Row-switched states in two-dimensional underdamped Josephson junction arrays

When magnetic flux moves across layered or granular superconductor structures, the passage of vortices can take place along channels which develop finite voltage, while the rest of the material remains in the zero-voltage state. We present analytical studies of an example of such mixed dynamics: the row-switched (RS) states in underdamped two-dimensional Josephson arrays, driven by a uniform DC current under external magnetic field but neglecting self-fields. The governing equations are cast into a compact differential-algebraic system which describes the dynamics of an assembly of Josephson oscillators coupled through the mesh current. We carry out a formal perturbation expansion, and obtain the DC and AC spatial distributions of the junction phases and induced circulating currents. We also estimate the interval of the driving current in which a given RS state is stable. All these analytical predictions compare well with our numerics. We then combine these results to deduce the parameter region (in the damping coefficient versus magnetic field plane) where RS states can exist.Comment: latex, 48 pages, 15 figs using psfi

A (Running) Bolt for New Reasons

We construct a four-parameter family of smooth, horizonless, stationary solutions of ungauged five-dimensional supergravity by using the four-dimensional Euclidean Schwarzschild metric as a base space and "magnetizing" its bolt. We then generalize this to a five-parameter family based upon the Euclidean Kerr-Taub-Bolt. These "running Bolt" solutions are necessarily non-static. They also have the same charges and mass as a non-extremal black hole with a classically-large horizon area. Moreover, in a certain regime their mass can decrease as their charges increase. The existence of these solutions supports the idea that the singularities of non-extremal black holes are resolved by low-mass modes that correct the singularity of the classical black hole solution on large (horizon-sized) scales.Comment: 25 pages, 3 figures, LaTeX; v2: minor changes, references adde

Star cluster formation and star formation: the role of environment and star-formation efficiencies

“The original publication is available at www.springerlink.com”. Copyright Springer. DOI: 10.1007/s10509-009-0088-5By analyzing global starburst properties in various kinds of starburst and post-starburst galaxies and relating them to the properties of the star cluster populations they form, I explore the conditions for the formation of massive, compact, long-lived star clusters. The aim is to determine whether the relative amount of star formation that goes into star cluster formation as opposed to field star formation, and into the formation of massive long-lived clusters in particular, is universal or scales with star-formation rate, burst strength, star-formation efficiency, galaxy or gas mass, and whether or not there are special conditions or some threshold for the formation of star clusters that merit to be called globular clusters a few billion years later.Peer reviewe

Central serous chorioretinopathy: An evidence-based treatment guideline.

Central serous chorioretinopathy (CSC) is a relatively common disease that causes vision loss due to macular subretinal fluid leakage and it is often associated with reduced vision-related quality of life. In CSC, the leakage of subretinal fluid through defects in the retinal pigment epithelial layer's outer blood-retina barrier appears to occur secondary to choroidal abnormalities and dysfunction. The treatment of CSC is currently the subject of controversy, although recent data obtained from several large randomized controlled trials provide a wealth of new information that can be used to establish a treatment algorithm. Here, we provide a comprehensive overview of our current understanding regarding the pathogenesis of CSC, current therapeutic strategies, and an evidence-based treatment guideline for CSC. In acute CSC, treatment can often be deferred for up to 3-4 months after diagnosis; however, early treatment with either half-dose or half-fluence photodynamic therapy (PDT) with the photosensitive dye verteporfin may be beneficial in selected cases. In chronic CSC, half-dose or half-fluence PDT, which targets the abnormal choroid, should be considered the preferred treatment. If PDT is unavailable, chronic CSC with focal, non-central leakage on angiography may be treated using conventional laser photocoagulation. CSC with concurrent macular neovascularization should be treated with half-dose/half-fluence PDT and/or intravitreal injections of an anti-vascular endothelial growth factor compound. Given the current shortage of verteporfin and the paucity of evidence supporting the efficacy of other treatment options, future studies-ideally, well-designed randomized controlled trials-are needed in order to evaluate new treatment options for CSC

Hyperon weak radiative decays in chiral perturbation theory

We investigate the leading-order amplitudes for weak radiative decays of hyperons in chiral perturbation theory. We consistently include contributions from the next-to-leading order weak-interaction Lagrangian. It is shown that due to these terms Hara's theorem is violated. The data for the decays of charged hyperons can be easily accounted for. However, at this order in the chiral expansion, the four amplitudes for the decays of neutral hyperons satisfy relations which are in disagreement with the data. The asymmetry parameters for all the decays can not be accounted for without higher-order terms. We shortly comment on the effect of the 27-plet part of the weak interaction.Comment: 8 pages of REVTeX and using macro-package "feynman.tex" (available at http://xxx.lanl.gov/ftp/hep-ph/papers/macros) for the 2 figure

The long-term survival chances of young massive star clusters

We review the long-term survival chances of young massive star clusters (YMCs), hallmarks of intense starburst episodes often associated with violent galaxy interactions. We address the key question as to whether at least some of these YMCs can be considered proto-globular clusters (GCs), in which case these would be expected to evolve into counterparts of the ubiquitous old GCs believed to be among the oldest galactic building blocks. In the absence of significant external perturbations, the key factor determining a cluster's long-term survival chances is the shape of its stellar initial mass function (IMF). It is, however, not straightforward to assess the IMF shape in unresolved extragalactic YMCs. We discuss in detail the promise of using high-resolution spectroscopy to make progress towards this goal, as well as the numerous pitfalls associated with this approach. We also discuss the latest progress in worldwide efforts to better understand the evolution of entire cluster systems, the disruption processes they are affected by, and whether we can use recently gained insights to determine the nature of at least some of the YMCs observed in extragalactic starbursts as proto-GCs. We conclude that there is an increasing body of evidence that GC formation appears to be continuing until today; their long-term evolution crucially depends on their environmental conditions, however.Comment: invited refereed review article; ChJA&A, in press; 33 pages LaTeX (2 postscript figures); requires chjaa.cls style fil

Astroglial d-serine is the endogenous co-agonist at the presynaptic NMDA receptor in rat entorhinal cortex

Presynaptic NMDA receptors facilitate the release of glutamate at excitatory cortical synapses and are involved in regulation of synaptic dynamics and plasticity. At synapses in the entorhinal cortex these receptors are tonically activated and provide a positive feedback modulation of the level of background excitation. NMDA receptor activation requires obligatory occupation of a co-agonist binding site, and in the present investigation we have examined whether this site on the presynaptic receptor is activated by endogenous glycine or d-serine. We used whole-cell patch clamp recordings of spontaneous AMPA receptor-mediated synaptic currents from rat entorhinal cortex neurones in vitro as a monitor of presynaptic glutamate release. Addition of exogenous glycine or d-serine had minimal effects on spontaneous release, suggesting that the co-agonist site was endogenously activated and likely to be saturated in our slices. This was supported by the observation that a co-agonist site antagonist reduced the frequency of spontaneous currents. Depletion of endogenous glycine by enzymatic breakdown with a bacterial glycine oxidase had little effect on glutamate release, whereas d-serine depletion with a yeast d-amino acid oxidase significantly reduced glutamate release, suggesting that d-serine is the endogenous agonist. Finally, the effects of d-serine depletion were mimicked by compromising astroglial cell function, and this was rescued by exogenous d-serine, indicating that astroglial cells are the provider of the d-serine that tonically activates the presynaptic NMDA receptor. We discuss the significance of these observations for the aetiology of epilepsy and possible targeting of the presynaptic NMDA receptor in anticonvulsant therapy. © 2014 Elsevier Ltd. All rights reserved

Have Superheavy Elements been Produced in Nature?

We discuss the possibility whether superheavy elements can be produced in Nature by the astrophysical rapid neutron capture process. To this end we have performed fully dynamical network r-process calculations assuming an environment with neutron-to-seed ratio large enough to produce superheavy nuclei. Our calculations include two sets of nuclear masses and fission barriers and include all possible fission channels and the associated fission yield distributions. Our calculations produce superheavy nuclei with A ~ 300 that however decay on timescales of days.Comment: 12 pages, 11 figure

Oxygen abundance in local disk and bulge: chemical evolution with a strictly universal IMF

The empirical differential oxygen abundance distribution (EDOD) is deduced from subsamples related to two different samples involving solar neighbourhood (SN) thick disk, thin disk, halo, and bulge stars. The EDOD of the SN thick + thin disk is determined by weighting the mass, for assumed SN thick to thin disk mass ratio within the range, 0.1-0.9. Inhomogeneous models of chemical evolution for the SN thick disk, the SN thin disk, the SN thick + thin disk, the SN halo, and the bulge, are computed assuming the instantaneous recycling approximation. The EDOD data are fitted, to an acceptable extent, by their TDOD counterparts provided (i) still undetected, low-oxygen abundance thin disk stars exist, and (ii) a single oxygen overabundant star is removed from a thin disk subsample. In any case, the (assumed power-law) stellar initial mass function (IMF) is universal but gas can be inhibited from, or enhanced in, forming stars at different rates with respect to a selected reference case. Models involving a strictly universal IMF (i.e. gas neither inhibited from, nor enhanced in, forming stars with respect to a selected reference case) can also reproduce the data. The existence of a strictly universal IMF makes similar chemical enrichment within active (i.e. undergoing star formation) regions placed in different environments, but increasing probability of a region being active passing from SN halo to SN thick + thin disk, SN thin disk, SN thick disk, and bulge. On the basis of the results, it is realized that the chemical evolution of the SN thick + thin disk as a whole cannot be excluded.Comment: 26 pages, 10 tables, and 5 figures; tables out of page are splitted in two parts in Appendix B; sects.4 and 5 rewritten for better understanding of the results; further references added. Accepted for publication in Astrophysics & Space Scienc