13,388 research outputs found
Carbide factor predicts rolling-element bearing fatigue life
Analysis was made to determine correlation between number and size of carbide particles and rolling-element fatigue. Correlation was established, and carbide factor was derived that can be used to predict fatigue life more effectively than such variables as heat treatment, chemical composition, and hardening mechanism
Highly ionized atoms in cooling gas
The ionization of low density gas cooling from a high temperature was calculated. The evolution during the cooling is assumed to be isochoric, isobaric, or a combination of these cases. The calculations are used to predict the column densities and ultraviolet line luminosities of highly ionized atoms in cooling gas. In a model for cooling of a hot galactic corona, it is shown that the observed value of N(N V) can be produced in the cooling gas, while the predicted value of N(Si IV) falls short of the observed value by a factor of about 5. The same model predicts fluxes of ultraviolet emission lines that are a factor of 10 lower than the claimed detections of Feldman, Brune, and Henry. Predictions are made for ultraviolet lines in cooling flows in early-type galaxies and clusters of galaxies. It is shown that the column densities of interest vary over a fairly narrow range, while the emission line luminosities are simply proportional to the mass inflow rate
Study of hot hardness characteristics of tool steels
Hardness measurements of tool steel materials in electric furnace at elevated temperatures and low oxygen environment are discussed. Development of equation to predict short term hardness as function of intial room temperature hardness of steel is reported. Types of steel involved in the process are identified
Moderate Asphericity of the SN 2002ic Circumstellar Envelope
The polarization of SN 2002ic interacting with a dense circumstellar envelope
is calculated in the context of the asymmetric version of a previously proposed
spherical interaction model. The circumstellar envelope is taken to be oblate.
The observed polarization (Wang et al. 2004) can be reproduced for an aspect
ratio of 0.65-0.7 assuming inclination angles >60 degrees. This model predicts
a weak sensitivity of the line profiles to the orientation, in agreement with
the absence of significant variations of the line profiles among SN 2002ic-like
supernovae. We propose a test for distinguishing between the binary and single
star progenitor scenarios based upon the polarization distribution function for
the growing sample of these events.Comment: 13 pages, 4 figs., ApJ, accepte
X-ray Spectroscopy of Candidate Ultracompact X-ray Binaries
We present high-resolution spectroscopy of the neutron star/low-mass X-ray
binaries (LMXBs) 4U 1850-087 and 4U 0513-40 as part of our continuing study of
known and candidate ultracompact binaries. The LMXB 4U 1850-087 is one of four
systems in which we had previously inferred an unusual Ne/O ratio in the
absorption along the line of sight, most likely from material local to the
binaries. However, our recent Chandra X-ray Observatory LETGS spectrum of 4U
1850-087 finds a Ne/O ratio by number of 0.22+/-0.05, smaller than previously
measured and consistent with the expected interstellar value. We propose that
variations in the Ne/O ratio due to source variability, as previously observed
in these sources, can explain the difference between the low- and
high-resolution spectral results for 4U 1850-087. Our XMM-Newton RGS
observation of 4U 0513-40 also shows no unusual abundance ratios in the
absorption along the line of sight. We also present spectral results from a
third candidate ultracompact binary, 4U 1822-000, whose spectrum is well fit by
an absorbed power-law + blackbody model with absorption consistent with the
expected interstellar value. Finally, we present the non-detection of a fourth
candidate ultracompact binary, 4U 1905+000, with an upper limit on the source
luminosity of < 1 x 10^{32} erg s^{-1}. Using archival data, we show that the
source has entered an extended quiescent state.Comment: 8 pages, 3 figures, accepted for publication to the Astrophysical
Journa
Chandra Observations of SN 2004et and the X-ray Emission of Type IIp Supernovae
We report the X-ray detection of the Type II-plateau supernova SN 2004et in
the spiral galaxy NGC 6946, using the Chandra X-Ray Observatory. The position
of the X-ray source was found to agree with the optical position within ~0.4
arcsec. Chandra also surveyed the region before the 2004 event, finding no
X-ray emission at the location of the progenitor. For the post-explosion
observations, a total of 202, 151, and 158 photons were detected in three
pointings, each ~29 ks in length, on 2004 October 22, November 6, and December
3, respectively. The spectrum of the first observation is best fit by a thermal
model with a temperature of kT=1.3 keV and a line-of-sight absorption of
N_H=1.0 x 10^{22} cm^{-2}. The inferred unabsorbed luminosity (0.4-8 keV) is
~4x10^{38} erg/s, adopting a distance of 5.5 Mpc. A comparison between hard and
soft counts on the first and third epochs indicates a softening over this time,
although there is an insufficient number of photons to constrain the variation
of temperature and absorption by spectral fitting. We model the emission as
arising from the reverse shock region in the interaction between the supernova
ejecta and the progenitor wind. For a Type IIP supernova with an extended
progenitor, the cool shell formed at the time of shock wave breakout from the
star can affect the initial evolution of the interaction shell and the
absorption of radiation from the reverse shock. The observed spectral softening
might be due to decreasing shell absorption. We find a pre-supernova mass loss
rate of (2-2.5)x 10^{-6} M_{\odot} /yr for a wind velocity of 10 kms, which is
in line with expectations for a Type IIP supernova.Comment: total 19 pages including 7 figures. ApJ, in press. See
http://spider.ipac.caltech.edu/staff/rho/preprint/SN2004etms.ps for the paper
including full resolution image
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