Heat capacity and phase transition of tetrahydrofuran clathrate hydrate

Heat capacity of tetrahydrofuran clathrate hydrate THF·16.81H₂O doped with KOH (x = 1.8 × 10⁻⁴ in the mole fraction of KOH in KOH and water) was measured in the temperature range 13–280 K. A sharp first-order phase transition having a large tail on the high temperature side was observed at 62 K and excess entropy due to the transition was determined to be 2.56JK⁻¹ (H₂O-mol)⁻¹. From a comparison with thermal behavior of hexagonal ice, it was indicated that this transition was related to ordering of protons in the host lattice.     

Nature of an electric-field-induced colloidal martensitic transition

We study the properties of a solid-solid close-packed to body-centered tetragonal transition in a colloidal suspension via fluorescence confocal laser scanning microscopy, in three dimensions and in real space. This structural transformation is driven by a subtle competition between gravitational and electric dipolar field energy, the latter being systematically varied via an external electric field. The transition threshold depends on the local depth in the colloidal sediment. Structures with order intermediate between close-packed and body-centered tetragonal were observed, with these intermediate structures also being stable and long lived. This is essentially a colloidal analogue of an "atomic-level" interfacial structure. We find qualitative agreement with theory (based purely on energetics). Quantitative differences can be attributed to the importance of entropic effects.     

Heat capacity of MnBr2·4H2O near the antiferromagnetic transition temperature

Heat capacity of MnBr₂·4H₂O has been measured in the critical region around the Neel temperature. The data can be fitted, over a restricted range of |t|⩽10⁻², to the asymptotic power law. The critical exponents and the amplitudesA andA′ are not consistent with any theoretic predictions. However when scaling constraints are imposed, their values agree with the parameters of Ising model. Corrections to scaling are necessary to extend the range of the fit to |t|>10⁻². The correction terms are asymmetric giving −1·15±0·25 as the ratio of the amplitudes of the lowest order correction terms,D andD′ above and belowT _c. This value is in agreement with the recent predictions of the renormalisation group theory.     

Transport coefficients near chiral phase transition

We analyze the transport properties of relativistic fluid composed of constituent quarks at finite temperature and density. We focus on the shear and bulk viscosities and study their behavior near chiral phase transition. We model the constituent quark interactions through the Nambu–Jona-Lasinio Lagrangian. The transport coefficients are calculated within kinetic theory under relaxation time approximation including in-medium modification of quasi-particles dispersion relations. We quantify the influence of the order of chiral phase transition and the critical end point on dissipative phenomena in such a medium.     

Observation of an intermediate phase near the α-β transition of quartz by heat capacity and neutron scattering measurements

Recent measurements of the heat capacity of quartz have shown an anomalous behaviour near the α-β transition of quartz. This result which is well correlated with a previous thermal expansion measurement shows the existence of an intermediate phase in a temperature range of 1.3°C above the temperature of the β-α transition upon cooling. Satellite peaks have been observed by neutron diffraction, showing that this phase is modulated.     

Heat capacity of RbMnF3 and EuO near the magnetic phase transitions

Precision measurements of C_p near the antiferromagnetic transition in RbMnF₃ and near the ferromagnetic transition in EuO yield critical exponents α = α′ = ?0.14 and α = α′ = ?0.04 respectively.     

Network traffic behaviour near phase transition point

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.     

Director dynamics near the nematic-smectic-A phase transition

The Landau-de Gennes model for the free energy of a nematic liquid crystal near the phase transition to the smectic A-phase is used to determine the frequency dependence of the fluctuation corrections to the Frank elastic constants. It is shown that the interaction of the fluctuations of the smectic order parameter and the director results in corrections to all the Frank elastic constants. In the low-frequency limit (ω→0), the corrections to the Frank elastic constants K ₂₂ and K ₃₃ are the largest, and decrease to zero in the infinite-frequency limit. The correction to K ₁₁ is negative, and vanishes in both limits. The absolute value of the correction to K ₁₁ is the largest at frequencies in the megahertz range. It is shown that in oriented nematics the interaction of the smectic fluctuations and the director limits deviations of the director from the direction of preferred orientation, as a result of which relaxation of both inhomogeneous and homogeneous distortions of the director field can be observed. It is also shown that this gives rise to a frequency interval in the megahertz range in which shear waves begin to propagate in the nematic. The propagation speed of these waves is roughly a hundred times smaller than that of sound and strongly depends on the direction of propagation. Zh. éksp. Teor. Fiz. 114, 2022–2033 (December 1998)     

Elastic anomalies near a surface-induced phase transition

An analysis is made of the influence of elastic degrees of freedom on a surface-induced phase transition. It is found that elastic interactions give rise to a nonlinear correction to the boundary conditions for the order parameter, with the result that the surface transition is of the second order despite the fact that a first order phase transition occurs in the bulk. The propagation of Rayleigh waves near such a transition is discussed.     

Quasiparticle picture of quarks near chiral phase transition

We study how the quasiparticle picture of the quark can be modified near but above the critical temperature (T _c) of the chiral phase transition; we incorporate into the quark self-energy the effects of the precursory soft modes of the phase transition, i.e. ‘para-σ(π) meson’. It is found that the quark spectrum has a three-peak structure near T _c: We show that the additional new spectra originate from the mixing between a quark (antiquark) and an antiquark-hole (quark-hole) caused by a “resonant scattering” of the quasi-fermions with the thermally-excited soft modes.     

Non-linear response to an external AC drive near the Kosterlitz Thouless phase transition

We discuss the effect of an external AC drive on the motion of vortices near the vortex unbinding transition in two-dimensional superfluids, and on the motion of the interface between a crystal and its melt at the roughening transition. Both belong to the Kosterlitz Thouless class of phase transitions. There are three length scales in the problem: the correlation length, a diffusion length which varies as and a length inversely related to the strength of the drive. A possible resonance experiment for helium crystals is discussed.     

Oscillations in ultrasonic attenuation near a phase transition

It is shown that the oscillations in ultrasonic attenuation observed in KH₂PO₄ near phase transition temperature cannot be due to velocity changes and interference of a coherent source with the echo as suggested by Steinitz et al. recently.     

Light scattering near phase transition points in solids

The present state of theoretical and experimental investigations of the light scattering near phase transition points in solids is reviewed. It is emphasized that the results available here may be understood on the ground of a simple but rather general phenomenological or semiphenomenological theory. From this point of view the anomaly of the total (integrated) light scattering intensity is considered with account taken of a coupling of the order parameter to other quantities including elastic strains and long-range electric fields. The temperature dependence of the scattered light spectral distribution is discussed in detail, the main attention being given to the so-called central peak problem. The influence of defects both on the total intensity and on the spectral distribution of the scattered light is also examined.     

Crystal shape near the faceting phase transition point

The critical behavior of an equilibrium shape of a crystal with the size much larger than the capillary length is studied near the faceting phase transition point.     

Kurtosis and compressibility near the chiral phase transition

The properties of net quark number fluctuations in the vicinity of the QCD chiral phase transition are discussed in terms of an effective chiral model in the mean-field approximation. We focus on the ratio of the fourth- to second-order cumulants (kurtosis) and the compressibility of the system and discuss their dependence on the pion mass. It is shown that near the chiral phase transition, both observables are sensitive to the value of mπ$m_{\pi }$. For physical mπ$m_{\pi }$, the kurtosis exhibits a peak whereas the inverse compressibility shows a dip at the pseudocritical temperature. These structures disappear for large mπ$m_{\pi }$. Our results, obtained in an effective model with two flavors, are qualitatively consistent with recent results of 2+1$2+1$ flavor lattice gauge theory. We also discuss the high- and low-temperature properties of these observables and the role of the coupling of the quark degrees of freedom to the Polyakov loop.     

Pion propagation near the QCD chiral phase transition

We point out that, in analogy with spin waves in antiferromagnets, all parameters describing the real-time propagation of soft pions at temperatures below the QCD chiral phase transition can be expressed in terms of static correlators. This allows, in principle, the determination of the soft pion dispersion relation on the lattice. Using scaling and universality arguments, we determine the critical behavior of the parameters of pion propagation. We predict that, when the critical temperature is approached from below, the pole mass of the pion drops despite the growth of the pion screening mass. This fact is attributed to the decrease of the pion velocity near the phase transition.