4,109 research outputs found
Synthesis and crystal structure of the first 6a-thiathiophthen metal complex [Mo(CO)_5PPh_(2]2)(Β΅-C_5H_2S_3)
The first 6a-thiathiophthen metal complex was prepared by treating M(CO_)5[PPh_2CS_2CH_2Cβ‘CH] with a catalytic amount of secondary amine or tertiary amine; the structure of the 6a-thiathiophthen molybdenum complex is confirmed by an X-ray diffraction analysis
QCD radiative correction to color-octet inclusive production at B Factories
In nonrelativistic Quantum Chromodynamics (NRQCD), we study the
next-to-leading order (NLO) QCD radiative correction to the color-octet
inclusive production at B Factories. Compared with the leading-order
(LO) result, the NLO QCD corrections are found to enhance the short-distance
coefficients in the color-octet production by a factor of about 1.9. Moreover, the
peak at the endpoint in the energy distribution predicted at LO can be
smeared by the NLO corrections, but the major color-octet contribution still
comes from the large energy region of . By fitting the latest data of
observed by Belle, we
find that the values of color-octet matrix elements are much smaller than
expected earlier by using the naive velocity scaling rules or extracted from
fitting experimental data with LO calculations. As the most stringent
constraint by setting the color-singlet contribution to be zero in
, we get an upper limit of the
color-octet matrix element, at NLO in .Comment: 18 pages, 8 figure
Coulomb Drag in Graphene
We study the Coulomb drag between two single graphene sheets in intrinsic and
extrinsic graphene systems with no interlayer tunneling. The general expression
for the nonlinear susceptibility appropriate for single-layer graphene systems
is derived using the diagrammatic perturbation theory, and the corresponding
exact zero-temperature expression is obtained analytically. We find that,
despite the existence of a non-zero conductivity in an intrinsic graphene
layer, the Coulomb drag between intrinsic graphene layers vanishes at all
temperatures. In extrinsic systems, we obtain numerical results and an
approximate analytical result for the drag resistivity , and
find that goes as at low temperature , as
for large bilayer separation and for high carrier density . We
also discuss qualitatively the effect of plasmon-induced enhancement on the
Coulomb drag, which should occur at a temperature of the order of or higher
than the Fermi temperature
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