10,599 research outputs found
The casting and powder-metallurgy forming of precipitation-hardenable stainless steels
Casting and powder metallurgy techniques for shaping precipitation hardened stainless steel
Implementation of mean-timing and subsequent logic functions on an FPGA
This article describes the implementation of a mean-timer and coincidence
logic on a Virtex-5 FPGA for trigger purposes in a particle physics experiment.
The novel feature is that the mean-timing and the coincidence logic are not
synchronized with a clock which allows for a higher resolution of approximately
400 ps, not limited by a clock frequency.Comment: 15 pages, 11 figure
Anomalous transport properties of the halfmetallic ferromagnets Co2TiSi, Co2TiGe, and Co2TiSn
In this work the theoretical and experimental investigations of Co2TiZ (Z =
Si, Ge, or Sn) compounds are reported. Half-metallic ferromagnetism is
predicted for all three compounds with only two bands crossing the Fermi energy
in the majority channel. The magnetic moments fulfill the Slater-Pauling rule
and the Curie temperatures are well above room temperature. All compounds show
a metallic like resistivity for low temperatures up to their Curie temperature,
above the resistivity changes to semiconducting like behavior. A large negative
magnetoresistance of 55% is observed for Co2TiSn at room temperature in an
applied magnetic field of 4T which is comparable to the large negative
magnetoresistances of the manganites. The Seebeck coefficients are negative for
all three compounds and reach their maximum values at their respective Curie
temperatures and stay almost constant up to 950 K. The highest value achieved
is -52muV/K m for Co2TiSn which is large for a metal. The combination of
half-metallicity and the constant large Seebeck coefficient over a wide
temperature range makes these compounds interesting materials for
thermoelectric applications and further spincaloric investigations.Comment: 4 pages 4 figure
Serendipitous XMM-Newton discovery of a cluster of galaxies at z=0.28
We report the discovery of a galaxy cluster serendipitously detected as an
extended X-ray source in an offset observation of the group NGC 5044. The
cluster redshift, z=0.281, determined from the optical spectrum of the
brightest cluster galaxy, agrees with that inferred from the X-ray spectrum
using the Fe K alpha complex of the hot ICM (z=0.27 +/- 0.01). Based on the 50
ks XMM observation, we find that within a radius of 383 kpc the cluster has an
unabsorbed X-ray flux, f_X (0.5-2 keV) = 3.34 (+0.08, -0.13) x 10^{-13}
erg/cm^2/s, a bolometric X-ray luminosity, L_X = 2.21 (+0.34, -0.19) x 10^{44}
erg/s, kT = 3.57 +/- 0.12 keV, and metallicity, 0.60 +/- 0.09 solar. The
cluster obeys the scaling relations for L_X and T observed at intermediate
redshift. The mass derived from an isothermal NFW model fit is, M_vir = 3.89
+/- 0.35 x 10^{14} solar masses, with a concentration parameter, c = 6.7 +/-
0.4, consistent with the range of values expected in the concordance
cosmological model for relaxed clusters. The optical properties suggest this
could be a ``fossil cluster''.Comment: 5 pages, 4 colour figures, accepted for publication in Ap
Chalcogen Height Dependence of Magnetism and Fermiology in FeTe_xSe_{1-x}
FeTexSe1-x (x=0, 0.25, 0.50, 0.75 and 1) system has been studied using
density functional theory. Our results show that for FeSe, LDA seems better
approximation in terms of magnitude of magnetic energy whereas GGA
overestimates it largely. On the other hand for FeTe, GGA is better
approximation that gives experimentally observed magnetic state. It has been
shown that the height of chalcogen atoms above Fe layers has significant effect
on band structure, electronic density of states (DOS) at Fermi level N(EF) and
Fermi surfaces. For FeSe the value of N(EF) is small so as to satisfy Stoner
criteria for ferromagnetism, (I\timesN(EF)\geq1) whereas for FeTe, since the
value of N(EF) is large, the same is close to be satisfied. Force minimization
done for FeTexSe1-x using supercell approach shows that in disordered system Se
and Te do not share same site and have two distinct z coordinates. This has
small effect on magnetic energy but no significant difference in band structure
and DOS near EF when calculated using either relaxed or average value of z for
chalcogen atoms. Thus substitution of Se at Te site decreases average value of
chalcogen height above Fe layers which in turn affect the magnetism and
Fermiology in the system. By using coherent-potential approximation for
disordered system we found that height of chalcogen atoms above Fe layer rather
than chalcogen species or disorder in the anion planes, affect magnetism and
shape of Fermi surfaces (FS), thus significantly altering nesting conditions,
which govern antiferromagnetic spin fluctuations in the system.Comment: 24 pages Text+Figs: comments/suggestions welcome
([email protected]
Galactic microwave emission at degree angular scales
We cross-correlate the Saskatoon Ka and Q-Band Cosmic Microwave Background
(CMB) data with different maps to quantify possible foreground contamination.
We detect a marginal correlation (2 sigma) with the Diffuse Infrared Background
Experiment (DIRBE) 240, 140 and 100 microm maps, but we find no significant
correlation with point sources, with the Haslam 408 MHz map or with the Reich
and Reich 1420 MHz map. The rms amplitude of the component correlated with
DIRBE is about 20% of the CMB signal. Interpreting this component as free-free
emission, this normalization agrees with that of Kogut et al. (1996a; 1996b)
and supports the hypothesis that the spatial correlation between dust and warm
ionized gas observed on large angular scales persists to smaller angular
scales. Subtracting this contribution from the CMB data reduces the
normalization of the Saskatoon power spectrum by only a few percent.Comment: Minor revisions to match published version. 14 pages, with 2 figures
included. Color figure and links at
http://www.sns.ias.edu/~angelica/foreground.htm
Quantum Fluctuations in the Chirped Pendulum
An anharmonic oscillator when driven with a fast, frequency chirped voltage
pulse can oscillate with either small or large amplitude depending on whether
the drive voltage is below or above a critical value-a well studied classical
phenomenon known as autoresonance. Using a 6 GHz superconducting resonator
embedded with a Josephson tunnel junction, we have studied for the first time
the role of noise in this non-equilibrium system and find that the width of the
threshold for capture into autoresonance decreases as the square root of T, and
saturates below 150 mK due to zero point motion of the oscillator. This unique
scaling results from the non-equilibrium excitation where fluctuations, both
quantum and classical, only determine the initial oscillator motion and not its
subsequent dynamics. We have investigated this paradigm in an electrical
circuit but our findings are applicable to all out of equilibrium nonlinear
oscillators.Comment: 5 pages, 4 figure
The Origin of the Intrinsic Scatter in the Relation Between Black Hole Mass and Bulge Luminosity for Nearby Active Galaxies
We investigate the origin of the intrinsic scatter in the correlation between
black hole mass (MBH) and bulge luminosity [L(bulge)] in a sample of 45
massive, local (z < 0.35) type~1 active galactic nuclei (AGNs). We derive MBH
from published optical spectra assuming a spherical broad-line region, and
L(bulge) from detailed two-dimensional decomposition of archival optical Hubble
Space Telescope images. AGNs follow the MBH-L(bulge) relation of inactive
galaxies, but the zero point is shifted by an average of \Delta log MBH ~ -0.3
dex. We show that the magnitude of the zero point offset, which is responsible
for the intrinsic scatter in the MBH-L(bulge) relation, is correlated with
several AGN and host galaxy properties, all of which are ultimately related to,
or directly impact, the BH mass accretion rate. At a given bulge luminosity,
sources with higher Eddington ratios have lower MBH. The zero point offset can
be explained by a change in the normalization of the virial product used to
estimate MBH, in conjunction with modest BH growth (~ 10%--40%) during the AGN
phase. Galaxy mergers and tidal interactions appear to play an important role
in regulating AGN fueling in low-redshift AGNs.Comment: To appear in ApJ; 67 pages, 56 figures, 4 tables, version with full
resolution figures at http://users.ociw.edu/mjkim/papers/scatter.pd
Violation of particle number conservation in the it GW approximation
We present a nontrivial model system of interacting electrons that can be solved analytically in the GW approximation. We obtain the particle number from the GW Green's function strictly analytically, and prove that there is a genuine violation of particle number conservation if the self-energy is calculated non-self-consistently from a zeroth order Green's function, as done in virtually all practical implementations. We also show that a simple shift of the self-energy that partially restores self-consistency reduces the numerical deviation significantly
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