T-matrix method formulation applied to the study of flexural waves scattering from a through obstacle in a plate

Elastic wave scattering in a flat thin plate hosting a through obstacle of arbitrary closed form is examined using a numerical technique based on the T-matrix approach, which is applied to describe of flexural waves in plates. The limiting cases of a hole and a rigid obstacle are considered. The vibrations of the plate are described by the Kirchhoff model. The far field backscattered amplitude as a function of wave frequency for inclusions of elliptic, triangular and square form with rounded corners is analysed numerically. Comparison of present results for circular obstacles with the analytical solutions obtained by other authors show excellent agreement.     

Steady-state vibrations of a thin two-layer plate with delamination

We consider the problem of harmonic vibrations of a thin two-layer plate with horizontal crack. The problem is solved with the help of the null-field approach. The influence of the shape of the crack contour on the amplitude-frequency characteristics of plate vibrations is investigated. Institute of Mathematics, Ukrainian Academy of Sciences, Kiev. Translated from Matematychni Metody ta Fizyko-Mekhanichni Polya, Vol. 41, No. 2, pp. 83–89, April–June, 1998.     

Synthesis of nanosized thin-film bimetallic catalysts based on mesoporous TiO2 for microstructured reactors

A synthetic procedure for the production of effective catalysts for the selective hydrogenation of organic substrates was developed, and the samples of thin-film Pt-Sn/TiO₂ materials, which are characterized by high dispersity and a narrow size distribution of bimetallic particles in a mesoporous matrix of titanium dioxide, were prepared. With the use of a set of physicochemical techniques (low-temperature nitrogen adsorption, X-ray diffraction analysis, thermal analysis, and transmission electron microscopy), the formation and surface properties of the mesoporous Pt-Sn/TiO₂ materials as powder and coatings on the surfaces of silica capillaries and plates were studied. Based on the effects of the sol composition and calcination temperature on the texture properties of TiO₂, an optimum sol composition (1Ti(O-iPr)₄: 0.009 F127: 0.13 HNO₃: 1.3 H₂O: 25 C₂H₅OH) and heat treatment conditions (calcination at 673 K; stepwise increase in the temperature) were determined to form a mesoporous coating with a specific surface area of 130 m²/g and an average pore diameter of 5.4 nm. It was found that the concentrations of metals (0.5–4 wt %), average particle sizes (1.0–3.5 nm), and particle size distributions in the Pt-Sn/TiO₂ materials can be mainly regulated by varying the nature of the solvent, the concentration of Pt-Sn carbonyl complexes, and the time of adsorption, whereas the electronic state of metals can be fine-tuned by thermal treatment conditions. In an oxidizing atmosphere, the Pt-Sn carbonyl complexes decomposed with the formation of a two-phase system (Pt○ and SnO₂). Thermal treatment in a vacuum and an inert or reducing atmosphere led to the formation of bimetallic phases (PtSn and Pt₃Sn), whose stucture was regulated by the composition of a gas atmosphere and by the calcination temperature.     

Microanalysis of geological samples by laser plasma ionization mass spectrometry (LIMS)

Laser plasma ionization mass spectrometry (LIMS) has been applied for in-situ microanalysis of minerals and inclusions in geo- and cosmochemical samples down to the ng/g concentration level. A great advantage of this method is that at high laser power densities (2×10¹⁰ W/cm²) used, most elements are ionized with about the same efficiency independent of chemistry and mineralogy of the samples. A procedure has been developed which allows quantitative analysis of about 30 trace elements with an accuracy of better than 25%.     

Raman spectra of single-crystal C60

We have analysed the Raman spectra of C₆₀ single crystals between room temperature and 10K and studied the temperature-induced phase transition in this material. The spectra show crystal field splitting of the internal Raman modes but no evidence for a line shift near the phase transition. The photo-induced transformation of the crystals and its implication on the interpretation of the Raman spectra is discussed. In the low temperature phase we observed two lines at 30 cm^–1 and 41 cm^–1 which we assign to the librational modes of the crystal.     

Development of a Ni–Pd/CeZrO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst for the effective conversion of methane into hydrogen-containing gas

The effects of the Pd content (0–1 wt %) and the synthesis method (joint impregnation with Ni + Pd and Pd/Ni or Ni/Pd sequential impregnation) on the physicochemical and catalytic properties of Ni–Pd/CeZrO₂/Al₂O₃ were studied in order to develop an efficient catalyst for the conversion of methane into hydrogen-containing gas. It was shown that variation in the palladium content and a change in the method used for the introduction of an active constituent into the support matrix make it possible to regulate the redox properties of nickel cations but do not affect the size of NiO particles (14.0 ± 0.5 nm) and the phase composition of the catalyst ((γ + δ)-Al₂O₃, CeZrO₂ solid solution, and NiO). It was established that the activity of Ni–Pd catalysts in the reaction of autothermal methane reforming depends on the method of synthesis and increases in the following order: Ni + Pd < Ni/Pd < Pd/Ni. It was found that, as the Pd content of the Ni–Pd/CeZrO₂/Al₂O₃ catalyst was decreased from 1 to 0.05 wt %, the ability for self-activation, high activity, and operational stability of the catalyst under the conditions of autothermal methane reforming remained unaffected: at 850°C, the yield of hydrogen was ~70% at a methane conversion of ~100% during a 24-h reaction.     

Heats of formation of boron hydride anions and dianions and their ammonium salts [BnHmy-][NH4+]y with y=1-2

Thermochemical parameters of the closo boron hydride BnHn2- dianions, with n=5-12, the B3H8- and B11H14- anions, and the B5H9 and B10H14 neutral species were predicted by high-level ab initio electronic structure calculations. Total atomization energies obtained from coupled-cluster CCSD(T)/complete basis set (CBS) extrapolated energies, plus additional corrections were used to predict the heats of formation of the simplest BnHmy- species in the gas phase in kcal/mol at 298 K: DeltaHf(B3H8-)=-23.1+/-1.0; DeltaHf(B5H52-)=119.4+/-1.5; DeltaHf(B6H62-)=64.1+/-1.5; and DeltaHf(B5H9)=24.1+/-1.5. The heats of formation of the larger species were evaluated by the G3 method from hydrogenation reactions (values at 298 K, in kcal/mol with estimated error bars of+/-3 kcal/mol): DeltaHf(B7H72-)=51.8; DeltaHf(B8H82-)=46.1; DeltaHf(B9H92-)=24.4; DeltaHf(B10H102-)=-12.5; DeltaHf(B11H112-)=-11.8; DeltaHf(B12H122-)=-86.3; DeltaHf(B11H14-)=-57.3; and DeltaHf(B10H14)=18.7. A linear correlation between atomization energies of the dianions and energies of the BH units was found. The heats of formation of the ammonium salts of the anions and dianions were predicted using lattice energies (UL) calculated from an empirical expression based on ionic volumes. The UL values (0 K) of the BnHn2- dianions range from 319 to 372 kcal/mol. The values of UL for the B3H8- and B11H14- anions are 113 and 135 kcal/mol, respectively. The calculated lattice energies and gas-phase heats of formation of the constituent ions were used to predict the heats of formation of the ammonium crystal salts [BnHmy-][NH4+]y. These results were used to evaluate the thermodynamics of the H2 release reactions from the ammonium hydro-borate salts.