Validation of a thermal decomposition mechanism of formaldehyde by detection of CH2O and HCO behind shock waves

The thermal decomposition of formaldehyde was investigated behind shock waves at temperatures between 1675 and 2080 K. Quantitative concentration time profiles of formaldehyde and formyl radicals were measured by means of sensitive 174 nm VUV absorption (CH₂O) and 614 nm FM spectroscopy (HCO), respectively. The rate constant of the radical forming channel (1a), CH₂O + M → HCO + H + M, of the unimolecular decomposition of formaldehyde in argon was measured at temperatures from 1675 to 2080 K at an average total pressure of 1.2 bar, k_1a = 5.0 × 10¹⁵ exp(‐308 kJ mol^?1/RT) cm³ mol^?1 s^?1. The pressure dependence, the rate of the competing molecular channel (1b), CH₂O + M → H₂ + CO + M, and the branching fraction β = k_1a/(kA_1a + k_1b) was characterized by a two‐channel RRKM/master equation analysis. With channel (1b) being the main channel at low pressures, the branching fraction was found to switch from channel (1b) to channel (1a) at moderate pressures of 1–50 bar. Taking advantage of the results of two preceding publications, a decomposition mechanism with six reactions is recommended, which was validated by measured formyl radical profiles and numerous literature experimental observations. The mechanism is capable of a reliable prediction of almost all formaldehyde pyrolysis literature data, including CH₂O, CO, and H atom measurements at temperatures of 1200–3200 K, with mixtures of 7 ppm to 5% formaldehyde, and pressures up to 15 bar. Some evidence was found for a self‐reaction of two CH₂O molecules. At high initial CH₂O mole fractions the reverse of reaction (6), CH₂OH + HCO ? CH₂O + CH₂O becomes noticeable. The rate of the forward reaction was roughly measured to be k₆ = 1.5 × 10¹³ cm³ mol^?1 s^?1. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 157–169 2004     

The effect of high electric fields on the structure and dielectric properties of the B2 phase

Dielectric studies are presented of a banana-shaped compound that exhibits the antiferroelectric B₂ phase. Upon application and subsequent removal of strong electric fields the textures and dielectric properties of the phase drastically change. Most notable is the huge increase of the low frequency permittivity. This behaviour would suggest the induction of ferroelectricity by the electric field.     

Untersuchungen über Papaverin

Ohne Zusammenfassung     

Total synthesis of the marine cytotoxic caulibugulones A-D

We report the first total synthesis of the cytotoxic marine alkaloids caulibugulone A-D. This synthesis confirmed the assigned structures and provided sufficient material for further biological testing.     

Photochromic reverse mode polymer dispersed liquid crystals

Control of light intensity and colour are two of the major features required in the realization of smart windows. We designed a bi-functional polymer dispersed liquid crystal (PDLC) film in order to satisfy such requirements, i.e. it is able both to modulate the optical transmission, if an external electric field is applied, and to change colour if exposed to sunlight. A monomer/liquid crystal mixture was doped with a small amount of photochromic material and homeotropically aligned by means of rough surfaces. A transparent and pale pink coloured film was achieved after photopolymerization. Such a film changes colour upon exposure for some seconds to sunlight or ultraviolet radiation in a persistent but reversible manner. In addition, the film appears transparent without the application of an electric field (OFF state) and becomes opaque on application of a driving voltage of about 75 V (ON state), and thus the film operates in reverse mode with respect to conventional PDLCs.     

PARTIAL VERSUS GENERAL STORAGE POLICY: COMMODITIES AND RESOURCES

This paper examines joint storage considerations when both commodities and resources can be stored, e.g., grain and water for irrigation. Results suggest that when separate agencies control public resource and commodity storage, suboptimal storage rules occur unless (i) each agency is sensitive to the policies of the other, (ii) commodity inventories are adjusted in response to prices, and (iii) resource inventories are adjusted in response to both commodity demand and resource supply conditions. For example, the common case where water storage depends on weather and reservoir conditions alone is not sufficiently general. The results imply that water management agencies that tend to be dominated by engineers and hydrological considerations need to incorporate economic considerations into decision processes.     

Studies on the chemical constituents of the South China Sea sponge Phacellia fusca

Three pyrrololactam alkaloids have been isolated from the marine sponge Phacellia fusca Schmidt collected from the South China Sea, and their structures were determined as 1–3 , on the grounds of spectral data. This is the first report of these compounds from this sponge. The structure of 1 was confirmed by X-ray analysis.     

Two- and three-dimensional analysis of bose-einstein correlations inπ +/K+p interactions at 250 GeV/c

The NA22 data onπ ^? π ^? correlations are analyzed in terms of a number of two- and three-dimensional parametrizations (Gaussian space-time, Goldhaber, Bowler string-like, Bertsch hydrodynamical, Kopylov-Podgoretskii, etc.). Contrary to the results obtained for e⁺e^? andµp collisions, the Goldhaber parametrization, as well as string-like models, fail in describing the hadron-hadron data. Better fits are obtained in the framework of surface-emitting fireball-like models, both when including and excluding hydrodynamical expansion of nuclear matter. Our results indicate that pion radiation occurs at earlier stages of matter evolution than in nuclear collisions.