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排序方式: 共有233条查询结果,搜索用时 15 毫秒
191.
A. K. Roy W. Baumann I. König G. Baumann S. Schulze M. Hietschold T. Mäder D. J. Nestler B. Wielage W. A. Goedel 《Analytical and bioanalytical chemistry》2010,396(5):1913-1919
Layers of alumina were deposited on to bundled carbon fibers in an atomic layer deposition (ALD) process via sequential exposure
to vapors of aluminium chloride and water, respectively. Scanning electron microscopic (SEM) images of the coated fibers revealed
that each individual fiber within a bundle was coated evenly and separately, fibers are not bridged by the coating. SEM and
transmission electron microscopic (TEM) images indicate that the coating was uniform and conformal with good adhesion to the
fiber surface. Average deposition rate, measured from SEM images, was 0.06 nm per cycle at 500 °C. SEM also revealed that
at deposition temperatures of 500 °C few of the fibers were damaged. At temperatures of 300 °C, no damaged fibers were observed,
the average deposition rate decreased down to 0.033 nm per cycle. Oxidation resistance of the alumina-coated fibers was characterized
by thermogravimetric analysis (TGA). The alumina coating improved oxidation resistance of the carbon fiber significantly.
Oxidation onset temperature was 600 °C for fibers coated with a 45 nm thick alumina. Uncoated fibers, on the other hand, started
to oxidize at temperatures as low as 250 °C. 相似文献
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Britta Vortmann-Westhoven Marcel Diehl Martin Winter Sascha Nowak 《Chromatographia》2018,81(7):995-1002
We present a method for the separation and determination of transition metals in electrolytes based on ion chromatography (IC) with post-column reaction (PCR) and serial conductivity and spectrophotometric detection. Three IC columns [Metrosep C4—250/4.0 (column A), Metrosep C6—250/4.0 (column B), and Nucleosil 100-5SA—250/4.6 (column C)] with different capacities, and stationary phases were used and compared with each other for method development. All spectrophotometric measurements were carried out with 4-(2-pyridylazo)resorcinol (PAR) as PCR reagent at a wavelength of 500 nm. To characterize the precision of the separation, the selectivity for the analysis of transition metals (nickel, cobalt, copper, and manganese) in the presence of large amounts of lithium and the resolution of the peaks were determined and compared with one another. Furthermore, the limits of detection (LOD) and quantification (LOQ) were determined for the transition metals. The LODs and LOQs determined by column C were as follows: cobalt (LOD/LOQ): 9.4 µg L?1/31.3 µg L?1, manganese (LOD/LOQ): 7.0 µg L?1/23.5 µg L?1, and nickel (LOD/LOQ): 6.3 µg L?1/21.1 µg L?1. Finally, the concentration of transition metal dissolution of the cathode material Li1Ni1/3Co1/3Mn1/3O2 (NCM) was investigated for different charge cut-off voltages by the developed IC method. 相似文献
196.
Maria Sdersten PhD Svante Granqvist Britta Hammarberg Annika Szabo 《Journal of voice》2002,16(3):356-371
Preschool teachers are at risk for developing voice problems such as vocal fatigue and vocal nodules. The purpose of this report was to study preschool teachers' voice use during work. Ten healthy female preschool teachers working at daycare centers (DCC) served as subjects. A binaural recording technique was used. Two microphones were placed on both sides of the subject's head, at equal distance from the mouth, and a portable DAT recorder was attached to the subject's waist. Recordings were made of a standard reading passage before work (baseline) and of spontaneous speech during work. The recording technique allowed separate analyses of the level of the background noise, and of the subjects' voice sound pressure level, mean fundamental frequency, and total phonation time. Among the results, mean background noise level for the ten DCCs was 76.1 dBA (range 73.0-78.2), which is more than 20 dB higher than what is recommended where speech communication is important (50-55 dBA). The subjects spoke on an average of 9.1 dB louder (p < 0.0001), and with higher mean fundamental frequency (247 Hz) during work as compared to the baseline (202 Hz) (p < 0.0001). Mean phonation time for the group was 17%, which was considered high. It was concluded that preschool teachers do have a highly vocally demanding profession. Important steps to reduce the vocal loading for this occupation would be to decrease the background noise levels and include pauses so that preschool teachers can rest their voices. 相似文献
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Dr. Patrick Rabe Jan Rinkel Britta Nubbemeyer Dr. Tobias G. Köllner Prof. Dr. Feng Chen Prof. Dr. Jeroen S. Dickschat 《Angewandte Chemie (International ed. in English)》2016,55(49):15420-15423
Genome sequences of social amoebae reveal the presence of terpene cyclases (TCs) in these organisms. Two TCs from Dictyostelium discoideum converted farnesyl diphosphate into (2S,3R,6S,9S)‐(?)‐protoillud‐7‐ene and (3S)‐(+)‐asterisca‐2(9),6‐diene. The enzyme mechanisms and EI‐MS fragmentations of the products were studied by labeling experiments. 相似文献
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