9,573 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
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
Short-term hot hardness characteristics of rolling-element steels
Short-term hot hardness studies were performed with five vacuum-melted steels at temperatures from 294 to 887 K (70 to 1140 F). Based upon a minimum Rockwell C hardness of 58, the temperature limitation on all materials studied was dependent on the initial room temperature hardness and the tempering temperature of each material. For the same room temperature hardness, the short-term hot hardness characteristics were identical and independent of material composition. An equation was developed to predict the short-term hardness at temperature as a function of initial room temperature hardness for AISI 52100, as well as the high-speed tool steels
An adjustable law of motion for relativistic spherical shells
A classical and a relativistic law of motion for an advancing shell are
deduced applying the thin layer approximation. A new parameter connected with
the quantity of absorbed matter in the expansion is introduced; this allows of
matching theory and observation.Comment: 15 pages, 10 figures and article in press; Central European Journal
of Physics 201
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
Influence of the r-mode instability on hypercritically accreting neutron stars
We have investigated an influence of the r-mode instability on
hypercritically accreting () neutron stars in
close binary systems during their common envelope phases based on the scenario
proposed by Bethe et al. \shortcite{bethe-brown-lee}. On the one hand neutron
stars are heated by the accreted matter at the stellar surface, but on the
other hand they are also cooled down by the neutrino radiation. At the same
time, the accreted matter transports its angular momentum and mass to the star.
We have studied the evolution of the stellar mass, temperature and rotational
frequency.
The gravitational-wave-driven instability of the r-mode oscillation strongly
suppresses spinning-up of the star, whose final rotational frequency is well
below the mass-shedding limit, typically as small as 10% of that of the
mass-shedding state. On a very short time scale the rotational frequency tends
to approach a certain constant value and saturates there as far as the amount
of the accreted mass does not exceed a certain limit to collapse to a black
hole. This implies that the similar mechanism of gravitational radiation as the
so-called Wagoner star may work in this process. The star is spun up by
accretion until the angular momentum loss by gravitational radiation balances
the accretion torque. The time-integrated dimensionless strain of the radiated
gravitational wave may be large enough to be detectable by the gravitational
wave detectors such as LIGO II.Comment: 6 pages, 3 figure
X-Ray Spectroscopy of the Low-Mass X-ray Binaries 2S 0918-549 and 4U1543-624: Evidence for Neon-Rich Degenerate Donors
We present high-resolution spectroscopy of the neutron-star/low-mass X-ray
binaries 2S 0918-549 and 4U 1543-624 with the High Energy Transmission Grating
Spectrometer onboard the Chandra X-ray Observatory and the Reflection Grating
Spectrometer onboard XMM-Newton. Previous low-resolution spectra of both
sources showed a broad line-like feature at 0.7 keV that was originally
attributed to unresolved line emission. We recently showed that this feature
could also be due to excess neutral Ne absorption, and this is confirmed by the
new high-resolution Chandra spectra. The Chandra spectra are each well fit by
an absorbed power-law + blackbody model with a modified Ne/O number ratio of
0.52+/-0.12 for 2S 0918-549 and 1.5+/-0.3 for 4U 1543-624, compared to the
interstellar-medium value of 0.18. The XMM spectrum of 2S 0918-549 is best fit
by an absorbed power-law model with a Ne/O number ratio of 0.46+/-0.03,
consistent with the Chandra result. On the other hand, the XMM spectrum of 4U
1543-624 is softer and less luminous than the Chandra spectrum and has a
best-fit Ne/O number ratio of 0.54+/-0.03. The difference between the measured
abundances and the expected interstellar ratio, as well as the variation of the
column densities of O and Ne in 4U 1543-624, supports the suggestion that there
is absorption local to these binaries. We propose that the variations in the O
and Ne column densities of 4U 1543-624 are caused by changes in the ionization
structure of the local absorbing material. It is important to understand the
effect of ionization on the measured absorption columns before the abundance of
the local material can be determined. This work supports our earlier suggestion
that 2S 0918-549 and 4U 1543-624 are ultracompact binaries with Ne-rich
companions.Comment: 11 pages, 5 figures, major revisions including addition of XMM
spectral analysis, accepted for publication in the Astrophysical Journal,
vol. 59
Spherically symmetric relativistic MHD simulations of pulsar wind nebulae in supernova remnants
Pulsars, formed during supernova explosions, are known to be sources of
relativistic magnetized winds whose interaction with the expanding supernova
remnants (SNRs) gives rise to a pulsar wind nebula (PWN). We present
spherically symmetric relativistic magnetohydrodynamics (RMHD) simulations of
the interaction of a pulsar wind with the surrounding SNR, both in particle and
magnetically dominated regimes. As shown by previous simulations, the evolution
can be divided in three phases: free expansion, a transient phase characterized
by the compression and reverberation of the reverse shock, and a final Sedov
expansion. The evolution of the contact discontinuity between the PWN and the
SNR (and consequently of the SNR itself) is almost independent of the
magnetization of the nebula as long as the total (magnetic plus particle)
energy is the same. However, a different behaviour of the PWN internal
structure is observable during the compression-reverberation phase, depending
on the degree of magnetization=2E The simulations were performed using the
third order conservative scheme by Del Zanna et al. (2003).Comment: 11 pages, Latex, 22 Encapsulated PostScript figures, accepted f or
publication on A&
Impacts of misalignment effects on the Muon Spectrometer Performance
The ATLAS detector, currently being installed at CERN, is designed to exploit the full potential of the LHC, identifying and providing highly accurate energy and momentum measurements of particles emerging from the LHC protonproton collisions with a centre-of-mass energy at 14 TeV, starting in 2007. High-momentum final-state muons are among the most promising signatures at the LHC, thanks to a high-resolution Muon Spectrometer with standalone triggering and momentum measurement. As well known, muons interact primarily trough their electromagnetic charge, but since they are 200 times more massive than the electrons they are less affected by the electric fields of the nuclei they encounter. Muons with an energy of more than a few GeV penetrate the calorimeter and can reach the Muon Spectrometer, which consists out of more than 1.200 single drift-tubes chambers. The correct alignment of the ATLAS Muon Spectrometer is crucial to ensure its design performance. This note documents the first attempt at using various misaligned Muonspectrometer layouts to study their impacts Muon Spectrometer performance
Aql X-1 in Outburst and Quiescence
We present photometry and spectroscopy of the soft x-ray transient Aql X-1.
Optical photometry during an active state shows a strong (0.6 mag peak-to-peak)
modulation at a period of 19 hours. Infrared (K'-band) photometry during a
quiescent state limits any ellipsoidal variations to <0.07 mag (peak-to-peak),
which implies an inclination i<31 (90% limit). Spectroscopy in a quiescent
state shows at most very small radial velocity variations, which implies a very
low inclination of i<12 (90% limit). The low inclination is rather unexpected
given the large photometric modulation seen in the active state. The upper
limit to the equivalent width of the anomalous Li 6707A line is <0.3A, which is
similar to the measured strength of this line in several other x-ray
transients.Comment: Accepted for publication in ApJ, 12 pages, 5 figure
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