Mössbauer study of nanodimensional nickel ferrite – mechanochemical synthesis and catalytic properties

Iron–nickel spinel oxide NiFe₂O₄ nanoparticles have been prepared by the combination of chemical precipitation and subsequent mechanical milling. For comparison, their analogue obtained by thermal synthesis is also studied. Phase composition and structural properties of iron–nickel oxides are investigated by X-ray diffraction and Mössbauer spectroscopy. Their catalytic behavior in methanol decomposition to CO and methane is tested. An influence of the preparation method on the reduction and catalytic properties of iron–nickel samples is established.     

Hilbert algebras as implicative partial semilattices

The infimum of elements a and b of a Hilbert algebra are said to be the compatible meet of a and b, if the elements a and b are compatible in a certain strict sense. The subject of the paper will be Hilbert algebras equipped with the compatible meet operation, which normally is partial. A partial lower semilattice is shown to be a reduct of such an expanded Hilbert algebra i ?both algebras have the same ?lters.An expanded Hilbert algebra is actually an implicative partial semilattice (i.e., a relative subalgebra of an implicative semilattice),and conversely.The implication in an implicative partial semilattice is characterised in terms of ?lters of the underlying partial semilattice.     

Selective spatial localization of the atom displacements in one-dimensional hybrid quasi-regular (Thue-Morse and Rudin-Shapiro)/periodic structures

We have studied the vibrational frequencies and atom displacements of one-dimensional systems formed by combinations of Thue-Morse and Rudin-Shapiro quasi-regular stackings with periodic ones. The materials are described by nearest-neighbor force constants and the corresponding atom masses. These systems exhibit differences in the frequency spectrum as compared to the original simple quasi-regular generations and periodic structures. The most important feature is the presence of separate confinement of the atom displacements in one of the parts forming the total composite structure for different frequency ranges, thus acting as a kind of phononic cavity.     

Thermal characterisation of micro-hotplates used in sensor structures

Micro-hotplates operated at elevated temperature form the basic element in several sensor devices, such as integrated calorimetric or Taguchi-type gas sensors and flow-rate sensors. In all of these applications thermal properties of the sensing elements play a determining role in functional operation, therefore, their accurate characterisation is essential. The micro-hotplates investigated were developed by one side porous silicon micro-machining technology, forming Pt micro-filaments embedded in non-stoichiometric silicon nitride, and suspended across a cavity. This work is dealing with the accurate temperature detection in the micro-scale by different measurement methods for the deduction of steady state and transient thermal properties from the results. Transient properties of the structure were investigated by application of a simplified thermal equivalent circuit model.     

Optical reflectance of blue bronze crystals near the Peierls transition

We report on the reflectance of blue bronze crystals in the visible frequency range as a function of temperature. The observed large oscillations in the reflectance at all wavelengths at temperatures near the Peierls transition are interpreted as interference effects stemming from a surface layer. It is found that the surface layer, which appears to be tied to fluctuations, can be as much as 1.6 microns thick.     

Structural and optical properties of thermally evaporated antimony telluride thin films

Antimony telluride thin films were prepared on the well-cleaned glass substrates under a pressure of 10 – 5 torr by thermal evaporation method. The thicknesses of the films were measured using Multiple Beam Interferometer (MBI) technique. The structure of the sample was analyzed by X-ray diffraction technique. The film attains crystalline structure as the temperature of the substrate is increased to 373 K. The d spacing and the lattice parameters of the sample were calculated. Optical behavior of the film samples with the various thicknesses was analyzed by obtaining their transmittance spectra in the wavelength range of 400 – 800 nm. The transmittance is found to decrease with increase in film thickness and also it falls steeply with decreasing wavelength. The optical constants were estimated and the results are discussed. The optical band gap energy decreases with increase in the film thickness. The optical transition in these films is found to be indirect and allowed. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

A Miura of the Painlevé I Equation and Its Discrete Analogs

We present Miura transformations for the continuous and several discrete Painlev\'e I equations. In the case of the continuous P_I, we use the Hamiltonian formulation of the Painlev\'e equations and show that there exists a Miura transformation between P_I and the binomial, second degree, equation of Cosgrove SD_V. In the case of the discrete P_I's we obtain two different kinds of Miuras. One kind relates a d-P_I to some other d-P_I while the other leads to discrete four-point equations which are the discrete analogs of the derivative of Cosgrove's equation SD_V.     

Application of quantum-chemical methods including density functional theory for the interpretation of isotropic hyperfine data. The example of azulenebenzoquinone

The radical anion of aceneazulenedione in which a benzoquinone is fused to an azulene moiety was generated by electrolysis and by reduction with the alkali metals in ethereal solvents. The hyperfine data could not be reproduced by standard Hückel calculations which usually give reliable predictions for the spin distribution in radical ions such as azulene quinones and a variety of extended π systems. However, PPP and, preferably,ab initio geometry optimisations followed by single-point calculations of the Fermi contact interaction with density functional theory, led to a straightforward assignment of the hyperfine coupling constants.