26,535 research outputs found
The effect of low mass substructures on the Cusp lensing relation
It has been argued that the flux anomalies detected in gravitationally lensed
QSOs are evidence for substructures in the foreground lensing haloes. In this
paper we investigate this issue in greater detail focusing on the Cusp relation
which corresponds to images of a source located to the cusp of the inner
caustic curve. We use numerical simulations combined with a Monte Carlo
approach to study the effects of the expected power law distribution of
substructures within LCDM haloes on the multiple images.
Generally, the high number of anomalous flux ratios in the cusp
configurations is unlikely explained by 'simple' perturbers (subhaloes) inside
the lensing galaxy, either modeled by point masses or extended NFW subhaloes.
We considered in our analysis a mass range of 10^5-10^7 Msun for the subhaloes.
We also demonstrate that including the effects of the surrounding mass
distribution, such as other galaxies close to the primary lens, does not change
the results. We conclude that triple images of lensed QSOs do not show any
direct evidence for dark dwarf galaxies such as cold dark matter substructure.Comment: 10 pages, 19 figures, Effects of different subhalos concentrations
discussed, analysis improved, accepted by MNRA
Sub-arcsecond Morphology of Planetary Nebulae
Planetary nebulae (PNe) can be roughly categorized into several broad
morphological classes. The high quality images of PNe acquired in recent years,
however, have revealed a wealth of fine structures that preclude simplistic
models for their formation. Here we present narrow-band, sub-arcsecond images
of a sample of relatively large PNe that illustrate the complexity and variety
of small-scale structures. This is especially true for bipolar PNe, for which
the images reveal multi-polar ejections and, in some cases, suggest turbulent
gas motions. Our images also reveal the presence or signs of jet-like outflows
in several objects in which this kind of component has not been previously
reported.Comment: 7 pages, 7 figures, Accepted for publication in PAS
All-optical transport and compression of ytterbium atoms into the surface of a solid immersion lens
We present an all-optical method to load 174Yb atoms into a single layer of
an optical trap near the surface of a solid immersion lens which improves the
numerical aperture of a microscope system. Atoms are transported to a region 20
um below the surface using a system comprised by three optical dipole traps.
The "optical accordion" technique is used to create a condensate and compress
the atoms to a width of 120 nm and a distance of 1.8 um away from the surface.
Moreover, we are able to verify that after compression the condensate behaves
as a two-dimensional quantum gas.Comment: 5 pages, 5 figure
Management arrangements for accommodating nonrice crops in rice-based irrigation systems: Proceedings of the First Progress Review and Coordination Workshop of the Research Network on Irrigation Management for Crop Diversification in Rice-Based Systems (IMCD), held in Quezon City, the Philippines, 10-14 December 1990
Irrigation management / Crops / Diversification / Rice / Irrigated farming / Policy / Research / Sri Lanka / Bangladesh / India / Indonesia / Malaysia / Nepal / Philippines / Thailand
Observationally-Motivated Analysis of Simulated Galaxies
The spatial and temporal relationships between stellar age, kinematics, and
chemistry are a fundamental tool for uncovering the physics driving galaxy
formation and evolution. Observationally, these trends are derived using
carefully selected samples isolated via the application of appropriate
magnitude, colour, and gravity selection functions of individual stars;
conversely, the analysis of chemodynamical simulations of galaxies has
traditionally been restricted to the age, metallicity, and kinematics of
`composite' stellar particles comprised of open cluster-mass simple stellar
populations. As we enter the Gaia era, it is crucial that this approach
changes, with simulations confronting data in a manner which better mimics the
methodology employed by observers. Here, we use the \textsc{SynCMD} synthetic
stellar populations tool to analyse the metallicity distribution function of a
Milky Way-like simulated galaxy, employing an apparent magnitude plus gravity
selection function similar to that employed by the RAdial Velocity Experiment
(RAVE); we compare such an observationally-motivated approach with that
traditionally adopted - i.e., spatial cuts alone - in order to illustrate the
point that how one analyses a simulation can be, in some cases, just as
important as the underlying sub-grid physics employed.Comment: Accepted for publication in PoS (Proceedings of Science): Nuclei in
the Cosmos XIII (Debrecen, Jul 2014); 6 pages; 3 figure
Valence-bond theory of highly disordered quantum antiferromagnets
We present a large-N variational approach to describe the magnetism of
insulating doped semiconductors based on a disorder-generalization of the
resonating-valence-bond theory for quantum antiferromagnets. This method
captures all the qualitative and even quantitative predictions of the
strong-disorder renormalization group approach over the entire experimentally
relevant temperature range. Finally, by mapping the problem on a hard-sphere
fluid, we could provide an essentially exact analytic solution without any
adjustable parameters.Comment: 5 pages, 3 eps figure
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