157 research outputs found
Investigative Ophthalmology & Visual Science A Journal of Dosic and Clinical Research Articles Non-Fluorescent Dye Staining of Primate Blue Cones
The intravitreal injection in macaque retina of the fluorescent dye Procion yellow can selectively label a specific cone population whose eccentricity distribution and angular separation are consistent with those of the blue-sensitive cones of human and non-human primate retinas. Because at the concentrations used the dye is poorly visible in conventional light microscopy, fluorescence microscopy is required for the observation of the stained cones. In this paper we describe several alternative methods for the staining of blue cones in primate retina, staining that can be visualized in conventional light microscopy and, with some methods, electron microscopy. Invest Ophthalmol Vis Sci 24:1449-1455, 198
Graphene-Quantum Dots Hybrid Photodetectors with Low Dark-Current Readout
Graphene-based photodetectors have shown responsivities up to 10A/W and
photoconductive gains up to 10 electrons per photon. These photodetectors
rely on a highly absorbing layer in close proximity of graphene, which induces
a shift of the graphene chemical potential upon absorption, hence modifying its
channel resistance. However, due to the semi-metallic nature of graphene, the
readout requires dark currents of hundreds of A up to mA, leading to high
power consumption needed for the device operation. Here we propose a novel
approach for highly responsive graphene-based photodetectors with orders of
magnitude lower dark current levels. A shift of the graphene chemical potential
caused by light absorption in a layer of colloidal quantum dots, induces a
variation of the current flowing across a metal-insulator-graphene diode
structure. Owing to the low density of states of graphene near the neutrality
point, the light-induced shift in chemical potential can be relatively large,
dramatically changing the amount of current flowing across the insulating
barrier, and giving rise to a novel type of gain mechanism. This readout
requires dark currents of hundreds of nA up to few A, orders of magnitude
lower than other graphene-based photodetectors, while keeping responsivities of
70A/W in the infrared, almost two orders of magnitude higher compared to
established germanium on silicon and indium gallium arsenide infrared
photodetectors. This makes the device appealing for applications where high
responsivity and low power consumption are required.Comment: 14 pages, 7 figure
Chaos and Complexity of quantum motion
The problem of characterizing complexity of quantum dynamics - in particular
of locally interacting chains of quantum particles - will be reviewed and
discussed from several different perspectives: (i) stability of motion against
external perturbations and decoherence, (ii) efficiency of quantum simulation
in terms of classical computation and entanglement production in operator
spaces, (iii) quantum transport, relaxation to equilibrium and quantum mixing,
and (iv) computation of quantum dynamical entropies. Discussions of all these
criteria will be confronted with the established criteria of integrability or
quantum chaos, and sometimes quite surprising conclusions are found. Some
conjectures and interesting open problems in ergodic theory of the quantum many
problem are suggested.Comment: 45 pages, 22 figures, final version, at press in J. Phys. A, special
issue on Quantum Informatio
Fluctuations in Nonequilibrium Statistical Mechanics: Models, Mathematical Theory, Physical Mechanisms
The fluctuations in nonequilibrium systems are under intense theoretical and
experimental investigation. Topical ``fluctuation relations'' describe
symmetries of the statistical properties of certain observables, in a variety
of models and phenomena. They have been derived in deterministic and, later, in
stochastic frameworks. Other results first obtained for stochastic processes,
and later considered in deterministic dynamics, describe the temporal evolution
of fluctuations. The field has grown beyond expectation: research works and
different perspectives are proposed at an ever faster pace. Indeed,
understanding fluctuations is important for the emerging theory of
nonequilibrium phenomena, as well as for applications, such as those of
nanotechnological and biophysical interest. However, the links among the
different approaches and the limitations of these approaches are not fully
understood. We focus on these issues, providing: a) analysis of the theoretical
models; b) discussion of the rigorous mathematical results; c) identification
of the physical mechanisms underlying the validity of the theoretical
predictions, for a wide range of phenomena.Comment: 44 pages, 2 figures. To appear in Nonlinearity (2007
From thermal rectifiers to thermoelectric devices
We discuss thermal rectification and thermoelectric energy conversion from
the perspective of nonequilibrium statistical mechanics and dynamical systems
theory. After preliminary considerations on the dynamical foundations of the
phenomenological Fourier law in classical and quantum mechanics, we illustrate
ways to control the phononic heat flow and design thermal diodes. Finally, we
consider the coupled transport of heat and charge and discuss several general
mechanisms for optimizing the figure of merit of thermoelectric efficiency.Comment: 42 pages, 22 figures, review paper, to appear in the Springer Lecture
Notes in Physics volume "Thermal transport in low dimensions: from
statistical physics to nanoscale heat transfer" (S. Lepri ed.
Estudio de la actividad antimicrobiana del fango termal de Copahue (Neuquén, Argentina)
Se investigó la actividad antimicrobiana del fango termal (Complejo Termal Copahue, Argentina) sobre microorganismos de la microbiota autóctona del hombre, agentes infecciosos de la comunidad, hospitalarios y cepas AT CC. Las cepas correspondieron a cocos Gram positivos, bacilos Gram negativos, levaduras y cepas AT CC. El fango se obtuvo de la Laguna Sulfurosa. La actividad inhibitoria se demostró utilizando fase líquida (FL) mediante la prueba de difusión en agar y por estudios de cinética bactericida. Con la primera se observó halo inhibitorio frente a Staphylococcus aureus y Cándida albicans, no visualizándose inhibición para el resto de los microorganismos. El estudio dinámico a través del tiempo sobre S. aureus, Enterococcus faecalis, Staphylococcus epidermis y C. albicans demostró acción inhibitoria antes de las 6 hs de incubación, mientras que no se observó inhibición frente a los bacilos Gram negativos. Es el primer trabajo que demuestra la actividad antimicrobiana de la FL sobre las cepas ensayadas.Facultad de Ciencias Médica
Estudio de la actividad antimicrobiana del fango termal de Copahue (Neuquén, Argentina)
Se investigó la actividad antimicrobiana del fango termal (Complejo Termal Copahue, Argentina) sobre microorganismos de la microbiota autóctona del hombre, agentes infecciosos de la comunidad, hospitalarios y cepas AT CC. Las cepas correspondieron a cocos Gram positivos, bacilos Gram negativos, levaduras y cepas AT CC. El fango se obtuvo de la Laguna Sulfurosa. La actividad inhibitoria se demostró utilizando fase líquida (FL) mediante la prueba de difusión en agar y por estudios de cinética bactericida. Con la primera se observó halo inhibitorio frente a Staphylococcus aureus y Cándida albicans, no visualizándose inhibición para el resto de los microorganismos. El estudio dinámico a través del tiempo sobre S. aureus, Enterococcus faecalis, Staphylococcus epidermis y C. albicans demostró acción inhibitoria antes de las 6 hs de incubación, mientras que no se observó inhibición frente a los bacilos Gram negativos. Es el primer trabajo que demuestra la actividad antimicrobiana de la FL sobre las cepas ensayadas.Facultad de Ciencias Médica
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
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