487 research outputs found
Breather solutions for a quasilinear (1+1)-dimensional wave equation
We consider the -dimensional quasilinear wave equation on 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 is even with and with and the delta distribution supported in . We assume that lies in a spectral gap of the operators on for all 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 explicitely given step potentials and periodic step potentials . In these examples we even find infinitely many distinct breathers
Breather solutions for a quasi‐linear (1+1)‐dimensional wave equation
We consider the (1 + 1)-dimensional quasi-linear wave equation 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 is even with ≢ 0 and with ∈ ℝ∖{0} and 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 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
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?
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
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
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
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
Silicon nitride (SiN) 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 SiN 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 SiN waveguides with light-emitting organic cladding materials in a hybrid approach. These SiN-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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