Towards understanding the influence of porosity on mechanical and fracture behaviour of quasi-brittle materials: experiments and modelling

In this work, porosity-property relationships of quasi-brittle materials are explored through a combined experimental and numerical approach. In the experimental part, hemihyrate gypsum plaster powder (\(\hbox {CaSO}_{4}\cdot 1/2\hbox {H}_{2}\hbox {O}\)) and expanded spherical polystyrene beads (1.5–2.0 mm dia.) have been mixed to form a model material with controlled additions of porosity. The expanded polystyrene beads represent pores within the bulk due to their light weight and low strength compared with plaster. Varying the addition of infill allows the production of a material with different percentages of porosity: 0, 10, 20, 30 and 31 vol%. The size and location of these pores have been characterised by 3D X-ray computed tomography. Beams of the size of \(20 \times 20 \times 150\) mm were cast and loaded under four-point bending to obtain the mechanical characteristics of each porosity level. The elastic modulus and flexural strength are found to decrease with increased porosity. Fractography studies have been undertaken to identify the role of the pores on the fracture path. Based on the known porosity, a 3D model of each microstructure has been built and the deformation and fracture was computed using a lattice-based multi-scale finite element model. This model predicted similar trends as the experimental results and was able to quantify the fractured sites. The results from this model material experimental data and the lattice model predictions are discussed with respect to the role of porosity on the deformation and fracture of quasi-brittle materials.     

APRIORI-SD: ADAPTING ASSOCIATION RULE LEARNING TO SUBGROUP DISCOVERY

This paper presents a subgroup discovery algorithm APRIORI-SD, developed by adapting association rule learning to subgroup discovery. The paper contributes to subgroup discovery, to a better understanding of the weighted covering algorithm, and the properties of the weighted relative accuracy heuristic by analyzing their performance in the ROC space. An experimental comparison with rule learners CN2, RIPPER, and APRIORI-C on UCI data sets demonstrates that APRIORI-SD produces substantially smaller rulesets, where individual rules have higher coverage and significance. APRIORI-SD is also compared to subgroup discovery algorithms CN2-SD and SubgroupMiner. The comparisons performed on U.K. traffic accident data show that APRIORI-SD is a competitive subgroup discovery algorithm.     

Moment-method analysis of volume dielectric scatterers. Four independent entire-domain solutions: Is entire-domain philosophy a luxury or necessity in the method of moments?

Four independent methods are presented for entire-domain (large-domain) moment-method analysis of lossy, inhomogeneous dielectric scatterers. They share two basic steps in solving volume integral equations: (1) the approximation of the scatterer geometry by large trilinear hexahedrons; and (2) the approximation of the unknown vector function in the hexahedrons by three-dimensional polynomials. The results are compared among themselves and with those obtained by subdomain (the only existing) methods, demonstrating great superiority of the entire-domain approach in solving three-dimensional scattering and interaction problems. © 1996 John Wiley & Sons, Inc.     

Encapsulation of thyme (Thymus serpyllum L.) aqueous extract in calcium alginate beads

BACKGROUND: Encapsulation of Thymus serpyllum L. aqueous extract within calcium alginate beads was studied in order to produce dosage formulations containing polyphenolic compounds. Electrostatic extrusion was applied for encapsulation of thyme aqueous extract in alginate gel beads. In addition to hydrogel beads, heat‐dried and freeze‐dried forms of beads were examined. METHODS: Encapsulation systems were examined and compared in order to choose the optimal one with respect to entrapment efficiency, preservation of antioxidant activity and thermal behaviour under heating conditions simulating the usual food processing. RESULTS: The beads obtained with approximately 2 mg g^?1 of gallic acid equivalents encapsulated in 0.015 g mL^?1 of alginate were spheres of a uniform size of about 730 µm. Encapsulation efficiency varied in the range 50‐80% depending on the encapsulation method. Besides, the analysis reveals that the encapsulation process and the material used did not degrade the bioactive compounds, as the total antioxidant content remained unchanged. This was verified by Fourier transform infrared analysis, which proved the absence of chemical interactions between extracted compounds and alginate. Addition of a filler substance, such as sucrose and inulin, in the dried product reduced its collapse and roundness distortion during drying process. CONCLUSION: This study demonstrates the potential of using hydrogel material for encapsulation of plant poplyphenols to improve their functionality and stability in food products. Copyright © 2011 Society of Chemical Industry     

The use of nanoclay in preparation of epoxy anticorrosive coatings

Epoxy/clay nanocomposites (NC) have become a very interesting topic among researchers in the past two decades because nanoclays have a positive effect on the mechanical, thermal and especially barrier and anticorrosive performances of the polymers. In this study epoxy NCs and NC-based epoxy coatings were prepared by the solution intercalation method using Cloisite 30B as nanoclay. WAXD and SEM analyses revealed that a mainly exfoliated structure was obtained in epoxy NC with 1 wt% clay content, while higher clay loadings reduced the number of exfoliated clay nanolayers and produced a mainly intercalated structure. EIS, TGA and DMA analyses showed that epoxy NCs with clay content below 5 wt% exhibited increased corrosion stability, thermal stability, glass transition temperature (T_g) and storage modulus (G′), in both glassy and rubbery states due to the nanoscale dispersion of Cloisite 30B and the barrier effect of individual nanolayers. Enhanced mechanical properties were also noticed at higher clay loadings, but the rate of improvement was lower. The highest extent of exfoliation and the most homogeneous macromolecular network was found for NC with 1 wt% of clay, leading to the highest improvement of thermal and anticorrosive properties. The salt spray test results showed that anticorrosive properties of epoxy coatings in the presence of 3 wt% and especially 1 wt% of Cloisite 30B were significantly better, thus indicating that nanoclay efficiently modifies the commercial epoxy coatings.     

Influence of discharge energy on machining characteristics in EDM

The machining characteristics of electrical discharge machining (EDM) directly depend on the discharge energy which is transformed into thermal energy in the discharge zone. The generated heat leads to high temperature, resulting in local melting and evaporation of workpiece material. However, the high temperature also impacts various physical and chemical properties of the tool and workpiece. This is why extensive knowledge of development and transformation of electrical energy into heat is of key importance in EDM. Based on the previous investigations, analytical dependence was established between the discharge energy parameters and the heat source characteristics in this paper. In addition, the thermal properties of the discharged energy were experimentally investigated and their influence on material removal rate, gap distance, surface roughness and recast layer was established. The experiments were conducted using copper electrode while varying discharge current and pulse duration. Analysis and experimental research conducted in this paper allow efficient selection of relevant parameters of discharge energy for the selection of most favorable EDM machining conditions.     

Comparison of different methods for the preparation of porous bone substitution materials and structural investigations by synchrotron μ‐computer tomography

The preparation of porous biomaterials for bone substitution is an important clinical issue in current biomedical technology because the ingrowth of bone can only occur if a suitable number of sufficiently large pores is available. Different procedures are compared here: The combined chemical‐thermal treatment of bovine and human cancellous bone, the calcination of bovine cancellous bone, mechanical hole‐drilling, and the extraction of porogens (in this case: salt crystals). The inner structure and the porosity of all samples were studied using high‐resolution synchrotron μ‐computer tomography.     

Regulation of International Watercourses under the UN/ECE Regional Agreements

Abstract

This article deals with the UN Economic Commission for Europe (UN/ECE) regional agreements, and their use as implementing instruments for protecting and managing international water courses. The background and issues of the regional instruments developed by the UN Economic Commission for Europe are addressed. The contents of the 1992 Helsinki Convention and its implementation are described, as well as the recent development of the Protocol on Water and Health. The relationship to the 1991 Espoo Convention and a comparison with the 1997 UN Convention on the Law of International Watercourses are also included. The potential of the UN/ECE conventions as tools to promote conflict prevention and dispute settlement is discussed. Lessons and conclusions are drawn from the experience on the management of transboundary waters in Europe.     

Fast ephemeral DNA damage upon BaP injection

Injection of high concentrations of benzo[a]pyrene (10-125 micrograms BaP/g body weight) into young frogs (Xenopus laevis), fish (Gambusia affinis) or tissue culture cells (L 5178 Y) in a state of logarithmic growth causes alterations in DNA. In frogs these alterations reach a maximum at 60-90 min after application, then they decrease and become undetectable after 3 h. Within 8-12 days after the single BaP dose, a new wave of DNA alterations can again be detected. Parallel measurements of mixed function oxygenases (MFO) showed no short term activity changes within the first day. There was, however, an increase of activity starting on the 8th day following injection in frogs, and lasting until day 14. DNA alterations have been assessed by two methods. One is a modification of the alkaline filter elution method of Kohn et al. (1976) and is believed to determine the number of events leading to single strand breaks at alkaline pH. The other method determines the number of S1 nuclease sensitive sites in highly purified native DNA. Both results were found to be highly correlated. The effect does not seem to be caused by an impurity, unless an unknown, very minor, and extraordinarily active component is present. The effect in frogs is linked to nutritional status. Frogs fed a carbohydrate-rich, protein-poor diet do not give the fast response. The fast effect cannot be blocked by application of Actinomycin, Cordycepin, and Chloramphenicol injected either 30 min before or simultaneously with the BaP. Benzo(e)pyrene, a non-tumorigenic isomer of BaP, does not cause any effects at similar doses.