AXIOM: advanced X-ray imaging of the magnetosphere

Planetary plasma and magnetic field environments can be studied in two complementary ways—by in situ measurements, or by remote sensing. While the former provide precise information about plasma behaviour, instabilities and dynamics on local scales, the latter offers the global view necessary to understand the overall interaction of the magnetospheric plasma with the solar wind. Some parts of the Earth’s magnetosphere have been remotely sensed, but the majority remains unexplored by this type of measurements. Here we propose a novel and more elegant approach employing remote X-ray imaging techniques, which are now possible thanks to the relatively recent discovery of solar wind charge exchange X-ray emissions in the vicinity of the Earth’s magnetosphere. In this article we describe how an appropriately designed and located X-ray telescope, supported by simultaneous in situ measurements of the solar wind, can be used to image the dayside magnetosphere, magnetosheath and bow shock, with a temporal and spatial resolution sufficient to address several key outstanding questions concerning how the solar wind interacts with the Earth’s magnetosphere on a global level. Global images of the dayside magnetospheric boundaries require vantage points well outside the magnetosphere. Our studies have led us to propose ‘AXIOM: Advanced X-ray Imaging of the Magnetosphere’, a concept mission using a Vega launcher with a LISA Pathfinder-type Propulsion Module to place the spacecraft in a Lissajous orbit around the Earth–Moon L1 point. The model payload consists of an X-ray Wide Field Imager, capable of both imaging and spectroscopy, and an in situ plasma and magnetic field measurement package. This package comprises a Proton-Alpha Sensor, designed to measure the bulk properties of the solar wind, an Ion Composition Analyser, to characterise the minor ion populations in the solar wind that cause charge exchange emission, and a Magnetometer, designed to measure the strength and direction of the solar wind magnetic field. We also show simulations that demonstrate how the proposed X-ray telescope design is capable of imaging the predicted emission from the dayside magnetosphere with the sensitivity and cadence required to achieve the science goals of the mission.     

Clay mineral variations in Holocene terrestrial sediments from the Indus Basin

We employed X-ray diffraction methods to quantify clay mineral assemblages in the Indus Delta and flood plains since ~ 14 ka, spanning a period of strong climatic change. Assemblages are dominated by smectite and illite, with minor chlorite and kaolinite. Delta sediments integrate clays from across the basin and show increasing smectite input between 13 and 7.5 ka, indicating stronger chemical weathering as the summer monsoon intensified. Changes in clay mineralogy postdate changes in climate by 5–3 ka, reflecting the time needed for new clay minerals to form and be transported to the delta. Samples from the flood plains in Punjab show evidence for increased chemical weathering towards the top of the sections (6–< 4 ka), counter to the trend in the delta, at a time of monsoon weakening. Clay mineral assemblages within sandy flood-plain sediment have higher smectite/(illite + chlorite) values than interbedded mudstones, suggestive of either stronger weathering or more sediment reworking since the Mid Holocene. We show that marine records are not always good proxies for weathering across the entire flood plain. Nonetheless, the delta record likely represents the most reliable record of basin-wide weathering response to climate change.     

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.     

Global airline networks and nodal regions

Transportation infrastructure has always played an important role in the economic fate of regions. In particular, airline networks have dramatically decreased the geographic and temporal constraints of moving people, goods and information; all of which are increasingly crucial inputs for the information economy. As a result, regions have become more concerned with both the quantity and quality of airline connections. The purpose of this paper is to examine the emerging global hierarchy of airline network connectivity. Using a proprietary database of nearly 900 airline carrier schedules from 2006, we examine regional connectivity between 4,650 worldwide origins and destinations. Through the use of network analysis and graph theoretical techniques, results indicate an increasingly complex web of nodal hierarchies in North America, Europe and Asia.

Sex offenders,housing and spatial restriction zones

Sex offenders are currently a major focus of crime control policies at the local, regional, state and federal levels throughout the United States. In part, the perceived threat of offender recidivism has motivated legislators to launch stringent community notification programs and to establish spatial restriction zones (SRZs) around schools, daycare facilities and public parks. The purpose of these restriction zones is to help protect children and minimize their exposure to convicted sex offenders living in the community. In addition to the concern that the implementation of SRZs dramatically reduces viable housing options for registered sex offenders, there are concerns that offenders will be forced to reside in socially disorganized areas that may encourage recidivism. The purpose of this paper is to explore the demographic and socioeconomic differences between areas inside and outside SRZs. Implications of these results for sex offender policies are discussed.

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.     

The effects of the San Francisco Bay plume on trace metal and nutrient distributions in the Gulf of the Farallones

The distributions of particulate elements (Al, P, Mn, Fe, Co, Cu, Zn, Cd, and Pb), dissolved trace metals (Mn, Fe, Co, Cu, Zn, and Cd), and dissolved nutrients (nitrate, phosphate, and silicic acid) were investigated in the Gulf of the Farallones, a region of high productivity that is driven by the dynamic mixing of the San Francisco Bay plume, upwelled waters, and California coastal surface waters. Particulate metals were separated into >10 and 0.4-10 μm size-fractions and further fractionated into leachable (operationally defined with a 25% acetic acid leach) and refractory particulate concentrations. Dissolved metals (< 0.4 μm pore-size filtrate) were separated into colloidal (0.03-0.4 μm) and soluble (<0.03 μm) fractions. The percent leachable particulate fractions ranged from 2% to 99% of the total particulate concentration for these metals with Mn and Cd being predominantly leachable and Fe and Al being predominantly refractory. The leachable particulate Pb concentration was associated primarily with suspended sediments from San Francisco Bay and was a tracer of the plume in coastal waters. The particulate trace metal data suggest that the leachable fraction was an available source of trace metal micronutrients to the primary productivity in coastal waters. The dissolved trace metals in the San Francisco Bay plume and freshly upwelled surface waters were similar in concentration, with the exception of Cu and Co, which exhibited relatively high concentrations in plume waters and served as tracers of this water mass. The dissolved data and estimates of the plume dynamics suggest that the impact of anthropogenic inputs of nutrients and trace metals in the San Francisco Bay plume contributes substantially to the concentrations found in the Gulf of the Farallones (10-50% of estimated upwelled flux values), but does not greatly disrupt the natural stoichiometric balance of trace metal and nutrient elements within coastal waters given the similarity in concentrations to sources in upwelled water. In all, the data from this study demonstrate that the flux of dissolved nutrients and bioactive trace metals from the San Francisco Bay plume contribute to the high and relatively constant phytoplankton biomass observed in the Gulf of the Farallones.