Resonant snubber based soft-switching inverters for electric propulsion drives

This paper summarizes recently developed soft-switching inverters and proposes two alternative options for electric propulsion drives. The newly developed soft-switching inverter employs an auxiliary switch and a resonant inductor per phase to produce a zero voltage across the main switch so that the main switch can turn on at the zero-voltage condition. Both the auxiliary switch and the resonant inductor are operating at a fractional duty, and thus are small in size as compared to the main inverter circuit components. Operation modes in a complete zero-voltage switching cycle for the single-phase soft-switching inverter are described in detail with graphical explanations. The circuit operation was first verified by a computer simulation and then tested with an 1-kW single-phase and an 100-kW three-phase inverters. Experimental results are presented to show the superior performance in efficiency improvement, EMI reduction, and dv/dt reduction of the proposed soft-switching inverters

A new method for microwave generation and data transmission using DFB laser based on fiber bragg gratings

A novel architecture for microwave/millimeter-wave signal generation and data modulation using a fiber-grating-based distributed feedback laser has been proposed in this letter. For demonstration, a 155.52-Mb/s data stream on a 16.9-GHz subcarrier has been transmitted and recovered successfully. It has been proved that this technology would be of benefit to future microwave data transmission systems. © 2006 IEEE

Simple technologies for fabrication of low-loss silica waveguides

A simple and reproducible technology is developed for the fabrication of low-loss silica waveguides on silicon substrates. The guiding layer is formed by changing the Si-O ratio composition of the SiO/sub 2/ layer. The waveguides can be made to have a good match to either optical fibres or guided-wave devices in III-V compound semiconductor

Multilevel converters for power system applications

Multilevel converters are emerging as a new breed of power converter options for power system applications. These converters are most suitable for high voltage high power applications because they connect devices in series without the need for component matching. One of the major limitations of the multilevel converters is the voltage unbalance between different levels. To avoid voltage unbalance between different levels, several techniques have been proposed for different applications. Excluding magnetic-coupled converters, this paper introduces three multilevel voltage source converters: (1) diode-clamp, (2) flying-capacitors, and (3) cascaded inverters with separate dc sources. The operation principle, features, constraints, and potential applications of these converters will be discussed

Adaptive online deployment for resource constrained mobile smart clients

Nowadays mobile devices are more and more used as a platform for applications. Contrary to prior generation handheld devices configured with a predefined set of applications, today leading edge devices provide a platform for flexible and customized application deployment. However, these applications have to deal with the limitations (e.g. CPU speed, memory) of these mobile devices and thus cannot handle complex tasks. In order to cope with the handheld limitations and the ever changing device context (e.g. network connections, remaining battery time, etc.) we present a middleware solution that dynamically offloads parts of the software to the most appropriate server. Without a priori knowledge of the application, the optimal deployment is calculated, that lowers the cpu usage at the mobile client, whilst keeping the used bandwidth minimal. The information needed to calculate this optimum is gathered on the fly from runtime information. Experimental results show that the proposed solution enables effective execution of complex applications in a constrained environment. Moreover, we demonstrate that the overhead from the middleware components is below 2%

Water vapor deposition from the inner gas coma onto the nucleus of Comet 67P/Churyumov-Gerasimenko

Rosetta has detected water ice existing on the surface of Comet 67P/Churyumov-Gerasimenko in various types of features. One of particular interest is the frost-like layer observed at the edge of receding shadows during the whole mission, interpreted as the recondensation of a thin layer of water ice. Two possible mechanisms, (1) subsurface ice sublimation and (2) gas coma deposition, have been proposed for producing this recondensation process and diurnal cycles of water ice. Previous studies have demonstrated both mechanisms based on simplified models. More precise and modern models are yet insufficient when addressing the gas-coma-deposition mechanism. We aim to study the recondensation from the inner water gas coma of the 67P/Churyumov-Gerasimenko with more physical constraints including the OSIRIS images, nucleus shape model, and insolation conditions. We compute, for the first time, the backflux distributions from the coma with various boundary conditions. Numerical simulations of this gas-coma-deposition process show that the equivalent water ice deposition can be up to several microns in an hour of accumulation time close to the perihelion passage, which is comparable with the simulation results of the other subsurface-ice sublimation mechanism

Enhancement of in vitro growth of papaya multishoots by aeration

Efficient micropropagation of papaya (Carica papaya L.) has become crucial for multiplication of specific sex types of papaya or transgenic lines resistant to virus infection. In this study, aeration at different intervals with a 0.02 mu m filter disc in the closure of culture flasks ensured exchange of gas components. The effect of aeration on development of multibuds to multishoots was investigated. Multibuds grown, in culture flasks after one-week without aeration followed by a two-week aeration treatment caused a 41% increase in the number of shoots greater than or equal to 0.5 cm, 42% increase in leaf expansion, and 17% increase in leaf numbers in comparison with unaerated materials. Ethylene and oxygen concentrations in the culture flasks were measured by gas chromatography and oxygen electrode at weekly intervals during the culture period. Oxygen concentrations were slightly different between aerated and unaerated culture flasks. Ethylene in the unaerated flask reached the highest level (0.11 ppm) 2 weeks after the treatment, while accumulation of ethylene in the aerated flasks was not detected. The multishoots grown for 3 weeks without aeration showed growth retardation on leaves and epinasty on petioles

Induced four fold anisotropy and bias in compensated NiFe/FeMn double layers

A vector spin model is used to show how frustrations within a multisublattice antiferromagnet such as FeMn can lead to four-fold magnetic anisotropies acting on an exchange coupled ferromagnetic film. Possibilities for the existence of exchange bias are examined and shown to exist for the case of weak chemical disorder at the interface in an otherwise perfect structure. A sensitive dependence on interlayer exchange is found for anisotropies acting on the ferromagnet through the exchange coupling, and we show that a wide range of anisotropies can appear even for a perfect crystalline structure with an ideally flat interface.Comment: 7 pages, 7 figure

A delta configured auxiliary resonant snubber inverter

A delta ({Delta}) configured auxiliary resonant snubber inverter is developed to overcome the voltage floating problem in a wye (Y) configured resonant snubber inverter. The proposed inverter is to connect auxiliary resonant branches between phase outputs to avoid a floating point voltage which may cause over-voltage failure of the auxiliary switches. Each auxiliary branch consists of a resonant inductor and a reverse blocking auxiliary switch. Instead of using an anti-paralleled diode to allow resonant current to flow in the reverse direction, as in the Y-configured version, the resonant branch in the {Delta}-configured version must block the negative voltage, typically done by a series diode. This paper shows single-phase and three-phase versions of {Delta}-configured resonant snubber inverters and describes in detail the operating principle of a single-phase version. The extended three-phase version is proposed with non-adjacent state space vector modulation. For hardware implementation, a single-phase 1-kW unit and a three-phase 100-kW unit were built to prove the concept. Experimental results show the superiority of the proposed topology

Post-Newtonian SPH calculations of binary neutron star coalescence. I. Method and first results

We present the first results from our Post-Newtonian (PN) Smoothed Particle Hydrodynamics (SPH) code, which has been used to study the coalescence of binary neutron star (NS) systems. The Lagrangian particle-based code incorporates consistently all lowest-order (1PN) relativistic effects, as well as gravitational radiation reaction, the lowest-order dissipative term in general relativity. We test our code on sequences of single NS models of varying compactness, and we discuss ways to make PN simulations more relevant to realistic NS models. We also present a PN SPH relaxation procedure for constructing equilibrium models of synchronized binaries, and we use these equilibrium models as initial conditions for our dynamical calculations of binary coalescence. Though unphysical, since tidal synchronization is not expected in NS binaries, these initial conditions allow us to compare our PN work with previous Newtonian results. We compare calculations with and without 1PN effects, for NS with stiff equations of state, modeled as polytropes with $\Gamma=3$. We find that 1PN effects can play a major role in the coalescence, accelerating the final inspiral and causing a significant misalignment in the binary just prior to final merging. In addition, the character of the gravitational wave signal is altered dramatically, showing strong modulation of the exponentially decaying waveform near the end of the merger. We also discuss briefly the implications of our results for models of gamma-ray bursts at cosmological distances.Comment: RevTeX, 37 pages, 17 figures, to appear in Phys. Rev. D, minor corrections onl