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排序方式: 共有111条查询结果,搜索用时 234 毫秒
41.
José Maurício A. Caiut Lucas A. Rocha Fernando A. Sigoli Younes Messaddeq Jeannette Dexpert-Ghys Sidney J.L. Ribeiro 《Journal of Non》2008,354(42-44):4795-4799
Boehmite–GPTS (GPTS-glycidoxypropyltrimethoxysilane) hybrids (BGS) have been prepared by the sol–gel methodology. Spectroscopic properties and structural features have been evaluated from the initial sols to xerogels as a function of composition. Eu3+-containing BGS samples were also prepared, and the Eu3+ 5D0 state emission quantum efficiency was observed to depend on the boehmite–siloxane interactions. Boehmite–siloxane heterocondensation was inferred from vibrational spectroscopy and 13C, 29Si, and 27Al nuclear magnetic resonance results. Unreacted epoxi groups could be identified in the final material being an important characteristic for the future applications. Good optical quality and mechanical properties lead to the preparation of thin films deposited on glass substrates by dip and spin-coating. Refractive index could be tuned by the relative boehmite and GPTS content. Waveguide properties have also been studied by m-lines spectroscopy and guided modes together with attenuation measurements suggest potential application of the prepared films in integrated optics. 相似文献
42.
Kathryn Barnes-Burroughs Christopher Watts Oren L. Brown Jeannette LoVetri 《Journal of voice》2005,19(3):411-419
The purpose of this investigation was to obtain information from professional singers active in performing of both classical and music theater repertoire with regard to the visual/kinesthetic effect of melodic contour in musical notation as it affects vocal timbre. The evaluation of data gathered during the study indicates that there is reason to investigate the resulting postural shifts of the head and neck because they are guided by visual maps of melodic contour and its inversion. Significantly, it was discovered that the tone quality produced when a singer's head and neck postures followed the natural melodic contour of the melody was in no case considered to be the most pleasing of the conditions studied and that, in many cases, the tone quality produced when a singer's head and neck postures followed a map of the inversion of the melodic contour was judged to be much improved. The results of the study also indicate that the development of new technology for the general teaching studio, designed to address these effects, may be useful to these singers. 相似文献
43.
The following paper summarises the mission analysis studies performed for the phase A of the solar electric propulsion option of the European Student Moon Orbiter (ESMO) mission. ESMO is scheduled to be launched in 2011, as an auxiliary payload on board an Ariane 5. Hence the lack of influence on the launch date. Two methods were devised to assess efficiently wide launch windows for the Earth-Moon transfer, they are presented below. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
44.
A metal-free method for enantioselective conjugate addition of a dimethylphenylsilyl group to α,β-unsaturated carbonyls is reported. Transformations are catalyzed by a chiral N-heterocyclic carbene (NHC), performed in an aqueous solution (3:1 mixture of water and tetrahydrofuran) and are operationally simpler to perform than the NHC-Cu-catalyzed variant. The chiral catalyst is generated from an enantiomerically pure imidazolinium salt (prepared in three steps) and a common organic amine base (dbu). NHC-catalyzed processes proceed with 5.0-12.5 mol % catalyst loading at 22 °C within 1-12 h, affording the desired β-silyl carbonyls in 85:15 to >98:2 enantiomeric ratio and in 50% to >98% yield. Cyclic enones or lactones and acyclic α,β-unsaturated ketones, esters, and aldehydes can be used as substrates. 相似文献
45.
Determination of genetic transferrin variants in human serum by high‐resolution capillary zone electrophoresis†
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Jitka Caslavska Jeannine Joneli Ursula Wanzenried Jeannette Schiess Christian Lanz Wolfgang Thormann 《Journal of separation science》2014,37(13):1663-1670
High‐resolution capillary zone electrophoresis in the routine arena with stringent quality assurance is employed for the determination of carbohydrate‐deficient transferrin in human serum. The assay comprises mixing of human serum with a FeIII‐containing solution prior to analysis of the iron‐saturated mixture in a dynamically double‐coated capillary using a commercial buffer at alkaline pH. In contrast to other assays, it provides sufficient resolution for proper recognition of genetic transferrin variants. Analysis of 7290 patient sera revealed 166 isoform patterns that could be assigned to genetic variants, namely, 109 BC, 53 CD, one BD and three CC variants. Several subtypes of transferrin D can be distinguished as they have large enough differences in pI values. Subtypes of transferrin C and B cannot be resolved. However, analysis of the detection time ratios of tetrasialo isoforms of transferrin BC and transferrin CD variants revealed multimodal frequency histograms, indicating the presence of subtypes of transferrin C, B and D. The data gathered over 11 years demonstrate the robustness of the high‐resolution capillary zone electrophoresis assay. This is the first account of a capillary zone electrophoresis based carbohydrate‐deficient transferrin assay with a broad overview on transferrin isoform patterns associated with genetic transferrin variants. 相似文献
46.
Determination of glyphosate and aminomethylphosphonic acid in aqueous soil matrices: A critical analysis of the 9‐fluorenylmethyl chloroformate derivatization reaction and application to adsorption studies
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María E. Báez Edwar Fuentes María José Espina Jeannette Espinoza 《Journal of separation science》2014,37(21):3125-3132
The assessment of the environmental fate of glyphosate and its degradation product (aminomethylphosphonic acid) is of great interest given the widespread use of the herbicide. Studies of adsorption–desorption and transport processes in soils require analytical methods with sensitivity, accuracy, and precision suitable for determining the analytes in aqueous equilibrium solutions of varied complexity. In this work, the effect of factors on the yield of the derivatization of both compounds with 9‐fluorenylmethyl chloroformate for applying in aqueous solutions derived from soils was evaluated through factorial experimental designs. Interference effects coming from background electrolytes and soil matrices were established. The whole method had a linear response up to 640 ng/mL (R2 > 0.999) under optimized conditions for high‐performance liquid chromatography with fluorescence detection. Limits of detection were 0.6 and 0.4 ng/mL for glyphosate and aminomethylphosphonic acid, respectively. The relative standard deviation was 4.4% for glyphosate (20 ng/mL) and 5.9% for aminomethylphosphonic acid (10 ng/mL). Adsorption of compounds on four different soils was assessed. Isotherm data fitted well the Freundlich model (R2 > 0.97). Kf constants varied between 93 ± 3.1 and 2045 ± 157 for glyphosate and between 99 ± 4.1 and 1517 ± 56 (μg1‐1/n mL1/n g–1) for aminomethylphosphonic acid, showing the broad range of applicability of the proposed method. 相似文献
47.
Jeannette Zarraga-Colina 《Surface science》2006,600(15):3058-3071
Model Pt-ceria catalysts have been prepared by the evaporation of Pt onto ceria (CeO2) films grown on Si(1 1 1) substrates. Photoelectron spectroscopy (XPS, UPS) data are used to characterise the surfaces and their adsorption characteristics, and CO oxidation has been used as a probe reaction to test the activity of the model catalysts.Pure ceria is catalytically-inactive under the test conditions employed, whereas the model Pt/ceria catalysts demonstrate high activity for CO oxidation. The model catalysts also reproduce many of the characteristics of their high-surface area analogues, including the possession of a characteristic light-off temperature, hysteresis in activity as a function of temperature and a negative-order dependence on the CO partial pressure.Many aspects of the behaviour of these catalysts are shown to be a direct result of the strong adsorption of CO. The sensitivity of the dispersed Pt towards oxidation is also experimentally-demonstrated and the importance of this phenomenon is discussed. 相似文献
48.
Cousinié S Gressier M Reber C Dexpert-Ghys J Menu MJ 《Langmuir : the ACS journal of surfaces and colloids》2008,24(12):6208-6214
This work focuses on the grafting of transition metal complexes on silica surface nanoparticles. Nanoscale silica particles in aqueous sols are used as starting silicated materials. We have undertaken the synthesis of europium(III) complexes containing organosilyldipyridine ligands, (EtO)3Si(CH2)3NHCH2-bipy (1) and (EtO)(CH3)2Si(CH2) 3NHCH 2-bipy (2), in view of a direct grafting reaction on silica nanoparticles. Reaction of one molar equivalent of 1 and 2 with Eu(tmhd)3 (tmhd= 2,2,6,6-tetramethyl-3,5-heptanedionato), as precursor, leads to octacoordinated silylated europium(III) complexes [Eu(tmhd)3(1)] (3) and [Eu(tmhd)3(2)] (4) as white solids in 34-54% yields. Europium complexes were characterized by elemental analysis, mass spectrometry, FT-IR, UV, and luminescence spectroscopies. These new complexes are reacting in a 1:10 (v/v) water and ethanol mixture with silica nanoparticles colloidal sol. Elemental analysis and thermogravimetric data indicated grafting ratios of 0.41 and 0.26 mmol of europium(III) complexes per gram of silica. Functionalized silica nanoparticles were characterized by DRIFT spectroscopy and TEM microscopy. The first analysis shows that the chemical integrity of the complexes is retained on the silica surface together with the size and the monodispersity of the nanoscale particles. As expected for europium(III) complexes, luminescence is observed under UV irradiation. Emission and excitation spectra indicate that the metal coordination environment is not modified on the silica surface. Moreover, the sharpness of the luminescence bands and the strong antenna effect are maintained when complexes are covalently bonded to silica. New luminescent europium(III) complexes grafted on silica nanoparticles are therefore obtained from our approach. 相似文献
49.
Stoesser R Klein J Peschke S Zehl A Cämmerer B Kroh LW 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,67(5):1161-1168
During the early stage of the Maillard reaction pyrazinium radical cations were detected by ESR within the reaction system d-glucose/glycine. The spectra were characterized by completely resolved hyperfine structure. The partial pressure of oxygen and the radical concentrations were measured directly in the reaction mixture by ESR using solutions of the spin probe TEMPOL and of DPPH, respectively. There are quantitative and qualitative relations of the actual concentration of the radical ions to the partial pressure of oxygen, the temperature-time regime and the mechanical mixing of the reaction system. These macroscopic parameters significantly affect both the induction period and the velocity of the time-dependent formation of free radicals. From in situ variations of p(O2) and p(Ar) including the connected mixing effects caused by the passing the gases through the reaction mixture, steric and chemical effects of the stabilization of the radical ions were established. The determination of suitable and relevant conditions for stabilization and subsequent radical reactions contributes to the elucidation of the macroscopically known antioxidant activity of Maillard products. 相似文献
50.
H.?S.?Barud C.?A.?RibeiroEmail author Marisa?S.?Crespi M.?A.?U.?Martines J.?Dexpert-Ghys R.?F.?C.?Marques Y.?Messaddeq S.?J.?L.?Ribeiro 《Journal of Thermal Analysis and Calorimetry》2007,87(3):815-818
Cellulose–phosphate composite
membranes have been prepared from bacterial cellulose membranes (BC) and sodium
polyphosphate solution. The structure and thermal behavior of the new composites
were evaluated by X-ray diffraction (XRD), 31P-nuclear
magnetic resonance (NMR), scanning electron microscopy (SEM), differential
scanning calorimetry (DSC), thermogravimetry (TG) and thermomechanical analysis
(TMA). From XRD analyses the Iα and Iβ cellulose crystalline phases
were identified together with crystalline sodium phosphate that covers the
cellulose microfibrils as revealed by SEM. 31P
NMR spectra show peaks assigned to Q0 and Q1
phosphate structures to be compared to the Q2 units
that characterize the precursor polyphosphate. Glass transition temperature, T
g, obtained from TMA curves
and thermal stability obtained from TG and DSC measurements, were observed
to be dependent on the phosphate content. 相似文献