3,289 research outputs found
Determination of physical and chemical states of lubricants in concentrated contacts, part 3
Solid and liquid thin films were analyzed by infrared emission Fourier microspectrophotometry. The apparatus used is a commercial absorption instrument modified to an emission instrument, comprising a rotating polarizing device, a miniature blackbody temperature reference adjustable in temperature and radiant flux and a microscope lens with a high numerical aperture in the entrance system for increased sensitivity and resolution. Studies of lubricant behavior in a simulated ball bearing showed the alignment of the fluid molecules in the Hertzian area. Polyphenyl ether plus 1% 1,1,2-trichloroethane (TCE) required lower shear rates for the same degree of alignment than without TCE. The experiment was run with 440 C stainless steel balls coated with TiN, a chemically inert material. In both cases, the alignment was strongly influenced by the presence of TCE. The results showed (1) the dependence of alignment of fluid molecules on flow and not on adsorption at metallic surfaces, (2) phase separation between lubricant and additive under high pressure which results in two phase flow and (3) reduction in traction of torque transmitting (traction) fluids
Community Efforts to Expand Dental Services for Low-Income People
Examines low-income patients' limited access to dental care, as well as state and community efforts to expand services, including changing Medicaid and State Children's Health Insurance Program reimbursement rates and licensing laws for preventive care
Suburban Poverty and the Health Care Safety Net
Examines trends in the number of suburban poor, their access to health care, and efforts to improve safety-net services in the suburbs of five cities. Explores causes of limited safety net capacity, community strategies, and policy implications
Infrared emission spectrophotometric study of the changes produced by TiN coating of metal surfaces in an operating EHD contact
Infrared emission spectra and related measurements were obtained from an operating ball/plate elastohydrodynamic (EHD) sliding contact under a variety of operating conditions. In order to be able to compare the effect of the ball surface, some of the balls were coated with a thin layer of titanium nitride (TiN) by vapor deposition. Polyphenyl ether (5P4E) was used as lubricant and 1 percent of 1,1,2-trichloroethane (TCE) as a surface-probing additive. TiN is chemically inert and its thermal conductivity is lower than that of steel. Therefore, the overall temperatures with TiN coated balls were higher. Nevertheless, no scuffing was observed with the coated balls under conditions giving rise to scuffing with the uncoated balls. Tractions were lower with the TiN coated balls and always when TCE was added to the 5P4E. These findings were found to be inversely related to the degree of polarization of the spectral emission bands. The intensity and the dichrosim of these bands were related to shear rates and inlet conditions of the EHD contact
Brightest Cluster Galaxies at the Present Epoch
We have observed 433 z<=0.08 brightest cluster galaxies (BCGs) in a full-sky
survey of Abell clusters. The BCG Hubble diagram is consistent to within 2% of
a Omega_m=0.3, Lambda=0.7 Hubble relation. The L_m-alpha relation for BCGs,
which uses alpha, the log-slope of the BCG photometric curve of growth, to
predict metric luminosity, L_m, has 0.27 mag residuals. We measure central
stellar velocity dispersions, sigma, of the BCGs, finding the Faber-Jackson
relation to flatten as the metric aperture grows to include an increasing
fraction of the total BCG luminosity. A 3-parameter "metric plane" relation
using alpha and sigma together gives the best prediction of L_m, with 0.21 mag
residuals. The projected spatial offset, r_x, of BCGs from the X-ray-defined
cluster center is a gamma=-2.33 power-law over 1<r_x<10^3 kpc. The median
offset is ~10 kpc, but ~15% of the BCGs have r_x>100 kpc. The absolute
cluster-dispersion normalized BCG peculiar velocity |Delta V_1|/sigma_c follows
an exponential distribution with scale length 0.39+/-0.03. Both L_m and alpha
increase with sigma_c. The alpha parameter is further moderated by both the
spatial and velocity offset from the cluster center, with larger alpha
correlated with the proximity of the BCG to the cluster mean velocity or
potential center. At the same time, position in the cluster has little effect
on L_m. The luminosity difference between the BCG and second-ranked galaxy, M2,
increases as the peculiar velocity of the BCG within the cluster decreases.
Further, when M2 is a close luminosity "rival" of the BCG, the galaxy that is
closest to either the velocity or X-ray center of the cluster is most likely to
have the larger alpha. We conclude that the inner portions of the BCGs are
formed outside the cluster, but interactions in the heart of the galaxy cluster
grow and extend the envelopes of the BCGs.Comment: Accepted for publication in the Astrophysical Journa
The Effect of Spatial Gradients in Stellar Mass-to-Light Ratio on Black Hole Mass Measurements
We have tested the effect of spatial gradients in stellar mass-to-light ratio
(Y) on measurements of black hole masses (MBH) derived from stellar orbit
superposition models. Such models construct a static gravitational potential
for a galaxy and its central black hole, but typically assume spatially uniform
Y. We have modeled three giant elliptical galaxies with gradients alpha = d(log
Y)/d(log r) from -0.2 to +0.1. Color and line strength gradients suggest mildly
negative alpha in these galaxies. Introducing a negative (positive) gradient in
Y increases (decreases) the enclosed stellar mass near the center of the galaxy
and leads to systematically smaller (larger) MBH measurements. For models with
alpha = -0.2, the best-fit values of MBH are 28%, 27%, and 17% lower than the
constant-Y case, in NGC 3842, NGC 6086, and NGC 7768, respectively. For alpha =
+0.1, MBH are 14%, 22%, and 17% higher than the constant-Y case for the three
respective galaxies. For NGC 3842 and NGC 6086, this bias is comparable to the
statistical errors from individual modeling trials. At larger radii, negative
(positive) gradients in Y cause the total stellar mass to decrease (increase)
and the dark matter fraction within one effective radius to increase
(decrease).Comment: 6 pages, 4 figures, 1 table. To appear in ApJ
Global Atmospheric Aerosol Modeling
Global aerosol models are used to study the distribution and properties of atmospheric aerosol particles as well as their effects on clouds, atmospheric chemistry, radiation, and climate. The present article provides an overview of the basic concepts of global atmospheric aerosol modeling and shows some examples from a global aerosol simulation. Particular emphasis is placed on the simulation of aerosol particles and their effects within global climate models
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