176,192 research outputs found
Coastal ocean processes symposium : a tribute to William D. Grant, September 27 - September 30, 1998
No full textThis report is a compilation of abstracts distrbuted at the Coastal Ocean Processes Symposium: A Tribute to Willam D.
Grant at the Woods Hole Oceanographic Institution from September 27 - September 30, 1998.Funding was provided by the Office of Naval Research under Contract No. N00014-98-1-0596,
the Rinehart Coastal Research Center and the United States Geological Survey
Trapping black hole remnants
No full textLarge extra dimensions lower the Planck scale to values soon accessible. The production of TeV mass black holes at the LHC is one of the most exciting predictions. However, the final phases of the black hole's evaporation are still unknown and there are strong indications that a black hole remnant can be left. Since a certain fraction of such objects would be electrically charged, we argue that they can be trapped. In this paper, we examine the occurrence of such charged black hole remnants. These trapped remnants are of high interest, as they could be used to closely investigate the evaporation characteristics. Due to the absence of background from the collision region and the controlled initial state, the signal would be very clear. This would allow to extract information about the late stages of the evaporation process with high precision
Clinical and cost-effectiveness of internal limiting membrane peeling for patients with idiopathic full thickness macular hole. Protocol for a Randomised Controlled Trial : FILMS (Full-thickness macular hole and Internal Limiting Membrane peeling Study)
No full textBackground: A full-thickness macular hole (FTMH) is a common retinal condition associated with impaired vision. Randomised controlled trials (RCTs) have demonstrated that surgery, by means of pars plana vitrectomy and post-operative intraocular tamponade with gas, is effective for stage 2, 3 and 4 FTMH. Internal limiting membrane (ILM) peeling has been introduced as an additional surgical manoeuvre to increase the success of the surgery; i.e. increase rates of hole closure and visual improvement. However, little robust evidence exists supporting the superiority of ILM peeling compared with no-peeling techniques. The purpose of FILMS (Fullthickness macular hole and Internal Limiting Membrane peeling Study) is to determine whether ILM peeling improves the visual function, the anatomical closure of FTMH, and the quality of life of patients affected by this disorder, and the cost-effectiveness of the surgery.
Methods/Design: Patients with stage 2–3 idiopathic FTMH of less or equal than 18 months duration (based on symptoms reported by the participant) and with a visual acuity ≤ 20/40 in the study eye will be enrolled in this FILMS from eight sites across the UK and Ireland. Participants will be randomised to receive combined cataract surgery (phacoemulsification and intraocular lens implantation) and pars plana vitrectomy with postoperative intraocular tamponade with gas, with or without ILM peeling. The primary outcome is distance visual acuity at 6 months. Secondary outcomes include distance visual acuity at 3 and 24 months, near visual acuity at 3, 6, and 24 months, contrast sensitivity at 6 months, reading speed at 6 months, anatomical closure of the macular hole at each time point (1, 3, 6, and 24 months), health related quality of life (HRQOL) at six months, costs to the health service and the participant, incremental costs per quality adjusted life year (QALY) and adverse events.
Discussion: FILMS will provide high quality evidence on the role of ILM peeling in FTMH surgery.
Trial registration: This trial is registered with Current Controlled Trials ISRCTN number 33175422 and Clinical Trials.gov identifier NCT00286507.Chief Scientist Office, Scotland (project ref no CZH/4/235), NHS GrampianPeer reviewedPublisher PD
Black hole attractors and the entropy function in four- and five-dimensional N=2 supergravity
No full textExtremal black holes in theories of gravity coupled to abelian gauge fields and neutral scalars, such as those arising in the low-energy description of compactifications of string theory on Calabi-Yau manifolds, exhibit the attractor phenomenon: on the event horizon the scalars settle to values determined by the charges carried by the black hole and independent of the values at infinity. It is so, because on the horizon the energy contained in vector fields acts as an effective potential (the black hole potential), driving the scalars towards its minima.
For spherically symmetric black holes in theories where gauge potentials appear in the Lagrangian solely through field strengths, the attractor phenomenon can be alternatively described by a variational principle based on the so-called entropy function, defined as the Legendre transform with respect to electric fields of the Lagrangian density integrated over the horizon. Stationarity conditions for the entropy function then take the form of attractor equations relating the horizon values of the scalars to the black hole charges, while the stationary value itself yields the entropy of the black hole.
In this study we examine the relationship between the entropy function and the black hole potential in four-dimensional N=2 supergravity and demonstrate that in the absence of higher-order corrections to the Lagrangian these two notions are equivalent. We also exemplify their practical application by finding a supersymmetric and a non-supersymmetric solution to the attractor equations for a conifold prepotential.
Exploiting a connection between four- and five-dimensional black holes we then extend the definition of the entropy function to a class of rotating black holes in five-dimensional N=2 supergravity with cubic prepotentials, to which the original formulation did not apply because of broken spherical symmetry and explicit dependence of the Lagrangian on the gauge potentials in the Chern-Simons term. We also display two types of solutions to the respective attractor equations.
The link between four- and five-dimensional black holes allows us further to derive five-dimensional first-order differential flow equations governing the profile of the fields from infinity to the horizon and construct non-supersymmetric solutions in four dimensions by dimensional reduction.
Finally, four-dimensional extremal black holes in N=2 supergravity can be also viewed as certain two-dimensional string compactifications with fluxes. Motivated by this fact the recently proposed entropic principle postulates as a probability measure on the space of these string compactifications the exponentiated entropy of the corresponding black holes. Invoking the conifold example we find that the entropic principle would favor compactifications that result in infrared-free gauge theories
The Black Hole Spin Controversy
No full textAstrophysical black holes are the simplest possible objects. They are completely described by only two parameters in general relativity, their mass and the specific angular momentum, spin. The spin is a fundamental characteristic of a black hole, but unlike mass it leaves a mark on space-time only very close to the event horizon, and is therefore more difficult to measure. The observational relevance of the spin comes from the fact that it sets the size scale of the last stable orbit around the accreting black hole, dragging the accretion disc farther in the faster it spins.
Black hole spin is a very controversial topic in both stellar and supermassive black holes. There are two methods to determine spin in binary systems, using either the direct disc continuum or the reflected emission. These can give significantly different values, and understanding the source of this discrepancy is important especially for interpreting AGN spin, where only the reflection method can be used.
We have strived to understand and carefully model the time-averaged energy spectra from several Galactic black hole binaries, in order to ultimately measure the black hole spin. Achieving this has required in-depth understanding of the instruments as well as the data analysis methods. The spin leaves only minor traces in the data, and these can be affected by calibration uncertainties, uncertainties in the models and systematic uncertainties. This knowledge is absolutely essential for a detailed analysis of all relativistically smeared atomic features seen in the time-averaged energy spectra of compact objects
What Price Determinism? The Hole Story!
No full textIn their modern classic ``What Price Substantivalism? The Hole Story'' Earman and Norton argued that substantivalism about spacetime points implies that general relativity is indeterministic and, for that reason, must be rejected as a candidate ontology for the theory. More recently, Earman has cottoned on to a related argument (in fact, related to a \emph{response} to the hole argument) that arises in the context of canonical general relativity, according to which the enforcing of determinism along standard lines---using the machinery of gauge theory---leads to a `frozen universe' picture (grounded in an absence of changes in values of general relativity's observables). \emph{Prima facie} this would seem to land the anti-substantivalist in waters at least as deep as those that Earman and Norton argued troubled substantivalism. In this paper I introduce the argument in what I think are clearer terms than Earman's, and assess his treatment of the problem. For the most part I agree with Earman about the nature of the problem, but I find aspects of his discussion wanting, especially as regards his proposed ontology. I argue that ontological sense can be made of the changelessness if a structuralist stance is adopted with respect to a natural class of observables
Internal limiting membrane peeling versus no peeling for idiopathic full-thickness macular hole: a pragmatic randomized controlled trial
No full text<p>Purpose: To determine whether internal limiting membrane (ILM) peeling is effective and cost effective compared with no peeling in patients with idiopathic stage 2 or 3 full-thickness maculay hole (FTMH).</p>
<p>Methods: This was a pragmatic multicenter randomized controlled trial. Eligible participants from nine centers were randomized to ILM peeling or no peeling (1:1 ratio) in addition to phacovitrectomy, including detachment and removal of the posterior hyaloid and gas tamponade. The primary outcome was distance visual acuity (VA) at 6 months after surgery. Secondary outcomes included hole closure, distance VA at other time points, near VA, contrast sensitivity, reading speed, reoperations, complications, resource use, and participant-reported health status, visual function, and costs.</p>
<p>Results: Of 141 participants randomized in nine centers, 127 (90%) completed the 6-month follow-up. Nonstatistically significant differences in distance visual acuity at 6 months were found between groups (mean difference, 4.8; 95% confidence interval [CI], −0.3 to 9.8; P = 0.063). There was a significantly higher rate of hole closure in the ILM-peel group (56 [84%] vs. 31 [48%]) at 1 month (odds ratio [OR]) at 1 month (odds ratio [OR, 6.23; 95% CI, 2.64–14.73; P < 0.001) with fewer reoperations (8 [12%] vs. 31 [48%]) performed by 6 months (OR, 0.14; 95% CI, 0.05–0.34; P < 0.001). Peeling the ILM is likely to be cost effective.</p>
<p>Conclusions: There was no evidence of a difference in distance VA after the ILM peeling and no-ILM peeling techniques. An important benefit in favor of no ILM peeling was ruled out. Given the higher anatomic closure and lower reoperation rates in the ILM-peel group, ILM peeling seems to be the treatment of choice for idiopathic stage 2 to 3 FTMH.</p>
Toxic dinoflagellates and marine mammal mortalities : proceedings of an expert consultation held at the Woods Hole Oceanographic Institution
No full textOn May 8 and 9, 1989, a consultation of experts was convened at the Woods Hole
Oceanographic Institution to discuss the possible link between natural biotoxins and recent mass mortalities of humpback whales and bottlenose dolphins along the eastern coast of the United States. The focus was on the possible role of dinoflagellate toxins in these events. The objectives of the meeting were to review and assess the existing evidence and to recommend research priorities and needs.Funding was provided by NOAA, National Marine Fisheries Service, Woods Hole Oceanographic
Institution Coastal Research Center through a grant from the Andrew W. Mellon Foundation and the Woods Hole Oceanographic Institution Sea Grant Program under Grant NA86-D-SW90 (Project R/B - 92 and M/O-2)
Hole dangling-bond capture cross-sections in a-Si:H
No full textIt is demonstrated that the occupation statistics for a Gaussian distribution of dangling bond states may account for the measured variation of hole mobility-lifetime values in hydrogenated amorphous silicon as the Fermi energy is systematically varied by doping from about 0.55 eV to 1.05 eV below the conduction band edge. An assessment of how the deduced dangling bond parameters may be influenced by underlying doping effects suggests that the minimum cross-section ratio for hole capture into charged (sh-) and neutral (sh0) dangling bond states requires that sh-/sh0 = 5. The capture of holes is consequently dominated by charged dangling bonds provided the Fermi energy lies within the upper half of the band-gap. Both sh- and sh0 are observed to depend upon temperature (T) as sh ? T-ß which may indicate the presence of tunnelling transitions between valence band tail states and dangling bonds
Shellfish closures in Massachusetts, status and options : proceedings of a Sea Grant-sponsored workshop held at the Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, March 22, 1989 : technical report
No full textThis report is a summary of a workshop on the problem of shellfish closures due to
microbial contamination in Massachusetts. The workshop, sponsored by the Woods Hole
Oceanographic Institution Sea Grant Program, was held on March 22, 1989, at the Woods
Hole Oceanographic Institution. Its principal aim was to keep the shellfishing community
informed about the status of shellfish closures throughout Massachusetts, the results of
recent research on microbial contamination of shellfish, and options for shellfisheries in the
region in the face of increasing closures of shellfish areas. Topics addressed by invited
speakers included 1) the history of shellfish closures in the state, 2) the fecal-coliform
standard and why it needs to be modified, 3) alternatives to the standard, and 4) shellfish
relay and depuration procedures used in other states. The workshop was attended by more
than 160 people, primarily shellfish officers, shellfish biologists, members of town
shellfish commissions and shellfishermen from Massachusetts.Funding for the workshop and preparation of this report was provided by
NOAA National Sea Grant Program Office. Department of Commerce.
under Grant No. NA-86-AA-D-SG090. Woods Hole Oceanographic Institution
Sea Grant Project Nos. M/0-2 and A/S-10-PD
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