Determination of stoichiometry of cadmium telluride by XPS

Summary The stoichiometry of cadmium telluride has been determined by the non-destructive technique of XPS. The determination has been based on differential photoionisation cross-sections, electron mean free paths and areas due to M₅ electrons of Cd and Te. The stoichiometry of Cd and Te determined by XPS has been found to be in good agreement with that obtained by analysing Cd and Te independently by chemical methods.     

Oxidation of thallium(I) by hexacyanoferrate(III) in aqueous acetic acid

The hexacyanoferrate(III)-thallium(I) reaction in aqueous acetic acid containing large concentrations of hydrochloric acid is considerably accelerated both by hydrogen and chloride ions as well as increasing acetic acid in the medium. The experimental results obey the rate law (1) where β₁ to β₆ are the cumulative stability constants of the species TlCl, TlCl, TlCl, HFe(CN), H₂Fe(CN) and H₃Fe(CN)₆ respectively and k_a and k_b are the rate constants associated with the mono- and di-protonated oxidant species. The main active species are H₂Fe(CN) and TlCl.     

Properties of amorphous and crystallizable hydrocarbon polymers. II. Rheology of linear and star-branched polybutadiene

Some results are reported on the linear viscoelastic properties of polybutadienes with narrow-molecular-weight distributions. The zero shear viscosity η₀ varies as M^3.4 in the linear samples, and viscosity enhancement is found in star-branched samples with long arms, in good agreement with results reported earlier by Kraus and Gruver. The temperature coefficient of viscosity appears to be slightly larger in stars when the arms become long. The steady state recoverable compliance J is 2.1 × 10 ^?7 cm²/dyn in linear samples of high molecular weight, but it increases to values as much as 10 times larger in the stars. The plateau modulus G, obtained from a composite curve for the linear samples, is 1.32 × 10⁷ dyn/cm². The terminal relaxation spectrum of the stars is too broad to allow an evaluation of plateau modulus.     

Hydromagnetic forced flow against a porous rotating disk

This paper deals with the steady forced flow of a viscous, incompressible and electrically conducting fluid against a porous rotating disk when a uniform magnetic field acts perpendicular to the disk surface. For small suction the equations of motion are integrated numerically by Kármán-Pohlhausen method, but for large suction a series solution in the inverse powers of the suction parameter is obtained. The effects of disk porosity and magnetic field on the various flow parameters are discussed in detail.     

Kinetics and mechanism of the oxidation of substituted benzaldehydes by benzyltrimethylammonium chlorobromate

The oxidation of 35 monosubstituted benzaldehydes by benzyltrimethylammonium chlorobromate (BTMACB) in aqueous acetic acid leads to the formation of the corresponding benzoic acids. The reaction is first order with respect to both benzaldehyde and BTMACB. The reaction failed to induce the polymerization of acrylonitrile. There is no effect of benzyltrimethylammonium chloride or potassium bromide on the reaction rate. The oxidation of [(2)H]benzaldehyde (PhCDO) indicated the presence of a substantial kinetic isotope effect. The effect of solvent composition indicated that the reaction rate increases with an increase in the polarity of the solvent. The rates of oxidation of meta- and para-substituted benzaldehydes were correlated in terms of Charton's triparametric LDR equation, whereas the oxidation of ortho-substituted benzaldehydes was correlated with the tetraparametric LDRS equation. The oxidation of para-substituted benzaldehydes is more susceptible to the delocalization effect, whereas the oxidation of ortho-and meta-substituted compounds displayed a greater dependence on the field effect. The positive value of eta suggests the presence of an electron-deficient reaction center in the rate-determining step. The reaction is subjected to steric hindrance by the ortho substituents.     

Energies and relative intensities of Kα3 and Kα4 x‐ray satellites of sulfur and sulfides by photon excitation

Energies and relative intensities of the K x‐ray satellites K_α4 and K_α3 of sulfur and two sulfides K₂S and FeS are measured by a wavelength dispersive spectrometer. The energy shifts of these satellites relative to the diagram line are compared with Dirac–Fock theoretical values. The energy shifts and relative intensities are examined for chemical effects. Supplementing the present data to the available data, Z dependence of K_α4/K_α3 intensity ratio is studied in the low Z region. Copyright © 2007 John Wiley & Sons, Ltd.     

Studies of β-turn opening with model peptides containing non-coded α-amino isobutyric acid

Single crystal X-ray diffraction studies show that among the three terminally protected model tripeptides I-III, Boc-Ile-Aib-Xx-OMe (Xx in peptide I: Val; II: Leu; III: Phe) with a centrally placed non-coded amino acid Aib (Aib: α-amino isobutyric acid), peptide I displays a conformational preference for β-turn, peptide II forms a hydrated β-turn representing the solvent mediated intermediate for the interconversion between β-turn and β-strand and peptide III adopts a completely unfolded β-strand like structure. By varying the steric bulk of the third residue, Xx(3), various conformations related to the structural interconversion between the β-turn and β-strand have been isolated. The peptide conformations in the solution phase have been probed by solvent dependent NMR titration and CD spectroscopy. Morphological studies with scanning electron microscopy (SEM) reveal that among the three peptides only peptide III can form filamentous fibrils in the solid state.     

Piezo rotary and axial vibrator (PRAV) characterization of a fresh coating during its drying

Using a piezo rotary and axial vibrator (PRAV) the viscoelastic properties of a fresh Al₂O₃ coating that is deposited on a well-chosen plate can be measured simultaneously during drying. There are three types of vibrations available to be excited and detected in their resonance modes, by measuring resonance frequencies f _k and half-widths h _k, before and after coating as a function of time: axial vibration, bending vibration to get the evolving Young’s modulus and rotary vibration to follow the viscosity increase during drying of the thin coating. This information is contained in the complex frequency shifts Ω_k = 2Δf _k /f _k + iΔh _k /f _k of the three vibration modes caused by the coating on the plate. A derivation of the relationships, their validation on Newtonian liquids and experimental applications carried out using the PRAV are given in the paper.