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Very-high-precision bound-state spectroscopy near a 85Rb Feshbach resonance
We precisely measured the binding energy ( epsilon /sub bind/) of a molecular state near the Feshbach resonance in a /sup 85/Rb Bose-Einstein condensate (BEC). Rapid magnetic-field pulses induced coherent atom-molecule oscillations in the BEC. We measured the oscillation frequency as a function of B field and fit the data to a coupled-channel model. Our analysis constrained the Feshbach resonance position [155.041(18) G], width [10.71(2) G], and background scattering length [-443(3)a/sub 0/] and yielded new values for the Rb interaction parameters. These results improved our estimate for the stability condition of an attractive BEC. We also found evidence for a mean-field shift to epsilon /sub bind
Investigation of the Neutron Form Factors by Inclusive Quasi-Elastic Scattering of Polarized Electrons off Polarized He: A Theoretical Overview
The theory of quasi-elastic inclusive scattering of polarized leptons off
polarized He is critically reviewed and the origin of different expressions
for the polarized nuclear response function appearing in the literature is
explained. The sensitivity of the longitudinal asymmetry upon the neutron form
factors is thoroughly investigated and the role played by the polarization
angle for minimizing the proton contribution is illustrated.Comment: Phys. Rev C in press; 9 figs. (available upon request
Detection of Atmospheric Cherenkov Radiation Using Solar Heliostat Mirrors
The gamma-ray energy region between 20 and 250 GeV is largely unexplored.
Ground-based atmospheric Cherenkov detectors offer a possible way to explore
this region, but large Cherenkov photon collection areas are needed to achieve
low energy thresholds. This paper discusses the development of a Cherenkov
detector using the heliostat mirrors of a solar power plant as the primary
collector. As part of this development, we built a prototype detector
consisting of four heliostat mirrors and used it to record atmospheric
Cherenkov radiation produced in extensive air showers created by cosmic ray
particles.Comment: 16 latex pages, 8 postscript figures, uses psfig.sty, to be published
in Astroparticle Physic
Excited Baryons in Lattice QCD
We present first results for the masses of positive and negative parity
excited baryons calculated in lattice QCD using an O(a^2)-improved gluon action
and a fat-link irrelevant clover (FLIC) fermion action in which only the
irrelevant operators are constructed with APE-smeared links. The results are in
agreement with earlier calculations of N^* resonances using improved actions
and exhibit a clear mass splitting between the nucleon and its chiral partner.
An correlation matrix analysis reveals two low-lying J^P=(1/2)^- states with a
small mass splitting. The study of different Lambda interpolating fields
suggests a similar splitting between the lowest two Lambda1/2^- octet states.
However, the empirical mass suppression of the Lambda^*(1405) is not evident in
these quenched QCD simulations, suggesting a potentially important role for the
meson cloud of the Lambda^*(1405) and/or a need for more exotic interpolating
fields.Comment: Correlation matrix analysis performed. Increased to 400
configurations. 22 pages, 13 figures, 15 table
Self-optimization, community stability, and fluctuations in two individual-based models of biological coevolution
We compare and contrast the long-time dynamical properties of two
individual-based models of biological coevolution. Selection occurs via
multispecies, stochastic population dynamics with reproduction probabilities
that depend nonlinearly on the population densities of all species resident in
the community. New species are introduced through mutation. Both models are
amenable to exact linear stability analysis, and we compare the analytic
results with large-scale kinetic Monte Carlo simulations, obtaining the
population size as a function of an average interspecies interaction strength.
Over time, the models self-optimize through mutation and selection to
approximately maximize a community fitness function, subject only to
constraints internal to the particular model. If the interspecies interactions
are randomly distributed on an interval including positive values, the system
evolves toward self-sustaining, mutualistic communities. In contrast, for the
predator-prey case the matrix of interactions is antisymmetric, and a nonzero
population size must be sustained by an external resource. Time series of the
diversity and population size for both models show approximate 1/f noise and
power-law distributions for the lifetimes of communities and species. For the
mutualistic model, these two lifetime distributions have the same exponent,
while their exponents are different for the predator-prey model. The difference
is probably due to greater resilience toward mass extinctions in the food-web
like communities produced by the predator-prey model.Comment: 26 pages, 12 figures. Discussion of early-time dynamics added. J.
Math. Biol., in pres
Electromagnetic Form Factors of the SU(3) Octet Baryons in the semibosonized SU(3) Nambu-Jona-Lasinio Model
The electromagnetic form factors of the SU(3) octet baryons are investigated
in the semibosonized SU(3) Nambu--Jona-Lasinio model (chiral quark-soliton
model). The rotational and strange quark mass corrections in linear
order are taken into account. The electromagnetic charge radii of the nucleon
and magnetic moments are also evaluated. It turns out that the model is in a
remarkable good agreement with the experimental data.Comment: RevTex is used. 37 pages. The final version to appear in Phys. Rev.
D. 13 figures are include
Demystifying an unidentified EGRET source by VHE gamma-ray observations
In a novel approach in observational high-energy gamma-ray astronomy,
observations carried out by imaging atmospheric Cherenkov telescopes provide
necessary templates to pinpoint the nature of intriguing, yet unidentified
EGRET gamma-ray sources. Using GeV-photons detected by CGRO EGRET and taking
advantage of high spatial resolution images from H.E.S.S. observations, we were
able to shed new light on the EGRET observed gamma-ray emission in the
Kookaburra complex, whose previous coverage in the literature is somewhat
contradictory. 3EGJ1420-6038 very likely accounts for two GeV gamma-ray sources
(E>1 GeV), both in positional coincidence with the recently reported pulsar
wind nebulae (PWN) by HESS in the Kookaburra/Rabbit complex. PWN associations
at VHE energies, supported by accumulating evidence from observations in the
radio and X-ray band, are indicative for the PSR/plerionic origin of spatially
coincident, but still unidentified Galactic gamma-ray sources from EGRET. This
not only supports the already suggested connection between variable, but
unidentified low-latitude gamma-ray sources with pulsar wind nebulae
(3EGJ1420-6038 has been suggested as PWN candidate previoulsy), it also
documents the ability of resolving apparently confused EGRET sources by
connecting the GeV emission as measured from a large-aperture space-based
gamma-ray instrument with narrow field-of-view but superior spatial resolution
observations by ground-based atmospheric Cherenkov telescopes, a very promising
identification technique for achieving convincing individual source
identifications in the era of GLAST-LAT.Comment: 4 pages, 5 figures, Accepted for publication in Astrophysics and
Space Science, Proc. of "The Multi-Messenger Approach to High-Energy
Gamma-ray Sources (Third Workshop on the Nature of Unidentified High-Energy
Sources)", Barcelona, July 4-7, 2006, one typo correcte
Evolution of active and polar photospheric magnetic fields during the rise of Cycle 24 compared to previous cycles
The evolution of the photospheric magnetic field during the declining phase
and minimum of Cycle 23 and the recent rise of Cycle 24 are compared with the
behavior during previous cycles. We used longitudinal full-disk magnetograms
from the NSO's three magnetographs at Kitt Peak, the Synoptic Optical Long-term
Investigations of the Sun (SOLIS) Vector Spectro-Magnetograph (VSM), the
Spectromagnetograph and the 512-Channel Magnetograph instruments, and
longitudinal full-disk magnetograms from the Mt. Wilson 150-foot tower. We
analyzed 37 years of observations from these two observatories that have been
observing daily, weather permitting, since 1974, offering an opportunity to
study the evolving relationship between the active region and polar fields in
some detail over several solar cycles. It is found that the annual averages of
a proxy for the active region poloidal magnetic field strength, the magnetic
field strength of the high-latitude poleward streams, and the time derivative
of the polar field strength are all well correlated in each hemisphere. These
results are based on statistically significant cyclical patterns in the active
region fields and are consistent with the Babcock-Leighton phenomenological
model for the solar activity cycle. There was more hemispheric asymmetry in the
activity level, as measured by total and maximum active region flux, during
late Cycle 23 (after around 2004), when the southern hemisphere was more
active, and Cycle 24 up to the present, when the northern hemisphere has been
more active, than at any other time since 1974. The active region net proxy
poloidal fields effectively disappeared in both hemispheres around 2004, and
the polar fields did not become significantly stronger after this time. We see
evidence that the process of Cycle 24 field reversal has begun at both poles.Comment: Accepted for publication in Solar Physic
CD9 co-operation with syndecan-1 is required for a major staphylococcal adhesion pathway
Epithelial colonization is a critical first step in bacterial pathogenesis. Staphylococcus aureus can utilize several host factors to associate with cells, including α5β1 integrin and heparan sulfate proteoglycans, such as the syndecans. Here, we demonstrate that a partner protein of both integrins and syndecans, the host membrane adapter protein tetraspanin CD9, is essential for syndecan-mediated staphylococcal adhesion. Fibronectin is also essential in this process, while integrins are only critical for post-adhesion entry into human epithelial cells. Treatment of epithelial cells with CD9-derived peptide or heparin caused significant reductions in staphylococcal adherence, dependent on both CD9 and syndecan-1. Exogenous fibronectin caused a CD9-dependent increase in staphylococcal adhesion, whereas blockade of β1 integrins did not affect adhesion but did reduce the subsequent internalization of adhered bacteria. CD9 disruption or deletion increased β1 integrin-mediated internalization, suggesting that CD9 coordinates sequential staphylococcal adhesion and internalization. CD9 controls staphylococcal adhesion through syndecan-1, using a mechanism that likely requires CD9-mediated syndecan organization to correctly display fibronectin at the host cell surface. We propose that CD9-derived peptides or heparin analogs could be developed as anti-adhesion treatments to inhibit the initial stages of staphylococcal pathogenesis
Caffeine for apnea of prematurity and brain development at 11Â years of age
Objective Caffeine therapy for apnea of prematurity has been reported to improve brain white matter microstructure at term-equivalent age, but its long-term effects are unknown. This study aimed to investigate whether caffeine affects (1) brain structure at 11 years of age, and (2) brain development from term-equivalent age to 11 years of age, compared with placebo. Methods Preterm infants born ≤1250 g were randomly allocated to caffeine or placebo. Magnetic resonance imaging (MRI) was performed on 70 participants (33 caffeine, 37 placebo) at term-equivalent age and 117 participants (63 caffeine, 54 placebo) at 11 years of age. Global and regional brain volumes and white matter microstructure were measured at both time points. Results In general, there was little evidence for differences between treatment groups in brain volumes or white matter microstructure at age 11 years. There was, however, evidence that the caffeine group had a smaller corpus callosum than the placebo group. Volumetric brain development from term-equivalent to 11 years of age was generally similar between treatment groups. However, there was evidence that caffeine was associated with slower growth of the corpus callosum, and slower decreases in axial, radial, and mean diffusivities in the white matter, particularly at the level of the centrum semiovale, over time than placebo. Interpretation This study suggests any benefits of neonatal caffeine therapy on brain structure in preterm infants weaken over time and are not clearly detectable by MRI at age 11 years, although caffeine may have long-term effects on corpus callosum development.Claire E. Kelly, Wenn Lynn Ooi, Joseph Yuan-Mou Yang, Jian Chen, Chris Adamson, Katherine J. Lee ... et al
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