31 research outputs found
Exact non-equilibrium current from the partition function for impurity transport problems
We study the partition functions of quantum impurity problems in the domain
of complex applied bias for its relation to the non-equilibrium current
suggested by Fendley, Lesage and Saleur (cond-mat/9510055). The problem is
reformulated as a certain generalization of the linear response theory that
accomodates an additional complex variable. It is shown that the mentioned
relation holds in a rather generic case in the linear response limit, or under
certain condition out of equilibrium. This condition is trivially satisfied by
the quadratic Hamiltonians and is rather restrictive for the interacting
models. An example is given when the condition is violated.Comment: 10 pages, RevTex. Final extended versio
Effects of spatially inhomogeneous atomic interactions on Bose-Einstein condensates in optical lattices
An interplay of optical lattices and nonlinear impurities in controlling the
dynamics of Bose-Einstein condensate bright solitons is investigated using
effective potential approach. The ability of pushing the solitons into or away
from the impurity region by changing both lattice and impurity parameters is
suggested. A possibility for the existence of stable fundamental gap solitons,
which appear to satisfy an inverted Vakhitov-Kolokolov criterion, is examined.Comment: 14 pages, 19 figure
Algebraic bright and vortex solitons in defocusing media
We demonstrate that spatially inhomogeneous defocusing nonlinear landscapes
with the nonlinearity coefficient growing toward the periphery as [1+abs(r)]**a
support one- and two-dimensional fundamental and higher-order bright solitons,
as well as vortex solitons, with algebraically decaying tails. The energy flow
of the solitons converges as long as nonlinearity growth rate exceeds the
dimensionality, i.e., a>D. Fundamental solitons are always stable, while
multipoles and vortices are stable if the nonlinearity growth rate is large
enough.Comment: 12 pages, 4 figure
Exchange Instabilities in Semiconductor Double Quantum Well Systems
We consider various exchange-driven electronic instabilities in semiconductor
double-layer systems in the absence of any external magnetic field. We
establish that there is no exchange-driven bilayer to monolayer charge transfer
instability in the double-layer systems. We show that, within the unrestricted
Hartree-Fock approximation, the low density stable phase (even in the absence
of any interlayer tunneling) is a quantum ``pseudospin rotated'' spontaneous
interlayer phase coherent spin-polarized symmetric state rather than the
classical Ising-like charge-transfer phase. The U(1) symmetry of the double
quantum well system is broken spontaneously at this low density quantum phase
transition, and the layer density develops quantum fluctuations even in the
absence of any interlayer tunneling. The phase diagram for the double quantum
well system is calculated in the carrier density--layer separation space, and
the possibility of experimentally observing various quantum phases is
discussed. The situation in the presence of an external electric field is
investigated in some detail using the
spin-polarized-local-density-approximation-based self-consistent technique and
good agreement with existing experimental results is obtained.Comment: 24 pages, figures included. Also available at
http://www-cmg.physics.umd.edu/~lzheng/preprint/ct.uu/ . Revised final
version to appear in PR
A Solvable Regime of Disorder and Interactions in Ballistic Nanostructures, Part I: Consequences for Coulomb Blockade
We provide a framework for analyzing the problem of interacting electrons in
a ballistic quantum dot with chaotic boundary conditions within an energy
(the Thouless energy) of the Fermi energy. Within this window we show that the
interactions can be characterized by Landau Fermi liquid parameters. When ,
the dimensionless conductance of the dot, is large, we find that the disordered
interacting problem can be solved in a saddle-point approximation which becomes
exact as (as in a large-N theory). The infinite theory shows a
transition to a strong-coupling phase characterized by the same order parameter
as in the Pomeranchuk transition in clean systems (a spontaneous
interaction-induced Fermi surface distortion), but smeared and pinned by
disorder. At finite , the two phases and critical point evolve into three
regimes in the plane -- weak- and strong-coupling regimes separated
by crossover lines from a quantum-critical regime controlled by the quantum
critical point. In the strong-coupling and quantum-critical regions, the
quasiparticle acquires a width of the same order as the level spacing
within a few 's of the Fermi energy due to coupling to collective
excitations. In the strong coupling regime if is odd, the dot will (if
isolated) cross over from the orthogonal to unitary ensemble for an
exponentially small external flux, or will (if strongly coupled to leads) break
time-reversal symmetry spontaneously.Comment: 33 pages, 14 figures. Very minor changes. We have clarified that we
are treating charge-channel instabilities in spinful systems, leaving
spin-channel instabilities for future work. No substantive results are
change
Quantum Transport in Semiconductor Nanostructures
I. Introduction (Preface, Nanostructures in Si Inversion Layers,
Nanostructures in GaAs-AlGaAs Heterostructures, Basic Properties).
II. Diffusive and Quasi-Ballistic Transport (Classical Size Effects, Weak
Localization, Conductance Fluctuations, Aharonov-Bohm Effect, Electron-Electron
Interactions, Quantum Size Effects, Periodic Potential).
III. Ballistic Transport (Conduction as a Transmission Problem, Quantum Point
Contacts, Coherent Electron Focusing, Collimation, Junction Scattering,
Tunneling).
IV. Adiabatic Transport (Edge Channels and the Quantum Hall Effect, Selective
Population and Detection of Edge Channels, Fractional Quantum Hall Effect,
Aharonov-Bohm Effect in Strong Magnetic Fields, Magnetically Induced Band
Structure).Comment: 111 pages including 109 figures; this review from 1991 has retained
much of its usefulness, but it was not yet available electronicall
sj-docx-1-wso-10.1177_17474930231217670 – Supplemental material for Lung cancer is associated with acute ongoing cerebral ischemia: A population-based study
Supplemental material, sj-docx-1-wso-10.1177_17474930231217670 for Lung cancer is associated with acute ongoing cerebral ischemia: A population-based study by Jonathan Naftali, Rani Barnea, Ruth Eliahou, Keshet Pardo, Assaf Tolkovsky, Meital Adi, Vadim Hasminski, Walid Saliba, Sivan Bloch, Guy Raphaeli, Avi Leader and Eitan Auriel in International Journal of Stroke</p
Functional Characterisation of Eel Dopamine D 2
International audienceIn various vertebrate species, dopamine (DA) exerts an inhibitory action on reproduction. In the European eel, DA plays a pivotal role in the inhibitory control of the gonadotrope function and the blockade of puberty. In vivo studies suggested that this effect is mediated by receptors pharmacologically related to the D2-family. In the European eel, two distinct D2 receptor (D2-R) paralogous genes have been identified (D2A-R and D2B-R) and both shown to be expressed in the pituitary. We investigated the potential role of each paralog in the control of gonadotrope function in this species. Eel recombinant D2A-R or D2B-R were expressed in HEK 293 cells, with a universal Gα subunit, and receptor activation was followed by inositol phosphate production. Recombinant D2-Rs exhibited a comparable affinity for DA, but differential affinities for mammalian D2-R agonists and antagonists, supporting subtle structure/activity differences. Further, using eel pituitary cell primary cultures, the expression by gonadotrope cells of both native eel D2-R paralogs was examined by in situ hybridisation of D2A-R or D2B-R transcripts, coupled to immunofluorescence of LHβ or FSHβ. LH and to a lesser extent, FSH cells expressed both D2-R transcripts, but with a clear predominance of D2B-R. Notably, D2B- R transcripts were detected on the majority of LH cells. Accordingly, using these cultures, we showed that DA potently inhibited basal and testosterone-stimulated LHβ expression and less potently basal and activin-stimulated FSHβ expression. We also tested some D2-R antagonists in order to select the most adequate one to be used in innovative protocols for induction of eel sexual maturation. We identified eticlopride as the most potent inhibitor of DA action on basal and stimulated LH expression in vitro. Our data suggest a differential functionalisation of the duplicated receptor genes and demonstrate that mainly D2B-R is involved in the dopaminergic inhibitory control of eel gonadotrope function