4,502 research outputs found
Sampling Rare Populations
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147111/1/rssa00397.pd
Post-prandial changes in salivary glucocorticoids: Effects of dietary cholesterol and associations with bile acid excretion
Mechanisms to explain post-prandial increases in circulating glucocorticoids are not well understood and may involve increased adrenal secretion and/or altered steroid metabolism. We have compared salivary levels of cortisol and cortisone levels in healthy male and female volunteers fed either a low or cholesterol-rich midday meal. Urinary levels of steroids, bile acids and markers of lipid peroxidation were also measured. Males and females showed expected circadian changes in salivary steroids and postprandial peaks within 1h of feeding. After a high-cholesterol meal, postprandial cortisol increases were higher in males whereas post-prandial cortisone levels were higher in females. Urinary cortisol but not cortisone levels were higher on the day when males and females ate a high-cholesterol meal. Urinary bile acid excretion and anti-oxidant markers of lipid peroxidation, thiobarbituric acid reactive substances (TBARS), and total phenol content were not affected by dietary cholesterol but tended to be higher in males. Cross-tabulation of correlation coefficients indicated positive associations between urinary markers of peroxidation, bile acids, and cortisol:cortisone ratios. We conclude that dietary cholesterol (a substrate for steroidogenesis) does not have an acute effect on adrenal glucocorticoid synthesis and that gender but not a high-cholesterol meal may influence the interconversion of cortisol and cortisone. Longer term studies of the effects of dietary cholesterol are needed to analyze the associations between bile acids, steroid metabolism, and secretion and lipid peroxidation.11pubpub
Remarks on evolution of space-times in 3+1 and 4+1 dimensions
A large class of vacuum space-times is constructed in dimension 4+1 from
hyperboloidal initial data sets which are not small perturbations of empty
space data. These space-times are future geodesically complete, smooth up to
their future null infinity, and extend as vacuum space-times through their
Cauchy horizon. Dimensional reduction gives non-vacuum space-times with the
same properties in 3+1 dimensions.Comment: 10pp, exposition improved; final versio
Isolating the effects of visual imagery on prospective memory
Two experiments investigated the role of visual imagery in prospective memory (PM). In experiment 1, 140 participants completed a general knowledge quiz which included a PM task of writing a letter ‘X’ next to any questions that referred to space. Participants either visualised themselves performing this task, verbalised an implementation intention about the task, did both, or did neither. Performance on the PM task was enhanced in both conditions involving visual imagery but not by implementation intentions alone. In experiment 2, 120 participants imagined themselves writing a letter ‘X’ next to questions about space, or in a bizarre imagery condition imagined themselves drawing an alien next to those questions. Relative to the control condition, PM was significantly enhanced when participants imagined writing a letter ‘X’ next to the target questions, but not by the bizarre imagery task. The findings indicate that the robust effects of imagery observed in retrospective memory also extend to PM
The validity of the Landau-Zener model for output coupling of Bose condensates
We investigate the validity of the Landau-Zener model in describing the
output coupling of Bose condensates from magnetic traps by a chirped
radiofrequency field. The predictions of the model are compared with the
numerical solutions of the Gross-Pitaevskii equation. We find a dependence on
the chirp direction, and also quantify the role of gravitation.Comment: 4 pages, Late
Radio Astronomy
Contains reports on three research projects.National Aeronautics and Space Administration (Grants No. NsG-250-62 and No. NsG-419)United States Navy, Office of Naval Research (Contract Nonr-3963(02)-Task 2)Lincoln Laboratory (Purchase Order DDL BB-107)United States ArmyUnited States NavyUnited States Air Force (Contract AF19(604)-7400
Measuring the temporal coherence of an atom laser beam
We report on the measurement of the temporal coherence of an atom laser beam
extracted from a Rb Bose-Einstein condensate. Reflecting the beam from a
potential barrier creates a standing matter wave structure. From the contrast
of this interference pattern, observed by magnetic resonance imaging, we have
deduced an energy width of the atom laser beam which is Fourier limited by the
duration of output coupling. This gives an upper limit for temporal phase
fluctuations in the Bose-Einstein condensate.Comment: 4 pages, 3 figure
Phase preparation by atom counting of Bose-Einstein condensates in mixed states
We study the build up of quantum coherence between two Bose-Einstein
condensates which are initially in mixed states. We consider in detail the two
cases where each condensate is initially in a thermal or a Poisson distribution
of atom number. Although initially there is no relative phase between the
condensates, a sequence of spatial atom detections produces an interference
pattern with arbitrary but fixed relative phase. The visibility of this
interference pattern is close to one for the Poisson distribution of two
condensates with equal counting rates but it becomes a stochastic variable in
the thermal case, where the visibility will vary from run to run around an
average visibility of In both cases, the variance of the phase
distribution is inversely proportional to the number of atom detections in the
regime where this number is large compared to one but small compared with the
total number of atoms in the condensates.Comment: 9 pages, 6 PostScript figure, submitted to PR
Moving Atom-Field Interactions: Quantum Motional Decoherence and Relaxation
The reduced dynamics of an atomic qubit coupled both to its own quantized
center of mass motion through the spatial mode functions of the electromagnetic
field, as well as the vacuum modes, is calculated in the influence functional
formalism. The formalism chosen can describe the entangled non-Markovian
evolution of the system with a full account of the coherent back-action of the
environment on the qubit. We find a slight increase in the decoherence due to
the quantized center of mass motion and give a condition on the mass and qubit
resonant frequency for which the effect is important. In optically resonant
alkali-metal atom systems, we find the effect to be negligibly small. The
framework presented here can nevertheless be used for general considerations of
the coherent evolution of qubits in moving atoms in an electromagnetic field.Comment: 9 pages, 1 figure, minor change
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