Variable structure control of a robotic arm in the presence of uncertainty

Based on the theory of variable structure systems (VSS), control system design for the trajectory control of robotic systems is presented. It is assumed that the parameters of the system are uncertain and unknown frictional torques are acting at the various joints of the arm. For simplicity, the control of a three-link PUMA arm is considered. For trajectory following, two control laws, C_H and C_θ, based on the choice of coordinates of the end effector or joint angles as the controlled outputs, respectively, are derived. It is seen that whereas control C_θ has no singularity, certain singular surfaces arise where feedback elements of C_H become infinity. These singular surfaces describe the boundary of the reachable region (workspace). Digital simulation results are presented to show that accurate trajectory following can be accomplished using the control C_H or C_θ for large maneuvers of the arm in spite of the uncertainty in the system.     

Analysis and design consideration of mean temperature differential Stirling engine for solar application

This article presents a technical innovation, study of solar power system based on the Stirling dish (SD) technology and design considerations to be taken in designing of a mean temperature differential Stirling engine for solar application. The target power source will be solar dish/Stirling with average concentration ratio, which will supply a constant source temperature of 320 °C. Hence, the system design is based on a temperature difference of 300 °C, assuming that the sink is kept at 20 °C. During the preliminary design stage, the critical parameters of the engine design are determined according to the dynamic model with losses energy and pressure drop in heat exchangers was used during the design optimisation stage in order to establish a complete analytical model for the engine. The heat exchangers are designed to be of high effectiveness and low pressure-drop. Upon optimisation, for given value of difference temperature, operating frequency and dead volume there is a definite optimal value of swept volume at which the power is a maximum. The optimal swept volume of 75 cm³ for operating frequency 75 Hz with the power is 250 W and the dead volume is of 370 cm³.     

Thermal Conductivity of Exfoliated p-Type Bismuth Antimony Telluride

A bulk p-type thermoelectric compound with nominal composition Bi_0.5Sb_1.5 Te₃ has been exfoliated using dimethyl sulfoxide as a solvent. Samples have been prepared from the exfoliated platelets by pressing followed by sintering or hot pressing. The exfoliated nanoplatelets have been characterized for size distribution and composition using scanning electron microscopy and energy-dispersive spectrometry. The smallest size platelet was 40 nm, and the maximum in the size distribution was near 80 nm. The exfoliated platelets and sintered sample showed significant deficiency in Sb and Te. The nonstoichiometry in the composition of the exfoliated platelets indicates that the mechanism of exfoliation may not be between quintuplets only, with other layers also being active. The composition of the hot-pressed sample remained closer to that of the bulk. Results of x-ray diffraction indicated the presence of Bi₂Te₃ and Bi_0.5Sb_1.5Te₃ phases and pure Te and Sb. Residual porosity was observed in the hot-pressed and sintered samples. The thermal conductivity of the samples was measured by transient thermoreflectance. The results showed that the thermal conductivity of the hot-pressed sample was reduced by a factor of two compared with that of the bulk as a result of the presence of a high density of interfaces and residual porosity. The thermal conductivity of the sintered sample showed an increase above that of the bulk sample, which is explained by the change in composition due to loss of Sb and Te.     

Municipal solid waste compost application improves productivity, polyphenol content, and antioxidant capacity of Mesembryanthemum edule

Organic wastes were successfully used as soil amendment to improve agrosystems productivity. Yet, the effectiveness of this practice to enhance plant antioxidant capacities has received little attention. Here, we assess the effect of municipal solid waste (MSW) compost (at 40 t ha(-1)) on growth, polyphenol contents and antioxidant activities of Mesembryanthemum edule. MSW compost application significantly increased the soil contents of carbon, nitrogen, calcium, phosphorus and potassium. This was associated with higher nutrient (N, P, and K) uptake, which likely led to the significant improvement of the plant biomass and relative growth rate (RGR) (+93% on average) as compared to the control. In the same way, the fertilizing effect of the added organic matter significantly enhanced the antioxidant potential M. edule, assessed by radical scavenging activity, iron reducing power and β-carotene bleaching capacity. This was associated with significantly higher antioxidant contents, mainly total phenols and flavonoids. Heavy metal (Pb, Cd, Cu, and Zn) concentrations were slightly increased upon compost application, but remained lower than phytotoxic values. Overall, our results point out that short-term MSW compost application at 40 t ha(-1) is efficient in enhancing the productivity together with the antioxidant potentiality of M. edule without any adverse environmental impact.     

Microscopic measurement of cellular infiltration in the rheumatoid arthritis synovial membrane: a comparison of semiquantitative and quantitative analysis

BACKGROUND: A significant proportion of burn patients with inhalation injuries incur difficulties with airway protection, dysphagia, and aspiration. In assessing the need for intubation in burn patients, the efficacy of fiberoptic laryngoscopy was compared with clinical findings and the findings of diagnostic tests, such as arterial blood gas analysis, measurement of carboxyhemoglobin levels, pulmonary function tests, and radiography of the lateral aspect of the neck. OBJECTIVE: To determine if these patients were at risk for aspiration or dysphagia, barium-enhanced fluoroscopic swallowing studies were performed. DESIGN: Prospective study. SETTINGS: Burn intensive care unit in an academic tertiary referral center. MAIN OUTCOME MEASURES: Need for endotracheal intubation and potential for aspiration. RESULTS: Six (55%) of 11 patients had clinical findings and symptoms that indicated, under traditional criteria, endotracheal intubation for airway protection. Visualization of the upper airway with fiberoptic laryngoscopy obviated the need for endotracheal intubation in all 11 patients. These patients also failed to evidence an increased risk of aspiration or other swallowing dysfunction. CONCLUSIONS: In comparison with other diagnostic criteria, fiberoptic laryngoscopy allows differentiation of those patients with inhalation injuries who, while at risk for upper airway obstruction, do not require intubation. These patients may be safely observed in a monitored setting with serial fiberoptic examinations, thus avoiding the possible complications associated with intubation of an airway with a compromised mucosalized surface. In these patients, swallowing abnormalities do not manifest.     

A wavelet-based technique for discrimination between faults and magnetizing inrush currents in transformers

This paper presents the development of a wavelet-based scheme, for distinguishing between transformer inrush currents and power system fault currents, which proved to provide a reliable, fast, and computationally efficient tool. The operating time of the scheme is less than half the power frequency cycle (based on a 5-kHz sampling rate). In this work, a wavelet transform concept is presented. Feature extraction and method of discrimination between transformer inrush and fault currents is derived. A 132/11-kV transformer connected to a 132-kV power system were simulated using the EMTP. The generated data were used by the MATLAB to test the performance of the technique as to its speed of response, computational burden and reliability. The proposed scheme proved to be reliable, accurate, and fast.     

Synthesis of poly(methylmethacrylate)/montmorillonite nanocomposites via in situ intercalative suspension and emulsion polymerization

Summary Na-montmorillonite (MMT) with cation exchange capacity (CEC) of 90 mEq/100g was converted to MMT-CTAB and MMT-CPC forms by the intercalation of Cetyltrimethylammonium bromide (CTAB) and Cetylpyridinium chloride (CPC), respectively. The intercalation of these surfactants onto the basal space of the montmorillonite was evidenced by fourier transform infrared spectroscopy (FTIR) and x-ray diffraction (XRD). The intercalation of the CPC expanded the basal space from 12.19 A^o to 21.47 A^o while in case of CTAB it was expanded to 19.35 A^o only. The (MMT-CPC) was subsequently used as a host for the preparation of PMMA nanocomposites via intercalative suspension and emulsion polymerization of methylmethacrylate (MMA) using benzoyl peroxide (BPO) and potassium persulphate (PPS) individually and simultaneously. The use of BPO and PPS together invoked better exfoliation but the yield did not change appreciably in comparison with using either of the initiators alone. Different structures were obtained with the variation of the preparation conditions; exfoliated and intercalated nanocomposites which were characterized by XRD, transmission electron microscope (TEM), thermal gravimetric analysis (TGA), and differential scanning calorimeter (DSC). The resultant nanocomposites exhibited improved thermal stability relative to the equivalent macrocomposites. No glass transition temperature (Tg) could be detected for the prepared nanocomposites which was assumed to result from the restricted molecular motion of the polymer chains.