632 research outputs found
Energy dependence of the freeze out eccentricity from the azimuthal dependence of HBT at STAR
Non-central heavy ion collisions create an out-of-plane-extended participant
zone that expands toward a more round state as the system evolves. The recent
RHIC Beam Energy Scan at sqrt{s_{NN}} of 7.7, 11.5, and 39 GeV provide an
opportunity to explore the energy dependence of the freeze out eccentricity.
The new low energy data from STAR complements high statistics data sets at
sqrt{s_{NN}} of 62.4 and 200 GeV. Hanbury-Brown-Twiss (HBT) interferometry
allows to determine the size of pion emitting source regions. The dependence of
the HBT radius parameters on azimuthal angle relative to the reaction plane
have been extracted. These dependencies can be related to the freeze out
eccentricity. The new results from STAR are consistent with a monotonically
decreasing freeze out eccentricity and constrain any minimum, suggested by
previously available data, to lie in the range between 11.5 and 39 GeV. Of
several models UrQMD appears to best predict the STAR and AGS data.Comment: 4 pages, 2 figures, Proceedings for the XXII International Conference
on Ultra-relativistic Nucleus-Nucleus Collisions (Quark Matter 2011), 22-28
May 2011, Annecy, Franc
The Morphology of Reionization in a Dynamically Clumpy Universe
A recent measurement of the Lyman-limit mean free path at suggests it
may have been very short, motivating a better understanding of the role that
ionizing photon sinks played in the reionization process. Accurately modeling
the sinks in reionization simulations is challenging because of the large
dynamic range required if gas structures on scales
contributed significant opacity. As a result, there is no consensus on how
important the sinks were in shaping reionization's morphology and its
observables. We address this question with a recently developed radiative
transfer code that includes a dynamical sub-grid model for the sinks based on
radiative hydrodynamics simulations. Compared to assuming a fully
pressure-smoothed IGM, our dynamical treatment reduces the predicted sizes of
ionized bubbles by under typical assumptions about reionization's
sources. Near the midpoint of reionization, the 21 cm power at
Mpc is reduced by a similar factor. These effects are more modest
than the power suppression resulting from the much higher
recombination rate in models that neglect pressure smoothing entirely. Whether
the sinks played a significant role in reionization's morphology depends on the
nature of its sources. For example, if reionization was driven by bright
() galaxies, the sinks reduce the large-scale 21 cm power by
at most , even if pressure smoothing is neglected. Conveniently, when
bright sources contribute significantly, the morphology in our dynamical
treatment can be reproduced to high accuracy with a uniform sub-grid clumping
factor that yields the same ionizing photon budget. By contrast, if galaxies drove reionization, an accurate model of the sinks' dynamics
is more important, with the uniform clumping model erring at the level.Comment: 17 pages, 12 figures, prepared for submission to MNRAS. Comments
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Synthesis and Supramolecular Structure of a (5-(3-(1H-tetrazol-5-yl)phenyl)-1H-tetrazole) Cobalt Complex
The reaction of CoCl2·6H2O with m-BDTH2 (1,3-benzeneditetrazol-5-yl) leads to [Co(C8H6N8)2(H2O)2(CH3CN)2]Cl2 (1). Both tetrazolic groups remain protonated existing in a 1H tautomeric form. A trifurcated chlorine atom and stacking interactions assemble compound 1 into a three-dimensional network
A nickel(II) complex with an unsymmetrical tetradentate chelating ligand derived from pyridine-2,6-dicarbaldehyde and 2-aminothiophenol
[(2-{[6-(1,3-BenzoÂthiaÂzol-2-yl)pyridin-2-yl]carbonylÂazaÂnidÂyl}phenÂyl)sulfÂanido]nickel(II), [Ni(CHNOS)], crystallizes in the centrosymmetric monoclinic space group with one molÂecule in the asymmetric unit. The expected ligand, a bis-Schiff base derived from pyridine-2,6-dicarbaldehyde and 2-aminoÂthioÂphenol, had modified in situ in a both unexpected and unsymmetrical fashion. One arm had cyclized to form a benzo[]thiaÂzol-2-yl functionality, while the imine linkage of the second arm had oxidized to an amide group. The geometry about the central Ni atom is distorted square-planar NS. The molÂecules form supraÂmolecular face-to-face dimers via rather strong ÏâÏ stacking interÂactions, with these dimers then linked into chains via pairwise CâHO interÂactions
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An undecanuclear ferrimagnetic Cu9Dy2 SMM achieved through ligand fine-tuning
We describe the concept of increasing the nuclearity of a previously reported high-spin Cu5Gd2 core using a âfine tuningâ ligand approach. Thus two Cu9Ln2 coordination clusters, with Ln = Dy (1), Gd(2) were synthesized with the Gd compound having a ground spin state of 17/2 and the Dy analogue showing SMM behavior in zero field
Synthesis of N-(2,4-dinitrophenyl) derivatives of D-ribosylamines; unexpected reaction and hydrolysis products
Reaction of 2,3-O-isopropylidene-d-ribofuranosylamine with 2,4-dinitrofluorobenzene afforded the crystalline 2,3-O-isopropylidene-N-(2,4-dinitrophenyl)-ÎČ-d-ribofuranosylamine (3) and a 1:1 crystalline complex of 2,3-O-isopropylidene-N-(2,4-dinitrophenyl-α-d-ribofuranosylamine and 2,3-O-isopropylidene-ÎČ-d-ribofuranose; controlled acidic hydrolysis of 3 afforded N-(2,4-dinitrophenyl-α-d-ribopyranosylamine and not the expected ÎČ-d-furanosylamine derivative. The structures of the new compounds were confirmed by NMR spectroscopy and X-ray crystallography
Tetranuclear CuII2DyIII2 coordination cluster as Suzuki (CâC) coupling reaction promoter
The air stable and high yielding tetranuclear coordination cluster [CuII2DyIII2L4(NO3)2(CH3CN)2]·2(CH3CN) promotes the Suzuki coupling reaction of phenylboronic acid with substituted aryl halides in environmentally benign conditions
Synthesis, structure and electrochemical characterization of the isopolytungstate (W4O16) held by MnII anchors within a superlacunary crown heteropolyanion {P8W48}
An isopolyanion {W4O16} within archetypal {P8W48} heteropolyanion assembly [(P8W48O184)(W4O16)K10Li4Mn10Na(H2O)50Cl2] 15- (Mn10W4-P8W48) has been synthesized by the reaction of the cyclic superlacunary anion [H7P8W48O184] 33â and Mn(ClO4)2.6H2O in I M LiCl soultion medium at pH 8. The isolated compound has been characterized by single crystal X-ray crystallography, powder X-ray diffraction (PXRD), Fourier-transform infrared (FTIR) spectroscopy, elemental analysis and thermogravimetric analysis. Electrochemical studies were also performed on Mn10W4-P8W48 confirmed the presence of Mn centres bonded to the tunsgtic framework. The novel polyanion [(P8W48O184)(W4O16)K10Li4Mn10Na(H2O)50Cl2] 15- is the first example of macrocyclic complex where an isopolyanion (W4O16) 8- is embedded within in the inner cavity of the {P8W48} and is placed in position by six MnII cations as anchors. Whereas, the exocyclic coordination of the four MnII atoms to {P8W48} yields extended structure by linking neighbouring polyanions through {WâOâMnâOâW} bridges. Further, the polyanion Mn10W4-P8W48 is the first derivative of {P8W48} with six MnII ions (largest) coordinated to the inner side the crown ring as anchors
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Systematic studies of hexanuclear {MIII4LnIII2} complexes (M = Fe, Ga; Ln = Er, Ho): structures, magnetic properties and SMM behavior
Four isostructural MIII4LnIII2 coordination clusters, [M4Ln2(ÎŒ3-OH)2(nbdea)4(C6H5COO)8]âąMeCN (M = Fe, Ln = Er (1); M = Ga, Ln = Er (2); M = Fe, Ln = Ho (3); M = Ga, Ln = Ho (4)) have been synthesized and characterized. Single-crystal X-ray diffraction and X-ray powder diffraction studies revealed that all four compounds crystallize isomorphously to each other, and to the previously reported MIII4DyIII2 (M = Fe or Ga) and FeIII4YIII2 analogues. DC magnetic susceptibility measurements for compounds 1-4, taken in combination with those for the FeIII4YIII2 analogue, indicated that the interactions between ErIII ions are weakly ferromagnetic and the FeIII-ErIII interactions are very weakly antiferromagnetic, while the HoIII-HoIII and FeIII-HoIII interactions are both negligible. By comparison, for the FeIII4DyIII2 analogue, the DyIII-DyIII interactions are antiferromagnetic while the FeIII-DyIII are ferromagnetic. Both Er analogues 1 and 2 display single-molecule magnet (SMM) behavior with the effective energy barrier Ueff increasing from 12.8 K (for Fe4Er2 1) to 53.5 K (for Ga4Er2 2), indicating that the very weak 3d-4f interaction enhances the QTM effect
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