Microwave harmonic mixing in iodine doped polyacetylene

Measurements of the temperature dependence of the conductivity and of the microwave harmonic mixing (MHM) signal produced by the non-ohmic behavior of iodine doped polyacetylene in the metallic regime are reported. The experimental results are consistent with fluctuation induced tunneling conduction between fibers. The theory has been adapted for low electric field strengths and microwave frequencies.     

Reference scales for the characterization of cationic electrophiles and neutral nucleophiles

Twenty-three diarylcarbenium ions and 38 pi-systems (arenes, alkenes, allyl silanes and stannanes, silyl enol ethers, silyl ketene acetals, and enamines) have been defined as basis sets for establishing general reactivity scales for electrophiles and nucleophiles. The rate constants of 209 combinations of these benzhydrylium ions and pi-nucleophiles, 85 of which are first presented in this article, have been subjected to a correlation analysis to determine the electrophilicity parameters E and the nucleophilicity parameters N and s as defined by the equation log k(20 degrees C) = s(N + E) (Mayr, H.; Patz, M. Angew. Chem., Int. Ed. Engl. 1994, 33, 938-957). Though the reactivity scales thus obtained cover more than 16 orders of magnitude, the individual rate constants are reproduced with a standard deviation of a factor of 1.19 (Table 1). It is shown that the reactivity parameters thus derived from the reactions of diarylcarbenium ions with pi-nucleophiles (Figure 3) are also suitable for characterizing the nucleophilic reactivities of alkynes, metal-pi-complexes, and hydride donors (Table 2) and for characterizing the electrophilic reactivities of heterosubstituted and metal-coordinated carbenium ions (Table 3). The reactivity parameters in Figure 3 are, therefore, recommended for the characterization of any new electrophiles and nucleophiles in the reactivity range covered. The linear correlation between the electrophilicity parameters E of benzhydryl cations and the corresponding substituent constants sigma(+) provides Hammett sigma(+) constants for 10 substituents from -1.19 to -2.11, i.e., in a range with only very few previous entries.     

Microwave photon - assisted tunneling in niobium triselenide,NbSe3.

Nonlinear conduction has been observed in NbSe₃ with microwave fields of amplitudes below the threshold field for nonlinear dc conduction at temperatures of about 25 K by the method of harmonic mixing. The observation is considered to support Bardeen's theory of tunneling assisted by photons whose frequency is the microwave frequency.     

Electron microprobe investigations on phase boundaries steel-enamel

Summary This report describes investigations carried out on a new type of enamel (Liberty Coat Enamel) for steel sheets from continuously cast material. Subsequent to technological tests, EPMA investigations were conducted to study the mechanism of enamel adherence. For this purpose, we employed our Concentration Mapping (CM) technique. In order to obtain representative data, a special evaluation method was used. The results, which are partly in contradiction with statements in the literature, suggest that the concept of enamel adherence reactions should be given further critical consideration.The paper has been presented at 12th Colloquium on Materials Analysis, Institute for Analytical Chemistry, Technical University in Vienna, May 13–15, 1985.     

Nearrings whose set of N-subgroups is linearly ordered

We consider zerosymmetric right nearrings whose lattice of N-subgroups is linearly ordered by inclusion and in which for every n ∈ N, there is x ∈ N such that x * n = n. All such nearrings with finitely many N-subgroups are constructed.