On "A Simple Protocol Whose Proof Isńt": The State Machine Approach

We discuss how to model a synchronous protocol (due to Aho, Ullman, and Yannakakis) using communicating finite state machines, and present a proof for its safety and liveness properties. Our proof is based on constructing a labeled finite reachability graph for the protocol. This reachability graph can be viewed as a sequential program whose safety and liveness properties can be stated and verified in a straightforward fashion.     

Effect of Rapid Solidification on Structure and Properties of Some Lead-Free Solder Alloys

Four of the binary lead-free solder alloys of compositions Sn-0.5Cu, Sn-3.5Ag, Sn-5Sb and Sn-9Zn, were rapidly solidified by melt-spinning technique as a technique for producing new alloy compositions. The results show that rapid solidification causes formation of some intermetallic compounds such as Ag₃Sn and Cu₆Sn₅ in the two alloys Sn-3.5Ag and Sn-0.5Cu, which cannot be formed at the equilibrium phase diagram at these compositions; contraction in the volume of the unit cell of the tetragonal Sn; reduction of the melting points due to the decrease in the crystalline size of Sn matrix; and formation of some vacancies in the resulting alloys, which cause reduction of the measured density than that calculated by mixture rule and increase the electrical resistivity.     

Electromagnetic scattered field time series from finite difference time domain trained time delay neural network

This paper uses time delay neural network (TDNN) for predicting electromagnetic (EM) fields scattered from dielectric objects (cylinder, cylinder‐hemisphere, and cylinder‐cone) using: (a) FDTD generated initial field data for similar conducting objects and (b) Statistical information for the nature of fields. Statistical data indicated that the scattered field nature is close to deterministic. The TDNN structure determination uses statistical data for fixing the number of delays and tabular technique to obtain the number of hidden neurons. The TDNN training uses the Levenberg‐Marquardt (LM) algorithm. The model outputs follow standard FDTD results closely.     

Isoform-dependent differences in feedback regulation and subcellular localization of serine acetyltransferase involved in cysteine biosynthesis from Arabidopsis thaliana

Serine acetyltransferase (SATase; EC 2.3.1.30), which catalyzes the formation of O-acetyl-L-serine (OAS) from acetyl-CoA and L-serine, plays a regulatory role in the biosynthesis of cysteine by its property of feedback inhibition by cysteine in bacteria and certain plants. Three cDNA clones encoding SATase isoforms (SAT-c, SAT-p, and SAT-m) have been isolated from Arabidopsis thaliana. However, the significance of the feedback regulation has not yet been clear in these different isoforms of SATase from A. thaliana. We constructed the overexpression vectors for cDNAs encoding three SATase isoforms of A. thaliana and analyzed the inhibition of SATase activity by cysteine using the recombinant SATase proteins. In the case of SAT-c, the activity was feedback-inhibited by a low concentration of cysteine (the concentration that inhibits 50% activity; IC50 = 1.8 microM). By contrast, SAT-p and SAT-m were feedback inhibition-insensitive isozymes. We also determined the subcellular localization of three SATase isozymes by the transient expression of fusion proteins of each SATase N-terminal region with jellyfish green fluorescent protein (GFP) in 4-week-old Arabidopsis leaves. The SAT-c-GFP fusion protein was stayed in cytosol, whereas SAT-p-GFP and SAT-m-GFP fusion proteins were localized in chloroplasts and in mitochondria, respectively. These results suggest that these three SATase isoforms, which are localized in the different organelles, are subjected to different feedback regulation, presumably so as to play the particular roles for the production of OAS and cysteine in Arabidopsis cells. Regulatory circuit of cysteine biosynthesis in the plant cells is discussed.     

Unboundedness detection for a class of communicating finite-state machines

Let M and N be two communicating finite-state machines that exchange one type of message. We discuss an algorithm to decide whether the communication between M and N is bounded. The algorithm is based on constructing a finite representation of the reachability tree of M and N assuming that M and N progress at equal speeds.     

The best keying protocol for sensor networks

Many sensor networks (especially networks of mobile sensors or networks that are deployed to monitor crisis situations) are deployed in an arbitrary and unplanned fashion. Thus, any sensor in such a network can end up being adjacent to any other sensor in the network. To secure the communications between every pair of adjacent sensors in such a network, each sensor $x$ in the network needs to store $n?1$ symmetric keys that sensor $x$ shares with all the other sensors, where $n$ is an upper bound on the number of sensors in the network. This storage requirement of the keying protocol is rather severe, especially when $n$ is large and the available storage in each sensor is modest. Earlier efforts to redesign this keying protocol and reduce the number of keys to be stored in each sensor have produced protocols that are vulnerable to impersonation, eavesdropping, and collusion attacks. In this paper, we present a fully secure keying protocol where each sensor needs to store $(n+1)/2$ keys, which is much less than the $n?1$ keys that need to be stored in each sensor in the original keying protocol. We also show that in any fully secure keying protocol, each sensor needs to store at least $(n?1)/2$ keys.     

Stabilization and pseudo-stabilization

Summary Astabilizing system is one which if started at any state is guaranteed to reach a state after which the system cannot deviate from its intended specification. In this paper, we propose a new variation of this notion, called pseudo-stabilization. Apseudo-stabilizing system is one which if started at any state is guaranteed to reach a state after which the system does not deriate from its intended specification. Thus, the difference between the two notions comes down to the difference between cannot and does not — a difference that hardly matters in many practical situations. As it happens, a number of well-known systems, for example the alternating-bit protocol, are pseudo-stabilizing but not stabilizing. We conclude that one should not try to make any such system stabilizing, especially if stabilization comes at a high price. 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 is currently an Associate Professor in the College of Computing at the Georgia Institute of Technology, having served previously on the faculty at Indiana University. He has broad research in theoretical issues of distributed and parallel computing, especially relating to problems of synchronization and fault tolerance. Mohamed Gawdat Gouda was born and raised in Egypt. His first bachelor degree was in engineering, and his second was in mathematics. Both degrees are from Cairo University. After his graduation, he moved to Canada where he obtained an MA in mathematics from York University, and a Master and a Ph.D. in computing science from the University of Waterloo. Later, he moved to the United states of America where he worked for the Honeywell Corporate Technology Center for three years. In 1980, he moved to the University of Texas at Austin, and has settled there ever since, except for one summer at Bell Labs, one summer at MCC, and one winter at the Eindhoven Technical University. Gouda currently holds the Mike A. Myer Centennial Professorship in Computing Science at the University of Texas at Austin. Gouda's area of research is distributed and concurrent computing. In this area, he has been working on: abstraction, nondeterminism, atomicity, convergence, stability, formality, correctness, efficiency, scientific elegance, and technical beauty (not necesarily in that order). Gouda was the founding Editor-in-Chief of the journal Distributed Computing, published by Springer-Verlag in 1985. He was the program committee chairman of the 1989 SIGCOMM Conference sponsored by ACM. He was the first program committee chairman for the International Conference on Network Protocols, established by the IEEE Computer Society in 1993. Gouda is an original member of the Austin Tuesday Afternoon Club. In his spare time, he likes to design network protocols and prove them correct for fun. Raymond E. Miller received his Ph.D. in 1957 from the University of Illinois, Champaign-Urbana. He was a Research Staff Member at IBM, Thomas J. Watson Research Center, Yorktown Heights, N.Y., from 1957 until 1980, Director of the School of Information and Computer Science at Georgia Tech from 1980 until 1987, and is currently a professor of computer science at the University of Maryland, College Park and Director of the NASA Center of Excellence in Space Data and Information Sciences at Goddard Space Flight Center. He has written over 90 technical papers in areas of theory of computation, machine organization, parellel computation and communication protocols. He is a Fellow of the IEEE and a Fellow of the American Association for the Advancement of Science. He has been active in the ACM and IEE/CS, and is a Board member of the Computing Research Association. In the IEEE/CS, he is a member of the Board of Governors and the 1991 Vice President for Educational Activities.