4,690 research outputs found
Mean Flow and Turbulence in a Laboratory Channel with Simulated Vegatation (HES 51)
U.S. Army Corps of Engineers, Waterways Experiment Station (Contract DACW39-94-K-0010)unpublishednot peer reviewe
River Bed Response to Channel Width Variation: Theory and Experiments (HES 49)
Illinois Water Resources Center (USGS Project 04 Contract 14-08-0004-G2017unpublishednot peer reviewe
Quiescent nuclear burning in low-metallicity white dwarfs
We discuss the impact of residual nuclear burning in the cooling sequences of
hydrogen-rich DA white dwarfs with very low metallicity progenitors
(). These cooling sequences are appropriate for the study of very old
stellar populations. The results presented here are the product of
self-consistent, fully evolutionary calculations. Specifically, we follow the
evolution of white dwarf progenitors from the zero-age main sequence through
all the evolutionary phases, namely the core hydrogen-burning phase, the
helium-burning phase, and the thermally pulsing asymptotic giant branch phase
to the white dwarf stage. This is done for the most relevant range of main
sequence masses, covering the most usual interval of white dwarf masses ---
from 0.53\, M_{\sun} to 0.83\, M_{\sun}. Due to the low metallicity of the
progenitor stars, white dwarfs are born with thicker hydrogen envelopes,
leading to more intense hydrogen burning shells as compared with their solar
metallicity counterparts. We study the phase in which nuclear reactions are
still important and find that nuclear energy sources play a key role during
long periods of time, considerably increasing the cooling times from those
predicted by standard white dwarf models. In particular, we find that for this
metallicity and for white dwarf masses smaller than about 0.6\, M_{\sun},
nuclear reactions are the main contributor to the stellar luminosity for
luminosities as low as \log(L/L_{\sun})\simeq -3.2. This, in turn, should
have a noticeable impact in the white dwarf luminosity function of
low-metallicity stellar populations.Comment: 4 pages, 3 figures. Accepted for publication in ApJ Letter
Adsorption and catalytic activity of glucose oxidase accumulated on OTCE upon the application of external potential
This article describes the adsorption of glucose oxidase (GOx) onto optically transparent carbon electrodes (OTCE) under the effect of applied potential and the analysis of the enzymatic activity of the resulting GOx/OTCE substrates. In order to avoid electrochemical interferences with the enzyme redox center, control electrochemical experiments were performed using flavin adenine dinucleotide (FAD) and GOx/OTCE substrates. Then, the enzyme adsorption experiments were carried out as a function of the potential applied (ranged from the open circuit potential to +950. mV), the pH solution, the concentration of enzyme, and the ionic strength on the environment. The experimental results demonstrated that an increase in the adsorbed amount of GOx on the OTCE can be achieved when the potential was applied. Although the increase in the adsorbed amount was examined as a function of the potential, a maximum enzymatic activity was observed in the GOx/OTCE substrate achieved at +800. mV. These experiments suggest that although an increase in the amount of enzyme adsorbed can be obtained by the application of an external potential to the electrode, the magnitude of such potential can produce detrimental effects in the conformation of the adsorbed protein and should be carefully considered. As such, the article describes a simple and rational approach to increase the amount of enzyme adsorbed on a surface and can be applied to improve the sensitivity of a variety of biosensors.Fil: Benavidez, Tomás Enrique. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto de Investigaciones en FĂsico-quĂmica de CĂłrdoba. Universidad Nacional de CĂłrdoba. Facultad de Ciencias QuĂmicas. Instituto de Investigaciones en FĂsico-quĂmica de CĂłrdoba; Argentina. University of Texas; Estados UnidosFil: Torrente, Daniel. University of Texas; Estados UnidosFil: Marucho, Marcelo. University of Texas; Estados UnidosFil: Garcia, Carlos D.. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto de Investigaciones en FĂsico-quĂmica de CĂłrdoba. Universidad Nacional de CĂłrdoba. Facultad de Ciencias QuĂmicas. Instituto de Investigaciones en FĂsico-quĂmica de CĂłrdoba; Argentina. University of Texas; Estados Unido
Integrated engineering and geomorphological analysis for assessing the performance of bendway weirs in Illinois streams
U.S. Department of the InteriorU.S. Geological SurveyOpe
Coherent structures in oscillatory flows within the laminar-to-turbulent transition regime for smooth and rough walls
This is an Accepted Manuscript of an article published by Taylor & Francis Group in [Journal of hydraulic research] on [2016], available online at: http://www.tandfonline.com/10.1080/00221686.2016.1174960We investigate coherent structures present in oscillatory boundary layers over smooth and rough beds for Reynolds numbers between 103 and 104, in the transition to turbulence regime. A two-camera 2D- particle image velocimetry (PIV) system was used to visualize coherent structures in an oscillatory-flow tunnel. The obtained results show that smooth-bed flow is populated by vortex-tube structures that are formed due to the Kelvin–Helmholtz instability. Three types of coherent structures are observed in the rough-wall experiments: vortices randomly distributed in space; turbulent bursts – spatial structures without a clear shape compared to vortices but with a longer life than the former; and shear layers of vortices originating due to flow separation from some of the grains on the bed. The reported study contributes to the description of coherent structures in oscillatory flows that are captured with the PIV technique, particularly a new structure in flows over rough beds in the transition to turbulence regime.Peer ReviewedPostprint (author's final draft
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