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

Physical Sciences and Mathematics Commons™

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

2007

Discipline
Institution
Keyword
Publication
Publication Type
File Type

Articles 5491 - 5520 of 5729

Full-Text Articles in Physical Sciences and Mathematics

Ichnofacies, Ichnocoenoses, And Ichnofabrics Of Quaternary Shallow-Marine To Dunal Tropical Carbonates: A Model And Implications, H. Allen Curran Jan 2007

Ichnofacies, Ichnocoenoses, And Ichnofabrics Of Quaternary Shallow-Marine To Dunal Tropical Carbonates: A Model And Implications, H. Allen Curran

Geosciences: Faculty Publications

A model of five ichnocoenoses within the Skolithos and Psilonichnus ichnofacies characterizes the modern, Holocene, and Pleistocene coastal-carbonate depositional environments and limestones of the Bahamas, as well as the Miami Limestone of south Florida. The subtidal to intertidal ichnocosnoses of the Skolithos ichnofacies are dominated by trace-making activities and trace fossils of callianassid shrimp, which can create distinctive and maximum ichnofabrics. Fossil Upogebia vasquezi burrows found in intertidal calcarenites and burrows of the trace fossil Psilonichnus upsilon, most common in beach backshore beds, have excellent potential as stratigraphic markers and can be used as indicators of past sea-level positions. …

Go to article

Paleoenvironmental Reconstruction Of The Middle Eocene Trieste-Pazin Basin (Croatia) From Benthic Foraminiferal Assemblages, Sanja ŽIvkovic, Bosiljka Glumac Jan 2007

Paleoenvironmental Reconstruction Of The Middle Eocene Trieste-Pazin Basin (Croatia) From Benthic Foraminiferal Assemblages, Sanja ŽIvkovic, Bosiljka Glumac

Geosciences: Faculty Publications

Foraminiferal assemblages from four stratigraphic sections of the Trieste-Pazin basin in central Istria, Croatia (southwestern Tethyan realm) were investigated to reconstruct paleoenvironmental conditions and to determine the age of these deposits. The following five Middle Eocene planktonic foraminiferal zones were identified from the range and frequency of foraminiferal species: Globigerinatheka kugleri/Morozovella aragonensis Zone (E9), Acarinina topilensis Zone (E10), Morozovelloides lehneri Zone (E11), Orbulinoides beckmanni Zone (E12), and Morozovelloides crassatus Zone (E13). A data set of benthic foraminifera relative frequency has been subjected to R- and Q-mode cluster analyses to demonstrate the linkage between taxa distribution and paleoenvironmental gradients. Benthic foraminiferal …

Go to article

Positive Solutions Of A Nonlinear Higher Order Boundary-Value Problem, John R. Graef, Johnny Henderson, Bo Yang Jan 2007

Positive Solutions Of A Nonlinear Higher Order Boundary-Value Problem, John R. Graef, Johnny Henderson, Bo Yang

Faculty Articles

The authors consider the higher order boundary-value problem u (n)(t) = q(t)f(u(t)), 0 ≤ t ≤ 1, u(i-1)(0) = u (n-2)(p) = u(n-1)(1) = 0, 1 ≤ i ≤ n -2, where n ≥ 4 is an integer, and p ∈ (1/2, 1) is a constant. Sufficient conditions for the existence and nonexistence of positive solutions of this problem are obtained. The main results are illustrated with an example.

Go to article

Environmental Abundance Of Anopheles (Diptera: Culicidae) Larval Habitats On Land Cover Change Sites In Karima Village, Mwea Rice Scheme, Kenya, Benjamin G. Jacob, Ephantus Muturi, Patrick Halbig, Joseph Mwangangi, R. K. Wanjogu, Enock Mpanga, Jose Funes, Josephat Shililu, John Githure, James L. Regens, Robert J. Novak Jan 2007

Environmental Abundance Of Anopheles (Diptera: Culicidae) Larval Habitats On Land Cover Change Sites In Karima Village, Mwea Rice Scheme, Kenya, Benjamin G. Jacob, Ephantus Muturi, Patrick Halbig, Joseph Mwangangi, R. K. Wanjogu, Enock Mpanga, Jose Funes, Josephat Shililu, John Githure, James L. Regens, Robert J. Novak

All Peer-Reviewed Publications

A study was carried out at Karima Village in the Mwea Rice Irrigation Scheme in Kenya to assess the impact of rice husbandry and associated land cover change for mosquito larval abundance. A multi-temporal, land use land cover (LULC) classification dataset incorporating distributions of Anopheles arabiensis aquatic larval habitats was produced in ERDAS Imagine version 8.7 using combined images from IKONOS at 4m spatial resolution from 2005 and Landsat Thematic Mapper (TM)™ classification data at 30-meters spatial resolution from 1988 for Karima. Of 207 larval habitats sampled, most were either canals (53.4%) or paddies (45.9%), and only one habitat was …

Go to article

Mosquito Larval Habitats In A Semiarid Ecosystem In Eritrea: Impact Of Larval Habitat Management On Anopheles Arabiensis Population, Josephat Shililu, Charles Mbogo, Tewolde Ghebremeskel, John Githure, Robert Novak Jan 2007

Mosquito Larval Habitats In A Semiarid Ecosystem In Eritrea: Impact Of Larval Habitat Management On Anopheles Arabiensis Population, Josephat Shililu, Charles Mbogo, Tewolde Ghebremeskel, John Githure, Robert Novak

All Peer-Reviewed Publications

This study investigated the impact of larval management and the temporal variation in larval productivity in Eritrea, a semiarid ecosystem. Results of this study show that mosquito breeding persists throughout the year mainly in stream bed pools. Anopheles arabiensis production in the ephemeral natural aquatic habitats such the streambed pools was high throughout the year and negatively associated with rainfall (r = -0.288, P = 0.047). High densities of An. arabiensis larvae were also recorded from canals and drainage channels at wells and communal water supply points. The numerous water supply locations and wells help sustain malaria transmission by serving …

Go to article

Tio2 Breakdown Under Pulsed Conditions, G. Zhao, R. P. Joshi, V. K. Lakdawala, E. Schamiloglu, H. Hjalmarson Jan 2007

Tio2 Breakdown Under Pulsed Conditions, G. Zhao, R. P. Joshi, V. K. Lakdawala, E. Schamiloglu, H. Hjalmarson

Electrical & Computer Engineering Faculty Publications

Model studies of current conduction and breakdown in TiO2 were carried out. Our simulation results indicate that electrical breakdown of TiO2 under multiple-pulsed conditions can occur at lower voltages as compared to quasi-dc biasing. This is in agreement with recent experimental data and is indicative of a cumulative phenomena. We demonstrate that the lower breakdown voltages observed in TiO2 under pulsed conditions is a direct rise-time effect, coupled with successive detrapping at the grain boundaries. 2007 American Institute of Physics.

Go to article

Using Pareto Fronts To Evaluate Polyp Detection Algorithms For Ct Colonography, Adam Huang, Jiang Li, Ronald M. Summers, Nicholas Petrick, Amy K. Hara Jan 2007

Using Pareto Fronts To Evaluate Polyp Detection Algorithms For Ct Colonography, Adam Huang, Jiang Li, Ronald M. Summers, Nicholas Petrick, Amy K. Hara

Electrical & Computer Engineering Faculty Publications

We evaluate and improve an existing curvature-based region growing algorithm for colonic polyp detection for our CT colonography (CTC) computer-aided detection (CAD) system by using Pareto fronts. The performance of a polyp detection algorithm involves two conflicting objectives, minimizing both false negative (FN) and false positive (FP) detection rates. This problem does not produce a single optimal solution but a set of solutions known as a Pareto front. Any solution in a Pareto front can only outperform other solutions in one of the two competing objectives. Using evolutionary algorithms to find the Pareto fronts for multi-objective optimization problems has been …

Go to article

Validating Pareto Optimal Operation Parameters Of Polyp Detection Algorithms For Ct Colonography, Jiang Li, Adam Huang, Nicholas Petrick, Jianhua Yao, Ronald M. Summers, Maryellen L. Giger (Ed.), Nico Karssemeijer (Ed.) Jan 2007

Validating Pareto Optimal Operation Parameters Of Polyp Detection Algorithms For Ct Colonography, Jiang Li, Adam Huang, Nicholas Petrick, Jianhua Yao, Ronald M. Summers, Maryellen L. Giger (Ed.), Nico Karssemeijer (Ed.)

Electrical & Computer Engineering Faculty Publications

We evaluated a Pareto front-based multi-objective evolutionary algorithm for optimizing our CT colonography (CTC) computer-aided detection (CAD) system. The system identifies colonic polyps based on curvature and volumetric based features, where a set of thresholds for these features was optimized by the evolutionary algorithm. We utilized a two-fold cross-validation (CV) method to test if the optimized thresholds can be generalized to new data sets. We performed the CV method on 133 patients; each patient had a prone and a supine scan. There were 103 colonoscopically confirmed polyps resulting in 188 positive detections in CTC reading from either the prone or …

Go to article

Modeling And Efficient Estimation Of Intra-Family Correlations, Roy Sabo Jan 2007

Modeling And Efficient Estimation Of Intra-Family Correlations, Roy Sabo

Mathematics & Statistics Theses & Dissertations

Familial data occur when observations are taken on multiple members of the same family. Due to relationships between these members, both genetic and by cohabitation, their response variables will likely exhibit some form of dependence. Most of the existing literature models this dependence with an equicorrelated structure. This structure is appropriate when the dependencies between family members are similar, such as in genetic studies, but not in cases where we expect the dependencies to differ, such as behavioral comparisons across different age groups. In this dissertation we first discuss an alternative structure based upon first-order autoregressive correlation. Specifically we create …

Go to article

Computer Simulation Of Glioma Growth And Morphology, Hermann B. Frieboes, John S Lowengrub, S Wise, X Zheng, Paul Macklin, Elaine L. Bearer, Vittorio Cristini Jan 2007

Computer Simulation Of Glioma Growth And Morphology, Hermann B. Frieboes, John S Lowengrub, S Wise, X Zheng, Paul Macklin, Elaine L. Bearer, Vittorio Cristini

Faculty, Staff and Student Publications

Despite major advances in the study of glioma, the quantitative links between intra-tumor molecular/cellular properties, clinically observable properties such as morphology, and critical tumor behaviors such as growth and invasiveness remain unclear, hampering more effective coupling of tumor physical characteristics with implications for prognosis and therapy. Although molecular biology, histopathology, and radiological imaging are employed in this endeavor, studies are severely challenged by the multitude of different physical scales involved in tumor growth, i.e., from molecular nanoscale to cell microscale and finally to tissue centimeter scale. Consequently, it is often difficult to determine the underlying dynamics across dimensions. New techniques …

Go to article

Structure And Biosynthesis Of Heat-Stable Antifungal Factor (Hsaf), A Broad-Spectrum Antimycotic With A Novel Mode Of Action, Fengan Yu, Kathia Zaleta-River, Xiangcheng Zhu, Justin Huffman, Jeffrey C. Millet, Steven D. Harris, Gary Y. Yuen, Xing-Cong Li, Liangcheng Du Jan 2007

Structure And Biosynthesis Of Heat-Stable Antifungal Factor (Hsaf), A Broad-Spectrum Antimycotic With A Novel Mode Of Action, Fengan Yu, Kathia Zaleta-River, Xiangcheng Zhu, Justin Huffman, Jeffrey C. Millet, Steven D. Harris, Gary Y. Yuen, Xing-Cong Li, Liangcheng Du

Department of Chemistry: Faculty Publications

A screen for antifungal compounds from Lysobacter enzymogenes strain C3, a bacterial biological control agent of fungal diseases, has previously led to the isolation of heat-stable antifungal factor (HSAF). HSAF exhibits inhibitory activities against a wide range of fungal species and shows a novel mode of antifungal action by disrupting the biosynthesis of a distinct group of sphingolipids. We have now determined the chemical structure of HSAF, which is identical to that of dihydromaltophilin, an antifungal metabolite with a unique macrocyclic lactam system containing a tetramic acid moiety and a 5,5,6-tricyclic skeleton. We have also identified the genetic locus responsible …

Go to article

Structure And Magnetic Properties Of Mn-Doped Zno Thin Films, Jun Zhang, Xingzhong Li, J. Shi, Yongfeng Lu, David J. Sellmyer Jan 2007

Structure And Magnetic Properties Of Mn-Doped Zno Thin Films, Jun Zhang, Xingzhong Li, J. Shi, Yongfeng Lu, David J. Sellmyer

David Sellmyer Publications

We report the structure and magnetic properties of Zn1-xMnxO thin films grown on Si(001) substrates by pulsed laser deposition. Structure and phase evolution with Mn doping has been studied using x-ray diffraction, electron diffraction, and high-resolution electron microscopy. The undoped and 1% Mn-doped ZnO films are completely (001) oriented, and further Mn doping deteriorates the (001) orientation. For Mn concentrations below 3%, only the hexagonal ZnO phase exists in the films without secondary phases. As the Mn concentration reaches 5%, secondary phase Mn2O3 was found aggregating at grain boundaries. All the Mn-doped films …

Go to article

Electrodeposition And Magnetic Properties Of Polypyrrole-Fe Nanocomposites, Mircea Chipara, Ralph Skomski, David J. Sellmyer Jan 2007

Electrodeposition And Magnetic Properties Of Polypyrrole-Fe Nanocomposites, Mircea Chipara, Ralph Skomski, David J. Sellmyer

David Sellmyer Publications

The synthesis, structure, and magnetic properties of a new composite material obtained by the codeposition of polypyrrole and iron, in the galvanostatic mode, using square wave potentials are reported. The effect of electrodeposition conditions (voltage and concentration of the electrolytes) on the magnetic properties of the nanocomposite is analyzed.

Go to article

Tem Study Of Fept And Fept:C Composite Double-Layered Thin Films, Xingzhong Li, T. George, Lingfang Jin, M. L. Yan, X. F. Xu, David J. Sellmyer Jan 2007

Tem Study Of Fept And Fept:C Composite Double-Layered Thin Films, Xingzhong Li, T. George, Lingfang Jin, M. L. Yan, X. F. Xu, David J. Sellmyer

David Sellmyer Publications

FePt films and FePt-based nano-composite films with the high-anisotropy L10 ordered phase have been extensively studied, since they have significant potential for extremely high-density perpendicular magnetic recording media and nano-composite permanent magnets [1]. Recently, new functional films were synthesized with a FePt:C composite layer on top of continuous FePt layer, in order to study the effect of the FePt layer on the ordering, orientation and magnetic properties of the composite layer. Transmission electron microscopy (TEM), together with X-ray diffraction, has been used to check the growth of the double-layered films and to study the microstructure, including the grain size, …

Go to article

Planar Hall Effect In Epitaxial Thin Films Of Magnetite, Y. Bason, L. Klein, H. Q. Wang, J. Hoffman, X. Hong, V. E. Henrich, C. H. Ahn Jan 2007

Planar Hall Effect In Epitaxial Thin Films Of Magnetite, Y. Bason, L. Klein, H. Q. Wang, J. Hoffman, X. Hong, V. E. Henrich, C. H. Ahn

Xia Hong Publications

We measured the planar Hall effect (PHE) of magnetite (Fe3O4) films between 150 and 350 K. The PHE was measured both with a constant magnetic field rotating in the plane of the sample and in a remanent state after applying a field in specific directions. The PHE amplitude decreases with temperature; however, it changes little between 300 and 350 K. The remanent PHE signal is as high as 10 V/A, larger than previously observed in manganite films. We also measured the PHE in the remanent state and found that its magnitude and stability make it a …

Go to article

Nanoscale Characterization Of Electronic And Electrical Properties Of Iii-Nitrides By Scanning Probe Microscopy, Brian J. Rodriguez, Alexei Gruverman, Robert J. Nemanich Jan 2007

Nanoscale Characterization Of Electronic And Electrical Properties Of Iii-Nitrides By Scanning Probe Microscopy, Brian J. Rodriguez, Alexei Gruverman, Robert J. Nemanich

Alexei Gruverman Publications

Recent interest in the technological potential of nitride-based semiconductors has led to the development and commercialization of a wide range of electronic devices. The nanoscale investigation of the electric properties of III-nitride thin films, bulk crystals, and heterostructures is of considerable interest for determining how interfaces, defects, and inversion domain boundaries affect device performance. The pyroelectric nature of wurtzitic III-nitrides is characterized by a spontaneous polarization that exists without the presence of an external field and by a polarization-bound surface charge. Scanning probe-based measurements of surface contact potentials and surface band bending in these materials, which are of crucial importance …

Go to article

Atomic Motion In Ferromagnetic Break Junctions: Comment And Response, S.-F. Shi, David C. Ralph, Andrei Sokolov, Chunjuan Zhang, Evgeny Y. Tsymbal, Jody G. Redepenning, Bernard Doudin Jan 2007

Atomic Motion In Ferromagnetic Break Junctions: Comment And Response, S.-F. Shi, David C. Ralph, Andrei Sokolov, Chunjuan Zhang, Evgeny Y. Tsymbal, Jody G. Redepenning, Bernard Doudin

Evgeny Tsymbal Publications

Authors’ response

In their comment, Shi and Ralph emphasize that conductance of Ni point contacts produced by an electro-migration technique can occasionally exhibit two-level fluctuations (TLF), mimicking the discrete steps in the conductance of the point contacts as a function of the applied magnetic-field direction. They explain the nature of these steps in terms of atomic motion rather than intrinsic electronic effect. We emphasize in this reply that our results, obtained on a different magnetic material synthesized by a different method, do not show a

Go to article

Acoustic Analog To Quantum Mechanical Level Splitting, Shawn A. Hilbert, Herman Batelaan Jan 2007

Acoustic Analog To Quantum Mechanical Level Splitting, Shawn A. Hilbert, Herman Batelaan

Department of Physics and Astronomy: Faculty Publications

A simple physical system is discussed that mirrors the quantum mechanical infinite square well with a central delta well potential. The physical realization consists of a continuous sound wave traveling in a pair of tubes separated by an adjustable diaphragm. The equivalence between the quantum system and the acoustic system is explored. The analytic solution to the quantum system exhibits level splitting as does the acoustic system.

Go to article

Chromatic Aberration Of Eyepieces In Early Telescopes, M. Eugene Rudd Jan 2007

Chromatic Aberration Of Eyepieces In Early Telescopes, M. Eugene Rudd

M. Eugene Rudd Publications

The twofold objective of this study is (1) to identify and give a brief review of the historical development of the various designs of early (pre-1850) telescope eyepieces, and (2) to determine by measurements and calculations the axial and lateral chromatic aberrations of a number of extant eyepieces from that period in order to provide basic data on which to judge the relative quality of different eyepiece forms. Eight distinct types of eyepieces containing one to five lens elements are discussed and illustrated. The second objective was addressed by measuring the focal lengths of the individual lens elements and the …

Go to article

Societal Adaptation To Decadal Climate Variability In The United States, Norman J. Rosenberg, Vikram M. Mehta, J Rolf Olsen, Hans Von Storch, Robert G. Varady, Michael J. Hayes, Donald A. Wilhite Jan 2007

Societal Adaptation To Decadal Climate Variability In The United States, Norman J. Rosenberg, Vikram M. Mehta, J Rolf Olsen, Hans Von Storch, Robert G. Varady, Michael J. Hayes, Donald A. Wilhite

United States Army Corps of Engineers, Omaha District

The search for evidence of decadal climatic variability (DCV) has a very long history. In the past decade, a research community has coalesced around a series of roughly biennial workshops that have emphasized description of past DCV events; their causes and their "teleconnections" responsible for droughts, floods, and warm and cold spells around the world; and recently, the predictability of DCV events. Researchers studying climate change put great emphasis on prospective impacts, but the DCV community has yet to do so. To begin rectifying this deficiency, a short but ambitious workshop was convened in Waikoloa, near Kona, Hawaii, from 26-28 …

Go to article

Corrosion Studies On The Uss Arizona With Application To A Japanese Midget Submarine, Brent M. Wilson, Donald L. Johnson, Hans Vantilburg, Matthew A. Russell, Larry E. Murphy, James D. Carr, Robert J. De Angelis, David L. Conlin Jan 2007

Corrosion Studies On The Uss Arizona With Application To A Japanese Midget Submarine, Brent M. Wilson, Donald L. Johnson, Hans Vantilburg, Matthew A. Russell, Larry E. Murphy, James D. Carr, Robert J. De Angelis, David L. Conlin

Department of Chemistry: Faculty Publications

The assessment of corrosion on the USS Arizona included the pioneering development of a minimum-impact cost-effective technique to determine the corrosion rate of steel-hulled shipwrecks in seawater. The technique, with potential application worldwide, is illustrated in this paper with the application to a World War II Japanese midget submarine submerged in deep waters off the Oahu, Hawaii, coast.

Go to article

Dna Multiplex Hybridization On Microarrays And Thermodynamic Stability In Solution: A Direct Comparison, Daniel J. Fish, M. Todd Horne, Greg P. Brewood, Jim P. Goodarzi, Saba Alemayehu, Ashwini Bhandiwad, Robert P. Searles, Albert S. Benight Jan 2007

Dna Multiplex Hybridization On Microarrays And Thermodynamic Stability In Solution: A Direct Comparison, Daniel J. Fish, M. Todd Horne, Greg P. Brewood, Jim P. Goodarzi, Saba Alemayehu, Ashwini Bhandiwad, Robert P. Searles, Albert S. Benight

Chemistry Faculty Publications and Presentations

Hybridization intensities of 30 distinct short duplex DNAs measured on spotted microarrays, were directly compared with thermodynamic stabilities measured in solution. DNA sequences were designed to promote formation of perfect match, or hybrid duplexes containing tandem mismatches. Thermodynamic parameters DeltaH degrees , DeltaS degrees and DeltaG degrees of melting transitions in solution were evaluated directly using differential scanning calorimetry. Quantitative comparison with results from 63 multiplex microarray hybridization experiments provided a linear relationship for perfect match and most mismatch duplexes. Examination of outliers suggests that both duplex length and relative position of tandem mismatches could be important factors contributing to …

Go to article

Solar Forcing Of Gulf Of California Climate During The Past 2000 Yr Suggested By Diatoms And Silicoflagellates, John A. Barron, David Bukry Jan 2007

Solar Forcing Of Gulf Of California Climate During The Past 2000 Yr Suggested By Diatoms And Silicoflagellates, John A. Barron, David Bukry

United States Geological Survey: Staff Publications

High-resolution records of the past 2000 yr are compared in a north–south transect (28° N to 24° N) of three cores from the eastern slopes of the Guaymas, Carmen, and Pescadero Basins of the Gulf of California (hereafter referred to as the “Gulf”). Evenly-spaced samples from the varved sediments in each core allow sample resolution ranging from ∼ 16 to ∼ 37 yr.

Diatoms and silicoflagellates capture the seasonal variation between a late fall to early spring period of high biosiliceous productivity, that is driven by northwest winds, and a summer period of warmer, more stratified waters during which these …

Go to article

Passive Aerobic Treatment Of Net-Alkaline, Iron-Laden Drainage From A Flooded Underground Anthracite Mine, Pennsylvania, Usa, Charles A. Cravotta Iii Jan 2007

Passive Aerobic Treatment Of Net-Alkaline, Iron-Laden Drainage From A Flooded Underground Anthracite Mine, Pennsylvania, Usa, Charles A. Cravotta Iii

United States Geological Survey: Staff Publications

This report evaluates the results of a continuous 4.5-day laboratory aeration experiment and the first year of passive, aerobic treatment of abandoned mine drainage (AMD) from a typical flooded underground anthracite mine in eastern Pennsylvania, USA. During 1991–2006, the AMD source, locally known as the Otto Discharge, had flows from 20 to 270 L/s (median 92 L/s) and water quality that was consistently suboxic (median 0.9 mg/L O2) and circumneutral (pH ~ 6.0; net alkalinity >10) with moderate concentrations of dissolved iron and manganese and low concentrations of dissolved aluminum (medians of 11, 2.2, and <0.2 mg/L, respectively). In 2001, the laboratory aeration experiment demonstrated rapid oxidation of ferrous iron (Fe2+) without …

Go to article

Late Cenozoic Climate Changes In China’S Western Interior: A Review Of Research On Lake Qinghai And Comparison With Other Records, Steven M. Colman, Shi-Yong Yua, Zhisheng Anc, Ji Shend, A.C.G. Henderson Jan 2007

Late Cenozoic Climate Changes In China’S Western Interior: A Review Of Research On Lake Qinghai And Comparison With Other Records, Steven M. Colman, Shi-Yong Yua, Zhisheng Anc, Ji Shend, A.C.G. Henderson

United States Geological Survey: Staff Publications

We review Late Cenozoic climate and environment changes in the western interior of China with an emphasis on lacustrine records from Lake Qinghai. Widespread deposition of red clay in the marginal basins of the Tibetan Plateau indicates that the Asian monsoon system was initially established by ~8 Ma, when the plateau reached a threshold altitude. Subsequent strengthening of the winter monsoon, along with the establishment of the Northern Hemisphere ice sheets, reflects a long-term trend of global cooling. The few cores from the Tibetan Plateau that reach back a million years suggest that they record the mid-Pleistocene transition from glacial …

Go to article

Sediment Geochemical Records Of Productivity And Oxygen Depletion Along The Margin Of Western North America During The Past 60,000 Years: Teleconnections With Greenland Ice And The Cariaco Basin, Walter E. Dean Jan 2007

Sediment Geochemical Records Of Productivity And Oxygen Depletion Along The Margin Of Western North America During The Past 60,000 Years: Teleconnections With Greenland Ice And The Cariaco Basin, Walter E. Dean

United States Geological Survey: Staff Publications

Many sediment records from the margins of the Californias (Alta and Baja) collected in water depths between 60 and 1200m contain anoxic intervals (laminated sediments) that can be correlated with interstadial intervals as defined by the oxygen-isotope composition of Greenland ice (Dansgaard–Oeschger, D–O, cycles). These intervals include all or parts of Oxygen Isotope Stage 3 (OIS3; 60–24 cal ka), the Bolling/Allerod warm interval (B/A; 15–13 cal ka), and the Holocene. This study uses organic carbon (Corg) and trace-element proxies for anoxia and productivity, namely elevated concentrations and accumulation rates of molybdenum and cadmium, in these laminated sediments to suggest that …

Go to article

Arsenic Incorporation Into Authigenic Pyrite, Bengal Basin Sediment, Bangladesh, Heather A. Lowers, George N. Breit, Andrea L. Foster, John Whitney, James Yount, Md. Nehal Uddin, Ad. Atual Muneem Jan 2007

Arsenic Incorporation Into Authigenic Pyrite, Bengal Basin Sediment, Bangladesh, Heather A. Lowers, George N. Breit, Andrea L. Foster, John Whitney, James Yount, Md. Nehal Uddin, Ad. Atual Muneem

United States Geological Survey: Staff Publications

Sediment from two deep boreholes (~400 m) approximately 90 km apart in southern Bangladesh was analyzed by X-ray absorption spectroscopy (XAS), total chemical analyses, chemical extractions, and electron probe microanalysis to establish the importance of authigenic pyrite as a sink for arsenic in the Bengal Basin. Authigenic framboidal and massive pyrite (median values 1500 and 3200 ppm As, respectively), is the principal arsenic residence in sediment from both boreholes. Although pyrite is dominant, ferric oxyhydroxides and secondary iron phases contain a large fraction of the sediment-bound arsenic between approximately 20 and 100 m, which is the depth range of wells …

Go to article

Dune Fields: Mid-Latitudes, J. Sun, Daniel R. Muhs Jan 2007

Dune Fields: Mid-Latitudes, J. Sun, Daniel R. Muhs

United States Geological Survey: Staff Publications

Large dune fields, or sand seas, are landscapes often thought to be found only in deserts beneath the great, subtropical high-pressure zones, where subsiding air suppresses rainfall. Dune fields are also quite common in mid-latitude regions, to the north and south of subtropical deserts (Fig. 1). Two major characteristics distinguish many mid-latitude dune fields from the sand seas of lower latitudes. One difference is that many of those in mid-latitudes are in semiarid, rather than arid climates, and therefore are not presently active. In this article, ‘active’ refers to eolian sand bodies that are not covered with vegetation, and where …

Go to article

Evaluation And Comparison Of Gross Primary Production Estimates For The Northern Great Plains Grasslands, Li Zhang, Bruce K. Wylie, Thomas Loveland, Eugene A. Fosnight, Larry L. Tieszen, Lei Ji, Tagir G. Gilmanov Jan 2007

Evaluation And Comparison Of Gross Primary Production Estimates For The Northern Great Plains Grasslands, Li Zhang, Bruce K. Wylie, Thomas Loveland, Eugene A. Fosnight, Larry L. Tieszen, Lei Ji, Tagir G. Gilmanov

United States Geological Survey: Staff Publications

Two spatially-explicit estimates of gross primary production (GPP) are available for the Northern Great Plains. An empirical piecewise regression (PWR) GPP model was developed from flux tower measurements to map carbon flux across the region. The Moderate Resolution Imaging Spectrometer (MODIS) GPP model is a process-based model that uses flux tower data to calibrate its parameters. Verification and comparison of the regional PWR GPP and the global MODIS GPP are important for the modeling of grassland carbon flux. This study compared GPP estimates from PWR and MODIS models with five towers in the grasslands. Among them, PWR GPP and MODIS …

Go to article

Conservation Genetics Of Snowy Plovers (Charadrius Alexandrinus) In The Western Hemisphere: Population Genetic Structure And Delineation Of Subspecies, W. Chris Funk, Thomas D. Mullins, Susan M. Haig Jan 2007

Conservation Genetics Of Snowy Plovers (Charadrius Alexandrinus) In The Western Hemisphere: Population Genetic Structure And Delineation Of Subspecies, W. Chris Funk, Thomas D. Mullins, Susan M. Haig

United States Geological Survey: Staff Publications

We examined the genetic structure of snowy plovers (Charadrius alexandrinus) in North America, the Caribbean, and the west coast of South America to quantify variation within and among breeding areas and to test the validity of three previously recognized subspecies. Sequences (676 bp) from domains I and II of the mitochondrial control region were analyzed for 166 snowy plovers from 20 breeding areas. Variation was also examined at 10 microsatellite loci for 144 snowy plovers from 14 breeding areas. The mtDNA and microsatellite data provided strong evidence that the Puerto Rican breeding group is genetically divergent from sites …

Go to article

First Prev Next Last