Heat transfers due to MHD-conjugate free convection from the isothermal horizontal circular cylinder while viscosity is a function of temperature is investigated. The governing equations of the flow and connected boun...Heat transfers due to MHD-conjugate free convection from the isothermal horizontal circular cylinder while viscosity is a function of temperature is investigated. The governing equations of the flow and connected boundary conditions are made dimensionless using a set of non-dimensional parameters. The governing equations are solved numerically using the finite difference method. Numerical results are obtained for various values of viscosity variation parameter, Prandtl number, magnetic parameter, and conjugate conduction parameter for the velocity and the temperature within the boundary layer as well as the skin friction coefficients and heat transfer rate along the surface.展开更多
We discuss in this paper a novel interpretation of Born rule as an approximated thermodynamic law which emerges from the interaction of a quantum system with a non-stationary thermal bath associated to vacuum fluctuat...We discuss in this paper a novel interpretation of Born rule as an approximated thermodynamic law which emerges from the interaction of a quantum system with a non-stationary thermal bath associated to vacuum fluctuations induced by external environment radiation. In particular we assume that vacuum polarization is a real non relativistic phenomena caused by hidden vacuum charge oscillations which diffuses heat energy in a dispersive and dissipative dielectric medium with a temperature dependent speed of propagation. We propose a model which couples vacuum wavefunctions to vacuum charge fluctuations and we deduce a temperature dependent running fine structure constant function proportional, at first approximation, to the squared of the effective electron charge and compatible with known experimental data. We interpret the vacuum symmetry breaking energy fluctuations induced in scattering experiments of particle physics and in laser assisted nuclear reactions as thermal quasi-monochromatic beams produced by the decay of hidden non equilibrium massive photons propagating with a variable light speed. We suggest, exploiting an old analogy between plasmons and pseudo Goldstone bosons, to interpret heat diffusion of this non relativistic polarized vacuum as a real De Broglie electromagnetic scalar wave associated to the radiation emitted by the hidden massive photons with acceleration proportional to vacuum Unruh like temperature. We predict a temperature dependent deviation from Coulomb law and a generalized dispersive law of these hidden unstable photons that could be revealed as not stationary coloured noise in experiments on anomalous heat diffusions associated to the decay of unstable accelerated pairs produced in nuclear physics experiments. We discuss then how our proposal of a temperature dependent non relativistic vacuum polarization might be applied to deduce a dynamic generalization of Born rule based on a realistic interpretation of quantum wavefunctions as averaged electromagnetic waves of hidden massive photons. Finally we suggest to test our time asymmetric model looking for very fast oscillating polarization thermal waves emitted during the not instantaneous wavefunction collapse and revealed as not stationary bulk heating effects in experiments on accelerated conductors and nanoconductors.展开更多
This paper deals with finite element study of the scanning induction heating of the magnetic steel sheets in transversal flux devices,taking into account the magnetic nonlinearity and the dependence on temperature of ...This paper deals with finite element study of the scanning induction heating of the magnetic steel sheets in transversal flux devices,taking into account the magnetic nonlinearity and the dependence on temperature of steel properties.The decrease of the non-uniformity of the transversal profile of sheet heating as effect of the magnetic or electromagnetic screening of the sheet lateral sides was proved.展开更多
In this paper, we construct the equations of generalized thermoelasicity for a non-homogeneous isotropic hollow cylider with a variable modulus of elasticity and thermal conductivity based on the Lord and Shulman theo...In this paper, we construct the equations of generalized thermoelasicity for a non-homogeneous isotropic hollow cylider with a variable modulus of elasticity and thermal conductivity based on the Lord and Shulman theory. The problem has been solved numerically using the finite element method. Numerical results for the displacement, the temperature, the radial stress, and the hoop stress distributions are illustrated graphically. Comparisons are made between the results predicted by the coupled theory and by the theory of generalized thermoelasticity with one relaxation time in the cases of temperature dependent and independent modulus of elasticity.展开更多
The work-hardening behaviour in an Fe-Mn-Si-Cr-Ni alloy has been investigated using tensile test at different temperatures and TEM observation. It was found that besides the intersection of εmartensite, the intersect...The work-hardening behaviour in an Fe-Mn-Si-Cr-Ni alloy has been investigated using tensile test at different temperatures and TEM observation. It was found that besides the intersection of εmartensite, the intersections of ε martensite with stacking fault and the cross-slip of dislocation which is difficult to occur in the alloy with low stacking fault energy are also important factors to the temperature dependent work-hardening behaviour.展开更多
GaSb p-channel metal-oxide-semiconductor field-effect transistors （MOSFETs） with an atomic layer deposited Al2O3 gate dielectric and a self-aligned Si-implanted source/drain are experimentally demonstrated. Temperat...GaSb p-channel metal-oxide-semiconductor field-effect transistors （MOSFETs） with an atomic layer deposited Al2O3 gate dielectric and a self-aligned Si-implanted source/drain are experimentally demonstrated. Temperature dependent electrical characteristics are investigated. Different electrical behaviors are observed in two temperature regions, and the un- derlying mechanisms are discussed. It is found that the reverse-bias pn junction leakage of the drain/substrate is the main component of the off-state drain leakage current, which is generation-current dominated in the low temperature regions and is diffusion-current dominated in the high temperature regions. Methods to further reduce the off-state drain leakage current are given.展开更多
The prime objective of the present study is to examine the effect of tempera- ture dependent viscosity/z（T） on the revolving axi-symmetric laminar boundary layer flow of an incompressible, electrically non-conductin...The prime objective of the present study is to examine the effect of tempera- ture dependent viscosity/z（T） on the revolving axi-symmetric laminar boundary layer flow of an incompressible, electrically non-conducting ferrofiuid in the presence of a stationary plate subjected to a magnetic field and maintained at a uniform temperature. To serve this purpose, the non-linear coupled partial differential equations are firstly converted into the ordinary differential equations using well-known similarity transformations. The popular finite difference method is employed to discretize the non-linear coupled differ- ential equations. These discretized equations are then solved using the Newton method in MATLAB, for which an initial guess is made with the help of the Flex PDE Solver. Along with the velocity profiles, the effects of temperature dependent viscosity are also examined on the skin friction, the heat transfer, and the boundary layer displacement thickness. The obtained results are presented numerically as well as graphically.展开更多
Physical implications of the activation energy derived from temperature dependent photoluminescence（PL） of In Ga Nbased materials are investigated, finding that the activation energy is determined by the thermal dec...Physical implications of the activation energy derived from temperature dependent photoluminescence（PL） of In Ga Nbased materials are investigated, finding that the activation energy is determined by the thermal decay processes involved.If the carrier escaping from localization states is responsible for the thermal quenching of PL intensity, as often occurs in In Ga N materials, the activation energy is related to the energy barrier height of localization states. An alternative possibility for the thermal decay of the PL intensity is the activation of nonradiative recombination processes, in which case thermal activation energy would be determined by the carrier capture process of the nonradiative recombination centers rather than by the ionization energy of the defects themselves.展开更多
Temperature dependent assembly of two novel Cd coordination polymers with the phen and H2MIP ligands （phen = 1,10-phenanthrolion and H2MIP = 5-methyl-isophthalic acid）, formulated as Cd2（MIP）2（phen）2 （1） and ...Temperature dependent assembly of two novel Cd coordination polymers with the phen and H2MIP ligands （phen = 1,10-phenanthrolion and H2MIP = 5-methyl-isophthalic acid）, formulated as Cd2（MIP）2（phen）2 （1） and Cd3（MIP）3（H2MIP）（phen）2 （2）. They have been structurally characterized by single-crystal X-ray diffraction, elemental analysis, FT-IR spectra and TGA. 1 crystallizes in the monoclinic space group P2/n, while 2 crystallizes in the triclinic space group P1. 1 shows a 2D （two-dimensional） plane and 2 shows a 1D （one-dimensional） chain. In addition, their solid-state luminescent properties have also been investigated.展开更多
Rare-earth calcium oxyborate crystals(RECa_(4)O(BO_(3))_(3),RECOB,RE:rare-earth elements)are a kind of multifunctional crystal materials.In this work,the temperature dependent behaviors of the electroelastic constants...Rare-earth calcium oxyborate crystals(RECa_(4)O(BO_(3))_(3),RECOB,RE:rare-earth elements)are a kind of multifunctional crystal materials.In this work,the temperature dependent behaviors of the electroelastic constants of NdCOB crystal were investigated over the temperature range of-80-200℃,and their temperature coefficients were evaluated.It is found that NdCOB crystal possesses minimal variation of relative dielectric permittivities(<3%).The temperature coefficient of frequency for ZY cut with width shear vibration mode is in the order of 0.07×10^(-4)/℃.The temperature coefficients of the elastic compliances are obtained to be in the range of-33.0×10^(-4)/℃-32.2×10^(-4)/℃.Particularly,the sand swere found to show low temperature coefficients of the elastic compliances,i.e.1.0×10^(-4)/℃and-0.4×10^(-4)/℃,respectively,indicating the existence of zero temperature coefficient of frequency crystal cut.Furthermore,the electromechanical coupling factors and piezoelectric coefficients as a function of temperature were studied.The electromechanical coupling factor kand piezoelectric coefficient dare determined to be~30.8%and~15.2 pC/N at room temperature,respectively.The large piezoelectric response and zero temperature coefficient of frequency indicate the potential usage of NdCOB crystal for piezoelectric frequency devices over a wide temperature range.展开更多
Based on the force-heat equivalence energy density principle,a theoretical model for magnetic metallic materials is developed,which characterizes the temperature-dependent magnetic anisotropy energy by considering the...Based on the force-heat equivalence energy density principle,a theoretical model for magnetic metallic materials is developed,which characterizes the temperature-dependent magnetic anisotropy energy by considering the equivalent relationship between magnetic anisotropy energy and heat energy;then the relationship between the magnetic anisotropy constant and saturation magnetization is considered.Finally,we formulate a temperature-dependent model for saturation magnetization,revealing the inherent relationship between temperature and saturation magnetization.Our model predicts the saturation magnetization for nine different magnetic metallic materials at different temperatures,exhibiting satisfactory agreement with experimental data.Additionally,the experimental data used as reference points are at or near room temperature.Compared to other phenomenological theoretical models,this model is considerably more accessible than the data required at 0 K.The index included in our model is set to a constant value,which is equal to 10/3 for materials other than Fe,Co,and Ni.For transition metals(Fe,Co,and Ni in this paper),the index is 6 in the range of 0 K to 0.65T_(cr)(T_(cr) is the critical temperature),and 3 in the range of 0.65T_(cr) to T_(cr),unlike other models where the adjustable parameters vary according to each material.In addition,our model provides a new way to design and evaluate magnetic metallic materials with superior magnetic properties over a wide range of temperatures.展开更多
Half-Heusler(HH)compounds have emerged as promising candidates for high-temperature thermoelectric power generation;however,their mechanical properties in service environments have been scarcely reported.In this study...Half-Heusler(HH)compounds have emerged as promising candidates for high-temperature thermoelectric power generation;however,their mechanical properties in service environments have been scarcely reported.In this study,the temperature dependences of the mechanical responses and failure mechanisms of an n-type ZrNiSn-based HH compound(Zr_(0.5)Hf_(0.5)NiSn_(0.985)Sb_(0.015))were systematically evaluated through high-temperature compression tests and microfractographic characterization.The test results indicated that the elastic modulus and ultimate compressive strength of Zr_(0.5)Hf_(0.5)NiSn_(0.985)Sb_(0.015)decreased with increasing temperature.The stress-strain behavior of the material changed from linear(300,500,and 700 K)to nonlinear(900 and 1100 K).Microfractography observations revealed that increasing the temperature reduced the strength of the grain boundary as well as aggravated oxidation and segregation on the fracture surface,which significantly impacted the macro-compressive behavior of Zr_(0.5)Hf_(0.5)NiSn_(0.985)Sb_(0.015)at elevated temperatures.Finally,a stress-strain relationship for the ZrNiSnbased HH was proposed to describe the change in the compressive response from linear to nonlinear with increasing temperature.The present study elucidates the load-carrying and failure mechanisms of Zr_(0.5)Hf_(0.5)NiSn_(0.985)Sb_(0.015)within its operational temperature range,providing valuable guidance for the mechanical design of HH thermoelectric devices over their entire service temperature range.展开更多
The long-lasting expectation“the hotter the engine,the better”calls for the development of high-temperature metallic alloys.Although the high specific strengths of titanium alloys are compelling for such application...The long-lasting expectation“the hotter the engine,the better”calls for the development of high-temperature metallic alloys.Although the high specific strengths of titanium alloys are compelling for such applications,their deleterious softening beyond 600℃ imposes serious limitations.Much has been known for decades regarding the phase metallurgy for precipitation strengthening design in titanium alloys,however,the other facile strength promotion mechanism,dispersion strengthening,remains comparatively less-explored and unutilized.The present research concerns the multi-scale dispersion strengthening in titanium alloys,with mechanistic emphases on the critical plasticity micro-events that affect strength preservation.Due to the simultaneous introduction of intragranular dispersoids and intergranular reinforcers,the current titanium alloys present superior engineering tensile strength of 519 MPa at 700℃.Throughout the examined 25-800℃ temperature range,noticeable softening induced by the thermal activation occurs above 600℃,accompanied by evident strength loss.The temperature-dependence transition of dominated softening mechanisms from dynamic recovery to dynamic recrystallization has been clarified by theoretical calculations.Furthermore,the strengthening effect of multi-scale architectures is underpinned as the enhanced dislocation strengthening owing to the introduction of thermally-stable heterointerfaces,which could generically guide the design of similar heat-resistant titanium alloys.展开更多
CdSxSe1-x quantum dots were fabricated by a simple spin-coating heat volatilization method on InP wafer.Temperature dependent photoluminescence of CdSxSe1-x quantum dots was carried out in a range of 10-300 K.The inte...CdSxSe1-x quantum dots were fabricated by a simple spin-coating heat volatilization method on InP wafer.Temperature dependent photoluminescence of CdSxSe1-x quantum dots was carried out in a range of 10-300 K.The integrated photoluminescence intensity revealed an anomalous behavior with increasing temperature in the range of 180-200 K.The band gap energy showed a redshift of 61.34 meV when the temperature increased from 10 to 300 K.The component ratio of S to Se in the CdSxSe1-x quantum dots was valued by both the X-ray diffraction data and photoluminescence peak energy at room temperature according to Vegard Law.Moreover,the parameters of the Varshni relation for CdS0.9Se0.1 materials were also obtained using photoluminescence peak energy as a function of temperature and the best-fit curve:α=(3.5 ± 0.1)10-4 eV/K,and β=210 ± 10 K (close to the Debye temperature θD of the material).展开更多
In this study, Al/p-Si and Al/Bi4Ti3O12/p-Si structures are fabricated and their interface states （Nss）, the values of series resistance （Rs）, and AC electrical conductivity （σac） are obtained each as a functio...In this study, Al/p-Si and Al/Bi4Ti3O12/p-Si structures are fabricated and their interface states （Nss）, the values of series resistance （Rs）, and AC electrical conductivity （σac） are obtained each as a function of temperature using admit- tance spectroscopy method which includes capacitance-voltage （C-V） and conductance-voltage （G-V） measurements. In addition, the effect of interfacial Bi4Ti3012 （BTO） layer on the performance of the structure is investigated. The voltage- dependent profiles of Nss and Rs are obtained from the high-low frequency capacitance method and the Nicollian method, respectively. Experimental results show that Nss and Rs, as strong functions of temperature and applied bias voltage, each exhibit a peak, whose position shifts towards the reverse bias region, in the depletion region. Such a peak behavior is attributed to the particular distribution of Nss and the reordering and restructuring of Nss under the effect of temperature. The values of activation energy （Ea）, obtained from the slope of the Arrhenius plot, of both structures are obtained to be bias voltage-independent, and the Ea of the metal-ferroelectric-semiconductor （MFS） structure is found to be half that of the metal-semiconductor （MS） structure. Furthermore, other main electrical parameters, such as carrier concentration of acceptor atoms （NA）, built-in potential （Vbi）, Fermi energy （EF）, image force barrier lowering （△φb）, and barrier height （φb）, are extracted using reverse bias C 2-V characteristics as a function of temperature.展开更多
The entropy analysis of viscoelastic fluid obeying the simplified Phan-ThienTanner(SPTT)model with variable thermophysical properties are obtained for laminar,steady state and fully developed Couette-Poiseuille flow.T...The entropy analysis of viscoelastic fluid obeying the simplified Phan-ThienTanner(SPTT)model with variable thermophysical properties are obtained for laminar,steady state and fully developed Couette-Poiseuille flow.The homotopy perturbation method(HPM)allows us to solve nonlinear momentum and energy differential equations.The Reynold’s model is used to describe the temperature dependency of thermophysical properties.Results indicate that the increase of the group parameter(Br=U)and the Brinkman number(Br)which show the power of viscous dissipation effect;increases the entropy generation while increasing fluid elasticity(εDe2)decreases the generated entropy.Increasing the Reynolds variational parameter(a)which control the level of temperature dependence of physical properties attenuate entropy generation when moving plate and applied pressure gradient have the opposite direction and decreases entropy generation when moving plate and applied pressure gradient have the same direction or both plates are at rest.Also,increasing elasticity reduces the difference between variable and constant thermophysical properties cases.These results may give guidelines for cost optimization in industrial processes.展开更多
This study aims to investigate turbulent plasma flow using the lattice Boltzmann(LB)method.A double population model D2Q9-D2Q4 is employed to calculate the plasma velocity and temperature fields.Along with the calcula...This study aims to investigate turbulent plasma flow using the lattice Boltzmann(LB)method.A double population model D2Q9-D2Q4 is employed to calculate the plasma velocity and temperature fields.Along with the calculation process a conversion procedure is made between the LB and the physical unit systems,so that thermo-physical properties variation is fully accounted for and the convergence is checked in physical space.The configuration domain and the boundary condition treatment are selected based on the most cited studies in order to illustrate a realistic situation.The jet morphology analysis gives credible results by comparison with commonly published works.It was demonstrated also that accounting for the substrate as wall boundary condition modify greatly the flow and temperature structures with may affect absolutely the particles behavior during its in-flight in the hot gas.展开更多
The current-voltage characteristics of 4H-SiC junction barrier Schottky （JBS） diodes terminated by an offset field plate have been measured in the temperature range of 25-300℃. An experimental barrier height value ...The current-voltage characteristics of 4H-SiC junction barrier Schottky （JBS） diodes terminated by an offset field plate have been measured in the temperature range of 25-300℃. An experimental barrier height value of about 0.5 eV is obtained for the Ti/4H-SiC JBS diodes at room temperature. A decrease in the experimental barrier height and an increase in the ideality factor with decreasing temperature are shown. Reverse recovery testing also shows the temperature dependence of the peak recovery current density and the reverse recovery time. Finally, a discussion of reducing the reverse recovery time is presented.展开更多
The steady-state fluorescence spectra and molecular dynamics simulations were explored to investigate the temperature dependent organization in some imidazolium ionic liquids：1-butyl-3-methylimidazolium hexafluo-roph...The steady-state fluorescence spectra and molecular dynamics simulations were explored to investigate the temperature dependent organization in some imidazolium ionic liquids：1-butyl-3-methylimidazolium hexafluo-rophosphate（[bmim][PF6]）,1-ethyl-3-methylimidazolium ethylsulfate（[emim][EtSO4]） and 1-butyl-3-methylimida-zolium tetrafluoroborate（[bmim][BF4]）.The pure room temperature ionic liquids（ILs） exhibit a large red shift at more than an excitation wavelength of around 340 nm,which demonstrates the heterogeneous nature of the liquids.Furthermore,the fluorescence spectra of the ionic liquids were found to be temperature-dependent.The emission intensity gradually decreased with increasing temperature for the neat ionic liquids and the mixed solutions of [bmim][BF4]-H2O,which was the special phenomena induced by not only the local structure but also the viscosity.The molecular dynamics simulation further confirms that the structures of ionic liquids are sensitive to the surroun-ding environment because of the aggregation degree of ILs.展开更多
文摘Heat transfers due to MHD-conjugate free convection from the isothermal horizontal circular cylinder while viscosity is a function of temperature is investigated. The governing equations of the flow and connected boundary conditions are made dimensionless using a set of non-dimensional parameters. The governing equations are solved numerically using the finite difference method. Numerical results are obtained for various values of viscosity variation parameter, Prandtl number, magnetic parameter, and conjugate conduction parameter for the velocity and the temperature within the boundary layer as well as the skin friction coefficients and heat transfer rate along the surface.
文摘We discuss in this paper a novel interpretation of Born rule as an approximated thermodynamic law which emerges from the interaction of a quantum system with a non-stationary thermal bath associated to vacuum fluctuations induced by external environment radiation. In particular we assume that vacuum polarization is a real non relativistic phenomena caused by hidden vacuum charge oscillations which diffuses heat energy in a dispersive and dissipative dielectric medium with a temperature dependent speed of propagation. We propose a model which couples vacuum wavefunctions to vacuum charge fluctuations and we deduce a temperature dependent running fine structure constant function proportional, at first approximation, to the squared of the effective electron charge and compatible with known experimental data. We interpret the vacuum symmetry breaking energy fluctuations induced in scattering experiments of particle physics and in laser assisted nuclear reactions as thermal quasi-monochromatic beams produced by the decay of hidden non equilibrium massive photons propagating with a variable light speed. We suggest, exploiting an old analogy between plasmons and pseudo Goldstone bosons, to interpret heat diffusion of this non relativistic polarized vacuum as a real De Broglie electromagnetic scalar wave associated to the radiation emitted by the hidden massive photons with acceleration proportional to vacuum Unruh like temperature. We predict a temperature dependent deviation from Coulomb law and a generalized dispersive law of these hidden unstable photons that could be revealed as not stationary coloured noise in experiments on anomalous heat diffusions associated to the decay of unstable accelerated pairs produced in nuclear physics experiments. We discuss then how our proposal of a temperature dependent non relativistic vacuum polarization might be applied to deduce a dynamic generalization of Born rule based on a realistic interpretation of quantum wavefunctions as averaged electromagnetic waves of hidden massive photons. Finally we suggest to test our time asymmetric model looking for very fast oscillating polarization thermal waves emitted during the not instantaneous wavefunction collapse and revealed as not stationary bulk heating effects in experiments on accelerated conductors and nanoconductors.
文摘This paper deals with finite element study of the scanning induction heating of the magnetic steel sheets in transversal flux devices,taking into account the magnetic nonlinearity and the dependence on temperature of steel properties.The decrease of the non-uniformity of the transversal profile of sheet heating as effect of the magnetic or electromagnetic screening of the sheet lateral sides was proved.
文摘In this paper, we construct the equations of generalized thermoelasicity for a non-homogeneous isotropic hollow cylider with a variable modulus of elasticity and thermal conductivity based on the Lord and Shulman theory. The problem has been solved numerically using the finite element method. Numerical results for the displacement, the temperature, the radial stress, and the hoop stress distributions are illustrated graphically. Comparisons are made between the results predicted by the coupled theory and by the theory of generalized thermoelasticity with one relaxation time in the cases of temperature dependent and independent modulus of elasticity.
文摘The work-hardening behaviour in an Fe-Mn-Si-Cr-Ni alloy has been investigated using tensile test at different temperatures and TEM observation. It was found that besides the intersection of εmartensite, the intersections of ε martensite with stacking fault and the cross-slip of dislocation which is difficult to occur in the alloy with low stacking fault energy are also important factors to the temperature dependent work-hardening behaviour.
基金Project supported by the National Basic Research Program of China(Grant No.2011CBA00602)the National Science and Technology Major Project of the Ministry of Science and Technology of China(Grant No.2011ZX02708-002)
文摘GaSb p-channel metal-oxide-semiconductor field-effect transistors （MOSFETs） with an atomic layer deposited Al2O3 gate dielectric and a self-aligned Si-implanted source/drain are experimentally demonstrated. Temperature dependent electrical characteristics are investigated. Different electrical behaviors are observed in two temperature regions, and the un- derlying mechanisms are discussed. It is found that the reverse-bias pn junction leakage of the drain/substrate is the main component of the off-state drain leakage current, which is generation-current dominated in the low temperature regions and is diffusion-current dominated in the high temperature regions. Methods to further reduce the off-state drain leakage current are given.
文摘The prime objective of the present study is to examine the effect of tempera- ture dependent viscosity/z（T） on the revolving axi-symmetric laminar boundary layer flow of an incompressible, electrically non-conducting ferrofiuid in the presence of a stationary plate subjected to a magnetic field and maintained at a uniform temperature. To serve this purpose, the non-linear coupled partial differential equations are firstly converted into the ordinary differential equations using well-known similarity transformations. The popular finite difference method is employed to discretize the non-linear coupled differ- ential equations. These discretized equations are then solved using the Newton method in MATLAB, for which an initial guess is made with the help of the Flex PDE Solver. Along with the velocity profiles, the effects of temperature dependent viscosity are also examined on the skin friction, the heat transfer, and the boundary layer displacement thickness. The obtained results are presented numerically as well as graphically.
基金Project supported by the National Key R&D Program of China(Grant Nos.2016YFB0401801 and 2016YFB0400803)the National Natural Science Foundation of China(Grant Nos.61674138,61674139,61604145,61574135,61574134,61474142,61474110,61377020,and 61376089)+1 种基金Science Challenge Project,China(Grant No.JCKY2016212A503)Beijing Municipal Science and Technology Project,China(Grant No.Z161100002116037)
文摘Physical implications of the activation energy derived from temperature dependent photoluminescence（PL） of In Ga Nbased materials are investigated, finding that the activation energy is determined by the thermal decay processes involved.If the carrier escaping from localization states is responsible for the thermal quenching of PL intensity, as often occurs in In Ga N materials, the activation energy is related to the energy barrier height of localization states. An alternative possibility for the thermal decay of the PL intensity is the activation of nonradiative recombination processes, in which case thermal activation energy would be determined by the carrier capture process of the nonradiative recombination centers rather than by the ionization energy of the defects themselves.
基金supported by the National Basic Research Program of China(973 Program,2012CB821702)the National Natural Science Foundation of China(21233009 and 21173221)the State Key Laboratory of Structural Chemistry
文摘Temperature dependent assembly of two novel Cd coordination polymers with the phen and H2MIP ligands （phen = 1,10-phenanthrolion and H2MIP = 5-methyl-isophthalic acid）, formulated as Cd2（MIP）2（phen）2 （1） and Cd3（MIP）3（H2MIP）（phen）2 （2）. They have been structurally characterized by single-crystal X-ray diffraction, elemental analysis, FT-IR spectra and TGA. 1 crystallizes in the monoclinic space group P2/n, while 2 crystallizes in the triclinic space group P1. 1 shows a 2D （two-dimensional） plane and 2 shows a 1D （one-dimensional） chain. In addition, their solid-state luminescent properties have also been investigated.
基金Project supported by the National Natural Science Foundation of China(51872165)the Primary Research&Development Plan of Shandong Province(2019JZZY010313)+1 种基金Shandong Provincial Natural Science Foundation(ZR2020KA003)the Shandong Province Innovative Talents Support Program(62350070311104)。
文摘Rare-earth calcium oxyborate crystals(RECa_(4)O(BO_(3))_(3),RECOB,RE:rare-earth elements)are a kind of multifunctional crystal materials.In this work,the temperature dependent behaviors of the electroelastic constants of NdCOB crystal were investigated over the temperature range of-80-200℃,and their temperature coefficients were evaluated.It is found that NdCOB crystal possesses minimal variation of relative dielectric permittivities(<3%).The temperature coefficient of frequency for ZY cut with width shear vibration mode is in the order of 0.07×10^(-4)/℃.The temperature coefficients of the elastic compliances are obtained to be in the range of-33.0×10^(-4)/℃-32.2×10^(-4)/℃.Particularly,the sand swere found to show low temperature coefficients of the elastic compliances,i.e.1.0×10^(-4)/℃and-0.4×10^(-4)/℃,respectively,indicating the existence of zero temperature coefficient of frequency crystal cut.Furthermore,the electromechanical coupling factors and piezoelectric coefficients as a function of temperature were studied.The electromechanical coupling factor kand piezoelectric coefficient dare determined to be~30.8%and~15.2 pC/N at room temperature,respectively.The large piezoelectric response and zero temperature coefficient of frequency indicate the potential usage of NdCOB crystal for piezoelectric frequency devices over a wide temperature range.
基金Project supported by the Natural Science Foundation of Chongqing(Grant No.CSTB2022NSCQ-MSX0391)。
文摘Based on the force-heat equivalence energy density principle,a theoretical model for magnetic metallic materials is developed,which characterizes the temperature-dependent magnetic anisotropy energy by considering the equivalent relationship between magnetic anisotropy energy and heat energy;then the relationship between the magnetic anisotropy constant and saturation magnetization is considered.Finally,we formulate a temperature-dependent model for saturation magnetization,revealing the inherent relationship between temperature and saturation magnetization.Our model predicts the saturation magnetization for nine different magnetic metallic materials at different temperatures,exhibiting satisfactory agreement with experimental data.Additionally,the experimental data used as reference points are at or near room temperature.Compared to other phenomenological theoretical models,this model is considerably more accessible than the data required at 0 K.The index included in our model is set to a constant value,which is equal to 10/3 for materials other than Fe,Co,and Ni.For transition metals(Fe,Co,and Ni in this paper),the index is 6 in the range of 0 K to 0.65T_(cr)(T_(cr) is the critical temperature),and 3 in the range of 0.65T_(cr) to T_(cr),unlike other models where the adjustable parameters vary according to each material.In addition,our model provides a new way to design and evaluate magnetic metallic materials with superior magnetic properties over a wide range of temperatures.
基金supported by the National Natural Science Foundation of China(NSFC)(Grant Nos.U2141208 and 12141203)Shengqiang Bai acknowledges the support from the International Partnership Program of the Chinese Academy of Sciences(Grant No.121631KYSB20200012).
文摘Half-Heusler(HH)compounds have emerged as promising candidates for high-temperature thermoelectric power generation;however,their mechanical properties in service environments have been scarcely reported.In this study,the temperature dependences of the mechanical responses and failure mechanisms of an n-type ZrNiSn-based HH compound(Zr_(0.5)Hf_(0.5)NiSn_(0.985)Sb_(0.015))were systematically evaluated through high-temperature compression tests and microfractographic characterization.The test results indicated that the elastic modulus and ultimate compressive strength of Zr_(0.5)Hf_(0.5)NiSn_(0.985)Sb_(0.015)decreased with increasing temperature.The stress-strain behavior of the material changed from linear(300,500,and 700 K)to nonlinear(900 and 1100 K).Microfractography observations revealed that increasing the temperature reduced the strength of the grain boundary as well as aggravated oxidation and segregation on the fracture surface,which significantly impacted the macro-compressive behavior of Zr_(0.5)Hf_(0.5)NiSn_(0.985)Sb_(0.015)at elevated temperatures.Finally,a stress-strain relationship for the ZrNiSnbased HH was proposed to describe the change in the compressive response from linear to nonlinear with increasing temperature.The present study elucidates the load-carrying and failure mechanisms of Zr_(0.5)Hf_(0.5)NiSn_(0.985)Sb_(0.015)within its operational temperature range,providing valuable guidance for the mechanical design of HH thermoelectric devices over their entire service temperature range.
基金financially supported by the National Key R&D Program of China(No.2021YFB3701203)the National Natural Science Foundation of China(Nos.U22A20113,52261135543,52171137 and 52071116)the Heilongjiang Touyan Team Program,Heilongjiang Provincial Natural Science Foundation of China(No.TD2020E001).
文摘The long-lasting expectation“the hotter the engine,the better”calls for the development of high-temperature metallic alloys.Although the high specific strengths of titanium alloys are compelling for such applications,their deleterious softening beyond 600℃ imposes serious limitations.Much has been known for decades regarding the phase metallurgy for precipitation strengthening design in titanium alloys,however,the other facile strength promotion mechanism,dispersion strengthening,remains comparatively less-explored and unutilized.The present research concerns the multi-scale dispersion strengthening in titanium alloys,with mechanistic emphases on the critical plasticity micro-events that affect strength preservation.Due to the simultaneous introduction of intragranular dispersoids and intergranular reinforcers,the current titanium alloys present superior engineering tensile strength of 519 MPa at 700℃.Throughout the examined 25-800℃ temperature range,noticeable softening induced by the thermal activation occurs above 600℃,accompanied by evident strength loss.The temperature-dependence transition of dominated softening mechanisms from dynamic recovery to dynamic recrystallization has been clarified by theoretical calculations.Furthermore,the strengthening effect of multi-scale architectures is underpinned as the enhanced dislocation strengthening owing to the introduction of thermally-stable heterointerfaces,which could generically guide the design of similar heat-resistant titanium alloys.
基金supported by the NSFC (No. 50532080)the Key Laboratory Projects of The Education Department of Liaoning Province (No. 20060131)
文摘CdSxSe1-x quantum dots were fabricated by a simple spin-coating heat volatilization method on InP wafer.Temperature dependent photoluminescence of CdSxSe1-x quantum dots was carried out in a range of 10-300 K.The integrated photoluminescence intensity revealed an anomalous behavior with increasing temperature in the range of 180-200 K.The band gap energy showed a redshift of 61.34 meV when the temperature increased from 10 to 300 K.The component ratio of S to Se in the CdSxSe1-x quantum dots was valued by both the X-ray diffraction data and photoluminescence peak energy at room temperature according to Vegard Law.Moreover,the parameters of the Varshni relation for CdS0.9Se0.1 materials were also obtained using photoluminescence peak energy as a function of temperature and the best-fit curve:α=(3.5 ± 0.1)10-4 eV/K,and β=210 ± 10 K (close to the Debye temperature θD of the material).
文摘In this study, Al/p-Si and Al/Bi4Ti3O12/p-Si structures are fabricated and their interface states （Nss）, the values of series resistance （Rs）, and AC electrical conductivity （σac） are obtained each as a function of temperature using admit- tance spectroscopy method which includes capacitance-voltage （C-V） and conductance-voltage （G-V） measurements. In addition, the effect of interfacial Bi4Ti3012 （BTO） layer on the performance of the structure is investigated. The voltage- dependent profiles of Nss and Rs are obtained from the high-low frequency capacitance method and the Nicollian method, respectively. Experimental results show that Nss and Rs, as strong functions of temperature and applied bias voltage, each exhibit a peak, whose position shifts towards the reverse bias region, in the depletion region. Such a peak behavior is attributed to the particular distribution of Nss and the reordering and restructuring of Nss under the effect of temperature. The values of activation energy （Ea）, obtained from the slope of the Arrhenius plot, of both structures are obtained to be bias voltage-independent, and the Ea of the metal-ferroelectric-semiconductor （MFS） structure is found to be half that of the metal-semiconductor （MS） structure. Furthermore, other main electrical parameters, such as carrier concentration of acceptor atoms （NA）, built-in potential （Vbi）, Fermi energy （EF）, image force barrier lowering （△φb）, and barrier height （φb）, are extracted using reverse bias C 2-V characteristics as a function of temperature.
文摘The entropy analysis of viscoelastic fluid obeying the simplified Phan-ThienTanner(SPTT)model with variable thermophysical properties are obtained for laminar,steady state and fully developed Couette-Poiseuille flow.The homotopy perturbation method(HPM)allows us to solve nonlinear momentum and energy differential equations.The Reynold’s model is used to describe the temperature dependency of thermophysical properties.Results indicate that the increase of the group parameter(Br=U)and the Brinkman number(Br)which show the power of viscous dissipation effect;increases the entropy generation while increasing fluid elasticity(εDe2)decreases the generated entropy.Increasing the Reynolds variational parameter(a)which control the level of temperature dependence of physical properties attenuate entropy generation when moving plate and applied pressure gradient have the opposite direction and decreases entropy generation when moving plate and applied pressure gradient have the same direction or both plates are at rest.Also,increasing elasticity reduces the difference between variable and constant thermophysical properties cases.These results may give guidelines for cost optimization in industrial processes.
基金supported in part by the Ministry of Higher Education and Scientific Research of TunisiaThe first author would like to thank particularly the University of Limoges for the computational facilities provided by CALI calculation centre,and the”Fonds de dotation PERENNE”for financial supports.
文摘This study aims to investigate turbulent plasma flow using the lattice Boltzmann(LB)method.A double population model D2Q9-D2Q4 is employed to calculate the plasma velocity and temperature fields.Along with the calculation process a conversion procedure is made between the LB and the physical unit systems,so that thermo-physical properties variation is fully accounted for and the convergence is checked in physical space.The configuration domain and the boundary condition treatment are selected based on the most cited studies in order to illustrate a realistic situation.The jet morphology analysis gives credible results by comparison with commonly published works.It was demonstrated also that accounting for the substrate as wall boundary condition modify greatly the flow and temperature structures with may affect absolutely the particles behavior during its in-flight in the hot gas.
基金Project supported by the National Natural Science Foundation of China (Grant No. 61006060)the 13115 Innovation Engineering of Shaanxi, China (Grant No. 2008ZDKG-30)the Key Laboratory Fund of Ministry of Education, China (Grant No. JY0100112501)
文摘The current-voltage characteristics of 4H-SiC junction barrier Schottky （JBS） diodes terminated by an offset field plate have been measured in the temperature range of 25-300℃. An experimental barrier height value of about 0.5 eV is obtained for the Ti/4H-SiC JBS diodes at room temperature. A decrease in the experimental barrier height and an increase in the ideality factor with decreasing temperature are shown. Reverse recovery testing also shows the temperature dependence of the peak recovery current density and the reverse recovery time. Finally, a discussion of reducing the reverse recovery time is presented.
基金Supported by the National Natural Science Foundation of China(No.20973192,11079007)
文摘The steady-state fluorescence spectra and molecular dynamics simulations were explored to investigate the temperature dependent organization in some imidazolium ionic liquids：1-butyl-3-methylimidazolium hexafluo-rophosphate（[bmim][PF6]）,1-ethyl-3-methylimidazolium ethylsulfate（[emim][EtSO4]） and 1-butyl-3-methylimida-zolium tetrafluoroborate（[bmim][BF4]）.The pure room temperature ionic liquids（ILs） exhibit a large red shift at more than an excitation wavelength of around 340 nm,which demonstrates the heterogeneous nature of the liquids.Furthermore,the fluorescence spectra of the ionic liquids were found to be temperature-dependent.The emission intensity gradually decreased with increasing temperature for the neat ionic liquids and the mixed solutions of [bmim][BF4]-H2O,which was the special phenomena induced by not only the local structure but also the viscosity.The molecular dynamics simulation further confirms that the structures of ionic liquids are sensitive to the surroun-ding environment because of the aggregation degree of ILs.
