Heterodyne performance of a quasioptical Schottky diode detector: Theoretical and experimental results

A detailed theoretical and experimental study of the heterodyne performance of a quasioptical Schottky diode detector is presented. The experimental results have been obtained by mixing the radiation from a FIR laser with the output of a 67–73 GHz Klystron. The heterodyne signal variation versus various parameters and its relation to the special case of two lasers mixing are described. The mixer characteristics are a NEP value of 2×10^?19W/Hz and a detector bandwidth of at least 9 GHz. Experimental evidence of harmonics generation of submillimetric frequencies at the diode junction is also presented.     

Algorithm 45. Automatic computation of improper integrals over a bounded or unbounded planar region

An automatic quadrature algorithm especially designed for double integration of functions with some form of singular behaviour on the boundary of the integration region is described, and its FORTRAN code is presented. The algorithm is based on the use of the product trapezoidal rule, after a non-linear transformation of the integrand in both variables renders a new integrand function whose derivatives vanish on the (transformed) boundary. Numerical results demonstrate the ability of the algorithm to obtain high accuracies in dealing automatically with pathological singularities of non-specific types.     

Computing turning points of curves implicitly defined by nonlinear equations depending on a parameter

Let the space curveL be defined implicitly by the (n, n+1) nonlinear systemH(u)=0. A new direct Newton-like method for computing turning points ofL is described that requires per step only the evaluation of one Jacobian and 5 function values ofH. Moreover, a linear system of dimensionn+1 with 4 different right hand sides has to be solved per step. Under suitable conditions the method is shown to converge locally withQ-order two if a certain discretization stepsize is appropriately chosen. Two numerical examples confirm the theoretical results.     

Schrankentreue Berechnung der Exponentialfunktion wesentlich-nichtnegativer Matrizen

An algorithm is proposed for computation of the exponential of a matrixX which uses the well known continued fraction expansion of tanhX. ForX essentially-nonnegative the following is proved: In interval arithmetic the algorithm is feasible, numerically convergent and bound conserving; after possibly a few initial steps it gives alternatively lower and upper bounds to the exact result.     

The computer generation of poisson random variables

An exact method for the generation of Poisson random variables on a computer is presented. The average time required per random variate decreases as the Poisson parameter tends to infinity.     

Solving linear systems by methods based on a probabilistic interpretation

In this paper it is demonstrated how the probabilistic concept of a stopping time in a random process may be used to generate an iterative method for solving a system of linear equations. Actually all known iterative approximation methods for solving linear equations are generated by various choices of a stopping time e. g. the point and block Jacobi methods, the point and block Gauss-Seidel Methods and overrelaxation methods are covered. The probabilistic approach offers—in a natural way—the possibility of adapting the solution technique to the special structure of the problem. Moreover, posterior bounds for the solution are constructed, which lead to faster convergence of the approximations than with usual prior bounds.     

On real factorizations of symmetric circulant sparse matrices

For the matricesA mentioned in the headline we determine the limit points up to which there is possible a real factorization of the formA=QQ ^T . HereQ=(q _ij ) is a circulant matrix, where from the elementsq _ij andq _ji withi≠j always one element is vanishing.     

Acute View Transport biofuels: Can they help limiting climate change without an upward impact on food prices?

Comprehensive life cycle assessments show that current transport biofuels often do worse than conventional fossil transport fuels as to the emission of greenhouse gases. Biofuels from microalgae grown with present technology and lignocellulosic biofuels from current arable land or land that is to be deforested are unlikely to do better regarding the emission of greenhouse gases than fossil transport fuels. When crops characterized by relatively low fossil fuel inputs and relatively high biomass yields are grown on abandoned agricultural and marginal soils which currently sequester little carbon, cropping for transport biofuels may help in limiting climate change without an impact on food prices. For such cropping one probably has to go beyond the market mechanism. Worldwide, there is some scope for the use of harvest residues in biofuel production. However, European arable soils show on average large losses of soil carbon and this rather favors increased addition of such residues to soils. Received: November 17, 2008; accepted: December 3, 2008     

Bacteriocins as food preservatives: Challenges and emerging horizons

ABSTRACT

The increasing demand for fresh-like food products and the potential health hazards of chemically preserved and processed food products have led to the advent of alternative technologies for the preservation and maintenance of the freshness of the food products. One such preservation strategy is the usage of bacteriocins or bacteriocins producing starter cultures for the preservation of the intended food matrixes. Bacteriocins are ribosomally synthesized smaller polypeptide molecules that exert antagonistic activity against closely related and unrelated group of bacteria. This review is aimed at bringing to lime light the various class of bacteriocins mainly from gram positive bacteria. The desirable characteristics of the bacteriocins which earn them a place in food preservation technology, the success story of the same in various food systems, the various challenges and the strategies employed to put them to work efficiently in various food systems has been discussed in this review. From the industrial point of view various aspects like the improvement of the producer strains, downstream processing and purification of the bacteriocins and recent trends in engineered bacteriocins has also been briefly discussed in this review.