On the energy dependence of hadronic BcB_c production

An estimate is presented of the production cross section of $B_c$ mesons between threshold and LHC energies using lowest-order perturbation theory and non-relativistic bound state approximation. It is shown that the ratio of the production cross sections for $B_c$ mesons and for $b$ quarks varies strongly with energy.Comment: 5 pages, 1 figure, Latex; Contribution to the 5th International Workshop on $B$-Physics at Hadron Machines, 1997, Los Angeles, California, US

Ryanodine Receptor Activation Induces Long-Term Plasticity of Spine Calcium Dynamics

A key feature of signalling in dendritic spines is the synapse-specific transduction of short electrical signals into biochemical responses. Ca2+ is a major upstream effector in this transduction cascade, serving both as a depolarising electrical charge carrier at the membrane and an intracellular second messenger. Upon action potential firing, the majority of spines are subject to global back-propagating action potential (bAP) Ca2+ transients. These transients translate neuronal suprathreshold activation into intracellular biochemical events. Using a combination of electrophysiology, two-photon Ca2+ imaging, and modelling, we demonstrate that bAPs are electrochemically coupled to Ca2+ release from intracellular stores via ryanodine receptors (RyRs). We describe a new function mediated by spine RyRs: the activity-dependent long-term enhancement of the bAP-Ca2+ transient. Spines regulate bAP Ca2+ influx independent of each other, as bAP-Ca2+ transient enhancement is compartmentalized and independent of the dendritic Ca2+ transient. Furthermore, this functional state change depends exclusively on bAPs travelling antidromically into dendrites and spines. Induction, but not expression, of bAP-Ca2+ transient enhancement is a spine-specific function of the RyR. We demonstrate that RyRs can form specific Ca2+ signalling nanodomains within single spines. Functionally, RyR mediated Ca2+ release in these nanodomains induces a new form of Ca2+ transient plasticity that constitutes a spine specific storage mechanism of neuronal suprathreshold activity patterns

Modulation of Elementary Calcium Release Mediates a Transition from Puffs to Waves in an IP3R Cluster Model

The oscillating concentration of intracellular calcium is one of the most important examples for collective dynamics in cell biology. Localized releases of calcium through clusters of inositol 1,4,5-trisphosphate receptor channels constitute elementary signals called calcium puffs. Coupling by diffusing calcium leads to global releases and waves, but the exact mechanism of inter- cluster coupling and triggering of waves is unknown. To elucidate the relation of puffs and waves, we here model a cluster of IP3R channels using a gating scheme with variable non-equilibrium IP3 binding. Hybrid stochastic and deterministic simulations show that puffs are not stereotyped events of constant duration but are sensitive to stimulation strength and residual calcium. For increasing IP3 concentration, the release events become modulated at a timescale of minutes, with repetitive wave-like releases interspersed with several puffs. This modulation is consistent with experimental observations we present, including refractoriness and increase of puff frequency during the inter-wave interval. Our results suggest that waves are established by a random but time-modulated appearance of sustained release events, which have a high potential to trigger and synchronize activity throughout the cell

Heidelberg coping scales for delusions: psychometric evaluation of an expert rating instrument

Background: Coping is of substantial relevance in the treatment and course of psychiatric disorders. Standardized instruments to assess coping with psychotic symptoms, particularly delusions, are rare. The aim of this study was to develop and evaluate the psychometric properties of a new instrument to assess coping strategies in the context of delusional experiences: the Heidelberg Coping Scales for Delusions (HCSD). Methods: Two hundred and twelve inpatients with schizophrenia spectrum disorders and affective disorders currently experiencing delusions were interviewed with the HCSD and other coping assessment instruments. Psychometric properties and factor structure were analyzed. Results: The HCSD showed good inter-rater reliability and convergent validity. Factor analysis yielded an interpretable structure with five factors: resource-oriented coping, medical care, distraction, cognitive coping, and depressive coping. Symptomatic behavior, due to its particular characteristics, was considered apart. Conclusion: The HCSD is a reliable and valid instrument for the assessment of coping strategies in patients with delusions. Further research is needed to evaluate coping changes over time and their influence on treatment and clinical outcomes. Copyright (C) 2012 S. Karger AG, Base

Light Gluinos and the Parton Structure of the Nucleon

We study the effects of light gluinos with mass below about 1 GeV on the nucleon parton densities and the running of alpha_(S). It is shown that from the available high-statistics DIS data no lower bound on the gluino mass can be derived. Also in the new kinematical region accessible at HERA the influence of such light gluinos on structure f unctions is found to be very small and difficult to detect. For use in more direct searches involving final state signatures we present a radiative estimate of the gluino distribution in the nucleon.Comment: 23 pages, LateX, 8 figures, MPI-PhT/94-22, LMU-3/9

PRODUCTION OF BcB_c MESONS IN HADRONIC COLLISIONS

We investigate hadroproduction of $B_c$ mesons from initial gluons using QCD perturbation theory and nonrelativistic bound state approximations. Our results obtained by two completely independent calculations are confronted with existing results which contradict each other. Moreover, we examine the approximation based on heavy quark fragmentation and determine the range of validity of it. Predictions for cross sections and differential distributions at Tevatron and LHC energies are presented.Comment: 10 Latex pages, 6 figures included by epsf.st

Photon Production from a Quark--Gluon Plasma

In-medium interactions of a particle in a hot plasma are considered in the framework of thermal field theory. The formalism to calculate gauge invariant rates for photon and dilepton production from the medium is given. In the application to a QED plasma, astrophysical consequences are pointed out. The photon production rate from strongly interacting quarks in the quark--gluon plasma, which might be formed in ultrarelativistic heavy ion collisions, is calculated in the previously unaccessible regime of photon energies of the order of the plasma temperature. For temperatures below the chiral phase transition, an effective field theory incorporating dynamical chiral symmetry breaking is employed, and perturbative QCD at higher temperatures. A smooth transition between both regions is obtained. The relevance to the soft photon problem and to high energy heavy ion experiments is discussed.Comment: Paper in ReVTeX. Figures and complete paper available via anonymous ftp, ftp://tpri6c.gsi.de/pub/phenning/hq95ga

RR--Parity Violating SUSY or Leptoquarks: Virtual Effects in Dilepton Production

In the Standard Model (SM), dilepton production in hadron--hadron collisions proceeds through the conventional Drell--Yan mechanism $q \bar{q} \rightarrow l^+ l^-$ with the exchange of a gauge boson. Some extensions of the SM contain a quark--lepton contact interaction {\it via} a $q l \phi$ Yukawa coupling, where $\phi$ is a scalar. Theories with scalar leptoquarks and $R$--parity violating SUSY models are the most important examples of such extensions. These Yukawa couplings induce a different dynamical configuration compared to the SM ($t$-channel vs. $s$-channel) in the $q\bar{q} \rightarrow l^+l^-$ process and thus offer the possibility of being identifiable upon imposition of suitable kinematic cuts. We discuss these effects in the context of the dilepton production in the CDF experiment, and explore consequences in the forthcoming Large Hadron Collider (LHC).Comment: LaTeX, 14 pages, 1 table, 5 figures (uuencoded postscript files added using figures option

Constraints on Light Gluinos from Tevatron Dijet Data

The effects of light, long-lived gluinos on $2\to 2$ processes at hadron colliders are examined. Such particles can mediate single squark resonant production via q\glu\to\sq\to q\glu which would significantly modify the dijet data sample. We find that squark masses in the range $130<m_{\tilde q}< 694, 595, 573$ GeV are excluded for gluino masses of $0.4, 1.3, 5.0$ GeV from existing UA2 and Tevatron data on dijet bump searches and angular distributions. Run II of the Tevatron has the capability of excluding this scenario for squark masses up to $\sim 1$ TeV.Comment: Includes new dijet analysis from D0. LaTex, 16 pages, 4 fig