41,738 research outputs found
A comprehensive analysis of cavitation and liquid impingement erosion data
Cavitation-erosion experimental data previously covering several materials tested in a rotating disk device and a magnetostriction apparatus were analyzed using new normalization and curve-fitting techniques. From this process a universal approach is derived which can include data from cavitation and liquid impingement studies for specific materials from different test devices
Universal approach to analysis of cavitation and liquid-impingement erosion data
Cavitation erosion experimental data was analyzed by using normalization and curve-fitting techniques. Data were taken from experiments on several materials tested in both a rotating disk device and a magnetostriction apparatus. Cumulative average volume loss rate and time data were normalized relative to the peak erosion rate and the time to peak erosion rate, respectively. From this process a universal approach was derived that can include data on specific materials from different test devices for liquid impingement and cavitation erosion studies
Spectral Efficiency of One-Bit Sigma-Delta Massive MIMO
We examine the uplink spectral efficiency of a massive MIMO base station employing a one-bit Sigma-Delta ( \Sigma \Delta ) sampling scheme implemented in the spatial rather than the temporal domain. Using spatial rather than temporal oversampling, and feedback of the quantization error between adjacent antennas, the method shapes the spatial spectrum of the quantization noise away from an angular sector where the signals of interest are assumed to lie. It is shown that, while a direct Bussgang analysis of the \Sigma \Delta approach is not suitable, an alternative equivalent linear model can be formulated to facilitate an analysis of the system performance. The theoretical properties of the spatial quantization noise power spectrum are derived for the \Sigma \Delta array, as well as an expression for the spectral efficiency of maximum ratio combining (MRC). Simulations verify the theoretical results and illustrate the significant performance gains offered by the \Sigma \Delta approach for both MRC and zero-forcing receivers
A hybrid computer program for rapidly solving flowing or static chemical kinetic problems involving many chemical species
A hybrid chemical kinetic computer program was assembled which provides a rapid solution to problems involving flowing or static, chemically reacting, gas mixtures. The computer program uses existing subroutines for problem setup, initialization, and preliminary calculations and incorporates a stiff ordinary differential equation solution technique. A number of check cases were recomputed with the hybrid program and the results were almost identical to those previously obtained. The computational time saving was demonstrated with a propane-oxygen-argon shock tube combustion problem involving 31 chemical species and 64 reactions. Information is presented to enable potential users to prepare an input data deck for the calculation of a problem
Pressure Drop Across Woven Screens Under Uniform and Nonuniform Flow Conditions
Tests were conducted to determine the experimental pressure drop and velocity data for water flowing through woven screens. The types of materials used are dutch twill and square weave fabrics. Pressure drop measures were made at four locations in a rectangular channel. The data are presented as change in pressure compared with the average entry velocity and the numerical relationship is determined by dividing the volumetric flow rate by the screen area open to flow. The equations of continuity and momentum are presented. A computer program listing an extension of a theoretical model and data from that computer program are included
Low radio frequency signatures of ram pressure stripping in Virgo spiral NGC 4254
We report the detection of extended low radio frequency continuum emission
beyond the optical disk of the spiral galaxy NGC 4254 using the Giant Metrewave
Radio Telescope. NGC 4254, which has an almost face-on orientation, is located
in the outskirts of the Virgo cluster. Since such extended emission is uncommon
in low inclination galaxies, we believe it is a signature of magnetised plasma
pushed out of the disk by ram pressure of the intracluster medium as NGC 4254
falls into the Virgo cluster. The detailed spectral index distribution across
NGC 4254 shows that the steepest spectrum alpha < -1 (S propto nu^{alpha})
arises in the gas beyond the optical disk. This lends support to the ram
pressure scenario by indicating that the extended emission is not from the disk
gas but from matter which has been stripped by ram pressure. The steeper
spectrum of the extended emission is reminiscent of haloes in edge-on galaxies.
The sharp fall in intensity and enhanced polarization in the south of the
galaxy, in addition to enhanced star formation reported by others provide
evidence towards the efficacy of ram pressure on this galaxy. HI 21cm
observations show that the gas in the north lags in rotation and hence is
likely the atomic gas which is carried along with the wind. NGC 4254 is a
particularly strong radio emitter with a power of 7x10^{22} Watts/Hz at 240
MHz. We find that the integrated spectrum of the galaxy flattens at lower
frequencies and is well explained by an injection spectrum with
alpha_0=-0.45+-0.12. We end by comparing published simulation results with our
data and conclude that ram pressure stripping is likely to be a significant
contributor to evolution of galaxies residing in X-ray poor groups and cluster
outskirts.Comment: 10 pages, 7 figures (figures 1,2 and 4 are in jpg format) and 2
tables; Accepted for publication in MNRA
On the origin of the various types of radio emission in GRS 1915+105
We investigate the association between the radio ``plateau'' states and the
large superluminal flares in GRS 1915+105 and propose a qualitative scenario to
explain this association. We identify several candidate superluminal flare
events from available monitoring data on this source and analyze the
contemporaneous RXTE pointed observations. We detect a strong correlation
between the average X-ray flux during the ``plateau'' state and the total
energy emitted in radio during the subsequent radio flare. We find that the
sequence of events is similar for all large radio flares with a fast rise and
exponential decay morphology. Based on these results, we propose a qualitative
scenario in which the separating ejecta during the superluminal flares are
observed due to the interaction of the matter blob ejected during the X-ray
soft dips, with the steady jet already established during the ``plateau''
state. This picture can explain all types of radio emission observed from this
source in terms of its X-ray emission characteristics.Comment: Corrected typo in the author names, contents unchanged, accepted in
Ap
Geometry of good sets in n-fold Cartesian product
We propose here a multidimensional generalisation of the notion of link
introduced in our previous papers and we discuss some consequences for
simplicial measures and sums of function algebras.Comment: 17 pages, no figures, no table
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