A general method for designing the transformer of flyback converters based on nonlinear FEA of electromagnetic field coupled with external circuit

This paper presents a general method for designing the transformer of flyback switching AC-DC converters based on nonlinear finite element analysis (FEA) of electromagnetic field coupled with external circuit. For that, the variation patterns of the PWM duty ratio and the current flowing through the windings of transformer versus the input voltage are introduced first, and then several important principles for the design of the transformer are given by using analytical method. As the magnetic saturation and control delay possess heavy influence on the safety of the operation, a MATLAB/Simulink based simulation model, in which both the nonlinear differential inductance and the control delay are included, is built to predict the converter transient performance. The nonlinear differential inductance is calculated by a general program of nonlinear 2-D FEA in Matlab/Simulink surrounding. By running the model, the performances of the converter with different loads and input voltages are obtained. Simulation results are in good agreement with theoretical analysis

A unified hybrid model with two level networks for peak current mode controlled buck-boost converters operating in DCM and CCM

Theis paper presents a unified hybrid model with two level networks for peak current mode controlled buck-boost converters operating in continuous conduction mode (CCM) and discontinuous conduction mode (DCM). It is a network model with two levels in which both a detailed switching model and a small signal average model are included correspondingly. The nonlinearity of some electronic components and the parasitical effects of circuit elements are considered. The nonlinear inductance is calculated by finite element analysis (FEA). The dynamical performance of the buck-boost converter can be obtained from the detailed switching model in the first level network, and then the frequency domain performance can be obtained from the average model in the second level network. As an automatic mechanism of exchanging data between two models is proposed, all the performances can be obtained automatically. By implementing the proposed model in Simulink surrounding, both the large signal transient performance and the frequency domain behavior of converters are obtained efficiently

Isolation of Stilbenoids and Lignans from Dendrobium hongdie

Purpose: To isolate and characterize chemical compounds of biological importance from the whole plant of Dendrobium hongdie.Methods: The whole plants of Dendrobium hongdie was extracted with ethanol (EtOH) and separated using silica gel, Sephadex LH-20 and MCI gel to isolate the pure compounds. Characterization of the isolated compounds was achieved using 1H and 13C nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS).Results: Nine compounds including two phenanthrenes, three bibenzyls, a phenanthraquinone, two lignans and a sterol were isolated from the extract. The structures of the compounds were elucidated as nudol (1), gigantol (2), batatasin III (3), tristin (4), moscatin (5), ephemeranthoquinone (6), (-)- syringaresinol (7), liriodendrin (8) and β-sitosterol (9).Conclusion: Nine compounds have been successfully isolated from D. hongdie for the first time. This plant is a potential source of some useful phytochemicals.Keywords: Dendrobium hongdie, Isolation, Stilbenoids, Lignans, Phytochemical

Adventitious shoot regeneration from in vitro stem explants of Phellodendron amurense

An efficient in vitro plant regeneration system from stem explants was established in Phellodendron amurense. Factors influencing shoot regeneration from stems including culture medium type, combinations of plant growth regulators and carbon source in the medium were investigated. Adventitious shoot regeneration was significantly influenced by the type of medium. Murashige and Skoog medium (MS) was the best for promoting shoot regeneration, followed by Gamborg medium (B5) and woody plant medium (WPM). The combination of 6-benzyladenine (BA) and naphthaleneacetic acid (NAA) produced better results for shoot regeneration. The optimum shoot regeneration frequency (74.5%) and number of shoots per explant (12.3) was achieved using MS medium supplemented with 29.7 M BA and 5.8 M NAA. High concentrations of BA and NAA in the medium inhibited shoot formation. Among the three sugars tested, 20 g dm-3 glucose was the optimum for shoot regeneration. Rooting of regenerated shoots was successful on 1/4-strength MS medium with the addition of 15.4 M IBA. Almost 100% plantlets survived acclimatization after transferred to soil.Key words: Phellodendron amurense, callus, shoot regeneration, stem explants

Stenting in small coronary arteries: initial experience with the Gianturco-roubin II stent

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Phytochemical Constituents and Pharmacological Activities of Plants from the Genus Adiantum: A Review

Adiantum is a genus of ca. 200 species in the family Adiantaceae, distributed extensively across the world from cool temperate zones to hot tropical regions. A lot of Adiantum species have been used in traditional Chinese medicine to cure human and animal diseases including relief of internal heat or fever, enhancement of urination, removal of urinary calculus, and sundry other curative claims. Chemical studies have shown the presence of various classes of compounds, the main ones being triterpenoids, flavonoids, phenyl propanoids, steroids, alicyclic acids, lipids and long-chain compounds. The extract of this genus as well as pure compounds isolated from it have been demonstrated to possess multiple pharmacological activities such as analgesic, antinociceptive, anti-implantation, and antimicrobial activities. In this review, we have addressed the phytochemistry and pharmacological activities of the Adiantum species in order to collate existing information on this plant as well as highlight its multi-activity properties as a medicinal agent.Keywords: Adiantum species, Adiantaceae, Phytochemical constituents, Pharmacological activities

Isolation and Characterization of Batatasin III and 3,4’- Dihydroxy-5-methoxybibenzyl: A Pair of Positional Isomers from Sunipia scariosa

Purpose: To isolate and characterize chemical compounds of biological importance from the whole plant of Sunipia scariosa.Methods: The whole plant of Sunipia scariosa was extracted with methanol (MeOH) and chromatographed on silica gel and sephadex LH-20 to afford the pure isolates. High perfomance liquild chromatography (HPLC) was used for further purification of the isolated compounds. Characterization ofthe isolated compounds was achieved by 1H and 13C nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS).Results: Batatasin III (3,3’-dihydroxy-5-methoxybibenzyl) and  3,4’-dihydroxy-5-methoxybibenzyl, a pair of positional isomers, were isolated from the whole plant of Sunipia scariosa. The yields of the two isomers were 60 and 40 %, respectively, from the mixture of two  compounds.Conclusion: Batatasin III and 3,4’-dihydroxy-5-methoxybibenzyl, a pair of positional isomers were successfully isolated from the whole plant of Sunipia scariosa for the first time.Keywords: Sunipia scariosa, Batatasin III, 3,4’-Dihydroxy-5-methoxybibenzyl, Isomer

Optimization of a five-phase E-core bearingless flux-switching permanent magnet motor for flywheel batteries

© 2018 IEEE. In this paper, a five-phase E-core bearingless fluxswitching permanent magnet (BSFPM) motor for flywheel batteries is proposed and optimized. First, the structure and the principle of the BSFPM motor are described simply. Second, the trial and error method is used to obtain the most reasonable relationship of center tooth arc width and edge tooth arc width, and then the electromagnetic torque and suspension force after optimization are got. The motor after optimization has smoother five-phase flux-linkage and the disturbance of the torque and suspension force decrease

Comparison of legal system of occupational safety and health between Hong Kong and Mainland China

2012-2013 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Skew angle optimization analysis of a permanent magnet synchronous motor for EVs

© 2018 IEEE. In this paper, the skew angle of the permanent magnet synchronous motor (PMSM) for electric vehicles (EVs) is studied. The stability of the output torque of the driving motor is important for the EVs. The influence of skew angle on the Back-electromotive force, cogging torque, and output torque are studied by finite element analysis. The optimum skew angle of the stator slot is analyzed for the prototype. The results show that the proposed PMSM has better comprehensive performance after the optimization of the skew angle