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951.
In order to demonstrate the adsorption of the nitrogen monoxide molecule (NO) on the LaO (001) surface of LaFeO3, we perform simulations based on density functional theory. The generalized gradient approximation (GGA) for the exchange-correlation energy functional indicates that the electronic state of the LaFeO3 bulk is an anti-ferromagnetic insulator with a local magnetic moment of 4.1 μB at each Fe atom. Using the ultrasoft pseudo-potential method with spin-polarized GGA, fully optimized internal parameters as well as charge and spin density are determined for the NO-adsorbed structure prepared in a slab model. The calculated adsorption energy of NO is around ? 1.4 eV on the LaO (001) surface of LaFeO3. This value decreases down to ? 4.46 eV at an oxygen vacancy site, where the nitrogen atom of NO is embedded in the 1st LaO layer forming a bond with Fe in the 2nd FeO layer. 相似文献
952.
Hitotsuyanagi Y Odagiri M Kato S Kusano J Hasuda T Fukaya H Takeya K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(10):2839-2846
Two bicyclic hexapeptides, allo-RA-V (4) and neo-RA-V (5), and one cyclic hexapeptide, O-seco-RA-V (6), were isolated from the roots of Rubia cordifolia?L. Their gross structures were elucidated on the basis of spectroscopic analysis and X-ray crystallography of compound 5. The absolute stereochemistry of compounds 4 and 5 were established by their total syntheses, and the absolute stereochemistry of compound 6 by chemical correlation with deoxybouvardin (3). Comparison of the 3D structures of highly active RA-VII (1) with less-active compounds 4 and 5 suggests that the orientation of the Tyr-5 and/or Tyr-6 phenyl rings plays a significant role in their biological activity. The isolation of peptides 4-6, along with compound 3, and the comparison of their structures seem to indicate that peptide 6 may be the common precursor to bicyclic peptides 3-5 in the plant. 相似文献
953.
Thorenz UR Kundel M Müller L Hoffmann T 《Analytical and bioanalytical chemistry》2012,404(8):2177-2183
In this work, we describe a simple diffusion capillary device for the generation of various organic test gases. Using a set of basic equations the output rate of the test gas devices can easily be predicted only based on the molecular formula and the boiling point of the compounds of interest. Since these parameters are easily accessible for a large number of potential analytes, even for those compounds which are typically not listed in physico-chemical handbooks or internet databases, the adjustment of the test gas source to the concentration range required for the individual analytical application is straightforward. The agreement of the predicted and measured values is shown to be valid for different groups of chemicals, such as halocarbons, alkanes, alkenes, and aromatic compounds and for different dimensions of the diffusion capillaries. The limits of the predictability of the output rates are explored and observed to result in an underprediction of the output rates when very thin capillaries are used. It is demonstrated that pressure variations are responsible for the observed deviation of the output rates. To overcome the influence of pressure variations and at the same time to establish a suitable test gas source for highly volatile compounds, also the usability of permeation sources is explored, for example for the generation of molecular bromine test gases. 相似文献
954.
Kundel M Thorenz UR Petersen JH Huang RJ Bings NH Hoffmann T 《Analytical and bioanalytical chemistry》2012,402(10):3345-3357
Knowledge of the composition and emission rates of iodine-containing volatiles from major widespread seaweed species is important
for modeling the impact of halogens on gas-phase atmospheric chemistry, new particle formation, and climate. In this work,
we present the application of mass spectrometric techniques for the quantification of short-lived iodine-containing volatiles
emitted by eight different seaweeds from the intertidal zone of Helgoland, Germany. A previously developed online time-of-flight
aerosol mass spectrometric method was used to determine I2 emission rates and investigate temporally resolved emission profiles. Simultaneously, iodocarbons were preconcentrated on
solid adsorbent tubes and quantified offline using thermodesorption–gas chromatography-mass spectrometry. The total iodine
content of the seaweeds was determined using microwave-assisted tetramethylammonium hydroxide extraction followed by inductively
coupled-plasma mass spectrometry analysis. The highest total iodine content was found in the Laminariales, followed by the
brown algae Ascophyllum nodosum, Fucus vesiculosus, Fucus serratus, and both red algae Chondrus crispus and Delesseria sanguinea. Laminariales were found to be the strongest I2 emitters. Time series of the iodine release of Laminaria digitata and Laminaria hyperborea showed a strong initial I2 emission when first exposed to air followed by an exponential decline of the release rate. For both species, I2 emission bursts were observed. For Laminaria saccharina und F. serratus, a more continuous I2 release profile was detected, however, F. serratus released much less I2. A. nodosum and F. vesiculosus showed a completely different emission behavior. The I2 emission rates of these species were slowly increasing with time during the first 1 to 2 h until a more or less stable I2 emission rate was reached. The lowest I2 emission rates were detected for the red algae C. crispus and D. sanguinea. Total iodocarbon emission rates showed almost the same general trend, however, the total iodocarbon emission rates were
about one to two orders of magnitude lower than those of molecular iodine, demonstrating that I2 is the major iodine containing volatile released by the investigated seaweed species. In addition, a clear dependency of
iodocarbon emission from the ozone level (0–150 ppb O3) was found for L. digitata. 相似文献
955.
A 48-year-old woman visited the authors' clinic because of aphonia. Laryngeal fiberscopic examination indicated laryngitis and bronchitis, and the authors recognized glottal incompetence when she tried to phonate. The authors performed a functional magnetic resonance imaging (f-MRI) study on the patient's first visit to their clinic and a second study 35 days after the first visit (30 days after the bronchitis and coughing had completely resolved). The brain activity shown on f-MRI differed markedly in the ordinary speaking and whispering phonation modes at the second visit. This suggests that whispering and pathological aphonia result from completely different brain activity, at least in this specific patient. 相似文献
956.
Misaki Katayama Koichi Sumiwaka Kazuhiro Hayashi Kazuhiko Ozutsumi Toshiaki Ohta Yasuhiro Inada 《Journal of synchrotron radiation》2012,19(5):717-721
A two‐dimensional imaging system of X‐ray absorption fine structure (XAFS) has been developed at beamline BL‐4 of the Synchrotron Radiation Center of Ritsumeikan University. The system mainly consists of an ionization chamber for I0 measurement, a sample stage, and a two‐dimensional complementary metal oxide semiconductor (CMOS) image sensor for measuring the transmitted X‐ray intensity. The X‐ray energy shift in the vertical direction, which originates from the vertical divergence of the X‐ray beam on the monochromator surface, is corrected by considering the geometrical configuration of the monochromator. This energy correction improves the energy resolution of the XAFS spectrum because each pixel in the CMOS detector has a very small vertical acceptance of ~0.5 µrad. A data analysis system has also been developed to automatically determine the energy of the absorption edge. This allows the chemical species to be mapped based on the XANES feature over a wide area of 4.8 mm (H) × 3.6 mm (V) with a resolution of 10 µm × 10 µm. The system has been applied to the chemical state mapping of the Mn species in a LiMn2O4 cathode. The heterogeneous distribution of the Mn oxidation state is demonstrated and is considered to relate to the slow delocalization of Li+‐defect sites in the spinel crystal structure. The two‐dimensional‐imaging XAFS system is expected to be a powerful tool for analyzing the spatial distributions of chemical species in many heterogeneous materials such as battery electrodes. 相似文献
957.
We prepared TiO2–ZrO2 binary oxide particles with various Ti/(Zr+Ti) mole ratios (x) from the solutions containing Ti(OC3H7i)4, Zr(OC3H7n)4 and acetylacetone (acac). The spherical particles of 1–5 μm in diameter were obtained via solvothermal treatment at 150 °C. The spheres were anatase at x=1 and amorphous at x=0–0.8. The spheres were thought to be formed through the moderate hydrolysis and nucleation provided by the chelation of the alkoxides by acac. Crystalline TiO2–ZrO2 particles were obtained by the heat treatment of the as-precipitated spheres, and the crystalline phase changed with the Ti/(Zr+Ti) mole ratios. Pure ZrO2 and TiO2, ZrO2 doped with Ti4+, TiO2 doped with Zr4+ and ZrTiO4 phases were produced, and the spherical shape remained after the heat treatment at 500–750 °C. 相似文献
958.
HP Komsa J Kotakoski S Kurasch O Lehtinen U Kaiser AV Krasheninnikov 《Physical review letters》2012,109(3):035503
Using first-principles atomistic simulations, we study the response of atomically thin layers of transition metal dichalcogenides (TMDs)-a new class of two-dimensional inorganic materials with unique electronic properties-to electron irradiation. We calculate displacement threshold energies for atoms in 21 different compounds and estimate the corresponding electron energies required to produce defects. For a representative structure of MoS_{2}, we carry out high-resolution transmission electron microscopy experiments and validate our theoretical predictions via observations of vacancy formation under exposure to an 80?keV electron beam. We further show that TMDs can be doped by filling the vacancies created by the electron beam with impurity atoms. Thereby, our results not only shed light on the radiation response of a system with reduced dimensionality, but also suggest new ways for engineering the electronic structure of TMDs. 相似文献
959.
960.