Rapid crack growth in a thermoelastic solid under mixed-mode thermomechanical loading

A two-dimensional steady-sate analysis of semi-infinite brittlecrack growth at a constant subcritical rate in an unboundedfully-coupled thermoelastic solid under mixed-mode thermomechanicalloading is made. The loading consists of normal and shear tractionsand heat fluxes applied as point sources (line loads in theout-of-plane direction). A related problem is solved exactly in an integral transformspace, and robust asymptotic forms used to reduce the originalproblem to a set of integral equations. The equations are partiallycoupled and exhibit operators of both Cauchy and Abel types,yet can be solved analytically. The temperature change field at a distance from the moving crackedge is then constructed, and its dominant term is found tobe controlled by the imposed heat fluxes. The role of this termis, indeed, enhanced if the heat fluxes serve to render thecrack as a net heat source/sink for the solid, as opposed tobeing a transmitter of heat across its plane. More generally,the influence of the thermoelastic coupling on this field, aswell as other functions, is found to increase with crack speed.     

Synthetic magnetic opals

We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there exists no report in literature on any BiNi compound which is magnetic.     

Regio- and stereoselective ring-opening metathesis polymerization of 3-substituted cyclooctenes

3-Substituted cis-cyclooctenes (3RCOEs, R = methyl, ethyl, hexyl, and phenyl) were synthesized and polymerized, and the polymers therefrom were hydrogenated to prepare model linear low density polyethylene (LLDPE) samples. The ring-opening metathesis polymerization (ROMP) of the 3RCOEs using Grubbs' catalyst proceeded in a regio- and stereoselective manner to afford polyoctenamers [poly(3RCOE)] exhibiting remarkably high head-to-tail regioregularity and high trans-stereoregularity. The overall selectivity increases with the increasing size of the R substituent. Hydrogenation of poly(3RCOE)s afforded precision LLDPEs with R substituents on every eighth backbone carbon.     

Mechanically versatile isosorbide-based thermoplastic copolyether-esters with a poly(ethylene glycol) soft segment

Segmented thermoplastic copolyether esters (TPEE's) with a partially renewable hard block containing isosorbide (ISB) and poly(ethylene glycol) (PEG) soft blocks were prepared by melt polycondensation. A range of compositions was accessible despite the relatively low reactivity of the sterically and electronically hindered ISB monomer. The small-scale reactions performed in the melt were limited in terms of achievable molar mass. This is attributed to the challenge of attaining stoichiometric balance in the feed and maintaining this balance throughout the high temperature (>200°C) reactions. Nevertheless, products were isolated that could be manipulated and melt-pressed into specimen for tensile testing. Varying the feed compositions gave rise to copolymers exhibiting a broad range of mechanical properties (elastic modulus from 1–66 MPa). These characteristics are consistent with a segmented polymer architecture with morphological features similar to commercially available TPEE counterparts. These results pave the way for more responsibly sourced building blocks being incorporated into materials with high market value potential.     

On the Use of ICP-MS for Measuring Plutonium in Urine

The analytical protocols currently used to measure plutonium in urinary excretion consist of radiochemical purification, the source preparation by electroplating and alpha spectrometry measurements. Such a procedure is of limited relevance to the individual monitoring of workers exposed to plutonium and mixed oxides. The use of ICP-MS, which takes much shorter counting time, was investigated with the aim of assessing the capabilities of this analytical tool for the determination of urinary excretion of plutonium. It has been shown that the detection level of 1 mBq·1^-1 could be achieved after a radiochemical purification process for a standard ICP-MS set-up.     

Biomimetic double network hydrogels: Combining dynamic and static crosslinks to enable biofabrication and control cell-matrix interactions

Hydrogels are promising candidates for recapitulation of the native extracellular matrix (ECM), yet recreating molecular and spatiotemporal complexity within a single network remains a challenge. Double network (DN) hydrogels are a promising step towards recapitulating the multicomponent ECM and have enhanced mechanical properties. Here, we investigate DNs based on dynamic covalent and covalent bonds to mimic the dynamicity of the ECM and enable biofabrication. We also investigate the spatiotemporal molecular attachment of a bioactive adhesive peptide within the networks. Using oxidized alginate (dynamic network, Schiff base) and polyethylene glycol diacrylate (static network, acrylate polymerization) we find an optimized procedure, where the dynamic network is formed first, followed by the static network. This initial dynamically cross-linked hydrogel imparts self-healing, injectability, and 3D printability, while the subsequent DN hydrogel improves the stability of the 3D gels and imparts toughness. Rheology and compression testing show that the toughening is due to the combination of energy dissipation (dynamic network) and elasticity (static network). Furthermore, where we place adhesive sites in the network matters; we find distinct differences when an adhesive peptide, Arg-Gly-Asp (RGD), is attached to the different networks. This DN strategy bring us closer to understanding and recreating the complex multicomponent ECM—pushing us past a materials view of cell adhesion—while enabling injectabiltiy and printing of tough hydrogels.     

Functional neural network analysis in frontotemporal dementia and Alzheimer's disease using EEG and graph theory

Background  

Although a large body of knowledge about both brain structure and function has been gathered over the last decades, we still have a poor understanding of their exact relationship. Graph theory provides a method to study the relation between network structure and function, and its application to neuroscientific data is an emerging research field. We investigated topological changes in large-scale functional brain networks in patients with Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD) by means of graph theoretical analysis of resting-state EEG recordings. EEGs of 20 patients with mild to moderate AD, 15 FTLD patients, and 23 non-demented individuals were recorded in an eyes-closed resting-state. The synchronization likelihood (SL), a measure of functional connectivity, was calculated for each sensor pair in 0.5–4 Hz, 4–8 Hz, 8–10 Hz, 10–13 Hz, 13–30 Hz and 30–45 Hz frequency bands. The resulting connectivity matrices were converted to unweighted graphs, whose structure was characterized with several measures: mean clustering coefficient (local connectivity), characteristic path length (global connectivity) and degree correlation (network 'assortativity'). All results were normalized for network size and compared with random control networks.