Search results for "thermal [correlation function]"
showing 10 items of 1923 documents
Anomalies in low-temperature lattice parameters of ErFeO3 and ErAlO3 single crystals: correlation with magnetic properties
2005
Abstract The paper presents the results of an experimental study of thermal expansion of isostructural orthorhombic ErFeO3 and ErAlO3 single crystals. Changes of lattice parameters have been investigated by X-ray measurements in the 10–300 K temperature range. Above ∼150 K, experimental results correspond well to the phonon mechanism. At low temperatures distinct anisotropic anomalies were observed in both compounds; and a correlation with the magnetic properties of the relevant ions is noted.
Vibrational properties of ZnTe at high pressures
2002
Raman spectra of ZnTe were measured under hydrostatic pressures up to 15 GPa at T = 300 K. Results for the frequencies of first- and second-order Raman features of the zincblende phase (0-9.5 GPa) are used to set up a rigid-ion model of the phonon dispersion relations under pressure. Calculated phonon densities of states, mode Gruneisen parameters and the thermal expansion coefficient as a function of pressure are discussed. The effect of pressure on the widths and intensities of Raman spectral features is considered. Raman spectra of high-pressure phases of ZnTe are reported. These spectra indicate the possible existence of a new phase near 13 GPa, intermediate between the cinnabar and ort…
Mixed Grotthuss and Vehicle Transport Mechanism in Proton Conducting Polymers from Ab initio Molecular Dynamics Simulations
2011
We elucidate the microscopic mechanism of long-range proton conduction in poly[vinyl phosphonic acid] (PVPA), a highly promising proton conducting polymer. Using a steered ab initio molecular dynamics approach, we characterize the charge transport functionality of acid groups interacting with nonbulk water molecules intercalated in the polymer. Our results show that in PVPA, unlike in Nafion, water has a local vehicle/carrier function for excess protons. This function must however be combined with the Grotthuss-type conduction mechanism that is supplied by the acid groups in order to yield long-range charge transport. As an additional aspect, we find that contrary to common intuition, syste…
In Situ Synthesis of Conducting Polymers: A Novel Approach toward Polymer Thermoelectrics
2020
The efficient conversion of thermal energy into electricity by means of durable and scalable solid-state thermoelectric devices has been a well stablished aim. Electrically conducting polymers have...
Real-time simulation and control system for the continuous casting process
2005
In this paper we present a real-time system which is used to simulate the unsteady-state continuous casting process and to control the secondary cooling water sprays. The aim of the control system is to keep the surface temperature of the slab constant with respect to time in spite of casting speed variations, and in this way minimize the formation of cracks in the final product. The simulator calculates the temperature distribution using a mathematical model based on a heat conduction formula with phase changes. The optimal spray water flow rates for each spray cooling zone will be calculated by minimizing the deviation between the target surface temperature and the calculated actual surfa…
Investigation on a Bio-Composite Material as Acoustic Absorber and Thermal Insulation
2020
In order to limit the anthropic emissions of CO2, research is currently investigating new materials for the building sector. The main purpose is the reduction in the embodied energy consumption, especially in the residential sector, and consequently the limitation of the direct and indirect utilization of fossil fuels, for the indoor heating, cooling, and ventilation services. Indeed, the residential sector is affected by a high energy demand, thus the choice of improved materials is fundamental to improve the sustainability. All phases: construction, building life, and dismantling are impacting in terms of resource and energy consumption, both associated with the emissions of pollutants in…
The effect of the axial heat transfer on space charge accumulation phenomena in HVDC cables
2020
To date, it has been widespread accepted that the presence of space charge within the dielectric of high voltage direct current (HVDC) cables is one of the most relevant issues that limits the growing diffusion of this technology and its use at higher voltages. One of the reasons that leads to the establishment of space charge within the insulation of cables is the temperature dependence of its conductivity. Many researchers have demonstrated that high temperature drop over the insulation layer can lead to the reversal of the electric field profile. In certain conditions, this can over-stress the insulation during polarity reversal (PR) and transient over voltages (TOV) events accelerating …
Fossil Fuel and Biofuel Boilers in Ukraine: Trends of Changes in Levelized Cost of Heat
2022
An increase in the share of renewables in heat supply systems is a promising direction to reach sustainable development goals and decarbonization. Decision makers should consider various factors, including energy market prices, the availability of biofuels, boiler and auxiliary equipment costs, logistic costs, and the taxation system. In the European Union, the energy crisis causes a rapid increase in fossil fuel prices. Moreover, the use of fossil fuels results in greenhouse gas emissions, which threatens the achievement of sustainable development goals. We studied the influence of the delivery cost and the value of environmental tax rates on the levelized cost of heat. Low-capacity boiler…
Graphene p-Type Doping and Stability by Thermal Treatments in Molecular Oxygen Controlled Atmosphere
2015
Doping and stability of monolayer low defect content graphene transferred on a silicon dioxide substrate on silicon are investigated by micro-Raman spectroscopy and atomic force microscopy (AFM) during thermal treatments in oxygen and vacuum controlled atmosphere. The exposure to molecular oxygen induces graphene changes as evidenced by a blue-shift of the G and 2D Raman bands, together with the decrease of I2D/IG intensity ratio, which are consistent with a high p-type doping (∼1013 cm-2) of graphene. The successive thermal treatment in vacuum does not affect the induced doping showing this latter stability. By investigating the temperature range 140-350 °C and the process time evolution, …
CdTe crystal growth process by the Bridgman method: numerical simulation
2001
Abstract Numerical simulation of the CdTe crystal growth process by the Bridgman method is made by using the commercial computational code FLUENT for the mathematical solution of the governing equations. To reduce computational effort, we have made use of a two level strategy. In the first level we have considered the whole system formed by the ampoule with the liquid–solid charge, the furnace, and the air between them. The heat transfer is assumed to occur by conduction, convection and radiation between the furnace and the ampoule, and only by conduction through the ampoule wall and the solid and liquid CdTe. In the second level we focus on the ampoule and its content, using the values of …