			Home About us Contact

Continuous Phase Transition (continuous + phase_transition)

Distribution by Scientific Domains

Physics and Astronomy	50%

Selected Abstracts

Convective Available Potential Energy (CAPE) in mixed phase cloud conditions

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 624 2007
B. Früh
Abstract An approximate but pragmatic approach is presented to define Convective Available Potential Energy (CAPE) in mixed phase cloud conditions. The underlying process calls for mixed (i.e. liquid and ice) phase parcels and assumes the liquid fraction to be a unique function of temperature. The approach is meant to represent average conditions. Differences between this and more traditional approaches are quantified and discussed for mean tropical conditions. Generally freezing increases parcel temperature and, hence, buoyancy. If freezing occurs isobarically (as was often assumed in the past), all water changes phase at a single level resulting in a discontinuity in buoyancy at that level. By contrast, the mixed phase parcel process implies a continuous phase transition in a finite range of temperatures Tfs , T , Tfe, leading to a gradual change of buoyancy with altitude and preventing any temperature inversion. The details of this gradual change depend on the choice of the specified temperature range [Tfs, Tfe]. High in the troposphere, where all water is frozen irrespective of the details, the differences between the buoyancy profiles are small (but finite). CAPE is very sensitive to the treatment of the freezing process. Isobaric freezing at a relatively high temperature (e.g. , 5 °C) in a reversible process may increase CAPE by a factor of 2 to 3, and this increase is similar in magnitude to the difference between the pseudo-adiabatic and the reversible processes for pure water parcels. Both of these processes are considered less realistic than the reversible mixed phase process with continuous freezing over a broad temperature range [Tfs, Tfe] = [,5 °C, , 40 °C]; the corresponding CAPE lies about half way between the reversible and irreversible pure water processes. For clouds with finite precipitation efficiency the effect of freezing is less pronounced than for reversible conditions. Copyright © 2007 Royal Meteorological Society [source]

The Structure-Controlling Solventless Synthesis and Optical Properties of Uniform Cu2S Nanodisks

CHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2008
Yu-Biao Chen Dr.
Abstract Uniform Cu2S nanodisks have been synthesized from a well-characterized layered copper thiolate precursor by structure-controlling solventless thermolysis at 200,220,°C under a N2 atmosphere. The development from small Cu2S nanoparticles (diameter ,3,nm) to nanodisks (diameter 8.3,nm) and then to faceted nanodisks (diameter 27.5,nm, thickness 12.7,nm) is accompanied by a continuous phase transition from metastable orthorhombic to monoclinic Cu2S, the ripening of small particles by aggregation, and finally the crystallization process. The growth of the nanoproduct is constrained by the crystal structure of the precursor and the in situ-generated thiol molecules. Such controlled anisotropic growth leads to a nearly constant thickness of faceted nanodisks with different diameters, which has been confirmed by TEM observations and optical absorption measurements. [source]

Monte Carlo Simulations of the 3D Ashkin,Teller Model: continuous phase transition lines

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003
G. Musia
Abstract Large-scale Monte Carlo simulations, based on the invariance of the Binder cumulant Q, for continuous phase transitions in the three-dimensional Ashkin,Teller spin-lattice model on a cubic lattice, have been performed. Using the universality hypotesis and the finite-size-scaling analysis, the Ising character of phase transitions from the antiferro- to paramagnetic phase, where the cumulant Q behavior is different than in the Ising model, is demonstrated. Some preliminary results demonstrating the existance of the tricritical points are also presented. [source]

Crystal structures, thermal expansion and phase transitions of mixed Pr1,xLaxAlO3 perovskites

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2009
Tetyana Basyuk
Abstract The crystal structures, thermal expansion and phase transitions of mixed Pr1,xLax AlO3 perovskites have been examined by using an in situ high resolution X-ray powder diffraction technique applying synchrotron radiation in a wide temperature range of 12,1173 K. At room temperature all samples in the PrAlO3,LaAlO3 pseudo-binary system adopt the rhombohedral perovskite-like structure. At elevated temperatures, all Pr1,xLax AlO3 compositions undergo continuous phase transitions from rhombohedral to cubic structures. The sequence of the low-temperature (LT) phase transformations Rc ,Imma ,C2/m has been observed in Pr1,xLax AlO3 samples. Temperatures of HT and LT phase transitions in Pr1,xLax AlO3 decrease with decreasing Pr content. Crystal structure parameters for all compositions Pr1,xLax AlO3 have been determined. Based on in situ powder diffraction and DTA/DSC data, the phase diagram of the PrAlO3,LaAlO3 pseudo-binary system has been constructed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]