Feedback equivalence of control systems

Cartan's method of equivalence is applied to the problem of equivalence of 2-state systems with scalar control under feedback. The differential invariants produced by the method completely characterize equivalence classes. The phenomenon of linearizability is associated with the presence of infinite Lie pseudogroups. The generic non-linearizable case has a geometrically defined variational problem which yields a time optimal closed loop control.     

Partial oxidation of methane over Rh/supported-ceria catalysts: Effect of catalyst reducibility and redox cycles

Partial oxidation of methane (POM) was studied over Rh/(Ce_0.56Zr_0.44)O_2−x, Rh/(Ce_0.91Gd_0.09)O_2−x, Rh/(Ce_0.71Gd_0.29)O_2−x and Rh/(Ce_0.88La_0.12)O_2−x. The effect of catalyst reducibility and redox cycles was investigated. It was found that the type of doped-ceria support and its reducibility played an important role in catalyst activity. It was also observed that redox cycles had a positive influence on H₂ production, which was enhanced as the number of redox cycle increased. Results of carbon formation are discussed as a function of ionic conductivity. Temperature programmed reduction (TPR) profiles, BET surface area, ionic conductivity and XRD patterns were determined to characterize catalysts. Catalytic tests revealed that of the materials tested, Rh/(Ce_0.56Zr_0.44)O_2−x was the most active material for the production of syngas, which correlates with its TPR profile. It was observed that doping CeO₂ with Zr, rather than with La or Gd caused an enhanced reducibility of Rh/supported-ceria catalysts.     

Children's deliberateness of planning according to task circumstances.

89 children ages 4 to 9 solved mazes varying in the presumed appropriateness of advance or improvisational planning. Using a between-Ss design, children's performance was compared in a standard condition that stressed accuracy in problem solving (designed to increase the importance of advance planning to avoid errors) and a variation stressing speed (designed to favor improvisational planning). Performance was compared by varying maze structure in terms of whether errors in route choices could be identified from a search of a small portion of the maze (favoring improvisation) or from a search through the entire maze (favoring advance planning). Children's planning strategies were stable over trials and had predictable effects on error rates. Children's usage of deliberate planning strategies was related to the circumstances of the problem, with more advanced planning when the structure of the mazes and instructions favored that strategy. Children used less advance planning when speed was a consideration and when the maze structure allowed avoidance of errors without extensive search. Results show that children's planning strategies are adapted to circumstances, and suggest that older children may be more proficient in this adaptation than are younger children. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Factors associated with acute and chronic pain following traumatic spinal cord injuries

Previous studies have estimated that between 25% and 45% of people with spinal cord injury report severe levels of chronic pain. Few studies have examined this longitudinally. This study examines the primary pain sites, intensity and variability of perceived pain in 76 patients, 6 weeks post injury and 45 patients from the same cohort, 8 year post discharge. Demographic information reveals a close similarity with the database (40,000) from Stover and Fine's cohort (1986). Data was assessed using visual analogue scales, measures were also taken of functional independence (FIM), emotional status and coping. At 6 weeks post injury, most pain is sited in the thoracic spine area, and in the upper and lower limbs. At 1 year post discharge, most pain is reported to be in the thoracic spine area, the lumbar region and the chest. Twenty-three per cent of the 6 week group reported that the intensity of their pain was severe, whilst at 1 year, 41% of the sample complained of severe pain. Factors associated with the pain at both time points were explored using correlational analyses. The emotional, functional and psychological factors that predict pain severity were explored using multiple regression analysis. Twenty-four per cent of those reporting moderate to severe pain at 6 weeks post injury were still reporting pain at 1 year post discharge. This study examines the relative contribution of psychological factors in reported pain.     

Neurobehavioral indicators of early brain insult in high-risk neonates.

Neurobehavioral (NB) performance was evaluated in 248 neurologically at-risk neonates at neonatal intensive care unit discharge to investigate the relation between behavior and brain insult. Six brain insult groups were defined on the basis of findings from cranial ultrasonography and brainstem auditory evoked response tests. The NB evaluation consisted of a modification and condensation of the Einstein Neonatal NB Assessment Scale and the assessment of activated motor patterns described by Katona. Logistic regression analysis of normal vs. abnormal judgments of behavioral categories revealed that, independent of the effects of prematurity, different patterns of NB abnormalities were associated with different degrees and types of brain insult. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Analysis and design of integrated active circulator antennas

A study on the analysis and design of active integrated antennas based on active quasi-circulators is reported in this paper. The antenna consists of a novel hybrid active circulator and a short-circuited quarter-wavelength microstrip antenna, which combine to form an active antenna with transmit and receive action at the same frequency. A full-wave model of the configuration using the extended finite-difference time-domain method is devised to analyze its operation, to study parasitic electromagnetic coupling effects, and to derive design guidelines. Experimental results for a hybrid model are also presented     

Elastic buckling of elliptical tubes

Hot-rolled and cold-formed structural steel tubular members of elliptical cross-section have recently been introduced into the construction sector. However, there is currently limited knowledge of their structural behaviour and stability, and comprehensive design guidance is not yet available. This paper examines the elastic buckling response of elliptical hollow sections in compression, which has been shown to be intermediate between that of circular hollow sections and flat plates. The transition between these two boundaries is dependant upon both the aspect ratio and relative thickness of the section. Based on the results of numerical and analytical studies, formulae to accurately predict the elastic buckling stress of elliptical tubes have been proposed, and shortcomings of existing expressions have been highlighted. Length effects have also been investigated. The findings have been employed to derive slenderness parameters in a system of cross-section classification for elliptical hollow sections, and form the basis for the development of effective section properties for slender elliptical tubes.