Cattle Temporal and Spatial Distribution in Midwestern Pastures Using Global Positioning (Three-year Progress Report)

Previous research has shown that grazing cattle tend to congregate in streamside zones of pastures to obtain water and shade for thermoregulation. However, problems associated with thermoregulation may be increased because of the presence of endophyte-infected tall fescue in pastures. Defining relationships between cattle distribution, such pasture characteristics as size, shape, shade distribution, botanical composition, and climatic factors related to heat stress, will provide the basis for the development and implementation of management practices that minimize nonpoint source pollution possibly associated with grazing cattle

Cattle Temporal & Spatial Distribution in Midwestern Pastures Using Global Positioning (A Three-Year Progress Report)

Eight pastures on five southern Iowa cow-calf farms were used to evaluate the effects of pasture characteristics and microclimatic conditions on cattle grazing cool-season grass pastures with streams and/or ponds. Pastures ranged from 19 to 309 acres and contained varying proportions of cool-season grasses, legumes, sedge, broadleaf weeds, brush, and bare ground. The percentages of pasture area that were shaded ranged from 19 to 73%. Cows were Angus and Angus-Cross on seven of the pastures, and Mexican Corriente on the remaining pasture. In spring, summer, and fall of 2007, 2008, and 2009, 2 to 3 cows per pasture were fitted with Global Positioning System (GPS) collars to record position at 10 minute intervals for periods of 5 to 14 days. Ambient temperature, black globe temperature, dew point, relative humidity, and wind speed and direction were collected with HOBO data loggers at ten minute intervals over the 2007, 2008, and 2009 grazing seasons on each farm. Streams, ponds, and fence lines were referenced on a geospatial map and used to establish zones in the pastures. Designated zones were: in the stream or pond, within 100 feet, or greater than 100 ft (uplands) from the stream or pond (water source). One hundred thirty-nine data sets were obtained throughout the three-year project. Mean proportions of observations when cattle were in the water source differed (P\u3c0.0001) between farms, but not between seasons (P=0.5824). Mean proportions of time cattle spent within 100, or greater 100 ft of the water source differed (P\u3c0.0001) among farms. The proportion of time cattle were within the streamside zone (defined as being in the water source or within 100 feet of the water source) increased with increasing ambient temperature, increasing the proportion of streamside zone within a pasture, increasing the proportion of total pasture shade within the streamside zone, and decreasing pasture size. Therefore, implementation of grazing management practices for the protection of pasture streams are more likely to be effective on small and/or narrow pastures in which cattle have less opportunity to locate in upland locations

Lift and drag effects of wing-tip rake

This report deals with a description and report of tests carried out at the Washington Navy Yard on models of the RAF-6, albatross and Slone airfoils to determine the effectiveness of the conventional wing-trailing edge being always longer than the leading edge. The results are compared with the values computed by standard formulae in use at the time the tests were conducted

First Passage Time in a Two-Layer System

As a first step in the first passage problem for passive tracer in stratified porous media, we consider the case of a two-dimensional system consisting of two layers with different convection velocities. Using a lattice generating function formalism and a variety of analytic and numerical techniques, we calculate the asymptotic behavior of the first passage time probability distribution. We show analytically that the asymptotic distribution is a simple exponential in time for any choice of the velocities. The decay constant is given in terms of the largest eigenvalue of an operator related to a half-space Green's function. For the anti-symmetric case of opposite velocities in the layers, we show that the decay constant for system length $L$ crosses over from $L^{-2}$ behavior in diffusive limit to $L^{-1}$ behavior in the convective regime, where the crossover length $L^*$ is given in terms of the velocities. We also have formulated a general self-consistency relation, from which we have developed a recursive approach which is useful for studying the short time behavior.Comment: LaTeX, 28 pages, 7 figures not include

Dispersion of imbibition fronts

We have studied the dispersive behaviour of imbibition fronts in a porous medium by X-ray tomography. Injection velocities were varied and the porous medium was initially prewetted or not. At low velocity in the prewetted medium, the imbibition profiles are found to be distinctly hyperdispersive. The profiles are anomalously extended when compared to tracer fronts exhibiting conventional (Gaussian) dispersion. We observe a strong velocity dependence of the exponent characterizing the divergence of the dispersion coefficient for low wetting-fluid saturation. Hyperdispersion is absent at high imbibition velocities or when the medium is not prewetted.Comment: 8 pages, 5 figures; submitted to Europhysics Letter

Analysis of the intraspinal calcium dynamics and its implications on the plasticity of spiking neurons

The influx of calcium ions into the dendritic spines through the N-metyl-D-aspartate (NMDA) channels is believed to be the primary trigger for various forms of synaptic plasticity. In this paper, the authors calculate analytically the mean values of the calcium transients elicited by a spiking neuron undergoing a simple model of ionic currents and back-propagating action potentials. The relative variability of these transients, due to the stochastic nature of synaptic transmission, is further considered using a simple Markov model of NMDA receptos. One finds that both the mean value and the variability depend on the timing between pre- and postsynaptic action-potentials. These results could have implications on the expected form of synaptic-plasticity curve and can form a basis for a unified theory of spike time-dependent, and rate based plasticity.Comment: 14 pages, 10 figures. A few changes in section IV and addition of a new figur

Dynamics of Wetting Fronts in Porous Media

We propose a new phenomenological approach for describing the dynamics of wetting front propagation in porous media. Unlike traditional models, the proposed approach is based on dynamic nature of the relation between capillary pressure and medium saturation. We choose a modified phase-field model of solidification as a particular case of such dynamic relation. We show that in the traveling wave regime the results obtained from our approach reproduce those derived from the standard model of flow in porous media. In more general case, the proposed approach reveals the dependence of front dynamics upon the flow regime.Comment: 4 pages, 2 figures, revte

Estimation of the hydraulic parameters of unsaturated samples by electrical resistivity tomography

In situ and laboratory experiments have shown that electrical resistivity tomography (ERT) is an effective tool to image transient phenomena in soils. However, its application in quantifying soil hydraulic parameters has been limited. In this study, experiments of water inflow in unsaturated soil samples were conducted in an oedometer equipped to perform three-dimensional electrical measurements. Reconstructions of the electrical conductivity at different times confirmed the usefulness of ERT for monitoring the evolution of water content. The tomographic reconstructions were subsequently used in conjunction with a finite-element simulation to infer the water retention curve and the unsaturated hydraulic conductivity. The parameters estimated with ERT agree satisfactorily with those determined using established techniques, hence the proposed approach shows good potential for relatively fast characterisations. Similar experiments could be carried out on site to study the hydraulic behaviour of the entire soil deposi