The melting line for ethylene on graphite

Using the minimum in the nuclear magnetic spin-lattice relaxation time versus temperature as an indicator of melting we have mapped out the solid-fluid phase boundary for ethylene adsorbed on graphite. At low coverages the ethylene forms a self-bound monolayer solid with a melting temperature of about 68 K. The molecules in the solid retain orientational mobility down to 55 K, the lowest temperatures explored.     

On the decrease in the temperature of contact melting in metal systems with intermetallic compounds

A sufficient condition for the manifestation of the ΔT effect is proposed on the basis of an analysis of published data and the results obtained by the authors. An attempt is made to justify the non-mandatory delay of critical nuclei of intermetallic compounds for the purpose of explaining metastable contact melting. The low-temperature character of contact melting under such conditions is determined by the nanocontact melting of contacting micro-(nano) protrusions of pure component and intermetallic compound.     

Calculating the low temperature vapour line by Monte Carlo

A combination of canonical and grand-canonical ensemble Monte Carlo calculations, together with the virial expansion, have been used to calculate the thermodynamic properties of the liquid/vapour co-existence curve of the (6 : 12) Lennard-Jones fluid for reduced temperatures, [Ttilde] ? 1·1. The results for the liquid density and energy and the latent heat of vaporization are believed to be precise, with the exception of the point at [Ttilde]=1·1 which may lie outside the range of the function fitting the liquid phase Monte Carlo data. The liquid density and the saturated vapour pressure are in very good agreement with the results of perturbation theory. The latent heat of vaporization does not agree well with the experimental data for argon though the fit to liquid density and internal energy is good.     

The melting line of the WCA lennard-jones reference system

Abstract

The Melting line of the WCA L-J reference system, i.e. the part of the L-J potential representing the repulsive forces, is determined by means of Monte Carlo calculations. The Gibbs free energy of the fluid is calculated by thermodynamic integration and that of the solid by using the Einstein-crystal method of Frenkel and Ladd (1984).     

Study of molecular line parameters down to very low temperature

The impact of precise spectroscopic measurements on the P(9) multiplet in the ν₃ band of ¹²CH₄, obtained using a newly developed cold Herriott cell coupled with a tunable diode laser spectrometer, is examined in the context of remote sensing of methane in the atmosphere. More specifically, the influence of the air-broadening temperature dependence, of line narrowing and of line-mixing effects is assessed when fitting high resolution atmospheric spectra recorded from a balloon in the solar occultation mode. This is achieved by considering residuals and retrieved methane volume mixing ratio profiles. By combining data from previous studies together with new measurements, the expression for the temperature dependence of the broadening coefficient has been revisited. It is shown that a correcting factor applied to the usual law gives better results, when considering all the available measurements from room temperature down to about 10–20 K, as compared to the usual expression of the width versus temperature. These results clearly demonstrate that collision broadening is more sensitive to long-range attractive forces when the temperature is decreased. PACS 33.70.Jg; 34.20.-b     

Volume dependence of the melting temperature for aluminium

We present a simple and straightforward relationship for evaluating the volume dependence of melting temperature based on the Lindemann’s melting equation (F.A. Lindemann, Z. Phys. 11 (1910) 609) and the Al’tshular et al. model for the volume dependence of the Gruneisen parameter (L.V. Al’tshuler, S.E. Brusnikin, E.A. Kuz’ menkov, J. Appl. Mech. Tech. Phys. 28 (1987) 129). The formula for the volume dependence of melting temperature obtained in the present study has been used to determine the results for aluminium up to a pressure range of 77 GPa. The results obtained for the melting temperature present a good agreement with the available experimental data.     

Boundary entropy of one-dimensional quantum systems at low temperature

The boundary beta function generates the renormalization group acting on the universality classes of one-dimensional quantum systems with boundary which are critical in the bulk but not critical at the boundary. We prove a gradient formula for the boundary beta function, expressing it as the gradient of the boundary entropy s at fixed nonzero temperature. The gradient formula implies that s decreases under renormalization, except at critical points (where it stays constant). At a critical point, the number exp((s) is the "ground-state degeneracy," g, of Affleck and Ludwig, so we have proved their long-standing conjecture that g decreases under renormalization, from critical point to critical point. The gradient formula also implies that s decreases with temperature, except at critical points, where it is independent of temperature. It remains open whether the boundary entropy is always bounded below.     

A new emission line in highly excited ZnO at low temperature

A new emission line from ZnO has been observed under strong u.v.-excitation at 4.2 K, which shifts to longer wavelengths with increasing excitation. The experimental results are described by a model involving the recombination of a bound exciton which transfers part of its energy to a free electron.     

Soft-disc melting in small systems

The location of melting for a soft-disc system of 32, 50 and 98 particles (N), respectively, is determined by molecular dynamics.     

Solid-solid phase transformation via virtual melting significantly below the melting temperature

A new phenomenon is theoretically predicted, namely, that solid-solid transformation with a relatively large transformation strain can occur through virtual melting along the interface at temperatures significantly (more than 100 K) below the melting temperature. The energy of elastic stresses, induced by transformation strain, increases the driving force for melting and reduces the melting temperature. Immediately after melting, the stresses relax and the unstable melt solidifies. Fast solidification in a thin layer leads to nanoscale cracking, which does not affect the thermodynamics and kinetics of solid-solid transformation. Seven theoretical predictions are in quantitative agreement with experiments conducted on the beta-->delta transformation in the HMX energetic crystal.     

Contact melting temperature of small-dimensional phases

Bulletin of the Russian Academy of Sciences: Physics - An attempt is made to derive the relation for the contact melting temperature of small-dimensional phases (nanoparticles, nanofilms) with...     

The Coulomb Gas at low temperature and low density

We study the quantum Coulomb Gas ofN particles with HamiltonianH at low temperature and negative values of the chemical potential. If is sufficiently negative the Coulomb gas is approximately a perfect rare gas of charged particles, as expected. The interesting fact is that for higher (but still negative) values of the gas changes to a rare gas of some atom or molecule (which is most likely neutral). The type of molecule is determined by the ground state of the HamiltonianH —N with center of mass motion removed.Dedicated to Roland DobrushinWork partially supported by U.S. National Science Foundation grant DMS 8600748 (J.C.), PHY 85-15288-(A03) (E.L.) and DMS-8601978 and DMS-8806731 (H.-T.Y.)     

Two-dimensional melting of dislocation vector systems

Dislocation vector systems with various dislocation core energies are simulated, and the nature and the mechanism of the melting phase transition there is determined by means of the energy, specific heat, dislocation density, renormalized coupling constant, shear modulus and orientational stiffness constant as well as microscopic configurations of dislocation vectors. For a system with a large core energy the melting transition is found to be continuous, caused by the dislocation unbinding mechanism predicted by Kosterlitz-Thouless and Halperin-Nelson-Young. For a system with a small core energy, grain boundary loops are nucleated in the process of melting and the phase transition turns out to be first order. The latter agrees with most of the computer experiments on atomistic systems.     

The epoxy-siloxane/Al composite coatings with low infrared emissivity for high temperature applications

Low infrared emissivity coatings with good thermal resistance were prepared by using epoxy-siloxane and aluminum as adhesive and pigment, respectively. The influence of chemical composition, surface texture, roughness and thickness on the infrared emissivity was systematically investigated. The detailed results of experimental investigation indicate that the cured composite coatings could possess low emissivity value. Due to reducing infrared absorption and forming uniform and compact char construction, the infrared emissivity decreases obviously. Both the surface roughness and thickness have a critical value, respectively. Too large roughness or thickness would not contribute to the decrease of the emissivity. Moreover, the composite coatings were tested for thermal stability in air to explore the effect of high-temperature environment on the emissivity. The results indicate that the composite coatings, still possessing low emissivity after the test, exhibit favorable thermal ageing and thermal shock resistance.     

Ultrasound for low temperature dyeing of wool with acid dye

The possibility of reducing the temperature of conventional wool dyeing with an acid levelling dye using ultrasound was studied in order to reach exhaustion values comparable to those obtained with the standard procedure at 98 °C, obtaining dyed samples of good quality. The aim was to develop a laboratory method that could be transferred at industrial level, reducing both the energy consumption and fiber damage caused by the prolonged exposure to high temperature without the use of polluting auxiliary agents.Dyeings of wool fabrics were carried out in the temperature range between 60 °C and 80 °C using either mechanical or ultrasound agitation of the bath and coupling the two methods to compare the results. For each dyeing, the exhaustion curves of the dye bath were determined and the better results of dyeing kinetics were obtained with ultrasound coupled with mechanical stirring. Hence the corresponding half dyeing times, absorption rate constants according to Cegarra-Puente modified equation and ultrasonic efficiency were calculated in comparison with mechanical stirring alone. In the presence of ultrasound the absorption rate constants increased by at least 50%, at each temperature, confirming the synergic effect of sonication on the dyeing kinetics. Moreover the apparent activation energies were also evaluated and the positive effect of ultrasound was ascribed to the pre-exponential factor of the Arrhenius equation. It was also shown that the effect of ultrasound at 60 °C was just on the dye bath, practically unaffecting the wool fiber surface, as confirmed by the results of SEM analysis.Finally, fastness tests to rubbing and domestic laundering yielded good values for samples dyed in ultrasound assisted process even at the lower temperature. These results suggest the possibility, thanks to the use of ultrasound, to obtain a well equalized dyeing on wool working yet at 60 °C, a temperature process strongly lower than 98 °C, currently used in industry, which damages the mechanical properties of the fibers.     

Disorder driven melting of the vortex line lattice

The 3D XY model with random in-plane couplings is simulated to model the phase diagram of a disordered type II superconductor as a function of temperature T and randomness strength p for fixed applied magnetic field. As p increases to a critical p(c), the first order vortex lattice melting line turns parallel to the T axis, continuing down to low temperatures, rather than ending at a critical point. Above p(c) preliminary results suggest the absence of a phase coherent vortex glass.