Fault-Tolerant Formation Driving Mechanism Designed for Heterogeneous MAVs-UGVs Groups

A fault-tolerant method for stabilization and navigation of 3D heterogeneous formations is proposed in this paper. The presented Model Predictive Control (MPC) based approach enables to deploy compact formations of closely cooperating autonomous aerial and ground robots in surveillance scenarios without the necessity of a precise external localization. Instead, the proposed method relies on a top-view visual relative localization provided by the micro aerial vehicles flying above the ground robots and on a simple yet stable visual based navigation using images from an onboard monocular camera. The MPC based schema together with a fault detection and recovery mechanism provide a robust solution applicable in complex environments with static and dynamic obstacles. The core of the proposed leader-follower based formation driving method consists in a representation of the entire 3D formation as a convex hull projected along a desired path that has to be followed by the group. Such an approach provides non-collision solution and respects requirements of the direct visibility between the team members. The uninterrupted visibility is crucial for the employed top-view localization and therefore for the stabilization of the group. The proposed formation driving method and the fault recovery mechanisms are verified by simulations and hardware experiments presented in the paper.     

Bestimmung des molekulargewichts von „mikrogelhaltigem”︁ polystyrol mit der ultrazentrifuge (methode archibald)

The weight average molecular weight M_w of a mixture of two polystyrenes with very high and relatively low molecular weights (M_w = 16.1 · 10⁶ and 98 · 10³ g/mole), as a model for polymers containing microgel, was determined by ultracentrifugation with the ARCHIBALD-methode. M_w decreases with increasing number of rotation N. The exact molecular weight can only be determined by extrapolation to N = 0. This value depends nearly completely on the molecular weight and weight percentage of the “microgel”. It is not suitable for the characterization of the whole sample.     

Das spezifische Brechungsinkrement eines statistischen Methylmethacrylat/Benzylacrylat/Styrol-Terpolymeren

The specific refractive index increments of a random methylmethacrylate/ benzylacrylate/styrene-terpolymer and of the three corresponding homopolymers was measured in several solvents and at six different wavelengths. With the known terpolymer composition and the specific refractive index increments of the homopolymers the specific refractive index increment of the terpolymer is calculated by means of an equation formerly derived. Calculated and experimental values are compared.     

Zur kinetik der acrylnitril-polymerisation

The heterogeneous bulk polymerization of acrylonitrile initiated by AIBN has been studied by means of an improved dilatometric technique and a new method of analysis, where the initial reaction rate (v_w)₀ results from the intercept of a straight line in a \documentclass{article}\pagestyle{empty}\begin{document}$ \frac {\ln \left( 1 \hbox{---} {\rm U} \right)} {{\rm e}^{{- 0,5} {\rm k}_{\rm s}{\rm t} \hbox{---} 1}}$\end{document} versus t plot. It has been found that the initial reaction rate is proportional to the square root of the initial catalyst concentration S₀. The ratio of the rate coefficients of propagation and termination\documentclass{article}\pagestyle{empty}\begin{document}$\frac { {\rm k}_{\rm a} } { {\rm k}_{ {\rm w}^{2} } } $\end{document} could be calculated from the slope of a straight line passing through the origin in a plot of (v_w)₀ versus \documentclass{article}\pagestyle{empty}\begin{document}$\sqrt { {\rm S}_{0} }$\end{document} and yielded a value of 280 mol 1^?1.     

Compatibility of polysaccharide/maleic copolymer blends. IV. Thermal behavior of hydroxypropyl cellulose‐containing blends

The compatibility of the hydroxypropyl cellulose (HPC) with maleic acid–vinyl acetate copolymer in the solid state was studied by thermogravimetry, thermo‐optical analysis, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and optical microscopy. It was established that physical interactions are prevalent in blends with a high content of HPC, whereas chemical interactions predominate in blends with a medium and low content of HPC. By increasing the temperature, the thermochemical reactions are favored. Thermal properties are dependent on the mixing ratio of the components. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2585–2597, 2003     

Messung der Selbstdiffusion im System Polystyrol-Benzol; Temperatur-, Konzentrations- und Molekulargewichtsabhängigkeit

Self-diffusion of benzene and polystyrene in the system benzene-polystyrene is studied by means of spin-echo-technique as function of temperature, concentration and polymer molecular weight. From the dependence of temperature the activation energies are calculated as function of concentration and molecular weight. The concentration dependence is discussed in terms of restricted diffusion and the Fujita Free-Volume-Theory. The computed free volume shows a significant maximum at 50°C. This effect may be attributed to a change in the mobility of the phenyl side groups of polystyrene and is vanishing with decreasing molecular weight. The free-volume-temperature curves are giving references to the glass transition.     

Enzymatic degradation of thermoresponsive poly(N‐isopropylacrylamide) grafted to carboxymethylcellulose copolymers

The enzymatic degradation of poly(N‐isopropyl acrylamide) (PNIPAM) grafted to carboxymethylcellulose (CMC) copolymers with a cellulasic preparation (Trichoderma viride) was studied. The enzymatic activity of the cellulasic preparation against CMC and the grafted copolymers was determined by the Petterson–Porath method, while their reduced viscosity variation in the presence of the same preparation was also followed. It has been shown that the enzymatic degradation behavior depends on the copolymer composition and the reaction temperature. Reducing sugars analysis showed that the experimental values for the grafted copolymers were higher than the calculated ones. At 50°C, the enzymatic reaction is completed in about 20 min for the copolymers, whereas for CMC it takes more than 40 min. It can be concluded that their enzymatic degradation is facilitated by the presence of the PNIPAM grafts. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1383–1386, 2003     

Zur oligomerenbildung bei der thermischen polymerisation von styrol

It is shown that in thermal polymerization of styrene four dimers and six trimers are formed by parallel occurring oligomerization reactions. With increasing temperature the rate of oligomerization increases more rapidly than the rate of polymerization. The relativ yields of the different oligomers depend on temperature, too.     

Struktur und eigenschaften von ABS-polymeren. IX. Quantitative untersuchungen zur morphologie von ABS-polymerisaten

The technological properties of ABS polymers largely depend on the structure of the elastomer phase as well as on the elastomer/thermoplast interface. The morphological structure of such polymers can be determined from electron micrographs of ultramicrotome sections – after selective contrasting of the polybutadiene phase – or of replicas of fracture surfaces after selective chemical degradation. The various ABS polymers are classified by their manufacturing processes and their morphologies and characterized by electron micrographs. The degree and place of grafting are of particular importance. The quantitative determination of the surface- and internal grafting is achieved by combining the determination of the degree of grafting (extraction), the evaluation of the results obtained on particle counting, and a morphometric process. It is demonstrated that the morphometric process can in general be applied for the quantitative determination of the contrastable component in two-phase polymers.     

Das Verhalten organischer Pigmente in Polymeren

The importance of colouring matter is of prime importance in the plastics industry. The individual behaviour of organic pigments in the various polymer materials necessitates, however, on the part of the plastics manufacturer a precise knowledge of ?which pigment for which plastic”?. For example, a well known Thioindigo pigment behaves very differently in various polymer materials : In polystyrene, depending on the concentration used, it is monomolecularly dissolved, in associated solution or present as undissolved particles. In PVC, however, the good migration fastness is indicative of the insolubility of the pigment in this medium and so it is not surprising that PVC is the ideal plastic medium for this pigment. The behaviour of organic pigments in polymers is largely a function of molecular structure, e. g. intermolecular H-bonds can cause a decrease in solubility of a pigment in a polymer material, which in turn results in improved migration fastness. This is demonstrated by the improved migration fastness of variously substituted β-hydroxy naphthoic acid arylamide derivatives. Many phenomena exist however, which as yet can only be explained on the basis of the crystal structure of the pigment particles, i. e. the presence of aggregates or agglomerates. Such a phenomenon is, for example, the dispersibility of pigments in polymers. Here pigment surface, wettability by polymer and intermolecular forces are all of importance. In general, the dispersibility is better the smaller the specific surface area, as is shown for a typical quinacridone pigment. The influence of the rate of wetting on dispersibility is demonstrated using polyethylene wax. A further effect, which demonstrates the intermolecular forces between pigment and polymer, is the way in which certain pigments influence the rate of crystallization of partly crystalline polymers. This itself is connected with the shape and size of the pigment particles embedded in the polymer material. Such effects are demonstrated by measurements on various polyethylene objects. The pigment in this case was a naphthalene tetra carbonic acid derivative in both cis and trans form with widely varying specific surface areas.