Residual CH Research Articles

Modification on the chloride binding capacity of alkali activated slag by applying calcium and aluminium containing phases

In this study, a modified alkali activated slag system is designed by introducing additional calcium and aluminum containing phases in the binder, aiming at promote the formation of Friedel's salt (Fs) within the reaction products and therefore achieve a better chloride binding capacity. The effect of calcium and alumina contents on phase composition, chloride binding behavior, pore structure and mechanical properties of alkali activated slag are investigated. The results show that the addition of Ca(OH)2 and nano γ-Al2O3 (CH and NA) results in the residual CH within the reaction products, but when in present of chloride, all residual CH transformed into Fs or other phases. The chloride binding capacity of the binder is obviously enhanced by CH and NA addition, owing to the increased ability to chemically bind chloride through Fs formation. There also exists an optimum Ca/Al ratio of the starting material regarding the chloride binding capacity. Adding CH coarsen the pore structure of the hydrated matrix by increase the amount of pores with the sizes larger than 200 nm, while NA exhibits a contrary effect. The chloride chemically binding behavior, namely the formation of Fs, slightly reduced the porosity of the binder. The strength results illustrate the negative effect of CH on compressive strength, and NA presents a positive effect, the modified binding system is able to provide a comparable mechanical property when compared with the reference alkali activated mixture.

A Study on Ordinary Portland Cement Blended with Rice Husk Ash and Metakaolin

This paper tries to investigate the effect of replacing Ordinary Portland cement (OPC) with Metakaolin (MK) and Rice husk ash (RHA) on the physicomechanical properties such as consistency, setting times, soundness and mortar compressive strength of ternary cement up to 40 % cement replacement. The soundness of the blended cement pastes and compressive strength of the blended mortars were conducted using Le Chatelier apparatus and Tonic Technic compression machine while the initial and final setting times were conducted on the blended cement paste using Vicat apparatus. Nineteen ternary cement mortars were prepared to comprise of OPC, RHA MK at different proportions and tested at 2, 7, 28 and 60 days. Results indicated that as RHA was gradually increased up to 25% at constant MK content, the volume expansion of the ternary cement paste increased gradually. On the other hand, as MK was increased from 5-25% at constant RHA, the volume expansion diminished. The water consistency of ternary cement paste experienced a variation as MK was increased up to 25 wt% at constant RHA up to 10 wt%. However, at 10 wt% constant RHA as MK was increased the water demand gradually increased. Similarly, an increase in RHA at constant MK increased the water demands of the ternary blends. An increase in RHA from 5-25 wt% at 5-25 wt% constant MK resulted in an acceleration in the initial and final setting times of cement blends. These accelerations could be attributed to the pozzolanic activity leading in shorter setting time. Whereas a series of accelerations and retardations of both setting times were experienced as the MK was increased from 5-25 wt% at 5-25 wt% constant RHA. It was observed that increment in the MK or RHA up to 10 wt% at constant RHA/MK up to 10 wt% resulted in improved mortar compressive strength of the ternary blend in comparison with control. This improvement was attributed to the high silica/alumina contribution to the matrix by MK inclusion, the C/S ratio in the cement matrix and RHA pozzolanic reactivity despite its unburnt carbon. All mortar compressive strength of the cement blends and control experienced an increase as the curing days were lengthened from 2 to 60 days. The enhanced strength compared with the control especially beyond 28 days could be attributed to the slow pozzolanic reaction resulting from the formation of additional CSH and CAH from the interaction of the residual CH and the silica available in the MK and RHA. The best compressive strength at 60 days was obtained at cement replaced with 15 wt% and 20 wt% at MK 5 wt% RHA producing a mortar compressive strength of 40.5 MPa.

A Hybrid Fuzzy-Genetic Algorithm for Performance Optimization of Cyber Physical Wireless Body Area Networks

The use of fuzzy decision-making in datapath selection extends the sensor network lifetime with a uniform distribution of routing load among network nodes. Fuzzy-logic based routing protocols are mostly designed for general wireless sensor networks (WSN). However, such protocols are not compatible with a Wireless Body Area Network (WBAN) comprised of biosensor nodes. WBAN nodes carry inferior computational, communication and energy resources as compared to general WSN nodes. A WBAN routing protocol needs to be designed as per IEEE 802.15.6 WBAN standards to meet high-end QoS requirements of medical applications. This paper presents a fuzzy-logic-based clustering protocol for data routing in WBANs. Nodes are grouped into clusters and cluster head nodes are selected through a Fuzzy-Genetic Algorithm termed as EB-fg-MADM. EB-fg-MADM makes an assessment of dual attributes of each cluster node in terms of node residual energy and CH selection cost. CH selection cost of a node is the forecasted value of network energy consumption if the node acts as a cluster head. EB-fg-MADM utilizes a fuzzy-TOPSIS function which makes a quantitative comparison of cluster nodes and selects the cluster head node possessing the aforementioned attributes closest to their ideally desired values. A Genetic Algorithm-based optimization process adapts the attribute weights for cluster head selection. EB-fg-MADM provides enhanced network lifetime with a uniform distribution of routing load. Protocol performance is obtained in terms of network lifetime, throughput and latency. Results are compared with existing WBAN routing protocols and are found to be better.

Genomewide association study of methane emissions in Angus beef cattle with validation in dairy cattle.

Methane (CH) is a product of enteric fermentation in ruminants, and it represents around 17% of global CH emissions. There has been substantial effort from the livestock scientific community toward tools that can help reduce this percentage. One approach is to select for lower emitting animals. To achieve this, accurate genetic parameters and identification of the genomic basis of CH traits are required. Therefore, the objectives of this study were 1) to perform a genomewide association study to identify SNP associated with several CH traits in Angus beef cattle (1,020 animals) and validate them in a lactating Holstein population (population 1 [POP1]; 205 animals); 2) to validate significant SNP for DMI and weight at test (WT) from a second Holstein population, from a previous study (population 2 [POP2]; 903 animals), in an Angus population; and 3) to evaluate 2 different residual CH traits and determine if the genes associated with CH also control residual CH traits. Phenotypes calculated for the genotyped Angus population included CH production (MeP), CH yield (MeY), CH intensity (MI), DMI, and WT. The Holstein population (POP1) was multiparous, with phenotypes on CH traits (MeP, MeY, and MI) plus genotypes. Additionally, 2 CH traits, residual genetic CH (RGM) and residual phenotypic CH (RPM), were calculated by adjusting MeP for DMI and WT. Estimated heritabilities in the Angus population were 0.30, 0.19, and 0.15 for MeP, RGM, and RPM, respectively, and genetic correlations of MeP with DMI and WT were 0.83 and 0.80, respectively. Estimated heritabilities in Holstein POP1 were 0.23, 0.30, and 0.42 for MeP, MeY, and MI, respectively. Strong associations with MeP were found on chromosomes 4, 12, 14, 20, and 30 at < 0.001, and those chromosomes also had significant SNP for DMI in Holstein POP1. In the Angus population, the number of significant SNP for MeP at < 0.005 was 3,304, and approximately 630 of those SNP also were important for DMI and WT. When a set (approximately 3,300) of significant SNP for DMI and WT in the Angus population was used to estimate genetic parameters for MeP and MeY in Holstein POP1, the genetic variance and, consequently, the heritability slightly increased, meaning that most of the genetic variation is largely captured by these SNP. Residual traits could be a good option to include in the breeding goal, as this would facilitate selection for lower emitting animals without compromising DMI and WT.

Observation of Evidence for the π*-σ* Hyperconjugation in the S1 State of o-, m-, and p-Fluorotoluenes by Double-Resonance Infrared Spectroscopy.

Drastic changes of the methyl internal rotation potential energy functions upon the electronic excitation have been reported for o- and m-fluorotolunes [ Okuyama , K. , Mikami , N. , and Ito , M. J. Phys. Chem. 1985 , 89 , 5617 - 5625 ], and their physical origin has been attributed to the π*-σ* hyperconjugation. To observe direct evidence of the π*-σ* hyperconjugation, double-resonance infrared spectroscopy was carried out in the CH stretching vibrational region in both the S0 and S1 states of jet-cooled o-, m-, and p-fluorotoluenes. In the spectra of both o- and m-fluorotoluenes, some of the methyl CH bands were red-shifted upon the electronic excitation while the residual CH bands stayed in the same frequency region. The normal-mode analysis demonstrated that the shift behavior correlates to the relative conformation between the methyl CH bond and the phenyl ring plane. This conformation-dependent methyl CH bond weakening clearly supports the presence of the π*-σ* hyperconjugation in o- and m-fluorotoluenes. The similar red-shift of the methyl CH bands upon the electronic excitation was seen also in p-fluorotoluene though the magnitude of the shift was much smaller. The mechanism of its internal rotation potential energy behavior, however, can be different from those of the o- and m-isomers.

Variations in the Nature of Triple Bonds: The N2, HCN, and HC2H Series

The inertness of molecular nitrogen and the reactivity of acetylene suggest there are significant variations in the nature of triple bonds. To understand these differences, we performed generalized valence bond as well as more accurate electronic structure calculations on three molecules with putative triple bonds: N2, HCN, and HC2H. The calculations predict that the triple bond in HC2H is quite different from the triple bond in N2, with HCN being an intermediate case but closer to N2 than HC2H. The triple bond in N2 is a traditional triple bond with the spins of the electrons in the bonding orbital pairs predominantly singlet coupled in the GVB wave function (92%). In HC2H, however, there is a substantial amount of residual CH(a(4)Σ(-)) fragment coupling in the triple bond at its equilibrium geometry with the contribution of the perfect pairing spin function dropping to 82% (77% in a full valence GVB calculation). This difference in the nature of the triple bond in N2 and HC2H may well be responsible for the differences in the reactivities of N2 and HC2H.

English

INTRODUCTION: The surgical treatment of cholesteatoma in paediatric age group has changed opinion many times in the evolution of cholesteatoma surgery. Intact canal wall technique allows provision for maintaining the depth of the middle ear and postoperative hearing is much better than in canal wall down procedure. Canal wall down method precludes regular cleaning of the large cavity left behind. In CWU method incidence of recurrent and residual CH are more than in CWD methods. It is more common because inspection of epi-tympanum and medial aspects of the ossicles is not possible in ICW procedures. As a result, the disease recurs within 6 to 12 months. MATERIALS AND METHODS: Fifty children attending the OPD of Government General Hospital Kurnool with CH, confirmed with CT scan are taken and subjected to ICW tympano-mastoidectomy with or without ossiculoplasty. They are followed for a period of 18 months for residual disease,auditory evaluation and otoscopic examination for graft take up. RESULTS: There was improvement in hearing in 78% of the patients. Graft healing was good in 80.85% of cases. Recurrence was seen in 19.15% of patients. 14% of the patients ICW had to be converted to a CWD procedure within 8 months. There were no reports of intra cranial complication in this series. CONCLUSION: ICW procedure in paediatric cholesteatoma gives better results if the disease is limited to the posterior mesotympanum and not beyond the auditus. Uneventful 18months follow up period was seen in 80.85% of the patients. Recurrent disease is less common if the mastoids are less pneumatized. Revision to CWD may be required in early recurrence; in this series it was 14% of the patients.

CO 2 savings affect the break-even distance of feedstock supply and digestate placement in biogas production

Anaerobic digestion promotes a valorisation of residual and dedicated biomass of agricultural origin. The EU Directive 2009/28/CE mandates a minimum 35% saving in greenhouse gas (GHG) emission for biofuels and bioliquids. National legislations add further limits, such as a 70 km maximum distance in the supply of biomass for energy uses (Short chain support scheme in Italy). In order to assess if the substitution of fossil fuels with biogas complies with such obligations and which are the factors most influencing GHG savings, a simulation study was carried out on a digester fed by maize silage, as many plants built in the frame of the current incentives. A simplified balance was drawn between the CO 2 emitted and saved by a 1000 kW el digester aimed for heat and electricity co-generation. The simulation output was the operational radius of feedstock supply and digestate disposal allowing a 35% CO 2 saving in a standard scenario. A sensitivity analysis was also run by varying several traits concerning process efficiency, feedstock characteristics, logistic aspects, plus the amount of net thermal energy actually exploited and CH 4 and N 2O emissions from the stored digestate. The standard scenario involving a 35% CO 2 saving allowed an operational radius of 192 km, almost three times as large as the maximum distance prescribed by the Short chain scheme. As an alternative, a 50% CO 2 saving was possible at a radius of 70 km. Varying the process, feedstock and logistic traits by ±10% determined variations in the break-even distance associated with a 35% CO 2 saving, ranging from ±20% (total solids; volatile solids; anaerobic biogasification potential; biogas CH 4 content), to ±15% (energy efficiency), to only ±5% (CO 2 emissions in the cropping phase; the carrying capacity of transport means). Actual heat utilisation and digestate GHG emissions, respectively set at 100% and 0% in the standard scenario, are traits with a high uncertainty in the normal practice. Therefore, a respective variation of −50% and +50% was adopted in the sensitivity analysis, determining in both cases a strong reduction (50%) of the break-even distance. In order to overcome the critical points represented by the amount of net thermal energy actually valorised and by GHG emissions from the stored digestate, special care is needed in planning biogas plants, in order to ensure a good utilisation of heat and recycle residual CH 4 within the process.

Evaluation of energy-conversion efficiencies in microbial fuel cells (MFCs) utilizing fermentable and non-fermentable substrates

We established the first complete electron-equivalent balances in microbial fuel cells (MFCs) fed with non-fermentable (acetate) and fermentable (glucose) electron donors by experimentally quantifying current, biomass, residual organic compounds, H 2, and CH 4 gas. The comparison of the two donors allowed us to objectively evaluate the diversion of electron flow to non-electricity sinks for fermentable donors, leading to different behaviors in energy-conversion efficiency (ECE) and potential efficiency (PE). Electrical current was the most significant electron sink in both MFCs, being 71% and 49%, respectively, of the initial COD applied. Biomass and residual organic compounds, the second and third greatest sinks, respectively, were greater in the glucose-fed MFC than in the acetate-fed MFC. We detected methane gas only in the glucose-fed MFC, and this means that anode-respiring bacteria (ARB) could out-compete acetoclastic methanogens. The ECE was 42% with acetate, but was only 3% with glucose. The very low ECE for glucose was mostly due to a large increase of the anode potential, giving a PE of only 6%. Although the glucose-fed MFC had the higher biomass density on its anode, it had a very low current density, which supports the fact that the density of ARB was very low. This led to slow kinetics for electron transfer to the anode and accentuated loss due to the substrate-concentration gradient in the anode-biofilm. The large drop of PE with low current, probably caused by a low ARB density and electron (e −) donor concentration, resulted in a poor maximum power density (9.8 mW/m 2) with glucose. In contrast, PE reached 59% along with high current for acetate and the maximum power density was 360 mW/m 2.

Variable carbon isotope fractionation expressed by aerobic CH 4-oxidizing bacteria

Carbon isotope fractionation factors reported for aerobic bacterial oxidation of CH 4 ( α CH 4 – CO 2 ) range from 1.003 to 1.039. In a series of experiments designed to monitor changes in the carbon isotopic fractionation of CH 4 by Type I and Type II methanotrophic bacteria, we found that the magnitude of fractionation was largely due to the first oxidation step catalyzed by methane monooxygenase (MMO). The most important factor that modulates the ( α CH 4 – CH 3 OH ) is the fraction of the total CH 4 oxidized per unit time, which strongly correlates to the cell density of the growth cultures under constant flow conditions. At cell densities of less than 0.1 g/L, fractionation factors greater than 1.03 were observed, whereas at cell densities greater than 0.5 g/L the fractionation factors decreased to as low as 1.002. At low cell densities, low concentrations of MMO limit the amount of CH 4 oxidized, while at higher cell densities, the overall rates of CH 4 oxidation increase sufficiently that diffusion of CH 4 from the gaseous to dissolved state and into the cells is likely the rate-determining step. Thus, the residual CH 4 is more fractionated at low cell densities, when only a small fraction of the total CH 4 has been oxidized, than at high cell densities, when up to 40% of the influent CH 4 has been utilized. Therefore, since Rayleigh distillation behavior is not observed, δ 13C values of the residual CH 4 cannot be used to infer the amount oxidized in either laboratory or field-studies. The measured ( α CH 4 – CH 3 OH ) was the same for both Type I and Type II methanotrophs expressing particulate or soluble MMO. However, large differences in the δ 13C values of biomass produced by the two types of methanotrophs were observed. Methylosinus trichosporium OB3b (Type II) produced biomass with δ 13C values about 15‰ higher than the dissimilated CO 2, whereas Methylomonas methanica (Type I) produced biomass with δ 13C values only about 6‰ higher than the CO 2. These effects were independent of the magnitude of the initial carbon isotope fractionation caused by MMO and were relatively constant despite changing ratios of assimilatory to dissimilatory carbon transformation by the organisms. This suggests that the difference in biomass carbon isotopes is primarily due to differences in the fractionation effect at the formaldehyde branch point in the metabolic pathway, rather than assimilation of CO 2 by Type II methanotrophs.

Mixed CH 4–CO 2 fluid inclusions in quartz from the South Wales Coalfield as suitable natural calibration standards for microthermometry and Raman spectroscopy

Laser Raman and microthermometric analysis have been used independently to calculate the molar proportions of mixed CH 4–CO 2 fluid inclusions in quartz from the South Wales Coalfield, UK. The respective ratios of the mean values obtained are 84 : 16 and 85 : 15 mol%. Therefore, the fluid inclusions are suitable for independently checking the validity of LRM and microthermometric data, and for determining the instrumental efficiency coefficient ξ of Raman microprobes. Individual fluid inclusions show consistent and reproducible phase transitions on heating and cooling between room temperature and − 196 °C. LRM tracking of these phase changes shows that on cooling CO 2 is strongly partitioned into a solid phase, thus purifying the residual CH 4 liquid down to − 196 °C at which point it freezes. Reheating results in the melting of the CH 4 solid to form co-existing liquid + vapour + solid ( L + V + S) CH 4 at the triple point of − 182.5 (± 1) °C. In these samples, this phase transition is exceptionally clear and reproducible making the inclusions suitable as a low temperature calibration standard for microthermometric studies. The Raman spectra for L, V and S methane are distinguishable, with a prominent peak at 2906 (± 1) cm − 1 for CH 4 ( S) at − 190 °C, compared with peak positions for CH 4 ( V) and CH 4 ( L) at − 105 °C at 2917 and 2910 (± 1) cm − 1 , respectively. Similar patterns apply to the CO 2 spectra. With change of aggregation the peak position shifts by up to 7 wave numbers. These data show that the Raman peak positions in natural inclusions depend not only on temperature and pressure as previously reported, but also on the state of matter in which the component occurs: L, V or S.

High-resolution methane profiles across anoxic brine–seawater boundaries in the Atlantis-II, Discovery, and Kebrit Deeps (Red Sea)

A decrease in temperature (Δ T up to 45.5 °C) and chloride concentration (ΔCl up to 4.65 mol/l) characterises the brine–seawater boundary in the Atlantis-II, Discovery, and Kebrit Deeps of the Red Sea, where redox conditions change from anoxic to oxic over a boundary layer several meters thick. High-resolution (100 cm) profiles of the methane concentration, stable carbon isotope ratio of methane, and redox-sensitive tracers (O 2, Mn 4+/Mn 2+, Fe 3+/Fe 2+, and SO 4 2−) were measured across the brine–seawater boundary layer to investigate methane fluxes and secondary methane oxidation processes. Substantial amounts of thermogenic hydrocarbons are found in the deep brines (mostly methane, with a maximum concentration up to 4.8×10 5 nmol/l), and steep methane concentration gradients mainly controlled by diffusive flow characterize the brine–seawater boundary (maximum of 2×10 5 nmol/l/m in Kebrit Deep). However, locally the actual methane concentration profiles deviate from theoretical diffusion-controlled concentration profiles and extremely positive δ 13C–CH 4 values can be found (up to +49‰ PDB in the Discovery Deep). Both, the actual CH 4 concentration profiles and the carbon-13 enrichment in the residual CH 4 of the Atlantis-II and Discovery Deeps indicate consumption (oxidation) of 12C-rich CH 4 under suboxic conditions (probably utilizing readily available—up to 2000 μmol/l—Mn(IV)-oxihydroxides as electron acceptor). Thus, a combined diffusion–oxidation model was used to calculate methane fluxes of 0.3–393 kg/year across the brine–seawater boundary layer. Assuming steady-state conditions, this slow loss of methane from the brines into the Red Sea bottom water reflects a low thermogenic hydrocarbon input into the deep brines.

Investigation on POM reaction in a new perovskite membrane reactor

A perovskite-type oxide of Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ (BSCFO) shows mixed (electronic/oxygen ionic) conductivity at high temperatures. Membrane made of the oxide has high oxygen permeability under air/helium oxygen partial pressure gradient. At 850°C, oxygen permeation rate maintained about 1.15 ml/cm 2 min for more than 1000 h under ambient air/helium oxygen gradient. A membrane reactor constructed from the oxide membrane was applied for the partial oxidation of methane (POM) to syngas, LiLaNiO x /γ-Al 2O 3 with 10 wt.% Ni loading was used as the packed catalyst. At the initial stage, oxygen permeation rate, methane conversion and CO selectivity were closely related with the state of the catalyst. Less than 21 h was needed for the oxygen permeation rate to reach its steady state. A membrane reactor made of BSCFO was successfully operated for POM reaction at 875°C for about 500 h without failure, with methane conversion of >97%, CO selectivity of >95% and oxygen permeation rate of about 11.5 ml/cm 2 min. Under membrane reaction condition, the POM reaction mechanism was suggested to obey the CRR (complete combustion of CH 4 to CO 2 and H 2O and a subsequent reforming reaction of the residual CH 4 and with CO 2 and H 2O to CO and H 2) mechanism.

Densification of hybrid silica–titania sol–gel films studied by ellipsometry and FTIR

Hybrid silica–titania films were prepared via sol–gel processing, by dip-coating on silicon wafer substrates, from organically-modified silane and titanium isopropoxide precursors. These hybrid sol–gel films were then subjected to selected heat treatments at temperatures up to 950°C and their densification was followed by ellipsometry and infrared absorption (FTIR) spectroscopy. The volume fraction of residual porosity was estimated, based on the refractive index data. A clear correlation was observed between the intensity of the infrared spectral shoulder near 1150 cm −1 and the porosity values, for the different heat treatment temperatures. For any treatment up to 950°C, the porosity of the hybrid silica–titania gel films was higher than that of the corresponding inorganic gel films, while both continuously decreased with increasing heat treatment temperature. The residual SiCH 3 groups, whose presence was identified in the hybrid silica–titania films until a temperature near 500°C, tend to be transformed into SiOH (silanol) groups as they are eliminated. Most silanol groups are eliminated at a temperature near 600°C. The hybrid silica–titania films were found to have a more porous and more compliant gel network than the corresponding inorganic films, while their structure appears to exhibit a smaller spread in the SiOSi intertetrahedral angle distribution.

How specific is the inhibition by methyl fluoride of acetoclastic methanogenesis in anoxic rice field soil?

Acetoclastic methanogens have been described to be inhibited at much lower concentrations of methyl fluoride, CH 3F, than H 2/CO 2-utilizing methanogens. Therefore, we tested whether CH 3F inhibition may be used to determine, in anoxic rice field soil, the contribution of H 2/CO 2-dependent methanogenesis to the total CH 4 production by comparing this technique with the incorporation of 14CO 2 into CH 4. In general, addition of 0.01–1% CH 3F to the gas phase resulted in an immediate partial inhibition of the total CH 4 production which lasted for at least 200 h. Inhibition increased with the logarithm of the initial CH 3F concentration up to about 0.2–0.6%. The initial CH 3F concentration slowly decreased with time, probably due to decomposition. CH 4 production sometimes completely recovered during the course of the experiment. The presence of CH 3F resulted in the accumulation of acetate, the final concentration of which was usually stoichiometrically related to the deficit in CH 4 production and increased with the initial CH 3F concentration. In some experiments, acetate accumulation was larger than expected from the CH 4 deficit and a substantial incorporation of 14CO 2 into acetate was observed. Hydrogen, on the other hand, was only slightly elevated in the presence of CH 3F. Addition of increasing CH 3F resulted in an increase of the percentage of H 2-dependent methanogenesis (measured by conversion of 14CO 2 to 14CH 4) demonstrating that acetoclastic methanogenesis was preferentially inhibited by CH 3F. However, the conversion of 14CO 2 to 14CH 4 was also slightly inhibited by CH 3F. Apparently, CH 3F inhibited the H 2-dependent methanogenesis to some extent, depending on the concentration of CH 3F applied. Indeed, the ratio between the residual CH 4 production rate and the fraction of CH 4 produced from 14CO 2 decreased with an increasing CH 3F concentration. A ratio of unity was obtained at initial CH 3F concentrations of 0.2–0.6% (58–174 μM). Both methods, i.e. inhibition using 0.5% CH 3F and conversion of 14CO 2 to 14CH 4, were applied to determine the temporal change of the contribution of H 2/CO 2-dependent methanogenesis to the total CH 4 production in two different batches of Italian rice field soil during a 120-days anoxic incubation period. The results of the two methods agreed well within the error of the methods and showed a relatively constant contribution of H 2/CO 2-dependent methanogenesis of about 25–30% as soon as CH 4 was produced at a steady rate and H 2 partial pressures had stabilized at about 1.5–2.5 Pa.

Inelastic electron tunneling spectroscopy of triethoxysilane on germania: a model study for silane-glass adhesion

IET spectra are presented for the first time for inorganic monolayers adsorbed on artificial tunnel barriers. They are obtained from hydrolyzed triethoxysilane (TES) monolayers introduced onto ultra-thin sputtered germania films incorporated in Al/germania/TES/Pb tunnel junctions. The minimum thickness required for germania film continuity is determined to be ∼ 1.5nm using a reliable method which is described. Three techniques are then used to dope the germania surface with TES; these are by exposure to: (i) TES vapor under a dry nitrogen atmosphere, (ii) TES vapor under a water vapor/nitrogen atmosphere, and (iii) aqueous acidic hydrolyzed TES solution. Vibrational spectra obtained using (i) and (iii) are similar; in both cases strong SiH stretching and bending modes are present at approximately 2000–2200 cm−1, and 900 cm−1 respectively. However, only very weak features due to residual CH species are present. These results confirm that the TES hydrolyses to a large degree and condenses on the germania surface. Spectra obtained using (ii) are similar to those obtained by the other two methods but also contain vibrational modes due to SiOSi stretching vibrations, which indicates that the TES not only hydrolyzes and condenses on the surface, but also polymerizes to form a hydrogenated polysiloxilane matrix. In contrast, spectra obtained for TES adsorbed on alumina using the same three techniques indicate that the TES neither hydrolyzes, condenses, nor polymerizes unless introduced from an aqueous acidic solution.

Carbon and hydrogen isotope fractionation during oxidation of methane by metal oxides at temperatures from 400° to 530°C

The oxidation of methane by metal oxides (Fe 2O 3, MnO 2 and CuO) in closed systems is controlled by the oxides and temperature. Abiogenic oxidation of methane can readily occur, even at temperatures below 200°C in the Earth's upper crust. The existence of residual CH 4 relatively enriched in 13C during oxidation can be explained by a kinetic isotope effect. The deuterium concentration of residual methane in the MnO 2 and CuO oxidation systems is controlled by a kinetic isotope effect, whereas for the Fe 2O 3 system, an isotope exchange between CH 4 and H 2O was observed. For the MnO 2 system, the temperature dependence of hydrogen isotope fractionation is similar to that for CuO, and was obtained as: 10 3(α H − 1) = 134 × 10 6 T 2−127 The relative change in the isotope concentrations in CH 4 during abiogenic oxidation is ΔH ΔC ≈ 21 at 200°C. This change is greater than that of other methane oxidation processes, indicating that carbon and hydrogen isotope compositions of methane may be useful in identifying abiogenic oxidation from other oxidation processes.

Effect of solvent removal technique on the matrix characteristics of polylactide/glycolide microspheres for peptide delivery

Porous salmon calcitonin (sCT)-loaded PLGA microspheres (size range 35–140μm) of varying matrix characteristics were prepared by an aqueous emulsification process using either a temperature gradient (Tmp) or dilution (Dil) of the continuous phase (CP). The Tmp technique resulted in microspheres with a hollow internal core and a porous wall. The core size and thickness of the porous wall were dependent on the temperature gradient used. A rapid ramp of temperature from 15 to 40°C resulted in a large core and a thin wall, while a gradual temperature rise resulted in a smaller core. The Dil technique produced microspheres with a uniform, honeycomb like pore structure without a core, pore size being dependent on the dilution volume used. The specific surface area was higher and bulk density lower for microspheres prepared by the Tmp technique while there was no significant difference in the peptide load (3.2–4.5%) between both techniques. A rapid removal of CH 2C1 2 was observed in case of the Tmp technique while the Dil technique facilitated a slower and gradual CH 2C1 2 removal. Residual CH 2Cl 2 was approximately < 10–20 ppm for microspheres prepared by the Tmp technique while the levels were 20–130 ppm for microspheres produced by the Dil technique. Higher retention of methanol (−15–50%) was observed in the droplet formation stage with the Tmp technique, subsequent removal of which affected the core size. In the Dil technique, very low levels of methanol (< 2%) were retained in the droplets soon after dispersion resulting in a uniform porous structure without core. Slower removal of methanol from the microspheres was partly responsible for the core formation.

The carbonation of hardened cement pastes

The microstructure of hardened pastes of C3S and a C3S/silica fume blend have been examined by transmission electron microscopy before and after partial carbonation in pure CO2 at a relative humidity of 72·6%. Fibrillar outer product C-S-H and the outer regions of inner product C-S-H gel carbonate without change of morphology to silica gel. Calcium carbonate is formed mainly in outer product regions as microcrystalline vaterite or calcite. Residual CH embedded in vaterite microcrystals is observed in the carbonated C3S pastes. It is proposed that outer product C-S-H and CH surfaces carbonate relatively rapidly, compared with inner regions of CH or the inner regions of inner product C-S-H, leading to a substantial level of carbonation of thin slices (0·4 mm) of paste within one day, with little further carbonation in the next few days. The implications for the theory of the kinetics of cement paste carbonation are discussed.

Study of the adsorption of H 2O+H 2 on oxygen contaminated Nb (110) surfaces at 110 K by ESD, AES and ELS

The adsorption of H 2O+H 2 on O contaminated Nb(110) at a temperature of 110 K has been studied by electron stimulated desorption (ESD), energy loss spectroscopy (ELS), and Auger electron spectroscopy (AES). ESD spectra show H + as the most important surface ion. The remaining 24% consists of H 2O +, OH + and O +. During adsorption three regions can be identified in the ion yield at increasing exposures of H 2O: (i) for O < Q < 1 L (H 2O) there is an increase of H +, O + and OH + surface ions, peaking at about 1 L (H 2O); (ii) for 1 < Q < 100L (H 2O) H 2O + increases, peaking at about 60 L (H 2O) while the other surface ions decrease; (iii) at Q > 1000 L (H 2O) H + tends to remain constant while H 2O +, O + and OH + disappear. of adsorption. AES spectra show an attenuation of the Nb (NVV) transition due to the H 2O adsorption. ELS reveals a loss at 20.8 eV, which should be identified with the O (2s) ionization, a shift of the Nb (4p) core level of approximately 5 eV and a broadness of the plasmon resonance at 8.7 eV. There is a contamination of the surface with C probably due to both the residual CH 4 and CO in the uhv system, or diffused from the bulk.