Performance of Halbach magnetized brushless AC motors

The steady-state performance of Halbach magnetized brushless ac machines when operated in constant torque and flux-weakening modes is investigated both theoretically and experimentally, with particular emphasis on the influence of cross-coupling magnetic saturation on the torque capability

A hybrid time-domain discontinuous Galerkin-boundary integral method for 3-D electromagnetic scattering analysis

published_or_final_versio

Phenolic Compound Profiles in Grape Skins of Cabernet Sauvignon, Merlot, Syrah and Marselan Cultivated in the Shacheng Area (China)

The phenolic compounds in the grape skins of Cabernet Sauvignon (CS), Merlot (ML), Syrah (SY) and Marselan (MS) from Shacheng, in China, were compared using HPLC-MS/MS. The results showed that the types and levels of phenolic compounds varied greatly with cultivars. Malvidin derivatives were the main anthocyanins. CS and ML showed a higher content of malvidin-3-O-(6-O-acetyl)-glucoside than malvidin-3-O-(trans-6-O- coumaryl)-glucoside, while SY and MS differed from CS and ML. ML had higher delphinidin and cyanidin derivatives, SY had higher peonidin derivatives, while malvidin and petunidin were higher in MS. The total content of flavonols, flavan-3-ols, phenolic acids and stilbenes in grape skins showed no difference among CS, ML and MS. Isorhamnetin-3-O-glucoside (CS, ML, MY), quercetin-3O-glucoside (SY), procyanidin trimer (SY, MS), procyanidin dimer (CS, ML), syringetin-3-O-glucoside, trans-cinnamic acid and resveratrol were the most abundant non-anthocyanin phenolic compounds. Cluster analysis showed that CS and ML, and SY and MS had similar phenolic profiles

Combining nano-silicon with oxide glass in anodes for Li-ion batteries

Vanadium-tellurite glasses (VT) have emerged as promising anode materials for lithium-ion batteries (LIBs). Despite this, the Li-ion storage capacity of the VT glass anode is still insufficient to meet the demands for the next generation of advanced LIBs. Silicon (Si) anode has ultrahigh theoretical capacity but suffers from significant volume expansion during lithiation and delithiation. In this work, we combined Si nanoparticles with VT glass to prepare Si@VT composite anode for LIBs. The composite was produced through heat-treatment at different temperatures, some of which were hot-pressed under the isostatic pressure of 100 MPa. The Si@VT composite exhibited a synergistic effect that integrated the strengths of both VT glass and Si, resulting in a substantial enhancement of its electrochemical performance. The systematic characterizations of the composite-based anodes revealed the optimal conditions for fabricating the high-performance Si@VT composite: a silicon fraction of 10 wt% and a hot-pressing temperature of 620 K. This composite stood out as the optimal choice, exhibiting a capacity of 353 mA h g−1 at 1 A g−1 after 1000 cycles. This capacity surpasses that of VT glass anode by over threefold and that of pure Si anode by twelvefold.</p

Rotor shaping method for torque ripple mitigation in variable flux reluctance machines

In this paper, four rotor shaping methods, i.e., eccentric circular, inverse cosine, inverse cosine with third harmonic, and multi-step shaping methods, are developed and compared for torque ripple mitigation in variable flux reluctance machines (VFRMs). By using a 6-stator-pole/7-rotor-pole (6/7) VFRM as an example, the design criterions and capabilities of these four methods are illustrated. It is found that all the rotor shaping methods are capable of torque ripple mitigation and applicable to all the VFRMs except those with 6 k /(6 i ± 2) k ( k , i = 1, 2, 3…) stator/rotor pole combinations. Moreover, the inverse cosine with third harmonic and multi-step shaping methods are found to have the best performance. They are able to reduce the torque ripple by 90% at a cost of only 3% torque density reduction. A 6/7 VFRM with both conventional and shaped rotors is prototyped and tested for verification

Effect of a Nonuniform Radial/Axial Tip Clearance on the Flow Field in a Mixed-Flow Pump

The effect of a nonuniform radial/axial tip clearance on the flow field in a mixed-flow pump was studied by numerical simulation of the unsteady flow in the pump with two tip clearance shapes using the standard Reynolds average Navier–Stokes turbulence model, and the equations were solved with the SIMPLEC computational algorithm. The external characteristics, distribution of static pressure, streamline flow of the tip clearance, and vorticity in the impeller are analyzed. The accuracy of numerical simulation was assessed by comparing experimental data with computational results. Although a nonuniform tip clearance leads to a decline in the pump head, which is more pronounced under part-load conditions, the configuration with a nonuniform tip clearance (c = 0.5–1 mm) provides the more uniform velocity and pressure distribution both in the circumferential and axial directions, as the leakage vortex intensity is weakened and its shedding is suppressed. The research results pointed the way for improving the unsteady flow in the mixed-flow pump.Изучено влияние неравномерного зазора на поле течения в радиально-осевом насосе с помощью численного моделирования нестационарного течения в насосе с зазором двух конфигураций на основе стандартной модели турбулентности RNG k , выполнено решение уравнений с применением алгоритма SIMPLE. Проанализированы внешние характеристики, распределение статического давления, потока в зазоре и турбулентности в импеллере. Проведена оценка достоверности численного моделирования путем сравнения экспериментальных данных с результатами расчетов. Показано, что неравномерный зазор вызывает уменьшение напора в насосе, что становится более выраженным в условиях частичного нагружения, но конфигурация с неравномерным зазором (с = 0,5 1,0 мм) обеспечивает более равномерные скорость и распределение давления в касательном и осевом направлениях, поскольку интенсивность обтекания с кольцевым вихрем уменьшается, а его сброс замедляется. Полученные результаты открывают путь к стабилизации нестационарного потока в радиально-осевом насосе

Possible Capture of keV Sterile Neutrino Dark Matter on Radioactive beta-decaying Nuclei

There exists an observed "desert" spanning six orders of magnitude between O(0.5) eV and O(0.5) MeV in the fermion mass spectrum. We argue that it might accommodate one or more keV sterile neutrinos as a natural candidate for warm dark matter. To illustrate this point of view, we simply assume that there is one keV sterile neutrino nu_4 and its flavor eigenstate nu_s weakly mixes with three active neutrinos. We clarify different active-sterile neutrino mixing factors for the radiative decay of nu_4 and beta decays in a self-consistent parametrization. A direct detection of this keV sterile neutrino dark matter in the laboratory is in principle possible since the nu_4 component of nu_e can leave a distinct imprint on the electron energy spectrum when it is captured on radioactive beta-decaying nuclei. We carry out an analysis of its signatures in the capture reactions nu_e + ^{3}H \to ^{3}He + e^- and nu_e + ^{106}Ru \to ^{106}Rh + e^- against the beta-decay backgrounds, and conclude that this experimental approach might not be hopeless in the long run.Comment: 14 pages, 3 figures, more discussions and references added. To appear in PL

Electrical transport studies of quench condensed Bi films at the initial stage of film growth: Structural transition and the possible formation of electron droplets

The electrical transport properties of amorphous Bi films prepared by sequential quench deposition have been studied in situ. A superconductor-insulator (S-I) transition was observed as the film was made increasingly thicker, consistent with previous studies. Unexpected behavior was found at the initial stage of film growth, a regime not explored in detail prior to the present work. As the temperature was lowered, a positive temperature coefficient of resistance (dR/dT > 0) emerged, with the resistance reaching a minimum before the dR/dT became negative again. This behavior was accompanied by a non-linear and asymmetric I-V characteristic. As the film became thicker, conventional variable-range hopping (VRH) was recovered. We attribute the observed crossover in the electrical transport properties to an amorphous to granular structural transition. The positive dR/dT found in the amorphous phase of Bi formed at the initial stage of film growth was qualitatively explained by the formation of metallic droplets within the electron glass.Comment: 7 pages, 6 figure

BESII Detector Simulation

A Monte Carlo program based on Geant3 has been developed for BESII detector simulation. The organization of the program is outlined, and the digitization procedure for simulating the response of various sub-detectors is described. Comparisons with data show that the performance of the program is generally satisfactory.Comment: 17 pages, 14 figures, uses elsart.cls, to be submitted to NIM