Search results for "GEM"
showing 10 items of 19240 documents
Unexpected Substituent Effects in the Iso-Heterocyclic Boulton-Katritzky Rearrangement of 3-Aroylamino-5-methyl-1,2,4-oxadiazoles: A Mechanistic Stud…
2019
The kinetics of the iso-heterocyclic mononuclear rearrangement of some 3-aroylamino-5-methyl-1,2,4-ozadiazoles was carefully examined under largely variable acidic or alkaline conditions. This reaction may proceed via two different mechanistic pathways (an uncatalyzed and a base-catalyzed one), as accounted for also by the evaluation of the relevant activation parameters. Substituent effects, as quantified by means of the Hammett’s equation, appear relatively modest; however, they reveal some interesting anomalies, which enabled us to draw a very precise picture of the intimate reaction course.
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…
Estimation des incertitudes de mesure sur bras polyarticulé portable par méthode de Monte Carlo
2013
International audience; Les bras polyarticulés portables ont progressivement évolué et sont de plus en plus utilisés dans l’industrie. Cependant, à l’heure actuelle, la traçabilité de ces dispositifs est difficile à effectuer et les incertitudes de mesures relatives à l’utilisation de ces appareils ne sont pas quantifiées. Le travail mené consiste à déterminer les incertitudes de mesures associées à la quantification, par un bras polyarticulé portable, des caractéristiques géométriques et dimensionnelles d’une pièce mécanique. Les travaux visant à élaborer un modèle d’incertitude de mesure, sont basés sur la méthode de Monte Carlo du supplément 1 du Guide pour l'expression de l'incertitude …
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…
Formation of dibutyl carbonate and butylcarbamate via CO2 insertion in titanium(IV) butoxide and reaction with n-butylamine
2016
Abstract The species resulting from insertion of 12CO2 and 13CO2 into titanium(IV) butoxide is for the first time fully characterized by means of infrared and nuclear magnetic resonance spectroscopy. Results show formation of Ti-monobutylcarbonate, that easily undergoes nucleophilic attack by an aliphatic amine. The hydrolysis of the resulting species produces butylcarbamate and dibutylcarbonate as the only main products. Characterization results of the carbonate-like adduct, along with its reactivity with amine molecules open the route to new ways of CO2 utilization as building block for valuable organic compounds.
Optimal Dynamic Portfolio Risk Management
2016
Numerous econometric studies report that financial asset volatilities and correlations are time-varying and predictable. Over the past decade, this knowledge has stimulated increasing interest in various dynamic portfolio risk control techniques. The two basic types of risk control techniques are: risk control across assets and risk control over time. At present, the two types of risk control techniques are not implemented simultaneously. There has been surprisingly little theoretical study of optimal dynamic portfolio risk management. In this paper, the author fills this gap in the literature by formulating and solving the multi-period portfolio choice problem. In terms of dynamic portfoli…
Modeling Rain Isotopic Composition under Orographic Control: A Landscape Approach for Hydrogeological Applications
2021
Oxygen isotopic composition is useful for individuating recharge areas of groundwater bodies by the comparison with those of local rainfalls. While on a global scale general relationships, such as the isotopic vertical gradient or continentality effects, efficiently describe spatial variations of the isotopic signature, hydrogeological applications need spatial models that are more focused on the effects of local topographic structures and/or subsoil geology. This work presents a case study in northeastern Sicily (Italy) characterized by complex geological and orographic structures, in which isotopic composition of rainfalls is governed by orographic effects and the varying initial composit…
Dimensionless Stage-Discharge Relationship for a Non-Linear Water Reservoir: Theory and Experiments
2020
In the field of hydrology, stage&ndash
Discussion of "Analysis of extreme rainfall trends in sicily for the evaluation of depth-duration-frequency curves in climate change scenarios" by Lo…
2016
In the original paper, the Authors investigated the presence of trends in extreme rainfall depths of duration d = 1, 3, 6, 12 and 24 hours, in Sicily. Trend analysis was performed by using the Mann-Kendal non-parametric test, which was applied at-site, for a number of 65 raingauges well distributed in the region, for the period 1950-2008. In order to overcome the gap of missing data, six years moving average series were considered in the Author’s analysis. In this discussion, the discussers highlighted some important observations about the paper presented by the Authors: i) The Authors applied the non-parametric Mann Kendall test to moving average series of rainfall data. The use of moving …
A novel comprehensive procedure for estimating greenhouse gas emissions from water resource recovery facilities
2017
The emissions of the major greenhouse gases (GHGs), i.e. carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) from water resource recovery facilities (WRRFs) are of increasing concern in the water industry. In order to produce useful and comparable information for monitoring, assessing, and reporting GHG emissions from WRRFs, there is a need for a generally accepted methodology for their quantification. This paper aims at proposing the first protocol for monitoring and accounting for GHG emissions from WRRFs, taking into account both direct and indirect internal emissions and focusing the attention on plant sections known to be primarily responsible for GHG emissions (i.e. oxidation…