Joint Cache Partition and Job Assignment on Multi-Core Processors

Multicore shared cache processors pose a challenge for designers of embedded systems who try to achieve minimal and predictable execution time of workloads consisting of several jobs. To address this challenge the cache is statically partitioned among the cores and the jobs are assigned to the cores so as to minimize the makespan. Several heuristic algorithms have been proposed that jointly decide how to partition the cache among the cores and assign the jobs. We initiate a theoretical study of this problem which we call the joint cache partition and job assignment problem. By a careful analysis of the possible cache partitions we obtain a constant approximation algorithm for this problem. For some practical special cases we obtain a 2-approximation algorithm, and show how to improve the approximation factor even further by allowing the algorithm to use additional cache. We also study possible improvements that can be obtained by allowing dynamic cache partitions and dynamic job assignments. We define a natural special case of the well known scheduling problem on unrelated machines in which machines are ordered by "strength". Our joint cache partition and job assignment problem generalizes this scheduling problem which we think is of independent interest. We give a polynomial time algorithm for this scheduling problem for instances obtained by fixing the cache partition in a practical case of the joint cache partition and job assignment problem where job loads are step functions

Effect of Nyquist Noise on the Nyquist Dephasing Rate in 2d Electron Systems

We measure the effect of externally applied broadband Nyquist noise on the intrinsic Nyquist dephasing rate of electrons in a two-dimensional electron gas at low temperatures. Within the measurement error, the phase coherence time is unaffected by the externally applied Nyquist noise, including applied noise temperatures of up to 300 K. The amplitude of the applied Nyquist noise from 100 MHz to 10 GHz is quantitatively determined in the same experiment using a microwave network analyzer.Comment: 5 pages, 4 figures. Author affiliation clarified; acknowledgements modified. Replacement reason clarifie

Electron transport through interacting quantum dots

We present a detailed theoretical investigation of the effect of Coulomb interactions on electron transport through quantum dots and double barrier structures connected to a voltage source via an arbitrary linear impedance. Combining real time path integral techniques with the scattering matrix approach we derive the effective action and evaluate the current-voltage characteristics of quantum dots at sufficiently large conductances. Our analysis reveals a reach variety of different regimes which we specify in details for the case of chaotic quantum dots. At sufficiently low energies the interaction correction to the current depends logarithmically on temperature and voltage. We identify two different logarithmic regimes with the crossover between them occurring at energies of order of the inverse dwell time of electrons in the dot. We also analyze the frequency-dependent shot noise in chaotic quantum dots and elucidate its direct relation to interaction effects in mesoscopic electron transport.Comment: 21 pages, 4 figures. References added, discussion slightly extende

Dynamic Analysis of a Rotating Shaft Subject to the Double Cutting Force and Time-varying Mass Effects of the Rod

AbstractThis paper investigates the dynamic behaviors of a rotating shaft subjected to the double cutting force and time-varying mass effects. The Timoshenko beam theory is used to model the rotating shaft, and the general boundary condition is assumed as the clamped-hinged supports. This system is used to simulate the manufacture process of the double turret CNC lathes, and the mass of the rod which is reduced gradually in cutting process. The system equations of motion are derived based on the global assumed mode method, and the dynamic responses of the system are obtained by Runge-Kutta numerical method. The transformation matrix is derived to make the equation of motion completing the boundary geometric constraints. The numerical results compare the dynamic response in different moving speeds and skew angles of the cutting forces with/without the time-varying mass effects. Additionally, this paper compares the response with single cutting force and double force. The results show that the double moving force system can reduce not only the machining time but also the amplitude of shaft vibration

A general T-matrix approach applied to two-body and three-body problems in cold atomic gases

We propose a systematic T-matrix approach to solve few-body problems with s-wave contact interactions in ultracold atomic gases. The problem is generally reduced to a matrix equation expanded by a set of orthogonal molecular states, describing external center-of-mass motions of pairs of interacting particles; while each matrix element is guaranteed to be finite by a proper renormalization for internal relative motions. This approach is able to incorporate various scattering problems and the calculations of related physical quantities in a single framework, and also provides a physically transparent way to understand the mechanism of resonance scattering. For applications, we study two-body effective scattering in 2D-3D mixed dimensions, where the resonance position and width are determined with high precision from only a few number of matrix elements. We also study three fermions in a (rotating) harmonic trap, where exotic scattering properties in terms of mass ratios and angular momenta are uniquely identified in the framework of T-matrix.Comment: 14 pages, 4 figure

Simplified amino acid alphabets based on deviation of conditional probability from random background

The primitive data for deducing the Miyazawa-Jernigan contact energy or BLOSUM score matrix consists of pair frequency counts. Each amino acid corresponds to a conditional probability distribution. Based on the deviation of such conditional probability from random background, a scheme for reduction of amino acid alphabet is proposed. It is observed that evident discrepancy exists between reduced alphabets obtained from raw data of the Miyazawa-Jernigan's and BLOSUM's residue pair counts. Taking homologous sequence database SCOP40 as a test set, we detect homology with the obtained coarse-grained substitution matrices. It is verified that the reduced alphabets obtained well preserve information contained in the original 20-letter alphabet.Comment: 9 pages,3figure

Superradiant and Aharonov-Bohm effect for the quantum ring exciton

The Aharonov-Bohm and superradiant effect on the redaitive decay rate of an exciton in a quantum ring is studied. With the increasing of ring radius, the exciton decay rate is enhanced by superradiance, while the amplitude of AB oscillation is decreased. The competition between these two effects is shown explicitly and may be observable in time-resolved exeriments.Comment: 4 pages, 2 figures, to appear in Solid State Communications (2004