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Contaminant transformation rates are routinely estimated from monitoring well data using a regression method based on a steady-state analytical model. This approach assumes one-dimensional solute transport in the presence of a continuous boundary concentration and a uniform first-order degradation coefficient. It must be recognized that this type of analysis is easily subject to misinterpretation, particularly when few monitoring points are used. This is because the dispersive nature of solute transport can produce concentration profiles which closely resemble those associated with a degrading contaminant even in the absence of any transformation processes. Monte Carlo analyses using simulated plumes suggest that this method may lead to significant overestimates of apparent transformation rates.

The problem of point defects diffusing anisotropically towards spheroidal sinks is solved using an analytical treatment. Depending on the ratios between the sink semi-axes (a0, b0) and the diffusivity main components (D⟂, Dz), two different situations are solved separately: the prolate and the oblate cases. For each case two boundary conditions are considered: a) periodic sink distribution and b) a constant boundary concentration condition. The results of this study allow to derive qualitative conclusions with respect to the influence of the diffusion anisotropy, the boundary conditions, and the cavity shape on the point defect concentration profiles around spheroidal sinks. In a coming paper these results are applied to study the diffusion of irradiation produced point defects towards cavities and to calculate defect bias and cavity sink strength. Mit einem analytischen Verfahren wird das Problem der Punktdefekte, die anisotrop zu spharoiden Senken diffundieren, gelost. In Abhangigkeit vom Verhaltnis zwischen den Senken-Halbachsen (a0, b0) und den Hauptkomponenten (D⟂, Dz) des Diffusionsvermogens, werden zwei unterschiedliche Situationen getrennt gelost: der gestreckte und der abgeplattete Fall. Fur jeden Fall werden zwei Grenzbedingungen betrachtet: a) eine periodische Senkenverteilung und b) eine konstante Konzentration der Grenzen. Die Ergebnisse dieser Untersuchung erlauben qualitative Schlusse bezuglich des Einflusses der Diffusionsanisotropie, der Grenzbedingungen und der Hohlraumform auf die Profile der Punktdefektkonzentration um spharoide Senken. In einer weiteren Arbeit werden diese Ergebnisse benutzt, um die Diffusion von strahlungsinduzierten Punktdefekten zu Hohlraumen zu untersuchen und Defektvorspannung und Hohlraumsenkenstarke zu berechnen.

The diffusion of sodium chloride, nitrite, and nitrate into beef, pork, and pork fat was studied by the porous disc technique. Total salt uptake and boundary concentration analyses were performed on beef. Various salt combinations and concentrations and various muscles were studied. Chloride diffusion was normal by all three methods of analysis, but skew boundaries and decreased uptake of nitrite were observed in the boundary measurements; diffusion rates of nitrite were constant in the porous disc method. Nitrite diffused slower than chloride in meat, but the rate of nitrate diffusion was sometimes greater than that of chloride. Comparison of the results of the steady state diffusion with the total uptake and boundary concentration showed the diffusion of nitrite to be governed by both physical and chemical factors.

The dependence of current-voltage characteristics, and potential distributions, on light intensity is measured at room temperature in thin photoconducting layers of polycrystalline Se. Theoretical calculations of the steady-state potential distribution of an illuminated metalsemiconductor contact, and mono- and bimolecular recombination, agree well with the experimental results. They show that the potential distribution, and therefore the current-voltage characteristic, are determined solely by the relation between the bulk and boundary concentrations of the one mobile carrier type. By fitting the experimental to the theoretical results, numerical values of carrier concentration p and mobility μ are obtained: μ ∼ 10−1 cm2/Vs, p ranges from 1011 cm−3 (in the dark) to 1013 cm−3 (for high intensity illumination). The boundary concentration pA ∼ 1012 cm−3 at the Se—Au contact was found to be independent of light intensity. An dunnen photoleitenden Schichten aus polykristallinem Selen wurden Strom-Spannungs-Kennlinien und Potentialverteilungen bei Zimmertemperatur in Abhangigkeit von der Bestrahlungsstarke gemessen. Mit den experimentellen Ergebnissen stimmen Berechnungen der stationaren Potentialverteilungen fur den belichteten Metall-Halbleiter-Kontakt bei mono- und bimolekularer Rekombination gut uberein. Sie zeigen, wie die Potentialverteilungen und damit auch die Strom-Spannungs-Kennlinien entscheidend durch das Verhaltnis der Rand- zur Innenkonzentration der einen beweglichen Ladungstragersorte bestimmt werden. Daruber hinaus erhalt man durch Anpassung der experimentellen an die theoretischen Ergebnisse numerische Werte fur die Ladungstragerkonzentration p und die Beweglichkeit μ. Fur die benutzten Schichten ergab sich μ ∼ 10−1 cm2/Vs sowie p ∼ 1011 cm−3 im Dunkeln bis p ∼ 1013 cm−3 bei starker Bestrahlung, dagegen eine von der Bestrahlungsstarke unabhangige Randkonzentration pA ∼ 1012 cm−3 an der Grenze Selen-Gold-Kontakt.