Optimal trajectory to overflow in a queue fed by a large number of sources

We analyse the deviant behavior of a queue fed by a large number of traffic streams. In particular, we explicitly give the most likely trajectory (or optimal path) to buffer overflow, by applying large deviations techniques. This is done for a broad class of sources, consisting of Markov fluid sources and periodic sources. Apart from a number of ramifications of this result, we present guidelines for the numerical evaluation of the optimal path.     

Development and validation of a liquid chromatography-electrospray tandem mass spectrometry method for mebendazole and its metabolites hydroxymebendazole and aminomebendazole in sheep liver

A quantitative liquid chromatography-electrospray tandem mass spectrometry method for the determination of mebendazole and its hydrolysed and reduced metabolites in sheep liver has been developed and validated. The benzimidazole substances were extracted with ethyl acetate after the sample mixture had been made alkaline. The HPLC separation was performed on a reversed-phase C18 column with gradient elution using a mobile phase consisting of water containing 0.1% formic acid and acetonitrile. The analytes were detected after atmospheric pressure electrospray ionization on a tandem quadrupole mass spectrometer in MS-MS mode. The components were measured by the MS-MS transitions of the molecular ion to the two most abundant daughter ions. The detection limits are lower than 1 microg kg(-1). For this application, the validation limit was set at 50 microg kg(-1). The examined validation parameters were in accordance with the permitted tolerances ranges stipulated in the proposed new European validation criteria for residue surveillance. For the three analytes, the overall recovery was higher than 90%. The RSD for the repeatability ranged from 5 to 11%. The range for the within-laboratory reproducibility was between 2 and 17%. The decision limits for mebendazole, the hydrolysed and the reduced metabolite were 56.6, 61.8 and 64.2 microg kg(-1), respectively. The detection capabilities for these substances were 60.0, 86.1 and 90.9 microg kg(-1), respectively.     

Local structure of the zeolitic catalytically active site during reaction

The structural changes of the catalytic active site that occur during catalytic reaction in an acidic zeolite are detected. The local structure of the zeolitic Br?nsted active site is a distorted tetrahedrally coordinated aluminum that has three short and one long aluminum-oxygen bond. Using in situ Al K edge X-ray absorption spectroscopy, the adsorption of a reactive intermediate in the oligomerization of ethene changed the local structure of the catalytic active site; the long aluminum oxygen bond is partially relaxed. At increasingly higher temperature, extensive coking of the catalyst frees the Br?nsted acid site from the reactive intermediate, restoring the asymmetric coordination. These measurements show that application of in situ Al K edge spectroscopy provides fundamental insight into the structure of zeolitic catalytically active sites during catalytic action.     

Collisional and photoinitiated reaction dynamics in the ground electronic state of Ca-HCl

Ca+HCl(upsilon,j) reactive collisions were studied for different rovibrational states of the HCl reactant using wave-packet calculations in reactant Jacobi coordinates. A recently proposed potential-energy surface was used with a barrier of approximately 0.4 eV followed by a deep well. The possibility of an insertion mechanism due to this last well has been analyzed and it was found that once the wave packet passes over the barrier most of it goes directly to CaCl+H products, which shows that the reaction dynamics is essentially direct. It was also found that there is no significant change in the reaction efficiency as a function of the initial HCl rovibrational state, because CaHCl at the barrier has an only little elongated HCl bond. Near the threshold for reaction with HCl(upsilon=0), however, the reaction shows significant steric effects for j > 0. In a complementary study, the infrared excitation from the Ca-HCl van der Waals well was simulated. The spectrum thus obtained shows several series of resonances which correspond to quasibound states correlating to excited HCl(upsilon) vibrations. The Ca-HCl binding energies of these quasibound states increase dramatically with upsilon, from 75 to 650 cm(-1), because the wave function spreads increasingly over larger HCl bond lengths. Thus it explores the region of the barrier saddle point and the deep insertion well. Although also the charge-transfer contribution increases with upsilon, the reaction probability for resonances of the upsilon=2 manifold, which are well above the reaction threshold, is still negligible. This explains the relatively long lifetimes of these upsilon=2 resonances. The reaction probability becomes significant at upsilon=3. Our simulations have shown that an experimental study of this type will allow a gradual spectroscopic probing of the barrier for the reaction.     

Beitrag zur potentiometrischen Untersuchung von Resorufin und einigen seiner Derivate

Zusammenfassung Durch potentiometrische Untersuchung des Verhaltens von Resorufin, o-Acetylresorufin und Äthoxyresorufin wurde festgelegt, unter welchen Bedingungen es zur Bildung von Semichinon kommt. Ferner wurden die Bedingungen für die titanometrische und stannometrische Bestimmung der angeführten Substanzen ermittelt.

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Summary Potentiometric investigation of the behavior of resorufin,o-acetylresorufin and ethoxyresorufin revealed the conditions that lead to the formation of semiquinone. The conditions for the titanometric and the stannometric determination of these materials were also established.

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Résumé On a établi les conditions de formation d'une hémiquinone, par l'étude potentiométrique du comportement de la résorufine, de l'o-acétylrésomfine et de l'éthoxyrésorufine. On en a déduit les conditions du titrage titanométrique et stannométrique de ces substances.

     

Mathematical model of suspension flocculation kinetics

A mathematical model of suspension flocculation kinetics which describes its evolution in a wide time interval, and later stages is presented. The rate constant of floc formation has been found. The calculated dependence of particle number in volume unit on time correlates well with experimental data.     

Effect of Through‐Bond Interaction on Conformation and Structure in Rod‐Shaped Donor–Acceptor Systems. Part 1

The crystal structures of five N‐arylpiperidin‐4‐one derivatives 2P2, 3P2, 5P2, 1P3 , and 2P3 are presented (Fig. 2 and Tables 1–5) and discussed together with the derivatives 1P2 and 4P2 published previously. In all but one structure, 1P2 , the aryl group is in an equatorial position. The piperidine ring adopts a normal chair conformation. In 1P2 , the piperidine ring central C? C bonds are significantly elongated, which is consistent with the idea that through‐bond interaction is more pronounced in the axial conformation. Through‐bond interaction also influences the pyramidalization at the piperidine C(4)‐atom in such a way that a strong interaction is directing the ethylene C‐atom C(9) into the axial direction.     

Device for automated spectrophotometric set-point titrations comprising an automatic correction for turbidity and dilution errors and its applications

Summary An automatic set-point titration with subtraction-photometric detection is used to determine Ca in turbid urine samples. The titration is carried out with EGTA at a pH of 8.5. The set-point solution contains the Zn-EGTA complex and zincon. Upon addition of Ca ions, Zn ions are set free, which are back-titrated till the original equilibrium situation is restored. Analyses of l-amounts of urine gave standard deviations of 2–3% rel. The recovery was 100% (150–400 mg/l). A titration took about 2 min making possible 200 analyses per day. The exponential transformation showed to be necessary for the analysis of turbid samples.

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Vorrichtung zur automatisierten spektralphotometrischen Titration bis zum vorgewählten Endpunkt mit automatischer Korrektur für Trübungs- und Verdünnungsfehler sowie ihre AnwendungenIII. Anwendung zur Titration von Calcium in trüben Harnproben

Zusammenfassung Eine automatische Titration mit vorgewähltem Endpunkt und mit subtraktions-photometrischer Detektion wurde zur Bestimmung von Calcium in trüben Harnproben angewendet. Die Titration wird mit ÄGTA bei einem pH-Wert von 8,5 vorgenommen. Die Endpunktslösung enthält Zn-ÄGTA-Komplex und Zinkon. Calciumionen aus der Probe setzen Zn(II) frei. Es wird mit ÄGTA titriert bis zum Anfangsgleichgewicht. Die Standardabweichung bei der Analyse von Proben von einigen l war ungefähr 2–3 % rel. Der gesamte Ca-Gehalt wurde zu 100% erfaßt (Bereich 150–400 mg/l). Die Titrationsdauer beträgt ungefähr 2 min; täglich können 200 Analysen ausgeführt werden. Für trübe Harnproben war eine exponentielle Transformation notwendig.

Part II: Z. Anal. Chem. 276, 181 (1975).