Immobilization of silver nanoparticles on polyethylene terephthalate

Two different procedures of grafting with silver nanoparticles (AgNP) of polyethylene terephthalate (PET), activated by plasma treatment, are studied. In the first procedure, the PET foil was grafted with biphenyl-4,4′-dithiol and subsequently with silver nanoparticles. In the second one, the PET foil was grafted with silver nanoparticles previously coated with the same dithiol. X-ray photoelectron spectroscopy and electrokinetic analysis were used for characterization of the polymer surface at different modification steps. Silver nanoparticles were characterized by ultraviolet-visible spectroscopy and by transmission electron microscopy (TEM). The first procedure was found to be more effective. It was proved that the dithiol was chemically bonded to the surface of the plasma-activated PET and that it mediates subsequent grafting of the silver nanoparticles. AgNP previously coated by dithiol bonded to the PET surface much less.     

Effect of severe plastic deformation on creep behaviour of a Ti–6Al–4V alloy

This paper examines the effect of severe plastic deformation on creep behaviour of a Ti–6Al–4V alloy. The processed material with an ultrafine-grained (UFG) structure (d ≈ 150 nm) was prepared by multiaxial forging. Uniaxial constant stress compression and constant load tensile creep tests were performed at 648–698 K and at stresses ranging between 300 and 600 MPa on the UFG processed alloy and, for comparison purposes, on its coarse-grained (CG) state. The values of the stress exponents of the minimum creep rate n and creep activation energy Q _c were determined. Creep behaviour was also investigated by nanoindentation method at room temperature under constant load. The microstructure was examined by transmission electron microscopy and scanning electron microscope equipped with an electron back scatter diffraction unit. The results of the uniaxial creep tests showed that the minimum creep rates of the UFG specimens are significantly higher in comparison with those of the CG state. However, the differences in the minimum creep rates of both states of alloy strongly decrease with increasing values of applied stress. The CG alloy exhibits better creep resistance than the UFG one over the stress range used; the minimum creep rate for the UFG alloy is about one to two orders of magnitude higher than that of the CG alloy. The indentation creep tests showed that annealing had little effect on the creep behaviour in UFG Ti alloy at room temperature.     

Atomistic simulations of dislocations and defects

This paper reviews selected recent research on the atomistic simulation of dislocation and defect properties of materials relevant to the multiscale modeling of plasticity and strength, with special emphasis on bcc metals and including work at extreme conditions. Current topics discussed include elasticity and ideal strength, dislocation structure and mobility, grain boundaries, point defects, and rapid resolidification, as well as noteworthy examples of research that directly impacts the issue of linking of length and/or time scales, as required in multiscale materials modeling. The work reviewed has been inspired by the recent international Workshop on Multiscale Modeling of Materials Strength and Failure held in October 2001 at Bodega Bay, California. This revised version was published online in June 2006 with corrections to the Cover Date.     

A Study of the Flow through Capillary Tubes Tuned for a Cooling Circuit with Saturated Fluorocarbon Refrigerants

Capillary tube expansion devices are widely used in refrigeration equipment; nevertheless, the mechanism of the flow is still not fully described and understood, so the experimental verification of most predictions is still necessary. A modified numerical model of capillary flow has been developed both for standard refrigerants and with emphasis for saturated fluorocarbon (C₂F_2n+2) refrigerants. These refrigerants have several unique properties (high dielectric performance, chemical stability, and radiation resistance). Therefore, they can be used in some special applications, where other common fluids cannot be applied. The main aim of this study was to prepare a practical capillary flow model, which would improve the procedure of predicting the behavior of capillary tubes for cooling circuits of particle detectors being built at the international CERN laboratory in Geneva. The generated numerical model was verified through available data from the literature and also via measurements performed in a real cooling circuit with pure, oil-free octafluoropropane (C₃F₈) refrigerant. Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.     

Ionic liquids and proteases: a clean alliance for semisynthesis

Herein we present the first report on protease-catalysed ligation of cleavage-sensitive peptide and protein fragments in ionic-liquid-containing solvent systems. By applying the newly established [MMIM][Me2PO4]/buffer mixture as a reaction medium, significant advantages over purely aqueous or conventional organic solvent-containing media could be identified, including in particular the use of active wild-type proteases as biocatalysts, the suppression of any competitive proteolytic side reactions, the high turnover rates compared to classical organic solvents and the high stability of chemically labile reactants.     

Creep in an electrodeposited nickel

This paper reports the experimental results on the creep behavior of electrodeposited ultrafine-grained nickel and its particle-reinforced nanocomposite. The objective of this research was to further improve the knowledge of the creep behavior of monolithic nickel and to explore the role of nano-sized SiO₂ particles in the potential creep strengthening of electrodeposited Ni nanocomposite. The creep behavior and microstructure of the pure ultrafine-grained nickel and its nanocomposite reinforced by 2 vol% nano-sized SiO₂ particles were studied at temperatures in the range from 293 to 573 K and at the applied tensile stresses between 100 and 800 MPa. The results indicate that the creep resistance of the nanocomposite may be noticeably improved compared to the monolithic nickel due to the interaction of the particles with dislocation motion. It was found that the applied stress interval can be divided into lower and higher stress intervals corresponding to dislocation (power-law) and exponential creep regions, respectively. Analysis of the creep data leads to the suggestion that the creep behavior of both electrodeposited nickel and its nanocomposite in power-law region may be grain boundary controlled. However, the mechanism responsible for the observed creep behavior at lower temperatures and the highest stresses is still not well established.     

Ermittlung der Warmrißanfälligkeit von Stählen beim Schweißen

Verfahren zur Kennzeichnung der Warmrißanfälligkeit von Stählen beim Schweißen. Warmzugversuche bei 400°C bis über 1390°C an einem Nickel-Chrom-Molybdän-Vanadin-Vergütungsstahl mit 0,22%C, 0,41%Mn, 1,10% Cr, 0,44% Mo und 2,80% Ni sowie dem zugehörigen Schweißgut. Ursachen der Warmrißbildung bei Temperaturen oberhalb 1380°C sowie bei 600 bis 100°C. Entmischungsrisse, Risse an Versetzungsreihen und ausscheidungsinduzierte Risse. Hinweise zur Vermeidung von Warmrissen beim Schweißen.     

Some results on sensitivity and robust stability of input-output systems governed by integral and differential equations

We consider input-output systems (not necessarily of feedback type) on the time domain [0, ) which are governed by nonlinear vector integral or differential equations that relate the input and the output. Assuming that these equations depend on a parameterA, describing perturbations, which is allowed to vary in a vicinity of a nominal valueA ₀ in a linear space, we study how strongly the output is affected by changes of (a)A ₀ when the input is fixed (insensitivity), and (b) the input whenA is fixed withA A ₀ being not too large (robust stability).The results are based on the theory of input-output systems over abstract extended spaces given in Parts I and II of [3]. We discuss nominal systems described by nonlinear Volterra and differential equations, and consider two types of possible perturbations. We also prove a simple result on systems governed by singular differential equations whose perturbations can change the order of the system.