Diameter Distribution of Spherical Primary Grains in the boolean model from small-angle scattering

A method for determining the size-distribution density of small spheres which are arranged, without any interaction between them, at random positions in space and form an isotropic twophase system is presented. In the case of higher volume fractions, frequent overlapping between the spheres is a logical consequence. This effect is an essential feature of the model itself and is well considered and observed. Stereological information, which contains all the necessary data about the unknown size distribution, is obtained from the angular intensity distribution (small-angle scattering experiment) of the particle system concerned. The resulting formula still includes, in a first representation, the volume fraction p as a free parameter. In a second step, a general analytical method for the determination of the volume fraction p from the set covariance of the considered random closed set is derived. Therefore, the unknown diameter distribution can be obtained in every detail, starting from the scattering curve of the sample, by way of two independent working steps.     

Zwei Dualräume der unendlichen,symmetrischen Gruppe

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Über das lexikographische und das kostarke Produkt von Mengensystemen

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Unusual and Novel C11H16 Hydrocarbons from the Southern Australian Brown Alga Dictyopteris acrostichoides (Phaeophyceae)

Unusual and novel C₁₁H₁₆ olefins with (E)- or (E,E)-configuration instead of the previously known (Z)- or (E,Z)-configuration at the double bond(s) within the longer side chain are the main products of the Australian phaeophyte Dictyopteris acrostichoides. This configuration anomaly refers to all four series of alicyclic C₁₁H₁₆ hydrocarbons, namely the disubstituted cyclopentenes and cyclopropanes, as well as the monosubstituted cycloheptadienes and cyclopentenes. Chiral compounds within the above series have the same absolute configuration. The two (cyclopent-3-enyl)hexa-1, 3-dienes 11 and 13 are found for the first time. The absolute configuration and optical purity of the hydrocarbons are determined by gas chromatography on modified cyclodextrins as chiral stationary phases. The synthesis of chiral references via lipase-catalyzed resolutions is described.     

Effect of water treatment on analyte and matrix ion yields in matrix-assisted time-of-flight secondary ion mass spectrometry: the case of insulin in and on hydroxycinnamic acid

A systematic study was performed to identify the origin of surprisingly high analyte-to-matrix yield ratios recently observed in time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis of oligo- and polypeptides mixed in matrices of alpha-cyano-4-hydroxycinnamic acid (4HCCA). Several sets of samples of porcine insulin in 4HCCA (1:3100 molar) were prepared from liquid solutions by a nebuliser technique, with more than one order of magnitude variation in sprayed material (substrate silicon). Following different periods of storage in air and/or vacuum as well as exposure to high-purity water, TOF-SIMS analysis was performed under oblique impact of 22 keV SF5+. Treatment with water involved either deposition of a droplet covering the whole sample for times between 1 and 20 min or spraying with water in droplet equivalent quantities. The analyte and matrix molecules were detected as protonated molecules (insulin also in doubly protonated form). Even the as-prepared samples usually showed insulin-to-4HCCA yield ratios exceeding the molar ratio of the mixed material. Upon ageing in vacuum the matrix ion yields remained constant but the analyte yields decreased, partly due to break-up of intrachain disulfide bonds. Water treatment resulted in a pronounced decrease in the 4HCCA yield, typically by a factor of five, in parallel with an increase of the insulin yield, by up to a factor of four. Evidence is provided that these changes occur concurrently with a partial dissolution of 4HCCA at the sample surface. The enhanced insulin yield was not correlated with the Na+ yield. The typically 20-fold increase in the insulin-to-4HCCA yield ratio, generated by water exposure of the samples, provides the explanation for the high yield ratios observed previously with water-treated samples. Spraying with water or repeated exposure to water droplets caused a pronounced degradation of the insulin parent yields in combination with an increasing appearance of signals due to the B- and A-chains of insulin. To clarify the issue of surface segregation, a few samples were prepared by spraying acetone-diluted solutions of insulin on previously deposited layers of 4HCCA. Whereas the insulin yields from as-prepared samples were rather low, the yields observed after water treatment were comparable with those observed with samples of insulin in 4HCCA. The results suggest that a large amount of insulin is present at the surface of samples prepared from liquid mixtures of insulin in 4HCCA. With both methods of sample preparation, however, high secondary ion yields of insulin were only obtained after exposure of the samples to water. The chemical changes responsible for this beneficial effect still need to be identified.     

Information on measurement uncertainty in test and product standards

According to ISO/IEC 17025, accreditation bodies generally accept that test procedures in normative documents have been validated. This contribution investigates, with respect to measurement uncertainty, the methodical basis of this practice in general and examines specifically two very different groups of products: asphalt, with its major components mineral aggregates and bitumen, and metal wire cloth. The author concludes that both the general and the specific situations are incoherent. The practice of accepting standardised test procedures a priori as validated does not have a sound basis in all cases. Both the concept, and the practical application, of validation or fitness for purpose vary in different product groups. The impact of this situation on the practice of accreditation should be taken into account in order to reduce market distortions in single-product groups. Laboratories face fundamental consequences from this practice.Presented at the Metro Trade Workshop on Traceability and Measurement Uncertainty in Testing, 30–31 January 2003, Berlin, Germany