4,025 research outputs found

    Exciton-Population Inversion and Terahertz Gain in Resonantly Excited Semiconductors

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    The build-up of exciton populations in resonantly laser excited semiconductors is studied microscopically. For excitation at the 2s2s-exciton resonance, it is shown that polarization with a strict ss-type radial symmetry can be efficiently converted into an incoherent pp-type population. As a consequence, inversion between the 2p2p and 1s1s exciton states can be obtained leading to the appearance of significant terahertz gain.Comment: 4 pages, 3 figure

    The Meaning of Animals

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    This research examines the social construction of animals by a rural Allegheny culture using a linguistic approach based on estimating the set of attributes associated with the words they used to describe animals. We asked 268 respondents to free-associate with the nouns, chicken and deer when seen in a context of other words related to nature. Their responses were coded and the frequencies of of words and word groupings were tabulated for sub-samples of differing age, gender and occupation. Response words were categorized into seven typologies including two affective types. The results indicate that except for possibly the very young, the social meanings of chicken and deer did not vary with gender, age or occupation. The respondents interpretation of living chicken was indistinguishable from that of unprepared food. Their interpretation of deer was broader and primarily one of interaction with a lesser adversary

    Spectral parameter power series method for discontinuous coefficients

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    Let (a,b) be a finite interval and 1/p, q, r be functions from L1(a,b). We show that a general solution (in the weak sense) of the equation (pu')'+qu = zru on (a,b) can be constructed in terms of power series of the spectral parameter z. The series converge uniformly on [a,b] and the corresponding coefficients are constructed by means of a simple recursive procedure. We use this representation to solve different types of eigenvalue problems. Several numerical tests are discussed
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