Ein Verfahren zur Stabilitätsfrage bei Matrizen-Eigenwertproblemen

Summary Given the eigenvalue problem (A–E) x=0 for real or complex matricesA the number of eigenvalues with positive real parts is determined without evaluating the caracteristical polynomial. A proceeding is developed here to transform the given matrixA into a reduced form by applying a finite series of elementary transformations upon the matrix. The elements of the reduced matrix allow immediately to solve the problem.     

Evaluation of the Sulfate Dynamics in Groundwater by Means of Environmental Isotopes

Abstract

Elevated sulfate concentrations and their heterogeneous distribution in the drinking water catchment area Torgau-Mockritz (Germany) were investigated by means of multiple isotope signatures such as δ³⁴S, δ¹⁸O-H₂O, δD, tritium, and ⁸⁵Kr. δ³⁴S values of the groundwater sulfate vary between -19…+ 37‰ CDT. No simple correlation exists between sulfate concentrations and δ³⁴S. Superimposition of different sulfur sources and mobilization processes combined with a complicated groundwater movement create a complex distribution pattern. The oxidation of reduced sedimentary sulfur has to be regarded as a main source of dissolved sulfate at least regionally. Tritium and ¹⁴C data revealed that old groundwater can be excluded as source for high sulfate contents. Correlated temporal variations in the concentrations of tritium and sulfate are observed in deeper sampling positions. Highly variable δ¹⁸O and δD, as detected in parts of the catchment area, indicate local influences of surface water infiltration into the aquifer. The spatial distribution of isotope signatures enables the identification of zones with descending younger water or hindered groundwater movement and hence provides useful hints for flow modeling.     

Transient processes in photogalvanic cells: Part III. The alternating current photogalvanic cell

An alternating current photogalvanic cell, having a symmetrical electrode configuration, is described. It uses the Ru(bipy)₃²⁺/Fe³⁺ system. The light beam alternately illuminates the two electrodes, yielding almost rectangular current/time and voltage/time responses. The main advantage of this type of a cell is a very stable power output. Unlike other cells, mass transport from one electrode to the other is not necessary, eliminating the disadvantage of slow diffusion processes. A computer simulation of this behaviour is presented. The long-term characteristics depend on the Fe³⁺/Fe²⁺ concentration ratio.     

Charge-Transfer-Übergänge im Pentacyano-benzonitril-ferrat (II)

Charge Transfer Transitions of Pentacyano-Benzonitrile-Ferrate(II) Pentacyano-benzontrile-ferrate(II) shows two charge transfer transitions, which are interpreted as central atom to benzonitrile transitions d-1π* and d-2π*. Selective excitation to the d-1π* state leads to a completely reversible photoreaction. An isosbestic point is observed at 398 nm in aqueous solution.     

ICP–MS trace-element analysis as a forensic tool

Careful tracing of evidence at the site of a crime must be performed before suspects can be convicted of a crime or homicide. Fingerprints and ballistic control samples are important evidence. A common method used to examine lead bullets is comparison of physical properties such as weight, dimensions, shape, and distinctive markings. However ballistic investigations, for example comparison of characteristic scratches and marks left on fired bullets, do not always give sufficient information. Ballistic abrasion patterns can change for a variety of reasons, e.g. deformation or mechanical strain. Sometimes only particles remain in a victims body. In such cases trace-element composition and lead-isotope ratios can be compared with those of controls. Elemental composition of particles and deformed bullets have been compared with the elemental fingerprints and isotope ratios of potential bullet types found on suspects. The applicability of the method was studied for two different cases. Data interpretation and several limitations of the technique are also discussed in this paper.     

Steroide und Sexualhormone. 260. Mitteilung. Limonoide Bitterstoffe V. Untersuchungen zur Stereochemie der C(8)-Alkylierung von 7-Oxo-13,17-secosteroiden

On the Stereochemistry of the C(8)-Alkylation of 7-Oxo-13,17-secosteroids It is shown that the title compounds, e.g. 10 , can be alkylated with methyl iodide under strongly basic conditions to afford 8α-methylated products, e.g. 11 (Scheme 1). The configuration was assigned by ¹³C-NMR.-spectroscopy, CD. measurements, and finally proved by a X-ray crystallographic structure analysis.     

Notizen zur Synthese von 2-Aminophenylsulfonen

Syntheses of some Alkyl, Cycloalkyl and Aryl 2-Aminophenyl Sulfones Syntheses of the alkyl, cycloalkyl and aryl 2-aminophenyl sulfones 10 were achieved by oxidation of the corresponding 2-nitrophenyl sulfides 7 to the 2-nitrophenyl sulfones 9 followed by ethanolic Béchamp-reduction. The sulfides 7 in turn were obtained either by reactions of 2-nitro-thiophenol ( 8 ) with the appropriate alkyl and cycloalkyl halides or of 2-chloro-nitrobenzene ( 5 ) with the relevant thiols. Condensation of 2-nitrobenzenesulfinic acid ( 3 ) with bromoacetic acid in aqueous alkaline solution led - presumably via 2-nitrophenylsulfonylacetic acid ( 4 ) - to methyl 2 nitrophenyl sulfone ( 1 ), reduction of which gave 2-aminophenyl methyl sulfone ( 2 ). Treatment of 2-aminothiophenol ( 11 ) with t-butyl alcohol in aqueous sulfuric acid gave 2-aminophenyl t-butyl sulfide ( 12 ), which was acetylated to o-t-butylthio-acetanilide ( 13 ). Oxidation of the latter to o-t-butylsulfonyl-acetanilide ( 14 ) followed by hydrolysis led to 2-aminophenyl t-butyl sulfone ( 15 ).