1,208 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
Realization of a Resonant Fermi Gas with a Large Effective Range
We have measured the interaction energy and three-body recombination rate for
a two-component Fermi gas near a narrow Feshbach resonance and found both to be
strongly energy dependent. Even for deBroglie wavelengths greatly exceeding the
van der Waals length scale, the behavior of the interaction energy as a
function of temperature cannot be described by atoms interacting via a contact
potential. Rather, energy-dependent corrections beyond the scattering length
approximation are required, indicating a resonance with an anomalously large
effective range. For fields where the molecular state is above threshold, the
rate of three-body recombination is enhanced by a sharp, two-body resonance
arising from the closed-channel molecular state which can be magnetically tuned
through the continuum. This narrow resonance can be used to study strongly
correlated Fermi gases that simultaneously have a sizeable effective range and
a large scattering length.Comment: to appear in Phys. Rev. Let
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
Radionuclide Contaminant Burdens in Arctic Marine Mammals Harvested During Subsistence Hunting
We conducted gamma spectrometric analyses on more than 200 arctic marine mammal tissue samples. These samples were primarily provided by subsistence hunters from northern Alaska, with a smaller number of samples from the Resolute region in Canada. The majority of samples (>90%) had detectable levels of the anthropogenic radionuclide 137Cs, with a mean level observed in all samples of 0.67 Bq/kg dry weight ± 0.81 (SD). Converted to wet weight, the mean was 0.21 Bq/kg ± 0.19 SD. The median activity observed was 0.45 Bq/kg dry weight (0.18 Bq/kg wet weight) with a range from detection limits to 6.7 Bq/kg dry weight (1.1 Bq/kg wet weight). These findings confirm expectations that current anthropogenic gamma emitter burdens in marine mammals used in the North American Arctic as subsistence food resources are well below activities that would normally merit public health concern (~1000 Bq/kg wet weight). Some differences among species and tissues were observed. Beluga tissues had slightly higher mean burdens of 137Cs overall, and epidermis and muscle tissues in bowhead and beluga whales typically had higher burdens than other tissues analyzed. Low levels of the neutron activation product 108mAg (half-life 418 yr.), probably bioaccumulated from bomb fallout sources, were observed in 16 of 17 beluga livers analyzed, but were not found in any other tissues of beluga or in any other species sampled. A subset of 39 samples of various tissues was analyzed for the alpha and beta emitters 239,240Pu and 90Sr. Plutonium levels were near the threshold of detectability (~0.1 Bq/kg dry weight) in 6 of the 39 samples; all other samples had no detectable plutonium. A detectable level of 90Sr (10.3 ± 1.0 Bq/kg dry weight) was observed in only one of the 39 samples analyzed, a bowhead epidermis sample. Although the accumulation of 108mAg has not been previously reported in any marine mammal livers, all of our analytical measurements indicate that only very low levels of anthropogenic radioactivity are associated with marine mammals harvested and consumed in the North American Arctic.On a effectuĂ© des analyses gamma-spectromĂ©triques sur plus de 200 Ă©chantillons de tissus prĂ©levĂ©s sur des mammifĂšres marins. La plupart de ces Ă©chantillons Ă©taient fournis par des chasseurs de subsistance de l'Alaska septentrional, et un petit nombre venaient de la rĂ©gion de Resolute au Canada. La majoritĂ© des Ă©chantillons (> 90 p. cent) contenaient des niveaux dĂ©tectables du radionuclĂ©ide anthropique 137Cs, avec un niveau moyen observĂ© dans tous les Ă©chantillons de 0,67 Bq/kg de poids sec ± 0,81 (Ă©cart-type). Convertie en poids frais, la moyenne Ă©tait de 0,21 Bq/kg ± 0,19 d'Ă©cart-type. L'activitĂ© mĂ©diane observĂ©e Ă©tait de 0,45 Bq/kg de poids sec (0,18 Bq/kg de poids frais) avec une fourchette allant des seuils de dĂ©tection jusqu'Ă 6,7 Bq/kg de poids sec (1,1 Bq/kg de poids frais). Ces rĂ©sultats confirment les rĂ©ponses prĂ©vues, Ă savoir que les charges actuelles des Ă©metteurs gamma anthropiques prĂ©sentes chez les mammifĂšres marins utilisĂ©s en AmĂ©rique du Nord comme ressource de subsistance sont bien infĂ©rieures aux niveaux qui voudraient normalement qu'on s'inquiĂšte pour la santĂ© publique (~1000 Bq/kg de poids frais). On a observĂ© certaines diffĂ©rences dans les espĂšces et les tissus. Dans l'ensemble, les tissus prĂ©levĂ©s sur le bĂ©louga contenaient des charges moyennes de 137Cs lĂ©gĂšrement plus Ă©levĂ©es, et l'Ă©piderme et les tissus musculaires de la baleine borĂ©ale et du bĂ©louga avaient gĂ©nĂ©ralement des charges supĂ©rieures Ă celles trouvĂ©es dans les autres tissus analysĂ©s. Dans 16 des 17 foies de bĂ©louga analysĂ©s, on a observĂ© de faibles niveaux du produit d'activation neutronique 108mAg (demi-vie 418 annĂ©es), dont la bioaccumulation est probablement due Ă des retombĂ©es de bombes atomiques, mais on n'en a observĂ© aucune trace dans les autres tissus du bĂ©louga ou de toute autre espĂšce Ă©chantillonnĂ©e. On a analysĂ© un sous-ensemble de 39 Ă©chantillons provenant de tissus divers pour savoir s'ils contenaient des Ă©metteurs alpha et bĂȘta 239,240Pu et 90Sr. Dans 6 des 39 Ă©chantillons, les niveaux de plutonium Ă©taient proches du seuil de dĂ©tectabilitĂ© (~ 0,1 Bq/kg de poids sec), et on n'a pas trouvĂ© de plutonium dĂ©tectable dans aucun des autres Ă©chantillons. On a observĂ© un niveau dĂ©tectable de 90Sr (10,3 ± 1,0 Bq/kg de poids sec) dans un seul des 39 Ă©chantillons analysĂ©s, soit un Ă©chantillon d'Ă©piderme de baleine borĂ©ale. Bien qu'on n'ait jamais rapportĂ© auparavant une accumulation de 108mAg dans le foie d'un mammifĂšre marin, toutes nos mesures analytiques rĂ©vĂšlent que les mammifĂšres marins faisant l'objet d'une activitĂ© d'exploitation et consommĂ©s dans l'Arctique nord-amĂ©ricain ne prĂ©sentent que de trĂšs faibles niveaux de radioactivitĂ© anthropique
The Effects of Degraded Digital Instrumentation and Control Systems on Human-system Interfaces and Operator Performance: HFE Review Guidance and Technical Basis
New and advanced reactors will use integrated digital instrumentation and control (I&C) systems to support operators in their monitoring and control functions. Even though digital systems are typically highly reliable, their potential for degradation or failure could significantly affect operator performance and, consequently, impact plant safety. The U.S. Nuclear Regulatory Commission (NRC) supported this research project to investigate the effects of degraded I&C systems on human performance and plant operations. The objective was to develop human factors engineering (HFE) review guidance addressing the detection and management of degraded digital I&C conditions by plant operators. We reviewed pertinent standards and guidelines, empirical studies, and plant operating experience. In addition, we conducted an evaluation of the potential effects of selected failure modes of the digital feedwater system on human-system interfaces (HSIs) and operator performance. The results indicated that I&C degradations are prevalent in plants employing digital systems and the overall effects on plant behavior can be significant, such as causing a reactor trip or causing equipment to operate unexpectedly. I&C degradations can impact the HSIs used by operators to monitor and control the plant. For example, sensor degradations can make displays difficult to interpret and can sometimes mislead operators by making it appear that a process disturbance has occurred. We used the information obtained as the technical basis upon which to develop HFE review guidance. The guidance addresses the treatment of degraded I&C conditions as part of the design process and the HSI features and functions that support operators to monitor I&C performance and manage I&C degradations when they occur. In addition, we identified topics for future research
L-Arginine promotes gut hormone release and reduces food intake in rodents
Aims: To investigate the anorectic effect of Lâarginine (LâArg) in rodents.
Methods: We investigated the effects of LâArg on food intake, and the role of the anorectic gut hormones glucagonâlike peptideâ1 (GLPâ1) and peptide YY (PYY), the Gâproteinâcoupled receptor family C group 6 member A (GPRC6A) and the vagus nerve in mediating these effects in rodents.
Results: Oral gavage of LâArg reduced food intake in rodents, and chronically reduced cumulative food intake in dietâinduced obese mice. Lack of the GPRC6A in mice and subdiaphragmatic vagal deafferentation in rats did not influence these anorectic effects. LâArg stimulated GLPâ1 and PYY release in vitro and in vivo. Pharmacological blockade of GLPâ1 and PYY receptors did not influence the anorectic effect of LâArg. LâArgâmediated PYY release modulated net ion transport across the gut mucosa. Intracerebroventricular (i.c.v.) and intraperitoneal (i.p.) administration of LâArg suppressed food intake in rats.
Conclusions: LâArg reduced food intake and stimulated gut hormone release in rodents. The anorectic effect of LâArg is unlikely to be mediated by GLPâ1 and PYY, does not require GPRC6A signalling and is not mediated via the vagus. I.c.v. and i.p. administration of LâArg suppressed food intake in rats, suggesting that LâArg may act on the brain to influence food intake. Further work is required to determine the mechanisms by which LâArg suppresses food intake and its utility in the treatment of obesity
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
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