38,111 research outputs found
Lunar concrete for construction
Feasibility of using concrete for lunar-base construction has been discussed recently without relevant data for the effects of vacuum on concrete. Experimental studies performed earlier at Los Alamos have shown that concrete is stable in vacuum with no deterioration of its quality as measured by the compressive strength. Various considerations of using concrete successfully on the moon are provided in this paper along with specific conclusions from the existing data base
SkyMapper and the Southern Sky Survey - a resource for the southern sky
SkyMapper is amongst the first of a new generation of dedicated, wide-field
survey telescopes. The 1.3m SkyMapper telescope features a 5.7 square degree
field-of-view Cassegrain imager and will see first light in late 2007. The
primary goal of the facility is to conduct the Southern Sky Survey a six
colour, six epoch survey of the southern sky. The survey will provide
photometry for objects between 8th and 23rd magnitude with global photometric
accuracy of 0.03 magnitudes and astrometry to 50 mas. This will represent a
valuable scientific resource for the southern sky and in addition provide a
basis for photometric and astrometric calibration of imaging data.Comment: 6 pages, 4 figures, proceedings of ESO Calibration Workshop 200
Lunar concrete for construction
Feasibility of using concrete for lunar base construction was discussed recently without relevant data for the effects of vacuum on concrete. Our experimental studies performed earlier at Los Alamos have shown that concrete is stable in vacuum with no deterioration of its quality as measured by the compressive strength. Various considerations of using concrete successfully on the Moon are provided in this paper, along with specific conclusions from the existing database
Bone loss and human adaptation to lunar gravity
Long-duration space missions and establishment of permanently manned bases on the Moon and Mars are currently being planned. The weightless environment of space and the low-gravity environments of the Moon and Mars pose an unknown challenge to human habitability and survivability. Of particular concern in the medical research community today is the effect of less than Earth gravity on the human skeleton, since the limits, if any, of human endurance in low-gravity environments are unknown. This paper provides theoretical predictions on bone loss and skeletal adaptation to lunar and other nonterrestrial-gravity environments based upon the experimentally derived relationship, density approximately (mass x gravity)(exp 1/8). The predictions are compared to skeletal changes reported during bed rest, immobilization, certrifugation, and spaceflight. Countermeasures to reduce bone losses in fractional gravity are also discussed
A Superbubble Feedback Model for Galaxy Simulations
We present a new stellar feedback model that reproduces superbubbles.
Superbubbles from clustered young stars evolve quite differently to individual
supernovae and are substantially more efficient at generating gas motions. The
essential new components of the model are thermal conduction, sub-grid
evaporation and a sub-grid multi-phase treatment for cases where the simulation
mass resolution is insufficient to model the early stages of the superbubble.
The multi-phase stage is short compared to superbubble lifetimes. Thermal
conduction physically regulates the hot gas mass without requiring a free
parameter. Accurately following the hot component naturally avoids overcooling.
Prior approaches tend to heat too much mass, leaving the hot ISM below K
and susceptible to rapid cooling unless ad-hoc fixes were used. The hot phase
also allows feedback energy to correctly accumulate from multiple, clustered
sources, including stellar winds and supernovae.
We employ high-resolution simulations of a single star cluster to show the
model is insensitive to numerical resolution, unresolved ISM structure and
suppression of conduction by magnetic fields. We also simulate a Milky Way
analog and a dwarf galaxy. Both galaxies show regulated star formation and
produce strong outflows.Comment: 13 pages, 13 figures; replaced with version accepted to MNRA
Energy Gaps and Kohn Anomalies in Elemental Superconductors
The momentum and temperature dependence of the lifetimes of acoustic phonons
in the elemental superconductors Pb and Nb was determined by resonant spin-echo
spectroscopy with neutrons. In both elements, the superconducting energy gap
extracted from these measurements was found to converge with sharp anomalies
originating from Fermi-surface nesting (Kohn anomalies) at low temperatures.
The results indicate electron many-body correlations beyond the standard
theoretical framework for conventional superconductivity. A possible mechanism
is the interplay between superconductivity and spin- or charge-density-wave
fluctuations, which may induce dynamical nesting of the Fermi surface
Constraining the Circumbinary Envelope of Z CMa via imaging polarimetry
Z CMa is a complex binary system, composed of a Herbig Be and an FU Ori star.
The Herbig star is surrounded by a dust cocoon of variable geometry, and the
whole system is surrounded by an infalling envelope. Previous
spectropolarimetric observations have reported a preferred orientation of the
polarization angle, perpendicular to the direction of a large, parsec-sized jet
associated with the Herbig star. The variability in the amount of polarized
light has been associated to changes in the geometry of the dust cocoon that
surrounds the Herbig star. We aim to constrain the properties of Z CMa by means
of imaging polarimetry at optical wavelengths. Using ExPo, a dual-beam imaging
polarimeter which operates at optical wavelengths, we have obtained imaging
(linear) polarimetric data of Z CMa. Our observations were secured during the
return to quiescence after the 2008 outburst. We detect three polarized
features over Z CMa. Two of these features are related to the two jets reported
in this system: the large jet associated to the Herbig star, and the micro-jet
associated to the FU Ori star. Our results suggest that the micro-jet extends
to a distance ten times larger than reported in previous studies. The third
feature suggests the presence of a hole in the dust cocoon that surrounds the
Herbig star of this system. According to our simulations, this hole can produce
a pencil beam of light that we see scattered off the low-density envelope
surrounding the system.Comment: Accepted for publication in A\&
Stellar Associations and their Field East of LMC 4 in the Large Magellanic Cloud
We report about the stellar content and the luminosity and mass functions of
three stellar associations and their field located on the north-east edge of
the super-bubble LMC 4 in the Large Magellanic Cloud.Comment: To be appeared in the meeting Proceedings of ``Modes of Star
Formation and the Origin of Field Populations'', Heidelberg, Germany, October
2000; to be published in the ASP Conference Series, edited by E. K. Grebel
and W. Brandne
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