Average Case Analysis of Disk Scheduling,Increasing Subsequences and Spacetime Geometry

We consider the problem of estimating the average tour length of the asymmetric TSP arising from the disk scheduling problem with a linear seek function and a probability distribution on the location of I/O requests. We provide a law of large numbers expression, for the expected tour size and compute it explicitely in the most interesting cases. We also provide finer asymptotic estimates in the case of a uniform request distribution. Our methods relate disk scheduling to the problem of finding the longest increasing subsequence in a permutation. Our tour length estimates also answer questions on the asymptotics of the connect-the dots problem with Lipschitz functions which was raised in Adv. Appl. Probab. 37, 571–603 (2005). In the last section we show that all the above problems can be interpreted naturally, in terms of Lorentzian geometry. We generalize the main results to this setting. Research partially supported by an IBM faculty award.     

Spatial Aliasing in Spherical Microphone Arrays

Performance of microphone arrays at the high-frequency range is typically limited by aliasing, which is a result of the spatial sampling process. This paper presents analysis of aliasing for spherical microphone arrays, which have been recently studied for a range of applications. The paper presents theoretical analysis of spatial aliasing for various sphere sampling configurations, showing how high-order spherical harmonic coefficients are aliased into the lower orders. Spatial antialiasing filters on the sphere are then introduced, and the performance of spatially constrained filters is compared to that of the ideal antialiasing filter. A simulation example shows how the effect of aliasing on the beam pattern can be reduced by the use of the antialiasing filters     

Jamming in Wireless Networks Under Uncertainty

Jamming is a form of a denial of service attack in which an adversary can degrade the quality of the reception by creating interference. One can study jamming both in the purpose of protecting a wireless network against such attack or, on the contrary, in order to efficiently disrupt the communications of some adversary. In both cases jamming is part of a conflict for which game theory is an appropriate tool. Here we investigate the effect of partially available information in which the user does not even know whether or not the jammer is indeed present. Moreover, the user does not know how jamming efforts are distributed among sub-carriers, nor does it know the fading channels gains. As an object function for the user we consider the SINR. We show that the problem can be formulated as a zero-sum game. We study independent fading channel gains scenario as well as the case of dependent fading channel gains, both in a discrete and a continuous versions. We show that in all the scenarii the jammer equalizes the quality of the best sub-carriers for the user on as low level as its power constraint allows. Meanwhile the user distributes his power among these jamming sub-carriers. We find the equilibrium strategies in closed form and specify the range of sub-carriers where the user can expect the jamming attack.     

Time sequential testing with fixed study time

We investigate sampling plans in time sequential testing af snrvival distributions, when the study time is fixed. We obtain the asymptotic value of optimal sampling plans as the error probabilities of the test approach zero.     

Implementing ISO 9000: performance improvement by first or second movers

When an organization implements a new managerial practice how should timing affect its decision? Should it be among the organizations that implement the new management practices early, i.e. first movers, or wait for others to implement and implement it a later time, i.e. second movers. The literature's findings with regard to many management practices, especially those that deal with quality, such as total quality management, suggest that while first movers implement a new management practice because of real needs and a high fit between what the practice suggests and their needs (technical efficiency), second movers implement the new management practice because of customer pressure and the fear of falling behind the competition (external pressure). Second movers just mimic first movers, and the new practice does not really fit with their operations. Thus, the new management practice achieves more for the first movers than the second movers. In this paper we ask whether this premise holds for the ISO 9000 quality standard, one which was specified in considerable detail by outside forces but was implemented in many different ways by organizations. Our results are based on a survey of 1150 quality managers who implemented ISO 9000. We find that learning is a more important factor than timing in explaining ISO 9000 performance. First movers achieve a high level of performance because they learn from their own experience, and second movers achieve a high level of performance because they learn from the experience of others. Whether an organization is a first mover or second, the ones that benefit from ISO 9000 are those who learn.     

Electrons retention model for localized charge inoxide-nitride-oxide (ONO) dielectric

An electrons retention model for localized charge, trapped in ONO stacked dielectric, is introduced utilizing the nitride read-only memory (NROM) device. The observed reduction in threshold voltage (retention loss) of a programmed cell is explained in terms of lateral charge redistribution in the nitride layer. Assuming a thermal emission mechanism, the energy levels of the electrons traps were extracted and found to be distributed continuously in the nitride band gap, with a median value of ~2.12 eV below the conduction band. Utilizing these findings, the model allows a prediction of the retention loss over wide range of temperatures, between 140°C-300°C, long times, up to 10 ⁷ s, large retention loss levels, ~90%, and programming windows, 1.9-3.3 V. Based on this work the ten-year relative retention loss at 140°C of an NROM cell is expected to be 14% (V_DS=0.1 V) and the equivalent uncycled product loss is expected to be 8%     

Control of a hybrid stochastic system

We consider in this paper a continuous-time stochastic hybrid control system with a finite time horizon. The objective is to minimize a linear function of the expected state trajectory. The state evolves according to a linear dynamics. However, the parameters of the state evolution equation may change at discrete times according to a controlled Markov chain which has finite state and action spaces. We use a procedure similar in form to the maximum principle; this determines a control strategy which is asymptotically optimal as the number of transitions during the finite time horizon grows to infinity.     

Using true concurrency to model execution of parallel programs

Parallel execution of a programR (intuitively regarded as a partial order) is usually modeled by sequentially executing one of the total orders (interleavings) into which it can be embedded. Our work deviates from this serialization principle by usingtrue concurrency to model parallel execution. True concurrency is represented via completions ofR tosemi total orders, called time diagrams. These orders are characterized via a set of conditions (denoted byCt), yielding orders or time diagrams which preserve some degree of the intended parallelism inR. Another way to express semi total orders is to use re-writing or derivation rules (denoted byCx) which for any programR generates a set of semi-total orders. This paper includes a classification of parallel execution into three classes according to three different types ofCt conditions. For each class a suitableCx is found and a proof of equivalence between the set of all time diagrams satisfyingCt and the set of all terminalCx derivations ofR is devised. This equivalence between time diagram conditions and derivation rules is used to define a novel notion of correctness for parallel programs. This notion is demonstrated by showing that a specific asynchronous program enforces synchronous execution, which always halts, showing that true concurrency can be useful in the context of parallel program verification.     

Stress concentration factors in two-dimensional composites: effects of material and geometrical parameters

In the study of fracture processes in composite materials, the interactions between broken and intact fibers are of critical importance. Indeed, the redistribution of stress from a failed fiber to its unfailed adjacent neighbors, and the stress concentration induced in these, determine the extent to which a break in one fiber will cause more breaks in neighboring fibers. The overall failure pattern is a direct function of the stress concentration factors (SCFs). In this paper, we propose a new model for the SCFs in two-dimensional unidirectional composites containing broken fibers. A closed-form expression is derived for the SCF profiles as a function of material and geometrical parameters. The model differs significantly from earlier schemes, as the local effect of a fiber break on nearest neighbors is much milder than previously calculated, both as a function of the inter-fiber distance and of the number of adjacent broken fibers. Comparison with experimental results for silicon-carbide/epoxy composites demonstrates the validity of the proposed scheme. Since the overall fracture pattern in fiber composites is a direct function of the SCFs, the model may help shed light on fracture nucleation and growth in composites.