The Stabilization of Metal Oxide Nanocrystals by the Addition of Alumina

A problem in the study of nanoparticles is that they will tend to grow at moderate temperatures. For example, most oxides (e.g. SnO₂, ZrO₂, MgO) will show significant grain growth at 400°C. This severely limits experimental studies that require measurements over an extensive temperature range. In this contribution we demonstrate that the incorporation of A1₂O₃, can significantly restrict grain growth in MgO and ZrO₂ even at high temperatures.     

Bacterial bioluminescence, bioelectromagnetics and function

The biological functions of light emission in bacterial bioluminescence are not always obvious, especially if the bacteria are in a free-living mode. Experimental evidence suggests that light emission confers benefit to the bacteria themselves such as through photoreactivation and involves as much as 20% of cell energy metabolism. A theoretical model shows if the effect is mediated solely by light then cells should be luminescent at both high and low cell densities, therefore raising doubt over the photoreactivation hypothesis and suggesting that another cofactor is involved. It has been postulated that bioelectromagnetics may be involved in biological processes and be involved with coordinated activity in quorate cells. The cell densities associated with autoinduction coincide with a large change in coupling efficiency in the millimeter and submillimeter spectral region. In this paper it is suggested that one function of bioluminescence is as a pump, involving millimeter and submillimeter wave coupling that is of benefit to the quorum. This may be related to the observation that millimeter wave radiation exposure has been reported to induce changes in DNA conformation and possibly gene expression. Agents that change DNA conformation in bioluminescent bacteria can cause increases in light emission. This work may have implications for electromagnetic fields as quorum-quenching agents.     

On a model for the Navier–Stokes equations using magnetization variables

It is known that in a classical setting, the Navier–Stokes equations can be reformulated in terms of so-called magnetization variables w that satisfy

(1)${?}_{t}w+(\mathbb{P}w?\mathrm{?})w+{(\mathrm{?}\mathbb{P}w)}^{?}w?\mathrm{\Delta }w=0,$

and relate to the velocity u via a Leray projection $u=\mathbb{P}w$. We will prove the equivalence of these formulations in the setting of weak solutions that are also in $L^{\infty }(0,T;H^{1/2})\cap L^2(0,T;H^{3/2})$ on the 3-dimensional torus.Our main focus is the proof of global well-posedness in $H^{1/2}$ for a new variant of (1), where $\mathbb{P}w$ is replaced by w in the second nonlinear term:

(2)${?}_{t}w+(\mathbb{P}w?\mathrm{?})w+\frac{1}{2}\mathrm{?}|w{|}^2?\mathrm{\Delta }w=0.$

This is based on a maximum principle, analogous to a similar property of the Burgers equations.     

Water-Soluble Polyelectrolytes with Ability to Remove Arsenic

Arsenic species can be removed from aqueous solutions using the liquid-phase polymer-based retention, LPR, technique. The LPR technique removes ionic species by functional groups of water-soluble polyelectrolytes (WSP) and then using a ultrafiltration membrane that does not let them pass through the membrane, thus separating them from the solution. The ability of WSP with groups (R)₄N⁺X⁻ to remove arsenate ions using LPR was studied. The interaction and arsenate anion retention capacity depended on: pH, the quaternary ammonium group's counter ion, and the ratio polymer: As(V), using different concentrations of As(V). Water-soluble polychelates were also used for one-step retention of As(III) in solution. The complex of poly(acrylic acid)-Sn, 10 and 20 wt-% of metal gave a high retention of As(III) species at pH 8, although the molar ratio polychelate: As(III) was 400:1. The enrichment method was used to determine the maximum retention capacity (C) for arsenate anions in aqueous solutions at pH 8. In similar conditions, the values of C were 142 mg g⁻¹ for P(ClAETA) and 75 mg g⁻¹ for P(SAETA). The combined treatment of arsenic aqueous solutions by electrocatalytic oxidation (EO) to convert the species of As(III) to As(V) with the LPR technique quantitatively removed arsenic.     

Numerical convergence properties of option pricing PDEs with uncertain volatility

The pricing equations derived from uncertain volatility modelsin finance are often cast in the form of nonlinear partial differentialequations. Implicit timestepping leads to a set of nonlinearalgebraic equations which must be solved at each timestep. Tosolve these equations, an iterative approach is employed. Inthis paper, we prove the convergence of a particular iterativescheme for one factor uncertain volatility models. We also demonstratehow non-monotone discretization schemes (such as standard Crank–Nicolsontimestepping) can converge to incorrect solutions, or lead toinstability. Numerical examples are provided.     

CrystalGrower: a generic computer program for Monte Carlo modelling of crystal growth

A Monte Carlo crystal growth simulation tool, CrystalGrower, is described which is able to simultaneously model both the crystal habit and nanoscopic surface topography of any crystal structure under conditions of variable supersaturation or at equilibrium. This tool has been developed in order to permit the rapid simulation of crystal surface maps generated by scanning probe microscopies in combination with overall crystal habit. As the simulation is based upon a coarse graining at the nanoscopic level features such as crystal rounding at low supersaturation or undersaturation conditions are also faithfully reproduced. CrystalGrower permits the incorporation of screw dislocations with arbitrary Burgers vectors and also the investigation of internal point defects in crystals. The effect of growth modifiers can be addressed by selective poisoning of specific growth sites. The tool is designed for those interested in understanding and controlling the outcome of crystal growth through a deeper comprehension of the key controlling experimental parameters.

Generic in silico methodology – CrystalGrower – for simulating crystal habit and nanoscopic surface topology to determine crystallisation free energies.     

Kinetic theory derivation of the transport coefficients of stochastic rotation dynamics

We use a kinetic theory approach to derive the continuum Navier-Stokes and heat conduction equations for stochastic rotation dynamics, a particle based algorithm for simulating a fluid. Hence we obtain expressions for the viscosity and thermal conductivity in two and three dimensions. The predictions are tested numerically and good agreement is found.     

Synthesis,characterization, and polychelatogenic properties of poly(acrylic acid-co-acrylamide)

The radical copolymerization of acrylic acid with acrylamide was carried out at different monomer ratios in solution (DMF) at 60°C. The corresponding homopolymers were also synthesized to compare their metal ion binding abilities. All the copolymers were characterized by elemental analysis. The metal ion binding properties of these water-soluble polymers with Cu(II), Co(II), Ni(II), Cd(II), Zn(II), Pb(II), Hg(II), Fe(III), and Cr(III) ions were investigated in aqueous solution using the Liquid-Phase Polymer-Based Retention (LPR) technique. Poly(acrylic acid-co-acrylamide) showed a higher retention compared to the homopolymers for all the metal ions except of Hg(II), which was not retained. Besides, the retention of Cd(II) is higher than that an addition of the retention of both homopolymers. It may be attributed to a synergic effect. Maximum capacity for Cu(II) at pH 5.0 was determined to be 1 mmol g⁻¹ (63.5 mg g⁻¹). © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2461–2467, 1997     

Pattern formation in binary fluids confined between rough, chemically heterogeneous surfaces

Using a mesoscale model for hydrodynamics, we simulate driven flow of AB binary fluids past surfaces that contain well-defined roughness or asperities. The geometry and wetting properties of the asperities are found to have a dramatic effect on the flow patterns. We isolate conditions where the A fluid forms vertical bands that bridge the asperities and an imposed shear (or pressure gradient) drives the system to form monodisperse droplets of A within the B fluid. The size of the droplets can be tailored by varying the morphology of the asperities. The surfaces needed to create this rich dynamical behavior are used as the stamps in microcontact printing; thus, the parameter space can readily be accessed experimentally, and the predictions suggest an efficient method for forming emulsions with well-controlled morphologies.