A fast and simple stretch-minimizing mesh parameterization
英语材基试卷
英文原版教材班“材料科学基础”考试试题试卷一Examination problems of the course of “fundament of materials science”姓名：班级：记分：1. Glossary (2 points for each)1) crystal structure:2) basis (or motif):3) packing fractor:4) slip system:5) critical size:6) homogeneous nucleation:7) coherent precipitate:8) precipitation hardening:9) diffusion coefficient:10) uphill diffusion:2. Determine the indices for the planes in the cubic unit cell shown in Figure 1. (5 points)Fig. 13. Determine the crystal structure for the following: (a) a metal with a0 =4.9489 Å, r = 1.75 Å and one atom per lattice point; (b) a metal with a0 = 0.42906 nm, r = 0.1858 nm and one atom per lattice point. (10 points)4-1. What is the characteristic of brinell hardness test, rockwell hardness test and Vickers hardness test? What are the effects of strain rate and temperature on the mechanical properties of metallic materials? (15 points)4-2. What are the effects of cold-work on metallic materials? How to eliminate those effects? And what is micro-mechanism for the eliminating cold-work effects? (15 points)5-1. Based on the Pb-Sn-Bi ternary diagram as shown in Fig. 2, try to(1)Show the vertical section of 40wt.%Sn; (4 points)(2) Describe the solidification process of the alloy 2# with very low cooling speed (includingphase and microstructure changes); (4 points)(3)Plot the isothermal section at 150o C. (7 points)Fig. 25-2. A 1mm sheet of FCC iron is used to contain N2in a heated exchanger at 1200o C. The concentration of N at one surface is 0.04 atomic percent and the concentration at the second surface is 0.005 atomic percent. At 1000 o C, if same N concentration is demanded at the second surface and the flux of N becomes to half of that at 1200o C, then what is the thickness of sheet?(15 points)6-1. Supposed that a certain liquid metal is undercooled until homogeneous nucleation occurs. (15 points)(1)How to calculate the critical radius of the nucleus required? Please give the deductionprocess.(2)For the Metal Ni, the Freezing Temperature is 1453︒C, the Latent Heat of Fusion is 2756J/cm3, and the Solid-liquid Interfacial Energy is 255⨯10-7 J/cm2. Please calculate the critical radius at 1353︒C. (Assume that the liquid Ni is not solidified.)6-2. Fig.3 is a portion of the Mg-Al phase diagram. (15 points)(1)If the solidification is too rapid, please describe the solidification process of Mg-10wt%Alalloy.(2)Please describe the equilibrium solidification process of Mg-20wt%Al alloy, and calculate theamount of each phase at 300︒C.Fig. 37-1. Figure 4 shows us the Al-Cu binary diagram and some microstructures found in a cooling process for an Al-4%Cu alloy. Please answer following questions according to this figure. (20 points)Fig. 4(1)What are precipitate, matrix and microconstituent? Please point them out in the in the figure and explain.(2)Why is need-like precipitate not good for dispersion strengthening? The typical microstructure shown in the figure is good or not? why?(3)Please tell us how to obtain the ideal microstructure shown in this figure.(4)Can dispersion strengthened materials be used at high temperature? Please give the reasons (comparing with cold working strengthening)7-2. Please answer following questions according to the time-temperature-transformation (TTT) diagram as shown in Fig. 5. (20 points)(1)What steel is this TTT diagram for? And what means P, B, and M in the figure? (2)Why dose the TTT diagram exhibi ts a ‘C’ shape?(3)Point out what microconstituent will be obtained after austenite is cooled according to the curves I, II, III and IV .(4)What is microstructural difference between the curve I and the curve II? (5)How to obtain the steel with the structure of(a) P+B(b) P+M+A (residual) (c) P+B+M+A (residual)(d) Full tempered martensiteIf you can, please draw the relative cooling curve or the flow chart of heat treatment.Fig. 5III III IV英文原版教材班“材料科学基础”考试试题答案Solution s of the course of “fundament of materials science”1. Glossary (2 points for each)1) The arrangement of the atoms in a material into a repeatable lattice.2) A group of atoms associated with a lattice.3) The fraction of space in a unit cell occupied by atoms.4) The combination of the slip plane and the slip direction.5) The minimum size that must be formed by atoms clustering together in the liquid before thesolid particle is stable and begins to grow.6) Formation of a critically sized solid from the liquid by the clustering together of a largenumber of atoms at a high undercooling (without an external interface).7) A precipitate whose crystal structure and atomic arrangement have a continuousrelationship with matrix from which precipitate is formed.8) A strengthening mechanism that relies on a sequence of solid state phase transformationsin a dispersion of ultrafine precipitates of a 2nd phase. This is same as age hardening. It is a form of dispersion strengthening.9) A temperature-dependent coefficient related to the rate at which atom, ion, or otherspecies diffusion. The DC depends on temperature, the composition and microstructure of the host material and also concentration of the diffusion species.10) A diffusion process in which species move from regions of lower concentration to that ofhigher concentration.2. Solution: A(-364), B(-340), C(346).3. Solution: (a)fcc; (b) bcc.4-1. What is the characteristic of brinell hardness test, rockwell hardness test and Vickers hardness test? What are the effects of strain rate and temperature on the mechanical properties of metallic materials? (15 points)4-2. What are the effects of cold-work on metallic materials? How to eliminate those effects? And what is micro-mechanism for the eliminating cold-work effects? (15 points)5-1. Based on the Pb-Sn-Bi ternary diagram as shown in Fig. 2, try to(1)Show the vertical section of 40wt.%Sn; (5 points)(2) Describe the solidification process of the alloy 2# with very low cooling speed (includingphase and microstructure changes); (5 points)(3)Plot the isothermal section at 150o C. (5 points)Fig. 25-2. A 1mm sheet of FCC iron is used to contain N2in a heated exchanger at 1200o C. The concentration of N at one surface is 0.04 atomic percent and the concentration at the second surface is 0.005 atomic percent. At 1000 o C, if same N concentration is demanded at the second surface and the flux of N becomes to half of that at 1200o C, then what is the thickness of sheet?(15 points)6-1. Supposed that a certain liquid metal is undercooled until homogeneous nucleation occurs. (15 points)(3)How to calculate the critical radius of the nucleus required? Please give the deductionprocess.(4)For the Metal Ni, the Freezing Temperature is 1453︒C, the Latent Heat of Fusion is 2756J/cm3, and the Solid-liquid Interfacial Energy is 255⨯10-7 J/cm2. Please calculate the critical radius at 1353︒C. (Assume that the liquid Ni is not solidified.)6-2. Fig.3 is a portion of the Mg-Al phase diagram. (15 points)(3)If the solidification is too rapid, please describe the solidification process of Mg-10wt%Alalloy.(4)Please describe the equilibrium solidification process of Mg-20wt%Al alloy, and calculate theamount of each phase at 300︒C.Fig. 37-1. Figure 4 shows us the Al-Cu binary diagram and some microstructures found in a cooling process for an Al-4%Cu alloy. Please answer following questions according to this figure. (20 points)Fig. 4(1)What are precipitate, matrix and microconstituent? Please point them out in the in the figure and explain.(2)Why is need-like precipitate not good for dispersion strengthening? The typical microstructure shown in the figure is good or not? why?(3)Please tell us how to obtain the ideal microstructure shown in this figure.(4)Can dispersion strengthened materials be used at high temperature? Please give the reasons (comparing with cold working strengthening)7-2. Please answer following questions according to the time-temperature-transformation (TTT) diagram as shown in Fig. 5. (20 points)(1)What steel is this TTT diagram for? And what means P, B, and M in the figure? (2)Why dose the TTT diagram exhibits a ‘C’ shape?(3)Point out what microconstituent will be obtained after austenite is cooled according to the curves I, II, III and IV .(4)What is microstructural difference between the curve I and the curve II? (5)How to obtain the steel with the structure of(a) P+B(b) P+M+A (residual) (c) P+B+M+A (residual)(d) Full tempered martensiteIf you can, please draw the relative cooling curve or the flow chart of heat treatment.Fig. 5III III IV英文原版教材班“材料科学基础”考试试题试卷二Examination problems of the course of “fundament of materials science”姓名：班级：记分：1. You would like to be able to physically separate different materials in a scrap recycling plant. Describe some possible methods that might be used to separate materials such as polymers, aluminum alloys, and steels from one another. (5 points)2. Plot the melting temperature of the elements in the 1A column of the periodic table versus atomic number (i.e., plot melting temperatures of Li through Cs). Discuss this relationship, based on atomic bonding and binding energy. (10 points)3.Above 882℃, titanium has a BCC crystal structure, with a = 0.332 nm. Below this temperature, titanium has a HCP structure, with a = 0.2978 nm and c = 0.4735 nm. Determine the percent volume change when BCC titanium transforms to HCP titanium. Is this a contraction or expansion? (10 points)4. The density of BCC iron is 7.882 g/cm3and the lattice parameter is 0.2866 nm whenhydrogen atoms are introduced at interstitial positions. Calculate (a) the atomic fraction of hydrogen atoms and (b) the number of unit cells required on average to contain one hydrogen atom. (15 points)5. A carburizing process is carried out on a 0.10% C steel by introducing 1.0% C at the surface at 980℃, where the iron is FCC. Calculate the carbon content at 0.01 cm, 0.05 cm, and 0.10 cm beneath the surface after 1 h. (15 points)6. The following data were collected from a standard 0.505-in.-diameter test specimen of acopper alloy (initial length (t o) = 2.0 in.):Load Gage Length Stress Strain(lb) (in.) (psi) (in/in.)0 2.00000 0 0.03,000 2.00167 15,000 0.0008356,000 2.00333 30,000 0.0016657,500 2.00417 37,500 0.0020859,000 2.0090 45,000 0.004510,500 2.040 52,500 0.0212,000 2.26 60,000 0.1312,400 2.50 (max load) 62,000 0.2511,400 3.02 (fracture) 57,000 0.51After fracture, the gage length is 3.014 in. and the diameter is 0.374 in. Plot the data and calculate (a) the 0.2% offset yield strength, (b) the tensile strength, (c) the modulus of elasticity, (d) the %Elongation, (e) the %Reduction in area, (f) the engineering stress at fracture, (g) the true stress at fracture, and (h) the modulus of resilience. (15 points)7. A 1.5-em-diameter metal bar with a 3-cm gage length is subjected to a tensile test. Thefollowing measurements are made.Change in Force (N) Gage length (cm) Diameter (cm)16,240 0.6642 1.202819,066 1.4754 1.088419,273 2.4663 0.9848Determine the strain hardening coefficient for the metal. Is the metal most likely to be FCC, BCC, or HCP? Explain.(15 points)8. Based on Hume-Rothery’s conditions, which of the following systems would be expected todisplay unlimited solid solubility? Explain. (15 points)(a) Au-Ag (b) Al-Cu (c) Al-Au (d)U-W(e) Mo-Ta (f) Nb-W (g) Mg-Zn (h) Mg-Cd英文原版教材班“材料科学基础”考试试题答案Solutions of the course of “fundament of materials science”1.Steels can be magnetically separated from the other materials; steel (or carbon-containing iron alloys) are ferromagnetic and will be attracted by magnets. Density differences could be used—polymers have a density near that of water; the specific gravity of aluminum alloys is around2.7;that of steels is between 7.5 and 8. Electrical conductivity measurements could be used—polymers are insulators, aluminum has a particularly high electrical conductivity.(5 points)2.T (o C)L i–180.7N a– 97.8K – 63.2R b– 38.9As the atomic number increases, the melting temperature decreases, (10 points)3. We can find the volume of each unit cell. Two atoms are present in both BCC and HCP titanium unit cells, so the volumes of the unit cells can be directly compared.V BCC = (0.332 nm)3 = 0.03659 nm3V HCP= (0.2978 nm)2(0.4735 nm)cos30 = 0.03637 nm3△V=x 100 =×100= -0.6%Therefore titanium contracts 0.6% during cooling. (10 points)4. (a) 7.882 g/cm3 =x = 0.0081 H atoms/cellThe total atoms per cell include 2 Fe atoms and 0.0081 H atoms. Thus:(10 points)(b) Since there is 0.0081 H/cell, then the number of cells containing H atoms is:cells = 1/0.0081 = 123.5 or 1 H in 123.5 cells (5 points)5. D = 0.23 exp[-32,900/(1.987)(1253)] = 42 × 10-8 cm2/sC x= 0.87% CC x= 0.43% CC x= 0.18% C(15 points)6. σ=FI (π/4)(0.505)2 = F/0.2ε = (l-2)/2(a) 0.2% offset yield strength = 45,000 psi(b)tensile strength = 62,000 psi(c) E = (30,000 - 0) / (0.001665 - 0) = 18 x 106 psi(d)%Elongation =(e) %Reduction in area =(f) engineering stress at fracture = 57,000 psi(g)true stress at fracture = 11,400 lb / (TC/4)(0.374)2= 103,770 psi (h) From the graph, yielding begins at about 37,500 psi. Thus:(15 points)7.Force(lb) Gage length(in.) Diameter(in.) True stress(psi) True strain(psi)16,240 3.6642 12.028 143 0.20019,066 4.4754 10.884 205 0.40019,273 5.4663 9.848 249 0.600σt=Kεt2or ln143=ln K + n ln0.2ln 249 = ln K + nln 0.6n=0.51A strain hardening coefficient of 0.51 is typical of FCC metals.(15 points)8.The Au–Ag, Mo–Ta, and Mg–Cd systems have the required radius ratio, the same crystal structures, and the same valences. Each of these might be expected to display complete solid solubility. [The Au –Ag and Mo –T a d o have isomorphous phase diagrams. In addition, the Mg–Cd alloys all solidify like isomorphous alloys; however a number of solid state phase transformations complicate the diagram.] (15 points)英文原版教材班“材料科学基础”考试试题试卷三Examination problems of the course of “fundament of materials science”姓名：班级：记分：1. You would like to be able to identify different materials without resorting to chemical analysis or lengthy testing procedures. Describe some possible testing and sorting techniques you might be able to use based on the physical properties of materials. (5 points)2. Plot the melting temperatures of elements in the 4A to 8-10 columns of the periodic table versus atomic number (i.e., plot melting temperatures of Ti through Ni, Zr through Pd, and Hf through Pt). Discuss these relationships, based on atomic bonding and binding energy, (a) as the atomic number increases in each row of the periodic table and (b) as the atomic number increases in each column of the periodic table. (10 points)3. Beryllium has a hexagonal crystal structure, with a o= 0.22858 nm and c o= 0.35842 nm. The atomic radius is 0.1143 nm, the density is 1.848 g/cm3, and the atomic weight is 9.01 g/mol. Determine (a) the number of atoms in each unit cell and (b) the packing factor in the unit cell.(10 points)4. Suppose we introduce one carbon atom for every 100 iron atoms in an interstitial position in BCC iron, giving a lattice parameter of 0.2867 nm. For the Fe-C alloy, find (a) the density and (b) the packing factor. (15 points)5. Iron containing 0.05% C is heated to 912oC in an atmosphere that produces 1.20% C at the surface and is held for 24 h. Calculate the carbon content at 0.05 cm beneath the surface if (a) the iron is BCC and (b) the iron is FCC. Explain the difference. (15 points)6. The following data were collected from a 0.4-in. diameter test specimen of poly vinyl chloride(l0 = 2.0 in):Load(lb) Gage Length(in.) Stress(psi) Strain(in/in.)0 2.00000 0 0.0300 2.00746 2,387 0.00373600 2.01496 4,773 0.00748900 2.02374 7,160 0.011871200 2.032 9,547 0.0161500 2.046 11,933 0.0231660 2.070 (max load) 13,206 0.0351600 2.094 12,729 0.0471420 2.12 (fracture) 11,297 0.06After fracture, the gage length is 2.09 in. and the diameter is 0.393 in. Plot the data and calculate (a) the 0.2% offset yield strength, (b) the tensile strength, (c) the modulus of elasticity, (d) the %Elongation, (e) the %Reduction in area, (f) the engineering stress at fracture, (g) the true stress at fracture, and (h) the modulus of resilience. (15 points)7. A titanium alloy contains a very fine dispersion of tiny Er203 particles. What will be the effectof these particles on the grain growth temperature and the size of the grains at any particular annealing temperature? Explain. (15 points)8. Suppose 1 at% of the following elements is added to copper (forming a separate alloy witheach element) without exceeding the solubility limit. Which one would be expected to give the higher strength alloy? Is any of the alloying elements expected to have unlimited solid solubility in copper?(a) Au (b) Mn (c) Sr (d) Si (e) Co (15 points)英文原版教材班“材料科学基础”考试试题答案Solutions of the course of “fundament of materials science”1.Steels can be magnetically separated from the other materials; steel (or carbon-containing iron alloys) are ferromagnetic and will be attracted by magnets. Density differences could be used—polymers have a density near that of water; the specific gravity of aluminum alloys is around2.7;that of steels is between 7.5 and 8. Electrical conductivity measurements could be used—polymers are insulators, aluminum has a particularly high electrical conductivity.(5 points)2. Ti –1668 Zr – 1852 Hf – 2227V –1900 Nb –2468 Ta – 2996Cr –1875 Mo–2610 W–3410Mn–1244 Tc –2200 Re–3180Fe –1538 Ru –2310 Os–2700Co –1495 Rh –1963 Ir –2447Ni –1453 Pd –1552 Pt –1769For each row, the melting temperature is highest when the outer “d” energy level is partly full. In Cr, there are 5 electrons in the 3d shell; in Mo, there are 5 electrons in the 4d shell; in W there are 4 electrons in the 5d shell. In each column, the melting temperature increases as the atomic number increases—the atom cores contain a larger number of tightly held electrons, making the metals more stable. (10 points)3.V= (0.22858 nm)2(0.35842 nm)cos 30 = 0.01622 nm3 = 16.22 × 10-24 cm3(a)From the density equation:1.848 g/cm3 =x = 2 atoms/cell(b)The packing factor (PF) is:PF == 0.77 (10 points)4. There is one carbon atom per 100 iron atoms, or 1 C/50 unit cells, or 1/50 C per unit cell:(a)(b)(15 points)5. t= (24 h)(3600 s/h) = 86,400 sD BCC = 0.011 exp[-20,900/(1.9871185)] = 1.54 × 10-6 cm2/sD FCC = 0.23 exp[-32,900/(1.987)(1185)] = 1.97×10-7 cm2/sBCC: = erf[0.0685] = 0.077C x= 1.11% CFCC: = erf[0.192] = 0.2139C x = 0.95% CFaster diffusion occurs in the looser packed BCC structure, leading to the higher carbon content at point “x”. (15 points)6. σ=F /(π/4)(0.4)2 = F/0.1257ε = (l-2)/2(a)0.2% offset yield strength = 11,600 psi(b) tensile strength = 12,729 psi(c) E= (7160 - 0) / (0.01187 - 0) = 603,000 psi(d)%Elongation =(e) %Reduction in area =(f) engineering stress at fracture = 11,297 psi(g)true stress at fracture = 1420 lb / (TC/4)(0.393)2= 11,706 psi (h) From the figure, yielding begins near 9550 psi. Thus:(15 points)7. These particles, by helping pin die grain boundaries, will increase the grain growth temperature and decrease the grain size. (15 points)8.The Cu-Sr alloy would be expected to be strongest (largest size difference). The Cu-Au alloy satisfies Hume-Rothery ’s conditions and might be expected to display complete solid solubility—in fact it freezes like an isomorphous series of alloys, but a number of solid state transformations occur at lower temperatures.(15 points)英文原版教材班“材料科学基础”考试试题试卷四Examination problems of the course of “fundament of materials science”姓名：班级：记分：1.Aluminum has a density of2.7 g/cm3. Suppose you would like to produce a compositematerial based on aluminum having a density of 1.5 g/cm3. Design a material that would have this density. Would introducing beads of polyethylene, with a density of 0.95 g/cm3, into the aluminum be a likely possibility? Explain. (5 points)2. (a) Aluminum foil used for storing food weighs about 0.3 g per square inch. How many atomsof aluminum are contained in this sample of foil?(b) Using the densities and atomic weights given in Appendix A, calculate and compare thenumber of atoms per cubic centimeter in (i) lead and (ii) lithium. (10 points)3. The density of potassium, which has the BCC structure and one atom per lattice point, is0.855 g/cm3. The atomic weight of potassium is 39.09 g/mol. Calculate (a) the latticeparameter; and (b) the atomic radius of potassium. (10 points)4. The density of a sample of HCP beryllium is 1.844 g/cm3 and the lattice parameters are a0=0.22858 nm and c0= 0.35842 nm. Calculate (a) the fraction of the lattice points that containvacancies and (b) the total number of vacancies in a cubic centimeter. (15 points)5. A ceramic part made of MgO is sintered successfully at 1700℃in 90 minutes. To minimizethermal stresses during the process, we plan to reduce the temperature to 1500℃. Which will limit the rate at which sintering can be done: diffusion of magnesium ions or diffusion of oxygen ions? What time will be required at the lower temperature? (15 points)6. (a) A thermosetting polymer containing glass beads is required to deflect 0.5 mm when aforce of 500 N is applied. The polymer part is 2 cm wide, 0.5 cm thick, and 10 cm long. If the flexural modulus is 6.9 GPa, determine the minimum distance between the supports. Will the polymer fracture if its flexural strength is 85 MPa? Assume that no plastic deformation occurs.(b) The flexural modulus of alumina is 45 x 106 psi and its flexural strength is 46,000 psi. Abar of alumina 0.3 in. thick, 1.0 in. wide, and 10 in. long is placed on supports 7 in. apart.Determine the amount of deflection at the moment the bar breaks, assuming that no plastic deformation occurs. (15 points)7. Based on the following observations, construct a phase diagram. Element A melts at 850°Cand element B melts at 1200°C. Element B has a maximum solubility of 5% in element A, and element A has a maximum solubility of 15% in element B. The number of degrees of freedom from the phase rule is zero when the temperature is 725°C and there is 35% B present. At room temperature 1% B is soluble in A and 7% A is soluble in B. (15 points)8.Suppose that age hardening is possible in the Al-Mg system (see Figure 10-11). (a)Recommend an artificial age-hardening heat treatment for each of the following alloys, and(b) compare the amount of the precipitate that forms from your treatment of each alloy. (i)Al-4% Mg (ii) Al-6% Mg (iii) Al-12% Mg (c) Testing of the alloys after the heat treatment reveals that little strengthening occurs as a result of the heat treatment. Which of the requirements for age hardening is likely not satisfied? (15 points)英文原版教材班“材料科学基础”考试试题答案Solutions of the course of “fundament of materials science”1. In order to produce an aluminum-matrix composite material with a density of 1.5 g/cm 3, we wouldneed to select a material having a density considerably less than 1.5 g/cm 3. While polyethylene’s density would make it a possibility, the polyethylene has a very low melting point compared to aluminum; this would make it very difficult to introduce the polyethylene into a solid aluminum matrix —processes such as casting or powder metallurgy would destroy the polyethylene .Therefore polyethylene would NOT be a likely possibility.One approach, however, might be to introduce hollow glass beads .Although ceramic glasses have densities comparable to that of aluminum, a hollow bead will have a very low density. The glass also has a high melting temperature and could be introduced into liquid aluminum for processing as a casting. (5 points)2. (a) In a one square inch sample:number ==6.69 × 1021 atoms(b) (i) In lead:= 3.3 × 1022 atoms/cm 3(ii) In lithium:= 4.63 × 1022 atoms/cm 3 (10 points)3. (a) Using Equation 3-5:0.855 g/cm 3 =a o 3 = 1.5189 × 10-22 cm 3 or a o = 5.3355 × 10-8 cm(b) From the relationship between atomic radius and lattice parameter:r == 2.3103 × 10-8cm (10 points)4. V u.c.= (0.22858 nm)2(0.35842 nm)cos30 = 0.01622 nm 3= 1.622 x 10~23 cm 3 (a) From the density equation:x = 1.9984fraction =29984.12 = 0.0008(b) number == 0.986 x 1020 vacancies/cm 3 (15 points)5. Diffusion of oxygen is the slower of the two, due to the larger ionic radius of the oxygen.D 1700= 0.000043 exp[-82,100/(1.987)(1973)] = 3.455 × 10-14 cm 2/sD1500= 0.000043 exp[-82,100/(1.987)(1773)] = 3.255 × 10-15 cm2/st1500 = D1700 t1700/D1500== 955 min = 15.9 h (15 points)6. (a) Solution:The minimum distance L between the supports can be calculated from the flexural modulus.L3 = 4w/z3δ(flexural modulus)/3FL3 = (4)(20 mm)(5 mm)3(0.5 mm)(6.9 GPA)(1000 MPa/GPa) / 500 NL3 = 69,000 mm3 or L = 41 mmThe stress acting on the bar when a deflection of 0.5 mm is obtained isσ= WL/2wh2 = (3)(500 N)(41 mm) / (2)(20 mm)(5 mm)2 = 61.5 MPaThe applied stress is less than the flexural strength of 85 MPa; the polymer is not expected to fracture.(b) Solution:The force required to break the bar isF = 2w/z2(flexural strength)/3LF= (2)(1 in)(0.3 in)2(46,000 psi / (3)(7 in.) = 394 lbThe deflection just prior to fracture is8 = FZ3/4wh3(flexural modulus)8 = (394 lb)(7 in)3/(4)(l in)(0.3 in)3(45 x 106 psi) = 0.0278 in. (15 points)7.(15 points)8. (a) The heat treatments for each alloy might be:Al-4% Mg Al-6% Mg Al-12% MgT Eutectic451°C 451°C 451°CT Solvs210°C 280°C 390°CSolutionTreat at: 210-451°C 280-451°C 390-451°CQuench Quench QuenchAge at: <210°C <280°C <390°C(b) Answers will vary depending on aging temperature selected. If all threeare aged at 200°C, as an example, the tie line goes from about 3.8 to 35% Mg:A1-4% Mg: %β = (4− 3.82)/(35 − 3.82) X 100 = 0.6%Al-6% Mg: %β = (6 − 3.82)/(35 − 3.82) X 100 = 7.1%Al-12% Mg: %β = (12 −3.82)/(35− 3.82) X 100 = 26.8%(c) Most likely, a coherent precipitate is not formed; simple dispersionstrengthening, rather than age hardening, occurs. (15 points)英文原版教材班“材料科学基础”考试试题试卷五Examination problems of the course of “fundament of materials science”姓名：班级：记分：1. You would like to design an aircraft that can be flown by human power nonstop for adistance of 30 km. What types of material properties would you recommend? What materials might be appropriate? (5 points)2. Boron has a much lower coefficient of thermal expansion than aluminum, even though bothare in the 3B column of the periodic table. Explain, based on binding energy, atomic size, and the energy well, why this difference is expected. (10 points)3. Determine the ASTM grain size number if 20 grains/square inch are observed at amagnification of 400. (10 points)4. We currently can successfully perform a carburizing heat treatment at 1200o C in 1 h. In aneffort to reduce the cost of the brick lining in our furnace, we propose to reduce the carburizing temperature to 950℃. What time will be required to give us a similar carburizing treatment? (15 points)5.The data below were obtained from a series of Charpy impact tests performed on foursteels, each having a different manganese content. Plot the data and determine (a) the transition temperature (defined by the mean of the absorbed energies in theductile and brittle regions) and (b) the transition temperature (defined as the temperature that provides 50 J absorbed energy). Plot the transition temperature versus manganese content and discuss the effect of manganese on the toughness of steel. What would be the minimum manganese allowed in the steel if a part is to be used at 0°C?Test temperature°C Impact snergy (J)0.30% Mn 0.39% Mn 1.01% Mn 1.55% Mn-100 2 5 5 15-75 2 5 7 25-50 2 12 20 45-25 10 25 40 700 30 55 75 11025 60 100 110 13550 105 125 130 14075 130 135 135 140100 130 135 135 140(15 points)。
新视野大学英语第五册单词(注释+例句)~
Unit 1 新视野大学英语第五册第一课A Technological Revolution in Education 课文生词讲解( new words study) prevalenta. (fml.)existing commonly, generally, or widely (in some place or at some time ); predominant(正式)（在某地或某时）流行的，盛行的；普遍的The habit of traveling by aircraft is becoming more prevalent each year.坐飞机旅行一年比一年普遍了。
One simple injection can help to protect you right through the cold months when flu is most prevalent.只要打上一针预防针就能帮助你度过流感盛行的寒冷月份。
continuityn. [U]uninterrupted connection or union (through time or space)连续性，连贯性There is no continuity of subject in a dictionary.词典的主题没有连续性。
This paper lacks continuity.这篇论文缺乏连贯性。
inherenta. existing as an essential constituent or characteristic; intrinsic固有的，内在的，天生的The communication skills that belong to each species of animal, including people, are not inherent.包括人在内的动物所具有的交际技能并不是天生的。
抑菌带宽度的英文
抑菌带宽度的英文The width of an antimicrobial band is a crucial factor in ensuring its effectiveness against various pathogens. It plays a significant role in the design of medical textiles and protective gear.In healthcare settings, the optimal width of an antimicrobial band is essential for preventing the spread of infections. A well-crafted band can act as a barrier, providing a first line of defense against harmful microorganisms.Research indicates that the width should be proportionate to the area it is intended to cover. For instance, a band for a surgical mask should be wide enough to secure a snug fit around the face, minimizing the entry of contaminants.Moreover, the material of the band also influences its width. Bands made from woven fabrics might require adifferent width than those made from non-woven materials, due to differences in stretch and durability.The incorporation of antimicrobial agents into the band's fibers can further enhance its width-related properties. These agents work to inhibit the growth of bacteria, fungi, and viruses, making the band an effective component of personal protective equipment.In conclusion, the width of an antimicrobial band is a multifaceted consideration that involves the balance between protection, comfort, and practicality. It must be carefully calibrated to meet the specific needs of the application and the individuals it is designed to protect.。
对熬夜的建议英语作文
对熬夜的建议英语作文In today's fast-paced society, many people find themselves pulling all-nighters for various reasons, whether it's to meet a deadline, study for an exam, or simply enjoy somelate-night entertainment. While staying up late may seem like a harmless habit, it can have significant effects on one's health and productivity. Here are some suggestions to make the most out of your late-night endeavors while minimizing the negative impacts:1. Plan Ahead: If you know you have to stay up late, try to prepare your day in advance. This might include getting a head start on your sleep the night before or planning lighter tasks for the following day to allow for recovery.2. Stay Hydrated and Snack Smart: Dehydration can exacerbate the effects of sleep deprivation. Drink plenty of water and opt for healthy snacks that can provide a steady source of energy without causing a sugar crash.3. Create a Comfortable Environment: Ensure your study or work area is well-lit and comfortable. A clutter-free space can help you focus better.4. Take Breaks: Every hour, take a short break to rest your eyes and stretch your body. This can help prevent fatigue and maintain alertness.5. Avoid Caffeine Overload: While a cup of coffee or tea can provide a much-needed energy boost, too much caffeine can lead to a jittery feeling and disrupt your sleep pattern for the following nights.6. Use Time Management Techniques: Techniques like the Pomodoro Technique, where you work for 25 minutes and then take a 5-minute break, can help you stay focused and efficient.7. Listen to Soothing Music: Soft, instrumental music can help create a calm atmosphere and reduce stress levels, making it easier to concentrate.8. Prioritize Tasks: Not all tasks are equally important. Identify which tasks are most urgent and tackle those first.9. Use Natural Light: If possible, work near a window where you can benefit from natural light. Natural light can help regulate your body's internal clock and improve alertness.10. Get Up and Move: Physical activity, even if it's just a short walk, can help you stay awake and alert.11. Avoid Electronic Devices Before Bed: The blue light emitted by phones, tablets, and computers can interfere with your sleep. Try to switch off these devices at least an hour before you plan to sleep.12. Seek Support: If you're consistently staying up late due to work or study demands, it might be helpful to talk to acounselor or a mentor about time management and stress reduction strategies.Remember, while occasional late nights are common, making it a habit can lead to serious health issues. It's important to balance the need to stay up late with the need for adequate rest. Prioritize your health and well-being, and use these tips to navigate the challenges of staying up late more effectively.。
如何更好的管理时间英语作文
如何更好的管理时间英语作文Time is one of the most precious resources we have in life. It is a finite and non-renewable commodity, and how we choose to use it can have a significant impact on our productivity, success, and overall well-being. Effective time management is a crucial skill that can help us achieve our goals, reduce stress, and live a more fulfilling life. In this essay, we will explore some strategies and techniques that can help us better manage our time and make the most of the hours we have.One of the fundamental principles of effective time management is to prioritize our tasks and activities. We often find ourselves overwhelmed by the sheer number of responsibilities and commitments we have, and it can be easy to get caught up in the urgency of the moment rather than focusing on what's truly important. By taking the time to identify our priorities and allocate our time accordingly, we can ensure that we're spending our time on the tasks that will have the greatest impact on our lives.One way to do this is to create a to-do list or a daily schedule thatoutlines our tasks and their level of importance. This can help us identify the high-priority items that require our immediate attention, as well as the lower-priority tasks that can be delegated or postponed. By focusing our energy on the most important tasks first, we can ensure that we're making progress towards our goals and avoiding the temptation to get sidetracked by less important activities.Another key aspect of effective time management is learning to say "no." In our modern, fast-paced world, we are often bombarded with requests and demands on our time, and it can be easy to overcommit ourselves. However, it's important to recognize that we have limited resources and that we need to be selective about the commitments we make. By learning to politely decline requests that don't align with our priorities or that would stretch us too thin, we can free up time to focus on the tasks that are truly important to us.In addition to prioritizing our tasks and learning to say "no," effective time management also involves developing strategies for minimizing distractions and staying focused. In today's digital age, we are constantly bombarded by notifications, emails, and social media updates, all of which can disrupt our productivity and pull us away from our important tasks. To combat this, we can try techniques like turning off our notifications, setting aside dedicated time for checking emails and social media, and using productivity apps orbrowser extensions to block distracting websites.Another useful strategy for better managing our time is to break down larger tasks into smaller, more manageable steps. This can help us avoid feeling overwhelmed and make it easier to make progress on our goals. By breaking down a large project into a series of smaller, more achievable tasks, we can create a sense of momentum and accomplishment that can help us stay motivated and on track.Finally, it's important to remember that effective time management is not just about being productive – it's also about taking care of ourselves. Burnout and stress can have a significant impact on our ability to manage our time effectively, so it's important to build in regular breaks and self-care activities into our schedules. This might involve taking a walk, practicing meditation or mindfulness, or simply taking a few minutes to step away from our work and recharge.In conclusion, effective time management is a crucial skill that can help us achieve our goals, reduce stress, and live a more fulfilling life. By prioritizing our tasks, learning to say "no," minimizing distractions, breaking down larger tasks, and taking care of ourselves, we can develop strategies and techniques that will help us better manage our time and make the most of the hours we have. With practice and dedication, we can all become more effective and efficient in our use of time, and reap the rewards of a life well-lived.。
由深至浅缝合技术在镜下治疗小肩袖损伤的临床应用
第24卷 第7期 中国内镜杂志 Vol. 24 No. 7 2018年7月 China Journal of Endoscopy Jul. 2018论 著收稿日期：2017-12-26*基金项目：东莞市社会科技发展（重点）项目（No ：201750715002435）[通信作者] 杜以宽，E-mail ：yikuan.du@DOI: 10.3969/j.issn.1007-1989.2018.07.006文章编号： 1007-1989（2018）07-0033-04由深至浅缝合技术在镜下治疗小肩袖损伤的临床应用*袁胜超，谭志超，杜以宽，林馥纯（广东省东莞市中医院 骨二科，广东 东莞 523000）摘要：目的 探讨关节镜下由深至浅缝合技术治疗小肩袖损伤的临床疗效。
方法 选取2014年1月-2016年6月肩关节镜下单锚钉微创手术技术修复小肩袖撕裂（肩袖撕裂口<1 cm）患者，探讨由深至浅缝合技术在镜下治疗小肩袖损伤的具体操作。
共选取33例患者。
其中，男14例，女19例，年龄38～75岁，平均57.2岁。
采用Constant 评分系统、美国加州大学肩关节评分系统（UCLA）、美国肩与肘协会评分系统（ASES）对手术前、手术后1年肩关节功能进行临床评估。
结果 Constant 评分从术前的（65.84±8.00）分增加至术后1年随访时的（84.73±6.24）分；UCLA 肩关节评分从术前的（17.63±3.11）分增加至末次随访时的（32.40±1.97）分；ASES 评分从术前的（78.80±7.02）分增加至末次随访时的（93.93±5.66）分；术前、术后比较差异均有统计学意义（P <0.01）。
结论 关节镜下由深至浅缝合技术治疗小肩袖损伤是一种简单有效的方法，是肩关节镜下缝合技术的一项创新和发展。
关键词： 由深至浅缝合；小肩袖损伤；关节镜中图分类号： R686 文献标识码： AClinical application of suture technique from the deep to shallow of arthroscopic rotator cuff repair for small rotator cuff tears *Sheng-chao Yuan, Zhi-chao Tan, Yi-kuan Du, Fu-chun Lin(Department of Orthopaedics, Dongguan Hospital of Traditional Chinese Medicine,Dongguan, Guangdong 523000, China)Abstract: Objective To discuss and evaluate the suture technique from the deep to shallow of arthroscopic rotator cuff repair and its clinical results. Methods From January 2014 to June 2016, the clinical data of 33 small tears patients treated by arthroscopic rotator cuff repair was reviewed. We discussed the specific operation in the suture technique from the deep to shallow of arthroscopic rotator cuff repair, 14 cases in men and 19 cases in women. The mean age was 57.2 (38 ~ 75) years old. All the tears were repaired under the arthroscope, and single metal suture anchor had been used in all the patients. Constant-Murley score, UCLA score and ASES score were adopted before operation and one year after the operation. Results The pre-operation and post-operation mean constant score was (65.84 ± 8.00) vs (84.73 ± 6.24), the mean UCLA score was (17.63 ± 3.11) vs (32.40 ± 1.97), the mean ASES score was (78.80 ± 7.02) vs (93.93 ± 5.66), there was significant differences between pre-operation and post-operation (P < 0.01). Conclusion It’s a simple and effective suture technique from the deep to shallow for small rotator cuff tears and it will be an innovation and development.Keywords: suture technique from the deep to shallow; small rotator cuff; arthroscope中国内镜杂志 第24卷肩袖是肩部力量最为集中的地方，对盂肱关节起到稳定、支撑的作用，尤其在肩关节频繁外展运动时，肩袖因摩擦、挤压而极易受到损伤，引发肌腱断裂或者无菌性炎症改变，称为肩袖损伤[1-4]。
2018高考英语阅读理解真题大全
2018高考英语阅读理解真题大全(附详解)(总47页)--本页仅作为文档封面，使用时请直接删除即可----内页可以根据需求调整合适字体及大小--2018高考英语阅读理解真题大全（附详解）1.Summer ActivitiesStudents should read the list with their parents/careers, and select two activities they would like to do. Forms will be available in school and online for them to indicate their choices and return to school. Before choices are finalised, parents/careers will be asked to sign to confirm their（1）Which activity will you choose if you want to go camping?....（2）What will the students do on Tuesday with Mrs. Wilson?to London.a parade and fireworks.central Paris.the WWI battlefields.（3）How long does Potty about Potter last?days.days.days.week.of us love July because it’s the month when nature’s berries and stone fruits are in abundance. These colourful and sweet jewels form British Columbia’s fields are little powerhouses of nutritional protection.Of the common berries, strawberries are highest in vitamin C, although, because of their seeds, raspberries contain a little more protein (蛋白质), iron and zinc (not that fruits have much protein). Blueberries are particularly high in antioxidants (抗氧化物质). The yellow and orange stone fruits such as peaches are high in the carotenoids we turn into vitamin A and which are antioxidants. As for cherries (樱桃), they are so delicious who caresHowever, they are rich in vitamin C.When combined with berries of slices of other fruits, frozen bananas make an excellent base for thick, cooling fruit shakes and low fat “ice cream”. For this purpose, select ripe bananas for freezing as they are much sweeter. Remove the skin and place them in plastic bags or containers and freeze. If you like, a squeeze of fresh lemon juice on the bananas will prevent them turning brown. Frozen bananas will last several weeks, depending on their ripeness and the temperature of the freezer.If you have a juicer, you can simply feed in frozen bananas and some berries or sliced fruit. Out comes a “soft-serve” creamy dessert, to be eaten right away. This makes a fun activity for a children’s party; they love feeding the fruit and frozen bananas into the top of the machine and watching the ice cream come out below.（1）What does the author seem to like about cherries?contain protein.are high in vitamin A.have a pleasant taste.are rich in antioxidants.（2）Why is fresh lemon juice used in freezing bananas?make them smell better.keep their colour.speed up their ripening.improve their nutrition.（3）What is “a juicer” in the last paragraph?dessert.drink.container.machine.（4）From which is the text probably taken?biology textbook.health magazine.research paper.travel brochure.and younger children are reading a lot less for fun, according to a Common Sense Media report published Monday.While the decline over the past decade is steep for teen readers, some data in the report shows that reading remains a big part of many children’s lives, and indicates how parents might help encourage more reading.According to the report’s key findings, “the proportion (比例) who say they ‘hardly ever’ read for fun has gone from 8 percent of 13-year-olds and 9 percent of 17-year-olds in 1984 to 22 percent and 27 percent respectively today.”The report data shows that pleasure reading levels for younger children, ages 2—8, remain largely the same. But the amount of time spent in reading each session has declined, from closer to an hour or more to closer to a half hour per session.When it comes to technology and reading, the report does little to counsel(建议) parents looking for data about the effect of e-readers and tablets on reading. It does point out that many parents still limit electronic reading, mainly due to concerns about increased screen time.The most hopeful data shared in the report shows clear evidence of parents serving as examples and important guides for their kids when it comes to reading. Data shows that kids and teens who do read frequently, compared to infrequent readers, have more books in the home, more books purchased for them, parents who read more often, and parents who set aside time for them to read.As the end of school approaches, and school vacation reading lists loom(逼近) ahead, parents might take this chance to step in and make their own summer reading list and plan a family trip to the library or bookstore.（1）What is the Common Sense Media report probably about?’s reading habits.of children’s books.’s after-class activities.relationships.（2）Where can you find the data that best supports "children are reading a lot less for fun"paragraph 2.paragraph 3.paragraph 4.paragraph 5.（3）Why do many parents limit electronic reading?are of poor quality.could be a waste of time.may ha rm children’s health.are expensive.（4）How should parents encourage their children to read more?as role models for them.then to write book reports.up reading groups for them.with their reading class teachers.’ve all been there: in a lift, in lin e at the bank or on an airplane, surrounded by people who are, like us, deeply focused on their smartphones or, worse, struggling with the uncomfortable silence.What’s the problemIt’s possible that we all have compromised conversational intelligence. It’s more likely that none of us start a conversation because it’s awkward and challenging, or we think it’s annoying and unnecessary. But the next time you find yourself among strangers, consider that small talk is worth the trouble. Experts say it’s an inv aluable social practice that results in big benefits.Dismissing small talk as unimportant is easy, but we can’t forget that deep relationships wouldn’teven exist if it weren’t for casual conversation. Small talk is the grease(润滑剂) for social communication, says Bernardo Carducci, director of the Shyness Research Institute at Indiana University Southeast. ＂Almost every great love story and each big business deal begins with small talk,＂ he explains. ＂The key to successful small talk is learning how to connect with others, not just communicate with them.＂In a 2014 study, Elizabeth Dunn, associate professor of psychology at UBC, invited people on their way into a coffee shop. One group was asked to seek out an interaction(互动) with its waiter; the other, to speak only when necessary. The results showed that those who chatted with their server reported significantly higher positive feelings and a better coffee shop experience. ＂It’s not that talking to the waiter is better than talking to your husband,＂ says Dunn. ＂But interactions with peripheral(边缘的) members of our social network matter for our well-being also.＂Dunn believes that people who reach out to strangers feel a significantly greater sense of belonging, a bond with others. Carducci believes developing such a sense of belonging starts with small talk. ＂Small talk is the basis of good manners,＂ he says.（1）What phenomenon is described in the first paragraph?to smartphones.behaviours in public places.of communication between strangers.with slow service.（2）What is important for successful small talk according to Carducci?good manners.to other people.on a topic.business deals.（3）What does the coffee-shop study suggest about small talk?improves family relationships.raises people’s confid ence.matters as much as a formal talk.makes people feel good.（4）What is the best title for the text?Countsof Making Small Talkof Small TalkSilence5.根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。
食品工艺学课件
⾷品⼯艺学课件Processing of fruitsInstructor: mingfeng zheng(郑明锋) phd.Email:vanheng@/doc/bca037d13186bceb19e8bb68.htmlCell: 138********注意：课件全部根据⽼师提供的ppt整理，在编号上可能会有些问题，所以⼤家将就着看，祝⼤家考试顺利。
Chapter one：introductionFruit quality and preprocessingObjectsThrough the introduction, the students knowThe relationship between quality of fruit and the processed product,The relationship between composition of fruit and the processed product,Quality attributes of fresh fruits, and quality measurementspreprocessing methods and technologies1.1 classification of fruitsFruits are commonly classified by growing region as follows. Temperate zone, subtropical, and tropical. Growing region and environmental conditions specific to each regionsignificantly affect fruit quality. Examples of fruit grown in each region are listed below:1) temperate zone fruits2) subtropical fruits3) tropical fruits(1) temperate zone fruitsPome fruits(仁果类): apple, asian pear (nashi), european pear, quince榅桲果Stone fruits: apricot杏, cherry, nectarine, peach, plumSmall fruits and berries: grape (european and american types), strawberry, raspberry, blueberry, blackberry, cranberry (2) subtropical fruitsCitrus fruits: grapefruit, lemon, lime, orange, pummelo, tangerine, and mandarinNoncitrus fruits: avocado, cherimaya, fig, kiwifruit, olive, pomegranate(3) tropical fruitsMajor tropical fruits: banana, mango, papaya, pineappleMinor tropical fruits: carambola, cashew apple, durian, guava,longan, lychee, mangosteen, passion fruit, rambutan1.2 quality of raw materialsThe quality of processed fruit products depends on their quality at the start of processing; How maturity at harvest, Harvesting methods,Post harvest handling proceduresMaintenance in fresh fruits between harvest and process initiation.Quality attributes of fresh fruitsAppearance、exture factors、flavor components、nutritional quality、safety factorsAppearance factorsSize、shape、color、freedom from defects and decay.Texture factorsFirmness, crispness, juiciness.Flavor componentsSweetness, sourness (acidity), astringency, (收敛),bitterness, aroma, off-flavors,Nutritional qualityFruit's content of vitamins (a and c are the most important in fruits), minerals, dietary fiber, carbohydrates, proteins. Safety factorsResidues of pesticides, presence of heavy metals, mycotoxins produced by certain species of fungi, microbial contamination.1.3 losses in fresh fruits after harvastWater loss,Physical injuries,physiological breakdown, decayLoss of acidity, flavor, color, and nutritive valueFactors influence fruit qualityIn the orchard,During transportation,Throughout the handling system (sorting, sizing, ripening, and storage).The total time between harvesting and processingMinimizing the delays throughout the post harvest handling system greatly reduces finality loss, especially in highly perishable fruits such as strawberries, blackberries, apricots, and cherries.1.4 contribution of fruits to human nutritionEnergy (calories)VitaminsMineralsDietary fiberThe us. Department of agriculture and other organizations currently encourage consumers to participate in the "five a day" program which focuses on consumption of five servings of either fruit or vegetables each day.Energy (calories)(1) carbohydrates: banana, breadfruit, raisin葡萄⼲(2) proteins & amino acids: nuts, dried apricot and fig(3) fats. Avocado, olive, nutsFruits typically contain between 10% and 25% carbohydrates, a small amount (less than1.0%) of proteins, and a very small amount (less than 0.5 %) of fat. Carbohydrates, sugars,and starches are broken down to co2, water, and energy during metabolism. Carbohydrates and fats provide most of the calories the body requires for heat and energy.Vitamins(1) fresh fruits and vegetables contribute about 91% of vitamin c, 48% of vitamin a, 27% of vitamin b6, 17% of thiamin硫胺(维⽣素b1) to diet.(2) the following fruits are important contributors (based on their vitamin content and the amount consumed) to the supply of indicated vitamins in the u.s. Diet:*vitamin a: apricot, peach, cherry, orange, watermelon, cantaloupe*vitamin c: strawberry, orange, grapefruit, banana, apple, cantaloupe* niacin烟酸: peach, banana, orange, apricot"*riboflavin核黄素: banana, peach, orange, apple* thiamin: orange, banana, grapefruit, appleMinerals(1) fresh fruits and vegetables contribute about 26% of the magnesium镁and 19% of the iron to the u.s. Diet.(2) the following fruits are important contributors to the supply of indicated minerals in the us. Diet:* potassium钾: banana, peach, orange, apple* phosphorus磷: banana, orange, peach, raisin, fig*calcium: tangerine, grapefruit, orange* iron: strawberry, banana, apple, orangeDietary fiber(1) all fruits and nuts contribute to the dietary fiber in the diet. Dietary fiber consists of cellulose, hemicellulose, lignin⽊质素, and pectic substances, which are derived primarily from fruit cell walls and skin.(2) the dietary fiber content of fruits ranges from 0.5-1.5% (fresh weight basis).(3) dietary fiber plays an important role in relieving constipation by increasing water-holding capacity of feces. Its consumption is also linked to decreased incidence of cardiovascular disease, diverticulosis, and colon cancer.factors influefncing composition and quality of fruitsPreharvest factors(1) genetic: selection of cultivars, differences in raw fruit composition, durability, and response to processing. Fruit cultivars grown for fresh market sale will not be the optimal cultivars for processing.(2) climatic: temperature, light, wind--climatic factors may have a strong influence on nutritional quality of fruits. Light intensity significantly affects vitamin concentration, and temperature influences transpiration rate, which will affect mineral uptake and metabolism. ?(3) cultural practices: soil type, soil nutrient and water supply, pruning修剪, thinning, pest control-fertilizer addition may significantly affect the mineral content of fruit.1. 5 maturity at harvest and harvesting methodMaturity at harvest is one of the primary factors affecting fruit composition, quality, and storage life. Although most fruits reach peak eating quality when harvested fully ripe, they are usually picked mature, but not ripe, to decrease mechanical damage during postharvest handling. Harvesting may also mechanically damage fruit; therefore, choice of harvest methodshould allow for maintenance of quality.Postharvest factors1) environmental，2) handling methods，3) time period between harvesting and consumption(1) environmentalTemperature, relative humidity, atmospheric composition,(2) handling methodsPostharvest handling systems involve the channels through which harvested fruit reaches the processing facility or consumer. Handling methods should be chosen such that they maintain fruit quality and avoid delays.(3) time period between harvesting and consumptionDelays between harvesting and cooling or processing may result in direct losses (due to water loss and decay) and indirect losses (decrease in flavor and nutritional quality).Fruit maturity, ripening, and quality relationshipsMaturity at harvest is the most important factor that determines storage life and final fruit quality. Immature fruits are of inferior quality when ripened. Overripe fruits are likely to become soft and with insipid flavor soon after harvest. Fruits picked either too early or too late in the season are more susceptible to physiological disorders and have a shorter storage life than those picked at mid-season.Maturity and ripeningIn general, fruits become sweeter, more colorful, and softer as they mature.Some fruits are usually picked mature but unripe so that they can withstand the postharvest handling system when shipped long distances. Most currently used maturity indices are based on a compromise between those indices that would ensure the best eating quality to the consumer and those that provide the needed flexibility in transportation and marketing.Carbohydrates（碳⽔化合物）Carbohydrates : fresh fruits vary greatly in their carbohydrate content, with a general range being between 10% and 25%;. The texture, taste, and food value of a fresh fruit is related to its carbohydrate content. Sucrose, glucose, and fructose are the primary sugars found in fruits.Fructose is sweeter than sucrose, and sucrose is sweeter than glucose.Starch is converted to sugar as the fruits mature and ripen.Proteins（蛋⽩质）Fruits contain less than 1% protein (as opposed to 9-20% protein in nuts such as almond, and walnut). Changes in the level and activity of proteins resulting from permeability changes in cell membranes may be involved in chilling injury. Enzymes, which catalyze metabolic processes in fruits, are proteins that are important in the reactions involved in fruit ripening and senescence.Enzymes in fruits：（Organic acids（有机酸）Organic acids are important intermediate products of metabolism. The krebs (tca) cycle is the main channel for the oxidation of organic acids in living cells, and it provides the energy required for maintenance of cell integrity. Organic acids aremetabolized into manyconstituents, including amino acids, which are the building blocks of proteins.Citric acid、malic acid、tartaric acid、oxalic acidPigments（⾊素）Pigments undergo many changes during the maturation and ripening of fruits.(1) loss of chlorophyll (green color), which is influenced by ph changes, oxidative conditions, and chlorophyllase action(2) synthesis and/or revelation of carotenoids (yellow and orange colors)(3) development of anthocyanins (red, blue, and purple colors.Beta-carotene is a precursor to vitamin a. Carotenoids are very stable and remain intact in fruit tissues, even when extensive senescence has occurred.Phenolic compounds（酚类化合物）Total phenolic content is higher in immature fruits than in mature fruits and is the main substrate involved in enzymatic browning of cut, or otherwise damaged, fruit tissues when exposed to air.Enzymatic browning（酶促褐变）Enzymatic browning occurs due to the oxidation of phenolic compounds and is mediated, in the presence of o2, by the enzyme polyphenoloxidase (ppo). The initial product of oxidation is usually o-quinone, which is highly unstable and undergoes polymerization to yield brown pigments of higher molecular weight. Polyphenoloxidase catalyzes the following tworeactions:Volatiles（挥发性）Volatiles are responsible for the characteristic aroma of fruits. They are present in extremely small quantities (c <100µg/g fresh wt.).Volatile compounds are largely esters（酯）, alcohols, acids, aldehydes（醛）, an d ketones (low-molecular weight compounds).VitaminsThe water-soluble vitamins includeVitamin c,Thiamin硫胺(维⽣素b1),Riboflavin核黄素,Niacin烟酸, vitamin b6,Folacin叶酸, vitamin b12, biotin维⽣素h. Fat soluble vitamins include vitamins a, d, e, and k.Fat-soluble vitamins are less susceptible to postharvest losses.Vitamin cAscorbic acid is most sensitive to destruction when the commodity is subjected to adverse handling and storage conditions. Losses are enhanced by extended storage, highertemperatures, low relative humidity, physical damage, and chilling injury. Postharvest losses in vitamins a and b are usually much smaller than losses in vitamin c.1.7 biological factors involved in postharvest deterioration (变坏) of fruits ?Respiration (呼吸作⽤)Ethylene productionTranspiration (蒸腾作⽤)Physiological disordersPhysical damagePathological breakdownRespirationStored organic materials (carbohydrates, proteins, fats) are broken down into simple end products with a release of energy. Oxygen (o2) is used in this process, and carbon dioxide (co2) is produced.The loss of stored food reserves in the commodity during respiration hastens senescence as the reserves that provide energy to maintain the commodity's living status are exhausted. ?Food value (energy value) for the consumer is lost; it has reduced flavor quality, with sweetness especially being lost; and salable dry weight is lost (especially important for commodities destined for dehydration). The energy released as heat.Ethylene productionEthylene, the simplest of the organic compounds affecting the physiological processes of plants, is produced by all tissues of higher plants. As a plant hormone, ethylene regulates many aspects of growth development, and senescence and is physiologically active in traceamounts (less than 0.1 ppm).Transpiration or water lossWater loss is the main cause of deterioration because it results not only direct quantitative.Losses (loss of salable weight) hut also in loss of its appearance, loss of cripsness, andjuiciness), and nutritional quality.The dermal system (outer protective coverings) governs the regulation of water loss by the commodity.Physiological disorders(1) freezing injury :usually results in immediate collapse of the tissues and total loss.(2) chilling injury when fruits (mainly those of tropical and subtropical origin) are held at temperatures above their freezing point and below 5-15℃, depending on the commodity. ?(3) heat injury results from exposure to direct sunlight or to excessively high temperatures.Symptoms include surface scalding, uneven ripening, excessive softening, and desiccation. ?(4) very low (<1%) oxygen and/or elevated (>20%) carbon dioxide concentration can result in physiological breakdown of all fruits.Physical damageVarious types of physical damage (surface injuries, impact bruising, vibration bruising, etc.) Are major contributors to deterioration. Mechanical injuries are not only unsightly, but also accelerate water loss, stimulate higher respiration and ethylene production rates, and favor decay incidence.Pathological breakdownDecay is one of the most common or apparent causes of deterioration; however, attack by many microorganisms usually follows mechanical injury or physiological breakdown, which allows entry to the microorganism. Pathogens can infect healthy tissues and become the primary cause of deterioration.Environmental factors influencing deterioration of fruits（影响⽔果变坏的环境因素）Temperature，Relative humidity，Air movement，Atmospheric composition，Ethylene，Harvesting procedures Postharvest handling proceduresDumping、Sorting、Sizing、Cooling、Storage、RipeningDumping：Fresh fruits should be handled with care throughout the postharvest handling system in order to minimize mechanical injuries. Dumping in water or in flotation tanks should be used for fruits. If dry dumping systems are used, they should be well padded bruising. Sorting：Manual sorting is usually carried out to eliminate fruit exhibiting defects or decay. For some fruits, it may also be necessary to sort the fruit into two or more classes of maturity or ripeness.Mechanical sorters, which operate on the basis of color, soluble solids, moisture, or fat content, are being implemented and may greatly reduce time and labor requirements. Sizing：In some cases, sizing the fruits into two or more size categories may be required before processing. Sizing can be done mechanically on the basis of fruit dimension or by weight.Mechanical sizing can be a major source of physical damage to the fruit if the machines are not adequately padded and adjusted to the minimum possible fruit drop heights Ripening：Ripening before processing may be required for certain fruits (banana, kiwifruit, mango, papaya, peach, pear, plum, melon) that are picked mature but unripe. Ethylene treatment can be used to obtain faster and more uniform ripening. The optimum temperature range for ripening is 15-25℃and, within this range, the higher the temperature, the faster the ripening. Relative humidity should be maintained between 90% and 95 % during ripening. Cooling：Cooling is utilized to remove field heat and lower the fresh fruit's temperature to near its optimum storage temperature. Cooling can be done using cold water (hydrocooling) or cold air (forced-air cooling or "pressure cooling"). Highly perishable fruits, such as strawberries, bush berries, and apricots, should be cooled to near 4℃within six hours of harvest. Other fruits should be cooled to their optimum temperature within twelve hours of harvest. Storage：Short-term or long-term storage of fresh fruits may be needed before processing to regulate the product flow and extend the processing season. The relative humidity in the storage facility should be kept between 90% and 95%.To reduce decay, elevated c02 (15-20%) may be added to the atmosphere within pallet covers for strawberries, bush berries, and cherries, and sulfur dioxide (200 ppm) fumigation may be used on grapes.1.8 quality measurementsMany quality measurements can be made before a fruit crop is picked in order to determine if proper maturity or degree of ripeness has developed.ColourColour may be measured with instruments or by comparing the colour of fruit on the tree with standard picture charts. TextureTexture may be measured by compression by hand or by simple type of plungers.Soluble solidsAs fruit mature on the tree its concentration of juice solids, which are mostly sugars, changes. The concentration of soluble solids in the juice can be estimated with arefractometer or a hydrometer液体⽐重计.Acid contentThe acid content of fruit changes with maturity and affects flavour. Acid concentration can be measured by a simple chemical titration on the fruit juice. But for many fruits the tartness and flavour are really affected by the ratio of sugar to acid. Sugar to acid ratioIn describing the taste of tartness of several fruits and fruit juices, the term "sugar to acid ratio" or "brix to acid ratio" are commonly used. The higher the brix the greater the sugar concentration in the juice; the higher the "brix to acid ratio" the sweeter and lees tart is the juice.1.9 preprocessing1.9.1 harvestingThe above and other measurements, plus experience, indicate when fruit is ready for harvesting and subsequent processing.1.9.2 reception - quality and quantity1.9.3 temporary storage before processing1.9.4 washingHarvested fruit is washed to remove soil, micro-organisms and pesticide residues.Fruit washing is a mandatory processing step; it would be wise to eliminate spoiled fruit before washing in order to avoid the pollution of washing tools and/or equipment and the contamination of fruit during washing.1.9.5 sortingFruit sorting covers two main separate processing operations:Removal of damaged fruit and any foreign bodies (which might have been left behind after washing);Qualitative sorting based on organoleptic criteria and maturity stage.Mechanical sorting for size is usually not done at the preliminary stage. The most important initial sorting is for variety and maturity.1.9.6 trimming and peeling (skin removal)This processing step aims at removing the parts of the fruit which are either not edible or difficult to digest especially the skin.Up to now the industrial peeling of fruit and vegetables was performed by three procedures: Mechanically;By using water steam;Chemically; this method consists in treating fruit and vegetables by dipping them in a caustic soda solution at a temperature of 90 to 100°c; the concentration of this solution as well asthe dipping or immersion time varying according to each specific case.1.9.7 cuttingThis step is performed according to the specific requirements of the fruit processing technology.1.9.8 blanchingA brief heat treatment to vegetables some fruits to inactivate oxidative enzyme systems such as catalase, peroxidase, polyphenoloxidase, ascorbic acid oxidase, and lipoxygenase. ?When the unblanched tissue is disrupted or bruised and exposed to air, these enzymes come in contact with substrates causing softening, discoloration, and the production of off flavors. ?It is most often standard practice to blanch fruits in order to prevent quality deterioration. ?Although the primary purpose of blanching is enzyme inactivation.There are several other benefits blanching initially cleanses the product;Decreases the microbial load,Preheats the product before processing.Softens the fruit, facilitates compact packing in the can.Expell intercellular gases in the raw fruitImproved heat transfer during heat processing.Water blanching is generally of the immersion type or spray type as the product moves on a conveyor.Steam blanching often involves belt or chain conveyors upon which the product moves through a tunnel containing live steam.adequacy of blanching is usually based on inactivation of one of the heat resistant enzymes (peroxidase or polyphenol oxidase).During the blanching process, it is imperative that certain enzymes that have the potential to cause flavour and textural changes be inactiviated. The process involves a brief heattreatment applied to most vegetables and also to some fruits in order to inactivate oxidative enzyme system such as catalase, peroxidase, polyphenoloxidase,ascorbic acid oxidase, and lipoxygenase.When unblanched tissue is disrupted or bruised and exposed to air,these enzymes come in contact with substrate causing softening,discoloration, and the production of off-flavours.Since this action can potentially occur during the period prior to heat processing, it is most often standard practice to blanch fruits in order to prevent quality deterioration.1.9.9 ascorbic/citric acid dipAscorbic acid or vitamin c minimises fruit oxidation primarily by acting as an antioxidant and itself becoming oxidised in preference to catechol⼉茶酚-tannin compounds.It has been found that increased acidity also helps retard oxidative colour changes and so ascorbic acid plus citric acid may be used together. Citric acid further reacts with (chelates) metal ions thus removing these catalysts of oxidation from the system.1.9.10 sulphur dioxide treatmentSulphur dioxide may function in several ways:Sulphur dioxide is an enzyme poison against common oxidising enzymes;It also has antioxidant properties; i.e., it is an oxygen acceptor (as is ascorbic acid);Further so2 minimises non enzymatic maillard type browning by reacting with aldehyde醛groups of sugars so that they are no longer free to combine with amino acids;Sulphur dioxide also interferes with microbial growth.In many fruit processing pre-treatments two factors must be considered:Sulphur dioxide must be given time to penetrate the fruit tissues;So2 must not be used in excess because it has a characteristic unpleasant taste and odour, and international food laws limit the so2 content of fruit products, especially of those which are consumer oriented (e.g. Except semi-processed products oriented to further industrial utilisation).5.2.11 sugar syrupSugar syrup addition is one of the oldest methods of minimising oxidation.Sugar syrup minimises oxidation by coating the fruit and thereby preventing contact withatmospheric oxygen.Sugar syrup also offers some protection against loss of volatile 挥发性的fruit esters 酯and itcontributes sweet taste to otherwise tart fruits.It is common today to dissolve ascorbic acid and citric acid in the sugar syrup for addedeffect or to include sugar syrup after an so 2 treatment.QuestionsWhat factors influence the quality of fruits after harvest?How to maintain the fruit in good quality before the processing begin?第⼀节果蔬原料特性新鲜果蔬原料的特点 ? 果蔬原料的化学成分原料的化学成分与加⼯的关系1.新鲜果蔬原料的特点易腐性、季节性、区域性2.果蔬中的化学成分（chemical composition in fruits and vegetables ）3.化学成分与加⼯的关系（relation between chemical composition and processing ）3.1 ⽔分(water)果蔬中⽔的含量：⼤多数在80%以上，含⽔量⾼的如冬⽠(wax gourd)可达96%以上。
英语作文-如何正确进行拉伸运动
英语作文-如何正确进行拉伸运动Stretching is an important part of any exercise routine, as it helps to improve flexibility, reduce the risk of injury, and enhance overall performance. However, many people do not know how to properly stretch or do not take the time to do so. In this article, we will discuss the importance of stretching and provide some tips on how to stretch correctly.First and foremost, it is important to understand why stretching is so crucial. When you stretch your muscles, you increase their flexibility and range of motion. This can help to improve your posture, reduce muscle tension, and prevent injuries. Additionally, stretching can help to improve circulation and reduce muscle soreness after a workout.To stretch correctly, it is important to warm up your muscles first. This can be done by doing some light cardio, such as jogging or jumping jacks, for 5-10 minutes. Once your muscles are warm, you can begin your stretching routine.When stretching, it is important to focus on all major muscle groups, including your legs, arms, back, and core. Hold each stretch for 15-30 seconds and repeat 2-3 times. Make sure to breathe deeply and relax into each stretch, avoiding any bouncing or jerking movements.Some common stretches include:1. Quadriceps stretch: Stand on one leg and grab your other foot behind you, bringing it towards your glutes.2. Hamstring stretch: Sit on the floor with one leg extended and the other bent. Reach towards your toes, keeping your back straight.3. Shoulder stretch: Bring one arm across your body and use your other arm to gently pull it towards you.4. Cat-cow stretch: Get on your hands and knees, arching your back up like a cat and then dropping it down like a cow.It is important to listen to your body while stretching and not push yourself too far. Stretching should not be painful, so if you feel any discomfort, ease off the stretch. Remember to stretch both sides of your body equally to maintain balance.In conclusion, stretching is a vital component of any exercise routine. By incorporating stretching into your workouts, you can improve your flexibility, reduce the risk of injury, and enhance your overall performance. Remember to warm up before stretching, focus on all major muscle groups, and listen to your body. With consistent stretching, you can achieve better results in your fitness journey.。
英语作文拉长
英语作文拉长精选英文英语作文拉长：The Art of Stretching: The Importance of Flexibility and How to Achieve ItStretching is often overlooked as a crucial component of physical fitness, yet it plays a vital role in maintaining flexibility, preventing injuries, and enhancing overall well-being. In today's fast-paced world, where our bodies are constantly subjected to stress and strain, learning the art of stretching is not just about attaining physical flexibility; it's also about nurturing a deeper connection with our bodies and promoting a balanced lifestyle.Why Is Stretching So Important?Stretching has numerous benefits, ranging from improving muscle elasticity to enhancing blood flow. A regular stretching routine can help alleviate muscle tightness, reducing the risk of injuries during physical activities. Additionally, stretching can promote relaxation, reducing stress and anxiety levels. By improving our flexibility, we can also enhance our range of motion, making daily tasks like bending, lifting, and reaching easier.How to Achieve Flexibility Through StretchingTo reap the benefits of stretching, it's essential to incorporate it into our daily routine. Here are some tips to help you achieve flexibility through stretching:1. Consistency Is Key: Just like any other fitness routine, consistency is crucial for achieving flexibility. Set aside a few minutes every day, whether it's in the morning, after a workout, or before bed, to stretch your body.2. Warm Up First: It's important to warm up your muscles before stretching. This can bedone through a light jog, some dynamic stretches, or a brief warm-up routine. Stretching cold muscles can lead to injury.3. Focus on Your Breathing: Breathing is an integral part of stretching. Focus on deep, slow breaths as you stretch, inhaling deeply and exhaling slowly. This will help you relax and enhance the effectiveness of your stretches.4. Stretch Slowly and Gently: Avoid bouncing or jerking your body into a stretch. Stretch slowly and gently, feeling the tension in your muscles as you move into the stretch. Hold each stretch for at least 15-30 seconds, allowing your muscles to relax and elongate.5. Stretch All Muscle Groups: Don't neglect any muscle group when stretching. Focus on stretching your legs, hips, back, shoulders, arms, and neck. By stretching all muscle groups, you can ensure balanced flexibility throughout your body.6. Listen to Your Body: Everyone's body is different, so it's important to listen to your body and stretch to your own comfort level. Don't push yourself too far or stretch beyond your range of comfort.In conclusion, stretching is an essential component of physical fitness and overall well-being. By incorporating a regular stretching routine into your daily life, you can improve your flexibility, reduce the risk of injuries, and promote relaxation and stress reduction. Remember, consistency is key, so make stretching a habit and enjoy the many benefits it brings to your life.中文对照翻译：伸展运dong的艺术：灵活性的重要性以及如何做到这一点伸展运dong作为身体健康的一个重要组成部分经常被忽视，但它在保持灵活性、防止受伤和增强整体健康方面发挥着至关重要的作用。
对电脑使用的建议英语作文
对电脑使用的建议英语作文Title: Suggestions for Computer Usage.In the digital age, computers have become an integral part of our daily lives. From work to entertainment, they play a crucial role in nearly every aspect of modern life. However, excessive or improper usage of computers can lead to various issues such as eye strain, neck pain, and even psychological problems. Therefore, it is essential to use computers responsibly and efficiently. Here are some suggestions for computer usage that can help you maximize its benefits while minimizing the associated risks.1. Take Regular Breaks: Extended periods of continuous computer usage can lead to eye strain, neck pain, and other muscular discomforts. To prevent these issues, it is recommended to take regular breaks. You can set a timer to remind yourself to take a break every 30 to 45 minutes. During these breaks, you can perform simple eye exercises, stretch your neck and shoulders, or even walk around for afew minutes to ease the tension.2. Adjust the Screen Brightness: The brightness of your computer screen can significantly affect your eyesight. If the screen is too bright, it can cause eye strain and fatigue. Conversely, if it is too dim, it can strain your eyes as well. Therefore, it is essential to adjust the screen brightness according to the lighting conditions of your environment. In general, it is recommended to keep the screen brightness at a level that is comfortable for your eyes.3. Maintain Good Posture: Sitting in front of a computer for long hours can lead to poor posture, which can further cause neck pain, backache, and other muscular issues. To avoid these problems, it is important to maintain good posture while using a computer. Ensure that your feet are flat on the floor, your back is straight, and your shoulders are relaxed. You can also use a standing desk or adjust the height of your chair to prevent long hours of sitting.4. Use Ergonomic Keyboards and Mice: Ergonomic keyboards and mice are designed to fit the contours of your hands and wrists, reducing the strain on your muscles and joints. Using these devices can help prevent carpal tunnel syndrome and other wrist-related injuries. When purchasing a keyboard or mouse, make sure to choose one that fits your hand size and preference.5. Protect Your Eyes: Computer screens emit blue light, which can potentially damage your eyes if exposed to for long periods. To protect your eyes, you can use blue light filters on your screen. These filters reduce the amount of blue light emitted, making it easier for your eyes to focus on the screen. Additionally, you can also consider wearing anti-glare glasses or adjusting the screen brightness to reduce eye strain.6. Secure Your Computer: With the increasing threat of cybercrime, it is crucial to secure your computer. Make sure to update your antivirus software regularly and avoid opening attachments or links from unknown sources. Additionally, create strong passwords for your computer andonline accounts, and do not store sensitive information on your computer unless absolutely necessary.7. Be Mindful of Your Online Behavior: The internet can be a great resource for learning and entertainment, but it is also important to be mindful of your online behavior. Avoid spreading misinformation, engaging in cyberbullying, or participating in any other unethical or illegal activities. Respect the privacy and rights of others and use the internet responsibly.In conclusion, computers are an essential part of modern life, but it is important to use them responsibly and efficiently. By following the suggestions mentioned above, you can maximize the benefits of computer usage while minimizing the associated risks. Remember to take regular breaks, adjust the screen brightness, maintain good posture, use ergonomic devices, protect your eyes, secure your computer, and be mindful of your online behavior. With these simple practices, you can enjoy the conveniences of computers while keeping yourself healthy and safe.。
玩电脑游戏的利英语作文
玩电脑游戏的利英语作文Playing computer games is a popular form of entertainment for many people around the world. There are both advantages and disadvantages to this activity. Let's discuss them in detail.One of the main benefits of playing computer games is that they can help improve cognitive skills. Many games require players to think critically, solve puzzles, and make quick decisions. This can help improve problem-solving abilities and enhance memory and concentration. Additionally, some games can help improve hand-eye coordination and reaction times.Another advantage of playing computer games is that they can provide a fun and enjoyable way to relax and unwind. After a long day at work or school, playing a game can be a great way to de-stress and escape from reality for a while. It can also be a social activity, as many games allow players to connect with friends and compete against each other online.However, there are also some disadvantages to playing computer games. One of the main concerns is that excessive gaming can lead to addiction. Some people may become so engrossed in a game that they neglect other responsibilities, such as work, school, or relationships. This can have negative consequences on their overall well-being.Another drawback of playing computer games is that they can be a sedentary activity. Sitting for long periods of time while gaming can lead to health problems such as obesity, poor posture, and eyestrain. It is important for gamers to take breaks, stretch, and exercise regularly to maintain their physical health.In conclusion, playing computer games can be a fun and enjoyable activity that offers a variety of benefits, such as improving cognitive skills and providing a way to relax. However, it is important to be mindful of the potential drawbacks, such as addiction and the negative impact on physical health. By balancing gaming with other activities and practicing moderation, it is possible to enjoy the benefits of gaming while minimizing the risks.玩电脑游戏是许多人世界各地的一种受欢迎的娱乐形式。
要适当玩游戏英语作文
要适当玩游戏英语作文标题，Enjoying Games in Moderation: A Beneficial Leisure Activity。
In today's fast-paced world, where the demands of work and study can be overwhelming, it is essential to find ways to unwind and relax. One popular method of relaxation is playing games. However, it is crucial to approach gaming with moderation and responsibility to ensure that it remains a healthy leisure activity. In this essay, we will explore the benefits of gaming in moderation and how to strike a balance between gaming and other aspects of life.First and foremost, gaming can provide an excellent way to relieve stress and escape from the pressures of daily life. Whether it's immersing oneself in an epic adventure, solving challenging puzzles, or competing against friendsin multiplayer games, gaming offers a temporary reprieve from the stresses and worries of the real world. Moreover, the sense of accomplishment and satisfaction that comesfrom overcoming obstacles in games can boost one's mood and self-esteem.Additionally, gaming can be an excellent way to sharpen cognitive skills and improve mental acuity. Many games require players to strategize, problem-solve, and think critically, which can help enhance cognitive functions such as memory, attention, and spatial awareness. For example, puzzle games like Sudoku and Tetris are known to improve logical thinking and pattern recognition skills. Similarly, strategy games like chess and real-time strategy games can enhance decision-making and planning abilities.Furthermore, gaming can also foster social connections and teamwork skills, especially in multiplayer games. Collaborating with others to achieve a common goal, communicating effectively, and learning to work as a team are essential skills that can be honed through gaming. Online gaming communities provide opportunities for players to interact, make friends, and even form lasting relationships with people from diverse backgrounds and cultures.However, despite the numerous benefits of gaming, it is crucial to approach it with moderation and responsibility. Excessive gaming can lead to various negative consequences, such as decreased productivity, impaired social relationships, and even health issues such as eyestrain and repetitive strain injuries. Therefore, it is essential to set limits on gaming time and prioritize other aspects of life, such as work, study, physical activity, and spending time with family and friends.To strike a balance between gaming and other responsibilities, it is helpful to establish a gaming schedule and stick to it. Set specific times for gaming each day or week and avoid letting it interfere with important tasks or commitments. Additionally, take regular breaks during gaming sessions to rest your eyes, stretch your muscles, and recharge your mind. It is also essential to be mindful of the content of the games you play and choose ones that are age-appropriate and align with your values and interests.In conclusion, gaming can be a beneficial leisure activity when enjoyed in moderation and approached responsibly. From relieving stress and enhancing cognitive skills to fostering social connections and teamwork abilities, gaming offers a wide range of benefits. However, it is essential to strike a balance between gaming and other aspects of life to ensure that it remains a healthy and enjoyable pastime. By setting limits, prioritizing responsibilities, and being mindful of content, one can maximize the positive aspects of gaming while minimizing the risks associated with excessive use.。
英语作文-如何进行科学合理的伸展运动
英语作文-如何进行科学合理的伸展运动Stretching is an essential part of any workout routine, as it helps to improve flexibility, reduce the risk of injury, and enhance overall athletic performance. However, in order to reap the full benefits of stretching, it is important to do so in a scientific and rational manner. In this article, we will discuss the key principles of effective stretching and provide some tips on how to incorporate it into your fitness regimen.First and foremost, it is important to understand the different types of stretching. There are two main categories: static stretching and dynamic stretching. Static stretching involves holding a position for a prolonged period of time, while dynamic stretching involves moving through a full range of motion in a controlled manner. Both types of stretching have their own unique benefits, and a well-rounded stretching routine should incorporate both.When it comes to static stretching, it is important to do so after a workout, when your muscles are warm and pliable. This will help to improve flexibility and range of motion, as well as reduce muscle soreness and stiffness. When performing static stretches, it is important to hold each position for at least 30 seconds, and to focus on the major muscle groups such as the hamstrings, quadriceps, calves, and shoulders.On the other hand, dynamic stretching is best done as a warm-up before a workout. This type of stretching helps to improve blood flow to the muscles, increase joint mobility, and enhance overall athletic performance. Some examples of dynamic stretches include leg swings, arm circles, and walking lunges. It is important to perform dynamic stretches in a controlled and deliberate manner, and to gradually increase the intensity as your muscles become more warmed up.In addition to understanding the different types of stretching, it is also important to pay attention to proper technique. When performing static stretches, it is important to focus on proper body alignment and form, and to avoid bouncing or jerking movements. This can lead to injury and will not effectively improve flexibility. When performingdynamic stretches, it is important to move through a full range of motion, and to focus on smooth and controlled movements.Furthermore, it is important to listen to your body and avoid overstretching. While it is normal to feel a mild discomfort during stretching, it is important to avoid any sharp or intense pain. This can be a sign of overstretching or potential injury, and it is important to back off and reevaluate your technique. It is also important to breathe deeply and rhythmically during stretching, as this can help to relax the muscles and improve the overall effectiveness of the stretch.In conclusion, incorporating stretching into your fitness routine is crucial for improving flexibility, reducing the risk of injury, and enhancing athletic performance. By understanding the different types of stretching, paying attention to proper technique, and listening to your body, you can ensure that your stretching routine is both effective and safe. So, the next time you hit the gym or head out for a run, be sure to incorporate some scientific and rational stretching into your workout routine. Your body will thank you for it!。
生活步调快慢的英语作文
生活步调快慢的英语作文英文回答：The pace of life has accelerated dramatically in recent decades. Technological advancements, globalization, and societal pressures have all contributed to a constant state of urgency and a feeling of being perpetually behind. The relentless pursuit of productivity and efficiency has left many individuals feeling overwhelmed, stressed, and disconnected from their true selves.On the other hand, a slower pace of life can offer numerous benefits. It allows individuals to prioritizetheir well-being, engage in meaningful relationships, and cultivate a sense of purpose and fulfillment. By embracing a more measured approach to life, people can reduce stress levels, improve their mental and physical health, and rediscover the joys of the present moment.Ultimately, the optimal pace of life is a personalchoice that depends on individual circumstances, values,and priorities. However, it is important to recognize the potential consequences of both a fast-paced and a slow-paced lifestyle and to make informed decisions about how to live one's life.中文回答：生活节奏的快慢之争由以下几个方面导致：1. 技术进步，科技的飞速发展促进了信息和通信的快速传播，让人们能够更轻松、更迅速地获取和处理信息。
我喜欢在有限的时间里完成很多事情英语作文
In today's fast-paced world, the ability to accomplish a multitude of tasks within limited timeframes has become a hallmark of efficiency and productivity. As an individual who thrives on the adrenaline rush that accompanies such endeavors, I find immense satisfaction in optimizing my time to tackle multiple responsibilities simultaneously. This essay explores the various dimensions of my affinity for multitasking, delving into the motivations, strategies, challenges, and rewards associated with this approach to managing my daily life.**Motivations: The Pursuit of Efficiency and Personal Growth**The primary driver behind my inclination towards multitasking lies in my unwavering commitment to maximizing efficiency. In a world where time is a precious commodity, I view multitasking as a means to stretch its value by accomplishing more within a given period. By juggling multiple tasks, I effectively reduce idle moments, minimize distractions, and ensure that every second is purposefully allocated. This approach not only enables me to meet pressing deadlines but also allows me to accommodate a diverse range of personal and professional interests, fostering a rich and fulfilling lifestyle.Moreover, multitasking serves as a catalyst for personal growth and skill development. Engaging in multiple tasks simultaneously requires cognitive flexibility, adaptability, and strong time management skills. These competencies are honed through the constant practice of prioritizing, planning, and executing tasks under pressure, ultimately contributing to my overall professional and personal competence. The continuous challenge of multitasking pushes me to expand my capacity, enhance my problem-solving abilities, and cultivate resilience, all of which are invaluable assets in today's dynamic world.**Strategies: Orchestrating Chaos with Structure and Discipline**Successfully managing multiple tasks in limited time requires a strategic and disciplined approach. To this end, I have developed several key strategies that enable me to maintain focus and productivity amidst the apparent chaos.Firstly, **prioritization** is paramount. I employ tools like the EisenhowerMatrix, categorizing tasks based on their urgency and importance, to ensure that my efforts are directed towards those with the greatest impact. This helps me avoid getting bogged down in trivial tasks while neglecting critical ones.Secondly, I rely heavily on **time blocking**, allocating specific time slots for each task or group of tasks. This technique creates a sense of structure and helps me maintain momentum by minimizing decision fatigue and context switching. I also incorporate buffer times between tasks to account for unforeseen delays or additional focus needed for complex assignments.Thirdly, I embrace **technology** as a powerful ally. Utilizing project management tools, digital calendars, and productivity apps enables me to streamline communication, automate repetitive tasks, and monitor progress efficiently. These tools also facilitate seamless collaboration with others, ensuring that even when working on multiple projects simultaneously, I can coordinate effectively and avoid misunderstandings or delays.Lastly, I prioritize **self-care** and **work-life balance**. Recognizing that sustained multitasking can be mentally and physically taxing, I integrate regular breaks, exercise, and mindfulness practices into my routine. These rejuvenating moments serve as vital pit stops, allowing me to recharge and maintain optimal performance levels throughout the day.**Challenges: Navigating Distractions, Overwhelm, and Quality Control** While multitasking offers numerous benefits, it is not without its challenges. The most prominent among these are managing distractions, coping with potential overwhelm, and maintaining high-quality output.**Distractions**, both external and internal, can easily derail a carefully planned multitasking schedule. To counteract this, I establish clear boundaries, using tools like website blockers, 'do not disturb' modes, and designated workspaces to minimize interruptions. Additionally, cultivating mental discipline through mindfulness and focus exercises helps me resist the allure of distracting thoughts and stay anchored in the present task.**Overwhelm** is another common pitfall in multitasking, particularly whenfaced with an overwhelming number of tasks or tight deadlines. To mitigate this, I regularly reassess and adjust my priorities, delegate tasks when possible, and practice self-compassion, acknowledging that it's impossible to do everything perfectly. Remembering that progress, not perfection, is the goal helps me maintain perspective and avoid burnout.Maintaining **quality control** while juggling multiple tasks can be a delicate balancing act. To ensure that each task receives the attention it deserves, I employ techniques like the Pomodoro Technique, dedicating focused, undistracted time to each task before moving on. Moreover, I make use of checklists, templates, and peer review processes to minimize errors and ensure consistency across multiple projects.**Rewards: The Satisfaction of Accomplishment and Continuous Learning** Despite the challenges, the rewards of multitasking are profound and deeply satisfying. Foremost among these is the **sense of accomplishment** derived from seeing numerous tasks completed within a short span of time. This tangible evidence of productivity fuels my motivation, instilling a sense of pride and boosting my self-confidence.Furthermore, multitasking fosters **continuous learning**. The exposure to diverse tasks and projects broadens my knowledge base, enhances my creativity, and accelerates my professional development. Each new challenge presents an opportunity to acquire new skills, adapt to different contexts, and solve problems in innovative ways, making every day a thrilling intellectual adventure.Lastly, multitasking contributes to my **resilience** and **adaptability**. The ability to navigate multiple demands and shifting priorities equips me with the agility needed to thrive in an ever-changing world. It instills in me a mindset of resourcefulness and perseverance, enabling me to face adversity head-on and emerge stronger.In conclusion, my affinity for multitasking stems from a deep-seated desire to maximize efficiency, foster personal growth, and lead a fulfilling life. Byemploying effective strategies, navigating challenges, and embracing the rewards, I have transformed what some might perceive as chaos into a well-choreographed dance of productivity. While multitasking is not without its difficulties, the satisfaction of accomplishing much in limited time, coupled with the continuous learning and personal development it fosters, makes it an exhilarating and rewarding way of life for me. In a world where time is finite but opportunities abound, multitasking allows me to seize the day and live life to its fullest potential.。
四年级踢足球注意事项英语作文
四年级踢足球注意事项英语作文Kicking the Ball with Safety in MindSoccer, or football as it is known in many parts of the world, is a thrilling and engaging sport that captivates millions of fans worldwide. However, with its fast-paced nature and physical demands, it's crucial to keep safety in mind while playing. Here are some essential things to consider when engaging in this beloved sport.1. Proper Warm-up and StretchingBefore kicking the ball, it's vital to warm up your muscles and joints to prevent injuries. Simple exercises like jogging, jumping jacks, and dynamic stretches can help increase blood flow and flexibility. Remember to stretch after the game too, to relax tight muscles and prevent stiffness.2. Wear Protective GearAppropriate footwear is essential in soccer. Ensure your cleats fit well and provide the necessary support and traction. Shin guards are also crucial, as they protect your legs from accidental impacts. Wearing a mouthguard can help prevent dental injuries, especially if you play in a contact league.3. Hydrate AdequatelySoccer can be a physically demanding sport, so staying hydrated is crucial. Drink plenty of water before, during, and after the game to replenish lost fluids and maintain your energy levels. Avoid sugary drinks, as they can lead to energy crashes.4. Know the RulesFamiliarize yourself with the rules of soccer, including fouls, penalties, and offside. Understanding the rules helps you play safely and avoid unnecessary collisions. Respect the referee's decisions and abide by the rules to ensure a fair and enjoyable game.5. Maintain AwarenessAlways be aware of your surroundings and the positions of your teammates and opponents. Avoid collisions by communicating clearly and looking up from the ball occasionally. Keep an eye on the referee for any signals or instructions.6. Play with RespectRespect your opponents, teammates, and the game itself. Avoid aggressive or violent behavior, as it can lead to injuries and damage the spirit of the game. Encourage fair play and positive sportsmanship.In conclusion, soccer is a fun and exciting sport, but safety should always be a priority. By following these simple tips, you can enjoy the game while minimizing the risk of injuries. Remember, it's not just about winning; it's about playing safely and having fun!。
家庭菜单制作英语作文
家庭菜单制作英语作文Title: Creating a Family Menu。
In today's fast-paced world, managing a household efficiently requires careful planning, especially when it comes to meal preparation. Developing a family menu not only ensures balanced nutrition but also saves time and money. Let's explore the steps involved in creating a family menu.Firstly, it's essential to consider the dietary needs and preferences of every family member. This includes any allergies, dietary restrictions, or food preferences. By understanding these requirements, we can tailor our menu to accommodate everyone's needs while still offering a variety of delicious options.Next, take inventory of what ingredients are already available in the pantry, refrigerator, and freezer. This step helps in minimizing waste and utilizing ingredientsthat may be nearing their expiration dates. It also serves as inspiration for meal ideas based on what ingredients are readily accessible.Once we have a clear understanding of our family's dietary needs and available ingredients, it's time to brainstorm meal ideas. A good approach is to plan meals for the entire week, taking into account breakfast, lunch, dinner, and snacks. Variety is key here to prevent meal fatigue and ensure everyone looks forward to mealtimes.When selecting recipes, consider factors such as cooking time, complexity, and nutritional value. Opt for recipes that are easy to prepare on busy days and reserve more elaborate dishes for weekends or special occasions. Additionally, aim for a balance of proteins, carbohydrates, fruits, vegetables, and healthy fats in each meal.After finalizing the meal plan for the week, create a shopping list based on the ingredients needed for each recipe. Organize the list by food categories to streamline the shopping process and minimize the chances of forgettingessential items. Remember to check for any staples that need replenishing, such as rice, pasta, spices, and condiments.When shopping for groceries, stick to the list as much as possible to avoid impulse purchases. Consider shopping at local markets or buying in bulk to save money,especially on items with longer shelf lives. Don't forget to check for any sales or discounts that can furtherstretch your budget.Once the groceries are purchased and brought home, it's time to prepare for the week ahead. Consider doing some meal prep in advance, such as chopping vegetables, marinating meats, or cooking grains. This not only saves time during busy weekdays but also encourages healthier eating habits by having nutritious ingredients readily available.Throughout the week, stay flexible with the menu plan and be open to making adjustments as needed. Life can be unpredictable, and there may be occasions when plans changeor unexpected events arise. Having a flexible attitude towards meal planning helps in adapting to these situations without causing undue stress.In conclusion, creating a family menu requires careful consideration of dietary needs, available ingredients, and meal preferences. By following a systematic approach, we can develop a menu that is nutritious, budget-friendly, and enjoyable for the entire family. With proper planning and organization, mealtime can become a stress-free and rewarding experience for everyone involved.。
杜绝眼睛的英文作文
杜绝眼睛的英文作文Title: Eliminating Eye Strain: A Comprehensive Guide。
In today's digital age, our eyes are constantly bombarded with screens, leading to a rise in eye strain and discomfort. It's crucial to address this issue to safeguard our visual health and overall well-being. This article aims to explore effective strategies to eliminate eye strain and promote healthier eye habits.First and foremost, proper ergonomics play a vital role in reducing eye strain. Ensure your workstation is set up correctly, with the monitor positioned at eye level and about an arm's length away. Adjust the brightness and contrast of your screen to comfortable levels, minimizing glare and reflections. Additionally, take regular breaks to rest your eyes and stretch your muscles, relieving tension and fatigue.Another essential aspect is practicing the 20-20-20rule. Every 20 minutes, take a 20-second break and focus on an object at least 20 feet away. This simple yet effective technique helps alleviate eye strain by giving your eyes a much-needed break from prolonged screen exposure.Furthermore, consider implementing blue light filterson your devices or wearing blue light-blocking glasses.Blue light emitted from screens can disrupt sleep patterns and contribute to eye strain. By reducing exposure to blue light, you can protect your eyes and improve your overall sleep quality.Moreover, proper lighting is crucial for reducing eye strain. Ensure your workspace is well-lit with indirect or natural lighting to minimize glare and harsh contrasts. Avoid working in overly dim or excessively bright environments, as both can strain your eyes and cause discomfort.In addition to environmental factors, adopting healthy lifestyle habits can also contribute to reducing eye strain. Stay hydrated by drinking plenty of water throughout theday, as dehydration can exacerbate dry eye symptoms. Incorporate foods rich in omega-3 fatty acids, vitamins A, C, and E into your diet to promote eye health.Furthermore, prioritize regular eye exams to monitor your visual health and address any underlying issues promptly. An optometrist can detect early signs of eye strain and prescribe corrective measures such as prescription glasses or contact lenses tailored to your needs.Lastly, practicing relaxation techniques such as meditation, deep breathing, or eye exercises can help alleviate eye strain and promote overall relaxation. Incorporate these techniques into your daily routine to reduce stress and tension in your eyes and body.In conclusion, by implementing these strategies and adopting healthy habits, you can effectively eliminate eye strain and promote long-term visual health. Remember to prioritize self-care and listen to your body's signals to prevent and address any discomfort promptly. Your eyes areprecious, so take proactive steps to protect them in today's screen-centric world.。
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A fast and simple stretch-minimizing mesh parameterizationShin YoshizawaAlexander BelyaevHans-Peter SeidelComputer Graphics Group,MPI Informatik,Saarbr¨u cken,GermanyPhone:[+49](681)9325-414Fax:[+49](681)9325-499E-mails:shin.yoshizawa belyaev hpseidel@mpi-sb.mpg.de(a)(b)(c)(d)Figure 1:Texture mapping of the Mannequin Head model with three mesh parameterizations used in our method.(a)Texture and model.(b)Floater’s shape preserving parameterization [6]is used as an initial mesh parameterization.(c)After a single optimization pass.(d)Our optimal low-stretch parameterization.AbstractWe propose a fast and simple method for generating a low-stretch mesh parameterization.Given a triangle mesh,we start from the Floater shape preserving parameterization and then im-prove the parameterization gradually.At each improvement step,we optimize the parameterization generated at the previous step by minimizing a weighted quadratic energy where the weights are chosen in order to minimize the parameterization stretch.This op-timization procedure does not generate triangle flips if the bound-ary of the parameter domain is a convex polygon.Moreover al-ready the first optimization step produces a high-quality mesh pa-rameterization.We compare our parameterization procedure with several state-of-art mesh parameterization methods and demon-strate its speed and high efficiency in parameterizing large and geometrically complex models.Keywords:mesh parameterization,stretch minimization,remesh-ing1IntroductionSurface parameterization consists of a surface decompo-sition into a set of patches,also referred to as an atlas of charts,and establishing one-to-one mappings between the patches and reference domains.Numerous applications of surface parameterization in computer graphics and geomet-ric modeling include texture mapping,shape morphing,sur-face reconstruction and repairing,and grid generation.In this paper,we deal with a planar parameterization for a triangle mesh approximating a smooth surface,a bijective mapping between the mesh and a triangulation of a planar polygon.An excellent survey of recent advances in mesh parameterization is given in [7],see also references therein.While various algorithms are developed for mesh param-eterization approaches based on solid mathematical the-ories (e.g.,conformal mappings),effective computational schemes for generating practically important low-stretch mesh parameterizations [15]have not yet been proposed.Consider a surface topologically equiva-lent to a disk and given parametrically by.The Jacobian matrix correspond-ing to the mapping is given by.The Jacobian determines all the first-order geometric proper-ties of the parameterization ,including the area,an-gle,and length distortions caused by the mapping .Denote by and the maximal and minimal singular values of .Consider the first fundamental form of :where ,,and .Then andare the eigenvalues of the metric tensor1It is convenient to use and for measuring various prop-erties of.For example,if,the parame-terization is conformal and mapping preservesangles.Since the conformal mappings are well understood math-ematically,discrete approximations of conformal mappingsare widely used for mesh parameterization purposes[9,10,4,8].However conformal mappings often produce highstretch regions where texture mappings have severe under-sampling artifacts.It is natural to measure the local stretch of mappingbycharacterizes the stretch of mapping.For each vertex in the parameter domain let us defineits stretch bywhere denotes the area of triangle and the sums are taken over all triangles surrounding mesh vertex corresponding to.Our method to build a low stretch mesh parameteriza-tion consists of several steps.First we construct an initial mesh parameterization using the Floater approach[6]:the boundary vertices of mesh are mapped into the boundary vertices of which form a polygon in the parameter plane and for each inner vertex of its corresponding vertex inside the polygon is selected such that the fol-lowing local quadratic energy(2)achieves its minimal value.Here are vertices corre-sponding to the mesh one-link neighbors of and are positive weights.Now the optimal positions for are found by solving a sparse system of linear equations(3)This computationally simple procedure produces a valid pa-rameterization of mesh and avoids triangleflips if the boundary of is a convex polygon[6].Now let us estimate local stretch for each inner vertex in the parametric plane.We redistribute the local stretches by assigning(4) in(2).The new positions of are now found by solving (3).We can think about vertices and corresponding en-ergies(2)in terms of a mass-spring system.For an area pre-serving parameterization,if a high(low)stretch is observed at,that is(),we relax(strengthen)the springs connected with by solving(3)with new weights (4).It works similarly for a general parameterization.Our idea to diffuse the local stretches iteratively by(1), (3),(4)can resemble the relaxation approach of Balmelli et al.[2].Notice however that in[2]the authors use a gradient-descent minimization approach(an explicit mesh evolution scheme)while our method is similar to quasi-Newton type minimization algorithms and an implicit mesh evolution scheme is used.One can alsofind a similarity between(2),(4)and Winslow’s variable diffusion method[18,3]for adaptive grid generation(see also[17]for a comprehensive analysis of numerical methods used to minimize Winslow’s variable diffusion functional).We start from the shape preserving parameterization of Floater[6,6]and then improve it gradually:is obtained from by solving (3)with weights defined byHere are the shape preserving weights proposed by Floater.The boundary vertices of the evolving mesh,,remainfixed.When solving(3)withnumerically we use as the initial guess for the numerical solver we employ.We use the stretch metric of Sander et al.[15]where the sums are taken over all the edges of meshes and.The angle distortion error is defined byEck et al.harmonic map[5]Floater’s shape preserving parameterization[6,6]Desbrun et al.intrinsic parameterization[4]Sander et al.stretch minimizing parameterization[15]Our single-step parameterizationOur optimal parameterizationThe subindex h in()in the bottom row of the above table shows the total number of optimization steps(3),(4) needed to generate.Tables1-12and Figures3and6present qualitative and visual comparisons of the above mesh parameterization schemes tested on various models topologically equivalent to a disk.The unit square is used as the parameter domain and for each models its the boundary vertices arefixed on the boundary of the square.The errors and computational times measured in seconds(s)and sometimes in minutes (m)and hours(h)are given.For the intrinsic parameterization method[4],we use the equal blending of the Dirichlet and Authalic energies for all the models,except for the Fish model(Table11)where we use only the Dirichlet energy in order to avoid triangleflips.Our single-step mesh parameterization procedure(gen-erating)is only slightly slower than the fast Floater and Eck et al.parameterization methods and faster than the in-trinsic parameterization of Desbrun et al.[4].Besides demonstrates competitive results in minimizing the stretch, edge,area,and angle distortions.Our optimal mesh parameterization procedure is also fast enough and sometimes achieves better results in stretch minimizing than the probabilistic minimization of Sander et al.[15]which is very slow.Moreover,by contrast with [15],does not generate parameter cracks(see Fig.6) because(3)acts like a diffusion process.Besides,if a very low stretch parameterization is needed,can be used as an initial parameterization for[15].Fig.7shows parameterization of the Mannequin Head model when the parameter domain has boundaries of various shapes.The left images show the parameteri-zation and corresponding texture mapping results when the boundary is the unit circle.The right images demonstrate similar results when the boundary of the parameter domain was obtained as the so-called natural boundary for the con-formal parameterization of[4].Notice that the stretch dis-tortions near the boundary are substantially reduced in the latter case.In Fig.8mesh parameterizations,,and are evaluated and compared using the checkerboard texture.Sometimes does not produce the best visual result be-cause of high anisotropy and is preferable.Finally,in Fig.9we analyze how the stretch distribution over a com-plex geometry model is changing during the optimization process.The top row of images presents the model(a decimated Max-Planck bust model)and re-sults of checkerboard texture mapping with,,and .The four remaining images of the model show the stretch distribution over the model for,,andparameterizations.The images demonstrate how well our stretch minimization procedures minimize and equalize the stretch.It is interesting to notice that near the mesh bound-ary the optimized meshes have large area and angle dis-tortions(the same effect is observed in all the other tested models)but relatively low stretch distortions.One can hope that an appropriate relaxation of boundary conditions will reduce those area and angle distortions while maintaining low stretch.Application to remeshing.In the right column of Fig.3 and in Fig.5we demonstrate how our mesh parameteriza-tion technique can be used for fast and high quality remesh-ing of complex surfaces.We have chosen the interactive geometry remeshing scheme of Alliez et al.[1]and imple-mented its main steps:1.Create a mesh parameterization.pute area,curvature,and control maps using hard-ware accelerated OpenGL commands.3.Sample points by applying an error diffusion to thecontrol map.4.Connect the points using the Delaunay triangulation.e the parameterization to map the points into3D.A conformal mesh parameterization is the best choice forthe described remeshing scheme.It is clear that the remeshing quality depends on the size of an image used for the hardware assisted acceleration:the bigger size,the better result.On the other side,the image size is restricted by the graphics card memory.It turns out that a high quality remeshing can be obtained even for a rel-atively small image size.Let us assume that we have two parameterizations of a3D mesh:a conformal parameter-4ization and an area-preserving one.Then let us the area-preserving parameterization for computing the control map and resampling the points via an error diffusion process.Fi-nally,the points are mapped from the area-preserving pa-rameterization to the conformal one and are connected us-ing the Delaunay triangulation.The above remeshing modification has one drawback:it requires two parameterizations,conformal and area-preserving.However since our low-stretch parameteriza-tion has nice area-preserving properties and the ini-tial Floater’s parameterization is close to a conformal one,we use and instead of the conformal and area-preserving parameterizations in the above modification of the interactive geometry remeshing scheme of Alliez et al.Right images(a)-(c)of Fig.3demonstrate results of thesingle-parameterization remeshing scheme if the discreteharmonic map parameterization[5],Floater’s shape pre-serving parameterization[6],and intrinsic discrete confor-mal parameterization are used,respectively.Right images(d)-(f)of Fig.3present our experiments with the double-parameterization remeshing scheme.We set Floater’s pa-rameterization as a substitute of a conformal param-eterization and used as an initial parameterization togenerate the stretch-minimizing parameterization of Sanderet al.[15]and and.These low-stretch parame-terizations were used as substitutes of an area-preservingparameterization.Fig.5presents remeshed Max-Planckbust and Stanford bunny models obtained by the remeshing schemes based on(from left to right),,and parameterizations(here using param-eterizations means that we use as a substitute of a con-formal parameterization and as a substitute of an areapreserving one).Notice that the double-parameterizationremeshing scheme with produces the best re-sults.4ConclusionWe have presented a fast and powerful method for gen-erating low-stretch mesh parameterizations and demon-strate its applicability to high quality texture mapping and remeshing.Our method is much faster than the stochas-tic stretch minimization procedure of Sander et al.[15] (note that their more recent coarse-to-fine stretch optimiza-tion procedure[14]is significantly faster than that of[15] but still slower than ours)and often produces better quality results.In particular,it does not generate parameter cracks.Our method is heuristic.At present we are not able to support it by rigorous mathematical results.In future we plan to extend our approach to sphericalparameterizations and use quadratic energies with matrix weights for incorporating an anisotropy in our optimization process.AcknowledgmentsThe authors would like to thank Hugues Hoppe for a helpful discussion and the anonymous reviewers of this paper for their valuable and constructive comments.The models are courtesy of the Stanford University(bunny and dragon),the University of Washington(mannequin head andfish),Cyberware Inc.(Igea), and MPI f¨u r Informatik(Max-Planck bust).References[1]P.Alliez,M.Meyer,and M.Desbrun.Interactive geometry remesh-ing.In Proceedings of ACM SIGGRAPH2002,pages347–354,2002.[2]L.Balmelli,G.Taubin,and F.Bernardini.Space-optimized texturemaps.In Proceedings of EUROGRAPHICS2002,pages411–420,2002.[3]W.Cao,W.Huang,and R.D.Russell.Approaches for generatingmoving adaptive meshes:location versus velocity.Appl.Numer.Math.,47:121–138,2003.[4]M.Desbrun,M.Meyer,and P.Alliez.Intrinsic parameterizations ofsurface meshes.In Proceedings of EUROGRAPHICS2002,pages209–218,2002.[5]M.Eck,T.DeRose,T.Duchamp,H.Hoppe,M.Lounsbery,andW.Stuetzl.Multiresolution analysis of arbitrary meshes.In Pro-ceedings of ACM SIGGRAPH1995,pages173–182,1995.[6]M.S.Floater.Parametrization and smooth approximation of surfaceputer Aided Geometric Design,14(3):231–250,1997.[7]M.S.Floater and K.Hormann.Recent advances in surface param-eterization.In Multiresolution in Geometric Modelling,pages259–284,2003.[8]X.Gu and S.-T.Yau.Global conformal surface parameterization.InProceedings of Eurographics Symposium on Geometry Processing2003,pages135–146,2003.[9]S.Haker,S.Angenent,A.Tannenbaum,R.Kikinis,G.Sapiro,andM.Halle.Conformal surface parameterization for texture map-ping.IEEE Transactions on Visualization and Computer Graphics,6(2):181–189,2000.[10] B.L´e vy and S.Petitjean.Least squares conformal maps for auto-matic texture atlas generations.In Proceedings of ACM SIGGRAPH2002,pages362–371,2002.[11]J.Maillot,H.Yahia,and A.Verroust.Interactive texture mapping.InProceedings of ACM SIGGRAPH1993,pages27–34,1993.[12] E.Praun and H.Hoppe.Spherical parametrization and remeshing.In Proceedings of ACM SIGGRAPH2003,pages340–349,2003.[13]W.H.Press,S.A.Teukolsky,W.T.Vetterling,and B.P.Flannery.Numerical Recipies in C.Cambridge University Press,1988.[14]P.V.Sander,S.J.Gortler,J.Snyder,and H.Hoppe.Signal-specialized parametrization.In Proceedings of Eurographics Work-shop on Rendering2002,pages87–98,2002.[15]P.V.Sander,J.Snyder,S.J.Gortler,and H.Hoppe.Texture mappingprogressive meshes.In Proceedings of ACM SIGGRAPH2001,pages409–416,2001.[16]O.Sorkine, D.Cohen-Or,R.Goldenthal,and D.Lischinski.Bounded-distortion piecewise mesh parameterization.In Proceed-ings of IEEE Visualization,pages355–362,2002.[17] A.M.Winslow.Numerical solution of the quasilinear poisson equa-tion in a put.Phys.,2:149–172,1967.[18] A.M.Winslow.Adaptive mesh zoning by equipotential method.Technical report,Lawrence Livermore Laboratory,1981.ReportUCID-19062.[19] E.Zhang,K.Mischaikow,and G.Turk.Feature-based surface pa-rameterization and texture mapping.Technical report,Georgia Insti-tute of Technology,2003.GVU Tech Report03-29.5P ARAMETERIZATION C URVATURE M AP T EXTURE M APPING P ARAMETER C RACKS ?R EMESHING [1](a)Harmonic map of Eck et al.[5]:time 0.37s,Stretch:6.661,Edge:0.997,Angle:0.068,Area:1.403(b)Floater shape preserving weights [6]:time 0.32s,Stretch:5.792,Edge:0.959,Angle:0.18,Area:1.373(c)Intrinsic parameterization of Desbrun et al.[4]:time 0.76s,Stretch:6.129,Edge:0.978,Angle:0.12,Area:1.388(d)Stretch minimization of Sander et al.[15]:time 23m,Stretch:1.327,Edge:0.539,Angle:0.274,Area:0.495(e)Ourparameterization:time 0.5s,Stretch:1.642,Edge:0.507,Angle:0.383,Area:0.871(f)Ourparameterization:time 1.09s,Stretch:1.382,Edge:0.4748,Angle:0.4132,Area:0.3832Figure 3:Comparison of various mesh parameterization schemes on the Mannequin Head model (,).6Stretch Angle(a) 6.65070.125(b) 5.91710.1995(c) 6.27510.1619(d) 1.3750.2952(e) 1.66910.3717() 1.40840.4479time Edge Area0.21s0.49350.84550.17s0.46480.84090.33s0.47530.84213s0.29960.30430.3s0.28620.3179Table2:Cat Head model:,Stretch Angle(a) 6.66170.0685(b) 5.79210.1807(c) 6.12950.1209(d) 1.32790.2744(e) 1.64250.3838() 1.3820.4132time Edge Area1.23s0.7563 1.02070.87s0.69760.95261.81s0.72320.97951h0.49550.42271.5s0.45510.46763.44s0.46610.3613Table4:Cat model:,Stretch Angle(a)18.0270.0361(b)15.9410.1441(c)16.9330.0857(d) 1.32570.2501(e) 2.20370.372() 1.53920.4905time Edge Area12.9s0.30250.50636.21s0.34120.565125.8s0.7602 1.00854.5h0.28330.433817.9s0.24770.387642.6s0.240.2375Table6:Fandisk model:,Stretch Angle(a)91795490.0915(b)11203180.3491(c)2319890.2707(d)7635.30.3544(e)313.640.6341() 3.56880.8253time Edge Area12.4s0.9729 1.51328.95s0.9983 1.572590.7s0.9845 1.542543.4h0.71930.666514.7s0.50410.807832.3s0.63990.5344Table8:Dragon Head model:,Stretch Angle(a) 3.47990.0542(b) 4.6760.1627(c)34.6210.1831(d) 1.30920.2265(e) 1.43730.3446() 1.3040.3923time Edge Area17.9s0.7097 1.09813.2s0.7241 1.0861231s0.7062 1.095755.6h0.49820.486822.5s0.45820.563279.8s0.61430.5241Table10:Stanford Bunny model:,Stretch Angle(a) 6.30610.0445(b) 6.0920.1782(c) 6.3060.0445(d) 2.56890.2444(e) 1.56830.3476() 1.50410.4678time Edge Area250s 1.2578 1.6936204s 1.25 1.691252.1m 1.2341 1.6924384s0.6598 1.2017848s0.59390.4812 Table12:Max-Planck bust model:,7Figure 4:Choosing smaller values for leads to a less aggressive stretch minimization.From left to right:parameterization ofMannequin Head with.Figure 5:Remeshing of Max-Planck bust model (three left images)and Stanford bunny (three right images)models.For each model remeshings according to ,,and are shown.See the text for details.Figure 6:Parameter cracks on various models textured with checkerboard texture.The images of the upper row demonstrate parameter cracks generated by the stretch-minimization method of Sander et al.[15].The images of the bottom row show the same parts of themodels parameterized by our.with circular parameter domain.Time:1.51s,Stretch:1.34,Edge:0.43,Angle:0.47,Area:0.4.with natural boundary [4].Time:1.67s,Stretch:1.68,Edge:0.5,Angle:0.37,Area:0.9.Figure 7:Using various parameter domains for .8Figure 8:Checkerboard texture mapping with(left),(mid-dle),and(right).Figure 9:Top row:a decimated Max-Planck bust model and re-sults of checkerboard texture mapping with ,,and pa-rameterizations.The four remaining images of the model show thedistribution of the vertex stretches over the model for,,and .Firstly coloring by stretch is used to com-pare and .Then the same coloring scheme on the stretchintervalis employed to compare the stretch distribu-tions for ,and .Here the bounds of the interval are equal to the maximal and minimal stretch values.9。