1,721,480 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“
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
Radiation-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
REMOTE MANAGEMENT OF RAIL TRAFFIC ON KOČEVSKA PROGA
No full textRegionalna železniška proga Grosuplje – Kočevje , imenovana tudi kočevska proga, je bila zgrajena leta 1893, kot del proge Ljubljana - Grosuplje - Kočevje. Proga naj bi imela predvsem gospodarski pomen. Proga je normalno obratovalo do šestdesetih let, ko je bila rekonstruirana cesta od Škofljice do Kočevja. Takrat je prišlo do upadanja tovornega prometa in drastičnega upadanja števila potnikov v potniškem prometu, tako da je v letih od 1968 do 1972 prišlo do ukinitve potniškega prometa. Od tedaj se na enotirni in ne elektrificirani kočevski progi odvija le tovorni promet pod posebnimi pogoji. Zaradi potrebe po ponovni vzpostavitvi potniškega prometa so leta 2008 začeli z obnovo proge. Proga je do danes obnovljena potrebno pa je še urediti signalnovarnostne naprave in center za daljinsko vodenje prometa. V diplomskem delu je predstavljeno kako opremiti in zavarovati progo in postaje od Grosuplja do Kočevja s sistemom za daljinsko vodenje železniškega prometa TRIS CTC.Regional railway line from Grosuplje to Kočevje, also known as »kočevska proga«, was built in 1893 as a part of the railway Ljubljana – Grosuplje – Kočevje. It was constructed primarily to improve the economy. The railway operated normally until 1960, when the reconstruction of the road from Škofljica to Kočevje ended, which had led to a drastic decrease in the number of freight transport and the number of passengers in commuter trains. Thus, during the years 1968 – 1972, the passenger traffic on the railways was cancelled. Since then, non-electrified monorail is used only for the transportation of goods under a special agreement. Due to the need of re-establishing the passenger transport, the reconstruction of the track began in 2008. The track reconstruction is finished, but signal safety devices and a remote traffic control center need to be regulated. In this thesis I propose how to equip and protect the railway and stations from Grosuplje to Kočevje with the remote railway traffic control system TRIS CTC
Feedback from central black holes in elliptical galaxies. III: models with both radiative and mechanical feedback
No full textFeedback from central black holes in elliptical galaxies. I: models with either radiative or mechanical feedback but not both
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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
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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