508 research outputs found
Modeling the Diversity of Type Ia Supernova Explosions
Type Ia supernovae (SNe Ia) are a prime tool in observational cosmology. A
relation between their peak luminosities and the shapes of their light curves
allows to infer their intrinsic luminosities and to use them as distance
indicators. This relation has been established empirically. However, a
theoretical understanding is necessary in order to get a handle on the
systematics in SN Ia cosmology. Here, a model reproducing the observed
diversity of normal SNe Ia is presented. The challenge in the numerical
implementation arises from the vast range of scales involved in the physical
mechanism. Simulating the supernova on scales of the exploding white dwarf
requires specific models of the microphysics involved in the thermonuclear
combustion process. Such techniques are discussed and results of simulations
are presented.Comment: 6 pages, ASTRONUM-2009 "Numerical Modeling of Space Plasma Flows",
Chamonix, France, July 2009, to appear in ASP Conf. Pro
Stellar neutrino energy loss rates due to Mg suitable for O+Ne+Mg core simulations
Neutrino losses from proto-neutron stars play a pivotal role to decide if
these stars would be crushed into black holes or explode as supernovae. Recent
observations of subluminous Type II-P supernovae (e.g., 2005cs, 2003gd, 1999br,
1997D) were able to rejuvenate the interest in 8-10 M stars which
develop O+Ne+Mg cores. Simulation results of O+Ne+Mg cores show varying results
in converting the collapse into an explosion. The neutrino energy loss rates
are important input parameters in core collapse simulations. Proton-neutron
quasi-particle random phase approximation (pn-QRPA) theory has been used for
calculation of neutrino energy loss rates due to Mg in stellar matter.
The rates are presented on a detailed density-temperature grid suitable for
simulation purposes. The calculated neutrino energy loss rates are enhanced up
to more than one order of magnitude compared to the shell model calculations
and favor a lower entropy for the core of these massive stars.Comment: 20 pages, 4 figures, 2 table
Количественный подход к анализу деятельности вуза и его подразделений
В работе обосновывается возможность, необходимость и правомерность количественного подхода к анализу деятельности вуза. Показана целесообразность использования для этих целей концентраций теории полезности, в частности аддитивных функций полезности. Сформулированы основные требования, которые необходимо учитывать при конструировании системы количественных показателей
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The impact of procurement method on costs of procurement
Collaborative working methods offer the hope of reduced waste, lower tendering costs and improved outputs. The costs of tendering may be influenced by the introduction of different working methods. Transaction cost economics appears to offer an analytical framework for studying the costs of tendering, but it is more to do with providing explanations at the institutional/industry level, not at the level of individual projects. Surveys and interviews were carried out with small samples in UK. The data show that that while tendering costs are not necessarily higher in collaborative working arrangements, there is no correlation between costs of tendering and the way the work is organized. Practitioners perceive that the benefits of working in collaborative procurement routes far outweigh the costs. Tendering practices can be improved to avoid waste, and the suggested improvements include restricting selective tendering lists to 23 bidders, letting bidders know who they are competing with, reimbursing tendering costs for aborted projects and ensuring that timely and comprehensive information is provided to bidders
Новые определения глубинного теплового потока Земли в Карпатском регионе
Встановлено нові значення глибинного теплового потоку Землі (ТП) у 44 пунктах та проведено незалежні повторні визначення ТП у 45 пунктах Карпатського регіону на родовищах нафти і газу. Визначено аномалії, які вірогідно пов'язані з підйомом глибинних флюїдів.The new values of deep heat flow (HF) are studied at 44 points, and the independent re-determinations of HF are executed at 45 points of the Carpathian region in the oil and gas fields. Anomalies presumably associated with the rise of deep fluids are found
Oxygen emission in remnants of thermonuclear supernovae as a probe for their progenitor system
Recent progress in numerical simulations of thermonuclear supernova
explosions brings up a unique opportunity in studying the progenitors of Type
Ia supernovae. Coupling state-of-the-art explosion models with detailed
hydrodynamical simulations of the supernova remnant evolution and the most
up-to-date atomic data for X-ray emission calculations makes it possible to
create realistic synthetic X-ray spectra for the supernova remnant phase.
Comparing such spectra with high quality observations of supernova remnants
could allow to constrain the explosion mechanism and the progenitor of the
supernova. The present study focuses in particular on the oxygen emission line
properties in young supernova remnants, since different explosion scenarios
predict a different amount and distribution of this element. Analysis of the
soft X-ray spectra from supernova remnants in the Large Magellanic Cloud and
confrontation with remnant models for different explosion scenarios suggests
that SNR 0509-67.5 could originate from a delayed detonation explosion and SNR
0519-69.0 from an oxygen-rich merger.Comment: 8 pages, 4 figures, MNRAS accepte
Nucleosynthesis in O-Ne-Mg Supernovae
We have studied detailed nucleosynthesis in the shocked surface layers of an
Oxygen-Neon-Magnesium core collapse supernova with an eye to determining if the
conditions are suitable for r process nucleosynthesis. We find no such
conditions in an unmodified model, but do find overproduction of N=50 nuclei
(previously seen in early neutron-rich neutrino winds) in amounts that, if
ejected, would pose serious problems for galactic chemical evolution.Comment: 12 pages, 1 figure, to be published in Astrophysical Journal Letter
From Microscales to Macroscales in 3D: Selfconsistent Equation of State for Supernova and Neutron Star Models
First results from a fully self-consistent, temperature-dependent equation of
state that spans the whole density range of neutron stars and supernova cores
are presented. The equation of state (EoS) is calculated using a mean-field
Hartree-Fock method in three dimensions (3D). The nuclear interaction is
represented by the phenomenological Skyrme model in this work, but the EoS can
be obtained in our framework for any suitable form of the nucleon-nucleon
effective interaction. The scheme we employ naturally allows effects such as
(i) neutron drip, which results in an external neutron gas, (ii) the variety of
exotic nuclear shapes expected for extremely neutron heavy nuclei, and (iii)
the subsequent dissolution of these nuclei into nuclear matter. In this way,
the equation of state is calculated across phase transitions without recourse
to interpolation techniques between density regimes described by different
physical models. EoS tables are calculated in the wide range of densities,
temperature and proton/neutron ratios on the ORNL NCCS XT3, using up to 2000
processors simultaneously.Comment: 6 pages, 11 figures. Published in conference proceedings Journal of
Physics: Conference Series 46 (2006) 408. Extended version to be submitted to
Phys. Rev.
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