Fine‐scale measurement of diffusivity in a microbial mat with nuclear magnetic resonance imaging

Noninvasive 1H‐nuclear magnetic resonance (NMR) imaging was used to investigate the diffusive properties of microbial mats in two dimensions. Pulsed field gradient NMR was used to acquire images of the H2O diffusion coefficient, Ds, and multiecho imaging NMR was used to obtain images of the water density in two structurally different microbial mats sampled from Solar Lake (Egypt). We found a pronounced lateral and vertical variability of both water density and water diffusion coefficient, correlated with the laminated and heterogeneous distribution of microbial cells and exopolymers within the mats. The average water density varied from 0.5 to 0.9, whereas the average water diffusion coefficient ranged from 0.4 to 0.9 relative to the values obtained in the stagnant water above the mat samples. The apparent water diffusivities estimated from NMR imaging compared well to apparent O2 diffusivities measured with a diffusivity microsensor. Analysis of measured O2 concentration profiles with a diffusion‐reaction model showed that both the magnitude of calculated rates and the depth distribution of calculated O2 consumption/production zones changed when the observed variations of diffusivity were taken into account. With NMR imaging, diffusivity can be determined at high spatial resolution, which can resolve inherent lateral and vertical heterogeneities found in most natural benthic systems

Progress in the synthesis and exploitation of catenanes since the Millennium

Catenanes – molecules consisting of interlocked macrocyclic rings – have been prepared by templation strategies for some thirty years. The utilization of CuI cation, aromatic donor–acceptor interactions and hydrogen bonding assisted self-assembly strategies has led to the construction of numerous examples of these aesthetically pleasing species. This review seeks to discuss key developments in the synthesis and functional application of catenanes that have occurred since the Millennium. The much expanded range of metal cation templates; the genesis and growth of anion templation, as well as the use of alternative supramolecular interactions (halogen bonding and radical templation) and thermodynamically controlled reactions to synthesize catenanes are detailed. The class of catenanes that may be described as “molecular machines” are then highlighted and to conclude, attempts to fabricate catenanes onto surfaces and into metal organic frameworks (MOFs) are discussed

Advances in anion supramolecular chemistry:from recognition to chemical applications

Since the start of this millennium, remarkable progress in the binding and sensing of anions has been taking place, driven in part by discoveries in the use of hydrogen bonding, as well as the previously under-exploited anion–π interactions and halogen bonding. However, anion supramolecular chemistry has developed substantially beyond anion recognition, and now encompasses a diverse range of disciplines. Dramatic advance has been made in the anion-templated synthesis of macrocycles and interlocked molecular architectures, while the study of transmembrane anion transporters has flourished from almost nothing into a rapidly maturing field of research. The supramolecular chemistry of anions has also found real practical use in a variety of applications such as catalysis, ion extraction, and the use of anions as stimuli for responsive chemical systems

Perfection of materials technology for producing improved Gunn-effect devices Interim scientific report

Chemical vapor deposition of epitaxial gallium arsenid

Direct neutron capture of 48Ca at kT = 52 keV

The neutron capture cross section of 48Ca was measured relative to the known gold cross section at kT = 52 keV using the fast cyclic activation technique. The experiment was performed at the Van-de-Graaff accelerator, Universitaet Tuebingen. The new experimental result is in good agreement with a calculation using the direct capture model. The 1/v behaviour of the capture cross section at thermonuclear energies is confirmed, and the adopted reaction rate which is based on several previous experimental investigations remains unchanged.Comment: 9 pages (uses Revtex), 2 postscript figures, accepted for publication as Brief Report in Phys. Rev.

Measurement of neutron capture on 48^{48}Ca at thermal and thermonuclear energies

At the Karlsruhe pulsed 3.75\,MV Van de Graaff accelerator the thermonuclear $^{48}$Ca(n,$\gamma$)$^{49}$Ca(8.72\,min) cross section was measured by the fast cyclic activation technique via the 3084.5\,keV $\gamma$-ray line of the $^{49}$Ca-decay. Samples of CaCO$_3$ enriched in $^{48}$Ca by 77.87\,\% were irradiated between two gold foils which served as capture standards. The capture cross-section was measured at the neutron energies 25, 151, 176, and 218\,keV, respectively. Additionally, the thermal capture cross-section was measured at the reactor BR1 in Mol, Belgium, via the prompt and decay $\gamma$-ray lines using the same target material. The $^{48}$Ca(n,$\gamma$)$^{49}$Ca cross-section in the thermonuclear and thermal energy range has been calculated using the direct-capture model combined with folding potentials. The potential strengths are adjusted to the scattering length and the binding energies of the final states in $^{49}$Ca. The small coherent elastic cross section of $^{48}$Ca+n is explained through the nuclear Ramsauer effect. Spectroscopic factors of $^{49}$Ca have been extracted from the thermal capture cross-section with better accuracy than from a recent (d,p) experiment. Within the uncertainties both results are in agreement. The non-resonant thermal and thermonuclear experimental data for this reaction can be reproduced using the direct-capture model. A possible interference with a resonant contribution is discussed. The neutron spectroscopic factors of $^{49}$Ca determined from shell-model calculations are compared with the values extracted from the experimental cross sections for $^{48}$Ca(d,p)$^{49}$Ca and $^{48}$Ca(n,$\gamma$)$^{49}$Ca.Comment: 15 pages (uses Revtex), 7 postscript figures (uses psfig), accepted for publication in PRC, uuencoded tex-files and postscript-files also available at ftp://is1.kph.tuwien.ac.at/pub/ohu/Ca.u

Yield response of corn in a Planosol soil to subsurface drainage with variable tile spacings

The Edina soil series of southeastern Iowa and northern Missouri are soils of relatively flat topography and poor internal drainage. The need for research data on the feasibility of drainage (both surface and subsurface) on the Edina soils was recognized at the time experiments were begun on the Southern Iowa Experimental Farm, Davis County, Iowa. The yield response of corn to surface drainage by bedding was summarized and reported by Beer et al.3 in 1961. Since initiation of the subsurface drainage experiment in 1949, data on crop-yield response to tile drainage have been collected. The purpose of this bulletin is to present the results of this study as related to the effects of tile drainage on crop yields, with the emphasis on corn, during the period of record. The nature of tile discharge during the growing seasons from 1951 to 1963 also is presented

Response of corn yields in a Planosol soil to surface drainage, cropping system and variable fertilizer treatments

The Edina soil series of southeastern Iowa and northern Missouri are areas of relatively flat topography and poor internal drainage. For these areas, where the topography and soils permit, surface drainage is the most practical method of removing excess water from the land. One method of surface drainage that has been used on the Edina soils is bedding, in which the field is divided into narrow-width plow lands with the deadfurrows running parallel to the prevailing land slope. Little is known about the relative returns from investment in a bedding system in comparison with other surface or subsurface drainage methods. Bedding requires that some topsoil be moved to obtain the desired grade for drainage. The effect on crop yields of topsoil removal and movement in land-forming operations such as bedding, however, is not quantitatively understood. It is the general purpose of this bulletin to present and analyze 6 years of corn-yield data involving drainage (bedded versus level), cropping and fertilizer variables from a study on the Southern Iowa Experimental Farm near Bloomfield

Comprehensive Survey of the Distribution of Colour and Phenolics of Different Red Grape Wine Vineyard Blocks from the Robertson Area in South Africa

Colour and phenolic content of red grapes are two of the most important constituents required to producea quality red wine. In the Robertson grape growing area, difficulty is sometimes experienced with colourdevelopment of grapes. This is especially linked to location and most probably greatly influenced byseason. Forty four vineyard blocks of the cultivars Pinotage, Merlot, Cabernet Sauvignon and Shiraz,were studied over 3 seasons primarily to focus on colour and phenolic content, but secondly on totalsoluble solids, titratable acidity and pH of the grapes. High performance liquid chromatography andspectrophotometric methods were used to determine various colour and phenolic parameters present atharvest. This data was used to indicate how colour and phenolic constitution of a part of the Robertsongrape growing area was distributed in relation to various factors, such as cultivar and season. GPS pointswere used to map data for the blocks visually. Results showed variable colour and phenolic content forthese grapes based on blocks and phenolic compounds investigated. Shiraz displayed a wider distributionof certain phenolic compounds over the three seasons than the other 3 cultivars. Seasonality had a greatinfluence on these results, with outlying blocks being identified

Photosynthesis-controlled calcification in a hypersaline microbial mat

We investigated the hypothesis that sulfate reduction rather than oxygenic photosynthesis promotes calcification in a hypersaline microbial mat by increasing the ion concentration product: ICP 5 [Ca2+] X [CO32-]. Pore‐water 3 calcium concentration profiles directly measured with microsensors show that calcium concentration in the photic zone decreased in illuminated mats and increased slightly in dark mats. High pH values in the photic zone of illuminated mats resulted in higher carbonate concentrations (2.25 mmol L-1) than in dark mats (0.75 mmol L-1), although the dissolved inorganic carbon (DIC) pore‐water concentration in the former was much lower (5.9 mmol L-1) than in the latter (9.9 mmol L-1). The pH‐induced rise in carbonate concentration in the light was the main factor influencing the ICP, while changes in Ca-1 concentration played a subsidiary role. Sulfate reduction did not result in a net pH increase in these mats, as rates in the photic zone were comparable between illuminated and dark mats (4 and 5 nmol cm-2 h-1, respectively), and pH increased in illuminated mats but not in dark mats. Calcium carbonate precipitation in the photic zone of these hypersaline mats is primarily controlled by photosynthesisinduced pH and carbonate concentration increases. However, heterotrophic bacteria, including sulfate reducers, play an important complementary role in calcification because they maintain high concentrations of DIC in the mat pore water