564 research outputs found
Coherent magnetic plasmon modes in a contacting gold nano-sphere chain on a gold Slab
A coupled magnetic resonator waveguide, composed of a contacting gold
nanosphere chain on a gold slab, is proposed and investigated. A broadband
coherent magnetic plasmon mode can be excited in this one dimensional
nanostructure. By employing the Lagrangian formalism and the Fourier transform
method, the dispersion properties of the wave vector and group velocity of the
magnetic plasmon mode are investigated. Small group velocity can be obtained
from this system which can be applied as subwavelength slow wave waveguides.Comment: 11pages, 5 figures, This work is published at Optics Express 19,
23782 (2011
Dark-pulse propagation in optical fibers
We report measurements of the reshaping of 0.3-psec dark pulses due to their passage through 10 m of single-mode optical fiber. The measurements were performed as a function of intensity and the observed strong reshaping agrees qualitatively with the predictions of the nonlinear Schrodinger equation which suggest that we have observed the formation of dark-pulse solitons.Peer reviewedElectrical and Computer Engineerin
Electronic and optical properties of electromigrated molecular junctions
Electromigrated nanoscale junctions have proven very useful for studying
electronic transport at the single-molecule scale. However, confirming that
conduction is through precisely the molecule of interest and not some
contaminant or metal nanoparticle has remained a persistent challenge,
typically requiring a statistical analysis of many devices. We review how
transport mechanisms in both purely electronic and optical measurements can be
used to infer information about the nanoscale junction configuration. The
electronic response to optical excitation is particularly revealing. We briefly
discuss surface-enhanced Raman spectroscopy on such junctions, and present new
results showing that currents due to optical rectification can provide a means
of estimating the local electric field at the junction due to illumination.Comment: 19 pages, 8 figures, invited paper for forthcoming special issue of
Journal of Physics: Condensed Matter. For other related papers, see
http://www.ruf.rice.edu/~natelson/publications.htm
Effective permittivity of random plasmonic composites
An effective-medium theory (EMT) is developed to predict the effective
permittivity \epsilon_eff of dense random dispersions of high
optical-conductivity metals such as Ag, Au and Cu. Dependence of \epsilon_eff
on the volume fraction \phi, a microstructure parameter \kappa related to the
static structure factor and particle radius a is studied. In the electrostatic
limit, the upper and lower bounds of \kappa correspond to Maxwell-Garnett and
Bruggeman EMTs respectively. Finite size effects are significant when
|\beta^2(ka/n)^3| becomes O(1) where \beta, k, and n denote the nanoparticle
polarizability, wavenumber and matrix refractive index respectively. The
coupling between the particle and effective medium results in a red-shift in
the resonance peak, a non-linear dependence of \epsilon_eff on \phi, and Fano
resonance in \epsilon_eff.Comment: Manuscript submitted to J. Opt. Soc. Am. B. 33 page
Simultaneous optical pulse compression and wing reduction
We report the compression of picosecond optical pulses with a simultaneous reduction of the pulse wings by using a combination of both the self-phase modulation and nonlinear birefringence effects in a modified optical-fiber pulse compressor.Peer reviewedElectrical and Computer Engineerin
Ultrafast light-controlled optical-fiber modulator
We report the ultrafast operation of a light-controlled optical-fiber modulator, driven by subpicosecond, compressed, and amplified (6000 A) dye laser pulses, controlling frequency doubled (5320 A) yttrium aluminum garnet laser pulses. The operation of the modulator is based on the optical Kerr effect, and its main component is 7 mm of single-mode optical fiber. Using this system as a light-controlled shutter, we produced either 0.4 ps green light pulses or 0.5 ps holes on the much longer duration second harmonic pulses.Peer reviewedElectrical and Computer Engineerin
DNA-based Self-Assembly of Chiral Plasmonic Nanostructures with Tailored Optical Response
Surface plasmon resonances generated in metallic nanostructures can be
utilized to tailor electromagnetic fields. The precise spatial arrangement of
such structures can result in surprising optical properties that are not found
in any naturally occurring material. Here, the designed activity emerges from
collective effects of singular components equipped with limited individual
functionality. Top-down fabrication of plasmonic materials with a predesigned
optical response in the visible range by conventional lithographic methods has
remained challenging due to their limited resolution, the complexity of
scaling, and the difficulty to extend these techniques to three-dimensional
architectures. Molecular self-assembly provides an alternative route to create
such materials which is not bound by the above limitations. We demonstrate how
the DNA origami method can be used to produce plasmonic materials with a
tailored optical response at visible wavelengths. Harnessing the assembly power
of 3D DNA origami, we arranged metal nanoparticles with a spatial accuracy of 2
nm into nanoscale helices. The helical structures assemble in solution in a
massively parallel fashion and with near quantitative yields. As a designed
optical response, we generated giant circular dichroism and optical rotary
dispersion in the visible range that originates from the collective
plasmon-plasmon interactions within the nanohelices. We also show that the
optical response can be tuned through the visible spectrum by changing the
composition of the metal nanoparticles. The observed effects are independent of
the direction of the incident light and can be switched by design between left-
and right-handed orientation. Our work demonstrates the production of complex
bulk materials from precisely designed nanoscopic assemblies and highlights the
potential of DNA self-assembly for the fabrication of plasmonic nanostructures.Comment: 5 pages, 4 figure
Zinc intake, status and indices of cognitive function in adults and children: a systematic review and meta-analysis
In developing countries, deficiencies of micronutrients are thought to have a major impact on child development; however, a consensus on the specific relationship between dietary zinc intake and cognitive function remains elusive. The aim of this systematic review was to examine the relationship between zinc intake, status and indices of cognitive function in children and adults. A systematic literature search was conducted using EMBASE, MEDLINE and Cochrane Library databases from inception to March 2014. Included studies were those that supplied zinc as supplements or measured dietary zinc intake. A meta-analysis of the extracted data was performed where sufficient data were available. Of all of the potentially relevant papers, 18 studies met the inclusion criteria, 12 of which were randomised controlled trials (RCTs; 11 in children and 1 in adults) and 6 were observational studies (2 in children and 4 in adults). Nine of the 18 studies reported a positive association between zinc intake or status with one or more measure of cognitive function. Meta-analysis of data from the adult’s studies was not possible because of limited number of studies. A meta-analysis of data from the six RCTs conducted in children revealed that there was no significant overall effect of zinc intake on any indices of cognitive function: intelligence, standard mean difference of <0.001 (95% confidence interval (CI) –0.12, 0.13) P=0.95; executive function, standard mean difference of 0.08 (95% CI, –0.06, 022) P=0.26; and motor skills standard mean difference of 0.11 (95% CI –0.17, 0.39) P=0.43. Heterogeneity in the study designs was a major limitation, hence only a small number (n=6) of studies could be included in the meta-analyses. Meta-analysis failed to show a significant effect of zinc supplementation on cognitive functioning in children though, taken as a whole, there were some small indicators of improvement on aspects of executive function and motor development following supplementation but high-quality RCTs are necessary to investigate this further
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