1,249 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.
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
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
Placebos in der Psychotherapieforschung – eine systematische Analyse am Beispiel der systematischen Desensibilisierung
Hintergrund: Die Voraussetzungen der randomisierten, Placebo-kontrollierten Evaluation - die Ununterscheidbarkeit der Therapiebedingungen für die Patienten und die Verblindung der Therapeuten - sind in der Psychotherapieforschung nicht uneingeschränkt gegeben. Das Ziel dieser qualitativen systematischen Übersichtsarbeit ist es, am Beispiel der systematischen Desensibilisierung (SD) die Vorgehensweisen zur Bestimmung der Behandlungsspezifität zu beschreiben und deren theoretische und praktische Implikationen zu diskutieren. Methodik: Auf der Basis einer systematischen Literaturrecherche in PsycINFO und PubMed für den Zeitraum von 1976-2015 wurden Psychotherapiestudien gesucht, in denen Patienten mit Angstsymptomen einer SD- oder Placebo-Gruppe zugewiesen und verglichen wurden. Nach Extraktion der gewählten Moderator-Variablen konnten 11 Studien eingeschlossen werden. Ergebnisse: Die Ergebnisse zu den spezifischen Effekten der SD waren nicht einheitlich. Eine durchgeführte Moderator-Analyse zeigte, dass der Nachweis spezifischer Effekte von der Glaubwürdigkeit des Placebos und dem dabei erlebten Ausmaß emotionaler Erfahrungen abhängig ist. Schlussfolgerung: Ob ein bestimmtes psychotherapeutisches Verfahren als spezifisch einzustufen ist, hängt von der Operationalisierung der Placebo-Kontrolle ab. Insbesondere bei SD scheint die Einschränkung des zu bearbeitenden Themas und in der Folge die Unterbindung der emotionalen Erfahrung des Patienten innerhalb der Kontrollbedingung eine Voraussetzung dafür zu sein, spezifische Effekte der SD zu finden
Rates for the reactions antiproton-proton --> pi phi and gamma phi
We study antiproton-proton annihilation at rest into and
. Rescattering by and
for states is sizable, of
order in the branching ratio, but
smaller than experiment. For the
rescattering contributions are negligible, but the channel is well
explained by a intermediate state combined with vector meson
dominance.Comment: 12 pages, plain latex, 2 postscript figures available upon request,
PSI-PR-93-2
Coherent Pion Radiation From Nucleon Antinucleon Annihilation
A unified picture of nucleon antinucleon annihilation into pions emerges from
a classical description of the pion wave produced in annihilation and the
subsequent quantization of that wave as a coherent state. When the constraints
of energy-momentum and iso-spin conservation are imposed on the coherent state,
the pion number distribution and charge ratios are found to be in excellent
agreement with experiment.Comment: LaTex, 8 text pages, 1 PostScript figure, PSI-PR-93-2
Universal Scaling of Wave Propagation Failure in Arrays of Coupled Nonlinear Cells
We study the onset of the propagation failure of wave fronts in systems of
coupled cells. We introduce a new method to analyze the scaling of the critical
external field at which fronts cease to propagate, as a function of
intercellular coupling. We find the universal scaling of the field throughout
the range of couplings, and show that the field becomes exponentially small for
large couplings. Our method is generic and applicable to a wide class of
cellular dynamics in chemical, biological, and engineering systems. We confirm
our results by direct numerical simulations.Comment: 4 pages, 3 figures, RevTe
Linguistic expert creation in online health practices
In this chapter, we explore how the construction of an expert identity varies across online e-health settings with different socio-technological features. Our methodology is qualitative in nature and draws on insights from discourse analysis, in particular positioning theory. Results show that four aspects of creating expertise are vital: the embeddedness of the posi-tioning strategies in the online health context, the interplay between these strategies within each setting, the interactivity of the medium, and the fact that not only professionals, but also clients and laypeople construct their expertise. The results reveal that previously found strategies to create expertise (e.g., using jargon or showing empathy) could be confirmed in our corpus, and that the interplay of several strategies is in fact needed to create credible and trustworthy expert identities for all participants involved. This interplay varies accord-ing to the practice
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