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191.
A 2D axisymmetric formulation for the solution of a directional solidification problem using an inverse finite-element method (IFEM) is presented. An algorithm developed by A. N. Alexandrou (Int. J. Numer. Methods Eng.28, 2383, 1989) has been modified and extended to include more general boundary conditions. The latter includes the explicit presence of an ampoule (with a complex shape) that contains the solid and the melt from which it is growing. Heat transfer between the ampoule and the external environment, time-dependent thermal boundary conditions, nonmonotonic temperature distributions, and species diffusion in the melt and crystal are also taken into account. Thus, our extended formulation encompasses a wider class of solidification problems than previous IFEM methods. Numerical experiments that illustrate the suitability of the extended IFEM are presented. In particular, we present a simulation of the directional solidification of zinc cadmium telluride using boundary conditions corresponding to an actual experiment scenario. 相似文献
192.
193.
Alexandre I. Danilenko 《Israel Journal of Mathematics》2006,156(1):341-358
LetG be a countable direct sum of finite groups. We construct an uncountable family of pairwise disjoint mixing (of any order)
rank-one strictly ergodic free actions ofG on a Cantor set. All of them possess the property of minimal self-joinings (of any order). Moreover, an example of rigid
weakly mixing rank-one strictly ergodic freeG-action is given.
The work was supported in part by CRDF, grant UM1-2546-KH-03. 相似文献
194.
195.
Mulholland AJ O'Leary RL Ramadas N Parr A Troge A Pethrick RA Hayward G 《Ultrasonics》2007,47(1-4):102-110
This paper investigates the use of magnetically active materials in the matching layer of a piezoelectric transducer. This then allows the performance of the device to be dynamically altered by applying an external field. The effect that this new matching layer has on the performance of a typical device is theoretically investigated here. It transpires that the additional flexibility of an active matching layer can be used to maintain the efficiency of the device as the external load is varied. 相似文献
196.
Alexandre?Ioan?RomoscanuEmail author Mahir?Behar?Sayir Klaus?H?usler Adam?Stewart?Burbidge 《Rheologica Acta》2003,42(5):462-476
In this work an instrument is described which measures the complex shear viscosity of liquids in the kHz frequency range. The instrument is driven electromagnetically and operates in resonant mode. The measurement of the primary data, from which the rheological properties of the fluid sample are inferred, does not include any deflection amplitude measuring step and is purely digital. Models allowing the interpretation of the probe primary data in terms of fluid complex viscosity are presented. The theoretically predicted mechanical behaviour of the probe is compared with the measured one and the rheometric ability of the device is discussed. 相似文献
197.
Copper‐Mediated Formation of Aryl,Heteroaryl, Vinyl and Alkynyl Difluoromethylphosphonates: A General Approach to Fluorinated Phosphate Mimics
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Maria V. Ivanova Dr. Alexandre Bayle Dr. Tatiana Besset Dr. Thomas Poisson Prof. Dr. Xavier Pannecoucke 《Angewandte Chemie (International ed. in English)》2015,54(45):13406-13410
A general and efficient access to aryl, heteroaryl, vinyl and alkynyl difluoromethylphosphonates is described. The developed methodology using TMSCF2PO(OEt)2, iodonium salts and a copper salt provided a straightforward manifold to reach these highly relevant products. The reaction proved to be highly functional group tolerant and proceeded under mild conditions, giving the corresponding products in good to excellent yields. This method represents the first general synthetic route to this important class of fluorinated scaffolds, which are well‐recognized as in vivo stable phosphate surrogates. 相似文献
198.
Electrolytic Macrocyclizations: Scalable Synthesis of a Diazonamide‐Based Drug Development Candidate
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Dr. Hui Ding Patrick L. DeRoy Christian Perreault Dr. Alexandre Larivée Dr. Arshad Siddiqui Dr. Charles G. Caldwell Susan Harran Prof. Dr. Patrick G. Harran 《Angewandte Chemie (International ed. in English)》2015,54(16):4818-4822
An electrochemical method to synthesize the core macrolactam of diazonamides is described. Large ring‐forming dehydrogenation is initiated by anodic oxidation at a graphite surface. The reaction requires no tailoring of the substrate and occurs at ambient temperature in aqueous DMF in an undivided cell open to air. This unique chemistry has enabled a concise, scalable preparation of DZ‐2384; a refined analog of diazonamide A slated for clinical development as a cancer therapeutic. 相似文献
199.
Vianney O. Santos Isabela R. Leite Alexandre G. Brolo Joel C. Rubim 《Journal of Raman spectroscopy : JRS》2016,47(6):674-680
The electrochemical conversion of CO2 into value‐added products using room temperature ionic liquids as solvent/electrolyte has been proposed as an alternative to minimize the environmental effects of CO2 emissions. A key issue in the design of electrochemical systems for the reduction of CO2 is the in situ identification of intermediate surface species as well as reaction products. Copper electrodes, besides being used as cathodes in the electrochemical reduction of CO2, present surface‐enhanced Raman scattering (SERS) when properly activated. In this sense, the electrochemical reduction of CO2 over a copper electrode in the room temperature ionic liquids 1‐n‐butyl‐3‐methyl imidazolium tetrafluoroborate (BMI.BF4) was investigated by cyclic voltammetry and by in situ SERS. The cyclic voltammetries have shown that the presence of CO2 on the BMI.BF4 anticipates the reduction of BMI+ to the corresponding carbene. Fourier‐transform‐SERS spectra excited at 1064 nm and SERS spectra excited at 632.8 nm have shown vibrational signals from adsorbed CO. These SERS results indicated that CO adsorbs on the copper surface at two different surface sites. The observation of a 2275 cm−1 vibration in the SERS spectra also confirmed the presence of chemically adsorbed CO2. Other products of CO2 reduction in BMI.BF4, besides CO, were identified, including BMI carbene and the BMI‐CO2 adduct. The SERS results also suggest that the presence of a thin film of Cu2O on the copper surface anticipates the reduction of CO2 to CO, an important component of syngas. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
200.
Alexandre Westermann Christophe Geantet Philippe Vernoux Stphane Loridant 《Journal of Raman spectroscopy : JRS》2016,47(10):1276-1279
In this work, the origin of the Raman defects band at 570 cm−1 of praseodymium‐doped ceria was revisited from in situ spectra using six different exciting lines between 458 and 785 nm at low temperatures after oxidizing or reducing treatment. The observation of overtones and the fast change of relative intensity with excitation wavelength were explained by a resonance effect around 514 nm, which involved a Pr4+ containing defect stabilized at the oxidized state leading to an absorption band around 530 nm. The reduction of Pr4+ cations contained in such defects modifies the electronic properties of praseodymium doped ceria inhibiting the resonance effect. Additionally, the number of D1 defects that involved Pr3+ cations and oxygen vacancies increased allowing them to be distinguished. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献