Backscattering of an intense laser beam by an electron

We present a novel, simple asymptotic expansion for the spectrum of radiation that is backscattered from a laser by a counterpropagating (or copropagating) electron. The solutions are presented in such a way that they explicitly show the relative merit of using an intense laser and of an energetic electron beam in x-ray production in the single particle regime. Simple scaling laws are given.     

Counter-Ion Influence on Polypyrrole Potentiometric pH Sensitivity

The pH sensitivity of conducting polymer films is an important issue from the sensor design point of view. The doping and supporting electrolyte anions effect on the potentiometric sensitivity and response time of polypyrrole (PPy) electrodes towards changes of solution pH were studied. It was found that (i) the response of PPy doped by easily exchangeable common anions (Cl^–, NO₃ ^–, ClO₄ ^–) in their solutions (KCl, KNO₃, NaClO₄) is slow. In contrast, (ii) polypyrrole films deposited in the presence of weak acid anions (phthalates, oxalates, salicylates) were characterised by instantaneous responses in the above mentioned solutions. On the basis of electrochemical experiments (open circuit potential vs. time dependencies, cyclic voltammetry, EQCM), the observed differences were attributed to different mechanisms of pH sensitivity of tested films. The long response times are related to the incorporation of the solution ions into the film in order to compensate charges created due to protonation. On the other hand, if the ion-exchange is hindered as in the case of (ii), instantaneous open circuit responses are observed due to polarisation of the oxidised polymer layer, analogously to the metal electrode. Moreover, for these films the internal pH buffering within the polymer membrane will weaken the pH change effect.The mechanisms were confirmed in the course of studying the pH effect in solutions containing anions easily (KCl, NaClO₄, KNO₃) or hardly exchangeable with polypyrrole (K₂SO₄, sodium poly(4-styrenesulphonate) solutions) acidified with H₂SO₄.     

An XeCl* Excimer Fluorescence Study on the Pulse Radiolysis of Xe–nCCl4 and Xe–SOCl2 Systems

The mechanism and kinetics of energy transfer from highly excited Xe states (E _ex > 9.5 eV), generated by a 12-ns electron beam, to chlorine donor molecules were deduced from time-resolved spectra of fluorescence in the region 240–340 nm. The emissions at 240–250 nm were assigned to Xe₂** excimers, and those at 308 and 340 nm to XeCl(B) and XeCl(C) states. Kinetic analysis of the recorded spectra for Xe–CCl₄ and Xe–SOCl₂ gas mixtures at constant xenon pressure and various pressures of molecular admixtures (0.1–1 Torr) allowed us to find the rate constants for the reactions (5) Xe** + RCI products, (6a) Xe** + RCl XeCl(B) + R*, and (6b) Xe** + RCl XeCl(C) + R*, where R is any radical.     

Spectral measurement of absorption by spectroscopic frequency-domain optical coherence tomography

A new method of measurement that essentially combines Fourier-domain optical coherence tomography with spectroscopy is introduced. By use of a windowed Fourier transform it is possible to obtain, in addition to the object structure, spectroscopic information such as the absorption properties of materials. The feasibility of this new method for performing depth-resolved spectroscopy is demonstrated with a glass filter plate. The results are compared with theoretically calculated spectra by use of the well-known spectral characteristics of the light source and the filter plate.     

STM/STS investigation of carbon nanotube junctions

In this paper we present scanning tunneling microscopy/spectroscopy investigations of multiwall carbon nanotube junctions. We concentrated on bent and narrowing junctions, which my be formed by introducing pentagon–heptagon defects into a hexagonal network of a carbon nanotube. It was expected that the defects introduced to the nanotube could cause changes in the local density of states. The scanning tunneling spectroscopy results were used to search for and identify these defects. We also discuss a hypothesis for a combination of a telescope junction and a pentagon–heptagon induced junction. PACS 68.37.Ef; 73.22.–f; 61.46.Fg; 71.20.Tx     

Computational studies of the cyclization of thiosemicarbazides

While typically cyclodehydration of thiosemicarbazides in acidic media leads to 1,3,4‐thiadiazoles, we have recently shown that under reflux conditions in anhydrous acetic acid the cyclization yields an imidazolidine derivative. The mechanism of this reaction has been characterized theoretically. Calculations indicate that this direction, facilitated by the presence of the ? CH₂CO₂? moiety in the N4 substituent is favored over the direction leading toward the thiadiazole product. Formation of the C? N bond that closes the five‐member ring appears to be concerted with the departure of ethanol molecule, although the proton transfer from the nitrogen atom to oxygen atom is much more advanced in the transition state. Copyright © 2007 John Wiley & Sons, Ltd.     

Room and high-temperature scanning tunnelling microscopy and spectroscopy (HT-STM/STS) investigations of surface nanomodifications created on the TiO2(1 1 0) surface

High-temperature scanning tunnelling microscopy, scanning tunnelling spectroscopy and current imaging tunnelling spectroscopy (HT-STM/STS/CITS) were used to study the topographic and electronic structures changes due to surface modifications of the TiO₂(1 1 0) surface caused by the STM tip. In situ high-temperature STM results showed that the created modifications were stable even at elevated temperatures. The STS/CITS results showed the presence of energy gap below the Fermi level on the untreated regions. The disappearance of energy gap below the Fermi level on the modifications created by the tip was observed. It is assumed that the presence of the tip can change the chemical stoichiometry of the surface from TiO_2−x towards Ti₂O₃.     

Storage Stability of Antioxidant in Milk Products Fermented with Selected Kefir Grain Microflora

The aim of the study was to assess the antioxidant potential of goat’s milk and whey from goat’s milk fermented with selected bacteria strains from kefir grain (L. plantarum, L. fermentum, L. rhamnosus and L. acidophilus) with regard to fermented cow’s milk with the same bacteria strains. The assessment of antioxidant potential was made by ABTS, DPPH, TPC and FRAP methods. The work also assessed metabolic activity of tested lactic acid bacteria using measurement of electrical impedance changes in the growing medium. The highest values describing the antioxidant potential were found for fermented milk by L. acidophilus. It was also found that the time of cooling storage causes significantly increasing the antioxidant potential of most analyzed samples. Metabolic activity of tested lactic acid bacteria was the highest for cow’s milk. The course of curves for goat’s milk and whey from goat’s milk was similar, which confirms the differences between cow and goat milk.     

Brucine and two solvates

The crystal structures of brucine (2,3‐di­methoxy­strychnidin‐10‐one), C₂₃H₂₆N₂O₄, brucine acetone solvate, C₂₃H₂₆N₂O₄·C₃H₆O, and brucine 2‐propanol solvate dihydrate, C₂₃H₂₆N₂O₄·C₃H₇O·2H₂O, have been determined. Crystals of brucine and its 2‐propanol solvate dihydrate exhibit similar monolayer sheet packing, whereas crystals of the acetone solvate adopt a different mode of packing, as brucine pillars. The solvent appears to control the brucine self‐assembly on the basis of common donor–acceptor properties of the surfaces.