Artificial neural networks are rapidly gaining popularity in the hard sciences and in social science. This article discusses neural networks as tools business researchers can use to analyze data. After providing a brief history of neural networks, the article describes limitations of multiple regression. Then, the characteristics and organization of neural networks are presented, and the article shows why they are an attractive alternative to regression. Shortcomings and applications of neural networks are reviewed, and neural network software is discussed.

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We show theoretically through computer simulations that phase-conjugate optical feedback that is realized through four-wave mixing can produce mode locking in multilongitudinal-mode semiconductor lasers. Phase-conjugate feedback, in contrast to ordinary optical feedback, directly couples pairs of longitudinal modes. For certain strengths of phase-conjugate reflectivities, the phases and beat frequencies of various longitudinal modes become locked in such a way that the laser produces ultrashort mode-locked pulses, even though the laser is pumped continuously.

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