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2000

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Articles 2461 - 2490 of 2647

Full-Text Articles in Physical Sciences and Mathematics

Track Theory Predictions For Single-Hit Cell Survival, Robert Katz, Francis Cucinotta Jan 2000

Track Theory Predictions For Single-Hit Cell Survival, Robert Katz, Francis Cucinotta

Robert Katz Publications

The track theory of cell survival after heavy-ion irradiation is based on the probability of survival after a single-particle transit, called ‘‘ion-kill’’ (not track core), joined to the cumulative effect of δ rays from adjacent ions in a beam, called ‘‘gamma-kill’’ (not penumbra). The model offers a set of equations containing four parameters, E0 and m for the single-hit multitarget statistical model for gamma-kill, and additionally σ0 and κ for ion-kill. A single set of parameters is used to fit a family of survival curves obtained with ions of different LET simultaneously.

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Holocene Environmental And Climatic Change In The Northern Great Plains As Recorded In The Geochemistry Of Sediments In Pickerel Lake, South Dakota, Walter E. Dean, Antje Schwalb Jan 2000

Holocene Environmental And Climatic Change In The Northern Great Plains As Recorded In The Geochemistry Of Sediments In Pickerel Lake, South Dakota, Walter E. Dean, Antje Schwalb

United States Geological Survey: Staff Publications

The sediments in Pickerel Lake, northeastern South Dakota, provide a continuous record of climatic and environmental change for the last 12000 yr. Sediments deposited between 12 and 6 ka (radiocarbon) show extreme variations in composition, oxygen and carbon isotopic composition of bulk carbonate, carbon isotopic composition of organic matter, and magnetic susceptibility. These variations reflect changes in sources of moisture, regional vegetation types, precipitation-evaporation balance, ground- and surface-water influx, water residence time, erosion, lake productivity, water level, and water temperature. The total carbonate content of late Pleistocene sediments steadily increased from <20% at the base of the core to as much as 80% in sediments deposited between 11 and 9 ka. By about 8 ka, the total carbonate content of the sediments had declined to about 40% where it remained with little variation for the past 8 kyr, suggesting relatively stable conditions. There are marked increases in values of δ13C and δ18O in bulk carbonate, …

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Dating Marine Terraces With Relative-Age And Correlated-Age Methods, Daniel R. Muhs Jan 2000

Dating Marine Terraces With Relative-Age And Correlated-Age Methods, Daniel R. Muhs

United States Geological Survey: Staff Publications

Coastal landforms, and particularly emergent marine terraces, a re amongt he most importantg eomorphicfe aturesi n studieso f Quaternarys eal evel fluctuationsa nd neotectonics. A general model, first articulated by Alexander (1953) and borne out by detailedr ecent studieso n many coastlinesi,s that emergent flights of erosional terraces and coral reefs (Fig. 1) are the resulto f glacioeustaticallyc ontrolledf luctuations of global sea level superimposed on steady uplift. Similiarity of U-series ages of coral from both constructional reefsi n the tropicsa nd erosionalt erracesi n midlatitudesh as provided a rigorous test of this model (Mesolella and others, 1969; Bloom and …

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Geomorphometry – Diversity In Quantitative Surface Analysis, Richard J. Pike Jan 2000

Geomorphometry – Diversity In Quantitative Surface Analysis, Richard J. Pike

United States Geological Survey: Staff Publications

A widening variety of applications is diversifying geomorphometry (digital terrain modelling), the quantitative study of topography. An amalgam of earth science, mathematics, engineering and computer science, the discipline has been revolutionized by the computer manipulation of gridded terrain heights, or digital elevation models (DEMs). Its rapid expansion continues. This article reviews the remarkable diversity of recent morphometric work in 15 selected topics and discusses their significance and prospects. The quantitative analysis of industrial microsurface topography is introduced to the earth science community. The 14 other topics are Internet access to geomorphometry; global DEMs; DEM modelling of channel networks; …

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Single-Dilution Enzyme-Linked Immunosorbent Assay For Quantification Of Antigen-Specific Salmonid Antibody, Stewart W. Alcorn, Ronald J. Pascho Jan 2000

Single-Dilution Enzyme-Linked Immunosorbent Assay For Quantification Of Antigen-Specific Salmonid Antibody, Stewart W. Alcorn, Ronald J. Pascho

United States Geological Survey: Staff Publications

An enzyme-linked immunosorbent assay (ELISA) was developed on the basis of testing a single dilution of serum to quantify the level of antibody to the p57 protein of Renibacterium salmoninarum in sockeye salmon (Oncorhynchus nerka). The levels of antibody were interpolated from a standard curve constructed by relating the optical densities (OD) produced by several dilutions of a high-titer rainbow trout (O. mykiss) antiserum to the p57 protein. The ELISA OD values produced by as many as 36 test sera on each microplate were compared with the standard curve to calculate the antigen-specific antibody activity. Repeated …

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Agroforestry In The United States: Research And Technology Transfer Needs For The Next Millennium Jan 2000

Agroforestry In The United States: Research And Technology Transfer Needs For The Next Millennium

United States Department of Agriculture, Forest Service / University of Nebraska-Lincoln: Faculty Publications

If society's needs and aspirations for forestderived goods, services, and amenities truely are to be met, we must find ways of augmenting traditional forestry by gleaning some portion of these benefits from agricultural lands. For example: windbreaks, riparian forest buffers, hybrid poplar trees, farm woodlots, and grazing/timber systems.

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Distribution, Speciation, And Transport Of Mercury In Stream-Sediment, Stream-Water, And Fish Collected Near Abandoned Mercury Mines In Southwestern Alaska, Usa, John E. Gray, Peter M. Theodorakos, Elizabeth A. Bailey, Ralph R. Turner Jan 2000

Distribution, Speciation, And Transport Of Mercury In Stream-Sediment, Stream-Water, And Fish Collected Near Abandoned Mercury Mines In Southwestern Alaska, Usa, John E. Gray, Peter M. Theodorakos, Elizabeth A. Bailey, Ralph R. Turner

United States Geological Survey: Staff Publications

Concentrations of total Hg, Hg(II), and methylmercury were measured in stream-sediment, stream-water, and fish collected downstream from abandoned mercury mines in southwestern Alaska to evaluate environmental effects to surrounding ecosystems. These mines are found in a broad belt covering several tens of thousands of square kilometers, primarily in the Kuskokwim River basin. Mercury ore is dominantly cinnabar (HgS), but elemental mercury (Hg °) is present in ore at one mine and near retorts and in streams at several mine sites. Approximately 1400 t of mercury have been produced from the region, which is approximately 99% of all mercury produced from …

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Negative Ph And Extremely Acidic Mine Waters From Iron Mountain, California, Darrell Kirk Nordstrom, Charles N. Alpers, Carol J. Ptacek, David W. Blowes Jan 2000

Negative Ph And Extremely Acidic Mine Waters From Iron Mountain, California, Darrell Kirk Nordstrom, Charles N. Alpers, Carol J. Ptacek, David W. Blowes

United States Geological Survey: Staff Publications

Extremely acidic mine waters with pH values as low as -3.6, total dissolved metal concentrations as high as 200 g/L, and sulfate concentrations as high as 760 g/L, have been encountered underground in the Richmond Mine at Iron Mountain, CA. These are the most acidic waters known. The pH measurements were obtained by using the Pitzer method to define pH for calibration of glass membrane electrodes. The calibration of pH below 0.5 with glass membrane electrodes becomes strongly nonlinear but is reproducible to a pH as low as -4. Numerous efflorescent minerals were found forming from these acid waters. These …

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Viability Of Piping Plover Charadrius Melodus Metapopulations, Jonathan H. Plissner, Susan M. Haig Jan 2000

Viability Of Piping Plover Charadrius Melodus Metapopulations, Jonathan H. Plissner, Susan M. Haig

United States Geological Survey: Staff Publications

The meta-population viability analysis package, vortex, was used to examine viability and recovery objectives for piping plovers Charadrius melodus, an endangered shorebird that breeds in three distinct regions of North America. Baseline models indicate that while Atlantic Coast populations, under current management practices, are at little risk of near-term extinction, Great Plains and Great Lakes populations require 36% higher mean fecundity for a significant probability of persisting for the next 100 years. Meta-population structure (i.e. the delineation of populations within the meta-population) and inter-population dispersal rates had varying effects on model results; however, spatially-structured meta-populations exhibited lower viability than …

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Aquatic Dissipation Of The Herbicide Triclopyr In Lake Minnetonka, Minnesota, Kurt D. Getsinger, David G. Petty, John D. Madsen, John G. Skogerboe, Bruce A. Houtman, William T. Haller, Alison M. Fox Jan 2000

Aquatic Dissipation Of The Herbicide Triclopyr In Lake Minnetonka, Minnesota, Kurt D. Getsinger, David G. Petty, John D. Madsen, John G. Skogerboe, Bruce A. Houtman, William T. Haller, Alison M. Fox

United States Army Corps of Engineers, Omaha District

A study of the aquatic fate of the triethylamine salt of triclopyr (3,5,6-trichloro-2- pyridinyloxyacetic acid) was conducted in three bays of Lake Minnetonka, Minnesota. Triclopyr is under review by the US Environmental Protection Agency as a selective aquatic herbicide. The primary purpose of this study was to determine dissipation rates of the parent active ingredient, triclopyr, and its major metabolites, 3,5,6-trichloropyridinol (TCP) and 3,5,6-trichloro-2-methoxypyridine (TMP) in selected matrices including water, sediment, plants, finfish and shellfish. Two 6.5- ha plots dominated by the weedy species Eurasian watermilfoil (Myriophyllum spicatum L) were treated with triclopyr-triethylammonum at a rate of 2.5mg AE liter …

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Geochemical And Mineralogical Evidence From Eolian Sediments For Northwesterly Mid-Holocene Paleowinds, Central Kansas, Usa, Alan F. Arbogast, Daniel R. Muhs Jan 2000

Geochemical And Mineralogical Evidence From Eolian Sediments For Northwesterly Mid-Holocene Paleowinds, Central Kansas, Usa, Alan F. Arbogast, Daniel R. Muhs

United States Geological Survey: Staff Publications

A prominent (4500 km2) dune field in the Great Plains is the Great Bend Sand Prairie of south-central Kansas. Dunes here overlie late Quaternary alluvium and were reactivated extensively in the late Holocene. Geomorphic and soil evidence suggests that the most likely eolian sand source is the Arkansas River valley to the northwest. Nevertheless, orientations of stabilized dunes indicate that the most recent dune-forming winds came from the south or southwest, in agreement with modern wind data.

Mineralogy and trace element concentrations in eolian sands of the Great Bend Sand Prairie are similar to those of the Arkansas …

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Geochemical Variations In Peoria Loess Of Western Iowa Indicate Paleowinds Of Midcontinental North America During Last Glaciation, Daniel R. Muhs, E. Arthur Bettis Iii Jan 2000

Geochemical Variations In Peoria Loess Of Western Iowa Indicate Paleowinds Of Midcontinental North America During Last Glaciation, Daniel R. Muhs, E. Arthur Bettis Iii

United States Geological Survey: Staff Publications

Peoria Loess deposited in western Iowa during the last glacial maximum (LGM) shows distinct geochemical and particle-size variations as a function of both depth and distance east of the Missouri River. Geochemical and particle-size data indicate that Peoria Loess in western Iowa probably had two sources: the Missouri River valley, and a source that lay to the west of the Missouri River. Both sources indicate that LGM paleowinds in western Iowa had a strong westerly component, similar to interpretations of previous workers. A compilation of loess studies in Iowa and elsewhere indicates that westerlv winds were dominant during loess transport …

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Effects Of Topography And Soil Properties On Recharge At Two Sites In An Agricultural Field, Geoffrey N. Delin, Richard W. Healy, Matthew K. Landon, John Karl Böhlke Jan 2000

Effects Of Topography And Soil Properties On Recharge At Two Sites In An Agricultural Field, Geoffrey N. Delin, Richard W. Healy, Matthew K. Landon, John Karl Böhlke

United States Geological Survey: Staff Publications

Field experiments were conducted from 1992 to 1995 to estimate ground water recharge rates at two sites located within a 2.7-hectare agricultural field. The field lies in a sand plain setting in central Minnesota and is cropped continuously in field corn. The sites are located at a topographically high (upland) site and a topographically low (lowland) site in an effort to quantify the effects of depression focusing of recharge. Three site-specific methods were used to estimate recharge rates: well hydrograph analysis, chlorofluorocarbon age dating, and an unsaturated zone water balance. All three recharge methods indicated that recharge rates at the …

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Multivariate Correlation Between Concentrations Of Selected Herbicides And Derivatives In Outflows From Selected U.S. Midwestern Reservoirs, R. Tauler, D. Barcelo, E. Michael Thurman Jan 2000

Multivariate Correlation Between Concentrations Of Selected Herbicides And Derivatives In Outflows From Selected U.S. Midwestern Reservoirs, R. Tauler, D. Barcelo, E. Michael Thurman

United States Geological Survey: Staff Publications

Multivariate correlations between the concentrations of selected herbicides and herbicide derivatives in outflows from selected reservoirs in the Midwestern United States for April 1992 through September 1993 were investigated using principal component analysis (PCA) and multivariate curve resolution (MCR). Two independent sources for alachlor ethanesulfonic acid, one major source related to spring flush and seasonal runoff and another minor source related to groundwater, were identified using PCA. Results of MCR provided a semiquantitative interpretation of the environmental sources of the observed herbicide concentrations in reservoir outflows and allowed the examination of their temporal and geographical distributions. Samples with higher herbicide …

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Nutrients In Groundwaters Of The Conterminous United States, 1992-1995, Bernard Nolan, Jeffrey Stoner Jan 2000

Nutrients In Groundwaters Of The Conterminous United States, 1992-1995, Bernard Nolan, Jeffrey Stoner

United States Geological Survey: Staff Publications

Results of a national water quality assessment indicate that nitrate is detected in 71% of groundwater samples, more than 13 times as often as ammonia, nitrite, organic nitrogen, and orthophosphate, based on a common detection threshold of 0.2 mg/L. Shallow groundwater (typically 5 m deep or less) beneath agricultural land has the highest median nitrate concentration (3.4 mg/L), followed by shallow groundwater beneath urban land (1.6 mg/L) and deeper groundwater in major aquifers (0.48 mg/L). Nitrate exceeds the maximum contaminant level, 10 mg/L as nitrogen, in more than 15% of groundwater samples from 4 of 33 major aquifers commonly used …

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Ecogeochemistry Of The Subsurface Food Web At Ph 0–2.5 In Iron Mountain, California, U.S.A., Eleanora I. Robbins, Teresa M. Rodgers, Charles N. Alpers, D. Kirk Nordstrom Jan 2000

Ecogeochemistry Of The Subsurface Food Web At Ph 0–2.5 In Iron Mountain, California, U.S.A., Eleanora I. Robbins, Teresa M. Rodgers, Charles N. Alpers, D. Kirk Nordstrom

United States Geological Survey: Staff Publications

Pyrite oxidation in the underground mining environment of Iron Mountain, California, has created the most acidic pH values ever reported in aquatic systems. Sulfate values as high as 120 000 mg 1-1 and iron as high as 27600mg 1-1 have been measured in the mine water, which also carries abundant other dissolved metals including Al, Zn, Cu, Cd, Mn, Sb and Pb. Extreme acidity and high metal concentrations apparently do not preclude the presence of an underground acidophilic food web, which has developed with bacterial biomass at the base and heliozoans as top predators. Slimes, oil-like films, flexible …

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Two-Dimensional Ferroelectrics, L. M. Blinov, V. M. Fridkin, S.P. Palto, A. V. Bune, Peter A. Dowben, Stephen Ducharme Jan 2000

Two-Dimensional Ferroelectrics, L. M. Blinov, V. M. Fridkin, S.P. Palto, A. V. Bune, Peter A. Dowben, Stephen Ducharme

Stephen Ducharme Publications

The investigation of the finite-size effect in ferroelectric crystals and films has been limited by the experimental conditions. The smallest demonstrated ferroelectric crystals had a diameter of ~ 200 A and the thinnest ferroelectric films were ~ 200 A thick, macroscopic sizes on an atomic scale. Langmuir - Blodgett deposition of films one monolayer at a time has produced high quality ferroelectric films as thin as 10 A, made from polyvinylidene fluoride and its copolymers. These ultrathin films permitted the ultimate investigation of finite-size effects on the atomic thickness scale. Langmuir ± Blodgett films also revealed the fundamental two-dimensional character …

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The Polarization Of Sb Overlayers On Nimnsb(100), Takashi Komesu, C.N. Borca, Hae-Kyung Jeong, Peter A. Dowben, Delia Ristoiu, J.P. Nozieres, Shane Stadler, Y.U. Idzerda Jan 2000

The Polarization Of Sb Overlayers On Nimnsb(100), Takashi Komesu, C.N. Borca, Hae-Kyung Jeong, Peter A. Dowben, Delia Ristoiu, J.P. Nozieres, Shane Stadler, Y.U. Idzerda

Peter Dowben Publications

We have investigated the induced polarization of paramagnetic Sb overlayers on the Heusler alloy NiMnSb. From combined X-ray absorption spectroscopy (XAS) and spin-polarized inverse photoemission spectroscopy (SPIPES), we can assign some of the unoccupied states of the Heusler alloy NiMnSb. With increasing thickness of the Sb overlayer, there is a decline in the density of states near the Fermi energy, as expected for a semimetal overlayer on a metallic substrate. While the Sb is polarized by the ferromagnetic NiMnSb substrate, consistent with the expectations of mean field theory, the polarization at the center of the surface/overlayer Brillouin zone cannot be …

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Sheep-Predation Behaviors Of Wild-Caught, Confined Coyotes: Some Historical Data, Ray T. Sterner, Kenneth Crane Jan 2000

Sheep-Predation Behaviors Of Wild-Caught, Confined Coyotes: Some Historical Data, Ray T. Sterner, Kenneth Crane

United States Department of Agriculture Wildlife Services: Staff Publications

As part of efforts to develop The Livestock Protection Collar (U.S. EPA Reg. No. 56228-22), we videotaped sheep-predation events by 23 (15 males and 8 females) wild-caught, confined coyotes (Canis latrans) in a 31 x 41 m enclosure. Coyotes were paired individually with a sheep (Ovis aries) during 1 h daily trials. Nineteen (13 males and 6 females) of the coyotes made 75 fatal attacks of 1 to 7 sheep each; 4 coyotes (2 males and 2 females) made no fatal attacks despite 19 to 39 daily pairings. Of coyotes that made fatal attacks, 13 (9 …

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Soil-Moisture Preferences And Soil-Use Behaviors Of Northern Pocket Gophers, Ray T. Sterner Jan 2000

Soil-Moisture Preferences And Soil-Use Behaviors Of Northern Pocket Gophers, Ray T. Sterner

United States Department of Agriculture Wildlife Services: Staff Publications

Factors affecting soil-contact and –manipulation behaviors of pocket gophers (Thomomys and Geomys spp.) are poorly understood. Delineation of these behaviors is crucial to development of new repellent systems that seek to exploit the fossorial activity of these rodents. In a laboratory study involving northern pocket gophers (Thomomys talpoides), I examined the effects(s) of gravimetric soil moisture (i.e., 0%, 5%, 10%, 15%, 20%, 25%) upon soil-contact and –use behaviors. Six gophers received successive, 0.5 h/day exposures to one of the moist soils compared to dry (0%) soil in a 2-choice apparatus. Times in each compartment and observed …

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Strychnine Alkaloid And Avian Reproduction: Effects Occur At Lower Dietary Concentrations With Mallard Ducks Than With Bobwhite Quail, C. A. Pedersen, R. T. Sterner, M. J. Goodall Jan 2000

Strychnine Alkaloid And Avian Reproduction: Effects Occur At Lower Dietary Concentrations With Mallard Ducks Than With Bobwhite Quail, C. A. Pedersen, R. T. Sterner, M. J. Goodall

United States Department of Agriculture Wildlife Services: Staff Publications

Separate subchronic reproductive toxicity studies were conducted using mallard ducks (Anas platyrhynchos) and northern bobwhite quail (Colinus virginianus). Three groups (32/group; 16 male-female pairs) of 17-week-old ducks (F0 generation) were fed Purina® Game Bird Breeder Layena® diets containing mean (±SD) 33.2 (±2.7), 68.9 (±1.8), and 140.9 (± 5.1) μg/g strychnine for 20 weeks, with some pairs in each group fed control diet during a subsequent 3-week recovery period. Three groups (32/group; 16 male-female pairs) of 19-week-old quail (F0 generation) were fed similar diets containing mean (±SD) 279.2 (±10.1), 557.4 (±43.5), and 1,113.6 (±46.6) μg/g …

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Boundary Controllability Of Thermoelastic Plates Via The Free Boundary Conditions, George Avalos, Irena Lasiecka Jan 2000

Boundary Controllability Of Thermoelastic Plates Via The Free Boundary Conditions, George Avalos, Irena Lasiecka

Department of Mathematics: Faculty Publications

Controllability properties of a partial differential equation (PDE) model describing a thermoelastic plate are studied. The PDE is composed of a Kirchoff plate equation coupled to a heat equation on a bounded domain, with the coupling taking place on the interior and boundary of the domain. The coupling in this PDE is parameterized by α > 0. Boundary control is exerted through the (two) free boundary conditions of the plate equation and through the Robin boundary condition of the temperature. These controls have the physical interpretation of inserted forces and moments and prescribed temperature, respectively, all of which act on the …

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Two-Groups With Few Conjugacy Classes, Nigel Boston, Judy L. Walker Jan 2000

Two-Groups With Few Conjugacy Classes, Nigel Boston, Judy L. Walker

Department of Mathematics: Faculty Publications

An old question of Brauer asking how fast numbers of conjugacy classes grow is investigated by considering the least number cn of conjugacy classes in a group of order 2n. The numbers cn are computed for n ≤ 14 and a lower bound is given for c15. It is observed that cn grows very slowly except for occasional large jumps corresponding to an increase in coclass of the minimal groups Gn. Restricting to groups that are 2-generated or have coclass at most 3 allows us to extend these computations.

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Translation Theorems For Fourier-Feynman Transforms And Conditional Fourier-Feynman Transforms, Seung Jun Change, Chull Park, David Skough Jan 2000

Translation Theorems For Fourier-Feynman Transforms And Conditional Fourier-Feynman Transforms, Seung Jun Change, Chull Park, David Skough

Department of Mathematics: Faculty Publications

Translation theorems for Wiener integrals were given by Cameron and Martin in [3] and by Cameron and Graves in [2]. Translation theorems for analytic Feynman integrals were given by Cameron and Storvick in [4], [7] and translation theorems for Feynman integrals on abstract Wiener and Hilbert spaces were given by Chung and Kang in [12].

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Groundwater-Level Changes In Nebraska - Spring 1999 To Spring 2000, Conservation Survey Division Jan 2000

Groundwater-Level Changes In Nebraska - Spring 1999 To Spring 2000, Conservation Survey Division

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Field Trip Guide (For The Nebraska Well Drillers Association) Eastern Nebraska Geology, S. Summerside, D. A. Eversoll, M. Kuzila, M. Joeckel Jan 2000

Field Trip Guide (For The Nebraska Well Drillers Association) Eastern Nebraska Geology, S. Summerside, D. A. Eversoll, M. Kuzila, M. Joeckel

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Exploiting Don't Cares To Enhance Functional Tests, Mark W. Weiss, Sharad C. Seth, Shashank K. Mehta, Kent L. Einspahr Jan 2000

Exploiting Don't Cares To Enhance Functional Tests, Mark W. Weiss, Sharad C. Seth, Shashank K. Mehta, Kent L. Einspahr

School of Computing: Conference and Workshop Papers

In simulation based design verification, deterministic or pseudo-random tests are used to check functional correctness of a design. In this paper we present a technique generating tests by specifying the don’t care inputs in the functional specifications so as to improve their coverage of both design errors and manufacturing faults. The don’t cares are chosen to maximize sensitization of signals in the circuit. The tests generated in this way require only a fraction of pseudo-exhaustive test patterns to achieve a high multiplicity of fault coverage.

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Prioritizing Test Cases For Regression Testing, Sebastian Elbaum, Alexey G. Malishevsky, Gregg Rothermel Jan 2000

Prioritizing Test Cases For Regression Testing, Sebastian Elbaum, Alexey G. Malishevsky, Gregg Rothermel

School of Computing: Technical Reports

Test case prioritization techniques schedule test cases in an order that increases their effectiveness in meeting some performance goal. One performance goal, rate of fault detection, is a measure of how quickly faults are detected within the testing process; an improved rate of fault detection can pro- vide faster feedback on the system under test, and let soft- ware engineers begin locating and correcting faults earlier than might otherwise be possible. In previous work, we re- ported the results of studies that showed that prioritization techniques can significantly improve rate of fault detection. Those studies, however, raised several additional questions: …

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Lsmac And Lsnait: Two Approaches For Cluster-Based Scalable Web Servers, Xuehong Gana, Trevor Schroeder, Steve Goddard, Byrav Ramamurthy Jan 2000

Lsmac And Lsnait: Two Approaches For Cluster-Based Scalable Web Servers, Xuehong Gana, Trevor Schroeder, Steve Goddard, Byrav Ramamurthy

School of Computing: Conference and Workshop Papers

Server responsiveness and scalability are more important than ever in today’s client/server dominated network environments. Recently, researchers have begun to consider cluster-based computers using commodity hardware as an alternative to expensive specialized hardware for building scalable Web servers. In this paper, we present performance results comparing two cluster-based Web servers based on different server infrastructures: MAC-based dispatching (LSMAC) and IP-based dispatching (LSNAT). Both cluster-based server systems were implemented as application-space programs running on commodity hardware. We point out the advantages and disadvantages of both systems. We also identify when servers should be clustered and when clustering will not improve performance.

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Optical Communication Networks For The Next-Generation Internet, Arun K. Somani, Byrav Ramamurthy Jan 2000

Optical Communication Networks For The Next-Generation Internet, Arun K. Somani, Byrav Ramamurthy

School of Computing: Faculty Publications

Computer and telecommunication networks are changing the world dramatically and will continue to do so in the foreseeable future. The Internet, primarily based on packet switches, provides very flexible data services such as e-mail and access to the World Wide Web. The Internet is a variable-delay, variable- bandwidth network that provides no guarantee on quality of service (QoS) in its initial phase. New services are being added to the pure data delivery framework of yesterday. Such high demands on capacity could lead to a “bandwidth crunch” at the core wide-area network, resulting in degradation of service quality. Fortunately, technological innovations …

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