Mitigating Circulating Common-Mode Currents Between Parallel Soft-Switched Drive Systems

A mathematical model that Is developed for a generalized drive system, including common-mode passive and active elements, is used to explore the issues of paralleling soft-switched resonant dc-link drive systems. Differences between the modulation pattern for each drive system cause common voltage disturbances, which lead to significant circulating currents between the drive systems. Control methods for actively compensating for common-mode circulating currents or reducing the common- mode voltage disturbances are investigated. Practical modifications to the drive system controls are implemented to reduce the circulating currents between paralleled systems.     

Pressure distribution in an assembly of wooden cylinders with various aspect ratios under uniaxial confined compression

Understanding how forces propagate in granular assemblages is important for equipment design and process control in many technologies. Yet, it remains poorly understood. In this study, a cuboidal assembly comprising cylinders of various lengths (aspect ratios AR ranging from 0.9 to 3.6) were subjected to uniaxial confined compression tests. Samples were vertically compressed until the top platen exerted a pressure of 50 kPa on the uppermost particles. This maximum pressure corresponds to the hydrostatic pressure of an approximately 15 m high column of chopped wood that may be encountered in real storage structures. The nonlinear loading curves were obtained depended on the aspect ratios of the cylinders. The modulus of elasticity, calculated from the linear elastic part of the stress–strain curve, monotonically decreased from 10.2 to 8.6 MPa as the aspect ratio increased from 1.2 to 3.6. The elastic modulus and volume fraction exhibited similar trends as functions of the aspect ratio. The horizontal-to-vertical pressure ratio was calculated as the horizontal pressure exerted on the wider walls to the vertical pressure exerted on the top lid during loading–unloading cycles. For ARs up to 3.6, the pressure ratio was approximately 0.31; for the longest cylinders (AR = 3.6), it decreased to approximately 0.27, probably because the assumption of the representative chamber volume was invalidated at this AR.     

Non-minimum-phase property of N-trailer kinematics resulting from off-axle interconnections

Off-axle interconnections between segments of N-trailer vehicles may imply specific oscillatory behaviour of trailers during vehicle manoeuvres. The paper reveals that this kind of oscillations is a direct consequence of the non-minimum-phase property of vehicle kinematics resulting from application of off-axle interconnections between vehicle segments. First we show the non-minimum-phase property for dynamics of a single pair of interconnected segments, and then how it propagates along the N-trailers equipped with arbitrary number of off-axle interconnections. By referring to available results for linear systems, we locally analyse linearly approximated vehicle kinematics around selected steady-motion conditions. We focus on the time-response effects like undershooting, zero-crossing, and overshooting caused by off-axle interconnections. We show how the number and type of interconnections influence the non-minimum-phase effects. Numerical results obtained for three-trailer kinematics validate theoretical considerations providing some quantitative view of the problem. Short discussion has been provided on the possible control-level consequences resulting from the non-minimum-phase property of N-trailers.     

Effect of metal purity and testing procedure on surface tension measurements of liquid tin

The surface tension of liquid tin of three different grades of purity (99.85, 99.96, and 99.999%) was measured by the classical sessile drop method over the temperature range 523–1023 K, in heating and cooling regimes. The results obtained show that the metal purity affects the values of surface tension and its temperature dependence. The highest values of surface tension and smooth linear temperature dependence were obtained in cooling regime for tin of the highest purity. With increasing content of impurities, both surface tension and its temperature coefficient decrease while the scatter of the data increases. The surface tension values measured on heating regime show higher scatter, compared to those obtained in cooling regime, and the temperature dependence of the surface tension is curvilinear rather than linear.     

The effect of change of voltage acceleration on temperatureactivation of oxide breakdown for ultrathin oxides

We report the effect of change of voltage acceleration on temperature dependence of oxide breakdown for ultra-thin oxides below 6 nm. The time- or charge-to-breakdown (T_BD/Q_BD) is directly measured over a wide range of temperatures (-30°C to 200°C) for several fixed voltages using different area capacitors and long-term stress. Using extensive experimental evidence, we unequivocally demonstrate that this strong temperature dependence of oxide breakdown on ultra-thin oxides is not a thickness effect as previously suggested at least for thickness range investigated in this work. It is a consequence of two experimental facts: 1) voltage-dependent voltage acceleration and 2) temperature-independent voltage acceleration within a fixed T_BD window. These results provide a coherent picture for T_BD in both voltage and temperature domains for ultra-thin oxides     

Electrocatalytic Determination of Glucose in a Ringer''s Solution by Pulse-Voltammetry

Improvement of the electrocatalytic method of glucose determination was achieved by applying the pulse voltammetry technique. This technique, compared. to previously applied cyclic voltammetry, enhances selectivity of a platinum-black working electrode for glucose measurement. A low catalytic load working electrode has been used which is less susceptible to poisoning and has longer term stability. With cyclic voltammetry previously applied, those electrodes were limited by their narrow concentration range for glucose detection. By applying a pulsing technique, these electrodes exhibit linearity up to a glucose concentration 200 mg/dl with correlation coefficients greater than 0.9. The pulse voltammetry diminishes interference by low molecular weight serum components such as serum urea. Concentrations from 20. to 40 mg/di had an interference of 4 percent compared to 40 percent with cyclic voltammetry. Further investigations are carried on to adopt pulse voltammetry for direct measurements of glucose in body fluids.     

PAN‐based fibers modified with two‐component ceramic nanoparticles

The authors determined conditions for manufacturing PAN precursor fibers containing a system of two nanoadditives, montmorillonite (MMT), and hydroxyapatite (HAp) in their structure. The PAN precursor fibers thus obtained are characterized by a tenacity of more than 30 cN/tex and a total volume of pores at the level of 0.29 cm³/g. Furthermore, it was found that the use of nanoadditives entails the remodeling of the paracrystalline structure of PAN fibers into a strictly crystalline one. This is accompanied by a decrease in spacing between MMT layers combined with their partial exfoliation. The fibers thus obtained, after being carbonized, will be used for medical applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009