28,450 research outputs found
ATP as a presynaptic modulator
© 2000 Elsevier Science Inc.There is considerable evidence that ATP acts as a fast transmitter or co-transmitter in autonomic and sensory nerves mostly through activation of ionotropic P2X receptors but also through metabotropic P2Y receptors. By analogy, the observations that ATP is released from stimulated central nervous
system (CNS) nerve terminals and that responses to exogenously added ATP can be recorded in central neurons, lead to the proposal that ATP might also be a fast transmitter in the CNS. However, in spite of
the robust expression of P2 receptor mRNA and binding to P2 receptors in the CNS, the demonstration of central purinergic transmission has mostly remained elusive. We now review evidence to suggest that ATP may also act presynaptically rather than solely postsynaptically in the nervous system.Fundação Ciência e Tecnologia and European nio
Mesonic states in the generalised Nambu-Jona-Lasinio theories
For any Nambu-Jona-Lasinio model of QCD with arbitrary nonlocal,
instantaneous, quark current-current confining kernels, we use a generalised
Bogoliubov technique to go beyond BCS level (in the large-Nc limit) so as to
explicitly build quark-antiquark compound operators for creating/annihilating
mesons. In the Hamiltonian approach, the mesonic bound-state equations appear
(from the generalised Bogoliubov transformation) as mass-gap-like equations
which, in turn, ensure the absence, in the Hamiltonian, of mesonic Bogoliubov
anomalous terms. We go further to demonstrate the one-to-one correspondence
between Hamiltonian and Bethe-Salpeter approaches to non-local NJL-type models
for QCD and give the corresponding "dictionary" necessary to "translate" the
amplitudes built using the graphical Feynman rules to the terms of the
Hamiltonian, and vice versa. We comment on the problem of multiple vacua
existence in such type of models and argue that mesonic states in the theory
should be prescribed to have an extra index - the index of the replica in which
they are created. Then the completely diagonalised Hamiltonian should contain a
sum over this new index. The method is proved to be general and valid for any
instantaneous quark kernel.Comment: LaTeX2e, uses aipproc class, Talk given at the conference "Quark
Confinement and the Hadron Spectrum VI", 21-25 September 2004, Sardinia,
Italy, to appear in Proceeding
Quantum field theory approach to the vacuum replica in QCD
Quantum field theory is used to describe the contribution of possible new QCD
vacuum replica to hadronic processes. This sigma-like new state has been
recently shown to be likely to appear for any realistic four-quark interaction
kernel as a consequence of chiral symmetry. The local operator creating the
replica vacuum state is constructed explicitly. Applications to physical
processes are outlined.Comment: LaTeX2e, 2 EPS figures, uses ws-procs9x6 (included) and epsfig
classes, Talk given at the conference "Quark Confinement and the Hadron
Spectrum V", 10-14 September 2002, Gargnano, Italy, to appear in Proceeding
The Electronic States of Two Oppositely doped Mott Insulators Bilayers
We study the effect of Coulomb interaction between two oppositely doped
low-dimensional tJ model systems. We exactly show that, in the one-dimensional
case, an arbitrarily weak interaction leads to the formation of charge neutral
electron-hole pairs. We then use two different mean-field theories to address
the two-dimensional case, where inter-layer excitons also form and condense. We
propose that this results in new features which have no analog in single
layers, such as the emergence of an insulating spin liquid phase. Our simple
bilayer model might have relevance to the physics of doped Mott insulator
interfaces and of the new four layer Ba2CaCu4O8 compound.Comment: 4 pages, 1 figur
Chiral corrections to baryon properties with composite pions
A calculational scheme is developed to evaluate chiral corrections to
properties of composite baryons with composite pions. The composite baryons and
pions are bound states derived from a microscopic chiral quark model. The model
is amenable to standard many-body techniques such as the BCS and RPA
formalisms. An effective chiral model involving only hadronic degrees of
freedom is derived from the macroscopic quark model by projection onto hadron
states. Chiral loops are calculated using the effective hadronic Hamiltonian. A
simple microscopic confining interaction is used to illustrate the derivation
of the pion-nucleon form factor and the calculation of pionic self-energy
corrections to the nucleon and Delta(1232) masses.Comment: 29 pages, Revtex, 4 ps figure
Magnetocaloric effect in integrable spin-s chains
We study the magnetocaloric effect for the integrable antiferromagnetic
high-spin chain. We present an exact computation of the Gr\"uneisen parameter,
which is closely related to the magnetocaloric effect, for the quantum spin-s
chain on the thermodynamical limit by means of Bethe ansatz techniques and the
quantum transfer matrix approach. We have also calculated the entropy S and the
isentropes in the (H,T) plane. We have been able to identify the quantum
critical points H_c^{(s)}=2/(s+1/2) looking at the isentropes and/or the
characteristic behaviour of the Gr\"uneisen parameter.Comment: 6 pages, 3 figure
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