1,217 research outputs found
All-Optical Production of a Degenerate Fermi Gas
We achieve degeneracy in a mixture of the two lowest hyperfine states of
Li by direct evaporation in a CO laser trap, yielding the first
all-optically produced degenerate Fermi gas. More than atoms are
confined at temperatures below K at full trap depth, where the Fermi
temperature for each state is K. This degenerate two-component mixture
is ideal for exploring mechanisms of superconductivity ranging from Cooper
pairing to Bose condensation of strongly bound pairs.Comment: 4 pgs RevTeX with 2 eps figs, to be published in Phys. Rev. Let
Bioaccumulation surveillance in Milford Haven Waterway
Biomonitoring of contaminants (metals, organotins, PAHs, PCBs) was
carried out along the Milford Haven Waterway (MHW) and at a reference site in the
Tywi Estuary during 2007-2008. The species used as bioindicators encompass a
variety of uptake routes - Fucus vesiculosus (dissolved contaminants); Littorina
littorea (grazer); Mytilus edulis and Cerastoderma edule (suspension feeders); and
Nereis diversicolor (omnivore which often reflects contaminants in sediment).
Differences in feeding strategy and habitat preference have subtle implications for
bioaccumulation trends though, with few exceptions, contaminant body burdens in
Milford Haven (MH) were higher than those at the Tywi reference site, reflecting
inputs.
Elevated concentrations of metals were occasionally observed at individual MH sites,
whilst As and Se (molluscs and seaweed) were, for much of MHW, consistently at the
higher end of the UK range. However, for the majority of metals, distributions in MH
biota were not exceptional by UK standards. Several metal-species combinations
indicated increases in bioavailability at upstream sites, which may reflect the
influence of geogenic or other land-based sources – perhaps enhanced by lower
salinity (greater proportions of more bioavailable forms).
TBT levels in MH mussels were below OSPAR toxicity thresholds and in the Tywi
were close to zero. Phenyltins were not accumulated appreciably in Mytilus, whereas
some Nereis populations may have been subjected to localized (historical) sources.
PAHs in Nereis tended to be evenly distributed across most sites, but with somewhat
higher values at Dale for acenaphthene, fluoranthene, pyrene, benzo(a)anthracene and
chrysene; naphthalenes tended to be enriched further upstream in the mid-upper
Haven (a pattern seen in mussels for most PAHs). Whilst concentrations in MH
mussels were mostly above reference site and OSPAR backgrounds, it is unlikely that
ecotoxicological guidelines would be exceeded.
PCBs in mussels were between upper and lower OSPAR guidelines and were unusual
in their distribution in that highest levels occurred at the mouth of MH.
Condition indices (CI) of bivalves (mussels and cockles) were highest at the Tywi
reference site and at the seaward end of MH, decreasing upstream along the
Waterway. There were a number of significant (negative) relationships between CI
and body burdens and multivariate analysis indicated that a combination of
contaminants could influence the pattern in condition (and sub-lethal responses such
as MT and TOSC) across sites. Cause and effect needs to be tested more rigorously in
future assessments
Strongly inhibited transport of a 1D Bose gas in a lattice
We report the observation of strongly damped dipole oscillations of a quantum
degenerate 1D atomic Bose gas in a combined harmonic and optical lattice
potential. Damping is significant for very shallow axial lattices (0.25 photon
recoil energies), and increases dramatically with increasing lattice depth,
such that the gas becomes nearly immobile for times an order of magnitude
longer than the single-particle tunneling time. Surprisingly, we see no
broadening of the atomic quasimomentum distribution after damped motion. Recent
theoretical work suggests that quantum fluctuations can strongly damp dipole
oscillations of 1D atomic Bose gas, providing a possible explanation for our
observations.Comment: 5 pages, 4 figure
Resonant control of elastic collisions in an optically trapped Fermi gas of atoms
We have loaded an ultracold gas of fermionic atoms into a far off resonance
optical dipole trap and precisely controlled the spin composition of the
trapped gas. We have measured a magnetic-field Feshbach resonance between atoms
in the two lowest energy spin-states, |9/2, -9/2> and |9/2, -7/2>. The
resonance peaks at a magnetic field of 201.5 plus or minus 1.4 G and has a
width of 8.0 plus or minus 1.1 G. Using this resonance we have changed the
elastic collision cross section in the gas by nearly 3 orders of magnitude.Comment: 4 pages, 3 figure
Regulation of surface architecture by symbiotic bacteria mediates host colonization
Microbes occupy countless ecological niches in nature. Sometimes these environments may be on or within another organism, as is the case in both microbial infections and symbiosis of mammals. Unlike pathogens that establish opportunistic infections, hundreds of human commensal bacterial species establish a lifelong cohabitation with their hosts. Although many virulence factors of infectious bacteria have been described, the molecular mechanisms used during beneficial host–symbiont colonization remain almost entirely unknown. The novel identification of multiple surface polysaccharides in the important human symbiont Bacteroides fragilis raised the critical question of how these molecules contribute to commensalism. To understand the function of the bacterial capsule during symbiotic colonization of mammals, we generated B. fragilis strains deleted in the global regulator of polysaccharide expression and isolated mutants with defects in capsule expression. Surprisingly, attempts to completely eliminate capsule production are not tolerated by the microorganism, which displays growth deficits and subsequent reversion to express capsular polysaccharides. We identify an alternative pathway by which B. fragilis is able to reestablish capsule production and modulate expression of surface structures. Most importantly, mutants expressing single, defined surface polysaccharides are defective for intestinal colonization compared with bacteria expressing a complete polysaccharide repertoire. Restoring the expression of multiple capsular polysaccharides rescues the inability of mutants to compete for commensalism. These findings suggest a model whereby display of multiple capsular polysaccharides provides essential functions for bacterial colonization during host–symbiont mutualism
Briefing: Young Coastal Scientists and Engineers Conference 2013
On 25–26 March 2013, 52 early career scientists and engineers, studying various aspects of coastal science, met at the University of Aberdeen for the ninth Young Coastal Scientists and Engineers Conference. The conference was jointly organised by the School of Engineering, University of Aberdeen, and Marine Scotland Science. Early-career scientists, researchers and practitioners presented 23 oral and 17 poster presentations over the 2-day meeting. The papers all had a coastal theme with a large diversity in the subjects covered, including waves, currents, tidal energy, coastal erosion, sediment transport, fluid mechanics and particle tracking. This briefing paper reports on the conference, and presents the keynote lecture and four papers voted to be of especially high quality by the panel of judges
The relationship between anxiety and acute mountain sickness.
INTRODUCTION: Whilst the link between physical factors and risk of high altitude (HA)-related illness and acute mountain sickness (AMS) have been extensively explored, the influence of psychological factors has been less well examined. In this study we aimed to investigate the relationship between 'anxiety and AMS risk during a progressive ascent to very HA. METHODS: Eighty health adults were assessed at baseline (848m) and over 9 consecutive altitudes during a progressive trek to 5140m. HA-related symptoms (Lake Louise [LLS] and AMS-C Scores) and state anxiety (State-Trait-Anxiety-Score [STAI Y-1]) were examined at each altitude with trait anxiety (STAI Y-2) at baseline. RESULTS: The average age was 32.1 ± 8.3 years (67.5% men). STAI Y-1 scores fell from 848m to 3619m, before increasing to above baseline scores (848m) at ≥4072m (p = 0.01). STAI Y-1 scores correlated with LLS (r = 0.31; 0.24-0.3; P<0.0001) and AMS-C Scores (r = 0.29; 0.22-0.35; P<0.0001). There was significant main effect for sex (higher STAI Y-1 scores in women) and altitude with no sex-x-altitude interaction on STAI Y-1 Scores. Independent predictors of significant state anxiety included female sex, lower age, higher heart rate and increasing LLS and AMS-C scores (p<0.0001). A total of 38/80 subjects (47.5%) developed AMS which was mild in 20 (25%) and severe in 18 (22.5%). Baseline STAI Y-2 scores were an independent predictor of future severe AMS (B = 1.13; 1.009-1.28; p = 0.04; r2 = 0.23) and STAI Y-1 scores at HA independently predicted AMS and its severity. CONCLUSION: Trait anxiety at low altitude was an independent predictor of future severe AMS development at HA. State anxiety at HA was independently associated with AMS and its severity
Ultrastable CO2 Laser Trapping of Lithium Fermions
We demonstrate an ultrastable CO2 laser trap that provides tight confinement
of neutral atoms with negligible optical scattering and minimal laser-noise-
induced heating. Using this method, fermionic 6Li atoms are stored in a 0.4 mK
deep well with a 1/e trap lifetime of 300 sec, consistent with a background
pressure of 10^(-11) Torr. To our knowledge, this is the longest storage time
ever achieved with an all-optical trap, comparable to the best reported
magnetic traps.Comment: 4 pages using REVTeX, 1 eps figur
All Optical Formation of an Atomic Bose-Einstein Condensate
We have created a Bose-Einstein condensate of 87Rb atoms directly in an
optical trap. We employ a quasi-electrostatic dipole force trap formed by two
crossed CO_2 laser beams. Loading directly from a sub-doppler laser-cooled
cloud of atoms results in initial phase space densities of ~1/200.
Evaporatively cooling through the BEC transition is achieved by lowering the
power in the trapping beams over ~ 2 s. The resulting condensates are F=1
spinors with 3.5 x 10^4 atoms distributed between the m_F = (-1,0,1) states.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let
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