1,900 research outputs found
Klassifizierung unbekannter Proben ökologischer und konventioneller Herkunft mittels FAS anhand von Trainingsdaten aus dem Vorjahr
Different sorts of apples coming from pairs of organic/conv. producers of different locations in Switzerland and Germany were retrospectively investigated in 2004 and prospectively classified in 2005 based on data measured by fluorescence-excitation-spectroscopy (FES) and subsequent discriminant analysis. The result was in 8 of 9 cases a correct identification of the method of production. In one case the data showed no difference
Large Eddy Simulation of Turbulent Channel Flows by the Rational LES Model
The rational large eddy simulation (RLES) model is applied to turbulent
channel flows. This approximate deconvolution model is based on a rational
(subdiagonal Pade') approximation of the Fourier transform of the Gaussian
filter and is proposed as an alternative to the gradient (also known as the
nonlinear or tensor-diffusivity) model. We used a spectral element code to
perform large eddy simulations of incompressible channel flows at Reynolds
numbers based on the friction velocity and the channel half-width Re{sub tau} =
180 and Re{sub tau} = 395. We compared the RLES model with the gradient model.
The RLES results showed a clear improvement over those corresponding to the
gradient model, comparing well with the fine direct numerical simulation. For
comparison, we also present results corresponding to a classical subgrid-scale
eddy-viscosity model such as the standard Smagorinsky model.Comment: 31 pages including 15 figure
Bacterial Respiration of Arsenate and Its Significance in the Environment
Although arsenic is a trace element in terms of its natural abundance, it nonetheless
has a common presence within the earth's crust. Because it is classified as a
group VB element in the periodic table, it shares many chemical and biochemical
properties in common with its neighbors phosphorus and nitrogen. Indeed, in the
case of this element's most oxidized (+5) oxidation state, arsenate [HAsO_4^(2-) or
As (V)], its toxicity is based on its action as an analog of phosphate. Hence,
arsenate ions uncouple the oxidative phosphorylation normally associated with
the enzyme glyceraldehyde 3-phosphate dehydrogenase, thereby preventing the
formation ofphosphoglyceroyl phosphate, a key high-energy intermediate in glycolysis.
To guard against this, a number of bacteria possess a detoxifying arsenate
reductase pathway (the arsC system) whereby cytoplasmic enzymes remove internal
pools of arsenate by achieving its reduction to arsenite [H_2AsO_3- or As
(III)]. However, because the arsenite product binds with internal sulfhydryl
groups that render it even more toxic than the original arsenate, efficient arsenite
efflux from the cell is also required and is achieved by an active ion ''pumping'' system (1). The details of this bacterial arsenic detoxification phenomenon have
been well established in the literature, and Chapter 10 in this volume provided
a thorough review. Here, we discuss bacterial respiration of arsenate and its significance
in the environment. As a biological phenomenon, respiratory growth
on arsenate is quite remarkable, given the toxicity of the element. Moreover, the
consequences of microbial arsenate respiration may, at times, have a significant
impact on environmental chemistry
- …