Filter networks for long cable drives and their influence on motor voltage distribution and common-mode currents

Filter networks for long cable drives have been studied in the last decade to solve the overvoltage problem at the motor terminals. However, little research has been dedicated to analyze their influence on the voltage distribution in the motor stator winding and on the circulation of the common-mode currents. In this paper, the project of dv/dt filters through simulation and analysis from previous work is extended, including the motor voltage distribution and common-mode current analysis. Simulation and experimental results are presented, demonstrating the usefulness of the filter networks on the motor overvoltage mitigation. Three filter topologies will be discussed and compared here: RLC filter at the motor terminals, RLC filter at the inverter output and reactor filter, which is extensively used in the industry. Simulation and experimental results demonstrate that the RLC filter at the inverter output is the most interesting solution among the main types of passive filter networks.     

Identification of hidden Markov models for ion channel currents.II. State-dependent excess noise

For pt.I see ibid., vol.46, no.7, p.1901 (1998). Hidden Markov modeling (HMM) techniques have been applied in the past few years to characterize single ion channel current events at low signal-to-noise ratios (SNRs). In this paper, an adaptation of the forward-backward procedure and Baum-Welch algorithm is presented to model ion channel kinetics under conditions of correlated and state-dependent excess noise like that observed in patch-clamp recordings. An autoregressive with additive nonstationary (ARANS) noise model is introduced to model the experimentally observed noise, and an algorithm called the Baum-Welch weighted least squares (BW-WLS) procedure is presented to re-estimate the noise model parameters along with the parameters of the underlying HMM. The performance of the algorithm is demonstrated with simulated data     

Gold-silicon nanofiber synthesized by femtosecond laser radiation for enhanced light absorptance

In this study, we devised a new concept for the precise nanofabrication of Au-Si fibrous nanostructures using megahertz femtosecond laser irradiation in air and atmospheric pressure conditions. The weblike fibrous nanostructures of Au thin layer on silicon substrate, which are proposed for the application of solar cells, exhibit a specific improvement of the optical properties in visible wavelength. Varying numbers of laser interaction pulses were used to control the synthesis of the nanofibrous structures. Electron microscopy analysis revealed that the nanostructures are formed due to the aggregation of polycrystalline nanoparticles of the respective constituent materials with diameters varying between 30 and 90 nm. Measurement of the reflectance through a spectroradiometer showed that the coupling of incident electromagnetic irradiation was greatly improved over the broadband wavelength range. Lower reflectance intensity was obtained with a higher number of laser pulses due to the bulk of gold nanoparticles being agglomerated by the mechanism of fusion. This forms interweaving fibrous nanostructures which reveal a certain degree of assembly.

PACS

81.05.Zx; 81.07.-b     

Analyzing unidentified locked-joint failures in kinematically redundant manipulators

Robots are frequently used for operations in hostile environments. The very nature of these environments, however, increases the likelihood of robot failures. Common failure-tolerance techniques rely on effective failure detection and identification. Since a failure may not always be successfully identified, or, even if identified, may not be identified soon enough, it becomes important to consider the behavior of manipulators with unidentified failures. This work investigates the behavior of robots experiencing unidentified locked-joint failures in a general class of tasks characterized by point-to-point motion. Based on the analysis, a procedure for workspace evaluation is developed that allows for the identification of regions in the manipulator's workspace in which tasks may be completed even with such failures. © 2005 Wiley Periodicals, Inc.     

Reciprocity-transposition-based sinusoidal pulsewidth modulation for diode-clamped multilevel converters

Modulation strategies for multilevel inverters have typically focused on synthesizing a desired set of three phase sinusoidal voltage waveforms using a fixed number of DC voltage levels. This results in the average current injection and hence the net power drawn from the multiple DC bus terminals to be unmatched and time varying. Subsequently, the DC-bus voltages are unregulated, requiring corrective control action to incorporated. In this paper, the principle of reciprocity transposition in introduced as a means for modeling the DC-bus current injection simultaneously as the modulation strategy is formulated. Furthermore, a new sinusoidal pulsewidth-modulation strategy that features constant and controllable current injection at the DC-bus terminals while maintaining output voltage waveform quality is introduced. The proposed strategy is general enough to be applied to converters with an even number of levels and an odd number of levels. Analytical results comparing the performance of the proposed modulator with a conventional multiple carrier modulator are presented for example multilevel converters with four and five levels. Computer simulation results verifying the analytical results are presented for a four-level converter.     

A MIMD implementation of a parallel Euler solver for unstructured grids

A mesh-vertex finite volume scheme for solving the Euler equations on triangular unstructured meshes is implemented on a MIMD (multiple instruction/multiple data stream) parallel computer. Three partitioning strategies for distributing the work load onto the processors are discussed. Issues pertaining to the communication costs are also addressed. We find that the spectral bisection strategy yields the best performance. The performance of this unstructured computation on the Intel iPSC/860 compares very favorably with that on a one-processor CRAY Y-MP/1 and an earlier implementation on the Connection Machine.The authors are employees of Computer Sciences Corporation. This work was funded under contract NAS 2-12961     

An interactive MOLP procedure using epsilon-constraints

Interactive multiobjective programming seeks to aid decision making in complex problems where it is difficult to explicitly state decision maker utility. A decision making aid is presented which uses a controlled pattern of objective attainments to generate new alternatives for decision maker selection. This procedure follows the concept of Steuer's algorithm, but avoids the need for filtering by use of constraints on objective attainment. In addition, the technique is not limited to original model corner points. The overall system seeks to obtain the benefits of Steuer's method, but requires only standard linear programming code, and adds the ability to identify improved solutions relative to Steuer's method when nonlinear utility exists.     

Multiple human cytochromes contribute to biotransformation of dextromethorphan in-vitro: role of CYP2C9, CYP2C19, CYP2D6, and CYP3A

Cytochromes mediating the biotransformation of dextromethorphan to dextrorphan and 3-methoxymorphinan, its principal metabolites in man, have been studied by use of liver microsomes and microsomes containing individual cytochromes expressed by cDNA-transfected human lymphoblastoid cells. In-vitro formation of dextrorphan from dextromethorphan by liver microsomes was mediated principally by a high-affinity enzyme (Km (substrate concentration producing maximum reaction velocity) 3-13 microM). Formation of dextrorphan from 25 microM dextromethorphan was strongly inhibited by quinidine (IC50 (concentration resulting in 50% inhibition) = 0.37 microM); inhibition by sulphaphenazole was approximately 18% and omeprazole and ketoconazole had minimal effect. Dextrorphan was formed from dextromethorphan by microsomes from cDNA-transfected lymphoblastoid cells expressing CYP2C9, -2C19, and -2D6 but not by those expressing CYP1A2, -2E1 or -3A4. Despite the low in-vivo abundance of CYP2D6, this cytochrome was identified as the dominant enzyme mediating dextrorphan formation at substrate concentrations below 10 microM. Formation of 3-methoxy-morphinan from dextromethorphan in liver microsomes proceeded with a mean Km of 259 microM. For formation of 3-methoxymorphinan from 25 microM dextromethorphan the IC50 for ketoconazole was 1.15 microM; sulphaphenazole, omeprazole and quinidine had little effect. 3-Methoxymorphinan was formed by microsomes from cDNA-transfected lymphoblastoid cells expressing CYP2C9, -2C19, -2D6, and -3A4, but not by those expressing CYP1A2 or -2E1. CYP2C19 had the highest affinity (Km = 49 microM) whereas CYP3A4 had the lowest (Km = 1155 microM). Relative abundances of the four cytochromes were determined in liver microsomes by use of the relative activity factor approach. After adjustment for relative abundance, CYP3A4 was identified as the dominant enzyme mediating 3-methoxymorphinan formation from dextromethorphan, although CYP2C9 and -2C19 were estimated to contribute to 3-methoxymorphinan formation, particularly at low substrate concentrations. Although formation of dextrorphan from dextromethorphan appears to be sufficiently specific to be used as an in-vitro or in-vivo index reaction for profiling of CYP2D6 activity, the findings raise questions about the specificity of 3-methoxymorphinan formation as an index of CYP3A activity.     

A current source PWM inverter with actively commutated SCRs

Conventional SCR based current source inverters suffer from poor waveform quality due to six step switching. Pulse width modulated current source inverters typically require gate turn off devices with reverse voltage blocking capability which have limited their application. In this paper, a new pulse width modulated current source inverter topology using one gate turn off switch and six SCRs is presented. The converter uses active commutation to realize pulse width modulation in a conventional SCR based current source inverter. Modulation techniques for the proposed inverter, simulation and experimental results are described in the paper. This topology is suitable for high performance, high power applications