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51.
低温恒能量同步荧光法同时快速检测食品中多种多环芳烃 总被引:1,自引:0,他引:1
恒能量同步荧光法应用于多环芳烃的检测可以提高选择性,低温可使谱带呈指纹特征,提供常温光谱无法获得的光谱细节信息,有助于实现对复杂基体中多环芳烃的检测。文章结合恒能量同步荧光扫描技术与斯波斯基低温技术,建立了食品中多种多环芳烃的低温恒能量同步荧光同时快速分析方法。对低油脂样品直接用正辛烷浸泡,高油脂样品也只需要增加皂化萃取,即可进行光谱扫描来检测食品样中的多种多环芳烃。对两种类型的实际样进行加标回收实验,回收率为80.2%~98.9%,定量工作曲线线性较好(r≥0.993 8)。该方法选择性好、操作简便快捷、费用低廉。 相似文献
52.
53.
The major objective of this work is to numerically investigate the interacting physical and chemical phenomena that characterize
the flow in a stabilized cool flame diesel fuel spray evaporation system. A two-phase RANS computational fluid dynamics code
has been developed and used to predict the characteristics of the developing turbulent, multiphase, multi-component, reactive
flow-field. The code employs a Eulerian–Lagrangian approach, taking into account the mass, momentum, thermal and turbulent
energy exchange between the phases. A variety of physical phenomena, such as turbulent dispersion, droplet evaporation, droplet-wall
collision, conjugate heat transfer, drift correction, two-way coupling are taken into account by implementing respective sub-models.
Two alternative modelling approaches for the simulation of cool flame reactions have been validated and evaluated by comparing
numerical predictions with experimental data from two atmospheric pressure, evaporating Diesel spray, Stabilized Cool Flame
reactors. Both models have achieved good quantitative agreement in the majority of the considered test cases. The results
have been used to estimate the local physical and chemical characteristic time scales of the occurring phenomena, thus allowing,
for the first time, the classification of stabilized cool flames. 相似文献
54.
Bruno Savard Haiou Wang Armin Wehrfritz Evatt R. Hawkes 《Proceedings of the Combustion Institute》2019,37(4):4655-4662
Rich premixed turbulent n-dodecane/air flames at diesel engine conditions are analyzed using direct numerical simulations. The conditions correspond to a parametric variation of the Engine Combustion Network Spray A (pressure 60 atm; oxidizer oxygen level and temperature 21% and 900 K, respectively; fuel temperature 363 K). Three simulations with equivalence ratios of 3, 5, and 7 are performed with a Karlovitz number (Ka, based on flame time) of order 100 to match the estimated Ka of the rich premixed combustion region in Spray A. At these conditions, the reference laminar flames exhibit a complex structure which involves both low-temperature chemistry (LTC) and high-temperature chemistry over a wide range of length scales. In the presence of turbulence, the flame structure is strongly affected in physical space and the reaction zone exhibits a very complex structure in which broken, distributed, and thin regions co-exist, especially for the leanest case. However, the contribution of the LTC pathway is only weakly affected by turbulence. In progress variable space, the mean flame structure, including the chemical source terms, is found to match remarkably well that of the corresponding unity Lewis number laminar flame, particularly for the 3 and 5 cases. This behavior is attributed to the strong turbulent mixing occurring throughout the flames/reaction zones, which suppresses differential diffusion effects. Nevertheless, large conditional fluctuations around the mean chemical source terms are identified. These are found to correlate very well with radical species mass fractions such as OH. In addition, a similar functional dependence is obtained from counterflow laminar flames. As such, it appears from these results that laminar flame models have a potential to be used to represent the thermochemical state of rich premixed turbulent flames under diesel engine conditions. 相似文献
55.
Svetlana V. Kirpichenko Bagrat A. Shainyan Erich Kleinpeter Sergey A. Shlykov Tran Dinh Phien Alexander I. Albanov 《Tetrahedron》2018,74(15):1859-1867
The 3,3-disubstitued 3-silaheterocyclohexane with an electronegative substituent at silicon, 3-fluoro-3-methyl-3-silatetrahydropyran 1, was synthesized, and its molecular structure and conformational properties studied by gas-phase electron diffraction (GED) and low temperature 13C and 19F NMR spectroscopy. Quantum-chemical calculations were carried out both for the isolated species and H-complexes in gas and in polar medium. The predominance of the 1-FeqMeax conformer (1-Feq:1-Fax ratio of 65:35, ΔG°?=?0.37?kcal/mol) determined from GED is close to the theoretically estimated conformational equilibrium, especially at the DFT level. In solution, low temperature NMR spectroscopy showed no decoalescence of the signals in 13C (down to 95?K) and 19F NMR spectra (down to 123?K). However, the calculated 19F chemical shift of ?173.6?ppm for the 1-FeqMeax conformer practically coincides with the experimentally observed value (?173 to ?175?ppm) as distinct from that for the 1-FaxMeeq conformer (?188.8?ppm), suggesting compound 1 to be anancomeric in solution, in compliance with its theoretical and experimental preference in the gas phase. 相似文献
56.
The synthesis of crystalline lead titanate powder by a generic low-temperature sol-gel approach is developed. Acetoin was added as ligand, instead of the commonly used alkanolamines, to ensure total dissolution of the precursor compounds. The feasibility of the acetoin-Ti isopropoxide complex as a new precursor of PbTiO3 perovskite particles via sol-gel method has been demonstrated. No excess lead has been introduced. Nanometric PbTiO3 crystallites have been formed at 400 °C under atmospheric pressure from titanium isopropoxide and lead acetate in alcoholic solution by remarkably low activation energy of crystallization process of 90 kJ mol−1. The powders show tetragonal lattice and dendritic morphology. In addition to the effect of heat-treatment temperature, time, and atmosphere, the sol chemistry particularly influenced the phase composition, particle size, and particle morphology. The use of different ligands significantly modified powder morphology. The extent of the crystallization was quantitatively evaluated by differential thermal analysis and analyzed by Johnson-Mehl-Avrami approach. The crystallization followed two rate regimes depending on the interval of the crystallized fraction. 相似文献
57.
We examined low-temperature synthetic route based on the amorphous nature of giant species to succeed to prepare Cs blue bronze (Cs0.3MoO3), which has never obtained by usual high-temperature methods, at ca. 680 K. Solid solutions (K1−xRbx)0.28MoO3 and (Li1−xNax)0.9Mo6O17 were also obtained at lower temperatures (ca. 670 K). For the latter system consisting of non-isostructural end members, Li0.9Mo6O17-structure type solid solution was formed even when 0.25<x<0.70, unlike the case by the usual high-temperature methods. Metastable mixed oxides Ln2Mo3O9 (Ln=La, Gd) were obtained, but not as single phases. 相似文献
58.
Geoffrey A. Ozin John G. McCaffrey J. Mark Parnis 《Angewandte Chemie (International ed. in English)》1986,25(12):1072-1085
Reactions of metal atoms with molecular hydrogen and alkanes are prototypical of more complex systems involving metal-mediated reactions in solution, on supports, and on surfaces. The simplicity of metal-atom reactions makes them particularly attractive for fundamental experimental and theoretical studies. Following the first reports of H2 and CH4 activation by photoexcited metal atoms in cryogenic matrices, the behavior of a number of transition-metal atoms in their ground and selected electronically excited states has been examined with molecular hydrogen, methane, and ethane. A wealth of structural, electronic, reactivity, and selectivity information is emerging from these studies and it is now becoming possible to recognize the controlling factors at work in these fundamental chemical reactions. In this article, some experimental results for a number of metal-atom systems, in particular, those involving silver, copper, manganese, and iron atoms, are presented along with a discussion of the factors that are believed to be important in the understanding of the observed physical and chemical behavior. 相似文献
59.
MoS2 是钼基加氢精制催化剂 [Co(Ni)Mo/γ Al2 O3]活性相的主要组份 ,其形态与结构对Co(Ni)Mo/γ Al2 O3的加氢脱硫 (HDS)、加氢脱氮 (HDN)活性的影响至关重要[1 ,2 ] .目前 ,人们通常使用的TPR方法虽可测定过渡金属硫化物的表面活性位 ,并可有效地区分位于催化剂活性相 (MoS2 slab)周边的硫物种 ,但对不同价态的钼尚无法鉴别[3] .本文制备了硫化态Mo/γ Al2 O3催化剂 ,以CO为探针分子 ,利用FTIR技术在液氮温度 (77K)下考察了催化剂的表面活性位 (钼物种 )及催化噻吩HDS的活性 .1 实… 相似文献
60.
采用溶胶-凝胶法低温制备了具有锐钛矿、板钛矿双晶型的TiO2薄膜. 分别利用X射线衍射(XRD)、透射电子显微镜(TEM)、UV-Vis透光率曲线和原子力显微镜(AFM)等手段对所得TiO2溶胶和薄膜进行了性能表征. 采用光催化降解罗丹明B水溶液评价TiO2薄膜的光催化活性. 结果发现, 所得TiO2薄膜具有较高的透明度和光催化活性. 同时, 考察了溶胶回流温度对所制备TiO2薄膜性能的影响, 发现升高溶胶回流温度可以完善薄膜的晶型, 增大薄膜的粗糙度, 从而提高薄膜的光催化活性. 溶胶回流温度为100 ℃时所制备的TiO2薄膜具有最高的光催化活性. 相似文献