183 research outputs found
Near streambed flow shapes microbial guilds within and across trophic levels in fluvial biofilms
Flow is an important physical driver of biofilm communities. Here, we tested the effects of the near bed flows in two mountainous stream reaches on the structure of biofilm microbial guilds (autotrophs, heterotrophic bacteria, and heterotrophic protists) within and across trophic levels. Near bed flow velocity and turbulent kinetic energy were important physical drivers for structuring the communities within and across guilds of the multitrophic fluvial biofilms. The effects of flow were nested in a seasonal and spatial (across-streams) context. Changes in physicochemical factors (temperature, light, dissolved carbon, and nutrients) along the reaches were alike in both streams suggesting that environmental boundary conditions at larger temporal scales were responsible for the seasonal differences of biofilm communities, whereas locally microbial diversity was shaped by near bed flow. Typically, the abundance of autotrophs increased with flow, indicating that biofilms shifted toward increasing autotrophy with increasing shear forces. Filamentous autotrophs seemed to provide protected habitats from the shear forces for smaller sized bacteria. Heterotrophic protist abundance decreased with flow leading to decreasing grazer to prey ratio. Bacteria thus benefitted from a reduction in grazing pressure at faster flowing, more turbulent sites. Our results suggest that near bed flow can impact the magnitude and direction of matter fluxes through the microbial food web and possibly affect ecosystem functioning of fluvial biofilms
Riccati-parameter solutions of nonlinear second-order ODEs
It has been proven by Rosu and Cornejo-Perez in 2005 that for some nonlinear
second-order ODEs it is a very simple task to find one particular solution once
the nonlinear equation is factorized with the use of two first-order
differential operators. Here, it is shown that an interesting class of
parametric solutions is easy to obtain if the proposed factorization has a
particular form, which happily turns out to be the case in many problems of
physical interest. The method that we exemplify with a few explicitly solved
cases consists in using the general solution of the Riccati equation, which
contributes with one parameter to this class of parametric solutions. For these
nonlinear cases, the Riccati parameter serves as a `growth' parameter from the
trivial null solution up to the particular solution found through the
factorization procedureComment: 5 pages, 3 figures, change of title and more tex
Nonlinear Bias and the Convective Fisher Equation
We combine random walks, growth and decay, and convection, in a Monte Carlo
simulation to model 1D interface dynamics with fluctuations. The continuum
limit corresponds to the deterministic Fisher equation with convection. We find
qualitatively the same type of asymmetry, as well as velocity difference, for
interface profiles moving in opposite directions. However a transition apparent
in the mean-field (continuum) limit is not found in the Monte Carlo simulation.Comment: 2.5 pages (texed) with 4 postscript figures, TeX 3.14t
Benefits of ecological engineering practices
With the intention to further promote the field of ecological engineering and the solutions it provides, a workshop on “Benefits of Ecological Engineering Practices” was held 3 December 2009. It was conducted by the International Ecological Engineering Society in Paris at the conference “Ecological Engineering: from Concepts to Application” organized by the Ecological Engineering Applications Group GAIE. This paper presents the results of the workshop related to three key questions: (1) what are the benefits of ecological engineering practices to human and ecosystem well-being, (2) which concepts are used or useful to identify, reference, and measure the benefits of ecological engineering practices, and (3) how and to whom shall benefits of ecological engineering practices be promoted. While benefits of ecological engineering practices are diverse, general conclusions can be derived to facilitate communication. Identifying benefits requires valuation frameworks reaching beyond the scope of ecology and engineering. A distinction between human and ecosystem well-being in this regard may not be easy or useful, but instead humans embedded in ecosystems should be addressed as a whole. The concepts of resource efficiency, ecosystem services, ecosystem health, and multifunctional land use could serve as suitable references to frame ecological engineering benefits, as well as referring to international political goals such as biodiversity protection, climate change mitigation and poverty reduction. Sector and application specific criteria of good practice could be worked out. Regional, area specific reference systems for sustainable development could provide comparative advantages for ecologically engineered solutions. Besides people with high decision making power and people with high motivation for change are good target groups to be addressed
Phase ordering and shape deformation of two-phase membranes
Within a coupled-field Ginzburg-Landau model we study analytically phase
separation and accompanying shape deformation on a two-phase elastic membrane
in simple geometries such as cylinders, spheres and tori. Using an exact
periodic domain wall solution we solve for the shape and phase ordering field,
and estimate the degree of deformation of the membrane. The results are
pertinent to a preferential phase separation in regions of differing curvature
on a variety of vesicles.Comment: 4 pages, submitted to PR
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Reply to: New Meta- and Mega-analyses of Magnetic Resonance Imaging Findings in Schizophrenia: Do They Really Increase Our Knowledge About the Nature of the Disease Process?
This work was supported by National Institute of Biomedical Imaging and Bioengineering Grant No. U54EB020403 (to the ENIGMA consortium)
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