3,400 research outputs found
Statistical mechanics of random two-player games
Using methods from the statistical mechanics of disordered systems we analyze
the properties of bimatrix games with random payoffs in the limit where the
number of pure strategies of each player tends to infinity. We analytically
calculate quantities such as the number of equilibrium points, the expected
payoff, and the fraction of strategies played with non-zero probability as a
function of the correlation between the payoff matrices of both players and
compare the results with numerical simulations.Comment: 16 pages, 6 figures, for further information see
http://itp.nat.uni-magdeburg.de/~jberg/games.htm
Two-population replicator dynamics and number of Nash equilibria in random matrix games
We study the connection between the evolutionary replicator dynamics and the
number of Nash equilibria in large random bi-matrix games. Using techniques of
disordered systems theory we compute the statistical properties of both, the
fixed points of the dynamics and the Nash equilibria. Except for the special
case of zero-sum games one finds a transition as a function of the so-called
co-operation pressure between a phase in which there is a unique stable fixed
point of the dynamics coinciding with a unique Nash equilibrium, and an
unstable phase in which there are exponentially many Nash equilibria with
statistical properties different from the stationary state of the replicator
equations. Our analytical results are confirmed by numerical simulations of the
replicator dynamics, and by explicit enumeration of Nash equilibria.Comment: 9 pages, 2x2 figure
Study of the and reactions close to threshold
Two--kaon production in proton--deuteron collisions has been studied at three
energies close to threshold using a calibrated magnetic spectrograph to measure
the final He and a vertex detector to measure the pair.
Differential and total cross sections are presented for the production of
--mesons, decaying through , as well as for prompt
production. The prompt production seems to follow phase space in both
its differential distributions and in its energy dependence. The amplitude for
the {He} reaction varies little for excess energies below 22
MeV and the value is consistent with that obtained from a threshold
measurement. The angular distribution of the decay pair shows that
near threshold the --mesons are dominantly produced with polarization
along the initial proton direction. No conclusive evidence for
production is found in the data.Comment: 13 figure
Growth Histories in Bimetric Massive Gravity
We perform cosmological perturbation theory in Hassan-Rosen bimetric gravity
for general homogeneous and isotropic backgrounds. In the de Sitter
approximation, we obtain decoupled sets of massless and massive scalar
gravitational fluctuations. Matter perturbations then evolve like in Einstein
gravity. We perturb the future de Sitter regime by the ratio of matter to dark
energy, producing quasi-de Sitter space. In this more general setting the
massive and massless fluctuations mix. We argue that in the quasi-de Sitter
regime, the growth of structure in bimetric gravity differs from that of
Einstein gravity.Comment: 28 pages + appendix, 11 figure
The CARMENES search for exoplanets around M dwarfs - Photospheric parameters of target stars from high-resolution spectroscopy
The new CARMENES instrument comprises two high-resolution and high-stability
spectrographs that are used to search for habitable planets around M dwarfs in
the visible and near-infrared regime via the Doppler technique. Characterising
our target sample is important for constraining the physical properties of any
planetary systems that are detected. The aim of this paper is to determine the
fundamental stellar parameters of the CARMENES M-dwarf target sample from
high-resolution spectra observed with CARMENES. We also include several M-dwarf
spectra observed with other high-resolution spectrographs, that is CAFE, FEROS,
and HRS, for completeness. We used a {chi}^2 method to derive the stellar
parameters effective temperature T_eff, surface gravity log g, and metallicity
[Fe/H] of the target stars by fitting the most recent version of the
PHOENIX-ACES models to high-resolution spectroscopic data. These stellar
atmosphere models incorporate a new equation of state to describe spectral
features of low-temperature stellar atmospheres. Since T_eff, log g, and [Fe/H]
show degeneracies, the surface gravity is determined independently using
stellar evolutionary models. We derive the stellar parameters for a total of
300 stars. The fits achieve very good agreement between the PHOENIX models and
observed spectra. We estimate that our method provides parameters with
uncertainties of {sigma} T_eff = 51 K, {sigma} log g = 0.07, and {sigma} [Fe/H]
= 0.16, and show that atmosphere models for low-mass stars have significantly
improved in the last years. Our work also provides an independent test of the
new PHOENIX-ACES models, and a comparison for other methods using
low-resolution spectra. In particular, our effective temperatures agree well
with literature values, while metallicities determined with our method exhibit
a larger spread when compared to literature results
Scientific, institutional and personal rivalries among Soviet geographers in the late Stalin era
Scientific, institutional and personal rivalries between three key centres of geographical research and scholarship (the Academy of Sciences Institute of Geography and the Faculties of Geography at Moscow and Leningrad State Universities) are surveyed for the period from 1945 to the early 1950s. It is argued that the debates and rivalries between members of the three institutions appear to have been motivated by a variety of scientific, ideological, institutional and personal factors, but that genuine scientific disagreements were at least as important as political and ideological factors in influencing the course of the debates and in determining their final outcome
Strong enhancement of spin fluctuations in the low-temperature-tetragonal phase of antiferromagnetically ordered La_{2-x-y}Eu_ySr_xCuO_4
Measurements of the static magnetization, susceptibility and ESR of Gd spin
probes have been performed to study the properties of antiferromagnetically
ordered La_{2-x-y}Eu_ySr_xCuO_4 (x less or equal 0.02) with the low temperature
tetragonal structure. According to the static magnetic measurements the CuO_2
planes are magnetically decoupled in this structural phase. The ESR study
reveals strong magnetic fluctuations at the ESR frequency which are not present
in the orthorhombic phase. It is argued that this drastic enhancement of the
spin fluctuations is due to a considerable weakening of the interlayer exchange
and a pronounced influence of hole motion on the antiferromagnetic properties
of lightly hole doped La_2CuO_4. No evidence for the stripe phase formation at
small hole doping is obtained in the present study.Comment: 10 pages, LaTeX, 3 EPS figures; to be published in Journal of
Physics: Condensed Matte
Nocturnal temperature controlled laminar airflow for treating atopic asthma: a randomised controlled trial
Objective To determine whether environmental control using nocturnal temperature controlled laminar airflow (TLA) treatment could improve the quality of life of patients with persistent atopic asthma. <br> <br>Design Randomised, double-blind, placebo-controlled, parallel-group trial. <br> <br>Setting Nineteen European asthma clinics. <br> <br>Participants 312 patients aged 7-70 with inadequately controlled persistent atopic asthma. <br> <br>Main outcome measure Proportion of patients with an increase of &gt;= 0.5 points in asthma quality of life score after 1 year of treatment. <br> <br>Results TLA devices were successfully installed in the bedrooms of 282 (90%) patients included in the primary efficacy analysis. There was a difference in treatment response rate between active (143 of 189, 76%) and placebo (56 of 92, 61%) groups, difference 14.8% (95% CI 3.1 to 26.5, p=0.02).(3) In patients aged &gt;= 12, on whom the study was powered, the difference in response rate was similar-active 106 of 143 (74%), placebo 42 of 70 (60%), difference 14.1% (0.6 to 27.7, p=0.059). There was a difference between groups in fractional exhaled nitric oxide change of -7.1 ppb (-13.6 to -0.7, p=0.03). Active treatment was associated with less increase in cat-specific IgE than placebo. There was no difference in adverse event rates between treatment groups. <br> <br>Conclusion Inhalant exposure reduction with TLA improves quality of life, airway inflammation and systemic allergy in patients with persistent atopic asthma. TLA may be a treatment option for patients with inadequately controlled persistent atopic asthma.funding agencies|Airsonett AB||National Institute for Health Research||National Institute for Health Research Biomedical Research Centre||MRC||Asthma UK Centre in Allergic Mechanisms of Asthma||</p
Search for the electric dipole excitations to the multiplet in Sn
The odd-mass Sn nucleus was investigated in nuclear resonance
fluorescence experiments up to an endpoint energy of the incident photon
spectrum of 4.1 MeV at the bremsstrahlung facility of the Stuttgart University.
More than 50 mainly hitherto unknown levels were found. From the measurement of
the scattering cross sections model independent absolute electric dipole
excitation strengths were extracted. The measured angular distributions
suggested the spins of 11 excited levels. Quasi-particle phonon model
calculations including a complete configuration space were performed for the
first time for a heavy odd-mass spherical nucleus. These calculations give a
clear insight in the fragmentation and distribution of the , , and
excitation strength in the low energy region. It is proven that the
component of the two-phonon quintuplet built on
top of the ground state is strongly fragmented. The theoretical
calculations are consistent with the experimental data.Comment: 10 pages, 5 figure
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