3,015 research outputs found
Flow and fracture of ice and ice mixtures
Frozen volatiles make up an important volume fraction of the low density moons of the outer solar system. Understanding the tectonic history of the surfaces of these moons, as well as the evolution of their interiors, requires knowledge of the mechanical strength of these icy materials under the appropriate planetary conditions (temperature, hydrostatic pressure, strain rate). Ongoing lab research is being conducted to measure mechanical properties of several different ices under conditions that faithfully reproduce condition both at the moons' surfaces (generally low temperature, to about 100 K, and low pressures) and in the deep interiors (warmer temperatures, pressures to thousands of atmospheres). Recent progress is reported in two different phases of the work: rheology of ices in the NH3-H2O system at temperatures and strain rates lower than ever before explored, with application to the ammonia-rich moons of Saturn and Uranus; and the water ice I yields II phase transformation, which not only applies directly to process deep in the interiors of Ganymede and Callisto, but holds implications for deep terrestrial earthquakes as well
Creep of ice: Further studies
Detailed studies have been done of ice creep as related to the icy satellites, Ganymede and Callisto. Included were: (1) the flow of high-pressure water ices II, III, and V, and (2) frictional sliding of ice I sub h. Work was also begun on the study of the effects of impurities on the flow of ice. Test results are summarized
The Internet, Not a Panacea: Distance Education in 2001: Working Paper Series--02-22
This paper directs attention to the conjunction among the hypertextural nature of the World Wide Web; recent literature and technical development in knowledge management; and the use of the World Wide Web for distance education, particularly in marketing contexts. We define and argue for the use of text-logging Internet applications based on HTML platforms as a significant component of university-level distance education
A Rapid Technique for Counting Cracks in Rocks
Using a scanning electron microscope (SEM) and an image analyzer, we have developed a technique for counting and measuring cracks in rocks which is more efficient than traditional techniques in which an operator performs all image analysis functions. The key aspect of the technique is that black-on-white tracings of fresh cracks, which can be made rather rapidly by an operator, are measured and digitized by an image analyzer. The most time-consuming step in the process has now become the generation of SEM micrographs and pertinent chemical (mineralogical) information, not the quantification of crack structure. The technique has been applied to two studies involving nuclear waste isolation in a granitic rock, Climax Stock (Nevada Test Site) quartz monzonite, a Cretaceous age rock which is structurally very inhomogeneous. One study detected a relationship between crack structure and distance from a hammer-drilled borehole; the other study was unable to detect a relationship between crack structure and gamma irradiation treatment in rocks loaded to near failure
Preference of Goats for Cool-Season Annual Clovers in the Southern United States
In the southern U.S.A., annual clovers provide high-quality winter and spring grazing for beef cattle and sheep. New Zealand data on white clover (Trifolium repens L.) suggests that goats do not prefer this plant as much as sheep (Clark et al., 1982) but little data are available on willingness of goats to consume different clover types in the USA
Parametric flutter studies of an arrow-wing configuration: Some early results
Some early experimental results from a combined experimental and analytical study being conducted at NASA-Langley of the transonic flutter characterisitics of a generic arrow wing configuration are presented. The planned study includes the parametric variation of a variety of structural and geometric characteristics. Presented here are flutter results of the basic arrow wing, for the basic wing with the addition of two simulated lower-surface-mounted engine nacelles, and for the basic wing with the addition of both the fin and the engine nacelles
Electrostatics and the Assembly of an RNA Virus
Electrostatic interactions play a central role in the assembly of
single-stranded RNA viruses. Under physiological conditions of salinity and
acidity, virus capsid assembly requires the presence of genomic material that
is oppositely charged to the core proteins. In this paper we apply basic
polymer physics and statistical mechanics methods to the self-assembly of a
synthetic virus encapsidating generic polyelectrolyte molecules. We find that
(i) the mean concentration of the encapsidated polyelectrolyte material depends
on the surface charge density, the radius of the capsid, and the linear charge
density of the polymer but neither on the salt concentration or the Kuhn
length, (ii) the total charge of the capsid interior is equal but opposite to
that of the empty capsid, a form of charge reversal. Unlike natural viruses,
synthetic viruses are predicted not to be under an osmotic swelling pressure.
The design condition that self-assembly only produces filled capsids is shown
to coincide with the condition that the capsid surface charge exceeds the
desorption threshold of polymer surface adsorption. We compare our results with
studies on the self-assembly of both synthetic and natural viruses.Comment: 41 pages, 4 figure
Synthesis and Cytotoxicity of Cyanoborane Adducts of N 6 -Benzoyladenine and 6-Triphenylphosphonylpurine
N
6
-Benzoyladenine-cyanoborane (2), and 6-triphenylphosphonylpurine-cyanoborane (3) were selected for
investigation of cytotoxicity in murine and human tumor cell lines, effects on human HL-60 leukemic
metabolism and DNA strand scission to determine the feasibility of these compounds as clinical
antineoplastic agents. Compounds 2 and 3 both showed effective cytotoxicity based on ED50 values less than
4 μg/ml for L1210, P388, HL-60, Tmolt3, HUT-78, HeLa-S3 uterine, ileum HCT-8, and liver Hepe-2.
Compound 2 had activity against ovary 1-A9, while compound 3 was only active against prostate PL and
glioma UM. Neither compound was active against the growth of lung 549, breast MCF-7, osteosarcoma
HSO, melanoma SK2, KB nasopharynx, and THP-1 acute monocytic leukemia. In mode of action studies in
human leukemia HL-60 cells, both compounds demonstrated inhibition of DNA and protein syntheses after
60 min at 100 μM. These compounds inhibited RNA synthesis to a lesser extent. The utilization of the DNA
template was suppressed by the compounds as determined by inhibition of the activities of DNA polymerase
α, m-RNA polymerase, r-RNA polymerase and t-RNA polymerase, which would cause adequate inhibition
of the synthesis of both DNA and RNA. Both compounds markedly inhibited dihydrofolate reductase
activity, especially in compound 2. The compounds appeared to have caused cross-linking of the DNA
strands after 24 hr at 100 μM in HL-60 cells, which was consistent with the observed increased in ct-DNA
viscosity after 24 hr at 100 μM. The compounds had no inhibitory effects on DNA topoisomerase I and II
activities or DNA-protein linked breaks. Neither compound interacted with the DNA molecule itself through
alkylation of the nucleotide bases nor caused DNA interculation between base pairs. Overall, these antineoplastic
agents caused reduction of DNA and protein replication, which would lead to killing of cancer
cells
Observation of magnetic circular dichroism in Fe L_{2,3} x-ray-fluorescence spectra
We report experiments demonstrating circular dichroism in the x-ray-fluorescence spectra of magnetic systems, as predicted by a recent theory. The data, on the L_{2,3} edges of ferromagnetic iron, are compared with fully relativistic local spin density functional calculations, and the relationship between the dichroic spectra and the spin-resolved local density of occupied states is discussed
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