10,384 research outputs found
Impact of Vegetative Treatment Systems on Multiple Measures of Antibiotic Resistance in Agricultural Wastewater
Wastewater is an important vector of antibiotic resistant bacteria and antibiotic resistance genes (ARB/G). While there is broad agreement that ARB/G from agricultural (ag) wastewaters can be transported through the environment and may contribute to untreatable infectious disease in humans and animals, there remain large knowledge gaps surrounding applied details on the types and amounts of ARB/G associated with different agricultural wastewater treatment options and different ag production systems. This study evaluates a vegetative treatment system (VTS) built to treat the wastewater from a beef cattle feedlot. Samples were collected for three years, and plated on multiple media types to enumerate tetracycline and cefotaxime-resistant bacteria. Enterobacteriaceae isolates (n = 822) were characterized for carriage of tetracycline resistance genes, and E. coli isolates (n = 673) were phenotyped to determine multi-drug resistance (MDR) profiles. Tetracycline resistance in feedlot runoff wastewater was 2-to-3 orders of magnitude higher compared to rainfall runoff from the VTS fields, indicating efficacy of the VTA for reducing ARB over time following wastewater application. Clear differences in MDR profiles were observed based on the specific media on which a sample was plated. This result highlights the importance of method, especially in the context of isolate-based surveillance and monitoring of ARB in agricultural wastewaters
Modeling the Behavior of the Surface to Liquid Interfaces in an Electrolytic Liquid
Understanding the mechanism for charge transfer between electrodes within an electrolyte dissolved in water is vital to better understanding the sources of electrical noise in the system. This research compares the electrical properties of liquid top gated graphene devices with the properties of two metal probes to model the system. By measuring the impedance of these systems at different frequencies, it is possible to develop a model of their electrical properties and to consider techniques to improve signal to noise at graphene interfaces
Expendable bubble tiltmeter for geophysical monitoring
An unusually rugged highly sensitive and inexpensive bubble tiltmeter has been designed, tested, and built in quantity. These tiltmeters are presently used on two volcanoes and an Alaskan glacier, where they continuously monitor surface tilts of geological interest. This paper discusses the
mechanical, thermal, and electric details of the meter, and illustrates its performance characteristics in both large ( > 10^(-4) radian) and small ( < 10^(-6) radian) tilt environments. The meter's ultimate sensitivity is better than 2 X 10^(-8) radians rms for short periods (hours), and its useful dynamic range is greater than 10^4. Included is a short description of field use of the instrument for volcano monitoring
The Role of Projection in the Control of Bird Flocks
Swarming is a conspicuous behavioural trait observed in bird flocks, fish
shoals, insect swarms and mammal herds. It is thought to improve collective
awareness and offer protection from predators. Many current models involve the
hypothesis that information coordinating motion is exchanged between neighbors.
We argue that such local interactions alone are insufficient to explain the
organization of large flocks of birds and that the mechanism for the exchange
of long-ranged information necessary to control their density remains unknown.
We show that large flocks self-organize to the maximum density at which a
typical individual is still just able to see out of the flock in many
directions. Such flocks are marginally opaque - an external observer can also
just still see a substantial fraction of sky through the flock. Although
seemingly intuitive we show that this need not be the case; flocks could easily
be highly diffuse or entirely opaque. The emergence of marginal opacity
strongly constrains how individuals interact with each other within large
swarms. It also provides a mechanism for global interactions: An individual can
respond to the projection of the flock that it sees. This provides for faster
information transfer and hence rapid flock dynamics, another advantage over
local models. From a behavioural perspective it optimizes the information
available to each bird while maintaining the protection of a dense, coherent
flock.Comment: PNAS early edition published online at
http://www.pnas.org/cgi/doi/10.1073/pnas.140220211
Synchronization of dynamical hypernetworks: dimensionality reduction through simultaneous block-diagonalization of matrices
We present a general framework to study stability of the synchronous solution
for a hypernetwork of coupled dynamical systems. We are able to reduce the
dimensionality of the problem by using simultaneous block-diagonalization of
matrices. We obtain necessary and sufficient conditions for stability of the
synchronous solution in terms of a set of lower-dimensional problems and test
the predictions of our low-dimensional analysis through numerical simulations.
Under certain conditions, this technique may yield a substantial reduction of
the dimensionality of the problem. For example, for a class of dynamical
hypernetworks analyzed in the paper, we discover that arbitrarily large
networks can be reduced to a collection of subsystems of dimensionality no more
than 2. We apply our reduction techique to a number of different examples,
including a class of undirected unweighted hypermotifs of three nodes.Comment: 9 pages, 6 figures, accepted for publication in Phys. Rev.
Genome Assembly Improvement and Mapping Convergently Evolved Skeletal Traits in Sticklebacks with Genotyping-by-Sequencing.
Marine populations of the threespine stickleback (Gasterosteus aculeatus) have repeatedly colonized and rapidly adapted to freshwater habitats, providing a powerful system to map the genetic architecture of evolved traits. Here, we developed and applied a binned genotyping-by-sequencing (GBS) method to build dense genome-wide linkage maps of sticklebacks using two large marine by freshwater F2 crosses of more than 350 fish each. The resulting linkage maps significantly improve the genome assembly by anchoring 78 new scaffolds to chromosomes, reorienting 40 scaffolds, and rearranging scaffolds in 4 locations. In the revised genome assembly, 94.6% of the assembly was anchored to a chromosome. To assess linkage map quality, we mapped quantitative trait loci (QTL) controlling lateral plate number, which mapped as expected to a 200-kb genomic region containing Ectodysplasin, as well as a chromosome 7 QTL overlapping a previously identified modifier QTL. Finally, we mapped eight QTL controlling convergently evolved reductions in gill raker length in the two crosses, which revealed that this classic adaptive trait has a surprisingly modular and nonparallel genetic basis
Modeling and analysis of systems with nonlinear functional dependence on random quantities
Many real-world systems exhibit noisy evolution; interpreting their
finite-time behavior as arising from continuous-time processes (in the It\^o or
Stratonovich sense) has led to significant success in modeling and analysis in
a variety of fields. Here we argue that a class of differential equations where
evolution depends nonlinearly on a random or effectively-random quantity may
exhibit finite-time stochastic behavior in line with an equivalent It\^o
process, which is of great utility for their numerical simulation and
theoretical analysis. We put forward a method for this conversion, develop an
equilibrium-moment relation for It\^o attractors, and show that this relation
holds for our example system. This work enables the theoretical and numerical
examination of a wide class of mathematical models which might otherwise be
oversimplified due to a lack of appropriate tools.Comment: 13 pages, 6 figure
When Pull Turns to Shove: A Continuous-Time Model for Opinion Dynamics
Accurate modeling of opinion dynamics has the potential to help us understand
polarization and what makes effective political discourse possible or
impossible. Here, we use physics-based methods to model the evolution of
political opinions within a continuously distributed population. We utilize a
network-free system of determining political influence and a local-attraction,
distal-repulsion dynamic for reaction to perceived content. Our approach allows
for the incorporation of intergroup bias such that messages from trusted
in-group sources enjoy greater leeway than out-group ones. We are able to
extrapolate these nonlinear microscopic dynamics to macroscopic population
distributions by using probabilistic functions representing biased
environments. The framework we put forward can reproduce real-world political
distributions and experimentally observed dynamics, and is amenable to further
refinement as more data becomes available.Comment: Main text and appendices: 14 pages including references, with 11
figure
Thermodynamic Studies of [H_(2)Rh(diphosphine)_2]^+ and [HRh(diphosphine)_(2)(CH_(3)CN)]^(2+) Complexes in Acetonitrile
Thermodynamic studies of a series of [H_(2)Rh(PP)_2]^+ and [HRh(PP)_(2)(CH_(3)CN)]^(2+) complexes have been carried out in acetonitrile. Seven different diphosphine (PP) ligands were selected to allow variation of the electronic properties of the ligand substituents, the cone angles, and the natural bite angles (NBAs). Oxidative addition of H_2 to [Rh(PP)_2]^+ complexes is favored by diphosphine ligands with large NBAs, small cone angles, and electron donating substituents, with the NBA being the dominant factor. Large pK_a values for [HRh(PP)_(2)(CH_(3)CN)]^(2+) complexes are favored by small ligand cone angles, small NBAs, and electron donating substituents with the cone angles playing a major role. The hydride donor abilities of [H_(2)Rh(PP)_2]^+ complexes increase as the NBAs decrease, the cone angles decrease, and the electron donor abilities of the substituents increase. These results indicate that if solvent coordination is involved in hydride transfer or proton transfer reactions, the observed trends can be understood in terms of a combination of two different steric effects, NBAs and cone angles, and electron-donor effects of the ligand substituents
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