Quadrocopter Hovering Using Position-estimation Information from Inertial Sensors and a High-delay Video System

The requirement that mobile robots become independent of external sensors, such as GPS, and are able to navigate in an environment by themselves, means that designers have few alternative techniques available. An increasingly popular approach is to use computer vision as a source of information about the surroundings. This paper presents an implementation of computer vision to hold a quadrocopter aircraft in a stable hovering position using a low-cost, consumer-grade, video system. However, such a system is not able to stabilize the aircraft on its own and must rely on a data-fusion algorithm that uses additional measurements from on-board inertial sensors. Special techniques had to be implemented to compensate for the increased delay in the closed-loop system with the computer vision system, i.e., video timestamping to determine the exact delay of the vision system and a slight modification of the Kalman filter to account for this delay. At the end, the validation results of the proposed filtering technique are presented along with the results of an autonomous flight as a proof of the proposed concept.     

Computing quadratic entropy in evolutionary trees

We note here that quadratic entropy, a measure of biological diversity introduced by C.R. Rao, is a variant of the weighted Wiener index, a graph invariant intensively studied in mathematical chemistry. This fact allows us to deduce some efficient algorithms for computing the quadratic entropy in the case of given tip weights, which may be useful for community biodiversity measures. Furthermore, on ultrametric phylogenetic trees, the maximum of quadratic entropy is a measure of pairwise evolutionary distinctness in conservation biology, introduced by S. Pavoine. We present an algorithm that maximizes this quantity in linear time, offering a significant improvement over the currently used quadratic programming approaches.     

Copolymerization of α-methylstyrene with N-alkylmaleimides

Summary Alternating copolymers of -methylstyrene (-MeSt) with N-alkylmaleimides (RMI; R=Et, n-Pr, iso-Pr, n-Bu, n-Hex) were prepared in Calvet differential microcalorimeter under different monomer-to-monomer ratios in the feed using AIBN as initiator. The equilibrium constants of CT-complex monomers have low values: 0.02–0.05 L.mol^-1 but the mechanism of copolymerization indicates the participation of CT-complex. Equilibrium constants and rate of decomposition under the TGA conditions are not dependent on steric factors, but the rate of copolymerization decreases with the increase of bulkiness of alkyl substituent. In high conversion copolymerization it was observed that in the presence of an excess of homopolymerizable RMI, alternating copolymers are quantitatively formed prior to the formation of poly(RMI).Dedicated to Professor Dragutin Fle on the occasion of his 70th birthday     

Direct-laser writing of striplines on AgCl single crystals

Experiments on a localized and controlled photo-reduction of silver were carried out on a AgCl single crystal that was exposed to a UV-laser light. Basic parameters such as the peak power and the total energy dose were varied. The study showed that for a pulsed-laser beam with a high peak power (>20 W) the ablation threshold of the AgCl was exceeded, while at lower peak powers no ablation was detected, only a change in the surface morphology. The degree of silver reduction was monitored using EDS microanalyses of the irradiated trace and the crystal matrix. We showed that the formation of photo-reduced silver aggregates decreases the ablation threshold and that the formation of a continuous silver trace on the AgCl single crystal is possible when the power density of the laser beam is further reduced.     

Existence of the Ba2Ti5O12 Phase in Ca-Doped TiO2-Rich BaTiO3

A TEM investigation was conducted on the structure of a second phase precipitated between the grains of a polycrystalline TiO₂-rich BaTiO₃ which was doped with 8 mol% Ca. This phase was identified as Ca-stabilized Ba₂Ti₅O₁₂ with a 10-layer orthorhombic structure and unit-cell parameters a=0.990, b=1.131, and c=2.330 nm.     

The effect of heating on the release of formaldehyde from durable-press finished fabrics

The effect of subsequent heating on formaldehyde release from DMDHEU-finished fabric has been examined. Formaldehyde release was higher at higher heating temperatures, but fabrics cured at higher temperatures showed less released formaldehyde. Adding urea reduced formaldehyde release.     

X-ray Diffraction and Microstructural Investigation of the Al2O3-La2O3-TiO2 System

The ternary phase diagram of Al₂O₃-La₂O₃-TiO₂ at 1400°C was determined with 12 compatibility triangles. Al₂O₃ stabilizes the A-site-deficient La_2/3TiO₃ perovskite structure. According to XRD and microstructural investigations, the solid solution extends along the La_2/3TiO₃-LaAlO₃ tie line from at least 4 mol% LaAlO₃ to pure LaAlO₃. With increasing LaAlO₃ content, the stabilized La_2/3TiO₃ structure changes from orthorombic via tetragonal to cubic.