QCD Phase Transitions, Volume 15
Schaefer, T.; Shuryak, E.
1999-03-20
The title of the workshop, ''The QCD Phase Transitions'', in fact happened to be too narrow for its real contents. It would be more accurate to say that it was devoted to different phases of QCD and QCD-related gauge theories, with strong emphasis on discussion of the underlying non-perturbative mechanisms which manifest themselves as all those phases. Before we go to specifics, let us emphasize one important aspect of the present status of non-perturbative Quantum Field Theory in general. It remains true that its studies do not get attention proportional to the intellectual challenge they deserve, and that the theorists working on it remain very fragmented. The efforts to create Theory of Everything including Quantum Gravity have attracted the lion share of attention and young talent. Nevertheless, in the last few years there was also a tremendous progress and even some shift of attention toward emphasis on the unity of non-perturbative phenomena. For example, we have seen some efforts to connect the lessons from recent progress in Supersymmetric theories with that in QCD, as derived from phenomenology and lattice. Another example is Maldacena conjecture and related development, which connect three things together, string theory, super-gravity and the (N=4) supersymmetric gauge theory. Although the progress mentioned is remarkable by itself, if we would listen to each other more we may have chance to strengthen the field and reach better understanding of the spectacular non-perturbative physics.
QCD PHASE TRANSITIONS-VOLUME 15.
SCHAFER,T.
1998-11-04
The title of the workshop, ''The QCD Phase Transitions'', in fact happened to be too narrow for its real contents. It would be more accurate to say that it was devoted to different phases of QCD and QCD-related gauge theories, with strong emphasis on discussion of the underlying non-perturbative mechanisms which manifest themselves as all those phases. Before we go to specifics, let us emphasize one important aspect of the present status of non-perturbative Quantum Field Theory in general. It remains true that its studies do not get attention proportional to the intellectual challenge they deserve, and that the theorists working on it remain very fragmented. The efforts to create Theory of Everything including Quantum Gravity have attracted the lion share of attention and young talent. Nevertheless, in the last few years there was also a tremendous progress and even some shift of attention toward emphasis on the unity of non-perturbative phenomena. For example, we have seen some. efforts to connect the lessons from recent progress in Supersymmetric theories with that in QCD, as derived from phenomenology and lattice. Another example is Maldacena conjecture and related development, which connect three things together, string theory, super-gravity and the (N=4) supersymmetric gauge theory. Although the progress mentioned is remarkable by itself, if we would listen to each other more we may have chance to strengthen the field and reach better understanding of the spectacular non-perturbative physics.
Volume phase transitions of cholesteric liquid crystalline gels
Matsuyama, Akihiko
2015-05-07
We present a mean field theory to describe anisotropic deformations of a cholesteric elastomer without solvent molecules and a cholesteric liquid crystalline gel immersed in isotropic solvents at a thermal equilibrium state. Based on the neoclassical rubber theory of nematic elastomers, we derive an elastic energy and a twist distortion energy, which are important to determine the shape of a cholesteric elastomer (or gel). We demonstrate that when the elastic energy dominates in the free energy, the cholesteric elastomer causes a spontaneous compression in the pitch axis and elongates along the director on the plane perpendicular to the pitch axis. Our theory can qualitatively describe the experimental results of a cholesteric elastomer. We also predict the first-order volume phase transitions and anisotropic deformations of a gel at the cholesteric-isotropic phase transition temperature. Depending on a chirality of a gel, we find a prolate or oblate shape of cholesteric gels.
Calculation of the volume effect at an electron phase transition in pure cerium and praseodymium
NASA Astrophysics Data System (ADS)
Ponomareva, S. A.; Koval', Yu. N.; Ponomarev, A. P.
2014-03-01
The experimental values of the volume effect at an electronic phase transition in several rare-earth metals are discussed. Specifically, volume changes at phase transitions in cerium and praseodymium are calculated using a semiphenomenological relationship derived in terms of the Falikov-Ramirez-Kimball model. A number of factors influencing the amount of the volume effect at electronic phase transitions are analyzed.
Deconfinement phase transition in a finite volume in the presence of massive particles
Ait El Djoudi, A.; Ghenam, L.
2012-06-27
We study the QCD deconfinement phase transition from a hadronic gas to a Quark-Gluon Plasma, in the presence of massive particles. Especially, the influence of some parameters as the finite volume, finite mass, flavors number N{sub f} on the transition point and on the order of the transition is investigated.
Pressure-induced volume collapse and structural phase transitions in SrRuO{sub 3}
Zhernenkov, Mikhail; Fabbris, Gilberto; Chmaissem, Omar; Mitchell, J.F.; Zheng, H.; Haskel, Daniel
2013-09-15
We report on the low temperature (6 K) structural properties of SrRuO{sub 3} under quasi-hydrostatic pressure studied by synchrotron X-ray powder diffraction in a diamond anvil cell. First principle calculations predict a first-order perovskite (Pv) to post-perovskite (pPv) phase transition at ∼40 GPa accompanied by a 1.9% volume collapse. Our results rule out the occurrence of a pPv phase to 54 GPa. Instead, we find a Pv to monoclinic to triclinic sequence of phase transitions. The monoclinic to triclinic phase transition at ∼38 GPa is accompanied by a 3.5% volume collapse. X-ray absorption spectroscopy indicates that this volume collapse is not accompanied by a change in Ru valence state. Our results should help guide improvements to theoretical treatments of this and other correlated d-electron systems based on density functional theory. - Graphical abstract: Unit cell volume as a function of pressure (T=6 K). Black squares and red circles correspond to Ne and He pressure media, respectively. Blue dashed lines are fit to the data before the volume collapse using a second-order Birch–Murnaghan equation of state excluding (lower curve) and including (upper curve) neutron diffraction data for the low temperature, ambient pressure volume. Dashed lines denote structural phase boundaries. Display Omitted - Highlights: • Crystal structure of SrRuO3 was studied under high pressure up to 54 GPa. • Pv to monoclinic to triclinic sequence of phase transitions was observed. • Transition to triclinic phase at ∼38 GPa is accompanied by a 3.5% volume collapse. • Volume collapse in SrRuO3 is not driven by a change in Ru valence state. • Pv-to-pPv phase transition predicted by DFT at 40 Gpa is not observed up to 54 GPa.
Multiphysics modelling of volume phase transition of ionic hydrogels responsive to thermal stimulus.
Li, Hua; Wang, Xiaogui; Wang, Zijie; Lam, K Y
2005-09-16
This paper presents the analysis of the volume phase transition of ionic thermo-sensitive hydrogels to thermal stimulus through mathematical modelling. The model is termed the multi-effect-coupling thermal-stimulus (MECtherm) model and it considers the effects of multi-phases and multi-physics. Its application to steady-state analysis of the hydrogels in swelling equilibrium is validated against available experimental data for the relation between volume swelling ratio and temperature, in which very good agreement is achieved. The phenomenon of volume phase transition is studied for the thermal-stimulus responsive hydrogel. The numerical studies predict well the influences of initially fixed charge density and initial volume fraction of polymeric network on the swelling equilibrium of the hydrogels.
Ghenam, L.; Djoudi, A. Ait El
2012-06-27
We study the finite size and finite mass effects for the thermal deconfinement phase transition in Quantum Chromodynamics (QCD), using a simple model of coexistence of hadronic (H) gas and quark-gluon plasma (QGP) phases in a finite volume. We consider the equations of state of the two phases with the QGP containing two massless u and d quarks and massive s quarks, and a hadronic gas of massive pions, and we probe the system near the transition. For this, we examine the behavior of the most important hydrodynamical quantities describing the system, at a vanishing chemical potential ({mu}= 0), with temperature and energy density.
Su, Wenjuan; Zhao, Kongshuang; Wei, Jingjing; Ngai, To
2014-11-21
Dielectric relaxation behaviors of three types of thermally sensitive poly(N-isopropylacrylamide) (PNIPAM) microgels with different cross-linking density distributions were investigated in a frequency range from 40 Hz to 110 MHz at temperatures from 15 °C to 55 °C. After eliminating the electrode polarization at low frequency, two remarkable relaxations were observed, one in the kHz frequency range and the other in the MHz range. The low-frequency relaxation is attributed to the counterion polarization in the whole measuring temperature range, while the relaxation at high-frequency is probably dominated by different polarization mechanisms depending on below or above the volume phase transition temperature (VPTT): it is considered as micro-Brownian motion of side groups of PNIPAM when T < VPTT and interfacial polarization when T > VPTT. The temperature dependence of the dielectric parameters for both the relaxations presents an abrupt change around 32.5 °C, indicating the occurrence of phase transition. Based on the analysis and discussion about the micro-Brownian motion of the side groups, a possible microstructure for the microgels before and after the collapse of PNIPAM was suggested. A dielectric model to describe the collapsing microgel suspension was proposed, from which the electrical and structural parameters of the suspension were calculated. The information on the internal structure and hydration dynamic behavior of microgels was obtained by using the thermodynamic parameters which were calculated based on the Eyring equation. Our results reveal that the spatial distribution of the cross-linking density distribution has almost no effect on the volume phase transition temperature, but markedly affects the swelling capacity of PNIPAM microgels at low temperatures.
Wolff, Manuel; Braun, Dieter; Nash, Michael A
2014-07-15
Environmentally responsive polymers are becoming increasingly important in the biomaterials field for use as diagnostic reagents, drug carriers, and tissue engineering scaffolds. Characterizing polymer phase transitions by cloud point curves typically requires large milliliter volumes of sample at high micromolar solution concentrations. Here we present a method based on quantification of thermophoretic Soret diffusion that allows determination of polymer phase transitions using only ~1 μL of liquid at dilute nanomolar concentrations, effectively reducing the amount of sample required by a factor of 10(6). We prepared an oligo(ethylene glycol) (OEG) methyl ether methacrylate copolymer via RAFT polymerization. End-group modification with fluorescent BODIPY-maleimide provided a dye-labeled pOEG-BODIPY conjugate with a lower critical solution temperature (LCST) in the range of ~25-35 °C. Thermophoresis measurements in dilute solution demonstrated a marked change in polymer thermodiffusion in the vicinity of the LCST. We measured the temperature dependence of thermodiffusion and transformed these data sets into sigmoidal curves characterizing the phase transition of the polymer. Finite element modeling suggested a correction to the measured values that brought the transition temperatures measured by thermophoresis into accord with the cloud point curves. Our results demonstrate that observation of polymer thermodiffusion in a low volume dilute format is a facile method for determining polymer phase transition temperatures.
Ultrasonic and Viscoelastic Properties of Small-Volume Mesogen Samples at the Phase Transition
NASA Astrophysics Data System (ADS)
Maksimochkin, G. I.; Pasechnik, S. V.; Usol'Zeva, N. V.; Bykova, V. V.
2010-06-01
The ultrasonic method is very informative for research of viscoelastic properties of mesogens at changing thermodynamic parameters of state. At phase transitions, anomalies of the velocity of propagation and coefficient of absorption of ultrasound waves as well as of viscoelastic properties are observed. These anomalies for liquid crystals are most pronounced at frequencies lower that 1 MHz. Up to now acoustic resonators with volumes of about 5 cm3 have been used, which considerably prevents the application of this method for science-based newly synthesized mesogenic compounds. This article presents experimental results obtained by means of a new resonator method with samples with volumes of 0.06 cm3 to 0.15 cm3. The velocity and coefficient of absorption of ultrasound were measured at frequencies from 0.68 MHz to 1.63 MHz for four mesogens: esters of alkyloxyphenylcyclo-hexane-2-carbonic acid and n-amylphenol. It has been shown that temperature dependencies of ultrasonic parameters obtained in small-volume cells correspond to those established previously by traditional methods using measuring cells with larger volumes. It is also shown that the temperature dependencies of the bulk viscosity and the bulk elasticity modulus derived from our ultrasonic measurements, in general features, duplicate the corresponding dependencies obtained by standard methods. It confirms that the proposed acoustic method is suitable for routine investigations of viscoelastic properties of small-volume samples of mesogenic compounds.
Guennou, Mael; Bouvier, Pierre; Garbarino, Gaston; Kreisel, Jens; Salje, Ekhard K H
2011-12-07
We report a pressure-dependent investigation of KMnF(3) by x-ray diffraction up to 30 GPa. The results are discussed in the framework of Landau theory and in relation to the isostructural phase transition in SrTiO(3). The phase transition temperature near 186 K in KMnF(3) shifts to room temperature at a critical pressure of P(c) = 3.4 GPa; the pressure dependence of the transition point follows ΔP(c)/ΔT(c) = 0.0315 GPa K(-1). The transition becomes second order under high pressure, close to the tricritical point. The phase transition is determined by the rotation of MnF(6) octahedra with their simultaneous expansion along the rotation axis. The rotation angle was found to increase to 10.5° at 24 GPa. An additional anomaly was observed at higher pressure around 25 GPa, suggesting a further phase transition.
NASA Astrophysics Data System (ADS)
Guennou, Mael; Bouvier, Pierre; Garbarino, Gaston; Kreisel, Jens; Salje, Ekhard K. H.
2011-12-01
We report a pressure-dependent investigation of KMnF3 by x-ray diffraction up to 30 GPa. The results are discussed in the framework of Landau theory and in relation to the isostructural phase transition in SrTiO3. The phase transition temperature near 186 K in KMnF3 shifts to room temperature at a critical pressure of Pc = 3.4 GPa the pressure dependence of the transition point follows ΔPc/ΔTc = 0.0315 GPa K-1. The transition becomes second order under high pressure, close to the tricritical point. The phase transition is determined by the rotation of MnF6 octahedra with their simultaneous expansion along the rotation axis. The rotation angle was found to increase to 10.5° at 24 GPa. An additional anomaly was observed at higher pressure around 25 GPa, suggesting a further phase transition.
NASA Astrophysics Data System (ADS)
Takigawa, T.; Araki, H.; Takahashi, K.; Masuda, T.
2000-11-01
The effects of mechanical stress on the volume phase transition of a poly(N-isopropylacrylamide) (PNIPA) gel as well as a copolymer gel composed of N-isopropylacrylamide (NIPA) and sodium acrylate (SA) were investigated in the relatively low stress region. The PNIPA gel without elongational stress showed the behavior close to the second order phase transition. The character of the first order transition became clear under tension, and the transition temperature increased with increasing applied stress. Similar behavior was observed for the NIPA-SA copolymer gel, but the copolymer gel showed the first order transition in the whole stress range investigated. The thermodynamical linear region, where the transition temperature varies linearly with applied stress, was narrower than the mechanical linear region determined by the stress-strain relation of the gels. The change in the transition behavior by the application of the mechanical stress originated chiefly from the volume change in the gels by the applied mechanical stress. It was found that the curve of the transition temperature against applied stress corresponds to the phase boundary between the swollen and collapsed phases for the gels. On the basis of the experimental data, a phenomenological model describing the volume phase transition of the polymer gels is proposed in the frame of the Landau-type free energy expression.
Superresolution Microscopy of the Volume Phase Transition of pNIPAM Microgels
NASA Astrophysics Data System (ADS)
Conley, Gaurasundar Marc; Nöjd, Sofi; Braibanti, Marco; Schurtenberger, Peter; Scheffold, Frank
Hierarchical polymer structures such as pNIPAM microgels have been extensively studied for their ability to undergo significant structural and physical transformations that can be controlled by external stimuli such as temperature, pH or solvent composition. Here we discuss in-situ three-dimensional superresolution microscopy of dye-labeled submicron sized PNiPAM microgels. We use direct STochastic Optical Reconstruction Microscopy (dSTORM) to study the internal density distribution and the particle-to-particle variability of the volume phase transition. Moreover we discuss the potential of this technique towards future applications to more complex architectures for example microgel with anisotropic shape or ones that are doped or decorated with nanoparticles.
Identification of volume phase transition of a single microgel particle using optical tweezers
NASA Astrophysics Data System (ADS)
Karthickeyan, D.; Gupta, Deepak K.; Tata, B. V. R.
2016-10-01
Poly (N-isopropyl acrylamide-co-acrylic acid) (PNIPAM-co-Aac) microgel particles are pH responsive and exhibit volume phase transition (VPT) upon variation of pH. Dynamic light scattering (DLS) is used conventionally to identify VPT and requires a dilute suspension with particle concentration ˜107 particles cm-3 and if particles are polydisperse in nature, DLS data interpretation is relatively difficult. Here we show that optical tweezers allow one to measure the VPT of a single microgel particle by measuring the optical trap stiffness, κ of trapped particle as a function of pH. We report here a sudden change in κ at VPT, which is shown to arise from a sudden decrease in particle diameter with a concomitant increase in the refractive index of the particle at VPT.
Large volume collapse observed in the phase transition in cubic PbCrO[subscript 3] perovskite
Xiao, Wansheng; Tan, Dayong; Xiong, Xiaolin; Liu, Jing; Xu, Jian
2010-08-27
When cubic PbCrO{sub 3} perovskite (Phase I) is squeezed up to {approx}1.6 GPa at room temperature, a previously undetected phase (Phase II) has been observed with a 9.8% volume collapse. Because the structure of Phase II can also be indexed into a cubic perovskite as Phase I, the transition between Phases I and II is a cubic to cubic isostructural transition. Such a transition appears independent of the raw materials and synthesizing methods used for the cubic PbCrO{sub 3} perovskite sample. In contrast to the high-pressure isostructural electronic transition that appears in Ce and SmS, this transition seems not related with any change of electronic state, but it could be possibly related on the abnormally large volume and compressibility of the PbCrO{sub 3} Phase I. The physical mechanism behind this transition and the structural and electronic/magnetic properties of the condensed phases are the interesting issues for future studies.
NASA Astrophysics Data System (ADS)
Gitterman, Moshe
2014-09-01
In discussing phase transitions, the first thing that we have to do is to define a phase. This is a concept from thermodynamics and statistical mechanics, where a phase is defined as a homogeneous system. As a simple example, let us consider instant coffee. This consists of coffee powder dissolved in water, and after stirring it we have a homogeneous mixture, i.e., a single phase. If we add to a cup of coffee a spoonful of sugar and stir it well, we still have a single phase -- sweet coffee. However, if we add ten spoonfuls of sugar, then the contents of the cup will no longer be homogeneous, but rather a mixture of two homogeneous systems or phases, sweet liquid coffee on top and coffee-flavored wet sugar at the bottom...
Yu, Yang; Beichel, Witali; Dlubek, Günter; Krause-Rehberg, Reinhard; Paluch, Marian; Pionteck, Jürgen; Pfefferkorn, Dirk; Bulut, Safak; Friedrich, Christian; Pogodina, Natalia; Krossing, Ingo
2012-05-21
Positron annihilation lifetime spectroscopy (PALS) was used to study a series of ionic liquids (ILs) with the 1-butyl-3-methylimidazolium cation ([C4MIM](+)) but different anions [Cl](-), [BF4](-), [PF6](-), [OTf](-), [NTf2](-), and [B(hfip)4](-) with increasing anion volumes. Changes of the ortho-positronium (o-Ps) lifetime parameters with temperature were observed for crystalline and amorphous (glass, supercooled, and normal liquid) states. Evidence for distinct phase transitions, e.g. melting, crystallization and solid-solid transitions, was observed in several PALS experiments. The o-Ps mean lifetime τ3 showed smaller values in the crystalline phase due to dense packing of the material compared to the amorphous phase. The o-Ps lifetime intensity I3 in the liquid state is clearly smaller than in the crystallized state. This behaviour can be attributed to a solvation of e(+) by the anions, which reduces the Ps formation probability in the normal and supercooled liquid. These phenomena were observed for the first time when applying the PALS technique to ionic liquids by us in one preliminary and in this work. Four of the ionic liquids investigated in this work ([BF4](-), [NTf2](-), [PF6](-) and [Cl](-) ILs) exhibit supercooled phases. The specific hole densities and occupied volumes of those ILs were obtained by comparing the local free volume with the specific volume from pressure-volume-temperature (PVT) experiments. From the o-Ps lifetime, the mean size vh of free volume holes of the four samples was calculated and compared with that calculated according to Fürth's hole theory. The hole volumes from both methods agree well. From the Cohen-Turnbull fitting of viscosity and conductivity against PALS/PVT results, the influence of the free volume on molecular transport properties was investigated.
Li, Tianjiao; Tang, Hui; Wu, Peiyi
2015-03-14
The deswelling and swelling behaviors of poly(2-isopropyl-2-oxazoline)-based hydrogel synthesized by a one-pot microwave-assisted solvent-free reaction were investigated. A distinct hydrophobic collapse of the hydrogel compared with the corresponding aqueous solution was observed by FT-IR spectroscopy combined with two-dimensional correlation spectroscopy (2DCOS) and perturbation-correlation moving-window (PCMW) analyses. The volume phase transition (VPT) temperature of 35 °C during heating and the transition temperature range of 41-30 °C during cooling were determined, indicating different dynamic transition mechanisms during heating and cooling. Water expulsion starting from the benzene ring-centered hydrophobic spots to the surroundings was revealed during deswelling. However, during swelling, although the rebuilding of cross-linking hydrogen bond bridges provided a channel-like microstructure to reswell the hydrogel gradually, a slow, unusual recovery of the amide hydrogen bonds to water molecules was observed.
NASA Astrophysics Data System (ADS)
Zhang, Fan; Wang, Jianchuan; Liu, Shuhong; Du, Yong
2016-10-01
Sn and Sn-based compounds have been attracting a great interest as promising alternative materials for commercial anodes in lithium ion batteries. In this study, the phase evolution of the Li-Sn system during the lithiated processes and the effect of the elastic-strain energies caused by volume change on the phase transition are investigated by means of first-principles calculations. Our calculated results demonstrate that the distorted Li7Sn3 crystal tends to be formed in order to decrease the elastic-strain energy. In addition, our work indicates that the whole lithiated processes under the elastically constrained condition could be classified into two steps. The first step is the two-phase equilibrium process, in which the thermodynamic driving force is large enough to facilitate the phase transition and the plateau voltage could be established. The second step is considered to be the selective equilibrium, in which the thermodynamic driving force is not enough to facilitate the nucleation of the new equilibrium phase due to the elastically constrained conditions and the plateau voltage unformed. Besides, we find that in the Li0.4Sn matrix the nucleation of the αSn is more preferential than the βSn due to the effects of the elastic-strain energies.
NASA Astrophysics Data System (ADS)
Bensalem, S.; Ait El Djoudi, A.
2016-10-01
This work deals with a statistical description of a thermally driven deconfining phase transition (DPT) from a hadronic gas consisting of massless pions to a color-singlet Quark- Gluon Plasma (QGP), in a finite volume. The thermodynamical approach, within a coexistence model is used to investigate the Quantum Chromo-Dynamics DPT occurring between the two phases, at vanishing chemical potential. Considering the color singletness condition for the QGP phase, with massless up and down quarks, the exact total partition function of the studied system is obtained and then employed to calculate mean values of physical quantities, well characterizing the system near the transition. The finite-size effects on the DPT have been investigated through the study of the thermal behavior of the order parameter, the susceptibility and the second cumulant of the probability density. The similarity between the susceptibility and the second cumulant representing the variance is probed for the studied DPT and a parameterization of the variance is proposed for the first time.
Cosmological phase transitions
Kolb, E.W. |
1993-10-01
If modern ideas about the role of spontaneous symmetry breaking in fundamental physics are correct, then the Universe should have undergone a series of phase transitions early in its history. The study of cosmological phase transitions has become an important aspect of early-Universe cosmology. In this lecture I review some very recent work on three aspects of phase transitions: the electroweak transition, texture, and axions.
NASA Astrophysics Data System (ADS)
Vojta, Matthias
2003-12-01
In recent years, quantum phase transitions have attracted the interest of both theorists and experimentalists in condensed matter physics. These transitions, which are accessed at zero temperature by variation of a non-thermal control parameter, can influence the behaviour of electronic systems over a wide range of the phase diagram. Quantum phase transitions occur as a result of competing ground state phases. The cuprate superconductors which can be tuned from a Mott insulating to a d-wave superconducting phase by carrier doping are a paradigmatic example. This review introduces important concepts of phase transitions and discusses the interplay of quantum and classical fluctuations near criticality. The main part of the article is devoted to bulk quantum phase transitions in condensed matter systems. Several classes of transitions will be briefly reviewed, pointing out, e.g., conceptual differences between ordering transitions in metallic and insulating systems. An interesting separate class of transitions is boundary phase transitions where only degrees of freedom of a subsystem become critical; this will be illustrated in a few examples. The article is aimed at bridging the gap between high-level theoretical presentations and research papers specialized in certain classes of materials. It will give an overview on a variety of different quantum transitions, critically discuss open theoretical questions, and frequently make contact with recent experiments in condensed matter physics.
Holographic magnetic phase transition
Lifschytz, Gilad; Lippert, Matthew
2009-09-15
We study four-dimensional interacting fermions in a strong magnetic field, using the holographic Sakai-Sugimoto model of intersecting D4- and D8-branes in the deconfined, chiral-symmetric parallel phase. We find that as the magnetic field is varied, while staying in the parallel phase, the fermions exhibit a first-order phase transition in which their magnetization jumps discontinuously. Properties of this transition are consistent with a picture in which some of the fermions jump to the lowest Landau level. Similarities to known magnetic phase transitions are discussed.
2011-05-01
Park, NC 27709-2211 15. SUBJECT TERMS Quantum Thoery Phase transitions Subir Sachdev Harvard University Office of Sponsored Research 1350...magnetism, and solvable models obtained from string theory. After introducing the basic theory, it moves on to a detailed description of the canonical...students and researchers in condensed matter physics and particle and string theory. Print | Close Quantum Phase Transitions 2nd Edition Subir Sachdev
Anderson, G.W.
1991-09-16
An analytic treatment of the one Higgs doublet, electroweak phase transition is given. The phase transition is first order, occurs by the nucleation of thin walled bubbles and completes at a temperature where the order parameter, {l_angle}{phi}{r_angle}{sub T} is significantly smaller than it is when the origin becomes absolutely unstable. The rate of anomalous baryon number violation is an exponentially function of {l_angle}{phi}{r_angle}{sub T}. In very minimal extensions of the standard model it is quite easy to increase {l_angle}{phi}{r_angle}{sub T} so that anomalous baryon number violation is suppressed after completion of the phase transition. Hence baryogenesis at the electroweak phase transition is tenable in minimal of the standard model. In some cases additional phase transitions are possible. For a light Higgs boson, when the top quark mass is sufficiently large, the state where the Higgs field has a vacuum expectation value {l_angle}{phi}{r_angle} = 246 GeV is not the true minimum of the Higgs potential. When this is the case, and when the top quark mass exceeds some critical value, thermal fluctuations in the early universe would have rendered the state {l_angle}{phi}{r_angle} = 246 GeV unstable. The requirement that the state {l_angle}{phi}{r_angle} = 246 GeV is sufficiently long lived constrains the masses of the Higgs boson and the top quark. Finally, we consider whether local phase transitions can be induced by heavy particles which act as seeds for deformations in the scalar field.
Anderson, G.W.
1991-09-16
An analytic treatment of the one Higgs doublet, electroweak phase transition is given. The phase transition is first order, occurs by the nucleation of thin walled bubbles and completes at a temperature where the order parameter, {l angle}{phi}{r angle}{sub T} is significantly smaller than it is when the origin becomes absolutely unstable. The rate of anomalous baryon number violation is an exponentially function of {l angle}{phi}{r angle}{sub T}. In very minimal extensions of the standard model it is quite easy to increase {l angle}{phi}{r angle}{sub T} so that anomalous baryon number violation is suppressed after completion of the phase transition. Hence baryogenesis at the electroweak phase transition is tenable in minimal of the standard model. In some cases additional phase transitions are possible. For a light Higgs boson, when the top quark mass is sufficiently large, the state where the Higgs field has a vacuum expectation value {l angle}{phi}{r angle} = 246 GeV is not the true minimum of the Higgs potential. When this is the case, and when the top quark mass exceeds some critical value, thermal fluctuations in the early universe would have rendered the state {l angle}{phi}{r angle} = 246 GeV unstable. The requirement that the state {l angle}{phi}{r angle} = 246 GeV is sufficiently long lived constrains the masses of the Higgs boson and the top quark. Finally, we consider whether local phase transitions can be induced by heavy particles which act as seeds for deformations in the scalar field.
NASA Astrophysics Data System (ADS)
Chen, Zhi; Yu, Clare C.
2006-03-01
Noise is present in many physical systems and is often viewed as a nuisance. Yet it can also be a probe of microscopic fluctuations. There have been indications recently that the noise in the resistivity increases in the vicinity of the metal-insulator transition. But what are the characteristics of the noise associated with well-understood first and second order phase transitions? It is well known that critical fluctuations are associated with second order phase transitions, but do these fluctuations lead to enhanced noise? We have addressed these questions using Monte Carlo simulations to study the noise in the 2D Ising model which undergoes a second order phase transition, and in the 5-state Potts model which undergoes a first order phase transition. We monitor these systems as the temperature drops below the critical temperature. At each temperature, after equilibration is established, we obtain the time series of quantities characterizing the properties of the system, i.e., the energy and magnetization per site. We apply different methods, such as the noise power spectrum, the Detrended Fluctuation Analysis (DFA) and the second spectrum of the noise, to analyze the fluctuations in these quantities.
Magnetic fields from phase transitions
NASA Astrophysics Data System (ADS)
Hindmarsh, Mark; Everett, Allen
1998-11-01
The generation of primordial magnetic fields from cosmological phase transitions is discussed, paying particular attention to the electroweak transition and to the various definitions of the ``average'' field that have been put forward. It is emphasized that only the volume average has dynamical significance as a seed for galactic dynamos. On rather general grounds of causality and energy conservation, it is shown that, in the absence of MHD effects that transfer power in the magnetic field from small to large scales, processes occurring at the electroweak transition cannot generate fields stronger than 10-20 G on a scale of 0.5 Mpc. However, it is implausible that this upper bound could ever be reached, as it would require all the energy in the Universe to be turned into a magnetic field coherent at the horizon scale. Non-linear MHD effects seem therefore to be necessary if the electroweak transition is to create a primordial seed field.
String mediated phase transitions
NASA Technical Reports Server (NTRS)
Copeland, ED; Haws, D.; Rivers, R.; Holbraad, S.
1988-01-01
It is demonstrated from first principles how the existence of string-like structures can cause a system to undergo a phase transition. In particular, the role of topologically stable cosmic string in the restoration of spontaneously broken symmetries is emphasized. How the thermodynamic properties of strings alter when stiffness and nearest neighbor string-string interactions are included is discussed.
Glass transition: 'Spin' fluctuations or free volume ?
NASA Astrophysics Data System (ADS)
Skomski, R.
1994-08-01
Using a simple but statistically well-defined Langevin soft-spin model, the behaviour of suddenly quenched glasses is investigated. The non-equilibrium phase diagram is calculated and utilized to discuss the dependence of the glass-transition temperature on the ground-state properties of the material. The true ground state of the model is ordered, but the glass state remains stable below a non-equilibrium glass-transition temperature T o < T eq, where T eq is the temperature of the accompanying equilibrium phase transition. As opposed to semiphenomenological free-volume theories, it is not necessary to fall back on temperature-dependent energy barriers to explain the glass transition. To rationalize the tendency towards glass formation we derive rules analogous to those known as Zachariasen rules in the case of inorganic glasses.
Emergence and Phase Transitions
NASA Astrophysics Data System (ADS)
Sikkema, Arnold
2006-05-01
Phase transitions are well defined in physics through concepts such as spontaneous symmetry breaking, order parameter, entropy, and critical exponents. But emergence --- also exhibiting whole-part relations (such as top-down influence), unpredictability, and insensitivity to microscopic detail --- is a loosely-defined concept being used in many disciplines, particularly in psychology, biology, philosophy, as well as in physics[1,2]. I will review the concepts of emergence as used in the various fields and consider the extent to which the methods of phase transitions can clarify the usefulness of the concept of emergence both within the discipline of physics and beyond.1. Robert B. Laughlin, A Different Universe: Reinventing Physics from the Bottom Down (New York: Basic Books, 2005). 2. George F.R. Ellis, ``Physics and the Real World'', Physics Today, vol. 58, no. 7 (July 2005) pp. 49-54.
Condensation phase transitions in ferrofluids.
Iskakova, L Yu; Smelchakova, G A; Zubarev, A Yu
2009-01-01
Experiments show that under suitable conditions magnetic particles in ferrofluids and other polar suspensions undergo condensation phase transitions and form dense liquidlike or solidlike phases. The problem of fundamental features and scenarios of the phase transitions is one of the central problems of the physics of these systems. This work deals with the theoretical study of scenarios of condensation phase transitions in ferrofluids, consisting of identical magnetic particles. Our results show that, unlike the classical condensation phase transitions, the appearance of the linear chains precedes the magnetic particle bulk condensation. The effect of the chains on the diagrams of the equilibrium phase transitions is studied.
Phase transition phenomenon: A compound measure analysis
NASA Astrophysics Data System (ADS)
Kang, Bo Soo; Park, Chanhi; Ryu, Doojin; Song, Wonho
2015-06-01
This study investigates the well-documented phenomenon of phase transition in financial markets using combined information from both return and volume changes within short time intervals. We suggest a new measure for the phase transition behaviour of markets, calculated as a return distribution conditional on local variance in volume imbalance, and show that this measure successfully captures phase transition behaviour under various conditions. We analyse the intraday trade and quote dataset from the KOSPI 200 index futures, which includes detailed information on the original order size and the type of each initiating investor. We find that among these two competing factors, the submitted order size yields more explanatory power on the phenomenon of market phase transition than the investor type.
Quantum phase transition in space
Damski, Bogdan; Zurek, Wojciech H
2008-01-01
A quantum phase transition between the symmetric (polar) phase and the phase with broken symmetry can be induced in a ferromagnetic spin-1 Bose-Einstein condensate in space (rather than in time). We consider such a phase transition and show that the transition region in the vicinity of the critical point exhibits scalings that reflect a compromise between the rate at which the transition is imposed (i.e., the gradient of the control parameter) and the scaling of the divergent healing length in the critical region. Our results suggest a method for the direct measurement of the scaling exponent {nu}.
NASA Astrophysics Data System (ADS)
Pan, Zan; Cui, Zhu-Fang; Chang, Chao-Hsi; Zong, Hong-Shi
2017-05-01
To investigate the finite-volume effects on the chiral symmetry restoration and the deconfinement transition for a quantum chromodynamics (QCD) system with Nf = 2 (two quark flavors), we apply the Polyakov-loop extended Nambu-Jona-Lasinio model by introducing a chiral chemical potential μ5 artificially. The final numerical results indicate that the introduced chiral chemical potential does not change the critical exponents, but shifts the location of critical end point (CEP) significantly; the ratios for the chiral chemical potentials and temperatures at CEP, μc/μ5c and Tc/T5c, are significantly affected by the system size R. The behavior is that Tc increases slowly with μ5 when R is “large” and Tc decreases first and then increases with μ5 when R is “small.” It is also found that for a fixed μ5, there is a Rmin, where the critical end point vanishes and the whole phase diagram becomes a crossover when R < Rmin. Therefore, we suggest that for the heavy-ion collision experiments, which is to study the possible location of CEP, the finite-volume behavior should be taken into account.
Phase transitions in disordered systems
NASA Astrophysics Data System (ADS)
Hrahsheh, Fawaz Y.
Disorder can have a wide variety of consequences for the physics of phase transitions. Some transitions remain unchanged in the presence of disorder while others are completely destroyed. In this thesis we study the effects of disorder on several classical and quantum phase transitions in condensed matter systems. After a brief introduction, we study the ferromagnetic phase transition in a randomly layered Heisenberg magnet using large-scale Monte-Carlo simulations. Our results provide numerical evidence for the exotic infinite-randomness scenario. We study classical and quantum smeared phase transitions in substitutional alloys A1-xBx. Our results show that the disorder completely destroys the phase transition with a pronounced tail of the ordered phase developing for all compositions x < 1. In addition, we find that short-ranged disorder correlations can have a dramatic effect on the transition. Moreover, we show an experimental realization of the composition-tuned ferromagnetic-to-paramagnetic quantum phase transition in Sr1-xCa xRuO3. We investigate the effects of disorder on first-order quantum phase transitions on the example of the N-color quantum Ashkin-Teller model. By means of a strong disorder renormalization group, we demonstrate that disorder rounds the first-order transition to a continuous one for both weak and strong coupling between the colors. Finally, we investigate the superfluid-insulator quantum phase transition of one-dimensional bosons with off-diagonal disorder by means of large-scale Monte-Carlo simulations. Beyond a critical disorder strength, we find nonuniversal, disorder dependent critical behavior.
Fluctuation driven electroweak phase transition
NASA Technical Reports Server (NTRS)
Gleiser, Marcelo; Kolb, Edward W.
1991-01-01
We examine the dynamics of the electroweak phase transition in the early Universe. For Higgs masses in the range 46 less than or = M sub H less than or = 150 GeV and top quark masses less than 200 GeV, regions of symmetric and asymmetric vacuum coexist to below the critical temperature, with thermal equilibrium between the two phases maintained by fluctuations of both phases. We propose that the transition to the asymmetric vacuum is completed by percolation of these subcritical fluctuations. Our results are relevant to scenarios of baryogenesis that invoke a weakly first-order phase transition at the electroweak scale.
Phase transitions in metastable phases of silicon
NASA Astrophysics Data System (ADS)
Zeng, Zhidan; Zeng, Qiaoshi; Mao, Wendy L.; Qu, Shaoxing
2014-03-01
Phase transitions in indentation induced Si-III/XII phases were investigated using a diamond anvil cell and nanoindentation combined with micro-Raman spectroscopy. The in situ high pressure Raman results demonstrate that the Si-III and Si-XII phases have very similar Raman spectra, indicating their relative amount cannot be determined if they are both present in a sample. The Si-III and Si-XII phases coexist in the indentations produced by a nanoindenter on a single crystalline silicon wafer as a result of the local residual compressive stresses near 1 GPa. High power laser annealing on the indentations can initiate a rapid Si-III/XII → Si-I phase transition. The newly formed polycrystalline Si-I phase initially has very small grain size, and the grains grow when the annealing time is extended. Si-IV phase was not observed in our experiment.
Learning phase transitions by confusion
NASA Astrophysics Data System (ADS)
van Nieuwenburg, Evert P. L.; Liu, Ye-Hua; Huber, Sebastian D.
2017-02-01
Classifying phases of matter is key to our understanding of many problems in physics. For quantum-mechanical systems in particular, the task can be daunting due to the exponentially large Hilbert space. With modern computing power and access to ever-larger data sets, classification problems are now routinely solved using machine-learning techniques. Here, we propose a neural-network approach to finding phase transitions, based on the performance of a neural network after it is trained with data that are deliberately labelled incorrectly. We demonstrate the success of this method on the topological phase transition in the Kitaev chain, the thermal phase transition in the classical Ising model, and the many-body-localization transition in a disordered quantum spin chain. Our method does not depend on order parameters, knowledge of the topological content of the phases, or any other specifics of the transition at hand. It therefore paves the way to the development of a generic tool for identifying unexplored phase transitions.
Phase transition in Liouville theory
Johnston, D. )
1989-11-15
We suggest that the vortices arising in a Kosterlitz-Thouless phase transition in Liouville theory correspond to transitions between different genera, producing the plumber's nightmare'' and other phases that have been predicted in fluid membrane theory from energetic considerations. This transition has previously been invoked by Cates to explain the degeneration of numerical simulations of Gaussian random surfaces into branched polymers. The difficulty in quantizing Liouville theory for {ital d}{gt}1 is conjectured to be due to our insistence on working at a fixed genus.
Phase transition in Liouville theory
NASA Astrophysics Data System (ADS)
Johnston, D.
1989-11-01
We suggest that the vortices arising in a Kosterlitz-Thouless phase transition in Liouville theory correspond to transitions between different genera, producing the ``plumber's nightmare'' and other phases that have been predicted in fluid membrane theory from energetic considerations. This transition has previously been invoked by Cates to explain the degeneration of numerical simulations of Gaussian random surfaces into branched polymers. The difficulty in quantizing Liouville theory for d>1 is conjectured to be due to our insistence on working at a fixed genus.
The general conditional equations which govern the phase equilibria in three-component systems are presented. Using the general conditional equations...a general method has been developed to precalculate the phase equilibria in three-component systems from first principle using computer technique...The method developed has been applied to several model examples and the system Ta-Hf-C. The phase equilibria in three-component systems calculated
Phase transitions in Abelian lattice gauge theories
NASA Astrophysics Data System (ADS)
Cheluvaraja, Srinath
2000-02-01
We study the phase transition in the U (1) lattice gauge theory using the Wilson-Polyakov line as the order parameter. The Wilson-Polyakov line remains very small at strong coupling and becomes non-zero at weak coupling, signalling a confinement-to-deconfinement phase transition. The decondensation of monopole loops is responsible for this phase transition. A finite size scaling analysis of the susceptibility of the Wilson line gives a ratio for icons/Journals/Common/gamma" ALT="gamma" ALIGN="TOP"/> /icons/Journals/Common/nu" ALT="nu" ALIGN="TOP"/> which is quite close to the corresponding value in the three-dimensional planar model. A scaling behaviour of the monopole loop distribution function is also established at the point of the second-order phase transition. A measurement of the plaquette susceptibility at the transition point shows that it does not scale with the four-dimensional volume as is expected of a first-order bulk transition.
Phase Transitions in Brownian Pumps
NASA Astrophysics Data System (ADS)
Dierl, Marcel; Dieterich, Wolfgang; Einax, Mario; Maass, Philipp
2014-04-01
We study stochastic particle transport between two reservoirs along a channel, where the particles are pumped against a bias by a traveling wave potential. It is shown that phase transitions of period-averaged densities or currents occur inside the channel when exclusion interactions between the particles are taken into account. These transitions reflect those known for the asymmetric simple exclusion process. We argue that their occurrence is a generic feature of Brownian motors operating in open systems.
Martensitic phase transition involving dislocations
NASA Astrophysics Data System (ADS)
Le, K. C.; Günther, C.
2015-06-01
A model of solid-solid phase transition involving dislocations in crystals is proposed within the nonlinear continuum dislocation theory (CDT). The co-existence of phases having piecewise constant plastic slip in laminates is possible for the two-well free energy density. The jumps of the plastic slip across the phase interfaces determine the surface dislocation densities at those incoherent boundaries. The number of phase interfaces should be determined by comparing the energy of dislocation arrays and the relaxed energy minimized among uniform plastic slips.
Liquid crystalline phase transitions in hydrogels
NASA Astrophysics Data System (ADS)
Alsayed, A. M.; Dogic, Z.; Islam, M. F.; Yodh, A. G.; Angler, A.; Discher, D. E.
2003-03-01
We investigate the isotropic-nematic (IN) phase transition of fd rods dissolved in P(NIPAAm) gel. The P(NIPAAm) gel exhibits a first order phase transition at 32 C from a low temperature expanded state to a high temperature collapsed state. Surprisingly we found it is possible to induce the nematic phase by keeping the volume of the gel constant and changing temperature. The sample exhibits a continuous and reversible transition from isotropic to nematic phase as the temperature is changed between 24-31 C. This unusual behavior is correlated with the presence of heterogeneities in the gel. Dissolving the rods into the gel effectively changes this concentration dependent lyotropic liquid crystal into temperature dependant system. The possibility that fd/gel system exhibits soft elasticity is currently being explored. Additionally we observe a temperature dependent nematic-smectic phase transition in this system and we studied its kinetics. This work is partially supported by NSF grants DMR-0203378, the PENN MRSEC, DMR-0079909, and NASA grant NAG8-2172.
Phase transitions in nuclear matter
Glendenning, N.K.
1984-11-01
The rather general circumstances under which a phase transition in hadronic matter at finite temperature to an abnormal phase in which baryon effective masses become small and in which copious baryon-antibaryon pairs appear is emphasized. A preview is also given of a soliton model of dense matter, in which at a density of about seven times nuclear density, matter ceases to be a color insulator and becomes increasingly color conducting. 22 references.
Su, Gehong; Zhou, Tao; Liu, Xifei; Zhang, Yulin
2017-10-04
In this study, temperature-dependent FTIR spectroscopy in combination with the perturbation-correlation moving-window (PCMW2D) technique and generalized two-dimensional (2D) correlation analysis was applied to investigate the phase transition mechanism of poly(N-vinylcaprolactam) (PVCL) hydrogel upon heating. In the conventional 1D FTIR spectra, the gradual dehydration of C-H groups, as well as the gradual dissociation of hydrogen bonds between C[double bond, length as m-dash]O groups and water molecules, was observed during phase transition. Moreover, we found that the rate at which water molecules were expelled out of the gel network during phase transition was changed to a sigmoid mode, rather than increasing linearly with increasing temperature. PCMW2D FTIR spectra revealed that the phase transition of PVCL hydrogel can be divided into two steps (named as I and II) upon heating, and we further determined the temperature regions of steps I and II to be 29.0-35.7 °C and 35.7-47.5 °C, respectively. Step I is the formation of hydrophobic domains in the gel, and step II is the chain collapse of the gel. Finally, with the help of generalized 2D correlation analysis, it was confirmed that the transformation of hydrogen bonds was the driving force of the hydrophobic domain formation process, while the hydrophobic interaction of C-H groups was the driving force for the chain collapse process. Combined with the obtained sequential orders of step I and step II, an integrated two-step phase transition mechanism of PVCL hydrogel upon heating was proposed.
Materials Science and Technology, Volume 5, Phase Transformations in Materials
NASA Astrophysics Data System (ADS)
Haasen, Peter
1996-12-01
This volume covers phase transformations, a general phenomenon central to understanding the behavior of materials and to creating high-performance materials. From the Contents: Pelton: Thermodynamics and Phase Diagrams of Materials. Murch: Diffusion in Crystalline Solids. Binder: Statistical Theories of Phase Transitions/Spinodal Decomposition. Wagner/Kampmann: Homogeneous Second Phase Precipitation. Purdy: Transformations Involving Interfacial Diffusion. Delaey: Diffusionless Transformations. Ruoff: High Pressure Phase Transformations. Pitsch/Inden: Atomic Ordering. Müller- Krumbhaar/Kurz: Solidification.
Sliding Over a Phase Transition
NASA Astrophysics Data System (ADS)
Tosatti, Erio; Benassi, Andrea; Vanossi, Andrea; Santoro, Giuseppe E.
2011-03-01
The frictional response experienced by a stick-slip slider when a phase transition occurs in the underlying solid substrate is a potentially exciting, poorly explored problem. We show, based on 2-dimensional simulations modeling the sliding of a nanotip, that indeed friction may be heavily affected by a continuous structural transition. First, friction turns nonmonotonic as temperature crosses the transition, peaking at the critical temperature Tc where fluctuations are strongest. Second, below Tc friction depends upon order parameter directions, and is much larger for those where the frictional slip can cause a local flip. This may open a route towards control of atomic scale friction by switching the order parameter direction by an external field or strain, with possible application to e.g., displacive ferroelectrics such as BaTi O3 , as well as ferro- and antiferro-distortive materials. Supported by project ESF FANAS/AFRI sponsored by the Italian Research Council (CNR).
Pressure induced phase transitions in ceramic compounds containing tetragonal zirconia
Sparks, R.G.; Pfeiffer, G.; Paesler, M.A.
1988-12-01
Stabilized tetragonal zirconia compounds exhibit a transformation toughening process in which stress applied to the material induces a crystallographic phase transition. The phase transition is accompanied by a volume expansion in the stressed region thereby dissipating stress and increasing the fracture strength of the material. The hydrostatic component of the stress required to induce the phase transition can be investigated by the use of a high pressure technique in combination with Micro-Raman spectroscopy. The intensity of Raman lines characteristic for the crystallographic phases can be used to calculate the amount of material that has undergone the transition as a function of pressure. It was found that pressures on the order of 2-5 kBar were sufficient to produce an almost complete transition from the original tetragonal to the less dense monoclinic phase; while a further increase in pressure caused a gradual reversal of the transition back to the original tetragonal structure.
Thermotropic and barotropic phase transitions on diacylphosphatidylethanolamine bilayer membranes.
Matsuki, Hitoshi; Endo, Shigeru; Sueyoshi, Ryosuke; Goto, Masaki; Tamai, Nobutake; Kaneshina, Shoji
2017-07-01
The bilayer phase transitions of four diacylphosphatidylethanolamines (PEs) with matched saturated acyl chains (Cn=12, 14, 16 and 18) and two PEs with matched unsaturated acyl chains containing a different kind of double bonds were observed by differential scanning calorimetry under atmospheric pressure and light-transmittance measurements under high pressure. The temperature-pressure phase diagrams for these PE bilayer membranes were constructed from the obtained phase-transition data. The saturated PE bilayer membranes underwent two different phase transitions related to the liquid crystalline (Lα) phase, the transition from the hydrated crystalline (Lc) phase and the chain melting (gel (Lβ) to Lα) transition, depending on the thermal history. Pressure altered the gel-phase stability of the bilayer membranes of PEs with longer chains at a low pressure. Comparing the thermodynamic quantities of the saturated PE bilayer membranes with those of diacylphosphatidylcholine (PC) bilayer membranes, the PE bilayer membranes showed higher phase-transition temperatures and formed more stable Lc phase, which originates from the strong interaction between polar head groups of PE molecules. On the other hand, the unsaturated PE bilayer membranes underwent the transition from the Lα phase to the inverted hexagonal (HII) phase at a high temperature and this transition showed a small transition enthalpy but high pressure-responsivity. It turned out that the kind of double bonds markedly affects both bilayer-bilayer and bilayer-nonbilayer transitions and the Lα/HII transition is a volume driven transition for the reconstruction of molecular packing. Further, the phase-transition behavior was explained by chemical potential curves of bilayer phases. Copyright © 2017 Elsevier B.V. All rights reserved.
Acoustic Detection of Phase Transitions at the Nanoscale
Vasudevan, Rama K.; Khassaf, Hamidreza; Cao, Ye; ...
2016-01-25
On page 478, N. Bassiri-Gharb and co-workers demonstrate acoustic detection in nanoscale volumes by use of an atomic force microscope tip technique. Elastic changes in volume are measured by detecting changes in resonance of the cantilever. Also, the electric field in this case causes a phase transition, which is modeled by Landau theory.
Phase transitions in random surfaces
NASA Astrophysics Data System (ADS)
Baig, M.; Espriu, D.; Wheater, J. F.
1989-03-01
We investigate the statistical properties of triangulated random surfaces of fixed connectivity embedded in d-dimensional space and weighted with an action that contains the extrinsic curvature of the surface as well as the usual Nambu-Goto term. Numerically, we find no second-order phase transition for finite values of the rigidity coupling, in contrast to results obtained by Kantor and Nelson using a different action. Rather, there is a third order "crumpling" transition which, however, is not associated with an infinite correlation length between the normals to the surface. We compare the Monte Carlo results with several approximations, particularly with the mean field solution of the model. Our results indicate that there are no fixed points other than those already found in perturbation theory. We comment on several other aspects of random surfaces.
Interacting Weyl fermions: Phases, phase transitions, and global phase diagram
NASA Astrophysics Data System (ADS)
Roy, Bitan; Goswami, Pallab; Juričić, Vladimir
2017-05-01
We study the effects of short-range interactions on a generalized three-dimensional Weyl semimetal, where the band touching points act as the (anti)monopoles of Abelian Berry curvature of strength n . We show that any local interaction has a negative scaling dimension -2 /n . Consequently, all Weyl semimetals are stable against weak short-range interactions. For sufficiently strong interactions, we demonstrate that the Weyl semimetal either undergoes a first-order transition into a band insulator or a continuous transition into a symmetry breaking phase. A translational symmetry breaking axion insulator and a rotational symmetry breaking semimetal are two prominent candidates for the broken symmetry phase. At the one-loop order, the correlation length exponent for continuous transitions is ν =n /2 , indicating their non-Gaussian nature for any n >1 . We also discuss the scaling of the thermodynamic and transport quantities in general Weyl semimetals as well as inside broken symmetry phases.
Phases and phase transitions in disordered quantum systems
NASA Astrophysics Data System (ADS)
Vojta, Thomas
2013-08-01
These lecture notes give a pedagogical introduction to phase transitions in disordered quantum systems and to the exotic Griffiths phases induced in their vicinity. We first review some fundamental concepts in the physics of phase transitions. We then derive criteria governing under what conditions spatial disorder or randomness can change the properties of a phase transition. After introducing the strong-disorder renormalization group method, we discuss in detail some of the exotic phenomena arising at phase transitions in disordered quantum systems. These include infinite-randomness criticality, rare regions and quantum Griffiths singularities, as well as the smearing of phase transitions. We also present a number of experimental examples.
Brain Performance versus Phase Transitions
NASA Astrophysics Data System (ADS)
Torres, Joaquín J.; Marro, J.
2015-07-01
We here illustrate how a well-founded study of the brain may originate in assuming analogies with phase-transition phenomena. Analyzing to what extent a weak signal endures in noisy environments, we identify the underlying mechanisms, and it results a description of how the excitability associated to (non-equilibrium) phase changes and criticality optimizes the processing of the signal. Our setting is a network of integrate-and-fire nodes in which connections are heterogeneous with rapid time-varying intensities mimicking fatigue and potentiation. Emergence then becomes quite robust against wiring topology modification—in fact, we considered from a fully connected network to the Homo sapiens connectome—showing the essential role of synaptic flickering on computations. We also suggest how to experimentally disclose significant changes during actual brain operation.
High pressure ferroelastic phase transition in SrTiO₃.
Salje, E K H; Guennou, M; Bouvier, P; Carpenter, M A; Kreisel, J
2011-07-13
High pressure measurements of the ferroelastic phase transition of SrTiO₃ (Guennou et al 2010 Phys. Rev. B 81 054115) showed a linear pressure dependence of the transition temperature between the cubic and tetragonal phase. Furthermore, the pressure induced transition becomes second order while the temperature dependent transition is near a tricritical point. The phase transition mechanism is characterized by the elongation and tilt of the TiO₆ octahedra in the tetragonal phase, which leads to strongly nonlinear couplings between the structural order parameter, the volume strain and the applied pressure. The phase diagram is derived from the Clausius-Clapeyron relationship and is directly related to a pressure dependent Landau potential. The nonlinearities of the pressure dependent strains lead to an increase of the fourth order Landau coefficient with increasing pressure and, hence, to a tricritical-second order crossover. This behaviour is reminiscent of the doping related crossover in isostructural KMnF₃.
Work and quantum phase transitions: quantum latency.
Mascarenhas, E; Bragança, H; Dorner, R; França Santos, M; Vedral, V; Modi, K; Goold, J
2014-06-01
We study the physics of quantum phase transitions from the perspective of nonequilibrium thermodynamics. For first-order quantum phase transitions, we find that the average work done per quench in crossing the critical point is discontinuous. This leads us to introduce the quantum latent work in analogy with the classical latent heat of first order classical phase transitions. For second order quantum phase transitions the irreversible work is closely related to the fidelity susceptibility for weak sudden quenches of the system Hamiltonian. We demonstrate our ideas with numerical simulations of first, second, and infinite order phase transitions in various spin chain models.
Dynamics of a Quantum Phase Transition
Zurek, Wojciech H.; Dorner, Uwe; Zoller, Peter
2005-09-02
We present two approaches to the dynamics of a quench-induced phase transition in the quantum Ising model. One follows the standard treatment of thermodynamic second order phase transitions but applies it to the quantum phase transitions. The other approach is quantum, and uses Landau-Zener formula for transition probabilities in avoided level crossings. We show that predictions of the two approaches of how the density of defects scales with the quench rate are compatible, and discuss the ensuing insights into the dynamics of quantum phase transitions.
Dynamical scheme for hadronization with first-order phase transition
NASA Astrophysics Data System (ADS)
Feng, Bohao; Xu, Zhe; Greiner, Carsten
2017-02-01
We present a dynamical scheme for hadronization with first-order confinement phase transition. The thermodynamical conditions of phase equilibrium, the fluid velocity profile, and the dissipative effect determine the macroscopic changes of the parton volume and the corresponding hadron volume during the phase transition. The macroscopic volume changes are the basis for building up a dynamical scheme by considering microscopic transition processes from partons to hadrons and backwards. The established scheme is proved by comparing the numerical results with the analytical solutions in the case of a one-dimensional expansion of a dissipative fluid with Bjorken boost invariance. The comparisons show almost perfect agreements, which demonstrate the applicability of the introduced scheme.
Cloud regimes as phase transitions
NASA Astrophysics Data System (ADS)
Stechmann, Samuel N.; Hottovy, Scott
2016-06-01
Clouds are repeatedly identified as a leading source of uncertainty in future climate predictions. Of particular importance are stratocumulus clouds, which can appear as either (i) closed cells that reflect solar radiation back to space or (ii) open cells that allow solar radiation to reach the Earth's surface. Here we show that these clouds regimes -- open versus closed cells -- fit the paradigm of a phase transition. In addition, this paradigm characterizes pockets of open cells as the interface between the open- and closed-cell regimes, and it identifies shallow cumulus clouds as a regime of higher variability. This behavior can be understood using an idealized model for the dynamics of atmospheric water as a stochastic diffusion process. With this new conceptual viewpoint, ideas from statistical mechanics could potentially be used for understanding uncertainties related to clouds in the climate system and climate predictions.
Aspects of the electroweak phase transition
Huet, P.
1992-11-01
The electroweak phase transition is reviewed in light of some recent developments. Emphasis is on the issue whether the transition is first or second order and its possible role in the generation of the baryon asymmetry of the universe.
Where the electroweak phase transition ends
NASA Astrophysics Data System (ADS)
Gürtler, M.; Ilgenfritz, E.-M.; Schiller, A.
1997-10-01
We give a more precise characterization of the end of the electroweak phase transition in the framework of the effective three-dimensional SU(2)-Higgs lattice model than has been given before. The model has now been simulated at gauge couplings βG=12 and 16 for Higgs boson masses M*H=70, 74, 76, and 80 GeV up to lattices 963 and the data have been used for reweighting. The breakdown of finite volume scaling of the Lee-Yang zeroes indicates the change from a first order transition to a crossover at λ3/g23=0.102(2) in rough agreement with results of Karsch, Neuhaus, Patkós, and Rank at βG=9 and smaller lattices. The infinite volume extrapolation of the discontinuity Δ<φ+φ>/g23 turns out to be zero at λ3/g23=0.107(2) being an upper limit. We comment on the limitations of the second method.
Current fluctuations at a phase transition
NASA Astrophysics Data System (ADS)
Gerschenfeld, A.; Derrida, B.
2011-10-01
The ABC model is a simple diffusive one-dimensional non-equilibrium system which exhibits a phase transition. Here we show that the cumulants of the currents of particles through the system become singular near the phase transition. At the transition, they exhibit an anomalous dependence on the system size (an anomalous Fourier's law). An effective theory for the dynamics of the single mode which becomes unstable at the transition allows one to predict this anomalous scaling.
Swarms, phase transitions, and collective intelligence
Millonas, M.M. . Dept. of Physics)
1992-01-01
A model of the collective behavior of a large number of locally acting organisms is proposed. The model is intended to be realistic, but turns out to fit naturally into the category of connectionist models, Like all connectionist models, its properties can be divided into the categories of structure, dynamics, and learning. The space in which the organisms move is discretized, and is modeled by a lattice of nodes, or cells. Each cell hag a specified volume, and is connected to other cells in the space in a definite way. Organisms move probabilistically between local cells in this space, but with weights dependent on local morphogenic substances, or morphogens. The morphogens are in turn are effected by the passage of an organism. The evolution of the morphogens, and the corresponding constitutes of the organisms constitutes the collective behavior of the group. The generic properties of such systems are analyzed, and a number of results are obtained. The model has various types of phase transitions and self-organizing properties controlled both by the level of the noise, and other parameters. It is hoped that the present mode; might serve as a paradigmatic example of a complex cooperative system in nature. In particular this model can be used to explore the relation of phase transitions to at least three important issues encountered in artificial life. Firstly, that of emergence as complex adaptive behavior. Secondly, as an exploration of second order phase transitions in biological systems. Lastly, to derive behavioral criteria for the evolution of collective behavior in social organisms. The model is then applied to the specific case of ants moving on a lattice. The local behavior of the ants is inspired by the actual behavior observed in the laboratory, and analytic results for the collective behavior are compared to the corresponding laboratory results. Monte carlo simulations are used as illustrations.
Swarms, phase transitions, and collective intelligence
Millonas, M.M.
1992-12-31
A model of the collective behavior of a large number of locally acting organisms is proposed. The model is intended to be realistic, but turns out to fit naturally into the category of connectionist models, Like all connectionist models, its properties can be divided into the categories of structure, dynamics, and learning. The space in which the organisms move is discretized, and is modeled by a lattice of nodes, or cells. Each cell hag a specified volume, and is connected to other cells in the space in a definite way. Organisms move probabilistically between local cells in this space, but with weights dependent on local morphogenic substances, or morphogens. The morphogens are in turn are effected by the passage of an organism. The evolution of the morphogens, and the corresponding constitutes of the organisms constitutes the collective behavior of the group. The generic properties of such systems are analyzed, and a number of results are obtained. The model has various types of phase transitions and self-organizing properties controlled both by the level of the noise, and other parameters. It is hoped that the present mode; might serve as a paradigmatic example of a complex cooperative system in nature. In particular this model can be used to explore the relation of phase transitions to at least three important issues encountered in artificial life. Firstly, that of emergence as complex adaptive behavior. Secondly, as an exploration of second order phase transitions in biological systems. Lastly, to derive behavioral criteria for the evolution of collective behavior in social organisms. The model is then applied to the specific case of ants moving on a lattice. The local behavior of the ants is inspired by the actual behavior observed in the laboratory, and analytic results for the collective behavior are compared to the corresponding laboratory results. Monte carlo simulations are used as illustrations.
Quantum phase transitions in disordered antiferromagnets
NASA Astrophysics Data System (ADS)
Yu, Rong
Recently quantum phase transitions have attracted the interest of both theorists and experimentalists in condensed matter physics. Quantum magnets provide a perfect playground for studying these phase transitions since they can be triggered by many control parameters such as frustration, lattice dimerization, and magnetic field. Most previous studies have focused on the magnetic properties in pure systems. In these systems, responses to the triggering parameters are found to be uniform, leading to homogeneous phases. However little progress has been made so far on the phase transitions and properties in disordered quantum magnets because they are more complicated systems, and few theoretical tools can be applied. In this thesis we use the stochastic series expansion quantum Monte Carlo method to study quantum phase transitions in disordered magnets. We find that disordered magnets can behave quite differently from pure systems. The system inhomogeneity can strongly affect phase transitions by changing their universality class. We also find order-disorder transitions are often accompanied by the appearance of novel quantum disordered phases, in which magnetic properties behave highly nontrivial, even singular. In this thesis two examples are studied in great detail. The first one is the phase diagram of an inhomogeneous, bond-diluted two-dimensional antiferromagnet near the percolation threshold. We show that the magnetic transition can be tuned by the inhomogeneity of the dilution from a classical percolation to a quantum phase transition. Interestingly the quantum transition still takes the nature of a renormalized percolative transition, with continuously varying critical exponents. A gapless quantum disordered phase with no magnetic long-range order but geometric percolation is found. The low-temperature uniform susceptibility diverges as a non-universal power-law of the temperature in this phase, indicating that this is a quantum Griffiths phase. In the second
Phase transitions of quadrupolar fluids
NASA Astrophysics Data System (ADS)
O'Shea, Seamus F.; Dubey, Girija S.; Rasaiah, Jayendran C.
1997-07-01
Gibbs ensemble simulations are reported for Lennard-Jones particles with embedded quadrupoles of strength Q*=Q/(ɛσ5)1/2=2.0 where ɛ and σ are the Lennard-Jones parameters. Calculations revealing the effect of the dispersive forces on the liquid-vapor coexistence were carried out by scaling the attractive r-6 term in the Lennard-Jones pair potential by a factor λ ranging from 0 to 1. Liquid-vapor coexistence is observed for all values of λ including λ=0 for Q*=2.0, unlike the corresponding dipolar fluid studied by van Leeuwen and Smit et al. [Phys. Rev. Lett. 71, 3991 (1993)] which showed no phase transition below λ=0.35 when the reduced dipole moment μ*=2.0. The simulation data are analyzed to estimate the critical properties of the quadrupolar fluid and their dependence on the strength λ of the dispersive force. The critical temperature and pressure show a clear quadratic dependence on λ, while the density is less confidently identified as being linear in λ. The compressibility is roughly linear in λ.
High pressure phase transition in Pr-monopnictides
Raypuria, Gajendra Singh E-mail: gsraypuria@gmail.com; Gupta, Dinesh Chandra
2015-06-24
The Praseodymium-monopnictides compounds have been found to undergo transition from their initial NaCl-type structure to high pressure body centered tetragonal (BCT) structure (distorted CsCl-type P4/mmm) using CTIP model. The calculated values of cohesive energy, lattice constant, phase transition pressure, relative volume collapse agree well with the available measured data and better than those computed by earlier workers.
Phase transition of La- chalcogenides under high pressure
Gupta, Dinesh Chandra; Raypuria, Gajendra Singh
2014-04-24
The lanthanum compounds have been found to undergo transition from their initial NaCl-type structure to high pressure body centered tetragonal (BCT) structure (distorted CsCl-type P4/mmm) using CTIP model. The calculated values of cohesive energy, lattice constant, phase transition pressure, relative volume collapse agree well with the available measured data and better than those computed by earlier workers.
Local bias-induced phase transitions
Seal, Katyayani; Baddorf, Arthur P.; Jesse, Stephen; Kalinin, Sergei V.; Nikiforov, Maxim; Proksch, Roger; Rodriguez, Brian J.; Maksymovych, Petro; Kholkin, Andrei L.
2008-11-27
Electrical bias-induced phase transitions underpin a wide range of applications from data storage to energy generation and conversion. The mechanisms behind these transitions are often quite complex and in many cases are extremely sensitive to local defects that act as centers for local transformations or pinning. Furthermore, using ferroelectrics as an example, we review methods for probing bias-induced phase transitions and discuss the current limitations and challenges for extending the methods to field-induced phase transitions and electrochemical reactions in energy storage, biological and molecular systems.
Local bias-induced phase transitions
Seal, Katyayani; Baddorf, Arthur P.; Jesse, Stephen; ...
2008-11-27
Electrical bias-induced phase transitions underpin a wide range of applications from data storage to energy generation and conversion. The mechanisms behind these transitions are often quite complex and in many cases are extremely sensitive to local defects that act as centers for local transformations or pinning. Furthermore, using ferroelectrics as an example, we review methods for probing bias-induced phase transitions and discuss the current limitations and challenges for extending the methods to field-induced phase transitions and electrochemical reactions in energy storage, biological and molecular systems.
Phase transitions in the web of science
NASA Astrophysics Data System (ADS)
Phillips, J. C.
2015-06-01
The Internet age is changing the structure of science, and affecting interdisciplinary interactions. Publication profiles connecting mathematics with molecular biology and condensed matter physics over the last 40 years exhibit common phase transitions indicative of the critical role played by specific interdisciplinary interactions. The strengths of the phase transitions quantify the importance of interdisciplinary interactions.
Cancer as a dynamical phase transition.
Davies, Paul Cw; Demetrius, Lloyd; Tuszynski, Jack A
2011-08-25
This paper discusses the properties of cancer cells from a new perspective based on an analogy with phase transitions in physical systems. Similarities in terms of instabilities and attractor states are outlined and differences discussed. While physical phase transitions typically occur at or near thermodynamic equilibrium, a normal-to-cancer (NTC) transition is a dynamical non-equilibrium phenomenon, which depends on both metabolic energy supply and local physiological conditions. A number of implications for preventative and therapeutic strategies are outlined.
Analysis of Nuclear Quantum Phase Transitions
Li, Z. P.; Meng, J.; Niksic, T.; Vretenar, D.; Lalazissis, G. A.; Ring, P.
2009-08-26
A microscopic analysis, based on nuclear energy density functionals, is presented for shape phase transitions in Nd isotopes. Low-lying excitation spectra and transition probabilities are calculated starting from a five-dimensional Hamiltonian, with parameters determined by constrained relativistic mean-field calculations for triaxial shapes. The results reproduce available data, and show that there is an abrupt change of structure at N = 90, that corresponds to a first-order quantum phase transition between spherical and axially deformed shapes.
Phase transition in a super superspin glass
NASA Astrophysics Data System (ADS)
Mathieu, R.; De Toro, J. A.; Salazar, D.; Lee, S. S.; Cheong, J. L.; Nordblad, P.
2013-06-01
We here confirm the occurrence of spin glass phase transition and extract estimates of associated critical exponents of a highly monodisperse and densely compacted system of bare maghemite nanoparticles. This system has earlier been found to behave like an archetypal spin glass, with, e.g., a sharp transition from paramagnetic to non-equilibrium behavior, suggesting that this system undergoes a spin glass phase transition at a relatively high temperature, Tg ∼ 140 K.
Geometric phases and quantum phase transitions in open systems.
Nesterov, Alexander I; Ovchinnikov, S G
2008-07-01
The relationship is established between quantum phase transitions and complex geometric phases for open quantum systems governed by a non-Hermitian effective Hamiltonian with accidental crossing of the eigenvalues. In particular, the geometric phase associated with the ground state of the one-dimensional dissipative Ising model in a transverse magnetic field is evaluated, and it is demonstrated that the related quantum phase transition is of the first order.
Quantum phase transitions in disordered magnets
NASA Astrophysics Data System (ADS)
Nozadze, David
We study the effects of quenched weak disorder on quantum phase transitions in disordered magnets. The presence of disorder in the system can lead to a variety of exotic phenomena, e.g., the smearing of transitions or quantum Griffiths singularities. Phase transitions are smeared if individual spatial regions can order independently of the bulk system. In paper I, we study smeared quantum phase transitions in binary alloys A1-xBx that are tuned by changing the composition x. We show that in this case the ordered phase is extended over all compositions x < 1. We also study the composition dependence of observables. In paper II, we investigate the influence of spatial disorder correlations on smeared phase transitions. As an experimental example, we demonstrate in paper III, that the composition-driven ferromagnetic-toparamagnetic quantum phase transition in Sr1-xCaxRuO3 is smeared. When individual spatial regions cannot order but fluctuate slowly, the phase transition is characterized by strong singularities in the quantum Griffiths phase. In paper IV, we develop a theory of the quantum Griffiths phases in disordered ferromagnetic metals. We show that the quantum Griffiths singularities are stronger than the usual power-law quantum Griffiths singularities in insulating magnets. In paper V, we present an efficient numerical method for studying quantum phase transitions in disordered systems with O(N) order parameter symmetry in the large-N limit. Our algorithm solves iteratively the large-N self-consistent equations for the renormalized distances from criticality. Paper VI is devoted to the study of transport properties in the quantum Griffiths phase associated with the antiferromagnetic quantum phase transition in a metal. We find unusual behavior of transport properties which is in contrast to the normal Fermi-liquid behavior.
Exploring structural phase transitions of ion crystals
Yan, L. L.; Wan, W.; Chen, L.; Zhou, F.; Gong, S. J.; Tong, X.; Feng, M.
2016-01-01
Phase transitions have been a research focus in many-body physics over past decades. Cold ions, under strong Coulomb repulsion, provide a repealing paradigm of exploring phase transitions in stable confinement by electromagnetic field. We demonstrate various conformations of up to sixteen laser-cooled 40Ca+ ion crystals in a home-built surface-electrode trap, where besides the usually mentioned structural phase transition from the linear to the zigzag, two additional phase transitions to more complicated two-dimensional configurations are identified. The experimental observation agrees well with the numerical simulation. Heating due to micromotion of the ions is analysed by comparison of the numerical simulation with the experimental observation. Our investigation implies very rich and complicated many-body behaviour in the trapped-ion systems and provides effective mechanism for further exploring quantum phase transitions and quantum information processing with ultracold trapped ions. PMID:26865229
First-Order Dynamical Phase Transitions
NASA Astrophysics Data System (ADS)
Canovi, Elena; Werner, Philipp; Eckstein, Martin
2014-12-01
Recently, dynamical phase transitions have been identified based on the nonanalytic behavior of the Loschmidt echo in the thermodynamic limit [Heyl et al., Phys. Rev. Lett. 110, 135704 (2013)]. By introducing conditional probability amplitudes, we show how dynamical phase transitions can be further classified, both mathematically, and potentially in experiment. This leads to the definition of first-order dynamical phase transitions. Furthermore, we develop a generalized Keldysh formalism which allows us to use nonequilibrium dynamical mean-field theory to study the Loschmidt echo and dynamical phase transitions in high-dimensional, nonintegrable models. We find dynamical phase transitions of first order in the Falicov-Kimball model and in the Hubbard model.
Microscopic Description of Nuclear Quantum Phase Transitions
Niksic, T.; Vretenar, D.; Lalazissis, G. A.; Ring, P.
2007-08-31
The relativistic mean-field framework, extended to include correlations related to restoration of broken symmetries and to fluctuations of the quadrupole deformation, is applied to a study of shape transitions in Nd isotopes. It is demonstrated that the microscopic self-consistent approach, based on global effective interactions, can describe not only general features of transitions between spherical and deformed nuclei, but also the singular properties of excitation spectra and transition rates at the critical point of quantum shape phase transition.
Astrophysical Implications of the QCD Phase Transition
Schaffner-Bielich, J.; Sagert, I.; Hempel, M.; Pagliara, G.; Fischer, T.; Mezzacappa, Anthony; Thielemann, Friedrich-Karl W.; Liebendoerfer, Matthias
2009-01-01
The possible role of a first order QCD phase transition at nonvanishing quark chemical potential and temperature for cold neutron stars and for supernovae is delineated. For cold neutron stars, we use the NJL model with a nonvanishing color superconducting pairing gap, which describes the phase transition to the 2SC and the CFL quark matter phases at high baryon densities. We demonstrate that these two phase transitions can both be present in the core of neutron stars and that they lead to the appearance of a third family of solution for compact stars. In particular, a core of CFL quark matter can be present in stable compact star configurations when slightly adjusting the vacuum pressure to the onset of the chiral phase transition from the hadronic model to the NJL model. We show that a strong first order phase transition can have a strong impact on the dynamics of core collapse supernovae. If the QCD phase transition sets in shortly after the first bounce, a second outgoing shock wave can be generated which leads to an explosion. The presence of the QCD phase transition can be read off from the neutrino and antineutrino signal of the supernova.
NASA Astrophysics Data System (ADS)
Shahnas, M. H.; Peltier, W. R.
2015-08-01
High-resolution seismic tomographic images from several subduction zones provide evidence for the inhibition of the downwelling of subducting slabs at the level of the 660 km depth seismic discontinuity. Furthermore, the inference of old (~140 Myr) sinking slabs below fossil subduction zones in the lower mantle has yet to be explained. We employ a control volume methodology to develop a new anelastically compressible model of three-dimensional thermal convection in the "mantle" of a terrestrial planet that fully incorporates the influence of large variations in material properties. The model also incorporates the influence of (1) multiple solid-solid pressure-induced phase transitions, (2) transformational superplasticity at 660 km depth, and (3) the high spin-low spin iron spin transition in ferropericlase at midmantle pressures. The message passing interface-parallelized code is successfully tested against previously published benchmark results. The high-resolution control volume models exhibit the same degree of radial layering as previously shown to be characteristic of otherwise identical 2-D axisymmetric spherical models. The layering is enhanced by the presence of moderate transformational superplasticity, and in the presence of the spin crossover in ferropericlase, stagnation of cold downwellings occurs in the range of spin crossover depths (~1700 km). Although this electronic spin transition has been suggested to be invisible seismically, recent high-pressure ab initio calculations suggest it to have a clear signature in body wave velocities which could provide an isochemical explanation of a seismological signature involving the onset of decorrelation between Vp and Vs that has come to be interpreted as requiring compositional layering.
Phase transitions in liquid crystal + aerosil gels
NASA Astrophysics Data System (ADS)
Ramazanoglu, Mehmet Kerim
Liquid Crystals (LCs) are found in many different phases, the most well-known, basic ones being Isotropic (I), Nematic (N), and Smectic-A (SmA). LCs show a rich variety of phase transitions between these phases. This makes them very interesting materials in which to study the basics of phase transitions and related topics. In the low symmetry phases, LCs show both positional and directional orders. X-ray scattering is an important tool to study these phase transitions as it probes the instantaneous positional correlations in these phases. Random forces have a nontrivial effect on ordering in nature, and the problem of phase transitions in the presence of a random field is a current and not well-understood topic. It has been found that aerosils posses a quenched randomness in the mixture of LC+aerosil samples, forming a gel random network which destroys long-range order (LRO) in the SmA phase. This can be modeled as a random field problem. In the N to SmA phase transition in 4O.8 LC (butyloxybenzlidene octylaniline), orientational order (N ) is modified by a 1-D density wave describing 2-D fluid layer spacing structure (SmA). Likewise the I to Sm A phase transition in 10CB LC (decylcyanobiphenyl), a transitional ordered phase develops without going through an orientational ordered phase. To study these phase transitions with aerosil dispersion carries the opportunity to probe the effect of induced quenched random disorder on phase transitions, which are 2nd order in the first case and 1st order in the second case. A two-component line-shape analysis is developed to define the phases in all temperature ranges. It consists of the thermal and the static structure factors. The reentered nematic (RN) phase of the [6:8]OCB+aerosil gels ([6:8]OCB is a mixture of hexyloxycyanobiphenyl and octyloxcyanobiphenyl) is another interesting case in which to study the quenched random disorder effects. The weak SmA phase of [6:8]OCB+aerosil gels is followed by a RN phase at low
Electroweak phase transition in ultraminimal technicolor
Jaervinen, Matti; Sannino, Francesco; Ryttov, Thomas A.
2009-05-01
We unveil the temperature-dependent electroweak phase transition in new extensions of the standard model in which the electroweak symmetry is spontaneously broken via strongly coupled, nearly conformal dynamics achieved by the means of multiple matter representations. In particular, we focus on the low energy effective theory introduced to describe ultra minimal walking technicolor at the phase transition. Using the one-loop effective potential with ring improvement, we identify regions of parameter space, which yield a strong first-order transition. A striking feature of the model is the existence of a second phase transition associated to the electroweak-singlet sector. The interplay between these two transitions leads to an extremely rich phase diagram.
Phase equilibria in the ternary system vanadium-niobium-carbon from 800C through the melting ranges of the cubic monocarbide solid solutions were...established on the basis of X-ray, melting point and metallographic studies. The phase equilibria above 1400C are presented in a three-dimensional...temperature-composition constitutional diagram, since the phase equilibria below 1400C were not thoroughly investigated due to kinetic problems. Vanadium
Generalized Entanglement and Quantum Phase Transitions
NASA Astrophysics Data System (ADS)
Somma, Rolando; Barnum, Howard; Knill, Emanuel; Ortiz, Gerardo; Viola, Lorenzo
2006-07-01
Quantum phase transitions in matter are characterized by qualitative changes in some correlation functions of the system, which are ultimately related to entanglement. In this work, we study the second-order quantum phase transitions present in models of relevance to condensed-matter physics by exploiting the notion of generalized entanglement [Barnum et al., Phys. Rev. A 68, 032308 (2003)]. In particular, we focus on the illustrative case of a one-dimensional spin-1/2 Ising model in the presence of a transverse magnetic field. Our approach leads to tools useful for distinguishing between the ordered and disordered phases in the case of broken-symmetry quantum phase transitions. Possible extensions to the study of other kinds of phase transitions as well as of the relationship between generalized entanglement and computational efficiency are also discussed.
Generalized Entanglement and Quantum Phase Transitions
NASA Astrophysics Data System (ADS)
Somma, Rolando; Barnum, Howard; Knill, Emanuel; Ortiz, Gerardo; Viola, Lorenzo
Quantum phase transitions in matter are characterized by qualitative changes in some correlation functions of the system, which are ultimately related to entanglement. In this work, we study the second-order quantum phase transitions present in models of relevance to condensed-matter physics by exploiting the notion of generalized entanglement [Barnum et al., Phys. Rev. A 68, 032308 (2003)]. In particular, we focus on the illustrative case of a one-dimensional spin-1/2 Ising model in the presence of a transverse magnetic field. Our approach leads to tools useful for distinguishing between the ordered and disordered phases in the case of broken-symmetry quantum phase transitions. Possible extensions to the study of other kinds of phase transitions as well as of the relationship between generalized entanglement and computational efficiency are also discussed.
Phase transitions in QCD and string theory
NASA Astrophysics Data System (ADS)
Campell, Bruce A.; Ellis, John; Kalara, S.; Nanopoulos, D. V.; Olive, Keith A.
1991-02-01
We develop a unified effective field theory approach to the high-temperature phase transitions in QCD and string theory, incorporating winding modes (time-like Polyakov loops, vortices) as well as low-mass states (pseudoscalar mesons and glueballs, matter and dilaton supermultiplets). Anomalous scale invariance and the Z3 structure of the centre of SU(3) decree a first-order phase transition with simultaneous deconfinement and Polyakov loop condensation in QCD, whereas string vortex condensation is a second-order phase transition breaking a Z2 symmetry. We argue that vortex condensation is accompanied by a dilaton phase transition to a strong coupling regime, and comment on the possible role of soliton degrees of freedom in the high-temperature string phase. On leave of absence from the School of Physics & Astronomy, University of Minnesota, Minneapolis, Minnesota, USA.
Phase transition of aragonite in abalone nacre
NASA Astrophysics Data System (ADS)
An, Yuanlin; Liu, Zhiming; Wu, Wenjian
2013-04-01
Nacre is composed of about 95 vol.% aragonite and 5 vol.% biopolymer and famous for its "brick and mortar" microstructure. The phase transition temperature of aragonite in nacre is lower than the pure aragonite. In situ XRD was used to identify the phase transition temperature from aragonite to calcite in nacre, based on the analysis of TG-DSC of fresh nacre and demineralized nacre. The results indicate that the microstructure and biopolymer are the two main factors that influence the phase transition temperature of aragonite in nacre.
Structural phase transition in lanthanum monochalcogenides induced by hydrostatic pressure
NASA Astrophysics Data System (ADS)
Varshney, Dinesh; Kaurav, N.; Sharma, P.; Shah, S.; Singh, R. K.
2004-11-01
An effective interionic interaction potential (EIOP) is developed to investigate the pressure induced phase transitions from NaCl-type (B1) to CsCl-type (B2) structure in lanthanum monochalcogenides LaX [X = S, Se, Te] compounds. The long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction up to second-neighbor ions within the Hafemeister and Flygare approach with modified ionic charge are properly incorporated in EIOP. The vdW coefficients are computed following the Slater-Kirkwood variational method, as both the ions are polarizable. The estimated value of the phase transition pressure (Pt) and the magnitude of the discontinuity in volume at the transition pressure are consistent with the reported data. A large volume discontinuity in the pressure-volume phase diagram identifies the structural phase transition from B1 to B2 structure. We also study the second order elastic constants for these La compounds. It appears that the vdW interaction is effective in determining the elastic and structural properties of these test compounds.
Magnetic Phase Transition in V2O3 Nanocrystals
Billinge, S.; Blagojevic, V.A.; Carlo, J.P.; Brus, L.E.; Steigerwald, M.L.; Uemura, Y.J.; Billinge, S.J.L.; Zhou, W.; Stephens, P.W.; Aczel, A.A.; Luke, G.M.
2010-09-30
V{sub 2}O{sub 3} nanocrystals can be synthesized through hydrothermal reduction in VO(OH){sub 2} using hydrazine as a reducing agent. Addition of different ligands to the reaction produces nanoparticles, nanorods, and nanoplatelets of different sizes. Small nanoparticles synthesized in this manner show suppression of the magnetic phase transition to lower temperatures. Using muon spin relaxation spectroscopy and synchrotron x-ray diffraction, we have determined that the volume fraction of the high-temperature phase, characterized by a rhombohedral structure and paramagnetism, gradually declines with decreasing temperature, in contrast to the sharp transition observed in bulk V{sub 2}O{sub 3}.
Magnetic Phase Transition in V2O3 Nanocrystals
V Blagojevic; J Carlo; L Brus; M Steigerwald; Y Uemura; S Billinge; W Zhou; P Stephens; A Aczel; G Luke
2011-12-31
V{sub 2}O{sub 3} nanocrystals can be synthesized through hydrothermal reduction in VO(OH){sub 2} using hydrazine as a reducing agent. Addition of different ligands to the reaction produces nanoparticles, nanorods, and nanoplatelets of different sizes. Small nanoparticles synthesized in this manner show suppression of the magnetic phase transition to lower temperatures. Using muon spin relaxation spectroscopy and synchrotron x-ray diffraction, we have determined that the volume fraction of the high-temperature phase, characterized by a rhombohedral structure and paramagnetism, gradually declines with decreasing temperature, in contrast to the sharp transition observed in bulk V{sub 2}O{sub 3}.
Discovering phase transitions with unsupervised learning
NASA Astrophysics Data System (ADS)
Wang, Lei
2016-11-01
Unsupervised learning is a discipline of machine learning which aims at discovering patterns in large data sets or classifying the data into several categories without being trained explicitly. We show that unsupervised learning techniques can be readily used to identify phases and phases transitions of many-body systems. Starting with raw spin configurations of a prototypical Ising model, we use principal component analysis to extract relevant low-dimensional representations of the original data and use clustering analysis to identify distinct phases in the feature space. This approach successfully finds physical concepts such as the order parameter and structure factor to be indicators of a phase transition. We discuss the future prospects of discovering more complex phases and phase transitions using unsupervised learning techniques.
Critical behaviours of contact near phase transitions
Chen, Y.-Y.; Jiang, Y.-Z.; Guan, X.-W.; Zhou, Qi
2014-01-01
A central quantity of importance for ultracold atoms is contact, which measures two-body correlations at short distances in dilute systems. It appears in universal relations among thermodynamic quantities, such as large momentum tails, energy and dynamic structure factors, through the renowned Tan relations. However, a conceptual question remains open as to whether or not contact can signify phase transitions that are insensitive to short-range physics. Here we show that, near a continuous classical or quantum phase transition, contact exhibits a variety of critical behaviours, including scaling laws and critical exponents that are uniquely determined by the universality class of the phase transition, and a constant contact per particle. We also use a prototypical exactly solvable model to demonstrate these critical behaviours in one-dimensional strongly interacting fermions. Our work establishes an intrinsic connection between the universality of dilute many-body systems and universal critical phenomena near a phase transition. PMID:25346226
Holographically Encoded Volume Phase Masks
2015-07-13
yÞAg; (6) where Ã and B̃ are the Fourier transforms of A and B, respec- tively, and fx and fy are the spatial frequencies along the x and y axes...collimated and directed onto a reflecting spatial light modulator (SLM). Applying the SLM encoding technique by Arrizón et al.,42 the incident beam was...converted into the LP11 and LP21 HOMs. These modes were selected because their spatial phase pattern match the HPM with the encoded four-sector binary
Magnetic fields from the electroweak phase transition
Tornkvist, O.
1998-02-01
I review some of the mechanisms through which primordial magnetic fields may be created in the electroweak phase transition. I show that no magnetic fields are produced initially from two-bubble collisions in a first-order transition. The initial field produced in a three-bubble collision is computed. The evolution of fields at later times is discussed.
Electrically driven phase transition in magnetite nanostructures.
Lee, Sungbae; Fursina, Alexandra; Mayo, John T; Yavuz, Cafer T; Colvin, Vicki L; Sofin, R G Sumesh; Shvets, Igor V; Natelson, Douglas
2008-02-01
Magnetite (Fe3O4), an archetypal transition-metal oxide, has been used for thousands of years, from lodestones in primitive compasses to a candidate material for magnetoelectronic devices. In 1939, Verwey found that bulk magnetite undergoes a transition at TV approximately 120 K from a high-temperature 'bad metal' conducting phase to a low-temperature insulating phase. He suggested that high-temperature conduction is through the fluctuating and correlated valences of the octahedral iron atoms, and that the transition is the onset of charge ordering on cooling. The Verwey transition mechanism and the question of charge ordering remain highly controversial. Here, we show that magnetite nanocrystals and single-crystal thin films exhibit an electrically driven phase transition below the Verwey temperature. The signature of this transition is the onset of sharp conductance switching in high electric fields, hysteretic in voltage. We demonstrate that this transition is not due to local heating, but instead is due to the breakdown of the correlated insulating state when driven out of equilibrium by electrical bias. We anticipate that further studies of this newly observed transition and its low-temperature conducting phase will shed light on how charge ordering and vibrational degrees of freedom determine the ground state of this important compound.
Electrically driven phase transition in magnetite nanostructures
NASA Astrophysics Data System (ADS)
Lee, Sungbae; Fursina, Alexandra; Mayo, John T.; Yavuz, Cafer T.; Colvin, Vicki L.; Sumesh Sofin, R. G.; Shvets, Igor V.; Natelson, Douglas
2008-02-01
Magnetite (Fe3O4), an archetypal transition-metal oxide, has been used for thousands of years, from lodestones in primitive compasses to a candidate material for magnetoelectronic devices. In 1939, Verwey found that bulk magnetite undergoes a transition at TV~120K from a high-temperature `bad metal' conducting phase to a low-temperature insulating phase. He suggested that high-temperature conduction is through the fluctuating and correlated valences of the octahedral iron atoms, and that the transition is the onset of charge ordering on cooling. The Verwey transition mechanism and the question of charge ordering remain highly controversial. Here, we show that magnetite nanocrystals and single-crystal thin films exhibit an electrically driven phase transition below the Verwey temperature. The signature of this transition is the onset of sharp conductance switching in high electric fields, hysteretic in voltage. We demonstrate that this transition is not due to local heating, but instead is due to the breakdown of the correlated insulating state when driven out of equilibrium by electrical bias. We anticipate that further studies of this newly observed transition and its low-temperature conducting phase will shed light on how charge ordering and vibrational degrees of freedom determine the ground state of this important compound.
IVUS coronary volume alignment for distinct phases
NASA Astrophysics Data System (ADS)
Matsumoto, Monica Mitiko Soares; Lemos, Pedro Alves; Furuie, Sergio Shiguemi
2009-02-01
Image-based intravascular ultrasound (IVUS) cardiac phase detection allows coronary volume reconstruction in different phases. Consecutive volumes are not necessarily spatially aligned due to longitudinal movement of the catheter. Besides ordinary pullback velocity, there is a relative longitudinal movement of the heart vessel walls and the transducer, due to myocardial contraction. In this manuscript, we aim to spatially align cardiac phase coronary IVUS volumes. In addition, we want to investigate this non-linear longitudinal catheter movement. With this purpose, we have analyzed 120 simulated IVUS images and 10 real IVUS pullbacks. We implemented the following methodology. Firstly, we built IVUS volume for each distinct phase. Secondly, each IVUS volume was transformed into a parametric signal of average frame intensity. We have used these signals to make correlation in space with a reference one. Then we estimated the spatial distance between the distinct IVUS volumes and the reference. We have tested in simulated images and real examinations. We have also observed similar pattern in real IVUS examinations. This spatial alignment method is feasible and useful as a step towards dynamic studies of IVUS examination.
Persistent homology analysis of phase transitions
NASA Astrophysics Data System (ADS)
Donato, Irene; Gori, Matteo; Pettini, Marco; Petri, Giovanni; De Nigris, Sarah; Franzosi, Roberto; Vaccarino, Francesco
2016-05-01
Persistent homology analysis, a recently developed computational method in algebraic topology, is applied to the study of the phase transitions undergone by the so-called mean-field XY model and by the ϕ4 lattice model, respectively. For both models the relationship between phase transitions and the topological properties of certain submanifolds of configuration space are exactly known. It turns out that these a priori known facts are clearly retrieved by persistent homology analysis of dynamically sampled submanifolds of configuration space.
Persistent homology analysis of phase transitions.
Donato, Irene; Gori, Matteo; Pettini, Marco; Petri, Giovanni; De Nigris, Sarah; Franzosi, Roberto; Vaccarino, Francesco
2016-05-01
Persistent homology analysis, a recently developed computational method in algebraic topology, is applied to the study of the phase transitions undergone by the so-called mean-field XY model and by the ϕ^{4} lattice model, respectively. For both models the relationship between phase transitions and the topological properties of certain submanifolds of configuration space are exactly known. It turns out that these a priori known facts are clearly retrieved by persistent homology analysis of dynamically sampled submanifolds of configuration space.
The deconfining phase transition in and out of equilibrium
NASA Astrophysics Data System (ADS)
Bazavov, Oleksiy
Recent experiments carried out at the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory provide strong evidence that a matter can be driven from a confined, low-temperature phase, observed in our every day world into a deconfined high-temperature phase of liberated quarks and gluons. The equilibrium and dynamical properties of the deconfining phase transition are thus of great theoretical interest, since they also provide an information about the first femtoseconds of the evolution of our Universe, when the hot primordial soup while cooling has undergone a chain of phase transitions. The aspects of the deconfining phase transition studied in this work include: the dynamics of the SU(3) gauge theory after the heating quench (which models rapid heating in the heavy-ion collisions), equilibrium properties of the phase transition in the SU(3) gauge theory with boundaries at low temperature (small volumes at RHIC suggest that boundary effects cannot be neglected and periodic boundary conditions normally used in lattice simulations do not correspond to the experimental situation), and a study of the order of the transition in U(1) gauge theory.
Theoretical Predictions of Phase Transitions at Ultra-high Pressures
NASA Astrophysics Data System (ADS)
Boates, Brian
2013-06-01
We present ab initio calculations of the high-pressure phase diagrams of important planetary materials such as CO2, MgSiO3, and MgO. For CO2, we predict a series of distinct liquid phases over a wide pressure (P) and temperature (T) range, including a first-order transition to a dense polymer liquid. We have computed finite-temperature free energies of liquid and solid CO2 phases to determine the melting curve beyond existing measurements and investigate possible phase separation transitions. The interaction of these phase boundaries with the mantle geotherm will also be discussed. Furthermore, we find evidence for a vast pressure-temperature regime where molten MgSiO3 decomposes into liquid SiO2 and solid MgO, with a volume change of approximately 1.2 percent. The demixing transition is driven by the crystallization of MgO ? the reaction only occurs below the high-pressure MgO melting curve. The predicted transition pressure at 10,000 K is in close proximity to an anomaly reported in recent laser-driven shock experiments of MgSiO3. We also present new results for the high-pressure melting curve of MgO and its B1-B2 solid phase transition, with a triple point near 364 GPa and 12,000 K.
Polymorphic Phase Transition in Superhydrous Phase B
Koch-Muller,M.; Dera, P.; Fei, Y.; Hellwig, H.; Liu, Z.; Van Orman, J.; Wirth, R.
2005-01-01
We synthesized superhydrous phase B (shy-B) at 22 GPa and two different temperatures: 1200 C (LT) and 1400 C (HT) using a multi-anvil apparatus. The samples were investigated by transmission electron microscopy (TEM), single crystal X-ray diffraction, Raman and IR spectroscopy. The IR spectra were collected on polycrystalline thin-films and single crystals using synchrotron radiation, as well as a conventional IR source at ambient conditions and in situ at various pressures (up to 15 GPa) and temperatures (down to -180 C). Our studies show that shy-B exists in two polymorphic forms. As expected from crystal chemistry, the LT polymorph crystallizes in a lower symmetry space group (Pnn2), whereas the HT polymorph assumes a higher symmetry space group (Pnnm). TEM shows that both modifications consist of nearly perfect crystals with almost no lattice defects or inclusions of additional phases. IR spectra taken on polycrystalline thin films exhibit just one symmetric OH band and 29 lattice modes for the HT polymorph in contrast to two intense but asymmetric OH stretching bands and at least 48 lattice modes for the LT sample. The IR spectra differ not only in the number of bands, but also in the response of the bands to changes in pressure. The pressure derivatives for the IR bands are higher for the HT polymorph indicating that the high symmetry form is more compressible than the low symmetry form. Polarized, low-temperature single-crystal IR spectra indicate that in the LT-polymorph extensive ordering occurs not only at the Mg sites but also at the hydrogen sites.
Structural Phase Transition of ThC Under High Pressure.
Yu, Cun; Lin, Jun; Huai, Ping; Guo, Yongliang; Ke, Xuezhi; Yu, Xiaohe; Yang, Ke; Li, Nana; Yang, Wenge; Sun, Baoxing; Xie, Ruobing; Xu, Hongjie
2017-03-07
Thorium monocarbide (ThC) as a potential fuel for next generation nuclear reactor has been subjected to its structural stability investigation under high pressure, and so far no one reported the observation of structure phase transition induced by pressure. Here, utilizing the synchrotron X-ray diffraction technique, we for the first time, experimentally revealed the phase transition of ThC from B1 to P4/nmm at pressure of ~58 GPa at ambient temperature. A volume collapse of 10.2% was estimated during the phase transition. A modulus of 147 GPa for ThC at ambient pressure was obtained and the stoichiometry was attributed to the discrepancy of this value to the previous reports.
Contemporary research of dynamically induced phase transitions
NASA Astrophysics Data System (ADS)
Hull, L. M.
2017-01-01
Dynamically induced phase transitions in metals, within the present discussion, are those that take place within a time scale characteristic of the shock waves and any reflections or rarefactions involved in the loading structure along with associated plastic flow. Contemporary topics of interest include the influence of loading wave shape, the effect of shear produced by directionality of the loading relative to the sample dimensions and initial velocity field, and the loading duration (kinetic effects, hysteresis) on the appearance and longevity of a transformed phase. These topics often arise while considering the loading of parts of various shapes with high explosives, are typically two or three-dimensional, and are often selected because of the potential of the transformed phase to significantly modify the motion. In this paper, we look at current work on phase transitions in metals influenced by shear reported in the literature, and relate recent work conducted at Los Alamos on iron's epsilon phase transition that indicates a significant response to shear produced by reflected elastic waves. A brief discussion of criteria for the occurrence of stress induced phase transitions is provided. Closing remarks regard certain physical processes, such as fragmentation and jet formation, which may be strongly influenced by phase transitions.
Contemporary Research of Dynamically Induced Phase Transitions
NASA Astrophysics Data System (ADS)
Hull, Lawrence
2015-06-01
Dynamically induced phase transitions in metals, within the present discussion, are those that take place within a time scale characteristic of the shock waves and any reflections or rarefactions involved in the loading structure along with associated plastic flow. Contemporary topics of interest include the influence of loading wave shape, the effect of shear produced by directionality of the loading relative to the sample dimensions and initial velocity field, and the loading duration (kinetic effects, hysteresis) on the appearance and longevity of a transformed phase. These topics often arise while considering the loading of parts of various shapes with high explosives, are typically two or three-dimensional, and are often selected because of the potential of the transformed phase to significantly modify the motion. In this paper, we look at current work on phase transitions in metals influenced by shear reported in the literature, and relate recent work conducted at Los Alamos on iron's epsilon phase transition that indicates a significant response to shear produced by reflected elastic waves. A brief discussion of criteria for the occurrence of stress induced phase transitions is provided. Closing remarks regard certain physical processes, such as fragmentation and jet formation, which may be strongly influenced by phase transitions. Supported by the DoD/DOE Joint Munitions Technology Development Program.
Cancer as a dynamical phase transition
2011-01-01
This paper discusses the properties of cancer cells from a new perspective based on an analogy with phase transitions in physical systems. Similarities in terms of instabilities and attractor states are outlined and differences discussed. While physical phase transitions typically occur at or near thermodynamic equilibrium, a normal-to-cancer (NTC) transition is a dynamical non-equilibrium phenomenon, which depends on both metabolic energy supply and local physiological conditions. A number of implications for preventative and therapeutic strategies are outlined. PMID:21867509
Supercooling and phase coexistence in cosmological phase transitions
Megevand, Ariel; Sanchez, Alejandro D.
2008-03-15
Cosmological phase transitions are predicted by particle physics models, and have a variety of important cosmological consequences, which depend strongly on the dynamics of the transition. In this work we investigate in detail the general features of the development of a first-order phase transition. We find thermodynamical constraints on some quantities that determine the dynamics, namely, the latent heat, the radiation energy density, and the false-vacuum energy density. Using a simple model with a Higgs field, we study numerically the amount and duration of supercooling and the subsequent reheating and phase coexistence. We analyze the dependence of the dynamics on the different parameters of the model, namely, the energy scale, the number of degrees of freedom, and the couplings of the scalar field with bosons and fermions. We also inspect the implications for the cosmological outcomes of the phase transition.
Electroweak phase transition in nearly conformal technicolor
Cline, James M.; Jaervinen, Matti; Sannino, Francesco
2008-10-01
We examine the temperature-dependent electroweak phase transition in extensions of the standard model in which the electroweak symmetry is spontaneously broken via strongly coupled, nearly conformal dynamics. In particular, we focus on the low energy effective theory used to describe minimal walking technicolor at the phase transition. Using the one-loop effective potential with ring improvement, we identify significant regions of parameter space which yield a sufficiently strong first-order transition for electroweak baryogenesis. The composite particle spectrum corresponding to these regions can be produced and studied at the Large Hadron Collider experiment. We note the possible emergence of a second phase transition at lower temperatures. This occurs when the underlying technicolor theory possesses a nontrivial center symmetry.
Theory of smeared quantum phase transitions.
Hoyos, José A; Vojta, Thomas
2008-06-20
We present an analytical strong-disorder renormalization group theory of the quantum phase transition in the dissipative random transverse-field Ising chain. For Ohmic dissipation, we solve the renormalization flow equations analytically, yielding asymptotically exact results for the low-temperature properties of the system. We find that the interplay between quantum fluctuations and Ohmic dissipation destroys the quantum critical point by smearing. We also determine the phase diagram and the behavior of observables in the vicinity of the smeared quantum phase transition.
Random fields at a nonequilibrium phase transition.
Barghathi, Hatem; Vojta, Thomas
2012-10-26
We study nonequilibrium phase transitions in the presence of disorder that locally breaks the symmetry between two equivalent macroscopic states. In low-dimensional equilibrium systems, such random-field disorder is known to have dramatic effects: it prevents spontaneous symmetry breaking and completely destroys the phase transition. In contrast, we show that the phase transition of the one-dimensional generalized contact process persists in the presence of random-field disorder. The ultraslow dynamics in the symmetry-broken phase is described by a Sinai walk of the domain walls between two different absorbing states. We discuss the generality and limitations of our theory, and we illustrate our results by large-scale Monte Carlo simulations.
Topics in Phase Transitions at Interfaces.
NASA Astrophysics Data System (ADS)
Nikas, Yvonne Jiang
This dissertation addresses three subjects in the area of phase transitions at interfaces. First, a study of wetting phenomena and wetting transitions in oil -water-surfactant mixtures is presented. We have studied the wetting phase behavior of this system systematically using mean-field approximations on a lattice model. Due to the delicate balance of interfacial tensions between various phases, the wetting phase diagrams are very profuse under the conditions of three-phase coexistence, and the reentrant wetting and dewetting transitions are very common. In the case of oil-water-microemulsion coexistence, we observe a first-order wetting transition by the microemulsion phase at the oil-water interface; the qualitative features of the transition agree with the experimental observations. In the second part of the dissertation, the phenomenon of surface melting is discussed. Using the molecular dynamics simulation technique, we monitor the melting process in a thin solid argon film adsorbed on graphite. Our study reveals that the melting begins from the surface and proceeds layer by layer. From diffusion coefficients data, we find that from the beginning of melting until the temperature reaches 97% of the melting temperature, the fraction of atoms in the liquid state increases as | ln(T_{m}-T)| in our five -layer system. Finally we present a study of the phase transitions in lipid monolayers at air-water interfaces. This study is mainly focused on the microscopic structures formed in monolayers at the transition from liquid to solid phase. We propose a lattice model, which captures all the essential features of the system, and combine analytical calculations, mean-field theory, and Monte Carlo simulations to study the behavior of the film at zero and finite temperatures. We find that for typical lipids, the striped phase has a lower energy than the hexagonal phase at zero temperature, but because the latter has a higher mixing entropy, there is a transition from the
Microgravity Two-Phase Flow Transition
NASA Technical Reports Server (NTRS)
Parang, M.; Chao, D.
1999-01-01
Two-phase flows under microgravity condition find a large number of important applications in fluid handling and storage, and spacecraft thermal management. Specifically, under microgravity condition heat transfer between heat exchanger surfaces and fluids depend critically on the distribution and interaction between different fluid phases which are often qualitatively different from the gravity-based systems. Heat transfer and flow analysis in two-phase flows under these conditions require a clear understanding of the flow pattern transition and development of appropriate dimensionless scales for its modeling and prediction. The physics of this flow is however very complex and remains poorly understood. This has led to various inadequacies in flow and heat transfer modeling and has made prediction of flow transition difficult in engineering design of efficient thermal and flow systems. In the present study the available published data for flow transition under microgravity condition are considered for mapping. The transition from slug to annular flow and from bubbly to slug flow are mapped using dimensionless variable combination developed in a previous study by the authors. The result indicate that the new maps describe the flow transitions reasonably well over the range of the data available. The transition maps are examined and the results are discussed in relation to the presumed balance of forces and flow dynamics. It is suggested that further evaluation of the proposed flow and transition mapping will require a wider range of microgravity data expected to be made available in future studies.
Shaping Crystal-Crystal Phase Transitions
NASA Astrophysics Data System (ADS)
Du, Xiyu; van Anders, Greg; Dshemuchadse, Julia; Glotzer, Sharon
Previous computational and experimental studies have shown self-assembled structure depends strongly on building block shape. New synthesis techniques have led to building blocks with reconfigurable shape and it has been demonstrated that building block reconfiguration can induce bulk structural reconfiguration. However, we do not understand systematically how this transition happens as a function of building block shape. Using a recently developed ``digital alchemy'' framework, we study the thermodynamics of shape-driven crystal-crystal transitions. We find examples of shape-driven bulk reconfiguration that are accompanied by first-order phase transitions, and bulk reconfiguration that occurs without any thermodynamic phase transition. Our results suggest that for well-chosen shapes and structures, there exist facile means of bulk reconfiguration, and that shape-driven bulk reconfiguration provides a viable mechanism for developing functional materials.
Mechanism of Diffuse Phase Transition in Relaxor Ferroelectrics
NASA Astrophysics Data System (ADS)
Tsurumi, Takaaki; Soejima, Kouji; Kamiya, Toshio; Daimon, Masaki
1994-04-01
Dielectric properties of lead magnesium niobate (PMN) and Ta-bearing strontium barium niobate (SBNT) were measured as a function of temperature, and the crystal structure of PMN was refined by the Rietveld analysis method. The results of structure refinement indicate that the volume of polar microregions (PMR) increases with decreasing temperature. The dielectric properties of PMN and SBNT are well explained by an advanced theory of dielectric dispersion. The anomalous behavior in dielectric permittivity (ɛ) observed on the low temperature side of T m, the temperature of ɛ maximum, is explained by simple dielectric relaxation, while on the high-temperature side of T m is explained by the volume increase of PMR. It is concluded that these is no phase transition around T m, and the diffuse phase transition is an overlapping phenomenon of volume increase of PMR, freezing process of fluctuating dipoles in PMR and dielectric dispersion around the measuring frequrncy. A model of diffuse phase transition and relaxor ferroelectrics is proposed. The difference between normal ferroelectrics and relaxor ferroelectrics is discussed from the viewpoints of spreading of soft-mode phonons and disorder in the crystals.
The α–β phase transition in volcanic cristobalite
Damby, David E.; Llewellin, Edward W.; Horwell, Claire J.; Williamson, Ben J.; Najorka, Jens; Cressey, Gordon; Carpenter, Michael
2014-01-01
Cristobalite is a common mineral in volcanic ash produced from dome-forming eruptions. Assessment of the respiratory hazard posed by volcanic ash requires understanding the nature of the cristobalite it contains. Volcanic cristobalite contains coupled substitutions of Al3+ and Na+ for Si4+; similar co-substitutions in synthetic cristobalite are known to modify the crystal structure, affecting the stability of the α and β forms and the observed transition between them. Here, for the first time, the dynamics and energy changes associated with the α–β phase transition in volcanic cristobalite are investigated using X-ray powder diffraction with simultaneous in situ heating and differential scanning calorimetry. At ambient temperature, volcanic cristobalite exists in the α form and has a larger cell volume than synthetic α-cristobalite; as a result, its diffraction pattern sits between ICDD α- and β-cristobalite library patterns, which could cause ambiguity in phase identification. On heating from ambient temperature, volcanic cristobalite exhibits a lower degree of thermal expansion than synthetic cristobalite, and it also has a lower α–β transition temperature (∼473 K) compared with synthetic cristobalite (upwards of 543 K); these observations are discussed in relation to the presence of Al3+ and Na+ defects. The transition shows a stable and reproducible hysteresis loop with α and β phases coexisting through the transition, suggesting that discrete crystals in the sample have different transition temperatures. PMID:25242910
The α-β phase transition in volcanic cristobalite.
Damby, David E; Llewellin, Edward W; Horwell, Claire J; Williamson, Ben J; Najorka, Jens; Cressey, Gordon; Carpenter, Michael
2014-08-01
Cristobalite is a common mineral in volcanic ash produced from dome-forming eruptions. Assessment of the respiratory hazard posed by volcanic ash requires understanding the nature of the cristobalite it contains. Volcanic cristobalite contains coupled substitutions of Al(3+) and Na(+) for Si(4+); similar co-substitutions in synthetic cristobalite are known to modify the crystal structure, affecting the stability of the α and β forms and the observed transition between them. Here, for the first time, the dynamics and energy changes associated with the α-β phase transition in volcanic cristobalite are investigated using X-ray powder diffraction with simultaneous in situ heating and differential scanning calorimetry. At ambient temperature, volcanic cristobalite exists in the α form and has a larger cell volume than synthetic α-cristobalite; as a result, its diffraction pattern sits between ICDD α- and β-cristobalite library patterns, which could cause ambiguity in phase identification. On heating from ambient temperature, volcanic cristobalite exhibits a lower degree of thermal expansion than synthetic cristobalite, and it also has a lower α-β transition temperature (∼473 K) compared with synthetic cristobalite (upwards of 543 K); these observations are discussed in relation to the presence of Al(3+) and Na(+) defects. The transition shows a stable and reproducible hysteresis loop with α and β phases coexisting through the transition, suggesting that discrete crystals in the sample have different transition temperatures.
Phase transitions in multiplicative competitive processes.
Shimazaki, Hideaki; Niebur, Ernst
2005-07-01
We introduce a discrete multiplicative process as a generic model of competition. Players with different abilities successively join the game and compete for finite resources. Emergence of dominant players and evolutionary development occur as a phase transition. The competitive dynamics underlying this transition is understood from a formal analogy to statistical mechanics. The theory is applicable to bacterial competition, predicting novel population dynamics near criticality.
Phase transitions in multiplicative competitive processes
Shimazaki, Hideaki; Niebur, Ernst
2005-07-01
We introduce a discrete multiplicative process as a generic model of competition. Players with different abilities successively join the game and compete for finite resources. Emergence of dominant players and evolutionary development occur as a phase transition. The competitive dynamics underlying this transition is understood from a formal analogy to statistical mechanics. The theory is applicable to bacterial competition, predicting novel population dynamics near criticality.
Friction forces on phase transition fronts
Mégevand, Ariel
2013-07-01
In cosmological first-order phase transitions, the microscopic interaction of the phase transition fronts with non-equilibrium plasma particles manifests itself macroscopically as friction forces. In general, it is a nontrivial problem to compute these forces, and only two limits have been studied, namely, that of very slow walls and, more recently, ultra-relativistic walls which run away. In this paper we consider ultra-relativistic velocities and show that stationary solutions still exist when the parameters allow the existence of runaway walls. Hence, we discuss the necessary and sufficient conditions for the fronts to actually run away. We also propose a phenomenological model for the friction, which interpolates between the non-relativistic and ultra-relativistic values. Thus, the friction depends on two friction coefficients which can be calculated for specific models. We then study the velocity of phase transition fronts as a function of the friction parameters, the thermodynamic parameters, and the amount of supercooling.
Thermogeometric phase transition in a unified framework
NASA Astrophysics Data System (ADS)
Banerjee, Rabin; Majhi, Bibhas Ranjan; Samanta, Saurav
2017-04-01
Using geomterothermodynamics (GTD), we investigate the phase transition of black hole in a metric independent way. We show that for any black hole, curvature scalar (of equilibrium state space geometry) is singular at the point where specific heat diverges. Previously such a result could only be shown by taking specific examples on a case by case basis. A different type of phase transition, where inverse specific heat diverges, is also studied within this framework. We show that in the latter case, metric (of equilibrium state space geometry) is singular instead of curvature scalar. Since a metric singularity may be a coordinate artifact, we propose that GTD indicates that it is the singularity of specific heat and not inverse specific heat which indicates a phase transition of black holes.
Quantum phase transitions with dynamical flavors
NASA Astrophysics Data System (ADS)
Bea, Yago; Jokela, Niko; Ramallo, Alfonso V.
2016-07-01
We study the properties of a D6-brane probe in the Aharony-Bergman-Jafferis-Maldacena (ABJM) background with smeared massless dynamical quarks in the Veneziano limit. Working at zero temperature and nonvanishing charge density, we show that the system undergoes a quantum phase transition in which the topology of the brane embedding changes from a black hole to a Minkowski embedding. In the unflavored background the phase transition is of second order and takes place when the charge density vanishes. We determine the corresponding critical exponents and show that the scaling behavior near the quantum critical point has multiplicative logarithmic corrections. In the background with dynamical quarks the phase transition is of first order and occurs at nonzero charge density. In this case we compute the discontinuity of several physical quantities as functions of the number Nf of unquenched quarks of the background.
High pressure phase transition in group III nitrides compounds
NASA Astrophysics Data System (ADS)
Soni, Shubhangi; Verma, S.; Kaurav, Netram; Choudhary, K. K.
2016-05-01
Using an effective interionic interaction potential (EIOP), the pressure induced structural phase transformation from ZnS-type (B3) to NaCl-type (B1) structure in group III Post-Transition Metal Nitrides [TMN; TM=Ga and Tl] were investigated. The long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction upto second-neighbor ions within the Hafemeister and Flygare approach with modified ionic charge are properly incorporated in the EIOP. The vdW coefficients are computed following the Slater-Kirkwood variational method, as both the ions are polarizable. The estimated value of the phase transition pressure (Pt) and the magnitude of the discontinuity in volume at the transition pressure are consistent as compared to the reported data.
Late-time cosmological phase transitions
NASA Technical Reports Server (NTRS)
Schramm, David N.
1991-01-01
It is shown that the potential galaxy formation and large scale structure problems of objects existing at high redshifts (Z approx. greater than 5), structures existing on scales of 100 M pc as well as velocity flows on such scales, and minimal microwave anisotropies ((Delta)T/T) (approx. less than 10(exp -5)) can be solved if the seeds needed to generate structure form in a vacuum phase transition after decoupling. It is argued that the basic physics of such a phase transition is no more exotic than that utilized in the more traditional GUT scale phase transitions, and that, just as in the GUT case, significant random Gaussian fluctuations and/or topological defects can form. Scale lengths of approx. 100 M pc for large scale structure as well as approx. 1 M pc for galaxy formation occur naturally. Possible support for new physics that might be associated with such a late-time transition comes from the preliminary results of the SAGE solar neutrino experiment, implying neutrino flavor mixing with values similar to those required for a late-time transition. It is also noted that a see-saw model for the neutrino masses might also imply a tau neutrino mass that is an ideal hot dark matter candidate. However, in general either hot or cold dark matter can be consistent with a late-time transition.
Late-time cosmological phase transitions
Schramm, D.N. Fermi National Accelerator Lab., Batavia, IL )
1990-11-01
It is shown that the potential galaxy formation and large-scale structure problems of objects existing at high redshifts (Z {approx gt} 5), structures existing on scales of 100M pc as well as velocity flows on such scales, and minimal microwave anisotropies ({Delta}T/T) {approx lt} 10{sup {minus}5} can be solved if the seeds needed to generate structure form in a vacuum phase transition after decoupling. It is argued that the basic physics of such a phase transition is no more exotic than that utilized in the more traditional GUT scale phase transitions, and that, just as in the GUT case, significant random gaussian fluctuations and/or topological defects can form. Scale lengths of {approximately}100M pc for large-scale structure as well as {approximately}1 M pc for galaxy formation occur naturally. Possible support for new physics that might be associated with such a late-time transition comes from the preliminary results of the SAGE solar neutrino experiment, implying neutrino flavor mixing with values similar to those required for a late-time transition. It is also noted that a see-saw model for the neutrino masses might also imply a tau neutrino mass that is an ideal hot dark matter candidate. However, in general either hot or cold dark matter can be consistent with a late-time transition. 47 refs., 2 figs.
Phase transitions in phosphatidylcholine multibilayers
Westerman, Philip W.; Vaz, Maria João; Strenk, Lawrence M.; Doane, J. William
1982-01-01
The 2H NMR spectrum of a multilamellar dispersion of 1-myristoyl-2-[14,14,14-2H3]myristoyl-sn-glycero-3-phosphocholine with 1 mol% cholesterol in excess water has been recorded at temperatures between -15°C and 36°C. Motionally averaged quadrupole coupling constants 〈νQ〉 and motionally induced asymmetry parameters η are obtained by spectral analysis. Values of these quantities indicate that, at temperatures below -4°C, any rotational motion of the molecules about their molecular long axis is slow on the NMR time scale. At temperatures immediately above the pretransition these same parameters show that a fast-rotational motion is occurring about the molecular long axis. This rotational motion is hindered in that the molecules flip about a twofold symmetry axis. Between -4°C and the pretransition, spectra appear as the superposition of two powder patterns, one corresponding to the pattern observed below -4°C and the other to the pattern above the pretransition. The relative contribution of the latter increases with temperature until the pretransition is reached. These data have been interpreted in two ways: either the sample between -4°C and the pretransition contains two populations of rapidly and slowly rotating molecules, or there is only a single population of molecules undergoing a 180° flipping motion on the time scale of the NMR measurement. The latter interpretation is more consistent with other experimental findings. At the temperature of the main transition the hydrocarbon chains melt. In the absence of cholesterol, spectra are more complex in that the line shape is reproduced by the superposition of three spectral powder patterns between -4°C and the pretransition and by the superposition of two spectral patterns above the pretransition. It is postulated that these two patterns observed above the pretransition are in direct correspondence to the two ripple structures observed by freeze-fracture electron microscopy in the absence of
Shape phase transitions and critical points
Alonso, C. E.; Arias, J. M.; Fortunato, L.; Vitturi, A.
2009-05-04
We investigate different aspects connected with shape phase transitions in nuclei and the possible occurrence of dynamical symmetries at the critical points. We discuss in particular the behaviour of the neighbour odd nuclei at the vicinity of the critical points in the even nuclei. We consider both the case of the transition from the vibrational behaviour to the gamma-unstable deformation (characterized within the collective Bohr hamiltonian by the E(5) critical point symmetry) and the case of the transition from the vibrational behaviour to the stable axial deformation (characterized by the X(5) symmetry). The odd particle is assumed to be moving in the three single particle orbitals j = 1/2,3/2,5/2, a set of orbitals that is known to lead to possible supersymmetric cases. The coupling of the odd particle to the Bohr hamiltonian does lead in fact in the former case at the critical point to the E(5/12) boson-fermion dynamical symmetry. An alternative approach to the two shape transitions is based on the Interacting Boson Fermion Model. In this case suitably parametrized boson-fermion hamiltonians can describe the evolution of the odd system along the shape transitions. At the critical points both energy spectra and electromagnetic transitions were found to display characteristic patterns similar to those displayed by the even nuclei at the corresponding critical point. The behaviour of the odd nuclei can therefore be seen as necessary complementary signatures of the occurrence of the phase transitions.
Entangled states and superradiant phase transitions
Aparicio Alcalde, M.; Cardenas, A. H.; Svaiter, N. F.; Bezerra, V. B.
2010-03-15
The full Dicke model is composed of a single bosonic mode and an ensemble of N identical two-level atoms. In the model, the coupling between the bosonic mode and the atoms generates resonant and nonresonant processes. We also consider a dipole-dipole interaction between the atoms, which is able to generate entangled states in the atomic system. By assuming thermal equilibrium with a reservoir at temperature {beta}{sup -1}, the transition from fluorescent to superradiant phase and the quantum phase transition are investigated. It is shown that the critical behavior of the full Dicke model is not modified by the introduction of the dipole-dipole interaction.
Jumping phase control in interband photonic transition.
Liu, Ye; Zhu, Jiang; Gao, Zhuoyang; Zhu, Haibin; Jiang, Chun
2014-03-10
Indirect interband photonic transition provides a nonmagnetic and linear scheme to achieve optical isolation in integrated photonics. In this paper, we demonstrate that the nonreciprocal transition can be induced through two pathways respectively by different modulation designs. At the end of those pathways, the two final modes have π phaseshift. We call this phenomenon jumping phase control since this approach provides a method to control the mode phase after the conversion. This approach also yields a novel way to generate nonreciprocal phaseshift and may contribute to chip-scale optoelectronic applications.
Metamagnetic Anomalies near Dynamic Phase Transitions
NASA Astrophysics Data System (ADS)
Riego, P.; Vavassori, P.; Berger, A.
2017-03-01
We report the existence of anomalous metamagnetic fluctuations in the vicinity of the dynamic phase transition (DPT) that do not occur for the corresponding thermodynamic behavior of simple ferromagnets. Our results demonstrate that key characteristics associated with the DPT are qualitatively different from conventional thermodynamic phase transitions. We also provide evidence that these differences are tunable by showing that the presence of metamagnetic fluctuations and the size of the critical scaling regime depend strongly on the amplitude of the oscillating field that is driving the DPT in the first place.
Solid-liquid phase transition in argon
NASA Technical Reports Server (NTRS)
Tsang, T.; Tang, H. T.
1978-01-01
Starting from the Lennard-Jones interatomic potential, a modified cell theory has been used to describe the solid-liquid phase transition in argon. The cell-size variations may be evaluated by a self-consistent condition. With the inclusion of cell-size variations, the transition temperature, the solid and liquid densities, and the liquid-phase radial-distribution functions have been calculated. These ab initio results are in satisfactory agreement with molecular-dynamics calculations as well as experimental data on argon.
Phase transition in sarcosine phosphite single crystals
NASA Astrophysics Data System (ADS)
Lemanov, V. V.; Popov, S. N.; Pankova, G. A.
2011-06-01
Single crystals of sarcosine phosphite (SarcH3PO3) have been grown. The amino acid sarcosine is an isomer of the protein amino acid alanine. Both amino acids are described by the same chemical formula but have different structures; or, more specifically, in contrast to the alanine molecule, the sarcosine molecule has a symmetric structure. It has been found that the sarcosine phosphite compound undergoes a structural phase transition at a temperature of approximately 200 K. This result has demonstrated that compounds of achiral amino acids are more susceptible to structural phase transitions.
Neimark, Alexander V; Vishnyakov, Aleksey
2006-05-18
Phase transformations in fluids confined to nanoscale pores, which demonstrate characteristic signatures of first-order phase transitions, have been extensively documented in experiments and molecular simulations. They are characterized by a pronounced hysteresis, which disappears above a certain temperature. A rigorous interpretation of these observations represents a fundamental problem from the point of view of statistical mechanics. Nanoscale systems are essentially small, finite volume systems, in which the concept of the thermodynamic limit is no longer valid, and the statistical ensembles are not equivalent. Here, we present a rigorous approach to the description and molecular simulations of phase transitions and criticality in small confined systems, as illustrated by the example of vapor-liquid transition (capillary condensation) in spherical cavities. The method is based on the analysis of the canonical ensemble isotherms, which can be generated by the gauge cell Monte Carlo simulation method. The method allows one to define the critical temperature of phase transition, conditions of phase equilibrium, limits of stability of metastable states, and nucleation barriers, which determine hysteretic phase transformations.
Thermodynamic geometry, phase transitions, and the Widom line.
Ruppeiner, G; Sahay, A; Sarkar, T; Sengupta, G
2012-11-01
A microscopic characterization, based on the thermodynamic curvature R, is proposed for first-order liquid-gas phase transitions. Near the critical point, where R is proportional to the correlation volume ξ(3), we propose that R takes the same value in the coexisting phases. This proposal allows a determination of the liquid-gas coexistence curve with no use of the problematic Maxwell equal area construction. Furthermore, |R| ~ ξ(3) allows a direct determination of the Widom line in the supercritical regime. We illustrate with input from the van der Waals model and the National Institute of Standards and Technology Chemistry WebBook.
Hysteresis in the phase transition of chocolate
NASA Astrophysics Data System (ADS)
Ren, Ruilong; Lu, Qunfeng; Lin, Sihua; Dong, Xiaoyan; Fu, Hao; Wu, Shaoyi; Wu, Minghe; Teng, Baohua
2016-01-01
We designed an experiment to reproduce the hysteresis phenomenon of chocolate appearing in the heating and cooling process, and then established a model to relate the solidification degree to the order parameter. Based on the Landau-Devonshire theory, our model gave a description of the hysteresis phenomenon in chocolate, which lays the foundations for the study of the phase transition behavior of chocolate.
Chaos: Butterflies also Generate Phase Transitions
NASA Astrophysics Data System (ADS)
Leplaideur, Renaud
2015-10-01
We exhibit examples of mixing subshifts of finite type and of continuous potentials such that there are phase transitions but the pressure is always strictly convex. More surprisingly, we show that the pressure can be analytic on some interval although there exist several equilibrium states.
Polymorphic phase transition mechanism of compressed coesite.
Hu, Q Y; Shu, J-F; Cadien, A; Meng, Y; Yang, W G; Sheng, H W; Mao, H-K
2015-03-20
Silicon dioxide is one of the most abundant natural compounds. Polymorphs of SiO₂ and their phase transitions have long been a focus of great interest and intense theoretical and experimental pursuits. Here, compressing single-crystal coesite SiO₂ under hydrostatic pressures of 26-53 GPa at room temperature, we discover a new polymorphic phase transition mechanism of coesite to post-stishovite, by means of single-crystal synchrotron X-ray diffraction experiment and first-principles computational modelling. The transition features the formation of multiple previously unknown triclinic phases of SiO₂ on the transition pathway as structural intermediates. Coexistence of the low-symmetry phases results in extensive splitting of the original coesite X-ray diffraction peaks that appear as dramatic peak broadening and weakening, resembling an amorphous material. This work sheds light on the long-debated pressure-induced amorphization phenomenon of SiO₂, but also provides new insights into the densification mechanism of tetrahedrally bonded structures common in nature.
Polymorphic phase transition mechanism of compressed coesite
NASA Astrophysics Data System (ADS)
Hu, Q. Y.; Shu, J.-F.; Cadien, A.; Meng, Y.; Yang, W. G.; Sheng, H. W.; Mao, H.-K.
2015-03-01
Silicon dioxide is one of the most abundant natural compounds. Polymorphs of SiO2 and their phase transitions have long been a focus of great interest and intense theoretical and experimental pursuits. Here, compressing single-crystal coesite SiO2 under hydrostatic pressures of 26-53 GPa at room temperature, we discover a new polymorphic phase transition mechanism of coesite to post-stishovite, by means of single-crystal synchrotron X-ray diffraction experiment and first-principles computational modelling. The transition features the formation of multiple previously unknown triclinic phases of SiO2 on the transition pathway as structural intermediates. Coexistence of the low-symmetry phases results in extensive splitting of the original coesite X-ray diffraction peaks that appear as dramatic peak broadening and weakening, resembling an amorphous material. This work sheds light on the long-debated pressure-induced amorphization phenomenon of SiO2, but also provides new insights into the densification mechanism of tetrahedrally bonded structures common in nature.
Caloric materials near ferroic phase transitions.
Moya, X; Kar-Narayan, S; Mathur, N D
2014-05-01
A magnetically, electrically or mechanically responsive material can undergo significant thermal changes near a ferroic phase transition when its order parameter is modified by the conjugate applied field. The resulting magnetocaloric, electrocaloric and mechanocaloric (elastocaloric or barocaloric) effects are compared here in terms of history, experimental method, performance and prospective cooling applications.
Caloric materials near ferroic phase transitions
NASA Astrophysics Data System (ADS)
Moya, X.; Kar-Narayan, S.; Mathur, N. D.
2014-05-01
A magnetically, electrically or mechanically responsive material can undergo significant thermal changes near a ferroic phase transition when its order parameter is modified by the conjugate applied field. The resulting magnetocaloric, electrocaloric and mechanocaloric (elastocaloric or barocaloric) effects are compared here in terms of history, experimental method, performance and prospective cooling applications.
Problem of phase transitions in nuclear structure
Scharff-Goldhaber, G
1980-01-01
Phase transitions between rotational and vibrational nuclei are discussed from the point of view of the variable moment of inertia model. A three-dimensional plot of the ground-state moments of inertia of even-even nuclei vs N and Z is shown. 3 figures. (RWR)
Double-Diffusive Layers and Phase Transitions
NASA Astrophysics Data System (ADS)
Dude, Sabine; Hansen, Ulrich
2015-04-01
Researching the thermal evolution of the Earth's mantle on numerical base is very challenging. During the last decade different approaches are put forward in oder to understand the picture of the today's Earth's mantle. One way is to incorporate all the known features and physics (plate tectonics, phase transitions, CMB-topography, ...) into numerical models and make them as complex (or 'complete') as possible to capture Earth's mantle processes and surface signals. Another way is, to take a step back and look at less complex models which account for single processes and their interaction and evolution. With these 'simpler' models one is able look in detail into the physical processes and dependencies on certain parameters. Since the knowledge of slab stagnation in the transitions zone of the Earth's mantle the question whether the mantle is or at least has been layered to some degree is still under debate. On this basis we address two important features that lead to layered mantle convection and may affect each other and with this the thermal evolution of the mantle. It is commonly known the main mantle mineral olivine pass through various phase changes with depth [1]. Detailed numerical studies had been carried out to ascertain the influence on convective motion and planetary evolution [2]. It is still heavily discussed whether the endothermic phase change at 660km depth can lead an isolated lower mantle. Most of the numerical studies favour a model which has phases of layering that are disrupted by catastrophic events. In the last years double-diffusive convection has also been intensively studied with regard to planetary mantle evolution such as pile formation and core-mantle boundary topography [3]. However, another striking feature still posing open questions are evolving layers self-organised from a previous non layered state. Considering a chemical component that influences the density of a fluid in addition to the temperature leads to dynamical phenomena
Meaning of activation energy in phospholipid multibilayers phase transitions.
Lonhus, K; Budianska, L; Lisetski, L
2017-08-01
The question of the activation energy of phase transitions in lyotropic liquid crystal phases of model phospholipid membranes was considered. In our experiments, we obtained DSC thermograms of hydrated DPPC and DMPC at different scanning rates, and activation energy values were determined by a modification of Kissinger non-isothermal kinetics method. Using this approach the equivalent order of reaction corresponding to the phase transition can be determined alongside the activation energy. The cooperativity of both main transition and pre-transition was shown to be strongly dependent on scanning rate, asymptotically tending to a certain value at high rates, which corresponds to the number of lipid molecules in two concentric layers of hexagonal tiling. Changes in pretransition activation energy are shown to be proportional to changes in the system volume during the pretransition process, while the tail-length dependent part of the main transition activation energy is proportional to the jump in the number of gauche isomers. Copyright © 2017. Published by Elsevier B.V.
Nonuniversal surface behavior of dynamic phase transitions
NASA Astrophysics Data System (ADS)
Riego, Patricia; Berger, Andreas
2015-06-01
We have studied the dynamic phase transition (DPT) of the kinetic Ising model in systems with surfaces within the mean-field approximation. Varying the surface exchange coupling strength Js, the amplitude of the externally applied oscillating field h0, and its period P , we explore the dynamic behavior of the layer-dependent magnetization and the associated DPTs. The surface phase diagram shows several features that resemble those of the equilibrium case, with an extraordinary bulk transition and a surface transition for high Js values, independent from the value of h0. For low Js, however, h0 is found to be a crucial parameter that leads to nonuniversal surface behavior at the ordinary bulk transition point. Specifically, we observed here a bulk-supported surface DPT for high field amplitudes h0 and correspondingly short critical periods Pc, whereas this surface transition simultaneous to the bulk one is suppressed for slow critical dynamics occurring for low values of h0. The suppression of the DPT for low h0 not only occurs for the topmost surface layer, but also affects a significant number of subsurface layers. We find that the key physical quantity that explains this nonuniversal behavior is the time correlation between the dynamic surface and bulk magnetizations at the bulk critical point. This time correlation has to pass a threshold value to trigger a bulk-induced DPT in the surface layers. Otherwise, dynamic phase transitions are absent at the surface in stark contrast to the equilibrium behavior of the corresponding thermodynamic Ising model. Also, we have analyzed the penetration depth of the dynamically ordered phase for the surface DPT that occurs for large Js values. Here we find that the penetration depth depends strongly on Js and behaves identically to the corresponding equilibrium Ising model.
Remarks on the Phase Transition in QCD
NASA Astrophysics Data System (ADS)
Wilczek, Frank
The significance of the question of the order of the phase transition in QCD, and recent evidence that real-world QCD is probably close to having a single second order transition as a function of temperature, is reviewed. Although this circumstance seems to remove the possibility that the QCD transition during the big bang might have had spectacular cosmological consequences, there is some good news: it allows highly non-trivial yet reliable quantitative predictions to be made for the behavior near the transition. These predictions can be tested in numerical simulations and perhaps even eventually in heavy ion collisions. The present paper is a very elementary discussion of the relevant concepts, meant to be an accessible introduction for those innocent of the renormalization group approach to critical phenomena and/or the details of QCD.
Phase transition in aluminous silica in the lowermost mantle
NASA Astrophysics Data System (ADS)
Tronnes, R. G.; Andrault, D.; Konopkova, Z.; Morgenroth, W.; Liermann, H.
2012-12-01
Lower mantle basaltic lithologies contain 35-40% Mg-perovskite, 20-30% Ca-perovskite, 15-25% Al-rich phases (NAL and Ca-ferrite phases) and 15-20% silica-dominated phases. The Fe-rich Mg-perovskite makes basaltic material denser than peridotite throughout the lower mantle below 720 km depth, with important implications for mantle dynamics. Partial separation of subducted basaltic crust from depleted lithosphere might occur within the strongly heterogeneous D" zone. Further details on phase transitions and equation of states for the various minerals, however, are needed for more complete insights. The silica-dominated phases have considerable solubility of alumina [1]. We investigated silica with 4 and 6 wt% alumina to 120 GPa, using LH-DAC at the Extreme Conditions Beamline (P02.2) at PETRA-III, DESY. Powdered glass mixed with 10-15 wt% Pt-powder was compressed and heated in NaCl pressure media in Re-gaskets. The transition from the CaCl2-structured phase to seifertite (alpha-PbO2-structure) occurs at about 116 GPa at 2500 K. This is intermediate between the transition pressures of about 122 GPa and 100-113 GPa reported for similar temperatures for pure SiO2 [2] and a basalt composition [1], respectively. The CaCl2-structured silica phase crystallized along with seifertite, consistent with a binary phase loop trending towards lower pressure with increasing Al-content. The presence of an Al-rich Ca-ferrite phase (near the MgAl2O4-NaAlSiO4-join) in basaltic material indicates that the Al-solubility limits for the silica-dominated phases in basaltic compositions may be similar to those in the binary system SiO2-AlO1.5. Based on the X-ray pattern refinement, our samples show no significant volume change across the transition. Even so, the transition could be associated with a significant density change if the Al substitution mechanisms are different in CaCl2-structured phase and seifertite. The most likely situation is that Al-substitution occurs via O-vacancies in the
Phase Space Transition States for Deterministic Thermostats
NASA Astrophysics Data System (ADS)
Ezra, Gregory; Wiggins, Stephen
2009-03-01
We describe the relation between the phase space structure of Hamiltonian and non-Hamiltonian deterministic thermostats. We show that phase space structures governing reaction dynamics in Hamiltonian systems, such as the transition state, map to the same type of phase space structures for the non-Hamiltonian isokinetic equations of motion for the thermostatted Hamiltonian. Our results establish a general theoretical framework for analyzing thermostat dynamics using concepts and methods developed in reaction rate theory. Numerical results are presented for the isokinetic thermostat.
Multiscale Modeling of Shock-Induced Phase Transitions in Iron
NASA Astrophysics Data System (ADS)
Carter, Emily; Caspersen, Kyle; Lew, Adrian; Ortiz, Michael
2004-03-01
Multiscale Modeling of Shock-Induced Phase Transitions in Iron Emily Carter, Kyle Caspersen, Adrian Lew and Michael Ortiz We investigate the bcc to hcp phase transition in iron under both pressure and shear. We use DFT to map out the energy landscape of uniformly deformed iron, including its equation of state and its elastic moduli as a function of volume. >From these data we construct a nonlinear-elastic energy density which gives the energy density for arbitrary - not necessarily small - deformations. The energy density contains two wells corresponding to the bcc and hcp phases. We take this multi-well energy density as a basis for the investigation of the effect of shear on the phase diagram of iron. We allow for mixed states consisting alternating lamellae of bcc and hcp phases, and, for each macroscopic deformation, we determine the optimal microstructure of the mixed state by energy minimization using a sequential-lamination algorithm. We find that the superposition of shearing deformation on a volume change has the effect of inducing mixed states of varying spatial complexity, and of markedly lowering the critical transformation pressure. Indeed, we find that shear must be taken into consideration in order to obtain agreement with measured transformation pressures. Finally, we demonstrate how the microstructure model can be integrated into large-scale finite element calculations of shocked iron.
Holographic phase transitions at finite chemical potential
NASA Astrophysics Data System (ADS)
Mateos, David; Matsuura, Shunji; Myers, Robert C.; Thomson, Rowan M.
2007-11-01
Recently, holographic techniques have been used to study the thermal properties of Script N = 2 super-Yang-Mills theory, with gauge group SU(Nc) and coupled to Nf << Nc flavours of fundamental matter, at large Nc and large 't Hooft coupling. Here we consider the phase diagram as a function of temperature and baryon chemical potential μb. For fixed μb < NcMq there is a line of first order thermal phase transitions separating a region with vanishing baryon density and one with nonzero density. For fixed μb>Nc Mq there is no phase transition as a function of the temperature and the baryon density is always nonzero. We also compare the present results for the grand canonical ensemble with those for canonical ensemble in which the baryon density is held fixed [1].
The comfortable driving model revisited: traffic phases and phase transitions
NASA Astrophysics Data System (ADS)
Knorr, Florian; Schreckenberg, Michael
2013-07-01
We study the spatiotemporal patterns resulting from different boundary conditions for a microscopic traffic model and contrast them with empirical results. By evaluating the time series of local measurements, the local traffic states are assigned to the different traffic phases of Kerner’s three-phase traffic theory. For this classification we use the rule-based FOTO-method, which provides ‘hard’ rules for this assignment. Using this approach, our analysis shows that the model is indeed able to reproduce three qualitatively different traffic phases: free flow (F), synchronized traffic (S), and wide moving jams (J). In addition, we investigate the likelihood of transitions between the three traffic phases. We show that a transition from free flow to a wide moving jam often involves an intermediate transition: first from free flow to synchronized flow and then from synchronized flow to a wide moving jam. This is supported by the fact that the so-called F → S transition (from free flow to synchronized traffic) is much more likely than a direct F → J transition. The model under consideration has a functional relationship between traffic flow and traffic density. The fundamental hypothesis of the three-phase traffic theory, however, postulates that the steady states of synchronized flow occupy a two-dimensional region in the flow-density plane. Due to the obvious discrepancy between the model investigated here and the postulate of the three-phase traffic theory, the good agreement that we found could not be expected. For a more detailed analysis, we also studied vehicle dynamics at a microscopic level and provide a comparison of real detector data with simulated data of the identical highway segment.
Phase Transformation Volume Change Control of Strain and Instability Mechanisms
NASA Astrophysics Data System (ADS)
Green, H. W.
2011-12-01
Phase transformations that are accompanied by significant change in volume self-organize the transformation process under stress to enhance strain and/or decrease stress. When the kinetics of the reaction are reasonably rapid, this occurs by nucleation and growth of phase(s) on grain boundaries of appropriate orientation to facilitate strain. When the kinetics of reaction are sluggish (ratio of nucleation rate to growth rate >> 1) and the reaction is polymorphic and exothermic, under specific conditions this process can lead to shearing instability in which the volume change of reaction drives runaway nucleation at stress concentrations leading to macroscopic faulting. Under these conditions, the detailed processes and microstructures produced depend on the sign of volume change but the failure is very similar whether volume change is positive or negative. The microstructures confirm that the mesoscale physics of this process (self-organization of primary features and nucleation/propagation of a fault) is the same as for brittle shear fracture, despite the large difference in the fundamental microscopic physics (formation of nanocrystalline microlenses instead of tensile cracks, and fault propagation by grain-boundary sliding rather than frictional sliding). When volume change is negative and the kinetics of reaction are less sluggish (ratio of nucleation rate to growth rate of order 1), nucleation of the new (denser) phase occurs preferentially on grain boundaries normal to maximum compression and new crystals nucleated on any orientation of grain boundary grow parallel to maximum compression. The result is stylolite-like volume loss normal to maximum compression. Observations of polyphase metamorphic rocks suggest that similar creep can occur during prograde metamorphism by nucleation of more-dense phases and less-dense phases on different populations of phase-boundary orientations such that the overall pattern achieves a macroscopic strain by volume transfer
Determining computational complexity from characteristic `phase transitions'
NASA Astrophysics Data System (ADS)
Monasson, Rémi; Zecchina, Riccardo; Kirkpatrick, Scott; Selman, Bart; Troyansky, Lidror
1999-07-01
Non-deterministic polynomial time (commonly termed `NP-complete') problems are relevant to many computational tasks of practical interest-such as the `travelling salesman problem'-but are difficult to solve: the computing time grows exponentially with problem size in the worst case. It has recently been shown that these problems exhibit `phase boundaries', across which dramatic changes occur in the computational difficulty and solution character-the problems become easier to solve away from the boundary. Here we report an analytic solution and experimental investigation of the phase transition in K -satisfiability, an archetypal NP-complete problem. Depending on the input parameters, the computing time may grow exponentially or polynomially with problem size; in the former case, we observe a discontinuous transition, whereas in the latter case a continuous (second-order) transition is found. The nature of these transitions may explain the differing computational costs, and suggests directions for improving the efficiency of search algorithms. Similar types of transition should occur in other combinatorial problems and in glassy or granular materials, thereby strengthening the link between computational models and properties of physical systems.
News and views in discontinuous phase transitions
NASA Astrophysics Data System (ADS)
Nagler, Jan
2014-03-01
Recent progress in the theory of discontinuous percolation allow us to better understand the the sudden emergence of large-scale connectedness both in networked systems and on the lattice. We analytically study mechanisms for the amplification of critical fluctuations at the phase transition point, non-self-averaging and power law fluctuations. A single event analysis allow to establish criteria for discontinuous percolation transitions, even on the high-dimensional lattice. Some applications such as salad bowl percolation, and inverse fragmentation are discussed.
Percolation quantum phase transitions in diluted magnets.
Vojta, Thomas; Schmalian, Jörg
2005-12-02
We show that the interplay of geometric criticality and quantum fluctuations leads to a novel universality class for the percolation quantum phase transition in diluted magnets. All critical exponents involving dynamical correlations are different from the classical percolation values, but in two dimensions they can nonetheless be determined exactly. We develop a complete scaling theory of this transition, and we relate it to recent experiments in La2Cu(1-p)(Zn,Mg)(p)O4. Our results are also relevant for disordered interacting boson systems.
Phase Transition of DNA Coated Nanogold Networks
NASA Astrophysics Data System (ADS)
Kiang, Ching-Hwa; Sun, Young; Harris, Nolan; Wickremasinghe, Nissanka
2004-03-01
Melting and hybridization of DNA-coated gold nanoparticle networks are investigated with optical absorption spectroscopy and tansmission electron microscopy. Single-stranded DNA-coated nanogold are linked with complementary, single-stranded linker DNA to form particle networks. Network formation results in a solution color change, which can be used for DNA detection. Compared to free DNA, networked DNA-nanoparticle systems result in a sharp melting transition. Melting curves calculated from percolation theory agree with our experimental results(1). (1) C.-H. Kiang, ``Phase Transition of DNA-Linked Gold Nanoparticles,'' Physica A, 321 (2003) 164--169.
Phase transitions in Pareto optimal complex networks
NASA Astrophysics Data System (ADS)
Seoane, Luís F.; Solé, Ricard
2015-09-01
The organization of interactions in complex systems can be described by networks connecting different units. These graphs are useful representations of the local and global complexity of the underlying systems. The origin of their topological structure can be diverse, resulting from different mechanisms including multiplicative processes and optimization. In spatial networks or in graphs where cost constraints are at work, as it occurs in a plethora of situations from power grids to the wiring of neurons in the brain, optimization plays an important part in shaping their organization. In this paper we study network designs resulting from a Pareto optimization process, where different simultaneous constraints are the targets of selection. We analyze three variations on a problem, finding phase transitions of different kinds. Distinct phases are associated with different arrangements of the connections, but the need of drastic topological changes does not determine the presence or the nature of the phase transitions encountered. Instead, the functions under optimization do play a determinant role. This reinforces the view that phase transitions do not arise from intrinsic properties of a system alone, but from the interplay of that system with its external constraints.
Dimensional phase transition in small Yukawa clusters
Sheridan, T. E.; Wells, K. D.
2010-01-15
We investigate the one- to two-dimensional zigzag transition in clusters consisting of a small number of particles interacting through a Yukawa (Debye) potential and confined in a two-dimensional biharmonic potential well. Dusty (complex) plasma clusters with n<=19 monodisperse particles are characterized experimentally for two different confining wells. The well anisotropy is accurately measured, and the Debye shielding parameter is determined from the longitudinal breathing frequency. Debye shielding is shown to be important. A model for this system is used to predict equilibrium particle configurations. The experiment and model exhibit excellent agreement. The critical value of n for the zigzag transition is found to be less than that predicted for an unshielded Coulomb interaction. The zigzag transition is shown to behave as a continuous phase transition from a one-dimensional to a two-dimensional state, where the state variables are the number of particles, the well anisotropy and the Debye shielding parameter. A universal critical exponent for the zigzag transition is identified for transitions caused by varying the Debye shielding parameter.
Phase transitions at high energy vindicate negative microcanonical temperature
NASA Astrophysics Data System (ADS)
Buonsante, P.; Franzosi, R.; Smerzi, A.
2017-05-01
The notion of negative absolute temperature emerges naturally from Boltzmann's definition of "surface" microcanonical entropy in isolated systems with a bounded energy density. Recently, the well-posedness of such construct has been challenged, on account that only the Gibbs "volume" entropy—and the strictly positive temperature thereof—would give rise to a consistent thermodynamics. Here we present analytical and numerical evidence that Boltzmann microcanonical entropy provides a consistent thermometry for both signs of the temperature. In particular, we show that Boltzmann (negative) temperature allows the description of phase transitions occurring at high energy densities, at variance with Gibbs temperature. Our results apply to nonlinear lattice models standardly employed to describe the propagation of light in arrays of coupled wave guides and the dynamics of ultracold gases trapped in optical lattices. Optically induced photonic lattices, characterized by saturable nonlinearity, are particularly appealing because they offer the possibility of observing states and phase transitions at both signs of the temperature.
Phase Transition and Elastic Properties of La-Compounds
Raypuria, G. S.; Singh, K. C.; Baraiya, A. K.; Gupta, D. C.
2011-07-15
The Phase transition and elastic properties of La-monochalcogenides have been investigated under pressure by means of a modified charge-transfer potential model which incorporates the Coulomb interaction modified by Coulomb screening due to the delocalization of electron of rare-earth atom leading to many-body interactions, covalency effect and overlap repulsion extended up to second-nearest neighbours. Under high pressure the coordination increases and they transform from rock-salt to CsCl structure. The calculated values of cohesive energy, lattice constant, phase transition pressure, relative volume collapse and harmonic elastic moduli their agree well with the available measured data and better than those computed by earlier workers. Present model is capable of explaining the Cauchy's discrepancy correctly.
Pressure induced structural phase transition of XC (X = Si, Ge, Sn)
NASA Astrophysics Data System (ADS)
Kaurav, N.; Verma, S.; Choudhary, K. K.; Sharma, U.; Shah, S.
2012-05-01
An effective interionic interaction potential (EIOP) is developed to investigate the pressure induced phase transitions from ZnS-type (B3) to NaCl-type (B1) in XC [X = Si, Ge, and Sn] compounds. The long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction up to second-neighbor ions within the Hafemeister and Flygare approach with modified ionic charge are properly incorporated in the EIOP. The vdW coefficients are computed following the Slater-Kirkwood variational method, as both the ions are polarizable. The estimated value of the phase transition pressure (Pt) and the magnitude of the discontinuity in volume at the transition pressure are consistent as compared to the reported data. The vast volume discontinuity in pressure volume phase diagram identifies the structural phase transition from B3 to B1 structure.
Pressure induced structural phase transition in IB transition metal nitrides compounds
Soni, Shubhangi; Kaurav, Netram Jain, A.; Shah, S.; Choudhary, K. K.
2015-06-24
Transition metal mononitrides are known as refractory compounds, and they have, relatively, high hardness, brittleness, melting point, and superconducting transition temperature, and they also have interesting optical, electronic, catalytic, and magnetic properties. Evolution of structural properties would be an important step towards realizing the potential technological scenario of this material of class. In the present study, an effective interionic interaction potential (EIOP) is developed to investigate the pressure induced phase transitions in IB transition metal nitrides TMN [TM = Cu, Ag, and Au] compounds. The long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction upto second-neighbor ions within the Hafemeister and Flygare approach with modified ionic charge are properly incorporated in the EIOP. The vdW coefficients are computed following the Slater-Kirkwood variational method, as both the ions are polarizable. The estimated value of the phase transition pressure (Pt) and the magnitude of the discontinuity in volume at the transition pressure are consistent as compared to the reported data.
Pressure induced structural phase transition in IB transition metal nitrides compounds
NASA Astrophysics Data System (ADS)
Soni, Shubhangi; Kaurav, Netram; Jain, A.; Shah, S.; Choudhary, K. K.
2015-06-01
Transition metal mononitrides are known as refractory compounds, and they have, relatively, high hardness, brittleness, melting point, and superconducting transition temperature, and they also have interesting optical, electronic, catalytic, and magnetic properties. Evolution of structural properties would be an important step towards realizing the potential technological scenario of this material of class. In the present study, an effective interionic interaction potential (EIOP) is developed to investigate the pressure induced phase transitions in IB transition metal nitrides TMN [TM = Cu, Ag, and Au] compounds. The long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction upto second-neighbor ions within the Hafemeister and Flygare approach with modified ionic charge are properly incorporated in the EIOP. The vdW coefficients are computed following the Slater-Kirkwood variational method, as both the ions are polarizable. The estimated value of the phase transition pressure (Pt) and the magnitude of the discontinuity in volume at the transition pressure are consistent as compared to the reported data.
Phase Transitions in Models of Bird Flocking
NASA Astrophysics Data System (ADS)
Christodoulidi, H.; van der Weele, K.; Antonopoulos, Ch. G.; Bountis, T.
2014-12-01
The aim of the present paper is to elucidate the transition from collective to random behavior exhibited by various mathematical models of bird flocking. In particular, we compare Vicsek's model [Vicsek et al., Phys. Rev. Lett. 75, 1226-1229 (1995)] with one based on topological considerations. The latter model is found to exhibit a first order phase transition from flocking to decoherence, as the "noise parameter" of the problem is increased, whereas Vicsek's model gives a second order transition. Refining the topological model in such a way that birds are influenced mostly by the birds in front of them, less by the ones at their sides and not at all by those behind them (because they do not see them), we find a behavior that lies in between the two models. Finally, we propose a novel mechanism for preserving the flock's cohesion, without imposing artificial boundary conditions or attractive forces.
Gravitational Waves from a Dark Phase Transition.
Schwaller, Pedro
2015-10-30
In this work, we show that a large class of models with a composite dark sector undergo a strong first order phase transition in the early Universe, which could lead to a detectable gravitational wave signal. We summarize the basic conditions for a strong first order phase transition for SU(N) dark sectors with n_{f} flavors, calculate the gravitational wave spectrum and show that, depending on the dark confinement scale, it can be detected at eLISA or in pulsar timing array experiments. The gravitational wave signal provides a unique test of the gravitational interactions of a dark sector, and we discuss the complementarity with conventional searches for new dark sectors. The discussion includes the twin Higgs and strongly interacting massive particle models as well as symmetric and asymmetric composite dark matter scenarios.
Structural phase transitions in layered perovskitelike crystals
Aleksandrov, K.S.
1995-03-01
Possible symmetry changes due to small tilts of octahedra are considered for layered perovskite-like crystals containing slabs of several ({ell}) layers of comer-sharing octahedra. In the crystals with {ell} > 1, four types of distortions are possible; as a rule, these distortions correspond to the librational modes of the parent lattice. Condensation of these soft modes is the reason for structural phase transitions or sequences of phase transitions. The results obtained are compared with the known experimental data for a number of layered ferroelectric and ferroelastic perovskite-like compounds. An application of the results to the initial stage of determining unknown structures is discussed with particular attention paid to high-temperature superconductors. 76 refs., 9 figs., 7 tabs.
Phase transition in the countdown problem
NASA Astrophysics Data System (ADS)
Lacasa, Lucas; Luque, Bartolo
2012-07-01
We present a combinatorial decision problem, inspired by the celebrated quiz show called Countdown, that involves the computation of a given target number T from a set of k randomly chosen integers along with a set of arithmetic operations. We find that the probability of winning the game evidences a threshold phenomenon that can be understood in the terms of an algorithmic phase transition as a function of the set size k. Numerical simulations show that such probability sharply transitions from zero to one at some critical value of the control parameter, hence separating the algorithm's parameter space in different phases. We also find that the system is maximally efficient close to the critical point. We derive analytical expressions that match the numerical results for finite size and permit us to extrapolate the behavior in the thermodynamic limit.
Phase transition in the countdown problem.
Lacasa, Lucas; Luque, Bartolo
2012-07-01
We present a combinatorial decision problem, inspired by the celebrated quiz show called Countdown, that involves the computation of a given target number T from a set of k randomly chosen integers along with a set of arithmetic operations. We find that the probability of winning the game evidences a threshold phenomenon that can be understood in the terms of an algorithmic phase transition as a function of the set size k. Numerical simulations show that such probability sharply transitions from zero to one at some critical value of the control parameter, hence separating the algorithm's parameter space in different phases. We also find that the system is maximally efficient close to the critical point. We derive analytical expressions that match the numerical results for finite size and permit us to extrapolate the behavior in the thermodynamic limit.
A nonequilibrium phase transition in immune response
NASA Astrophysics Data System (ADS)
Zhang, Wei; Qi, An-Shen
2004-07-01
The dynamics of immune response correlated to signal transduction in immune thymic cells (T cells) is studied. In particular, the problem of the phosphorylation of the immune-receptor tyrosine-based activation motifs (ITAM) is explored. A nonlinear model is established on the basis of experimental observations. The behaviours of the model can be well analysed using the concepts of nonequilibrium phase transitions. In addition, the Riemann-Hugoniot cusp catastrophe is demonstrated by the model. Due to the application of the theory of nonequilibrium phase transitions, the biological phenomena can be clarified more precisely. The results can also be used to further explain the signal transduction and signal discrimination of an important type of immune T cell.
Gravitational Waves from a Dark Phase Transition
NASA Astrophysics Data System (ADS)
Schwaller, Pedro
2015-10-01
In this work, we show that a large class of models with a composite dark sector undergo a strong first order phase transition in the early Universe, which could lead to a detectable gravitational wave signal. We summarize the basic conditions for a strong first order phase transition for SU (N ) dark sectors with nf flavors, calculate the gravitational wave spectrum and show that, depending on the dark confinement scale, it can be detected at eLISA or in pulsar timing array experiments. The gravitational wave signal provides a unique test of the gravitational interactions of a dark sector, and we discuss the complementarity with conventional searches for new dark sectors. The discussion includes the twin Higgs and strongly interacting massive particle models as well as symmetric and asymmetric composite dark matter scenarios.
Phase transitions: An overview with a view
Gleiser, M.
1997-10-01
The dynamics of phase transitions plays a crucial role in the so- called interface between high energy particle physics and cosmology. Many of the interesting results generated during the last fifteen years or so rely on simplified assumptions concerning the complex mechanisms typical of nonequilibrium field theories. After reviewing well-known results concerning the dynamics of first and second order phase transitions, I argue that much is yet to be understood, in particular in situations where homogeneous nucleation theory does not apply. I present a method to deal with departures from homogeneous nucleation, and compare its efficacy with numerical simulations. Finally, I discuss the interesting problem of matching numerical simulations of stochastic field theories with continuum models.
Electroweak monopoles and the electroweak phase transition
NASA Astrophysics Data System (ADS)
Arunasalam, Suntharan; Kobakhidze, Archil
2017-07-01
We consider an isolated electroweak monopole solution within the Standard Model with a nonlinear Born-Infeld extension of the hypercharge gauge field. Monopole (and dyon) solutions in such an extension are regular and their masses are predicted to be proportional to the Born-Infeld mass parameter. We argue that cosmological production of electroweak monopoles may delay the electroweak phase transition and make it more strongly first order for monopole masses M≳ 9.3 {\\cdot } 10^3 TeV, while the nucleosynthesis constraints on the abundance of relic monopoles impose the bound M≲ 2.3\\cdot 10^4 TeV. The monopoles with a mass in this shallow range may be responsible for the dynamical generation of the matter-antimatter asymmetry during the electroweak phase transition.
Phase transitions in unstable cancer cell populations
NASA Astrophysics Data System (ADS)
Solé, R. V.
2003-09-01
The dynamics of cancer evolution is studied by means of a simple quasispecies model involving cells displaying high levels of genetic instability. Both continuous, mean-field and discrete, bit-string models are analysed. The string model is simulated on a single-peak landscape. It is shown that a phase transition exists at high levels of genetic instability, thus separating two phases of slow and rapid growth. The results suggest that, under a conserved level of genetic instability the cancer cell population will be close to the threshold level. Implications for therapy are outlined.
Evolution of structure during phase transitions
Martin, J.E.; Wilcoxon, J.P.; Anderson, R.A.
1996-03-01
Nanostructured materials can be synthesized by utilizing the domain growth that accompanies first-order phase separation. Structural control can be achieved by appropriately selecting the quench depth and the quench time, but in order to do this in a mindful fashion one must understand the kinetics of domain growth. The authors have completed detailed light scattering studies of the evolution of structure in both temperature- and field-quenched phase transitions in two and three dimensional systems. They have studied these systems in the quiescent state and in shear and have developed theoretical models that account for the experimental results.
Structural phase transitions in monolayer molybdenum dichalcogenides
NASA Astrophysics Data System (ADS)
Choe, Duk-Hyun; Sung, Ha June; Chang, Kee Joo
2015-03-01
The recent discovery of two-dimensional materials such as graphene and transition metal dichalcogenides (TMDs) has provided opportunities to develop ultimate thin channel devices. In contrast to graphene, the existence of moderate band gap and strong spin-orbit coupling gives rise to exotic electronic properties which vary with layer thickness, lattice structure, and symmetry. TMDs commonly appear in two structures with distinct symmetries, trigonal prismatic 2H and octahedral 1T phases which are semiconducting and metallic, respectively. In this work, we investigate the structural and electronic properties of monolayer molybdenum dichalcogenides (MoX2, where X = S, Se, Te) through first-principles density functional calculations. We find a tendency that the semiconducting 2H phase is more stable than the metallic 1T phase. We show that a spontaneous symmetry breaking of 1T phase leads to various distorted octahedral (1T') phases, thus inducing a metal-to-semiconductor transition. We discuss the effects of carrier doping on the structural stability and the modification of the electronic structure. This work was supported by the National Research Foundation of Korea (NRF) under Grant No. NRF-2005-0093845 and Samsung Science and Technology Foundation under Grant No. SSTFBA1401-08.
Extracellular ice phase transitions in insects.
Hawes, T C
2014-01-01
At temperatures below their temperature of crystallization (Tc), the extracellular body fluids of insects undergo a phase transition from liquid to solid. Insects that survive the transition to equilibrium (complete freezing of the body fluids) are designated as freeze tolerant. Although this phenomenon has been reported and described in many Insecta, current nomenclature and theory does not clearly delineate between the process of transition (freezing) and the final solid phase itself (the frozen state). Thus freeze tolerant insects are currently, by convention, described in terms of the temperature at which the crystallization of their body fluids is initiated, Tc. In fact, the correct descriptor for insects that tolerate freezing is the temperature of equilibrium freezing, Tef. The process of freezing is itself a separate physical event with unique physiological stresses that are associated with ice growth. Correspondingly there are a number of insects whose physiological cryo-limits are very specifically delineated by this transitional envelope. The distinction also has considerable significance for our understanding of insect cryobiology: firstly, because the ability to manage endogenous ice growth is a fundamental segregator of cryotype; and secondly, because our understanding of internal ice management is still largely nascent.
A magnetic phase transition temperature calibration device
NASA Astrophysics Data System (ADS)
Garcia, F.; Cernicchiaro, G. R. C.; Takeuchi, A. Y.
1999-04-01
We have devised a technique of manufacturing temperature sensor calibration devices based on the magnetic properties of the pseudobinary compounds of formula (RxR1-x')Co2, where R and R' are heavy rare earth elements. The device is a solid sensor which provides an easily detectable first order magnetic phase transition at fixed temperature points. It is known that a first order magnetic phase transition from ferrimagnetism to paramagnetism is observed in compounds as TmCo2 (3.70 K), ErCo2 (32.05 K), HoCo2 (77.12 K), and DyCo2 (136.55 K). These transitions correspond to a large anomaly in the characteristic properties as function of temperature. In this work, we present the electrical resistivity and magnetization measurements of (Er, Ho)Co2 series and DyCo2 compounds showing the viability of the proposed devices from 32.05 up to 136.55 K. This range can be extended below and above by substitution of the chemical components and the stoichiometric composition. The number of transitions can be fixed by a convenient arrangement of several elements.
Gravitational phase transitions with an exclusion constraint in position space
NASA Astrophysics Data System (ADS)
Chavanis, Pierre-Henri
2014-01-01
We discuss the statistical mechanics of a system of self-gravitating particles with an exclusion constraint in position space in a space of dimension d. The exclusion constraint puts an upper bound on the density of the system and can stabilize it against gravitational collapse. We plot the caloric curves giving the temperature as a function of the energy and investigate the nature of phase transitions as a function of the size of the system and of the dimension of space in both microcanonical and canonical ensembles. We consider stable and metastable states and emphasize the importance of the latter for systems with long-range interactions. For d ≤ 2, there is no phase transition. For d > 2, phase transitions can take place between a "gaseous" phase unaffected by the exclusion constraint and a "condensed" phase dominated by this constraint. The condensed configurations have a core-halo structure made of a "rocky core" surrounded by an "atmosphere", similar to a giant gaseous planet. For large systems there exist microcanonical and canonical first order phase transitions. For intermediate systems, only canonical first order phase transitions are present. For small systems there is no phase transition at all. As a result, the phase diagram exhibits two critical points, one in each ensemble. There also exist a region of negative specific heats and a situation of ensemble inequivalence for sufficiently large systems. We show that a statistical equilibrium state exists for any values of energy and temperature in any dimension of space. This differs from the case of the self-gravitating Fermi gas for which there is no statistical equilibrium state at low energies and low temperatures when d ≥ 4. By a proper interpretation of the parameters, our results have application for the chemotaxis of bacterial populations in biology described by a generalized Keller-Segel model including an exclusion constraint in position space. They also describe colloids at a fluid
Topological phase transitions in frustrated magnets
NASA Astrophysics Data System (ADS)
Southern, B. W.; Peles, A.
2006-06-01
The role of topological excitations in frustrated Heisenberg antiferromagnets between two and three spatial dimensions is considered. In particular, the antiferromagnetic Heisenberg model on a stacked triangular geometry with a finite number of layers is studied using Monte Carlo methods. A phase transition that is purely topological in nature occurs at a finite temperature for all film thicknesses. The results indicate that topological excitations are important for a complete understanding of the critical properties of the model between two and three dimensions.
Nonequilibrium Phase Transitions. Appendix A-F
1988-09-20
equilibrium whereas the dissipation of energy goes to zero as the excess energy vanishes at equilibrium. In a system that is not isolated the dissipation...polymer molecule cannot undergo a phase transition with zero change in free energy unless it does so with no change in conformation. This is the...solidification can never occur with a zero change in free energy . Only when the polymer molecule has a reasonable probability of occupying the same conformation
Gravitation, phase transitions, and the big bang
Krauss, L.M.
1982-11-08
Introduced here is a model of the early universe based on the possibility of a first-order phase transition involving gravity, and arrived at by a consideration of instabilities in the semiclassical theory. The evolution of the system is very different from the standard Friedmann-Robertson-Walker big-bang scenario, indicating the potential importance of semiclassical finite-temperature gravitational effects. Baryosynthesis and monopole production in this scenario are also outlined.
Phase transitions in Nowak Sznajd opinion dynamics
NASA Astrophysics Data System (ADS)
Wołoszyn, Maciej; Stauffer, Dietrich; Kułakowski, Krzysztof
2007-05-01
The Nowak modification of the Sznajd opinion dynamics model on the square lattice assumes that with probability β the opinions flip due to mass-media advertising from down to up, and vice versa. Besides, with probability α the Sznajd rule applies that a neighbour pair agreeing in its two opinions convinces all its six neighbours of that opinion. Our Monte Carlo simulations and mean-field theory find sharp phase transitions in the parameter space.
Fluorescence study on the phase transition of hydrogen-bonding gels
NASA Astrophysics Data System (ADS)
Yılmaz, Yaşar
2002-11-01
A technique based on steady-state fluorescence measurements is introduced to study the discontinuous volume phase transition of hydrogen-bonding gel. The fluorescence light intensity of pyranine (1-Hydroxypyrene-3, 6, 8-trisulfonic acid) bonded to the gel by means of methacryl amino-propyl-trimethyl ammonium chloride was monitored during the swelling of poly(methacrylic acid-co-dimethyl acrylamide) copolymer in water as a function of temperature. A discontinuous volume phase transition around 60 °C and an additional phase around 30 °C, which may be interpreted as the freely fluctuating phase in a collapsed state, were observed when the fluorescence intensity changes.
LDRD final report : raman spectroscopic measurements to monitor the HMX beta-delta phase transition.
Renlund, Anita Mariana; Tappan, Alexander Smith; Miller, Jill C.
2000-11-01
The HMX {beta}-{delta} solid-solid phase transition, which occurs as HMX is heated near 170 C, is linked to increased reactivity and sensitivity to initiation. Thermally damaged energetic materials (EMs) containing HMX therefore may present a safety concern. Information about the phase transition is vital to predictive safety models for HMX and HMX-containing EMs. We report work on monitoring the phase transition with real-time Raman spectroscopy aimed towards obtaining a better understanding of physical properties of HMX through the phase transition. HMX samples were confined in a cell of minimal free volume in a displacement-controlled or load-controlled arrangement. The cell was heated and then cooled at controlled rates while real-time Raman spectroscopic measurements were performed. Raman spectroscopy provides a clear distinction between the phases of HMX because the vibrational transitions of the molecule change with conformational changes associated with the phase transition. Temperature of phase transition versus load data are presented for both the heating and cooling cycles in the load-controlled apparatus, and general trends are discussed. A weak dependence of the temperature of phase transition on load was discovered during the heating cycle, with higher loads causing the phase transition to occur at a higher temperature. This was especially true in the temperature of completion of phase transition data as opposed to the temperature of onset of phase transition data. A stronger dependence on load was observed in the cooling cycle, with higher loads causing the reverse phase transitions to occur at a higher cooling temperature. Also, higher loads tended to cause the phase transition to occur over a longer period of time in the heating cycle and over a shorter period of time in the cooling cycle. All three of the pure HMX phases ({alpha}, {beta} and {delta}) were detected on cooling of the heated samples, either in pure form or as a mixture.
Phase transitions in planar bilayer membranes.
White, S H
1975-01-01
Temperature-dependent structural changes in planar bilayer membranes formed from glycerol monooleate (GMO) dispersed in various n-alkane solvents (C12-C17) have been studied using precise measurements of specific geometric capacitance (Cg). Cg generally increases as temperature (T) decreases. A change in the slope of Cg(T) occurs between 15 and 18 degrees C for all solvent systems examined. Measurements of the interfacial tension (gamma) of the bulk GMO-alkane dispersions against 0.1 M NaCl show that gamma generally decreases with decreasing temperature. The data can be fitted with two straight lines of different slope which intersect on the average at 17 degrees C. Pagano et al. (1973, Science (Wash. D.C.). 181:557) have shown using calorimetry that GMO has a phase transition at about 15 degrees C. Thus, the changes in Cg and gamma with temperature are likely to result from a GMO phase transition. A second structural change is observed to occur between 5 and 10 degrees C which has not been detected calorimetrically. Calculations of Cg based on various estimates of the hydrocarbon dielectric coefficient (epsilon-b) and/or hydrocarbon thickness (delta-b) leads to models for the structure of the bilayer above and below the phase transition temperature. PMID:1111634
Dynamical quantum phase transitions (Review Article)
NASA Astrophysics Data System (ADS)
Zvyagin, A. A.
2016-11-01
During recent years the interest to dynamics of quantum systems has grown considerably. Quantum many body systems out of equilibrium often manifest behavior, different from the one predicted by standard statistical mechanics and thermodynamics in equilibrium. Since the dynamics of a many-body quantum system typically involve many excited eigenstates, with a non-thermal distribution, the time evolution of such a system provides an unique way for investigation of non-equilibrium quantum statistical mechanics. Last decade such new subjects like quantum quenches, thermalization, pre-thermalization, equilibration, generalized Gibbs ensemble, etc. are among the most attractive topics of investigation in modern quantum physics. One of the most interesting themes in the study of dynamics of quantum many-body systems out of equilibrium is connected with the recently proposed important concept of dynamical quantum phase transitions. During the last few years a great progress has been achieved in studying of those singularities in the time dependence of characteristics of quantum mechanical systems, in particular, in understanding how the quantum critical points of equilibrium thermodynamics affect their dynamical properties. Dynamical quantum phase transitions reveal universality, scaling, connection to the topology, and many other interesting features. Here we review the recent achievements of this quickly developing part of low-temperature quantum physics. The study of dynamical quantum phase transitions is especially important in context of their connection to the problem of the modern theory of quantum information, where namely non-equilibrium dynamics of many-body quantum system plays the major role.
Recent theoretical advances on superradiant phase transitions
NASA Astrophysics Data System (ADS)
Baksic, Alexandre; Nataf, Pierre; Ciuti, Cristiano
2013-03-01
The Dicke model describing a single-mode boson field coupled to two-level systems is an important paradigm in quantum optics. In particular, the physics of ``superradiant phase transitions'' in the ultrastrong coupling regime is the subject of a vigorous research activity in both cavity and circuit QED. Recently, we explored the rich physics of two interesting generalizations of the Dicke model: (i) A model describing the coupling of a boson mode to two independent chains A and B of two-level systems, where chain A is coupled to one quadrature of the boson field and chain B to the orthogonal quadrature. This original model leads to a quantum phase transition with a double symmetry breaking and a fourfold ground state degeneracy. (ii) A generalized Dicke model with three-level systems including the diamagnetic term. In contrast to the case of two-level atoms for which no-go theorems exist, in the case of three-level system we prove that the Thomas-Reich-Kuhn sum rule does not always prevent a superradiant phase transition.
New photosensitive systems for volume phase holography
NASA Astrophysics Data System (ADS)
Bianco, Andrea; Colella, Letizia; Galli, Paola; Zanutta, Alessio; Bertarelli, Chiara
2017-05-01
Volume phase holographic elements are becoming attractive thanks to the large efficiency and good optical quality. They are based on photosensitive materials where a modulation of the refractive index is induced. In this paper, we highlight the strategies to obtain a change in the refractive index in a dielectric material, namely a change in the material density and/or in the molecular polarizability. Moreover, we show the results achieved for materials that undergo the photo-Fries reaction as function of the molecular structure and the illumination conditions. We also report the results on a system based on the diazo Meldrum's acid where volatile molecules are produced upon light exposure.
Structural phase transition and electronic properties in samarium chalcogenides
Panwar, Y. S.; Aynyas, Mahendra; Pataiya, J.; Sanyal, Sankar P.
2016-05-06
The electronic structure and high pressure properties of samarium monochalcogenides SmS, SmSe and SmTe have been reported by using tight binding linear muffin-tin-orbital (TB-LMTO) method within the local density approximation (LDA). The total energy as a function of volume is evaluated. It is found that these monochalcogenides are stable in NaCl-type structure under ambient pressure. We predict a structural phase transition from NaCl-type (B{sub 1}-phase) structure to CsCl-type (B{sub 2}-type) structure for these compounds. Phase transition pressures were found to be 1.7, 4.4 and 6.6 GPa, for SmS, SmSe and SmTe respectively. Apart from this, the lattice parameter (a{sub 0}), bulk modulus (B{sub 0}), band structure (BS) and density of states (DOS) are calculated. From energy band diagram we observed that these compounds exhibit metallic character. The calculated values of equilibrium lattice parameter and phase transition pressure are in general good agreement with available data.
Phase Transitions in Model Active Systems
NASA Astrophysics Data System (ADS)
Redner, Gabriel S.
The amazing collective behaviors of active systems such as bird flocks, schools of fish, and colonies of microorganisms have long amazed scientists and laypeople alike. Understanding the physics of such systems is challenging due to their far-from-equilibrium dynamics, as well as the extreme diversity in their ingredients, relevant time- and length-scales, and emergent phenomenology. To make progress, one can categorize active systems by the symmetries of their constituent particles, as well as how activity is expressed. In this work, we examine two categories of active systems, and explore their phase behavior in detail. First, we study systems of self-propelled spherical particles moving in two dimensions. Despite the absence of an aligning interaction, this system displays complex emergent dynamics, including phase separation into a dense active solid and dilute gas. Using simulations and analytic modeling, we quantify the phase diagram and separation kinetics. We show that this nonequilibrium phase transition is analogous to an equilibrium vapor-liquid system, with binodal and spinodal curves and a critical point. We also characterize the dense active solid phase, a unique material which exhibits the structural signatures of a crystalline solid near the crystal-hexatic transition point, as well as anomalous dynamics including superdiffusive motion on intermediate timescales. We also explore the role of interparticle attraction in this system. We demonstrate that attraction drastically changes the phase diagram, which contains two distinct phase-separated regions and is reentrant as a function of propulsion speed. We interpret this complex situation with a simple kinetic model, which builds from the observed microdynamics of individual particles to a full description of the macroscopic phase behavior. We also study active nematics, liquid crystals driven out of equilibrium by energy-dissipating active stresses. The equilibrium nematic state is unstable in these
High-pressure phase transition in ZnSe
NASA Astrophysics Data System (ADS)
Köfferlein, M.; Karzel, H.; Potzel, W.; Schiessl, W.; Steiner, M.; Kalvius, G. M.; Mitchell, D. W.; Das, T. P.
1994-12-01
A high-pressure Mössbauer spectrometer for the 93.3-keV resonance in67Zn and an X-ray diffractometer of the Guinier type are used to investigate67ZnSe powder at high external pressures. At ˜ 13 GPa, a phase transition from the zinc blende to the fcc (NaCl) structure is observed. The transition is accompanied by a 15.2% decrease of the volume of the unit cell. The Lamb-Mössbauer factor (LMF) increases from f=0.53% at ambient pressure to f=1.07% at 6.1 GPa. It then decreases to f=0.91% as the pressure is further increased to 8.2 GPa. This behavior is investigated by lattice-dynamical calculations using an 11-parameter rigid-ion model. The decrease of the LMF at high pressures is caused by the softening of the TA phonon modes, which occurs already far below the phase transition. The s-electron density ρ(0) at the67Zn nucleus increases with reduced volume. The change of ρ(0) as well as theoretical Hartree-Fock cluster calculations show that covalency of bonding 4s/4p states of Zn and Se plays an essential role and determines the isomer shift.
Phase transitions in complex network dynamics
NASA Astrophysics Data System (ADS)
Squires, Shane
Two phase transitions in complex networks are analyzed. The first of these is a percolation transition, in which the network develops a macroscopic connected component as edges are added to it. Recent work has shown that if edges are added "competitively" to an undirected network, the onset of percolation is abrupt or "explosive." A new variant of explosive percolation is introduced here for directed networks, whose critical behavior is explored using numerical simulations and finite-size scaling theory. This process is also characterized by a very rapid percolation transition, but it is not as sudden as in undirected networks. The second phase transition considered here is the emergence of instability in Boolean networks, a class of dynamical systems that are widely used to model gene regulation. The dynamics, which are determined by the network topology and a set of update rules, may be either stable or unstable, meaning that small perturbations to the state of the network either die out or grow to become macroscopic. Here, this transition is analytically mapped onto a well-studied percolation problem, which can be used to predict the average steady-state distance between perturbed and unperturbed trajectories. This map applies to specific Boolean networks with few restrictions on network topology, but can only be applied to two commonly used types of update rules. Finally, a method is introduced for predicting the stability of Boolean networks with a much broader range of update rules. The network is assumed to have a given complex topology, subject only to a locally tree-like condition, and the update rules may be correlated with topological features of the network. While past work has addressed the separate effects of topology and update rules on stability, the present results are the first widely applicable approach to studying how these effects interact. Numerical simulations agree with the theory and show that such correlations between topology and update
Phase transitions of ε-HNIW in compound systems
Zhang, Jing-yuan; Guo, Xue-yong Jiao, Qing-jie; Zhang, Pu
2016-05-15
The heat-induced phase transitions of ε-HNIW, both neat and coated with various additives used in plastic bonded explosives, were investigated using powder X-ray diffraction and differential scanning calorimetry. It was found that ε-HNIW, after being held at 70°C for 60 h, remained in the ε-phase. Applying other conditions, various phase transition parameters were determined, including T{sub c} (the critical phase transition temperature), T{sub 50} (the temperature at which 50% of the phase transition is complete) and T{sub 180} (the percentage of γ-HNIW present in samples heated to 180°C). According to the above three parameters, additives were divided into three categories: those that delay phase transition, those that raise the critical temperature and the transition rate, and those that promote the phase transition. Based on the above data, a phase transition mechanism is proposed.
The transition to chaotic phase synchronization
NASA Astrophysics Data System (ADS)
Mosekilde, E.; Laugesen, J. L.; Zhusubaliyev, Zh. T.
2012-08-01
The transition to chaotic phase synchronization for a periodically driven spiral-type chaotic oscillator is known to involve a dense set of saddle-node bifurcations. By following the synchronization transition through the cascade of period-doubling bifurcations in a forced Rössler system, this paper describes how these saddle-node bifurcations arise and how their characteristic cyclic organisation develops. We identify the cycles that are involved in the various saddle-node bifurcations and descibe how the formation of multi-layered resonance cycles in the synchronization domain is related to the torus doubling bifurcations that take place outside this domain. By examining a physiology-based model of the blood flow regulation to the individual functional unit (nephron) of the kidney we demonstrate how a similar bifurcation structure may arise in this system as a response to a periodically varying arterial blood pressure. The paper finally discusses how an alternative transition to chaotic phase synchronization may occur in the mutual synchronization of two chaotically oscillating period-doubling systems.
Quantum Phase Transitions in Antiferromagnets and Superfluids
NASA Astrophysics Data System (ADS)
Sachdev, Subir
2000-03-01
A general introduction to the non-zero temperature dynamic and transport properties of low-dimensional systems near a quantum phase transition shall be presented. Basic results will be reviewed in the context of experiments on the spin-ladder compounds. Recent large N computations (M. Vojta and S. Sachdev, Phys. Rev. Lett. 83), 3916 (1999) on an extended t-J model motivate a global scenario of the quantum phases and transitions in the high temperature superconductors, and connections will be made to numerous experiments. A universal theory (S. Sachdev, C. Buragohain, and M. Vojta, Science, in press M. Vojta, C. Buragohain, and S. Sachdev, cond- mat/9912020) of quantum impurities in spin-gap antiferromagnets near a magnetic ordering transition will be compared quantitatively to experiments on Zn doped Y Ba2 Cu3 O7 (Fong et al.), Phys. Rev. Lett. 82, 1939 (1999)
Phase transitions of nuclear matter beyond mean field theory
Tran Huu Phat; Nguyen Tuan Anh; Nguyen Van Long; Le Viet Hoa
2007-10-15
The Cornwall-Jackiw-Tomboulis (CJT) effective action approach is applied to study the phase transition of nuclear matter modeled by the four-nucleon interaction. It is shown that in the Hartree-Fock approximation (HFA) a first-order phase transition takes place at low temperature, whereas the phase transition is of second order at higher temperature.
Kuramoto-type phase transition with metronomes
NASA Astrophysics Data System (ADS)
Boda, Sz; Ujvári, Sz; Tunyagi, A.; Néda, Z.
2013-11-01
Metronomes placed on the perimeter of a disc-shaped platform, which can freely rotate in a horizontal plane, are used for a simple classroom illustration of the Kuramoto-type phase transition. The rotating platform induces a global coupling between the metronomes, and the strength of this coupling can be varied by tilting the metronomes’ swinging plane relative to the radial direction on the disc. As a function of the tilting angle, a transition from spontaneously synchronized to unsynchronized states is observable. By varying the number of metronomes on the disc, finite-size effects are also exemplified. A realistic theoretical model is introduced and used to reproduce the observed results. Computer simulations of this model allow a detailed investigation of the emerging collective behaviour in this system.
Dynamical phase transitions in quantum mechanics
NASA Astrophysics Data System (ADS)
Rotter, Ingrid
2012-02-01
The nucleus is described as an open many-body quantum system with a non-Hermitian Hamilton operator the eigenvalues of which are complex, in general. The eigenvalues may cross in the complex plane (exceptional points), the phases of the eigenfunctions are not rigid in approaching the crossing points and the widths bifurcate. By varying only one parameter, the eigenvalue trajectories usually avoid crossing and width bifurcation occurs at the critical value of avoided crossing. An analog spectroscopic redistribution takes place for discrete states below the particle decay threshold. By this means, a dynamical phase transition occurs in the many-level system starting at a critical value of the level density. Hence the properties of the low-lying nuclear states (described well by the shell model) and those of highly excited nuclear states (described by random ensembles) differ fundamentally from one another. The statement of Niels Bohr on the collective features of compound nucleus states at high level density is therefore not in contradiction to the shell-model description of nuclear (and atomic) states at low level density. Dynamical phase transitions are observed experimentally in different quantum mechanical systems by varying one or two parameters.
Magnetoelastic effects on antiferromagnetic phase transitions (invited)
Wolf, W.P.; Huan, C.H.A.
1988-04-15
The effect of elastic strains on antiferromagnetic phase transitions is considered. For cases in which the magnetic and chemical unit cells coincide, the combination of a strain and an applied field is found to lead to the possibility of a linear magnetoelastic (LME) coupling which may induce antiferromagnetic order, even in the normally paramagnetic phase. Such an effect can, in principle, destroy any second-order phase transition. An order of magnitude estimate shows that the effect is small but not negligible, and that it may explain a number of unusual effects observed in dysprosium aluminum garnet, including anomalous neutron scattering, magnetic hysteresis and magnetostriction. Similar strain-induced effects may be important in many other antiferromagnets, including CoF/sub 2/, FeF/sub 2/, MnF/sub 2/, and ..cap alpha..Fe/sub 2/O/sub 3/, as well as in mixed crystals with the same structures. Strain gradients may produce similar effects in other antiferromagnets which are magnetoelectric, including DyPO/sub 4/, DyAlO/sub 3/, and Cr/sub 2/O/sub 3/.
Pressure dependence of band-gap and phase transitions in bulk CuX (X = Cl, Br, I)
Azhikodan, Dilna; Nautiyal, Tashi; Sharma, S.
2016-05-06
Usually a phase transition, in theoretical studies, is explored or verified by studying the total energy as a function of the volume considering various plausible phases. The intersection point, if any, of the free energy vs. volume curves for the different phases is then the indicator of the phase transition(s). The question is, can the theoretical study of a single phase alone indicate a phase transition? i.e. can we look beyond the phase under consideration through such a study? Using density-functional theory, we report a novel approach to suggest phase transition(s) through theoretical study of a single phase. Copper halides have been engaged for this study. These are direct band-gap semiconductors, with zinc blende structure at ambient conditions, and are reported to exhibit many phase transitions. We show that the study of volume dependence of energy band-gap in a single phase facilitates looking beyond the phase under consideration. This, when translated to pressures, reflects the phase transition pressures for CuX (X = Cl, Br, I) with an encouraging accuracy. This work thus offers a simple, yet reliable, approach based on electronic structure calculations to investigate new semiconducting materials for phase changes under pressure.
Phases and phase transitions in the algebraic microscopic shell model
NASA Astrophysics Data System (ADS)
Georgieva, A. I.; Drumev, K. P.
2016-01-01
We explore the dynamical symmetries of the shell model number conserving algebra, which define three types of pairing and quadrupole phases, with the aim to obtain the prevailing phase or phase transition for the real nuclear systems in a single shell. This is achieved by establishing a correspondence between each of the pairing bases with the Elliott's SU(3) basis that describes collective rotation of nuclear systems. This allows for a complete classification of the basis states of different number of particles in all the limiting cases. The probability distribution of the SU(3) basis states within theirs corresponding pairing states is also obtained. The relative strengths of dynamically symmetric quadrupole-quadrupole interaction in respect to the isoscalar, isovector and total pairing interactions define a control parameter, which estimates the importance of each term of the Hamiltonian in the correct reproduction of the experimental data for the considered nuclei.
Chiral phase transition from string theory.
Parnachev, Andrei; Sahakyan, David A
2006-09-15
The low energy dynamics of a certain D-brane configuration in string theory is described at weak t'Hooft coupling by a nonlocal version of the Nambu-Jona-Lasinio model. We study this system at finite temperature and strong t'Hooft coupling, using the string theory dual. We show that for sufficiently low temperatures chiral symmetry is broken, while for temperatures larger then the critical value, it gets restored. We compute the latent heat and observe that the phase transition is of the first order.
Early Work on Defect Driven Phase Transitions
NASA Astrophysics Data System (ADS)
Kosterlitz, J. Michael; Thouless, David J.
2016-12-01
This article summarizes the early history of the theory of phase transitions driven by topological defects, such as vortices in superfluid helium films or dislocations and disclinations in two-dimensional solids. We start with a review of our two earliest papers, pointing out their errors and omissions as well as their insights. We then describe the work, partly done by Kosterlitz but mostly done by other people, which corrected these oversights, and applied these ideas to experimental systems, and to numerical and experimental simulations.
Dependence of phase transitions on small changes
NASA Astrophysics Data System (ADS)
Stoop, R.
1993-06-01
In this contribution, the generalized thermodynamic formalism is applied to a nonhyperbolic dynamical system in two comparable situations. The change from one situation to the other is small in the sense that the grammar and the singularities of the system are preserved. For the discussion of the effects generated by this change, the generalized entropy functions are calculated and the sets of the specific scaling functions which reflect the phase transition of the system are investigated. It is found that even under mild variations, this set is not invariant.
Quantum coherence and quantum phase transitions
Li, Yan-Chao; Lin, Hai-Qing
2016-01-01
We study the connections between local quantum coherence (LQC) based on Wigner-Yanase skew information and quantum phase transitions (QPTs). When applied on the one-dimensional Hubbard, XY spin chain with three-spin interaction, and Su-Schrieffer-Heeger models, the LQC and its derivatives are used successfully to detect different types of QPTs in these spin and fermionic systems. Furthermore, the LQC is effective as the quantum discord (QD) in detecting QPTs at finite temperatures, where the entanglement has lost its effectiveness. We also demonstrate that the LQC can exhibit different behaviors in many forms compared with the QD. PMID:27193057
Phase transition of physically confined 2-decanol
NASA Astrophysics Data System (ADS)
Griffin, Harrisonn; Amanuel, Samuel
2014-03-01
We have studied phase transition of physically confined 2-decanol in nano porous silica using power compensated differential scanning calorimeter (DSC). Like bulk, the physically confined also exhibit hysteresis between its melting and freezing temperature. However, its thermal history plays significant role in determining its freezing temperature. The melting temperature, on the other hand, did not show similar changes with respect to thermal history, suggesting that it is truly driven thermodynamically rather than kinetically. In addition, there seems to be a cutoff in size where crystallization front could not proceed.
Raman Spectroscopic and Ultrasonic Measurements to Monitor the HMX ( ) Phase Transition
GIESKE,JOHN H.; MILLER,JILL C.; RENLUND,ANITA M.; TAPPAN,ALEXANDER S.
1999-10-14
The HMX {beta}-{delta} solid-solid phase transition, which occurs as HMX is heated near 170 C, is clearly linked to increased reactivity and sensitivity to initiation. Thermally damaged energetic materials (EMs) containing HMX therefore may present a safety concern. Information about the phase transition is vital to a predictive safety model for HMX and HMX-containing EMs. We report work in progress on monitoring the phase transition with real-time Raman spectroscopy and ultrasonic measurements aimed towards a better understanding of physical properties through the phase transition. HMX samples were confined with minimal free volume.in a cell with constant volume. The cell was heated at a controlled rate and real-time Raman spectroscopic or ultrasonic measurements were performed. Raman spectroscopy provides a clear distinction between the two phases because the vibrational transitions of the molecule change with confirmational changes associated with the phase transition. Ultrasonic time-of-flight measurements provide an additional method of distinguishing the two phases because the sound speed through the material changes with the phase transition. Ultrasonic attenuation measurements also provide information about microstructural changes such as increased porosity due to evolution of gaseous decomposition products.
Quantum Phase Transition in Josephson Junction Arrays
NASA Astrophysics Data System (ADS)
Moon, K.; Girvin, S. M.
1997-03-01
One-dimensional Josephson junction arrays of SQUIDS exhibit a novel superconductor-insulator phase transition. The critical regime can be accessed by tuning the effective Josephson coupling energy using a weak magnetic field applied to the SQUIDS. The role of instantons induced by quantum fluctuations will be discussed. One novel feature of these systems which can be explained in terms of quantum phase slips is that in some regimes, the array resistance decreases with increasing length of the array. We calculate the finite temperature crossover function for the array resistance and compare our theoretical results with the recent experiments by D. Haviland and P. Delsing at Chalmers. This work is supported by DOE grant #DE-FG02-90ER45427 and by NSF DMR-9502555.
Phase transitions in fluids and biological systems
NASA Astrophysics Data System (ADS)
Sipos, Maksim
metric to 16S rRNA metagenomic studies of 6 vertebrate gastrointestinal microbiomes and find that they assembled through a highly non-neutral process. I then consider a phase transition that may occur in nutrient-poor environments such as ocean surface waters. In these systems, I find that the experimentally observed genome streamlining, specialization and opportunism may well be generic statistical phenomena.
Nuclear Binding Near a Quantum Phase Transition
NASA Astrophysics Data System (ADS)
Elhatisari, Serdar; Li, Ning; Rokash, Alexander; Alarcón, Jose Manuel; Du, Dechuan; Klein, Nico; Lu, Bing-nan; Meißner, Ulf-G.; Epelbaum, Evgeny; Krebs, Hermann; Lähde, Timo A.; Lee, Dean; Rupak, Gautam
2016-09-01
How do protons and neutrons bind to form nuclei? This is the central question of ab initio nuclear structure theory. While the answer may seem as simple as the fact that nuclear forces are attractive, the full story is more complex and interesting. In this work we present numerical evidence from ab initio lattice simulations showing that nature is near a quantum phase transition, a zero-temperature transition driven by quantum fluctuations. Using lattice effective field theory, we perform Monte Carlo simulations for systems with up to twenty nucleons. For even and equal numbers of protons and neutrons, we discover a first-order transition at zero temperature from a Bose-condensed gas of alpha particles (4He nuclei) to a nuclear liquid. Whether one has an alpha-particle gas or nuclear liquid is determined by the strength of the alpha-alpha interactions, and we show that the alpha-alpha interactions depend on the strength and locality of the nucleon-nucleon interactions. This insight should be useful in improving calculations of nuclear structure and important astrophysical reactions involving alpha capture on nuclei. Our findings also provide a tool to probe the structure of alpha cluster states such as the Hoyle state responsible for the production of carbon in red giant stars and point to a connection between nuclear states and the universal physics of bosons at large scattering length.
Nuclear Binding Near a Quantum Phase Transition.
Elhatisari, Serdar; Li, Ning; Rokash, Alexander; Alarcón, Jose Manuel; Du, Dechuan; Klein, Nico; Lu, Bing-Nan; Meißner, Ulf-G; Epelbaum, Evgeny; Krebs, Hermann; Lähde, Timo A; Lee, Dean; Rupak, Gautam
2016-09-23
How do protons and neutrons bind to form nuclei? This is the central question of ab initio nuclear structure theory. While the answer may seem as simple as the fact that nuclear forces are attractive, the full story is more complex and interesting. In this work we present numerical evidence from ab initio lattice simulations showing that nature is near a quantum phase transition, a zero-temperature transition driven by quantum fluctuations. Using lattice effective field theory, we perform Monte Carlo simulations for systems with up to twenty nucleons. For even and equal numbers of protons and neutrons, we discover a first-order transition at zero temperature from a Bose-condensed gas of alpha particles (^{4}He nuclei) to a nuclear liquid. Whether one has an alpha-particle gas or nuclear liquid is determined by the strength of the alpha-alpha interactions, and we show that the alpha-alpha interactions depend on the strength and locality of the nucleon-nucleon interactions. This insight should be useful in improving calculations of nuclear structure and important astrophysical reactions involving alpha capture on nuclei. Our findings also provide a tool to probe the structure of alpha cluster states such as the Hoyle state responsible for the production of carbon in red giant stars and point to a connection between nuclear states and the universal physics of bosons at large scattering length.
Phase transition in the ABC model
NASA Astrophysics Data System (ADS)
Clincy, M.; Derrida, B.; Evans, M. R.
2003-06-01
Recent studies have shown that one-dimensional driven systems can exhibit phase separation even if the dynamics is governed by local rules. The ABC model, which comprises three particle species that diffuse asymmetrically around a ring, shows anomalous coarsening into a phase separated steady state. In the limiting case in which the dynamics is symmetric and the parameter q describing the asymmetry tends to one, no phase separation occurs and the steady state of the system is disordered. In the present work, we consider the weak asymmetry regime q=exp(-β/N), where N is the system size, and study how the disordered state is approached. In the case of equal densities, we find that the system exhibits a second-order phase transition at some nonzero βc. The value of βc=2π(3) and the optimal profiles can be obtained by writing the exact large deviation functional. For nonequal densities, we write down mean-field equations and analyze some of their predictions.
Phase transition in the ABC model.
Clincy, M; Derrida, B; Evans, M R
2003-06-01
Recent studies have shown that one-dimensional driven systems can exhibit phase separation even if the dynamics is governed by local rules. The ABC model, which comprises three particle species that diffuse asymmetrically around a ring, shows anomalous coarsening into a phase separated steady state. In the limiting case in which the dynamics is symmetric and the parameter q describing the asymmetry tends to one, no phase separation occurs and the steady state of the system is disordered. In the present work, we consider the weak asymmetry regime q=exp(-beta/N), where N is the system size, and study how the disordered state is approached. In the case of equal densities, we find that the system exhibits a second-order phase transition at some nonzero beta(c). The value of beta(c)=2pi square root 3 and the optimal profiles can be obtained by writing the exact large deviation functional. For nonequal densities, we write down mean-field equations and analyze some of their predictions.
Phase transitions of monolayers on graphene
NASA Astrophysics Data System (ADS)
Kahn, Joshua; Dzyubenko, Boris; Vilches, Oscar; Cobden, David
We have studied physisorbed layers of monatomic and diatomic gases on graphene. We used devices in which few-layer graphene, ranging from monolayer to trilayer, is suspended across a trench between two platinum contacts and are cleaned by thermal and current annealing. We found that the density of adsorbates is revealed by the conductance, similar to the case with nanotubes. The conductance change for a monolayer can be large. On trilayer graphene the adsorbed gases can be seen to exhibit transitions between two-dimensional phases identical to those on bulk graphite, including incommensurate and commensurate solid, fluid and vapor and multiple layers. New features appear in the conductance at the boundaries of the commensurate phase of Kr. We are able to measure single-particle binding energies very accurately and see how it depends on thickness; investigate the effects of changing disorder by gradually current annealing; and search for new phases in the case of monolayer graphene where atoms adsorbed on both sides can interact. We can map out the 2d phase diagrams very quickly by ohmic heating, which gives nearly instantaneous control of the temperature.
Phase transitions in Thirring’s model
NASA Astrophysics Data System (ADS)
Campa, Alessandro; Casetti, Lapo; Latella, Ivan; Pérez-Madrid, Agustín; Ruffo, Stefano
2016-07-01
In his pioneering work on negative specific heat, Walter Thirring introduced a model that is solvable in the microcanonical ensemble. Here, we give a complete description of the phase-diagram of this model in both the microcanonical and the canonical ensemble, highlighting the main features of ensemble inequivalence. In both ensembles, we find a line of first-order phase transitions which ends in a critical point. However, neither the line nor the point have the same location in the phase-diagram of the two ensembles. We also show that the microcanonical and canonical critical points can be analytically related to each other using a Landau expansion of entropy and free energy, respectively, in analogy with what has been done in (Cohen and Mukamel 2012 J. Stat. Mech. P12017). Examples of systems with certain symmetries restricting the Landau expansion have been considered in this reference, while no such restrictions are present in Thirring’s model. This leads to a phase diagram that can be seen as a prototype for what happens in systems of particles with kinematic degrees of freedom dominated by long-range interactions.
Phase transitions and doping in semiconductor nanocrystals
NASA Astrophysics Data System (ADS)
Sahu, Ayaskanta
impurities (or doping) allows further control over the electrical and optical properties of nanocrystals. However, while impurity doping in bulk semiconductors is now routine, doping of nanocrystals remains challenging. In particular, evidence for electronic doping, in which additional electrical carriers are introduced into the nanocrystals, has been very limited. Here, we adopt a new approach to electronic doping of nanocrystals. We utilize a partial cation exchange to introduce silver impurities into cadmium selenide (CdSe) and lead selenide (PbSe) nanocrystals. Results indicate that the silver-doped CdSe nanocrystals show a significant increase in fluorescence intensity, as compared to pure CdSe nanocrystals. We also observe a switching from n- to p-type doping in the silver-doped CdSe nanocrystals with increased silver amounts. Moreover, the silver-doping results in a change in the conductance of both PbSe and CdSe nanocrystals and the magnitude of this change depends on the amount of silver incorporated into the nanocrystals. In the bulk, silver chalcogenides (Ag2E, E=S, Se, and Te) possess a wide array of intriguing properties, including superionic conductivity. In addition, they undergo a reversible temperature-dependent phase transition which induces significant changes in their electronic and ionic properties. While most of these properties have been examined extensively in bulk, very few studies have been conducted at the nanoscale. We have recently developed a versatile synthesis that yields colloidal silver chalcogenide nanocrystals. Here, we study the size dependence of their phase-transition temperatures. We utilize differential scanning calorimetry and in-situ X-ray diffraction analyses to observe the phase transition in nanocrystal assemblies. We observe a significant deviation from the bulk alpha (low-temperature) to beta (high-temperature) phase-transition temperature when we reduce their size to a few nanometers. Hence, these nanocrystals provide great
Kinetics of silica-phase transitions
Duffy, C.J.
1993-07-01
In addition to the stable silica polymorph quartz, several metastable silica phases are present in Yucca Mountain. The conversion of these phases to quartz is accompanied by volume reduction and a decrease in the aqueous silica activity, which may destabilize clinoptilolite and mordenite. The primary reaction sequence for the silica phases is from opal or glass to disordered opal-CT, followed by ordering of the opal-CT and finally by the crystallization of quartz. The ordering of opal-CT takes place in the solid state, whereas the conversion of opal-CT takes place through dissolution-reprecipitation involving the aqueous phase. It is proposed that the rate of conversion of opal-CT to quartz is controlled by diffusion of defects out of a disordered surface layer formed on the crystallizing quartz. The reaction rates are observed to be dependent on temperature, pressure, degree of supersaturation, and pH. Rate equations selected from the literature appear to be consistent with observations at Yucca Mountain.
Multifractality and Network Analysis of Phase Transition
Li, Wei; Yang, Chunbin; Han, Jihui; Su, Zhu; Zou, Yijiang
2017-01-01
Many models and real complex systems possess critical thresholds at which the systems shift dramatically from one sate to another. The discovery of early-warnings in the vicinity of critical points are of great importance to estimate how far the systems are away from the critical states. Multifractal Detrended Fluctuation analysis (MF-DFA) and visibility graph method have been employed to investigate the multifractal and geometrical properties of the magnetization time series of the two-dimensional Ising model. Multifractality of the time series near the critical point has been uncovered from the generalized Hurst exponents and singularity spectrum. Both long-term correlation and broad probability density function are identified to be the sources of multifractality. Heterogeneous nature of the networks constructed from magnetization time series have validated the fractal properties. Evolution of the topological quantities of the visibility graph, along with the variation of multifractality, serve as new early-warnings of phase transition. Those methods and results may provide new insights about the analysis of phase transition problems and can be used as early-warnings for a variety of complex systems. PMID:28107414
Gravitational waves from the electroweak phase transition
Leitao, Leonardo; Mégevand, Ariel; Sánchez, Alejandro D. E-mail: megevand@mdp.edu.ar
2012-10-01
We study the generation of gravitational waves in the electroweak phase transition. We consider a few extensions of the Standard Model, namely, the addition of scalar singlets, the minimal supersymmetric extension, and the addition of TeV fermions. For each model we consider the complete dynamics of the phase transition. In particular, we estimate the friction force acting on bubble walls, and we take into account the fact that they can propagate either as detonations or as deflagrations preceded by shock fronts, or they can run away. We compute the peak frequency and peak intensity of the gravitational radiation generated by bubble collisions and turbulence. We discuss the detectability by proposed spaceborne detectors. For the models we considered, runaway walls require significant fine tuning of the parameters, and the gravitational wave signal from bubble collisions is generally much weaker than that from turbulence. Although the predicted signal is in most cases rather low for the sensitivity of LISA, models with strongly coupled extra scalars reach this sensitivity for frequencies f ∼ 10{sup −4} Hz, and give intensities as high as h{sup 2}Ω{sub GW} ∼ 10{sup −8}.
Gama, S.; de Campos, A.; Coelho, A. A.; Alves, C. S.; Ren, Y.; Garcia, F.; Brown, D. E.; da Silva, L. M.; Magnus, A.; Carvalho, G.; Gandra, G. C.; dos Santos, A. O.; Cardoso, L. P.; von Ranke, P. J.; X-Ray Science Division; Univ. Federal de Sao Paulo; Unv. Estadual de Champinas; Univ. Estadual de Maringa Lab. Nacional de Luz Sincrotron; Northern Univ.; Univ. de Estado do Rio de Janerio
2009-01-01
First order phase transitions for materials with exotic properties are usually believed to happen at fixed values of the intensive parameters (such as pressure, temperature, etc.) characterizing their properties. It is also considered that the extensive properties of the phases (such as entropy, volume, etc.) have discontinuities at the transition point, but that for each phase the intensive parameters remain constant during the transition. These features are a hallmark for systems described by two thermodynamic degrees of freedom. In this work it is shown that first order phase transitions must be understood in the broader framework of thermodynamic systems described by three or more degrees of freedom. This means that the transitions occur along intervals of the intensive parameters, that the properties of the phases coexisting during the transition may show peculiar behaviors characteristic of each system, and that a generalized Clausius-Clapeyron equation must be obeyed. These features for the magnetic case are confirmed, and it is shown that experimental calorimetric data agree well with the magnetic Clausius-Clapeyron equation for MnAs. An estimate for the point in the temperature-field plane where the first order magnetic transition turns to a second order one is obtained (the critical parameters) for MnAs and Gd{sub 5}Ge{sub 2}Si{sub 2} compounds. Anomalous behavior of the volumes of the coexisting phases during the magnetic first order transition is measured, and it is shown that the anomalies for the individual phases are hidden in the behavior of the global properties as the volume.
Quark–hadron phase transition in massive gravity
Atazadeh, K.
2016-11-15
We study the quark–hadron phase transition in the framework of massive gravity. We show that the modification of the FRW cosmological equations leads to the quark–hadron phase transition in the early massive Universe. Using numerical analysis, we consider that a phase transition based on the chiral symmetry breaking after the electroweak transition, occurred at approximately 10 μs after the Big Bang to convert a plasma of free quarks and gluons into hadrons.
Quark-hadron phase transition in massive gravity
NASA Astrophysics Data System (ADS)
Atazadeh, K.
2016-11-01
We study the quark-hadron phase transition in the framework of massive gravity. We show that the modification of the FRW cosmological equations leads to the quark-hadron phase transition in the early massive Universe. Using numerical analysis, we consider that a phase transition based on the chiral symmetry breaking after the electroweak transition, occurred at approximately 10 μs after the Big Bang to convert a plasma of free quarks and gluons into hadrons.
Does sex induce a phase transition?
NASA Astrophysics Data System (ADS)
de Oliveira, P. M. C.; Moss de Oliveira, S.; Stauffer, D.; Cebrat, S.; Pękalski, A.
2008-05-01
We discovered a dynamic phase transition induced by sexual reproduction. The dynamics is a pure Darwinian rule applied to diploid bit-strings with both fundamental ingredients to drive Darwin's evolution: (1) random mutations and crossings which act in the sense of increasing the entropy (or diversity); and (2) selection which acts in the opposite sense by limiting the entropy explosion. Selection wins this competition if mutations performed at birth are few enough, and thus the wild genotype dominates the steady-state population. By slowly increasing the average number m of mutations, however, the population suddenly undergoes a mutational degradation precisely at a transition point mc. Above this point, the “bad” alleles (represented by 1-bits) spread over the genetic pool of the population, overcoming the selection pressure. Individuals become selectively alike, and evolution stops. Only below this point, m < mc, evolutionary life is possible. The finite-size-scaling behaviour of this transition is exhibited for large enough “chromosome” lengths L, through lengthy computer simulations. One important and surprising observation is the L-independence of the transition curves, for large L. They are also independent on the population size. Another is that mc is near unity, i.e. life cannot be stable with much more than one mutation per diploid genome, independent of the chromosome length, in agreement with reality. One possible consequence is that an eventual evolutionary jump towards larger L enabling the storage of more genetic information would demand an improved DNA copying machinery in order to keep the same total number of mutations per offspring.
Pressure induced phase transition in CeN with NaCl-type structure
NASA Astrophysics Data System (ADS)
Dubey, R.; Singh, S.; Sarwan, M.
2015-02-01
We have expressed the Gibbs free energy for CeN compound as a function of pressure and charge transfer through improved interaction potential model (IIPM). The lattice energy in it has been represented by an IIPM which include Coulomb interaction, three body interaction, polarizability effect and overlap repulsive interaction. The phase transition pressure and relative compression reveal that this compound shows a B1-B2 phase transition and this approach are found to be the experimental data in future. The phase transition pressures and volume collapses obtained from this model show a generally good agreement with available results.
First Principles Theory of the hcp-fcc Phase Transition in Cobalt.
Lizárraga, Raquel; Pan, Fan; Bergqvist, Lars; Holmström, Erik; Gercsi, Zsolt; Vitos, Levente
2017-06-19
Identifying the forces that drive a phase transition is always challenging. The hcp-fcc phase transition that occurs in cobalt at ~700 K has not yet been fully understood, although early theoretical studies have suggested that magnetism plays a main role in the stabilization of the fcc phase at high temperatures. Here, we perform a first principles study of the free energies of these two phases, which we break into contributions arising from the vibration of the lattice, electronic and magnetic systems and volume expansion. Our analysis of the energy of the phases shows that magnetic effects alone cannot drive the fcc-hcp transition in Co and that the largest contribution to the stabilization of the fcc phase comes from the vibration of the ionic lattice. By including all the contributions to the free energy considered here we obtain a theoretical transition temperature of 825 K.
NASA Astrophysics Data System (ADS)
Boguslavskii, Yu.; Achmetshackirova, Kh.; Drabkin, S.
1998-09-01
Based on the deformation theory of plasticity the problem of pressure distribution in a compressed layer at phase transition experiencing a plane plastic deformation is considered. It is found that in the pressure distribution near the phase boundaries anomalies emerge in the form of a “step” or a local maximum caused by volume jumps at phase transition. It is shown that these anomalies and differences in yield limits of the phases can lead to essential change of pressure in the center of the layer in comparison with its value in absence of phase transition, but under equal external load. The maximal value of external load admitting the considered solution is found. The kinetics of possible isothermal regimes of phase transition leading to change in the time-pressure distribution in the plastic layer is investigated.
Weyl semimetals and topological phase transitions
NASA Astrophysics Data System (ADS)
Murakami, Shuichi
Weyl semimetals are semimetals with nondegenerate 3D Dirac cones in the bulk. We showed that in a transition between different Z2 topological phases, i.e. between the normal insulator (NI) and topological insulator (TI), the Weyl semimetal phase necessarily appears when inversion symmetry is broken. In the presentation we show that this scenario holds for materials with any space groups without inversion symmetry. Namely, let us take any band insulator without inversion symmetry, and assume that the gap is closed by a change of an external parameter. In such cases we found that the system runs either into (i) a Weyl semimetal or (ii) a nodal-line semimetal, but no insulator-to-insulator transition happens. This is confirmed by classifying the gap closing in terms of the space groups and the wavevector. In the case (i), the number of Weyl nodes produced at the gap closing ranges from 2 to 12 depending on the symmetry. In (ii) the nodal line is protected by mirror symmetry. In the presentation, we explain some Weyl semimetal and nodal-line semimetals which we find by using this classification. As an example, we explain our result on ab initio calculation on tellurium (Te). Tellurium consists of helical chains, and therefore lacks inversion and mirror symmetries. At high pressure the band gap of Te decreases and finally it runs into a Weyl semimetal phase, as confirmed by our ab initio calculation. In such chiral systems as tellurium, we also theoretically propose chiral transport in systems with such helical structures; namely, an orbital magnetization is induced by a current along the chiral axis, in analogy with a solenoid.
Phase transitions in Ge-Sb phase change materials
Raoux, Simone; Virwani, Kumar; Hitzbleck, Martina; Salinga, Martin; Madan, Anita; Pinto, Teresa L.
2009-03-15
Thin films of the phase change material Ge-Sb with Ge concentrations between 7.3 and 81.1 at. % were deposited by cosputtering from elemental targets. Their crystallization behavior was studied using time-resolved x-ray diffraction, Auger electron spectroscopy, differential scanning calorimetry, x-ray reflectivity, profilometry, optical reflectivity, and resistivity versus temperature measurements. It was found that the crystallization temperature increases with Ge content. Calculations of the glass transition temperature (which is a lower limit for the crystallization temperature T{sub x}) also show an increase with Ge concentration closely tracking the measured values of T{sub x}. For low Ge content samples, Sb x-ray diffraction peaks occurred during a heating ramp at lower temperature than Ge diffraction peaks. The appearance of Ge peaks is related to Ge precipitation and agglomeration. For Ge concentrations of 59.3 at. % and higher, Sb and Ge peaks occurred at the same temperature. Upon crystallization, film mass density and optical reflectivity increase as well as electrical contrast (ratio of resistivity in amorphous phase to crystalline phase) all showed a maximum for the eutectic alloy (14.5 at. % Ge). For the alloy with 59.3 at. % Ge there was very little change in any of these parameters, while the alloy with 81.1 at. % Ge behaved opposite to a typical phase change alloy and showed reduced mass density and reflectivity and increased resistivity.
Phase transitions in biogenic amorphous calcium carbonate
NASA Astrophysics Data System (ADS)
Gong, Yutao
Geological calcium carbonate exists in both crystalline phases and amorphous phases. Compared with crystalline calcium carbonate, such as calcite, aragonite and vaterite, the amorphous calcium carbonate (ACC) is unstable. Unlike geological calcium carbonate crystals, crystalline sea urchin spicules (99.9 wt % calcium carbonate and 0.1 wt % proteins) do not present facets. To explain this property, crystal formation via amorphous precursors was proposed in theory. And previous research reported experimental evidence of ACC on the surface of forming sea urchin spicules. By using X-ray absorption near-edge structure (XANES) spectroscopy and photoelectron emission microscopy (PEEM), we studied cross-sections of fresh sea urchin spicules at different stages (36h, 48h and 72h after fertilization) and observed the transition sequence of three mineral phases: hydrated ACC → dehydrated ACC → biogenic calcite. In addition, we unexpectedly found hydrated ACC nanoparticles that are surrounded by biogenic calcite. This observation indicates the dehydration from hydrated ACC to dehydrated ACC is inhibited, resulting in stabilization of hydrated ACC nanoparticles. We thought that the dehydration was inhibited by protein matrix components occluded within the biomineral, and we designed an in vitro assay to test the hypothesis. By utilizing XANES-PEEM, we found that SM50, the most abundant occluded matrix protein in sea urchin spicules, has the function to stabilize hydrated ACC in vitro.
Nowikovsky, Karin; Schweyen, Rudolf J; Bernardi, Paolo
2009-05-01
Regulation of mitochondrial volume is a key issue in cellular pathophysiology. Mitochondrial volume and shape changes can occur following regulated fission-fusion events, which are modulated by a complex network of cytosolic and mitochondrial proteins; and through regulation of ion transport across the inner membrane. In this review we will cover mitochondrial volume homeostasis that depends on (i) monovalent cation transport across the inner membrane, a regulated process that couples electrophoretic K(+) influx on K(+) channels to K(+) extrusion through the K(+)-H(+) exchanger; (ii) the permeability transition, a loss of inner membrane permeability that may be instrumental in triggering cell death. Specific emphasis will be placed on molecular advances on the nature of the transport protein(s) involved, and/or on diseases that depend on mitochondrial volume dysregulation.
Volume Phase Masks in Photo-Thermo-Refractive Glass
2014-10-06
2014 Approved for public release; distribution is unlimited. Volume phase masks in photo-thermo-refractive glass The views, opinions and/or findings...Triangle Park, NC 27709-2211 photothermorefractive glass , volume hologram, volume phase mask REPORT DOCUMENTATION PAGE 11. SPONSOR/MONITOR’S REPORT...in photo-thermo-refractive glass Report Title In many applications such as beam shaping, mode conversion, and phase encoding it is necessary to alter
Thermodynamics of the ferromagnetic phase transition in nearly half metallic CoS2 at high pressures
Elkin, F. S.; Zibrov, I. P.; Novikov, A. P.; Khasanov, S. S.; Sidorov, V. A.; Petrova, A. E.; Lograsso, Thomas A.; Thompson, J. D.; Stishov, S. M.
2013-12-06
The volume change and heat capacity at the ferromagnetic phase transition in COS2 were measured at high pressures using X-rays generated by the Argonne synchrotron light source and by ac-calorimetry, respectively. The transition entropy, calculated on the basis of these experimental data, drops along the transition line due to quantum degradation, as required by Nernst's law. The volume change increases strongly along the transition line, which is explained by specifics of the compressibility difference of coexisting phases that results from nearly half metallic nature of the ferromagnetic phase of COS2. (C) 2013 Elsevier Ltd. All rights reserved.
Exotic quantum phase transitions of strongly interacting topological insulators
NASA Astrophysics Data System (ADS)
Slagle, Kevin; You, Yi-Zhuang; Xu, Cenke
2015-03-01
Using determinant quantum Monte Carlo simulations, we demonstrate that an extended Hubbard model on a bilayer honeycomb lattice has two novel quantum phase transitions. The first is a quantum phase transition between the weakly interacting gapless Dirac fermion phase and a strongly interacting fully gapped and symmetric trivial phase, which cannot be described by the standard Gross-Neveu model. The second is a quantum critical point between a quantum spin Hall insulator with spin Sz conservation and the previously mentioned strongly interacting fully gapped phase. At the latter quantum critical point the single-particle excitations remain gapped, while spin and charge gaps both close. We argue that the first quantum phase transition is related to the Z16 classification of the topological superconductor 3He-B phase with interactions, while the second quantum phase transition is a topological phase transition described by a bosonic O (4 ) nonlinear sigma model field theory with a Θ term.
High-pressure phase transition observed in barium hydride
NASA Astrophysics Data System (ADS)
Smith, Jesse S.; Desgreniers, Serge; Tse, John S.; Klug, Dennis D.
2007-08-01
The pressure-dependent structural and vibrational properties of barium hydride have been studied up to 22 GPa at room temperature by means of powder x-ray diffraction, Raman spectroscopy, and first-principles calculations. At ambient conditions, BaH2 crystallizes in the cotunnite structure (Pnma). A reversible, first-order structural phase transition is observed at 1.6 GPa. The high-pressure phase can be indexed by a hexagonal unit cell with a proposed Ni2In structure (P63/mmc), with the Ba and H atoms in special positions. The experimental volume compression of the high-pressure phase yields an isothermal bulk modulus B0=24(1) GPa (B0' fixed at 4.13). This compares favorably with the results of the first-principles calculations, which reproduce the first-order nature of the transition. The relevance of these results is discussed in the contexts of metal hydrides in particular and ionic AX2(A =metal) compounds in general.
Valleytronics and phase transition in silicene
NASA Astrophysics Data System (ADS)
Aftab, Tayyaba
2017-03-01
Magnetic and transport properties of silicene in the presence of perpendicular electromagnetic fields and a ferromagnetic material are studied. It is shown that for small exchange field, the magnetic moment associated with each valley is opposite for the other and it gives a shift in band energy, by a Zeeman-like coupling term. Thus opening a new horizon for valley-orbit coupling. Magnetic proximity effect is seen to adjust the spintronics of each valley. Valley polarization is calculated using the semi classical formulation of electron dynamics. It can be modified and measured due to its contribution in Hall conductivity. Quantum phase transitions are observed in silicene, providing a tool to control the topological state experimentally. The strong dependence of the physical properties on valley degree of freedom is an important step towards valleytronics.
Switchable Metal-Insulator Phase Transition Metamaterials.
Hajisalem, Ghazal; Nezami, Mohammadreza S; Gordon, Reuven
2017-05-10
We investigate the switching of a gap plasmon tunnel junction between conducting and insulating states. Hysteresis is observed in the second and the third harmonic generation power dependence, which arises by thermally induced disorder ("melting") of a two-carbon self-assembled monolayer between an ultraflat gold surface and metal nanoparticles. The hysteresis is observed for a variety of nanoparticle sizes, but not for larger tunnel junctions where there is no appreciable tunneling. By combining quantum corrected finite-difference time-domain simulations with nonlinear scattering theory, we calculate the changes in the harmonic generation between the tunneling and the insulating states, and good agreement is found with the experiments. This paves the way to a new class of metal-insulator phase transition switchable metamaterials, which may provide next-generation information processing technologies.
Scaling theory of topological phase transitions
NASA Astrophysics Data System (ADS)
Chen, Wei
2016-02-01
Topologically ordered systems are characterized by topological invariants that are often calculated from the momentum space integration of a certain function that represents the curvature of the many-body state. The curvature function may be Berry curvature, Berry connection, or other quantities depending on the system. Akin to stretching a messy string to reveal the number of knots it contains, a scaling procedure is proposed for the curvature function in inversion symmetric systems, from which the topological phase transition can be identified from the flow of the driving energy parameters that control the topology (hopping, chemical potential, etc) under scaling. At an infinitesimal operation, one obtains the renormalization group (RG) equations for the driving energy parameters. A length scale defined from the curvature function near the gap-closing momentum is suggested to characterize the scale invariance at critical points and fixed points, and displays a universal critical behavior in a variety of systems examined.
MAGNETIC FIELDS FROM QCD PHASE TRANSITIONS
Tevzadze, Alexander G.; Kisslinger, Leonard; Kahniashvili, Tina; Brandenburg, Axel
2012-11-01
We study the evolution of QCD phase transition-generated magnetic fields (MFs) in freely decaying MHD turbulence of the expanding universe. We consider an MF generation model that starts from basic non-perturbative QCD theory and predicts stochastic MFs with an amplitude of the order of 0.02 {mu}G and small magnetic helicity. We employ direct numerical simulations to model the MHD turbulence decay and identify two different regimes: a 'weakly helical' turbulence regime, when magnetic helicity increases during decay, and 'fully helical' turbulence, when maximal magnetic helicity is reached and an inverse cascade develops. The results of our analysis show that in the most optimistic scenario the magnetic correlation length in the comoving frame can reach 10 kpc with the amplitude of the effective MF being 0.007 nG. We demonstrate that the considered model of magnetogenesis can provide the seed MF for galaxies and clusters.
Generalized fidelity susceptibility at phase transitions
NASA Astrophysics Data System (ADS)
You, Wen-Long; He, Li
2015-05-01
In the present work, we investigate the intrinsic relation between quantum fidelity susceptibility (QFS) and the dynamical structure factor. We give a concise proof of the QFS beyond the perturbation theory. With the QFS in the Lehmann representation, we point out that the QFS is actually the negative-two-power moment of dynamical structure factor and illuminate the inherent relation between physical quantities in the linear response theory. Moreover, we discuss the generalized fidelity susceptibility (GFS) of any quantum relevant operator, that may not be coupled to the driving parameter, and present similar scaling behaviors. Finally, we demonstrate that the QFS cannot capture the fourth-order quantum phase transition in a spin-1/2 anisotropic XY chain in the transverse alternating field, while a lower-order GFS can seize the criticalities.
Information Dynamics at a Phase Transition
NASA Astrophysics Data System (ADS)
Sowinski, Damian; Gleiser, Marcelo
2017-03-01
We propose a new way of investigating phase transitions in the context of information theory. We use an information-entropic measure of spatial complexity known as configurational entropy (CE) to quantify both the storage and exchange of information in a lattice simulation of a Ginzburg-Landau model with a scalar order parameter coupled to a heat bath. The CE is built from the Fourier spectrum of fluctuations around the mean-field and reaches a minimum at criticality. In particular, we investigate the behavior of CE near and at criticality, exploring the relation between information and the emergence of ordered domains. We show that as the temperature is increased from below, the CE displays three essential scaling regimes at different spatial scales: scale free, turbulent, and critical. Together, they offer an information-entropic characterization of critical behavior where the storage and fidelity of information processing is maximized at criticality.
Traffic volume and collisions involving transit and nontransit vehicles.
Ragland, D R; Hundenski, R J; Holman, B L; Fisher, J M
1992-10-01
This study reports an analysis of collisions occurring between public transit vehicles operated by the San Francisco Municipal Railway System (Muni), the public transit agency for the City of San Francisco, and nontransit vehicles. The analysis, focusing on weekday collisions during 1987, demonstrated a strong association between hourly transit collisions rates and hourly traffic volume. The collision rate varied from 0.01 per 1,000 Muni vehicle-hours of operation during the interval 5 A.M. to 6 A.M., a time of very low traffic volume, to 0.93 (approximately 1 collision per 1,000 Muni vehicle-hours of operation) during the interval 5 P.M. to 6 P.M., a time of very high traffic volume. Using a power function to predict either the total number of collisions, or the rate of collisions per 1,000 Muni vehicle-hours, almost 90% of total variation was accounted for by traffic volume. A very similar pattern was found for collisions judged either avoidable or unavoidable. A peak in the collision rate between 2 A.M. and 3 A.M. could not be accounted for by traffic volume alone. That peak occurred in the one-hour interval following the 2 A.M. closing of bars in San Francisco, and was composed entirely of a sharp increase in unavoidable collisions. Increasing traffic volume appeared to operate through two mechanisms: (i) an increase in the number of opportunities for a collision, defined as a quantity proportional to the product of the number of Muni and non-Muni vehicles; (ii) an increase in the probability of a collision occurring between any given pair of vehicles.
Phase Transitions in Living Neural Networks
NASA Astrophysics Data System (ADS)
Williams-Garcia, Rashid Vladimir
Our nervous systems are composed of intricate webs of interconnected neurons interacting in complex ways. These complex interactions result in a wide range of collective behaviors with implications for features of brain function, e.g., information processing. Under certain conditions, such interactions can drive neural network dynamics towards critical phase transitions, where power-law scaling is conjectured to allow optimal behavior. Recent experimental evidence is consistent with this idea and it seems plausible that healthy neural networks would tend towards optimality. This hypothesis, however, is based on two problematic assumptions, which I describe and for which I present alternatives in this thesis. First, critical transitions may vanish due to the influence of an environment, e.g., a sensory stimulus, and so living neural networks may be incapable of achieving "critical" optimality. I develop a framework known as quasicriticality, in which a relative optimality can be achieved depending on the strength of the environmental influence. Second, the power-law scaling supporting this hypothesis is based on statistical analysis of cascades of activity known as neuronal avalanches, which conflate causal and non-causal activity, thus confounding important dynamical information. In this thesis, I present a new method to unveil causal links, known as causal webs, between neuronal activations, thus allowing for experimental tests of the quasicriticality hypothesis and other practical applications.
Phase transitions in Hidden Markov Models
NASA Astrophysics Data System (ADS)
Bechhoefer, John; Lathouwers, Emma
In Hidden Markov Models (HMMs), a Markov process is not directly accessible. In the simplest case, a two-state Markov model ``emits'' one of two ``symbols'' at each time step. We can think of these symbols as noisy measurements of the underlying state. With some probability, the symbol implies that the system is in one state when it is actually in the other. The ability to judge which state the system is in sets the efficiency of a Maxwell demon that observes state fluctuations in order to extract heat from a coupled reservoir. The state-inference problem is to infer the underlying state from such noisy measurements at each time step. We show that there can be a phase transition in such measurements: for measurement error rates below a certain threshold, the inferred state always matches the observation. For higher error rates, there can be continuous or discontinuous transitions to situations where keeping a memory of past observations improves the state estimate. We can partly understand this behavior by mapping the HMM onto a 1d random-field Ising model at zero temperature. We also present more recent work that explores a larger parameter space and more states. Research funded by NSERC, Canada.
Global quantum discord and quantum phase transition in XY model
Liu, Si-Yuan; Zhang, Yu-Ran; Yang, Wen-Li; Fan, Heng
2015-11-15
We study the relationship between the behavior of global quantum correlations and quantum phase transitions in XY model. We find that the two kinds of phase transitions in the studied model can be characterized by the features of global quantum discord (GQD) and the corresponding quantum correlations. We demonstrate that the maximum of the sum of all the nearest neighbor bipartite GQDs is effective and accurate for signaling the Ising quantum phase transition, in contrast, the sudden change of GQD is very suitable for characterizing another phase transition in the XY model. This may shed lights on the study of properties of quantum correlations in different quantum phases.
Topological and geometrical aspects of phase transitions
NASA Astrophysics Data System (ADS)
Santos, F. A. N.; Rehn, J. A.; Coutinho-Filho, M. D.
2014-03-01
In the first part of this review, we use a topological approach to describe the frustration- and field-induced phase transitions exhibited by the infinite-range XY model on the AB2 chain, including noncollinear spin structures. For this purpose, we have computed the Euler characteristic, χ, as well as other topological invariants, which are found to behave similarly as a function of the energy level in the context of Morse theory. Our findings and those available in the literature suggest that the cusp-like singularity exhibited by χ at the critical energy, Ec, put together with the divergence of the density of Jacobian's critical points emerge as necessary and sufficient conditions for the occurrence of finite-temperature topology-induced phase transitions. In the second part, we present an alternative solution of the Ising chain in a field under free and periodic boundary conditions, in the microcanonical, canonical, and grand canonical ensembles, from a unified combinatorial and topological perspective. In particular, the computation of the per-site entropy as a function of the energy unveils a residual value for critical values of the magnetic field, a phenomenon for which we provide a topological interpretation and a connection with the Fibonacci sequence. We also show that, in the thermodynamic limit, the per-site microcanonical entropy is equal to the logarithm of the per-site Euler characteristic. Finally, we emphasize that our combinatorial approach to the canonical ensemble allows exact computation of the thermally averaged value <χ>(T) of the Euler characteristic; our results show that the conjecture <χ>(Tc)= 0, where Tc is the critical temperature, is valid for the Ising chain.
Formamidinium iodide: crystal structure and phase transitions
Goodilin, Eugene A.; Tarasov, Alexey B.; Dorovatovskii, Pavel V.
2017-01-01
At a temperature of 100 K, CH5N2 +·I− (I), crystallizes in the monoclinic space group P21/c. The formamidinium cation adopts a planar symmetrical structure [the r.m.s. deviation is 0.002 Å, and the C—N bond lengths are 1.301 (7) and 1.309 (8) Å]. The iodide anion does not lie within the cation plane, but deviates from it by 0.643 (10) Å. The cation and anion of I form a tight ionic pair by a strong N—H⋯I hydrogen bond. In the crystal of I, the tight ionic pairs form hydrogen-bonded zigzag-like chains propagating toward [20-1] via strong N—H⋯I hydrogen bonds. The hydrogen-bonded chains are further packed in stacks along [100]. The thermal behaviour of I was studied by different physicochemical methods (thermogravimetry, differential scanning calorimetry and powder diffraction). Differential scanning calorimetry revealed three narrow endothermic peaks at 346, 387 and 525 K, and one broad endothermic peak at ∼605 K. The first and second peaks are related to solid–solid phase transitions, while the third and fourth peaks are attributed to the melting and decomposition of I. The enthalpies of the phase transitions at 346 and 387 K are estimated as 2.60 and 2.75 kJ mol−1, respectively. The X-ray powder diffraction data collected at different temperatures indicate the existence of I as the monoclinic (100–346 K), orthorhombic (346–387 K) and cubic (387–525 K) polymorphic modifications. PMID:28435723
Magnetically ordered phase near transition to Bose-glass phase
NASA Astrophysics Data System (ADS)
Syromyatnikov, A. V.; Sizanov, A. V.
2017-01-01
We discuss a magnetically ordered ("superfluid") phase near quantum transition to the Bose-glass phase in a simple modeling system, a Heisenberg antiferromagnet with spatial dimension d >2 in an external magnetic field with disorder in exchange coupling constants. Our analytical consideration is based on hydrodynamic description of long-wavelength excitations. Results obtained are valid in the entire critical region near the quantum critical point (QCP), allowing us to describe a possible crossover from one critical behavior to another. We demonstrate that the system behaves in full agreement with predictions by M. P. Fisher et al. [Phys. Rev. B 40, 546 (1989), 10.1103/PhysRevB.40.546] in close vicinity to the QCP. We find as an extension to that analysis that the anomalous dimension η =2 -d and β =ν d /2 , where β and ν are critical exponents of the order parameter and the correlation length, respectively. The density of states per spin of low-energy localized excitations is found to be independent of d ("superuniversal"). We show that many recent experimental and numerical results obtained in various three-dimensional (3D) systems can be described by our formulas using percolation critical exponents. Then, it is a possibility that a percolation critical regime arises in the ordered phase in some 3D systems not very close to the QCP.
Determination of void volume in normal phase liquid chromatography.
Jiang, Ping; Wu, Di; Lucy, Charles A
2014-01-10
Void volume is an important fundamental parameter in chromatography. Little prior discussion has focused on the determination of void volume in normal phase liquid chromatography (NPLC). Various methods to estimate the total void volume are compared: pycnometry; minor disturbance method based on injection of weak solvent; tracer pulse method; hold-up volume based on unretained compounds; and accessible volume based on Martin's rule and its descendants. These are applied to NPLC on silica, RingSep and DNAP columns. Pycnometry provides a theoretically maximum value for the total void volume and should be performed at least once for each new column. However, pycnometry does not reflect the volume of adsorbed strong solvent on the stationary phase, and so only yields an accurate void volume for weaker mobile phase conditions. 1,3,5-Tri-t-butyl benzene (TTBB) results in hold-up volumes that are convenient measures of the void volume for all eluent conditions on charge-transfer columns (RingSep and DNAP), but is weakly retained under weak eluent conditions on silica. Injection of the weak mobile phase component (hexane) may be used to determine void volume, but care must be exercised to select the appropriate disturbance feature. Accessible volumes, that are determined using a homologous series, are always biased low, and are not recommended as a measure of the void volume. Copyright © 2013 Elsevier B.V. All rights reserved.
Thermotropic and barotropic phase transitions of dilauroylphosphatidylcholine bilayer.
Tada, Kaori; Goto, Masaki; Tamai, Nobutake; Matsuki, Hitoshi; Kaneshina, Shoji
2008-06-01
The bilayer phase transitions of dilauroylphosphatidylcholine (DLPC), containing two linear acyl chains with 12 carbon atoms, were observed by means of differential scanning calorimetry (DSC) under ambient pressure and light transmittance under high pressure. When the heating scan for the DLPC bilayer in 50 wt.% aqueous ethylene glycol (EG) solution began at -30 degrees C after cold storage, the DSC thermogram showed two endothermic peaks at 1.7 and 4.5 degrees C, which correspond to the transition from the lamellar crystalline (Lc) phase to the intermediate liquid crystalline (Lx) phase and the transition from the Lx phase to the liquid crystalline (L) phase, respectively. Extremely large enthalpy change (32.9 kJ mol(-1)) is characteristic of the Lc/Lx phase transition. The DSC thermogram for the heating scan beginning from -10 degrees C showed a single endothermic peak with 9.2 kJ mol(-1) at -0.4 degrees C, which was assigned as the so-called main transition between the metastable ripple gel (P'(beta)) and metastable Lalpha phases. The DLPC bilayer under high pressure underwent three kinds of transitions in EG solution, whereas only one transition was observed in water under high pressure. The middle-temperature transition in EG solution could be assigned to the main transition because of its consistency with the main transition in water. The lower-temperature transition is probably assigned as transition from the Lc phase to the P'(beta) phase. Since the slope (dT/dp) of the Lc/P'(beta) phase boundary is smaller than that for the main transition, the Lc/P'(beta) phase boundary and the main transition curves crossed each other at 40 MPa on the temperature-pressure phase diagram. The higher-temperature transition in EG solution refers to the transition from the Lx phase to the Lalpha phase. The Lx phase disappeared at about 180 MPa, and the direct transition from the P'(beta) phase to the Lalpha phase was observed at high pressures above 180 MPa.
The Phase Transition of Zn0.854Cu0.146O Under High Pressure
Y Jin; J Zhang; P Zhu; W Gao; Q Cui
2011-12-31
Pressure induced phase transition of hexagonal Zn{sub 0.854}Cu{sub 0.146}O is studied by using synchrotron angle dispersive X-ray diffraction (ADXRD) up to 43.1 GPa at room temperature. A structural transformation from a hexagonal phase to a cubic phase is observed, which starts at 10.2 GPa and finishes at about 16.5 GPa. The phase transition leads to a volume collapse of 17% at 10.2 GPa. The cubic phase of Zn{sub 0.854}Cu{sub 0.146}O remains stable up to the highest experiment pressure. The pressure-volume data are fitted with the Birch-Murnaghan equation of state. The bulk modulus obtained upon compression from the fitting are 175(2) and 259(6) GPa for the hexagonal and cubic phases, respectively.
Hexagonal and nematic phases of chains. I - Correlation functions. II - Phase transitions
NASA Technical Reports Server (NTRS)
Selinger, Jonathan V.; Bruinsma, Robijn F.
1991-01-01
The statistical mechanics of a system of semiflexible chains, which can represent polymer liquid crystals, long-chain biomolecules, stiff wormlike micelles, or columns of discotic liquid crystals, are examined. A continuum theory is used to calculate static correlation functions in the hexagonal and nematic phases. Two correlation functions are considered: (1) the structure factor which describes fluctuations in the density; and (2) the director fluctuation spectrum, which describes fluctuations in the local optical axis. In addition, a model is developed for the phase transitions of a system of infinitely long, semiflexible chains which interact through a steric, excluded-volume repulsion. The model yields generic phase diagrams in terms of pressure or density vs. persistence length or temperature.
Estimation of liquid volume fraction using ultrasound transit time spectroscopy
NASA Astrophysics Data System (ADS)
Al-Qahtani, Saeed M.; Langton, Christian M.
2016-12-01
It has recently been proposed that the propagation of an ultrasound wave through complex structures, consisting of two-materials of differing ultrasound velocity, may be considered as an array of parallel ‘sonic rays’, the transit time of each determined by their relative proportion; being a minimum (t min) in entire higher velocity material, and a maximum (t max) in entire lower velocity material. An ultrasound transit time spectrum (UTTS) describes the proportion of sonic rays at an individual transit time. It has previously been demonstrated that the solid volume fraction of a solid:liquid composite, specifically acrylic step-wedges immersed in water, may be reliably estimated from the UTTS. The aim of this research was to investigate the hypothesis that the volume fraction of a two-component liquid mixture, of unequal ultrasound velocity, may also be estimated by UTTS. A through-transmission technique incorporating two 1 MHz ultrasound transducers within a horizontally-aligned cylindrical tube-housing was utilised, the proportion of silicone oil to water being varied from 0% to 100%. The liquid volume fraction was estimated from the UTTS at each composition, the coefficient of determination (R 2%) being 98.9 ± 0.7%. The analysis incorporated a novel signal amplitude normalisation technique to compensate for absorption within the silicone oil. It is therefore envisaged that the parallel sonic ray concept and the derived UTTS may be further applied to the quantification of liquid mixture composition assessment.
Gravitational waves from global second order phase transitions
Jr, John T. Giblin; Price, Larry R.; Siemens, Xavier; Vlcek, Brian E-mail: larryp@caltech.edu E-mail: bvlcek@uwm.edu
2012-11-01
Global second-order phase transitions are expected to produce scale-invariant gravitational wave spectra. In this manuscript we explore the dynamics of a symmetry-breaking phase transition using lattice simulations. We explicitly calculate the stochastic gravitational wave background produced during the transition and subsequent self-ordering phase. We comment on this signal as it compares to the scale-invariant spectrum produced during inflation.
Nonequilibrium quantum phase transitions in the Dicke model.
Bastidas, V M; Emary, C; Regler, B; Brandes, T
2012-01-27
We establish a set of nonequilibrium quantum phase transitions in the Dicke model by considering a monochromatic nonadiabatic modulation of the atom-field coupling. For weak driving the system exhibits a set of sidebands which allow the circumvention of the no-go theorem which otherwise forbids the occurrence of superradiant phase transitions. At strong driving we show that the system exhibits a rich multistable structure and exhibits both first- and second-order nonequilibrium quantum phase transitions.
Phase transitions in the Nb-D(H) system: Superlattice reflections near the '-US phase transition
Chasnov, R.; Birnbaum, H.K.; Shapiro, S.M.
1986-02-01
An experimental study of NbD/sub x/(H/sub x/) alloys (0.70 < x < 0.85) in the vicinity of the '-US phase transition was conducted using x-ray and elastic neutron scattering techniques in the temperature range 300 < T < 473 K. ''Superlattice'' reflections between the Bragg peaks of the bcc ' phase were observed for both x-ray and neutron scattering but there were significant differences between observations carried out with the two types of radiation. The temperature dependence of these weak reflections was determined in the ' phase. These superlattice reflections were interpreted as being due to periodic modulations of the metal lattice caused by the partial ordering of deuterium atoms in the ' phase.
Chiral phase transition in lattice QCD as a metal-insulator transition
Garcia-Garcia, Antonio M.; Osborn, James C.
2007-02-01
We investigate the lattice QCD Dirac operator with staggered fermions at temperatures around the chiral phase transition. We present evidence of a metal-insulator transition in the low lying modes of the Dirac operator around the same temperature as the chiral phase transition. This strongly suggests the phenomenon of Anderson localization drives the QCD vacuum to the chirally symmetric phase in a way similar to a metal-insulator transition in a disordered conductor. We also discuss how Anderson localization affects the usual phenomenological treatment of phase transitions a la Ginzburg-Landau.
Blackburn, J.C.; Kilpatrick, P.K. )
1993-04-01
The effects of added salt (CsOH, CsCl), long-chain carboxylic acid, and long-chain alcohol on the lyotropic liquid crystalline phase behavior in the cesium n-tetradecanoate (CsTD)-water system is reported. The transitional region between the hexagonal (H) and lamellar (L) phases was the compositional range of focus. Three transitional phases were observed: (i) the ribbon (R) phase, a biaxial phase consisting of cylinders of ellipsoidal cross section; (ii) the viscous isotropic (VI) phase, an isotropic phase thought to consist of interconnected rods on an Ia3d lattice; and (iii) the intermediate (Int) phase, a uniaxial anisotropic phase thought to consist of interconnected rods on a planar lattice. The effect of the additives was to decrease the interfacial curvature of the surfactant head group layer by varying head group repulsion and by varying the surfactant tail volume relative to the surfactant head group area. These changes resulted in formation of transitional phases seeming to possess curvature between that of the cylindrical H phase and the planar L phase. The ionic repulsion between carboxylate head groups was reduced by the addition of CsOH or CsCl, and resulted in destabilization of the VI phase and the formation of the anisotropic Int phase. With the addition of cosurfactants, n-tetradecanoic acid (TDA) and 1-tetradecanol (TDOH), no Int phase was observed. With 7 wt% added TDA the R phase was stabilized up to temperatures of 336 K, above the 330 K temperature limit in the binary CsTD-D[sub 2]O system. In all four systems, sufficient additive (5-10 wt%) resulted in a transition to the L phase, which was stable over a large portion of the compositional range. In order of apparently decreasing mean curvature, the phase sequence is: hexagonal, ribbon, viscous isotropic, intermediate, and lamellar.
Structural and phase transitions of one and two polymer mushrooms
NASA Astrophysics Data System (ADS)
Yang, Delian; Wang
2012-02-01
A polymer mushroom here refers to a group of n homopolymer chains end-grafted at the same point on a flat, impenetrable and homogeneous substrate. Using lattice self-consistent field (LSCF) calculations with the Kronecker δ-function interactions (instead of the commonly used nearest-neighbor interactions), we have studied the structures of one and two polymer mushrooms in an explicit solvent as a function of the polymer volume fraction, the solvent quality characterized by the Flory-Huggins χ parameter, and the distance between the two mushrooms. We have constructed phase diagrams of these systems showing the coil-globule transition (CGT) of one mushroom and how it is coupled with the fused-separated transition (FST) of two mushrooms. Since LSCF results are exact only in the limit of n->∞, we also use the newly proposed fast lattice Monte Carlo (FLMC) simulations^1 with the same Hamiltonian as in LSCF theory to examine how this limit is approached with increasing n. Direct comparisons between LSCF and FLMC results without any parameter-fitting quantify the fluctuation/correlation effects neglected in LSCF theory. We also find a second-order symmetric-asymmetric transition (SAT) for one-mushroom system in the globule state, and examine its coupling with CGT and FST. [1] Q. Wang, Soft Matter, 5, 4564 (2009); 6, 6206 (2010).
Volume-based considerations for the metal-insulator transition of CMR oxides
Neumeier, J.J. |; Hundley, M.F.; Cornelius, A.L.; Andres, K.
1998-03-01
The sensitivity of {rho} [electrical resistivity] to changes in volume which occur through: (1) applied pressure, (2) variations in temperature, and (3) phase transitions, is evaluated for some selected CMR oxides. It is argued that the changes in volume associated with phase changes are large enough to produce self pressures in the range of 0.18 to 0.45 GPa. The extreme sensitivity of the electrical resistivity to pressure indicates that these self pressures are responsible for large features in the electrical resistivity and are an important component for occurrence the metallicity below {Tc}. It is suggested that this is related to a strong volume dependence of the electron phonon coupling in the CMR oxides.
QCD phase transition with chiral quarks and physical quark masses.
Bhattacharya, Tanmoy; Buchoff, Michael I; Christ, Norman H; Ding, H-T; Gupta, Rajan; Jung, Chulwoo; Karsch, F; Lin, Zhongjie; Mawhinney, R D; McGlynn, Greg; Mukherjee, Swagato; Murphy, David; Petreczky, P; Renfrew, Dwight; Schroeder, Chris; Soltz, R A; Vranas, P M; Yin, Hantao
2014-08-22
We report on the first lattice calculation of the QCD phase transition using chiral fermions with physical quark masses. This calculation uses 2+1 quark flavors, spatial volumes between (4 fm)(3) and (11 fm)(3) and temperatures between 139 and 196 MeV. Each temperature is calculated at a single lattice spacing corresponding to a temporal Euclidean extent of N(t) = 8. The disconnected chiral susceptibility, χ(disc) shows a pronounced peak whose position and height depend sensitively on the quark mass. We find no metastability near the peak and a peak height which does not change when a 5 fm spatial extent is increased to 10 fm. Each result is strong evidence that the QCD "phase transition" is not first order but a continuous crossover for m(π) = 135 MeV. The peak location determines a pseudocritical temperature T(c) = 155(1)(8) MeV, in agreement with earlier staggered fermion results. However, the peak height is 50% greater than that suggested by previous staggered results. Chiral SU(2)(L) × SU(2)(R) symmetry is fully restored above 164 MeV, but anomalous U(1)(A) symmetry breaking is nonzero above T(c) and vanishes as T is increased to 196 MeV.
Liquid–liquid phase transition in hydrogen by coupled electron–ion Monte Carlo simulations
Pierleoni, Carlo; Morales, Miguel A.; Rillo, Giovanni; ...
2016-04-20
The phase diagram of high-pressure hydrogen is of great interest for fundamental research, planetary physics, and energy applications. A first-order phase transition in the fluid phase between a molecular insulating fluid and a monoatomic metallic fluid has been predicted. The existence and precise location of the transition line is relevant for planetary models. Recent experiments reported contrasting results about the location of the transition. Theoretical results based on density functional theory are also very scattered. We report highly accurate coupled electron-ion Monte Carlo calculations of this transition, finding results that lie between the two experimental predictions, close to that measuredmore » in diamond anvil cell experiments but at 25-30 GPa higher pressure. Here, the transition along an isotherm is signaled by a discontinuity in the specific volume, a sudden dissociation of the molecules, a jump in electrical conductivity, and loss of electron localization.« less
Liquid–liquid phase transition in hydrogen by coupled electron–ion Monte Carlo simulations
Morales, Miguel A.; Rillo, Giovanni; Holzmann, Markus; Ceperley, David M.
2016-01-01
The phase diagram of high-pressure hydrogen is of great interest for fundamental research, planetary physics, and energy applications. A first-order phase transition in the fluid phase between a molecular insulating fluid and a monoatomic metallic fluid has been predicted. The existence and precise location of the transition line is relevant for planetary models. Recent experiments reported contrasting results about the location of the transition. Theoretical results based on density functional theory are also very scattered. We report highly accurate coupled electron–ion Monte Carlo calculations of this transition, finding results that lie between the two experimental predictions, close to that measured in diamond anvil cell experiments but at 25–30 GPa higher pressure. The transition along an isotherm is signaled by a discontinuity in the specific volume, a sudden dissociation of the molecules, a jump in electrical conductivity, and loss of electron localization. PMID:27099295
Anomalous Change in Temperature during the Pressure-Induced Phase Transition of KI
NASA Astrophysics Data System (ADS)
Nomura, Motoyuki; Harino, Hideo; Itoh, Tsukasa
1990-11-01
Temperature changes associated with the pressure-induced phase transition of KI were observed. Two kinds of temperature signals were detected, one of which is endothermic due to the adiabatic expansion of the pressure transmitting liquid brought about by the discontinuous decrease in the sample volume. The other is an exothermic one transmitted from the sample by radiation, which means heating of a sample at the forward transition. The latter signal consists of a spike accompanied by a small but long-tailed signal. The heating at the forward transition is inconsistent with the negative slope of the phase boundary in the accepted pressure-temperature phase diagram. Although the pattern of temperature signals observed seems to support the transition mechanism of the nucleation of B2 and its growth, this mechanism contradicts the behavior of the fracture plane of KI which suggests some kind of Martesite transformation. In a reverse transition, complicated temperature signals were detected.
On the existence of vapor-liquid phase transition in dusty plasmas
Kundu, M.; Sen, A.; Ganesh, R.; Avinash, K.
2014-10-15
The phenomenon of phase transition in a dusty-plasma system (DPS) has attracted some attention in the past. Earlier Farouki and Hamaguchi [J. Chem. Phys. 101, 9876 (1994)] have demonstrated the existence of a liquid to solid transition in DPS where the dust particles interact through a Yukawa potential. However, the question of the existence of a vapor-liquid (VL) transition in such a system remains unanswered and relatively unexplored so far. We have investigated this problem by performing extensive molecular dynamics simulations which show that the VL transition does not have a critical curve in the pressure versus volume diagram for a large range of the Yukawa screening parameter κ and the Coulomb coupling parameter Γ. Thus, the VL phase transition is found to be super-critical, meaning that this transition is continuous in the dusty plasma model given by Farouki and Hamaguchi. We provide an approximate analytic explanation of this finding by means of a simple model calculation.
Highly birefringent crystal for Raman transitions with phase modulators
NASA Astrophysics Data System (ADS)
Arias, Nieves; Abediyeh, Vahide; Hamzeloui, Saeed; Jeronimo-Moreno, Yasser; Gomez, Eduardo
2016-05-01
We present a system to excite Raman transitions with minimum phase noise. The system uses a phase modulator to generate the phase locked beams required for the transition. We use a long calcite crystal to filter out one of the sidebands, avoiding the cancellation that appears at high detunings for phase modulation. The measured phase noise is limited by the quality of the microwave synthesizer. We use the calcite crystal a second time to produce a co-propagating Raman pair with perpendicular polarizations to drive velocity insensitive Raman transitions. Support from CONACYT and Fundacion Marcos Moshinsky.
Van der Waals phase transition in the framework of holography
NASA Astrophysics Data System (ADS)
Zeng, Xiao-Xiong; Li, Li-Fang
2017-01-01
Phase structure of the quintessence Reissner-Nordström-AdS black hole is probed by the nonlocal observables such as holographic entanglement entropy and two point correlation function. Our result shows that, as the case of the thermal entropy, both the observables exhibit the Van der Waals-like phase transition. To reinforce this conclusion, we further check the equal area law for the first order phase transition and critical exponent of the heat capacity for the second order phase transition. We also discuss the effect of the state parameter on the phase structure of the nonlocal observables.
Potekhin, S A; Senin, A A; Abdurakhmanov, N N; Khusainova, R S
2008-11-01
Scanning microcalorimetry has been used to study the high pressure effect on the main transition from the ripple gel P'(beta) phase to the liquid crystal (L(alpha)) phase in DPPC (dipalmitoylphosphatidylcholine). It has been demonstrated that an increase of the pressure by 200 MPa shifts the transition to higher temperatures by 36.4 degrees. The pressure increase does not affect the cooperativity of transition but reduces noticeably its enthalpy. The changes of the molar partial volume, isothermal compressibility as well as volume thermal expansibility during transition in DPPC suspension have been estimated. It has been shown that monovalent ions (Na(+), Cl(-)) in solution slightly affect the main thermodynamic parameters of the transition. Calcium ions significantly decrease distinction in compressibility and thermal expansibility between liquid-crystal and ripple gel phases of lipid suspension, which in its turn reflects less difference in their volume fluctuations.
Quantum thermodynamic cycle with quantum phase transition
NASA Astrophysics Data System (ADS)
Ma, Yu-Han; Su, Shan-He; Sun, Chang-Pu
2017-08-01
With the Lipkin-Meshkov-Glick (LMG) model as an illustration, we construct a thermodynamic cycle composed of two isothermal processes and two isomagnetic field processes, and we study the thermodynamic performance of this cycle accompanied by the quantum phase transition (QPT). We find that for a finite particle system working below the critical temperature, the efficiency of the cycle is capable of approaching the Carnot limit when the external magnetic field λ1 corresponding to one of the isomagnetic processes reaches the cross point of the ground states' energy level, which can become the critical point of the QPT in the large-N limit. Our analysis proves that the system's energy level crossings at low-temperature limits can lead to a significant improvement in the efficiency of the quantum heat engine. In the case of the thermodynamics limit (N →∞ ) , the analytical partition function is obtained to study the efficiency of the cycle at high- and low-temperature limits. At low temperatures, when the magnetic fields of the isothermal processes are located on both sides of the critical point of the QPT, the cycle reaches maximum efficiency, and the Carnot efficiency can be achieved. This observation demonstrates that the QPT of the LMG model below critical temperature is beneficial to the thermodynamic cycle's operation.
Phononic Crystal Tunable via Ferroelectric Phase Transition
NASA Astrophysics Data System (ADS)
Xu, Chaowei; Cai, Feiyan; Xie, Shuhong; Li, Fei; Sun, Rong; Fu, Xianzhu; Xiong, Rengen; Zhang, Yi; Zheng, Hairong; Li, Jiangyu
2015-09-01
Phononic crystals (PCs) consisting of periodic materials with different acoustic properties have potential applications in functional devices. To realize more smart functions, it is desirable to actively control the properties of PCs on demand, ideally within the same fabricated system. Here, we report a tunable PC made of Ba0.7Sr0.3Ti O3 (BST) ceramics, wherein a 20-K temperature change near room temperature results in a 20% frequency shift in the transmission spectra induced by a ferroelectric phase transition. The tunability phenomenon is attributed to the structure-induced resonant excitation of A0 and A1 Lamb modes that exist intrinsically in the uniform BST plate, while these Lamb modes are sensitive to the elastic properties of the plate and can be modulated by temperature in a BST plate around the Curie temperature. The study finds opportunities for creating tunable PCs and enables smart temperature-tuned devices such as the Lamb wave filter or sensor.
Phase transitions in random quantum satisfiability
NASA Astrophysics Data System (ADS)
Laumann, Chris; Moessner, Roderich; Scardicchio, Antonello; Sondhi, Shivaji
2009-03-01
The potential power of quantum computers is a subject of great current interest and the raison d'etre for the intense effort and progress to build them. Naturally much theoretical interest has focused on algorithms that outperform their classical counterpart but recent developments in quantum complexity theory suggest that we already know problems, those shown to be QMA-complete, whose worst case instances would take a quantum computer exponentially long to solve. As in classical complexity theory the supposed difficulty of QMA complete problems follows from the existence of polynomial transformations relating any of the large class of QMA problems to instances of QMA-complete questions. This does not directly address the question of why this problem has hard instances and what features they posses. In this work we attempt to investigate the features of hard instances of a QMA complete problem introduced by S. Bravyi: quantum k-SAT. We use techniques of statistical physics of disordered systems in order to study a random ensemble of quantum k-SAT instances parametrized by clause density α in a program that is analogous to recent studies of classical random k-SAT. We establish a phase transition in satisfiability as a function of clause density and show that the problem almost always reduces to identifying a classical graph property.
Emergence and reduction combined in phase transitions
NASA Astrophysics Data System (ADS)
Butterfield, Jeremy; Bouatta, Nazim
2012-06-01
In another paper (Butterfield 2011), one of us argued that emergence and reduction are compatible, and presented four examples illustrating both. The main purpose of this paper is to develop this position for the example of phase transitions. We take it that emergence involves behaviour that is novel compared with what is expected: often, what is expected from a theory of the system's microscopic constituents. We take reduction as deduction, aided by appropriate definitions. Then the main idea of our reconciliation of emergence and reduction is that one makes the deduction after taking a limit of an appropriate parameter N. Thus our first main claim will be that in some situations, one can deduce a novel behaviour, by taking a limit N → ∞. Our main illustration of this will be Lee-Yang theory. But on the other hand, this does not show that the N = ∞ limit is "physically real". For our second main claim will be that in such situations, there is a logically weaker, yet still vivid, novel behaviour that occurs before the limit, i.e. for finite N. And it is this weaker behaviour which is physically real. Our main illustration of this will be the renormalization group description of cross-over phenomena.
Quantum thermodynamic cycle with quantum phase transition.
Ma, Yu-Han; Su, Shan-He; Sun, Chang-Pu
2017-08-01
With the Lipkin-Meshkov-Glick (LMG) model as an illustration, we construct a thermodynamic cycle composed of two isothermal processes and two isomagnetic field processes, and we study the thermodynamic performance of this cycle accompanied by the quantum phase transition (QPT). We find that for a finite particle system working below the critical temperature, the efficiency of the cycle is capable of approaching the Carnot limit when the external magnetic field λ_{1} corresponding to one of the isomagnetic processes reaches the cross point of the ground states' energy level, which can become the critical point of the QPT in the large-N limit. Our analysis proves that the system's energy level crossings at low-temperature limits can lead to a significant improvement in the efficiency of the quantum heat engine. In the case of the thermodynamics limit (N→∞), the analytical partition function is obtained to study the efficiency of the cycle at high- and low-temperature limits. At low temperatures, when the magnetic fields of the isothermal processes are located on both sides of the critical point of the QPT, the cycle reaches maximum efficiency, and the Carnot efficiency can be achieved. This observation demonstrates that the QPT of the LMG model below critical temperature is beneficial to the thermodynamic cycle's operation.
Phase transitions in models of human cooperation
NASA Astrophysics Data System (ADS)
Perc, Matjaž
2016-08-01
If only the fittest survive, why should one cooperate? Why should one sacrifice personal benefits for the common good? Recent research indicates that a comprehensive answer to such questions requires that we look beyond the individual and focus on the collective behavior that emerges as a result of the interactions among individuals, groups, and societies. Although undoubtedly driven also by culture and cognition, human cooperation is just as well an emergent, collective phenomenon in a complex system. Nonequilibrium statistical physics, in particular the collective behavior of interacting particles near phase transitions, has already been recognized as very valuable for understanding counterintuitive evolutionary outcomes. However, unlike pairwise interactions among particles that typically govern solid-state physics systems, interactions among humans often involve group interactions, and they also involve a larger number of possible states even for the most simplified description of reality. Here we briefly review research done in the realm of the public goods game, and we outline future research directions with an emphasis on merging the most recent advances in the social sciences with methods of nonequilibrium statistical physics. By having a firm theoretical grip on human cooperation, we can hope to engineer better social systems and develop more efficient policies for a sustainable and better future.
Consistent lattice Boltzmann equations for phase transitions.
Siebert, D N; Philippi, P C; Mattila, K K
2014-11-01
Unlike conventional computational fluid dynamics methods, the lattice Boltzmann method (LBM) describes the dynamic behavior of fluids in a mesoscopic scale based on discrete forms of kinetic equations. In this scale, complex macroscopic phenomena like the formation and collapse of interfaces can be naturally described as related to source terms incorporated into the kinetic equations. In this context, a novel athermal lattice Boltzmann scheme for the simulation of phase transition is proposed. The continuous kinetic model obtained from the Liouville equation using the mean-field interaction force approach is shown to be consistent with diffuse interface model using the Helmholtz free energy. Density profiles, interface thickness, and surface tension are analytically derived for a plane liquid-vapor interface. A discrete form of the kinetic equation is then obtained by applying the quadrature method based on prescribed abscissas together with a third-order scheme for the discretization of the streaming or advection term in the Boltzmann equation. Spatial derivatives in the source terms are approximated with high-order schemes. The numerical validation of the method is performed by measuring the speed of sound as well as by retrieving the coexistence curve and the interface density profiles. The appearance of spurious currents near the interface is investigated. The simulations are performed with the equations of state of Van der Waals, Redlich-Kwong, Redlich-Kwong-Soave, Peng-Robinson, and Carnahan-Starling.
Consistent lattice Boltzmann equations for phase transitions
NASA Astrophysics Data System (ADS)
Siebert, D. N.; Philippi, P. C.; Mattila, K. K.
2014-11-01
Unlike conventional computational fluid dynamics methods, the lattice Boltzmann method (LBM) describes the dynamic behavior of fluids in a mesoscopic scale based on discrete forms of kinetic equations. In this scale, complex macroscopic phenomena like the formation and collapse of interfaces can be naturally described as related to source terms incorporated into the kinetic equations. In this context, a novel athermal lattice Boltzmann scheme for the simulation of phase transition is proposed. The continuous kinetic model obtained from the Liouville equation using the mean-field interaction force approach is shown to be consistent with diffuse interface model using the Helmholtz free energy. Density profiles, interface thickness, and surface tension are analytically derived for a plane liquid-vapor interface. A discrete form of the kinetic equation is then obtained by applying the quadrature method based on prescribed abscissas together with a third-order scheme for the discretization of the streaming or advection term in the Boltzmann equation. Spatial derivatives in the source terms are approximated with high-order schemes. The numerical validation of the method is performed by measuring the speed of sound as well as by retrieving the coexistence curve and the interface density profiles. The appearance of spurious currents near the interface is investigated. The simulations are performed with the equations of state of Van der Waals, Redlich-Kwong, Redlich-Kwong-Soave, Peng-Robinson, and Carnahan-Starling.
The control of developmental phase transitions in plants.
Huijser, Peter; Schmid, Markus
2011-10-01
Plant development progresses through distinct phases: vegetative growth, followed by a reproductive phase and eventually seed set and senescence. The transitions between these phases are controlled by distinct genetic circuits that integrate endogenous and environmental cues. In recent years, however, it has become evident that the genetic networks that underlie these phase transitions share some common factors. Here, we review recent advances in the field of plant phase transitions, highlighting the role of two microRNAs - miR156 and miR172 - and their respective targets during these transitions. In addition, we discuss the evolutionary conservation of the functions of these miRNAs in regulating the control of plant developmental phase transitions.
Uniaxial phase transition in Si: Ab initio calculations
NASA Astrophysics Data System (ADS)
Cheng, C.
2003-04-01
Based on a previously proposed thermodynamic analysis, [C. Cheng, W. H. Huang, and H. J. Li, Phys. Rev. B 63, 153202 (2001)] we study the relative stabilities of five Si phases under uniaxial compression using ab initio methods. The five phases are diamond, βSn, simple-hexagonal (sh), simple-cubic, and hexagonal closed-packed structures. The possible phase-transition patterns were investigated by considering the phase transitions between any two chosen phases of the five phases. By analyzing the different contributions to the relative phase stability, we identified the most important factors in reducing the phase-transition pressures at uniaxial compression. We also show that it is possible to have phase transitions occur only when the phases are under uniaxial compression, in spite of no phase transition when under hydrostatic compression. Taking all five phases into consideration, the phase diagram at uniaxial compression was constructed for pressures up to 20 GPa. The stable phases were found to be diamond, βSn, and sh structures, i.e., the same as those when under hydrostatic condition. According to the phase diagram, direct phase transition from the diamond to the sh phase is possible if the applied uniaxial pressures, on increasing, satisfy the condition Px>Pz. Similarly, the sh-to-βSn transition on increasing pressures is also possible if the applied uniaxial pressures are varied from the condition of Px>Pz, on which the phase of sh is stable to the condition Px
Unconventional phase transitions in a constrained single polymer chain
NASA Astrophysics Data System (ADS)
Klushin, L. I.; Skvortsov, A. M.
2011-11-01
Phase transitions were recognized among the most fascinating phenomena in physics. Exactly solved models are especially important in the theory of phase transitions. A number of exactly solved models of phase transitions in a single polymer chain are discussed in this review. These are three models demonstrating the second order phase transitions with some unusual features: two-dimensional model of β-structure formation, the model of coil-globule transition and adsorption of a polymer chain grafted on the solid surface. We also discuss models with first order phase transitions in a single macromolecule which admit not only exact analytical solutions for the partition function with explicit finite-size effects but also the non-equilibrium free energy as a function of the order parameter (Landau function) in closed analytical form. One of them is a model of mechanical desorption of a macromolecule, which demonstrates an unusual first order phase transition with phase coexistence within a single chain. Features of first and second order transitions become mixed here due to phase coexistence which is not accompanied by additional interfacial free energy. Apart from that, there exist several single-chain models belonging to the same class (adsorption of a polymer chain tethered near the solid surface or liquid-liquid interface, and escape transition upon compressing a polymer between small pistons) that represent examples of a highly unconventional first order phase transition with several inter-related unusual features: no simultaneous phase coexistence, and hence no phase boundary, non-concave thermodynamic potential and non-equivalence of conjugate ensembles. An analysis of complex zeros of partition functions upon approaching the thermodynamic limit is presented for models with and without phase coexistence.
Glass transitions in nanoscale heated volumes of thin polystyrene films
NASA Astrophysics Data System (ADS)
Li, Alex G.; Burggraf, Larry W.
2010-12-01
Glass transitions in confined polystyrene films on a silicon substrate were studied using atomic force microscopy incorporating a thermal tip. Three-dimensional spatial nanoconfinements were achieved by controlling size and boundary conditions of small heated volumes of polymer nanostrands drawn from the polymer surface with the thermal tip, using appropriate loads and temperatures at the tip-polymer contact. Finite element analysis was performed to model mechanical contact and thermal transport, including the effects of contact radius, film thickness, and load on temperature and pressure distributions in the confined volume at the contact. The glass transition temperature (Tg) was measured by observing the softening of polymers with increasing temperature. The measured surface Tg exhibited a strong size dependence, while the subsurface Tg increased with decreasing the distance to the substrate. A large increase in the surface Tg was observed when the radius of contact was reduced below about 10 nm. The increase in the glass transition temperature at the surface was attributed to the presence of surface and line tension at the nanometer contact, while the enhanced Tg near the substrate was attributed to the pinning effects that reduces the mobility of the polymer molecules in the film over several hundreds of nanometers away from the polymer-substrate interface.
Interplay between micelle formation and waterlike phase transitions
NASA Astrophysics Data System (ADS)
Heinzelmann, G.; Figueiredo, W.; Girardi, M.
2010-02-01
A lattice model for amphiphilic aggregation in the presence of a structured waterlike solvent is studied through Monte Carlo simulations. We investigate the interplay between the micelle formation and the solvent phase transition in two different regions of temperature-density phase diagram of pure water. A second order phase transition between the gaseous (G) and high density liquid (HDL) phases that occurs at very high temperatures, and a first order phase transition between the low density liquid (LDL) and (HDL) phases that takes place at lower temperatures. In both cases, we find the aggregate size distribution curve and the critical micellar concentration as a function of the solvent density across the transitions. We show that micelle formation drives the LDL-HDL first order phase transition to lower solvent densities, while the transition G-HDL is driven to higher densities, which can be explained by the markedly different degrees of micellization in both cases. The diffusion coefficient of surfactants was also calculated in the LDL and HDL phases, changing abruptly its behavior due to the restructuring of waterlike solvent when we cross the first order LDL-HDL phase transition. To understand such behavior, we calculate the solvent density and the number of hydrogen bonds per water molecule close to micelles. The curves of the interfacial solvent density and the number of hydrogen bonds per water molecule in the first hydration signal a local phase change of the interfacial water, clarifying the diffusion mechanism of free surfactants in the solvent.
Theory of volume transition in polyelectrolyte gels with charge regularization.
Hua, Jing; Mitra, Mithun K; Muthukumar, M
2012-04-07
We present a theory for polyelectrolyte gels that allow the effective charge of the polymer backbone to self-regulate. Using a variational approach, we obtain an expression for the free energy of gels that accounts for the gel elasticity, free energy of mixing, counterion adsorption, local dielectric constant, electrostatic interaction among polymer segments, electrolyte ion correlations, and self-consistent charge regularization on the polymer strands. This free energy is then minimized to predict the behavior of the system as characterized by the gel volume fraction as a function of external variables such as temperature and salt concentration. We present results for the volume transition of polyelectrolyte gels in salt-free solvents, solvents with monovalent salts, and solvents with divalent salts. The results of our theoretical analysis capture the essential features of existing experimental results and also provide predictions for further experimentation. Our analysis highlights the importance of the self-regularization of the effective charge for the volume transition of gels in particular, and for charged polymer systems in general. Our analysis also enables us to identify the dominant free energy contributions for charged polymer networks and provides a framework for further investigation of specific experimental systems.
Fcc r arrow bct phase transition in Th at extreme compressions: Theory
Eriksson, O. ); Soederlind, P. ); Wills, J.M. )
1992-06-01
The experimentally observed fcc{r arrow}bct crystallographic phase transition in Th, at {similar to}1 Mbar, is reproduced by means of full-potential, linear-muffin-tin-orbitals calculations. Both the calculated volume and pressure for which the transition occurs, agrees with the experimental data. The calculated pressure dependence of the {ital c}/{ital a} ratio of the bct structure is also in good agreement wtih experimental data. Calculations for La predict the fcc phase to be stable over the bct phase up to {similar to}7 Mbar.
78 FR 30951 - SBIR/STTR Phase I to Phase II Transition Benchmarks
Federal Register 2010, 2011, 2012, 2013, 2014
2013-05-23
... From the Federal Register Online via the Government Publishing Office SMALL BUSINESS ADMINISTRATION SBIR/STTR Phase I to Phase II Transition Benchmarks AGENCY: U.S. Small Business Administration. ACTION: Notice for Small Business Innovation Research Program Phase I to Phase II Transition...
Strain glass state as the boundary of two phase transitions
Zhou, Zhijian; Cui, Jian; Ren, Xiaobing
2015-01-01
A strain glass state was found to be located between B2-B19’ (cubic to monoclinic) phase transition and B2-R (cubic to rhombohedral) phase transition in Ti49Ni51 alloys after aging process. After a short time aging, strong strain glass transition was observed, because the size of the precipitates is small, which means the strain field induced by the precipitates is isotropic and point-defect-like, and the distribution of the precipitates is random. After a long time aging, the average size of the precipitates increases. The strong strain field induced by the precipitates around them forces the symmetry of the matrix materials to conform to the symmetry of the crystalline structure of the precipitates, which results in the new phase transition. The experiment shows that there exists no well-defined boundary in the evolution from the strain glass transition to the new phase transition. Due to its generality, this glass mediated phase transition divergence scheme can be applied to other proper material systems to induce a more important new phase transition path, which can be useful in the field of phase transition engineering. PMID:26307500
Order of the deconfining phase transition in SU(3) lattice gauge theory
Fukugita, M. ); Okawa, M. ); Ukawa, A. )
1989-10-23
The nature of the finite-temperature deconfining phase transition is studied by Monte Carlo simulation on lattices ranging over 8{sup 3}{times}4 to 36{sup 3}{times}4. The spatial-volume dependence of the susceptibility and the mass gap strongly support a first-order transition. This is corroborated by an explicit construction of the effective {ital Z}(3) spin system whose dominant two-spin couplings are found to be all positive.
Quantum phase transitions in the presence of disorder and dissipation
NASA Astrophysics Data System (ADS)
Kotabage, Chetan
A quantum phase transition is a phase transition at absolute zero occurring under variations in an external non-thermal parameter such as magnetic field or pressure. Quantum phase transitions are one among the important topics currently investigated in condensed matter physics. They are observed in various systems, e.g., in the ferromagnetic-paramagnetic phase transition in LiHoF 4 or in the superconductor-metal phase transition in nanowires. A particular class of quantum phase transitions, which is phase transitions in the presence of disorder and dissipation, is investigated here. An example of this class is the ferromagnetic-paramagnetic phase transition in Ni 1-xVx or CePd 1-xRhx caused by variations in chemical composition. In these system, disorder is due to random positions of doping element and the dynamics of order-parameter fluctuations is dissipative due to conduction electrons. These quantum phase transitions are explained using the following approach: The Landau-Ginzberg-Wilson functional, which is derived from a microscopic Hamiltonian, is treated by the strong-disorder renormalization group method. For ohmic damping, phase transitions are strongly influenced by disorder and the critical point is an infinite-randomness fixed point, which is in the universality class same as that of the random transverse-field Ising model. The scaling form of observable quantities is activated type rather than conventional power-law type. For superohmic damping, the strong-disorder renormalization group method yields one of the recursion relationships different from ohmic damping. This difference indicates a more conventional transition for superohmic damping.
Method for identifying and probing phase transitions in materials
Asay, Blaine W.; Henson, Bryan F.; Sander, Robert K.; Robinson, Jeanne M.; Son, Steven F.; Dickson, Peter M.
2002-01-01
The present invention includes a method for identifying and probing phase transitions in materials. A polymorphic material capable of existing in at least one non-centrosymmetric phase is interrogated with a beam of laser light at a chosen wavelength and frequency. A phase transition is induced in the material while it is interrogated. The intensity of light scattered by the material and having a wavelength equal to one half the wavelength of the interrogating laser light is detected. If the phase transition results in the production of a non-centrosymmetric phase, the intensity of this scattered light increases; if the phase transition results in the disappearance of a non-centrosymmetric phase, the intensity of this scattered light decreases.
Pressure-Induced Phase Transitions of n-Tridecane
NASA Astrophysics Data System (ADS)
Yamashita, Motoi
Pressure-induced phase transition behavior of n-tridecane from the ordered phase through the rotator phase into the liquid phase has been investigated by using Fourier transform infrared spectroscopy at 25 °C. The transition between the ordered and rotator phases has been observed in the pressure range of 270-220 MPa and the transition between the rotator and liquid phases has been observed in the pressure range of 171-112 MPa, within the experimental error of ±50 MPa. The populations of the -gtg- + -gtg'-, -gg- and gt- defects determined from the methylene wagging mode are smaller in the rotator phase than in the liquid phase and are smaller under higher pressure in both of the rotator and liquid phases. A relationship has been found between the conformation and the intensity of the 890 cm-1 band, which has been assigned as the methyl rocking mode and has been considered as insensitive to conformation.
Broadening of a nonequilibrium phase transition by extended structural defects.
Vojta, Thomas
2004-08-01
We study the effects of quenched extended impurities on nonequilibrium phase transitions in the directed percolation universality class. We show that these impurities have a dramatic effect: they completely destroy the sharp phase transition by smearing. This is caused by rare strongly coupled spatial regions which can undergo the phase transition independently from the bulk system. We use extremal statistics to determine the stationary state as well as the dynamics in the tail of the smeared transition, and we illustrate the results by computer simulations.
Bi-phase transition diagrams of metallic thin multilayers
Li, J.C.; Liu, W.; Jiang, Q. . E-mail: jiangq@jlu.edu.cn
2005-02-01
Phase transitions of metallic multilayers induced by differences in interface energy are considered thermodynamically, based on a thermodynamic model for interface energy and the Goldschmidt premise for lattice contraction. Bi-phase transition diagrams of Co/Cr, Zr/Nb, Ti/Nb and Ti/Al multilayers are constructed, which are in agreement with experimental results.
On the Phase Transition of N-Isopropylcarbazole.
1986-05-01
vacinity of the phase transition (ca. T 137 + 40 K). We propose a semiquantitative interpretation of the phase transition in NIPC based on this assumption...the order parameter fluctuations in the vacinity of TO . V. Conclusions. The elastic properties of NIPC in the temperature range 90 K - 295 K have
Quantum Monte Carlo simulation of topological phase transitions
NASA Astrophysics Data System (ADS)
Yamamoto, Arata; Kimura, Taro
2016-12-01
We study the electron-electron interaction effects on topological phase transitions by the ab initio quantum Monte Carlo simulation. We analyze two-dimensional class A topological insulators and three-dimensional Weyl semimetals with the long-range Coulomb interaction. The direct computation of the Chern number shows the electron-electron interaction modifies or extinguishes topological phase transitions.
Surface phonons near structural phase transitions of fluoridic perovskites
NASA Astrophysics Data System (ADS)
Prade, J.; Kulkarni, A. D.; De Wette, F. W.; Reiger, R.; Schröder, U.; Kress, W.
1989-04-01
The fluoridic perovskite KMnF 3 exhibits an antiferrodistortive phase transition which goes along with a soft mode at the R-point of the Brillouin zone. We investigate in this paper the surface phonons of the KF(001) surface at temperatures near this phase transition. The calculations are carried out for relaxed and reconstructed (001) slabs.
The Condensation Phase Transition in Random Graph Coloring
NASA Astrophysics Data System (ADS)
Bapst, Victor; Coja-Oghlan, Amin; Hetterich, Samuel; Raßmann, Felicia; Vilenchik, Dan
2016-01-01
Based on a non-rigorous formalism called the "cavity method", physicists have put forward intriguing predictions on phase transitions in diluted mean-field models, in which the geometry of interactions is induced by a sparse random graph or hypergraph. One example of such a model is the graph coloring problem on the Erdős-Renyi random graph G( n, d/ n), which can be viewed as the zero temperature case of the Potts antiferromagnet. The cavity method predicts that in addition to the k-colorability phase transition studied intensively in combinatorics, there exists a second phase transition called the condensation phase transition (Krzakala et al. in Proc Natl Acad Sci 104:10318-10323, 2007). In fact, there is a conjecture as to the precise location of this phase transition in terms of a certain distributional fixed point problem. In this paper we prove this conjecture for k exceeding a certain constant k 0.
Chiral phase transition in QED3 at finite temperature
NASA Astrophysics Data System (ADS)
Yin, Pei-Lin; Xiao, Hai-Xiao; Wei, Wei; Feng, Hong-Tao; Zong, Hong-Shi
2016-12-01
In the framework of Dyson-Schwinger equations, we employ two kinds of criteria (one kind is the chiral condensate, the other kind is thermodynamic quantities, such as the pressure, the entropy, and the specific heat) to investigate the nature of chiral phase transitions in QED3 for different fermion flavors. It is found that the chiral phase transitions in QED3 for different fermion flavors are all typical second-order phase transitions; the critical temperature and order of the chiral phase transition obtained from the chiral condensate and susceptibility are the same with that obtained by the thermodynamic quantities, which means that they are equivalent in describing the chiral phase transition; the critical temperature decreases as the number of fermion flavors increases and there is a boundary that separates the Tc-Nf plane into chiral symmetry breaking and restoration regions.
Thermodynamic phase transition of a black hole in rainbow gravity
NASA Astrophysics Data System (ADS)
Feng, Zhong-Wen; Yang, Shu-Zheng
2017-09-01
In this letter, using the rainbow functions that were proposed by Magueijo and Smolin, we investigate the thermodynamics and the phase transition of rainbow Schwarzschild black hole. First, we calculate the rainbow gravity corrected Hawking temperature. From this modification, we then derive the local temperature, free energy, and other thermodynamic quantities in an isothermal cavity. Finally, we analyze the critical behavior, thermodynamic stability, and phase transition of the rainbow Schwarzschild black hole. The results show that the rainbow gravity can stop the Hawking radiation in the final stages of black holes' evolution and lead to the remnants of black holes. Furthermore, one can observe that the rainbow Schwarzschild black hole has one first-order phase transition, two second-order phase transitions, and three Hawking-Page-type phase transitions in the framework of rainbow gravity theory.
Pressure-Induced Phase Transition and Mechanical Properties of Mg2Sr Intermetallics
Yan, Haiyan; Han, Xingming; Zheng, Baobing
2016-01-01
A pressure-induced phase transition of Mg2Sr intermetallics from the low-pressure C14-type phase to an orthorhombic phase (space group Cmcm, Z = 4) at a high pressure of 21.0 GPa was firstly predicted using first-principles calculations combined with unbiased swarm structure searching techniques. The phase transition was identified as a first-order nature with a volume drop of 4.7%, driven by the softening of elastic behavior at high pressure. Further phonon calculations indicate that the newly predicted orthorhombic phase is dynamically stable at high pressure and ambient pressure. The mechanical properties including the elastic anisotropy of this orthorhombic phase were thus fully studied at ambient pressure. The elastic anisotropy behavior of this orthorhombic phase was investigated by the distributions of elastic moduli. The evidence of the bonding nature of Mg–Sr was also manifested by density of states (DOS) and electronic localization function (ELF) calculations. PMID:28774023
Electron microscopy: Phase transition singled out
Browning, Nigel D.
2013-04-23
One of the fundamental challenges within nanotechnology is to understand and control how nanoscale properties are initiated, evolve, and eventually terminate as a system moves from an individual nanostructure towards the meso- and macro-scale ensembles that are used in most applications. The ability to directly observe individual nanostructures and characterize their structure and composition has long been within the purview of transmission electron microscopy (TEM). The almost ubiquitous application of spherical aberration correction in TEM and in scanning-TEM (STEM) that has occurred over the last 10 years, now means it is possible to routinely characterize such nanostructures with both atomic resolution and sensitivity [1,2]. The development of temporal resolution in the TEM and the ability to study fast dynamics, on the other hand, has only recently come to the forefront of instrumentation development and is currently defined by two different approaches in the use of photoemission sources: the single shot s-ns dynamic TEM (DTEM) [3] and the stroboscopic ps-fs 4-D EM [4]. In the case of the DTEM, the goal is to observe the longer timescale irreversible structural changes that occur during nucleation and growth phenomena (here the single shot approach means there are enough electrons in a single pulsed beam to form a complete image). The 4-D EM focuses on a stroboscopic approach with the goal of studying very rapid reversible effects that occur during phase transitions (here an image is composed of thousands of pump-probe events each occurring with exactly the same time signature, with an individual pulse containing only a few electrons).
Pressure-induced phase transition and polymerization of tetracyanoethylene (TCNE)
NASA Astrophysics Data System (ADS)
Tomasino, Dane; Chen, Jing-Yin; Kim, Minesob; Yoo, Choong-Shik
2013-03-01
We have studied the pressure-induced physical and chemical transformations of tetracyanoethylene (TCNE or C6N4) in diamond anvil cells using micro-Raman spectroscopy, laser-heating, emission spectroscopy, and synchrotron x-ray diffraction. The results indicate that TCNE in a quasi-hydrostatic condition undergoes a shear-induced phase transition at 10 GPa and then a chemical change to two-dimensional (2D) C=N polymers above 14 GPa. These phase and chemical transformations depend strongly on the state of stress in the sample and occur sluggishly in non-hydrostatic conditions over a large pressure range between 7 and 14 GPa. The x-ray diffraction data indicate that the phase transition occurs isostructurally within the monoclinic structure (P21/c) without any apparent volume discontinuity and the C=N polymer is highly disordered but remains stable to 60 GPa—the maximum pressure studied. On the other hand, laser-heating of the C=N polymer above 25 GPa further converts to a theoretically predicted 3D C-N network structure, evident from an emergence of new Raman νs(C-N) at 1404 cm-1 at 25 GPa and the visual appearance of translucent solid. The C-N product is, however, unstable upon pressure unloading below 10 GPa, resulting in a grayish powder that can be considered as nano-diamonds with high-nitrogen content at ambient pressure. The C-N product shows a strong emission line centered at 640 nm at 30 GPa, which linearly shifts toward shorter wavelength at the rate of -1.38 nm/GPa. We conjecture that the observed red shift upon unloading pressure is due to increase of defects in the C-N product and thereby weakening of C-N bonds.
RNA Denaturation: Excluded Volume, Pseudoknots, and Transition Scenarios
NASA Astrophysics Data System (ADS)
Baiesi, M.; Orlandini, E.; Stella, A. L.
2003-11-01
A lattice model of RNA denaturation which fully accounts for the excluded volume effects among nucleotides is proposed. A numerical study shows that interactions forming pseudoknots must be included in order to get a sharp continuous transition. Otherwise a smooth crossover occurs from the swollen linear polymer behavior to highly ramified, almost compact conformations with secondary structures. In the latter scenario, which is appropriate when these structures are much more stable than pseudoknot links, probability distributions for the lengths of both loops and main branches obey scaling with nonclassical exponents.
Fluctuation-driven electroweak phase transition. [in early universe
NASA Technical Reports Server (NTRS)
Gleiser, Marcelo; Kolb, Edward W.
1992-01-01
We examine the dynamics of the electroweak phase transition in the early Universe. For Higgs masses in the range 46 less than or = M sub H less than or = 150 GeV and top quark masses less than 200 GeV, regions of symmetric and asymmetric vacuum coexist to below the critical temperature, with thermal equilibrium between the two phases maintained by fluctuations of both phases. We propose that the transition to the asymmetric vacuum is completed by percolation of these subcritical fluctuations. Our results are relevant to scenarios of baryogenesis that invoke a weakly first-order phase transition at the electroweak scale.
Fluctuation-driven electroweak phase transition. [in early universe
NASA Technical Reports Server (NTRS)
Gleiser, Marcelo; Kolb, Edward W.
1992-01-01
We examine the dynamics of the electroweak phase transition in the early Universe. For Higgs masses in the range 46 less than or = M sub H less than or = 150 GeV and top quark masses less than 200 GeV, regions of symmetric and asymmetric vacuum coexist to below the critical temperature, with thermal equilibrium between the two phases maintained by fluctuations of both phases. We propose that the transition to the asymmetric vacuum is completed by percolation of these subcritical fluctuations. Our results are relevant to scenarios of baryogenesis that invoke a weakly first-order phase transition at the electroweak scale.
Insight into Structural Phase Transitions from Density Functional Theory
NASA Astrophysics Data System (ADS)
Ruzsinszky, Adrienn
2014-03-01
Structural phase transitions caused by high pressure or temperature are very relevant in materials science. The high pressure transitions are essential to understand the interior of planets. Pressure or temperature induced phase transitions can be relevant to understand other phase transitions in strongly correlated systems or molecular crystals.Phase transitions are important also from the aspect of method development. Lower level density functionals, LSDA and GGAs all fail to predict the lattice parameters of different polymorphs and the phase transition parameters at the same time. At this time only nonlocal density functionals like HSE and RPA have been proved to resolve the geometry-energy dilemma to some extent in structural phase transitions. In this talk I will report new results from the MGGA_MS family of meta-GGAs and give an insight why this type of meta-GGAs can give a systematic improvement of the geometry and phase transition parameters together. I will also present results from the RPA and show a possible way to improve beyond RPA.
Pressure-driven phase transition mechanisms revealed by quantum chemistry: l-serine polymorphs.
Rychkov, Denis A; Stare, Jernej; Boldyreva, Elena V
2017-03-01
The present study delivers a computational approach for the understanding of the mechanism of phase transitions between polymorphs of small organic molecules. By using state of the art periodic DFT calculations augmented with dispersion corrections and an external stress tensor together with gas-phase cluster calculations, we thoroughly explained the reversible phase transitions of three polymorphs of the model system, namely crystalline l-serine in the pressure range up to 8 GPa. This study has shown that at the macroscopic level the main driving force of the phase transitions is the decrease in the volume of the crystal unit cell, which contributes to the enthalpy difference between the two forms, but not to the difference in their internal crystal energies. At the microscopic level we suggest that hydrogen bond overstrain leads to a martensitic-like, cooperative, displacive phase transition with substantial experimental hysteresis, while no such overstrain was found for the "normal type", atom per atom, reconstructive phase transition. The predicted pressures for the phase transitions deducted by the minimum enthalpy criterion are in reasonable agreement with the observed ones. By delivering unambiguous explanations not provided by previous studies and probably not accessible to experiment, this work demonstrates the predictive and explanatory power of quantum chemistry, confirming its indispensable role in structural studies.
Quantum phase transitions of topological insulators without gap closing.
Rachel, Stephan
2016-10-12
We consider two-dimensional Chern insulators and time-reversal invariant topological insulators and discuss the effect of perturbations breaking either particle-number conservation or time-reversal symmetry. The appearance of trivial mass terms is expected to cause quantum phase transitions into trivial phases when such a perturbation overweighs the topological term. These phase transitions are usually associated with a bulk-gap closing. In contrast, the chiral Chern insulator is unaffected by particle-number breaking perturbations. Moreover, the [Formula: see text] topological insulator undergoes phase transitions into topologically trivial phases without bulk-gap closing in the presence of any of such perturbations. In certain cases, these phase transitions can be circumvented and the protection restored by another U(1) symmetry, e.g. due to spin conservation. These findings are discussed in the context of interacting topological insulators.
CO2 Capture from Flue Gas by Phase Transitional Absorption
Liang Hu
2009-06-30
A novel absorption process called Phase Transitional Absorption was invented. What is the Phase Transitional Absorption? Phase Transitional Absorption is a two or multi phase absorption system, CO{sub 2} rich phase and CO{sub 2} lean phase. During Absorption, CO{sub 2} is accumulated in CO{sub 2} rich phase. After separating the two phases, CO{sub 2} rich phase is forward to regeneration. After regeneration, the regenerated CO{sub 2} rich phase combines CO{sub 2} lean phase to form absorbent again to complete the cycle. The advantage for Phase Transitional Absorption is obvious, significantly saving on regeneration energy. Because CO{sub 2} lean phase was separated before regeneration, only CO{sub 2} rich phase was forward to regeneration. The absorption system we developed has the features of high absorption rate, high loading and working capacity, low corrosion, low regeneration heat, no toxic to environment, etc. The process evaluation shows that our process is able to save 80% energy cost by comparing with MEA process.
The OCD phase transition and supernova core collapse
Gentile, N.A.; Mathews, G.J.; Wilson, J.R.
1993-10-01
We examine the implications for stellar core collapse of a phase transition occurring at densities of a few times nuclear matter density. We use an equation of state that describes a phase transition between bulk nuclear matter and a phase consisting of unbound quarks and gluons. We analyze the effect on the prompt shock, the production of strange matter, and the effect on the neutrino signal and the delayed mechanism.
Quantum phase transition in strongly correlated systems
NASA Astrophysics Data System (ADS)
Jiang, Longhua
In this thesis, we investigated the strongly correlated phenomena in bilayer quantum Hall effect, inhomogeneous superconductivity and Boson Hubbard model. Bilayer quantum Hall system is studied in chapter 2. By using the Composite Boson (CB) theory developed by J. Ye, we derive the ground state, quasihole and a quasihole-pair wave functions from the CB theory and its dual action. We find that the ground state wave function is the product of two parts, one in the charge sector which is the well known Halperin's (111) wave function and the other in the spin sector which is non-trivial at any finite d due to the gapless mode. So the total groundstate wave function differs from the well known (111) wave function at any finite d. In addition to commonly known multiplicative factors, the quasihole and quasihole-pair wave functions also contain non-trivial normalization factors multiplying the correct ground state wave function. Then we continue to study the quantum phase transition from the excitonic superfluid (ESF) to a possible pseudo-spin density wave (PSDW) at some intermediate distances driven by the magneto-roton minimum collapsing at a finite wavevector. We analyze the properties of the PSDW and explicitly show that a square lattice is the favored lattice. We suggest that correlated hopping of vacancies in the active and passive layers in the PSDW state leads to very large and temperature-dependent drag, consistent with the experimental data. Comparisons with previous microscopic numerical calculations are made. Further experimental implications are given. In chapter 3, we investigate inhomogeneous superconductivity. Starting from the Ginzburg-Landau free energy describing the normal state to Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state transition, we evaluate the free energy of seven most common lattice structures: stripe, square, triangular, Simple Cubic (SC), Face centered Cubic (FCC), Body centered Cubic (BCC) and Quasicrystal (QC). We find that the stripe
Explosive transitions to synchronization in networks of phase oscillators
Leyva, I.; Navas, A.; Sendiña-Nadal, I.; Almendral, J. A.; Buldú, J. M.; Zanin, M.; Papo, D.; Boccaletti, S.
2013-01-01
The emergence of dynamical abrupt transitions in the macroscopic state of a system is currently a subject of the utmost interest. The occurrence of a first-order phase transition to synchronization of an ensemble of networked phase oscillators was reported, so far, for very particular network architectures. Here, we show how a sharp, discontinuous transition can occur, instead, as a generic feature of networks of phase oscillators. Precisely, we set conditions for the transition from unsynchronized to synchronized states to be first-order, and demonstrate how these conditions can be attained in a very wide spectrum of situations. We then show how the occurrence of such transitions is always accompanied by the spontaneous setting of frequency-degree correlation features. Third, we show that the conditions for abrupt transitions can be even softened in several cases. Finally, we discuss, as a possible application, the use of this phenomenon to express magnetic-like states of synchronization. PMID:23412391
The electroweak phase transition in the Inert Doublet Model
Blinov, Nikita; Profumo, Stefano; Stefaniak, Tim E-mail: profumo@ucsc.edu
2015-07-01
We study the strength of a first-order electroweak phase transition in the Inert Doublet Model (IDM), where particle dark matter (DM) is comprised of the lightest neutral inert Higgs boson. We improve over previous studies in the description and treatment of the finite-temperature effective potential and of the electroweak phase transition. We focus on a set of benchmark models inspired by the key mechanisms in the IDM leading to a viable dark matter particle candidate, and illustrate how to enhance the strength of the electroweak phase transition by adjusting the masses of the yet undiscovered IDM Higgs states. We argue that across a variety of DM masses, obtaining a strong enough first-order phase transition is a generic possibility in the IDM. We find that due to direct dark matter searches and collider constraints, a sufficiently strong transition and a thermal relic density matching the universal DM abundance is possible only in the Higgs funnel regime.
The electroweak phase transition in the Inert Doublet Model
Blinov, Nikita; Profumo, Stefano; Stefaniak, Tim
2015-07-21
We study the strength of a first-order electroweak phase transition in the Inert Doublet Model (IDM), where particle dark matter (DM) is comprised of the lightest neutral inert Higgs boson. We improve over previous studies in the description and treatment of the finite-temperature effective potential and of the electroweak phase transition. We focus on a set of benchmark models inspired by the key mechanisms in the IDM leading to a viable dark matter particle candidate, and illustrate how to enhance the strength of the electroweak phase transition by adjusting the masses of the yet undiscovered IDM Higgs states. We argue that across a variety of DM masses, obtaining a strong enough first-order phase transition is a generic possibility in the IDM. We find that due to direct dark matter searches and collider constraints, a sufficiently strong transition and a thermal relic density matching the universal DM abundance is possible only in the Higgs funnel regime.
The effects of Venusian mantle convection with multiple phase transitions
NASA Technical Reports Server (NTRS)
Steinbach, V.; Yuen, D. A.; Christensen, U. R.
1992-01-01
Recently there was a flurry of activities in studying the effects of phase transitions in the Earth's mantle. From petrological and geophysical considerations, phase-transitions would also play an important role in venusian dynamics. The basic differences between the two planets are the surface boundary conditions, both thermally and mechanically. In this vein we have studied time-dependent mantle convection with multiple phase transitions and depth-dependent thermal expansivity (alpha is approximately rho(exp -6)), based on high-pressure and temperature measurements. Both the olivine-spinel and spinel-perovskite transitions were simulated by introducing an effective thermal expansivity, as described. Used together with the extended Boussinesq Approximation this method serves as a powerful tool to examine the effects of phase transitions on convection at relatively low computational costs.
High pressure structural phase transitions of PbPo
NASA Astrophysics Data System (ADS)
Bencherif, Y.; Boukra, A.; Zaoui, A.; Ferhat, M.
2012-09-01
First-principles calculations have been performed to investigate the high pressure phase transitions and dynamical properties of the less known lead polonium compound. The calculated ground state parameters for the NaCl phase show good agreement with the experimental data. The obtained results show that the intermediate phase transition for this compound is the orthorhombic Pnma phase. The PbPo undergoes from the rocksalt to Pnma phase at 4.20 GPa. Further structural phase transition from intermediate to CsCl phase has been found at 8.5 GPa. In addition, phonon dispersion spectra were derived from linear-response to density functional theory. In particular, we show that the dynamical properties of PbPo exhibit some peculiar features compared to other III-V compounds. Finally, thermodynamics properties have been also addressed from quasiharmonic approximation.
Deviatoric stress-induced phase transitions in diamantane
Yang, Fan; Lin, Yu; Dahl, Jeremy E. P.; Carlson, Robert M. K.; Mao, Wendy L.
2014-10-21
The high-pressure behavior of diamantane was investigated using angle-dispersive synchrotron x-ray diffraction (XRD) and Raman spectroscopy in diamond anvil cells. Our experiments revealed that the structural transitions in diamantane were extremely sensitive to deviatoric stress. Under non-hydrostatic conditions, diamantane underwent a cubic (space group Pa3) to a monoclinic phase transition at below 0.15 GPa, the lowest pressure we were able to measure. Upon further compression to 3.5 GPa, this monoclinic phase transformed into another high-pressure monoclinic phase which persisted to 32 GPa, the highest pressure studied in our experiments. However, under more hydrostatic conditions using silicone oil as a pressure medium, the transition pressure to the first high-pressure monoclinic phase was elevated to 7–10 GPa, which coincided with the hydrostatic limit of silicone oil. In another experiment using helium as a pressure medium, no phase transitions were observed to the highest pressure we reached (13 GPa). In addition, large hysteresis and sluggish transition kinetics were observed upon decompression. Over the pressure range where phase transitions were confirmed by XRD, only continuous changes in the Raman spectra were observed. This suggests that these phase transitions are associated with unit cell distortions and modifications in molecular packing rather than the formation of new carbon-carbon bonds under pressure.
First-Principles Study of Pressure-Induced Phase Transition in CuGaO2
NASA Astrophysics Data System (ADS)
Jiang, Cheng-Lu; Liu, Qi-Jun; Liu, Zheng-Tang
2017-02-01
We have studied the structural, elastic, electronic properties, and pressure-induced phase transition of CuGaO2 by using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). The obtained ground state properties of three phases were in agreement with previous works. The calculated enthalpy variations with pressure showed that the structural phase transition ( β → 3R/2H) appeared at 65.5 ± 1 GPa. The changes in volume and band gap of β phase showed that there was a break between 30 and 40 GPa. The independent elastic constants of three phases were calculated. The 3R, 2H, and β phases were all mechanical stability and behaved in ductile manner under zero pressure.
Ethylene Epoxidation at the Phase Transition of Copper Oxides.
Greiner, Mark T; Jones, Travis E; Klyushin, Alexander; Knop-Gericke, Axel; Schlögl, Robert
2017-08-30
Catalytic materials tend to be metastable. When a material becomes metastable close to a thermodynamic phase transition it can exhibit unique catalytic behavior. Using in situ photoemission spectroscopy and online product analysis, we have found that close to the Cu2O-CuO phase transition there is a boost in activity for a kinetically driven reaction, ethylene epoxidation, giving rise to a 20-fold selectivity enhancement relative to the selectivity observed far from the phase transition. By tuning conditions toward low oxygen chemical potential, this metastable state and the resulting enhanced selectivity can be sustained. Using density functional theory, we find that metastable O precursors to the CuO phase can account for the selectivity enhancements near the phase transition.
Homogeneous nucleation of a noncritical phase near a continuous phase transition
Sear, Richard P.
2001-06-01
Homogeneous nucleation of a new phase near a second, continuous, transition, is considered. The continuous transition is in the metastable region associated with the first-order phase transition, one of whose coexisting phases is nucleating. Mean-field calculations show that as the continuous transition is approached, the size of the nucleus varies as the response function of the order parameter of the continuous transition. This response function diverges at the continuous transition, as does the temperature derivative of the free-energy barrier to nucleation. This rapid drop of the barrier as the continuous transition is approached means that the continuous transition acts to reduce the barrier to nucleation at the first-order transition. This may be useful in the crystallization of globular proteins.
Problem-Solving Phase Transitions During Team Collaboration.
Wiltshire, Travis J; Butner, Jonathan E; Fiore, Stephen M
2017-02-18
Multiple theories of problem-solving hypothesize that there are distinct qualitative phases exhibited during effective problem-solving. However, limited research has attempted to identify when transitions between phases occur. We integrate theory on collaborative problem-solving (CPS) with dynamical systems theory suggesting that when a system is undergoing a phase transition it should exhibit a peak in entropy and that entropy levels should also relate to team performance. Communications from 40 teams that collaborated on a complex problem were coded for occurrence of problem-solving processes. We applied a sliding window entropy technique to each team's communications and specified criteria for (a) identifying data points that qualify as peaks and (b) determining which peaks were robust. We used multilevel modeling, and provide a qualitative example, to evaluate whether phases exhibit distinct distributions of communication processes. We also tested whether there was a relationship between entropy values at transition points and CPS performance. We found that a proportion of entropy peaks was robust and that the relative occurrence of communication codes varied significantly across phases. Peaks in entropy thus corresponded to qualitative shifts in teams' CPS communications, providing empirical evidence that teams exhibit phase transitions during CPS. Also, lower average levels of entropy at the phase transition points predicted better CPS performance. We specify future directions to improve understanding of phase transitions during CPS, and collaborative cognition, more broadly. Copyright © 2017 Cognitive Science Society, Inc.
Capillary Condensation in Polymer Blends: an Analysis of Phase Transitions
NASA Astrophysics Data System (ADS)
Ilie, Carolina C.; Jira, Nicholas C.; Evans, Ian R.; Cohen, Matthew; D'Rozario, Julia R.; Romano, Marie T.; Sabirianov, Ildar
We explore herein the capillary condensation for various geometries. Capillary condensation is studied in the presence of van der Waals forces. We derive the grand free energy, and we analyze the phase transitions, the absorption isotherms and the triple point. Phase transitions between full, empty and two films are investigated and the shape of the liquid is calculated. We also analyze an important application of wetting phenomena and capillary condensation in binary polymer blends and investigate the type of wetting transitions presented and the phase diagram. SUNY Oswego SCAC Grant, NSF Noyce Grant.
Tunable Bragg filters with a phase transition material defect layer
Wang, Xi; Gong, Zilun; Dong, Kaichen; ...
2016-01-01
We propose an all-solid-state tunable Bragg filter with a phase transition material as the defect layer. Bragg filters based on a vanadium dioxide defect layer sandwiched between silicon dioxide/titanium dioxide Bragg gratings are experimentally demonstrated. Temperature dependent reflection spectroscopy shows the dynamic tunability and hysteresis properties of the Bragg filter. Temperature dependent Raman spectroscopy reveals the connection between the tunability and the phase transition of the vanadium dioxide defect layer. This work paves a new avenue in tunable Bragg filter designs and promises more applications by combining phase transition materials and optical cavities.
Disorder-induced rounding of certain quantum phase transitions.
Vojta, Thomas
2003-03-14
We study the influence of quenched disorder on quantum phase transitions in systems with overdamped dynamics. For Ising order-parameter symmetry disorder destroys the sharp phase transition by rounding because a static order parameter can develop on rare spatial regions. This leads to an exponential dependence of the order parameter on the coupling constant. At finite temperatures the static order on the rare regions is destroyed. This restores the phase transition and leads to a double-exponential relation between critical temperature and coupling strength. We discuss the behavior based on Lifshitz-tail arguments and illustrate the results by simulations of a model system.
Superradiant phase transitions with three-level systems
NASA Astrophysics Data System (ADS)
Baksic, Alexandre; Nataf, Pierre; Ciuti, Cristiano
2013-02-01
We determine the phase diagram of N identical three-level systems interacting with a single photonic mode in the thermodynamical limit (N→∞) by accounting for the so-called diamagnetic term and the inequalities imposed by the Thomas-Reich-Kuhn (TRK) oscillator strength sum rule. The key role of transitions between excited levels and the occurrence of first-order phase transitions is discussed. We show that, in contrast to two-level systems, in the three-level case the TRK inequalities do not always prevent a superradiant phase transition in the presence of a diamagnetic term.
Problem of Phase Transition in Spin-fluctuation Theory
NASA Astrophysics Data System (ADS)
Melnikov, N. B.; Paradezhenko, G. V.
A first-order phase transition is a characteristic feature of the Gaussian approximation in spin-fluctuation theory. We describe a method for taking into account the fourth-order terms of the free energy expansion using partial averaging. In the example of the Ising model, we show that renormalization of the magnetic susceptibility leads to the second-order phase transition, which is experimentally observed in metals. Near the phase transition, we use the parameter substitution method to compute temperature dependencies. We perform a qualitative analysis and explain the mechanism of the renormalization.
Geometrical phase transitions on hierarchical lattices and universality
NASA Astrophysics Data System (ADS)
Hauser, P. R.; Saxena, V. K.
1986-12-01
In order to examine the validity of the principle of universality for phase transitions on hierarchical lattices, we have studied percolation on a variety of hierarchical lattices, within exact position-space renormalization-group schemes. It is observed that the percolation critical exponent νp strongly depends on the topology of the lattices, even for lattices with the same intrinsic dimensions and connectivities. These results support some recent similar results on thermal phase transitions on hierarchical lattices and point out the possible violation of universality in phase transitions on hierarchical lattices.
Topology-driven magnetic quantum phase transition in topological insulators.
Zhang, Jinsong; Chang, Cui-Zu; Tang, Peizhe; Zhang, Zuocheng; Feng, Xiao; Li, Kang; Wang, Li-Li; Chen, Xi; Liu, Chaoxing; Duan, Wenhui; He, Ke; Xue, Qi-Kun; Ma, Xucun; Wang, Yayu
2013-03-29
The breaking of time reversal symmetry in topological insulators may create previously unknown quantum effects. We observed a magnetic quantum phase transition in Cr-doped Bi2(SexTe1-x)3 topological insulator films grown by means of molecular beam epitaxy. Across the critical point, a topological quantum phase transition is revealed through both angle-resolved photoemission measurements and density functional theory calculations. We present strong evidence that the bulk band topology is the fundamental driving force for the magnetic quantum phase transition. The tunable topological and magnetic properties in this system are well suited for realizing the exotic topological quantum phenomena in magnetic topological insulators.
Sim, Taeyong; Choi, Ahnryul; Lee, Soeun; Mun, Joung Hwan
2017-10-01
The transition phase of a golf swing is considered to be a decisive instant required for a powerful swing. However, at the same time, the low back torsional loads during this phase can have a considerable effect on golf-related low back pain (LBP). Previous efforts to quantify the transition phase were hampered by problems with accuracy due to methodological limitations. In this study, vector-coding technique (VCT) method was proposed as a comprehensive methodology to quantify the precise transition phase and examine low back torsional load. Towards this end, transition phases were assessed using three different methods (VCT, lead hand speed and X-factor stretch) and compared; then, low back torsional load during the transition phase was examined. As a result, the importance of accurate transition phase quantification has been documented. The largest torsional loads were observed in healthy professional golfers (10.23 ± 1.69 N · kg(-1)), followed by professional golfers with a history of LBP (7.93 ± 1.79 N · kg(-1)), healthy amateur golfers (1.79 ± 1.05 N · kg(-1)) and amateur golfers with a history of LBP (0.99 ± 0.87 N · kg(-1)), which order was equal to that of the transition phase magnitudes of each group. These results indicate the relationship between the transition phase and LBP history and the dependency of the torsional load magnitude on the transition phase.
NASA Astrophysics Data System (ADS)
Kinelovskii, S. A.; Maevskii, K. K.
2017-02-01
The shock-wave synthesis and compaction using powder mixtures are the one of perspective directions of new materials creation. The results of numerical experiments on modeling of shock wave loading of mixtures with allowance for phase transition components in their composition are presented. The significant change in volume in the region of phase transition components included in the mixtures allows us to expand the range of variation of thermodynamic parameters of the mixtures under shock wave loading. The calculation model is based on the assumption that all components of mixture under shock-wave loading are in thermodynamic equilibrium (model TEC). The model TEC allows us to describe the region of the polymorphic phase transition, considering the material in the region of phase transition as a mixture of low-pressure phase and high-pressure phase. The good agreement of these model calculations with the data of different authors defined on the basis of experiments is obtained. Thermodynamic parameters of the nitrides mixture, solid and porous mixtures with quartz as component were reliably described. This model is useful for determining the compositions and volume fractions of the components of the mixture to obtain the specified parameters of solid and porous materials under shock-wave loading.
High pressure phase transition and variation of elastic constants of diluted magnetic semiconductors
NASA Astrophysics Data System (ADS)
Varshney, Dinesh; Sharma, P.; Kaurav, N.; Shah, S.; Singh, R. K.
2004-11-01
A theoretical study of the high-pressure phase transition and elastic behavior in diluted magnetic semiconductors Zn0.83Mn0.17Se, using a three-body interaction (TBI) potential caused by the electron-shell deformation of the overlapping ions is carried out. The estimated values of phase transition pressure and the vast volume discontinuity in pressure-volume (PV) phase diagram indicate the structural phase transition from zincblende (B3) to rock salt (B1). The variation of second-order elastic constants with pressure resembles that observed in some binary semiconductors. The inconsistency in the deduced value of pressure derivative of second order elastic constant with the available data is attributed to the fact that we derive expressions neglecting thermal effects and assuming the overlap repulsion significant only up to nearest neighbors. The vdW interaction is effective in obtaining the thermodynamical parameters such as Debye temperature, Gruneisen parameter, thermal expansion coefficient, compressibility as well phase stability in diluted magnetic semiconductors. It is revealed that TBI model has a promise to predict the phase transition pressure and the pressure variation of elastic constants of other semiconductors as well.
Reentrant phase transitions of higher-dimensional AdS black holes in dRGT massive gravity
NASA Astrophysics Data System (ADS)
Zou, De-Cheng; Yue, Ruihong; Zhang, Ming
2017-04-01
We study the P- V criticality and phase transition in the extended phase space of anti-de Sitter (AdS) black holes in higher-dimensional de Rham, Gabadadze and Tolley (dRGT) massive gravity, treating the cosmological constant as pressure and the corresponding conjugate quantity is interpreted as thermodynamic volume. Besides the usual small/large black hole phase transitions, the interesting thermodynamic phenomena of reentrant phase transitions (RPTs) are observed for black holes in all d≥6-dimensional spacetime when the coupling coefficients c_i m^2 of massive potential satisfy some certain conditions.
Safety performance of traffic phases and phase transitions in three phase traffic theory.
Xu, Chengcheng; Liu, Pan; Wang, Wei; Li, Zhibin
2015-12-01
Crash risk prediction models were developed to link safety to various phases and phase transitions defined by the three phase traffic theory. Results of the Bayesian conditional logit analysis showed that different traffic states differed distinctly with respect to safety performance. The random-parameter logit approach was utilized to account for the heterogeneity caused by unobserved factors. The Bayesian inference approach based on the Markov Chain Monte Carlo (MCMC) method was used for the estimation of the random-parameter logit model. The proposed approach increased the prediction performance of the crash risk models as compared with the conventional logit model. The three phase traffic theory can help us better understand the mechanism of crash occurrences in various traffic states. The contributing factors to crash likelihood can be well explained by the mechanism of phase transitions. We further discovered that the free flow state can be divided into two sub-phases on the basis of safety performance, including a true free flow state in which the interactions between vehicles are minor, and a platooned traffic state in which bunched vehicles travel in successions. The results of this study suggest that a safety perspective can be added to the three phase traffic theory. The results also suggest that the heterogeneity between different traffic states should be considered when estimating the risks of crash occurrences on freeways.
Pontine respiratory activity involved in inspiratory/expiratory phase transition
Mörschel, Michael; Dutschmann, Mathias
2009-01-01
Control of the timing of the inspiratory/expiratory (IE) phase transition is a hallmark of respiratory pattern formation. In principle, sensory feedback from pulmonary stretch receptors (Breuer–Hering reflex, BHR) is seen as the major controller for the IE phase transition, while pontine-based control of IE phase transition by both the pontine Kölliker–Fuse nucleus (KF) and parabrachial complex is seen as a secondary or backup mechanism. However, previous studies have shown that the BHR can habituate in vivo. Thus, habituation reduces sensory feedback, so the role of the pons, and specifically the KF, for IE phase transition may increase dramatically. Pontine-mediated control of the IE phase transition is not completely understood. In the present review, we discuss existing models for ponto-medullary interaction that may be involved in the control of inspiratory duration and IE transition. We also present intracellular recordings of pontine respiratory units derived from an in situ intra-arterially perfused brainstem preparation of rats. With the absence of lung inflation, this preparation generates a normal respiratory pattern and many of the recorded pontine units demonstrated phasic respiratory-related activity. The analysis of changes in membrane potentials of pontine respiratory neurons has allowed us to propose a number of pontine-medullary interactions not considered before. The involvement of these putative interactions in pontine-mediated control of IE phase transitions is discussed. PMID:19651653
Computer simulation of fluid phase transitions
NASA Astrophysics Data System (ADS)
Wilding, Nigel B.
2001-11-01
The goal of accurately locating fluid phase boundaries by means of computer simulation is hampered by difficulties associated with sampling both coexisting phases in a single simulation. We explain the background to these difficulties and describe how they can be tackled using a synthesis of biased Monte Carlo sampling and histogram extrapolation methods, in conjunction with a standard fluid simulation algorithm. The combined approach provides a powerful method for tracing fluid phase boundaries.
Phase transitions in ferroelectric silicon doped hafnium oxide
NASA Astrophysics Data System (ADS)
Böscke, T. S.; Teichert, St.; Bräuhaus, D.; Müller, J.; Schröder, U.; Böttger, U.; Mikolajick, T.
2011-09-01
We investigated phase transitions in ferroelectric silicon doped hafnium oxide (FE-Si:HfO2) by temperature dependent polarization and x-ray diffraction measurements. If heated under mechanical confinement, the orthorhombic ferroelectric phase reversibly transforms into a phase with antiferroelectric behavior. Without confinement, a transformation into a monoclinic/tetragonal phase mixture is observed during cooling. These results suggest the existence of a common higher symmetry parent phase to the orthorhombic and monoclinic phases, while transformation between these phases appears to be inhibited by an energy barrier.
On the theory of phase transitions in magnetic fluids
Zubarev, A. Yu. Iskakova, L. Yu.
2007-11-15
Particles of magnetic fluids (ferrofluids), as is known from experiments, can condense to bulk dense phases at low temperatures (that are close to room temperature) in response to an external magnetic field. It is also known that a uniform external magnetic field increases the threshold temperature of the observed condensation, thus stimulating the condensation process. Within the framework of early theories, this phenomenon is interpreted as a classical gas-liquid phase transition in a system of individual particles involved in a dipole-dipole interaction. However, subsequent investigations have revealed that, before the onset of a bulk phase transition, particles can combine to form a chain cluster or, possibly, a topologically more complex heterogeneous cluster. In an infinitely strong magnetic field, the formation of chains apparently suppresses the onset of a gas-liquid phase transition and the condensation of magnetic particles most likely proceeds according to the scenario of a gas-solid phase transition with a wide gap between spinodal branches. This paper reports on the results of investigations into the specific features of the condensation of particles in the absence of an external magnetic field. An analysis demonstrates that, despite the formation of chains, the condensation of particles in this case can proceed according to the scenario of a gas-liquid phase transition with a critical point in the continuous binodal. Consequently, a uniform magnetic field not only can stimulate the condensation phase transition in a system of magnetic particles but also can be responsible for a qualitative change in the scenario of the phase transition. This inference raises the problem regarding a threshold magnetic field in which there occurs a change in the scenario of the phase transition.
Goldwire, H.C. Jr.; Rodean, H.C.; Cederwall, R.T.; Kansa, E.J.; Koopman, R.P.; McClure, J.W.; McRae, T.G.; Morris, L.K.; Kamppinen, L.; Kiefer, R.D.
1983-10-01
The Coyote series of liquefied natural gas (LNG) spill experiments was performed at the Naval Weapons Center (NWC), China Lake, California, during the summer and fall of 1981. These tests were a joint effort of the Lawrence Livermore National Laboratory (LLNL) and the NWC and were sponsored by the US Department of Energy (DOE) and the Gas Research Institute. There were ten Coyote experiments, five primarily for the study of vapor dispersion and burning vapor clouds, and five for investigating the occurrence of rapid-phase-transition (RPT) explosions. Each of the last four of the five RPT tests consisted of a series of three spills. Seven experiments were with LNG, two were with liquid methane (LCH/sub 4/), and one was with liquid nitrogen (LN/sub 2/). Three arrays of instrumentation were deployed. An array of RPT diagnostic instruments was concentrated at the spill pond and was operated during all of the tests, vapor burn as well as RPT. The wind-field array was operated during the last nine experiments to define the wind direction and speed in the area upwind and downwind of the spill pond. The gas-dispersion array was deployed mostly downwind of the spill pond to measure gas concentration, humidity, temperature, ground heat flux, infrared (IR) radiation, and flame-front passage during three of the vapor dispersion and burn experiments (Coyotes 3, 5, and 6). High-speed color motion pictures were taken during every test, and IR imagery (side and overhead) was obtained during some vapor-burn experiments. Data was obtained by radiometers during Coyotes 3, 6, and 7. This report presents a comprehensive selection of the data obtained. It does not include any data analysis except that required to determine the test conditions and the reliability of the data. Data analysis is to be reported in other publications. 19 references, 76 figures, 13 tables.
Phase transitions in simplified models with long-range interactions
NASA Astrophysics Data System (ADS)
Rocha Filho, T. M.; Amato, M. A.; Mello, B. A.; Figueiredo, A.
2011-10-01
We study the origin of phase transitions in several simplified models with long-range interactions. For the self-gravitating ring model, we are unable to observe a possible phase transition predicted by Nardini and Casetti [Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.80.060103 80, 060103R (2009).] from an energy landscape analysis. Instead we observe a sharp, although without any nonanalyticity, change from a core-halo to a core-only configuration in the spatial distribution functions for low energies. By introducing a different class of solvable simplified models without any critical points in the potential energy we show that a behavior similar to the thermodynamics of the ring model is obtained, with a first-order phase transition from an almost homogeneous high-energy phase to a clustered phase and the same core-halo to core configuration transition at lower energies. We discuss the origin of these features for the simplified models and show that the first-order phase transition comes from the maximization of the entropy of the system as a function of energy and an order parameter, as previously discussed by Hahn and Kastner [Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.72.056134 72, 056134 (2005); Eur. Phys. J. BEPJBFY1434-602810.1140/epjb/e2006-00100-7 50, 311 (2006)], which seems to be the main mechanism causing phase transitions in long-range interacting systems.
Thin Film Phase Transition Materials Development Program
1985-04-01
clearly appropriate. Re ference 1. Verleur, Barker and Berglund, Phys. Rev. 172, 788 (1968). r 2U VOUGHT S MOT H 8000A 803-14A *ALL SAPPHIRE #RES. RAT...shift can occur effect- ing a change from equally spaced V ions to a homopolar V-V bonding pairs. These two transitions occur similtaneously in pure...The secondary homopolar V-V bonding/metallic V-V bonding transition, is also effected by the Ti substitu- tion because the 3d* configuration
Orientational phase transitions and the assembly of viral capsids
NASA Astrophysics Data System (ADS)
Dharmavaram, Sanjay; Xie, Fangming; Klug, William; Rudnick, Joseph; Bruinsma, Robijn
2017-06-01
We present a Landau theory for large-l orientational phase transitions and apply it to the assembly of icosahedral viral capsids. The theory predicts two distinct types of ordering transitions. Transitions dominated by the l =6 ,10 ,12 , and 18 icosahedral spherical harmonics resemble robust first-order phase transitions that are not significantly affected by chirality. The remaining transitions depend essentially on including mixed l states denoted as l =15 +16 corresponding to a mixture of l =15 and l =16 spherical harmonics. The l =15 +16 transition is either continuous or weakly first-order and it is strongly influenced by chirality, which suppresses spontaneous chiral symmetry breaking. The icosahedral state is in close competition with states that have tetrahedral, D5, and octahedral symmetries. We present a group-theoretic method to analyze the competition between the different symmetries. The theory is applied to a variety of viral shells.
Space shuttle phase B extension, volume 1
NASA Technical Reports Server (NTRS)
1971-01-01
In order to define a system which would significantly reduce payload delivery costs, activities were extended to modifications of the reusable space shuttle design concept. Considered were systems using orbiters with external propellant tanks and an interim expendable booster which allowed phased development of the usable orbiter and booster. Analyzed were: Merits of internal and external propellant tanks and the impact of external LH2 compared to L02 and LH2; impact of cargo bay size; impact abort; merit of expendable booster options; and merit of a phased development program. Studies showed that external L02/LH2 and the continued use of the J-2S engine on the orbiter reduced program cost and risk.
Preliminary CALS Phase II Architecture. Volume 19
1989-07-03
IDEF ICAM Definition Languages 5 IDEFO ICAM Definition Language: Activity Modeling IDEFIX ICAM Definition Language: Data Modeling 3 IDS Integrated Design...level. At the Conceptual Description level, data are defined by an integrated semantic data model, such as those produced using the IDEFIX modeling...Architecture with the dominate focus on the data dictionary for the IWSDB, represented by an IDEFIX semantic data model. It is at this level that CALS Phase II
Simulation of structural phase transitions in NiTi
NASA Astrophysics Data System (ADS)
Mutter, Daniel; Nielaba, Peter
2010-12-01
By means of molecular-dynamics simulations, temperature-driven diffusionless structural phase transitions in equiatomic and nearly equiatomic ordered nickel-titanium alloys were investigated. For this purpose, a model potential from the literature was adopted [W. S. Lai and B. X. Liu, J. Phys.: Condens. Matter 12, L53 (2000)10.1088/0953-8984/12/5/101], which is based on the tight-binding model in second moment approximation. The model predicts a stable B19' phase at low temperatures and a nearly cubic B2 phase at high temperatures. After an analysis of crystallography and energetics of the emerging structures, the experimentally known strong dependence of transition temperatures on composition is confirmed and related to lattice instability. Free-energy calculations finally give insight into the driving forces of the phase transitions and reveal free energy barriers inhibiting them below the transition temperatures.
D2-D1 phase transition of columnar liquid crystals
NASA Astrophysics Data System (ADS)
Sun, Y. F.; Swift, J.
1986-04-01
The D2-D1 phase transition in columnar liquid crystals of the HAT series [e.g., HAT11 (triphenelene hexa-n-dodecanoate)] is discussed within the framework of Landau theory. The order parameters which describe the transition are abstracted from a tensor density function, and are associated with two irreducible representations of the symmetry group of the high-temperature D2 phase. A mechanism for a first-order transition is then suggested in accordance with both theoretical considerations and the experimental result for the D2-D1 transition. Two possible arrangements of the herringbone structure of the D1 phase are obtained, each of which gives six orientational states in the low-temperature D1 phase.
Quantum phase transition detected through one-dimensional ballistic conductance
NASA Astrophysics Data System (ADS)
Bayat, Abolfazl; Kumar, Sanjeev; Pepper, Michael; Bose, Sougato
2017-07-01
A quantum phase transition is an unequivocal signature of strongly correlated many-body physics. Signatures of such phenomena are yet to be observed in ballistic transport through quantum wires. Recent developments in quantum wires have made it possible to enhance the interaction between the electrons. Here we show that hitherto unexplained anticrossing between conduction energy subbands, observed in such experiments, can be explained through a simple yet effective discretized model which undergoes a second-order quantum phase transition within the Ising universality class. Accordingly, we observe how the charge distribution, transverse to the direction of the wire, will vary across the phase transition. We show that data coming from three different samples with differing electron densities and gate voltages show a remarkable universal scaling behavior, determined by the relevant critical exponent, which is only possible near a quantum phase transition.
Intrinsic response of polymer liquid crystals in photochemical phase transition
Ikeda, Tomiki; Sasaki, Takeo; Kim, Haengboo )
1991-01-24
Time-resolved measurements were performed on the photochemically induced isothermal phase transition of polymer liquid crystals (PLC) with mesogenic side chains of phenyl benzoate (PAPB3) and cyanobiphenyl (PACB3) under conditions wherein the photochemical reaction of the doped photoresponsive molecule (4-butyl-4-{prime}-methoxyazobenzene, BMAB) was completed within {approximately} 10 ns, and the subsequent phase transition of the matrix PLC from nematic (N) to isotropic (I) state was followed by time-resolved measurements of the birefringence of the system. Formation of a sufficient amount of the cis isomer of BMAB with a single pulse of a laser lowered the N-I phase transition temperature of the mixture, inducing the N-I phase transition of PLCs isothermally in a time range of {approximately} 200 ms. This time range is comparable to that of low molecular weight liquid crystals, indicating that suppression in mobility of mesogens in PLCs does not affect significantly the thermodynamically controlled process.
Depressed Phase Transition in Solution-Grown VO2 Nanostructures
Whittaker, L.; Jaye, C; Fu, Z; Fischer, D; Banerjee, S
2009-01-01
The first-order metal-insulator phase transition in VO{sub 2} is characterized by an ultrafast several-orders-of-magnitude change in electrical conductivity and optical transmittance, which makes this material an attractive candidate for the fabrication of optical limiting elements, thermochromic coatings, and Mott field-effect transistors. Here, we demonstrate that the phase-transition temperature and hysteresis can be tuned by scaling VO{sub 2} to nanoscale dimensions. A simple hydrothermal protocol yields anisotropic free-standing single-crystalline VO{sub 2} nanostructures with a phase-transition temperature depressed to as low as 32 C from 67 C in the bulk. The observations here point to the importance of carefully controlling the stochiometry and dimensions of VO{sub 2} nanostructures to tune the phase transition in this system.
Depressed phase transition in solution-grown VO2 nanostructures.
Whittaker, Luisa; Jaye, Cherno; Fu, Zugen; Fischer, Daniel A; Banerjee, Sarbajit
2009-07-01
The first-order metal-insulator phase transition in VO(2) is characterized by an ultrafast several-orders-of-magnitude change in electrical conductivity and optical transmittance, which makes this material an attractive candidate for the fabrication of optical limiting elements, thermochromic coatings, and Mott field-effect transistors. Here, we demonstrate that the phase-transition temperature and hysteresis can be tuned by scaling VO(2) to nanoscale dimensions. A simple hydrothermal protocol yields anisotropic free-standing single-crystalline VO(2) nanostructures with a phase-transition temperature depressed to as low as 32 degrees C from 67 degrees C in the bulk. The observations here point to the importance of carefully controlling the stoichiometry and dimensions of VO(2) nanostructures to tune the phase transition in this system.
Magnetic phase transitions in samarium iron garnet
NASA Astrophysics Data System (ADS)
Geller, S.; Balestrino, G.
1980-05-01
Mössbauer spectroscopy has shown that there are at least three magnetic phases of samarium iron garnet and possibly five, if spin reorientations that are not abrupt are assumed to occur between these phases. The easy magnetic axes are: [111], 560>T>~60 K; [110], ~45>T>~18 K; [100], ~10>T>=5 K. The spin reorientations are estimated to occur between ~60 and ~45 K and between ~18 and ~10 K. While the phases with the [111] and [110] easy magnetic axis have been reported before, this is the first report of the lowest-temperature phase with [100] easy magnetic axis, and of the possible spin reorientations. If the latter exist, the lowest-temperature phase cannot be tetragonal; it is most likely orthorhomic. The sequence of magnetic space groups is: R3¯c',[111]-->F2'd'-->Fdd'd', [110]-->I2'c'-->Ibc'a', [100].
Magnetic phase transitions in samarium iron garnet
Geller, S.; Balestrino, G.
1980-05-01
Moessbauer spectroscopy has shown that there are at least three magnetic phases of samarium iron garnet and possibly five, if spin reorientations that are not abrupt are assumed to occur between these phases. The easy magnetic axes are: (111), 560>T> or approx. =60 K; (110), approx. 45>T> or approx. =18 K; (100), approx. 10>T > or = 5 K. The spin reorientations are estimated to occur between approx. 60 and approx. 45 K and between approx. 18 and approx. 10 K. While the phases with the (111) and (110) easy magnetic axis have been reported before, this is the first report of the lowest-temperature phase with (100) easy magnetic axis, and of the possible spin reorientations. If the latter exist, the lowest-temperature phase can not be tetragonal; it is most likely orthorhombic. The sequence of magnetic space groups is: R3c', (111) ..-->.. F2'/d' ..-->.. Fdd'd', (110) ..-->.. I2'/c' ..-->.. Ibc'a', (100).
Thermodynamic properties and phase transitions in CO2 molecular clusters
NASA Technical Reports Server (NTRS)
Etters, R. D.; Flurchick, K.; Pan, R. P.; Chandrasekharan, V.
1981-01-01
The thermodynamic properties of (CO2)N molecular aggregates of size N between 2 and 13 have been investigated. These crystallites exhibit well defined orientational order-disorder rotational transitions accompanied by a structural transition into a plastic crystallite phase. In addition, they exhibit melting and disassociation transitions. It is shown that the interpretation of experimental data, based upon dimer properties, depends crucially on these results. Equilibrium structures and orientations are also given.
Decoupling of structural and electronic phase transitions in VO2.
Tao, Zhensheng; Han, Tzong-Ru T; Mahanti, Subhendra D; Duxbury, Phillip M; Yuan, Fei; Ruan, Chong-Yu; Wang, Kevin; Wu, Junqiao
2012-10-19
Using optical, TEM, and ultrafast electron diffraction experiments we find that single crystal VO(2) microbeams gently placed on insulating substrates or metal grids exhibit different behaviors, with structural and metal-insulator transitions occurring at the same temperature for insulating substrates, while for metal substrates a new monoclinic metal phase lies between the insulating monoclinic phase and the metallic rutile phase. The structural and electronic phase transitions in these experiments are strongly first order and we discuss their origins in the context of current understanding of multiorbital splitting, strong correlation effects, and structural distortions that act cooperatively in this system.
Structure, Hydrodynamics, and Phase Transition of Freely Suspended Liquid Crystals
NASA Technical Reports Server (NTRS)
Clark, Noel A.
2000-01-01
Smectic liquid crystals are phases of rod shaped molecules organized into one dimensionally (1D) periodic arrays of layers, each layer being between one and two molecular lengths thick. In the least ordered smectic phases, the smectics A and C, each layer is a two dimensional (2D) liquid. Additionally there are a variety of more ordered smectic phases having hexatic short range translational order or 2D crystalline quasi long range translational order within the layers. The inherent fluid-layer structure and low vapor pressure of smectic liquid crystals enable the long term stabilization of freely suspended, single component, layered fluid films as thin as 30A, a single molecular layer. The layering forces the films to be an integral number of smectic layers thick, quantizing their thickness in layer units and forcing a film of a particular number of layers to be physically homogeneous with respect to its layer structure over its entire area. Optical reflectivity enables the precise determination of the number of layers. These ultrathin freely suspended liquid crystal films are structures of fundamental interest in condensed matter and fluid physics. They are the thinnest known stable condensed phase fluid structures and have the largest surface-to-volume ratio of any stable fluid preparation, making them ideal for the study of the effects of reduced dimensionality on phase behavior and on fluctuation and interface phenomena. Their low vapor pressure and quantized thickness enable the effective use of microgravity to extend the study of basic capillary phenomena to ultrathin fluid films. Freely suspended films have been a wellspring of new liquid crystal physics. They have been used to provide unique experimental conditions for the study of condensed phase transitions in two dimensions. They are the only system in which the hexatic has been unambiguously identified as a phase of matter, and the only physical system in which fluctuations of a 2D XY system and
Colossal magnetic phase transition asymmetry in mesoscale FeRh stripes
NASA Astrophysics Data System (ADS)
Uhlíř, V.; Arregi, J. A.; Fullerton, E. E.
2016-10-01
Coupled order parameters in phase-transition materials can be controlled using various driving forces such as temperature, magnetic and electric field, strain, spin-polarized currents and optical pulses. Tuning the material properties to achieve efficient transitions would enable fast and low-power electronic devices. Here we show that the first-order metamagnetic phase transition in FeRh films becomes strongly asymmetric in mesoscale structures. In patterned FeRh stripes we observed pronounced supercooling and an avalanche-like abrupt transition from the ferromagnetic to the antiferromagnetic phase, while the reverse transition remains nearly continuous over a broad temperature range. Although modest asymmetry signatures have been found in FeRh films, the effect is dramatically enhanced at the mesoscale. The activation volume of the antiferromagnetic phase is more than two orders of magnitude larger than typical magnetic heterogeneities observed in films. The collective behaviour upon cooling results from the role of long-range ferromagnetic exchange correlations that become important at the mesoscale and should be a general property of first-order metamagnetic phase transitions.
Colossal magnetic phase transition asymmetry in mesoscale FeRh stripes
Uhlíř, V.; Arregi, J. A.; Fullerton, E. E.
2016-01-01
Coupled order parameters in phase-transition materials can be controlled using various driving forces such as temperature, magnetic and electric field, strain, spin-polarized currents and optical pulses. Tuning the material properties to achieve efficient transitions would enable fast and low-power electronic devices. Here we show that the first-order metamagnetic phase transition in FeRh films becomes strongly asymmetric in mesoscale structures. In patterned FeRh stripes we observed pronounced supercooling and an avalanche-like abrupt transition from the ferromagnetic to the antiferromagnetic phase, while the reverse transition remains nearly continuous over a broad temperature range. Although modest asymmetry signatures have been found in FeRh films, the effect is dramatically enhanced at the mesoscale. The activation volume of the antiferromagnetic phase is more than two orders of magnitude larger than typical magnetic heterogeneities observed in films. The collective behaviour upon cooling results from the role of long-range ferromagnetic exchange correlations that become important at the mesoscale and should be a general property of first-order metamagnetic phase transitions. PMID:27725642
The QCD phase transitions: From mechanism to observables
Shuryak, E.V.
1997-09-22
This paper contains viewgraphs on quantum chromodynamic phase transformations during heavy ion collisions. Some topics briefly described are: finite T transitions of I molecule pairs; finite density transitions of diquarks polymers; and the softtest point of the equation of state as a source of discontinuous behavior as a function of collision energy or centrality.
Phase transitions in two-line ferrihydrite nanoparticles
NASA Astrophysics Data System (ADS)
Rani, Chandni; Tiwari, S. D.
2017-08-01
Two-line ferrihydrite nanoparticles are synthesized by a chemical method. The sample is characterized with X-ray diffractometer, thermogravimetric analyzer, differential scanning calorimeter, and vibrating sample magnetometer. The system is found to undergo two-phase transitions on heating. Nature of these transitions and magnetic behavior of original and heated samples are reported.
Quark-gluon plasma phase transition using cluster expansion method
NASA Astrophysics Data System (ADS)
Syam Kumar, A. M.; Prasanth, J. P.; Bannur, Vishnu M.
2015-08-01
This study investigates the phase transitions in QCD using Mayer's cluster expansion method. The inter quark potential is modified Cornell potential. The equation of state (EoS) is evaluated for a homogeneous system. The behaviour is studied by varying the temperature as well as the number of Charm Quarks. The results clearly show signs of phase transition from Hadrons to Quark-Gluon Plasma (QGP).
Hawking-Page phase transition on the brane
Chamblin, A.; Karch, A.
2005-09-15
We show that the Hawking-Page phase transition of a conformal field theory on AdS{sub d-1} weakly coupled to gravity has a dual bulk description in terms of a phase transition between a black string and a thermal gas on AdS{sub d}. At even lower temperatures the black string develops a Gregory Laflamme instability, which is dual to black hole evaporation in the boundary theory.
Partial dynamical symmetry at critical points of quantum phase transitions.
Leviatan, A
2007-06-15
We show that partial dynamical symmetries can occur at critical points of quantum phase transitions, in which case underlying competing symmetries are conserved exactly by a subset of states, and mix strongly in other states. Several types of partial dynamical symmetries are demonstrated with the example of critical-point Hamiltonians for first- and second-order transitions in the framework of the interacting boson model, whose dynamical symmetries correspond to different shape phases in nuclei.
Raman study of magnetic phase transitions of hexagonal manganites
NASA Astrophysics Data System (ADS)
Nam, Ji-Yeon; Hien, Nguyen T. M.; Huyen, Nguyen T.; Han, Kiok; Chen, Xiang-Bai; Cheong, S. W.; Lee, D.; Noh, T. W.; Sung, N. H.; Cho, B. K.; Yang, In-Sang
2014-03-01
Results of Raman studies of magnetic phase transitions of hexagonal LuMnO3 single crystal and HoMnO3 thin films are compared directly with the results of magnetic measurements. Our results show that the temperature dependent Raman study of magnon scattering provides a simple and accurate method for investigating magnetic phase transitions, especially in HoMnO3 thin films. In single crystal, our optical method provides results as good as magnetization measurements.
Phase transitions in nanostructured potassium nitrate
NASA Astrophysics Data System (ADS)
Naberezhnov, Aleksandr; Koroleva, Ekaterina; Rysiakiewicz-Pasek, Ewa; Fokin, Aleksandr; Sysoeva, Anna; Franz, Alexandra; Seregin, Maksim; Tovar, Mihael
2014-11-01
Dielectric properties and temperature evolution of the crystal structure of nanocomposites on the basis of porous glasses and KNO3 embedded into the pores have been studied on heating and cooling. It is shown that the stability of the ferroelectric phase depends on nanoparticle sizes and temperature prehistory of sample preparation and measurement procedure. The temperature interval, where the ferroelectric phase exists, increases on decreasing of the nanoparticle size. In the composite of KNO3 and porous glasses with the average pore diameters of 7 nm, the ferroelectric phase becomes stable down to 100 K after the first heating-cooling circle.
Bubble nucleation and growth in very strong cosmological phase transitions
NASA Astrophysics Data System (ADS)
Mégevand, Ariel; Ramírez, Santiago
2017-06-01
Strongly first-order phase transitions, i.e., those with a large order parameter, are characterized by a considerable supercooling and high velocities of phase transition fronts. A very strong phase transition may have important cosmological consequences due to the departures from equilibrium caused in the plasma. In general, there is a limit to the strength, since the metastability of the old phase may prevent the transition to complete. Near this limit, the bubble nucleation rate achieves a maximum and thus departs from the widely assumed behavior in which it grows exponentially with time. We study the dynamics of this kind of phase transitions. We show that in some cases a gaussian approximation for the nucleation rate is more suitable, and in such a case we solve analytically the evolution of the phase transition. We compare the gaussian and exponential approximations with realistic cases and we determine their ranges of validity. We also discuss the implications for cosmic remnants such as gravitational waves.
Liquid-Liquid Phase Transition and Glass Transition in a Monoatomic Model System
Xu, Limei; Buldyrev, Sergey V.; Giovambattista, Nicolas; Stanley, H. Eugene
2010-01-01
We review our recent study on the polyamorphism of the liquid and glass states in a monatomic system, a two-scale spherical-symmetric Jagla model with both attractive and repulsive interactions. This potential with a parametrization for which crystallization can be avoided and both the glass transition and the liquid-liquid phase transition are clearly separated, displays water-like anomalies as well as polyamorphism in both liquid and glassy states, providing a unique opportunity to study the interplay between the liquid-liquid phase transition and the glass transition. Our study on a simple model may be useful in understanding recent studies of polyamorphism in metallic glasses. PMID:21614201
Structural phase transition and antiferromagnetic transition of Tb3RuO7
NASA Astrophysics Data System (ADS)
Hinatsu, Yukio; Doi, Yoshihiro
2014-12-01
Magnetic properties and structural phase transition of terbium ruthenate Tb3RuO7 are investigated through magnetic susceptibility, specific heat, high-temperature X-ray diffraction and differential scanning calorimetry measurements. The structural phase transition from space group P21nb to Cmcm has been observed at 402 K. Tb3RuO7 shows an antiferromagnetic transition at 17 K. In addition, another magnetic anomaly has been found at 10 K. Analysis of the magnetic specific heat for Tb3RuO7 indicates that the magnetic transitions at 10 and 17 K are due to the magnetic ordering of Tb3+ and Ru5+ ions, respectively.
Giant elastic tunability in strained BiFeO3 near an electrically induced phase transition
Yu, Pu; Vasudevan, Rama K.; Tselev, Alexander; ...
2015-01-01
Elastic anomalies are signatures of phase transitions in condensed matters and have traditionally been studied using various techniques spanning from neutron scattering to static mechanical testing. Here, using band-excitation elastic/piezoresponse spectroscopy, we probed sub-MHz elastic dynamics of a tip bias-induced rhombohedral–tetragonal phase transition of strained (001)-BiFeO3 (rhombohedral) ferroelectric thin films from ~103 nm3 sample volumes. Near this transition, we observed that the Young's modulus intrinsically softens by over 30% coinciding with 2-3 folds enhancement of local piezoresponse. Coupled with phase-field modeling, we also addressed the influence of polarization switching and mesoscopic structural heterogeneities (e.g., domain walls) on the kinetics ofmore » this phase transition, thereby providing fresh insights into the morphotropic phase boundary (MPB) in ferroelectrics. Moreover, the giant electrically tunable elastic stiffness and corresponding electromechanical properties observed here suggest potential applications of BiFeO3 in next-generation frequency-agile electroacoustic devices, based on utilization of the soft modes underlying successive ferroelectric phase transitions.« less
Giant elastic tunability in strained BiFeO3 near an electrically induced phase transition
Li, Q; Cao, Y.; Yu, P.; Vasudevan, R. K.; Laanait, N.; Tselev, A.; Xue, F.; Chen, L. Q.; Maksymovych, P.; Kalinin, S. V.; Balke, N.
2015-01-01
Elastic anomalies are signatures of phase transitions in condensed matters and have traditionally been studied using various techniques spanning from neutron scattering to static mechanical testing. Here, using band-excitation elastic/piezoresponse spectroscopy, we probed sub-MHz elastic dynamics of a tip bias-induced rhombohedral−tetragonal phase transition of strained (001)-BiFeO3 (rhombohedral) ferroelectric thin films from ∼103 nm3 sample volumes. Near this transition, we observed that the Young's modulus intrinsically softens by over 30% coinciding with two- to three-fold enhancement of local piezoresponse. Coupled with phase-field modelling, we also addressed the influence of polarization switching and mesoscopic structural heterogeneities (for example, domain walls) on the kinetics of this phase transition, thereby providing fresh insights into the morphotropic phase boundary in ferroelectrics. Furthermore, the giant electrically tunable elastic stiffness and corresponding electromechanical properties observed here suggest potential applications of BiFeO3 in next-generation frequency-agile electroacoustic devices, based on the utilization of the soft modes underlying successive ferroelectric phase transitions. PMID:26597483
Phase transition process in DDAB supported lipid bilayer
NASA Astrophysics Data System (ADS)
Isogai, Takumi; Nakada, Sakiko; Yoshida, Naoya; Sumi, Hayato; Tero, Ryugo; Harada, Shunta; Ujihara, Toru; Tagawa, Miho
2017-06-01
We report the results of microscope measurements examining the phase transition process of a cationic lipid, Dimethyldioctadecylammonium bromide (DDAB) supported lipid bilayer (SLB). Due to lateral fluidity and strong electrostatic interaction with DNA, SLB serves as a fluid substrate for assembling 2D lattices of DNA functionalized nanoparticles (DNA-NPs): lipid molecules work as carriers for transporting DNA-NPs. By fluorescence microscopy and atomic force microscopy (AFM), two types of phase transitions, which correspond to liquid crystalline-gel and liquid crystalline-interdigitated gel (LβI) ones, were observed in DDAB SLB during cooling. In thermal equilibrium at room temperature both gel and LβI phases have enough adsorbed amounts of DNA-NPs which indicate that both domains have enough surface charge densities for adsorbing DNA-NPs, however, during phase transition DNA-NPs preferably distributed into LβI phase.
Thermodynamic phase transitions in a frustrated magnetic metamaterial.
Anghinolfi, L; Luetkens, H; Perron, J; Flokstra, M G; Sendetskyi, O; Suter, A; Prokscha, T; Derlet, P M; Lee, S L; Heyderman, L J
2015-09-21
Materials with interacting magnetic degrees of freedom display a rich variety of magnetic behaviour that can lead to novel collective equilibrium and out-of-equilibrium phenomena. In equilibrium, thermodynamic phases appear with the associated phase transitions providing a characteristic signature of the underlying collective behaviour. Here we create a thermally active artificial kagome spin ice that is made up of a large array of dipolar interacting nanomagnets and undergoes phase transitions predicted by microscopic theory. We use low energy muon spectroscopy to probe the dynamic behaviour of the interacting nanomagnets and observe peaks in the muon relaxation rate that can be identified with the critical temperatures of the predicted phase transitions. This provides experimental evidence that a frustrated magnetic metamaterial can be engineered to admit thermodynamic phases.
Models for a liquid-liquid phase transition
NASA Astrophysics Data System (ADS)
Buldyrev, S. V.; Franzese, G.; Giovambattista, N.; Malescio, G.; Sadr-Lahijany, M. R.; Scala, A.; Skibinsky, A.; Stanley, H. E.
2002-02-01
We use molecular dynamics simulations to study two- and three-dimensional models with the isotropic double-step potential which in addition to the hard core has a repulsive soft core of larger radius. Our results indicate that the presence of two characteristic repulsive distances (hard core and soft core) is sufficient to explain liquid anomalies and a liquid-liquid phase transition, but these two phenomena may occur independently. Thus liquid-liquid transitions may exist in systems like liquid metals, regardless of the presence of the density anomaly. For 2D, we propose a model with a specific set of hard core and soft core parameters, that qualitatively reproduces the phase diagram and anomalies of liquid water. We identify two solid phases: a square crystal (high density phase), and a triangular crystal (low density phase) and discuss the relation between the anomalies of liquid and the polymorphism of the solid. Similarly to real water, our 2D system may have the second critical point in the metastable liquid phase beyond the freezing line. In 3D, we find several sets of parameters for which two fluid-fluid phase transition lines exist: the first line between gas and liquid and the second line between high-density liquid (HDL) and low-density liquid (LDL). In all cases, the LDL phase shows no density anomaly in 3D. We relate the absence of the density anomaly with the positive slope of the LDL-HDL phase transition line.
Paraelectric-antiferroelectric phase transition in achiral liquid crystals
NASA Astrophysics Data System (ADS)
Pociecha, Damian; Gorecka, Ewa; Čepič, Mojca; Vaupotič, Nataša; Gomola, Kinga; Mieczkowski, Jozef
2005-12-01
Critical freezing of molecular rotation in an achiral smectic phase, which leads to polar ordering through the second order paraelectric-antiferroelectric (Sm-A→Sm-APA) phase transition is studied theoretically and experimentally. Strong softening of the polar mode in the Sm-A phase and highly intensive dielectric mode in the Sm-APA phase are observed due to weak antiferroelectric interactions in the system. In the Sm-APA phase the dielectric response behaves critically upon biasing by a dc electric field. Such a behavior is found general for the antiferroelectric smectic phase with significant quadrupolar interlayer coupling.
Modeling liquid-liquid phase transitions and quasicrystal formation
NASA Astrophysics Data System (ADS)
Skibinsky, Anna
In this thesis, studies which concern two different subjects related to phase transitions in fluids and crystalline solids are presented. Condensed matter formation, structure, and phase transitions are modeled using molecular dynamics simulations of simple discontinuous potentials with attractive and repulsive interactions. Novel phase diagrams are proposed for quasicrystals, crystals, and liquids. In the first part of the thesis, the formation of a quasicrystal in a two dimensional monodisperse system is investigated using molecular dynamics simulations of hard sphere particles interacting via a two-dimensional square-well potential. It is found that for certain values of the square-well parameters more than one stable crystalline phase can form. By quenching the liquid phase at a very low temperature, an amorphous phase is obtained. When this the amorphous phase is heated, a quasicrystalline structure with five-fold symmetry forms. From estimations of the Helmholtz potentials of the stable crystalline phases and of the quasicrystal, it is concluded that within a specific temperature range, the observed quasicrystal phase can be the stable phase. The second part of the thesis concerns a study of the liquid-liquid phase transition for a single-component system in three dimensions, interacting via an isotropic potential with a repulsive soft-core shoulder at short distance and an attractive well at an intermediate distance. The potential is similar to potentials used to describe such liquid systems as colloids, protein solutions, or liquid metals. It is shown that the phase diagram for such a potential can have two lines of first-order fluid-fluid phase transitions: one separating a gas and a low-density liquid (LDL), and another between the LDL and a high-density liquid (HDL). Both phase transition lines end in a critical point, a gas-LDL critical point and, depending on the potential parameters, either a gas-HDL critical point or a LDL-HDL critical point. A
Discontinuous phase transitions via cooperative contagion
NASA Astrophysics Data System (ADS)
Ghanbarnejad, Fakhteh; Cai, Weiran; Chen, Li; Grassberger, Peter
2015-03-01
We study the spreading of two diseases that interact cooperatively (the presence of one helps the other one to spread) on different network topologies, and with two microscopic realizations, both of which are stochastic versions of an SIR type studied by us recently in mean field approximation. We had shown that cooperativity can lead to discontinuous transitions (DT). However, due to the rapid mixing implied by the mean field assumption, DTs were seen only when there were finite (non-zero) densities of sick individuals in the initial state.In this paper we find that the results for the stochastic model depend strongly on the underlying network. In particular, DTs are found when there are few short but many long loops: (i) No DTs exist on trees, due to the absence of loops; (ii) On 2-d lattices with local contacts there are no DTs either, but because of too many short loops; (iii) We do find DTs on Erdos-Renyi (ER) networks, on d-dimensional lattices with d >= 4 ,and on 2-d lattices with sufficiently long-ranged contacts; (iv) On 3-d lattices with local contacts the results depend on the microscopic details of the implementation. All found discontinuous transitions are of ``hybrid'' type, i.e. they display also scaling features usually associated with continuous transitions.
Generic finite size scaling for discontinuous nonequilibrium phase transitions into absorbing states
NASA Astrophysics Data System (ADS)
de Oliveira, M. M.; da Luz, M. G. E.; Fiore, C. E.
2015-12-01
Based on quasistationary distribution ideas, a general finite size scaling theory is proposed for discontinuous nonequilibrium phase transitions into absorbing states. Analogously to the equilibrium case, we show that quantities such as response functions, cumulants, and equal area probability distributions all scale with the volume, thus allowing proper estimates for the thermodynamic limit. To illustrate these results, five very distinct lattice models displaying nonequilibrium transitions—to single and infinitely many absorbing states—are investigated. The innate difficulties in analyzing absorbing phase transitions are circumvented through quasistationary simulation methods. Our findings (allied to numerical studies in the literature) strongly point to a unifying discontinuous phase transition scaling behavior for equilibrium and this important class of nonequilibrium systems.
Pressure-induced series of phase transitions in sodium azide
NASA Astrophysics Data System (ADS)
Zhu, Hongyang; Zhang, Fuxiang; Ji, Cheng; Hou, Dongbin; Wu, Jianzhe; Hannon, Trevor; Ma, Yangzhang
2013-01-01
The phase analysis of sodium azide (NaN3) has been investigated by in situ synchrotron X-ray diffraction measurements in a diamond anvil cell up to 52.0 GPa at room temperature. Three pressure-induced phase transitions were observed. The phase transition pressures were determined to be 0.3, 17.3, and 28.7 GPa verified by three different pressure transmitting media. The first high pressure phase, α-NaN3 (0.3 ˜ 17.3 GPa), was identified to be monoclinic with a C2/m space group. The β-NaN3 to α-NaN3 transition is a second-order phase transition, accompanied by the shearing of the Na-layers and the tilting of the azide chains. The second high pressure phase, γ-NaN3 (18.4 ˜ 28.7 GPa), has a lower symmetry than the α-NaN3. A further phase transition of γ-NaN3 to δ-NaN3 at 28.7 GPa was observed.
Phase Transitions in Antibody Solutions: from Pharmaceuticals to Human Disease
NASA Astrophysics Data System (ADS)
Wang, Ying; Lomakin, Aleksey; Benedek, George; Dana Farber Cancer Institute Collaboration; Amgen Inc. Collaboration
2014-03-01
Antibodies are very important proteins. Natural antibodies play essential role in the immune system of human body. Pharmaceutical antibodies are used as drugs. Antibodies are also indispensable tools in biomedical research and diagnostics. Recently, a number of observations of phase transitions of pharmaceutical antibodies have been reported. These phase transitions are undesirable from the perspective of colloid stability of drug solutions in processing and storage, but can be used for protein purification, X-ray crystallography, and improving pharmokinetics of drugs. Phase transitions of antibodies can also take place in human body, particularly in multiple myeloma patients who overproduce monoclonal antibodies. These antibodies, in some cases, crystallize at body temperature and cause severe complications called cryoglobulinemia. I will present the results of our current studies on phase transitions of both pharmaceutical antibodies and cryoglobulinemia-associated antibodies. These studies have shown that different antibodies have different propensity to undergo phase transitions, but their phase behavior has universal features which are remarkably different from those of spherical proteins. I will discuss how studies of phase behavior can be useful in assessing colloid stability of pharmaceutical antibodies and in early diagnostics of cryoglobulinemia, as well as general implications of the fact that some antibodies can precipitate at physiological conditions.
Density Functional Theory for Phase-Ordering Transitions
Wu, Jianzhong
2016-03-30
Colloids display astonishing structural and dynamic properties that can be dramatically altered by modest changes in the solution condition or an external field. This complex behavior stems from a subtle balance of colloidal forces and intriguing mesoscopic and macroscopic phase transitions that are sensitive to the processing conditions and the dispersing environment. Whereas the knowledge on the microscopic structure and phase behavior of colloidal systems at equilibrium is now well-advanced, quantitative predictions of the dynamic properties and the kinetics of phase-ordering transitions in colloids are not always realized. Many important mesoscopic and off-equilibrium colloidal states remain poorly understood. The proposed research aims to develop a new, unifying approach to describe colloidal dynamics and the kinetics of phase-ordering transitions based on accomplishments from previous work for the equilibrium properties of both uniform and inhomogeneous systems and on novel concepts from the state-of-the-art dynamic density functional theory. In addition to theoretical developments, computational research is designed to address a number of fundamental questions on phase-ordering transitions in colloids, in particular those pertinent to a competition of the dynamic pathways leading to various mesoscopic structures, off-equilibrium states, and crystalline phases. By providing a generic theoretical framework to describe equilibrium, metastable as well as non-ergodic phase transitions concurrent with the colloidal self-assembly processes, accomplishments from this work will have major impacts on both fundamental research and technological applications.
NASA Astrophysics Data System (ADS)
Samanta, Sudeshna; Li, Quanjun; Cheng, Benyuan; Huang, Yanwei; Pei, Cuiying; Wang, Qinglin; Ma, Yanzhang; Wang, Lin
2017-01-01
A comprehensive understanding of the physical origins of the phase transition behaviors of transition metal oxides is still complex due to the interplay among competing interactions of comparable strengths tuning their nature. Widespread interest in such phase transitions has motivated explorations of nanocrystalline vanadium dioxide (VO2) in various forms and a long-running debate persists over the roles played by electron-electron correlation with lattice distortion. External stimuli like pressure and temperature have strong effects on the appearance, stability, and spacial distribution of the high-resistive (HR) and low-resistive (LR) phases accompanying their structural modification. Our comprehensive experiments establish the pressure-induced and thermally driven evolution of phase coexistence in VO2(A ) nanorods. Our experimental evidence supports coexisting HR and LR phases, where compression suppressed coexistence at ˜7 GPa, followed by a semiconductor-semiconductor transition at around ˜10 GPa with the absence of pressure-induced metallization. X-ray diffraction revealed lattice distortion with local microscopic strain inhomogeneity in the nanorods, without any discontinuity in the pressure-volume data. We further investigated the vibrational modes and relaxations of the samples related to their thermal expansions. We also found that the pressure-dependent hierarchy of microstructural densification contributed significantly to the resulting transport properties.
Phase transition properties of YbN under pressure
NASA Astrophysics Data System (ADS)
Singh, Sanjay Kumar; Rana, P.; Nayak, V.; Verma, U. P.
2013-06-01
In the present paper, we have investigated the phase transition properties of Ytterbium nitride (YbN) under high pressure by using the full potential linear augmented plane wave plus local orbitals approach within the framework of density functional theory as implanted in the WIEN2k package. In this approach the generalized gradient approximation (GGA) is chosen for the exchange-correlation functional energy optimization for calculating the total energy. At ambient conditions YbN stabilize in NaCl (B1 phase) structure characterized by the space group Fm-3m. Under compression, it undergoes first-order structural transition from Fm-3m to Pm-3m (B2) phase at 51.73 GPa. On further increasing pressure it goes to body centred tetragonal (BCT) phase at 79.56 GPa. Under ambient conditions, the energy in B1 phase is found to be lower than that of B2 phase. At high pressures beyond B1 to B2 phase transition, the energy of B2 phase is found to be slightly lower than that in B1 phase. The structural properties viz., equilibrium lattice constants, bulk modulus, its pressure derivative and total energy are calculated in four different phases i.e. B1, B2, B3 (zinc blende), and BCT phases and compared with previous calculations and available experimental data.
Microscopic analysis of order parameters in nuclear quantum phase transitions
Li, Z. P.; Niksic, T.; Vretenar, D.; Meng, J.
2009-12-15
Microscopic signatures of nuclear ground-state shape phase transitions in Nd isotopes are studied using excitation spectra and collective wave functions obtained by diagonalization of a five-dimensional Hamiltonian for quadrupole vibrational and rotational degrees of freedom, with parameters determined by constrained self-consistent relativistic mean-field calculations for triaxial shapes. As a function of the physical control parameter, the number of nucleons, energy gaps between the ground state and the excited vibrational states with zero angular momentum, isomer shifts, and monopole transition strengths exhibit sharp discontinuities at neutron number N=90, which is characteristic of a first-order quantum phase transition.
Writhe induced phase transition in unknotted self-avoiding polygons
NASA Astrophysics Data System (ADS)
Dagrosa, E.; Owczarek, A. L.; Prellberg, T.
2017-09-01
Recently it has been argued that weighting the writhe of unknotted self-avoiding polygons can be related to possible experiments that turn double stranded DNA. We first solve exactly a directed model and demonstrate that in such a subset of polygons the problem of weighting their writhe is associated with a phase transition. We then analyse simulations using the Wang-Landau algorithm to observe scaling in the fluctuations of the writhe that is compatible with a second-order phase transition in a undirected self-avoiding polygon model. The transition can be clearly detected when the polygon is stretched with a strong pulling force.
Exotic phase transitions of k -cores in clustered networks
NASA Astrophysics Data System (ADS)
Bhat, Uttam; Shrestha, Munik; Hébert-Dufresne, Laurent
2017-01-01
The giant k -core—maximal connected subgraph of a network where each node has at least k neighbors—is important in the study of phase transitions and in applications of network theory. Unlike Erdős-Rényi graphs and other random networks where k -cores emerge discontinuously for k ≥3 , we show that transitive linking (or triadic closure) leads to 3-cores emerging through single or double phase transitions of both discontinuous and continuous nature. We also develop a k -core calculation that includes clustering and provides insights into how high-level connectivity emerges.
Phase Transition to Bundles of Flexible Supramolecular Polymers
NASA Astrophysics Data System (ADS)
Huisman, B. A. H.; Bolhuis, P. G.; Fasolino, A.
2008-05-01
We report Monte Carlo simulations of the self-assembly of supramolecular polymers based on a model of patchy particles. We find a first-order phase transition, characterized by hysteresis and nucleation, toward a solid bundle of polymers, of length much greater than the average gas phase length. We argue that the bundling transition is the supramolecular equivalent of the sublimation transition, which results from a weak chain-chain interaction. We provide a qualitative equation of state that gives physical insight beyond the specific values of the parameters used in our simulations.
Constant volume gas cell optical phase-shifter
Phillion, Donald W.
2002-01-01
A constant volume gas cell optical phase-shifter, particularly applicable for phase-shifting interferometry, contains a sealed volume of atmospheric gas at a pressure somewhat different than atmospheric. An optical window is present at each end of the cell, and as the length of the cell is changed, the optical path length of a laser beam traversing the cell changes. The cell comprises movable coaxial tubes with seals and a volume equalizing opening. Because the cell is constant volume, the pressure, temperature, and density of the contained gas do not change as the cell changes length. This produces an exactly linear relationship between the change in the length of the gas cell and the change in optical phase of the laser beam traversing it. Because the refractive index difference between the gas inside and the atmosphere outside is very much the same, a large motion must be made to change the optical phase by the small fraction of a wavelength that is required by phase-shifting interferometry for its phase step. This motion can be made to great fractional accuracy.
Pore volume accessibility of particulate and monolithic stationary phases.
Urban, Jiří
2015-05-29
A chromatographic characterization of pore volume accessibility for both particulate and monolithic stationary phases is presented. Size-exclusion calibration curves have been used to determine the pore volume fraction that is accessible for six alkylbenzenes and twelve polystyrene standards in tetrahydrofuran as the mobile phase. Accessible porosity has been then correlated with the size of the pores from which individual compounds are just excluded. I have determined pore volume accessibility of commercially available columns packed with fully and superficially porous particles, as well as with silica-based monolithic stationary phase. I also have investigated pore accessibility of polymer-based monolithic stationary phases. Suggested protocol is used to characterize pore formation at the early stage of the polymerization, to evaluate an extent of hypercrosslinking during modification of pore surface, and to characterize the pore accessibility of monolithic stationary phases hypercrosslinked after an early termination of polymerization reaction. Pore volume accessibility was also correlated to column efficiency of both particulate and monolithic stationary phases. Copyright © 2015 Elsevier B.V. All rights reserved.
New numerical method to study phase transitions and its applications
Lee, Jooyoung; Kosterlitz, J.M.
1991-11-01
We present a powerful method of identifying the nature of transitions by numerical simulation of finite systems. By studying the finite size scaling properties of free energy barrier between competing states, we can identify unambiguously a weak first order transition even when accessible system sizes are L/{xi} < 0.05 as in the five state Potts model in two dimensions. When studying a continuous phase transition we obtain quite accurate estimates of critical exponents by treating it as a field driven first order transition. The method has been successfully applied to various systems.
Phase transitions in biogenic amorphous calcium carbonate
Gong, Yutao U. T.; Killian, Christopher E.; Olson, Ian C.; Appathurai, Narayana P.; Amasino, Audra L.; Martin, Michael C.; Holt, Liam J.; Wilt, Fred H.; Gilbert, P. U. P. A.
2012-01-01
Crystalline biominerals do not resemble faceted crystals. Current explanations for this property involve formation via amorphous phases. Using X-ray absorption near-edge structure (XANES) spectroscopy and photoelectron emission microscopy (PEEM), here we examine forming spicules in embryos of Strongylocentrotus purpuratus sea urchins, and observe a sequence of three mineral phases: hydrated amorphous calcium carbonate (ACC·H2O) → dehydrated amorphous calcium carbonate (ACC) → calcite. Unexpectedly, we find ACC·H2O-rich nanoparticles that persist after the surrounding mineral has dehydrated and crystallized. Protein matrix components occluded within the mineral must inhibit ACC·H2O dehydration. We devised an in vitro, also using XANES-PEEM, assay to identify spicule proteins that may play a role in stabilizing various mineral phases, and found that the most abundant occluded matrix protein in the sea urchin spicules, SM50, stabilizes ACC·H2O in vitro. PMID:22492931
Kinetics of solid-solid phase transitions in metals using proton radiography (u)
Schwartz, Cynthia L; Rigg, Paulo A; Hixson, Rob S; Jensen, Brian J
2011-01-25
When a compressed material changes phase it doesn't do so instantly. Instead it transitions through a mixed phase as it transforms to the end state phase for a given pressure, volume and temperature. Common phase diagrams show the phase boundaries as sharp lines when compression has been slowly applied and held for an infinite amount of time. When the compression is applied with high strain rate, however, the phase boundaries are no longer crisp as the kinetic effects of the crystal reorientation delay the transitions, resulting in regions of mixed phase. This opens up the possibility that some degree of metastability exists for such transition in dynamic compression. The compression path can go past the equilibrium phase boundary and the transition happen from a metastable state because of the very short timescale of the compression process. Molecular dynamics (MD) simulations recently have been used to examine shock-induced phase transitions in single crystal materials illustrating an orientation dependence of the transition stress, mechanisms, kinetics, and Hugoniot response. For example, the [100] orientation of iron had a simulated transition stress higher than the experimentally determined polycrystalline value of 13 GPa by 2 GPa. Previously, dynamic experiments on iron have observed a non-zero transition time and width in the solid-solid {alpha}-{var_epsilon} phase transition. Using Proton Radiography at the Los Alamos Neutron Science Center, we have performed plate impact experiments on iron to further study the {alpha}-{var_epsilon} phase transition which occurs at 13 GPa. A 40mm bore powder gun was coupled to a proton radiography beam line and imaging system and synchronized to the impact of the projectile on the target sample with the proton beam pattern. A typical experimental configuration for the iron study, as shown below in 3 color-enhanced radiographs, is a 40mm diameter aluminum sabot impacting a 40mm diameter sample of polycrystalline ARMCO iron
Solid-solid phase transitions via melting in metals.
Pogatscher, S; Leutenegger, D; Schawe, J E K; Uggowitzer, P J; Löffler, J F
2016-04-22
Observing solid-solid phase transitions in-situ with sufficient temporal and spatial resolution is a great challenge, and is often only possible via computer simulations or in model systems. Recently, a study of polymeric colloidal particles, where the particles mimic atoms, revealed an intermediate liquid state in the transition from one solid to another. While not yet observed there, this finding suggests that such phenomena may also occur in metals and alloys. Here we present experimental evidence for a solid-solid transition via the formation of a metastable liquid in a 'real' atomic system. We observe this transition in a bulk glass-forming metallic system in-situ using fast differential scanning calorimetry. We investigate the corresponding transformation kinetics and discuss the underlying thermodynamics. The mechanism is likely to be a feature of many metallic glasses and metals in general, and may provide further insight into phase transition theory.
Solid-solid phase transitions via melting in metals
NASA Astrophysics Data System (ADS)
Pogatscher, S.; Leutenegger, D.; Schawe, J. E. K.; Uggowitzer, P. J.; Löffler, J. F.
2016-04-01
Observing solid-solid phase transitions in-situ with sufficient temporal and spatial resolution is a great challenge, and is often only possible via computer simulations or in model systems. Recently, a study of polymeric colloidal particles, where the particles mimic atoms, revealed an intermediate liquid state in the transition from one solid to another. While not yet observed there, this finding suggests that such phenomena may also occur in metals and alloys. Here we present experimental evidence for a solid-solid transition via the formation of a metastable liquid in a `real' atomic system. We observe this transition in a bulk glass-forming metallic system in-situ using fast differential scanning calorimetry. We investigate the corresponding transformation kinetics and discuss the underlying thermodynamics. The mechanism is likely to be a feature of many metallic glasses and metals in general, and may provide further insight into phase transition theory.
Spin-current probe for phase transition in an insulator
Qiu, Zhiyong; Li, Jia; Hou, Dazhi; Arenholz, Elke; N'Diaye, Alpha T.; Tan, Ali; Uchida, Ken-ichi; Sato, Koji; Okamoto, Satoshi; Tserkovnyak, Yaroslav; Qiu, Z. Q.; Saitoh, Eiji
2016-01-01
Spin fluctuation and transition have always been one of the central topics of magnetism and condensed matter science. Experimentally, the spin fluctuation is found transcribed onto scattering intensity in the neutron-scattering process, which is represented by dynamical magnetic susceptibility and maximized at phase transitions. Importantly, a neutron carries spin without electric charge, and therefore it can bring spin into a sample without being disturbed by electric energy. However, large facilities such as a nuclear reactor are necessary. Here we show that spin pumping, frequently used in nanoscale spintronic devices, provides a desktop microprobe for spin transition; spin current is a flux of spin without an electric charge and its transport reflects spin excitation. We demonstrate detection of antiferromagnetic transition in ultra-thin CoO films via frequency-dependent spin-current transmission measurements, which provides a versatile probe for phase transition in an electric manner in minute devices. PMID:27573443
Spin-current probe for phase transition in an insulator.
Qiu, Zhiyong; Li, Jia; Hou, Dazhi; Arenholz, Elke; N'Diaye, Alpha T; Tan, Ali; Uchida, Ken-Ichi; Sato, Koji; Okamoto, Satoshi; Tserkovnyak, Yaroslav; Qiu, Z Q; Saitoh, Eiji
2016-08-30
Spin fluctuation and transition have always been one of the central topics of magnetism and condensed matter science. Experimentally, the spin fluctuation is found transcribed onto scattering intensity in the neutron-scattering process, which is represented by dynamical magnetic susceptibility and maximized at phase transitions. Importantly, a neutron carries spin without electric charge, and therefore it can bring spin into a sample without being disturbed by electric energy. However, large facilities such as a nuclear reactor are necessary. Here we show that spin pumping, frequently used in nanoscale spintronic devices, provides a desktop microprobe for spin transition; spin current is a flux of spin without an electric charge and its transport reflects spin excitation. We demonstrate detection of antiferromagnetic transition in ultra-thin CoO films via frequency-dependent spin-current transmission measurements, which provides a versatile probe for phase transition in an electric manner in minute devices.
Solid–solid phase transitions via melting in metals
Pogatscher, S.; Leutenegger, D.; Schawe, J. E. K.; Uggowitzer, P. J.; Löffler, J. F.
2016-01-01
Observing solid–solid phase transitions in-situ with sufficient temporal and spatial resolution is a great challenge, and is often only possible via computer simulations or in model systems. Recently, a study of polymeric colloidal particles, where the particles mimic atoms, revealed an intermediate liquid state in the transition from one solid to another. While not yet observed there, this finding suggests that such phenomena may also occur in metals and alloys. Here we present experimental evidence for a solid–solid transition via the formation of a metastable liquid in a ‘real' atomic system. We observe this transition in a bulk glass-forming metallic system in-situ using fast differential scanning calorimetry. We investigate the corresponding transformation kinetics and discuss the underlying thermodynamics. The mechanism is likely to be a feature of many metallic glasses and metals in general, and may provide further insight into phase transition theory. PMID:27103085
Spin-current probe for phase transition in an insulator
Qiu, Zhiyong; Li, Jia; Hou, Dazhi; Arenholz, Elke; N’Diaye, Alpha T.; Tan, Ali; Uchida, Ken-ichi; Sato, Koji; Okamoto, Satoshi; Tserkovnyak, Yaroslav; Qiu, Z. Q.; Saitoh, Eiji
2016-08-30
Spin fluctuation and transition have always been one of the central topics of magnetism and condensed matter science. Experimentally, the spin fluctuation is found transcribed onto scattering intensity in the neutron-scattering process, which is represented by dynamical magnetic susceptibility and maximized at phase transitions. Importantly, a neutron carries spin without electric charge, and therefore it can bring spin into a sample without being disturbed by electric energy. However, large facilities such as a nuclear reactor are necessary. Here we present that spin pumping, frequently used in nanoscale spintronic devices, provides a desktop microprobe for spin transition; spin current is a flux of spin without an electric charge and its transport reflects spin excitation. Additionally, we demonstrate detection of antiferromagnetic transition in ultra-thin CoO films via frequency-dependent spin-current transmission measurements, which provides a versatile probe for phase transition in an electric manner in minute devices.
Spin-current probe for phase transition in an insulator
Qiu, Zhiyong; Li, Jia; Hou, Dazhi; ...
2016-08-30
Spin fluctuation and transition have always been one of the central topics of magnetism and condensed matter science. Experimentally, the spin fluctuation is found transcribed onto scattering intensity in the neutron-scattering process, which is represented by dynamical magnetic susceptibility and maximized at phase transitions. Importantly, a neutron carries spin without electric charge, and therefore it can bring spin into a sample without being disturbed by electric energy. However, large facilities such as a nuclear reactor are necessary. Here we present that spin pumping, frequently used in nanoscale spintronic devices, provides a desktop microprobe for spin transition; spin current is amore » flux of spin without an electric charge and its transport reflects spin excitation. Additionally, we demonstrate detection of antiferromagnetic transition in ultra-thin CoO films via frequency-dependent spin-current transmission measurements, which provides a versatile probe for phase transition in an electric manner in minute devices.« less
Spin-current probe for phase transition in an insulator
NASA Astrophysics Data System (ADS)
Qiu, Zhiyong; Li, Jia; Hou, Dazhi; Arenholz, Elke; N'diaye, Alpha T.; Tan, Ali; Uchida, Ken-Ichi; Sato, Koji; Okamoto, Satoshi; Tserkovnyak, Yaroslav; Qiu, Z. Q.; Saitoh, Eiji
2016-08-01
Spin fluctuation and transition have always been one of the central topics of magnetism and condensed matter science. Experimentally, the spin fluctuation is found transcribed onto scattering intensity in the neutron-scattering process, which is represented by dynamical magnetic susceptibility and maximized at phase transitions. Importantly, a neutron carries spin without electric charge, and therefore it can bring spin into a sample without being disturbed by electric energy. However, large facilities such as a nuclear reactor are necessary. Here we show that spin pumping, frequently used in nanoscale spintronic devices, provides a desktop microprobe for spin transition; spin current is a flux of spin without an electric charge and its transport reflects spin excitation. We demonstrate detection of antiferromagnetic transition in ultra-thin CoO films via frequency-dependent spin-current transmission measurements, which provides a versatile probe for phase transition in an electric manner in minute devices.
First-order phase transitions in the real microcanonical ensemble
NASA Astrophysics Data System (ADS)
Schierz, Philipp; Zierenberg, Johannes; Janke, Wolfhard
2016-08-01
We present a simulation and data analysis technique to investigate first-order phase transitions and the associated transition barriers. The simulation technique is based on the real microcanonical ensemble where the sum of kinetic and potential energy is kept constant. The method is tested for the droplet condensation-evaporation transition in a Lennard-Jones system with up to 2048 particles at fixed density, using simple Metropolis-like sampling combined with a replica-exchange scheme. Our investigation of the microcanonical ensemble properties reveals that the associated transition barrier is significantly lower than in the canonical counterpart. Along the line of investigating the microcanonical ensemble behavior, we develop a framework for general ensemble evaluations. This framework is based on a clear separation between system-related and ensemble-related properties, which can be exploited to specifically tailor artificial ensembles suitable for first-order phase transitions.
Irreversible phase transitions and wave propagation in silicate geologic materials
Swegle, J.W. )
1990-08-15
Shock and unloading experiments on quartz and silicate rocks indicate that the release adiabats lie below the Hugoniot. The hysteresis and energy dissipation inherent in this situation have important wave propagation implications. On loading, there is a pressure-induced transition to the stishovite phase which does not occur under conditions of thermodynamic equilibrium, in that the Hugoniot passes through a metastable mixed-phase region for several tens of GPa. One interpretation of the unloading data is that the transition is not reversible, and the phase mixture remains frozen on unloading. However, material strength may also play a role. A complete thermodynamically consistent equation of state which includes phase transitions and strength effects has been developed and used to examine shock and release data on quartz and silicate rocks in order to quantify the kinetics of the reverse transition and to separate the hysteretic effects due to reverse phase transition kinetics from those due to material strength. The model allows quantitative determination of the effect of reverse transition kinetics on ground shock propagation in silicate materials.
Irreversible phase transitions and wave propagation in silicate geologic materials
Swegle, J.W.
1989-08-01
Shock and unloading experiments on quartz and silicate rocks indicate that the release adiabats lie below the Hugoniot. The hysteresis and energy dissipation inherent in this situation have important wave propagation implications. On loading, there is a pressure-induced transition to the stishovite phase which is not abrupt, with the Hugoniot passing through a metastable mixed phase region for several tens of GPa. One interpretation of the unloading data is that the transition is not reversible, and the material remains in a frozen phase mixture on initial unloading. However, material strength may also play a role. A complete thermodynamically consistent EOS which includes phase transitions and strength effects has been developed and used to examine shock and release data on quartz and silicate rocks in order to quantify the kinetics of the reverse transition and to separate the hysteretic effects due to phase transition kinetics from those due to material strength. The model also allows quantitative determination of the effect of transition kinetics on ground shock propagation in silicate materials. 51 refs., 46 figs., 3 tabs.
Irreversible phase transition and wave propagation in silicate geologic materials
Swegle, J.W.
1989-01-01
Shock and unloading experiments on quartz and silicate rocks indicate the release adiabats lie below the Hugoniot. The hysteresis and energy dissipation inherent in this situation have important wave propagation implications. On loading, there is pressure-induced transition to the stishovite phase which is not abrupt, with the Hugoniot passing through a metastable mixed phase region for several tens of GPa. One interpretation of the unloading data is that the transition is not reversible, and the material remains in a frozen phase mixture on initial unloading. However, material strength may also play a role. A complete thermodynamically consistent EOS which includes phase transitions and strength effects has been developed and used to examine shock and release data on quartz and silicate rocks in order to quantify the kinetics of the reverse transition and to separate the hysteretic effects due to phase transition kinetics from those due to material strength. The model allows quantitative determination of the effect of transition kinetics on ground shock propagation in silicate materials. 7 refs., 6 figs.
Microstructural fingerprints of phase transitions in shock-loaded iron
NASA Astrophysics Data System (ADS)
Wang, S. J.; Sui, M. L.; Chen, Y. T.; Lu, Q. H.; Ma, E.; Pei, X. Y.; Li, Q. Z.; Hu, H. B.
2013-01-01
The complex structural transformation in crystals under static pressure or shock loading has been a subject of long-standing interest to materials scientists and physicists. The polymorphic transformation is of particular importance for iron (Fe), due to its technological and sociological significance in the development of human civilization, as well as its prominent presence in the earth's core. The martensitic transformation α-->ɛ (bcc-->hcp) in iron under shock-loading, due to its reversible and transient nature, requires non-trivial detective work to uncover its occurrence. Here we reveal refined microstructural fingerprints, needle-like colonies and three sets of {112}<111> twins with a threefold symmetry, with tell-tale features that are indicative of two sequential martensitic transformations in the reversible α-->ɛ phase transition, even though no ɛ is retained in the post-shock samples. The signature orientation relationships are consistent with previously-proposed transformation mechanisms, and the unique microstructural fingerprints enable a quantitative assessment of the volume fraction transformed.
The formation of topological defects in phase transitions
NASA Technical Reports Server (NTRS)
Hodges, Hardy M.
1989-01-01
It was argued, and fought through numerical work that the results of non-dynamical Monte Carlo computer simulations cannot be applied to describe the formation of topological defects when the correlation length at the Ginzburg temperature is significantly smaller than the horizon size. To test the current hypothesis that infinite strings at formation are essentially described by Brownian walks of size the correlation length at the Ginzburg temperature, fields at the Ginzburg temperature were equilibrated. Infinite structure do not exist in equilibrium for reasonable definitions of the Ginzburg temperature, and horizons must be included in a proper treatment. A phase transition, from small-scale to large-scale string or domain wall structure, is found to occur very close to the Ginzburg temperature, in agreement with recent work. The formation process of domain walls and global strings were investigated through the breaking of initially ordered states. To mimic conditions in the early Universe, cooling times are chosen so that horizons exist in the sample volume when topological structure formation occurs. The classical fields are evolved in real-time by the numerical solution of Langevin equations of motion on a three dimensional spatial lattice. The results indicate that it is possible for most of the string energy to be in small loops, rather than in long strings, at formation.
Cascading dynamics on random networks: crossover in phase transition.
Liu, Run-Ran; Wang, Wen-Xu; Lai, Ying-Cheng; Wang, Bing-Hong
2012-02-01
In a complex network, random initial attacks or failures can trigger subsequent failures in a cascading manner, which is effectively a phase transition. Recent works have demonstrated that in networks with interdependent links so that the failure of one node causes the immediate failures of all nodes connected to it by such links, both first- and second-order phase transitions can arise. Moreover, there is a crossover between the two types of transitions at a critical system-parameter value. We demonstrate that these phenomena can occur in the more general setting where no interdependent links are present. A heuristic theory is derived to estimate the crossover and phase-transition points, and a remarkable agreement with numerics is obtained.
Cascading dynamics on random networks: Crossover in phase transition
NASA Astrophysics Data System (ADS)
Liu, Run-Ran; Wang, Wen-Xu; Lai, Ying-Cheng; Wang, Bing-Hong
2012-02-01
In a complex network, random initial attacks or failures can trigger subsequent failures in a cascading manner, which is effectively a phase transition. Recent works have demonstrated that in networks with interdependent links so that the failure of one node causes the immediate failures of all nodes connected to it by such links, both first- and second-order phase transitions can arise. Moreover, there is a crossover between the two types of transitions at a critical system-parameter value. We demonstrate that these phenomena can occur in the more general setting where no interdependent links are present. A heuristic theory is derived to estimate the crossover and phase-transition points, and a remarkable agreement with numerics is obtained.
Domain wall formation in late-time phase transitions
NASA Technical Reports Server (NTRS)
Kolb, Edward W.; Wang, Yun
1992-01-01
We examine domain wall formulation in late time phase transitions. We find that in the invisible axion domain wall phenomenon, thermal effects alone are insufficient to drive different parts of the disconnected vacuum manifold. This suggests that domain walls do not form unless either there is some supplemental (but perhaps not unreasonable) dynamics to localize the scalar field responsible for the phase transition to the low temperature maximum (to an extraordinary precision) before the onset of the phase transition, or there is some non-thermal mechanism to produce large fluctuations in the scalar field. The fact that domain wall production is not a robust prediction of late time transitions may suggest future directions in model building.
Structural phase transitions and topological defects in ion Coulomb crystals
Partner, Heather L.; Nigmatullin, Ramil; Burgermeister, Tobias; Keller, Jonas; Pyka, Karsten; Plenio, Martin B.; Retzker, Alex; Zurek, Wojciech Hubert; del Campo, Adolfo; Mehlstaubler, Tanja E.
2014-11-19
We use laser-cooled ion Coulomb crystals in the well-controlled environment of a harmonic radiofrequency ion trap to investigate phase transitions and defect formation. Topological defects in ion Coulomb crystals (kinks) have been recently proposed for studies of nonlinear physics with solitons and as carriers of quantum information. Defects form when a symmetry breaking phase transition is crossed non-adiabatically. For a second order phase transition, the Kibble-Zurek mechanism predicts that the formation of these defects follows a power law scaling in the rate of the transition. We demonstrate a scaling of defect density and describe kink dynamics and stability. We further discuss the implementation of mass defects and electric fields as first steps toward controlled kink preparation and manipulation.
Origin of time before inflation from a topological phase transition
NASA Astrophysics Data System (ADS)
Bellini, Mauricio
2017-09-01
We study the origin of the universe (or pre-inflation) by suggesting that the primordial space-time in the universe suffered a global topological phase transition, from a 4D Euclidean manifold to an asymptotic 4D hyperbolic one. We introduce a complex time, τ, such that its real part becomes dominant after started the topological phase transition. Before the big bang, τ is a space-like coordinate, so that can be considered as a reversal variable. After the phase transition is converted in a causal variable. The formalism solves in a natural manner the quantum to classical transition of the geometrical relativistic quantum fluctuations: σ, which has a geometric origin.
Computation of temperature induced phase transitions at high pressure
NASA Astrophysics Data System (ADS)
Belonoshko, Anatoly
2014-03-01
Phase transitions at high pressure and temperature is perhaps one of the most controversial topics in high pressure science. There is a number of theoretical methods developed recently to address this problem. Unfortunately, none of them is fully satisfactory, considering stringent requirements to accuracy of the computed free energies of the involved phases. This, in part, explains the variety of the suggested methods. The experimental data is rather controversial as well, probably because the experiments at extreme conditions are difficult. I will provide overview of the theoretical methods that are applied for the computation and simulation of T-induced phase transitions. Both liquid-solid and solid-solid transitions will be covered. Possible sources of the disagreement between theoretical methods as well as between theory and experiment will be illustrated by examples. Insight from simulations will be used to suggest alternative explanations of experimental data. The optimal, at present, method to compute the transitions will be suggested.
Nonthermal solid-to-solid phase transitions in tungsten
NASA Astrophysics Data System (ADS)
Giret, Yvelin; Daraszewicz, Szymon L.; Duffy, Dorothy M.; Shluger, Alexander L.; Tanimura, Katsumi
2014-09-01
The ab initio calculations of phonon dispersions and nonthermal forces along structural deformation paths were used to study nonthermal solid-to-solid phase transitions in photoexcited tungsten. We assumed that electronic excitation can be described by an electronic temperature and demonstrated that nonthermal, i.e., caused purely by electronic excitation, bcc-to-fcc and bcc-to-hcp phase transitions can occur for electronic temperatures between 1.7 and 4.3 eV. These transitions result from soft modes along the Σ line of the Brillouin zone. Structural path calculations at different electronic temperatures indicate that both transitions are likely to take place in nonequilibrium conditions. We further predict that transient fcc and hcp phases of tungsten could be observed for several ps.
Pressure-induced reversible phase transition in thiourea dioxide crystal
Wang, Qinglei; Yan, Tingting; Zhu, Hongyang; Cui, Qiliang; Zou, Bo E-mail: zoubo@jlu.edu.cn; Wang, Kai E-mail: zoubo@jlu.edu.cn
2015-06-28
The effect of high pressure on the crystal structure of thiourea dioxide has been investigated by Raman spectroscopy and angle-dispersive X-ray diffraction (ADXRD) in a diamond anvil cell up to 10.3 GPa. The marked changes in the Raman spectra at 3.7 GPa strongly indicated a structural phase transition associated with the distortions of hydrogen bonding. There were no further changes up to the maximum pressure of 10.3 GPa and the observed transition was completely reversible when the system was brought back to ambient pressure. This transition was further confirmed by the changes of ADXRD spectra. The high-pressure phase was indexed and refined to an orthorhombic structure with a possible space group Pbam. The results from the first-principles calculations suggested that this phase transition was mainly related to the changes of hydrogen-bonded networks in thiourea dioxide.
Role of phonons in the metal-insulator phase transition.
NASA Technical Reports Server (NTRS)
Langer, W. D.
1972-01-01
Review, for the transition series oxides, of the Mattis and Lander model, which is one of electrons interacting with lattice vibrations (electron and phonon interaction). The model displays superconducting, insulating, and metallic phases. Its basic properties evolve from a finite crystallographic distortion associated with a dominant phonon mode and the splitting of the Brillouin zone into two subzones, a property of simple cubic and body centered cubic lattices. The order of the metal-insulator phase transition is examined. The basic model has a second-order phase transition and the effects of additional mechanisms on the model are calculated. The way in which these mechanisms affect the magnetically ordered transition series oxides as described by the Hubbard model is discussed.
Probing phase transitions of vortex matter by Josephson plasma resonance
NASA Astrophysics Data System (ADS)
Matsuda, Yuji
2001-03-01
The vortex matter in high-Tc superconductors exhibits a fascinatingly rich phase diagram with a variety of phase transitions. Recent investigations have revealed that the vortex phase is comprised of three distinct phases; vortex liquid, vortex glass, and Bragg glass. The most direct way to clarify the nature of these vortex phases and the phase transitions among them is to measure the interlayer phase coherence, because the CuO2 layers are connected by the Josephson effect. A most powerful probe for the interlayer phase coherence is the Josephson plasma resonance (JPR) which provides a direct measurement of the Josephson coupling energy U_J. Josephson plasma is a collective oscillation of Cooper pairs through the insulating layers. In Bi_2Sr_2CaCu_2O_8+d with large anisotropy, a very precise determination of UJ is possible because the plasma frequency ω_pl falls within the microwave window. Here we report the detailed and quantitative study of UJ in the vortex liquid, Bragg glass and vortex glass phases of Bi_2Sr_2CaCu_2O_8+d by the JPR. The measurements revealed distinct features in the T- and H-dependencies of ω_pl for each of these three vortex phases. When going across either the Bragg-to-vortex glass or the Bragg-to-liquid transition line, ω_pl shows a dramatic change. We provide a quantitative discussion on the properties of these phase transitions, including the first order nature of the Bragg-to-vortex glass transition.
Sample-dependent phase transitions in disordered exclusion models
NASA Astrophysics Data System (ADS)
Enaud, C.; Derrida, B.
2004-04-01
We give numerical evidence that the location of the first-order phase transition between the low- and the high-density phases of the one-dimensional asymmetric simple exclusion process with open boundaries becomes sample dependent when quenched disorder is introduced for the hopping rates.
Synchronization of Oscillators: An Ideal Introduction to Phase Transitions
ERIC Educational Resources Information Center
English, L. Q.
2008-01-01
The spontaneous synchronization of phase-coupled, non-identical oscillators is explored numerically via the famous Kuramoto model. The conditions for synchronization are examined as a function of the coupling network. I argue that such a numerical exploration provides a feasible way to introduce the topic of phase transitions early in the physics…
Synchronization of Oscillators: An Ideal Introduction to Phase Transitions
ERIC Educational Resources Information Center
English, L. Q.
2008-01-01
The spontaneous synchronization of phase-coupled, non-identical oscillators is explored numerically via the famous Kuramoto model. The conditions for synchronization are examined as a function of the coupling network. I argue that such a numerical exploration provides a feasible way to introduce the topic of phase transitions early in the physics…
Effect of dimensionality on vapor-liquid phase transition
Singh, Sudhir Kumar
2014-04-24
Dimensionality play significant role on ‘phase transitions’. Fluids in macroscopic confinement (bulk or 3-Dimensional, 3D) do not show significant changes in their phase transition properties with extent of confinement, since the number of molecules away from the surrounding surfaces is astronomically higher than the number of molecules in close proximity of the confining surfaces. In microscopic confinement (quasi 3D to quasi-2D), however, the number of molecules away from the close proximity of the surface is not as high as is the case with macroscopic (3D) confinement. Hence, under the same thermodynamic conditions ‘phase transition’ properties at microscopic confinement may not remain the same as the macroscopic or 3D values. Phase transitions at extremely small scale become very sensitive to the dimensions as well as the surface characteristics of the system. In this work our investigations reveal the effect of dimensionality on the phase transition from 3D to quasi-2D to 2D behavior. We have used grand canonical transition matrix Monte Carlo simulation to understand the vapor–liquid phase transitions from 3D to quasi-2D behavior. Such studies can be helpful in understanding and controlling the fluid film behaviour confined between solid surfaces of few molecular diameters, for example, in lubrication applications.
The Improper Ferroelectric Phase Transition of Magnesium-Chloride Boracite
NASA Astrophysics Data System (ADS)
Arakelian, Henry Edward
Laser Raman backscattering has been used to determine the Raman scattering strength as a function of temperature, in the ferroelectric phase of magnesium-chloride (Mg-Cl) boracite. Raman spectroscopy looks directly at the optical phonon responsible for the ferroelectric phase transition, at 142 cm('-1). Ferroelectricity may be explained by the Landau theory of second order phase transitions. The thermodynamic Gibbs potential is assumed to be expandable in terms of the phase transition's order parameter. Within this context there are two models, one proposed by V. Dvorak and another by A. Levanyuk, to explain the coupled (improper) phase transition of boracite. Dvorak takes the primary order parameter to be the lattice distorting mode, while Levanyuk assigns the polar mode as the order parameter. Both models adequately predict dielectric susceptibility vs. temperature. It is shown here how to calculate, for any coupled phase transition, the dielectric susceptibility, oscillator strength, spontaneous polarization, and polarization-optic coefficient. The polarization-optic coefficient is necessary to calculate the total Raman scattering strength. An expression is developed where the scattering strength is written as a combination of derivatives of the Gibbs potential and the Bose population factor. The models of Levanyuk and Dvorak are computer simulated and predict very different behavior of the scattering strength. The Dvorak model predicts a strong divergence in the intensity of Raman scattering at the critical temperature. The results of experiment do not show such a divergence and therefore confirm the Levanyuk model.
Quantum phase transition in Bose-Fermi mixtures
Ludwig, D.; Moroz, S.; Wetterich, C.; Floerchinger, S.
2011-09-15
We study a quantum Bose-Fermi mixture near a broad Feshbach resonance at zero temperature. Within a quantum field theoretical model, a two-step Gaussian approximation allows us to capture the main features of the quantum phase diagram. We show that a repulsive boson-boson interaction is necessary for thermodynamic stability. The quantum phase diagram is mapped in chemical-potential and density space, and both first- and second-order quantum phase transitions are found. We discuss typical characteristics of the first-order transition, such as hysteresis or a droplet formation of the condensate, which may be searched for experimentally.
Non-equilibrium quantum phase transition via entanglement decoherence dynamics
Lin, Yu-Chen; Yang, Pei-Yun; Zhang, Wei-Min
2016-01-01
We investigate the decoherence dynamics of continuous variable entanglement as the system-environment coupling strength varies from the weak-coupling to the strong-coupling regimes. Due to the existence of localized modes in the strong-coupling regime, the system cannot approach equilibrium with its environment, which induces a nonequilibrium quantum phase transition. We analytically solve the entanglement decoherence dynamics for an arbitrary spectral density. The nonequilibrium quantum phase transition is demonstrated as the system-environment coupling strength varies for all the Ohmic-type spectral densities. The 3-D entanglement quantum phase diagram is obtained. PMID:27713556
Non-equilibrium quantum phase transition via entanglement decoherence dynamics.
Lin, Yu-Chen; Yang, Pei-Yun; Zhang, Wei-Min
2016-10-07
We investigate the decoherence dynamics of continuous variable entanglement as the system-environment coupling strength varies from the weak-coupling to the strong-coupling regimes. Due to the existence of localized modes in the strong-coupling regime, the system cannot approach equilibrium with its environment, which induces a nonequilibrium quantum phase transition. We analytically solve the entanglement decoherence dynamics for an arbitrary spectral density. The nonequilibrium quantum phase transition is demonstrated as the system-environment coupling strength varies for all the Ohmic-type spectral densities. The 3-D entanglement quantum phase diagram is obtained.
Isotropic-nematic transition and cholesteric phases of helical Yukawa rods
NASA Astrophysics Data System (ADS)
Kuhnhold, A.; Schilling, T.
2016-11-01
We present a Monte Carlo simulation study of helical Yukawa rods as a model for chiral liquid crystal mesogens. To simulate the cholesteric phase, we introduce a new simulation method that uses soft walls and self-determined boundary conditions. We observe that the isotropic-nematic phase transition is shifted to lower volume fractions with decreasing salt concentration as well as with increasing internal pitch of the rods. For particular sets of interaction parameters, the sense of the cholesteric pitch inverts, i.e., depending on concentration, mesogens of a given handedness can produce cholesteric phases of both chiral senses.
Crystal structure, phase transition, and disorder in pyridinium methanesulfonate
NASA Astrophysics Data System (ADS)
Jesariew, Dominik; Ilczyszyn, Maria M.
2017-05-01
Thermal analysis, X-ray diffraction and vibrational spectroscopy have been used to investigate pyridinium methanesulfonate in order to verify its crystal structure and to have insight into its anomalous dynamical properties. This compound undergoes a solid-solid, reversible phase transition at 255.8/266.8 K (cooling/heating). It crystallizes in non-centrosymmetric Pna21 space group at the high-temperature phase (I) and in centrosymmetric Pbca one at the low-temperature phase (II). The entropy gain occurred at the II→I transition has shown that two independent orientations of ions in the disorder phase (I) are allowed. Infrared spectra have confirmed that the pyridinium cation as well as the -CH3 group of the anion exhibit changes in their dynamics when entering the phase I. These spectra have also suggested residual disorder of both, the pyridinium cation and the -CH3 group, in the low temperature phase (II).
Shear induced phase transitions induced in edible fats
NASA Astrophysics Data System (ADS)
Mazzanti, Gianfranco; Welch, Sarah E.; Marangoni, Alejandro G.; Sirota, Eric B.; Idziak, Stefan H. J.
2003-03-01
The food industry crystallizes fats under different conditions of temperature and shear to obtain products with desired crystalline phases. Milk fat, palm oil, cocoa butter and chocolate were crystallized from the melt in a temperature controlled Couette cell. Synchrotron x-ray diffraction studies were conducted to examine the role of shear on the phase transitions seen in edible fats. The shear forces on the crystals induced acceleration of the alpha to beta-prime phase transition with increasing shear rate in milk fat and palm oil. The increase was slow at low shear rates and became very strong above 360 s-1. In cocoa butter the acceleration between beta-prime-III and beta-V phase transition increased until a maximum of at 360 s-1, and then decreased, showing competition between enhanced heat transfer and viscous heat generation.
Finite-temperature phase transitions in the ionic Hubbard model
NASA Astrophysics Data System (ADS)
Kim, Aaram J.; Choi, M. Y.; Jeon, Gun Sang
2014-04-01
We investigate paramagnetic metal-insulator transitions in the infinite-dimensional ionic Hubbard model at finite temperatures. By means of the dynamical mean-field theory with an impurity solver of the continuous-time quantum Monte Carlo method, we show that an increase in the interaction strength brings about a crossover from a band insulating phase to a metallic one, followed by a first-order transition to a Mott insulating phase. The first-order transition turns into a crossover above a certain critical temperature, which becomes higher as the staggered lattice potential is increased. Further, analysis of the temperature dependence of the energy density discloses that the intermediate metallic phase is a Fermi liquid. It is also found that the metallic phase is stable against strong staggered potentials even at very low temperatures.
Experimental observation of phase-flip transitions in the brain
NASA Astrophysics Data System (ADS)
Dotson, Nicholas M.; Gray, Charles M.
2016-10-01
The phase-flip transition has been demonstrated in a host of coupled nonlinear oscillator models, many pertaining directly to understanding neural dynamics. However, there is little evidence that this phenomenon occurs in the brain. Using simultaneous microelectrode recordings in the nonhuman primate cerebral cortex, we demonstrate the presence of phase-flip transitions between oscillatory narrow-band local field potential signals separated by several centimeters. Specifically, we show that sharp transitions between in-phase and antiphase synchronization are accompanied by a jump in synchronization frequency. These findings are significant for two reasons. First, they validate predictions made by model systems. Second, they have potentially far reaching implications for our understanding of the mechanisms underlying corticocortical communication, which are thought to rely on narrow-band oscillatory synchronization with specific relative phase relationships.
Theory of interfacial phase transitions in surfactant systems
NASA Astrophysics Data System (ADS)
Shukla, K. P.; Payandeh, B.; Robert, M.
1991-06-01
The spin-1 Ising model, which is equivalent to the three-component lattice gas model, is used to study wetting transitions in three-component surfactant systems consisting of an oil, water, and a nonionic surfactant. Phase equilibria, interfacial profiles, and interfacial tensions for three-phase equilibrium are determined in mean field approximation, for a wide range of temperature and interaction parameters. Surfactant interaction parameters are found to strongly influence interfacial tensions, reducing them in some cases to ultralow values. Interfacial tensions are used to determine whether the middle phase, rich in surfactant, wets or does not wet the interface between the oil-rich and water-rich phases. By varying temperature and interaction parameters, a wetting transition is located and found to be of the first order. Comparison is made with recent experimental results on wetting transitions in ternary surfactant systems.
Third-order phase transition in random tilings
NASA Astrophysics Data System (ADS)
Colomo, F.; Pronko, A. G.
2013-10-01
We consider the domino tilings of an Aztec diamond with a cut-off corner of macroscopic square shape and given size and address the bulk properties of tilings as the size is varied. We observe that the free energy exhibits a third-order phase transition when the cut-off square, increasing in size, reaches the arctic ellipse—the phase separation curve of the original (unmodified) Aztec diamond. We obtain this result by studying the thermodynamic limit of a certain nonlocal correlation function of the underlying six-vertex model with domain wall boundary conditions, the so-called emptiness formation probability (EFP). We consider EFP in two different representations: as a τ function for Toda chains and as a random matrix model integral. The latter has a discrete measure and a linear potential with hard walls; the observed phase transition shares properties with both Gross-Witten-Wadia and Douglas-Kazakov phase transitions.
Non-linear dielectric effect in the isotropic phase above the isotropic-cholesteric phase transition
NASA Astrophysics Data System (ADS)
Mukherjee, Prabir K.; Chakraborty, Sumanta; Rzoska, Sylwester J.
2011-11-01
Using the Landau-de Gennes theory, the temperature, pressure and frequency dependence of the non-linear effect in the isotropic phase above the isotropic-cholesteric phase transition is calculated. The influence of pressure on the isotropic-cholesteric phase transition is discussed by varying the coupling between the orientational order parameter and the macroscopic polarization of polar cholesterics. Comparing the results of the calculations with existing data, we finally conclude that the model provides a description of the isotropic-cholesteric transition that takes all experimentally known features of the unusual negative and positive pretransitional effect in the isotropic phase of the system into account in a qualitatively correct way.
Going full circle: phase-transition thermodynamics of ionic liquids.
Preiss, Ulrich; Verevkin, Sergey P; Koslowski, Thorsten; Krossing, Ingo
2011-05-27
We present the full enthalpic phase transition cycle for ionic liquids (ILs) as examples of non-classical salts. The cycle was closed for the lattice, solvation, dissociation, and vaporization enthalpies of 30 different ILs, relying on as much experimental data as was available. High-quality dissociation enthalpies were calculated at the G3 MP2 level. From the cycle, we could establish, for the first time, the lattice and solvation enthalpies of ILs with imidazolium ions. For vaporization, lattice, and dissociation enthalpies, we also developed new prediction methods in the course of our investigations. Here, as only single-ion values need to be calculated and the tedious optimization of an ion pair can be circumvented, the computational time is short. For the vaporization enthalpy, a very simple approach was found, using a surface term and the calculated enthalpic correction to the total gas-phase energy. For the lattice enthalpy, the most important constituent proved to be the calculated conductor-like screening model (COSMO) solvation enthalpy in the ideal electric conductor. A similar model was developed for the dissociation enthalpy. According to our assessment, the typical error of the lattice enthalpy would be 9.4 kJ mol(-1), which is less than half the deviation we get when using the (optimized) Kapustinskii equation or the recent volume-based thermodynamics (VBT) theory. In contrast, the non-optimized VBT formula gives lattice enthalpies 20 to 140 kJ mol(-1) lower than the ones we assessed in the cycle, because of the insufficient description of dispersive interactions. Our findings show that quantum-chemical calculations can greatly improve the VBT approaches, which were parameterized for simple, inorganic salts with ideally point-shaped charges. In conclusion, we suggest the term "augmented VBT", or "aVBT", to describe this kind of theoretical approach.
Three-dimensional mantle dynamics with an endothermic phase transition
NASA Technical Reports Server (NTRS)
Honda, S.; Balachandar, S.; Yuen, D. A.; Reuteler, D.
1993-01-01
3D convection for the spinel to perovskite phase change has been simulated numerically. Results for Rayleigh (Ra) numbers of 0(10 exp 6) show intermittent layering with a strong robust plume rising through the phase boundary. Many descending instabilities are deflected but merging cold sheets come together at a junction. A pool of cold material accumulates underneath in the phase-transition zone. A strong gravitational instability results, which precipitates a rapid and massive discharge of upper-mantle material.
Phase transition and properties of a compact star
Sharma, B. K.; Panda, P. K.; Patra, S. K.
2007-03-15
We investigate the phase transition to a deconfined phase and the consequences in the formation of neutron stars. We use the recently proposed effective-field-theory-motivated relativistic mean-field theory for the hadrons and the MIT bag model and color-flavor locked (CFL) phase for the quark matter to get the appropriate equation of state. The properties of the stars are then calculated. The differences between unpaired and CFL quark matter are discussed.
Three-dimensional mantle dynamics with an endothermic phase transition
NASA Technical Reports Server (NTRS)
Honda, S.; Balachandar, S.; Yuen, D. A.; Reuteler, D.
1993-01-01
3D convection for the spinel to perovskite phase change has been simulated numerically. Results for Rayleigh (Ra) numbers of 0(10 exp 6) show intermittent layering with a strong robust plume rising through the phase boundary. Many descending instabilities are deflected but merging cold sheets come together at a junction. A pool of cold material accumulates underneath in the phase-transition zone. A strong gravitational instability results, which precipitates a rapid and massive discharge of upper-mantle material.
Adaptive Competition, Market Efficiency, and Phase Transitions
NASA Astrophysics Data System (ADS)
Savit, Robert; Manuca, Radu; Riolo, Rick
1999-03-01
In many social and biological systems agents simultaneously and adaptively compete for limited resources, thereby altering their environment. We analyze a simple model that incorporates fundamental features of such systems. If the space of strategies available to the agents is small, the system is in a phase in which all information available to the agents' strategies is traded away, and agents' choices are maladaptive, resulting in a poor collective utilization of resources. For larger strategy spaces, the system is in a phase in which the agents are able to coordinate their actions to achieve a better utilization of resources. The best utilization of resources occurs at a critical point, when the dimension of the strategy space is on the order of the number of agents.
Solid-solid phase transition measurements in iron
Schwartz, Cynthia Louise
2010-01-01
Previously, dynamic experiments on iron have observed a non-zero transition time and width in the solid-solid {alpha}-{var_epsilon} phase transition. Using Proton Radiography at the Los Alamos Neutron Science Center, we have performed plate impact experiments on iron to further study the {alpha}-{var_epsilon} phase transition which occurs at 13GPa. A 40mm bore powder gun was coupled to a proton radiography beam line and imaging system and synchronized to the impact of the projectile on the target sample with the proton beam pattern. A typical experimental configuration for the iron study, as shown below in 3 color-enhanced radiographs, is a 40mm diameter aluminum sabot impacting a 40mm diameter of polycrystalline ARMCO iron. The iron is backed by a sapphire optical window for velocimetry measurements. The aluminum flyer on the left of the iron is barely visible for visual display purposes. Direct density jumps were measured which corresponded to calculations to within 1% using a Wondy mUlti-phase equation of state model. In addition, shock velocities were measured using an edge fitting technique and followed that edge movement from radiograph to radiograph, where radiographs are separated in time by 500 ns. Preliminary measurements give a shock velocity (P1 wave) of 5.251 km/s. The projectile velocity was 0.725 km/s which translate to a peak stress of 17.5 GPa. Assuming the P1 wave is instantaneous, we are able to calibrate the chromatic, motion, object and camera blur by measuring the width of the P1 wave. This approximation works in this case since each of the two density jumps are small compared to the density of the object. Subtracting the measured width of the P1 wave in quadrature from the width of the P2 wave gives a preliminary measurement of the transition length of 265 {mu}m. Therefore, a preliminary measured phase transition relaxation time {tau} = transition length/u{sub s} = 265 {mu}m/5.251 km/s = 50 ns. Both Boettger and Jensen conclude that the
Multiple Phase Transition in Unconventional Superconducting Films
NASA Astrophysics Data System (ADS)
Miyawaki, N.; Higashitani, S.
2016-10-01
When Andreev bound states are formed at the surfaces of a superconducting film, there may arise, as the ground state of the film, a superconducting state with broken time-reversal symmetry (T). In this state, Cooper pairs with a finite center-of-mass momentum q are formed without external fields. We focus on the T-breaking state in a d-wave superconducting film and investigate the effect of the Fermi surface shape on its stability region in the T-D^{-1} phase diagram (T: temperature, D: film thickness). The phase boundaries separating the normal state, the T-breaking superconducting state, and the trivial (q = 0 ) superconducting state are determined for various Fermi surface shapes ranging from cylindrical to square. It is found that the region of the T-breaking phase is substantially enlarged when the Fermi surface is square-shaped. This is mainly because the critical thickness D_c between the normal and T-breaking states is significantly reduced when the Fermi surface has a good nesting property.
Multiple Phase Transition in Unconventional Superconducting Films
NASA Astrophysics Data System (ADS)
Miyawaki, N.; Higashitani, S.
2017-06-01
When Andreev bound states are formed at the surfaces of a superconducting film, there may arise, as the ground state of the film, a superconducting state with broken time-reversal symmetry (T). In this state, Cooper pairs with a finite center-of-mass momentum q are formed without external fields. We focus on the T-breaking state in a d-wave superconducting film and investigate the effect of the Fermi surface shape on its stability region in the T-D^{-1} phase diagram ( T: temperature, D: film thickness). The phase boundaries separating the normal state, the T-breaking superconducting state, and the trivial (q = 0) superconducting state are determined for various Fermi surface shapes ranging from cylindrical to square. It is found that the region of the T-breaking phase is substantially enlarged when the Fermi surface is square-shaped. This is mainly because the critical thickness D_c between the normal and T-breaking states is significantly reduced when the Fermi surface has a good nesting property.
Quark-hadron phase transition and strangeness conservation constraints
NASA Astrophysics Data System (ADS)
Saeed-Uddin
1999-01-01
The implications of the strangeness conservation in a hadronic resonance gas (HRG) on the expected phase transition to the quark gluon plasma (QGP) are investigated. It is assumed that under favourable conditions a first order hadron-quark matter phase transition may occur in the hot hadronic matter such as those produced in the ultra-relativistic heavy-ion collisions at CERN and BNL. It is however shown that the criteria of strict strangeness conservation in the HRG may not permit the occurrence of a strict first order equilibrium quark-hadron phase transition unlike a previous study. This emerges as a consequence of the application of a realistic equation of state (EOS) for the HRG and QGP phases, which account for the finite-size effect arising from the short range hard-core hadronic repulsion in the HRG phase and the perturbative QCD interactions in the QGP phase. For a first order hadron-quark matter phase transition to occur one will therefore require large fluctuations in the critical thermal parameters, which might arise due to superheating, supercooling or other nonequlibrium effects. We also discuss a scenario proposed earlier, leading to a possible strangeness separation process during hadronization.
Mapping the QCD Phase Transition with Accreting Compact Stars
Blaschke, D.; Poghosyan, G.; Grigorian, H.
2008-10-29
We discuss an idea for how accreting millisecond pulsars could contribute to the understanding of the QCD phase transition in the high-density nuclear matter equation of state (EoS). It is based on two ingredients, the first one being a ''phase diagram'' of rapidly rotating compact star configurations in the plane of spin frequency and mass, determined with state-of-the-art hybrid equations of state, allowing for a transition to color superconducting quark matter. The second is the study of spin-up and accretion evolution in this phase diagram. We show that the quark matter phase transition leads to a characteristic line in the {omega}-M plane, the phase border between neutron stars and hybrid stars with a quark matter core. Along this line a drop in the pulsar's moment of inertia entails a waiting point phenomenon in the accreting millisecond pulsar (AMXP) evolution: most of these objects should therefore be found along the phase border in the {omega}-M plane, which may be viewed as the AMXP analog of the main sequence in the Hertzsprung-Russell diagram for normal stars. In order to prove the existence of a high-density phase transition in the cores of compact stars we need population statistics for AMXPs with sufficiently accurate determination of their masses, spin frequencies and magnetic fields.
NASA Astrophysics Data System (ADS)
Xiao, Bing
investigated the electronic structures and magnetism of R-VO2 using exchange-correlation functionals of all five rungs on Jacob's ladder. Our calculations show that all semilocal functionals (LSDA, GGAs and meta-GGAs) and hybrid functionals (HSE06) stabilize the spin-polarized states (ferromagnetic and anti-ferromagnetic states) over non-magentic state, which are completely opposite to experimental observation. Suprisingly, LSDA gives the best energetic descriptions for magnetic and non-magnetic phases of R-VO2 among semilocal functionals and HSE06. Othwerwise, RPA calculations are highly dependent on the inputs in the spin polarized case. With PBE inputs, RPA also fails, giving lower energies for spin-polarized states than for the non-magnetic phase. Meawhile, the results are reversed using LSDA inputs. From the computed equilibrium cell volume, we observe the error cancellation in the exchange-correlation hole of most semilocal functionals in the spin-polarized calculations. LSDA and RPA do not fit to this picture. By analyzing the local magnetic moments of vanadium atoms, it is found that the magnetic property predicted from meta-GGA can be related to its exchange enhancement factor. The physisorption of a molecule on a transition metal surface is also another difficult problem in DFT because of the long-range van der Waals interactions. The recently developed MGGA_MS family of density functionals is able to capture a portion of intermediate range dispersion interactions. Therefore, we employed MGGA_MS2 to study the physisorption of CO2 on Pt (111) surface, and the results are compared to those of PBE, PBE+D2 and optB88-vdW methods. The computed binding curves comfirm that that MGGA_MS2 indeed captures the van der Waals interactions near the equilibrium binding distance, and the obtained binding distance is also in good agreement with PBE+D2 and optB88-vdW calculations. By computing the electron density difference map (EDDM), we find that the electron densities of CO2 and
Quantum Phase Transition and Entanglement in Topological Quantum Wires.
Cho, Jaeyoon; Kim, Kun Woo
2017-06-05
We investigate the quantum phase transition of the Su-Schrieffer-Heeger (SSH) model by inspecting the two-site entanglements in the ground state. It is shown that the topological phase transition of the SSH model is signified by a nonanalyticity of local entanglement, which becomes discontinuous for finite even system sizes, and that this nonanalyticity has a topological origin. Such a peculiar singularity has a universal nature in one-dimensional topological phase transitions of noninteracting fermions. We make this clearer by pointing out that an analogous quantity in the Kitaev chain exhibiting the identical nonanalyticity is the local electron density. As a byproduct, we show that there exists a different type of phase transition, whereby the pattern of the two-site entanglements undergoes a sudden change. This transition is characterised solely by quantum information theory and does not accompany the closure of the spectral gap. We analyse the scaling behaviours of the entanglement in the vicinities of the transition points.
Phase transitions in the assembly of multivalent signalling proteins
Li, Pilong; Banjade, Sudeep; Cheng, Hui-Chun; Kim, Soyeon; Chen, Baoyu; Guo, Liang; Llaguno, Marc; Hollingsworth, Javoris V.; King, David S.; Banani, Salman F.; Russo, Paul S.; Jiang, Qiu-Xing; Nixon, B. Tracy; Rosen, Michael K.
2013-04-08
Cells are organized on length scales ranging from angstrom to micrometers. However, the mechanisms by which angstrom-scale molecular properties are translated to micrometer-scale macroscopic properties are not well understood. Here we show that interactions between diverse synthetic, multivalent macromolecules (including multi-domain proteins and RNA) produce sharp liquid-liquid-demixing phase separations, generating micrometer-sized liquid droplets in aqueous solution. This macroscopic transition corresponds to a molecular transition between small complexes and large, dynamic supramolecular polymers. The concentrations needed for phase transition are directly related to the valency of the interacting species. In the case of the actin-regulatory protein called neural Wiskott-Aldrich syndrome protein (N-WASP) interacting with its established biological partners NCK and phosphorylated nephrin1, the phase transition corresponds to a sharp increase in activity towards an actin nucleation factor, the Arp2/3 complex. The transition is governed by the degree of phosphorylation of nephrin, explaining how this property of the system can be controlled to regulatory effect by kinases. The widespread occurrence of multivalent systems suggests that phase transitions may be used to spatially organize and biochemically regulate information throughout biology.
Pressure-induced phase transitions of indium selenide
NASA Astrophysics Data System (ADS)
Rasmussen, Anya Marie
In2Se3 has potential as a phase-change material for memory applications. Understanding its phase diagram is important to achieve controlled switching between phases. Pressure-dependent phase transitions of In2Se3 bulk powders and nanowire samples were studied at room temperature and at elevated temperatures using synchrotron x-ray diffraction and diamond-anvil cells (DACs). alpha-In2Se3 transforms into the beta phase at 0.7 GPa, an order of magnitude lower than phase-transition critical pressures in typical semiconductors. The bulk moduli are reported and the c/a ratio for the beta phase is shown to have a highly nonlinear dependence on pressure. gamma-In2Se3, metastable under ambient conditions, transforms into to the high-pressure beta phase between 2.8 GPa and 3.2 GPa in bulk powder samples and at slightly higher pressures, between 3.2 GPa and 3.7 GPa in nanowire samples. While the gamma phase bulk modulus is similar to that of the beta phase, the decrease due to pressure in the unit cell parameter ratio, c/a, is less than half the decrease seen in the beta phase. Using high-temperature DACs, we investigated how elevated temperatures and pressures affect the crystal structure of In 2Se3. From these measurements, the high-pressure beta phase was found to be metastable. The high-pressure beta phase transitions into the high-temperature beta phase at temperatures above 380 °C.
NASA Astrophysics Data System (ADS)
Yılmaz, Yaşar
2007-06-01
Transition between collapsed state phases and discontinuous volume phase transition for a hydrogen bonding gel, poly(methacrylic acid-co-dimethyl acrylamide), were observed by using both the volume measurements and fluorescence intensity of the pyranine fluoroprobe (8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt) bonded to the gel by means of electrostatic interactions. In the collapsed state, while there is no appreciable change in the volume of the gel, a considerable variation in the fluorescence intensity occurred around 30°C signaling a second order phase transition between collapsed state phases, from relatively frozen to a fluctuating phase. Our analysis of the data around 30°C indicates that the critical point of gel volume transition belongs to the so-called mean-field universality class, as predicted in Onuki [Phys. Rev. A 38, 2192 (1988)] and by Golubovic and Lubensky [Phys. Rev. Lett. 63, 1082 (1989)]. The relaxation time for the equilibrium swelling critically depends on the temperature and diverges near 60°C, where both fluorescence intensity and the volume of the gel change drastically and indicate the discontinuous volume phase transition. The swelling kinetics of the critical gel during the discontinuous volume phase transition can be modeled best with the first term in the expansion of the Li-Tanaka equation for a long initial period of the swelling time.
Extended ensemble theory, spontaneous symmetry breaking, and phase transitions
NASA Astrophysics Data System (ADS)
Xiao, Ming-wen
2006-09-01
In this paper, as a personal review, we suppose a possible extension of Gibbs ensemble theory so that it can provide a reasonable description of phase transitions and spontaneous symmetry breaking. The extension is founded on three hypotheses, and can be regarded as a microscopic edition of the Landau phenomenological theory of phase transitions. Within its framework, the stable state of a system is determined by the evolution of order parameter with temperature according to such a principle that the entropy of the system will reach its minimum in this state. The evolution of order parameter can cause a change in representation of the system Hamiltonian; different phases will realize different representations, respectively; a phase transition amounts to a representation transformation. Physically, it turns out that phase transitions originate from the automatic interference among matter waves as the temperature is cooled down. Typical quantum many-body systems are studied with this extended ensemble theory. We regain the Bardeen Cooper Schrieffer solution for the weak-coupling superconductivity, and prove that it is stable. We find that negative-temperature and laser phases arise from the same mechanism as phase transitions, and that they are unstable. For the ideal Bose gas, we demonstrate that it will produce Bose Einstein condensation (BEC) in the thermodynamic limit, which confirms exactly Einstein's deep physical insight. In contrast, there is no BEC either within the phonon gas in a black body or within the ideal photon gas in a solid body. We prove that it is not admissible to quantize the Dirac field by using Bose Einstein statistics. We show that a structural phase transition belongs physically to the BEC happening in configuration space, and that a double-well anharmonic system will undergo a structural phase transition at a finite temperature. For the O(N)-symmetric vector model, we demonstrate that it will yield spontaneous symmetry breaking and produce
NASA Technical Reports Server (NTRS)
1986-01-01
The conceptual designs and programmatics for a Space Station Nonhuman Life Sciences Research Facility (LSRF) are highlighted. Conceptual designs and programmatics encompass an Initial Orbital Capability (IOC) LSRF, a growth or Follow-on Orbital Capability (FOC), and the transitional process required to modify the IOC LSRF to the FOC LSRF.
Mochida, Tomoyuki; Ishida, Mai; Tominaga, Takumi; Takahashi, Kazuyuki; Sakurai, Takahiro; Ohta, Hitoshi
2017-05-31
In recent years, ionic plastic crystals have attracted much attention. Many metallocenium salts exhibit plastic phases, but factors affecting their phase transitions are yet to be elucidated. To investigate these factors, we synthesized octamethylferrocenium salts with various counteranions [Fe(C5Me4H)2]X ([1]X; X(-) = B(CN)4(-), C(CN)3(-), N(CN)2(-), FSA (= (SO2F)2N(-)), FeCl4(-), GaCl4(-) and CPFSA (= CF2(SO2CF2)2N(-))) and elucidated their crystal structures and phase behavior. Correlations between the crystal structures and phase sequences, and the shapes and volumes of the anions are discussed. Except for [1][CPFSA], these salts exhibit phase transitions to plastic phases at or above room temperature (TC = 298-386 K), and the plastic phases exhibit either NaCl- or anti-NiAs-type structures. X-ray crystal structure analyses of these salts at 100 K revealed that they have structures in which cations and anions are alternately arranged, with the exception of [1][CPFSA]. [1][CPFSA] exhibits a structure in which anions and cations are separately stacked to form columns. [1][N(CN)2] exhibits a polar crystal structure that undergoes a monotropic phase transition to a centrosymmetric structure. The magnetic susceptibilities of room-temperature plastic crystals [1][GaCl4] and [1][FeCl4] were investigated; the latter exhibits a small ferromagnetic interaction at low temperatures.
Observation of the Photon-Blockade Breakdown Phase Transition
NASA Astrophysics Data System (ADS)
Fink, J. M.; Dombi, A.; Vukics, A.; Wallraff, A.; Domokos, P.
2017-01-01
Nonequilibrium phase transitions exist in damped-driven open quantum systems when the continuous tuning of an external parameter leads to a transition between two robust steady states. In second-order transitions this change is abrupt at a critical point, whereas in first-order transitions the two phases can coexist in a critical hysteresis domain. Here, we report the observation of a first-order dissipative quantum phase transition in a driven circuit quantum electrodynamics system. It takes place when the photon blockade of the driven cavity-atom system is broken by increasing the drive power. The observed experimental signature is a bimodal phase space distribution with varying weights controlled by the drive strength. Our measurements show an improved stabilization of the classical attractors up to the millisecond range when the size of the quantum system is increased from one to three artificial atoms. The formation of such robust pointer states could be used for new quantum measurement schemes or to investigate multiphoton phases of finite-size, nonlinear, open quantum systems.
A comparison of observables for solid-solid phase transitions
Smilowitz, Laura B; Henson, Bryan F; Romero, Jerry J
2009-01-01
The study of solid-solid phase transformations is hindered by the difficulty of finding a volumetric probe to use as a progress variable. Solids are typically optically opaque and heterogeneous. Over the past several years, second harmonic generation (SHG) has been used as a kinetic probe for a solid-solid phase transition in which the initial and final phases have different symmetries. Bulk generation of SHG is allowed by symmetry only in noncentrosymmetric crystallographic space groups. For the organic energetic nitramine octahydro-1,3 ,5,7 -tetranitro-1,3 ,5,7 -tatrazocine (HMX), the beta phase is centro symmetric (space group P2{sub 1}/c) and the delta phase iS noncentrosymmetric (space group P6{sub 1}22) making SHG an extremely sensitive, essentially zero background probe of the phase change progress. We have used SHG as a tool to follow the progress of the transformation from beta to delta phase during the solid-solid transformation. However, kinetic models of the transformation derived using different observables from several other groups have differed, showing later onset for the phase change and faster progression to completion. In this work, we have intercompared several techniques to understand these differences. The three techniques discussed are second harmonic generation, Raman spectroscopy, and differential scanning calorimetry (DSC). The progress of the beta to delta phase transition in HMX observed with each of these different probes will be discussed and advantages and disadvantages of each technique described. This paper compares several different observables for use in measuring the kinetics of solid-solid phase transitions. Relative advantages and disadvantages for each technique are described and a direct comparison of results is made for the beta to delta polymorphic phase transition of the energetic nitramine, octahydro-1,3,5,7-tetranitro-1,3,5,7-tatrazocine.
Multiple quantum phase transitions of plutonium compounds
Matsumoto, Munehisa; Yin, Quan; Otsuki, Junya; Savrasov, Sergey Y.
2011-07-22
We show by quantum Monte Carlo simulations of realistic Kondo lattice models derived from electronicstructure calculations that multiple quantum critical points can be realized in plutonium-based materials. We place representative systems, including PuCoGa5, on a realistic Doniach phase diagram and identify the regions where the magnetically mediated superconductivity could occur. The solution of an inverse problem to restore the quasiparticle renormalization factor for f electrons is shown to be sufficiently good to predict the trends among Sommerfeld coefficients and magnetism. A suggestion on the possible experimental verification for this scenario is given for PuAs.
Selle, J E
1992-06-26
Attempts were made to apply the Kaufman method of calculating binary phase diagrams to the calculation of binary phase diagrams between the rare earths, actinides, and the refractory transition metals. Difficulties were encountered in applying the method to the rare earths and actinides, and modifications were necessary to provide accurate representation of known diagrams. To calculate the interaction parameters for rare earth-rare earth diagrams, it was necessary to use the atomic volumes for each of the phases: liquid, body-centered cubic, hexagonal close-packed, and face-centered cubic. Determination of the atomic volumes of each of these phases for each element is discussed in detail. In some cases, empirical means were necessary. Results are presented on the calculation of rare earth-rare earth, rare earth-actinide, and actinide-actinide diagrams. For rare earth-refractory transition metal diagrams and actinide-refractory transition metal diagrams, empirical means were required to develop values for the enthalpy of vaporization for rare earth elements and values for the constant (C) required when intermediate phases are present. Results of using the values determined for each element are presented.
Mirmelstein, A.; Podlesnyak, Andrey A.; dos Santos, Antonio M.; Ehlers, Georg; Kerbel, O.; Matvienko, V.; Sefat, A. S.; Saporov, B.; Halder, G. J.; Tobin, J. G.
2015-08-03
The pressure-induced structural phase transition in the intermediate-valence compound CeNi has been investigated by x-ray and neutron powder diffraction techniques. It is shown that the structure of the pressure-induced CeNi phase (phases) can be described in terms of the Pnma space group. Equations of state for CeNi on both sides of the phase transition are derived and an approximate P-T phase diagram is suggested for P<8 GPa and T<300 K. The observed Cmcm→Pnma structural transition is then analyzed using density functional theory calculations, which successfully reproduce the ground state volume, the phase transition pressure, and the volume collapse associated with the phase transition.
NASA Astrophysics Data System (ADS)
Mirmelstein, A.; Podlesnyak, A.; dos Santos, Antonio M.; Ehlers, G.; Kerbel, O.; Matvienko, V.; Sefat, A. S.; Saparov, B.; Halder, G. J.; Tobin, J. G.
2015-08-01
The pressure-induced structural phase transition in the intermediate-valence compound CeNi has been investigated by x-ray and neutron powder diffraction techniques. It is shown that the structure of the pressure-induced CeNi phase (phases) can be described in terms of the P n m a space group. Equations of state for CeNi on both sides of the phase transition are derived and an approximate P-T phase diagram is suggested for P <8 GPa and T <300 K. The observed C m c m →P n m a structural transition is analyzed using density functional theory calculations, which successfully reproduce the ground state volume, the phase transition pressure, and the volume collapse associated with the phase transition.
Mirmelstein, A.; Podlesnyak, Andrey A.; dos Santos, Antonio M.; ...
2015-08-03
The pressure-induced structural phase transition in the intermediate-valence compound CeNi has been investigated by x-ray and neutron powder diffraction techniques. It is shown that the structure of the pressure-induced CeNi phase (phases) can be described in terms of the Pnma space group. Equations of state for CeNi on both sides of the phase transition are derived and an approximate P-T phase diagram is suggested for P<8 GPa and T<300 K. The observed Cmcm→Pnma structural transition is then analyzed using density functional theory calculations, which successfully reproduce the ground state volume, the phase transition pressure, and the volume collapse associated withmore » the phase transition.« less
Antikaon condensation and deconfinement phase transition in neutron stars
Gu Jianfa; Guo Hua; Xu Furong; Li Xiguo; Liu Yuxin
2006-05-15
Antikaon condensation and deconfinement phase transition in neutron stars are investigated in a chiral hadronic model (also referred as to the FST model) for the hadronic phase and in the MIT bag model for the deconfined quark matter phase. It is shown that the existence of quark matter phase makes antikaon condensation impossible in neutron stars. The properties of neutron stars are sensitive to the bag constant. For the small values of the bag constant, the pure quark matter core appears and hyperons are strongly suppressed in neutron stars, whereas for the large bag constant, the hadron-quark mixed phase exists in the center of neutron stars. The maximum masses of neutron stars with the quark matter phase are lower than those without the quark matter phase; meanwhile, the maximum masses of neutron stars with the quark matter phase increase with the bag constant.
More is the Same; Phase Transitions and Mean Field Theories
NASA Astrophysics Data System (ADS)
Kadanoff, Leo P.
2009-12-01
This paper is the first in a series that will look at the theory of phase transitions from the perspectives of physics and the philosophy of science. The series will consider a group of related concepts derived from condensed matter and statistical physics. The key technical ideas go under the names of "singularity", "order parameter", "mean field theory", "variational method", "correlation length", "universality class", "scale changes", and "renormalization". The first four of these will be considered here. In a less technical vein, the question here is how can matter, ordinary matter, support a diversity of forms. We see this diversity each time we observe ice in contact with liquid water or see water vapor (steam) come up from a pot of heated water. Different phases can be qualitatively different in that walking on ice is well within human capacity, but walking on liquid water is proverbially forbidden to ordinary humans. These differences have been apparent to humankind for millennia, but only brought within the domain of scientific understanding since the 1880s. A phase transition is a change from one behavior to another. A first order phase transition involves a discontinuous jump in some statistical variable. The discontinuous property is called the order parameter. Each phase transition has its own order parameter. The possible order parameters range over a tremendous variety of physical properties. These properties include the density of a liquid-gas transition, the magnetization in a ferromagnet, the size of a connected cluster in a percolation transition, and a condensate wave function in a superfluid or superconductor. A continuous transition occurs when the discontinuity in the jump approaches zero. This article is about statistical mechanics and the development of mean field theory as a basis for a partial understanding of phase transition phenomena. Much of the material in this review was first prepared for the Royal Netherlands Academy of Arts and
Molecular Dynamics Simulations of Ferroelectric Phase Transitions
NASA Astrophysics Data System (ADS)
Yu, Rici; Krakauer, Henry
1997-03-01
Based on an analysis of the wavevector dependence of the lattice instabilities in KNbO_3, we proposed a real-space chain-like instability and a scenario of sequential freezing out or onset of coherence of these instabilities, which qualitatively explains the sequence of observed temperature-dependent ferroelectric phases.(R. Yu and H. Krakauer, Phys. Rev. Lett. 74), 4067 (1995). We suggested that this chain-like instability should also be found in BaTiO_3, and this has been subsequently confirmed by Ghosez et al.(P. Ghosez et al.), Proc. 4th Williamsburg Workshop on First-Principles Calculations for Ferroelectrics, to be published We will present molecular dynamics simulations on BaTiO_3, using effective Hamiltonians constructed from first-principles calculations,(W. Zhong, D. Vanderbilt, and K. M. Rabe, Phys. Rev. Lett. 73), 1861 (1994). that reproduce the essential features of diffuse x-ray scattering measurements in the cubic, tetragonal, orthorhombic, and rhombohedral phases. The good agreement supports the interpretation of real-space chain-formation. Simulations for KNbO3 may also be reported.
Unusually sharp paramagnetic phase transition in thin film Fe3Pt invar
NASA Astrophysics Data System (ADS)
Drisko, Jasper; Cumings, John
2013-03-01
Invar alloys, typically 3d transition metal rich systems, are most commonly known for their extremely low coefficients of thermal expansion (CTE) over a wide range of temperatures close to room temperature. This anomalous behavior in the CTE lends Invar to a variety of important applications in precision mechanical devices, scientific instruments, and sensors, among others. Many theoretical models of Invar have been proposed over the years, the most promising of which is a system described by two coexisting phases, one high-spin high-volume and the other low-spin low-volume, that compete to stabilize the volume of the material as the temperature is changed. However, no theory has yet been able to explain all experimental observations across the range of Invar alloys, especially at finite temperature. We have fabricated thin films of a Fe3Pt Invar alloy and investigate them using Lorentz Transmission Electron Microscopy (TEM). 23nm films are deposited onto SiN membrane substrates via radio-frequency magnetron sputtering from a pure Fe target decorated with Pt pieces. We observe novel magnetic domain structures and an unusually sharp phase transition between ferromagnetic (FM) and paramagnetic (PM) regions of the film under a temperature gradient. This sharp transition suggests that the FM-to-PM transition may be first order, perhaps containing a structural-elastic component to the order parameter. However, electron diffraction reveals that both the FM and PM regions have the same FCC crystal structure.
High-pressure phase transitions in rare earth metal thulium to 195 GPa.
Montgomery, Jeffrey M; Samudrala, Gopi K; Tsoi, Georgiy M; Vohra, Yogesh K
2011-04-20
We have performed image plate x-ray diffraction studies on a heavy rare earth metal, thulium (Tm), in a diamond anvil cell to a pressure of 195 GPa and volume compression V/V₀ = 0.38 at room temperature. The rare earth crystal structure sequence, hcp →Sm-type→ dhcp →fcc → distorted fcc, is observed in Tm below 70 GPa with the exception of a pure fcc phase. The focus of our study is on the ultrahigh-pressure phase transition and Rietveld refinement of crystal structures in the pressure range between 70 and 195 GPa. The hexagonal hR-24 phase is seen to describe the distorted fcc phase between 70 and 124 GPa. Above 124 ± 4 GPa, a structural transformation from hR 24 phase to a monoclinic C 2/m phase is observed with a volume change of -1.5%. The equation of state data shows rapid stiffening above the phase transition at 124 GPa and is indicative of participation of f-electrons in bonding. We compare the behavior of Tm to other heavy rare-earths and heavy actinide metals under extreme conditions of pressure.
Quantum phase transitions in bosonic heteronuclear pairing Hamiltonians
Hohenadler, M.; Silver, A. O.; Bhaseen, M. J.; Simons, B. D.
2010-07-15
We explore the phase diagram of two-component bosons with Feshbach resonant pairing interactions in an optical lattice. It has been shown in previous work to exhibit a rich variety of phases and phase transitions, including a paradigmatic Ising quantum phase transition within the second Mott lobe. We discuss the evolution of the phase diagram with system parameters and relate this to the predictions of Landau theory. We extend our exact diagonalization studies of the one-dimensional bosonic Hamiltonian and confirm additional Ising critical exponents for the longitudinal and transverse magnetic susceptibilities within the second Mott lobe. The numerical results for the ground-state energy and transverse magnetization are in good agreement with exact solutions of the Ising model in the thermodynamic limit. We also provide details of the low-energy spectrum, as well as density fluctuations and superfluid fractions in the grand canonical ensemble.
Discrete-to-continuous transition in quantum phase estimation
NASA Astrophysics Data System (ADS)
Rządkowski, Wojciech; Demkowicz-Dobrzański, Rafał
2017-09-01
We analyze the problem of quantum phase estimation in which the set of allowed phases forms a discrete N -element subset of the whole [0 ,2 π ] interval, φn=2 π n /N , n =0 ,⋯,N -1 , and study the discrete-to-continuous transition N →∞ for various cost functions as well as the mutual information. We also analyze the relation between the problems of phase discrimination and estimation by considering a step cost function of a given width σ around the true estimated value. We show that in general a direct application of the theory of covariant measurements for a discrete subgroup of the U(1 ) group leads to suboptimal strategies due to an implicit requirement of estimating only the phases that appear in the prior distribution. We develop the theory of subcovariant measurements to remedy this situation and demonstrate truly optimal estimation strategies when performing a transition from discrete to continuous phase estimation.
Quantum phase transition in a common metal.
Yeh, A; Soh, Yeong-Ah; Brooke, J; Aeppli, G; Rosenbaum, T F; Hayden, S M
2002-10-03
The classical theory of solids, based on the quantum mechanics of single electrons moving in periodic potentials, provides an excellent description of substances ranging from semiconducting silicon to superconducting aluminium. Over the last fifteen years, it has become increasingly clear that there are substances for which the conventional approach fails. Among these are certain rare earth compounds and transition metal oxides, including high-temperature superconductors. A common feature of these materials is complexity, in the sense that they have relatively large unit cells containing heterogeneous mixtures of atoms. Although many explanations have been put forward for their anomalous properties, it is still possible that the classical theory might suffice. Here we show that a very common chromium alloy has some of the same peculiarities as the more exotic materials, including a quantum critical point, a strongly temperature-dependent Hall resistance and evidence for a 'pseudogap'. This implies that complexity is not a prerequisite for unconventional behaviour. Moreover, it should simplify the general task of explaining anomalous properties because chromium is a relatively simple system in which to work out in quantitative detail the consequences of the conventional theory of solids.
Non-equilibrium phase transitions in a liquid crystal
NASA Astrophysics Data System (ADS)
Dan, K.; Roy, M.; Datta, A.
2015-09-01
The present manuscript describes kinetic behaviour of the glass transition and non-equilibrium features of the "Nematic-Isotropic" (N-I) phase transition of a well known liquid crystalline material N-(4-methoxybenzylidene)-4-butylaniline from the effects of heating rate and initial temperature on the transitions, through differential scanning calorimetry (DSC), Fourier transform infrared and fluorescence spectroscopy. Around the vicinity of the glass transition temperature (Tg), while only a change in the baseline of the ΔCp vs T curve is observed for heating rate (β) > 5 K min-1, consistent with a glass transition, a clear peak for β ≤ 5 K min-1 and the rapid reduction in the ΔCp value from the former to the latter rate correspond to an order-disorder transition and a transition from ergodic to non-ergodic behaviour. The ln β vs 1000/T curve for the glass transition shows convex Arrhenius behaviour that can be explained very well by a purely entropic activation barrier [Dan et al., Eur. Phys. Lett. 108, 36007 (2014)]. Fourier transform infrared spectroscopy indicates sudden freezing of the out-of-plane distortion vibrations of the benzene rings around the glass transition temperature and a considerable red shift indicating enhanced coplanarity of the benzene rings and, consequently, enhancement in the molecular ordering compared to room temperature. We further provide a direct experimental evidence of the non-equilibrium nature of the N-I transition through the dependence of this transition temperature (TNI) and associated enthalpy change (ΔH) on the initial temperature (at fixed β-values) for the DSC scans. A plausible qualitative explanation based on Mesquita's extension of Landau-deGennes theory [O. N. de Mesquita, Braz. J. Phys. 28, 257 (1998)] has been put forward. The change in the molecular ordering from nematic to isotropic phase has been investigated through fluorescence anisotropy measurements where the order parameter, quantified by the
Non-equilibrium phase transitions in a liquid crystal.
Dan, K; Roy, M; Datta, A
2015-09-07
The present manuscript describes kinetic behaviour of the glass transition and non-equilibrium features of the "Nematic-Isotropic" (N-I) phase transition of a well known liquid crystalline material N-(4-methoxybenzylidene)-4-butylaniline from the effects of heating rate and initial temperature on the transitions, through differential scanning calorimetry (DSC), Fourier transform infrared and fluorescence spectroscopy. Around the vicinity of the glass transition temperature (Tg), while only a change in the baseline of the ΔCp vs T curve is observed for heating rate (β) > 5 K min(-1), consistent with a glass transition, a clear peak for β ≤ 5 K min(-1) and the rapid reduction in the ΔCp value from the former to the latter rate correspond to an order-disorder transition and a transition from ergodic to non-ergodic behaviour. The ln β vs 1000/T curve for the glass transition shows convex Arrhenius behaviour that can be explained very well by a purely entropic activation barrier [Dan et al., Eur. Phys. Lett. 108, 36007 (2014)]. Fourier transform infrared spectroscopy indicates sudden freezing of the out-of-plane distortion vibrations of the benzene rings around the glass transition temperature and a considerable red shift indicating enhanced coplanarity of the benzene rings and, consequently, enhancement in the molecular ordering compared to room temperature. We further provide a direct experimental evidence of the non-equilibrium nature of the N-I transition through the dependence of this transition temperature (TNI) and associated enthalpy change (ΔH) on the initial temperature (at fixed β-values) for the DSC scans. A plausible qualitative explanation based on Mesquita's extension of Landau-deGennes theory [O. N. de Mesquita, Braz. J. Phys. 28, 257 (1998)] has been put forward. The change in the molecular ordering from nematic to isotropic phase has been investigated through fluorescence anisotropy measurements where the order parameter, quantified by the
How tetraquarks can generate a second chiral phase transition
Pisarski, Robert D.; Skokov, Vladimir V.
2016-09-09
We consider how tetraquarks can affect the chiral phase transition in theories like QCD, with light quarks coupled to three colors. For two flavors the tetraquark field is an isosinglet, and its effect is minimal. For three flavors, however, the tetraquark field transforms in the same representation of the chiral symmetry group as the usual chiral order parameter, and so for very light quarks there may be two chiral phase transitions, which are both of first order. In QCD, results from the lattice indicate that any transition from the tetraquark condensate is a smooth crossover. In the plane of temperature, T, and quark chemical potential, μ, though, a crossover line for the tetraquark condensate is naturally related to the transition line for color superconductivity. For four flavors we suggest that a triquark field, antisymmetric in both flavor and color, combine to form hexaquarks.
How tetraquarks can generate a second chiral phase transition
Pisarski, Robert D.; Skokov, Vladimir V.
2016-09-09
We consider how tetraquarks can affect the chiral phase transition in theories like QCD, with light quarks coupled to three colors. For two flavors the tetraquark field is an isosinglet, and its effect is minimal. For three flavors, however, the tetraquark field transforms in the same representation of the chiral symmetry group as the usual chiral order parameter, and so for very light quarks there may be two chiral phase transitions, which are both of first order. In QCD, results from the lattice indicate that any transition from the tetraquark condensate is a smooth crossover. In the plane of temperature, T, and quark chemical potential, μ, though, a crossover line for the tetraquark condensate is naturally related to the transition line for color superconductivity. For four flavors we suggest that a triquark field, antisymmetric in both flavor and color, combine to form hexaquarks.
Dynamical Symmetry Breaking and Phase Transitions in Driven Diffusive Systems
NASA Astrophysics Data System (ADS)
Baek, Yongjoo; Kafri, Yariv; Lecomte, Vivien
2017-01-01
We study the probability distribution of a current flowing through a diffusive system connected to a pair of reservoirs at its two ends. Sufficient conditions for the occurrence of a host of possible phase transitions both in and out of equilibrium are derived. These transitions manifest themselves as singularities in the large deviation function, resulting in enhanced current fluctuations. Microscopic models which implement each of the scenarios are presented, with possible experimental realizations. Depending on the model, the singularity is associated either with a particle-hole symmetry breaking, which leads to a continuous transition, or in the absence of the symmetry with a first-order phase transition. An exact Landau theory which captures the different singular behaviors is derived.
Nonequilibrium phase transition in a driven Potts model with friction.
Iglói, Ferenc; Pleimling, Michel; Turban, Loïc
2011-04-01
We consider magnetic friction between two systems of q-state Potts spins which are moving along their boundaries with a relative constant velocity ν. Due to the interaction between the surface spins there is a permanent energy flow and the system is in a steady state, which is far from equilibrium. The problem is treated analytically in the limit ν=∞ (in one dimension, as well as in two dimensions for large-q values) and for v and q finite by Monte Carlo simulations in two dimensions. Exotic nonequilibrium phase transitions take place, the properties of which depend on the type of phase transition in equilibrium. When this latter transition is of first order, a sequence of second- and first-order nonequilibrium transitions can be observed when the interaction is varied. ©2011 American Physical Society
How tetraquarks can generate a second chiral phase transition
Pisarski, Robert D.; Skokov, Vladimir V.
2016-09-09
We consider how tetraquarks can affect the chiral phase transition in theories like QCD, with light quarks coupled to three colors. For two flavors the tetraquark field is an isosinglet, and its effect is minimal. For three flavors, however, the tetraquark field transforms in the same representation of the chiral symmetry group as the usual chiral order parameter, and so for very light quarks there may be two chiral phase transitions, which are both of first order. In QCD, results from the lattice indicate that any transition from the tetraquark condensate is a smooth crossover. In the plane of temperature,more » T, and quark chemical potential, μ, though, a crossover line for the tetraquark condensate is naturally related to the transition line for color superconductivity. For four flavors we suggest that a triquark field, antisymmetric in both flavor and color, combine to form hexaquarks.« less
Phase transitions in traffic flow on multilane roads.
Kerner, Boris S; Klenov, Sergey L
2009-11-01
Based on empirical and numerical analyses of vehicular traffic, the physics of spatiotemporal phase transitions in traffic flow on multilane roads is revealed. The complex dynamics of moving jams observed in single vehicle data measured by video cameras on American highways is explained by the nucleation-interruption effect in synchronized flow, i.e., the spontaneous nucleation of a narrow moving jam with the subsequent jam dissolution. We find that (i) lane changing, vehicle merging from on-ramps, and vehicle leaving to off-ramps result in different traffic phases-free flow, synchronized flow, and wide moving jams-occurring and coexisting in different road lanes as well as in diverse phase transitions between the traffic phases; (ii) in synchronized flow, the phase transitions are responsible for a non-regular moving jam dynamics that explains measured single vehicle data: moving jams emerge and dissolve randomly at various road locations in different lanes; (iii) the phase transitions result also in diverse expanded general congested patterns occurring at closely located bottlenecks.
Multiferroic Phases and Transitions in Ferroelectric Lead Titanate Nanodots
Xu, Tao; Shimada, Takahiro; Uratani, Yoshitaka; Wang, Xiaoyuan; Wang, Jie; Kitamura, Takayuki
2017-01-01
Discovery of novel phases and their associated transitions in low-dimensional nanoscale systems is of central interest as the origin of emergent phenomena and new device paradigms. Although typical ferroelectrics such as PbTiO3 exhibit diverse phase transition sequences, the conventional incompatible mechanisms of ferroelectricity and magnetism keep them as simply nonmagnetic phases, despite the immense practical prospective of multiferroics in novel functional devices. Here, we demonstrate using density function theory that PbTiO3 nanodots exhibit unconventional multiferroic phase transitions. The nanosize and nonstoichiometric effects intrinsic to nanodots bring about the coexistence of ferromagnetism with the host electric polarization, mediated by the termination and surface morphology. We also predict the key features of the size-dependent phase diagram of nanodots that involve a rich sequence of ferroelectric-multiferroic-ferromagnetic/nonmagnetic (FE-MF-FM/NM) multiferroic phase transitions. The present work thus provides an avenue to realizing multiferroics and multifunctional oxides in low-dimensional systems. PMID:28367955
Investigation of Dielectric Properties of Liquid Crystals near Phase Transitions
NASA Astrophysics Data System (ADS)
Kordell, Michael; Lawson, Tracy; Prayaga, Chandra; Ujj, Laszlo
2010-03-01
Precise capacitance measurement has been performed near the phase transitions of scientifically important liquid crystals such as 8-CB. The details of the measurements to get high precision data on dielectric constant and its temperature dependence will be presented. The results show significant changes of the dielectric properties of the liquid crystal near the smectic-to-nematic and nematic-to-liquid phase transitions attributed to structural changes of the relevant phases. In order to measure the details of the functional dependence near the phase transition, the temperature was varied with milliKelvin precision. The data was obtained using a self-assembled RC circuit with phase sensitive lock-in amplifier detection. Calibration of the device was made by measuring known standard capacitances. In order to get high accuracy the measurement was completely computer controlled. The Method applied here will contribute to the better understanding of thermodynamic behavior of liquid crystals and can be routinely used to characterize novel materials showing phase transitions.
Phase transition and electronic properties of SbI3: First-principles calculations
NASA Astrophysics Data System (ADS)
Sun, Xiao-Xiao; Li, Cong; Hou, Qing-Yu; Zhang, Yue
2017-06-01
We have performed the first-principles pseudopotential calculations to investigate the structural phase transition and electronic properties of SbI3 considering several possible phases as a function of pressure from 0 GPa to 100 GPa. Our calculations show that this material undertakes a structural transformation from the R-3 phase to high-pressure P21/c phase at about 6.5 GPa with a relative volume collapse of 4.3%. We also have investigated the elastic properties and energy band structure of SbI3 under hydrostatic pressure. The calculation suggests that the R-3 phase is a semiconductor with an indirect band gap of about 2.16 eV at 0 Gpa. Under the influence of pressure, we have found that high-pressure P21/c phase has transformed to metal at about 55 GPa.
Structural phase transition and antiferromagnetic transition of Tb{sub 3}RuO{sub 7}
Hinatsu, Yukio Doi, Yoshihiro
2014-12-15
Magnetic properties and structural phase transition of terbium ruthenate Tb{sub 3}RuO{sub 7} are investigated through magnetic susceptibility, specific heat, high-temperature X-ray diffraction and differential scanning calorimetry measurements. The structural phase transition from space group P2{sub 1}nb to Cmcm has been observed at 402 K. Tb{sub 3}RuO{sub 7} shows an antiferromagnetic transition at 17 K. In addition, another magnetic anomaly has been found at 10 K. Analysis of the magnetic specific heat for Tb{sub 3}RuO{sub 7} indicates that the magnetic transitions at 10 and 17 K are due to the magnetic ordering of Tb{sup 3+} and Ru{sup 5+} ions, respectively. - Graphical abstract: Temperature dependence of the magnetic specific heat divided by temperature (C{sub mag}/T) and the magnetic entropy (S{sub mag}) for Tb{sub 3}RuO{sub 7}. Two-step magnetic transition has been observed. - Highlights: • Tb{sub 3}RuO{sub 7} shows an antiferromagnetic transition at 17 K. • Specific heat measurements confirmed the occurrence of two-step magnetic transition. • The phase transition from space group P2{sub 1}nb to Cmcm has been observed at 402 K.
A raman study of hydrostatic pressure induced phase transitions in Rb2KInF6 crystals
NASA Astrophysics Data System (ADS)
Vtyurin, A. N.; Krylov, A. S.; Goryainov, S. V.; Krylova, S. N.; Oreshonkov, A. S.; Voronov, V. N.
2012-05-01
The Raman spectra of the elpasolite (Rb2KInF6) crystal have been studied in the pressure range from 0 to 5.3 GPa at a temperature of 295 K. A phase transition at a pressure of approximately 0.9 GPa has been found. An analysis of the variations in the spectral parameters has led to the conclusion that the phase transition to a distorted phase is accompanied by the doubling of the volume of the primitive cell of the initial cubic phase. Numerical calculations of the lattice dynamics in the Rb2KInF6 crystal have been performed. The numerical simulation has established that the phase transition at a pressure of 0.9 GPa is associated with condensation of the F lg mode. A probable high-pressure phase is the phase with space group C2/ m.
Transition Path Sampling Method and Its Application in Argon Phase Transition
NASA Astrophysics Data System (ADS)
Li, Bingxi
Rare events during both physical and chemical transitions are of great significance to under- stand the evolution of systems from one stable state to another. Solid-solid phase transition is a fundamental problem in this field and a lot of experimental and theoretical efforts have been made into tackling it. However Molecular Dynamics simulation in this field encounters the problem that these transitions occur too rarely to be observed within current simulations. Thus the Transition Path Sampling (TPS) method is designed to tackle this issue. The phase transition between face centered cubic (fcc) and hexagonal close packed (hcp) phases in argon solid at 40K is investigated with TPS method. TPS is a rare event sampling methodology, which combine Molecular Dynamics and Monte Carlo. Molecular Dynamics is used to generate the whole trajectory from an assigned starting point, based on the time evolution of the system. Monte Carlo is applied to select a structure from the known phase transition trajectories as the starting point. This is an importance sampling process and the acceptance probability for starting point selection depends on its equilibrium probability in the ensemble of interest. With TPS method, the sampling of trajectories can be efficiently performed in the phase transition trajectories ensemble. The sampling process will yield energetically favorable trajectories. A phase transition trajectory is required to initialize the Molecular Dynamics Transition Path Sampling process. This trajectory can be generated with Variable Cell Nudged Elastic Band (VCNEB) method, which determines Ar fcc to hcp transition at 0K. The configuration of transition state in VCNEB trajectory is selected as the initial state to start TPS calculation. An atomistic description of the mechanism of the fcc-to- hcp transformation in solid argon is then obtained from Molecular Dynamics transition path sampling simulations. We show that the transition barrier at 40 K under ambient
Tools for Studying Quantum Emergence near Phase Transitions
NASA Astrophysics Data System (ADS)
Imada, Masatoshi; Onoda, Shigeki; Mizusaki, Takahiro; Watanabe, Shinji
2003-12-01
We review recent studies on developing tools for quantum complex phenomena. The tools have been applied for clarifying the perspective of the Mott transitions and the phase diagram of metals, Mott insulators and magnetically ordered phases in the two-dimensional Hubbard model. The path-integral renormalization-group (PIRG) method has made it possible to numerically study correlated electrons even with geometrical frustration effects without biases . It has numerically clarified the phase diagram at zero temperature, T = 0, in the parameter space of the onsite Coulomb repulsion, the geometrical frustration amplitude and the chemical potential. When the bandwidth is controlled at half filling, the first-order transition between insulating and metallic phases is evidenced. In contrast, the filling-control transition shows diverging critical fluctuations for spin and charge responses with decreasing doping concentration. Near the Mott transition, a nonmagnetic spin-liquid phase appears in a region with large frustration effects. The phase is characterized remarkably by gapless spin excitations and the vanishing dispersion of spin excitations. Magnetic orders quantum mechanically melt through diverging magnon mass. The correlator projection method (CPM) is formulated as an extension of the operator projection theory. This method also allows an extension of the dynamical mean-field theory (DMFT) with systematic inclusion of the momentum dependence in the self-energy. It has enabled determining the phase diagram at T > 0, where the boundary surface of the first-order metal-insulator transition at half filling terminates on the critical end curve at T = Tc. The critical end curve is characterized by the diverging compressibility. The single particle spectra show strong renormalization of low-energy spectra, generating largely momentum dependent and flat dispersion. The results of two tools consistently suggest that the strong competitions of various phases with underlying
Microrheology close to an equilibrium phase transition
Reinhardt, J.; Scacchi, A.; Brader, J. M.
2014-04-14
We investigate the microstructural and microrheological response to a tracer particle of a two-dimensional colloidal suspension under thermodynamic conditions close to a liquid-gas phase boundary. On the liquid side of the binodal, increasing the velocity of the (repulsive) tracer leads to the development of a pronounced cavitation bubble, within which the concentration of colloidal particles is strongly depleted. The tendency of the liquid to cavitate is characterized by a dimensionless “colloidal cavitation” number. On the gas side of the binodal, a pulled (attractive) tracer leaves behind it an extended trail of colloidal liquid, arising from downstream advection of a wetting layer on its surface. For both situations the velocity dependent friction is calculated.
Structural transitions in condensed colloidal virus phases
NASA Astrophysics Data System (ADS)
Schmidt, Nathan; Barr, Steve; Udit, Andrew; Gutierrez, Leonardo; Nguyen, Thanh; Finn, M. G.; Luijten, Erik; Wong, Gerard
2010-03-01
Analogous to monatomic systems colloidal phase behavior is entirely determined by the interaction potential between particles. This potential can be tuned using solutes such as multivalent salts and polymers with varying affinity for the colloids to create a hierarchy of attractions. Bacteriophage viruses are a naturally occurring type of colloidal particle with characteristics difficult to achieve by laboratory synthesis. They are monodisperse, nanometers in size, and have heterogeneous surface charge distributions. We use the MS2 and Qbeta bacteriophages (diameters 27-28nm) to understand the interplay between different attraction mechanisms on nanometer-sized colloids. Small Angle X-ray Scattering (SAXS) is used to characterize the inter-particle interaction between colloidal viruses using several polymer species and different salt types.
Phase transitions in predator-prey systems
NASA Astrophysics Data System (ADS)
Nagano, Seido; Maeda, Yusuke
2012-01-01
The relationship between predator and prey plays an important role in ecosystem conservation. However, our understanding of the principles underlying the spatial distribution of predators and prey is still poor. Here we present a phase diagram of a predator-prey system and investigate the lattice formation in such a system. We show that the production of stable lattice structures depends on the limited diffusion or migration of prey as well as higher carrying capacity for the prey. In addition, when the prey's growth rate is lower than the birth rate of the predator, global prey lattice formation is initiated by microlattices at the center of prey spirals. The predator lattice is later formed in the predator spirals. But both lattice formations proceed together as the prey growth rate increases.
Structural phase transition and phonon instability in Cu12Sb4S13
NASA Astrophysics Data System (ADS)
May, A. F.; Delaire, O.; Niedziela, J. L.; Lara-Curzio, E.; Susner, M. A.; Abernathy, D. L.; Kirkham, M.; McGuire, M. A.
2016-02-01
A structural phase transition has been discovered in the synthetic tetrahedrite Cu12Sb4S13 at approximately 88 K. Upon cooling, the material transforms from its known cubic symmetry to a tetragonal unit cell that is characterized by an in-plane ordering that leads to a doubling of the unit cell volume. Specific heat capacity measurements demonstrate a hysteresis of more than two degrees in the associated anomaly. A similar hysteresis was observed in powder x-ray diffraction measurements, which also indicate a coexistence of the two phases, and together these results suggest a first-order transition. This structural transition coincides with a recently-reported metal-insulator transition, and the structural instability is related to the very low thermal conductivity κ in these materials. Inelastic neutron scattering was used to measure the phonon density of states in Cu12Sb4S13 and Cu10Zn2Sb4S13 , both of which possess a localized, low-energy phonon mode associated with strongly anharmonic copper displacements that suppress κ . In Cu12Sb4S13 , signatures of the phase transition are observed in the temperature dependence of the localized mode, which disappears at the structural transition. In contrast, in the cubic Zn-doped material, the mode is at slightly higher-energy but observable for all temperatures, though it softens upon cooling.
Structural phase transition and phonon instability in Cu12Sb4S13
May, Andrew F.; Delaire, Olivier A.; Niedziela, Jennifer L.; ...
2016-02-08
In this study, a structural phase transition has been discovered in the synthetic tetrahedrite Cu12Sb4S13 at approximately 88 K. Upon cooling, the material transforms from its known cubic symmetry to a tetragonal unit cell that is characterized by an in-plane ordering that leads to a doubling of the unit cell volume. Specific heat capacity measurements demonstrate a hysteresis of more than two degrees in the associated anomaly. A similar hysteresis was observed in powder x-ray diffraction measurements, which also indicate a coexistence of the two phases, and together these results suggest a first-order transition. This structural transition coincides with amore » recently-reported metal-insulator transition, and the structural instability is related to the very low thermal conductivity κ in these materials. Inelastic neutron scattering was used to measure the phonon density of states in Cu12Sb4S13 and Cu10Zn2Sb4S13, both of which possess a localized, low-energy phonon mode associated with strongly anharmonic copper displacements that suppress κ. In Cu12Sb4S13, signatures of the phase transition are observed in the temperature dependence of the localized mode, which disappears at the structural transition. In contrast, in the cubic Zn-doped material, the mode is at slightly higher-energy but observable for all temperatures, though it softens upon cooling.« less
Solid state phase transitions characterized by ESR and XAS
NASA Astrophysics Data System (ADS)
Acrivos, Juana Vivó
2000-12-01
Measurements of the relaxation time, τ of electron systems to a disturbance, by two different spectroscopic methods are examined in detail, with the purpose to establish how the presence of fluctuations near a solid state phase transition are made evident in insulators, conductors and superconductors. The absolute temperature and the relaxation time determine the thermodynamic stability of the electronic system near a phase transition by the Uncertainty Principle. At a given temperature T, Landau and Lifshitz obtain the stability from the lower limit of the uncertainty in entropy in units of the Boltzmann constant, Δ S/ kB<<1 when Tτ>>3.82 K ps. Magnetic resonance can measure τ>>10 -10 s, when v=9 GHz. X-ray spectroscopy can measure τ<10 -16s for hv>5 keV. The results extract information about phenomena that occur at the phase transition by following the evolution of spectral features versus T and crystal orientation. Electron spin resonance identifies the phase transition by the evolution of doublet, triplet and antiferromagnetic resonance, and energy loss. Analysis of the X-ray absorption near an element edge determines one, the relative valence: V(Cu in chains)- V(Cu in planes) ≈1 in YBa 2Cu 3O 7- δ, two, the appearance of allowed Cu K pre-edge quadrupole transitions at Tc, three, the enhancement of Ba L3,2 edge transitions by an order of magnitude, just above Tc, at a crystal orientation of the c-axis to the X-ray polarization vector of 8 π/18, and four, difference X-ray absorption spectra, relative to the transition temperature, identify the bonds as well as the atoms involved in the transition. The figure abstract shows the changes in electron density obtained by temperature difference X-ray absorption near the Y K-edge in YBa 2Cu 3O 7- δ below Tc.
NASA Technical Reports Server (NTRS)
1986-01-01
Lockheed Missiles and Space Company's conceptual designs and programmatics for a Space Station Nonhuman Life Sciences Research Facility (LSRF) are presented. Conceptual designs and programmatics encompass an Initial Orbital Capability (IOC) LSRF, a growth or follow-on Orbital Capability (FOC), and the transitional process required to modify the IOC LSFR to the FOC LSFR. The IOC and FOC LSFRs correspond to missions SAAX0307 and SAAX0302 of the Space Station Mission Requirements Database, respectively.
Enantiotropic phase transition in a binuclear tin complex with an O,N,O'-tridentate ligand.
Schwarzer, Anke; Paul, Lydia E H; Böhme, Uwe
2013-11-01
The crystal structure of chlorido{μ-2-[(2-oxidobenzylidene)amino]ethanolato-κ(4)O,N,O':O'}{2-[(2-oxidobenzylidene)amino]ethanolato-κ(3)O,N,O'}trivinylditin(IV), [Sn2(C2H3)3(C9H9NO2)2Cl], is disordered above 178 K. A doubling of the unit-cell volume is observed on cooling. The asymmetric unit at 93 K contains two ordered molecules. The phase transition corresponds to an order-disorder transition of one vinyl group bound to the Sn(IV) atom.
Optical Sensor for Characterizing the Phase Transition in Salted Solutions
Claverie, Rémy; Fontana, Marc D.; Duričković, Ivana; Bourson, Patrice; Marchetti, Mario; Chassot, Jean-Marie
2010-01-01
We propose a new optical sensor to characterize the solid-liquid phase transition in salted solutions. The probe mainly consists of a Raman spectrometer that extracts the vibrational properties from the light scattered by the salty medium. The spectrum of the O – H stretching band was shown to be strongly affected by the introduction of NaCl and the temperature change as well. A parameter SD defined as the ratio of the integrated intensities of two parts of this band allows to study the temperature and concentration dependences of the phase transition. Then, an easy and efficient signal processing and the exploitation of a modified Boltzmann equation give information on the phase transition. Validations were done on solutions with varying concentration of NaCl. PMID:22319327
Thermal phase transition in a QCD-like holographic model
Evans, Nick; Threlfall, Ed
2008-11-15
We investigate the high-temperature phase of a dilaton flow deformation of the anti-de Sitter/conformal field theory correspondence. We argue that these geometries should be interpreted as the N=4 gauge theory perturbed by a SO(6) invariant scalar mass and that the high-temperature phase is just the well-known anti-de Sitter-Schwarzschild solution. We compute, within supergravity, the resulting Hawking-Page phase transition, which in this model can be interpreted as a deconfining transition in which the vacuum expectation value for the operator TrF{sup 2} dissolves. In the presence of quarks the model also displays a simultaneous chiral symmetry restoring transition with the Goldstone mode and other quark bound states dissolving into the thermal bath.
GENERAL: Canonical Entropy and Phase Transition of Rotating Black Hole
NASA Astrophysics Data System (ADS)
Zhao, Ren; Wu, Yue-Qin; Zhang, Li-Chun
2008-07-01
Recently, the Hawking radiation of a black hole has been studied using the tunnel effect method. The radiation spectrum of a black hole is derived. By discussing the correction to spectrum of the rotating black hole, we obtain the canonical entropy. The derived canonical entropy is equal to the sum of Bekenstein-Hawking entropy and correction term. The correction term near the critical point is different from the one near others. This difference plays an important role in studying the phase transition of the black hole. The black hole thermal capacity diverges at the critical point. However, the canonical entropy is not a complex number at this point. Thus we think that the phase transition created by this critical point is the second order phase transition. The discussed black hole is a five-dimensional Kerr-AdS black hole. We provide a basis for discussing thermodynamic properties of a higher-dimensional rotating black hole.
Phase transition in spin systems with various types of fluctuations
MIYASHITA, Seiji
2010-01-01
Various types ordering processes in systems with large fluctuation are overviewed. Generally, the so-called order–disorder phase transition takes place in competition between the interaction causing the system be ordered and the entropy causing a random disturbance. Nature of the phase transition strongly depends on the type of fluctuation which is determined by the structure of the order parameter of the system. As to the critical property of phase transitions, the concept “universality of the critical phenomena” is well established. However, we still find variety of features of ordering processes. In this article, we study effects of various mechanisms which bring large fluctuation in the system, e.g., continuous symmetry of the spin in low dimensions, contradictions among interactions (frustration), randomness of the lattice, quantum fluctuations, and a long range interaction in off-lattice systems. PMID:20689226
Dark matter as the trigger of strong electroweak phase transition
Chowdhury, Talal Ahmed; Nemevšek, Miha; Senjanović, Goran; Zhang, Yue E-mail: miha@ictp.it E-mail: yuezhang@ictp.it
2012-02-01
In this paper, we propose a new possible connection between dark matter relic density and baryon asymmetry of the universe. The portal between standard model sector and dark matter not only controls the relic density and detections of dark matter, but also allows the dark matter to trigger the first order electroweak phase transition. We discuss systematically possible scalar dark matter candidates, starting from a real singlet to arbitrary high representations. We show that the simplest realization is provided by a doublet, and that strong first-order electroweak phase transition implies a lower bound on the dark matter direct detection rate. The mass of dark matter lies between 45 and 80 GeV, allowing for an appreciable invisible decay width of the Standard Model Higgs boson, which is constrained to be lighter than 130 GeV for the sake of the strong phase transition.
A MATLAB GUI to study Ising model phase transition
NASA Astrophysics Data System (ADS)
Thornton, Curtislee; Datta, Trinanjan
We have created a MATLAB based graphical user interface (GUI) that simulates the single spin flip Metropolis Monte Carlo algorithm. The GUI has the capability to study temperature and external magnetic field dependence of magnetization, susceptibility, and equilibration behavior of the nearest-neighbor square lattice Ising model. Since the Ising model is a canonical system to study phase transition, the GUI can be used both for teaching and research purposes. The presence of a Monte Carlo code in a GUI format allows easy visualization of the simulation in real time and provides an attractive way to teach the concept of thermal phase transition and critical phenomena. We will also discuss the GUI implementation to study phase transition in a classical spin ice model on the pyrochlore lattice.
Local measurements of phase transitions in Bacteriorhodopsin membrane
NASA Astrophysics Data System (ADS)
Proksch, R.; Nikiforov, M. P.; Hohlbauch, S.; King, W. P.; Antoraz Contera, S.; Voïtchovsky, K.; Kalinin, S. V.
2010-03-01
Phase transitions play an important role in biology. Specifically the thermodynamic stability of internal membrane proteins is an important issue of biophysics. Purple membrane from Halobacterium halobium contain bacteriorhodopsin (bR), an integral protein 70-80% of whole mass is intramembraneous. There are heated debates in the field about the parameters of thermal denaturation of bR, such as the denaturation temperature, enthalpy etc. Recently, bR was proposed as a component of biomolecular electronics. Thus, reliable information about the phase transitions of supported samples of bR membranes is necessary. Phase transitions in polymer/biopolymer materials are associated with the large changes in mechanical properties of the samples. We developed the technique for the measurements of the temperature dependence of the mechanical properties with high spatial resolution. This technique is based on the measurements of the contact stiffness of the atomic force microscopy tip -- sample system as a function of temperature.
Phase Transitions and Equilibrium Measures in Random Matrix Models
NASA Astrophysics Data System (ADS)
Martínez-Finkelshtein, A.; Orive, R.; Rakhmanov, E. A.
2015-02-01
The paper is devoted to a study of phase transitions in the Hermitian random matrix models with a polynomial potential. In an alternative equivalent language, we study families of equilibrium measures on the real line in a polynomial external field. The total mass of the measure is considered as the main parameter, which may be interpreted also either as temperature or time. Our main tools are differentiation formulas with respect to the parameters of the problem, and a representation of the equilibrium potential in terms of a hyperelliptic integral. Using this combination we introduce and investigate a dynamical system (system of ODEs) describing the evolution of families of equilibrium measures. On this basis we are able to systematically derive a number of new results on phase transitions, such as the local behavior of the system at all kinds of phase transitions, as well as to review a number of known ones.
Charge crossover at the U(1)-Higgs phase transition
Freire, Filipe; Litim, Daniel F.
2001-08-15
The type-I region of phase transitions at finite temperature of the U(1)-Higgs theory in 3+1 dimensions is investigated in detail using a Wilsonian renormalization group. We consider, in particular, the quantitative effects induced through the crossover of the scale-dependent Abelian charge from the Gaussian to a nontrivial Abelian fixed point. As a result, the strength of the first-order phase transition is weakened. Analytical solutions to approximate flow equations are obtained, and all characteristics of the phase transition are discussed and compared to the results obtained from perturbation theory. In addition, we present a detailed quantitative study regarding the dependence of the physical observables on the coarse-graining scheme. This results in error bars for the regularization scheme (RS) dependence. We find quantitative evidence for an intimate link between the RS dependence and truncations of flow equations.
Gravitational radiation from first-order phase transitions
Child, Hillary L.; Giblin, John T. Jr. E-mail: giblinj@kenyon.edu
2012-10-01
It is believed that first-order phase transitions at or around the GUT scale will produce high-frequency gravitational radiation. This radiation is a consequence of the collisions and coalescence of multiple bubbles during the transition. We employ high-resolution lattice simulations to numerically evolve a system of bubbles using only scalar fields, track the anisotropic stress during the process and evolve the metric perturbations associated with gravitational radiation. Although the radiation produced during the bubble collisions has previously been estimated, we find that the coalescence phase enhances this radiation even in the absence of a coupled fluid or turbulence. We comment on how these simulations scale and propose that the same enhancement should be found at the Electroweak scale; this modification should make direct detection of a first-order electroweak phase transition easier.
On the structural phase transition in rare earth elpasolites
NASA Astrophysics Data System (ADS)
Selgert, P.; Lingner, C.; Lüthi, B.
1984-09-01
The structural phase transition in two representatives of the rare earth elpasolite fluorides, Rb2NaHoF6 and Rb2NaTmF6, are studied in detail. The symmetry of the soft mode is determined from Raman spectra, X-ray and neutron powder diffraction data to be Γ{4/+}. From the temperature dependence of the elastic constants of both compounds, estimates of various phase transition parameters are given, e.g. strain soft mode coupling constant and soft mode frequency. The softening of the elastic constants for T>T c is explained by the strain coupling to the fluctuations of the soft mode coordinates. The energy of the soft phonon at the zone boundary is estimated from the data and compared with that of K2ReCl6. The phase transition mechanisms in rare earth elpasolites and hexahalometallates are discussed.
Superionic phase transition of doped fluorites
NASA Astrophysics Data System (ADS)
den Hartog, H. W.; van der Veen, J.
1988-02-01
In this paper we present new results of specific-heat experiments on superionic mixtures of cubic lead fluoride and some rare-earth fluorides. The results depend very strongly on the rare-earth ion; for samples doped with LaF3 we observe a peak in the specific heat as a function of T, which is located at an approximately fixed position. This peak, which is due to the superionic transition, increases in width with increasing concentrations of LaF3. If we add YbF3, however, the position of the peak varies. It appears that in samples doped with a few mol % YbF3 there are two peaks in the ``specific-heat spectrum'': one very similar to the peak observed in pure PbF2 and a second peak situated at significantly lower temperatures. The results are discussed in view of the experimental data on the clustering properties of the different solid solutions. In addition, we treat some of the specific-heat data with theoretical models, which have been proposed by Vlieg, den Hartog, and Winnink. This analysis suggests that due to the introduction of La impurities the formation of Frenkel pairs is more difficult. The introduction of Yb impurities, however, leads to additional Frenkel-pair formation, because Pb1-xYbxF2+x clusters, consisting of more than one Yb-F interstitial pair, trap extra interstitial F- ions. Because the energy of these extra trapped interstitial F- ions is lower than the energy of free anion interstitials, this leads to an enhancement of the formation of Frenkel pairs.
Guan, Shu-Hui; Liu, Zhi-Pan
2016-02-14
Structural inhomogeneity is ubiquitous in solid crystals and plays critical roles in phase nucleation and propagation. Here, we develop a heterogeneous solid-solid phase transition theory for predicting the prevailing heterophase junctions, the metastable states governing microstructure evolution in solids. Using this theory and first-principles pathway sampling simulation, we determine two types of heterophase junctions pertaining to metal α-ω phase transition at different pressures and predict the reversibility of transformation only at low pressures, i.e. below 7 GPa. The low-pressure transformation is dominated by displacive Martensitic mechanism, while the high-pressure one is controlled by the reconstructive mechanism. The mechanism of α-ω phase transition is thus highly pressure-sensitive, for which the traditional homogeneous model fails to explain the experimental observations. The results provide the first atomic-level evidence on the coexistence of two different solid phase transition mechanisms in one system.
Structural and topological phase transitions on the German Stock Exchange
NASA Astrophysics Data System (ADS)
Wiliński, M.; Sienkiewicz, A.; Gubiec, T.; Kutner, R.; Struzik, Z. R.
2013-12-01
We find numerical and empirical evidence for dynamical, structural and topological phase transitions on the (German) Frankfurt Stock Exchange (FSE) in the temporal vicinity of the worldwide financial crash. Using the Minimal Spanning Tree (MST) technique, a particularly useful canonical tool of the graph theory, two transitions of the topology of a complex network representing the FSE were found. The first transition is from a hierarchical scale-free MST representing the stock market before the recent worldwide financial crash, to a superstar-like MST decorated by a scale-free hierarchy of trees representing the market’s state for the period containing the crash. Subsequently, a transition is observed from this transient, (meta)stable state of the crash to a hierarchical scale-free MST decorated by several star-like trees after the worldwide financial crash. The phase transitions observed are analogous to the ones we obtained earlier for the Warsaw Stock Exchange and more pronounced than those found by Onnela-Chakraborti-Kaski-Kertész for the S&P 500 index in the vicinity of Black Monday (October 19, 1987) and also in the vicinity of January 1, 1998. Our results provide an empirical foundation for the future theory of dynamical, structural and topological phase transitions on financial markets.