Molecular Hydrogen Emission from Protoplanetary Disks: Effects of X-ray Irradiation and Dust Evolution

Detailed models for the density and temperature profiles of gas and dust in protoplanetary disks are constructed by taking into account X-ray and UV irradiation from a central T Tauri star, as well as dust size growth and settling toward the disk midplane. The spatial and size distributions of dust grains are numerically computed by solving the coagulation equation for settling dust particles, with the result that the mass and total surface area of dust grains per unit volume of the gas in the disks are very small, except at the midplane. The H2 level populations and line emission are calculated using the derived physical structure of the disks. X-ray irradiation is the dominant heating source of the gas in the inner disk and in the surface layer, while the UV heating dominates otherwise. If the central star has strong X-ray and weak UV radiation, the H2 level populations are controlled by X-ray pumping, and the X-rayinduced transition lines could be observable. If the UV irradiation is strong, the level populations are controlled by thermal collisions or UV pumping, depending on the dust properties. As the dust particles evolve in the disks, the gas temperature at the disk surface drops because the grain photoelectric heating becomes less efficient. This makes the level populations change from LTE to non-LTE distributions, which results in changes to the line ratios. Our results suggest that dust evolution in protoplanetary disks could be observable through the H2 line ratios. The emission lines are strong from disks irradiated by strong UV and X-rays and possessing small dust grains; such disks will be good targets in which to observe H2 emission.

Low-frequency electrical response to microbial induced sulfide precipitation

We investigated the sensitivity of low-frequency electrical measurements to microbe-induced metal sulfide precipitation. Three identical sand-packed monitoring columns were used; a geochemical column, an electrical column and a control column. In the first experiment, continuous upward flow of nutrients and metals in solution was established in each column. Cells of Desulfovibrio vulgaris (D. vulgaris) were injected into the center of the geochemical and electrical columns. Geochemical sampling and post-experiment destructive analysis showed that microbial induced sulfate reduction led to metal precipitation on bacteria cells, forming motile biominerals. Precipitation initially occurred in the injection zone, followed by chemotactic migration of D. vulgaris and ultimate accumulation around the nutrient source at the column base. Results from this experiment conducted with metals show (1) polarization anomalies, up to 14 mrad, develop at the bacteria injection and final accumulation areas, (2) the onset of polarization increase occurs concurrently with the onset of lactate consumption, (3) polarization profiles are similar to calculated profiles of the rate of lactate consumption, and (4) temporal changes in polarization and conduction correlate with a geometrical rearrangement of metal-coated bacterial cells. In a second experiment, the same biogeochemical conditions were established except that no metals were added to the flow solution. Polarization anomalies were absent when the experiment was replicated without metals in solution. We therefore attribute the polarization increase observed in the first experiment to a metal-fluid interfacial mechanism that develops as metal sulfides precipitate onto microbial cells and form biominerals. Temporal changes in polarization and conductivity reflect changes in (1) the amount of metal-fluid interfacial area, and (2) the amount of electronic conduction resulting from microbial growth, chemotactic movement and final coagulation. This polarization is correlated with the rate of microbial activity inferred from the lactate concentration gradient, probably via a common total metal surface area effect.

The application of calcined natural dolomitic rock as a solid base catalyst in triglyceride transesterification for biodiesel synthesis

Natural dolomitic rock has been investigated in the transesterification of C-4 and C-8 triglycerides and olive oil with a view to determining its viability as a solid base catalyst for use in biodiesel synthesis. XRD reveals that the dolomitic rock comprised 77% dolomite and 23% magnesian calcite. The generation of basic sites requires calcination at 900 degrees C, which increases the surface area and transforms the mineral into MgO nanocrystallites dispersed over CaO particles. Calcined dolomitic rock exhibits high activity towards the liquid phase transesterification of glyceryl tributyrate and trioctanoate, and even olive oil, with methanol for biodiesel production.

Preparation and characterisation of supported L(a0.)8Sr(0.2)MnO(3+x)

Three supported La0.8Sr0.2MnO3+x catalysts were prepared, one supported on lanthanum-stabilised alumina and two supported on a NiAl2O4 spinel. The catalysts were characterised using X-ray diffraction, transmission electron microscopy and surface area measurements following heat-treatments at temperatures up to 1200 degreesC in air. In the alumina-supported catalyst, a reaction occurred between the active phase and the support at high temperatures, indicating that these materials would be unsuitable for high temperature catalytic combustion. Only in the NiAl2O4-supported catalysts were the supported perovskite phases found to be stable at high temperature. These catalysts showed good methane combustion activity. (C) 2001 Elsevier Science B.V. All rights reserved.

The removal of dyes from textile wastewater: a study of the physical characteristics and adsorption mechanisms of diatomaceous earth

The feasibility of using diatomite for the removal of the problematic reactive dyes as well as basic dyes from textile wastewater was investigated. Methylene blue, Cibacron reactive black and reactive yellow dyes were considered. Physical characteristics of diatomite such as pH(solution), pH(ZPC), surface area, Fourier transform infrared, and scanning electron microscopy were investigated. The surface area of diatomite was found to be 27.80 m(2) g(-1) and the pH(ZPC) occurred around pH of 5.4. The results indicated that the surface charge of diatomite decreased as the pH of the solution increased with the maximum methylene blue removal from aqueous solution occurring at basic pH of around (1011). Adsorption isotherms of diatomite with methylene blue, hydrolysed reactive black and yellow dyes were constructed at different pH values, initial dye concentrations and particle sizes. The experimental results were fitted to the Langmuir, Freundlich, and Henry models. The study indicated that electrostatic interactions play an important role in the adsorption of dyes onto diatomite. A model of the adsorption mechanism of methylene blue onto diatomite is proposed. (C) 2003 Elsevier Ltd. All rights reserved.

The preparation and properties of coprecipitated Cu-Zr-Y and Cu-Zr-La catalysts used for the steam reforming of methanol

A series of Cu-zirconia catalysts containing various additives (Y2O3, La2O3, Al2O3 and CeO2) have been prepared by coprecipitation and their activities and stabilities under operating conditions have been obtained for the steam reforming of methanol. It has been found that an yttria-promoted catalyst containing 30 mol% Cu and 20 mol% of Y2O3 is not only very active but is also very stable under reaction conditions. The yttria appears to stabilise a high copper surface area and may also have a slight promotional effect on the copper. The results obtained with this material compare very favourably with data for the best catalysts reported in the literature. (C) 2007 Published by Elsevier B.V.

Modification of chitin properties for enzymatic deacetylation

Chitins produced via a conventional chemical route as well as from a new biological process were modified to increase the efficiency of enzymatic deacetylation reactions for the production of novel biological chitosan. These modified chitins were reacted for 24h with extracellular fungal enzymes from Colletotrichum lindemuthianum. The chemical and physical properties of the various substrates were analysed and their properties related to the effectiveness in the deacetylation reaction. Modifications of the chitins affected the degree of deacetylation with varied effects. Without further modification to reduce crystallinity and to open up the solid substrate structure, the chitins were found to be poor substrates for the heterogeneous solid-liquid enzymatic catalysis. It was found that the solvent and drying method used in modifying the chitins had significant impact on the final efficiency of the enzymatic deacetylation reaction. The most successful modifications through freeze drying of a colloidal chitin suspension increased the degree of enzymatic deacetylation by 20 fold. These processes reduce the crystallinity of the chitin making it easier for the enzymes to access their internal structure. X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and BET isotherm analysis are employed to characterise the modified chitins to ascertain the degree of crystallinity, porous structure, surface area, and morphology.

Paracetamol-Loaded Poly(ε-caprolactone) Layered Silicate Nanocomposites

The work described in this paper demonstrates a combined novel approach to the preparation of drug loaded poly(e-caprolactone) layered silicate nanocomposites using hot melt extrusion, a continuous process in contrast to the normal batch type processing used to prepare polymeric drug delivery systems, and most significantly the use of high surface area, large aspect ratio inorganic nanoplatelets to retard drug release. The methodology and results described in this article are significant and could equally be applied to the controlled/retarded release of any bio-active molecule (pharmaceutical, nutraceutical, protein, DNA/iRNA, anti-microbial, anti-coagulant, etc.) from biopolymers and the production of medical devices from such composite materials.

Population pharmacokinetic and pharmacogenetic analysis of 6-mercaptopurine in paediatric patients with acute lymphoblastic leukaemia

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT center dot The cytotoxic effects of 6-mercaptopurine (6-MP) were found to be due to drug-derived intracellular metabolites (mainly 6-thioguanine nucleotides and to some extent 6-methylmercaptopurine nucleotides) rather than the drug itself. center dot Current empirical dosing methods for oral 6-MP result in highly variable drug and metabolite concentrations and hence variability in treatment outcome. WHAT THIS STUDY ADDS center dot The first population pharmacokinetic model has been developed for 6-MP active metabolites in paediatric patients with acute lymphoblastic leukaemia and the potential demographic and genetically controlled factors that could lead to interpatient pharmacokinetic variability among this population have been assessed. center dot The model shows a large reduction in interindividual variability of pharmacokinetic parameters when body surface area and thiopurine methyltransferase polymorphism are incorporated into the model as covariates. center dot The developed model offers a more rational dosing approach for 6-MP than the traditional empirical method (based on body surface area) through combining it with pharmacogenetically guided dosing based on thiopurine methyltransferase genotype. To investigate the population pharmacokinetics of 6-mercaptopurine (6-MP) active metabolites in paediatric patients with acute lymphoblastic leukaemia (ALL) and examine the effects of various genetic polymorphisms on the disposition of these metabolites. Data were collected prospectively from 19 paediatric patients with ALL (n = 75 samples, 150 concentrations) who received 6-MP maintenance chemotherapy (titrated to a target dose of 75 mg m(-2) day(-1)). All patients were genotyped for polymorphisms in three enzymes involved in 6-MP metabolism. Population pharmacokinetic analysis was performed with the nonlinear mixed effects modelling program (nonmem) to determine the population mean parameter estimate of clearance for the active metabolites. The developed model revealed considerable interindividual variability (IIV) in the clearance of 6-MP active metabolites [6-thioguanine nucleotides (6-TGNs) and 6-methylmercaptopurine nucleotides (6-mMPNs)]. Body surface area explained a significant part of 6-TGNs clearance IIV when incorporated in the model (IIV reduced from 69.9 to 29.3%). The most influential covariate examined, however, was thiopurine methyltransferase (TPMT) genotype, which resulted in the greatest reduction in the model's objective function (P

SERS enhancement by aggregated Au colloids: effect of particle size

Aggregated Au colloids have been widely used as SERS enhancing media for many years but to date there has been no systematic investigation of the effect of the particle size on the enhancements given by simple aggregated Au colloid solutions. Previous systematic studies on isolated particles in solution or multiple particles deposited onto surfaces reported widely different optimum particle sizes for the same excitation wavelength and also disagreed on the extent to which surface plasmon absorption spectra were a good predictor of enhancement factors. In this work the spectroscopic properties of a range of samples of monodisperse Au colloids with diameters ranging from 21 to 146 nm have been investigated in solution. The UV/visible absorption spectra of the colloids show complex changes as a function of aggregating salt (MgSO4) concentration which diminish when the colloid is fully aggregated. Under these conditions, the relative SERS enhancements provided by the variously sized colloids vary very significantly across the size range. The largest signals in the raw data are observed for 46 nm colloids but correction for the total surface area available to generate enhancement shows that particles with 74 nm diameter give the largest enhancement per unit surface area. The observed enhancements do not correlate with absorbance at the excitation wavelength but the large differences between differently sized colloids demonstrate that even in the randomly aggregated particle assemblies studied here, inhomogeneous broadening does not mask the underlying changes due to differences in particle diameter.

Liquid marble formation using hydrophobic powders

This work aims to investigate and quantitatively measure “liquid marble” phenomena using hydrophobic powders (granules). The hydrophobic powders based on a copper substrate were prepared by a silver deposition technique of particle sizes 9 µm, 20 µm and 320 µm and of contact angle with water approaching 160°. The hydrophobic powder poly-methylmethacralate (PMMA) particle size 42 µm and contact angle of 120° was also used to determine the effect of powder density on liquid marble stability. The experimental investigations indicated that for successful formation of liquid marbles a number of variables in addition to hydrophobicity need to be considered, namely: powder density; powder particle size; powder shape; liquid marble formation technique. It was found that liquid marbles were formed using all four powders to varying extents, with a low powder particle size forming more stable liquid marbles. In a series of gravimetric tests, adhered powder mass on liquid marbles was found to be directly proportional to the water droplet surface area. A more complete coverage of the water drops were found with PMMA powder than the hydrophobic granules. Moreover, a further procedure was developed to increase the mechanical strength of the liquid marble, by polymerising methylmethacrylate (MMA) on the surface of a PMMA powder – liquid marble, with the aim of maintaining water within a more robust PMMA – liquid marble shell. This technique may prove to be a novel way of encapsulating drug compounds, such as gentamicin sulphate, for PMMA bone cement.

Ionic liquids as solvent and solvent additives for the synthesis of sol-gel materials

The ionic liquid (IL) 1-butyl-3-methylimidazolium chloride was used as a drying control chemical additive in the synthesis of silica sol-gel materials with and without methanol as a co-solvent. The resulting gels were characterized by using thermogravimetric analysis, differential scanning calorimetry, infrared spectroscopy and water sorption kinetics. Calcined gels were analyzed using scanning electron microscopy and nitrogen adsorption isotherms for surface area and pore volume determination. Non-calcined gels were monolithic and showed general cloudiness with lesser degrees observed at higher IL volumes. Calcinations resulted in the formation of powders with increased available surface area as the amount of IL volume was increased. This is consistent with an increase in respective pore volume but a general decrease in average pore size. The resulting materials exhibited conventional structural microdomains, in contrast to periodicity reported when other ionic liquids were used as templates.

Wear paths produced by individual hip-replacement patients— A large-scale, long-term follow-up study

Wear particle accumulation is one of the main contributors to osteolysis and implant failure in hip replacements. Altered kinematics produce significant differences in wear rates of hip replacements in simulator studies due to varying degrees of multidirectional motion. Gait analysis data from 153 hip-replacement patients 10-years post-operation were used to model two- and three-dimensional wear paths for each patient. Wear paths were quantified in two dimensions using aspect ratios and in three dimensions using the surface areas of the wear paths, with wear-path surface area correlating poorly with aspect ratio. The average aspect ratio of the patients wear paths was 3.97 (standard deviation ¼ 1.38), ranging from 2.13 to 10.86. Sixty percent of patients displayed aspect ratios between 2.50 and 3.99. However, 13% of patients displayed wear paths with aspect ratios 45.5, which indicates reduced multidirectional motion. The majority of total hip replacement (THR) patients display gait kinematics which produce multidirectional wear paths, but a significant minority display more linear paths.

Influence of preparation conditions on the characteristics of activated carbons produced in laboratory and pilot scale systems

The central theme of this investigation is to evaluate the feasibility of using bituminous coal as a precursor material for the production of chars and activated carbons using physical and chemical activation processes. The chemical activation process was accomplished by impregnating the raw materials with different dehydrating agents in different ratios and concentrations, prior to heat treatment (ZnCl2, KCl, KOH, NaOH and Fe2(SO4)3·xH2O). Steam activation of the precursor material was adopted for the preparation of activated carbon using physical activation technology. Different types of bituminous coal; namely, contaminated Columbian (contaminated with pet. coke), pure Columbian, Venezuelan and New Zealand bituminous coal were used in the production processes. BET surface area, micropore area, pore size distribution and total pore volume of the chars and activated carbons were determined from N2 adsorption/desorption isotherm, measured at 77 K. Charring conditions, charring temperature of 800 °C and charring time of 4 h, proved to be the optimum conditions for preparing chars. Contaminated Columbian were found to be the best precursor material for the production of char with reasonable physical characteristics (surface area = 138.1 m2 g-1 and total pore volume of 8.656 × 10-0.2 cm3 g-1). An improvement in the physical characteristics of the activated carbons was obtained upon the treatment of coal with dehydrating agents. Contaminated Columbian treated with 10 wt% ZnCl2 displayed the highest surface area and total pore volume (surface area = 231.5 m2 g-1 and total pore volume = 0.1227 cm3 g-1) with well-developed microporisity (micropore area = 92.3 m2 g-1). Venezuelan bituminous coal using the steam activation process was successful in producing activated carbon with superior physical characteristics (surface area = 863.50 m2 g-1, total pore volume = 0.469 cm3 g-1 and micropore surface area = 783.58 m2 g-1).

Separation of acid-dyes mixture by bamboo derived active carbon

In the present study, the activated carbon is produced using phosphoric acid treatment of the waste bamboo scaffolding and activated at either 400 or 600 °C. The effect of acid to bamboo ratio (Xp) up to 2.4 has been studied. The BET surface area increased with increasing Xp and activating temperature. BET surface area up to 2500 m2/g carbon has been produced. In order to simulate effluent treatment from textile industry, the produced carbon was tested for its dye adsorption capacities. Two acid dyes with different molecular sizes were used, namely Acid Yellow 117 (AY117) and Acid Blue 25 (AB25). In a single component system, it was found that dye with smaller molecular size, AB25, was readily adsorbed onto the carbon while the larger size dye, AY117, showed little adsorption. As a result, it is possible to tailor-make the carbon for the adsorption of dye mixtures in industrial applications, especially textile dyeing, i.e. molecular sieve effect. A binary AY117–AB25 mixture was used to test the possibility of the molecular sieve effect. Furthermore, experimental results were fitted to equilibrium isotherm models, Langmuir, Freundlich and Sips for the single component system. For the binary component system, extended single-component equilibrium isotherm models were used to predict the experimental data.