Factors Associated With Excessive Migration in Bone Impaction Hip Revision Surgery A Radios
因子载荷系数英文
因子载荷系数英文Factor loading coefficients, also known as factor loadings, are essential statistical measures used in factor analysis. They quantify the relationship between observed variables and latent factors in a model. In this article, we will explore the concept of factor loading coefficients in the field of statistics.Introduction to Factor Loading CoefficientsFactor loading coefficients play a crucial role in understanding the underlying structure of a set of observed variables. They indicate the strength and direction of the relationship between the observed variables and the latent factors. The coefficients can range from -1 to 1, with values closer to -1 or 1 indicating a stronger relationship.Interpretation of Factor Loading CoefficientsTo interpret factor loading coefficients, it is important to consider both the magnitude and sign of the coefficients. A positive coefficient indicates a positive relationship between the observed variable and the latent factor, while a negative coefficient indicates a negative relationship.The magnitude of the coefficient represents the strength of the relationship. Higher magnitudes suggest a stronger association between the observed variable and the latent factor. However, it is important to note that the absolute value of the coefficient is more meaningful than the magnitude itself.Importance of Factor Loading CoefficientsFactor loading coefficients are used to assess the quality of the factor model. They help researchers determine which observed variables are most strongly related to each latent factor. By examining the coefficients, researchers can identify the key variables that contribute most to a specific factor.Moreover, factor loading coefficients can be used to determine the reliability and validity of a measure. A measure is considered reliable when its observed variables load highly on their designated factors. Conversely, measures with low factor loading coefficients may indicate measurement errors or weak variables.Calculation of Factor Loading CoefficientsFactor loading coefficients can be calculated using various methods, such as principal component analysis (PCA) or maximum likelihood estimation (MLE). These methods aim to estimate the associations between observed variables and latent factors based on the data collected.PCA is a commonly used method for factor analysis. It transforms the observed variables into an orthogonal set of factors. The factor loading coefficients in PCA represent the correlation between the observed variables and the factors.MLE, on the other hand, estimates the parameters of a statistical model by maximizing the likelihood function. In factor analysis, MLE is used to estimate the factor loading coefficients by maximizing the likelihood of the observed data given the latent factors.Limitations of Factor Loading CoefficientsWhile factor loading coefficients provide valuable insights, they have certain limitations. First, they are sample-specific and may vary across different samples. Therefore, caution should be exercised when generalizing findings based on specific factor loading coefficients.Second, the interpretation of factor loading coefficients depends on the context and underlying theory. A coefficient considered substantial in one study may not be significant in another. Thus, it is essential to consider the specific research question and theoretical framework when interpreting the coefficients.ConclusionFactor loading coefficients are fundamental statistical measures in factor analysis. They help researchers understand the relationship between observed variables and latent factors. By interpreting these coefficients, researchers can identify key variables, assess measure reliability, and evaluate the quality of a factor model.It is crucial to consider the magnitude and sign of the coefficients when interpreting their meaning. However, it is important to recognize the limitations of factor loading coefficients, as they are sample-specific and context-dependent. Overall, factor loading coefficients provide valuable insights into the underlying structure of a set of observed variables.。
Certaintyfactors
MB(H, E) − MD(H, E) cf = 1 − min [MB(H, E), MD(H, E)]
Consider a simple rule:
IF A is X THEN B is Y
In usual cases experts are not absolute certain that a rule holds and the expert usually can associate a certainty factor with each possible value B given that A has value X.
Basic probability theory Bayesian reasoning Uncertainty factor
Certainty factors
Certainty factor theory is a popular alternative to Bayesian reasoning. Introduced by the developers of MYCIN expert system because of:
Combining the views of different experts
Large expert systems usually combine the knowledge and expertise of a number of experts. Unfortunately, experts seldom reach exactly the same conclusions. Usually, experts have contradictory opinions and produce conflicting rules. To resolve the conflict, the knowledge engineer has to attach a weight to each expert and then calculate the composite conclusion.
Conversion Factors
CONVERSION fACTORSThe following table gives conversion factors from various units of measure to SI units . It is reproduced from NIST Special Publication 811, Guide for the Use of the International System of Units (SI) . The table gives the factor by which a quantity expressed in a non-SI unit should be multiplied in order to calculate its value in the SI . The SI values are expressed in terms of the base, supple-mentary, and derived units of SI in order to provide a coherent presentation of the conversion factors and facilitate computations (see the table “International System of Units” in this section) . If desired, powers of ten can be avoided by using SI prefixes and shifting the decimal point if necessary .Conversion from a non-SI unit to a different non-SI unit may be carried out by using this table in two stages, e .g .,1 cal th = 4 .184 J1 Btu IT = 1 .055056 E+03 JThus,1 Btu IT = (1 .055056 E+03 ÷ 4 .184) cal th = 252 .164 cal th Conversion factors are presented for ready adaptation to com-puter readout and electronic data transmission . The factors are written as a number equal to or greater than one and less than ten with six or fewer decimal places . This number is followed by the letter E (for exponent), a plus or a minus sign, and two digits that indicate the power of 10 by which the number must be multiplied to obtain the correct value . For example:3 .523 907 E-02 is 3 .523 907 × 10–2or0 .035 239 07Similarly:3 .386 389 E+03 is 3 .386 389 × 103or3 386 .389A factor in boldface is exact; i .e ., all subsequent digits are zero . All other conversion factors have been rounded to the figures given in accordance with accepted practice . Where less than six digits after the decimal point are shown, more precision is not warranted .It is often desirable to round a number obtained from a conver-sion of units in order to retain information on the precision of the value . The following rounding rules may be followed:1 . If the digits to be discarded begin with a digit less than 5, thedigit preceding the first discarded digit is not changed .Example: 6 .974 951 5 rounded to 3 digits is 6 .972 . If the digits to be discarded begin with a digit greater than5, the digit preceding the first discarded digit is increasedby one .Example: 6 .974 951 5 rounded to 4 digits is 6 .9753 . If the digits to be discarded begin with a 5 and at least oneof the following digits is greater than 0, the digit precedingthe 5 is increased by 1 .Example: 6 .974 851 rounded to 5 digits is 6 .974 94 . If the digits to be discarded begin with a5 and all of the fol-lowing digits are 0, the digit preceding the 5 is unchangedif it is even and increased by one if it is odd . (Note that thismeans that the final digit is always even .)Examples:6 .974 951 5 rounded to7 digits is 6 .974 9526 .974 950 5 rounded to7 digits is 6 .974 950ReferenceTaylor, B . N ., Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 1995 Edition, Superintendent of Documents, U .S . Government Printing Office, Washington, DC 20402, 1995 .Factors in boldface are exactTo convert from to Multiply by abampere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ampere (A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.0E+01 abcoulomb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .coulomb (C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.0E+01 abfarad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .farad (F) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.0E+09 abhenry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .henry (H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.0E–09 abmho . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .siemens (S) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.0E+09 abohm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ohm (Ω) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.0E–09 abvolt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .volt (V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.0E–08 acceleration of free fall, standard (g n) . . . . . . . . . . . . . . . . . . .meter per second squared (m/s2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9.806 65E+00 acre (based on U .S . survey foot)9 . . . . . . . . . . . . . . . . . . . . . . . . . .square meter (m2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 .046 873 E+03 acre foot (based on U .S . survey foot)9 . . . . . . . . . . . . . . . . . .cubic meter (m3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .233 489 E+03 ampere hour (A ∙ h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .coulomb (C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.6E+03ångström (Å) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .meter (m) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.0E–10ångström (Å) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .nanometer (nm) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.0E–01 apostilb (asb) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .candela per meter squared (cd/m2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 .183 098 E–01 are (a) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .square meter (m2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.0E+02 astronomical unit (ua or AU) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .meter (m) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .495 979 E+11 atmosphere, standard (atm) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .pascal (Pa) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.013 25 E+05 atmosphere, standard (atm) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .kilopascal (kPa) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.013 25E+02 atmosphere, technical (at)10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .pascal (Pa) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9.806 65E+04 atmosphere, technical (at)10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .kilopascal (kPa) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9.806 65E+019 The U .S . survey foot equals (1200/3937) m . 1 international foot = 0 .999998 survey foot .10 One technical atmosphere equals one kilogram-force per square centimeter (1 at = 1 kgf/cm2) .1-28To convert from to Multiply bybar (bar) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .pascal (Pa) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.0E+05 bar (bar) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .kilopascal (kPa) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.0E+02 barn (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .square meter (m2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.0E–28 barrel [for petroleum, 42 gallons (U .S .)](bbl) . . . . .cubic meter (m3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .589 873 E–01 barrel [for petroleum, 42 gallons (U .S .)](bbl) . . . . .liter (L) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .589 873 E+02 biot (Bi) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ampere (A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.0E+01 British thermal unit IT (Btu IT)11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule (J) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .055 056 E+03 British thermal unit th (Btu th)11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule (J) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .054 350 E+03 British thermal unit (mean) (Btu) . . . . . . . . . . . . . . . . . . . . . . . . .joule (J) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .055 87 E+03 British thermal unit (39 ºF) (Btu) . . . . . . . . . . . . . . . . . . . . . . . . . .joule (J) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .059 67 E+03 British thermal unit (59 ºF) (Btu) . . . . . . . . . . . . . . . . . . . . . . . . . .joule (J) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .054 80 E+03 British thermal unit (60 ºF) (Btu) . . . . . . . . . . . . . . . . . . . . . . . . . .joule (J) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .054 68 E+03 British thermal unit IT foot per hour square foot degree Fahrenheit[Btu IT ∙ ft/(h ∙ ft2∙ ºF)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .watt per meter kelvin [W/(m ∙ K)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .730 735 E+00 British thermal unit th foot per hour square foot degree Fahrenheit[Btu th ∙ ft/(h ∙ ft2∙ ºF)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .watt per meter kelvin [W/(m ∙ K)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .729 577 E+00 British thermal unit IT inch per hour square foot degree Fahrenheit[Btu IT ∙ in/(h ∙ ft2∙ ºF)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .watt per meter kelvin [W/(m ∙ K)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .442 279 E–01 British thermal unit th inch per hour square foot degree Fahrenheit[Btu th ∙ in/(h ∙ ft2∙ ºF)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .watt per meter kelvin [W/(m ∙ K)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .441 314 E–01 British thermal unit IT inch per second square foot degree Fahrenheit[Btu IT ∙ in/(s ∙ ft2∙ ºF)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .watt per meter kelvin [W/(m ∙ K)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 .192 204 E+02 British thermal unit th inch per second square foot degree Fahrenheit[Btu th ∙ in/(s ∙ ft2∙ ºF)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .watt per meter kelvin [W/(m ∙ K)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 .188 732 E+02 British thermal unit IT per cubic foot(Btu IT/ft3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule per cubic meter (J/m3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 .725 895 E+04 British thermal unit th per cubic foot(Btu th/ft3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule per cubic meter (J/m3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 .723 403 E+04 British thermal unit IT per degree Fahrenheit(Btu IT/ºF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule per kelvin (J/k) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .899 101 E+03 British thermal unit th per degree Fahrenheit(Btu th/ºF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule per kelvin (J/k) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .897 830 E+03 British thermal unit IT per degree Rankine(Btu IT/ºR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule per kelvin (J/k) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .899 101 E+03 British thermal unit th per degree Rankine(Btu th/ºR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule per kelvin (J/k) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .897 830 E+03 British thermal unit IT per hour (Btu IT/h) . . . . . . . . . . . . .watt (W) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 .930 711 E–01 British thermal unit th per hour (Btu th/h) . . . . . . . . . . . . . .watt (W) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 .928 751 E–01 British thermal unit IT per hour square foot degree Fahrenheit[Btu IT/(h ∙ ft2∙ ºF)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .watt per square meter kelvin[W/(m2 ∙ K)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 .678 263 E+00 British thermal unit th per hour square foot degree Fahrenheit[Btu th/(h ∙ ft2 ∙ ºF)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .watt per square meter kelvin[W/(m2∙ K)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 .674 466 E+00 British thermal unit th per minute (Btu th/min) . . . . .watt (W) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .757 250 E+01 British thermal unit IT per pound (Btu IT/lb) . . . . . . . . .joule per kilogram (J/kg) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.326E+03 British thermal unit th per pound (Btu th/lb) . . . . . . . . . .joule per kilogram (J/kg) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 .324 444 E+03 British thermal unit IT per pound degree Fahrenheit[Btu IT/(lb ∙ ºF)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule per kilogram kelvin (J/(kg ∙ K)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.1868E+03 British thermal unit th per pound degree Fahrenheit[Btu th/(lb ∙ ºF)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule per kilogram kelvin [J/(kg ∙ K)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.184E+03 British thermal unit IT per pound degree Rankine[Btu IT/(lb ∙ ºR)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule per kilogram kelvin [J/(kg ∙ K)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.1868E+03 British thermal unit th per pound degree Rankine[Btu th/(lb ∙ ºR)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule per kilogram kelvin [J/(kg ∙ K)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.184 E+03 British thermal unit IT per second (Btu IT/s) . . . . . . . . . .watt (W) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .055 056 E+03 British thermal unit th per second (Btu th/s) . . . . . . . . . . .watt (W) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .054 350 E+0311 The Fifth International Conference on the Properties of Steam (London, July 1956) defined the International Table calorie as 4 .1868 J . Therefore the exact conversion factor for the International Table Btu is 1 .055 055 852 62 kJ . Note that the notation for the International Table used in this listing is subscript “IT” . Similarily, the notation for thermochemical is subscript “th .” Further, the thermochemical Btu, Btu th, is based on the thermochemical calorie, cal th, where cal th = 4 .184 J exactly .To convert from to Multiply by British thermal unit IT per second square foot degree Fahrenheit[Btu IT/(s ∙ ft2 ∙ ºF)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .watt per square meter kelvin[W/(m2 ∙ K)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 .044 175 E+04 British thermal unit th per second square foot degree Fahrenheit[Btu th/(s ∙ ft2 ∙ ºF)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .watt per square meter kelvin[W/(m2 ∙ K)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 .042 808 E+04 British thermal unit IT per square foot(Btu IT/ft2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule per square meter (J/m2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .135 653 E+04 British thermal unit th per square foot(Btu th/ft2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule per square meter (J/m2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .134 893 E+04 British thermal unit IT per square foot hour[(Btu IT/(ft2 ∙ h)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .watt per square meter (W/m2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 .154 591 E+00 British thermal unit th per square foot hour[Btu th/(ft2 ∙ h)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .watt per square meter (W/m2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 .152 481 E+00 British thermal unit th per square foot minute[Btu th/(ft2 ∙ min)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .watt per square meter (W/m2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .891 489 E+02 British thermal unit IT per square foot second[(Btu IT/(ft2 ∙ s)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .watt per square meter (W/m2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .135 653 E+04 British thermal unit th per square foot second[Btu th/(ft2 ∙ s)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .watt per square meter (W/m2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .134 893 E+04 British thermal unit th per square inch second[Btu th/(in2 ∙ s)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .watt per square meter (W/m2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .634 246 E+06 bushel (U .S .) (bu) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .cubic meter (m3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 .523 907 E–02 bushel (U .S .) (bu) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .liter (L) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 .523 907 E+01 calorie IT (cal IT)11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule (J) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.1868E+00 calorie th (cal th)11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule (J) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.184E+00 calorie (cal) (mean) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule (J) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 .190 02 E+00 calorie (15 ºC) (cal15) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule (J) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 .185 80 E+00 calorie (20 ºC) (cal20) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule (J) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 .181 90 E+00 calorie IT, kilogram (nutrition)12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule (J) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.1868E+03 calorie th, kilogram (nutrition)12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule (J) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.184E+03 calorie (mean), kilogram (nutrition)12 . . . . . . . . . . . . . . . . . .joule (J) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 .190 02 E+03 calorie th per centimeter second degree Celsius[cal th/(cm ∙ s ∙ ºC)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .watt per meter kelvin [W/(m ∙ K)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.184E+02 calorie IT per gram (cal IT/g) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule per kilogram (J/kg) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.1868E+03 calorie th per gram (cal th/g) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule per kilogram (J/kg) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.184E+03 calorie IT per gram degree Celsius[cal IT/(g ∙ ºC)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule per kilogram kelvin [J/(kg ∙ K)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.1868E+03 calorie th per gram degree Celsius[cal th/(g ∙ ºC)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .joule per kilogram kelvin [J/(kg ∙ K)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.184E+03 calorie IT per gram kelvin [cal IT/(g ∙ K)] . . . . . . . . . . . . . . . . .joule per kilogram kelvin [J/(kg ∙ K)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.1868E+03 calorie th per gram kelvin [cal th/(g ∙ K)] . . . . . . . . . . . . . . . . . .joule per kilogram kelvin [J/(kg ∙ K)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.184E+03 calorie th per minute (cal th/min) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .watt (W) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 .973 333 E–02 calorie th per second (cal th/s) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .watt (W) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.184E+00 calorie th per square centimeter (cal th/cm2) . . . . . . . . . . .joule per square meter (J/m2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.184E+04 calorie th per square centimeter minute[cal th/(cm2∙ min)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .watt per square meter (W/m2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 .973 333 E+02 calorie th per square centimeter second[cal th/(cm2∙ s)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .watt per square meter (W/m2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.184E+04 candela per square inch (cd/in2) . . . . . . . . . . . . . . . . . . . . . . . . . . . .candela per square meter (cd/m2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .550 003 E+03 carat, metric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .kilogram (kg) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.0E–04 carat, metric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .gram (g) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.0E–01 centimeter of mercury (0 ºC)13 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .pascal (Pa) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .333 22 E+03 centimeter of mercury (0 ºC)13 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .kilopascal (kPa) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .333 22 E+00 centimeter of mercury, conventional (cmHg)13 . .pascal (Pa) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .333 224 E+0312 The kilogram calorie or “large calorie” is an obsolete term used for the kilocalorie, which is the calorie used to express the energy content of foods . However, in practice, the prefix “kilo” is usually omitted .13 Conversion factors for mercury manometer pressure units are calculated using the standard value for the acceleration of gravity and the density of mercury at the stated temperature . Additional digits are not justified because the definitions of the units do not take into account the compressibility of mercury or the change in density caused by the revised practical temperature scale, ITS-90 . Similar comments also apply to water manometer pressure units . Conversion factors for conventional mercury and water manometer pressure units are based on ISO 31-3 .。
干细胞最新突破消息,干细胞有什么用途,注意利弊
干细胞最新突破消息，干细胞有什么用途，注意利弊干细胞新突破消息，干细胞有什么用途，注意利弊！在现代医学的探索中，干细胞技术的发展不仅令人兴奋，也带来了前所未有的可能性。
干细胞疗法是一种具有自我复制和多向分化潜能的细胞，它们可以分化为人体中任何类型的细胞，如肌肉细胞、神经细胞或肝细胞等。
那么，干细胞有什么用途呢？干细胞可以帮助治多种病：例如，对于心脏病患者，干细胞可以对于新的心肌细胞生长，心脏功能；对于糖尿患者，干细胞可以生成新的胰岛细胞，帮助调控血糖；对于帕森病患者，干细胞可以生成神经细胞，缓解症状。
此外，干细胞疗法可以提高人体的免疫、减缓衰老过程、并可以用于美容领域！需要注意的是，虽然干细胞疗法有诸多好处，但也存在一些风险。
研究发现，越是能变化多端的干细胞，其致瘤性也越大，面对的伦理困境也越大，我们也不能忽视其可能带来的副作用。
干细胞副作用可以从两个层面来考虑：一是与移植过程有关的技术问题，二是生物学反应引发的副作用。
在技术层面上，任何操作都存在风险，包括感染、出血以及麻晬相关的风险等。
而在干细胞操作中，如何精确地将干细胞定位到受损区域，也是一大挑战。
如果不能准确地达到目标区域，可能会导致效果不佳甚至产生新的问题。
Stem cell side effects can be considered from two levels: one is the technical problems related to the transplant process, and the other is the side effects caused by biological reactions. On a technical level, there are risks associated with any operation.从生物学角度来讲，干细胞可能导致副作用主要涉及免疫反应和肿瘤形成。
当体内植入异体干细胞时，患者的免役系统可能会将其视为外来入侵者，并发起攻击，这就可能发生免役排斥反应。
英语作文关于环境问题
Environmental issues have become a global concern that affects every individual on our planet.The degradation of the environment is a complex problem that requires a multifaceted approach to address.In this essay,we will delve into the various aspects of environmental problems,their causes,and potential solutions.Introduction to Environmental IssuesThe Earths environment is under immense pressure due to human activities.From deforestation and habitat destruction to pollution and climate change,the consequences are farreaching and often irreversible.The loss of biodiversity,the depletion of natural resources,and the disruption of ecosystems are just a few examples of the challenges we face.Causes of Environmental Problems1.Industrialization and Urbanization:The rapid growth of industries and urban areas has led to significant pollution.Factories emit harmful gases and chemicals into the air and water,contributing to air and water pollution.2.Deforestation:The clearing of forests for agriculture,logging,and urban expansion has resulted in the loss of habitats for countless species and the release of carbon dioxide into the atmosphere.3.Overconsumption:The modern lifestyle,characterized by high consumption rates, generates a massive amount of waste,leading to landfill overflow and pollution.4.Agricultural Practices:The use of chemical fertilizers and pesticides in agriculture not only affects the quality of soil and water but also harms the health of humans and wildlife.5.Climate Change:The increase in greenhouse gas emissions,primarily from the burning of fossil fuels,is causing global temperatures to rise,leading to a myriad of environmental problems such as melting ice caps,rising sea levels,and extreme weather events.Effects of Environmental Problems1.Health Impacts:Pollution and climate change can lead to respiratory diseases, heatrelated illnesses,and the spread of vectorborne diseases.2.Economic Consequences:The degradation of the environment can lead to reducedagricultural productivity,loss of tourism revenue due to environmental degradation,and increased costs associated with disaster recovery.3.Social Implications:Environmental issues can lead to conflicts over resources, displacement of communities,and increased social inequality.Solutions to Environmental Problems1.Sustainable Practices:Adopting sustainable practices in agriculture,industry,and urban planning can help reduce the environmental impact of human activities.2.Renewable Energy:Transitioning to renewable energy sources such as solar,wind,and hydroelectric power can significantly reduce greenhouse gas emissions.3.Conservation Efforts:Protecting and restoring natural habitats,as well as implementing conservation programs for endangered species,can help preserve biodiversity.4.Waste Management:Implementing effective waste management strategies,including recycling and reducing waste production,can help mitigate the problem of pollution.5.Public Awareness and Education:Raising public awareness about the importance of environmental conservation and educating individuals on sustainable practices can lead to behavioral changes that benefit the environment.ConclusionAddressing environmental issues is a collective responsibility that requires the cooperation of governments,businesses,and individuals.By understanding the causes and effects of environmental problems and implementing sustainable solutions,we can work towards a healthier and more sustainable future for our planet.It is crucial that we act now,as the consequences of inaction will be felt by future generations and the planet itself.。
国外商学院人力资源14 blcm Interventions Organisation
Change in Organisations at the Larger-System Level – Interorganisational Larger System Level Changes fail when there is:
Insufficient goal and measurement clarity Imbalance of power between the organizations Imbalance of expertise, status or prestige Overconfident, unrealistic ideas about control over key variables Lack of a contingency plan Lack of perceived equity
•Markets & Products •Community, Education and Direct •Corporate Center •Global Supply Chain •Corporate finance
IKEA
Centralised, Functional
Decentralised, Divisional
Change in Organisations at the Larger-System Level – Change Focus
Revolutionary, focus on the big picture: organization’s purpose, mission, strategy, leadership and culture, e.g. Evolutionary, focus on organizational design and structure, information systems, management practices, e.g.
林木病理学_东北林业大学中国大学mooc课后章节答案期末考试题库2023年
林木病理学_东北林业大学中国大学mooc课后章节答案期末考试题库2023年1.According to plant pathology, which of the following is not caused by viraldiseases?答案:Bacterial gall on the stem2.Parasite is答案:an organism that grows part or all of the time on or within another organism of a different species(known as its host),and from which it derives all or part of its food.3. A pathogen is答案:an organism that causes disease.4.Biotic disease is答案:Disease caused by living organisms.5.Host is答案:An organism upon which an organism of a different species grows and from which all or most of its food is derived.6.which feature is not characteristic of mushroom structure?答案:leaf7.What is plant disease?答案:sustained physiological and structural damage to plant tissues caused by biological and non-biological agents ending sometimes in plant death.8.abiotic disease is答案:Disease resulting from nonliving agents.9.Saprophyte is答案:An organism that lives on dead organic matter.10.What is the definition of obligate parasite?答案:A parasite that is incapable of existing independently of living tissues.11.What is the definition of Facultative saprophytes?答案:are mostly parasitic, but have the faculty to live on dead organic matter, like Phytophthora spp.12.What is the definition of toxicity?答案:The inherent ability of a toxicant to damage plants and animals. 13.What is the possible diameter for mushroom spores?答案:10μm14.which of the following cells or structures are associated with sexualreproduction in fungi?答案:ascospores15.All fungi share which of the following characteristics?答案:heterotrophic16.chestnut blight is a kind of _____ disease.答案:Infectious17.Crown gall often grows on willow in Sun Island Park，Crown gall is a _____disease.答案:Bacterial18.对Forest decline正确的理解的是答案:森林衰退19.Diplodia Blight of Pines（松枯梢病）is casused by Sphaeropsis sapinea, syn.Diplodia pinea，which of the following is the correct description of thedisease.答案:A fungal infectious disease20.According to the knowledge of Plant Pathology, the correct description of thevirus is:答案:Viruses are too small to be seen even with the aid of a powerful lightmicroscope.Viruses are systemic pathogens.21.Viruses are characteristically composed of which one?答案:a protein coata nucleic acid core22.The correct description of fungi is答案:Fungi are heterotrophs that feed by absorptionFungi play key roles in nutrient cycling, ecological interactions, and human welfareFungi produce spores through sexual or asexual life cyclesFungi have radiated into a diverse set of lineages23.Which are biotic factors in the following items？答案:Bacteria Fungi。
AMOS词句中英文对照
AMOS词句中英⽂对照AMOS词句中英⽂对照王超整理Covariance 协⽅差（共变关系）Data Files 数据⽂件的连结设定File Manager ⽂件管理Interface Properties 界⾯属性Analysis Properties 分析属性Object Properties 对象属性Variables in Model 模型中的变量Variables in Dataset 数据⽂件中的变量Parameters 参数Diagram 绘图Draw Observed 描绘观察变量Draw Unobserved 描绘潜在变量Draw Path 描绘单向路径图Draw Covariance 描绘双向协⽅差图Figure Caption 图⽰标题（图形标题）Draw Indicator Variable 描绘指标变量Draw Unique Variable 描绘误差变量Zoom In 放⼤图⽰Zoom Out 缩⼩图⽰Loupe 放⼤镜检视Redraw diagram 重新绘制图形Identified 被识别unidentified ⽆法识别undo 撤销redo 恢复（重做）Copy to clipboafd 复制到剪切板Deselect all 解除选取全部对象Duplicate 复制对象Erase 删除对象Move Parameter 移动参数位置Reflect 映射指标变量Rotate 旋转指标变量Shape of Object 改变对象形状Space Horizontally 调整选取对象的⽔平距离Space Vertically调整选取对象的垂直距离Drag Properties 拖动对象属性Fit to Page 适合页⾯Touch up 模型图最适接触Model-Fit 模型适配度Calculate Estimates 计算估计值Stop Calculate Estimates停⽌计算估计值程序Manage Groups 管理群组/ 多群组设定Manage Models 管理模型/ 多重模型设定Modeling Lab 模型实验室Toggle Observed / Unobserved 改变观察变量/潜在变量Degree of Freedom ⾃由度的信息Specification Search 模型界定的搜寻Multiple-Group Analysis 多群组分析Bayesian estimation 适⽤于⼩样本的贝⽒估计法Data imputation 缺失值数据替代法List Font 字型Smart 对称性Outline 呈现路径图的线条Square 以⽅型⽐例绘图Golden 以黄⾦分割⽐例绘图Customize 定制功能列Seed Manager 种⼦管理Draw Covariances 描绘协⽅差双箭头图Growth Curve Model 增长曲线模型Name Parameters 增列参数名称Name Unobserved Variables 增列潜在变量名称Resize Observed Variables 重新设定观察变量⼤⼩Standardized RMR 增列标准化RMR值Plugins 增列Commands 命令Categories 分类Parameter Formats 参数格式Computation Summary 计算摘要Files in current directory ⽬前⽬录中的⽂件Standardized estimates 标准化估计Unstandardized estimates 未标准化估计View the input path diagram-Model specification显⽰输⼊的路径图View the output path diagram 显⽰输出结果的路径图Default model 预设模型Saturated model 饱和模型Independent model 独⽴模型1 variable is unnamed ⼀个变量没有名称Nonpositive definite matrices ⾮正定矩阵Portrait 肖像照⽚格式（纵向式的长⽅形：⾼⽐宽的长度长）Landscape 风景照⽚格式（横向式长⽅形：宽⽐⾼的长度长）Page Layout 页⾯配置Orientation ⽅向Apply 应⽤Latent variables 潜在变量Latent independent潜在⾃变量（因变量）Exogenous variables外因变量Latent dependent潜在依变量（果变量）Endogenous variables内因变量Draw a latent variable or add an indicator to a latent variable 描绘潜在变量或增画潜在变量的指标变量Rotate the indicators of a latent variable 旋转潜在变量的指标变量Error variable 误差变量Draw paths-single headed arrows 描绘单向箭头的路径Draw covariances-double headed arrows 描绘协⽅差（双向箭头）的路径Add a unique variable to an existing variable 增列误差变量到已有的变量中Residual variables 残差变量（误差变量）Minimization history 极⼩化过程的统计量Squared multiple correlations 多元相关平⽅/复相关系数平分Indirect, direct ＆ Total effects 间接效果、直接效果与总效果Sample moments样本协⽅差矩阵或称样本动差Implied moments 隐含协⽅差矩阵或称隐含动差Residual moments 残差矩阵或称残差动差Modification indices 修正指标Factor score weights 因素分数加权值Covariance estimates 协⽅差估计值Critical ratios for difference差异值的临界⽐值/ 差异值的Z检验Test for normality and outliers正态性与极端值的检验Observed information matrix 观察的信息矩阵Threshold for modification indices修正指标临界值的界定Means and intercepts 平均数与截距Page Setpage 设定打印格式Decimails⼩数点位数Column spacing 表格栏宽度Maximum number of table columns 表格字段的最⼤值Table Rules 表格范例Table Border 表格边框线Analysis Summary 分析摘要表Notes for Group 组别注解Fill color 形状背景的颜⾊Line width 边框线条的粗度Very Thin ⾮常细Very Thick ⾮常粗Fill style 填充样式Transparent 颜⾊透明Solid 完全填满Regular 正常字型Italic 斜体字型Bold 粗体字型Bold Italic粗斜体字型Set Default 设为默认值Set Default Object Properties 预设对象属性Pen width 对象框线Fill style 对象内样式Parameter orientation 参数呈现⽅向The path diagram 绘制的路径图中Normal template AMOS内定的⼀般样板格式中Visibility 可见性：显⽰设定项⽬在路径图上Use visibility setting 使⽤可见设置Show picture 显⽰图形对象Drag properties from object to object 将对象的属性在对象间拖动Height ⾼度X coordinate X坐标-⽔平位置Y coordinate Y坐标-垂直位置Parameter constraints 参数标签名称Preserve symmetries 保留对称性Zoom in on an area that you select 扩⼤选取的区域View a smaller area of the path diagram 将路径图的区域放⼤View a larger area of the path diagram 将路径图的区域缩⼩Show the entire page on the screen 将路径图整页显⽰在屏幕上Resize the path diagram to fit on a page 重新调整路径图的⼤⼩以符合编辑画⾯（路径图呈现于编辑窗⼝页⾯内）Examine the path diagram with the loupe 以放⼤镜检核路径图Multiple-Group Analysis 多群体的分析Specification Search 模型界定的搜寻Select one object at a time ⼀次选取单⼀对象Iteration 8 迭代次数为8Pairwise Parameter Comparisons 成对参数⽐较Varance-Covariance Matrix of Estimates 估计值间⽅差协⽅差矩阵Output输出结果标签钮Minimization history 最⼩化过程Standardized estimates 标准化的估计值Squared multiple estimates 多元相关的平⽅Indirect, direct ＆ total effects间接效果、直接效果与总效果Sample moments 观察样本协⽅差矩阵Implied moments 隐含协⽅差矩阵Residual moments 残差矩阵Modification indices 修正指标Tests for normality and outlies 检验正态性与异常值AMOS的五种选项估计法：Maximum likelihood 极⼤似然法，简称ML法Generalized least squares ⼀般化最⼩平⽅法，简称GLS法Unweighted least squares 未加权最⼩平⽅法，简称ULS法Scale-free least squares 尺度⾃由最⼩平⽅法，简称SFLS法Asymptotically distribution free 渐近分布⾃由法，简称ADF法“错误提⽰”部分：An error occurred while checking for missing data in the group, Group number 1.You have not supplied enough information to allow computing the sample variances and covariances. You must supply exactly one of the following: 没有提供⾜够的信息，因⽽⽆法计算样本的⽅差与协⽅差，使⽤者必须正确提供：a. The sample variance-covariance matrix. a. 样本⽅差-协⽅差矩阵b. The sample correlation matrix and the sample standard deviations b.样本相关矩阵与样本的标准差；c. Raw data. c.原始资料。
Vitiating Factors
Vitiating FactorsCircumstances that make a legal transaction void are known as “vitiating circumstances”, because they invalidate the affected transaction. When a legal transaction (such as a contract) is made void, it is as though that transaction had never been entered into at all. It is wiped out as from its very beginning (ab initio). As a consequence 结果of this, any legal obligation that were created by that transaction are discharged, and any money paid or property transferred must be given back, so that neither party retains any benefit under the vitiated transaction.•Mistake•Misrepresentation•Unconscionable conduct 过度的行为•Undue influence 不正当压力•Duress 强迫•Misleading conduct 令人误解的行为•Illegality 违法Duress·Duress exists when one party uses, of threatens恐吓to use, unlawful force武力or harm to obtain the other party’s agreement.·The forces or harm may be physical harm to the person, or economic harm, or illegal actions over their goods ( such as refusing to return goods), t·a contract can be set aside on grounds of duress if the threats of violence are made either directly against the contracting party, or against a person who is related or close to themBarton v Armstrong B 买了A 股份，之后说是A 恐吓，后发现有其他原因Once B had proved that A had made the threats, A was under an onus to show the threats had not contributed to B’s dicision to enter the contract. The court found that even though there were other reasons for agreeing to buy the shares, A had not been able to show that his threats had not contributed to B’s decision. It was therefore open to B to avoid the contract if he wished.·Threats of economic harm rather than physical harm may constitute duressNorth Ocean Shipping Co Lth v Hyundai Construction Co LtdUndue Influence不正当压力Where ascendant 优越的party takes improper不适当的advantage of position of dominance 优势，统治over the dependent party，and the transaction may be set aside as void ab initio.When the parties to a transaction have some other pre- existing relationship, such as when a parent enters a contract with their child (solicitor律师& client, doctor & patient, guardian & ward, religious advisor 宗教的顾问& believer, trustee 托管人& beneficiary受益人) one of the parties may have a position of dominance, control or influence over the other, so that the weaker party is not really able to exercise their independent judgment独立的判断in deciding whether or not to contract.Certain relationship inevitably必然地give one party a controlling degree of influence over the other. When such a relationship exists between contracting parties, it is presumed that a contract between them is made because the controlling party used undue influence to obtain the consent of the weaker party.·The onus 责任，义务is then on the controlling party to rebut 反驳this presumption, failing which the weaker party can have the contract set aside as void. Allcard v Skinner A把物业给religious，5年后要拿回noThe relationship between A and the religious order was that of devotee and religious adviser, one of the relationships giving rise to a presumption of undue influence. If A had sought to recover the gift while she was still a member of the order, or shortly after leaving it, the presumption would have applied and, unless the order could prove that the transaction was not result of undue influence, the contract would have been set aside as void. But A had waited too long after leaving the order before asking to get her property back. The court held that, by failing to take any action to avoid the transaction within a reasonable time, A had in effect affirmed the transaction when she was no longer under any undue influence.·In other relationships, there is no presumption of undue influence but it is open to the weaker party to prove that, in the particular circumstances of the case, the relationship was such as to give the stronger party a general controlling influence over the weaker party’s decision making. The contract may be set aside as void unless the stronger party can prove that the weaker party’s decision on enter the contract was not in fact made because any undue influence.Johnson v Buttress B很老，唔识字，要依靠J，J带B去找律师转物业，B死后儿子上诉V oidable on grounds of undue influenceUnconscionable conduct过度的行为Arise when the inequality between contracting parties is serious and obvious, and the stronger party takes advantage of this to an extent that good conscience should not allow. In such circumstances, the weaker party can have the affected transaction set aside as void, on grounds of unconscionable conduct.·A contract will only be set aside for unconscionable dealing under the general law if the disadvantage of the weaker party is obvious to the stronger party, or if the circumstances raise the likelihood of some such disadvantage, putting the stronger party on inquiry.Commercial Bank of Australia Ltd v Amadio A骗父母抵押物业向银行借钱，A无钱还，银行收物业The mortgage should be set asideMistakeTypes of mistake①Common: where the parties think they have reached objective agreement but in turns out that they have not.- McRae v Commonwealth Disposals Commission M bid 了C的烂船，查后发现没有That is the sale of non- existent thing, and such agreements are not normallyenforceable. However, the C had in effect guaranteed the existence of the tanker they sold to M- Leaf v International Galleries L在I处买画，都以为是名家画，但不是The mistake did not justify setting the contract aside as void.②Mutua l: where the parties reach objective agreement, but that agreement is based on some assumed fact or facts about which they are both wrong- Raffles v Wichelhaus W要R用P船运货，R以为是另外一同名船There is no objective agreement because of mutual mistake, the contract will be void in common law- Goldsbrough Mort & Co v Quinn G租Q的地，都以为对方给转让费There had been sufficient agreementApplying the objective test, there was only on interpretation解释that areasonable person could put on the words used, ie that the seller (Q) would pay the costs of conversion.③Unilateral: where the parties reach objective agreement but one of the parties is mistaken about some assumed fact, while the other knows the true facts.- Taylor v Johnson J卖10acres地$15,000/acre, 写错成共$15,000 The contract should be set aside because buyer acted unconscientiously, deliberately setting out to prevent seller becoming aware of the mistake.④Mistake as to terms of contractSmith v HughesMisrepresentationRepresentations are statements of apparent fact, made with the intention of inducing the other party to enter the contract, but for which there is no intention (objectively judged) to be contractually liable. If representations are untrue that is misrepresentations. Misrepresentations do not create liability for breach of contract because representations do not become terms of contract.①The misrepresentation is one of past or existing fact·therefore it cannot be a statement of opinion. However, there are exceptions, eg if the representor never held that opinion or lied about it②The representation must be untrue·Silence alone is not a misrepresentation at common law. No duty to disclose material facts (caveat emptor applies)·However, there are some exceptions requiring disclosure:-When a ‘half-truth’ is made, ie when the representor has failed to make fulldisclosure-Subsequent discovery the statement is false-The statement was true when made but becomes untrue later:With v O’Flanagan③The misrepresentation was addressed to the party misled before or when thecontract was made· Plaintiff must show they were the intended recipient of the false statement. Only those who directly or indirectly act on the false statement can obtain a remedy for the misrepresentation④The representation was intended to induce and had in fact induced the other partyinto the contract·Plaintiff must show the misrepresentation both intended to induce and wassuccessful in inducing the contract⑤Has the innocent party suffered any loss?·If there is no damage suffered from the misrepresentation, there is no action Remedies:•Misrepresentation may make a contract voidable. This may give rise to the equitable remedy of rescission (or cancellation of the contract). The innocent party may also possibly claim damages. The types of remedies available depend on whether the misrepresentation was:•Fraudulent: rescission and/or damages for deceit are available (see Derry v Peek for the criteria for fraudulent misrepresentation)•Negligent: rescission and/or damages for negligence are available (see Shaddock v Parramatta City Council for the criteria to establish a duty of care in negligent misrep’n)•Innocent: rescission only under the Fair Trading Act 1999 (Vic) s 32OAIllegal contractsIn the general law, a transaction may be considered illegal if it contravenes违反public policy. The courts treat such contracts either as void (non-existent) or as legally unenforceable.Contracts illegal at common law:①Restraint约束of trade: restraint of trade is prime facie illegal and void unless itis in the parties’ and the public’s interests. The restraint of trade must also bereasonable in time and spaceNordenfelt v Maxim Nordenfelt Guns & Ammunition Co LtdN卖枪厂给M，承诺25年内不加入全球任何枪公司The clause was reasonable, and therefore enforceable②in employment contracts, restraint on confidential info may be valid, but won’textend to ordinary info and skillsLinder v Murdock’s Garage M要L离职后不能再镇上工作In a majority decision, the restraint clause was held to be unreasonable in extent, making it contrary to public policy and therefore unenforceable.Q4. Consent(unconscionable conduct) 對方更有bargaining powerA签约出版笑话，版权得5%The major issue in this question is whether Ann Onymous can avoid her contract with the publisher for unconscionability. She has two avenues in this regard.I.Unconscionability – Common LawWhere there is unequal bargaining power between contracting parties, and that unequal bargaining power is used to exact oppressive or harsh terms, courts are increasingly inclined to set aside such contracts.In the arts or entertainment industry, it has been recognised that there is unequal bargaining power since a “struggling artist” has limited access to public exposure. In Schroeder Music Publishing v Macaulay, a musician who signed an oppressive contract with a publisher was able to have the contract set aside for unconscionability. Apart from the contract being a restraint of trade in that case, the terms of the contract were unduly harsh.As in Ann’s case, the publisher took full copyright in the composer’s work and was under no obligation to publish any of it. Similarly to our case, the royalties agreement was heavily weighed in favour of the publisher.An important factor in cases involving unconscionability is whether the plaintiff has received or been encouraged to seek independent legal advice (See CBA v Amadio). There is no evidence here of Ann seeking independent advice before agreeing to these harsh terms.If Ann is compelled to write material with little in return, then this is arguably an unconscionable contract.II Unconscionability – StatutoryPart IVA Trade Practices Act 1974 (Cth) gives alternative redress against unconscionable conduct while preserving the common Law in this regard (see s5IAA).Section 51AB prohibits unconscionable conduct in the supply of goods or services. This section is unlikely to assist Ann Onymous here. She must be dealing with a “corporation” to employ this section and this is unclear from the facts. Even if the other contracting party is a corporation, they are not supplying but acquiring Ann’s services. Additionally the services (in this case the jokes provided) must be for “personal domestic or household use” to meet the requirements of s51AB(5); arguably these jokes are supplied by Ann for commercial purposes involving publication.Sec 51AC of the legislation might assist Ann here. This section mirrors s51AB by providing that a corporation or a person must not engage in conduct that is unconscionable in a business transaction.This section applies to both the provision of services and the acquisition of services.Section 51AC(1)(b) would apply to Ann’s situation providing that the publisher is a corporation.Section 51AC(4) sets out some factors that the Court may have regard to in determining the unconscionability of conduct. These include:(a)the relative bargaining strengths of the parties (as discussed above)(b)whether as a result of conduct engaged in by the acquirer (the publisher in this case), the smallbusiness supplier (Ann) was required to comply with conditions that were not reasonablynecessary to protect the legitimate interests of the acquirer. (It is not likely that the publisherneeds to exact such harsh terms)(c)the ability of the small business supplier (Ann) to understand any documents. (This seemsinconclusive in our case. More information is required).(d)Whether undue influence or unfair tactics were used (This is unknown here).(e) A comparison with how the small business supplier (Ann) would have fared with other acquirers(publishers). (This is unknown on our facts).(f)How other similar suppliers are treated.(g)(h)The applicability of industry codes(i)Any unreasonable failures of disclosure by the acquirer.(j)The extent to which the acquirer was willing to negotiate(k)The extent to which the parties acted in good faith etc.Q7. Contact illegalityT帮M运野，超重被抓，M唔肯俾钱The major issue for discussion in this question is illegality in contract law. The contract, in this problem, may be categorised as a contract illegal by statute (since there is legislation specifically prohibiting and penalising the overloading of a truck).In general, courts are loathe to assist parties in contracts illegal by statute. However, the contract here is not illegal as formed or in its inception. The parties did not intend to engage in an illegal transaction. In this case, the contract is illegal only as performed.In such a case, where there is only mere incidental illegality, the courts are generally prepared to hold the parties to their contractual obligations, and take the view that any breach of law is independent of the contract and may be separately punished. Here, the subject matter is legal (it involves the transport of goods). Accordingly, the courts are likely to enforce this contract.This was the view of the courts in St John Shipping Corporation v Joseph Rank Ltd. In that case, a shipowner overloading a ship in breach of statute, and therefore liable to a penalty under the statute, was entitled to payment for freight, because the object of the statute was not to prohibit contracts but to prevent overloading.R骗奶奶D担保在银行借钱，R还不了钱，银行要D负责Eastpac Bank wants to enforce its contract of guarantee. Dorothy may be able to argue that they cannot on the basis of lack of real and informed consent. That is that the necessary element of consent to form a contract is missing. She may argue non est factum, but this is unlikely to succeed as she does not satisfy the criteria (she knows what she is signing although she does not appreciate what the legal effects are). Undue influence is not going to work here as against Rhonda and Dorothy because there is no contract between them, however there may be a case of undue influence of the bank over Dorothy. This is on the basis of a relationship of confidence and dependence as Dorothy has banked with Eastpac Bank for 35 years and the bank knows she is elderly and frail. This is also unlikely to succeed as she does not place trust and confidence in the bank, rather she trusts her family.The main basis for lack of consent is unconscionable conduct, requiring the following:•Stronger party vis-a-vis a weaker party.•Weaker party under a special disability.•Stronger party aware of disability•Stronger party takes advantage unconscientiously of weaker party’s special disability.The facts are similar to Commercial Bank v Amadio. The bank is the stronger party, Dorothy the weaker party, having special disabilities. The bank knows that she relies on her family. It also knows that she is getting no benefit from this guarantee (that is, the home loan is not for her). She is elderly and they sign the contract at her house and importantly, the bank does not satisfy itself that Dorothy knows what liability she is incurring. The bank has not told her or required her to get independent legal advice.Glossary of key legal words/terms relating to the above problems:。
BASL and EPF2 act independently to
Plant Signaling & Behavior 5:3, 278-280; March 2010; © 2010 Landes BiosciencearticLe addenduM278 Plant Signaling & Behavior Volume 5 issue 3Key words: stomata, development, meristemoids, asymmetric cell division, leaf epidermis, cell polarity, peptide signal Submitted: 11/16/09Accepted: 11/18/09Previously published online:/journals/psb/article/10704*Correspondence to: Julie E. Gray; Email: j.e.gray@Addendum to: Hunt L, Gray JE. Signaling peptide EPF2 controls asymmetric cell divisions during stomatal development. Current Biol 2009; 19:864-9; PMID: 19398336; DOI:10.1016/j.cub.2009.03.069.The initiation of stomatal develop-ment in the developing Arabidopsis epidermis is characterized by an asym-metric ‘entry’ division in which a small cell, known as a meristemoid, and a larger daughter cell is formed. The meristemoid may undergo further asymmetric divi-sions, regenerating a meristemoid each time, before differentiating into a guard mother cell which divides symmetrically to form a pair of guard cells surround-ing a stomatal pore. Recently EPF2 and BASL have emerged as regulators of these asymmetric divisions and here we present results indicating that these two factors operate independently to control stomatal development.EPF Peptides Regulate Asymmetric Divisions of Stomatal PrecursorsSeveral factors that regulate asymmet-ric cell divisions involved in the differ- entiation of specialized plant cell types have been identified from molecular genetic studies, including putative tran-scription factors, receptors, phosphatases, kinases and proteases.1 Recently, we and others reported putative peptide ligands for the receptor-like protein TMM which regulates both the number and spacing of stomata during epidermal develop-ment.2,3 EPIDERMAL PATTERNING FACTORs 1 and 2 (EPF1 and EPF2) are members of a family of secretory peptides, all with previously unknown function.4-6 EPF1 and EPF2 are both specifically expressed in stomatal precursor cells. Knockdown mutants of epf1 exhibit pairs of adjacent stomata in their epidermis,and epf2 mutants are characterized by increased stomatal density and the pres-ence of an abnormally large proliferation of arrested meristemoids. Thus EPF1 functions to orientate asymmetric divi-sions of meristemoids and prevent sto-mata from forming in contact with one another, whereas EPF2 acts to restrict the number of ‘entry’ and asymmetric divi-sions of meristemoids and to promote the differentiation of daughter cells into pave-ment cells.Polarized Cellular Expressionof BASL Occurs Prior to Asymmetric Division A novel protein, BREAKING OF ASYMMETRY IN THE STOMATAL LINEAGE (BASL), which accumulates in stomatal precursor cells has also recently been reported.7 Interestingly, BASL accu-mulates in a distinct polarized pattern inside stomatal precursor cells, marking the periphery of those cells about to undergo an asymmetric division. Knockdown basl mutants show extra symmetric divisions of meristemoids and BASL is therefore proposed to be necessary for promoting correctly orientated asymmetric divisions of stomatal precursors. Epigenetic studies have shown that double mutants epf1;basl and tmm;basl have additive phenotypes relative to the single mutants suggesting that BASL acts independently of these previously characterised stomatal devel-opment regulators. As EPF2 and BASL are both expressed in stomatal precursor cells and are both involved in regulating their asymmetric divisions, we investi-gated whether EPF2 and BASL could actBASL and EPF2 act independently to regulate asymmetric divisions during stomatal developmentLee Hunt and Julie E. Gray*Department of Molecular Biology and Biotechnology; University of Sheffield; Sheffield, UK Plant Signaling & Behavior 279articLe addenduMarticLe addenduMreduction in the number of paired or clus-tered stomata in basl-4;epf2-1 (p > 0.016) (Fig. 1F ). Neither basl-4 nor epf2-1 showed any obvious effect on growth rate or leaf shape, but basl-4;epf2-1 plants developed narrow twisted leaves, perhaps because of their considerably reduced number of epi-dermal pavement cells.To confirm that the additional small epidermal cells that we found in our mutants were the result of excessive asym-metric or symmetric divisions of meriste-moids we expressed the pTMM:GUS-GFP gene construct which is specifically expressed in stomatal lineage cells, in each of our genetic backgrounds and observed GUS and GFP cellular expression patterns (Fig. 2C ). GUS staining and GFP fluo-rescence directed by the TMM promoter indicted that the additional small epider-mal cells that we observed in our single and double mutants were indeed arrested stomatal lineage cells.ConclusionsThe recently reported Arabidopsis gene products BASL and EPF2 are both involved in regulating the asymmetric cell division programthat leads to stomatal development. Lack of BASL expression leads to a large number of symmetric rather than asymmetric divisions of sto-matal precursors, and lack of EPF2 leads to excessive numbers of asymmetric divi-sions. Our analysis of the double mutant basl-4;epf2-1 suggests however, that BASL and EPF2 operate independently to regu-late asymmetric divisions during stomatal development.References1. Bergmann DC, Sack FD. Stomatal development.Annu Rev Plant Biol 2007; 58:163-81.2. Casson S, Gray JE. Influence of environmental fac-tors on stomatal development. New Phytol 2008; 178:9-23.3. Abrash EB, Bergmann DC. Asymmetric cell divi-sions: a view from plant development. Dev Cell 2009; 16:783-96.4. Hara K, Kajita R, Torii KU, Bergmann DC, KakimotoT. The secretory peptide gene EPF1 enforces the stomatal one-cell-spacing rule. Genes Dev 2007; 21:1720-5.5. Hara K, Yokoo T, Kajita R, Onishi T, Yahata S,Peterson KM, et al. Epidermal cell density is auto-regulated via a secretory peptide, EPIDERMAL PATTERNING FACTOR 2 in Arabidopsis leaves. Plant Cell Physiol 2009; 50:1019-31.6. Hunt L, Gray JE. Signaling peptide EPF2 controlsasymmetric cell divisions during stomatal develop-ment. Current Biol 2009; 19:864-9.1A–D ). Stomatal density was not altered in fully expanded leaves of either basl-4 orbasl-4;epf2-1 in comparison to the wild-type control (Col-0) but was significantly higher in epf2-1 (p < 0.003) than wild-type or basl-4;epf2-1 (p < 0.03) (Fig. 1E ).In contrast to basl-1 and basl-2,7 basl-4 didnot show increased stomatal density. This may be explained by the different tissue examined as Dong et al. examined coty-ledons, whereas we used mature leaves. There were however clearly more clus-tered stomata in basl-4 than wild-type and the epf2-1 mutation caused a significanttogether to regulate this step in stomatal parison of Single basl and epf2 Mutants with the Double Mutant, basl ;epf2The basl-4;epf2-1 leaf epidermis con-tained large numbers of additional small cells which appeared to be the result of increases in both symmetric and asymmet-ric divisions of stomatal lineage cells. This resulted in a reduced density of mature tessellated epidermal pavement cells (Fig. BaSL & ePF2 act independently. cleared normarski images of abaxial epidermis of (a) basl-4, (c) epf2-1, (d) basl-4;epf2-1 leaves approximately 2 cm in length. gc, pair of guard cells; pc, pavement cell; m, meristemoids. *indicates meristemoids that have undergone an abnormal symmetric division. Scale bar = 30 µm. (e) densities of stomatal and (F) stomatal clusters of abaxial surface of fully expanded leaves. error Bars are SeM. Photographs of mature plants of col-0 (G) and basl-4;epf2-1 (H). Scale bar = 3 cm. Plant transformation, plant material, GuS staining and microsco-py were as described in.6 basl-4 (SALK_086936) was obtained from NASC and verified by PCR with primers 5'-ctc GtG aca aaG aaa cac aaa ca-3', 5'-Gaa tct aca aca ttG Gaa ccc taa a-3'. crosses between basl-4 and epf2-1 were verified by PCR.280 Plant Signaling & Behavior Volume 5 issue 37. Dong J, MacAlister CA, Bergmann DC. BASL con-trols asymmetric cell division in Arabidopsis. Cell 2009; 137:1320-30.8. Nadeau JA, Sack FD. Control of stomatal distribu-tion on the Arabidopsis leaf surface. Science 2002; 296:1697-700.Figure 2.additional small epidermal cells in basl-4;epf2-1 are stomatal lineage cells. col-0, epf2-1, basl-4 and basl-4;epf2-1 mutants expressing the pTMM:GUS-GFP transcriptional reporter histochemically stained for GUS (A–D) or examined under UV fluorescence (E–H). Staining and fluorescence are not from the same plant. Scale bar (a–d) = 40 µm, (e–H) = 20 µm. three independent lines of basl-4;epf2-1 expressing pTMM:GUS-GFP 8 were obtained and all showed similar staining or GFP fluorescence pattern.。
Unitarily invariant norms related to factors
Don Hadwin
Keywords: semi-finite factors, unitarily invariant norms, s-numbers, Ky Fan norms. MSC2000: 46L10; 46L51
1
Introduction
F.J. Murray and J.von Neumann [15, 16, 17, 26, 27] introduced and studied certain algebras of Hilbert space operators. Those algebras are now called “Von Neumann algebras.” They are strong-operator closed self-adjoint subalgebras of all bounded linear transformations on a Hilbert space. Factors are von Neumann algebras whose centers consist of scalar multiples of the identity operator. Every von Neumann algebra is a direct sum (or “direct integral”) of factors. Thus factors are the building blocks for general von Neumann algebras. Murray and von Neumann [15] classified factors into type In , I∞ , II1 , II∞ , III factors. Type In and I∞ factors are full matrix algebras: Mn (C) and B(H). Type In and II1 factors are called finite factors. There is a unique faithful normal tracial state on a finite factor. 1
20.Equipment design considerations for large scale cell culture
21Equipment design considerations for large scale cell cultureDavid M.MarksDME Alliance Incorporated ,5012Medical Center Circle ,Allentown ,PA 18106,USA (e -mail :david .marks @dmealliance .com )Received 28June 2002;accepted in revised form 3February 2003Key words :Bioreactor,Cell culture,Large scale,Mass transfer,Mixing,Scale up,Stirred tankAbstractEquipment design is frequently recognized as a key component in the success of GMP biologics manufacturing,but is not always implemented with full appreciation of the processing implications.In the case of mammalian cell culture,there are some recognized issues and risks that develop when transitioning to a large scale of operation.The developing demand for cell culture production capacity in the biopharmaceutical industry has led to a progressive increase in the scale of operation in the last decade.This review will provide a high level summary of the documented process difficulties unique to serum-free large scale (LS)cell culture,analyze the engineering constraints typical of these processes,and suggest some practical equipment design considerations to enhance the productivity,reliability and operability of such systems under GMP manufacturing conditions.A systems approach will be used to establish a good LS bioreactor design practice,providing a discussion on gas distribution,agitation,vessel design,SIP/CIP and control issues.Introductionscale bioreactor to produce a production scale yield.However,the price for this productivity bonus is the The success of biopharmaceutical manufacturers in acceptance of greater risk associated with a more filling parenteral drug pipelines has fueled speculation complex process.As very few biopharmaceutical that the world’s cell culture production capacity will manufacturers have been able to justify the im-be insufficient for the growing demand for mono-plementation of perfusion technology for large scale clonal antibody and recombinant protein production GMP production,the scope of this paper will be in coming years.This has stimulated an increased limited to LS stirred tank bioreactors that are operated interest in large-scale (.10,000liter)production tech-in batch and fed-batch modes.niques.The conventional approach to large scale Several alternative technologies show promise,biologics production is through a stirred tank bio-notably transgenic plants and animals,but a trans-reactor.Several biopharmaceutical genic production facility has yet to be licensed by a have invested in LS stirred-tank cell culture manufac-regulatory agency for the production of human thera-turing capability by implementing production bio-peutics.As these processes are still in their pioneering reactors at 10,000to 20,000liter scale (Glaser 2000).stage of development,the approach represents signifi-Perfusion technology is available to support com-cant risk in terms of uncertainties regarding the time mercial production without a large equipment scale required for process development and regulatory hur-up.A variety of cell retention devices have been dles.In addition,it remains to be proven that the developed for use in stirred perfusion bioreactors capital savings in replacing the cell culture unit opera-(Woodside et al.1998).These devices allow media tion are not offset or exceeded by the increases in replenishment without a loss of viable cells,support-purification costs (Morrow 2002).Therefore the ing higher cell densities and extended production stirred tank bioreactor is expected to remain the time.Perfusion is attractive because it enables a pilot biologics workhorse and most viable approach for2003Kluwer Academic Publishers .Printed in the Netherlands .Cytotechnology 42: 21–33, 2003.22GMP production of complex proteins in the foresee-the hydrodynamic shear effects on animal cells(Leist able future.et al.1990).Problems associated with nutrient,pH Early initiatives with LS cell culture production and dissolved oxygen gradients due to poor mixing approached bioreactor design in much the same way can develop in systems with inadequate agitation.As as one would design a microbial fermentor.The we shall see in the discussion that follows,many of microbial design conventions and rules of thumb for the mixing problems experienced in LS cell culture agitation,vessel geometry and aeration were often result from an erroneous view of the sensitivity of applied,if for no other reason than the fact that there mammalian cell lines to mechanical agitation. were no established conventions for cell culture and Oxygen,a key nutrient for aerobic organisms, there was no evidence that these methods would not requires constant replenishment for cell growth to work.Subsequent studies have demonstrated that continue.Atfirst consideration,the oxygen transfer there are unique challenges presented by a LS cell requirement for LS cell culture would seem relatively culture process,which necessitate a different ap-easy to accomplish because animal cell respiration proach to equipment design and scale up.rates are substantially lower than that of microbialorganisms.However,unlike microbial fermentations,animal cells cannot tolerate voluminous sparging in Agitation and aeration conjunction with mechanical gas dispersion to maxi-mize aeration.The shear sensitivity of mammalian At large scale,the agitation and aeration characteris-cells places practical constraints upon the mass trans-tics of the bioreactor are critical and clearly the most fer technologies that can be used.Oxygen transfer, difficult aspect of scale up.The LS cell culture issues then,becomes progressively more difficult as one can be differentiated into three categories for this scales up the process,as the mass transfer efficiency discussion:of stirred tank bioreactors will generally degrade as 1.Factors that contribute to physical cell damage or scale is increased.Likewise,the ability to removelysis.carbon dioxide produced by cell respiration is also 2.Concentration gradients resulting from poor mix-affected,and problems associated with high CO2 ing.accumulation have been documented for LS cell 3.Problems associated with inadequate gas-liquid culture systems as well(Garnier et al.1996;Kimuraphase mass transfer.and Miller1996;DeZengotita et al.1998;Taticek etal.1998).Of the factors that can lead to physical cell damage,the two principal mechanisms are agitation inducedhydrodynamic shear and bubble damage caused by Mass transfergas sparging.Animal cells,unlike microbial organ-isms,lack a protective cell wall and are therefore Mass transfer in stirred tank bioreactors can be ac-relatively sensitive to disruptive physical forces in the complished via a gas permeable membrane,surface fluid.A culture’s‘shear sensitivity’is influenced by aeration,and subsurface sparging.Aeration by choice of cell line,presence of key nutrients,con-of a permeable membrane has been demonstrated in centration of inhibitory cell metabolites and batch age bioreactors up to150liters(Lehmann et al.1988; (cells are more susceptible to shear damage in lag and Vorlop et al.1989)but has not proven scalable for stationary phases).Though the focus of this discus-commercial GMP applications.Surface aeration oc-sion is on equipment design,it is recognized that the curs in all stirred tank bioreactors,and is often suffi-problem of shear damage in cell culture is multifa-cient alone for mass transfer in small-scale systems. ceted,requiring consideration of process methods and However,the contribution of surface aeration to the medium composition as well.overall mass transfer requirements of the culture is Bioreactor mixing is always an issue at large scale,much less significant at large scale.The mass transfer as the time required to achieve bulk homogeneity is contribution from surface aeration diminishes rapidly generally longer asfluid volume is increased(Enfors as one scales up the process because there is an et al.2001).For cell culture process,mixing is an approximate log-log relationship between production even greater concern because of the gentle agitation scale and the surface area available for mass transfer systems that are typically implemented to minimize in a bioreactor vessel(Figure1).Even when used in23 conjunction with a surface agitator,surface aeration is surface of objects immersed in thefluid,creating ausually only practical at small scale.Therefore,the protective layer that mitigates the adverse effects of only viable method to meet the mass transfer require-sparge bubbles in serum-free medium.The use of ments of LS cell culture is through a subsurface Pluronic surfactants should be restrained,as they are introduction of sparge bubbles through the culture also known to create problems with foaming,down-medium.stream processing and loss of mass transfer efficiency. One cannot adequately address the mass transfer Another problem associated with mass transfer issues within LS cell culture without also considering LS cell culture is a progressive increase in the partial the damaging effects of sparge bubbles.Bubble ef-pressure of carbon dioxide(pCO)as the batch pro-2fects are widely regarded as the principle cause of cell gresses.A high concentration of dissolved carbon damage in mammalian cell culture using serum-free dioxide can have an inhibitory effect on cell growth medium.It is postulated that cells collect along the and will drive the culture pH more acetic because itgas-liquid interface of the sparge bubbles as they rise will increase the concentration of H CO.This prob-23within the vessel,and then are exposed to damaging lem occurs when the rate of CO stripping is less than2effects when the bubble bursts at the liquid surface the rate of oxygen transfer.It has been noted in cell (Handa et al.1987;Chalmers1994).Some studies culture systems that deliver oxygen by membrane have also suggested that cells are damaged when they diffusion or very small bubbles that dissolve before are captured by sparge bubbles and sequestered in the reaching the surface of the medium.As the only foam layer at the surface.Detrimental effects have remaining method of eliminating metabolically pro-been noted at sparge rates as low as0.05VVM.duced CO is through surface mass transfer(Mitchell-2Studies on the effects of bubbles have demon-Logean and Murhammer1997)it is not surprising that strated a linear relationship between the specific gas larger bioreactors are more susceptible to this phe-¨flow rate and the cell death rate(Jobses et al.1990).nomenon.The degree of the cellular damage is dictated by Production bioreactors should be designed to bioreactor design and operation,as well as the cell achieve an oxygen transfer capacity that will at least line characteristics,media formulation,and nutritional match the oxygen uptake rate of the culture at the state of the cells.The conventional approach to ad-harvest cell density.The rate of oxygen transfer in a dressing bubble damage is to add0.5to3g/liter bioreactor is directly proportional to the system massPluronic F68,a non-ionic surfactant copolymer of transfer coefficient,k a,which is a function ofLpolyoxyethylene and polyoxypropylene.It coats the medium constituents,vessel geometry,gas distribu-tion design,operating pressure and vessel agitation.Itis normal to experience some loss in mass transferefficiency when stirred tank bioreactors are scaled up.The k a for production-sized bioreactors can diminishLby as much as1/2that of similar pilot scale reactors.To compensate,mass transfer performance can beboosted through oxygen enrichment,increased spargeflow,and improved mixing.Oxygen enrichment willincrease the mass transfer driving force(C*-C)byincreasing the O concentration in the gas phase.The2oxygen transfer rate is directly proportional to themass transfer driving force in accordance with theequation OTR5k a(C*-C),where C is the oxygenLconcentration of the gas phase and C*is the oxygenconcentration that would be in equilibrium with theliquid phase.Spargeflow,typically scaled by VesselVolumes per Minute(VVM),dictates the rate ofoxygen delivery to the system and the number ofbubbles available for aeration.An increase in the O2massflow rate per unit volume will improve k a due Figure1.Surface area per unit volume diminishes exponentially Lwith increase in batch size.to greater surface area available for mass transfer,24though the degree of freedom in this area is limited bythe aforementioned problems with bubble damage andfoaming.The mass transfer efficiency of a culture canalso be improved by better agitation.Fluid mixingwill affect a remarkable improvement on k a becauseLa well-agitated vessel prevents bubble coalescing andmaintains bubbles in suspension for a longer period oftime.Both spargeflow and agitation parameters ex-hibit a linear relationship with k a,a relationship thatLcan be characterized for the specific operating anddesign configuration of each bioreactor.In most LScell culture systems the disruptive energy released bybubble bursting is at least an order of magnitudegreater than that of mixing induced hydrodynamicshear.This a strategy of keeping the spargerate at a minimum and focusing on oxygen enrich-ment and mixing improvements to achieve the neces-sary oxygen transfer rate.Figure2.The‘Elephant Ear’Low Shear impeller is designed todistributefluid shear equally along the trailing edge of each blade Mixing(from ABEC Incorporated with permission).Early concerns about thefluid shear produced byagitation led to the predominant use of marine im-eddies becomes significant as they approach the size pellers,as well as the development of a variety of of the cell(McQueen et al.1987).Detrimental effects ‘low shear’pitched blade impellers in the1980s.have been shown to occur when the Kolmogorov eddy These mixers provide gentle bulk mixing without the length drops below1/2–2/3times the diameter of the vigorousfluid turbulence typical of microbial fermen-cellular unit(Croughan et al.1989).This is usually tors(Figure2).Subsequent studies have indicated that not problematic for suspension cell culture,where shear stress in the bulkfluid is not as significant a there are freefloating cells on the order of10–20m m. factor as it was once thought to be(Chisti1993).Anchorage-dependant cells,however,frequently re-quire100–200m m diameter microcarrier beads toprovide a growth substrate.These are much moresensitive to the shear effects of microeddies due to to the culture(Kioukia et al.1996).Nevertheless,their large size(Croughan et al.1987).When scaling bubble damage can be mitigated by Pluronic F68as up,it can be difficult to provide sufficient agitation to previously discussed,and so it is still prudent to use keep the microcarriers in suspension while maintain-low-shear mixing technology to avoid unnecessary ing the Kolmogorov size above the threshold that localizedfluid turbulence.Mechanical mixing be-strips cells from the substrate,which may partially comes a process constraint where localizedfluid shear explain the prevalence of suspension cell culture at is produced by eddies in the wake of impeller rge scale.The potential for cell damage resulting from localized Poor mixing is a common problem with LS cell fluid shear can be quantified by examining the small-culture,leading to undesirable concentration gradients est of the turbulentfluid eddies,commonly called and diminished mass transfer efficiency within the Kolmogorov eddies,which can be calculated for a bioreactor(Nienow et al.1996).In addition,con-bioreactor vessel as a function of kinematic viscosity centration gradients can be exacerbated in high-den-and local power per unit mass in accordance with the sity cultures by the formation of cell aggregates or 43equation,l5y/´,where l5Kolmogorov eddy agglomerates within the turbulent eddies of thefluid. size,y5kinematic viscosity,and´5localized power In poorly mixed systems,these aggregates can be-dissipated per unit e large enough to create segregated cellular The risk of cell damage resulting from these micro clumps that establish concentration gradients within25 the culture(Ozturk1996).The impact on the hetero-specified with a generous safety factor with regard to geneity of the culture can adversely affect cellular capacity and turndown control.growth and productivity(Sen et al.2001).The Oxygen Uptake Rate for a given cell line Mixing can be improved by(1)increasing the cultured at the desired harvest cell density can be used agitation speed,(2)increasing the diameter of the to establish the minimum required bioreactor k a,orL impeller,and(3)adding impellers to the system.oxygen transfer threshold,below which respiration some studies suggest that mixing time is becomes growth limiting(Figure3).For each equip-independent of impeller type in systems with equiva-ment design and operating configuration,this oxygen lent power input and tank geometry(baffled tank;1:1transfer threshold can be characterized as an exponen-liquid aspect ratio)(Nienow1997).In systems with tial function of spargeflow rate and mixing speed goodfluid circulation patterns,the medium mixing is(Figure4).If we consider all of the design constraints related to the power per unit volume imparted by the discussed thus far,we can construct a process oper-agitation system,which is defined by the equation ating window within which agitation and aeration 35P/V5N N D r/V,where N5impeller power num-parameters are sufficient to achieve the desired cell p i pber,N5agitation speed,D5impeller diameter,r5density(Figure5).The specific boundaries of this imedium density and V5medium volume.As indi-window ultimately must be determined experimental-cated by this equation,the mixing energy imparted to ly for each cell line and equipment configuration.As the medium is very sensitive to both agitation speed cell density increases,the area of the operating win-and impeller diameter.However,the Kolmogorov dow diminishes until one or more of the process eddy size is also dictated by the power input,which constraints becomes growth limiting.The scale up defines a limitation where the hydrodynamic shear objective is to make this operating window as large as becomes damaging to the cells.The equation for possible,maximizing the degrees of freedom for each Kolmogorov eddy length can be employed in con-process parameter.junction with the power equation to predict this limitfor design purposes,using the cube of the impellerdiameter as an estimate of volume for the calculationof localized power dissipated per unit mass(Nelson1988).Moreover,these formulas predict that theKolmogorov eddy size in the medium is inverselyproportional tofluid density,which exacerbates theproblem approaching the end of the batch when bothcell density and oxygen demand are at their highestlevel.Scale upCell culture bioreactors are usually scaled up withsimilar vessel geometries to duplicate pilot scalemixing patterns,but beyond that there are no reliablescaling parameters that correlate well with productionperformance.For lack of a better method,aeration andagitation systems are often scaled by equivalent VVMand impeller tip speed,but these criteria are notreliable indicators that can be used to predict theperformance characteristics and productivity of a LScell culture system(Aunins and Henzler1993).Pro-cessing parameters are ultimately chosen by empiricalobservations of the sparge rates and agitation speedsFigure3.At constant k a,the bioreactor mass transfer performanceLrequired to scale the k a of the system.For that can be characterized in terms of an exponential relationship be-Lreason,aeration and agitation systems are usually tween aeration and agitation(modeled data).26These constraints clearly have the greatest impact onthe design of the agitator and gas distribution systems.Both of these critical systems have a significantimpact on the mass transfer characteristics of theequipment.Gas distribution designEquipment gas distribution systems typically utilizethermal massflow controllers to meter aeration to thebioreactor.Oxygen is frequently used to supplementair for a reduced spargeflow rate,thereby mitigatingthe problems associated with sparge bubbles.Bio-reactor aeration systems may also include carbondioxide gas for pH control,and nitrogen for dissolvedoxygen probe calibration and control.These gases arecombined in a0.2m m sterilefilter,which provides a Figure4.In any given set of equipment and operating conditions,dual function of mixing the gases and removing the relationship between aeration and agitation can be characterized biologic contaminates.for several oxygen transfer thresholds(modeled data).Gas spargers used in GMP equipment must bedesigned such that they are easily cleanable,steam When designing equipment for LS cell culture,onesterilizable,and free draining.In practice,it is dif-must take into account all of the common scale upficult to achieve ideal GMP construction in conjunc-problems previously discussed,as well as environ-tion with optimal mass transfer performance.The mental and nutritional requirements of the cells.designs in common use are the point sparger,ringsparger,and frit sparger.Each represents a compro-mise in the performance or operability of the system.The sparger selection for a given application shouldbe one that will provide the best GMP operation andmeet the minimum mass transfer requirements at thesame time.Ideally,spargers should be designed todisperse bubbles sufficiently to avoid coalescence intolarger bubbles as they rise within the vessel.Thepressure drop across the sparger should be sufficientto ensure uniformflow distribution,but not so great asto create a turbulent jet that could potentially damagecells.At least one study has suggested that an exces-sive pressure drop across the sparger can affect cellgrowth(Murhammer and Goochee1990).A goodrule of thumb is to size the sparger such that thepressure drop is0.5–2.5psi throughout the antici-pated operating range.Point spargers are the simplest of designs,pro-viding a single bullet-shaped nozzle through whichgas is introduced to the vessel.The simplicity of thisdesign makes it preferable from a GMP perspectivebecause it is the easiest to clean and sterilize.Theorifice on the tip of the point sparger is designed to Figure5.The objective of equipment design for LS cell culture isprovideflow restriction such that a continuous stream to mitigate process constraints such that the process operatingwindow is as large as possible.of bubbles is provided throughout the entire opera-27 tional gasflow range.The principle disadvantage of damaging to cells,cultures with micro-sparging sys-point spargers is that there is little control of bubble tems are more susceptible to bubble damage at low size,and large bubbles provide relatively little bubbleflow rates.In high density CHO and BHK cultures, surface area for mass transfer.bubble damage has been documented at sparge rates Ring spargers are often employed to increase the above0.054VVM using a0.15m m sparger,and surface area available for mass transfer by creating above0.025VVM using a0.5m m sparger(Qi et al. multiple smaller bubbles.The air nozzles on this2001).sparger are drilled on the bottom of a tubular ring such The frit porosity is chosen to optimize the balance that it can freely drain to meet GMP requirements.between oxygen transfer and CO stripping within the2Therefore,ring spargers need to be inserted in a medium.If the bubbles are too small,they will specific orientation and should be indexed to the dissolve before reaching the surface–effectivelyvessel nozzle.If used in conjunction with a bottom-removing the CO stripping capability of the sparge.2mounted agitator,ring spargers are usually designed If the bubbles are too large,the sparge rate will need in the shape of a shepherd’s crook instead of a full to be increased to compensate for the loss of mass ring,to allow for installation clearance relative to the transfer area.An experimental study of high density agitator shaft.In practical comparison with the point CHO culture at500L scale has suggested an optimum sparge design,ring spargers often do not provide a pure oxygen bubble size of approximately2–3mmsignificant enough improvement in the mass transfer diameter,which is sufficiently large to affect CO2 performance to justify the added expense and cleaning stripping while minimizing the total sparge rate(Gray difficulties introduced.et al.1996).Larger bubbles may be necessary to Frit spargers utilize a porous tube to create produce the same effect in LS cell culture systems. thousands of very small bubbles within the bioreactor Manufacturers generally recommend frit porosities of vessel.The miniature bubbles produced by a frit are2–5m m.The length of the frit element is then sized to ideal for mass transfer because they provide ample create a reasonable pressure drop across the sparger. gas-liquid surface area and allow additional contact The principle problem with frit-type spargers is the time for gasses to reach equilibrium(Figure6).The difficulty cleaning the porous element.In non-GMP frit itself,usually constructed of sintered stainless applications they are typically cleaned by a caustic steel or porous Teflon,can be sized to create a soak followed by thermal oxidation of any organic uniform curtain of bubbles with a fairly narrow size residuals in a dry heat oven.However,it is extremely distribution.Bubble size if further affected by sparge difficult if not impossible to validate that all process rate and Pluronic F68concentration.As smaller bub-residuals imbedded in the frit have been removed. bles tend to create higher shear gradients that are Therefore the frit elements used in GMP cell cultureFigure6.In comparison with ring spargers(left),frit spargers(right)produce thousands of miniature bubbles,which optimize the bubble-liquid interface area available for mass transfer(from Mott Corporation with permission).28are generally considered disposable.Replacement chanical seals–is critical to the success of LS cell sparge elements are either attached via an aseptic culture.Magnetic coupling systems are available as a connection or rewelded to the sparge insert tube.replacement for mechanical seals,but have not gained Over-foaming can become problematic if the sur-widespread acceptance for LS manufacturing(per-factant level and sparge rates are too high,especially haps because of torque limitations and perceived when the bubble size is very small(as produced by a cleaning and maintenance difficulties).A good refer-frit-type sparger).The surface foam layer threatens ence for GMP agitation design in this application is the cell culture process when it is high enough to the ASME BPE standard(American Society of Me-entrain foam in the gas exhaust line and foul the vent chanical Engineers2002)section DS-4.8,which illus-filter.Several devices have been developed for foam trates specific preferred and recommended design separation from the bioreactor off-gas stream,but practices to ensure the sterility and cleanability of their application is costly and not recommended for bioprocessing equipment.Both top and bottom long-term aseptic applications such as GMP cell mounted drives have been used for cell culture, culture.A variety of antifoam and defoaming agents though large systems frequently do not have the are commercially available to address the foam layer,ceiling clearance required for maintenance and re-but these chemicals can degrade mass transfer per-moval of top-mounted agitators.Impeller installation formance and create difficulties in downstream pro-and removal also presents a problem at large scale,as cessing.If possible,its best to avoid conditions that cell culture impellers are frequently too large tofit are conducive to excessive foam build up in thefirst through a standard vessel manway.This may require place.the installation of an oversized manway or full open-ing head,as well as the overhead lifting mechanismsrequired for handling.Agitator design The agitator positioning in stirred tank vessels maybe specified with either angular off-center positioning Cell culture impellers are typically sized at1/3to1/2or centerline orientation.Angular off-center drives are of the vessel diameter.If space allows,additional installed with an agitator shaft angle that is positioned impellers can be added to improve mixing.Since the approximately15degrees off the vertical centerline of Kolmogorov eddies occur in the local turbulent zone the vessel so as to collapse thefluid vortex on the adjacent to each impeller,the addition of a second or ed in conjunction with axialflow impel-third impeller is an effective strategy to improve lers,these drive orientations are commonly employed mixing without significantly contributing to the prob-in pilot scale cell culture bioreactors because they can lem of hydrodynamic shear from micro eddies.It is be implemented in an unbaffled tank-thereby remov-best to use axialflow impellers with good pumping ing the need for baffles that complicate the cleaning of characteristics,such as marine,hydrofoil or low shear the vessel and are perceived as a contributor to pitched blade designs,to provide good vertical mix-hydrodynamic shear stress on the cells.Angular off-ing.Axialflow impellers improve mass transfer ef-center agitators have been used in LS cell culture ficiency by increasing the average residence time of systems as well,but require a structurally robust the bubbles.These impellers should be spaced at least design because the unbalancedfluid forces in the one impeller diameter from each other and from the bioreactor can become severe when the power de-surface of the medium.If an impeller operates too livered by the agitator exceeds3HP(Perry and Green close to the liquid surface,it can create a vortex that1997).entrains air bubbles from the headspace,mimicking Centerline agitators create relatively balancedfluid the damaging effects of the sparge bubbles(Kunas forces in comparison with angular systems,but re-and Papoutsakis1990).quire the addition of2–4baffles to ensure uniform Agitation systems present some unique operational mixing.Vessel baffles,vertical metal strips that are challenges in LS cell culture applications.These equally spaced in radial positions along the tank wall, systems are required to maintain a long-term aseptic are typically designed with a width1/10to1/12of environment,and thefinancial loss associated with a the tank diameter and extend the full tangent height of contamination at this stage is substantial.Therefore,the vessel.In GMP applications,they should be seal the sanitary design detail of the agitator internals-welded to the tank wall and constructed so as to avoid including impeller construction,couplings and me-sharp edges,corners,cracks and crevices.Despite the。
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RAND Europe
4.1.2 Habits and patterns of behaviour can impede adherence to good practice guidelines .............................................................................. 38 4.1.3 Reconciling personal judgement with guidelines involves assessing the available evidence ........................................................... 38 4.1.4 Team working and human factors influence good practice behaviours .......................................................................................... 38 4.1.5 Morale, workload and resources need to be effectively managed to enable doctors to make good decisions ........................................... 38 4.1.6 Organisational culture may obstruct ongoing improvement and negatively affect standards of care ....................................................... 38 Bibliography 41 Benchmarking bibliography ....................................................................................... 50 Appendix A: Rapid Evidence Assessment – detailed methodology ............................. 53 Appendix B: Key Informant Interview topic guide .................................................... 59 Appendix C: Template for benchmarking analysis .................................................... 63 Appendix D: Benchmarking background data .......................................................... 67
产品对番茄的影响英语作文
产品对番茄的影响英语作文Title: The Impact of Products on Tomatoes。
Tomatoes, a staple in many cuisines worldwide, have garnered attention not only for their culinary versatility but also for their nutritional value. However, the influence of products on tomatoes extends beyond mere consumption. From farming practices to packaging and transportation, various products play a significant role in shaping the journey of tomatoes from farm to table. This essay delves into the multifaceted impact of products on tomatoes.To begin with, agricultural products such as fertilizers, pesticides, and herbicides profoundly affect the growth and quality of tomatoes. While fertilizers enhance soil fertility and promote plant growth, excessive use can lead to nutrient imbalances and environmental pollution. Similarly, pesticides and herbicides helpcontrol pests and weeds, safeguarding tomato crops fromdamage. Nonetheless, their indiscriminate use raises concerns about chemical residues on tomatoes and environmental degradation.Moreover, advancements in agricultural technology have introduced innovative products like genetically modified organisms (GMOs) and hydroponic systems. GMO tomatoes, engineered for traits such as disease resistance and extended shelf life, have sparked debates regarding food safety and ethical implications. On the other hand, hydroponic cultivation eliminates the need for soil, conserves water, and enables year-round production, revolutionizing traditional farming practices.In the realm of food processing and preservation, a myriad of products is utilized to enhance the shelf life and appeal of tomatoes. Canning, freezing, and drying are common methods employed to preserve tomatoes and create various products such as sauces, purees, and sun-dried tomatoes. Additives like citric acid and ascorbic acid are incorporated to maintain color, flavor, and nutritional value during processing. While these products extend theavailability of tomatoes beyond their harvest season, concerns about additives' health effects persist among consumers.Packaging materials also exert a notable influence on tomatoes, affecting their freshness, safety, and environmental footprint. Traditional packaging options like cardboard boxes and plastic bags provide protection during transportation but may contribute to food waste and plastic pollution. Alternatively, innovative packaging solutions such as biodegradable films and compostable trays offereco-friendly alternatives, aligning with consumer preferences for sustainable practices.Furthermore, transportation products like refrigerated trucks and containers facilitate the global trade of tomatoes, enabling year-round availability in diverse markets. However, long-distance transportation entails energy consumption and carbon emissions, prompting initiatives to optimize logistics and promote local sourcing. Additionally, packaging materials and transportation products collectively contribute to thecarbon footprint associated with tomatoes, prompting stakeholders to explore eco-friendly alternatives and mitigate environmental impact.In the retail sector, marketing products like labels, advertisements, and promotions influence consumer perceptions and purchasing decisions. Labels indicating organic, non-GMO, or locally sourced tomatoes appeal to health-conscious and environmentally conscious consumers seeking sustainable options. Moreover, promotional campaigns and point-of-sale displays create demand for tomato products, driving sales and market competitiveness.In conclusion, the impact of products on tomatoes transcends their role in consumption, encompassing various stages from cultivation to retail. Agricultural products, processing methods, packaging materials, and marketing strategies collectively shape the production, distribution, and consumption of tomatoes. While innovations offer opportunities for efficiency, quality, and sustainability, they also pose challenges related to environmental, health, and ethical considerations. Thus, a holistic approach isimperative to navigate the complex interplay between products and tomatoes, ensuring a balance between progress and responsibility in the food industry.。
Revealed
Evolving patterns of international trade∗James Proudman,Bank of England†Stephen Redding,New College,Oxford and CEPR‡23rd March,1998AbstractTheoretical models of growth and trade suggest that patterns of international specialisation are inherently dynamic and evolve endoge-nously over time.Initial comparative advantages are either reinforcedor gradually unwound with the passage of time.This paper puts for-ward an empirical framework to evaluate the dynamics of internationaltrade patterns,that uses techniques widely employed in the cross-country literature on income convergence.Applying this frameworkto industry-level data,wefind evidence of significant differences ininternational trade dynamics among the G5economies.J.E.L.CLASSIFICATION:C10,F10,030KEYWORDS:Distribution Dynamics,International Trade,Markov Chains, Revealed Comparative AdvantageAll Figures and Tables are at the end of the paper∗The views expressed in this paper are those of the authors and do not necessarily reflect those of the Bank of England.A substantial amount of this research was un-dertaken while Stephen Redding was also at the Bank of England.We would like to thank Mary Amiti,Andrew Bernard,Christopher Bliss,Gavin Cameron,Cecilia Garcia-Penalosa,Nigel Jenkinson,Danny Quah,Andrew Scott,Jon Temple,Peter Westaway,and participants in seminars at the Bank of England,the Royal Economic Society1997and the European Economic Association1997for their helpful comments.We are grateful to Jon Temple forfirst suggesting the use of formal indices of mobility.We are also grateful to Kee Law,Mark Thirlwell,and Colin Webb for their help with the data.We would like to thank(without implicating)Danny Quah for making the TSRF econometrics package available to us.The usual disclaimer applies.†Monetary Analysis(Division2),HO-4,Bank of England,Threadneedle Street, London.EC2R8AH.Tel:01716015955.Fax:01716015953.E-mail: james.proudman@.‡New College,Oxford.OX13BN.Tel:01865279482.Fax:01865279590.E-mail: stephen.redding@.11IntroductionA number of dynamic models of international trade have emerged over recent years(selected examples include Krugman(1987),Grossman and Helpman (1991)and Rivera-Batiz and Romer(1991)),in which rates of economic growth and patterns of international trade are jointly and endogenously de-termined.The exact specification of the growth process varies from paper to paper,but an important subset of this literature(of which the three papers cited above are all examples)emphasises the links between international trade and endogenous technological change.In the presence of country-specific knowledge spillovers or local increas-ing returns to scale in individual sectors,it is easy to derive the theoreti-cal result that initial comparative advantages and patterns of international trade will be reinforced or‘locked-in’over time(see,for example,Krug-man(1987)and Grossman and Helpman(1991)Chapter8).However,it is equally clear that this prediction of‘persistence’in international trade flows is very sensitive to the assumptions made about knowledge spillovers. If ideas spillover across economies,or there are variations in either the rate at which learning by doing occurs or the productivity of Research and De-velopment(R&D)expenditures,then initial patterns of international trade may instead change or exhibit‘mobility’over time(Brezis et al.(1993)and Grossman and Helpman(1991),Chapter7).Thus,whether international tradeflows persist or exhibit mobility over time is ultimately an empirical question.The objective of this paper is to provide an empirical framework within which it is possible to address ques-tions of international trade dynamics.The empirical framework consists of two components.Thefirst is a measure of an economy’s pattern of in-ternational specialisation at any given point in time.This is provided by the distribution of a modified version of Balassa’s(1965)index of‘Revealed Comparative Advantage’(RCA)across industries.The second element is a2technique for analysing the evolution of this measure of international special-isation over time.This is achieved using a model of distribution dynamics, introduced into the cross-country literature on income convergence by Quah (1993),(1996a)and(1996c).The paper is structured as follows.Section2presents a relatively stan-dard theoretical model of international trade and endogenous technological change,that combines elements from Dornbusch et al.(1977),Krugman (1987)and Bernard and Jones(1994,1996).This is used to derive the basic theoretical prediction that international tradeflows may exhibit either per-sistence or mobility over time.Section3introduces an empirical framework for analysing international trade ter Sections implement this empirical methodology using industry-level manufacturing data from the G5 economies.The dynamics of patterns of international trade are analysed in two stages.First,Section4undertakes the preliminary data analysis.Measures of RCA are presented for the manufacturing sectors of France,Germany, Japan,the United Kingdom and the United States,and the evolution of patterns of international trade over time is analysed graphically.Second, the model of distribution dynamics is estimated econometrically in Section 5.Transition probability matrices are presented for each of the G5economies and for the sample formed by pooling observations across economies.The extent of persistence and mobility in patterns of international trade is quan-tified using formal indices of mobility.Wefind evidence of significant dif-ferences in international trade dynamics among the G5economies.Interest-ingly,France exhibits the most mobility and Japan the least.Japan is also the only G5economy to experience an increase in the degree of international specialisation over time.Section6summarises our conclusions.32A theoretical model of international trade dynamicsThis Section presents a simple theoretical model of international trade and endogenous technological change.The model uncovers some forces that lead to persistence in patterns of international trade and other conflicting influ-ences that tend to induce mobility.Static equilibrium is determined exactly as in the standard Ricardian model with a continuum of goods(Dornbusch et al.(1977)).There are two economies(home and foreign)and A ij denotes the productivity of labour in sector j of economy i∈{H,F}.Each econ-omy may produce any of afixed number of goods indexed by j∈[0,n].An individual good j will be produced in home(H)if and only if the unit cost of producing that good in home is below or equal to that in foreign(F),w H(t) w F(t)≤A Hj(t)A F j(t)(1)where w H and w F are the home and foreign wage rates respectively.If we denote home productivity relative to foreign by B j≡A Hj/A F j, and index goods so that higher values of j correspond to lower values of home productivity relative to foreign(B j),then the right-hand side of(??)may be illustrated diagrammatically by the downward sloping curve in Figure ??.Given a value for the home relative wage w H/w F,all goods j≤˜j in Figure??are produced in home and all goods j>˜j are produced in foreign.˜j denotes the limit good such that home’s relative wage is exactly equal to home productivity relative to foreign’s.In static equilibrium,home’s relative wage is pinned down by the ad-ditional requirement that home income equals world expenditure on home goods(or alternatively that trade is balanced).Under the assumption that instantaneous utility is a symmetric,Cobb-Douglas function of the con-sumption of each good j(with the elasticity of instantaneous utility with respect to the consumption of each good equal toβ),this condition may be4expressed as,w H w F =D˜j,where D˜j≡˜j.β1−˜j.β.¯L∗¯L(2)where¯L and¯L∗are the home and foreign supplies of labour respectively, and the right-hand side of(??)is illustrated diagrammatically by the upward sloping curve in Figure??.Static equilibrium is defined by the intersection of the two curves,where both(??)and(??)are satisfied.<Figure1about here>Within this framework,the evolution of patterns of international trade over time is determined by rates of technological progress in each sector of the two economies.A wide range of empirical evidence exists that learning by doing is an important source of productivity improvement.For exam-ple,Lucas(1993)cites evidence that each doubling of cumulative output of ‘Liberty Ships’in14US shipyards during World War II was associated with a reduction in man-hours required per ship of between12and24per cent. By definition,learning by doing is associated with actual experience of the production process and will thus occur in an individual sector of a particular economy.At the same time,it is plausible that production knowledge may spillover across economies,and we wish to allow technology in each sector to transferred from a leading to a follower economy.Therefore,technological progress is assumed to occur endogenously as a result of both learning by doing and(unless the economy is the world tech-nological leader in a particular sector)technological transfer.The particular specification chosen combines the model of learning by doing in Krugman (1987)with one of technological transfer in Bernard and Jones(1996)(see also Bernard and Jones(1994)).Specifically,A ij(t)is assumed to evolve over time as follows,lnA ij(t)A ij(t−1)=γij+ψj ln(1+L ij(t−1))+λj lnA Xj(t−1A ij(t−1)(3)5γij,ψij,λij≥0∀i,jwhere A Xj denotes productivity in sector j in whichever of the two economies i∈{H,F}is the world’s technological leader,γij is a sector and country-specific constant reflecting the exogenous determinants of rates of techno-logical change,ψj parameterises the rate of learning by doing,andλj char-acterises the rate of technological catch-up.Throughout the analysis,tech-nological change is modelled as a pure externality of current production and is therefore consistent with the assumption of perfect competition in the Ricardian model.Equation(??)implies that,in each sector j of the two economies i,the evolution of productivity relative to the world technological leader may be expressed as,lnA ij(t)A Xj(t)=γij−γXj+ψj ln1+L ij(t−1)1+L Xj(t−1)−λj.lnA ij(t−1)A Xj(t−1)(4)The dynamics of international trade patterns are fully characterised by the static equilibrium conditions(??)and(??),together with the specifi-cation of productivity growth in equations(??)and(??).Initial levels of productivity determine the pattern of comparative advantage and interna-tional specialisation.The pattern of international specialisation(with its associated allocation of labour across sectors)then affects rates of produc-tivity growth and hence the evolution of international tradeflows over time.On the one hand,the presence of sector-specific learning by doing means that initial patterns of international specialisation will tend to be reinforced over time.On the other hand,technological transfer and differences in the exogenous rates of productivity growth across sectors may both be respon-sible for reversing initial patterns of international specialisation-depending6upon the correlation between initial levels of relative productivity and the steady-state levels implicit in equation(??).For example,consider two special cases.First,suppose that there is a common rate of exogenous technological change across all sectors and economies(γHj=γF j=γfor all j)and no international knowledge spillovers(λj=0for all j).Static equilibrium at time t implies that home will specialise completely in the production of the range of goods j∈[0,˜j] and foreign in goods j∈(˜j,n].That is,in home,L j(t)>0for j∈[0,˜j] and L j(t)=0for j∈(˜j,n],while in foreign L j(t)=0for j∈[0,˜j]and L j(t)>0for j∈(˜j,n].It follows immediately,from(??)and the param-eter restrictions imposed above,that home productivity relative to foreign will rise in the sectors where home initially specialises and fall in the sec-tors where home does not initially specialise.As a result,initial patterns of international specialisation persist and will become increasingly locked-in over time(as in Krugman(1987)).Second,suppose that there is no sector-specific learning by doing(ψj=0 for all j);nonetheless,exogenous technological progress occurs at varying rates across sectors and economies(γij>0for all i,j,γHj=γF j for all j) and is accompanied by knowledge spillovers(λj>0for all j).Suppose also that those sectors in which home productivity is initially less than foreign are the same sectors in whichγH>γF,and that the converse is also true.Then, from equation(??),sectors where home productivity is initially less than foreign will become-in steady-state-sectors in which home productivity exceeds foreign.This is sufficient(though not necessary)for initial patterns of international specialisation to be reversed over time.11Remember that it is relative values of AHj/A F j across sectors j that matter for comparative advantage and international specialisation.73Empirical modelling of trade dynamicsThus,economic theory pin-points some forces that lead to persistence in international tradeflows and others that induce mobility.Whether initial patterns of international trade are reinforced or reversed over time is there-fore an empirical question.This Section proposes an empirical framework for analysing the dynamics of international tradeflows.The framework will enable the question of persistence versus mobility to be addressed,while also yielding information about other related aspects of international trade dynamics-for example,whether the overall degree of international special-isation is rising over time.The extent of specialisation in an individual sector is characterised us-ing a modified version of Balassa’s(1965)index of Revealed Comparative Advantage(RCA).2An economy i’s RCA in sector j is given by the ratio of its share of exports in sector j to its average export share in all sectors,3RCA ij=Z ij/ i Z ij1Nj(Z ij/iZ ij)(5)where Z ij denotes the value of economy i’s exports in sector j.RCA yields information about the pattern of international specialisation insofar as it evaluates an economy’s export share in an individual sector relative to some benchmark-namely,the economy’s average export share in all sectors.The pattern of international specialisation at any one point in time t is characterised by the distribution of RCA across sectors.A value of RCA ij above unity indicates an industry in which economy i’s share of exports exceeds its average share in all industries:that is,an industry in which economy i specialises.2For a more recent application of Balassa’s original index,see Dollar and Wolff(1993).3Balassa(1965)’s actual measure of RCA is the ratio of economy i’s export share in sector j to its share of total exports of all sectors.This measure suffers from the disadvantage that its arithmetic mean is not necessarily equal to one,and may vary both across economies and over time.The measure used in this paper is formally equivalent to normalising Balassa’s measure by its cross-sectional mean.See Appendix B for further discussion.8Evaluating the dynamics of patterns of international specialisation over time involves an analysis of the evolution of the entire cross-section distri-bution of RCA.Issues such as persistence versus mobility in international tradeflows correspond to questions of intra-distribution dynamics.What is the probability that a sector moves from one quartile of the RCA distribu-tion to another?Are the sectors in which RCA ij>1at time t+k(k≥1) the same sectors as at time t?Changes in the overall degree of international specialisation may be evaluated by analysing the evolution of the external shape of the RCA distribution.Do we observe an increasing specialisation in a limited subset of industries(a polarisation of the RCA distribution towards extreme values),or has the degree of international specialisation remained broadly unchanged?The evolution of the RCA distribution over time may be modelled for-mally,employing techniques already used in the cross-country growth litera-ture to analyse income convergence(see Quah(1993),(1996a)and(1996c)). Thus,denote RCA by the measure x and its distribution across sectors at time t by F t(x).Corresponding to F t,we may define a probability measure λt where∀x∈ ,λt((−∞,x])=F t(x).Following Quah op cit.,the evo-lution of the distribution of RCA over time is then modelled in terms of a stochastic difference equation,λt=P∗(λt−1,u t),integer t(6) where{u t:integer t}is a sequence of disturbances and P∗is an operator that maps disturbances and probability measures into probability measures. For simplicity,we assume that this stochastic difference equation isfirst-order and that the operator P∗is time invariant.Even so,equation(??)is intractable and cannot be directly estimated.However,setting the distur-bances u to zero and iterating the stochastic difference equation forwards, we obtain,9λt+s=P∗(λt+s−1,0)=P∗(P∗(λt+s−2,0),0)...(7)=P∗(P∗(P∗...(P∗(λt,0),0)...0),0)=(P∗)sλtIf the space of possible values of RCA is divided into a number of distinct, discrete cells,P∗becomes a matrix of transition probabilities which may be estimated by counting the number of transitions out of and into each cell.4 From these transition probabilities,one is able to characterise the extent of mobility between different segments of the RCA distribution.Furthermore, by taking the limit s→∞in equation(??),one obtains the implied ergodic RCA distribution,which provides information concerning the evolution of the external shape of the RCA distribution.4Preliminary data analysisThe empirical methodology outlined above is used in the remainder of this paper to analyse the evolution of patterns of international specialisation in the manufacturing sectors of the G5.The techniques used enable a wide range of issues concerning international trade dynamics to be addressed.For example,we consider the extent to which there are changes in patterns of specialisation over time and at what levels of specialisation the greatest de-gree of mobility is observed.It is possible to examine whether international trade dynamics are different in the US from Japan or the major European economies.We evaluate the degree to which each economy is increasingly specialising in small sub-sets of manufacturing sectors.This Section presents the RCA data on patterns of specialisation in the G5economies,and looks informally at changes in international specialisation over time.The following Section estimates the formal model of distribution 4More generally,if we continue to treat RCA as a continuous variable,one may estimate the stochastic kernel associated with P∗(see for example Quah(1996c)).However,in the present application,there are too few cross-sectional units to permit such estimation.10dynamics econometrically.The source for all the data is the OECD’s Bilat-eral Trade Database(BTD).This provides consistent information on exports to the OECD and15trade partners for22manufacturing industries for the period1970-93.5We begin by characterising the distribution of RCA at any one point in time in the United Kingdom and the United States,before widening the analysis to encompass the other three members of the G5.Ta-ble1presents measures of RCA for the United Kingdom in each of the22 manufacturing industries in the sample for the period1970-93.For ease of exposition,the data are presented in the form offive-year averages.<Table1about here>Table2presents exactly the same information for the United States. From a comparison of the tables,the two economies’patterns of international specialisation show several similarities,although there are also important differences.In Table3,we list all the UK and US industries in which RCA exceeds one in either or both of the periods1970-4and1990-3.Industries in which an RCA is either acquired or lost in each economy during the sample period are denoted by italics.In thefirst of these two periods,industries in which the United Kingdom had an RCA and the United States did not were Petroleum Refining,Metal Products,Nonferrous Metals,Pharmaceuticals and Other Manufacturing;industries in which the US had an RCA but the UK did not were Motor Vehicles and Communication.<Table2about here>Table3also makes clear that the industries in which an economy has an RCA change substantially over time.On the one hand,between the periods 1970-4and1990-3,the United Kingdom lost its RCA in Electrical Machin-ery,Non-electrical Machinery,Metal Products and Non-ferrous Metals.On the other hand,the United Kingdom gained an RCA in Industrial Chem-icals and Communication.In the United States,a comparison of patterns5Further details concerning the data used,including an industrial classification,are contained in Appendix A.11of international specialisation in1970-4and1990-3reveals the acquisition of an RCA in Food and Drink and Paper and Printing,combined with the loss of an RCA in Motor Vehicles.<Table3about here>Exactly the same analysis is undertaken for the other three members of the G5.Table4lists all the French,German and Japanese industries in which RCA exceeds one in either or both of the periods1970-4and 1990-3.6Again,changes in patterns of international specialisation occur. The case of Japan is particularly worthy of note,where an RCA is lost in Rubber and Plastic,Textiles and Clothing and Other Manufacturing, and an RCA is acquired in Non-electrical Machinery,Electrical Machinery, Motor Vehicles and Computers.From these two tables alone,patterns of international specialisation in France and Germany appear to be less mobile than those in Japan and the United Kingdom.Tables3and4provide one means of analysing the dynamics of pat-terns of international specialisation.Although some interesting information can be obtained,the conclusions that may be drawn from these tables are necessarily limited.First,the analysis is concerned with only two of the five-year periods.Second and more importantly,by restricting attention to movements of RCA above or below the value of one,one loses a vast amount of information on changes in the degree of specialisation in individ-ual industries.Movements between other segments of the RCA distribution are also of interest.For example,between1970-4and1980-4,RCA in the US Textiles and Clothing rose to173%of its original value,while that in the US Ferrous Metals industry fell to64%of its initial value.Neither of these substantial changes in patterns of international specialisation enters into Table3.<Table4about here>6In the interests of brevity,actual values of RCA are not reported.This information is available from the author on request.12A more complete-although still informal-analysis of international trade dynamics is undertaken for the United Kingdom in Figures2-7.In Figure2, UK industries are ordered in terms of increasing RCA for the period1970-4, and the cross-section distribution of RCA is graphed.Figures3,4,5and 6preserve the same ordering of industries and plot the RCA distribution for the periods1975-79,1980-4,1985-9and1990-3respectively.Figure7 re-orders industries in terms of increasing RCA for the period1990-3,and again graphs the cross-section distribution of RCA.Taken together,Figures2-6yield information concerning intra-distribution dynamics.If patterns of international specialisation in the United Kingdom exhibited substantial persistence,one would expect the distribution of RCA to remain very similar across successive time periods.Industries with high values of RCA in1970-4would also have high values of RCA in1990-3.In fact,what one observes is considerable mobility in international tradeflows in the United Kingdom-particularly in the middle of the distribution.For example,between1970-4and1985-9,the UK’s RCA in Motor Vehicles fell from0.94to0.48,before rising to0.67in1990-3.A similar analysis is undertaken for each of the G5economies.If indus-tries are ordered in terms of increasing RCA for the period1970-4,and the cross-section distribution of RCA in successive time periods is graphed,the story again appears to be one of considerable mobility-afinding that will be confirmed in the formal analysis to follow.Figures2-7may also be used to gain information about changes in the overall degree of international specialisation in the United Kingdom -changes in the external shape of the cross-section distribution of RCA. If the United Kingdom were increasingly specialising in a limited subset of industries,one would observe RCA systematically increasing in specific sec-tors and systematically decreasing in others,so that the distribution of RCA would exhibit an increasing mass at extreme values of RCA.A comparison of Figures2and7in particular reveals no evidence of this being the case.13With the exception of Japan(to be discussed in the following Section),the same is also true for each of the other G5economies.<Figures2-7about here>5Econometric estimationThis Section estimates the formal model of distribution dynamics introduced above econometrically.If the space of possible values of RCA is divided into m discrete cells,the operator P∗in equations(??)and(??)becomes an m×m matrix of transition probabilities,λt=P∗.λt−1(8) The matrix P∗contains elements p kl,each of which denotes the proba-bility that an industry moves from cell k to cell l(where k,l∈{1,...,m}) and which may be estimated by counting the number of transitions out of and into each cell.All empirical estimation was undertaken using Danny Quah’s TSRF econometrics package.7In each case,the boundaries between cells were chosen such that industry-year observations are divided roughly equally between the grid cells.In order to provide a benchmark against which to compare the results for individual economies,we begin by pooling observations across economies. Table5presents the estimated transition probability matrix for the pooled sample(implicitly,we assume that the stochastic process determining the evolution of RCA in each economy is the same).The interpretation of this table is as follows.The numbers in parentheses in thefirst column are the total number of industry-year observations beginning in a particular cell, while thefirst row of numbers denotes the upper endpoint of the corre-sponding grid cell.Thereafter each row denotes the estimated probability of passing from one state into another.For example,the second row of 7Responsibility for any results,opinions and errors is of course solely the authors’.14numbers presents(reading across from the second to thefifth column)the probability of remaining in the lowest RCA state and then the probability of moving into the lower-intermediate,higher-intermediate and highest RCA states successively.Thefinal row of the upper section of the table gives the implied ergodic distribution,while,in the lower section of the table,the one-year transition probability matrix is iteratedfive times.<Table5about here>Transition probability matrices are then estimated for each of the G5 economies individually(allowing the stochastic process shaping the evolu-tion of RCA to vary across economies).The results of this estimation are presented in Tables6and7.The interpretation of the tables is directly analogous,except that the one-year transition probability matrix iterated five times is now omitted.<Tables6and7about here>Estimated values of transition probabilities close to one along the diag-onal are indicative of persistence in the distribution of RCA across sectors, while large off-diagonal terms imply greater mobility.The results for in-dividual G5economies in Tables6and7confirm the mainfinding in the informal analysis of the previous Section.That is,there is evidence of a relatively high degree of mobility in patterns of international specialisation. For example,in France the probability of moving out of one grid cell after one year ranges from11%-27%,while in the United States the same prob-ability varies from10%-21%.Iterating the one-year transition matrixfive times(not shown in Tables6and7),the extent of mobility is brought out more strongly:for France,the probability of remaining in the same cell over thefive-year period ranges from64%to only37%.In each of the G5economies and in the pooled sample,mobility is highest in the middle of the distribution(out of the lower-and upper-intermediate grid cells).Of the six matrices of estimated transition probabilities,a com-parison of diagonal and off-diagonal terms suggests that those for France and15。
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（二）寒邪 cold factor
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superficial
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Factors Associated With Excessive Migration in Bone Impaction Hip Revision SurgeryA Radiostereometric Analysis StudyRob G.H.H.Nelissen,MD,PhD,*Edward R.Valstar,MSc,PhD,* Ruud G.Po¨ll,MD,PhD,*Eric H.Garling,MSc,*and Ronald Brand,MSc,PhD†Abstract:A prospective radiostereometric analysis(RSA)study of18patients withcemented revision hip surgery and impaction grafting with an Exeter stem was donewith a follow-up of2years for all patients.All factors that could influence migration(ie,micromotion)of the stem were analyzed with a repeated measurements analysisof variance.Two groups could be identified:a stable group and a continuousmigrating group.Two factors significantly influenced micromotion during the fol-low-up measurements.Thefirst factor was the Paprosky classification(the bigger thedefect,the higher the micromotion).The second factor was cement mantle defects inՆ1Gruen zones.The migrating hip stems had more Gruen zones with cementmantle defects(45%)compared with the stable prostheses(21%).The effect of thefirst factor on micromotion was limited and probably clinically less relevant.Becausethe cement mantle defects found in this study were caused by poor instrumentation,the second factor stresses the importance of good instrumentation,which is essentialto make this technically demanding technique effective in creating a stable stem–allograft construct in the defective femoral canal.Key words:migration,cementedhip revision,tapered polished stems,bone impaction grafting.Copyright2002,Elsevier Science(USA).All rights reserved.Increasing numbers of total hip arthroplasties are done annually;estimations of about1million total hip arthroplasties worldwide have been made.Be-cause revision rates at10-year follow-up range from7%to13%[1],an increasing number of revision hip arthroplasties is expected.The common factor for aseptical loosening of prostheses is loss of bone stock of the proximal femur[2]. Reconstruction of this bone loss with tight pack-ing of morcellized cancellous bone–graft combined with a cemented stem is a widely used technique in revision surgery of the hip.This technique shows favorable clinical and radiographic results[3].Some histologic studies showed signs of allograft bone remodeling[4–6],whereas others showed signs of allograft bone necrosis[7,8].In2impaction grafting studies[9,10],concern was raised about the tech-nique of cemented revision with impacted bone chips.It was noticed that massive early migration could occur with subsequent early prosthesis fail-ure.In impaction grafting of bone defects after revi-sion hip arthroplasty,the graft behaves as a friableFrom the Departments of*Orthopaedic Surgery and†Medical Sta-tistics,Leiden University Medical Center,Leiden,The Netherlands.Submitted September21,2001;accepted April30,2002.No benefits or funds were received in support of this study.Reprint requests:Rob G.H.H.Nelissen,MD,PhD,Depart-ment of Orthopaedic Surgery,Leiden University Medical Center,PO Box9600,2300RC Leiden,The Netherlands.E-mail:r.g.h.h.nelissen@lumc.nlCopyright2002,Elsevier Science(USA).All rights reserved.0883-5403/02/1707-0009$35.00/0doi:10.1054/arth.2002.34532The Journal of Arthroplasty Vol.17No.72002826aggregate.Its resistance to complex forces depends on grading,normal load,and compaction.Ulti-mately the quality of the impacted bone and its remodeling potency determine prosthetic stability. The presence or absence of allograft bone remodel-ing might initiate a failure scenario.Several factors influence the success of this revision technique; patient factors(preoperative femoral defects and potency of allograft remodeling),technical factors (degree of bone impaction,allograft bone chip size, cementing technique),and postoperative rehabili-tation factors.Viability and extent of bone graft remodeling[6,8]influencing particle size has been discussed by others[11].Evaluation of surgical fac-tors,which probably are not only of more impor-tance to the success or failure of this technique,but also can be changed easily,has not been addressed in relation to micromotion of the hip stem.Exper-imental studies showed that migration of the im-plant relative to the host–bone occurred immedi-ately after operation but decreased at a later stage during follow-up[8,12].The construct of prosthe-sis,cement,and allograft can be considered as a unit that has to stabilize with respect to the host–bone. Stabilization of migration of this unit after a longer period is a reflection of a viable remodeled allograft, which is present at18months postoperatively[6]. In contrast,continuous migration reflects a nonvi-able,nonremodeled allograft.The latter is probably identical to a failed revision impaction grafting pro-cedure.The use of impacted morcellized cancellous allograft in the proximal femur followed by inser-tion of a cemented implant is believed to reconsti-tute the proximal femur gradually through substi-tution and incorporation of the allograft into the host–bone[4–7].Although several authors reported on the viability of the grafted femur[4,6,8],little is known about the biomechanical performance of this revision tech-nique:How does the prosthesis–cement–allograft construct migrate in the host femur,and which fac-tors influence migration?Will the prosthetic stem continue to migrate in the allograft impacted femoral canal,or does it stabilize at a certain time in follow-up?Stabilization means resorption of the allograft bone construct stops,and the construct becomes via-ble.The aim of this study is to identify which factors are associated with excessive migration in bone im-paction hip revision surgery.Material and MethodsA prospective study of18patients who under-went revision surgery of a primary total hip pros-thesis was carried out at the Leiden University Medical Center.The procedure was done with im-paction grafting and a tapered cemented stem(Ex-eter;Stryker Howmedica Osteonics Corp,Allen-dale,NJ).The institutional ethics committee approved the study,and the patients gave informed consent.The mean age of the patients was63Ϯ13.4 years,and mean body mass index was26Ϯ2.6 kg/m2.The preoperative femoral defect was classi-fied according to Paprosky[13].Patients had the following femoral defects:1type2A,10type2C,3 type2B,and4type3.Diagnosis was osteoarthritis in5hips and rheumatoid arthritis in13hips.Dur-ing the2-year follow-up period,1patient died(1 year postoperatively).All revision surgeries were done through a direct lateral approach to the hip.The impaction grafting procedure was done as previously described by one of the authors[3,6,14].Surgery was done by2 experienced surgeons;in10cases,surgery was done by1author(R.G.P.),and the other8eight cases,surgery was done by another author (R.G.H.H.N.).All allograft bone used was stored atϪ80°C.The cancellous allograft bone was mor-cellized to a chip size of approximately2to4mm with a bone mill.The graft was washed once,after which autologous bone marrow with blood from the exposed femur and acetabulum was added.The hip prosthesis was cemented using Simplex P gen-tamicin-impregnated cement(Stryker Howmedica Osteonics Corp,Allendale,NJ).The patients were evaluated preoperatively.Post-operatively,clinical evaluations were done(Harris hip score[15]),and RSA radiographs were taken. Postoperatively,patients were kept from weight bearing until thefirst RSA radiograph was obtained at thefifth postoperative day.The postoperative regimen was different between the2surgeons re-gardless of the preoperative femoral defect.Thefirst author(R.G.H.H.N.)allowed patients to ambulate with50%weight bearing with2crutches from the 5th day postoperatively until6weeks postopera-tively,when full weight bearing was allowed.The other author(R.G.P.)had patients ambulating with15%weight bearing with crutches during the first6postoperative weeks;after that time,patients were allowed50%weight bearing until3months postoperatively,when full weight bearing was al-lowed.Follow-up evaluations were immediately postop-eratively,and6weeks,3months,6months,12 months,18months,and2years postoperatively. Immediately postoperative standard anteroposte-rior and lateral radiographs of the hip were ob-Factors for Migration in Hip Revision•Nelissen et al.827tained.On the anteroposterior radiographs,the ce-ment mantle was divided into7zones according to Gruen,McNeice,and Amstutz[16].Zone1is lo-cated adjacent to the greater trochanter,and zone7 is located at the calcar.In the standard anteropos-terior radiographs,the orientation of the stem(ie, varus or valgus),the cement mantle thickness,and the position of the distal cement plug were mea-sured.The presence of bone remodeling or cortical bone resorption was scored.A cement mantle thickness ofϽ2mm in1of the7Gruen zones on the anteroposterior radiograph was considered in-sufficient[17–21].Alignment of the hip stem with the axis of the femur within3°of varus or valgus was considered neutral.Finally,on the anteropos-terior radiograph of the femur,an index was calcu-lated at the distal border of the lesser trochanter. This femur–stem index is the anteroposterior diam-eter of the femur(inner aspect of cortex)divided by the anteroposterior diameter of the prosthesis(an index of2means a diameter of the femur that is twice as big as the prosthetic stem).During the operation,6to81-mm tantalum balls (Industrial Techtonics,Ann Arbor,MI)were in-serted in the greater and lesser trochanteric region of the femur.To be able to assess the position of the implant accurately,the hip stem was modified by the manufacturer.One marker was attached to the shoulder of the prosthesis,and another was at-tached to the tip of the prosthesis.The center of the head of the prosthesis was used as a third prosthesis marker.The RSA setup consists of2synchronized roent-gen tubes positioned at approximately1.5m above the radiograph,each projected at one half of a roentgenfilm(35cmϫ43cm).The exposure of this roentgenfilm was simultaneous by both roent-gen tubes.The angle of each roentgen tube with the vertical was20°.A Plexiglas calibration box(Medis, Leiden,The Netherlands)with121-mm tantalum markers on the upper plane and26on the bottom plane was used.The marker positions were deter-mined accurately by a mechanical measuring de-vice.These box markers define the coordinate sys-tem and determine the roentgen foci positions.The patient is positioned above the calibration box.The coordinates of the bone and prosthesis markers on the radiographs were measured.The assessment of the marker coordinates,the3-dimensional recon-struction of marker positions,and the micromotion calculations were done with specialized RSA soft-ware(RSA-CMS,Medis,Leiden,The Nether-lands)[22–24].Thefirst RSA examination served as a reference baseline.All future micromotion evaluations were related to the relative position of the prosthesis with respect to the bone at that time.Migration of the stem could be expressed as translation movements along the3orthogonal axes:longitudinal,trans-verse,and sagittal.Prostheses were designated as either stable or migrating.Two criteria were used to distinguish the migrating prostheses from the stable prostheses. Thefirst criterion for a migrating prosthesis was translation alongՆ1of the axes ofϾ2mm at 1-year follow-up.The second criterion was a migra-tion rate ofՆ0.5mm along1of the axes during the 2nd year of follow-up.If1of these2criteria were met,the patient was assigned to the migrating group.Because our point of interest was migration throughout the follow-up period,the total migra-tion was determined by the sum of the translations along the3orthogonal axes.This total length of the translation vector was used to define total migra-tion.An analysis of variance(ANOVA)with re-peated measurements was done with correction for follow-up time,Paprosky femoral defects,surgeon (and postoperative rehabilitation regimen),and fe-mur–stem index as covariant.Because the number of patients was small in the Paprosky2C and3 defect group,these2classes of defect were com-bined for the ANOVA test(ie,3classes were ana-lyzed:2A,2B,and2C combined with3).Mean values and SDs were calculated for all variables.To compare the differences between migrating and stable prostheses,Student t-tests were used.To test the intraobserver and interobserver measurement error of the cement thickness measurements,a paired-samples t-test(95%confidence interval) was used.ResultsClinical ResultsFourteen hip prostheses were inserted in neutral alignment(0.9°Ϯ1.5°),and4stems were inserted in varus alignment(range,4°–6°).The mean pre-operative Harris hip score was33Ϯ11.5points;the postoperative score increased to74Ϯ13.2points. All patients had pain relief at the latest follow-up compared with the preoperative follow-up.In Fig.1,the mean cement mantle thickness in the7Gruen zones is given for the migrating hip stems and the stable hip stems.The migrating hip stems had more Gruen zones with cement mantle defects(eg,0mm of cement[25of the56scored Gruen zones,45%])compared with the stable pros-theses(15of the70Gruen zones,21%).Especially828The Journal of Arthroplasty Vol.17No.7October2002at the medial (zone V and VI)and distal parts (zone IV)of the prostheses,cement mantle defects were found.The reproducibility of these cement mantle thickness measurements has been tested by means of an intraobserver and interobserver test with 2observers;no signi ficant differences for either of these tests were found.Radiologic scoring for the presence of osseous integration of the morcellized allograft by presence of trabecular bone at the final follow-up showed an equal distribution of bone remodeling between mi-grating and stable prostheses in all Gruen zones.The femur –stem diameter index between the mi-grating hip stems (2.4Ϯ0.39)was not statistically signi ficant different from the stable hip stems (2.1Ϯ0.17).Radiostereometric Analysis ResultsMicromotion along the 3orthogonal axes in the stable and migrating groups 5during the 2-year follow-up is shown in Tables 1and 2and Figs.2and 3.The largest amount of micromotion occurred during the first 3postoperative months.Transla-tions of the hip stem in both groups were mainly present along the longitudinal axis.In the migrating group,translations were present along the trans-verse (Ϫ1.7Ϯ1.67mm)and the sagittal (1.1Ϯ2.95mm)axes.The migration along the transverseaxis probably is caused by a varus rotation.The migration along the sagittal axis probably is caused by antetorsion rotation.In the migrating stems group,the largest micromotion was seen along the longitudinal axis:18.6mm at 2-year follow-up (Fig.3).In this case,micromotions found along the transverse (7.3mm)and sagittal axis (3.5mm)also were the largest in this study.This patient had a femoral stem –femur diameter index of 3.1and no cement stop.ANOVA showed that only follow-up moment and preoperative femoral defect had a statistically signi ficant effect on the total translation (ANOVA,P ϭ.001).No effect on migration was present for the surgeon (postoperative ambulation regimen),the cement mantle thickness,or the femur –stem index.The total micromotion of the hip stems in the preoperative Paprosky 2A femoral defects was 0.35mm (range,0.12-0.58mm;95%con fidence inter-val)less micromotion compared with the Paprosky 2C and 3groups (ANOVA;P ϭ.001).The total mi-cromotion in the preoperative Paprosky 2B group was 0.14mm (range,0.03-0.25mm;95%con fi-dence interval)less than the Paprosky 2C and 3groups (ANOVA;P ϭ.02).DiscussionIn this study,2factors could be identi fied to in fluence migration of the hip stems.The first factor was the extent of the femoral defect,and the second factor was the presence of cement mantle defects.The association between the extent of the femoral defect (Paprosky classi fication)and total migration of the stem in the allograft-impacted femoral canal could be anticipated,but the differences in migra-tion between the Paprosky groups are small.Be-cause the differences in stem migration between an intact femoral canal and a defective canal are prob-ably clinically less important,the allograft impac-tion revision technique provides a clinically stable construct for the cemented stem,even in extensive femoral defects.The mechanical goal of the opera-tion is providing enough initial stability of the ce-ment –implant –allograft construct.When stabilityisFig.1.Median and range of the average cement thickness in the migrating prostheses and the stable prostheses.Table 1.Mean Translations (mm)and SDs of the Migrating ProsthesesPostoperative6wk3mo6mo9mo1y1.5y2yTransverse 0Ϫ0.51Ϯ0.87Ϫ0.71Ϯ1.07Ϫ0.76Ϯ1.02Ϫ0.66Ϯ1.11Ϫ1.12Ϯ1.36Ϫ1.32Ϯ1.88Ϫ1.74Ϯ1.67Longitudinal 0Ϫ2.56Ϯ3.69Ϫ3.27Ϯ3.91Ϫ4.36Ϯ5.21Ϫ5.16Ϯ5.93Ϫ5.56Ϯ5.71Ϫ6.58Ϯ5.60Ϫ7.53Ϯ5.90Sagittal0.66Ϯ1.000.96Ϯ1.39 1.30Ϯ2.54 1.09Ϯ2.27 1.06Ϯ2.40 1.34Ϯ2.64 1.10Ϯ2.95Factors for Migration in Hip Revision •Nelissen et al.829achieved at operation,further restoration of the integrity of the proximal femur occurs as the graft is progressively revascularized and replaced by host –bone in the postoperative period [6].In vitro studies show that the mechanical (ie,axial and torsional)stability of the cemented femoral component in impaction grafting is only slightly less compared with the primary cemented stem [25].Mechanical sequelae,which occur in a postopera-tive biologic environment,are less predictive but determine the incorporation of allograft bone with host –bone.During the creeping substitution of al-lograft bone by host –bone,the stability of the ce-ment implant –allograft construct can be endan-gered.In this study,the highest increase in migration occurred the first 3months after surgery and is higher than the mean 1.06mm migration in the primary Exeter stem that was found in another RSA study [26].Another study [27]found that the highest migration with this impaction grafting revi-sion technique occurred during the first postopera-tive weeks.This early subsidence of the prosthesis probably is related to additional allograft compac-tion when patients are mobilized.We did not find any difference in total migration comparing the 2postoperative rehabilitation protocols (ie,immedi-ate weight bearing vs no weight bearing for 6weeks).Some authors [3]stated that the Exeter stem continues to migrate during its entire life span owing to its stem design.In 96%of cases,Ͻ2mm of migration was noticed,however.Migration of the Exeter stem was stated to be nil in 36%of cases [28]and to occur in 1case out of 56cases in another study [3].All these migration measurements were made on conventional radiographs with their sub-sequent measurement inaccuracies [6,22].In our study,the Exeter stems showed either stabilizing migration of the stems along the 3cardinal axes or an overall mean continuous migration.The migra-tory pattern in the migrating group was subsidence and a possible varus rotation and antetorsion.This pattern probably was due to either cement defects at the medial Gruen zones or less impacted allograft chips.The latter could not be substantiated with our data because no effect of the surgeon was found on migration,and the radiographic appearance of the allograft bone incorporation at the Gruen zones was identical between the stable and migrating groups.The second factor in fluencing the migration of the hip stems was the presence of a thincementFig. 2.Subsidence of the stems in the stable prostheses (n ϭ10).Table 2.Mean Translations (mm)and SDs of the Stable ProsthesesPostoperative6wk3mo6mo9mo1y1.5y2yTransverse 0Ϫ0.16Ϯ0.43Ϫ0.20Ϯ0.46Ϫ0.18Ϯ0.51Ϫ0.18Ϯ0.57Ϫ0.03Ϯ0.410.04Ϯ0.54Ϫ0.06Ϯ0.50Longitudinal 0Ϫ0.21Ϯ0.27Ϫ0.43Ϯ0.36Ϫ0.66Ϯ0.47Ϫ0.85Ϯ0.50Ϫ0.98Ϯ0.54Ϫ1.08Ϯ0.74Ϫ1.21Ϯ0.76Sagittal0.10Ϯ0.420.11Ϯ0.360.17Ϯ0.500.14Ϯ0.390.14Ϯ0.380.17Ϯ0.500.21Ϯ0.61830The Journal of Arthroplasty Vol.17No.7October 2002mantle or possible cement mantle defects.All 8continuous migrating hip stems had cement mantle defects (Ͻ2mm cement)in at least 2Gruen zones.In the stable hip stem group,5of 10stable hip stems had a cement mantle defect in 2Gruen zones.The cement mantle should allow for a smooth transition of forces from the femoral component to the adja-cent bone.Because the bone –graft deforms perma-nently during the process of creeping substitution,defects might cause progressive migration and fail-ure of the hip stem.Also,this type of stem probably eventually would loosen,in the presence of sub-stantial migration because the latter should be iden-tical to cement mantle defects;this is illustrated by the different migratory patterns of the stabilized and the continuous migrating hip stems.Stabiliza-tion of stem migration is probably identical to a viable bone –graft,which in some cases also can exist after an initial postoperative high migration ratio.Whether this hip stem will stabilize depends on the extent of the femoral defect and probably on the type of instruments.Some authors [10]showed the Exeter tamp has a different con figuration (ie,shorter and smaller distally)than the de finitive prostheses.Consequently an insuf ficient cement mantle is created,which might explain the high initial migration in our study and that of oth-ers [27].Many articles [18,19,26,29–31]link thelongevity of a cemented hip stem to the adequacy of the cement mantle,and cement defects might be a factor for failure.In a retrieval study [19],cement fractures had a relationship with loosening of the prosthesis in the long run.Prosthesis survival is multifactorial.RSA of the prosthesis can address fixation factors that cannot be measured reproducibly and accurately on con-ventional radiographs.The revision technique of morcellized allograft impaction with a cemented tapered polished stem is a technically demanding technique,which can be technically successful.Postoperatively,irreversible deformation occurs af-ter loading of the impacted morcellized grafts,re-sulting in stem migration [32].In a fair amount of hip stems,stabilization of this migration occurs.The extent and stabilization of migration depend on several factors as addressed previously.Continued migration after 1.5to 2years seems to have a high likelihood of future failure,however,compared with a stable stem –cement –allograft construct [33].ConclusionTwo factors could be identi fied in fluencing the stem migration in allograft impaction revision of a hip prosthesis:the extent of the femoral defectsandFig. 3.Subsidence of the stems in the migrat-ing prostheses (n ϭ8).Factors for Migration in Hip Revision •Nelissen et al.831the presence of cement mantle defects.The effect of thefirst factor on micromotion was limited and 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