Non-Darcy flow characteristics of water as influenced by clay concentration

The flow of water through saturated samples of montmorillonite and kaolinite was studied to help clarify the existence and nature of non-Darcian flow. No threshold gradients were found in any of the samples studied. Non-Darcy flow was found in 9, 30 and 40 weight percent montmorillonite samples but not in a 50 weight percent montmorillonite or in kaolinite samples. The possible causes of the non-Darcian flow are discussed. A refined technique using a pressure transducer was developed to measure hydraulic conductivities. The hydraulic conductivities of several types of samples under varying conditions were measured. Transport equations for convective diffusion in porous media were derived and tested for capillaries, porous diaphragms, sand columns and clay plugs.U.S. Department of the InteriorU.S. Geological SurveyOpe

Structural basis of Lewis(b) antigen binding by the Helicobacter pylori adhesin BabA

Helicobacter pylori is a leading cause of peptic ulceration and gastric cancer worldwide. To achieve colonization of the stomach, this Gram-negative bacterium adheres to Lewis(b) (Le(b)) antigens in the gastric mucosa using its outer membrane protein BabA. Structural information for BabA has been elusive, and thus, its molecular mechanism for recognizing Le(b) antigens remains unknown. We present the crystal structure of the extracellular domain of BabA, from H. pylori strain J99, in the absence and presence of Le(b) at 2.0- and 2.1-Å resolutions, respectively. BabA is a predominantly α-helical molecule with a markedly kinked tertiary structure containing a single, shallow Le(b) binding site at its tip within a β-strand motif. No conformational change occurs in BabA upon binding of Le(b), which is characterized by low affinity under acidic [K D (dissociation constant) of ~227 μM] and neutral (K D of ~252 μM) conditions. Binding is mediated by a network of hydrogen bonds between Le(b) Fuc1, GlcNAc3, Fuc4, and Gal5 residues and a total of eight BabA amino acids (C189, G191, N194, N206, D233, S234, S244, and T246) through both carbonyl backbone and side-chain interactions. The structural model was validated through the generation of two BabA variants containing N206A and combined D233A/S244A substitutions, which result in a reduction and complete loss of binding affinity to Le(b), respectively. Knowledge of the molecular basis of Le(b) recognition by BabA provides a platform for the development of therapeutics targeted at inhibiting H. pylori adherence to the gastric mucosa

Characterization of U-Mo Foils for AFIP-7

Twelve AFIP in-process foil samples, fabricated by either Y-12 or LANL, were shipped from LANL to PNNL for potential characterization using optical and scanning electron microscopy techniques. Of these twelve, nine different conditions were examined to one degree or another using both techniques. For this report a complete description of the results are provided for one archive foil from each source of material, and one unirradiated piece of a foil of each source that was irradiated in the Advanced Test Reactor. Additional data from two other LANL conditions are summarized in very brief form in an appendix. The characterization revealed that all four characterized conditions contained a cold worked microstructure to different degrees. The Y-12 foils exhibited a higher degree of cold working compared to the LANL foils, as evidenced by the highly elongated and obscure U-Mo grain structure present in each foil. The longitudinal orientations for both of the Y-12 foils possesses a highly laminar appearance with such a distorted grain structure that it was very difficult to even offer a range of grain sizes. The U-Mo grain structure of the LANL foils, by comparison, consisted of a more easily discernible grain structure with a mix of equiaxed and elongated grains. Both materials have an inhomogenous grain structure in that all of the characterized foils possess abnormally coarse grains

Physics on the edge: contour dynamics, waves and solitons in the quantum Hall effect

We present a theoretical study of the excitations on the edge of a two-dimensional electron system in a perpendicular magnetic field in terms of a contour dynamics formalism. In particular, we focus on edge excitations in the quantum Hall effect. Beyond the usual linear approximation, a non-linear analysis of the shape deformations of an incompressible droplet yields soliton solutions which correspond to shapes that propagate without distortion. A perturbative analysis is used and the results are compared to analogous systems, like vortex patches in ideal hydrodynamics. Under a local induction approximation we find that the contour dynamics is described by a non-linear partial differential equation for the curvature: the modified Korteweg-de Vries equation. PACS number(s): 73.40.Hm, 02.40.Ma, 03.40.Gc, 11.10.LmComment: 15 pages, 12 embedded figures, submitted to Phys. Rev.

Expanding Stereochemical and Skeletal Diversity Using Petasis Reactions and 1,3-Dipolar Cycloadditions

A short and modular synthetic pathway using intramolecular 1,3-dipolar cycloaddition reactions and yielding functionalized isoxazoles, isoxazolines, and isoxazolidines is described. The change in shape of previous compounds and those in this study is quantified and compared using principal moment-of-inertia shape analysis.Chemistry and Chemical Biolog