Search results for "CATA"

SiC MOSFET vs SiC/Si Cascode short circuit robustness benchmark

2019

Abstract Nowadays, MOSFET SiC semiconductors short circuit capability is a key issue. SiC/Si Cascodes are compound semiconductors that, in some aspects, show a similar MOSFET behaviour. No interlayer dielectric insulation suggests, in theory, Cascode JFETs as more robust devices. The purpose of this paper is to compare the drift and degradation of two commercial devices static parameters by exposing them to different levels of repetitive 1.5 μs short-circuit campaigns at 85% of its breakdown voltage. Short-circuit time has been set experimentally, and longer times result in catastrophic failure of MOSFET devices due to over self-heating. For this purpose, pre- and post-test short circuit ch…

Analysis of 7Be and 210Pb concentration and 7Be/210Pb activity ratio in ground level air in Palermo (Italy)

2019

A series of measurements of particulate samples collected on paper filters in Palermo (Italy) during 1995–2005 has been performed to detect 210Pb air activity concentration and, along with previous similar data on 7Be, to evaluate their activity ratio. Average values for the daily activity concentrations of 7Be and 210Pb are found to be 4.7 and 0.6 mBq/m3 , respectively, 9.8 being the average activity ratio. Data confirm a seasonal behavior for both radionuclides. A correlation between 7Be and 210Pb air activity concentrations seems to exist, despite their different origins. The time behaviors of both 7Be and 210Pb air concentrations and 7Be/ 210Pb activity ratio have been compared with som…

Origin of Enzymatic Kinetic Isotope Effects in Human Purine Nucleoside Phosphorylase

2017

Here we report a study of the effect of heavy isotope labeling on the reaction catalyzed by human purine nucleoside phosphorylase (hPNP) to elucidate the origin of its catalytic effect and of the enzymatic kinetic isotope effect (EKIE). Using quantum mechanical and molecular mechanical (QM/MM) molecular dynamics (MD) simulations, we study the mechanism of the hPNP enzyme and the dynamic effects by means of the calculation of the recrossing transmission coefficient. A free energy surface (FES), as a function of both a chemical and an environmental coordinate, is obtained to show the role of the environment on the chemical reaction. Analysis of reactive and nonreactive trajectories allows us …

Unravelling the kinetics and molecular mechanism of the degenerate Cope rearrangement of bullvalene

2020

The kinetics and molecular mechanism of the gas phase degenerate Cope rearrangement (DCR) of bullvalene have been investigated by applying quantum mechanical calculations. Highly accurate energies (CBS-QB3 and CBS-APNO) and RRKM calculations were employed to study the kinetics and ‘fall-off’ behavior. It was found that the DCR of bullvalene (C3v) occurs through a bishomoaromatic transition structure (C2v) with an energy barrier of ∼49 kJ mol−1. The calculated activation energy and enthalpy were in good agreement with the available values in the literature, but lower than those of common Cope rearrangement; this result is related to the high stabilization energy due to the interaction of the…

Sensitive Assays by Nucleophile-Induced Rearrangement of Photoactivated Diarylethenes.

2018

Upon light-induced isomerization, diarylethenes (DAEs) equipped with reactive aldehyde moieties rearrange selectively in the presence of amines, accompanied by decoloration. In a comprehensive study, the probe structure was optimized with regard to its inherent reactivity in the nucleophile-triggered rearrangement reaction. Detailed structure−reactivity relationships could be derived, in particular with regard to the type of integrated (het)aryl moieties as well as the location of the formyl residue, and the probes’ intrinsic reactivity with primary and secondary amines was optimized. Utilizing an ancillary base, the initially formed rearrangement product can engage in a subsequent catalyti…

A solvent-directed stereoselective and electrocatalytic synthesis of diisoeugenol.

2018

A stereoselective and electrocatalytic coupling reaction of isoeugenol has been reported for the first time in a 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP)/boron-doped diamond (BDD) electrode system. This particular C-C bond formation and diastereoselectivity is driven by a solvate interaction between the radical species and another isoeugenol molecule. Due to an electrocatalytic cycle, only understoichiometric amounts of charge are necessary. Since electric current is directly employed as the oxidant, the reaction is metal and reagent-free. In addition, the electrolysis can be conducted in a very simple undivided beaker-type cell under constant current conditions. Therefore, the protocol is …

Catalytic epoxidation using dioxidomolybdenum(VI) complexes with tridentate aminoalcohol phenol ligands

2019

Reaction of the tridentate aminoalcohol phenol ligands 2,4-di-tert-butyl-6-(((2 hydroxyethyl)(methyl)amino)methyl)phenol (H2L1) and 2,4-di-tert-butyl-6-(((1-hydroxybutan-2-yl)amino)methyl)phenol (H2L2) with [MoO2(acac)2] in methanol solutions resulted in the formation of [MoO2(L1)(MeOH)] (1) and [MoO2(L2)(MeOH)] (3), respectively. In contrast, the analogous reactions in acetonitrile afforded the dinuclear complexes [Mo2O2(μ-O)2(L1)2] (2) and [Mo2O2(μ-O)2(L2)2] (4). The corresponding reactions with the potentially tetradentate ligand 3-((3,5-di-tert-butyl-2-hydroxybenzyl)(methyl)amino)propane-1,2-diol (H3L3) led to the formation of the mononuclear complex [MoO2(L3)(MeOH)] (5) in methanol whi…

Iminium Catalysis (n → π*)

2016

The Taming of Redox‐Labile Phosphidotitanocene Cations

2019

International audience; Tame d0 phosphidotitanocene cations stabilized with a pendant tertiary phosphane arm are reported. These compounds were obtained by one-electron oxidation of d1 precursors with [Cp2Fe][BPh4]. The electronic structure of these compounds was studied experimentally (EPR, UV/Vis, and NMR spectroscopy, X-ray diffraction analysis) and through DFT calculations. The theoretical analysis of the bonding situation by using the electron localization function (ELF) shows the presence of π-interactions between the phosphido ligand and Ti in the d0 complexes, whereas dπ–pπ repulsion prevents such interactions in the d1 complexes. In addition, CH–π interactions were observed in seve…

Oxidovanadium(V) amine bisphenolates as epoxidation, sulfoxidation and catechol oxidation catalysts

2017

Air-stable oxidovanadium(V) complexes with tetradentate amine bisphenolate ligands were made by the reaction of VOSO4·xH2O and ligand precursors in MeOH solutions. Isolated compounds were studied as catechol oxidase models as well as catalysts for epoxidation and sulfoxidation reactions. All compounds can catalyse such oxidation reactions without notable structure-activity correlations. The 51V NMR studies indicate that the complexes turn to the number of different species during the catalytic experiments. peerReviewed