Soft Matter in a Tight Spot: Nanorheology of Confined Liquids and Block Copolymers

The linear frequency-dependent shear rheology and force–distance profiles of molecularly-thin fluids of very different structure were contrasted: a globular molecule octamethylcyclotetrasiloxane (OMCTS), branched alkanes (3-methylundecane and squalane), and a polymer brush in near-theta solution (polystyrene-polyvinylpyridine). In each case the data suggest a prolongation of the longest relaxation time (τ₁) with increasing compression. At frequencies ω > 1/τ₁ the shear response was “solid-like”, but at ω < 1/τ₁ it was “liquid-like”. OMCTS under mild compression exhibited seeming power-law viscoelastic behavior with G′(ω) = G″(ω) over a wide frequency range. Of the branched-molecule fluids, 3-methylundecane exhibited oscillatory force–distance profiles; this confirms prior computer simulations. But squalane (6 pendant methyl groups in an alkane chain 24 carbons long) showed one sole broad attractive minimum. Polymer brushes in a near-theta solvent exhibited changes qualitatively similar to those OMCTS, in particular, a smooth progression of longest relaxation time, generating a transition from “liquid-like” to “solid-like” shear rheology with decreasing film thickness. The common trend of shear response in these systems, in spite of important differences in molecular structure and force–distance profiles, is emphasized.     

Design criteria for functional data bases

A functional data base is characterized as a collection of functions and its language as a collection of operators. The data base design criteria are established in terms of the functional properties, “redundancy” and “semantic content”. The behavior of data base operators is analyzed under these criteria to detect redundancies and compute the semantic content of a data model, to evaluate and compare data models. The correspondence between these criteria and the relational normalization theory is established.     

Information markets over trust networks

Information markets are inefficient. Information products have large upfront development costs, yet their duplication costs are negligibly small; and they are experience goods with high costs of marketing and promotion. As a result, either winner-take-all markets are created through large and expensive promotional campaigns, or artificial monopoly power is conferred by the government through copyright protection, or both, to prevent the collapse of these markets from intense price competition and piracy. Such inefficiency creates opportunities to design more efficient markets by utilizing new technologies. Trust networks provide such an opportunity where the network infrastructure acts not only as a distribution system for information products, but also as an advertising and promotion medium, a payment and pricing mechanism, a guarantee and insurance service, and a copyright enforcement and dispute resolution tool. Such a network-centric market place is proposed to remedy many of the shortcomings of mass markets by relying on peer-to-peer distribution, peer-to-peer payments, and peer-to-peer enforcement of trust and integrity. Analytical models are presented to show that such a market place for information goods can scale up to satisfy large markets without expensive promotions and advertising campaigns, create customized products with dynamic pricing, reduce entry costs by eliminating the distinction between buyers and sellers, and eliminate the need for copyright protection.     

Removal of hexavalent chromium anions via polymer enhanced ultrafiltration using a fully ionized polyelectrolyte

A fully ionized polyelectrolyte was synthesized for Cr(VI) removal from aqueous solutions by continuous polymer enhanced ultrafiltration (PEUF). Effect of operating parameters such as pH, loading, polymer, and competing ion concentrations were examined. Highest Cr(VI) retention was obtained at a loading of 0.01 at pH 4. Increasing both polymer and chromate concentrations at a fixed loading of 0.01 decreased the retention which demonstrated the effect of crowding. In the presence of competing anions such as chloride and sulfate, Cr(VI) retention decreased for all of the pH values studied. Even at high competing anion concentrations, significant retentions of Cr (VI) were obtained.     

Stochastic elastic–plastic finite elements

A computational framework has been developed for simulations of the behavior of solids and structures made of stochastic elastic–plastic materials. Uncertain elastic–plastic material properties are modeled as random fields, which appear as the coefficient term in the governing partial differential equation of mechanics. A spectral stochastic elastic–plastic finite element method with Fokker–Planck–Kolmogorov equation based probabilistic constitutive integrator is proposed for solution of this non-linear (elastic–plastic) partial differential equation with stochastic coefficient. To this end, the random field material properties are discretized, in both spatial and stochastic dimension, into finite numbers of independent basic random variables, using Karhunen–Loève expansion. Those random variables are then propagated through the elastic–plastic constitutive rate equation using Fokker–Planck–Kolmogorov equation approach, to obtain the evolutionary material properties, as the material plastifies. The unknown displacement (solution) random field is then assembled - using polynomial chaos - as a function of known basic random variables and unknown deterministic coefficients, which are obtained by minimizing the error of finite representation, by Galerkin technique.     

Voltammetric behavior of nicotine at pencil graphite electrode and its enhancement determination in the presence of anionic surfactant

The electrochemical oxidation of nicotine was studied in aqueous as well as micellar media at a pencil graphite electrode using cyclic, differential pulse and square-wave voltammetric techniques. The compound was oxidized irreversibly at low positive potentials in one (in acidic and neutral media) or two (in alkaline media) oxidation steps. The response was evaluated with respect to pH, scan rate, addition of surfactant and other variables. For analytical purposes, very resolved voltammetric peaks at +0.84 V (versus Ag/AgCl) were obtained in phosphate buffer at pH 7.0 containing 2 mM sodium dodecylsulfate using square-wave mode. The process could be used to determine nicotine concentrations in the range of 7.6–107.5 μM with a detection limit of 2.0 μM (0.33 mg L⁻¹). The proposed method was applied to the determination of nicotine in different brands of commercial cigarettes.     

Influences of sex and seasons on levels of heavy metals in tissues of green tiger shrimp (Penaeus semisulcatus de Hann, 1844)

Seasonal changes in heavy metal (Ag, Cr, Ni, Pb, Cu, Fe, Zn) concentrations in muscle, gill, hepatopancreas and gonad tissues of both male and female green tiger shrimp (Penaeus semisulcatus) from Iskenderun Bay (Northern East Mediterranean Sea, Turkey) were measured for a year period by using ICP-AES. The relationships in various heavy metal concentrations in organs were compared according to sex and seasons. Heavy metal content varied with type of metals, seasons and sex. Accumulations also differed significantly in certain organs. Metal concentrations (as μg g⁻¹ w.w.) were highest in male gonads whereas lowest in the muscle of all shrimp species. From the human consumption point of view, heavy metal concentrations except for copper in male and female green tiger shrimp’s muscle were below the admissible limits. Thus, precautions should be taken on account of higher content of heavy metals as well as in other organs that could be affected by industrial pollution.     

Synthesis and characterization of thiophene functionalized polystyrene copolymers and their electrochemical properties

Thiophene functionalized polystyrene samples (TFPS) were synthesized by atom transfer radical polymerization (ATRP) of styrene, followed by Suzuki coupling with 3‐thiophene (Th) boronic acid. Conducting graft polymer of TFPS with thiophene was achieved at 1.5 V in tetrabutylammonium tetrafluoroborate/dichloromethane (TBAFB/DM) by electrochemical methods. Spectroelectrochemical analysis of the resulting copolymers [P(TFPS‐co‐Th)] reflected electronic transitions at 449, 721 and 880 nm, revealing π ? π* transition, polaron and bipolaron band formation, respectively. We also successfully established the utilization of dual type complementary colored polymer electrochromic devices using P(TFPS‐co‐Th)/poly(3,4‐ethylenedioxythiophene (PEDOT) in sandwich configuration. The switching ability, stability and optical memory of the electrochromic device were investigated by UV–visible spectrophotometry and cyclic voltammetry. Device switches between brown and blue color with a switching time of 1.3 s were prepared with optical contrast (%ΔT) of 25 %. Copyright © 2005 Society of Chemical Industry     

3D Modeling of Ripping Process

Due to environmental constraints and limitations on blasting, ripping as a ground loosening and breaking method has become more popular than drilling and blasting method in both mining and civil engineering applications. The best way of estimating the rippability of rocks is to conduct direct ripping runs in the field. However, it is not possible to conduct direct ripping runs in all sites using different dozer types. Therefore, the utilization of numerical modeling of ripping systems becomes unavoidable. A complex ripping system can better be understood with three-dimensional (3D) models rather than two-dimensional models. In this study, 3D distinct element program called 3DEC was used to investigate the ripping process. First, the ripping mechanisms were investigated and then the individual factors that affect the rippability performance of dozers were reviewed. The rippabilities of rocks depend not only on the rock properties, but also machine or dozer properties. Thus, ripper production and rock rippability with D8 type of dozers were also determined by direct ripping runs on different open pit lignite mines within the scope of this research. Production values obtained from numerical modeling were compared with field production values obtained from the case studies. This comparison shows that the model gives consistent and adequate results. Hence, a link has been established between the field results and the 3D models.     

Microstructure evolution of Al–Si alloys under shear loading

In this paper, an attempt is made to predict the microstructure evolution in Al–Si alloy two-dimensional (2D) system under shear loading conditions. The importance of damage accumulation events in delamination wear is studied. The conducted molecular dynamics (MD) simulations are based on the Modified Embedded Atom Method (MEAM). As a result a cohesive zone type of model relating the shear stress and the shear displacement has been suggested.