Lost heat capacity and entropy in the helical magnet MnSi

The heat capacity of MnSi at B = 0 and B = 4 T was measured in the temperature range 2.5-100 K. To analyze the data, calculations of the phonon spectrum and phonon density of states in MnSi were performed. The calculated phonon frequencies were confirmed by means of inelastic neutron scattering. The analysis of the data suggests the existence of negative contributions to the heat capacity and entropy of MnSi at T > T(c) that may imply a specific ordering in the spin subsystem in the paramagnetic phase of MnSi.     

On the correlation between thermal expansion coefficient and heat capacity of argon cryocrystals

A detailed analysis of the correlation between the volumetric thermal expansion coefficient o(T) and heat capacity C(T) of a rare-gas (Ar) cryocrystal has been performed. It has been shown that there is a clear correlation dependence o(C) not only in the low-temperature range, where it is linear and known as the Grüneisen law, but also in a significantly wider temperature range (up to the melting point of argon). The dependence o(C) substantially deviates from the low-temperature linear behavior when the heat capacity reaches the classical Dulong-Petit limit of 3R.     

Electron heat capacity and lattice properties of Americium

The temperature dependence of the electron heat capacity of americium is calculated using the concepts on the electronic structure and magnetic properties of this element. The Debye temperature, the thermal expansion coefficient, and the bulk modulus of americium are determined on the basis of the results of calculations and experimental data on heat capacity.     

氩离子原子过程参数的系统计算与评估：Ⅰ电子碰撞激发

利用准相对论扭曲波玻恩近似加交换方法，在组态平均近似下，系统地计算了类氢、类氦、类锂氩离子n≤6的各组态之间的碰撞激发过程截面。并和已有的理论结果进行了详细的对比分析。计算结果和相对论扭曲波近似的计算结果符合得很好，相对偏差一般都小于10％。由于没有考虑共振效应。计算的结果与强耦合方法的计算结果在入射电子能量较低的情况下有较大偏差，其他情况则符合较好，相对偏差一般在15％以内。该方法可以方便地计算大量应用所需的原子过程参数。     

Anomalous influence of spin fluctuations on the heat capacity and entropy in a strongly correlated helical ferromagnet MnSi

The influence of spin fluctuations on the thermodynamic properties of a helical ferromagnet MnSi has been investigated in the framework of the Hubbard model with the electronic spectrum determined from the first-principles LDA + U + SO calculation, which is extended taking into account the Hund coupling and the Dzyaloshinskii–Moriya antisymmetric exchange. It has been shown that the ground state of the magnetic material is characterized by large zero-point fluctuations, which disappear at the temperature T* (<T _c is the temperature of the magnetic phase transition). In this case, the entropy abruptly increases, and a lambdashaped anomaly appears in the temperature dependence of the heat capacity at constant volume (C _V (T)). In the temperature range T* < T < T _c , thermal fluctuations lead to the disappearance of the inhomogeneous magnetization. The competition between the increase in the entropy due to paramagnon excitations and its decrease as a result of the reduction in the amplitude of local magnetic moments, under the conditions of strong Hund exchange, is responsible for in the appearance of a “shoulder” in the dependence C _V (T)).     

利用简单方法分析定压热容Cp和熵S对压强与温度的依赖性

假设α(T,p)Bτ(T,p)=α(T0,O)Bτ(T0,0),并运用考虑热压项之后的Tait方程,提出了一种简单而直接的方法来计算不同温度和压强条件下定压热容Cp和熵S的值．将这种方法应用于NaCl晶体和液体甲醇,计算值与可提供的数据吻合得很好．     

Relativistic Boltzmann theory for a plasma: I. The entropy production

An expression for the entropy production has been derived on the basis of which it is argued that the choice of reference frame as proposed by Landau and Lifshitz is to be preferred rather than any other possibility.     

Negative entropy,energy, and heat capacity in connection with surface tension: Artifact of a model or real?

It is only byneglecting self-adsorption (a treatment referred to as “pure-energy,” PE) that one gets textbook thermodynamics of a surface, based upon the tensionL as a function of temperatureT, and one finds negative specific heat for hot water. Any lower critical point and PE provides the other exciting negatives: nicotine-and-water is an example. In order toinclude adsorption,L must be known in terms ofT and chemical potentials asindependent variables; this forces measurement of the tension of curved menisci. Will the minus signs remain?     

On the time and cell dependence of the coarse-grained entropy. I

We consider a finite, thermally isolated, classical system which passes from an equilibrium state $\text{A}$ by the removal of an internal constraint to another equilibrium state $\text{B}$ after an empirical relaxation time. In the phase space of the system, cells are introduced according to the set of measuring instruments used and their experimental inaccuracies. It is shown that the coarse-grained entropy S_cg(t) tends to its new equilibrium value in general faster than the expectation values of the macroscopic variables to their new equilibrium values. We then investigate the dependence of S_cg(t) on the size of the phase cells. For fixed t, we find a lower bound on S_cg(t) by doing to the limit of infinite accuracy of the measuring instruments. In the limit t → ∞, this lower bound on S_cg(t) also converges to the equilibrium entropy of $\text{B}$. These properties strongly support the opinion that S_cg(t) is a proper microscopic expression for the entropy for equilibrium and nonequilibrium. Finally, explicit calculations of S_cg(t) for the model of a point particle enclosed in a one-dimensional box are presented which confirm the general results.     

The properties of argon at its triple point

Using the interaction energy between argon atoms deduced in a previous paper from the properties of the crystal and the gas and regarding the liquid as an approximately equimolar mixture of structures with coordination numbers z = 12 and z = 8 we have calculated the total energy of the liquid at the triple point in good agreement with experiment.     

Elastic properties and heat capacity of opal matrices and related 3D-nanocomposite materials

The elastic properties of opal matrices and related 3D-nanocomposites, as well as their heat capacity, have been investigated. The velocities and attenuation coefficients of longitudinal and transverse waves have been measured at room temperature. The Debye temperature has been calculated from the velocities of ultrasound. The temperature dependence of the heat capacity of the opal matrix has been studied. It has been shown that the low-temperature part of this dependence contains contributions proportional to the first and third powers of the temperature. It has been found that the Debye temperatures determined from the velocities of ultrasound and those obtained from the heat capacity differ significantly.     

The temperature dependence of nanocrystal heat capacity

The temperature dependence of the specific (per atom) entropy and heat capacity of a nanocrystal is studied using a nanocrystal model in the form of a rectangular parallelepiped with variable surface shape. Accounting for the temperature dependence of the surface energy showed that the temperature dependence of the surface contribution to specific entropy is described by the same function that determines the temperature dependence of the isochoric heat capacity of a macrocrystal. Thus, at T → 0 K at T/Θ > 2 the surface contribution to the specific heat is zero. The maximal surface contribution to specific heat is reached at T/Θ = 0.2026 and is equal to c _st/k _B = 1.0115 (where k _B is the Boltzmann constant, Θ is the characteristic temperature depending both on the size and the shape of the nanocrystal). The applicability of the Grüneisen rule for a nanocrystal both at low and high temperatures is studied. It has been found that a case when the surface contribution to specific heat would be negative c(N) < c(∞), i.e. c _st(N) < 0 can occur for nanocrystals with a noncubic habitus.     

Calculation of radiative heat transfer in argon arc plasmas

Radiation emission and absorption in arc plasmas are important energy transfer processes. Exact calculations, though possible in principle, are usually impossible in practice because of the need to treat a large number of spectral lines and also the continuum radiation in the whole spectrum range. Recently, we have used an approximate method of partial characteristics to evaluate the radiation intensities, radiation fluxes and the divergence of radiation fluxes for SF₆ arc plasma with cylindrical symmetry. In this paper, we have extended our calculations toargon arc plasmas for the plasma pressures of 0.1, 0.5 and 1.0 MPa. We have calculated the coefficients of absorption for Ar plasmas at temperatures from 300 to 35 000 K, and have used these coefficients to calculate the partial characteristics. Both the continuum and the line spectra have been included in calculations. We have taken into account the radiative photo-recombination and bremsstrahlung for the continuous spectrum, and over 500 spectral lines for the discrete spectra.The method of partial characteristics has been applied to three-dimensional calculations of radiative heat transfer — i.e. radiation intensity, radiation flux and its divergence — in simplified temperature profiles. Conclusions have been made concerning validity and utilization of the method of partial characteristics in general gas dynamics problems.     

D-Dimensional ideal gas in parastatistics: Thermodynamic properties

We consider a parastatistics ideal gas with energy spectrum ¦k¦ (>0) or even more generally in ad-dimensional box with volumeV (periodic boundary conditions), the numberN of the gas particles being well determined (real particles) or not (quasiparticles). We calculate the main thermodynamic quantities (chemical potential, internal energy, specific heatC, equation of state, latent heat, average numbers of particles) for arbitraryd, ,T (temperature), andp (maximal number of particles per state allowed in the parastatistics). The main asymptotic regimes are worked out explicitly. In particular, the Bose-Einstein condensation for fixed densityN/V appears as a nonuniform convergence in thep limit, in complete analogy with the standard critical phenomena that appear in interacting systems in theN limit. The system behaves essentially like a Fermi-Dirac one forall finite values ofp, and reveals a Bose-Einstein behavioronly in thep limit. For instance, at low temperaturesC T ifp< andC T ^d/ ifp. Finally, the Sommerfeld integral and its expansion are generalized to an arbitrary, finitep.     

The effect of turbulence-radiation interaction on radiative entropy generation and heat transfer

The analysis under the second law of thermodynamics is the gateway for optimisation in thermal equipments and systems. Through entropy minimisation techniques it is possible to increase the efficiency and overall performance of all kinds of thermal systems. Radiation, being the dominant mechanism of heat transfer in high-temperature systems, plays a determinant role in entropy generation within such equipments. Turbulence is also known to be a major player in the phenomenon of entropy generation. Therefore, turbulence-radiation interaction is expected to have a determinant effect on entropy generation. However, this is a subject that has not been dealt with so far, at least to the extent of the authors’ knowledge. The present work attempts to fill that void, by studying the effect of turbulence-radiation interaction on entropy generation. All calculations are approached in such a way as to make them totally compatible with standard engineering methods for radiative heat transfer, namely the discrete ordinates method. It was found that turbulence-radiation interaction does not significantly change the spatial pattern of entropy generation, or heat transfer, but does change significantly their magnitude, in a way approximately proportional to the square of the intensity of turbulence.     

Measured collisional radiative coefficients of the 4p groups of the argon I and argon II systems

We determine the r¹ (p) coefficients of the argon I 4p ¹P₁ state (2p₂ with Paschen notation) with the λ = 696.5 nm line and of the argon II 4p ²D_{$\text{5}\text{2}$} state with the λ = 488.0 nm line in a highly ionized, low temperature (T_{e = 3?4 eV}), magnetically confined (0.2 T) plasma of a hollow cathode arc with electron densities n_e between 10¹⁹ and 10²⁰ m^?3. The neutral density n₀ is 10¹⁹ m^?3 or less. The r¹ (4p) values are (6 ± 2) × 10^?5 for argon I and (5 ± 2) × 10^?4 for argon II.     

The heat capacity of a mixed titanate superconductor

The heat capacity of semiconducting Sr_0.925Ba_0.075TiO₃ has been measured between 0.3 and 4°K. The superconducting transition is observed at 0.5°K. An anomaly in the normal-state heat capacity is interpreted as a change in the number of valleys in the conduction band.     

Low frequency longitudinal waves in argon hot cathode discharges. I

Experimental investigation of low-frequency longitudinal waves in argon low-current thermionic cathode discharges at the pressure from 10 Pa to 100 Pa is described. The longitudinal waves are generated in the discharge volume forpd _ac Pa. cm if the thermionic emission-discharge current ratio,I _em/I _d, is greater than 30.