Disorder is good for you: the influence of local disorder on strain localization and ductility of strain softening materials

We formulate a generic concept model for the deformation of a locally disordered, macroscopically homogeneous material which undergoes irreversible strain softening during plastic deformation. We investigate the influence of the degree of microstructural heterogeneity and disorder on strain localization (formation of a macroscopic shear band) in such materials. It is shown that increased microstructural heterogeneity delays strain localization and leads to an increase of the plastic regime in the macroscopic stress–strain curves. The evolving strain localization patterns are characterized.     

From Primary MSC Culture of Adipose Tissue to Immortalized Cell Line Producing Cytokines for Potential Use in Regenerative Medicine Therapy or Immunotherapy

For twenty-five years, attempts have been made to use MSCs in the treatment of various diseases due to their regenerative and immunomodulatory properties. However, the results are not satisfactory. Assuming that MSCs can be replaced in some therapies by the active factors they produce, the immortalized MSCs line was established from human adipose tissue (HATMSC1) to produce conditioned media and test its regenerative potential in vitro in terms of possible clinical application. The production of biologically active factors by primary MSCs was lower compared to the HATMSC1 cell line and several factors were produced only by the cell line. It has been shown that an HATMSC1-conditioned medium increases the proliferation of various cell types, augments the adhesion of cells and improves endothelial cell function. It was found that hypoxia during culture resulted in an augmentation in the pro-angiogenic factors production, such as VEGF, IL-8, Angiogenin and MCP-1. The immunomodulatory factors caused an increase in the production of GM-CSF, IL-5, IL-6, MCP-1, RANTES and IL-8. These data suggest that these factors, produced under different culture conditions, could be used for different medical conditions, such as in regenerative medicine, when an increased concentration of pro-angiogenic factors may be beneficial, or in inflammatory diseases with conditioned media with a high concentration of immunomodulatory factors.     

A model of formation of fixed charge in thermal silicon dioxide

A quantitative model of formation of fixed charge (Q _f ) in silicon dioxide during thermal oxidation of silicon is developed. The value of Q _f is governed by the number of interstitial silicon atoms in the vicinity of the Si-SiO₂ interface; these atoms are formed as a result of the processes of their generation and recombination at the interface and also due to their diffusion to the depth of dioxide. The model makes it possible to describe a decrease in the fixed charge as the oxidation temperature is increased and in the case of annealing in neutral media for silicon dioxide on silicon with orientations (100) and (111) in a wide range of temperatures.     

Cyclization in vinyl-divinyl copolymerization

It was found by analysis of the composition and n.m.r. behaviour of low-conversion soluble copolymers of styrene (S) with 5–60 wt% of ethylene dimethacrylate (EDMA) that cyclization strongly predominates in crosslinking copolymerization. The results suggest that, especially at a higher content of the divinyl component, compact structures are formed with the character of microgel-like particles. At a higher EDMA content, this component is incorporated into the copolymer only as a unit with a pendant double bond and the content of crosslinks (EDMA units with both vinyls reacted) does not further increase with increasing EDMA content. The pendant vinyls in the particle cores are already so immobilized or sterically hindered that they are unable to react even with small molecules of the monomer. Procedures for the determination of copolymerization parameters for pairs of mono- and divinyl monomers, usually neglecting cyclization, were revised. An analysis of the theoretical model of crosslinking copolymerization with weak cyclization and experimental results obtained with the S-EDMA system with prevailing cyclization show that the copolymerization parameters need not be too much distorted, if they have been determined from the content of the mono- and divinylic components of the copolymer.     

Contamination of chicken carcasses in Gauteng, South Africa, by Salmonella, Listeria monocytogenes and Campylobacter

The presence of the foodborne pathogens, Salmonella spp., Listeria monocytogenes and Campylobacter spp., on 99 fresh and frozen chicken carcasses sourced from various retailers in Gauteng, South Africa, was investigated. Using culture methods, 60.6% of the carcasses were found to be contaminated with one or more pathogens, with 19.2%, 19.2% and 32.3% of the carcasses being found to harbour Salmonella, L. monocytogenes and Campylobacter, respectively. The extent of contamination with one or more pathogens was not significantly different (p>0.1) between fresh or frozen samples or between samples from butcheries, supermarkets or street vendors. Significantly more (p<0.1) fresh carcasses from butcheries than from other outlets were contaminated with Salmonella, while more fresh carcasses from supermarkets were contaminated with Campylobacter. The proportion of carcasses with L. monocytogenes from all sources were similar. Polymerase chain reaction (PCR) results indicate an even higher extent of pathogen contamination, but the PCR techniques need to be further refined before they can be used routinely.     

Social Interaction in YouTube Text‐Based Polylogues: A Study of Coherence

Since YouTube was launched, its emblematic video‐sharing facility has attracted considerable attention as a social networking system of cultural production. In addition to vlogging, YouTube offers a text facility through which YouTubers share and negotiate opinions. However, research into the latter is scarce, especially within language‐based disciplines (Androutsopoulos & Beiβwenger 2009; Zelenkauskaite & Herring 2008). This article contributes to addressing this imbalance by focusing on YouTube text‐based ‘conversation’ (Herring 2010a). Specifically, it examines coherence in a corpus of YouTube postings in Spanish. Although coherence has been the object of much academic debate in other forms of computer‐mediated communication, no empirical analysis of coherence in YouTube text has been undertaken to date. Results underline the conversational potential of this facility.     

Liquid chromatography of polymer mixtures applying combination of exclusion and full adsorption mechanisms. I. Analysis of polystyrene in its mixture with polymethylmethacrylate single column/single eluent approach

Components of polymer mixtures with different chemical composition can be separated by liquid chromatography by applying appropriate conditions (column packing, eluent, temperature, and pressure) in which just one type of macromolecule is eluted in the size exclusion mode while the other component is fully retained within on column packing. The feasibility of this idea has been demonstrated using the mixtures of polystyrene (PS) plus polymethylmethacrylate (PMMA) with silica gel as the column packing and toluene as an eluent. The PMMA was retained by the silica get at ambient temperature and moderate pressures of several MPa while the PS was eluted by a typical SEC mecahanism. Furthermore, the molar mass distribution of the PS could be determined in one step with the same precision as if injected alone. Surprisingly large amounts of PMMA were trapped within the column prior to its SEc characteristics being influenced. After a series of analyses the column has to be regenerated with a brief flushing with a desorbing liquid, tetrahydrofuran in the system studied. The re-equilibrization of the column with the initial eluent, toluene, was fast and a new series of analyses could be started soon after the characterization step had seen finished. © 1995 John Wiley & Sons, Inc.     

Model of thermal oxidation of silicon with diffusion coefficient relaxation

Based on the bulk oxidation model, taking into account the effect of internal mechanical stresses and time relaxation of the oxidizer diffusion coefficient in dioxide, the effects observed during ordinary, fast, and multistage thermal oxidation of silicon were quantitatively analyzed. Substrates with different crystallographic orientations were used.