2,529 research outputs found
Nanophotonic boost of intermolecular energy transfer
We propose a scheme for efficient long-range energy transfer between two
distant light emitters separated by more than one wavelength of light, i.e.
much beyond the classical Forster radius. A hybrid nanoantenna-waveguide system
mediates the transmission of energy, showing enhancements up to 10^8 as
compared to vacuum. Our model shows how energy transfer in nanostructured media
can be boosted, beyond the simple donor Purcell enhancement, and in particular
for large donor-acceptor separations. The scheme we propose connects realistic
emitters and could lead to practical on-chip implementations.Comment: 9 pages, 4 figure
The Westerbork HI Survey of Spiral and Irregular Galaxies I. HI Imaging of Late-type Dwarf Galaxies
Neutral hydrogen observations with the Westerbork Synthesis Radio Telescope
are presented for a sample of 73 late-type dwarf galaxies. These observations
are part of the WHISP project (Westerbork HI Survey of Spiral and Irregular
Galaxies). Here we present HI maps, velocity fields, global profiles and radial
surface density profiles of HI, as well as HI masses, HI radii and line widths.
For the late-type galaxies in our sample, we find that the ratio of HI extent
to optical diameter, defined as 6.4 disk scale lengths, is on average 1.8+-0.8,
similar to that seen in spiral galaxies. Most of the dwarf galaxies in this
sample are rich in HI, with a typical M_HI/L_B of 1.5. The relative HI content
M_HI/L_R increases towards fainter absolute magnitudes and towards fainter
surface brightnesses. Dwarf galaxies with lower average HI column densities
also have lower average optical surface brightnesses. We find that lopsidedness
is as common among dwarf galaxies as it is in spiral galaxies. About half of
the dwarf galaxies in our sample have asymmetric global profiles, a third has a
lopsided HI distribution, and about half shows signs of kinematic lopsidedness.Comment: Accepted for publication in A&A. 18 pages. 39 MB version with all
figures is available http://www.robswork.net/publications/WHISPI.ps.g
Fast outflow of neutral and ionized gas from the radio galaxy 3C 293
We detect a fast outflow of neutral and ionized gas with velocities up to
about 1000 km/s from the central region of radio galaxy 3C 293. With optical
spectroscopy we locate the bulk of the ionized gas outflow at the position of a
bright radio hot-spot in the inner radio jet, about 1 kpc east of the nucleus.
Given the presence of large amounts of cold gas and the distorted morphology of
the radio jet in this region, we argue that the ISM is pushed out by a severe
interaction with the radio plasma. The similarity of the outflow of HI with the
ionized gas outflow that we see at the position of the radio hot-spot suggests
that despite the high energies involved in the jet-ISM interaction, part of the
gas stays, or becomes again, neutral. In this paper we also present the
detection of HI emission in three nearby companions of 3C 293.Comment: 8 pages, 4 figures. Proceedings of the "Extra-planar Gas" conference,
Dwingeloo, the Netherlands, June 7-11, 2004. To appear in ASP Conference
Series, ed. R. Brau
Using negative detections to estimate source finder reliability
We describe a simple method to determine the reliability of source finders
based on the detection of sources with both positive and negative total flux.
Under the assumption that the noise is symmetric and that real sources have
positive total flux, negative detections can be used to assign to each positive
detection a probability of being real. We discuss this method in the context of
upcoming, interferometric HI surveys.Comment: Accepted for publication on the 2012 PASA source finding special
issu
IC 4200: a gas-rich early-type galaxy formed via a major merger
We present the result of radio and optical observations of the S0 galaxy IC
4200. We find that the galaxy hosts 8.5 billion solar masses of HI rotating on
a ~90 deg warped disk extended out to 60 kpc from the centre of the galaxy.
Optical spectroscopy reveals a simple-stellar-population-equivalent age of 1.5
Gyr in the centre of the galaxy and V- and R-band images show stellar shells.
Ionised gas is observed within the stellar body and is kinematically decoupled
from the stars and characterised by LINER-like line ratios.We interpret these
observational results as evidence for a major merger origin of IC 4200, and
date the merger back to 1-3 Gyr ago.Comment: Accepted for publication in Astronomy & Astrophysics; 18 pages, 13
figures; the tables of Appendix C can be downloaded at
http://www.astro.rug.nl/~pserra/IC420
Cooperative scattering and radiation pressure force in dense atomic clouds
We consider the collective scattering by a cloud of two-level atoms
driven by an uniform radiation field. Dense atomic clouds can be described by a
continuous density and the problem reduces to deriving the spectrum of the
atom-atom coupling operator. For clouds much larger than the optical
wavelength, the spectrum is treated as a continuum, and analytical expressions
for several macroscopic quantities, such as scattered radiation intensity and
radiation pressure force, are derived. The analytical results are then compared
to the exact -body solution and with those obtained assuming a symmetric
timed Dicke state. In contrast with the symmetric timed Dicke state, our
calculations takes account of the back action of the atoms on the driving field
leading to phase shifts due to the finite refraction of the cloud
Asymmetric Synthesis of New Chiral Europium N,N'-Disuccinate Complexes:Shift Reagents for Aqueous Solutions and Application in the Enantiomeric Excess Determination of Amino Acids
The synthesis of new chiral N,N'-disuccinate ligands (R,R)-8, (R,R)-9, and (S,S)-10 from (5R)- or (SS)-(menthyloxy)-2(5H)-furanone is described. These ligands, after complexation with EuCl3.6H(2)O, are highly suitable as chiral shift reagents for the enantiomeric excess determination of amino acids and alpha-alkylated amino acids in aqueous solutions. Resolution experiments using various amino acids and their derivatives and a study of the pH dependency of the induced diastereomeric shift differences are included
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