Phase transition in swollen gels

Summary The photoelastic behaviour of two networks — polyacrylamide (PAAm) and of a network prepared by the copolymerization of acrylamide with 5 mol.% sodium methacrylate — was investigated in water-acetone mixtures. For the PAAm network the dependence of all photoelastic characteristics on the composition of the mixture is continuous. At 54 vol.% acetone in the mixture, the ionized network undergoes a transition which gives rise to jumpwise changes in the shear modulus, deformational-optical coefficient, C, and in the refractive index of the gel, n_g. While in the collapsed state the optical anisotropy of the statistical segment is negative, –3×10^–24 cm³ (indicating an interaction between the side chains), in the expanded state it is positive, 0.5 × 10^–24 cm³. The dependence of all optical characteristics on the composition of the mixtures suggests that: (a) in both networks we have a transition between two conformational states of the chain; while for the ionized network the transition is a discrete one, for the nonionized network it takes place in the range between 30 and 45 vol.% acetone in the mixture; (b) in both networks the gels are optically homogeneous throughout the whole range of compositions of the mixtures (and thus also in the close vicinity of the collapse of the ionized network).     

Effect of artificial weathering and temperature cycling on the performance of coating systems used for wooden windows

The effects of ultraviolet light irradiation and water spray and temperature cycling on the color stability of waterborne coating systems on spruce were investigated. The test samples were treated with three coating systems (white and brown pigmented acrylate waterborne coatings systems with different layering) from six producers. The artificial weathering was carried out based on standardized (504 h) and increased weathering parameters (504 h). Thirty cycles of temperature changes were performed. Discoloration suggesting the rate of degradation process and color stability was measured by a spectrophotometer in L*a*b* color space. The results showed greater color stability of white coating systems during both experiments. The producer of acrylate coatings with iodopropynyl butyl carbamate and permethrin as biocides and benzotriazole, silicon dioxide and methylsiloxane as additives was characterized by the best coatings performance. The most sensitive color parameter to describe the surface quality as a result of irradiation and water spray has proven to be a change of lightness. A tendency towards degradation with increasing lightness was observed during weathering. The effect of temperature itself on color change was minimal. Scanning electron microscopy and energy dispersive spectroscopy revealed microscopic changes of coatings caused by artificial weathering.     

Distribution of exogenous heavy metals in the hepatocytes of calves: a morphometric study

The objective of this study was to evaluate the presence of heavy metals in the hepatocytes of the animals fed a cadmium-supplemented diet and also receiving zinc and/or selenium in the injection form. The experiment involved four groups of calves (6-8, both sexes) receiving the heavy metals in various combinations for 95 days. Electron micrographs of liver cells were prepared and statistically evaluated using Student's t-test. A modified morphometric apparatus was used for morphometric examination. Exogenous cadmium showed marked accumulation in the hepatocytes. If, however, the cadmium diet was combined with zinc or selenium administration the amount of the reduction product was much lower.     

A feasibility study of using CeO2 as a surrogate material during the investigation of UO2 thermal conductivity enhancement

A possible substitution of UO₂ for research purposes is the cerium dioxide (CeO₂) owing to its chemical and physical properties. Neutronic properties are different and fission is absent in the case of CeO₂; however, similarities were studied recently to have a possibility to compare the neutronic influence of secondary additives into the matrix. This paper deals with increasing the thermal conductivity of UO₂ nuclear fuel on surrogate material (CeO₂); the main focus of the research is given on the sintering behaviour of CeO₂. The incorporation of highly thermally conductive material (SiC) is the investigated concept of thermal conductivity enhancement. Conventional sintering and spark plasma sintering (SPS) were applied to compare the behaviour of CeO₂ and UO₂ reported in the literature. High temperature thermal conductivity measurements did not confirm the positive influence of SiC additive inside the CeO₂ matrix mainly due to grain boundary disruptions. Similar behaviour was also previously reported for UO₂ pellets with SiC.     

Exploring fluorescence antibunching in solution to determine the stoichiometry of molecular complexes

Fluorescence antibunching is a well-known technique for determining the number of independent emitters per molecule or molecular complex. It was rarely applied to autofluorescent proteins due to the necessity of collecting large numbers of fluorescence photons from a single molecule, which is usually impossible to achieve with rather photolabile autofluorescent proteins. Here, we measure fluorescence antibunching on molecules in solution, allowing us to accumulate data over a large number of molecules. We use that method for determining an average stoichiometry of molecular complexes. The proposed method is absolute in the sense that it does not need any calibration or referencing. We develop the necessary theoretical background and check the method on pure dye solutions and on molecular complexes with known stoichiometry.     

High-rate low-temperature dc pulsed magnetron sputtering of photocatalytic TiO2 films: the effect of repetition frequency

The article reports on low-temperature high-rate sputtering of hydrophilic transparent TiO₂ thin films using dc dual magnetron (DM) sputtering in Ar + O₂ mixture on unheated glass substrates. The DM was operated in a bipolar asymmetric mode and was equipped with Ti(99.5) targets of 50 mm in diameter. The substrate surface temperature T_surf measured by a thermostrip was less than 180 °C for all experiments. The effect of the repetition frequency f_r was investigated in detail. It was found that the increase of f_r from 100 to 350 kHz leads to (a) an improvement of the efficiency of the deposition process that results in a significant increase of the deposition rate a_D of sputtered TiO₂ films and (b) a decrease of peak pulse voltage and sustaining of the magnetron discharge at higher target power densities. It was demonstrated that several hundreds nm thick hydrophilic TiO₂ films can be sputtered on unheated glass substrates at a_D = 80 nm/min, T_surf < 180 °C when high value of f_r = 350 kHz was used. Properties of a thin hydrophilic TiO₂ film deposited on a polycarbonate substrate are given.     

Relationship of iso‐α‐acid content and endogenous antioxidative potential during storage of lager beer

One of the critical issues regarding the quality of beer is the change in its chemical composition that occurs during storage. Decomposition of iso‐α‐acids results in an undesirable decrease in bitterness as well as a deterioration in the sensory profile of the beer. These changes are caused by the susceptibility of iso‐α‐acids to degradation owing to the influence of reactive oxygen species and light. The aim of this study was to investigate the influence of storage conditions (temperature, light) on the degradation of iso‐α‐acids during aging, with the main focus on monitoring the relationship between the turnover of iso‐α‐acids, the sulphur dioxide content and the antioxidative potential of stored beer as measured by electron spin resonance spectroscopy. In agreement with previous investigations, a significant decrease in the content of bitter compounds (up to 18 % relative to the original level, depending on storage conditions) was observed. A significant decrease in the antioxidant potential of beer was recorded simultaneously and the data confirmed a strong correlation between these parameters. The decline in beer bitterness could become a marker for estimating oxidative damage during storage. Copyright © 2014 The Institute of Brewing & Distilling     

Experimental Investigation of the Properties of Lime-Based Plaster-Containing PCM for Enhancing the Heat-Storage Capacity of Building Envelopes

Experimental analysis of a wide range of properties of a lightweight plaster which should enhance the heat-storage capacity of building envelopes is presented. The basic physical characteristics, namely, the bulk density, matrix density, total open porosity, and pore-size distribution are measured at first. Then, the compressive strength is determined for an assessment of mechanical performance of the plaster. The thermal conductivity and thermal diffusivity are studied using an impulse technique. Differential scanning calorimetry measurements are performed as well, in order to identify the temperature range and latent heat of the phase change and to determine the specific heat capacity as a function of temperature. Durability properties are assessed using the measurement of the water absorption coefficient and sorption and desorption isotherms. The experimental results indicate a good capability of the designed plaster to moderate effectively the interior climate of buildings.     

Formulating the template ILP consistency problem as a constraint satisfaction problem

Inductive Logic Programming (ILP) deals with the problem of finding a hypothesis covering positive examples and excluding negative examples, where both hypotheses and examples are expressed in first-order logic. In this paper we employ constraint satisfaction techniques to model and solve a problem known as template ILP consistency, which assumes that the structure of a hypothesis is known and the task is to find unification of the contained variables. In particular, we present a constraint model with index variables accompanied by a Boolean model to strengthen inference and hence improve efficiency. The efficiency of models is demonstrated experimentally.