248 research outputs found
Maximum black-hole spin from quasi-circular binary mergers
Black holes of mass M must have a spin angular momentum S below the Kerr
limit chi = S/M^2 < 1, but whether astrophysical black holes can attain this
limiting spin depends on their accretion history. Gas accretion from a thin
disk limits the black-hole spin to chi_gas < 0.9980 +- 0.0002, as
electromagnetic radiation from this disk with retrograde angular momentum is
preferentially absorbed by the black hole. Extrapolation of
numerical-relativity simulations of equal-mass binary black-hole mergers to
maximum initial spins suggests these mergers yield a maximum spin chi_eq <
0.95. Here we show that for smaller mass ratios q = m/M << 1, the superradiant
extraction of angular momentum from the larger black hole imposes a fundamental
limit chi_lim < 0.9979 +- 0.0001 on the final black-hole spin even in the
test-particle limit q -> 0 of binary black-hole mergers. The nearly equal
values of chi_gas and chi_lim imply that measurement of supermassive black-hole
spins cannot distinguish a black hole built by gas accretion from one assembled
by the gravitational inspiral of a disk of compact stellar remnants. We also
show how superradiant scattering alters the mass and spin predicted by models
derived from extrapolating test-particle mergers to finite mass ratios.Comment: final version accepted in PRD, new Fig.4 and discussio
Cigarette smoking in an adolescent psychiatric population
Objective. To examine the relationship between cigarette smoking and psychiatric symptomatology in an outpatient psychiatric population of adolescents.Method. A retrospective analysis was done of 934 patient charts at an outpatient psychiatric centre.Results. 48.4% of the psychiatric sample reported regular smoking behaviour, which is substantially more than the 18.1 % prevalence found in a local epidemiological study. Incomparing smokers and non-smokers within the psychiatric sample, it was noted that smokers were significantly younger and scored somewhat higher on depression ratingscales than non-smokers. A logistical regression, using quasi-Newton estimation, was chosen as the most suitable statistical method for building a classificatory model ofsmoking. Two continuous variables, age and the Hamilton depression score, along with 39 discrete variables, were chosen for modelling purposes. Model building was conducted in a hierarchical fashion, starting with demographic variables, the variable selection beingcontrolled by using chi-square tests of model differences. A predictive model of smoking with nine variables was finally selected.Conclusions. As a whole the results support the strong association between smoking and psychiatric problems, but in this adolescent sample smoking is more likely to be partof a general risk-taking behaviour pattern than an attempt to medicate depression. Anti-tobacco campaigns that highlight the risks of smoking are therefore open invitationsfor adolescents to take up the habit
Methods to improve recruitment to randomised controlled trials : Cochrane systematic review and meta-analysis
Peer reviewedPublisher PD
Monitoring Volcanoes by Use of Air-Dropped Sensor Packages
Sensor packages that would be dropped from airplanes have been proposed for pre-eruption monitoring of physical conditions on the flanks of awakening volcanoes. The purpose of such monitoring is to gather data that could contribute to understanding and prediction of the evolution of volcanic systems. Each sensor package, denoted a volcano monitoring system (VMS), would include a housing with a parachute attached at its upper end and a crushable foam impact absorber at its lower end (see figure). The housing would contain survivable low-power instrumentation that would include a Global Positioning System (GPS) receiver, an inclinometer, a seismometer, a barometer, a thermometer, and CO2 and SO2 analyzers. The housing would also contain battery power, control, data-logging, and telecommunication subsystems. The proposal for the development of the VMS calls for the use of commercially available sensor, power, and telecommunication equipment, so that efforts could be focused on integrating all of the equipment into a system that could survive impact and operate thereafter for 30 days, transmitting data on the pre-eruptive state of a target volcano to a monitoring center. In a typical scenario, VMSs would be dropped at strategically chosen locations on the flanks of a volcano once the volcano had been identified as posing a hazard from any of a variety of observations that could include eyewitness reports, scientific observations from positions on the ground, synthetic-aperture-radar scans from aircraft, and/or remote sensing from aboard spacecraft. Once dropped, the VMSs would be operated as a network of in situ sensors that would transmit data to a local monitoring center. This network would provide observations as part of an integrated volcano-hazard assessment strategy that would involve both remote sensing and timely observations from the in situ sensors. A similar strategy that involves the use of portable sensors (but not dropping of sensors from aircraft) is already in use in the Volcano Disaster Assistance Program (VDAP), which was developed by the U.S. Geological Survey and the U.S. Office of Foreign Disaster Assistance to respond to volcanic crises around the world. The VMSs would add a greatly needed capability that would enable VDAP response teams to deploy their volcano-monitoring equipment in a more timely manner with less risk to personnel in the field
Occurrence of Chaceon Larvae in Plankton Samples from Slope Waters of the Northeastern Gulf of Mexico
Geographic, seasonal, and bathymetric distributions of Chaceon larvae are described for the northeastern Gulf of Mexico
Occurrence of Chaceon Larvae in Plankton Samples from Slope Waters of the Northeastern Gulf of Mexico
Geographic, seasonal, and bathymetric distributions of Chaceon larvae are described for the northeastern Gulf of Mexico
Sensitivity, Specificity and the Hybridization Isotherms of DNA Chips
Competitve hybridization, at the surface and in the bulk, lowers the
sensitivity of DNA chips. Competitive surface hybridization occurs when
different targets can hybridize with the same probe. Competitive bulk
hybridization takes place when the targets can hybridize with free
complementary chains in the solution. The effects of competitive hybridization
on the thermodynamically attainable performance of DNA chips are quantified in
terms of the hybridization isotherms of the spots. These relate the equilibrium
degree of the hybridization to the bulk composition. The hybridization isotherm
emerges as a Langmuir isotherm modified for electrostatic interactions within
the probe layer. The sensitivity of the assay in equilibrium is directly
related to the slope of the isotherm. A simpler description is possible in
terms of s specifying the bulk composition corresponding to 50%
hybridization at the surface. The effects of competitive hybridization are
important for the quantitative analysis of DNA chip results especially when
used to study point mutations.Comment: 18 pages and 7 figures. To be published in Biophys.
1980: Abilene Christian College Bible Lectures - Full Text
UNTIL HE COMES
Being the Abilene Christian University Annual Bible Lectures 1980
Published by Abilene Christian University Book Store
ACU Station Abilene, Texas 7969
4-(8-Ethoxy-2,3-dihydro-1H-cyclopenta[c]quinolin-4-yl)butane-1-peroxol
In the title molecule, C18H23NO3, the hydroperoxybutyl substituent is nearly fully extended, with the four torsion angles in the range 170.23 (10)–178.71 (9)°. The O—O distance in the hydroperoxide group is 1.4690 (13) Å. This group acts as an intermolecular hydrogen-bond donor to a quinoline N atom. This results in dimeric units about the respective inversion centers, with graph-set notation R
2
2(18)
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