1,708 research outputs found

    Flow and transport experiments for a streambank seep originating from a preferential flow pathway

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    Streambank seeps commonly originate from localized heterogeneity or preferential flow pathways (PFPs) in riparian floodplains. However, limited field data have been reported on ground water seep flows and solute transport to seeps from PFPs. The objective of this research was to build upon previous floodplain-scale investigations of PFPs by analyzing seep discharge and transport characteristics through a single PFP. An important research question was whether this PFP could be conceptualized as a homogeneous, one-dimensional flow path. Streambank seep discharge measurements were obtained by inducing a hydraulic head in a trench injection system. Also, co-injection of Rhodamine WT (RhWT) and a potassium chloride (KCl) tracer over a 60-min period was used to investigate transport dynamics. Seep discharge and breakthrough curves for electrical conductivity (EC) and RhWT were measured at the streambank using a lateral flow collection device. The breakthrough curves were fit to one-dimensional convective-dispersion equations (CDEs) to inversely estimate solute transport parameters. The PFP from which the seep originated was clean, coarse gravel (6% by mass less than 2.0 mm) surrounded by gravel with finer particles (20% by mass less than 2.0 mm). Located approximately 2 m from the trench, the seep (50 cm by 10 cm area) required at least 40 cm of hydraulic head for flow to emerge at the streambank. At a higher hydraulic head of 125 cm, seep discharge peaked at 3.5 L/min. This research verified that localized PFPs can result in the rapid transport of water (hydraulic conductivity on the order of 400 m/d) and solutes once reaching a sufficient near-bank hydraulic head. A one-dimensional equilibrium CDE was capable of simulating the EC (R2 = 0.94) and RhWT (R2 = 0.91) breakthrough curves with minimal RhWT sorption (distribution coefficient, Kd, equal to 0.1 cm3/g). Therefore, the PFP could be conceptualized as a one-dimensional, homogenous flow and transport pathway. These results are consistent with previous research observing larger-scale phosphorus transport

    X-ray Properties of Black-Hole Binaries

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    We review the properties and behavior X-ray binaries that contain an accreting black hole. The larger majority of such systems are X-ray transients, and many of them were observed in daily pointings with RXTE throughout the course of their outbursts. The complex evolution of these sources is described in terms of common behavior patterns illustrated with comprehensive overview diagrams for six selected systems. Central to this comparison are three X-ray states of accretion, which are reviewed and defined quantitatively. Each state yields phenomena that arise in strong gravitational fields. We sketch a scenario for the potential impact of black hole observations on physics and discuss a current frontier topic: the measurement of black hole spin.Comment: 39 pages, 12 figures, ARAA, vol. 44, in pres

    Effects of Environmental Cold on the Preruminant Calf

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    This study examined effects of sustained environmental cold on growth and health of dairy calves. Functional measures of energy metabolism, fat-soluble vitamin and mineral status, and immune competency were also evaluated. Newborn calves were assigned to warm or cold environments for 7wk. Cold environment temperature were maintained as close to 2°C as possible. Frequent wetting of the environment and calves augmented effects of the cold. The warm environment was maintained as close to 15°C as possible and humidity was not manipulated. Preventative medications or vaccinations were not administered. All calves were fed a non-medicated MR (20% CP and 20% fat fed at .45 kg/d) and non-medicated starter ad libitum. Cold environment averaged 12 o C lower than warm environment during the study period. Humidity averaged 10% higher in the cold environment. Respiratory health of the warm environment calves was moderately better than that of cold environment calves. Scour scores were unaffected by cold exposure. Growth rate was unaffected by environmental temperature; however, cold environment calves consumed more starter from wk 5 to 7. Blood glucose concentrations were lower and NEFA concentrations were higher in cold environment calves, indicative of a state of mild negative energy balance. Serum cytokine and fat-soluble vitamin concentrations, and antibody responses to vaccination were not impacted by sustained exposure to cold

    The hydraulic conductivity structure of gravel-dominated vadose zones within alluvial floodplains

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    The floodplains of many gravel-bed streams have a general stratigraphy that consists of a layer of topsoil covering gravel-dominated subsoil. Previous research has demonstrated that this stratigraphy can facilitate preferential groundwater flow through focused linear features, such as paleochannels, or gravelly regions within the vadose zone. These areas within the floodplain vadose zone may provide a route for interactions between the floodplain surface and alluvial groundwater, effectively extending the hyporheic zone across the floodplain during high stream stage. The objective of this research was to assess the structure and scale of texture heterogeneity within the vadose zone within the gravel subsoils of alluvial floodplains using resistivity data combined with hydraulic testing and sediment sampling of the vadose zone. Point-scale and broad-scale methodologies in combination can help us understand spatial heterogeneity in hydraulic conductivity without the need for a large number of invasive hydraulic tests. The evaluated sites in the Ozark region of the United States were selected due to previous investigations indicating that significant high conductivity flow zones existed in a matrix which include almost no clay content. Data indicated that resistivity corresponded with the fine content in the vadose zone and subsequently corresponds to the saturated hydraulic conductivity. Statistical analysis of resistivity data, and supported by data from the soil sampling and permeameter hydraulic testing, identified isolated high flow regions and zones that can be characterized as broad-scale high hydraulic conductivity features with potentially significant consequences for the migration of water and solutes and therefore are of biogeochemical and ecological significance

    Charge- And Angle-correlated Inelasticities In Collisions Of Bare Fast Carbon Ions With Neon

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    We have studied the detailed energy balance in collisions of 10-MeV C6+ ions with Ne. In these collisions, the Ne is multiply ionized and the C ion may emerge as either C6+ or C5+. Projectile energy loss and scattering angle for a given carbon-ion charge state were determined in a high-resolution magnetic spectrograph and were measured in coincidence with the formation of a given Ne recoil-ion charge state. The amount of energy transferred to the continuum electrons exceeds, by far, the sum of the values of the ionization potentials. © 1988 The American Physical Society

    Catalysts for long-life closed-cycle CO2 lasers

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    Long-life, closed-cycle operation of pulsed CO2 lasers requires catalytic CO-O2 recombination both to remove O2, which is formed by discharge-induced CO2 decomposition, and to regenerate CO2. Platinum metal on a tin (IV) oxide substrate (Pt/SnO2) has been found to be an effective catalyst for such recombination in the desired temperature range of 25 to 100 C. This paper presents a description of ongoing research at NASA-LaRC on Pt/SnO2 catalyzed CO-O2 recombination. Included are studies with rare-isotope gases since rare-isotope CO2 is desirable as a laser gas for enhanced atmospheric transmission. Results presented include: (1) achievement of 98% to 100% conversion of a stoichiometric mixture of CO and O2 to CO2 for 318 hours (greater than 1 x 10 to the 6th power seconds), continuous, at a catalyst temperature of 60 C, and (2) development of a technique verified in a 30-hour test, to prevent isotopic scrambling when CO-18 and O-18(2) are reacted in the presence of a common-isotope Pt/Sn O-16(2) catalyst

    Fat-Soluble Vitamin and Micromineral Concentrations in Preruminant Dairy Calves Fed to Achieve Different Growth Rates

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    Effects of neonatal growth rate on plasma concentrations of fat-soluble vitamins, zinc, and copper in preruminant calves were evaluated. Calves were assigned to dietary treatments designed to achieve three targeted rates of gain [No-Growth (NG) = 0.0 kg/d, Low-Growth (LG) = 0.55 kg/d, or High-Growth (HG) = 1.2 kg/d] over a 7 wk period. MR intakes needed to achieve specified growthrates were estimated using the NRC Nutrient Requirements of Dairy Cattle calf model computer program. Calves were fed a 30% CP, 20% fat, MR reconstituted to 14% DM. Because vitamin levels in the MR were based on DM intake of HG calves, NG and LG calves were supplemented with additional vitamins once weekly to compensate for reduced MR consumption. Growth rates for NG (0.11 kg/d), LG (0.58 kg/d), and HG (1.16 kg/d) calves differed throughout the study. Although vitamins A and D, and Zn concentrations were unaffected by growth rate, their concentrations increased and Zn/Cu concentrations decreased with time. Throughout the study their concentrations remained within normal ranges for the preruminant calf. Vitamin E and copper were affected by growth rate. At wk 7, HG calves had lower vitamin E concentrations than LG and NG calves. Copper concentrations were greater for HG calves than LG and NG calves from wk 4 to wk 7. Copper and vitE concentrations, however, remained within ranges considered normal for preruminant calves. These results suggest that growth rate during the neonatal period influences vitE and Cu availabilit

    Stage-dependent transient storage of phosphorus in alluvial floodplains

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    Models for contaminant transport in streams commonly idealize transient storage as a well-mixed but immobile system. These transient storage models capture rapid (near-stream) hyporheic storage and transport, but do not account for large-scale, stage-dependent interaction with the alluvial aquifer. The objective of this research was to document transient storage of phosphorus (P) in coarse gravel alluvium potentially influenced by large-scale, stage-dependent preferential flow pathways (PFPs). Long-term monitoring was performed at floodplain sites adjacent to the Barren Fork Creek and Honey Creek in northeastern Oklahoma. Based on results from subsurface electrical resistivity mapping which was correlated to hydraulic conductivity data, observation wells were installed both in higher hydraulic conductivity and lower hydraulic conductivity subsoils. Water levels in the wells were monitored over time, and water samples were obtained from the observation wells and the stream to document P concentrations at multiple times during high flow events. Contour plots indicating direction of flow were developed using water table elevation data. Contour plots of total P concentrations showed the alluvial aquifer acting as a transient storage zone, with P-laden stream water heterogeneously entering the aquifer during the passage of a storm pulse, and subsequently re-entering the stream during baseflow conditions. Some groundwater in the alluvial floodplains had total P concentrations that mirrored the streams’ total P concentrations. A detailed analysis of P forms indicated that particulate P (i.e. P attached to particulates greater than 0·45 μm) was a significant portion of the P transport. This research suggests the need for more controlled studies on stage-dependent transient storage in alluvial systems
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