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41.
We propose an efficient scheme for camera motion characterization in MPEG‐compressed video. The proposed scheme detects six types of basic camera motions through threshold‐based qualitative interpretation, in which fixed thresholds are applied to motion model parameters estimated from MPEG motion vectors (MVs). The efficiency and robustness of the scheme are validated by the experiment with real compressed video sequences. 相似文献
42.
Kyutae Lim Sang Seol Lee 《Antennas and Propagation, IEEE Transactions on》1995,43(11):1325-1328
An exact analytic solution of a plane electromagnetic (EM) wave scattered by an eccentric multilayered sphere (EMS) is obtained. It is assumed that the layers are perfect dielectrics and that the innermost core is a perfectly conducting sphere. Each center of a layer is translated along the incident axis. All fields are expanded in terms of the spherical vector wave functions with unknown expansion coefficients. The addition theorem for spherical wave functions is used prior to applying the boundary conditions. The unknown coefficients are determined by solving a system of linear equations derived from the boundary conditions. Numerical results of the scattering cross sections are presented on the plane of φ=0 degrees and φ=90 degrees. The convergence of modal solutions and the characteristics of patterns are examined with various geometries and permittivity distributions 相似文献
43.
TH Lim HS An T Hasegawa L McGrady KY Hasanoglu CR Wilson 《Canadian Metallurgical Quarterly》1995,20(23):2565-8; discussion 2569
STUDY DESIGN: A biomechanical study was performed to investigate a relation between the bone mineral density of the vertebral body and the number of loading cycles to induce fatigue loosening of an anterior vertebral screw. OBJECTIVES: The objective of this study was to investigate the potential usefulness of dual energy x-ray absorptiometry of measuring bone mineral density of the vertebral body in predicting the fatigue loosening of th anterior vertebral screw. SUMMARY OF BACKGROUND DATA: Loosening of the vertebral body screw is a well know failure in spinal instrumentation, and more commonly observed than pullout failure. The relation between bone mineral density and pullout strength of the screw has been investigated previously, but no studies are available on the fatigue loosening in anterior spinal fixation. METHODS: Bone mineral density was measured using dual energy x-ray absorptiometry and the screw loosening was produce by a cyclic loading in the cephalad-caudal direction. Screw loosening was defined as 1 mm displacement of the screw relative to bone, and the number of loading cycles to induce the screw loosening was obtained and statistically correlated with bone mineral density. RESULTS: There was a positive correlation between the number of loading cycles to induce screw loosening and bone mineral density (R = 0.8, P < 0.01). The average number of loading cycles to induce screw loosening was significantly less for specimens with bone mineral density < 0.45 g/cm2 compared to those with bone mineral density > or = g/cm2. CONCLUSIONS: These findings suggest that bone mineral density may be a good predictor of anterior vertebral screw loosening. Bone mineral density < 0.45 g/cm2 may be critical value of loosening of the anterior vertebral body screw. However, further biomechanical and clinical studies are required before using threshold value clinically. 相似文献
44.
Kim S. Jeong S. Lee Y.T. Kim D.-H. Lim J.-S. Seo K.-S. Nam S. 《Electronics letters》2002,38(13):622-623
A new ultra-wideband, low-loss and small-size coplanar waveguide (CPW) to coplanar strip (CPS) transition which can be used from DC to 110 GHz is presented. The proposed transition connects CPW with CPS by the reformed air-bridge. Two ground planes of CPW are tied at their ends by a line and the centre of the line is connected to the ground strip of CPS by another line. Owing to the symmetry of the proposed structure, the currents of two ground planes of CPW are combined with the same phase and transferred to the ground strip of CPS. With height of 3 μm, the signal line of CPW passes over two connecting lines and is connected to the signal strip of CPS. For the back-to-back transition structure, insertion loss <1 dB and return loss >15 dB are obtained from 0.5 to 110 GHz 相似文献
45.
Core–shell type nanoparticles of poly(L ‐lactide)/poly(ethylene glycol) (LE) diblock copolymer were prepared by a dialysis technique. Their size was confirmed as 40–70 nm using photon correlation spectroscopy. The 1H‐NMR analysis confirmed the formation of core–shell type nanoparticles and drug loading. The particle size, drug loading, and drug release rate of the LE nanoparticles were slightly changed by the initial solvents that were used. The drug release behavior of LE core–shell type nanoparticles showed an initial burst during the first 12 h and then a sustained release until 100 h. The degradation behavior of LE block copolymer nanoparticles was divided into three phases: the initial rapid degradation phase, the stationary phase, and the rapid degradation phase until complete degradation. It was suggested that lidocaine release kinetics were predominantly governed by the diffusion mechanism in the initial burst phase and after that by both of the diffusion and degradation mechanisms. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2625–2634, 2002 相似文献
46.
The intent of this paper is to design a high-frequency transformer that is to be incorporated into the DC/DC pulsewidth-modulated switch-mode power supplies by two different technical approaches: a conventional wound-coil magnetic using copper wires, and a planar magnetic with layered copper tracks on laminated printed circuit board. Comparisons will be made between the two approaches in terms of profile: mounting height and surface area, and performance: power losses and efficiency. Other indicators like temperature rise and leakage inductance that causes electromagnetic interference, and cost, materials, and process fluency are also to be looked into. A sandwiched configuration for primary and secondary windings is proposed for the planar type. Issues arising and typical phenomena encountered will be discussed in detail. Primarily, the dominating factor in performance, cost effectiveness, or circuit compactness that restrains the choice of a particular type is to be evaluated. 相似文献
47.
Security of the Cao-Li public key cryptosystem 总被引:1,自引:0,他引:1
Lim Lek Heng 《Electronics letters》1998,34(2):170-172
The author shows that the Cao-Li cryptosystem proposed [1991] is not secure. Its private key can be reconstructed from its public key using elementary means such as LU-decomposition and the Euclidean algorithm 相似文献
48.
A new method of thin section preparation of III-V semiconductors and multilayers for transmission electron microscopy (TEM) is presented that exhibits considerable advantages over conventional methods such as ion beam milling and jet thinning. GaAs thin films and multilayers of GaAs/In chi Ga1-chi As/GaAs are grown over an etch release layer of AlAs on GaAs substrates by molecular beam epitaxy (MBE). Planar TEM sections prepared by selective etching from these samples show improved ability to image film morphology and dislocation arrangements, and the resulting large thin electron transparent areas facilitate dislocation density measurements and detection of spatial variations. Avoidance of radiation effects and wedge shaping, both common to ion milled samples, allows this method to be used to prepare uniform thickness standards of single layer GaAs films for EDS analysis or lattice imaging. 相似文献
49.
An integral method is investigated and developed in the current work. The effects of the parameters of inlet distortions
on the trend of downstream flow feature in compressor are simulated. Other than the drag-to-lift ratio of the blade and the
inlet incidence angle, it is found that the distorted inlet velocity is another essential parameter to control the distortion
in propagation. Based on this study, a novel critical distortion line and corresponding critical distortion factor are proposed
to express the effect of the two essential inlet parameters on the propagation of distortion, namely, the inlet incidence
angle and the distorted inlet velocity. From the viewpoint of compressor efficiency, the propagation of inlet flow distortion
is further described by a compressor critical performance and its critical characteristic. The results present a useful physical
insight to an axial flow compressor behavior and asymptotic behavior of the propagation of inlet distortion, and confirm the
active role of compressor in determining the velocity distribution when compressor responds to an inlet flow distortion.
Received: 20 December 2001 / Accepted: 21 August 2002
The authors would like to thank HQ RSAF for permission to publish this work, their financial support and encouragement. The
first author wants to acknowledge Prof. Frank Marble of California Institute of Technology, for bringing the problem to the
author's attention and for his helpful discussion. 相似文献
50.
In the design of a digital filter, the frequency response is often optimized to meet a given set of specifications on a dense grid of frequency points. The density of the frequency grid points must be sufficiently high so that the frequency response of the filter does not violate the specifications at frequencies in between the grid points. However, the computational complexity of the design process and the storage requirements of the computer increase with the number of frequency grid points. We propose a novel dynamic: grid point allocation technique for the design of minimax optimum FIR filter. It uses a sparse frequency grid but will produce a design that is the same as one designed on very dense frequency grid points. It requires significantly less computer time and memory resources compared with fixed grid point algorithms 相似文献