16,355 research outputs found
Electroencephalographic studies of sleep
Various experimental studies on sleep are described. The following areas are discussed: (1) effect of altered day length on sleep, (2) effect of a partial loss of sleep on subsequent nocturnal sleep; (3) effect of rigid control over sleep-wake-up times; (4) sleep and wakefulness in a time-free environment; (5) distribution of spindles during a full night of sleep; and (6) effect on sleep and performance of swiftly changing shifts of work
Multiangle static and dynamic light scattering in the intermediate scattering angle range
We describe a light scattering apparatus based on a novel optical scheme
covering the scattering angle range 0.5\dg \le \theta \le 25\dg, an
intermediate regime at the frontier between wide angle and small angle setups
that is difficult to access by existing instruments. Our apparatus uses
standard, readily available optomechanical components. Thanks to the use of a
charge-coupled device detector, both static and dynamic light scattering can be
performed simultaneously at several scattering angles. We demonstrate the
capabilities of our apparatus by measuring the scattering profile of a variety
of samples and the Brownian dynamics of a dilute colloidal suspension
What are the most effective nonpharmacologic therapies for irritable bowel syndrome?
Herbal formulations, certain probiotics, elimination diets based on immunoglobulin G (IgG) antibodies, cognitive behavioral therapy, and self-help books have been shown to decrease global symptoms of irritable bowel syndrome (IBS) and improve overall quality of life (strength of recommendation [SOR ]: B). For patients with severe refractory IBS, hypnosis has been shown to relieve symptoms (SOR : B). Soluble fiber is more effective than insoluble fiber at improving global IBS symptom ratings (SOR : C)
Decoherence and Quantum Fluctuations
We show that the zero-point fluctuations of the intrinsic electromagnetic
environment limit the phase coherence time in all mesoscopic systems at low
temperatures. We derive this quantum noise limited dephasing time and its
temperature dependence in the crossover to the thermal regime. Our results
agree well with most experiments in 1D systems.Comment: 4 pages & 1 figur
Ground-state cooling of a trapped ion Using long-wavelength radiation
We demonstrate ground-state cooling of a trapped ion using radio-frequency (rf) radiation. This is a powerful tool for the implementation of quantum operations, where rf or microwave radiation instead of lasers is used for motional quantum state engineering. We measure a mean phonon number of n¯=0.13(4) after sideband cooling, corresponding to a ground-state occupation probability of 88(7)%. After preparing in the vibrational ground state, we demonstrate motional state engineering by driving Rabi oscillations between the |n=0⟩ and |n=1⟩ Fock states. We also use the ability to ground-state cool to accurately measure the motional heating rate and report a reduction by almost 2 orders of magnitude compared with our previously measured result, which we attribute to carefully eliminating sources of electrical noise in the system
Nonequilibrium brittle fracture propagation: Steady state, oscillations and intermittency
A minimal model is constructed for two-dimensional fracture propagation. The
heterogeneous process zone is presumed to suppress stress relaxation rate,
leading to non-quasistatic behavior. Using the Yoffe solution, I construct and
solve a dynamical equation for the tip stress. I discuss a generic tip velocity
response to local stress and find that noise-free propagation is either at
steady state or oscillatory, depending only on one material parameter. Noise
gives rise to intermittency and quasi-periodicity. The theory explains the
velocity oscillations and the complicated behavior seen in polymeric and
amorphous brittle materials. I suggest experimental verifications and new
connections between velocity measurements and material properties.Comment: To appear in Phys. Rev. Lett., 6 pages, self-contained TeX file, 3
postscript figures upon request from author at [email protected] or
[email protected], http://cnls-www.lanl.gov/homepages/rafi/rafindex.htm
The first high-amplitude delta Scuti star in an eclipsing binary system
We report the discovery of the first high-amplitude delta Scuti star in an
eclipsing binary, which we have designated UNSW-V-500. The system is an
Algol-type semi-detached eclipsing binary of maximum brightness V = 12.52 mag.
A best-fitting solution to the binary light curve and two radial velocity
curves is derived using the Wilson-Devinney code. We identify a late A spectral
type primary component of mass 1.49+/-0.02 M_sun and a late K spectral type
secondary of mass 0.33+/-0.02 M_sun, with an inclination of 86.5+/-1.0 degrees,
and a period of 5.3504751+/-0.0000006 d. A Fourier analysis of the residuals
from this solution is performed using PERIOD04 to investigate the delta Scuti
pulsations. We detect a single pulsation frequency of f_1 = 13.621+/-0.015 c/d,
and it appears this is the first overtone radial mode frequency. This system
provides the first opportunity to measure the dynamical mass for a star of this
variable type; previously, masses have been derived from stellar evolution and
pulsation models.Comment: 7 pages, 6 figures, 2 tables, for submission to MNRAS, v2: paper size
change, small typographical changes to abstrac
Identification of a nearby stellar association in the Hipparcos catalog: implications for recent, local star formation
The TW Hydrae Association (~55 pc from Earth) is the nearest known region of
recent star formation. Based primarily on the Hipparcos catalog, we have now
identified a group of 9 or 10 co-moving star systems at a common distance (~45
pc) from Earth that appear to comprise another, somewhat older, association
(``the Tucanae Association''). Together with ages and motions recently
determined for some nearby field stars, the existence of the Tucanae and TW
Hydrae Associations suggests that the Sun is now close to a region that was the
site of substantial star formation only 10-40 million years ago. The TW Hydrae
Association represents a final chapter in the local star formation history.Comment: 5 pages incl figs and table
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