Free volume and permeabilities of O2 and H2 in Nafion membranes for polymer electrolyte fuel cells

The mechanism of gas permeation in Nafion membranes for polymer electrolyte fuel cells has been investigated from the viewpoint of free volume. Three different samples, a membrane with ionic exchange capacity (IEC) = 0.92 meq/g, and recast samples with IEC = 0.92 and 1.00 meq/g were used after drying. Free volume was quantified using the positron annihilation lifetime (PAL) technique and gas permeabilities were measured for O₂ and H₂ as functions of temperature and relative humidity. Good linear correlations between the logarithm of the permeabilities at different temperatures and reciprocal free volume indicate that gas permeation in dry Nafion is governed by the free volume. Nevertheless permeabilities are much smaller than the corresponding flexible chain polymer with a similar free volume size due to stiff chains of the perfluoroethylene backbone. In highly hydrated Nafion above 60% relative humidity, where the O₂ permeability varies oppositely to the free volume, gas permeation proved to be controlled by the gradual increase in overall flexibility of the Nafion–water system.     

KINEMATIC VISCOSITY-TEMPERATURE BEHAVIOR OF HEAVY TBP-FRACTIONS (455°C+) OF ARABIAN CRUDE OILS

A generalized kinematic viscosity-temperature correlation for undefined liquid heavy petroleum fractions has been developed to represent the data for a wide range of temperature from 100°C to 200°C. The correlation is based on the experimental kinematic viscosity data of true boiling point fractions of four Arabian crude oils. The characterization property required for estimation is 50% boiling point. The proposed correlation fits the experimental data with an overall absolute error of 6.1%. Experimental measurements of kinematic viscosity of heavy true boiling point fractions of Arabian crude oils were also obtained in order to develop the proposed correlation.     

Molecular characterization of erythrocyte glucose-6-phosphate dehydrogenase deficiency in Al-Ain District, United Arab Emirates

Operational skills involved in controlling a motor vehicle were measured in two groups of very healthy elderly drivers and a young control group to test the hypothesis that there are age-related declines in operational performance that may influence driver safety. An actual behind-the-wheel, standardized road test was employed using a motor vehicle equipped with sensors to record speed, braking activity, and lane position, as well as direction and magnitude of front-wheel and eye-movement excursions. The data from these sensors were used as dependent measures of operational performance. Older drivers made fewer steering and eye-movement excursions and drifted across the center line more frequently than the young control group. Younger drivers drove significantly faster and executed more braking applications than did their older counterparts. The motor-vehicle operational performance of older healthy drivers was related to visual-spatial attentional declines and the useful field of vision associated with the normal aging process.     

Conical magnetic bearings with radial and thrust control

Conical magnetic bearings with radial and thrust (axial) control are discussed. First a model of the conical bearing is made in state variable form. Airgap flux, airgap displacement, and velocity are used as state variables. A control method based on recent developments in control theory is proposed. The method is called Q-parameterization theory and is used to design a stabilizing controller for the system which, without control, is unstable in nature. The controller parameters are chosen using console (a software tandem for interactive optimization-based design) so that all design requirements are satisfied. Digital simulation was used to verify the proposed control method. Transient responses, forced responses in all three directions (vertical, horizontal, and axial), and the interactions between them are obtained. The results obtained are satisfactory and suggest the robustness of the proposed technique     

Asymptotics of Largest Components in Combinatorial Structures

Given integers m and n, we study the probability that structures of size n have all components of size at most m. The results are given in term of a generalized Dickman function of n/m.     

Direct Instantaneous Torque Control in Direct Drive Permanent Magnet Synchronous Motors—a New Approach

In this paper, a novel direct instantaneous torque control scheme for a direct drive (DD) permanent magnet synchronous motor (PMSM) is presented. A hybrid control structure combining the internal model principle and the variable structure control (VSC) approach is proposed. First, a variable structure torque controller is adopted to regulate the torque angle increment according to the torque feedback error. Second, the appropriate control voltage vector is determined using the reference stator flux vector and the estimated dynamic back electromotive force (EMF) vector, as an internal model, in a deadbeat control manner. Subsequently, better disturbance rejection can be obtained with the proposed cascaded control structure. To robustly obtain the instantaneous torque and flux information, a robust adaptive motor model is proposed. The Lyapunov stability theory is used to analyze the stability of the augmented robust adaptive motor model and to give a guideline for tuning model parameters. Experimental results are presented to demonstrate the validity and effectiveness of the proposed instantaneous torque control scheme.     

Optimisation of solar photovoltaic (PV) parameters using meta-heuristics

Microsystem Technologies - This paper presents a critical analysis of the meta-heuristic techniques used in various researches on the optimisation of photovoltaic (PV) parameters, which involves...     

Adaptive fuzzy fault-tolerant control using Nussbaum-type function with state-dependent actuator failures

Neural Computing and Applications - This paper presents an adaptive fuzzy fault-tolerant tracking control for a class of unknown multi-variable nonlinear systems, with external disturbances,...