11,898 research outputs found
Dispersive spherical optical model of neutron scattering from Al27 up to 250 MeV
A spherical optical model potential (OMP) containing a dispersive term is
used to fit the available experimental database of angular distribution and
total cross section data for n + Al27 covering the energy range 0.1- 250 MeV
using relativistic kinematics and a relativistic extension of the Schroedinger
equation. A dispersive OMP with parameters that show a smooth energy dependence
and energy independent geometry are determined from fits to the entire data
set. A very good overall agreement between experimental data and predictions is
achieved up to 150 MeV. Inclusion of nonlocality effects in the absorptive
volume potential allows to achieve an excellent agreement up to 250 MeV.Comment: 13 figures (11 eps and 2 jpg), 3 table
Empirical studies of open source evolution
Copyright @ 2008 Springer-VerlagThis chapter presents a sample of empirical studies of Open Source Software (OSS) evolution. According to these studies, the classical results from the studies of proprietary software evoltion, such as Lehman’s laws of software evolution, might need to be revised, if not fully, at least in part, to account for the OSS observations. The book chapter also summarises what appears to be the empirical
status of each of Lehman’s laws with respect to OSS and highlights the threads to
validity that frequently emerge in these empirical studies. The chapter also discusses
related topics for further research
Dynamical Systems On Three Manifolds Part II: 3-Manifolds,Heegaard Splittings and Three-Dimensional Systems
The global behaviour of nonlinear systems is extremely important in control
and systems theory since the usual local theories will only give information
about a system in some neighbourhood of an operating point. Away from that
point, the system may have totally different behaviour and so the theory
developed for the local system will be useless for the global one.
In this paper we shall consider the analytical and topological structure of
systems on 2- and 3- manifolds and show that it is possible to obtain systems
with 'arbitrarily strange' behaviour, i.e., arbitrary numbers of chaotic
regimes which are knotted and linked in arbitrary ways. We shall do this by
considering Heegaard Splittings of these manifolds and the resulting systems
defined on the boundaries.Comment: 15 pages with 9 pictures. Accepted by Int. J. of Bifurcation and
Chao
Pilot study of vegetation in the Alchichica-Perote region by remote sensing
A study of the application of satellite images to the identification of vegetation in a small area corresponding to the arid zone of Veracruz and part of Puebla is presented. This study is accomplished by means of images from the LANDSAT satellite obtained on January 19 and May 23, 1973. The interpretation of the different maps is made on the basis of information from the data bank of the Flora de Veracruz program, and various surveys made by land and air
Bethe-Salpeter equation for doubly heavy baryons in the covariant instantaneous approximation
In the heavy quark limit, a doubly heavy baryon is regarded as composed of a
heavy diquark and a light quark. We establish the Bethe-Salpeter (BS) equations
for the heavy diquarks and the doubly heavy baryons, respectively, to leading
order in a expansion. The BS equations are solved numerically under
the covariant instantaneous approximation with the kernels containing scalar
confinement and one-gluon-exchange terms. The masses for the heavy diquarks and
the doubly heavy baryons are obtained and the non-leptonic decay widths for the
doubly heavy baryons emitting a pseudo-scalar meson are calculated within the
model.Comment: Corrections to the text, two references added, version accepted for
publication in Physical Review
Tailor-made directional emission in nanoimprinted plasmonic-based light-emitting devices
We demonstrate an enhanced and tailor-made directional emission of light-emitting devices using nanoimprinted hexagonal arrays of aluminum nanoparticles. Fourier microscopy reveals that the luminescence of the device is not only determined by the material properties of the organic dye molecules but is also strongly influenced by the coherent scattering resulting from periodically arranged metal nanoparticles. Emitters can couple to lattice-induced hybrid plasmonic–photonic modes sustained by plasmonic arrays. Such modes enhance the spatial coherence of an emitting layer, allowing the efficient beaming of the emission along narrow angular and spectral ranges. We show that tailoring the separation of the nanoparticles in the array yields an accurate angular distribution of the emission. This combination of large-area metal nanostructures fabricated by nanoimprint lithography and light-emitting devices is beneficial for the design and optimization of solid-state lighting systems
On Phase Transitions to Cooperation in the Prisoner's Dilemma
Game theory formalizes certain interactions between physical particles or
between living beings in biology, sociology, and economics, and quantifies the
outcomes by payoffs. The prisoner's dilemma (PD) describes situations in which
it is profitable if everybody cooperates rather than defects (free-rides or
cheats), but as cooperation is risky and defection is tempting, the expected
outcome is defection. Nevertheless, some biological and social mechanisms can
support cooperation by effectively transforming the payoffs. Here, we study the
related phase transitions, which can be of first order (discontinous) or of
second order (continuous), implying a variety of different routes to
cooperation. After classifying the transitions into cases of equilibrium
displacement, equilibrium selection, and equilibrium creation, we show that a
transition to cooperation may take place even if the stationary states and the
eigenvalues of the replicator equation for the PD stay unchanged. Our example
is based on adaptive group pressure, which makes the payoffs dependent on the
endogeneous dynamics in the population. The resulting bistability can invert
the expected outcome in favor of cooperation.Comment: For related work see http://www.soms.ethz.ch
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