305,281 research outputs found
De stempels van Ommoord
No full textDe tussenmaten in de stempels van Ommoord. Een onderzoek naar nieuwe domeinen binnen de maat en schaal van de stempels in Ommoord
Stability of organic molecules against shocks in the young Solar nebula
No full textOne of the fundamental astrobiology questions is how life has formed in our Solar System. In this context the formation and stability of abiotic organic molecules such as CH(4), formic acid and amino acids, is important for understanding how organic material has formed and survived shocks and energetic particle impact from winds in the early Solar System. Shock waves have been suggested as a plausible scenario to create chondrules, small meteoritic components that have been completely molten by energetic events such as shocks and high velocity particle impacts. We study here the formation and destruction of certain gas-phase molecules such as methane and water during such shock events and compare the chemical timescales with the timescales for shocks arising from gravitational instabilities in a protosolar nebula
Photometric∕spectroscopic analyses and magnetic activity in young late-type stars
No full text15th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun -- JUL 21-25, 2008 -- St Andrews, SCOTLANDWe present preliminary results of a study in progress based on photometric and spectroscopic observations of young weak-line T Tauri and post-T Tauri stars just arriving on the Zero Aye Main Sequence. The study is part of a project based on high-resolution spectra obtained with FOCES@CAHA (Spain) and SARG@TNG (Spain) and contemporaneous photometry performed at Catania (Italy) and TUBITAK (Turkey) observatories. The main aim is to investigate the topology of magic active regions at photospheric and chromospheric levels in young single stars. Since our targets arc slow rotators, with rotation periods longer than about 2 days, we are able to apply the spectroscopic technique hawed on line-depth ratio for the measure of the photospheric temperature modulation. These stars. possible members of Stellar Kinematic Groups, display emission cores to the Call H&K and IRT lines, as well as a conspicuous filling-in of the H alpha core. Moreover. we derive lithium abundance. and measure rotational and radial velocities. In several cases we detect a clear rotational modulation of brightness. In this work we briefly mention some preliminary results obtained for SAO 51891. We have also developed a spot/plage model to he applied to the data deriving the spot parameters (filling factor and temperature) and recovering information about the chromospheric inhomogeneities (flux contrast and filling factor). This study will contribute to explore the correlations between global stellar parameters anti spot/plage characteristics in;tars with different activity level and evolutionary stage.Royal Astron Soc, Scottish Univ Phys Alliance, European Space Agcy, NASA Astrobiol InstItalian Ministry dell'Istruzione, Universitate Ricerca (MIUR)We thank the OACt, TNG, CAHA, and TUG teams for the assistance during the observations. This work has been supported by the Italian Ministry dell'Istruzione, Universitate Ricerca (MIUR) which is greatfully acknowledged. This research has made use of SIMBAD and VIZIER databases, operated at CDS, Strasbourg (France)
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
The formation of brown dwarfs and low-mass stars by disc fragmentation
No full textWe suggest that a high proportion of brown dwarfs are formed by gravitational fragmentation of massive extended discs around Sun‐like stars. We argue that such discs should arise frequently, but should be observed infrequently, precisely because they fragment rapidly. By performing an ensemble of radiation‐hydrodynamic simulations, we show that such discs typically fragment within a few thousand years to produce mainly brown dwarfs (including planetary‐mass brown dwarfs) and low‐mass hydrogen‐burning stars. Subsequently most of the brown dwarfs are ejected by mutual interactions. We analyse the properties of these objects that form by disc fragmentation, and compare them with observations
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
Introducing a Hybrid Method of Radiative Transfer in Smoothed Particle Hydrodynamics
No full textWe present a new method of incorporating radiative transfer into Smoothed Particle Hydrodynamics (SPH). There have been many recent attempts at radiative transfer in SPH [10, 11, 5, 13], however these are becoming increasingly complex, with some methods requiring the photosphere to be mapped (which is often of non‐trivial geometric shape), and extra conditions to be applied there (matching atmospheres as in [2], or specifying cooling at the photosphere as in [5]). The method of identifying the photosphere is usually a significant addition to the total simulation runtime, and often requires extra free parameters, the changing of which will affect the final results. Our method is not affected by such concerns, as the photosphere is constructed implicitly by the algorithm without the need for extra free parameters. The algorithm used is a synergy of two current formalisms for radiative effects: a) the polytropic cooling formalism proposed by [12], and b) flux‐limited diffusion, used by many authors to simulate radiation transport in the optically thick regime (e.g. [5]). We present several tests of this method
Author, publisher and bookseller : a tripartite synergy in Nigerian book industry
No full textThis work is about the roles of Author, Publisher and Bookseller in Book development in
Nigeria. The paper started by delving into the history of Book Publishing in Nigeria after
which it proceeded by defining who an author, a publisher, and a bookseller is and
expatiated on the indispensable roles of these key actors in Nigerian Book Industry and in
the emerging Information Society. Furthermore, the various constraints to book
development were identified while the paper advised on how the Book Industry can be
further promoted in Nigeria. However, the paper concluded and made recommendations
on how the Book sector can help in enhancing scholarship in the country
Stellar or Non-Stellar Light? Determining Near-Infrared Contamination in Low Mass X-ray Binaries
No full textLow-mass X-ray binary (LMXB) systems are comprised of a low-mass, K or M dwarflike star orbiting a compact object. Stellar black hole masses and their distributions are important inputs for binary evolution and supernova models. Currently, the main limiting factor in determining accurate black hole masses in LMXBs is the uncertainty of the orbital inclination angle due to an unknown amount of contaminating light in the near infrared. If present, this light dilutes the ellipsoidal variations of the low-mass secondary star, and thus gives the appearance of a lower orbital inclination system. It has been generally thought that the near infrared ellipsoidal light curves of these systems were relatively uncontaminated and represented primarily the light from the low-mass secondary star; however, recent disk and jet models have thrust this thinking into question. We combine our data from the Spitzer Space Telescope with our ground-based optical and near infrared data for several LMXBs to characterize and derive the amount of light contaminating the near-infrared ellipsoidal variations of the low-mass secondary star
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