A mathematical model for pollution in a river and its remediation by aeration

We present a simple mathematical model for river pollution and investigate the effect of aeration on the degradation of pollutant. The model consists of a pair of coupled reaction–diffusion–advection equations for the pollutant and dissolved oxygen concentrations, respectively. The coupling of these equations occurs because of reactions between oxygen and pollutant to produce harmless compounds. Here we consider the steady-state case in one spatial dimension. For simplified cases the model is solved analytically. We also present a numerical approach to the solution in the general case. The extension to the transient spatial model is relatively straightforward. The study is motivated by the crucial problem of water pollution in many countries and specifically within the Tha Chin River in Thailand. For such real situations, simple models can provide decision support for planning restrictions to be imposed on farming and urban practices.     

Outputs and time lags for linear bioreactors

Linear systems of convection reaction-diffusion equations for bioreactors are shown to have a structure which allows a geometric factorization of steady state problems giving a significant reduction in their dimensionality. Moreover, convection dominated linear systems with quasisymmetric reaction terms may be further simplified by matrix transformations, which uncouple the differential equations. The boundary conditions are also uncoupled when the diagonal diffusivity matrix D governing diffusion in the bioparticle is a scalar multiple of the corresponding matrix H describing the diffusivity characteristic of the fluid boundary layers around the bioparticles. The dominant transient behaviour of the systems may be handled by establishing an analogous system of time independent equations for mean action time variables and higher moments. These equations have the same amenable structure. Outputs, time lags and various mean residence and first passage times, associated with establishing steady outputs from a concentration free initial state, can be expressed in terms of the steady state solutions and mean action time variables.     

Turbulent free convection heat transfer to power-law fluids from arbitrary geometric configurations

The problem of turbulent free convection heat transfer from curved surfaces to non-Newtonian power-law fluids has been investigated using the Nakayama-Koyama solution methodology. The scheme is designed to deal with bodies of arbitrary geometric configurations and hence can be viewed as a generalized version of the Shenoy-Mashelkar approach for turbulent free convection heat transfer from a flat vertical plate to a power-law fluid. The surface wall temperature is allowed to vary in the streamwise direction in an arbitrary fashion, and calculations are carried out for the turbulent free convection about the horizontal circular cylinder and sphere for illustrative purposes. Available theoretical and experimental data have been compared with the predictions of the present analysis and the comparison of results has been found to be reasonably good.     

Dactylospongiaquinone, a new meroterpenoid from the Australian marine sponge Dactylospongia n. sp.

Chemical investigation of the sponge Dactylospongia n. sp. collected near Mooloolaba, S.E. Queensland, has led to the isolation of dactylospongiaquinone (7) together with the known quinones (2-5). The new metabolite 7 possesses a different carbon framework from the known dictyoceratidaquinone (9) and is suggested to possess a cis-fused ring junction by extensive NOESY studies combined with molecular modelling calculations. The relative stereochemistry of the previously described cyclospongiaquinone-1 (3) and dehydrocyclospongiaquinone-1 (4) is also assigned on the basis of NOESY analyses. Full NMR spectroscopic assignments are provided for all compounds.     

Inhibitory Effects of Erythrosine/Curcumin Derivatives/Nano-Titanium Dioxide-Mediated Photodynamic Therapy on Candida albicans

This study focuses on the role of photosensitizers in photodynamic therapy. The photosensitizers were prepared in combinations of 110/220 µM erythrosine and/or 10/20 µM demethoxy/bisdemethoxy curcumin with/without 10% (w/w) nano-titanium dioxide. Irradiation was performed with a dental blue light in the 395–480 nm wavelength range, with a power density of 3200 mW/cm² and yield of 72 J/cm². The production of ROS and hydroxyl radical was investigated using an electron paramagnetic resonance spectrometer for each individual photosensitizer or in photosensitizer combinations. Subsequently, a PrestoBlue^® toxicity test of the gingival fibroblast cells was performed at 6 and 24 h on the eight highest ROS-generating photosensitizers containing curcumin derivatives and erythrosine 220 µM. Finally, the antifungal ability of 22 test photosensitizers, Candida albicans (ATCC 10231), were cultured in biofilm form at 37 °C for 48 h, then the colonies were counted in colony-forming units (CFU/mL) via the drop plate technique, and then the log reduction was calculated. The results showed that at 48 h the test photosensitizers could simultaneously produce both ROS types. All test photosensitizers demonstrated no toxicity on the fibroblast cells. In total, 18 test photosensitizers were able to inhibit Candida albicans similarly to nystatin. Conclusively, 20 µM bisdemethoxy curcumin + 220 µM erythrosine + 10% (w/w) nano-titanium dioxide exerted the highest inhibitory effect on Candida albicans.     

EFFECT OF USING DISPERSANTS DURING THE MIXING OF AGGREGATES WITH POLYMER-MODIFIED ASPHALTS: A CASE STUDY FOR NOVOPHALT

The present work explores the use of dispersants in lowering the viscosity of asphalt mastics. The study includes the use of three different types of dispersants during the mixing of fine aggregates with one specific type of polymer-modified asphalt, namely, Novophalt that has been selected for a case study. The effect of the dispersants on the selection of the mixing temperature is elucidated. A distinction is made between a lubricant and a dispersant by observing the Theological behavior of the aggregate-asphalt systems under different conditions. It is also shown that stearic acid which acts more like a lubricant has the potential to lower compaction temperatures during the paving of roads.     

Determination of aqueous acid‐dissociation constants of aspartic acid using PCM/DFT method

Determination of acid‐dissociation constants, pK_a, of aspartic acid in aqueous solution, using density functional theory calculations combined with the conductor‐like polarizable continuum model (CPCM) and with integral‐equation‐formalism polarizable continuum model (IEFPCM) based on the UAKS and UAHF radii, was carried out. The computed pK_a values derived from the CPCM and IEFPCM with UAKS cavity model of bare structures of the B3LYP/6‐31+G(d,p)‐optimized tetrahydrated structures of aspartic acid species are mostly close to the experimental pK_a values. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008