8,551 research outputs found
Transient Response of Shells of Revolution by Direct Integration and Modal Superposition Methods
The results of an analytical effort to obtain and evaluate transient response data for a cylindrical and a conical shell by use of two different approaches: direct integration and modal superposition are described. The inclusion of nonlinear terms is more important than the inclusion of secondary linear effects (transverse shear deformation and rotary inertia) although there are thin-shell structures where these secondary effects are important. The advantages of the direct integration approach are that geometric nonlinear and secondary effects are easy to include and high-frequency response may be calculated. In comparison to the modal superposition technique the computer storage requirements are smaller. The advantages of the modal superposition approach are that the solution is independent of the previous time history and that once the modal data are obtained, the response for repeated cases may be efficiently computed. Also, any admissible set of initial conditions can be applied
Vibration characteristics of ring-stiffened orthotropic shells of revolution
Computer program solves vibration modes and frequencies of thin shells of revolution having general meridional curvature and orthotropic elastic properties in order to evaluate the dynamic behavior of structures with thin shelled components
Theoretical determination of lifetimes of metastable states in Sc III and Y III
Lifetimes of the first two metastable states in Sc^{2+} and Y^{2+} are
determined using the relativistic coupled-cluster theory. There is a
considerable interest in studying the electron correlation effects in these
ions as though their electronic configurations are similar to the neutral
alkali atoms, their structures are very different from the latter. We have made
a comparative study of the correlation trends between the above doubly ionized
systems with their corresponding neutral and singly ionized iso-electronic
systems. The lifetimes of the excited states of these ions are very important
in the field of astrophysics, especially for the study of post-main sequence
evolution of the cool giant stars.Comment: 13 pages, 1 figure and 5 table
LOTIS, Super-LOTIS, Sloan Digital Sky Survey, and Tautenburg Observations of GRB 010921
We present multi-instrument optical observations of the High Energy Transient Explorer (HETE-2) and In-terplanetary Network error box of GRB 010921. This event was the first gamma-ray burst (GRB) partly localized by HETE-2 that has resulted in the detection of an optical afterglow. In this Letter, we report the earliest known observations of the GRB 010921 field, taken with the 0.11 m Livermore Optical Transient Imaging System (LOTIS) telescope, and the earliest known detection of the GRB 010921 optical afterglow, using the 0.5 m Sloan Digital Sky Survey Photometric Telescope (SDSS PT). Observations with the LOTIS telescope began during a routine sky patrol 52 minutes after the burst. Observations were made with the SDSS PT, the 0.6 m Super-LOTIS telescope, and the 1.34 m Tautenburg Schmidt telescope 21.3, 21.8, and 37.5 hr, respectively, after the GRB. In addition, the host galaxy was observed with the US Naval Observatory Flagstaff Station 1.0 m telescope 56 days after the burst. We find that at later times ( t \u3e1 day after the burst), the optical afterglow exhibited a power-law decline with a slope of α - 1.75 + or - 0.28. However, our earliest observations show that this power-law decline cannot have extended to early times ( t \u3c 0.035 days)
Association Between Advanced Age and Vascular Disease in Different Arterial Territories A Population Database of Over 3.6 Million Subjects
ObjectivesThis study sought to determine the relationship between vascular disease in different arterial territories and advanced age.BackgroundVascular disease in the peripheral circulation is associated with significant morbidity and mortality. There is little data to assess the prevalence of different phenotypes of vascular disease in the very elderly.MethodsOver 3.6 million self-referred participants from 2003 to 2008 who completed a medical and lifestyle questionnaire in the United States were evaluated by screening ankle brachial indices <0.9 for peripheral artery disease (PAD), and ultrasound imaging for carotid artery stenosis (CAS) >50% and abdominal aortic aneurysm (AAA) >3 cm. Participants were stratified by decade of life. Multivariate logistic regression analysis was used to estimate odds of disease in different age categories.ResultsOverall, the prevalence of PAD, CAS, and AAA, was 3.7%, 3.9%, and 0.9%, respectively. Prevalence of any vascular disease increased with age (40 to 50 years: 2%, 51 to 60 years: 3.5%, 61 to 70 years: 7.1%, 71 to 80 years: 13.0%, 81 to 90 years: 22.3%, 91 to 100 years: 32.5%; p < 0.0001). Prevalence of disease in each vascular territory increased with age. After adjustment for sex, race/ethnicity, body mass index, family history of cardiovascular disease, smoking, diabetes, hypertension, hypercholesterolemia, and exercise, the odds of PAD (odds ratio [OR]: 2.14; 95% confidence interval [CI]: 2.12 to 2.15), CAS (OR: 1.80; 95% CI: 1.79 to 1.81), and AAA (OR: 2.33; 95% CI: 2.30 to 2.36) increased with every decade of life.ConclusionsThere is a dramatic increase in the prevalence of PAD, CAS, and AAA with advanced age. More than 20% and 30% of octogenarians and nonagenarians, respectively, have vascular disease in at least 1 arterial territory
The HgMn Binary Star Phi Herculis: Detection and Properties of the Secondary and Revision of the Elemental Abundances of the Primary
Observations of the Mercury-Manganese star Phi Herculis with the Navy
Prototype Optical Interferometer (NPOI) conclusively reveal the previously
unseen companion in this single-lined binary system. The NPOI data were used to
predict a spectral type of A8V for the secondary star Phi Her B. This
prediction was subsequently confirmed by spectroscopic observations obtained at
the Dominion Astrophysical Observatory. Phi Her B is rotating at 50 +/-3
km/sec, in contrast to the 8 km/sec lines of Phi Her A. Recognizing the lines
from the secondary permits one to separate them from those of the primary. The
abundance analysis of Phi Her A shows an abundance pattern similar to those of
other HgMn stars with Al being very underabundant and Sc, Cr, Mn, Zn, Ga, Sr,
Y, Zr, Ba, Ce, and Hg being very overabundant.Comment: Accepted to ApJ, 45 pages, 11 figure
Exact time evolution and master equations for the damped harmonic oscillator
Using the exact path integral solution for the damped harmonic oscillator it
is shown that in general there does not exist an exact dissipative Liouville
operator describing the dynamics of the oscillator for arbitrary initial bath
preparations. Exact non-stationary Liouville operators can be found only for
particular preparations. Three physically meaningful examples are examined. An
exact new master equation is derived for thermal initial conditions. Second,
the Liouville operator governing the time-evolution of equilibrium correlations
is obtained. Third, factorizing initial conditions are studied. Additionally,
one can show that there are approximate Liouville operators independent of the
initial preparation describing the long time dynamics under appropriate
conditions. The general form of these approximate master equations is derived
and the coefficients are determined for special cases of the bath spectral
density including the Ohmic, Drude and weak coupling cases. The connection with
earlier work is discussed.Comment: to be published in Phys. Rev.
LOTIS, Super-LOTIS, SDSS and Tautenburg Observations of GRB 010921
We present multi-instrument optical observations of the High Energy Transient
Explorer (HETE-2)/Interplanetary Network (IPN) error box of GRB 010921. This
event was the first gamma ray burst (GRB) localized by HETE-2 which has
resulted in the detection of an optical afterglow. In this paper we report the
earliest known observations of the GRB010921 field, taken with the 0.11-m
Livermore Optical Transient Imaging System (LOTIS) telescope, and the earliest
known detection of the GRB010921 optical afterglow, using the 0.5-m Sloan
Digital Sky Survey Photometric Telescope (SDSS PT). Observations with the LOTIS
telescope began during a routine sky patrol 52 minutes after the burst.
Observations were made with the SDSS PT, the 0.6-m Super-LOTIS telescope, and
the 1.34-m Tautenburg Schmidt telescope at 21.3, 21.8, and 37.5 hours after the
GRB, respectively. In addition, the host galaxy was observed with the USNOFS
1.0-m telescope 56 days after the burst. We find that at later times (t > 1 day
after the burst), the optical afterglow exhibited a power-law decline with a
slope of . However, our earliest observations show that
this power-law decline can not have extended to early times (t < 0.035 day).Comment: AASTeX v5.x LaTeX 2e, 6 pages with 2 postscript figures, will be
submitted to ApJ Letter
Binarity at the L/T brown dwarf transition
Current atmospheric models cannot reproduce some of the characteristics of
the transition between the L dwarfs with cloudy atmospheres and the T dwarfs
with dust-depleted photospheres. It has been proposed that a majority of the
L/T transition brown dwarfs could actually be a combinaison of a cloudy L dwarf
and a clear T dwarf. Indeed binarity seems to occur more frequently among L/T
transition brown dwarfs.
We aim to refine the statistical significance of the seemingly higher
frequency of binaries. Co-eval binaries would also be interesting test-beds for
evolutionary models. We obtained high-resolution imaging for six mid-L to
late-T dwarfs, with photometric distances between 8 and 33pc, using the
adaptive optics systems NACO at the VLT, and the Lick system, both with the
laser guide star.
We resolve none of our targets. Combining our data with published results, we
obtain a frequency of resolved L/T transition brown dwarfs of (31+21-15)%,
compared to (21+10-7)% and (14+14-7)% for mid-L and T dwarfs (90% of confidence
level). These fractions do not significantly support, nor contradict, the
hypothesis of a larger binary fraction in the L/T transition. None of our
targets has companions with effective temperatures as low as 360-1000K at
separations larger than 0.5".Comment: 6 pages, 4 figures, accepted by A&
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