1566543
Minimizing Mean Flow Time with Error Constraint
Abstract. We consider the problem of minimizing mean flow time for the Imprecise Computation Model introduced by Lin et al. A task system TS=({Ti},{r(Ti)},{d(Ti)},{m(Ti)},{o(Ti)})  consists of a set of n  independent tasks, where r(Ti),d(Ti),m(Ti) , and o(Ti)  denote the ready time, deadline, execution time of the mandatory part, and execution time of the optional part of Ti , respectively. Given a task system TS  and an error threshold K , our goal is to find a preemptive schedule on one processor such that the average error is no more than K  and the mean flow time of the schedule is minimized. Such a schedule is called an optimal schedule. In this article we show that the problem of finding an optimal schedule is NP-hard, even if all tasks have identical ready times and deadlines. A pseudopolynomial-time algorithm is given for a set of tasks with identical ready times and deadlines, and oppositely ordered mandatory execution times and total execution times (i.e., there is a labeling of tasks such that m(Ti)≤ m(Ti+1)  and m(Ti)+o(Ti)≥ m(Ti+1)+o(Ti+1)  for each 1≤ i<n  ). Finally, polynomial-time algorithms are given for (1) a set of tasks with identical ready times, and similarly ordered mandatory execution times and total execution times and (2) a set of tasks with similarly ordered ready times, deadlines, mandatory execution times, and total execution times.
7180182
Minimizing mean flow time with error constraint
In a new model of task systems studied by J.W.S. Liu et al. (1987) each task is logically decomposed into two subtasks, mandatory and optional. The authors discuss preemptively scheduling this kind of task system on p>or=1 identical processors so as to minimize the mean flow time. Given a task system and an error threshold K, the goal is to find a preemptive schedule such that each task is executed in the interval of its release time and deadline, the average error is no more than K, and the mean flow time of the schedule is minimized. Such a schedule is called an optimal schedule. It is shown that the problem of finding an optimal schedule is NP-hard for each p>or=1, even if all tasks have the same ready time and deadline. For a single processor, a pseudo-polynomial time algorithm and polynomial time algorithms for various special cases of the problem are given.<<ETX>>
26809229
Packing Squares into a Square
Abstract The problem of determining whether a set of rectangles can be orthogonally packed into a larger rectangle has been studied as a geometric packing problem and as a floor planning problem. Recently, there is some renewed interest in this problem, as it is related to a job scheduling problem in a partitionable mesh connected system. In this paper we show that the problem of deciding whether a set of squares can be packed into a larger square is strongly NP-complete, answering an open question posed by Li and Cheng.
29097074
Analysis on the Session Life Time Distribution of Gnutella
15727543
Securing Mobile Agents for Electronic Commerce: An Experiment
Mobile software agents are becoming a major trend of distributed systems in the next decade. Electronic commerce and information retrieval are two prospective applications of mobile agents. Nevertheless, security is a crucial concern for such systems. Attacks to agents by malicious hosts are the most challenging part of the problem unsolved. In this paper, a Shopping Information Agent System (SIAS) is built based on mobile agent technology. Possible security attacks by malicious hosts to agents in the system are discussed, and solutions to prevent these attacks are presented. Security of the solutions is analysed, and the performance overhead introduced is evaluated.
8508688
New algorithms for the rectilinear Steiner tree problem
An approach to constructing the rectilinear Steiner tree (RST) of a given set of points in the plane, starting from a minimum spanning tree (MST), is discussed. The main idea in this approach is to find layouts for the edges of the MST that maximize the overlaps between the layouts, thus minimizing the cost (i.e. wire length) of the resulting rectilinear Steiner tree. Two algorithms for constructing rectilinear Steiner trees from MSTs, which are optimal under the conditions that the layout of each edge of the MST is an L shape or any staircase, respectively, are described. The first algorithm has linear time complexity and the second algorithm has a higher polynomial time complexity. Steiner trees produced by the second algorithm have a property called stability, which allows the rerouting of any segment of the tree, while maintaining the cost of the tree, and without causing overlaps with the rest of the tree. Stability is a desirable property in VLSI global routing applications. >
1861595
Charge optimization of the interface between protein kinases and their ligands
Examining the potential for electrostatic complementarity between a ligand and a receptor is a useful technique for rational drug design, and can demonstrate how a system prioritizes interactions when allowed to optimize its charge distribution. In this computational study, we implemented the previously developed, continuum solvent-based charge optimization theory with a simple, quadratic programming algorithm and the UHBD Poisson-Boltzmann solver. This method allows one to compute the best set of point charges for a ligand or ligand region based on the ligand and receptor shape, and the receptor partial charges, by optimizing the binding free energy obtained from a continuum-solvent model. We applied charge optimization to a fragment of the heat-stable protein kinase inhibitor (PKI) of protein kinase A (PKA), to three flavopiridol inhibitors of CDK2, and to cyclin A which interacts with CDK2 to regulate the cell cycle. We found that a combination of global (involving every charge) and local (involving only charges in a local region) optimization can give useful hints for designing better inhibitors. Although some parts of an inhibitor may already contribute significantly to binding, we found that they could still be the most important targets for modifications to obtain stronger binders. In studying the binding of flavopiridol inhibitors to CDK2, comparable binding affinity could be obtained regardless of whether the net charges of the inhibitors were constrained to -2, -1, 0, 1, or 2 during the optimization. This provides flexibility in inhibitor design when a certain net charge of the inhibitor is desired in addition to strong binding affinity. For the study of the PKA-PKI and CDK2-cyclin A interfaces, we identified residues whose charge distributions are already close to optimal and those whose charge distributions could be refined to further improve binding.
15615911
Time-varying shortest path problems with constraints
The shortest path problem is considered with yet another extension. The transit times b(x,y,u) and the arc costs c(x,y,u) on arc (x,y) vary as a function of the departure time u at the beginning vertex of the arc. The problem considered is to find the shortest path between a pair of nodes such that the total traverse time is lesser than some specified value T. Waiting times at nodes are considered as decision variables in this paper as well. Three variations of the problem are analyzed in which the waiting times are allowed to be arbitrary, the waiting times are zero and the waiting time has an upper bound at each vertex. Algorithms are also discussed to solve the problem. Some of the applications of the problem are encountered in communication networks and freight delivery problems. Suppose that some freight is to be sent from one city to another in a network before a deadline T. Different types of freight services with different costs and transit times are available between the two cities. An optimal solution would have to specify the route as well as the waiting times of the freight at each city so that the overall cost is minimum. A dynamic programming approach is used to compute the shortest path from the origin node to the destination node. Three cases are considered for the waiting times and an algorithm is suggested for each of those cases. This problem is obviously an NP-Complete problem as it is more difficult to solve than a problem with constant transit times and arc costs such as the previous problem which is NP-Complete. Some definitions: Waiting time w(x i) at a vertex x i is a nonnegative integer with an upper bound U x >= 0. Let P be a path from vertex x 1 to x r. The departure time T(x i) at a vertex x i can be expressed as below: T(x 1) = w(x 1) The departure time for all other vertices on the path can be expressed recursively as : The time of path P is defined as T(x r) where x r is the final node on the path..
35666520
Automatic Lyrics Alignment on Popular Music