Intimal hyperplasia following implantation of helical-centreline and straight-centreline stents in common carotid arteries in healthy pigs: influence of intraluminal flow?

Intimal hyperplasia (IH) is a leading cause of obstruction of vascular interventions, including arterial stents, bypass grafts and arteriovenous grafts and fistulae. Proposals to account for arterial stent-associated IH include wall damage, low wall shear stress (WSS), disturbed flow and, although not widely recognized, wall hypoxia. The common non-planarity of arterial geometry and flow, led us to develop a bare-metal, nitinol, self-expanding stent with three-dimensional helical-centreline geometry. This was deployed in one common carotid artery of healthy pigs, with a straight-centreline, but otherwise identical (conventional) stent deployed contralaterally. Both stent types deformed the arteries, but the helical-centreline device additionally deformed them helically and caused swirling of intraluminal flow. At sacrifice, one month post stent deployment, histology revealed significantly less IH in the helical-centreline than straight-centreline stented vessels. Medial cross-sectional area was not significantly different in helical-centreline than straight-centreline stented vessels. By contrast, luminal cross-sectional area was significantly larger in helical-centreline than straight-centreline stented vessels. Mechanisms considered to account for those results include enhanced intraluminal WSS and enhanced intraluminal blood–vessel wall mass transport, including of oxygen, in the helical-centreline stented vessels. Consistent with the latter proposal, adventitial microvessel density was lower in the helical-centreline stented than straight-centreline stented vessels.     

Effects of Copper Plasticity on the Induction of Stress in Silicon from Copper Through-Silicon Vias (TSVs) for 3D Integrated Circuits

Finite element modeling (FEM) has been undertaken to characterize the effect of copper (Cu) elasto-plastic behavior on the induction of stress in 3D crystalline silicon (Si) systems incorporating Cu through-silicon vias (TSVs). Using a linear isotropic hardening model, simulations of thermal annealing cycles in Cu TSVs indicate that, for sufficient anneal temperatures, plastic yield within the Cu leads to substantial residual stress in the neighboring Si following cool-down. Simulated Si stress profiles of annealed isolated TSVs agreed with experimental Raman microscopy measurements of post-anneal stress profiles in Si near isolated 5 × 25 μm cylindrical TSVs on a 300 mm Si wafer. Simulations were expanded to investigate the impact of Cu plasticity (yield stress and tangent modulus) on the residual stress profile in Si near isolated TSVs and linear TSV arrays. The results show that the magnitude and extent of the TSV-induced stress field in Si is a non-monotonic function of Cu yield stress. Moreover, the tensile or compressive nature of TSV-induced stress within and outside linear TSV arrays is also a strong function of the Cu yield stress. The simulated impact of Cu tangent modulus on TSV-induced stress in Si is less substantial. The implications of these results for TSV layout with respect to active device placement in a 3D system are discussed.     

Influence of H+ ion irradiation on the surface and microstructural changes of a nuclear graphite

Despite the significant importance of nuclear graphite as a promising plasma-facing component material in all thermonuclear fusion devices, its physico-chemical microstructural behavior under severe irradiation conditions was poorly understood. To provide a wide range of information and understanding about the structure change of nuclear graphite under energetic hydrogen ion irradiation, we therefore carried out a systematic study with employing various characterization tools such as scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoemission spectroscopy (XPS). Furthermore, we suggested possible surface chemical erosion mechanism from the observed physico-chemical microstructural changes.     

Structural characterisation and bioactivities of hybrid carrageenan-like sulphated galactan from red alga Furcellaria lumbricalis

The red alga, Furcellaria lumbricalis from the coast of the Prince Edward Island (PEI) in Atlantic Canada, was extracted with hot water and fractionated with 0.125 M KCl to obtain a carrageenan-like polysaccharide. The polysaccharide was further purified on ion-exchange and gel-permeation chromatography to yield a fraction (FB1) of uniform size and charge, with an average molecular weight of 428 kD. Oligosaccharides generated with acid hydrolysis of FB1 were sequenced using the electrospray ionisation collision induced dissociation tandem mass spectrometry (ES-CID-MS/MS) technique. On the basis of chemical and spectroscopic analysis, FB1 was characterised to be composed of 1,4-linked 3,6-anhydro-galactose (40%), 1,3-linked 4-sulphated-galactose (30%), 1,3-linked galactose (20%), 1,4-linked galactose (8%) and 1,4-linked 3-O-methyl-galactose (2%), which makes it be a novel sulphated galactan hybrid. The β-secretase (BACE) inhibition and immunomodulation activities of FB1-derived oligosaccharides were evaluated in vitro.     

A mechanistic study on the hydrogen trapping property and the subsequent electrochemical corrosion behavior of quenched and tempered steel

The hydrogen-facilitated anodic dissolution of steel is an interesting experimental phenomenon, but the persistent gaps in this knowledge area are great. The changes in the Tafel slopes and the reaction rates of steel that has been cathodically charged with hydrogen are interpreted mainly in the context of hydrogen trapping and de-trapping behaviors of steel using a variety of electrochemical methods. This study reveals that the increase in the anodic current density and the decrease in the polarization resistance are attributed primarily to the hydrogen-induced lattice expansion. Based on the Tafel-slope change, the oxidation of hydrogen cation partly contributed to the increase in the total anodic current density together with the dominant anodic reaction of the steel dissolution. The electrochemical permeation measurements showed much slower effusion kinetics of the hydrogen that has been trapped at the ε-carbide particles, and the trapping and de-trapping behavior at the fine particles are one of the controlling factors of the hydrogen-enhanced anodic dissolution of steel. From an engineering aspect, it is believed that the current study will provide an important insight into future perspectives on stress corrosion cracking failure occurring in various high-strength steels.     

Shearing of γ′ precipitates by a〈1 1 2〉 dislocation ribbons in Ni-base superalloys: A phase field approach

The phase field model of dislocations has been used to study the propagation of dislocation ribbons with an overall Burgers vector of a〈1 1 2〉 through a simulated Ni-base superalloy. The driving force for dislocation dissociation reactions and formation of planar faults is incorporated into the free energy functional using periodic functions specially fitted to ab initio γ-surface data. The model shows that the mechanism of cutting of the γ′ precipitates by these ribbons exhibits significant dependence on stress magnitude, orientation and precipitate shape. In the case of mixed screw–edge ribbons a change of shearing mode is observed, from stacking fault shear to anti-phase boundary shear, when the applied stress approaches the yield of the material. This transition is absent in pure edge ribbons.     

Biosorption of Hg from aqueous solutions by crab carapace

Carapace from the edible crab was assessed for the biosorption of Hg from aqueous solutions. Batch adsorption studies were used to determine the effects of contact time, pH, concentration, particle size and Cu(II) as a co-ion. The removal of Hg was fast and efficient, attaining >80.0% from 500 mg/L by 60 min. Specific uptake increased from 0.1 to 13.0mg/g as initial concentration increased from 0.5 to 1000 mg/L while the removal efficiency decreased from 100.0% over the 0.5-10.0mg/L range to 65.0% at 1000 mg/L. As particle size decreases from >2.5 to <0.15 mm, the Hg uptake increased from 1.4 to 8.3mg/g. In binary metal solutions, Cu(II) reduced the Hg removal by 80.0% while the presence of Hg increased Cu(II) removal by approximately 7.0%. Crab carapace is a readily available alkaline waste and easily processed into durable granular forms. Therefore, it offers potential as a low-cost alternative to commercial adsorbents or as a complimentary polishing process for the removal of Hg from acidic solutions.     

Development of a tubular microbial fuel cell (MFC) employing a membrane electrode assembly cathode

Tubular microbial fuel cells (MFC) with air cathode might be amenable to scale-up but with increasing volume a mechanically robust, cost-effective cathode structure is required. Membrane electrode assemblies (MEA) are investigated in a tubular MFC using cost-effective cation (CEM) or anion (AEM) exchange membrane. The MEA fabrication mechanically combines a cathode electrode with the membrane between a perforated cylindrical polypropylene shell and tube. Hydrogel application between membrane and cathode increases cathode potential by ∼100 mV over a 0–5.5 mA range in a CEM-MEA. Consequently, 6.1 W m⁻³ based on reactor liquid volume (200 cm³) are generated compared with 5 W m⁻³ without hydrogel. Cathode potential is also improved in AEM-MEA using hydrogel. Electrochemical Impedance Spectroscopy (EIS) to compare MEA's performance suggests reduced impedance and enhanced membrane–cathode contact area when using hydrogel. The maximum coulombic efficiency observed with CEM-MEA is 71% and 63% with AEM-MEA. Water loss through the membrane varies with external load resistance, indicating that total charge transfer in the MFC is related to electro-osmotic drag of water through the membrane. The MEA developed here has been shown to be mechanically robust, operating for more than six month at this scale without problem.     

Using the tabulated diffusion flamelet model ADF-PCM to simulate a lifted methane-air jet flame

Two formulations of a turbulent combustion model based on the approximated diffusion flame presumed conditional moment (ADF-PCM) approach [J.-B. Michel, O. Colin, D. Veynante, Combust. Flame 152 (2008) 80-99] are presented. The aim is to describe autoignition and combustion in nonpremixed and partially premixed turbulent flames, while accounting for complex chemistry effects at a low computational cost. The starting point is the computation of approximate diffusion flames by solving the flamelet equation for the progress variable only, reading all chemical terms such as reaction rates or mass fractions from an FPI-type look-up table built from autoigniting PSR calculations using complex chemistry. These flamelets are then used to generate a turbulent look-up table where mean values are estimated by integration over presumed probability density functions. Two different versions of ADF-PCM are presented, differing by the probability density functions used to describe the evolution of the stoichiometric scalar dissipation rate: a Dirac function centered on the mean value for the basic ADF-PCM formulation, and a lognormal function for the improved formulation referenced ADF-PCMχ. The turbulent look-up table is read in the CFD code in the same manner as for PCM models. The developed models have been implemented into the compressible RANS CFD code IFP-C3D and applied to the simulation of the Cabra et al. experiment of a lifted methane jet flame [R. Cabra, J. Chen, R. Dibble, A. Karpetis, R. Barlow, Combust. Flame 143 (2005) 491-506]. The ADF-PCMχ model accurately reproduces the experimental lift-off height, while it is underpredicted by the basic ADF-PCM model. The ADF-PCMχ model shows a very satisfactory reproduction of the experimental mean and fluctuating values of major species mass fractions and temperature, while ADF-PCM yields noticeable deviations. Finally, a comparison of the experimental conditional probability densities of the progress variable for a given mixture fraction with model predictions is performed, showing that ADF-PCMχ reproduces the experimentally observed bimodal shape and its dependency on the mixture fraction, whereas ADF-PCM cannot retrieve this shape.