170,175 research outputs found
The influence of magnetic fields, turbulence, and UV radiation on the formation of supermassive black holes
No full text<p>Context. The seeds of the supermassive black holes with masses of similar to 10(9) M-circle dot observed already at z similar to 6 may have formed through the direct collapse of primordial gas in T-vir greater than or similar to 10(4) K halos, whereby the gas must stay hot (similar to 10(4) K) in order to avoid fragmentation.</p><p>Aims. The interplay between magnetic fields, turbulence, and a UV radiation background during the gravitational collapse of primordial gas in a halo is explored; in particular, the possibilities for avoiding fragmentation are examined.</p><p>Methods. Using an analytical one-zone model, the evolution of a cloud of primordial gas is followed from its initial cosmic expansion through turnaround, virialization, and collapse up to a density of 10(7) cm(-3).</p><p>Results. It was found that in halos with no significant turbulence, the critical UV background intensity (J(21)(crit)) for keeping the gas hot is lower by a factor similar to 10 for an initial comoving magnetic field B-0 similar to 2 nG than for the zero-field case, and even lower for stronger fields. In turbulent halos, J(21)(crit) is found to be a factor similar to 10 lower than for the zero-field-zero-turbulence case, and the stronger the turbulence (more massive halo and/or stronger turbulent heating), the lower J(21)(crit).</p><p>Conclusions. The reduction in J(21)(crit) is particularly important, since it exponentially increases the number of halos exposed to a super-critical radiation background.</p>
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Logistiek en automatisering in de transporttechniek: Bijdragen lustrumsymposium
No full textSymposium gehouden ter gelegenheid van 35 jaar Dispuut Transportkunde, Technische Universiteit Delft, en 30 jaar Laboratorium voor Transporttechniek, Technische Universiteit Delft, en 15 jaar Afdeling Transportkunde, Koninklijk Instituut van Ingenieurs. In dit symposium wordt aandacht besteed aan het logistieke- en automatiseringsaspect van magazijnen en terminals, plaatsen waar vervoersmodaliteiten en goederenstromen elkaar ontmoeten en goederen worden overgeslagen, opgeslagen en gedistribueerd. Zowel bij de operationele fase als in de ontwerpfase van de werktuigen en van het al of niet geautomatiseerde systeem speelt simulatie een steeds belangrijkere rol. Distributiemagazijnen, distributiecentra, bulkterminals en container terminals worden behandeld.Mechanical, Maritime and Materials Engineerin
The fundamentals of three-dimensional chip curl, chip breaking and chip control
No full textElectrical Engineering, Mathematics and Computer Scienc
Mitomycin C in highly myopic eyes - Author reply
No full textOphthalmology. 2005 Feb;112(2):208-18; discussion 219.
Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes.
Gambato C, Ghirlando A, Moretto E, Busato F, Midena E.
SourceRefractive Surgery Service and Antimetabolite Therapy Research Unit, Department of Ophthalmology, University of Padova, Padova, Italy.
Abstract
PURPOSE: To evaluate the role of topical mitomycin C in corneal wound healing (CWH) after photorefractive keratectomy (PRK) in highly myopic eyes.
DESIGN: Prospective, double-masked, randomized clinical trial.
PARTICIPANTS: Seventy-two eyes of 36 patients affected by high (>7 diopters) myopia.
METHODS: In each patient, one eye was randomly assigned to PRK with intraoperative topical 0.02% mitomycin C application, and the fellow eye was treated with a placebo. Postoperatively, mitomycin C-treated eyes received artificial tears (3 times daily, tapered in 3 months), whereas the fellow eye was treated with fluorometholone sodium 2% and artificial tears (3 times daily, tapered in 3 months).
MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), contrast sensitivity, manifest refraction, and biomicroscopy. Contrast sensitivity was determined using the Pelli-Robson chart. Corneal confocal microscopy documented CWH.
RESULTS: Mean follow-up was 18 months (range, 12-36). No side effects or toxic effects were documented. At 12-month follow-up examination, UCVAs (logarithm of the minimum angle of resolution) were 0.4+/-0.48 and 0.5+/-0.53 (P = .03) in mitomycin C-treated eyes and corticosteroid-treated eyes, respectively. At 1 year, corneal haze developed in 20% of corticosteroid-treated eyes, versus 0% of mitomycin C-treated eyes. At 12, 24, and 36 months, corneal confocal microscopy showed activated keratocytes and extracellular matrix significantly more evident in untreated eyes (Ps = 0.004, 0.024, and 0.046, respectively).
CONCLUSION: Topical intraoperative application of 0.02% mitomycin C can reduce haze formation in highly myopic eyes undergoing PRK.
Comment in
Ophthalmology. 2006 Feb;113(2):357; author reply 357-8
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Effects of turbulence and rotation on protostar formation as a precursor to seed black holes
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