225 research outputs found
Women in modern economic society: demographic and geographic images and realities
With the approach of the Fourth World Conference on Women
in Beijing, it is appropriate for scholars to reflect on the status of
women in modern society, on the changes that ha ve occurred in
that status, and on the plans for future changes
Sterically restricted tin phosphines, stabilized by weak intramolecular donor-acceptor interactions
Funding: Engineering and Physical Sciences Research Council (EPSRC)Four related sterically restricted pen-substituted acenaphthenes have been prepared containing mixed tin phosphorus moieties in the proximal 5,6-positions (Acenap[SnR3][(PPr2)-Pr-i]; Acenap = acenaphthene-5,6-diyl; R-3 = Ph-3 (1), Ph2Cl (2), Me2Cl (3), Bu2Cl (4)). The degree of intramolecular P-Sn bonding within the series was investigated by X-ray crystallography, solution and solid-state NMR spectroscopy, and density functional theory (DFT/B3LYP/SBKJC/PCM) calculations. All members of the series adopt a conformation such that the phosphorus lone pair is located directly opposite the tin center, promoting an intramolecular donor acceptor P -> Sn type interaction. The extent of covalent bonding between Sn and P is found to be much greater in triorganotin chlorides 2-4 in comparison with the triphenyl derivative 1. Coordination of a highly electronegative chlorine atom naturally increases the Lewis acidity of the tin center, enhancing the Ip(P)-sigma*(Sn-Y) donor acceptor 3c-4e type interaction, as indicated by conspicuously short Sn-P peri distances and significant (1)J(P-31,Sn-119) spin spin coupling constants (SSCCs) in the range 740-754 Hz. Evidence supporting the presence of this interaction was also found in solid-state NMR spectra of some of the compounds which exhibit an indirect spin spin coupling on the same order of magnitude as observed in solution. DFT calculations confirm the increased covalent bonding between P and Sn in 2-4, with notable WBIs of ca. 0.35 obtained, in comparison to 0.1 in 1.PostprintPeer reviewe
Nota del curatore
The authors thank EPSRC and NSERC (Canada) for financial support.Reactions of the dianion [Te(tBuN)P(Îź-NtBu)2P(NtBu)Te]2â with I2 or [Cp*RhCl2]2 unexpectedly produced complexes of the novel spirocyclic Te5 dianion [{tBuN(Te)P(Îź-NtBu)2P(Te)NtBu}2Îź-Te]2â, which is N,Nâ˛-coordinated to two Na+ ions in the disodium derivative and adopts a Te,Teâ˛,Teâ˛â˛-bonding mode in the Cp*Rh complex.PostprintPeer reviewe
Toward Unbiased Galaxy Cluster Masses from Line of Sight Velocity Dispersions
We study the use of red sequence selected galaxy spectroscopy for unbiased
estimation of galaxy cluster masses. We use the publicly available galaxy
catalog produced using the semi-analytic model of De Lucia & Blaizot (2007) on
the Millenium Simulation (Springel et al. 2005). We explore the impacts on
selection using galaxy color, projected separation from the cluster center, and
galaxy luminosity. We study the relationship between cluster mass and velocity
dispersion and identify and characterize the following sources of bias and
scatter: halo triaxiality, dynamical friction of red luminous galaxies and
interlopers. We show that due to halo triaxiality the intrinsic scatter of
estimated line of sight dynamical mass is about three times larger (30-40%)
than the one estimated using the 3D velocity dispersion (~12%) and a small bias
(~1%) is induced. We find evidence of increasing scatter as a function of
redshift and provide a fitting formula to account for it. We characterize the
amount of bias and scatter introduced by dynamical friction when using
subsamples of red-luminous galaxies to estimate the velocity dispersion. We
study the presence of interlopers in spectroscopic samples and their effect on
the estimated cluster dynamical mass. Our results show that while cluster
velocity dispersions extracted from a few dozen red sequence selected galaxies
do not provide precise masses on a single cluster basis, an ensemble of cluster
velocity dispersions can be combined to produce a precise calibration of a
cluster survey mass observable relation. Currently, disagreements in the
literature on simulated subhalo velocity dispersion mass relations place a
systematic floor on velocity dispersion mass calibration at the 15% level in
mass. We show that the selection related uncertainties are small by comparison,
providing hope that with further improvements this systematic floor can be
reduced.Comment: submitted to Ap
Synthesis and characterization of novel organic heteroatom compounds from reaction of Woollinsâ Reagent with various organic substrates
A series of new selenium-containing heteroatom compounds were synthesized in good yields by the reactions of Woollinsâ reagent with various organic substrates such as cyclohexanamine, N-benzoylbenzamide, benzoic anhydride, 4-fluoro-N-(2-oxo-2-phenylethyl)benzamide, N-benzoylbenzamide, benzoic anhydride, 3-(bromomethyl)benzonitrile, 1,2-diphenylethane-1,2-diol and sodium alcoholate. Three representative X-ray structures are described.PostprintPostprintPeer reviewe
Anatomical relations of the superficial sensory branches of the radial nerve: a cadaveric study with clinical implications
Explicit Computation of Input Weights in Extreme Learning Machines
We present a closed form expression for initializing the input weights in a
multi-layer perceptron, which can be used as the first step in synthesis of an
Extreme Learning Ma-chine. The expression is based on the standard function for
a separating hyperplane as computed in multilayer perceptrons and linear
Support Vector Machines; that is, as a linear combination of input data
samples. In the absence of supervised training for the input weights, random
linear combinations of training data samples are used to project the input data
to a higher dimensional hidden layer. The hidden layer weights are solved in
the standard ELM fashion by computing the pseudoinverse of the hidden layer
outputs and multiplying by the desired output values. All weights for this
method can be computed in a single pass, and the resulting networks are more
accurate and more consistent on some standard problems than regular ELM
networks of the same size.Comment: In submission for the ELM 2014 Conferenc
Spirocyclic, macrocyclic and ladder complexes of coinage metals and mercury with dichalcogeno P2N2-supported anions
Financial support from the EPSRC and NSERC (Canada) is acknowledged.Metathetical reactions of alkaliâmetal derivatives of the dianion [tBuN(Se)P(Îź-NtBu)2P(Se)NtBu]2â (2Se2â) with Ag(NHC)Cl, Ag[BF4], AuCl(THT) and HgCl2, as well as the reaction of 2S2â with AuCl(THT) were investigated. The observed products all incorporate the monoprotonated ligands 2SeHâ or 2SHâ in a variety of structural arrangements around the metal centres, including tetrameric and trimeric macrocycles [Ag and Au (E = Se)], a ladder (Au, E = S) and a spirocycle (Hg); the ladder contains both the dianion 2S2â and the monoanion 2SHâ as ligands linking three Au2 units. All complexes have been characterised in the solid state by single crystal X-ray analyses and in solution by multinuclear (1H, 31P and 77Se) NMR spectra.PostprintPeer reviewe
Gravitational Flexion by Elliptical Dark Matter Haloes
We present equations for the gravitational lensing flexion expected for an
elliptical lens mass distribution. These can be reduced to one-dimensional
finite integrals, thus saving significant computing time over a full
two-dimensional calculation. We estimate constraints on galaxy halo
ellipticities for a range of potential future surveys, finding that the
constraints from the two different types of flexion are comparable and are up
to two orders of magnitude tighter than those from shear. Flexion therefore
appears to be a very promising potential tool for constraining the shapes of
galaxy haloes from future surveys.Comment: 7 pages, 5 figures, submitted to MNRA
Sterically encumbered tin and phosphorus peri-substituted acenaphthenes
The work in this project was supported by the Engineering and Physical Sciences Research Council (EPSRC), EaStCHEM and the University of St Andrews.A group of sterically encumbered peri-substituted acenaphthenes have been prepared, containing tin moieties at the 5,6-positions in 1 â 3 ([Acenap(SnR3)2], Acenap = acenaphthene-5,6-diyl; R3 = Ph3 ( 1 ), Me3 ( 2 ); [(Acenap)2(SnMe2)2] ( 3 )) and phosphorus functional groups at the proximal peri-positions in 4 and 5 ([Acenap(PR2)(PiPr2)] R2 = Ph2 ( 4 ), Ph(iPr) ( 5 )). Bis(stannane) structures 1 â 3 are dominated by repulsive interactions between the bulky tin groups, leading to peri-distances approaching the sum of van der Waals radii. Conversely, the quasi-linear CPh-P¡¡¡P three-body fragments found in bis(phosphine) 4 suggest the presence of a lp(P)âĎ*(PâC) donorâacceptor 3c-4e type interaction, supported by a notably short intramolecular P¡¡¡P distance and notably large JPP through-space coupling (180 Hz). Severely strained bis(sulfides) 4-S and 5-S , experiencing pronounced in-plane and out-of-plane displacements of the exocyclic peri-bonds, have also been isolated following treatment of 4 and 5 with sulfur. The resulting nonbonded intramolecular P¡¡¡P distances, âź4.05 Ă
and âź12% longer than twice the van der Waals radii of P (3.60 Ă
), are among the largest ever reported peri-separations, independent of the heteroatoms involved, and comparable to the distance found in 1 containing the larger Sn atoms (4.07 Ă
). In addition we report two metal complexes with square planar [( 4 )PtCl2] ( 4-Pt ) and octahedral cis-[( 4 )Mo(CO)4] ( 4-Mo ) geometries. In both complexes the bis(phosphine) backbone is distorted, but notably less so than in bis(sulfide) 4-S . All compounds were fully characterized, and except for bis(phosphine) 5 , crystal structures were determined.PostprintPostprintPeer reviewe
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