14,397 research outputs found
Cedar River at Cedar Rapids, Iowa
For thirty-seven years we have noted with regret the gradual increase in the pollution of our river, in fact the increase has been quite rapid during recent years. During that time the inhabitants on the banks have increased three-fold while the amount of pollution that is put into the river has increased probably three-thousand-fold. A third of a century ago the Chlorine as Chlorides was three parts per million, the normal amount for unpolluted water in this region; now it is ten. A half a century ago when the Cedar Rapids water works were first built, raw water was put into the mains and for twelve years used for drinking water by a large per cent of the inhabitants
Methods of isolation and identification of pathogenic and potential pathogenic bacteria from skins and tannery effluents
Currently there is no standard protocol available within the leather industry to isolate and identify pathogenic bacteria from hides, skins or tannery effluent. This study was therefore carried out to identify simple but effective methods for isolation and identification of bacterial pathogens from the effluent and skins during leather processing. Identification methods based on both phenotypic and genotypic characteristics were investigated. Bacillus cereus and Pseudomonas aeruginosa were used as indicator bacteria to evaluate the isolation and identification methods. Decontaminated calfskins were inoculated with a pure culture of the above mentioned bacterial species followed by a pre-tanning and chromium tanning processes. Effluent samples were collected and skins were swabbed at the end of each processing stage. Bacterial identification was carried out based on the phenotypic characteristics; such as colony appearance on selective solid media, cell morphology following a standard Gram-staining and spore staining techniques, and biochemical reactions, e.g., the ability of a bacterial species to ferment particular sugars and ability to produce certain enzymes. Additionally, an identification system based on bacterial phenotypic characteristics, known as Biolog® system was applied. A pulsed-filed gel electrophoresis (PFGE) method for bacterial DNA fingerprinting was also evaluated and used for the identification of the inoculated bacteria. The methods described in the study were found to be effective for the identification of pathogenic bacteria from skins and effluent
Case-control study of arsenic in drinking water and lung cancer in California and Nevada.
Millions of people are exposed to arsenic in drinking water, which at high concentrations is known to cause lung cancer in humans. At lower concentrations, the risks are unknown. We enrolled 196 lung cancer cases and 359 controls matched on age and gender from western Nevada and Kings County, California in 2002-2005. After adjusting for age, sex, education, smoking and occupational exposures, odds ratios for arsenic concentrations ≥85 µg/L (median = 110 µg/L, mean = 173 µg/L, maximum = 1,460 µg/L) more than 40 years before enrollment were 1.39 (95% CI = 0.55-3.53) in all subjects and 1.61 (95% CI = 0.59-4.38) in smokers. Although odds ratios were greater than 1.0, these increases may have been due to chance given the small number of subjects exposed more than 40 years before enrollment. This study, designed before research in Chile suggested arsenic-related cancer latencies of 40 years or more, illustrates the enormous sample sizes needed to identify arsenic-related health effects in low-exposure countries with mobile populations like the U.S. Nonetheless, our findings suggest that concentrations near 100 µg/L are not associated with markedly high relative risks
An electron Talbot interferometer
The Talbot effect, in which a wave imprinted with transverse periodicity
reconstructs itself at regular intervals, is a diffraction phenomenon that
occurs in many physical systems. Here we present the first observation of the
Talbot effect for electron de Broglie waves behind a nanofabricated
transmission grating. This was thought to be difficult because of Coulomb
interactions between electrons and nanostructure gratings, yet we were able to
map out the entire near-field interference pattern, the "Talbot carpet", behind
a grating. We did this using a Talbot interferometer, in which Talbot
interference fringes from one grating are moire'-filtered by a 2nd grating.
This arrangement has served for optical, X-ray, and atom interferometry, but
never before for electrons. Talbot interferometers are particularly sensitive
to distortions of the incident wavefronts, and to illustrate this we used our
Talbot interferometer to measure the wavefront curvature of a weakly focused
electron beam. Here we report how this wavefront curvature demagnified the
Talbot revivals, and we discuss applications for electron Talbot
interferometers.Comment: 5 pages, 5 figures, updated version with abstrac
Bulk phase behaviour of binary hard platelet mixtures from density functional theory
We investigate isotropic-isotropic, isotropic-nematic and nematic-nematic
phase coexistence in binary mixtures of circular platelets with vanishing
thickness, continuous rotational degrees of freedom and radial size ratios
up to 5. A fundamental measure density functional theory, previously
used for the one-component model, is proposed and results are compared against
those from Onsager theory as a benchmark. For the system
displays isotropic-nematic phase coexistence with a widening of the biphasic
region for increasing values of . For size ratios , we
find demixing into two nematic states becomes stable and an
isotropic-nematic-nematic triple point can occur. Fundamental measure theory
gives a smaller isotropic-nematic biphasic region than Onsager theory and
locates the transition at lower densities. Furthermore, nematic-nematic
demixing occurs over a larger range of compositions at a given value of
than found in Onsager theory. Both theories predict the same
topologies of the phase diagrams. The partial nematic order parameters vary
strongly with composition and indicate that the larger particles are more
strongly ordered than the smaller particles
Multi-objective evolutionary–fuzzy augmented flight control for an F16 aircraft
In this article, the multi-objective design of a fuzzy logic augmented flight controller for a high performance fighter jet (the Lockheed-Martin F16) is described. A fuzzy logic controller is designed and its membership functions tuned by genetic algorithms in order to design a roll, pitch, and yaw flight controller with enhanced manoeuverability which still retains safety critical operation when combined with a standard inner-loop stabilizing controller. The controller is assessed in terms of pilot effort and thus reduction of pilot fatigue. The controller is incorporated into a six degree of freedom motion base real-time flight simulator, and flight tested by a qualified pilot instructor
Computing the Casimir energy using the point-matching method
We use a point-matching approach to numerically compute the Casimir
interaction energy for a two perfect-conductor waveguide of arbitrary section.
We present the method and describe the procedure used to obtain the numerical
results. At first, our technique is tested for geometries with known solutions,
such as concentric and eccentric cylinders. Then, we apply the point-matching
technique to compute the Casimir interaction energy for new geometries such as
concentric corrugated cylinders and cylinders inside conductors with focal
lines.Comment: 11 pages, 18 figure
The effects of spatial resolution and dimensionality on modeling regional-scale hydraulics in a multichannel river
As modeling capabilities at regional and global scales improve, questions remain regarding the appropriate process representation required to accurately simulate multichannel river hydraulics. This study uses the hydrodynamic model LISFLOOD-FP to simulate patterns of water surface elevation (WSE), depth, and inundation extent across a ∼90 km, anabranching reach of the Tanana River, Alaska. To provide boundary conditions, we collected field observations of bathymetry and WSE during a 2 week field campaign in summer 2013. For the first time at this scale, we test a simple, raster-based model's capabilities to simulate 2-D, in-channel patterns of WSE and inundation extent. Additionally, we compare finer resolution (≤25 m) 2-D models to four other models of lower dimensionality and coarser resolution (100–500 m) to determine the effects of simplifying process representation. Results indicate that simple, raster-based models can accurately simulate 2-D, in-channel hydraulics in the Tanana. Also, the fine-resolution, 2-D models produce lower errors in spatiotemporal outputs of WSE and inundation extent compared to coarse-resolution, 1-D models: 22.6 cm versus 56.4 cm RMSE for WSE, and 90% versus 41% Critical Success Index values for simulating inundation extent. Incorporating the anabranching channel network using subgrid representations for smaller channels is important for simulating accurate hydraulics and lowers RMSE in spatially distributed WSE by at least 16%. As a result, better representation of the converging and diverging multichannel network by using subgrid solvers or downscaling techniques in multichannel rivers is needed to improve errors in regional to global-scale models
The geometry of nonlinear least squares with applications to sloppy models and optimization
Parameter estimation by nonlinear least squares minimization is a common
problem with an elegant geometric interpretation: the possible parameter values
of a model induce a manifold in the space of data predictions. The minimization
problem is then to find the point on the manifold closest to the data. We show
that the model manifolds of a large class of models, known as sloppy models,
have many universal features; they are characterized by a geometric series of
widths, extrinsic curvatures, and parameter-effects curvatures. A number of
common difficulties in optimizing least squares problems are due to this common
structure. First, algorithms tend to run into the boundaries of the model
manifold, causing parameters to diverge or become unphysical. We introduce the
model graph as an extension of the model manifold to remedy this problem. We
argue that appropriate priors can remove the boundaries and improve convergence
rates. We show that typical fits will have many evaporated parameters. Second,
bare model parameters are usually ill-suited to describing model behavior; cost
contours in parameter space tend to form hierarchies of plateaus and canyons.
Geometrically, we understand this inconvenient parametrization as an extremely
skewed coordinate basis and show that it induces a large parameter-effects
curvature on the manifold. Using coordinates based on geodesic motion, these
narrow canyons are transformed in many cases into a single quadratic, isotropic
basin. We interpret the modified Gauss-Newton and Levenberg-Marquardt fitting
algorithms as an Euler approximation to geodesic motion in these natural
coordinates on the model manifold and the model graph respectively. By adding a
geodesic acceleration adjustment to these algorithms, we alleviate the
difficulties from parameter-effects curvature, improving both efficiency and
success rates at finding good fits.Comment: 40 pages, 29 Figure
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