4,675 research outputs found
Black Hole - Neutron Star Mergers as Central Engines of Gamma-Ray Bursts
Hydrodynamic simulations of the merger of stellar mass black hole - neutron
star binaries (BH/NS) are compared with mergers of binary neutron stars
(NS/NS). The simulations are Newtonian, but take into account the emission and
backreaction of gravitational waves. The use of a physical nuclear equation of
state allows us to include the effects of neutrino emission. For low neutron
star to black hole mass ratios the neutron star transfers mass to the black
hole during a few cycles of orbital decay and subsequent widening before
finally being disrupted, whereas for ratios near unity the neutron star is
already distroyed during its first approach. A gas mass between about 0.3 and
about 0.7 solar masses is left in an accretion torus around the black hole and
radiates neutrinos at a luminosity of several 10^{53} erg/s during an estimated
accretion time scale of about 0.1 s. The emitted neutrinos and antineutrinos
annihilate into electron-positron pairs with efficiencies of 1-3% percent and
rates of up to 2*10^{52} erg/s, thus depositing an energy of up to 10^{51} erg
above the poles of the black hole in a region which contains less than 10^{-5}
solar masses of baryonic matter. This could allow for relativistic expansion
with Lorentz factors around 100 and is sufficient to explain apparent burst
luminosities of up to several 10^{53} erg/s for burst durations of
approximately 0.1-1 s, if the gamma emission is collimated in two moderately
focussed jets in a fraction of about 1/100-1/10 of the sky.Comment: 8 pages, LaTex, 4 postscript figures, 2 tables. ApJ Letters,
accepted; revised and shortened version, Fig. 2 change
Space processing of chalcogenide glass
A program was conducted to develop the technique of space processing for chalcogenide glass, and to define the process and equipment necessary. In the course of this program, successful long term levitation of objects in a 1-g environment was achieved. Glass beads 4 mm diameter were containerless melted and fused together
Hope and Inquietudes in Nucleo-cosmochronology
Critical views are presented on some nucleo-cosmochronological questions.
Progress has been made recently in the development of the 187Re-187Os
cosmochronometry. From this, there is good hope for this clock to become of the
highest quality for the nuclear dating of the Universe. The simultaneous
observation of Th and U in ultra-metal-poor stars would also be a most
interesting prospect. In contrast, a serious inquietude is expressed about the
reliability of the chronometric attempts based on the classical 232Th-238U and
235U-238U pairs, as well as on the Th (without U) abundance determinations in
ultra-metal poor stars.Comment: 9 pages, no figures; ASP Conference Series: "Astrophysical Ages and
Time Scales
Sina Fabian: Boom in der Krise. Konsum, Tourismus, Autofahren in Westdeutschland und Großbritannien 1970–1990, Göttingen:: Vandenhoeck & Ruprecht 2016, 494 S.
Exploring the opportunities and perceived success of internationalization strategies in Malaysian SME’s
There is a complete transforming process all around the global economy. Technological displacement is displacing all the business activities into information oriented or information based activities. Internationalization has the great contribution in the fundamental changes which took place all over the world. In fact due to internationalization a revolution has been introduce globally. Due to the web there is availability of extended opportunities for Malaysian customer and small & medium enterprises (SME‟s). There is a need of an orderly frame work, due to limited research on the role of internet in international marketing. In order to have the better understanding to the role of internet in international marketing strategy, it is needed to examine the purpose for which SME‟s use the internet in the international marketing context(Shanker & Meyer, 2009). This paper will be providing a significant contribution in the development of internationalization process among Malaysian SME's. This paper will also help Malaysian SME's to improve their internationalization strategies in contrast with the electronic commerce
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