2,147 research outputs found
The Chemistry of Selected Food Stuffs and Condiments
This 17 page thesis discusses the composition of various foods, including milk, butter, bread and wine
Harpacticoid copepods associated with <i>Spartina alterniflora</i> culms from the marshes of Cocodrie, Louisiana (Crustacea, Copepoda)
Seven harpacticoid copepods have been found living on the lower parts of Spartina alterniflora culms, from Cocodrie marshes in Louisiana (U.S.A.). This contribution deals exclusively with the systematics of these species. Mesochra wolskii Jakubisiak is redescribed and a new key to the species of the genus is given. M. neotropica Jakobi is allocated to the genus Amphibiperita n. gen. and is redescribed and discussed in detail. A new laophontid species, F. mangalis n. sp. is described and placed together with Laophonte chathamensis Sars in the genus Folioquinpesn. gen. Some amendations on the description of Schizopera knabeni Lang are given and the peculiar shape of the furcal setae of Nannopus palustris Brady is illustrated
Discovery of a candidate quiescent low-mass X-ray binary in the globular cluster NGC 6553
This paper reports the search for quiescent low-mass X-ray binaries (qLMXBs)
in the globular cluster (GC) NGC 6553 using an XMM-Newton observation designed
specifically for that purpose. We spectrally identify one candidate qLMXB in
the core of the cluster, based on the consistency of the spectrum with a
neutron star H-atmosphere model at the distance of NGC 6553. Specifically, the
best-fit radius found using the three XMM European Photon Imaging Camera
spectra is R_NS=6.3(+2.3)(-0.8) km (for M_NS=1.4 Msun) and the best-fit
temperature is kTeff=136 (+21)(-34) eV. Both physical parameters are in
accordance with typical values of previously identified qLMXBs in GC and in the
field, i.e., R_NS~5-20 km and kTeff~50-150 eV. A power-law (PL) component with
a photon index Gamma=2.1(+0.5)(-0.8) is also required for the spectral fit and
contributes to ~33% of the total flux of the X-ray source. A detailed analysis
supports the hypothesis that the PL component originates from nearby sources in
the core, unresolved with XMM. The analysis of an archived Chandra observation
provides marginal additional support to the stated hypothesis. Finally, a
catalog of all the sources detected within the XMM field of view is presented
here.Comment: 10 pages, 5 figures, 3 tables. Accepted to ApJ (to be published in
August 2011
A Method for Distinguishing Between Transiently Accreting Neutron Stars and Black Holes, in Quiescence
We fit hydrogen atmosphere models to the X-ray data for four neutron stars
(three from a previous paper, plus 4U 2129+47) and six black hole candidates
(A0620-00, GS 2000+25, GS 1124-68, GS 2023+33, GRO J1655-40, and GRO J0422+32).
While the neutron stars are similar in their intrinsic X-ray spectra (similar
effective temperatures and emission area radii ~10 km), the spectra of two
black hole candidates are significantly different, and the spectra of the
remaining four are consistent with a very large parameter space that includes
the neutron stars. The spectral differences between the neutron stars and black
hole candidates favors the interpretation that the quiescent neutron star
emission is predominantly thermal emission from the neutron star surface. Our
work suggests that an X-ray spectral comparison in quiescence provides an
additional means for distinguishing between neutron stars and black holes. The
faint X-ray sources in globular clusters are also a class of objects which can
be investigated in this manner.Comment: 33 pages, including 3 ps figures, LaTeX. To appear in Ap
Chandra Observation of Quiescent Low-Mass X-ray Binaries in the Globular Cluster NGC 6304
This paper presents the analysis of candidate quiescent low mass xray binarie
(qLMXBs) observed during a short Chandra/ACIS observation of the globular
cluster (GC) NGC 6304. Two out of the three candidate qLMXBs of this cluster,
XMMU 171433-292747 and XMMU 171421-292917, lie within the field of view. This
permits comparison with the discovery observation of these sources. The one in
the GC core -- XMMU 171433-292747 -- is spatially resolved into two separate
X-ray sources, one of which is consistent with a pure H-atmosphere qLMXB, and
the other is an X-ray power-law spectrum source. These two spectral components
separately account for those observed from XMMU 171433-292747 in its discovery
observation. We find that the observed flux and spectral parameters of the
H-atmosphere spectral components are consistent with the previous observation,
as expected from a qLMXB powered by deep crustal heating. XMMU 171421-292917
also has neutron star atmosphere spectral parameters consistent with those in
the XMM-Newton observation and the observed flux has decreased by a factor
0.54^{+0.30}_{-0.24}.Comment: Accepted for publication in ApJ. 6 pages, 1 figur
Recommended from our members
The influence of contextual reward statistics on risk preference
Decision theories mandate that organisms should adjust their behaviour in the light of the contextual reward statistics. We tested this notion using a gambling choice task involving distinct contexts with different reward distributions. The best fitting model of subjects' behaviour indicated that the subjective values of options depended on several factors, including a baseline gambling propensity, a gambling preference dependent on reward amount, and a contextual reward adaptation factor. Combining this behavioural model with simultaneous functional magnetic resonance imaging we probed neural responses in three key regions linked to reward and value, namely ventral tegmental area/substantia nigra (VTA/SN), ventromedial prefrontal cortex (vmPFC) and ventral striatum (VST). We show that activity in the VTA/SN reflected contextual reward statistics to the extent that context affected behaviour, activity in the vmPFC represented a value difference between chosen and unchosen options while VST responses reflected a non-linear mapping between the actual objective rewards and their subjective value. The findings highlight a multifaceted basis for choice behaviour with distinct mappings between components of this behaviour and value sensitive brain regions
Millimeter-wave diode-grid phase shifters
Monolithic diode grids have been fabricated on 2-cm square gallium-arsenide wafers with 1600 Schottky-barrier varactor diodes. Shorted diodes are detected with a liquid-crystal technique, and the bad diodes are removed with an ultrasonic probe. A small-aperture reflectometer that uses wavefront division interference was developed to measure the reflection coefficient of the grids. A Phase shift of 70° with a 7-dB loss was obtained at 93 GHz when the bias on the diode grid was changed from -3 V to 1 V. A simple transmission-line grid model, together with the measured low-frequency parameters for the diodes, was shown to predict the measured performance over the entire capacitive bias range of the diodes, as well as over the complete reactive tuning range provided by a reflector behind the grid, and over a wide range of frequencies form 33 GHz to 141 GHz. This shows that the transmission-line model and the measured low-frequency diode parameters can be used to design an electronic beam-steering array and to predict its performance. An electronic beam-steering array made of a pair of grids using state-of-the-art diodes with 5-Ω series resistances would have a loss of 1.4 dB at 90 GHz
Millimeter-Wave Diode-Grid Frequency Doubler
Monolithic diode grid were fabricated on 2-cm^2 gallium-arsenide wafers in a proof-of-principle test of a quasi-optical varactor millimeter-wave frequency multiplier array concept. An equivalent circuit model based on a transmission-line analysis of plane wave illumination was applied to predict the array performance. The doubler experiments were performed under far-field illumination conditions. A second-harmonic conversion efficiency of 9.5% and output powers of 0.5 W were achieved at 66 GHz when the diode grid was pumped with a pulsed source at 33 GHz. This grid had 760 Schottky-barrier varactor diodes. The average series resistance was 27 Ω, the minimum capacitance was 18 fF at a reverse breakdown voltage of -3 V. The measurements indicate that the diode grid is a feasible device for generating watt-level powers at millimeter frequencies and that substantial improvement is possible by improving the diode breakdown voltage
Development Of An 80'-Diameter Ribbon Drogue Parachute For The NASA X-38 Vehicle
The NASA X-38 program required a larger, more robust drogue parachute. A multi-organizational team from NASA, Sandia National Laboratories, United Space Alliance, and Pioneer Aerospace Corporation has developed and tested a new 80-ft.-dia., quarter-spherical, ribbon drogue parachute. The design requirements, design specifics, margin analyses, and results of testing are all discussed herein. Some of the weight advantages of switching from Kevlar to Zylon for radial, line and riser materials are presented
Enhancing Mosquito-Borne Disease Surveillance in Florida
The University of Florida, IFAS, Florida Medical Entomology Laboratory developed online graphic visuals to assist Florida mosquito control districts and health departments in maximizing the potential of their individual surveillance programs for mosquito-borne diseases through a better understanding and interpretation of surveillance data. Using data generated by the Florida Department of Health, we developed Geographic Information System (GIS) based maps with animation (video) to bring surveillance results to life. Our GIS video is the first of its kind in mosquito-borne disease surveillance and will aid in refining the science of preventing mosquito-borne diseases outbreaks
- …