Pose consensus in networks of heterogeneous robots with variable time delays

This paper proposes a novel pose (position and orientation) consensus controller for networks of heterogeneous robots modeled in the operational space. The proposed controller is a distributed proportional plus damping scheme that, with a slight modification, solves both the leader–follower and leaderless consensus problems. A singularity‐free representation, unit quaternion, is used to describe the robots orientation, and the network is represented by an undirected and connected interconnection graph. Furthermore, it is shown that the controller is robust to interconnection variable time delays. Experiments with a network of two 6‐degrees‐of‐freedom robots are presented to illustrate the performance of the proposed scheme. Copyright © 2014 John Wiley & Sons, Ltd.     

Study on the RF Sputtered hydrogenated amorphous silicon–germanium thin films

In this study mechanical and electrical properties of the RF sputtered hydrogenated amorphous silicon germanium thin films deposited at room temperature have been discussed. Interesting correlation between the resistance and the flow of hydrogen is observed. Further, both band and hopping conduction mechanisms are found to exist simultaneously for the studied amorphous silicon germanium films.     

Microcrystalline to nanocrystalline silicon phase transition in hydrogenated silicon-carbon alloy films

Different classes of interesting materials (such as protocrystalline, microcrystalline and nanocrystalline) have been grown under conditions very near to those for the microcrystalline phase. In spite of the importance of these materials, a clear picture regarding their phase transitions is missing. A smooth transition from the microcrystalline to the nanocrystalline silicon phase, distinctly different from an abrupt order-disorder phase transition, has been demonstrated, for the first time, in hydrogenated silicon-carbon alloy films, prepared from a silane-methane gas mixture highly diluted in hydrogen, by varying the rf power in a plasma enhanced chemical vapour deposition system. The study has also provided the signature of medium range order in hydrogenated silicon-carbon alloy films.     

Formation of ge nanocrystals in SiO2 by electron beam evaporation

Ge nanocrystals were formed by electron beam evaporation on SiO2 covered Si substrates. The size and distribution of the nanocrystals were studied by atomic force microscopy, scanning electron microscopy and cross-sectional transmission electron microscopy. Dependencies of the nanocrystal size, of the nanocrystal surface coverage, and sheet resistance obtained by van der Pauw method of the Ge layer have been found on the evaporation time. The suggested growth mechanism for the formation of nanocrystals is the Volmer-Weber type. The sheet resistance exhibited a power dependence on the nanocrystal size.     

Cyclic chronopotentiometry as a detection tool for flowing solution systems

Cyclic chronopotentiometry provides a very simple detection method, which may be particularly useful in capillary electrophoresis (CE) and microseparation systems. It has been shown that for disk microelectrodes it is possible to define safe reduction and oxidation currents that would never lead to the formation of H2 or O2 gas bubbles, even if they are applied for an indefinitely long time period. During end-column CE detection, currents passing through the working microelectrode can be completely controlled by the external electronic circuit and they are not affected by the separation current. Consequently, problems created by the offset potential in CE can be completely eliminated. The detection can be accomplished through a variety of different mechanisms; however, generation of the electrode response as a result of analyte adsorption seems to be most common. The method is applicable to many analytes, which do not have to be electroactive. The analytical signal is obtained by monitoring the change in the average electrode potential (calculated for either a cathodic or an anodic half-cycle) caused by an analyte interacting with the electrode. The analytical signal is proportional to the analyte concentration, within a concentration range extending over approximately 2 orders of magnitude.     

Truncation error in mesh‐free particle methods

A truncation error analysis has been developed for the approximation of spatial derivatives in smoothed particle hydrodynamics (SPH) and related first‐order consistent methods such as the first‐order form of the reproducing kernel particle method. Error is shown to depend on both the smoothing length h and the ratio of particle spacing to smoothing length, Δx/h. For uniformly spaced particles in one dimension, analysis shows that as h is reduced while maintaining constant Δx/h, error decays as h² until a limiting discretization error is reached, which is independent of h. If Δx/h is reduced while maintaining constant h (i.e. if the number of neighbours per particle is increased), error decreases at a rate which depends on the kernel function's smoothness. When particles are distributed non‐uniformly, error can grow as h is reduced with constant Δx/h. First‐order consistent methods are shown to remove this divergent behaviour. Numerical experiments confirm the theoretical analysis for one dimension, and indicate that the main results are also true in three dimensions. This investigation highlights the complexity of error behaviour in SPH, and shows that the roles of both h and Δx/h must be considered when choosing particle distributions and smoothing lengths. Copyright © 2005 John Wiley & Sons, Ltd.     

Correlation between structural and opto-electronic properties of a-Si1 − xCx:H films deposited by plasma enhanced chemical vapour deposition

Hydrogenated amorphous silicon carbon alloy films of different carbon content were prepared by Plasma Enhanced Chemical Vapor Deposition using silane and methane with helium dilution and were characterized to study their opto-electronic, structural and defective properties. A linear correlation between micro structural disorder and overall disorder has been demonstrated. Further, it has been shown that the increase in the intrinsic disorder leads to an increase in the defect density while the increase in voids results in the decrease in the mass density for the studied films.     

Correlation of structure and optical properties of an annealed hydrogenated amorphous silicon-carbon alloy film

A hydrogenated amorphous silicon-carbon (a-Si_0.76C_0.24:H) film has been prepared via the glow discharge decomposition of SiH₄ and C₂H₄. The optical constants of this alloy film have been determined as a function of annealing temperature T_a for photon energies between 1.5 and 4.75 eV. The refractive index n and its imaginary part k show small but significant variation with annealing temperature. The optical energy gap E_opt also exhibits interesting variation with annealing temperature, decreasing with increasing annealing temperature up to T_a = 650°C and then increasing above this temperature. Further, E_opt is found to be correlated with the inverse of the full width at half-maximum of the Si---C and the Si---O IR stretch absorption mode, which seems to indicate that the changes in E_opt are structural in origin and that phonon order correlates well with electronic order.