1,500 research outputs found
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
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
Striped antiferromagnetic order and electronic properties of stoichiometric LiFeAs from first-principles calculations
We investigate the structural, electronic, and magnetic properties of
stoichiometric LiFeAs by using state-of-the-arts first-principles method. We
find the magnetic ground-state by comparing the total energies among all the
possible magnetic orders. Our calculated internal positions of Li and As are in
good agreement with experiment. Our results show that stoichiometric LiFeAs has
almost the same striped antiferromagnetic spin order as other FeAs-based parent
compounds and tetragonal FeSe do, and the experimental fact that no magnetic
phase transition has been observed at finite temperature is attributed to the
tiny inter-layer spin coupling
Investigation of optimal Split ratio for high-speed permanent-magnet brushless machines
The split ratio, i.e., the ratio of rotor outer diameter to stator outer diameter, is one of the most vital design parameters for permanent-magnet (PM) machines due to its significant impact on the machine torque or power density. However, it has been optimized analytically in the existing papers with due account only for the stator copper loss, which is reasonable for low-to-medium speed PM machines. For high-speed PM machines (HSPMMs), the negligence of stator iron loss and the mechanical stress on the rotor will lead to a deviation of optimal split ratio and actual torque capability. In this paper, the optimal split ratio of HSPMM is investigated analytically with the consideration of stator iron loss as well as the mechanical stress on the rotor. The influence of air-gap length and rotor pole pairs on the optimal split ratio is elaborated. Both the analytical and finite-element analysis reveal that the optimal split ratio for HSPMM will be significantly reduced, when stator iron loss and mechanical constraints are taken into account
Measurement of the Intrinsic Radiopurity of Cs-137/U-235/U-238/Th-232 in CsI(Tl) Crystal Scintillators
The inorganic crystal scintillator CsI(Tl) has been used for low energy
neutrino and Dark Matter experiments, where the intrinsic radiopurity is an
issue of major importance. Low-background data were taken with a CsI(Tl)
crystal array at the Kuo-Sheng Reactor Neutrino Laboratory. The pulse shape
discrimination capabilities of the crystal, as well as the temporal and spatial
correlations of the events, provide powerful means of measuring the intrinsic
radiopurity of Cs-137 as well as the U-235, U-238 and Th-232 series. The event
selection algorithms are described, with which the decay half-lives of Po-218,
Po-214, Rn-220, Po-216 and Po-212 were derived. The measurements of the
contamination levels, their concentration gradients with the crystal growth
axis, and the uniformity among different crystal samples, are reported. The
radiopurity in the U-238 and Th-232 series are comparable to those of the best
reported in other crystal scintillators. Significant improvements in
measurement sensitivities were achieved, similar to those from dedicated
massive liquid scintillator detector. This analysis also provides in situ
measurements of the detector performance parameters, such as spatial
resolution, quenching factors, and data acquisition dead time.Comment: 28 pages, 12 figure
Partial wave analysis of J/\psi \to \gamma \phi \phi
Using events collected in the BESII detector, the
radiative decay is
studied. The invariant mass distribution exhibits a near-threshold
enhancement that peaks around 2.24 GeV/.
A partial wave analysis shows that the structure is dominated by a
state () with a mass of
GeV/ and a width of GeV/. The
product branching fraction is: .Comment: 11 pages, 4 figures. corrected proof for journa
Measurements of the observed cross sections for exclusive light hadrons containing at , 3.650 and 3.6648 GeV
By analyzing the data sets of 17.3, 6.5 and 1.0 pb taken,
respectively, at , 3.650 and 3.6648 GeV with the BES-II
detector at the BEPC collider, we measure the observed cross sections for
, , ,
and at the three energy
points. Based on these cross sections we set the upper limits on the observed
cross sections and the branching fractions for decay into these
final states at 90% C.L..Comment: 7 pages, 2 figure
- …