40,798 research outputs found
Materials thermal and thermoradiative properties/characterization technology
Reliable properties data on well characterized materials are necessary for design of experiments and interpretation of experimental results. The activities of CINDAS to provide data bases and predict properties are discussed. An understanding of emissivity behavior is important in order to select appropriate methods for non-contact temperature determination. Related technical issues are identified and recommendations are offered
Detection of changes in the characteristics of a Gauss-Markov process
Sequential detection of changes in Gauss-Markov process achieved through probability ratio tes
Noncommutative D-Brane in Non-Constant NS-NS B Field Background
We show that when the field strength H of the NS-NS B field does not vanish,
the coordinates X and momenta P of an open string endpoints satisfy a set of
mixed commutation relations among themselves. Identifying X and P with the
coordinates and derivatives of the D-brane world volume, we find a new type of
noncommutative spaces which is very different from those associated with a
constant B field background.Comment: 11 pages, Latex, minor modification
Iron Emission in the z=6.4 Quasar SDSS J114816.64+525150.3
We present near-infrared J and K-band spectra of the z = 6.4 quasar SDSS
J114816.64+525150.3 obtained with the NIRSPEC spectrograph at the Keck-II
telescope, covering the rest-frame spectral regions surrounding the C IV 1549
and Mg II 2800 emission lines. The iron emission blend at rest wavelength
2900-3000 A is clearly detected and its strength appears nearly
indistinguishable from that of typical quasars at lower redshifts. The Fe II /
Mg II ratio is also similar to values found for lower-redshift quasars,
demonstrating that there is no strong evolution in Fe/alpha broad-line emission
ratios even out to z=6.4. In the context of current models for iron enrichment
from Type Ia supernovae, this implies that the SN Ia progenitor stars formed at
z > 10. We apply the scaling relations of Vestergaard and of McLure & Jarvis to
estimate the black hole mass from the widths of the C IV and Mg II emission
lines and the ultraviolet continuum luminosity. The derived mass is in the
range (2-6)x10^9 solar masses, with an additional uncertainty of a factor of 3
due to the intrinsic scatter in the scaling relations. This result is in
agreement with the previous mass estimate of 3x10^9 solar masses by Willott,
McLure, & Jarvis, and supports their conclusion that the quasar is radiating
close to its Eddington luminosity.Comment: To appear in ApJ Letter
A Tidal Flare Candidate in Abell 1795
As part of our ongoing archival X-ray survey of galaxy clusters for tidal
flares, we present evidence of an X-ray transient source within 1 arcmin of the
core of Abell 1795. The extreme variability (a factor of nearly 50), luminosity
(> 2 x 10^42 erg s^{-1}), long duration (> 5 years) and supersoft X-ray
spectrum (< 0.1 keV) are characteristic signatures of a stellar tidal
disruption event according to theoretical predictions and to existing X-ray
observations, implying a massive >~10^5 M_sun black hole at the centre of that
galaxy. The large number of X-ray source counts (~700) and long temporal
baseline (~12 years with Chandra and XMM-Newton) make this one of the
best-sampled examples of any tidal flare candidate to date. The transient may
be the same EUV source originally found contaminating the diffuse ICM
observations of Bowyer et al. (1999), which would make it the only tidal flare
candidate with reported EUV observations and implies an early source luminosity
1-2 orders of magnitude greater. If the host galaxy is a cluster member then it
must be a dwarf galaxy, an order of magnitude less massive than the quiescent
galaxy Henize 2-10 which hosts a massive black hole that is difficult to
reconcile with its low mass. The unusual faintness of the host galaxy may be
explained by tidal stripping in the cluster core.Comment: Accepted by MNRAS 2013 July 23. 27 pages, 10 figure
Modulation of inherent dynamical tendencies of the bisabolyl cation via preorganization in epi-isozizaene synthase.
The relative importance of preorganization, selective transition state stabilization and inherent reactivity are assessed through quantum chemical and docking calculations for a sesquiterpene synthase (epi-isozizaene synthase, EIZS). Inherent reactivity of the bisabolyl cation, both static and dynamic, appears to determine the pathway to product, although preorganization and selective binding of the final transition state structure in the multi-step carbocation cascade that forms epi-isozizaene appear to play important roles
Self-shadowing Effects of Slim Accretion Disks in Active Galactic Nuclei: Diverse Appearance of the Broad-line Region
Supermassive black holes in active galactic nuclei (AGNs) undergo a wide
range of accretion rates, which lead to diversity of appearance. We consider
the effects of anisotropic radiation from accretion disks on the broad-line
region (BLR), from the Shakura-Sunyaev regime to slim disks with
super-Eddington accretion rates. The geometrically thick funnel of the inner
region of slim disks produces strong self-shadowing effects that lead to very
strong anisotropy of the radiation field. We demonstrate that the degree of
anisotropy of the radiation fields grows with increasing accretion rate. As a
result of this anisotropy, BLR clouds receive different spectral energy
distributions depending on their location relative to the disk, resulting in
diverse observational appearance of the BLR. We show that the self-shadowing of
the inner parts of the disk naturally produces two dynamically distinct regions
of the BLR, depending on accretion rate. These two regions manifest themselves
as kinematically distinct components of the broad H line profile with
different line widths and fluxes, which jointly account for the Lorentzian
profile generally observed in narrow-line Seyfert 1 galaxies. In the time
domain, these two components are expected reverberate with different time lags
with respect to the varying ionizing continuum, depending on the accretion rate
and the viewing angle of the observer. The diverse appearance of the BLR due to
the anisotropic ionizing energy source can be tested by reverberation mapping
of H and other broad emission lines (e.g., \feii), providing a new tool
to diagnose the structure and dynamics of the BLR. Other observational
consequences of our model are also explored.Comment: emulatapj style, 15 pages, 6 figures, in pres
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