Analysis and design of DSP-based dual-loop controlled UPS inverters

This paper presents a novel digital dual-loop control scheme of the PWM (Pulse with modulate) inverter. Deadbeat control technique are employed to enhance the performance. Half switching period delayed sampling and control timing strategy is used to improve the system dynamic response. Simulation and experimental results presented in the paper verified the validity of the proposed control scheme.     

Indirect estimation of cable tension during gymnastic movements on rings

Knowledge of external forces acting on an athlete is often required to study performance and injury mechanisms, but direct measurements are difficult to obtain. While transducers in the rings cables typically measure external forces experienced by gymnasts performing static balances and swinging movements on rings, this solution is not always acceptable and an accurate technique that does not hinder the gymnasts’ performances is desirable. This study evaluates a video-based technique for estimating cable tension on the rings apparatus. Static loading of a rings frame coupled with a planar video analysis of the mandatory damped elastic devices (DEDs) provided a tension-deflection calibration curve. Three-dimensional video and cable tension data were obtained for two male gymnasts performing static balances and dynamic swinging movements. Cable tension was measured using a force link while a planar video analysis determined time histories of the DED deflections. Combined cable tension time histories were estimated fromrelative DED deflections coupled with the tension-deflection calibration curve and the orientation of the rings cables, and were compared to measured values to evaluate the proposed technique. For static balances the RMS difference between measured and estimated combined cable tension was 83 N. For dynamic swinging movements the maximum RMS difference was 189 N, equivalent to a 4% difference when expressed as a percentage of the peak value. The indirect video-based technique developed in this study accurately estimates combined cable tension throughout movements on rings and may be considered for studies where a remote measurement is required. There is potential for the technique to be extended to other sporting situations, where indirect accurate estimates of external forces acting on an athlete are needed.     

Comparison of numerical and analytical solutions for fly casting dynamics

This paper presents an approximate analytical model of the dynamics of a tapered fly line during a standard overhead cast. During casting, the line forms a nonlinear propagating wave that is frequently referred to as a ‘loop’ by fly casters. The geometry of the loop is described by three distinct parts: a straight bottom segment (attached to a stationary fly rod), a semi-circular segment that is propagating (i.e. the loop), and a straight top segment that is also propagating, (i.e. the traveling line). A fly (particle) is attached at the end of the traveling line. A work-energy balance yields the velocity of the fly as a function of the length of the traveling line. For a uniform fly line (level line), a closed-form solution is found, while for a tapered fly line, the solution is obtained by quadrature. A critical loop diameter arises in the analysis, and it determines whether the final velocity of the fly is greater or lesser than the initial velocity of the traveling line. The analytical solutions are critically compared against numerical solutions of a general model for fly line dynamics that relaxes many of the assumptions employed in the analytical model. The agreement between the two solutions remains close during the loop propagation phase, provided a significant amount of fly line remains in the traveling line. However, as the traveling line vanishes and the loop ‘turns over’, the two solutions diverge abruptly due to the many simplifying assumptions employed in the analytical model.     

Cycling on rollers: influence of tyre pressure and cross section on power requirements

The resistance against a cyclist while riding on rollers is due mainly to rolling resistance produced by the deformation of the tyre as it rolls against small diameter drums. Resistance is then combined with wheel speed to set power output. The effect of tyre pressure and cross-section on power was investigated by systematically altering the pressure (552 kPa, 690 kPa, and 827 KPa) in a 20c, 23c, 25c, and 28c tyre of the same design while riding at a wheel speed of 45 kph. Average power over 1 minute was measured with a Power Tap Hub (Tune Corporation, Cambridge, Massachusetts, USA) on five occasions. Statistical significance was evaluated at p < 0.05. Power requirements increased significantly with each reduction in tyre pressure for all tyres and pressures except the 25c between 690 and 827 kPa. The 20c tyre required significantly more power from the cyclist at each tested tyre pressure when compared to the other tyres (which were not different from each other). The differences in resistance from tyre size were not observed when ridden on the road. Additionally, a slightly different tyre design from the same manufacturer responded similarly in the 20c, but was significantly different in the 23c size. It was also observed that power requirements increased significantly when both the wheels were ridden on the rollers as compared to just the rear wheel. These results indicate that the power requirements may be significantly altered by the cyclist by adjusting tyre pressure, tyre cross-section size, tyre type, and with the number of wheels contacting the rollers. However, the magnitude of these power requirements may not be suitable for intense workouts of trained cyclists.     

Editorial zum Themenheft: ,,Datenbanksysteme”

Ohne Zusammenfassung     

Personal digital assistant-based drug information sources: potential to improve medication safety.

OBJECTIVES: This study compared the potential for personal digital assistant (PDA)-based drug information sources to minimize potential medication errors dependent on accurate and complete drug information at the point of care. METHODS: A quality and safety framework for drug information resources was developed to evaluate 11 PDA-based drug information sources. Three drug information sources met the criteria of the framework: Eprocrates Rx Pro, Lexi-Drugs, and mobileMICROMEDEX. Medication error types related to drug information at the point of care were then determined. Forty-seven questions were developed to test the potential of the sources to prevent these error types. Pharmacists and physician experts from Creighton University created these questions based on the most common types of questions asked by primary care providers. Three physicians evaluated the drug information sources, rating the source for each question: 1=no information available, 2=some information available, or 3 = adequate amount of information available. RESULTS: The mean ratings for the drug information sources were: 2.0 (Eprocrates Rx Pro), 2.5 (Lexi-Drugs), and 2.03 (mobileMICROMEDEX). Lexi-Drugs was significantly better (mobileMICROMEDEX t test; P=0.05; Eprocrates Rx Pro t test; P=0.01). CONCLUSION: Lexi-Drugs was found to be the most specific and complete PDA resource available to optimize medication safety by reducing potential errors associated with drug information. No resource was sufficient to address the patient safety information needs for all cases.     

Euclidean Geometry in Two Medieval Islamic Encyclopaedias

Two early encyclopaedic treatises, written in Arabic, include extensive discussion of geometry. Although both the Rasā'il Ikhwān al-Safā' and the Kitāb al-Shifā' fall within the Euclidean tradition, their style and content differ radically. The Neo-Pythagorean and Neo-Platonic Ikhwān al-Safā' place mathematics at the head of their encyclopaedia, but develop their discussion of geometry using a "sub-Euclidean" approach. Ibn Sīnā, whose orientation is broadly Aristotelian, includes an epitome of Euclid's Elements in its entirety, yet modifies the text at numerous points.