45,654 research outputs found
Dual-side and three-dimensional microelectrode arrays fabricated from ultra-thin silicon substrates
A method for fabricating planar implantable microelectrode arrays was demonstrated using a process that relied on ultra-thin silicon substrates, which ranged in thickness from 25 to 50 µm. The challenge of handling these fragile materials was met via a temporary substrate support mechanism. In order to compensate for putative electrical shielding of extracellular neuronal fields, separately addressable electrode arrays were defined on each side of the silicon device. Deep reactive ion etching was employed to create sharp implantable shafts with lengths of up to 5 mm. The devices were flip-chip bonded onto printed circuit boards (PCBs) by means of an anisotropic conductive adhesive film. This scalable assembly technique enabled three-dimensional (3D) integration through formation of stacks of multiple silicon and PCB layers. Simulations and measurements of microelectrode noise appear to suggest that low impedance surfaces, which could be formed by electrodeposition of gold or other materials, are required to ensure an optimal signal-to-noise ratio as well a low level of interchannel crosstalk
Degenerate states of narrow semiconductor rings in the presence of spin orbit coupling: Role of time-reversal and large gauge transformations
The electron Hamiltonian of narrow semiconductor rings with the Rashba and
Dresselhaus spin orbit terms is invariant under time-reversal operation
followed by a large gauge transformation. We find that all the eigenstates are
doubly degenerate when integer or half-integer quantum fluxes thread the
quantum ring. The wavefunctions of a degenerate pair are related to each other
by the symmetry operation. These results are valid even in the presence of a
disorder potential. When the Zeeman term is present only some of these
degenerate levels anticross
Self-shadowing Effects of Slim Accretion Disks in Active Galactic Nuclei: Diverse Appearance of the Broad-line Region
Supermassive black holes in active galactic nuclei (AGNs) undergo a wide
range of accretion rates, which lead to diversity of appearance. We consider
the effects of anisotropic radiation from accretion disks on the broad-line
region (BLR), from the Shakura-Sunyaev regime to slim disks with
super-Eddington accretion rates. The geometrically thick funnel of the inner
region of slim disks produces strong self-shadowing effects that lead to very
strong anisotropy of the radiation field. We demonstrate that the degree of
anisotropy of the radiation fields grows with increasing accretion rate. As a
result of this anisotropy, BLR clouds receive different spectral energy
distributions depending on their location relative to the disk, resulting in
diverse observational appearance of the BLR. We show that the self-shadowing of
the inner parts of the disk naturally produces two dynamically distinct regions
of the BLR, depending on accretion rate. These two regions manifest themselves
as kinematically distinct components of the broad H line profile with
different line widths and fluxes, which jointly account for the Lorentzian
profile generally observed in narrow-line Seyfert 1 galaxies. In the time
domain, these two components are expected reverberate with different time lags
with respect to the varying ionizing continuum, depending on the accretion rate
and the viewing angle of the observer. The diverse appearance of the BLR due to
the anisotropic ionizing energy source can be tested by reverberation mapping
of H and other broad emission lines (e.g., \feii), providing a new tool
to diagnose the structure and dynamics of the BLR. Other observational
consequences of our model are also explored.Comment: emulatapj style, 15 pages, 6 figures, in pres
Semiclassical Green Function in Mixed Spaces
A explicit formula on semiclassical Green functions in mixed position and
momentum spaces is given, which is based on Maslov's multi-dimensional
semiclassical theory. The general formula includes both coordinate and momentum
representations of Green functions as two special cases of the form.Comment: 8 pages, typeset by Scientific Wor
Experimental Demonstration of Quantum State Multi-meter and One-qubit Fingerprinting in a Single Quantum Device
We experimentally demonstrate in NMR a quantum interferometric multi-meter
for extracting certain properties of unknown quantum states without resource to
quantum tomography. It can perform direct state determinations,
eigenvalue/eigenvector estimations, purity tests of a quantum system, as well
as the overlap of any two unknown quantum states. Using the same device, we
also demonstrate one-qubit quantum fingerprinting
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