Modeling the inhibitory effects of organic acids on bacteria.

The inhibitory effect of acids on microbial growth has long been used to preserve foods from spoilage. While much of the effect can be accounted for by pH, it is well known that different organic acids vary considerably in their inhibitory effects. Because organic acids are not members of a homologous series, but vary in the numbers of carboxy groups, hydroxy groups and carbon-carbon double bonds in the molecule, it has typically not been possible to predict the magnitude, or in some cases even the direction, of the change in inhibitory effect upon substituting one acid for another or to predict the net result in food systems containing more than one acid. The objective of this investigation was to attempt to construct a mathematical model that would enable such prediction as a function of the physical and chemical properties of organic acids. Principal Components Analysis (PCA) was applied to 11 properties for each of 17 acids commonly found in food systems; this resulted in four significant principal components (PCs), presumably representing fundamental properties of the acids and indicating each acid's location along each of these four scales. These properties correspond to polar groups, the number of double bonds, molecular size, and solubility in non-polar solvents. Minimum inhibitory concentrations (MICs) for each of eight acids for six test microorganisms were determined at pH 5.25. The MICs for each organism were modeled as a function of the four PCs using partial least squares (PLS) regression. This produced models with high correlations for five of the bacteria (R2 = 0.856, 0.941, 0.968, 0.968 and 0.970) and one with a slightly lower value (R2 = 0.785). Acid susceptible organisms (Bacillus cereus, Bacillus subtilis, and Alicyclobacillus) exhibited a similar response pattern. There appeared to be two separate response patterns for acid resistant organisms; one was exhibited by the two lactobacilli studied and the other by E. coli. Predicting the inhibitory effects of the organic acids as a function of their chemical and physical properties is clearly possible.     

All-Optoelectronic Terahertz Imaging Systems and Examples of Their Application

We give an overview over several all-optoelectronic measurement systems which we have developed for transmittive and reflective imaging in the terahertz (THz) frequency range. The systems employ either pulsed or continuous-wave THz radiation. In both cases, they work on the basis of single-pixel scanning. Addressing the potential for imaging in the medical and dental field, and the application of THz radiation for industrial surface and interface characterization, we explore dark-field imaging where the imaging contrast originates from diffraction and scattering effects coming from topography or refractive-index variations.     

Comparison of clustering approaches with application to dual colour protein data

Cells communicate with their environment via proteins, located at the plasma membrane separating the interior of a cell from its surroundings. The spatial distribution of these proteins in the plasma membrane under different physiological conditions is of importance, since this may influence their signal transmission properties. In this study, the authors compare different methods such as hierarchical clustering, extensible Markov models and the gammics method for analysing such a spatial distribution. The methods are examined in a simulation study to determine their optimal use. Afterwards, they analyse experimental imaging data and extend these methods to simulate dual colour data.Inspec keywords: proteins, molecular biophysics, cellular biophysics, biomembranes, Markov processes, bioinformatics, statistical analysisOther keywords: clustering approaches, dual colour protein data, cell communication, plasma membrane, spatial protein distribution, signal transmission, hierarchical clustering, extensible Markov models, gammics method, experimental imaging data     

A Bayesian approach to information fusion for evaluating the measurement uncertainty

The Bayesian approach to uncertainty evaluation is a classical example of the fusion of information from different sources. Basically, it is founded on both the knowledge about the measurement process and the influencing quantities and parameters. The knowledge about the measurement process is primarily represented by the so-called model equation, which forms the basic relationship for the fusion of all involved quantities. The knowledge about the influencing quantities and parameters is expressed by their degree of belief, i.e. appropriate probability density functions that usually are obtained by utilizing the principle of maximum information entropy and the Bayes theorem. Practically, the Bayesian approach to uncertainty evaluation is put into effect by employing numerical integration techniques, preferably Monte-Carlo methods. Compared to the ISO-GUM procedure, the Bayesian approach does not have any restrictions with respect to nonlinearities and calculation of confidence intervals.     

针对高速应用的电流反馈运算放大器

电流反馈运算放大器架构现已成为针对多类应用的主要解决方案,该放大器架构具有很多优势,并且几乎可用于任何需要运算放大器的产品设计中.     

Optically reconfigurable azobenzene polymer-based fiber Bragg filter

Optically writable, thermally erasable surface relief gratings in thin Disperse Red 1 polymethyl methacrylate azopolymer films were used to demonstrate an arbitrarily reconfigurable fiber Bragg filter. Gratings were optically written on azopolymer-coated side-polished fiber blocks, and a write-erase-write cycle was demonstrated. Finite difference time domain simulations reveal that this optically reconfigurable device concept can be optimized in a silicon-on-insulator waveguide platform.     

Zerstörungsfreie Eigenspannungsmessungen an Turbinen- und Generatorwellen

Anwendung des Nockenverfahrens bei Eigenspannungsmessungen an Wellen aus mit Chrom, Molybdän und Nickel legiertem Vergütungsstahl. Ermittlung der in den Randschichten herrschenden Eigenspannungen an tangential umlaufenden Bahnen. Erprobung des Nockenverfahrens im Betrieb bei Messungen in größerem Umfang. Aussagen über die Größe der Eigenspannungen und deren Abhängigkeit vom Wellendurchmesser. Untersuchung der rotationssymmetrischen Verteilung der Eigenspannungen und deren Änderung in Wellenlängsrichtung.