Specifics about Specific Ion Adsorption from Heterodyne-Detected Second Harmonic Generation

Ion specific outcomes at aqueous interfaces remain among the most enigmatic phenomena in interfacial chemistry. Here, charged fused silica/water interfaces have been probed by homodyne- and heterodyne-detected (HD) second harmonic generation (SHG) spectroscopy at pH 7 and pH 5.8 and for concentrations of LiCl, NaCl, NaBr, NaI, KCl, RbCl, and CsCl ranging from 10 mc microM to several 100 mM. For ionic strengths around 0.1 mM to 1 mM, SHG intensities increase reversibly by up to 15% compared to the condition of zero added salt because of optical phase matching and electrical double layer. For ionic strengths above 1 mM, use of any combination of cations and anions produces decreases in SHG response by as much as 50%, trending with ion softness when compared to the condition of zero added salt. Gouy- Chapman model fits to homodyned SHG intensities for the alkali halides studied here show charge densities increase significantly with decreasing cation size. HD-SHG measurements indicate diffuse layer properties probed by the SHG process are invariant with ion identity, while Stern layer properties, as reported by chi(2), are subject to ion specificity for the ions surveyed in this work in the order of chi(2)RbCl = 1/2 chi(2)NaCl = 1/4 chi(2)NaI .Comment: Pre-edited version, 15 manuscript pages, 2 tables, 5 figures. Supporting Information available up request to the corresponding autho

Energy Conversion via Metal Nanolayers

Current approaches for electric power generation from nanoscale conducting or semiconducting layers in contact with moving aqueous droplets are promising as they show efficiencies of around 30%, yet even the most successful ones pose challenges regarding fabrication and scaling. Here, we report stable, all-inorganic single-element structures synthesized in a single step that generate electrical current when alternating salinity gradients flow along its surface in a liquid flow cell. Nanolayers of iron, vanadium, or nickel, 10 to 30 nm thin, produce open-circuit potentials of several tens of millivolt and current densities of several microA cm^(−2) at aqueous flow velocities of just a few cm s^(−1). The principle of operation is strongly sensitive to charge-carrier motion in the thermal oxide nanooverlayer that forms spontaneously in air and then self-terminates. Indeed, experiments suggest a role for intraoxide electron transfer for Fe, V, and Ni nanolayers, as their thermal oxides contain several metal-oxidation states, whereas controls using Al or Cr nanolayers, which self-terminate with oxides that are redox inactive under the experimental conditions, exhibit dramatically diminished performance. The nanolayers are shown to generate electrical current in various modes of application with moving liquids, including sliding liquid droplets, salinity gradients in a flowing liquid, and in the oscillatory motion of a liquid without a salinity gradient

Geological and Structural Interpretation of Part of the Buem Formation, Ghana, Using Aerogeophysical Data

Airborne magnetic and radiometric datasets were processed to interpret the geology of part of the Buem formation and estimate the depth to basement of magnetic source in the area. The study was aimed at mapping lithology, delineating structural lineaments and their trends as well as estimating the depth to magnetic source bodies of the area. The data processing steps involved advance improved enhancement filters such as reduction to the pole, analytic signal and first vertical derivative, Tilt angle derivative and these helped delineate geological structures and lithology within the Buem formation. The radiometric datasets displaying the geochemical information on potassium, thorium and uranium concentrations within the study area proved valuable in delineating the Buem shales, sandstones, basalts and part of the Voltaian sediments that underlie the Buem formation of the area. Lineament analysis using the rose diagram showed that the area is dominated by north-south (NS) and east-west (EW) trending lineaments. Depths to the magnetic source bodies were estimated using Werner deconvolution method, indicating two depth source models. The depth of the magnetic body produced from the dike model ranged from 101.15 m to 1866.34 m and that of the contact model ranged from 100.36 m to 983.709 m. Keywords: Buem formation, aeromagnetic, radiometric, hydrothermal, alteration, mineralization

Sero-epidemiology of toxoplasmosis amongst pregnant women in the greater Accra region of Ghana

Objectives: To investigate Toxoplasma infection among pregnant women in relation to exposure to infection risk, age and pregnancy-related risk factors. Design and Methods: This cross-sectional study involved 294 pregnant women attending ante-natal clinic in Accra who consented to participate. Personal and Toxoplasma infection risk related data were obtained by questionnaire interviews. Venous blood was safely drawn from each participant and spun to obtain sera.Each of the 159 randomly selected serum samples was tested for specific anti-Toxoplasma (anti-T. gondii) antibodies IgG, IgA and IgM using a commercial ELISA kit (Calbiotech Inc., CA). ELISA results were correlated with exposure to possible infection risk factorsas well as age and pregnancy-related risk factors. Results: The 159 women aged 15-40 years in their first, second and third trimesters, numbered 29, 70 and 60, respectively. An overall anti-T. gondii antibodies IgG, IgA and IgM seroprevalence of 92.5% (147/159)was recorded, with 4.1% (6/147) of them having anti- IgG only. The remaining 88.7% (141/159) had anti- Toxoplasma antibodies IgG, IgA and IgM in various combinations and consisted of 17.7% (25/141) in their first, 44.0% (62/141) in their second, and 38.3% (54/141) in their third, trimesters. Twelve women (7.6%) were seronegative for all 3 antibodies Conclusions: Seroprevalence was high among the women and exposure to contact with cats’ faeces was found to be the major T. gondii infection risk factor. Age and pregnancy-related risk factors did not have association with T. gondii infection within the limitationsof this study

Beyond the Gouy-Chapman Model with Heterodyne-Detected Second Harmonic Generation

We report ionic strength-dependent phase shifts in second harmonic generation (SHG) signals from charged interfaces that verify a recent model in which dispersion between the fundamental and second harmonic beams modulates observed signal intensities. We show how phase information can be used to unambiguously separate the chi(2) and interfacial potential-dependent chi(3) terms that contribute to the total signal and provide a path to test primitive ion models and mean field theories for the electrical double layer with experiments to which theory must conform. Finally, we demonstrate the new method on supported lipid bilayers and comment on the ability of our new instrument to identify hyper-Rayleigh scattering contributions to common homodyne SHG measurements in reflection geometries.Comment: 21 manuscript pages, four figures, 10 pages supporting information included, pre-edited versio

Energy Conversion via Metal Nanolayers

Current approaches for electric power generation from nanoscale conducting or semi-conducting layers in contact with moving aqueous droplets are promising as they show efficiencies of around 30 percent, yet, even the most successful ones pose challenges regarding fabrication and scaling. Here, we report stable, all-inorganic single-element structures synthesized in a single step that generate electrical current when alternating salinity gradients flow along its surface in a liquid flow cell. 10 nm to 30 nm thin nanolayers of iron, vanadium, or nickel produce several tens of mV and several microA cm^-2 at aqueous flow velocities of just a few cm s^-1. The principle of operation is strongly sensitive to charge-carrier motion in the thermal oxide nano-overlayer that forms spontaneously in air and then self terminates. Indeed, experiments suggest a role for intra-oxide electron transfer for Fe, V, and Ni nanolayers, as their thermal oxides contain several metal oxidation states, whereas controls using Al or Cr nanolayers, which self-terminate with oxides that are redox inactive under the experimental conditions, exhibit dramatically diminished performance. The nanolayers are shown to generate electrical current in various modes of application with moving liquids, including sliding liquid droplets, salinity gradients in a flowing liquid, and in the oscillatory motion of a liquid without a salinity gradient.Comment: Pre-edited final version, 16 pages main text, 5 figure

Pesticide exposures in a malarious and predominantly farming area in Central Ghana

In areas where malaria is endemic, pesticides are widely deployed for vector control, which has contributed to reductions in malaria deaths. Pesticide use for agrarian purposes reduces pest populations, thus improving crop production and post-harvest losses. However, adverse health effects have been associated with pesticide exposure, ranging from skin irritation to neurotoxicity and carcinogenicity. Though misuse of these pesticides can lead to widespread potential dangers, the debilitating effects are usually underappreciated in many developing countries. To evaluate the pattern of pesticide usage among rural communities in the Kintampo area of Ghana, a cross-sectional survey was conducted among 1455 heads of households randomly sampled from among 29,073 households in the Kintampo Health and Demographic Surveillance System area of Ghana to estimate the prevalence of pesticide use and indications for use among this rural populace. Seventy-one percent (1040/1455) of household heads reported having used pesticides on either their farms or homes, most commonly for control of weeds (96.4%, 1003/1040) or insects (85.4%, 888/1040). Dichlorodiphenyltrichloroethane (DDT) was used by 22.9% (238/1040) of respondents. The majority of households who reported use of pesticides said women in their households assisted in the spraying efforts (69.3%, 721/1040); of these women, 50.8% (366/721) did so while carrying their babies on their backs. Only 28.9% (301/1040) of the study participants wore protective devices during pesticide applications. Frequent symptoms that were reported after spraying, included cough (32.3%; 336/1040), difficulty in breathing (26.7%; 278/1040) and skin irritation (39.0%; 406/1040). Pesticide use among community members in the Kintampo area of Ghana is common and its potential health impacts warrant further investigation.Key words: Pesticide, malaria, prevalence, Kintampo, dichlorodiphenyltrichloroethane

Low-Energy (\u3c 20 eV) and High-Energy (1000 eV) Electron-Induced Methanol Radiolysis of Astrochemical Interest

We report the first infrared study of the low-energy (\u3c 20 eV) electron-induced reactions of condensed methanol. Our goal is to simulate processes which occur when highenergy cosmic rays interact with interstellar and cometary ices, where methanol, a precursor of several prebiotic species, is relatively abundant. The interactions of high-energy radiation, such as cosmic rays (Emax ~1020 eV), with matter produce large numbers of low-energy secondary electrons, which are known to initiate radiolysis reactions in the condensed phase. Using temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS), we have investigated low-energy (5–20 eV) and high-energy (~1000 eV) electron-induced reactions in condensed methanol (CH3OH). IRAS has the benefit that it does not require thermal processing prior to product detection. Using IRAS, we have found evidence for the formation of ethylene glycol (HOCH2CH2OH), formaldehyde (CH2O), dimethyl ether (CH3OCH3), methane (CH4), carbon dioxide (CO2), carbon monoxide (CO), and the hydroxyl methyl radical (•CH2OH) upon both low-energy and high-energy electron irradiation of condensed methanol at ~85 K. Additionally, TPD results, presented herein, are similar for methanol films irradiated with both 1000 eV and 20 eV electrons. These IRAS and TPD findings are qualitatively consistent with the hypothesis that high-energy condensed phase radiolysis is mediated by low-energy electron-induced reactions. Moreover, methoxymethanol (CH3OCH2OH) could serve as a tracer molecule for electron-induced reactions in the interstellar medium. The results of experiments such as ours may provide a fundamental understanding of how complex organic molecules (COM) are synthesized in cosmic ices

Influence of time and ageing conditions on the properties of ferrihydrite

Natural conversion of ferrihydrite (Fh), a widespread Fe(iii)-oxyhydroxide mineral at the Earth's surface, to thermodynamically more stable iron oxides such as goethite (Gt) and hematite (Hm) is a slow process that spans months to years. Here we examined the effects of synthesis and storage conditions on the hydration, the ratio of tetrahedral to octahedral iron sites, and the transformation of naturally aged 2-line Fh at room temperature and mildly acidic pH over an ageing period of 5 years. Fh samples synthesized and aged in either aerobic or anaerobic conditions were characterized over time by XRD, SEM, thermogravimetric analysis - mass spectroscopy (TGA-MS), and X-ray absorption spectroscopies (XANES and XMCD). The findings show that the ratio of tetrahedral to octahedral Fe(iii) sites in Fh is correlated to its extent of hydration, with fresher Fh samples exhibiting a higher ratio and more bound water. Fresh Fh aged in aerobic conditions has similar bound inorganic carbon, is more hydrated, and has less tetrahedral Fe(iii) than that aged in anaerobic conditions. Hence, for relatively fresh Fh there is a link between Fh properties and storage conditions. However, the long-term ageing characteristics, such as the transformation rate and relative phase fraction of Gt and Hm products, are not noticeably impacted by storage conditions. TGA-MS measurements coupled with O K-edge XANES spectra confirm that Fh tends to lose its hydration as it ages, as expected. Corresponding Fe L2,3-edge XMCD spectra reveal that this dehydration is coupled to a steady decrease in the ratio of tetrahedral to octahedral Fe(iii) sites. In addition to the obvious constraints these findings place on making comparisons across Fh samples of different age and environmental settings, they also highlight that Fh structure, and consequently magnetism, are linked to its bound water content