Numerical analysis of the width of fracture process zone in concrete beams

There are two ways of modelling cracking in concrete structures using a finite element method (FEM). In the first concept crack is considered as densely distributed throughout the finite area of element. The alternative approach assumes an isolated sharp interelement crack. The first concept of microcracked band is often used during numerical computations of concrete structures and a crack band model can be applied in design practice where relatively simple methods of calculations are preferred. In this model the width of microcracked zone, which is called the width of fracture process zone, is the additional parameter of tensile concrete.In this paper, the influence of the fracture process zone width on numerical calculations in case of bent concrete beams is analyzed. The results of numerical simulations are presented and compared with those obtained during the experiment. The crack band model proposed by Hillerborg [Cement and Concrete Research, 6 (1976) 773–782] has been used in numerical calculations and six different widths of fracture process zone have been modelled in the analyzed specimen. When comparing the obtained FEM-results their significant differences according to the width of fracture process zone have been observed. On the basis of the performed analysis it may be concluded that the width of fracture process zone taken in numerical simulations does have an influence on FEM-results.     

Development and Validation of Europium-Sensitized Luminescence (ESL) Method for the Determination of Tetracycline Residues in Milk

The development of a fast and reliable screening method for the determination of tetracycline residues in milk is described and compared to high-performance liquid chromatography. The method is based on europium-sensitized luminescence: The emissive properties of the lanthanide cation are used as a fingerprint of europium (III) complexation with tetracycline. The optimization of the extraction and purification procedures provided a simple and convenient route to prepare stable tetracycline samples that can safely resist freezing cycles. The method is validated for the first time in milk matrix: The results show that accuracy and precision of the method meet complaints with the criteria of the Commission Decision 2002/657/EC. The proposed method has a false compliant rate (β error) lower than 5%.     

Synthesis and characterization of a new family of photoactive liquid crystalline polyesters based on α‐methylstilbene

A liquid crystal polyester and two liquid crystal copolyesters containing α‐methylstilbene moieties and aliphatic or aromatic spacers in the backbone were synthesized in good yields, with the aim of using them for photosensitive microcapsule preparation. The synthesized polymers were fully characterized with respect to thermal stability, type of mesophase, molecular weight and E–Z photoisomerization. Combination of monomers with different structures allowed adjustment of the polymer characteristics such as degree of crystallinity and glass transition temperature, as verified using X‐ray diffraction, polarized optical microscopy and differential scanning calorimetry. Quantitative ¹H NMR and UV‐visible experiments were performed in order to investigate E–Z photoisomerization after photoirradiation at 364 nm. Finally, a membrane based on one of these polymers was prepared and it was found that its wettability increased on photoirradiation. © 2013 Society of Chemical Industry     

Production of microparticles from milk fat products using the Supercritical Melt Micronization (ScMM) process

The ScMM (Supercritical Melt Micronization) process was applied for the production of microparticles from anhydrous milk fat (AMF) and a diacylglycerol-based modified milk fat (D-AMF). Both fats were able to dissolve ca. 30 wt% CO₂ in the studied pressure and temperature ranges, being the CO₂ amount slightly higher for AMF. A melting point depression was observed in both systems in the presence of CO₂. Two powder morphologies were obtained (spherical hollow particles and a mass sponge-like broken particles) depending on the ScMM process conditions. The concentration of CO₂ in the fat melt was the main process variable affecting the particle morphology, followed by the temperature of the melt. The small broken particles originated from the breakage of spherical fat particles that solidified before all CO₂ could escape from the atomized droplets. While the hollow spheres had a tendency to agglomerate, the broken microparticles constituted a free-flowing powder as long as they were stored at low temperatures (up to −18 °C). Both types of particles have a potential for being incorporated in refrigerated or frozen food products as a structuring agent.     

Ion bombardment induced surface electrical degradation monitoring by means of luminescence in aluminas

Oxide ceramics for use as electrical insulators in future fusion devices, will be exposed to ionization and displacement damage (neutrons, gammas, ion bombardment). Enhanced oxygen loss due to ion bombardment increases surface electrical conductivity, and at the same time the surface emits light due to ion beam induced luminescence (IBIL). Results for 3 types of α-alumina and sapphire measuring electrical surface conductivity and IBIL as a function of dose at different temperatures between 20 and 200 °C, show a clear correlation between luminescence and surface electrical degradation. This indicates the potential to remotely monitor insulating material degradation not only in ITER and beyond, but also in the more immediate in-reactor experiments required for materials testing. Partial reduction of degradation by heating in air suggests the possibility for in situ recovery of the insulating properties.     

Evaluation of Alternative Preservation Treatments (Water Heat Treatment,Ultrasounds, Thermosonication and UV-C Radiation) to Improve Safety and Quality of Whole Tomato

Previously optimised postharvest treatments were compared to conventional chlorinated water treatment in terms of their effects on the overall quality of tomato (‘Zinac’) during storage at 10 °C. The treatments in question were water heat treatment (WHT?=?40 °C, 30 min), ultrasounds (US?=?45 kHz, 80 %, 30 min), thermosonication (TS?=?40 °C, 30 min, 45 kHz, 80 %) and ultraviolet irradiation (UV-C: 0.97 kJ m^?2). The quality factors evaluated were colour, texture, sensorial analysis, mass loss, antioxidant capacity, total phenolic content, peroxidase and pectin methylesterase enzymatic activities, and microbial load reduction. The results demonstrate that all treatments tested preserve tomato quality to some extent during storage at 10 °C. WHT, TS and UV-C proved to be more efficient on minimising colour and texture changes with the additional advantage of microbial load reduction, leading to a shelf life extension when compared to control trials. However, at the end of storage, with exception of WHT samples, the antioxidant activity and phenolic content of treated samples was lower than for control samples. Moreover, sensorial results were well correlated with instrumental colour experimental data. This study presents alternative postharvest technologies that improve tomato (Zinac) quality during shelf life period and minimise the negative impact of conventional chlorinated water on human safety, health and environment.     

Electrochemical performance of carbon gels with variable surface chemistry and physics

This study describes the electrochemical characterization of N-doped carbon xerogels in the form of microspheres and of carbon aerogels with varied porosities and surface oxygen complexes. The interfacial capacitance of N-doped carbon xerogels decreased with increased micropore surface area as determined by N₂ adsorption at ?196 °C. The interfacial capacitance showed a good correlation with the areal N_XPS concentration, and the best correlation with the areal concentration of pyrrolic or pyridonic nitrogen functionalities. The gravimetric capacitance decreased with greater xerogel microsphere diameter. The interfacial capacitance of carbon aerogels increased with higher percentage of porosity as determined from particle and true densities. The interfacial capacitance showed a linear relationship with the areal oxygen concentration and with the areal concentrations of CO- and CO₂-evolving groups.     

Rheological characterization of edible films made from collagen colloidal particle suspensions

A rheological characterization of collagen edible films is proposed through the experimental evaluation of shear elastic modulus, toughness, hydration capability and stress and stretch ratio at fracture. These properties are obtained from hydration, simple extension and compression tests and analyzed through the BST (Blatz, Sharda, & Tschoegl, 1974) hyperelastic model. Also precursor collagen particle suspensions, with solid concentrations in the range 0.5–4% w/w, are studied to evaluate their thixotropic responses in sudden imposed shear rates and shear loops. These responses are a consequence of particle aggregations leading to cluster formations. The particle size distribution function of suspensions is determined via scanning electron microscopy. Films are formed by casting and then fixed through either a coagulation process with a salt solution or a chemical process involving covalent cross-links with glutaraldehyde. Results indicate that these collagen films behave as colloidal particulate networks composed of particles and clusters. Also it is found that the fractal dimension of clusters is an intrinsic property of collagen particle suspensions, independently from the maturation time. Clusters in these suspensions are formed with a rather open architecture (low fractal value) due to rather large particle attractive forces. The evaluation of the BST rheological parameters allows one the estimation of the energy amount required to get film fracture for different collagen and cross-linker concentrations. Since the final films have to satisfy several quality requirements before using, the interplay between their stiffness and toughness is presented and discussed.