946 research outputs found
A Memristor as Multi-Bit Memory: Feasibility Analysis
The use of emerging memristor materials for advanced electrical devices such as multi-valued logic is expected to outperform today's binary logic digital technologies. We show here an example for such non-binary device with the design of a multi-bit memory. While conventional memory cells can store only 1 bit, memristors-based multi-bit cells can store more information within single device thus increasing the information storage density. Such devices can potentially utilize the non-linear resistance of memristor materials for efficient information storage. We analyze the performance of such memory devices based on their expected variations in order to determine the viability of memristor-based multi-bit memory. A design of read/write scheme and a simple model for this cell, lay grounds for full integration of memristor multi-bit memory cell
Excitonic instability and electric-field-induced phase transition towards a two dimensional exciton condensate
We present an InAs-GaSb-based system in which the electric-field tunability
of its 2D energy gap implies a transition towards a thermodynamically stable
excitonic condensed phase. Detailed calculations show a 3 meV BCS-like gap
appearing in a second-order phase transition with electric field. We find this
transition to be very sharp, solely due to exchange interaction, and so, the
exciton binding energy is greatly renormalized even at small condensate
densities. This density gradually increases with external field, thus enabling
the direct probe of the Bose-Einstein to BCS crossover.Comment: LaTex, 11 pages, 3 ps figures, To appear in PR
Shot noise suppression in multimode ballistic Fermi conductors
We have derived a general formula describing current noise in multimode
ballistic channels connecting source and drain electrodes with Fermi electron
gas. In particular (at ), the expression describes the
nonequilibrium ''shot'' noise, which may be suppressed by both Fermi
correlations and space charge screening. The general formula has been applied
to an approximate model of a 2D nanoscale, ballistic MOSFET. At large negative
gate voltages, when the density of electrons in the channel is small, shot
noise spectral density approaches the Schottky value , where
is the average current. However, at positive gate voltages, when the
maximum potential energy in the channel is below the Fermi level of the
electron source, the noise can be at least an order of magnitude smaller than
the Schottky value, mostly due to Fermi effects.Comment: 4 page
Current noise in long diffusive SNS junctions in the incoherent MAR regime
Spectral density of current fluctuations at zero frequency is calculated for
a long diffusive SNS junction with low-resistive interfaces. At low
temperature, T << Delta, the subgap shot noise approaches linear voltage
dependence, S=(2/ 3R)(eV + 2Delta), which is the sum of the shot noise of the
normal conductor and voltage independent excess noise. This result can also be
interpreted as the 1/3-suppressed Poisson noise for the effective charge q =
e(1+2Delta/eV) transferred by incoherent multiple Andreev reflections (MAR). At
higher temperatures, anomalies of the current noise develop at the gap
subharmonics, eV = 2Delta/n. The crossover to the hot electron regime from the
MAR regime is analyzed in the limit of small applied voltages.Comment: improved version, to be published in Phys. Rev.
What you know can influence what you are going to know (especially for older adults)
Stimuli related to an individual's knowledge/experience are often more memorable than abstract stimuli, particularly for older adults. This has been found when material that is congruent with knowledge is contrasted with material that is incongruent with knowledge, but there is little research on a possible graded effect of congruency. The present study manipulated the degree of congruency of study material with participants’ knowledge. Young and older participants associated two famous names to nonfamous faces, where the similarity between the nonfamous faces and the real famous individuals varied. These associations were incrementally easier to remember as the name-face combinations became more congruent with prior knowledge, demonstrating a graded congruency effect, as opposed to an effect based simply on the presence or absence of associations to prior knowledge. Older adults tended to show greater susceptibility to the effect than young adults, with a significant age difference for extreme stimuli, in line with previous literature showing that schematic support in memory tasks particularly benefits older adults
The use of ocular coherence tomography in evaluating optic nerve health in eyes with large disc size
Large discs are often associated with large cups; in order to exclude glaucomatous cupping a good objective tool is needed. The purpose of this study is to evaluate ocular coherence tomography (OCT) optic nerve head (ONH) parameters as indicators of ocular health in subjects with large discs. Eighty-one eyes of 53 healthy patients were evaluated; 46 eyes had large discs (disc area ≥2.6 mm2) and 35 eyes had regular size discs (disc area <2.6 mm2). All subjects underwent OCT. All ONH parameters were documented, including vertical integrated rim area (VIRA), horizontal integrated rim width (HIRW), rim area, cup area, cup-to-disc (CD) area ratio, horizontal cup to disc ratio (HCDR), vertical cup to disc ratio (VCDR), cup area topography, and cup volume. In addition, OCT retinal nerve fiber layer (RNFL) global mean thickness and four quadrants mean thicknesses were analyzed. All cup parameters were significantly higher in the large disc group compared to the normal disc group. The parameters estimating the rim varied between the groups: in the large disc group VIRA was significantly lower while HIRW was significantly higher, compared to the control group. Rim area was the only parameter with similar values in both groups (1.52±0.24 mm2 and 1.6±0.3 mm2 in the large and regular disc groups, respectively). Correlation analysis revealed significant positive association between disc area and cup parameters in the large disc group. In contrast, in the regular disc group, disc area was positively associated with rim parameters. Rim area might serve as an indicator for ocular health in large discs with large cups
Dynamical effects of an unconventional current-phase relation in YBCO dc-SQUIDs
The predominant d-wave pairing symmetry in high temperature superconductors
allows for a variety of current-phase relations in Josephson junctions, which
is to a certain degree fabrication controlled. In this letter we report on
direct experimental observations of the effects of a non-sinusoidal
current-phase dependence in YBCO dc-SQUIDs, which agree with the theoretical
description of the system.Comment: 4 pages, 4 ps figures, to apprear in Phys. Rev. Let
Non-equilibrium current noise in mesoscopic disordered SNS junctions
Current noise in superconductor-normal metal-superconductor (SNS) junctions
is calculated within the scattering theory of multiple Andreev reflections
(MAR). It is shown that the noise exhibits subharmonic gap singularities at
, both in single-mode junctions with arbitrary
transparency and in multi-mode disordered junctions. The subharmonic
structure is superimposed with monotonic increase of the effective transferred
charge with decreasing bias voltage. Other features of the
noise include a step-like increase of in junctions with small , and a
divergence at small voltages and excess noise , where is the excess current, at large voltages, in
junctions with diffusive transport.Comment: 5 page
Effect of screening on shot noise in diffusive mesoscopic conductors
Shot noise in diffusive mesoscopic conductors, at finite observation
frequencies (comparable to the reciprocal Thouless time
), is analyzed with an account of screening. At low frequencies,
the well-known result is recovered. This result is valid at
arbitrary for wide conductors longer than the screening length.
However, at least for two very different systems, namely, wide and short
conductors, and thin conductors over a close ground plane, noise approaches a
different fundamental level, , at .Comment: 5 pages, 3 figures. Published version. Also available in the
journal's format at
http://hana.physics.sunysb.edu/~yehuda/cv/papers/shotnoise.pd
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