864 research outputs found
1/m_b^2 correction to the left-right lepton polarization asymmetry in the decay B -> X_s mu^+ mu^-
Using a known result by Falk et al. for the 1/m_b^2 correction to the
dilepton invariant mass spectrum in the decay B \rightarrow X_s \mu^+ \mu^-, we
calculate the 1/m_b^2 correction to the left-right muon polarization asymmetry
in this decay. Employing an up-to-date range of values for the non-perturbative
parameter \lambda_1, we find that the correction is much smaller than it should
have been expected from the previous work by Falk et al.Comment: 8 pages, 2 figures included. Uses epsf.sty and rotate.sty. To appear
in Physical Review D. The complete postscript file is also available from URL
ftp://feynman.t30.physik.tu-muenchen.de/pub/preprints/ tum_t31_98_96.ps.g
QCD Improved Constraints on the Minimal Supergravity Model
Recent advances in the QCD corrections to decay in the MSSM
include i.) evaluation of the relevant operators, Wilson coefficients and
anomalous dimension matrix elements for the various MSSM effective theories
valid at scales beyond , ii.) calculations of most of the needed
anomalous dimension matrix elements to next-to-leading order for scales
m_b\alt Q , and iii.) calculations of virtual and
bremsstrahlung corrections to the decay operators at scale
. We assemble all these known results to gain an estimate of for the parameter space of the minimal supergravity model (mSUGRA).
We find a much reduced scale dependence of our result compared to usual
leading-log evaluations. Comparison with the latest CLEO results yields
stringent constraints on parameter space. Much of mSUGRA parameter space is
ruled out for , especially for large . We compare these
results with other constraints from cosmology and non-standard vacua. Also, we
compare with expectations for discovering mSUGRA at LEP2, the Tevatron and the
CERN LHC.Comment: 14 pages REVTEX plus 7 PS figures; this version contains revised
figures and text due to discovery of a bug in the program used to generate
results for the previous version of this manuscrip
High Spectral Resolution Observations of the Massive Stars in the Galactic Center
We present high-resolution near-infrared spectra, obtained with the NIRSPEC
spectrograph on the W. M. Keck II Telescope, of a collection of hot, massive
stars within the central 25 arcseconds of the Galactic center. We have
identified a total of twenty-one emission-line stars, seven of which are new
radial velocity detections with five of those being classified as He I
emission-line stars for the first time. These stars fall into two categories
based on their spectral properties: 1) those with narrow 2.112, 2.113 micron He
I doublet absorption lines, and 2) those with broad 2.058 micron He I emission
lines. These data have the highest spectral resolution ever obtained for these
sources and, as a result, both components of the absorption doublet are
separately resolved for the first time. We use these spectral features to
measure radial velocities. The majority of the measured radial velocities have
relative errors of 20 kms, smaller than those previously obtained with
proper-motion or radial velocity measurements for similar stellar samples in
the Galactic center. The radial velocities estimated from the He I absorption
doublet are more robust than those previously estimated from the 2.058 micron
emission line, since they do not suffer from confusion due to emission from the
surrounding ISM. Using this velocity information, we agree that the stars are
orbiting in a somewhat coherent manner but are not as defined into a disk or
disks as previously thought. Finally, multi-epoch radial velocity measurements
for IRS 16NE show a change in its velocity presumably due to an unseen stellar
companion.Comment: ApJ accepted, 42 pages, 16 figure
Phase fluctuations and the pseudogap in YBa2Cu3Ox
The thermodynamics of the superconducting transition is studied as a function
of doping using high-resolution expansivity data of YBa2Cu3Ox single crystals
and Monte-Carlo simulations of the anisotropic 3D-XY model. We directly show
that Tc of underdoped YBa2Cu3Ox is strongly suppressed from its mean-field
value (Tc-MF) by phase fluctuations of the superconducting order parameter. For
overdoped YBa2Cu3Ox fluctuation effects are greatly reduced and Tc ~ Tc-MF . We
find that Tc-MF exhibits a similar doping dependence as the pseudogap energy,
naturally suggesting that the pseudogap arises from phase-incoherent Cooper
pairing.Comment: 9 pages, 3 Figure
Free energy barrier for melittin reorientation from a membrane-bound state to a transmembrane state
An important step in a phospholipid membrane pore formation by melittin
antimicrobial peptide is a reorientation of the peptide from a surface into a
transmembrane conformation. In this work we perform umbrella sampling
simulations to calculate the potential of mean force (PMF) for the
reorientation of melittin from a surface-bound state to a transmembrane state
and provide a molecular level insight into understanding peptide and lipid
properties that influence the existence of the free energy barrier. The PMFs
were calculated for a peptide to lipid (P/L) ratio of 1/128 and 4/128. We
observe that the free energy barrier is reduced when the P/L ratio increased.
In addition, we study the cooperative effect; specifically we investigate if
the barrier is smaller for a second melittin reorientation, given that another
neighboring melittin was already in the transmembrane state. We observe that
indeed the barrier of the PMF curve is reduced in this case, thus confirming
the presence of a cooperative effect
Rare earth magnetism in CeFeAsO: A single crystal study
Single crystals of CeFeAsO, large enough to study the anisotropy of the
magnetic properties, were grown by an optimized Sn-flux technique. The high
quality of our single crystals is apparent from the highest residual
resistivity ratio, RRR = 12, reported among undoped RFeAsO compounds (R=rare
earth) as well as sharp anomalies in resistivity, specific heat, C(T), and
thermal expansion at the different phase transitions. The magnetic
susceptibility chi(T) presents a large easy-plane anisotropy consistent with
the lowest crystal electric field doublet having a dominant Gamma_6 character.
Curie-Weiss like susceptibilities for magnetic field parallel and perpendicular
to the crystallographic c-axis do not reveal an influence of a staggered field
on the Ce site induced by magnetic ordering of the Fe. Furthermore, the
standard signatures for antiferromagnetic order of Ce at T_N = 3.7 K observed
in chi(T) and C(T) are incompatible with a Zeeman splitting Delta = 10 K of the
CEF ground state doublet at low temperature due to the Fe-magnetic order as
previously proposed. Our results can be reconciled with the earlier observation
by assuming a comparatively stronger effect of the Ce-Ce exchange leading to a
reduction of this Zeeman splitting below 15 K.Comment: 15 pages, 6 figures, added section on magn. susceptibilit
Respostas de forrageiras a nutrientes em solos da planície sedimentar do Rio Taquari, Pantanal Mato-Grossense.
A adicao de fosforo e micronutrientes nao acusou aumento na producao de massa verde de Stylosanthes hamatanem de Pueraria phaseoloides em "cordilheiras" com mata onde o solo arenoso e fertil. O estudo da fertilidade em casa de vegetacao com tres series de Podzol hidromorfico, que representam a catena deste solo na sub-regiao de Nhecolandia e Paiaguas, apresentou dados variavies. Ha deficiencias generalizadas de macronutrientes e as doses testadas de micronutrientes foram aparentemente inadequadas, principalmente o boro, que foi toxico. Em experimento de introducao de forrageiras em "cordilheiras" de media fertilidade, uma adubacao basica (calcario, fosforo, potassio, nitrogenio, enxofre e molibdenio) nao apresentou resposta. Na "cordilheira" de baixa fertilidade, a adicao dos nutrientes nao contribuiu para o estabelecimento de maior numero de especies. Adubacao basica (calcario, fosforo, potassio e enxofre) no "caronal" contribuiu para maior producao e estabelecimento de muitas especies e proporcionou maior crescimento a algumas plantas no periodo de afloramento do lencol freatico.bitstream/item/37694/1/CT08.pd
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