130,556 research outputs found
Thermal disk winds in x-ray binaries: realistic heating and cooling rates give rise to slow, but massive, outflows
No full textA number of X-ray binaries exhibit clear evidence for the presence of disk winds in the high/soft state. A promising driving mechanism for these outflows is mass loss driven by the thermal expansion of X-ray heated material in the outer disk atmosphere. Higginbottom & Proga recently demonstrated that the properties of thermally driven winds depend critically on the shape of the thermal equilibrium curve, since this determines the thermal stability of the irradiated material. For a given spectral energy distribution, the thermal equilibrium curve depends on an exact balance between the various heating and cooling mechanisms at work. Most previous work on thermally driven disk winds relied on an analytical approximation to these rates. Here, we use the photoionization code cloudy to generate realistic heating and cooling rates which we then use in a 2.5D hydrodynamic model computed in ZEUS to simulate thermal winds in a typical black hole X-ray binary. We find that these heating and cooling rates produce a significantly more complex thermal equilibrium curve, with dramatically different stability properties. The resulting flow, calculated in the optically thin limit, is qualitatively different from flows calculated using approximate analytical rates. Specifically, our thermal disk wind is much denser and slower, with a mass-loss rate that is a factor of two higher and characteristic velocities that are a factor of three lower. The low velocity of the flow— km s−1—may be difficult to reconcile with observations. However, the high mass-loss rate—15 × the accretion rate—is promising, since it has the potential to destabilize the disk. Thermally driven disk winds may therefore provide a mechanism for state changes
Jubiliejaus proga
No full text1968 m. lapkričio 14–16 d. Šiaulių K. Preikšo pedagoginio instituto dvidešimtmečio proga įvykusioje konferencijoje pranešimus skaitė ir visuomenės mokslų atstovai, tarp jų ir filosofai. B. Genzelis perskaitė pranešimą „Lietuvos kultūrinio palikimo vertinimo kriterijaus klausimu“, A. Gaigalaitė – „Istorijos mokslo Lietuvoje istoriografijos klausimu“, E. Gendrolis – „V. Leninas apie metodologinius materialistinės pasaulėžiūros formavimosi pagrindus“, J. Ažubalis – „Religinės pažiūros į moterį kritika Lietuvos ateistinėje 1940–1965 m. literatūroje“
Feedback from central black holes in elliptical galaxies. I: models with either radiative or mechanical feedback but not both
No full textFeedback from central black holes in elliptical galaxies. III: models with both radiative and mechanical feedback
No full textRadiation-driven accretion disk winds
No full textThe concept of an ‘effective' Eddington limit as a lower bound on the system luminosity required for mass loss to be radiation pressure driven is discussed and shown to fall in the interesting regime for high-state non-magnetic CV (nMCV). The results of recent hydrodynamical models of radiation-driven disk winds (Proga et al. 1998, Proga 1999) are summarised. Mass loss rates predicted by these models are then compared with observational constraints. It is shown that either mass accretion rates in high-state nMCV are a factor of 2–3 larger than presently supposed or that radiation pressure alone is not quite sufficient to drive the observed hypersonic flows
Line-driven Disk Winds in Activ Galactic Nuclei: The Critical Importance of Ionization and Radiative Transfer
No full textAccretion disk winds are thought to produce many of the characteristic features seen in the spectra of active galactic nuclei (AGNs) and quasi-stellar objects (QSOs). These outflows also represent a natural form of feedback between the central supermassive black hole and its host galaxy. The mechanism for driving this mass loss remains unknown, although radiation pressure mediated by spectral lines is a leading candidate. Here, we calculate the ionization state of, and emergent spectra for, the hydrodynamic simulation of a line-driven disk wind previously presented by Proga & Kallman. To achieve this, we carry out a comprehensive Monte Carlo simulation of the radiative transfer through, and energy exchange within, the predicted outflow. We find that the wind is much more ionized than originally estimated. This is in part because it is much more difficult to shield any wind regions effectively when the outflow itself is allowed to reprocess and redirect ionizing photons. As a result, the calculated spectrum that would be observed from this particular outflow solution would not contain the ultraviolet spectral lines that are observed in many AGN/QSOs. Furthermore, the wind is so highly ionized that line driving would not actually be efficient. This does not necessarily mean that line-driven winds are not viable. However, our work does illustrate that in order to arrive at a self-consistent model of line-driven disk winds in AGN/QSO, it will be critical to include a more detailed treatment of radiative transfer and ionization in the next generation of hydrodynamic simulations
LAUDACIJA DOC. LIONGINUI PAŽŪSIUI ŠV. JERONIMO PREMIJOS ĮTEIKIMO PROGA 2011 M. RUGSĖJO 30 D., ARSENALE, VILNIUJE
No full texthttp://www.llvs.lt/?item=567&lang=lt
2011 metais ilgamečiui Vertimo studijų katedros dėstytojui, ne vienos vertėjų kartos mokytojui, kalbininkui, vertėjui, docentui daktarui LIONGINUI PAŽŪSIUI skirta Šv. Jeronimo premija už užsienio literatūros vertimus į lietuvių kalbą. Lietuvos literatūros vertėjų sąjunga įvertino visokeriopą laureato indėlį į meninio vertimo teoriją, kritiką ir vertėjų ugdymą, virtuoziškus poezijos vertimus bei ypatingą dėmesį žodžio skambesiui. Vertimo studijos sveikina kolegą ir spausdina profesorės Ligijos Kaminskienės laudaciją, pasakytą premijos įteikimo proga 2011 m. rugsėjo 30 d., Vilniuje
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
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
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