Genes required for in situ sediment survival of Shewanella oneidensis MR-1.

We determined the function of one sediment-survival gene, examining mexF in greater detail. The protein encoded by mexF shares high homology with MexF in pathogenic Pseudomonas where it has been shown to confer a multidrug resistance phenotype on its host. We determined that mexF in MR-1 also functions in multidrug resistance, although additional substrates, including those that may be found in sediment remain to be elucidated. We propose that similar genes, present in the genomes of both pathogenic and nonpathogenic bacteria, have persisted over time in order to combat natural (such as plant- and bacterial-derived antimicrobials) as well as man-made toxins.We developed a modified version of the traditional signature-tagged mutagenesis (STM) procedure, incorporating microarray technology to streamline the entire screening process. We also identified a mini-Tn10 transposon that is capable of randomly mutagenizing model bacteria of the gamma- and delta- Proteobacteria. This system can therefore be applied to a wide variety of environmentally significant bacteria to answer questions of ecological or economical importance. This is the first study to use STM in studying bacteria of environmental significance.We identified 47 genes required for sediment survival of MR-1. We validate our STM screening method by identifying genes that would be expected to enhance sediment survival (e.g., chemotaxis genes) or would be required for growth with Fe(III) (i.e., gspN, a gene within an operon that was shown previously to be required for Fe(III) reduction). We describe the putative sediment functions of many groups of these genes, and we propose roles for phage- and transposon-related genes, as well as many genes involved in defensive mechanisms, such as multidrug resistance.We examined survival of Shewanella oneidensis MR-1 in sediment microcosms under various respiratory conditions. MR-1 was able to maintain its population in aerobic, transitory, and unamended anaerobic sediments; however, under Fe(III)-reducing conditions, the addition of lactate or an electron shuttle/Fe(III) chelator was required for maintenance of inoculum concentration and for growth in some instances. Loss of numbers in the absence of these compounds may result from direct competition with indigenous bacteria, such as Geobacter species, that are better suited physiologically for obtaining energy from Fe(III) reduction

Morphologic signatures of autogenic waterfalls: A case study in the San Gabriel Mountains, California

Waterfalls are powerful agents of geomorphic work as they can erode at different ratesthan surrounding reaches, thereby setting the pace of landscape evolution. Waterfalls can form due to external perturbation of river base level, lithologic heterogeneity, and internal feedbacks (i.e., autogenic dynamics). While criteria for identification of waterfalls formed by lithologic heterogeneity and external perturbation are well documented, there has been no systematic description of how to identify self-formed (autogenic) waterfalls, therein limiting assessment of the ubiquity of self-formed waterfalls and their influence on past environmental forcing encoded in topography. Based on the assumption that autogenic waterfalls form from a specific type of bedrock bedform known as cyclic steps, we propose that autogenic waterfalls should form in series with waterfall height and spacing between waterfalls set primarily by channel slope. We use high resolution topography in the San Gabriel Mountains, California, to identify 360 waterfalls and show that waterfalls tend to form at channel slopes >3%, coinciding with the onset of Froude supercritical flow, and that the waterfall height to spacing ratio increases with channel slope; consistent with cyclic step theory and previous laboratory experiments. Our results imply that in unglaciated mountain ranges with relatively uniform rock strength, the majority of waterfalls may be autogenic in origin

Vegetation Communities of Ledges State Park, Boone County, Iowa

The vegetation of Ledges State Park was sampled with 54 plots placed in representative plant communities throughout the park. The plots were ordinated by tree species and compared with topography. Seven major vegetation types were defined: Quercus alba type ,Quercus alba-Quercus rubra type, Quercus rubra type, Quercus rubra-Tilia americana type, Tilia americana type,Juglans nigra type, and slump forest type. A vegetation map of the park was constructed using field data and aerial photography. In comparison with eastern Iowa forests, the forests of Ledges State Park are a western extension of the species-rich eastern forests with the addition of xeric elements common in the Ledges but not as common in the east. Forests of the xeric uplands of the Ledges State Park do not succeed toward maple-basswood as in eastern Iowa, but remain oak dominated. The slump forest, a new vegetation community unique to the Ledges, is described

Crystal structures and freezing of dipolar fluids

We investigate the crystal structure of classical systems of spherical particles with an embedded point dipole at T=0. The ferroelectric ground state energy is calculated using generalizations of the Ewald summation technique. Due to the reduced symmetry compared to the nonpolar case the crystals are never strictly cubic. For the Stockmayer (i.e., Lennard-Jones plus dipolar) interaction three phases are found upon increasing the dipole moment: hexagonal, body-centered orthorhombic, and body-centered tetragonal. An even richer phase diagram arises for dipolar soft spheres with a purely repulsive inverse power law potential $\sim r^{-n}$. A crossover between qualitatively different sequences of phases occurs near the exponent $n=12$. The results are applicable to electro- and magnetorheological fluids. In addition to the exact ground state analysis we study freezing of the Stockmayer fluid by density-functional theory.Comment: submitted to Phys. Rev.

An interactive multimedia continuously learning helpdesk system : (when Hal met Sally)

Thesis (S.B. and M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.Includes bibliographical references (leaves 65-72).by Marion L. Groh.S.B.and M.Eng

Vesicles in solutions of hard rods

The surface free energy of ideal hard rods near curved hard surfaces is determined to second order in curvature for surfaces of general shape. In accordance with previous results for spherical and cylindrical surfaces it is found that this quantity is non-analytical when one of the principal curvatures changes signs. This prohibits writing it in the common Helfrich form. It is shown that the non-analytical terms are the same for any aspect ratio of the rods. These results are used to find the equilibrium shape of vesicles immersed in solutions of rod-like (colloidal) particles. The presence of the particles induces a change in the equilibrium shape and to a shift of the prolate-oblate transition in the vesicle phase diagram, which are calculated within the framework of the spontaneous curvature model. As a consequence of the special form of the energy contribution due to the rods these changes cannot be accounted for by a simple rescaling of the elastic constants of the vesicle as for solutions of spherical colloids or polymers.Comment: 11 pages, 7 figures, submitted to Phys. Rev.

Flora and Phytogeographical History of Ledges State Park, Boone County, Iowa

The Ledges State Park flora includes 437 species of vascular plants, several of which are unusual for central Iowa. The flora is surprisingly diverse considering its western location. The current distributions and occurrences of plants in the Ledges suggest the influence of historic plant migrations. The Ledges flora is composed of three elements, eastern mesophytic species, southern zerophytic species and northern boreal species. The dissected topography of the Ledges State Park has allowed boreal species, relics of northern forests, to persist in the protected canyon habitats

Observed crustal uplift near the Southern Patagonian Icefield constrains improved viscoelastic Earth model

Thirty‒one GPS geodetic measurements of crustal uplift in southernmost South America determined extraordinarily high trend rates (> 35 mm/yr) in the north‒central part of the Southern Patagonian Icefield. These trends have a coherent pattern, motivating a refined viscoelastic glacial isostatic adjustment model to explain the observations. Two end‒member models provide good fits: both require a lithospheric thickness of 36.5 ± 5.3 km. However, one end‒member has a mantle viscosity near η =1.6 ×1018 Pa s and an ice collapse rate from the Little Ice Age (LIA) maximum comparable to a lowest recent estimate of 1995–2012 ice loss at about −11 Gt/yr. In contrast, the other end‒member has much larger viscosity: η = 8.0 ×1018 Pa s, half the post–LIA collapse rate, and a steadily rising loss rate in the twentieth century after AD 1943, reaching −25.9 Gt/yr during 1995–2012.Fil: Lange, H.. Technische Universitaet Dresden; AlemaniaFil: Casassa, G.. Centro de Estudios Cientificos; Chile. Universidad de Magallanes; ChileFil: Ivins, E. R.. Institute of Technology. Jet propulsion Laboratory; Estados UnidosFil: Schroeder, L.. Technische Universitaet Dresden; AlemaniaFil: Fritsche, M.. Technische Universitaet Dresden; AlemaniaFil: Richter, Andreas Jorg. Technische Universitaet Dresden; Alemania. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas. Departamento de Astrometría; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Groh, A.. Technische Universitaet Dresden; AlemaniaFil: Dietrich, R.. Technische Universitaet Dresden; Alemani

Orientational order in dipolar fluids consisting of nonspherical hard particles

We investigate fluids of dipolar hard particles by a certain variant of density-functional theory. The proper treatment of the long range of the dipolar interactions yields a contribution to the free energy which favors ferromagnetic order. This corrects previous theoretical analyses. We determine phase diagrams for dipolar ellipsoids and spherocylinders as a function of the aspect ratio of the particles and their dipole moment. In the nonpolar limit the results for the phase boundary between the isotropic and nematic phase agree well with simulation data. Adding a longitudinal dipole moment favors the nematic phase. For oblate or slightly elongated particles we find a ferromagnetic liquid phase, which has also been detected in computer simulations of fluids consisting of spherical dipolar particles. The detailed structure of the phase diagram and its evolution upon changing the aspect ratio are discussed in detail.Comment: 35 pages LaTeX with epsf style, 11 figures in eps format, submitted to Phys. Rev.

Magnetization of ferrofluids with dipolar interactions - a Born--Mayer expansion

For ferrofluids that are described by a system of hard spheres interacting via dipolar forces we evaluate the magnetization as a function of the internal magnetic field with a Born--Mayer technique and an expansion in the dipolar coupling strength. Two different approximations are presented for the magnetization considering different contributions to a series expansion in terms of the volume fraction of the particles and the dipolar coupling strength.Comment: 19 pages, 11 figures submitted to PR