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2010

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Articles 6631 - 6660 of 6945

Full-Text Articles in Physical Sciences and Mathematics

Linear Programming Models For Multi-Channel P2p Streaming Systems, Miao Wang, Lisong Xu, Byrav Ramamurthy Jan 2010

Linear Programming Models For Multi-Channel P2p Streaming Systems, Miao Wang, Lisong Xu, Byrav Ramamurthy

School of Computing: Conference and Workshop Papers

Most of the commercial P2P video streaming deployments support hundreds of channels and are referred to as multichannel systems. Measurement studies show that bandwidth resources of different channels are highly unbalanced and thus recent research studies have proposed various protocols to improve the streaming qualities for all channels by enabling cross-channel cooperation among multiple channels. However, there is no general framework for comparing existing and potential designs for multi-channel P2P systems. The goal of this paper is to establish tractable models for answering the fundamental question in multi-channel system designs: Under what circumstances, should a particular design be used to …

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Spatio-Temporal Soil Moisture Measurement With Wireless Underground Sensor Networks, Xin Dong, Mehmet C. Vuran Jan 2010

Spatio-Temporal Soil Moisture Measurement With Wireless Underground Sensor Networks, Xin Dong, Mehmet C. Vuran

School of Computing: Conference and Workshop Papers

In this paper, the estimation distortion of distributed soil moisture measurement using Wireless Underground Sensor Networks (WUSNs) is investigated. The main focus of this paper is to analyze the impact of the environment and network parameters on the estimation distortion of the soil moisture.More specifically, the effects of rainfall, soil porosity, and vegetation root zone are investigated by exploiting a rainfall model, in addition to the effects of sampling rate, network topology, and measurement signal noise ratio. Spatio-temporal correlation is characterized to develop a measurement distortion model with respect to these factors. The evaluations reveal that with porous soil and …

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Cost Efficiency Of Anycast-Based Forwarding In Duty-Cycled Wsns With Lossy Channel, Yuyan Xue, Mehmet C. Vuran, Byrav Ramamurthy Jan 2010

Cost Efficiency Of Anycast-Based Forwarding In Duty-Cycled Wsns With Lossy Channel, Yuyan Xue, Mehmet C. Vuran, Byrav Ramamurthy

School of Computing: Conference and Workshop Papers

Anycasting has been proposed recently as an efficient communication method for asynchronous duty-cycled wireless sensor networks. However, the interdependencies between end-toend communication cost and the anycasting design parameters have not been systematically studied. In this paper, a statistical endtoend cost model is presented to capture the end-to-end latency and energy consumption of anycasting operation under a realistic wireless channel model. By exploring the relationship between the end-to-end cost efficiency and the forwarding decision dependent anycasting design parameters, two anycasting forwarding metrics are proposed for fully distributed forwarding decision. By exploring the relationship among the preamble length, the size of the …

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Stochastic Analysis Of Energy Consumption In Wireless Sensor Networks, Yunbo Wang, Mehmet C. Vuran, Steve Goddard Jan 2010

Stochastic Analysis Of Energy Consumption In Wireless Sensor Networks, Yunbo Wang, Mehmet C. Vuran, Steve Goddard

School of Computing: Conference and Workshop Papers

Limited energy resources in increasingly sophisticated wireless sensor networks (WSNs) call for a comprehensive crosslayer analysis of energy consumption in a multi-hop network. For reliability analysis in such networks, the statistical information about energy consumption and lifetime is required. However, traditional energy analysis approaches only focus on the average energy consumed. In this paper, instead, we provide a stochastic analysis of the energy consumption in a random network environment. Accordingly, a comprehensive cross-layer analysis framework, which employs a stochastic queueing model, is developed. Using this framework, the distribution of energy consumption for nodes in WSNs during a given time period …

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A First Practical Algorithm For High Levels Of Relational Consistency, Shant Karakashian, Robert J. Woodward, Christopher Reeson, Berthe Y. Choueiry, Christian Bessiere Jan 2010

A First Practical Algorithm For High Levels Of Relational Consistency, Shant Karakashian, Robert J. Woodward, Christopher Reeson, Berthe Y. Choueiry, Christian Bessiere

School of Computing: Conference and Workshop Papers

Consistency properties and algorithms for achieving them are at the heart of the success of Constraint Programming. In this paper, we study the relational consistency property R(*,m)C, which is equivalent to m-wise consistency proposed in relational databases. We also define wR(*,m)C, a weaker variant of this property. We propose an algorithm for enforcing these properties on a Constraint Satisfaction Problem by tightening the existing relations and without introducing new ones. We empirically show that wR(*,m)C solves in a backtrackfree manner all the instances of some CSP benchmark classes, thus hinting at the tractability …

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A Partial Taxonomy Of Substitutability And Interchangeability, Shant Karakashian, Robert J. Woodward, Berthe Y. Choueiry, Steven D. Prestwich, Eugene C. Freuder Jan 2010

A Partial Taxonomy Of Substitutability And Interchangeability, Shant Karakashian, Robert J. Woodward, Berthe Y. Choueiry, Steven D. Prestwich, Eugene C. Freuder

School of Computing: Conference and Workshop Papers

Substitutability, interchangeability and related concepts in Constraint Programming were introduced approximately twenty years ago and have given rise to considerable subsequent research. We survey this work, classify, and relate the different concepts, and indicate directions for future work, in particular with respect to making connections with research into symmetry breaking. This paper is a condensed version of a larger work in progress.

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A Novel Weighted-Graph-Based Grouping Algorithm For Metadata Prefetching, Peng Gu, Jun Wang, Yifeng Zhu, Hong Jiang, Pengju Shang Jan 2010

A Novel Weighted-Graph-Based Grouping Algorithm For Metadata Prefetching, Peng Gu, Jun Wang, Yifeng Zhu, Hong Jiang, Pengju Shang

School of Computing: Faculty Publications

Although data prefetching algorithms have been extensively studied for years, there is no counterpart research done for metadata access performance. Existing data prefetching algorithms, either lack of emphasis on group prefetching, or bearing a high level of computational complexity, do not work well with metadata prefetching cases. Therefore, an efficient, accurate, and distributed metadata-oriented prefetching scheme is critical to leverage the overall performance in large distributed storage systems. In this paper, we present a novel weighted-graph-based prefetching technique, built on both direct and indirect successor relationship, to reap performance benefit from prefetching specifically for clustered metadata servers, an arrangement envisioned …

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Xlp: A Cross-Layer Protocol For Efficient Communication In Wireless Sensor Networks, Mehmet C. Vuran, Ian F. Akyildiz Jan 2010

Xlp: A Cross-Layer Protocol For Efficient Communication In Wireless Sensor Networks, Mehmet C. Vuran, Ian F. Akyildiz

School of Computing: Faculty Publications

Severe energy constraints of battery-powered sensor nodes necessitate energy-efficient communication in Wireless Sensor Networks (WSNs). However, the vast majority of the existing solutions is based on classical layered protocols approach, which leads to significant overhead. It is much more efficient to have a unified scheme which blends common protocol layer functionalities into a cross-layer module. In this paper, a cross layer protocol (XLP) is introduced, which achieves congestion control, routing, and medium access control in a cross-layer fashion. The design principle of XLP is based on the cross-layer concept of initiative determination, which enables receiver-based contention, initiative-based forwarding, local …

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Nebraska Statewide Groundwater-Level Monitoring Report 2010, J. T. Korus, M. E. Burbach, L. M. Howard, R. M. Joeckel Jan 2010

Nebraska Statewide Groundwater-Level Monitoring Report 2010, J. T. Korus, M. E. Burbach, L. M. Howard, R. M. Joeckel

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Isomer Identification And Resolution In Small Gold Clusters, Wei Huang, Rhitankar Pal, Lei-Ming Wang, Xiao Cheng Zeng, Lai-Sheng Wang Jan 2010

Isomer Identification And Resolution In Small Gold Clusters, Wei Huang, Rhitankar Pal, Lei-Ming Wang, Xiao Cheng Zeng, Lai-Sheng Wang

Xiao Cheng Zeng Publications

A variety of experimental techniques are used to resolve energetically close isomers of Au7 − and Au8 − by combining photoelectron spectroscopy and ab initio calculations. Two structurally distinct isomers are confirmed to exist in the cluster beam for both clusters. Populations of the different isomers in the cluster beam are tuned using Ar-tagging, O2-titration, and isoelectronic atom substitution by Cu and Ag. A new isomer structure is found for Au7 −, which consists of a triangular Au6 unit with a dangling Au atom. Isomer-specific photoelectron spectra of Au8 − are obtained …

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Longitudinal Scaling Property Of The Charge Balance Function In Au + Au Collisions At √Snn= 200 Gev, B. I. Abelev, M. M. Aggarwal, Z. Ahammed, A. V. Alakhverdyants, I. Alekseev, B. D. Anderson, D. Arkhipkin, G. S. Averichev, J. Balewski, L. S. Barnby, S. Bültmann, I. Koralt, D. Plyku Jan 2010

Longitudinal Scaling Property Of The Charge Balance Function In Au + Au Collisions At √Snn= 200 Gev, B. I. Abelev, M. M. Aggarwal, Z. Ahammed, A. V. Alakhverdyants, I. Alekseev, B. D. Anderson, D. Arkhipkin, G. S. Averichev, J. Balewski, L. S. Barnby, S. Bültmann, I. Koralt, D. Plyku

Physics Faculty Publications

We present measurements of the charge balance function, from the charged particles, for diverse pseudorapidity and transverse momentum ranges in Au + Au collisions at √sNN = 200 GeV using the STAR detector at RHIC. We observe that the balance function is boost-invariant within the pseudorapidity coverage [ − 1.3 , 1.3 ] . The balance function properly scaled by the width of the observed pseudorapidity window does not depend on the position or size of the pseudorapidity window. This scaling property also holds for particles in different transverse momentum ranges. In addition, we find that the width …

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Holdrege: Nebraska's State Soil Jan 2010

Holdrege: Nebraska's State Soil

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Melting Alpine Glaciers Enrich High-Elevation Lakes With Reactive Nitrogen, Jasmine E. Saros, Kevin C. Rose, David W. Clow, Verlin C. Stevens, Andrea B. Nurse, Heather A. Arnett, Jeffery R. Stone, Craig E. Williamson, Alexander P. Wolfe Jan 2010

Melting Alpine Glaciers Enrich High-Elevation Lakes With Reactive Nitrogen, Jasmine E. Saros, Kevin C. Rose, David W. Clow, Verlin C. Stevens, Andrea B. Nurse, Heather A. Arnett, Jeffery R. Stone, Craig E. Williamson, Alexander P. Wolfe

Department of Earth and Atmospheric Sciences: Faculty Publications

Alpine glaciers have receded substantially over the last century in many regions of the world. Resulting changes in glacial runoff not only affect the hydrological cycle, but can also alter the physical (i.e., turbidity from glacial flour) and biogeochemical properties of downstream ecosystems. Here we compare nutrient concentrations, transparency gradients, algal biomass, and fossil diatom species richness in two sets of high-elevation lakes: those fed by snowpack melt alone (SF lakes) and those fed by both glacial and snowpack meltwaters (GSF lakes). We found that nitrate (NO3-) concentrations in the GSF lakes were 1-2 orders of magnitude …

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Centennial Eolian Cyclicity In The Great Plains, Usa: A Dominant Climate Pattern Of Wind Transport Over The Past 4000 Years?, Antje Schwalb, Walter E. Dean, Sherilyn C. Fritz, Christoph E. Geiss, Bernd Kromer Jan 2010

Centennial Eolian Cyclicity In The Great Plains, Usa: A Dominant Climate Pattern Of Wind Transport Over The Past 4000 Years?, Antje Schwalb, Walter E. Dean, Sherilyn C. Fritz, Christoph E. Geiss, Bernd Kromer

Department of Earth and Atmospheric Sciences: Faculty Publications

Proxy evidence at decadal resolution from Late Holocene sediments from Pickerel Lake, northeastern South Dakota, shows distinct centennial cycles (400-700 years) in magnetic susceptibility; contents of carbonate, organic carbon, and major elements; abundance in ostracodes; and δ18O and δ13C values in calcite. Proxies indicate cyclic changes in eolian input, productivity, and temperature. Maxima in magnetic susceptibility are accompanied by maxima in aluminum and iron mass accumulation rates (MARs), and in abundances of the ostracode Fabaeformiscandona rawsoni. This indicates variable windy, and dry conditions with westerly wind dominance, including during the Medieval Climate Anomaly. Maxima in …

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Millennial-Scale Climate Variability During The Last Glacial Period In The Tropical Andes, Sherilyn C. Fritz, P. A. Baker, E. Ekdahl, G. O. Seltzer, L. R. Stevens Jan 2010

Millennial-Scale Climate Variability During The Last Glacial Period In The Tropical Andes, Sherilyn C. Fritz, P. A. Baker, E. Ekdahl, G. O. Seltzer, L. R. Stevens

Department of Earth and Atmospheric Sciences: Faculty Publications

Millennial-scale climate variation during the Last Glacial period is evident in many locations worldwide, but it is unclear if such variation occurred in the interior of tropical South America, and, if so, how the low-latitude variation was related to its high-latitude counterpart. A high-resolution record, derived from the deep drilling of sediments on the floor of Lake Titicaca in the southern tropical Andes, is presented that shows clear evidence of millennial-scale climate variation between ~60 and 20 ka BP. This variation is manifested by alternations of two interbedded sedimentary units. The two units have distinctive sedimentary, geochemical, and paleobiotic properties …

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Groundwater Recharge In Natural Dune Systems And Agricultural Ecosystems In The Thar Desert Region, Rajasthan, India, Bridget Scanlon, Abhijit Mukherjee, John B. Gates, Robert C. Reedy, Amarendra K. Sinha Jan 2010

Groundwater Recharge In Natural Dune Systems And Agricultural Ecosystems In The Thar Desert Region, Rajasthan, India, Bridget Scanlon, Abhijit Mukherjee, John B. Gates, Robert C. Reedy, Amarendra K. Sinha

Department of Earth and Atmospheric Sciences: Faculty Publications

Water and nutrient availability for crop production are critical issues in (semi)arid regions. Unsaturated-zone Cl tracer data and nutrient (NO3 and PO4) concentrations were used to quantify recharge rates using the Cl mass balance approach and nutrient availability in the Thar Desert, Rajasthan, India. Soil cores were collected in dune/interdune settings in the arid Thar Desert (near Jaisalmer) and in rain-fed (nonirrigated) and irrigated cropland in the semiarid desert margin (near Jaipur). Recharge rates were also simulated using unsaturated zone modeling. Recharge rates in sparsely vegetated dune/interdune settings in the Jaisalmer study area are 2.7-5.6 mm/year (2-3% …

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Stratigraphic Signature Of The Late Palaeozoic Ice Age In The Parmeener Supergroup Of Tasmania, Se Australia, And Inter-Regional Comparisons, Christopher R. Fielding, Tracy D. Frank, John L. Isbell, Lindsey C. Henry, Eugene W. Domack Jan 2010

Stratigraphic Signature Of The Late Palaeozoic Ice Age In The Parmeener Supergroup Of Tasmania, Se Australia, And Inter-Regional Comparisons, Christopher R. Fielding, Tracy D. Frank, John L. Isbell, Lindsey C. Henry, Eugene W. Domack

Department of Earth and Atmospheric Sciences: Faculty Publications

Recent research in eastern Australia has established that rather than being a single, long-lived epoch, the late Palaeozoic Ice Age comprised a series of glacial intervals each 1–8 million years in duration, separated by non-glacial intervals of comparable duration. In order to test whether the glacial events recognized in New South Wales and Queensland have broader extent, we conducted a reappraisal of the Parmeener Supergroup of Tasmania, southeast Australia. A facies analysis of the Pennsylvanian to Permian section was carried out, allowing rationalization of the succession into four recurrent facies associations: a) glacigenic facies association, restricted to the basal Pennsylvanian/earliest …

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Tetrapod Fauna Of The Lowermost Usili Formation (Songea Group, Ruhuhu Basin) Of Southern Tanzania, With A New Burnetiid Record, Christian A. Sidor, Kenneth D. Angielczyk, D. Marie Weide, Roger M. H. Smith, Sterling J. Nesbitt, Linda A. Tsuji Jan 2010

Tetrapod Fauna Of The Lowermost Usili Formation (Songea Group, Ruhuhu Basin) Of Southern Tanzania, With A New Burnetiid Record, Christian A. Sidor, Kenneth D. Angielczyk, D. Marie Weide, Roger M. H. Smith, Sterling J. Nesbitt, Linda A. Tsuji

Department of Earth and Atmospheric Sciences: Faculty Publications

Vertebrate fossils from the Ruhuhu Basin of southern Tanzania have been known for over 75 years, but the details of their stratigraphic distribution remain imperfectly understood. Recent fieldwork in the Upper Permian Usili Formation (Songea Group) has led to the discovery of a tetrapod assemblage in a conglomeratic unit at its base. The fossils are concentrated in matrix-supported intraformational clay pebble conglomerates interpreted as mass flow deposits in wide, shallow channels in the distal reaches of an alluvial fan. Included in this new collection are fossils representing the first record of a burnetiid therapsid from Tanzania. The anatomy of the …

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Improved Algorithm For Modis Satellite Retrievals Of Aerosol Optical Thickness Over Land In Dusty Atmosphere: Implications For Air Quality Monitoring In China, Jun Wang, Xiaoguang Xu, R. Spurr, Yuxuang Wang, Easan Drury Jan 2010

Improved Algorithm For Modis Satellite Retrievals Of Aerosol Optical Thickness Over Land In Dusty Atmosphere: Implications For Air Quality Monitoring In China, Jun Wang, Xiaoguang Xu, R. Spurr, Yuxuang Wang, Easan Drury

Department of Earth and Atmospheric Sciences: Faculty Publications

A new algorithm, using the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite reflectance and aerosol single scattering properties simulated from a chemistry transport model (GEOS-Chem), is developed to retrieve aerosol optical thickness (AOT) over land in China during the spring dust season. The algorithmfirst uses a “dynamic lower envelope” approach to sample theMODIS dark-pixel reflectance data in lowAOT conditions, to derive the local surface visible (0.65 μm)/near infrared (NIR, 2.1 μm) reflectance ratio. Joint retrievals of AOT at 0.65 μm and surface reflectance at 2.1 μm are then performed, based on the time, location, and spectraldependent single scattering properties of the …

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The Heavily Polluted Atmosphere Of The Daz White Dwarf Galex J193156.8+011745, Stephane Vennes, Adéla Kawka, Péter Németh Jan 2010

The Heavily Polluted Atmosphere Of The Daz White Dwarf Galex J193156.8+011745, Stephane Vennes, Adéla Kawka, Péter Németh

Aerospace, Physics, and Space Science Faculty Publications

We report on the discovery of a new heavily polluted white dwarf. The DAZ white dwarf GALEX J193156.8+011745 was identified in a joint Galaxy Evolution Explorer (GALEX)/GSC survey of ultraviolet-excess objects. Optical spectra obtained at ESO New Technology Telescope show strong absorption lines of magnesium and silicon, and a detailed abundance analysis based on Very Large Telescope-Kueyen UVES spectra reveal super-solar abundances of silicon and magnesium and near-solar abundances of oxygen, calcium and iron. The overall abundance pattern bears the signature of on-going accretion on to the white dwarf atmosphere. The infrared spectral energy distribution shows an excess in the …

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Chandra Observations Of The Radio Galaxy 3c 445 And The Hot Spot X-Ray Emission Mechanism, Eric S. Perlman, Markos Georganopoulos, Emily M. May, Deosthenes Kazanas Jan 2010

Chandra Observations Of The Radio Galaxy 3c 445 And The Hot Spot X-Ray Emission Mechanism, Eric S. Perlman, Markos Georganopoulos, Emily M. May, Deosthenes Kazanas

Aerospace, Physics, and Space Science Faculty Publications

We present new Chandra observations of the radio galaxy 3C 445, centered on its southern radio hot spot. Our observations detect X-ray emission displaced upstream and to the west of the radio-optical hot spot. Attempting to reproduce both the observed spectral energy distribution and the displacement excludes all one-zone models. Modeling of the radio-optical hot spot spectrum suggests that the electron distribution has a low-energy cutoff or break approximately at the proton rest mass energy. The X-rays could be due to external Compton scattering of the cosmic microwave background coming from the fast (Lorentz factor Γ ≈ 4) part of …

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Chandra Observations Of The Radio Galaxy 3c 445 And The Hot Spot X-Ray Emission Mechanism, Eric S. Perlman, Markos Georganopoulos, Emily M. May, Demosthenes Kazanas Jan 2010

Chandra Observations Of The Radio Galaxy 3c 445 And The Hot Spot X-Ray Emission Mechanism, Eric S. Perlman, Markos Georganopoulos, Emily M. May, Demosthenes Kazanas

Aerospace, Physics, and Space Science Faculty Publications

We present new Chandra observations of the radio galaxy 3C 445, centered on its southern radio hot spot. Our observations detect X-ray emission displaced upstream and to the west of the radio-optical hot spot. Attempting to reproduce both the observed spectral energy distribution and the displacement excludes all one-zone models. Modeling of the radio-optical hot spot spectrum suggests that the electron distribution has a low-energy cutoff or break approximately at the proton rest mass energy. The X-rays could be due to external Compton scattering of the cosmic microwave background coming from the fast (Lorentz factor Γ ≈ 4) part of …

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A Multi-Wavelength Spectral And Polarimetric Study Of The Jet Of 3c 264, Eric S. Perlman Jan 2010

A Multi-Wavelength Spectral And Polarimetric Study Of The Jet Of 3c 264, Eric S. Perlman

Aerospace, Physics, and Space Science Faculty Publications

We present a comprehensive multi-band spectral and polarimetric study of the jet of 3C 264 (NGC 3862). Included in this study are three Hubble Space Telescope (HST) optical and ultraviolet polarimetry data sets, along with new and archival Very Large Array radio imaging and polarimetry, a re-analysis of numerous HST broadband data sets from the near infrared to the far ultraviolet, and a Chandra ACIS-S observation. We investigate similarities and differences between optical and radio polarimetry, in both degree of polarization and projected magnetic field direction. We also examine the broadband spectral energy distribution of both the nucleus and jet …

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Model Of Sprite Luminous Trail Caused By Increasing Streamer Current, Ningyu Liu Jan 2010

Model Of Sprite Luminous Trail Caused By Increasing Streamer Current, Ningyu Liu

Aerospace, Physics, and Space Science Faculty Publications

This study investigates a possible physical mechanism responsible for the occurrence of the luminous trail of sprite streamers, which is also known as "afterglow." According to streamer modeling results, when sprite streamers propagate with expansion, acceleration and brightening, the total current flowing through the streamer body also increases. The increasing current results in the rise of the electric field in the streamer channel far behind the streamer head, which leads to effective production of N₂ excited states by electron impact excitation and then the glowing trail.

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Acceleration Of Suprathermal Particles By Compressional Plasma Wave Trains In The Solar Wind, Ming Zhang Jan 2010

Acceleration Of Suprathermal Particles By Compressional Plasma Wave Trains In The Solar Wind, Ming Zhang

Aerospace, Physics, and Space Science Faculty Publications

This paper presents a calculation of particle acceleration by an idealized compressional plasma wave train. In this model, suprathermal particles, such as pickup ions, are continuously injected into a wave train consisting of a series of compression or rarefaction regions. The momentum distribution of particles will become broader and broader as they go through the wave train, which is very similar to diffusion in momentum space. The acceleration process is very fast: it does not take too many wave cycles even with a small compression amplitude to reach an asymptotic steady state momentum distribution. In the absence of large-scale adiabatic …

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Diffusion Of Relativistic Runaway Electrons And Implications For Lightning Initiation, Joseph R. Dwyer Jan 2010

Diffusion Of Relativistic Runaway Electrons And Implications For Lightning Initiation, Joseph R. Dwyer

Aerospace, Physics, and Space Science Faculty Publications

Using detailed Monte Carlo simulations, the diffusion coefficients for relativistic runaway electron avalanches in air are found for the range of electric field strengths applicable to thunderclouds. Diffusion causes runaway electron avalanches to spread perpendicular to and parallel to the avalanche direction, resulting in much smaller peak conductivities than would be inferred otherwise. The idea that runaway electron avalanches seeded by extensive cosmic ray air showers may initiate lightning has gained considerable popularity in recent years. However, using the diffusion coefficients calculated in this paper along with the avalanche multiplication limit from X-ray and positron feedback, it is found that …

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First Results On Terrestrial Gamma Ray Flashes From The Fermi Gamma-Ray Burst Monitor, Michael S. Briggs, Joseph R. Dwyer Jan 2010

First Results On Terrestrial Gamma Ray Flashes From The Fermi Gamma-Ray Burst Monitor, Michael S. Briggs, Joseph R. Dwyer

Aerospace, Physics, and Space Science Faculty Publications

The Gamma-ray Burst Monitor (GBM) on the Fermi Gamma-ray Space Telescope detected 12 intense terrestrial gamma ray flashes (TGFs) during its first year of observation. Typical maximum energies for most of the TGFs are ∼30 MeV, with one TGF having a 38 MeV photon; two of the TGFs are softer and longer than the others. After correcting for instrumental effects, a representative bright TGF is found to have a fluence of ∼0.7 photons cm-2. Pulses are either symmetrical or have faster risetimes than fall times; they are well fit with Gaussian or lognormal functions. The fastest risetime observed was 7 …

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Thunderstorm Characteristics Associated With Rhessi Identified Terrestrial Gamma Ray Flashes, Michael E. Splitt, Steven M. Lazarus, Diana H. Barnes, Joseph R. Dwyer, Hamid K. Rassoul, David M. Smith, Bryna J. Hazelton, Brian W. Grefenstette Jan 2010

Thunderstorm Characteristics Associated With Rhessi Identified Terrestrial Gamma Ray Flashes, Michael E. Splitt, Steven M. Lazarus, Diana H. Barnes, Joseph R. Dwyer, Hamid K. Rassoul, David M. Smith, Bryna J. Hazelton, Brian W. Grefenstette

Aerospace, Physics, and Space Science Faculty Publications

The characteristics of thunderstorms that produce terrestrial gamma-ray flashes (TGFs) observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) are determined using climatological and meteorological data. RHESSI observed TGFs follow diurnal, seasonal, and geographic patterns that are very similar to those of thunderstorms confirming, in part, that these events are directly connected to thunderstorm activity. The TGF producing thunderstorms are shown to be closely associated with tall (ranging from 13.6 km to 17.3 km) tropical thunderstorm systems, a finding that is consistent with theoretical expectations from models of relativistic breakdown that relate the source region to the spectral …

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Magnetic Cloud Boundary Layer Of 9 November 2004 And Its Associated Space Weather Effects, Pingbing Zuo, Fengsi Wei, Xueshang Feng, Xiaojun Xu, Wenbin Song Jan 2010

Magnetic Cloud Boundary Layer Of 9 November 2004 And Its Associated Space Weather Effects, Pingbing Zuo, Fengsi Wei, Xueshang Feng, Xiaojun Xu, Wenbin Song

Aerospace, Physics, and Space Science Faculty Publications

On 9 November 2004, the WIND spacecraft detected a magnetic cloud boundary layer (MCBL) during the interval from 19:07 UT to 20:30 UT. Within the MCBL, there is intense southward magnetic field and the dynamic pressure is rather high, which makes it much geoeffective. Twenty-three minutes later, the MCBL arrived on the magnetopause. An intense geomagnetic storm main phase was driven by the sustaining strong southward magnetic field within the MCBL. During the passage of the MCBL, a typical magnetospheric substorm was triggered. The substorm onset was synthetically identified by the aurora breakup, magnetic dipolarization, dispersionless particle injection, Pi2 pulsation, …

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Isolation And Identification Of A New Acetildenafil Analogue Used To Adulterate A Dietary Supplement: Dimethylacetildenafil, Ali̇ Hakan Göker, Maksut Coşkun, Mehmet Alp Jan 2010

Isolation And Identification Of A New Acetildenafil Analogue Used To Adulterate A Dietary Supplement: Dimethylacetildenafil, Ali̇ Hakan Göker, Maksut Coşkun, Mehmet Alp

Turkish Journal of Chemistry

A new sildenafil analogue was found to have been added illegally to a dietary supplement marketed for the enhancement of sexual function. The structure was determined as 5-(2-ethoxy-5- {[4-(3,5-dimethyl)piperazin-1-yl]-acetyl}phenyl)-1,6-dihydro-1-methyl-3- propyl-7H-pyrazolo [4,3-d]pyrimidin-7-one. Owing to the inclusion of a dimethyl group in acetildenafil, the detected compound was called dimethylacetildenafil. The sample was purified with column chromatography. The IR, LC/MS (ESI), and completely assigned NMR data of dimethylacetildenafil are reported for the first time. The structure was compared with that of acetildenafil and the results showed that the ethyl substitution at the 4-position of the piperazine ring had been replaced by a 3,5-dimethyl …

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