4,643 research outputs found
Integrated Flexible Ocular Coil for Power and Data Transfer in Retinal Prostheses
A microfabricated and fully-implantable coil for use as a power and data transfer component for retinal prostheses is presented. Compared with traditional hand-made ocular coils, this parylene-based device is thin and flexible with 10 turns of thin-film metal wires and a thickness of less than 10 µm. In addition, the entire coil structure can be heat-formed on a mold to match the eye's curvature for extraocular implantation. Because it is made using parylene thin-film technology, this coil can be directly integrated with multielectrode arrays and with parylene-based packages incorporating application specific integrated circuits (ASICs) or discrete electrical components such as chip capacitors. This coil thus enables the fabrication and implantation of a fully microfabricated system for retinal prostheses
Weak and Strong coupling regimes in plasmonic-QED
We present a quantum theory for the interaction of a two level emitter with
surface plasmon polaritons confined in single-mode waveguide resonators. Based
on the Green's function approach, we develop the conditions for the weak and
strong coupling regimes by taking into account the sources of dissipation and
decoherence: radiative and non-radiative decays, internal loss processes in the
emitter, as well as propagation and leakage losses of the plasmons in the
resonator. The theory is supported by numerical calculations for several
quantum emitters, GaAs and CdSe quantum dots and NV centers together with
different types of resonators constructed of hybrid, cylindrical or wedge
waveguides. We further study the role of temperature and resonator length.
Assuming realistic leakage rates, we find the existence of an optimal length at
which strong coupling is possible. Our calculations show that the strong
coupling regime in plasmonic resonators is accessible within current technology
when working at very low temperatures (<4K). In the weak coupling regime our
theory accounts for recent experimental results. By further optimization we
find highly enhanced spontaneous emission with Purcell factors over 1000 at
room temperature for NV-centers. We finally discuss more applications for
quantum nonlinear optics and plasmon-plasmon interactions.Comment: published as Phys. Rev. B 87, 115419 (2013
Enhanced dispersion interaction in confined geometry
The dispersion interaction between two point-like particles confined in a
dielectric slab between two plates of another dielectric medium is studied
within a continuum (Lifshitz) theory. The retarded (Casimir-Polder) interaction
at large inter-particle distances is found to be strongly enhanced as the
mismatch between the dielectric permittivities of the two media is increased.
The large-distance interaction is multiplied due to confinement by a factor of
at zero temperature, and by
at finite temperature, \gamma=\ein(0)/\eout(0)
being the ratio between the static dielectric permittivities of the inner and
outer media. This confinement-induced amplification of the dispersion
interaction can reach several orders of magnitude.Comment: 4 page
Recording advances for neural prosthetics
An important challenge for neural prosthetics research is to record from populations of neurons over long periods of time, ideally for the lifetime of the patient. Two new advances toward this goal are described, the use of local field potentials (LFPs) and autonomously positioned recording electrodes. LFPs are the composite extracellular potential field from several hundreds of neurons around the electrode tip. LFP recordings can be maintained for longer periods of time than single cell recordings. We find that similar information can be decoded from LFP and spike recordings, with better performance for state decodes with LFPs and, depending on the area, equivalent or slightly less than equivalent performance for signaling the direction of planned movements. Movable electrodes in microdrives can be adjusted in the tissue to optimize recordings, but their movements must be automated to be a practical benefit to patients. We have developed automation algorithms and a meso-scale autonomous electrode testbed, and demonstrated that this system can autonomously isolate and maintain the recorded signal quality of single cells in the cortex of awake, behaving monkeys. These two advances show promise for developing very long term recording for neural prosthetic applications
Diffraction of light by a planar aperture in a metallic screen
We present a complete derivation of the formula of Smythe [Phys.Rev.72, 1066
(1947)] giving the electromagnetic field diffracted by an aperture created in a
perfectly conducting plane surface. The reasoning, valid for any excitating
field and any hole shape, makes use only of the free scalar Green function for
the Helmoltz equation without any reference to a Green dyadic formalism. We
compare our proof with the one previously given by Jackson and connect our
reasoning to the general Huygens Fresnel theorem.Comment: J. Math. Phys. 47, 072901 (2006
Nonequilibrium models of relativistic heavy-ion collisions
To be published in J. Phys. G - Proceedings of SQM 2004 : We review the results from the various hydrodynamical and transport models on the collective flow observables from AGS to RHIC energies. A critical discussion of the present status of the CERN experiments on hadron collective flow is given. We emphasize the importance of the flow excitation function from 1 to 50 A.GeV: here the hydrodynamic model has predicted the collapse of the v2-flow ~ 10 A.GeV; at 40 A.GeV it has been recently observed by the NA49 collaboration. Since hadronic rescattering models predict much larger flow than observed at this energy we interpret this observation as evidence for a first order phase transition at high baryon density r b. Moreover, the connection of the elliptic flow v2 to jet suppression is examined. It is proven experimentally that the collective flow is not faked by minijet fragmentation. Additionally, detailed transport studies show that the away-side jet suppression can only partially (< 50%) be due to hadronic rescattering. Furthermore, the change in sign of v1, v2 closer to beam rapidity is related to the occurence of a high density first order phase transition in the RHIC data at 62.5, 130 and 200 A.GeV
Quantum and statistical fluctuations in dynamical symmetry breaking
Dynamical symmetry breaking in an expanding nuclear system is investigated in
semi-classical and quantum framework by employing a collective transport model
which is constructed to mimic the collective behavior of expanding systems. It
is shown that the fluctuations in collective coordinates during the expansion
are developed mainly by the enhancement of the initial fluctuations by the
driving force, and that statistical and quantum fluctuations have similar
consequences. It is pointed out that the quantal fluctuations may play an
important role in the development of instabilities by reducing the time needed
to break the symmetry, and the possible role of quantal fluctuations in
spinodal decomposition of nuclei is discussed.Comment: 19 Latex pages including 6 figure
Unitary model for the reaction and the magnetic dipole moment of the
Radiative pion photoproduction in the resonance region is
studied with the aim to access the magnetic dipole moment. We
present a unitary model of the () reactions, where the rescattering is included in an on-shell
approximation. In this model, the low energy theorem which couples the process in the limit of a soft final photon to the process is exactly satisfied. We study the sensitivity of the
process at higher values of the final photon
energy to the magnetic dipole moment. We compare our results
with existing data and give predictions for forthcoming measurements of angular
and energy distributions. It is found that the photon asymmetry and a helicity
cross section are particularly sensitive to the magnetic dipole
moment.Comment: 23 pages, 18 figure
Andreev tunnelling in quantum dots: A slave-boson approach
We study a strongly interacting quantum dot connected to a normal and to a
superconducting lead. By means of the slave-boson technique we investigate the
low temperature regime and discuss electrical transport through the dot. We
find that the zero bias anomaly in the current-voltage characteristics which is
associated to the occurance of the Kondo resonance in the quantum dot, is
enhanced in the presence of superconductivity, due to resonant Andreev
scattering.Comment: 4 pages, 1 figur
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