1,289 research outputs found
Plasticity of GABA(B) receptor-mediated heterosynaptic interactions at mossy fibers after status epilepticus
Several neurotransmitters, including GABA acting at presynaptic GABAB receptors, modulate glutamate release at synapses between hippocampal mossy fibers and CA3 pyramidal neurons. This phenomenon gates excitation of the hippocampus and may therefore prevent limbic seizure propagation. Here we report that status epilepticus, triggered by either perforant path stimulation or pilocarpine administration, was followed 24 hr later by a loss of GABAB receptor-mediated heterosynaptic depression among populations of mossy fibers. This was accompanied by a decrease in the sensitivity of mossy fiber transmission to the exogenous GABAB receptor agonist baclofen. Autoradiography revealed a reduction in GABAB receptor binding in the stratum lucidum after status epilepticus. Failure of GABAB receptor-mediated modulation of mossy fiber transmission at mossy fibers may contribute to the development of spontaneous seizures after status epilepticus
Extragalactic Relativistic Jets and Nuclear Regions in Galaxies
Past years have brought an increasingly wider recognition of the ubiquity of
relativistic outflows (jets) in galactic nuclei, which has turned jets into an
effective tool for investigating the physics of nuclear regions in galaxies. A
brief summary is given here of recent results from studies of jets and nuclear
regions in several active galaxies with prominent outflows.Comment: 5 pages; contribution to ESO Astrophysical Symposia, "Relativistic
Astrophysics and Cosmology", eds. B. Aschenbach, V. Burwitz, G. Hasinger, B.
Leibundgut (Springer: Heidelberg 2006
Compact jets as probes for sub-parsec scale regions in AGN
Compact relativistic jets in active galactic nuclei offer an effective tool
for investigating the physics of nuclear regions in galaxies. The emission
properties, dynamics, and evolution of jets in AGN are closely connected to the
characteristics of the central supermassive black hole, accretion disk and
broad-line region in active galaxies. Recent results from studies of the
nuclear regions in several active galaxies with prominent outflows are reviewed
in this contribution.Comment: AASLaTeX, 5 pages, 4 figures. Accepted in Astrophysics and Space
Scienc
The relationship of leaf photosynthetic traits - V-cmax and J(max) - to leaf nitrogen, leaf phosphorus, and specific leaf area: a meta-analysis and modeling study
Great uncertainty exists in the global exchange of carbon between the atmosphere and the terrestrial biosphere. An important source of this uncertainty lies in the dependency of photosynthesis on the maximum rate of carboxylation (Vcmax) and the maximum rate of electron transport (Jmax). Understanding and making accurate prediction of C fluxes thus requires accurate characterization of these rates and their relationship with plant nutrient status over large geographic scales. Plant nutrient status is indicated by the traits: leaf nitrogen (N), leaf phosphorus (P), and specific leaf area (SLA). Correlations between Vcmax and Jmax and leaf nitrogen (N) are typically derived from local to global scales, while correlations with leaf phosphorus (P) and specific leaf area (SLA) have typically been derived at a local scale. Thus, there is no global-scale relationship between Vcmax and Jmax and P or SLA limiting the ability of global-scale carbon flux models do not account for P or SLA. We gathered published data from 24 studies to reveal global relationships of Vcmax and Jmax with leaf N, P, and SLA. Vcmax was strongly related to leaf N, and increasing leaf P substantially increased the sensitivity of Vcmax to leaf N. Jmax was strongly related to Vcmax, and neither leaf N, P, or SLA had a substantial impact on the relationship. Although more data are needed to expand the applicability of the relationship, we show leaf P is a globally important determinant of photosynthetic rates. In a model of photosynthesis, we showed that at high leaf N (3 gmâ2), increasing leaf P from 0.05 to 0.22 gmâ2 nearly doubled assimilation rates. Finally, we show that plants may employ a conservative strategy of Jmax to Vcmax coordination that restricts photoinhibition when carboxylation is limiting at the expense of maximizing photosynthetic rates when light is limiting
An Adaptive Secondary Mirror demonstrator: Construction and Preliminary Evaluation
Adaptive optics combines technologies that enable the correction of the wavefront distortion caused by the earthâs atmospheric turbulence in real time. Adaptive secondary mirror (ASM) systems have been proposed and are now being developed. ASMs have advantages over conventional AO systems in terms of throughput, polarisation and IR emissivity. Previously, we reported the design of an ASM demonstrator along with its predicted performance. This paper reports the construction techniques and the results from the preliminary static and dynamic testing of such a demonstrator. In particular assembly methods that preserve the optical quality of the mirror are presented along with experimentally measured mirror influence functions and closed loop tip/tilt performance
The Ising-Kondo lattice with transverse field: an f-moment Hamiltonian for URu2Si2?
We study the phase diagram of the Ising-Kondo lattice with transverse
magnetic field as a possible model for the weak-moment heavy-fermion compound
URu2Si2, in terms of two low-lying f singlets in which the uranium moment is
coupled by on-site exchange to the conduction electron spins. In the mean-field
approximation for an extended range of parameters, we show that the conduction
electron magnetization responds logarithmically to f-moment formation, that the
ordered moment in the antiferromagnetic state is anomalously small, and that
the Neel temperature is of the order observed. The model gives a qualitatively
correct temperature-dependence, but not magnitude, of the specific heat. The
majority of the specific heat jump at the Neel temperature arises from the
formation of a spin gap in the conduction electron spectrum. We also discuss
the single-impurity version of the model and speculate on ways to increase the
specific heat coefficient. In the limits of small bandwidth and of small
Ising-Kondo coupling, we find that the model corresponds to anisotropic
Heisenberg and Hubbard models respectively.Comment: 20 pages RevTeX including 5 figures (1 in LaTeX, 4 in uuencoded EPS),
Received by Phys. Rev. B 19 April 199
K-Pi=6+ and 8- isomer decays in HF-172 and DELTA-K=8 E1 transition rates
A recoil-shadow measurement of isomer decay in 172Hf has revealed many weak gamma-ray transitions. One of these is a sevenfold K-forbidden E1 transition from the K(pi) = 8- isomer (T1/2 = 163 ns) to the K(pi) = 0+ ground-state band. The low hindrance factor for this transition in Hf-172 is compared with the hindrance factors for other DELTAK = 8 E1 transitions
Possible symmetries of the superconducting order parameter in a hexagonal ferromagnet
We study the order parameter symmetry in a hexagonal crystal with co-existing
superconductivity and ferromagnetism. An experimental example is provided by
carbon-based materials, such as graphite-sulfur composites, in which an
evidence of such co-existence has been recently discovered. The presence of a
non-zero magnetization in the normal phase brings about considerable changes in
the symmetry classification of superconducting states, compared to the
non-magnetic case.Comment: 4 pages, REVTe
Resolution of the w-179-isomer anomaly: exposure of a Fermi-aligned s-band
The K-pi = 35-/2, five-quasiparticle isomer in W-179 is shown to decay into the region of a backbend in the 7-/2[514] band, allowing for the first time the identification of a full set of aligned-band states. Destructive interference results from level mixing in the band-crossing region. The deduced gamma-ray branching ratios are used to establish the mixing matrix elements and to show that the aligned band has a high value of the K quantum number. The properties of well-defined alignment and yet also high K provide the first clear example of a Fermi-aligned s band. The anomalous decay of the isomer itself is now explained
Proton polarizability contribution to the hyperfine splitting in muonic hydrogen
The contribution of the proton polarizability to the ground state hyperfine
splitting in muonic hydrogen is evaluated on the basis of modern experimental
and theoretical results on the proton polarized structure functions. The value
of this correction is equal to 4.6(8)\cdot 10^{-4} times the Fermi splitting
E_F.Comment: 10 pages (revtex), 5 figure
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