Control of chaotic dynamical systems using radial basis function network approximators

This paper presents a general control method based on radial basis function networks (RBFNs) for chaotic dynamical systems. For many chaotic systems that can be decomposed into a sum of a linear and a nonlinear part, under some mild conditions the RBFN can be used to well approximate the nonlinear part of the system dynamics. The resulting system is then dominated by the linear part, with some small or weak residual nonlinearities due to the RBFN approximation errors. Thus, a simple linear state-feedback controller can be devised, to drive the system response to a desirable set-point. In addition to some theoretical analysis, computer simulations on two representative continuous-time chaotic systems (the Duffing and the Lorenz systems) are presented to demonstrate the effectiveness of the proposed method.     

COMPARISON OF PROBE METHODS FOR MEASUREMENT OF BUBBLE PROPERTIES

Direct quantitative comparisons of four different probe methods were performed for determination of local gas holdup, vertical bubble length, bubble rising velocity, and bubble frequency. The methods include vertically projecting electroresistivity, horizontally projecting electroresistivity, U-shape light reflection, and light transmission. The measured bubble properties strongly depended on the size and configuration of the probe tips. The light transmission probe developed in this work can be used to determine the bubble properties effectively. In order to minimize interferences with bubble flow, the size of probe tip should be small as possible and its configuration must be vertically projecting.     

Nucleation and growth of aluminium oxide on silicon in the CVD process

Films of aluminium oxide have been formed on single crystal silicon substrates using AlCl₃-CO₂-H₂ gas mixtures in a cold-walled chemical vapour deposition (CVD) reactor. The nucleation and subsequent growth of the deposit have been observed under the varying process parameters. It is found that the nucleation and growth of the Al₂O₃ are dependent on the H₂O flux and H₂O supersaturation. An activation energy of 34.8 Kcal mol^–1 is obtained for the growth rate indicating that the CVD of Al₂O₃ on silicon is a thermally activated process and limited by surface reaction. Scanning electron micrographs (SEM) show that the deposited films are amorphous at low temperature, 850° C, but change to fine grained polycrystalline structure at high temperature, 1000° C.     

Effect of bipolar plate materials on the stress distribution and interfacial contact resistance in PEM fuel cell

In polymer electrolyte fuel cell (PEFC) system, ideal structural integrity design takes into account the end-to-end load transfer mechanism. Hence, structural durability of cell is dependent of individual layers response to the external clamp loading. Since failure modes of each layer differ from another, multidisciplinary approach is needed to innovative designs. Bipolar plate (BPP) of PEFC is multi-functional layer that has a significant potential for research to avoid its structural failure as well as neighboring layers. To this end, present work investigates the effect of BPP materials on the stress transfer as well as distribution in cell layers based on theoretical investigation for clamping load. Gas-diffusion layer (GDL) / BPP interface has drawn considerable interest among researchers due to its susceptibility for damage failure and other related losses. Hence, investigating the interfacial behavior and relating this to the electrical contact resistance is the key feature in proposed investigation.     

Antioxidant activities from the aerial parts of Platycodon grandiflorum

In order to obtain basic data necessary for the utilisation of aerial parts from Platycodon grandiflorum as a functional substance in Korea, the antioxidant activities of solvent fractions from the ethanol extract of P. grandiflorum aerial parts were examined. The butanol fraction from P. grandiflorum showed the most potent antioxidant activities in each assay, showing 91.31% in the DPPH radical scavenging method, 99.62% in the ABTS radical scavenging method, 7.84% in the reducing power method, and 1.29% in the FRAP method at a concentration of 10 mg/ml. The DPPH, ABTS, reducing power, and FRAP assay indicated that the butanol fraction of aerial parts of P. grandiflorum was the most potent radical-scavengers and reducing agents compared to the other two extracts. Therefore, our study verified that the butanol fraction has strong antioxidant activities which are correlated with its high level of phenolics, particularly luteolin-7-O-glucoside and apigenin-7-O-glucoside. This extract of P. grandiflorum aerial parts can be utilised as an effective and safe source of functional food materials such as natural antioxidants.     

A low-loss single-pole six-throw switch based on compact RF MEMS switches

A low-loss single-pole six-throw (SP6T) switch using very compact metal-contact RF microelectromechanical system (MEMS) series switches is presented. The metal-contact MEMS switch has an extremely compact active area of 0.4 mm /spl times/ 0.3 mm, thus permitting the formation of an SP6T MEMS switch into the RF switch with a total area of 1 mm/sup 2/. The MEMS switch shows an effective spring constant of 746 N/m and an actuation time of 8.0 /spl mu/s. It has an isolation loss from -64.4 to -30.6dB and an insertion loss of 0.08-0.19 dB at 0.5-20 GHz. Furthermore, in order to evaluate RF performances of the SP6T MEMS switch, as well as those of the single-pole single-throw RF MEMS series switch, we have performed small-signal modeling based on a parameter-extraction method. Accurate agreement between the measured and modeled RF performances demonstrates the validity of the small-signal model. The SP6T switch performed well with an isolation loss from -62.4 to -39.1dB and an insertion loss of 0.19-0.70 dB from dc to 6 GHz between the input port and each output port.     

A new 4H-SiC normally off lateral channel vertical JFET with extremely low power losses: source inserted double-gate structure with a supplementary highly doped region

A novel silicon carbide (SiC) normally off lateral channel vertical junction field-effect transistor (LC-VJFET), namely a source-inserted double-gate structure with a supplementary highly doped region (SHDR), was proposed for achieving extremely low power losses in high-power switching applications. The proposed architecture was based on the combination of an additional source electrode inserted between two adjacent surface gate electrodes and a unique SHDR in the vertical channel region. Two-dimensional numerical simulations for the static and resistive switching characteristics were performed to analyze and optimize the SiC LC-VJFET structures for this purpose. Based on the simulation results, the excellent performance of the proposed structure was compared with optimized conventional structures with regard to total power losses. Finally, the proposed structure showed about a 20% reduction in on-state loss (P/sub on/) compared to the conventional structures, due to the effective suppression of the JFET effect. Furthermore, the switching loss (P/sub sw/) of the proposed structure was found to be much lower than the results of the conventional structures, about a 75% /spl sim/ 95% reduction, by significantly reducing both input capacitance (C/sub iss/) and reverse transfer capacitance (C/sub rss/) of the device.     

Simulated fault injection: a methodology to evaluate fault tolerantmicroprocessor architectures

A simulation-based fault-injection methodology for validating fault-tolerant microprocessor architectures is described. The approach uses mixed-mode simulation (electrical/logic analysis), and injects transient errors in run-time to assess the resulting fault-impact. To exemplify the methodology, a fault-tolerant architecture which models the digital aspects of a dual-channel, real-time jet-engine controller is used. The level of effectiveness of the dual configuration with respect to single and multiple transients is measured. The results indicate 100% coverage of single transients. Approximately 12% of the multiple transients affect both channels; none result in controller failure since two additional levels of redundancy exist     

Modeling of power supply noise in large chips using the circuit-based finite-difference time-domain method

In this paper, a multilayered on-chip power distribution network consisting of two million passive elements has been modeled using the finite-difference time-domain (FDTD) method. In this method, a branch capacitor has been used. The use of the branch capacitor is important for simulating multilayered power grids. In addition, a method for including the CMOS inverter characteristics into the FDTD simulation has been presented. As an example of the application of this method, an H-tree clock network was simulated to compute the power supply noise distribution across an entire chip. Various scenarios with varying decoupling capacitances, load capacitances, number of clock buffers, and rise times have been analyzed to demonstrate the importance of circuit nonlinearity on power supply noise. Also, a method has been presented for analyzing package and board planes. Based on the methods presented, the interaction between chip and package has been discussed for capturing the resonant behavior that is otherwise absent when each section of the system is analyzed separately.