NEC

About: NEC is a company organization based out in Tokyo, Japan. It is known for research contribution in the topics: Signal & Layer (electronics). The organization has 33269 authors who have published 57670 publications receiving 835952 citations. The organization is also known as: NEC Corporation & NEC Electronics Corporation.

On the computational complexity of approximating distributions by probabilistic automata

Abstract: We introduce a rigorous performance criterion for training algorithms for probabilistic automata (PAs) and hidden Markov models (HMMs), used extensively for speech recognition, and analyze the complexity of the training problem as a computational problem. The PA training problem is the problem of approximating an arbitrary, unknown source distribution by distributions generated by a PA. We investigate the following question about this important, well-studied problem: Does there exist an efficient training algorithm such that the trained PAs provably converge to a model close to an optimum one with high confidence, after only a feasibly small set of training data? We model this problem in the framework of computational learning theory and analyze the sample as well as computational complexity. We show that the number of examples required for training PAs is moderate—except for some log factors the number of examples is linear in the number of transition probabilities to be trained and a low-degree polynomial in the example length and parameters quantifying the accuracy and confidence. Computationally, however, training PAs is quite demanding: Fixed state size PAs are trainable in time polynomial in the accuracy and confidence parameters and example length, but not in the alphabet size unless RP e NP. The latter result is shown via a strong non-approximability result for the single string maximum likelihood model probem for 2-state PAs, which is of independent interest.

Focused ion beam applications to solid state devices

Abstract: The current state of focused ion beam (FIB) applications in relation to solid state devices is reviewed, and recent use of FIB technology for lithography, etching, deposition, and doping are described. Etching and deposition have become essential processes for failure analysis and for mask repair in silicon ULSL production. Furthermore, the FIB doping technique has been used to fabricate quantum effect devices.

Person location system

Abstract: A person location system comprises radio base stations and a radio central station, all stations being connected to a public switched telephone network. The base stations respectively cover small areas, or "microcells", in one of which is located a user station, and the central station covers an area containing all of the microcells. The central station receives a polling signal containing the user's address via the telephone network and broadcasts a copy of the polling signal. A management center is connected to the telephone network for transmitting the polling signal to the central station when a location demand arises. Each base station is responsive to the polling signal from the central station for returning field intensity data of the user station through the telephone network to the management center if the polling signal identifies the user station.

Magnetic random access memory circuit

Abstract: A magnetic random access memory circuit comprises first and second row decoders receiving a part of a given address, first and second column decoders receiving the other part of a given address, a plurality of pairs of sense lines connected between output terminals of the first row decoder and output terminals of the second row decoder, each pair of sense lines being located adjacent to each other, a plurality of word lines connected between output terminals of the first column decoder and output terminals of the second column decoder, and extending to intersect the sense lines so that intersections of the sense lines and the word lines are located in the form of a matrix. A memory array includes a plurality of cell pairs distributed over the matrix, each cell pair including a memory cell and a reference cell located adjacent to each other. Each of the memory cell and the reference cell includes a magneto-resistive element. The memory cell and the reference cell of each cell pair are located at intersections of one word line and one pair of sense lines, respectively. The memory cell of the each cell pair is connected between one sense line of the one pair of sense lines and the one word line, and the reference cell of the each cell pair is connected between the other sense line of the one pair of sense lines and the one word line.