4,434 research outputs found
Common learning
Consider two agents who learn the value of an unknown parameter by observing a sequence of private signals. The signals are independent and identically distributed across time but not necessarily across agents. We show that when each agent's signal space is finite, the agents will commonly learn the value of the parameter, that is, that the true value of the parameter will become approximate common knowledge. The essential step in this argument is to express the expectation of one agent's signals, conditional on those of the other agent, in terms of a Markov chain. This allows us to invoke a contraction mapping principle ensuring that if one agent's signals are close to those expected under a particular value of the parameter, then that agent expects the other agent's signals to be even closer to those expected under the parameter value. In contrast, if the agents' observations come from a countably infinite signal space, then this contraction mapping property fails. We show by example that common learning can fail in this case
Low Head Power Generation With Bulb Turbines
Because of uncertainties, delays, and high costs associated with alternative electric energy sources, many agencies responsible for generation of electrical power are investigating means of replacing or supplementing their existing hydroelectric facilities. In the head range between 10 and 60 feet, the bulb-type generating unit, in which the generator is enclosed in a metal capsule within the water passage, has many advantages, including higher efficiency and lower cost, over other types of turbines. Two of the municipalities in the United States which have recently conducted feasibility studies for installing bulb turbines in their systems are the City of Idaho Falls, Idaho, and the City of Vanceburg, Kentucky. For the City of Idaho Falls, International Engineering Company, Inc. prepared feasibility studies which demonstrated that for 7 MW units installed in existing plants, (I) bulb turbines are more economical than comparable conventional (vertical shaft Kaplan) units, (2) installation of new bulb turbine units is preferable to rehabilitating and/or relocating the existing generating units, and (3) the cost of energy generated by the proposed bulb turbine installations would be less than that from alternative sources of energy. At locations at existing dams on the Ohio River, the Vanceburg Electric Light, Heat and Power System studied installations comprised of 3 - 23 MW bulb turbines per plant and also found that the cost of energy from these facilities would be less than from other sources
Imaging a 1-electron InAs quantum dot in an InAs/InP nanowire
Nanowire heterostructures define high-quality few-electron quantum dots for
nanoelectronics, spintronics and quantum information processing. We use a
cooled scanning probe microscope (SPM) to image and control an InAs quantum dot
in an InAs/InP nanowire, using the tip as a movable gate. Images of dot
conductance vs. tip position at T = 4.2 K show concentric rings as electrons
are added, starting with the first electron. The SPM can locate a dot along a
nanowire and individually tune its charge, abilities that will be very useful
for the control of coupled nanowire dots
Using ultra-thin parylene films as an organic gate insulator in nanowire field-effect transistors
We report the development of nanowire field-effect transistors featuring an
ultra-thin parylene film as a polymer gate insulator. The room temperature,
gas-phase deposition of parylene is an attractive alternative to oxide
insulators prepared at high temperatures using atomic layer deposition. We
discuss our custom-built parylene deposition system, which is designed for
reliable and controlled deposition of <100 nm thick parylene films on III-V
nanowires standing vertically on a growth substrate or horizontally on a device
substrate. The former case gives conformally-coated nanowires, which we used to
produce functional -gate and gate-all-around structures. These give
sub-threshold swings as low as 140 mV/dec and on/off ratios exceeding at
room temperature. For the gate-all-around structure, we developed a novel
fabrication strategy that overcomes some of the limitations with previous
lateral wrap-gate nanowire transistors. Finally, we show that parylene can be
deposited over chemically-treated nanowire surfaces; a feature generally not
possible with oxides produced by atomic layer deposition due to the surface
`self-cleaning' effect. Our results highlight the potential for parylene as an
alternative ultra-thin insulator in nanoscale electronic devices more broadly,
with potential applications extending into nanobioelectronics due to parylene's
well-established biocompatible properties
InAs nanowire transistors with multiple, independent wrap-gate segments
We report a method for making horizontal wrap-gate nanowire transistors with
up to four independently controllable wrap-gated segments. While the step up to
two independent wrap-gates requires a major change in fabrication methodology,
a key advantage to this new approach, and the horizontal orientation more
generally, is that achieving more than two wrap-gate segments then requires no
extra fabrication steps. This is in contrast to the vertical orientation, where
a significant subset of the fabrication steps needs to be repeated for each
additional gate. We show that cross-talk between adjacent wrap-gate segments is
negligible despite separations less than 200 nm. We also demonstrate the
ability to make multiple wrap-gate transistors on a single nanowire using the
exact same process. The excellent scalability potential of horizontal wrap-gate
nanowire transistors makes them highly favourable for the development of
advanced nanowire devices and possible integration with vertical wrap-gate
nanowire transistors in 3D nanowire network architectures.Comment: 18 pages, 5 figures, In press for Nano Letters (DOI below
Correlation-induced conductance suppression at level degeneracy in a quantum dot
The large, level-dependent g-factors in an InSb nanowire quantum dot allow
for the occurrence of a variety of level crossings in the dot. While we observe
the standard conductance enhancement in the Coulomb blockade region for aligned
levels with different spins due to the Kondo effect, a vanishing of the
conductance is found at the alignment of levels with equal spins. This
conductance suppression appears as a canyon cutting through the web of direct
tunneling lines and an enclosed Coulomb blockade region. In the center of the
Coulomb blockade region, we observe the predicted correlation-induced
resonance, which now turns out to be part of a larger scenario. Our findings
are supported by numerical and analytical calculations.Comment: 5 pages, 4 figure
Test of a Jastrow-type wavefunction for a trapped few-body system in one dimension
For a system with interacting quantum mechanical particles in a
one-dimensional harmonic oscillator, a trial wavefunction with simple structure
based on the solution of the corresponding two-particle system is suggested and
tested numerically. With the inclusion of a scaling parameter for the distance
between particles, at least for the very small systems tested here the ansatz
gives a very good estimate of the ground state energy, with the error being of
the order of ~1% of the gap to the first excited state
Signatures of Wigner Localization in Epitaxially Grown Nanowires
It was predicted by Wigner in 1934 that the electron gas will undergo a
transition to a crystallized state when its density is very low. Whereas
significant progress has been made towards the detection of electronic Wigner
states, their clear and direct experimental verification still remains a
challenge. Here we address signatures of Wigner molecule formation in the
transport properties of InSb nanowire quantum dot systems, where a few
electrons may form localized states depending on the size of the dot (i.e. the
electron density). By a configuration interaction approach combined with an
appropriate transport formalism, we are able to predict the transport
properties of these systems, in excellent agreement with experimental data. We
identify specific signatures of Wigner state formation, such as the strong
suppression of the antiferromagnetic coupling, and are able to detect the onset
of Wigner localization, both experimentally and theoretically, by studying
different dot sizes.Comment: 4 pages, 4 figure
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