41,668 research outputs found
The numerical analysis of the rotational theory for the formation of lunar globules
The morphology of lunar globules is studied through the application of a numerical analysis of their rotation in space during cooling. It is assumed that molten rock is shot from the surface of the moon, solidifies in space above the moon and then falls back to the surface. The rotational theory studied makes the following assumptions: the volume of the molten rock does not change during cooling; the angular momentum is conserved; there are no internal motions because of the high viscosity of the molten rock, i.e., in equilibrium the globule is rotating as a rigid body; finally, the kinetic reaction of the globule to the forces is fast relative to the rate of cooling, i.e., the globule reaches equilibrium at constant energy. These assumptions are subjected to numerical analysis yielding good agreement between the actual globule shapes and the numerical results, but leaving some doubt as to the validity of the rotational theory due to the failure to establish the existence of true local minima and an incomplete understanding of the thermokentics
Construction and Calibration of a Streaked Optical Spectrometer for Shock Temperature
Here we describe the implementation and calibration of a streaked visible
spectrometer (SVS) for optical pyrometry and emission/absorption spectroscopy
on light gas gun platforms in the UC Davis Shock Compression Laboratory. The
diagnostic consists of an optical streak camera coupled to a spectrometer to
provide temporally and spectrally-resolved records of visible emission from
dynamically-compressed materials. Fiber optic coupling to the sample enables a
small diagnostic footprint on the target face and flexibility of operation on
multiple launch systems without the need for open optics. We present the
details of calibration (time, wavelength and spectral radiance) for absolute
temperature determination and present benchmark measurements of system
performance.Comment: 6 pages, 3 figures Davies, E., et al. (accepted). In J. Lane, T.
Germann, and M. Armstrong (Eds.), 21st Biennial APS Conference on Shock
Compression of Condensed Matter (SCCM19). AIP Publishin
S190 interpretation techniques development and application to New York State water resources
The author has identified the following significant results. The program has demonstrated that Skylab imagery can be utilized to regularly monitor eutrophication indices of lakes, such as chlorophyll concentration and photic zone depth. The relationship between the blue to green reflectance ratio and chlorophyll concentration was shown, along with changes in lake properties caused by chlorophyll, lignin, and humic acid using reflectance ratios and changes. A data processing technique was developed for detecting atmospheric fluctuations occurring over a large lake
Electronic structure and the glass transition in pnictide and chalcogenide semiconductor alloys. Part II: The intrinsic electronic midgap states
We propose a structural model that treats in a unified fashion both the
atomic motions and electronic excitations in quenched melts of pnictide and
chalcogenide semiconductors. In Part I (submitted to J. Chem. Phys.), we argued
these quenched melts represent aperiodic -networks that are highly
stable and, at the same time, structurally degenerate. These networks are
characterized by a continuous range of coordination. Here we present a
systematic way to classify these types of coordination in terms of discrete
coordination defects in a parent structure defined on a simple cubic lattice.
We identify the lowest energy coordination defects with the intrinsic midgap
electronic states in semiconductor glasses, which were argued earlier to cause
many of the unique optoelectronic anomalies in these materials. In addition,
these coordination defects are mobile and correspond to the transition state
configurations during the activated transport above the glass transition. The
presence of the coordination defects may account for the puzzling discrepancy
between the kinetic and thermodynamic fragility in chalcogenides. Finally, the
proposed model recovers as limiting cases several popular types of bonding
patterns proposed earlier, including: valence-alternation pairs, hypervalent
configurations, and homopolar bonds in heteropolar compounds.Comment: 17 pages, 15 figures, revised version, final version to appear in J.
Chem. Phy
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Strength of the DTM RapidSteel 1.0 Material
This paper reports the results of a study into the strength of the DTM RapidSteel 1.0 material.
Elastic modulus and strength of the metal/copper composite material was investigated as a
function of the distance from the point of copper infiltration, the furnace cycle duration, and the
furnace type. The microstructure of the RapidSteel material was also examined in an attempt to
understand the science behind the infiltration process. The results have implications for the
design of tools to be made using the RapidTool process in situations where the tool will be used
as a production tool, rather than a prototype tool.Mechanical Engineerin
Relation between socioeconomic deprivation and death from a first myocardial infarction in Scotland: population based analysis
No abstract available
Imaging the Near Field
In an earlier paper we introduced the concept of the perfect lens which
focuses both near and far electromagnetic fields, hence attaining perfect
resolution. Here we consider refinements of the original prescription designed
to overcome the limitations of imperfect materials. In particular we show that
a multi-layer stack of positive and negative refractive media is less sensitive
to imperfections. It has the novel property of behaving like a fibre-optic
bundle but one that acts on the near field, not just the radiative component.
The effects of retardation are included and minimized by making the slabs
thinner. Absorption then dominates image resolution in the near-field. The
deleterious effects of absorption in the metal are reduced for thinner layers.Comment: RevTeX, (9 pages, 8 figures
Access to dental care by young South Australian adults
The document attached has been archived with permission from the Australian Dental Association (9th Jan 2008). An external link to the publisher’s copy is included.Background: Despite reported concern over the dental care of young adults little research has been done on their use of dental services in Australia. The aim of this study was to investigate the patterns of dental utilization of young South Australian adults aged 20-24 years. Methods: A random sample of 2300 young adults was selected from the electoral roll. Partial or complete addresses and possible phone numbers were obtained for 1921 persons. Telephone interviews were conducted for 1261 subjects to obtain information on socio- demographics, health behaviour and dental visiting (response rate 65.6 per cent). Results: One third of young adults (34 per cent) had not made a dental visit in the previous two years and 38 per cent usually visited for a problem rather than a check-up. Making a dental visit in the last two years was significantly associated with a number of socio- demographic variables including age and gender, with holders of private dental insurance and those who have not avoided care because of cost having higher odds of making a visit and males and government concession card holders having lower odds of visiting. Usual reason for visiting a dentist for a problem was significantly associated with no private dental insurance, holding a government concession card, no tertiary education and avoiding care because of cost. Conclusions: This study suggests that demographic and economic factors influenced use of dental services and reason for visiting of young South Australian adults.KF Roberts-Thomson, JF Stewar
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