Search results for "thermal [correlation function]"
showing 10 items of 1923 documents
An analytical model of heat transfer and fluid dynamic performances of an unconventional NTR engine for manned interplanetary missions
2009
Abstract An analytical model of fluid flow and heat transfer of a Nuclear Thermal Rocket (NTR) engine concept is presented. The engine is based on the direct conversion of the kinetic energy of the fission fragments (FFs) into the propellant enthalpy. The FFs can escape from an extremely thin layer of fissionable material: a sufficiently large surface coated with few micrometers of Americium 242m, confined by a neutron moderator–reflector, may become a critical reactor. Three dimensional coupled CFD-Monte Carlo simulations have already been presented in Di Piazza and Mulas (2006) . In this paper, an analytical integral 1-D model of fluid dynamics and heat transfer is built in order to fores…
Allosteric Models for Multimeric Proteins: Oxygen-Linked Effector Binding in Hemocyanin
2005
In many crustaceans, changing concentrations of several low molecular weight compounds modulates hemocyanin oxygen binding, resulting in lower or higher oxygen affinities of the pigment. The nonphysiological effector caffeine and the physiological modulator urate, the latter accumulating in the hemolymph of the lobster Homarus vulgaris during hypoxia, increase hemocyanin oxygen affinity and decrease cooperativity of oxygen binding. To derive a model that describes the mechanism of allosteric interaction between hemocyanin and oxygen in the presence of urate or caffeine, studies of oxygen, urate, and caffeine binding to hemocyanin were performed. Exposure of lobster hemocyanin to various pH …
Dynamic fluctuations of dipolar semiflexible filaments
2005
On the basis of the model of a flexible magnetic filament, the characteristics of their thermal fluctuations are considered. The crossover of the time dependence of the mean quadratic displacement from t(3/4) to t(1/2) at the magnetic field increase is found. Two characteristic mechanisms of the magnetization relaxation time distribution--straightening of the thermal undulations and excitation of the bending modes of the free ends under the action of an ac magnetic field--are described. In both cases, the characteristic scaling law omega(-3/4) of the magnetic susceptibility in a high-frequency range is found.
Use of thermography in the diagnosis of pressure ulcers category I: A protocol proposal
2016
ressure ulcers (PU) category I are defined by intact skin with non-blanchable erythema of a localized area, usually over a bony prominence. Although they are often underdiagnosed, they may indicate “at risk” persons. There are available different procedures to diagnose pressure ulcers category I, such as but these methods can produce a misdiagnosis. Infrared thermal imaging may be helpful to resolve his conflict. We propose a protocol to observational and prospective study for the diagnosis of PU category I using thermography. Sin financiación No data (2016) UEV
Ascorbic Acid Is the Only Bioactive That Is Better Preserved by High Hydrostatic Pressure than by Thermal Treatment of a Vegetable Beverage
2010
Variations in levels of antioxidant compounds (ascorbic acid, total phenolics, and total carotenoids), total antioxidant capacity, and color changes in a vegetable (tomato, green pepper, green celery, onion, carrot, lemon, and olive oil) beverage treated by high hydrostatic pressure (HHP) were evaluated in this work. The effects of HHP treatment, four different pressures (100, 200, 300, and 400 MPa) and four treatment times for each pressure (from 120 to 540 s) were compared with those of thermal treatment (90-98 °C for 15 and 21 s). High pressure treatment retained significantly more ascorbic acid in the vegetable beverage than thermal treatment. However, no significant changes in total ph…
Laser induced thermal profiles in thermally and optically thin films
1988
The temperature field generated by the weak absorption of a gaussian laser beam in an optically and thermally thin film bounded by two transparent plates is discussed. An analytical solution of the problem is presented together with an algorithm for the numerical integration. The influence of the finite thermal conductivity of the plates is shown in an example.
Resistive state of quasi-one-dimensional superconductors: Fluctuations vs. sample inhomogeneity
2007
The shape of experimentally observed R(T) transition of thin superconducting wires is analyzed. Broadening of the transition in quasi-1-dimensional superconducting channels is typically associated with phase slip mechanism provided by thermal or quantum fluctuations. It is shown that consideration of inevitable geometrical inhomogeneity and finite dimensions of real samples studied in experiments is of primary importance for interpretation of results. The analysis is based on experimental fact that for many superconducting materials the critical temperature is a function of characteristic dimension of a low-dimensional system: film thickness or wire cross section
Transition to ballistic regime for heat transport in helium II
2014
The size-dependent and flux-dependent effective thermal conductivity of narrow capillaries filled with superfluid helium is analyzed from a thermodynamic continuum perspective. The classical Landau evaluation of the effective thermal conductivity of quiescent superfluid, or the Gorter-Mellinck regime of turbulent superfluids, are extended to describe the transition to ballistic regime in narrow channels wherein the radius $R$ is comparable to (or smaller than) the phonon mean-free path $\ell$ in superfluid helium. To do so we start from an extended equation for the heat flux incorporating non-local terms, and take into consideration a heat slip flow along the walls of the tube. This leads f…
Non-isothermal crystallization kinetics of PET
2000
The crystallization kinetics of poly(ethylene terephthalate) was studied using constant cooling rate, isothermal and quenching experiments. A non-isothermal crystallization kinetics equation based on a single mechanism was used to analyze the data. Different mechanisms of crystallization at low, intermediate, and high cooling rates were hypothesized based on deviation of the experimental data from the single mechanism model.
Structural transformations in amorphous selenium as studied by the differential thermal analysis and exoelectron emission technique
2007
The parameters (temperature, activation energy) of the surface and volume glass transition (retrification process) in amorphous selenium produced by rapid quenching of the liquid phase have been determined using the EEE and DTA techniques. EEE is a surface effect connected with structural transformations in the surface layer whereas the DTA measurements give the information about the transformations occurring in the volume of the sample. It has been found that the surface retrification of selenium occurs with activation energy smaller than the volume retrification, both observed in the first heating run. The value of activation energy for the volume retrification measured in the second DTA …