8,470 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
X-ray Emission from SN 2012ca: A Type Ia-CSM Supernova Explosion in a Dense Surrounding Medium
X-ray emission is one of the signposts of circumstellar interaction in
supernovae (SNe), but until now, it has been observed only in core-collapse
SNe. The level of thermal X-ray emission is a direct measure of the density of
the circumstellar medium (CSM), and the absence of X-ray emission from Type Ia
SNe has been interpreted as a sign of a very low density CSM. In this paper, we
report late-time (500--800 days after discovery) X-ray detections of SN 2012ca
in {\it Chandra} data. The presence of hydrogen in the initial spectrum led to
a classification of Type Ia-CSM, ostensibly making it the first SN~Ia detected
with X-rays. Our analysis of the X-ray data favors an asymmetric medium, with a
high-density component which supplies the X-ray emission. The data suggest a
number density cm in the higher-density medium, which is
consistent with the large observed Balmer decrement if it arises from
collisional excitation. This is high compared to most core-collapse SNe, but it
may be consistent with densities suggested for some Type IIn or superluminous
SNe. If SN 2012ca is a thermonuclear SN, the large CSM density could imply
clumps in the wind, or a dense torus or disk, consistent with the
single-degenerate channel. A remote possibility for a core-degenerate channel
involves a white dwarf merging with the degenerate core of an asymptotic giant
branch star shortly before the explosion, leading to a common envelope around
the SN.Comment: 11 pages, 4 figures. Accepted to MNRA
Residual mean first-passage time for jump processes: theory and applications to L\'evy flights and fractional Brownian motion
We derive a functional equation for the mean first-passage time (MFPT) of a
generic self-similar Markovian continuous process to a target in a
one-dimensional domain and obtain its exact solution. We show that the obtained
expression of the MFPT for continuous processes is actually different from the
large system size limit of the MFPT for discrete jump processes allowing
leapovers. In the case considered here, the asymptotic MFPT admits
non-vanishing corrections, which we call residual MFPT. The case of L/'evy
flights with diverging variance of jump lengths is investigated in detail, in
particular, with respect to the associated leapover behaviour. We also show
numerically that our results apply with good accuracy to fractional Brownian
motion, despite its non-Markovian nature.Comment: 13 pages, 8 figure
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
Caractérisation électromagnétique des matériaux magnétiques anisotropes : vers une nouvelle approche de la détermination de la largeur de raie à mi-hauteur
National audienceCette étude présente une nouvelle méthode de caractérisation électromagnétique des ferrites aimantés, par nature anisotropes. Plutôt que de mesurer directement les éléments complexes du tenseur de perméabilité et la permittivité scalaire, nous proposons une technique large bande permettant de remonter au facteur d’amortissement. Ce paramètre est en effet essentiel à la détermination du comportement dynamique des ferrites polycristallins. Il constitue l’unique paramètre dynamique d’entrée d’un outil de simulation que nous avons développé pour l’aide à la conception des dispositifs hyperfréquences à ferrite. Les autres paramètres d’entrée étant les propriétés statiques du ferrite. La méthode large bande proposée est basée sur l’utilisation d’une ligne coaxiale. L’échantillon de ferrite est aimanté selon la direction de propagation
YAPA: A generic tool for computing intruder knowledge
Reasoning about the knowledge of an attacker is a necessary step in many
formal analyses of security protocols. In the framework of the applied pi
calculus, as in similar languages based on equational logics, knowledge is
typically expressed by two relations: deducibility and static equivalence.
Several decision procedures have been proposed for these relations under a
variety of equational theories. However, each theory has its particular
algorithm, and none has been implemented so far. We provide a generic procedure
for deducibility and static equivalence that takes as input any convergent
rewrite system. We show that our algorithm covers most of the existing decision
procedures for convergent theories. We also provide an efficient
implementation, and compare it briefly with the tools ProVerif and KiSs
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