2,275 research outputs found
Many-body wave scattering by small bodies
Scattering problem by several bodies, small in comparison with the
wavelength, is reduced to linear algebraic systems of equations, in contrast to
the usual reduction to some integral equations
Phase mapping of ultrashort pulses in bimodal photonic structures: A window on local group velocity dispersion
The amplitude and phase evolution of ultrashort pulses in a bimodal waveguide structure has been studied with a time-resolved photon scanning tunneling microscope (PSTM). When waveguide modes overlap in time intriguing phase patterns are observed. Phase singularities, arising from interference between different modes, are normally expected at equidistant intervals determined by the difference in effective index for the two modes. However, in the pulsed experiments the distance between individual singularities is found to change not only within one measurement frame, but even depends strongly on the reference time. To understand this observation it is necessary to take into account that the actual pulses generating the interference signal change shape upon propagation through a dispersive medium. This implies that the spatial distribution of phase singularities contains direct information on local dispersion characteristics. At the same time also the mode profiles, wave vectors, pulse lengths, and group velocities of all excited modes in the waveguide are directly measured. The combination of these parameters with an analytical model for the time-resolved PSTM measurements shows that the unique spatial phase information indeed gives a direct measure for the group velocity dispersion of individual modes. As a result interesting and useful effects, such as pulse compression, pulse spreading, and pulse reshaping become accessible in a local measuremen
Nanorod optical antennas for dipolar transitions
Optical antennas link objects to light. Here, we analyze metal nanorod
antennas as cavities with variable reflection coefficients to derive the
interaction of dipolar transitions with radiation through the antenna modes.
The presented analytical model accurately describes the complete emission
process, and is summarized in a phase-matching equation. We show how antenna
modes evolve as they become increasingly more bound, i.e. plasmonic. The
results illustrate why efficient antennas should not be too plasmonic, and how
subradiant even modes can evolve into weakly-interacting dark modes. Our
description is valid for the interaction of nanorods with light in general, and
is thus widely applicable.Comment: 10 pages, 4 figures, submitte
A monopole antenna at optical frequencies: single-molecule near-field measurements
We present a monopole antenna for optical frequencies (~600 THz) and discuss near-field measurements with single fluorescent molecules as a technique to characterize such antennas. The similarities and differences between near-field antenna measurements at optical and radio frequencies are discussed in detail. Two typical antenna properties, polarization selectivity and resonances, are studied for the optical monopole by direct near-field measurements and finite integration technique calculations. The antenna is driven by the local field of a sub-wavelength aperture. This gives rise to a dependence of the antenna response on the orientation of the local field vector, in an analogous way to the polarization selectivity of linear wire antennas. The antenna resonances are studied by varying the antenna length. Typical monopole resonances are demonstrated. The finite conductivity of metals at optical frequencies (in combination with the antenna radius) causes the wavelength of the surface charge density oscillation (surface plasmon polariton) along the antenna to be shortened in comparison to the free space wavelength. As a result, resonances for the optical monopole antenna occur at much shorter relative lengths than for conventional radio monopole antennas\ud
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A new and versatile method for the successful conversion of AFLP-TM markers into simple single locus markers
Genetic markers can efficiently be obtained by using amplified fragment length polymorphism (AFLP) fingerprinting because no prior information on DNA sequence is required. However, the conversion of AFLP markers from complex fingerprints into simple single locus assays is perceived as problematic because DNA sequence information is required for the design of new locus-specific PCR primers. In addition, single locus polymorphism (SNP) information is required to design an allele-specific assay. This paper describes a new and versatile method for the conversion of AFLP markers into simple assays. The protocol presented in this paper offers solutions for frequently occurring pitfalls and describes a procedure for the identification of the SNP responsible for the AFLP. By following this approach, a high success rate for the conversion of AFLP markers into locus-specific markers was obtained
Optical Albedo Theory of Strongly-Irradiated Giant Planets: The Case of HD 209458b
We calculate a new suite of albedo models for close-in extrasolar giant
planets and compare with the recent stringent upper limit for HD 209458b of
Rowe et al. using MOST. We find that all models without scattering clouds are
consistent with this optical limit. We explore the dependence on wavelength and
waveband, metallicity, the degree of heat redistribution, and the possible
presence of thermal inversions and find a rich diversity of behaviors.
Measurements of transiting extrasolar giant planets (EGPs) at short wavelengths
by MOST, Kepler, and CoRoT, as well as by proposed dedicated multi-band
missions, can complement measurements in the near- and mid-IR using {\it
Spitzer} and JWST. Collectively, such measurements can help determine
metallicity, compositions, atmospheric temperatures, and the cause of thermal
inversions (when they arise) for EGPs with a broad range of radii, masses,
degrees of stellar insolation, and ages. With this paper, we reappraise and
highlight the diagnostic potential of albedo measurements of hot EGPs shortward
of 1.3 m.Comment: 6 pages, 1 table, 1 color figure; accepted to the Astrophysical
Journa
An Interacting Galaxy System Along a Filament in a Void
Cosmological voids provide a unique environment for the study of galaxy
formation and evolution. The galaxy population in their interior have
significantly different properties than average field galaxies. As part of our
Void Galaxy Survey (VGS), we have found a system of three interacting galaxies
(VGS_31) inside a large void. VGS_31 is a small elongated group whose members
are embedded in a common HI envelope. The HI picture suggests a filamentary
structure with accretion of intergalactic cold gas from the filament onto the
galaxies. We present deep optical and narrow band H_alpha data, optical
spectroscopy, near-UV and far-UV GALEX and CO(1-0) data. We find that one of
the galaxies, a Markarian object, has a ring-like structure and a tail evident
both in optical and HI. While all three galaxies form stars in their central
parts, the tail and the ring of the Markarian object are devoid of star
formation. We discuss these findings in terms of a gravitational interaction
and ongoing growth of galaxies out of a filament. VGS_31 is one of the first
observed examples of a filamentary structure in a void. It is an important
prototype for understanding the formation of substructure in a void. This
system also shows that the galaxy evolution in voids can be as dynamic as in
high density environments.Comment: 17 pages, 8 figures, accepted for publication in A
Benchmarking Burgerzaken : een empirisch onderzoek naar de kostendoelmatigheid van burgerzaken
De noodzaak van productiviteitsgroei in de publieke sector is nu groter dan ooit. Aan deze noodzaak liggen twee ontwikkelingen ten grondslag. In de eerste plaats staan de financiën van de publieke sector onder druk als gevolg van bezuinigingen. In de tweede plaats worden er op de langere termijn knelpunten op de arbeidsmarkt verwacht als gevolg van vergrijzing en ontgroening van de bevolking. In de marksector dwingen concurrentieoverwegingen organisaties ertoe om voortdurend aandacht te hebben voor productiviteitsverbetering en deze waar mogelijk te realiseren. In de publieke sector ontbreken de prikkels van de markt en lijken productiviteitsverbeteringen moeizaam tot stand te komen
KK246, a dwarf galaxy with extended H I disk in the Local Void
We have found that KK 246, the only confirmed galaxy located within the
nearby Tully Void, is a dwarf galaxy with an extremely extended H I disk and
signs of an H I cloud with anomalous velocity. It also exhibits clear
misalignment between the kinematical major and minor axes, indicative of an
oval distortion, and a general misalignment between the H I and optical major
axes. We measure a H I mass of 1.05 +- 0.08 x 10^8 M_sun, and a H I extent 5
times that of the stellar disk, one of the most extended H I disks known. We
estimate a dynamical mass of 4.1 x 10^9 M_sun, making this also one of the
darkest galaxies known, with a mass-to-light ratio of 89. The relative
isolation and extreme underdense environment make this an interesting case for
examining the role of gas accretion in galaxy evolution.Comment: 15 pages, 8 figures, 2 tables, accepted for publication in A
The non-linguistic status of the Symmetry Condition in signed languages: Evidence from a comparison of signs and speechaccompanying representational gestures
Since Battison (1978), it has been noted in many signed languages that the Symmetry Condition constrains the form of two-handed signs in which two hands move independently. The Condition states that the form features (e.g., the handshapes and movements) of the two hands are 'symmetrical'. The Symmetry Condition has been regarded in the literature as a part of signed language phonology. In this study, we examine the linguistic status of the Symmetry Condition by comparing the degree of symmetry in signs from Sign Language of the Netherlands and speech-accompanying representational gestures produced by Dutch speakers. Like signed language, such gestures use hand movements to express concepts, but they do not constitute a linguistic system in their own right. We found that the Symmetry Condition holds equally well for signs and spontaneous gestures. This indicates that this condition is a general cognitive constraint, rather than a constraint specific to language. We suggest that the Symmetry Condition is a manifestation of the mind having one active 'mental articulator' when expressing a concept with hand movement
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