Solid-state ion-selective electrodes for the potentiometric determination of hexacyanoferrate (II)

Hexacyanoferrate(II)-sensing electrodes were prepared by mixing Ag₂S and Ag₄Fe (CN)₆. The 6:1 Ag₂S/Ag₄Fe (CN)₆ provided the best potentiometric response and speed of response. The log concentration vs. potential curves were linear with Nernstian slope (14.8 mV/decade) over the range 10^?1-10^?6 M hexacyanoferrate (II) at pH 7.00 with constant ionic strength. Interferences included iodide, sulfide and bromide. This electrode was used as indicator in potentiometric titrations of hexacyanoferrate (II).     

Electronic transport in graphene nanostructures on SiO2

We report two experiments on graphene nanostructures. The first was performed on a graphene nanoribbon, where the nature of electronic transport was investigated in detail. Electrons or holes are found to localize in pockets of the potential along the ribbon. Transport is governed by the joint action of localization and Coulomb interaction. The temperature-dependence of the conductance shows activated behavior at temperatures above a few Kelvin. The activation energy retraces the edges of Coulomb blockade diamonds found in nonlinear transport. In the second experiment the metallic tip of a low-temperature scanning force microscope was scanned above a graphene quantum dot. In addition to the familiar Coulomb blockade fringes, localized states are detected forming in the constrictions connecting the dot to source and drain.     

Singlet-triplet transition tuned by asymmetric gate voltages in a quantum ring

Wave-function and interaction effects in the addition spectrum of a Coulomb-blockaded many-electron quantum ring are investigated as a function of asymmetrically applied gate voltages and magnetic field. Hartree and exchange contributions to the interaction are quantitatively evaluated at a crossing between states extended around the ring and states which are more localized in one arm of the ring. A gate tunable singlet-triplet transition of the two uppermost levels of this many-electron ring is identified at zero magnetic field.     

Transport in graphene nanostructures

Graphene nanostructures are promising candidates for future nanoelectronics and solid-state quantum information technology. In this review we provide an overview of a number of electron transport experiments on etched graphene nanostructures. We briefly revisit the electronic properties and the transport characteristics of bulk, i.e., two-dimensional graphene. The fabrication techniques for making graphene nanostructures such as nanoribbons, single electron transistors and quantum dots, mainly based on a dry etching ??paper-cutting?? technique are discussed in detail. The limitations of the current fabrication technology are discussed when we outline the quantum transport properties of the nanostructured devices. In particular we focus here on transport through graphene nanoribbons and constrictions, single electron transistors as well as on graphene quantum dots including double quantum dots. These quasi-one-dimensional (nanoribbons) and quasi-zero-dimensional (quantum dots) graphene nanostructures show a clear route of how to overcome the gapless nature of graphene allowing the confinement of individual carriers and their control by lateral graphene gates and charge detectors. In particular, we emphasize that graphene quantum dots and double quantum dots are very promising systems for spin-based solid state quantum computation, since they are believed to have exceptionally long spin coherence times due to weak spin-orbit coupling and weak hyperfine interaction in graphene.     

Coherent nonlinear transport in quantum rings

While equilibrium properties of mesoscopic systems are well understood, many questions are still debated concerning the non-equilibrium properties, which govern nonlinear transport. Nonlinear transport measurements have been performed on two-terminal semiconductor quantum rings in the open regime, where the rings are used as electron interferometers and show the Aharonov–Bohm effect. We observe a magnetic field asymmetry of the nonlinear conductance, compatible with the non-validity of the Onsager–Casimir relations out-of-equilibrium. In particular, the voltage-antisymmetric part of the nonlinear conductance of these two-terminal devices is not phase rigid, as it is the case for the linear conductance. We show that this asymmetry is directly related to the electronic phase accumulated by the electrons along the arms of the ring and can be tuned using an electrostatic gate.     

Antibiotika aus actinomyceten. zur chemischen konstitution des antibiotikums griseorhodin A : I—isolierung und struktur von zwei abbauprodukten

On treating of griseorhodin A with pyridine at 100°C several degradation products of the antibiotic are formed. Two of these compounds have been isolated. Substance 1a was shown to be 2,5,8-trihydroxy-7-methoxynaphthoquinone-(1,4). The second degradation product 2a is a derivative of isocoumarin.     

Separation of metals by liquid surfactant membranes containing crown ether carboxylic acids

A water-in-oil-in-water emulsion liquid membrane system is used to transport alkali metal and alkaline earth cations from an external alkaline aqueous source phase through an organic membrane containing a crown ether carboxylic acid and into the internal acidic aqueous phase of the emulsion droplet. The influence of varying the crown ether carboxylic acid structure upon the selectivity and efficiency of competitive metal ion transport is examined.     

Charging effects of ErAs islands embedded in AlGaAs heterostructures

Self-assembled ErAs islands were grown on GaAs between a two-dimensional electron gas (2DEG) and a backgate electrode by molecular-beam epitaxy. The islands have overlapping Schottky barriers that form an insulating potential barrier. A TiAu topgate was added by shadow mask evaporation. Thermal activation and charging experiments were employed to gain insight into the electronic properties of the ErAs island systems. In addition the 2DEG was characterized as a function of topgate and backgate voltage.     

Zur manometrischen Mikrobestimmung des Kohlenstoffs und Wasserstoffs in organischen Verbindungen

Zusammenfassung Eine manometrische Mikrobestimmungsmethode für Kohlenstoff und Wasserstoff in organischen Verbindungen wurde ausgearbeitet. Die Verbrennung der Substanz erfolgt im Stickstoffstrom unter Zusatz einer bestimmten Menge Sauerstoff. Zur Oxydation noch unverbrannter Substanzdämpfe dient eine auf 750° C erhitzte, 16 cm lange Katalysatorschicht aus einem Gemisch von Kupfer- und Kobaltoxid. Wasser und Kohlendioxid werden in zwei Kühlfallen mit Kohlensäureschnee bzw. flüssiger Luft ausgefroren und anschließend in zwei evakuierte Quecksilbermanometer gleichzeitig verdampft. Aus den Druckzunahmen berechnet man den Kohlenstoff- und Wasserstoffgehalt der analysierten Substanz. Die Bestimmungsmethode ist universell anwendbar, wie die Analysenergebnisse von Verbindungen verschiedenster Zusammensetzung und unterschiedlichen Verhaltens zeigen. Eine vollständige Analyse beansprucht zirka 20 Minuten. Die Analysenresultate einer Testsubstanz wurden statistisch ausgewertet. Bei einer vorgegebenen statistischen SicherheitS von 95% betragen die Streubereiche ±x für die Kohlenstoffwerte ±x _C =0,42% und für die Wasserstoffwerte ±x_H = ±0,27%.

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Summary A method has been worked out for the manometric microdetermination of carbon and hydrogen in organic compounds. The sample is burned in a stream of nitrogen with the addition of a certain amount of oxygen. The still unburned vapors from the sample are oxidized by means of a layer of catalyst consisting of a mixture of copper-and cobalt oxide and heated to 750° C. Water and carbon dioxide are frozen out in two cooling vessels surrounded by solid carbon dioxide and liquid air respectively and subsequently volatilized simultaneously into two evacuated mercury manometers. The carbon and hydrogen content of the sample are determined from the increases in pressure. The procedure is applicable in all cases as shown by the analytical data obtained from compounds with most varied compositions and varied behaviour. A complete analysis consumes about 20 minutes. The analytical results from a test substance were evaluated statistically. With an accepted accuracyS of 95%, the deviation ranges ±x for the carbon contents are ±x_C = 0.42% and for the hydrogen values ±x_H = ±0.27%.

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Résumé On a mis au point une méthode manométrique pour le microdosage du carbone et de l'hydrogène dans les composés organiques. La combustion de la substance s'effectue sous courant d'azote, additionné d'une quantité déterminée d'oxygène. Pour oxyder les vapeurs de la substance qui n'a pas encore brûlé, on utilise une couche de catalyseur, longue de 16 cm, chauffée à 750° C et composée d'un mélange d'oxydes de cuivre et de cobalt. On condense l'eau et le gaz carbonique dans deux pièges refroidis par de la neige carbonique ou par de l'air liquide, et, pour finir, on les vaporise simultanément dans deux manomètres à mercure où l'on a fait le vide. A partir de l'augmentation de pression, on calcule la teneur en carbone et en hydrogène de la substance analysée. La méthode de dosage est universellement applicable, comme le montrent les résultats d'analyse de composés de diverses compositions et de propriétés différentes. Une analyse complète demande environ 20 minutes. On a utilisé statistiquement les résultats d'analyse d'une substance étalon. En comptant sur une limite de confianceS, statistiquement de 95%, les domaines de dispersion ±x atteignent ±x_C = 0,42% pour les valeurs du carbone et ±x_H = 0,27% pour les valeurs de l'hydrogène.