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.

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.

Mineralogy of selected geological deposits from the United Kingdom and the Republic of Ireland as possible capping materials for low-level radioactive waste disposal facilities

Solid low-level radioactive waste (LLW) is currently being disposed at a number of facilities in the United Kingdom (UK). The safety of these facilities relies to some extent on the use of engineered barriers, such as a cap, to isolate the waste and protect the environment. Generally, the material used as the barrier layer within such a cap should be of low permeability and it should retain this property over long timescales (beyond a few decades normally required for facilities containing non-radioactive wastes). The objective of this research is to determine the mineralogy of selected geological deposits from the UK and Ireland as part of a larger project to examine their suitability as a capping material, particularly on LLW sites. Mineral transformations, as a result of future climate change, may impact on the long-term performance of the cap and even the disposal facility. X-ray diffraction (XRD) was carried-out on the sand, silt and clay fractions of the London Clay, Belfast Upper Boulder Clay, Irish Glacial Till, Belfast Sleech, and Ampthill Clay geological deposits. Minerals were present that could pose both positive and negative effects on the long-term performance of the cap. Smectite, which has a high shrink swell potential, may produce cracks in London Clay, Belfast Upper Boulder Clay and Ampthill Clay capping material during dry, hotter periods as a possible consequence of future climate change; thus, resulting in higher permeability. Ampthill Clay and Belfast Sleech had elevated amounts of organic matter (OM) at 5.93% and 5.88%, respectively, which may also contribute to cracking. Over time, this OM may decompose and result in increased permeability. Gypsum (CaSO4) in the silt and sand fractions of Ampthill Clay may reduce the impact of erosion during wetter periods if it is incorporated into the upper portion of the cap. There are potential negative effects from the acidity created by the weathering of pyrite (FeS2) present in the silt and sand fractions of Belfast Sleech and Ampthill Clay that could impede the growth of grasses used to stabilize the surface of the capping material if this material is used as part of the vegetative soil layer. Additionally, acidic waters generated from pyrite weathering could negatively impact the lower lying capping layers and the disposal facility in general. However, the calcium carbonate (CaCO3) present in the silt and sand fractions of these deposits, and dolomite (CaMg(CO3)2) in Belfast Sleech, may counter act the acidity.

Scanning electron microscopy study of microstructural evolution of electroless nickel-phosphorus deposits with heat treatment

This paper follows previous X-ray diffraction work on crystallisation and phase transformation of electroless nickel–phosphorus deposits, concentrating on microstructural changes. Amorphous or nanocrystalline coatings, depending on their phosphorus content, were heat treated at temperatures between 100 and 500 °C for 1 h. Changes in microstructure after the heat treatment were examined using high-resolution field emission scanning electron microscope. Crystallisation and grain growth effects are observed, as well as some inherent defect structures in the coatings and their changes. These are compared with the previous X-ray diffraction work and in general, good agreement is observed. The complementary strength and weakness of the different characterisation techniques are discussed.

An Antennas and Propagation Approach to Improving Physical Layer Performance in Wireless Body Area Networks

A combined antennas and propagation study has been undertaken with a view to directly improving link conditions for wireless body area networks. Using tissue-equivalent numerical and experimental phantoms representative of muscle tissue at 2.45 GHz, we show that the node to node [S-21] path gain performance of a new wearable integrated antenna (WIA) is up to 9 dB better than a conventional compact Printed-F antenna, both of which are suitable for integration with wireless node circuitry. Overall, the WIA performed extremely well with a measured radiation efficiency of 38% and an impedance bandwidth of 24%. Further benefits were also obtained using spatial diversity, with the WIA providing up to 7.7 dB of diversity gain for maximal ratio combining. The results also show that correlation was lower for a multipath environment leading to higher diversity gain. Furthermore, a diversity implementation with the new antenna gave up to 18 dB better performance in terms of mean power level and there was a significant improvement in level crossing rates and average fade durations when moving from a single-branch to a two-branch diversity system.

Through-thickness control of polymer bioresorption via electron beam irradiation

Predicable and controlled degradation is not only central to the accurate delivery of bioactive agents and drugs, it also plays a vital role in key aspects of bone tissue engineering. The work addressed in this paper investigates the utilisation of e-beam irradiation in order to achieve a controlled (surface) degradation profile. This study focuses on the modification of commercially and clinically relevant materials, namely poly(L-lactic acid) (PLLA), poly(L-lactide-hydroxyapatite) (PLLA-HA), poly(L-lactide-glycolide) co-polymer (PLG) and poly(L-lactide-DL-lactide) co-polymer (PLDL). Samples were subjected to irradiation treatments using a 0.5 MeV electron beam with delivered surface doses of 150 and 500 kGy. In addition, an acrylic attenuation shield was used for selected samples to control the penetration of the e-beam. E-beam irradiation induced chain scission in all polymers, as characterized by reduced molecular weights and glass transition temperatures (T-g). Irradiation not only produced changes in the physical properties of the polymers but also had associated effects on surface erosion of the materials during hydrolytic degradation. Moreover, the extent to which both mechanical and hydrolytic degradation was observed is synonymous with the estimated penetration of the beam (as controlled by the employment of an attenuation shield). (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Alkynyl-Bridged Ruthenium(II) 4 '-Diferroceny1-2,2 ':6 ',2 ''-terpyridine Electron Transfer Complexes: Synthesis, Structures, and Electrochemical and Spectroscopic Studiese

The novel ligand 4'-diferrocenylallcyne-2,2':6',2 ''-terpyridine (7; Fc-C C-Fc-tpy; tpy = terpyridyl; Fc = ferrocenyl) and its Ru2+ complexes 8-10 have been synthesized and characterized by single-crystal X-ray diffraction, cyclic voltammetry, and UV-vis and luminescence spectroscopy. Electrochemical data and UV absorption and emission spectra indicate that the insertion of an ethynyl group causes delocalization of electrons in the extended pi* orbitals. Cyclic voltammetric measurements of 7 show two successive reversible one-electron-oxidation processes with half-wave potentials of 0.53 and 0.78 V. The small variations of the E-1/2 values for the Fe2+/Fe3+ redox couples after the coordination of the Ru2+ ion suggest a weak interaction between the Ru2+ and Fe2+ centers. After insertion of an ethynyl group, UV-vis absorption spectra show a red shift of the absorption peak of the (1)[(d(pi)(Fe))(6)]->(1)[(d(pi)(Fe))(5)(pi*(Ru)(tpy))(1)] MMLCT of the Ru2+ complexes. The Ru2+ complex 8 exhibits the strongest luminescence intensity (lambda(em)(max) 712 nm, Phi(em) = 2.63 x 10(-4), tau = 323 ns) relative to analogous ferrocene-based terpyridine Ru(II) complexes in H2O/CH3CN (4/1 v/v) solution.

A comprehensive aerosol spray method for the rapid photocatalytic grid area analysis of semiconductor photocatalyst thin films

Indicator inks, previously shown to be capable of rapidly assessing photocatalytic activity via a novel photo-reductive mechanism, were simply applied via an aerosol spray onto commercially available pieces of Activ (TM) self-cleaning glass. Ink layers could be applied with high evenness of spread, with as little deviation as 5% upon UV-visible spectroscopic assessment of 25 equally distributed positions over a 10 cm x 10 cm glass cut. The inks were comprised of either a resazurin (Rz) or dichloroindophenol (DCIP) redox dye with a glycerol sacrificial electron donor in an aqueous hydroxyethyl cellulose (HEC) polymer media. The photo-reduction reaction under UVA light of a single spot was monitored by UV-vis spectroscopy and digital images attained from a flat-bed scanner in tandem for both inks. The photo-reduction of Rz ink underwent a two-step kinetic process, whereby the blue redox dye was initially reduced to a pink intermediate resorufin (Rf) and subsequently reduced to a bleached form of the dye. In contrast, a simple one-step kinetic process was observed for the reduction of the light blue redox dye DCIP to its bleached intermediates. Changes in red-green-blue colour extracted from digital images of the inks were inversely proportional to the changes seen at corresponding wavelengths via UV-visible absorption spectroscopy and wholly indicative of the reaction kinetics. The photocatalytic activity areas of cuts of Activ (TM) glass, 10 cm x 10 cm in size, were assessed using both Rz and DCIP indicator inks evenly sprayed over the films: firstly using UVA lamp light to activate the underlying Activ (TM) film (1.75 mW cm(-2)) and secondly under solar conditions (2.06 +/- 0.14 mW cm(-2)). The photo-reduction reactions were monitored solely by flat-bed digital scanning. Red-green-blue values of a generated 14 x 14 grid (196 positions) that covered the entire area of each film image were extracted using a Custom-built program entitled RGB Extractor(C). A homogenous degradation over the 196 positions analysed for both Rz (Red colour deviation = 19% UVA, 8% Solar: Green colour deviation = 17% UVA, 12% Solar) and DCIP (Red colour deviation = 22% UVA, 16% Solar) inks was seen in both UVA and solar experiments, demonstrating the consistency of the self-cleaning titania layer on Activ (TM). The method presented provides a good solution for the high-throughput photocatalytic screening of a number of homogenous photocatalytically active materials simultaneously or numerous positions on a single film; both useful in assessing the homogeneity of a film or determining the best combination of reaction components to produce the optimum performance photocatalytic film. (C) 2010 Elsevier B.V. All rights reserved.

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.

The alteration of the structural properties and photocatalytic activity of TiO2 following exposure to non-linear irradiation sources

When TiO2 powder was irradiated with a laser light (>0.8 MW peak pulse power (PPP) at 355 nm) a visible change in its colour from white to dark blue was observed. The initial rate of change of the total colour difference was related to the laser light intensity and the longer the irradiation time the more substantial the colour change. The result of X-ray diffraction (XRD) studies showed that the crystal structure of the TiO2 developed a more rutile form after laser exposure. ESR studies indicated that the colour change was associated with the generation of Ti(III) species in the photocatalyst. Electron microscopic studies showed that more spherical shaped particles of TiO2 were observed after laser treatment although the average particle size remained largely unchanged. No significant changes in the band gap or the surface area of the laser modified TiO2 were observed. The laser modified photocatalyst showed no enhancement in activity for the destruction of methylene blue, rhodamine B and stearic acids, indicating that the rutile/anatase ratio is unimportant in the destruction of the test pollutants used in this work, via TiO2 photocatalysis

Laser-Driven Fast Electron Collimation in Targets with Resistivity Boundary

We demonstrate experimentally that the relativistic electron flow in a dense plasma can be efficiently confined and guided in targets exhibiting a high-resistivity-core-low-resistivity-cladding structure analogous to optical waveguides. The relativistic electron beam is shown to be confined to an area of the order of the core diameter (50 mu m), which has the potential to substantially enhance the coupling efficiency of electrons to the compressed fusion fuel in the Fast Ignitor fusion in full-scale fusion experiments.

Observation of annular electron beam transport in multi-TeraWatt laser-solid interactions

Electron energy transport experiments conducted on the Vulcan 100 TW laser facility with large area foil targets are described. For plastic targets it is shown, by the plasma expansion observed in shadowgrams taken after the interaction, that there is a transition between the collimated electron flow previously reported at the 10 TW power level to an annular electron flow pattern with a 20 degrees divergence angle for peak powers of 68 TW. Intermediate powers show that both the central collimated flow pattern and the surrounding annular-shaped heated region can co-exist. The measurements are consistent with the Davies rigid beam model for fast electron flow (Davies 2003 Phys. Rev. E 68 056404) and LSP modelling provides additional insight into the observed results.

A COMPARISON OF EXPERIMENTAL AND THEORETICAL ELECTRON-ENERGY DISTRIBUTION-FUNCTIONS IN A MULTICUSP ION-SOURCE

Experimental and theoretical electron energy distribution functions (EEDFS) measured in and calculated for the driver of a multicusp ion source operating in hydrogen are compared. The results show that atomic physics based theoretical models can accurately predict the EEDF in such discharges if some appropriate experimentally determined quantities are used as input parameters. The magnitude and shape of the EEDF is found to be particularly sensitive to the effective surface area to volume ratio for electrons.

Ruthenium(II) bis(terpyridine) electron transfer complexes with alkynyl-ferrocenyl bridges: synthesis, structures, and electrochemical and spectroscopic studies

Two novel alkynyl-bridged symmetric bis-tridentate ligands 1,2-bis(1'-[4'-(2,2':6', 2 ''-terpyridinyl)]-ferrocenyl)ethyne (3a; tpy-Fc-C C-Fc-tpy; Fc = ferrocenyl; tpy = terpyridyl) and 1,4-bis(1'-[4'-(2,2':6', 2 ''-terpyridinyl)]ferrocenyl)-1,3-butadiyne (3b; tpy-Fc-C C-C C-Fc-tpy) and their Ru2+ complexes 6a and 6b have been synthesized and characterized by cyclic voltammetry, UV-vis and luminescence spectroscopy, and in the case of 3b by single-crystal X-ray diffraction. Cyclic voltammograms of both compounds, 3a and 3b, display two severely overlapping ferrocene-based oxidative peaks with only one reductive peak. The redox behavior of 6a and 6b is dominated by the Ru2+/Ru3+ redox couple (E-1/2 from 1.33 to 1.34 V), the Fe2+/Fe3+ redox couples (E-1/2 from 0.46 to 0.80 V), and the tpy/tpy(-)/tpy(2-)redox couples (E-1/2 from -1.19 to -1.48 V). The UV-vis spectra of 6a and 6b show absorption bands assigned to the (1)[(d(pi)(Fe))(6)] -> (1)[(d(pi)(Fe))(5)(pi*(Ru)(tpy))(1)] MMLCT transition at similar to 555 nm. Complexes 6a and 6b are luminescent in H2O-CH3CN (4 : 1, v/v) solution at room temperature, and 6b exhibits the strongest luminescence intensity (lambda(em)(max): 710 nm, Phi(em): 2.28 x 10(-4), tau: 358 ns) relative to analogous ferrocene-based bis(terpyridine) Ru(II) complexes reported so far.