2,277 research outputs found
The Nelson and Winter Models RevisitedPrototypes for Computer-Based Reconstruction of Schumpeterian Competition
The report deals with the reconstruction and further development of the models of industrial dynamics developed by Nelson and Winter and summarised in their famous 1982-book. The basic idea underlying the Nelson and Winter models is that a verbal account of Schumpeterian competition can naturally be transformed into a description of a computational process in which firms not only make short-term production decisions and investment decisions but also performs a search for new technologies. The latter search is successful in a probabilistic manner, and its successes and failures determine an evolutionary process of the industry. Although the simulation models of Nelson and Winter have played a central role the ‘take-off’ of evolutionary economics, they have never been fully documented and their differences have never been explored. The resulting problems are obvious for students who start from Nelson’s and Winter’s most famous accounts, but even for researchers with a full collection of the underlying research papers, the situation is quite confusing. The report tries to make things easier by presenting overviews of the structure of Nelson and Winter models as well as fully implemented versions of their simulation models – especially NELWIN78 based on ch. 13 of the 1982-book and NELWIN77 based on ch. 12. The report furthermore presents a computer-based environment (implemented in MAPLE V Rev2) for revision of the models and for analysis of the overwhelming number of data resulting from simulation runs.Evolutionary economic modelling, simulation of industrial dynamics, Schumpeterian competit
Lattice thermal conductivity of TiZrHfNiSn half-Heusler alloys calculated from first principles: Key role of nature of phonon modes
In spite of their relatively high lattice thermal conductivity
, the XNiSn (X=Ti, Zr or Hf) half-Heusler compounds are good
thermoelectric materials. Previous studies have shown that can
be reduced by sublattice-alloying on the X-site. To cast light on how the alloy
composition affects , we study this system using the phonon
Boltzmann-transport equation within the relaxation time approximation in
conjunction with density functional theory.The effect of alloying through
mass-disorder scattering is explored using the virtual crystal approximation to
screen the entire ternary TiZrHfNiSn phase diagram. The
lowest lattice thermal conductivity is found for the TiHfNiSn
compositions; in particular, there is a shallow minimum centered at
TiHfNiSn with taking values between 3.2 and 4.1 W/mK
when the Ti content varies between 20 and 80\%. Interestingly, the overall
behavior of mass-disorder scattering in this system can only be understood from
a combination of the nature of the phonon modes and the magnitude of the mass
variance. Mass-disorder scattering is not effective at scattering acoustic
phonons of low energy. By using a simple model of grain boundary scattering, we
find that nanostructuring these compounds can scatter such phonons effectively
and thus further reduce the lattice thermal conductivity; for instance,
TiHfNiSn with a grain size of nm experiences a 42\%
reduction of compared to that of the single crystal
Laser-induced solid-solid phase transition in As under pressure: A theoretical prediction
In Arsenic a pressure-induced solid-solid phase transition from the A7 into
the simple cubic structure has been experimentally demonstrated [Beister et
al., Phys. Rev. B 41, 5535 (1990)]. In this paper we present calculations,
which predict that this phase transition can also be induced by an ultrashort
laser pulse in As under pressure. In addition, calculations for the
pressure-induced phase transition are presented. Using density functional
theory in the generalized gradient approximation, we found that the
pressure-induced phase transition takes place at 26.3 GPa and is accompanied by
a volume change "Delta V" = 0.5 bohr^3/atom. The laser-induced phase transition
is predicted for an applied pressure of 23.8 GPa and an absorbed laser energy
of 2.8 mRy/atom.Comment: 9 pages, 5 figures Changes to content To be published in New Journal
of Physics (accepted for publication
Growth performance, carcass and non-carcass characteristics of Mubende and Mubende×Boer crossbred goats under different feeding regimes
IACHEC CROSS-CALIBRATION OF CHANDRA, NuSTAR, SWIFT, SUZAKU, XMM-NEWTON WITH 3C 273 ANDPKS 2155-304
On behalf of the International Astronomical Consortium for High Energy Calibration, we present results from the cross-calibration campaigns in 2012 on 3C 273 and in 2013 on PKS 2155-304 between the then active X-ray observatories Chandra, NuSTAR, Suzaku, Swift, and XMM-Newton. We compare measured fluxes between instrument pairs in two energy bands, 1–5 keV and 3–7 keV, and calculate an average cross-normalization constant for each energy range. We review known cross-calibration features and provide a series of tables and figures to be used for evaluating cross-normalization constants obtained from other observations with the above mentioned observatories.United States. National Aeronautics and Space Administration (Smithsonian Astrophysical Observatory. Contract SV3-73016)United States. National Aeronautics and Space Administration. (Grant NNX09AE58G
The class of the locus of intermediate Jacobians of cubic threefolds
We study the locus of intermediate Jacobians of cubic threefolds within the
moduli space of complex principally polarized abelian fivefolds, and its
generalization to arbitrary genus - the locus of abelian varieties with a
singular odd two-torsion point on the theta divisor. Assuming that this locus
has expected codimension (which we show to be true for genus up to 5), we
compute the class of this locus, and of is closure in the perfect cone toroidal
compactification, in the Chow, homology, and the tautological ring.
We work out the cases of genus up to 5 in detail, obtaining explicit
expressions for the classes of the closures of the locus of products of an
elliptic curve and a hyperelliptic genus 3 curve, in moduli of principally
polarized abelian fourfolds, and of the locus of intermediate Jacobians in
genus 5. In the course of our computation we also deal with various
intersections of boundary divisors of a level toroidal compactification, which
is of independent interest in understanding the cohomology and Chow rings of
the moduli spaces.Comment: v2: new section 9 on the geometry of the boundary of the locus of
intermediate Jacobians of cubic threefolds. Final version to appear in
Invent. Mat
Short Telomeres in Hatchling Snakes: Erythrocyte Telomere Dynamics and Longevity in Tropical Pythons
Telomere length (TL) has been found to be associated with life span in birds and humans. However, other studies have demonstrated that TL does not affect survival among old humans. Furthermore, replicative senescence has been shown to be induced by changes in the protected status of the telomeres rather than the loss of TL. In the present study we explore whether age- and sex-specific telomere dynamics affect life span in a long-lived snake, the water python (Liasis fuscus)
Homogeneous cosmologies with cosmological constant
Spatially homogeneous cosmological models with a positive cosmological
constant are investigated, using dynamical systems methods. We focus on the
future evolution of these models. In particular, we address the question
whether there are models within this class that are de Sitter-like in the
future, but are tilted.Comment: 10 pages, 13 eps-figures. Submitted to Phys. Rev.
Inflationary Cosmology and Quantization Ambiguities in Semi-Classical Loop Quantum Gravity
In loop quantum gravity, modifications to the geometrical density cause a
self-interacting scalar field to accelerate away from a minimum of its
potential. In principle, this mechanism can generate the conditions that
subsequently lead to slow-roll inflation. The consequences for this mechanism
of various quantization ambiguities arising within loop quantum cosmology are
considered. For the case of a quadratic potential, it is found that some
quantization procedures are more likely to generate a phase of slow--roll
inflation. In general, however, loop quantum cosmology is robust to ambiguities
in the quantization and extends the range of initial conditions for inflation.Comment: 15 pages, 8 figure
Thermal Evolution of Compact Stars
A collection of modern, field-theoretical equations of state is applied to
the investigation of cooling properties of compact stars. These comprise
neutron stars as well as hypothetical strange matter stars, made up of
absolutely stable 3-flavor strange quark matter. Various uncertainties in the
behavior of matter at supernuclear densities, e.g., hyperonic degrees of
freedom, behavior of coupling strengths in matter, pion and meson condensation,
superfluidity, transition to quark matter, absolute stability of strange quark
matter, and last but not least the many-body technique itself are tested
against the body of observed cooling data.Comment: 41 pages, revised versio
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