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排序方式: 共有389条查询结果,搜索用时 15 毫秒
81.
An attempt was made to prepare polyvinyl chloride (PVC)/thermosetting polyurethane (PU) blends via direct formation of the thermosetting minor phase from its reactants during blending into PVC. Chemorheological approaches were employed in order to investigate the formation reaction of PU. The results of chemorheological analyses were utilized to adjust appropriate reactive blending temperature. PVC/PU reactive blending process was carried out in a laboratory internal mixer. PVC and PU reactive mixture were fed into the internal mixer using two different feed orders. In the first method, porous particles of PVC and liquid mixture of PU monomers were premixed in a high-speed mixer at ambient temperature. The blending was then followed by processing the prepared paste in the preheated internal mixer. In the second method, PVC was loaded into the internal mixer. Afterward, PU reactive compound was introduced into the PVC after torque equilibrium. For both feed orders, the PU content of blends and rotor speed were among parameters studied. The mechanical properties of PVC/PU blends prepared by reactive blending and pure PVC showed that incorporation of PU elastomer into PVC through the proposed reactive blending technique resulted in an increase in the elongation at break and toughness of the brittle PVC. 相似文献
82.
A finite difference technique is developed to predict the second stage creep displacement rates and stress analysis of a short fiber metal matrix composite subjecting to a constant axial load through a micromechanical approach. The technique is capable to take into account the presence of interfacial debonding as one of the main factors affecting the creep performance of short fiber composites. The exponential law is adopted to describe the matrix creep behavior. Also, a model for prediction of interfacial debonding at fiber/matrix interface is developed using a stress based method. The obtained results could greatly help to better understand the flow pattern of matrix material and the load transfer mechanism between fiber and matrix with and without the presence of interfacial debond. The predicted strain rate by the proposed approach exhibits good agreement with the experimental results. 相似文献
83.
This paper presents a technique for designing a broad-band partially adaptive antenna using a new recursive fan filter. Each beamformer is designed using recursive two-pole sections. This method reduces the number of taps of the fan filter considerably. Interferences occurring in the sidelobes as well as the mainlobe of the desired pattern and having the same frequency as the desired signal and overlap in bandwidths are cancelled effectively independent of frequency 相似文献
84.
Ehsan Hashemi Maani Ghaffari Jadidi Navid Ghaffari JadidiAuthor vitae 《Robotics and Autonomous Systems》2011,59(11):930-942
The purpose of this study is to suggest and examine a PI–fuzzy path planner and associated low-level control system for a linear discrete dynamic model of omni-directional mobile robots to obtain optimal inputs for drivers. Velocity and acceleration filtering is also implemented in the path planner to satisfy planning prerequisites and prevent slippage. Regulated drivers’ rotational velocities and torques greatly affect the ability of these robots to perform trajectory planner tasks. These regulated values are examined in this research by setting up an optimal controller. Introducing optimal controllers such as linear quadratic tracking for multi-input–multi-output control systems in acceleration and deceleration is one of the essential subjects for motion control of omni-directional mobile robots. The main topics presented and discussed in this article are improvements in the presented discrete-time linear quadratic tracking approach such as the low-level controller and combined PI–fuzzy path planner with appropriate speed monitoring algorithm such as the high-level one in conditions both with and without external disturbance. The low-level tracking controller presented in this article provides an optimal solution to minimize the differences between the reference trajectory and the system output. The efficiency of this approach is also compared with that of previous PID controllers which employ kinematic modeling. Utilizing the new approach in trajectory-planning controller design results in more precise and appropriate outputs for the motion of four-wheeled omni-directional mobile robots, and the modeling and experimental results confirm this issue. 相似文献
85.
Nasser Nikfarjam Matineh Ghomi Tarun Agarwal Mahnaz Hassanpour Esmaeel Sharifi Danial Khorsandi Moonis Ali Khan Filippo Rossi Arianna Rossetti Ehsan Nazarzadeh Zare Navid Rabiee Davoud Afshar Massoud Vosough Tapas Kumar Maiti Virgilio Mattoli Eric Lichtfouse Franklin R. Tay Pooyan Makvandi 《Advanced functional materials》2021,31(42):2104148
Excessive and unwarranted administration of antibiotics has invigorated the evolution of multidrug-resistant microbes. There is, therefore, an urgent need for advanced active compounds. Ionic liquids with short-lived ion-pair structures are highly tunable and have diverse applications. Apart from their unique physicochemical features, the newly discovered biological activities of ionic liquids have fascinated biochemists, microbiologists, and medical scientists. In particular, their antimicrobial properties have opened new vistas in overcoming the current challenges associated with combating antibiotic-resistant pathogens. Discussions regarding ionic liquid derivatives in monomeric and polymeric forms with antimicrobial activities are presented here. The antimicrobial mechanism of ionic liquids and parameters that affect their antimicrobial activities, such as chain length, cation/anion type, cation density, and polymerization, are considered. The potential applications of ionic liquids in the biomedical arena, including regenerative medicine, biosensing, and drug/biomolecule delivery, are presented to stimulate the scientific community to further improve the antimicrobial efficacy of ionic liquids. 相似文献
86.
87.
Multipath fading channel significantly modifies the shape of pulses in ultra-wideband (UWB) communications and makes it difficult to distinguish between different pulse shapes. Hence, channel effects must be compensated for. A technique is introduced to extract and estimate the UWB channel impulse response from the distorted signal. 相似文献
88.
Evidence is presented showing that the presence of the commonly used anti-reflection coating material Ta2O5 on the free surface of contact metallization can either suppress or enhance, depending on the system, the interaction that
takes place at elevated temperatures between the metallization and the underlying Si. The cap layer is shown to suppress both
the generation and annihilation of vacancies at the free surface of the metal which are necessary to support metal-Si interactions.
Evidence is also presented indicating that the mechanical condition of the free metal surface has a significant effect on
the metal-silicon reaction rate. 相似文献
89.
H. Navid R.T. Fenner F. Nadiri G.A. Webster 《International Journal of Pressure Vessels and Piping》1985,18(4):241-254
Stress intensity factors for both internal and external semi-circular and semi-elliptical surface cracks in internally pressurised thick-walled cylinders of radius ratios between 2 and 3 are presented for a wide range of crack sizes. These solutions were obtained using the boundary integral equation (BIE) method for three-dimensional numerical stress analysis. Hoop strain distributions at the outer circumference of the cylinder are also presented for some external cracks, and shown to be useful for experimentally monitoring crack growth. 相似文献
90.
Removal of copper from molybdenite concentrate by mesophilic and extreme thermophilic microorganisms
Hadi Abdollahi Zahra Manafi Ziaedin Shafaei Sied Mohammad Noaparast Navid Manafi Moorkani 《矿业科学技术学报(英文版)》2013,23(6):827-834
Mixed mesophilic and extreme thermophilic bioleaching were evaluated to remove copper from the molybdenite concentrate. Bioleaching tests were carried out in shake flasks and in a 50-L bioreactor. The shake flask tests were performed with different inoculum size, solids density, pH, and temperature in order to identify optimum conditions. The highest amount of copper elimination, 75% was obtained with extreme thermophilic microorganisms (at 12% inoculation, 10% solids, 65 °C and a pH of 1.5). The highest copper elimination by mesophilic microorganisms was 55% (at 12% inoculation, 5% solids, 30 °C at pH 2). The optimum conditions in shake flask tests were applied to 7 days batch tests in a 50-L bioreactor. Extreme thermophilic experiment gave the best copper elimination of 60% (at 12% inoculation, 10% solids, 65 °C and pH 1.5). Mesophilic test removed 50% of the copper (at 12% inoculation, 10% solids, 35 °C at pH 2). 相似文献