90,841 research outputs found
Analysis of wear-debris from full-scale bearing fatigue tests using the ferrograph
The ferrograph was used to determine the types and quantities of wear particles generated during full-scale bearing fatigue tests. Deep-groove ball bearings made from AISI 52100 steel were used. A MIL-L-23699 tetraester lubricant was used in a recirculating lubrication system containing a 49 mm absolute filter. Test conditions included a maximum Hertz stress of 2.4 GPa, a shaft speed of 15,000 rpm, and a lubricant supply temperature of 74 C (165 F). Four fatigue failures were detected by accelerometers in this test set. In general, the ferrograph was more sensitive (up to 23 hr) in detecting spall initiation than either accelerometers or the normal spectrographic oil analysis. Four particle types were observed: normal rubbing wear particles, spheres, nonferrous particles, and severe wear (spall) fragments
Ferrographic analysis of wear particles from sliding elastohydrodynamic experiments
The Ferrograph was used to analyze wear debris generated in a sliding elastohydrodynamic contact. The amount of wear debris correlates well with the ratio of film thickness to composite surface roughness (A ratio). The general wear level parameter and the wear severity index yielded similar correlations with average A ratios. Essentially all the generated wear particles were of the normal rubbing wear type. The Ferrograph was more sensitive in detecting the wear debris than was the commonly used emission spectrograph
Use of thin ionization calorimeters for measurements of cosmic ray energy spectra
The reliability of performing measurements of cosmic ray energy spectra with a thin ionization calorimeter was investigated. Monte Carlo simulations were used to determine whether energy response fluctuations would cause measured spectra to be different from the primary spectra. First, Gaussian distributions were assumed for the calorimeter energy resolutions. The second method employed a detailed Monte Carlo simulation of cascades from an isotropic flux of protons. The results show that as long as the energy resolution does not change significantly with energy, the spectral indices can be reliably determined even for sigma sub e/e = 50%. However, if the energy resolution is strongly energy dependent, the measured spectra do not reproduce the true spectra. Energy resolutions greatly improving with energy result in measured spectra that are too steep, while resolutions getting much worse with energy cause the measured spectra to be too flat
Ferrographic analysis of wear debris generated in a sliding elastohydrodynamic contact
The ferrograph was used to analyze wear debris generated in a sliding elastohydrodynamic contact. The amount of wear debris correlates well with the ratio of film thickness to composite surface roughness. Essentially all of the generated wear particles were of the normal rubbing wear type
Molecfit: A general tool for telluric absorption correction II. Quantitative evaluation on ESO-VLT X-Shooter spectra
Context: Absorption by molecules in the Earth's atmosphere strongly affects
ground-based astronomical observations. The resulting absorption line strength
and shape depend on the highly variable physical state of the atmosphere, i.e.
pressure, temperature, and mixing ratio of the different molecules involved.
Usually, supplementary observations of so-called telluric standard stars (TSS)
are needed to correct for this effect, which is expensive in terms of telescope
time. We have developed the software package molecfit to provide synthetic
transmission spectra based on parameters obtained by fitting narrow ranges of
the observed spectra of scientific objects. These spectra are calculated by
means of the radiative transfer code LBLRTM and an atmospheric model. In this
way, the telluric absorption correction for suitable objects can be performed
without any additional calibration observations of TSS. Aims: We evaluate the
quality of the telluric absorption correction using molecfit with a set of
archival ESO-VLT X-Shooter visible and near-infrared spectra. Methods: Thanks
to the wavelength coverage from the U to the K band, X-Shooter is well suited
to investigate the quality of the telluric absorption correction with respect
to the observing conditions, the instrumental set-up, input parameters of the
code, the signal-to-noise of the input spectrum, and the atmospheric profiles.
These investigations are based on two figures of merit, I_off and I_res, that
describe the systematic offsets and the remaining small-scale residuals of the
corrections. We also compare the quality of the telluric absorption correction
achieved with moelcfit to the classical method based on a telluric standard
star. (Abridged)Comment: Acc. by A&A; Software available via ESO:
http://www.eso.org/sci/software/pipelines/skytools
The survival and destruction of X-ray coronae of early-type galaxies in the rich cluster environments: a case study of Abell 1367
A new Chandra observation of the northwest region of the galaxy cluster A1367
reveals four cool galaxy coronae (0.4 - 1.0 keV) embedded in the hot
intracluster medium (ICM) (5 - 6 keV). While the large coronae of NGC 3842 and
NGC 3837 appear symmetric and relaxed, the galaxy coronae of the \lsim L*
galaxies (NGC 3841 and CGCG 97090) are disturbed and being stripped. Massive
galaxies, with dense cooling cores, are better able to resist ram pressure
stripping and survive in rich environments than \lsim L* galaxies whose
galactic coronae are much less dense. The survival of these cool coronae
implies that thermal conduction from the hot surrounding ICM has to be
suppressed by a factor of at least 60, at the corona boundary. Within the
galaxy coronae of NGC 3842 and NGC 3837, stellar mass loss or heat conduction
with the Spitzer value may be sufficient to balance radiative cooling. Energy
deposition at the ends of collimated jets may heat the outer coronae, but allow
the survival of a small, dense gas core (e.g., NGC 3842 in A1367 and NGC 4874
in Coma). The survived X-ray coronae become significantly smaller and fainter
with the increasing ambient pressure.Comment: 11 pages, 7 figures, emulateapj5, accepted by Ap
Reinforced structural plastics
Reinforced polyimide structures are described. Reinforcing materials are impregnated with a suspension of polyimide prepolymer and bonded together by heat and pressure to form a cured, hard-reinforced, polyimide structure
Direct constraints on the dark matter self-interaction cross-section from the merging galaxy cluster 1E0657-56
We compare new maps of the hot gas, dark matter, and galaxies for 1E0657-56,
a cluster with a rare, high-velocity merger occurring nearly in the plane of
the sky. The X-ray observations reveal a bullet-like gas subcluster just
exiting the collision site. A prominent bow shock gives an estimate of the
subcluster velocity, 4500 km/s, which lies mostly in the plane of the sky. The
optical image shows that the gas lags behind the subcluster galaxies. The
weak-lensing mass map reveals a dark matter clump lying ahead of the
collisional gas bullet, but coincident with the effectively collisionless
galaxies. From these observations, one can directly estimate the cross-section
of the dark matter self-interaction. That the dark matter is not fluid-like is
seen directly in the X-ray -- lensing mass overlay; more quantitative limits
can be derived from three simple independent arguments. The most sensitive
constraint, sigma/m<1 cm^2/g, comes from the consistency of the subcluster
mass-to-light ratio with the main cluster (and universal) value, which rules
out a significant mass loss due to dark matter particle collisions. This limit
excludes most of the 0.5-5 cm^2/g interval proposed to explain the flat mass
profiles in galaxies. Our result is only an order-of-magnitude estimate which
involves a number of simplifying, but always conservative, assumptions;
stronger constraints may be derived using hydrodynamic simulations of this
cluster.Comment: Text clarified; some numbers changed slightly for consistency with
final version of the accompanying lensing paper. 6 pages, uses emulateapj.
ApJ in pres
Quantized transport, strain-induced perfectly conducting modes and valley filtering on shape-optimized graphene Corbino devices
The extreme mechanical resilience of graphene and the peculiar coupling it
hosts between lattice and electronic degrees of freedom have spawned a strong
impetus towards strain-engineered graphene where, on the one hand, strain
augments the richness of its phenomenology and makes possible new concepts for
electronic devices and, on the other hand, new and extreme physics might take
place. Here, we demonstrate that the shape of substrates supporting graphene
sheets can be optimized for approachable experiments where strain-induced
pseudomagnetic fields (PMF) can be tailored by pressure for directionally
selective electronic transmission and pinching-off of current flow down to the
quantum channel limit. The Corbino-type layout explored here furthermore allows
filtering of charge carriers according to valley and current direction, which
can be used to inject or collect valley-polarized currents, thus realizing one
of the basic elements required for valleytronics. Our results are based on a
framework developed to realistically determine the combination of strain,
external parameters, and geometry optimally compatible with the target spatial
profile of a desired physical property --- the PMF in this case. Characteristic
conductance profiles are analyzed through quantum transport calculations on
large graphene devices having the optimal shape.Comment: 5+7 figures. Supporting information include
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