491 research outputs found
Observation of Intensity Statistics of Light Transmitted Through 3D Random Media
We experimentally observe the spatial intensity statistics of light
transmitted through three-dimensional isotropic scattering media. The intensity
distributions measured through layers consisting of zinc oxide nanoparticles
differ significantly from the usual Rayleigh statistics associated with
speckle, and instead are in agreement with the predictions of mesoscopic
transport theory, taking into account the known material parameters of the
samples. Consistent with the measured spatial intensity fluctuations, the total
transmission fluctuates. The magnitude of the fluctuations in the total
transmission is smaller than expected on the basis of quasi-one-dimensional
(1D) transport theory, which indicates that quasi-1D theories cannot fully
describe these open three-dimensional media.Comment: 4 pages 3 figure
Focusing Light through Random Photonic Media by Binary Amplitude Modulation
We study the focusing of light through random photonic materials using
wavefront shaping. We explore a novel approach namely binary amplitude
modulation. To this end, the light incident to a random photonic medium is
spatially divided into a number of segments. We identify the segments that give
rise to fields that are out of phase with the total field at the intended focus
and assign these a zero amplitude, whereas the remaining segments maintain
their original amplitude. Using 812 independently controlled segments of light,
we find the intensity at the target to be 75 +/- 6 times enhanced over the
average intensity behind the sample. We experimentally demonstrate focusing of
light through random photonic media using both an amplitude only mode liquid
crystal spatial light modulator and a MEMS-based spatial light modulator. Our
use of Micro Electro-Mechanical System (MEMS)-based digital micromirror devices
for the control of the incident light field opens an avenue to high speed
implementations of wavefront shaping
Scattering Lens Resolves sub-100 nm Structures with Visible Light
The smallest structures that conventional lenses are able to optically
resolve are of the order of 200 nm. We introduce a new type of lens that
exploits multiple scattering of light to generate a scanning nano-sized optical
focus. With an experimental realization of this lens in gallium phosphide we
have succeeded to image gold nanoparticles at 97 nm optical resolution. Our
work is the first lens that provides a resolution in the nanometer regime at
visible wavelengths.Comment: 4 pages, 3 figure
Immobilization of invertase in conducting polymer matrices
Cataloged from PDF version of article.This paper reports a novel approach in the electrode immobilization of an enzyme, invertase, by
electrochemical polymerization of pyrrole in the presence of enzyme. The polypyrrolelinvertase and
polyamide/polypyrrole/invertase electrodes were constructed by the entrapment of enzyme in
conducting matrices during electrochemical polymerization of pyrrole. This study involves the
preparation and characterization of polypyrrole/invertase and polyamidelpolypyrrolelinvertase
electrodes under conditions compatible with the enzyme. It demonstrates the effects of pH and
temperature on the properties of enzyme electrode. Enzyme leakage tests were carried out during
reuse number studies. The preparation of enzyme electrodes was done in two different electrolyte/
solvent systems. The enzyme serves as a sucrose electrode and retains its activity for several
months. (c) 1997 Elsevier Science Limited. All rights reserve
Polypyrrole grafts with poly[(methyl methacrylate)-CO-(2-(N-pyrrolyl)ethyl methacrylate)]
Cataloged from PDF version of article.Conducting polymer grafts of pyrrole and poly[(methyl methacrylate)-co-(2-
(N-pyrrolyl) ethyl methacrylate)] containing 0.7% PEMA units were prepared
by potentiostatic anodic polymerization of pyrrole in different electrolytic
media. Grafting between copolymer and pyrrole was achieved in media where
tetrabutylammonium fluoroborate and sodium perchlorate were used as the
supporting electrolytes. Characterizations were made by using IT-IR, DSC,
TGA, SEM, CV, and elemental analysis. The conductivities of the resultant
polymers seemed to be in the order of pure polypyrrole prepared under the
same conditions. Copyright o 1997 Elsevier Scienc
Solutions of the Einstein-Dirac and Seiberg-Witten Monopole Equations
We present unique solutions of the Seiberg-Witten Monopole Equations in which
the U(1) curvature is covariantly constant, the monopole Weyl spinor consists
of a single constant component, and the 4-manifold is a product of two Riemann
surfaces of genuses p_1 and p_2. There are p_1 -1 magnetic vortices on one
surface and p_2 - 1 electric ones on the other, with p_1 + p_2 \geq 2 p_1 =
p_2= 1 being excluded). When p_1 = p_2, the electromagnetic fields are
self-dual and one also has a solution of the coupled euclidean
Einstein-Maxwell-Dirac equations, with the monopole condensate serving as
cosmological constant. The metric is decomposable and the electromagnetic
fields are covariantly constant as in the Bertotti-Robinson solution. The
Einstein metric can also be derived from a K\"{a}hler potential satisfying the
Monge-Amp\`{e}re equations.Comment: 22 pages. Rep. no: FGI-99-
Conducting polymer composites of polypyrrole and a poly(arylene ether ketone)
Electrically conducting composites of polypyrrole and a poly(arylene ether ketone) were synthesized by electroinitiated polymerization of pyrrole on a poly(arylene ether ketone)-coated platinum electrode. The electrolysis medium was water and p-toluene sulfonic acid. The conductivities of the composites were in the range 1-10 S/cm. The composites were characterized by scanning electron microscopy, Fourier transform infrared, and thermal analyses. The composites were found to be composed of bilayers which can be peeled into two free-standing polymer films. The solution side of the polypyrrole layer of the alloy film contains globular structures, whereas the other side is smoother
Conducting polymer composites of polypyrrole and polyimide
Polymeric composites with conductivities ranging from 1 to 10 S/cm were prepared by electrochemically polymerizing pyrrole in a matrix of polyimide. The polyimide/polypyrrole (PI/PPy) composites were characterized by SEM, TGA, FT-IR and electrical conductivity measurements. The cyclic voltammetry technique was used to determine the electroactivity and the electrochemical properties of PPy and PI/PPy. Copyright © 1996 by Marcel Dekker, Inc
Conducting polymer composites of polypyrrole and polyindene
Polypyrrole-polyindene composites were prepared via electrochemical methods. Two different approaches were utilized. In the first, the electro-initiated polymerization of indene on a platinum electrode was achieved at 2.0 V versus Ag/Ag+ in acetonitrile. Then the polyindene-coated electrode was used for the electrochemical polymerization of pyrrole at 1.0 V versus Ag/Ag+. In the second case, electrochemical coating of platinum electrode with polypyrrole at 1.0 V versus Ag/Ag+ was carried out and indene was polymerized on the conducting polymer at 2.0 V versus Ag/Ag+ in acetonitrile medium. The characterizations of these composites were done by FT-IR, scanning electron microscopy (SEM) and thermal gravimetric analysis (TGA). Electrical conductivities were evaluated by two-probe and four-probe methods
- …