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941.
Alexander Meduna 《Acta Informatica》1996,33(5):457-462
The syntactic complexity of context-free grammars defined over word monoids is investigated. It is demonstrated that every
recursively enumerable language can be defined by a ten-nonterminal context-free grammar over a word monoid generated by an
alphabet and six words of length two. Open problems are formulated.
Received October 10, 1994/February 23, 1995 相似文献
942.
G. Sajeevkumar R. Raveendran B. S. Remadevi Alexander Varghese Vaidyan 《Bulletin of Materials Science》2004,27(4):323-325
Ammonium hydrogend-tartrate (d-AHT) single crystals were grown in silica gel. The growth features of these crystals with variation of parameters like specific
gravity of the gel, gel pH, acid concentrations, concentration of the feed solution and gel age were studied in detail. 相似文献
943.
Alexander L. Fetter 《Journal of Low Temperature Physics》1998,113(3-4):189-194
A vortex in a trapped Bose-Einstein condensate can experience at least two Types of instabilities. (1). Macroscopic hydrodynamic motion of the vortex core relative to the center of mass of the condensate requires some process to dissipate energy. (2). Microscopic small-amplitude normal modes can also induce an instability. In one specific example, the vortex core again moves relative to the overall center of mass, suggesting that there may be only a single physical mechanism. 相似文献
944.
945.
EH Uhlenhuth PE Alexander GM Dempsey W Jones BS Coleman AM Swiontek 《Canadian Metallurgical Quarterly》1998,47(1-3):183-190
Heart sounds produce an incessant noise during lung sounds recordings. This noise severely contaminates the breath sounds signal and interferes in the analysis of lung sounds. In this paper, the use of a wavelet transform domain filtering technique as an adaptive de-noising tool, implemented in lung sounds analysis, is presented. The multiresolution representations of the signal, produced by wavelet transform, are used for signal structure extraction. In addition, the use of hard thresholding in the wavelet transform domain results in a separation of the nonstationary part of the input signal (heart sounds) from the stationary one (lung sounds). Thus, the location of the heart sound noise (1st and 2nd heart sound peaks) is automatically detected, without requiring any noise reference signal. Experimental results have shown that the implementation of this wavelet-based filter in lung sound analysis results in an efficient reduction of the superimposed heart sound noise, producing an almost noise-free output signal. Due to its simplicity and its fast implementation the method can easily be used in clinical medicine. 相似文献
946.
947.
948.
Mandelbaum Avi Massey William A. Reiman Martin I. Stolyar Alexander Rider Brian 《Telecommunication Systems》2002,21(2-4):149-171
We consider a Markovian multiserver queueing model with time dependent parameters where waiting customers may abandon and subsequently retry. We provide simple fluid and diffusion approximations to estimate the mean, variance, and density for both the queue length and virtual waiting time processes arising in this model. These approximations, which are generated by numerically integrating only 7 ordinary differential equations, are justified by limit theorems where the arrival rate and number of servers grow large. We compare our approximations to simulations, and they perform extremely well. 相似文献
949.
950.
Alexander E. Braun 《集成电路应用》2007,(1):47-47
边缘缺陷率已成为器件制造的重要问题,然而相当多的器件制造商认为.目前对晶圆边缘进行检测的能力还远远不够。虽然有些解决方案的表现还不错.但是它们似乎主要针对的是晶圆制造商,重点关注的是晶圆上的碎片和裂缝等物理损伤。 相似文献