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
2015-05-01
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. PMID:25956120
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.
Volume phase transitions of cholesteric liquid crystalline gels
NASA Astrophysics Data System (ADS)
Matsuyama, Akihiko
2015-05-01
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.
Salt effect on volume phase transition of a gel.
Annaka, Masahiko; Amo, Yuko; Sasaki, Shigeo; Tominaga, Yasunori; Motokawa, Keiko; Nakahira, Takayuki
2002-03-01
The salt effect on the phase transition of N-isopropylacrylamide (NIPA) gel was studied for alkali-metal chlorides (NaCl, KCl, and CsCl). Low-frequency Raman scattering experiment was conducted to know the dynamic state of water molecule under the presence of salt and its correlation to macroscopic phase behavior of the gel was investigated together with the thermodynamic activities of water molecule of aqueous alkali-metal chloride solutions. The series of swelling experiment reveal that the change in the gel volume phase transition strongly depends on the salt concentration and is related to the dehydration with respect to hydrophobic hydration. From the analysis of the reduced low-frequency Raman spectra in water and aqueous alkali-metal chlorides solutions by the use of the relaxation mode that takes into account the inertia and the non-white effects, the characteristic values of aqueous salt solutions (i.e., relaxation time and modulation speed) indicate that the addition of alkali-metal chloride to gel fluid affects the disruption of water molecules in the hydration shell around the NIPA gel and the formation of the hydrogen-bonded network structure of water around themselves, as a result of which the gel collapses. The chemical potential and the dynamic nature of water molecule at the transition points are well correlated: the chemical potentials at the transition points are almost constant whereas the structure of bulk water is changed by addition of alkali-metal chlorides or change in temperature. These results strongly suggest that the swelling ratio of N-isopropylacrylamide gel is a function of hydration degree, which is regulated by the chemical potential of water. PMID:11909100
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.
Effects of strongly selective additives on volume phase transition in gels
NASA Astrophysics Data System (ADS)
Uematsu, Yuki; Araki, Takeaki
2012-07-01
We investigate volume phase transition in gels immersed in mixture solvents, on the basis of a three-component Flory-Rehner theory. When the selectivity of the minority solvent component to the polymer network is strong, the gel tends to shrink with an increasing concentration of the additive, regardless of whether it is good or poor. This behavior originates from the difference of the additive concentration between inside and outside the gel. We also found the gap of the gel volume at the transition point can be controlled by adding the strongly selective solutes. By dissolving a strongly poor additive, for instance, the discontinuous volume phase transition can be extinguished. Furthermore, we observed that another volume phase transition occurs far from the original transition point. These behaviors can be well explained by a simplified theory neglecting the nonlinearity of the additive concentration.
Temperature-dependent phase transitions of a complex biological membrane in zeptoliter volumes
Nikiforov, Maxim; Hohlbauch, Sophia; King, William P; Voitchovsky, K; Contera, S Antoranz; Jesse, Stephen; Kalinin, Sergei V; Proksch, Roger
2011-01-01
Phase transitions in purple membrane have been a topic of debate for the past two decades. In this work we present studies of a reversible transition of purple membrane in the 50 60 C range in zeptoliter volumes under different heating regimes (global heating and local heating). The temperature of the reversible phase transition is 52 5 C for both local and global heating, supporting the hypothesis that this transition is mainly due to a structural rearrangement of bR molecules and trimers. To achieve high resolution measurements of temperature-dependent phase transitions, a new scanning probe microscopy-based method was developed. We believe that our new technique can be extended to other biological systems and can contribute to the understanding of inhomogeneous phase transitions in complex systems.
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.
Open volume defects and magnetic phase transition in Fe{sub 60}Al{sub 40} transition metal aluminide
Liedke, M. O. Anwand, W.; Butterling, M.; Wagner, A.; Bali, R.; Cornelius, S.; Potzger, K.; Trinh, T. T.; Salamon, S.; Walecki, D.; Smekhova, A.; Wende, H.
2015-04-28
Magnetic phase transition in the Fe{sub 60}Al{sub 40} transition metal aluminide from the ferromagnetic disordered A2-phase to the paramagnetic ordered B2-phase as a function of annealing up to 1000 °C has been investigated by means of magneto-optical and spectroscopy techniques, i.e., Kerr effect, positron annihilation, and Mössbauer spectroscopy. The positron annihilation spectroscopy has been performed in-situ sequentially after each annealing step at the Apparatus for In-situ Defect Analysis that is a unique tool combining positron annihilation spectroscopy with temperature treatment, material evaporation, ion irradiation, and sheet resistance measurement techniques. The overall goal was to investigate the importance of the open volume defects onto the magnetic phase transition. No evidence of variation in the vacancy concentration in matching the magnetic phase transition temperature range (400–600 °C) has been found, whereas higher temperatures showed an increase in the vacancy concentration.
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...
Yang, Man; Zhao, Kongshuang
2015-10-15
A new experimental result from dielectric spectroscopy of poly(N-isopropylacrylamide)/poly(acrylic acid) semi-interpenetrating polymer network (PNIPAM/PAA SIPN) microgel, which undergoes significant volume phase transition, is reported. Two significant dielectric relaxations were observed around 0.1-0.5 MHz and 1-5 MHz, respectively. The high-frequency relaxation is attributed to the migration of counterions tangentially and radially along the domain formed by linear PAA chains (counterion polarization). The temperature dependence of the domain size obtained from this relaxation shows that the SIPN microgel with higher content of PAA has better thermal response and swelling property. The low-frequency relaxation shows two separate mechanisms below and above the volume phase transition temperature (VPTT), which are dominated by different relaxation processes, respectively: micro-Brownian movement of solvated side groups of PNIPAM dominates when T < VPTT, while the interfacial polarization does when T > VPTT. A dielectric model was proposed to describe the collapsed microspheres suspension, from which the electrical parameters of microgel were calculated. The permittivity of microgel shows that a special ordered arrangement of water molecules is formed in microgel with less PAA. Thermodynamic parameters obtained from Eyring equation reveal that the difference in PAA content has a great influence on the thermodynamics of the phase transition process. Besides, it was found that the VPTT of the SIPN microgel was significantly increased compared with pure PNIPAM hydrogel microspheres. The essence of anomalous VPTT revealed by relaxation mechanism is the difference in composition content leading to different hydrophilic/hydrophobic and electrostatic interaction. Determining the reason for anomalous VPTT is of instructive significance to understand the volume phase transition of complex polymer materials. PMID:26401730
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.
Photoinduced phase transitions.
Bennemann, K H
2011-02-23
Optically induced ultrafast electronic excitations with sufficiently long lifetimes may cause strong effects on phase transitions like structural and nonmetal→metal ones and on supercooling, supersaturation, etc. Examples are the transitions diamond→graphite, graphite→graphene, non-metal→metal, solid→liquid and vapor→liquid, solid. Photoinduced formation of graphene and water condensation of saturated or supersaturated vapor due to increased bonding amongst water molecules are of particular interest. These nonequilibrium transitions are an ultrafast response, on a few hundred fs time scale, to the fast low to large energy electronic excitations. The energy of the photons is converted into electronic energy via electronic excitations changing the cohesive energy. This changes the chemical potential controlling the phase transition. In view of the advances in laser optics photon induced transitions are expected to become an active area in nonequilibrium physics and phase transition dynamics. Conservation laws like energy or angular momentum conservation control the time during which the transitions occur. Since the photon induced effects result from weakening or strengthening of the bonding between the atoms or molecules transitions like solid/liquid, etc can be shifted in both directions. Photoinduced transitions will be discussed from a unified point of view. PMID:21411879
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)
Anderson, Gregory Wayne
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,
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.
Capitani, F; Trequattrini, F; Palumbo, O; Paolone, A; Postorino, P
2016-03-24
A detailed Raman study has been carried out on the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14-TFSI) over a wide pressure (0-8 GPa) and temperature (100-300 K) range. The explored thermodynamic region allowed us to study the evolution of the system across different solid and liquid phases. Calculated Raman spectra remarkably helped in the spectral data analysis. In particular, the pressure behavior of the most intense Raman peak and the shape analysis of the ruby fluorescence (used as a local pressure gauge) allowed us to identify a liquid-solid transition around 2.2 GPa at T = 300 K. The low-frequency Raman signal as well as the absence of remarkable spectral shape modifications on crossing the above threshold and the comparison with the spectra of the crystalline phase suggest a glassy nature of the high-pressure phase. A detailed analysis of the pressure dependence of the relative concentration of two conformers of TFSI allowed us to obtain an estimate of the volume variation between trans-TFSI and the smaller cis-TFSI, which is the favored configuration on applying the pressure. Finally, the combined use of both visual inspection and Raman spectroscopy confirmed the peculiar sequence of phase transitions observed as a function of temperature at ambient pressure and the different spectral/morphological characteristics of the two crystalline phases. PMID:26937556
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.
Vadlamani, Bhaskar S; An, Ke; Jagannathan, M.; Ravi Chandran, K.
2014-01-01
The design and performance of a novel in-situ electrochemical cell that greatly facilitates the neutron diffraction study of complex phase transitions in small volume electrodes of Li-ion cells, is presented in this work. Diffraction patterns that are Rietveld-refinable could be obtained simultaneously for all the electrodes, which demonstrates that the cell is best suited to explore electrode phase transitions driven by the lithiation and delithiation processes. This has been facilitated by the use of single crystal (100) Si sheets as casing material and the planar cell configuration, giving improved signal-to-noise ratio relative to other casing materials. The in-situ cell has also been designed for easy assembly and to facilitate rapid experiments. The effectiveness of cell is demonstrated by tracking the neutron diffraction patterns during the charging of graphite/LiCoO2 and graphite/LiMn2O4 cells. It is shown that good quality neutron diffraction data can be obtained and that most of the finer details of the phase transitions, and the associated changes in crystallographic parameters in these electrodes, can be captured.
Xiao, Bin; Kegler, Philip; Gesing, Thorsten M; Robben, Lars; Blanca-Romero, Ariadna; Kowalski, Piotr M; Li, Yan; Klepov, Vladislav; Bosbach, Dirk; Alekseev, Evgeny V
2016-01-18
By applying high temperature (1270 K) and high pressure (3.5 GPa), significant changes occur in the structural volume and crystal topology of ThMo2 O8 , allowing the formation of an unexpected new ThMo2 O8 polymorph (high-temperature/high-pressure (HT/HP) orthorhombic ThMo2 O8 ). Compared with the other three ThMo2 O8 polymorphs prepared at the ambient pressure (monoclinic, orthorhombic, and hexagonal phases), the molar volume for the quenched HT/HP-orthorhombic ThMo2 O8 is decreased by almost 20 %. As a result of such a dramatic structural transformation, a permanent high-pressure quenchable state is able to be sustained when the pressure is released. The crystal structures of the three ambient ThMo2 O8 phases are based on three-dimensional (3D) frameworks constructed from corner-sharing ThOx (x=6, 8, or 9) polyhedra and MoO4 tetrahedra. The HT/HP-orthorhombic ThMo2 O8 , however, crystallizes in a novel structural topology, exhibiting very dense arrangements of ThO11 and MoO4+1 polyhedra connecting along the crystallographic c axis. The phase transitions among all four of these ThMo2 O8 polymorphs are unveiled and fully characterized with regard to the structural transformation, thermal stability, and vibrational properties. The complementary first principles calculations of Gibbs free energies reveal the underlying energetics of the phase transition, which support the experimental findings. PMID:26626413
Patra, Leena; Messman, Jamie M; Toomey, Ryan G
2013-01-01
Ellipsometry in an inverted configuration was used to characterize the temperature-dependent swelling of thin (100 nm) coatings of photo-cross-linked poly(cyclopropylacrylamide), or poly(CPAAm), and poly(vinylisobutyramide), or poly(NVIBAm). Both polymers contained 3 mole % of methacroylaminobenzophenone (MnBP) as the photo-cross-linking unit. Poly(CPAAm-co-MnBP) showed a continuous, 2nd order deswelling transition between 10 and 70 oC with no hysteresis. Poly(NVIBAm), on the other hand showed a discontinuous, 1st order deswelling transition at 45 oC with a hysteresis in the swelling curve. The differences in the swelling transitions can be interpreted within the context of the cloud-point measurements of the uncross-linked polymers. Whereas poly(NVIBAm-co-MnBP) has a significant off-zero critical point (>10 wt% polymer) at 36oC, poly(CPAAm-co-MnBP) has a critical point at zero concentration and 23 oC. Concurrent measurements of the infrared vibrations of the amide groups in both polymers further revealed that the amide group in poly(CPAAm-co-MnBP) maintains a constant hydrogen-bonding environment throughout the volume-phase transition. Poly(NVIBAm-co-MnBP), on the other hand, has a concentration dependent hydrogen bonding environment around the carbonyl group, which is consistent with an off-zero concentration in the cloud point curve.
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}.
Theory of antiferroelectric phase transitions
NASA Astrophysics Data System (ADS)
Tolédano, Pierre; Guennou, Mael
2016-07-01
At variance with structural ferroic phase transitions which give rise to macroscopic tensors coupled to macroscopic fields, criteria defining antiferroelectric (AFE) phase transitions are still under discussion due to the absence of specific symmetry properties characterizing their existence. They are recognized by the proximity of a ferroelectric (FE) phase induced under applied electric field, with a double hysteresis loop relating the induced polarization to the electric field and a typical anomaly of the dielectric permittivity. Here, we show that there exist indeed symmetry criteria defining AFE transitions. They relate the local symmetry of the polar crystallographic sites emerging at an AFE phase transition with the macroscopic symmetry of the AFE phase. The dielectric properties of AFE transitions are deduced from a Landau theoretical model in which ferroelectric and ferrielectric phases are shown to stabilize as the result of specific symmetry-allowed couplings of the AFE order parameter with the field-induced polarization.
Phase Transitions for Suspension Flows
NASA Astrophysics Data System (ADS)
Iommi, Godofredo; Jordan, Thomas
2013-06-01
This paper is devoted to studying the thermodynamic formalism for suspension flows defined over countable alphabets. We are mostly interested in the regularity properties of the pressure function. We establish conditions for the pressure function to be real analytic or to exhibit a phase transition. We also construct an example of a potential for which the pressure has countably many phase transitions.
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.
Transition of Bery Phase and Pancharatnam Phase and Phase Change
NASA Astrophysics Data System (ADS)
Fu, Guolan; Pan, Hui; Wang, Zisheng
2016-07-01
Berry Phase and time-dependent Pancharatnam phase are investigated for nuclear spin polarization in a liquid by a rotation magnetic field, where two-state mixture effect is exactly included in the geometric phases. We find that when the system of nuclear spin polarization is in the unpolarized state, the transitive phenomena of both Berry phase and Pancharatnam phase are taken place. For the polarized system, in contrast, such a transition is not taken place. It is obvious that the transitions of geometric phase correspond to the phase change of physical system.
Cavagnoli, Rafael; Menezes, Debora P.; Providencia, Constanca
2009-06-03
In the present work we study the hadron-quarkphase transition with boson condensation by investigating the binodal surface and extending it to finite temperature in order to mimic the QCD phase diagram.
Holographic approach to phase transitions
Franco, Sebastian; Garcia-Garcia, Antonio M.; Rodriguez-Gomez, Diego
2010-02-15
We provide a description of phase transitions at finite temperature in strongly coupled field theories using holography. For this purpose, we introduce a general class of gravity duals to superconducting theories that exhibit various types of phase transitions (first or second order with both mean and non-mean field behavior) as parameters in their Lagrangian are changed. Moreover the size and strength of the conductivity coherence peak can also be controlled. Our results suggest that certain parameters in the gravitational dual control the interactions responsible for binding the condensate and the magnitude of its fluctuations close to the transition.
Phase transition of holographic entanglement entropy in massive gravity
NASA Astrophysics Data System (ADS)
Zeng, Xiao-Xiong; Zhang, Hongbao; Li, Li-Fang
2016-05-01
The phase structure of holographic entanglement entropy is studied in massive gravity for the quantum systems with finite and infinite volumes, which in the bulk is dual to calculating the minimal surface area for a black hole and black brane respectively. In the entanglement entropy-temperature plane, we find for both the black hole and black brane there is a Van der Waals-like phase transition as the case in thermal entropy-temperature plane. That is, there is a first order phase transition for the small charge and a second order phase transition at the critical charge. For the first order phase transition, the equal area law is checked and for the second order phase transition, the critical exponent of the heat capacity is obtained. All the results show that the phase structure of holographic entanglement entropy is the same as that of thermal entropy regardless of the volume of the spacetime on the boundary.
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.
Non-equilibrium phase transitions
Mottola, E.; Cooper, F.M.; Bishop, A.R.; Habib, S.; Kluger, Y.; Jensen, N.G.
1998-12-31
This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Non-equilibrium phase transitions play a central role in a very broad range of scientific areas, ranging from nuclear, particle, and astrophysics to condensed matter physics and the material and biological sciences. The aim of this project was to explore the path to a deeper and more fundamental understanding of the common physical principles underlying the complex real time dynamics of phase transitions. The main emphasis was on the development of general theoretical tools to deal with non-equilibrium processes, and of numerical methods robust enough to capture the time-evolving structures that occur in actual experimental situations. Specific applications to Laboratory multidivisional efforts in relativistic heavy-ion physics (transition to a new phase of nuclear matter consisting of a quark-gluon plasma) and layered high-temperature superconductors (critical currents and flux flow at the National High Magnetic Field Laboratory) were undertaken.
Phase Transitions in Dipalmitoylphosphatidylcholine Monolayers.
Zuo, Yi Y; Chen, Rimei; Wang, Xianju; Yang, Jinlong; Policova, Zdenka; Neumann, A Wilhelm
2016-08-23
A self-assembled phospholipid monolayer at an air-water interface is a well-defined model system for studying surface thermodynamics, membrane biophysics, thin-film materials, and colloidal soft matter. Here we report a study of two-dimensional phase transitions in the dipalmitoylphosphatidylcholine (DPPC) monolayer at the air-water interface using a newly developed methodology called constrained drop surfactometry (CDS). CDS is superior to the classical Langmuir balance in its capacity for rigorous temperature control and leak-proof environments, thus making it an ideal alternative to the Langmuir balance for studying lipid polymorphism. In addition, we have developed a novel Langmuir-Blodgett (LB) transfer technique that allows the direct transfer of lipid monolayers from the droplet surface under well-controlled conditions. This LB transfer technique permits the direct visualization of phase coexistence in the DPPC monolayer. With these technological advances, we found that the two-dimensional phase behavior of the DPPC monolayer is analogous to the three-dimensional phase transition of a pure substance. This study has implications in the fundamental understanding of surface thermodynamics as well as applications such as self-assembled monolayers and pulmonary surfactant biophysics. PMID:27479299
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.
Polarized gravitational waves from cosmological phase transitions
NASA Astrophysics Data System (ADS)
Kisslinger, Leonard; Kahniashvili, Tina
2015-08-01
We estimate the degree of circular polarization for the gravitational waves generated during the electroweak and QCD phase transitions from the kinetic and magnetic helicity generated by bubble collisions during those cosmological phase transitions.
Acoustic Detection of Phase Transitions at the Nanoscale
Vasudevan, Rama K.; Khassaf, Hamidreza; Cao, Ye; Zhang, Shujun; Tselev, Alexander; Carmichael, Ben D.; Okatan, Mahmut Baris; Jesse, Stephen; Chen, Long-Qing; Alpay, S. Pamir; et al
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 transition dynamics and gravitational waves
Megevand, Ariel
2009-04-20
During a first-order phase transition, gravitational radiation is generated either by bubble collisions or by turbulence. For phase transitions which took place at the electroweak scale and beyond, the signal is expected to be within the sensitivity range of planned interferometers such as LISA or BBO. We review the generation of gravitational waves in a first-order phase transition and discuss the dependence of the spectrum on the dynamics of the phase transition.
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.
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. PMID:25019721
Nonequilibrium dynamics of phase transitions
NASA Astrophysics Data System (ADS)
Gagne, Carmen Jeanne
2001-11-01
Phase transitions occur in such diverse and important systems as ferromagnets, liquid crystals and the early Universe. The dynamics of phase transitions such as these have been studied for decades, but the analytical models still need a great deal of improvement before they can adequately describe all time stages and regions under the coexistence curve. Numerical studies can supplement these analytical theories, but they need to accurately describe the continuum equations that they are intended to solve. This thesis describes a method for removing the lattice- spacing and renormalization-mass dependence of Langevin simulations of phase mixing in (2 + 1)-dimensional asymmetric Ginzburg-Landau models with short-ranged interactions. Also, the spread in the order parameter near the critical value of the control parameter due to critical slowing down is used to more accurately determine this value of the control parameter in these simulations. In addition, a new method is proposed for quantifying the departure from equilibrium. The method explores the behavior of the rate of change of the momentum-integrated structure function, ΔStot( t), as it evolves in time. As an illustration, we examine a (1 + 1)-dimensional model of a stochastic Ginzburg-Landau model at varying cooling rates. We show that ΔStot(t) displays a peak which scales with cooling time-scale as t1/2q in the over-damped limit and t1/3q in the underdamped limit. The peak amplitude was found to scale with cooling time-scale as t6/5q in all viscosities studied.
NASA Astrophysics Data System (ADS)
García-Sánchez, Eduardo; Mendoza-Huizar, Luis H.; Ramírez-García, Uriel; Sustaita, Ireri A.; Alvarado, Francisco
2015-04-01
In this work, we have analyzed the experimental pressure-temperature behavior at the isotropic-nematic phase transition of the liquid crystals PAP, 5CB, MBBA, and EBBA at 1 atm by using the HERSW Convex Peg model in conjunction with the IPCM model. We have calculated the molecular volume values for the hard and attractive cores from theoretical quantum calculations at the PM3, PM6, B3LYP/6-311++G(d,p)//PM6, and M06/6-311++G(d,p)//PM6 levels of theory. The results suggest that the best theoretical prediction of the experimental pressure-temperature behavior is obtained when the molecular volume is evaluated at the DFT level.
NASA Astrophysics Data System (ADS)
Trenkler, Johann
We have observed two length scales in the critical x-ray diffuse scattering (CDS) from a VH0.525 crystal above the beta1-beta 2 phase transition where a sharp Lorentzian profile in the CDS was superimposed on a broader one. While no sharp component appeared in transmission geometry with high-energy x-rays, no broad component was detected in an experiment confined to a near-surface volume. Based on HERDA- and SNMS-measurements, the decay of the mosaic spread with increasing penetration, a larger d-spacing in the skin layer than in the bulk, and the above x-ray experiments, we conclude that the sharp component arises in the presence of a "defective" near-surface volume, while the broad component is associated with the pure bulk. For the defective skin layer, we observed a continuous phase transition allowing us to extract a tricritical exponent beta below TC, and tricritical exponents nu1 and gamma 1 for small reduced temperatures t = T/ TC -- 1. For larger t, the exponents nu and gamma are altered within the experimental range of t. Furthermore, the CDS of the defective skin layer is very anisotropic . The bulk, however, displays a strong discontinuous phase transition. This is not associated with a crossing of a two-phase region, nor with the small concentration H/V gradient within the upper 200 A, nor with a local (near-surface) ternary phase diagram due to an oxygen gradient in this region. The bulk displays an almost isotropic diffuse intensity above TC. In this work, we discuss the scaling and crossover behavior in the skin layer, the change of the order of the phase transition from the bulk to the skin layer associated with a change in the sign of the fourth order term in the Landau free energy expansion and the change of the correlation length with temperature, crystallographic direction and penetration. Furthermore, we qualitatively simulate the short-range order via Krivoglaz-Clapp-Moss and the Chepulskii-Bugaev RING approximations, taking into account the
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.
Phase Transition of Diluted Magnetic Semiconductor
NASA Astrophysics Data System (ADS)
Li, M. K.; Lee, S. J.; Yuldashev, S. U.; Ihm, G.; Kang, T. W.
2011-12-01
Three types of phase transitions in diluted magnetic semiconductor, first-order, second-order and mixed-order, are found in theory. Especially the mixed type transition shows two steps transition and novel specific heat property. Specific heat properties disclose a possible meta ferromagnetic phase confirmed by the experimental qualitative result.
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.
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.
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.
Phase transitions in semidefinite relaxations
Javanmard, Adel; Montanari, Andrea; Ricci-Tersenghi, Federico
2016-01-01
Statistical inference problems arising within signal processing, data mining, and machine learning naturally give rise to hard combinatorial optimization problems. These problems become intractable when the dimensionality of the data is large, as is often the case for modern datasets. A popular idea is to construct convex relaxations of these combinatorial problems, which can be solved efficiently for large-scale datasets. Semidefinite programming (SDP) relaxations are among the most powerful methods in this family and are surprisingly well suited for a broad range of problems where data take the form of matrices or graphs. It has been observed several times that when the statistical noise is small enough, SDP relaxations correctly detect the underlying combinatorial structures. In this paper we develop asymptotic predictions for several detection thresholds, as well as for the estimation error above these thresholds. We study some classical SDP relaxations for statistical problems motivated by graph synchronization and community detection in networks. We map these optimization problems to statistical mechanics models with vector spins and use nonrigorous techniques from statistical mechanics to characterize the corresponding phase transitions. Our results clarify the effectiveness of SDP relaxations in solving high-dimensional statistical problems. PMID:27001856
Phase transitions in semidefinite relaxations.
Javanmard, Adel; Montanari, Andrea; Ricci-Tersenghi, Federico
2016-04-19
Statistical inference problems arising within signal processing, data mining, and machine learning naturally give rise to hard combinatorial optimization problems. These problems become intractable when the dimensionality of the data is large, as is often the case for modern datasets. A popular idea is to construct convex relaxations of these combinatorial problems, which can be solved efficiently for large-scale datasets. Semidefinite programming (SDP) relaxations are among the most powerful methods in this family and are surprisingly well suited for a broad range of problems where data take the form of matrices or graphs. It has been observed several times that when the statistical noise is small enough, SDP relaxations correctly detect the underlying combinatorial structures. In this paper we develop asymptotic predictions for several detection thresholds, as well as for the estimation error above these thresholds. We study some classical SDP relaxations for statistical problems motivated by graph synchronization and community detection in networks. We map these optimization problems to statistical mechanics models with vector spins and use nonrigorous techniques from statistical mechanics to characterize the corresponding phase transitions. Our results clarify the effectiveness of SDP relaxations in solving high-dimensional statistical problems. PMID:27001856
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.
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.
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.
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
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.
Pressure-induced phase transition in pentacene
NASA Astrophysics Data System (ADS)
Farina, L.; Brillante, A.; Della Valle, R. G.; Venuti, E.; Amboage, M.; Syassen, K.
2003-07-01
We have recently studied two solid phases of bulk pentacene (polymorphs H and C) by means of lattice phonon Raman spectroscopy. The assignment, previously based on lattice dynamics calculations alone, is now verified by X-ray diffraction measurements, conclusively confirming the existence of both polymorphs. Furthermore, Raman phonon spectra indicate a pressure-induced phase transition where the polymorph C (lower density phase) transforms to the H form (higher density phase). The onset pressure for the phase transition is only 0.2 GPa. The phase change is irreversible.
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.
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.
Topological phase transitions in the gauged BPS baby Skyrme model
NASA Astrophysics Data System (ADS)
Adam, C.; Naya, C.; Romanczukiewicz, T.; Sanchez-Guillen, J.; Wereszczynski, A.
2015-05-01
We demonstrate that the gauged BPS baby Skyrme model with a double vacuum potential allows for phase transitions from a non-solitonic to a solitonic phase, where the latter corresponds to a ferromagnetic liquid. Such a transition can be generated by increasing the external pressure P or by turning on an external magnetic field H. As a consequence, the topological phase where gauged BPS baby skyrmions exist, is a higher density phase. For smaller densities, obtained for smaller values of P and H, a phase without solitons is reached. We find the critical line in the P, H parameter space. Furthermore, in the soliton phase, we find the equation of state for the baby skyrmion matter V = V( P,H) at zero temperature, where V is the "volume", i.e., area of the solitons.
Automatic contrast phase estimation in CT volumes.
Sofka, Michal; Wu, Dijia; Sühling, Michael; Liu, David; Tietjen, Christian; Soza, Grzegorz; Zhou, S Kevin
2011-01-01
We propose an automatic algorithm for phase labeling that relies on the intensity changes in anatomical regions due to the contrast agent propagation. The regions (specified by aorta, vena cava, liver, and kidneys) are first detected by a robust learning-based discriminative algorithm. The intensities inside each region are then used in multi-class LogitBoost classifiers to independently estimate the contrast phase. Each classifier forms a node in a decision tree which is used to obtain the final phase label. Combining independent classification from multiple regions in a tree has the advantage when one of the region detectors fail or when the phase training example database is imbalanced. We show on a dataset of 1016 volumes that the system correctly classifies native phase in 96.2% of the cases, hepatic dominant phase (92.2%), hepatic venous phase (96.7%), and equilibrium phase (86.4%) in 7 seconds on average. PMID:22003696
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}.
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}.
Phase transitions and convection in icy satellites
NASA Technical Reports Server (NTRS)
Bercovici, D.; Schubert, G.; Reynolds, R. T.
1986-01-01
The effects of solid-solid phase changes on subsolidus convection in the large icy moons of the outer solar system are considered. Phase transitions affect convection via processes that distort the phase change boundary and/or influence buoyancy through thermal expansion. Linear stability analyses are carried out for ice layers with a phase change at the midplane. Two exothermic phase transitions (ice I - ice II, ice VI - ice VIII) and two endothermic transitions (ice I - ice III, ice II - ice V) are considered. For the exothermic cases, the phase change can either impede or enhance whole-layer convection. For the endothermic cases, the phse change always inhibits whole-layer convective overturn and tends to enforce two-layer convection. These results play some constraints on possible models of icy satellite evolution and structure.
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
Thermal Phase Transitions in Finite Quantum Systems
Dean, D.J.
2001-10-18
In this Proceedings, the author will describe the behavior of two different quantum-mechanical systems as a function of increasing temperature. While these systems are somewhat different, the questions addressed are very similar, namely, how does one describe transitions in phase of a finite many-body system; how does one recognize these transitions in practical calculations; and how may one obtain the order of the transition.
Phase transition model for community detection
NASA Astrophysics Data System (ADS)
Wu, Jianshe; Lu, Rui; Jiao, Licheng; Liu, Fang; Yu, Xin; Wang, Da; Sun, Bo
2013-03-01
Motivated by social and biological interactions, a novel type of phase transition model is provided in order to investigate the emergence of the clustering phenomenon in networks. The model has two types of interactions: one is attractive and the other is repulsive. In each iteration, the phase of a node (or an agent) moves toward the average phase of its neighbors and moves away from the average phase of its non-neighbors. The velocities of the two types of phase transition are controlled by two parameters, respectively. It is found that the phase transition phenomenon is closely related to the topological structure of the underlying network, and thus can be applied to identify its communities and overlapping groups. By giving each node of the network a randomly generated initial phase and updating these phases by the phase transition model until they reach stability, one or two communities will be detected according to the nodes’ stable phases, confusable nodes are moved into a set named Of. By removing the detected communities and the nodes in Of, another one or two communities will be detected by an iteration of the algorithm, …. In this way, all communities and the overlapping nodes are detected. Simulations on both real-world networks and the LFR benchmark graphs have verified the efficiency of the proposed scheme.
Nuclear binding near a quantum phase transition
NASA Astrophysics Data System (ADS)
Lee, Dean
2016-03-01
I review recent ab initio results by the Nuclear Lattice Effective Field Theory Collaboration showing that nature lies close to a quantum phase transition between an alpha-particle gas and nuclear liquid. I discuss the control parameter of this transition and the implications for clustering in nuclei and improving ab initio nuclear structure calculations.
Phase transitions three-component superfluid
NASA Astrophysics Data System (ADS)
Carlstrom, Johan; Babaev, Egor
2014-03-01
We discuss phase transitions in three-component models of superfluidity and superconductivity. We present Monte Carlo simulations showing that for certain types of inter-component interactions, these systems exhibit novel types of first order phase transitions that are driven by spin-waves. Supported by NSF CAREER Award DMR-0955902, Knut and Alice Wallenberg Foundation through the Royal Swedish Academy of Sciences andSwedish Research Council.
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.
Modelling of phase transitions: do it yourself
NASA Astrophysics Data System (ADS)
Medved', I.; Huckaby, D. A.; Trník, A.; Valovičová, L'
2013-01-01
We present the basics of a powerful contemporary statistical mechanical technique that can be used by students to explore first-order phase transitions by themselves and for models of their own construction. The technique is a generalization of the well-known Peierls argument and is applicable to various models on a lattice. We illustrate the technique with the help of two simple models that were recently used to simulate phase transitions on surfaces.
Higgs couplings and electroweak phase transition
NASA Astrophysics Data System (ADS)
Katz, Andrey; Perelstein, Maxim
2014-07-01
We argue that extensions of the Standard Model (SM) with a strongly first-order electroweak phase transition generically predict significant deviations of the Higgs couplings to gluons, photons, and Z bosons from their SM values. Precise experimental measurements of the Higgs couplings at the LHC and at the proposed next-generation facilities will allow for a robust test of the phase transition dynamics. To illustrate this point, in this paper we focus on the scenario in which loops of a new scalar field are responsible for the first-order phase transition, and study a selection of benchmark models with various SM gauge quantum numbers of the new scalar. We find that the current LHC measurement of the Higgs coupling to gluons already excludes the possibility of a first-order phase transition induced by a scalar in a sextet, or larger, representation of the SU(3) c . Future LHC experiments (including HL-LHC) will be able to definitively probe the case when the new scalar is a color triplet. If the new scalar is not colored, an electron-positron Higgs factory, such as the proposed ILC or TLEP, would be required to test the nature of the phase transition. The extremely precise measurement of the Higgsstrahlung cross section possible at such machines will allow for a comprehensive and definitive probe of the possibility of a first-order electroweak phase transition in all models we considered, including the case when the new scalar is a pure gauge singlet.
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.
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.
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.
Continuous and discontinuous topological quantum phase transitions
NASA Astrophysics Data System (ADS)
Roy, Bitan; Goswami, Pallab; Sau, Jay D.
2016-07-01
The continuous quantum phase transition between noninteracting, time-reversal symmetric topological and trivial insulators in three dimensions is described by the massless Dirac fermion. We address the stability of this quantum critical point against short range electronic interactions by using renormalization group analysis and mean field theory. For sufficiently weak interactions, we show that the nature of the direct transition remains unchanged. Beyond a critical strength of interactions we find that either (i) there is a direct first order transition between two time reversal symmetric insulators or (ii) the direct transition is eliminated by an intervening time reversal and inversion odd "axionic" insulator. We also demonstrate the existence of an interaction driven first order quantum phase transition between topological and trivial gapped states in lower dimensions.
Monoclinic phases arising across thermal inter-ferroelectric phase transitions
NASA Astrophysics Data System (ADS)
Gu, Yijia; Xue, Fei; Lei, Shiming; Lummen, Tom T. A.; Wang, Jianjun; Gopalan, Venkatraman; Chen, Long-Qing
2014-07-01
Thermotropic phase boundaries (TPBs), as thermal analogs of morphotropic phase boundaries (MPBs), are associated with the thermal inter-ferroelectric phase transitions. Similar to an MPB, a TPB exhibits a characteristically flattened energy profile which favors polarization rotation, thus giving rise to a structurally bridging low-symmetry phase. We report on the kinetic process of thermal inter-ferroelectric phase transitions in BaTiO3 and KNbO3 using the phase-field method. The domain structures are found to play key roles in stabilizing the monoclinic phase. In simple domain structures, the monoclinic phase is a transient phase and cannot be stabilized into its neighboring phase regimes. However, by introducing structural inhomogeneity (orthogonal in-plane domain twins), we found that the monoclinic phase can be stabilized over a range of over 100 K across the transition. As a result, the piezoelectric properties are enhanced due to the stabilized monoclinic phase. In addition to the emergence of new piezoelectric components with monoclinic symmetry, most of the original components present in the tetragonal symmetry also show substantial enhancement with the rotation of polarization.
Thermochromic phase transitions in two aromatic tetrachlorocuprates
NASA Astrophysics Data System (ADS)
Mostafa, M. Fareed; Abdel-Kader, M. M.; Arafat, S. S.; Kandeel, E. M.
1991-06-01
Bis(para-toluidinium)2 tetrachlorocuprate and bis(para-chloroanilinium)2 tetrachlorocuprate crystallize in a perovskite-related layer structure. The former crystallizes in an orthorhombic unit cell with a = 6.911 Å, b = 7.052 Å and c = 33.182 Å. It undergoes a thermochromic first order phase transition from a yellow low temperature phase to a dark orange high temperature phase at T = 300 ± 3K with a 10° thermal hysteresis. The latter compound undergoes two thermochromic transitions expressed by the relation. Orange Phase (I) rightleftarrows294 K Yellow Phase (II) rightleftarrows214K Green Phase (III). Both compounds are ferromagnetic at low temperture with exchange interactions J/k = 17.5° and 20° for the two compounds respectively.
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. PMID:23215170
Sensitivity analysis of volume scattering phase functions.
Tuchow, Noah; Broughton, Jennifer; Kudela, Raphael
2016-08-01
To solve the radiative transfer equation and relate inherent optical properties (IOPs) to apparent optical properties (AOPs), knowledge of the volume scattering phase function is required. Due to the difficulty of measuring the phase function, it is frequently approximated. We explore the sensitivity of derived AOPs to the phase function parameterization, and compare measured and modeled values of both the AOPs and estimated phase functions using data from Monterey Bay, California during an extreme "red tide" bloom event. Using in situ measurements of absorption and attenuation coefficients, as well as two sets of measurements of the volume scattering function (VSF), we compared output from the Hydrolight radiative transfer model to direct measurements. We found that several common assumptions used in parameterizing the radiative transfer model consistently introduced overestimates of modeled versus measured remote-sensing reflectance values. Phase functions from VSF data derived from measurements at multiple wavelengths and a single scattering single angle significantly overestimated reflectances when using the manufacturer-supplied corrections, but were substantially improved using newly published corrections; phase functions calculated from VSF measurements using three angles and three wavelengths and processed using manufacture-supplied corrections were comparable, demonstrating that reasonable predictions can be made using two commercially available instruments. While other studies have reached similar conclusions, our work extends the analysis to coastal waters dominated by an extreme algal bloom with surface chlorophyll concentrations in excess of 100 mg m^{-3}. PMID:27505819
Phase transitions at high pressure in tetracyanoethylene
NASA Astrophysics Data System (ADS)
Mukhopadhyay, R.; Deb, S. K.; Das, Amitabh; Chaplot, S. L.
2009-11-01
We report in situ x-ray diffraction studies in tetracyanoethylene (TCNE) at high pressure using diamond anvil cell (DAC) at Elettra synchrotron source, Trieste, Italy. Experiments were performed with both the polymorphic phases (monoclinic and cubic) of TCNE as the starting phase. While starting with monoclinic (the high temperature stable) TCNE, it was found that the Bragg peaks get broadened with increase of pressure and above 5 GPa only few broad peaks remained to be observed. On release of pressure from 6.4 GPa, when the sample started turning black, the diffraction pattern at ambient pressure corresponds to cubic, the other crystalline phase of TCNE. Results reconfirm the monoclinic to cubic transition at high pressure but via an intermediate 'disordered' phase. This settles a number of conflicting issues. TCNE represents only system, which undergoes transition from one crystalline to another crystalline phase via a 'disordered' metastable phase at high pressure. When the starting phase was cubic (the low temperature stable) no apparent phase transition was observed up to 10.8 GPa.
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.
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.
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.
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.
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. 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
2014-01-01
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
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.
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.
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 loop quantum gravity
NASA Astrophysics Data System (ADS)
Mäkelä, Jarmo
2016-04-01
We point out that with a specific counting of states loop quantum gravity implies that black holes perform a phase transition at a certain characteristic temperature TC . In this phase transition the punctures of the spin network on the stretched horizon of the black hole jump, in effect, from the vacuum to the excited states. The characteristic temperature TC may be regarded as the lowest possible temperature of the hole. From the point of view of a distant observer at rest with respect to the hole, the characteristic temperature TC corresponds to the Hawking temperature of the hole.
Network traffic behaviour near phase transition point
NASA Astrophysics Data System (ADS)
Lawniczak, A. T.; Tang, X.
2006-03-01
We explore packet traffic dynamics in a data network model near phase transition point from free flow to congestion. The model of data network is an abstraction of the Network Layer of the OSI (Open Systems Interconnect) Reference Model of packet switching networks. The Network Layer is responsible for routing packets across the network from their sources to their destinations and for control of congestion in data networks. Using the model we investigate spatio-temporal packets traffic dynamics near the phase transition point for various network connection topologies, and static and adaptive routing algorithms. We present selected simulation results and analyze them.
Queueing phase transition: theory of translation.
Romano, M Carmen; Thiel, Marco; Stansfield, Ian; Grebogi, Celso
2009-05-15
We study the current of particles on a lattice, where to each site a different hopping probability has been associated and the particles can move only in one direction. We show that the queueing of the particles behind a slow site can lead to a first-order phase transition, and derive analytical expressions for the configuration of slow sites for this to happen. We apply this stochastic model to describe the translation of mRNAs. We show that the first-order phase transition, uncovered in this work, is the process responsible for the classification of the proteins having different biological functions. PMID:19519001
Holographic endpoint of spatially modulated phase transition
Ooguri, Hirosi; Park, Chang-Soon
2010-12-15
In a previous paper [S. Nakamura, H. Ooguri, and C. S. Park, Phys. Rev. D 81, 044018 (2010)], we showed that the Reissner-Nordstroem black hole in the five-dimensional anti-de Sitter space coupled to the Maxwell theory with the Chern-Simons term is unstable when the Chern-Simons coupling is sufficiently large. In the dual conformal field theory, the instability suggests a spatially modulated phase transition. In this paper, we construct and analyze nonlinear solutions which describe the endpoint of this phase transition. In the limit where the Chern-Simons coupling is large, we find that the phase transition is of the second order with the mean field critical exponent. However, the dispersion relation with the Van Hove singularity enhances quantum corrections in the bulk, and we argue that this changes the order of the phase transition from the second to the first. We compute linear response functions in the nonlinear solution and find an infinite off-diagonal DC conductivity in the new phase.
Transition to turbulence in pipe flow as a phase transition
NASA Astrophysics Data System (ADS)
Vasudevan, Mukund; Hof, Björn
2015-11-01
In pipe flow, turbulence first arises in the form of localized turbulent patches called puffs. The flow undergoes a transition to sustained turbulence via spatio-temporal intermittency, with puffs splitting, decaying and merging in the background laminar flow. However, the due to mean advection of the puffs and the long timescales involved (~107 advective time units), it is not possible to study the transition in typical laboratory set-ups. So far, it has only been possible to indirectly estimate the critical point for the transition. Here, we exploit the stochastic memoryless nature of the puff decay and splitting processes to construct a pipe flow set-up, that is periodic in a statistical sense. It then becomes possible to study the flow for sufficiently long times and characterize the transition in detail. We present measurements of the turbulent fraction as a function of Reynolds number which in turn allows a direct estimate of the critical point. We present evidence that the transition has features of a phase transition of second order.
On configurational weak phase transitions in graphene
NASA Astrophysics Data System (ADS)
Sfyris, Dimitris
2016-07-01
We report a study on configurational weak phase transitions for a freestanding monolayer graphene. Firstly, we characterize weak transformation neighborhoods by suitably bounding the metric components. Then, we distinguish between structural and configurational phase changes and elaborate on the second class of them. We evaluate the irreducible invariant subspaces corresponding to these phase changes and lay down symmetry-breaking as well as symmetry-preserving stretches. In the reduced bifurcation diagram, symmetry-preserving stretches are related to a turning point with a change of stability but not of symmetry. Symmetry-breaking stretches are related to a first-order weak phase transition. We evaluate symmetry-breaking stretches as well as their generating cosets. The reduced bifurcation diagram consists of three transcritical bifurcating curves which are all unstable but can be stabilized producing a subcritical bifurcation. We, also, shortly comment on the hysteretical behavior that might appear in this case.
Annotated Bibliography on Transition from School to Work. Volume 2.
ERIC Educational Resources Information Center
Leach, Lynda N.; Harmon, Adrienne S.
This second volume of an annotated bibliography on transition from school to work focuses on evaluation methodology, efficacy of secondary and transitional services, and related topics. The bibliography's scope includes English-language journal articles, books, and reports, originally published from 1977 through 1987. For each of the 368 entries,…
Black Hole Phase Transition in Massive Gravity
NASA Astrophysics Data System (ADS)
Ning, Shou-Li; Liu, Wen-Biao
2016-07-01
In massive gravity, some new phenomena of black hole phase transition are found. There are more than one critical points under appropriate parameter values and the Gibbs free energy near critical points also has some new properties. Moreover, the Maxwell equal area rule is also investigated and the coexistence curve of the black hole is given.
Dual condensate and QCD phase transition
Zhang Bo; Bruckmann, Falk; Fodor, Zoltan; Szabo, Kalman K.; Gattringer, Christof
2011-05-23
The dual condensate is a new QCD phase transition order parameter, which connnects confinement and chiral symmetry breaking as different mass limits. We discuss the relation between the fermion spectrum at general boundary conditions and the dual condensate and show numerical results for the latter from unquenched SU(3) lattice configurations.
Theory and phenomenology of electroweak phase transitions
NASA Astrophysics Data System (ADS)
Patel, Hiren H.
An open problem in cosmology is to explain the origin of baryon abundance implied by observational cosmology. Among the many proposed explanations, electroweak baryogenesis is particularly attractive in that its ingredients is discoverable by modern experiments. The analysis of the electroweak phase transition in the early universe comprises an integral component within the larger study of electroweak baryogenesis. In this work, I make a detailed investigation of the conventional analysis of the electroweak phase transition commonly found in literature, and explicitly demonstrate that results are not independent of the choice of gauge. In its place, I provide a manifestly gauge-independent method for the analysis, review sources of theoretical and numerical uncertainties, and explore avenues for further development. Next, I explore the dynamics of the electroweak phase transition in two minimal extensions of the Standard Model of particle physics. Within these simple models, I describe a novel pattern of electroweak symmetry breaking favorable for baryogenesis that can serve as a paradigm for phase transition analysis in more complicated models.
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.
Application of epidemic models to phase transitions
NASA Astrophysics Data System (ADS)
Bilge, A. H.; Pekcan, Ö.; Gürol, M. V.
2012-11-01
The Susceptible-Infected-Recovered (SIR) and Susceptible-Exposed-Infected-Recovered (SEIR) models describe the spread of epidemics in a society. In the typical case, the ratio of the susceptible individuals fall from a value S 0 close to 1 to a final value Sf , while the ratio of recovered individuals rise from 0 to Rf = 1 - Sf . The sharp passage from the level zero to the level Rf allows also the modeling of phase transitions by the number of "recovered" individuals R(t) of the SIR or SEIR model. In this article, we model the sol-gel transition for polyacrylamide-sodium alginate (SA) composite with different concentrations of SA as SIR and SEIR dynamical systems by solving the corresponding differential equations numerically and we show that the phase transitions of "classical" and "percolation" types are represented, respectively, by the SEIR and SIR models.
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
Nonuniversal surface behavior of dynamic phase transitions.
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 J(s), the amplitude of the externally applied oscillating field h(0), 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 J(s) values, independent from the value of h(0). For low J(s), however, h(0) 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 h(0) and correspondingly short critical periods P(c), whereas this surface transition simultaneous to the bulk one is suppressed for slow critical dynamics occurring for low values of h(0). The suppression of the DPT for low h(0) 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 J(s) values. Here we find that the penetration depth depends strongly on J(s) and behaves identically to the corresponding equilibrium Ising model. PMID:26172695
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.
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 transitions in nonequilibrium traffic theory
Zhang, H.M.
2000-02-01
This paper uses the center difference scheme of Lax-Friedrichs to numerically solve a newly developed continuum traffic flow theory and the kinematic theory of Lighthill and Whitham, and Richards, and it studies the flow-concentration phase transitions in flow containing both shock and rarefaction waves. A homogeneous road with finite length was modeled by both theories. Numerical simulations show that both theories yield nearly identical results for two representative Riemann problems--one has a shock solution and the other a rarefaction wave solution. Their phase transition curves, however, are different: those derived from the new theory have two branches--one for acceleration flow and one for deceleration flow, whereas those derived from the LWR theory comprise a single curve--the equilibrium curve. The phase transition curves in the shock case agree well with certain experimental observations but disagree with others. This disagreement may be resolved by studying transitions among nonequilibrium states, which awaits further development of a more accurate finite difference approximation of the nonequilibrium theory.
Phase transition theory of sprite halo
NASA Astrophysics Data System (ADS)
Hiraki, Yasutaka
2010-04-01
We present the phase transition theory for sprite halo using measurable lightning parameters (charge moment and discharge time) on the basis of steady state thermodynamics. A halo is located at the upper part of the tree-like structure of a sprite and is produced through electron impact excitation of neutral species under the lightning-induced electric field. We proposed in our previous studies that the occurrence criteria for halos and sprites are characterized by the above lightning parameters, and additionally, the intensity of a halo weakens rapidly with an increase in the discharge time T. We assume that this phenomenon is quite similar to the phase transition between the vapor and the liquid states of water; here the analogy is between the accelerated electrons and the water molecules. We demonstrate analytically a phase transition for a simply modeled halo based on the quasistatic theory of lightning-induced electric field. Choosing the luminosity of a halo as an order parameter, we show that it has a dependence of T-0.25 - Tc-0.25 near the critical point Tc, which is characteristic of the phase transition. Furthermore, the critical time scale Tc ≈ 5.5 ms is provided naturally from our modeling and is somewhat larger than the typical time scale of the halo luminosity in observations. We consider that this kind of formalism is useful in understanding the detailed relationship between lightning activity and occurrence of halos. We discuss this point for future observations along with the possibilities of the transition model of column and carrot structures.
Understanding topological phase transition in monolayer transition metal dichalcogenides
NASA Astrophysics Data System (ADS)
Choe, Duk-Hyun; Sung, Ha-Jun; Chang, K. J.
2016-03-01
Despite considerable interest in layered transition metal dichalcogenides (TMDs), such as M X2 with M =(Mo ,W ) and X =(S ,Se ,Te ) , the physical origin of their topological nature is still poorly understood. In the conventional view of topological phase transition (TPT), the nontrivial topology of electron bands in TMDs is caused by the band inversion between metal d - and chalcogen p -orbital bands where the former is pulled down below the latter. Here, we show that, in TMDs, the TPT is entirely different from the conventional speculation. In particular, M S2 and M S e2 exhibits the opposite behavior of TPT such that the chalcogen p -orbital band moves down below the metal d -orbital band. More interestingly, in M T e2 , the band inversion occurs between the metal d -orbital bands. Our findings cast doubts on the common view of TPT and provide clear guidelines for understanding the topological nature in new topological materials to be discovered.
Topological phase transition in layered transition metal dichalcogenides
NASA Astrophysics Data System (ADS)
Choe, Duk-Hyun; Sung, Ha-Jun; Chang, Kee Joo
Despite considerable interests in transition metal dichalcogenides (TMDs), such as MX2 with M = (Mo, W) and X = (S, Se, Te), the physical origin of their topological nature is still in its infancy. The conventional view of topological phase transition (TPT) in TMDs is that the band inversion occurs between the metal d and chalcogen p orbital bands. More precisely, the former is pulled down below the latter. Here we introduce an explicit scheme for analyzing TPT in topological materials and find that the TPT in TMDs is different from the conventional speculation. When the 1T phase undergoes a structural transformation to the 1T' phase in monolayer MX2, the band topology changes from trivial to non-trivial, leading to the TPT. We discuss the exact role of the metal d and chalcogen p orbital bands during the TPT. Our finding would provide clear guidelines for understanding the topological nature not only in TMDs but also in other topological materials yet to be explored.
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.
Phase transition to turbulence in a pipe
NASA Astrophysics Data System (ADS)
Goldenfeld, Nigel
Leo Kadanoff taught us much about phase transitions, turbulence and collective behavior. Here I explore the transition to turbulence in a pipe, showing how a collective mode determines the universality class. Near the transition, turbulent puffs decay either directly or through splitting, with characteristic time-scales that exhibit a super-exponential dependence on Reynolds number. Direct numerical simulations reveal that a collective mode, a so-called zonal flow emerges at large scales, activated by anisotropic turbulent fluctuations, as represented by Reynolds stress. This zonal flow imposes a shear on the turbulent fluctuations that tends to suppress their anisotropy, leading to a Landau theory of predator-prey type, in the directed percolation universality class. Stochastic simulations of this model reproduce the functional form and phenomenology of pipe flow experiments. Talk based on work performed with Hong-Yan Shih and Tsung-Lin Hsieh. This work was partially supported by the National Science Foundation through Grant NSF-DMR-1044901.
Phase transitions in soft-committee machines
NASA Astrophysics Data System (ADS)
Biehl, M.; Schlösser, E.; Ahr, M.
1998-10-01
Equilibrium statistical physics is applied to the off-line training of layered neural networks with differentiable activation functions. A first analysis of soft-committee machines with an arbitrary number (K) of hidden units and continuous weights learning a perfectly matching rule is performed. Our results are exact in the limit of high training temperatures (β → 0). For K = 2 we find a second-order phase transition from unspecialized to specialized student configurations at a critical size P of the training set, whereas for K >= 3 the transition is first order. The limit K → ∞ can be performed analytically, the transition occurs after presenting on the order of NK/β examples. However, an unspecialized metastable state persists up to P propto NK2/β.
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.
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.
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. PMID:26565451
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. PMID:23005354
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.
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.
Generalized phase transitions in Lovelock gravity
NASA Astrophysics Data System (ADS)
Camanho, Xián O.; Edelstein, José D.; Giribet, Gastón; Gomberoff, Andrés
2014-09-01
We investigate a novel mechanism for phase transitions that is a distinctive feature of higher-curvature gravity theories. For definiteness, we bound ourselves to the case of Lovelock gravities. These theories are known to have several branches of asymptotically anti-de Sitter solutions. Here, extending our previous work, we show that phase transitions among some of these branches are driven by a thermalon configuration: a bubble separating two regions of different effective cosmological constants, generically hosting a black hole in the interior. Above some critical temperature, this thermalon configuration is preferred with respect to the finite-temperature anti-de Sitter space, triggering a sophisticated version of the Hawking-Page transition. After being created, the unstable bubble configuration can in general dynamically change the asymptotic cosmological constant. While this phenomenon already occurs in the case of a gravity action with square curvature terms, we point out that in the case of Lovelock theory with cubic (and higher) terms new effects appear. For instance, the theory may admit more than one type of bubble and branches that are in principle free of pathologies may also decay through the thermalon mechanism. We also find ranges of the gravitational couplings for which the theory becomes sick. These add up to previously found restrictions to impose tighter constraints on higher-curvature gravities. The results of this paper point to an intricate phase diagram which might accommodate similarly rich behavior in the dual conformal field theory side.
Phase Transitions in Delaunay Potts Models
NASA Astrophysics Data System (ADS)
Adams, Stefan; Eyers, Michael
2016-01-01
We establish phase transitions for certain classes of continuum Delaunay multi-type particle systems (continuum Potts models) with infinite range repulsive interaction between particles of different type. In one class of the Delaunay Potts models studied the repulsive interaction is a triangle (multi-body) interaction whereas in the second class the interaction is between pairs (edges) of the Delaunay graph. The result for the edge model is an extension of finite range results in Bertin et al. (J Stat Phys 114(1-2):79-100, 2004) for the Delaunay graph and in Georgii and Häggström (Commun Math Phys 181:507-528, 1996) for continuum Potts models to an infinite range repulsion decaying with the edge length. This is a proof of an old conjecture of Lebowitz and Lieb. The repulsive triangle interactions have infinite range as well and depend on the underlying geometry and thus are a first step towards studying phase transitions for geometry-dependent multi-body systems. Our approach involves a Delaunay random-cluster representation analogous to the Fortuin-Kasteleyn representation of the Potts model. The phase transitions manifest themselves in the percolation of the corresponding random-cluster model. Our proofs rely on recent studies (Dereudre et al. in Probab Theory Relat Fields 153:643-670, 2012) of Gibbs measures for geometry-dependent interactions.
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
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.
Structural phase transition and electronic properties in samarium chalcogenides
NASA Astrophysics Data System (ADS)
Panwar, Y. S.; Aynyas, Mahendra; Pataiya, J.; Sanyal, Sankar P.
2016-05-01
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 (B1-phase) structure to CsCl-type (B2-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 (a0), bulk modulus (B0), 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
NASA Astrophysics Data System (ADS)
Gai, Yue; Song, Dong-Po; Watkins, James
Brush block copolymers synthesized via living ring-opening metathesis polymerization (ROMP) offer unique advantages as templates for functional hybrid materials. Unlike linear block copolymer, the bottlebrush polymer phase transition not only depends on volume fractions of the two blocks but also on side chain length. Here we report the morphology transitions of PS-b-PEO bottlebrush copolymer (BBCP) as a function of PEO side chain length and block volume fraction. For the BBCPs with similar side chain lengths, highly ordered lamellar morphologies were observed with PEO volume fractions in a wide range from 32 vol% to 72 vol%, which is significantly different from that of traditional linear block copolymers. This study will lay the groundwork for nanostructure fabrications using the BBCPs and provides new insights into the phase behavior of the new type of materials. This work was supported by NSF center for Hierarchical Manufacturing at the University of Massachusetts, Amherst.
Structural phase transition in evolving networks.
Kim, Sang-Woo; Noh, Jae Dong
2009-08-01
A network as a substrate for dynamic processes may have its own dynamics. We propose a model for networks which evolve together with diffusing particles through a coupled dynamics and investigate emerging structural property. The model consists of an undirected weighted network of fixed mean degree and randomly diffusing particles of fixed density. The weight w of an edge increases by the amount of traffics through its connecting nodes or decreases by a constant factor. Edges are removed with the probability P(rew)=1/(1+w) and replaced by new ones having w=0 at random locations. We find that the model exhibits a structural phase transition between the homogeneous phase characterized by an exponentially decaying degree distribution and the heterogeneous phase characterized by the presence of hubs. The hubs emerge as a consequence of a positive feedback between the particle and the edge dynamics. PMID:19792212
Polymer physics of intracellular phase transitions
NASA Astrophysics Data System (ADS)
Brangwynne, Clifford P.; Tompa, Peter; Pappu, Rohit V.
2015-11-01
Intracellular organelles are either membrane-bound vesicles or membrane-less compartments that are made up of proteins and RNA. These organelles play key biological roles, by compartmentalizing the cell to enable spatiotemporal control of biological reactions. Recent studies suggest that membrane-less intracellular compartments are multicomponent viscous liquid droplets that form via phase separation. Proteins that have an intrinsic tendency for being conformationally heterogeneous seem to be the main drivers of liquid-liquid phase separation in the cell. These findings highlight the relevance of classical concepts from the physics of polymeric phase transitions for understanding the assembly of intracellular membrane-less compartments. However, applying these concepts is challenging, given the heteropolymeric nature of protein sequences, the complex intracellular environment, and non-equilibrium features intrinsic to cells. This provides new opportunities for adapting established theories and for the emergence of new physics.
Phase transitions of ɛ-HNIW in compound systems
NASA Astrophysics Data System (ADS)
Zhang, Jing-yuan; Guo, Xue-yong; Jiao, Qing-jie; Zhang, Pu
2016-05-01
The heat-induced phase transitions of ɛ-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 ɛ-HNIW, after being held at 70°C for 60h, remained in the ɛ-phase. Applying other conditions, various phase transition parameters were determined, including Tc (the critical phase transition temperature), T50 (the temperature at which 50% of the phase transition is complete) and T180 (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.
Thin film phase transition materials development program
NASA Astrophysics Data System (ADS)
Case, W. E.
1985-04-01
A number of application concepts have emerged based on the idea that a phase transition thin film such as vanadium dioxide provides a high resolution, two-dimensional format for switching, recording, and processing optical signals. These applications range from high density optical disk recording systems and optical data processing to laser protection devices, infrared FLIRS and seekers, laser radar systems and IR scene simulators. All application candidates have a potential for providing either a totally new capability, an improved performance, a lower cost, or combinations of the three. Probably of greatest significance is the emergence of agile sensor concepts arising out of some of the film's special properties. These are represented by the above FLIRs, seekers and laser radar systems. A three year research program has been completed to advance the state-of-the-art in the preparation and characterization of selected thin film phase transition materials. The objectives of the program were: (1) to expand the data base and improve operational characteristics of Vought prepared vanadium dioxide thin films, (2) to evolve process chemistry and subsequently characterize several new program materials, including rare-earth chalcogenides, organic semiconductor charge complexes, alloys of transition metal oxides, and metal-insulator cermets, and (3) to spin-off new applications and concepts.
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)
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.
Transitional Bubble in Periodic Flow Phase Shift
NASA Technical Reports Server (NTRS)
Talan, M.; Hourmouziadis, Jean
2004-01-01
One particular characteristic observed in unsteady shear layers is the phase shift relative to the main flow. In attached boundary layers this will have an effect both on the instantaneous skin friction and heat transfer. In separation bubbles the contribution to the drag is dominated by the pressure distribution. However, the most significant effect appears to be the phase shift on the transition process. Unsteady transition behaviour may determine the bursting of the bubble resulting in an un-recoverable full separation. An early analysis of the phase shift was performed by Stokes for the incompressible boundary layer of an oscillating wall and an oscillating main flow. An amplitude overshoot within the shear layer as well as a phase shift were observed that can be attributed to the relatively slow diffusion of viscous stresses compared to the fast change of pressure. Experiments in a low speed facility with the boundary layer of a flat plate were evaluated in respect to phase shift. A pressure distribution similar to that on the suction surface of a turbomachinery aerofoil was superimposed generating a typical transitional separation bubble. A periodically unsteady main flow in the suction type wind tunnel was introduced via a rotating flap downstream of the test section. The experiments covered a range of the three similarity parameters of momentum-loss-thickness Reynolds-number of 92 to 226 and Strouhal-number (reduced frequency) of 0.0001 to 0.0004 at the separation point, and an amplitude range up to 19 %. The free stream turbulence level was less than 1% .Upstream of the separation point the phase shift in the laminar boundary layer does not appear to be affected significantly bay either of the three parameters. The trend perpendicular to the wall is similar to the Stokes analysis. The problem scales well with the wave velocity introduced by Stokes, however, the lag of the main flow near the wall is less than indicated analytically. The separation point
Phase transitions in least-effort communications
NASA Astrophysics Data System (ADS)
Prokopenko, Mikhail; Ay, Nihat; Obst, Oliver; Polani, Daniel
2010-11-01
We critically examine a model that attempts to explain the emergence of power laws (e.g., Zipf's law) in human language. The model is based on the principle of least effort in communications—specifically, the overall effort is balanced between the speaker effort and listener effort, with some trade-off. It has been shown that an information-theoretic interpretation of this principle is sufficiently rich to explain the emergence of Zipf's law in the vicinity of the transition between referentially useless systems (one signal for all referable objects) and indexical reference systems (one signal per object). The phase transition is defined in the space of communication accuracy (information content) expressed in terms of the trade-off parameter. Our study explicitly solves the continuous optimization problem, subsuming a recent, more specific result obtained within a discrete space. The obtained results contrast Zipf's law found by heuristic search (that attained only local minima) in the vicinity of the transition between referentially useless systems and indexical reference systems, with an inverse-factorial (sub-logarithmic) law found at the transition that corresponds to global minima. The inverse-factorial law is observed to be the most representative frequency distribution among optimal solutions.
Exploiting phase transitions for fusion optimization problems
NASA Astrophysics Data System (ADS)
Svenson, Pontus
2005-05-01
Many optimization problems that arise in multi-target tracking and fusion applications are known to be NP-complete, ie, believed to have worst-case complexities that are exponential in problem size. Recently, many such NP-complete problems have been shown to display threshold phenomena: it is possible to define a parameter such that the probability of a random problem instance having a solution jumps from 1 to 0 at a specific value of the parameter. It is also found that the amount of resources needed to solve the problem instance peaks at the transition point. Among the problems found to display this behavior are graph coloring (aka clustering, relevant for multi-target tracking), satisfiability (which occurs in resource allocation and planning problem), and the travelling salesperson problem. Physicists studying these problems have found intriguing similarities to phase transitions in spin models of statistical mechanics. Many methods previously used to analyze spin glasses have been used to explain some of the properties of the behavior at the transition point. It turns out that the transition happens because the fitness landscape of the problem changes as the parameter is varied. Some algorithms have been introduced that exploit this knowledge of the structure of the fitness landscape. In this paper, we review some of the experimental and theoretical work on threshold phenomena in optimization problems and indicate how optimization problems from tracking and sensor resource allocation could be analyzed using these results.
Phase transitions of Dirac electrons in bismuth.
Li, Lu; Checkelsky, J G; Hor, Y S; Uher, C; Hebard, A F; Cava, R J; Ong, N P
2008-07-25
The Dirac Hamiltonian, which successfully describes relativistic fermions, applies equally well to electrons in solids with linear energy dispersion, for example, in bismuth and graphene. A characteristic of these materials is that a magnetic field less than 10 tesla suffices to force the Dirac electrons into the lowest Landau level, with resultant strong enhancement of the Coulomb interaction energy. Moreover, the Dirac electrons usually come with multiple flavors or valley degeneracy. These ingredients favor transitions to a collective state with novel quantum properties in large field. By using torque magnetometry, we have investigated the magnetization of bismuth to fields of 31 tesla. We report the observation of sharp field-induced phase transitions into a state with striking magnetic anisotropy, consistent with the breaking of the threefold valley degeneracy. PMID:18653888
Finitely Generated Multifractals Can Display Phase Transitions
NASA Astrophysics Data System (ADS)
Huillet, Thierrey; Jeannet, Bernard
1996-02-01
A new class of multifractal objects (“skewed” multifractals) is introduced, the mutiplicative generator of which has a finite number of branches of different real-valued depths. Both microscopic and macroscopic scales are represented by such objects, each of these corresponding to a specific thermodynamical regime. In the “diluted” regime, the partition function Z_t is exactly renormalizable which means in the sequel, as is the case in the general multifractal theory, that t^{-1} log Z_t as a non trivial limit as t tends to infinity. In the “condensed” one the partition function converges. Details about the transition between these two regimes are given. Une nouvelle classe de “multifractales” est introduite, pour laquelle le générateur présente un nombre fini de branches de longueur variable à valeurs réelles. Les échelles macroscopiques et microscopiques sont représentables par de tels objets, chacune d'elles correspondant à un régime thermodynamique spécifique. Dans la phase “diluée”, la fonction de partition Z_t est exactement renormalisable, en ce sens (classique) que la limite quand trightarrow infty de t^{-1} log Z_t est non triviale. Dans la phase “condensée” la fonction de partition converge. Les détails thermodynamiques concernant cette transition de phase sont fournis.
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.
Topological Phase Transition without Gap Closing
Ezawa, Motohiko; Tanaka, Yukio; Nagaosa, Naoto
2013-01-01
Topological phase transition is accompanied with a change of topological numbers. According to the bulk-edge correspondence, the gap closing and the breakdown of the adiabaticity are necessary at the phase transition point to make the topological number ill-defined. However, the gap closing is not always needed. In this paper, we show that two topological distinct phases can be continuously connected without gap closing, provided the symmetry of the system changes during the process. Here we propose the generic principles how this is possible by demonstrating various examples such as 1D polyacetylene with the charge-density-wave order, 2D silicene with the antiferromagnetic order, 2D silicene or quantum well made of HgTe with superconducting proximity effects and 3D superconductor Cu doped Bi2Se3. It is argued that such an unusual phenomenon can occur when we detour around the gap closing point provided the connection of the topological numbers is lost along the detour path. PMID:24071900
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.
Jahn-Teller solitons, structural phase transitions, and phase separation.
Clougherty, Dennis P
2006-02-01
It is demonstrated that under common conditions a molecular solid subject to Jahn-Teller interactions supports stable Q-ball-like nontopological solitons. Such solitons represent a localized lump of excess electric charge in periodic motion accompanied by a time-dependent shape distortion of a set of adjacent molecules. The motion of the distortion can correspond to a true rotation or to a pseudorotation about the symmetric shape configuration. These solitons are stable for Jahn-Teller coupling strengths below a critical value; however, as the Jahn-Teller coupling approaches this critical value, the size of the soliton diverges signaling an incipient structural phase transition. The soliton phase mimics features commonly attributed to phase separation in complex solids. PMID:16486846
Jahn-Teller Solitons, Structural Phase Transitions, and Phase Separation
NASA Astrophysics Data System (ADS)
Clougherty, Dennis P.
2006-02-01
It is demonstrated that under common conditions a molecular solid subject to Jahn-Teller interactions supports stable Q-ball-like nontopological solitons. Such solitons represent a localized lump of excess electric charge in periodic motion accompanied by a time-dependent shape distortion of a set of adjacent molecules. The motion of the distortion can correspond to a true rotation or to a pseudorotation about the symmetric shape configuration. These solitons are stable for Jahn-Teller coupling strengths below a critical value; however, as the Jahn-Teller coupling approaches this critical value, the size of the soliton diverges signaling an incipient structural phase transition. The soliton phase mimics features commonly attributed to phase separation in complex solids.
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.
Pressure dependence of band-gap and phase transitions in bulk CuX (X = Cl, Br, I)
NASA Astrophysics Data System (ADS)
Azhikodan, Dilna; Nautiyal, Tashi; Sharma, S.
2016-05-01
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.
Is ``metamictization`` of zircon a phase transition?
Salje, E.K.H.; Chrosch, J.; Ewing, R.C.
1999-07-01
Metamictization is the transition from the crystalline to an aperiodic or amorphous state due to alpha-decay event damage from constituent radionuclides ({sup 238}U, {sup 235}U, and {sup 232}Th) and their daughters. However, this transformation in minerals is part of a larger class of radiation-induced transformations to the amorphous state that has received considerable recent attention as a result of ion- and electron-beam experiments on metals, intermetallics, simple oxides, and complex ceramics and minerals. Diffuse X-ray scattering from single crystals of metamict zircon reveals residual crystallinity even at high fluences (up to 7.2 {times} 10{sup 18} {alpha}-decay events/g). The experimental evidence does not suggest that radiation-induced amorphization is a phase transition. The observations are in good agreement with a nonconvergent, heterogeneous model of amorphization in which damage production is a random process of cascade formation and overlap at increasing fluence. Instead of an amorphization transition, the existence of a percolation transition is postulated. At the level of radiation damage near the percolation point, the heterogeneous strain broadening of X-ray diffraction profiles is reduced whereas the particle-size broadening increases. Simultaneously, the macroscopic swelling of the zircon becomes larger than the maximum expansion of the unit-cell parameters. A suitable empirical parameter that characterizes this transition is the flux, D{sub s}, at which the macroscopic expansion is identical to the maximum expansion of the crystallographic unit cell. In zircon, D{sub s} = 3.5{center_dot}10{sup 18} {alpha}-decay events/g.
Quantum coherence and quantum phase transitions
NASA Astrophysics Data System (ADS)
Li, Yan-Chao; Lin, Hai-Qing
2016-05-01
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.
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
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
Evolutionary Phase Transitions in Random Environments.
Skanata, Antun; Kussell, Edo
2016-07-15
We present analytical results for long-term growth rates of structured populations in randomly fluctuating environments, which we apply to predict how cellular response networks evolve. We show that networks which respond rapidly to a stimulus will evolve phenotypic memory exclusively under random (i.e., nonperiodic) environments. We identify the evolutionary phase diagram for simple response networks, which we show can exhibit both continuous and discontinuous transitions. Our approach enables exact analysis of diverse evolutionary systems, from viral epidemics to emergence of drug resistance. PMID:27472146
Evolutionary Phase Transitions in Random Environments
NASA Astrophysics Data System (ADS)
Skanata, Antun; Kussell, Edo
2016-07-01
We present analytical results for long-term growth rates of structured populations in randomly fluctuating environments, which we apply to predict how cellular response networks evolve. We show that networks which respond rapidly to a stimulus will evolve phenotypic memory exclusively under random (i.e., nonperiodic) environments. We identify the evolutionary phase diagram for simple response networks, which we show can exhibit both continuous and discontinuous transitions. Our approach enables exact analysis of diverse evolutionary systems, from viral epidemics to emergence of drug resistance.
Berry phase transition in twisted bilayer graphene
NASA Astrophysics Data System (ADS)
Rode, Johannes C.; Smirnov, Dmitri; Schmidt, Hennrik; Haug, Rolf J.
2016-09-01
The electronic dispersion of a graphene bilayer is highly dependent on rotational mismatch between layers and can be further manipulated by electrical gating. This allows for an unprecedented control over electronic properties and opens up the possibility of flexible band structure engineering. Here we present novel magnetotransport data in a twisted bilayer, crossing the energetic border between decoupled monolayers and coupled bilayer. In addition a transition in Berry phase between π and 2π is observed at intermediate magnetic fields. Analysis of Fermi velocities and gate induced charge carrier densities suggests an important role of strong layer asymmetry for the observed phenomena.
Bound entanglement in quantum phase transitions
Baghbanzadeh, S.; Alipour, S.; Rezakhani, A. T.
2010-04-15
We investigate quantum phase transitions in which a change in the type of entanglement from bound entanglement to either free entanglement or separability may occur. In particular, we present a theoretical method to construct a class of quantum spin-chain Hamiltonians that exhibit this type of quantum criticality. Given parameter-dependent two-site reduced density matrices (with prescribed entanglement properties), we lay out a reverse construction for a compatible pure state for the whole system, as well as a class of Hamiltonians for which this pure state is a ground state. This construction is illustrated through several examples.
Evaluation of proximity devices, volume 2, phase 3
NASA Astrophysics Data System (ADS)
Nixon, J. H.; Hipp, J. E.; Green, T. C.; Murch, G. H.; Cater, J. P.
1982-12-01
Phase 1 of this three phase program consisted of test evaluations of commercially available proximity warning devices. Phase 2 resulted in the design and development of a microprocessor based distributed sensor ac electrometer that measures the electrostatic field at locations along a crane boom. In volume 1 of phase 2 the electrostatic fields around a crane boom were measured by the instrument at high voltage powerlines of various voltages and geometries. Volume 2 of phase 2 contains the appendixes.
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.
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.
Phase Transitions of Single Semistiff Polymer Chains
NASA Astrophysics Data System (ADS)
Bastolla, Ugo; Grassberger, Peter
1997-12-01
We study numerically a lattice model of semiflexible homopolymers with nearest neighbor (nn) attraction and energetic preference for straight joints between bonded monomers. For this we use a new Monte Carlo algorithm, the “prunedenriched Rosenbluth Method” (PERM). It is very efficient both for relatively open configurations at high temperatures and for compact and frozen-in low- T states. This allows us to study in detail the phase diagram as a function of nn attraction ɛ and stiffness x. It shows a θ-collapse line with a transition from open coils (small ɛ) to molten compact globules (large ɛ) and a freezing transition toward a state with orientational global order (large stiffness x). Qualitatively this is similar to a recently studied mean-field theory [S. Doniach, T. Garel, and H. Orland (1996), J. Chem. Phys. 105(4), 1601], but there are important differences in details. In contrast to the mean-field theory and to naive expectations, the θ-temperature increases with stiffness x. The freezing temperature increases even faster, and reaches the θ-line at a finite value of x. For even stiffer chains, the freezing transition takes place directly, without the formation of an intermediate globular state. Although being in conflict with mean-field theory, the latter had been conjectured already by Doniach et al. on the basis of heuristic arguments and of low-statistics Monte Carlo simulations. Finally, we discuss the relevance of the present model as a very crude model for protein folding.
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.
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}.
Gravitational waves from the electroweak phase transition
NASA Astrophysics Data System (ADS)
Leitao, Leonardo; Mégevand, Ariel; Sánchez, Alejandro D.
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 ~ 10-4 Hz, and give intensities as high as h2ΩGW ~ 10-8.
Automated determination of volume phase hologram parameters
NASA Astrophysics Data System (ADS)
Brown, Robert D.; Stanley, James H.
2015-03-01
Commercially available ray tracing programs by themselves are not adequate for modelling optical systems with holographic gratings. In this paper, we describe a suite of tools that we have developed specifically for working with volume phase holograms. One tool measures the diffraction efficiency of a grating with respect to angle and position. Our automated measurement process is described. The measured diffraction data is analyzed to extract key grating parameters; such as, grating thickness and index modulation. The theoretical basis for this analysis is described. The extracted grating parameters can be used to ray trace expected performance for comparison with direct measurements. Such a methodology has allowed us to develop modelling capabilities that can be confidently used to compare design options and guide development activities. In our environment, data is collected and grating parameters are extracted using LabView; ray tracing is performed using Zemax. The concepts, however, are quite general. An example of measuring a grating recorded in a photopolymer and extracting its grating parameters is given. Results are compared to published datasheet specifications.
Phase transitions in supercritical explosive percolation
NASA Astrophysics Data System (ADS)
Chen, Wei; Nagler, Jan; Cheng, Xueqi; Jin, Xiaolong; Shen, Huawei; Zheng, Zhiming; D'Souza, Raissa M.
2013-05-01
Percolation describes the sudden emergence of large-scale connectivity as edges are added to a lattice or random network. In the Bohman-Frieze-Wormald model (BFW) of percolation, edges sampled from a random graph are considered individually and either added to the graph or rejected provided that the fraction of accepted edges is never smaller than a decreasing function with asymptotic value of α, a constant. The BFW process has been studied as a model system for investigating the underlying mechanisms leading to discontinuous phase transitions in percolation. Here we focus on the regime α∈[0.6,0.95] where it is known that only one giant component, denoted C1, initially appears at the discontinuous phase transition. We show that at some point in the supercritical regime C1 stops growing and eventually a second giant component, denoted C2, emerges in a continuous percolation transition. The delay between the emergence of C1 and C2 and their asymptotic sizes both depend on the value of α and we establish by several techniques that there exists a bifurcation point αc=0.763±0.002. For α∈[0.6,αc), C1 stops growing the instant it emerges and the delay between the emergence of C1 and C2 decreases with increasing α. For α∈(αc,0.95], in contrast, C1 continues growing into the supercritical regime and the delay between the emergence of C1 and C2 increases with increasing α. As we show, αc marks the minimal delay possible between the emergence of C1 and C2 (i.e., the smallest edge density for which C2 can exist). We also establish many features of the continuous percolation of C2 including scaling exponents and relations.
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.
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.
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.
High-pressure phase transitions of strontianite
NASA Astrophysics Data System (ADS)
Speziale, S.; Biedermann, N.; Reichmann, H. J.; Koch-Mueller, M.; Heide, G.
2015-12-01
Strontianite (SrCO3) is isostructural to aragonite, a major high-pressure polymorph of calcite. Thus it is a material of interest to investigate the high-pressure phase behavior of aragonite-group minerals. SrCO3 is a common component of natural carbonates and knowing its physical properties at high pressures is necessary to properly model the thermodynamic properties of complex carbonates, which are major crustal minerals but are also present in the deep Earth [Brenker et al., 2007] and control carbon cycling in the Earth's mantle. The few available high-pressure studies of SrCO3 disagree regarding both pressure stability and structure of the post-aragonite phase [Lin & Liu, 1997; Ono et al., 2005; Wang et al. 2015]. To clarify such controversies we investigated the high-pressure behavior of synthetic SrCO3 by Raman spectroscopy. Using a diamond anvil cell we compressed single-crystals or powder of strontianite (synthesized at 4 GPa and 1273 K for 24h in a multi anvil apparatus), and measured Raman scattering up to 78 GPa. SrCO3 presents a complex high-pressure behavior. We observe mode softening above 20 GPa and a phase transition at 25 - 26.9 GPa, which we interpret due to the CO3 groups rotation, in agreement with Lin & Liu [1997]. The lattice modes in the high-pressure phase show dramatic changes which may indicate a change from 9-fold coordinated Sr to a 12-fold-coordination [Ono, 2007]. Our results confirm that the high-pressure phase of strontianite is compatible with Pmmn symmetry. References Brenker, F.E. et al. (2007) Earth and Planet. Sci. Lett., 260, 1; Lin, C.-C. & Liu, L.-G. (1997) J. Phys. Chem. Solids, 58, 977; Ono, S. et al. (2005) Phys. Chem. Minerals, 32, 8; Ono, S. (2007) Phys. Chem. Minerals, 34, 215; Wang, M. et al. (2015) Phys Chem Minerals 42, 517.
Quantum phase transitions in frustrated magnetic systems
NASA Astrophysics Data System (ADS)
Wölfle, P.; Schmitteckert, P.
2015-07-01
We review our recent work on quantum phase transitions in frustrated magnetic systems. In the first part a Pseudo Fermion Functional Renormalization Group (PFFRG) method is presented. By using an exact representation of spin 1/2 operators in terms of pseudofermions a quantum spin Hamiltonian may be mapped onto an interacting fermion system. For the latter an FRG treatment is employed. The results for the J1-J2 model and similar models of frustrated interaction show phase diagrams in agreement with those obtained by other methods, but give more detailed information on the nature of correlations, in particular in the non-magnetic phases. Applications of PFFRG to geometrically frustrated systems and to highly anisotropic Kitaev type models are also reported. In the second part the derivation of quantum spin models from the microscopic many-body Hamiltonian is discussed. The results for multiband systems with strong spin-orbit interaction encountered in the iridates class of compounds are shown to resolve some of the questions posed by experiment.
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.
Phase transitions in femtosecond laser ablation
NASA Astrophysics Data System (ADS)
Povarnitsyn, Mikhail E.; Khishchenko, Konstantin V.; Levashov, Pavel R.
2009-03-01
In this study we simulate an interaction of femtosecond laser pulses (100 fs, 800 nm, 0.1-10 J/cm 2) with metal targets of Al, Au, Cu, and Ni. For analysis of laser-induced phase transitions, melting and shock waves propagation as well as material decomposition we use an Eulerian hydrocode in conjunction with a thermodynamically complete two-temperature equation of state with stable and metastable phases. Isochoric heating, material evaporation from the free surface of the target and fast propagation of the melting and shock waves are observed. On rarefaction the liquid phase becomes metastable and its lifetime is estimated using the theory of homogeneous nucleation. Mechanical spallation of the target material at high strain rates is also possible as a result of void growth and confluence. In our simulation several ablation mechanisms are taken into account but the main issue of the material is found to originate from the metastable liquid state. It can be decomposed either into a liquid-gas mixture in the vicinity of the critical point, or into droplets at high strain rates and negative pressure. The simulation results are in agreement with available experimental findings.
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.
Thermodynamics of the ferromagnetic phase transition in nearly half metallic CoS2 at high pressures
NASA Astrophysics Data System (ADS)
Elkin, F. S.; Zibrov, I. P.; Novikov, A. P.; Khasanov, S. S.; Sidorov, V. A.; Petrova, A. E.; Lograsso, T. A.; Thompson, J. D.; Stishov, S. M.
2014-03-01
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.
Topological classification of dynamical phase transitions
NASA Astrophysics Data System (ADS)
Vajna, Szabolcs; Dóra, Balázs
2015-04-01
We study the nonequilibrium time evolution of a variety of one-dimensional (1D) and two-dimensional (2D) systems (including SSH model, Kitaev-chain, Haldane model, p +i p superconductor, etc.) following a sudden quench. We prove analytically that topology-changing quenches are always followed by nonanalytical temporal behavior of return rates (logarithm of the Loschmidt echo), referred to as dynamical phase transitions (DPTs) in the literature. Similarly to edge states in topological insulators, DPTs can be classified as being topologically protected or not. In 1D systems the number of topologically protected nonequilibrium time scales are determined by the difference between the initial and final winding numbers, while in 2D systems no such relation exists for the Chern numbers. The singularities of dynamical free energy in the 2D case are qualitatively different from those of the 1D case; the cusps appear only in the first time derivative.
Scaling theory of topological phase transitions.
Chen, Wei
2016-02-10
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. PMID:26790004
Shape phase transition in Nd-152144 isotopes
NASA Astrophysics Data System (ADS)
Gupta, J. B.
2015-10-01
Background: The Z =60 Nd-152144 isotopes span the spherical to the well-deformed collective nuclear structures. The shape phase transition at N =86 -88 and N =88 -90 is intermediate between (Ba,Ce) and (Sm,Gd). The role of the Z =64 subshell closure in this forms an interesting subject of study. Objective: To analyze these complex features of the Nd spectra and the effects of the Z =64 subshell by comparing with predictions from the microscopic dynamic pairing plus quadrupole model to explain the shape transition at N =86 -90 . Method: Empirical analysis of the Nd spectra is illustrated. The K -band structures of the collective Iπ=2+ states in Nd-152144 are described. The predicted B (E 2 ) values and the interband B (E 2 ) ratios are compared with experimental data. The potential-energy surfaces of Nd-152146 are illustrated, and the role of protons and neutrons filling the Nilsson orbits is described. Results: The different effects of the Z =64 subshell on the ground-state band and the excited vibrational bands of Nd-148146 are illustrated. Conclusion: The important role of the dynamics of the nucleus, besides the static features, is made more transparent.
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.
Phase Transitions in Networks of Memristive Elements
NASA Astrophysics Data System (ADS)
Sheldon, Forrest; di Ventra, Massimiliano
The memory features of memristive elements (resistors with memory), analogous to those found in biological synapses, have spurred the development of neuromorphic systems based on them (see, e.g.,). In turn, this requires a fundamental understanding of the collective dynamics of networks of memristive systems. Here, we study an experimentally-inspired model of disordered memristive networks in the limit of a slowly ramped voltage and show through simulations that these networks undergo a first-order phase transition in the conductivity for sufficiently high values of memory, as quantified by the memristive ON/OFF ratio. We provide also a mean-field theory that reproduces many features of the transition and particularly examine the role of boundary conditions and current- vs. voltage-controlled networks. The dynamics of the mean-field theory suggest a distribution of conductance jumps which may be accessible experimentally. We finally discuss the ability of these networks to support massively-parallel computation. Work supported in part by the Center for Memory and Recording Research at UCSD.
Survey of CRISM Transition Phase Observations
NASA Astrophysics Data System (ADS)
Seelos, F. P.; Murchie, S. L.; Choo, T. H.; McGovern, J. A.
2006-12-01
The Mars Reconnaissance Orbiter (MRO) transition phase extends from the end of aerobraking (08/30/06) to the start of the Primary Science Phase (PSP) (11/08/2006). Within this timeframe, the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) will acquire Mars scene observations in association with the deployment of the telescope cover (09/27/06) and during the operational checkout of the full science payload (09/29/06 - 10/05/06). The CRISM cover opening sequence includes scene observations that will be used to verify deployment and to validate the on-orbit instrument wavelength calibration. The limited cover opening observation set consists of: 1. A hyperspectral nadir scan acquired as the cover is deployed (first light) 2. A single targeted (gimbaled) hyperspectral observation in the northern plains 3. A restricted duration nadir multispectral strip The high level objectives for the science payload checkout are to obtain observations in support of in-flight wavelength, radiometric, and geometric instrument calibration, to acquire data that will contribute to the development of a first-order hyperspectral atmospheric correction, and to exercise numerous spacecraft and instrument observing modes and strategies that will be employed during PSP. The science payload checkout also enables a unique collaboration between the Mars Express OMEGA and CRISM teams, with both spectrometers slated to observe common target locations with a minimal time offset for the purpose of instrument cross-calibration. The priority CRISM observations for the payload checkout include: 1. Multispectral nadir and hyperspectral off-nadir targeted observations in support of the cross-calibration experiment with OMEGA 2. Terminator-to-terminator multispectral data acquisition demonstrating the strategy that will be used to construct the global multispectral survey map 3. Terminator-to-terminator atmospheric emission phase function (EPF) data acquisition demonstrating the observation
Pressure driven spin crossover and isostructural phase transition in LaFeO{sub 3}
Javaid, Saqib; Javed Akhtar, M. Younas, Muhammad; Ahmad, Irfan; Shah, Shafqat H.; Ahmad, Iftikhar
2013-12-28
We have studied the behavior of LaFeO{sub 3} under pressure (P) using density functional theory (DFT) and atomistic simulations. Ground state structural properties of LaFeO{sub 3} are correctly described by atomistic simulations. The effect of high pressure shows that there is an isotropic compression up to 100 GPa. However, DFT calculations show that within pressure range 0 < P < 32.4 GPa, LaFeO{sub 3} retains its ground state electronic structure. On the other hand, at P ∼32.4 GPa high to low spin magnetic phase transition is observed, which is accompanied by 6.9% volume collapse of LaFeO{sub 3} unit cell, while retaining the ground state orthorhombic crystal structure, i.e., isostructural phase transition. Furthermore, the band gap is closed leading insulator to metal transition. This differing behavior observed by the two techniques can be attributed to the omission of magnetic effects in static simulations. The simultaneous magnetic, electrical, and structural (volume collapse) phase transitions of LaFeO{sub 3} under compression as revealed by DFT calculations corroborate experimental findings. From these results, we can elaborate the mechanism of phase transition in LaFeO{sub 3}: increasing crystal field induces a high spin to low spin transition, which in turn drives the electrical transitions and volume collapse.
NASA Astrophysics Data System (ADS)
Matsuoka, Tatsuro; Nakamura, Shunsuke; Yamaguchi, Tsuyoshi; Koda, Shinobu
2012-01-01
Temperature dependence of partial molar volume of 4-amino-4‧-nitrobiphenyl (ANB) and 4,4‧-dinitrobiphenyl (DNB) in the isotropic phase of 4-n-pentyl-4‧-cyanobiphenyl (5CB) was determined. Addition of ANB to 5CB causes increase of isotropic-nematic phase transition temperature (TIN) [1]. The decrease of partial molar volume of ANB was observed while the increase of partial molar volume of DNB and triphenyl phosphite (TPP) [8] was observed with approaching TIN. The anomalous behavior of partial molar volume was discussed using treatments similar to that of other thermodynamic derivatives in the I-N transition.
Structural phase transition of BaZrO{sub 3} under high pressure
Yang, Xue; Li, Quanjun; Liu, Ran; Liu, Bo; Zhang, Huafang; Jiang, Shuqing; Zou, Bo; Cui, Tian; Liu, Bingbing; Liu, Jing
2014-03-28
We studied the phase transition behavior of cubic BaZrO{sub 3} perovskite by in situ high pressure synchrotron X-ray diffraction experiments up to 46.4 GPa at room temperature. The phase transition from cubic phase to tetragonal phase was observed in BaZrO{sub 3} for the first time, which takes place at 17.2 GPa. A bulk modulus 189 (26) GPa for cubic BaZrO{sub 3} is derived from the pressure–volume data. Upon decompression, the high pressure phase transforms into the initial cubic phase. It is suggested that the unstable phonon mode caused by the rotation of oxygen octahedra plays a crucial role in the high pressure phase transition behavior of BaZrO{sub 3}.
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.
A Direct Method for Viewing Ferromagnetic Phase Transition.
ERIC Educational Resources Information Center
Lue, Chin-Shan
1994-01-01
Provides a method, using the Rowland ring as a specimen, to observe the phase transition process directly on the oscilloscope and even extract the critical exponent of ferromagnetic transition. Includes theory, experimental setup, and results. (MVL)
Pressure-induced phase transition in CrO2.
Alptekin, Sebahaddin
2015-12-01
The ab initio constant pressure molecular dynamics technique and density functional theory with generalized gradient approximation (GGA) was used to study the pressure-induced phase transition of CrO2. The phase transition of the rutile (P42/mnm) to the orthorhombic CaCl2 (Pnnm) structure at 30 GPa was determined successfully in a constant pressure simulation. This phase transition was analyzed from total energy calculations and, from the enthalpy calculation, occurred at around 17 GPa. Structural properties such as bulk modules, lattice parameters and phase transition were compared with experimental results. The phase transition at 12 ± 3 GPa was in good agreement with experimental results, as was the phase transition from the orthorhombic CaCl2 (Pnnm) to the monoclinic (P21/c) structure also found at 35 GPa. PMID:26541468
Diffuse phase transition of Fe doped lead ytterbium tantalate ceramics
NASA Astrophysics Data System (ADS)
Rout, Dibyaranjan; Subramanian, V.; Hariharan, K.; Sivasubramanian, V.
2006-02-01
The effect of different concentration of Fe on the phase transition behavior of Lead ytterbium tantalate is investigated by dielectric and differential scanning calrimetry measurements. The samples are prepared through solid state reaction method and it has been found that the sintering temperature significantly lowered when the proportion of Pb(Fe 1/2Ta 1/2)O 3 increased. It has been observed that the doping in small amounts (0≤ x≤0.2) of Fe could meliorate the dielectric and ferroelectric properties. The diffuseness in the mode of phase transition increases and the phase transition temperature decreases as a function of Fe content. It is revealed that the dielectric data and heat capacity data follow a similar trend in the variation of the mode of phase transition and phase transition temperatures. The phase transition temperature values obtained from the heat capacity measurement well agreed with the values obtained from dielectric measurement.
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.
The Roberge-Weiss phase transition and its endpoint
NASA Astrophysics Data System (ADS)
Kouno, Hiroaki; Sakai, Yuji; Kashiwa, Kouji; Yahiro, Masanobu
2009-11-01
The Roberge-Weiss (RW) phase transition in the imaginary chemical potential region is analyzed by the Polyakov-loop extended Nambu-Jona-Lasinio (PNJL) model. In the RW phase transition, the charge-conjugation symmetry is spontaneously broken, while the extended {\\mathbb Z}_{3} symmetry (the RW periodicity) is preserved. The RW transition is of second order at the endpoint. At the zero chemical potential, a crossover deconfinement transition appears as a remnant of the second-order RW phase transition at the endpoint, while the charge-conjugation symmetry is always preserved.
Main phase transitions in supported lipid single-bilayer.
Charrier, A; Thibaudau, F
2005-08-01
We have studied the phase transitions of a phospholipidic single-bilayer supported on a mica substrate by real-time temperature-controlled atomic force microscopy. We show the existence of two phase transitions in this bilayer that we attribute to two gel (L(beta))/fluid (L(alpha)) transitions, corresponding to the independent melting of each leaflet of the bilayer. The ratio of each phase with temperature and the large broadening of the transitions' widths have been interpreted through a basic thermodynamic framework in which the surface tension varies during the transitions. The experimental data can be fit with such a model using known thermodynamic parameters. PMID:15879467
Topological phase transition of a Josephson junction and its dynamics
NASA Astrophysics Data System (ADS)
Hutasoit, Jimmy; Marciani, Marco; Tarasinski, Brian; Beenakker, Carlo
A Josephson junction formed by a superconducting ring interrupted by a semiconductor nanowire can realize a zero-dimensional class D topological superconductor. By coupling the Josephson junction to a ballistic wire and altering the strength of the coupling, one can drive this topological superconductor through a topological phase transition. We study the compressibility of the junction as a probe of the topological phase transition. We also study the dynamics of the phase transition by studying the current pulse injected into the wire.
Quantum phase transition of condensed bosons in optical lattices
Liang Junjun; Liang, J.-Q.; Liu, W.-M.
2003-10-01
In this paper we study the superfluid-Mott-insulator phase transition of ultracold dilute gas of bosonic atoms in an optical lattice by means of Green function method and Bogliubov transformation as well. The superfluid-Mott-insulator phase transition condition is determined by the energy-band structure with an obvious interpretation of the transition mechanism. Moreover the superfluid phase is explained explicitly from the energy spectrum derived in terms of Bogliubov approach.
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.
Theory of volume transition in polyelectrolyte gels with charge regularization.
Hua, Jing; Mitra, Mithun K; Muthukumar, M
2012-04-01
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. PMID:22482584
Theory of volume transition in polyelectrolyte gels with charge regularization
NASA Astrophysics Data System (ADS)
Hua, Jing; Mitra, Mithun K.; Muthukumar, M.
2012-04-01
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.
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.
Raman study of thermochromic phase transition in tungsten trioxide nanowires
NASA Astrophysics Data System (ADS)
Lu, Dong Yu; Chen, Jian; Chen, Huan Jun; Gong, Li; Deng, Shao Zhi; Xu, Ning Sheng; Liu, Yu Long
2007-01-01
Tungsten trioxide (WO3) nanowires were synthesized by thermal evaporation of tungsten powder in two steps: tungsten suboxide (WO3-x) nanowires were synthesized, and then oxidized in O2 ambient and transformed into WO3 nanowires. Raman spectroscopy was applied to study the thermochromic phase transition of one-dimensional WO3 nanowires. From the temperature dependence of the characteristic mode at 33cm-1 in WO3, the phase transition temperature was determined. It was found that the phase transition of WO3 nanowires was reversible and the phase transition temperatures were even lower than that of WO3 nanopowder.
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. PMID:25192088
NASA Astrophysics Data System (ADS)
Nishio-Hamane, Daisuke; Dekura, Haruhiko; Seto, Yusuke; Yagi, Takehiko
2015-05-01
A post-cotunnite phase transition in zirconia (ZrO2) at high pressure was investigated by synchrotron X-ray diffraction measurements and ab initio calculations based on density functional theory. This study successfully demonstrated a cotunnite- to Fe2P-type phase transition. Static enthalpy difference (Δ H) calculations predicted the appearance of the Fe2P phase at 124 GPa (LDA) and 143 GPa (GGA), and experimental trials demonstrated the coexistence of the Fe2P and cotunnite phases at 175 GPa after heating to 3,000 K. Both phases were quenchable to ambient conditions. The volume of the Fe2P phase was slightly less (~Δ 0.6 %) than that of the cotunnite phase over the experimental pressure range, indicating that the Fe2P phase is the higher pressure phase. The coexistence of both phases in this study may be attributed to the slow kinetics of the phase transition resulting from the close structural relationship of the two phases. An Fe2P-type structural model can be derived by applying a simple operation to the cotunnite-type structure, consisting of a 1/2 shift of several zirconium arrangements parallel to the b-axis of the cotunnite-type unit cell. It is concluded that the high-pressure cotunnite-to-Fe2P phase transition may be a common trend in many dioxides.
Liquid-liquid phase transition in hydrogen by coupled electron-ion Monte Carlo simulations
NASA Astrophysics Data System (ADS)
Pierleoni, Carlo; Morales, Miguel A.; Rillo, Giovanni; Holzmann, Markus
2016-05-01
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.
Liquid-liquid phase transition in hydrogen by coupled electron-ion Monte Carlo simulations.
Pierleoni, Carlo; Morales, Miguel A; Rillo, Giovanni; Holzmann, Markus; Ceperley, David M
2016-05-01
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
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
Phase transitions in a gas of anyons
NASA Astrophysics Data System (ADS)
MacKenzie, R.; Nebia-Rahal, F.; Paranjape, M. B.; Richer, J.
2010-10-01
We continue our numerical Monte Carlo simulation of a gas of closed loops on a 3 dimensional lattice, however, now in the presence of a topological term added to the action which corresponds to the total linking number between the loops. We compute the linking number using a novel approach employing certain notions from knot theory. Adding the topological term converts the particles into anyons. Interpreting the model as an effective theory that describes the 2+1-dimensional Abelian Higgs model in the asymptotic strong-coupling regime, the topological linking number simply corresponds to the addition to the action of the Chern-Simons term. The system continues to exhibit a phase transition as a function of the vortex mass as it becomes small. We find the following new results. The Chern-Simons term has no effect on the Wilson loop. On the other hand, it does effect the ’t Hooft loop of a given configuration, adding the linking number of the ’t Hooft loop with all of the dynamical vortex loops. We find the unexpected result that both the Wilson loop and the ’t Hooft loop exhibit a perimeter law even though there are no massless particles in the theory, in both phases of the theory. It should be noted that our method suffers from numerical instabilities if the coefficient of the Chern-Simons term is too large; thus, we have restricted our results to small values of this parameter. Furthermore, interpreting the lattice loop gas as an effective theory describing the Abelian Higgs model is only known to be true in the infinite coupling limit; for strong but finite coupling this correspondence is only a conjecture, the validity of which is beyond the scope of this article.
Phase transitions in a gas of anyons
MacKenzie, R.; Nebia-Rahal, F.; Paranjape, M. B.; Richer, J.
2010-10-01
We continue our numerical Monte Carlo simulation of a gas of closed loops on a 3 dimensional lattice, however, now in the presence of a topological term added to the action which corresponds to the total linking number between the loops. We compute the linking number using a novel approach employing certain notions from knot theory. Adding the topological term converts the particles into anyons. Interpreting the model as an effective theory that describes the 2+1-dimensional Abelian Higgs model in the asymptotic strong-coupling regime, the topological linking number simply corresponds to the addition to the action of the Chern-Simons term. The system continues to exhibit a phase transition as a function of the vortex mass as it becomes small. We find the following new results. The Chern-Simons term has no effect on the Wilson loop. On the other hand, it does effect the 't Hooft loop of a given configuration, adding the linking number of the 't Hooft loop with all of the dynamical vortex loops. We find the unexpected result that both the Wilson loop and the 't Hooft loop exhibit a perimeter law even though there are no massless particles in the theory, in both phases of the theory. It should be noted that our method suffers from numerical instabilities if the coefficient of the Chern-Simons term is too large; thus, we have restricted our results to small values of this parameter. Furthermore, interpreting the lattice loop gas as an effective theory describing the Abelian Higgs model is only known to be true in the infinite coupling limit; for strong but finite coupling this correspondence is only a conjecture, the validity of which is beyond the scope of this article.
On the existence of vapor-liquid phase transition in dusty plasmas
NASA Astrophysics Data System (ADS)
Kundu, M.; Avinash, K.; Sen, A.; Ganesh, R.
2014-10-01
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.
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.
Electrical Dissipation Measurement of Polymer Phase Transitions
NASA Technical Reports Server (NTRS)
Long, E. R., R; Schuszler, A., II
1983-01-01
Technique measures solid/solid, glass/rubber, and liquid/liquid transition temperatures in polymers having dipole moments. Technique based on change in dipole packing that occurs with each transition and measured as change in electrical dissipation factor. Change in dipole packing occuring with each transition sensed by effect on dissipation factor.
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. PMID:25493907
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 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.
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.
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.
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
Strain glass state as the boundary of two phase transitions
NASA Astrophysics Data System (ADS)
Zhou, Zhijian; Cui, Jian; Ren, Xiaobing
2015-08-01
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.
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.
Dynamics of a photoinduced phase transition in polydiacetylene crystals
NASA Astrophysics Data System (ADS)
Koshihara, S.; Tokura, Y.; Takeda, K.; Koda, T.
1995-09-01
The dynamical process of the photoinduced phase transition in polydiacetylene (PDA) single crystals has been investigated by time-resolved spectroscopy with varying temperature, excitation photon energy, and intensity. The photoinduced phase transition can be driven bidirectionally between the two (A and B) phases by dichromatic irradiation of a laser pulse, when the temperature of the PDA crystal is kept around the phase transition temperature (Tc). It was found that primary process of the photoinduced phase transition is mostly completed within 50 ns. In addition, occurrence of a transient domain injection has been confirmed at temperatures far below and above Tc. Together with the time-resolved measurement of photocurrent, we have found a close correlation between the photocurrent intensity and the phase conversion efficiency. This suggests that the domain walls separating the A and B phases can carry the charge.
Liquid liquid phase transition in Stillinger Weber silicon
NASA Astrophysics Data System (ADS)
Beaucage, Philippe; Mousseau, Normand
2005-04-01
It was recently demonstrated that Stillinger-Weber silicon undergoes a liquid-liquid first-order phase transition deep into the supercooled region (Sastry and Angell 2003 Nat. Mater. 2 739). Here we study the effects of perturbations on this phase transition. We show that the order of the liquid-liquid transition changes with negative pressure. We also find that the liquid-liquid transition disappears when the three-body term of the potential is strengthened by as little as 5%. This implies that the details of the potential could affect strongly the nature and even the existence of the liquid-liquid phase.
Transformation of phase transitions driven by an anisotropic random field
NASA Astrophysics Data System (ADS)
Popa-Nita, V.; Kralj, Samo
2005-04-01
We carry out a comparative study of the influence of a random anisotropy field on continuous and discontinuous phase transitions. The ordered phase, which is reached via a continuous symmetry breaking phase transition, is characterized by an order parameter and by a corresponding hydrodynamic continuum field. We assume that the response of the hydrodynamic field to the imposed disorder results in a domainlike pattern of the system. For a strong enough disorder both transitions become gradual. For weaker disorder strengths the disorder converts a second order transition into a discontinuous one.
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.
Pressure-induced phase transitions and metallization in VO2
NASA Astrophysics Data System (ADS)
Bai, Ligang; Li, Quan; Corr, Serena A.; Meng, Yue; Park, Changyong; Sinogeikin, Stanislav V.; Ko, Changhyun; Wu, Junqiao; Shen, Guoyin
2015-03-01
We report the results of pressure-induced phase transitions and metallization in VO2 based on synchrotron x-ray diffraction, electrical resistivity, and Raman spectroscopy. Our isothermal compression experiments at room temperature and 383 K show that the room temperature monoclinic phase (M 1 ,P 21/c ) and the high-temperature rutile phase (R ,P 42/m n m ) of VO2 undergo phase transitions to a distorted M 1 monoclinic phase (M 1' ,P 21/c ) above 13.0 GPa and to an orthorhombic phase (CaCl2-like, P n n m ) above 13.7 GPa, respectively. Upon further compression, both high-pressure phases transform into a new phase (phase X ) above 34.3 and 38.3 GPa at room temperature and 383 K, respectively. The room temperature M 1 -M 1' phase transition structurally resembles the R -CaCl2 phase transition at 383 K, suggesting a second-order displacive type of transition. Contrary to previous studies, our electrical resistivity results, Raman measurements, as well as ab initio calculations indicate that the new phase X , rather than the M 1' phase, is responsible for the metallization under pressure. The metallization mechanism is discussed based on the proposed crystal structure.
Critical linear thermal expansion in the smectic- A phase near the nematic-smectic phase transition
NASA Astrophysics Data System (ADS)
Anesta, E.; Iannacchione, G. S.; Garland, C. W.
2004-10-01
Recent high-resolution x-ray investigations of the smectic- A (SmA) phase near the nematic-to-SmA transition provide information about the critical behavior of the linear thermal expansion coefficient α‖ parallel to the director. Combining such data with available volume thermal expansion αV data yields the in-plane linear expansion coefficient α⊥ . The critical behaviors of α‖ and α⊥ are the same as those for αV and the heat capacity Cp . However, for any given liquid crystal, α‖(crit) and α⊥(crit) differ in sign. Furthermore, the quantity α‖(crit) is positive for SmAd partial bilayer smectics, while it is negative for nonpolar SmAm monomeric smectics. This feature is discussed in terms of the molecular structural aspects of these smectic phases.
Phase transitions and domain structures in multiferroics
NASA Astrophysics Data System (ADS)
Vlahos, Eftihia
2011-12-01
Thin film ferroelectrics and multiferroics are two important classes of materials interesting both from a scientific and a technological prospective. The volatility of lead and bismuth as well as environmental issues regarding the toxicity of lead are two disadvantages of the most commonly used ferroelectric random access memory (FeRAM) materials such as Pb(Zr,Ti)O3 and SrBi2Ta2O9. Therefore lead-free thin film ferroelectrics are promising substitutes as long as (a) they can be grown on technologically important substrates such as silicon, and (b) their T c and Pr become comparable to that of well established ferroelectrics. On the other hand, the development of functional room temperature ferroelectric ferromagnetic multiferroics could lead to very interesting phenomena such as control of magnetism with electric fields and control of electrical polarization with magnetic fields. This thesis focuses on the understanding of material structure-property relations using nonlinear optical spectroscopy. Nonlinear spectroscopy is an excellent tool for probing the onset of ferroelectricity, and domain dynamics in strained ferroelectrics and multiferroics. Second harmonic generation was used to detect ferroelectricity and the antiferrodistortive phase transition in thin film SrTiO3. Incipient ferroelectric CaTiO3 has been shown to become ferroelectric when strained with a combination of SHG and dielectric measurements. The tensorial nature of the induced nonlinear polarization allows for probing of the BaTiO3 and SrTiO3 polarization contributions in nanoscale BaTiO3/SrTiO3 superlattices. In addition, nonlinear optics was used to demonstrate ferroelectricity in multiferroic EuTiO3. Finally, confocal SHG and Raman microscopy were utilized to visualize polar domains in incipient ferroelectric and ferroelastic CaTiO3.
Replacing energy by von Neumann entropy in quantum phase transitions
Kopp, Angela; Jia Xun; Chakravarty, Sudip . E-mail: sudip@physics.ucla.edu
2007-06-15
We propose that quantum phase transitions are generally accompanied by non-analyticities of the von Neumann (entanglement) entropy. In particular, the entropy is non-analytic at the Anderson transition, where it exhibits unusual fractal scaling. We also examine two dissipative quantum systems of considerable interest to the study of decoherence and find that non-analyticities occur if and only if the system undergoes a quantum phase transition.
Chiral phase transition in peripheral heavy-ion collisions
Ayala, Alejandro; Bashir, Adnan; Raya, Alfredo; Sanchez, Angel
2009-04-20
It has been recently realized that in peripheral heavy-ion collisions at high energies, a sizable magnetic field is produced in the interaction region. Although this field becomes weak at the proper times when the chiral phase transition is believed to occur, it is still significant so as to ask whether it influences such transition. We use the linear sigma model to study the chiral phase transition in the presence of weak magnetic fields.
Reexamination of entanglement and the quantum phase transition
Yang, M.-F.
2005-03-01
We show that, for an exactly solvable quantum spin model, a discontinuity in the first derivative of the ground-state concurrence appears in the absence of a quantum phase transition. It is opposed to the popular belief that the nonanalyticity property of ground-state concurrence can be used to determine quantum phase transitions. We further point out that the analyticity property of the ground-state concurrence in general can be more intricate than that of the ground-state energy. Thus there is no one-to-one correspondence between quantum phase transitions and the nonanalyticity property of the concurrence. Moreover, we show that the von Neumann entropy, as another measure of entanglement, cannot reveal quantum phase transitions in the present model. Therefore, in order to link with quantum phase transitions, some other measures of entanglement are needed.
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.
Technical feasibility of transition phase tests in TREAT. [LMFBR
Stewart, R.R.; Bauer, T.H.; Hoff, O.I.; Koyama, K.; Stephenson, M.E.; Kraft, T.E.
1982-01-01
Understanding the behavior of molten fuel-steel mixtures subjected to fission heating within a HCDA environment is essential to continuing the mechanistic description of the whole-core accident into the transition phase, and further to a permanent subcritical and safe fuel debris configuration. Fundamentally, the RX1 TREAT test will simulte the transition phase of a HCDA (the accident phase in which the fuel in individual subassemblies melts and becomes a heat-generating pool of molten fuel and boiling steel). This assessment of the feasibility of such a test indicates that a transition phase test can be achieved in TREAT, at power levels simulating decay heat.
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.
Reentrant topological phase transitions in a disordered spinless superconducting wire
NASA Astrophysics Data System (ADS)
Rieder, Maria-Theresa; Brouwer, Piet W.; Adagideli, İnanç
2013-08-01
In a one-dimensional spinless p-wave superconductor with coherence length ξ, disorder induces a phase transition between a topologically nontrivial phase and a trivial insulating phase at the critical mean-free path l=ξ/2. Here, we show that a multichannel spinless p-wave superconductor goes through an alternation of topologically trivial and nontrivial phases upon increasing the disorder strength, the number of phase transitions being equal to the channel number N. The last phase transition, from a nontrivial phase into the trivial phase, takes place at a mean-free path l=ξ/(N+1), parametrically smaller than the critical mean-free path in one dimension. Our result is valid in the limit that the wire width W is much smaller than the superconducting coherence length ξ.
Wetting transitions in two-, three-, and four-phase systems.
Hejazi, Vahid; Nosonovsky, Michael
2012-01-31
We discuss wetting of rough surfaces with two-phase (solid-liquid), three-phase (solid-water-air and solid-oil-water), and four-phase (solid-oil-water-air) interfaces mimicking fish scales. We extend the traditional Wenzel and Cassie-Baxter models to these cases. We further present experimental observations of two-, three-, and four-phase systems in the case of metal-matrix composite solid surfaces immersed in water and in contact with oil. Experimental observations show that wetting transitions can occur in underwater oleophobic systems. We also discuss wetting transitions as phase transitions using the phase-field approach and show that a phenomenological gradient coefficient is responsible for wetting transition, energy barriers, and wetting/dewetting asymmetry (hysteresis). PMID:22054126
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. PMID:27530509
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.
Metamagnetic Phase Transition in a Diruthenium Compound with Interpenetrating Sublattices
Fishman, Randy Scott; Miller, Joel S.
2011-01-01
The diruthenium compound [Ru2(O2CMe)4]3[Cr(CN)6] may be the only known material that con- tains two weakly-coupled, magnetically-ordered sublattices occupying the same three-dimensional volume. Due to the strong easy-plane anisotropy on each Ru2 complex, the moment of each sub- lattice is constrained to one of the eight cubic diagonals. At low fields, the two sublattices are antiferromagnetically aligned by weak dipolar and deformation energies. But above a metamagnetic critical field of about 1000 Oe, the sublattice moments become ferromagnetically aligned and the net magnetization increases dramatically. We have successfully modeled this metamagnetic tran- sition by assuming that the individual sublattice spin configurations are only weakly distorted by the magnetic field. This model suggests that the ground state of each sublattice undergoes a phase transition at a pressure of about 7 kbar. The drop in the sublattice moment and the rise in the sublattice susceptibility above 7 kbar can be explained by a high- to low-spin transition (S = 3/2 to 1/2) on the mixed-valent diruthenium complexes.
Phase transition in the Jarzynski estimator of free energy differences.
Suárez, Alberto; Silbey, Robert; Oppenheim, Irwin
2012-05-01
The transition between a regime in which thermodynamic relations apply only to ensembles of small systems coupled to a large environment and a regime in which they can be used to characterize individual macroscopic systems is analyzed in terms of the change in behavior of the Jarzynski estimator of equilibrium free energy differences from nonequilibrium work measurements. Given a fixed number of measurements, the Jarzynski estimator is unbiased for sufficiently small systems. In these systems the directionality of time is poorly defined and the configurations that dominate the empirical average, but which are in fact typical of the reverse process, are sufficiently well sampled. As the system size increases the arrow of time becomes better defined. The dominant atypical fluctuations become rare and eventually cannot be sampled with the limited resources that are available. Asymptotically, only typical work values are measured. The Jarzynski estimator becomes maximally biased and approaches the exponential of minus the average work, which is the result that is expected from standard macroscopic thermodynamics. In the proper scaling limit, this regime change has been recently described in terms of a phase transition in variants of the random energy model. In this paper this correspondence is further demonstrated in two examples of physical interest: the sudden compression of an ideal gas and adiabatic quasistatic volume changes in a dilute real gas. PMID:23004704
Phase transition in the Jarzynski estimator of free energy differences
NASA Astrophysics Data System (ADS)
Suárez, Alberto; Silbey, Robert; Oppenheim, Irwin
2012-05-01
The transition between a regime in which thermodynamic relations apply only to ensembles of small systems coupled to a large environment and a regime in which they can be used to characterize individual macroscopic systems is analyzed in terms of the change in behavior of the Jarzynski estimator of equilibrium free energy differences from nonequilibrium work measurements. Given a fixed number of measurements, the Jarzynski estimator is unbiased for sufficiently small systems. In these systems the directionality of time is poorly defined and the configurations that dominate the empirical average, but which are in fact typical of the reverse process, are sufficiently well sampled. As the system size increases the arrow of time becomes better defined. The dominant atypical fluctuations become rare and eventually cannot be sampled with the limited resources that are available. Asymptotically, only typical work values are measured. The Jarzynski estimator becomes maximally biased and approaches the exponential of minus the average work, which is the result that is expected from standard macroscopic thermodynamics. In the proper scaling limit, this regime change has been recently described in terms of a phase transition in variants of the random energy model. In this paper this correspondence is further demonstrated in two examples of physical interest: the sudden compression of an ideal gas and adiabatic quasistatic volume changes in a dilute real gas.
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.
Phase transition in the assignment problem for random matrices
NASA Astrophysics Data System (ADS)
Esteve, J. G.; Falceto, F.
2005-12-01
We report an analytic and numerical study of a phase transition in a P problem (the assignment problem) that separates two phases whose representatives are the simple matching problem (an easy P problem) and the traveling-salesman problem (a NP-complete problem). Like other phase transitions found in combinatoric problems (K-satisfiability, number partitioning) this can help to understand the nature of the difficulties in solving NP problems an to find more accurate algorithms for them.
Geodesics in information geometry: classical and quantum phase transitions.
Kumar, Prashant; Mahapatra, Subhash; Phukon, Prabwal; Sarkar, Tapobrata
2012-11-01
We study geodesics on the parameter manifold for systems exhibiting second order classical and quantum phase transitions. The coupled nonlinear geodesic equations are solved numerically for a variety of models which show such phase transitions in the thermodynamic limit. It is established that both in the classical as well as in the quantum cases, geodesics are confined to a single phase and exhibit turning behavior near critical points. Our results are indicative of a geometric universality in widely different physical systems. PMID:23214748
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. PMID:26764651
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
Micellar structures in lyotropic liquid crystals and phase transitions
NASA Astrophysics Data System (ADS)
Saupe, A.; Xu, S. Y.; Plumley, Sulakshana; Zhu, Y. K.; Photinos, P.
1991-05-01
The formation of micellar nematics is discussed with emphasis on the transitions between nematic phases and nematic-smectic transitions. Phase diagrams for MTAB/l-decanol/D,O systems show a direct transition between uniaxial nematics. Electrical conductivity and birefringence measurements on a mixture of sodium decylsulfate. 1-decanol, D,O demonstrate, on the other hand, the existence of a biaxial nemantic range that separates the Uniaxial nematics. On a mixture of cesium perflouroctanoate and H 2O the electrical conductivity and rotational viscosity are used to discuss the relevant features of nematic-lamellar-smectic transitions. The formation of elongated ribbon-like micelles at the nematic-smectic transition is suggested. Transitions between different nematic phases in the MTAB system may be connected with a structural change from long micelles with a fairly circular cross section to similar micelles with a more elliptical cross section.
NASA Astrophysics Data System (ADS)
Lin, Xianqing; Ni, Jun
2016-08-01
First-principles calculations have been performed to study the energetic, electronic, and magnetic properties of substitutional 3d transition metal dopants in monoclinic transition metal dichalcogenides (TMDs) as topological insulators ( 1 T ' - MX 2 with M = (Mo, W) and X = (S, Se)). We find various favorite features in these doped systems to introduce magnetism and other desirable electronic properties: (i) The Mn embedded monoclinic TMDs are magnetic, and the doped 1 T ' - MoS 2 still maintains the semiconducting character with high concentration of Mn, while an electronic phase transition occurs in other Mn doped monoclinic TMDs with an increasing concentration of Mn. Two Mn dopants prefer the ferromagnetic coupling except for substitution of the nearest Mo atoms in 1 T ' - MoS 2 , and the strength of exchange interaction shows anisotropic behavior with dopants along one Mo zigzag chain having much stronger coupling. (ii) The substitutional V is a promising hole dopant, which causes little change to the energy dispersion around the conduction and valence band edges in most systems. In contrast, parts of the conduction band drop for the electron dopants Co and Ni due to the large structural distortion. Moreover, closing band gaps of the host materials are observed with increasing carrier concentration. (iii) Single Fe dopant has a magnetic moment, but it also dopes electrons. When two Fe dopants have a small distance, the systems turn into nonmagnetic semiconductors. (iv) The formation energies of all dopants are much lower than those in hexagonal TMDs and are all negative in certain growth conditions, suggesting possible realization of the predicted magnetism, electronic phase transitions as well as carrier doping in 1 T ' - MX 2 based topological devices.