70,012 research outputs found
Unifying Requirements and Code: an Example
Requirements and code, in conventional software engineering wisdom, belong to
entirely different worlds. Is it possible to unify these two worlds? A unified
framework could help make software easier to change and reuse. To explore the
feasibility of such an approach, the case study reported here takes a classic
example from the requirements engineering literature and describes it using a
programming language framework to express both domain and machine properties.
The paper describes the solution, discusses its benefits and limitations, and
assesses its scalability.Comment: 13 pages; 7 figures; to appear in Ershov Informatics Conference, PSI,
Kazan, Russia (LNCS), 201
A Class of Functional Equations of Neutral Type
Class of functional integral equations in space of continuous function
Electron-hole pairs during the adsorption dynamics of O2 on Pd(100) - Exciting or not?
During the exothermic adsorption of molecules at solid surfaces dissipation
of the released energy occurs via the excitation of electronic and phononic
degrees of freedom. For metallic substrates the role of the nonadiabatic
electronic excitation channel has been controversially discussed, as the
absence of a band gap could favour an easy coupling to a manifold of
electronhole pairs of arbitrarily low energies. We analyse this situation for
the highly exothermic showcase system of molecular oxygen dissociating at
Pd(100), using time-dependent perturbation theory applied to first-principles
electronic-structure calculations. For a range of different trajectories of
impinging O2 molecules we compute largely varying electron-hole pair spectra,
which underlines the necessity to consider the high-dimensionality of the
surface dynamical process when assessing the total energy loss into this
dissipation channel. Despite the high Pd density of states at the Fermi level,
the concomitant non-adiabatic energy losses nevertheless never exceed about 5%
of the available chemisorption energy. While this supports an electronically
adiabatic description of the predominant heat dissipation into the phononic
system, we critically discuss the non-adiabatic excitations in the context of
the O2 spin transition during the dissociation process.Comment: 20 pages including 7 figures; related publications can be found at
http://www.fhi-berlin.mpg.de/th/th.html [added two references, changed
V_{fsa} to V_{6D}, modified a few formulations in interpretation of spin
asymmetry of eh-spectra, added missing equals sign in Eg.(2.10)
Linear response in infinite nuclear matter as a tool to reveal finite size instabilities
Nuclear effective interactions are often modelled by simple analytical
expressions such as the Skyrme zero-range force. This effective interaction
depends on a limited number of parameters that are usually fitted using
experimental data obtained from doubly magic nuclei. It was recently shown that
many Skyrme functionals lead to the appearance of instabilities, in particular
when symmetries are broken, for example unphysical polarization of odd-even or
rotating nuclei. In this article, we show how the formalism of the linear
response in infinite nuclear matter can be used to predict and avoid the
regions of parameters that are responsible for these unphysical instabilities.Comment: Based on talk presented at 18th Nuclear Physics Workshop "Maria and
Pierre Curie", 2011, Kazimierz, Polan
Non-empirical pairing energy density functional. First order in the nuclear plus Coulomb two-body interaction
We perform systematic calculations of pairing gaps in semi-magic nuclei
across the nuclear chart using the Energy Density Functional method and a {\it
non-empirical} pairing functional derived, without further approximation, at
lowest order in the two-nucleon vacuum interaction, including the Coulomb
force. The correlated single-particle motion is accounted for by the SLy4
semi-empirical functional. Rather unexpectedly, both neutron and proton pairing
gaps thus generated are systematically close to experimental data. Such a
result further suggests that missing effects, i.e. higher partial-waves of the
NN interaction, the NNN interaction and the coupling to collective
fluctuations, provide an overall contribution that is sub-leading as for
generating pairing gaps in nuclei. We find that including the Coulomb
interaction is essential as it reduces proton pairing gaps by up to 40%.Comment: 6 pages, 1 figure, accepted for publication in EPJ
Spontaneous Spin Polarization in Quantum Wires
A number of recent experiments report spin polarization in quantum wires in
the absence of magnetic fields. These observations are in apparent
contradiction with the Lieb-Mattis theorem, which forbids spontaneous spin
polarization in one dimension. We show that sufficiently strong interactions
between electrons induce deviations from the strictly one-dimensional geometry
and indeed give rise to a ferromagnetic ground state in a certain range of
electron densities.Comment: 4 pages, 4 figure
On the role of physisorption states in molecular scattering: A semi-local density-functional theory study on O2/Ag(111)
We simulate the scattering of O from Ag(111) with classical dynamics
simulations performed on a six-dimensional potential energy surface calculated
within semi-local density-functional theory (DFT). The enigmatic experimental
trends that originally required the conjecture of two types of repulsive walls,
arising from a physisorption and chemisorption part of the interaction
potential, are fully reproduced. Given the inadequate description of the
physisorption properties in semi-local DFT, our work casts severe doubts on the
prevalent notion to use molecular scattering data as indirect evidence for the
existence of such states.Comment: 5 pages, 4 figure
Formation of Chain-Folded Structures from Supercooled Polymer Melts
The formation of chain-folded structures from the melt is observed in
molecular dynamics simulations resembling the lamellae of polymer crystals.
Crystallization and subsequent melting temperatures are related linearly to the
inverse lamellar thickness. Analysis of the single chain conformations in the
crystal shows that most chains reenter the same lamella by tight backfolds.
Simulations are performed with a mesoscopic bead-spring model including a
specific angle bending potential. They demonstrate that chain stiffness alone,
without an attractive inter-particle potential, is a sufficient driving force
for the formation of chain-folded lamellae.Comment: 4 pages, 5 figure
Three-dimensional fast electron transport for ignition-scale inertial fusion capsules
Three-dimensional hybrid PIC simulations are presented to study electron
energy transport and deposition in a full-scale fast ignition configuration.
Multi-prong core heating close to ignition is found when a few GA, few PW beam
is injected. Resistive beam filamentation in the corona seeds the 3D current
pattern that penetrates the core. Ohmic heating is important in the low-density
corona, while classical Coulomb deposition heats the core. Here highest energy
densities (few Tbar at 10 keV) are observed at densities above 200 g/cc. Energy
coupling to the core ranges from 20 to 30%; it is enhanced by beam collimation
and decreases when raising the beam particle energy from 1.5 to 5.5 MeV.Comment: 5 pages, 5 figure
Coupling of non-crossing wave modes in a two-dimensional plasma crystal
We report an experimental observation of coupling of the transverse vertical
and longitudinal in-plane dust-lattice wave modes in a two-dimensional complex
plasma crystal in the absence of mode crossing. A new large diameter rf plasma
chamber was used to suspend the plasma crystal. The observations are confirmed
with molecular-dynamics simulations. The coupling manifests itself in traces of
the transverse vertical mode appearing in the measured longitudinal spectra and
vice versa. We calculate the expected ratio of the trace to the principal mode
with a theoretical analysis of the modes in a crystal with finite temperature
and find good agreement with the experiment and simulations.Comment: 4 figures, 5 pages, accepted for publication in PRL Nov 201
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