Trace element abundance determinations by Synchrotron X Ray Fluorescence (SXRF) on returned comet nucleus mineral grains

Trace element analyses were performed on bulk cosmic dust particles by Proton Induced X Ray Emission (PIXE) and Synchrotron X Ray Fluorescence (SXRF). When present at or near chondritic abundances the trace elements K, Ti, Cr, Mn, Cu, Zn, Ga, Ge, Se, and Br are presently detectable by SXRF in particles of 20 micron diameter. Improvements to the SXRF analysis facility at the National Synchrotron Light Source presently underway should increase the range of detectable elements and permit the analysis of smaller samples. In addition the Advanced Photon Source will be commissioned at Argonne National Laboratory in 1995. This 7 to 8 GeV positron storage ring, specifically designed for high-energy undulator and wiggler insertion devices, will be an ideal source for an x ray microprobe with one micron spatial resolution and better than 100 ppb elemental sensitivity for most elements. Thus trace element analysis of individual micron-sized grains should be possible by the time of the comet nucleus sample return mission

The arithmetic of hyperelliptic curves

We summarise recent advances in techniques for solving Diophantine problems on hyperelliptic curves; in particular, those for finding the rank of the Jacobian, and the set of rational points on the curve

Persistence and the Random Bond Ising Model in Two Dimensions

We study the zero-temperature persistence phenomenon in the random bond $\pm J$ Ising model on a square lattice via extensive numerical simulations. We find strong evidence for ` blocking\rq regardless of the amount disorder present in the system. The fraction of spins which {\it never} flips displays interesting non-monotonic, double-humped behaviour as the concentration of ferromagnetic bonds $p$ is varied from zero to one. The peak is identified with the onset of the zero-temperature spin glass transition in the model. The residual persistence is found to decay algebraically and the persistence exponent $\theta (p)\approx 0.9$ over the range $0.1\le p\le 0.9$. Our results are completely consistent with the result of Gandolfi, Newman and Stein for infinite systems that this model has ` mixed\rq behaviour, namely positive fractions of spins that flip finitely and infinitely often, respectively. [Gandolfi, Newman and Stein, Commun. Math. Phys. {\bf 214} 373, (2000).]Comment: 9 pages, 5 figure

Design of testbed and emulation tools

The research summarized was concerned with the design of testbed and emulation tools suitable to assist in projecting, with reasonable accuracy, the expected performance of highly concurrent computing systems on large, complete applications. Such testbed and emulation tools are intended for the eventual use of those exploring new concurrent system architectures and organizations, either as users or as designers of such systems. While a range of alternatives was considered, a software based set of hierarchical tools was chosen to provide maximum flexibility, to ease in moving to new computers as technology improves and to take advantage of the inherent reliability and availability of commercially available computing systems

The Railroad’s Impact on Land Values in the Upper Great Plains at the Closing of the Frontier

We show that the impact of transportation improvements on land values is complex with a direct, positive relationship on the price of land and also a positive relationship with the ratio of improved acres to total acres, another important influence on the per acre price of land. We construct a two step estimation that removes the impact of transportation outlets on the ratio of improved to total acres before including the transportation variables and the adjusted ratio variable as independent variables in a regression on price per acre. This estimation gives us the expected positive impact of railroads on land price. We also use Box-Cox regressions to show the semi-log form, a common model specification, may be inappropriate for our data and possibly then for other land price research.Box-Cox, Railroads, Great Plains

Multidisciplinary research in the space sciences

Research activities were carried out in the following areas during this reporting period: (1) astrophysics; (2) climate and atmospheric modeling; and (3) climate applications of earth observations & geological studies. An ultra-low-noise 115 GHz receiver based upon a superconducting tunnel diode mixer has been designed and constructed. The first laboratory tests have yielded spectacular results: a single-sideband noise temperature of 75 K considerably more sensitive than any other receiver at this frequency. The receiver will replace that currently in use on the Columbia-GISS CO Sky Survey telescope. The 1.2 meter millimeter-wave telescope at Columbia University has been used to complete two large-scale surveys of molecular matter in the part of the inner galaxy which is visible from the Northern hemisphere (the first galactic quadrant); one of the distant galaxy and one of the solar neighborhood. The research conducted during the past year in the climate and atmospheric modeling programs has been focused on the development of appropriate atmospheric and upper ocean models, and preliminary applications of these models. Principal models are a one-dimensional radiative-convective model, a three-dimensional global climate model, and an upper ocean model. During the past year this project has focused on development of 2-channel satellite analysis methods and radiative transfer studies in support of multichannel analysis techniques

Longitudinal photo-documentation: recording living walls

This working paper advocates a methodological approach to the study of street art and graffiti that is based on the documentation of single sites over time. Longitudinal photo-documentation is a form of data collection that allows street art and graffiti to be examined as visual dialogue. By capturing everyday forms of public mark making alongside both more recognizably ‘artistic’ images, and more visually ‘offensive’ tags, we aim to attend to graffiti and street art’s existence within a field of social interaction. We describe a relevant analytic tool drawn from ethnomethodology and conversation analysis – the next turn proof procedure – which may be adapted in order to study street art and graffiti as a form of asynchronous, yet sequential, communication. This form of analysis departs from existent forms of analysis in that it is not concerned with the semiotics or iconography of decontextualized individual photographs of street art or graffiti. We present a worked analytic example to demonstrate the utility of longitudinal photo-documentation in making visible the dialogue amongst artists, writers and community members, and we employ the principles of the next turn proof procedure to illustrate the ways in which each party shows their understanding of the prior work on the wall via their own contribution to the ‘conversation.