1,722,362 research outputs found
PRIORITIZED CHANNEL ASSIGNMENT IN A CELLULAR RADIO NETWORK
No full textDimensioning procedures for prioritized channel assignment in a cellular radio network are considered. Under the cutoff priority discipline, the prioritized channel assignment procedures for a single cell and multicell system are formulated as nonlinear discrete capacity allocation problems. Exact incremental algorithms which efficiently solve the proposed problems are devised based on the properties of the blocking probabilities of new calls and handoff calls. Given the number of available frequency channels together with the arrival rates and the GOS for both types of calls in each cell, algorithm SP1 generates an optimal channel assignment which ensures priority for handoff calls. Given the arrival rates and distinct GOS's for new and handoff calls, algorithm SP2 finds the minimum number of channels required in each cell. Algorithm MP extends algorithm SP1 to a multicell system and provides the prioritized channel assignment for all cells in the system. Due to their simplicity, our algorithms run very fast and can be implemented adoptively in the practical systems. It is also shown that they are appropriate for the fair allocation of frequency channels among the cells throughout the entire system
Development of an efficient algorithm for global optimization by simplex elimination
No full textAn efficient multi-start algorithm for global optimization is developed by introducing multi-dimensional simplexes as new expression units of attraction regions. The region elimination method generally consists of making a set of eliminated regions called attraction regions, checking adjacency between the current design point and the attraction region, and quitting local optimization for the attracted design points. The efficiency of the elimination method is considerably enhanced by supplementing general simplexes and their neighborhoods to conventional units of attraction regions of points and lines. To show the effectiveness of the proposed algorithm, mathematical problems from the literature are solved and the results are compared with several well-known multi-start algorithms. The present algorithm produces the global optimum in all problems more efficiently than the variants of the multi-start method. Several types of truss, frame, and composite material structures are optimized as engineering applications. Many local optima are found and the differences among the local optima are not negligibly small. These results suggest that an efficient and reliable global optimizer is strongly required in some fields of engineering optimization
Microplasticity phenomena in thermomechanically strained nickel thin films
No full textMagnetron sputtered Ni thin films on both oxidised Si (100) and alpha-Al(2)O(3) (0001) substrates of thickness 150-1000 nm were tested thermomechanically with a wafer curvature system, as well as in situ in a transmission electron microscope. The films on oxidised Si have a {111}-textured columnar microstructure with a mean grain size similar to the film thickness. On (0001) alpha-Al2O3 a near single crystal epitaxy with two growth variants is achieved leading to a significantly larger grain size. The thermo-mechanical testing was analysed in terms of the room temperature/high temperature flow stresses in the films and the observed thermoelastic slopes. It was found that the room temperature flow stresses increased with decreasing film thickness until a plateau of similar to 1100 MPa was reached for films thinner than 400 nm. This plateau is attributed to the present experiments exerting insufficient thermal strain to induce yielding in these thinner films. At 500 degrees C the compressive flow stresses of the films show a competition between dislocation and diffusion mediated plasticity. A size effect is also observed in the thermoelastic slopes of the films, with thinner films coming closer to the slope predicted by mismatch in thermal expansion coefficients. It is put forward here that this is due to a highly inhomogeneous stress distribution in the films arising from the grain size distribution.X1156Nsciescopu
Adaptive noise cancelling based on independent component analysis
No full textA method for adaptive noise cancelling based on independent component analysis (ICA) is presented. Although the conventional least-mean-squares (LMS) algorithm removes noise components based on second-order correlation, the proposed algorithm can utilise higher-order statistics. Experimental results show that the proposed algorithm provides considerable performance improvement.This work was supported by the Brain Science & Engineering Research Program sponsored by Korean Ministry of Science and Technology
Improvement of the dynamic properties of a steel-composite hybrid flexspline of a harmonic drive
No full textThe harmonic drive is a special gear-drive speed reduction system whose operation principle is based on elastic deformation rather than rigid-body motion of the general gearing system. I;rom the components of the harmonic drive, the flexspline is the key element for the transmission of motion. It must be flexible in the radial direction, but must be stiff in the torsional direction to accurately transmit rotational motion. Because the contradictory dual role of the flexspline cannot be satisfied effectively with conventional isotropic materials, but can be achieved with anisotropic composite materials, in this paper the cup section of the flexspline was hybridly manufactured by laying-up composite material on the inside surface of the steel cup section. The static and dynamic characteristics of the hybrid flexspline were investigated with respect to the fibre volume fraction, stacking sequence and the mass ratio of the composite to steel. (C) 1997 Elsevier Science Ltd
An efficient postbuckling analysis technique for composite stiffened curved panels
No full textSeveral efficient techniques are presented for the postbuckling analysis of composite stiffened structures in this paper. Some aerospace structures allow local buckling in order to increase structural efficiency. This idea may be a very effective design concept, but it takes a great deal of time in structural design. Due to its geometrical and material nonlinearity, the postbuckling analysis process requires a long computational time. fit this report, to reduce the computational time, efficient analysis techniques are proposed. A change in the element type used, separation of the linear response region, and the termination of the analysis after ultimate failure of the structure were applied to the analysis. As a result. about 80% of the computational time was reduced with high accuracy
A filter bank approach to independent component analysis and its application to adaptive noise cancelling
No full textWe present a filter bank (FB) approach to perform independent component analysis for adaptive noise cancelling. This approach is based on FBs, and its decimation provides much less computational complexity and faster convergence speed than the time-domain approach. In addition, the approach does not have a performance limitation unlike the frequency-domain approach. One can select the number of filters in the FB regardless of reverberation and implement the method to fit for parallel processing. We verify the effectiveness of the FB approach through simulations on adaptive noise cancelling. (C) 2003 Elsevier B.V. All rights reserved.This work was supported as the Brain Neuroinformatics Research Program sponsored
by Korean Ministry of Science and Technology
The multilayer modified Stoney's formula for the laminated polymer composites on a silicon substrate
No full textThe thermomechanical behavior of multilayer structures is a subject of perennial interest. Stoney's formula has long been one of the most important tools for understanding thermomechanical stress for single-layered structures like spin-coated polyimides or deposited metal thin film on substrates. In today's microelectronics, however, as multilayer substrates have become widely available, the "modified version" of Stoney's formula for multilayer applications is not only useful but necessary. While the majority of reports in the literature have focused on single-layer analysis, in this study, we examined an extended usage of Stoney's formula for multilayer analysis. A simple model, the multilayer-modified Stoney's formula, which predicts the stress contribution of each individual layer is proposed and verified through experiments and numerical analysis. Using various kinds of materials employed in a typical lamination-based multichip module technology, the thermomechanical behavior of the lamination-based multilayer substrates was measured by a laser profilometry during thermal cycling. The measured values were compared with calculated values using the multilayer-modified Stoney's formula. (C) 1999 American Institute of Physics. [S0021-8979(99)05822-3]
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