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The Choptank River is an estuary, tributary of the Chesapeake Bay, and an ecosystem in decline due partly to excessive nutrient and sediment loads from agriculture. The Conservation "Effects Assessment Project for the Choptank Riv...
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The Choptank River is an estuary, tributary of the Chesapeake Bay, and an ecosystem in decline due partly to excessive nutrient and sediment loads from agriculture. The Conservation "Effects Assessment Project for the Choptank River watershed was established to evaluate the effectiveness of conservation practices on water quality within this watershed. Several measurement frameworks are being used to assess conservation practices. Nutrients (nitrogen and phosphorus) and herbicides (atrazine and metolachlor) are monitored within 15 small, agricultural subwatersheds and periodically in the lower portions of the river estuary. Initial results indicate that land use within these subwatersheds is a major determinant of nutrient concentration in streams. In addition, the ~(18)O isotope signature of nitrate was used to provide a landscape assessment of denitrification processes in the presence of the variable land use. Herbicide concentrations were not correlated to land use, suggesting that herbicide delivery to the streams is influenced by other factors and/or processes. Remote sensing technologies have been used to scale point measurements of best management practice effectiveness from field to subwatershed and watershed scales. Optical satellite (SPOT-5) data and ground-level measurements have been shown to be effective for monitoring nutrient uptake by winter cover crops in fields with a wide range of management practices. Synthetic Aperture Radar (RADARSAT-1) data have been shown to detect and to characterize accurately the hydrology (hydroperiod) of forested wetlands at landscape and watershed scales. These multiple approaches are providing actual data for assessment of conservation practices and to help producers, natural resource managers, and policy makers maintain agricultural production while protecting this unique estuary.
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State-of-the-art design of communication networks is characterized by the ubiquitous appearance of computer technology. All significant message-switching systems designed in the last ten years have used stored program processor co...
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State-of-the-art design of communication networks is characterized by the ubiquitous appearance of computer technology. All significant message-switching systems designed in the last ten years have used stored program processor controlled switching. Sophisticated terminals are also using small computers, and are otherwise dominated by the use of digital electronics. The telecommunications technological environment is characterized by rapidly changing cost-benefit relationships among system components, due primarily to the cost decline of digital logic.
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Muscular dystrophies are individually rare genetic disorders that cause much chronic disability, affecting young children and adults. In the past 20 years, more than 30 genetic types of muscular dystrophy have been defined. During...
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Muscular dystrophies are individually rare genetic disorders that cause much chronic disability, affecting young children and adults. In the past 20 years, more than 30 genetic types of muscular dystrophy have been defined. During this time, precise diagnosis, genetic counselling, and medical management have improved. These advances in medical practice have occurred while definitive therapies based on an improved knowledge of disease pathogenesis are awaited. A wide range of therapeutic options have been tested in animal models, and some are being tested in clinical trials. Various therapeutic targets are being investigated, from personalised medicines targeting specific mutations and drugs targeting cellular pathways to gene-based and cell-based therapies.
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Recently, high-transition-temperature (high-T_c) superconductivity was discovered in the iron pnictide RFeAsO_(1-x)F_x (R, rare-earth metal) family of materials. We use neutron scattering to study the structural and magnetic phase...
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Recently, high-transition-temperature (high-T_c) superconductivity was discovered in the iron pnictide RFeAsO_(1-x)F_x (R, rare-earth metal) family of materials. We use neutron scattering to study the structural and magnetic phase transitions in CeFeAsO_(1-x)F_x as the system is tuned from a semimetal to a high-T_c superconductor through fluorine (F) doping, x. In the undoped state, CeFeAsO develops a structural lattice distortion followed by a collinear antiferromagnetic order with decreasing temperature. With increasing fluorine doping, the structural phase transition decreases gradually and vanishes within the superconductivity dome near x = 0.10, whereas the antiferromagnetic order is suppressed before the appearance of superconductivity for x > 0.06, resulting in an electronic phase diagram remarkably similar to that of the high-T_c copper oxides. Comparison of the structural evolution of CeFeAsO_(1-x)F_x with other Fe-based superconductors suggests that the structural perfection of the Fe-As tetrahedron is important for the high-T_c superconductivity in these Fe pnictides.
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We use neutron scattering to study the spin and lattice structure of single-crystal SrFe_2As_2, the parent compound of the FeAs-based superconductor (Sr,K)Fe_2As_2. We find that SrFe_2As_2 exhibits an abrupt structural phase trans...
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We use neutron scattering to study the spin and lattice structure of single-crystal SrFe_2As_2, the parent compound of the FeAs-based superconductor (Sr,K)Fe_2As_2. We find that SrFe_2As_2 exhibits an abrupt structural phase transition at 220 K, where the structure changes from tetragonal with lattice parameters c>a=b to orthorhombic with c > a > b. At almost the same temperature, Fe spins develop a collinear antiferromagnetic structure along the orthorhombic a axis with spin direction parallel to this a axis. These results are consistent with earlier work on the RFeAsO (R=rare earth) families of materials and on BaFe_2As_2, and therefore suggest that static antiferromagnetic order is ubiquitous for the parent compounds of these FeAs-based high-transition temperature superconductors.
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We use powder neutron diffraction to study the spin and lattice structures of polycrystalline samples of nonsuperconducting PrFeAsO and superconducting PrFeAsO_(0.85)F_(0.15) and PrFeAsO_(0.85).We find that PrFeAsO exhibits abrupt...
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We use powder neutron diffraction to study the spin and lattice structures of polycrystalline samples of nonsuperconducting PrFeAsO and superconducting PrFeAsO_(0.85)F_(0.15) and PrFeAsO_(0.85).We find that PrFeAsO exhibits abrupt structural phase transitions at 153 K followed by static long-range antiferromagnetic order at 127 K. Both the structural distortion and magnetic order are similar to other rare-earth oxypnictides. Electron doping the system with either fluorine or oxygen deficiency suppresses the structural distortion and static long-range antiferromagnetic order, therefore placing these materials into the same class of FeAs-based superconductors.
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