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排序方式: 共有63条查询结果,搜索用时 15 毫秒
1.
Spectroscopic characterization of mineral crystals produced by the bacterium Azospirillum brasilense
Kamnev AA Antonyuk LP Chernyshev AV Ignatov VV De Vargas MC 《Analytical and bioanalytical chemistry》1996,355(5-6):739-741
The results of spectroscopic structural and trace elemental analyses of mineral crystals produced by the soil nitrogen-fixing bacterium Azospirillum brasilense cultivated in a synthetic medium are presented and discussed. The mineral formed is shown to have a structure close to struvite (MgNH(4)PO(4) x 6H(2)O; ASTM file No. 15-762) with some differences which may be attributed to the presence of isomorphic admixtures of other cations (struvite is known to have a variety of forms). AAS/AES and ion chromatography analyses for a number of biologically important microelements and their role in the formation of the crystal structure, as well as some questions related to biomineralization are also discussed. 相似文献
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Katiuska Araujo Marinela Colina Román Mazurek José Delgado Hilda Ledo Elizabeth Gutierrez Lenín Herrera 《Fresenius' Journal of Analytical Chemistry》1996,355(3-4):319-320
The mercury concentrations in wastewater and sewage sludge of a stabilization pond system have been evaluated. The system is built by three parallel facultative ponds followed by two systems of three maturation ponds in series. The samples of wastewater and sludge were digested using nitric acid and placed into a Parr-type bomb for 4 h at 110° C. Mercury was measured by Cold Vapour Atomic Absorption Spectrometry (CV-AAS) at 253.7 nm with sodium tetrahydroborate as reductant. The methodologies were checked with an USEPA quality control sample, a standard reference material from NIST and with another method of mineralization (cold mineralization) showing good results. Concentrations of mercury in wastewater between 1.47 ± 0.75 gl–1 have been found at the entrance of the system and 0.74 ± 0.0 gl–1 at the exit, while in sludge the results were between 0.29 ± 0.12 gkg–1 in the facultative pond and 0.04 ± 0.02 gkg–1 in the second maturation pond (exit). 相似文献
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Alejandro Colina Betzabé Sulbarán-de-Ferrer Cateryna Aiello Alexis Ferrer 《Applied biochemistry and biotechnology》2003,108(1-3):715-724
Xylanase production of Trichoderma reesei Rut C-30 was examined at different initial pH values (4.8, 5.9, and 7.0) on rice straw in shake flasks, and in a fermentor,
for the best pH condition. Enzyme performance was tested on ammonia-treated dwarf elephant grass. The maximum xylanase activities,
92 and 122 IU/mL, were obtained at pH 4.8 in the shake flasks and fermentor, respectively, in which good growth of the fungus
was observed during the first 24 h and consumption of proteins dissolved from the rice straw caused the pH to rise later to
values between 6.4 and 6.7 (optimal for xylanase production). The xylanases from T. reesei were as effective as Multifect XL, a commercial enzyme preparation, in hydrolyzing ammonia-treated elephant grass. 相似文献
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EI Rodriguez Martinez CI Barriga-Paulino MI Zapata CC Chinchilla AM López-Jiménez CM Gómez 《BMC neuroscience》2012,13(1):104-23
ABSTRACT: BACKGROUND: The peri-adolescent period is a crucial developmental moment of transition from childhood to emergent adulthood. The present report analyses the differences in Power Spectrum (PS) of the Electroencephalogram (EEG) between late childhood (24 children between 8 and 13 years old) and young adulthood (24 young adults between 18 and 23 years old). RESULTS: The narrow band analysis of the Electroencephalogram was computed in the frequency range of 0--20 Hz. The analysis of mean and variance suggested that six frequency ranges presented a different rate of maturation at these ages, namely: low delta, delta-theta, low alpha, high alpha, low beta and high beta. For most of these bands the maturation seems to occur later in anterior sites than posterior sites. Correlational analysis showed a lower pattern of correlation between different frequencies in children than in young adults, suggesting a certain asynchrony in the maturation of different rhythms. The topographical analysis revealed similar topographies of the different rhythms in children and young adults. Principal Component Analysis (PCA) demonstrated the same internal structure for the Electroencephalogram of both age groups. Principal Component Analysis allowed to separate four subcomponents in the alpha range. All these subcomponents peaked at a lower frequency in children than in young adults. CONCLUSIONS: The present approaches complement and solve some of the incertitudes when the classical brain broad rhythm analysis is applied. Children have a higher absolute power than young adults for frequency ranges between 0-20 Hz, the correlation of Power Spectrum (PS) with age and the variance age comparison showed that there are six ranges of frequencies that can distinguish the level of EEG maturation in children and adults. The establishment of maturational order of different frequencies and its possible maturational interdependence would require a complete series including all the different ages. 相似文献
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Journal of Solid State Electrochemistry - UV/Vis absorption spectroelectrochemistry is a very promising analytical technique due to the complementary information that is simultaneously obtained... 相似文献
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Ana Erica Paramo Susana Palmero Aranzazu Heras Alvaro Colina David Ibañez 《Electroanalysis》2016,28(4):890-897
The purpose of this work is to develop simple and reproducible ways to fabricate carbon nanofibers (CNFs) electrodes. Disposable CNFs electrodes were fabricated after filtering CNFs through polytetrafluoroethylene filters (PTFE), using directly as electrodes these filters with the CNFs film. The electrochemical behaviour of CNFs/PTFE electrodes were tested with ferrocenemethanol and tris(2,2′‐bypyridyl)dichlororuthenium(II) (Ru(bipy)32+). As a proof of concept of the analytical usefulness of the CNFs/PFTE electrodes, the study of vitamin B12 was carried out. Multivariate calibrate has been successfully used to determine vitamin B12 in a complex medium with vitamins B1 and B6 as interferents. 相似文献
10.
B. ZanfrogniniA. Colina A. HerasC. Zanardi R. SeeberJ. López-Palacios 《Polymer Degradation and Stability》2011,96(12):2112-2119
Poly(3,4-ethylendioxythiophene) films were electropolymerized in aqueous medium without using any surfactant, on glassy carbon electrodes. UV/Vis and Raman spectroelectrochemical techniques were used to analyze the degradation of the polymer film occurring at different pH values. Spectroelectrochemistry has proven to be a very useful analytical tool for this purpose, thanks to its ability to provide information not only about the extent of degradation, but also about mechanistic aspects of the process. From our results we extracted important information about the main factors that play a role in the degradation, in particular about the influence of repetitive doping and de-doping cycles and of photo-induced processes, as a function of the characteristics of the solution, i.e. of pH. 相似文献