A two-dimensional homogenized model for a pile of thin elastic sheets with frictional contact

The present paper deals with the computational simulation of a pile of thin sheets. The sheets are not laminated or glued, but they interact by frictional contact. In general, it is not possible to perform a full-scale finite element contact computation for piles containing thousands of sheets; the problem size becomes too large, and numerical solution methods suffer from severe convergence problems due to the large number of strongly coupled contact conditions. In this paper, a macroscopic material model is presented for the two-dimensional case. The pile of sheets is homogenized by introducing an effective anisotropic constitutive law, which is motivated by formulations of the theory of elasto-plasticity. This macroscopic material law models the behavior of a pile of sheets, allowing for no tensile stresses in the direction normal to the sheets and obeying Coulomb??s law of friction in the tangential contact plane. Applying this macroscopic material model, an equivalent homogeneous body can be treated using much coarser discretizations. Computational results for the problems are provided, and a comparison with simplified contact computations is done.     

Pyrene-adamantane-β-cyclodextrin: An efficient host–guest system for the biofunctionalization of SWCNT electrodes

The design of nanostructured biological architectures based on host–guest interactions between β-cyclodextrin and adamantane was investigated on SWCNT coatings using glucose oxidase (GOX) as biomolecule model. β-Cyclodextrin tagged GOX was immobilized on adamantane functionalized carbon nanotubes, deposited on platinum electrodes. Different functionalization techniques to attach “pyrene adamantane” on nanotubes were studied and compared in terms of the performances of the subsequently constructed glucose biosensors. The best results were obtained by dipping the nanotube deposit into a pyrene-adamantane solution followed by electropolymerization of the adsorbed pyrene monolayer. The constructed biosensor exhibited a good linear response toward glucose concentrations between 2 × 10⁻⁷ M and 1.6 × 10⁻³ M. The maximum current density and glucose sensitivity were 154.9 μA cm⁻² and 14.4 mA M⁻¹ cm⁻², respectively.     

Conformation in solution of side-chain liquid crystal polymers as a function of the mesogen-graft amount

The conformation of side-chain liquid crystal polymers with different mesogen-graft amounts has been studied by small-angle neutron scattering in dilute solutions of toluene-d8 and THF-d8. It is shown that the radius of gyration increases by about twofold when the mesogen-graft amount increases from 0 to 100%, which suggests that the persistence length of the backbone increases by about 4-fold. Comparison with the results reported in the literature on the melt state suggests that the persistence length is not an intrinsic property of side chain liquid crystal polymers, but depends on inter-chain interactions.     

A new silver sulfadiazine water soluble gel

Silver sulfadiazine is the most commonly used topical antibacterial agent for the treatment of burn wounds. It has many clinical advantages, including a broad spectrum of antimicrobial activity, low toxicity, and minimal pain on application. The current formulation of silver sulfadiazine contains a lipid soluble carrier, polypropylene glycol, that has certain disadvantages, including pseudo-eschar formation and the need for twice daily application. The purpose of this investigation was to describe a new formulation of silver sulfadiazine in a water soluble gel, poloxamer 188. The antibacterial activity of this new gel has been compared to that of the commercially available silver sulfadiazine cream by in vitro and in vivo testing. The results of the in vitro antibacterial testing of these two different agents demonstrated the superiority of the new gel formulation. In experimental wounds, the antibacterial activity of the gel and the commercially available silver sulfadiazine cream were not significantly different when applied once a day. The antibacterial activity of the gel when applied once a day was comparable to that encountered by twice daily applications of the silver sulfadiazine cream by experimental wounds. The major advantage of this gel was its ease of application and removal that is attributed to its water solubility.     

Resistive Switching of Individual,Chemically Synthesized TiO2 Nanoparticles

Resistively switching devices are considered promising for next‐generation nonvolatile random‐access memories. Today, such memories are fabricated by means of “top–down approaches” applying thin films sandwiched between nanoscaled electrodes. In contrast, this work presents a “bottom–up approach” disclosing for the first time the resistive switching (RS) of individual TiO₂ nanoparticles (NPs). The NPs, which have sizes of 80 and 350 nm, respectively, are obtained by wet chemical synthesis and thermally treated under oxidizing or vacuum conditions for crystallization, respectively. These NPs are deposited on a Pt/Ir bottom electrode and individual NPs are electrically characterized by means of a nanomanipulator system in situ, in a scanning electron microscope. While amorphous NPs and calcined NPs reveal no switching hysteresis, a very interesting behavior is found for the vacuum‐annealed, crystalline TiO_2–x NPs. These NPs reveal forming‐free RS behavior, dominantly complementary switching (CS) and, to a small degree, bipolar switching (BS) characteristics. In contrast, similarly vacuum‐annealed TiO₂ thin films grown by atomic layer deposition show standard BS behavior under the same conditions. The interesting CS behavior of the TiO_2–x NPs is attributed to the formation of a core–shell‐like structure by re‐oxidation of the reduced NPs as a unique feature.     

Evaluation of DNA extraction methods for Bacillus anthracis spores spiked to food and feed matrices at biosafety level 3 conditions

The DNA extraction efficiency from milk, whey, soy, corn gluten meal, wheat powders and heat-treated corn grain that were spiked with Bacillus anthracis and Bacillus thuringiensis spores was determined. Two steps were critical: lysis of the spores and binding of the free DNA to the DNA binding magnetic beads in the presence of the interfering powders. For the guanidine-thiocyanate based Nuclisens lysis buffer from Biomerieux we found that between 15 and 30% of the spores survived the lysis step. As most lysis buffers in DNA/RNA extraction kits are guanidine based it is likely that other lysis buffers will show a similar partial lysis of the Bacillus spores. Our results show that soybean flour and wheat flour inhibited the DNA extraction process strongest, leading to unreliable DNA extractions when using too much of the matrix. For corn gluten meal, heat-treated corn grain and milk powders, DNA extraction efficiencies in the presence of 100mg and 10mg of powder resulted in 70%-95% reduced DNA recoveries. The inhibition was, however, reliable and intermediate compared to the inhibition by soy and wheat. Whey powder had the lowest inhibitory effect on DNA-extraction efficiency and recoveries of 70-100% could be reached when using 10mg of powder. The results show that reducing the amount of matrix leads to better DNA-extraction efficiencies, particularly for strongly inhibiting powders such as soy and wheat. Based on these results, a standard protocol to directly isolate DNA from micro-organisms present in complex matrixes such as food and feed powders was designed.     

Large‐scale Synthesis of Urchin‐like Mesoporous TiO2 Hollow Spheres by Targeted Etching and Their Photoelectrochemical Properties

A versatile targeted etching strategy is developed for the large‐scale synthesis of urchin‐like mesoporous TiO₂ hollow spheres (UMTHS) with tunable particle size. Its key feature is the use of a low‐temperature hydrothermal reaction of surface‐fluorinated, amorphous, hydrous TiO₂ solid spheres (AHTSS) under the protection of a polyvinylpyrrolidone (PVP) coating. With the confinement of PVP and water penetration, the highly porous AHTSS are selectively etched and hollowed by fluoride without destroying their spherical morphology. Meanwhile TiO₂ hydrates are gradually crystallized and their growth is preferentially along anatase (101) planes, reconstructing an urchin‐like shell consisting of numerous radially arranged single‐crystal anatase nanothorns. Complex hollow structures, such as core–shell and yolk–shell structures, can also be easily synthesized via additional protection of the interior by pre‐filling AHTSS with polyethylene glycol (PEG). The hollowing transformation is elucidated by the synergetic effect of etching, PVP coating, low hydrothermal reaction temperature, and the unique microstructure of AHTSS. The synthesized UMTHS with a large surface area of up to 128.6 m² g^‐1 show excellent light‐harvesting properties and present superior performances in photocatalytic removal of gaseous nitric oxide (NO) and photoelectrochemical solar energy conversion as photoanodes for dye‐sensitized mesoscopic solar cells.     

Influence of absorbable dusting powders on wound infection

OBJECTIVE: To investigate the lymphocyte subpopulations (T4, T8 and macrophages) and major histocompatibility (MHC) II antigens in patients with superficial bladder cancer before and after intravesical instillations of recombinant interferon-gamma (IFN-gamma). PATIENTS AND METHODS: Four intravesical weekly instillations of either 1.3 mg (20 patients, group A) or 0.7 mg (11 patients, group B) IFN-gamma were administered in 31 evaluable patients (28 men and three women, mean age 68.5 years). The CD4+, CD8+, CD68+ and HLA-DR antigens were detected immunohistochemically in tumours and a marker tumour before and after intravesical instillations. RESULTS: The median number of T4 lymphocytes increased from 15 per high-power field (HPF) to 27.5 in group A (P = 0.0029) and to 45 in group B (P = 0.0117). Macrophages increased from 6 cells/HPF to 15 cells/HPF in group A (P = 0.0029) and from 2 to 8.75 cells/HPF in group B (P = 0.0117). The T8 lymphocyte subpopulation decreased from 4 to 3 cells/HPF (P = 0.0231) in group A and from 5 to 2 cells/HPF (P = 0.0759) in group B. The median percentage of HLA-DR antigens increased from 1.5% to 18% in general, (P < 0.001), from 2.5% to 15% in group A (P = 0.0064) and from 0% to 20% in group B (P = 0.0077). The induction of HLA-DR antigens was statistically significant in those receiving the lower dose (from 0% before instillation to 20% afterward, P = 0.0277), while it was not with the higher dose (from 0% to 5%, P = 0.068). Irrespective of the dose of IFN used. T4 lymphocytes and macrophages increased significantly after treatment in patients in whom the tumour HLA-DR antigens were either up-regulated or remained stable. The median net increase in T4 cells was 17.5 and 30 cells/HPF for groups A and B, respectively (P = 0.0429). CONCLUSION: T4 lymphocytes, macrophages and HLA-DR antigens increased after intravesical IFN-gamma in patients with superficial bladder cancer, but T8 lymphocytes decreased. Irrespective of the drug dose used, patients with either upregulated or stable HLA-DR antigens after treatment showed the same pattern of changes in the lymphocyte subpopulations. The two doses generally had the same effect on the immunological variables assessed but the lower dose was more effective in inducing HLA-DR antigens and in increasing the number of T4 lymphocytes in the tumours.