Preliminary evaluation of radar imagery of Yellowstone Park, Wyoming

Evaluation of radar imagery of Yellowstone Park, Wyomin

Improving the fatigue resistance of adhesive joints in laminated wood structures

The premature fatigue failure of a laminated wood/epoxy test beam containing a cross section finger joint was the subject of a multi-disciplinary investigation. The primary objectives were to identify the failure mechanisms which occurred during the finger joint test and to provide avenues for general improvements in the design and fabrication of adhesive joints in laminated wood structures

Mineralization of an Axially Aligned Collagenous Matrix: A Morphological Study

Bone can be described as a highly ordered composite of type I collagen integrated with an inorganic mineral phase. In vitro models of bone mineralization using collagenous substrates have been reported in the literature. This study reports an in vitro system of mineralized reconstituted collagen fibers, with aligned fibrillar substructure. The collagen fibers were mineralized in a double diffusion chamber saturated with respect to calcium and phosphate. The morphology and ultrastructure of the mineral precipitate were evaluated as a function of the pH of the incubating media. Brushite crystal was observed at acidic pH. Large rectangular crystals formed at pH 5.15 and appear to associate with the collagen fibers. At neutral and alkaline pHs, hydroxyapatite crystals were observed in association with the collagen fibers . Spherical aggregates of hydroxyapatite crystals were seen at neutral and alkaline pHs, but these structures were reduced in size when formed on collagen at alkaline pH. On close examination these spherical structures were found to be hollow when viewed in cross section. The crystals precipitated within the interior of the collagen fiber at neutral and alkaline pHs were comparable in both size and shape to crystals observed in mineralized turkey tendon and skeletal tissues. These preliminary observations indicate that with further refinement the reconstituted collagen fibers may prove useful in model systems for the study of collagen mediated mineralization in vitro. In addition, mineralization of collagenous matrices may lead to the development of biomaterials for bone repair and replacement

Shields for Enhanced Protection Against High-Speed Debris

A report describes improvements over the conventional Whipple shield (two thin, spaced aluminum walls) for protecting spacecraft against high-speed impacts of orbiting debris. The debris in question arises mainly from breakup of older spacecraft. The improved shields include exterior "bumper" layers composed of hybrid fabrics woven from combinations of ceramic fibers and high-density metallic wires or, alternatively, completely metallic outer layers composed of high-strength steel or copper wires. These shields are designed to be light in weight, yet capable of protecting against orbital debris with mass densities up to about 9 g/cubic cm, without generating damaging secondary debris particles. As yet another design option, improved shields can include sparsely distributed wires made of shape memory metals that can be thermally activated from compact storage containers to form shields of predetermined shape upon arrival in orbit. The improved shields could also be used to augment shields installed previously

Computing Accurate Age and Distance Factors in Cosmology

As the universe expands astronomical observables such as brightness and angular size on the sky change in ways that differ from our simple Cartesian expectation. We show how observed quantities depend on the expansion of space and demonstrate how to calculate such quantities using the Friedmann equations. The general solution to the Friedmann equations requires a numerical solution which is easily coded in any computing language (including EXCEL). We use these numerical calculations in four student projects that help to build their understanding of high-redshift phenomena and cosmology. Instructions for these projects are available as supplementary materials.Comment: accepted for publication in the American Journal of Physic

Self-dual vortices in a Maxwell-Chern-Simons model with non-minimal coupling

We find self-dual vortex solutions in a Maxwell-Chern-Simons model with anomalous magnetic moment. From a recently developed N=2-supersymmetric extension, we obtain the proper Bogomol'nyi equations together with a Higgs potential allowing both topological and non-topological phases in the theory.Comment: 12 pages, 9 figures, 2 tables; some typos corrected, one reference updated. To be published in the Int. J. Mod. Phys. A (1999

Complex network analysis of literary and scientific texts

We present results from our quantitative study of statistical and network properties of literary and scientific texts written in two languages: English and Polish. We show that Polish texts are described by the Zipf law with the scaling exponent smaller than the one for the English language. We also show that the scientific texts are typically characterized by the rank-frequency plots with relatively short range of power-law behavior as compared to the literary texts. We then transform the texts into their word-adjacency network representations and find another difference between the languages. For the majority of the literary texts in both languages, the corresponding networks revealed the scale-free structure, while this was not always the case for the scientific texts. However, all the network representations of texts were hierarchical. We do not observe any qualitative and quantitative difference between the languages. However, if we look at other network statistics like the clustering coefficient and the average shortest path length, the English texts occur to possess more clustered structure than do the Polish ones. This result was attributed to differences in grammar of both languages, which was also indicated in the Zipf plots. All the texts, however, show network structure that differs from any of the Watts-Strogatz, the Barabasi-Albert, and the Erdos-Renyi architectures

Theory of Activated Transport in Bilayer Quantum Hall Systems

We analyze the transport properties of bilayer quantum Hall systems at total filling factor $\nu=1$ in drag geometries as a function of interlayer bias, in the limit where the disorder is sufficiently strong to unbind meron-antimeron pairs, the charged topological defects of the system. We compute the typical energy barrier for these objects to cross incompressible regions within the disordered system using a Hartree-Fock approach, and show how this leads to multiple activation energies when the system is biased. We then demonstrate using a bosonic Chern-Simons theory that in drag geometries, current in a single layer directly leads to forces on only two of the four types of merons, inducing dissipation only in the drive layer. Dissipation in the drag layer results from interactions among the merons, resulting in very different temperature dependences for the drag and drive layers, in qualitative agreement with experiment.Comment: 4 pages, 2 figure