Torque redistribution and time regulation methods for actuator of fault-tolerant parallel robots

In this article, we investigate and employ torque redistribution and time regulation approaches to track a preplanned trajectory while avoiding actuator saturation for redundantly actuated, fault-tolerant parallel robots encountering actuator failure. The torque redistribution method utilizes actuation redundancies (if available) after joint failure and/or saturation to alter the torque requirements of the joints so as to avoid saturation. The time regulation method is based upon the alteration of the time to completion of the defined joint-space trajectory. By searching for a suitable time scaling factor to change (reduce) the inertia load requirements, the robot attempts to slow down or speed up as it moves along the defined trajectory to avoid saturation. The preferred implementation strategy is to use the torque redistribution approach when redundancy is available and actuation capacity is sufficient, otherwise the time regulation approach is employed. For both methods, the computed torque technique, consisting of a model reference algorithm in the feedforward process, and a proportional plus integral plus derivative (PID) controller, to deal with modeling errors and disturbances in the feedback process, are utilized.     

Analysis of gross error rates in operation of commercial nuclear power stations

Experience in operation of US commercial nuclear power plants is reviewed over a 25-moth period. The reports accumulated in that period on events of human error and component failure are examined to evaluate gross operator error rates. The impact of such errors on plant operation and safety is examined through the use of proper taxonomies of error, tasks and failures. Four categories of human errors are considered; namely, operator, maintenance, installation and administrative. The computed error rates are used to examine appropriate operator models for evaluation of operator reliability. Human error rates are found to be significant to a varying degree in both BWR and PWR. This emphasizes the import of considering human factors in safety and reliability analysis of nuclear systems. The results also indicate that human errors, and especially operator errors, do indeed follow the exponential reliability model.     

Analysis of coherence,strain, thermal vibration and preferred orientation in carbons by X-Ray diffraction

In ideal graphitic layers the inter-atomic (or inter-unit cell) distances l and the number of atoms (or unit cells) n(l) at a distance from any atom (or unit cell) chosen as origin may be represented by sets l and n(l) which define the structure. In the defective lattice theory presented here the structure of diffusely scattering (the so-called amorphous) carbons are likewise defined by the two sets, however n(l)'s are modified by a probability (coherence probability) function g(l) and l's are modified for dispersion (strain effects). It is shown that the coherence probability function can be determined from the atomic radial distribution curves without a priori knowledge of distortion and temperature diffuse scattering. Analytical expressions have been developed that permit analysis of distortion and temperature diffuse scattering from the observed profiles of the diffuse peaks and from the atomic radial distribution functions. In analyzing the distortion, Gauss', Gauchy's and Laplace's distributions are considered. It is demonstrated that distortion could be responsible for the diffuseness of the diffraction profiles of carbons to a greater extent than the coherence probability, the so-called domain or particle size effect. It is also shown that the integrated intensities, I(φ), of the (00l) reflections of anisotropic, e.g. pyrolytic, carbons are related to the angle φ that the diffraction vector makes with the pole of the sample by I(φ) = K exp (?p²sin²φ) in which K is the proportionality constant and p is the characteristic parameter of the sample. The equation has a reasonably sound physical basis and has been found to be applicable to samples having a wide range of preferred orientations.     

Design of a small single-purpose nuclear desalination plant compatible with the local resources in the middle east

Present plans in the Middle East involve the construction of several nuclear power plants with desalination capabilities to provide power and water to meet the requirements of the anticipated growth in the industrial sector and development of new settlements to improve the socio-economical aspects of population distribution. This effort has been matched by a program initiated by the Development Consultants Association (DCA) to provide the necessary training, manpower and expertise necessary for adequate involvement in siting, design, construction and operation of both nuclear and desalination plants.

In this paper results of the preliminary stages of the design of a 2.6 million gallons per day (1000 cubic meters/day) single-purpose 40 MW thermal MSF-heavy water nuclear plant are reported. Design objectives and philosophy are reviewed. A descriprion is given of the neutronic, thermal, control and mechanical design parameters of the plant. The design is based on utilization of available local material, technology and manpower. The feasibility of production of heavy water in the fertilizer production plants and the extraction of natural uranium from the phospahate mines on the Red Sea coast are considered pointing out further stages of development and future plans.     

Effect of Low Concentration Sn Doping on Optical Properties of CdS Films Grown by CBD Technique

Thin and transparent films of doped cadmium sulfide (CdS) were obtained on commercial glass substrates by Chemical Bath Deposition (CBD) technique. The films were doped with low concentration of Sn, and annealed in air at 300 °C for 45 min. The morphological characterization of the films with different amounts of dopant was made using SEM and EDAX analysis. Optical properties of the films were evaluated by measuring transmittance using the UV-vis spectrophotometer. A comparison of the results revealed that lower concentration of Sn doping improves transmittance of CdS films and makes them suitable for application as window layer of CdTe/CIGS solar cells.     

Probing metabolic stability of CdSe nanoparticles: alkaline extraction of free cadmium from liver and kidney samples of rats exposed to CdSe nanoparticles

Cadmium selenide nanoparticles (CdSe NPs) exhibit novel optoelectronic properties for potential biomedical applications. However, their metabolic stability is not fully understood because of the difficulties in measurement of free Cd from biological tissues of exposed individuals. In this study, alkaline dissolution with tetramethylammonium hydroxide (TMAH) is demonstrated for selective determination of free Cd and intact NPs from liver and kidney samples of animals that were exposed to thiol-capped CdSe NPs. Aqueous suspensions of CdSe NPs (3.2 nm) were used to optimize the conditions for extracting free Cd without affecting NPs. Nanoparticles were found to aggregate when heated in TMAH without releasing any significant Cd to solution. Performance of the method in discriminating free Cd and intact NPs were verified by Dogfish Liver (DOLT-4) certified reference material. The samples from the animals were digested in 4 mL TMAH at 70 °C to extract free Cd followed by analysis of aqueous phase by ICP-MS. Both liver and kidney contained significant levels of free Cd. Total Cd was higher in the liver, while kidney accumulated mostly free Cd such that up to 47.9% of total Cd in the kidney was free Cd when NPs were exposed to UV-light before injection.