485 research outputs found
Equianalytic and equisingular families of curves on surfaces
We consider flat families of reduced curves on a smooth surface S such that
each member C has the same number of singularities of fixed singularity types
and the corresponding (locally closed) subscheme H of the Hilbert scheme of S.
We are mainly concerned with analytic resp. topological singularity types and
give a sufficient condition for the smoothness of H (at C). Our results for
S=P^2 seem to be quite sharp for families of cuves of small degree d.Comment: LaTeX v 2.0
Cooperation and Self-Regulation in a Model of Agents Playing Different Games
A simple model for cooperation between "selfish" agents, which play an
extended version of the Prisoner's Dilemma(PD) game, in which they use
arbitrary payoffs, is presented and studied. A continuous variable,
representing the probability of cooperation, [0,1], is assigned to
each agent at time . At each time step a pair of agents, chosen at
random, interact by playing the game. The players update their using a
criteria based on the comparison of their utilities with the simplest estimate
for expected income. The agents have no memory and use strategies not based on
direct reciprocity nor 'tags'. Depending on the payoff matrix, the systems
self-organizes - after a transient - into stationary states characterized by
their average probability of cooperation and average equilibrium
per-capita-income . It turns out that the model
exhibit some results that contradict the intuition. In particular, some games
which - {\it a priory}- seems to favor defection most, may produce a relatively
high degree of cooperation. Conversely, other games, which one would bet that
lead to maximum cooperation, indeed are not the optimal for producing
cooperation.Comment: 11 pages, 3 figures, keybords: Complex adaptive systems, Agent-based
models, Social system
Cohomological characterizations of projective spaces and hyperquadrics
We confirm Beauville's conjecture that claims that if the p-th exterior power
of the tangent bundle of a smooth projective variety contains the p-th power of
an ample line bundle, then the variety is either the projective space or the
p-dimensional quadric hypersurface.Comment: Added Lemma 2.8 and slightly changed proof of Lemma 6.2 to make them
apply for torsion-free sheaves and not only to vector bundle
Thermodynamic properties of excess-oxygen-doped La2CuO4.11 near a simultaneous transition to superconductivity and long-range magnetic order
We have measured the specific heat and magnetization {\it versus} temperature
in a single crystal sample of superconducting LaCuO and in a
sample of the same material after removing the excess oxygen, in magnetic
fields up to 15 T. Using the deoxygenated sample to subtract the phonon
contribution, we find a broad peak in the specific heat, centered at 50 K. This
excess specific heat is attributed to fluctuations of the Cu spins possibly
enhanced by an interplay with the charge degrees of freedom, and appears to be
independent of magnetic field, up to 15 T. Near the superconducting transition
(=0)= 43 K, we find a sharp feature that is strongly suppressed when
the magnetic field is applied parallel to the crystallographic c-axis. A model
for 3D vortex fluctuations is used to scale magnetization measured at several
magnetic fields. When the magnetic field is applied perpendicular to the
c-axis, the only observed effect is a slight shift in the superconducting
transition temperature.Comment: 8 pages, 8 figure
Quantification of a lubricant transfer process that enhances the sliding life of a MoS2 coating
Measurements of Branching Ratios
Using data collected by the fixed target Fermilab experiment FOCUS, we
measure the branching ratios of the Cabibbo favored decays , , and relative to to be
, , and ,
respectively. We report the first observation of the Cabibbo suppressed decay
and we measure the branching ratio relative to
to be . We also set 90%
confidence level upper limits for and relative to to
be 0.12 and 0.05, respectively. We find an indication of the decays and and set
90% confidence level upper limits for the branching ratios with respect to
to be 0.12 and 1.72, respectively. Finally, we
determine the 90% C.L. upper limit for the resonant contribution relative to to be 0.10.Comment: 14 pages, 8 figure
Study of Hadronic Five-Body Decays of Charmed Mesons
We study the decay of D+ and Ds+ mesons into charged five body final states,
and report the discovery of the decay mode D+ -> K+K-Pi+Pi+Pi-, as well as
measurements of the decay modes D+ -> K-Pi+Pi+Pi+Pi-, Ds+ -> K+K-Pi+Pi+Pi-, Ds+
-> PhiPi+Pi+Pi- and D+/Ds+ -> Pi+Pi+Pi+Pi-Pi-. An analysis of the resonant
substructure is also included, with evidence suggesting that both decays
proceed primarily through an a1 vector resonance.Comment: 11 pages, 3 figure
Dalitz plot analysis of D_s+ and D+ decay to pi+pi-pi+ using the K-matrix formalism
FOCUS results from Dalitz plot analysis of D_s+ and D+ to pi+pi-pi+ are
presented. The K-matrix formalism is applied to charm decays for the first time
to fully exploit the already existing knowledge coming from the light-meson
spectroscopy experiments. In particular all the measured dynamics of the S-wave
pipi scattering, characterized by broad/overlapping resonances and large
non-resonant background, can be properly included. This paper studies the
extent to which the K-matrix approach is able to reproduce the observed Dalitz
plot and thus help us to understand the underlying dynamics. The results are
discussed, along with their possible implications on the controversial nature
of the sigma meson.Comment: To be submitted to Phys.Lett.B A misprint corrected in formula
Quantum transport through STM-lifted single PTCDA molecules
Using a scanning tunneling microscope we have measured the quantum
conductance through a PTCDA molecule for different configurations of the
tip-molecule-surface junction. A peculiar conductance resonance arises at the
Fermi level for certain tip to surface distances. We have relaxed the molecular
junction coordinates and calculated transport by means of the Landauer/Keldysh
approach. The zero bias transmission calculated for fixed tip positions in
lateral dimensions but different tip substrate distances show a clear shift and
sharpening of the molecular chemisorption level on increasing the STM-surface
distance, in agreement with experiment.Comment: accepted for publication in Applied Physics
Studies of correlations between D and mesons in high energy photoproduction
Studies of correlations for a large sample of events containing
fully and partially reconstructed pairs of charmed mesons recorded by the
Fermilab photoproduction experiment FOCUS (FNAL-E831) are presented.
Correlations between and mesons are used to study heavy quark
production dynamics. We present results for fully and partially reconstructed
charm pairs and comparisons to a recent version of \textsc{Pythia} with default
parameter settings. We also comment on the production of in our
data.Comment: 14 pages, 4 figure
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