RAFT-mediated emulsion polymerization of styrene using a non-ionic surfactant

We report the successful RAFT-mediated emulsion polymerization of styrene using a non-ionic surfactant (Brij98), the highly reactive 1-phenylethyl phenyldithioacetate (PEPDTA) RAFT agent, and water-soluble initiator ammonium persulfate (APS). The molar ratio of RAFT agent to APS was identical in all experiments. Most of the monomer was contained within the micelles, analogous to microemulsion or miniemulsion systems but without the need of shear, sonication, cosurfactant, or a hydrophobe. The number-average molecular weight increased with conversion and the polydispersity index was below 1.2. This ideal 'living' behavior was only found when molecular weights of 9000 and below were targeted. It was postulated that the rapid transportation of RAFT agent from the monomer swollen micelles to the growing particles was fast on the polymerization timescale, and most if not all the RAFT agent is consumed within the first 10% conversion. In addition, it was postulated that the high nucleation rate from the high rate of exit ( of the R radical from the RAFT agent) and high entry rate from water-phase radicals ( high APS concentration) reduced the effects of 'superswelling' and therefore a similar molar ratio of RAFT agent to monomer was maintained in all growing particles. The high polydispersity indexes found when targeting molecular weights greater than 9000 were postulated to be due to the lower nucleation rate from the lower weight fractions of both APS and RAFT agent. In these cases, 'superswelling' played a dominant role leading to a heterogeneous distribution of RAFT to monomer ratios among the particles nucleated at different times.

Cloud-point extraction and preconcentration of cyanobacterial toxins (microcystins) from natural waters using a cationic surfactant

A new cloud-point extraction and preconcentration method, using a cationic, surfactant, Aliquat-336 (tricaprylyl-methy;ammonium chloride), his-been developed for the determination of cyanobacterial toxins, microcystins, in natural waters. Sodium sulfate was used to induce phase separation at 25 degreesC. The phase behavior of Aliquat-336 with respect to concentration of Na2SO4 was studied. The cloud-point system revealed a very high phase volume ratio compared to other established systems of nonionic, anionic, and cationic surfactants: At pH 6-7, it showed an outstanding selectivity in ahalyte extraction for anionic species. Only MC-LR and MC-YR, which are known to be predominantly anionic, were extracted (with averaged recoveries of 113.9 +/- 9% and 87.1 +/- 7%, respectively). MC-RR, which is likely to be amphoteric at the above pH range, was. not cle tectable in.the extract. Coupled to HPLC/UV separation and detection, the cloud-point extraction method (with 2.5 mM Aliquat-336 and 75 mM Na2SO4 at 25 degreesC) offered detection limits of 150 +/- 7 and 470 +/- 72 pg/mL for MC-LR and MC-YR, respectively, in 25 mL of deionized water. Repeatability of the method was 7.6% for MC-LR and 7.3% for MC-YR: The cloud-point extraction process can be. completed within 10-15 min with no cleanup steps required. Applicability of the new method to the determination of microcystins in real samples was demonstrated using natural surface waters, collected from a local river and a local duck pond spiked with realistic. concentrations of microcystins. Effects of salinity and organic matter (TOC) content in the water sample on the extraction efficiency were also studied.

Explaining point variability in the eastern Victoria river region, northern territory

This paper constructs a reduction sequence model for north Australian points from the eastern Victoria River region, and identifies a single continuum linking unifacial and bifacial point forms, with some divergence from this single reduction trajectory dependent upon artefact size. Chronological changes in reduction intensity between 5,000BP and the present are found to coincide with typological variation in points as well as changing emphasis on the extendibility of point reduction. It is suggested that changes in the extendibility of point reduction can be linked to intensified ENSO-driven climatic variability in the late Holocene that likely increased economic risk and warranted a substantial technological response, including the use of retouched toolkits with potential for longer use-lives.

Application of heterogeneous vacancy solution theory to characterization of microporous solids

The vacancy solution theory of adsorption is re-formulated here through the mass-action law, and placed in a convenient framework permitting the development of thermodynamic ally consistent isotherms. It is shown that both the multisite Langmuir model and the classical vacancy solution theory expression are special cases of the more general approach when the Flory-Huggins activity coefficient model is used, with the former being the thermodynamically consistent result. The improved vacancy solution theory approach is further extended here to heterogeneous adsorbents by considering the pore-width dependent potential along with a pore size distribution. However, application of the model to numerous hydrocarbons as well as other adsorptives on microporous activated carbons shows that the multisite model has difficulty in the presence of a pore size distribution, because pores of different sizes can have different numbers of adsorbed layers and therefore different site occupancies. On the other hand, use of the classical vacancy solution theory expression for the local isotherm leads to good simultaneous fit of the data, while yielding a site diameter of about 0.257 nm, consistent with that expected for the potential well in aromatic rings on carbon pore surfaces. It is argued that the classical approach is successful because the Flory-Huggins term effectively represents adsorbate interactions in disguise. When used together with the ideal adsorbed solution theory the heterogeneous vacancy solution theory successfully predicts binary adsorption equilibria, and is found to perform better than the multisite Langmuir as well as the heterogeneous Langmuir model. (C) 2001 Elsevier Science Ltd. All rights reserved.

Gray's model of personality and aggregate level factor analysis

Previous research shows that correlations tend to increase in magnitude when individuals are aggregated across groups. This suggests that uncorrelated constellations of personality variables (such as the primary scales of Extraversion and Neuroticism) may display much higher correlations in aggregate factor analysis. We hypothesize and report that individual level factor analysis can be explained in terms of Giant Three (or Big Five) descriptions of personality, whereas aggregate level factor analysis can be explained in terms of Gray's physiological based model. Although alternative interpretations exist, aggregate level factor analysis may correctly identify the basis of an individual's personality as a result of better reliability of measures due to aggregation. We discuss the implications of this form of analysis in terms of construct validity, personality theory, and its applicability in general. Copyright (C) 2003 John Wiley Sons, Ltd.

HPGR model verification and scale-up

This paper summarises test results that were used to validate a model and scale-up procedure of the high pressure grinding roll (HPGR) which was developed at the JKMRC by Morrell et al. [Morrell, Lim, Tondo, David,1996. Modelling the high pressure grinding rolls. In: Mining Technology Conference, pp. 169-176.]. Verification of the model is based on results from four data sets that describe the performance of three industrial scale units fitted with both studded and smooth roll surfaces. The industrial units are currently in operation within the diamond mining industry and are represented by De Beers, BHP Billiton and Rio Tinto. Ore samples from the De Beers and BHP Billiton operations were sent to the JKMRC for ore characterisation and HPGR laboratory-scale tests. Rio Tinto contributed an historical data set of tests completed during a previous research project. The results conclude that the modelling of the HPGR process has matured to a point where the model may be used to evaluate new and to optimise existing comminution circuits. The model prediction of product size distribution is good and has been found to be strongly dependent of the characteristics of the material being tested. The prediction of throughput and corresponding power draw (based on throughput) is sensitive to inconsistent gap/diameter ratios observed between laboratory-scale tests and full-scale operations. (C) 2004 Elsevier Ltd. All rights reserved.

The cost of uniqueness in groundwater model calibration

Calibration of a groundwater model requires that hydraulic properties be estimated throughout a model domain. This generally constitutes an underdetermined inverse problem, for which a Solution can only be found when some kind of regularization device is included in the inversion process. Inclusion of regularization in the calibration process can be implicit, for example through the use of zones of constant parameter value, or explicit, for example through solution of a constrained minimization problem in which parameters are made to respect preferred values, or preferred relationships, to the degree necessary for a unique solution to be obtained. The cost of uniqueness is this: no matter which regularization methodology is employed, the inevitable consequence of its use is a loss of detail in the calibrated field. This, ill turn, can lead to erroneous predictions made by a model that is ostensibly well calibrated. Information made available as a by-product of the regularized inversion process allows the reasons for this loss of detail to be better understood. In particular, it is easily demonstrated that the estimated value for an hydraulic property at any point within a model domain is, in fact, a weighted average of the true hydraulic property over a much larger area. This averaging process causes loss of resolution in the estimated field. Where hydraulic conductivity is the hydraulic property being estimated, high averaging weights exist in areas that are strategically disposed with respect to measurement wells, while other areas may contribute very little to the estimated hydraulic conductivity at any point within the model domain, this possibly making the detection of hydraulic conductivity anomalies in these latter areas almost impossible. A study of the post-calibration parameter field covariance matrix allows further insights into the loss of system detail incurred through the calibration process to be gained. A comparison of pre- and post-calibration parameter covariance matrices shows that the latter often possess a much smaller spectral bandwidth than the former. It is also demonstrated that, as all inevitable consequence of the fact that a calibrated model cannot replicate every detail of the true system, model-to-measurement residuals can show a high degree of spatial correlation, a fact which must be taken into account when assessing these residuals either qualitatively, or quantitatively in the exploration of model predictive uncertainty. These principles are demonstrated using a synthetic case in which spatial parameter definition is based oil pilot points, and calibration is Implemented using both zones of piecewise constancy and constrained minimization regularization. (C) 2005 Elsevier Ltd. All rights reserved.

Characterization of activated carbons using liquid phase adsorption

A modification of the Dubinin-Radushkevich pore filling model by incorporation of the repulsive contribution to the pore potential, and of bulk non-ideality, is proposed in this paper for characterization of activated carbon using liquid phase adsorption. For this purpose experiments have been performed using ethyl propionate, ethyl butyrate, and ethyl isovalerate as adsorbates and the microporous-mesoporous activated carbons Filtrasorb 400, Norit ROW 0.8 and Norit ROX 0.8 as adsorbents. The repulsive contribution to the pore potential is incorporated through a Lennard-Jones intermolecular potential model, and the bulk-liquid phase non-ideality through the UNIFAC activity coefficient model. For the characterization of activated carbons, the generalized adsorption isotherm is utilized with a bimodal gamma function as the pore size distribution function. It is found that the model can represent the experimental data very well, and significantly better than when the classical energy-size relationship is used, or when bulk non-ideality is neglected. Excellent agreement between the bimodal gamma pore size distribution and DFT-cum-regularization based pore size distribution is also observed, supporting the validity of the proposed model. (C) 2001 Elsevier Science Ltd. All rights reserved.

Combined hydraulic and biological modelling and full-scale validation of SBR process

The biological reactions during the settling and decant periods of Sequencing Batch Reactors (SBRs) are generally ignored as they are not easily measured or described by modelling approaches. However, important processes are taking place, and in particular when the influent is fed into the bottom of the reactor at the same time (one of the main features of the UniFed process), the inclusion of these stages is crucial for accurate process predictions. Due to the vertical stratification of both liquid and solid components, a one-dimensional hydraulic model is combined with a modified ASM2d biological model to allow the prediction of settling velocity, sludge concentration, soluble components and biological processes during the non-mixed periods of the SBR. The model is calibrated on a full-scale UniFed SBR system with tracer breakthrough tests, depth profiles of particulate and soluble compounds and measurements of the key components during the mixed aerobic period. This model is then validated against results from an independent experimental period with considerably different operating parameters. In both cases, the model is able to accurately predict the stratification and most of the biological reactions occurring in the sludge blanket and the supernatant during the non-mixed periods. Together with a correct description of the mixed aerobic period, a good prediction of the overall SBR performance can be achieved.

Modelling the activated sludge flocculation process combining laser light diffraction particle sizing and population balance modelling (PBM)

A technique based on laser light diffraction is shown to be successful in collecting on-line experimental data. Time series of floc size distributions (FSD) under different shear rates (G) and calcium additions were collected. The steady state mass mean diameter decreased with increasing shear rate G and increased when calcium additions exceeded 8 mg/l. A so-called population balance model (PBM) was used to describe the experimental data, This kind of model describes both aggregation and breakage through birth and death terms. A discretised PBM was used since analytical solutions of the integro-partial differential equations are non-existing. Despite the complexity of the model, only 2 parameters need to be estimated: the aggregation rate and the breakage rate. The model seems, however, to lack flexibility. Also, the description of the floc size distribution (FSD) in time is not accurate.

Quantitative prediction of phase diagrams for polymer partitioning in aqueous two-phase systems

Published polymer distribution data for aqueous poly(ethylene glycol)/dextran mixtures have been reassessed to illustrate the feasibility of their quantitative characterization in terms of the Flory-Huggins theory of polymer thermodynamics. Phase diagrams predicted by this characterization procedure provide better descriptions of the experimental data than those based on an earlier, oversimplified treatment in similar terms. (C) 2003 Wiley Periodicals, Inc.

Deriving matrix of peptide-MHC interactions in diabetic mouse by genetic algorithm

Finding motifs that can elucidate rules that govern peptide binding to medically important receptors is important for screening targets for drugs and vaccines. This paper focuses on elucidation of peptide binding to I-A(g7) molecule of the non-obese diabetic (NOD) mouse - an animal model for insulin-dependent diabetes mellitus (IDDM). A number of proposed motifs that describe peptide binding to I-A(g7) have been proposed. These motifs results from independent experimental studies carried out on small data sets. Testing with multiple data sets showed that each of the motifs at best describes only a subset of the solution space, and these motifs therefore lack generalization ability. This study focuses on seeking a motif with higher generalization ability so that it can predict binders in all A(g7) data sets with high accuracy. A binding score matrix representing peptide binding motif to A(g7) was derived using genetic algorithm (GA). The evolved score matrix significantly outperformed previously reported

Equilibrium swelling measurements of network and semicrystalline polymers in supercritical carbon dioxide using high-pressure NMR

The extent of swelling of cross-linked poly(dimethylsiloxane) and linear low-density poly(ethylene) in supercritical CO2 has been investigated using high-pressure NMR spectroscopy and microscopy. Poly(dimethylsiloxane) was cross-linked to four different cross-link densities and swollen in supercritical CO2. The Flory-Huggins interaction parameter, x, was found to be 0.62 at 300 bar and 45 degrees C, indicating that supercritical CO2 is a relatively poor solvent compared to toluene or benzene. Linear low-density poly(ethylene) was shown to exhibit negligible swelling upon exposure to supercritical CO2 up to 300 bar. The effect Of CO2 pressure on the amorphous region of the poly(ethylene) was investigated by observing changes in the H-1 T-2 relaxation times of the polymer. These relaxation times decreased with increasing pressure, which was attributed to a decrease in mobility of the polymer chains as a result of compressive pressure.

Molecular dynamics characterization of n-octyl-beta-D-glucopyranoside micelle structure in aqueous solution

n-Octyl-beta-D-glueopyranoside (OG) is a non-ionic glycolipid, which is used widely in biotechnical and biochemical applications. All-atom molecular dynamics simulations from two different initial coordinates and velocities in explicit solvent have been performed to characterize the structural behaviour of an OG aggregate at equilibrium conditions. Geometric packing properties determined from the simulations and small angle neutron scattering experiment state that OG micelles are more likely to exist in a non-spherical shape, even at the concentration range near to the critical micelle concentration (0.025 M). Despite few large deviations in the principal moment of inertia ratios, the average micelle shape calculated from both simulations is a prolate ellipsoid. The deviations at these time scales are presumably the temporary shape change of a micelle. However, the size of the micelle and the accessible surface areas were constant during the simulations with the micelle surface being rough and partially elongated. Radial distribution functions computed for the hydroxyl oxygen atoms of an OG show sharper peaks at a minimum van der Waals contact distance than the acetal oxygen, ring oxygen, and anomeric carbon atoms. This result indicates that these atoms are pointed outwards at the hydrophilic/hydrophobic interface, form hydrogen bonds with the water molecules, and thus hydrate the micelle surface effectively. (c) 2005 Elsevier Inc. All rights reserved.