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Examines the behavior of thermal expansion coefficients in models of solids with different pairwise interaction potentials. Evaluation of the role of various nonlinear effects caused by the specificity of pairwise potentials; Consideration of three types of pairwise potentials; Utilization of a system of units in which the size, weight, and interaction energy of particles are equal to zero.

This paper shows the results obtained in controlling a mobile robot by means of local recurrent neural networks based on a radial basis function (RBF) type architecture. The model used has a Finite Impulse Response (FIR) filter feeding back each neuron's output to its own input, while using another FIR filter as a synaptic connection. The network parameters (coefficients of both filters) are adjusted by means of the gradient descent technique, thus obtaining the stability conditions of the process. As a practical application the system has been successfully used for controlling a wheelchair, using an architecture made up by a neurocontroller and a neuroidentifier. The role of the latter, connected up in parallel with the wheelchair, is to propagate the control error to the neurocontroller, thus cutting down the control error in each working cycle. [ABSTRACT FROM AUTHOR]

The sensorial system developed is based on the emission of an infrared beam, recovering the reflected beam and measuring distances to significant points in the environment. This system is able to detect and model obstacles in unknown environments. Features of the capture system allow large fields of view to be caught at short distances, aiding the robot's mobility. Several algorithms are used to find the formation centre of the image and so model the distortion introduced by the wide-angle lens. Parameters of the optical model are inserted into the calibration matrix to obtain the camera model. We present also an algorithm which extracts the points on the image that belong to the laser beam. All of the above work is in unknown environments with variable conditions of illumination. The robot's trajectory is obtained and modified in real time, with a spline function, using four different reference systems. Finally, empirical tests have been carried out on a mobile platform, using a CCD camera with a wide-angle lens of 65° and 110°, a 15 mW laser emitter and a frame grabber for image processing. [ABSTRACT FROM AUTHOR]

• Hierarchically micro-mesoporous SiOC-CD were obtained from HF etching of SiOC • Better electrochemical response when both micro and slit-shape mesopores are present • SiOC-DC materials pyrolyzed at 1200 °C display a C s of up to 100 Fg−1 at 40 Ag−1 • SiOC-DCmaterials pyrolyzed at 1200 °C show an energy density of up to 28 W h Kg−1 [Display omitted] Hierarchically micro/mesoporous silicon oxycarbide derived carbon (SiOC-DC) materials have been successfully prepared by HF selective removing of silica nano-domains present in SiOC. Dense carbon enriched SiOC materials are obtained by pyrolysis from 1100 to 1400 °C of novel sol-gel hybrids which contain both Si–H and Si-Ph bonds. The pyrolysis temperature deeply affects the etching process, major differences are observed between the sample pyrolyzed at 1100 °C and at higher temperatures. Those differences are directly associated to the evolution of the phase separation of SiOC into SiO 2 and SiC, which facilitates the selective extraction of silica nano-domains and the formation of micro/mesoporous SiOC-DC materials with high specific surface areas (SSAs) and high pore volumes. The SiOC-DC sample pyrolyzed at 1200 °C displays very promising results of specific capacitance (90–100 Fg−1 at 40 Ag−1), relatively high energy density (28 W h Kg−1) at a low power density (0.10 kW kg−1), and a significant performance at high power density (10 W h Kg−1 at 49 kW kg−1), taking into account the low potential window of inorganic liquid electrolyte used (0.9 V). We have found that the presence of micropores but even more, the presence of slit-shape mesopores (D meso 3–10 nm) is crucial in order to explain the electrochemical response of these materials. [ABSTRACT FROM AUTHOR]

This paper studies the problem of controlling the movements of a handicapped person's motorized wheelchair from a practical point of view. The control system implemented has been divided into two levels: the “low level”, consisting of an electronic system which directly controls the drivers of the chair's motors, with a classic PID (proportional-integral-derivative) control loop. The aim of this level is to ensure that the speeds of each one of the wheels is similar to the input speed of these control boards. The second control level (“high level”), implemented by means of neural techniques, ensures that the linear and angular speeds of the wheelchair are those indicated by a trajectory generator. A new recurrent model is used as the neural network, for which the stability conditions of the complete control system are obtained and various practical tests are carried out, which show the correct performance of the actual system implemented. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations of two types of isolated siloxane dendrimers of various generations (from the 2nd to the 8th) have been performed for temperatures ranging from 150 K to 600 K. The first type of dendrimer molecules has short spacers consisting of a single oxygen atom. In the dendrimers of the second type, spacers are longer and comprised of two oxygen atoms separated by a single silicon atom. A comparative analysis of molecular macroscopic parameters such as the gyration radius and the shape factor as well as atom distributions within dendrimer interior has been performed for varying generation number, temperature, and spacer length. It has been found that the short-spacer dendrimers of the 7th and 8th generations have a stressed central part with elongated bonds and deformed valence angles. Investigation of the time evolution of radial displacements of the terminal Si atoms has shown that a fraction of the Si groups have a reduced mobility. Therefore, rather long time trajectories (of the order of tens of nanoseconds) are required to study dendrimer intramolecular dynamics. [ABSTRACT FROM AUTHOR]

The potential application of silicon oxycarbonitride (SiOCN), silicon oxycarbide (SiOC) and silicon oxycarbide–SiC (SiOC–SiC) for photothermal devices such as volumetric solar absorbers has been studied evaluating the response to thermal shock from a Fresnel lens. The accelerated ageing test comprises fast heating (32 °C min−1) and cooling rates (27 °C min−1) from 100 to 1000 °C and dwelling times of 10 min. Porous materials (SiOCNp and SiOCp) failed the thermal shock tests; they were massively degraded by the formation of a large depression in the focus of solar radiation. Dense materials (SiOCd and SiOC–SiCd) withstood 100 cycles of thermal shock ageing tests due to the formation of a protective silica layer. The absorptance values for dense materials remained fairly constant before and after thermal shock tests: from 94.5 to 94.3% for SiOCd and from 93.3 to 93.3% for SiOC–SiCd. These preliminary studies indicate their potential for high-temperature solar receiver applications. [ABSTRACT FROM AUTHOR]