University of Stuttgart

About: University of Stuttgart is a education organization based out in Stuttgart, Germany. It is known for research contribution in the topics: Laser & Finite element method. The organization has 27715 authors who have published 56370 publications receiving 1363382 citations. The organization is also known as: Universität Stuttgart.

Passive high-power microwave components

Abstract: This review discusses the present state-of-the-art of passive high-power microwave components for applications in microwave systems for RF plasma generation and heating, plasma diagnostics, plasma and microwave materials processing, spectroscopy, communication, radar ranging and imaging, and for drivers of next generation high-field-gradient electron-positron linear colliders. The paper reports on high-power components for overmoded high-power transmission systems such as smooth-wall waveguides, HE/sub 11/ hybrid mode waveguides and quasi-optical TEM/sub 00/ beam waveguides. These include various types of mode converters, polarizers, cross-section tapers, bends, mode selective filters, pulse compressors, DC-breaks, directional couplers, beam combiners and dividers, vacuum windows, and instruments for mode analysis. Problems of ohmic attenuation and unwanted conversion to parasitic modes are discussed in detail and rules for alignment requirements are given. In the case of waveguide transmission, this review mainly concentrates on circular waveguide components but also deals with rectangular waveguide.

Synthesis and Reactions of Optically Active Cyanohydrins

Abstract: Cyanohydrins have always held a place of importance both as technical products and as reagents in organic chemistry. It is surprising, therefore, that optically active Cyanohydrins have been extensively investigated and employed for syntheses relatively recently. This can be explained by the fact that only in the past few years have enzymatic methods made chiral Cyanohydrins readily available in high optical purity. Chiral Cyanohydrins are widespread in nature in the form of the respective glycosides and serve roughly 3000 plants and many insects as antifeedants. For the preparative organic chemist, this class of compounds offers an enormous synthetic potential for making other chiral compounds accessible. In a few instances, the pharmacological principle of a drug also incorporates a chiral cyanohydrin as constitutive structural element. In the development of novel, physiologically active compounds all possible stereo-isomers must be synthesized and investigated with respect to their activity range and the pathway of their metabolic transformations and/or degradation. The development of simple synthetic procedures for such compounds, which also entail a high degree of stereoselectivity, therefore has prime importance. To this end chiral Cyanohydrins may serve as stereochemically pure starting materials. In the present review, the following topics will be addressed: enantioselective addition of hydrogen cyanide (HCN), catalysed by the enzymes (R)-and (S)-oxynitrilase, to aldehydes and Ketones yielding (R) and (S) cyanohydrins, respectivity; enantioselective addition of HCN to aldehydes catalyzed by cyclic dipeptides; enantioselective esterification of racemic ocyanohydrins and enantioselective hydrolysis of cyanohydrin esters caytalyzed by lipases and esterases, reprectively; transformation of the nitrile groups of chiral cyanohydrins to provide optically active -hydroxycarboxylic acids, aldehydes, and ketones, as well as 2-amino alcohols; sulfonylation of the OH group of chiral cyanohydrins to furnish optically active -sulfonyloxynitriles which undergo SN2 displacement of the activated OH group yielding α-azido-,α -amino, and α-fluoronitriles with inverted configuration.

WATER, METHANE, AND CARBON DIOXIDE PRESENT IN THE DAYSIDE SPECTRUM OF THE EXOPLANET HD 209458b

Abstract: Using the NICMOS instrument on the Hubble Space Telescope, we have measured the dayside spectrum of HD 209458b between 1.5 and 2.5 μm. The emergent spectrum is dominated by features due to the presence of methane (CH4) and water vapor (H2O), with smaller contributions from carbon dioxide (CO2). Combining this near-infrared spectrum with existing mid-infrared measurements shows the existence of a temperature inversion and confirms the interpretation of previous photometry measurements. We find a family of plausible solutions for the molecular abundance and detailed temperature profile. Observationally resolving the ambiguity between abundance and temperature requires either (1) improved wavelength coverage or spectral resolution of the dayside emission spectrum or (2) a transmission spectrum where abundance determinations are less sensitive to the temperature structure.