79 research outputs found
Approximate k-state solutions to the Dirac-Yukawa problem based on the spin and pseudospin symmetry
Using an approximation scheme to deal with the centrifugal
(pseudo-centrifugal) term, we solve the Dirac equation with the screened
Coulomb (Yukawa) potential for any arbitrary spin-orbit quantum number
{\kappa}. Based on the spin and pseudospin symmetry, analytic bound state
energy spectrum formulas and their corresponding upper- and lower-spinor
components of two Dirac particles are obtained using a shortcut of the
Nikiforov-Uvarov method. We find a wide range of permissible values for the
spin symmetry constant C_{s} from the valence energy spectrum of particle and
also for pseudospin symmetry constant C_{ps} from the hole energy spectrum of
antiparticle. Further, we show that the present potential interaction becomes
less (more) attractive for a long (short) range screening parameter {\alpha}.
To remove the degeneracies in energy levels we consider the spin and pseudospin
solution of Dirac equation for Yukawa potential plus a centrifugal-like term. A
few special cases such as the exact spin (pseudospin) symmetry Dirac-Yukawa,
the Yukawa plus centrifugal-like potentials, the limit when {\alpha} becomes
zero (Coulomb potential field) and the non-relativistic limit of our solution
are studied. The nonrelativistic solutions are compared with those obtained by
other methods.Comment: 21 pages, 6 figure
Approximate relativistic bound state solutions of the Tietz-Hua rotating oscillator for any -state
Approximate analytic solutions of the Dirac equation with Tietz-Hua (TH)
potential are obtained for arbitrary spin-orbit quantum number using the
Pekeris approximation scheme to deal with the spin-orbit coupling terms In the
presence of exact spin and pseudo-spin (pspin) symmetric limitation, the bound
state energy eigenvalues and associated two-component wave functions of the
Dirac particle moving in the field of attractive and repulsive TH potential are
obtained using the parametric generalization of the Nikiforov-Uvarov (NU)
method. The cases of the Morse potential, the generalized Morse potential and
non-relativistic limits are studied.Comment: 19 pages; 7 figures; Few-Body Systems (2012) (at press
Analysis of the intraspinal calcium dynamics and its implications on the plasticity of spiking neurons
The influx of calcium ions into the dendritic spines through the
N-metyl-D-aspartate (NMDA) channels is believed to be the primary trigger for
various forms of synaptic plasticity. In this paper, the authors calculate
analytically the mean values of the calcium transients elicited by a spiking
neuron undergoing a simple model of ionic currents and back-propagating action
potentials. The relative variability of these transients, due to the stochastic
nature of synaptic transmission, is further considered using a simple Markov
model of NMDA receptos. One finds that both the mean value and the variability
depend on the timing between pre- and postsynaptic action-potentials. These
results could have implications on the expected form of synaptic-plasticity
curve and can form a basis for a unified theory of spike time-dependent, and
rate based plasticity.Comment: 14 pages, 10 figures. A few changes in section IV and addition of a
new figur
The T=0 neutron-proton pairing correlations in the superdeformed rotational bands around 60Zn
The superdeformed bands in 58Cu, 59Cu, 60Zn, and 61Zn are analyzed within the
frameworks of the Skyrme-Hartree-Fock as well as Strutinsky-Woods-Saxon total
routhian surface methods with and without the T=1 pairing correlations. It is
shown that a consistent description within these standard approaches cannot be
achieved. A T=0 neutron-proton pairing configuration mixing of
signature-separated bands in 60Zn is suggested as a possible solution to the
problem.Comment: 9 ReVTex pages, 10 figures, submitted to Phys. Rev.
Bound state solutions of the Dirac-Rosen-Morse potential with spin and pseudospin symmetry
The energy spectra and the corresponding two- component spinor wavefunctions
of the Dirac equation for the Rosen-Morse potential with spin and pseudospin
symmetry are obtained. The wave ( state) solutions for this
problem are obtained by using the basic concept of the supersymmetric quantum
mechanics approach and function analysis (standard approach) in the
calculations. Under the spin symmetry and pseudospin symmetry, the energy
equation and the corresponding two-component spinor wavefunctions for this
potential and other special types of this potential are obtained. Extension of
this result to state is suggested.Comment: 18 page
How Gibbs distributions may naturally arise from synaptic adaptation mechanisms. A model-based argumentation
This paper addresses two questions in the context of neuronal networks
dynamics, using methods from dynamical systems theory and statistical physics:
(i) How to characterize the statistical properties of sequences of action
potentials ("spike trains") produced by neuronal networks ? and; (ii) what are
the effects of synaptic plasticity on these statistics ? We introduce a
framework in which spike trains are associated to a coding of membrane
potential trajectories, and actually, constitute a symbolic coding in important
explicit examples (the so-called gIF models). On this basis, we use the
thermodynamic formalism from ergodic theory to show how Gibbs distributions are
natural probability measures to describe the statistics of spike trains, given
the empirical averages of prescribed quantities. As a second result, we show
that Gibbs distributions naturally arise when considering "slow" synaptic
plasticity rules where the characteristic time for synapse adaptation is quite
longer than the characteristic time for neurons dynamics.Comment: 39 pages, 3 figure
Mineralocorticoid receptors dampen glucocorticoid receptor sensitivity to stress via regulation of FKBP5
Responding to different dynamic levels of stress is critical for mammalian survival. Disruption of mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) signaling is proposed to underlie hypothalamic-pituitary-adrenal (HPA) axis dysregulation observed in stress-related psychiatric disorders. In this study, we show that FK506-binding protein 51 (FKBP5) plays a critical role in fine-tuning MR:GR balance in the hippocampus. Biotinylated-oligonucleotide immunoprecipitation in primary hippocampal neurons reveals that MR binding, rather than GR binding, to the Fkbp5 gene regulates FKBP5 expression during baseline activity of glucocorticoids. Notably, FKBP5 andMR exhibit similar hippocampal expression patterns in mice and humans, which are distinct from that of the GR. Pharmacological inhibition and region- and cell type-specific receptor deletion in mice further demonstrate that lack of MR decreases hippocampal Fkbp5 levels and dampens the stress-induced increase in glucocorticoid levels. Overall, our findings demonstrate that MR-dependent changes in baseline Fkbp5 expression modify GR sensitivity to glucocorticoids, providing insight into mechanisms of stress homeostasis.Diabetes mellitus: pathophysiological changes and therap
The use of phenome-wide association studies (PheWAS) for exploration of novel genotype-phenotype relationships and pleiotropy discovery
The field of phenomics has been investigating network structure among large arrays of phenotypes, and genome-wide association studies (GWAS) have been used to investigate the relationship between genetic variation and single diseases/outcomes. A novel approach has emerged combining both the exploration of phenotypic structure and genotypic variation, known as the phenome-wide association study (PheWAS). The Population Architecture using Genomics and Epidemiology (PAGE) network is a National Human Genome Research Institute (NHGRI)-supported collaboration of four groups accessing eight extensively characterized epidemiologic studies. The primary focus of PAGE is deep characterization of well-replicated GWAS variants and their relationships to various phenotypes and traits in diverse epidemiologic studies that include European Americans, African Americans, Mexican Americans/Hispanics, Asians/Pacific Islanders, and Native Americans. The rich phenotypic resources of PAGE studies provide a unique opportunity for PheWAS as each genotyped variant can be tested for an association with the wide array of phenotypic measurements available within the studies of PAGE, including prevalent and incident status for multiple common clinical conditions and risk factors, as well as clinical parameters and intermediate biomarkers. The results of PheWAS can be used to discover novel relationships between SNPs, phenotypes, and networks of interrelated phenotypes; identify pleiotropy; provide novel mechanistic insights; and foster hypothesis generation. The PAGE network has developed infrastructure to support and perform PheWAS in a high-throughput manner. As implementing the PheWAS approach has presented several challenges, the infrastructure and methodology, as well as insights gained in this project, are presented herein to benefit the larger scientific community
Narcolepsy and adjuvanted pandemic influenza A (H1N1) 2009 vaccines – Multi-country assessment
Background: In 2010, a safety signal was detected for narcolepsy following vaccination with Pandemrix, an AS03-adjuvanted monovalent pandemic H1N1 influenza (pH1N1) vaccine. To further assess a possible association and inform policy on future use of adjuvants, we conducted a multi-country study of narcolepsy and adjuvanted pH1N1 vaccines. Methods: We used electronic health databases to conduct a dynamic retrospective cohort study to assess narcolepsy incidence rates (IR) before and during pH1N1 virus circulation, and after pH1N1 vaccination campaigns in Canada, Denmark, Spain, Sweden, Taiwan, the Netherlands, and the United Kingdom. Using a case-control study design, we evaluated the risk of narcolepsy following AS03- and MF59-adjuvanted pH1N1 vaccines in Argentina, Canada, Spain, Switzerland, Taiwan, and the Netherlands. In the Netherlands, we also conducted a case-coverage study in children born between 2004 and 2009. Results: No changes in narcolepsy IRs were observed in any periods in single study sites except Sweden and Taiwan; in Taiwan incidence increased after wild-type pH1N1 virus circulation and in Sweden (a previously identified signaling country), incidence increased after the start of pH1N1 vaccination. No association was observed for Arepanrix-AS03 or Focetria-MF59 adjuvanted pH1N1 vaccines and narcolepsy in children or adults in the case-control study nor for children born between 2004 and 2009 in the Netherlands case-coverage study for Pandemrix-AS03. Conclusions: Other than elevated narcolepsy IRs in the period after vaccination campaigns in Sweden, we did not find an association between AS03- or MF59-adjuvanted pH1N1 vaccines and narcolepsy in children or adults in the sites studied, although power to evaluate the AS03-adjuvanted Pandemrix brand vaccine was limited in our study
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