Motion planning in velocity affine mechanical systems

We address the motion planning problem in specific mechanical systems whose linear and angular velocities depend affinely on control. The configuration space of these systems encompasses the rotation group, and the motion planning involves the system orientation. Derivation of the motion planning algorithm for velocity affine systems has been inspired by the continuation method. Performance of this algorithm is illustrated with examples of the kinematics of a serial nonholonomic manipulator, the plate-ball kinematics and the attitude control of a rigid body.     

A model of smoothing slide ball-burnishing and an analysis of the parameter interaction

The paper analyses a model of smoothing ball-burnishing which takes into account the mechanical properties of the workpiece, the geometry of the workpiece-tool contact area as well as the stereometry of the machined surface. It allows the determination of the dependence of the tip displacement of the machined surface asperities on the burnishing tool pressure. In the model-based research the effect of the particular parameters of the burnishing process on the tip displacement was defined. The optimum value of the displacement and the pressure it takes under various burnishing conditions were calculated. The analysis results were verified experimentally.     

Effect of metal purity and testing procedure on surface tension measurements of liquid tin

The surface tension of liquid tin of three different grades of purity (99.85, 99.96, and 99.999%) was measured by the classical sessile drop method over the temperature range 523–1023 K, in heating and cooling regimes. The results obtained show that the metal purity affects the values of surface tension and its temperature dependence. The highest values of surface tension and smooth linear temperature dependence were obtained in cooling regime for tin of the highest purity. With increasing content of impurities, both surface tension and its temperature coefficient decrease while the scatter of the data increases. The surface tension values measured on heating regime show higher scatter, compared to those obtained in cooling regime, and the temperature dependence of the surface tension is curvilinear rather than linear.     

Monitoring of transient temperature and thermal stresses in pressure components of steam boilers

Two methods of solving the transient inverse heat conduction problens in complex shaped elements are presented in this paper. The time-space temperature distribution in whole element cross-section is reconstructed using the measured temperature histories at several points placed inside the element or on its easily accessible outer surface. Thermal stresses are then evaluated involving Finite Element Analysis. In both methods the heat transfer coefficient at the element inner surface is the unknown value. Four examples are presented, two for one method showing the high accuracy of the presented methods and possibility of their practical application.     

Syntheses of 1,2,4-triazolo[4,3-c]pteridines. Potential substrates for xanthine oxidase

A synthetic route for the preparation of 9-phenyl-1,2,4-triazolo[4,3-c]pteridines 8 is described. Their reactivities towards xanthine oxidase from Arthrobacter M-4 are determined and compared with the pteridine derivatives 6-phenylpteridin-4[3H]-thione 5, 6-phenyl-4-thiomethylpteridine 6, 4-hydrazino-6-phenylpteridine 7, 3-N-methyl-6-phenylpteridin-4[3H]-thione 19, 4-amino-6-phenylpteridine 22 and 1-N-methyl-6-phenylpteridin-4[1H]-one 24, in order to inspect a possible influence of pyrimidine ring substitution pattern on their interaction with the bacterial enzyme. It has been suggested that a planar structure of the pteridine moiety and the substituents could be an important factor that so far has been overlooked when considering the enzyme activity. Some literature data are also discussed in view of revision of structure assignment of the compounds 12, 14, and 17. This revised version was published online in August 2006 with corrections to the Cover Date.     

Wetting and Interfacial Chemistry of SnZnCu Alloys with Cu and Al Substrates

Wetting of Cu and Al pads by Sn-Zn eutectic-based alloys with 0.5, 1, and 1.5 wt.% of Cu was studied at 250 °C, in the presence of ALU33® flux, with wetting times of 15, 30, 60, and 180 s, respectively. With increasing wetting time the wetting angle decreases only slightly and the angles on Cu pads are higher than those on Al pads. Selected, solidified solder-pad couples were cross-sectioned and subjected to SEM-EDS study of the interfacial microstructure. The results revealed that the microstructure of the SnZnCu/Cu interface is much different from SnZnCu/Al interface. In the first case continuous interlayers are observed while in the latter case there is no interlayer but the alloy dissolves the substrate along grain boundaries.     

Depth Dependence of Nanoindentation Pile-Up Patterns in Copper Single Crystals

A study of the dependence of nanoindentation pile-up patterns on the indentation load and crystallographic orientation is presented. Three different orientations—(001), (011), and (111)—of single crystal copper were investigated. Experiments were conducted on a CSM ultra-nanoindentation tester using a Berkovich tip. The topographic images were obtained using an atomic force microscope. The evolution of pile-up patterns with different applied loads was observed. The results show that for applied loads equal to 0.45 mN and smaller the pile-up patterns do not depend on the crystallographic orientation of the indented surface; instead, they depend on the tip’s geometry. On the other hand, in the case of indentation loads bigger than 2 mN, pile-up patterns on the surfaces of (001)-, (011)-, and (111)-oriented single crystals have fourfold, twofold, and sixfold (or threefold) symmetry, respectively. An intermediate state was also reported. Furthermore, a detailed analysis of residual impressions with maximal applied loads equal to 2 mN and bigger reveals that both pile-up and sink-in patterns are present.     

Vibrational spectra of functionalized fullerenes containing amide

The set of three new hydrogen bonding functionalized fullerenes containing amide (PCB-t-BA, PCB-n-BA, and MPCB-t-BA) was investigated using the infrared absorption and Raman scattering spectroscopies. Additionally, the quantum chemical calculations of the equilibrium geometry and normal mode vibrations of the molecules were performed. Role of hydrogen bonds (HB) in the investigated samples was under our particular attention. Bifurcated HB was suggested.     

Determination of trace selenium on hanging copper amalgam drop electrode

Hanging copper amalgam drop electrode has been applied for trace determination of selenium by cathodic stripping analysis. Detection limit for Se(IV) as low as 0.25 nM (0.02 μg L⁻¹) at deposition time (120 s) could be obtained. For seven successive determinations of Se(IV) at concentration of 5 nM relative standard deviation was 2.3% (n = 7). Interferences from selected metals and surfactant substances were examined. Absence of copper ions in sample solution causes easier optimization and makes method less vulnerable on contamination. The developed method was validated by analysis of certified reference materials (BCRs) and applied to selenium determinations in natural water samples, snow, mushrooms and ox liver.     

Influence of chemical and physical characteristics of cement kiln dusts (CKDs) on their hydration behavior and potential suitability for soil stabilization

The interaction of CKDs with a given soil depends on the chemical and physical characteristics of the CKDs. Hence, the characterization of CKDs and their hydration products may lead to better understanding of their suitability as soil stabilizers. In the present article, four different CKD powders are characterized and their hydration products are evaluated. A detailed chemical (X-ray diffraction), thermogravimetric and morphological (scanning electron microscope) analyses of both the CKD powders and the hydrated CKD pastes are presented. In general, high free-lime content (~ 14–29%) CKDs, when reacted with water produced significant amounts of calcium hydroxide, ettringite and syngenite. These CKDs also developed higher unconfined compressive strength and higher temperature of hydration compared to CKDs with lower amounts of free-lime. An attempt was made to qualitatively correlate the performance of CKD pastes with the chemical and physical characteristics of the original CKD powders and to determine their potential suitability as soil stabilizers. To that effect a limited unconfined compressive strength testing of CKD-treated kaolinite clays was performed. The results of this study suggest that both the compressive strength and the temperature of hydration of the CKD paste can give early indications of the suitability of particular CKD for soil stabilization.