Kind Of Phase Transition Research Articles

NANOSCALE EFFECTS OF SURFACES AND LUBRICANTS ON FRICTION

Nanoscale frictional phenomena at solid–solid surfaces with lubricants are studied numerically using a lattice model which consists of two rigid substrates and a monolayer of lubricant molecules. The maximum static frictional force, which works on the driven upper solid, is always finite and obeys a certain scaling relation. The lubricant layer, however, shows a kind of phase transition from a pinned state to free sliding state when the strength of the interaction potential with the substrates decreases. We discuss the peculiar pinning mechanism of the upper substrate in the presence of a lubricant monolayer.

Structure solution in binary systems under high pressure: phase decomposition and phase synthesis

There are binary systems (compounds) for which no structural solution can be found for a new high-pressure state by assuming a single phase. In accordance with Gibb's phase rule, an additional variable--composition--leads to an additional degree of freedom for a binary system (one more than in a one-component system). Although the bulk composition of a system may remain fixed, compositional variation between phases should be taken into account when considering phase transitions under pressure in binary compounds. This approach allows for a binary system the following kinds of phase transitions that are not possible in a one-component system: (i) phase (compound) decomposition into two phases with different compositions; (ii) phase synthesis from two initial phases; and (iii) phase separation from an initial phase into phases of different compositions. Examples of these kinds of high-pressure transformations and structure solution are given for the following binary systems: In-Bi, In-Sn, Hg-Sn, Cd-Sb and Sn-Bi.

Effect of ω-Hydrogenation on the Adsorption of Fluorononanols at the Hexane/Water Interface: Pressure Effect on the Adsorption of Fluorononanols

The interfacial tension gamma of the hexane solution of 1H,1H-perfluorononanol (FDFC(9)OH) and its omega-hydrogenated analogue, 1H,1H,9H-perfluorononanol (HDFC(9)OH), against water was measured as a function of pressure and concentration at 298.15 K in order to clarify the effect of omega-dipole on the orientation of fluorononanol molecules from the viewpoint of volume. The adsorbed films of both alcohols exhibit two kinds of phase transitions among three different states: the gaseous, expanded, and condensed states. The partial molar volume changes of adsorption - in the expanded and condensed states were evaluated and compared between the two systems. The - values of both alcohols are negative, and thus the alcohol molecules have smaller volume in the adsorbed film than in the bulk solution. Furthermore, the value was obtained through the evaluation of by the density measurement of the bulk hexane solution. It was found that the value of HDFC(9)OH is smaller than that of FDFC(9)OH in the condensed state. On the basis of three matters concerning the molecular structure of alcohols, the occupied area at the interface, and the orientation of FDFC(9)OH in the adsorbed film deduced from the earlier results of X-ray reflectivity measurement, the mean tilt angle of HDFC(9)OH from the interface normal in the condensed film was estimated to be 15 degrees . The thermodynamic estimation demonstrated here is highly valuable one to provide structure information on an adsorbed film.

Effect of pressure on the electrical resistivity of double perovskite Sr [formula omitted]FeW [formula omitted]Mo [formula omitted]O [formula omitted

The electrical resistivity of Sr 2 FeW 0.75 Mo 0.25 O 6 has been measured under high pressure in order to make the transport properties of this compound clear. The resistivity decreased with increasing pressure and the magnitude of pressure coefficient below 1 GPa is larger than that above 1 GPa. It is found that the electrical resistivity shows a T - 1 / 4 temperature dependence, which implies that the conduction of electrons is mainly dominated by a variable range hopping. The coefficient of T - 1 / 4 is decreased by applying pressure and is different between, below and above 1 GPa. These results suggest that a kind of phase transition or crossover occurs around 1 GPa.

Discovery of new phase and analysis of phase relationships in BaBiO 3 with thermal analyses

Structural phase transition of BaBiO 3 was investigated by using thermal analyses such as dilatometry, differential scanning calorimetry (DSC) and quantitative differential thermal analysis (DTA). First order phase transition, corresponding to so far reported structural one from monoclinic- to rhombohedral-distorted perovskite, was detected at 160 °C both in thermal expansion and DSC for the first time. Two kinds of phase transitions were also detected for the first time at 520 and 620 °C with dilatometry and quantitative DTA, respectively. High-temperature X-ray diffraction measurement revealed that crystal structure more than 620 °C was face centered cubic perovskite with ordered arrangement of Bi 3+ and Bi 5+. In 520–620 °C, X-ray diffraction peaks which indicated existence of superstructure were observed, which had been already proposed by electron diffraction measurement.

Finding of an unexpected thermal anomaly at very low temperatures due to water confined within a globular protein, bovine serum albumin

Heat capacities and enthalpy relaxation rates of completely anhydrous bovine serum albumin (BSA) and hydrous BSA with 1.85% (w/w) water were measured by using an adiabatic calorimeter to examine the thermal behavior at low temperatures of a small amount of water left within the globular protein molecule. The heat capacities of the hydrous BSA were larger a little on account of the presence of water molecules. In addition, two new phenomena appeared for the hydrous BSA while not for the anhydrous one: spontaneous exothermic and endothermic effects depending on the pre-cooling rates were observed and interpreted as due to a glass transition. Anomalous behavior of heat capacities was found in 60–140 K and recognized as potentially originating from a kind of phase transition. It is suggested that the water left a little within the BSA is responsible for both the phenomena occurring at low temperatures.

The structure of F420-dependent methylenetetrahydromethanopterin dehydrogenase: a crystallographic `superstructure' of the selenomethionine-labelled protein crystal structure

The diffraction pattern of native protein crystals of F(420)-dependent methylenetetrahydromethanopterin dehydrogenase from Methanopyrus kandleri shows weak additional reflections compared with the selenomethionine-labelled protein crystals, indicating a doubled c unit-cell parameter. These reflections indicate small reorientations of the hexameric structural units, breaking the translational symmetry. TLS refinement of the selenomethionine-labelled protein structure at 1.55 A resolution revealed an anisotropic rigid-body libration of the hexameric units. The anisotropy is consistent with the static reorientation in the native protein crystals. These results are discussed as related to the crystal packing. The relation between the two structures suggests an analogy to structural changes during certain kinds of phase transitions that have been well studied in inorganic structural chemistry.

A New Percolation Model with Two Threshold Points

A new percolation model of plane percolation is considered. When many small squares are inserted into a cubic lattice, we can expect two kinds of phase transitions: One is formation of an essentially string consisting of chained squares which is expanding from end to end, and another is formation of a huge plane expanding over our system.

Vortex glass transition in a YBa 2Cu 3O 7− δ film with patterned pinning geometry

We report on multiterminal transport measurement in YBa 2Cu 3O y films, where a vortex flow channel is artificially introduced in a strong pinning environment with columnar defects. The samples were prepared by partially masked heavy-ion irradiation. Two kinds of phase transitions with different transition temperatures, T VG and T BG, which correspond to the vortex glass transition and the Bose glass transition, are observed for the unirradiated region and the irradiated one, respectively. At high field, the situation of T VG< T BG, where the flux flow in unirradiated channel is confined between Bose glass solids of the irradiated region, is realized. The vortex velocity distribution is almost homogeneous inside the channel. Around the boundary, however, we find that the vortices flowing in the unirradiated channel drag the vortices of the Bose glass solid in the irradiated region.

Classical equilibrium thermostatistics, “Sancta sanctorum of Statistical Mechanics” from nuclei to stars

Equilibrium statistics of Hamiltonian systems is correctly described by the microcanonical ensemble. Classically this is the manifold of all points in the N-body phase space with a given total energy. Due to Boltzmann–Planck's principle, e S = tr( δ( E− H)), its geometrical size is related to the entropy S( E, N, V,…). This definition does not invoke any information theory, no thermodynamic limit, no extensivity, and no homogeneity assumption. Therefore, it describes the equilibrium statistics of extensive as well of non-extensive systems. Due to this fact it is the fundamental definition of any classical equilibrium statistics. It addresses nuclei and astrophysical objects as well. S( E, N, V,…) is multiply differentiable everywhere, even at phase transitions. All kind of phase transitions can be distinguished sharply and uniquely for even small systems. In contrast to the canonical theory, what is even more important, is that the region of phase space which corresponds to phase separation is accessible, where the most interesting phenomena occur. No deformed q-entropy is needed for equilibrium. Boltzmann–Planck is the only appropriate statistics independent of whether the system is small or large, whether the system is ruled by short- or long range forces.

A New Thermodynamics from Nuclei to Stars

Equilibrium statistics of Hamiltonian systems is correctly described by the microcanonical ensemble. Classically this is the manifold of all points in the $N-$body phase space with the given total energy. Due to Boltzmann's principle, $e^S=tr(\delta(E-H))$, its geometrical size is related to the entropy $S(E,N,...)$. This definition does not invoke any information theory, no thermodynamic limit, no extensivity, and no homogeneity assumption, as are needed in conventional (canonical) thermo-statistics. Therefore, it describes the equilibrium statistics of extensive as well of non-extensive systems. Due to this fact it is the {\em fundamental} definition of any classical equilibrium statistics. It can address nuclei and astrophysical objects as well. All kind of phase transitions can be distinguished sharply and uniquely for even small systems. It is further shown that the second law is a natural consequence of the statistical nature of thermodynamics which describes all systems with the same -- redundant -- set of few control parameters simultaneously. It has nothing to do with the thermodynamic limit. It even works in systems which are by far {\em larger} than any thermodynamic "limit".

Electron localization-delocalization transitions in dissociation of the C4- anion: a large-D analysis.

We present a study, employing high level ab initio methods, of electron localization-delocalization transitions along the dissociation path of the C4- anion to C2 and C2-. We find that at the equilibrium geometry, the symmetrical and nonsymmetrical configurations of the linear C4- anion are almost isoenergetic. However, along a collinear dissociation path, the dipole moment drops abruptly to zero when the separation between the two middle carbon nuclei reaches about R = 2.15 angstroms. The dipole moment remains zero until about R = 2.78 angstroms, and then continuously increases as dissociation proceeds. This behavior is analogous to critical phenomena: The abrupt drop to zero of the dipole moment resembles a first-order phase transition, the later steady rise resembles a continuous phase transition. We show that a simple sub-Hamiltonian model, corresponding to the large-dimension limit for an electron in the field of four collinear carbon atoms, exhibits both kinds of phase transitions along the dissociation path.

Time evolution, cyclic solutions and geometric phases for the generalized time-dependent harmonic oscillator

The generalized time-dependent harmonic oscillator is studied. Though several approaches to the solution of this model have been available, yet a new approach is presented here, which is very suitable for the study of cyclic solutions and geometric phases. In this approach, finding the time evolution operator for the Schr\"odinger equation is reduced to solving an ordinary differential equation for a c-number vector which moves on a hyperboloid in a three-dimensional space. Cyclic solutions do not exist for all time intervals. A necessary and sufficient condition for the existence of cyclic solutions is given. There may exist some particular time interval in which all solutions with definite parity, or even all solutions, are cyclic. Criterions for the appearance of such cases are given. The known relation that the nonadiabatic geometric phase for a cyclic solution is proportional to the classical Hannay angle is reestablished. However, this is valid only for special cyclic solutions. For more general ones, the nonadiabatic geometric phase may contain an extra term. Several cases with relatively simple Hamiltonians are solved and discussed in detail. Cyclic solutions exist in most cases. The pattern of the motion, say, finite or infinite, can not be simply determined by the nature of the Hamiltonian (elliptic or hyperbolic, etc.). For a Hamiltonian with a definite nature, the motion can changes from one pattern to another, that is, some kind of phase transition may occur, if some parameter in the Hamiltonian goes through some critical value.

Low-temperature heat capacities and derived thermodynamic functions of cyclohexane

Abstract The low-temperature heat capacities of cyclohexane were measured in the temperature range from 78 to 350 K by means of an automatic adiabatic calorimeter equipped with a new sample container adapted to measure heat capacities of liquids. The sample container was described in detail. The performance of this calorimetric apparatus was evaluated by heat capacity measurements on water. The deviations of experimental heat capacities from the corresponding smoothed values lie within 0.3%, while the inaccuracy is within 0.4%, compared with the reference data in the whole experimental temperature range. Two kinds of phase transitions were found at 186.065 and 279.684 K corresponding solid-solid and solid-liquid phase transitions, respectively. The entropy and enthalpy of the phase transition, as well as the thermodynamic functions {H(T)-H 298.15 K} and {S (T)-S298.15 K}, were derived from the heat capacity data. The mass fraction purity of cyclohexane sample used in the present calorimetric study was de...

Quantum orders in an exact soluble model.

We find all the exact eigenstates and eigenvalues of a spin-1/2 model on square lattice: H=16g Sum S(y)(i)S(x)(i + empty set x)S(y)(i + empty set x + empty set y)S(x)(i + empty set y). We show that the ground states for g < 0 and g > 0 have different quantum orders described by Z2A and Z2B projective symmetry groups. The phase transition at g = 0 represents a new kind of phase transition that changes quantum orders but not symmetry. Both the Z2A and Z2B states contain Z2 lattice gauge theories at low energies. They have robust topologically degenerate ground states and gapless edge excitations.

Influence of long-range effects on the critical behavior of three-dimensional systems

The Padé-Borel resummation technique is used to describe field-theoretically, in the two-loop approximation, the behavior of Ising systems with long-range effects directly in a three-dimensional space. The renormalization-group equations are analyzed and the fixed points governing the critical behavior of the system are determined. It is shown that the long-range effects can bring about a change in both the regime of critical behavior and the kind of phase transition.

Phase transitions in self-gravitating systems: self-gravitating fermions and hard-sphere models.

We discuss the nature of phase transitions in self-gravitating systems both in the microcanonical and in the canonical ensemble. We avoid the divergence of the gravitational potential at short distances by considering the case of self-gravitating fermions and hard-sphere models. Depending on the values of the parameters, three kinds of phase transitions (of zero, first, and second order) are evidenced. They separate a "gaseous" phase with a smoothly varying distribution of matter from a "condensed" phase with a core-halo structure. We propose a simple analytical model to describe these phase transitions. We determine the value of energy (in the microcanonical ensemble) and temperature (in the canonical ensemble) at the transition point and we study their dependence on the degeneracy parameter (for fermions) or on the size of the particles (for a hard-sphere gas). Scaling laws are obtained analytically in the asymptotic limit of a small short distance cutoff. Our analytical model captures the essential physics of the problem and compares remarkably well with the full numerical solutions. We also stress some analogies with the liquid-gas transition and with the Blume-Emery-Griffiths model with infinite range interactions. In particular, our system presents two tricritical points at which the transition passes from first order to second order.

Reaction dynamics and statistical theory for the growth of hydrogen bonding clusters

The similarities between the formation of hydrogen bonds and polycondensation reactions are stated from the statistical viewpoint, and then taking the hydrogen bonding system of AaDd type as an example, the growing process of hydrogen bonding clusters is investigated in terms of the theory of reaction dynamics and statistical theory for polymeric reactions. The two methods lead to the same conclusions, stating that the statistical theory for polymerization is applicable to the hydrogen bonding systems. Based on this consideration, the explicit relationship between the conversions of proton-donors and proton-acceptors and the Gibbs free energy of the system under study is given. Furthermore, the sol-gel phase transition is predicted to take place in some hydrogen bonding systems, and the corresponding generalized scaling laws describing this kind of phase transition are obtained.

Phase transition in an asymmetric generalization of the zero-temperatureq-state Potts model

An asymmetric generalization of the zero-temperature q-state Potts model on a one-dimensional lattice, with and without boundaries, has been studied. The dynamics of the particle number, and especially the large time behavior of the system, has been analyzed. In the thermodynamic limit, the system exhibits two kinds of phase transitions, a static and a dynamic phase transition.

Phase transition in an asymmetric generalization of the zero-temperature Glauber model.

An asymmetric generalization of the zero-temperature Glauber model on a lattice is introduced. The dynamics of the particle-density and especially the large-time behavior of the system is studied. It is shown that the system exhibits two kinds of phase transitions, a static one and a dynamic one.