4,888 research outputs found
The 10 to the 8th power bit solid state spacecraft data recorder
The results are summarized of a program to demonstrate the feasibility of Bubble Domain Memory Technology as a mass memory medium for spacecraft applications. The design, fabrication and test of a partially populated 10 to the 8th power Bit Data Recorder using 100 Kbit serial bubble memory chips is described. Design tradeoffs, design approach and performance are discussed. This effort resulted in a 10 to the 8th power bit recorder with a volume of 858.6 cu in and a weight of 47.2 pounds. The recorder is plug reconfigurable, having the capability of operating as one, two or four independent serial channel recorders or as a single sixteen bit byte parallel input recorder. Data rates up to 1.2 Mb/s in a serial mode and 2.4 Mb/s in a parallel mode may be supported. Fabrication and test of the recorder demonstrated the basic feasibility of Bubble Domain Memory technology for such applications. Test results indicate the need for improvement in memory element operating temperature range and detector performance
The Weyl map and bundle gerbes
Available online 5 December 2019.We introduce the notion of a general cup product bundle gerbe and use it to define the Weyl bundle gerbe on T x SU(n)/T. The Weyl map from T x SU(n)/T to SU(n) is then used to show that the pullback of the basic bundle gerbe on SU(n) defined by the second two authors is stably isomorphic to the Weyl bundle gerbe as SU(n)-equivariant bundle gerbes. Both bundle gerbes come equipped with connections and curvings and by considering the holonomy of these we show that these bundle gerbes are not D-stably isomorphic.Kimberly E. Becker, Michael K. Murray, Daniel Stevenso
VPMS J1342+2840 - an unusual quasar from the variability and proper motion survey
We report the discovery of the highly peculiar, radio-loud quasar VPMS
J1342+2840 (z ~ 1.3) from the variability and proper motion survey. We present
spectroscopic, imaging and photometric observations. The unusual spectrum shows
a strong depression of the continuum over a wide wavelength range in the blue
part without the typical structures of broad absorption line (BAL) troughs. The
image of the quasar is unresolved and there is no evidence for a foreground
object on the line of sight. The broad-band spectral energy distribution is not
consistent with obvious dust reddening with the standard SMC extinction curve.
The downturn of the continuum flux of VPMS J1342+2840 at short wavelengths can
be caused by dust reddening only if the reddening curve is steeper then the SMC
curve in the ultraviolet and is very flat at longer wavelengths. Alternatively,
the dominant spectral features can be explained by low-ionization BALs forming
unusually wide, overlapping absorption troughs.Comment: 4 pages, 3 figures, accepted for publication in A&A Letter
LegumeGRN: A Gene Regulatory Network Prediction Server for Functional and Comparative Studies
Building accurate gene regulatory networks (GRNs) from high-throughput gene expression data is a long-standing challenge. However, with the emergence of new algorithms combined with the increase of transcriptomic data availability, it is now reachable. To help biologists to investigate gene regulatory relationships, we developed a web-based computational service to build, analyze and visualize GRNs that govern various biological processes. The web server is preloaded with all available Affymetrix GeneChip-based transcriptomic and annotation data from the three model legume species, i.e., Medicago truncatula, Lotus japonicus and Glycine max. Users can also upload their own transcriptomic and transcription factor datasets from any other species/organisms to analyze their in-house experiments. Users are able to select which experiments, genes and algorithms they will consider to perform their GRN analysis. To achieve this flexibility and improve prediction performance, we have implemented multiple mainstream GRN prediction algorithms including co-expression, Graphical Gaussian Models (GGMs), Context Likelihood of Relatedness (CLR), and parallelized versions of TIGRESS and GENIE3. Besides these existing algorithms, we also proposed a parallel Bayesian network learning algorithm, which can infer causal relationships (i.e., directionality of interaction) and scale up to several thousands of genes. Moreover, this web server also provides tools to allow integrative and comparative analysis between predicted GRNs obtained from different algorithms or experiments, as well as comparisons between legume species. The web site is available at http://legumegrn.noble.org
Nature and statistical properties of quasar associated absorption systems in the XQ-100 Legacy Survey
We statistically study the physical properties of a sample of narrow
absorption line (NAL) systems looking for empirical evidences to distinguish
between intrinsic and intervening NALs without taking into account any a priori
definition or velocity cut-off. We analyze the spectra of 100 quasars with 3.5
< z < 4.5, observed with X-shooter/VLT in the context of the XQ-100
Legacy Survey. We detect a 8 excess in the number density of
absorbers within 10,000 km/s of the quasar emission redshift with respect to
the random occurrence of NALs. This excess does not show a dependence on the
quasar bolometric luminosity and it is not due to the redshift evolution of
NALs. It extends far beyond the standard 5000 km/s cut-off traditionally
defined for associated absorption lines. We propose to modify this definition,
extending the threshold to 10,000 km/s when also weak absorbers (equivalent
width < 0.2 \AA) are considered. We infer NV is the ion that better traces the
effects of the quasar ionization field, offering the best statistical tool to
identify intrinsic systems. Following this criterion we estimate that the
fraction of quasars in our sample hosting an intrinsic NAL system is 33
percent. Lastly, we compare the properties of the material along the quasar
line of sight, derived from our sample, with results based on close quasar
pairs investigating the transverse direction. We find a deficiency of cool gas
(traced by CII) along the line of sight associated with the quasar host galaxy,
in contrast with what is observed in the transverse direction.Comment: 18 pages, 13 figures, 5 table
Implications of Dramatic Broad Absorption Line Variability in the Quasar FBQS J1408+3054
We have observed a dramatic change in the spectrum of the formerly heavily
absorbed `overlapping-trough' iron low-ionization broad absorption line
(FeLoBAL) quasar FBQS J1408+3054. Over a time span of between 0.6 to 5
rest-frame years, the Mg II trough outflowing at 12,000 km/s decreased in
equivalent width by a factor of two and the Fe II troughs at the same velocity
disappeared. The most likely explanation for the variability is that a
structure in the BAL outflow moved out of our line of sight to the ultraviolet
continuum emitting region of the quasar's accretion disk. Given the size of
that region, this structure must have a transverse velocity of between 2600
km/s and 22,000 km/s. In the context of a simple outflow model, we show that
this BAL structure is located between approximately 5800 and 46,000
Schwarzschild radii from the black hole. That distance corresponds to 1.7 to 14
pc, 11 to 88 times farther from the black hole than the H-beta broad-line
region. The high velocities and the parsec-scale distance for at least this one
FeLoBAL outflow mean that not all FeLoBAL outflows can be associated with
galaxy-scale outflows in ultraluminous infrared galaxies transitioning to
unobscured quasars. The change of FBQS J1408+3054 from an FeLoBAL to a LoBAL
quasar also means that if (some) FeLoBAL quasars have multiwavelength
properties which distinguish them from HiBAL quasars, then some LoBAL quasars
will share those properties. Finally, we extend previous work on how
multiple-epoch spectroscopy of BAL and non-BAL quasars can be used to constrain
the average lifetime of BAL episodes (currently >60 rest-frame years at 90%
confidence).Comment: Final version to appear in MNRAS: references added and factor of 2
underestimate of accretion disk size corrected, resulting in absorber
constrained to be somewhat closer to the black hole. For an animated gif
showing the spectral evolution of the broad absorption line troughs in this
quasar, see http://www.yorku.ca/phall/film19952009.gi
Optical identification of the 3C 58 pulsar wind nebula
We have performed a deep optical imaging of 3C 58 SNR with the NOT in the B
and V bands to detect the optical counterpart of the associated pulsar
J0295+6449 and its torus-like wind nebula visible in X-rays. We analyzed our
data together with the archival data obtained with the Chandra in X-rays and
with the Spitzer in the mid-IR. We detect a faint extended elliptical object
with B=24.06 and V=23.11 whose peak brightness and center position are
consistent at the sub-arcsecond level with the position of the pulsar. Its
morphology and orientation are in excellent agreement with the torus-like
pulsar nebula, seen almost edge on in X-rays although its extension is only
about a half of that in X-rays. In the optical we likely see only the brightest
central part of the torus with the pulsar. The object is identical to the
counterpart of the torus recently detected in the mid-IR. The estimated pulsar
contribution to the optical flux is less than 10%. Combinig the optical/mid-IR
fluxes and X-ray power-law spectrum extracted from the spatial region
constrained by the optical/IR source extent we compile a tentative
multi-wavelength spectrum of the central part of the nebula. Within
uncertainties of the interstellar extinction it is reminiscent of either the
Crab or B0540-69 pulsar wind nebula spectra. The properties of the object
strongly suggest it to be the optical counterpart of the 3C 58 pulsar + its
wind nebula system, making 3C 58 the third member of such a class of the
torus-like systems identified in the optical and mid-IR.Comment: 12 pages including 7 figures, submitted for publication in A&A. For
high resolution images, see http://www.ioffe.ru/astro/NSG/obs/3C58
Polarization properties of broad absorption line QSOs : new statistical clues
We report the results of statistical tests performed on a sample of 139 broad
absorption line (BAL) QSOs with good quality optical spectra and/or optical
polarization data. Correlations between optical indices and the polarization
degree p_0 are systematically searched for. In order to identify the most
important correlations, we perform a principal component analysis with a sample
of 30 BAL QSOs and eight quantities (including p_0). Most of the variance in
the data is contained in two principal components (PC): PC1 is mainly dominated
by the correlation between the balnicity index BI and the strength of the feii
emission, and may be driven by the accretion rate of matter onto the central
compact object. The variance in PC2 is essentially due to the anti-correlation
between p_0 and the detachment index DI. PC2 may be related to the orientation
of the BAL QSOs with respect to the line of sight. We also consider a
spectropolarimetric sample of 21 BAL QSOs for which we define four indices
describing the polarization properties of the absorption and emission lines. We
find a possible anti-correlation between the detachment index and a quantity SI
which measures the ratio of the depths of the civ absorption in the polarized
flux and in the total flux. This correlation indicates that in BAL QSOs with P
cygni profiles, the BAL troughs in the polarized flux are nearly as deep as in
the total flux while, in BAL QSOs with detached absorptions, the BAL troughs in
the polarized flux are much weaker than in the total flux. We show that our
main results may be explained in the framework of a 'two-component' wind model.
In this model, the broad absorption occurs in a dense equatorial wind emerging
from the accretion disk, while scattering and polarization mainly take place in
a polar region.Comment: 18 pages, 8 figures, to be published in Astronomy & Astrophysic
LegumeGRN: a gene regulatory network prediction server for functional and comparative studies
Building accurate gene regulatory networks (GRNs) from high-throughput gene expression data is a long-standing challenge. However, with the emergence of new algorithms combined with the increase of transcriptomic data availability, it is now reachable. To help biologists to investigate gene regulatory relationships, we developed a web-based computational service to build, analyze and visualize GRNs that govern various biological processes. The web server is preloaded with all available Affymetrix GeneChip-based transcriptomic and annotation data from the three model legume species, i.e., Medicago truncatula, Lotus japonicus and Glycine max. Users can also upload their own transcriptomic and transcription factor datasets from any other species/organisms to analyze their in-house experiments. Users are able to select which experiments, genes and algorithms they will consider to perform their GRN analysis. To achieve this flexibility and improve prediction performance, we have implemented multiple mainstream GRN prediction algorithms including co-expression, Graphical Gaussian Models (GGMs), Context Likelihood of Relatedness (CLR), and parallelized versions of TIGRESS and GENIE3. Besides these existing algorithms, we also proposed a parallel Bayesian network learning algorithm, which can infer causal relationships (i.e., directionality of interaction) and scale up to several thousands of genes. Moreover, this web server also provides tools to allow integrative and comparative analysis between predicted GRNs obtained from different algorithms or experiments, as well as comparisons between legume species. The web site is available at http://legumegrn.noble.org.Oklahoma Center for The Advancement of Science and Technology: (OCAST Grant No. PSB11-031)
Discovery of X-ray Pulsations from the Compact Central Source in the Supernova Remnant 3C 58
We report on high time resolution observations of the SNR 3C 58 using the
High Resolution Camera on the Chandra X-ray Observatory. These data show a
point-like central source, from which we detect 65.68 ms pulsations at 6.7
sigma significance. We interpret these pulsations as corresponding to a young
rotation-powered pulsar (PSR J-205+6449) which is associated with, and powers,
3C 58. Analysis of archival RXTE data from three years earlier confirms these
pulsations, and allows us to determine a spin-down rate of P-dot=1.93x10^-13
s/s. Assuming a magnetic dipole model for PSR J0205+6449, we infer a surface
magnetic field of 3.6x10^12 G. The characteristic age for this pulsar is 5400
yr, indicating either that 3C 58 was not the supernova of 1181 CE, or that the
pulsar's initial spin period was ~60 ms.Comment: 11 pages, 4 figures, 1 tabl
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