Open Access. Powered by Scholars. Published by Universities.®

Digital Commons Network™

Open Access. Powered by Scholars. Published by Universities.®

2008

Discipline
Institution
Keyword
Publication
Publication Type
File Type

Articles 11761 - 11790 of 13173

Full-Text Articles in Entire DC Network

Considering Operational Issues For Multiagent Conceptual Inferencing In A Distributed Information Retrieval Application, Leen-Kiat Soh Jan 2008

Considering Operational Issues For Multiagent Conceptual Inferencing In A Distributed Information Retrieval Application, Leen-Kiat Soh

School of Computing: Faculty Publications

Our system, based on a multiagent framework called collaborative understanding of distributed knowledge (CUDK), is designed with the overall goal of balancing agents’ conceptual learning and task accomplishment. The tradeoff between the two is that while conceptual learning allows an agent to improve its own concept base, it could be counter-productive: conceptual learning is time consuming and requires processing resources necessary for the agent to accomplish its tasks. In our current phase of research, we investigate the roles of resource and knowledge constraints, environmental factors (such as the frequency of queries), and learning mechanisms in a CUDK-based distributed information retrieval …

Go to article

Partial Forwarding Scheme For Dynamic Window Resizing In Live P2p Streaming Systems, Zhipeng Ouyang, Lisong Xu, Byrav Ramamurthy Jan 2008

Partial Forwarding Scheme For Dynamic Window Resizing In Live P2p Streaming Systems, Zhipeng Ouyang, Lisong Xu, Byrav Ramamurthy

School of Computing: Conference and Workshop Papers

Peer-to-peer (P2P) streaming systems, in which individual nodes or peers operated by ordinary Internet users collaborate to serve video streams, have recently aroused considerable interest in both academia and industry. An important problem in P2P streaming systems is how to reduce their consumed bandwidth, which is a major concern of Internet service providers. Our work is motivated by the fact that a user may dynamically change the size of a window displaying a video stream according to his/her personal choice, a scenario we refer to as dynamic window resizing. In this paper, we propose a scheme called the Partial Forwarding …

Go to article

A Security Framework For Wireless Sensor Networks Utilizing A Unique Session Key, Yong Wang, Byrav Ramamurthy, Yuyan Xue, Xukai Zou Jan 2008

A Security Framework For Wireless Sensor Networks Utilizing A Unique Session Key, Yong Wang, Byrav Ramamurthy, Yuyan Xue, Xukai Zou

School of Computing: Conference and Workshop Papers

Key management is a core mechanism to ensure the security of applications and network services in wireless sensor networks. It includes two aspects: key distribution and key revocation. Many key management protocols have been specifically designed for wireless sensor networks. However, most of the key management protocols focus on the establishment of the required keys or the removal of the compromised keys. The design of these key management protocols does not consider the support of higher level security applications. When the applications are integrated later in sensor networks, new mechanisms must be designed. In this paper, we propose a security …

Go to article

Providing Reliable Data Transport For Dynamic Event Sensing In Wireless Sensor Networks, Yuyan Xue, Byrav Ramamurthy, Yong Wang Jan 2008

Providing Reliable Data Transport For Dynamic Event Sensing In Wireless Sensor Networks, Yuyan Xue, Byrav Ramamurthy, Yong Wang

School of Computing: Conference and Workshop Papers

In this paper, we propose a Loss Tolerant Reliable (LTR) data transport mechanism for dynamic Event Sensing (LTRES) in WSNs. In LTRES, a reliable event sensing requirement at the transport layer is dynamically determined by the sink. A distributed source rate adaptation mechanism is designed, incorporating a loss rate based lightweight congestion control mechanism, to regulate the data traffic injected into the network so that the reliability requirement can be satisfied. An equation based fair rate control algorithm is used to improve the fairness among the LTRES flows sharing the congestion path. The performance evaluations show that LTRES can provide …

Go to article

A Key Management Protocol For Wireless Sensor Networks With Multiple Base Stations, Yong Wang, Byrav Ramamurthy, Yuyan Xue Jan 2008

A Key Management Protocol For Wireless Sensor Networks With Multiple Base Stations, Yong Wang, Byrav Ramamurthy, Yuyan Xue

School of Computing: Conference and Workshop Papers

Most of the proposed key management protocols for wireless sensor networks (WSNs) in the literature assume that a single base station is used and that the base station is trustworthy. However, there are applications in which multiple base stations are used and the security of the base stations must be considered. This paper investigates a key management protocol in wireless sensor networks which include multiple base stations. We consider the situations in which both the base stations and the sensor nodes can be compromised. The proposed key management protocol, mKeying, includes two schemes, a key distribution scheme, mKeyDist, supporting multiple …

Go to article

Computation Of A Face Attractiveness Index Based On Neoclassical Canons, Symmetry, And Golden Ratios, Kendra Schmid, David Marx, Ashok Samal Jan 2008

Computation Of A Face Attractiveness Index Based On Neoclassical Canons, Symmetry, And Golden Ratios, Kendra Schmid, David Marx, Ashok Samal

School of Computing: Faculty Publications

Analysis of attractiveness of faces has long been a topic of research. Literature has identified many different factors that can be related to attractiveness. In this research we analyze the role of symmetry, neoclassical canons, and golden ratio in the determination of attractiveness of a face. We focus on the geometry of a face and use actual faces for our analysis. We find there are some differences in the criteria used by males and females to determine attractiveness. The model we have developed to predict the attractiveness of a face using its geometry is accurate with low residual errors.

Go to article

Cross-Layer Packet Size Optimization For Wireless Terrestrial, Underwater, And Underground Sensor Networks, Mehmet C. Vuran, Ian F. Akyildiz Jan 2008

Cross-Layer Packet Size Optimization For Wireless Terrestrial, Underwater, And Underground Sensor Networks, Mehmet C. Vuran, Ian F. Akyildiz

School of Computing: Conference and Workshop Papers

In this paper, a cross-layer solution for packet size optimization in wireless sensor networks (WSN) is introduced such that the effects of multi-hop routing, the broadcast nature of the physical wireless channel, and the effects of error control techniques are captured. A key result of this paper is that contrary to the conventional wireless networks, in wireless sensor networks, longer packets reduce the collision probability. Consequently, an optimization solution is formalized by using three different objective functions, i.e., packet throughput, energy consumption, and resource utilization. Furthermore, the effects of end-to-end latency and reliability constraints are investigated that may be required …

Go to article

Design Of A Wireless Vision Sensor For Object Tracking In Wireless Vision Sensor Networks, Mauricio Casarest, Mehmet C. Vuran, Senem Velipasalar Jan 2008

Design Of A Wireless Vision Sensor For Object Tracking In Wireless Vision Sensor Networks, Mauricio Casarest, Mehmet C. Vuran, Senem Velipasalar

School of Computing: Conference and Workshop Papers

The integration of CMOS cameras with embedded processors and wireless communication devices has enabled the development of distributed wireless vision systems. Wireless Vision Sensor Networks (WVSNs), which consist of wirelessly connected embedded systems with vision and sensing capabilities, provide wide variety of application areas that have not been possible to realize with the wall-powered vision systems with wired links or scalar-data based wireless sensor networks. In this paper, the design of a middleware for a wireless vision sensor node is presented for the realization of WVSNs. The implemented wireless vision sensor node is tested through a simple vision application to …

Go to article

Atlantic And Pacific Sst Influences On Medieval Drought In North America Simulated By The Community Atmospheric Model, Song Feng, Robert Oglesby, Clinton M. Rowe, David B. Loope, Qi Hu Jan 2008

Atlantic And Pacific Sst Influences On Medieval Drought In North America Simulated By The Community Atmospheric Model, Song Feng, Robert Oglesby, Clinton M. Rowe, David B. Loope, Qi Hu

Department of Earth and Atmospheric Sciences: Faculty Publications

Severe drought is arguably one of the greatest recurring natural disasters that strikes North America. A synthesis of multiproxy data shows that North America was in the grip of a severe centennial-scale drought during medieval times (800–1300 AD). In this study, the Community Atmospheric Model (CAM) is used to investigate the role of sea surface temperature (SST) anomalies from the North Atlantic and the tropical Pacific Ocean on this megadrought. These anomalies are obtained from proxy reconstructions of SST. Four model experiments with prescribed SST anomalies in the tropical Pacific and/or North Atlantic Ocean were made. The CAM results captured …

Go to article

Life In A Temperate Polar Sea: A Unique Taphonomic Window On The Structure Of A Late Cretaceous Arctic Marine Ecosystem, Karen Chin, John Bloch, Arthur Sweet, Justin Tweet, Jaelyn Eberle, Stephen Cumbaa, Jakub Witowski, David M. Harwood Jan 2008

Life In A Temperate Polar Sea: A Unique Taphonomic Window On The Structure Of A Late Cretaceous Arctic Marine Ecosystem, Karen Chin, John Bloch, Arthur Sweet, Justin Tweet, Jaelyn Eberle, Stephen Cumbaa, Jakub Witowski, David M. Harwood

Department of Earth and Atmospheric Sciences: Faculty Publications

As the earth faces a warming climate, the rock record reminds us that comparable climatic scenarios have occurred before. In the Late Cretaceous, Arctic marine organisms were not subject to frigid temperatures but still contended with seasonal extremes in photoperiod. Here, we describe an unusual fossil assemblage from Devon Island, Arctic Canada, that offers a snapshot of a ca 75 MYR ago marine paleoecosystem adapted to such conditions. Thick siliceous biogenic sediments and glaucony sands reveal remarkably persistent high primary productivity along a high-latitude Late Cretaceous coastline. Abundant fossil feces demonstrate that this planktonic bounty supported benthic invertebrates and large, …

Go to article

Elevated Primary Productivity Of Calcareous Nannoplankton Associated With Ocean Anxoic Event 1b During The Aptian/Albian Transition (Early Cretaceous), Emily L. Browning, David K. Watkins Jan 2008

Elevated Primary Productivity Of Calcareous Nannoplankton Associated With Ocean Anxoic Event 1b During The Aptian/Albian Transition (Early Cretaceous), Emily L. Browning, David K. Watkins

Department of Earth and Atmospheric Sciences: Faculty Publications

Previous isotopic investigations of Aptian/Albian oceanic anoxic event (OAE) 1b from the western North Atlantic (Blake Nose) posited that increased sea surface temperatures and decreased salinity led to stratification of the upper water column, resulting in lowered dissolved oxygen and enhanced organic matter preservation. We examined calcareous nannofossils from the same site in the western North Atlantic (Blake Nose) to evaluate changes in surface water conditions prior to, during, and after the Aptian/Albian OAE1b. The results of our analysis conflict somewhat with the previous interpretation that OAE1b at Blake Nose was linked to water column stratification. The signal from calcareous …

Go to article

Seismic Facies And Stratigraphy Of The Cenozoic Succession In Mcmurdo Sound, Antarctica: Implications For Tectonic, Climatic And Glacial History, Christopher R. Fielding, Joanne Whittaker, Stuart A. Henrys, Terry J. Wilson, Timothy R. Naish Jan 2008

Seismic Facies And Stratigraphy Of The Cenozoic Succession In Mcmurdo Sound, Antarctica: Implications For Tectonic, Climatic And Glacial History, Christopher R. Fielding, Joanne Whittaker, Stuart A. Henrys, Terry J. Wilson, Timothy R. Naish

Department of Earth and Atmospheric Sciences: Faculty Publications

Integration of data from fully cored stratigraphic holes with an extensive grid of seismic reflection lines in McMurdo Sound, Antarctica, has allowed the formulation of a new model for the evolution of the Cenozoic Victoria Land Basin of the West Antarctic Rift. The Early Rift phase (Eocene to Early Oligocene) is recorded by wedges of strata confined by early extensional faults, and which contain seismic facies consistent with drainage via coarse-grained fans and deltas into discrete, actively subsiding grabens and half-grabens. The Main Rift phase (Early Oligocene to Early Miocene) is represented by a lens of strata that thickens symmetrically …

Go to article

Chloride And The Environmental Isotopes As The Indicators Of The Groundwater Recharge In The Gobi Desert, Northwest China, J. Z. Ma, Z. Ding, John B. Gates, Y. Su Jan 2008

Chloride And The Environmental Isotopes As The Indicators Of The Groundwater Recharge In The Gobi Desert, Northwest China, J. Z. Ma, Z. Ding, John B. Gates, Y. Su

Department of Earth and Atmospheric Sciences: Faculty Publications

The long term recharge in Gobi Desert from Hexi Corridor to Inner Mongolia Plateau was estimated to Be 1 mm year-1 by using the chloride mass balance method from one unsaturated zone profile, which shows that no effective modern recharge is taking place. A good rainfall database from Zhangye provides definition of the stable isotopic composition of modern rainfall. The signature of groundwater from the late Pleistocene differs markedly from that of the Holocene, shown clearly by the compositions of -10.5‰ δ18O as compared with values of -7‰ at the present day. It is apparent that the …

Go to article

Seismic Facies And Stratigraphy Of The Cenozoic Succession In Mcmurdo Sound, Antarctica: Implications For Tectonic, Climatic And Glacial History, Christopher R. Fielding, J. Whittaker, Stuart A. Henrys, T. J. Wilson, T. R. Naish Jan 2008

Seismic Facies And Stratigraphy Of The Cenozoic Succession In Mcmurdo Sound, Antarctica: Implications For Tectonic, Climatic And Glacial History, Christopher R. Fielding, J. Whittaker, Stuart A. Henrys, T. J. Wilson, T. R. Naish

Department of Earth and Atmospheric Sciences: Faculty Publications

A new stratigraphic model is presented for the evolution of the Cenozoic Victoria Land Basin of the West Antarctic Rift, based on integration of seismic reflection and drilling data. The Early Rift phase (?latest Eocene to Early Oligocene) comprises wedges of strata confined by early extensional faults, and which contain seismic facies consistent with drainage via coarse-grained fans and deltas into discrete, actively subsiding grabens and half-grabens. The Main Rift phase (Early Oligocene to Early Miocene) comprises a lens of strata that thickens symmetrically from the basin margins into a central depocenter, and in which stratal events pass continuously over …

Go to article

An Observational Analysis And Evaluation Of Land Surface Model Accuracy In The Nebraska Sand Hills, David B. Radell, Clinton M. Rowe Jan 2008

An Observational Analysis And Evaluation Of Land Surface Model Accuracy In The Nebraska Sand Hills, David B. Radell, Clinton M. Rowe

Department of Earth and Atmospheric Sciences: Faculty Publications

In this study, the influence of subsurface water on the energy budget components of three locations with heterogeneous land surfaces in the Nebraska Sand Hills are examined through observations and use of the Noah land surface model (LSM). Observations of the four primary components of the surface energy budget are compared for a wet interdunal meadow valley, a dry interdunal valley, and a dunal upland location. With similar atmospheric forcing at each site, it was determined that differences in the partitioning of the mean diurnal net radiation (Rnet) existed among the three locations due to the influence …

Go to article

Improved Algorithm For Modis Satellite Retrievals Of Aerosol Optical Depths Over Western North America, Easan Drury, Daniel J. Jacob, Jun Wang, Robert J.D. Spurr, Kelly Chance Jan 2008

Improved Algorithm For Modis Satellite Retrievals Of Aerosol Optical Depths Over Western North America, Easan Drury, Daniel J. Jacob, Jun Wang, Robert J.D. Spurr, Kelly Chance

Department of Earth and Atmospheric Sciences: Faculty Publications

Quantitative evaluation of chemical transport models (CTMs) with aerosol optical depth (AOD) products retrieved from satellite backscattered reflectances can be compromised by inconsistent assumptions of aerosol optical properties and errors in surface reflectance estimates. We present an improved AOD retrieval algorithm for the MODIS satellite instrument using locally derived surface reflectances and CTM aerosol optical properties for the 0.47, 0.65, and 2.13 μm MODIS channels. Assuming negligible atmospheric reflectance at 2.13 μm in cloud-free conditions, we derive 0.65/2.13 surface reflectance ratios at 1° X 1.25° horizontal resolution for the continental United States in summer 2004 from the subset of top-of-atmosphere …

Go to article

The Optimal Bulk Wind Differential Depth And The Utility Of The Upper-Tropospheric Storm-Relative Flow For Forecasting Supercells, Adam L. Houston, Richard L. Thompson, Roger Edwards Jan 2008

The Optimal Bulk Wind Differential Depth And The Utility Of The Upper-Tropospheric Storm-Relative Flow For Forecasting Supercells, Adam L. Houston, Richard L. Thompson, Roger Edwards

Department of Earth and Atmospheric Sciences: Faculty Publications

An analysis of 4 yr of Rapid Update Cycle-2 (RUC-2) derived soundings in proximity to radar-observed supercells and nonsupercells is conducted in an effort to answer two questions: 1) over what depth is the fixed-layer bulk wind differential (BWD; the vector difference between the wind velocity at a given level and the wind velocity at the surface) the best discriminator between supercell and nonsupercell environments and 2) does the upper-tropospheric storm-relative flow (UTSRF) discriminate between the environments of supercells and nonsupercells? Previous climatologies of sounding-based supercell forecast parameters have documented the ability of the 0–6-km BWD in delineating supercell from …

Go to article

Aspects Of Producing, Directing, Conditioning, Impinging And Detecting Spectroscopic Electromagnetic Radiation From Small Spots On Samples, Martin M. Liphardt, Ping He, Blaine D. Johs, Galen L. Pfeiffers, James D. Welch, John A. Woollam Jan 2008

Aspects Of Producing, Directing, Conditioning, Impinging And Detecting Spectroscopic Electromagnetic Radiation From Small Spots On Samples, Martin M. Liphardt, Ping He, Blaine D. Johs, Galen L. Pfeiffers, James D. Welch, John A. Woollam

Department of Electrical and Computer Engineering: Faculty Publications

Sytems and mehtods for providing and enhancing electromagnetic radiation beam radail energy homogeneity and intensity vs. wavelength content, for reliably directing electromagnetic radiation emitted by a source thereof in a common direction, for achromatically reducing spot size on a sample (eg. liquid cavity containing lenses and low aberration 1:1 imaging systems modified to perform as spatial filters), and for directing directing different wavelengths into different detectors, in ellipsometer, polarizer or the like systems.

Go to article

System And Method Ofselectively Monitoring Sample Front And Backside Reflections In Ellipsometer And The Like Systems, James D. Welch, John A. Woollam, Martin M Liphardt Jan 2008

System And Method Ofselectively Monitoring Sample Front And Backside Reflections In Ellipsometer And The Like Systems, James D. Welch, John A. Woollam, Martin M Liphardt

Department of Electrical and Computer Engineering: Faculty Publications

A spectrophotometer, reflectometer, ellipsometer polarimeter or the like system having a detector means for independently intercepting electromagnetic radiation reflected from a sample frontside or backside, and methodology for pursuing less correlated determination of refractive index and thickness values.

Go to article

Sample Editions Of The Oxford Hebrew Bible: Deuteronomy 32:1-9, 1 Kings 11:1-8, And Jeremiah 27:1-10 (34 G), Sidnie White Crawford, Jan Joosten, Eugene Ulrich Jan 2008

Sample Editions Of The Oxford Hebrew Bible: Deuteronomy 32:1-9, 1 Kings 11:1-8, And Jeremiah 27:1-10 (34 G), Sidnie White Crawford, Jan Joosten, Eugene Ulrich

Department of Classics and Religious Studies: Faculty Publications

The following sample editions illustrate the theory and method of the Oxford Hebrew Bible. The Deuteronomy sample, edited by Sidnie White Crawford, concerns a text with one ancient edition, while the Kings sample, edited by Jan Joosten, and the Jeremiah sample, edited by Eugene Ulrich, concern texts with two ancient editions. The arguments that justify the editorial decisions are presented in the apparatuses and text-critical commentaries. (The detailed introductory chapters are not included.) The critical texts, following the conventions discussed in the previous article, contain the following sigla: a superlinear circlet to indicate an entry in the apparatus where the …

Go to article

Network Coding For Wdm All-Optical Multicast, Eric D. Manley, Jitender S. Deogun, Lisong Xu, Dennis R. Alexander Jan 2008

Network Coding For Wdm All-Optical Multicast, Eric D. Manley, Jitender S. Deogun, Lisong Xu, Dennis R. Alexander

School of Computing: Technical Reports

Network coding has become a useful means for achieving efficient multicast, and the optical community has started to examine its application to optical networks. However, a number of challenges, including limited processing capability and coarse bandwidth granularity, need to be overcome before network coding can be effectively used in optical networks. In this paper, we address some of these problems. We consider the problem of finding efficient routes to use with coding, and we study the effectiveness of using network coding for optical-layer dedicated protection of multicast traffic. We also propose architectures for all-optical circuits capable of performing the processing …

Go to article

Short-Term Memory, Working Memory, And Executive Functioning In Preschoolers: Longitudinal Predictors Of Mathematical Achievement At Age 7 Years, Rebecca Bull, Kimberly Andrews Espy, Sandra A. Wiebe Jan 2008

Short-Term Memory, Working Memory, And Executive Functioning In Preschoolers: Longitudinal Predictors Of Mathematical Achievement At Age 7 Years, Rebecca Bull, Kimberly Andrews Espy, Sandra A. Wiebe

Department of Educational Psychology: Faculty Publications

This study examined whether measures of short-term memory, working memory, and executive functioning in preschool children predict later proficiency in academic achievement at 7 years of age (third year of primary school). Children were tested in preschool (M age = 4 years, 6 months) on a battery of cognitive measures, and mathematics and reading outcomes (from standardized, norm-referenced school-based assessments) were taken on entry to primary school, and at the end of the first and third year of primary school. Growth curve analyses examined predictors of math and reading achievement across the duration of the study and revealed that …

Go to article

Effects, Uptake, And Fate Of 2,4,6-Trinitrotoluene Aged In Soil In Plants And Worms, Elly Ph Best, Henry E. Tatem, Kaaren N. Geter, Melissa L. Wells, Brian K. Lane Jan 2008

Effects, Uptake, And Fate Of 2,4,6-Trinitrotoluene Aged In Soil In Plants And Worms, Elly Ph Best, Henry E. Tatem, Kaaren N. Geter, Melissa L. Wells, Brian K. Lane

United States Army Corps of Engineers, Omaha District

The present study was aimed at providing data to be used at predicting exposure-based effects of 2,4,6-trinitrotoluene (TNT) aged in soil on endpoint organisms representing two trophic levels. These data can be used to define criteria or reference values for environmental management and conducting specific risk assessment. Long-term exposure tests were conducted to evaluate sublethal toxicity and uptake of aged soil-based explosives, with TNT as the main contaminant. In these tests, plants were exposed for 55 d, and biomass and explosives residues were determined. Worms were exposed for 28 and 42 d, and biomass, number, and tissue residues were determined. …

Go to article

Plant-Feeding Hemiptera And Orthoptera Communities In Native And Restored Mesic Tallgrass Prairies, Kristine T. Nemec, Thomas B. Bragg Jan 2008

Plant-Feeding Hemiptera And Orthoptera Communities In Native And Restored Mesic Tallgrass Prairies, Kristine T. Nemec, Thomas B. Bragg

United States Army Corps of Engineers, Omaha District

Aboveground Hemiptera and Orthoptera communities were compared among three native and three restored mesic tallgrass prairies along the Platte River in central Nebraska to assess both the relative success of restored sites and the relationship between insect and plant communities. Hemiptera and Orthoptera were sampled using sweep nets in early June, mid-July, and mid-August 2000. Plant species composition was assessed in early June and mid-August. A total of 89 Auchenorrhyncha (71 Cicadellidae, 15 Fulgoroidea, and 3 Membracidae) and 23 orthopterans (15 Acrididae and 8 Tettigoniidae) were collected. Eighty-five plant species were observed in combined study sites. Shannon diversity was significantly …

Go to article

Towards Universal Cover Decoding, Nathan Axvig, Deanna Dreher, Katherine Morrison, Eric T. Psota, Lance C. Pérez, Judy L. Walker Jan 2008

Towards Universal Cover Decoding, Nathan Axvig, Deanna Dreher, Katherine Morrison, Eric T. Psota, Lance C. Pérez, Judy L. Walker

Department of Mathematics: Faculty Publications

Low complexity decoding of low-density paritycheck (LDPC) codes may be obtained from the application of iterative message-passing decoding algorithms to the bipartite Tanner graph of the code. Arguably, the two most important decoding algorithms for LDPC codes are the sum-product decoder and the min-sum (MS) decoder. On a bipartite graph without cycles (a tree), the sum-product decoder minimizes the probability of bit error, while the min-sum decoder minimizes the probability of word error [9]. While the behavior of sum-product and min-sum is easily understood when operating on trees, their behavior becomes much more difficult to characterize when the Tanner graph …

Go to article

Ldpc Codes From Voltage Graphs, Christine A. Kelley, Judy L. Walker Jan 2008

Ldpc Codes From Voltage Graphs, Christine A. Kelley, Judy L. Walker

Department of Mathematics: Faculty Publications

Several well-known structure-based constructions of LDPC codes, for example codes based on permutation and circulant matrices and in particular, quasi-cyclic LDPC codes, can be interpreted via algebraic voltage assignments. We explain this connection and show how this idea from topological graph theory can be used to give simple proofs of many known properties of these codes. In addition, the notion of abelianinevitable cycle is introduced and the subgraphs giving rise to these cycles are classified. We also indicate how, by using more sophisticated voltage assignments, new classes of good LDPC codes may be obtained.

Go to article

Average Min-Sum Decoding Of Ldpc Codes, Nathan Axvig, Deanna Dreher, Katherine Morrison, Eric T. Psota, Lance C. Pérez, Judy L. Walker Jan 2008

Average Min-Sum Decoding Of Ldpc Codes, Nathan Axvig, Deanna Dreher, Katherine Morrison, Eric T. Psota, Lance C. Pérez, Judy L. Walker

Department of Mathematics: Faculty Publications

Simulations have shown that the outputs of minsum (MS) decoding generally behave in one of two ways: the output either eventually stabilizes at a codeword or eventually cycles through a finite set of vectors that may include both codewords and non-codewords. This inconsistency in MS across iterations has significantly contributed to the difficulty in studying the performance of this decoder. To overcome this problem, a new decoder, average min-sum (AMS), is proposed; this decoder outputs the average of the min-sum output vectors over a finite set of iterations. Simulations comparing MS, AMS, linear programming (LP) decoding, and maximum likelihood (ML) …

Go to article

Numerical Simulation Of A Novel Blast Wave Mitigation Device, Zhenbi Su, Wen Peng, Zhaoyan Zhang, George Gogos, Reed Skaggs, Bryan Cheeseman Jan 2008

Numerical Simulation Of A Novel Blast Wave Mitigation Device, Zhenbi Su, Wen Peng, Zhaoyan Zhang, George Gogos, Reed Skaggs, Bryan Cheeseman

Department of Mechanical and Materials Engineering: Faculty Publications

This paper proposes a novel blast wave mitigation device, consisting of a piston–cylinder assembly. A shock wave is induced inside the device when it is subject to a blast wave. The shock wave propagates inside the device and is reflected repeatedly. The physical processes within the blast wave mitigation device are simulated numerically. Numerical predictions are in excellent agreement with analytical solutions for special cases of the investigated problem that are available in the literature. The peak pressure on the base of the device caused by the blast wave is studied using a number of design parameters. The numerical simulation …

Go to article

Highly Resolved Absolute Cross-Sections For Dissociative Electron Attachment To Sf5cf3, K. Graupner, L. M. Graham, T. A. Field, Christopher A. Mayhew, Ilya I. Fabrikant, T. M. Miller, M. Braun, M.-W. Ruf, Harmut Hotop Jan 2008

Highly Resolved Absolute Cross-Sections For Dissociative Electron Attachment To Sf5cf3, K. Graupner, L. M. Graham, T. A. Field, Christopher A. Mayhew, Ilya I. Fabrikant, T. M. Miller, M. Braun, M.-W. Ruf, Harmut Hotop

Ilya Fabrikant Publications

Using two complementary experimental methods, we have measured partial (mass-resolved) cross-sections for dissociative electron attachment to the molecule trifluoromethyl sulfurpentafluoride (SF5CF3) at the gas temperature TG = 300K over a broad range of electron energies (E = 0.001–12 eV).

Go to article

Relativistic Magnetic Monopole Flux Constraints From Rice, Daniel P. Hogan, Dave Z. Besson, John P. Ralston, Ilya Kravchenko, D. Seckel Jan 2008

Relativistic Magnetic Monopole Flux Constraints From Rice, Daniel P. Hogan, Dave Z. Besson, John P. Ralston, Ilya Kravchenko, D. Seckel

Department of Physics and Astronomy: Faculty Publications

We report an upper limit on the flux of relativistic monopoles based on the nonobservation of in-ice showers by the Radio Ice Cherenkov Experiment (RICE) at the South Pole.We obtain a 95% C.L. limit of order 10-18 (cm2 s sr)-1 for intermediate-mass monopoles of 107 ≤ γ ≤ 1012 at the anticipated energy Etot = 1016 GeV. This bound is over an order of magnitude stronger than all previously published experimental limits for this range of boost parameters γ and exceeds 2 orders of magnitude improvement over most of the range. We review …

Go to article

First Prev Next Last