442,086 research outputs found
Surface temperatures and glassy state investigations in tribology, part 4
Measurements were made of the limiting shear stress for two naphthenic oils of differing molecular weight and three blends of the lower molecular weight oil and polyalkylmethacrylate polymers of differing molecular weight. The two base oils reached the same limiting shear stress for the same temperature and pressure. This was also true for all the polymer solutions although the polymer reduced the limiting shear stress by about 15 percent. It is shown that limiting stress is more a function of material type than viscosity or molecular weight. A new falling body viscometer was constructed to operate to 230 C and 0.6 GPa. Another viscometer was constructed to extend the pressure range to 1.1 GPa. A concentrated contact simulator was developed which allows recording of the traction force while the slide-roll ratio is continuously varied and the rolling speed is maintained essentially constant by a single drive motor. The configuration is that of a crowned roller against a disk. Measurement of lubricant minimum film thickness of elliptical EHD contacts of various aspect ratios were made by optical interferometry. The data collected were used to evaluate the Hamrock and Dowson minimum film thickness model over a range of contract ellipticity ratio where the major axis of the contact ellipse was aligned both parallel and perpendicular to the direction of motion. A statistical analysis of the measured film thickness data showed that on the average the experimental data were 30 percent greater than the film thickness predicted by the model. Preliminary development of the application of a scanning infrared radiation system to a tribo-system was completed
Electric Dipole Moments in the Generic Supersymmetric Standard Model
The generic supersymmetric standard model is a model built from a
supersymmetrized standard model field spectrum the gauge symmetries only. The
popular minimal supersymmetric standard model differs from the generic version
in having R-parity imposed by hand. We review an efficient formulation of the
model and some of the recently obtained interesting phenomenological features,
focusing on one-loop contributions to fermion electric dipole moments.Comment: 1+7 pages Revtex 3 figures incoporated; talk at NANP'0
Surface temperatures and glassy state investigations in tribology, part 3
Research related to the development of the limiting shear stress rheological model is reported. Techniques were developed for subjecting lubricants to isothermal compression in order to obtain relevant determinations of the limiting shear stress and elastic shear modulus. The isothermal compression limiting shear stress was found to predict very well the maximum traction for a given lubricant. Small amounts of side slip and twist incorporated in the model were shown to have great influence on the rising portion of the traction curve at low slide-roll ratio. The shear rheological model was also applied to a Grubin-like elastohydrodynamic inlet analysis for predicting film thicknesses when employing the limiting shear stress model material behavior
Investigations of lubricant rheology as applied to elastohydrodynamic lubrication
Measurements of lubricant shear rheological behavior in the amorphous solid region and near the liquid-solid transition are reported. Elastic, plastic and viscous behavior was observed. A shear rheological model based on primary laboratory data is proposed for concentrated contact lubrication. The model is a Maxwell model modified with a limiting shear stress. Three material properties are required: low shear stress viscosity, limiting elastic shear modulus, and the limiting shear stress the material can withstand. All three are functions of temperature and pressure. In applying the model to EHD contacts the predicted response possesses the characteristics expected from several experiments reported in the literature
Strings And Dyonic Plasmas
Recently Olesen has shown the existence of dual string solutions to the
equations of ideal Magnetohydrodynamics that describe the long wavelength
properties of electrically charged plasmas. Here, we extend these solutions to
include the case of plasmas consisting of point like dyons, which carry both
electric and magnetic charge. Such strings are dyonic in that they consist of
both magnetic and electric flux. We contrast some physical features of dyonic
plasmas with those of the purely electric or magnetic type, particularly in
relation to the validity of the ideal approximation.Comment: 11 pages, LaTeX, no figure
Is H3+ cooling ever important in primordial gas?
Studies of the formation of metal-free Population III stars usually focus
primarily on the role played by H2 cooling, on account of its large chemical
abundance relative to other possible molecular or ionic coolants. However,
while H2 is generally the most important coolant at low gas densities, it is
not an effective coolant at high gas densities, owing to the low critical
density at which it reaches local thermodynamic equilibrium (LTE) and to the
large opacities that develop in its emission lines. It is therefore possible
that emission from other chemical species may play an important role in cooling
high density primordial gas. A particularly interesting candidate is the H3+
molecular ion. This ion has an LTE cooling rate that is roughly a billion times
larger than that of H2, and unlike other primordial molecular ions such as H2+
or HeH+, it is not easily removed from the gas by collisions with H or H2. It
is already known to be an important coolant in at least one astrophysical
context -- the upper atmospheres of gas giants -- but its role in the cooling
of primordial gas has received little previous study. In this paper, we
investigate the potential importance of H3+ cooling in primordial gas using a
newly-developed H3+ cooling function and the most detailed model of primordial
chemistry published to date. We show that although H3+ is, in most
circumstances, the third most important coolant in dense primordial gas (after
H2 and HD), it is nevertheless unimportant, as it contributes no more than a
few percent of the total cooling. We also show that in gas irradiated by a
sufficiently strong flux of cosmic rays or X-rays, H3+ can become the dominant
coolant in the gas, although the size of the flux required renders this
scenario unlikely to occur.Comment: 60 pages, 22 figures. Submitted to MNRA
HESS J1507-622: an unique unidentified source off the Galactic Plane
Galactic very high energy (VHE, > 100 GeV) gamma ray sources in the inner
Galaxy H.E.S.S. survey tend to cluster within 1 degree in latitude around the
Galactic plane. HESS J1507-622 instead is unique, since it is located at
latitude of ~3.5 degrees. HESS J1507-622 is slightly extended over the PSF of
the instrument and hence its Galactic origin is clear. The search for
counterparts in other wavelength regimes (radio, infrared and X-rays) failed to
show any plausible counterparts; and given its position off the Galactic plane
and hence the absorption almost one order of magnitude lower, it is very
surprising to not see any counterparts especially at X-rays wavelengths (by
ROSAT, XMM Newton and Chandra). Its latitude implies that it is either rather
close, within about 1 kpc, or is located well off the Galactic plane. And also
the models reflect the uniqueness of this object: a leptonic PWN scenario would
place this source due to its quite small extension to multi-kpc distance
whereas a hadronic scenario would preferentially locate this object at
distances of < 1 kpc where the density of target material is higher
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