1,497 research outputs found
High-resolution Earth-based lunar radar studies: Applications to lunar resource assessment
The lunar regolith will most likely be a primary raw material for lunar base construction and resource extraction. High-resolution radar observations of the Moon provide maps of radar backscatter that have intensity variations generally controlled by the local slope, material, and structural properties of the regolith. The properties that can be measured by the radar system include the dielectric constant, density, loss tangent, and wavelength scale roughness. The radar systems currently in operation at several astronomical observatories provide the ability to image the lunar surface at spatial resolutions approaching 30 m at 3.8 cm and 12.6 cm wavelengths and approximately 500 m at 70 cm wavelength. The radar signal penetrates the lunar regolith to a depth of 10-20 wavelengths so the measured backscatter contains contributions from the vacuum-regolith interface and from wavelength-scale heterogeneities in the electrical properties of the subsurface material. The three wavelengths, which are sensitive to different scale structures and scattering volumes, provide complementary information on the regolith properties. Aims of the previous and future observations include (1) analysis of the scattering properties associated with fresh impact craters, impact crater rays, and mantled deposits; (2) analysis of high-incidence-angle observations of the lunar mare to investigate measurement of the regolith dielectric constant and hence porosity; (3) investigation of interferometric techniques using two time-delayed observations of the same site, observations that require a difference in viewing geometry less than 0.05 deg and, hence, fortuitous alignment of the Earth-Moon system when visible from Arecibo Observatory
Microwave scattering and emission properties of large impact craters on the surface of Venus
Many of the impact craters on Venus imaged by the Magellan synthetic aperture radar (SAR) have interior floors with oblique incidence angle backscatter cross sections 2 to 16 times (3 dB to 12 dB) greater than the average scattering properties of the planet's surface. Such high backscatter cross sections are indicative of a high degree of wavelength-scale surface roughness and/or a high intrinsic reflectivity of the material forming the crater floors. Fifty-three of these (radar) bright floored craters are associated with 93 percent of the parabolic-shaped radar-dark features found in the Magellan SAR and emissivity data, features that are thought to be among the youngest on the surface of Venus. It was suggested by Campbell et al. that either the bright floors of the parabolic feature parent craters are indicative of a young impact and the floor properties are modified with time to a lower backscatter cross section or that they result from some property of the surface or subsurface material at the point of impact or from the properties of the impacting object. As a continuation of earlier work we have examined all craters with diameters greater than 30 km (except 6 that were outside the available data) so both the backscatter cross section and emissivity of the crater floors could be estimated from the Magellan data
Regional institutions and the environment in Central and Eastern Europe
AbstractThis contribution is based on a set of reflections presented at the REGov Workshop. These reflections were offered as part of a panel discussion around the topic “Environmental regions in multilevel governance.” Additional presentations provided in the context of this panel discussion include those of Ron Witt, United Nations Environment Programme, and Olivier Graefe, University of Fribourg (this volume). Webcasts of all presentations are available at http://www.reg-observatory.org/outputs.html
Estimating Lunar Pyroclastic Deposit Depth from Imaging Radar Data: Applications to Lunar Resource Assessment
Lunar pyroclastic deposits represent one of the primary anticipated sources of raw materials for future human settlements. These deposits are fine-grained volcanic debris layers produced by explosive volcanism contemporaneous with the early stage of mare infilling. There are several large regional pyroclastic units on the Moon (for example, the Aristarchus Plateau, Rima Bode, and Sulpicius Gallus formations), and numerous localized examples, which often occur as dark-halo deposits around endogenic craters (such as in the floor of Alphonsus Crater). Several regional pyroclastic deposits were studied with spectral reflectance techniques: the Aristarchus Plateau materials were found to be a relatively homogeneous blanket of iron-rich glasses. One such deposit was sampled at the Apollo 17 landing site, and was found to have ferrous oxide and titanium dioxide contents of 12 percent and 5 percent, respectively. While the areal extent of these deposits is relatively well defined from orbital photographs, their depths have been constrained only by a few studies of partially filled impact craters and by imaging radar data. A model for radar backscatter from mantled units applicable to both 70-cm and 12.6-cm wavelength radar data is presented. Depth estimates from such radar observations may be useful in planning future utilization of lunar pyroclastic deposits
A Chandra X-Ray Survey of Ultraluminous Infrared Galaxies
We present results from Chandra observations of 14 ultraluminous infrared
galaxies (ULIRGs; log(L_IR/L_Sun) >= 12) with redshifts between 0.04 and 0.16.
The goals of the observations were to investigate any correlation between
infrared color or luminosity and the properties of the X-ray emission and to
attempt to determine whether these objects are powered by starbursts or active
galactic nuclei (AGNs). The sample contains approximately the same number of
high and low luminosity objects and ``warm'' and ``cool'' ULIRGs. All 14
galaxies were detected by Chandra. Our analysis shows that the X-ray emission
of the two Seyfert 1 galaxies in our sample are dominated by AGN. The remaining
12 sources are too faint for conventional spectral fitting to be applicable.
Hardness ratios were used to estimate the spectral properties of these faint
sources. The photon indices for our sample plus the Chandra-observed sample
from Ptak et al.(2003) peak in the range of 1.0-1.5, consistent with
expectations for X-ray binaries in a starburst, an absorbed AGN, or hot
bremsstrahlung from a starburst or AGN. The values of photon index for the
objects in our sample classified as Seyferts (type 1 or 2) are larger than 2,
while those classified as HII regions or LINERs tend to be less than 2. The
hard X-ray to far-infrared ratios for the 12 weak sources are similar to those
of starbursts, but we cannot rule out the possibility of absorbed, possibly
Compton-thick, AGNs in some of these objects. Two of these faint sources were
found to have X-ray counterparts to their double optical and infrared nuclei.Comment: 40 pages, 5 tables, 14 figures, accepted by Ap
Near-field radiative heat transfer between macroscopic planar surfaces
Near-field radiative heat transfer allows heat to propagate across a small
vacuum gap in quantities that are several orders of magnitude greater then the
heat transfer by far-field, blackbody radiation. Although heat transfer via
near-field effects has been discussed for many years, experimental verification
of this theory has been very limited. We have measured the heat transfer
between two macroscopic sapphire plates, finding an increase in agreement with
expectations from theory. These experiments, conducted near 300 K, have
measured the heat transfer as a function of separation over mm to m and as
a function of temperature differences between 2.5 and 30 K. The experiments
demonstrate that evanescence can be put to work to transfer heat from an object
without actually touching it
Marshall University Music Department Presents a Faculty Recital, J.D. Folsom, Trumpet, William B. Stacy, French Horn, John H. Mead, Trombone
https://mds.marshall.edu/music_perf/1138/thumbnail.jp
Suzaku Observations of Local Ultraluminous Infrared Galaxies
We report the results from our analysis of {\it Suzaku} XIS (0.5-10 keV) and
HXD/PIN (15-40 keV) observations of five well-known local ULIRGs: {\em IRAS}
F05189-2524, {\em IRAS} F08572+3915, Mrk 273, PKS 1345+12, and Arp 220. The XIS
observations of F05189-2524 and Mrk 273 reveal strong iron lines consistent
with Fe K and changes in spectral shapes with respect to previous {\it
Chandra} and {\it XMM-Newton} observations. Mrk 273 is also detected by the
HXD/PIN at 1.8-. For F05189-2524, modeling of the data from the
different epochs suggests that the change in spectral shape is likely due to
the central source switching off, leaving behind a residual reflection
spectrum, or an increase in the absorbing column. An increase in the covering
fraction of the absorber can describe the spectral variations seen in Mrk 273,
although a reduction in the intrinsic AGN luminosity cannot be formally ruled
out. The {\it Suzaku} spectra of Mrk 273 are well fit by a ~94% covering
fraction model with a column density of cm. The
absorption-corrected log[ / ] ratio is consistent
with those found in PG Quasars. The 0.5-10 keV spectrum of PKS 1345+12 and Arp
220 seem unchanged from previous observations and their hard X-ray emission is
not convincingly detected by the HXD/PIN. The large column density derived from
CO observations and the large equivalent width of an ionized Fe line in Arp 220
can be reconciled by an ionized reflection model. F08572+3915 is undetected in
both the XIS and HXD/PIN, but the analysis of unpublished {\em Chandra} data
provides a new measurement at low energies.Comment: 37 pages including 4 tables and 10 figures. Accepted for publication
in ApJ. It is tentatively scheduled to appear in the January 20, 2009 issue
of Ap
Sex Differences in the Kinetic Profiles of d- and l- Methylphenidate in the Brains of Adult Rats
OBJECTIVE: Methylphenidate is commonly used in the treatment of Attention Deficit Hyperactivity Disorder and narcolepsy. Methylphenidate is administered as a racemic mixture of the d- and l- threo enantiomers; however, the d-enantiomer is primarily responsible for the pharmacologic activity. Previous studies of the behavioral effects of methylphenidate have highlighted sex differences in the responsiveness to the drug, namely an increased sensitivity of females to its stimulatory effects. These differences may be due to differences in the uptake, distribution, and elimination of methylphenidate from male and female brains. Therefore, we compared the pharmacokinetics of d- and l- threo methylphenidate in the brains of male and female rats.
MATERIALS AND METHODS: Adult male and female Sprague-Dawley rats were injected with 5 mg/kg d, l- threo methylphenidate, and whole brains were collected at various time points following injection. We measured methylphenidate concentrations utilizing chiral high pressure liquid chromatography followed by mass spectrometry.
RESULTS: Females exhibited consistently higher brain concentrations of both d- and l- methylphenidate and a slower clearance of methylphenidate from brain as compared to males, particularly with the active d-enantiomer.
CONCLUSIONS: The increased sensitivity of females to methylphenidate may be partially explained by an increase in total brain exposure to the drug
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