Electrochemically-Switched 2nd Order Non-Linear Optical Response in an Arylimido-Polyoxometalate with High Contrast and Cyclability

Electrochemically switched 2^nd order non-linear optical responses have been demonstrated for the first time in polyoxometalates (POMs), with an arylimido-derivative showing a leading combination of high on/off contrast (94 %), high visible transparency, and cyclability. Spectro-electrochemical and TD-DFT studies indicate that the switch-off results from weakened charge transfer (CT) character of the electronic transitions in the reduced state. This represents the first study of an imido-POM reduced state, and demonstrates the potential of POM hybrids as electrochemically activated molecular switches.     

Percolative transport in the vicinity of charge-order ferromagnetic transition in a hole-doped manganite

We report measurements of non-linear charge transport in epitaxial (La_1−x Pr _x )_0.7Ca_0.3MnO₃ thin films fabricated on (100) oriented SrTiO₃ single crystals by pulsed laser deposition. The end members of this series, namely Pr_0.7Ca_0.3MnO₃ and La_0.7Ca_0.3MnO₃ are canonical charge-ordered (CO) and ferromagnetic manganites, respectively. The onset of the CO state in Pr_0.7Ca_0.3MnO₃ is manifested by a pronounced insulating behavior below ∼ 200 K. The CO state remains stable even when a large (∼ 2×10⁵ V/cm) electric field is applied across the thin film samples. However, on substitution of Pr with La, a crossover from the highly resistive CO state to a state of metallic character is observed at relatively low electric fields. The current-voltage characteristics of the samples at low temperatures show hysteretic and history dependent effects. The electric field driven charge transport in the system is modelled on the basis of an inhomogeneous medium consisting of ferromagnetic metallic clusters dispersed in a CO background.     

Thin-layer separation and low-temperature luminescence measurement of mixtures of carcinogens

Low-temperature fluorescence and phosphorescence characteristics of a number of polynuclear aromatic hydrocarbons are reported. Complex mixtures of hydrocarbons are studied to determine the selectivity of low-temperature luminescence measurement. Low-temperature fluorimetry is applied to measure several hydrocarbon carcinogens after ethanolic extraction from thin-layer chromatograms. The method described permits determination of ca. 0.1 μg of most of the potent carcinogens.     

A measurement of direct photon production at large pT at the CERN ISR

We have measured direct photon production in pp collisions at the CERN intersecting storage rings for c.m. energies 31 < √s < 63 GeV and transverse momenta up to 9GeV/c, using segmented lead/liquid-argon calorimeters. The ratio of direct photon to π⁰ production is significantly larger than zero, starting at p_T ≈ 4 GeV/c and increasing to values of about 0.4 at 9GeV/c. No significant √s dependence is seen.     

Molecular orbital momentum distributions and binding energies for H2O using an electron impact coincidence spectrometer

The construction and operation of an instrument which uses the techniques of coincidence counting and electron impact spectroscopy is reported for the study of molecular ionization at large momentum transfer in which the two outgoing electrons are detected at 45° to the incident beam. Variation of the incident energy provides binding-energy spectra for Xe, CH₄ and H₂O up to 45 eV. Alternatively variation of the azimuthal angle (symmetric, non-coplanar geometry) gives a measure of the electron momentum distribution for any selected orbital in the binding-energy spectrum. Momentum distributions for the four valence orbitals of H₂O are compared with various wavefunctions from the literature.     

Correlation effects and electron momentum distributions in the valence orbitals of ethylene

The non-coplanar symmetric (e, 2e) reaction has been applied to C₂H₄ at 1000-eV incident electron energy. An ion state at 27.4 eV separation en     

A second-order iterative technique for differential-integral systems

This note considers the optimal control of a system represented by nonlinear differential-integral equations with a general cost function. A second-order iterative method of solution based on the fixed-point contraction mapping principle is proposed.     

N-terminal and internal sequence determination of microgram amounts of proteins separated by isoelectric focusing in immobilized pH gradients

Isolation of microgram amounts of proteins and submicrogram quantities of peptides in a form suitable for sequence analysis is a key step in high sensitivity protein sequencing technology. Recently, methods have been developed which allow the direct, high yield, recovery of microgram amounts of sequenceable proteins separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis or two-dimensional gel electrophoresis. In the present publication, we describe an extension of these methods to obtain N-terminal or internal sequence information from proteins separated by isoelectric focusing in polyacrylamide gels containing immobilized pH gradients. For N-terminal sequence analysis, separated proteins were electrophoretically transferred (electroblotted) onto chemically-modified glass fiber sheets, a support compatible with Edman degradation chemistry. Transferred protein bands were detected on the support, cut out and directly inserted into the cartridge of a gas-phase protein sequenator. For internal sequence analysis, separated proteins were electrophoretically transferred onto nitrocellulose. Protein bands were detected by staining, cut out and the proteins subjected to enzymatic digestion directly on the support. The resulting cleavage fragments (peptides) were released into the supernatant where they were recovered and separated by narrow-bore reversed-phase high performance liquid chromatography for sequence analysis. The potential of this methodology is illustrated by the comparative peptide mapping of isoforms of bovine carbonic anhydrase.