Influence of Threshold Stress on the Estimation of the Weibull Statistics

The influence of threshold stress on the estimation of the Weibull statistics is discussed in terms of the Akaike information criterion. Numerical simulations show that, if sample data are limited in number and threshold stress is not too large, the two-parameter Weibull distribution is still a preferred choice. For example, the fit of strength data of glass and ceramics to the two- and three-parameter Weibull distributions is compared.     

The impact of relative radiometric calibration on the accuracy of kNN-predictions of forest attributes

The k-nearest-neighbour (kNN) algorithm is widely applied for the estimation of forest attributes using remote sensing data. It requires a large amount of reference data to achieve satisfactory results. Usually, the number of available reference plots for the kNN-prediction is limited by the size of the area covered by a terrestrial reference inventory and remotely sensed imagery collected from one overflight. The applicability of kNN could be enhanced if adjacent images of different acquisition dates could be used in the same estimation procedure. Relative radiometric calibration is a prerequisite for this. This study focuses on two empirical calibration methods. They are tested on adjacent LANDSAT TM scenes in Austria. The first, quite conventional one is based on radiometric control points in the overlap area of two images and on the determination of transformation parameters by linear regression. The other, recently developed method exploits the kNN-cross-validation procedure. Performance and applicability of both methods as well as the impact of phenology are discussed.     

Preparation and characterization of lanthanum silicon nitride

Lanthanum silicon nitride (LaSi₃N₅) powder has been prepared under the relatively mild conditions of 1400 ° C and 1 atm nitrogen. Chemical, X-ray diffraction, solid state nuclear magnetic resonance spectra and morphological information on this powder is presented. The X-ray diffraction data and previously published information have been used to develop a more complete specification of the unit cell dimensions.²⁹Si magic-angle spinning nuclear magnetic resonance spectra of LaSi₃N₅ show two chemical shifts at –64.5 and –56.5 p.p.m. These shifts reflect two electronically different types of silicon which have been attributed to the effects of quadrupolar¹³⁹La nuclei and their spatial arrangements around silicon atoms.     

Synthesis of 2-amino-6-(2-formyl-5-hydroxymethyl-1-pyrrolyl-)hexanoic acid

Summary The title compound has been synthesized by a novel route fromN -trifluoroacetyl lysine methyl ester and 2,9-dimethyldeca-2,8-diene-4,7-dione. Transformation of the pyrrole substituents and easy cleavage of protecting groups yields the compound in samples of high purity.

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Synthese der 2-Amino-6-(2-formyl-5-hydroxymethyl-l-pyrrolyl)-hexansäure

Zusammenfassung Die Titelverbindung wird auf einem neuen Weg ausN -Trifluoracetyllysinmethylester und 2,9-Dimethyldeca-2,8-dien-4,7-dion synthetisiert. Nach Umwandlung der Pyrrolsubstituenten und Abspaltung der Schutzgruppen unter milden Bedingungen erhält man die Titelverbindung in hoher Reinheit.

     

Diffusion of the hydroxide-ion in liquid CaO-Al2O3-slags by application of Fourier-Transform-lnfrared-Spectroscopy

Water vapour is soluted in liquid CaO-Al₂O₃-slags as OH^?-ion. To determine the diffusion coefficient a capillary technique is used. Roughly 5 cm long platinum capillaries filled with liquid slag are equilibrated at 1500 and 1600 °C and bar different times and then are quenched in liquid D₂O. By dividing these capillaries into roughly 3 mm long segments enough sample substance is won to obtain FT-IR spectra of the OH-band. From measurement of the integral extinction of the OH-band and OH^?-concentration profile through the capillary is obtained. FT-IR-spectroscopy is very suitable for this capillary technique because it needs only very little sample substance.     

Bitterstoffe beim Erhitzen von Saccharose, Maltose und Prolin 2. Mitteilung

Summary In addition to the mono- and dipyrrolidinohexosereductones described recently (Z Lebensm Unters Forsch (1984) 178:356) two further bittertasting compounds were isolated from heated mixtures of proline and sucrose (molar ratio 3: 1, 190 °C, 30 min) and also synthesized, namely 2,3-bis-(1-pyrrolidinyl)2-cyclopenten-l-one and 2,3-bis(1-pyrrolidinyl)-5methyliden-2-cyclopenten-l-one. The recognition thresholds (mmol/1) are 0.15–0.25 and 0.06–0.12 respectively. Both compounds have a burning bitter taste character. From a maltose-proline reaction mixture 2--glucosyl-5-hydroxy-5-methyl-4-piperidinyl-2-cyclopenten-1-one was isolated. When the dihydroxypyranone VI was heated with proline, 2,5-dihydroxy-5-methyl-4-prohnyl-2-cyclopenten-1-one and the cyclopent(b)azepinones XI and XII were among the compounds formed. These compounds also have a bitter taste character.Zusammenfassung Zusätzlich zu den kürzlich beschriebenen Mono- and Dipyrrolidinohexosereduktionen (Z Lebensm Unters Forsch (1984) 178:356) wurden zwei weitere bittere Verbindungen aus erhitzten Mischungen von Prolin and Saccharose (Molverhältnis 3:1, 190 °C, 30 min) isoliert and synthetisiert. Es handelt sich um 2,3-Bis-(1-Pyrrolidinyl)-2-cyclopenten-1-on und 2,3-Bis-(1-Pyrrolidinyl)-5-methyliden-2-cyclopenten-1-on. Die Erkennungsschwellenwerte (mmol/1) sind 0,15-0,25 and 0,06-0,12. Beide Verbindungen haben einen brennend-bitteren Geschmack. Aus einem Maltose-Prolin-Umsetzungsgemisch gelang die Isolierung des 2--Glucosyl-5-hydroxy-5-methyl-4-piperidinyl-2-cyclopenten-1-ons. Bei der Reaktion des Dihydropyranons VI mit Prolin wurden u. a. das 2,5-Dihydroxy-5-methyl-4-prolinyl2-cyclopenten-1-on sowie die Cyclopent(b)azepinone XI and XII gebildet. Diese Verbindungen sind ebenfalls mehr oder weniger stark bitter.     

Probing the Conformation States of Neurotensin Receptor 1 Variants by NMR Site-Directed Methyl Labeling

G protein-coupled receptors (GPCRs) are key players in mediating signal transduction across the cell membrane. However, due to their intrinsic instability, many GPCRs are not suitable for structural investigations. Various approaches have been developed in recent years to remedy this situation, ranging from the use of more native membrane mimetics to protein-stabilization methods. The latter approach typically results in GPCRs that contain various numbers of mutations. However, probing the functionality of such variants by in vitro and in vivo assays is often time consuming. In addition, to validate the suitability of such GPCRs for structural investigations, an assessment of their conformation state is required. NMR spectroscopy has been proven to be suitable to probe the conformation state of GPCRs in solution. Here, by using chemical labeling with an isotope-labeled methyl probe, we show that the activity and the conformation state of stabilized neurotensin receptor 1 variants obtained from directed evolution can be efficiently assayed in 2D NMR experiments. This strategy enables the quantification of the active and inactive conformation states and the derivation of an estimation of the basal as well as agonist-induced activity of the receptor. Furthermore, this assay can be used as a readout when re-introducing agonist-dependent signaling into a highly stabilized, and thus rigidified, receptor by mutagenesis. This approach will be useful in cases where low production yields do not permit the addition of labeled compounds to the growth medium and where 1D NMR spectra of selectively ¹⁹F-labeled receptors are not sufficient to resolve signal overlap for a more detailed analysis.     

Mechanical Properties and Oxidation Behavior of Al2O3–AlN–TiN Composites

The study examines the effect which the composition of hot-pressed electroconductive ceramics has on their structure, mechanical properties, and oxidation behavior, for ceramics of the type AIN–Al₂O₃–42 wt% TiN, differing in the AIN/Al₂O₃ ratio. The results are physico-mechanical property data, including density, hardness, strength, fracture toughness, and wear resistance. A correlation was found between the wear resistance and fracture toughness. The analysis of oxidation products revealed the formation of α-Al₂O₃ and rutile in the temperature range from 600° to 1100°C and aluminum titanate above 1200°C. The spallation of the oxide layer caused low oxidation resistance of Al₂O₃-rich composites above 1250°C. The oxidation of composites was compared with the oxidation of pure TiN. The relationship is discussed between material properties, composition, phases, and processing parameters.