Energy-optimal gait analysis of quadruped robots

It is important for walking robots such as quadruped robots to have an efficient gait. Since animals and insects are the basic models for most walking robots, their walking patterns are good examples. In this study, the walking energy consumption of a quadruped robot is analyzed and compared with natural animal gaits. Genetic algorithms have been applied to obtain the energy-optimal gait when the quadruped robot is walking with a set velocity. In this method, an individual in a population represents the walking pattern of the quadruped robot. The gait (individual) which consumes the least energy is considered to be the best gait (individual) in this study. The energy-optimal gait is analyzed at several walking velocities, since the amount of walking energy consumption changes if the walking velocity of the robot is changed. The results of this study can be used to decide what type of gait should be generated for a quadruped robot as its walking velocity changes. This work was presented, in part, at the Sixth International Symposium on Artificial Life and Robotics, Tokyo, Japan, January 15–17, 2001.     

The Influence of Volts/Hertz Control on Filter Impedance Effects in VSI-Fed Induction Machines

The use of a transient volts/hertz controller can produce great improvement in the dynamic behavior of a voltage source inverter (VSI)-fed induction machine with a dc link filter. The effects of transient volts/hertz control are investigated and methods for selecting the proper controller gain GW for a wide range of systems are given. The information is presented in terms of 1) the upper and lower critical gains (GWCU and GWCL) needed to ensure stability, 2) a form of optimum gain (GWB) which gives the best dynamic performance for a specific machine and operating point, and 3) an acceptable gain (GWA) which gives acceptable dynamic performance over a range of operating conditions. Utilizing nondimensional parameters, eigen-values, and root locus plots, the values of the gains of the volts/hertz control are studied for a wide range of parameters. Graphs of the critical gains and methods of choosing GWB and GWA are presented. The results indicate that volts/hertz control can always be used to improve system dynamics, and with properly chosen controller gain the dynamic performance of the inverter-filter-motor system is typically better than the motor alone for a wide range of motor sizes and operating conditions.     

Orientation Control of ZnO Thin Film Prepared by CVD

A series of materials represented by the formula Ni_1;Mo_1–/3O₄, where -1/5 1/3, were prepared by calcination of layered ammonium nickel molybdates having a general formula (NH₄)H_2xNi_3-xO(OH)(MoO₄)₂, where 0 x 3/2. Phase determination using high temperature X-ray diffraction studies showed that the variable stoichiometry of the precursor phase that allowed for Ni/Mo ratios between 0.75 and 1.5 led to the formation of a single phase of the form Ni_1;Mo_1–/3O₄ following calcination. AC impedance spectroscopy was used to investigate the electronic conductivity of the materials. The defect chemistry of these ternary ionic materials was modeled to correlate the electronic conductivity with the structure.     

Transformation of bile acids and sterols by clostridia (fusiform bacteria) in Wistar rats

The effects on bile acid and sterol transformation of clostridia (fusiform bacteria), the dominant intestinal bacteria in rodents (ca. 10¹⁰ counts per g wet feces) were examined in Wistar rats. After inoculation of clostridia into germ-free rats and into rats previously inoculated solely with Escherichia coli, most of the endogenous bile acids were deconjugated, and cholic acid and chenodeoxycholic acid were 7α-dehydroxylated to deoxycholic acid and lithocholic acid, respectively. Tauro-β-muricholic acid, another major bile acid in rats, was deconjugated, but only part of it (ca. 30%) was transformed into hyodeoxycholic acid. Cholesterol and sitosterol were also reduced to coprostanol and sitostanol, respectively. Escherichia coli transformed neither bile acids nor sterols. These data suggest that clostridia play an imporant role in the formation of secondary bile acids and coprostanol in rats.     

Structural changes of Nb2O5 and V2O5 as rechargeable cathodes for lithium battery

The structural changes of T-Nb₂O₅ and V₂O₅ cathodes with discharge and recharge were investigated by X-ray photoelectron spectroscopy (ESCA) and X-ray diffractometory etc.ESCA spectra of the discharge products shows that M⁵⁺ is reduced to a lower valence state such as M⁴⁺ on the discharge, and the chemical bond between Li⁺ inserted into the oxide and O^2? of the oxide exhibits a higher ionic character than that of Li₂O. X-ray diffraction measurement shows that T-Nb₂O₅ gives the reversible structural change accompanying the disorder and order of the atomic arrangement on the charge-discharge cycling. On the other hand, V₂O₅ takes two discharge steps, within the 1st step of which it gives the reversible lattice change along b-axis caused by the intercalation of Li⁺ into the oxide layer, whereas within the 2nd step it is considered that the reaction in the charge-discharge takes place in the vicinity of the surface of the oxide particle. In both oxides, ternary phases such as Li_xM₂O₅ are produced as discharge products, where x is at least 2 for Nb₂O₅ and x is at least 3 for V₂O₅.     

Substituent effects in heterogeneous catalysis: VIII. Reactions of 2-methyl- and 2-ethylcyclohexanone with deuterium catalyzed by platinum metals

2-Methyl and 2-ethyl derivatives of cyclohexanone were allowed to react with deuterium in tBuOD using platinum group metals as catalysts. The product alcohols and the remaining ketone were examined by mass spectrometry. Over Ru, Os, and Ir, the simple addition of two deuterium atoms to the carbonyl linkage was predominant, accompanied by little isotopic exchange. Over Pt, however, isotopic exchange was significant and over Rh and Pd quite extensive. The samples obtained over Rh and Pd were further analyzed by NMR spectroscopy to determine the loci of the incorporated deuterium atoms. Deuterium exchange over Pd was almost entirely confined to the C(2) and C(6) positions, while that over Rh was smeared beyond these positions. These results can be accounted for by assuming the intermediacy of π-absorbed π-oxaallylic species on Pd and of αβ-diadsorbed species on Rh.     

Circuit realisation of negative-impedance convertor at v.h.f.

A circuit realisation of a v.h.f. negative-impedance convertor (n.i.c.) is presented. Using simultaneous multiple negative feedback, a stable operation is obtained to approximately 15% of fT. Using transistors with an fT of 1.1 GHz, the realised n.i.c. circuit operates to 160 MHz.