1,723 research outputs found
Coulomb displacement energies, energy differenced and neutron skins
A Fock space representation of the monopole part of the Coulomb potential is
presented. Quantum effects show through a small orbital term in . Once
it is averaged out, the classical electrostatic energy emerges as an
essentially exact expression, which makes it possible to eliminate the
Nolen-Schiffer anomaly, and to estimate neutron skins and the evolution of
radii along yrast states of mirror nuclei. The energy differences of the latter
are quantitatively reproduced by the monopole term and a schematic multipole
one.Comment: 4 pages, 3 figures, Revte
Autosis: a new addition to the cell death tower of babel
Autophagy is a cellular recycling and stress response that
degrades organelles and long-lived proteins and serves to
protect cells from the potential damage induced by dysfunctional
organelles and protein aggregates.1 Autophagy can
also be used as a recycling or salvage process to provide
amino acids, nucleotides and other building blocks to protect
cells from some, but not all, forms of starvation
The Lazy Bureaucrat Scheduling Problem
We introduce a new class of scheduling problems in which the optimization is
performed by the worker (single ``machine'') who performs the tasks. A typical
worker's objective is to minimize the amount of work he does (he is ``lazy''),
or more generally, to schedule as inefficiently (in some sense) as possible.
The worker is subject to the constraint that he must be busy when there is work
that he can do; we make this notion precise both in the preemptive and
nonpreemptive settings. The resulting class of ``perverse'' scheduling
problems, which we denote ``Lazy Bureaucrat Problems,'' gives rise to a rich
set of new questions that explore the distinction between maximization and
minimization in computing optimal schedules.Comment: 19 pages, 2 figures, Latex. To appear, Information and Computatio
Isobaric multiplet yrast energies and isospin non-conserving forces
The isovector and isotensor energy differences between yrast states of
isobaric multiplets in the lower half of the region are quantitatively
reproduced in a shell model context. The isospin non-conserving nuclear
interactions are found to be at least as important as the Coulomb potential.
Their isovector and isotensor channels are dominated by J=2 and J=0 pairing
terms, respectively. The results are sensitive to the radii of the states,
whose evolution along the yrast band can be accurately followed.Comment: 4 pages, 4 figures. Superseeds second part of nucl-th/010404
The Role of Fission in Neutron Star Mergers and Its Impact on the r-Process Peaks
Comparing observational abundance features with nucleosynthesis predictions of stellar evolution or explosion simulations, we can scrutinize two aspects: (a) the conditions in the astrophysical production site and (b) the quality of the nuclear physics input utilized. We test the abundance features of r-process nucleosynthesis calculations for the dynamical ejecta of neutron star merger simulations based on three different nuclear mass models: The Finite Range Droplet Model, the (quenched version of the) Extended Thomas Fermi Model with Strutinsky Integral, and the Hartree-Fock-Bogoliubov mass model. We make use of corresponding fission barrier heights and compare the impact of four different fission fragment distribution models on the final r-process abundance distribution. In particular, we explore the abundance distribution in the second r-process peak and the rare-earth sub-peak as a function of mass models and fission fragment distributions, as well as the origin of a shift in the third r-process peak position. The latter has been noticed in a number of merger nucleosynthesis predictions. We show that the shift occurs during the r-process freeze-out when neutron captures and β-decays compete and an (n,γ)-(γ,n) equilibrium is no longer maintained. During this phase neutrons originate mainly from fission of material above A = 240. We also investigate the role of β-decay half-lives from recent theoretical advances, which lead either to a smaller amount of fissioning nuclei during freeze-out or a faster (and thus earlier) release of fission neutrons, which can (partially) prevent this shift and has an impact on the second and rare-earth peak as well.Peer reviewe
r-PROCESS CALCULATIONS WITH A MICROSCOPIC DESCRIPTION OF THE FISSION PROCESS
We computed the fission properties of nuclei in the range of 84 ≤
Z ≤ 120 and 118 ≤ N ≤ 250 using the Barcelona–Catania–Paris–Madrid
(BCPM) Energy Density Functional (EDF). For the first time, a set of
spontaneous and neutron-induced fission rates were obtained from a microscopic calculation of nuclear collective inertias. These fission rates were
used as a nuclear input in the estimation of nucleosynthesis yields on neutron star mergers. We founded that the increased stability against the
fission process predicted by the BCPM allows the formation of nuclei up
to A = 286. This constitutes a first step in a systematic exploration of
different sets of fission rates on r-process abundance predictionsS.A.G., G.M.P. and M.-R.W. acknowledge support from the Helmholtz
Association through the Nuclear Astrophysics Virtual Institute (VH-VI417), and the BMBF-Verbundforschungsprojekt number 05P15RDFN1.
M.-R.W. acknowledges support from the Villum Foundation (Project No.
13164) and the Danish National Research Foundation (DNRF91). The work
of L.M.R. was supported in part by the Spanish Ministerio de EconomĂa y
Competitividad (MINECO), under contracts Nos. FIS2012-34479, FPA2015-
65929, FIS2015-63770 and by the Consolider-Ingenio 2010 Program MULTIDAR
Electron fraction constraints based on Nuclear Statistical Equilibrium with beta equilibrium
The electron-to-nucleon ratio or electron fraction is a key parameter in many
astrophysical studies. Its value is determined by weak-interaction rates that
are based on theoretical calculations subject to several nuclear physics
uncertainties. Consequently, it is important to have a model independent way of
constraining the electron fraction value in different astrophysical
environments. Here we show that nuclear statistical equilibrium combined with
beta equilibrium can provide such a constraint. We test the validity of this
approximation in presupernova models and give lower limits for the electron
fraction in type Ia supernova and accretion-induced collapse.Comment: 10 pages, 9 figures, Astronomy and Astrophysic
Presupernova collapse models with improved weak-interaction rates
Improved values for stellar weak interaction rates have been recently
calculated based upon a large shell model diagonalization. Using these new
rates (for both beta decay and electron capture), we have examined the
presupernova evolution of massive stars in the range 15-40 Msun. Comparing our
new models with a standard set of presupernova models by Woosley and Weaver, we
find significantly larger values for the electron-to-baryon ratio Ye at the
onset of collapse and iron core masses reduced by approximately 0.1 Msun. The
inclusion of beta-decay accounts for roughly half of the revisions, while the
other half is a consequence of the improved nuclear physics. These changes will
have important consequences for nucleosynthesis and the supernova explosion
mechanism.Comment: 4 pages, 2 figure
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