Solid-state relaxations in poly(ethylene oxide). II. Study using the spin-labeling technique

Poly(ethylene oxide) (PEO) was spin-labeled with 3-chlorocarbonyl-2,2,5,5-tetramethylpyrroline-1-oxyl. Correlation times were calculated from 173 to 375°K. For estimating slow-motion rotational correlation times three models were used: Brownian diffusion, “moderate jump” diffusion, and “large jump” diffusion. Analysis of the changes in the extrema separation and spectra shape with temperature strongly suggests the presence of β and γ processes in solid poly(ethylene oxide). The Brownian diffusion model gives, for the γ relaxation, an activation energy of 8 kcal mole^?1 which is in good agreement with that found using dielectric relaxation measurements.     

Zur Auswertung flammenspektrometrischer Absorptionsmessungen nach dem Quotientenverfahren

Zusammenfassung Es wird festgestellt, unter welchen Voraussetzungen die Auswertung flammenspektrometrischer Absorptionsmessungen nach dem Quotientenverfahren zulässig ist. Danach wird der relative Fehler der Konzentrationsermittlung berechnet, wenn man das Steigungsmaß der Eichgeraden willkürlich zu 1 annimmt. Für die annähernde Ermittlung bzw. Kontrolle des Steigungsmaßes wird ein einfaches Verfahren angegeben sowie der relative Fehler dieser Bestimmung.

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Summary The presuppositions for the evaluation of flame photometric absorption measurements by the quotient method are examined. The relative error of the concentration is calculated for an arbitrary value = 1 of the gradient of the calibration curve. A simple method is described for the approximate determination and control of the gradient and the relative error of this determination is given.

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Unterstützt mit Mitteln der Deutschen Forschungsgemeinschaft.     

A LEED study of the deposition of carbon on platinum crystal surfaces

The deposition of carbon is studied by LEED on four platinum crystal faces: two low-index surfaces Pt(100), Pt(111)and two stepped surfaces Pt(S) ? [5(100) × (111)], a vicinal of (100), Pt(S)?[6(111) × (100)], a vicinal of (111). Carbon, generated by flowing ethylene onto the hot platinum, causes the formation of a graphitic overlayer and surface rearrangements of the substrate. The threshold temperature for graphitization is the lowest on Pt(100). The overlayer exhibits a single preferred orientation on Pt(100), several orientations on Pt(111) and its vicinal. Ordered carbon structures can be detected on the vicinal of (111) for low carbon doses. The orientations found in spot patterns (perfect registry) or ring-like patterns (imperfect alignment) can be associated with a coincidence-site lattice condition at the Pt/C interface. Faceting is observed except on Pt(111); the vicinal of (100) is particularly unstable. The stepped array on the vicinal of (111) starts to disorder at 350°C and can be converted into a hill and valley configuration at higher temperatures and carbon doses. Implications for catalytic studies are discussed.     

Über spezielle Klassen von Schwartz-Räumen II

Ohne Zusammenfassung     

Kinetic glucose determination with glucose dehydrogenase

Ohne Zusammenfassung

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Kinetic glucose determination with glucose dehydrogenase

     

A modified K-matrix approach to many-channel processes

The definition of a K-matrix, that does not have the direct channel singularities of the scattering amplitude, is not unique. Different choices lead to different integral equations for K with different physical content. We discuss the choice where the intermediate states have a simple off-shell behaviour for each partial wave. Crossing leads to an identification of the singularities of the K-matrix elements and to an iterative method of finding the scattering amplitude starting from a “bare” world.     

The determination of metals in petroleum samples by atomic absorption spectrometry : Part II. Determination of nickel

Some atomic absorption characteristics of xylene solutions of eight organometallic compounds of nickel in air—acetylene and nitrous oxide—acetylene flames are described. Different absorbances from various nickel organometallic compounds were observed; these differences were not eliminated by using the nitrous oxide—acetylene flame. Serious errors may arise when different organometallic compounds are used for calibration in the determination of nickel in xylene solutions of various petroleum samples. These errors are much less pronounced when nickel is determined by a standard addition technique. The effects of different sample matrices are discussed.