Chiral Phase Transition at Finite Isospin Density in Linear Sigma Model

Using the linear sigma model, we have introduced the pion isospin chemical potential. The chiral phase transition is studied at finite temperatures and finite isospin densities. We have studied the μ-T phase diagram for the chiral phase transition and found the transition cannot happen below a certain low temperature because of the Bose-Einstein condensation in this system. Above that temperature, the chiral phase transition is studied by the isotherms of pressure versus density. We indicate that the transition, in the chiral limit, is a first-order transition from a low-density phase to a high-density phase like a gas-liquid phase transition.     

Phase transformations during the growth of paracetamol crystals from the vapor phase

Phase transformations during the growth of paracetamol crystals from the vapor phase are studied by differential scanning calorimetry. It is found that the vapor-crystal phase transition is actually a superposition of two phase transitions: a first-order phase transition with variable density and a second-order phase transition with variable ordering. The latter, being a diffuse phase transition, results in the formation of a new, “pretransition,” phase irreversibly spent in the course of the transition, which ends in the appearance of orthorhombic crystals. X-ray diffraction data and micrograph are presented.     

Hydrogen-bond topology and the ice VII/VIII and ice Ih/XI proton-ordering phase transitions

The existence of an ice Ih/XI proton-ordering transition to a low-temperature ferroelectric phase has sparked considerable debate in the literature. Electronic density functional theory calculations, extended using graph invariants, confirm that a transition to a low-temperature ferroelectric phase should occur. The predicted transition at 98 K is in qualitative agreement with the observed transition at 72 K, and the low-temperature phase is the ferroelectric phase determined in diffraction experiments. The theoretical methods used to predict the phase transition are validated by comparing their prediction to the well-characterized ice VII/VIII proton-ordering transition.     

Vapor-crystal phase transition in synthesis of paracetamol films by vacuum evaporation and condensation

We report on the structural and technological investigations of the vapor-crystal phase transition during synthesis of paracetamol films of the monoclinic system by vacuum evaporation and condensation in the temperature range 220–320 K. The complex nature of the transformation accompanied by the formation of a gel-like phase is revealed. The results are interpreted using a model according to which the vapor-crystal phase transition is not a simple first-order phase transition, but is a nonlinear superposition of two phase transitions: a first-order transition with a change in density and a second-order phase transition with a change in ordering. Micrographs of the surface of the films are obtained at different phases of formation.     

Micromagnetic imaging to determine the nature of the ferromagnetic phase transition in La(0.7)Ca(0.3)MnO3

There is considerable controversy surrounding the nature of the paramagnetic to ferromagnetic phase transition in La(0.7)Ca(0.3)MnO3. We have used transmission electron microscopy to determine whether the phase transition is first or second order. On warming through the transition point, the ferromagnetic phase retreats from the sample surface as it is replaced by the paramagnetic phase. This coexistence of ferromagnetic and paramagnetic phases indicates a primarily first order transition. However, there is also continuous loss of magnetization which precedes the phase transition. We compare this with the phase transition in nickel, an archetypal second order ferromagnet.     

Expanding the thermodynamical potential and analysis of the possible phase diagram of deconfinement in the FL model

Deconfinement phase transition is studied in the FL model at finite temperature and chemical potential. At MFT approximation, phase transition can only be first order in the whole μ-T phase plane. Using a Landau expansion, we further study the phase transition order and the possible phase diagram of deconfinement. We discuss the possibilities of second order phase transitions in the FL model. From our analysis, if the cubic term in the Landau expansion could be cancelled by the higher order fluctuations, second order phase transition may occur. By an ansatz of the Landau parameters, we obtain a possible phase diagram with both the first and second order phase transitions, including the tri-critical point which is similar to that of the chiral phase transition.     

A polymerization-depolymerization model for generation of contractile force during bacterial cell division

We have investigated the pressure-induced phase transition of NiO and other structural properties using three-body potential approach. NiO undergoes phase transition from B1 (rocksalt) to B2 (CsCl) structure associated with a sudden collapse in volume showing first-order phase transition. A theoretical study of high pressure phase transition and elastic behaviour in transition metal compounds using a three-body potential caused by the electron shell deformation of the overlapping ion was carried out. The phase transition pressure and other properties predicted by our model is closer to the phase transition pressure predicted by Eto et al.      

Parastatistics and phase transition from a cluster as a fluctuation to a cluster as a distinguishable object

A phase transition of the first kind is a jump of a function, a phase transition of the second kind is a jump of its first derivative, a phase transition of the third kind, a jump of the second derivative. A phase transition from one statistic to another is very gradual, but finally it is as considerable as the phase transition of the first kind. However, we cannot introduce a clearly defined parameter to which this transition corresponds. This is due to the fact that the fluctuations near the critical point are huge, and this violates, in the vicinity of that point, the main law of equilibrium thermodynamics, which asserts that fluctuations are relatively small. The paper describes the transition in the supercritical fluid region of equilibrium thermodynamics from parastatistics to mixed statistics, in which the Boltzmann statistics is realized for long-living clusters. In economics this corresponds to a negative nominal credit rate. Examples of this non-standard situation are presented.     

QED effects on phase transition and Ruppeiner geometry of Euler-Heisenberg-AdS black holes

Considering the quantum electrodynamics (QED) effect, we study the phase transition and Ruppeiner geometry of Euler-Heisenberg anti-de Sitter black holes in the extended phase space. For negative and small positive QED parameters, we observe a small/large black hole phase transition and reentrant phase transition, respectively, whereas a large positive value of the QED parameter ruins the phase transition. Phase diagrams for each case are explicitly shown. Then, we construct the Ruppeiner geometry in thermodynamic parameter space. Different features of the corresponding scalar curvature are shown for both the small/large black hole phase transition and reentrant phase transition cases. Of particular interest is the additional region of positive scalar curvature, indicating a dominant repulsive interaction among black hole microstructures, for the black hole with a small positive QED parameter. Furthermore, universal critical phenomena are observed for the scalar curvature of Ruppeiner geometry. These results indicate that the QED parameter has a crucial influence on the black hole phase transition and microstructure.     

Nature of the high-pressure transition in Fe2O3 hematite

We present a new method to separate the crystallographic and electronic phase transitions in hematite using x-ray emission spectroscopy and x-ray diffraction. Our observations, based on the behavior of a metastable high-pressure phase in the stability domain of the low-pressure phase, show that the electronic transition is preempted by the crystallographic transition. The former occurs only afterwards in the high-pressure phase, possibly as a result of a Mott transition. The idea that the electronic transition drives the transition in hematite is therefore invalidated. Such methods should help elucidate the mechanics and the driving forces behind a number of first-order high-pressure phase transitions.     

2PI effective action and evolution equations of \mathcal{N} = 4 super Yang–Mills

We study the possibility of phase transitions between Lifshitz black holes and other configurations by using free energies explicitly. A phase transition between Lifshitz soliton and Lifshitz black hole might not occur in three dimensions. We find that a phase transition between Lifshitz and BTZ black holes is unlikely to occur because they have different asymptotes. Similarly, we point out that any phase transition between Lifshitz and black branes is unlikely to occur in four dimensions since they have different asymptotes. This is consistent with the necessary condition for taking a phase transition in a gravitational system, which requires the same asymptote.     

Features of sound propagation in the vicinity of “symmetry-dictated” isostructural phase transitions in ferroelastics

Using a proper ferroelastic phase transition of the tension-compression type as an example, it is shown that, if the order parameter characterizing a structural phase transition allows the existence of a third-power invariant in the Landau potential, then there must be “symmetry-dictated” isostructural phase transition lines in the vicinity of the line of that structural phase transition. These isostructural transitions may manifest themselves both directly and as supercritical anomalies in the behavior of elastic moduli and lattice parameters. These effects are discovered and investigated without invoking the perturbation theory in terms of which the second-order phase transitions are commonly described. A hypothesis is made on the basis of the results obtained that the sound velocity anomalies observed in orthoclase and sanidine crystals are due to the super-critical behavior of the lattice parameters in the vicinity of a symmetry-dictated isostructural phase transition in the prototype phase of these crystals.     

Two scenarios for colloidal phase transitions

A two-dimensional assembly of charged colloidal particles induced by an alternating electric field was studied in real space by means of digital video microscopy. Phase transitions occur from a highly ordered colloidal monolayer to an isotropic suspension by changing the field strength or frequency (in the appropriate range). In particular, it is found that the strength-dependent phase transition is an infinite-order phase transition, in contrast with the frequency-dependent phase transition, which is a second-order phase transition.     

On the type of a phase transition in the system of exciton polaritons in an optical microcavity

The type of a phase transition in the quasi-equilibrium system of exciton polaritons in a two-dimensional optical microcavity has been analyzed. It has been shown that, although the system contains two types of bosons undergoing mutual transformations into each other, only one phase transition to the superfluid state with the quasilong-range order occurs in the two-dimensional system. This phase transition is a Kosterlitz-Thouless phase transition. A new physical implementation—excitons in a photon crystal—has been proposed for the Bose condensation of exciton polaritons. The superfluid properties of the ordered phase are discussed, and the superfluid density and Kosterlitz-Thouless transition temperature have been calculated in the low-density approximation.     

窗口声阻抗对锆相变动力学的影响

基于磁驱动加载装置CQ-4开展了锆的斜波压缩相变实验,研究了锆样品后表面窗口声阻抗对相变波形的影响.实验结果显示,锆后表面为较低声阻抗窗口(自由面和LiF窗口)时,相变起始对应的特征粒子速度约331.0 m/s,而高阻抗蓝宝石窗口时,特征粒子速度约301.9 m/s,特征速度对应的压力从约9.14 GPa下降到8.27 GPa.相变对应的速度特征拐点是与多种因素相关的实验信息,因此它对应的压力并不是材料属性参数相变压力.结合基于热力学Helmholtz自由能的多相状态方程和非平衡相变动力学方程开展了锆的相变动力学数值模拟研究,相变弛豫时间为30 ns,计算结果与三种情况的实验结果符合良好,可以较好地模拟斜波压缩下锆的弹塑性转变、相变等物理过程.在压力-比容和温度-压力热力学平面,相变前锆的准等熵线与冲击绝热线差异很小,相变后准等熵线都位于冲击绝热线下方,随着压力的增加准等熵线和冲击绝线偏差越来越大,温度-压力平面中在20 GPa时相差约100 K.相变开始后,由于相变引起比容的间断,导致锆的拉氏声速迅速下降约7%,相变完成后拉氏声速恢复到体波声速.     

Coupled m-component fields with cubic anisotropy

The critical behavior at phase transitions of two coupled, m-component systems with cubic anisotropy is studied by a simplified model in which the fluctuations are partially considered. The phase transition could be a new fluctuation-induced first order transition into the anisotropic phase, or a new second order phase transition. Unlike in uncoupled systems, the second order phase transition could be into either the anisotropic or isotropic phase. As expected, upon suppression of fluctuations, all results reduce to those of mean field theory.     

Comparison of the ferromagnetic phase transitions in La0.7Ca0.3MnO3 and single crystal nickel by micromagnetic imaging

There is considerable controversy surrounding the nature of the paramagnetic to ferromagnetic phase transition in La_0.7Ca_0.3MnO₃. We have used transmission electron microscopy to perform micromagnetic imaging in order to determine whether the phase change is first or second order. On warming through the transition point, the ferromagnetic phase retreats from the sample surface as it is replaced by the paramagnetic phase. This coexistence of ferromagnetic and paramagnetic phases indicates a primarily first-order transition. However, there is also a continuous loss of magnetization which precedes the phase transition. We compare this with the ferromagnetic transition in nickel which displays a purely continuous phase change. We discuss the accuracy and range of applicability of the micromagnetic imaging techniques of electron holography and Fresnel imaging which were used in this investigation.     

High-energy x-ray diffraction study on phase transition asymmetry of plastic crystal neopentylglycol

As a prototype material of colossal barocaloric effects, neopentylglycol is investigated by combining high-precision differential scanning calorimetric measurement and high-energy x-ray diffraction measurement. The diffraction data at constant temperatures indicate a first-order phase transition with thermal hysteresis as well as the phase transition asymmetry, specifically, the phase transition is completed faster at cooling than at heating. The analysis of resulting pair distribution function confirms the intermolecular disorder in the high-temperature phase. The phase transition asymmetry is quantitatively characterized by time-resolved x-ray diffraction, which is in agreement with the thermal measurement. Also, such an asymmetry is observed to be suppressed at high pressures.     

Formation kinetics of brittle phase nuclei in hydrogenated metals under loading

It is shown that the formation of the brittle phase in hydrogenated metal under external loading is a first-order phase transition. The basic equation of the evolution of elastic stress in a uniform and isotropic hydrogenated metal during the formation of a brittle hydride phase is derived and its solution is found. Based on this data, the time dependences of all characteristics of the phase transition into a brittle phase are found; namely, the densities of nuclei of the hydride phase, the size distribution, and the formation rates of the hydride phase nuclei are found. The characteristic time of the transition into the brittle phase is found.