Gravin orchestrates protein kinase A and 2-adrenergic receptor signaling critical for synaptic plasticity and memory

A kinase-anchoring proteins (AKAPs) organize compartmentalized pools of protein kinase A (PKA) to enable localized signaling events within neurons. However, it is unclear which of the many expressed AKAPs in neurons target PKA to signaling complexes important for long-lasting forms of synaptic plasticity and memory storage. In the forebrain, the anchoring protein gravin recruits a signaling complex containing PKA, PKC, calmodulin, and PDE4D (phosphodiesterase 4D) to the β2-adrenergic receptor. Here, we show that mice lacking the α-isoform of gravin have deficits in PKA-dependent long-lasting forms of hippocampal synaptic plasticity including β2-adrenergic receptor-mediated plasticity, and selective impairments of long-term memory storage. Furthermore, both hippocampal β2-adrenergic receptor phosphorylation by PKA, and learning-induced activation of ERK in the CA1 region of the hippocampus are attenuated in mice lacking gravin-α. We conclude that gravin compartmentalizes a significant pool of PKA that regulates learning-induced β2-adrenergic receptor signaling and ERK activation in the hippocampus in vivo, thereby organizing molecular interactions between glutamatergic and noradrenergic signaling pathways for long-lasting synaptic plasticity, and memory storage

BPS Solutions and New Phases of Finite-Temperature Strings

All high-temperature phases of the known N=4 superstrings in five dimensions can be described by the universal thermal potential of an effective four-dimensional supergravity. This theory, in addition to three moduli s, t, u, contains non-trivial winding modes that become massless in certain regions of the thermal moduli space, triggering the instabilities at the Hagedorn temperature. In this context, we look for exact domain wall solutions of first order BPS equations. These solutions preserve half of the supersymmetries, in contrast to the usual finite-temperature weak-coupling approximation, and as such may constitute a new phase of finite-temperature superstrings. We present exact solutions for the type-IIA and type-IIB theories and for a self-dual hybrid type-II theory. While for the heterotic case the general solution cannot be given in closed form, we still present a complete picture and a detailed analysis of the behaviour around the weak and strong coupling limits and around certain critical points. In all cases these BPS solutions have no instabilities at any temperature. Finally, we address the physical meaning of the resulting geometries within the contexts of supergravity and string theory.Comment: 47 pages, 3 eps figures, Latex, version to be published in Nucl. Phys. B, one refernce added, minor correction

Far-infrared line and dust emission from H II regions and photodissociation regions

We explore the effect of varying the spectral energy distribution of the incident continuum, by simultaneously and self-consistently computing the structure of an H II region and a photodissociation region that are in pressure equilibrium. The results of the calculations are applied to extragalactic observations. The intensity ratio diagrams of far-infrared (FIR) emission for Herschel bands (70, 110, 160, 250, 350, and 500 {\mu}m) and the contribution from H II regions for these specific FIR emissions are presented for the first time. With these diagrams, we compare the predicted FIR continuum intensity ratios of M82 with observations by Herschel.Comment: 27 pages, 8 figures, 2 tables, accepted by Ap

Identifying Sparse Low-Dimensional Structures in Markov Chains: A Nonnegative Matrix Factorization Approach

We consider the problem of learning low-dimensional representations for large-scale Markov chains. We formulate the task of representation learning as that of mapping the state space of the model to a low-dimensional state space, called the kernel space. The kernel space contains a set of meta states which are desired to be representative of only a small subset of original states. To promote this structural property, we constrain the number of nonzero entries of the mappings between the state space and the kernel space. By imposing the desired characteristics of the representation, we cast the problem as a constrained nonnegative matrix factorization. To compute the solution, we propose an efficient block coordinate gradient descent and theoretically analyze its convergence properties.Comment: Accepted for publication in American Control Conference (ACC) Proceedings, 202

Gamma-Ray Bursts in Circumstellar Shells: A Possible Explanation for Flares

It is now generally accepted that long-duration gamma ray bursts (GRBs) are due to the collapse of massive rotating stars. The precise collapse process itself, however, is not yet fully understood. Strong winds, outbursts, and intense ionizing UV radiation from single stars or strongly interacting binaries are expected to destroy the molecular cloud cores that give birth to them and create highly complex circumburst environments for the explosion. Such environments might imprint features on GRB light curves that uniquely identify the nature of the progenitor and its collapse. We have performed numerical simulations of realistic environments for a variety of long-duration GRB progenitors with ZEUS-MP, and have developed an analytical method for calculating GRB light curves in these profiles. Though a full, three-dimensional, relativistic magnetohydrodynamical computational model is required to precisely describe the light curve from a GRB in complex environments, our method can provide a qualitative understanding of these phenomena. We find that, in the context of the standard afterglow model, massive shells around GRBs produce strong signatures in their light curves, and that this can distinguish them from those occurring in uniform media or steady winds. These features can constrain the mass of the shell and the properties of the wind before and after the ejection. Moreover, the interaction of the GRB with the circumburst shell is seen to produce features that are consistent with observed X-ray flares that are often attributed to delayed energy injection by the central engine. Our algorithm for computing light curves is also applicable to GRBs in a variety of environments such as those in high-redshift cosmological halos or protogalaxies, both of which will soon be targets of future surveys such as JANUS or Lobster.Comment: 12 pages, 5 figures, Accepted by Ap

Thermal Tachyon Cosmology

We show that in a multi D\={D} branes system with high temperature, there may exist a thermal cosmological phase before usual tachyon inflation. Though this thermal phase can be very transitory, it may has some interesting applications for early tachyon/brane cosmology.Comment: 5 pages, no figures. new version with 6 pages, part paragraphs were rewritten and title was slightly changed, to publish in PL

A hybrid Si@FeSiy/SiOx anode structure for high performance lithium-ion batteries via ammonia-assisted one-pot synthesis

Synthesised via planetary ball-milling of Si and Fe powders in an ammonia (NH3) environment, a hybrid Si@FeSiy/SiOx structure shows exceptional electrochemical properties for lithium-ion battery anodes, exhibiting a high initial capacity of 1150 mA h g−1 and a retention capacity of 880 mA h g−1 after 150 cycles at 100 mA g−1; and a capacity of 560 mA h g−1 at 4000 mA g−1. These are considerably high for carbon-free micro-/submicro-Si-based anodes. NH3 gradually turns into N2 and H2 during the synthesis, which facilitates the formation of highly conductive FeSiy (y = 1, 2) phases, whereas such phases were not formed in an Ar atmosphere. Milling for 20–40 h leads to partial decomposition of NH3 in the atmosphere, and a hybrid structure of a Si core of mixed nanocrystalline and amorphous Si domains, shelled by a relatively thick SiOx layer with embedded FeSi nanocrystallites. Milling for 60–100 h results in full decomposition of NH3 and a hybrid structure of a much-refined Si-rich core surrounded by a mantle of a relatively low level of SiOx and a higher level of FeSi2. The formation mechanisms of the SiOx and FeSiy phases are explored. The latter structure offers an optimum combination of the high capacity of a nanostructural Si core, relatively high electric conductivity of the FeSiy phase and high structural stability of a SiOx shell accommodating the volume change for high performance electrodes. The synthesis method is new and indispensable for the large-scale production of high-performance Si-based anode materials

Hagedorn Inflation: Open Strings on Branes Can Drive Inflation

We demonstrate an inflationary solution to the cosmological horizon problem during the Hagedorn regime in the early universe. Here the observable universe is confined to three spatial dimensions (a three-brane) embedded in higher dimensions. The only ingredients required are open strings on D-branes at temperatures close to the string scale. No potential is required. Winding modes of the strings provide a negative pressure that can drive inflation of our observable universe. Hence the mere existence of open strings on branes in the early hot phase of the universe drives Hagedorn inflation, which can be either power law or exponential. We note the amusing fact that, in the case of stationary extra dimensions, inflationary expansion takes place only for branes of three or less dimensions.Comment: Talk given by Katherine Frees

Sparticle spectrum and dark matter in type I string theory with an intermediate scale

The supersymmetric particle spectrum is calculated in type I string theories formulated as orientifold compactifications of type IIB string theory. A string scale at an intermediate value of $10^{11}-10^{12}$ GeV is assumed and extra vector-like matter states are introduced to allow unification of gauge coupling constants to occur at this scale. The qualitative features of the spectrum are compared with Calabi-Yau compactification of the weakly coupled heterotic string and with the eleven dimensional supergravity limit of $M$-theory. Some striking differences are observed. Assuming that the lightest neutralino provides the dark matter in the universe, further constraints on the sparticle spectrum are obtained. Direct detection rates for dark matter are estimated.Comment: LaTeX file (10 pages+10 figures), improved references, v3: typos fixed, accepted for publication in Physics Letters