The new generation of L. C. columns; A critical evaluation of their systems compatibility and performance

Summary The demand for faster, more economic and convenient high-efficiency LC analyses has led to the development of microbore and fast columns. However, to utilize their benefits, the low column dispersions produced by these new technologies necessitate low external variances in the total system.This paper describes the determination of the external variance of microbore, fast and conventional LC systems by a column method. Compatibility with the relevant column technologies is evaluated by a method involving the comparison of the external and column dispersions.Direct comparison of chromatograms of an 8-component mixture, on a set of columns of various diameters and lengths, shows the relative speed, economy and sensitivity obtainable in practice.The problem of reduced sample loadability is considered and the practical solution of peak compression illustrated.Part of this work was presented during a poster session at the 15th International Symposium on Chromatography in Nürnberg, October 1984.     

Two-dimensional choked transonic flow

Summary Choked transonic flow about a thin two-dimensional airfoil in a wide wind tunnel is analyzed. Asymptotic expansions are constructed in terms of the transonic similarity variableK _T as K_T0 (and the tunnel height), in an inner region, near the body, and in an outer region, near the walls, and are matched. The inner expansion consists of sonic free flow plus a correction. The outer expansion accounts for the meeting of the sonic line and the limit characteristic at the wall. The magnitude of the correction to sonic free flight at the body as well as the dependence of the choking Mach number on the wind tunnel height are determined. A boundary value problem is formulated to determine the correction to the free flight sonic flow.

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Zusammenfassung Es wird die schallnahe Sperrströmung um einen zweidimensionalen Flügel in einem weiten Windkanal analysiert. Asymptotische Reihenentwicklungen werden in der transsonischen Ähnlich-KeitsvariablenK _T im inneren Bereich in der Nähe des Körpers und im äußeren Bereich nahe der Wandung konstruiert und verglichen. Die innere Reihenentwicklung besteht aus freier Schallströmung und einem Korrektionsglied. Die äußere Reihenentwicklung steht für das Zusammentreffen der Schallinie und der Grenzcharacteristik an der Wandung. Es werden die Größe des Korrektionsgliedes zur freien Schallströmung am Körper, als auch die Abhängigkeit der Machschen Zahl der freien Strömung von der Höhe des Windkanals bestimmt. Ein Randwertproblem wird formuliert um die Korrektur zur freien Schallströmung zu bestimmen.

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Research partly sponsored by AFOSR under Grant No. 82-0155 and by NSF under Grant DMS-8401738. The U.S. Government is authorized to reproduce and distribute reprints notwithstanding any copyright notation thereon.     

Simplifying assumptions for the order of partitioned multivalue methods

In solving a system of ordinary differential equations by multivalue methods, the concept of partitioning such a method into two parts corresponding to internal and external computations has recently been introduced by Burrage and Butcher [3]. In this paper the order conditions for such methods will be given and simplifying assumptions for them derived. Various examples are presented and, in particular, a new class of methods is introduced and its order properties are studied.     

Antibacterial activity of native plants from Northwest Argentina against phytopathogenic bacteria

Abstract

Extracts from aerial parts of medicinal plants from northwest Argentina were screened for antibacterial activity against the phytopathogenic strains namely CECT 124 (Pseudomonas corrugata), CECT 126 (P. syringae pv. tomato), CECT 225 (Erwinia carotovora var. carotovora), CECT 472 (Agrobacterium tumefaciens) and CECT 792 (Xanthomonas campestres pv. vesicatoria). Leaves and stems of Aspidosperma quebracho-blanco, Schinus fasciculatus, S. gracilipes, Amphilophium cynanchoides and Tecoma stans were separately extracted with solvents of increasing polarity to obtain the dichloromethane (fCH₂Cl₂), ethyl acetate (fEtAc) and methanol extracts (fMeOH), respectively. Among the thirty extracts tested, only fEtAc from leaves and stems of S. fasciculatus reached the IC₅₀ against the five bacterial strains tested (IC₅₀?=?0.9?mg/ml). The fEtAc from the leaves contained kaempferol, quercetin and agathisflavone which had moderate to strong antibacterial activity. This extract and its identified flavonoids showed synergic (CECT 124,126 and 792) or additive effects (CECT 472 and 225) in mixtures with Kocide 3000.     

Light Fluence Rate and Tissue Oxygenation (StO2) Distributions Within the Thoracic Cavity of Patients Receiving Intraoperative Photodynamic Therapy for Malignant Pleural Mesothelioma

The distributions of light and tissue oxygenation (S_tO₂) within the chest cavity were determined for 15 subjects undergoing macroscopic complete resection followed by intraoperative photodynamic therapy (PDT) as part of a clinical trial for the treatment of malignant pleural mesothelioma (MPM). Over the course of light delivery, detectors at each of eight different sites recorded exposure to variable fluence rate. Nevertheless, the treatment-averaged fluence rate was similar among sites, ranging from a median of 40–61 mW cm⁻² during periods of light exposure to a detector. S_tO₂ at each tissue site varied by subject, but posterior mediastinum and posterior sulcus were the most consistently well oxygenated (median S_tO₂ >90%; interquartile ranges ~85–95%). PDT effect on S_tO₂ was characterized as the S_tO₂ ratio (post-PDT S_tO₂/pre-PDT S_tO₂). High S_tO₂ pre-PDT was significantly associated with oxygen depletion (S_tO₂ ratio < 1), although the extent of oxygen depletion was mild (median S_tO₂ ratio of 0.8). Overall, PDT of the thoracic cavity resulted in moderate treatment-averaged fluence rate that was consistent among treated tissue sites, despite instantaneous exposure to high fluence rate. Mild oxygen depletion after PDT was experienced at tissue sites with high pre-PDT S_tO₂, which may suggest the presence of a treatment effect.     

Relationship between chain length, disorder, and resistivity in polypyrrole films

The effects of the polymerization temperature and of voltammetric cycling on the chain length and the resistivity of polypyrrole films are investigated. The studies provide further proof for the existence of at least two different types of polypyrrole, the so-called PPy I and PPy II. As the electropolymerization of conjugated systems in contrast to normal polymerization reactions is a fully activated process, the generation of these different types of PPy depends on experimental parameters such as temperature or formation potentials. UV-vis measurements demonstrate that PPy II comprises significantly shorter chains than PPy I (8-12 vs 32-64 units); moreover, film conductivity is found to increase with the fraction of PPy II. This fraction is changed via the polymerization temperature as well as by cyclic voltammetry, both of which can induce a metal-insulator transition. The counter-intuitive relationship between resistivity and chain length is interpreted in terms of disorder-dominated transport, in which the shorter chains of PPy II support the formation of delocalized electronic states, thereby increasing the localization length. Thus, our results are in agreement with recent broadband reflectivity measurements.     

Bio-based nanostructured carbons toward sustainable technologies

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