Combinatorial Algorithms for the Unsplittable Flow Problem

We provide combinatorial algorithms for the unsplittable flow problem (UFP) that either match or improve the previously best results. In the UFP we are given a (possibly directed) capacitated graph with n vertices and m edges, and a set of terminal pairs each with its own demand and profit. The objective is to connect a subset of the terminal pairs each by a single flow path subject to the capacity constraints such that the total profit of the connected pairs is maximized.We consider three variants of the problem. First is the classical UFP in which the maximum demand is at most the minimum edge capacity. It was previously known to have an O(√m) approximation algorithm; the algorithm is based on the randomized rounding technique and its analysis makes use of the Chernoff bound and the FKG inequality.We provide a combinatorial algorithm that achieves the same approximation ratio and whose analysis is considerably simpler. Second is the extended UFP in which some demands might be higher than edge capacities. Our algorithm for this case improves the best known approximation ratio. We also give a lower bound that shows that the extended UFP is provably harder than the classical UFP. Finally, we consider the bounded UFP in which the maximum demand is at most 1/K times the minimum edge capacity for some K > 1. Here we provide combinatorial algorithms that match the currently best known algorithms. All of our algorithms are strongly polynomial and some can even be used in the online setting.     

Model-based low-level control in flexible manufacturing systems

Low-level (supervisory) control of flexible manufacturing systems (FMS) assures conflict-free operation and enforces production requirements such as priorities. It forms a crucial link between medium and higher-level decision making, on the one hand, and the various machine-controllers and servomechanisms on the other. In the absence of a suitable control methodology, ad hoc development is the current practice and compromised results at high cost are far too common. Here we described a model-based framework for a new, systematic approach to supervisory control.     

The Sales Tax Puzzle – Has the law of demand been repealed?

TRA86 removed the deductibility of state and local sales taxes from U.S. personal income taxes. This effectively increased the price to state governments of sales tax revenue relative to income tax revenues. This implies that state reliance on income taxes relative to sales taxes should have increased after TRA86 was implemented. Leading public finance economists investigated this in the period shortly following the reform and invariably found that the predicted substitution of income for sales taxes did not take place. In fact, several studies noted that state dependence on the sales tax increased relative to income taxes – hence the Sales Tax Puzzle. Several experts tried to rationalize their non-findings. These rationalizations are unconvincing. This paper asserts that the puzzle may be resolved in two different ways. The first, seemingly trivial, is that the analysis must incorporate sufficient time so as to allow for relatively complex adjustments. Our contributions here are to anchor this obvious point with a theoretical model related to earlier work of the authors, and an explicit empirical examination of the lag structures of individual states reactions to the comprehensive tax reform. The second demonstrates that the analysis must take into account regional shifts that were taking place in the U.S. during this period. When such compositional shifts involving political and deductibility patterns are explicitly introduced into the model, the paradoxical findings are resolved both in the long and in the short run. Our contribution here is a demonstration that the use of detailed state-level data, unlike any of the earlier work in this area, allows for the inclusion in the analysis of inter-regional shifts in various parameters. An additional contribution is the explicit use and emphasis of the propensity to itemize as an independent variable. The use of this variable ties this area of analysis of post tax reform behavior into a hitherto untapped strand of public-finance literature. The variable is both theoretically interesting, and proves to have experienced compositional shift patterns which help resolve the sales-tax puzzle paradox.     

A Hybrid AlGaInAs–Silicon Evanescent Amplifier

We report a hybrid AlGaInAs-silicon evanescent amplifier incorporating a silicon waveguide with a III-V gain medium. The optical mode of the hybrid amplifier is mostly confined to the silicon waveguide and evanescently coupled to the AlGaInAs quantum-well (QW) region where optical gain is provided by electrical current injection. These two different material systems are bonded by low-temperature oxygen plasma assisted wafer bonding at 300 degC. The fabricated device shows 13 dB of maximum chip gain with 11 dBm of output saturation power. Evanescent coupling allows a lower active region confinement factor to provide a higher saturation output power than amplifiers with centered QWs, which is important for applications that require linear amplification     

Electing a leader in a ring with link failures

Summary We investigate the message complexity of electing a leader in a ring of asynchronous processors. Our work deviates from the previous works on electing a leader in that we consider the effect of link failures. A link is said to fail if some message sent through it never reaches its destination. We distinguish the case where n is known from the case n unknown. Our main result is a O(n · log n) algorithm for electing a leader on a n-processor ring (the case n is known).     

A fair protocol for signing contracts

Two parties, A and B, want to sign a contract C over a communication network. To do so, they must simultaneously exchange their commitments to C. Since simultaneous exchange is usually impossible in practice, protocols are needed to approximate simultaneity by exchanging partial commitments in piece-by-piece manner. During such a protocol, one party or another may have a slight advantage; a fair protocol keeps this advantage within acceptable limits. A new protocol is proposed. It is fair in the sense that, at any stage in its execution, the conditional probability that one party cannot commit both parties to the contract given that the other party can, is close to zero. This is true even if A and B have vastly different computing powers and is proved under very weak cryptographic assumptions     

A uniform-complexity treatment of encryption and zero-knowledge

We provide a treatment of encryption and zero-knowledge in terms of uniform complexity measures. This treatment is appropriate for cryptographic settings modeled by probabilistic polynomial-time machines. Our uniform treatment allows the construction of secure encryption schemes and zero-knowledge proof systems (for allNP) using only uniform complexity assumptions. We show that uniform variants of the two definitions of security, presented in the pioneering work of Goldwasser and Micali, are in fact equivalent. Such a result was known before only for nonuniform formalization. Nonuniformity is implicit in all previous treatments of zero-knowledge in the sense that a zero-knowledge proof is required to “leak no knowledge” onall instances. For practical purposes, it suffices to require that it isinfeasible to find instances on which a zero-knowledge proof “leaks knowledge.” We show how to construct such zero-knowledge proof systems for every language inNP, using only a uniform complexity assumption. Properties of uniformly zero-knowledge proofs are investigated and their utility is demonstrated. This research was partially supported by the Fund for Basic Research Administered by the Israeli Academy of Sciences and Humanities. Revision of this work was supported by Grant No. 89-00312 from the United States-Israel Binational Science Foundation (BSF), Jerusalem, Israel.     

解读DOCSIS 2.0技术

新的应用是否需要新的技术?或者，新的技术是否会产生新的应用?在不同的情况下，这一由来已久的问题的答案也各不相同。但就有线宽带市场而言，对这两个问题的回答都是肯定的。     

A perfect zero-knowledge proof system for a problem equivalent to the discrete logarithm

An interactive proof system is calledperfect zero-knowledge if the probability distribution generated by any probabilistic polynomial-time verifier interacting with the prover on input theoremϕ, can be generated by another probabilistic polynomial-time machine which only getsϕ as input (and interacts with nobody!). In this paper we present aperfect zero-knowledge proof system for a decision problem which is computationally equivalent to the Discrete Logarithm Problem. Doing so we provide additional evidence to the belief thatperfect zero-knowledge proof systems exist in a nontrivial manner (i.e., for languages not inBPP). Our results extend to the logarithm problem in any finite Abelian group. This research was partially supported by the Fund for Basic Research Administered by the Israeli Academy of Sciences and Humanities. An early version of this paper appeared inAdvances in Cryptology —Crypto 88 (Proceedings), S. Goldwasser (ed.), pp. 57–70, Lecture Notes in Computer Science, vol. 403, Springer-Verlag, Berlin, 1990.