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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Accreditation and quality assurance 4 (1999), S. 349-351 
    ISSN: 1432-0517
    Keywords: Key words Accuracy ; Analytical quality assurance ; Clinical chemistry ; Metrology ; Laboratory medicine ; Traceability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract  In a recent Letter to the Editor, Dr. B. Neidhart questioned the need to make clinical chemical measurement results traceable to international standards and to incorporate the principles of analytical quality assurance into clinical chemistry. An analysis of the arguments presented shows that modern laboratory medicine has to deliver accurate results, which are comparable over space and time, in order to improve the accuracy of diagnostic tools and minimize cost. The means to achieve accuracy and comparability are metrological traceability and quality assurance as supported by many national and international initiatives.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract  The uncertainty budget of the determination of cholesterol in a reference material (freeze-dried human serum) by isotope dilution mass spectrometry (IDMS) was evaluated. Measurements were run on a GC/quadrupole MS. A nested experimental design combined with a corresponding model for the analysis of variance (ANOVA) revealed the components making up the total uncertainty of the determinations. The coefficient of variation (CV) of the sole GC/MS-step was 0.47%, while that of the sample preparation including hydrolyzation, extraction and derivatization was 0.84%. This made the in-laboratory (overall) CV 0.96%. In addition, there was a vial-to-vial effect of 1.00% probably due to both inhomogeneity of the pooled material and lack of reproducibility of the filling procedure (including freeze drying) of the supplier as well as the reconstitution prior to use in the laboratory. These contributions sum up to an overall CV of a single determination of about 1.4%.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of medicinal chemistry 6 (1963), S. 192-194 
    ISSN: 1520-4804
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 6779-6800 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: It was recently reported that multiple-quantum NMR coherences could apparently be observed in water and other concentrated samples, in direct violation of established theory. These results were previously explained in a dressed-state framework as manifestations of the coupling between the spins and the coil (quantized radiation damping). Here we provide details of previously communicated experimental explorations of these effects [J. Chem. Phys. 96, 1659 (1992)], and we extend these results to multicomponent samples. We observe cross peaks between independent molecules in solution in two-dimensional experiments, including spectra with multiple-quantum coherence transfer echoes; we also demonstrate coherence transfer between solvent and (dilute) solute molecules. However, we show that these intermolecular cross peaks are induced by a mechanism which is local in nature, and thus radiation damping (either classical or quantized) cannot provide the bulk of the explanation for their occurrence. Simulations and analytical results show that the dipolar demagnetizing field can account for many of these surprising effects, although a complete picture must be more complex.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 2418-2420 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The controlled growth of SiC heteropolytypic structures consisting of hexagonal and cubic polytypes has been performed by solid-source molecular-beam epitaxy. On on-axis substrates, 4H/3C/4H–SiC(0001) and 6H/3C/6H–SiC(0001) structures were obtained by first growing the 3C–SiC layer some nanometer thick at lower substrate temperatures (T=1550 K) and Si-rich conditions and a subsequent growth of α-SiC on top of the 3C–SiC layer at higher T (1600 K) under more C-rich conditions. On off-axis substrates, multiheterostructures consisting of 4H/3C- or 6H/3C-stacking sequences were also obtained by first nucleating selectively one-dimensional wire-like 3C–SiC on the terraces of well-prepared off-axis α-SiC(0001) substrates at low T(〈1500 K). Next, SiC was grown further in a step-flow growth mode at higher T and Si-rich conditions. After the growth, many wire-like regions consisting of 3C–SiC were found also within the hexagonal layer material matrix indicating a simultaneous step-flow growth of both the cubic and the hexagonal SiC material. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 1204-1206 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial growth of 6H–SiC on 6H–SiC(0001) via two-dimensional nucleation was realized at 930 °C by solid-source molecular beam epitaxy using the alternate supply of Si and C. The deposition was controlled to an atomic level by surface superstructures. The growth was started on the ((square root of)3×(square root of)3)R30° surface which turns into the (1×1) phase upon deposition of about 1 monolayer silicon and recurs after subsequent deposition of about 1 monolayer carbon. Deviations from the monolayer deposition and, moreover, growth around substrate related defects result in the deposition of 3C–SiC. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 2981-2983 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The growth kinetics of Si dots grown on 6H-SiC(0001) by molecular beam epitaxy were studied in real time by reflection high-energy electron diffraction. The critical thickness for the Stranski–Krastanov growth mode transition was found to be kinetically delayed leading to a gradual decrease of this thickness with increasing temperature (T). At T〈625 °C and coverages below the critical thickness, a post-deposition evolution of dots is clearly established. The dot growth process is, under these conditions, mainly determined by the mass transfer out of the two-dimensional layer towards the Si dots. The dots grown on top of a 1 monolayer (ML) thick wetting layer are quantum sized with typical dimensions of 5–6 nm in height and 20–30 nm in diameter after a long post-deposition evolution times at 2–3 ML coverages. Above 625 °C and coverages above the critical thickness, the dot growth is only determined by surface-diffusion kinetics resulting in the growth of larger dots. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Fresenius' journal of analytical chemistry 365 (1999), S. 569-573 
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract As a consequence of the globalisation of trade and industry and other human activities, reliability of and confidence in measurement results is increasingly required, also in the field of chemical analysis, so that measurements made in one country will be accepted in other countries without the necessity to repeat them. The prerequisite for confidence is comparability on the basis of known uncertainties which in turn are based on traceability to recognised references. Traceability structures for chemical measurements are required which, by providing calibration means traceable to national standards, allow uncertainty statements to be made at field level, thus establishing comparability. Such traceability structures are now being developed in all industrialised countries. To ensure international comparability, mutual recognition of the national activities in metrology in chemistry is required in addition. The Mutual Recognition Agreement (MRA) for national measurement standards and calibration certificates issued by national metrology institutes, which is currently under way within the framework of the Metre Convention, aimes at providing the necessary international confidence for all kinds of measurements. The field of chemical analysis is included in the international metrological infrastructure through the new Consultative Committee for Amount of Substance (CCQM). Carefully selected key comparison measurements, which cover the most important areas where traceability is required, and which are carried out by national metrology institutes in cooperation with other national institutes entrusted with the provision of part of the national references for chemical measurements, form the basis for declarations of equivalence under the MRA. The results of the first key comparisons and studies carried out so far clearly show that the group of laboratories involved in the key comparisons is capable of establishing the international references (key comparison reference values) for chemical measurements with sufficient accuracy, also in complicated matrices.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 193 (1966), S. 235-245 
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Zusammenfassung Zur Messung trägerkonzentrationsabhängiger Absorptionsprozesse in Halbleitern führt man Photoabsorptionsmessungen durch, d.h. Messung des optischen Absorptionsbeitrags photoelektrisch erzeugter Träger. Hierzu wird ein Doppelwechsellichtverfahren angegeben, bei dem sowohl die Meßlichtquelle, die das Licht für die Absorptionsmessung liefert, als auch die Photolichtquelle, die die Überschußträger erzeugt, Wechsellichtquellen sind. Durchsetzt das mitω 1-modulierte Meßlicht die Probe, deren Durchlässigkeit durch die Photolichtquelle mitω 2 moduliert ist, so erhält man hinter der Probe ein mit der Differenzfrequenzω 1−ω 2 moduliertes Lichtsignal. Dieses wird selektiv nachgewiesen, es ist ein Maß für den Absorptionsquerschnitt der Überschußträger. Bei diesem Verfahren werden keine hohen Anforderungen an die spektrale Reinheit des Meß- bzw. Photostrahls gestellt, weshalb es anderen Verfahren zur Photoabsorptionsmessung überlegen ist. Die Möglichkeiten der Anwendung des Verfahrens werden diskutiert. Als Beispiele wurden Photoabsorptionsspektren an Germanium und Silizium gemessen.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Microchimica acta 94 (1988), S. 175-177 
    ISSN: 1436-5073
    Keywords: reflectance ; infrared
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract An integrating sphere is used together with a Fourier transform spectrometer for directional-hemispherical reflectance measurements in the spectral range from 1μm to 15μm. Comparisons with PTB's fundamental sphere reflectometer around 1μm show that the uncertainty of the infrared measurements is ±0.01.
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