919 research outputs found
Comparison of Gatifloxacin Versus Levofloxacin in the Treatment of Adults with Bacterial Infections: A Double-Blind, Randomized Trial in China
Random Field Models for Relaxor Ferroelectric Behavior
Heat bath Monte Carlo simulations have been used to study a four-state clock
model with a type of random field on simple cubic lattices. The model has the
standard nonrandom two-spin exchange term with coupling energy and a random
field which consists of adding an energy to one of the four spin states,
chosen randomly at each site. This Ashkin-Teller-like model does not separate;
the two random-field Ising model components are coupled. When , the
ground states of the model remain fully aligned. When , a
different type of ground state is found, in which the occupation of two of the
four spin states is close to 50%, and the other two are nearly absent. This
means that one of the Ising components is almost completely ordered, while the
other one has only short-range correlations. A large peak in the structure
factor appears at small for temperatures well above the transition
to long-range order, and the appearance of this peak is associated with slow,
"glassy" dynamics. The phase transition into the state where one Ising
component is long-range ordered appears to be first order, but the latent heat
is very small.Comment: 7 pages + 12 eps figures, to appear in Phys Rev
Correlation energy of a two-dimensional electron gas from static and dynamic exchange-correlation kernels
We calculate the correlation energy of a two-dimensional homogeneous electron
gas using several available approximations for the exchange-correlation kernel
entering the linear dielectric response of the system.
As in the previous work of Lein {\it et al.} [Phys. Rev. B {\bf 67}, 13431
(2000)] on the three-dimensional electron gas, we give attention to the
relative roles of the wave number and frequency dependence of the kernel and
analyze the correlation energy in terms of contributions from the plane. We find that consistency of the kernel with the electron-pair
distribution function is important and in this case the nonlocality of the
kernel in time is of minor importance, as far as the correlation energy is
concerned. We also show that, and explain why, the popular Adiabatic Local
Density Approximation performs much better in the two-dimensional case than in
the three-dimensional one.Comment: 9 Pages, 4 Figure
Design of Experiments for Screening
The aim of this paper is to review methods of designing screening
experiments, ranging from designs originally developed for physical experiments
to those especially tailored to experiments on numerical models. The strengths
and weaknesses of the various designs for screening variables in numerical
models are discussed. First, classes of factorial designs for experiments to
estimate main effects and interactions through a linear statistical model are
described, specifically regular and nonregular fractional factorial designs,
supersaturated designs and systematic fractional replicate designs. Generic
issues of aliasing, bias and cancellation of factorial effects are discussed.
Second, group screening experiments are considered including factorial group
screening and sequential bifurcation. Third, random sampling plans are
discussed including Latin hypercube sampling and sampling plans to estimate
elementary effects. Fourth, a variety of modelling methods commonly employed
with screening designs are briefly described. Finally, a novel study
demonstrates six screening methods on two frequently-used exemplars, and their
performances are compared
Body-centered-cubic Ni and its magnetic properties
The body-centered-cubic (bec) phase of Ni, which does not exist in nature, has been achieved as a thin film on GaAs(001) at 170 K via molecular beam epitaxy. The bec Ni is ferromagnetic with a Curie temperature of 456 K and possesses a magnetic moment of 0.52 \uc2\ub1 0.08 \uce\ubcB/atom. The cubic magneto-crystalline anisotropy of bec Ni is determined to be +4.0 \uc3\u97 105 ergs \uc2\ub7 cm-3, as opposed to -5.7 \uc3\u97 10 4 ergs \uc2\ub7 cm-3 for the naturally occurring face-centered-cubic (fcc) Ni. This sharp contrast in the magnetic anisotropy is attributed to the different electronic band structures between bec Ni and fcc Ni, which are determined using angle-resolved photoemission with synchrotron radiation
Measurements of J/psi Decays into 2(pi+pi-)eta and 3(pi+pi-)eta
Based on a sample of 5.8X 10^7 J/psi events taken with the BESII detector,
the branching fractions of J/psi--> 2(pi+pi-)eta and J/psi-->3(pi+pi-)eta are
measured for the first time to be (2.26+-0.08+-0.27)X10^{-3} and
(7.24+-0.96+-1.11)X10^{-4}, respectively.Comment: 11 pages, 6 figure
BESII Detector Simulation
A Monte Carlo program based on Geant3 has been developed for BESII detector
simulation. The organization of the program is outlined, and the digitization
procedure for simulating the response of various sub-detectors is described.
Comparisons with data show that the performance of the program is generally
satisfactory.Comment: 17 pages, 14 figures, uses elsart.cls, to be submitted to NIM
Measurements of the Mass and Full-Width of the Meson
In a sample of 58 million events collected with the BES II detector,
the process J/ is observed in five different decay
channels: , , (with ), (with
) and . From a combined fit of all five
channels, we determine the mass and full-width of to be
MeV/ and
MeV/.Comment: 9 pages, 2 figures and 4 table. Submitted to Phys. Lett.
A Measurement of Psi(2S) Resonance Parameters
Cross sections for e+e- to hadons, pi+pi- J/Psi, and mu+mu- have been
measured in the vicinity of the Psi(2S) resonance using the BESII detector
operated at the BEPC. The Psi(2S) total width; partial widths to hadrons,
pi+pi- J/Psi, muons; and corresponding branching fractions have been determined
to be Gamma(total)= (264+-27) keV; Gamma(hadron)= (258+-26) keV, Gamma(mu)=
(2.44+-0.21) keV, and Gamma(pi+pi- J/Psi)= (85+-8.7) keV; and Br(hadron)=
(97.79+-0.15)%, Br(pi+pi- J/Psi)= (32+-1.4)%, Br(mu)= (0.93+-0.08)%,
respectively.Comment: 8 pages, 6 figure
Study of
New data are presented on from a sample of 58M
events in the upgraded BES II detector at the BEPC. There is a
conspicuous signal for and a peak at higher mass which
may be fitted with . From a combined analysis with
data, the branching ratio
is at the 95%
confidence level.Comment: 11 pages, 5 figures. Submitted to Phys. Lett.
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