209 research outputs found
Intermediate (S=1) spin state in five-coordinate cobalt(III): Magnetic properties of N-o-hydroxy-benzamido-meso-tetraphenylporphyrin cobalt(III), Co(N-NCO(o-O)C6H4-tpp)
The crystal structures of paramagnetic N-o-oxido-benzimido-meso-tetraphenylporphyrinato (-kappa(4),N-1,N-2,N-3,N-5,kappa O-2) cobalt(III) [Co(N-NCO(o-O)C6H4-tpp); 2] (S = 1) and diamagnetic N-o-oxido-benzimido-meso-tetraphenylporphyrinato (-kappa(4), N-1, N-2, N-3, N-5, kappa O-2) gallium( III) chloroform center dot methanol solvate [Ga(N-NCO(o-O)C6H4-tpp)center dot 0.5CHCl(3)center dot MeOH; 3 center dot 0.5CHCl(3) center dot MeOH] (S = 0) were determined. The coordination sphere around Co(III) in 2 [or Ga(III) in 3 center dot 0.5CHCl(3)center dot MeOH] is described as five-coordinate distorted trigonal bipyramid (DTBP) with O(1), N(1)and N(3) [or O(2), N(1), N(3)] lying in the equatorial plane for 2 [or 3 center dot 0.5CHCl(3)center dot MeOH]. The magnitude of axial (D) zero-field splitting (ZFS) for the Co(III) (S = 1) in 2 was determined as approximately 107 cm(-1) by paramagnetic susceptibility measurements. The compound (2) reacts in donor solvent such as pyridine to form six-coordinate diamagnetic species of the type Co(N-NCO(o-O) C6H4-tpp)(py) (4), whose H-1 NMR spectra can be interpreted as for Co(III) in an octahedral environment
Obstructions to the Existence of Sasaki-Einstein Metrics
We describe two simple obstructions to the existence of Ricci-flat Kahler
cone metrics on isolated Gorenstein singularities or, equivalently, to the
existence of Sasaki-Einstein metrics on the links of these singularities. In
particular, this also leads to new obstructions for Kahler-Einstein metrics on
Fano orbifolds. We present several families of hypersurface singularities that
are obstructed, including 3-fold and 4-fold singularities of ADE type that have
been studied previously in the physics literature. We show that the AdS/CFT
dual of one obstruction is that the R-charge of a gauge invariant chiral
primary operator violates the unitarity bound.Comment: 35 pages, 1 figure; references and a footnote adde
Crystal structure and two-stage hydrolysis of dimethoxo(meso-tetra(4-methoxyphenylporphyrinato))tin(IV), Sn(tmpp)(OMe)(2)
In this work, we determine the crystal structure of dimethoxo(meso-tetra(4-methoxyphenylporphyrinato))tin(IV), Sn(tmpp)(OMe)(2) (1). Experimental results indicate that the tin atom has an octahedral geometry. The geometry around the tin center has Sn(1)-O(5) = 2.020(6), Sn(1)-O(6) = 2.003(7) Angstrom and an average Sn(1)-N = 2.10(1) Angstrom. The two methoxo groups are unidentately coordinated to the tin(IV) atom. Two-stage hydrolysis of Sn(tmpp)(OMe)(2) in CDCl3 was observed by H-1 and C-13 NMR spectroscopy. Compound (1) crystallizes in the space group P2(1)/n with a = 14.7492(1), b = 19.2022(3), c = 16.0806(2) Angstrom, beta = 94.104(1)degrees and Z = 4
The PHENIX Experiment at RHIC
The physics emphases of the PHENIX collaboration and the design and current
status of the PHENIX detector are discussed. The plan of the collaboration for
making the most effective use of the available luminosity in the first years of
RHIC operation is also presented.Comment: 5 pages, 1 figure. Further details of the PHENIX physics program
available at http://www.rhic.bnl.gov/phenix
Measurement of the W+W-gamma Cross Section and Direct Limits on Anomalous Quartic Gauge Boson Couplings at LEP
The process e+e- -> W+W-gamma is analysed using the data collected with the
L3 detector at LEP at a centre-of-mass energy of 188.6GeV, corresponding to an
integrated luminosity of 176.8pb^-1. Based on a sample of 42 selected W+W-
candidates containing an isolated hard photon, the W+W-gamma cross section,
defined within phase-space cuts, is measured to be: sigma_WWgamma = 290 +/- 80
+/- 16 fb, consistent with the Standard Model expectation. Including the
process e+e- -> nu nu gamma gamma, limits are derived on anomalous
contributions to the Standard Model quartic vertices W+W- gamma gamma and W+W-Z
gamma at 95% CL: -0.043 GeV^-2 < a_0/Lambda^2 < 0.043 GeV^-2 0.08 GeV^-2 <
a_c/Lambda^2 < 0.13 GeV^-2 0.41 GeV^-2 < a_n/Lambda^2 < 0.37 GeV^-2
Production of Single W Bosons at \sqrt{s}=189 GeV and Measurement of WWgamma Gauge Couplings
Single W boson production in electron-positron collisions is studied with the
L3 detector at LEP. The data sample collected at a centre-of-mass energy of
\sqrt{s} = 188.7GeV corresponds to an integrated luminosity of 176.4pb^-1.
Events with a single energetic lepton or two acoplanar hadronic jets are
selected. Within phase-space cuts, the total cross-section is measured to be
0.53 +/- 0.12 +/- 0.03 pb, consistent with the Standard Model expectation.
Including our single W boson results obtained at lower \sqrt{s}, the WWgamma
gauge couplings kappa_gamma and lambda_gamma are determined to be kappa_gamma =
0.93 +/- 0.16 +/- 0.09 and lambda_gamma = -0.31 +0.68 -0.19 +/- 0.13
Search for an invisibly decaying Higgs boson in e^+e^- collisions at \sqrt{s} = 183 - 189 GeV
A search for a Higgs boson decaying into invisible particles is performed
using the data collected at LEP by the L3 experiment at centre-of-mass energies
of 183 GeV and 189 GeV. The integrated luminosities are respectively 55.3 pb^-1
and 176.4 pb^-1. The observed candidates are consistent with the expectations
from Standard Model processes. In the hypothesis that the production cross
section of this Higgs boson equals the Standard Model one and the branching
ratio into invisible particles is 100%, a lower mass limit of 89.2 GeV is set
at 95% confidence level
Search for Neutral Higgs Bosons of the Minimal Supersymmetric Standard Model in e+e- Interactions at \sqrt{s} = 189 GeV
A search for the lightest neutral scalar and neutral pseudoscalar Higgs
bosons in the Minimal Supersymmetric Standard Model is performed using 176.4
pb^-1 of integrated luminosity collected by L3 at a center-of-mass energy of
189 GeV. No signal is observed, and the data are consistent with the expected
Standard Model background. Lower limits on the masses of the lightest neutral
scalar and pseudoscalar Higgs bosons are given as a function of tan(beta).
Lower mass limits for tan(beta)>1 are set at the 95% confidence level to be m_h
> 77.1 GeV and m_A > 77.1 GeV
Measurement of Bose-Einstein Correlations in e+e- -> W+W- at root(s)=189GeV
We investigate Bose-Einstein correlations (BEC) in W-pair production at
root(s)=189GeV using the L3 detector at LEP. We observe BEC between particles
from a single W decay in good agreement with those from a light-quark Z decay
sample. We investigate their possible existence between particles coming from
different W's. No evidence for such inter-W BEC is found
Measurement of the Lifetime of the Tau Lepton
The tau lepton lifetime is measured with the L3 detector at LEP using the
complete data taken at centre-of-mass energies around the Z pole resulting in
tau_tau = 293.2 +/- 2.0 (stat) +/- 1.5 (syst) fs. The comparison of this result
with the muon lifetime supports lepton universality of the weak charged current
at the level of six per mille. Assuming lepton universality, the value of the
strong coupling constant, alpha_s is found to be alpha_s(m_tau^2) = 0.319 +/-
0.015(exp.) +/- 0.014 (theory)
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