337 research outputs found
Robust plasmon waveguides in strongly-interacting nanowire arrays
Arrays of parallel metallic nanowires are shown to provide a tunable, robust,
and versatile platform for plasmon interconnects, including high-curvature
turns with minimum signal loss. The proposed guiding mechanism relies on gap
plasmons existing in the region between adjacent nanowires of dimers and
multi-wire arrays. We focus on square and circular silver nanowires in silica,
for which excellent agreement between both boundary element method and multiple
multipolar expansion calculations is obtained. Our work provides the tools for
designing plasmon-based interconnects and achieving high degree of integration
with minimum cross talk between adjacent plasmon guides.Comment: 4 pages, 5 figure
Quantification of the performance of chaotic micromixers on the basis of finite time Lyapunov exponents
Chaotic micromixers such as the staggered herringbone mixer developed by
Stroock et al. allow efficient mixing of fluids even at low Reynolds number by
repeated stretching and folding of the fluid interfaces. The ability of the
fluid to mix well depends on the rate at which "chaotic advection" occurs in
the mixer. An optimization of mixer geometries is a non trivial task which is
often performed by time consuming and expensive trial and error experiments. In
this paper an algorithm is presented that applies the concept of finite-time
Lyapunov exponents to obtain a quantitative measure of the chaotic advection of
the flow and hence the performance of micromixers. By performing lattice
Boltzmann simulations of the flow inside a mixer geometry, introducing massless
and non-interacting tracer particles and following their trajectories the
finite time Lyapunov exponents can be calculated. The applicability of the
method is demonstrated by a comparison of the improved geometrical structure of
the staggered herringbone mixer with available literature data.Comment: 9 pages, 8 figure
Atomic-scale confinement of optical fields
In the presence of matter there is no fundamental limit preventing
confinement of visible light even down to atomic scales. Achieving such
confinement and the corresponding intensity enhancement inevitably requires
simultaneous control over atomic-scale details of material structures and over
the optical modes that such structures support. By means of self-assembly we
have obtained side-by-side aligned gold nanorod dimers with robust
atomically-defined gaps reaching below 0.5 nm. The existence of
atomically-confined light fields in these gaps is demonstrated by observing
extreme Coulomb splitting of corresponding symmetric and anti-symmetric dimer
eigenmodes of more than 800 meV in white-light scattering experiments. Our
results open new perspectives for atomically-resolved spectroscopic imaging,
deeply nonlinear optics, ultra-sensing, cavity optomechanics as well as for the
realization of novel quantum-optical devices
Anyons in a weakly interacting system
We describe a theoretical proposal for a system whose excitations are anyons
with the exchange phase pi/4 and charge -e/2, but, remarkably, can be built by
filling a set of single-particle states of essentially noninteracting
electrons. The system consists of an artificially structured type-II
superconducting film adjacent to a 2D electron gas in the integer quantum Hall
regime with unit filling fraction. The proposal rests on the observation that a
vacancy in an otherwise periodic vortex lattice in the superconductor creates a
bound state in the 2DEG with total charge -e/2. A composite of this
fractionally charged hole and the missing flux due to the vacancy behaves as an
anyon. The proposed setup allows for manipulation of these anyons and could
prove useful in various schemes for fault-tolerant topological quantum
computation.Comment: 7 pages with 3 figures. For related work and info visit
http://www.physics.ubc.ca/~fran
Hydraulic & Design Parameters in Full-Scale Constructed Wetland & Treatment Units: Six Case Studies
The efficiency of pond and constructed wetland (CW) treatment systems, is influenced by the internal hydrodynamics and mixing interactions between water and aquatic vegetation. In order to contribute to current knowledge of how emergent real vegetation affects solute mixing, and on what the shape and size effects are on the mixing characteristics, an understanding and quantification of those physical processes and interactions was evaluated.
This paper presents results from tracer tests conducted during 2015-2016 in six full-scale systems in the UK under different flow regimes, operational depths, shapes and sizes, and in-/outlet configurations. The aim is to quantify the hydraulic performance and mixing characteristics of the treatment units, and to investigate the effect of size and shape on the mixing processes. Relative comparison of outlet configuration, inflow conditions, and internal features between the six different treatment units showed variations in residence times of up to a factor of 3. A key outcome of this study, demonstrated that the width is a more important dimension for the efficiency of the unit compared to the depth. Results underlined the importance of investigating hydrodynamics and physics of flow in full-size units to enhance treatment efficiency and predictions of water quality models
Mode imaging and selection in strongly coupled nanoantennas
The number of eigenmodes in plasmonic nanostructures increases with
complexity due to mode hybridization, raising the need for efficient mode
characterization and selection. Here we experimentally demonstrate direct
imaging and selective excitation of the bonding and antibonding plasmon mode in
symmetric dipole nanoantennas using confocal two-photon photoluminescence
mapping. Excitation of a high-quality-factor antibonding resonance manifests
itself as a two-lobed pattern instead of the single spot observed for the broad
bonding resonance, in accordance with numerical simulations. The two-lobed
pattern is observed due to the fact that excitation of the antibonding mode is
forbidden for symmetric excitation at the feedgap, while concomitantly the mode
energy splitting is large enough to suppress excitation of the bonding mode.
The controlled excitation of modes in strongly coupled plasmonic nanostructures
is mandatory for efficient sensors, in coherent control as well as for
implementing well-defined functionalities in complex plasmonic devices.Comment: 11 pages, 5 figures, 1 supplementary informatio
A multiplex marker set for microsatellite typing and sexing of sooty terns Onychoprion fuscatus
OBJECTIVES: Seabirds have suffered dramatic population declines in recent decades with one such species being the sooty tern Onychoprion fuscatus. An urgent call to re-assess their conservation status has been made given that some populations, such as the one on Ascension Island, South Atlantic, have declined by over 80% in three generations. Little is known about their population genetics, which would aid conservation management through understanding ecological processes and vulnerability to environmental change. We developed a multiplex microsatellite marker set for sooty terns including sex-typing markers to assist population genetics studies. RESULTS: Fifty microsatellite loci were isolated and tested in 23 individuals from Ascension Island. Thirty-one were polymorphic and displayed between 4 and 20 alleles. Three loci were Z-linked and two autosomal loci deviated from Hardy-Weinberg equilibrium. The remaining 26 autosomal loci together with three sex-typing makers were optimised in seven polymerase chain reaction plexes. These 26 highly polymorphic markers will be useful for understanding genetic structure of the Ascension Island population and the species as a whole. Combining these with recently developed microsatellite markers isolated from Indian Ocean birds will allow for assessment of global population structure and genetic diversity
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