Using Krylov subspace and spectral methods for solving complementarity problems in many‐body contact dynamics simulation

Many‐body dynamics problems are expected to handle millions of unknowns when, for instance, investigating the three‐dimensional flow of granular material. Unfortunately, the size of the problems tractable by existing numerical solution techniques is severely limited on convergence grounds. This is typically the case when the equations of motion embed a differential variational inequality problem that captures contact and possibly frictional interactions between rigid and/or flexible bodies. As the size of the physical system increases, the speed and/or the quality of the numerical solution decreases. This paper describes three methods – the gradient projected minimum residual method, the preconditioned spectral projected gradient with fallback method, and the modified proportioning with reduced gradient projection method – that demonstrate better scalability than the projected Jacobi and Gauss–Seidel methods commonly used to solve contact problems that draw on a differential‐variational‐inequality‐based modeling approach. Copyright © 2013 John Wiley & Sons, Ltd.     

Bioactive cotton fabrics containing chitosan and biologically active substances extracted from plants

The paper studies the obtaining of bioactive textiles using chitosan-coated fabrics, in which biologically active substances contained by Viola Tricolor (VT) – an extract of three Viola species (Violaceae) – were immobilized. Chitosan was applied on cotton fabric or on chemically modified cotton (having reactive –CHO or carboxymethyl groups), as tripolyphosphate (TPP) crosslinked fine particles, or by use of glutaraldehyde crosslinking agent. The amount of VT retained on the fabrics was found to depend on the procedure of chitosan application on the cotton. The obtained bioactive textiles are expected to have antioxidant activity due to the biologically active substances from VT; they can be used for obtaining clothes for people with allergies or other skin problems, assuring a controlled release of biomolecules. The study focuses on the in vitro release of VT retained on the fabrics, as well as on its antioxidant activity.     

Considerations on Drying Frozen Spruce Wood and Effects upon Its Properties

The aricle presents the results of a research performed in order to establish whether drying lumber from frozen state (in winter) has repercussions upon its properties, compared to drying under the same conditions lumber parts originating from the same log and position within the log section but that were not frozen prior to drying. To this purpose, spruce (Picea abies L.) lumber specimens, 35 mm and 55 mm thick, cut from the same log, half frozen at ? 30°C and half unfrozen, were dried under the same conditions in a climate chamber. Some mechanical properties (hardness, bending strength, and modulus elasticity in static bending), as well as workability (expressed by means of the absorbed power and specific resistance to cutting during milling), were determined The results revealed slight differences between the frozen and the unfrozen samples both during the drying process and afterwards. It was noticed that a significant amount of water was removed from wood during the very beginning of the heating phase (thawing). With regards to wood properties after drying, a slight lowering of the mechanical properties and better workability could be established for the initially frozen samples.     

Biohybrid Nanostructured Iron Oxide Nanoparticles and Satureja hortensis to Prevent Fungal Biofilm Development

Cutaneous wounds are often superinfected during the healing process and this leads to prolonged convalescence and discomfort. Usage of suitable wound dressings is very important for an appropriate wound care leading to a correct healing. The aim of this study was to demonstrate the influence of a nano-coated wound dressing (WD) on Candida albicans colonization rate and biofilm formation. The modified WD was achieved by submerging the dressing pieces into a nanofluid composed of functionalized magnetite nanoparticles and Satureja hortensis (SO) essential oil (EO). Chemical composition of the EO was established by GC-MS. The fabricated nanostructure was characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Differential Thermal Analysis (DTA) and Fourier Transform-Infrared Spectroscopy (FT-IR). The analysis of the colonized surfaces using (Scanning Electron Microscopy) SEM revealed that C. albicans adherence and subsequent biofilm development are strongly inhibited on the surface of wound dressing fibers coated with the obtained nanofluid, comparing with regular uncoated materials. The results were also confirmed by the assay of the viable fungal cells embedded in the biofilm. Our data demonstrate that the obtained phytonanocoating improve the resistance of wound dressing surface to C. albicans colonization, which is often an etiological cause of local infections, impairing the appropriate wound healing.     

Hybrid magnetite nanoparticles/Rosmarinus officinalis essential oil nanobiosystem with antibiofilm activity

Biofilms formed by fungal organisms are associated with drastically enhanced resistance against most antimicrobial agents, contributing to the persistence of the fungi despite antifungal therapy. The purpose of this study is to combine the unique properties of nanoparticles with the antimicrobial activity of the Rosmarinus officinalis essential oil in order to obtain a nanobiosystem that could be pelliculised on the surface of catheter pieces, in order to obtain an improved resistance to microbial colonization and biofilm development by Candida albicans and C. tropicalis clinical strains. The R. officinalis essential oils were extracted in a Neo-Clevenger type apparatus, and its chemical composition was settled by GC-MS analysis. Functionalized magnetite nanoparticles of up to 20 nm size had been synthesized by precipitation method adapted for microwave conditions, with oleic acid as surfactant. The catheter pieces were coated with suspended core/shell nanoparticles (Fe₃O₄/oleic acid:CHCl₃), by applying a magnetic field on nanofluid, while the CHCl₃ diluted essential oil was applied by adsorption in a secondary covering treatment. The fungal adherence ability was investigated in six multiwell plates, in which there have been placed catheters pieces with and without hybrid nanoparticles/essential oil nanobiosystem pellicle, by using culture-based methods and confocal laser scanning microscopy (CLSM). The R. officinalis essential oil coated nanoparticles strongly inhibited the adherence ability and biofilm development of the C. albicans and C. tropicalis tested strains to the catheter surface, as shown by viable cell counts and CLSM examination. Due to the important implications of Candida spp. in human pathogenesis, especially in prosthetic devices related infections and the emergence of antifungal tolerance/resistance, using the new core/shell/coated shell based on essential oil of R. officinalis to inhibit the fungal adherence could be of a great interest for the biomedical field, opening new directions for the design of film-coated surfaces with antibiofilm properties.     

MEASUREMENT OF RADIATION INDUCED LOCALIZED ABSORPTION IN CHROMATOGRAPHIC ELUENTS BY MEANS OF THE CO LASER AND THE PZT PYROELECTRIC DETECTOR

Abstract

Combined use of the CO laser and PZT piezoelectric detector is proposed as a sensitive and specific detector for gas chromatography. The feasibility of this detection scheme is demonstrated for a model mixture containing varying proportions of acetone in water. After separation on a GC column, spectra of both constituents were recorded in the 1600 cm^?1 to 1900 cm^?1 range that encompasses the characteristic frequency of C=O bond in acetone. Reasonably high sensitivity (mass concentration limit is 1.2x10^?8 g acetone) and a good degree (factor 530) of spectral discrimination was achieved by a proper selection of analytical wavelengths.     

Thermal analysis control of in-mould and ladle inoculated grey cast irons

The effect of addition of 0.05wt.% to 0.25 wt.% Ca, Zr, Al-FeSi alloy on in-ladle and in-mould inoculation of grey cast irons was investigated. In the present paper, the conclusions drawn are based on thermal analysis. For the solidification pattern, some specific cooling curves characteristics, such as the degree of undercooling at the beginning of eutectic solidification and at the end of solidification, as well as the recalescence level, are identified to be more influenced by the inoculation technique. The degree of eutectic undercooling of the electrically melted base iron having 0.025% S, 0.003% AI and 3.5% Ce is excessively high (39 - 40℃), generating a relatively high need for inoculation. Under these conditions, the in-mould inoculation has a more significant effect compared to ladle inoculation, especially at lower inoculant usage (less than 0.20 wt.%). Generally, the efficiency of 0.05wt.% - 0.15wt.% of alloy for in-mould inoculation is comparable to, or better than, that of 0.15wt.% - 0.25wt.% addition in ladle inoculation procedures. In order to secure stable and controlled processes, representative thermal analysis parameters could be used, especially in thin wall grey iron castings production.     

ZnO nanoparticles supported on mesoporous MCM-41 and SBA-15: a comparative physicochemical and photocatalytic study

A simple solvothermal impregnation method was used to prepare ZnO nanoparticles supported on MCM-41 and SBA-15. X-ray powder diffraction, N₂ adsorption–desorption, Electron Probe Micro Analysis (EPMA), and UV–vis spectroscopy were used to characterize the prepared materials. The influence of the ZnO loading of different supports on the structural characteristics and the photocatalytic activity toward degradation of methylene blue in water under ultraviolet irradiation were investigated. Wide angle X-ray diffraction and UV–vis Diffuse Reflectance confirmed the existence of ZnO phase. A much smaller influence of impregnation with ethanolic zinc salt solution on the porosity was observed for SBA-15 compared with MCM-41. Finally, the adsorption and photocatalytic activity of the ZnO/mesoporous materials depend on porous characteristics of the support materials.     

Friction reduction in rolling bearing by using polymer additives

The friction torque on the outer ring of a tapered roller bearing has been experimentally measured for a mineral oil (base oil), as well as for samples of the base oil additived with low‐density polyethylene. The data show an important reduction of friction by introducing the polymer into the base oil due to the film formed by the adsorption of macromolecular coils on the solid surface. The effectiveness of macromolecular additive contribution to friction behaviour is described in terms of polymer efficiency, which shows maximum values at low polymer concentrations. Copyright © 2009 John Wiley & Sons, Ltd.     

Enhanced Bio-Electrochemical Reduction of Carbon Dioxide by Using Neutral Red as a Redox Mediator

Microbial electrosynthetic cells containing Methylobacterium extorquens were studied for the reduction of CO₂ to formate by direct electron injection and redox mediator-assisted approaches, with CO₂ as the sole carbon source. The formation of a biofilm on a carbon felt (CF) electrode was achieved while applying a constant potential of −0.75 V versus Ag/AgCl under CO₂-saturated conditions. During the biofilm growth period, continuous H₂ evolution was observed. The long-term performance for CO₂ reduction of the biofilm with and without neutral red as a redox mediator was studied by an applied potential of −0.75 V versus Ag/AgCl. The neutral red was introduced into the systems in two different ways: homogeneous (dissolved in solution) and heterogeneous (electropolymerized onto the working electrode). The heterogeneous approach was investigated in the microbial system, for the first time, where the CF working electrode was coated with poly(neutral red) by the oxidative electropolymerization thereof. The formation of poly(neutral red) was characterized by spectroscopic techniques. During long-term electrolysis up to 17 weeks, the formation of formate was observed continuously with an average Faradaic efficiency of 4 %. With the contribution of neutral red, higher formate accumulation was observed. Moreover, the microbial electrosynthetic cell was characterized by means of electrochemical impedance spectroscopy to obtain more information on the CO₂ reduction mechanism.