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41.
Degradation of friction-reducing effectiveness of dilute poly(ethylene oxide) solutions subjected to continuous agitation is examined in disk flow. A residual or steady-state effectiveness is observed which disappears only at a sufficiently high Reynolds number. The onset of friction reduction appears to occur within the transition region and seems to be independent of solution concentration. The onset of degradation also appears to be independent of concentration. Prior shear working is shown to have a significant effect on residual friction-reducing effectiveness only when the shear working is performed in a more intense shear field than that in which the friction-reducing effectiveness is evaluated. Degradation of friction-reducing effectiveness is compared to corresponding changes in viscosity-average molecular weight. The experimental results are interpreted in terms of a model of the interaction between polymer molecules and the turbulent flow field. 相似文献
42.
Bachan S. Rawat Amar N. Goswami Sri Krishna 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1980,30(1):557-562
Isobaric vapour-liquid equilibria for the ternary system hexane-benezene-sulpholane have been determined at 760 mmHg pressure. The data have been compared with those calculated using the NRTL equation. The NRTL constants obtained from the literature were evaluated from ternary liquid-liquid equilibrium data for this system. The agreement between experimental and calculated values is reasonable. 相似文献
43.
A simple and stereoselective synthesis of (Z)-13-hexadecen-11-yn-1-yl acetate, the major component of the sex pheromone ofThaumetopoea pityocampa (Denis and Schiff.) is described. The procedure essentially involves formylation of a terminal acetylene to the corresponding aldehyde followed by a stereochemically controlled Wittig reaction, which has been studied under a variety of conditions. 相似文献
44.
AbstractCross-validation of soft computing techniques needs to be done efficiently to avoid overfitting and underfitting. This is more important in petroleum reservoir characterisation applications where the often-limited training and testing data subsets represent Wells with known and unknown target properties, respectively. Existing data stratification strategies have been haphazardly chosen without any experimental basis. In this study, the optimal training–testing stratification proportions have been rigorously investigated using the prediction of porosity and permeability of petroleum reservoirs as an experimental case. The comparative performances of seven traditional and advanced machine learning techniques were considered. The overall results suggested a recommendable optimum training stratification that could serve as a good reference for researchers in similar applications. 相似文献
45.
This paper focuses on the promise of globally linearized control (GLC) structure in the realm of strongly nonlinear reactor system control. The proposed nonlinear control strategy is comprised of: (i) an input-output linearizing state feedback law (transformer), (ii) a state observer, and (iii) an external linear controller. The synthesis of discrete-time GLC controller for single-input single-output diabatic continuous stirred tank reactor (DCSTR) has been studied first, followed by the synthesis of feedforward/feedback controller for the same reactor having dead time in process as well as in disturbance. Subsequently, the multivariable GLC structure has been designed and then applied on multi-input multi-output DCSTR system. The simulation study shows high quality performance of the derived nonlinear controllers. The better-performed GLC in conjunction with reduced-order observer has been compared with the conventional proportional integral controller on the example reactor and superior performance has been achieved by the proposed GLC control scheme. 相似文献
46.
Amar C. Garg 《Engineering Fracture Mechanics》1986,23(6):1031-1050
Fracture surface morphological studies of graphite/epoxy (T300/934) laminates have been performed to distinguish between mode I and mode II interlaminar and intralaminar fractures. Additionally, the effect of a few hygrothermal conditions on mode I fracture surface is also assessed. Centre notched tension, compact tension, double cantilever beam and cracked lap shear specimens have been used to study these fracture modes. While mode I fracture is characterized by branched cracks between fibers, river pattern and chevron markings on resin rich zones, the epoxy hackles dominate mode II fracture surface. The interlaminar and intralaminar fractures can be distinguished by fiber spacings and some matrix features. The effect of increase in temperature and/or moisture is seen to cause reduction in matrix microcracking and increase in fiber pullout in mode I. 相似文献
47.
Pragati A. Shinde Vaibhav C. Lokhande Amar M. Patil Taeksoo Ji Chandrakant D. Lokhande 《International Journal of Hydrogen Energy》2018,43(5):2869-2880
In present study, new strategy is employed to build composite nanostructure and asymmetric configuration to enhance the capacitive performance of supercapacitor device. The WO3-MnO2 composite with mesoporous structure is prepared by single-step hydrothermal method and used to gain superior electrochemical performance in asymmetric configuration. A binder-free and additive-less WO3-MnO2 composite electrode exhibits high specific capacitance of 609 F g?1 at a scan rate of 5 mV s?1. The flexible asymmetric supercapacitor device with WO3-MnO2 as a positive electrode and WO3 as a negative electrode demonstrates stable operating potential window of 1.4 V with specific capacitance of 103 F g?1 at a scan rate of 5 mV s?1 and energy density of 24.13 Wh kg?1 at power density of 915 W kg?1. Furthermore, WO3-MnO2//WO3 device exhibits good cycle life with capacity retention of 95% after 2500 cycles and excellent mechanical flexibility. These results reveal the potential of WO3-MnO2 composite electrode for fabrication of high-performance supercapacitors. 相似文献
48.
Sustainable biocomposites have gained considerable interest as an alternative to conventional composites in recent years due to their cost-effectiveness and environmental friendliness. The aim of this study was to investigate the performance and durability behavior of biocomposites from sustainable biocarbon (BC) as compared to conventional established fillers. The poly(butylene terephthalate) (PBT) and its composites reinforced with BC, talc, and glass fiber (GF) were prepared and the durability performances was investigated. The study showed that BC/PBT biocomposites provided a lighter weight alternative to traditionally used fillers. After undergoes thermo-oxidative aging, the mechanical properties of BC/PBT biocomposite were deteriorated. The GF/PBT showed the most stable in retaining its mechanical properties in comparison to the talc/PBT and BC/PBT. The aging behavior and mechanism of the PBT composites were discussed. This study provides further insight on the durability-related properties progression of biocomposites as compared to traditional used fillers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47722. 相似文献
49.
Speech coders operating at low bit rates necessitate efficient encoding of the linear predictive coding (Lpc) coefficients. Line spectral Frequencies (Lsf) parameters are currently one of the most efficient choices of transmission parameters for theLpc coefficients. In this paper, an optimized trellis coded vector quantization (Tcvq) scheme for encoding theLsf parameters is presented. When the selection of a proper distortion measure is the most important issue in the design and operation of the encoder, an appropriate weighted distance measure has been used during theTcvq construction process. We further applied the optimizedTcvq system for encoding theLsf parameters of the us Federal Standard (Fs1016) 4.8 kbps speech coder. At lower bit rates, objective and subjective evaluation results show that the incorporatedLsf tcvq encoder performs better than the 34 bits/frameLsf scalar quantizer used originally in the fs1016 coder. The subjective tests reveal also that the 27 bit/frame scheme produces equivalent perceptual quality to that when theLsf parameters are unquantized. 相似文献
50.
Hlne Lange Patricia Taillandier Jean‐Pierre Riba 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2001,76(5):501-505
Escherichia coli and Saccharomyces cerevisiae suspensions were submitted to controlled shear stress. Above a threshold value shear stress induced a decrease in micro‐organism viability. The threshold of shear stress efficiency depended on the micro‐organisms, being between 1292 Pa and 2770 Pa for S cerevisiae, and about 1250 Pa for E coli. Above 1810 Pa, E coli cells were disrupted whereas the S cerevisiae cells remained intact. The higher the cellular concentration, the greater the rate of decrease in viability. Viability loss was influenced by the number of passages through the experimental shear stress device and by exposure time. © 2001 Society of Chemical Industry 相似文献