Showing papers on "Phase transition published in 1999"
TL;DR: The universe itself is thought to have passed through several phase transitions as the high-temperature plasma formed by the big bang cooled to form the world as we know it today as mentioned in this paper.
Abstract: Nature abounds with phase transitions. The boiling and freezing of water are everyday examples of phase transitions, as are more exotic processes such as superconductivity and superfluidity. The universe itself is thought to have passed through several phase transitions as the high-temperature plasma formed by the big bang cooled to form the world as we know it today.
3,749 citations
01 Jan 1999
641 citations
TL;DR: In this article, a lattice gas model with biased random walkers is presented to mimic the pedestrian counter flow in a channel under the open boundary condition of constant density, and the transition point is given by pc=0.45±0.01, not depending on the system size.
Abstract: A lattice gas model with biased random walkers is presented to mimic the pedestrian counter flow in a channel under the open boundary condition of constant density. There are two types of walkers without the back step: the one is the random walker going to the right and the other is the random walker going to the left. It is found that a dynamical jamming transition from the freely moving state at low density to the stopped state at high density occurs at the critical density. The transition point is given by pc=0.45±0.01, not depending on the system size. The transition point depends on the strength of drift and decreases with increasing drift. Also, we present the extended model to take into account the traffic rule in which a pedestrian walks preferably on the right-hand side of the channel.
487 citations
TL;DR: In this article, the phase diagram of strongly interacting matter as a function of temperature and baryon number density is explored, using a class of models for two-flavor QCD in which the interaction between quarks is modelled by that induced by instantons.
422 citations
TL;DR: In this paper, the phase diagram of the hot electroweak phase transition has been studied by four-dimensional lattice simulations and a continuum extrapolation is done, showing that the phase transition is first order for Higgs-boson masses.
Abstract: We study the hot electroweak phase transition by four-dimensional lattice simulations and give the phase diagram. A continuum extrapolation is done. We find that the phase transition is first order for Higgs-boson masses ${m}_{H}l66.5\ifmmode\pm\else\textpm\fi{}1.4\mathrm{GeV}$. Above this end point a rapid crossover occurs. Our result agrees with that of the dimensional reduction approach. It also indicates that the fermionic sector of the standard model (SM) may be included perturbatively. We obtain that the end point in the SM is $72.4\ifmmode\pm\else\textpm\fi{}1.7\mathrm{GeV}$. Thus, the LEP Higgs-boson mass lower bound excludes any electroweak phase transition in the SM.
319 citations
TL;DR: In this article, a 3D cellular automaton (CA) model for the prediction of dendritic grain structures formed during solidification is presented, which is built on the basis of a 3-D CA algorithm.
Abstract: A three-dimensional (3-D) model for the prediction of dendritic grain structures formed during solidification is presented. This model is built on the basis of a 3-D cellular automaton (CA) algorithm. The simulation domain is subdivided into a regular lattice of cubic cells. Using physically based rules for the simulation of nucleation and growth phenomena, a state index associated with each cell is switched from zero (liquid state) to a positive value (mushy and solid state) as solidification proceeds. Because these physical phenomena are related to the temperature field, the cell grid is superimposed to a coarser finite element (FE) mesh used for the solution of the heat flow equation. Two coupling modes between the microscopic CA and macroscopic FE calculations have been designed. In a so-called “weak” coupling mode, the temperature of each cell is simply interpolated from the temperature of the FE nodes using a unique solidification path at the macroscopic scale. In a “full” coupling mode, the enthalpy field is also interpolated from the FE nodes to the CA cells and a fraction of solid increment is computed for each mushy cell using a truncated Scheil microsegregation model. These fractions of solid increments are then fed back to the FE nodes in order to update the new temperature field, thus accounting for a more realistic release of the latent heat (i.e., the solidification path is no longer unique). Special dynamic allocation techniques have been designed in order to minimize the computation costs and memory size associated with a very large number of cells (typically 107 to 108). The potentiality of the CAFE model is demonstrated through the predictions of typical grain structures formed during the investment casting and continuous casting processes.
300 citations
TL;DR: In this article, the authors review progress in the understanding of gravitational thermodynamics and pinpoint the error in the proof that all systems have positive specific heat and say when it can occur and discuss the development of the thermal runaway in both the gravothermal catastrophe and its inverse.
Abstract: Starting from Antonov's discovery that there is no maximum to the entropy of a gravitating system of point particles at fixed energy in a spherical box if the density contrast between centre and edge exceeds 709, we review progress in the understanding of gravitational thermodynamics. We pinpoint the error in the proof that all systems have positive specific heat and say when it can occur. We discuss the development of the thermal runaway in both the gravothermal catastrophe and its inverse. The energy range over which microcanonical ensembles have negative heat capacity is replaced by a first order phase transition in the corresponding canonical ensembles. We conjecture that all first order phase transitions may be viewed as caused by negative heat capacities of units within them. We find such units in the theory of ionization, chemical dissociation and in the Van der Waals gas so these concepts are applicable outside the realm of stars, star clusters and black holes.
300 citations
TL;DR: The structure of CaTiO3 has been studied at high temperatures by powder neutron diffraction methods as mentioned in this paper, and two phase transitions are evident, with an intermediate tetragonal (I/mcm) structure forming near 1500 K and a primitive cubic structure above 1580 K. Detailed Rietveld analyses of the data suggest there may also be a phase transition from the room temperature Pbnm structure to an orthorhombic Cmcm structure around 1380 K, which is a remarkable feature of the results.
Abstract: The structure of CaTiO3 has been studied at high temperatures by powder neutron diffraction methods. From inspection of the diffraction data two phase transitions are evident, with an intermediate tetragonal (I/mcm) structure forming near 1500 K and a primitive cubic structure above 1580 K. Detailed Rietveld analyses of the data suggest there may also be a phase transition from the room temperature Pbnm structure to an orthorhombic Cmcm structure around 1380 K. A remarkable feature of the results is the regular variation in the out-of-phase octahedral tilt angle over the entire temperature range.
277 citations
TL;DR: The "shape hysteresis" in the GUVs is reversible and largely independent of the temperature scan rate, and a surprising behavior is observed, showing a sequence of different vesicle shapes as follows: spherical-polygonal-ellipsoidal.
273 citations
TL;DR: In this paper, a brief history of neutron stars and supernovae recent developments are discussed, and the nuclear to quark matter phase transition and its mixed phases with intriguing structures are treated.
Abstract: After a brief history of neutron stars and supernovae recent developments are discussed. Based on modern nucleon-nucleon potentials more reliable equations of state for dense nuclear matter have been constructed. Furthermore, phase transitions such as pion, kaon and hyperon condensation, superfluidity and quark matter can occur in cores of neutron stars. Specifically, the nuclear to quark matter phase transition and its mixed phases with intriguing structures is treated. Rotating neutron stars with and without phase transitions are discussed and compared to observed masses, radii and glitches. The observations of possible heavy $\sim 2M_\odot$ neutron stars in X-ray binaries and QPO's require relatively stiff equation of states and restricts strong phase transitions to occur at very high nuclear densities only.
266 citations
TL;DR: In this paper, it was shown that a system of self-propelled particles exhibits spontaneous symmetry breaking and self-organization in one dimension, in contrast with previous analytical predictions.
Abstract: We demonstrate that a system of self-propelled particles exhibits spontaneous symmetry breaking and self-organization in one dimension, in contrast with previous analytical predictions. To explain this surprising result we derive a new continuum theory that can account for the development of the symmetry broken state and belongs to the same universality class as the discrete self-propelled particle model.
TL;DR: In this paper, a first order phase transition was found in liquid carbon using atomistic simulation methods and Brenner's bond order potential, which is the first nonempirical evidence of a liquid-liquid transition between thermodynamically stable fluids.
Abstract: A first order phase transition is found in liquid carbon using atomistic simulation methods and Brenner{close_quote}s bond order potential. The phase line is terminated by a critical point at 8801thinspthinspK and 10.56thinspthinspGPa and by a triple point on the graphite melting line at 5133thinspthinspK and 1.88thinspthinspGPa. The phase change is associated with density and structural changes. The low-density liquid is predominantly sp bonded with little sp{sup 3} character. The high-density liquid is mostly sp{sup 3} bonded with little sp character. This is the first nonempirical evidence of a liquid-liquid transition between thermodynamically stable fluids. {copyright} {ital 1999} {ital The American Physical Society}
TL;DR: In this article, a solvent-induced phase transition in pentacene thin films, from a thin film phase to a bulk-like phase, was reported, where the plane spacing of the entire layer shifts abruptly from the elongated (001) plane spacing to the bulk value.
Abstract: We report a solvent-induced phase transition in pentacene thin films, from a “thin film” phase to a bulk-like phase. X-ray diffraction indicates that as-deposited thermally evaporated pentacene films consist mainly of (001)-oriented pentacene with an elongated (001) plane spacing of 15.5±0.1 A, and a minor amount with a (001) plane spacing of 14.5±0.1 A. When such films are exposed to solvents such as acetone, isopropanol, or ethanol, the plane spacing of the entire layer shifts abruptly from the elongated (001) plane spacing to the bulk value and this shift is accompanied by a macroscopic change in film morphology. While molecular ordering is maintained as indicated by x-ray diffraction, thin film transistor performance is severely degraded, most likely as a result of the morphological changes in the film.
TL;DR: The examination of phase transitions and critical phenomena has dominated statistical physics for the latter half of this century--there is a great theoretical challenge in solving special statistical mechanical models and beautiful experimental results have elucidated the singularities in phase transitions.
Abstract: The examination of phase transitions and critical phenomena has dominated statistical physics for the latter half of this century--there is a great theoretical challenge in solving special statistical mechanical models. Additionally, beautiful experimental results have elucidated the singularities (critical behavior) that occur in phase transitions. Although a few spectacular successes in the exact solution of simple models have occurred, interesting systems have mostly proven to be intractable from the analytic perspective. Because many physically disparate systems show identical critical behavior, identifying and understanding general principles of universality and their relationship to microscopic symmetries are of fundamental importance
TL;DR: In this article, the transition from the 1A1 low-spin state at low temperatures to the 5T2 high-spin states at elevated temperatures is accompanied by a large increase in metal-ligand bond lengths.
TL;DR: A bulk transition between a highly ordered smectic and an isotropic phase induces a sharp change from a rigid to a soft behavior, with consequent effects on the tack properties of the liquid crystalline polymer and on the dewetting dynamics of a liquid on its surface.
Abstract: The spreading velocity of liquids on the surface of a liquid crystalline polymer can be tremendously affected by a slight temperature change. Indeed, a bulk transition between a highly ordered smectic and an isotropic phase induces a sharp change from a rigid to a soft behavior, with consequent effects on the tack properties of the liquid crystalline polymer and on the dewetting dynamics of a liquid on its surface.
TL;DR: In this paper, the existence and stability of stationary solutions of an integrodifferential model for phase transitions was studied, which is a gradient flow for a free energy functional with general nonlocal integrals penalizing spatial nonuniformity.
Abstract: We study the existence and stability of stationary solutions of an integrodifferential model for phase transitions, which is a gradient flow for a free energy functional with general nonlocal integrals penalizing spatial nonuniformity. As such, this model is a nonlocal extension of the AllenCahn equation, which incorporates long-range interactions. We find that the set of stationary solutions for this model is much larger than that of the AllenCahn equation.
TL;DR: The high-temperature phase transitions of cubic perovskites have been studied using powder neutron diffraction and the Rietveld method as discussed by the authors, and the transition from the tetragonal to cubic phase is consistent with a continuous phase transition.
Abstract: The high-temperature phase transitions of ${\mathrm{SrZrO}}_{3}$ have been studied using powder neutron diffraction and the Rietveld method. The material is tetragonal $(I4/mcm)$ between \ensuremath{\sim}1020 and 1360 K. At higher temperatures (g1360 K) the structure was found to be the ideal cubic perovskite $(Pm3\ifmmode\bar\else\textasciimacron\fi{}m).$ From the neutron-diffraction data and the space-group assignments, the transition from the tetragonal to cubic phase is consistent with a continuous phase transition. The angle of tilt of the oxygen octahedron in the tetragonal phase is taken to be the order parameter and its temperature variation is typical of a tricritical phase transition.
TL;DR: In this paper, electrical conductivity measurements indicate that fluid hydrogen achieves the minimum conductivity of a metal at 140 GPa, ninefold initial liquid hydrogen density of states with a Fermi surface and 2600 K.
Abstract: Electrical conductivity measurements indicate that fluid hydrogen achieves the minimum conductivity of a metal at 140 GPa, ninefold initial liquid-${\mathrm{H}}_{2}$ density, and 2600 K. Metallization density is defined to be that at which the electronic mobility gap ${E}_{g}$ is reduced by pressure to ${E}_{g}\ensuremath{\sim}{k}_{B}T,$ at which point ${E}_{g}$ is filled in by fluid disorder to produce a metallic density of states with a Fermi surface and the minimum conductivity of a metal. High pressures and temperatures were obtained with a two-stage gun, which accelerates an impactor up to 7 km/sec. A strong shock wave is generated on impact with a holder containing liquid hydrogen at 20 K. The impact shock is split into a shock wave reverberating in hydrogen between two stiff ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ anvils. This compression heats hydrogen quasi-isentropically to about twice its melting temperature and lasts \ensuremath{\sim}100 ns, sufficiently long to achieve equilibrium and sufficiently short to preclude loss of hydrogen by diffusion and chemical reactions. The measured conductivity increases four orders of magnitude in the range 93 to 140 GPa and is constant at 2000 (\ensuremath{\Omega} ${\mathrm{c}\mathrm{m})}^{\mathrm{\ensuremath{-}}1}$ from 140 to 180 GPa. This conductivity is that of fluid Cs and Rb undergoing the same transition at 2000 K. This measured value is within a factor of 5 or less of hydrogen conductivities calculated with (i) minimum conductivity of a metal, (ii) Ziman model of a liquid metal, and (iii) tight-binding molecular dynamics. At metallization this fluid is \ensuremath{\sim}90 at. % ${\mathrm{H}}_{2}$ and 10 at. % H with a Fermi energy of \ensuremath{\sim}12 eV. Fluid hydrogen at finite temperature undergoes a Mott transition at ${D}_{m}^{1/3}{a}^{*}=0.30,$ where ${D}_{m}$ is the metallization density and ${a}^{*}$ is the Bohr radius of the molecule. Metallization occurs at a lower pressure in the fluid than predicted for the solid probably because crystalline and orientational phase transitions in the ordered solid do not occur in the fluid and because of many-body and structural effects. Tight-binding molecular dynamics calculations by Lenosky et al. suggest that fluid metallic hydrogen is a novel state of condensed matter. Protons are paired transiently and exchange on a timescale of a few molecular vibrational periods, $\ensuremath{\sim}{10}^{\ensuremath{-}14}\mathrm{sec}.$ Also, the kinetic, vibrational, and rotational energies of the dynamically paired protons are comparable.
TL;DR: In this article, the authors investigated the diffuse phase transition accompanying the formation of submicrometric ferromagnetic-metallic (FM) domains embedded in the antiferromagnetic charge-ordered state, which is caused by quenched random field originating from Cr impurities substituted on the Mn sites.
Abstract: We have investigated the diffuse phase transition accompanying the formation of submicrometric ferromagnetic-metallic (FM) domains embedded in the antiferromagnetic charge-ordered state in ${\mathrm{Nd}}_{1/2}{\mathrm{Ca}}_{1/2}{\mathrm{MnO}}_{3}$ crystals, which is caused by quenched random field originating from Cr impurities substituted on the Mn sites. The fraction of the FM phase volume or the size of the FM cluster can be controlled to a large extent by the magnetic-field annealing as well as the Cr content. The observed phenomena are reminiscent of those of relaxor ferroelectrics composed of ferroelectric clusters embedded in paraelectric matrix.
TL;DR: In this paper, the lattice models of traffic are proposed to describe the jamming transition in traffic flow on a highway in terms of thermodynamic terminology of phase transitions and critical phenomena.
Abstract: The lattice models of traffic are proposed to describe the jamming transition in traffic flow on a highway in terms of thermodynamic terminology of phase transitions and critical phenomena. They are the lattice versions of the hydrodynamic model of traffic. Two lattice models are presented: one is described by the differential-difference equation where time is a continuous variable and space is a discrete variable, and the other is the difference equation in which both time and space variables are discrete. We apply the linear stability theory and the nonlinear analysis to the lattice models. It is shown that the time-dependent Ginzburg–Landau (TDGL) equation is derived to describe the traffic flow near the critical point. A thermodynamic theory is formulated for describing the phase transitions and critical phenomena. It is also shown that the perturbed modified Korteweg-de Vries (MKdV) equation is derived to describe the traffic jam.
TL;DR: 31P-NMR indicates the coexistence, within a certain range of temperatures, of lamellar and hexagonal phases, or hexagonal phase precursors, relevant in the interpretation of certain forms of interfacial enzyme activation and in the regulation and dynamics of the bilayer structure of cell membranes.
TL;DR: In this paper, a discrete convolution model for Ising-like phase transitions is derived as an l 2-gradient flow for a Helmholtz free energy functional with general long range interactions.
Abstract: We study a discrete convolution model for Ising-like phase transitions. This nonlocal model is derived as an l
2-gradient flow for a Helmholtz free energy functional with general long range interactions. We construct traveling waves and stationary solutions, and study their uniqueness and stability. In particular, we find some criteria for “propagation” and “pinning”, and compare our results with those for a previously studied continuum convolution model.
TL;DR: In this article, the crystal structure and a phase transition of gadolinium orthoborate, GdBO3, were studied by electron diffraction and X-ray powder diffraction.
Abstract: The crystal structure and a phase transition of gadolinium orthoborate, GdBO3, were studied by electron diffraction and X-ray powder diffraction. GdBO3 crystallizes in the vaterite structure (LT), in a rhombohedral space group R32 with the lattice constants of a = 6.6357(2) A and c = 26.706(1) A. The structure of the LT phase was derived from the hexagonal YBO3 structure and refined using X-ray powder diffraction data. The structure consists of tetrahedral polyborate group B3O99- and the gadolinium atoms, located respectively on the 3-fold screw axis and a general position. The material undergoes a first-order phase transition with a large thermal hysteresis. The high-temperature (HT) phase crystallizes in a calcite related structure with the lattice constants of a = 4.1154(2) and c = 8.592(1) A, which consists of planer triangular borate group BO33-. The observed large thermal hysteresis of the phase transition is mainly caused by a structural change of the borate group, from B3O99- in the LT phase to BO...
TL;DR: In this article, a detailed computer simulation study of Gay-Berne particles interacting via a potential parametrized to reflect the anisotropic forces based on a fit to a realistic mesogenic molecule is presented.
Abstract: The Gay–Berne potential is proving to be a valuable model with which to investigate the behavior of liquid crystals using computer simulation techniques. The potential contains four independent parameters which control the anisotropy in the attractive and repulsive interactions. The choice of these parameters is not straightforward and it would seem that those employed in some simulations are not strictly appropriate for mesogenic rodlike molecules. Here we report a detailed computer simulation study of Gay–Berne particles interacting via a potential parametrized to reflect the anisotropic forces based on a fit to a realistic mesogenic molecule. The behavior of the phases and the transitions between them have been investigated for a system of 2000 particles using isothermal–isobaric Monte Carlo simulations. At low pressures, this Gay–Berne mesogen exhibits isotropic, smectic A and smectic B phases but, as the pressure is increased, so a nematic phase is added to the sequence. The nature of the phase transitions and the phase diagram are compared where possible with those of real mesogens. The structures of the four phases have been investigated in detail for a larger system of 16 000 particles using canonical molecular dynamics simulations at state points taken from the phase diagram determined from the Monte Carlo simulations. A wide range of singlet and pair distribution functions were evaluated together with orientational correlation coefficients and, for the smectic phases, a bond orientation correlation function. The results for these properties were used to identify the phases, to consider their structure at a quantitative level and, where possible, to make contact with experimental studies and the predictions of theories of liquid crystals. It would appear that with this parametrization, the Gay–Berne potential provides a powerful tool with which to understand the behavior of real liquid crystals and to test the predictions of theory.
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TL;DR: In this paper, the authors review different aspects of field theory at zero and finite temperature, related to the theory of phase transitions, and discuss different renormalization conditions for the effective potential at zero temperature.
Abstract: We review different aspects of field theory at zero and finite temperature, related to the theory of phase transitions. We discuss different renormalization conditions for the effective potential at zero temperature, emphasizing in particular the MS-bar renormalization scheme. Finite temperature field theory is discussed in the real and imaginary time formalisms, showing their equivalence in simple examples. Bubble nucleation by thermal tunneling, and the subsequent development of the phase transition is described in some detail. Some attention is also devoted to the breakdown of the perturbative expansion and the infrared problem in the finite temperature field theory. Finally the application to baryogenesis at the electroweak phase transition is done in the Standard Model and in the Minimal Supersymmetric Standard Model. In all cases we have translated the condition of not washing out any previously generated baryon asymmetry by upper bounds on the Higgs mass.
TL;DR: In this paper, it has been suggested that the structural phase transition is driven by a band Jahn-Teller distortion involving redistribution of electrons between 3d sub-bands of different symmetries.
Abstract: Polarized neutron scattering has been used to determine the changes in the distribution of unpaired electrons which take place in the martensitic transition in Ni2MnGa. Ni2MnGa is a ferromagnetic Heusler alloy which undergoes a reversible transition at about 220 K from a high temperature cubic phase to a low temperature tetragonal one. It has been suggested, on the basis of band structure calculations, that the structural phase transition is driven by a band Jahn-Teller distortion involving redistribution of electrons between 3d sub-bands of different symmetries. The results of the neutron scattering experiments show that the transition from the cubic to the tetragonal phase is accompanied by a transfer of magnetic moment from Mn to Ni. The unpaired electrons in the cubic phase have overall eg symmetry. In the tetragonal phase, the degeneracy of the eg and t2g bands is raised and the unpaired electrons are redistributed in such a way that the sub-bands based on orbitals extending towards the c-axis are preferentially occupied. Although the experimental moments differ in detail from those expected from band structure calculations, the change in symmetry of the magnetization distribution is consistent with a band Jahn-Teller origin for the phase transition.
TL;DR: The one-dimensional lattice hydrodynamic model of traffic is extended to the two-dimensional traffic flow and it is shown that the phase transition among the freely moving phase, the coexisting phase, and the uniformly congested phase occurs below the critical point.
Abstract: Phase transition and critical phenomenon are investigated in the two-dimensional traffic flow numerically and analytically. The one-dimensional lattice hydrodynamic model of traffic is extended to the two-dimensional traffic flow in which there are two types of cars (northbound and eastbound cars). It is shown that the phase transition among the freely moving phase, the coexisting phase, and the uniformly congested phase occurs below the critical point. Above the critical point, no phase transition occurs. The value a(c) of the critical point decreases as increasing fraction c of the eastbound cars for c
TL;DR: In this article, the authors report that sol-gel coating of and subsequent heat treatment at relatively low temperature greatly improves the structural stability of cathodes and exhibit excellent structural stability, retaining 86 and 84 %, respectively, of their initial capacities after 47 cycles between 4.4 and at the rate.
Abstract: We report that sol‐gel coating of and subsequent heat‐treatment at relatively low temperature greatly improve the structural stability of cathodes. Coated materials heat‐treated at 400 and exhibit excellent structural stability, retaining 86 and 84 %, respectively, of their initial capacities after 47 cycles between 4.4 and at the rate. This is attributed to the disappearance of the transition to a hexagonal phase from a monoclinic phase at during cycling, a result of the formation of nonuniform distribution throughout the particle, i.e., higher concentration near the particle surface. In contrast, coated heat‐treated at that shows unifom distribution throughout the particles exhibits this phase transition during cycling, as does uncoated , leading to 51 % capacity loss after 47 cycles. This phase transition also increases cation disorder upon cycling. ©2000 The Electrochemical Society
TL;DR: In this paper, the authors focus on the entropic depletion interaction as a means to tune the range of attraction between colloids and show that meta-stable critical fluctuations may enhance the rate of crystal nucleation.
Abstract: Increase in visible order can be associated with an increase in microscopic disorder. This phenomenon leads to many counter-intuitive phenomena such as entropy driven crystallization and phase separation. I devote special attention to the entropic depletion interaction as a means to tune the range of attraction between colloids. The range of the intermolecular potential determines whether or not stable liquid-vapor coexistence is possible. For short range attraction, the liquid-vapor transition may be located below the sublimation line. Under those conditions, meta-stable critical fluctuations may enhance the rate of crystal nucleation