Electrical current distribution across a metal-insulator-metal structure during bistable switching

Combining scanning electron microscopy (SEM) and electron-beam-induced current (EBIC) imaging with transport measurements, it is shown that the current flowing across a two-terminal oxide-based capacitor-like structure is preferentially confined in areas localized at defects. As the thin-film device switches between two different resistance states, the distribution and intensity of the current paths, appearing as bright spots, change. This implies that switching and memory effects are mainly determined by the conducting properties along such paths. A model based on the storage and release of charge carriers within the insulator seems adequate to explain the observed memory effect.Comment: 8 pages, 7 figures, submitted to J. Appl. Phy

Radical Alkynylations with EthynylBenziodoXolones: from Photocatalysis to Direct Excitation

Ethynylbenziodoxolones (EBXs) have recently emerged as potent reagents for the alkynylation of radicals. Their combination with photocatalysis allows the synthesis of valuable alkynes at room temperature. Herein, we discuss two photomediated strategies for the synthesis of internal alkynes. The first transformation is a 1,2-oxyalkynylation of N- and O-alkenes using 4ClCzIPN as a photocatalyst. The second strategy makes use of EBXs as strong photooxidants allowing the oxidation of a variety of substrates with no need for a photocatalyst

Silylium-Catalyzed Activation of Donor- Acceptor Strained Rings and Annulation with Indoles

Leveraging the unique reactivity profile of donor-acceptor aminocyclopropanes and cyclobutanes allows the preparation of complex nitrogen-substituted molecules. While most reports focus on donor-acceptor strained rings with two geminal carbonyl groups as acceptors, mono carbonyl acceptor systems, despite their synthetic relevance, have been considerably less studied. Herein we describe catalytic annulation reactions ofaminocyclopropane and aminocyclobutane monoesters employing silylium catalysis to activate these less reactive donor-acceptor systems

Polarization states of polydomain epitaxial Pb(Zr1-xTix)O3 thin films and their dielectric properties

Ferroelectric and dielectric properties of polydomain (twinned) single-crystal Pb(Zr1-xTix)O3 thin films are described with the aid of a nonlinear thermodynamic theory, which has been developed recently for epitaxial ferroelectric films with dense laminar domain structures. For Pb(Zr1-xTix)O3 (PZT) films with compositions x = 0.9, 0.8, 0.7, 0.6, 0.5, and 0.4, the "misfit strain-temperature" phase diagrams are calculated and compared with each other. It is found that the equilibrium diagrams of PZT films with x > 0.7 are similar to the diagram of PbTiO3 films. They consist of only four different stability ranges, which correspond to the paraelectric phase, single-domain tetragonal ferroelectric phase, and two pseudo-tetragonal domain patterns. In contrast, at x = 0.4, 0.5, and 0.6, the equilibrium diagram displays a rich variety of stable polarization states, involving at least one monoclinic polydomain state. Using the developed phase diagrams, the mean out-of-plane polarization of a poled PZT film is calculated as a function of the misfit strain and composition. Theoretical results are compared with the measured remanent polarizations of PZT films grown on SrTiO3. Dependence of the out-of-plane dielectric response of PZT films on the misfit strain in the heterostructure is also reported.Comment: 23 pages, 4 figure

Characterization of the Active Site of Acetylcholinesterases by Application of Sterically Modified Acetylcholine Homologues

Our aim was to find steric limitations for the model of the active site of acetylcholinesterase and cho1inesterase. For thi<s purpose we used homologues of acetylcholine with hydrocarbon chains of increasing size at the cationic head. Catalysis of hydrolysis ceased for both enzymes, when the methyl groups of the cationic head of acetylcholine were substituted by three n-propyl groups. With data already documented in the literature and our additional experiments, under the same conditions, we were able to present models of the active sites for both enzymes

Pollinator Selection, Quantitative Genetics, and Predicted Evolutionary Responses of Floral Traits in Penstemon Centranthifolius (Scrophulariaceae)

Much of the remarkable diversity of angiosperm flowers is thought to have evolved in response to selection by animal pollinators. Selection during pollination can readily be documented, but the extent to which it leads to evolutionary change depends on the genetic basis of floral traits. Here we combine estimates of genetic variance and covariance for several traits of flowers and inflorescences in a wild plant species, with estimates of natural selection by hummingbird pollinators. Analysis of phenotypic selection through two components of pollination success indicates direct selection of plants toward larger size and toward bearing shorter flowers that produce more nectar. Predictions of selection response that account for genetic correlations among traits generally exceed the simple predictions based on apparent selection and heritabilities of single traits. This underscores the importance of genetic correlations and demonstrates that univariate, strictly phenotypic, analyses of natural selection can be misleading. A sample of fruits from one of the two years of our study also indicates that total selection at the end of the reproductive cycle is weaker than selection during pollination. Thus a second caution is in order, against relying too strongly on differential pollination success as an estimate of overall selection

DISTRIBUTION AND KINETICS OF 14C-VECURONIUM IN RATS AND MICE

The distribution and kinetics of 14C-vecuronium were studied in rats and mice. 14C-Vecuronium accumulated rapidly in the liver. Both unchanged and metabolized vecuronium were excreted with the bile into the intestines and stomach. Reabsorption in the gut was probably responsible for an enterohepatic increase in radioactivity in the liver after one hour. Excretion through the kidneys increased continuously from low values after the initial peak. Binding in compartments with acid mucopolysaccharides such as cartilage, connective tissue etc., was less important. Bloodbrain barrier and placenta were permeable only to a small degre

Interaction particles from the surface of the curved pipeline

The interaction of the agglomerated fine dust particles from the surface of the rotary pyleprovoda, given deposit formation evaluation. The interaction of large particles to the surface of the rotary pyleprovoda. The analysis of hydrodynamic phenomena in the means of protection against wear