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.     

Phase Equilibrium and Critical Phenomena in the n-Pentan–Water and n-Hexane–Water Systems at High Temperatures and Pressures

Russian Physics Journal - PVTx-properties of the H2O – n-C5H12 and H2O – n-C6H14 mixtures are measured in the temperature range 303-680 K at pressures up to 60 MPa. The measurements...     

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).     

Preparation and Physical Properties of Carbon Nanotubes–PVA Nanocomposites

Nanocomposite materials were prepared by incorporating multiwall carbon nanotubes (MWNTs), obtained by acetylene catalytic chemical vapor deposition (CCVD) on Co/Fe‐modified MgO, within poly(vinyl alcohol) (PVA). Before incorporation, nanotubes were oxidized to obtain better compatibilization with the polymer. It has been found that the addition of COOH‐functionalized and purified MWNTs improves the mechanical response, increases the glass transition temperature, and delays the thermal oxidation of PVA. Furthermore, the PVA crystallinity seems to be enhanced by the presence of nanotubes.     

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...     

Phase Transformations in Nd–Fe–B-Based Alloys under High Pressure Torsion at Different Temperatures

In this work, we studied the behavior of the Nd–Dy–Fe–Co–Cu–B alloy for permanent magnets under high pressure torsion (HPT). In the initial state of the studied alloy, it mainly contained the crystalline phase τ₁ (Nd, Dy)₂(Fe, Co, Cu) ₁₄B. After HPT at room temperature (T_HPT = 30°C), a mixture of an amorphous phase with nanocrystalline inclusions of the τ₁ phase is observed in the alloy. In the equilibrium phase diagram, this state is equivalent to a mixture of the τ₁ phase with the melt at the temperature T_eff= ∼1100°C. The thus determined T_eff value is called the effective temperature. When the T_HPT temperature of the HPT treatment increases to 300 and 400°C, the amorphous phase disappears, and the Fe₂B and γ-Fe phases appear instead. In the equilibrium phase diagram, this state is equivalent to a mixture of phases τ₁+ Fe₂B + γ-Fe, which is observed in the temperature range from ∼950 to ∼1050°C. We explain this phenomenon by the fact that with an increase in the HPT temperature T_HPT, the rate of formation of defects during deformation remains constant, but the rate of their thermal relaxation (annihilation) increases. This is equivalent to decrease in the effective temperature T_eff in the equilibrium phase diagram. The previously predicted decrease in T_eff with an increase in T_HPT is observed for the first time.

     

Solving the Dyson–Schwinger Equation at Zero and Finite Temperatures

The properties of the solutions of the truncated Dyson–Schwinger equation for the quark propagator at finite temperatures within the rainbow-ladder approximation are analysed in some detail.     

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.     

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.     

Tracy–Widom at High Temperature

We investigate the marginal distribution of the bottom eigenvalues of the stochastic Airy operator when the inverse temperature \(\beta \) tends to \(0\) . We prove that the minimal eigenvalue, whose fluctuations are governed by the Tracy–Widom \(\beta \) law, converges weakly, when properly centered and scaled, to the Gumbel distribution. More generally we obtain the convergence in law of the marginal distribution of any eigenvalue with given index \(k\) . Those convergences are obtained after a careful analysis of the explosion times process of the Riccati diffusion associated to the stochastic Airy operator. We show that the empirical measure of the explosion times converges weakly to a Poisson point process using estimates proved in Dumaz and Virág (Ann Inst H Poincaré Probab Statist 49(4):915–933, 2013). We further compute the empirical eigenvalue density of the stochastic Airy ensemble on the macroscopic scale when \(\beta \rightarrow 0\) . As an application, we investigate the maximal eigenvalues statistics of \(\beta _N\) -ensembles when the repulsion parameter \(\beta _N\rightarrow 0\) when \(N\rightarrow +\infty \) . We study the double scaling limit \(N\rightarrow +\infty , \beta _N \rightarrow 0\) and argue with heuristic and numerical arguments that the statistics of the marginal distributions can be deduced following the ideas of Edelman and Sutton (J Stat Phys 127(6):1121–1165, 2007) and Ramírez et al. (J Am Math Soc 24:919–944, 2011) from our later study of the stochastic Airy operator.     

Shock Melting Temperature of Initially Porous Iron and Indication for Melting Curve of Iron at High Pressures

The melting curve of iron is crucial for modelling of the earth‘s internal heat structures and to understand melting of solids at high pressures. However, the measured melting temperatures of iron at high pressures are disparate so far. We measured the shocked interface (porous iron/sapphire window) temperatures of a kind of porous iron.By using a model for shock temperature measurement [High Pressures Res. 2 (1990) 159] and the previous results of sound velocity measurements [Chin. Phys. Lett. 18 (2001) 852], we determine the melting temperatures of iron at shock compression high pressures of 145 and 171 GPa. They are consistent with the results reported by other shock compression experiments. Based on the possible different melting mechanisms of iron in diamond anvil cell and in shock compression, the corrected melting temperatures of iron at high pressures become more consistent.     

Novel Superconducting Electrides in Ca–S System under High Pressures

Due to their unique structure properties,most of the electrides that possess extra electrons locating in interstitial regions as anions are insulators.Metallic and superconducting electrides are very rare under ambient conditions.We systematically search possible compounds in Ca-S systems stabilized under various pressures up to 200 GPa,and investigate their crystal structures and properties using first-principles calculations.We predict a series of novel stoichiometries in Ca-S systems as potential superconductors,including P2_1/m Ca_3S, Pnma C_a3S,Pnma Ca_2S,Cmcm Ca_2S,Fddd CaS_2,Immm CaS_3 and C2/c CaS_4.The P4mbm Ca_3S phase exhibits a maximum T_c value of ～20K.It is interesting to notice that the P2_1/m Ca_3S and Pnma Ca_2S stabilized at 60 and 50 GPa behave as superconducting electrides with critical temperatures T_c of 7.04 K and 0.26 K,respectively.More importantly,our results demonstrate that P2_1/m Ca_3S and Pnma Ca_2S are dynamically stable at 5 GPa and 0 GPa,respectively,indicating a high possibility to be quenched to ambient condition or synthesized using the large volume press.     

Electrical Resistance and Magnetoresistance of Cd3As2–30 mol % MnAs under High Pressures

Physics of the Solid State - The paper presents the results of a study on the Electrical resistance and magneto-resistance (MR) of the composite, consisting of a Dirac semimetal Cd3As2 and 30 mol %...     

Chemical Synthesis and Characterization of Flaky h-BCN at High Pressure and High Temperature

Hexagonal boron carbonitrogen （h-BCN） compound is synthesized from a mixture of boron powder and CNH compound prepared by pyrolysis of melamine （CaH6N6） under high temperature （1400-1500℃） and high pressure （5.0-5.5 GPa）. X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and Raman spec- troscopy are used to determine the chemical composition and bonds of the product. The results show that the product has composition of B0.18C0.64N0.16 （near BC4N） and atomic-level hybrid. X-ray diffraction analysis indicates that the powder has a hexagonal network structure. Scanning and transmission electron microscopy results suggest that h-BCN compound morphology is mainly flaky in width about 1 μm and thickness 200nm.     

Autoadhesion of High‐Molecular‐Weight Monodisperse Glassy Polystyrene at Unexpectedly Low Temperatures

Abstract

Healing of symmetric interfaces of amorphous anionically polymerized high‐ and ultrahigh‐molecular weight (HMW and UHMW, respectively) polystyrene (PS) in a range of the weight‐average molecular weight M _w from 102.5 (M _w/M _n = 1.05) to 1110 kg/mol (M _w/M _n = 1.15) was followed at a constant healing temperature, T _h, well below the glass transition temperature of the polymer bulk [T _g‐bulk = 105–106°C as measured by differential scanning calorimeter (DSC)]. The bonded interfaces were shear fractured in tension on an Instron tester at ambient temperature. Autoadhesion at symmetric HMW PS–HMW PS and UHMW PS–UHMW PS interfaces was detected mechanically after healing at T _h = 38°C for 107 hr, and even at 24°C (for longer healing times). The occurrence of autoadhesion between the surfaces of the UHMW PS with M _w = 1110 kg/mol at 24°C implies that the glass transition temperature at the interface, T _{g‐interface}, of this polymer was a least lower: by 82°C than its DSC T _g‐bulk, by 30–40°C than the Vogel temperature, T _∞—the lowest theoretical value of a kinetic T _g‐bulk at infinite long time—and by 20°C than T ₂ (a “true” thermodynamic T _g‐bulk corresponding to a second‐order phase transition temperature). To our knowledge, this is the first observation of such nature, which gives further evidence of the lowering of the T _g at polymeric surfaces and the persistence of this effect at early stages of healing of polymer–polymer interfaces.     

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.     

Interface Instability of Diamond Crystals at High Temperature and High Pressure

Diamond growth instability at high temperature and high pressure (HPHT) has been elucidated by observing the cellular interface in diamond crystals.The HPHT diamond crystals grow layer by layer from solution of carbon in the molten catalyst.In the growth of any other cyrstals from solution,the growth interface is not stable and should be of the greatest significance to understand further the diamond growth mechanism.During the diamond growth,the carbon atoms are delivered to the growing diamond crystal by diffusion through a diamond crystal-solution boundary layer.In front of the boundary layer,there is a narrow constitutional supercooling zone related to the solubility difference between diamond and graphite in the molten catalyst.The diamond growth stability is broken,and the flat or planar growth interface transforms into a cellular interface due to the light supercooling.The phenomenon of solute trails in the diamonds was observed,the formation of solute trails was closely associated with the cellular interface.