A Modified Linear Sampling Method Valid for all Frequencies and an Application to the Inverse Inhomogeneous Medium Problem

We consider the inverse inhomogeneous medium scattering problem in acoustics where one tries to recover the support of anomalies in a medium by interrogating the region of interest with plane waves at fixed frequency. We discuss the validity of the Linear Sampling Method (LSM) for solving this inverse problem, and its connection to an unusual eigenvalue problem. It turns out that the existence of non-trivial solutions of the so-called interior transmission eigenvalue problem results in the failure of the LSM. We then propose a modification of the LSM that avoids these shortcomings and is numerically sound. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Coupled-mode theory of a fiber laser-amplifier

Abstract

The behavior of a fiber laser-amplifier is considered, including the effects of mode coupling, radiation losses, and noise. In the linear regime, a competitive effect between mode coupling and losses is present, in the sense that mode coupling tends to equalize the gains of different modes, while radiation losses favor low-order modes. Thus, single-mode amplification and collective amplification are predominant, respectively, in the weak and strong coupling case. In the saturated regime a mode coupling effect is found that is independent of fiber imperfections and relies on the nonlinear nature of the process.     

Microwave Induced Reaction of H-Dimethylphosphonate with Styrene Oxide

Microwave catalyzed reaction of a neat mixture of styrene oxide and H-dimethylphosphonate furnished dimethyl methylphosphonate, trimethylphosphate, phenylacetaldehyde, 1-methoxy-2-phenylethanol, 1-phenylethleneglycol, cis- and trans-1,3-diphenylcyclobutanes, hydrogen 1-(2-phenylethyl)methylphosphinate, (1-phenylethyl)dimethylphosphonate, and (1-phenylethyl)dimethylphosphonate via free radical processes.     

Relative stability of the2 A 1g and2 E g states of the C2H 6 + ion

Anab initio study of the relative stability for the states² A _1g and² E _g of C₂H ₆ ⁺ has been carried out. The results of the Open Shell Restricted Hartree-Fock calculations lead to assign the² A _{1 g} as the ground state of the molecule in agreement with previous SCF calculations.The correlation energy associated to both states has been calculated within the correlation hole model and the results, contrary to those obtained from Configuration Interaction calculations, do not alter qualitatively the conclusions from SCF.     

Untersuchung der Umsetzung von Schwefel mit Natriumnitrit in DMF,DMSO und HMPT

Investigation of the Reaction of Sulfur with Sodium Nitrite in DMF, DMSO, and HMPA The mechanism of the title reaction has been elucidated by VIS/UV, IR, ¹⁵N NMR, and ESR spectrometric measurements, gas analysis, and chromatography. The course of the complex reaction and the great number of products — nitrous oxide, nitric oxide, sodium thiosulfate, sulfate, polysulfides, polythionates, nitrate — can be explained with the assumption that at first perthionitrates NaS_xNO₂ are formed, which are decomposed either to give dinitrogen monoxide and thiosulfate, or, react with nitrite to yield nitrate and perthionitrite NaS₂NO which dissociates reversibly into sodium trisulfide(-I) and nitrogen monoxide. (The details of the two main series of competitive and consecutive reaction steps can be seen from the tabular summary at the end of the text). The characteristic colour change during the reaction from blue-Green to orange-red is due to the formation of the two coloured species: S₃^? (blue, λ_max = 620 nm, g = 2.029) and ONSS^? (red, λ_max = 448 nm, δ(¹⁵N) = 334 ppm, ref. K¹⁵NO₃).     

Electron and ion beam induced heating effects in solids measured by laser interferometry

A sensitive interferometric technique has been applied for studying the thermal displacement of thin film heated by electron or ion beams. The steady state displacement has been measured and we discuss the dependence on material properties and film thickness showing that this method has a potential for in-situ monitoring of thin-film deposition or etching. Transient effects are studied in a thin quartz plate and the propagation velocity of thermal waves is measured.Our colleague Martin Nonnenmacher passed away May 1992. We deplore his early death deeply and acknowledge gratefully the excellent cooperation with him.     

Mössbauer Spectra of Clays and Ceramics

The physical, chemical and mineralogical aspects of the use of Mössbauer spectroscopy in studies of clay-based ceramics are described. Mössbauer spectra of pottery clays fired under oxidising, reducing and changing conditions are explained, and the possibilities of using Mössbauer spectra to derive information on the firing temperatures and the kiln atmosphere during firing in antiquity are discussed and illustrated by examples.