Thermodynamical Phase Equilibrium of Iron Nitrides at Low Temperatures

The presence of α-Fe(N),γ‘-Fe4N and ε-Fe2N1-x phases and the phase equilibrium between αFe(N) and γ′-Fe4N,and γ′-Fe4N and ε-Fe2N1-x have been studied at low temperatures below 350℃ ,according to the binary Fe-N phase diagram calculated using the sublattice-compound energy model,The α-Fe(N),γ′-Fe4N and ε-Fe2N1-x phases would be thermodynamically stable at the low temperatures.Thermodynamic phase equilibrium of the iron nitrides is supproted by the experimental results,explaining the phase formation and its stability in the Fe-N system at low temperatures.     

Current-Voltage Characteristics of Molecular Devices at Low Bias

We use density functional theory and the Green function formalism with charge energy effect included in the self-consistent calculation of the I-V characteristics of a single benzene ring with an appendage of cf3, and identify some interesting properties of the I-V characteristics at low bias. The molecule picks up a fractional charge at zero bias, then the additional fractional charge produces a barrier on the junction of the molecule and contacts to perturb current flow on the molecule. This phenomenon may be useful for the design of future molecular devices.     

The Griineisen Parameter of NaC1 at High Pressures and Temperatures： a Molecular Dynamics Study

The isotherms and Grǖneisen parameters are calculated by using the molecular dynamics (MD) method with an improved Tosi-Fumi pair potential. The results show that the approximate power law dependence of the Grǖneisen parameter on compression γ=γ0（V/V0）^q, with q≈1.078, holds in the temperature range from 298 to 1073K and pressure range from 0 to 60 GPa, and that the Grfineisen parameter for a given density of 2.16 g/cm^3 varies with temperature in a wind range from 300 to I O000 K, expressed by γ=1.052 0.582exp(-T/ 4878.56).     

Equation of State of the Fluid He-Ne Binary Mixtures at High Pressures and High Temperatures

The fluid variational free energy model is applied to calculate the equation of state (EOS) of the fluid (Ne/3,2He/3) mixtures at 296K. The pair potential is used to describe the He-Ne interaction. The calculated EOSs at 296Kare compared with the experiments for solid Ne(He)2. The validity of the potential and the calculated model is verified by comparison. The present model is extended to calculate the equation of state of the fluid He-Ne mixtures with different He:Ne compositions in the pressure 0-160 GPa and temperature up to 10000 K.     

Theoretical Study of the Opacity for Mixture Materials at High Temperatures

Using a detailed configuration accounting model with term structures treated by the umresolved transition array model,we have extensively investigated the opacitiesof mixture materials.For plasmas at the temperature of 250 eV and density of 1 g/cm^3,our calculated Rosseland mean opacities are in good agreement with other theoretical results.A high increase in the Rosseland mean opacity to 2944cm^2/g is achieved for a multi-element mixture compared to the value of 1729cm^2/g for pure gold.Various mixtures at other plasma conditions are also studied.     

The Kac Version of the Sherrington–Kirkpatrick Model at High Temperatures

We study the Kac version of the Sherrington–Kirkpatrick (SK) model of a spin glass, i.e., a spin glass with long- but finite-range interaction on and Gaussian mean zero couplings. We prove that for all < 1, the free energy of this model converges to that of the SK model as the range of the interaction tends to infinity. Moreover, we prove that for all temperatures for which the infinite-volume Gibbs state is unique, the free energy scaled by the square root of the volume converges to a Gaussian with variance c _, , where ^–1 is the range of the interaction. Moreover, at least for almost all values of , this variance tends to zero as goes to zero, the value in the SK model. We interpret our finding as a weak indication that at least at high temperatures, the SK model can be seen as a reasonable asymptotic model for lattice spin glasses.     

Disordering in Stone—Wales Graphene at High Temperatures

JETP Letters - Thermally activated structural disordering is numerically studied in Stone—Wales graphene, which is a recently predicted new allotropic modification of graphene. The elastic...     

Magnetic and Thermal Behaviour of One-Dimensional Antiferromagnetic Spin-1 Ising Chain at Low Temperatures

We investigate magnetic and thermal behaviours of one-dimensional antiferromagnetic spin-i Ising chain with single-ion anisotropy at very low temperatures using the classical transfer matrix technique. Magnetic plateaus, phase diagram, specific heat, susceptibility of the spin chain have been evaluated numerically from the free energy. The results are in good agreement with the experimental data for the spin-1 compounds [Ni2 （Medpt）2 （μ- ox）（H2O）2]（ClO4）22H2O, [Ni2（Medpt）2（μ-ox）（μ-N3）]（ClO4）0.5H2O, Ni（C2H8N2）Ni（CN）4 and Ni（C10H8N2）2 Ni（CN）4·H2O.     

High Two-Beam Coupling Coefficients of Monolithic Small Molecule at Low Electric Field

A novel full-functional photorefractive small molecular material, (9-ethyl-9H-carbazol-3-ylmethylene)-(4-nitrophenyl)-amine (ECYENPA), was synthesized and its photorefractivity was studied by two-beam coupling experiments at a wavelength of 632.8nm. The glass transition temperature of ECYENPA, as low as -5℃, results in the chromophore being orientated easily at room temperature. High two-beam coupling coefficient was obtained to be 232cm^-1 at an electric field of 44.6 V/μm.     

Neutrino Mean Free Path in Strange Matter at High Temperatures

We investigate the condition that the neutrino energies E_v can be considered to be small enough to be neglected in the energy momentum conservation equation in the reactions d+v_e → u+e^- and u+e^- → d+v_e. It can be simply expressed as E_v < 4α_cμ_e/π, where α_c is the strong coupling constant and μ_e is the electron chemical potential. Then for E_v < 4α_cμ_e/π, we generalize the mean free path for nondegenerate neutrinos given by Iwamoto and obtain a formula that is valid for both nondegenerate and degenerate neutrinos. We also model the mean free path for both nondegenerate and degenerate neutrinos with energies E_v < 4α_cμ_e/π.     

Boron–Carbon Nanocomposites Fabricated at High Pressures and Temperatures

Interaction of amorphous boron and C₆₀ fullerite is analyzed at pressures of 2.0 and 7.7. GPa and temperatures of 600–1800°C. Effect of pressure and temperature on the material structure is studied, temperatures for synthesis of boron carbide and diamond are found, and the sequence of transformations of the carbon component is determined. Ultrasonic method is used to measure elastic moduli of the samples, and the dependences of the moduli on the structure are analyzed. It is demonstrated that the boron–carbon nanocomposite synthesized at relatively low pressure (2.0 GPa) and temperature (about 1000°C) exhibits high elastic parameters (bulk modulus, B ≈ 75.3–84.0 GPa; Young modulus, E ≈ 108–119 GPa; and shear modulus, G ≈ 43–47 GPa at a density of about 2.2 g/cm³). The results can be used for development of novel nanocomposite materials.     

Magnetic Susceptibility of Intermetallic Compounds in a REM—Al System at High Temperatures

The Faraday method is used to study for the first time the temperature dependence of the magnetic susceptibility of intermetallic compounds of rare-earth metals (REM = Gd, Dy, Ho, and Er) with aluminum in a wide temperature interval from room temperature to 1700°C encompassing their solid state, melting process, and liquid state. It is established that for all examined compounds, except the Gd–Al system, the dependence (T) is linear. It is described by the modified Curie–Weiss law for solid and liquid compounds of the Gd–Al system. The Curie paramagnetic temperature _p, the Curie–Weiss constant C, the temperature-independent susceptibility component, and the effective magnetic moments _eff per REM atom are calculated on a computer by the least-squares method based on the dependence ^–1(T). The indirect exchange interaction parameter of the examined compounds is also calculated semi-empirically.     

Numerical Simulation of the Movement of Frenkel–Kontorova Dislocations in Aluminum Single Crystals at Low Temperatures

The motion of Frenkel–Kontorova dislocations in the single crystals of aluminum at low temperatures has been studied, by means of the computer simulation. It is shown that the dislocation movement is realized by the quantum tunneling of the kinks of dislocations through the Peierls barriers. It is shown that the action of the Peierls high barrier is analogous to the action of low temperatures, and if the Peierls barrier overcome, the dislocation moves unevenly, accelerating under the action of the Peierls barrier and slowing down after overcoming the Peierls barrier. Based on the numerical experiment, the mean free path of dislocation, the distance between the Peierls potential barriers and the width of the Peierls barrier are calculated. The computed values correspond to the real values.     

Low‐temperature and high-pressure apparatus developed at ISSP,University of Tokyo

A high-pressure apparatus with cubic-anvil device has been successfully working for more than 10 years at low temperatures down to 2?K under quasi-hydrostatic pressure up to 10?GPa in study of solid-state physics. Main parts of it are composed of a set of compact cubic-anvils, a top-loading high-pressure cryostat and a 250?ton press. All the particulars of the cubic-anvil apparatus are given, including pressure calibrations at low temperature.     

Effect of γ-Radiation on the Conduction Phenomena of Amorphous As4Se4Te2 at Low Temperatures

The I–V characteristic of amorphous As₄Se₄Te₂ was studied at relatively low temperature ranging from – 158°C to –67°C. Three distinct regions of current-voltage range were observed and discussed on the basis of space-charge limited-current mechanism. A number of conduction parameters were calculated for fresh and γ-radiation samples. The effect of γ-radiation and thermal annealing process on the conduction behaviour of the test sample and on the conduction parameters were also discussed.     

A New High Power Microwave Source Operated at Low Magnetic Field

A new tpye of high power microwave souce operated at low magnetic filed is proposed and studied by the particle-in-cell (PIC) method.An oversized uniform backward-wave-oscillator-like structure is connected to a tapered slow-wave structure by a resonalt cavity.In this device,the electron beam current is effectively used to yield microwaves with high efficientcy,and the mode is locked in a wide range of diode voltage to reduce the requirement to the voltage wave form.The PIC siumlation results show that a peak microwave power of 2.1 GW (averaged 1.1GW) with a pure TM01 mode at 10.7GHz is radiated with 4.1GW input beam power,the frequency remains approximately the same when the diode voltage changed from 300kV to 700kV.     

The Preparation and Study on Ultrahigh Molecular Weight Polypropylene Gel‐spun Fibers

A novel polypropylene (PP) fiber was prepared by using gel spinning/crystallization from dilute solutions of ultrahigh molecular weight isotactic polypropylene (i‐UHMWPP), and subsequently drawing at various temperatures. The influence of drawing temperature on the properties of the resulted fibers was investigated. We found that the draw‐ability and mechanical as well as crystallization properties of the fibers obtained were dramatically improved with increasing drawing temperature. When the drawing temperature is below the α‐crystal relaxation temperature of PP, which was measured by wide‐angle X‐ray diffraction (WAXD) analysis as 100–120°C, the fibers are characterized by lower crystallinity and smaller crystals with less perfection, resulting in brittle fracture and subsequently poor mechanical durability. With drawing at temperatures above the α‐crystal relaxation temperature of PP, a novel UHMWPP fiber with Young's modulus of 27 GPa and tensile strength of 1.3 GPa was obtained. Higher crystallinity and larger crystals with better perfection and orientation were observed in this fiber.     

Study on Phase Formation and Evolution of High Impact Polystyrene with Poly(Cis‐Butadiene) Rubber Blends

Phase formation and evolution of high‐impact polystyrene with poly(cis‐butadiene) rubber blends was studied. The characteristic length, L, was defined to describe the size of particles, and the graph‐estimation method was introduced to determine the width of the distribution of L. Based on the method, the distribution of L proved to be a log‐normal distribution and the distribution width of L was calculated. The phase structure was also discussed in the wave‐number space. The correlation distance, a _c , was defined and computed, applying light‐scattering theory to power spectrum images obtained by 2‐dimensional Fourier transformation (2DFT). The change of a _c was in accord with that of L, which meant 2DFT was valid to study the phase structure. A fractal dimension, D _c , was introduced to describe the uniformity of the spatial distribution. The result showed that D _c was an effective parameter to study the distribution of particles of the dispersed phase.     

Molecular‐dynamics simulation of YBa2Cu3O7 at high temperatures

Molecular-dynamics simulation of YBa₂Cu₃O₇ is carried out to study the oxygen-atom distribution at high temperatures as the system undergoes the orthorhombic-to-tetragonal phase transition. While at the transition the one-dimensional arrangement of oxygen atoms in the Cul(0,0,0)-O4(0, 1/2, 0) chains begins to disorder, at temperatures above the transition the simulation also indicates the presence of a few vacancies at the O1(0, 0, z) sites. At still higher temperatures vacancies occur at all the oxygen sites. The simulation utilises an interatomic potential based on an unscreened rigid-ion model which was earlier found to be useful in understanding the structure, phonon density of states, and related properties. The thermal expansion, as obtained from the zero-pressure simulation, is in reasonable agreement with the observations of Jorgensen et al. on the oxygen-deficient system. The melting temperature obtained from the simulation is also in fair agreement with experiment.     

Phase Behavior of Poly(Ethylene Oxide) Studied by Modulated‐Temperature DSC—Influence of the Molecular Weight

Abstract

Melting and crystallization behavior of poly(ethylene oxide) (PEO) with different molecular weight was investigated by modulated‐temperature differential scanning calorimetry (MT‐DSC)—step‐scan alternating DSC. It was found that by separating the reversing and nonreversing components of the (total) heat flow, PEO 10000, which exhibits the highest degree of crystallinity, shows the smallest nonreversing signal during crystallization. This effect can be attributed to the favorable structural features associated with spacial alignment. On the other hand, the crystallization process of PEO with molecular weight of 3400 is hindered by a relatively high content of end groups that may cause defects in the crystal lattice. For PEO 35000, low segmental mobility and chain entanglements lower the rate of crystallization. The area of the reversing component of PEO melting for different molecular weight fractions confirms that for PEO 10000, recrystallization is less intensive than for both the lower and higher molecular weight analogues.