5,325 research outputs found
Realizing lateral wrap-gated nanowire FETs: Controlling gate length with chemistry rather than lithography
An important consideration in miniaturizing transistors is maximizing the
coupling between the gate and the semiconductor channel. A nanowire with a
coaxial metal gate provides optimal gate-channel coupling, but has only been
realized for vertically oriented nanowire transistors. We report a method for
producing laterally oriented wrap-gated nanowire field-effect transistors that
provides exquisite control over the gate length via a single wet etch step,
eliminating the need for additional lithography beyond that required to define
the source/drain contacts and gate lead. It allows the contacts and nanowire
segments extending beyond the wrap-gate to be controlled independently by
biasing the doped substrate, significantly improving the sub-threshold
electrical characteristics. Our devices provide stronger, more symmetric gating
of the nanowire, operate at temperatures between 300 to 4 Kelvin, and offer new
opportunities in applications ranging from studies of one-dimensional quantum
transport through to chemical and biological sensing.Comment: 16 pages, 5 figures. Submitted version, published version available
at http://http://pubs.acs.org/journal/nalef
A Wideband, Four-Element, All-Digital Beamforming System for Dense Aperture Arrays in Radio Astronomy
Densely-packed, all-digital aperture arrays form a key area of technology
development required for the Square Kilometre Array (SKA) radio telescope. The
design of real-time signal processing systems for digital aperture arrays is
currently a central challenge in pathfinder projects worldwide. We describe
interim results of such work; an heirarchical, frequency-domain beamforming
architecture for synthesising a sky beam from the wideband antenna feeds of
digital aperture arrays.Comment: 4 pages, 6 figure
Industry reallocations in a globalizing economy
We distill the main insights from recent trade models on firms responses to globalisation. Our primary aim is to assess the economic impact and the welfare implications of the resulting reallocation of resources across firms and countries. In sodoing, we bring theory into life through the numerical implementation of a theoretical framework calibrated on European data, which encompasses aspects of economic geography, firm heterogeneity, and firms organizational choices. Our final purpose isto provide a comprehensive background for empirical investigations and to stimulate further theoretical research.international integration, resource reallocation, economic geography, firm heterogeneity, multinationals
Gravity on a Little Warped Space
We investigate the consistent inclusion of 4D Einstein gravity on a truncated
slice of AdS_5 whose bulk-gravity and UV scales are much less than the 4D
Planck scale, M_* << M_{Pl}. Such "Little Warped Spaces" have found
phenomenological utility and can be motivated by string realizations of the
Randall-Sundrum framework. Using the interval approach to brane-world gravity,
we show that the inclusion of a large UV-localized Einstein-Hilbert term allows
one to consistently incorporate 4D Einstein gravity into the low-energy theory.
We detail the spectrum of Kaluza-Klein metric fluctuations and, in particular,
examine the coupling of the little radion to matter. Furthermore, we show that
Goldberger-Wise stabilization can be successfully implemented on such spaces.
Our results demonstrate that realistic low-energy effective theories can be
constructed on these spaces, and have relevance for existing models in the
literature.Comment: 1+24 page
Motion of vortices in inhomogeneous Bose-Einstein condensates
We derive a general and exact equation of motion for a quantised vortex in an
inhomogeneous two-dimensional Bose-Einstein condensate. This equation expresses
the velocity of a vortex as a sum of local ambient density and phase gradients
in the vicinity of the vortex. We perform Gross-Pitaevskii simulations of
single vortex dynamics in both harmonic and hard-walled disk-shaped traps, and
find excellent agreement in both cases with our analytical prediction. The
simulations reveal that, in a harmonic trap, the main contribution to the
vortex velocity is an induced ambient phase gradient, a finding that
contradicts the commonly quoted result that the local density gradient is the
only relevant effect in this scenario. We use our analytical vortex velocity
formula to derive a point-vortex model that accounts for both density and phase
contributions to the vortex velocity, suitable for use in inhomogeneous
condensates. Although good agreement is obtained between Gross-Pitaevskii and
point-vortex simulations for specific few-vortex configurations, the effects of
nonuniform condensate density are in general highly nontrivial, and are thus
difficult to efficiently and accurately model using a simplified point-vortex
description.Comment: 13 pages, 8 figure
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