Measuring morphological features using light-scattering spectroscopy and Fourier-domain low-coherence interferometry.

We present measurements of morphological features in a thick turbid sample using light-scattering spectroscopy (LSS) and Fourier-domain low-coherence interferometry (fLCI) by processing with the dual-window (DW) method. A parallel frequency domain optical coherence tomography (OCT) system with a white-light source is used to image a two-layer phantom containing polystyrene beads of diameters 4.00 and 6.98 mum on the top and bottom layers, respectively. The DW method decomposes each OCT A-scan into a time-frequency distribution with simultaneously high spectral and spatial resolution. The spectral information from localized regions in the sample is used to determine scatterer structure. The results show that the two scatterer populations can be differentiated using LSS and fLCI.

Shallow water model for aluminium electrolysis cells with variable top and bottom

The MHD wave instability in commercial cells for electrolytic aluminium production is often described using ‘shallow water’ models. The model [1] is extended for a variable height cathode bottom and anode top to account for realistic cell features. The variable depth of the two fluid layers affects the horizontal current density, the wave development and the stability threshold. Instructive examples for the 500 kA cell are presented.

Finance for water and sanitation as a public service

Drawing on empirical evidence gathered through the PSIRU database, this contribution aims at addressing the potential of public finance to enhance the provision of water supply and sanitation as a public service. It highlights the problems associated with (and the disappointing results obtained from) resort to Private Sector Participation and private finance, both historically and in the last 15-20 years, in developed and developing countries. It also addresses the advantages of using public finance as a more cost-effective and equitable instrument to achieve developmental objectives such as the expansion of service coverage and development of water and sanitation infrastructure. The potential of public operations in maximising developmental impact from the social, economic and environmental points of view is then explored referring to specific examples from a variety of countries and regions. These include the in-house restructuring of public operations to enhance transparency, accountability and effectiveness, as well as the use of Public-Public Partnerships (PUPs) to build capacity. Attention is devoted to the specific financial requirements of expanding sewerage services at global level to achieve MDGs or broader developmental goals. These requirements are revisited in light of a regional breakdown of coverage gaps, available resources and development aid flows. These findings challenge the established view among international and bilateral agencies that expanding sewerage services in developing countries is excessively costly and should be abandoned as a priority because unaffordable. This contribution draws on a number of PSIRU Reports, and particularly the following. - http://www.psiru.org/reports/2008-03-W-sewers.pdf - http://boell-latinoamerica.org/download_es/agua08_privatizacion_LA_2007.pdf - http://boell-latinoamerica.org/download_es/agua08_agua_un_servicio_publico.pdf - http://www.psiru.org/reports/2006-03-W-investment.pdf All PSIRU Reports are accessible at http://www.psiru.org/publicationsindex.asp.

Kinetic studies of the effect of varnish on water loss by glass-ionomer cements

OBJECTIVES: This paper reports a study of the water loss behaviour of two commercial glass-ionomer cements coated with varnishes. METHODS: For each cement (Fuji IX Fast or Chemflex), specimens (6mmdiameterx2mm depth) were prepared and cured for 10min at 37 degrees C. They were exposed to a desiccating environment over H(2)SO(4) either uncoated or coated with the appropriate varnish (Fuji Varnish, a solvent-based lacquer, or Fuji Coat, a light-cured varnish). Four specimens were prepared for each material. They were weighed at hourly intervals for 6h, daily for up to 5 days, then weekly thereafter until equilibration. RESULTS: Unlike the uncoated specimens, water loss from varnished cements was not Fickian, but followed the form: mass loss=A/t+B, where t is time, A and B are constants specific to each cement/varnish combination. A varied from 1.22 to 1.30 (mean 1.26, standard deviation 0.04), whereas B varied from 1.54 to 2.09 (mean -1.83, standard deviation 0.29). At equilibrium, varnished specimens lost much less water than unvarnished ones (p>0.01) but there was no significant difference between the solvent-based and the light-cured varnishes. SIGNIFICANCE: Varnishes protect immature glass-ionomer cements from drying out by altering the mechanism of water loss. This slows the rate of drying but does not necessarily change the total amount of water retained. It confirms that, in clinical use, glass-ionomer restoratives should be varnished to allow them to mature satisfactorily.

Rare-earth nitroquinolinates: Visible-light-sensitizable near-infrared emitters in aqueous solution

Water-soluble, stable, and easily synthesizable 1:4 complexes of rare-earth ions with 8-hydroxy-5-nitroquinolinate ligands have been prepared. These complexes can be sensitized by visible light with wavelengths up to 480 nm and show near-infrared emission in aqueous solution. The incorporation of a nitro group in the quinoline moiety shifts its absorption bands to longer wavelengths and also increases its molar absorptivity by a factor of 2.5, thereby significantly enhancing its light-harvesting power. The presence of the nitro group also increases the solubility of the resulting complexes, making them water-soluble. (c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007.

Habitat utilization by juvenile hawksbill turtles (Eretmochelys imbricata, Linnaeus, 1766) around a shallow water coral reef

Contemporary studies of sea turtle diving behaviour are generally based upon sophisticated techniques such as the attachment of time depth recorders. However, if the risks of misinterpretation are to be minimized, it is essential that electronic data are analysed in the light of first-hand observations. To this aim, we set out to make observations of juvenile hawksbill turtles (Eretmochelys imbricata , Linnaeus, 1766) foraging and resting in a shallow water coral reef habitat around the granitic Seychelles (4degrees'S, 55degrees'E). Data were collected from six study sites characterized by a shallow reef plateau (

Hydrophobic substances induce water stress in microbial cells

Ubiquitous noxious hydrophobic substances, such as hydrocarbons, pesticides and diverse industrial chemicals, stress biological systems and thereby affect their ability to mediate biosphere functions like element and energy cycling vital to biosphere health. Such chemically diverse compounds may have distinct toxic activities for cellular systems; they may also share a common mechanism of stress induction mediated by their hydrophobicity. We hypothesized that the stressful effects of, and cellular adaptations to, hydrophobic stressors operate at the level of water : macromolecule interactions. Here, we present evidence that: (i) hydrocarbons reduce structural interactions within and between cellular macromolecules, (ii) organic compatible solutes-metabolites that protect against osmotic and chaotrope-induced stresses-ameliorate this effect, (iii) toxic hydrophobic substances induce a potent form of water stress in macromolecular and cellular systems, and (iv) the stress mechanism of, and cellular responses to, hydrophobic substances are remarkably similar to those associated with chaotrope-induced water stress. These findings suggest that it may be possible to devise new interventions for microbial processes in both natural environments and industrial reactors to expand microbial tolerance of hydrophobic substances, and hence the biotic windows for such processes.

An Investigation into the Optimum Thickness of Titanium Dioxide Thin Films Synthesized by Using Atmospheric Pressure Chemical Vapour Deposition for Use in Photocatalytic Water Oxidation

Twenty eight films of titanium dioxide of varying thickness were synthesised by using atmospheric pressure chemical vapour deposition (CVD) of titanium(IV) chloride and ethyl acetate onto glass and titanium substrates. Fixed reaction conditions at a substrate temperature of 660 degrees C were used for all depositions, with varying deposition times of 5-60 seconds used to control the thickness of the samples. A sacrificial electron acceptor system composed of alkaline sodium persulfate was used to determine the rate at which these films could photo-oxidise water in the presence of 365 nm light. The results of this work showed that the optimum thickness for CVD films on titanium substrates for the purposes of water oxidation was approximate to 200 nm, and that a platinum coating on the reverse of such samples leads to a five-fold increase in the observed rate of water oxidation.

The photo-oxidation of water by sodium persulfate, and other electron acceptors, sensitised by TiO2

A number of different electron acceptors are tested for efficacy in the oxidation of water to oxygen, photocatalysed by titanium dioxide. The highly UV-absorbing metal ion electron acceptors, Ce4+ and Fe3+, appear ineffective at high concentration (10(-2) M), due to UV-screening, but more effective at lower concentrations (10(-3) M). The metal-depositing electron acceptor, Ag+, is initially effective, but loses activity upon prolonged irradiation due to metal deposition which promotes electron-hole recombination as well as UV-screening the titania particles. Most striking of the electron acceptors tested is persulfate, particularly in alkaline solution (0.1 M NaOH). The kinetics of the photo-oxidation of water by persulfate, photocatalysed by titania are studied as a function of pH, [S2O82-] and incident light intensity (I). The initial rate of water oxidation increases with pH, is directly proportional to the concentration of persulfate present and depends upon I-0.6. The TiO2/alkaline persulfate photosystem is robust and shows very little evidence of photochemical wear upon repeated irradiation. The results of this work are discussed with regard to previous work in this area and current mechanistic thinking. The formal quantum efficiency of the TiO2/alkaline persulfate photosystem was estimated as ca. 2%. (C) 2004 Elsevier B.V. All rights reserved.

Photo-oxidation of water sensitized by TiO2 and WO3 in presence of different electron acceptors

The photo-oxidation of water is studied in presence of UV-light (lambda

Detoxification of water by semiconductor photocatalysis

An overview of the use of semiconductor photocatalysis for water purification is given. The basic principles of semiconductor photocatalysis are described along with the current understanding of the underlying reaction mechanism(s) and how it fits in with the major features of the observed Langmuir-Hinshelwood-type kinetics of pollutant destruction. These features are illustrated based on literature on the destruction of aqueous solutions of 4-chlorophenol as a pollutant, using titanium dioxide as the photocatalyst. The range of organic and inorganic pollutants that can be destroyed by semiconductor photocatalysis are reported and discussed. The basic considerations that need to be made when designing a reactor for semiconductor photocatalysis are considered. These include: the nature of the reactor glass, the type of illumination source, and the nature and type of semiconductor photocatalyst. The key basic photoreactor designs are reported and discussed, including external illumination, annular, and circular photoreactors. Actual designs that have been used for fixed and thin falling film semiconductor photocatalyst reactors are illustrated and their different features discussed. Basic non-concentrating and concentrating solar photoreactors for semiconductor photocatalysis are also reported. The design features of the major commercial photocatalytic reactor systems for water purification are reported and illustrated. Several case studies involving commercial photocatalytic reactors for water purification are reported. An attempt is made briefly to compare the efficacy of semiconductor photocatalysis for water purification with that of other, more popular and prevalent water purification processes. The future of semiconductor photocatalysis as a method of purifying water is considered.

Platinum and Palladium in Semiconductor Photocatalytic Systems FACTORS AFFECTING THE PURIFICATION OF WATER AND AIR

A wide range of organic pollutants can be destroyed by semiconductor photocatalysis using titania. The purification of water and air contaminated with organic pollutants has been investigated by semiconductor photocatalysis for many years and in attempts to improve the purification rate platinum and palladium have been deposited, usually as fine particles, on the titania surface. Such deposits are expected to improve the rate of reduction of oxygen and so reduce the probability of electron-hole recombination and increase the overall rate of the reaction. The effectiveness of the deposits is reviewed here and appears very variable with reported rate enhancement factors ranging from 8 to 0.1. Semiconductor photocatalysis can be used to purify air (at temperatures > 100 degrees C) and Pt deposits can markedly improve the overall rate of mineralisation. However, volatile organic compounds containing an heteroatom can deactivate the photocatalyst completely and irreversibly. Factors contributing to the success of the processes are considered. The use of chloro-Pt(IV)-titania and other chloro-platinum group metals-titania complexes as possible visible light sensitisers for water and air purification is briefly reviewed.

Bromate removal from drinking water by semiconductor photocatalysis

The semiconductor photocatalyst, platinised titanium dioxide, Pt/TiO2, is used to promote the destruction of bromate ions to bromide and oxygen by 254 nm ultraviolet light. The kinetics of bromate removal are first order with respect to [BrO3-] and are inhibited, although not completely, by competitive adsorption by other anions, including bromide and sulfate ions. The Pt/TiO2 can be used not only as a powder dispersion, but also as a thin film in a flow reactor for the destruction of bromate ions. Copyright (C) 1996 Elsevier Science Ltd