Delay Optimal Scheduling in a Two-Hop Vehicular Relay Network

We study a scheduling problem in a wireless network where vehicles are used as store-and-forward relays, a situation that might arise, for example, in practical rural communication networks. A fixed source node wants to transfer a file to a fixed destination node, located beyond its communication range. In the absence of any infrastructure connecting the two nodes, we consider the possibility of communication using vehicles passing by. Vehicles arrive at the source node at renewal instants and are known to travel towards the destination node with average speed v sampled from a given probability distribution. The source node communicates data packets (or fragments) of the file to the destination node using these vehicles as relays. We assume that the vehicles communicate with the source node and the destination node only, and hence, every packet communication involves two hops. In this setup, we study the source node’s sequential decision problem of transferring packets of the file to vehicles as they pass by, with the objective of minimizing delay in the network. We study both the finite file size case and the infinite file size case. In the finite file size case, we aim to minimize the expected file transfer delay, i.e., expected value of the maximum of the packet sojourn times. In the infinite file size case, we study the average packet delay minimization problem as well as the optimal tradeoff achievable between the average queueing delay at the source node buffer and the average transit delay in the relay vehicle.     

New applications of Orthomin(1) algorithm for K-eigenvalue problem in Reactor Physics

This paper presents some new investigations on the use of Orthomin(1) algorithm for the solution of K-eigenvalue problem in Nuclear Reactor Physics. The algorithm was first used by Suetomi and Sekimoto [Conjugate gradient like methods and their application to eigenvalue problems for neutron diffusion equations, Annals of Nuclear Energy, 18(4) (1991) 205–227.] to find fundamental mode solution of K-eigenvalue problem based on multi-group neutron diffusion theory. It was shown to be an efficient alternative to the conventional methods based on power iterations. The use of this algorithm needs software development to evaluate product of coefficient matrices with vectors. Here, it is shown that the algorithm can also be applied to the K-eigenvalue equation cast in terms of fission matrix. This opens up the possibility of using conventional well-established diffusion codes to implement Orthomin(1) so that new software is not needed. Apart from this, a remarkable feature of Orthomin(1) brought out in this paper is its utility to find higher mode solutions of the K-eigenvalue problem. This procedure is radically different from the methods commonly used for finding higher K-modes. It may also be of interest for finding higher mode eigensolutions in other scientific fields.     

Compact notch loaded half disk patch antenna for dualband operation

In this article, microstrip patch antenna loaded with two symmetrical vertical notches and shorting pin is investigated for dualband operation using circuit theory concept based on modal expansion cavity model. It is found that the antenna resonates at 2.84 and 6.33 GHz for upper and lower resonance frequencies respectively. The bandwidth of the compact notch loaded antenna at lower resonance frequency is 9.94 % (theoretical) and 6.67 % (simulated) whereas at upper resonance frequency, it is 12.99 % (theoretical) and 11.59 % (simulated). The compact notch loaded antenna characteristics are compared with other proposed radiating structures. The theoretical results are compared with IE3D simulation as well as reported experimental results and they are in close agreement.     

Laboratory investigation of indirect tensile strength using roofing polyester waste fibers in hot mix asphalt

The vast quantity of waste materials (such as roofing polyester waste fibers) accumulating throughout the world is creating costly disposal problem. The use of these materials was proved to be economical, environmentally sound and effective in increasing the performance properties of the asphalt mixture in recent years. The primary objective of this research was to determine whether homogeneously dispersed roofing waste polyester fibers improve the indirect tensile strength (ITS) and moisture susceptibility properties of asphalt concrete mixtures containing various lengths and percentages of the fiber in various aggregate sources. The experimental design included the use of three aggregate sources, two lengths (0.635 cm (1/4 in.) and 1.270 cm (1/2 in.)) of this fiber, and two fiber contents (0.35% and 0.50% by weight of total mixture). The results of the experiments found that, in general, the addition of the polyester fiber was beneficial in improving the wet tensile strength and tensile strength ratio (TSR) of the modified mixture, increasing the toughness value in both dry and wet conditions, and increasing the void content, the asphalt content, the unit weight, and the Marshall stability.     

The effect of materials testing modes on finite element simulation of hard machining via the use of internal state variable plasticity model coupled with experimental study

To understand the true nature of hard turning mechanics, a numerical model that incorporates an internal state variable plasticity model via a material user subroutine has been developed with the material constants obtained from the compression and tension tests. A global material failure/damage evolution model was implemented to simulate chip formation that solely depends on the material deformation state. Orthogonal hard turning experiments were performed to validate the numerical model. The purpose of this work was to determine the material property differences under the different stress states by using numerical simulations. The numerical and experimental results illustrated that the material constants from the compression tests captured the true nature of a hard machining process as compression dominates the of material deformation process in hard machining.     

A stochastic control approach for scheduling multimedia transmissions over a polled multiaccess fading channel

We develop scheduling strategies for carrying multimedia traffic over a polled multiple access wireless network with fading. We consider a slotted system with three classes of traffic (voice, streaming media and file transfers). A Markov model is used for the fading and also for modeling voice packet arrivals and streaming arrivals. The performance objectives are a loss probability for voice, mean network delay for streaming media, and time average throughput for file transfers. A central scheduler (e.g., the access point in a single cell IEEE 802.11 wireless local area network (WLAN)) is assumed to be able to keep track of all the available state information and make the scheduling decision in each slot (e.g., as would be the case for PCF mode operation of the IEEE 802.11 WLAN). The problem is modeled as a constrained Markov decision problem. By using constraint relaxations (a linear relaxation and Whittle type relaxations) an index based policy is obtained. For the file transfers the decision problem turns out to be one with partial state information. Numerical comparisons are provided with the performance obtained from some simple policies. This work was supported by a research grant from Intel Technology India Pvt. Ltd. Munish Goyal obtained his Masters and PhD degree in telecommunications from the Indian Institute of Science, Bangalore, India and the B.E. degree in Electronics and Communication from the Indian Institute of Technology, Roorkee, India. Currently, he is a postdoctoral research fellow at the ARC Center of Excellence for Mathematics and Statistics of Complex Systems, University of Melbourne, Australia. His research interests include modelling, analysis and control problems arising in stochastic systems especially telecommunication systems. Anurag Kumar obtained his B.Tech. degree from the Indian Institute of Technology at Kanpur, and the PhD degree from Cornell University, both in Electrical Engineering. He was then with Bell Laboratories, Holmdel, N.J., for over 6 years. Since 1988 he has been with the Indian Institute of Science (IISc), Bangalore, in the Dept. of Electrical Communication Engineering, where he is now a Professor, and is also the Chairman of the department. From 1988 to 2003 he was the Coordinator at IISc of the Education and Research Network Project (ERNET), India’s first wide-area packet switching network. His area of research is communication networking, specifically, modeling, analysis, control and optimisation problems arising in communication networks and distributed systems. Recently his research has focused primarily on wireless networking. He has been elected Fellow of the IEEE, and the Indian National Science Academy (INSA), both from 2006, and has been a Fellow of the Indian National Academy of Engineering (INAE) since 1998. He is an associate editor of IEEE Transactions on Networking, and of IEEE Communications Surveys and Tutorials. He is a coauthor of the advanced text-book “Communication Networking: An Analytical Approach,” by Kumar, Majunath and Kuri, published by Morgan-Kaufman/Elsevier. Vinod Sharma received his B.Tech in Electrical Engineering from Indian Institute of Technology, New Delhi in 1978 and PhD in Electrical and Computer Engineering from Carnegie Mellon University in 1984. He worked in Northeastern University and University of California at Los Angeles before joining Indian Instutute of Science in 1988 where currently he is a Professor. He has held visiting positions at INRS Montreal, Helsinki University of Technology, Tokyo University of Science, Institute Mittag-Leffler and INRIA, Sophia Antipolis. His current interests are in Communication Networks, Wireless Communications and Queueing Theory.     

Comparative performance analysis of versions of TCP in a local network with a mobile radio link

The scenario is that a bulk data transfer is being performed over a TCP connection, from a host on a local area network (LAN) to a mobile host attached to the LAN by a radio link. In an earlier work we had assumed that packet losses in a TCP connection over a radio link are statistically independent. In this paper, we extend this analysis to a Rayleigh fading link, which we model by a two-state Markov model. The bulk throughputs of TCP-OldTahoe and TCP-Tahoe are compared with and without fading, for various average signal-to-noise ratios. We also study the performance with a link protocol on the wireless link, and study the effect of varying the link packet size, the number of link packet attempts, and the vehicle speed. For the parameters of the BSD UNIX implementation, over a 1.5 Mbps wireless link, we find that, with fading, a signal-to-noise ratio of at least 30 dB is required to get reasonable throughput with TCP Tahoe or OldTahoe; this corresponds to at least 100 times more power than is needed without fading. For fixed signal-to-noise ratio, as the vehicle speed varies there are roughly 3 regions of performance: at very low speeds (pedestrian speeds) the throughput is very good; at low vehicular speeds the throughput deteriorates, and again becomes very good at higher vehicle speeds. The speeds corresponding to the various regions depend on the parameters of the link protocol. This work was done while the first author was on Sabbatical at WINLAB, Rutgers University     

Aerosol Synthesis of Lipid Nanoparticles: Relating Crystallinity to Simulated Evaporation Rates

The degree of crystallinity of nanometer size lipid matrices governs drug loading and release rates. Recently, droplet-phase aerosol synthesis was used to prepare lipid nanoparticles of stearic acid and achieve control over their crystallinity using precursor solvents with differing vapor pressures. The present work aims at examining relationships between solvent evaporation rate and extent of evaporative cooling, during drop evaporation, on the crystallinity of the resulting lipid nanoparticles. A stationary drop model was developed to study evaporation of submicron-sized solution drops, of stearic acid in organic solvents, by including mechanisms of solvent vapor pressure depression by the solute, heat and mass transfer between the drop ensemble and suspending gas, Kelvin (curvature) effect, noncontinuum vapor transfer effects, and changes in activity coefficients of solute and solvent with changing concentrations. It was found that increasing estimated evaporation rates correlated with decreasing measured crystallinity. Higher evaporation rates also led to greater evaporative cooling and lower drop temperatures. The rate of change of supersaturation in solution drops under fast evaporation was shown to be an order of magnitude higher than that for slow evaporation. The modeled evaporation rate and drop temperature depend primarily on vapor pressure and enthalpy of vaporization of the precursor solvent. This suggests that selection of precursor solvents, with desired physical properties, can be used to control crystallinity, and related drug release behavior of lipid nanoparticles made through aerosol synthesis routes.

Copyright 2012 American Association for Aerosol Research     

Refolding of biotech therapeutic proteins expressed in bacteria: review

The efficiency of the protein refolding process lies in identification of the optimal conditions. However, a number of challenges need to be overcome to achieve this. This review first describes the protein refolding process that is utilized presently for production of protein therapeutics. Next, it discusses the various shortcomings that exist with respect to the present approach. The focus of the paper is on presentation of the significant advancements that have been made in the past decade in the various aspects of protein folding, including use of bioinformatics, mechanistic modeling, analytical monitoring, process optimization, use of additives, high throughput development, on‐column refolding, Quality by Design (QbD), Process Analytical Technology (PAT), and process intensification. Finally, an approach is proposed that incorporates the best practices that have been identified in the various areas. The paper is expected to be of interest to those in academia and industry working in the area of protein refolding. © 2013 Society of Chemical Industry.