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991.
Carlos B. da Silva Pedro Neto José C. F. Pereira 《Theoretical and Computational Fluid Dynamics》2009,23(4):287-296
Direct and large-eddy simulations (DNS/LES) of accelerating round jets are used to analyze the effects of acceleration on
the kinematics of vortex rings in the near field of the jet (x/D < 12). The acceleration is obtained by increasing the nozzle jet velocity with time, in a previously established (steady)
jet, and ends once the inlet jet velocity is equal to twice its initial value. Several acceleration rates (α = 0.02–0.6) and Reynolds numbers (Re
D
= 500–20000) were simulated. Acceleration maps were used to make a detailed study of the kinematics of vortex rings in accelerating
jets. One of the effects of the acceleration is to cause a number of new primary and secondary vortex merging events that
are absent from steady jets. As the acceleration rate α increases, both the number of primary merging events between rings
and the axial position where these take place decreases. The statistics for the speed of the starting ring that forms at the start of the acceleration phase for each simulation, agree well with the statistics for the “front” speed
observed by Zhang and Johari (Phys Fluids 8:2185–2195, 1996). Acceleration maps and flow visualizations show that during the
acceleration phase the near field coherent vortices become smaller and are formed at an higher frequency than in the steady
jet, and their (mean) shedding frequency increases linearly with the acceleration rate. Finally, it was observed that the
acceleration decreases the spreading rate of the jet, in agreement with previous experimental works.
相似文献
992.
芳胺和芳酮所形成的希夫碱在无水三氯化铝或二异丙胺锂与氯化锌乙醚溶液存在下和腈类化合物加成,制备了一些文献中未报导过的3-氨基-2-烯亚胺,并经元素分析、1H NMR,13C NMR和MS确证. 相似文献
993.
Pedro H. Ferri Carlito Lariucci Leon I. B. Homar Raquel F. Santos Elaine R. Maia Lourivaldo S. Santos Ivo Vencato 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(1):118-120
The crystal structure and absolute configuration of the title compound, C17H21BrO8, have been determined by X‐ray analysis. They confirmed the 1′R absolute configuration at the 1′‐bromoethyl moiety which has been assigned previously on the basis of chemical and spectroscopic data. Cohesion of the crystal can be attributed to weak intermolecular C—H?O and van der Waals interactions. 相似文献
994.
Ya Zou Víctor Bonal Sergio Moles Quintero Dr. Pedro G. Boj Dr. José M. Villalvilla Dr. José A. Quintana Dr. Guangwu Li Shaofei Wu Dr. Qing Jiang Dr. Yong Ni Prof. Juan Casado Prof. María A. Díaz-García Prof. Jishan Wu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(35):15037-15044
Perylene-fused, aggregation-free polycyclic aromatic hydrocarbons with partial zigzag periphery ( ZY-01 , ZY-02 , and ZY-03 ) were synthesized. X-ray crystallographic analysis reveals that there is no intermolecular π–π stacking in any of the three molecules, and as a result, they show moderate-to-high photoluminescence quantum yield in both solution and in the solid state. They also display the characteristic absorption and emission spectra of perylene dyes. ZY-01 and ZY-02 with a nearly planar π-conjugated skeleton exhibit amplified spontaneous emission (ASE) when dispersed in polystyrene thin films. Solution-processed distributed feedback lasers have been fabricated using ZY-01 and ZY-02 as active gain materials, both showing narrow emission linewidth (<0.4 nm) at wavelengths around 515 and 570 nm, respectively. In contrast, ZY-03 did not show ASE and lasing, presumably due to its highly twisted backbone, which facilitates nonradiative internal conversion and intersystem crossing. 相似文献
995.
Alonso Alain Lázaro Mariano Lázaro Pedro Lázaro David Alvear Daniel 《Journal of Thermal Analysis and Calorimetry》2020,140(1):263-273
Journal of Thermal Analysis and Calorimetry - Understanding a material’s fire behaviour implies to know the thermal decomposition processes. Thermal analysis techniques are widely employed to... 相似文献
996.
997.
Gilberto Casillas Juan Pedro Palomares-Báez José Luis Rodríguez-López Junhang Luo Arturo Ponce Rodrigo Esparza 《哲学杂志》2013,93(35):4437-4453
There is strong interest in studying changes in mechanical properties with reducing grain size. The rational is that consequent dislocation glide cannot be sustained, resulting in an increase in material strength. However, this comes with the cost of a reduction in ductility. It has been shown that coherent twin boundaries in nanostructured Cu improve the ductility to 14% [Lu et al., Science 324 (2009) p. 349]. In this paper, we report for the first time the compression of individual nanoparticles using an in situ force probing holder in the transmission electron microscope. Four types of nanoparticles were tested, three with twin boundaries (decahedra, icosahedra and a single twin) and one free of defects (octahedral). Our results indicate the yield strength of the twinned nanoparticles is between 0.5 and 2.0 GPa. The total malleability for the twinned particles range from 80 to 100%. In addition, experimental results were reproduced by MD simulations of the compression phenomena and suggest that the outstanding mechanical properties are related with partial dislocation multiplication at twin boundaries. 相似文献
998.
Amanda Carla Quintas de Medeiros Vieira Graziella Silvestre Marques Cybelly Marques de Melo Keyla Emanuelle Ramos da Silva Larissa Araújo Rolim Maria do Carmo Alves de Lima Suely Lins Galdino Ivan da Rocha Pitta Pedro José Rolim Neto 《Journal of Thermal Analysis and Calorimetry》2014,115(3):2339-2349
LPSF/GQ-130 is a drug candidate, according to reports about its significant anti-inflammatory activity and non-toxicity demonstrated in an acute preclinical study. Despite this, knowledge of its physical–chemical properties is insufficient for the development of medicines. Thus, this work aimed to characterize the raw material at its molecular, particle, and agglomerate level as well as evaluate its thermal compatibility to pharmaceutical excipients. Through spectrometric techniques the molecular structure of the substance was confirmed. For thermal analysis its melting (171.3–176.5 °C) and degradation (238.3–297.4 °C) ranges, besides its purity (99.37 %), were determined. The kinetic non-isothermal degradation supplied the order of thermal reaction (0), the activation energy (96.14 kJ mol?1) and the frequency factor (3.130 × 10?7 min?1). The diffraction of X-rays presented well defined signs in the angles 5.5°, 16.3°, and 44.18° 2θ, suggesting crystalline structure. Scanning electronic microscopy exhibited needle morphology. LPSF/GQ-130 presented Type-III isotherm adsorption/desorption, with a superficial area of 81.3529 m2 g?1 and water content calculated at 1 % using the Karl Fisher method. Laser granulometry calculated its granulometry between 11.65 and 13.10 μm, thus it was characterized as a very fine powder. The prototype was classified as insoluble in water (<0.0187 μg mL?1) and soluble in acetone and acetonitrile, and exhibits instability in basic pH (100 %) and oxidative conditions (30–70 %). In thermal compatibility the excipients PVP K-30, Compritol® 888 ATO, and MYRJ® 59 seem to exercise a protective thermal activity for the prototype. 相似文献
999.
Methoxycarbonylation of olefins catalyzed by palladium(II) complexes containing naphthyl(diphenyl)phosphine ligands 下载免费PDF全文
Santiago Zolezzi Sergio A. Moya Gonzalo Valdebenito Gabriel Abarca Jose Parada Pedro Aguirre 《应用有机金属化学》2014,28(5):364-371
Palladium(II) complexes containing phosphine donor ligands derived from naphthyl(diphenyl)phosphine were synthesized and characterized by NMR and elemental analysis. The complexes were studied as catalyst precursors in the methoxycarbonylation reaction of several aromatic and aliphatic olefins under mild conditions. The catalysts reported high chemoselectivities (over 96%) and regioselectivities between 44% and 93% for different olefins. The best results were obtained over a styrene substrate with 97% of conversion after 6 h of reaction, with high regioselectivity (93%). Kinetic studies permitted the determination of the rate law (v = k [substrate]1.21±0.02 [catalyst]0.94±0.11 [acid]0.52±0.03 [MeOH]0.53±0.05 [CO]0.65±0.03) for methoxycarbonylation of styrene. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献