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Temperature Evolution (temperature + evolution)
Selected AbstractsExciton,phonon interaction and Raman spectra of [(CH3)2NH2]5Cd2CuCl11 crystalsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2004V. Kapustianik Abstract Temperature evolution of the exciton,phonon interaction (EPI) in ((CH3)2NH2)5Cd2CuCl11 solid solution was studied on the basis of absorption spectroscopy data. The obtained values of effective phonon energies were compared with the data of Raman spectroscopy. It is shown that the (T) and E, parameters of Urbach's rule show the continuous anomalous change characteristic of the second-order phase transition at T1 = 176 K. The anomalous behaviour of the EPI and other spectral parameters at T0 = 310,315 K was related to the complex co-operative effect involving weakening of the hydrogen bonds and variation of the Jahn,Teller distortion of metal,halogen polyhedra with temperature. This process takes place only within the copper,chlorine sublattice and due to this would be hardly related to the usual phase transition. At the same time, the considered temperature change of the tetragonal distortion of the metal,halogen octahedra is followed by nonfulfillment of Urbach's rule in the temperature range TT0. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] On the optimal cooling strategy for variable-speed continuous castingINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2002D. Constales Abstract In this paper, we consider the inverse problem of determining the optimal cooling parameters for continuous casting under changing casting speed. We rely on automatic differentiation to support different search methods for the parameter values that will minimize a given cost functional, which can include a variety of criteria: surface temperature evolution and variation, interface position, full solidification point. In the direct problem we use a fixed-domain transformation to solve the corresponding free-boundary problem to high accuracy. Numerical experiments are provided to illustrate and support the effectiveness of the present concept. Copyright © 2001 John Wiley & Sons, Ltd. [source] Dependence of small-angle neutron scattering contrast on the difference in thermal expansions of phases in two-phase alloysJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2009Pavel Strunz Theoretical expressions describing small-angle neutron scattering (SANS) contrast dependence on temperature in the region where no phase-composition changes occur were derived for two-phase Ni superalloys. The theory is based on the difference in thermal expansion of the two primary phases, , and ,,. The simulations show that the scattering contrast temperature evolution is significant enough to be considered in in situ SANS experiments with superalloys at elevated temperatures. The simulations performed show that the magnitude of the scattering contrast at room temperature is firmly connected with the particular shape of the scattering contrast temperature dependence. This fact can be used for determination of the scattering contrast without a knowledge of the compositions of the individual phases. The theoretical expressions derived for scattering contrast were proven experimentally on an Ni,Fe-base alloy, DT706. The evolution of lattice parameters of both the matrix and the precipitate phases was obtained from an in situ wide-angle neutron diffraction experiment. The theoretical scattering contrast dependence was then successfully fitted to the measured SANS integral intensity. [source] Amphibolites with staurolite and other aluminous minerals: calculated mineral equilibria in NCFMASHJOURNAL OF METAMORPHIC GEOLOGY, Issue 1 2000Arnold Amphibolite facies mafic rocks that consist mainly of hornblende, plagioclase and quartz may also contain combinations of chlorite, garnet, epidote, and, more unusually, staurolite, kyanite, sillimanite, cordierite and orthoamphiboles. Such assemblages can provide tighter constraints on the pressure and temperature evolution of metamorphic terranes than is usually possible from metabasites. Because of the high variance of most of the assemblages, the phase relationships in amphibolites depend on rock composition, in addition to pressure, temperature and fluid composition. The mineral equilibria in the Na2O,CaO,FeO,MgO,Al2O3,SiO2,H2O (NCFMASH) model system demonstrate that aluminium content is critical in controlling the occurrence of assemblages involving hornblende with aluminous minerals such as sillimanite, kyanite, staurolite and cordierite. Except in aluminous compositions, these assemblages are restricted to higher pressures. The iron to magnesium ratio (XFe), and to a lesser extent, sodium to calcium ratio, have important roles in determining which (if any) of the aluminous minerals occur under particular pressure,temperature conditions. Where aluminous minerals occur in amphibolites, the P,T,X dependence of their phase relationships is remarkably similar to that in metapelitic rocks. The mineral assemblages of Fe-rich amphibolites are typically dominated by garnet- and staurolite-bearing assemblages, whereas their more Mg-rich counterparts contain chlorite and cordierite. Assemblages involving staurolite,hornblende can occur over a wide range of pressures (4,10 kbar) at temperatures of 560,650 °C; however, except in the more aluminous, iron-rich compositions, they occupy a narrow pressure,temperature window. Thus, although their occurrence in ,typical' amphibolites may be indicative of relatively high pressure metamorphism, in more aluminous compositions their interpretation is less straightforward. [source] Titan's damp ground: Constraints on Titan surface thermal properties from the temperature evolution of the Huygens GCMS inletMETEORITICS & PLANETARY SCIENCE, Issue 11 2006Ralph D. Lorenz The model parameters are adjusted to match the recorded temperature history of a nearby heater, taking into account heat losses by conduction to the rest of the probe and to Titan's cold atmosphere. The model suggests that after impact when forced convective cooling ceased, the inlet temperature rose from ,110 K to an asymptotic value of only ,145 K. This requires that the inlet was embedded in a surface that acted as an effective heat sink, most plausibly interpreted as wet or damp with liquid methane. The data appear inconsistent with a tar or dry, fine-grained surface, and the inlet was not warm enough to devolatilize methane hydrate. [source] An implementation of radiative transfer in the cosmological simulation code gadgetMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2009Margarita Petkova ABSTRACT We present a novel numerical implementation of radiative transfer in the cosmological smoothed particle hydrodynamics (SPH) simulation code gadget. It is based on a fast, robust and photon-conserving integration scheme where the radiation transport problem is approximated in terms of moments of the transfer equation and by using a variable Eddington tensor as a closure relation, following the Optically Thin Variable Eddington Tensor suggestion of Gnedin & Abel. We derive a suitable anisotropic diffusion operator for use in the SPH discretization of the local photon transport, and we combine this with an implicit solver that guarantees robustness and photon conservation. This entails a matrix inversion problem of a huge, sparsely populated matrix that is distributed in memory in our parallel code. We solve this task iteratively with a conjugate gradient scheme. Finally, to model photon sink processes we consider ionization and recombination processes of hydrogen, which is represented with a chemical network that is evolved with an implicit time integration scheme. We present several tests of our implementation, including single and multiple sources in static uniform density fields with and without temperature evolution, shadowing by a dense clump and multiple sources in a static cosmological density field. All tests agree quite well with analytical computations or with predictions from other radiative transfer codes, except for shadowing. However, unlike most other radiative transfer codes presently in use for studying re-ionization, our new method can be used on-the-fly during dynamical cosmological simulation, allowing simultaneous treatments of galaxy formation and the re-ionization process of the Universe. [source] Dynamics of molecules in crystals from multi-temperature anisotropic displacement parameters.ACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2000A new model for analysing the temperature evolution of anisotropic displacement parameters (ADP's) is presented. It allows for a separation of temperature-dependent from temperature-independent contributions to ADP's and provides a fairly detailed description of the temperature-dependent large-amplitude molecular motions in crystals in terms of correlated atomic displacements and associated effective vibrational frequencies. It can detect disorder in the crystal structure, systematic error in the diffraction data and the effects of non-spherical electron-density distributions on ADP's in X-ray data. The analysis requires diffraction data measured at multiple temperatures. [source] Dynamics of molecules in crystals from multi-temperature anisotropic displacement parameters.ACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2000The temperature evolution of atomic anisotropic displacement parameters (ADP's) of perdeuterobenzene and of urea in the temperature range between 12 and 123,K is investigated in terms of the model presented in paper I. For the benzene molecule, the temperature-dependent contributions to the ADP's are well described by three molecular librations and three molecular translations. For the urea molecule, the analysis revealed a low-frequency high-amplitude normal mode (~64,cm,1), which combines out-of-plane deformations of the NH2 groups with molecular libration. The pyramidalization motion allows the hydrogen-bonding pattern to be retained quite well, whereas this pattern is heavily distorted in the higher-frequency molecular librations. The results presented for urea go a step beyond those obtainable in a conventional rigid-body or segmented-rigid-body analysis because they show how correlations of atomic displacements in molecular crystals can be determined from the temperature evolution of ADP's. For both molecules, the analysis reveals temperature-independent contributions to the ADP's accounting for the high-frequency internal vibrations. It is the first time that such contributions have been extracted directly from single-crystal diffraction data for light atoms like hydrogen and deuterium as well as for heavier atoms like carbon, nitrogen and oxygen. These contributions agree well with those calculated from independent spectroscopic information. [source] Numerical parameter study of the thermal behaviour of a gypsum plaster board at fire temperaturesFIRE AND MATERIALS, Issue 2 2008Luc Wullschleger Abstract Based on a comparison between the measured and the calculated temperature evolutions within a gypsum plaster board subject to fire, a numerical parameter study regarding the material properties of gypsum at elevated temperatures has been carried out. This allowed quantifying the individual influence of different quantities and their deviations on the calculated thermal behaviour of this material. Copyright © 2007 John Wiley & Sons, Ltd. [source] Heat and mass transfer during microwave-convective dryingAICHE JOURNAL, Issue 1 2010Stefan J. Kowalski Abstract The article presents a mathematical model of drying that describes the kinetics of combined microwave-convective drying for the process as a whole. Based on this model, the drying curves and the temperature evolutions of the drying body were constructed by a number of computer-simulated drying programs, which were chosen to follow the respective experimental processes carried out on a cylindrical sample made of kaolin. The experimental data allowed both the estimate of material coefficients arising in the model and the validation of the theory. A very satisfactory correlation of the theoretical predictions with the experimental data is found. The main novelty of this article is the mathematically complete drying model that describes all periods of the microwave-convective drying process. Application of such a complete model is necessary if we want to optimize drying processes with respect to drying time and consumption of energy via computer simulations. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Spectroscopic ellipsometry of SrTiO3 crystals applied to antiferrodistortive surface phase transitionPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2010Alexandr Dejneka Abstract This work is devoted to the ellipsometric study of antiferrodistortive (AFD) ,,, cubic-to-tetragonal phase transition (PT) of SrTiO3 surface. Strong influence of surface defect structure on magnitude and temperature evolutions of surface refractive index related to PT was found and investigated. It is shown that even small surface imperfections result in enhancement and strong changes of the surface refractive index when approaching the temperature of PT. This effect is caused by emergence and evolutions in the surface of the structural changes corresponding to order parameter at the temperatures sufficiently higher than transition temperature in the bulk. In the case of structurally perfect crystal surface, the features of the temperature dependence of surface refractive index appeared to be very small and visible at the temperatures a little smaller than transition temperature for bulk that agrees well with predictions of Kaganov,Omel'yanchuk theory. [source] | ||||||||||||||||