1,767 research outputs found
Quarks, Gluons and Frustrated Antiferromagnets
The Contractor Renormalization Group method (CORE) is used to establish the
equivalence of various Hamiltonian free fermion theories and a class of
generalized frustrated antiferromagnets. In particular, after a detailed
discussion of a simple example, it is argued that a generalized frustrated
SU(3) antiferromagnet whose single-site states have the quantum numbers of
mesons and baryons is equivalent to a theory of free massless quarks.
Furthermore, it is argued that for slight modification of the couplings which
define the frustrated antiferromagnet Hamiltonian, the theory becomes a theory
of quarks interacting with color gauge-fields.Comment: 21 pages, Late
Shaped nozzles for cryogenic buffer gas beam sources
Cryogenic buffer gas beams are important sources of cold molecules. In this
work we explore the use of a converging-diverging nozzle with a buffer-gas
beam. We find that, under appropriate circumstances, the use of a nozzle can
produce a beam with improved collimation, lower transverse temperatures, and
higher fluxes per solid angle
Photoassociation of cold atoms with chirped laser pulses: time-dependent calculations and analysis of the adiabatic transfer within a two-state model
This theoretical paper presents numerical calculations for photoassociation
of ultracold cesium atoms with a chirped laser pulse and detailed analysis of
the results. In contrast with earlier work, the initial state is represented by
a stationary continuum wavefunction. In the chosen example, it is shown that an
important population transfer is achieved to vibrational levels in
the vicinity of the v=98 bound level in the external well of the
potential. Such levels lie in the energy range swept by
the instantaneous frequency of the pulse, thus defining a ``photoassociation
window''. Levels outside this window may be significantly excited during the
pulse, but no population remains there after the pulse. Finally, the population
transfer to the last vibrational levels of the ground (6s + 6s)
is significant, making stable molecules. The results are interpreted in the
framework of a two state model as an adiabatic inversion mechanism, efficient
only within the photoassociation window. The large value found for the
photoassociation rate suggests promising applications. The present chirp has
been designed in view of creating a vibrational wavepacket in the excited state
which is focussing at the barrier of the double well potential.Comment: 49 pages, 9 figures, submitted to Phys. Rev.
Electrostatic guiding of the methylidyne radical at cryogenic temperatures
We have produced a cryogenic buffer-gas cooled beam of the diatomic molecular
radical CH (methylidyne). This molecule is of interest for studying cold
chemical reactions and fundamental physics measurements. Its light mass and
ground-state structure make it a promising candidate for electrostatic guiding
and Stark deceleration, which allows for control over its kinetic energy. This
control can facilitate studies of reactions with tuneable collision energies
and trapping for precise spectroscopic studies. Here, we have demonstrated
electrostatic guiding of CH with fluxes up to molecules per steradian
per pulseComment: 10 pages, 10 figure
Composition of fish communities in macrotidal salt marshes of the Mont Saint-Michel bay (France)
At least 100 fish species are known to be present in the intertidal areas (estuaries, mudflats and salt marshes) of Mont Saint-Michel Bay. These and other comparable shallow marine coastal waters, such as estuaries and lagoons, play a
nursery role for many fish species. However, in Europe little attention has been paid to the value of tidal salt marshes for fishes. Between March 1996 and April 1999, 120 tides were sampled in a tidal creek. A total of 31 species were caught. This community was largely dominated by mullets (Liza ramada represent 87% of the total biomass) and sand gobies(Pomatoschistus minutus and P. lozanoi represent 82% of the total numbers). These species and also Gasterosteus aculeatus, Syngnathus rostellatus, Dicentrarchus labrax, Mugil spp., Liza aurata and Sprattus sprattus were the most frequent species (>50% of monthly frequency of occurrence). In Europe, salt marshes and their creeks are flooded only during high spring tides. So, fishes only invade this environment during short immersion periods, and no species can be considered as marsh
resident. But, the salt marsh was colonized by fish every time the tide reached the creek, and during the short time of flood, dominant fishes fed actively and exploited the high productivity. Nevertheless, this study shows that there is little interannual variation in the fish community and there are three ‘ seasons ’ in the fish fauna of the marsh. Marine straggler and marine estuarine dependent species colonize marshes between spring (recruitment period in the bay) and autumn before returning into deeper adjacent waters. Estuarine fishes are present all year round with maximum abundances in the end of summer. The presence of fishes confirms that this kind of wetland plays an important trophic and nursery role for these species. Differences in densities and stages distribution of these species into Mont Saint-Michel systems (tidal mudflats, estuaries and tidal salt marshes) can reduce the trophic competition
Very-High-Energy -Ray Observations of the Blazar 1ES 2344+514 with VERITAS
We present very-high-energy -ray observations of the BL Lac object
1ES 2344+514 taken by the Very Energetic Radiation Imaging Telescope Array
System (VERITAS) between 2007 and 2015. 1ES 2344+514 is detected with a
statistical significance above background of in hours
(livetime) of observations, making this the most comprehensive very-high-energy
study of 1ES 2344+514 to date. Using these observations the temporal properties
of 1ES 2344+514 are studied on short and long times scales. We fit a constant
flux model to nightly- and seasonally-binned light curves and apply a
fractional variability test, to determine the stability of the source on
different timescales. We reject the constant-flux model for the 2007-2008 and
2014-2015 nightly-binned light curves and for the long-term seasonally-binned
light curve at the level. The spectra of the time-averaged emission
before and after correction for attenuation by the extragalactic background
light are obtained. The observed time-averaged spectrum above 200 GeV is
satisfactorily fitted () by a power-law function with
index and extends to at least 8
TeV. The extragalactic-background-light-deabsorbed spectrum is adequately fit
() by a power-law function with index while an F-test indicates that the power-law with
exponential cutoff function provides a marginally-better fit ( =
) at the 2.1 level. The source location is found to be
consistent with the published radio location and its spatial extent is
consistent with a point source.Comment: 7 pages, 2 figures. Published in Monthly Notices of the Royal
Astronomical Societ
Shaped nozzles for cryogenic buffer-gas beam sources
Cryogenic buffer-gas beams are important sources of cold molecules. In this work we explore the use of a converging-diverging nozzle with a buffer-gas beam. We find that, under appropriate circumstances, the use of a nozzle can produce a beam with improved collimation, lower transverse temperatures, and higher fluxes per solid angle
Use of Medicare claims to rank hospitals by surgical site infection risk following coronary artery bypass graft surgery
ObjectiveTo evaluate whether longitudinal insurer claims data allow reliable identification of elevated hospital surgical site infection (SSI) rates.DesignWe conducted a retrospective cohort study of Medicare beneficiaries who underwent coronary artery bypass grafting (CABG) in US hospitals performing at least 80 procedures in 2005. Hospitals were assigned to deciles by using case mix-adjusted probabilities of having an SSI-related inpatient or outpatient claim code within 60 days of surgery. We then reviewed medical records of randomly selected patients to assess whether chart-confirmed SSI risk was higher in hospitals in the worst deciles compared with the best deciles.ParticipantsFee-for-service Medicare beneficiaries who underwent CABG in these hospitals in 2005.ResultsWe evaluated 114,673 patients who underwent CABG in 671 hospitals. In the best decile, 7.8% (958/12,307) of patients had an SSI-related code, compared with 24.8% (2,747/11,068) in the worst decile ([Formula: see text]). Medical record review confirmed SSI in 40% (388/980) of those with SSI-related codes. In the best decile, the chart-confirmed annual SSI rate was 3.2%, compared with 9.4% in the worst decile, with an adjusted odds ratio of SSI of 2.7 (confidence interval, 2.2-3.3; [Formula: see text]) for CABG performed in a worst-decile hospital compared with a best-decile hospital.ConclusionsClaims data can identify groups of hospitals with unusually high or low post-CABG SSI rates. Assessment of claims is more reproducible and efficient than current surveillance methods. This example of secondary use of routinely recorded electronic health information to assess quality of care can identify hospitals that may benefit from prevention programs
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