Transport mechanism of hydrogen through oxide film formed on zircaloy-4

The diffusion behavior of hydrogen in the oxide films of zircaloy-4 specimens containing different size of Zr(Fe,Cr)₂ precipitates was examined. In the case of the specimen containing fine precipitates, hydrogen diffused uniformly through the zirconium oxide phase. The diffusion coefficient was 2·10⁻²¹ m²·s⁻¹ at room temperature and 6·10⁻¹⁹ m²·s⁻¹ at 673 K. The transport rate of hydrogen in the oxide film of the specimen containing coarse precipitates was significantly higher than that of the specimen containing fine ones at both room temperature and 673 K.     

Rare-earth elemental analysis of banded iron-formations by instrumental neutron activation analysis

Representative banded iron-formations (BIFs) from various locations of the eastern Indian geological belt were investigated by instrumental neutron activation analysis (INAA). After pre-concentration, irradiation was carried out using a neutron flux of 5.1·10¹⁶ m⁻²·s⁻¹, 1.0·10¹⁵ m⁻²·s⁻¹ and 3.7·10¹⁵ m⁻²s⁻¹, with thermal, epi-thermal and fast neutrons, respectively. The activities in these samples were measured by a HPGe detector. Ten rare-earth elements, such as La, Ce, Nd, Sm, Eu, Tb, Ho, Tm, Yb and Lu, have been qualitatively identified and quantitatively estimated in these samples. The present investigation is an example of employing a pre-concentration method for high iron-containing ores prior to neutron activation analysis.     

Contribution to the external gamma dose rate from <Superscript>137</Superscript>Cs and <Superscript>40</Superscript>K activity concentrations determined in the vertical profile of sandy beaches

Sampling sites, located along the Calabria and Basilicata Regions coastal beaches (south of Italy), were selected to assess the external gamma dose rate in air, 1 m above ground, and to estimate the fraction attributable to the radiocesium and radiopotassium contents along the vertical sand profile. Mean values for the gamma dose rate were: 76±30 nGy·h⁻¹. ¹³⁷Cs and ⁴⁰K deposition densities in sand samples were determined for each sampling site (mean values 0.24±0.22 kBq·m⁻² and 178±88 kBq·m⁻², respectively). The ¹³⁷Cs external dose rate contribution was assessed using a Monte Carlo simulation code. The method gives an estimation of the contribution to the external gamma dose rate of each sand layer along the vertical profile. The dose rate associated with the ¹³⁷Cs content in sand was 0.16±0.14 nGy·h⁻¹. The cosmic radiation and ⁴⁰K contributions to the external gamma dose rate were estimated using the UNSCEAR methodologies. The values obtained were 34±3 nGy·h⁻¹ and 18±9 nGy·h⁻¹, respectively.     

The thermal decomposition of N , N -dimethyl-3-oxaglutaramic acid and the kinetics of its second-stage thermal decomposition reaction

N,N-dimethyl-3-oxa-glutaramic acid was purified and characterized by ¹H-NMR, Fourier transform infrared spectroscopy (FT-IR) and elemental analysis. The thermal decomposition of the title compound was studied by means of thermogravimetry differential thermogravimetry (TG-DTG) and FT-IR. The kinetic parameters of its second-stage decomposition reaction were calculated and the decomposition mechanism was discussed. The kinetic model function in a differential form, apparent activation energy and pre-exponential constant of the reaction are 3/2 [(1−α)^1/3−1]⁻¹, 203.75 kJ·mol⁻¹ and 10^17.95s⁻¹, respectively. The values of ΔS ^≠, ΔH ^≠ and ΔG ^≠ of the reaction are 94.28 J·mol⁻¹·K⁻¹, 203.75 kJ·mol⁻¹ and 155.75 kJ·mol⁻¹, respectively. Supported by the National Natural Science Foundation of China (Grant No. 20106009)     

A facile gamma-ray method for radiodegradation of bilirubin in chloroform

Kinetics and concentration profile associated with the regulated radiodegradation of bilirubin in an organic solvent were assessed. The pure unconjugated specimen was prepared in chloroform (40.0 μM). The depletion of bilirubin was almost linear with dose, and complete degradation was accomplished with doses in excess of 100 Gy. The method was also evaluated for the explicit production of the long-wavelength isomer of biliverdin, which was characterized spectrometrically by an absorbance band in the region 600–650 nm. Results including differences in air, N₂ and O₂ purged samples are presented to identify the atmospheric medium for optimum production of biliverdin. The process was regulated by controlling the dose. The general rate constant of the depletion process was estimated at a dose rate of 5.67·10⁻²Gy·s⁻¹. The method is a convenient substitute for light illumination studies of bilirubin. This revised version was published online in July 2006 with corrections to the Cover Date.     

<Emphasis Type="Italic">Ab initio</Emphasis> study of the reaction path of the reaction HNCO+CN

We report ab initio UMP2 calculations of the reaction of CN with HNCO using 6-311G(d,p) basis sets. The obtained results show that the reaction has two product channels: HNCO+CN→HCN+NCO (1) and HNCO+CN→HNCN+CO (2). Channel (1) is a hydrogen abstraction reaction, which is a concerted process. The calculated potential energy barrier is 20.80 kJ/mol at UMP2(full)/6-311G(d,p) level. In the range of reaction temperature (1000-2100 K), the conventional transition theory rate constant for channel (1) ranges from 0.32×10⁻¹¹ to 6.9×10⁻¹¹cm³· mol⁻¹· s⁻¹, which is close to the experimental value. Channel (2) is a stepwise reaction involving an intermediate during the process of reaction. The UMP2(full)/6-311G(d,p) potential energy barrier is 83.42 kJ/mol for the rate-controlling step, which is much higher than that of channel (1).     

Light sensitivity and potential stability of electrically conducting polymers commonly used in solid contact ion-selective electrodes

The results of a systematic study of the light sensitivity and long-term potential stability (30 days) of poly(pyrrole) (PPy), poly(3-octylthiophene) (POT), poly(3,4-ethylenedioxythiophene) (PEDOT), poly(aniline) (PANI) and plasticised poly(vinyl chloride) (PVC) containing 20% (m/m) PANI are reported. Thin films were prepared either electrochemically or by the solution casting technique. This fundamental study is of importance because conducting polymers (CP) are commonly used as ion-to-electron transduction materials in all-solid-state solid contact ion-selective electrodes. The potential stability test done in 0.1 M KCl (pH 7.5) simulates the extreme situation when the CP-based SC becomes in direct contact with water. Films prepared of a nanodispersion of PANI showed both good potential stability and insensitivity to light even under illumination with very intensive light (>10⁵ lx). In contrary, it was observed that POT is very light-sensitive. Upon illumination with intensive light, the potential responses of POT films prepared by solution casting and electropolymerisation were 315 and 590 mV, respectively. A room light sensitivity of approximately −10 to −15 mV was observed for these films. The other CPs in this study were insensitive to room light (∼150 lx), but were light-sensitive under illumination with intensive light. The potential drift of PPy(Cl) is below −10 μV/h (3–30 days), whereas the other most stable CPs in this study had a slightly higher potential drift.     

Theoretical study of bifurcated bent blue-shifted hydrogen bonds CH<Subscript>2</Subscript>···Y

Ab initio quantum chemistry methods were applied to study the bifurcated bent hydrogen bonds Y··· H₂CZ (Z = O, S, Se) and Y···H₂CZ₂ (Z = F, Cl, Br) (Y = Cl⁻, Br⁻) at the MP2/6-311++G(d,p) and MP2/6-311++G(2df,2p) levels. The results show that in each complex there are two equivalent blue-shifted H-bonds Y···H-C, and that the interaction energies and blue shifts are large, the energy of each Y···H-C H-bond is 15–27 kJ/mol, and Δr(CH) = −0.1 − −0.5 pm and Δv(CH) = 30 − 80 cm⁻¹. The natural bond orbital analysis shows that these blue-shifted H-bonds are caused by three factors: large rehybridization; small direct intermolecular hyperconjugation and larger indirect intermolecular hyperconjugation; large decrease of intramolecular hyperconjugation. The topological analysis of electron density shows that in each complex there are three intermolecular critical points: there is one bond critical point between the acceptor atom Y and each hydrogen, and there is a ring critical point inside the tetragon YHCH, so these interactions are exactly H-bonding.     

Anaerobic baffled reactor treatment of biodiesel-processing wastewater with high strength of methanol and glycerol: reactor performance and biogas production

Biodiesel-processing factories employing the alkali-catalyzed transesterification process generate a large amount of wastewater containing high amount of methanol, glycerol, and oil. As such, wastewater has high potential to produce biogas using anaerobic treatment. The aim of this research was to investigate the performance of an anaerobic baffled reactor for organic removal and biogas production from biodiesel wastewater. The effect of different organic loading rates, varying from 0.5 kg m⁻³ d⁻¹ to 3.0 kg m⁻³ d⁻¹ of chemical oxygen demand, was determined using three 22 L reactors, each comprising five separate compartments. Wastewater was pretreated with chemical coagulants to partially remove oil prior to experimentation. Results show that the anaerobic baffled reactor operated at 1.5 kg m⁻³ d⁻¹ of chemical oxygen demand and ten days of hydraulic retention time provided the best removal efficiencies of 99 % of chemical oxygen demand, 100 % of methanol, and 100 % of glycerol. Increasing the organic loading rate over 1.5 kg m⁻³ d⁻¹ of chemical oxygen demand led to excessive accumulation of volatile fatty acids thereby making the pH drop to a value unfavorable for methanogenesis. The biogas production rate was 12 L d⁻¹ and the methane composition accounted for 64–74 %. Phase-separated characteristics revealed that the highest chemical oxygen demand removal percentage was achieved in the first compartment and the removal efficiency gradually decreased longitudinally. A scanning electron microscopic study indicated that the most predominant group of microorganisms residing on the external surface of the granular sludge was Methanosarcina.     

Photochemical and photophysical properties ofmeso-tetraferrocenylporphyrin. Quenching ofmeso-tetraphenylporphyrin by ferrocene

It was found that the quantum yield of the fluorescence ofmeso-tetraferrocenylporphyrin (TFcP) is at most 3.0·10⁻⁵, and that of the triplet state of FTcP is at least 200 times lower than the quantum yield ofmeso-tetraphenylporphyrin (TPP). Excitation of TFcP in CCl₄ by light with λ>410 nm results in the oxidation of TFcP. The singlet and triplet excited states of TPP in toluene and acetonitrile are quenched by ferrocene with rate constants of 1.2·10¹⁰ and 1.7·10¹⁰, (4.6±0.5)·10⁸ and (1.37±0.21)·10⁹ L mol⁻¹ s⁻¹, respectively. The quenching mechanisms are discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1924–1927, October, 1999.     

The open-close mechanism of M2 channel protein in influenza A virus:A computational study on the hydrogen bonds and cation-π interactions among His37 and Trp41

The M2 protein from influenza A virus is a tetrameric ion channel. It was reported that the permeation of the ion channel is correlated with the hydrogen bond network among His37 residues and the cation-π interactions between His37 and Trp41. In the present study,the hydrogen bonding network of 4-methyl-imidazoles was built to mimic the hydrogen bonds between His37 residues,and the cation-π interactions between 4-methyl-imidazolium and indole systems were selected to represent the interac-tions between His37 and Trp41. Then,quantum chemistry calculations at the MP2/6-311G level were carried out to explore the properties of the hydrogen bonds and the cation-π interactions. The calcula-tion results indicate that the binding strength of the N-H···N hydrogen bond between imidazole rings is up to -6.22 kcal·mol-1,and the binding strength of the strongest cation-π interaction is up to -18.8 kcal·mol-1(T-shaped interaction) or -12.3 kcal·mol-1(parallel stacking interaction). Thus,the calcu-lated binding energies indicate that it is possible to control the permeation of the M2 ion channel through the hydrogen bond network and the cation-π interactions by altering the pH values.     

Atmospheric deposition fluxes of <Superscript>7</Superscript>Be, <Superscript>210</Superscript>Pb and <Superscript>210</Superscript>Po at Xiamen,China

The atmospheric deposition fluxes of ⁷Be, ²¹⁰Pb and ²¹⁰Po at Xiamen were measured. The samples were collected from March 2004 to April 2005 and the sampling period was one month. The ⁷Be and ²¹⁰Pb activity were measured using HPGe γ-spectrometer after concentration using Fe(OH)₃ co-precipitation method. The ²¹⁰Po was counted with an α-spectrometer after the sample was digested and spontaneous plated onto a silver planchet. At Xiamen, the atmospheric deposition fluxes of ⁷Be varied between 0.11 and 2.93 Bq·m⁻²·d⁻¹ and the average was 1.64 Bq·m⁻²·d⁻¹; ²¹⁰Pb fluxes varied between 0.04 and 0.85 Bq·m⁻²·d⁻¹, and the average was 0.51 Bq·m⁻²·d⁻¹; ²¹⁰Po fluxes varied between 0.002 and 0.133 Bq·m⁻²·d⁻¹, and the average was 0.061 Bq·m⁻²·d⁻¹. There were positive correlations between the deposition fluxes of ⁷Be, ²¹⁰Pb or ²¹⁰Po and the amount of precipitation. The residence time of aerosols varied between 6.0 and 54.0 days with a mean of 27.1 days, which were calculated by ²¹⁰Po/²¹⁰Pb fluxes ratios.     

Fallout of7Be in Damascus City

Atmospheric fallout of⁷Be was measured over a 2 year period (January 1995–January 1997) at Damascus city (33 N^o, 727 m above sea level). The annual total deposition of⁷Be was found to be 420 and 634 Bq·m⁻² for 1995 and 1996, respectively, reflecting a Mediterranean climate where two well recognized periods are dominant (wet and dry). The depositions in the wet periods were 303 Bq·m⁻² and 517 Bq·m⁻² for 1995 and 1996, respectively, while unexpected equal deposition rates in the two dry periods were found to be about 117 Bq·m⁻². In addition, monthly deposition rate of⁷Be showed a maxima in February in 1995 and January for 1996. Moreover, a comparison has been set for our measurements and other data obtained at different locations in the world.     

The Ethanol Tolerance of <Emphasis Type="Italic">Pachysolen tannophilus</Emphasis> in Fermentation on Xylose

The influence of ethanol on fermentation by Pachysolen tannophilus was studied. When xylose utilization rate was 80%, ethanol concentration began to decline. Fermentation of P. tannophilus was affected by ethanol addition in the beginning of fermentation; average xylose consumption rate was 0.065 g·l⁻¹·h⁻¹, and maximum specific growth rate was 0.07 h⁻¹ at 28 g·l⁻¹ ethanol, comparing with the average xylose consumption rate of 0.38 g·l⁻¹·h⁻¹ and maximum specific growth rate of 0.14 h⁻¹ in fermentation with no ethanol addition; P. tannophilus stopped growth at 40 g·l⁻¹ ethanol. When the initial ethanol concentration was 30 g·l⁻¹, the addition of glucose in xylose media made the growth of P. tannophilus better, and the most favorable glucose concentration was 15 g·l⁻¹ with the highest biomass of 1.51 g·l⁻¹ as compared with that of 0.95 g·l⁻¹ in pure xylose media.     

Evaluation of Multiple Corona Reactor Modes and the Application in Odor Removal

Effects of multiple corona reactor modes on pulse characteristics, energy transfer efficiency, and odor (H₂S and NH₃) removal were investigated experimentally by the wire-plate corona reactor(s). The removal efficiency of H₂S was only 91% and the energy consumption was 16.1 Wh m⁻³ by the single mode with a gas-flow rate of 23 m³ h⁻¹ and an initial concentration of 200 mg m⁻³. At the same experimental conditions, almost 100% removal efficiency was achieved and the energy consumption was only 12.8 and 14.9 Wh m⁻³ by the series and parallel modes. In the case of 50 mg m⁻³ NH₃ removal at the same gas-flow rate, the removal efficiencies with the single mode, the series and parallel modes were 64, 92 and 70%, respectively. The energy requirement did not increase at the same residence time under the experimental conditions of the single mode with a gas-flow rate of 11.5 m³ h⁻¹ and the series or parallel mode with a gas-flow rate of 23.0 m³ h⁻¹. The experimental results indicate that the series and parallel modes are effective in saving energy consumption, improving removal ability and efficiency, especially for the series mode.     

Concentrations atmospheriques de85Kr dans les hemispheres nord et sud

The evolution of⁸⁵Kr concentrations in the atmosphere has been followed in the Northern hemisphere (France) from June 1966 to February 1979 and in the Southern hemisphere from March 1968 to October 1977 (Tahiti and Terre Adélie). The growth observed during the years 1966–1968 (1.8 pCi·m⁻³ per year) in the Northern hemisphere did not continue in 1969, 1970, 1971, during which period a constant level at 14.8 pCi·m⁻³ per year and even a decrease (12.9 pCi·m⁻³ in 1971) were noticed; this was followed by a new increase of about 0.9 pCi·m⁻³ per year. In the Southern hemisphere, a regular groth from 1968 to 1974 (0.9 pCi·m⁻³ per year) was followed by values stabilized around 14.5 pCi·m⁻³. The curve illustrating the evolution of the Krypton specific activity in the Northern hemisphere from 1954 to February 1979 shows that this increased in a discontinuous way from 1 to 40 disintegrations per minute; nevertheless the present atmospheric activity is very low with a value of only 8·10⁻⁵ MPC.      

Evaluation of <Superscript>137</Superscript>Cs soil-to-plant transfer: Natural and model experiments

Soil and meadow grass were sampled in the whole territory of Lithuania in 1992–2000. For the laboratory experiment, spring wheat Triticum aestivum L. “Nandu” was used because its root system type is similar to that of perennial meadow grass. The ¹³⁷Cs soil-to-plant transfer factor of spring wheat was determined and the results were compared with the predicted values using a compartment model of soil-to-plant transfer and with the results of the field experiment. The results of comparing the measured and calculated transfer factor using the model show rather good coincidence, however, the calculated values were overestimated. The reason for overestimation can be that the uptake rate is not influenced only by the soil-to-plant transfer. The results of the model experiment (from 0.005 m²·kg⁻¹ to 0.053 m²·kg⁻¹) are close to those of the field measurements for grass (from 0.013 m²·kg⁻¹ in 1992–1995 to 0.10 m²·kg⁻¹ in 1999–2000).     

Determination of carbon impurities in epitaxial layers from semiconductor silicon by means of charged particles

The energy-dependent range of charged particles in activation analysis according to the reaction¹²C(d,n)¹³N permits the method to be applied to carbon determination in model epitaxial layers of sufficient thickness. We investigated 100 μm epitaxial layers of the n-type and undoped 50 μ layers as to p⁻ Czochralski substrates. Deuterons were slowed down with Cu and Ta foils having a limiting energy of 13.5 MeV, to 4.2 MeV and 2.9 MeV, respectively. In the resulting activation depths of 52 and 102 μm, the sensitivity of the method, which is 3·10¹⁴ at ·cm⁻³C at E_d=10 MeV in silicon, is reduced to 25% and 10%, respectively. An optimal flux of 0.9 μA·cm⁻² was maintained. After irradiation, 20 or 10 μm were etched off. The sample was inductively fused at 1500 K in a Pb₃O₄/B₂O₃ mixture.¹³N was passed with He as carrier gas into an absorption vessel kept at 77 K, and its activity was measured in γ, γ-coincidence.     

Preliminary kinetic characterization of xylose reductase and xylitol dehydrogenase extracted from Candida guilliermondii FTI 20037 cultivated in sugarcane bagasse hydrolysate for xylitol production

Candida guilliermondii FTI 20037 was cultured in sugarcane bagasse hydrolysate supplemented with 2.0 g/L of (NH₄)₂SO₄, 0.1 g/L of CaCl₂·2H₂O, and 20.0 g/L of rice bran at 35°C; pH 4.0; agitation of 300 rpm; and aeration of 0.4, 0.6, or 0.8 vvm. The high xylitol production (20.0 g/L) and xylose reductase (XR) activity (658.8 U/mg of protein) occurred at an aeration of 0.4 vvm. Under this condition, the xylitol dehydrogenase (XD) activity was low. The apparent K _M for XR and XD against substrates and cofactors were as follows: for XR, 6.4×10⁻² M (xylose) and 9.5×10⁻³ mM (NADPH); for XD, 1.6×10⁻¹ M (xylitol) and 9.9×10⁻² mM (NAD+). Because XR requires about 10-fold less xylose and cofactor than XD for the condition in which the reaction rate is half of the V _max, some interference on the overall xylitol production by the yeast could be expected.