COMPUTER AIDED DESIGN OF HORN RADIATORS FOR SATELLITE COMMUNICATION BY LEAST SQUARES OPTIMIZATION

Computer aided design optimization of corrugated horns became a powerful tool to reduce development costs on the one hand and to improve performance of space antennas on the other. In this paper the physical model is outlined, based on Maxwell's equations, and it is shown how a complete numerical simulation of a circular corrugated horn can be achieved, assuming that the interior geometry of the horn is known. In order to compute the electromagnetic properties of a horn, the so-called scattering matrix is assembled. This matrix is needed to relate mode amplitudes of reflected and transmitted waves in horn sections with different diameters. Envelope functions, determined by a few geometric design parameters, are used to describe the inner geometry of a horn. These parameters are applied to formulate a least squares optimization problem. As a starting point, an amplitude spectrum in the aperture has to be determined which radiates a given far field. The differences between those amplitudes and the amplitudes predicted by the model are to become as small as possible by adapting the design variables. Moreover, the return loss is to be minimized. The resulting least squares optimization problem can be solved by a standard sequential quadratic programming (SQP) code after a suitable transformation into a nonlinear programming problem, by which typical features of Gauss-Newton methods are retained. Some numerical results are included to show the successful application of the introduced advance to design a circular corrugated horn which radiates a given far field.     

AUTOMATIC EXTRACTING AS AN INTERACTIVE PROCESS

In our study we have tried to evaluate most of the existing methods of automatic extracting and to combine them into one single system for text reduction. Hitherto, all existing automatic extracting systems have produced only extracts of documents: they select certain sentences from the full text and list them in text order.

Despite the result that statistical methods can be used for extracting German language texts (and that similar methods show best results for German and English texts) the main outcome of this study was that computer-based methods for text extracting can alter the whole extracting and abstracting process as such and lead to completely new and as yet unknown aspects of text reduction: the tailormade extract and extracting as an interactive process.     

Phosphorus detection in vitrified bacteria by cryo‐STEM annular dark‐field analysis

Bacterial cells often contain dense granules. Among these, polyphosphate bodies (PPBs) store inorganic phosphate for a variety of essential functions. Identification of PPBs has until now been accomplished by analytical methods that required drying or chemically fixing the cells. These methods entail large electron doses that are incompatible with low‐dose imaging of cryogenic specimens. We show here that Scanning Transmission Electron Microscopy (STEM) of fully hydrated, intact, vitrified bacteria provides a simple means for mapping of phosphorus‐containing dense granules based on quantitative sensitivity of the electron scattering to atomic number. A coarse resolution of the scattering angles distinguishes phosphorus from the abundant lighter atoms: carbon, nitrogen and oxygen. The theoretical basis is similar to Z contrast of materials science. EDX provides a positive identification of phosphorus, but importantly, the method need not involve a more severe electron dose than that required for imaging. The approach should prove useful in general for mapping of heavy elements in cryopreserved specimens when the element identity is known from the biological context.     

DIFFUSION of LOW-MOLECULAR COMPOUNDS IN FOOD MODEL SYSTEMS

The diffusion of NaCl and isopropanol was studied in a matrix of pure gel and one containing either carbohydrates, proteins or fat using the concentration-distance method. Concentrations of NaCl were measured by conductivity, those of isopropanol by gas chromatography. Diffusion experiments have shown that the temperature dependence of the diffusion coefficient is in accordance with an Arrhenius approach.
Experimental and predicted diffusion coefficients didnot agree satisfactorily when only models of mere obstruction were considered. Including the effect of hydration by values obtained from pure gels, experimental diffusion coefficients range throughout between the calculated values of mere obstruction and those obtained from a mathematical combination of obstruction and maximum hydration.     

NMR Study of Adsorbate Self-Diffusion in Porous Glasses

The NMR pulsed field gradient technique was used to study molecular transport in porous glasses. The adsorbent materials were produced by leaching phase-separated sodium-boron-silica glasses of different composition, then heat-treating. The pore diameters of the glass samples produced were within the interval 0.8 to 50 nm. Water, methanol, dodecane, and do-decene were used as adsorbates. The coefficients of adsorbate self-diffusion were found to decrease with decreasing pore diameter. In comparison with the neat liquids, a reduction in the adsorbate mobility (up to two orders of magnitude) was observed. For the larger pores, that decrease may be attributed to the tortuosity of the adsorbent, whereas the low diffusivities in the porous glasses with small pores are a consequence of the stabilizing effect of the rigid adsorbent framework.     

A simple and stable autofocusing protocol for long multidimensional live cell microscopy

Focus maintenance is a challenging problem in multidimensional wide‐field microscopy. Most automated microscopes use software algorithms, which are applied to z‐sections of the object, to select for the plane with the best signal to noise ratio. When applied automatically in multidimensional imaging applications, autofocus routines significantly increase light exposure and can become cytotoxic if applied too frequently. In addition, automated focusing procedures can readily focus on unwanted high contrast objects. By labelling a defined position with a fluorescent marker, we were able to separate the focusing procedure from the actual image acquisition positions and therefore overcome some of the major drawbacks of routine autofocus procedures. To implement this method in a multidimensional acquisition experiment, we created a visual basic‐based program, which is run prior to each image acquisition. This technique allows tight control of focus whilst keeping light toxicity in live cell imaging experiments to a minimum.     

CONSISTENT INFINITESIMAL FINITE-ELEMENT CELL METHOD: THREE-DIMENSIONAL VECTOR WAVE EQUATION

To calculate the unit-impulse response matrix of an unbounded medium for use in a time-domain analysis of unbounded medium–structure interaction, the consistent infinitesimal finite-element cell method is developed for the three-dimensional vector wave equation. This is a boundary finite-element procedure. The discretization is only performed on the structure–medium interface, yielding a reduction of the spatial dimension by 1. The procedure is rigorous in the radial direction and exact in the finite-element sense in the circumferential directions. In contrast to the boundary-element procedure, the consistent infinitesimal finite-element cell method does not require a fundamental solution and incorporates interfaces extending from the structure–medium interface to infinity compatible with similarity without any additional computational effort. A general anisotropic material can be processed. The derivation is based on the finite-element formulation and on similarity.     

Evaluation of a CPU Scheduling Mechanism for Multimedia Systems

Multimedia applications handling audio and video data have to obey time characteristics of these media types. Besides a basic functionality to express time relations, correctness with respect to time constraints requires mechanisms which lead to favoured processing of multimedia operations. CPU scheduling techniques based on the experience from real-time operating systems offer a solution and provide multimedia applications with the ability to meet time-related quality of service requirements. This paper discusses mechanisms to express time in multimedia systems and describes an implementation of a CPU scheduler designed to run under IBM's UNIX derivate AIX. The evaluation of the implementation based on measurements shows that the scheduler is able to support the time requirements of multimedia applications and that such mechanisms are indeed necessary since otherwise deadline violations occur.