Next-generation wireless networks will support a wide range of data rates over several frequency bands and require adaptive and programmable system resources. Radio transceivers used in these wireless networks will incorporate self-calibration and full programmability to support their high performance and adaptivity. Low power designs at the circuit architectural, and overall system levels will enable longer battery life for portable devices. Many additional challenges exist in implementing high data rate programmable orthogonal frequency division multiplexing (OFDM) multiple-input/multiple-output (MIMO) radio transceivers that cover different frequency bands, maintain low current consumption, and are low cost. This article is an examination of the challenges in implementing high data rate programmable orthogonal frequency division multiplexing multiple-input/multiple-output radio transceivers that cover different frequency bands, maintain low current consumption, and are low cost. 相似文献
For the first time, a low cost, high performance and environmentally friendly heterogeneous catalyst derived from waste filter press cake (FPC) from a sugar manufacturing facility was used for the production of biodiesel. This industrial waste was calcined in air at 900 °C for 2 h to convert it into an active CaO‐based catalyst (FPC‐HT). In addition, the calcium oxide nanoparticles (FPC‐NAC) were synthesized by surfactant‐hydration treatment of FPC‐HT. The synthesized catalysts were characterized by XRD, FTIR, SEM, TEM and BET analysis. These calcium oxide catalysts were used for a transesterification reaction between canola oil and methanol to produce biodiesel. The results show that the FPC‐NAC has higher catalytic activity than FPC‐HT under optimized reaction conditions. Therefore, this economic catalyst is able to catalyze the transesterification of canola oil to its methyl esters in 1.5 h with yields above 96 %. 相似文献
A steady-state three-dimensional non-isothermal computational fluid dynamics (CFD) model of a proton exchange membrane fuel cell is presented. Conservation of mass, momentum, species, energy, and charge, as well as electrochemical kinetics are considered. In this model, the effect of interfacial contact resistance is also included. The numerical solution is based on a finite-volume method. In this study the effects of flow channel dimensions on the cell performance are investigated. Simulation results indicate that increasing the channel width will improve the limiting current density. However, it is observed that an optimum shoulder size of the flow channels exists for which the cell performance is the highest. Polarization curves are obtained for different operating conditions which, in general, compare favorably with the corresponding experimental data. Such a CFD model can be used as a tool in the development and optimization of PEM fuel cells. 相似文献
In this paper, a new linear theory for bending stress-strain analysis of a cracked beam has been developed. A displacement field has been suggested for the beam strain and stress calculations. The bending differential equation for the beam has been written using equilibrium equations. The required constant for this model is also obtained from fracture mechanics. The bending equation has been solved for a simply supported beam with rectangular cross-section and the results are compared with finite element and empirical results. There is an excellent agreement between theoretical results and those obtained by numerical and empirical methods. The model developed in this research is a simple and precise approximation of the behavior of the cracked beams in bending. 相似文献
In most blast loading structure analyses, it is assumed that the load acts uniformly on a target area. For the rationable design, it is useful to have a quantitative criterion to determine at which maximum distance the standoff can be placed to assume a uniform pressure distribution. Surprisingly, no standard criterion was found in the literature and the effect of blast wave clearing was not considered as well. In this paper, pressure histories applied on structures are calculated considering the non‐uniform loading characteristic as well as pressure relief from the edges. Additionally, the effects of various parameters on uniformity of impulse distribution are investigated. The results have shown that the effect of pressure relief on impulse uniformity is very important, especially when the blast wave is attenuated. This phenomenon leads an optimum distance at which impulse distribution is the most uniform. 相似文献
Nowadays, automatic speech emotion recognition has numerous applications. One of the important steps of these systems is the feature selection step. Because it is not known which acoustic features of person’s speech are related to speech emotion, much effort has been made to introduce several acoustic features. However, since employing all of these features will lower the learning efficiency of classifiers, it is necessary to select some features. Moreover, when there are several speakers, choosing speaker-independent features is required. For this reason, the present paper attempts to select features which are not only related to the emotion of speech, but are also speaker-independent. For this purpose, the current study proposes a multi-task approach which selects the proper speaker-independent features for each pair of classes. The selected features are then given to the classifier. Finally, the outputs of the classifiers are appropriately combined to achieve an output of a multi-class problem. Simulation results reveal that the proposed approach outperforms other methods and offers higher efficiency in terms of detection accuracy and runtime.
This paper develops a novel robust tracking model predictive control (MPC) without terminal constraint for discrete-time nonlinear systems capable to deal with changing setpoints and unknown non-additive bounded disturbances. The MPC scheme without terminal constraint avoids difficult computations for the terminal region and is thus simpler to design and implement. However, the existence of disturbances and/or sudden changes in a setpoint may lead to feasibility and stability issues in this method. In contrast to previous works that considered changing setpoints and/or additive slowly varying disturbance, the proposed method is able to deal with changing setpoints and non-additive non-slowly varying disturbance. The key idea is the addition of tightened input and state (tracking error) constraints as new constraints to the tracking MPC scheme without terminal constraints based on artificial references. In the proposed method, the optimal tracking error converges asymptotically to the invariant set for tracking, and the perturbed system tracking error remains in a variable size tube around the optimal tracking error. Closed-loop input-to-state stability and recursive feasibility of the optimization problem for any piece-wise constant setpoint and non-additive disturbance are guaranteed by tightening input and state constraints as well as weighting the terminal cost function by an appropriate stabilizing weighting factor. The simulation results of the satellite attitude control system are provided to demonstrate the efficiency of the proposed predictive controller. 相似文献