Kind Of Phase Transition Research Articles

Cosmic Evolution from Phase Transition of Three-Dimensional Flat Space

Flat space cosmology spacetimes are exact time-dependent solutions of three-dimensional gravity theories, such as Einstein gravity or topologically massive gravity. We exhibit a novel kind of phase transition between these cosmological spacetimes and the Minkowski vacuum. At sufficiently high temperature, (rotating) hot flat space tunnels into a universe described by flat space cosmology.

Critical conditions of entropy-driving nucleation in binary colloidal system

In a binary colloidal hard-sphere system, due to the entropic depletion interactions, large spheres may be pushed to pack into clusters. If a cluster is taken as a new kind of component, then the binary colloidal system turns to be a ternary one and it therefore can be dealt in the framework of a multi-component system. It is known that, under certain conditions, a cluster can grow larger and larger and turn into a nucleation, even a kind of phase transition will take place. In this paper, the critical conditions, including the critical size of the nucleating cluster and the corresponding volume fraction of the colloidal system, were determined by analyzing entropy variation through the multi-component of Carnahan–Starling (CS) state equation and the principle of entropy maximum. The results obtained in this way are in good agreement with that of the experiments. In addition, the results also show that, when the critical volume fraction of the system increases from 0.18 to 0.19, the cluster’s density ϕ will change from 0.74 to 0.58. Except for the size ratio of large to small spheres, the critical size of the nucleating cluster is almost independent of its density and the volume fraction of the system.

Temperature Dependence of Magnetic Parameters in FePt Nanoparticles

Here, particular focus is placed on the atomic alignment and the order–disorder phase transition of the FePt alloy with the aid of a model that can describe realistic phenomena. Here, we present a method to study the order–disorder phenomena of FePt alloys. We will discuss the increase in the coercivity of FePt nanoparticles by an increasing annealing temperature for annealed FePt nanoparticles. According to the experimental evidence, we will present a model for explaining spin-glass-like behavior of these particles during the annealing procedure. In the phase transition from disordered FCC to ordered FCT in FePt nano-particles can be treated by first-order phase transitions. So, the mean field approach can be used in order to model this kind of phase transition. In nanoparticles, which are synthetized by sol–gel methods, the short range parameter is predominant because in these kinds of preparations, the long range order takes a lot of time to happen. By using a short range parameter, we are able to use the mean field approach, which considers the diffusion of atoms to the near neighborhood sites. The effects of random exchange and random magnetocrystalline anisotropy are known as the main results of coercivity reduction in magnetic nanoparticles. These effects are strongly dependent to the annealing temperature of nanoparticles. During disorder–order transition, these two effects are max. As transition continues, these effects vanish and coercivity of nanoparticles increases. Here, we will add these two effects to the Hamiltonian of the FePt system. With increasing the annealing temperature, the fraction of the FePt nanoparticles with a FCC disordered phase vanishes, which leads to decrease in the amount of 〈j〉. During the annealing process, the $\frac{c}{a}$ ratio varies as a function of the annealing temperature. The relation between the $\frac{c}{a}$ ratio and the annealing temperature is derived. The derived $\frac{c}{a}$ ratio and coercivity formulas are compared with experimental results. The results are in a good agreement with experimental data.

Approximation by rational functions on compact nowhere dense subsets of the complex plane

Let \(X\) be a compact nowhere dense subset of the complex plane, and let \(dA\) denote two-dimensional or area measure on \(X\). Let \(R(X)\) denote the uniform closure of the rational functions having no poles on \(X\), and for each \(p,\, 1\le p<\infty \), let \(R^p(X)\) be the closure of \(R(X)\) in the \(L^p(X, dA)\)-norm. Since \(X\) has no interior \(R^p(X)=L^p(X)\) whenever \(1\le p <2\), but for \(p=2\) a kind of phase transition occurs that can be quite striking at times. Our main goal here is to study the manner in which similar phase transitions can occur at any value of \(p, \, 2\le p < \infty \).

Modulation of the boundary between hierarchically differentiated domains in a self-organizing neural system

It is known that an abstract model with linear and distance-dependent interactions can develop a topographic connection structure in an input-output two-layer system. We expand the model by reflecting the effects of correlations between propagating neural firings and investigate the emergent properties in the resulting nonlinear model. It is found that the output layer can separate into several ones between which topographic connections develop. This result shows that hierarchically differentiated cortical sections, developing on a lattice structure, can regulate their boundary through Hebbian plasticity. We further argue that the phenomenon of cortical area differentiation can be described as a kind of phase transition.

Linear higher derivative field theories, entanglement entropy and quantum phase transition

Quantum systems described by linear, higher order spatial derivatives of the field exhibit a new kind of phase transition as the coupling strength of the higher order terms varies.This essentially happens because a fundamental change in the ratio of ground state energy eigenvalues, between linear and non-linear regime, takes place which leads to excitation of higher modes. The new phase has inverse relation with area.

Optical features of A2BX4 ferroic nanocomposites with the incommensurate phase

In this paper, we report on the experimental studies of optical birefringence of A2BX4 (K2ZnCl4, Rb2ZnCl4, and K2SeO4) type of crystals in a wide temperature range which show para-electric, ferroelectric properties with incommensurate phases for the 633nm wavelength. We found that with the decrease of the nanocrystallite sizes, temperature range of the incommensurate phase is enhanced. At the same time the ferroelectricity disappeared at crystallite sizes below 8nm due to nano-confinement effects which change the electron–phonon anharmonic interactions which are responsible for such kinds of phase transitions. Additional superposition of the external electric field leads to drastic changes in the relative amount of the ferroelectrics and incommensurate phases. The effect is explained within the Landau–Ginzburg phenomenological approach with Lifshitz invariant. Additional confirmation of the observed effects was obtained by optical second harmonic generation. During the decrease of the nanocrystallite sizes below 12nm there occurs some harmonic soliton waves which are propagated in several directions parallel to the crystallographic axes. Despite the absence of the long-range disorder there occurs some non-centrosymmetry.

Two kinds of phase transitions in a voting model

In this paper, we discuss a voting model with two candidates, C0 and C1. We consider two types of voters—herders and independents. The voting of independents is based on their fundamental values, while the voting of herders is based on the number of previous votes. We can identify two kinds of phase transitions. One is an information cascade transition similar to a phase transition seen in the Ising model. The other is a transition of super and normal diffusions. These phase transitions coexist. We compared our results to the conclusions of experiments and identified the phase transitions in the upper limit of the time t by using the analysis of human behavior obtained from experiments.

Pressure effects on grain boundary, electrical and vibrational properties of the polycrystalline BaTeO3

The evolutions of alternate current (AC) impedance spectra, direct current (DC) resistivity and Raman spectra in polycrystalline BaTeO3 have been investigated at high pressures. The abrupt changes observed in electrical transport measurements at 12.73 GPa indicated a kind of phase transition, which was confirmed to be related to the structural phase transition by high-pressure Raman scattering experiments. From the impedance spectra, both grain resistance and grain boundary resistance decreased with increasing pressure, and two clear discontinuities occurred at 12.73 GPa and 17.47 GPa, respectively. After the transition, the contribution to the total resistance by the grain boundary effect dramatically declined and the grain resistance began to play a dominant role. Besides, the electric polarization process was changed due to the phase transition, and it led to a significant rise of the relaxation frequency. From the decompression impedance spectra, it could be clearly seen that the phase transition was irreversible, and it was probably attributed to the irreversible change of the grain boundary for the two different crystal structures. By varying the temperature, the transport behaviour at high pressure was still of semiconductor type but with different slopes for the ambient and high-pressure phases. High-pressure Raman measurements revealed an irreversible structural phase transition occurring above 15 GPa, and the results were consistent with the observed changes of the electrical properties at high pressures.

Order-disorder transition in a model with two symmetric absorbing states

We study a model of two-dimensional interacting monomers which has two symmetric absorbing states and exhibits two kinds of phase transition; one is an order-disorder transition and the other is an absorbing phase transition. Our focus is around the order-disorder transition, and we investigate whether this transition is described by the critical exponents of the two-dimensional Ising model. By analyzing the relaxation dynamics of "staggered magnetization," the finite-size scaling, and the behavior of the magnetization in the presence of a symmetry-breaking field, we show that this model should belong to the Ising universality class. Our results along with the universality hypothesis support the idea that the order-disorder transition in two-dimensional models with two symmetric absorbing states is of the Ising universality class, contrary to the recent claim [K. Nam et al., J. Stat. Mech.: Theory Exp. (2011) L06001]. Furthermore, we illustrate that the Binder cumulant could be a misleading guide to the critical point in these systems.

Mean-field-like behavior of the generalized voter-model-class kinetic Ising model

We analyze a kinetic Ising model with suppressed bulk noise, which is a prominent representative of the generalized voter model phase transition. On the one hand, we discuss the model in the context of social systems and opinion formation in the presence of a tunable social temperature. On the other hand, we characterize the abrupt phase transition. The system shows nonequilibrium dynamics in the presence of absorbing states. We slightly change the system to get a stationary-state model variant exhibiting the same kind of phase transition. Using a Fokker-Planck description and comparing to mean-field calculations, we investigate the phase transition, finite-size effects, and the effect of the absorbing states resulting in a dynamic slowing down.

Vortices in superconducting nano-networks with anti-dots array

AbstractVortices (magnetic flux quanta) in the superconducting networks perforated with anti-dots (holes) arrays behave as electrons in atomic lattice of crystals. Repulsive and attractive interaction among vortices and anti-dots resemble to those among electrons and atoms in crystals. To confirm the variety of the vortex physics similar to the solid state physics, we have fabricated such superconducting networks with antidots array in metallic, inter-metallic and high-T c superconductors (HTSCs), and have measured magneto-resistance of vortex-flow. In these materials, we have observed integer-matching at the matching fields and fractional-matching effect between them. Most of them are well explained by commensurability between Abrikosov vortex lattice and anti-dots array. Furthermore, the effect of the anti-dots array in HTSCs appears as another kind of phase transitions instead of to the first-order melting transition of vortex lattice in pristine samples.

Thermodynamics of Size Effect on Phase Transition Temperatures of Dispersed Phases

An equation for a phase transition in a dispersed system has been proposed, and the applications of the equation in various kinds of phase transitions have been discussed. The determinate relation ...

Phase transition in saturated porous media: Pore-fluid segregation in consolidation

Consider the consolidation process typical of soils; this phenomenon is expected not to exhibit a unique state of equilibrium, depending on external loading and constitutive parameters. Beyond the standard solution also, pore-fluid segregation can arise. Pore-fluid segregation has been recognized as a phenomenon typical of the short time behavior of a saturated porous slab or a saturated porous sphere, during consolidation. In both circumstances, the Biot three-dimensional model provides time increasing values of the water pressure (and fluid mass density) at the center of the slab (or of the sphere), at early times, if the Lamé constant μ of the skeleton is different from zero. This localized pore-fluid segregation is known in the literature as the Mandel–Cryer effect. In this paper, a nonlinear poromechanical model is formulated. The model is able to describe the occurrence of two states of equilibrium and the switching from one to the other by considering a kind of phase transition. Extending the classical Biot theory, a more than quadratic strain energy potential is postulated, depending on the strain of the porous material and the variation of the fluid mass density (measured with respect to the skeleton reference volume). When the consolidating pressure is strong enough, the existence of two distinct minima is proven.

Thermotropic and Barotropic Phase Transitions of Dialkyldimethylammonium Bromide Bilayer Membranes: Effect of Chain Length

The bilayer phase transitions of dialkyldimethylammonium bromides (2C(n)Br; n = 12, 14, 16) were observed by differential scanning calorimetry and high-pressure light-transmittance measurements. Under atmospheric pressure, the 2C(12)Br bilayer membrane underwent the stable transition from the lamellar crystal (L(c)) phase to the liquid crystalline (L(α)) phase. The 2C(14)Br bilayer underwent the main transition from the metastable lamellar gel (L(β)) phase to the metastable L(α) phase in addition to the stable L(c)/L(α) transition. For the 2C(16)Br bilayer, moreover, three kinds of phase transitions were observed: the metastable main transition, the metastable transition from the metastable lamellar crystal (L(c(2))) phase to the metastable L(α) phase, and the stable lamellar crystal (L(c(1)))/L(α) transition. The temperatures of all the phase transitions elevated almost linearly with increasing pressure. The temperature (T)-pressure (p) phase diagrams of the 2C(12)Br and 2C(14)Br bilayers were simple, but that of the 2C(16)Br bilayer was complex; that is, the T-p curves for the metastable main transition and the L(c(2))/L(α) transition intersect at ca. 25 MPa, which means the inversion of the relative phase stability between the metastable phases of L(β) and L(c(2)) above and below the pressure. Moreover, the T-p curve of the L(c(2))/L(α) transition was separated into two curves under high pressure, and as a result, the pressure-induced L(c(2P)) phase appeared in between. Thermodynamic quantities for phase transitions of the 2C(n)Br bilayers increased with an increase in alkyl-chain length. The chain-length dependence of the phase-transition temperature for all kinds of transitions observed suggests that the stable L(c(1))/L(α) transition incorporates the metastable L(c(2))/L(α) transition in the bilayers of 2C(n)Br with shorter alkyl chains, and the main-transition of the 2C(12)Br bilayer would occur at a temperature below 0 °C.

An apparent critical point in binary mixtures of nitrotoluene with alkanes: Experimental and simulation study

We report an experimental and simulation study of binary mixtures of o- and m-nitrotoluene with decane and hexadecane. Mixtures of o-nitrotoluene with alkanes form a classical critical mixtures, but m-nitrotoluene / n - alkane mixtures show an apparent critical point, which lies in a metastable, experimentally inaccessible state, below the melting point, affecting physical and chemical properties of this systems in the stable liquid phase. The presence of the apparent critical point in this mixture has been experimentally observed by Nonlinear Dielectric Effect (NDE) measurements as an anomalous increase in the NDE values typical of critical concentrations. The phase diagram of this mixture shows evidence that the system freezes in the homogenous phase and its melting point is higher than its critical temperature [1-3]. For such a system, we performed Monte Carlo simulations aimed at analysing the kind of phase transitions observed, and the conditions of their occurrence in a nonpolar/dipolar mixture. We perform studies for classical critical systems of o-nitrotoluene with decane and hexadecane The enthalpy, configurational energy and radial distribution function have been estimated by the MC simulation method in the NPT system. Immiscibility conditions according to Schoen and Hoheisel [4] approach are also discussed.

Transition into the Supersolid (SS) State, Supersolid Density ρ ss and the Critical Velocity V c to Destroy the SS State

We have reported the onset of the vortex fluid (VF) state in hcp solid 4He below an onset temperature To (Penzev et al. in Phys. Rev. Lett. 101:065301, 2008). We have also shown the transition from the VF state into the supersolid (SS) state, which is characterized by a supersolid density and macroscopic coherence, below a transition (Kubota et al. in J. Low Temp. Phys. 158:572, 2010; Shimizu et al. in arXiv:0903.1326, 2009; Yagi et al. in J. Low Temp. Phys., QFS2010, 2011) at Tc, as well as a critical velocity for the destruction of the SS state. Here we describe further confirming evidence of the phase transition into the SS state, namely, we report here some other observations than the hysteretic behavior. We find some other features which indicate a clear change of the properties in the hcp 4He below the same Tc as hysteretic behavior, reported in Kubota et al. (J. Low Temp. Phys. 158:572, 2010), Shimizu et al. (arXiv:0903.1326, 2009), Yagi et al. (J. Low. Temp. Phys., QFS2010, 2011). It was discovered by detailed study of the torsional oscillator (TO) drive velocity Vac dependence of the nonlinear rotational susceptibility (NLRS) of the VF state. We discuss the features of the VF to SS transition. The large ratio between To and Tc may indicate large fluctuations of the system and it may give a basis for the vortex state (Fisher et al. in Phys. Rev. B 43(1):130, 1991) appearance in the hcp 4He, as seen in the new type of superconductors. We discuss a question related to the observation of the VF phase with specific dynamic features (Nemirovskii et al. in arXiv:0907.0330, 2009), coexisting with the SS phase and a possible new kind of phase transition coexisting with the SS phase and a possible new kind of phase transition for the VF to SS transition.

Preparation of LaNi 1 − xFe xO 3 single phase and characterization of their phase transition behaviors

Optimization of preparation conditions of single phase LaNi 1 − x Fe x O 3, which is a candidate cathode material for solid oxide fuel cells (SOFC), by solid state reaction method was examined. We have found that heat treatment under O 2 atmosphere is effective to prevent the generation of impurities with Ni valence less than 3+ and succeeded in the preparation of single phase specimens with x = 1.0 ~ 0.3. Using thermal analyses, Mössbauer spectroscopy and high temperature X-ray diffraction measurement, phase diagram of LaNi 1 − x Fe x O 3 has been constructed. Three kinds of phase transitions were observed in LaNi 1 − x Fe x O 3 and their phase boundary has been determined. Magnetic phase transition from antiferromagnetic to paramagnetic was observed for the specimens with x = 1.0 ~ 0.8. The magnetic phase transition temperature decreased with decreasing x and disappeared above room temperature in the specimens with x lower than 0.7. For LaFeO 3, structural phase transition from orthorhombic distorted perovskite to trigonal distorted one was observed at 980 °C. By Ni substitution, high temperature trigonal phase varied to rhombohedral phase with decreasing structural phase transition temperature. Since neither phase transition nor oxygen nonstoichiometry was observed for the specimens with LaNi 0.6Fe 0.4O 3 and LaNi 0.7Fe 0.3O 3 from room temperature to 1000 °C, they can be regarded as promising candidate for cathode material of SOFC.

Modern Rheology on a Stock Market: Fractional Dynamics of Indices

This paper presents an exactly solvable (by applying the fractional calculus) the rheological model of fractional dynamics of financial market conformed to the principle of no arbitrage present on financial market. The rheological model of fractional dynamics of financial market describes some singular, empirical, speculative daily peaks of stock market indices, which define crashes as a kind of phase transition. In the frame of the model the plastic market hypothesis and financial uncertainty principle were formulated, which proposed possible scenarios of some market crashes. The brief presentation of the model was made in our earlier work (and references therein). The rheological model of fractional dynamics of financial market is a deterministic model and it is complementary to already existing other ones; together with them it oers possibility for thorough and widespread technical analysis of crashes. The constitutive, fractional integral equation of the model is an analogy of the corresponding one, which defines the fractional Zener model of plastic material. The fractional Zener model is the canonical one for modern rheology, polymer physics and biophysics concerning non-Debye relaxation of viscoelastic biopolymers. The useful approximate solution of the constitutive equation of the rheological model of fractional dynamics of financial market consists of two parts: (i) the first one connected with long-term memory present in the system, which is proportional to the generalized exponential function defined by the Mittag‐Leer function and (ii) the second one describing oscillations (e.g. beats or oscillations having two slightly shifted frequences). The shape exponent leading the Mittag‐Leer function, defines here the order of the phase transition between bullish and bearish states of the financial market, in particular, for recent hossa and bessa on some small, middle and large stock markets. It happened that this solution also successfully estimated some long-term price dynamics on the hypothetical market in United States.

Simulation of pedestrian flow through a “T” intersection: A multi-floor field cellular automata approach

There are several ways to study pedestrian dynamics, such as the macroscopic hydrodynamics, molecular dynamics with social force, and cellular automata (CA) with mean field approach. In recent years, the cellular automata approach has received growing interest from researchers. Because this approach is not only to save the computing time but also to reduce the complexity of the problem. In this presentation, we report the study of the conformation of congestion in a “T” intersection by using a cellular automata procedure with multi-floor fields. By using the multi-floor fields, we can mimic the pedestrian flow from several entrances to different exits firstly, and we can simulate the different pedestrian speed by changing the controlling parameter. Our results show, there are some kinds of phase transition in this system.