Simulation Support to EPR-based Dentin Characterization

Treatment of dental caries as one of the most economically relevant human disease can rely only on the understanding of the caries progress through dentin. As it can be seen from the frequency of tooth decay among different animals, its existence and progress strongly depend on the mineral part arrangement, especially on the orientation of the hydroxyapatite (HA) crystals, which resist the mechanical and chemical stress very anisotropically. It is therefore not surprising that different attempts have been made to unravel the mystery of dentin growth and HA crystals arrangement. By dentin irradiation with gamma-rays, very stable CO₃ ^? radicals are generated within HA crystals which due to the anisotropic magnetic coupling enable detection of their orientational distribution via angular-dependent electron paramagnetic resonance spectroscopy. The latter can be significantly enhanced if the whole angular dependence can be fitted simultaneously within certain dentin structural models. As shown in this work, even subtle information like the orientation of the tubules relative to the pulp or the orientation of HA crystals relative to the tubules can be extracted. The sensitivity to different sample geometry is discussed to provide the best possible characterization.     

The RATIO method for time‐resolved Laue crystallography

A RATIO method for analysis of intensity changes in time‐resolved pump–probe Laue diffraction experiments is described. The method eliminates the need for scaling the data with a wavelength curve representing the spectral distribution of the source and removes the effect of possible anisotropic absorption. It does not require relative scaling of series of frames and removes errors due to all but very short term fluctuations in the synchrotron beam.     

Optical properties of semiconducting iron disilicide thin films

The iron silicides samples were prepared by annealing of iron films evaporated onto silicon wafers and capped with amorphous silicon thin overlayers. Semiconducting FeSi₂ phase is formed by annealing at the temperatures from 550°C to 850°C. The optical properties of the FeSi₂ layers have been deduced from reflectance and transmittance measurements carried out in the temperature range of (77–380) K. The spectral dependence of the absorption coefficient favours direct allowed transitions with forbidden energy gap of 0.87eV at the room temperature. The application of a simple three-parameter semiempirical formula to the temperature dependence of the direct energy gaps leads to the following best fit parameters: the band gap at zero temperature E _g (0) = (0.895 ± 0.004)eV, the dimensionless coupling parameter S = 2.0 ± 0.3, and the average phonon energy <hw> = (46 ± 8)meV. By examining all the reported triplets of parameters for -FeSi₂ fabricated by different techniques and thermal processes, an obvious discrepancy can be found for the lattice coupling parameter and average phonon energy, although the bandgaps at 0 K are very similar. Unlike the theoretical prediction and the earlier reported result, our results do not show any evidence of a particularly strong electron-phonon interaction, which would give the lower carrier mobilities. -FeSi₂ seems to be an intriguing material where states with energies near the band edges permit ambiguous interpretation of the character of transitions. From optical model for the thin film-substrate system we found the index of refraction to be (5–5.9) in the photon energy interval from 0.65 to 1.15eV. There is also indication of an additional higher-energy absorption edge at l.05eV.     

Radionuclide concentrations in samples of medicinal herbs and effective dose from ingestion of ¹³⁷Cs and natural radionuclides in herbal tea products from Serbian market

The objective of this study is to evaluate natural and artificial radioactivity levels in 18 different samples of medicinal herbs from Serbian market. The activity concentrations of (238)U, (232)Th, (40)K, and (137)Cs were measured using gamma spectroscopy system with a high-purity germanium detector. The activity concentrations of (238)U, (232)Th, (40)K, and (137)Cs were found to be in a range of 0.6-8.2, 1.7-15.1, 126-1243.7, and 0.3-8.8 Bq/kg, respectively. The annual whole body doses from ingestion of (137)Cs and natural radionuclides for an adult person who consumed herbal tea from these medicinal herbs were found to be 2.5-469.9 nSv for (137)Cs, 0.7-9.7 nSv for (238)U, 0.3-2.8 nSv for (232)Th, and 1026.0-10,132.0 nSv for (40)K. These doses are not hazardous to public health. The obtained results were compared with correspondent studies conducted worldwide.     

On a Construction of Fast Direct Solvers

Fast direct solvers for the Poisson equation with homogeneous Dirichlet and Neumann boundary conditions on special triangles and tetrahedra are constructed. The domain given is extended by symmetrization or skew symmetrization onto a rectangle or a rectangular parallelepiped and a fast direct solver is used there. All extendable domains are found. Eigenproblems are also considered.     

Macrodefect-Free Materials: Modification of Interfaces in Cement Composites by Polymer Grafting

MDF materials are chemically bonded ceramic materials free of the macrodefects typical of hydraulic cement-based materials. MDF materials arising through reactions of sulfo-aluminate-ferrite belitic (SAFB) clinkers and/or Portland cements (PC) with two types of water-soluble polymer (hydroxy-propylmethyl cellulose {HPMC}, polyphosphate glass {poly-P}) are discussed. Mixes of low energy SAFB clinkers with Portland cement, HPMC and, especially poly-P comprise promising cross-linked compositions additional to the better known MDF materials formed from high alumina cement with polyvinylalcohol/acetate. The principles of co-ordination of P and C atoms (of the polymer) with Al and Fe atoms (originating from the cement) are highlighted from spectroscopic information on next-nearest-neighbour interactions, along with the effects of second co-ordination spheres. Polymers modify the interface through functional bonding/grafting of polymer chains onto the surfaces of cement grains. Both the cross-linked atomic structure and the interface coincide well with the model of functional polymers and represent a new type of atomic-level structure in polymer-modified cements. Interpretation is based on previous magnetic resonance and thermal analysis studies. The compactness of Al(Fe)-O-P cross-links reduces transport through the interfaces, increasing the interfacial interactions and resisting the unfavourable uptake of moisture and carbonation.     

Theoretical study of the helio hydrogen cyanide dication HeCNH2+

The structure and stability of the helio hydrogen cyanide molecular ion, HeCNH²⁺, is investigated by standard quantum chemical methods. Single reference calculations are carried out using second-order perturbation theory (MP2), the coupled cluster expansion in the CCSD approximation, and the hybrid approach using a perturbative estimate of the triple excitation energy component designated CCSD(T). Multireference calculations using a complete active space (CASSCF) and a second-order perturbation theory estimate of correlation effects (CASPT2) are reported.