Search results for "dire"

High pressure theoretical and experimental analysis of the bandgap of BaMoO4, PbMoO4, and CdMoO4

2019

We have investigated the origin of the bandgap of BaMoO4, PbMoO4, and CdMoO4 crystals on the basis of optical absorption spectroscopy experiments and ab initio electronic band structure, density of states, and electronic localization function calculations under high pressure. Our study provides an accurate determination of the bandgaps Eg and their pressure derivatives d E g / dP for BaMoO4 (4.43 eV, −4.4 meV/GPa), PbMoO4 (3.45 eV, −53.8 meV/GPa), and CdMoO4 (3.71 eV, −3.3 meV/GPa). The absorption edges were fitted with the Urbach exponential model which we demonstrate to be the most appropriate for thick crystals with direct bandgaps. So far, the narrowing of the bandgap of distinct PbMoO4…

2018

Damping distances of surface plasmon polariton modes sustained by different thin titanium nitride (TiN) films are measured at the telecom wavelength of 1.55 μm. The damping distances are correlated to the electrical direct current resistivity of the films sustaining the surface plasmon modes. It is found that TiN/Air surface plasmon mode damping distances drop non-linearly from 40 to 16μm as the resistivity of the layers increases from 28 to 130μΩ.cm, respectively. The relevance of the direct current (dc) electrical resistivity for the characterization of TiN plasmonic properties is investigated in the framework of the Drude model, on the basis of parameters extracted from spectroscopic ell…

The Role of Right Interpretation of Space Charge Distribution for Optimized Design of HVDC Cables

2019

In the field of high-voltage transmission systems, different degradation phenomena affect the reliability of the employed components. In particular, under dc stress, the space charge accumulation phenomenon is believed to be the most responsible of the dielectrics lifetime reduction. To measure the accumulated space charges in flat specimens, the pulsed electro-acoustic (PEA) method is one of the most used techniques. The working principle of the PEA cell is based on the acoustic waves propagation and detection. As is well known, the acoustic waves propagating in different means are partially transmitted and partially reflected. Therefore, the piezoelectric sensor of the PEA cell is subject…

Effect of Polarity Reversal on the Partial Discharge Phenomena

2020

In the field of High Voltage Direct Current (HVDC) transmission, the space charge accumulation phenomenon and the Partial Discharges (PD) phenomena are considered the main causes of dielectric ageing. During the years, the degradation effect of both phenomena under constant DC stress has been widely studied by several researchers. In case of polarity reversal, typically carried out to control bi-directional power flow between interconnected High Voltage transmission systems, the space charge movement may not synchronously follow the electric field polarity. This could make the moment of reversing polarity a very critical one, where space charge injected during preceding polarity produces hi…

Parameter sensitivity of flux-linkage based sensorless control for permanent magnet synchronous motors

2017

Sensorless control can be utilized to reduce cost, size and total complexity of a motor drive or enhance reliability of the system. This paper first presents a sensorless control algorithm for a surface permanent-magnet synchronous motor (SPMSM) based on estimated flux linkages and stator currents. Within the algorithm, rotor position error can be predicted by comparing the estimated currents with measured stator currents. Performance of the sensorless control based on flux-linkages and the dependency of the algorithm on motor parameters is then numerically investigated via simulations. It is found from the investigation that the accuracy of the method depends on the motor working condition…

Determination of impurity distributions in ingots of solar grade silicon by neutron activation analysis

2017

AbstractIn a series of crystallization experiments, the directional solidification of silicon was investigated as a low cost path for the production of silicon wafers for solar cells. Instrumental neutron activation analysis was employed to measure the influence of different crystallization parameters on the distribution of 3d-metal impurities of the produced ingots. A theoretical model describing the involved diffusion and segregation processes during the solidification and cooling of the ingots could be verified by the experimental results. By successive etching of the samples after the irradiation, it could be shown that a layer of at least 60 μm of the samples has to be removed to get r…

Review of the PEA Method for Space Charge Measurements on HVDC Cables and Mini-Cables

2019

This review takes into account articles and standards published in recent years concerning the application of the Pulsed Electro Acoustic (PEA) method for space charge measurement on High Voltage Direct Current (HVDC) cables and mini-cables. Since the 80s, the PEA method has been implemented for space charge measurements on flat specimens in order to investigate space charge phenomena and to evaluate the ageing of dielectrics. In recent years, this technique has been adapted to cylindrical geometry. Several studies and experiments have been carried out on the use of the PEA method for full size cables and HVDC cable models. The experiments have been conducted using different arrangements of…

Optical quantum information processing and storage

2018

Here we report our recent experimental progresses in optical quantum information processing. In particular, the following topics are included. First, we extend the heralding scheme to multi-mode states and demonstrate heralded creation of qutrit states. Next, we demonstrate storage of single-photon states and synchronized release of them. Then, we demonstrate real-time acquisition of quadrature values of heralded states by making use of an exponentially rising shape of wave-packets. Finally, we demonstrate cluster states in an arbitrarily long chain in the longitudinal direction.

Intermolecular and Intramolecular Transamidation Reactions

2006

The amide functional group is resonance stabilised and direct reaction with amines is known to be difficult. Facile amide exchange reactions would enable the synthesis of important new amide based molecules, therefore transamidation reactions represent an important step in this direction. In order to ensure a transamidation reaction takes place, special requirements and conditions are required. According to the different structural characteristics of the carbox-amide group and types of activation, the most relevant examples of this reaction will be reviewed.

Half-sandwich complexes of molybdenum-(III), -(IV) and -(V) with P–O and P–N bifunctional ligands Ph2PCH2X (X = 2-oxazolinyl, or C(O)NPh2)

2000

International audience; The reaction of the ligands Ph2PCH2X (X = 2-oxazolinyl, I; or C(O)NPh2, II) with the half-sandwich molybdenum(III) precursors [Mo(η-C5R5)(μ-Cl)2]2 (R = H or Me) has been investigated. Ligand I reacts with both complexes to form the corresponding adducts [Mo(η-C5R5)Cl2(Ph2PCH2C3H4NO)] (R = H, 1; or Me, 2). The reaction between I and [MoCp*Cl4] (Cp* = η-C5Me5) affords [MoCp*Cl4(Ph2PCH2C3H4NO-κ1P)] as a kinetic isomer, which then transforms quantitatively to [MoCp*Cl3(Ph2PCH2C3H4NO-κ2P,N)]+Cl−, 3. Ligand II reacts with [MoCp(μ-Cl)2]2 (Cp = η-C5H5) to afford the adduct [CpMoCl2{Ph2PCH2C(O)NPh2-κ2P,O}], 4, as an equilibrium mixture of two isomers. Longer reaction times in…