10,663 research outputs found
Gear mesh compliance modeling
A computer model has been constructed to simulate the compliance and load sharing in a spur gear mesh. The model adds the effect of rim deflections to previously developed state-of-the-art gear tooth deflection models. The effects of deflections on mesh compliance and load sharing are examined. The model can treat gear meshes composed to two external gears or an external gear driving an internal gear. The model includes deflection contributions from the bending and shear in the teeth, the Hertzian contact deformations, and primary and secondary rotations of the gear rims. The model shows that rimmed gears increase mesh compliance and, in some cases, improve load sharing
Study of an advanced transport airplane design concept known as Flatbed
The design concept and configuration of the Flatbed transport aircraft are presented. The Flatbed configuration combines into one frame, the ability to haul cargo, virtually unrestrained by cross sectional dimensions of the fuselage. The feasibility and capability of the Flatbed is discussed in depth
Radial Color Gradients in K+A Galaxies in Distant Clusters of Galaxies
Galaxies in rich clusters with z 0.3 are observed to have a higher
fraction of photometrically blue galaxies than their nearby counterparts. This
raises the important question of what environmental effects can cause the
termination of star formation between z 0.3 and the present. The star
formation may be truncated due to ram-pressure stripping, or the gas in the
disk may be depleted by an episode of star formation caused by some external
perturbation. To help resolve this issue, surface photometry was carried out
for a total of 70 early-type galaxies in the cluster Cl1358+62, at z
0.33, using two-color images from the Hubble Archive. The galaxies were divided
into two categories based on spectroscopic criteria: 24 are type K+A (e.g.,
strong Balmer lines, with no visible emission lines), while the remaining 46
are in the control sample with normal spectra. Radial color profiles were
produced to see if the K+A galaxies show bluer nuclei in relation to their
surrounding disks. Specifically, a linear gradient was fit to the radial color
profile of each galaxy. We find that the K+A galaxies on average tend to have
slightly bluer gradients towards the center than the normals. A
Kolmogorov-Smirnov two-sample test has been applied to the two sets of color
gradients. The result of the test indicates that there is only a 2%
probability that the K+A and normal samples are drawn from the same parent
distribution. There is a possible complication from a trend in the apparent
magnitude vs. color gradient relation, but overall our results favor the
centralized star formation scenario as an important process in the evolution of
galaxies in dense clusters.Comment: 16 pages, 12 figures, accepted for publication in A
Cosmology with velocity dispersion counts: an alternative to measuring cluster halo masses
The evolution of galaxy cluster counts is a powerful probe of several
fundamental cosmological parameters. A number of recent studies using this
probe have claimed tension with the cosmology preferred by the analysis of the
Planck primary CMB data, in the sense that there are fewer clusters observed
than predicted based on the primary CMB cosmology. One possible resolution to
this problem is systematic errors in the absolute halo mass calibration in
cluster studies, which is required to convert the standard theoretical
prediction (the halo mass function) into counts as a function of the observable
(e.g., X-ray luminosity, Sunyaev-Zel'dovich flux, optical richness). Here we
propose an alternative strategy, which is to directly compare predicted and
observed cluster counts as a function of the one-dimensional velocity
dispersion of the cluster galaxies. We argue that the velocity dispersion of
groups/clusters can be theoretically predicted as robustly as mass but, unlike
mass, it can also be directly observed, thus circumventing the main systematic
bias in traditional cluster counts studies. With the aid of the BAHAMAS suite
of cosmological hydrodynamical simulations, we demonstrate the potential of the
velocity dispersion counts for discriminating even similar CDM models.
These predictions can be compared with the results from existing redshift
surveys such as the highly-complete Galaxy And Mass Assembly (GAMA) survey, and
upcoming wide-field spectroscopic surveys such as the Wide Area Vista
Extragalactic Survey (WAVES) and the Dark Energy Survey Instrument (DESI).Comment: 15 pages, 13 figures. Accepted for publication in MNRAS. New section
on cosmological forecasts adde
Electron Neutrino Mass Measurement by Supernova Neutrino Bursts and Implications on Hot Dark Matter
We present a new strategy for measuring the electron neutrino mass (\mnue)
by future detection of a Galactic supernova in large underground detectors such
as the Super-Kamiokande (SK). This method is nearly model-independent and one
can get a mass constraint in a straightforward way from experimental data
without specifying any model parameters for profiles of supernova neutrinos. We
have tested this method using virtual data generated from a numerical model of
supernova neutrino emission by realistic Monte-Carlo simulations of the SK
detection. It is shown that this method is sensitive to \mnue of 3 eV
for a Galactic supernova, and this range is as low as the prediction of the
cold+hot dark matter scenario with a nearly degenerate mass hierarchy of
neutrinos, which is consistent with the current observations of solar and
atmospheric neutrino anomalies and density fluctuations in the universe.Comment: 4 pages including 1 figure, accepted by Phys. Rev. Let
Large-Scale Bulk Motions Complicate the Hubble Diagram
We investigate the extent to which correlated distortions of the luminosity
distance-redshift relation due to large-scale bulk flows limit the precision
with which cosmological parameters can be measured. In particular, peculiar
velocities of type 1a supernovae at low redshifts may prevent a sufficient
calibration of the Hubble diagram necessary to measure the dark energy equation
of state to better than 10%, and diminish the resolution of the equation of
state time-derivative projected for planned surveys. We consider similar
distortions of the angular-diameter distance, as well as the Hubble constant.
We show that the measurement of correlations in the large-scale bulk flow at
low redshifts using these distance indicators may be possible with a cumulative
signal-to-noise ratio of order 7 in a survey of 300 type 1a supernovae spread
over 20,000 square degrees.Comment: 6 pages; 4 figure
Non-Gaussianity from Self-Ordering Scalar Fields
The Universe may harbor relics of the post-inflationary epoch in the form of
a network of self-ordered scalar fields. Such fossils, while consistent with
current cosmological data at trace levels, may leave too weak an imprint on the
cosmic microwave background and the large-scale distribution of matter to allow
for direct detection. The non-Gaussian statistics of the density perturbations
induced by these fields, however, permit a direct means to probe for these
relics. Here we calculate the bispectrum that arises in models of self-ordered
scalar fields. We find a compact analytic expression for the bispectrum,
evaluate it numerically, and provide a simple approximation that may be useful
for data analysis. The bispectrum is largest for triangles that are aligned
(have edges ) as opposed to the local-model
bispectrum, which peaks for squeezed triangles (), and
the equilateral bispectrum, which peaks at . We
estimate that this non-Gaussianity should be detectable by the Planck satellite
if the contribution from self-ordering scalar fields to primordial
perturbations is near the current upper limit.Comment: 11 pages, 1 figur
Large Extra Dimensions, Sterile neutrinos and Solar Neutrino Data
Solar, atmospheric and LSND neutrino oscillation results require a light
sterile neutrino, , which can exist in the bulk of extra dimensions.
Solar , confined to the brane, can oscillate in the vacuum to the zero
mode of and via successive MSW transitions to Kaluza-Klein states of
. This new way to fit solar data is provided by both low and
intermediate string scale models. From average rates seen in the three types of
solar experiments, the Super-Kamiokande spectrum is predicted with 73%
probability, but dips characteristic of the 0.06 mm extra dimension should be
seen in the SNO spectrum.Comment: 4 pages, 2 figure
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