排序方式: 共有143条查询结果,搜索用时 15 毫秒
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We describe a simple and efficient procedure for the preparation of sulfuric acid ([3-(3-silicapropyl)sulfanyl]propyl)ester (3) by the reaction of 3-(thio(propy-3-yl)silica)-propanol (2) and chlorosulfonic acid in chloroform. 3-(Thio(propy-3-yl)silica)-propanol was prepared by the reaction of 3-mercaptopropylsilica (MPS) with 3-chloropropanol in refluxing toluene. This solid sulfuric acid ([3-(3-silicapropyl)sulfanyl]propyl)ester is employed as a new catalyst for the formylation of alcohols with ethyl formate under mild and heterogeneous conditions at room temperature with good to excellent yields. Also, 3 can catalyze the acetylation of various alcohols by the reaction of alcohols with ethyl acetate under reflux conditions or with acetic anhydride at room temperature. 相似文献
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Dariush Kokabi 《Materials Science & Technology》2020,36(15):1639-1647
The paper aims at understanding the microstructure evolution of the diffusion brazing of γ-TiAl intermetallic compound using two Ni-based filler metals, a ternary Ni-Si-B, and a quinary Ni-Cr-Fe-Si-B. It was found that the joint region comprised of two distinct zones: analogous reaction layers adjacent to the TiAl substrates and a solidified zone at the middle of the joint region. The reaction layers consisted of separate intermetallic phases regions including ternary and binary Ti-Ni-Al intermetallic compounds. The solidified zone mainly composed of the Al1-xNi3Six isostructural solid solution and athermally Ni-boride or Ni-Cr rich borides containing eutectic microstructures at the joint centerline. The maximum shear strength was 240?MPa, and obtained by using Ni-Cr-Fe-Si-B filler metal. Fracture of the joint with Ni-Cr-Fe-Si-B filler occurred in the reaction layer/solidified zone interface, but joint with Ni-Si-B filler was fractured at solidified zone. 相似文献
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This note shows that the input targets of proposed model by Kuosmanen and Kazemi Matin (2009) (http://dx.doi.org/10.1016/j.ejor.2007.09.040 and http://dx.doi.org/10.1016/j.omega.2008.11.002) may not be less than the input targets of proposed model by Lozano and Villa (2006) (http://dx.doi.org/10.1016/j.cor.2005.02.031). 相似文献
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Salar Azizi Mansour Taheri Dariush Mowla 《Numerical Heat Transfer, Part A: Applications》2013,63(8):659-677
A two-fluid model (TFM) based on the kinetic theory was used to study the heat transfer of gas-solid flows in a vertical pneumatic conveyor. A 2-D, vertical pipe with 1.1 m length and 0.017 m internal diameter was chosen as the computation domain. Pipeline has 0.86 m heat transfer section after a 0.28 m developing section. It was found that the voidage has minimum and dimensionless velocities, and temperatures have maximum values in the centerline. A convective heat transfer coefficient decreases along the pipeline, and it was found that the heat transfer coefficient of gas-solid flow is greater than clean gas. 相似文献
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In this paper, secure channel coding schemes based on turbo codes are suggested for time reversal ultra wideband (TR-UWB)
systems. Turbo code has the capability of error correction near Shannon’s limit. Adding security to turbo code is an attractive
idea since it could reduce the overall processing cost of providing secure coded data and enjoys the advantages of high-speed
encryption and decryption with high security, smaller encoder and decoder size and greater efficiency. The proposed turbo
code schemes are labeled as follows: secure puncturing rate, secure frame length, and secure interleaving. Using these scenarios,
secure turbo code is defined in a way that the redundant information used for error correction is not pre-determined by the
nature of the error correction part of the algorithm but it can be chosen arbitrarily out of the whole set of possible strings.
The lower bound of bit error probability for secure turbo code schemes in AWGN and TR-UWB systems are evaluated. Analytical
and simulation results show secure turbo code performance is very satisfying. Various crypto-analytical attacks are investigated
against these schemes. Based on this analysis, secure turbo code structures changed during the encryption procedure to increase
the complexity of linear and differential cryptanalysis. It is seen that the performance of conventional turbo code and random
frame length with Poisson distribution are the same. Comparing these schemes shows, secure interleaving approach has the best
performance and secure puncturing rate the worst, but the latter provides the most security. The enhanced security of UWB,
due to rich multipath nature of UWB channel, could be exploited. Due to space-time focusing property of time reversal UWB,
there is an environmental confidentiality (or spatial security), which is additional security for secure turbo code in this
system. Using secure turbo code, it is possible to increase the transmission range of UWB systems. 相似文献
68.
In this study, a new mathematical approach for evaluating of a de-oiling hydrocyclone efficiency has been developed. This new model uses the flow pattern of disperse phase and the boundary layer separation theory. In the present model unlike the other existing models, it is assumed that the droplet concentration in the radial direction is not uniform within the hydrocyclone. The hydrocyclone separation efficiency is calculated considering the droplet size distribution of the feed and the boundary layer thickness. The present approach considers the effects of droplet load, hydrocyclone geometry, mean droplet size and flow rate on the efficiency. The model is validated by comparison of the calculated separation efficiency with several previous experimental studies. 相似文献
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Sina Amini Dariush Mowla Mahdi Golkar Feridun Esmaeilzadeh 《Chemical Engineering Research and Design》2012
In this study, a mathematical model is developed to predict the efficiency of a down-hole oil–water separation hydrocyclone. In the proposed model, the separation efficiency is determined based on droplet trajectory of a single oil droplet through the continuous-phase. The droplet trajectory model is developed using a Lagrangian approach in which single droplets are traced in the continuous-phase. The droplet trajectory model uses the swirling flow of the continuous-phase to trace the oil droplets. By applying the droplet trajectory, a trial and error approach is used to determine the size of the oil droplet that reaches the reverse flow region, where they can be separated. The required input for the proposed model is hydrocyclone geometry, fluid properties, inlet droplet size distribution and operational conditions at the down hole. The model is capable of predicting the hydrocyclone hydrodynamic flow field, namely, the axial, tangential and radial velocity distributions of the continuous-phase. The model was then applied for some case studies from the field tested DOWS systems which exist in the literature. The results show that the proposed model can predict well the split ratio and separation efficiency of the hydrocyclone. Moreover, the results of the proposed model can be used as a preliminary evaluation for installing a down-hole oil–water separation hydrocyclone system in a producing well. 相似文献
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Haider N. Sultani Ibrahim Morgan Hidayat Hussain Andreas H. Roos Haleh H. Haeri Goran N. Kaluerovi Dariush Hinderberger Bernhard Westermann 《International journal of molecular sciences》2021,22(13)
Multicomponent reactions, especially the Ugi-four component reaction (U-4CR), provide powerful protocols to efficiently access compounds having potent biological and pharmacological effects. Thus, a diverse library of betulinic acid (BA), fusidic acid (FA), cholic acid (CA) conjugates with TEMPO (nitroxide) have been prepared using this approach, which also makes them applicable in electron paramagnetic resonance (EPR) spectroscopy. Moreover, convertible amide modified spin-labelled fusidic acid derivatives were selected for post-Ugi modification utilizing a wide range of reaction conditions which kept the paramagnetic center intact. The nitroxide labelled betulinic acid analogue 6 possesses cytotoxic effects towards two investigated cell lines: prostate cancer PC3 (IC50 7.4 ± 0.7 μM) and colon cancer HT29 (IC50 9.0 ± 0.4 μM). Notably, spin-labelled fusidic acid derivative 8 acts strongly against these two cancer cell lines (PC3: IC50 6.0 ± 1.1 μM; HT29: IC50 7.4 ± 0.6 μM). Additionally, another fusidic acid analogue 9 was also found to be active towards HT29 with IC50 7.0 ± 0.3 μM (CV). Studies on the mode of action revealed that compound 8 increased the level of caspase-3 significantly which clearly indicates induction of apoptosis by activation of the caspase pathway. Furthermore, the exclusive mitochondria targeting of compound 18 was successfully achieved, since mitochondria are the major source of ROS generation. 相似文献