IGS Near Real-Time Products and Their Applications

The primary IGS products, including precise GPS orbits, Earth orientation parameters, and estimated and predicted GPS satellite clocks, are no longer used exclusively for essential geodetic support of scientic research. They are increasingly being used by a wide range of non-academic applications. In these applications, timeliness is extremely critical. To address the timeliness issue, the strengths and weaknesses of current IGS production processes are discussed, new ways to improve the timeliness and quality are explored, and recommendations are proposed to fulfill the application requirements. ? 2001 John Wiley & Sons, Inc.     

The Cold War and geography’s quantitative revolution: Some messy reflections on Barnes’ geographical underworld

A response to a recent paper by Barnes, arguing that the origins of geography’s quantitative revolution were not as monofocused as he suggests.     

Sex Offender Residential Movement Patterns: A Markov Chain Analysis

This article introduces a new approach to the analysis of changes in sex offender residences over time. Using a Markov chain framework, we analyze residential movement patterns of registered sex offenders in Hamilton County, Ohio, over a three-year period (2005–2007). Results indicate a 46 percent reduction in offenders violating spatial restriction zone policy as compared to a counterfactual case where offenders move as a function of housing distributions. Strong legacy effects are also found as offenders previously in violation of restriction policies move into other restricted zones at a higher rate than offenders who were previously in compliance with the policy. Parcels that previously were home to registered offenders also continue to attract offenders in future periods. Although we find differences in the probabilities of attracting offenders for parcels outside and inside restricted zones that are consistent with offender restrictive policies, these differences are actually significantly smaller than what holds under the counterfactual. Parcels in restricted zones continue to attract offenders at a higher rate than expected, despite the policy restrictions.     

Salt terrains of Iran

Salt only survives at outcrop in desert climates, and southern Iran has more than its share of salt mountains created by rising diapirs. With their white salt cliffs and creeping salt glaciers, these constitute amazing landscapes with collapsing dolines that feed into spectacularly decorated caves.     

Comparing the CO and HI Distributions in Nearby Spiral Galaxies at High Resolution

With wide-field CO maps of spiral galaxies at ～6′′resolution provided by the BIMA Survey of Nearby Galaxies (BIMA SONG),it is now feasible to compare the CO and HI distributions in disks onscales of ～1 kpc or less. The results of such a comparisonsuggest that, when azimuthally averaged, the ratio of CO to HIemission, and by implication the molecular-to-atomic gas ratio, isdetermined by the midplane interstellar pressure, with the ISMmetallicity as a secondary factor. A variety of observed phenomena,including the inhibition of molecular cloud and star formation in theouter disks of galaxies, can be understood in terms of thisdependence. We present recent data on the edge-on galaxy NGC 891 thatallow a comparison of the vertical distribution of CO and HI, and willtherefore provide an independent test of these ideas.     

The distribution of water ice in the interior of Comet Tempel 1

The Deep Impact flyby spacecraft includes a 1.05 to 4.8 μm infrared (IR) spectrometer. Although ice was not observed on the surface in the impact region, strong absorptions near 3 μm due to water ice are detected in IR measurements of the ejecta from the impact event. Absorptions from water ice occur throughout the IR dataset beginning three seconds after impact through the end of observations, ∼45 min after impact. Spatially and temporally resolved IR spectra of the ejecta are analyzed in conjunction with laboratory impact experiments. The results imply an internal stratigraphy for Tempel 1 consisting of devolatilized materials transitioning to unaltered components at a depth of approximately one meter. At greater depths, which are thermally isolated from the surface, water ice is present. Up to depths of 10 to 20 m, the maximum depths excavated by the impact, these pristine materials consist of very fine grained (∼1±1 μm) water ice particles, which are free from refractory impurities.     

Lake Missoula and the Scablands,Washington, USA

Gigantic floods that, for just a few days, had flow rates many times greater than the combined flows of all the other rivers of the world put together. Sounds ridiculous, and it's almost inconceivable, but it's real, and it all happened at the end of the last Ice Age. The water came from Lake Missoula, which exists no more, but the effects are still to be seen in the landscapes, most notably in the vast scablands of eastern Washington.     

A spatio-temporal model of housing prices based on individual sales transactions over time

A spatio-temporal model of housing price trends is developed that focuses on individual housing sales over time. The model allows for both the spatio-temporal lag effects of previous sales in the vicinity of each housing sale, and for general autocorrelation effects over time. A key feature of this model is the recognition of the unequal spacing between individual housing sales over time. Hence the residuals are modeled as a first-order autoregressive process with unequally spaced events. The maximum-likelihood estimation of this model is developed in detail, and tested in terms of simulations based on selected data. In addition, the model is applied to a small data set in the Philadelphia area.