507 research outputs found
Facile access to functionalized chiral secondary benzylic boronic esters via catalytic asymmetric hydroboration
Allylic and homoallylic phosphonates bearing an aryl or heteroaryl substituent at the γ- or δ-position undergo rhodium-catalyzed asymmetric hydroboration by pinacolborane to give functionalized chiral secondary benzylic boronic esters in yields up to 86% and enantiomer ratios up to 99 : 1. Compared to minimally-functionalized terminal and 1,1-disubstituted vinyl arenes, there are relatively few reports of efficient catalytic asymmetric hydroboration (CAHB) of more highly functionalized internal alkenes. Phosphonate substrates bearing a variety of common heterocyclic ring systems, including furan, indole, pyrrole and thiophene derivatives, as well as those bearing basic nitrogen substituents (e.g., morpholine and pyrazine) are tolerated, although donor substituents positioned in close proximity of the alkene can influence the course of the reaction. Stereoisomeric (E)- and (Z)-substrates afford the same major enantiomer of the borated product. Deuterium-labelling studies reveal that rapid (Z)- to (E)-alkene isomerization accounts for the observed (E/Z)-stereoconvergence during CAHB. The synthetic utility of the chiral boronic ester products is illustrated by stereospecific C–B bond transformations including stereoretentive electrophile promoted 1,2-B-to-C migrations, stereoinvertive SE2 reactions of boron-ate complexes with electrophiles, and stereoretentive palladium- and rhodium-catalyzed cross-coupling protocols
High photon energy spectroscopy of NiO: experiment and theory
We have revisited the valence band electronic structure of NiO by means of
hard x-ray photoemission spectroscopy (HAXPES) together with theoretical
calculations using both the GW method and the local density approximation +
dynamical mean-field theory (LDA+DMFT) approaches. The effective impurity
problem in DMFT is solved through the exact diagonalization (ED) method. We
show that the LDA+DMFT method alone cannot explain all the observed structures
in the HAXPES spectra. GW corrections are required for the O bands and Ni-s and
p derived states to properly position their binding energies. Our results
establish that a combination of the GW and DMFT methods is necessary for
correctly describing the electronic structure of NiO in a proper ab-initio
framework. We also demonstrate that the inclusion of photoionization cross
section is crucial to interpret the HAXPES spectra of NiO.We argue that our
conclusions are general and that the here suggested approach is appropriate for
any complex transition metal oxide.Comment: 16 pages, 5 figure
Influence of some added electrolytes on the surface and thermodynamic properties of cetylpyridinium chloride in aqueous medium
561-568The effect of some added electrolytes, viz. NaCl, CaCl2 and AlCl3, on the critical micelle concentration (CMC), maximum surface excess concentration (Gmax) and minimum area per molecule (Amin) at air-liquid interface of a cationic surfactant cetylpyridinium chloride (CPC) in aqueous solutions have been studied at 288.15, 293.15 and 298.15 K using tensiometric method. The effect of an added electrolyte on decreasing CMC of CPC is found to be in the order (AlCl3) > (CaCl2) > (NaCl), which falls in the same order as of the moles chloride ions furnished by each mole of the added electrolyte. The Gmax decreases with increasing temperature and electrolyte concentration leading to an enhanced available area per molecule at the air-liquid interface. The process of micellization and adsorption of CPC at air-liquid interface are both favoured by exothermic enthalpy change as well as entropy gain. The observed features such as lowering of CMC, higher thermodynamic micellar stability, more relaxed surfactant molecules at the interface, due to an added electrolyte, may be exploited for improving the efficiency of the surfactant as a detergent, solubilizing agent, froth floatation process for concentrating ores, petroleum oil recovery and oil spill management
Influence of some added electrolytes on the surface and thermodynamic propertiesof cetylpyridinium chloride in aqueous medium
The effect of some added electrolytes, viz. NaCl, CaCl2 and AlCl3, on the critical micelle concentration (CMC),maximum surface excess concentration (Γmax) and minimum area per molecule (Amin) at air-liquid interface of a cationicsurfactant cetylpyridinium chloride (CPC) in aqueous solutions have been studied at 288.15, 293.15 and 298.15 K usingtensiometric method. The effect of an added electrolyte on decreasing CMC of CPC is found to be in the order (AlCl3) >(CaCl2) > (NaCl), which falls in the same order as of the moles chloride ions furnished by each mole of the addedelectrolyte. The Γmax decreases with increasing temperature and electrolyte concentration leading to an enhanced availablearea per molecule at the air-liquid interface. The process of micellization and adsorption of CPC at air-liquid interface areboth favoured by exothermic enthalpy change as well as entropy gain. The observed features such as lowering of CMC,higher thermodynamic micellar stability, more relaxed surfactant molecules at the interface, due to an added electrolyte,may be exploited for improving the efficiency of the surfactant as a detergent, solubilizing agent, froth floatation process forconcentrating ores, petroleum oil recovery and oil spill management
The Gribov-Zwanziger action in the presence of the gauge invariant, nonlocal mass operator in the Landau gauge
We prove that the nonlocal gauge invariant mass dimension two operator
can be consistently added to the
Gribov-Zwanziger action, which implements the restriction of the path
integral's domain of integration to the first Gribov region when the Landau
gauge is considered. We identify a local polynomial action and prove the
renormalizability to all orders of perturbation theory by employing the
algebraic renormalization formalism. Furthermore, we also pay attention to the
breaking of the BRST invariance, and to the consequences that this has for the
Slavnov-Taylor identity.Comment: 30 page
Gridded and direct Epoch of Reionisation bispectrum estimates using the Murchison Widefield Array
We apply two methods to estimate the 21~cm bispectrum from data taken within
the Epoch of Reionisation (EoR) project of the Murchison Widefield Array (MWA).
Using data acquired with the Phase II compact array allows a direct bispectrum
estimate to be undertaken on the multiple redundantly-spaced triangles of
antenna tiles, as well as an estimate based on data gridded to the -plane.
The direct and gridded bispectrum estimators are applied to 21 hours of
high-band (167--197~MHz; =6.2--7.5) data from the 2016 and 2017 observing
seasons. Analytic predictions for the bispectrum bias and variance for point
source foregrounds are derived. We compare the output of these approaches, the
foreground contribution to the signal, and future prospects for measuring the
bispectra with redundant and non-redundant arrays. We find that some triangle
configurations yield bispectrum estimates that are consistent with the expected
noise level after 10 hours, while equilateral configurations are strongly
foreground-dominated. Careful choice of triangle configurations may be made to
reduce foreground bias that hinders power spectrum estimators, and the 21~cm
bispectrum may be accessible in less time than the 21~cm power spectrum for
some wave modes, with detections in hundreds of hours.Comment: 19 pages, 10 figures, accepted for publication in PAS
The Infrared Behaviour of the Pure Yang-Mills Green Functions
We review the infrared properties of the pure Yang-Mills correlators and
discuss recent results concerning the two classes of low-momentum solutions for
them reported in literature; i.e. decoupling and scaling solutions. We will
mainly focuss on the Landau gauge and pay special attention to the results
inferred from the analysis of the Dyson-Schwinger equations of the theory and
from "{\it quenched}" lattice QCD. The results obtained from properly
interplaying both approaches are strongly emphasized.Comment: Final version to be published in FBS (54 pgs., 11 figs., 4 tabs
A Microbe Associated with Sleep Revealed by a Novel Systems Genetic Analysis of the Microbiome in Collaborative Cross Mice.
The microbiome influences health and disease through complex networks of host genetics, genomics, microbes, and environment. Identifying the mechanisms of these interactions has remained challenging. Systems genetics in laboratory mice (Mus musculus) enables data-driven discovery of biological network components and mechanisms of host-microbial interactions underlying disease phenotypes. To examine the interplay among the whole host genome, transcriptome, and microbiome, we mapped QTL and correlated the abundance of cecal messenger RNA, luminal microflora, physiology, and behavior in a highly diverse Collaborative Cross breeding population. One such relationship, regulated by a variant on chromosome 7, was the association of Odoribacter (Bacteroidales) abundance and sleep phenotypes. In a test of this association in the BKS.Cg-Dock7m +/+ Leprdb/J mouse model of obesity and diabetes, known to have abnormal sleep and colonization by Odoribacter, treatment with antibiotics altered sleep in a genotype-dependent fashion. The many other relationships extracted from this study can be used to interrogate other diseases, microbes, and mechanisms
Population Preference of Net Texture prior to Bed Net Trial in Kala-Azar–Endemic Areas
Prior to a community-based efficacy trial of long-lasting insecticidal nets (LLINs) in the prevention of visceral leishmaniasis (VL; also called kala-azar), a pilot study on preference of tools was held in endemic areas of India and Nepal in September 2005
Time-independant stochastic quantization, DS equations, and infrared critical exponents in QCD
We derive the equations of time-independent stochastic quantization, without
reference to an unphysical 5th time, from the principle of gauge equivalence.
It asserts that probability distributions that give the same expectation
values for gauge-invariant observables are physically
indistiguishable. This method escapes the Gribov critique. We derive an exact
system of equations that closely resembles the Dyson-Schwinger equations of
Faddeev-Popov theory, which we then solve non-perturbatively for the critical
exponents that characterize the asymptotic form at of the
tranverse and longitudinal parts of the gluon propagator in Landau gauge, D^T
\sim (k^2)^{-1-\a_T} and D^L \sim a (k^2)^{-1-\a_L}, and obtain \a_T = -
2\a_L \approx - 1.043 (short range), and \a_L \approx 0.521, (long range).
Although the longitudinal part vanishes with the gauge parameter in the
Landau gauge limit, , there are vertices of order , so the
longitudinal part of the gluon propagator contributes in internal lines,
replacing the ghost that occurs in Faddeev-Popov theory. We compare our results
with the corresponding results in Faddeev-Popov theory.Comment: 50 pages, 2 figure
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