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排序方式: 共有120条查询结果,搜索用时 0 毫秒
81.
Shayan Ehsani Mohammad Ghodsi Ahmad Khajenezhad Hamid Mahini Afshin Nikzad 《Information Processing Letters》2012,112(4):118-123
We study the optimal pricing strategy for profit maximization in presence of network externalities where a decision to buy a product depends on the price offered to the buyer and also on the set of her friends who have already bought that product. We model the network influences by a weighted graph where the utility of each buyer is the sum of her initial value on the product, and the linearly additive influence from her friends. We assume that the buyers arrive online and the seller should offer a price to each buyer when she enters the market. We also take into account the manufacturing cost. In this paper, we first assume that the monopolist defines a unique price for the product and commits to it for all buyers. In this case, we present an FPTAS algorithm that approximates the optimal price with a high probability. We also prove that finding the optimum price is NP-hard. Second, we consider a market with positive network externalities and assume that the monopolist could offer a private price to each customer. We prove that this problem is also hard to approximate for linear influences. On the positive side, we present a polynomial time algorithm for the problem when influences are symmetric. At last, we show that the seller has more ability to extract influences with price discrimination. 相似文献
82.
Cost/time estimation in flat plate processing (FPP) is a complex system of man–work–environment–organization. As the share and impact of physical, psychological, personal, and other characteristics of human in this complex system becomes bigger, the state of FPP time estimation changes from well defined to ill-defined (uncertain). Due to so many inter-related, imprecise, and ill-defined factors involved in activity time, it is too complicated; time consuming and expensive to model these factors into a universally accepted activity time/cost estimation system using mathematical or even analytical–experimental approaches. This paper addresses the issue of uncertainty treatment in activity time estimation in FPP. The emphasis is placed on modeling of non-random uncertainties using fuzzy sets. 相似文献
83.
This paper investigates the role of computer simulation in evaluating the performance of a container terminal in relation to its handling techniques and their impact on the capacity of terminal. The paper investigates and compares two different operational systems (current and proposed) statistically via a simulation model. The paper also addresses issues such as the performance criteria and the model parameters to propose an operational method that reduces port terminal congestion and increases the capacity of terminal. 相似文献
84.
Aero‐structural dynamics of a flexible hub connection for load reduction on two‐bladed wind turbines 下载免费PDF全文
In this study, an innovative concept for load reduction on the two‐bladed Skywind 3.4 MW prototype is presented. The load reduction system consists of a flexible coupling between the hub mount, carrying the drive train components including the hub assembly, and a nacelle carrier supported by the yaw bearing. This paper intends to assess the impact of introducing a flexible hub connection on the system dynamics and the aero‐elastic response to aerodynamic load imbalances. In order to limit the rotational joint motion, a cardanic spring‐damper element is introduced between the hub mount and the nacelle carrier flange, which affects the system response and the loads. A parameter variation of the stiffness and damping of the connecting spring‐damper element has been performed in the multi‐body simulation solver Simpack. A deterministic, vertically sheared wind field is applied to induce a periodic aerodynamic imbalance on the rotor. The aero‐structural load reduction mechanisms of the coupled system are thereby identified. It is shown that the fatigue loads on the blades and the turbine support structure are reduced significantly. For a very low structural coupling, however, the corresponding rotational deflections of the hub mount exceed the design limit of operation. The analysis of the interaction between the hub mount motion and the blade aerodynamics in a transient inflow environment indicates a reduction of the angle of attack amplitudes and the corresponding fluctuations of the blade loading. Hence, it can be concluded that load reduction is achieved by a combination of reduced structural coupling and a mitigation of aerodynamic load imbalances. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
85.
Henry Medeiros Donghun Kim Jianxin Sun Hariharan Seshadri Shayan Ali Akbar Noha M. Elfiky Johnny Park 《野外机器人技术杂志》2017,34(7):1203-1224
Dormant pruning of fruit trees is one of the most costly and labor‐intensive activities in specialty crop production. We present a system that solves the first step in the process of automated pruning: accurately measuring and modeling the fruit trees. Our system employs a laser sensor to collect observations of fruit trees from multiple perspectives, and it uses these observations to measure parameters needed for pruning. A split‐and‐merge clustering algorithm divides the collected data into three sets of points: trunk candidates, junction point candidates, and branches. The trunk candidates and junction point candidates are then further refined by a robust fitting algorithm that models as cylinders each segment of the trunk and primary branches. In this work, we focus on measuring the diameters of the primary branches and the trunk, which are important factors in dormant pruning and can be obtained directly from the cylindrical models. We show that the results are qualitatively satisfactory using synthetic and real data. Our experiments with three synthetic and three real apple trees of two different varieties showed that the system is able to identify the primary branches with an average accuracy of 98% and estimate their diameters with an average error of 0.6 cm. Although the current implementation of the system is too slow for large‐scale practical applications (it can measure approximately two trees per hour), our study shows that the proposed approach may serve as a fundamental building block of robotic pruners in the near future. 相似文献
86.
Johan Karlsson Stephany Y. Tzeng Shayan Hemmati Kathryn M. Luly Olivia Choi Yuan Rui David R. Wilson Kristen L. Kozielski Alfredo Quiñones-Hinojosa Jordan J. Green 《Advanced functional materials》2021,31(17):2009768
Clinical translation of polymer-based nanocarriers for systemic delivery of RNA has been limited due to poor colloidal stability in the blood stream and intracellular delivery of the RNA to the cytosol. To address these limitations, this study reports a new strategy incorporating photocrosslinking of bioreducible nanoparticles for improved stability extracellularly and rapid release of RNA intracellularly. In this design, the polymeric nanocarriers contain ester bonds for hydrolytic degradation and disulfide bonds for environmentally triggered small interfering RNA (siRNA) release in the cytosol. These photocrosslinked bioreducible nanoparticles (XbNPs) have a shielded surface charge, reduced adsorption of serum proteins, and enable superior siRNA-mediated knockdown in both glioma and melanoma cells in high-serum conditions compared to non-crosslinked formulations. Mechanistically, XbNPs promote cellular uptake and the presence of secondary and tertiary amines enables efficient endosomal escape. Following systemic administration, XbNPs facilitate targeting of cancer cells and tissue-mediated siRNA delivery beyond the liver, unlike conventional nanoparticle-based delivery. These attributes of XbNPs facilitate robust siRNA-mediated knockdown in vivo in melanoma tumors colonized in the lungs following systemic administration. Thus, biodegradable polymeric nanoparticles, via photocrosslinking, demonstrate extended colloidal stability and efficient delivery of RNA therapeutics under physiological conditions, and thereby potentially advance systemic delivery technologies for nucleic acid-based therapeutics. 相似文献
87.
Shayan Eslami J. Francisco Miranda Luis Mourão Paulo J. Tavares P. M. G. P. Moreira 《The International Journal of Advanced Manufacturing Technology》2018,99(1-4):127-136
The use of friction stir welding (FSW) to join thermoplastics has proven to produce strong welds with good surface quality when compared to conventional welding methods. In this study, a Teflon stationary shoulder was developed to weld 3-mm-thick plates of high molecular weight polyethylene in butt-joint configuration. Different sets of welding parameters were chosen and tested to evaluate their effect on the weld strength. Also, in order to increase joint performance, the temperature generated during welding was measured. For that purpose, thermocouples were located underneath of the weld nugget surface to measure the generated frictional heat for different tool diameters and parameters. Tool diameter and rotational and welding speeds are the most influential parameters regarding the welding temperature; however, all the input parameters had statistically significant effect on the weld quality. Unlike FSW in metals, using this tool, the heat is generated mainly by surface contact of the rotating probe and copper sleeve than the base material. The strongest welded joint was able to withstand 97% of the force that is necessary to fracture the base material, without using an external heating source. 相似文献
88.
Shayan Farahvash Mohsen Kavehrad 《International Journal of Wireless Information Networks》2000,7(4):197-210
Behavior of co-channel interference in fixed wireless cellular systems, such as millimeter-waves Local Multipoint Distribution Service (LMDS), is different compared to what has been established for mobile microwave systems. This is due to utilization of a high-gain antenna for the subscriber. In this paper, first the analysis of signal-to-interference ratio (SIR) is presented for line-of-sight and nearly line-of-sight LMDS architecture. In this analysis, the effects of precipitation and foliage attenuation and depolarization have been considered. These two parameters have negligible effect on the microwave mobile systems but in millimeter-wave range are among the most important factors in the link budget. To mitigate the fading due to shadowing by buildings and trees, a highly overlapped architecture and macro-diversity are proposed. After analysis of downlink SIR in previously proposed cellular systems, a cellular architecture is proposed based on polarization interleaving and frequency segmentation which has a much higher SIR yield. The statistical assessment of SIR is accomplished by assuming lognormal distribution for the received signals. 相似文献
89.
B. V. Suresh Kumar Siddaramaiah M. B. Shayan K. S. Manjula C. Ranganathaiah G. V. Narasimha Rao B. Basavalingu K. Byrappa 《Journal of Polymer Research》2010,17(1):135-142
Polymer-Zeolites composites have been prepared, using castor oil based polyurethane (PU) as a host and AlPO4-5 as particulate filler. The prepared PU/zeolite composites have been characterized for mechanical properties such as tensile strength and tensile modulus. These PU composites exhibited an improved mechanical performance compared to the unfilled PU. Thermo gravimetric analyzer (TGA) curve shows that all the chain-extended PUs are stable up to 250 °C and maximum weight loss occurs at 490 °C. The thermal stability of composites increases with increase in zeolite content. Microcrystalline parameters and micro voids of composites have been measured by using wide-angle X-ray scattering (WAXS) and Positron Annihilation Lifetime (PALS) methods respectively. The microcrystalline parameters and micro-voids from PALS indicate the interaction of the filler with the matrix is stronger beyond 5% of the filler which reflect the mechanical performance as well. Surface morphology of composites has been studied using Scanning Electron Microscopy (SEM). The photomicrograph of SEM indicates a uniform distribution of zeolite filler in the PU matrix. 相似文献
90.
Simge Uzun Shayan Seyedin Amy L. Stoltzfus Ariana S. Levitt Mohamed Alhabeb Mark Anayee Christina J. Strobel Joselito M. Razal Genevieve Dion Yury Gogotsi 《Advanced functional materials》2019,29(45)
Textile‐based electronics enable the next generation of wearable devices, which have the potential to transform the architecture of consumer electronics. Highly conductive yarns that can be manufactured using industrial‐scale processing and be washed like everyday yarns are needed to fulfill the promise and rapid growth of the smart textile industry. By coating cellulose yarns with Ti3C2Tx MXene, highly conductive and electroactive yarns are produced, which can be knitted into textiles using an industrial knitting machine. It is shown that yarns with MXene loading of ≈77 wt% (≈2.2 mg cm?1) have conductivity of up to 440 S cm?1. After washing for 45 cycles at temperatures ranging from 30 to 80 °C, MXene‐coated cotton yarns exhibit a minimal increase in resistance while maintaining constant MXene loading. The MXene‐coated cotton yarn electrode offers a specific capacitance of 759.5 mF cm?1 at 2 mV s?1. A fully knitted textile‐based capacitive pressure sensor is also prepared, which offers high sensitivity (gauge factor of ≈6.02), wide sensing range of up to ≈20% compression, and excellent cycling stability (2000 cycles at ≈14% compression strain). This work provides new and practical insights toward the development of platform technology that can integrate MXene in cellulose‐based yarns for textile‐based devices. 相似文献