Sublethal Stress In Escherichia-Coli - Function Of Salinity

Sublethal stress in Escherichia coli was detected in various test media after exposure (in vitro) to seawater of various salinities. Stress was measured with an electrochemical detection technique and a,-galactosidase assay. Test media included EC medium, medium A-1, and tryptic soy broth modified to contain lactose for /?-galactosidase assay experiments. Stress was defined as the difference between a predicted electrochemical response time calculated for unstarved cells from a standard curve and the observed electrochemical response time for cells starved in seawater. The higher the salinity, the greater the stress for all test media examined. Stress was most pronounced in EC and was attributed primarily to initial die-off of starved cells exposed to the test medium at the elevated temperature of 44.5°C. Lag time and growth rates in test media were not significantly affected by salinity. fl-Galactosidase specific activity, assayed in starved cells after transfer to an induction medium at 44.5°C for 150 min, was inversely related to the salinity of the starved cell suspension. The consequences of these observations with respect to coliform enumeration methods are discussed

Net and Acoustic Examination of Bathypelagic Nekton on the Mid-Atlantic Ridge

Spatial distributions of organisms play a key role in facilitating trophic interactions, which influence pelagic ecosystem structure and function. This study combines discrete net trawl sampling with continuous acoustic measurements to investigate the distribution of bathypelagic (1000- 3000 m depth) nekton biomass along the Mid-Atlantic Ridge from Iceland to the Azores. Two, previously unknown, acoustic scattering layers (ASLs) were observed using 18 kHz echosounder data. The first extended approximately 200 m from 2000 m depth and was ubiquitous wherever bottom depth allowed. The second, found within the 1500-2000 m depth stratum, only occurred south of the Sub-Polar Front. Backscatter from the 2000 m ASL was attributed to fish from a suite of bathypelagic species observed throughout the study area, rather than any specific group. No general increase in backscatter, as a proxy for pelagic nekton biomass, was observed in close proximity to the bottom (≤ 200 m), but previously unreported localized concentrations of backscatter were observed when bottom topography was steep. Together these observations demonstrate higher complexity in the spatial structuring of bathypelagic ecosystems than has been previously reported and is likely to affect local ecosystem function

Anisotropy and shear-velocity heterogeneities in the upper mantle

Long-period surface waves are used to map lateral heterogeneities of velocity and anisotropy in the upper mantle. The dispersion curves are expanded in spherical harmonics up to degree 6 and inverted to find the depth structure. The data are corrected for the effect of surface layers and both Love and Rayleigh waves are used. Shear wave velocity and shear polarization anisotropy can be resolved down to a depth of about 450 km. The shear wave velocity distribution to 200 km depth correlates with surface tectonics, except in a few anomalous regions. Below that depth the correlation vanishes. Cold subducted material shows up weakly at 350 km as fast S-wave anomalies. In the transition region a large scale pattern appears with fast mantle in the South-Atlantic. S-anisotropy at 200 km can resolve uprising or downwelling currents under some ridges and subduction zones. The Pacific shows a NW-SE fabric

Gravitational Waves: Just Plane Symmetry

We present some remarkable properties of the symmetry group for gravitational plane waves. Our main observation is that metrics with plane wave symmetry satisfy every system of generally covariant vacuum field equations except the Einstein equations. The proof uses the homothety admitted by metrics with plane wave symmetry and the scaling behavior of generally covariant field equations. We also discuss a mini-superspace description of spacetimes with plane wave symmetry.Comment: 10 pages, TeX, uses IOP style file

Interpreting the Spatial Distribution of Bathypelagic Nekton Along the Mid-Atlantic Ridge

The spatial distribution of organisms plays a key role in facilitating biological processes, such as trophic interactions, which govern ecosystem structure and function. Attempts to understand bathypelagic (1000-4000 m depth) ecosystem dynamics have been hampered by the coarse temporal-spatial resolution and static nature of most sampling strategies. This study combines a traditional approach, based on discrete net trawls sampling small volumes, with the continuous full water column coverage provided by fisheries acoustics to investigate the distribution of biomass along the Mid-Atlantic Ridge (MAR). The limited trawl samples have been interpreted as showing a positive relationship between the presence of the MAR in the bathypelagic depth zone and biomass of bathypelagic fish species. Using 18 kHz echosounder data we explored this apparent association, and used comparisons of trawl data with the acoustic backscatter distribution to provide insights into how the distribution of biomass may influence trophic interactions in the bathypelagos. As such, this research provides a valuable case study of the potential contribution of acoustics to ecosystem studies, both within fisheries management and in a wider biological context

Electronic theory for superconductivity in Sr2_2RuO4_4: triplet pairing due to spin-fluctuation exchange

Using a two-dimensional Hubbard Hamiltonian for the three electronic bands crossing the Fermi level in Sr$_2$RuO$_4$ we calculate the band structure and spin susceptibility $\chi({\bf q}, \omega)$ in quantitative agreement with nuclear magnetic resonance (NMR) and inelastic neutron scattering (INS) experiments. The susceptibility has two peaks at {\bf Q}$_i = (2\pi/3, 2\pi/3)$ due to the nesting Fermi surface properties and at {\bf q}$_i = (0.6\pi, 0)$ due to the tendency towards ferromagnetism. Applying spin-fluctuation exchange theory as in layered cuprates we determine from $\chi({\bf q}, \omega)$, electronic dispersions, and Fermi surface topology that superconductivity in Sr$_2$RuO$_4$ consists of triplet pairing. Combining the Fermi surface topology and the results for $\chi({\bf q}, \omega)$ we can exclude $s-$ and $d-$wave symmetry for the superconducting order parameter. Furthermore, within our analysis and approximations we find that $f$-wave symmetry is slightly favored over p-wave symmetry due to the nesting properties of the Fermi surface.Comment: 5 pages, 5 figures, misprints correcte

Hot Accretion With Conduction: Spontaneous Thermal Outflows

Motivated by the low-collisionality of gas accreted onto black holes in Sgr A* and other nearby galactic nuclei, we study a family of 2D advective accretion solutions with thermal conduction. While we only impose global inflow, the accretion flow spontaneously develops bipolar outflows. The role of conduction is key in providing the extra degree of freedom (latitudinal energy transport) necessary to launch these rotating thermal outflows. The sign of the Bernoulli constant does not discriminate between inflowing and outflowing regions. Our parameter survey covers mass outflow rates from ~ 0 to 13% of the net inflow rate, outflow velocities from ~0 to 11% of the local Keplerian velocity and outflow opening angles from ~ 0 to 60 degs. As the magnitude of conduction is increased, outflows can adopt a conical geometry, pure inflow solutions emerge, and the limit of 2D non-rotating Bondi-like solutions is eventually reached. These results confirm that radiatively-inefficient, hot accretion flows have a hydrodynamical propensity to generate bipolar thermal outflows.Comment: 38 pages, 10 figures, accepted for publication in Ap

Efficient computation of matched solutions of the Kapchinskij-Vladimirskij envelope equations for periodic focusing lattices

A new iterative method is developed to numerically calculate the periodic, matched beam envelope solution of the coupled Kapchinskij-Vladimirskij (KV) equations describing the transverse evolution of a beam in a periodic, linear focusing lattice of arbitrary complexity. Implementation of the method is straightforward. It is highly convergent and can be applied to all usual parameterizations of the matched envelope solutions. The method is applicable to all classes of linear focusing lattices without skew couplings, and also applies to all physically achievable system parameters -- including where the matched beam envelope is strongly unstable. Example applications are presented for periodic solenoidal and quadrupole focusing lattices. Convergence properties are summarized over a wide range of system parameters.Comment: 20 pages, 5 figures, Mathematica source code provide

Quantum state tomography by continuous measurement and compressed sensing

The need to perform quantum state tomography on ever larger systems has spurred a search for methods that yield good estimates from incomplete data. We study the performance of compressed sensing (CS) and least squares (LS) estimators in a fast protocol based on continuous measurement on an ensemble of cesium atomic spins. Both efficiently reconstruct nearly pure states in the 16-dimensional ground manifold, reaching average fidelities FCS = 0.92 and FLS = 0.88 using similar amounts of incomplete data. Surprisingly, the main advantage of CS in our protocol is an increased robustness to experimental imperfections