2,402 research outputs found
Vertical quantum wire realized with double cleaved-edge overgrowth
A quantum wire is fabricated on (001)-GaAs at the intersection of two
overgrown cleaves. The wire is contacted at each end to n+ GaAs layers via
two-dimensional (2D) leads. A sidegate controls the density of the wire
revealing conductance quantization. The step height is strongly reduced from
2e^2/h due to the 2D-lead series resistance. We characterize the 2D density and
mobility for both cleave facets with four-point measurements. The density on
the first facet is modulated by the substrate potential, depleting a 2um wide
strip that defines the wire length. Micro-photoluminescence shows an extra peak
consistent with 1D electron states at the corner.Comment: 4 pages, 4 figure
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This image smells good: Effects of image information scent in search engine results pages
Users are confronted with an overwhelming amount of web pages when they look for information on the Internet. Current search engines already aid the user in their information seeking tasks by providing textual results but adding images to results pages could further help the user in judging the relevance of a result. We investigated this problem from an Information Foraging perspective and we report on two empirical studies that focused on the information scent of images. Our results show that images have their own distinct "smell" which is not as strong as that of text. We also found that combining images and text cues leads to a stronger overall scent. Surprisingly, when images were added to search engine results pages, this did not lead our participants to behave significantly differently in terms of effectiveness or efficiency. Even when we added images that could confuse the participants' scent, this had no significantly detrimental impact on their behaviour. However, participants expressed a preference for results pages which included images. We discuss potential challenges and point to future research to ensure the success of adding images to textual results in search engine results pages. © 2011 ACM
Combustion of solid fuel in very low speed oxygen streams
In reduced gravity, the combustion of solid fuel in low-speed flow can be studied. The flame behavior in this low-speed regime will fill a void in our understanding of the flow effect on combustion. In addition, it is important for spacecraft fire safety considerations. In this work, modeling and experimental work on low-speed forced-concurrent-flow flame spread are carried out. In addition, experiments on reduced-gravity buoyant-flow flame spread are performed
Fluctuation-Driven Molecular Transport in an Asymmetric Membrane Channel
Channel proteins, that selectively conduct molecules across cell membranes,
often exhibit an asymmetric structure. By means of a stochastic model, we argue
that channel asymmetry in the presence of non-equilibrium fluctuations, fueled
by the cell's metabolism as observed recently, can dramatically influence the
transport through such channels by a ratchet-like mechanism. For an
aquaglyceroporin that conducts water and glycerol we show that a previously
determined asymmetric glycerol potential leads to enhanced inward transport of
glycerol, but for unfavorably high glycerol concentrations also to enhanced
outward transport that protects a cell against poisoning.Comment: REVTeX4, 4 pages, 3 figures; Accepted for publication in Phys. Rev.
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Tunneling in Fractional Quantum Hall line junctions
We study the tunneling current between two counterpropagating edge modes
described by chiral Luttinger liquids when the tunneling takes place along an
extended region. We compute this current perturbatively by using a tunnel
Hamiltonian. Our results apply to the case of a pair of different
two-dimensional electron gases in the fractional quantum Hall regime separated
by a barrier, e. g. electron tunneling. We also discuss the case of strong
interactions between the edges, leading to nonuniversal exponents even in the
case of integer quantum Hall edges. In addition to the expected nonlinearities
due to the Luttinger properties of the edges, there are additional interference
patterns due to the finite length of the barrier.Comment: 7 pages, RevTex, 12 figs, submitted to Phys Rev
Four-point measurements of n- and p-type two-dimensional systems fabricated with cleaved-edge overgrowth
We demonstrate a contact design that allows four-terminal magnetotransport
measurements of cleaved-edge overgrown two-dimensional electron and hole
systems. By lithographically patterning and etching a bulk-doped surface layer,
finger-shaped leads are fabricated, which contact the two-dimensional systems
on the cleave facet. Both n- and p-type two-dimensional systems are
demonstrated at the cleaved edge, using Si as either donor or acceptor,
dependent on the growth conditions. Four-point measurements of both gated and
modulation-doped samples yield fractional quantum Hall features for both n- and
p-type, with several higher-order fractions evident in n-type modulation-doped
samples.Comment: 3 pages, 3 figure
Dynamics of Nucleation in the Ising Model
Reactive pathways to nucleation in a three-dimensional Ising model at 60% of
the critical temperature are studied using transition path sampling of single
spin flip Monte Carlo dynamics. Analysis of the transition state ensemble (TSE)
indicates that the critical nuclei are rough and anisotropic. The TSE,
projected onto the free energy surface characterized by cluster size, N, and
surface area, S, indicates the significance of other variables in addition to
these two traditional reaction coordinates for nucleation. The transmission
coefficient along N is ~ 0.35, and this reduction of the transmission
coefficient from unity is explained in terms of the stochastic nature of the
dynamic model.Comment: In press at the Journal of Physical Chemistry B, 7 pages, 8 figure
Classical-to-stochastic Coulomb blockade cross-over in aluminum arsenide wires
We report low-temperature differential conductance measurements in aluminum
arsenide cleaved-edge overgrown quantum wires in the pinch-off regime. At zero
source-drain bias we observe Coulomb blockade conductance resonances that
become vanishingly small as the temperature is lowered below . We
show that this behavior can be interpreted as a classical-to-stochastic Coulomb
blockade cross-over in a series of asymmetric quantum dots, and offer a
quantitative analysis of the temperature-dependence of the resonances
lineshape. The conductance behavior at large source-drain bias is suggestive of
the charge density wave conduction expected for a chain of quantum dots.Comment: version 2: new figure 4, refined discussio
Smoothing a Rock by Chipping
We investigate an idealized model for the size reduction and smoothing of a
polygonal rock due to repeated chipping at corners. Each chip is sufficiently
small so that only a single corner and a fraction of its two adjacent sides are
cut from the object in a single chipping event. After many chips have been cut
away, the resulting shape of the rock is generally anisotropic, with facet
lengths and corner angles distributed over a broad range. Although a
well-defined shape is quickly reached for each realization, there are large
fluctuations between realizations.Comment: 7 pages, 10 figures, 2-column revtex4 format; version 2: final
published form in PRE; contains minor changes in response to referee comment
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