6,809 research outputs found

    The Gaussian formula and spherical aberration of the static and moving curved mirrors from Fermat's principle

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    The Gaussian formula and spherical aberrations of the static and relativistic curved mirrors are analyzed using the optical path length (OPL) and Fermat's principle. The geometrical figures generated by the rotation of conic sections about their symmetry axes are considered for the shapes of the mirrors. By comparing the results in static and relativistic cases, it is shown that the focal lengths and the spherical aberration relations of the relativistic mirrors obey the Lorentz contraction. Further analysis of the spherical aberrations for both static and relativistic cases have resulted in the information about the limits for the paraxial approximation, as well as for the minimum speed of the systems to reduce the spherical aberrations.Comment: 15 pages, 7 figures, uses iopart. Major revisions on the physical interpretations of the results. Accepted for publication in J. Op

    Investment of migrant remittances : some evidence from anthropology

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    Thesis (M.C.P.)--Massachusetts Institute of Technology, Dept. of Urban Studies and Planning, 1984.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ROTCH.Bibliography: leaves 36-38.by Joy Eliza Hecht.M.C.P

    Developments in Television Viewership

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    In recent years the ways in which we watch television has changed, and so has the television we watch. “Binge watching,” almost the Oxford English Dictionary’s Word of the Year in 2013, has taken a firm hold on the American television audience who now watches television not according to the broadcast schedule but on its own terms. So, too, has the practice of engaging with other audience members, be they friends, family, or strangers, while watching a show by using a secondary device – a “second screen.” These practices have been developing for some time, and as technology adapts to facilitate them the denizens of television viewers now consider them normal. The questions that follow are whether these new ways to watch television change the TV programs themselves, and whether the viewers’ emotional response to the shows is changing, too. If it is accepted as standard that audiences will watch multiple episodes of one show in a row, instead of waiting for a weekly release of a single episode, are the episodes being written with that consumption pattern in mind? Do the old conventions written into television shows to help the viewer remember what happened in the weeks before still apply? And, if viewers are looking at their second screens to follow the national response on Twitter v at the same time as they are watching a show, can they be as emotionally engaged with the show as they would be if they were focusing on the single, primary screen? There have been some studies that investigate these questions and others like them, and there is a plethora of written work ranging from scholarly papers to blog posts. The opinion columns of magazines and newspapers are full of think pieces on the effects of binge watching and the state of television today. My thesis incorporates existing research and writing with a historical overview of changes to television technology over time, as well as the results of an original survey distributed to my social network with the goal of reaching an understanding of how people are watching television and using the technology in their own lives

    Amplitude control of quantum interference

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    Usually, the oscillations of interference effects are controlled by relative phases. We show that varying the amplitudes of quantum waves, for instance by changing the reflectivity of beam splitters, can also lead to quantum oscillations and even to Bell violations of local realism. We first study theoretically a generalization of the Hong-Ou-Mandel experiment to arbitrary source numbers and beam splitter transmittivity. We then consider a Bell type experiment with two independent sources, and find strong violations of local realism for arbitrarily large source number NN; for small NN, one operator measures essentially the relative phase of the sources and the other their intensities. Since, experimentally, one can measure the parity of the number of atoms in an optical lattice more easily than the number itself, we assume that the detectors measure parity.Comment: 4 pages; 4 figure

    Zur methodik der ninhydrinreaktion und papierchromatographie im zusammenhang mit untersuchungen uber gerinnungsphysiologisch interessierende phosphatide

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    In view of other researches, the authors have studied the ninhydrin reaktion in order to obtain evidence of free amino-N of phosphatides and their fission products. Apart from the study of paper chromatography of nitrogenated lipoids, the details of general interest are given of the technique used by the authors. Description is given of a series of experiments of paper chromatography with cephaline, more or less purified by precipitation or dialysis, and with preparations made amino-free by the method of VAN SLYKE, before and after hydrolysis. Glutamic acid and sphingosine have been found in the hydrolysates along with cholamine and serine. The results could be explained, according to the Discussion, by the hypothesis of disposed phosphatides in chain or ring form. The authors have also proved the presence in the phosphatides of bound amino-N which cannot be eliminated by VAN SLYKE 's method; and thus they have given an explanation of the fact observed previously that the determination of amino-N by VAN SLYKE gives higher values in the phosphatides before hydrolysis than after hydrolysis

    Measurement of atomic diffraction phases induced by material gratings

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    Atom-surface interactions can significantly modify the intensity and phase of atom de Broglie waves diffracted by a silicon nitride grating. This affects the operation of a material grating as a coherent beam splitter. The phase shift induced by diffraction is measured by comparing the relative phases of serveral interfering paths in a Mach-Zehnder Na atom interferometer formed by three material gratings. The values of the diffraction phases are consistent with a simple model which includes a van der Waals atom-surface interaction between the Na atoms and the silicon nitride grating bars.Comment: 4 pages, 5 figures, submitted to PR

    Coherence properties of infrared thermal emission from heated metallic nanowires

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    Coherence properties of the infrared thermal radiation from individual heated nanowires are investigated as function of nanowire dimensions. Interfering the thermally induced radiation from a heated nanowire with its image in a nearby moveable mirror, well-defined fringes are observed. From the fringe visibility, the coherence length of the thermal emission radiation from the narrowest nanowires was estimated to be at least 20 um which is much larger than expected from a classical blackbody radiator. A significant increase in coherence and emission efficiency is observed for smaller nanowires.Comment: 4 pages,figures include
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