452 research outputs found
Cut-wire-pair structures as two-dimensional magnetic metamaterials
We study numerically and experimentally magnetic metamaterials based on
cut-wire pairs instead of split-ring resonators. The cut-wire pair planar
structure is extended in order to create a truly two-dimensional metamaterial
suitable for scaling to optical frequencies. We fabricate the cut-wire
metamaterial operating at microwave frequencies with lattice spacing around 10%
of the free-space wavelength, and find good agreement with direct numerical
simulations. Unlike the structures based on split-ring resonators, the
nearest-neighbor coupling in cut-wire pairs can result in a magnetic stop-band
with propagation in the transverse direction
Molecular interconversion behaviour in comprehensive two-dimensional gas chromatography
Comprehensive two-dimensional gas chromatography (GC x GC) is shown to provide information on dynamic molecular behaviour (interconversion), with the interconversion process occurring on both columns in the coupled-column experiment. The experiment requires suitable adjustment of both experimental conditions and relative dimensions of each of the columns. In this case, a longer column than normally employed in GC x GC allows sufficient retention duration on the second column, which permits the typical plateau-shape recognised for the interconversion process to be observed. The extent of interconversion depends on prevailing temperature, retention time, and the phase type. Polyethylene glycol-based phases were found to result in high interconversion kinetics, although terephthalic acid-terminated polyethylene glycol had a lesser extent of interconversion. Much less interconversion was seen for phenyl-methylpolysiloxane and cyclodextrin phases. This suggests that for the oximes, interconversion largely occurs in the stationary phase. Examples of different extents of interconversion in both dimensions are shown, including peak coalescence on the first column with little interconversion on the second column
Ideal and nonideal electromagnetic cloaks
We employ the analytical results for the spatial transformation of the
electromagnetic fields to obtain and analyze explicit expressions for the
structure of the electromagnetic fields in invisibility cloaks, beam splitters,
and field concentrators. We study the efficiency of nonideal electromagnetic
cloaks and discuss the effect of scattering losses on the cloak invisibility.Comment: 4 pages, 2 figure
Transformation Optics for Plasmonics
A new strategy to control the flow of surface plasmon polaritons at metallic
surfaces is presented. It is based on the application of the concept of
Transformation Optics to devise the optical parameters of the dielectric medium
placed on top of the metal surface. We describe the general methodology for the
design of Transformation-Optical devices for surface plasmons and analyze, for
proof-of-principle purposes, three representative examples with different
functionalities: a beam shifter, a cylindrical cloak and a ground-plane cloak.Comment: 15 pages, 3 figure
Deep subcutaneous application of poly-L-lactic acid as a filler for facial lipoatrophy in HIV-infected patients
Introduction: Facial lipoatrophy is a crucial problem of HIV-infected patients undergoing highly active antiretroviral therapy (HAART). Poly-L-lactic acid (PLA), provided as New-Fill(R)/Sculptra(TM), is known as one possible treatment option. In 2004 PLA was approved by the FDA as Sculptra(TM) for the treatment of lipoatrophy of the face in HIV-infected patients. While the first trials demonstrated relevant efficacy, this was to some extent linked to unwanted effects. As the depth of injection was considered relevant in this context, the application modalities of the preparation were changed. The preparation was to be injected more deeply into subcutaneous tissue, after increased dilution. Material and Methods: To test this approach we performed a pilot study following the new recommendations in 14 patients. Results: While the efficacy turned out to be about the same, tolerability was markedly improved. The increase in facial dermal thickness was particularly obvious in those patients who had suffered from lipoatrophy for a comparatively small period of time. Conclusion: With the new recommendations to dilute PLA powder and to inject it into the deeper subcutaneous tissue nodule formation is a minor problem. However, good treatment results can only be achieved if lipoatrophy is not too intense; treatment intervals should be about 2 - 3 weeks. Copyright (C) 2005 S. Karger AG, Basel
General Relativity in Electrical Engineering
In electrical engineering metamaterials have been developed that offer
unprecedented control over electromagnetic fields. Here we show that general
relativity lends the theoretical tools for designing devices made of such
versatile materials. Given a desired device function, the theory describes the
electromagnetic properties that turn this function into fact. We consider media
that facilitate space-time transformations and include negative refraction. Our
theory unifies the concepts operating behind the scenes of perfect invisibility
devices, perfect lenses, the optical Aharonov-Bohm effect and electromagnetic
analogs of the event horizon, and may lead to further applications
A comparative study of semiconductor-based plasmonic metamaterials
Recent metamaterial (MM) research faces several problems when using
metal-based plasmonic components as building blocks for MMs. The use of
conventional metals for MMs is limited by several factors: metals such as gold
and silver have high losses in the visible and near-infrared (NIR) ranges and
very large negative real permittivity values, and in addition, their optical
properties cannot be tuned. These issues that put severe constraints on the
device applications of MMs could be overcome if semiconductors are used as
plasmonic materials instead of metals. Heavily doped, wide bandgap oxide
semiconductors could exhibit both a small negative real permittivity and
relatively small losses in the NIR. Heavily doped oxides of zinc and indium
were already reported to be good, low loss alternatives to metals in the NIR
range. Here, we consider these transparent conducting oxides (TCOs) as
alternative plasmonic materials for many specific applications ranging from
surface-plasmon-polariton waveguides to MMs with hyperbolic dispersion and
epsilon-near-zero (ENZ) materials. We show that TCOs outperform conventional
metals for ENZ and other MM-applications in the NIR.Comment: 16 pages, 7 figure
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