Quantum theory of spontaneous and stimulated emission of surface plasmons

We introduce a quantization scheme that can be applied to surface waves propagating along a plane interface. An important result is the derivation of the energy of the surface wave for dispersive non-lossy media without invoking any specific model for the dielectric constant. Working in Coulomb's gauge, we use a modal representation of the fields. Each mode can be associated with a quantum harmonic oscillator. We have applied the formalism to derive quantum-mechanically the spontaneous emission rate of surface plasmon by a two-level system. The result is in very good agreement with Green's tensor approach in the non-lossy case. Green's approach allows also to account for losses, so that the limitations of a quantum approach of surface plasmons are clearly defined. Finally, the issue of stimulated versus spontaneous emission has been addressed. Because of the increasing density of states near the asymptote of the dispersion relation, it is quantitatively shown that the stimulated emission probability is too small to obtain gain in this frequency region.Comment: 14 pages, 5 figures, submitted to Phys. Rev. B

Technical Assessments of Future European Space Transportation Options

The paper describes some of the most recent activities in Germany in the technical assessment of future European launcher architecture. In focus is a joint effort of DLR-SART with German launcher industry in the definition of a next generation upper-medium class expendable TSTO with an initial operational capability after 2020. Involved companies are EADS astrium and MT Aerospace. This DLR-agency funded study WOTAN investigates fully cryogenic launchers as well as those with a combination of solid and cryogenic stages, fulfilling a requirement of 5000 kg single payload into GTO. Solid strap-on boosters should allow both versions further payload growth capability. In its second part the paper analyzes options for new liquid fuel upper stages to be put on the P80 solid first stage of the Vega small launcher. Versions with storable as well as cryogenic propellants are investigated in a preliminary launcher system lay-out and their technical viability is critically assessed

Pro- and anti-inflammatory cytokines in threatened miscarriages

OBJECTIVE: The purpose of this study was to evaluate circulating and intracellular levels of Th1 and Th2 cytokines in women with threatenedmiscarriage (TM) and subsequent outcome. STUDY DESIGN: Plasma levels of tumor necrosis factor (TNF)-receptors 1 and 2, TNF , interferon gamma (IFN ), and interleukins (IL) -6 and -10 were measured by flow cytometric bead assays in 80 women with TM: 53 women with normal outcome and 27 women who miscarried. Fluorescent antibody labeling was also performed on whole blood in a subgroup of 27 women of TM: 16 women with normal outcome and 11 women who miscarried. RESULTS: Monocyte expression of TNF and circulating levels of TNF , IFN , IL-10, IL-6, and TNF-R1 were significantly lower, whereas circulating levels of TNF /IL-10, IFN /IL-10, and TNF /IL-6 ratios were significantly higher, in women with TM who subsequently miscarried, compared with the women with normal outcome. CONCLUSION: An increased Th1 type of immune response, which was similar to that observed in preterm delivery, was found in TM cases that were complicated by a subsequent miscarriage.peer-reviewe

The detectability of extrasolar planet surroundings - I. Reflected-light photometry of unresolved rings

It is expected that the next generation of high-contrast imaging instruments will deliver the first unresolved image of an extrasolar planet. The emitted thermal infrared light from the planet should show no phase effect assuming the planet is in thermal equilibrium. But the reflected visible light will vary versus the phase angle. Here, we study the photometric variation of the reflected light versus the orbital phase of a ringed extrasolar planet. We show that a ring around an extrasolar planet, both obviously unresolved, can be detected by its specific photometric signature. A simple quantitative model is discussed, taking into account the basic optical and geometrical properties of the ringed planet.Comment: Keywords: Stars: planetary systems -- Planets: rings -- Extrasolar planet characterization. 10 pages, 16 figures. Published version is A&A 420, 1153-1162 (2004), available online at http://www.edpsciences.org/articles/aa/abs/2004/24/aa0720/aa0720.htm

Magnetic reversals in a simple model of MHD

We study a simple magnetohydrodynamical approach in which hydrodynamics and MHD turbulence are coupled in a shell model, with given dynamo constrains in the large scales. We consider the case of a low Prandtl number fluid for which the inertial range of the velocity field is much wider than that of the magnetic field. Random reversals of the magnetic field are observed and it shown that the magnetic field has a non trivial evolution linked to the nature of the hydrodynamics turbulence.Comment: 4 pages, submitted to PR