3,729 research outputs found
New Visible Light-triggered Photocatalytic Trifluoromethylation Reactions of Carbonâcarbon Multiple Bonds and (Hetero)aromatic Compounds
Visible-light-photocatalyzed methods employed insynthetic transformations present attractive properties such asenvironmentally friendly, safety, availability and excellent functionalgroup tolerance. In this venue, research on the visible-lightphotocatalytic incorporation of the trifluoromethyl CF3 moiety intoorganic substrates, in particular, has contributed to a clear evolutionof the very field of photocatalysis. Outer-sphere electron transfersbetween photocatalysts and trifluoromethyl sources supply CF3radicals efficiently in clean and controlled ways, capable of effectingnumerous synthetic transformations and functionalization on organicsubstrates and compounds with pharmacological activity instraightforward manners. Although this particular area is constantlyevolving and reviewed, the last five years have experienced anoutburst of seminal and significant photocatalytic trifluoromethylationexamples that are leading the way and opening new syntheticavenues. Recent review articles on Ru- and Ir- based photocatalytictrifluoromethylation reactions have borne witness of this evolution.Although this account will show the new Ru- and Ir-basedphotocatalytic trifluoromethylations, Sections 2 and 3 will alsoillustrate other photocatalytic systems, such as organic dyes, organicsemiconductors and newly-developed all-organic photocatalysts. All the known and reviewed strategies for photocatalytictrifluoromethylation reactions of olefins and (hetero)aromaticcompounds will not be discussed but will be summarized in twoFigures (Figures 4 and 5), and new examples (2015-present) will bepresented and discussed.Fil: Barata Vallejo, Sebastian. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica. Departamento de QuĂmica OrgĂĄnica; ArgentinaFil: Postigo, Jose Alberto. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica. Departamento de QuĂmica OrgĂĄnica; Argentin
Stau relic density at the Big-Bang nucleosynthesis era consistent with the abundance of the light element nuclei in the coannihilation scenario
We calculate the relic density of stau at the beginning of the Big-Bang
Nucleosynthesis (BBN) era in the coannihilation scenario of minimal
supersymmetric standard model (MSSM). In this scenario, stau can be long-lived
and form bound states with nuclei. We put constraints on the parameter space of
MSSM by connecting the calculation of the relic density of stau to the
observation of the light elements abundance, which strongly depends on the
relic density of stau. Consistency between the theoretical prediction and the
observational result, both of the dark matter abundance and the light elements
abundance, requires the mass difference between the lighter stau and the
lightest neutralino to be around 100MeV, the stau mass to be 300 -- 400 GeV,
and the mixing angle of the left and right-handed staus to be
.Comment: 9 pages, 5 figures, figure 5 correcte
Non-Abelian Medium Effects in Quark-Gluon Plasma
Based on the kinetic theory, the non-Abelian medium property of hot
Quark-Gluon Plasma is investigated. The nonlinearity of the plasma comes from
two aspects: The nonlinear wave-wave interaction and self-interaction of color
field. The non-Abelian color permittivity is obtained by expanding the kinetic
equations to third order. As an application, the nonlinear Landau damping rate
and the nonlinear eigenfrequency shift are calculated in the longwave length
limit.Comment: 12 pages(Revtex), no figure
Big-bang nucleosynthesis with a long-lived charged massive particle including He spallation processes
We propose helium-4 spallation processes induced by long-lived stau in
supersymmetric standard models, and investigate an impact of the processes on
light elements abundances. We show that, as long as the phase space of helium-4
spallation processes is open, they are more important than stau-catalyzed
fusion and hence constrain the stau property.Comment: 12 pages, 4 figures, 1 table, references added, all figures correcte
Real Space Imaging of Spin Polarons in Zn Doped SrCu2(BO3)2
We report on the real space profile of spin polarons in the quasi
two-dimensional frustrated dimer spin system SrCu2(BO3)2 doped with 0.16% of
Zn. The 11B nuclear magnetic resonance spectrum exhibits 15 additional boron
sites near non-magnetic Zn impurities. With the help of exact diagonalizations
of finite clusters, we have deduced from the boron spectrum the distribution of
local magnetizations at the Cu sites with fine spatial resolution, providing
direct evidence for an extended spin polaron. The results are confronted with
those of other experiments performed on doped and undoped samples of
SrCu2(BO3)2.Comment: 9 pages, 11 figures, including supplemental materials. accepted for
publication in PR
Investigation of passive flow control techniques to enhance the stall characteristics of a microlight aircraft
This report investigates the enhancement of aerodynamic stall characteristics of a Skyranger microlight aircraft by the use of passive flow control techniques, namely vortex generators and turbulators. Each flow control device is designed and scaled to application conditions. Force balance measurements and surface oil flow visualisation are carried out on a half-model of the microlight to further investigate the nature of the flow on the aircraft with and without the flow control devices. The results indicate a clear advantage to the use of turbulators compared with vortex generators. Turbulators increased the maximum lift coefficient by 2.8%, delayed the onset of stall by increasing the critical angle by 17.6% and reduced the drag penalty at both lower (pre-stall) and higher angles of attack by 8% compared to vortex generators. With vortex generators applied, the results indicated a delayed stall with an increase in the critical angle by 2% and a reduced drag penalty at higher angles of attack
Quantitative assessment of people-oriented forestry in Bangladesh: A case study in the Tangail forest division
ArticleJOURNAL OF ENVIRONMENTAL MANAGEMENT. 88(1): 83-92 (2008)journal articl
Avoiding zero probability events when computing Value at Risk contributions
This paper is concerned with the process of risk allocation for a generic
multivariate model when the risk measure is chosen as the Value-at-Risk (VaR).
We recast the traditional Euler contributions from an expectation conditional
on an event of zero probability to a ratio involving conditional expectations
whose conditioning events have stricktly positive probability. We derive an
analytical form of the proposed representation of VaR contributions for various
parametric models. Our numerical experiments show that the estimator using this
novel representation outperforms the standard Monte Carlo estimator in terms of
bias and variance. Moreover, unlike the existing estimators, the proposed
estimator is free from hyperparameters
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