1,246 research outputs found
04051 Abstracts Collection -- Perspectives Workshop: Empirical Theory and the Science of Software Engineering
From 25.01.04 to 29.01.04, the Dagstuhl Seminar 04051 ``Perspectives Workshop: Empirical Theory and the Science of Software Engineering\u27\u27 was held
in the International Conference and Research Center (IBFI), Schloss Dagstuhl.
During the seminar, several participants presented their current
research, and ongoing work and open problems were discussed. Abstracts of
the presentations given during the seminar as well as abstracts of
seminar results and ideas are put together in this paper. The first section
describes the seminar topics and goals in general.
Links to extended abstracts or full papers are provided, if available
Hybrid evolutionary oligopolies and the dynamics of corporate social responsibility
The diffusion of corporate social responsibility is investigated by employing a hybrid evolutionary game where a firm chooses between being either socially responsible, which implies devoting a fraction of its profit to social projects, or non-socially responsible. Consumers prize socially responsible companies by paying a higher reservation price for their products. The hybrid evolutionary framework is characterized by a quantity dynamics that describes the oligopolistic competition given firms’ belief about the composition of the industry. At regular intervals of time, this belief is endogenously updated by a retrospective comparison on the profits obtained and on the basis of an evolutionary mechanism. Assuming that firms are Nash players, that is at each instant of time they produce the Nash equilibrium-in-belief quantity, the investigation of the model reveals that an industry homogeneously populated by socially responsible firms is a stable equilibrium when the fraction of profits earmarked for socially responsible activities is sufficiently limited. However, the extra marginal profits of a socially responsible firm are reduced when the number of competitors increases, impeding the diffusion of socially responsible companies. In particular, the trade-off between a higher net margin on sales obtained by socially responsible firms and a lower level of production that reduces the profit gap between a socially responsible firm and the rest of the market shows that an increased size of the industry favors mixed oligopolies. Moreover, imposing the hypothesis of neutrality of CSR activities, the model reveals that being socially responsible is an evolutionarily stable strategy for firms and is convenient for customers. Relaxing the hypothesis of Nash players by introducing boundedly rational firms that decide their level of production according to a partial adjustment toward the best reply, the robustness of these results is confirmed
Binary black holes on a budget: Simulations using workstations
Binary black hole simulations have traditionally been computationally very
expensive: current simulations are performed in supercomputers involving dozens
if not hundreds of processors, thus systematic studies of the parameter space
of binary black hole encounters still seem prohibitive with current technology.
Here we show how the multi-layered refinement level code BAM can be used on
dual processor workstations to simulate certain binary black hole systems. BAM,
based on the moving punctures method, provides grid structures composed of
boxes of increasing resolution near the center of the grid. In the case of
binaries, the highest resolution boxes are placed around each black hole and
they track them in their orbits until the final merger when a single set of
levels surrounds the black hole remnant. This is particularly useful when
simulating spinning black holes since the gravitational fields gradients are
larger. We present simulations of binaries with equal mass black holes with
spins parallel to the binary axis and intrinsic magnitude of S/m^2= 0.75. Our
results compare favorably to those of previous simulations of this particular
system. We show that the moving punctures method produces stable simulations at
maximum spatial resolutions up to M/160 and for durations of up to the
equivalent of 20 orbital periods.Comment: 20 pages, 8 figures. Final version, to appear in a special issue of
Class. Quantum Grav. based on the New Frontiers in Numerical Relativity
Conference, Golm, July 200
Quasi-equilibrium binary black hole sequences for puncture data derived from helical Killing vector conditions
We construct a sequence of binary black hole puncture data derived under the
assumptions (i) that the ADM mass of each puncture as measured in the
asymptotically flat space at the puncture stays constant along the sequence,
and (ii) that the orbits along the sequence are quasi-circular in the sense
that several necessary conditions for the existence of a helical Killing vector
are satisfied. These conditions are equality of ADM and Komar mass at infinity
and equality of the ADM and a rescaled Komar mass at each puncture. In this
paper we explicitly give results for the case of an equal mass black hole
binary without spin, but our approach can also be applied in the general case.
We find that up to numerical accuracy the apparent horizon mass also remains
constant along the sequence and that the prediction for the innermost stable
circular orbit is similar to what has been found with the effective potential
method.Comment: 6 pages, 3 figures, 1 tabl
Initial data for binary neutron stars with arbitrary spins
In general neutron stars in binaries are spinning. Due to the existence of
millisecond pulsars we know that these spins can be substantial. We argue that
spins with periods on the order a few dozen milliseconds could influence the
late inspiral and merger dynamics. Thus numerical simulations of the last few
orbits and the merger should start from initial conditions that allow for
arbitrary spins. We discuss quasi-equilibrium approximations one can make in
the construction of binary neutron star initial data with spins. Using these
approximations we are able to derive two new matter equations. As in the case
of irrotational neutron star binaries one of these equations is algebraic and
the other elliptic. If these new matter equations are solved together with the
equations for the metric variables following the Wilson-Mathews or conformal
thin sandwich approach one can construct neutron star initial data. The spin of
each star is described by a rotational velocity that can be chosen freely so
that one can create stars in arbitrary rotation states. Our new matter
equations reduce to the well known limits of both corotating and irrotational
neutron star binaries.Comment: 9 page
The fission yeast cytokinesis formin Cdc12p is a barbed end actin filament capping protein gated by profilin
Cytokinesis in most eukaryotes requires the assembly and contraction of a ring of actin filaments and myosin II. The fission yeast Schizosaccharomyces pombe requires the formin Cdc12p and profilin (Cdc3p) early in the assembly of the contractile ring. The proline-rich formin homology (FH) 1 domain binds profilin, and the FH2 domain binds actin. Expression of a construct consisting of the Cdc12 FH1 and FH2 domains complements a conditional mutant of Cdc12 at the restrictive temperature, but arrests cells at the permissive temperature. Cells overexpressing Cdc12(FH1FH2)p stop growing with excessive actin cables but no contractile rings. Like capping protein, purified Cdc12(FH1FH2)p caps the barbed end of actin filaments, preventing subunit addition and dissociation, inhibits end to end annealing of filaments, and nucleates filaments that grow exclusively from their pointed ends. The maximum yield is one filament pointed end per six formin polypeptides. Profilins that bind both actin and poly-l-proline inhibit nucleation by Cdc12(FH1FH2)p, but polymerization of monomeric actin is faster, because the filaments grow from their barbed ends at the same rate as uncapped filaments. On the other hand, Cdc12(FH1FH2)p blocks annealing even in the presence of profilin. Thus, formins are profilin-gated barbed end capping proteins with the ability to initiate actin filaments from actin monomers bound to profilin. These properties explain why contractile ring assembly requires both formin and profilin and why viability depends on the ability of profilin to bind both actin and poly-l-proline
BSSN in Spherical Symmetry
The BSSN (Baumgarte-Shapiro-Shibata-Nakamura) formulation of the Einstein
evolution equations is written in spherical symmetry. These equations can be
used to address a number of technical and conceptual issues in numerical
relativity in the context of a single Schwarzschild black hole. One of the
benefits of spherical symmetry is that the numerical grid points can be tracked
on a Kruskal--Szekeres diagram. Boundary conditions suitable for puncture
evolution of a Schwarzschild black hole are presented. Several results are
shown for puncture evolution using a fourth--order finite difference
implementation of the equations.Comment: This is the final version to be published in CQG. It contains much
more information and detail than the original versio
Impurity Effects in Two-Electron Coupled Quantum Dots: Entanglement Modulation
We present a detailed analysis of the electronic and optical properties of
two-electron quantum dots with a two-dimensional Gaussian confinement
potential. We study the effects of Coulomb impurities and the possibility of
manipulate the entanglement of the electrons by controlling the confinement
potential parameters. The degree of entanglement becomes highly modulated by
both the location and charge screening of the impurity atom, resulting two
regimes: one of low entanglement and other of high entanglement, with both of
them mainly determined by the magnitude of the charge. It is shown that the
magnitude of the oscillator strength of the system could provide an indication
of the presence and characteristics of impurities that could largely influence
the degree of entanglement of the system.Comment: Regular Article (Journal of Physics B, in press), 9 pages, 10 figure
Parity-Affected Superconductivity in Ultrasmall Metallic Grains
We investigate the breakdown of BCS superconductivity in {\em ultra}\/small
metallic grains as a function of particle size (characterized by the mean
spacing between discrete electronic eigenstates), and the parity ( =
even/odd) of the number of electrons on the island. Assuming equally spaced
levels, we solve the parity-dependent BCS gap equation for the order parameter
. Both the critical level spacing and the
critical temperature at which are parity
dependent, and both are so much smaller in the odd than the even case that
these differences should be measurable in current experiments.Comment: 4 pages RevTeX, 1 encapsulated postscript figure, submitted to
Physical Review Letter
A robust Pax7EGFP mouse that enables the visualization of dynamic behaviors of muscle stem cells.
BACKGROUND: Pax7 is a transcription factor involved in the specification and maintenance of muscle stem cells (MuSCs). Upon injury, MuSCs leave their quiescent state, downregulate Pax7 and differentiate, contributing to skeletal muscle regeneration. In the majority of regeneration studies, MuSCs are isolated by fluorescence-activated sorting (FACS), based on cell surface markers. It is known that MuSCs are a heterogeneous population and only a small percentage of isolated cells are true stem cells that are able to self-renew. A strong Pax7 reporter line would be valuable to study the in vivo behavior of Pax7-expressing stem cells.
METHODS: We generated and characterized the muscle properties of a new transgenic Pax7EGFP mouse. Utilizing traditional immunofluorescence assays, we analyzed whole embryos and muscle sections by fluorescence microscopy, in addition to whole skeletal muscles by 2-photon microscopy, to detect the specificity of EGFP expression. Skeletal muscles from Pax7EGFP mice were also evaluated in steady state and under injury conditions. Finally, MuSCs-derived from Pax7EGFP and control mice were sorted and analyzed by FACS and their myogenic activity was comparatively examined.
RESULTS: Our studies provide a new Pax7 reporter line with robust EGFP expression, detectable by both flow cytometry and fluorescence microscopy. Pax7EGFP-derived MuSCs have identical properties to that of wild-type MuSCs, both in vitro and in vivo, excluding any positional effect due to the transgene insertion. Furthermore, we demonstrated high specificity of EGFP to label MuSCs in a temporal manner that recapitulates the reported Pax7 expression pattern. Interestingly, immunofluorescence analysis showed that the robust expression of EGFP marks cells in the satellite cell position of adult muscles in fixed and live tissues.
CONCLUSIONS: This mouse could be an invaluable tool for the study of a variety of questions related to MuSC biology, including but not limited to population heterogeneity, polarity, aging, regeneration, and motility, either by itself or in combination with mice harboring additional genetic alterations
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