487 research outputs found

    Breather solutions for a quasilinear (1+1)-dimensional wave equation

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    We consider the (1+1)(1 + 1)-dimensional quasilinear wave equation g(x)wttwxx+h(x)(wt3)t=0g(x)w_{tt} − w_{xx} + h(x)(w^3_t)_t = 0 on R×R\mathbb{R}\times\mathbb{R} which arises in the study of localized electromagnetic waves modeled by Kerr-nonlinear Maxwell equations. We are interested in time-periodic, spatially localized solutions. Here gL(R)g\in L^{\infty}(\mathbb{R}) is even with g≢0g\not\equiv 0 and h(x)=γδ0(x)h(x) = \gamma\delta_0(x) with γR\{0}\gamma\in\mathbb{R}\backslash\{0\} and δ0\delta_0 the delta distribution supported in 00. We assume that 00 lies in a spectral gap of the operators Lk=d2dx2k2ω2gL_k = \frac{d^2}{dx^2}-k^2\omega^2g on L2(R)L^2(\mathbb{R}) for all k2Z+1k\in 2\mathbb{Z}+1 together with additional properties of the fundamental set of solutions of LkL_k. By expanding ww into a Fourier series in time we transfer the problem of finding a suitably defined weak solution to finding a minimizer of a functional on a sequence space. The solutions that we have found are exponentially localized in space. Moreover, we show that they can be well approximated by truncating the Fourier series in time. The guiding examples, where all assumptions are fulfilled, are explicitely given step potentials and periodic step potentials gg. In these examples we even find infinitely many distinct breathers

    Breather solutions for a quasi‐linear (1+1)‐dimensional wave equation

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    We consider the (1 + 1)-dimensional quasi-linear wave equation ()+h()(3)=0()_{} − _{} + ℎ()(^{3}_{} )_{} = 0 on ℝ×ℝ that arises in the study of localized electromagnetic waves modeled by Kerr-nonlinear Maxwell equations. We are interested in time-periodic, spatially localized solutions. Here (R) ∈ ^{∞}(ℝ) is even with ≢ 0 and h()=0()ℎ() = _{0}() with ∈ ℝ∖{0} and 0_{0} the delta-distribution supported in 0. We assume that 0 lies in a spectral gap of the operators _{} = − \frac {d^{2}}{d^{2}} − ^{2}^{2} on 2(R)^{2}(ℝ) for all ∈ 2ℤ+1 together with additional properties of the fundamental set of solutions of _{}. By expanding into a Fourier series in time, we transfer the problem of finding a suitably defined weak solution to finding a minimizer of a functional on a sequence space. The solutions that we have found are exponentially localized in space. Moreover, we show that they can be well approximated by truncating the Fourier series in time. The guiding examples, where all assumptions are fulfilled, are explicitly given step potentials and periodic step potentials . In these examples, we even find infinitely many distinct breathers

    Paper Session I-C - Autonomous Microgravity Industrial Carrier (AMICA) Initiative

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    GE Astro-Space Division, Pnnceton, New Jersey, has joined with MBB-ERNO of Germany* Aerltalla, and MATRA, in proposing a program employing two spacecraft which would offer flight opportunities to the space science community in the 1990s. The first of these spacecraft would be obtained by transfer of the European Retrievable Carrier (EURECA) to this initiative. EURECA is a spacecraft currently under development, scheduled for launch in May 1991 and retrieval in January 1992. The second spacecraft, called the - Autonomous Microgravity Industrial Carrier (AMIGA), would also be built, as a\u27 duplicate of EURECA... The entire program is referred to as the AMIGA Initiative. AMICA Is a free-flyer spacecraft that features the highest degree of mlcrogravlty, extended flight duration, cleanliness, retrlevablllty and re-flight. \u27It. Is therefore a key element 1n the 1990s Industrialization of space. The program evolves from the EURECA. program which will in 11991 carry a variety of experiments In Solar Physics, Atmospheric Physics, Gamma-Ray Astronomy, Astrophysics* Materials Science, Life Science, and technology development. The EURECA spacecraft, in turn, employs techniques used in the Shuttle Pallet Satellite. AMIGA, therefore, represents a low-risk approach based on extensive space flight experience

    Erneuerbare Energien - Energiewirtschaftsgesetz: Wie sollte ein zukunftsfähiges Energieversorgungssystem aussehen?

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    Wie könnte ein zukunftsfähiges Energieversorgungssystem aussehen und welche Bedeutung hat dabei das Erneuerbare-Energien-Gesetz? Prof. Dr. Rainer Frank Elsässer, E.ON AG, vermisst u.a. die europäische Perspektive. Für Bernhard Hillebrand, EEFA, Münster, und Prof. Dr. Wolfgang Ströbele, Universität Münster, ist der Ausbau regenerativer Energiequellen allenfalls eine langfristige Option. Stephan Kohler, dena, Berlin, plädiert für eine "Innovationsoffensive". Prof. Dr. Uwe Leprich, Hochschule für Technik und Wirtschaft, Saarbrücken, betont die Notwendigkeit einer stärkeren Dezentralisierung des Energieversorgungssystems

    Star formation environments and the distribution of binary separations

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    We have carried out K-band speckle observations of a sample of 114 X-ray selected weak-line T Tauri stars in the nearby Scorpius-Centaurus OB association. We find that for binary T Tauri stars closely associated to the early type stars in Upper Scorpius, the youngest subgroup of the OB association, the peak in the distribution of binary separations is at 90 A.U. For binary T Tauri stars located in the direction of an older subgroup, but not closely associated to early type stars, the peak in the distribution is at 215 A.U. A Kolmogorov-Smirnov test indicates that the two binary populations do not result from the same distibution at a significance level of 98%. Apparently, the same physical conditions which facilitate the formation of massive stars also facilitate the formation of closer binaries among low-mass stars, whereas physical conditions unfavorable for the formation of massive stars lead to the formation of wider binaries among low-mass stars. The outcome of the binary formation process might be related to the internal turbulence and the angular momentum of molecular cloud cores, magnetic field, the initial temperature within a cloud, or - most likely - a combination of all of these. We conclude that the distribution of binary separations is not a universal quantity, and that the broad distribution of binary separations observed among main-sequence stars can be explained by a superposition of more peaked binary distributions resulting from various star forming environments. The overall binary frequency among pre-main-sequence stars in individual star forming regions is not necessarily higher than among main-sequence stars.Comment: 7 pages, Latex, 4 Postscript figures; also available at http://spider.ipac.caltech.edu/staff/brandner/pubs/pubs.html ; accepted for publication in ApJ Letter

    Nonlocal thermoelectricity in a Cooper-pair splitter

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    We investigate the nonlocal thermoelectric transport in a Cooper-pair splitter based on a double-quantum-dot-superconductor three-terminal hybrid structure. We find that the nonlocal coupling between the superconductor and the quantum dots gives rise to nonlocal thermoelectric effects which originate from the nonlocal particle-hole breaking of the system. We show that Cooper-pair splitting induces the generation of a thermo-current in the superconducting lead without any transfer of charge between the two normal metal leads. Conversely, we show that a nonlocal heat exchange between the normal leads is mediated by non-local Andreev reflection. We discuss the influence of finite Coulomb interaction and study under which conditions nonlocal power generation becomes possible, and when the Cooper-pair splitter can be employed as a cooling device.Comment: 12 pages, 7 figure

    Kernheizwerke : technische Konzepte und Marktpotentiale ; BMFT Fördervorhaben AB 0158. Zusammenfassung des Gesamtprojekts

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    Die Ziele dieser Arbeit waren: * die bisher bekannten Heizreaktorkonzepte bezüglich der Auslegung, Sicherheitseigenschaften und Kosten zu analysieren und den Stand der Technik sowie die Anforderung aus sicherheitstechnischer und betrieblicher Sicht darzustellen, * schwerpunktmäßig Beurteilung wichtiger neuer Auslegungsprinzipien wie thermohydraulisches und reaktordynamisches Verhalten von Reaktoren mit zweiphasigem Leichtwasser-Naturumlauf und reaktorphysikalische Auslegungsfragen bei solchen Anlagen wie Moderatordichtekoeffizienten und Abbrandverhalten bei sehr langen Brennstoffzyklen. * Beurteilung des Kernverhaltens von Heizreaktoren bei hypothetischer Annahme des totalen Ausfalls der Wärmeabfuhr durch Kernschmelz-Simulationsrechnungen mit dem Programmsystem KESS-2, * systematischer Vergleich der Kernheizwerke mit fossilen Alternativsystemen und Abschätzung von technischen und wirtschaftlichen Potentialen in der Niedertemperaturwärmeversorgung der Bundesrepublik Deutschland sowie eine Untersuchung der Exportchancen, * Analyse der umweltbezogenen Aspekte bei Kernheizwerken im Vergleich zu den Alternativsystemen, * Untersuchung der Einsatzmöglichkeiten von Kernheizwerken

    Lasing in Si₃N₄-organic hybrid (SiNOH) waveguides

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    Silicon nitride (Si3_{3}N4_{4}) waveguides offer low-loss wave propagation over a wide spectral range including visible wavelengths and lend themselves to photonic integrated circuits for bio-photonic applications. The Si3_{3}N4_{4} device portfolio, however, is so far limited to passive devices that need to be fed by external light sources. This often requires delicate and costly fiber-chip coupling schemes that are subject to stringent alignment tolerances. In this paper, we present and investigate a class of lasers that combine Si3_{3}N4_{4} waveguides with light-emitting organic cladding materials in a hybrid approach. These Si3_{3}N4_{4}-organic hybrid (SiNOH) lasers are operated by optical pumping from the top with low alignment precision. We theoretically and experimentally investigate different SiNOH laser concepts based on spiral-shaped ring resonators and distributed feedback (DFB) resonators. While our devices are designed for an emission wavelength of approximately 600 nm, the SiNOH laser concept can be transferred to a large range of wavelengths in the visible spectrum. The devices are amenable to cost-efficient mass production and have the potential to address a wide range of applications in bio-photonics and point-of-care diagnostics
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