2,645 research outputs found
A Macroevolutionary Perspective on Multiple Sexual Traits in the Phasianidae (Galliformes)
Traits involved in sexual signaling are ubiquitous among animals. Although a single trait appears sufficient to convey information, many sexually dimorphic species exhibit multiple sexual signals, which may be costly to signalers and receivers. Given that one signal may be enough, there are many microevolutionary hypotheses to explain the evolution of multiple signals. Here we extend these hypotheses to a macroevolutionary scale and compare those predictions to the patterns of gains and losses of sexual dimorphism in pheasants and partridges. Among nine dimorphic characters, including six intersexual signals and three indicators of competitive ability, all exhibited both gains and losses of dimorphism within the group. Although theories of intersexual selection emphasize gain and elaboration, those six characters exhibited greater rates of loss than gain; in contrast, the competitive traits showed a slight bias towards gains. The available models, when examined in a macroevolutionary framework, did not yield unique predictions, making it difficult to distinguish among them. Even with this limitation, when the predictions of these alternative models were compared with the heterogeneous patterns of evolution of dimorphism in phasianids, it is clear that many different selective processes have been involved in the evolution of sexual signals in this group
Multiplicity Fluctuations in the Pion-Fireball Gas
The pion number fluctuations are considered in the system of pions and large
mass fireballs decaying finally into pions. A formulation which gives an
extension of the model of independent sources is suggested. The grand canonical
and micro-canonical ensemble formulations of the pion-fireball gas are
considered as particular examples.Comment: 13 pages, 4 figure
Fluctuations and Deconfinement Phase Transition in Nucleus-Nucleus Collisions
We propose a method to experimentally study the equation of state of strongly
interacting matter created at the early stage of nucleus--nucleus collisions.
The method exploits the relation between relative entropy and energy
fluctuations and equation of state. As a measurable quantity, the ratio of
properly filtered multiplicity to energy fluctuations is proposed. Within a
statistical approach to the early stage of nucleus-nucleus collisions, the
fluctuation ratio manifests a non--monotonic collision energy dependence with a
maximum in the domain where the onset of deconfinement occurs.Comment: revised version to be published in Phys. Lett.
Diffractive eta_c photo-and electroproduction with the perturbative QCD Odderon
Using a set of new odderon states, we calculate their contribution to the
diffractive eta_c photo- and electroproduction process. Compared to previous
simple 3-gluon exchange calculations we find an enhancement of about one order
of magnitude in the cross section. The t-dependence of the cross section
exhibits a dip structure in the small t region.Comment: 16 pages, 3 eps figure
Numerical Hermitian Yang-Mills Connections and Vector Bundle Stability in Heterotic Theories
A numerical algorithm is presented for explicitly computing the gauge
connection on slope-stable holomorphic vector bundles on Calabi-Yau manifolds.
To illustrate this algorithm, we calculate the connections on stable monad
bundles defined on the K3 twofold and Quintic threefold. An error measure is
introduced to determine how closely our algorithmic connection approximates a
solution to the Hermitian Yang-Mills equations. We then extend our results by
investigating the behavior of non slope-stable bundles. In a variety of
examples, it is shown that the failure of these bundles to satisfy the
Hermitian Yang-Mills equations, including field-strength singularities, can be
accurately reproduced numerically. These results make it possible to
numerically determine whether or not a vector bundle is slope-stable, thus
providing an important new tool in the exploration of heterotic vacua.Comment: 52 pages, 15 figures. LaTex formatting of figures corrected in
version 2
Challenges for standardization of Clostridium difficile typing methods
Typing of Clostridium difficile facilitates understanding of the epidemiology of the infection. Some evaluations have shown that certain strain types (for example, ribotype 027) are more virulent than others and are associated with worse clinical outcomes. Although restriction endonuclease analysis (REA) and pulsed-field gel electrophoresis have been widely used in the past, PCR ribotyping is the current method of choice for typing of C. difficile. However, global standardization of ribotyping results is urgently needed. Whole-genome sequencing of C. difficile has the potential to provide even greater epidemiologic information than ribotyping
Event-by-Event Fluctuations in Heavy Ion Collisions and the QCD Critical Point
The event-by-event fluctuations of suitably chosen observables in heavy ion
collisions at SPS, RHIC and LHC can tell us about the thermodynamic properties
of the hadronic system at freeze-out. By studying these fluctuations as a
function of varying control parameters, it is possible to learn much about the
phase diagram of QCD. As a timely example, we stress the methods by which
present experiments at the CERN SPS can locate the second-order critical
endpoint of the first-order transition between quark-gluon plasma and hadron
matter. Those event-by-event signatures which are characteristic of freeze-out
in the vicinity of the critical point will exhibit nonmonotonic dependence on
control parameters. We focus on observables constructed from the multiplicity
and transverse momenta of charged pions. We first consider how the
event-by-event fluctuations of such observables are affected by Bose-Einstein
correlations, by resonances which decay after freeze-out and by fluctuations in
the transverse flow velocity. We compare our thermodynamic predictions for such
noncritical event-by-event fluctuations with NA49 data, finding broad
agreement. We then focus on effects due to thermal contact between the observed
pions and a heat bath with a given (possibly singular) specific heat, and due
to the direct coupling between the critical fluctuations of the sigma field and
the observed pions. We also discuss the effect of the pions produced in the
decay of sigma particles just above threshold after freeze-out on the inclusive
pion spectrum and on multiplicity fluctuations. We estimate the size of these
nonmonotonic effects which appear near the critical point, including
restrictions imposed by finite size and finite time, and conclude that they
should be easily observable.Comment: 58 pages, 2 figures; to appear in Phys. Rev.
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