Wave-vector diagrams for two-dimensional photonic crystals

Photonic crystals exhibit band gaps, meaning that electromagnetic fields cannot propagate in them for specific ranges of wavelengths and directions. The calculation of band structure diagrams has been intensively studied and is now well understood. In contrast to that, so-called wave-vector diagrams (i.e. dispersion surfaces, depicting the loci of all relevant wave vectors at a fixed wavelength) are less known and used. In principle, they show how the effective index of the structure depends on the direction of propagation. A method to calculate explicitly wave-vector diagrams for two-dimensional photonic crystals is derived which leads finally to quadratic eigenvalue problems. Results for square and triangular lattices are presented and some applications are discussed.     

Synthesis of (±)-Desmarestene and (±)-Viridiene,the Two Sperm Releasing and Attracting Pheromones from the Brown Algae Desmarestia aculeata and Desmarestia viridis

Desmarestene 1 6-(1Z,3-butadienyl)-1,4-cycloheptadiene and viridiene 3 cis-3-(1Z, 3-butadienyl)-4-vinylcyclopentene are chemical messengers for male gametes of the brown algae Desmarestia aculeate and Desmarestia viridis. Total syntheses of 1 , 3 and their stereoisomers 1a , 3a - c are reported. Gas-chromatographic comparison of synthetic 1 and 3 with the corresponding natural products has established their structural identity.     

Structure Determination of a New Spirobicyclic Triterpenoid from Iris foetidissima

The novel iridal 10 has been isolated from rhizome extracts of Iris foetidissima. Its structure was established by spectroscopic methods and oxidative degradation. Final proof of the spirobicyclic nature of the compound – a new feature in the triterpenoid field – was afforded by the correlations observed in the 2D-HMBC- (¹H-detected multiple-bond heteronuclear multiple-quantum coherence) spectrum. The possible biogenesis of this unusual compound is discussed.     

Massenspektrometrische untersuchungen zur elementaranalyse organischer verbindungen—III: Verbrennungsvorgänge im leeren rohr

A measuring system is described which permits study of all stages of combustion processes as functions of carrier gas, temperature, residence time and tube filling. The organic sample is fed at constant speed into a stream of carrier gas. The mixture reaches the combustion chamber within a few milliseconds via a transfer capillary. With the help of a viscous inlet system, a sample of the resulting reaction products is taken and fed into a mass spectrometer. Reaction time and temperature can be adjusted within wide ranges or varied continuously. A plot of the extent of reaction of the various combustion products against temperature at a chosen reaction time yields an oxidation-thermogram which gives a clear picture of the combustion process. It is evident from thermograms of selected compounds that the samples decompose in the presence of oxygen at appreciably lower temperatures than in inert gas. The primary step of the decomposition is “oxidative pyrolysis” which often leads to other products than “inert pyrolysis”. The intermediate products found are partly structurally specific and, especially with nitrogen-containing samples, are numerous and long-lived (for example, carbon monoxide, nitric oxide, cyanogen, hydrocyanic acid, cyanic acid and methyl cyanate). The notorious “difficult combustibility” is largely due to the fact that carbon monoxide, cyanic and hydrocyanic acids undergo complete combustion only at very high temperature. The combustion properties of the “empty tube” can be improved noticeably by a filling of quartz wool and markedly by partly filling with platinum wool.