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2006

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Articles 4711 - 4740 of 4906

Full-Text Articles in Physical Sciences and Mathematics

Structure And Magnetism Of Atomically Thin Fe Layers On Flat And Vicinal Pt Surfaces, D. Repetto, T. Y. Lee, S. Rusponi, Jan Honolka, K. Kuhnke, Violetta Sessi, Ulrich Starke, H. Brune, P. Gambardella, C. Carbone, Axel Enders, K. Kern Jan 2006

Structure And Magnetism Of Atomically Thin Fe Layers On Flat And Vicinal Pt Surfaces, D. Repetto, T. Y. Lee, S. Rusponi, Jan Honolka, K. Kuhnke, Violetta Sessi, Ulrich Starke, H. Brune, P. Gambardella, C. Carbone, Axel Enders, K. Kern

Axel Enders Publications

Ultrathin Fe films on Pt substrates have been investigated under ultrahigh vacuum conditions by scanning tunneling microscopy, low energy electron diffraction, magneto-optical Kerr effect, x-ray magnetic circular dichroism measurements, and Kerr microscopy. We present a comparison between Fe films on flat Pt(111) and stepped Pt(997), with particular focus on the magnetic anisotropy in the submonolayer thickness range below 0.2 monolayer coverage, and above the spin reorientation transition at 3 monolayer thickness. The comparison of structure and magnetism suggests that the perpendicular easy axis found for films thinner than three monolayers is due to dominating contributions from both film interfaces to …

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Effect Of Method Of Delivering Nicarbazin To Mallards On Plasma 4,4′-Dinitrocarbanilide Levels And Reproduction, C. A. Yoder, J. K. Graham, L. A. Miller, K. S. Bynum, J. J. Johnston, M. J. Goodall Jan 2006

Effect Of Method Of Delivering Nicarbazin To Mallards On Plasma 4,4′-Dinitrocarbanilide Levels And Reproduction, C. A. Yoder, J. K. Graham, L. A. Miller, K. S. Bynum, J. J. Johnston, M. J. Goodall

United States Department of Agriculture Wildlife Services: Staff Publications

Nicarbazin (NCZ), a coccidiostat used in the poultry industry, has been developed as a contraceptive for resident Canada geese. We tested the efficacy of NCZ as a contraceptive using mallards (Anas platyrhynchos) as a model for Canada geese. Nicarbazin-treated corn was fed ad libitum for 14 d at 0, 750, 1,000, or 1,500 ppm. Plasma and egg levels of 4,4′-dinitrocarbanilide (DNC), the active anticoccidial component of NCZ, differed among treatment groups in a dose-response relationship, but plasma levels did not differ between sexes. Nicarbazin caused a decrease in egg weight, but there was no effect of NCZ on …

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Magic Alkali-Fullerene Compound Clusters Of Extreme Thermal Stability, Axel Enders, N. Malinowski, D. Ievlev, E. Zurek, Jochen Autschbach, Klaus Kern Jan 2006

Magic Alkali-Fullerene Compound Clusters Of Extreme Thermal Stability, Axel Enders, N. Malinowski, D. Ievlev, E. Zurek, Jochen Autschbach, Klaus Kern

Axel Enders Publications

The thermal stability of free pure C60-, as well as C60-alkali, and -alkaline-earth metal compound clusters is investigated. We find that small (C60) m-clusters (m ≤ 6) decay at comparatively low temperatures below 400 K, as a consequence of weak intermolecular van der Waals interaction. Adding barium or potassium to the clusters dramatically increases the decay temperatures for “magic” configurations of (C60)mBa2m−1 and (C60)mK2m, which reach values as high as 1780 K. Contrary to common belief, the superstable compound …

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Search For R-Parity Violating Supersymmetry Via The Llē Couplings Λ121, Λ122 Or Λ133 In Pp Collisions At √ S = 1.96 Tev, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, Do Collaboration Jan 2006

Search For R-Parity Violating Supersymmetry Via The Llē Couplings Λ121, Λ122 Or Λ133 In Pp Collisions At √ S = 1.96 Tev, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, Do Collaboration

Kenneth Bloom Publications

A search for gaugino pair production with a trilepton signature in the framework of R-parity violating supersymmetry via the couplings λ121, λ122, or λ133 is presented. The data, corresponding to an integrated luminosity of L ≈ 360 pb−1, were collected from April 2002 to August 2004 with the D∅ detector at the Fermilab Tevatron Collider, at a center-of-mass energy of √s = 1.96 TeV. This analysis considers final states with three charged leptons with the flavor combinations eel, μμl, and eeτ (l = e or μ). No evidence for supersymmetry is …

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Why Is The Number Of Dna Bases 4?, Bo Deng Jan 2006

Why Is The Number Of Dna Bases 4?, Bo Deng

Department of Mathematics: Faculty Publications

In this paper we construct a mathematical model for DNA replication based on Shannon’s mathematical theory for communication. We treatDNAreplication as a communication channel. We show that the mean replication rate is maximal with four nucleotide bases under the primary assumption that the pairing time of the G–C bases is between 1.65 and 3 times the pairing time of the A–T bases.

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Understanding Farmers’ Forecast Use From Their Beliefs, Values, Social Norms, And Perceived Obstacles*, Q. Steven Hu, Lisa M. Pytlikzillig, Gary D. Lynne, Alan Tomkins, William J. Waltman, Michael J. Hayes, Kenneth Hubbard, Ikrom Artikov, Stacey Hoffman, Donald A. Wilhite Jan 2006

Understanding Farmers’ Forecast Use From Their Beliefs, Values, Social Norms, And Perceived Obstacles*, Q. Steven Hu, Lisa M. Pytlikzillig, Gary D. Lynne, Alan Tomkins, William J. Waltman, Michael J. Hayes, Kenneth Hubbard, Ikrom Artikov, Stacey Hoffman, Donald A. Wilhite

Department of Earth and Atmospheric Sciences: Faculty Publications

Although the accuracy of weather and climate forecasts is continuously improving and new information retrieved from climate data is adding to the understanding of climate variation, use of the forecasts and climate information by farmers in farming decisions has changed little. This lack of change may result from knowledge barriers and psychological, social, and economic factors that undermine farmer motivation to use forecasts and climate information. According to the theory of planned behavior (TPB), the motivation to use forecasts may arise from personal attitudes, social norms, and perceived control or ability to use forecasts in specific decisions. These attributes are …

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The Earth All Around Us: Selected Building Stone In Lincoln, Nebraska. A Walking Tour, William J. Wayne Jan 2006

The Earth All Around Us: Selected Building Stone In Lincoln, Nebraska. A Walking Tour, William J. Wayne

Department of Earth and Atmospheric Sciences: Faculty Publications

Stone has been a primary building material for millennia. Cities, therefore, are treasure troves of earth materials. A wide variety of stones from many places are used for walls, as foundations to support entire buildings, as trim, and more recently as cladding (facing, an overlay). The Earth science teacher can find, in the limited space of an urban environment, a superb collection of stones with which to introduce students to these materials. The surfaces of stones on the outsides of buildings illustrate the durability and the vulnerability of each kind of stone to the local climate. And the history of …

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Modeling Blackbird Abundance In The Prairie Pothole Region Using A Hierarchical Spatial Model, Greg M. Forcey, George M. Linz, Wayne E. Thogmartin, William J. Bleier Jan 2006

Modeling Blackbird Abundance In The Prairie Pothole Region Using A Hierarchical Spatial Model, Greg M. Forcey, George M. Linz, Wayne E. Thogmartin, William J. Bleier

United States Department of Agriculture Wildlife Services: Staff Publications

Blackbirds are ubiquitous members of the avian fauna in the Prairie Pothole Region. However, their abundance combined with their food habits make blackbirds significant agricultural pests on sunflower. Cost estimates for blackbird damage to sunflower in the northern Great Plains range from 4-11 million U.S. dollars per year. Because of their economic impact on agriculture, it is imperative to understand the environmental factors that influence blackbird abundance patterns. This study attempts to quantify the effects of landscape-level land use and climate patterns on blackbird abundance in the Prairie Pothole Region of the United States.

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Red-Winged Blackbird (Agelaius Phoeniceus) Reproduction In North Dakota, Rachel M. Bush, Mark E. Clark, Wendy L. Read, George M. Linz Jan 2006

Red-Winged Blackbird (Agelaius Phoeniceus) Reproduction In North Dakota, Rachel M. Bush, Mark E. Clark, Wendy L. Read, George M. Linz

United States Department of Agriculture Wildlife Services: Staff Publications

No abstract provided.

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Groundwater-Level Changes In Nebraska, Spring 2000 To Spring 2006/ Density Of Registered Irrigation Wells In Nebraska August 2005, Conservation Survey Division Jan 2006

Groundwater-Level Changes In Nebraska, Spring 2000 To Spring 2006/ Density Of Registered Irrigation Wells In Nebraska August 2005, Conservation Survey Division

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Evaluating The Effectiveness Of Slicing For Model Reduction Of Concurrent Object-Oriented Programs, Matthew B. Dwyer, John Hatcliff, Matthew Hoosier, Venkatesh Ranganath, Robby, Todd Wallentine Jan 2006

Evaluating The Effectiveness Of Slicing For Model Reduction Of Concurrent Object-Oriented Programs, Matthew B. Dwyer, John Hatcliff, Matthew Hoosier, Venkatesh Ranganath, Robby, Todd Wallentine

School of Computing: Book Chapters

Model checking techniques have proven effective for checking a number of non-trivial concurrent object-oriented software systems. However, due to the high computational and memory costs, a variety of model reduction techniques are needed to overcome current limitations on applicability and scalability. Conventional wisdom holds that static program slicing can be an effective model reduction technique, yet anecdotal evidence is mixed, and there has been no work that has systematically studied the costs/benefits of slicing for model reduction in the context of model checking source code for realistic systems. In this paper, we present an overview of the sophisticated Indus program …

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A Maximum-Likelihood Approach To Symbolic Indirect Correlation, Ashutosh Joshi, George Nagy, Daniel Lopresti, Sharad C. Seth Jan 2006

A Maximum-Likelihood Approach To Symbolic Indirect Correlation, Ashutosh Joshi, George Nagy, Daniel Lopresti, Sharad C. Seth

School of Computing: Conference and Workshop Papers

Symbolic Indirect Correlation (SIC) is a nonparametric method that offers significant advantages for recognition of ordered unsegmented signals. A previously introduced formulation of SIC based on subgraph-isomorphism requires very large reference sets in the presence of noise. In this paper, we seek to address this issue by formulating SIC classification as a maximum likelihood problem. We present experimental evidence that demonstrates that this new approach is more robust for the problem of online handwriting recognition using noisy input.

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On Reoptimizing Multi-Class Classifiers, Kun Deng, Chris Bourke, Stephen Scott, Robert E. Schapire, N. V. Vinodchandran Jan 2006

On Reoptimizing Multi-Class Classifiers, Kun Deng, Chris Bourke, Stephen Scott, Robert E. Schapire, N. V. Vinodchandran

School of Computing: Technical Reports

Significant changes in the instance distribution or associated cost function of a learning problem require one to reoptimize a previously learned classifier to work under new conditions. We study the problem of reoptimizing a multi-class classifier based on its ROC hypersurface and a matrix describing the costs of each type of prediction error. For a binary classifier, it is straightforward to find an optimal operating point based on its ROC curve and the relative cost of true positive to false positive error. However, the corresponding multi-class problem (finding an optimal operating point based on a ROC hypersurface and cost matrix) …

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Automated Generation Of Context-Aware Tests, Zhimin Wang, Sebastian Elbaum, David Rosenblum Jan 2006

Automated Generation Of Context-Aware Tests, Zhimin Wang, Sebastian Elbaum, David Rosenblum

School of Computing: Technical Reports

The incorporation of context-awareness capabilities into pervasive applications allows them to leverage contextual information to provide additional services while maintaining an acceptable quality of service. These added capabilities, however, introduce a distinct input space that can affect the behavior of these applications at any point during their execution, making their validation quite challenging. In this paper, we introduce an approach to improve the test suite of a context-aware application by identifying context-aware program points where context changes may affect the application’s behavior, and by systematically manipulating the context data fed into the application to increase its exposure to potentially valuable …

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Scaling A Dataflow Testing Methodology To The Multiparadigm World Of Commercial Spreadsheets, Marc Randall Fisher Ii, Gregg Rothermel, Tyler Creelan, Margaret Burnett Jan 2006

Scaling A Dataflow Testing Methodology To The Multiparadigm World Of Commercial Spreadsheets, Marc Randall Fisher Ii, Gregg Rothermel, Tyler Creelan, Margaret Burnett

School of Computing: Technical Reports

Spreadsheets are widely used but often contain faults. Thus, in prior work we presented a dataflow testing methodology for use with spreadsheets, which studies have shown can be used cost-effectively by end-user programmers. To date, however, the methodology has been investigated across a limited set of spreadsheet language features. Commercial spreadsheet environments are multiparadigm languages, utilizing features not accommodated by our prior approaches. In addition, most spreadsheets contain large numbers of replicated formulas that severely limit the efficiency of dataflow testing approaches. We show how to handle these two issues with a new dataflow adequacy criterion and automated detection of …

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Dynamic Lightpath Scheduling In Next-Generation Wdm Optical Networks, Lu Shen, Ajay Todimala, Byrav Ramamurthy, Xi Yang Jan 2006

Dynamic Lightpath Scheduling In Next-Generation Wdm Optical Networks, Lu Shen, Ajay Todimala, Byrav Ramamurthy, Xi Yang

School of Computing: Conference and Workshop Papers

Lightpath scheduling is an important capability in next-generation wavelength-division multiplexing (WDM) optical networks to reserve resources in advance for a specified time period while provisioning end-to-end lightpaths. In this study, we propose an approach to support dynamic lightpath scheduling in such networks. To minimize blocking probability in a network that accommodates dynamic scheduled lightpath demands (DSLDs), resource allocation should be optimized in a dynamic manner. However, for the network users who desire deterministic services, resources must be reserved in advance and guaranteed for future use. These two objectives may be mutually incompatible. Therefore, we propose a two-phase dynamic lightpath scheduling …

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Spatial Correlation-Based Collaborative Medium Access Control In Wireless Sensor Networks, Mehmet C. Vuran, Ian F. Akyildiz Jan 2006

Spatial Correlation-Based Collaborative Medium Access Control In Wireless Sensor Networks, Mehmet C. Vuran, Ian F. Akyildiz

School of Computing: Faculty Publications

Wireless Sensor Networks (WSN) are mainly characterized by dense deployment of sensor nodes which collectively transmit information about sensed events to the sink. Due to the spatial correlation between sensor nodes subject to observed events, it may not be necessary for every sensor node to transmit its data. This paper shows how the spatial correlation can be exploited on the Medium Access Control (MAC) layer. To the best of our knowledge, this is the first effort which exploits spatial correlation in WSN on the MAC layer. A theoretical framework is developed for transmission regulation of sensor nodes under a distortion …

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Burrows Dug By Large Vertebrates Into Rain-Moistened Middle Jurassic Sand Dunes, David B. Loope Jan 2006

Burrows Dug By Large Vertebrates Into Rain-Moistened Middle Jurassic Sand Dunes, David B. Loope

Department of Earth and Atmospheric Sciences: Faculty Publications

In south-central Utah, eolian cross-strata of the Escalante Member of the Entrada Sandstone contain inclined, cylindrical burrows up to 63 cm in diameter and 305 cm long. Of the 14 large tunnels located during this study, 12 descend from second- and third-order bounding surfaces that formed on the lee slopes of large dune ridges, well above the water table. The tunnels are inclined 15°–22°; one tunnel ends in an expanded chamber. Eolian cross-strata fill proximal portions of four of the tunnels and indicate that after abandonment, sand drifts migrated as much as a meter into the open shafts. Structureless sand …

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Coupling Between Primary Terrestrial Succession And The Trophic Development Of Lakes At Glacier Bay, Alaska, D. R. Engstrom, Sherilyn C. Fritz Jan 2006

Coupling Between Primary Terrestrial Succession And The Trophic Development Of Lakes At Glacier Bay, Alaska, D. R. Engstrom, Sherilyn C. Fritz

Department of Earth and Atmospheric Sciences: Faculty Publications

The natural eutrophication of lakes is still an accepted concept in limnology, arising as it does from the earliest efforts to classify lakes and place them in an evolutionary sequence. Recent studies of newly formed lakes at Glacier Bay, Alaska, only partially support this idea, and suggest more variable trends in lake trophic development which are under local (catchment-level) control. Here we use sediment cores from several lakes in Glacier Bay National Park to examine the relationship between successional changes in catchment vegetation and trends in water-column nitrogen (a limiting nutrient) and lake primary production. Terrestrial succession at Glacier Bay …

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Isopiestic Measurement Of The Osmotic Coefficients Of Aqueous {Xh2So4 + (1−X)Fe2(So4)3} Solutions At 298.15 And 323.15 K, Mariano Velazquez-Rivera, Donald Palmer, Richard Kettler Jan 2006

Isopiestic Measurement Of The Osmotic Coefficients Of Aqueous {Xh2So4 + (1−X)Fe2(So4)3} Solutions At 298.15 And 323.15 K, Mariano Velazquez-Rivera, Donald Palmer, Richard Kettler

Department of Earth and Atmospheric Sciences: Faculty Publications

This study measures the osmotic coefficients of {xH2SO4 +(1−x)Fe2 (SO4)3}(aq) solutions at 298.15 and 323.15 K that have ionic strengths as great as 19.3 mol•kg-1, using the isopiestic method. Experiments utilized both aqueous NaCl and H2SO4 as reference solutions. Equilibrium values of the osmotic coefficient obtained using the two different reference solutions were in satisfactory internal agreement. The solutions follow generally the Zdanovskii empirical linear relationship and yield values of aw for the Fe2 (SO4)3–H2O binary system at 298.15 …

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Reconstructing Sea-Level Change From The Internal Architecture Of Stromatolite Reefs: An Example From The Mesoproterozoic Sulky Formation, Dismal Lakes Group, Arctic Canada, L C. Kah, Julie K. Bartley, Tracy D. Frank, Timothy W. Lyons Jan 2006

Reconstructing Sea-Level Change From The Internal Architecture Of Stromatolite Reefs: An Example From The Mesoproterozoic Sulky Formation, Dismal Lakes Group, Arctic Canada, L C. Kah, Julie K. Bartley, Tracy D. Frank, Timothy W. Lyons

Department of Earth and Atmospheric Sciences: Faculty Publications

The Mesoproterozoic Dismal Lakes Group, arctic Canada, contains a relatively thin, yet regionally extensive stromatolitic reef complex that developed subtidally during a major transgression, shoaled to sea level, and was overlain by intertidal to supratidal carbonate and evaporite strata. The September Lake reef complex exhibits a complex internal architecture that records the interaction between stromatolite growth and changes in accommodation space derived from both higher order (4th- or 5th-order, parasequence-scale) changes in sea level and the variable bathymetry of the sea floor. Reef growth, which was initiated during three sea-level cycles, records progressive marine transgression over depositional lows that were …

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The Solar Flare Of The 14th Of July 2000 (L3+C Detector Results), Pablo Achard, Gyöngyi Baksay, László A. Baksay, K Dehmelt, Marcus Hohlmann, D Rembeczki, Z Szillasi, I Vodopianov, The L3 Collaboration Jan 2006

The Solar Flare Of The 14th Of July 2000 (L3+C Detector Results), Pablo Achard, Gyöngyi Baksay, László A. Baksay, K Dehmelt, Marcus Hohlmann, D Rembeczki, Z Szillasi, I Vodopianov, The L3 Collaboration

Aerospace, Physics, and Space Science Faculty Publications

Aims.Several experiments have reported observations on possible correlations between the flux of high energy muons and intense solar flares. If confirmed, these observations would have significant implications for acceleration processes in the heliosphere able to accelerate protons and other ions to energies of at least tens of GeV. Methods.The solar flare of the 14 of July 2000 offered a unique opportunity for the L3+C experiment to search for a correlated enhancement in the flux of muons using the L3 precision muon spectrometer. Its capabilities for observing a directional excess in the flux of muons above 15 GeV (corresponding to primary …

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A Multisite Photometric Campaign On The Pre-Main-Sequence Δ Scuti Pulsator Ip Persei, Vincenzo Ripepi, T D. Oswalt Jan 2006

A Multisite Photometric Campaign On The Pre-Main-Sequence Δ Scuti Pulsator Ip Persei, Vincenzo Ripepi, T D. Oswalt

Aerospace, Physics, and Space Science Faculty Publications

We present the results of a photometric multisite campaign on the δ Scuti Pre-Main-Sequence star IP Per. Nine telescopes have been involved in the observations, with a total of about 190 h of observations over 38 nights. Present data confirms the multiperiodic nature of this star and leads to the identification of at least nine pulsational frequencies. Comparison with the predictions of linear non-adiabatic radial pulsation models allowed us to identify only five of the nine observed frequencies, and to constrain the position of IP Per in the HR diagram. The latter is in good agreement with the empirical determination …

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Whole Earth Telescope Observations Of The Zz Ceti Star Hl Tau 76, Noël Dolez, Matt A. Wood, Thomas J. Ahrens, Nicole Silvestri Jan 2006

Whole Earth Telescope Observations Of The Zz Ceti Star Hl Tau 76, Noël Dolez, Matt A. Wood, Thomas J. Ahrens, Nicole Silvestri

Aerospace, Physics, and Space Science Faculty Publications

This paper analyses the Whole Earth Telescope observations of HL Tau 76, the first discovered pulsating DA white dwarf. The star was observed during two Whole Earth Telescope campaigns. It was a second priority target during the XCOV13 campaign in 1996 and the first priority one during the XCOV18 campaign in 1999. The 1999 campaign reached 66.5% duty cycle. With a total duration of 18 days, the frequency resolution achieved is 0.68 μHz. With such a frequency resolution, we were able to find as many as 78 significant frequencies in the power spectrum, of which 34 are independent frequencies after …

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The Rapidly Pulsating Subdwarf B Star Pg 1325+101 Ii. Structural Parameters From Asteroseismology, Stéphane Charpinet, T D. Oswalt, Mark J. Rudkin, Kyle B. Johnston Jan 2006

The Rapidly Pulsating Subdwarf B Star Pg 1325+101 Ii. Structural Parameters From Asteroseismology, Stéphane Charpinet, T D. Oswalt, Mark J. Rudkin, Kyle B. Johnston

Aerospace, Physics, and Space Science Faculty Publications

We present a detailed analysis of the rapidly pulsating subdwarf B star (or EC14026 star) PG 1325+101. This analysis exploits the outcome of dedicated multisite observations using time-series photometry that revealed the presence of (at least) 15 periodicities in the luminosity modulation of this star (Silvotti et al. 2006, A&A, 459, 557, Paper I). Based on high-S/N, medium-resolution spectra obtained at the Steward Observatory's 2.3 m Telescope and at the 6.5 m MMT Telescope, new NLTE spectroscopic derivations of the atmospheric parameters of PG 1325+101 are presented. The mean values of T eff = 35 050 ± 220 K, log …

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The Rapidly Pulsating Subdwarf B Star Pg 1325+101 I. Oscillation Modes From Multisite Observations, R Silvotti, T D. Oswalt, Mark J. Rudkin, Kyle B. Johnston Jan 2006

The Rapidly Pulsating Subdwarf B Star Pg 1325+101 I. Oscillation Modes From Multisite Observations, R Silvotti, T D. Oswalt, Mark J. Rudkin, Kyle B. Johnston

Aerospace, Physics, and Space Science Faculty Publications

In this article we present the results of 215 h of time-series photometry on the rapidly pulsating subdwarf B star PG 1325+101 (Teff - 35 000 K, log g = 5.8, log N(Hs)/N(H) = -1.7), obtained during 25 days of observation in Spring 2003 from nine different sites. As in previous observations, the temporal spectrum is dominated by the main peak at 7255.55 μHz, with an amplitude of about 2.7% which, however, is dropped to about 1.7% in February 2005. No secondary peaks close to the dominant pulsation mode are clearly detected. In addition, at least fourteen more pulsation frequencies …

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Runaway Breakdown In The Jovian Atmospheres, Joseph R. Dwyer, Lee M. Coleman, Ramon E. Lopez, Ziad H. Saleh, D. Concha, Michael G. Brown, Hamid K. Rassoul Jan 2006

Runaway Breakdown In The Jovian Atmospheres, Joseph R. Dwyer, Lee M. Coleman, Ramon E. Lopez, Ziad H. Saleh, D. Concha, Michael G. Brown, Hamid K. Rassoul

Aerospace, Physics, and Space Science Faculty Publications

Using detailed Monte Carlo calculations, the properties of runaway breakdown in the atmospheres of the four gas giant planets in our solar system are investigated, and the runaway avalanche lengths and average runaway electron kinetic energies are presented as a function of atmospheric electric field strengths. The runaway breakdown threshold field for the Jovian atmospheres is found to be 10 times smaller than the conventional breakdown field when hydrometeors are present, compared to 3 times smaller for Earth's atmosphere, indicating that runaway breakdown processes may be much more efficient in the gas giants than on Earth. In the Earth's atmosphere, …

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Correlation Between Energetic Ion Enhancements And Heliospheric Current Sheet Crossings In The Outer Heliosphere, John D. Richardson, Edward C. Stone, Ace C. Cummings, Justin C. Kasper, Ming Zhang, Leonard F. Burlaga, Nudel F. Ness, Ying Liu Jan 2006

Correlation Between Energetic Ion Enhancements And Heliospheric Current Sheet Crossings In The Outer Heliosphere, John D. Richardson, Edward C. Stone, Ace C. Cummings, Justin C. Kasper, Ming Zhang, Leonard F. Burlaga, Nudel F. Ness, Ying Liu

Aerospace, Physics, and Space Science Faculty Publications

Voyagers 1 and 2 observed highly-variable beams of energetic ions in the foreshock region upstream of the termination shock (TS). At Voyager 2 (V2), the ion intensities are generally not related to the plasma properties. At Voyager 1 (V1), the beams are often coincident with crossings of the heliospheric current sheet (HCS). The V1 intensity peaks occur when the HCS is crossed from negative to positive magnetic polarities and V1 is within a few AU of the TS. Two mechanisms are considered: current sheet drift and streaming of ions from the TS along magnetic field lines which are parallel to …

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Origin Of Heavy Ions In Upstream Events Near The Earth's Bow Shock, Mihir I. Desai, Glenn M. Mason, Joseph E. Mazur, Joseph R. Dwyer Jan 2006

Origin Of Heavy Ions In Upstream Events Near The Earth's Bow Shock, Mihir I. Desai, Glenn M. Mason, Joseph E. Mazur, Joseph R. Dwyer

Aerospace, Physics, and Space Science Faculty Publications

We have surveyed the ∼20-160 keV/nucleon heavy ion composition of 2102 upstream events observed by the Wind/STEP instrument near the Earth's bow shock over a complete solar cycle from day 325, 1994 through day 90, 2006. Our main results are: (1) During solar minimum conditions, both the C/O and Fe/O ratios are similar to the corresponding values measured in the solar wind and/or CIRs. (2) During solar maximum conditions, the C/O ratio is similar to that measured in SEP and CME-driven IP shock events, while the Fe/O ratio lies between the values measured in IP shock and SEP events. We …

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Propagation Speed Of Runaway Electron Avalanches, Lee M. Coleman, Joseph R. Dwyer Jan 2006

Propagation Speed Of Runaway Electron Avalanches, Lee M. Coleman, Joseph R. Dwyer

Aerospace, Physics, and Space Science Faculty Publications

Simulations of relativistic runaway breakdown (RRB) are performed as functions of both time and space, resulting in explicit calculations of e-folding lengths (λ) and times (τ). The ratio of λ to τ agrees well with the speed of the avalanche, which ranges from 2.61 × 108 m sˉ¹ to 2.72 × 108 m sˉ¹. Thus, using the speed of light, c, for the ratio of λ to τ can cause a 10% error when estimating λ from τ. A 10% error in λ will cause a factor of three error in the predicted number of runaway electrons for every ten …

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