1,186 research outputs found
Growth of Intermediate-Mass Black Holes in Globular Clusters
We present results of numerical simulations of sequences of binary-single
scattering events of black holes in dense stellar environments. The simulations
cover a wide range of mass ratios from equal mass objects to 1000:10:10 solar
masses and compare purely Newtonian simulations to simulations in which
Newtonian encounters are interspersed with gravitational wave emission from the
binary. In both cases, the sequence is terminated when the binary's merger time
due to gravitational radiation is less than the arrival time of the next
interloper. We find that black hole binaries typically merge with a very high
eccentricity (0.93 < e < 0.95 pure Newtonian; 0.85 < e < 0.90 with
gravitational wave emission) and that adding gravitational wave emission
decreases the time to harden a binary until merger by ~ 30% to 40%. We discuss
the implications of this work for the formation of intermediate-mass black
holes and gravitational wave detection.Comment: 28 pages including 9 figures, submitted to Ap
Four-Body Effects in Globular Cluster Black Hole Coalescence
In the high density cores of globular clusters, multibody interactions are
expected to be common, with the result that black holes in binaries are
hardened by interactions. It was shown by Sigurdsson & Hernquist (1993) and
others that 10 solar mass black holes interacting exclusively by three-body
encounters do not merge in the clusters themselves, because recoil kicks the
binaries out of the clusters before the binaries are tight enough to merge.
Here we consider a new mechanism, involving four-body encounters. Numerical
simulations by a number of authors suggest that roughly 20-50% of binary-binary
encounters will eject one star but leave behind a stable hierarchical triple.
If the orbital plane of the inner binary is strongly tilted with respect to the
orbital plane of the outer object, a secular Kozai resonance, first
investigated in the context of asteroids in the Solar System, can increase the
eccentricity of the inner body significantly. We show that in a substantial
fraction of cases the eccentricity is driven to a high enough value that the
inner binary will merge by gravitational radiation, without a strong
accompanying kick. Thus the merged object remains in the cluster; depending on
the binary fraction of black holes and the inclination distribution of
newly-formed hierarchical triples, this mechanism may allow massive black holes
to accumulate through successive mergers in the cores of globular clusters. It
may also increase the likelihood that stellar-mass black holes in globular
clusters will be detectable by their gravitational radiation.Comment: Submitted to ApJ Letters (includes emulateapj.sty
Using AVIRIS In The NASA BAA Project To Evaluate The Impact Of Natural Acid Drainage On Colorado Watersheds
The Colorado Geological Survey and the co-authors of this paper were awarded one of 15 NASA Broad Agency Announcement (BAA) grants in 2001. The project focuses on the use of hyperspectral remote sensing to map acid-generating minerals that affect water quality within a watershed, and to identify the relative contributions of natural and anthropogenic sources to that drainage. A further objective is to define the most cost-effective remote sensing instrument configuration for this application
The Kepler End-to-End Model: Creating High-Fidelity Simulations to Test Kepler Ground Processing
The Kepler mission is designed to detect the transit of Earth-like planets around Sun-like stars by observing 100,000 stellar targets. Developing and testing the Kepler ground-segment processing system, in particular the data analysis pipeline, requires high-fidelity simulated data. This simulated data is provided by the Kepler End-to-End Model (ETEM). ETEM simulates the astrophysics of planetary transits and other phenomena, properties of the Kepler spacecraft and the format of the downlinked data. Major challenges addressed by ETEM include the rapid production of large amounts of simulated data, extensibility and maintainability
Theoretical Risk of Genetic Reassortment Should Not Impede Development of Live, Attenuated Rift Valley Fever (RVF) Vaccines Commentary on the Draft WHO RVF Target Product Profile
In November 2019, The World Health Organization (WHO) issued a draft set of Target Product Profiles (TPPs) describing optimal and minimally acceptable targets for vaccines against Rift Valley fever (RVF), a Phlebovirus with a three segmented genome, in both humans and ruminants. The TPPs contained rigid requirements to protect against genomic reassortment of live, attenuated vaccines (LAVs) with wild-type RVF virus (RVFV), which place undue constraints on development and regulatory approval of LAVs. We review the current LAVs in use and in development, and conclude that there is no evidence that reassortment between LAVs and wild-type RVFV has occurred during field use, that such a reassortment event if it occurred would have no untoward consequence, and that the TPPs should be revised to provide a more balanced assessment of the benefits versus the theoretical risks of reassortment
Survey of the quality of experimental design, statistical analysis and reporting of research using animals
For scientific, ethical and economic reasons, experiments involving animals should be appropriately designed, correctly analysed and transparently reported. This increases the scientific validity of the results, and maximises the knowledge gained from each experiment. A minimum amount of relevant information must be included in scientific publications to ensure that the methods and results of a study can be reviewed, analysed and repeated. Omitting essential information can raise scientific and ethical concerns. We report the findings of a systematic survey of reporting, experimental design and statistical analysis in published biomedical research using laboratory animals. Medline and EMBASE were searched for studies reporting research on live rats, mice and non-human primates carried out in UK and US publicly funded research establishments. Detailed information was collected from 271 publications, about the objective or hypothesis of the study, the number, sex, age and/or weight of animals used, and experimental and statistical methods. Only 59% of the studies stated the hypothesis or objective of the study and the number and characteristics of the animals used. Appropriate and efficient experimental design is a critical component of high-quality science. Most of the papers surveyed did not use randomisation (87%) or blinding (86%), to reduce bias in animal selection and outcome assessment. Only 70% of the publications that used statistical methods described their methods and presented the results with a measure of error or variability. This survey has identified a number of issues that need to be addressed in order to improve experimental design and reporting in publications describing research using animals. Scientific publication is a powerful and important source of information; the authors of scientific publications therefore have a responsibility to describe their methods and results comprehensively, accurately and transparently, and peer reviewers and journal editors share the responsibility to ensure that published studies fulfil these criteria
Explorations, Vol. 3, No. 3
Cover: Artwork by Marcia Spencer, University of Maine art student.
Articles include: Characterization of Normal and Carcinogen Induced Neoplastic Cells of Teleost Origin, by Tim Lyden
Attitutdes and Opinions of Maine Dairy Farmers, by John Muth and James Leiby
Background: the quest for the eighteen month oyster, by Kevin Scully
The Quest for the Eighteen Month Oyster, by Kevin Scully
Measurement of Surface Tension of Kraft Black Liquor, by Jayalakshmi Jaya Krishnagopalan
From the former student, by Jayalakshmi Krishnagopalan
From the faculty advisor, by Ivar H. Stockel
Aquatic Fungal Decomposers in Two Adjacent Maine Lakes of Different Acidity, by Peter Wagner
Studies on a New Mouse Mutation, by Luanne L. Peters
Opportunities for Students: Maine Agricultural Experiment Station Research Programs, by Mark W. Anderson
Experimental Embryogenesis in Red Pine, by Judy C. Gates
The V-Notched Lobster in Maine, by Cheryl Waltz
Undernutrition in a Pediatric Population, by Paula Quatromoni
From the Advisor
Archaeology of the Central Maine Coast, by Douglas Kellogg
Marketing Strategies for Computer Consultants in Small Business, by Kimberly Dagher
Our Cover Artist
From the Advisor, by James Lineha
Regulation of oligodendrocyte progenitor cell maturation by PPARδ: effects on bone morphogenetic proteins
In EAE (experimental autoimmune encephalomyelitis), agonists of PPARs (peroxisome proliferator-activated receptors) provide clinical benefit and reduce damage. In contrast with PPARγ, agonists of PPARδ are more effective when given at later stages of EAE and increase myelin gene expression, suggesting effects on OL (oligodendrocyte) maturation. In the present study we examined effects of the PPARδ agonist GW0742 on OPCs (OL progenitor cells), and tested whether the effects involve modulation of BMPs (bone morphogenetic proteins). We show that effects of GW0742 are mediated through PPARδ since no amelioration of EAE clinical scores was observed in PPARδ-null mice. In OPCs derived from E13 mice (where E is embryonic day), GW0742, but not the PPARγ agonist pioglitazone, increased the number of myelin-producing OLs. This was due to activation of PPARδ since process formation was reduced in PPARδ-null compared with wild-type OPCs. In both OPCs and enriched astrocyte cultures, GW0742 increased noggin protein expression; however, noggin mRNA was only increased in astrocytes. In contrast, GW0742 reduced BMP2 and BMP4 mRNA levels in OPCs, with lesser effects in astrocytes. These findings demonstrate that PPARδ plays a role in OPC maturation, mediated, in part, by regulation of BMP and BMP antagonists
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How are management fashions institutionalized? The role of institutional work
We explore how transitory management fashions become institutionalized. Based on the concepts of institutional entrepreneurship and institutional work, we postulate that fashionable management practices acquire permanence when they are anchored within fieldwide institutions. The building of such institutions requires various types of institutional work, including political work, technical work and cultural work. Based on a review of the empirical literature on various management fashions, we identify the actors engaging in these different types of works, and their skills. Our results suggest that the institutionalization effect is stronger if more types of institutional work are deployed and if the skill sets of the involved actors vary. We also argue that institutional construction in the case of management fashions is likely to take the form of decentralized `partaking' rather than being led by a single dominant institutional entrepreneur. We conclude with implications for the study of management fashions and the role of agency in institutionalization
Epidemic space
The aim of this article is to highlight the importance of 'spatiality' in understanding the materialization of risk society and cultivation of risk sensibilities. More specifically it provides a cultural analysis of pathogen virulence (as a social phenomenon) by means of tracing and mapping the spatial flows that operate in the uncharted zones between the microphysics of infection and the macrophysics of epidemics. It will be argued that epidemic space consists of three types of forces: the vector, the index and the vortex. It will draw on Latour's Actor Network Theory to argue that epidemic space is geared towards instability when the vortex (of expanding associations and concerns) displaces the index (of finding a single cause)
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