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The thermodynamic model of hysteresis in phase transitions based on the regular solution theory, previously developed, was applied to the solid phases of C(1)H(4) and C(2)H(4). The width and height of the hysteresis loops for these systems were calculated and compared with the experimental data; agreement was satisfactory.
A brief review is given of the theoretical models and calculational methods used to study the main phase transition in phospholipid membranes with particular emphasis on recent progress. The models are discussed in terms of the mechanical variables and the various interactions which are necessary to describe the phase transition. Theoretical results are presented for the transitional properties and how the phase equilibria are affected by "impurities" such as cholesterol, proteins and anaesthetics.
Pressure-induced phase transitions in liquid phosphorus have been studied by constant-pressure first-principles molecular dynamics simulations. By compressing a low-pressure liquid which consists of the tetrahedral P4 molecules, a structural phase transition from the molecular to polymeric liquid (a high-pressure phase) observed in the recent experiment by Katayama et al. [Nature (London) 403, 170 (2000)] was successfully realized. It is found that this transition is caused by a breakup of the tetrahedral molecules with large volume contraction. The same transition is also realized by heating. This indicates that only the polymeric liquid can stably exist at high temperature.
Differential scanning calorimetry (DSC) and low-temperature X-ray diffraction studies showed that 2-thio-(5,5-dimethyl-1,3,2-dioxaphosphorinanyl)2'-oxo-dineopentyl-thiophosphate (compound 1) undergoes reversible phase transition at 203 K related to the change of symmetry of the crystallographic unit. Solid state NMR spectroscopy was used to establish the dynamic processes of aliphatic groups and the phosphorus skeleton. 13C and 31P variable temperature NMR studies as well as T1 and T1rho measurements of relaxation times revealed the different mode of molecular motion for each neopentyl residue directly bonded to phosphorus. It is concluded that molecular dynamics of aliphatic groups causes different van der Waals interactions in the crystal lattice and is the driving force of phase transition for compound 1. Finally, we showed that very sharp phase transition temperature makes compound 1 an excellent candidate as a low-temperature NMR thermometer in the solid phase.
We report that the properties of the isotropic to nematic liquid crystalline phase transition of F-actin depend critically on the average filament length. For average filament lengths longer than 2 microm, we confirm previous findings that the phase transition is continuous in both alignment and concentration. For average filament lengths shorter than 2 microm, we show for the first time a first order transition with a clear discontinuity in both alignment and concentration. Tactoidal droplets of coexisting isotropic and nematic phases, differing in concentration by approximately 30%, form over the course of hours and appear to settle into near equilibrium metastable states.
The Glauber model on a one-dimensional lattice with boundaries (for the ferromagnetic and antiferromagnetic cases) is considered. The large-time behavior of the one-point function is studied. It is shown that at any temperature, the system shows a dynamical phase transition. The dynamical phase transition is controlled by the rate of spin flip at the boundaries, and is a discontinuous change of the derivative of the relaxation time towards the stationary configuration.
The fluorescence spectra of 6-propionyl-2-(dimethylamino)naphthalene (Prodan) and 6-dodecanoyl-2-(dimethylamino)naphthalene (Laurdan) in bilayer membranes of 1,2-distearoylphosphatidylcholine (DSPC) were observed as a function of pressure at constant temperature. The emission spectra of Prodan and Laurdan varied with the pressure-induced states of bilayer membranes. The maximum emission wavelength (lambda(max)) of Prodan characteristic of the liquid crystalline (L(alpha)), lamellar gel (L(beta)') and pressure-induced interdigitated gel (L(beta)I) phases of the DSPC bilayer was 480, 440 and 500 nm, respectively. On the other hand, the lambda(max) of Laurdan characteristic of the L(alpha) and L(beta)' phases was 480 and 440 nm in a similar manner as Prodan probe. However, no change in the lambda(max) was observed in spite of the occurrence of the interdigitation of bilayer. Since the lambda(max) reflects the solvent property around the probe molecules, we could speculate about the location of fluorescent probe in the bilayer membranes. In the L(alpha) phase the same chromophore group of Prodan and Laurdan probes distributes around phosphate group of lipid (i.e., polar region). The transformation of bilayer into the L(beta)' phase causes the Prodan and Laurdan molecules to move into the glycerol backbone (i.e., less polar) region. In the ripple gel (P(beta)') phase, the emission spectrum of Prodan shows a broad peak at about 480 nm and a shoulder around 440 nm, which means that the Prodan molecules are widespread over the wide range from the glycerol backbone to the hydrophilic part of bilayer. The P(beta)'/L(beta)I phase transition causes the Prodan molecule to squeeze out from the glycerol backbone region and to move the hydrophilic region near the bilayer surface. Contrarily, the Laurdan molecule was not squeezed out from the glycerol backbone region because the long acyl chain of Laurdan serves as an anchor in the hydrophobic core of bilayer. The ratio of fluorescence intensity of Prodan at 480 nm to that at 440 nm, F(480)/F(440), is available to observation of bilayer phase transitions. The plot of F(480)/F(440) versus pressure seems to be useful for the recognition of bilayer phase transition, especially the bilayer interdigitation.
We investigate a traffic model in which cars either move freely with quenched intrinsic velocities or belong to clusters formed behind slower cars. In each cluster, the next-to-leading car is allowed to pass and resume free motion. The model undergoes a phase transition from a disordered phase for the high passing rate to a jammed phase for the low rate. In the disordered phase, the cluster size distribution decays exponentially in the large size limit. In the jammed phase, the distribution of finite clusters is independent on the passing rate, but it accounts only for a fraction of all cars; the "excessive" cars form an infinite cluster moving with the smallest velocity. Mean-field equations, describing the model in the framework of Maxwell approximation, correctly predict the existence of phase transition and adequately describe the disordered phase; properties of the jammed phase are studied numerically.
We model the dynamical behavior of the neuropil, the densely interconnected neural tissue in the cortex, using neuropercolation approach. Neuropercolation generalizes phase transitions modeled by percolation theory of random graphs, motivated by properties of neurons and neural populations. The generalization includes (1) a noisy component in the percolation rule, (2) a novel depression function in addition to the usual arousal function, (3) non-local interactions among nodes arranged on a multi-dimensional lattice. This paper investigates the role of non-local (axonal) connections in generating and modulating phase transitions of collective activity in the neuropil. We derived a relationship between critical values of the noise level and non-locality parameter to control the onset of phase transitions. Finally, we propose a potential interpretation of ontogenetic development of the neuropil maintaining a dynamical state at the edge of criticality.
The effect of 1-anilinonaphthalene-8-sulfonate (ANS) on the thermotropic phase transition of dipalmitoylphosphatidylcholine (DPPC) bilayers was examined by differential scanning calorimetry. The main phase transition temperature was found to be shifted to lower values in the presence of the probe. The shift strongly depends on pH and the presence of salts. This indicates that the penetration of the probe of the hydrocarbon moiety of the bilayer is influenced by coulombic interactions. Pretransition phenomena are also affected. The implications for the interpretation of experimental data of biomembrane studies are discussed.
In this paper we study a microcanonical lattice gas model with a constrained average volume. We show that the caloric curve explicitly depends on the considered transformation of the volume with the excitation energy and so does not bear direct information on the characteristics of the phase transition. Conversely, partial energy fluctuations are demonstrated to be a direct measure of the equation of state. Since the heat capacity has a negative branch in the phase transition region, the presence of abnormally large kinetic energy fluctuations is a signal of the liquid-gas phase transition.
Unsonicated liposomes prepared from dimyristoyl phosphatidylcholine were nearly completely dissolved during a 3 h incubation with rat plasma at or close to the phase-transition temperature of 24 degrees C. At 37 or 15 degrees C virtually no liposomal disintegration was observed even after 24 h of incubation. The liposomal solubilization, which was monitored by turbidity measurements or by determination of phospholipid sedimentability, was accompanied by the formation of a phospholipid-protein complex similar or identical to the one we previously reported to be formed from sonicated liposomes of egg phosphatidylcholine (Scherphof, G., Roerdink, F., Waite, M. and Parks, J. (1978) Biochim. Biophys. Acta 542, 296--307). Unsonicated multilamellar liposomes made of egg phosphatidylcholine were completely resistant to the dissolving potency of plasma when incubated at 37 degrees C. Liposomes from equimolar mixtures of dimyristoyl and dipalmitoyl phosphatidylcholine were only degraded by plasma in the temperature range between 30 and 35 degrees C at which temperature this cocrystallizing phospholipid mixture undergoes a phase transition. However, even at these temperatures the rate of dissolution of this mixture was significantly lower than of dimyristoyl phosphatidylcholine at 24 degrees C. In the dissolving process of this mixture a slight preference for the lower-melting component was observed. The ability of cholesterol to completely abolish the susceptibility of dimyristoyl phosphatidylcholine liposomes to plasma at a 1:2 molar ratio of cholesterol to phospholipid substantiates the essential role of the phase transition in the process of liposome solubilization. When liposomes of the monotectic mixtures dimyristoyl and distearoyl phosphatidylcholine or dilauroyl and distearoyl phosphatidylcholine were incubated with plasma at temperatures in between those at which the constituent lipids undergo a phase change in the mixture, the liposomes were slowly dissolved. Under those conditions a selective removal of the lipids in the liquid-crystalline phase was observed. It is concluded that for the plasma-induced dissolution of unsonicated liposomes, which is most probably achieved by interaction with (apo)lipoproteins, the presence of phase boundaries is required in much the same way as was first reported for phospholipases by Op den Kamp, J.A.F., de Gier, J. and Van Deenen, L.L.M. (1974) Biochim. Biophys. Acta 345, 253--256).
We consider how the Lee-Yang description of phase transitions in terms of partition function zeros applies to nonequilibrium systems. Here, one does not have a partition function; instead we consider the zeros of a steady-state normalization factor in the complex plane of the transition rates. We obtain the exact distribution of zeros in the thermodynamic limit for a specific model, the boundary-driven asymmetric simple exclusion process. We show that the distributions of zeros at the first- and the second-order nonequilibrium phase transitions of this model follow the patterns known in the Lee-Yang equilibrium theory.
Three accurate X-ray diffraction experiments (Mo Kalpha, T = 190, 240 and 298 K) were carried out to track the temperature dependence of the electron density in the cubic perovskite potassium manganese trifluoride, KMnF3, from room temperature to just above that of the phase transition to the tetragonal structure (186 K), and to correlate the parameters of the critical points with the phase-transition mechanism. The data obtained were approximated by the Hansen-Coppens multipole model expanded up to hexadecupoles; the anharmonicity of the atomic displacements up to the fourth level was considered. Topological analysis shows only two types of chemical bond at room temperature, Mn-F and K-F. However, at low temperature the K-F bonds blocking the rotation of the MnF6 octahedra are weakened and new Mn-K bonds are formed to keep the crystal structure from disintegrating. The Mn-K bonds become stronger as the temperature approaches 186 K. This rearrangement of chemical bonds can be regarded as a precursor effect, which starts 50-60 degrees above the phase-transition temperature. The effective one-particle potential of the F atom has a single minimum at 298 K and four well separated minima (with a shift of 0.2 A from the equilibrium position towards the structural holes) at 190 K. Parameters of the critical points of the electron density indicate closed-shell type interactions between K-F and Mn-K pairs, whereas the Mn-F bond can be considered as an intermediate type. The topology of the electrostatic potentials is discussed as well.
This study was designed to investigate the effects of the He-Ne laser (632.8 nm of wavelength, 8.5 mW in power, Senko Med. Co. Ltd., Tokyo, Japan) on the phase transition temperature of dipalmitoyl phosphatidylcholine (DPPC) membranes. Liposomal bilayers of DPPC (12.5 mM) were obtained with ultrasonification for 45 min at 40 degrees C and refrigerated for 2-3 days at 5 degrees C. The bilayers vesicle solution was divided into 3-ml working aliquots, which were assigned to three groups. The aliquots in Group 1 were used as controls without irradiation and the aliquots in Groups 2 and 3 were irradiated in 37 degrees C baths for 15 to 30 min, respectively. To determine phase transition temperature, optical density (%T; percent of permittance) of each aliquot was measured spectrophotomechanically at a wavelength of 440 nm while increasing its temperature at a rate of 0.5 degrees C every minute. Main phase transition temperatures in Groups 1, 2, and 3 were 41.54 +/- 0.23 degrees C (n = 10), 41.50 +/- 0.27 degrees C (n = 10), and 41.30 +/- 0.36 degrees C (n = 10), respectively. No significant difference between the nonirradiation and irradiation groups was established. These results suggest that irradiations of low-power He-Ne lasers up to 30 min do not change important physical characteristics of artificial DPPC membranes.
Stochastic dynamical systems are shown to exhibit the same order-disorder phase transitions that have been found in chaotic map lattices. Phase diagrams are obtained for diffusively coupled two-dimensional (2D) lattices, using two stochastic maps and a chaotic one, for both square and triangular geometries, with simultaneous updating. We show how the use of triangular geometry reduces (or even eliminates) the reentrant behavior found in the phase diagrams for the square geometry. This is attributed to the elimination (via frustration) of the antiferromagnetic clusters common to simultaneous updating of square lattices. We also evaluate the critical exponents for the stochastic maps in the triangular lattices. The strong similarities in the phase diagrams and the consistency between the critical exponents of one stochastic map and the chaotic one, evaluated in an early work by Marcq et al. [Phys. Rev. Lett. 77, 4003 (1996); Phys. Rev. E 55, 2606 (1997)] suggest that the "sign-persistence," defined as the probability that the local map keeps the sign of the local variable in one iteration, plays a fundamental role in the presence of continuous phase transitions in coupled map lattices, and is a basic ingredient for models that belong to this weak Ising universality. However, the fact that the second stochastic map, which has an extremely simple local dynamics, seems to fall in the 2D Ising universality class, suggests that some minimal local complexity is also needed to generate the specific correlations that end up giving non-Ising critical behavior.
PURPOSE: Lenses from selenite-treated animals develop reversible "cold cataract" at a lower temperature than is required for lenses from age-matched control animals. This unexplained, stabilized phase transition is readily observed in intact lenses 36 to 48 hours after treatment and occurs in lenses before the appearance of the irreversible nuclear opacity observed 72 to 96 hours after treatment. The objective of this study was to investigate factors that may be responsible for this difference. METHODS: Preweanling rats were injected with sodium selenite. Lens extracellular water volume was measured using 14C-inulin. Free amino acids were analyzed using precolumn derivatization and high performance liquid chromatography. Soluble protein was isolated from lenses of control, and treated animals and temperature-dependent changes in light scattering were measured at 490 nm. RESULTS: Lens extracellular water was increased by the selenite treatment, with a concurrent 10% decrease in intracellular volume. Solutions of soluble protein from lenses of selenite-treated animals after postinjection hours 24 and 48 had higher critical phase transition temperatures (Tc) compared to similar proteins from control lenses. From 24 to 72 hours after injection, the free amino acid content of the lens increased 42%. Taurine levels were unchanged over the same period. The addition of 7 mM glycine and 7 mM proline to solutions of soluble protein (96 mg ml-1) decreased the phase transition temperature. Taurine (14 mM) had a similar effect. Combining taurine and the glycine plus proline solutions had an additive effect in lowering the Tc. CONCLUSIONS: Increases in free amino acid concentration occur in lenses in response to the stress imposed by a systemic dose of selenite. The altered polyion content in lenses from selenite-treated animals, before nuclear cataract formation, contributes to the greater thermal stability of transparency in these lenses, thus lowering the temperature at which "cold cataract" forms.
We propose a new approach to study quantum phase transitions in low-dimensional lattice models. It is based on studying the von Neumann entropy of two neighboring central sites in a long chain. It is demonstrated that the procedure works equally well for fermionic and spin models, and the two-site entropy is a better indicator of quantum phase transition than calculating gaps, order parameters, or the single-site entropy. The method is especially convenient when the density-matrix renormalization-group algorithm is used.