Aggregate accessibility to population at the county level: U.S. 1940–2000

 A classic study by Harris (1954) shows a map of U.S. national accessibility. Harris argued that access to population and income represents a critical factor for location analysis. Such maps and analyses are now readily produced by geographical information systems, allowing experimentation with various parameters, and explorations of changes. By comparing changes in these measurements we can develop a synthetic picture of the impacts of population redistribution. This paper offers a comprehensive review of these calculations and illustrates their use with maps from county population in the continental U.S. from 1940 through to 2000. Received: September 2002 / Accepted: January 2003 RID="*" ID="*" Previous versions of this paper were presented to the Initiative in Population Research (IPR) workshop at the Ohio State University (Horner) and to the Center for Spatially Integrated Social Sciences (CSISS) Summer Workshop in Accessibility (O'Kelly). Thanks to the referees for helpful comments.     

Refractory organic carbon in particle-size fractions of arable soils II: organic carbon in relation to mineral surface area and iron oxides in fractions <6 μm

The interaction of organic compounds with the mineral phase is considered as one stabilization mechanism for organic carbon (OC) in soils. The objective of this study is to assess the role of mineral surfaces for the long-term stabilization of OC in arable soils, with special emphasis on iron oxides. Soil samples were taken from two contrasting treatment types, i.e. fertilized plots and C-depleted plots, in long-term agroecosystem experiments. The soil organic carbon pool of the C-depleted plots is considered to show a lower contribution of labile compounds and consequently to be relatively enriched in refractory compounds compared with the fertilized counterparts. In fractions <6 μm, OC was studied in relation to total mineral surface area, surface area contributed by oxides and silicates, and the content and type of iron oxides (dithionite and oxalate extractable iron, Fe_d and Fe_o). In two sandy soils, OC contents were linearly related to total mineral surface area and the content of the two iron oxide fractions (Fe_d and Fe_o). The surface area developed by the silicates was low and thus the surface area contribution from oxides was dominant in fractions <6 μm. In contrast to the sandy soils, in a loamy soil OC was not correlated with surface area or the iron oxide content. However, the different soils agreed with respect to the behavior of C in density fractions: losses of OC occurred mainly from the light fraction (2 g cm⁻³), whereas C in the heavy fraction (>2 g cm⁻³) proved to be stable. For the sandy soils, mineral surface area appears to control the storage of OC in fine fractions. Given the dominant surface area contribution from oxides, OC storage here primarily depends on the oxides. The C-depleted plots in particular show that surface area controls the accumulation of refractory C. The interaction of organic compounds with the mineral phase, mainly with the surface of oxides, seems to be a major mechanism for the long-term stabilization of OC in these sandy soils. An interaction with minerals seems to be important for stabilizing OC also in the loamy soil, although this is not reflected by a proportional relation between OC and surface area across the fractions.     

Pedestal craters on Ganymede

The high-resolution Voyager images of Ganymede show a class of fresh craters 6–89 km in diameter which is distinguished by an ejecta blanket similar to those seen for some types of Martian craters. One hundred and eighty-five were identified and studied for trends with respect to latitude, longitude, and terrain type. No correlation of the ratio of ejecta diameter to crater diameter was found as a function of latitude or longitude, and there is only a suggestion of a trend in this ratio with respect to major terrain types. Central peak frequency is greatest for the smaller crater diameters. Central pit occurrence dominates central peak occurrence at crater diameters ?35 km. We conclude that the ejecta morphology probably results from impact into an icy target. The question of whether atmospheric ejecta-particle drag contributes to ejecta blanket morphologies on planets with an atmospheric cannot be resolved entirely from the Voyager images. The image resolution is insufficient to show diagnostic flow features on the ejecta, if they exist, or to detect evidence of any other ejecta deposits which would lie beyond the pedestal, predicted by some researchers to exist only on bodies with an atmosphere.     

Seismic refraction, isotropic anisotropic seismic tomography on an ancient monument (Antonino and Faustina temple ad 141)

This paper describes the results of using geophysical techniques to investigate three columns of the Pronaos of the Antonino and Faustina temple ( AD  141) in Rome, Italy; the columns are of cipollino marble which shows alternate sequences of mica and calcite beds. We applied seismic refraction using traditional interpretation, and seismic transmission tomography. The comparison between the results of the refraction study and the 2D and 3D isotropic tomographic analyses suggested anisotropic characteristics for the marble, and this prompted us to perform a further tomographic experiment, taking into account these characteristics of the material. Assuming an elliptical model, the main directions of anisotropy were detected. Two velocity fields corresponding to the main directions of the anisotropy were measured and anomalies such as cracks and fractures were noted. The conjugate-gradient algorithm was used to invert the data. The results of the isotropic and anisotropic models were compared. The correlation between the methods highlighted the characteristics of the marble, i.e. anisotropy, depth of the weathering, fractures and small cracks. The results show that the material of the columns is in reasonable condition, with the exception of a surface area 6 cm to 15 cm deep that we estimate has been weathered for 2000 years, and that has been particularly affected by pollution in the last century.     

Three-dimensional earthquake locations and upper crustal structure of the Sannio-Matese region (southern Italy)

The Sannio-Matese region is one of the most seismically active regions of Italy and has been struck by large historical earthquakes. At present, the area is characterized by low magnitude background seismicity and small seismic sequences following M4 main events. In this paper, we show Vp and Vp/Vs models and 3D locations for a complete set of earthquakes occurring in the period 1991–2001. We observe a significant crustal heterogeneity, with large scale east-verging high Vp fault-related-folds, stacked by the Pliocene compression. The relocated earthquakes cluster along a 70° east-dipping, NW-striking plane located at the border of the high Vp thrust units. Normal fault earthquakes related to the young and active extension occur within these high Vp zones, interpreted as high strength material. We expect large future earthquakes to occur within these high Vp zones actually characterized by low magnitude seismicity at their borders.     

The first multi-model ensemble of regional climate simulations at kilometer-scale resolution part 2: historical and future simulations of precipitation

This paper presents the first multi-model ensemble of 10-year, “convection-permitting” kilometer-scale regional climate model (RCM) scenario simulations downscaled from selected CMIP5 GCM projections for historical and end of century time slices. The technique is to first downscale the CMIP5 GCM projections to an intermediate 12–15 km resolution grid using RCMs, and then use these fields to downscale further to the kilometer scale. The aim of the paper is to provide an overview of the representation of the precipitation characteristics and their projected changes over the greater Alpine domain within a Coordinated Regional Climate Downscaling Experiment Flagship Pilot Study and the European Climate Prediction system project, tasked with investigating convective processes at the kilometer scale. An ensemble of 12 simulations performed by different research groups around Europe is analyzed. The simulations are evaluated through comparison with high resolution observations while the complementary ensemble of 12 km resolution driving models is used as a benchmark to evaluate the added value of the convection-permitting ensemble. The results show that the kilometer-scale ensemble is able to improve the representation of fine scale details of mean daily, wet-day/hour frequency, wet-day/hour intensity and heavy precipitation on a seasonal scale, reducing uncertainty over some regions. It also improves the representation of the summer diurnal cycle, showing more realistic onset and peak of convection. The kilometer-scale ensemble refines and enhances the projected patterns of change from the coarser resolution simulations and even modifies the sign of the precipitation intensity change and heavy precipitation over some regions. The convection permitting simulations also show larger changes for all indices over the diurnal cycle, also suggesting a change in the duration of convection over some regions. A larger positive change of frequency of heavy to severe precipitation is found. The results are encouraging towards the use of convection-permitting model ensembles to produce robust assessments of the local impacts of future climate change.

     

Heavy metals in the Ventspils Harbour: normalization based on a multi-parameter dataset

Heavy metals were investigated in the sediments of the Ventspils Harbour located in north-west Latvia (eastern Baltic Sea). Sediment samples were analysed for major and trace metals by ICP-AES, supplemented by inorganic and organic carbon as well as grain-size distributions. Principal component analysis of the data resulted in two main parameter clusters associated with Ca- and Al-rich material and indicated differing behaviour of Pb, Cu, Zn, N and P. Normalization with respect to Ca and Al by least absolute values regression removed the spatial pattern of sediment metal content in the harbour. High residual concentrations at individual sites were associated with local contaminations, whereas the overall concentration pattern was governed by the transport of riverine fine material. Dilution with coarser, quartz-rich marine sediments led to a pronounced heavy metal concentration drop towards the harbour gates. High mixing was an important feature of sediment dynamics in the Ventspils Harbour, hampering contaminant source identification and sediment monitoring.     

Biometric and Genetic Analysis of the Marine Rissoid Rissoa auriscalpium (Gastropoda, Prosobranchia) and its Ecological Implications

Abstract. Two forms of Rissoa auriscalpium were found in Posidonia oceanica beds around the Island of Ischia (Gulf of Naples). In order to investigate their taxonomical value and to quantify the discriminating features found, the radular, conchometric, genetic, and ecological features of the two forms were analyzed. Ecological observations showed that the distribution of the two forms is strongly correlated with hydrodynamic factors.