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1999

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Articles 2161 - 2190 of 2348

Full-Text Articles in Physical Sciences and Mathematics

X-Ray Crystal Structures And The Facile Oxidative (Au−C) Cleavage Of The Dimethylaurate(I) And Tetramethylaurate(Iii) Homologues, Dunming Zhu, Sergey V. Lindeman, Jay K. Kochi Jan 1999

X-Ray Crystal Structures And The Facile Oxidative (Au−C) Cleavage Of The Dimethylaurate(I) And Tetramethylaurate(Iii) Homologues, Dunming Zhu, Sergey V. Lindeman, Jay K. Kochi

Chemistry Faculty Research and Publications

Dimethylaurate(I) has been prepared as the crystalline tetrabutylammonium salt for comparison with the known tetramethylaurate(III) analogue. The linear structure of dimethylaurate(I) and the square-planar structure of tetramethylaurate(III) have both been confirmed by X-ray crystallography. One-electron oxidation of dimethylaurate(I) by either ferrocenium or arenediazonium cations produces the metastable dimethylgold(II) intermediate, which can be trapped as the paramagnetic 9,10-phenanthrenequinone (PQ) adduct. Otherwise, dimethylgold(II) is subject to rapid reductive elimination of ethane and affords metallic gold (mirror). The analogous oxidation of tetramethylaurate(III) by ferrocenium, arenediazonium, or nitrosonium cations also proceeds via electron transfer to generate the putative tetramethylgold(IV) intermediate. The highly unstable (CH …

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Affinity Chromatography: A Review Of Clinical Applications, David S. Hage Jan 1999

Affinity Chromatography: A Review Of Clinical Applications, David S. Hage

David Hage Publications

Affinity chromatography is a type of liquid chromatography that makes use of biological-like interactions for the separation and specific analysis of sample components. This review describes the basic principles of affinity chromatography and examines its use in the testing of clinical samples, with an emphasis on HPLCbased methods. Some traditional applications of this approach include the use of boronate, lectin, protein A or protein G, and immunoaffinity supports for the direct quantification of solutes. Newer techniques that use antibody-based columns for on- or off-line sample extraction are examined in detail, as are methods that use affinity chromatography in combination with …

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Biogenic Silica Records From The Bdp93 Drill Site And Adjacent Areas Of The Selenga Delta, Lake Baikal, Siberia, Steven M. Colman, John A. Peck, Josephine Hatton, Eugene B. Karabanov, John W. King Jan 1999

Biogenic Silica Records From The Bdp93 Drill Site And Adjacent Areas Of The Selenga Delta, Lake Baikal, Siberia, Steven M. Colman, John A. Peck, Josephine Hatton, Eugene B. Karabanov, John W. King

United States Geological Survey: Staff Publications

Biogenic silica contents of sediments on the lower Selenga Delta and Buguldeika saddle in Lake Baikal show distinct fluctuations that reflect changes in diatom productivity, and ultimately, climate. The pattern of the upper 50 m of the section, dating from about 334 ka, is similar to that of the marine oxygen isotope record, increasingly so as the younger sediments become progressively finer grained and less locally derived with time. The last two interglaciations are marked by biogenic silica abundances similar to those of the Holocene. The equivalent of marine oxygenisotope stage 3 is distinctly intermediate in character between full glacial …

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The Carbon Cycle And Biogeochemical Dynamics In Lake Sediments, Walter E. Dean Jan 1999

The Carbon Cycle And Biogeochemical Dynamics In Lake Sediments, Walter E. Dean

United States Geological Survey: Staff Publications

The concentrations of organic carbon (OC) and CaCO3 in lake sediments are often inversely related. This relation occurs in surface sediments from different locations in the same lake, surface sediments from different lakes, and with depth in Holocene sediments. Where data on accumulation rates are available, the relation holds for organic carbon and CaCO3 accumulation rates as well. An increase of several percent OC is accompanied by a decrease of several tens of percent CaCO3 indicating that the inverse relation is not due to simple dilution of one component by another. It appears from core data that …

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200,000 Years Of Climate Change Recorded In Eolian Sediments Of The High Plains Of Eastern Colorado And Western Nebraska, Daniel R. Muhs, James Swinehart, David Loope, John N. Aleinikoff, Josh Been Jan 1999

200,000 Years Of Climate Change Recorded In Eolian Sediments Of The High Plains Of Eastern Colorado And Western Nebraska, Daniel R. Muhs, James Swinehart, David Loope, John N. Aleinikoff, Josh Been

United States Geological Survey: Staff Publications

Loess and eolian sand cover vast areas of the western Great Plains of Nebraska, Kansas and Colorado (Fig. 1). In recent studies of Quaternary climate change, there has been a renewed interest in loess and eolian sand. Much of the attention now given to loess stems from new studies of long loess sequences that contain detailed records of Quaternary glacial-interglacial cycles, thought to be a terrestrial equivalent to the foraminiferal oxygen isotope record in deep-sea sediments (Fig. 2). Loess is also a direct record of atmospheric circulation, and identification of loess paleowinds in the geologic record can test atmospheric general …

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Slip-Parallel Seismic Lineations On The Northern Hayward Fault, California, Felix Waldhauser, William L. Ellsworth, Alex Cole Jan 1999

Slip-Parallel Seismic Lineations On The Northern Hayward Fault, California, Felix Waldhauser, William L. Ellsworth, Alex Cole

United States Geological Survey: Staff Publications

A high-resolution relative earthquake location procedure is used to image the fine-scale seismicity structure of the northern Hayward fault, California. The seismicity defines a narrow, near-vertical fault zone containing horizontal alignments of hypocenters extending along the fault zone. The lineations persist over the 15-year observation interval, implying the localization of conditions on the fault where brittle failure conditions are met. The horizontal orientation of the lineations parallels the slip direction of the fault, suggesting that they are the result of the smearing of frictionally weak material along the fault plane over thousands of years.

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Late Quaternary Loess In Northeastern Colorado: Part I—Age And Paleoclimatic Significance, Daniel R. Muhs, John N. Aleinikoff, Thomas W. Stafford Jr., Rolf Kihl, Josh Been, Shannon A. Mahan, Scott Cowherd Jan 1999

Late Quaternary Loess In Northeastern Colorado: Part I—Age And Paleoclimatic Significance, Daniel R. Muhs, John N. Aleinikoff, Thomas W. Stafford Jr., Rolf Kihl, Josh Been, Shannon A. Mahan, Scott Cowherd

United States Geological Survey: Staff Publications

Loess in eastern Colorado covers an estimated 14,000 km2, and is the westernmost part of the North American midcontinent loess province. Stratigraphic studies indicate there were two periods of loess deposition in eastern Colorado during late Quaternary time. The first period spanned ca. 20,000 to 12,000 14C yr B.P. (ca. 20–14 ka) and correlates reasonably well with the culmination and retreat of Pinedale glaciers in the Colorado Front Range during the last glacial maximum. The second period of loess deposition occurred between ca. 11,000 and 9,000 14C yr B.P. This interval may be Holocene or may …

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Late Quaternary Loess In Northeastern Colorado: Part Ii—Pb Isotopic Evidence For The Variability Of Loess Sources, John N. Aleinikoff, Daniel R. Muhs, Rebecca R. Sauer, C. Mark Fanning Jan 1999

Late Quaternary Loess In Northeastern Colorado: Part Ii—Pb Isotopic Evidence For The Variability Of Loess Sources, John N. Aleinikoff, Daniel R. Muhs, Rebecca R. Sauer, C. Mark Fanning

United States Geological Survey: Staff Publications

A new application of the Pb isotopic tracer technique has been used to determine the relative importance of different silt sources for late Wisconsin loess in the central Great Plains of eastern Colorado. Samples of the Peoria Loess collected throughout the study area contain K-feldspar derived from two isotopically and genetically distinct sources: (1) glaciogenic material from Early and Middle Proterozoic crystalline rocks of the Colorado province, and (2) volcaniclastic material from the Tertiary White River Group exposed on the northern Great Plains. Pb isotopic compositions of K-feldspar in loess from two dated vertical sections (at Beecher Island and Last …

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Predation Of Artificial Ground Nests On White-Tailed Prairie Dog Colonies, Bruce W. Baker, Thomas R. Stanley, James A. Sedgwick Jan 1999

Predation Of Artificial Ground Nests On White-Tailed Prairie Dog Colonies, Bruce W. Baker, Thomas R. Stanley, James A. Sedgwick

United States Geological Survey: Staff Publications

Prairie dog (Cynomys spp.) colonies are unique to prairie and shrub-steppe landscapes. However, widespread eradication, habitat loss, and sylvatic plague (Yersinia pestis) have reduced their numbers by 98% since historical times. Birds associated with prairie dogs also are declining. Potential nest predators, such as coyotes (Canis latrans), swift foxes (Vulpes velox), and badgers (Taxidea taxus), may be attracted to colonies where a high concentration of prairie dogs serve as available prey. Increased abundance of small mammals, including prairie dogs, also may increase the risk of predation for birds nesting on colonies. …

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Atrazine Degradation In A Small Stream In Iowa, Dana W. Kolpin, Stephen J. Kalkhoff Jan 1999

Atrazine Degradation In A Small Stream In Iowa, Dana W. Kolpin, Stephen J. Kalkhoff

United States Geological Survey: Staff Publications

A study was conducted during 1990 through an 11.2-km reach of Roberts Creek in northeastern Iowa to determine the fate of atrazine in a surface water environment. Water samples were collected at ~1-month intervals from April through November during stable low to medium flow conditions and analyzed for atrazine and two of its initial biotic degradation products, desethylatrazine and deisopropylatrazine. Samples were collected on the basis of a Lagrangian model of streamflow in order to sample the same parcel of water as it moved downstream. Atrazine concentrations substantially decreased (roughly 25-60% ) between water entering and exiting the study reach …

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Are Shifts In Herbicide Use Reflected In Concentration Changes In Midwestern Rivers?, William Battaglin, Donald Goolsby Jan 1999

Are Shifts In Herbicide Use Reflected In Concentration Changes In Midwestern Rivers?, William Battaglin, Donald Goolsby

United States Geological Survey: Staff Publications

In many Midwestern rivers, elevated concentrations of herbicides occur during runoff events for 1-3 months following application. The highest or “peak” herbicide concentration often occurs during one of these runoff events. Herbicide concentrations in rivers are affected by a number of factors, including herbicide use patterns within the associated basin. Changing agricultural practices, reductions in recommended and permitted herbicide applications, shifts to new herbicides, and greater environmental awareness in the agricultural community have resulted in changes to herbicide use patterns. In the Midwestern United States, alachlor use was much larger in 1989 than in 1995, while acetochlor was not used …

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Negative Ph, Efflorescent Mineralogy, And Consequences For Environmental Restoration At The Iron Mountain Superfund Site, California, D. Kirk Nordstrom, Charles N. Alpers Jan 1999

Negative Ph, Efflorescent Mineralogy, And Consequences For Environmental Restoration At The Iron Mountain Superfund Site, California, D. Kirk Nordstrom, Charles N. Alpers

United States Geological Survey: Staff Publications

The Richmond Mine of the Iron Mountain copper deposit contains some of the most acid mine waters ever reported. Values of pH have been measured as low as -3.6, combined metal concentrations as high as 200 g/liter, and sulfate concentrations as high as 760 g/liter. Copious quantities of soluble metal sulfate salts such as melanterite, chalcanthite, coquimbite, rhomboclase, voltaite, copiapite, and halotrichite have been identified, and some of these are forming from negative-pH mine waters. Geochemical calculations show that, under a mine-plugging remediation scenario, these salts would dissolve and the resultant 600,000-m3 mine pool would have a pH of …

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Trapping Considerations For The Fossorial Pocket Gopher, Gary W. Witmer, Rex Marsh, George Matschke Jan 1999

Trapping Considerations For The Fossorial Pocket Gopher, Gary W. Witmer, Rex Marsh, George Matschke

United States Department of Agriculture Wildlife Services: Staff Publications

Fossorial mammals such as the pocket gopher (Thomomys spp.) are well adapted to life in an underground closed burrow system. These animals can have considerable influence on ecosystems and can cause significant damage to agricultural crops, forest resources, and field machinery. The research and management of pocket gopher populations poses many challenges to land managers and research biologists. Both live-trapping for research purposes and kill trapping for control purposes are important tools for working with pocket gophers. Trapping can be an effective and efficient tool if the proper traps are used and trappers are trained to place traps properly …

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Transition From Research To Operations: Arktos - A Knowledge-Based Sea Ice Classification System, Cheryl Bertoia, Denise Gineris, Kim Partington, Leen-Kiat Soh, Costas Tsatsoulis Jan 1999

Transition From Research To Operations: Arktos - A Knowledge-Based Sea Ice Classification System, Cheryl Bertoia, Denise Gineris, Kim Partington, Leen-Kiat Soh, Costas Tsatsoulis

School of Computing: Conference and Workshop Papers

ARKTOS is a fully automated intelligent system that classifies sea ice and that is now being used by the U.S. National Ice Center (NIC) for daily operations related to the NIC’s task of mapping the ice covered oceans. In this paper we describe the process of taking a research project and transitioning it to an operational environment. We discuss the theoretical methodologies implemented in ARKTOS, and how ARKTOS was developed, tested, and finally moved to operations.

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Empirical Computation Of Reject Ratio In Vlsi Testing, Shashank K. Mehta, Sharad C. Seth Jan 1999

Empirical Computation Of Reject Ratio In Vlsi Testing, Shashank K. Mehta, Sharad C. Seth

School of Computing: Conference and Workshop Papers

Among significant components of testing cost are testlength, reject ratio, and lost-yield. In this paper a new approach is proposed to estimate the reject ratio. The empirical model is based on test-data properties that are believed to be invariant for a wide range of manufacturing technologies and types of tests. The analysis is carried out entirely in terms of the device test data, as might be available from wafer probe. Experimental results demonstrate robustness of the model.

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A Synthesis For Testability Scheme For Finite State Machines Using Clock Control, Kent L. Einspahr, Shashank K. Mehta, Sharad C. Seth Jan 1999

A Synthesis For Testability Scheme For Finite State Machines Using Clock Control, Kent L. Einspahr, Shashank K. Mehta, Sharad C. Seth

School of Computing: Faculty Publications

A new method is proposed for improving the testability of a finite state machine (FSM) during its synthesis. The method exploits clock control to enhance the controllability and observability of machine states. With clock control it is possible to add new state transitions during testing. Therefore, it is easier to navigate between states in the resulting test machine. Unlike prior work, where clock control is added to the circuit as a postdesign step, here, clock control is considered in conjunction with a symbolic scheme for encoding the states of the FSM. The encoding is shown to result in significant reductions …

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A Dual Encryption Protocol For Scalable Secure Multicasting, Lakshminath R. Dondeti, Sarit Mukherjee, Ashok K. Samal Jan 1999

A Dual Encryption Protocol For Scalable Secure Multicasting, Lakshminath R. Dondeti, Sarit Mukherjee, Ashok K. Samal

School of Computing: Conference and Workshop Papers

In this paper we propose a dual encryption protocol for scalable secure multicasting. Multicasting is a scalable solution for group communication. It howevel; poses several unique security problems. We use hierarchical subgrouping to achieve scalability. Third party hosts or members of the multicast group are designated as subgroup managers. They are responsible for secret key distribution and group membership management at the subgroup level. Unlike existing secure multicast protocols, our protocol need not trust the subgroup managers with the distribution of data encryption keys. The dual encryption protocol proposed in this paper distributes encrypted data encryption keys via subgroup managers. …

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Resource News-Spring 1999 Jan 1999

Resource News-Spring 1999

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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2018 Nebraska Water Leaders Academy - Final Report, Mark E. Burbach Jan 1999

2018 Nebraska Water Leaders Academy - Final Report, Mark E. Burbach

Conservation and Survey Division: Faculty and Staff Publications

Nineteen participants completed the 2018 Water Leaders Academy bringing the total number of graduates to 120 since the inception of the program in 2011. Assessment of participants’ transformational leadership skills, champion of innovation skills, water knowledge and engagement, civic capacity, and entrepreneurial leadership behaviors showed a significant increase over the course of the year, from both participants’ and their raters’ perspectives. Feedback from participants was highly positive and constructive. Participant concerns were addressed, and only minor changes are planned for the 2019 Academy curriculum. Results of the program assessment indicate that the curriculum is meeting Academy objectives. Most importantly, Alumni …

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Hydrologic Setting Of Two Interdunal Valleys In The Central Sand Hills Nebraska, D. C. Gosselin, S. Drda, F. E. Harvey, J. Goeke Jan 1999

Hydrologic Setting Of Two Interdunal Valleys In The Central Sand Hills Nebraska, D. C. Gosselin, S. Drda, F. E. Harvey, J. Goeke

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Reconnaissance Water Quality Study Of The Dakota Aquifer In Lancaster County, Nebraska, J. Anderson, D. D. Gosselin Jan 1999

Reconnaissance Water Quality Study Of The Dakota Aquifer In Lancaster County, Nebraska, J. Anderson, D. D. Gosselin

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Groundwater-Level Changes In Nebraska, 1996, Abraham H. Chen, Mohan J. Khisty Jan 1999

Groundwater-Level Changes In Nebraska, 1996, Abraham H. Chen, Mohan J. Khisty

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Douglas County Test Hole Logs, Raymond R. Burchett, Frank A. Smith Jan 1999

Douglas County Test Hole Logs, Raymond R. Burchett, Frank A. Smith

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Hamilton County Test Hole Logs, Perry B. Wigley Jan 1999

Hamilton County Test Hole Logs, Perry B. Wigley

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Sarpy County Test Hole Logs, Raymond R. Burchett, Frank A. Smith Jan 1999

Sarpy County Test Hole Logs, Raymond R. Burchett, Frank A. Smith

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Wayne County Test Hole Logs, Sue Olafsen Lackey, Frank A. Smith, Raymond R. Burchett Jan 1999

Wayne County Test Hole Logs, Sue Olafsen Lackey, Frank A. Smith, Raymond R. Burchett

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Stanton County Test Hole Logs, Sue Olafsen Lackey, Frank A. Smith, Raymond R. Burchett Jan 1999

Stanton County Test Hole Logs, Sue Olafsen Lackey, Frank A. Smith, Raymond R. Burchett

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Phelps County Test Hole Logs, S. E. Summerside Jan 1999

Phelps County Test Hole Logs, S. E. Summerside

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Analysis Of The Gal-Chen–Zhang Single-Doppler Velocity Retrieval, Steven Lazarus, Alan Shapiro, Kelvin Droegemeier Jan 1999

Analysis Of The Gal-Chen–Zhang Single-Doppler Velocity Retrieval, Steven Lazarus, Alan Shapiro, Kelvin Droegemeier

Ocean Engineering and Marine Sciences Faculty Publications

The authors present herein an analysis of a single-Doppler velocity retrieval (SDVR) technique whereby the unobserved wind components are determined from single-Doppler radar data. The analysis is designed to provide information about the behavior and/or sensitivity of the SDVR scheme as a function of various internal and external parameters as well as about observational errors and weights. Results presented for retrieval of both the mean and local flow indicate that the SDVR breaks down if the reflectivity gradient vanishes or if a reflectivity isoline is locally perpendicular to the radar beam. In the absence of reflectivity or radial velocity errors, …

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A Coupled Bio-Optical And Mixed Layer Model For The Equatorial Pacific, James Vincent Koziana Jan 1999

A Coupled Bio-Optical And Mixed Layer Model For The Equatorial Pacific, James Vincent Koziana

OES Theses and Dissertations

A one dimensional coupled bio-optical and mixed layer model is developed and applied to problems involving the role of phytoplankton-induced turbidity (PIT) on the vertical structure and heating of the upper ocean in the Equatorial Pacific Ocean. The bio-optical and mixed layer model for optically pure sea water was forced with climatological environmental conditions to provide a reference simulation for 140°W in the eastern Equatorial Pacific Ocean. This reference simulation was used for comparison to other simulations which considered the effects of variations in wind stress and solar input for a homogeneous chlorophyll a profile and variations in the magnitude …

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