231,117 research outputs found
Direct torque control of brushless DC drives with reduced torque ripple
The application of direct torque control (DTC) to brushless ac drives has been investigated extensively. This paper describes its application to brushless dc drives, and highlights the essential differences in its implementation, as regards torque estimation and the representation of the inverter voltage space vectors. Simulated and experimental results are presented, and it is shown that, compared with conventional current control, DTC results in reduced torque ripple and a faster dynamic response
Advances on creep–fatigue damage assessment in notched components
In this paper, the extended Direct Steady Cyclic Analysis method (eDSCA) within the Linear Matching Method Framework (LMMF) is combined with the Stress Modified Ductility Exhaustion method and the modified Cavity Growth Factor (CGF) for the first time. This new procedure is used to systematically investigate the effect of several load parameters including load level, load type and creep dwell duration on the creep–fatigue crack initiation process in a notched specimen. The results obtained are verified through a direct comparison with experimental results available in the literature demonstrating great accuracy in predicting the crack initiation life and the driving mechanisms. Furthermore, this extensive numerical study highlighted the possible detrimental effect of the creep–ratchetting mechanism on the crack growth process. This work has a significant impact on structural integrity assessments of complex industrial components and for the better understanding of creep–fatigue lab scale tests
An efficient method for computing unsteady transonic aerodynamics of swept wings with control surfaces
A transonic equivalent strip (TES) method was further developed for unsteady flow computations of arbitrary wing planforms. The TES method consists of two consecutive correction steps to a given nonlinear code such as LTRAN2; namely, the chordwise mean flow correction and the spanwise phase correction. The computation procedure requires direct pressure input from other computed or measured data. Otherwise, it does not require airfoil shape or grid generation for given planforms. To validate the computed results, four swept wings of various aspect ratios, including those with control surfaces, are selected as computational examples. Overall trends in unsteady pressures are established with those obtained by XTRAN3S codes, Isogai's full potential code and measured data by NLR and RAE. In comparison with these methods, the TES has achieved considerable saving in computer time and reasonable accuracy which suggests immediate industrial applications
Zero Modes of Matter Fields on Scalar Flat Thick Branes
Zero modes of various matters with spin 0, 1 and 1/2 on a class of scalar
flat thick branes are discussed in this paper. We show that scalar field with
spin 0 is localized on all thick branes without additional condition, while
spin 1 vector field is not localized. In addition, for spin 1/2 fermionic
field, the zero mode is localized on the branes under certain conditions.Comment: 11 pages,no figure
Kernel Regression For Determining Photometric Redshifts From Sloan Broadband Photometry
We present a new approach, kernel regression, to determine photometric
redshifts for 399,929 galaxies in the Fifth Data Release of the Sloan Digital
Sky Survey (SDSS). In our case, kernel regression is a weighted average of
spectral redshifts of the neighbors for a query point, where higher weights are
associated with points that are closer to the query point. One important design
decision when using kernel regression is the choice of the bandwidth. We apply
10-fold cross-validation to choose the optimal bandwidth, which is obtained as
the cross-validation error approaches the minimum. The experiments show that
the optimal bandwidth is different for diverse input patterns, the least rms
error of photometric redshift estimation arrives at 0.019 using color+eClass as
the inputs, the less rms error amounts to 0.020 using ugriz+eClass as the
inputs. Here eClass is a galaxy spectra type. Then the little rms scatter is
0.021 with color+r as the inputs.Comment: 6 pages,2 figures, accepted for publication in MNRA
Directional excitation of graphene surface plasmons
We propose a scheme to directionally couple light into graphene plasmons by
placing a graphene sheet on a magneto-optical substrate. When a magnetic field
is applied parallel to the surface, the graphene plasmon dispersion relation
becomes asymmetric in the forward and backward directions. It is possible to
achieve unidirectional excitation of graphene plasmons with normally incident
illumination by applying a grating to the substrate. The directionality can be
actively controlled by electrically gating the graphene, or by varying the
magnetic bias. This scheme may have applications in graphene-based
opto-electronics and sensing
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