Statistical framework for estimating GNSS bias

We present a statistical framework for estimating global navigation satellite system (GNSS) non-ionospheric differential time delay bias. The biases are estimated by examining differences of measured line integrated electron densities (TEC) that are scaled to equivalent vertical integrated densities. The spatio-temporal variability, instrumentation dependent errors, and errors due to inaccurate ionospheric altitude profile assumptions are modeled as structure functions. These structure functions determine how the TEC differences are weighted in the linear least-squares minimization procedure, which is used to produce the bias estimates. A method for automatic detection and removal of outlier measurements that do not fit into a model of receiver bias is also described. The same statistical framework can be used for a single receiver station, but it also scales to a large global network of receivers. In addition to the Global Positioning System (GPS), the method is also applicable to other dual frequency GNSS systems, such as GLONASS (Globalnaya Navigazionnaya Sputnikovaya Sistema). The use of the framework is demonstrated in practice through several examples. A specific implementation of the methods presented here are used to compute GPS receiver biases for measurements in the MIT Haystack Madrigal distributed database system. Results of the new algorithm are compared with the current MIT Haystack Observatory MAPGPS bias determination algorithm. The new method is found to produce estimates of receiver bias that have reduced day-to-day variability and more consistent coincident vertical TEC values.Comment: 18 pages, 5 figures, submitted to AM

The dwarf low surface brightness population in different environments of the Local Universe

The nature of the dwarf galaxy population as a function of location in the cluster and within different environments is investigated. We have previously described the results of a search for low surface brightness objects in data drawn from an East-West strip of the Virgo cluster (Sabatini et al., 2003) and have compared this to a large area strip outside of the cluster (Roberts et al., 2004). In this talk I compare the East-West data (sampling sub-cluster A and outward) to new data along a North-South cluster strip that samples a different region (part of sub-cluster A, and the N,M clouds) and with data obtained for the Ursa Major cluster and fields around the spiral galaxy M101. The sample of dwarf galaxies in different environments is obtained from uniform datasets that reach central surface brightness values of ~26 B mag/arcsec^2 and an apparent B magnitude of 21 (M_B=-10 for a Virgo Cluster distance of 16 Mpc). We discuss and interpret our results on the properties and distribution of dwarf low surface brightness galaxies in the context of variuos physical processes that are thought to act on galaxies as they form and evolve.Comment: 10 pages, 3 figures, to appear in "Dark Galaxies and Lost Baryons", IAU244 conference proceeding

Cation composition effects on oxide conductivity in the Zr_2Y_2O_7-Y_3NbO_7 system

Realistic, first-principles-based interatomic potentials have been used in molecular dynamics simulations to study the effect of cation composition on the ionic conductivity in the Zr2Y2O7-Y3NbO7 system and to link the dynamical properties to the degree of lattice disorder. Across the composition range, this system retains a disordered fluorite crystal structure and the vacancy concentration is constant. The observed trends of decreasing conductivity and increasing disorder with increasing Nb5+ content were reproduced in simulations with the cations randomly assigned to positions on the cation sublattice. The trends were traced to the influences of the cation charges and relative sizes and their effect on vacancy ordering by carrying out additional calculations in which, for example, the charges of the cations were equalised. The simulations did not, however, reproduce all the observed properties, particularly for Y3NbO7. Its conductivity was significantly overestimated and prominent diffuse scattering features observed in small area electron diffraction studies were not always reproduced. Consideration of these deficiencies led to a preliminary attempt to characterise the consequence of partially ordering the cations on their lattice, which significantly affects the propensity for vacancy ordering. The extent and consequences of cation ordering seem to be much less pronounced on the Zr2Y2O7 side of the composition range.Comment: 22 pages, 8 figures, submitted to Journal of Physics: Condensed Matte

Materials Balance for Bromine, Chlorine, Sulfur, and Nitrogen in Europe

An understanding of the flow of toxic materials through industry and into the environment is one of the major tasks for the IIASA Study, "The Future Environments for Europe: Some Implications, of Alternative Development Paths". Toxic chemicals represent a great threat to the environment, and yet they are commonly used in industrial societies. A sustainable development path would require that usage and disposal of toxic chemicals be compatible with the long-term health of humans and the natural environment. Examining the current and past flows of these materials is a starting point for understanding options for management of their use and disposal, and the impact these options might have on the economy and society. The method chosen to analyze this problem is a materials balance approach in which toxic chemicals are traced as they move through the industrial economy; from extraction to production to intermediate uses and finally to end uses. The methodology and its advantages and disadvantages are discussed in some detail in Chapter 2. The implementation of this approach will become apparent in Chapters 3 through 6 as four individual chemical elements are studied. The four elements examined are bromine, chlorine, sulfur and nitrogen. These chemicals were chosen from a list of 15 which were of particular interest because of the exceptional biological activity of many of the compounds derived from them. The major goal of the project was to develop process-product flow diagrams for these elements showing their pathways through the industrial economy. Each of Chapters 3 through 6 contains a discussion of production processes, major uses, process-product flow diagram(s) and an Appendix with detailed information about the chemical transformations involved in each of the processes. In addition, further investigations including quantitative analysis and discussions of the applicability of this approach for a given element are included in some of the Chapters. Chapter 3, Bromine, presents a detailed qualitative material balance and a more aggregated quantitative material balance for the Netherlands and the United States for 1978 and 1985. The selection of these two countries was based solely on available data. Although the U.S. is not formally part of the study, it is useful as it more closely represents the Western European consumption pattern on average than the Netherlands. While the quantitative analysis focuses only on two countries for two years, it does demonstrate both the qualitative and quantitative aspects of the material balance approach. Bromine consumption is an interesting case as it has been heavily impacted by the phase-out of leaded gasoline and strong market shifts are expected in the future. Chapter 4, Chlorine, presents an in-depth qualitative materials balance and a look at the pathways of chlorine into the environment based on its pattern of end-use consumption. Currently, millions of tons of chlorine are produced each year for use as a disinfectant and in the organic and inorganic chemical industries. Many of the end-uses of chlorine result in eventual releases into the environment of various compounds which have a significant effect on environmental quality. Organic chlorine compounds are of great use to man because they are not readily biodegradable and they are chemically stable. However, because of these qualities they represent some of the most difficult disposal problems of any anthropogenic material. Chapter 5, Sulfur, presents a thorough qualitative analysis of the industrial processes and an in-depth discussion of the applicability of the materials balance approach to sulfur. A large portion of anthropogenically mobilized sulfur is from the burning of fossil fuels and the smelting of ores, two processes where sulfur is not an intentional product, simply an unavoidable one. The bulk of scientific study of sulfur wastes is concentrated on these areas due to their contribution to the acid rain problem. The analysis presented here shows that over half of the total anthropogenic sulfur budget in Europe is from industrial sources other than fossil fuels and ore smelting. This is a fairly surprising result. Thus, the flow of sulfur through the industrial economy in Europe is significant and greater understanding of the eventual disposal of this sulfur is needed. In addition, sulfuric acid is the number one industrial chemical based on the tonnage of production. It is used in a myriad of industries where it is generally consumed in the process and not embodied in the end product. This presents difficulties in the implementation of the materials balance analysis for sulfur. Chapter 6, Nitrogen, presents the process-product flow diagram for nitrogen. About 95% of the anthropogenically mobilized nitrogen is in the form of ammonia. Therefore, this chapter concentrates on the production and eventual end-uses of ammonia. While the process-product diagram is quite thorough, due to time constraints, further discussion and analysis of nitrogen is left as a future research topic. This report is the first step toward completing the task of understanding the impact of toxic materials in Europe. Future analysts may use the process-product diagrams and the analysis presented in this report as a starting point for a historical reconstruction which then could be used for building future scenarios of chemical flows of toxic materials

Feed intake, gastrointestinal system and body composition in reindeer calves fed early harvested first cut timothy silage (Phleum pratense)

Early harvested first cut (EFC) timothy silage was fed to five reindeer calves (Rangifer tarandus tarandus L.) taken from their natural summer pasture and brought to Tromsø for feeding trial. The calves were housed indoors in metabolism cages and fed EFC timothy silage ad lib. during the trial, which lasted from late November 1994 until the end of February 1995, when animals subsequently were slaughtered. Daily feed intake, gastrointestinal (GI) anatomy, body weight and body composition of the animals were examined. Timothy silage {Phleum praténse) was harvested 21 June, 1994 in Tromsø, prewilted and stored as round bales containing 97% leaves. The EFC silage contained 42.1% dry matter (DM), and 18.1% crude protein, 20.7% cellulose, 16.9% hemicellulose and 28.0% water soluble carbohydrates (WSC) of DM. Mean feed intake (DM) 24 hours after the trial started (day 1) was 9-4 g/kg body mass (BM) (S.D.+ 3-9), while the mean daily DM intake during days 15-74 comprised 24.2 g/kg BM (S.D.+ 6.1). All animals except one gained body weight during the trial. The median (range) BM at start and at slaughter was 48.5 kg (34.5¬58.0 kg) and 50.0 kg (42.0-53.5 kg), respectively. Median (range) carcass weight % of BM was 58.0% (51.2-58.7%) and muscle index value 0.0132 (0.0106-0.0176). The median reticulo-rumen (RR) content wet weight (WW) was 4601 g (range 2697-5000 g) comprising 9.3% of the BM, and 85.1% of the total gastrointestinal wet weight content. The median (range) gastrointestinal tract weight was 14.1% of BM (10.7-16.4%). Based on feed intake during the trial and body composition at slaughtet we conclude that first cut timothy silage is suitable as emergency feed to reindeer, as long as it is harvested in early growth stage with high proportion of leaves

Foreword: Mississippi College Law Review - Symposium on Bankruptcy Law

Symposium - An Analysis of Developments in Bankruptcy Law - Forewor