A definitive RNAA method for determination of selenium in biological samples: uncertainty evaluation and assessment of degree of accuracy

This article describes work on the development of a highly accurate RNAA method for determination of selenium in biological samples. The analytical post-irradiation procedure is based on a combination of cation-exchange and extraction chromatography with final selective and quantitative fixation of selenium on a column packed with 3,3′-diaminobenzidine (DAB) supported on Amberlite XAD4, followed by gamma-ray spectrometric measurement. The suitability and accuracy of the method was demonstrated by analysing CRMs with certified selenium content. The uncertainty budget for Se determination in standard reference material Peach Leaves NBS 1547 was estimated; the combined standard uncertainty was calculated as 1.7%. The described method fulfils all the criteria for definitive methods. It was subsequently used for determination of selenium in biological materials intended as new CRMs and proficiency test samples.     

On the flow of chemically reacting gaseous mixture

We consider the Cauchy problem for the system of equations governing flow of isothermal reactive mixture of compressible gases. Our main contribution is to prove sequential stability of weak solutions when the state equation essentially depends on the species concentration and the viscosity coefficients vanish on vacuum. Moreover, under additional assumption on the “cold” component of the pressure in the regions of small density, we prove the existence of weak solutions for arbitrary large initial data.     

Investigation of the low-frequency vibrations of crystalline tartaric acid using terahertz spectroscopy and solid-state density functional theory

The room temperature and cryogenic terahertz (THz) spectra (10-95 cm(-1)) of l-tartaric acid and dl-tartaric acid were investigated. At 293 K, the l-tartaric acid spectrum showed four absorption features at 36.4, 61.6, 78.7, and 87.3 cm(-1) in the experimental spectrum. Once cooled to 78 K, these features narrowed and shifted to 35.9, 63.4, 81.1, and 90.1 cm(-1). The THz spectrum of dl-tartaric acid is significantly different, containing only a single absorption at 79.9 cm(-1) at room temperature, which shifts to 82.9 cm(-1) at 78 K. Solid-state density functional theory calculations [B3LYP/6-311G(2d,2p)] were performed to simulate the crystalline structure of both molecular solids and to assign the observed spectral features to specific atomic motions. The THz spectrum of l-tartaric acid is particularly interesting in that it contains a theoretically unaccounted for spectral feature that may arise from second-order phonon processes and also exhibits an anomalous red-shifting absorption feature with cooling that is shown to originate from negative thermal expansion of the crystal.     

Laser cleaning of copper roofing sheets subjected to long-lasting environmental corrosion

The study was concerned with the effect of the laser fluence and pulse duration on the microstructure of copper roofing of the Wilanów Palace in Warsaw (Poland) subjected to environmental degradation since the turn 19th century. The techniques used for the microstructure examinations included: SEM+EDS, X-ray diffraction analysis, surface profiling and colour analysis. The measurements of colour of the laser-cleaned surfaces showed that series of 100-μs pulses offer the most effective cleaning. It was also found that by controlling the number of laser pulses it is possible to control the roughness of the cleaned surface.     

The effect of carbon nanotubes on epoxy matrix nanocomposites

The paper concerns thermal properties of epoxy/nanotubes composites for aircraft application. In this work, influence of carbon nanotubes on thermal stability, thermal conductivity, and crosslinking density of epoxy matrix was determined. Three kinds of nanotubes were used: non-modified with 1- and 1.5-μm length, and 1-μm length modified with amino groups. Scanning electron microscopy observations were done for examining dispersion of nanotubes in the epoxy matrix. Glass transition temperature (T _g) was readout from differential scanning calorimetry. From dynamic mechanical analysis, crosslinking density was calculated for epoxy and its composites. Also, thermogravimetric analysis was done to determine influence of nanotubes addition on thermal stability and decomposition process of composites. Activation energy was calculated from TGA curves by Flynn–Wall–Ozawa method. Thermal diffusivity was also measured. SEM images proved the uniform dispersion of carbon nanotubes without any agglomerates. It was found that nanotubes modified with amino groups lead to the increase of epoxy matrix crosslinking density. The significant increase in T _g was also observed. On the other hand, addition of carbon nanotubes leads to the decrease of thermal stability of polymer due to the increase of thermal diffusivity.     

Cellulose-TiO2 nanocomposite with enhanced UV–Vis light absorption

TiO₂/N-cellulose nanocomposite was successfully prepared in the (cyclohexyl)hexyl-dimethylammonium acetate–dimethyl sulfoxide solution. The obtained composite was characterized with various techniques like UV–Vis/DR, FTIR/DRS, X-ray diffraction, thermogravimetric analysis, DLS method and BET SSA measurements. TiO₂/N-cellulose nanocomposite exhibited high UV–Vis light absorption with energy gap shifted to the visible region. Additive of TiO₂/N photocatalyst to cellulose-IL-DMSO solution leads to obtaining the material with higher thermostability and limited photoactivity.