9,928 research outputs found
System for measuring passenger reaction to transportation-vehicle vibration
Equipment is capable of measuring frequencies from 0 to 50 Hz and is portable, light, inexpensive, and easily adaptable to field operations. System could be used in situations where it is necessary to record simultaneously subject response to other types of physical measurement or stimuli, such as temperature, noise, or pressure
Lithium and Lithium Depletion in Halo Stars on Extreme Orbits
We have determined Li abundances in 55 metal-poor (3.6 < [Fe/H] < -0.7) stars
with extreme orbital kinematics. We find the Li abundance in the Li-plateau
stars and examine its decrease in low-temperature, low-mass stars. The Li
observations are primarily from the Keck I telescope with HIRES (spectral
resolution of ~48,000 and median signal-to-noise per pixel of 140). Abundances
or upper limits were determined for Li for all the stars with typical errors of
0.06 dex. Our 14 stars on the Li plateau give A(Li) = log N(Li)/N(H) + 12.00 of
2.215 +-0.110, consistent with earlier results. We find a dependence of the Li
abundance on metallicity as measured by [Fe/H] and the Fe-peak elements [Cr/H]
and [Ni/H], with a slope of ~0.18. We also find dependences of A(Li) with the
alpha elements, Mg, Ca, and Ti. For the n-capture element, Ba, the relation
between A(Li) and [Ba/H] has a shallower slope of 0.13; over a range of 2.6 dex
in [Ba/H], the Li abundance spans only a factor of two. We examined the
possible trends of A(Li) with the characteristics of the orbits of our halo
stars, but find no relationship with kinematic or dynamic properties. The stars
cooler than the Li plateau are separated into three metallicity subsets. The
decrease in A(Li) sets in at hotter temperatures at high metallicities than at
low metallicities; this is in the opposite sense of the predictions for Li
depletion from standard and non-standard models.Comment: 29 pages including 3 tables and 12 figures Accepted by The
Astrophysical Journal, for the 1 November 2005 issue, v. 63
ALMA polarimetric studies of rotating jet/disk systems
We have recently obtained polarimetric data at mm wavelengths with ALMA for
the young systems DG Tau and CW Tau, for which the rotation properties of jet
and disk have been investigated in previous high angular resolution studies.
The motivation was to test the models of magneto-centrifugal launch of jets via
the determination of the magnetic configuration at the disk surface. The
analysis of these data, however, reveals that self-scattering of dust thermal
radiation dominates the polarization pattern. It is shown that even if no
information on the magnetic field can be derived in this case, the polarization
data are a powerful tool for the diagnostics of the properties and the
evolution of dust in protoplanetary disks.Comment: 9 pages, 3 figures, to appear in "Jet Simulations, Experiments and
Theory. Ten years after JETSET, what is next ?", C. Sauty ed., Springer
Natur
Impact of age and race on outcomes of a program to prevent excess weight gain and disordered eating in adolescent girls
Interpersonal psychotherapy (IPT) prevents weight gain and reduces loss-of-control (LOC)-eating in adults. However, IPT was not superior to health-education (HE) for preventing excess weight gain and reducing LOC-eating over 1-year in adolescent girls at risk for excess weight gain and eating disorders. Limited data suggest that older and non-White youth may be especially responsive to IPT. In secondary analyses, we examined if age or race moderated weight and LOC-eating outcomes. The 113 participants (12–17 years; 56.6% White) from the original trial were re-contacted 3 years later for assessment. At baseline and follow-up visits through 3 years, we assessed BMI, adiposity by dual energy X-ray absorptiometry, and LOC-eating presence. In linear mixed models, baseline age moderated 3-year BMI outcome; older girls in IPT had the lowest 3-year BMI gain compared to younger girls in IPT and all girls in HE, p = 0.04. A similar pattern was observed for adiposity. Race moderated 3-year LOC-eating; non-White girls in IPT were most likely to abstain from LOC-eating at 3 years compared to all other girls, p = 0.04. This hypothesis-generating analysis suggests future studies should determine if IPT is especially efficacious at reducing LOC-eating in older, non-White adolescents
Finite-Band-width Effects on the Transition Temperature and NMR Relaxation Rate of Impure Superconductors
We study the thermodynamic properties of impure superconductors by explicitly
taking into consideration the finiteness of electronic bandwidths within the
phonon-mediated Eliashberg formalism. For a finite electronic bandwidth, the
superconducting transition temperature, , is suppressed by nonmagnetic
impurity scatterings. This is a consequence of a reduction in the effective
electron-phonon coupling, . The reduced is
reflected in the observation that the coherence peak in , where
is the nuclear spin-lattice relaxation time and is the temperature,
is enhanced by impurity scatterings for a finite bandwidth. Calculations are
presented for and as bandwidths and impurity scattering rates
are varied. Implications for doped C superconductors are discussed in
connection with and measurements.Comment: 10 pages. REVTeX. 5 postscript figures. Scheduled to be published in
Physical Review B, March 1. The previous submission is revised and two
figures are adde
Theory of Distinct Crystal Structures of Polymerized Fullerides AC60, A=K, Rb, Cs: the Specific Role of Alkalis
The polymer phases of AC60 form distinct crystal structures characterized by
the mutual orientations of the (C60-)n chains. We show that the direct electric
quadrupole interaction between chains always favors the orthorhombic structure
Pmnn with alternating chain orientations. However the specific quadrupolar
polarizability of the alkali metal ions leads to an indirect interchain
coupling which favors the monoclinic structure I2/m with equal chain
orientations. The competition between direct and indirect interactions explains
the structural difference between KC60 and RbC60, CsC60.Comment: 4 pages, 2 figures, 1 tabl
Collapse and black hole formation in magnetized, differentially rotating neutron stars
The capacity to model magnetohydrodynamical (MHD) flows in dynamical,
strongly curved spacetimes significantly extends the reach of numerical
relativity in addressing many problems at the forefront of theoretical
astrophysics. We have developed and tested an evolution code for the coupled
Einstein-Maxwell-MHD equations which combines a BSSN solver with a high
resolution shock capturing scheme. As one application, we evolve magnetized,
differentially rotating neutron stars under the influence of a small seed
magnetic field. Of particular significance is the behavior found for
hypermassive neutron stars (HMNSs), which have rest masses greater the mass
limit allowed by uniform rotation for a given equation of state. The remnant of
a binary neutron star merger is likely to be a HMNS. We find that magnetic
braking and the magnetorotational instability lead to the collapse of HMNSs and
the formation of rotating black holes surrounded by massive, hot accretion tori
and collimated magnetic field lines. Such tori radiate strongly in neutrinos,
and the resulting neutrino-antineutrino annihilation (possibly in concert with
energy extraction by MHD effects) could provide enough energy to power
short-hard gamma-ray bursts. To explore the range of outcomes, we also evolve
differentially rotating neutron stars with lower masses and angular momenta
than the HMNS models. Instead of collapsing, the non-hypermassive models form
nearly uniformly rotating central objects which, in cases with significant
angular momentum, are surrounded by massive tori.Comment: Submitted to a special issue of Classical and Quantum Gravity based
around the New Frontiers in Numerical Relativity meeting at the Albert
Einstein Institute, Potsdam, July 17-21, 200
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