Surface sulfur measurements on stratospheric particles

The surface chemistries of three particulate samples collected from the lower stratosphere have been determined using a Scanning Auger Microprobe (SAM). These samples are typical of the most abundant natural and anthropogenic particles observed within the stratosphere in the >2µm diameter size fraction. Successive sputtering and analysis below the first few adsorbed monolayers of all particles shows the presence of a thin <150A) sulphur layer. These sulphur regions probably formed by surface reaction of sulphur-rich aerosols with each particle within the stratosphere. Settling rate calculations show that a typical sphere (10µm diameter) may reside within the aerosol layer for ~20 days and thus, provide a qualitative guide to surface sulphur reaction rates.

The thermal decomposition of hydronium jarosite and ammoniojarosite

The thermal decomposition of hydronium jarosite and ammoniojarosite was studied using thermogravimetric analysis and mass spectrometry, in situ synchrotron X-ray diffraction and infrared emission spectroscopy. There was no evidence for the simultaneous loss of water and sulfur dioxide during the desulfonation stage as has previously been reported for hydronium jarosite. Conversely, all hydrogen atoms are lost during the dehydration and dehydroxylation stage from 270 to 400 °C and no water, hydroxyl groups or hydronium ions persist after 400 °C. The same can be said for ammoniojarosite. The first mass loss step during the decomposition of hydronium jarosite has been assigned to the loss of the hydronium ion via protonation of the surrounding hydroxyl groups to evolve two water molecules. For ammoniojarosite, this step corresponds to the protonation of a hydroxyl group by ammonium, so that ammonia and water are liberated simultaneously. Iron(II) sulfate was identified as a possible intermediate during the decomposition of ammoniojarosite (421–521 °C) due to a redox reaction between iron(III) and the liberated ammonia during decomposition. Iron(II) ions were also confirmed with the 1,10-phenanthroline test. Iron(III) sulfate and other commonly suggested intermediates for hydronium and ammoniojarosite decomposition are not major crystalline phases; if they are formed, then they most likely exist as an amorphous phase or a different low temperature phases than usual.

Deposition of hydrocarbon molecules on diamond (001) surfaces : atomic scale modeling

The impact induced chemisorption of hydrocarbon molecules (CH3 and CH2) on H-terminated diamond (001)-(2x1) surface was investigated by molecular dynamics simulation using the many-body Brenner potential. The deposition dynamics of the CH3 radical at impact energies of 0.1-50 eV per molecule was studied and the energy threshold for chemisorption was calculated. The impact-induced decomposition of hydrogen atoms and the dimer opening mechanism on the surface was investigated. Furthermore, the probability for dimer opening event induced by chemisorption of CH, was simulated by randomly varying the impact position as well as the orientation of the molecule relative to the surface. Finally, the energetic hydrocarbons were modeled, slowing down one after the other to simulate the initial fabrication of diamond-like carbon (DLC) films. The structure characteristic in synthesized films with different hydrogen flux was studied. Our results indicate that CH3, CH2 and H are highly reactive and important species in diamond growth. Especially, the fraction of C-atoms in the film having sp(3) hybridization will be enhanced in the presence of H atoms, which is in good agreement with experimental observations. (C) 2002 Elsevier Science B.V. All rights reserved.

Effect of reactive bed mineralogy on arsenic retention and permeability of synthetic arsenic-containing acid mine drainage

Successive alkalinity producing systems (SAPSs) are widely used for treating acid mine drainage (AMD) and alleviating clogging commonly occurring in limestone systems due to an amorphous ferric precipitate. In this study, iron dust, bone char, micrite and their admixtures were used to treat arseniccontaining AMD. A particular interest was devoted to arsenic removal performance, mineralogical constraints on arsenic retention ability and permeability variation during column experiment for 140 days. The results showed that the sequence of the arsenic removal capacity was as follows: bone char > micrite > iron dust. The combination of 20% v/v iron dust and 80% v/v bone char/micrite columns can achieve better hydraulic conductivity and phosphorus-retention capacity than single micrite and bone char columns. The addition of iron dust created reductive environment and resulted in the transformation of coating material from colloidal phase to secondary mineral phase, such as green rust and phosphoerrite, which obviously ameliorates hydraulic conductivity of systems. The sequential extraction experiments indicated that the stable fractions of arsenic in columns were enhanced with help of iron dust compared to single bone char and micrite columns. A combination of iron dust and micrite/bone char represented a potential SAPS for treating As-containing AMD.

Improving power quality in low-voltage networks containing distributed energy resources

Severe power quality problems can arise when a large number of single-phase distributed energy resources (DERs) are connected to a low-voltage power distribution system. Due to the random location and size of DERs, it may so happen that a particular phase generates excess power than its load demand. In such an event, the excess power will be fed back to the distribution substation and will eventually find its way to the transmission network, causing undesirable voltage-current unbalance. As a solution to this problem, the article proposes the use of a distribution static compensator (DSTATCOM), which regulates voltage at the point of common coupling (PCC), thereby ensuring balanced current flow from and to the distribution substation. Additionally, this device can also support the distribution network in the absence of the utility connection, making the distribution system work as a microgrid. The proposals are validated through extensive digital computer simulation studies using PSCADTM

Insights into the mechanism of the reaction between ttrachloro-p-bnzoquinone and hydrogen peroxide and their implications in the catalytic role of water molecules in producing the hydroxyl radial

Detailed mechanisms for the formation of hydroxyl or alkoxyl radicals in the reactions between tetrachloro-p-benzoquinone (TCBQ) and organic hydroperoxides are crucial for better understanding the potential carcinogenicity of polyhalogenated quinones. Herein, the mechanism of the reaction between TCBQ and H2O2 has been systematically investigated at the B3LYP/6-311++G** level of theory in the presence of different numbers of water molecules. We report that the whole reaction can easily take place with the assistance of explicit water molecules. Namely, an initial intermediate is formed first. After that, a nucleophilic attack of H2O2 onto TCBQ occurs, which results in the formation of a second intermediate that contains an OOH group. Subsequently, this second intermediate decomposes homolytically through cleavage of the O-O bond to produce a hydroxyl radical. Energy analyses suggest that the nucleophilic attack is the rate-determining step in the whole reaction. The participation of explicit water molecules promotes the reaction significantly, which can be used to explain the experimental phenomena. In addition, the effects of F, Br, and CH3 substituents on this reaction have also been studied.

Evidence for the adsorption of molecules at special sites located at copper/zinc oxide interfaces. Part 2. -- A fourier-transform infrared spectroscopy study of methanol adsorption on reduced and oxidised Cu/ZnO/SiO2 catalysts

FTIR spectra are reported of methanol adsorbed at 295 K on ZnO/SiO 2, on reduced Cu/ZnO/SiO2 and on Cu/ZnO/SiO2 which had been preoxidised by exposure to nitrous oxide. Methanol on ZnO/SiO2 gave methoxy species on ZnO and SiO, in addition to both strongly and weakly physisorbed methanol on SiO2. The corresponding adsorption of methanol on reduced Cu/ZnO/SiO2 also gave methoxy species on Cu and a small amount of bridging formate. Reaction of methanol with a reoxidised Cu/ZnO/SiO2 catalyst resulted in an enhanced quantity of methoxy species on Cu. Heating adsorbed species on Cu/ZnO/SiO2 at 393 K led to the loss of methoxy groups on Cu and the concomitant formation of formate species on both ZnO and Cu. The comparable reaction on a reoxidised Cu/ZnO/SiO2 catalyst gave an increased amount of formate species on ZnO and this correlated with an increased quantity of methoxy groups lost from Cu. An explanation is given in terms of adsorption of formate and formaldehyde species at special sites located at the copper/zinc oxide interface.

Evidence for the adsorption of molecules at special sites located at copper/zinc oxide interfaces: Part 1. -- A Fourier-transform infrared study of formic acid and formaldehyde adsorption on reduced and oxidised Cu/ZnO/SiO2 catalysts

Fourier-transform infrared (FTIR) spectra are reported of formic acid and formaldehyde on ZnO/SiO2, reduced Cu/ZnO/SiO2 and reoxidised Cu/ZnO/SiO2 catalyst. Formic acid adsorption on ZnO/SiO2 produced mainly bidentate zinc formate species with a lesser quantity of unidentate zinc formate. Formic acid on reduced Cu/ZnO/SiO2 catalyst resulted not only in the formation of bridging copper formate structures but also in an enhanced amount of formate relative to that for ZnO/SiO2 catalyst. Formic acid on reoxidised Cu/ZnO/SiO2 gave unidentate formate species on copper in addition to zinc formate moieties. The interaction of formaldehyde with ZnO/SiO2 catalyst resulted in the formation of zinc formate species. The same reaction on reduced Cu/ZnO/SiO2 catalyst gave bridging formate on copper and a remarkable increase in the quantity of formate species associated with the zinc oxide. Adsorption of formaldehyde on a reoxidised Cu/ZnO/SiO2 catalyst produced bridging copper formate and again an apparent increase in the concentration of zinc formate species. An explanation in terms of the adsorption of molecules at special sites located at the interface between copper and zinc oxide is given.

Evidence for the adsorption of molecules at special sites located at copper/zinc oxide interfaces. Part 3. -- Fourier-transform infrared study of methyl formate adsorption on reduced and oxidised Cu/ZnO/SiO2 catalysts

FTIR spectra are reported of methyl formate adsorbed at 295 K on ZnO/SiO2, reduced Cu/ZnO/SiO2 and on Cu/ZnO/SiO2 which had been preoxidised by exposure to nitrous oxide. Methyl formate on ZnO/SiO2 gave adsorbed zinc formate species and strongly physisorbed molecular methanol on silica. The comparable reaction of methyl formate with reduced Cu/ZnO/SiO2 catalyst produced bridging formate species on copper and a diminished quantity of zinc formate relative to that formed on ZnO/SiO2 catalyst. This effect is explained in terms of site blockage on the ZnO surface by small copper clusters. Addition of methyl formate to a reoxidised Cu/ZnO/SiO2 catalyst produced a considerably greater amount of formate species on zinc oxide and methoxy groups on copper were detected. The increase in concentration of zinc formate species was rationalised in terms of rearrangement of unidentate copper formate species to become bonded to copper and zinc oxide sites located at the interface between these two components.

MS-based metabolomics facilitates the discovery of in vivo functional small molecules with a diversity of biological contexts

In vivo small molecules as necessary intermediates are involved in numerous critical metabolic pathways and biological processes associated with many essential biological functions and events. There is growing evidence that MS-based metabolomics is emerging as a powerful tool to facilitate the discovery of functional small molecules that can better our understanding of development, infection, nutrition, disease, toxicity, drug therapeutics, gene modifications and host-pathogen interaction from metabolic perspectives. However, further progress must still be made in MS-based metabolomics because of the shortcomings in the current technologies and knowledge. This technique-driven review aims to explore the discovery of in vivo functional small molecules facilitated by MS-based metabolomics and to highlight the analytic capabilities and promising applications of this discovery strategy. Moreover, the biological significance of the discovery of in vivo functional small molecules with different biological contexts is also interrogated at a metabolic perspective.

Sulfur resistant emissions catalyst

A catalyst comprising one or more complex oxides having a nominal compn. as set out in formula (1): AxB1-y-zMyPzOn (1) wherein A is selected from one or more group III elements including the lanthanide elements or one or more divalent or monovalent cations; B is selected from one or more elements with at. no. 22 to 24, 40 to 42 and 72 to 75; M is selected from one or more elements with at. no. 25 to 30; P is selected from one or more elements with at. no. 44 to 50 and 76 to 83; x is defined as a no. where 0

The effect of nitroxides on swarming motility and biofilms, multicellular behaviors in Pseudomonas aeruginosa

The ability of NO to induce biofilm dispersion has been well established. Here we investigated the effect of nitroxides (sterically hindered nitric oxide analogues) on biofilm formation and swarming motility in Pseudomonas aeruginosa. A transposon mutant unable to produce nitric oxide endogenously (nirS) was deficient in swarming motility relative to wild type and the complemented strain. Moreover, expression of the nirS gene was up-regulated by 9.65-fold in wild type swarming cells when compared to planktonic cells. Wild type swarming levels were substantially restored upon exogenous addition of nitroxide containing compounds, consistent with the hypothesis that NO is necessary for swarming motility. Here, we showed that nitroxides not only mimicked the dispersal activity of NO, but also prevented biofilms from forming in flow cell chambers. In addition, a nirS transposon mutant was deficient in biofilm formation relative to wild type and the complemented strain, thus implicating NO in the formation of biofilms. Intriguingly despite its stand alone action in inhibiting biofilm formation and promoting dispersal, a nitroxide partially restored the ability of a nirS mutant to form biofilms.

Spin-coated carbon

We describe a novel and facile approach to covalently graft molecules containing stable free radicals onto carbon surfaces including graphene, carbon nanotubes, glassy carbon and carbon fibres. The new technique employs a stable aryl nitroxide radical diazonium tetrafluoroborate salt. The salt may be isolated and added to carbon surfaces in solution, suspension or electrochemically and represents a convenient, versatile and highly efficient means to adorn graphitic materials with large numbers of free radical spin systems

Containing Queensland prickly pear : buffer zones, closer settlement, whiteness

By 1925, the introduced prickly pear (Opuntia and Nopalea spp.) covered up to 60 million acres of Queensland and New South Wales in what was perceived as prime agricultural land. After 40 years of experimentation, all Queensland Government strategies had failed. Faced with this failure and a diminishing expectation that the land would ever be conquered, buffer zones were proposed by the newly formed Queensland Prickly Pear Land Commission. A close reading of government documents, newspaper reports and local histories about these buffer zones shows how settler anxieties over who could or should occupy the land shaped the kinds of strategies recommended and adopted in relation to this alien species. Physical and cultural techniques were used to manage the uneasy coexistence between prickly pear, on the one hand, and farmers and graziers on the other. Furthermore, this environmental history challenges the notion of racially homogenous closer settlement under the White Australia Policy, showing the many different kinds of livelihood and labour in prickly pear land in the 1920s.

The α5 subunit regulates the expression and function of α4*-containing neuronal nicotinic acetylcholine receptors in the ventral-tegmental area

Human genetic association studies have shown gene variants in the α5 subunit of the neuronal nicotinic receptor (nAChR) influence both ethanol and nicotine dependence. The α5 subunit is an accessory subunit that facilitates α4* nAChRs assembly in vitro. However, it is unknown whether this occurs in the brain, as there are few research tools to adequately address this question. As the α4*-containing nAChRs are highly expressed in the ventral tegmental area (VTA) we assessed the molecular, functional and pharmacological roles of α5 in α4*-containing nAChRs in the VTA. We utilized transgenic mice α5+/+(α4YFP) and α5-/-(α4YFP) that allow the direct visualization and measurement of α4-YFP expression and the effect of the presence (α5+/+) and absence of α5 (-/-) subunit, as the antibodies for detecting the α4* subunits of the nAChR are not specific. We performed voltage clamp electrophysiological experiments to study baseline nicotinic currents in VTA dopaminergic neurons. We show that in the presence of the α5 subunit, the overall expression of α4 subunit is increased significantly by 60% in the VTA. Furthermore, the α5 subunit strengthens baseline nAChR currents, suggesting the increased expression of α4* nAChRs to be likely on the cell surface. While the presence of the α5 subunit blunts the desensitization of nAChRs following nicotine exposure, it does not alter the amount of ethanol potentiation of VTA dopaminergic neurons. Our data demonstrates a major regulatory role for the α5 subunit in both the maintenance of α4*-containing nAChRs expression and in modulating nicotinic currents in VTA dopaminergic neurons. Additionally, the α5α4* nAChR in VTA dopaminergic neurons regulates the effect of nicotine but not ethanol on currents. Together, the data suggest that the α5 subunit is critical for controlling the expression and functional role of a population of α4*-containing nAChRs in the VTA.