1,721,070 research outputs found
ANALYSIS AND MEASUREMENT OF BIREFRINGENCE IN SINGLE-MODE FIBERS USING THE BACKSCATTERING METHOD
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Almost tight upper bound for finding Fourier coefficients of bounded pseudo-Boolean functions
No full textA k-bounded pseudo-Boolean function is a real-valued function on {0, 1}(n) that can be expressed as a sum of functions depending on at most k input bits. The k-bounded functions play an important role in a number of areas including molecular biology, biophysics, and evolutionary computation. We consider the problem of finding the Fourier coefficients of k-bounded functions, or equivalently, finding the coefficients of multilinear polynomials on {-1, 1}(n) of degree k or less. Given a k-bounded function f with m non-zero Fourier coefficients for constant k, we present a randomized algorithm to find the Fourier coefficients of f with high probability in O(m logn) function evaluations. The best known upper bound was O(lambda(n, m)m log n), where lambda(n, m) is between n(1/2) and n depending on m. Our bound improves the previous bound by a factor of Omega(n(1/2)). It is almost tight with respect to the lower bound Omega(mlogn/logm). In the process, we also consider the problem of finding k-bounded hypergraphs with a certain type of queries under an oracle with one-sided error. The problem is of self interest and we give an optimal algorithm for the problem. (C) 2010 Elsevier Inc. All rights reserved
A CMOS frequency synthesizer block for MB-OFDM UWB systems
No full textA CMOS frequency synthesizer block for multi-band orthogonal frequency division multiplexing ultra-wideband systems is proposed. The proposed frequency synthesizer adopts a double-conversion architecture for simplicity and to mitigate spur suppression requirements for out-of-band interferers in 2.4 and 5 GHz bands. Moreover, the frequency synthesizer can consist of the fewest nonlinear components, such as divide-by-Ns and a mixer with the proposed frequency plan, leading to the generation of less spurs. To evaluate the feasibility of the proposed idea, the frequency synthesizer block is implemented in 0.18-mu m CMOS technology. The measured sideband suppression ratio is about 32 dBc, and the phase noise is -105 dBc/Hz at an offset of 1 MHz. The fabricated chip consumes 17.6 mA from a 1.8 V supply, and the die-area including pads is 0.9 x 1.1 mm(2)
USE OF POLARIZATION OPTICAL-TIME DOMAIN REFLECTOMETRY FOR OBSERVATION OF THE FARADAY-EFFECT IN SINGLE-MODE FIBERS
No full textAutomating strategies of emergency operation for optimal shutdown in pressurized water reactors
No full textIn this paper, the automating strategies of emergency operation are proposed for achieving optimal shutdown in pressurized water reactors, These strategies can make emergency operation optimal, and as well they considerably lengthen the operator response time, Decision-making and control are investigated in order to develop the automating strategies, In decision-making, diagnostic trees are established to automate the diagnostic tasks for selecting appropriate emergency operations, and the decision-making procedure is developed to automate some decisions which must be made on a plant-and event-specific basis, In control, cooldown is planned by establishing operational goals, forming strategies, and specifying operational means and constraints, The reference set points of the controlled parameters are adaptively adjusted through fuzzy reasoning for optimal cooldown and depressurization. The validation of the proposed strategies was carried out using the micro-simulator for the Kori Unit 2 with steam generator tube rupture events, The results indicated that the automated emergency operation successfully drove the plant at full power to a cold shutdown state with all the operational constraints satisfied
Thermal power estimation by fouling phenomena compensation using wavelet and principal component analysis
No full textA small percentage of reactor thermal power can be overestimated because of fouling phenomena in a secondary feedwater flowmeter. This study proposes a signal processing technique for the compensation of a degraded flowmeter such a secondary feedwater flowmeter in nuclear power plants. The technique proposed is mainly focused on noise classification and step-by-step noise reduction. The noises focused are classified into the rapid distortion caused by environmental interference, the flow fluctuation according to plant state transition and the degradation by fouling phenomena qualitatively. The multi-step de-noising technique reduces each noise by three techniques step-by-step. The wavelet analysis as a low frequency pass filter to remove the rapid distortion, the linear principal component analysis (PCA) to pl edict a steady-state value from the fluctuation, and the non-linear PCA implemented as an autoassociative neural network (AANN) to predict an original value from the signal including fouling phenomena are developed. The main purpose of this approach is to make an AANN concentrate on compensating the degradation by fouling phenomena itself. For the demonstration the signals from a simulator and signal modeling were used so that the role and the performance of each noise removal step was represented. In addition a thermal power deviation estimator is proposed to recognize the degradation effect of each operating parameter for reactor thermal power calculation. (C) 1000 Published by Elsevier Science S.A. All rights reserved
Development of a need-oriented steam turbine cycle simulation toolbox
No full textWe call an electric generation mechanism, whose working fluid is water, as a steam turbine cycle or Rankine cycle. A steam turbine cycle has been adopted in fossil-fuel or nuclear power plants because it is suitable for large-scale and continuous operation. To check the performance level of a steam turbine cycle, performance tests are carried out according to the performance test codes (PTCs) provided by the authorized institute. However, authors found that it was too difficult to follow the PTCs in actual plants. The reason is signal reliability and the prerequisites of the PTCs. The effort to overcome these shortcomings already started and some commercial solutions were also developed. These solutions include a general-purpose simulation code with signal validation techniques. Despite these achievements, performance engineers are suffering from the inconsistency between their previous performance analysis work and new performance analysis tools. This study proposed the solution, a need-oriented turbine cycle simulation toolbox, which is another general-purpose simulation code with the signal validation method based on multivariate statistics. This toolbox removed the inconsistency by customizing the actual needs of performance engineers. The accuracy of the developed simulation code was validated with other commercial turbine cycle simulation codes
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