Search results for "CAPA"
showing 10 items of 1965 documents
Derivation of a Homogenized Two-Temperature Model from the Heat Equation
2014
This work studies the heat equation in a two-phase material with spherical inclusions. Under some appropriate scaling on the size, volume fraction and heat capacity of the inclusions, we derive a coupled system of partial differential equations governing the evolution of the temperature of each phase at a macroscopic level of description. The coupling terms describing the exchange of heat between the phases are obtained by using homogenization techniques originating from [D. Cioranescu, F. Murat: Coll\`ege de France Seminar vol. 2. (Paris 1979-1980) Res. Notes in Math. vol. 60, pp. 98-138. Pitman, Boston, London, 1982.]
Partial discharges behavior under different rectified waveforms
2017
In this work, a previous software used to simulate partial discharges (PDs) under Alternating Current (AC) stress has been modified in order to evaluate the PDs behavior under a voltage stress close to the Direct Current (DC) waveform. By using a full-wave and a half-wave rectifier, the specimen with an air void defects has been subjected to a gradual constant stress. Finally, a capacitive filter has been inserted in order to produce a steadier voltage supply. Simulation results show that under an almost DC waveform, the PDs activity become less compared to AC stress.
Preparation, Characterisation and Dielectric Properties of YBa2Cu3O7-δ/ Insulator-Heterostructures
1996
YBa 2 Cu 3 O 7-δ /insulator/Au-heterostructures on SrTiO 3 or LaAlO 3 substrates were prepared to study the properties of the materials SrTiO 3 , BaTiO 3 and Ceo 2 . X-ray diffraction measurements in Bragg-Brentano geometry show c-axis-oriented growth for the superconductor and the insulators SrTiO 3 and CeO 2 . Typical values for the rocking curve width of the different insulating films are between 0.4° and 0.8°. The highest breakdown fields are measured for the insulator SrTiO 3 with +37.5 kV/mm and -8.8 kV/mm. The permittivity for CeO 2 is independent of applied field and only weakly temperature dependent. This is in contrast to the perovskite type insulators, where the permittivity depe…
The α and γ plasma modes in plasma-enhanced atomic layer deposition with O2-N2 capacitive discharges
2017
Two distinguishable plasma modes in the O2–N2 radio frequency capacitively coupled plasma (CCP) used in remote plasma-enhanced atomic layer deposition (PEALD) were observed. Optical emission spectroscopy and spectra interpretation with rate coefficient analysis of the relevant processes were used to connect the detected modes to the α and γ modes of the CCP discharge. To investigate the effect of the plasma modes on the PEALD film growth, ZnO and TiO2 films were deposited using both modes and compared to the films deposited using direct plasma. The growth rate, thickness uniformity, elemental composition, and crystallinity of the films were found to correlate with the deposition mode. In re…
Radiation resistance of nanolayered silicon nitride capacitors
2020
Abstract Single-layered and multi-layered 20–60 nm thick silicon nitride (Si3N4) dielectric nanofilms were fabricated using a low-pressure chemical vapour deposition (LPCVD) method. The X-ray photoelectron spectroscopy (XPS) confirmed less oxygen content in the multi-layered nanofilms. The capacitors with Si3N4 multilayer demonstrated a tendency to a higher breakdown voltage compared to the capacitors with Si3N4 single layer. Si3N4 nanofilms and capacitors with Si3N4 dielectric were exposed to 1 kGy dose of gamma photons. Fourier transform infrared (FTIR) spectroscopy analysis showed that no modifications of the chemical bonds of Si3N4 were present after irradiation. Also, gamma irradiation…
Analytical solution for the diffusion of a capacitor discharge generated magnetic field pulse in a conductor
2016
Powerful forces arise when a pulse of a magnetic field in the order of a few tesla diffuses into a conductor. Such pulses are used in electromagnetic forming, impact welding of dissimilar materials and grain refinement of solidifying alloys. Strong magnetic field pulses are generated by the discharge current of a capacitor bank. We consider analytically the penetration of such pulse into a conducting half-space. Besides the exact solution we obtain two simple self-similar approximate solutions for two sequential stages of the initial transient. Furthermore, a general solution is provided for the external field given as a power series of time. Each term of this solution represents a self-sim…
Deposition of binder-free oxygen-vacancies NiCo2O4 based films with hollow microspheres via solution precursor thermal spray for supercapacitors
2019
Abstract Hollow micro-/nanostructures and oxygen vacancies are highly desirable for supercapacitors due to high active surface area and outstanding electrochemical properties. In order to benefiting from the both effect, binder-free oxygen-vacancies NiCo2O4 based films with hollow microspheres were pioneering directly deposited via one kind thermal spray technology, named solution precursor thermal spray (SPTS) process. To our best knowledge, the rapid one-step SPTS route was firstly employed to synthesize and deposit NiCo2O4 films for supercapacitor applications. The CV data clearly demonstrated that the specific capacitances of more oxygen-deficient NiCo2O4 electrodes with hollow microsph…
Unveiling the Occurrence of Co(III) in NiCo Layered Electroactive Hydroxides: The Role of Distorted Environments
2020
Co- and Ni-based layered hydroxides constitute a unique class of two-dimensional inorganic materials with exceptional chemical diversity, physicochemical properties and outstanding performance as supercapacitors and overall water splitting catalysts. Recently, the occurrence of Co(III) in these phases has been proposed as a key factor that enhance their electrochemical performance. However, the origin of this centers and control over its contents remains as an open question. We employed the Epoxide Route to synthesize a whole set of α-NiCo layered hydroxides. The PXRD and XAS characterization alert about the occurrence of Co(III) as a consequence of the increment in the Ni content. DFT+U si…
Single Enantiomer’s Urge to Crystallize in Centrosymmetric Space Groups: Solid Solutions of Phenylpiracetam
2017
A detailed thermochemical and structural study of the phenylpiracetam enantiomer system was performed by characterizing the solid solutions, rationalizing the structural driving force for their formation, as well as identifying a common structural origin responsible for the formation of solid solutions of enantiomers. Enantiomerically pure phenylpiracetam forms two enantiotropically related polymorphs (enant–A and enant–B). The transition point (70(7) °C) was determined based on isobaric heat capacity measurements. Structural studies revealed that enant–A and enant–B crystallize in space groups P1 (Z′ = 4) and P212121 (Z′ = 2), respectively. However, pseudoinversion centers were present res…
Analysis of drought and vulnerability in the North Darfur region of Sudan
2018
North Darfur of Sudan is located on the edge of the Sahara Desert and endures frequent droughts due to water shortages and high summer temperatures. Monitoring and understanding drought characteristics are essential for integrated drought risk mitigation and prevetion of land degradation. This study evaluates drought conditions in North Darfur by analyzing the spatiotemporal distribution of drought using three drought indices (Standardized Precipitation Index, Vegetation Condition Index, and Soil Moisture Content Index) and their combined drought index (CDI) from 2004 to 2013. Biophysical and socioeconomic indicators are further used to measure vulnerability to drought risk and its three co…