3,180 research outputs found
Investigations of the g factors and local structure for orthorhombic Cu^{2+}(1) site in fresh PrBa_{2}Cu_{3}O_{6+x} powders
The electron paramagnetic resonance (EPR) g factors g_x, g_y and g_z of the
orthorhombic Cu^{2+}(1) site in fresh PrBa_{2}Cu_{3}O_{6+x} powders are
theoretically investigated using the perturbation formulas of the g factors for
a 3d^9 ion under orthorhombically elongated octahedra. The local orthorhombic
distortion around the Cu^{2+}(1) site due to the Jahn-Teller effect is
described by the orthorhombic field parameters from the superposition model.
The [CuO6]^{10-} complex is found to experience an axial elongation of about
0.04 {\AA} along c axis and the relative bond length variation of about 0.09
{\AA} along a and b axes of the Jahn-Teller nature. The theoretical results of
the g factors based on the above local structure are in reasonable agreement
with the experimental data.Comment: 6 pages, 1 figur
Complex Behavior in Simple Models of Biological Coevolution
We explore the complex dynamical behavior of simple predator-prey models of
biological coevolution that account for interspecific and intraspecific
competition for resources, as well as adaptive foraging behavior. In long
kinetic Monte Carlo simulations of these models we find quite robust 1/f-like
noise in species diversity and population sizes, as well as power-law
distributions for the lifetimes of individual species and the durations of
quiet periods of relative evolutionary stasis. In one model, based on the
Holling Type II functional response, adaptive foraging produces a metastable
low-diversity phase and a stable high-diversity phase.Comment: 8 pages, 5 figure
Search for via the transition at LHCb and factory
It is interesting to study the characteristics of the whole family of
which contains two different heavy flavors. LHC and the proposed factory
provide an opportunity because a large database on the family will be
achieved. and its excited states can be identified via their decay modes.
As suggested by experimentalists, is not easy to be
clearly measured, instead, the trajectories of and occurring in
the decay of () can be unambiguously
identified, thus the measurement seems easier and more reliable, therefore this
mode is more favorable at early running stage of LHCb and the proposed
factory. In this work, we calculate the rate of
in terms of the QCD multipole-expansion and the numerical results indicate that
the experimental measurements with the luminosity of LHC and factory are
feasible.Comment: 12 pages, 1 figures and 4 tables, acceptted by SCIENCE CHINA Physics,
Mechanics & Astronomy (Science in China Series G
Collapses and revivals of exciton emission in a semiconductor microcavity: detuning and phase-space filling effects
We investigate exciton emission of quantum well embedded in a semiconductor
microcavity. The analytical expressions of the light intensity for the cases of
excitonic number state and coherent state are presented by using secular
approximation. Our results show that the effective exciton-exciton interaction
leads to the appearance of collapse and revival of the light intensity. The
revival time is twice compared the coherent state case with that of the number
state. The dissipation of the exciton-polariton lowers the revival amplitude
but does not alter the revival time. The influences of the detuning and the
phase-space filling are studied. We find that the effect of the higher-order
exciton-photon interaction may be removed by adjusting the detuning.Comment: 7 pages, 3 figure
NRQCD Analysis of Bottomonium Production at the Tevatron
Recent data from the CDF collaboration on the production of spin-triplet
bottomonium states at the Tevatron p \bar p collider are analyzed within the
NRQCD factorization formalism. The color-singlet matrix elements are determined
from electromagnetic decays and from potential models. The color-octet matrix
elements are determined by fitting the CDF data on the cross sections for
Upsilon(1S), Upsilon(2S), and Upsilon(3S) at large p_T and the fractions of
Upsilon(1S) coming from chi_b(1P) and chi_b(2P). We use the resulting matrix
elements to predict the cross sections at the Tevatron for the spin-singlet
states eta_b(nS) and h_b(nP). We argue that eta_b(1S) should be observable in
Run II through the decay eta_b -> J/psi + J/psi.Comment: 20 pages, 3 figure
Gluon fragmentation to ^3D_J quarkonia
We present a calculation of the leading order QCD fragmentation functions for
gluons to split into spin-triplet D-wave quarkonia. We apply them to evaluate
the gluon fragmentation contributions to inclusive ^3D_J quarkonium production
at large transverse momentum processes like the Tevatron and find that the
D-wave quarkonia, especially the charmonium 2^{--} state, could be observed
through color-octet mechanism with present luminosity. Since there are
distinctively large gaps between the contributions of two different (i.e,
color-singlet and color-octet) quarkonium production mechanisms, our results
may stand as a unique test to NRQCD color-octet quarkonium production
mechanism.Comment: 15 pages in LaTex (2 figures in PS-file
Elusive vector glueball
If the vector glueball exists in the mass range that theory suggests, its
resonance production cross section can be seen in e+e- annihilation only if the
decay width is very narrow (< a few MeV). Otherwise it willbe observed only
indirectly through its mixing with psi(2S). A few tests of the glueball-psi'
mixing are proposed for future charm factories.Comment: One misleading short sentence delete
k-Component q-deformed charge coherent states and their nonclassical properties
k-Component q-deformed charge coherent states are constructed, their
(over)completeness proved and their generation explored. The q-deformed charge
coherent states and the even (odd) q-deformed charge coherent states are the
two special cases of them as k becomes 1 and 2, respectively. A D-algebra
realization of the SU(1,1) generators is given in terms of them. Their
nonclassical properties are studied and it is shown that for , they
exhibit two-mode q-antibunching, but neither SU(1,1) squeezing, nor one- or
two-mode q-squeezing.Comment: LaTeX, 29 pages, 2 Postscript figures, minor change
A Crucial Test for Color-Octet Production Mechanism in Z^0 Decays
The direct production rates of -wave charmonia in the decays of is
evaluated. The color-octet production processes are shown to have distinctively large branching ratios, the same order
of magnitude as that of prodution, as compared with other -wave
charmonium production mechanisms. This may suggest a crucial channel to test
the color-octet mechanism as well as to observe the -wave charmonium states
in decays. In addition, a signal for the charmonium as strong as
or with large transverse momentum at the Tevatron should
also be observed.Comment: 14 pages in LaTex (3 figures in PS-file
Thermal Impact on Spiking Properties in Hodgkin-Huxley Neuron with Synaptic Stimulus
The effect of environmental temperature on neuronal spiking behaviors is
investigated by numerically simulating the temperature dependence of spiking
threshold of the Hodgkin-Huxley neuron subject to synaptic stimulus. We find
that the spiking threshold exhibits a global minimum in a "comfortable
temperature" range where spike initiation needs weakest synaptic strength,
indicating the occurrence of optimal use of synaptic transmission in neural
system. We further explore the biophysical origin of this phenomenon in ion
channel gating kinetics and also discuss its possible biological relevance in
information processing in neural systems.Comment: 10 pages, 4 figure
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