649 research outputs found
On the vanishing viscosity limit in a disk
We say that the solution u to the Navier-Stokes equations converges to a
solution v to the Euler equations in the vanishing viscosity limit if u
converges to v in the energy norm uniformly over a finite time interval.
Working specifically in the unit disk, we show that a necessary and sufficient
condition for the vanishing viscosity limit to hold is the vanishing with the
viscosity of the time-space average of the energy of u in a boundary layer of
width proportional to the viscosity due to modes (eigenfunctions of the Stokes
operator) whose frequencies in the radial or the tangential direction lie
between L and M. Here, L must be of order less than 1/(viscosity) and M must be
of order greater than 1/(viscosity)
Setting up tracking tools for NuFact bowtie decay ring studies
This paper describes the setting up of ray-tracing tools, and preliminary beam dynamics studies concerning the NuFact bowtie decay ring
Polynuclear formation in aqueous solutions containing iron (III) and selected carboxylic acids
Thesis (M.A.)--Boston UniversityOver the past several years various workers have accumulated evidence for the existence of polynuclear complexes of a number of metal ions. In this connection it has been established that iron(III) forms polynuclear species with a variety of common complexing agents. In the present work an investigation was carried out on systems containing iron(III) and selected carboxylic acids. An attempt was made to classify the systems according to whether or not they formed polynuclear species. For some systems it was established under what conditions polynuclear species are present and under what conditions they are not present. [TRUNCATED
On the flow map for 2D Euler equations with unbounded vorticity
In Part I, we construct a class of examples of initial velocities for which
the unique solution to the Euler equations in the plane has an associated flow
map that lies in no Holder space of positive exponent for any positive time. In
Part II, we explore inverse problems that arise in attempting to construct an
example of an initial velocity producing an arbitrarily poor modulus of
continuity of the flow map.Comment: http://iopscience.iop.org/0951-7715/24/9/013/ for published versio
Analysis of complex singularities in high-Reynolds-number Navier-Stokes solutions
Numerical solutions of the laminar Prandtl boundary-layer and Navier-Stokes
equations are considered for the case of the two-dimensional uniform flow past
an impulsively-started circular cylinder. We show how Prandtl's solution
develops a finite time separation singularity. On the other hand Navier-Stokes
solution is characterized by the presence of two kinds of viscous-inviscid
interactions that can be detected by the analysis of the enstrophy and of the
pressure gradient on the wall. Moreover we apply the complex singularity
tracking method to Prandtl and Navier-Stokes solutions and analyze the previous
interactions from a different perspective
An olfactory subsystem that detects carbon disulfide and mediates food-related social learning
In mammals, pheromones and other social cues can promote mating or aggression behaviors; can communicate information about social hierarchies, genetic identity and health status; and can contribute to associative learning. However, the molecular, cellular, and neural mechanisms underlying many olfactory-mediated social interactions remain poorly understood. Here, we show a specialized olfactory subsystem that includes olfactory sensory neurons (OSNs) expressing the receptor guanylyl cyclase GC-D, the cyclic nucleotide-gated channel subunit CNGA3, and the carbonic anhydrase isoform CAII (GC-D(+) OSNs) is required for the acquisition of socially transmitted food preferences (STFPs) in mice
Ammonia emissions from cattle urine and dung excreted on pasture
Twelve cattle were kept for three days in a circular area of 16 m radius on short pasture and fed with freshly-cut pasture. Ammonia (NH<sub>3</sub>) emissions from the urine and dung excreted by the cattle were measured with a micrometeorological mass-balance method, during the cattle presence and for 10 subsequent days. Daily-integrated emission rates peaked on Day 3 of the experiment (last day of cattle presence) and declined steadily for five days thereafter. Urine patches were the dominant sources for these emissions. On Day 9, a secondary emissions peak occurred, with dung pats likely to be the main sources. This interpretation is based on simultaneous observations of the pH evolution in urine patches and dung pats created next to the circular plot. Feed and dung samples were analysed to estimate the amounts of nitrogen (N) ingested and excreted. Total N volatilised as NH<sub>3</sub> was 19.8 (± 0.9)% of N intake and 22.4 (± 1.3)% of N excreted. The bimodal shape of the emissions time series allowed to infer separate estimates for volatilisation from urine and dung, respectively, with the result that urine accounted for 88.6 (± 2.6)% of the total NH<sub>3</sub> emissions. The emissions from urine represented 25.5 (± 2.0)% of the excreted urine-N, while the emissions from dung amounted to 11.6 (± 2.7)% of the deposited dung-N. Emissions from dung may have continued after Day 13 but were not resolved by the measurement technique. A simple resistance model shows that the magnitude of the emissions from dung is controlled by the resistance of the dung crust
Viscous-Inviscid Interactions in a Boundary-Layer Flow Induced by a Vortex Array
In this paper we investigate the asymptotic validity of boundary layer
theory. For a flow induced by a periodic row of point-vortices, we compare
Prandtl's solution to Navier-Stokes solutions at different numbers. We
show how Prandtl's solution develops a finite time separation singularity. On
the other hand Navier-Stokes solution is characterized by the presence of two
kinds of viscous-inviscid interactions between the boundary layer and the outer
flow. These interactions can be detected by the analysis of the enstrophy and
of the pressure gradient on the wall. Moreover we apply the complex singularity
tracking method to Prandtl and Navier-Stokes solutions and analyze the previous
interactions from a different perspective
First hints of new sensors
A mechanism by which plants detect and respond to oxygen starvation has been known for some years. Three recent papers suggest that we haven’t been seeing the full picture
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