1,684 research outputs found
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
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
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
Brane-Antibrane Systems at Finite Temperature and Phase Transition near the Hagedorn Temperature
In order to study the thermodynamic properties of brane-antibrane systems, we
compute the finite temperature effective potential of tachyon T in this system
on the basis of boundary string field theory. At low temperature, the minimum
of the potential shifts towards T=0 as the temperature increases. In the
D9-antiD9 case, the sign of the coefficient of |T|^2 term of the potential
changes slightly below the Hagedorn temperature. This means that a phase
transition occurs near the Hagedorn temperature. On the other hand, the
coefficient is kept negative in the Dp-antiDp case with p <= 8, and thus a
phase transition does not occur. This leads us to the conclusion that only a
D9-antiD9 pair and no other (lower dimensional) brane-antibrane pairs are
created near the Hagedorn temperature. We also discuss a phase transition in
NS9B-antiNS9B case as a model of the Hagedorn transition of closed strings.Comment: 28 pages, 3 figures, minor errors correcte
Combining the Muon Anomalous Magnetic Moment with other Constraints on the CMSSM
We combine the constraint suggested by the recent BNL E821 measurement of the
anomalous magnetic moment of the muon on the parameter space of the constrained
MSSM (CMSSM) with those provided previously by LEP, the measured rate of b to s
gamma decay and the cosmological relic density Omega-hsquared. Our treatment of
Omega-hsquared includes carefully the direct-channel Higgs poles in
annihilation of pairs of neutralinos chi and a complete analysis of chi -
slepton coannihilation. We find excellent consistency between all the
constraints for tan beta > 10 and mu > 0, for restricted ranges of the CMSSM
parameters m_0 and m_1/2. All the preferred CMSSM parameter space is within
reach of the LHC, but may not be accessible to the Tevatron collider, or to a
first-generation e^+ e^- linear collider with centre-of-mass energy below 1.2
TeV.Comment: 14 pages, 3 eps figures, for a version with high-resolution figures,
go to http://www.hep.umn.edu/~olive/ENO4.p
Intracellular mechanisms underlying the nicotinic enhancement of LTP in the rat dentate gyrus
We have previously shown that activation of nicotinic acetylcholine receptors (nAChRs) enhanced long-term potentiation (LTP) in the rat dentate gyrus in vitro via activation of α7 nAChR. In the present studies, mechanisms underlying the acute and chronic nicotinic enhancement of LTP were examined. In particular, the involvement of activation of intracellular kinases was examined using selective kinase antagonists, and the effects of enhancing cholinergic function with positive allosteric modulators of the α7 nAChR and with acetylcholinesterase (AChE) inhibitors were also investigated. Activation of extracellular signal-regulated kinase (ERK) and cAMP-dependent protein kinase (PKA) was found to be involved in the induction of the acute nicotinic enhancement of LTP, although not control LTP. In contrast, activation of the tyrosine kinase Src, Ca2+-calmodulin-dependent protein kinase II, Janus kinase 2 and p38 mitogen-activated protein kinase was not involved in the acute nicotinic enhancement of LTP, although Src activation was necessary for control LTP. Moreover, activation of phosphoinositide 3-kinase was involved in the acute nicotinic enhancement of LTP to a much lesser extent than in control LTP. Chronic nicotine enhancement of LTP was found to be dependent on PKA, ERK and Src kinases. Acute nicotinic enhancement of LTP was occluded by chronic nicotine treatment. The positive allosteric modulator PNU-120596 was found to strongly reduce the threshold for nicotinic enhancement of LTP, an affect mediated via the α7 nAChR as it was blocked by the selective antagonist methyllycaconitine. The AChE inhibitors tacrine and physostigmine enhanced control LTP
Solutions of Several Coupled Discrete Models in terms of Lame Polynomials of Order One and Two
Coupled discrete models abound in several areas of physics. Here we provide
an extensive set of exact quasiperiodic solutions of a number of coupled
discrete models in terms of Lame polynomials of order one and two. Some of the
models discussed are (i) coupled Salerno model, (ii) coupled Ablowitz-Ladik
model, (iii) coupled saturated discrete nonlinear Schrodinger equation, (iv)
coupled phi4 model, and (v) coupled phi6 model. Furthermore, we show that most
of these coupled models in fact also possess an even broader class of exact
solutions.Comment: 31 pages, to appear in Pramana (Journal of Physics) 201
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