Modeling void growth in polycrystalline materials

Most structural materials are polycrystalline aggregates whose constituent crystals are irregular in shape, have anisotropic mechanical properties and contain a variety of defects, resulting in very complicated damage evolution. Failure models of these materials remain empirically calibrated due to the lack of a thorough understanding of the controlling processes at the scale of the materials’ heterogeneity, i.e. the mesoscale. This paper describes a novel formulation for a quantitative, microstructure-sensitive three-dimensional mesoscale prediction of ductile damage of polycrystalline materials, in the important void growth phase of the process. Specifically, we have extended a formulation based on fast Fourier transforms to compute growth of intergranular voids in porous polycrystalline materials. In this way, two widely used micromechanical formulations, i.e. polycrystal plasticity and dilatational plasticity, have been efficiently combined, with crystals and voids represented explicitly, to predict porosity evolution. The proposed void growth algorithm is first validated by comparison with corresponding finite-element unit cell results. Next, in order to isolate the influence of microstructure on void growth, the extended formulation is applied to a face-centered cubic polycrystal with uniform texture and intergranular cavities, and to a porous material with homogenous isotropic matrix and identical initial porosity distribution. These simulations allow us to assess the effect of the matrix’s polycrystallinity on porosity evolution. Microstructural effects, such as the influence of the Taylor factor of the crystalline ligaments linking interacting voids, were predicted and qualitatively confirmed by post-shocked microstrostructural characterization of polycrystalline copper.     

Rare Glutamic Acid Methyl Ester Peptaibols from Sepedonium ampullosporum Damon KSH 534 Exhibit Promising Antifungal and Anticancer Activity

Fungal species of genus Sepedonium are rich sources of diverse secondary metabolites (e.g., alkaloids, peptaibols), which exhibit variable biological activities. Herein, two new peptaibols, named ampullosporin F (1) and ampullosporin G (2), together with five known compounds, ampullosporin A (3), peptaibolin (4), chrysosporide (5), c(Trp-Ser) (6) and c(Trp-Ala) (7), have been isolated from the culture of Sepedonium ampullosporum Damon strain KSH534. The structures of 1 and 2 were elucidated based on ESI-HRMSⁿ experiments and intense 1D and 2D NMR analyses. The sequence of ampullosporin F (1) was determined to be Ac-Trp¹-Ala²-Aib³-Aib⁴-Leu⁵-Aib⁶-Gln⁷-Aib⁸-Aib⁹-Aib¹⁰-GluOMe¹¹-Leu¹²-Aib¹³-Gln¹⁴-Leuol¹⁵, while ampullosporin G (2) differs from 1 by exchanging the position of Gln⁷ with GluOMe¹¹. Furthermore, the total synthesis of 1 and 2 was carried out on solid-phase to confirm the absolute configuration of all chiral amino acids as L. In addition, ampullosporin F (1) and G (2) showed significant antifungal activity against B. cinerea and P. infestans, but were inactive against S. tritici. Cell viability assays using human prostate (PC-3) and colorectal (HT-29) cancer cells confirmed potent anticancer activities of 1 and 2. Furthermore, a molecular docking study was performed in silico as an attempt to explain the structure-activity correlation of the characteristic ampullosporins (1–3).     

Effect of interpass temperature on microstructure,impact toughness and fatigue crack propagation in joints welded using the GTAW process on steel ASTM A743-CA6NM

Mainly due to their great toughness, martensitic stainless steels are used for manufacturing hydraulic turbines. However, these steels have some restrictions regarding regions recovered by welding, mainly due to the formation of non-quenched martensite, which causes a reduction in toughness. Considering repair of hydraulic turbines, there is a great interest in developing welding procedures that increase impact toughness and avoid post-welding heat treatment (TTPS). This study aims to analyse the influence of interpass temperature on microstructure, impact toughness and fatigue crack propagation in multipass welded joints on martensitic stainless steel CA6NM, using AWS410NiMo filler metal and the gas tungsten arc welding (GTAW) process. In the sample with interpass temperature of 80°C, influence of the interpass temperature on the formation of ferrite δ, with intragranular formation in the two-phase δ field, was observed, while in the sample welded at 150°C, the formation of ferrite δδ occurred mainly in the single-phase field. The change in the formation of ferrite δ, with the low interpass temperature, promoted an increase in impact toughness and a decrease in the fatigue crack propagation when compared with the sample welded with a higher interpass temperature. The results obtained indicate that the TIG process is an excellent alternative for the repair of CA6NM steel, with a significant influence from the interpass temperature.     

Cellular Integrin α5β1 and Exosomal ADAM17 Mediate the Binding and Uptake of Exosomes Produced by Colorectal Carcinoma Cells

Approximately 25% of colorectal cancer (CRC) patients develop peritoneal metastasis, a condition associated with a bleak prognosis. The CRC peritoneal dissemination cascade involves the shedding of cancer cells from the primary tumor, their transport through the peritoneal cavity, their adhesion to the peritoneal mesothelial cells (PMCs) that line all peritoneal organs, and invasion of cancer cells through this mesothelial cell barrier and underlying stroma to establish new metastatic foci. Exosomes produced by cancer cells have been shown to influence many processes related to cancer progression and metastasis. In epithelial ovarian cancer these extracellular vesicles (EVs) have been shown to favor different steps of the peritoneal dissemination cascade by changing the functional phenotype of cancer cells and PMCs. Little is currently known, however, about the roles played by exosomes in the pathogenesis and peritoneal metastasis cascade of CRC and especially about the molecules that mediate their interaction and uptake by target PMCs and tumor cells. We isolated exosomes by size−exclusion chromatography from CRC cells and performed cell-adhesion assays to immobilized exosomes in the presence of blocking antibodies against surface proteins and measured the uptake of fluorescently-labelled exosomes. We report here that the interaction between integrin α5β1 on CRC cells (and PMCs) and its ligand ADAM17 on exosomes mediated the binding and uptake of CRC-derived exosomes. Furthermore, this process was negatively regulated by the expression of tetraspanin CD9 on exosomes.     

Immunomodulatory Properties of Umbilical Cord Blood-Derived Small Extracellular Vesicles and Their Therapeutic Potential for Inflammatory Skin Disorders

Umbilical cord blood (UCB) has long been seen as a rich source of naïve cells with strong regenerative potential, likely mediated by paracrine signals. More recently, small extracellular vesicles (sEV), such as exosomes, have been shown to play essential roles in cell-to-cell communication, via the transport of numerous molecules, including small RNAs. Often explored for their potential as biomarkers, sEV are now known to have regenerative and immunomodulating characteristics, particularly if isolated from stem cell-rich tissues. In this study, we aim to characterize the immunomodulating properties of umbilical cord blood mononuclear cell-derived sEV (UCB-MNC-sEV) and explore their therapeutic potential for inflammatory skin diseases. UCB-MNC-sEV were shown to shift macrophages toward an anti-inflammatory phenotype, which in turn exert paracrine effects on fibroblasts, despite previous inflammatory stimuli. Additionally, the incubation of PBMC with UCB-MNC-sEV resulted in a reduction of total CD4⁺ and CD8⁺ T-cell proliferation and cytokine release, while specifically supporting the development of regulatory T-cells (Treg), by influencing FOXP3 expression. In a 3D model of psoriatic skin, UCB-MNC-sEV reduced the expression of inflammatory and psoriatic markers IL6, IL8, CXCL10, COX2, S100A7, and DEFB4. In vivo, UCB-MNC-sEV significantly prevented or reversed acanthosis in imiquimod-induced psoriasis, and tendentially increased the number of Treg in skin, without having an overall impact on disease burden. This work provides evidence for the anti-inflammatory and tolerogenic effect of UCB-MNC-sEV, which may be harnessed for the treatment of Th17-driven inflammatory skin diseases, such as psoriasis.     

Synthesis and characterization of zirconium ionomer dispersions

Water-based ionomer dispersions were formed by post-polymerization addition of zirconium species to polymer latices prepared from butyl methacrylate (BMA), butyl acrylate (BA) and acrylic acid (AA) by semicontinuous emulsion polymerization. The mole fraction of AA in the latex particles was kept at 10 mole% in all cases whereas the ratio of BA to BMA was varied. A method was established which allowed zirconium in the form of ammonium zirconium carbonate (AZC) to be successfully introduced into the latices without affecting their colloidal stability. Dynamic light scattering was used to determine average particle size in diluted latices. The structure and properties of cast ionomer films were investigated by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), tensile strength and swelling measurements. Fourier transform infrared spectroscopy (FTIR) was used to investigate the nature of the carboxylate bonding.     

Mitotic, but not meiotic, oriented cell divisions in rat spermatogenesis

The process of mammalian spermatogenesis involves both mitosis and meiosis at the same developmental age. Most previous studies have focused on mitotic spindle orientation during development, but not during meiotic division. Therefore, we asked whether there is a difference between mitotic and meiotic germ cell spindle orientation during rat spermatogenesis. Our results showed that mitotic spindles of spermatogonia were mainly oriented with angles ranging from 60 to 90 degrees, perpendicular in relation to the basement membrane of the seminiferous tubules. On the other hand, meiotic spindles showed a random orientation. Nocodazole treatment (at a concentration that depolymerizes only astral microtubules) induced a significant increase in cells with an angle between 0 and 30 degrees (parallel) in relation to the basement membrane. Meiotic spindles did not show a significant change in their orientation after the Nocodazole treatment. Therefore, our results suggest differences between the mechanisms controlling positioning and orientation of mitotic and meiotic spindles during rat spermatogenesis. It seems that a phylogenetically conserved programme controls the mitotic spindle orientation in organisms ranging from worms to mammals.     

Making the case for grid-connected photovoltaics in Brazil

In the developed world, grid-connected photovoltaics (PVs) are the fastest-growing segment of the energy market. From 1999 to 2009, this industry had a 42% compound annual growth-rate. From 2009 to 2013, it is expected to grow to 45%, and in 2013 the achievement of grid parity – when the cost of solar electricity becomes competitive with conventional retail (including taxes and charges) grid-supplied electricity – is expected in many places worldwide. Grid-connected PV is usually perceived as an energy technology for developed countries, whereas isolated, stand-alone PV is considered as more suited for applications in developing nations, where so many individuals still lack access to electricity. This rationale is based on the still high costs of PV when compared with conventional electricity. We make the case for grid-connected PV generation in Brazil, showing that with the declining costs of PV and the rising prices of conventional electricity, urban populations in Brazil will also enjoy grid parity in the present decade. We argue that governments in developing nations should act promptly and establish the mandates and necessary conditions for their energy industry to accumulate experience in grid-connected PV, and make the most of this benign technology in the near future.