Structure elucidation of polyene systems with extensive charge delocalization-carbocations from allylic carotenols

[structure: see text] The structures of two diastereomeric cations, readily prepared from beta, beta-caroten-4-ol (1) by treatment with trifluoroacetic acid, have been determined by NIR and NMR spectroscopy, resulting in the complete structure elucidation of the most extensively delocalized carbocations so far described. Higher partial charge was observed toward the center of the polyene chain (larger filled red circles). Bond reversion occurs in the central region of the molecule.     

Majority voting leads to unanimity

We consider a situation where society decides, through majority voting in a secret ballot, between the alternatives of ‘reform’ and ‘status quo’. Reform is assumed to create a minority of winners, while being efficient in the Kaldor–Hicks sense. We explore the consequences of allowing binding transfers between voters conditional on the chosen alternative. In particular, we establish conditions under which the winners wish to compensate all losers, thus leading to unanimity for reform, rather than compensating some losers to form a non-maximal majority. The analysis employs concepts from cooperative game theory.      

Denotational semantics for intuitionistic type theory using a hierarchy of domains with totality

A modified version of Normann's hierarchy of domains with totality [9] is presented and is shown to be suitable for interpretation of Martin-L?f's intuitionistic type theory. This gives an interpretation within classical set theory, which is natural in the sense that -types are interpreted as sets of pairs and -types as sets of choice functions. The hierarchy admits a natural definition of the total objects in the domains, and following an idea of Berger [3] this makes possible an interpretation where a type is defined to be true if its interpretation contains a total object. In particular, the empty type contains no total objects and will therefore be false (in any non-empty context). In addition, there is a natural equivalence relation on the total objects, so we derive a hierarchy of topological spaces (quotient spaces wrt. the Scott topology), and give a second interpretation using this hierarchy. Received: 11 December 1995 / Revised version: 14 October 1996     

Studies on the mechanism of the Carr-Price blue colour reaction

The reaction of retinoids (retinol, retinyl acetate and anhydroretinol) with Br?nsted acids was studied as a model system for the Carr-Price reaction. The anhydroretinylic cation was characterised by VIS and 2D NMR spectroscopy, including an estimate of the charge distribution and region of bond inversion, observed in a mixture of identified E/Z isomers. Products obtained by quenching with NaOMe-MeOH were identified by HPLC and MS. The classical Carr-Price reaction between retinol (vitamin A) and the Lewis acid SbCl(3) in saturated chloroform solution was reinvestigated by VIS, NMR, EPR, dynamic light scattering and chemical quenching. Whereas product instability and failure to provide informative NMR spectra indicated a radical cation, EPR results excluded free-radical species. Dynamic light scattering experiments, in comparison with model systems, revealed strong aggregation for the Carr-Price complex, rationalizing the low stability, NMR problems and dimerisation observed by chemical quenching. The VIS data support structural similarity of the blue Carr-Price product with the delocalized anhydroretinylic cation, and a detailed structure of the antimony complex is evaluated.     

Experiments on sound generation in corrugated pipes with flow

The article reports acoustic measurements on short corrugated pipes with flow. Such pipes might generate high sound levels associated with length resonances. One of the main objectives of the study was to estimate the location of the effective sources by studying the energy flow through the pipes. It was found that a short section of corrugations will only produce sound effectively when placed at the inflow end, while for fully corrugated pipes, the sound-producing regions are located around the pressure maxima of the observed standing waves. It was further found that the net energy flow is in the upstream direction for nearly the complete length of pipe.     

Adsorption of phenol and benzyl alcohol onto surfactant modified silica

The adsorption of the surfactant, dodecyltrimethylammonium bromide, DTAB, and the co-adsorption of the additives phenol and benzyl alcohol, onto silica from aqueous solutions are investigated. The adsorption of DTAB is found to increase with increasing alcohol concentration in solutions where the DTAB concentration is below the cmc. Moreover, the corresponding adsorption of DTAB decreases when the DTAB concentration is above the cmc. The co-adsorption of the alcohol is found to increase with increasing alcohol concentration, and benzyl alcohol co-adsorbs more strongly than phenol. The surfactant modified silica shows a very high ability to incorporate phenol and benzyl alcohol. The results are discussed in relation to solubilization site and surfactant aggregate shape.     

Two-dimensional LC-MS fractioning and cross-matching of mass spectrometric data for rational identification of bioactive compounds in crude extracts

Bioprospecting aims at the identification of biological compounds with novel properties. Identification of such compounds in crude complex biological extracts is a comprehensive challenge. As a large number of extracts must be screened for successful identification of one potential promising lead, rational screening strategies must be developed. Here we report on a novel two stage rational LC-MS strategy of extracts already pre-screened and proven to contain bioactive compound(s). All extracts are initially fractionated using one and the same LC condition with parallel mass spectrometric detection. Fractions containing bioactive compound(s) are then subjected to a second fractional stage using two different chromatographic conditions. Mass detection is also included at this stage, and a cross-matching algorithm for comparison of processed mass chromatograms from the two dimensions was developed. The algorithm reports only masses present in bioactive fractions in both dimensions and enable therefore an efficient identification of potential masses that causes the bioactivity. This mass list can be used to search in natural compound database(s) for a rapid evaluation if the mass belongs to an already identified compound or if it is a potentially new one. This strategy enables thorough screening of several hundred crude extracts in one week on one single instrument.     

Modeling of micromachined silicon–polymer 2-2 composite matching layers for 15 MHz ultrasound transducers

Silicon–polymer composites fabricated by micromachining technology offer attractive properties for use as matching layers in high frequency ultrasound transducers. Understanding of the acoustic behavior of such composites is essential for using them as one of the layers in a multilayered transducer structure. This paper presents analytical and finite element models of the acoustic properties of silicon–polymer composites in 2-2 connectivity. Analytical calculations based on partial wave solutions are applied to identify the resonance modes and estimate effective acoustic material properties. Finite Element Method (FEM) simulations were used to investigate the interaction between the composite and the surrounding load medium, either a fluid or a solid, with emphasis on the acoustic impedance of the composite. Composites with lateral periods of 20, 40 and 80 μm were fabricated and used as acoustic matching layers for air-backed transducers operating at 15 MHz. These composites were characterized acoustically, and the results were compared with analytical calculations. The analytical model shows that at low to medium silicon volume fraction, the first lateral resonance in the silicon–polymer 2-2 composite is defined by the composite period, and this lateral resonant frequency is at least 1.2 times higher than that of a piezo-composite with the same polymer filler. FEM simulations showed that the effective acoustic impedance of the silicon–polymer composite varies with frequency, and that it also depends on the load material, especially whether this is a fluid or a solid. The estimated longitudinal sound velocities of the 20 and 40 μm period composites match the results from analytical calculations within 2.7% and 2.6%, respectively. The effective acoustic impedances of the 20 and 40 μm period composites were found to be 10% and 26% lower than the values from the analytical calculations. This difference is explained by the shear stiffness in the solid, which tends to even out the surface displacements of the composites.