Braess’s paradox exposes a counterintuitive phenomenon that when travelers selfishly choose their routes in a network, removing links can improve the overall network performance. Under the model of nonatomic selfish routing, we characterize the topologies of k-commodity undirected and directed networks in which Braess’s paradox never occurs. Our results strengthen Milchtaich’s series-parallel characterization (Milchtaich, Games Econom. Behav. 57(2), 321–346 (2006)) for the single-commodity undirected case. 相似文献
A cable-driven parallel manipulator is a manipulator whose end-effector is driven by a number of parallel cables instead of
rigid links. Since cables always have more flexibility than rigid links, a cable manipulator bears a concern of possible vibration.
Thus, investigation of vibration of cable manipulators caused by cable flexibility is important for applications requiring
high system stiffness or bandwidth. This paper provides a vibration analysis of general 6-DOF cable-driven parallel manipulators.
Based on the analysis of the natural frequencies of the multibody system, the study demonstrates that a cable manipulator
can be designed stiff enough for special applications like the cable-manipulator based hardware-in-the-loop simulation of
contact dynamics. Moreover, under an excitation, a cable may vibrate not only in its axial direction, but also in its transversal
direction. The paper also analyzes the vibration of cable manipulators caused by cable flexibilities in both axial and transversal
directions. It is shown that the vibration of a cable manipulator due to the transversal vibration of cables can be ignored
comparing to that due to the axial flexibility of cables. 相似文献
The goal of holographic particle velocimetry is to infer fluid velocity patterns from images reconstructed from doubly exposed holograms of fluid volumes seeded with small particles. The advantages offered by in-line holography in this context usually make it the method of choice, but seeding densities sufficient to achieve high spatial resolution in the sampling of the velocity fields cause serious degradation, through speckle, of the signal-to-noise ratio in the reconstructed images. The in-line method also leads to a great depth of field in paraxial viewing of reconstructed images, making it essentially impossible to estimate particle depth with useful accuracy. We present here an analysis showing that these limitations can be circumvented by variably scaled correlation, or wavelet transformation. The shift variables of the wavelet transform are provided automatically by the optical correlation methodology. The variable scaling of the wavelet transform derives, in this case, directly from the need to accommodate varying particle depths. To provide such scaling, we use a special optical system incorporating prescribed variability in spacings and focal length of lenses to scan through the range of particle depths.
Calculation shows, among other benefits, improvement by approximately two orders of magnitude in depth resolution. A much higher signal-to-noise ratio together with faster data extraction and processing should be attainable.
The mirror-confinement-type electron cyclotron resonance (MCECR) plasma source has high plasma density and high electron temperature, and it is quite useful in many plasma processing, and has been used for etching and thin-film deposition. In this paper, the carbon films about 50 nm thickness were deposited on Si (1 0 0) by MCECR plasma sputtering the sintered carbon target with the argon plasma, and its properties were studied. The bonding structure of the film was analyzed by using the X-ray photoelectron spectropscopy (XPS) and the nanostructure was evaluated with the high-resolution transmission electron microscopy (HRTEM). The tribological properties (friction coefficient, wear rate, and wear life) of the film was investigated by using the pin-on-disk tribometer under the conditions that the normal load is 1 N and the sliding velocity is 0.05 m/s. The nanohardness of the films was measured by using the nanoindenter under conditions that the maximum displacement is 30 nm and the maximum load is 500 μN. The optical properties were measured by using the ellipsometer. The residual stress was measured with a surface profilometer. The surface morphology was studied by using the atomic force microscope (AFM). 相似文献