1,546 research outputs found
Higher Order Two Step Mechanisms in Nucleon Antinucleon Annihilation and the OZI Rule
We evaluate three meson doorway mechanisms for nucleon-antinucleon
annihilation at rest for the first time. Detailed results are presented for the
final state phi pi0 originating from the 3S1 initial state and for the phi rho
channel originating from 1S0. The results presented also include the improved
contributions from two meson doorway states and from the tree diagrams. For all
the channels considered a consistent explanation of large and small OZI
violations emerges.Comment: 18 pages, 2 PostScript figures, will be published in Eur. Phys. J.
Noise sustained propagation: Local versus global noise
We expand on prior results on noise supported signal propagation in arrays of
coupled bistable elements. We present and compare experimental and numerical
results for kink propagation under the influence of local and global
fluctuations. As demonstrated previously for local noise, an optimum range of
global noise power exists for which the medium acts as a reliable transmission
``channel''. We discuss implications for propagation failure in a model of
cardiac tissue and present a general theoretical framework based on discrete
kink statistics. Valid for generic bistable chains, the theory captures the
essential features ob served in our experiments and numerical simulations.Comment: 1 latex file 20 pages, 9 figures. Accepted for publication in
Physical Review
A simple Monte Carlo model for crowd dynamics
In this paper we introduce a simple Monte Carlo method for simulating the
dynamics of a crowd. Within our model a collection of hard-disk agents is
subjected to a series of two-stage steps, implying (i) the displacement of one
specific agent followed by (ii) a rearrangement of the rest of the group
through a Monte Carlo dynamics. The rules for the combined steps are determined
by the specific setting of the granular flow, so that our scheme should be
easily adapted to describe crowd dynamics issues of many sorts, from stampedes
in panic scenarios to organized flow around obstacles or through bottlenecks.
We validate our scheme by computing the serving times statistics of a group of
agents crowding to be served around a desk. In the case of a size homogeneous
crowd, we recover intuitive results prompted by physical sense. However, as a
further illustration of our theoretical framework, we show that heterogeneous
systems display a less obvious behavior, as smaller agents feature shorter
serving times. Finally, we analyze our results in the light of known properties
of non-equilibrium hard-disk fluids and discuss general implications of our
model.Comment: to be published in Physical Review
An algorithm for clock synchronization with the gradient property in sensor networks
We introduce a distributed algorithm for clock synchronization in sensor
networks. Our algorithm assumes that nodes in the network only know their
immediate neighborhoods and an upper bound on the network's diameter.
Clock-synchronization messages are only sent as part of the communication,
assumed reasonably frequent, that already takes place among nodes. The
algorithm has the gradient property of [2], achieving an O(1) worst-case skew
between the logical clocks of neighbors. As in the case of [3,8], the
algorithm's actions are such that no constant lower bound exists on the rate at
which logical clocks progress in time, and for this reason the lower bound of
[2,5] that forbids constant skew between neighbors does not apply
The effect of hidden color channels on nucleon-nucleon interaction in quark model
In the framework of constituent quark model, the effect of hidden color
channels on the nucleon-nucleon () interaction is studied. By adjusting the
color confinement strength between the hidden color channels and color singlet
channels and/or between the hidden color channels and hidden color channels,
the experimental data of to partial-wave phase shifts of
scattering can be fitted well. The results show that the hidden color channel
coupling might be important in producing the intermediate-range attraction of
interaction. The deuteron properties and dibaryon candidates have also
been studied with this model.Comment: 11 pages, 9 figure
Data sources for rescuing the rich heritage of Mediterranean historical surface climate data
10.1002/gdj3.4Availability of long-term and high-quality instrumental climate records is still insufficient and the rich heritage of meteorological surface observations is largely underexploited in many parts of the world. This is particularly striking over the Greater Mediterranean region (GMR), where meteorological observations have been taken since the 18th century at some locations. The lack of high quality and long series here is despite this region being regarded as a climate change hot spot. This article mainly assesses relevant sources containing Mediterranean historical climate data and metadata either from online repositories worldwide or physical archives, with the emphasis here on the rich holdings kept at French archives. A particular case study is the data rescue (DARE) program undertaken by the Algerian National Meteorological Service, as well as some of the past and ongoing projects and initiatives aimed at enhancing climate data availability and accessibility over the GMR. Our findings point to the high potential for undertaking DARE activities over the GMR and the need for bringing longer and higher quality climate time series to support a diverse number of scientific and technical assessments and policies
OZI Rule Violation in p pbar Annihilation into phi pi pi by Two Step Processes
The phi pi+ pi- production in p pbar annihilation at rest is strongly
enhanced by a two step mechanism with intermediate K Kbar pi pi states. The
relative yield of the phi production due to the resonant final state
interaction decreases with increasing total energy of the p pbar system.Comment: 18 pages, 9 PostScript figure
On the relationship of the scaled phase space and Skyrme-coherent state treatments of proton antiproton annihilation at rest
We discuss pion multiplicities and single pion momentum spectra from proton
antiproton annihilation at rest. Both the scaled phase space model and the
Skyrme-coherent state approach describe these observables well. In the coherent
state approach the puzzling size of the scale parameter relating the phase
space integrals for different multiplicities is replaced by a well defined
weight function. The strength of this function is determined by the intensity
of the classical pion field and its spatial extent is of order 1 fm.Comment: 11 pages including 4 figures(postscript
- …