Solution modules and system equivalence

In this paper we consider a system as a relation between input, internal variables and output. This relation is given by the solution space of the system's equations. For time invariant linear systems in differential operator representation the solution space carries a K[s]-module structure defined by the ordinary differential operator. This algebraic structure is exploited systematically to develop a self-contained theory of strict system equivalence in time domain.

The module of free motions is considered as space of initial conditions. An algebraic characterization of systems having the same solution space is presented. System homomorphisms are defined as special K[s] homomorphisms between the solution modules. Two systems are called system-equivalent, if there exists a system-isomorphism between their solution spaces. It turns out that, this concept coincides with Rosenbrock's concept of strict. system equivalence. It. is shown that further concepts and results of linear system theory (construction of a state-space model in time domain, controllability and observability criteria, uniqueness theorem of linear realization theory) can be derived within this framework.     

Stability and robustness properties of universal adaptive controllers for first-order linear systems

Quite recently, examples of non-linear adaptive controllers have been found that adaptively stabilize any scalar first-order linear system. In this paper we describe two general classes of such ‘universal’ adaptive stabilizers that include the previously proposed controllers as special cases, Different types of perturbations of these controllers are studied and we report on extensive simulation experiments. Our results demonstrate considerable qualitative differences in the dynamical behaviour of various adaptive universal stabilizers. While the previously proposed controllers all exhibit the bursting phenomena, we give an explicit example of a stabilizing controller that does not show bursting behaviour.     

Friction in hip-joint prostheses and its influence on the fixation of the artificial head

The head of an implanted hip joint endoprosthesis is exposed to torques, which are transferred during gait due to the friction between the head and the cup prosthesis. In prostheses with ceramic ball heads, which are widely used now, and in which the head is fixed onto the stem by conical clamping, these torques could possibly affect the connection. In this study, torques transferred from the cup to the head are compared to the torques which are required to loosen the head from the metallic spigot. The results show that for the investigated head and taper types and sizes, under normal conditions the connection is safe with respect to undesired rotation. However, it is shown that for polluted sliding surfaces the fixation strength could possibly be exceeded. © 1998 Kluwer Academic Publishers     

Investigations of the molar heat capacity at low temperatures in the TiH x system

Results from heat capacity measurements in the temperature range 1.8–10 K on TiH _x samples with different x values are communicated. From the coefficients of the electronic heat capacity the dependence of the density of states N(E _F) on the x value for the cubic and the tetragonal TiH _x phases is discussed, and is compared with similar results from susceptibility measurements. The estimated value for the electron-phonon interaction parameter excludes superconductivity for TiH _x . An additional lattice contribution to the heat capacity of TiH _x samples with x < 1.7 was observed and seems to be related to a low-frequency anomaly in the phonon spectra.     

The relation between SAR imagery and regional sea ice ridging characteristics from BEPERS-88

Abstract

In the Bothnian Experiment in Preparation for ERS-1 (BEPERS-88) airborne laser profiles and Synthetic Aperture Radar (SAR) images were obtained simultaneously over the pack ice in the Bay of Bothnia, Baltic Sea. The possibility of mapping ice ridging characteristics using SAR has been analysed. SAR intensity histograms and ridging statistics have been compared in regions with length scales from 3 to 23 km. The measures for the intensity of ridging were taken from the profilometer data as functions of the number of ridges and mean ridge height. The results show that, from SAR intensity distribution, an average of 10 per cent upper tail divided by the overall average is a good predictor for the ridging intensity. This predictor explains 80-90 per cent of the variance.     

The Bothnian Experiment in Preparation for ERS-1, 1988 BEPERS-88) — an overview

Abstract

BEPERS-88 was an extensive field campaign on the use of Synthetic Aperture Radar (SAR) in sea ice remote sensing in the Baltic Sea. This experiment was performed in order to study the possibilities of using the ERS-1 satellite SAR (and radar altimeter) in connection with the brackish ice in the Baltic Sea. The Canada Centre for Remote Sensing CV-580 C/X-band SAR was flown and an extensive validation programme was carried out. The data have been used for SAR image analysis, backscatter investigations, geophysical validation of SAR over sea ice, and evaluation of the potentials of SAR in operational ice information services. The results indicate that SAR can be used to discriminate between ice and open water, classify ice types into thrcc categories, quantify ice ridging intensity, and determine the ice drift. As an operational tool SAR is expected to be an excellent complement to NOAA imagery and ground truth.     

Immobilization of a biologically active coating on a hydrophobic L-lactide-ɛ-caprolactone copolymer

The electron beam radiation induced grafting method was used to attach a reactive polyacrylamide (PAA) layer (20 wt %) on the surface of a biodegradable poly-L-lactide-co--caprolactone (PLLA-co-CL). The biocompatibility of graft–polymer obtained was studied by cytotoxicity test and no signs of toxicity were observed. Heparin and sol–gel-produced silica-gel coatings were successfully attached on the top of the polymeric material produced. The amount of heparin immobilized directly on the surface can be controlled by reaction conditions: reaction time, temperature and pH of the incubation solution. By using acidic conditions, up to 98 µg cm^-2 of heparin was immobilized on the surface. The sol–gel-produced silica-gel layer formed by dipping technique was 30 µm thick and the cracking of the layer was minimal after bending several times to 90°. © 1999 Kluwer Academic Publishers     

Investigation of turbulence rotation in the SOL and plasma edge of W7-X for different magnetic configurations

The W7-X stellarator is optimized with respect to neoclassical transport. Therefore turbulent transport plays an important role. It is equipped with an inertial cooled graphite divertor which intersects the island chain at the plasma edge depending on the magnetic configuration. Additional control coils and the plasma current modify the iota profile at the plasma edge and shift the position of the island chain. To monitor the effects on the poloidal propagation velocity in the scrape-off layer(SOL) and the plasma edge, an O-mode Poloidal Correlation Reflectometer(PCR) is used which simultaneously monitors the propagation of low-k turbulence. Operating in the density range of 0.6?×?10~(19) m~(-3) to2?×?10~(19) m~(-3) it covers a large part of the SOL and the plasma edge and allows for the experimental determination in the last closed flux surface(LCFS) and the associated shear layer in low to middensity discharges. In this paper it is shown that the propagation in the shear layer and its vicinity is determined best, when based on an elliptical model. Different magnetic configurations with magnetic edge topology of five independent islands for ι?=?1 and six linked islands for ι?=?0.81 are investigated. Also the effects of the plasma current and additional control coils on the edge magnetic topology are studied. The coherence spectra of antenna pairs for different poloidal separations is investigated. Using a decomposition method for the measured coherence spectra the characterization of turbulence spectra is possible with respect to e.g. broad band turbulence and quasi coherent modes.A strong reduction of the broad band turbulence is observed in the vicinity of the LCFS which is evidence for the suppression of low-k turbulence at the shear layer.