Surviving conduction symmetries in non-linear response

In linear response, the electric conductance of mesoscopic, two-terminal devices is symmetric with respect to the direction of an external magnetic field. The conductance symmetry, in general, breaks down in the non-linear regime of transport. Here we consider semiconductor quantum dots and show certain symmetries survive in the non-linear conductance with respect to the bias voltage and magnetic field that can be measured.     

Chromatography of aromatic compounds on anion-exchange resins

Complex mixtures of aromatic compounds can be rapidly separated on anion-exchangers in the acetate form with acetic acid as eluent and determined automatically by recording the absorbance in the ultraviolet. Carboxylates are separated by ion-exchange. Hydrogen bonds between non-disso-ciated acids and the counter-ions influence the distribution coefficients. Hydrogen-bonding with the resin has a marked effect on the sorption of solutes containing phenolic protons. Intramolecular hydrogen-bonding depresses their sorption. Hydrophobic interactions have a predominant influence with hydrocarbons and with phenolic compounds containing non-polar aliphatic substituents. The relative importance of these interactions increases with a decreased ion-exchange capacity of the resin.     

Sorption of aldonic acids from ethyl alcohol-water solutions on anion exchangers

Aldonic acids can be retained quantitatively from ethyl alcohol-water solutions by means of anion exchangers in the sulfate form. After the sorption step the aldonic acids can be easily displaced by washing with water. The sorption is explained by a partition mechanism of the same type as demonstrated in earlier work with strongly polar non-electrolytes. Precautions have to be taken to prevent uptake by means of an ion exchange mechanism. The method permits a separation from exchangeable anions and from non-adsorbable solutes.     

Separation of sugar derivatives by partition chromatography on anion-exchange resins

The separation of a number of sugar derivatives such as methyl, ethyl, benzyl, hydroxyethyl erners and various glycosides has been studied. An efficient separation of most species was obtained in 94% ethanol using an anion-exchange resin in its sulfate form. The eluate concentration was determined automatically using the orcinol method.     

Reversible Insertion of Methyl Isothiocyanate into Copper(I) Aryloxides

MeNCS undergoes insertion into the copper(I)-aryloxide bond to form [N-methylimino(aryloxy)methanethiolato]copper(I) complexes. This insertion occurs in the absence of ancillary ligands unlike the analogous insertion of PhNCS. The reaction with 4-methylphenoxide results in the formation of hexakis[[N-methylimino(4-methylphenoxy)methanethiolato]copper(I)] (1), which has been characterized by X-ray crystallography. Crystal data for 1: hexagonal R&thremacr;, a = 12.365(3) ?, c = 36.734(16) ?, gamma = 120 degrees, Z = 3, V = 4863(3) ?(3), R = 0.0306. Reactions of 2,6-dimethyl- and 4-chlorophenoxides also result in analogous copper(I) complexes 2 and 3. Addition of stochiometric amounts of PPh(3) to the oligomeric complexes typically results in the extrusion of MeNCS. The ease of extrusion is dependent on the substituents on the aryloxide, and this deinsertion is accelerated by water. However, the extrusion reaction is slow enough in the case of the N-methylimino(2,6-dimethylphenoxy)methanethiolate complex and the isolation of an intermediate monomeric product bis(triphenylphosphine)[N-methylimino(2,6-dimethylphenoxy)methanethiolato]copper(I) (4) is possible. Crystal data for 4: triclinic P&onemacr;, a = 10.088(2) ?, b = 11.302(1) ?, c = 17.990(2) ?, alpha = 94.06(1) degrees, beta = 95.22(2) degrees, gamma = 103.94(1) degrees, Z = 2, V = 1974.4(7) ?(3), R = 0.0361. In the presence of of PPh(3), the insertion reaction becomes reversible. This allows the exchange of the heterocumulene MeNCS or the aryloxy group in these molecules with another heterocumulene or a phenol, respectively, when catalytic amounts of PPh(3) are added. Oligomers with exchanged heterocumulmes and phenols could be characterized by independent synthesis.     

Kinetics of wetting of a compacted powder by aqueous solutions of surface active agents

Summary The capillary rise of aqueous solutions of anionic wetting agents into a compacted powder of an organic chromium complex is discussed on the basis of the Washburn-Rideal equation expanded to account for the porous structure parameters.At the porosity 1 —/6, corresponding to the loosest packing of monodisperse spheres the penetration rate is found to be mostly governed by the effective tensions operative at the moving three phase line of contact in case no deflocculation intervenes.

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Zusammenfassung Der Kapillaraufstieg wässeriger Lösungen anionischer Netzmittel in gepreßtem Pulver eines organischen Chrom-Komplexes wird durch die erweiterte Gleichung vonWashburn-Rideal wiedergegeben, in der die Parameter der porösen Struktur mit einbezogen werden.Bei der Porosität 1 —/6, die der lockersten Anordnung gleichförmiger Kugeln entspricht, wird die Eindringgeschwindigkeit meistens durch die an der sich bewegenden Dreiphasengrenze wirkenden Grenzflächenspannungen bestimmt, wenn keine Peptisation eintritt.

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Paper presented at the XII Intern. Congr. Fat Research, Milan, September 1974.     

“Cautious” utility maximization and iterated weak dominance

This paper examines the implications of assuming that rational players in a two-player noncooperative game maximize expected utility using cautious beliefs; i.e., beliefs that give positive probability to all rational strategies of the other players. The result is a solution concept that captures some of the flavor of but is not equivalent to the iterated elimination of weakly dominated strategies. The solution concept yields attractive results for some games, but suffers from nonexistence problems in other games. We interpret the nonexistence problems as showing that it is logically inconsistent to assume that rational players analyze all games on the basis of cautious expected utility maximization.We would like to thank Pierpaolo Battigalli, two anonymous referees, and an editor for helpful comments. Tilman Börgers gratefully acknowledges financial assistance from the Schweizerischer Nationalfonds.     

Utilization of ion exchangers in analytical chemistry XXVI : Application of the ion-exchange method to solutions containing oxidants

The free acid form of a cation-exchange resin of the sulfonated hydrocarbon type (Dowex 50) can be used for a quantitative liberation of the corresponding acids from salt solutions containing oxidants that are reduced by phenolic resins. Positive results have been obtained with solutions containing bromate, iodate, periodate, molybdate, and chromate. With permanganate a partial reduction occurs which prevents the application of the ion-exchange method for quantitative separation of solutions containing permanganate.