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排序方式: 共有194条查询结果,搜索用时 15 毫秒
41.
In this work, we explore the refractive index of the phasmidic columnar liquid crystal for homeotropic oriented samples (column perpendicular to the plates). To measure the ordinary index no of the columnar liquid crystal C10, a simple and accurate method is presented using the deflection by reflection of a laser beam (λ = 633nm) through a prismatic phasmidic thin film placed between two glass plates in the homeotropic orientation. For the C10 samples, we found no = 1.5512 ± 0.0002 at T = 100°C. We used the same method to determine the isotropic index nl of the isotropic phase and found nl = 1.5301 ± 0.0002 at T = 120°C. Using the precision of the same method in polychromatic laser beam, we measured the variation of the ordinary index with the wavelength λ and characterize the dispersion by the known Cauchy's dispersion relationship no = A + B/λ2. We deduce an estimation of the birefringence for several samples. 相似文献
42.
T(2) contrast is gaining importance in high field strength MRI. We report a strategy for developing a T(2) contrast agent from paramagnetic metal ions synthesized within an engineered protein cage. The manganese-ferritin nanocomposite showed high T(2) relaxivity indicating its potential as an ultrasensitive T(2) contrast agent. 相似文献
43.
Sana Bannour Kamel Abderrazak Hatem Mhiri Georges Le Palec 《Optics & Laser Technology》2012,44(8):2459-2468
Laser welding processes are widely used for fabrications in many engineering applications such as aerospace and automotives. In this paper, a moving distributed heat source model based on Goldak's method [1] has been implemented into finite volume thermal simulations in order to predict temperature distributions during the welding process of a magnesium alloy and to study the effects of variations in thermal properties, absorption coefficient and gas shielding on the computed temperature distributions and weld pool dimensions. The main conclusion is the significant effects of varying the thermal conductivity and absorption coefficient of magnesium. Also, it has been seen that the shielding gas, besides its main role of protection against oxidation, has a significant effect on the width of the weld pool. Finally, the obtained results have been compared to the experimental ones and a satisfactory correlation has been observed, indicating the reliability of the model developed in this study. 相似文献
44.
Choudhari Dinkar Chakravarty Debamitra Lande Dipali N. Parveen Sana Gejji Shridhar P. Kodam Kisan M. Salunke-Gawali Sunita 《Structural chemistry》2019,30(6):2257-2270
Structural Chemistry - Homologated (N)-n-alkylammonium salts of 2-bromo-3-oxido-1,4-naphthoquinone (BS-1 to BS-8) have been synthesized and characterized from the single crystal X-ray diffraction... 相似文献
45.
46.
In this work, we study theoretically the thermal decomposition of weak dative complexes (namely, the complexes between BH3, BeH2, or LiH and ammonia or water). The most accurate calculations have been carried out at the MP 4sdtq/6-311++G (3df,2p) level on MP 2full/6-31G ** fully optimized geometries. The transition structures for hydrogen evolution are described. The rate constants were obtained using conventional transition-state theory. Stability conditions for the complexes were considered. Water complexes are less stable than are the corresponding ammonia derivatives. Lithium complexes seem to be very unstable. It seems that beryllium compounds could be synthesized. Borane derivatives are known experimentally. We find, as observed, that the first hydrogen evolution occurs only above room temperature. Iminoborane seems not to be easily accessible under pyrolysis conditions. Other reactions require less activation energy. Finally, the early stages of the ammonia–borane pyrolysis and paths to open-chain polymers as well as to cyclic structures are described. © 1993 John Wiley & Sons, Inc. 相似文献
47.
Five hydrogen abstraction reactions, CH4 + R CH3 + HR have been studied usingab initio SCF and CI methods. R was successively chosen as H, CH3, NH2, OH and F. Geometries were fully optimized at SCF level and energies were computed at CI level for products, reactants and transition states. Quadratic hypersurfaces were fitted in the neighborhood of the most important points of the potential energy hypersurfaces and vibrational analysis were performed thereupon. Wigner's and Christov's approximations were used to obtain an idea of the importance of tunneling of H atoms through the reaction barrier, and this effect was shown to be non-negligible. Finally, rate constant calculation were carried out at different temperatures.Chercheur Qualifié au Fonds National Belge de la Recherche Scientifique. 相似文献
48.
Yulu Yang Yang Tang Haomin Jiang Yongmei Chen Pingyu Wan Maohong Fan Rongrong Zhang Sana Ullah Lun Pan Ji-Jun Zou Mengmeng Lao Wenping Sun Chao Yang Gengfeng Zheng Qiling Peng Ting Wang Yonglan Luo Xuping Sun Alexander S. Konev Oleg V. Levin Panagiotis Lianos Zhuofeng Hu Zhurui Shen Qinglan Zhao Ying Wang Nadia Todorova Christos Trapalis Matthew V. Sheridan Haipeng Wang Ling Zhang Songmei Sun Wenzhong Wang Jianmin Ma 《中国化学快报》1990,30(12):2089-2109
In this roadmap, we address the development and perspectives of hydrogen evolution reaction, oxygen reduction reaction, oxygen evolution reaction, carbon dioxide reduction reaction and nitrogen reduction. 相似文献
49.
Sanaâ Majid Mamia El Rhazi Aziz Amine Antonella Curulli Giuseppe Palleschi 《Mikrochimica acta》2003,143(2-3):195-204
Carbon paste electrodes modified with conducting polymers for sensitive and selective determination of lead are presented. A novel method for generating a reproducible polymer-coated electrode surface is developed. We prove that 1,8-diaminonaphthalene (1,8-DAN) mixed with a carbon paste electrode leads to a conducting polymer in acidic medium while, in the same medium, this polymer is known to be non-conducting on platinum electrode. The electrode behaviour of poly(1,8-DAN), electropolymerised into carbon paste, was investigated by cyclic voltammetry in the presence of the ferri-ferrocyanide couple.A carbon paste electrode modified with poly(1,8-DAN) was used to determine Pb2+ in aqueous solutions. Pb2+ ions were firstly complexed and then electrochemically deposited by a potential step to –0.9V. The accumulated lead after reduction was anodically stripped by differential pulse voltammetry. Different parameters, such as pH of the solution, preconcentration time, and electropolymerisation procedures were studied.For a preconcentration time of ten minutes, the calibration graph was linear from 40 to 2070ngmL–1 with r2=0.998. The detection limit was found to be 30ngmL–1, and the relative standard deviation was 6%. 相似文献
50.
Sana Tfaili Cyril Gobinet Gwendal Josse Jean-François Angiboust Arlette Baillet Michel Manfait Olivier Piot 《Analytical and bioanalytical chemistry》2013,405(4):1325-1332
Caffeine is utilised as a reference for permeation studies in dermatology and cosmetology. The present work aimed to monitor the permeation of a caffeine solution through the skin. For this purpose, Raman and infrared studies were performed. Raman microspectroscopy permitted a dynamic follow-up of the caffeine diffusion. In complementary, infrared microimaging provided information of the caffeine localization in the skin by applying multivariate statistical processing on skin tissue sections. Herein, we prove the possibility of tracking low concentrations of caffeine through the skin and we highlight some experimental limitations of vibrational spectroscopies. 相似文献