Showing papers on "Phase transition published in 1977"
TL;DR: In this article, the effect of more than ninety lipid-soluble compounds on the phase transition behavior ofdl-α-dipalmitoyl lecithin bilayer has been examined by differential scanning calorimetry.
Abstract: The effect of more than ninety lipid-soluble compounds on the phase transition behavior ofdl-α-dipalmitoyl lecithin bilayer has been examined by differential scanning calorimetry. The type of effect on the phase transition profile depends on the nature of the additive, whereas the extent of the effect depends on the concentration. The compounds examined include uncouplers, alkanols, fatty acids, detergents, organic solvents, ionophores, inorganic ions, and some commonly used spin-labelled and fluorescent membrane probes. A qualitatively distinct effect of several of these additives on the phase transition behavior of bilayer provides a method of determining the nature of the perturbation they induce in the bilayer organization. The observations are consistent with the hypothesis that the type of effect induced by an additive on the phase transition profile of the bilayer is related to the position of localization of the additive along the thickness of the bilayer. At least four different types of modified transition profiles that are related to changes in bilayer fluidity can be distinguished. These correspond to the localization of the additive in phosphorylcholine (type D), glycerol backbone (type B), C1–C8 methylene (type A), C9–C16 methylene (type C) region of the bilayer. A possible relationship between the type of phase transition profiles of modified liposomes and the physiological effects of drugs is also discussed.
481 citations
362 citations
TL;DR: In this article, a density-functional theory capable of predicting free energies and spatially dependent number densities of simple classical fluids is applied to the case of argon films in the presence of a solid carbon dioxide substrate.
Abstract: A density-functional theory capable of predicting free energies and spatially dependent number densities of simple classical fluids is applied to the case of argon films in the presence of a solid carbon dioxide substrate. For pressures less than the saturated vapor pressure, a new phase transition for which the order parameter is the film thickness is described. The phases are the usual unsaturated film and a one- or two-atomic-layer structure localized at the argon-C${\mathrm{O}}_{2}$ interface.
360 citations
TL;DR: In this paper, the electroclinic effect of chiral molecules was studied in the second order, smectic-$A$---smectic/$C$ phase transition.
Abstract: When a smetic-$A$ phase is composed of chiral molecules, it exhibits an electroclinic effect, i.e., a direct coupling of molecular tilt to applied field. The pretransitional behavior of the electroclinic effect in the $A$ phase is used to study the critical behavior near the second order, smectic-$A$---smectic-$C$ phase transition. This behavior is measured by monitoring the change in birefringence of a sample as the electroclinic effect causes a tilt of the molecules. A large pretransitional effect is measured, and constants describing the critical behavior are determined.
342 citations
TL;DR: In this article, the authors examined the statistical interdependence of the faster rotational reorientation of the individual spinbearing molecules and the (slower) director or order-parameter fluctuations.
Abstract: The theory of spin relaxation for liquid crystals is examined with the objective of properly analyzing the statistical interdependence of the faster rotational reorientation of the individual spin‐bearing molecules and the (slower) director or order‐parameter fluctuations. The analysis is presented in terms of a composite Markov process including both types of motions. It is shown that one recovers a sum of spectral‐density terms which, in lowest order in fluctuations, correspond to (1) reorientation of the molecule relative to the equilibrium potential of mean torque, (2) effects of director fluctuations, and (3) a negative cross‐term between these two processes which bears a simple relation to (2). Detailed results are given for the particular models of director fluctuations in the nematic phase, quasicritical order fluctuations on either side of the isotropic–nematic phase transition, and slow fluctuations in the local structure. Effects of localized cooperative modes of molecular reorientation are als...
320 citations
TL;DR: In this article, the Hartree-Fock approach is used to explain the properties of metal-insulators and other related phase transitions, as observed in V2O3 and several other materials.
Abstract: Mott insulators are identified here with ordinary magnetic insulators. The insulating gap, local moment, and effective spin hamiltonian aspects are qualitatively explained by means of a novel set of solutions of the Hartree-Fock equations. The apparent conflict between Bloch's theorem and localized-electron phenomenology is thereby resolved in an elementary manner. This Hartree-Fock approach also sheds considerable light on the physical mechanisms responsible for the associated metal-insulator (Mott) and other related phase transitions, as observed in V2O3 and several other materials. With some generalizations and refinements, this theoretical picture is shown to also account semiquantitatively for a number of detailed properties of NiO and CoO, two of the most extensively studied Mott insulator materials. A wide variety of experimental data for NiO is surveyed in order to determine reasonable values for its effective Hubbard hamiltonian parameters, suitably generalized for the 3d electrons. The ...
305 citations
TL;DR: In this paper, low-energy-electron-diffraction studies of carefully cleaned and annealed surfaces of molybdenum and tungsten (100) showed that a phase transition can be induced by lowering the temperature below 300 K. The phase transition is reversible and seemingly second order.
Abstract: Low-energy-electron-diffraction studies of carefully cleaned and annealed surfaces of molybdenum (100) and tungsten (100) show that a phase transition can be induced by lowering the temperature below 300 K. The periodicity of the "reconstructed" surface is believed to be due to the formation of a displacement wave with a wavelength which is $2a$ ($a$ is the lattice parameter) for W(100) and $\ensuremath{\sim}2.2a$ for Mo(100). The phase transition is reversible and seemingly second order. It appears possible that displacements of this type also occur in chemisorption on these surfaces.
300 citations
TL;DR: In this article, a general phenomenological theory of spin-glasses is presented, which predicts the weak singularities (like cusps) of susceptibilities and specific heat near the transition point TsG and also predicts generally the divergence of the second derivative of the nonlinear susceptibilities with respect to a magnetic field in zero field at Tsa.
Abstract: A general phenomenological theory of spin-glasses is presented, which predicts the weak singularities (like cusps) of susceptibilities and specific heat near the transition point TsG and also predicts generally the divergence of the second derivative of the nonlinear suscepti bility with respect to a magnetic field in zero field at Tsa. A similar second derivative of specific heat is also shown to diverge at Tsa except for the molecular field theory. Scaling equations of state for magnetization m and spin-glass order-parameter q are derived, which yield new scaling relations of critical exponents for m(T), q(T), X,(T), Co(T) and the corresponding nonlinear quantities. These general results explain qualitatively very well the magnetic field dependence of magnetization and specific heat observed experimentally. A non-uniform phenomenological Hamiltonian is also proposed for the rcnormalization group approach, which yields the critical dimensionality d,=6, as usuaL Intermediate random statistics and real replica method are p;oposed. There is also presented an exactly soluble model showing a spin-glass like phase transition.
298 citations
TL;DR: In this paper, the properties of magnetic systems with competing ferromagnetic and antiferromagnetic inter-actions are investigated and a few exact results are obtained; the possibility of exact solutions comes from the fact that the distribution of ferro-and antiferromeagnetic bonds is assumed to obey certain rules, instead of being completely random.
Abstract: Magnetic systems with competing ferromagnetic and antiferromagnetic inter- actions are investigated and a few exact results are obtained. The possibility of exact solutions comes from the fact that the distribution of ferro- and antiferromagnetic bonds is assumed to obey certain rules, instead of being completely random. The ground state, however, has the character of a spin glass. Two of our models have the property that they have no phase transi- tion in the case of one-dimensional (Ising) spins, whereas there is a phase transition for two- dimensional (XY) spins. The phase transition disappears again for high values of the spin dimensionality n. In a particular case of a three-dimensional. X Y model, the susceptibility has been calculated at high and IOW temperatures; it has a maximum at some temperature, but a speculative argument is given that there is actually no kink.
294 citations
TL;DR: In this paper, phase diagrams for both molecular and metallic hydrogen-helium mixtures were analyzed in detail, and it was concluded that at the temperatures and pressures of interest (T ≈ 10^4 K, P ≈ 1-10 Mbar), both phases are fluid, but the transition between them might nevertheless be first-order.
Abstract: Hydrogen and helium are the major constituents of Jupiter and Saturn, and phase transitions can have important effects on the planetary structure. In this paper, the relevant phase diagrams and microscopic transport properties are analyzed in detail. The following paper (Paper II) applies these results to the evolution and present dynamic structure of the Jovian planets. Pure hydrogen is first discussed, especially the nature of the molecular-metallic transition and the melting curves for the two phases. It is concluded that at the temperatures and pressures of interest (T ≈ 10^4 K, P ≈ 1-10 Mbar), both phases are fluid, but the transition between them might nevertheless be first-order. The insulator-metal transition in helium occurs at a much higher pressure (~ 70 Mbars) and is not of interest. The phase diagrams for both molecular and metallic hydrogen-helium mixtures are discussed. In the metallic mixture, calculations indicate a miscibility gap for T ≾ 10^4 K. Immiscibility in the molecular mixture is more difficult to predict but almost certainly occurs at much lower temperatures. A fluid-state model is constructed which predicts the likely topology of the threedimensional
phase diagram. The greater solubility of helium in the molecular phase leads to the prediction that the He/H mass ratio is typically twice as large in the molecular phase as in the coexisting metallic phase. Under these circumstances a "density inversion" is possible in which the molecular phase becomes more dense than the metallic phase. The partitioning of minor constituents is also considered: The deuterium/hydrogen mass ratio is essentially the same for all coexisting hydrogen-helium phases, at least for T ≳ 5000 K. The partitioning of H_2O, CH_4, and NH_3 probably favors the molecular (or helium-rich) phase. Substances with high conduction electron density (e.g., AI) may partition into the metallic phase. Electronic and thermal conductivities, viscosity, helium diffusivity, and Soret coefficient are evaluated for the fluid molecular and metallic phases, all to at least order-of-magnitude accuracy. The properties of the metallic phase are typical of a liquid alkali metal, and those of the molecular
phase are typical of a dense neutral fluid (except that the conductivities may be almost metallic at the transition pressure). The opacities of molecular hydrogen and solar-composition mixtures are discussed for T ≈ 500 K, where molecular hydrogen alone may be insufficiently opaque to
ensure convection in the Jovian planets. Sufficient opacity to initiate convection is probably supplied by the minor constituents. Current uncertainties are assessed.
218 citations
TL;DR: In this article, the authors considered the phase II of solid CH4 in nuclear spin species equilibration and proposed two adjustable parameters to adapt the assumed crystal potential to the actual situation in the solid state of CH4.
Abstract: Thermal, spectroscopic, and other properties of methane solids, especially those concerning Phase II of solid CH4 in nuclear spin species equilibration, are theoretically studied from a unified point of view, i.e., the extended James–Keenan model. It assumes a rigid lattice and treats the molecular motions with respect to the rotational degress of freedom in the crystal potential given by Yasuda [Prog. Theor. Phys. 45, 1361 (1971)]. Two adjustable parameters are introduced in order to adapt the assumed crystal potential to the actual situation in the solid state of CH4. Most of the calculations are carried out in the framework of the molecular field method in quantum statistical mechanics. The eight‐sublattice antiferrorotational structure is assigned to Phase II. Thus we have two kinds of site Hamiltonians in this phase, the symmetry groups of which are the direct product groups ?hOh and ?dD2d. Basis functions are doubly symmetry adapted under each of these symmetry groups. Rotational functions are inclu...
TL;DR: In this article, it was shown from a general point of view that the coexistence of ferro-and antiferromagnetism with a symmetry-breaking is possible in certain itinerant electron systems where the wave vector dependent susceptibility χ q 0 without the electron-electron interaction has two peaks at q = 0 and q = Q, the Antiferromagnetic vector.
TL;DR: In this article, the frequency dependance of the proton spin-lattice relaxation time T1 at several temperatures and pressures in TTF-TCNQ(D4) and TTF(D 4)-TCNsQ was analyzed.
Abstract: This paper presents the frequency dependance of the proton spin-lattice relaxation time T1 at several temperatures and pressures in TTF-TCNQ(D4) and TTF(D4)-TCNQ. It is shown that only backward (q = 2 kF) and forward (q = 0) scatterings contribute to the nuclear relaxation induced by the modulation of the hyperfine field in these one-dimensional conductors. At medium fields, H 0 ~ 30 kOe, the frequency dependence of T1 originates from the diffuse character of the spin density wave excitations around q = 0, leading to T1-1 αH0- 1/2 . The enhancement of T1 -1, is at low fields, limited by the existence of a finite interchain coupling (tunnelling type). We find, within a RPA analysis, close correlations between the pressure and temperature dependences of the spin excitations diffusion constant and the collision time derived from the longitudinal conductivity. The interpretation of the NMR data in terms of a Hubbard model excludes both big U and small U pictures. However, we point out the importance of the electron-electron interactions on the relaxation rate of TTF-TCNQ. We derive a ratio U/4 t II ~ 0.9 for the TCNQ chain. We also assume that besides charge density waves fluctuations existing between 300 K and the phase transition at 53 K, electron-electron interactions make an important contribution to the temperature dependence of the spin susceptibility. Finally, we give a unified description of quasi one dimensional conductors in which the various systems are classified according to the transverse tunnelling coupling and the electron lifetime. It follows from this description that for TTF-TCNQ and its derivatives, transverse couplings (tunnelling and Coulomb) are large enough to justify the use of a mean-field theory.
IBM1
TL;DR: In this paper, an Ising model with infinite-ranged interaction with statistically independent site fields with Gaussian distribution is considered and the model is solved exactly and exhibits both an independent spin phase and a ferromagnetic phase, separated by a line of second-order phase transitions.
Abstract: We consider an Ising model with infinite-ranged interaction with statistically independent site fields with Gaussian distribution. The model is solved exactly and exhibits both an independent spin phase and a ferromagnetic phase, separated by a line of second-order phase transitions. We also establish that the replica technique yields exact results in the present model but not in the related random exchange system.
TL;DR: It is found that it is the vesicle size which limits the cooperativity of the transition in the small, single-bilayer vesicles, and for the possibility of achieving lateral communication in the plane of the membrane.
TL;DR: In an attempt to understand the mechanism by which a structural change of membrane lipids affects transport functions, the temperature dependence of transport rate has been measured to below the low temperature end of the fluid in equilibrium ordered phase transition of the membrane Lipids.
Abstract: In an attempt to understand the mechanism by which a structural change of membrane lipids affects transport functions, the temperature dependence of transport rate has been measured to below the low temperature end of the fluid in equilibrium ordered phase transition of the membrane lipids. The unsaturated fatty acid requiring Escherichia coli strain T105 was supplemented with either trans-delta9-octadecenoate or trans-delta9-hexadecenoate or supplemented with and subsequently starved for cis-delta9-octadecenoate. Fluid in equilibrium ordered phase transitions measured in whole cells using the fluorescence probe N-phenyl-1-naphthylamine were compared with the temperature dependence of beta-glucoside and beta-galactoside transport. In addition to the previously observed downward "break" in the Arrhenius plot of transport rate which occurred near the middle of the phase transition temperature range, a second upward "break" was observed which could be correlated with the low-temperature end of the phase transition. These experiments are interpreted in terms of a partitioning of transport proteins between ordered and fluid domains which is described by a lateral distribution coefficient, k. This distribution coefficient varies with the membrane lipid composition as well as with the transport system. Values for k suggest a 2-20-fold preference for the partitioning of transport proteins into the fluid parts of the membrane.
TL;DR: In this paper, the average thermodynamic properties of small (N?13) clusters of atoms were calculated using the Monte Carlo method and the melting points predicted by these tests did not differ by more than 5%.
Abstract: The Monte Carlo method is used to calculate the average thermodynamic properties of small (N?13) clusters of atoms. All cluster sizes studied exhibit fairly sharp solid–liquid, as well as liquid–gas, transitions. In addition, some of the larger clusters also undergo structural transitions between different isomeric forms. The solid–liquid transition temperature is determined by four independent tests. The melting points predicted by these tests do not differ by more than 5%.
TL;DR: In this paper, the changes in rheological parameters and effective viscosity across mantle polymorphic phase transitions and the variations of these quantities with temperature and pressure throughout the earth's mantle were studied.
Abstract: We study the changes in rheological parameters and effective viscosity across mantle polymorphic phase transitions and the variations of these quantities with temperature and pressure throughout the earth's mantle. The intrinsic activation energy for oxygen ion diffusion in oxides E0* is shown to be systematically related to oxygen ion packing by E0*(kcal/mol) = (187±16) - (3.8±0.8) Vo=(A3), where Vo= is the volume per oxygen ion at zero pressure and 25°C. This relation allows the change in activation energy δE0* across a polymorphic phase transition to be estimated from the associated change in density. Under the assumptions that the activation volume V* remains constant or decreases across a phase transition and that the activation energy for subsolidus creep is equal to the activation energy for O= diffusion, we use δE0* in a general non-Newtonian flow law to estimate the increase in effective viscosity η and the decrease in activation volume V* across a phase transition. By modeling V* and the activation energy by using thermodynamical and mechanical relations for elastic continua and data from seismically derived earth models for relevant elastic parameters, we are able to estimate better the increases in viscosity across polymorphic phase transitions and throughout an adiabatic mantle. Our best models of mantle viscosity have (1) η increasing by less than an order of magnitude across any phase transition, (2) η essentially constant throughout the lower mantle, and (3) η in the lower mantle no more than 2 orders of magnitude greater than η in the upper mantle.
TL;DR: In this article, the adsorption of a charged macromolecule to a charged surface under the influence of a weak electrostatic attraction is investigated, and the probability density P(x,N) to find the end point of a molecule with N monomer units at distance x from the surface is calculated analytically.
Abstract: The adsorption of a charged macromolecule to a charged surface under the influence of a weak electrostatic attraction is investigated. The probability density P(x,N) to find the end point of a molecule with N monomer units at distance x from the surface is calculated analytically. In the limit N to infinity this function shows a phase transition at a critical value ( theta c) of the adsorption energy in units if kBT: for theta > theta cP(x,N) is peaked near the surface and the molecule is effectively adsorbed to the surface; for theta < theta c the heat motion is strong enough to remove the molecule from the surface and P(x,N) is effectively constant throughout the whole available volume. A possible role of such conformational phase transitions in the regulation of cellular metabolism is briefly commented on.
TL;DR: Measurements indicate that dP m/dTm at all pressures is in agreement with the 1 atm value of delta H/Tm delta V within experimental error where Tm and Pm are the temperature and pressure of the phase transition, respectively.
Abstract: The effect of pressure on the phase transition temperature for the dipalmitoyllecithin bilayer was redetermined by following the volume change accompanying the transition. These measurements were carried out isothermally with the transition from the ordered to the disordered phase induced by decreasing the pressure. This contrasts with our previous measurements which were carried out at constant pressure and increasing temperature. The transition at every temperature was sharp and confirmed our previous observation that the volume change associated with the transition (0.033 mL g-1) is invariant with pressure. However, our present measurements, in contrast to our previous results, indicate that dP m/dTm at all pressures is in agreement with the 1 atm value of delta H/Tm delta V within experimental error where Tm and Pm are the temperature and pressure of the phase transition, respectively. These results, which are now in agreement with all other known pressure data, indicate that the entropy change associated with the transition is invariant with pressure.
TL;DR: In this paper, the role of fluctuations and the self-consistency of mean field theory are assessed in a simple fashion for a variety of phase transitions, and it is suggested that this simple selfconsistent approach to Landau theory should be incorporated in the teaching of elementary phase transition phenomena.
Abstract: By applying a real space version of the Ginzburg criterion, the role of fluctuations and thence the self‐consistency of mean field theory are assessed in a simple fashion for a variety of phase transitions. It is shown that in using this approach the concept of ’’marginal dimensionality’’ emerges in a natural way. For example, it is shown that for many homogeneous structural transformations the marginal dimensionality is two, so that mean field theory will be valid for real three‐dimensional systems. It is suggested that this simple self‐consistent approach to Landau theory should be incorporated in the teaching of elementary phase transition phenomena.
TL;DR: The reported phase diagrams are the first to describe binary mixtures in which one lipid is charged and the second lipid uncharged and the problem of solid phases with different crystalline conformations as it relates to the occurrence of a pretransition in phosphatidylcholines and its absence in phosph atidylserines.
TL;DR: In this article, a theory for the line width of crystal-field excitations in metallic rare-earth systems were the damping is due to conduction electron-hole excitations.
Abstract: A theory is developed for the line width of crystal-field excitations in metallic rare-earth systems were the damping is due to conduction electron-hole excitations. First the single ion or dilute alloy case is studied. As an example the theory is applied to Ce in LaAl2 and compared with recent experiments. Then the case of a regular lattice of rare-earth ions is considered. The theory is applied to theΓ
1 –Γ
4 system. Special attention is paid to the behaviour of the central peak near an induced-moment phase transition. It is shown that the dynamics of the conduction electrons leads to observable effects in the centralpeak intensity and can not be neglected as it is usually done. The theoretical predictions are in agreement with recent experimental findings on Pr3Tl.
TL;DR: In this article, the authors compared the pretransitional fluctuations of the Rayleigh-Benard or convective instability for a binary mixture and compared to the one component case, showing that the critical mode of the soft phase transition is more stable than that of the pure fluid RayleighBenard instability.
Abstract: The pretransitional fluctuations of the Rayleigh-Benard or convective instability are obtained for a binary mixture and compared to the one component case. There are now enhanced concentration fluctuations and although the velocity fluctuations are critically enhanced, they are weaker by a factor of D/χ. The behaviour of the critical (soft) mode is compared to the fluctuations in the order parameter obtained for a classical analysis of a phase transition. The region around the instability where the classical treatment of the order parameter fluctuations is invalid is increased in the binary case by a factor of (χ/D)1/2 over that of the pure fluid Rayleigh-Benard instability.
TL;DR: In this article, the generalized van der Waals (GVDW) theory was extended to fluids of anisotropic molecules interacting through angledependent potentials which can be broken up into strong short-ranged repulsions and weak long-ranged attractions.
Abstract: We extend the generalized van der Waals (GVDW) theory to fluids of anisotropic molecules interacting through angle‐dependent potentials which can be broken up into strong short‐ranged repulsions and weak long‐ranged attractions. This approach provides a description of the gas–liquid phase transition in which corresponding states behavior breaks down with increasing anisotropy of the molecular (hard rod) shape. Allowing for the orientational order characterizing nematic phases of liquid crystals, we propose a GVDW form for the Helmholtz free energy A as a functional of the orientational distribution f (Ω). The molecular shape repulsions vrep are treated within the approximation of scaled particle theory. The long‐range attractions vattr enter directly through a mean field average which explicitly excludes the relative positions denied to a pair of molecules because of their anisotropic cores. For the special case in which vrep→vhardsphere and vattr → vdispersion ? −Ciso/r6ij ‐ Can cos2ϑij/r6ij (here ϑij is...
TL;DR: The second order phase transition in biphenyl has been monitored using some lines unique to the Raman spectrum of the low temperature phase as discussed by the authors, and a 33 cm − 1 interval observed in the crystal at 4.2 K is estimated to be about 40 cm −1.
TL;DR: In this paper, a paramagnetic (I)-ferromagnetic (II)-sinusoidal (III) phase diagram near a Lifshitz point is studied for the case of uniaxial magnetization.
Abstract: A paramagnetic (I)-ferromagnetic (II)-sinusoidal (III) phase diagram near a Lifshitz point is studied for the case of uniaxial magnetization. The shape of the phase diagram in the vicinity of this point is determined. It is found that the II \ensuremath{\rightleftarrows} III phase transition line is tangent to the order-disorder (I \ensuremath{\rightleftarrows} II and I \ensuremath{\rightleftarrows} III) transition line at the Lifshitz point. The II \ensuremath{\rightleftarrows} III phase transition is shown to be first order, with latent heat and metastability regions. The behavior of magnetic susceptibility is determined. Binary alloy systems are suggested in which the considered type of phase diagram may be expected.
TL;DR: In this article, a phase diagram is constructed which is consistent with both calorimetric and neutron scattering results, and a formula relating the domain size to the shift in transition temperature gives r = 50' A for the mean radius of the domains.