9,008 research outputs found
Calculation of skin-stiffener interface stresses in stiffened composite panels
A method for computing the skin-stiffener interface stresses in stiffened composite panels is developed. Both geometrically linear and nonlinear analyses are considered. Particular attention is given to the flange termination region where stresses are expected to exhibit unbounded characteristics. The method is based on a finite-element analysis and an elasticity solution. The finite-element analysis is standard, while the elasticity solution is based on an eigenvalue expansion of the stress functions. The eigenvalue expansion is assumed to be valid in the local flange termination region and is coupled with the finite-element analysis using collocation of stresses on the local region boundaries. Accuracy and convergence of the local elasticity solution are assessed using a geometrically linear analysis. Using this analysis procedure, the influence of geometric nonlinearities and stiffener parameters on the skin-stiffener interface stresses is evaluated
The Effect of Biased Communications On Both Trusting and Suspicious Voters
In recent studies of political decision-making, apparently anomalous behavior
has been observed on the part of voters, in which negative information about a
candidate strengthens, rather than weakens, a prior positive opinion about the
candidate. This behavior appears to run counter to rational models of decision
making, and it is sometimes interpreted as evidence of non-rational "motivated
reasoning". We consider scenarios in which this effect arises in a model of
rational decision making which includes the possibility of deceptive
information. In particular, we will consider a model in which there are two
classes of voters, which we will call trusting voters and suspicious voters,
and two types of information sources, which we will call unbiased sources and
biased sources. In our model, new data about a candidate can be efficiently
incorporated by a trusting voter, and anomalous updates are impossible;
however, anomalous updates can be made by suspicious voters, if the information
source mistakenly plans for an audience of trusting voters, and if the partisan
goals of the information source are known by the suspicious voter to be
"opposite" to his own. Our model is based on a formalism introduced by the
artificial intelligence community called "multi-agent influence diagrams",
which generalize Bayesian networks to settings involving multiple agents with
distinct goals
Changes in Dark Matter Properties After Freeze-Out
The properties of the dark matter that determine its thermal relic abundance
can be very different from the dark matter properties today. We investigate
this possibility by coupling a dark matter sector to a scalar that undergoes a
phase transition after the dark matter freezes out. If the value of Omega_DM
h^2 calculated from parameters measured at colliders and by direct and indirect
detection experiments does not match the astrophysically observed value, a
novel cosmology of this type could provide the explanation. This mechanism also
has the potential to account for the "boost factor" required to explain the
PAMELA data.Comment: 5 pages; v2: Fixed minor typo, added short discussion of application
to PAMELA and appropriate references, results unchange
Socioeconomic disadvantage in childhood as a predictor of excessive gestational weight gain and obesity in midlife adulthood.
BackgroundLower childhood socioeconomic position is associated with greater risk of adult obesity among women, but not men. Pregnancy-related weight changes may contribute to this gender difference. The objectives of this study were to determine the associations between: 1. childhood socioeconomic disadvantage and midlife obesity; 2. excessive gestational weight gain (GWG) and midlife obesity; and 3. childhood socioeconomic disadvantage and excessive GWG, among a representative sample of childbearing women.MethodsWe constructed marginal structural models for seven measures of childhood socioeconomic position for 4780 parous women in the United States, using National Longitudinal Survey of Youth (1979-2010) data. Institute of Medicine definitions were used for excessive GWG; body mass index ≥30 at age 40 defined midlife obesity. Analyses were separated by race/ethnicity. Additionally, we estimated controlled direct effects of childhood socioeconomic disadvantage on midlife obesity under a condition of never gaining excessively in pregnancy.ResultsLow parental education, but not other measures of childhood disadvantage, was associated with greater midlife obesity among non-black non-Hispanic women. Among black and Hispanic mothers, childhood socioeconomic disadvantage was not consistently associated with midlife obesity. Excessive GWG was associated with greater midlife obesity in all racial/ethnic groups. Childhood socioeconomic disadvantage was not statistically significantly associated with excessive GWG in any group. Controlled direct effects were not consistently weaker than total effects.ConclusionsChildhood socioeconomic disadvantage was associated with adult obesity, but not with excessive gestational weight gain, and only for certain disadvantage measures among non-black non-Hispanic mothers. Prevention of excessive GWG may benefit all groups through reducing obesity, but excessive GWG does not appear to serve as a mediator between childhood socioeconomic position and adult obesity in women
The WIRED Survey. IV. New Dust Disks from the McCook & Sion White Dwarf Catalog
We have compiled photometric data from the Wide-field Infrared Survey
Explorer All Sky Survey and other archival sources for the more than 2200
objects in the original McCook & Sion Catalog of Spectroscopically Identified
White Dwarfs. We applied color-selection criteria to identify 28 targets whose
infrared spectral energy distributions depart from the expectation for the
white dwarf photosphere alone. Seven of these are previously known white dwarfs
with circumstellar dust disks, five are known central stars of planetary
nebulae, and six were excluded for being known binaries or having possible
contamination of their infrared photometry. We fit white dwarf models to the
spectral energy distributions of the remaining ten targets, and find seven new
candidates with infrared excess suggesting the presence of a circumstellar dust
disk. We compare the model dust disk properties for these new candidates with a
comprehensive compilation of previously published parameters for known white
dwarfs with dust disks. It is possible that the current census of white dwarfs
with dust disks that produce an excess detectable at K-band and shorter
wavelengths is close to complete for the entire sample of known WDs to the
detection limits of existing near-IR all-sky surveys. The white dwarf dust disk
candidates now being found using longer wavelength infrared data are drawn from
a previously underrepresented region of parameter space, in which the dust
disks are overall cooler, narrower in radial extent, and/or contain fewer
emitting grains.Comment: accepted for publication in The Astrophysical Journal; 34 pages, 5
figures, 5 tables; added missing reference in Section 2 (p. 7
The Extremely Red Objects Found Thus Far in the Caltech Faint Galaxy Redshift Survey
We discuss the very red objects found in the first field of the Caltech Faint
Galaxy Redshift Survey, for which the observations and analysis are now
complete. In this field, which is 15 arcmin and at J005325+1234 there are
195 objects with mag, of which 84% have redshifts. The sample
includes 24 spectroscopically confirmed Galactic stars, 136 galaxies, three
AGNs, and 32 objects without redshifts.
About 10% of the sample has mag. Four of these objects have
redshifts, with . Three of these are based on absorption
features in the mid-UV, while the lowest redshift object shows the standard
features near 4000\AA. Many of the objects still without redshifts have been
observed spectroscopically, and no emission lines were seen in their spectra.
We believe they are galaxies with that are red due to their
age and stellar content and not to some large amount of internal reddening from
dust.
Among the many other results from this survey of interest here is a
determination of the median extinction in the mid-UV for objects with strong
emission line spectra at . The result is extinction by a factor
of 2 at 2400\AA.Comment: 6 pages, Latex, with 2 figures. To be published in the proceedings of
the conference "Infrared Surveys: A Prelude to SIRTF
New Challenges For Wind Shock Models: The Chandra Spectrum Of The Hot Star Delta Orionis
The Chandra spectrum of delta Ori A shows emission lines from hydrogen- and helium-like states of Si, Mg, Ne, and O, along with N VII Lyalpha and lines from ions in the range Fe XVII-Fe XXI In contrast to the broad lines seen in zeta Pup and zeta Ori (850 +/- 40 and 1000 +/- 240 km s(-1) half-width at half-maximum [HWHM], respectively), these lines are broadened to only 430 +/- 60 km s(-1) HWHM. This is much lower than the measured wind terminal velocity of 2000 km s(-1). The forbidden, intercombination, and resonance (fir) lines from He-like ions indicate that the majority of the X-ray line emission does not originate at the base of the wind, in agreement with the standard wind shock models for these objects. However, in that model the X-ray emission is distributed throughout an expanding, X-ray-absorbing wind, and it is therefore surprising that the emission lines appear relatively narrow, unshifted, and symmetric. We compare the observed line profiles to recent detailed models for X-ray line pro le generation in hot stars, but none of them offers a fully satisfactory explanation for the observed line profiles
Bounding the approach to oligarchy in a variant of the yard-sale model
We present analytical results for the Gini coefficient of economic inequality
under the dynamics of a modified Yard-Sale Model of kinetic asset exchange. A
variant of the Yard-Sale Model is introduced by modifying the underlying binary
transaction of the classical system. It is shown that the Gini coefficient is
monotone under the resulting dynamics but the approach to oligarchy, as
measured by the Gini index, can be bounded by a first-order differential
inequality used in conjunction with the differential Gronwall inequality. The
asymptotics of the modified system, with a redistributive tax, are derived and
shown to agree with the original, taxed Yard-Sale Model, which implies the
modified system is as suitable for matching real wealth distributions
The Effect of Porosity on X-ray Emission Line Profiles from Hot-Star Winds
We investigate the degree to which the nearly symmetric form of X-ray
emission lines seen in Chandra spectra of early-type supergiant stars could be
explained by a possibly porous nature of their spatially structured stellar
winds. Such porosity could effectively reduce the bound-free absorption of
X-rays emitted by embedded wind shocks, and thus allow a more similar
transmission of red- vs. blue-shifted emission from the back vs. front
hemispheres. For a medium consisting of clumps of size l and volume filling
factor f, in which the `porosity length' h=l/f increases with local radius as h
= h' r, we find that a substantial reduction in wind absorption requires a
quite large porosity scale factor h' > 1, implying large porosity lengths h >
r. The associated wind structure must thus have either a relatively large scale
l~ r, or a small volume filling factor f ~ l/r << 1, or some combination of
these. The relatively small-scale, moderate compressions generated by intrinsic
instabilities in line-driving seem unlikely to give such large porosity
lengths, leaving again the prospect of instead having to invoke a substantial
(ca. factor 5) downward revision in assumed mass-loss rates.Comment: 6 pages in apj-emulate; 3 figures; submitted to Ap
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