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61.
Both the enantiomers of sclerosporin and sclerosporal were synthesized from (-)-carvone. (4R,9R,10S)-(+)-Sclerosporin and (4R,9R,10S)-(-)-sclerosporal were identified as the natural enantiomers by a comparison of their CD-spectra. An intramolecular Diels-Alder route was proved to be an efficient method of preparing sufficient amounts of (+)- for the biological study. 相似文献
62.
Bertrand Lombard 《Accreditation and quality assurance》2006,11(1-2):94-100
Given the current interest in measurement uncertainty (MU) in food microbiology, in particular for laboratory accreditation
purposes, and the need to have harmonized reference documents specifically in that area at the international level, ISO is
conducting works to meet this need. An ISO Technical Specification (ISO/TS 19036) is being prepared on MU estimation for quantitative
determinations. A global approach has been chosen, based on the reproducibility standard deviation of the final result of
the measurement process. Three possibilities are envisaged for the estimation of the reproducibility standard deviation, in
a decreasing order of preference: The intra-laboratory standard deviation, the inter-laboratory standard deviation derived
from method validation, and the inter-laboratory standard deviation derived from proficiency testing.The uncertainty of qualitative
determinations is still under investigation, and will be covered by a separate ISO publication.
Presented at AOAC Europe/Eurachem Symposium March 2005, Brussels, Belgium 相似文献
63.
The processes going on in silver-doped GeO2 films during air-heating were investigated by XPS, TEM, IR and UV-visible spectroscopy methods. Silver was shown to interact with the GeO2 matrix at 500-600 °C to give silver germanate which was decomposed on further heating to form GeO2 and silver nanoparticles, 10-35 nm in size, absorbing in the plasmon resonance region (λmax = 415 nm). The silver nanoparticles are located deep in the films and encapsulated by oxide particles. 相似文献
64.
Two of the most important structural controls on the properties of borosilicate glasses and glass melts are the variation between three- and four-coordination of network-forming boron cations, and the extent of mixing of Si and B. The effects of composition on these key parameters are relatively well studied. However, proposed mechanisms could be better constrained by testing with another, independent parameter that can also strongly affect the network. Here we present some of the first quantitative structural data on the effects of high pressure on the network structure of a sodium borosilicate glass. Using high-resolution 11B and 17O NMR on a sample melted at 5 GPa, we demonstrate that the formation of tetrahedral boron from trigonal boron is indeed closely coupled to the conversion of non-bridging to bridging oxygens. The increased fraction of tetrahedral boron at high pressure also causes increased mixing of boron and silicate structural units, as oxygens bridging between two BO4 groups are energetically relatively unfavorable. 相似文献
65.
Oxides-based glass-ceramics have been intensively studied and while they exhibit exceptional thermo-mechanical properties, their transparency in the infrared is limited to the 3 μm region. In this paper we describe a new type of glass-ceramics which are transparent up to 11 μm and based on the controlled nucleation and crystallization of cesium chloride sub-micron particles inside a Ge-Sb-S glass matrix. The evolution of the optical transmission versus annealing time and temperature has been investigated. Observations under scanning electronic microscopy as well as X-ray diffraction indicate that the crystalline phase is a primitive cubic cell with a parameter slightly inferior to that of pure CsCl and that the grain sizes are about 100 nm. A preliminary test on fracture propagation shows a much better resistance of glass-ceramics to cracks than the corresponding pure glass matrix. 相似文献
66.
Thin GexSb40−xS60 (x=5, 15, 20, 25 and 27) chalcogenide films have been investigated by X-ray photoelectron spectroscopy (XPS). X-ray photoelectron spectra show that there is a peculiarity in the relative intensity ratio of the Sb 4d photoelectron peak associated with Sb2S3 to the Sb 4d photoelectron peak associated Sb2S5 at an average co-ordination number Z of 2.65-2.67. After contamination and photo-oxidation layers were removed from the surface of the films, X-ray photoelectron spectra were measured again. It has been found that binding energies of the Ge 2p and Sb 3d3/2 photoelectron peaks, which reflect the electronic structure at lower core energy levels, are independent of Z. However, the binding energies of the Ge 3d and Sb 4d photoelectron peaks are more sensitive to Z and have a discontinuity at Z=2.65. 相似文献
67.
Iêda Maria Garcia dos Santos Rafael Carlos Martins Moreira Ronan Lebullenger Edson Roberto Leite Elson Longo 《Journal of Non》2003,319(3):304-310
PbO-Bi2O3-Ga2O3 glasses present interesting properties such as good transmission in the mid-infrared region, high magnetic Verdet constant and non-linear properties. The processing of these heavy-metal-oxide (HMO) glasses is limited by the high corrosive nature of the melt, even in relation to noble metal crucibles. In this work, three kinds of ceramic crucibles (alumina, tin oxide and zirconia) were tested for melting HMO glasses. The main physical properties of the prepared glasses, such as the characteristic temperatures, optical transmission were studied in function of the crucible nature, time/temperature melting parameters. The incorporation of crucible material in the glasses was determined by ICP and atomic absorption. The maximum glass contamination from the crucible was 2.9, 1.6 and 3.6 mol% for Al2O3, SnO2 and ZrO2 crucibles, respectively, when melting was done at 900 °C/240 min, for zirconia crucibles and at 1000 °C/60 min, for the other two crucibles. The evolution of the physical properties was discussed as a function of contamination degree. 相似文献
68.
Anita Schmidt 《Accreditation and quality assurance》2001,6(6):277-278
The 5th Eurolab Symposium on 4th and 5th October in Edinburgh was the highlight event of Eurolab in 2000, Eurolab’s 10th anniversary
year. Under the title: ”Confidence in Testing Services – new expectations, new rules, new challenges” it reflected recent
changes and developments in the laboratory scene and focussed on new tasks and challenges. The most essential changes for
laboratories are connected with the new standard ISO/IEC 17025 ”General requirements for the competence of testing and calibration
laboratories”. Keywords in this respect are uncertainty of measurement and traceability to SI units, requirements on personnel,
proficiency testing, customer orientation, and management systems. 相似文献
69.
Tomislav Ivankovic Antonija Rajic Sanja Ercegovic Razic Sabine Rolland du Roscoat Zenun Skenderi 《Molecules (Basel, Switzerland)》2022,27(6)
Wool is considered to possibly exhibit antibacterial properties due to the ability of wool clothing to reduce the build-up of odor, which arises from the microbial activity of skin microbiota. Indeed, when tested with a widely used agar diffusion plate test method, even wool or other textiles not treated with any antimicrobial agent can be interpreted to show certain antibacterial effects due to the lack of growth under the specimen, as instructed in ISO 20645:2004 standard. Therefore, we analyzed in detail what happens to bacterial cells in contact with untreated wool and cotton fabric placed on inoculated agar plates by counting viable cells attached to the specimens after 1 and 24 h of contact. All wool and several cotton samples showed no growth under the specimen. Nevertheless, it was shown without a doubt that neither textile material kills bacteria or inhibits cell multiplication. A reasonable explanation is that bacterial cells firmly attach to wool fibers forming a biofilm during multiplication. When the specimen was lifted off the nutrient agar surface, the cells in the form of biofilm remained attached to the wool fibers, removing the biomass and resulting in a clear, no growth zone underneath it. By imaging the textile specimens with X-ray microtomography, we concluded that the degree of attachment could be dependent on surface topography. The results indicate that certain textiles, in this case, wool, could exhibit antibacterial properties by removing excess bacteria that grow on the textile/skin interface when taken off the body. 相似文献
70.
Juan José Tarí José Francisco Molina Juan Luis Castejón 《European Journal of Operational Research》2007
Recent research into quality management has examined the relationship between quality management and performance. The purpose of this study is to identify the relationships between quality management practices, and to examine the direct and indirect effects of these practices on quality outcomes by means of replication research. The paper uses a path analysis and a research model is tested using cross-section data collected from 106 certified firms in Spain. The findings support the relationships between quality management practices and the positive impact of these practices on quality outcomes. Evidence is also found confirming previous research showing that a firm could transfer the organizational forms and behaviours underlying quality management to other countries with similar cultures. However, as minor differences emerge, managers should consider the cultural issues. The contribution of the paper is that it provides empirical support for direct and indirect effects of quality management on performance in Spain compared to previous studies carried out in USA and Korea. 相似文献