20,784 research outputs found
Inhibition by ATP of hippocampal synaptic transmission requires localized extracellular catabolism by ecto-nucleotidases into adenosine and channeling to adenosine A1 receptors
© 1998 Society for NeuroscienceATP analogs substituted in the γ-phosphorus (ATPγS, β, γ-imido-ATP, and β, γ-methylene-ATP) were used to probe the involvement of P2 receptors in the modulation of synaptic transmission in the hippocampus, because their extracellular catabolism was virtually not detected in CA1 slices. ATP and γ-substituted analogs were equipotent to inhibit synaptic transmission in CA1 pyramid synapses (IC50 of 17–22 μM). The inhibitory effect of ATP and γ-phosphorus-substituted ATP analogs (30 μM) was not modified by the P2 receptor antagonist suramin (100 μM), was inhibited by 42–49% by the ecto-5’- nucleotidase inhibitor and α, β-methylene ADP (100 μM), was inhibited by 74–85% by 2 U/ml adenosine deaminase (which converts adenosine into its inactive metabolite-inosine), and was nearly prevented by the adenosine A1 receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (10 nM). Stronger support for the involvement of extracellular adenosine formation as a main requirement for the inhibitory effect of ATP and γ-substituted ATP analogs was the observation that an inhibitor of adenosine uptake, dipyridamole (20 μM), potentiated by 92–124% the inhibitory effect of ATP and γ-substituted ATP analogs (10 μM), a potentiation similar to that obtained for 10 μM adenosine (113%). Thus, the present results indicate that inhibition by extracellular ATP of hippocampal synaptic transmission requires localized extracellular catabolism by ectonucleotidases and channeling of the generated adenosine to adenosine A1 receptors.This work was supported by Junta Nacional de Investigação Cientifica e Tecnológica,
Praxis XXI, Gulbenkian Foundation, and European Union (BIOMED 2 programme
On the nature of the spin-polarized hole states in a quasi-two-dimensional GaMnAs ferromagnetic layer
A self-consistent calculation of the density of states and the spectral
density function is performed in a two-dimensional spin-polarized hole system
based on a multiple-scattering approximation. Using parameters corresponding to
GaMnAs thin layers, a wide range of Mn concentrations and hole densities have
been explored to understand the nature, localized or extended, of the
spin-polarized holes at the Fermi level for several values of the average
magnetization of the Mn ystem. We show that, for a certain interval of Mn and
hole densities, an increase on the magnetic order of the Mn ions come together
with a change of the nature of the states at the Fermi level. This fact
provides a delocalization of spin-polarized extended states anti-aligned to the
average Mn magnetization, and a higher spin-polarization of the hole gas. These
results are consistent with the occurrence of ferromagnetism with relatively
high transition temperatures observed in some thin film samples and
multilayered structures of this material.Comment: 3 page
Magnetic ordering in GaAlAs:Mn double well structure
The magnetic order in the diluted magnetic semiconductor barrier of double
AlAs/GaAs: Mn quantum well structures is investigated by Monte Carlo
simulations. A confinement adapted RKKY mechanism is implemented for indirect
exchange between Mn ions mediated by holes. It is shown that, depending on the
barrier width and the hole concentration a ferromagnetic or a spin-glass order
can be established.Comment: 3 figure
P-248 Futility and utility of two-stage hepatectomy
Meeting abstract in the European-Society-for-Medical-Oncology (ESMO) 21st World Congress on Gastrointestinal Cancer.info:eu-repo/semantics/publishedVersio
A dynamical point of view of Quantum Information: entropy and pressure
Quantum Information is a new area of research which has been growing rapidly
since last decade. This topic is very close to potential applications to the so
called Quantum Computer. In our point of view it makes sense to develop a more
"dynamical point of view" of this theory. We want to consider the concepts of
entropy and pressure for "stationary systems" acting on density matrices which
generalize the usual ones in Ergodic Theory (in the sense of the Thermodynamic
Formalism of R. Bowen, Y. Sinai and D. Ruelle). We consider the operator
acting on density matrices over a finite
-dimensional complex Hilbert space where and , are
operators in this Hilbert space. is not a linear operator. In
some sense this operator is a version of an Iterated Function System (IFS).
Namely, the , , play the role of the
inverse branches (acting on the configuration space of density matrices )
and the play the role of the weights one can consider on the IFS. We
suppose that for all we have that . A
family determines a Quantum Iterated Function System
(QIFS) , $\mathcal{F}_W=\{\mathcal{M}_N,F_i,W_i\}_{i=1,...,
k}.
A dynamical point of view of Quantum Information: Wigner measures
We analyze a known version of the discrete Wigner function and some
connections with Quantum Iterated Funcion Systems. This paper is a follow up of
"A dynamical point of view of Quantum Information: entropy and pressure" by the
same authors
Asteroseismic Theory of Rapidly Oscillating Ap Stars
This paper reviews some of the important advances made over the last decade
concerning theory of roAp stars.Comment: 9 pages, 5 figure
Melting of immiscible physical and compatibilized polymer blends in single screw extruders
Melting is a major step in plasticating single screw extrusion, but most of the existing phenomenological know how was gathered by performing Maddock-type experiments with homopolymers. Given the current widespread industrial use of polymer blends, it is worth determining whether the same mechanisms and mathematical models apply, or whether different sequences develop. This work reports the results of Maddock-type experiments using a PA6/PP blend, both in its immiscible and compatibilized varieties. A melting mechanism combining the features of the classical Tadmor mechanism and of the dispersed melting mechanism, also previously reported in the literature, was observed
Melting of polymer blends and concomitant morphology development in single screw extruders
The current understanding of the melting stage in single screw extruders results from pioneering research
efforts that were initiated in the fifties and continued for more than thirty years. Most of these theoretical and
experimental studies used homopolymers as model systems, whereas in industrial practice there has been a considerable
evolution in terms of the complexity of the materials being extruded. This work reports an attempt to monitor the
melting sequence and the morphology development of immiscible physical and chemically compatibilized PA6/PP
blends. A hybrid melting mechanism, incorporating elements of the Tadmor and of the Dispersive melting mechanisms
seems to develop; the early stages of morphology development seem to be similar to those observed in the Haake mixer
and Twin-screw extruder
Morphology development of immiscible polymer blends during melting in single-screw extruders : effect of composition and compatibilization
Melting in single screw extruders began to be studied in the fifties, based on the pioneering work of Maddock. Most theoretical and experimental studies used homopolymers as model systems. However, in practice, there has been a considerable evolution in terms of the complexity of the materials being extruded. In the case of polymer blends, the morphology developed during melting should determine the final blend properties. Therefore, this work aims at investigating the morphology evolution during the melting stage of immiscible physical and chemically compatibilized PA6/PP blends. In general, the sequence of steps of morphology evolution reported for twin screw extruders and batch mixers was observed, though adapted to the flow kinematics along a helical single screw channel. The global morphological development is not affected by blend composition, but distinct domains seem to be formed when in situ reactive compatibilization takes place
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