582 research outputs found
Identification of the Microlens in Event MACHO-LMC-20
We report on the identification of the lens responsible for microlensing
event MACHO-LMC-20. As part of a \textit{Spitzer}/IRAC program conducting
mid-infrared follow-up of the MACHO Large Magellanic Cloud microlensing fields,
we discovered a significant flux excess at the position of the source star for
this event. These data, in combination with high resolution near-infrared
\textit{Magellan}/PANIC data has allowed us to classify the lens as an early M
dwarf in the thick disk of the Milky Way, at a distance of kpc. This
is only the second microlens to have been identified, the first also being a M
dwarf star in the disk. Together, these two events are still consistent with
the expected frequency of nearby stars in the Milky Way thin and thick disks
acting as lenses.Comment: 6 pages, 4 figures, submitted to ApJ Letter
Recent results on strangeness production from NA49
We present a summary of measurements of strange particles performed by the
experiment NA49 in inelastic p+p interactions, as well as semi-central C+C and
Si+Si, central Pb+Pb, and minimum bias Pb+Pb collisions in the energy range
= 6.3 - 17.3 GeV. New results on , and
production in minimum bias Pb+Pb collisions at = 8.7 and 17.3
are shown. Furthermore the strangeness enhancement factor at =
17.3 GeV is presented and compared to the results from NA57 and STAR. Energy
dependence of strange particle yields normalized to pion yields is presented.
New data on production are shown at = 17.3
GeV. Furthermore we present the energy dependence of and
fluctuations. The data are compared with model predictions.Comment: 9 pages, 7 figures, Submitted to J. Phys. G (Proceedings of the
International Conference on Strangeness in Quark Matter, Buzios, Rio de
Janeiro, Brazil, September 27 - October 2, 2009
Spitzer/IRAC Limits to Planetary Companions of Fomalhaut and epsilon Eridani
Fomalhaut and epsilon Eridani are two young, nearby stars that possess
extended debris disks whose structures suggest the presence of perturbing
planetary objects. With its high sensitivity and stable point spread function,
Spitzer/IRAC is uniquely capable of detecting cool, Jupiter-like planetary
companions whose peak emission is predicted to occur near 4.5 um. We report on
deep IRAC imaging of these two stars, taken at 3.6 and 4.5 um using subarray
mode and in all four channels in wider-field full array mode. Observations
acquired at two different telescope roll angles allowed faint surrounding
objects to be separated from the stellar diffraction pattern. No companion
candidates were detected at the reported position of Fomalhaut b with 3 sigma
model-dependent mass upper limits of 3 MJ (for an age of 200 Myr). Around
epsilon Eridani we instead set a limit of 4 and <1 MJ (1 Gyr model age) at the
inner and outer edge of the sub-millimeter debris ring, respectively. These
results are consistent with non-detections in recent near-infrared imaging
searches, and set the strongest limits to date on the presence of planets
outside epsilon Eridani sub-millimeter ring.Comment: Accepted by The Astrophysical Journal. Request electronic-only plates
to M. Marengo ([email protected]
Usability of Image Generation Platforms to Produce Oblique World Views
The interpretation of oblique aerial views in UAV operations is an important task, yet one that provides unique challenges. The human visual system is mal-adapted to visual perception from the air, especially when oblique views are involved. Hence, UAV operators have to be given training in the interpretation of oblique aerial visual stimuli. A novel way to train operators on how to accurately inspect and perceive oblique aerial images is to administer multiple trials of discrimination tasks for paired oblique images. In discrimination training, trainees view pairs of oblique aerial views and determine whether the images are taken from comparable positions, or contain similar information, etc. For such training, a number of images need to be developed. There are a number of ways that these training images can be generated: The methods differ in the amount of detail they provide and with respect to the resources they require for their development. This paper examines the feasibility and usability of different methods of image generation for aerial UAV imagery. Development of stimuli from sources such as aerial photographs, web-based models, and off-the-shelf simulations are discussed
Interacting particles at a metal-insulator transition
We study the influence of many-particle interaction in a system which, in the
single particle case, exhibits a metal-insulator transition induced by a finite
amount of onsite pontential fluctuations. Thereby, we consider the problem of
interacting particles in the one-dimensional quasiperiodic Aubry-Andre chain.
We employ the density-matrix renormalization scheme to investigate the finite
particle density situation. In the case of incommensurate densities, the
expected transition from the single-particle analysis is reproduced. Generally
speaking, interaction does not alter the incommensurate transition. For
commensurate densities, we map out the entire phase diagram and find that the
transition into a metallic state occurs for attractive interactions and
infinite small fluctuations -- in contrast to the case of incommensurate
densities. Our results for commensurate densities also show agreement with a
recent analytic renormalization group approach.Comment: 8 pages, 8 figures The original paper was splitted and rewritten.
This is the published version of the DMRG part of the original pape
Suppression of spatiotemporal chaos in the oscillatory CO oxidation on Pt(110) by focused laser light
Chemical turbulence in the oscillatory catalytic CO oxidation on Pt(110) is suppressed by means of focused laser light. The laser locally heats the platinum surface which leads to a local increase of the oscillation frequency, and to the formation of a pacemaker which emits target waves. These waves slowly entrain the medium and suppress the spatiotemporal chaos present in the absence of laser light. Our experimental results are confirmed by a detailed numerical analysis of one- and two-dimensional media using the Krischer-Eiswirth-Ertl model for CO oxidation on Pt110. Different control regimes are identified and the dispersion relation of the system is determined using the pacemaker as an externally tunable wave source
Deciphering the genome structure and paleohistory of _Theobroma cacao_
We sequenced and assembled the genome of _Theobroma cacao_, an economically important tropical fruit tree crop that is the source of chocolate. The assembly corresponds to 76% of the estimated genome size and contains almost all previously described genes, with 82% of them anchored on the 10 _T. cacao_ chromosomes. Analysis of this sequence information highlighted specific expansion of some gene families during evolution, for example flavonoid-related genes. It also provides a major source of candidate genes for _T. cacao_ disease resistance and quality improvement. Based on the inferred paleohistory of the T. cacao genome, we propose an evolutionary scenario whereby the ten _T. cacao_ chromosomes were shaped from an ancestor through eleven chromosome fusions. The _T. cacao_ genome can be considered as a simple living relic of higher plant evolution
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