1999-01-28 - ECVS - European College of Veterinary …

合集下载

Inversion of band limited TEM responses

Geophysical Prospecting,1999,47,551–564Inversion of band-limited TEM responses1Flemming Effersø,2Esben Auken2and Kurt Ingvard Sørensen2AbstractIt is shown that the electromagnetic(EM)spectrum is characterized by strong amplitude-modulated transmitters operating in the target bandwidth of transient electromagnetic(TEM)measurements.As these transmitters cause signiﬁcant noise in TEM soundings,it is mandatory to band-limit the input signals to improve the signal-to-noise ratio and thereby the depth of exploration.Band-limitation will distort the TEM responses,which leads to erroneous inversion results if the applied low-pass ﬁlters are not accounted for in the inversion scheme.We incorporate the low-pass ﬁlters in the inversion scheme and test the inversion approach on theoretical andﬁeld data.Inversion of band-limited theoretical responses results in recovery of erroneous resistivity models if theﬁlters are not included in the inversion scheme.By contrast, inversion of band-limited theoretical andﬁeld data,for which the applied low-pass ﬁlters are included in the inversion scheme,leads to recovery of similar resistivity models,independent of the applied cut-off frequencies.IntroductionThe transient electromagnetic(TEM)method has been used extensively in Denmark over the last rge TEM surveys are carried out for delineating the low-resistivity,impermeable boundaries of regional aquifers in sedimentary areas(Auken et al.1994;Christensen and Sørensen1994;Sørensen1996).Delineation plays a major role in the long-term planning of water supply and assists in planning remediation measures to improve contaminated ground water resources.In the literature there are several papers on noise rejection for TEM systems(e.g. Macnae,Lamontagne and West1984;McCracken,Oristaglio and Hohmann1986). The emphasis in these papers is on rejection of incoherent noise basically arising from lightning discharges and phase-coherent power-line noise.However,both theoretical and experimental studies suggest that amplitude-modulated(AM)long wave and very low frequency(VLF)transmitters cause high-amplitude input signals in TEM receivers that are not sufﬁciently band-limited.When the AM transmitter noise is sampled on logarithmically spaced gates and subsequently stacked,the standard deviation of the input signal will exhibit a t¹1proportionality,compared with a t¹1/2 dependence(Munkholm and Auken1996)for white noise.The level of the AM 1Received April1998,revision accepted December1998.2Department of Earth Sciences,Aarhus University,Finlandsgade6,8200Aarhus N,Denmark.᭧1999European Association of Geoscientists&Engineers551552F.Effersø,E.Auken and K.I.Sørensentransmitter noise is often orders of magnitude higher than the background noise level so that the signal-to-noise(S/N)ratio is lowered at the early and medium decay times. Low-pass(LP)ﬁlters are used in most commercial TEM receivers to suppress the AM transmitter noise.However,the LPﬁlters distort the early and medium part of the decay curve due to damping of the high-frequency content.The level of distortion depends on several factors such as cut-off frequency and subsurface resistivities.Thus, LPﬁlters must be incorporated in the inversion scheme such that the calculated forward response is subject to the sameﬁltering as the measured response.Firstly,we characterize the EM noise spectrum based on numerical simulations and on measured noise.Secondly,we quantify the distortion of responses due to band-limitation for a number of typical resistivity models.The band-limitations are based on cut-off frequencies typically used in commercial instruments.Finally,it is demon-strated that distortion due to band-limitation can be modelled in the inversion scheme by including the LPﬁlters in the forward response.This approach is tested on theoretical data as well as onﬁeld data.The EM noise spectrumEM noise can be divided into two major types,namely that arising from(i)natural sources and(ii)cultural sources.The noise spectrum has diurnal,annual and geographical variations.In the following a brief review of the sources is given.A more thorough discussion of the EM noise spectrum has been given by Macnae et al.(1984), McCracken et al.(1986)and Spies and Frischknecht(1991).For natural sources the EM noise below1Hz arises mainly from complex interactions between the solar wind and the Earth’s stationary magneticﬁeld.Of more interest in TEM soundings is the spectrum above1Hz.The major contributor above1Hz is lightning discharge from thunderstorms.Distant thunderstorm activity produces a background noise level,whereas strong sferics arise from nearby or intermediate distances.Theseﬁelds travel in the Earth–ionosphere cavity.Sferics occur worldwide with a frequency ofϷ100per second.In populated areas cultural sources increase the overall noise level.In these areas the power distribution grid is one of the main noise contributors,resulting in spectral peaks at50/60Hz and associated odd harmonics.Although the voltage waveform is kept sinusoidal at50/60Hz,the current producing the perturbingﬁeldsﬂuctuates from the sinusoidal waveform due to the varying load on the grid.High-amplitude,broadband transients also occur occasionally.Furthermore,spectral peaks arising from AM transmitters around the globe contribute signiﬁcant noise.These amplitude-modulated signals are transmitted with high power,such that the signals appear as distinct spectral lines,orders of magnitude higher than the ambient EM noise.The electromagnetic ﬁeld from radio waves is plane-polarized and can be treated as a plane wave a few skin depths away from the transmitter antenna.The major noise contribution stems from the magneticﬁeld,as the noise contribution from the electricalﬁeld is negligible if the receiver coil is adequately shielded.᭧1999European Association of Geoscientists&Engineers,Geophysical Prospecting,47,551–564Inversion of band-limited TEM responses553Suppression of EM noiseIn transient electromagnetic instruments,several techniques are applied to suppress the EM noise.Firstly,the decay signal is integrated in gates having exponentially increasing width as a function of decay time(log-gating).The integration serves two major functions:(i)it reduces the dynamic range of the input signal and(ii)it reduces the bandwidth,as an integrator is inherently an LPﬁlter with a frequency response of a sinc-function.Secondly,a synchronous detection technique(gate-stacking)is used in which the polarity of the transmitter wave is alternated between half-cycles. Synchronous detection removes the offset in the receiver ampliﬁers and makes it possible to use repetition frequencies of f/N,reducing power-line noise and increasing the S/N ratio at later times.f is the50/60Hz power-line frequency and N is an even number.In order to reduce high-amplitude AM transmitter noise,most transient electro-magnetic instruments are segmented such that each segment is band-limited by LP ﬁlters.The instrumentation is designed so that the bandwidth is broad at early time segments and narrow at late time segments.However,application of LPﬁlters distorts the TEM response due to damping of the high-frequency content,as the cut-off frequency must be low enough to obtain a satisfactory S/N ratio.In order to characterize the EM noise,two data sets were measured with a prototype TEM instrument(Sørensen1997).The data sets were collected with a10kHz and a 500kHz LPﬁlter,respectively.The noise measurements were log-gated and gate-stacked(10000time series),and the mean and the standard deviations were calculated (Fig.1).Figure1a shows that the mean of the500kHz noise is about an order of magnitude higher at early times compared with the mean of the10kHz noise.The standard deviation falls off as t¹1for the500kHz noise,whereas the10kHz noise contains two time dependences.At times earlier than10¹3s,the standard deviation exhibits a t¹1time dependence,whereas a t¹1/2time dependence is seen for times later than10¹3s.In our experience the standard deviation,as in the case of the broadband(500kHz) measurement in Fig.1a,always exhibits a t¹1time dependence when the bandwidth is 100kHz or higher.These observations indicate that the EM noise spectrum is coloured because a white noise spectrum,as shown by Munkholm and Auken(1996),is expected to show a t¹1/2dependence when log-gated.Munkholm and Auken(1996) showed that several spectral peaks are present in the EM noise spectrum,indicating that the EM noise spectrum is coloured,and they recognized these as VLF and LF radio transmitters.In order to test the above-mentioned observations,a numerical simulation of a log-gated and gate-stacked TEM receiver system was made.In the simulation two cases of noise spectra were considered:(i)a white noise spectrum and(ii)a noise spectrum containing a simulated AM transmitter in an otherwise white noise spectrum(AM noise spectrum).Figures1c and d show three simulations:(i)a white noise spectrum, (ii)an AM noise spectrum and(iii)an AM noise spectrum band-limited with a10kHz ᭧1999European Association of Geoscientists&Engineers,Geophysical Prospecting,47,551–564554F .Effersø,E.Auken and K.I.Sørensen᭧1999European Association of Geoscientists &Engineers,Geophysical Prospecting ,47,551–564Figure 1.(a)and (b)Mean and standard deviation,respectively,of real noise data measured with a 10and a 500kHz LP ﬁlter.The mean of the 500kHz data is signiﬁcantly higher,about an order of magnitude at early times,than the mean of the 10kHz data.For the 10kHz data the standard deviation has a t ¹1time dependence at early times,and a t ¹1/2time dependence at late times.The 500kHz noise data has a t ¹1dependence in the entire time range.(c)and (d)Numerical simulations of two noise spectra subjected to log-gating and gate-stacking.(c)and (d)show the mean and the standard deviations,respectively.One curve represents a white noise spectrum,the second curve represents a white noise spectrum superimposed with excess white noise in the frequency range 239–249kHz (AM noise spectrum),and the third curve is the AM noise spectrum band-limited with a 10kHz LP ﬁlter (thick curve).LPﬁlter.The AM transmitter was simulated by multiplying a white noise spectrum by a factor of100in the frequency range239–249kHz.This frequency range was chosen to simulate the high-amplitude LF radio transmitter present in Denmark.Log-gating was performed by equidistantly sampling and averaging over the samples within the time range of the gate.The mean and the standard deviation were calculated for100 realizations of noise spectra,shown in Figs1c and d,respectively.Figure1c shows that the mean of the AM noise isϷ5–10times higher than the mean of the band-limited noise,up to about10¹2s.Figure1d shows that the standard deviation of the AM noise exhibits a t¹1time dependence,whereas the band-limited AM noise exhibits a t¹1dependence at early times and a t¹1/2dependence at late times.In conclusion the standard deviation of the broadband measurement(500kHz)of the real noise and the broadband simulation of the AM noise spectrum indicate that the real EM noise spectrum is coloured as it shows a t¹1fall-off.The simulation,as well as observation of the EM spectrum,suggests that the t¹1fall-off(as opposed to a t¹1/2 fall-off for white noise)is probably due to the AM transmitters.The means of the real and the simulated noise indicate that band-limitation of the noise spectrum signiﬁcantly reduces the noise amplitude.Accordingly,band-limitation of TEM responses will improve the S/N ratio and thereby enhance the depth of exploration of TEM soundings.The inversion approachWe have implemented a numerical code for forward and inverse modelling of one-dimensional TEM data.The forward code includes modelling of LPﬁlters and any piece-wise linear transmitter waveform(Raiche1984;Asten1987;Fitterman and Anderson1987).The frequency-to time-domain transform is implemented as a straightforward Fourier transform(Anderson1982;Newman,Hohmann and Anderson1986).Even though this approach is slightly more computationally intensive,it has,in our experience,some advantages over the commonly used Gaver–Stehfest inverse Laplace transform method(Knight and Raiche1982).The Gaver–Stehfest algorithm may show instability,and it provides an accuracy of no better than four digits.If LPﬁlters are applied in the Laplace domain,inaccurate responses result due to instability of the inverse Laplaceﬁlter even when implemented in double precision.The implementation of the inverse Fourier transform approach follows that of Newman et al.(1986).The real and the imaginary parts of the frequency-domain response represent the spectrum of a causal function,suggesting that the transforma-tion from the frequency domain to the time domain is obtained by means of either a cosine or a sine transform.The step response is obtained fromfðt;pÞ¼¹2p∞Im½Fðq;pÞÿqcosðq tÞd qð1ÞInversion of band-limited TEM responses555᭧1999European Association of Geoscientists&Engineers,Geophysical Prospecting,47,551–564orf ðt ;p Þ¼¹2p ∞0Re ½F ðq ;p Þÿq sin ðq t Þd q ;ð2Þand the impulse response from d f ðt ;p Þd t ¼2p ∞0Im ½F ðq ;p Þÿsin ðq t Þd q ð3Þord f ðt ;p Þd t ¼¹2p ∞0Re ½F ðq ;p Þÿcos ðq t Þd q ;ð4Þwhere p is the model vector and F (q ,t )is the frequency-domain kernel.Johansen and Sørensen (1979)showed that the cosine and the sine transforms can be stated as J ¹1/2and J 1/2transforms,respectively,so that 2 ∞0F ðx Þcos sin ð2p sx Þd x ¼r1=2 ∞0f 1ðl Þl J ϯ1=2ðl r Þd l ;ð5Þwhere r ¼s (2p )1/2,l ¼x (2p )1/2and f 1(l )¼f (l /(2p )1/2)l 1/2.The integral in (5)is evaluated using the fast digital Hankel ﬁlters computed by Christensen (1990).The Hankel ﬁlters consist of precalculated ﬁlter coefﬁcients,and the calculation is conducted as a discrete convolution between the ﬁlter coefﬁcients and the frequency-domain kernels.The TEM inversion is carried out as an iterative damped least-squares approach (Menke 1989),formally writingm n þ1¼m n þðG T n C ¹1d G n þa I Þ¹1G T n C ¹1d ðd obs ¹d n Þ;ð6Þwhere m denotes the model vector,G n is the Jacobian matrix,C d is the data covariance matrix,a is the damping factor,I is the identity matrix,d obs denotes the observed data vector and d n denotes the forward data vector based on the previous model vector m n .The model parameter analysis is based on the linear approximation to the covariance of the estimation error,C est (Jackson 1979;Menke 1989),C est ¼ðG T C ¹1d G Þ¹1;ð7Þwhere G is based on the ﬁnal model obtained in the inversion.The data ﬁt is determined by the data residual,RES ,given by RES ¼1N N n ¼1ðy n ¹d n Þ2j n v u u t ;ð8Þwhere d n denotes the observed data,y n denotes the predicted data,j n denotes the relative standard deviation and N is the number of data points.556F .Effersø,E.Auken and K.I.Sørensen᭧1999European Association of Geoscientists &Engineers,Geophysical Prospecting ,47,551–564Band-limitation of TEM responsesBand-limitation of TEM responses introduces errors due to damping of the high-frequency content.These errors depend on the cut-off frequency,transmitter waveform and subsurface resistivities.Hence TEM instruments are traditionally designed with a system bandwidth varying with the time segment.In early time segments the system has a broad bandwidth,which is gradually narrowed with increasingly later time segments.In this paper the effect of analog electronicﬁlters is modelled by digital,ﬁrst-order Butterworthﬁlters.Theﬁltered response is obtained by imposing the multiplication theorem on(1),formally writingfðt;pÞ¼¹2p∞Im½Fðq;pÞHðqÞÿqcosðq tÞd q;ð9Þwhere H(q)is the frequency response of the digitalﬁlter.For instance,aﬁrst-order LP Butterworthﬁlter is given byH1ðqÞ¼11þi q=q cð10Þwhere q c is the cut-off frequency.Distortion of TEM responsesIn order to quantify the distortion of the TEM responses due to band-limitation,aﬁlter index,FI,is used,given byFI¼f nðtÞ¹f fðtÞf nðtÞ;ð11Þwhere f n and f f are the unﬁltered andﬁltered responses,respectively.FI is used to assess the relative difference between theﬁltered and unﬁltered responses for a given resistivity model.Figure2a shows theoretical,LP-ﬁltered,TEM responses generated for a three-layer model(model A,Fig.2c).This model consists of a10Q m layer of inﬁnite thickness, overlain by a100Q m(100m thick)layer,overlain by an upper30Q m(30m thick) layer.Geologically,this model corresponds to a basement of highly conductive clays overlain by a coarse-grained sand/gravel overlain by a clay till.In addition to the unﬁltered response,the data include band-limited responses in the range from50to 400kHz.As expected,the distortion becomes larger and more prolonged as the cut-off frequency decreases.Figure2b shows theﬁlter indices,FI,of theﬁltered responses in Fig.2a.If theﬁrst three microseconds are neglected,where some of the curves have sign shifts,we see that FI becomes higher at lower cut-off frequencies,as suggested by Fig.2a.Moreover,it is seen that an increase of the cut-off frequency by a factor of two increases FI by a factor of two at late times.Figure2d shows theoretical,LP-ﬁltered,TEM responses generated for a three-layer model(model B,Fig.2f).This model consists of a10Q m layer of inﬁnite thickness,Inversion of band-limited TEM responses557᭧1999European Association of Geoscientists&Engineers,Geophysical Prospecting,47,551–564558F.Effersø,E.Auken and K.I.Sørensen᭧1999European Association of Geoscientists&Engineers,Geophysical Prospecting,47,551–564Inversion of band-limited TEM responses559 overlain by a100Q m(70m thick)layer,overlain by an upper1000Q m(50m thick) layer.This model is similar to model A except that the upper layer consists of a thick unsaturated zone of sand instead of till.Figure2e shows the FI for the responses in Fig. 2d.Weﬁnd the same tendency for this model,namely that the distortion increases with decreasing cut-off paring the FI for models A and B,it is seen that the distortions of the responses for model B are signiﬁcantly higher(about a factor of100), but approach those for model A at late times.Inversion of theoretical dataIn order to test the effect of modelling the LPﬁlters in the inversion scheme, theoretical response data were generated for models A and B.The responses consist of an early time(6m s to1ms)segment and a late time(0.1ms to8ms) segment.A200kHz and a450kHz LPﬁlter and a40kHz and a450kHz LPﬁlter were applied to the early time and late time segments,respectively.The40and the 200kHz cut-off frequencies simulate the bandwidth of the receiver system,whereas the450kHz cut-off frequency simulates the bandwidth of the receiver coil.These cut-off frequencies were chosen as they are typical of those applied in commercial TEM instruments.The theoretical data were modelled in two ways:one in which the LPﬁlters were included in the inversion scheme,and one in which theﬁlters were excluded from the inversion.The inversion results for model A are shown in Fig.3,and the inversion results for model B appear in Fig.4.Figure3c shows that a good model recovery and dataﬁt with a residual of0.84is obtained when the LPﬁlters are included in the inversion scheme.The parameter analysis shows that all model parameters are well determined with uncertainties less than10%.In the case where theﬁlters were excluded in the inversion,the data were modelled by a three-and a four-layer model(Figs3d and e).The three-layer model results in a poor dataﬁt,whereas the four-layer model produced a satisfactory dataﬁt with a residual of1.13.However,neither the three-layer model nor the four-layer model resulted in a good recovery of the original model.Of the model parameters in the three-layer model,only the third-layer resistivity resembles that of the initial model. The parameter analysis suggests,however,that all the model parameters are well determined.The four-layer model suffers from a false low resistivity:a top layer that does not resemble the top layer in the initial model.If theﬁrst layer is neglected the remainder of the model is very much like the initial model.The analysis shows that the top-layer parameters are completely undetermined and the other model parameters are Figure2.(a)Theoretical responses generated for model A in(c).The responses include an unﬁltered response in addition to four responsesﬁltered with,respectively,50,100,200and 400kHzﬁrst-order LPﬁlters.(b)Filter index(FI)for the responses in(a).(d)Theoretical responses for model B in(f).The LPﬁlters are the same as in Fig.3a.(e)FI for the responses in (d).The3%line shown in(b)and(e)indicates the assumed noise level in the data.᭧1999European Association of Geoscientists&Engineers,Geophysical Prospecting,47,551–564slightly less well determined compared with the inversion with the ﬁlter included.Thus,in this case it is necessary to add a false layer to the initial model when the ﬁlters are not included in the inversion scheme.For model B (Fig.4),the inversion with LP ﬁlters produces a good model recovery and data ﬁt.In the inversion with LP ﬁlters excluded,the data were modelled with two three-layer models,namely one with all the data points and the other with the two data points (6–10m s)removed.For the inversion with all data (no ﬁlters),a poor model recovery is obtained with a residual of 4.8.In the modelling where the ﬁrst two data560F .Effersø,E.Auken and K.I.Sørensen᭧1999European Association of Geoscientists &Engineers,Geophysical Prospecting ,47,551–564Figure 3.Theoretical data (error bars)in (a)and (b)generated for model A are shown as thin curves in (c)–(e).The theoretical data were generated using a 200and a 450kHz LP ﬁlter in the early time segment,and a 40and a 450kHz ﬁlter in the late time segment.3%and 5%white noise was added to the early and the late time segments,respectively.The theoretical data were inverted with and without the LP ﬁlters included in the inversion scheme.The model response based on inclusion of the LP ﬁlters and the inverted model are shown in (a)(curve)and (c)(thick),respectively.In the inversion scheme without inclusion of the LP ﬁlters,the data were interpreted by (d)a three-layer model and (e)a four-layer model.Model responses for the three-layer (thin curve)and the four-layer (thick curve)models are shown in (e).points were removed,the initial model is signiﬁcantly better recovered with a residual of 0.92.All model parameters are determined better than 10%.In conclusion,the effect of the LP ﬁlters is more pronounced at early times in the high-resistivity model (model B)compared with the low-resistivity model (model A).For the high-resistivity model,a reasonable model recovery is obtained by removing the ﬁrst data points,whereas for the low-resistivity model the effect is more smeared out and it is not possible to recover the model by removing the early data points.Inversion of ﬁeld dataThe inversion approach was applied to ﬁeld data acquired at different cut-off frequencies.The geological model of the ﬁeld site is considered to be a 40m thick till on top of T ertiary ᭧1999European Association of Geoscientists &Engineers,Geophysical Prospecting ,47,551–564Figure 4.Similar annotations as in Fig.3apply to Fig.4where the theoretical data were generated for model B shown as thin curves in (c)–(e).In the inversion scheme without the inclusion of the LP ﬁlters,the theoretical data were inverted (d)using the full data set and (e)with the ﬁrst two data points removed.low-resistivity clays.Data were measured with a prototype TEM system.A receiver coil with a bandwidth of 1MHz and an effective receiver area of 60m 2was used.The data were acquired in the central loop conﬁguration using a square of 40m ×40m transmitter loop and a transmitter current of 7.6A.Three different ﬁrst-order LP ﬁlters with cut-off frequencies of 10,50and 100kHz were used to collect separate data sets.The data sets were modelled using LP ﬁlters with the same cut-off frequencies as were applied in measuring the data.In Figs 5a and b,the inversion results are shown for the 10and 100kHz data,and the inversion results for all the cut-off frequencies are shown in Figs 5c–e.As can be seen,it is possible to recover the same four-layer model within the uncertainties of the model parameters for all three data sets.However,the model parameter analysis shows that application of very low cut-off frequencies (10kHz)may increase the parameter uncertainty of the uppermost layers due to the lack of the high frequencies.᭧1999European Association of Geoscientists &Engineers,Geophysical Prospecting ,47,551–564Figure 5.Field data (error bars)measured with (a)a 10kHz ﬁrst-order LP ﬁlter and (b)a 100kHz ﬁrst-order LP ﬁlter together with four-layer model responses (curve).(c)–(e)Inverted models obtained from ﬁeld data collected with the 10,50and 100kHz LP ﬁlters.Identical LP ﬁlters used to collect the data were included in the inversion scheme.ConclusionsMeasured noise and simulation of the EM noise spectrum indicates that high-power amplitude-modulated VLF and LF radio transmitters are signiﬁcant contributors to the overall noise level.The standard deviation of log-gated real noise exhibits a characteristic t¹1time dependence,being indicative of a coloured noise spectrum. Measurements of the real noise spectrum and simulated noise spectra show that band-limitation dampens the noise amplitudes signiﬁcantly and thereby the inﬂuence of the AM transmitters.The noise reduction improves the S/N ratio and therefore the depth of exploration in TEM soundings.Due to the AM transmitters it is mandatory to band-limit TEM responses to obtain a satisfactory depth of exploration.However,band-limitation will distort the TEM responses because of the damping of the high-frequency content.The distortion is dependent on several factors such as cut-off frequency and subsurface resistivities.The distortion increases at lower cut-off frequencies and higher resistivities.It is demonstrated that distortions due to cut-off frequencies applied in commercial TEM instruments can lead to incorrect inversion results if the low-passﬁlters are not included in the inversion scheme.We have shown that for both theoretical andﬁeld data the applied low-passﬁlters can be incorporated in the inversion scheme.The inversion results obtained this way demonstrate that similar resistivity models within the uncertainties of the model parameters can be recovered,independent of the applied cut-off frequency.ReferencesAnderson W.L.1982.Nonlinear least-squares inversion of transient soundings for a central loop system(Subprogram NLSTCI).US Geological Survey Open-File Report82-1129,85.Asten M.W.1987.Full transmitter waveform transient electromagnetic modeling and inversion for soundings over coal measures.Geophysics52,279–288.Auken E.,Christensen N.B.,Sørensen K.I.and Effersørge scale hydrogeological investigation in the Beder area–a case study.Symposium on the Application of Geophysics to Engineering and Environmental Problems(SAGEEP),Boston,USA,Expanded Abstracts, 615–628.Christensen N.B.1990.Optimized fast Hankel transformﬁlters.Geophysical Prospecting38, 545–568.Christensen N.B.and Sørensen K.I.1994.Integrated use of electromagnetic methods for hydrogeological investigations.Symposium on the Application of Geophysics to Engineering and Environmental Problems(SAGEEP),Boston,USA,Expanded Abstracts, 163–176.Fitterman D.V.and Anderson W.L.1987.Effect of transmitter turn-off time on transient soundings.Geoexploration24,131–146.Jackson D.D.1979.The use of a priori data to resolve non-uniqueness in linear inversion. Geophysical Journal of the Royal Astronomical Society57,137–157.Johansen H.K.and Sørensen K.1979.Fast Hankel transforms.Geophysical Prospecting27, 876–901.᭧1999European Association of Geoscientists&Engineers,Geophysical Prospecting,47,551–564。

EN 1999-815-EC

COMMISSION DECISIONof7December1999adopting measures prohibiting the placing on the market of toys and childcare articles intended to be placed in the mouth by children under three years of age made of soft PVC containing one or more of the substances di-iso-nonyl phthalate(DINP),di(2-ethylhexyl)phthalate(DEHP),dibutyl phthalate(DBP),di-iso-decyl phthalate(DIDP),di-n-octyl phthalate(DNOP),and butylbenzyl phtha-late(BBP)(notified under document number C(1999)4436)(Text with EEA relevance)(1999/815/EC)THE COMMISSION OF THE EUROPEAN COMMUNITIES,Having regard to the Treaty establishing the European Community,Having regard to Council Directive92/59/EEC of29June1992 on general product safety(1),and in particular Article9thereof,Whereas:(1)Pursuant to Article3of Directive92/59/EEC,producersare obliged to place only safe products on the market;the Directive stresses in particular the need to ensure ahigh level of protection of the health and safety ofchildren;(2)Article9of the Directive provides that the Commissionmay,under certain conditions and in conformity withthe procedure set out in the Directive,adopt a decisionrequiring Member States to take temporary measures toprevent,restrict or submit to particular conditions theplacing on the market of a product,or requiring itswithdrawal from the market,if it presents a serious andimmediate risk to the health and safety of consumers;(3)The Commission may adopt such a decision with regardto a product which,in accordance with informationprovided by a Member State,presents a serious andimmediate risk and in respect of which one or moreMember States have adopted measures entailing restric-tions on the marketing of the product or requiring itswithdrawal from the market;(4)Such a decision is subject to the conditions that MemberStates differ on the adoption of measures to deal withthe risk in question;that the risk cannot be dealt with ina manner compatible with the urgency of the case underthe other procedures laid down by the specificCommunity legislation applicable to the product orcategory of products concerned;that the risk can beeliminated effectively only by adopting appropriatemeasures applicable at Community level,in order toensure the protection of the health and safety ofconsumers and the proper functioning of the internalmarket;(5)The Danish authorities have informed the Commission,in four notifications presented in April and July1997under Article8of Directive92/59/EEC,of the seriousand immediate risk presented by certain soft PVCteething rings containing the phthalates DINP,DEHP,DBP,DIDP,DNOP and BBP;(6)The Spanish authorities have informed the Commission,in a notification presented in the same framework inFebruary1998,of the risk presented by a soft PVCimitation fruit containing the phthalate DINP,intendedfor children;(7)The Greek authorities adopted on15January1999measures concerning the withdrawal from the market ofsoft PVC childcare articles intended for teething byinfants and the prohibition of the import and marketingof certain soft PVC toys intended for children under theage of three years;(8)The Austrian authorities adopted on4August1998alaw prohibiting toys containing phthalates;intended forchildren of less than three years of age,which are,undernormal and foreseeable conditions of use,sucked,chewed or otherwise frequently placed in the mouth;(9)The Danish authorities issued on15March1999aStatutory Order prohibiting the production,import andmarketing of childcare articles intended or likely to beplaced in mouth,and of toys,and products which mustbe expected to be used as toys by children under the ageof three years,or parts thereof,containing more than0,05%of phthalates;(10)The Swedish authorities adopted on10June1999,ameasure prohibiting the marketing and sale of phthalate-containing toys and childcare articles intended for chil-dren under three years of age and which can be put inthe mouth;(11)The Finnish authorities adopted on23September1999,a Resolution of the Council of State prohibiting child-care articles and toys which can be put into the mouthby children under three years of age which are made ofsoft PVC and contain more than0,05%by weight ofDINP,DEHP,DBP,DIDP,DNOP or BBP;(1)OJ L228,11.8.1992,p.24.(12)The Italian authorities adopted on30September1999ameasure prohibiting the marketing of soft plastic toysfor children under three years of age intended or likelyto be put in the mouth,containing more than0,05%ofDINP,DIDP,DEHP,DBP,DNOP or BBP;in addition theItalian authorities notified the Commission on14June1999within the framework of Directive98/34/EC ofthe European Parliament and of the Council(1)as lastamended by Directive98/48/EC(2),of a draft measureprohibiting the use of four phthalates(DIDP,DEHP,DINP,DBP)in plastic materials and elastomers andrestricting the use of certain other phthalates to amaximum of5%by weight in childcare articles;(13)The French authorities adopted on5July1999ameasure suspending the marketing,production,importand export and ordering a withdrawal of certain toysand childcare articles intended for placing in the mouthby children under36months in soft PVC containingDINP,DIDP,DEHP,DBP,DNOP and BBP;they have inaddition notified the Commission within the frameworkof Directive98/34/EC of a draft measure prohibiting theuse of DINP,DIDP,DEHP,DBP,DNOP and BBP in toysand childcare articles intended for placing in the mouthby children under three years of age;(14)The German authorities notified the Commission on24August1999within the framework of Directive98/34/EC of a draft measure prohibiting the marketing,production and import of teething rings and certainplastic toys for children up to three years of age entirelyor partly made of plastic materials,of which the plasticparts are intended or can be foreseen to be put in themouth,containing more than0,1%of any phthalates;(15)All the abovementioned notifications and measuresrelate to the risks associated with exposure of children tophthalates and concern childcare products and/or toysmade of soft PVC containing certain phthalates whichare intended or Likely to be placed in the mouth byyoung children;(16)The Commission adopted,on1July1998recommenda-tion98/485/EC(3)on phthalates in certain childcarearticles and toys,on the basis of the scientific knowledgethen available,inviting Member States to monitor thelevel of phthalate migration from the products in ques-tion,taking into account the opinion of the ScientificCommittee on Toxicity,Ecotoxicity and the Environ-ment(SCTEE)of24April1998,and to take the meas-ures required to ensure a high level of child healthprotection;(17)The Scientific Committee on Toxicity,Ecotoxicity andthe Environment(SCTEE),consulted by the Commission,in its opinion on phthalates in toys of27November1998,taking into account the results of the most recentrelevant studies,has confirmed that there are groundsfor concern with the low safety margins as regards theexposure of children to the phthalate DEHP and DINP,in connection with the use of certain toys and childcarearticles made of soft PVC containing these substances;(18)The SCTEE has come to this conclusion on the basis,inter alia,of adverse effects of DINP for liver and kidneyand testicular damage caused by DEHP observed in labo-ratory tests;.it therefore appears that under certainconditions these substances may have serious adversehealth effects:(19)In the light of the SCTEE opinion,the Commissionconsiders that young children who use certain toys andchildcare articles which are placed in the mouth,madeof phthalate-containing soft PVC,may be subject to dailylevels of exposure to DINP and DEHP higher than thelevels deemed to be safe;(20)The SCTEE found the release of the other phthalates(DNOP,DIDP,BBP and DBP)to be low and to presentno risk under current conditions of use.The Committeeobserved that a larger release would occur if they wereused as plasticisers in higher concentrations;(21)The Commission considers that,should the use ofDNOP,DIDP,BBP and DBP be allowed to replace DINPand DEHP,as a consequence of the prohibition of thesetwo substances as plasticisers in the products in ques-tion,the exposure of children to them would increaseand consequently the risk would be higher.Therefore,the Commission,adopting a precautionary approach,considers that this Decision should also apply to them;(22)Young children are also exposed to phthalates fromsources other than PVC toys and childcare articles,butthe level of exposure due to these sources cannot,according to the SCTEE opinion,be quantified becauseof lack of sufficient data;the existence of such additionalexposure should however be taken into account inmanaging the risks in question;(23)Although the serious effects mentioned above do notbecome manifest until some time after exposure,the riskassociated with the products in question is an immediateone because it is directly associated with exposure to thephthalates;such products.following the normal periodof use by a child,may lead to significant exposure withserious effects later in life;(24)Therefore,the Commission considers that toys andchildcare articles for young children made of soft PVCcontaining phthalates arc liable to present a serious andimmediate risk to health;1p.37.(2)OJ L217,5.8.1998,p.18.(3)OJ L217,5.8.1998,p.35.(25)The products which pose the abovementioned risks aretoys and childcare articles which.are intended to beplaced in the mouth by young children and are made ofsoft PVC containing one or more of the phthalates inquestion,because they are expected to be placed in themouth for periods long enough and in a way liable togive rise to daily phthalate-extraction above the levelsdeemed to be safe;this Decision concerns,taken intoaccount the nature of the risk,both products producedin the Community and imported products;(26)Denmark,Austria,Greece,Finland,Sweden,Italy,Franceand Germany have decided to submit the productsbelonging to the category in question to restrictivemeasures with different scope,aimed at eliminating theuse of phthalates in this application;the Commissionhas ascertained,that Member States differ on the adop-tion of measures to deal with the risk in question;(27)Because of the differences between Member States andbetween the scope of the measures taken by certainMember States,a Community measure is necessary toeliminate the risk and effectively ensure a consistenthigh level of protection of child health and the properfunctioning of the internal market;(28)Council Directive76/769/EEC of27July1976on theapproximation of the laws,regulations and adminis-trative provisions of the Member States relating torestrictions on the marketing and use of certaindangerous substances and preparations(1),as lastamended by Directive1999/77/EC(2)applies todangerous substances and preparations,but does not yetcontain provisions concerning phthalates;CouncilDirective88/378/EEC of3May1988on the approx-imation of the laws of the Member States concerning thesafety of toys(3),as last amended by Directive93/68/EEC(4),as regards dangerous substances refers to therelevant Community legislation relating to certain cate-gories of products or to the prohibition,restriction ofuse or labelling of certain dangerous substances andpreparations;it does not apply to childcare articles anddoes not provide for an emergency procedure;(29)The Danish authorities requested the Commission on15April1998to adopt a decision introducing restrictivemeasures in relation to the products in question,incompliance with Article9of Directive92/59/FEC;(30)The European Parliament,in its resolution on aconsumer policy action plan,adopted on4May1999,has called on the Commission to take steps in removingphthalates from PVC toys intended for babies and youngchildren(5);(31)The SCTEE,consulted by the Commission.hasconcluded in its opinion of28September1999onTNO,LGC and United States CPSC reports on phthalate-migration test validation that none of the phthalate-migration test methods which have been subject to vali-dation attempts is currently suitable for controlpurposes;(32)In the absence of a test method of phthalate migrationthat has been validated and standardised at Communitylevel,it is not currently feasible to guarantee a consis-tently high level of child health protection by layingdown limits on the migration of these substances fromthe toys and childcare articles in question,and to ensurestandard and non-discriminatory application of theselimits;furthermore it is at present very difficult to estab-lish phthalate migration limits which take account of thecontribution to phthalate child exposure from sourcesother than PVC toys and childcare articles;(33)The scientific evidence on phthalate migration-testmethods mentioned above,which has been made avail-able recently,has shown that Recommendation98/485/EC is not sufficient to ensure a consistent high levelof child health protection;it is now urgent to prohibitrapidly the placing on the market of toys and childcarearticles intended to be placed in the mouth by childrenunder three years,because it has now become evidentthat there is no other effective control measure currentlyavailable for regulatory purposes;(34)The Commission has presented a proposal for anamendment to Directive76/769/EEC on restrictions onthe marketing and use of dangerous substances andpreparations prohibiting,the use of DINP,DEHP,DIDP;DNOP,DBP and BBP in toys and childcare articles madeof soft PVC and intended to be put in the mouth bychildren under the age of three.Furthermore,the placingon the market of such products is not allowed if theycontain the mentioned phthalates;the proposal aims,inaddition,at ensuring that other toys and childcarearticles of soft PVC intended for children under the ageof three and which could be put in the mouth shouldbear a label in order to ensure that the children do notput them in the mouth;(35)In order to ensure a consistent high level of child healthprotection throughout the EU,in the period precedingthe adoption by the European Parliament and theCouncil of the proposed Directive and its implementa-tion by the Member States,and given that toys andchildcare articles of soft PVC containing phthalatesintended for placing in the mouth by children underthree years of age present a serious and immediate risk,it is necessary to prohibit immediately their placing onthe market;1p.201.(2)OJ L207,6.8.1999,p.18.(3)OJ L187,16.7.1988,p.1.(4)OJ L220,30.8.1993,p.1.(5)OJ C279,1.10.1999,p.86.(36)All the relevant phthalates must be covered by thisDecision in order to eliminate those which are presentlyused and prevent use of the others which pose compar-able risks for child health;(37)This Decision should eliminate the deliberate use of therelevant phthalates as plastisizers in the products inquestion.while acknowledging the possibility of theirpresence at a trace level of up to0,1%by weight whichis considered a level allowing for non-intended impuri-ties not giving rise to concern for child health; (38)The duration of the validity of this Decision is limited tothree months;period of validity may be prolonged ifnecessary;(39)Pursuant to Article11(3)of Directive92/59/EECMember States shall take all necessary measures toimplement the decision adopted within less than10days;(40)The measures provided for in this Decision are inaccordance with the opinion of the EmergenciesCommittee,HAS ADOPTED THIS DECISION:Article1This Decision shall apply to toys and childcare articles:—made of,or in part made of;soft PVC containing more than 0,1%by weight of one or more of the following substances:—di-isononyl phthalate(DINP)CAS No28553-12-0 Einecs No249-079-5,—di(2-ethylhexyl)phthalate(DEHP)CAS No117-81-7 Einecs No204-211-0,—di-n-octyl phthalate(DNOP)CAS No117-84-0Einecs No204-214-7,—di-iso-decyl phthalate(DIDP)CAS No26761-40-0 Einecs No247-977-1,—butyl benzyl phthalate(BBP)CAS No85-68-7Einecs No201-622-7,—dibutyl phthalate(DBP)CAS No84-74-2Einecs No 201-557-4,—intended to be placed in the mouth by children of less than three years of age.Article2For the purposes of this Decision:—a‘toy’shall mean any product designed or clearly intended for use in play by children,—childcare article shall mean any product intended to facili-tate sleep,relaxation.the feeding of children,or sucking on the part of children.Article3Member States shall prohibit the placing on the market of the toys and childcare articles referred to in Article1.Article4Member States shall take the measures necessary to comply with this Decision within less than10days of its notification. They shall forthwith inform the Commission thereof.Article5This Decision shall be applicable until8March2000.Article6This Decision is addressed to the Member States.Done at Brussels,7December1999.For the CommissionDavid BYRNEMember of the Commission。

Journal of the European Ceramic Society 19(1999)

Correlation between Microstructure andConductance in NTC Thermistors Produced from Oxide PowdersG.D.C.Csete de Gyo rgyfalva,*A.N.Nolte and I.M.ReaneyDepartment of Engineering Materials,Sir Robert Had®eld Building,University of She eld,She eld,S13JD,UKAbstractA detailed study of spinel-structured Ni 1Àx Mn 2+x O 4formed by a mixed oxide route has shown that when x %0a high proportion of NiO is residual in the sin-tered ceramic.Wickham (Wickham,D.G.,Solid phase equilibria in the system NiO±Mn 2O 3±O 2.J.Inorg.Chem.,1964,26,1369±1377)demonstrated that the spinel phase decomposes in air above 900 C.Sintering in this system is usually per-formed around 1200 C.Decomposition of the spi-nel phase is therefore inevitable.The e ect of decomposition on the microstructure and electrical properties of Ni 1Àx Mn 2+x O 4based ceramics is discussed.#1999Elsevier Science Limited.All rights reservedKeywords :microstructure,electrical conductivity,spinels,thermistors.1IntroductionNegative temperature coe cient (NTC)thermistors are found in an ever increasing number of electrical and electronic products.Ni 1Àx Mn 2+x O 4,where x denotes the deviation from the stoichiometric 1:1NiO:Mn 2O 3ratio,o ers a range of properties that are suitable for most temperature sensing applications.When x =0,(nickel manganite,NiMn 2O 4),the solid solution has an inverse cubic spinel structure,based on a 2Â2Â2array of face centred cubic (fcc)oxygen subunits.When x =1,Mn 3O 4is present which is a tetragonally distorted spinel.The properties routinely used to characterise NTC thermistors are resistance,R 1and R 2,at 25 C (T 1)and 85 (T 2)and a B value (with units of tem-perature in Kelvin)which is a measure of the sensi-tivity of the device over a given temperature range:BT 1T 2T 2ÀT 1ln R 1R 2IThe exact mode of conduction in nickel manga-nite is poorly understood,but several modelsinvoke the small polaron theory.1,2Small polaron conduction is sometimes referred to as a `hopping'mechanism,as it involves the transfer of polarisa-tion from one cation to another.In the nickel manganite system,it has been postulated that the mixed valence,Mn 4+,Mn 3+cations present on the octahedral sites give rise to these small polaron pathways.1The octahedral cations in the spinel structure lie in chains along some <110>direc-tions.These vectors represent the smallest inter-cationic distances within the unit cell.Another important parameter when considering applications for Ni 1Àx Mn 2+x O 4ceramics is their thermal stability or aging characteristics (changes in conductance over long periods,i.e.lifetime of the component).Reports indicate that better ther-mal stability is found in tetragonal ceramics rather than cubic materials though the conductivity of the latter is 10to 100times higher.2,3This could be explained by a reduction in the concentration of Mn 4+compared to Mn 2+and Mn 3+or possibly by the presence of planar defects such as ferroelas-tic domain walls.4Ni 1Àx Mn 2+x O 4ceramics have been prepared by the carbonate and oxalate methods,in addi-tion to the more conventional mixed oxide route.5Irrespective of the preparation route,sintering (typically around 1200 C)is always carried out above the decomposition temperature in air for the system ($900 C)as discussed by Wickham.5Con-sequently,ceramics ®red using conventional pro-cessing will contain multiple phases,e.g.NiO fromJournal of the European Ceramic Society 19(1999)857±860#1999Elsevier Science LimitedPrinted in Great Britain.All rights reservedP I I :S 0955-2219(98)00331-80955-2219/99/$-see front matter857*To whom correspondence should be addressed.Fax:+44-(0)114-222-5943;e-mail:mtp96gdc@she the decomposed spinel and Mn-rich regions,3,6,7in accordance with the equation:xiwn III2y43x xiy 3Àx3xi II 3À3x a 3Àxwn II 2x a 3Àx wn III2O4 x6O2PIt is the intention of this paper to demonstrate how the degree of decomposition from single phase in¯uences conductivity and,in particular,aging. X-ray di raction and transmission electron micro-scopy will be used to monitor the degree of decomposition and accelerated aging tests(470 C) will be performed.2Experimental ProcedureThe NiO and Mn2O3powders in a1:1Mn2O3:NiO molar ratio were weighed out using an electronic balance( 0.01g)and transferred to a poly-propylene vessel with a charge of ZrO2milling media(the weight of ZrO2varied with the weight of the batch being processed).The batch was mil-led for6h to reduce particle size distribution to a mean of6"m and a maximum of12"m then drawn through a suction®lter.The resulting slurry was dried in a70 C oven overnight.The dried powder was calcined in a mullite crucible at900 C for16h and subjected to a further6h milling under the above conditions.One one cm diameter pellets were pressed from the powders and sintered at 1250 C,achieving densities better than95%. Microstructural and structural characterisation were carried out using transmission electron microscopy(TEM)and X-ray di raction(XRD), respectively.XRD was performed on solid cera-mics and loose powders using a Phillips PW1050 di ractometer with a Cu K source.A0.02 step size was used at a scan rate of0.5 minÀ1.TEM samples were prepared by grinding the ceramic to a thickness of20"m and ion beam milling to per-foration.Images were obtained using JEOL200CX and3010TEMs:the latter was equipped with a LINK energy dispersive X-ray detector. Accelerated aging tests were carried out using a non-induction wound furnace held at470 C.Tem-perature¯ux was monitored in the furnace using a thermocouple mounted immediately adjacent to the test piece.Platinum wires leading to a high precision HP4284A LCR meter were used to make contact to the electroded surface of the cera-mic.Changes in the resistance of the leads and contacts as a function of temperature were taken into account by performing a closed circuit run.Typically,temperature varied within a 0.2 C range over10h.3Results and DiscussionWickham,5in his study of the Ni1Àx Mn2+x O4solid solution,demonstrated that above900 C decom-position occurs resulting in the formation of NiO and a Mn-rich spinel phase.The higher the tem-perature above the onset of the decomposition reaction,the more rapid the rate.In order to study the decomposition reaction in more detail and its potential e ect on electrical properties,single phase ceramics(within the sensitivity of conventional XRD)were fabricated,as demonstrated in Fig.1. Figure2shows a series of XRD traces from single phase samples heat treated at1000,1100and 1200 C for1h.The evolution of peaks corres-ponding to NiO can be observed in accordance with the predictions of Wickham.6The relative intensities of the NiO peaks(marked)increase with increasing temperature.Figure3is a bright®eld(BF)TEM image showing a typical region of spinel grains in single phase material.The grain boundaries and interiors are free from second phase.Inset in Fig.3is a <110>zone axis di raction pattern(ZADP)from one of the spinel grains in the image.Figure4isaFig.1.XRD trace of single phase ceramic.Note absence ofNiOpeaks.Fig.2.XRD spectra of samples held at1000,1100,1200 c for1h.NiO peaks are marked.858G.D.C.Csete de GyoÈrgyfalva et al.BFTEM image obtained from a sample decom-posed for9h at1250 C.Inset is a<110>ZADP pattern from the imaged region.The fundamental re¯ections can be indexed according to a<110> zone axis from rock salt structured NiO.The weak re¯ections at half integer positions arise from regions of spinel phase,observed as dark contrast. Rock salt(NiO)and spinel structured compounds invariably exhibit a cube//cube orientation rela-tionship.Oxides with the rock salt structure are based around single fcc oxygen subunits whereas spinel structured compounds have a2Â2Â2fcc oxygen sublattice.In order to study the aging characteristics of the ceramics as a function of decomposition,con-ductance measurements were performed over10h at470 C 0.2 C.Figure5shows the change in conductance normalised to the initial value,against time at470 C for(A)single phase spinel and(B) `partially'decomposed spinel(heat treated for9h at1250 C).The single phase sample showed a negligible drift in resistivity over the test period, whereas the`partially'decomposed sample exhib-ited a steady decline in conductance.Di erences in the absolute starting values can be attributed to small variations in the dimensions of the samples. Figures6and7are XRD traces showing the samples before and after the accelerated aging experiments.Figure6,which corresponds to Fig.5(A)(decomposed),shows a reduction intheFig.4.BFTEM image of spinel regions in a NiO matrix.Insetis a<110>ZADP from the NiO.Faint re¯ections are presentat half integer positions arising from the dark regions ofspinel.Fig.5.Graph showing normalised conductance versus time at470 C for(A)single phase and(B)decomposed(9h at1250 C)material.Fig.6.XRD spectra of single phase sample(A)before and(B)after acceleratedaging.Fig.7.XRD spectra of decomposed sample(A)before and(B)after acceleratedaging.Fig.3.BFTEM image of spinel grains in single phase mate-rial.Inset is a<110>zone axis di raction pattern(ZADP)from a spinel grain.NTC thermistors produced from oxide powders859intensity of the NiO peaks(A)before and(B)after the experiment.However,Fig.7,which corre-sponds to Fig.5(B)(single phase),shows traces that are identical(A)before and(B)after.It is thought that the accelerated aging at470 C leads to NiO being re-absorbed into the ceramic during the lifetime of the experiment.It is proposed that the decomposition reaction occurs homogeneously throughout the ceramic,and the NiO is intimately mixed with the spinel phase,as evidenced by Fig.4. The reverse process may therefore occur relatively quickly because of the short di usion distances involved(of the order of nm according to Fig.4). However,it should be noted that aging at room temperature may be related to di erent phenomena than suggested by these accelerated tests.4Conclusions.The reaction between NiO and Mn2O3pro-ceeds forwards slowly at temperatures less than900 C,but will reverse as temperature increases above this value..The rate of decomposition increases with increasing temperature resulting in amicrostructure of intimately mixed NiO and Mn-rich spinel..Initial investigations indicate that a single phase ceramic gives rise to substantial improvements in thermal stability under accelerated aging.References1.Brabers,V.A.M.and Terhell,J.,Electrical conductivityand cation valencies in nickel manganite.Phys.Stat.Sol.(a),1982,69,325±332.2.Dorris,S.E.and Mason,T.O.,Electrical properties andcation valences in Mn3O4.J.Am.Ceram.Soc.,1988, 71(5),379±385.3.Rousset,A.,Larange,A.,Brieu,M.,Couderc,J.andLegros,R.,In¯uence de la microstructure sur la stabilite electrique des thermistance.C.T.N Journ.de Phys.III, 1992,4,833±845.4.Macklen,E.D.,Electric conductivity and cation distribu-tion in nickel manganite.J.Phys.Chem.Solids,1986, 47(11),1073±1079.5.Wickham,D.G.,Solid phase equilibria in the systemNiO±Mn2O3±O2.J.Inorg.Chem.,1964,26,1369±1377.6.Feltz,A.,Topfer,J.and Schirrmeister,F.,Conductivitydata and preparation routes for NiMn2O4thermistor ceramics.J.Eur.Ceram.Soc.,1992,9,187±191.7.Jung,J.,Topfer,J.,Murbe,J.and Feltz,A.,Micro-structure and phase development in NiMn2O4spinel ceramics during isothermal sintering.J.Europ.Ceram.Soc.,1990,6,351±359.860G.D.C.Csete de GyoÈrgyfalva et al.。

THE EUROPEAN PHYSICAL JOURNAL B

Eur.Phys.J.B1,327–331(1998)Eﬀect of surface electricﬁeld on the anchoringof nematic liquid crystalsG.Barbero1,a,L.R.Evangelista2,and N.V Madhusudana31Dipartimento di Fisica del Politecnico and Istituto Nazionale della Materia Corso Duca degli Abruzzi24,10129Torino,Italia 2Departamento de Fisica,Universitade Estadual de Maringa,Avenida Colombo3690,87020-900,Maringa,Parana,Brazil3Raman Research Institute,C.V.Raman Avenue,Bangalore560080,IndiaReceived:29September1997/Received inﬁnal from:10November1997/Accepted:18November1997Abstract.We analyse the inﬂuence of adsorbed ions and the resulting surface electricﬁeld and its gradienton the anchoring properties of nematics with ionic conductivity.We take into account two physical mech-anisms for the coupling of the nematic director with the surface electricﬁeld:(i)the dielectric anisotropyand(ii)the coupling of the quadrupolar component of theﬂexoelectric coeﬃcient with theﬁeld gradient.It is shown that for suﬃciently largeﬁelds near saturated coverage of the adsorbed ions,there can be aspontaneous curvature distortion in the cell even when the anchoring energy is inﬁnitely strong.We alsodiscuss the director distortion when the anchoring energy of the surface isﬁnite.PACS.61.30.-v Liquid crystals–61.30.Gd Orientational order of liquid crystals;electric and magneticﬁeld eﬀects on order–61.30.Cz Theory and models of liquid crystal structure1IntroductionAs in any other sample of condensed matter,the surface and interfacial properties of nematic liquid crystals(NLC) are rather complex.In many physical studies as well as practical devices like displays,it is necessary to anchor the orientation of the nematic director at appropriate sur-faces in speciﬁc directions.Several techniques have been invented for this purpose[1,2].In practice the anchor-ing has to be characterized by an angle dependent energy density and the simplest form proposed by Rapini and Pa-poular[3]consistent with the symmetry of the NLC has the following form:F s=−1a e-mail:barbero@polito.it devices the power consumption has to be reduced to the absolute minimum,and special care is taken to purify the sample.On the other hand,the eﬀect ofﬁnite conductiv-ity has very interesting consequences,for example leading to a‘nonlocal’character of the anchoring energy itself. Indeed there have been experimental studies[8,9]which have clearly demonstrated the necessity to take into ac-count the inﬂuence of adsorbed charges on the surfaces in understanding the anchoring properties as functions of thickness and conductivity.In theﬁrst theoretical models the attention was conﬁned to the coupling of the surface electricﬁeld produced by the adsorbed charges with the dielectric anisotropy of the medium.All liquid crystals haveﬂexoelectric properties,and in particular the nonzero quadrupole density arising out of the orientational order in the medium[10]couples with electricﬁeld gradients which can be quite large near the surfaces.In the present paper we will discuss the gen-eral electrostatic problem near surfaces which incorpo-rates both the dielectric andﬂexoelectric properties of the medium.The previous treatments of the problem[11–15] were based on the naive assumption that the dielectric and theﬂexoelectric torques are reduced to only surface con-tributions,ignoring the elastic torque completely.These were balanced by the torque due to the anchoring energy at the surface.In turn the problem was simply treated as a renormalization in the eﬀective anchoring energy. This approach implies that in the case of strong anchoring there cannot be an instability due to the surface electric ﬁeld.In this paper we present a more general analysis328The European Physical Journal B of this problem and show that even in the case of w→∞,a curvature instability can indeed occur above a thresholddouble layer potential.If w isﬁnite,the threshold poten-tial naturally gets reduced.2Theoretical modelWe consider the speciﬁc case of an NLC conﬁned betweentwo glass plates treated for homeotropic alignment,i.e.,the easy axis n0is along z,the normal to the surface.θ(z)is the polar angle made by the director with respect to thez-axis.The problem is considered to be one-dimensional,i.e.,we assume that the surface has uniform properties inthe xy-plane.As we mentioned in Section1,the medium isassumed to contain ionic impurities,and the surface selec-tively adsorbs one type of ions(usually positively charged)with an adsorption energy E.As is well known in the elec-trolyte theory,such an adsorption produces a counterioncloud over a depth L d,called the Debye screening length[16–18].In turn,there is an electricﬁeld which is verystrong near the surface(=E)and decays as we moveaway from it.As such,there is a fairly strongﬁeld gra-dient near the surface.In usual liquid crystals,L d d,where d is the thickness of the sample.Hence,it is suﬃ-cient to treat the case of a semi-inﬁnite sample boundedat z=0.The free energy density of the bulk NLC has thefollowing contributions:(i)the elastic part which is given byf el=12K33(n×∇×n)2;(2)(ii)dielectric coupling with the electricﬁeld given byf diel=−a2Kθ 2(z)−a2sin[2θ(z)]θ (z)E(z),(5)whereθ =dθ/d z and e=(e1+e3)is the sum of the two ﬂexoelectric coeﬃcients deﬁned in equation(4).The surface energy which is generally assumed to be of the Rapini-Papoular form given by equation(1)can have another contribution if the molecules are polar and the anchoring is homeotropic[19].It is now experimentally established that there is a surface polarization P s in such a case[20–22].The angle dependent part of the total surface energy density now becomes[23,24]f s=−12w cos2θ0−P s E0cosθ0,(6) whereθ0and E0are the values of the polar tilt angle and the electricﬁeld at the surface(z=0).Equation(6)was used to describe planar to homeotropic transitions at the nematic surface[25].The equilibrium conﬁguration in the bulk medium is given as usual by the Euler-Lagrange equation which yieldsKθ (z)−a2E (z)sin[2θ(z)]=0,(7) which has to be solved with the boundary conditions−Kθ +14πE2(z)+eE (z)θ=0,(10)for the Euler-Lagrange equation,and−Kθ +(eE0+w+P s E0)θ0=0,(11) for the boundary condition at z=0.We recall that the electricﬁeld E(z)is generated in the present problem because of the adsorbed ions on the surfaces and the counterion cloud forming the diﬀuse dou-ble layer in the liquid crystal.Theﬁeld distribution in this case is well known and it can be written to a very good approximation as[16]E(z)=E0exp(−z/L d).(12) The total energy for unit surface area is given byF=∞f d z+f s=∞18πE2(z)θ2(z)−eE(z)θ(z)θ (z)d z+1G.Barbero et al.:Surfaceﬁeld and anchoring energy329 3AnalysisTheﬁeld which acts as the source term for the instability(see Eq.(10))is localized close to the limiting surface atz=0.Thus it is appropriate to consider an approximatesolution of the formθ(z)=θ0+∆θ[1−exp(−z/L d)]=θb−∆θexp(−z/L d),(14)whereθb is the value ofθin the bulk(i.e.at z L d).The bulk energy density now takes the simple formf=12L d +a4πE20L dθb∆θ+eE0(∆θ)2,(17) and C=a4L d +eE032πE20L d+w+E0P s2+a16πE20L d+w+P s E0@(∆θ)=2α∆θ−βθb=0,(23)and∂F∂(∆θ)2=2α>0,(25) and the Hessian determinantH=∂2F∂θ2b−∂2F16πE20L d+2e2L d+w>0,(27)andK3+a4πE20L d+K3+a2+a2L d−4πa L d(29)and theﬁelds corresponding to zero crossings ofµaregiven by[26]E0=8πeθ8πea L2d.(30)We can now discuss diﬀerent possibilities.4.1Nematic with negative dielectric anisotropy, a<0In this case the term in the square root of equation(30)is always positive and larger in magnitude than theﬁrstterm.Hence in general there are two values of the surfaceﬁeld,one negative and another positive,corresponding todiﬀerent species of adsorbed charges,between which thehomeotropic anchoring is stable,and beyond which it getsdestabilized.If theﬂexoelectric coeﬃcient e is positive,thenegative thresholdﬁeld is much larger than the positive330The European Physical Journal B ﬁeld,and vice versa for a negative e.The physical meaningof these results is obvious:while a negative a leads to aninstability of the director if the electricﬁeld is large enoughand has either sign,theﬂexoelectric term stabilizes thehomeotropic alignment for one of the signs of theﬁeldgradient depending on its own sign.4.2Nematic with positive dielectric anisotropy, a>0In this case two possibilities have to be considered accord-ing to the value of a.If a<8πK(31)the term in the square root is still positive,but smaller in magnitude than theﬁrst term in equation(30).The insta-bility occurs for some value of theﬁeld,but the homeotro-pic alignment gets restabilized at a second higher thresh-oldﬁeld in view of the quadratic dependence of the stabi-lizing dielectric torque on theﬁeld.The sign of e decides the sign of theﬁeld for which the destabilization occurs: for positive e,E0also should be positive,i.e.theﬁeld gradient should be negative,and vice versa.If a>8πK(32)the term under the square root becomes negative and there cannot be any destabilization of the homeotropic alignment.The case when a=0will be discussed separately.5Threshold values forﬁnite anchoring energy When the anchoring energy isﬁnite,the zero crossings in relations(27,28)have to be numerically evaluated for given material parameters and the value of w.This has been done,and as can be expected,as w gets smaller,the thresholdﬁeld needed for instability becomes lower.For example,if w=10−2erg/cm2,which corresponds to an extrapolation length of∼0.5µm,which can be attained in the laboratory[8],and a=−1,P s=−10−3esu[23,24], L d=0.1µm[17,18],K=10−7dyn[27],the threshold double layer potential is about22mV for e=+5×10−4 esu and∼30mV for e=−5×10−4esu[28].These values are easily attained in conducting nematic liquid crystals [17,18].We consider now two simple limiting cases.5.1Threshold for a dielectrically isotropic mediumFor simplicity we assume that P s=0in further analysis. In this case,when a=0,the stability conditions equa-tions(27,28)read as2e2L d +w>0,(33)andK3w−eE02|e|K3e−3e2+2Kw3e+3e2+2KweL d.(38)E3is of course positive for positive e.This means that thethreshold occurs for a double layer potential[27,28]V th∼K5×10−4∼10−3stat V∼0.3V.(39)Indeed such voltages are possible across double layers[29].5.2Threshold for a nonﬂexoelectric mediumIn this case e=0and as before we assume P s=0.Nowthe instability threshold,which can occur only if a<0,is given by| a|2L d+w<0,(40)and−2a4πK12E20−KwL d| a|,(42)whose form is reminiscent of the condition for Freedericksztransition.Again we get a double layer threshold voltagefor a=−4to be V th∼1V;of the same order as in theprevious case.The above analysis shows that even when the anchor-ing energy w is considered to be inﬁnite,a suﬃcientlyG.Barbero et al.:Surfaceﬁeld and anchoring energy331strong surface electricﬁeld generated by adsorbed ions can lead to a destabilization of the homeotropic alignment.If the dielectric anisotropy is negative and theﬂexoelectric coeﬃcient e is positive,and the anchoring energy is mod-erate,the destabilizing double layer voltage can be quite low,of the order of0.1V,which can be easily attained in practical cases.Similar considerations are valid for planar alignment. In this case it is easier to destabilize nematic liquid crystals with positive a and for a positive surfaceﬁeld,materials with negative e.6ConclusionsWe have reexamined the inﬂuence of adsorbed ions on the orientation of nematic liquid crystals doped with ionic im-purities.The earlier approaches treated the problem only for the case of a weak surface anchoring,and treated the eﬀect of the double layer potential as a purely surface ef-fect,ignoring the elastic distortion in the bulk.In this approximation,the surface electricﬁeld just renormalizes theﬁnite anchoring energy at the surface and hence it does not inﬂuence the director proﬁle if the anchoring is strong.We have removed this limitation in our analysis and shown that the surface electricﬁeld can aﬀect the bulk orientation of the director by distorting the director pro-ﬁle near the surface.Indeed such a distortion is found even when w→∞.This destabilization has two origins,due to both the dielectric anisotropy coupling with E20,and to theﬂexoelectric coeﬃcient e=e1+e3coupling with the strongﬁeld gradient near the surface.For homeotropic anchoring,a positive sign of e leads to a destabilization of the director for a negativeﬁeld gradient and hence a positive surfaceﬁeld,and is the origin of destabilization in materials with positive a.In this case at a second larger threshold the director proﬁle gets restabilized in view of the E2-dependence of the dielectric coupling.In the case of negative dielectric anisotropy materials,such a restabi-lization is not possible.In fact it is often found that it is rather diﬃcult to get a homeotropic alignment of materi-als with negative dielectric anisotropy[29].We feel that the phenomena discussed in this paper can account for these experimental results.Many thanks are due to A.K.Zvezdin for useful discussions. This work has been partially supported by Istituto Nazionale della Materia and by Dipartimento di Fisica del Politecnico di Torino in the framework of the collaboration between Politec-nico di Torino and the Raman Research Institute.References1.J.Cognard,Mol.cryst.Liq.Cryst.Suppl.Ser.1,1(1982).2. B.Jerome,Rep.Prog.Phys.54,391(1991).3. A.Rapini,M.Papoular,J.Phys.Colloq.France30,C4-54(1969).4.K.Okano,J.Murakami,J.Phys.Colloq.France40,C3-525(1979).5.G.Barbero,G.Durand,in Liquid Crystals in ComplexGeometries,edited by G.P.Crawford,S.Zumer(Francis, Taylor,London,1996).6.H.Yokoyama,Mol.Cryst.Liq.Cryst.165,265(1988).7.G.Barbero,G.Durand,J.Phys.France,51,281(1990).8.L.M.Blinov,A.Yu.Kabaenkov,A.A.Sonin,Liq.Cryst.5,645(1989).9. B.Valenti,M.Grillo,G.Barbero,P.Taverna Valabrega,Europhys.Lett.12,407(1990).10.J.Prost,J.P.Marcerou,J.Phys.France38,315(1977).11. A.V.Kaznachev,A.A.Sonin,Soviet Phys.Solid State25,528(1983).12. A.A.Sonin,A.V.Kaznachev,Soviet Phys.Solid State26,486(1984).13.G.Barbero,G.Durand,Liq.Cryst.2,401,(1987).14. A.L.Alexe-Ionescu,G.Barbero,A.G.Petrov,Phys.Rev.E48,R1631(1993).15.V.G.Nazarenko,vrentovich,Phys.Rev.E49,R990(1994).16.J.Israelachvili,Intermolecular and Surface Forces(Aca-demic Press,London,1985).17.R.N.Thurston,J.Appl.Phys.55,4154(1984).18.R.N.Thurston,J.Cheng,R.B.Meyer,G.D.Boyd,J.Appl.Phys.56,264(1984).19.M.Osipov,T.J.Sluckin,S.J.Cox,Phys.Rev.E55,464(1997)20.P.Guyot-Sionnest,H.Hsiung,Y.R.Shen,Phys.Rev.Lett.57,2963(1986).vrentovich,T.Ya.Marusy,Yu.A.Reznikov,V.V.Sergan,Mol.Cryst.Liq.Cryst.192,239(1990).vrentovich,V.G.Nazarenko,V.V.Sergan,G.Durand,Phys.Rev.A45,6969(1992).23. A.G.Petrov,A.Derzhanski,Mol.Cryst.Liq.Cryst.Lett.41,41(1977).24.M.Monkade,Ph.Martinot-Lagarde,G.Durand,Euro-phys.Lett.2,299(1986).25.J.D.Parson,Phys.Rev.Lett.41,877(1978).26.Of course asθb=∆θwhen w→∞,the problem canbe simpliﬁed very much,and the total energy given by equation(19)is now of the form F=Γθ2b,whereΓis a quadratic expression in E0,and naturally w drops out of the problem.The zero crossings ofΓnow yield the thresh-old values for E0and they are exactly the same as in equa-tion(30).27.P.G.de Gennes,J.Prost,The Physics of Liquid Crystals(Clarendon Press,Oxford,1993).28.N.V.Madhusudana,G.Durand,J.Phys.Lett.France46,L-200(1985).29.G.Basappa,N.V.Madhusudana,to be published.。

美国1999高中物理竞赛题及答案

The values of some possibly useful constants are given below:
mass of electron mass of proton electronic charge speed of light Coulomb’s constant permittivity constant
[A] 0.85v
[B] 0.80v
[C] 0.75v
[D] 0.70v
[E] 0.65v
2. Hercules and Ajax horizontally push in the same direction on a 1200 kg crate. Hercules pushes with a force of 500 newtons and Ajax pushes with a force of 300 newtons. If a frictional force provides 200 newtons of resistance, what is the acceleration of the crate?
[A] (2/5)m
[B] 2m
[C] (5/2)m
[பைடு நூலகம்] 5m
[E] 10m
8. A large beach ball is dropped from the ceiling of a school gymnasium to the floor about 10 meters below. Which of the following graphs would best represent its velocity as a function of time?
permeability constant gravitational constant mass of Earth radius of Earth gravitational field speed of sound (200 C)

英国化学奥林匹克竞赛UKChO近5年真题汇总

曲网左ψ}≡矣闫刃型璇UKChO⅛N 4>αJ血254ff 3sl 阳 rS a H S i ^≡H I(UKCHO砂邨Mnfl-ZEII le ⅜w]B B 楙E左聊回醐-。

a -R )⅛Im w>回JΣΠH g ≡l 圈#茁昔肆砌召3聲-H IKI 俳4H ⅜≡O 命W >酸嶷曲呻何-»觀迪羽血÷2戏3課叶7髒聖样母7l g >κg l汞糰芽闫器関UKChO≡54ff刘墜□四那>+剤和就≥4ffs ≡報娜软測閒・血妙岂阳砂滋s ÷完弃—翦淆妙吸—T O CB一2・ThjSquestion ωa b o H detec-≡∙gm o φc u φs ΞSeptember 224∙ the BBC announced 59l r a d k >astronomers had discovered -he ・30ω→ ComP 一exmolecce ∙O da φ≡∙SPaC e ∙FOUnd in .Sagittahus- B2(N)∙—Ihe ωrg e sαstar-forming region 3OUr GalaXy IthiSis -he firsi molecule defected ∖M ≡abranched CarbonChaim The SyStematiC namefor-he molecuφis 2∙me3y1propane Mrile∙ -tWaSfoundiobeA nitrileis ω molecule in WhiChOne Of-heCarbonShas a=iple bond-Onitrogen,(a) (D=)DraW the StrUC c r e and g_ve 5esysαemabcnameOfanothernitrile .SomedcWHh2,me-<PΓOPanenMle .AS=OnomerS are nowIooking for the nextSerieSOfnit2esWith5eformuωCSHD N ・(b)DraWa 一二heISOmehC nitriles Wi 5the formuωCSH ⅛∙ MoSiOfthemo_ecu_es defectedby radk>-as≡τonomers 3∙IeSS ac-iveregions OfSPaCe φn d O have -5'e arstructures Theωrges -So farde-ectedhas ≡eUn-ike-y ∙look5∙gfornluωH p z∙(C)DraW -he S-HJCtUreOf ≡e-inear moφcu φWiih ≡e formula X o --z ∙The Signa-S de-ec-ed 55eradio WaVeregionOf 5e elec-romagneuc SPeCtrUm are due OKansibons between r θa t δ∙n a - energy-e v e ω・each OfWhiCh has ω PartiCU ωr energy, Mo-ecu-es have many roiauona- energy -eve-s avai_ab_e ~0 Ihem ・ each -eve-With a different energy beingSPeCmed by ≡e SO-Ca 一Ied65Γb o n ωquancm number ∙ J. WhiCh ωk e s ≡,一eger <ωE φω fromO UPWards ・Theenergy (3∙jou_es) Of≡e S rog o-na -energy-eveLEyisgivenbythefofmu-ω EJ關h ×BX J(JH)WhereBU ≡erotauonωConStasOf 一he3o-φ0⊂-φ (inHZ)h Mp-anck ∙sCOnSta H M 6.626×12∙Js ・ and一<≡∙3OffreqUenCyf(HZ)hasenergy hM f oou-es) TWO Signa ωhavebeendetected due一oZ o l z - O s e2016年考题2. ThlS question is about the ChOmiStry Of tungstenThe ChemIStry Of the transition metal tungsten has Cenain SimilaritieS to that Of the mai∩∙group element SUlfUr SinCe both atoms have a total Of SiX VaIenCeelectrons. BOth elements reach their maximum ÷6 OXidatiOnStateS when COmblned Wrth electronegative elementsfluorine and OXygeITWhilSt tungsten(VI) fluonde is USed in the Semi∞nductorindustry, the OXide is USed in electrochromic windows.TheSe Change ∞lour When an electrical VOltage is applied,as ShOWn in the airσaft WindOWS On the right.MoSt tungsten OCCUfS naturally in the tungstate anion,WO42", analogous to the sulfate. SO42". A COmmOn tungsten mineral is Scheelite, CaICiUm tungstate, CdWO4.(a)DraW a StrUctUre ShOWing the bonding in the WθΛ ion and give the O-W-O bond angle.Treatment Of SCheellte Wlth aqueous SOdiUm CarbOnate gives a SOlutKXI Of SOdiUm tungstate and a White insoluble salt. AdditiOn Of hydrochloric add to aqueous SOdiUm tungstate PrOdUCeS tungstic acid. WhiCh On heating gives Iungsten(VI) oxide. ThiS may be reduced Wrth hydrogen to give PUre UJngSten metal.(b)(i) GiVe the equation for the reaction between SCheeIite and aqueous SodiUmCart)Onate.(ii) GiVe the equation for the reactiOn Of aqueous SOdiUm tungstate Wrth hydrochloric acid and SUggeSt a StrUctUre for tungstic acid・(Iii) GiVe the equation for the formation Of tungsten(VI) OXKje from tungstic aαd.(iv) GiVe the equation for the (OrmatiOn tungsten metal.In electrochromic Windows. a VOltage is applied between a WanSParent Iayer Of Iungsten(VI) OXkje and a SOUrCe Of ions SUCh as a IrthIUm SaIt・and the following reacbo∩ takes PIaCe during wħich SOme Of the IrthiUm ions are in∞rporated into the StrUCtUre Of the oxide:WO3÷ xU* ÷ Xe- ---------- ► LiXWo3The PrOdUct t Li1WO3. is known as a tungsten bronze, and its ColoUr depends On the ValUe Of x. The VaIUe Of X Can Vary from O to 1： a typical ValUe giving a blue-black COlOUr is When X = 0.3.(C) (i) CaIcUlate the OXidatiOn State Of the tungsten When X= 1 ・(ii) CakXIIate the average OXidatiOn State Of the tungsten When X = 0.3.BOth elemental SUlfUr and tungsten react Wrth fluorir»e gas to form the hexafluorides. SFe and WF6are both gases at r∞m temperature and PreSSUre. Wrth WF6being the most dense gas known Underthese ∞nditio∩s. WF6is extremely toxic due to its rapid reaction With Water to form twoSUbStances. In COntrast, SF6is inert in Water and non-toxic・(d)By assuming air to be made UP Of nItrOgen gas OnM CaICUlate the densities Of SF e and WF6relative to air.(e)CaleUlate the actual density Of WFβ(g) in g cm"3 at 298 K and Standard PreSSUre.(f)SUggeSt an equation for the reaction Of WF e Wfth water.2017年考题ThiS question is about the Green POOl Of RiOWhen the Water in the diving PoOI at the RiO OlymPiC GameS turned green, it WaS SUggeSted that Ihe growth Of algae WaS to blame; this WaS StrOngM COnteSted by the organisers. EVen after Ihe OffiCial report WaS PUbliShed t there is StiIl much SPeCUIation as to theactual reason behind the ∞tour Change-One Of the most COmmOnfy USed ComPOUndS in thechlorination Of SWimming POoIS is SOdiUmhypochlorite・ NaCIO.(a)Determine the OXidatiOn State Of ChiOrine inSOdiUm hypochlorite, NaelO.OnCe dissolved, an equilibrium is established between CIO" and its COnjUgate acid.(b)GrVe an equation for this equilibrium.ThiS equilibrium is highly PH dependent and Un der acidic co nd tons ChIOrine is produced.(C) GiVe an equation for the generation Of cħlorine from hypochlorite and HCLThe Organisers eventually explained the green COlOUr in the POOI as being due to the growth Of algae after the i∩advertent addition Of a Iarge quantity Of hydrogen PerOXide. WhiCh destroyed thehypochk>rrte and formed ChlOride ions.(d)GiVe an equation for the reaction between hydrogen PeroXkJe and hypochlorite.KyPoChlOrrteS also have a tendency to react Wrth ammonia and ammonia-like ComPOUndS to form ∞mpou∩ds COntaining nitrogen and ChlOnne. One SUCh COmPOUnd is nitrogen trichloride. WhiCh Can CaUSe eyeirritation and Ihe distinctive SmeIl Of Swimmlng p∞ls(e)(i) GiVe an equation for the formation Of nitrogen trichloride.(ii) DraW a StrUCtUre for nitrogen trichloride, ShOWing its shape, and State the approximate CkN-Cl bond angle.DePending On reacting ratios, another POSSibIe OUtCOme Of Ihe reaction between ammonia and hypoChlorrte is the formation Of hydrazine. H2N-NH2. and ChlOride ions.(O GrVe an equation for this reaction.COPPer(II) SUtfate is SOmetimeS added to SWimming POOIS and this WaS also suggested as the CaUSe Of the green ∞lour. COPPer(II) ions Wefe also blamed for the green t int given to Ihe bleached hair Of the AmeriCan SWimmer Ryan LoChte・ The COPPer(Il) ions precipitate On the hair due to the high PH OfCertain sħamp∞s・(g)SUggeSt a formula for the blue PreCiPitate On Ryan LOChte,s h.2018年考题4. ThiS question is about COUgh SUPPreSSantSIn SePtember 2017. the UK Prime MiniSter l ThereSa May, had a bad ∞υgh during her SPeeCh at the ConSerVatiVe Party COnferenCe- The COUgh suppressant drugOextromethorphan, WhiCh is PreSent in ∞ugh remedies SUCh as BenyIin®. CoUld have helped her out. ThiS questiOn is about the SyntheSlS Of dextromethorphan. The SyntheSiS involves the formation Of SOme Str(Jng b∞ds and SOme StabIe CarbOCations.DeXtromethorphan is Onen administered as the hydrobromide monohydrate salt.(a) In the anSWer b∞k. Ci rCle the atom in dextromethorphan that is PrOtOnated in the salt. (b) Determine the molecular formula Of dextromethorphan and hence CaIaJlate Ihe molar mass Of thedextromethorphan hydrobromkie monohydrate salt. The SyntheSiS Of dextRxnethorphan takes a number Of StePS. PteaSe note that in the SChemeS describing the Synthesis, by-products Of the reactions are not always shown.The SyntheSiS Of dextromethorphan begins With the SyntheSiS Of COmPoUnd F.1 MgS∞h ICO 2 SOCh ------------------------ COmPOUnd A ■ COmPOUnd B 3 M ZMzOIR 3100 Cm t (v9rybΦM1716 Cm ' (3hΛφ)A COmPOUnd D c ∙ - W 2 HZH 2O♦ CoIOUrIeSS gas X π⅞o∕∙ mass of 44 01 g moi 1COnIPOUnd C♦COmPOUnd ECOmPOUnd FDraW the StUCtUreS Of COmPOUndS A. B. C. D. E and g‘COmPOUnd CCOmPOUnd EO δ2019年考题4・ ThiS question is about CarbOn dioxideThe food and drink industries USe a IOt OfCarbon dioxide DUring SUmmer 2018, a globalShOrtage Ied to SUPermarketS Iimiting frozenfood deliveries and ratbning beer. ThiS isironic COnSidering the do∞mented rise Ofatmospheric CO2 IeVeIs.(a) (i) DraW dot and CrOSS diagrams forCarbon dioxide and CartXXI monoxide.(Ii) CalaJlate the difference in the OXIdatiOn State between the CarbOnS in CarbOn dioxide and in CarbOn monoxide・The EngIiSh ChemiSt WiIliam Henry StUdied the equilibria When a gas dissolves in a IiqUid He PrOPOSed Ihat Ihe ConCentratiOn Of a gas dissolved in a IlqUld IS ProPOrt)Onal to the gas' PartiaI PreSSUre When in the gas phase. The PrOPOrti∞alrty fac tor is CaIIed the Henry l S IaW ∞nstant. The Henry S IaW ConStant for 82 is 3.3 × 1(Γ2 mol dm'3 atm"1.SeaIed COntainerS Of fizzy drinks COntain dissolved CQ. ThiS dissolved CO： is in equilibrium With a SmaIl quantity Of gase∞s CQ at the top Of the COn tain er.(b) (i) The Partial PreSSUre Of CO2gas in a 250 αn3 Can Of fizzy drink is 3.0 atm at25 0C. What is the COnCentratiOn Of CO2 in the fizzy drink?(H) What mass Of CO2 is ClISSOIVed in a 250 cm3 Can Of fizzy drink?(III)If the Can c∞ta∣ned Onty the mass Of C O? CaICUIated in Part (O) as a gas. CaIaJlate the PreSSUre in Ihe Can When it is StOred at 25 °C.(IV)Under What ∞nditio∩s WoUId CO2 gas be most SOlUble jn water?TiCk the COrreet OPtiOn in the anSWer b∞klet:•high PreSSUre and IOW temperature•high PreSSUre and high temperature•IoW PreSSUre and IOW temperature•IOW PreSSUre and high temperature2020年考题2. ThiS question is about hydrogen as a fuelCart)On dioxide emissions from fossil fuelsare a major factor in Climate change.Hydrogen is a Potenual alternative tofossil fuels. PrOViding ,dean energy* WrthOnly Water as a byproduct. The UK govemmentis in vestIgatlng COnVeftIng the naturalgas ghd to Carry hydrogen instead.FOr this question・ assume all PrOCeSSeStake PIaCe at 298 K.EnthaIPy Change Of formation Of CH4(g). ∆∕^f = -74.8 kJ moΓ'EnthaIPy Change Of formation Of CO?(g). Δ∕Λ = -393.5 kJ moΓ1EnthaIPy Change Of (Ofmation Of H2O(∣> ∆∕^f ≡ -285 8 kJ mol*1EntroPy Change Of formation Of H2O(I). ∆^e f = -163.0 J K*1moΓ1One IOW COSt method for PrOdUCing hydrogen is reforming methane. ThoUgh this PrOdUCeS CO2, this Can be easily captured. The reforming ProCeSS Can be represented by the OVeraH reaction:CH4(g) ÷ 2H2O(I) -→ CO2(g) + 4H2(g)(a) CalCUIate the enthalpy Change for this reaction.EleCtr OIySiS Of Water is another method Of producing hydrogen On a Iarge SCaIe .it OJrrently ∞sts more than reforming methane.In POIymer electrolyte membrane electrolysts, PfOlOnS are transferred thr∞gh a membrane between Ihe two electrodes. The two half reactions are:1.2H2O(l) → O2(g) + 4Hφ(aq) + 4eβ2.2H∙(aq) ÷ 2e" → H2(g)WhiCh Of these half reactions OCeUrS at the cathode?。

RD活动的就业效应：基于中国数据的实证分析

R&D活动的就业效应基于中国数据的实证分析论文导读:：的一份失业研究报告显示。

是技术进步（胡鞍钢。

就业形势严峻。

就技术落后国家的实际情况而言。

论文关键词：R&，D，技术进步，就业，技术落后一、引言2009年，我国城镇登记失业人数首次突破900万，就业形势严峻。

CICC（中国国际金融有限公司）2010年公布的宏观经济形势预测显示，中国劳动力市场2011年劳动力供给可能增长3900万，其中包括了2500万失去与之前4万亿经济刺激计划相关联工作的临时工；与此同时，新增就业岗位可能只有800万个，就业压力明显。

奥肯定律表明，经济增长率与失业率之间存在着一种稳定的关系，诸多经验研究也证实了该关系在美国曾长期存在。

国内学者运用中国数据进行检验时，却得出奥肯定律在中国并不适用的结论；另一方面，通过对就业弹性的考察发现，我国经济增长的就业弹性自上世纪90年代开始呈现出下降趋势毕业论文模板，2005年之后的就业弹性徘徊在0.06-0.08之间，说明我国经济增长创造就业的能力在下降，中国经济进入“无就业增长”[①]时代。

归纳国内学者对“无就业增长”原因的研究，主要存在三种观点：一是经济体制改革（齐建国、常进雄；常云昆等）；二是产业结构转变（蔡昉、都阳；谌新民等）；三是技术进步（胡鞍钢；袁志刚；张军等）。

早在1994年，OECD的一份失业研究报告显示，增加就业不能从放弃技术进步，实施保护主义中寻找解决途径，而应从改进市场流动性，恢复经济与社会适应变化的能力来增加就业，在其对策建议中，首先就是加强技术知识的创造和扩散。

作为实现技术进步的最基本手段，将R&D活动纳入到分析就业问题中具有一定的理论意义和现实意义。

本文旨在明确R&D活动与就业之间是否存在一定的关系？其具体的传导途径是什么？并结合技术落后国家（中国）的实际情况进行理论与实证分析。

本文接下来的安排是：第二部分是R&D、技术进步与就业的相关文献综述；第三部分是所需变量的选取及测算；第四部分是实证分析；最后是本文的相关结论中国期刊全文数据库。

1999滑铁卢竞赛试题答案

( x – 2)( x + 1) = 0
∴ x = 2 or x = –1
Solution 2 1 6 x2 – x – 6 1– – 2 = x x x2 x 2 – x – 2) – 4 ( = x2 –4 2 2 (since x – x – 2 = 0 ) x 2 But x – x – 2 = ( x – 2)( x + 1) = 0 ∴ x = 2 or x = –1. x = –1, Substituting x = 2, or –4 –4 = 4 1 = –1. = –4 =
y
6
–3
–1 O
x
Solution 3 Let the equation of the parabola be y = a( x + 2)2 + c . Since (0, 6) is on parabola, 6 = 4 a + c , and ( –1, 0) is on parabola, 0 = a + c . Solving, a = 2, c = – 2. ∴ Equation is y = 2( x + 2)2 – 2 . 3. (a) How many equilateral triangles of side 1 cm, placed as shown in the diagram, are needed to completely cover the interior of an equilateral triangle of side 10 cm?
(b)
If the point P( – 3, 2) is on the line 3 x + 7ky = 5 , what is the value of k? Solution Since P is on the line, its coordinates must satisfy the equation of the line. Thus, 3( – 3) + 7k (2) = 5 14 k = 14 k =1

大学英文成绩单模板

Note:
Compulsor y
Elective
xxxx xxxx
xxxx xxxx
Selected
xx xx
Total xx xx
Note:
GPA Qualification Result
xxx Date of Graduation:
xxxxxxxxx
No. of Graduate Certificate
xx
xx xx xx xx xx xx
International Trade Formal Logic
3 70 Career Instruction 2 78 Mandarin
xx xx
Compulsory Courses
Total Credits
Specialty Elective Courses
x xx x xx x xx x xx
xx xx xx xx
x Practise of International Trade
x xx x x
x History of Taxes in China x Property Assessment
xx
Economics
x x xx xx xx xx xx
xx xx
Political Economics Deng Xiaoping's Theory Foundamentals of Computer Accounting
xxxx xx
Microeconomics
xx xx Probablity Theory & Mathematical Statistics
Student ID Number: XXXXXXX

1999-468-EC

COUNCIL DECISIONof17July2006amending Decision1999/468/EC laying down the procedures for the exercise of implementingpowers conferred on the Commission(2006/512/EC)THE COUNCIL OF THE EUROPEAN UNION,Having regard to the Treaty establishing the European Community,and in particular the third indent of Article202 thereof,Having regard to the proposal from the Commission,Having regard to the Opinion of the European Parliament(1),Whereas:(1)The Council adopted Decision1999/468/EC of28June1999laying down the procedures for the exercise ofimplementing powers conferred on the Commission(2).That Decision provided for a limited number ofprocedures for the exercise of such powers.(2)That Decision should be amended in order to introduce anew type of procedure for the exercise of implementingpowers,the regulatory procedure with scrutiny,whichallows the legislator to oppose the adoption of draftmeasures where it indicates that the draft exceeds theimplementing powers provided for in the basicinstrument,or that the draft is incompatible with theaim or the content of that instrument or fails torespect the principles of subsidiarity or proportionality.(3)It is necessary to follow the new regulatory procedurewith scrutiny for measures of general scope designed toamend non-essential elements of a basic instrumentadopted in accordance with the procedure referred toin Article251of the Treaty,including by deletingsome of those elements or by supplementing theinstrument by the addition of new non-essentialelements.(4)In this same framework,it should be ensured that theEuropean Parliament receives better information on thework of committees,HAS DECIDED AS FOLLOWS:Article1Decision1999/468/EC is hereby amended as follows:1.at the end of recital5,the following shall be added:‘with the exception of those governing the regulatory procedure with scrutiny’;2.after recital(7),the following recital shall be inserted:‘(7a)It is necessary to follow the regulatory procedure with scrutiny as regards measures of general scope whichseek to amend non-essential elements of a basicinstrument adopted in accordance with theprocedure referred to in Article251of the Treaty,inter alia by deleting some of those elements or bysupplementing the instrument by the addition of newnonessential elements.This procedure should enablethe two arms of the legislative authority to scrutinisesuch measures before they are adopted.The essentialelements of a legislative act may only be amended bythe legislator on the basis of the Treaty;’;3.recital(10)shall be replaced by the following:‘(10)The third purpose of this Decision is to improve information to the European Parliament byproviding that the Commission should inform it ona regular basis of committee proceedings,that theCommission should transmit to it documents relatedto activities of committees and inform it whenever theCommission transmits to the Council measures orproposals for measures to be taken;particularattention will be paid to the provision of informationto the European Parliament on the proceedings ofcommittees in the framework of the regulatoryprocedure with scrutiny,so as to ensure that theEuropean Parliament takes a decision within thestipulated deadline.’;4.in Article1:‘5a’shall be inserted between‘5’and‘and6’in the last line;(1)Not yet published in the Official Journal.(2)OJ L184,17.7.1999,p.23.5.in Article2:(a)in the first paragraph the words‘1.Without prejudice toparagraph2,’shall be inserted at the beginning of thetext;(b)the following paragraph shall be added:‘2.Where a basic instrument,adopted in accordancewith the procedure referred to in Article251of theTreaty,provides for the adoption of measures ofgeneral scope designed to amend non-essentialelements of that instrument,inter alia by deleting someof those elements or by supplementing the instrument bythe addition of new non-essential elements,thosemeasures shall be adopted in accordance with the regu-latory procedure with scrutiny.’;6.in Article4(2)and Article5(2),the terms‘and(4)’shall beadded after‘Article205(2)’;7.after Article5,the following Article shall be inserted:‘Article5aRegulatory procedure with scrutiny1.The Commission shall be assisted by a RegulatoryProcedure with Scrutiny Committee composed of the repre-sentatives of the Member States and chaired by the repre-sentative of the Commission.2.The representative of the Commission shall submit tothe Committee a draft of the measures to be taken.The Committee shall deliver its opinion on the draft within a time-limit which the chairman may lay down according to the urgency of the matter.The opinion shall be delivered by the majority laid down in Article205(2)and(4)of the Treaty in the case of decisions which the Council is required to adopt on a proposal from the Commission.The votes of the representatives of the Member States within the Committee shall be weighted in the manner set out in that Article.The chairman shall not vote.3.If the measures envisaged by the Commission are inaccordance with the opinion of the Committee,the following procedure shall apply:(a)the Commission shall without delay submit the draftmeasures for scrutiny by the European Parliament andthe Council;(b)the European Parliament,acting by a majority of itscomponent members,or the Council,acting by a qualified majority,may oppose the adoption of the said draft by the Commission,justifying their opposition by indicating that the draft measures proposed by the Commission exceed the implementing powers provided for in the basic instrument or that the draft is not compatible with the aim or the content of the basic instrument or does not respect the principles of subsi-diarity or proportionality;(c)if,within three months from the date of referral to them,the European Parliament or the Council opposes the draft measures,the latter shall not be adopted by the Commission.In that event,the Commission may submit to the Committee an amended draft of the measures or present a legislative proposal on the basis of the Treaty;(d)if,on expiry of that period,neither the EuropeanParliament nor the Council has opposed the draft measures,the latter shall be adopted by the Commission.4.If the measures envisaged by the Commission are not in accordance with the opinion of the Committee,or if no opinion is delivered,the following procedure shall apply:(a)the Commission shall without delay submit a proposalrelating to the measures to be taken to the Council and shall forward it to the European Parliament at the same time;(b)the Council shall act on the proposal by a qualifiedmajority within two months from the date of referral to it;(c)if,within that period,the Council opposes the proposedmeasures by a qualified majority,the measures shall not be adopted.In that event,the Commission may submit to the Council an amended proposal or present a legi-slative proposal on the basis of the Treaty;(d)if the Council envisages adopting the proposed measures,it shall without delay submit them to the European Parliament.If the Council does not act within the two-month period,the Commission shall without delay submit the measures for scrutiny by the European Parliament;(e)the European Parliament,acting by a majority of itscomponent members within four months from the forwarding of the proposal in accordance with point(a),may oppose the adoption of the measures inquestion,justifying their opposition by indicating that the proposed measures exceed the implementing powers provided for in the basic instrument or are not compatible with the aim or the content of the basic instrument or do not respect the principles of subsi-diarity or proportionality;(f)if,within that period,the European Parliament opposesthe proposed measures,the latter shall not be adopted.In that event,the Commission may submit to the Committee an amended draft of the measures or present a legislative proposal on the basis of the Treaty;(g)if,on expiry of that period,the European Parliament hasnot opposed the proposed measures,the latter shall be adopted by the Council or by the Commission,as the case may be.5.By way of derogation from paragraphs3and4,a basic instrument may in duly substantiated exceptional cases provide:(a)that the time-limits laid down in paragraphs3(c),4(b)and4(e)shall be extended by an additional month,when justified by the complexity of the measures;or(b)that the time-limits laid down in paragraphs3(c),4(b)and4(e)shall be curtailed where justified on the grounds of efficiency.6.A basic instrument may provide that if,on imperative grounds of urgency,the timelimits for the regulatory procedure with scrutiny referred to in paragraphs3,4and 5cannot be complied with,the following procedure shall apply:(a)if the measures envisaged by the Commission are inaccordance with the opinion of the Committee,theCommission shall adopt the measures,which shall imme-diately be implemented.The Commission shall withoutdelay communicate them to the European Parliament andto the Council;(b)within a time-limit of one month following that commu-nication,the European Parliament,acting by a majorityof its component members,or the Council,acting by aqualified majority,may oppose the measures adopted bythe Commission,on the grounds that the measuresexceed the implementing powers provided for in thebasic instrument or are not compatible with the aim orthe content of the basic instrument or do not respect theprinciples of subsidiarity or proportionality;(c)in the event of opposition by the European Parliament orthe Council,the Commission shall repeal the measures.Itmay however provisionally maintain the measures inforce if warranted on health protection,safety or envi-ronmental grounds.In that event,it shall without delaysubmit to the Committee an amended draft of themeasures or a legislative proposal on the basis of theTreaty.The provisional measures shall remain in forceuntil they are replaced by a definitive instrument.’.8.In Article7(3)at the end of the first sentence,the followingshall be added:‘following arrangements which ensure that the transmission system is transparent and that the information forwarded and the various stages of the procedure are identified.’.Article2This Decision shall take effect on the day following that of its publication in the Official Journal of the European Union.Done at Brussels,17July2006.For the CouncilThe PresidentE.TUOMIOJA。

DIRECTIVE 2002-95-EC RoHS

DIRECTIVE2002/95/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCILof27January2003on the restriction of the use of certain hazardous substances in electrical and electronic equipmentTHE EUROPEAN PARLIAMENT AND THE COUNCIL OF THE EUROPEAN UNION,Having regard to the Treaty establishing the European Commu-nity,and in particular Article95thereof,Having regard to the proposal from the Commission(1),Having regard to the opinion of the Economic and Social Committee(2),Having regard to the opinion of the Committee of Regions(3),Acting in accordance with the procedure laid down in Article 251of the Treaty in the light of the joint text approved by the Conciliation Committee on8November2002(4),Whereas:(1)The disparities between the laws or administrativemeasures adopted by the Member States as regards therestriction of the use of hazardous substances in elec-trical and electronic equipment could create barriers totrade and distort competition in the Community andmay thereby have a direct impact on the establishmentand functioning of the internal market.It thereforeappears necessary to approximate the laws of theMember States in this field and to contribute to theprotection of human health and the environmentallysound recovery and disposal of waste electrical and elec-tronic equipment.(2)The European Council at its meeting in Nice on7,8and9December2000endorsed the Council Resolution of4December2000on the precautionary principle.(3)The Commission Communication of30July1996onthe review of the Community strategy for waste manage-ment stresses the need to reduce the content of hazar-dous substances in waste and points out the potentialbenefits of Community-wide rules limiting the presenceof such substances in products and in productionprocesses.(4)The Council Resolution of25January1988on aCommunity action programme to combat environmentalpollution by cadmium(5)invites the Commission topursue without delay the development of specificmeasures for such a programme.Human health also hasto be protected and an overall strategy that in particularrestricts the use of cadmium and stimulates research intosubstitutes should therefore be implemented.The Reso-lution stresses that the use of cadmium should be limitedto cases where suitable and safer alternatives do notexist.(5)The available evidence indicates that measures on thecollection,treatment,recycling and disposal of wasteelectrical and electronic equipment(WEEE)as set out inDirective2002/96/EC of27January2003of theEuropean Parliament and of the Council on waste elec-trical and electronic equipment(6)are necessary toreduce the waste management problems linked to theheavy metals concerned and the flame retardantsconcerned.In spite of those measures,however,signifi-cant parts of WEEE will continue to be found in thecurrent disposal routes.Even if WEEE were collectedseparately and submitted to recycling processes,itscontent of mercury,cadmium,lead,chromium VI,PBBand PBDE would be likely to pose risks to health or theenvironment.(6)Taking into account technical and economic feasibility,the most effective way of ensuring the significant reduc-tion of risks to health and the environment relating tothose substances which can achieve the chosen level ofprotection in the Community is the substitution of thosesubstances in electrical and electronic equipment by safeor safer materials.Restricting the use of these hazardoussubstances is likely to enhance the possibilities andeconomic profitability of recycling of WEEE anddecrease the negative health impact on workers in recy-cling plants.(7)The substances covered by this Directive are scientificallywell researched and evaluated and have been subject todifferent measures both at Community and at nationallevel.(8)The measures provided for in this Directive take intoaccount existing international guidelines and recommen-dations and are based on an assessment of availablescientific and technical information.The measures arenecessary to achieve the chosen level of protection of(1)OJ C365E,19.12.2000,p.195and OJ C240E,28.8.2001,p.303.(2)OJ C116,20.4.2001,p.38.(3)OJ C148,18.5.2001,p.1.(4)Opinion of the European Parliament of15May2001(OJ C34E,7.2.2002,p.109),Council Common Position of4December2001(OJ C90E,16.4.2002,p.12)and Decision of the European Parlia-ment of10April2002(not yet published in the Official Journal).Decision of the European Parliament of18December2002andDecision of the Council of16December2002.(5)OJ C30,4.2.1988,p.1.(6)See page24of this Official Journal.human and animal health and the environment,havingregard to the risks which the absence of measures wouldbe likely to create in the Community.The measuresshould be kept under review and,if necessary,adjustedto take account of available technical and scientific infor-mation.(9)This Directive should apply without prejudice toCommunity legislation on safety and health require-ments and specific Community waste management legis-lation,in particular Council Directive91/157/EEC of18March1991on batteries and accumulators containingcertain dangerous substances(1).(10)The technical development of electrical and electronicequipment without heavy metals,PBDE and PBB shouldbe taken into account.As soon as scientific evidence isavailable and taking into account the precautionary prin-ciple,the prohibition of other hazardous substances andtheir substitution by more environmentally friendly alter-natives which ensure at least the same level of protectionof consumers should be examined.(11)Exemptions from the substitution requirement should bepermitted if substitution is not possible from the scien-tific and technical point of view or if the negative envir-onmental or health impacts caused by substitution arelikely to outweigh the human and environmental bene-fits of the substitution.Substitution of the hazardoussubstances in electrical and electronic equipment shouldalso be carried out in a way so as to be compatible withthe health and safety of users of electrical and electronicequipment(EEE).(12)As product reuse,refurbishment and extension of life-time are beneficial,spare parts need to be available.(13)The adaptation to scientific and technical progress of theexemptions from the requirements concerning phasingout and prohibition of hazardous substances should beeffected by the Commission under a committee proce-dure.(14)The measures necessary for the implementation of thisDirective should be adopted in accordance with CouncilDecision1999/468/EC of28June1999laying downthe procedures for the exercise of implementing powersconferred on the Commission(2),HAVE ADOPTED THIS DIRECTIVE:Article1ObjectivesThe purpose of this Directive is to approximate the laws of the Member States on the restrictions of the use of hazardous substances in electrical and electronic equipment and to contri-bute to the protection of human health and the environmen-tally sound recovery and disposal of waste electrical and elec-tronic equipment.Article2Scope1.Without prejudice to Article6,this Directive shall apply to electrical and electronic equipment falling under the cate-gories1,2,3,4,5,6,7and10set out in Annex IA to Direc-tive No2002/96/EC(WEEE)and to electric light bulbs,and luminaires in households.2.This Directive shall apply without prejudice to Commu-nity legislation on safety and health requirements and specific Community waste management legislation.3.This Directive does not apply to spare parts for the repair, or to the reuse,of electrical and electronic equipment put on the market before1July2006.Article3DefinitionsFor the purposes of this Directive,the following definitions shall apply:(a)‘electrical and electronic equipment’or‘EEE’means equip-ment which is dependent on electric currents or electro-magnetic fields in order to work properly and equipment for the generation,transfer and measurement of such currents and fields falling under the categories set out in Annex IA to Directive2002/96/EC(WEEE)and designed for use with a voltage rating not exceeding1000volts for alternating current and1500volts for direct current;(b)‘producer’means any person who,irrespective of the sellingtechnique used,including by means of distance communi-cation according to Directive97/7/EC of the European Parliament and of the Council of20May1997on the protection of consumers in respect of distance contracts(3):(i)manufactures and sells electrical and electronic equip-ment under his own brand;(ii)resells under his own brand equipment produced by other suppliers,a reseller not being regarded as the‘producer’if the brand of the producer appears on theequipment,as provided for in subpoint(i);or (iii)imports or exports electrical and electronic equipment on a professional basis into a Member State. Whoever exclusively provides financing under or pursuant to any finance agreement shall not be deemed a‘producer’unless he also acts as a producer within the meaning of subpoints(i) to(iii).(1)OJ L78,26.3.1991,p.38.Directive as amended by CommissionDirective98/101/EC(OJ L1,5.1.1999,p.1).(2)OJ L184,17.7.1999,p.23.(3)OJ L144, 4.6.1997,p.19.Directive as amended by Directive2002/65/EC(L271,9.10.2002,p.16).Article4Prevention1.Member States shall ensure that,from1July2006,new electrical and electronic equipment put on the market does not contain lead,mercury,cadmium,hexavalent chromium,poly-brominated biphenyls(PBB)or polybrominated diphenyl ethers (PBDE).National measures restricting or prohibiting the use of these substances in electrical and electronic equipment which were adopted in line with Community legislation before the adoption of this Directive may be maintained until1July 2006.2.Paragraph1shall not apply to the applications listed in the Annex.3.On the basis of a proposal from the Commission,the European Parliament and the Council shall decide,as soon as scientific evidence is available,and in accordance with the prin-ciples on chemicals policy as laid down in the Sixth Commu-nity Environment Action Programme,on the prohibition of other hazardous substances and the substitution thereof by more environment-friendly alternatives which ensure at least the same level of protection for consumers.Article5Adaptation to scientific and technical progress1.Any amendments which are necessary in order to adapt the Annex to scientific and technical progress for the following purposes shall be adopted in accordance with the procedure referred to in Article7(2):(a)establishing,as necessary,maximum concentration valuesup to which the presence of the substances referred to in Article4(1)in specific materials and components of elec-trical and electronic equipment shall be tolerated;(b)exempting materials and components of electrical and elec-tronic equipment from Article4(1)if their elimination or substitution via design changes or materials and compo-nents which do not require any of the materials or substances referred to therein is technically or scientifically impracticable,or where the negative environmental,health and/or consumer safety impacts caused by substitution are likely to outweigh the environmental,health and/or consumer safety benefits thereof;(c)carrying out a review of each exemption in the Annex atleast every four years or four years after an item is added to the list with the aim of considering deletion of materials and components of electrical and electronic equipment from the Annex if their elimination or substitution via design changes or materials and components which do not require any of the materials or substances referred to inArticle4(1)is technically or scientifically possible,provided that the negative environmental,health and/or consumer safety impacts caused by substitution do not outweigh the possible environmental,health and/or consumer safety benefits thereof.2.Before the Annex is amended pursuant to paragraph1, the Commission shall inter alia consult producers of electrical and electronic equipment,recyclers,treatment operators,envir-onmental organisations and employee and consumer ments shall be forwarded to the Committee referred to in Article7(1).The Commission shall provide an account of the information it receives.Article6ReviewBefore13February2005,the Commission shall review the measures provided for in this Directive to take into account,as necessary,new scientific evidence.In particular the Commission shall,by that date,present propo-sals for including in the scope of this Directive equipment which falls under categories8and9set out in Annex IA to Directive2002/96/EC(WEEE).The Commission shall also study the need to adapt the list of substances of Article4(1),on the basis of scientific facts and taking the precautionary principle into account,and present proposals to the European Parliament and Council for such adaptations,if appropriate.Particular attention shall be paid during the review to the impact on the environment and on human health of other hazardous substances and materials used in electrical and elec-tronic equipment.The Commission shall examine the feasibility of replacing such substances and materials and shall present proposals to the European Parliament and to the Council in order to extend the scope of Article4,as appropriate.Article7Committee1.The Commission shall be assisted by the Committee set up by Article18of Council Directive75/442/EEC(1).2.Where reference is made to this paragraph,Articles5and 7of Decision1999/468/EC shall apply,having regard to Article8thereof.The period provided for in Article5(6)of Decision1999/468/ EC shall be set at three months.3.The Committee shall adopt its rules of procedure.(1)OJ L194,25.7.1975,p.39.Article8PenaltiesMember States shall determine penalties applicable to breaches of the national provisions adopted pursuant to this Directive. The penalties thus provided for shall be effective,proportionate and dissuasive.Article9Transposition1.Member States shall bring into force the laws,regulations and administrative provisions necessary to comply with this Directive before13August2004.They shall immediately inform the Commission thereof.When Member States adopt those measures,they shall contain a reference to this Directive or be accompanied by such a refer-ence on the occasion of their official publication.The methods of making such a reference shall be laid down by the Member States.2.Member States shall communicate to the Commission the text of all laws,regulations and administrative provisions adopted in the field covered by this Directive.Article10Entry into forceThis Directive shall enter into force on the day of its publica-tion in the Official Journal of the European Union.Article11AddresseesThis Directive is addressed to the Member States.Done at Brussels,27January2003.For the European ParliamentThe PresidentP.COXFor the CouncilThe PresidentG.DRYSANNEXApplications of lead,mercury,cadmium and hexavalent chromium,which are exempted from the requirementsof Article4(1)1.Mercury in compact fluorescent lamps not exceeding5mg per lamp.2.Mercury in straight fluorescent lamps for general purposes not exceeding:—halophosphate10mg—triphosphate with normal lifetime5mg—triphosphate with long lifetime8mg.3.Mercury in straight fluorescent lamps for special purposes.4.Mercury in other lamps not specifically mentioned in this Annex.5.Lead in glass of cathode ray tubes,electronic components and fluorescent tubes.6.Lead as an alloying element in steel containing up to0,35%lead by weight,aluminium containing up to0,4%leadby weight and as a copper alloy containing up to4%lead by weight.7.—Lead in high melting temperature type solders(i.e.tin-lead solder alloys containing more than85%lead),—lead in solders for servers,storage and storage array systems(exemption granted until2010),—lead in solders for network infrastructure equipment for switching,signalling,transmission as well as network management for telecommunication,—lead in electronic ceramic parts(e.g.piezoelectronic devices).8.Cadmium plating except for applications banned under Directive91/338/EEC(1)amending Directive76/769/EEC(2)relating to restrictions on the marketing and use of certain dangerous substances and preparations.9.Hexavalent chromium as an anti-corrosion of the carbon steel cooling system in absorption refrigerators.10.Within the procedure referred to in Article7(2),the Commission shall evaluate the applications for:—Deca BDE,—mercury in straight fluorescent lamps for special purposes,—lead in solders for servers,storage and storage array systems,network infrastructure equipment for switching, signalling,transmission as well as network management for telecommunications(with a view to setting a specific time limit for this exemption),and—light bulbs,as a matter of priority in order to establish as soon as possible whether these items are to be amended accordingly.(1)OJ L186,12.7.1991,p.59.(2)OJ L262,27.9.1976,p.201.。

17 EU and Ireland欧洲和爱尔兰

The EU is run by five institutions, each playing a specific role:
• European Parliament
– elected by the peoples of the Member States
• Council of the Union
• • • •
for food products, and for tariff wall for industrial products Political relations with UK unequal Modernization had yet to happen Economy opened up and modernized only in the late 1960s Accompanied by measures to attract FDI (Foreign Direct Investment)
Funds
• Cohesion Funds, 1986 (economic and
social cohesion became EU objectives • Single market program 1992 • Successive Enlargement to 28 Members • Successive CAP Reforms
• This decision was taken on political rather than
EU and Ireland
Impacts
A BRIEF HISTORY OF THE EU
The European Union has gone through many incarnations since its origins fifty-plus years ago.

2003年全国大学生英语竞赛C类初赛真题及答案

2003 National English Contest for College Students（Preliminary）Part I Listening Comprehension（30 minutes，30 points）Section A Dialogues（10 points）Directions：In this section ，you will hear 10 short dialogues．At the end of each dialogue，a question will be asked about what was said．Both the dialogue and the question will be read only once．After each question there will be a pause．during the pause，you must read the four choices marked A，B，C and D，and decide which is the best answer．Then m ark the corresponding letter on the Answer Sheet with a single line through the center．1．A．A sales clerk．B．A police officer C．A tailor．D．A nurse．2．A．By train．B．She walks C．By car．D．By bus．3．A．Fish is the only dish left．B．Chicken is the only dish left．C．V egetarian meals are not offered．D．There aren't any vegetarian meals left．4．A．He starts work next weekend．B．He'll be away．C．He'll be in the mountains．D．He's moving to Florida．5．A．In an elevator．B．At a dress store．C．On the seventh floor．D．At a department store．6．A．They felt it was disorganized．B．They were pleased with its Asian content．C．They felt it lacked Asian content．D．They felt it ignored recent events．7．A．He doesn't have enough time．B．He doesn't have a watch．C．The library doesn't have the articles he wants．D．He can't find the library．8．A．He wants the woman to dine out with them．B．He wants to work tomorrow．C．He wants the woman to finish dinner first．D．He wants to pay for the dinner．9．A．Twice a day．B．Twice a week．C．Once a week．D．Daily．10．A．At two o'clock．B．At four o'clock．C．At three thirty D．At eight o'clock．Section B News Items（10 points）Directions：In this section，you will hear 10 pieces of short news from BBC or VOA．There will be a question following each piece of news．Write down the answer to each question in no more than 15 words．11._______________________________________12_______________________________________13._______________________________________14_______________________________________15_______________________________________16_______________________________________17_______________________________________18._______________________________________19_______________________________________20._______________________________________Section C Compound Dictation（10 points）Directions：In this section，you will hear a passage three times．When the passage is read for the first time，you should listen carefully for its general idea．Then listen to the passage again．When the passage is read for the second time，you are required to fill in the blanks numbered from 21 to 28 with the exact words you have just heard．For blanks numbered from 29 to 30，you are required to fill in the missing information．Y ou can either use the exact words you have just heard or write down the main points in your own words．Finally，when the passage is read for the third time，you should check what you have written and rewrite the correct answers on the Answer Sheet．Although general Motors and General Electric are large multinational companies with operations around the globe，there are numerous smaller companies that engage in international trade．Because 95percent of the world's population and two-thirds of its(21)_____ power are located outside the United States，it is important for American(22)_____to be present in foreign markets．However，before we explain the different methods by which a company may (23)_____in international trade，we might first consider some important (24)_____that U.S．companies often fail to study before they sell products in a foreign country．These factors are (25)_____with differences in language，in values and attitudes，and in political (26)_____．When (27)_____Coca-Cola into the Chinese market in 1920，the company used a group of Chinese symbols that，when spoken，sounded like Coca-Cola．However，when read，these symbols meant，“a female horse fattened with wax”．Upon reentering the Chinese market in the 1970s，Coca-Cola used a series of Chinese (28)_____that translates into“happiness in the mouth”．(29)_________________________．Culture is the total pattern of human behavior that is practiced by a particular group of people．(30)_________________________．Part II Vocabulary and Structure（15 minutes，30 points）Section A Multiple Choice（20 points）Directions：Questions 31-50 constitute a complete passage．There are 20blanks in the passage．For each blank there are four choices marked A，B，C and D．Choose the one that best completes the sentence．Then mark the corresponding letter on the Answer Sheet with a single line through the centre．31．Senior Metropolitan police officers tried to dismiss the Noting Hill race riots which raged for five nights over the August bank holiday in 1958 as the work of“ruffians ，both colored and white”hell-bent on hooliganism ，according to _____ official files．A．recent revealed B．newly released C．previous disclosing D．earlier exposing32．But police eyewitness reports in the secret papers_____ that they wereoverwhelmingly the work of a white working class mob out to get the“niggers”．A．contain B．convince C．consist D．confirm 33．The ferocity of the Noting Hill“racial riots”，as the press called them at the time，shocked Britain into_____ for the first time that it was not above the kind of racial conflict then being played out in the American deep south．A．realizing B．witnessing C．watching D．identifying 34．The carnival，which will_____ the streets of west London _____more than 1.5 million people this weekend，was started in 1959 as a direct response to the riots．A．crowd；of B．pour；for C．fill；with D．emerge；in35．While senior officers tried to play down the racial aspects of the riots，the internal Metropolitan police files released this month at the public record office confirm that the disturbances were overwhelmingly _____ by 300 to 400 strong“Keep Britain White” mobs ，many of them Teddy boys armed with iron bars ，butcher's knives and weighted leather belts，who went“nigger-hunting”among the West Indian residents of Noting Hill and Noting Dale．A．erupted B．commenced C．triggered D．inaugurated36．The first night left five black men _____ on the pavements of Noting Hill．A．lying unconscious B．there died C．feel faint D．serious hurt37．The battles raged over the bank holiday weekend as the black _____responded in kind with counterattacks by large groups of“men of color”similarly armed．A．column B．army C．brigade D．community 38．Thomas Williams was stopped by the police as he came out of Bluey's Club on Talbot Road，Noting Hill．He _____a piece of iron down his left trouser leg，a petrol bomb in his right pocket and a razor blade in his inside breast pocket：“I have to protect myself，”he told the arresting officer．A．found to have B．was found to have C．found having D．was found having39．The _____ files，which were sealed under the 75-year rule but have been released early，show that senior officers tried to convince the then home secretary，“Rab”Butler，that there was not a racial element to the rioting．A．forbidden B．confidential C．incredible D．strict 40．In his official report，Detective Sergeant M.Walters of the Notting Hill police said the national press had been wrong to portray the“widespread series of street disturbances”as“racial”riots：“Whereas there certainly was some _____ feeling between white and colored residents in this area，it is abundantly clear much of the trouble was caused by ruffians，both colored and white，who seized on this opportunity to indulge in hooliganism ．”A．ill B．Sick C．painful D．hurt41．But the police witness statements and private statistics _____ ．A．told differently B．interpreted in a different wayC．existed m any differences D．told a different story42．The Met com missioner was told that _____ the 108people who were charged with offences ranging from grievous bodily harm to affray and riot and possessing offensive weapons，72 were white and 36 were “colored”．A．for B．From C．of D．in43．It is popularly believed that the riot began on the night of Saturday，August 20，when a 400-strong crowd of white men，_____“Teds”，attacked houses occupied by West Indians．A．they are all B．many of them C．some were D．most of them belong to44．Among the _____ was Majbritt Morrison ，a young white Swedish bride of a Jamaican．A．offenders B．rioters C．victims D．residents45．She was pelted with stones，glass and wood，and _____ in the back with an iron bar as she tried to get home．A．bruised B．struck C．patted D．scratched 46．The internal police witness statements provide graphic evidence of the motives of the mobs—at one point crowds several thousand strong roamed the streets of Notting Hill，_____ homes and attacking any West Indian they could find．A．plunging into B．breaking into C．seeking for D．searching for47．PC Richard Bedford said he had seen a mob of 300 to 400 white people in Bramley Road _____：“We will kill all black bastards．Why don't you send them home？”A．shouting B．to cry C．utter D．announced48．PC Ian McQueen on the same night said he was told：“Mind your own _____，cops．Keep out of it．We will settle these niggers our way．We'll murder the bastards．” A．matters B．affair C．things D．business49．The disturbances continued night after night until they finally petered out on September 5．At the Old Bailey Judge Salmon later handed down exemplary _____ of four years each on nine white youths who had gone“nigger hunting”．A．decisions B．statements C．trials D．sentences50．While those dealt with by the courts were overwhelmingly white ，the large number of black people also arrested and the official _____ there had not been a racial motive ensured a legacy of black mistrust of the Metropolitan police that has never really been eradicated．A．persistence B．perseverance C．insistence D．instanceSection B Error Correction（10points）Directions：The following passage contains 9 errors．In each case only one word is involved．Y ou should proofread the passage on the Answer Sheet and correct it in the following way：EXAMPLEOne night，quite late，I was still awake in the room I am shared with 1. ammy husband．I was lying on my right side and can hear a child crying． 2. couldGetting up，I went ∧ see if our son was all right． 3. to He was sleeping soundly，breathing deeply and gently． 4. √ The ZipperWhatever did we do before the invention of the zipper？In 1893 the world's first zipper was produced in Chicago．Although the inventor claimed that it was a reliable fasteningfor clothing，this was not the case．The Chicago zipper sprang 51．______ open without warning，or jammed shut，and it swiftly lostpopularity．Twenty years ago a Swedish-born engineer called 52．______ Sundback solved the problem．He attached tiny cups to thebacks of the interlocked teeth，and this meant that the teeth 53．______ could be enmeshed more firmly and reliably．At first zippers were made of metal．They were heavy，andif they got stuck it was difficult to free．Then came nylon 54．______ zippers which were lighter and easier to use，and had smallerteeth．The fashion industry liked the new zippers far betterbecause they didn‟t distort the line of the garment or weighing 55．______ down light fabrics．They were also easier for the machiniststo fit into the garment．Meanwhile a new fastening agent made its appearance atthe end of the twenty century: velcro. V elcro is another product 56．______ made from nylon．Nylon is a very tough synthetic fibre firstdeveloped in the 1930s，and bearing a name to mind the wearer 57．______of the two places where it was developed：NY for New Y ork andLON for London．V elcro is made with very small nylon hooks onone side of the fastening which caught tiny looped whiskers on the 58．______ other side of the fastening．It is strong and durable．V elcro is used on clothing，luggages and footwear．It is quick 59．______and easy to fasten and unfasten，and has taken a large part ofthe zipper's share of the market．It is also used in ways a zippercannot be used—for instance as an easily changed fastening onplaster casts，and to hold furnishing fabrics in a position．60．______ Part III Situational Dialogues（5 minutes，10 points）Directions：Complete the following dialogues by choosing the best answer．Then mark the corresponding letter on the Answer Sheet with a single line through the centre．61．Rob：Hey Jill，you're looking great．Jill：Thanks，Rob．____________Rob：Well，you did it．How？Jill：I jog every morning，and I go to aerobics every other day．A．I bought this dress yesterday．Really smart．B．Y ou are looking fine too．C．I'm recovering my strength after the flu．D．My New Year's resolution was to get in shape．62．Bob：Hi Jane．How are you？Jane：____________I didn't sleep a wink last night．The people next door were making a lot of noise again till very late at night．A．I'm feeling a bit out of sorts this morning．B．Fine，thank you．And you？C．I slept like a log and didn't want to get out of bed．D．It seems a bit unusual，you know．63．Ann ：Aah！He's gorgeous！Look at those big，golden paws．When did you get him？Roger：Y esterday．____________Ann ：Oh，right．What kind is she？Roger：A Labrador．A．Susan's got a more beautiful one．B．What's up？C．It's a she actually．D．Isn't it right？64．Tina：Wow，look at all the things on sale．____________Andrew：Y es，look，this shirt is 50 ％off．Tina：And look at these shoes．They are 30 ％off the normal price．A．I'd like to buy a skirt．B．There are some real bargains．C．Are the prices reasonable？D．These shoes are the same as mine．65．Woman：Have you finished the packaging？Man ：____________Woman：Good．Because the truck will be coming soon，this is a rush job．A．Don't hurry m or I'll break the glass．B．Almost．I just have to wrap the glass and put it into boxes．C．No，I haven't．Why didn't you help me with it？D．Y es，I have．What else can I do for you？66．Customs Officer ：________________________Mrs．John son ：No，nothing at all．Customs Officer ：No perfume，alcohol or cigarettes？Mrs．John son ：Well，I have 200 cigarettes；that's all．A．Do you have anything in the bag，ma'am？B．Do you have anything to declare，ma'am？C．Do you want to buy something，ma'am？D．Is there anything I can do for you，ma'am？67．Linda：Hello．I'd like to send this package，please．Clerk：____________________________________Linda：First class．How long will that take？Clerk：About three days．A．How would you like to send it？B．Which class are you in？C．Where do you want to send it to？D．Which class is it in？68．Assistant：Can I help you？Colin ：Y es，it's about this sports shirt．I washed it the other day．The colour ran and it shrank．Assistant：Oh dear，I see．________________________Colin ：I'm afraid not．Assistant：I'm sorry，but I'm not allowed to change anything without a receipt．A．Did you buy it here？B．Would you want to change it？C．Do you have the receipt？D．Could you tell me who sold it to you？69．James：Could I have my bill，please？Can I pay by credit card or eurocheque？Receptionist：____________James：I'll pay by credit card，then．Receptionist：That's fine．I hope you enjoyed your stay here．A．Here's your bill．B．Sorry，we don't take credit card．C．Y ou can pay by eurocheque．D．Y es，we take both．70．Husband：When is our anniversary？Wife：________________________Husband：No，it's just that I bought these flowers for you and I was hoping today was the day．A．Hmm ．．．I can't remember either．Why？B．Hey，are these flowers for me？C．Who cares？Do you want to give me a surprise？D．Are you joking？Have you really forgotten again？Part IV Reading Comprehension（25 minutes，40 points）Section A Multiple Choice（10 points）Directions：There is one reading passage in this part．The passage is followed by 5 questions or unfinished statements．For each of them there are four choices marked A，B，C and D．You should decide on the best choice and mark the corresponding letter on the Answer Sheet with a single line through the centre．Questions 71 to 75 are based on the following passage：Taking a peep at what's going on in your headCARL Filer，18，a star salesman at a B＆Q hardware store in the UK，was called up for promotion within one week of starting work．But，instead of being made supervisor，he was sacked—after his employers saw the results of his psychometric test．Y ou might think that anyone who answers that he“strongly disagrees he is an over-achiever is asking for trouble，but Mr Filer already thought he had proved himself more than capable．This year，nearly half of UK firms—46 percent—will use psychometric tests to select trainees，compared with just 17 percent in 2000，according to a report for GTI，a publisher of graduate career guides．These tests，which rate candidates‟ ability and gauge their personality，have been usedin the UK since the 1980s．But assorted studies have shown most people—graduates in particular—are wholly cynical about the idea of their personality being“measured．“People tend to see them as either too silly or too clever， says Clive Fletcher，professor of occupational psychology at University of London．“But all the evidence indicates the tests do have some value．The first personality test as we know it，was developed by the American army in 1917 to filter out weak recruits．But it was not until the 1980s that the tests became popular in Britain．With a rising number of graduates going for a decreasing number of jobs，organizations began to see psychometric testing as a cheap，reliable alternative to the expensive，time-consuming interview．But today the tests are becoming alarmingly sophisticated and are edging towards probing the“dark side：pathology and personality disorders．Increasingly，tests are being used to try to detect promising young graduates who may，later in life，fly off the rails（go crazy）；or to stop psychopaths（having mental disorder）getting recruited．In the future，interviewees could even be given a mouth swab to reveal the genetic and biological markers of personality．“We are heading for the era of genetic screening，”warns Carolyn Jones，of the Institute for Employment Rights．“I think these tests are very flawed．And there are other problems with the tests．For starters，it is possible to fake it—even the test producers agree on this．But they have made it as hard as possible．For example，look at whether you agree or disagree with the following two statements：“New ideas come easily to me and“I find generating new concepts difficult． How long did it take you to realize they both could mean the same thing？The main argument，however，is that the tests are invalid and cannot quantify（put a numerical value on）something as changeable as personality．The golden rule is then，that a psychometric test should never be used as the sole basis of selection，but should always be followed by interviews．71．Most people's attitude towards the psychometric test is ______．A．contemptuous B．favorable C．tolerant D．confounded72．Which of the following is one of the reasons why psychometric testing wins an advantage over interviews？A．It doesn't cost any money．B．It requires no equipment．C．It is time-saving．D．It can be done within seconds．73．Which of the following statements is the author's idea？A．Psychometric tests are defective．B．Psychometric tests should not be the only way to recruit promising young graduates．C．Psychometric tests are invalid and cannot quantify something changeable as personality．D．Psychometric tests are golden rules．74．The test producers make the tests very complicated to ______．A．avoid cheating B．improve genetic screeningC．find out the best ideas D．generate new concepts75．Which of the following is not true according to the passage？A．The American army developed the first personality test to screen out weak recruits．B．In the future，interviewers could give a mouth swab to reveal interviewees‟ symptoms．C．There are possibilities for starters to cheat in the psychometric tests．D．Interviews still play an important role in evaluating interviewees．Section B Short Answer Questions（30 points）Directions：In this part there are 3 passages with 15 questions or incomplete statements．Read the passages carefully．Then answer the questions in the fewest possible words（not exceeding 10 words）．Remember to rewrite the answers on the Answer Sheet．Questions 76 to 80 are based on the following passage：The 8 Steps of Social Invention1．Get ready to play．Like other types of creativity，social inventiveness flourishes when you begin thinking outside conventional boundaries．Charlie Girsch，a St．Paul，Minnesota-based creativity consultant，suggests that you start by playing with obviously absurd explanations for everyday events．“If traffic is slow，you'll be tem pted to say，…Hmm．Must be an accident up ahead．‟ Instead，try saying，…Must be a family of turtles crossing the highway‟or…I expect there's some kind of alien abduction going on．‟Y ou'll be amazed how soon you will be look ing at familiar problems in new ways．”Girsch's book，Fanning the Creative Spirit（Creativity Central，1999）has scores of other exercises for limbering up the inventive part of your brain．2．Generate a zillion far-fetched ideas．Concerned about the homeless in your neighborhood？Imagine a Homeless Parliament，a Homeless Circus，homeless families forming an orchestra，a homeless museum ．．．and on and on．Generate like mad with no regard for feasibility in order，as social invention pioneer Nicholas Albery advises，to“overcome e worthy-but-dull ideas．”Eventually the two or three best ideas will begin to stand out．3．Take your wildest idea and bring it down to earth．How about that Homeless Circus？Could it turn into a forum for homeless people to display their creative talents？A performance series about homelessness？A neighborhood carnival with the homeless as guests of honor？Y our flakiest idea may have a germ of brilliance that actually makes it more attractive，and thus more feasible （and fundable），than its worthy-but-dull cousins．4．Look for in venations that solve more than one problem．The Slow Food Movement，born in Italy，boosts local farmers and regional cuisine traditions and restaurateurs and the same time that it“feeds”our hunger for authentic tastes，healthy eating，and a more leisurely，saner style of life．5．Accentuate the positive．“A very common question that I get when I work with people in communities is…Whydoesn't anybody care about our problems？‟”notes M chael Patterson，a social inventor and activist in Massachusetts．“What a worthless question．…Why‟？questions are for philosophers．Ask…How‟？and…What‟？questions—they are a lot more practical．”For instance，Patterson asks，“What would you do if you knew you couldn't fail？”6．Give it a rest．Walk away from your favorite idea for a while，forget about it，let it sleep．With your conscious mind out of the way，your subconscious gets to fiddle with the concept for a while，and you just might have an unexpected insight or breakthrough．7．Practice“yes and”in stead of“yes but”．No matter how tempted you are to say“Y es，but this will be hard because，”or“Yes，but a million other people are doing this，”shift the conjunction to“and”and see what sort of positive refinement or change emerges．“Y es，and we could concentrate on immigrants．”“Y es，and we can make it open to all ages．”8．Get your idea into the world．This is the tough part．Y ou might seek out the help of activists who will take a shine to your ideas．Or become an organizer yourself．Paul Glove，a New Y ork social inventor，coun-sels：“If you have an idea you believe in，write a pamphlet with your phone number on it and post it in Laundromats and bookstores．If three people call you，have lunch with them and call yourselves an organization．If five people call，meet with them and issue a press release．” Presto，you're launched．76．To generate far-fetched ideas helps to ______．77．Michael Patterson wants us to come up with“How”？and“What”？instead of“Why”？questions because he considers they are more practical than ______．78．The pur pose to practice“yes and”instead of“yes but”is to make yourself more ______．79．According to the article，when one has difficulty developing his favorite idea，he should ______．80．One should not only generate far-fetched ideas but also ______ because the latter step is the nearest to reality．Questions 81 to 85 are based on the following passage：Thin Slice of TV Has Big MarketIt is too early to write an obituary for bulky picture tubes，which will remain the most affordable TV sets for years to come．But，analysts and industry executives insist that thin screens already have started to become the dominant format for TV sets in the digital era．Sharp price cuts have brought plasma sets and other thin，flat televisions out of high-end electronic boutiques and into thousands of mass-market outlets such as Cosco，a wholesale buying club in the US，best known for offering members bulk items and big discounts．The least expensive plasma sets still cost a hefty US ＄3，000or more ，yet sales are growing so rapidly that many manufacturers are racing to boost production．That increase，combined with expanding production capacity and improved technology，could push the price of plasma sets down by one-third next year，according to analyst Richard Doherty of Envisioneering Group，a US research firm．But manufacturers are not just competing with each other；they are also trying to fend off challenges from competing thin-screen technologies，such as liquid crystal displays（LCD）．The demand for thin screens is fuelled in part by the advent of DVDs and digital TV broadcasts，which offer more detailed pictures and more lifelike colors than conventional analog TV signals．To see the difference，consumers need a set that can pack more information onto the screen than their current TVs can．This sharpness is most vivid on screens that are 40inches diagonal or larger．At that size，however，traditional direct view and projection TVs are so bulky that many consumers have trouble finding a place for them at home．Hence the interest in thin screens—models slender and light enough to hang on a wall．The glass panels at the heart of plasma and LCD sets come mainly from about a dozen companies with factories in Japan，South Korea and，increasingly，China．About 800，000 plasma panels will be shipped this year around the world，analysts say．That is a tiny amount compared with the overall market for TVs，which was about 140 million sets last year．But，industry experts said 2003would be a“breakout year” or plasma because shipments should double．Helping drive the growth are new or expanded manufacturing facilities．For example，Japanese electronics giant NEC last year doubled the capacity of its Japanese factory—reaching 300，000to 400，000 plasma panels．And it plans to double it again in 2003，officials said．As competition has heated up during the last four years，prices have fallen more than 50 percent．According to“NPD Tec world”，the average price of a plasma display sold in the US dropped from US ＄12，700in January 1999 to US ＄6，100in October 2002．The best markets for plasma screens have been in Asia，and about half of the sets have gone to businesses instead of homes．LCD TVs carry a premium price—they can be 10 times as expensive as a comparable tube-driven television—that knocks them out of most buye rs‟ budgets．But LCD panels are quickly taking over the market for computer monitors，and the tens of millions of panels being produced for that segment will help push down prices for LCD TVs，analysts predicted．Sharp Electronics，for one，is betting heavily on LCDs．Its chairman，Toshiaki Urushisako，has predicted that Sharp will switch completely from conventional tube sets to LCD TVs in Japan by 2005．Flat-panel refers to wafer-thin（3 inches or less）TVs，whereas flat-screen may actually describe traditional cathode-ray-tube sets（CRTs）whose glass front lacks the distorting curve that TVs have had for 50 years．Be aware of two things：One，flat-panel technology may not be high-definition TV；for eventual HDTV reception，some of these sets will require a separate HD tuner．Two，some flat-panel TVs are just the panel and lack speakers and sometimes。

北京第二外国语学院1999年研究生入学考试：英语写作

北京第二外国语学院1999年研究生入学考试：英语写作Read the following article carefully and then write a composition about 1500words. In the first part of yo ur writing, you should give a brief summary of the article. In the second part, make comments on the art icle. And in the last part, give your solutions to the present problem of the reempliyment for people who have been laid off in China.Startups To the Rescuein Europe, small companies are where the action isLeopoldo Fernandez Pujals has a tempting recipe for a continent that craves jobs. A decade ago. as m ore Spanish women began entering the workforce, the Cuban- American marketer sensed Spain’s grow ing appetite for fast food ,so he invested $80,000 to start a pizza- delivery service in Madrid, Now, Tele Pizza boasts$2060 million in sales and employs 6,000workers.Since going public on the Spanish Bolsa in late 1996, Telepizza’s shares have soared from $14to $123, and its market cap now tops$1.3billion, Says Pujals, a 50-year –old Vietnam war veteran: “More and m ore people are asking me: ‘What’s our secret?’”No wonder. At a time when Europe’s industrial giants continue to shed workers, a raft of small, dynamic companies such as Pujals’are emerging. They are creating jobs and spurring economic regeneration-d espite obstacles such as heavy taxes and red tape that have long discouraged the Continent’s entrepre neurs. Indeed, Europe’s hot growth companies are showing a remarkable ability to take advantage of th e Continent’s growing trend toward deregulation, its nascent secondary stock markets, and the rapid sp read of the internet, which puts companies in inatant touch with new customers. Says Juan Roure, a pr ofessor at IESE Business School in Barcelona: “These are the companies that are most effectively crea ting value and jobs, They are Changing the rules of how to compete in their markets.”Smaller growth companies have gone largely unnoticed among Europe’s political elite until recently. But their continued success is vital if the Continent is to reduce the rands of its 19 million unemployed. A n ew study by Europe’s 500 Association, a nonprofit group linked to the European Foundation of Entrepre neurship Research, identified 500small and midsize companies whose sales-and emplyment ranks-are soaring. Conducted by IP S trategies., an independent consultant, the study found that both service co mpanies and small-scale manufacturers are providing entry –level jobs needed to combat Europe’s 11 %jobless rate. Moreover, they aren’s just clustered around tech zones such as Munich and Cambridge but are dotted across the Continent.。

Hippocampal BDNF mediates the efficacy of exercise

Hippocampal BDNF mediates the efﬁcacy of exerciseon synaptic plasticity and cognitionShoshanna Vaynman,1Zhe Ying1and Fernando Gomez-Pinilla1,21Department of Physiological Science,UCLA,621Charles E.Young Drive,Los Angeles,CA90095,USA2Division of Neurosurgery,UCLA Brain Injury Research Centre,Los Angeles90095,California,USAKeywords:CREB,exercise,learning and memory,Morris water maze,synapsin IAbstractWe found that a short exercise period enhanced cognitive function on the Morris water maze(MWM),such that exercised animals were signiﬁcantly better than sedentary controls at learning and recalling the location of the platform.Theﬁnding that exercise increased brain-derived neurotrophic factor(BDNF),a molecule important for synaptic plasticity and learning and memory,impelled us to examine whether a BDNF-mediated mechanism subserves the capacity of exercise to improve hippocampal-dependent learning.A speciﬁc immunoadhesin chimera(TrkB-IgG),that mimics the BDNF receptor,TrkB,to selectively bind BDNF molecules, was used to block BDNF in the hippocampus during a1-week voluntary exercise period.After this,a2-trial-per-day MWM was performed for5consecutive days,succeeded by a probe trial2days later.By inhibiting BDNF action we blocked the beneﬁt of exercise on cognitive function,such that the learning and recall abilities of exercising animals receiving the BDNF blocker were reduced to sedentary control levels.Inhibiting BDNF action also blocked the effect of exercise on downstream systems regulated by BDNF and important for synaptic plasticity,cAMP response-element-binding protein(CREB)and synapsin I.Speciﬁc to exercise,we found an association between CREB and BDNF expression and cognitive function,such that animals who were the fastest learners and had the best recall showed the highest expression of BDNF and associated CREB mRNA levels.Theseﬁndings suggest a functional role for CREB under the control of BDNF in mediating the exercise-induced enhancement in learning and memory.Our results indicate that synapsin I might also contribute to this BDNF-mediated mechanism.IntroductionOver the past two decades,both animal and human studies have shown the capacity of exercise to beneﬁt cognitive function.Notably, exercise enhances memory and cognition(Fordyce&Wehner,1993; Kramer et al.,1999),facilitates functional recovery following brain injury(Grealy et al.,1999),and counteracts the mental decline associated with ageing(Laurin et al.,2001).A characteristicﬁnding is the exercise-induced increase in brain-derived neurotrophic factor (BDNF)in the hippocampus,an area involved in learning and memory formation(Neeper et al.,1997;Vaynman et al.,2003).Given the importance of BDNF for synaptic plasticity and learning and memory, it has been proposed that these exercise-induced increases in hippocampal BDNF levels might underlie the ability of exercise to enhance cognitive function.Nevertheless,the central question remains whether the exercise-induced enhancement in learning and memory is dependent upon the action of hippocampal BDNF during exercise. BDNF is a member of the neurotrophin family known to play a prominent role in the survival,growth,and maintenance of neurons during development(Leibrock et al.,1989;Barde,1994)and more recently,the ability to modulate synaptic-plasticity in the adult brain (Lo,1995).This capability of BDNF to impact synaptic plasticity can be seen in the diverse tasks it manages;BDNF regulates axonal and dendritic branching and remodelling(Shimada et al.,1998;Lom& Cohen-Cory,1999;McAllister et al.,1999;Yacoubian&Lo,2000),synaptogenesis in arborizing axon terminals(Alsina et al.,2001),the efﬁcacy of synaptic transmission(Lohof et al.,1993;Kang& Schuman,1995;Boulanger&Poo,1999;Kaﬁtz et al.,1999),and the functional maturation of excitatory and inhibitory synapses(Seil& Drake-Baumann,2000;Rutherford et al.,1998;Vicario-Abejon et al., 1998).BDNF gene deletion or inhibition(Figurov et al.,1996;Kang et al.,1997)produces a deﬁcit in long-term potentiation(LTP),the transcription-dependent electrophysiological correlate of learning and memory(Nguyen&Kandel,1996).Moreover,this deﬁcit in synaptic function can be amended by the exogenous application(Patterson et al.,1996)or overexpression(Korte et al.,1995)of BDNF. Previously,we found that exercise induces synaptic plasticity markers in the hippocampus through a BDNF-mediated mechanism, particularly increasing the mRNA levels of calcium and cAMP response-element-binding(CREB)protein and synapsin I(Gomez-Pinilla et al.,2001;Vaynman et al.,2003).CREB is one of the best described stimulus-induced transcriptional regulators,notable for its involvement in adaptive responses(Finkbeiner et al.,1997;Finkbe-iner,2000),but particularly famous for its evolutionary conserved role in long-term memory(LTM)formation(Dash et al.,1990;Bourt-chouladze et al.,1994;Frank&Greenberg,1994;Tully et al.,1994; Yin et al.,1995;Abel&Kandel,1998).Synapsin I is a presynaptic phosphoprotein,which has been shown to modulate transmitter release (Jovanovic et al.,2000),the formation and maintenance of the presynaptic structure(Melloni et al.,1994;Takei et al.,1995)and axonal elongation(Akagi et al.,1996).Although previous work has shed some light on underlying synaptic plasticity changes the brain undergoes with exercise,the mechanismsCorrespondence:Dr Fernando Gomez-Pinilla,as above.E-mail:Fgomezpi@Received9April2004,revised23August2004,accepted2September2004European Journal of Neuroscience,Vol.20,pp.2580–2590,2004ªFederation of European Neuroscience Societies doi:10.1111/j.1460-9568.2004.03720.xresponsible for bestowing the exercise-induced enhancement in cognitive function are as yet poorly understood.Therefore,in this current study we investigated the causal link between exercise-induced cognitive improvement and BDNF action.To block the action of BDNF,we employed a speciﬁc immunoadhesin chimera(TrkB-IgG) that mimics the BDNF receptor,TrkB,to selectively bind BDNF molecules.We injected TrkB-IgGs into the hippocampus before the start of wheel running,using a microbead vehicle that enables the inhibitory effect of the BDNF blocker to last throughout the1-week exercise period,and measured Morris water maze(MWM)perform-ance and mRNA levels of BDNF,TrkB,synapsin I and CREB.It is of signiﬁcant clinical interest to determine if exercise utilizes BDNF action to exert its beneﬁcial effects on neuronal and cognitive plasticity,as exercise may be potentially combined with other interventions which might impact BDNF-mediated mechanisms. Materials and methodsExercise paradigmAdult male Sprague-Dawley(Charles River)rats(3months old)were randomly assigned into four groups:sedentary with cytochrome C (cytC)injection(sed⁄cytC;n¼7);exercise with cytC injection (exc⁄cytC;n¼7);sedentary with TrkB-IgG injection(sed⁄TrkB-IgG;n¼7);and exercise with TrkB-IgG injection(exc⁄TrkB-IgG; n¼7).All rats were housed individually in standard polyethylene cages in a12⁄12h light⁄dark cycle at22–24°C,with food and water available ad libitum.We chose a voluntary exercise paradigm because it simulates aspects of human behaviour in which animals choose how much to run.The exercise rats were given access to a wheel (diameter¼31.8cm,width¼10cm)that freely rotated against a resistance of100g,attached to a receiver that monitored revolutions every hour(VitalViewer Data Acquisition System software,Mini Mitter Company,Inc.,Sunriver,OR,USA).All groups were allowed to acclimate to their respective environments for1week before the start of experiments.Animals were exercised for a period of1week before MWM training,during which respective drug treatments were given to groups.The choice of a short1-week exercise period was based upon theﬁndings that4days of exercise are sufﬁcient to enhance performance on the MWM task(Shaw et al.,2003)and increase the expression of synaptic plasticity markers believed to underlie mechanisms supporting cognitive function(Molteni et al., 2002;Vaynman et al.,2003).As in Shaw et al.(2003),in order to reproduce the effects of a short exercise period on cognitive function, we required that each rat ran a minimum of100m each night.The control rats were conﬁned to a cage with no access to a running wheel. Animals continued in their respective experimental conditions for the duration of the experiment.All animals were killed by decapitation the morning following the last treatment day and their hippocampi were rapidly dissected out,immediately placed on dry ice,and stored at )70°C.These studies were performed in accordance with the United State National Institute of Health Guide for the Care and Use of Laboratory Animals and were approved by UCLA Animal Research Committees.DrugsRecombinant human TrkB-IgG chimera was acquired from R&D System,Inc.(Minneapolis,MN,USA)in powder form.This chimerical protein comprises the intracellular domains of human TrkB and the Fc domain of IgG,and has been shown to be a highly potent and speciﬁc antagonist of BDNF action(Shelton et al.,1995).We used cytochrome C(cytC),obtained in powder from Sigma (St.Louis,MO,USA)as the control drug as it has been used as a standard control for microbead injections(Lom&Cohen-Cory,1999; Vaynman et al.,2003).CytC was dissolved in sterile distilled water, with stock concentration of100ng⁄l L.Fluorescent latex microbeads, used as the vehicle for drug insertion into the hippocampus,were purchased from Lumaﬂour Corp.,Naple,FL.The sterile phosphate-buffered saline(PBS)containing0.1%bovine serum albumin(BSA) was added to the vial to prepare a stock solution(100l g⁄mL). Preparation of microbeadsInfusion of TrkB-IgGs was achieved by coupling them to microbeads, which we have previously used as a reservoir for the successful delivery of viable inhibitors into the hippocampus(Vaynman et al., 2003).We prepared microbeads(Lumaﬂour,Naples,FL,USA)by the methods described previously(Riddle et al.,1997;Lom&Cohen-Cory,1999).Brieﬂy,these consisted of coating the microbeads with each drug via passive absorbency by incubating overnight at4°C with a1:5mix of microbeads to TrkB-IgG(5l g⁄l L in PBS with BSA, Croll et al.,1998)and cytC(100ng⁄l L in sterile water,Lom& Cohen-Cory,1999).The morning after coating the microbeads,the solution was centrifuged at14000g for30min and the microbeads were resuspended in sterile water at a10%concentration.These two drugs were administered via injection ofﬂuorescent latex microbeads directly into the right hippocampus,resulting in a consistent and effective blockade of targets as shown in the results.In a previous publication,we have shown that microbead inhibition was effective for3days(Vaynman et al.,2003).In a new set of studies,in which we used the same protocol,we have found that microbead inhibition lasts up to7days(our unpublished observations).Previous studies by Quattrochi et al.,(1989),Riddle et al.(1995,1997)and Lom& Cohen-Cory(1999)have reported successful delivery by microbeads of bioactive agents such as neurotrophins and neurotransmitter agonists⁄antagonists into highly localized brain regions.Injection of drugs into the hippocampusExercise and sedentary rats received TrkB-IgG or the standard control cytC injection.We used a unilateral injection to the right hippocampus to be consistent with previous blocking experiments(Vaynman et al., 2003).We did not use the contralateral hippocampus as a control because a unilateral injection can cause changes on the contralateral side due to connectingﬁbres(Amaral&Witter,1989).Injections were given to all animals once before the onset of the running period,and administered early in the morning such that an ample recovery time permitted all animals to begin running that same evening.All animals were anaesthetized by isoﬂurane(2–2.5%)utilizing the Mobile Laboratory Animal Anaesthesia System,and positioned in a stereo-taxic apparatus that was used to secure the animal and to measure the sight for injection.TrkB-IgG or cytC imbedded in microbeads was injected into the right hippocampus(3.8mm posterior to Bregma, 1mm from the midline,and3.7mm vertically)using a Hamilton syringe in a volume of2l L over15min.The location of microbead injection was veriﬁed by histological examination of selected brains, as previously described(Quattrochi et al.,1989;Riddle et al.,1995). We visually inspected all the brains at the time of dissection and only those showing characteristic markings of microbeads of the right hippocampus were used for mRNA measurements.The microbead injection site was additionally veriﬁed byﬂorescence microscopy (shown in Fig.1),using an Olympus BX51microscope.Exercise,BDNF and learning2581ª2004Federation of European Neuroscience Societies,European Journal of Neuroscience,20,2580–2590Cognitive testingTo evaluate the effect of exercise and TrkB-IgG inhibition of BDNF activity on memory functions,all rats were tested,using the Morris water maze,for spatial memory acquisition and retention (Morris et al .,1982;Sutherland et al.,1982).The swimming pool (130cm diameter,50cm height)was divided into four quadrants.As previously discussed in Molteni et al .(2002),the quadrant housing the escape platform (12cm diameter),was ﬁxed in a permanent position 2cm under the water surface during the course of the MWM training procedure and was deﬁned as the target zone.The water,kept at a steady 22±2°C,was made opaque with white nontoxic biodegradable dye to prevent the rats from seeing the platform.The rats were trained in the MWM for 5consecutive days using the challenging 2-trial-per-day regimen previously found to discern learning difference in exercise and sedentary animals (van Praag et al .,1999).We changed the 6day training paradigm to a 5day training paradigm which was more conducive to assessing the shorter exercise period we employed (Shaw et al .,2003).Overall,the 2-trial-per-day,5day MWM training paradigm was chosen for optimal discernment of learning differences in animals exposed to a short-term exercise regimen.The animals were placed into the tank facing the wall from one of the equally spaced start locations,which were randomly altered every trial.Spatial reference cues around the pool were maintained constant through out the duration of the MWM training and probe trials.Each trial lasted until the rat found the platform or for a maximum duration of 60s.If the rat failed to ﬁnd the platform,it was gently placed on the platform.At the end of each trial,the rat was allowed to rest on the platform for 10s.The time to reach the platform (escape latency)was recorded for each animal.To assess spatial memory retention,a probe trial was performed 2days after the last training trial,during which the platform was removed from the pool,while all other factors remained constant.As previously described (Molteni et al .,2002,2004),rats were allowed to swim for 60s,during which the percentage of time spent in each quadrant was calculated and their swim paths were semiautomatically recorded by a video tracking system (Smart:Spontaneous Motor Activity Recording and Tracking.#35E4F-FA9,Pan Laboratory s.l).The location of the platform was designated as quadrant P (Fig.2B).Isolation of total RNA and real-time quantitative reverse transcription-polymerase chain reactionTotal RNA was isolated using RNA STAT-60kit (TEL-TEST,Inc.,Friendswood,TX,USA)as per the manufacturer’s protocol.Quan-tiﬁcation was carried out by absorption at 260nm.The mRNAs forBDNF,TrkB,CREB and synapsin I were measured by real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR)using a PE Applied Biosystems prism model 7700sequence detection instrument,which directly detects the RT-PCR product without downstream processing.This is achieved by monitoring the increase in ﬂuorescence of a dye-labelled DNA probe,one that is speciﬁc for the factor of interest plus another speciﬁc for glyceraldyehyde-3-phosphate dehydrogenase (GAPDH)gene,which has been previously used as a successful endogenous assay control (Griesbach et al .,2002;Molteni et al .,2002).Total RNA (100ng)was converted into cDNA using TaqMan EZ RT-PCR core reagents (Perkin-Elmer,Branchburg,NJ,USA).The sequences of probes,forward and reverse primers,designed by Integrated DNA Technologies (Coralville,IA,USA)were:BDNF (5¢-AGTCATTTGCGCACAACTTTAAAAGTCTGCATT-3¢);forward (5¢-GGACATATCCATGACCAGAAAGAAA-3¢);reverse (5¢-GCAACAAACCACAACATTATCGAG-3¢);TrkB (5¢-TGC ACGTCTGGCCGCTCCTAACC-3¢);forward (5¢-CCCAATTGTGGTCTGCCG-3¢);reverse (5¢-CTTCCCTTCCTCCACCGTG-3¢);CREB (5¢.-CATGGCACGTAATGGAGACTACCGCA-3¢.);forward (5¢.-CCGCCAGCATGCCTTC-3¢.);reverse (5¢.-TGCAGCCCAATGACCAAA-3¢.);Fig .1.Tissue section in the sagittal plane of the right hippocampus,showing the microbead injection site concentrated in the stratum lacunosum moleculare (slm)using ﬂorescence microscopy.Hippocampal areas have been labelled for convenience;CA1,CA2andCA3.2582S.Vaynman et al .ª2004Federation of European Neuroscience Societies,European Journal of Neuroscience ,20,2580–2590synapsin I(5¢.-CATGGCACGTAATGGAGACTACCGCA-3¢.);forward(5¢.-CCGCCAGCATGCCTTC-3¢.);reverse(5¢.-TGCAGCCCAATG ACCAAA-3¢.).The endogenous control probe,speciﬁc for the GAPDH gene, served to standardize the amount of RNA sample and consisted of the following oligonucleotide sequence(5¢.-CCGACTCTTGCCCTTC GAAC-3¢.).The RT-reaction steps consisted of an initial2-min incubation step at50°C to activate uracil glycosylase(UNG)and were followed by30min of reverse transcription at60°C.A completion step for UNG deactivation was performed for5min at 95°C.The40cycles of two-step PCR-reaction consisted of a20-s period at94°C and a1-min period at62°C.Western blotTo get a better measure of the active sate of CREB,the expression of p-CREB was assessed by immunoblotting.Hippocampal tissue was homogenized in a lysis buffer containing137m m NaCl,20m m Tris-HCl pH8.0,1%NP40,10%glycerol,1m m PMSF,10l g⁄mL aprotinin,0.1m m benzethonium chloride and0.5m m sodium vanadate.The homogenates were then centrifuged,the supernatants were collected and total protein concentration was determined according to the Micro BCA procedure(Pierce,Rockford,IL, USA),using BSA as standard.Equal amounts(25l g)of protein samples were separated by electrophoresis on a10%polyacrilamide gel and electrotransferred to a nitrocellulose membrane.Theﬁlters were blocked with5%nonfat milk.Membranes were then incubated with anti-actin antibody(1:2000,Santa Cruz Biotechnology,Santa Cruz,CA,USA)and anti-p-CREB antibody(1:1000,Upstate, Lake Placid,NY,USA),followed by anti-rabbit IgG horseradish peroxidase-conjugate.After rinsing with buffer,the immunocom-plexes were visualized by chemiluminescence using the ECL kit (Amersham Pharmacia Biotech Inc.,Piscataway,NJ,USA)accord-ing to the manufacturer’s instructions.Theﬁlm signals were digitally scanned and quantiﬁed using NIH Image software, normalized for actin level.Statistical analysesWe used GAPDH for RT-PCR as an internal standard as described previously in our other studies(Molteni et al.,2002).Quantiﬁcation of the TaqMan RT-PCR results was performed by plotting ﬂuorescent signal intensities against the number of PCR cycles on a semilogarithmic scale.A threshold cycle(C T)was designated as the ampliﬁcation cycle at which theﬁrst signiﬁcant increase in ﬂuorescence occurred.The C T value of each sample was compared to that of the internal standard.These processes were fully automated and carried out using the ABI sequence detector software version 1.6.3(PE Biosystem).Taqman EZ RT-PCR values for BDNF,TrkB,CREB,and synapsin I were corrected by subtracting values for GAPDH as described previously(Greisbach et al.,2002; Molteni et al.,2002).These corrected values were used to make cross group comparisons.The mean values for the mRNA levels were computed for all four groups following completion of exercise and MWM training and compared using analysis of variance (anova).The analysis of maze data was performed in accordance with techniques described in Molteni et al.(2002),using an anova with repeated measures.The mean values of distances(Km)run over the exercise period were computed for the exercise groups and compared using t-test.A Fischer-test was used for cross group comparisons.A Scheffe F-test was used to compare learning differences between days for each group.Results were expressed as the mean percent of control values for graphic clarity and represent the mean±SEM.We used a regression analysis to evaluate the association between mRNA expression for all the combinations of BDNF,TrkB,CREB and synapsin I,for each of the four groups. Additionally,we used regression analysis to evaluate the association between mRNA expression and MWM performance,both the acquisition(escape latency slope)and the consolidation phase (percentage time spent in P quadrant during probe trial),in each group.ResultsMicrobead injection siteWe inspected the microbead injection location viaﬂuorescence imaging.As shown in Fig.1,the microbead carrier is centralized to the injection site,in the stratum lacunosum moleculare(slm)of the hippocampus,while the drug transported is free to disperse to other areas of the hippocampus.Our microbead infusion site is consistent with our previous study,which used drug blockers coupled to microbeads(Vaynman et al.,2003).MWM performance:learning acquisitionTo assess spatial learning acquisition,we used a challenging2-trial-per-day paradigm,which has proven to be sufﬁciently sensitive for discerning learning differences between exercise and sedentary animals(van Praag et al.,1999).Animals were trained every day for5consecutive days on the MWM task.Results showed that the escape latencies were similar between all four groups on days1and2 of MWM training(Fig.2).We found a signiﬁcant difference in latency between the exc⁄cytC group and all the other three groups(sed⁄cytC, exc⁄TrkB-IgG,and sed⁄TrkB-IgG;Fig.2).We found that exc⁄cytC rats had signiﬁcantly shorter escape latencies on day3 (14.57±2.71s,P<0.01),day4(8.5±2.47s,P<0.05),and day 5(6.93±0.99s,P<0.05)of MWM training than sed⁄cytC control rats(31.58±3.63s,26.71±4.74s,and20.5±2.78s,respectively; Fig.2).Injection of TrkB-IgGs into the hippocampus signiﬁcantly abrogated the effect of exercise on MWM training performance, reducing the escape latency of exc⁄TrkB-IgG rats on days3 (34.2±2.39s,P<0.01),4(25.25±4.38s,P<0.05),and5 (19.94±3.18s,P<0.05)to sed⁄cytC control level(Fig.2).In contrast,TrkB-IgG injection did not have any signiﬁcant effect on sedentary rats;the sed⁄IgG group had similar escape latencies on days 3(30±4.92s),4(25.64±5.92s),and5(18.21±5.05s)to those of sed⁄cytC controls(Fig.2).The performance of groups during the acquisition phase can be better appreciated by looking at the slope of the escape latencies between groups.The exc⁄cytC group had a signiﬁcantly(P<0.05) steeper escape latency slope(m¼12.29)than the sed⁄cytC control group(m¼)8.66),illustrating that the exc⁄cytC rats had acquired the MWM task faster than sed⁄cytC control rats.Inhibiting BDNF action with TrkB-IgGs eliminated the increased rate of learning acquisition produced by exercise,as exc⁄TrkB-IgG(m¼)8.88)and sed⁄cytC control animals had a similar slope of acquisition.TrkB-IgG seemed to have no effect on MWM acquisition during sedentary conditions as there was no signiﬁcant difference in the slopes of sed⁄IgG animals(m¼)7.33)and sed⁄cytC controls.To determine when a signiﬁcant enhancement in MWM acqui-sition occurred,we performed an anova between days for eachExercise,BDNF and learning2583ª2004Federation of European Neuroscience Societies,European Journal of Neuroscience,20,2580–2590group.We found that escape latency in the exc ⁄cytC control group was signiﬁcantly reduced on day 3of MWM training (as compared with days 1and 2),indicating that they had a signiﬁcant improvement in learning acquisition on day 3of MWM training (ààP <0.01,Fig.2).In contrast,both sedentary groups,i.e.sed ⁄cytC and sed ⁄TrkB-IgG,did not show a signiﬁcant reduction in escape latency until day 4(as compared with days 1and 2,**P <0.01;Fig.2).We found that the exc ⁄TrkB-IgG group retained the signiﬁcant within group improvement on day 3(ààP <0.01;Fig.2),but that the performance of the exc ⁄cytC group was also signiﬁcantly better than exc ⁄TrkB-IgG rats on day 3(between groups,P <0.01;Fig.2).MWM performance:memory retentionTo evaluate memory retention,we performed a probe trial 2days after the last MWM training day.Rats were allowed to swim for 60s in the pool in which they received their training,but with the escape platform removed.The percentage of time spent in the probe quadrant,which previously housed the platform (quadrant P),was calculated for each animal.We found that the exc ⁄cytC group showed a clear preference for the P quadrant over sed ⁄cytC rats,as they spent a signiﬁcantly (P <0.05)greater percentage of time in quadrant P (48.27±3.14%)than sed ⁄cytC controls (33.95±4.64%).Administration of TrkB-IgG fully prevented the exercise-induced preference for the target quadrant,such that there was no difference between the amount of time spent by exc ⁄TrkB-IgG rats (32.13±3.22%)and sed ⁄cytC controls in quadrant P (Fig.3A).TrkB-IgG seemed not to affect the preference of sed ⁄TrkB-IgG rats for quadrant P,as there was no signiﬁcant difference in the percentage of time spent in quadrant P between sed ⁄TrkB-IgG (31.63±3.26%)and sedentary control rats (Fig.3A).We found that the results of our study showed an effect of blocking BDNF action during exercise,as sedentary groups,sed ⁄cytC and sed ⁄TrkB-IgG,did not show any signiﬁcant differ-ences in their escape latencies and preference for the target zone (quadrant P)in the MWM task,as would be achieved if BDNF was blocked during the actual MWM task (Mu et al .,1999).This effect was reproduced and very apparent in our mRNA results,discussed in the subsequent sections.We recorded the running distances for each exercise group and found that the average distance (Km)run over the 1-week period did not differ signiﬁcantly between the exercise groups,exc ⁄cytC (6.83±1.91)and exc ⁄TrkB-IgG (7.30±2.11).Effect of exercise and BDNF blockage on the mRNA levels of BDNF and its TrkB receptorBDNF uses TrkB as the primary receptor to transduce activity into signal transduction cascades (Barbacid,1994).Accordingly,we quantiﬁed hippocampal TrkB as well as BDNF mRNA levels in exercised animals.We found that exercise signiﬁcantly (P <0.05)increased the mRNA levels of BDNF (130±13%)and its TrkB receptor (120±6%)in the hippocampus above sed ⁄cytC controls% t i m e i n p r o b e q u a d r a n tABexc/cytC sed/cytC exc/TrkB-IgG sed/TrkB-IgGexc/cytC *sed/cytc exc/TrkB-IgG sed/TrkB-IgGEBBEBEBEEBPFig .3.Effect of blocking BDNF action during the exercise period on memory retention using the probe trial on the MWM task.(A)Exercise increased the memory retention on the MWM task as indicated by the ﬁnding that exercised animals spent signiﬁcantly more time in quadrant P than sedentary controls (exc ⁄cytC vs.sed ⁄cytC).Blocking BDNF action during exercise abolished this exercise-induced preference for the P quadrant (exc ⁄TrkB-IgG vs.exc ⁄cytC),such that exercised animals receiving the BDNF blocker spent as much time in the P quadrant as sedentary control animals (exc ⁄TrkB-IgG vs.sed ⁄cytC).Blocking BDNF action did not have an effect on the preference of sedentary animals for the P quadrant (sed ⁄TrkB-IgG vs.sed ⁄cytC).(B)Representative samples of trials traveled during the probe test (B,begin,E,end,P ,quadrant which previously housed the platform),illustrating the marked preference of the exc ⁄ctyC group for the P quadrant as compared to all other groups.Each value represents the mean ±SEM (anova ,Fischer test,*P <0.05).2584S.Vaynman et al .ª2004Federation of European Neuroscience Societies,European Journal of Neuroscience ,20,2580–2590。

1999年世界大学生数学竞赛复试试题及详细答案

−1 6n . ∞
if n is divisible by 5, otherwise it is
1 5·6n . n
Thus,
k=1
p5k is
1 5
+
4 5·6n
if n is divisible by 5, otherwise it is
−
3. Assume that x1 , . . . , xn ≥ −1 and
i=1
x3 i = 0. Prove that
n
xi ≤
i=1
n 3.
(20 points)
2
Solution. The inequality 3 1 1 0 ≤ x3 − x + = (x + 1) x − 4 4 2 holds for x ≥ −1. Substituting x1 , . . . , xn , we obtain
∞
f (x) =
k=1
p k xk =
x + x2 + x3 + x4 + x5 + x6 6
n
.
(The last equality can be easily proved by induction.)
∞
Our goal is to compute the sum
k=1 ∞
π π p5k . Let ε = cos 25 + i sin 25 be the ﬁrst 5th root of unity. Then
6th INTERNATIONAL COMPETITION FOR UNIVERSITY STUDENTS IN MATHEMATICS Keszthely, 1999. Problems and solutions on the second day

海口“PEP”2024年10版小学6年级第9次英语第2单元测验试卷

海口“PEP”2024年10版小学6年级英语第2单元测验试卷考试时间：90分钟（总分:140）B卷考试人：_________题号一二三四五总分得分一、综合题(共计100题)1、What do you call a place where you can see dinosaurs?A. MuseumB. ZooC. AquariumD. Park答案: A2、填空题：I can ______ (克服) obstacles in my path.3、选择题：What is the name of the famous beach in Rio de Janeiro?A. CopacabanaB. IpanemaC. BondiD. Waikiki4、填空题：The first university in the world was established in ______ (摩洛哥).5、听力题：The weather is _____ outside today. (nice)6、听力题：The chemical symbol for titanium is ______.7、What do you call the study of chemicals and their properties?A. BiologyB. ChemistryC. PhysicsD. Geology答案:B8、What do you call the place where you go to learn?A. SchoolB. StoreC. ParkD. Library答案:A9、听力题：I can ______ (draw) a map of my town.10、Which fruit is yellow and curved?A. AppleB. OrangeC. BananaD. Grape答案:C11、填空题：A lemur is found in ________________ (马达加斯加).12、填空题：My favorite outdoor activity is ______.13、填空题：The skunk can spray a ______ (臭味) for defense.14、What do we call the act of taking something from one place to another?A. TransportingB. MovingC. TransferringD. Conveying答案：A15、听力题：A saturated solution is one in which the maximum amount of solute has been ______.16、听力题：A ________ is a long period of dry weather.17、填空题：My dad, ______ (我爸爸), plays the guitar in a band.Did you ever watch a _______ (小蛇) slither?19、What do you use to write on paper?A. BrushB. PencilC. ScissorsD. Ruler答案: B20、选择题：What is the name of the insect that makes silk?A. AntB. ButterflyC. SilkwormD. Bee21、填空题：We learn about ______ (数学) in school.22、What color is the sky on a clear day?A. GreenB. BlueC. RedD. Yellow答案：B23、What is the main ingredient in salad?A. FruitB. Leafy greensC. MeatD. Cheese答案:B24、听力题：A chemical reaction can be reversible or _____.25、What is the currency used in the United States?A. EuroB. YenC. DollarD. Pound答案:C26、听力题：What do you want for ________?The turtle crawls slowly on the ______.28、填空题：I feel _______ when I sing.29、填空题：The cat catches a _______ (猫抓住一只_______).30、填空题：A ____(mixed-use development) combines residential and commercial spaces.31、听力题：The first successful heart surgery was performed by _______.32、What do you wear on your feet?A. HatB. GlovesC. ShoesD. Belt33、What is the largest land animal?A. RhinocerosB. GiraffeC. ElephantD. Hippopotamus34、填空题：We have a ______ (有趣的) discussion in class.35、填空题：I enjoy making ________ (名词) for my toys to play with in their own world.36、听力题：The __________ of a bee is essential for making honey.37、听力题：Chemical reactions can produce gases, liquids, or ______.38、听力题：A soluble substance can easily _______ in a liquid.39、填空题：The country known for its folklore is ________ (爱尔兰).My brother is interested in ____.41、听力题：My sister loves to ________.42、听力题：The chemical formula for hydrochloric acid is __________.43、填空题：My grandma tells me stories about ______ (动物). They are always very ______ (有趣).44、填空题：The _____ (环境保护) initiatives promote planting more trees.45、填空题：The invention of the steam locomotive revolutionized _____ travel.46、听力题：The stars are ________ in the sky.47、听力题：A __________ is a type of bond formed by sharing electrons.48、What is the opposite of "big"?A. LargeB. SmallC. HugeD. Giant答案: B49、What is the main ingredient in guacamole?A. TomatoB. AvocadoC. OnionD. Pepper答案:B50、What is the name of the star at the center of our solar system?A. MoonB. SunC. EarthD. Mars答案:B51、a Desert is mainly located in __________. (非洲) 填空题：The Saha52、What is the name of the famous painting by Leonardo da Vinci?A. Starry NightB. Mona LisaC. The ScreamD. Girl with a Pearl Earring答案: B. Mona Lisa53、听力题：The __________ of a frog helps it jump.54、What is the color of a bluebird?A. RedB. GreenC. BlueD. Yellow答案:C55、听力题：The process of rusting is an example of a __________ reaction.56、听力题：The __________ is a famous body of water in the Caribbean.57、听力题：The baby is very ___. (happy)58、听力题：Many different cultures can be found in _______.59、听力题：I have a _____ (goal) to achieve.60、填空题：The __________ Sea is famous for its saltwater. (死海)61、填空题：My sister is a good __________. (歌手)62、填空题：I can _______ very fast.63、听力题：Photosynthesis takes place mainly in the _____ (leaves) of plants.The capital of Myanmar is _____.65、听力题：A ______ is a type of bond where electrons are transferred.66、What is the tallest mountain in the world?A. K2B. Mount EverestC. KilimanjaroD. Denali答案:B67、What is 3 + 4?a. 6b. 7c. 8d. 9答案:B68、What is the main ingredient in mayonnaise?A. OilB. EggsC. VinegarD. Mustard答案:A. Oil69、填空题：I love to watch ________ (家庭电影) with my siblings.70、听力题：An alkali metal is very ______ reactive.71、填空题：The invention of the printing press was a key moment in _____ history.72、What is the capital of Thailand?A. BangkokB. HanoiC. JakartaD. Kuala Lumpur答案: A. Bangkok73、听力题：The process of thermal decomposition breaks down compounds using ______.What is the name of the desert in northern Africa?A. SaharaB. GobiC. KalahariD. Mojave75、听力题：She likes to __________ in the evening.76、填空题：The iguana basks in the _______ (阳光).77、填空题：The _____ (果汁) comes from fresh fruits.78、How many wheels does a bicycle have?A. OneB. TwoC. ThreeD. Four答案: B79、听力题：Chemical reactions can be represented using ________ equations.80、听力题：A chemical that acts as a nucleophile donates ______.81、听力题：The cat is ________ on the sofa.82、填空题：The __________ (历史研究) involves analyzing primary sources.83、What do you call a person who writes stories?A. AuthorB. EditorC. JournalistD. Poet答案:A84、听力题：A balanced chemical equation has the same number of atoms on both _____.85、What do you call the study of plants?A. BotanyB. ZoologyC. EcologyD. Agriculture答案:A86、填空题：The ______ (小鸡) hatched from an egg yesterday.87、听力题：The ______ is very knowledgeable about science.88、填空题：The __________ is a famous city known for its museums. (巴黎)89、填空题：The __________ (海岸) is perfect for swimming.90、填空题：The ________ (海洋探险) unveils new species.91、听力题：We should ________ our hands before eating.92、What do you call a scientist who studies rocks?A. BiologistB. GeologistC. ChemistD. Physicist答案: B93、选择题：What do we celebrate on December 25th?A. HalloweenB. ThanksgivingC. ChristmasD. New Year's94、What is a common pet that purrs?A. DogB. CatC. FishD. Rabbit95、填空题：The kangaroo hops across the _________. (平原)96、Which insect makes a web?A. AntB. BeeC. SpiderD. Fly答案: C97、How many players are on a hockey team?A. FiveB. SixC. SevenD. Eight98、填空题：The snail carries its _______ (壳) on its back.99、ts can grow in ______ (水) like water lilies. 填空题：Some pla100、填空题：The __________ tells us it will be sunny next week. (天气预报)。