192,318 research outputs found

    Modulation of the Curie Temperature in Ferromagnetic/Ferroelectric Hybrid Double Quantum Wells

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    We propose a ferromagnetic/ferroelectric hybrid double quantum well structure, and present an investigation of the Curie temperature (Tc) modulation in this quantum structure. The combined effects of applied electric fields and spontaneous electric polarization are considered for a system that consists of a Mn \delta-doped well, a barrier, and a p-type ferroelectric well. We calculate the change in the envelope functions of carriers at the lowest energy sub-band, resulting from applied electric fields and switching the dipole polarization. By reversing the depolarizing field, we can achieve two different ferromagnetic transition temperatures of the ferromagnetic quantum well in a fixed applied electric field. The Curie temperature strongly depends on the position of the Mn \delta-doped layer and the polarization strength of the ferroelectric well.Comment: 9 pages, 5 figures, to be published in Phys. Rev. B (2006) minor revision: One of the line types is changed in Fig.

    Entropy of the Randall-Sundrum brane world with the generalized uncertainty principle

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    By introducing the generalized uncertainty principle, we calculate the entropy of the bulk scalar field on the Randall-Sundrum brane background without any cutoff. We obtain the entropy of the massive scalar field proportional to the horizon area. Here, we observe that the mass contribution to the entropy exists in contrast to all previous results, which is independent of the mass of the scalar field, of the usual black hole cases with the generalized uncertainty principle.Comment: 12 pages. The improved version published in Phys. Rev.

    The Ties that Bind: Asian American Communities without \u27\u27Ethnic Spaces in Southeast Michigan

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    According to the 2000 census, over 12 million Asian Americans, almost 70 percent of them either immigrants who came to the U.S. after 1970 or their children, comprised an ethnically and socioeconomically diverse population that was more regionally dispersed throughout the U.S. than ever before. (Lai and Arguelles, 2003). Despite these transitions and increasing heterogeneity, discourses about Asian American communities have focused on ethnic enclaves such as Chinatowns, Koreatowns, and Little Saigons where coethnic residents, businesses, services, institutions and organizations exist and interact in urban or suburban physical spaces of the bicoastal United States (Fong, 1994; Li, 1999; Zhou and Bankston, 1988). According to Kathleen Wong (Lau), these tangible markers tied to space are often privileged as authentic Asian American communities while those without demographic concentrations and geographically bound enclaves are less advanced communities; as a result, [w]hat is not recognized in the literature is the \u27localness\u27 of this production. [1997:83]

    The Effectiveness of a Contact Filter for the Removal of Iron from Ground Water

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    Various types of modified filters were investigated to replace greensand filters which clogged when removing ground water. A properly designed uniform-grain sized filter can increase the filtration time more than ten times that of ordinary sand or greensand filters. The filter medium was obtained by passing commercial filter material between two standard sieves of a close size range, so that the resulting medium was of a uniform size. The head loss rate on such a medium was independent of the filter depth and was inversely proportional to the almost 3/2 power of the grain size. On the other hand, the filter depth was almost linearly proportional to the time of protective action. The effects of the grain size, filter depth, and filter material on the filter run were evaluated with a synthetic iron water; and optimum filter depths for each unisized material were determined. At identical filtration conditions, anthracite had a 70 to 110% longer filter run than the sand medium, and it was attributed to the greater porosity of the former. Expectedly, the time to reach initial leakage of the iron floc was greater with the coarse and more porous medium. but was reduced to an insignificant amount when the filter depth was increased to three to six feet. The performance of unisized filters on permanganate-treated ground water was much better than that of fine-grained greensand. Applicability of experimental data on an existing filtration theory was investigatedThe work upon which this report is based was supported by funds (Proj. A-025-ALAS) provided by the United States Department of the Interior, Office of Water Resources Research, as authorized under the Water Resources Act of 1964

    Pulsar Velocity with Three-Neutrino Oscillations in Non-adiabatic Processes

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    We have studied the position dependence of neutrino energy on the Kusenko-Segr\`{e} mechanism as an explanation of the proper motion of pulsars. The mechanism is also examined in three-generation mixing of neutrinos and in a non-adiabatic case. The position dependence of neutrino energy requires the higher value of magnetic field such as B3×1015B\sim 3\times 10^{15} Gauss in order to explain the observed proper motion of pulsars. It is shown that possible non-adiabatic processes decrease the neutrino momentum asymmetry, whereas an excess of electron neutrino flux over other flavor neutrino fluxes increases the neutrino momentum asymmetry. It is also shown that a general treatment with all three neutrinos does not modify the result of the two generation treatment if the standard neutrino mass hierarchy is assumed.Comment: 8 pages, REVTEX, no figure