610 research outputs found
Simulating merging binary black holes with nearly extremal spins
Astrophysically realistic black holes may have spins that are nearly extremal
(i.e., close to 1 in dimensionless units). Numerical simulations of binary
black holes are important tools both for calibrating analytical templates for
gravitational-wave detection and for exploring the nonlinear dynamics of curved
spacetime. However, all previous simulations of binary-black-hole inspiral,
merger, and ringdown have been limited by an apparently insurmountable barrier:
the merging holes' spins could not exceed 0.93, which is still a long way from
the maximum possible value in terms of the physical effects of the spin. In
this paper, we surpass this limit for the first time, opening the way to
explore numerically the behavior of merging, nearly extremal black holes.
Specifically, using an improved initial-data method suitable for binary black
holes with nearly extremal spins, we simulate the inspiral (through 12.5
orbits), merger and ringdown of two equal-mass black holes with equal spins of
magnitude 0.95 antialigned with the orbital angular momentum.Comment: 4 pages, 2 figures, updated with version accepted for publication in
Phys. Rev. D, removed a plot that was incorrectly included at the end of the
article in version v
Power of Three
The strained relationship between communities and police worsens every day and will continue to without change. Our podcast tells the stories of different situations that support this claim. Then three speakers tell how these strained relations can lead to violent confrontations between officers and civilians through discussion with our differed opinions. The book Outcasts United is repeatedly referenced throughout the entire podcast by including certain stories from the book that go hand-in-hand with the real life situations. There are three main topics in the podcast, the first talks about two unarmed black civilians who were shot to death. The second is an interview with a Veteran police officer who shares his opinion on what the cause of this distrust is. The last topic is about the city of San Bernardino and how they are trying to fix it
The RRAT Trap: Interferometric Localization of Radio Pulses from J0628+0909
We present the first blind interferometric detection and imaging of a
millisecond radio transient with an observation of transient pulsar J0628+0909.
We developed a special observing mode of the Karl G. Jansky Very Large Array
(VLA) to produce correlated data products (i.e., visibilities and images) on a
time scale of 10 ms. Correlated data effectively produce thousands of beams on
the sky that can localize sources anywhere over a wide field of view. We used
this new observing mode to find and image pulses from the rotating radio
transient (RRAT) J0628+0909, improving its localization by two orders of
magnitude. Since the location of the RRAT was only approximately known when
first observed, we searched for transients using a wide-field detection
algorithm based on the bispectrum, an interferometric closure quantity. Over 16
minutes of observing, this algorithm detected one transient offset roughly 1'
from its nominal location; this allowed us to image the RRAT to localize it
with an accuracy of 1.6". With a priori knowledge of the RRAT location, a
traditional beamforming search of the same data found two, lower significance
pulses. The refined RRAT position excludes all potential multiwavelength
counterparts, limiting its optical luminosity to L_i'<1.1x10^31 erg/s and
excluding its association with a young, luminous neutron star.Comment: Submitted to ApJ, 7 pages, 5 figure
Characterization of a Novel Origin Recognition Complex-Like Complex: Implications for DNA Recognition, Cell Cycle Control, and Locus-Specific Gene Amplification
The origin recognition complex (ORC) plays a central role in eukaryotic DNA replication. Here we describe a unique ORC-like complex in Tetrahymena thermophila, TIF4, which bound in an ATP-dependent manner to sequences required for cell cycle-controlled replication and gene amplification (ribosomal DNA [rDNA] type I elements). TIF4's mode of DNA recognition was distinct from that of other characterized ORCs, as it bound exclusively to single-stranded DNA. In contrast to yeast ORCs, TIF4 DNA binding activity was cell cycle regulated and peaked during S phase, coincident with the redistribution of the Orc2-related subunit, p69, from the cytoplasm to the macronucleus. Origin-binding activity and nuclear p69 immunoreactivity were further regulated during development, where they distinguished replicating from nonreplicating nuclei. Both activities were lost from germ line micronuclei following the programmed arrest of micronuclear replication. Replicating macronuclei stained with Orc2 antibodies throughout development in wild-type cells but failed to do so in the amplification-defective rmm11 mutant. Collectively, these findings indicate that the regulation of TIF4 is intimately tied to the cell cycle and developmentally programmed replication cycles. They further implicate TIF4 in rDNA gene amplification. As type I elements interact with other sequence-specific single-strand breaks (in vitro and in vivo), the dynamic interplay of Orc-like (TIF4) and non-ORC-like proteins with this replication determinant may provide a novel mechanism for regulation
Momentum flow in black-hole binaries: II. Numerical simulations of equal-mass, head-on mergers with antiparallel spins
Research on extracting science from binary-black-hole (BBH) simulations has
often adopted a "scattering matrix" perspective: given the binary's initial
parameters, what are the final hole's parameters and the emitted gravitational
waveform? In contrast, we are using BBH simulations to explore the nonlinear
dynamics of curved spacetime. Focusing on the head-on plunge, merger, and
ringdown of a BBH with transverse, antiparallel spins, we explore numerically
the momentum flow between the holes and the surrounding spacetime. We use the
Landau-Lifshitz field-theory-in-flat-spacetime formulation of general
relativity to define and compute the density of field energy and field momentum
outside horizons and the energy and momentum contained within horizons, and we
define the effective velocity of each apparent and event horizon as the ratio
of its enclosed momentum to its enclosed mass-energy. We find surprisingly good
agreement between the horizons' effective and coordinate velocities. To
investigate the gauge dependence of our results, we compare pseudospectral and
moving-puncture evolutions of physically similar initial data; although
spectral and puncture simulations use different gauge conditions, we find
remarkably good agreement for our results in these two cases. We also compare
our simulations with the post-Newtonian trajectories and near-field
energy-momentum. [Abstract abbreviated; full abstract also mentions additional
results.]Comment: Submitted to Phys. Rev.
Odonata of Cape York, Australia
46 p. : ill., map ; 24 cm.Includes bibliographical references (p. 44-45)
Reducing spurious gravitational radiation in binary-black-hole simulations by using conformally curved initial data
At early times in numerical evolutions of binary black holes, current
simulations contain an initial burst of spurious gravitational radiation (also
called "junk radiation") which is not astrophysically realistic. The spurious
radiation is a consequence of how the binary-black-hole initial data are
constructed: the initial data are typically assumed to be conformally flat. In
this paper, I adopt a curved conformal metric that is a superposition of two
boosted, non-spinning black holes that are approximately 15 orbits from merger.
I compare junk radiation of the superposed-boosted-Schwarzschild (SBS) initial
data with the junk of corresponding conformally flat, maximally sliced (CFMS)
initial data. The SBS junk is smaller in amplitude than the CFMS junk, with the
junk's leading-order spectral modes typically being reduced by a factor of
order two or more.Comment: Submitted to Class. Quantum Grav. for inclusion in the "Numerical
Relativity & Data Analysis 2008 proceedings" special issu
Decision Tree Classifiers for Star/Galaxy Separation
We study the star/galaxy classification efficiency of 13 different decision
tree algorithms applied to photometric objects in the Sloan Digital Sky Survey
Data Release Seven (SDSS DR7). Each algorithm is defined by a set of parameters
which, when varied, produce different final classification trees. We
extensively explore the parameter space of each algorithm, using the set of
SDSS objects with spectroscopic data as the training set. The
efficiency of star-galaxy separation is measured using the completeness
function. We find that the Functional Tree algorithm (FT) yields the best
results as measured by the mean completeness in two magnitude intervals: () and (). We compare the performance of the
tree generated with the optimal FT configuration to the classifications
provided by the SDSS parametric classifier, 2DPHOT and Ball et al. (2006). We
find that our FT classifier is comparable or better in completeness over the
full magnitude range , with much lower contamination than all but
the Ball et al. classifier. At the faintest magnitudes (), our classifier
is the only one able to maintain high completeness (80%) while still
achieving low contamination (). Finally, we apply our FT classifier
to separate stars from galaxies in the full set of SDSS
photometric objects in the magnitude range .Comment: Submitted to A
FDR Stabilizer Selection Using Simple Soil Tests
69A355184710Most local agencies that use full-depth reclamation (FDR) choose the stabilizer to be used by selecting a vendor rather than performing test on the pavement materials. Most of the methods available for selecting the technique or additive to be used rely on a sieve test and the plastic index (PI). The PI is not sensitive at the low values found in materials like the glacial tills common across the northeast. However the Sand Equivalent (SE) is more sensitive in those materials and can be performed quickly. Five soils were tested to see if the SE with a sieve test could be used to discern if asphalt emulsion would be a good stabilizer additive for FDR. A proposed new matrix for which stabilizer technique or additive was proposed. Three sets of pavement materials (surface asphalt concrete and base gravels) were then tested to confirm the proposed stabilizer selection matrix. The results confirmed that the SE test may be a good alternative for local agencies trying to decide which stabilizer to use
Subsequent Surgery After Revision Anterior Cruciate Ligament Reconstruction: Rates and Risk Factors From a Multicenter Cohort
BACKGROUND: While revision anterior cruciate ligament reconstruction (ACLR) can be performed to restore knee stability and improve patient activity levels, outcomes after this surgery are reported to be inferior to those after primary ACLR. Further reoperations after revision ACLR can have an even more profound effect on patient satisfaction and outcomes. However, there is a current lack of information regarding the rate and risk factors for subsequent surgery after revision ACLR.
PURPOSE: To report the rate of reoperations, procedures performed, and risk factors for a reoperation 2 years after revision ACLR.
STUDY DESIGN: Case-control study; Level of evidence, 3.
METHODS: A total of 1205 patients who underwent revision ACLR were enrolled in the Multicenter ACL Revision Study (MARS) between 2006 and 2011, composing the prospective cohort. Two-year questionnaire follow-up was obtained for 989 patients (82%), while telephone follow-up was obtained for 1112 patients (92%). If a patient reported having undergone subsequent surgery, operative reports detailing the subsequent procedure(s) were obtained and categorized. Multivariate regression analysis was performed to determine independent risk factors for a reoperation.
RESULTS: Of the 1112 patients included in the analysis, 122 patients (11%) underwent a total of 172 subsequent procedures on the ipsilateral knee at 2-year follow-up. Of the reoperations, 27% were meniscal procedures (69% meniscectomy, 26% repair), 19% were subsequent revision ACLR, 17% were cartilage procedures (61% chondroplasty, 17% microfracture, 13% mosaicplasty), 11% were hardware removal, and 9% were procedures for arthrofibrosis. Multivariate analysis revealed that patients aged <20 years had twice the odds of patients aged 20 to 29 years to undergo a reoperation. The use of an allograft at the time of revision ACLR (odds ratio [OR], 1.79; P = .007) was a significant predictor for reoperations at 2 years, while staged revision (bone grafting of tunnels before revision ACLR) (OR, 1.93; P = .052) did not reach significance. Patients with grade 4 cartilage damage seen during revision ACLR were 78% less likely to undergo subsequent operations within 2 years. Sex, body mass index, smoking history, Marx activity score, technique for femoral tunnel placement, and meniscal tearing or meniscal treatment at the time of revision ACLR showed no significant effect on the reoperation rate.
CONCLUSION: There was a significant reoperation rate after revision ACLR at 2 years (11%), with meniscal procedures most commonly involved. Independent risk factors for subsequent surgery on the ipsilateral knee included age <20 years and the use of allograft tissue at the time of revision ACLR
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