102,346 research outputs found
Negative Differential Resistivity and Positive Temperature Coefficient of Resistivity effect in the diffusion limited current of ferroelectric thin film capacitors
We present a model for the leakage current in ferroelectric thin- film
capacitors which explains two of the observed phenomena that have escaped
satisfactory explanation, i.e. the occurrence of either a plateau or negative
differential resistivity at low voltages, and the observation of a Positive
Temperature Coefficient of Resistivity (PTCR) effect in certain samples in the
high-voltage regime. The leakage current is modelled by considering a
diffusion-limited current process, which in the high-voltage regime recovers
the diffusion-limited Schottky relationship of Simmons already shown to be
applicable in these systems
Entangling power of the quantum baker's map
We investigate entanglement production in a class of quantum baker's maps.
The dynamics of these maps is constructed using strings of qubits, providing a
natural tensor-product structure for application of various entanglement
measures. We find that, in general, the quantum baker's maps are good at
generating entanglement, producing multipartite entanglement amongst the qubits
close to that expected in random states. We investigate the evolution of
several entanglement measures: the subsystem linear entropy, the concurrence to
characterize entanglement between pairs of qubits, and two proposals for a
measure of multipartite entanglement. Also derived are some new analytical
formulae describing the levels of entanglement expected in random pure states.Comment: 22 pages, 11 figure
GIS Characterization of Beaver Watershed
Beaver Reservoir watershed is located in Northwest Arkansas including portions of Madison, Washington, Benton, Carroll, Franklin and Crawford counties. This watershed is important to the Northwest Arkansas region because it supplies most of the drinking water for the major towns and cities, and several rural water systems. The watershed consists of 308,971 ha with elevations ranging from approximately 341 m to 731 m above mean sea level. It includes the Springfield Plateau and the Boston Mountains provinces within the Ozark Plateau physiographic region. There are approximately 581 km of streams, 532 km of shore line, and 3712 km of roads in the watershed most of which are city streets and rural roads. The soils in the watershed vary extensively and are quite complex due to the differences in parent material, topography and time. Most parent material of the soils in the Springfield Plateau is limestone, whereas in the Boston Mountains the dominant parent material is sandstone and shale. The differences in soils have led to the differences in landuse and land cover. The near surface geology in the watershed is also divided by physiographic provinces. Most of the Springfield Plateau surface geology is limestone, whereas the Boston Mountains are primarily sandstone and shale. Spatial details of the streams, roads, soils and geology attributes in the watershed are presented in this report. The GIS database and characterization of the watershed offers an excellent beginning to future research and modeling of various water quality parameters in this and other watersheds
Impact of layer defects in ferroelectric thin films
Based on a modified Ising model in a transverse field we demonstrate that
defect layers in ferroelectric thin films, such as layers with impurities,
vacancies or dislocations, are able to induce a strong increase or decrease of
the polarization depending on the variation of the exchange interaction within
the defect layers. A Green's function technique enables us to calculate the
polarization, the excitation energy and the critical temperature of the
material with structural defects. Numerically we find the polarization as
function of temperature, film thickness and the interaction strengths between
the layers. The theoretical results are in reasonable accordance to
experimental datas of different ferroelectric thin films.Comment: 17 pages, 8 figure
Investigation of the Statistical and Spatial Distributions of Mercury Contaminated Fish, Surface Waters and Soils in Arkansas
Mercury (Hg) contamination of fish is a widespread problem throughout much of the United States and the world (Louisiana WWW page, 1997). Levels ofHg in fish suffic1ent to exceed the FDA action level of 1 mg kg-1 have been found in many water bodies, including some in Arkansas and Louisiana. As a result of the serious public health ramifications for developing fetuses and for people that subsist on native fish, fish consumption advisories due to Hg contamination have been issued in 29 states. Contamination of surface water bodies by Hg results from deforestation, forest fires, fossil fuels, mining, natural emissions and commercial emissions (Armstrong, 1994). In addition, Hg has a high affinity for organic matter in soil and sediments, and therefore, long-term storage of Hg is an environmental problem. An excellent review of the integration and synthesis of recent work on Hg pollution is given in several papers edited by Watras and Huckabee (1994). The general consensus of the reports in this document seems to be that increases in Hg levels can be attributed to one or more of several mechanisms including atmospheric deposition, acidification of soils and lakes by sulfur deposition followed by an increased sulfate reduction, and transport from other source areas
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