On the linear friction welding process of aluminum alloys: Experimental insights through process monitoring

Linear friction welding is a solid-state joining process for non-axisymmetric components in which joining of materials is obtained through the relative motion of two components under pressure. In the process the heat source is given by the frictional forces work decaying into heat determining a local softening of the material and eventually bonding conditions. A dedicated fixture was equipped with sensors for the in-process acquisition of variables regarding kinematics, dynamics and temperature levels. The results of an experimental campaign aimed to weld AA6082-T6 aluminum alloy parts are presented and a process window is identified for the used alloy.     

Low temperature dyeing of wool fabric by acid dye after UV irradiation

The aim of the work was to improve wool’s dyeability using acid dye through a simple pretreatment with ultraviolet (UV) irradiation. Different radiation doses were investigated using both a laboratory UV lamp and a semi-industrial apparatus. UV-treated fabrics were characterized in terms of morphological, chemical and physical properties by SEM, FTIR-ATR spectra, water contact angle measurements, bursting and pilling test. The pre-treated samples were then dyed with an acid dye at different dyeing temperatures to compare the results with the untreated fabric. Final bath exhaustion reached, kinetic curves and colour measurements were evaluated. Moreover, the colour levelness of the dyeings obtained on fabrics with and without irradiation was assessed. Finally, dyeing fastness to washing and rubbing were determined according to ISO standard methods.     

Protein Synthesis Inhibition Activity by Strawberry Tissue Protein Extracts during Plant Life Cycle and under Biotic and Abiotic Stresses

Ribosome-inactivating proteins (RIPs), enzymes that are widely distributed in the plant kingdom, inhibit protein synthesis by depurinating rRNA and many other polynucleotidic substrates. Although RIPs show antiviral, antifungal, and insecticidal activities, their biological and physiological roles are not completely understood. Additionally, it has been described that RIP expression is augmented under stressful conditions. In this study, we evaluated protein synthesis inhibition activity in partially purified basic proteins (hereafter referred to as RIP activity) from tissue extracts of Fragaria × ananassa (strawberry) cultivars with low (Dora) and high (Record) tolerance to root pathogens and fructification stress. Association between the presence of RIP activity and the crop management (organic or integrated soil), growth stage (quiescence, flowering, and fructification), and exogenous stress (drought) were investigated. RIP activity was found in every tissue tested (roots, rhizomes, leaves, buds, flowers, and fruits) and under each tested condition. However, significant differences in RIP distribution were observed depending on the soil and growth stage, and an increase in RIP activity was found in the leaves of drought-stressed plants. These results suggest that RIP expression and activity could represent a response mechanism against biotic and abiotic stresses and could be a useful tool in selecting stress-resistant strawberry genotypes.     

Polymeric scaffolds for cardiac tissue engineering: requirements and fabrication technologies

Cardiac tissue engineering (TE) is an emerging field, whose main goal is the development of innovative strategies for the treatment of heart diseases, with the aim of overcoming the drawbacks of traditional therapies. One of these strategies involves the implantation of three‐dimensional matrices (scaffolds) capable of supporting tissue formation. Scaffolds designed and fabricated for such application should meet several requirements, concerning both the scaffold‐forming materials and the properties of the scaffold itself. A scaffold for cardiac TE should be biocompatible and biodegradable, mimic the properties of the native cardiac tissue, provide a mechanical support to the regenerating heart and possess an interconnected porous structure to favour cell migration, nutrient and oxygen diffusion, and waste removal. Moreover, the mimesis of myocardium characteristic anisotropy is attracting increasing interest to provide engineered constructs with the possibility to be structurally and mechanically integrated in native tissue. Several conventional and non‐conventional fabrication techniques have been explored in the literature to produce polymeric scaffolds meeting all these requirements. This review describes these techniques, with a focus on their advantages and disadvantages, and their flexibility, with the final goal of providing the reader with the primal knowledge necessary to develop an effective strategy in cardiac TE. © 2013 Society of Chemical Industry     

A dynamic programming strategy to balance exploration and exploitation in the bandit problem

The K-armed bandit problem is a well-known formalization of the exploration versus exploitation dilemma. In this learning problem, a player is confronted to a gambling machine with K arms where each arm is associated to an unknown gain distribution. The goal of the player is to maximize the sum of the rewards. Several approaches have been proposed in literature to deal with the K-armed bandit problem. This paper introduces first the concept of “expected reward of greedy actions” which is based on the notion of probability of correct selection (PCS), well-known in simulation literature. This concept is then used in an original semi-uniform algorithm which relies on the dynamic programming framework and on estimation techniques to optimally balance exploration and exploitation. Experiments with a set of simulated and realistic bandit problems show that the new DP-greedy algorithm is competitive with state-of-the-art semi-uniform techniques.     

Sr-containing hydroxyapatite: morphologies of HA crystals and bioactivity on osteoblast cells

A series of Sr-substituted hydroxyapatites (HA), of general formula Ca_(10 ? x)Sr_x(PO₄)₆(OH)₂, where x = 2 and 4, were synthesized by solid state methods and characterized extensively. The reactivity of these materials in cell culture medium was evaluated, and the behavior towards MG-63 osteoblast cells (in terms of cytotoxicity and proliferation assays) was studied. Future in vivo studies will give further insights into the behavior of the materials.A paper by Lagergren et al. (1975), concerning Sr-substituted HA prepared by a solid state method, reports that the presence of Sr in the apatite composition strongly influences the apatite diffraction patterns. Zeglinsky et al. (2012) investigated Sr-substituted HA by ab initio methods and Rietveld analyses and reported changes in the HA unit cell volume and shape due to the Sr addition.To further clarify the role played by the addition of Sr on the physico-chemical properties of these materials we prepared Sr-substituted HA compositions by a solid state method, using different reagents, thermal treatments and a multi-technique approach. Our results indicated that the introduction of Sr at the levels considered here does influence the structure of HA. There is also evidence of a decrease in the crystallinity degree of the materials upon Sr addition. The introduction of increasing amounts of Sr into the HA composition causes a decrease in the specific surface area and an enrichment of Sr-apatite phase at the surface of the samples. Bioactivity tests show that the presence of Sr causes changes in particle size and/or morphology during soaking in MEM solution; on the contrary the morphology of pure HA does not change after 14 days of reaction. The presence of Sr, as Sr-substituted HA and SrCl_2, in cultures of human MG-63 osteoblasts did not produce any cytotoxic effect. In fact, Sr-substituted HA increased the proliferation of osteoblast cells and enhanced cell differentiation: Sr in HA has a positive effect on MG-63 cells. In contrast, Sr ions alone, at the concentrations released by Sr-HA (1.21–3.24 ppm), influenced neither cell proliferation nor differentiation. Thus the positive effects of Sr in Sr-HA materials are probably due to the co-action of other ions such as Ca and P.