BeO高压相变和声子谱的第一性原理计算

采用第一性原理方法计算了BeO在零温时的高压相变和三种结构在零温零压时的声子谱.相变的计算表明,在122GPa左右的压力下BeO会发生从纤锌矿(B4)结构到氯化钠(B1)结构的相变,而闪锌矿(B3)结构在零温零压下是一种可能的亚稳态结构.采用冷声子方法计算了这三种结构的BeO在零温零压下的声子谱.计算结果表明:B1结构在零温零压下是一种不稳定的结构;尽管B4结构和B3结构具有明显的相似性,仍然可以通过声子谱来很好的区分.最后根据准简谐近似理论计算得到了BeO的高温高压相图.     

用压力传感器和温度传感器测量绝对零度

介绍用绝对零度球体与压力传感器和温度传感器配合,在定容条件下测量气体的压强与温度,采用外推法估算理想气体可以达到的最低温度(绝对零度)的摄氏温度值,替代原先用玻璃管测体积和水银温度计测温度。使用新的绝对零度实验装置,可以更明显地观察分析热力学现象,并使测得的绝对零度值较为精确。     

A new representation for the supercurrent in He-A and its zero temperature limit

A new representation for the thermal Green's function of ³He-A and its zero the corresponding supercurrent at an arbitrary temperature. Expansion of this general expression in the orbital vector gradients is considered at zero temperature; the widely accepted first-order contribution with the anomalous part and the second-order corrections to it are obtained, thus confirming the existence of the anomalous current at zero temperature.     

Long-range correlations and generic scale invariance in classical fluids and disordered electron systems

Long-ranged, or power-law, behavior of correlation functions in both space and time is discussed for classical systems and for quantum systems at finite temperature, and is compared with the corresponding behavior in quantum systems at zero temperature. The origin of the long-ranged correlations is explained in terms of soft modes. In general, correlations at zero temperature are of longer range than their finite-temperature or classical counterparts. This phenomenon is due to additional soft modes that exist at zero temperature.     

Mean Field Dilute Ferromagnet: High Temperature and Zero Temperature Behavior

We study the mean field dilute model of a ferromagnet. We find and prove an expression for the free energy density at high temperature, and at temperature zero. We find the critical line of the model, separating the phase with zero magnetization from the phase with symmetry breaking. We also compute exactly the entropy at temperature zero, which is strictly positive. The physical behavior at temperature zero is very interesting and related to infinite dimensional percolation, and suggests possible behaviors at generic low temperatures. Lastly, we provide a complete solution for a (partially) annealed model. Our results hold both for the Poisson and the Bernoulli versions of the model.     

基于多参数模型的非分散红外光谱气体检测稳定性方法研究

针对非分散红外光谱传感器零点和温度漂移问题,建立了一种基于零气光强、参考光强、标准温度、环境温度、温度漂移系数等多参数模型,对红外传感器长期连续运行中存在的零点和温度漂移进行自动校正和补偿。测试结果和长时间应用表明,仪器在各种变换的环境条件下检测精度均小于5%F.S。CO₂的平均检测精度从未综合处理前的9.26%提高到了处理后的1.23%,CH₄的平均检测精度从未综合处理前的10.61%提高到了处理后的0.70%,克服了很多气体检测仪存在的稳定性差,标定周期短等不足,有效提高了仪器的检测精度、稳定性,降低了维护成本。     

Thermal behaviour of the planar spin chain with competing interactions up to third neighbours

The 1D classical planar model with competing interactions up to third neighbours is exactly studied at finite temperature by the transfer matrix method. The third neighbour interaction enters first an second order phase transition and full frustration lines at zero temperature. In particular, we have studied the static structure factorS(q) to understand the finite temperature short range order (SRO). This results strictly related to the zero temperature long range order (LRO) and coexistence of SRO configurations in the neighborhood of the zero temperature first order transition lines is clearly demonstrated. We have also found the signal of the full frustration of our model in a two equal weight peaks profile ofS(q) in the neighborhood of the ferro-antiferromagnetic boundary on which the chain breaks itself at zero temperature in two ferromagnetic sublattices the angle in between being arbitrary.     

用压力传感器和温度传感器测量绝对零度

介绍用贮气球体与压力传感器和温度传感器配合,在定容条件下测量气体的压强与温度,采用外推法估算理想气体可以达到的最低温度,即绝对零度的摄氏温度值,替代原先用玻璃管测体积和水银温度计测温度.使用这种绝对零度实验装置,可以更明显地观察分析热力学现象,并使测得的绝对零度值较为精确.     

Principle of Unattainability of absolute zero temperature,the Third Law of Thermodynamics,and projective quantum measurements

The Principle of Unattainability rules out the attainment of absolute zero temperature by any finite physical means, no matter how idealised they could be. Nevertheless, we clarify that the Third Law of Thermodynamics, as defined by Nernst's heat theorem statement, is distinct from the Principle of Unattainability in the sense that the Third Law is mathematically equivalent only to the unattainability of absolute zero temperature by quasi-static adiabatic processes. This, on the one hand, leaves open the possibility of attainability of absolute zero by non-adiabatic means, without violating the Third Law. On the other hand, we point out some apparent incompatibility between the Postulate of Projective Measurement in quantum mechanics and the Principle of Unattainability in that projective measurements of energy could result in zero temperature.     

A Low Temperature Analysis of the Boundary Driven Kawasaki Process

Low temperature analysis of nonequilibrium systems requires finding the states with the longest lifetime and that are most accessible from other states. We determine these dominant states for a one-dimensional diffusive lattice gas subject to exclusion and with nearest neighbor interaction. They do not correspond to lowest energy configurations even though the particle current tends to zero as the temperature reaches zero. That is because the dynamical activity that sets the effective time scale, also goes to zero with temperature. The result is a non-trivial asymptotic phase diagram, which crucially depends on the interaction coupling and the relative chemical potentials of the reservoirs.     

A first-principles study on the structural and elastic properties and the equation of state of wurtzite-type cadmium selenide under pressure

A first-principles investigation on the crystal structural and elastic properties and the equation of state of wurtzite-type cadmium selenide (w-CdSe) has been conducted using the plane-wave pseudo-potential density functional theory and the quasi-harmonic Debye model. The elastic constants, the aggregate elastic moduli, the elastic anisotropy, and Poisson's ratio under pressure have been investigated. Our calculated equilibrium lattice constants, the elastic constants, and the aggregate elastic moduli at zero pressure are in good agreement with the experimental data and other theoretical results. The variations in the compressional and shear elastic wave velocities with pressure at zero temperature up to pressure 2.7 GPa have been studied; the computed Debye temperature at zero pressure and zero temperature is in reasonable agreement with the result of Bonello et al., In addition, the equation of state of w-CdSe in the pressure range of 0–2.7 GPa and up to a temperature of 900 K has also been obtained.     

CERNOX CX-SD低温温度计使用方法

随着超导技术的飞速发展,超导装置运行过程中极低温测量技术成为一个重要的研究课题.国际上发展了许多特殊的温度测量方法,以精确测量绝对零度附近mK甚至μK量级的温度,同时对于需要具有较大温度变化范围的温度测量,例如从室温到绝对零度附近的温度测量也开发出了性能优越的温度计.在超导托卡马克核聚变实验装置的设计运行过程中,美国L...     

Absolute zero and its unattainability

The unattainability of absolute zero is deduced from two general conditions concerning temperature scales. It is also shown that the existence of a universal lower bound of temperature may not be inferred from the zero of the current absolute scale.     

Zero Temperature Limit for Directed Polymers and Inviscid Limit for Stationary Solutions of Stochastic Burgers Equation

We consider a space-continuous and time-discrete polymer model for positive temperature and the associated zero temperature model of last passage percolation type. In our previous work, we constructed and studied infinite-volume polymer measures and one-sided infinite minimizers for the associated variational principle, and used these objects for the study of global stationary solutions of the Burgers equation with positive or zero viscosity and random kick forcing, on the entire real line. In this paper, we prove that in the zero temperature limit, the infinite-volume polymer measures concentrate on the one-sided minimizers and that the associated global solutions of the viscous Burgers equation with random kick forcing converge to the global solutions of the inviscid equation.     

Droplet Shapes for a Class of Models in \mathbb{Z}^2 at Zero Temperature

In this work we consider the Wulff construction at zero temperature for a class of Gibbs models and study the shape of the obtained droplets. Considering zero temperature we avoid all difficulties connected with the competition between energy and entropy. It allows us to study a quite wide class of models which provides a variety of shapes. The motivations of the study come from attempts to describe isotropic properties of some models on 2D lattice at zero temperature. The studied models are binary (the spin space is 0,1) with a ferromagnetic behavior such that the potential functions are not equal to zero only for some tiles with size 3×3. In fact, we study herein droplet shapes of a subclass of the ferromagnetic models with potential functions as mentioned above. This subclass of models is defined by a condition called regularity. We call the model classified here as having regular micro-boundaries. Several examples of non-regular models are also presented.     

Collisional damping of giant monopole and quadrupole resonances

Collisional damping widths of giant monopole and quadrupole excitations for ¹²⁰Sn and ²⁰⁸Pb at zero and finite temperatures are calculated within Thomas-Fermi approximation by employing the microscopic in-medium cross-sections of Li and Machleidt and the phenomenological Skyrme and Gogny forces, and are compared with each other. The results for the collisional widths of giant monopole and quadrupole vibrations at zero temperature as a function of the mass number show that the collisional damping of giant monopole vibrations accounts for about 30 - 40% of the observed widths at zero temperature, while for giant quadrupole vibrations it accounts for only 20 - 30% of the observed widths at zero temperature. Received: 9 January 2001 / Accepted: 29 March 2001     

Zero energy and thermodynamic equilibrium

Using path integral techniques, it is shown that the real time formalism for finite temperature field theory requires an extra Feynman rule for Feynman diagrams carrying zero-external energies. This is related to a general principle governing the use of equilibrium finite temperature field theory. It is shown that only with this extra Feynman rule does the real time formalism become consistent for zero energy calculations. It is also used to understand the problem of the lack of analyticity at zero external four-momenta encountered in finite temperature field theory diagrams.     

Transitions to the Fulde-Ferrell-Larkin-Ovchinnikov phases at low temperature in two dimensions

We explore the nature of the transition to the Fulde-Ferrell-Larkin- Ovchinnikov superfluid phases in the low temperature range in two dimensions, for the simplest isotropic BCS model. This is done by applying the Larkin-Ovchinnikov approach to this second order transition. We show that there is a succession of transitions toward ever more complex order parameters when the temperature goes to zero. This gives rise to a cascade with, in principle, an infinite number of transitions. Except for one case, the order parameter at the transition is a real superposition of cosines with equal weights. The directions of these wavevectors are equally spaced angularly, with a spacing which goes to zero when the temperature goes to zero. This singular behaviour in this T = 0 limit is deeply linked to the two-dimensional nature of the problem.     

On the zero temperature statistics for the density of gap states of hydrogenated amorphous silicon

It is shown that one may obtain much larger value of density-of-states in the gap of hydrogenated amorphous silicon than real value, if the zero temperature statistics is used in studying that material. So care must be taken when one employs zero temperature statistics in studying the density-of-states of amorphous materials.     

Doubly ordered superconducting state in a doped antiferromagnet

In a weakly doped quasi-two-dimensional antiferromagnet with a Fermi contour in the form of small pockets, the Coulomb repulsion gives rise to a doubly ordered superconducting state of coexisting condensates with a large pair momentum and a zero one. The pairing with the large momentum determines the superconducting transition temperature, below which the order with zero momentum coexists as an induced order until the temperature corresponding to the initiation of the phonon pairing mechanism is reached. The superconductivity-induced orbital current density wave eliminates the pairing-repulsion-caused zero points from the two-gap quasiparticle spectrum and leads to a deviation of the relative phase of the superconducting order parameter components from π.