Eigenvalues of Two Parameter Polynomial Operator Pencils of Waveguide Type

The spectral structure of two parameter unbounded operator pencils of waveguide type is studied. Theorems on discreteness of the spectrum for a fixed parameter are proved. Variational principles for real eigenvalues in some parts of the root zones are established. In the case of n = 1 (quadratic pencils) domains containing the spectrum are described (see Fig. 1–3). Conditions in the definition of the pencils of waveguide type arise naturally from physical problems and each of them has a physical meaning. In particular a connection between the energetic stability condition and a perturbation problem for the coefficients is given.     

The Mechanism of Photochemical Release of Nitric Oxide from S-Nitrosoglutathione

Abstract— Laser flash photolysis of S-nitroso complexes of glutathione (GSNO) and bovine serum albumin (BSANO) via excitation at 355 nm has been used to investigate the photogeneration of nitric oxide (NO) and subsequent radical reactions. In the case of GSNO, liberation of NO was confirmed by its oxidation of oxyhemoglobin to met hemoglobin. Initial NO release is via homolytic cleavage of the S-N bond to produce the glutathione thiyl radical, GS, which can subsequently react with (a) ground-state GSNO (k= 1.7 × 10⁹M^?1/i> s^?1) to yield additional NO and oxidized glutathione, GSSG; and (b) oxygen (k= 3.0 × 10⁹M^?1 s^?1) to give the glutathione peroxy radical, GSOO, which subsequently reacts with ground-state GSNO (k= 3.8 × 10⁸M^?1 s^?1), also producing additional NO and GSSG. The relative concentrations of oxygen and GSNO in the system determine the major pathway for removal of G'. These secondary reactions occur at such high rates that they preclude radical recombination under low-intensity irradiation conditions. The quantum yield of overall loss of GSNO thus varies with both GSNO and oxygen concentrations; a value of 0.66 was determined for an aerated solution of GSNO (0.86 mM). In the case of GSNO, therefore, generation of NO is not due solely to homolysis of the S-N bond; secondary reactions of the radicals formed lead to further NO liberation. In rationalizing the known phototoxicity of GSNO, possible contributions from thiyl and thiyl-derived radicals should be considered. In contrast to GSNO, direct excitation of BSANO (containing one bound NO group per molecule) led to photodecomposition with a quantum yield of 0.09 but no evidence was obtained for liberation of NO into the bulk medium.     

Modeling of asymmetric membrane formation by dry-casting method

Many polymeric membranes are produced by phase inversion technique invented by Loeb and Sourirajan in 1962. The dry-casting method is one of the major phase inversion techniques in which a homogeneous polymer solution consisting of solvent(s) and nonsolvent(s) is cast on a support and then evaporation of the casting solution takes place under convective conditions. In this paper, we model membrane formation by the dry-casting method. The model takes into account film shrinkage, evaporative cooling, coupled heat, and mass transfer and incorporates practical and reliable diffusion theory as well as complex boundary conditions especially at the polymer solution/air interface. The predictions from the model provide composition paths, temperature, and thickness of the solution. By plotting the composition paths on the ternary phase diagram, we ascertain the general structural characteristics of the membranes prepared from particular casting conditions. The predictive ability of the model was evaluated by comparing the results with the experimental data obtained from gravimetric measurements for cellulose acetate (CA)–acetone–water system. In an attempt to illustrate the importance of diffusion formalism on the predictions, recently proposed multicomponent diffusion theory and its simplified forms were utilized in the model. The computational results show that the critical factor for capturing the accurate behavior of membrane formation is the diffusion formalism utilized in the model.     

Hydrolytic polycondensation of alkoxysilanes and modification of polymerization reactions

Polymers having oxide network chains are produced by hydrolytic polycondensation of metal alkoxides and alkoxysilanes. Molecular morphology and molecular size distribution of these inorganic polymers are strongly affected by certain nonchemical parameters. Included among these parameters is the molecular separation of interacting species during the polymerization. There is strong evidence that the molecular size expansion occurs by two distinct processes: initially by a gradual “growth” process, and later by “recombination” of high-molecular weight species. The later process often leads to a bi-modal molecular size distribution. The concentration of water-rich siloxane solutions leads to significant molecular size expansion by further oxide network formation. No similar polymer size growth occurs during the concentration of alcohol based solutions. This difference in the polymeric activities can be related to the difference in the terminal bond under the two different conditions.     

Recognition-induced transformation of microspheres into vesicles: morphology and size control

Polystyrene functionalized with diamidopyridine (DAP) recognition units self-assembles in nonpolar media to form thermally reversible micrometer-scale spherical aggregates. The size and the thermal stability of these microspheres can be controlled by the molecular weight of the polymer. The addition of thymine-functionalized polymer to these self-assembled microspheres converted them into vesicular aggregates with a controlled size. The morphology change was reversible: the addition of DAP-functionalized polymer converted the vesicles back to microspheres.     

Hydrophobic cryogels for DNA adsorption: Effect of embedding of monosize microbeads into cryogel network on their adsorptive performances

As alternative hydrophobic adsorbent for DNA adsorption, supermacroporous cryogel disks were synthesized via free radical polymerization. In this study, we have prepared two kinds of cryogel disks: (i) poly(2‐hydroxyethyl methacrylate‐N‐methacryloyl‐l ‐tryptophan) [p(HEMA‐MATrp)] cryogel containing specific hydrophobic ligand MATrp; and (ii) monosize p(HEMA‐MATrp) particles synthesized via suspension polymerization embedded into p(HEMA) cryogel structure to obtain p(HEMA‐MATrp)/p(HEMA) composite cryogel disks. These cryogel disks containing hydrophobic functional group were characterized via swelling studies, Fourier transform infrared spectroscopy, elemental analysis, surface area measurements and scanning electron microscopy. DNA adsorption onto both p(HEMA‐MATrp) cryogel and p(HEMA‐MATrp)/p(HEMA) composite cryogels was investigated. Maximum adsorption of DNA on p(HEMA‐MATrp) cryogel was found to be 15 mg/g polymer. Otherwise, p(HEMA‐MATrp)/p(HEMA) composite cryogels significantly increased the DNA adsorption capacity to 38 mg/g polymer. Composite cryogels could be used repeatedly without significant loss on adsorption capacity after 10 repetitive adsorption–desorption cycles. Copyright © 2013 John Wiley & Sons, Ltd.     

Natural and artificial radioactivity levels of greenhouse soils and relations with soil properties

Journal of Radioanalytical and Nuclear Chemistry - In this study, natural (226Ra, 232Th, 40K) and artificial (137Cs) radionuclide activity concentration levels of 63 greenhouse soils collected from...     

Heavy Metal Removal from Synthetic Solutions with Magnetic Beads Under Magnetic Field

The aim of this study is to prepare magnetic beads which can be used for the removal of heavy metal ions from synthetic solutions. Magnetic poly(ethylene glycol dimethacrylate‐vinyl imidazole) [m‐poly(EGDMA‐VIM)] beads were produced by suspension polymerization in the presence of magnetite Fe₃O₄ nano‐powder. The specific surface area of the m‐poly(EGDMA‐VIM) beads was found to be 63.1 m²/g with a size range of 150–200 µm in diameter and the swelling ratio was 85%. The average Fe₃O₄ content of the resulting m‐poly(EGDMA‐VIM) beads was 12.4%. The maximum binding capacities of the m‐poly(EGDMA‐VIM) beads were 32.4 mg/g for Cu²⁺, 45.8 mg/g for Zn²⁺, 84.2 mg/g for Cd²⁺and 134.5 mg/g for Pb²⁺. The affinity order on mass basis is Pb²⁺>Cd²⁺>Zn²⁺>Cu²⁺. Equilibrium data agreed well with the Langmuir model. pH significantly affected the binding capacity of the magnetic beads. Binding of heavy metal ions from synthetic wastewater was also studied. The binding capacities were 26.2 mg/g for Cu²⁺, 33.7 mg/g for Zn²⁺, 54.7 mg/g for Cd²⁺ and 108.4 mg/g for Pb²⁺. The magnetic beads could be regenerated up to about 97% by treating with 0.1 M HNO₃. These features make m‐poly(EGDMA‐VIM) beads a potential candidate for support of heavy metal removal under magnetic field.