13,328 research outputs found
Quantum Emitters near Layered Plasmonic Nanostructures: Decay Rate Contributions
We introduce a numerical framework for calculating decay rate contributions
when excited two-level quantum emitters are located near layered plasmonic
nanostructures, particularly emphasizing the case of plasmonic nanostructures
atop metal substrates where three decay channels exist: free space radiation,
Ohmic losses, and excitation of surface plasmon polaritons (SPPs). The
calculation of decay rate contributions is based on Huygen's equivalence
principle together with a near-field to far-field transformation of the local
electric field, thereby allowing us to discern the part of the electromagnetic
field associated with free propagating waves rather than SPPs. The methodology
is applied to the case of an emitter inside and near a gap-plasmon resonator,
emphasizing strong position and orientation dependencies of the total decay
rate, contributions of different decay channels, radiation patterns, and
directivity of SPP excitation
How Efficient is Rotational Mixing in Massive Stars ?
The VLT-Flames Survey for Massive Stars (Evans05,Evans06) provides recise
measurements of rotational velocities and nitrogen surface abundances of
massive stars in the Magellanic Clouds. Specifically, for the first time, such
abundances have been estimated for stars with significant rotational
velocities. This extraordinary data set gives us the unique possibility to
calibrate rotationally and magnetically induced mixing processes. Therefore, we
have computed a grid of stellar evolution models varying in mass, initial
rotational velocity and chemical composition. In our models we find that
although magnetic fields generated by the Spruit-Taylor dynamo are essential to
understand the internal angular momentum transport (and hence the rotational
behavior), the corresponding chemical mixing must be neglected to reproduce the
observations. Further we show that for low metallicities detailed initial
abundances are of prime importance, as solar-scaled abundances may result in
significant calibration errors.Comment: To appear in the proceedings of "First Stars III", Santa Fe, New
Mexico, July 16-20, 2007, 3 pages, 3 figure
How Efficient is Rotational Mixing in Massive Stars ?
The VLT-Flames Survey for Massive Stars (Evans05,Evans06) provides recise
measurements of rotational velocities and nitrogen surface abundances of
massive stars in the Magellanic Clouds. Specifically, for the first time, such
abundances have been estimated for stars with significant rotational
velocities. This extraordinary data set gives us the unique possibility to
calibrate rotationally and magnetically induced mixing processes. Therefore, we
have computed a grid of stellar evolution models varying in mass, initial
rotational velocity and chemical composition. In our models we find that
although magnetic fields generated by the Spruit-Taylor dynamo are essential to
understand the internal angular momentum transport (and hence the rotational
behavior), the corresponding chemical mixing must be neglected to reproduce the
observations. Further we show that for low metallicities detailed initial
abundances are of prime importance, as solar-scaled abundances may result in
significant calibration errors.Comment: To appear in the proceedings of "First Stars III", Santa Fe, New
Mexico, July 16-20, 2007, 3 pages, 3 figure
Gradient metasurfaces: a review of fundamentals and applications
In the wake of intense research on metamaterials the two-dimensional
analogue, known as metasurfaces, has attracted progressively increasing
attention in recent years due to the ease of fabrication and smaller insertion
losses, while enabling an unprecedented control over spatial distributions of
transmitted and reflected optical fields. Metasurfaces represent optically thin
planar arrays of resonant subwavelength elements that can be arranged in a
strictly or quasi periodic fashion, or even in an aperiodic manner, depending
on targeted optical wavefronts to be molded with their help. This paper reviews
a broad subclass of metasurfaces, viz. gradient metasurfaces, which are devised
to exhibit spatially varying optical responses resulting in spatially varying
amplitudes, phases and polarizations of scattered fields. Starting with
introducing the concept of gradient metasurfaces, we present classification of
different metasurfaces from the viewpoint of their responses, differentiating
electrical-dipole, geometric, reflective and Huygens' metasurfaces. The
fundamental building blocks essential for the realization of metasurfaces are
then discussed in order to elucidate the underlying physics of various physical
realizations of both plasmonic and purely dielectric metasurfaces. We then
overview the main applications of gradient metasurfaces, including waveplates,
flat lenses, spiral phase plates, broadband absorbers, color printing,
holograms, polarimeters and surface wave couplers. The review is terminated
with a short section on recently developed nonlinear metasurfaces, followed by
the outlook presenting our view on possible future developments and
perspectives for future applications.Comment: Accepted for publication in Reports on Progress in Physic
Plasmonic metagratings for simultaneous determination of Stokes parameters
Measuring light's state of polarization is an inherently difficult problem,
since the phase information between orthogonal polarization states is typically
lost in the detection process. In this work, we bring to the fore the
equivalence between normalized Stokes parameters and diffraction contrasts in
appropriately designed phase-gradient birefringent metasurfaces and introduce a
concept of all-polarization birefringent metagratings. The metagrating, which
consists of three interweaved metasurfaces, allows one to easily analyze an
arbitrary state of light polarization by conducting simultaneous (i.e.,
parallel) measurements of the correspondent diffraction intensities that reveal
immediately the Stokes parameters of the polarization state under examination.
Based on plasmonic metasurfaces operating in reflection at the wavelength of
800 nm, we design and realize phase-gradient birefringent metasurfaces and the
correspondent metagrating, while experimental characterization of the
fabricated components convincingly demonstrates the expected functionalities.
We foresee the use of the metagrating in compact polarimetric setups at any
frequency regime of interest
Transgendered in Alaska: Navigating the Changing Legal Landscape for Change in Gender Petitions
Background: Detecting intracellular bacterial symbionts can be challenging when they persist at very low densities. Wolbachia, a widespread bacterial endosymbiont of invertebrates, is particularly challenging. Although it persists at high titers in many species, in others its densities are far below the detection limit of classic end-point Polymerase Chain Reaction (PCR). These low-titer infections can be reliably detected by combining PCR with DNA hybridization, but less elaborate strategies based on end-point PCR alone have proven less sensitive or less general. Results: We introduce a multicopy PCR target that allows fast and reliable detection of A-supergroup Wolbachia -even at low infection titers -with standard end-point PCR. The target is a multicopy motif (designated ARM: A-supergroup repeat motif) discovered in the genome of wMel (the Wolbachia in Drosophila melanogaster). ARM is found in at least seven other Wolbachia A-supergroup strains infecting various Drosophila, the wasp Muscidifurax and the tsetse fly Glossina. We demonstrate that end-point PCR targeting ARM can reliably detect both high-and low-titer Wolbachia infections in Drosophila, Glossina and interspecific hybrids. Conclusions: Simple end-point PCR of ARM facilitates detection of low-titer Wolbachia A-supergroup infections. Detecting these infections previously required more elaborate procedures. Our ARM target seems to be a general feature of Wolbachia A-supergroup genomes, unlike other multicopy markers such as insertion sequences (IS)
Beam-Size Invariant Spectropolarimeters Using Gap-Plasmon Metasurfaces
Metasurfaces enable exceptional control over the light with surface-confined
planar components, offering the fascinating possibility of very dense
integration and miniaturization in photonics. Here, we design, fabricate and
experimentally demonstrate chip-size plasmonic spectropolarimeters for
simultaneous polarization state and wavelength determination.
Spectropolarimeters, consisting of three gap-plasmon phase-gradient
metasurfaces that occupy 120{\deg} circular sectors each, diffract normally
incident light to six predesigned directions, whose azimuthal angles are
proportional to the light wavelength, while contrasts in the corresponding
diffraction intensities provide a direct measure of the incident polarization
state through retrieval of the associated Stokes parameters. The
proof-of-concept 96-{\mu}m-diameter spectropolarimeter operating in the
wavelength range of 750-950nm exhibits the expected polarization selectivity
and high angular dispersion. Moreover, we show that, due to the circular-sector
design, polarization analysis can be conducted for optical beams of different
diameters without prior calibration, demonstrating thereby the beam-size
invariant functionality. The proposed spectropolarimeters are compact,
cost-effective, robust, and promise high-performance real-time polarization and
spectral measurements
Hyperpolarizability effects in a Sr optical lattice clock
We report the observation of the higher order frequency shift due to the
trapping field in a Sr optical lattice clock. We show that at the magic
wavelength of the lattice, where the first order term cancels, the higher order
shift will not constitute a limitation to the fractional accuracy of the clock
at a level of . This result is achieved by operating the clock at
very high trapping intensity up to kW/cm and by a specific study of
the effect of the two two-photon transitions near the magic wavelength
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