First principles investigation of binary intermetallics in Mg-Al-Ca-Sn alloy:Stability,electronic structures,elastic properties and thermodynamic properties

The structural stability, electronic structures, elastic properties and thermodynamic properties of the main binary phases Mg_（17）Al_（12）, Al_2Ca, Mg_2 Sn and Mg_2 Ca in Mg-Al-Ca-Sn alloy were determined from the first-principles calculation. The calculated lattice parameters are in good agreement with the experimental and literature values. The calculated heats of formation and cohesive energies show that Al_2Ca has the strongest alloying ability and structural stability. The densities of states（DOS）, Mulliken electron occupation number, metallicity and charge density difference of these compounds are given. The elastic constants of Mg_（17）Al_（12）, Al_2Ca, Mg_2 Sn and Mg_2 Ca phases are calculated, and the bulk moduli, shear moduli, elastic moduli and Poisson ratio are derived. The calculations of thermodynamic properties show that the Gibbs free energies of Al_2Ca and Mg_2 Sn are lower than that of Mg_（17）Al_（12）, which indicates that Al_2Ca and Mg_2 Sn are more stable than Mg_（17）Al_（12） phase. Hence, the heat resistance of Mg-Al-based alloys can be improved by adding Ca and Sn additions.

First-principle calculations of ductile CeAg intermetallic compound

The first-principle calculations were performed to investigate the structural,mechanical,electronic and thermal properties of the binary ductile intermetallic compound CeAg with B2（CsCl） structure.The calculated value of lattice constant a0 for CeAg with generalized gradient approximation is 3.713-,which is in better agreement with experimental data than local spin density approximation.The negative energy of formation implies that CeAg with B2 structure is thermodynamically stable phase.The greater separation between the d bands of Ce and Ag results in weaker bond hybridization of Ce d—Ag d,which prevents formation of directional covalent bonding.The three independent elastic constants（C11,C12 and C44） are derived and the bulk modulus,shear modulus,elastic modulus,anisotropy factor,and Poisson ratio are determined to be 57.6 GPa,15.8 GPa,43.4 GPa,3.15 and 0.374,respectively.The elastic constants meet all the mechanical stability criteria.The value of Pugh＇s criterion is 3.65.The ductility of CeAg is predicted if Pugh＇s criterion is greater than 1.75.Furthermore,the variations of volume,bulk modulus,heat capacity,and thermal expansion coefficient with temperature and/or pressure were calculated and discussed.

Elastic and thermodynamic properties of Re_2N at high pressure and high temperature

First principles calculations are preformed to systematically investigate the elastic and thermodynamic properties of Re2N at high pressure and high temperature. The Re2N exhibits a clear elastic anisotropy and the elastic constants C11 and C33 vary rapidly in comparison with the variations in C12, C13 and C44 at high pressure. In addition, bulk modulus B, elastic modulus E, and shear modulus Gas a function of crystal orientations for Re2N are also investigated for the first time. The tensile directional dependences of the elastic modulus obey the following trend： [0001] [1211] [1010] [1011]EEEE〉〉〉 . The shear moduli of Re2N within the （0001） basal plane are the smallest and greatly reduce the resistance of against large shear deformations. Based on the quasi-harmonic Debye model, the dependences of Debye temperature, Grüneisen parameter, heat capacity and thermal expansion coefficient on the temperature and pressure are explored in the whole pressure range from 0 to 50 GPa and temperature range from 0 to 1600 K.

Elastic Tensor and Thermodynamic Property of Magnesium Silicate Perovskite from First-principles Calculations

The thermodynamic and elastic properties of magnesium silicate （MgSiO3） perovskite at high pressure are investigated with the quasi-harmonic Debye model and the first-principles method based on the density functional theory. The obtained equation of state is consistent with the available experimental data. The heat capacity and the thermal expansion coefficient agree with the observed values and other calculations at high pressures and temperatures. The elastic constants are calculated using the finite strain method. A complete elastic tensor of MgSiO3 perovskite is determined in the wide pressure range. The geologically important quantities： Young＇s modulus, Poisson＇s ratio, Debye temperature, and crystal anisotropy, are derived from the calculated data.

Linear correlations of formation enthalpies/bulk modules and atomic volumes observed in Pt-Zr compounds by ab initio calculation

118 kinds of Pt-Zr phases were established and investigated by considering various structures. Then the related physical properties, such as structural stability, lattice constants, formation enthalpies, elastic constants and bulk moduli, are obtained by ab initio calculations. Based on the calculated results of formation enthalpies, the ground-state convex hull is derived for the Pt-Zr system. The calculated physical data would provide a basis for further thermodynamic calculations and atomistic simulations. For these Pt-Zr compounds, it is found there are a positive linear correlation between the formation enthalpies and atomic volumes, and a negative linear correlation between the bulk modules and atomic volumes.

Study on structural,mechanical and thermodynamic properties of TiAl alloy under high pressure based on first-principles

The effect of pressure on structural, mechanical properties as well as the temperature dependence of thermodynamic properties of TiAl alloy are investigated by implementing first-principles calculations. The results show that the volume decrea-ses with the pressure increasing. We calculated the CtJ at various pressures and all the results satisfy mechanical stability crite-ria, thus the TiAl alloy is mechanically stable. The elastic constants？ bulk modulus and shear modulus calculated are well in a-greement with the calculated values at zero the pressure. The bulk modulus and shear modulus increase with the pressure in-creasing, which reflects the deformation resistance, and accordingly, deformation resistance can be strengthened with the in-crease of pressure. The brittle nature of TiAl alloy turns to ductile nature in 10 - 20 GPa . The Debye temperature, linear ther-mal expansion and heat capacity are calculated using the quasi-harmonic Debye model under the pressure ranging from 0 to 50 GPa and the temperature ranging from 0 to 1 000 K, which are useful to investigate the effect of temperature and pressure on thermodynamic parameters. Finally, electronic structure is calculated at various pressures,and it can be found that the peak intensity decreases with increasing pressure and the the strength of d-d orbital of Ti is weakened but the ductility is enhanced.

Elasticity solution of laminated beams with temperature-dependent material properties under a combination of uniform thermo-load and mechanical loads

An exact solution for simply-supported laminated beams with material properties variable with temperature under a combination of uniform thermo-load and mechanical loads was investigated,based on the two-dimensional(2-D)thermo-elasticity theory.Firstly,the beam was divided into a series of layers with uniform material properties along the interfaces of the beam.The uniform thermo-load acted on each layer was transformed into a combination of the normal surface forces acted at the two ends and the transverse thermo-load.Secondly,the state space method was employed to obtain the general solutions of displacements and stresses in an arbitrary layer.Thirdly,based on the interfacial continuity conditions between adjacent layers,the relations of displacement and stress components between the top and bottom layers of the beam were recursively derived by use of the transfer-matrix method.The unknowns in the solutions can be solved by the mechanical loads acted on the top and bottom surfaces.The convergence of the present solutions was checked.The comparative study of the present solutions with the Timoshenko’s solutions and the finite element(FE)solutions was carried out.The effects of material properties variable with temperature on the thermo-elastic behavior of laminated beams were discussed in detail.

Elastic and Thermodynamic Properties of CdSe from First-Principles Calculations

The lattice parameters, bulk modulus, phase transition pressure, and temperature dependencies of the elastic constants cij of CdSe are investigated by using the Cambridge Serial Total Energy Package （CASTEP） program in the frame of Density Functional Theory （DFT）. It is found that the phase transitions from the ZB structure to the RS structure and from WZ structure to RS structure are 2.2 GPa and 2.8 GPa, respectively. Our results agree well with the available experimental data and other theoretical results. The aggregate elastic modulus （B, G, E, A ）, the Poisson＇s ratio （v）, the Griuneisen parameter （γ）, the Debye temperature θD on pressure and temperature are also successfully obtained.

Theoretical solution of a spherically isotropic hollow sphere for dynamic thermoelastic problems

The separation of variables method was successfully used to resolve the spherically symmetric dynamic thermoelastic problem for a spherically isotropic elastic hollow sphere. Use of the integral transform can be avoided by means of this method, which is also appropriate for an arbitrary thickness hollow sphere subjected to arbitrary thermal and mechanical loads. Numerical results are presented to show the dynamic stress responses in the uniformly heated hollow spheres.

First-Principle Calculations for Elastic and Thermodynamic Properties of Diamond

The elastic constants and thermodynamic properties of diamond are investigated by using the CRYSTALO3 program. The lattice parameters, the bulk modulus, the heat capacity, the Gruneieen parameter, and the Debye temperature are obtained. The results are in good agreement with the available experimental and theoretical data. Moreover, the relationship between V/V0 and pressure, the elastic constants under high pressure are successfully obtained. Especially, the elastic constants of diamond under high pressure are firstly obtained theoretically. At the same time, the variations of the thermal expansion α with pressure P and temperature Tare obtained systematically in the ranges of 0-870 GPa and 0-1600 K.

Theoretical Calculations for Structural, Elastic and Thermodynamic Properties of MgB2 under High Pressure

We have investigated the structural and elastic properties of MgB2 under high pressures using the full- potential linearized muffin-tin orbital （FP-LMTO） scheme within the generalized gradient approximation correction （GGA） in the frame of density functional theory. The calculated pressure dependence of the normalized volume is in excellent agreement with the experimental results. At the same time the elastic constants and acoustic anisotropy as a function of applied pressure are presented. Through the quasi-harmonic Debye model, we also investigate the thermodynamic properties of MgB2.

Phase transition, thermodynamic and elastic properties of ZrC

First principles calculation and quasi-harmonic Debye model were used to obtain more physical properties of zirconium carbide under high temperature and high pressure.The results show that the B1structure of ZrC is energetically more favorable with lower heat of formation than the B2structure,and that mechanical instability and positive heat of formation induce the inexistence of the B2structure at normal pressure.It is also found that the B1structure would transform to the B2structure under high pressure below the critical point of V/V0=0.570.In addition,various thermodynamic and elastic properties of ZrC are obtained within the temperature range of0-3000K and the pressure range of0-100GPa.The calculated results not only are discussed and understood in terms of electronic structures,but also agree well with corresponding experimental data in the literature.

Henriksen and Flora （1999） Revisited A Literature Review on Third-Person Effects and Children/Adolescents＊

In this literature review on TPE （third-person effects） and the behavioral consequences on children, the research questions posed are how the body of knowledge has evolved since the first empirical evidence of TPE among children and what knowledge gaps that remain. The traceable developments are two： （1） Compared to the vast amount of articles on TPE in general, the 5 9 identified on the topic of children are few and two thirds actually focus on adolescents/young adults rather than children. The reason put forward for studying younger children is the urge to prevent risky behavior through media literacy programs or pro-social advertisements; and （2） The studies have not primarily addressed results to support occurrence of TPE among children. Rather they support parental TPE or among the adolescents that TPE and reverse TPE occur due to certain kind of media content. The discussion on knowledge gaps that remain follow three themes： （1） Differentiations between self and others are in psychological studies implied to occur among children between the ages of 3-4 years old, yet no study address how children develop TPE; （2） There is a tendency to follow the more general development within TPE research with the renewed interest in behavioral consequences. But the primary behavioral consequence studied in TPE in general and within studies of TPE and children is support for censorship. Few studies address ＂real＂ behavioral consequences like parental mediation; and （3） There is also a need for more theoretically coherent research on the importance of social distance.

Elasticity under pressure and thermal property of Mg2La from first-principles calculations

The elastic properties, thermodynamic and electronic structures of Mg_2La were investigated by using first-principles. The calculated results show that pressure affects the elastic constants of C_(11) more than that of C_(12) and C_(44). Specifically, higher pressure leads to greater bulk modulus(B), shear modulus(G), and elastic modulus(E). We predict B/G and anisotropy factor A based on the calculated elastic constants. The Debye temperature also increases with increasing pressure. Based on the quasi-harmonic Debye model, we examined the thermodynamic properties. These properties include the normalized volume(V/V_0), bulk modulus(B), heat capacity(C_v), thermal expansion coefficient(α), and Debye temperature(■). Finally, the electronic structures associated with the density of states(DOS) and Mulliken population are analyzed.

First Principles Study of AI-Li Intermetallic Compounds

The structural properties, heats of formation, elastic properties, and electronic structures of four compositions of binary A1-Li intermetallics, A13Li, A1Li, A12Li3, and A14Li9, are ana- lyzed in detail by using density functional theory. The calculated formation heats indicate a strong chemical interaction between A1 and Li for all the A1-Li intermetallics. In partic- ular, in the Li-rich A1-Li compounds, the thermodynamic stability of intermetallics linearly decreases with increasing concentration of.Li. According to the computational single crystal elastic constants, all the four A1-Li intermetallic compounds considered here are mechani- cally stable. The polycrystalline elastic modulus and Poisson＇s ratio have been deduced by using Voigt, Reuss, and Hill approximations, and the calculated ratios of bulk modulus to shear modulus indicate that the four compositions of binary A1-Li intermetallics are brittle materials. With the increase of Li concentration, the bulk modulus of A1-Li intermetallics decreases in a linear manner.

Analytical Bond-order Potential for hcp-Y

The lattice parameters, elastic constants, cohesive energy, structural energy differences, as well as the properties of point defects and planar defects of hexagonal closepacked yttrium （hcpY） have been studied with ab initio density functional theory for constructing an ex tensive database. Based on an analytical bondorder poial scheme, empirical manybody interatomic potential for hcpY has been developed. The model is fitted to some properties of Y, e.g., the lattice parameters, elastic constants, bulk modulus, cohesive energy, vacancy formation energy, and the structural energy differences. The present potential has ability to reproduce defect properties including the selfinterstitial atoms formation energies, vacancy formation energy, divacancy binding energy, as well as the bulk properties and the thermal dynamic properties.

Structural, thermodynamics and elastic properties of Mg_(17)Al_(12), Al_2Y and Al_4Ba phases by first-principles calculations

Structural stabilities, thermodynamics stabilities, elastic properties and electronic structures of Mgl7Al12, Al2Y and AlaBa phases were analyzed by first-principles calculations with Castep and Drool3 program based on the density functional theory. The calculated results of heat of formation indicate that AI2Y phase has the strongest alloying ability. The calculated thermodynamic properties show that the thermal stability of these compounds gradually increases in the order ofMgl7Al12, A12Y and Al4Ba phases. Y or Ba addition to the Mg-Al alloys could improve the heat resistance. The calculated bulk modulus B, shear modulus G, elastic modulus E and Poisson ratio v show that the adding Y or Ba to Mg-Al alloys could promote the brittleness and stiffness, and reduce tenacity and plasticity by forming Al4Ba and Al2Y phases. The calculated cohesive energy and density of state （DOS） show that Al2Y has the strongest structural stability, then AlaBa and finally Mg17Al12. The calculated electronic structures show that Al2Y has the strongest structure stability because of the strong ionic bonds and covalent bonds combined action.

热波探针灵敏度的理论分析

当一束聚焦的、调制的激励激光照射固体材料时，表面上除了产生周期性的温 度分布，还产生局部的周期性形变。在形变区域，探测激光束的反射光受到周期性的偏 转。研究了这种周期性偏转与材料性质和激励激光束参数之间的关系。从热弹性学基本 方程出发建立了数学模型。利用Ｈａｎｋｅｌ积分变换方法得到了交变偏转角的积分表达 式。给出了对于单晶硅的若干计算机模拟结果。

Thermoelastic coupling problems caused by thermal contact resistance:A discontinuous Galerkin finite element approach

A discontinuous Galerkin (DG) finite element method is presented to solve the thermoelastic coupling problems caused by temperature and pressure dependent thermal contact resistance (TCR).The whole analysis is made up of two parts,thermal and mechanical analysis.In thermal analysis,the DG method is employed to simulate the temperature jump phenomenon,which satisfies the imperfect thermal contact condition in a straightforward manner.In mechanical analysis,the impenetrability condition is fulfilled through a DG approach with penalty functions.The Picard iteration procedure with a relaxation technique is also adopted to accelerate the rate of convergence and avoid numerical instability.Numerical examples show that the present method is an attractive approach for solving thermoelastic coupling problems caused by TCR.The methodology can also be expanded to solve problems with friction finite deformation contact,node-to-segment contact and node-to-surface contact,etc.in a straightforward manner.

A new interpretation of internal-variable theory in finite thermo-viscoelasticity

Based on the non-equilibrium thermodynamics,an internal-variable theory in thermo-viscoelasticity at finite deformation was proposed by Huang in 1999.In this theory,a modified stretch of the molecular chain was introduced,and hence the molecular network model in rubber elasticity was extended to take into account the viscous and thermal effects of the material.The viscous dissipation of the material can then be described by means of these internal variables,which appear in the expression of the modified stretch.In order to give a clearer explanation on the physical implication of the internal variables,a connection between the internal-variable theory and theoretical formulation based on the multiplicative decomposition of the deformation gradient in existing literature is presented in this paper,which allows the above internal-variable theory to be more systematic.