Microstructure and its relationship to deformation processes in amorphous polymer glasses

The microdeformation morphology of a number of vinyl polymers with bulky side chains (type I) and arylene polymers with flexible oxygen linkages (type II) was studied by electron microscopy. The polyarylenes crazed only near the glass transition while the polyvinyls exhibited a crazing regime that extended to liquid nitrogen temperatures. In addition significantly less plastic strain was localized in type II glass crazes relative to those in type I glasses. In compatible blends of polystyrene (PS) and 2,6-dimethyl poly(phenylene oxide) (2MPPO), ca. 30% 2MPPO was sufficient to induce a transition from type I to type II crazing behavior. Small amounts of PS suppressed the low-temperature 2MPPO β relaxation but enhanced the intermediate transition of 2MPPO at higher temperatures. Blending increased the conformational energy of the 2MPPO chain and improved interchain packing. The propensity for the polymer glass to form sharp shear bands at the expense of diffuse bands was increased by a decrease in the conformation energy of the polymer chain and an improvement in the glassy state packing.     

Influence of chitosan characteristics on coagulation and flocculation of organic suspensions

Several samples of chitosan with different degrees of deacetylation and of different molecular weights were tested for the coagulation–flocculation of organic suspensions. Organic suspensions were prepared by mixing mushroom powder with tap water. Experiments were carried out at pH 5, pH 7, and pH 9. Because decreasing the pH reduced the amount of chitosan required to reach the required turbidity, at pH 9, a high concentration of chitosan was required to achieve the required treatment levels, whereas the difference was less significant between pH 7 and pH 5 (the required concentration of chitosan was halved). Though viscosity, correlated to the molecular weight of chitosan, affected treatment performance, its influence on the efficiency of coagulation–flocculation could be substantially reduced by slightly increasing the concentration of the polymer. This is of importance in the processing of industrial effluents: the aging of a chitosan solution, which may cause partial depolymerization, and loss of viscosity, will have a limited impact on process efficiency. The degree of deacetylation also has a limited effect on treatment performance, especially when the degree of deacetylation exceeds 90%. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2070–2079, 2005     

Alcohol-induced changes of {beta}-lactoglobulin - retinol-binding stoichiometry

It has been demonstrated using CD that ethanol induces importantsecondary structure changes of ß-lactoglobulin. CDspectra indicate that ß-lactoglobulin secondary structure,which is mainly composed of ß-strands, becomes mostly-helical under the influence of the solvent polarity changes.The midpoint of ß-strand/-helix transition in ß-lactoglobulinis observed at dielectric constant {small tilde}60 (35% ethanol;v/v). According to CD measurements, the ethanol-dependent secondarystructure changes are reversible. The alkylation of lysines-NH₂ in ß-lactoglobulin weakens the central ß-barrelstructure, since the ß-strand/-helix transition midpointof alkylated ß-lactoglobulin is shifted to lower ethanolconcentration (25% ethanol; v/v). ß-Lactoglobulinstructural changes are triggering the dissociation of the ß-lactoglobulin- retinol complex as judged from complete quenching of its fluorescencein ethanol concentration >30% (v/v). However, in 20% ethanol(v/v), ß-lactoglobulin still retains most of its nativesecondary structure as shown by CD and, in this condition, oneß-lactoglobulin molecule binds an additional secondretinol molecule. This suggests that the highly populated speciesobserved around 20% ethanol (v/v) might represent an intermediatestate able to bind two molecules of retinol.     

Synthesis, characterization, and catalytic properties of polysiloxanes with pendant 4-(3-pyridinyl)butyl and 4-(1-oxypyridin-3-yl)butyl groups

New silane monomers with the pendant 4-(3-pyridine)butyl group have been synthesized by hydrosilation of 3-(3-butenyl)pyridine with Me _n Si(OEt)_3-n H (n=0, 1) using a platinum catalyst. Only -addition products were observed. The products were characterized by elemental analysis, infrared,¹H- and¹³C-NMR spectroscopy, and gas chromatography-mass spectrometry. Hydrolysis-polycondensation of the difunctional monomer with a basic catalyst, Me₄NOH, gave a mixture of cyclic oligomers, principally cyclic tetramer, and linear homopolymer. Under similar reaction conditions, the trifunctional monomer gave crosslinked material which was soluble in common organic solvents. The linear homopolymer and crosslinked polymer were trimethylsilyl end-blocked with hexamethyldisilazane. The cyclic and end-blocked polymers were characterized by elemental analysis and spectroscopic methods. Molecular weights of the polymers were obtained by end-group analysis using¹H-NMR spectral data, size exclusion chromatography, and direct insertion-probe mass spectrometry. The cyclic, linear, and crosslinked materials were N-oxidized withm-chloroperoxybenzoic acid and characterized by spectroscopic methods. The polymeric N-oxide derivatives were shown to be effective transacylation catalysts in the synthesis of mixed carboxylic acid anhydrides in immiscible solvents (H₂O/CH₂Cl₂) under phase-transfer conditions. The implications of the results on the mechanism of catalysis are discussed.     

Retrograde Densification of Calcined and Glass Precursors of Approximate (Bi,Pb)2Sr2Ca2Cu3O10 Stoichiometry

Retrograde densification of pelletized calcines and glasses having an approximate (Bi,Pb)₂Sr₂Ca₂Cu₃O₁₀ starting stoichiometry and sintered at ∼850°C can be described by first-order rate equations. Retrograde densification in the calcine precursors was largely due to the development of open pores, and was approximately proportional to the concentration of the (Bi,Pb)₂Sr₂CaCu₃O₁₀ phase. In the glasses, retrograde densification is mainly caused by porosity accompanying the growth of a needlelike Sr─Ca─Cu─O phase, together with (Bi,Pb)₂Sr₂Ca₂Cu₃O₁₀ and (Bi,Pb)₂Sr₂CaCu₂O₈.     

Response to walnut olfactory and visual cues by the parasitic wasp Diachasmimorpha juglandis

Diachasmimorpha juglandis is a specialist parasitoid attacking fly larvae in the genus Rhagoletis that feed exclusively on walnut fruit husks. In a free-foraging assay comparing response to uninfested, infested, and mechanically damaged fruits, we first determined that D. juglandis use host feeding damage on the fruit as a cue for host presence. In another free-foraging assay that used artificial walnut models and wind tunnel experiments, D. juglandis distinguished infested from uninfested fruits by using either olfactory or visual cues separately. However, the response rate of wasps in the wind tunnel was raised considerably when visual cues were also available. We analyzed the volatile compounds emitted by cohorts of uninfested, mechanically damaged, and infested fruits 1, 3, 5, 8, and 10 days after oviposition by flies into the infested fruits. Total volatile emissions did not differ significantly among treatments, but quantitative changes in volatiles distinguished infested fruits from uninfested and damaged fruits. The fact that parasitoids did not distinguish between infested and damaged fruits in assays where damage was visible indicates that they rely on visual cues when those are available.     

The Effects of Power Law Fluid Rheology on Coil Heat Transfer for Agitated Vessel in the Transitional Flow Regime

A CFD model of heat transfer from power‐law fluids to helical cooling coils in the transitional flow regime of a baffled tank mixed with a pitched blade turbine was developed with Fluent^TM. The model captured local temperature and velocity gradients. Simulations were run, varying Re, Pr, K and n. The results indicate that a Sieder‐Tate type correlation, with the exponent on and the coefficient in front of the Reynolds number being a function of n, is recommended for estimating ho. Also, a new two coil bank design was found to be more efficient when 450 < Re < 650.     

A scalable solution to the nearest neighbor search problem through local-search methods on neighbor graphs

Pattern Analysis and Applications - Nearest neighbor search is a powerful abstraction for data access; however, data indexing is troublesome even for approximate indexes. For intrinsically...     

Flocking of Multi-agent Systems with Unknown Nonlinear Dynamics and Heterogeneous Virtual Leader

This paper investigates the flocking control of multi-agent systems with unknown nonlinear dynamics while the virtual leader information is heterogeneous. The uncertain nonlinearity in the virtual leader information is considered, and the weaker constraint on the velocity information measurements is assumed. In addition, a bounded assumption on the unknown nonlinear dynamics is also considered. It is weaker than the Lipschitz condition adopted in the most flocking control methods. To avoid fragmentation, we construct a new potential function based on the penalty idea when the initial network is disconnected. A dynamical control law including a adjust parameter is designed to achieve the stable flocking. It is proven that the velocities of all agents approach to consensus and no collision happens between the mobile agents. Finally, several simulations verify the effectiveness of the new design, and indicate that the proposed method has high convergence and the broader applicability in practical applications with more stringent restrictions.

     

An investigation of phase transformation behavior in sputter-deposited PtMn thin films

Sputter-deposited, equiatomic PtMn thin films have application in giant magnetoresistive spin valves, tunneling magnetoresistive spin valves, and magnetic random access memory. However, the as-deposited films are found to be a disordered A1 phase in a paramagnetic state rather than an antiferromagnetic phase with L1₀ structure, which is needed for device operation. Therefore, a postannealing step is required to induce the phase transformation from the asdeposited A1 face-centered-cubic phase to the antiferromagnetic L1₀ phase. The A1 to L1₀ metastable transformation was studied by x-ray diffraction and differential-scanning calorimetry. An exothermic transformation enthalpy of −12.1 kJ/mol of atoms was determined. The transformation kinetics were simulated using the Johnson-Mehl-Avrami analysis.