Dynamic optimization of an industrial semi-batch nylon 6 reactor with end point constraints and stopping conditions

In this study, optimal vapor release rate (or pressure) histories have been generated for an industrial semi-batch nylon 6 reactor using Pontryagin's minimum principle. The batch time has been taken as the objective function, which is to be minimized. The pressure is constrained to lie between a lower and an upper limit. The temperature, a state variable, is also constrained to lie between 220°C and 270°C in order to ensure single-phase polymerization. Optimization has been carried out with a single end-point constraint (on monomer conversion) and a stopping condition (obtaining a product having a desired degree of polymerization, μ_n). Techniques have been developed to overcome the discontinuities present in the model, as well as to take care of state variable constraints. The effects of various physical and computational variables on the optimal pressure history and the corresponding batch time have been studied. It is found that the optimal batch time is almost 50% of the industrial value used currently. Interestingly, the optimal pressure history is quite similar qualitatively with the current practice though quantitatively there is a significant difference. Improvements in reactor operation along these lines have been reported. © 1996 John Wiley & Sons, Inc.     

Bibliography of literature on reliability in automotive industries

This paper presents a brief introduction and selective up-to-date references related to automotive reliability.     

Wireless Fading Paradigm for Antenna Array Receiver for a Disk-Type Cluster of Scatterers

This correspondence presents a signal processing based alternate approach for simulating the flat fading narrowband wireless channels for the antenna array receivers under the time-varying environment, in which the discrete disk of scatterers is incorporated around the mobile wireless transmitter to model the spreading of azimuth. The disk-type cluster of scatterers continuously changes due to the movement of the mobile wireless transmitter. Under this time-varying environment, each scatterer, at the successive stages of the disk, is correlated with the scatterers at the preceding stages of the disk using the second-order autoregressive process AR(2). At the receiver, one signal waveform is associated with each element of the antenna array taking into account the spread in azimuth of the received signal. The correlation of the fading waveforms generated by using the presented paradigm is compared with the expected analytical correlation results, which clearly manifests that the simulation results are consistent with the findings based on Jakes’ model. Moreover, the presented discrete disk-type cluster of scatterers fading model may be used to generate/simulate the variable diameter ring-type cluster of scatterers fading paradigm. The proposed channel model may play a significant role in the emerging field of wireless signal processing for the latest mobile communication systems.     

Causal memory: definitions,implementation, and programming

Summary The abstraction of a shared memory is of growing importance in distributed computing systems. Traditional memory consistency ensures that all processes agree on a common order of all operations on memory. Unfortunately, providing these guarantees entails access latencies that prevent scaling to large systems. This paper weakens such guarantees by definingcausal memory, an abstraction that ensures that processes in a system agree on the relative ordering of operations that arecausally related. Because causal memory isweakly consistent, it admits more executions, and hence more concurrency, than either atomic or sequentially consistent memories. This paper provides a formal definition of causal memory and gives an implementation for message-passing systems. In addition, it describes a practical class of programs that, if developed for a strongly consistent memory, run correctly with causal memory. Mustaque Ahamad is an Associate Professor in the College of Computing at the Georgia Institute of Technology. He received his M.S. and Ph.D. degrees in Computer Science from the State University of New York at Stony Brook in 1983 and 1985 respectively. His research interests include distributed operating systems, consistency of shared information in large scale distributed systems, and replicated data systems. James E. Burns received the B.S. degree in mathematics from the California Institute of Technology, the M.B.I.S. degree from Georgia State University, and the M.S. and Ph.D. degrees in information and computer science from the Georgia Institute of Technology. He served on the faculty of Computer Science at Indiana University and the College of Computing at the Georgia Institute of Technology before joining Bellcore in 1993. He is currently a Member of Technical Staff in the Network Control Research Department, where he is studying the telephone control network with special interest in behavior when faults occur. He also has research interests in theoretical issues of distributed and parallel computing especially relating to problems of synchronization and fault tolerance.This work was supported in part by the National Science Foundation under grants CCR-8619886, CCR-8909663, CCR-9106627, and CCR-9301454. Parts of this paper appeared in S. Toueg, P.G. Spirakis, and L. Kirousis, editors,Proceedings of the Fifth International Workshop on Distributed Algorithms, volume 579 ofLecture Notes on Computer Science, pages 9–30, Springer-Verlag, October 1991The photograph of Professor J.E. Burns was published in Volume 8, No. 2, 1994 on page 59This author's contributions were made while he was a graduate student at the Georgia Institute of Technology. No photograph and biographical information is available for P.W. Hutto Gil Neiger was born on February 19, 1957 in New York, New York. In June 1979, he received an A.B. in Mathematics and Psycholinguistics from Brown University in Providence, Rhode Island. In February 1985, he spent two weeks picking cotton in Nicaragua in a brigade of international volunteers. In January 1986, he received an M.S. in Computer Science from Cornell University in Ithaca, New York and, in August 1988, he received a Ph.D. in Computer Science, also from Cornell University. On August 20, 1988, Dr. Neiger married Hilary Lombard in Lansing, New York. He is currently a Staff Software Engineer at Intel's Software Technology Lab in Hillsboro, Oregon. Dr. Neiger is a member of the editorial boards of theChicago Journal of Theoretical Computer Science and theJournal of Parallel and Distributed Computing.     

Synthesis,characterization, and swelling behavior evaluation of hydrogels based on Gum ghatti and acrylamide for selective absorption of saline from different petroleum fraction–saline emulsions

In this research article, the synthesis of Gum ghatti and acrylamide based superabsorbents under pressure with N,N′‐methylene bisacrylamide as a crosslinker and an ascorbic acid–potassium persulfate redox pair as an initiator is reported. To study the impact of the different reaction variables on the water absorbance of the candidate polymer, different reaction parameters, including the reaction time, amount of solvent, pH of the medium, initiator ratio, pressure, and monomer and crosslinker concentrations, were optimized. The candidate polymer was characterized with different techniques, including Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, differential thermal analysis, differential thermogravimetry, and X‐ray diffraction. The crosslinked product was found to be thermally more stable than the initial backbone. The swelling capacity of the synthesized polymer was investigated in deionized water as a function of time, temperature, and pH of the swelling medium. Moreover, the effects of the ionic strengths of different cations on the swelling capacity of the candidate polymer were studied with different salt solutions. The tendency of absorbency for these hydrogels in salt solutions was found to be in the following order: Na⁺ > Ba²⁺ > Fe³⁺ > Sn⁴⁺ for NaCl, BaCl₂, FeCl₃, and SnCl₄ salt solutions. Further, the candidate polymer was used for the selective absorption of saline water from different petroleum fraction–saline emulsions. The results showed that the saline absorption capacities of the hydrogels were 667, 610, 646, and 680% in kerosene–saline, diesel–saline, petrol–saline, and petroleum ether–saline emulsions, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Ultracompact beam splitters based on plasmonic nanoslits

An ultracompact plasmonic beam splitter is theoretically and numerically investigated. The splitter consists of a V-shaped nanoslit in metal films. Two groups of nanoscale metallic grooves inside the slit (A) and at the small slit opening (B) are investigated. We show that there are two energy channels guiding light out by the splitter: the optical and the plasmonic channels. Groove A is used to couple incident light into the plasmonic channel. Groove B functions as a plasmonic scatter. We demonstrate that the energy transfer through plasmonic path is dominant in the beam splitter. We find that more than four times the energy is transferred by the plasmonic channel using structures A and B. We show that the plasmonic waves scattered by B can be converted into light waves. These light waves redistribute the transmitted energy through interference with the field transmitted from the nanoslit. Therefore, different beam splitting effects are achieved by simply changing the interference conditions between the scattered waves and the transmitted waves. The impact of the width and height of groove B are also investigated. It is found that the plasmonic scattering of B is changed into light scattering with increase of the width and the height of B. These devices have potential applications in optical sampling, signal processing, and integrated optical circuits.     

Fast computation of the discrete Hartley transform

The discrete Hartley transform (DHT) is a real‐valued transform closely related to the discrete Fourier transform (DFT) of a real‐valued spectrum which preserves some useful properties of DFT. In this paper, an algorithm is proposed to realize one‐dimensional DHT with sequence length N=2^{(2 × m)}, m?2. The proposed algorithm requires fewer multiplications than some of the algorithms in the literature. Copyright © 2008 John Wiley & Sons, Ltd.