Radial transport in a porous medium with Dirichlet, Neumann and Robin-type inhomogeneous boundary values and general initial data: analytical solution and evaluation

The analytical solution is presented to the convection–diffusion equation describing the concentration of solutes in a radial velocity field due to extracting groundwater from or injecting water into an aquifer with arbitrary initial concentration data F(r), with r the radial distance, and an inhomogeneous mixed boundary condition G(t), with t the time, at the well radius r = r ₀. The analytical solution is obtained with a generalized Hankel transformation or with a Laplace transformation. The Hankel transformation turns out to be easier for G = 0, F ≠ 0, while the Laplace transformation is easier for F = 0, G ≠ 0. Both techniques can, however, deal with the full problem. The representation found by the generalized Hankel transform can also be found by the Laplace transform, through modification of the contour through the complex plane in the Bromwich integral for the inverse Laplace transform to the real axis. In practice, the numerical evaluation of the integral representation is difficult, due to the oscillating behavior of the integrands. A more appropriate numerical inversion procedure is also suggested, which circumvents the integration of the oscillating integrands, by an alternative modification of the contour in the Bromwich integral such that the new contour follows the steepest descent path starting from a saddle point at the real axis.     

Risk factors for Salmonella dublin infections on dairy farms

A case-control investigation of the risk factors for Salmonella dublin infections on 126 dairy farms identified the following variables as being significantly associated with infection: standardized farm size and presence of water courses. Contrary to expectations, contact with cattle from other farms when the animals were turned out to grass was negatively associated with S. dublin infection. The purchase of cattle from other farms was a risk factor. There were more infections when feed consisted of grass alone than when grass was supplemented with maize or grass silage. S. dublin infections were strongly correlated with liver fluke infections.     

Strategy for solving semi-analytically three-dimensional transient flow in a coupled <Emphasis Type="Italic">N</Emphasis>-layer aquifer system

Efficient strategies for solving semi-analytically the transient groundwater head in a coupled N-layer aquifer system , i = 1, ... , N, with radial symmetry, with full z-dependency, and partially penetrating wells are presented. Aquitards are treated as aquifers with their own horizontal and vertical permeabilities. Since the vertical direction is fully taken into account, there is no need to pose the Dupuit assumption, i.e., that the flow is mainly horizontal. To solve this problem, integral transforms will be employed: the Laplace transform for the t-variable (with transform parameter p), the Hankel transform for the r-variable (with transform parameter α) and a particular form of a generalized Fourier transform for the vertical direction z with an infinite set of eigenvalues (with the discrete index m). It is possible to solve this problem in the form of a semi-analytical solution in the sense that an analytical expression in terms of the variables r and z, transform parameter p, and eigenvalues of the generalized Fourier transform can be given or in terms of the variables z and t, transform parameter α, and eigenvalues . The calculation of the eigenvalues and the inversion of these transformed solutions can only be done numerically. In this context the application of the generalized Fourier transform is novel. By means of this generalized Fourier transform, transient problems with horizontal symmetries other than radial can be treated as well. The notion of analytical solution versus numerical solution is discussed and a classification of analytical solutions is proposed in seven classes. The expressions found in this paper belong to Class 6, meaning that the transformed solutions are written in terms of eigenvalues which depend on one transform parameter (here p or α). Earlier solutions to the transient problem belong to Class 7, where the eigenvalues depend on two transform parameters. The theory is applied to three examples.     

Remembering Can Cause Inhibition: Retrieval-Induced Inhibition as Cue Independent Process.

Previous experiments have mostly relied on recall as a dependent measure to assess whether retrieval of information from memory causes inhibition of related information. This study aimed to measure this inhibition in a more direct way. In Experiment 1, it was shown that repeated retrieval of exemplars from a category resulted in longer recognition latencies to nonretrieved exemplars from that same category, compared with recognition latencies to control exemplars. Experiment 2 obtained the same pattern of results using a lexical decision task. This was the 1st time that retrieval-induced forgetting was demonstrated on an implicit test of memory. To exclude noninhibitory explanations of the data, the exemplars were presented in both experiments without their categories as cues. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

When observing gaze shifts of others enhances object desirability.

The present research explored when observing gaze shifts of another person, involving both the observer and a specific object, enhances desirability of the gazed-at object. Specifically, we offer an initial attempt to test the idea that a three-step sequence consisting of direct gaze at the observer, followed by object-directed gaze and then by direct gaze at the observer, cues the desirability of an object to the observer and hence increases the perceived desirability of the gazed-at object. We examined this hypothesis in three experiments by manipulating eye-gaze shifts and including a no-gaze control condition. In line with our prediction, results showed that the dynamic sequence of gaze shifts indeed increases perceived object desirability. These findings provide new evidence that a sequence of gaze behavior involving the observer and an object plays an important role in influencing affective evaluation of objects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Measuring driving knowledge2

Several new driving knowledge tests and a conventional written test are compared with respect to their correlations with real driving performance. It is found that a theoretical knowledge test, using slides of simple real-traffic situations, correlates higher with real driving performance than the conventional test. Therefore, as a licensing device, it is recommended to use the described slide test instead of written multiple choice tests.