4,411 research outputs found
Local Out-Tournaments with Upset Tournament Strong Components I: Full and Equal {0,1}-Matrix Ranks
A digraph D is a local out-tournament if the outset of every vertex is a tournament. Here, we use local out-tournaments, whose strong components are upset tournaments, to explore the corresponding ranks of the adjacency matrices. Of specific interest is the out-tournament whose adjacency matrix has boolean, nonnegative integer, term, and real rank all equal to the number of vertices, n. Corresponding results for biclique covers and partitions of the digraph are provided
Recommended from our members
Validating Dose Uncertainty Estimates Produced by AUTODIRECT: An Automated Program to Evaluate Deformable Image Registration Accuracy.
Deformable image registration is a powerful tool for mapping information, such as radiation therapy dose calculations, from one computed tomography image to another. However, deformable image registration is susceptible to mapping errors. Recently, an automated deformable image registration evaluation of confidence tool was proposed to predict voxel-specific deformable image registration dose mapping errors on a patient-by-patient basis. The purpose of this work is to conduct an extensive analysis of automated deformable image registration evaluation of confidence tool to show its effectiveness in estimating dose mapping errors. The proposed format of automated deformable image registration evaluation of confidence tool utilizes 4 simulated patient deformations (3 B-spline-based deformations and 1 rigid transformation) to predict the uncertainty in a deformable image registration algorithm's performance. This workflow is validated for 2 DIR algorithms (B-spline multipass from Velocity and Plastimatch) with 1 physical and 11 virtual phantoms, which have known ground-truth deformations, and with 3 pairs of real patient lung images, which have several hundred identified landmarks. The true dose mapping error distributions closely followed the Student t distributions predicted by automated deformable image registration evaluation of confidence tool for the validation tests: on average, the automated deformable image registration evaluation of confidence tool-produced confidence levels of 50%, 68%, and 95% contained 48.8%, 66.3%, and 93.8% and 50.1%, 67.6%, and 93.8% of the actual errors from Velocity and Plastimatch, respectively. Despite the sparsity of landmark points, the observed error distribution from the 3 lung patient data sets also followed the expected error distribution. The dose error distributions from automated deformable image registration evaluation of confidence tool also demonstrate good resemblance to the true dose error distributions. Automated deformable image registration evaluation of confidence tool was also found to produce accurate confidence intervals for the dose-volume histograms of the deformed dose
Light Dark Matter Detection Prospects at Neutrino Experiments
We consider the prospects for the detection of relatively light dark matter
through direct annihilation to neutrinos. We specifically focus on the
detection possibilities of water Cherenkov and liquid scintillator neutrino
detection devices. We find in particular that liquid scintillator detectors may
potentially provide excellent detection prospects for dark matter in the 4-10
GeV mass range. These experiments can provide excellent corroborative checks of
the DAMA/LIBRA annual modulation signal, but may yield results for low mass
dark matter in any case. We identify important tests of the ratio of electron
to muon neutrino events (and neutrino versus anti-neutrino events), which
discriminate against background atmospheric neutrinos. In addition, the
fraction of events which arise from muon neutrinos or anti-neutrinos (
and ) can potentially yield information about the branching
fractions of hypothetical dark matter annihilations into different neutrino
flavors. These results apply to neutrinos from secondary and tertiary decays as
well, but will suffer from decreased detectability.Comment: 13 pages, 2 figures, pdflatex, references, one figure and comments on
electron neutrino bounds and on spin-dependent scattering limits added.
Figures updated
First Measurement of a Rapid Increase in the AGN Fraction in High-Redshift Clusters of Galaxies
We present the first measurement of the AGN fraction in high-redshift
clusters of galaxies (z~0.6) with spectroscopy of one cluster and archival data
for three additional clusters. We identify 8 AGN in all four of these clusters
from the Chandra data, which are sensitive to AGN with hard X-ray (2-10keV)
luminosity L_{X,H} > 10^43 erg/s in host galaxies more luminous than a rest
frame M_R < -20 mag. This stands in sharp contrast to the one AGN with L_{X,H}
> 10^43 erg/s we discovered in our earlier study of eight low-redshift clusters
with z=0.06-0.31 (average z~0.2). Three of the four high-redshift cluster
datasets are sensitive to nearly L_{X,H} > 10^42 erg/s and we identify seven
AGN above this luminosity limit, compared to two in eight, low-redshift
clusters. Based on membership estimates for each cluster, we determine that the
AGN fraction at z~0.6 is f_A(L_X>10^42;M_R<-20) = 0.028 (+0.019/-0.012) and
f_A(L_X>10^43;M_R<-20) = 0.020 (+0.012/-0.008). These values are approximately
a factor of 20 greater than the AGN fractions in lower-redshift (average z~0.2)
clusters of galaxies and represent a substantial increase over the factors of
1.5 and 3.3 increase, respectively, in the measured space density evolution of
the hard X-ray luminosity function over this redshift range. Potential
systematic errors would only increase the significance of our result. The
cluster AGN fraction increases more rapidly with redshift than the field and
the increase in cluster AGN indicates the presence of an AGN Butcher-Oemler
Effect.Comment: ApJL Accepted, 5 pages, 2 figure
Northrop Grumman TR202 LOX/LH2 Deep Throttling Engine Technology Project Status
NASA's Propulsion and Cryogenic Advanced Development (PCAD) project is currently developing enabling propulsion technologies in support of future lander missions. To meet lander requirements, several technical challenges need to be overcome, one of which is the ability for the descent engine(s) to operate over a deep throttle range with cryogenic propellants. To address this need, PCAD has enlisted Northrop Grumman Aerospace Systems (NGAS) in a technology development effort associated with the TR202 engine. The TR202 is a LOX/LH2 expander cycle engine driven by independent turbopump assemblies and featuring a variable area pintle injector similar to the injector used on the TR200 Apollo Lunar Module Descent Engine (LMDE). Since the Apollo missions, NGAS has continued to mature deep throttling pintle injector technology. The TR202 program has completed two series of pintle injector testing. The first series of testing used ablative thrust chambers and demonstrated igniter operation as well as stable performance at discrete points throughout the designed 10:1 throttle range. The second series was conducted with calorimeter chambers and demonstrated injector performance at discrete points throughout the throttle range as well as chamber heat flow adequate to power an expander cycle design across the throttle range. This paper provides an overview of the TR202 program, describing the different phases and key milestones. It describes how test data was correlated to the engine conceptual design. The test data obtained has created a valuable database for deep throttling cryogenic pintle technology, a technology that is readily scalable in thrust level
- …