Peak-to-average ratio reduction scheme for multi-carrier systems with block-based channel estimation

A simple scheme is proposed to reduce the peak-to-average ratio (PAPR) for multi-carrier systems with block-based channel estimation, where each user simultaneously transmits multiple traffic blocks across the frequency, and the channel estimation is done within each block. Unlike most existing schemes, the proposed scheme does not require additional side information or estimation at the receiver. Results indicate significant improvements in both the PAPR and cubic metric reduction.     

A feedback-based implementation scheme for batch process optimization

The terminal-cost optimization of a control–affine nonlinear system leads to a discontinuous solution that can be characterized in a piecewise manner. To implement such an optimal trajectory despite disturbances and parametric uncertainty, a cascade optimization scheme is proposed in this paper, where optimal reference signals are tracked. Optimality is achieved by the appropriate definition of reference signals (input bounds, state constraints, or switching functions) to track in various sub-intervals. Furthermore, conservatism is introduced into the optimization problem to ensure satisfaction of path constraints in the presence of uncertainty. Finally, the proposed cascade optimization scheme is illustrated on a simulation of a fed-batch penicillin fermentation plant.     

Modeling and analysis of miniaturized methanol reformer for fuel cell powered mobile applications

In this paper a miniaturized packed bed reactor is analyzed, in which autothermal reforming of methanol occurs to produce sufficient hydrogen for generating 100 W of power. Mass balance equations are developed for each species in the reactor and an energy balance is developed for modeling non-isothermal operation. The pressure drop is modeled via the Ergun equation. Simulations are conducted in MATLAB to determine the effect of process parameters (e.g. steam to methanol ratio, inlet pressure, inlet temperature) on the production of hydrogen. It is shown that the pressure drop is negligible. Simulation results are compared with experimental results from the literature and it shown that there is excellent agreement between the simulation results and experimental results. Process conditions that lead to the generation of sufficient hydrogen for generating 100 W of power are developed.     

Capacity of wireless erasure networks

In this paper, a special class of wireless networks, called wireless erasure networks, is considered. In these networks, each node is connected to a set of nodes by possibly correlated erasure channels. The network model incorporates the broadcast nature of the wireless environment by requiring each node to send the same signal on all outgoing channels. However, we assume there is no interference in reception. Such models are therefore appropriate for wireless networks where all information transmission is packetized and where some mechanism for interference avoidance is already built in. This paper looks at multicast problems over these networks. The capacity under the assumption that erasure locations on all the links of the network are provided to the destinations is obtained. It turns out that the capacity region has a nice max-flow min-cut interpretation. The definition of cut-capacity in these networks incorporates the broadcast property of the wireless medium. It is further shown that linear coding at nodes in the network suffices to achieve the capacity region. Finally, the performance of different coding schemes in these networks when no side information is available to the destinations is analyzed.     

Acquisition of troubleshooting skills in a computer simulation: Worked example vs. conventional problem solving instructional strategies

In a computer-based simulation of a chemical processing plant, the differential effects of three instructional strategies for learning how to troubleshoot the plant’s malfunctions were investigated. In an experiment concerning learners’ transfer performance and mental effort, the simulation presented the three strategies to three groups of learners and measured their performance on the transfer tasks. In this experiment, conventional problem solving was contrasted with two worked example strategies. The results indicated a significant difference between practicing problem solving and using worked examples. Learners who practiced problem solving in an interactive simulation outperformed the learners who studied computer-based worked examples. They also invested lower mental effort in transfer tasks. When accounting for the difference in the learners’ domain knowledge, the strategies were not significantly different among the more experienced learners. For the less experienced learners, those who practiced problem solving significantly outperformed their worked example counterparts. Among all participants and also among less experienced learners the problem solving group invested significantly lower mental effort in the performance of transfer tasks. Based on the results of this study, the authors recommend the use of the conventional problem solving strategy with or without worked examples for learning complex skills.     

Robust state feedback synthesis for control of non-square multivariable nonlinear systems

In this paper, a robust nonlinear controller is designed in the Input/Output (I/O) linearization framework, for non-square multivariable nonlinear systems that have more inputs than outputs and are subject to parametric uncertainty. A nonlinear state feedback is synthesized that approximately linearizes the system in an I/O sense by solving a convex optimization problem online. A robust controller is designed for the linear uncertain subsystem using a multi-model H₂/H_∞ synthesis approach to ensure robust stability and performance of non-square multivariable, nonlinear systems. This methodology is illustrated via simulation of a regulation problem in a continuous stirred tank reactor.     

Modeling and Simulation of the 1,3‐Butadiene Extraction Process at Turndown Capacity

As cracker feed around the globe is trending towards lighter feedstocks, butadiene production facilities worldwide are now run at turndown capacities. Models are developed to study how operation at turndown ratios of feed rates affects the purity of 1,3‐butadiene. The optimal solvent‐to‐feed ratio was found to be in the range of 6–7 when the plant is run at normal throughput; however, it is necessary to change the solvent‐to‐feed ratio in the range of 10–11 when the plant is operating at turndown capacity. Dynamic simulations indicate that the effect of fluctuations in the feed flow rate on product purity can be minimized by a ratio controller to change the solvent flow rate and a composition controller to alter the side‐draw flow rate.     

Robust controller synthesis for multivariable nonlinear systems with unmeasured disturbances

This work concerns robust controller synthesis using the differential geometric concepts for minimum phase nonlinear systems with unmeasurable disturbances. A pseudo-linearization of the disturbance model at the input-output linearization stage is applied to yield a linear subsystem for controller design. Based on this linear model, a multi-loop controller framework is implemented, whereby μ-synthesis is used to design off-line robust controller in the outer loop while state feedback is implemented in the inner loop. Through proper selection of weights, the outer robust controller is explicitly designed to address both uncertainty and disturbance rejection whereas the inner controller is used for on-line static state feedback. Numerical simulations are used to illustrate robustness of the controller for multi-input multi-output temperature control in two non-isothermal continuous stirred tank reactors in series.     

Sliding mode control of I/O linearizable systems with uncertainty

In this paper we explore the application of sliding mode control to process control problems. Sliding mode control is presented as a natural tool for robust design of state feedback controllers for minimum phase input–output linearizable systems with uncertainty. An example is presented to illustrate some of the issues involved in the design of sliding mode robust controllers.