A statistical model of fracture for a 2D hexagonal mesh: The Cell Network Model of Fracture for the bamboo Guadua angustifolia

A 2D, hexagonal in geometry, statistical model of fracture is proposed. The model is based on the drying fracture process of the bamboo Guadua angustifolia. A network of flexible cells are joined by brittle junctures of fixed Young moduli that break at a certain thresholds in tensile force. The system is solved by means of the Finite Element Method (FEM). The distribution of avalanche breakings exhibits a power law with exponent −2.93(9), in agreement with the random fuse model (Bhattacharyya and Chakrabarti, 2006) [1].     

Polyethylene glycol functionalized gold nanoparticles: the influence of capping density on stability in various media

Thiol-terminated polyethylene glycol (PEG) is commonly used to functionalize the surface of gold nanoparticles (AuNPs) in order to improve their in vivo stability and to avoid uptake by the reticular endothelial system. Although it has been reported that AuNPs functionalized with tethered PEG are stable in biological media, the influence of chain density remains unclear. This study investigates the influence of PEG capping density on the stability of washed and dried AuNPs in: water, phosphate-buffered saline solution (PBS), phosphate-buffered saline solution containing bovine serum albumin (PBS/BSA), and dichloromethane (DCM). PEG coating had a dramatic effect on stability enabling stable suspensions to be produced in all the media studied. A linear relationship was observed between capping density and stability in water and DCM with a somewhat lower stability observed in PBS and PBS/BSA. A maximum PEG loading level of ∼14 wt.% was achieved, equivalent to a PEG surface density of ∼1.13 chains/nm².     

The constitutive transport element (CTE) of Mason-Pfizer monkey virus (MPMV) accesses a cellular mRNA export pathway

The constitutive transport elements (CTEs) of type D retroviruses are cis-acting elements that promote nuclear export of incompletely spliced mRNAs. Unlike the Rev response element (RRE) of human immunodeficiency virus type 1 (HIV-1), CTEs depend entirely on factors encoded by the host cell genome. We show that an RNA comprised almost entirely of the CTE of Mason-Pfizer monkey virus (CTE RNA) is exported efficiently from Xenopus oocyte nuclei. The CTE RNA and an RNA containing the RRE of HIV-1 (plus Rev) have little effect on export of one another, demonstrating differences in host cell requirements of these two viral mRNA export pathways. Surprisingly, even very low amounts of CTE RNA block export of normal mRNAs, apparently through the sequestration of cellular mRNA export factors. Export of a CTE-containing lariat occurs when wild-type CTE, but not a mutant form, is inserted into the pre-mRNA. The CTE has two symmetric structures, either of which supports export and the titration of mRNA export factors, but both of which are required for maximal inhibition of mRNA export. Two host proteins bind specifically to the CTE but not to non-functional variants, making these proteins candidates for the sequestered mRNA export factors.     

A note on time integrators in water-wave simulations

The importance of a suitable temporal integrator for fully nonlinear simulations of surface gravity waves is emphasized. Via numerical examples, it is demonstrated that constant-step procedures are inefficient. This relates to the practice of energy-conserving symplectic integration, assuming constant time steps, and is compared to direct numerical simulations using Runge–Kutta integrators with variable time-step control. It is concluded that the latter with automatic variable time-step control is the more efficient, and should be applied. The practice and efficiency of a stabilization procedure for the time-step selection is described and illustrated. An important point of the method is that the linear part of the prognostic equations is integrated analytically, which means that this part is obtained to machine presicion for any (large) time step (time interval). The evolution and instabilities of highly nonlinear water waves in three dimensions are exemplified through an accurate and efficient time-integration procedure. We are grateful to Professor J. N. Newman for his longstanding and pioneering contributions to the research field of marine hydrodynamics. His analytical and numerical works on fundamental and industrial problems in relation to water waves and their interaction with floating bodies have inspired us and many fellow scientist world wide over long time.     

The effects of firing conditions on the properties of electrophoretically deposited titanium dioxide films on graphite substrates

Thick anatase films were fabricated on graphite substrates using a method of anodic aqueous electrophoretic-deposition using oxalic acid as a dispersant. Thick films were subsequently fired in air and in nitrogen at a range of temperatures. The morphology and phase composition were assessed and the photocatalytic performance was examined by the inactivation of Escherichia coli in water. It was found that the transformation of anatase to rutile is enhanced by the presence of a graphite substrate through reduction effects. The use of a nitrogen atmosphere allows higher firing temperatures, results in less cracking of the films and yields superior bactericidal performance in comparison with firing in air. The beneficial effects of a nitrogen firing atmosphere on the photocatalytic performance of the material are likely to be a result of the diffusion of nitrogen and carbon into the TiO₂ lattice and the consequent creation of new valence band states.