Single-phase to three-phase power conversion interface

This study proposes a single-phase to three-phase power conversion interface which converts the power from a single-phase utility to three-phase power for a three-phase load. The proposed single-phase to three-phase power conversion interface comprises a bridge-type switch set, a set of three-phase inductors, a transformer set and a set of three-phase capacitors. A current-mode control controls the switching of bridge-type switch set, to generate a set of nonzero-sequence (NZS) currents and a set of zero-sequence (ZS) currents. The transformer set is used to decouple the NZS currents and the ZS currents. The NZS currents are used to generate a high-quality three-phase voltage that supplies power to a three-phase load. The ZS currents flow to the single-phase utility so that the utility current is sinusoidal and in phase with the utility voltage. Accordingly, only a bridge-type switch set is used in the single-phase to three-phase power conversion interface to simply the power circuit. A prototype is developed and tested to verify the performance of the proposed single-phase to three-phase power conversion interface.     

An orthogonal peak detector for multiphase sinusoidal signals

A novel sinusoidal amplitude detector is proposed. This detector is based on the characteristic of orthogonal pairs. The salient point of this algorithm is that it can be applied in multiphase systems. The transient performance of this detector is very good, due to its fast response characteristic. The proposed detector is implemented and tested in three multiphase systems to verify its performance     

Second-order harmonic distortion and optimal fiber length in erbium-doped fiber amplifiers

The gain of an erbium-doped fiber amplifier (EDFA) operating in the kHz regimes and its second-order harmonic distortion (SBD) are studied. Using the rate and beam-propagation equations, we have shown the dependences of the distortion on the pump power, the modulation frequency, and the position along the fiber. Moreover, it is found that the SHD is the smallest when the fiber has an optimal length for the maximum gain. A relation between the optimal length and fiber parameters is presented for calculating easily the optimal fiber length in an EDFA.     

Force model identification for magnetic suspension systems viamagnetic field measurement

In magnetic suspension analysis, a simplified model of the current-to-distance relationship is not sufficient to design an optimal control. Due to the nonlinearity of the magnetic field, an accurate model, which is a function of the suspended object, suspension distance, core material, and operation conditions, is difficult to obtain. An improved force-model-identification method for magnetic suspension systems establishes reliable parameters for describing the magnetic field characteristics. The parameter for each test sample can be calculated under the specified operating conditions after some magnetic field measurements. The results lead to effective controller design for magnetic suspension systems     

Non-equilibrium chemical potential and stress-induced migration of polymers in tubes

A non-equilibrium chemical potential depending on the viscous pressure tensor is used to describe shear-induced diffusion in polymer solutions flowing along cylindrical tubes. Our results generalize previous ones in three main aspects: a Flory-Huggins expression for the equilibrium contribution to the chemical potential is used instead of the ideal-gas like expression, the full expression for the steady-state compliance of the solution is taken into account instead of only the polymer contribution, and the influence of the solute molecular mass is explicitly considered. As a qualitatively new result of considerable practical interest, it stands the prediction that in some circumstances, a dynamical instability may appear, which accelerates and enhances the separation process.     

Higher-order fluxes and the speed of thermal waves

By following the formalism of extended irreversible thermodynamics, we obtain a hierarchy of evolution equations for the higher-order fluxes in heat conduction. We study the influence of the higher-order fluxes on the speed of thermal waves in the second-, third and fourth-order approximations, as well as in the asymptotic limit of infinite higher-order fluxes.     

The decision model of task allocation for constrained stochastic distributed systems

In distributed systems, an application program is divided into several software modules, which need to be allocated to processors connected by communication links. The distributed system reliability (DSR) could be defined as the probability of successfully completing the distributed program. Previous studies about optimal task allocation with respect to DSR focused on the effects of the inter-connectivity of processors, the failure rates of the processors, and the failure rates of the communication links. We are the first to study the effects of module software reliabilities and module execution frequencies on the optimal task allocation. By viewing each module as a state in the Markov process, we build a task allocation decision model to maximize DSR for distributed systems with 100% reliable network. In this model, the DSR is derived from the module software reliabilities, the processor hardware reliabilities, the transition probabilities between modules, and the task allocation matrix. Resource constraints of memory space limitation and computation load limitation on each processor are considered. The constraint of total system cost, including the execution cost, the communication cost, and the failure cost, is also considered. We solve the problem by Constraint Programming using the ILOG SOLVER library. We then apply the proposed model to a case extended from previous studies. Finally, a sensitivity analysis is performed to verify the effects of module software reliabilities and processor hardware reliabilities on the DSR and on the task allocation decision.     

Investigation of effects of virtual reality environments on learning performance of technical skills

Practical training is what brings imagination and creativity to fruition, which relies significantly on the relevant technical skills needed. Thus, the current study has placed its emphasis on strengthening the learning of technical skills with emerging innovations in technology, while studying the effects of employing such technologies at the same time. As for the students who participated in the study, technical skills had been cultivated in the five dimensions of knowledge, comprehension, simulation, application, and creativity, in accordance to the set teaching objectives and the taxonomy for students learning outcome, while the virtual reality learning environment (VRLE) has also been developed to meet different goals as the various technical skills were being examined. In terms of the nature of technology, operation of machines, selection of process parameters, and process planning in technical skills, VRLE has also designed the six modules of “learning resource”, “digital content”, “collaborative learning”, “formative evaluation”, “simulation of manufacturing process”, and “practical exercise” in particular for providing students with assistance in the development on their technical skills on a specific, gradual basis. After assessing the technical skills that have been developed for the time period of one semester, the students have reported finding VRLE to be a significantly effective method when considering the three dimensions of “operation of machines”, “selection of process parameter”, and “process planning”, though not so much so when it came to the dimension of “nature of technology”. Among the six modules, “simulation of manufacturing process” and “practical exercise” were the two that were most preferred by students for the three dimensions considered.     

Antibacterial and biodegradable properties of polyhydroxyalkanoates grafted with chitosan and chitooligosaccharides via ozone treatment

Acrylic acid was grafted to ozone‐treated poly(3‐hydroxybutyric acid) (PHB) and poly(3‐hydroxybutyric acid‐co‐3‐hydroxyvaleric acid) (PHBV) membranes. The resulting membranes were further grafted with chitosan (CS) or chitooligosaccharide (COS) via esterification. These CS‐ or COS‐grafted membranes showed antibacterial activity against Escherichia coli, Pseudomonas aeruginosa, methicilin‐resistant Staphylococcus aureus (MRSA), and S. aureus. The antibacterial activity to E. coli was the highest, whereas the antibacterial activity to MRSA was the lowest among these four bacteria tested. Acrylic acid grafting can increase the biodegradability with Alcaligens faecalis, whereas CS and COS grafting can reduce the biodegradability. In addition, CS‐grafted PHBV membrane showed higher antibacterial activity and lower biodegradability than COS‐grafted PHBV membrane. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 12: 2797–2803, 2003