Synthesis and magnetorheological characteristics of ribbon‐like,polypyrrole‐coated carbonyl iron suspensions under oscillatory shear

One of the crucial problems of classical magnetorheological (MR) fluids is their high rate of sedimentation. This disadvantage may be substantially eliminated using core‐shell particles. The aim of this study is to prepare spherical carbonyl iron (CI) particles coated with conducing polymer polypyrrole (PPy) with ribbon‐like morphology. Scanning electron microscopy proved the formation of the ribbon‐like layer onto CI particles while Fourier transform infrared spectroscopy confirmed the chemical structure of PPy. The magnetic properties observed via vibrating sample magnetometer showed decreased magnetization saturation of core‐shell‐structured particles due to the existence of non‐magnetic surface layer. MR measurements performed under oscillatory shear flow as a function of the applied magnetic flux density, temperature, and particle concentration showed that core‐shell particle‐based MR suspension exhibits sufficient MR performance for practical applications. Moreover, the suspension stability is promoted significantly when core‐shell particles are used as a dispersed phase. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Assessment of Flooding Risk to Cultural Heritage in Historic Sites

Fluvial flooding in August 2002 affected a number of structures in the Czech Republic. Considerable damage was observed particularly in the historic city of Prague. Extensive investigations indicated that main observed causes of damage could be classified into geotechnical aspects, inadequate structural properties, and insufficient communication. After the flooding responsible authorities have considered permanent and temporary protective measures to reduce adverse consequences of flooding in the future. Decisions concerning expensive measures should be preferably based on risk optimization, taking into account potential societal and economic consequences and losses of cultural heritage values. General framework of the risk assessment is thus proposed considering specific issues of cultural heritage. Such an assessment needs a theoretical model suitable for predicting flows and extents of future floods. For that reason, the authors statistically analyzed hydrologic data for annual maximum flows of the Vltava River in Prague dating back to 1827. Pearson III and lognormal distributions seem to be suitable models for a considered sample. Estimations of extreme flows, needed for assessment of flooding risk to endangered sites and decisions on protective measures, are provided for different return periods.     

The replacement of the fantasied oedipal child: A disruptive effect of sibling loss on the mother-infant relationship.

Presents the case of a 30-yr-old woman whose sibling had died during adolescence and who experienced her own child, almost 2 decades later, as a replacement for the lost sibling. This process was facilitated by the oedipal meaning of her sibling and by the interference in her family's ability to mourn the death of the child. The case illustrates the manner in which these conflicts were activated during the patient's pregnancy and how they subsequently interfered in the developing mother–infant relationship prior to intervention. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stability of partial difference equations governing control gains in infinite-dimensional backstepping

We examine the stability properties of a class of LTV difference equations on an infinite-dimensional state space that arise in backstepping designs for parabolic PDEs. The nominal system matrix of the difference equation has a special structure: all of its powers have entries that are −1, 0, or 1, and all of the eigenvalues of the matrix are on the unit circle. The difference equation is driven by initial conditions, additive forcing, and a system matrix perturbation, all of which depend on problem data (for example, viscosity and reactivity in the case of a reaction–diffusion equation), and all of which go to zero as the discretization step in the backstepping design goes to zero. All of these observations, combined with the fact that the equation evolves only in a number of steps equal to the dimension of its state space, combined with the discrete Gronwall inequality, establish that the difference equation has bounded solutions. This, in turn, guarantees the existence of a state-feedback gain kernel in the backstepping control law. With this approach we greatly expand, relative to our previous results, the class of parabolic PDEs to which backstepping is applicable.     

Studies on interactions between metmyoglobin and heparin

Butyric acid is released from milk by pre-intestinal lipases during suckling. It is also known to inhibit bacterial growth. To investigate whether butyric acid may be a significant factor in controlling bacterial growth in the stomach of pre-weaned animals, the ability of butyric acid to inhibit growth of selected bacteria was tested over physiological ranges of pH and butyric acid concentrations. Six enteric and environmental strains of bacteria were used: two strains of Escherichia coli, Klebsiella pneumoniae, Enterococcus faecium, Enterococcus faecalis, and Enterococcus casseliflavus. At pH 4.5 and 5.0, the growth of all organisms was significantly inhibited in the presence of butyrate, and in some cases growth was completely arrested. At pH 6.0, butyric acid did not affect bacterial growth until the concentration reached 40 mM. The maximum concentration of butyric acid available in cow's milk after incubation with pre-gastric lipase is approximately 16 mM, which would be sufficient to prevent growth of the organisms tested at pH values occurring in the stomach. Therefore, butyric acid inhibition of bacterial growth may explain in part, the role of pre-intestinal lipases in young animals' natural defenses against bacteria in ingested food prior to weaning.     

Polyaniline nanotubes: conditions of formation

The courses of aniline oxidation with ammonium peroxydisulfate in aqueous solutions of strong (sulfuric) and in weak (acetic) acids, followed by temperature and acidity changes, are different. In solutions of sulfuric acid, granular polyaniline (PANI) was produced; in solutions of acetic acid, PANI nanotubes were obtained. The external diameter of the nanotubes was 100–300 nm, the internal cavity 20–100 nm, and the length extended to several micrometres. The morphology of PANI, granular or tubular, depends on the acidity conditions during the reaction rather than on the chemical nature of the acid. PANI nanotubes were also produced when aniline was oxidized in the absence of any acid. The bulk conductivity of PANI prepared in solutions of acetic acid was 0.08–0.27 S cm^?1, depending on the acid concentration. Protonated PANI prepared in sulfuric and acetic acids were deprotonated with ammonium hydroxide to obtain PANI bases and the ammonium salt of the protonating acid. FTIR spectroscopy showed the differences in the molecular structure of the PANI bases. Irrespective of whether the polymerization was performed in solutions of sulfuric or acetic acid, PANI had hydrogen sulfate counter‐ions only. The PANI morphology is thus not controlled by the nature of counter‐ions. The acidity of the reaction medium determines the protonation of monomer, oligomer and polymer species. The chemistry of aniline oxidation is likely to be affected especially by the protonation of an intermediate in the pernigraniline form. It is proposed that, in the course of aniline oxidation, pH‐dependent self‐assembly of aniline oligomers predetermines the final PANI morphology. Copyright © 2005 Society of Chemical Industry     

Diffusion of One‐ and Two‐Component Fluids into Polymeric Membranes

The starting point of this paper is a model of the non‐Fickian diffusion of a simple fluid into a polymeric medium that has been introduced in El Afif and Grmela (2002). The model is extended to a mixture consisting of two simple fluids and one polymeric medium. The effects of the polymeric medium on diffusion are included in the formulations through the use of relative momenta playing the role of internal variables. In ternary mixtures, new phenomena arise due to cross‐coupling effects. As a consequence, the single diffusion Deborah number in binary mixtures becomes a 2 × 2 matrix in ternary mixtures. Two specific examples for which experimental data are available are investigated in detail.     

Influence of Oxygen Content on Formation of Yttrium α-SiAlON Ceramics

Low porosity α- and β-SiAION composite material was prepared when the powder mixture intended for preparation of yttrium α-SiAlON, with the formula Y_0.4Si_12–m+n Al_m+nO_nN_16–n, was attritor milled in isopropyl alcohol or contained excess oxygen (n > 0.6). The region of stability of single-phase yttrium α-SiAlON was smaller at lower temperatures. Wet milling (in isopropyl alcohol) of AIN powder was found to introduce excess oxygen into the milled powder.     

Effect of the directional crystallization on microstructure of Ti46Al-5Nb-1W

Ti-Al based intermetallic alloys are promising for various applications in aerospace and automobile industry. Their favorable properties, such as low density and good corrosion resistance, are accompanied on the other hand by low toughness and very difficult metallurgy. One of the possibilities to improve the toughness of Ti-46Al-5Nb-1W (,, at. fraction) alloy consists in change of their microstructure into lamellar microstructure, which can be reached moreover by directional crystallization. This experiment is described in this paper. Samples of the Ti-46Al-5Nb-1W (,, at. fraction) alloy prepared by plasma and vacuum-induction metallurgy were subjected to directional crystallization. Cooling rates were constant and ranged from 5.56 × 10-6 m/s to 1.18 × 10 -4 m/s. Directional crystallization has been accomplished in ceramic tubes made of corundum-Al2O3. The samples were studied by metallographic and chemical analysis.Lamellar microstructure of the samples was found to consist of α2- and γ-phase lamellas. Moreover, ceramic particles Al2O3 were found to be present in the samples. Distribution of the alloying elements in the samples was homogenous.     

Fluorescent Nanodiamonds Embedded in Biocompatible Translucent Shells

High pressure high temperature (HPHT) nanodiamonds (NDs) represent extremely promising materials for construction of fluorescent nanoprobes and nanosensors. However, some properties of bare NDs limit their direct use in these applications: they precipitate in biological solutions, only a limited set of bio‐orthogonal conjugation techniques is available and the accessible material is greatly polydisperse in shape. In this work, we encapsulate bright 30‐nm fluorescent nanodiamonds (FNDs) in 10–20‐nm thick translucent (i.e., not altering FND fluorescence) silica shells, yielding monodisperse near‐spherical particles of mean diameter 66 nm. High yield modification of the shells with PEG chains stabilizes the particles in ionic solutions, making them applicable in biological environments. We further modify the opposite ends of PEG chains with fluorescent dyes or vectoring peptide using click chemistry. High conversion of this bio‐orthogonal coupling yielded circa 2000 dye or peptide molecules on a single FND. We demonstrate the superior properties of these particles by in vitro interaction with human prostate cancer cells: while bare nanodiamonds strongly aggregate in the buffer and adsorb onto the cell membrane, the shell encapsulated NDs do not adsorb nonspecifically and they penetrate inside the cells.