Search results for "Optical"
showing 10 items of 7671 documents
Ab initio molecular dynamics studies of Au38(SR)24 isomers under heating
2019
Despite the great success in achieving monodispersity for a great number of monolayer-protected clusters, to date little is known about the dynamics of these ultra-small metal systems, their decomposition mechanisms, and the energy that separates their structural isomers. In this work, we use density functional theory (DFT) to calculate and compare the ground state energy and the Born-Oppenheimer molecular dynamics of two well-known Au 38 (SCH 2 CH 2 Ph) 24 nanocluster isomers. The aim is to shed light on the energy difference between the two clusters isomers and analyze their decomposition mechanisms triggered by high temperatures. The results demonstrate that the energy that separates the…
Different Space Charge Behavior of Materials Used in AC and DC Systems
2017
The aim of the present work is to evaluate the behavior, from the space charge accumulation phenomenon point of view, of three different XLPE specimens used as insulation materials in high voltage systems. Considering that under DC stress the charge accumulation is more relevant as compared to the AC case, in the specimens for DC applications additives are typically added. In this work, three different specimens are analyzed. One is a free additive sample used conventionally under AC stress and two others include different additives that are used under DC stress. In order to measure the space charge accumulation, the Pulsed Electro Acoustic (PEA) method has been employed. For each sample, t…
Kinetics of block-copolymer aggregation in super critical CO2
2002
Small angle X-ray and neutron scattering (SAXS and SANS) are used to obtain structural information on the aggregation behavior of block-copolymers dissolved in supercritical CO2. The SANS technique is used to provide a detailed structural model for the micellar aggregates, which form below the critical micellization density (CMD), that we defined in our previous work. The SAXS technique (with a synchrotron source) is used to provide the first experimental information concerning the kinetic features of both formation and decomposition of such aggregates as soon as pressure jumps are applied to the solutions across the CMD. 2002 Elsevier Science B.V. All rights reserved.
Magnetic Ion Exchange Interactions in NiO—MgO Solid Solutions
2006
In this work, a review of recent experimental data and their interpretation for NicMg1−c O solid solutions is given. In particular, the influence of exchange interactions between Ni2+ ions on the structural, optical, magnetic, and vibrational properties is discussed.
Microwave-based gas sensor with phthalocyanine film at room temperature
2013
Abstract This work presents the development of a microwave gas sensor at room temperature. The design of the sensor includes a coplanar grounded wave guide where is deposited a molecular gas sensing material. In this study, the sensitive material is a thin layer of cobalt phthalocyanine (CoPc), sensitive to ammonia and toluene. Submitted to an electromagnetic incident wave in the microwave range, the sensor response is a reflected wave. In the presence of pollutant, the reflected wave shape is specific to the species concentrations. The results interpretation is led at each frequency by the evaluation of the reflected coefficient, which traduces the ratio between the reflected wave over the…
Phase Stability of Natural Ni0.75Mg0.22Ca0.03CO3 Gaspeite Mineral at High Pressure and Temperature
2020
[EN] Divalent metal carbonates play an important role in Earth's carbon cycle, but the effect of chemical substitution is still poorly known. In this work, we have studied the structural and vibrational properties of natural mineral gaspeite (Ni0.75Mg0.22Ca0.03CO3) under high pressure and temperature using in situ synchrotron X-ray diffraction and Raman spectroscopy in diamond-anvil cells. These experiments have been complemented by ab initio simulations. Synchrotron high-pressure XRD measurements at room temperature using He as the pressure transmitting medium have shown that the calcite-type structure is stable up to 23.3 GPa. A bulk modulus at zero pressure of B-0 = 105(2) GPa with B-0' …
Crystalline-Size Dependence of Dual Emission Peak on Hybrid Organic Lead-Iodide Perovskite Films at Low Temperatures
2018
In this work, we have investigated the crystalline-size dependence of optical absorption and photoluminescence emission of CH3NH3PbI3 films, which is necessary to identify the potential practical applications of the gadgets based on perovskite films. This study was carried out at low temperatures to minimize the extra complexity induced by thermal effects. The purpose was to clarify the origin of the dual emission peak previously reported in the literature. We found that the grain size is responsible for the appearance or disappearance of this dual emission on CH3NH3PbI3 at low temperatures, whereas we have inferred that the thickness of the perovskite layer is a much more important factor …
Treatment of Herráez equation correlating viscosity in binary liquid mixtures exhibiting strictly monotonous distribution
2013
Recently, Herraez et al. proposed a new correlation equation, which introduces a correcting polynomial as an exponential-acting upon the molar fraction of one of mixture components. This equation is found to be widely applicable with more reasonable accuracy in systems exhibiting monotonous distribution than those presenting an extremum. In previous works, we have found that the first adjustable parameter of this equation is a universal exponent (0.5 or 1) for dioxane–water and isobutyric acid–water mixtures characterising the presence of solute–solute or solute–solvent interaction at very high dilution. In this work, we have tested this equation in 48 systems, and we have noted that severa…
Observable Streaming Potential in Membranes
2003
Theories describing the electrokinetic processes in membranes usually involve nonobservable variables. One of these phenomena is the streaming potential, i.e., the electric potential generated by a pressure difference imposed across the membrane system. In this work the streaming potential is successfully described by using observable variables in the framework of thermodynamics of irreversible processes. The observable electric potential is the central quantity of the transport equations. The relaxation with time of this electric potential difference is well explained by the solute flux in these transport equations. The fluxes and forces defined in the formulation permit one to analyze the…
Evaluating Thermal Corrections for Adsorption Processes at the Metal/Gas Interface
2019
International audience; Adsorption and desorption steps are key for active catalysts and rely on a subtle balance between enthalpic and entropic terms. While the enthalpic term is becoming ever more accurate through density functional development, the entropic term remains underrated and its precise determination a great challenge. In this work, we have performed extensive first principles thermodynamic integration (TI) simulations for the 1 adsorption of small (e.g., CO) to larger (e.g., phenol) molecules at metallic surfaces and compared their adsorption free energies to the values obtained by vertical, static statistical mechanics approximations to thermal corrections invoking three diff…