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  • 2010-2014  (68)
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  • 1
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    Three-dimensional flow in centered pool-riffle sequences (2013)
    Wiley
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    Publikationsdatum: 2013-01-17
    Beschreibung: Pool-riffle sequences are geomorphological features of many streams, thought to contribute to the hydrodynamic variability necessary to support healthy habitat conditions. Due to this fact, the addition of artificial pools and riffles is a common alternative for restoration projects on channelized streams. In this paper, detailed three-dimensional (3-D) flow measurements conducted on a scale model of an existing pool-riffle design implemented as part of a restoration project is presented. The design incorporated the basic features of natural pool-riffle sequences but maintained the deepest part of the pool in the center of the cross section and away from the banks. Results showed that the 3-D flow patterns were qualitatively different for two discharge conditions tested. The lower discharge case was strongly affected by the topography, displaying a pattern consistent with a secondary flow generated by the curvature of the streamlines. The higher discharge case was less affected by the topography, presenting a secondary flow pattern similar to that observed over a flat bed and typically associated with turbulence anisotropy. Self-maintenance and flow variability were also investigated. Even though convergence of the values of bed shear stresses at pool and riffle sections with increasing discharge did take place, reversal conditions did not occur. The difference in flow structure with flow stage was also reflected in the spatial flow variability, the lower discharge displaying larger variability than the higher discharge. The higher discharge generated a level of variability comparable with the values obtained over a flat bed.
    Print ISSN: 0043-1397
    Digitale ISSN: 1944-7973
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geographie
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
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    Sediment mobility and bed armoring in the St Clair River: insights from hydrodynamic modeling (2012)
    Wiley
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    Publikationsdatum: 2012-04-15
    Beschreibung: The lake levels in Lake Michigan-Huron have recently fallen to near historical lows, as has the elevation difference between Lake Michigan-Huron compared to Lake Erie. This decline in lake levels has the potential to cause detrimental impacts on the lake ecosystems, together with social and economic impacts on communities in the entire Great Lakes region. Results from past work suggest that morphological changes in the St Clair River, which is the only natural outlet for Lake Michigan-Huron, could be an appreciable factor in the recent trends of lake level decline. A key research question is whether bed erosion within the river has caused an increase in water conveyance, therefore, contributed to the falling lake level. In this paper, a numerical modeling approach with field data is used to investigate the possibility of sediment movement in the St Clair River and assess the likelihood of morphological change under the current flow regime. A two-dimensional numerical model was used to study flow structure, bed shear stress, and sediment mobility/armoring over a range of flow discharges. Boundary conditions for the numerical model were provided by detailed field measurements that included high-resolution bathymetry and three-dimensional flow velocities. The results indicate that, without considering other effects, under the current range of flow conditions, the shear stresses produced by the river flow are too low to transport most of the coarse bed sediment within the reach and are too low to cause substantial bed erosion or bed scour. However, the detailed maps of the bed show mobile bedforms in the upper St Clair River that are indicative of sediment transport. Relatively high shear stresses near a constriction at the upstream end of the river and at channel bends could cause local scour and deposition. Ship-induced propeller wake erosion also is a likely cause of sediment movement in the entire reach. Other factors that may promote sediment movement, such as ice cover and dredging in the lower river, require further investigation. Copyright © 2012 John Wiley & Sons, Ltd.
    Print ISSN: 0197-9337
    Digitale ISSN: 1096-9837
    Thema: Geographie , Geologie und Paläontologie
    Publiziert von Wiley
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
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    The effects of floodplain soil heterogeneity on meander planform shape (2012)
    Wiley
    Details
    Publikationsdatum: 2012-09-13
    Beschreibung: Past analytical studies of meander planform development have mostly focused on the complexity of the governing equations, i.e., hydrodynamics, and less so on the stream bank resistance to erosion, whose spatial heterogeneity is difficult to describe deterministically. This motivated the use of a Monte Carlo approach to examine the effects of floodplain soils and their distribution on planform development, with the goal of including bank erosion properties in the analysis. Simulated bank erosion rates are controlled by the resistance to hydraulic erosion of the bank soils using an excess shear stress approach. The spatial distribution of critical shear stress across the floodplain is delineated on a rectangular, equidistant grid with varying degrees of variability. The corresponding erodibility coefficient is computed using a field-derived empirical relation. For a randomly disturbed distribution, in which the mean resistance to erosion exponentially increases away from the valley centerline, two relevant parameters are identified: the standard deviation of the critical shear stress distribution, which controls skewness and variability of the channel centerline, and the cross-valley increase in soil resistance, which constrains lateral migration and also affects bend skewness. For a purely random distribution, migrated centerlines exhibit larger variability for increasing spatial scales of floodplain soil heterogeneity. For equal stochastic variability of the corresponding governing parameters, relating meander migration to hydraulic erosion of the bank soils produces more variability and shape complexity than the “classic” bank migration approach of Ikeda et al. (1981), which relates migration rate to excess velocity at the outer bank. Finally, the proposed stochastic approach provides a foundation for estimating a suitable spatial density of measurements to characterize the physical properties of floodplain soils and vegetation.
    Print ISSN: 0043-1397
    Digitale ISSN: 1944-7973
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geographie
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
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    Reduction of wind stress due to swell at high wind conditions (2012)
    Wiley
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    Publikationsdatum: 2012-05-19
    Beschreibung: Wind stress over the ocean depends on the sea surface roughness which is determined by the sea state. On one hand, underdeveloped wind seas, rougher than their fully developed counterpart, increase the drag. On the other hand, the presence of swell can modify wind stress by modifying the wind sea roughness. This latter mechanism is believed to have a great impact at high winds whenever underdeveloped local waves coexist with swell. Detailed measurements of wind stress and wavefield in fetch-limited growth conditions were made in an area subjected to strong and persistent winds. Through the analysis of wavefield observations, it is found that the presence of swell dampens the short wind waves. The observed attenuation is greater for younger wind seas and decreases as the wind waves become older. Results obtained from modeling the interaction of wind waves and the air flow above point out that the attenuation of short wind waves causes a reduction of the wave-supported stress, which in turn decreases the total wind stress.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
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    Suppression of leukemia development caused by PTEN loss [Cell Biology] (2011)
    National Academy of Sciences
    Details
    Publikationsdatum: 2011-01-26
    Beschreibung: Multiple genetic or molecular alterations are known to be associated with cancer stem cell formation and cancer development. Targeting such alterations, therefore, may lead to cancer prevention. By crossing our previously established phosphatase and tensin homolog (Pten)-null acute T-lymphoblastic leukemia (T-ALL) model onto the recombination-activating gene 1−/− background, we show that the lack of variable, diversity and joining [V(D)J] recombination completely abolishes the Tcrα/δ-c-myc translocation and T-ALL development, regardless of β-catenin activation. We identify mammalian target of rapamycin (mTOR) as a regulator of β-selection. Rapamycin, an mTOR-specific inhibitor, alters nutrient sensing and blocks T-cell differentiation from CD4−CD8− to CD4+CD8+, the stage where the Tcrα/δ-c-myc translocation occurs. Long-term rapamycin treatment of preleukemic Pten-null mice prevents Tcrα/δ-c-myc translocation and leukemia stem cell (LSC) formation, and it halts T-ALL development. However, rapamycin alone fails to inhibit mTOR signaling in the c-KitmidCD3+Lin− population enriched for LSCs and eliminate these cells. Our results support the idea that preventing LSC formation and selectively targeting LSCs are promising approaches for antileukemia therapies.
    Print ISSN: 0027-8424
    Digitale ISSN: 1091-6490
    Thema: Biologie , Medizin , Allgemeine Naturwissenschaft
    Publiziert von National Academy of Sciences
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
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    Observation and measurement of temperature rise and distribution on GaAs photo-cathode wafer with a 532nm drive laser and a thermal imaging camera (2011)
    Elsevier
    Details
    Publikationsdatum: 2011-03-01
    Print ISSN: 0168-9002
    Digitale ISSN: 1872-9576
    Thema: Physik
    Publiziert von Elsevier
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
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    Elastic scattering and total reaction cross section for the Be7 + Al27 system at near-barrier energies (2014)
    American Physical Society (APS)
    Details
    Publikationsdatum: 2014-04-25
    Beschreibung: Author(s): V. Morcelle, R. Lichtenthäler, R. Linares, M. C. Morais, V. Guimarães, A. Lépine-Szily, P. R. S. Gomes, J. Lubian, D. R. Mendes Junior, P. N. De Faria, A. Barioni, L. R. Gasques, J. M. B. Shorto, K. C. C. Pires, J. C. Zamora, R. P. Condori, V. Scarduelli, J. J. Kolata, H. Amro, F. D. Becchetti, H. Jiang, E. F. Aguilera, D. Lizcano, E. Martinez-Quiroz, and H. Garcia Elastic scattering angular distributions of the radioactive weakly bound Be7 on Al27 have been measured at energies near the Coulomb barrier. The interaction optical potential is investigated by using different potentials. Total reaction cross sections have also been obtained. [Phys. Rev. C 89, 044611] Published Thu Apr 24, 2014
    Schlagwort(e): Nuclear Reactions
    Print ISSN: 0556-2813
    Digitale ISSN: 1089-490X
    Thema: Physik
    Publiziert von American Physical Society (APS)
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
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    Modification of Meander Migration by Bank Failures (2014)
    Wiley
    Details
    Publikationsdatum: 2014-04-03
    Beschreibung: Meander migration and planform evolution depend on the resistance to erosion of the floodplain materials. To date, research to quantify meandering river adjustment has largely focused on resistance to erosion properties that vary horizontally. This paper evaluates the combined effect of horizontal and vertical floodplain material heterogeneity on meander migration by simulating fluvial erosion and cantilever and planar bank mass failure processes responsible for bank retreat. The impact of streambank failures on meander migration is conceptualized in our RVR Meander model through a bank armoring factor associated with the dynamics of slump blocks produced by cantilever and planar failures. Simulation periods smaller than the time to cutoff areconsidered, such that all planform complexity is caused by bank erosion processes and floodplain heterogeneity and not by cutoff dynamics. Cantilever failure continuously affects meander migration, because it is primarily controlled by the fluvial erosion at the bank toe. Hence, it impacts migration rates and meander shapes through the horizontal and vertical distribution of erodibility of floodplain materials. Planar failures are more episodic. However, in floodplain areas characterized by less cohesive materials, they can affect meander evolution in a sustained way and produce preferential migration patterns. Model results show that besides the hydrodynamics, bed morphology and horizontal floodplain heterogeneity, floodplain stratigraphy can significantly affect meander evolution, both in terms of migration rates and planform shapes. Specifically, downstream meander migration can either increase or decrease with respect to the case of a homogeneous floodplain; lateral migration generally decreases as result of bank protection due to slump blocks; and the effect on bend skewness depends on the location and volumes of failed bank material caused by cantilever and planar failures along the bends, with possible achievement of downstream bend skewness under certain conditions. Therefore, floodplain stratigraphy must be accounted for when estimating meander migration within floodplains. Results also suggest that the generation of slump blocks due to mass failure mechanisms and their effect on rates of bank erosion must be included explicitly in models of meander migration: tweaking the bank erodibility parameters for fluvial erosion to indirectly account for those processes cannot sufficiently reproduce their effects on meander migration patterns, because slump block generation depends on river planform configuration, direction of migration, and location of the river bends with respect to the floodplain material patches.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
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    Adatoms and Anderson localization in graphene (2014)
    American Physical Society (APS)
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    Publikationsdatum: 2014-08-23
    Beschreibung: Author(s): Jose H. García, Bruno Uchoa, Lucian Covaci, and Tatiana G. Rappoport We address the nature of the disordered state that results from the adsorption of adatoms in graphene. For adatoms that sit at the center of the honeycomb plaquette, as in the case of most transition metals, we show that the ones that form a zero-energy resonant state lead to Anderson localization i... [Phys. Rev. B 90, 085425] Published Fri Aug 22, 2014
    Schlagwort(e): Surface physics, nanoscale physics, low-dimensional systems
    Print ISSN: 1098-0121
    Digitale ISSN: 1095-3795
    Thema: Physik
    Publiziert von American Physical Society (APS)
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
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    Price Explosiveness, Speculation, and Grain Futures Prices (2014)
    Oxford University Press
    Details
    Publikationsdatum: 2014-12-13
    Beschreibung: A recently developed testing procedure is used to detect and date-stamp explosive episodes ("bubbles") in corn, soybean, and wheat futures markets during 2004–2013. We find that the markets experienced price explosiveness only approximately two percent of the time and, when bubbles do occur, they are generally short-lived and small in magnitude. The correspondence between observed price spikes and bubbles is rather low, with a large portion of the price explosiveness occurring during downward price movements. Commodity index trader positions do not significantly affect the probability of a positive bubble occurring in grain futures markets, which directly contradicts the argument (the "Masters Hypothesis") that waves of index investment distorted underlying supply-and-demand relationships and led to a series of massive bubbles in agricultural futures markets. In addition, commodity index trader positions tend to reduce negative bubble occurrence, while general speculative activity as measured by Working's T reduces the probability of a positive bubble. There is some evidence that the positions of noncommercial traders have a direct effect on positive bubble occurrence, but the effect declines when accounting for the composition of other traders in the market. Overall, speculation has little effect or negative effects on price explosiveness. Finally, positive bubbles are more likely to occur in the presence of low inventories, strong exports, a weak U.S. dollar, and booming economic growth, whereas negative bubbles are more likely to occur with large inventories, weak exports, and stagnant economic growth.
    Schlagwort(e): D84 - Expectations ; Speculations, G12 - Asset Pricing ; Trading volume ; Bond Interest Rates, G13 - Contingent Pricing ; Futures Pricing, G14 - Information and Market Efficiency ; Event Studies, Q13 - Agricultural Markets and Marketing ; Cooperatives ; Agribusiness, Q41 - Demand and Supply
    Print ISSN: 0002-9092
    Digitale ISSN: 1467-8276
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft , Wirtschaftswissenschaften
    Publiziert von Oxford University Press
    Standort Signatur Erwartet Verfügbarkeit
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