23,768 research outputs found
Speed Scaling for Energy Aware Processor Scheduling: Algorithms and Analysis
We present theoretical algorithmic research of processor scheduling in an energy aware environment using the mechanism of speed scaling. We have two main goals in mind. The first is the development of algorithms that allow more energy efficient utilization of resources. The second goal is to further our ability to reason abstractly about energy in computing devices by developing and understanding algorithmic models of energy management. In order to achieve these goals, we investigate three classic process scheduling problems in the setting of a speed scalable processor.
Integer stretch is one of the most obvious classical scheduling objectives that has yet to be considered in the speed scaling setting. For the objective of integer stretch plus energy, we give an online scheduling algorithm that, for any input, produces a schedule with integer stretch plus energy that is competitive with the integer stretch plus energy of any schedule that finishes all jobs.
Second, we consider the problem of finding the schedule, S, that minimizes some quality of service objective Q plus B times the energy used by the processor. This schedule, S, is the optimal energy trade-off schedule in the sense that: no schedule can have better quality of service given the current investment of energy used by S, and, an additional investment of one unit of energy is insufficient to improve the quality of service by more than B. When Q is fractional weighted flow, we show that the optimal energy trade-off schedule is unique and has a simple structure, thus making it easy to check the optimality of a schedule. We further show that the optimal energy trade-off schedule can be computed with a natural homotopic optimization algorithm.
Lastly, we consider the speed scaling problem where the quality of service objective is deadline feasibility and the power objective is temperature. In the case of batched jobs, we give a simple algorithm to compute the optimal schedule. For general instances, we give a new online algorithm and show that it has a competitive ratio that is an order of magnitude better than the best previously known for this problem
Thermal conductivity in harmonic lattices with random collisions
We review recent rigorous mathematical results about the macroscopic
behaviour of harmonic chains with the dynamics perturbed by a random exchange
of velocities between nearest neighbor particles. The random exchange models
the effects of nonlinearities of anharmonic chains and the resulting dynamics
have similar macroscopic behaviour. In particular there is a superdiffusion of
energy for unpinned acoustic chains. The corresponding evolution of the
temperature profile is governed by a fractional heat equation. In non-acoustic
chains we have normal diffusivity, even if momentum is conserved.Comment: Review paper, to appear in the Springer Lecture Notes in Physics
volume "Thermal transport in low dimensions: from statistical physics to
nanoscale heat transfer" (S. Lepri ed.
Dynamical scaling of the DNA unzipping transition
We report studies of the equilibrium and the dynamics of a general set of
lattice models which capture the essence of the force-induced or mechanical DNA
unzipping transition. Besides yielding the whole equilibrium phase diagram in
the force vs temperature plane, which reveals the presence of an interesting
re-entrant unzipping transition for low T, these models enable us to
characterize the dynamics of the process starting from a non-equilibrium
initial condition. The thermal melting of the DNA strands displays a model
dependent time evolution. On the contrary, our results suggest that the
dynamical mechanism for the unzipping by force is very robust and the scaling
behaviour does not depend on the details of the description we adopt.Comment: 6 pages, 4 figures, A shorter version of this paper appeared in Phys.
Rev. Lett. 88, 028102 (2002
Towards the Distributed Burning Regime in Turbulent Premixed Flames
Three-dimensional numerical simulations of canonical statistically-steady
statistically-planar turbulent flames have been used in an attempt to produce
distributed burning in lean methane and hydrogen flames. Dilatation across the
flame means that extremely large Karlovitz numbers are required; even at the
extreme levels of turbulence studied (up to a Karlovitz number of 8767)
distributed burning was only achieved in the hydrogen case. In this case,
turbulence was found to broaden the reaction zone visually by around an order
of magnitude, and thermodiffusive effects (typically present for lean hydrogen
flames) were not observed. In the preheat zone, the species compositions differ
considerably from those of one-dimensional flames based a number of different
transport models (mixture-averaged, unity Lewis number, and a turbulent eddy
viscosity model). The behaviour is a characteristic of turbulence dominating
non-unity Lewis number species transport, and the distinct limit is again
attributed to dilatation and its effect on the turbulence. Peak local reaction
rates are found to be lower in the distributed case than in the lower Karlovitz
cases but higher than in the laminar flame, which is attributed to effects that
arise from the modified fuel-temperature distribution that results from
turbulent mixing dominating low Lewis number thermodiffusive effects. Finally,
approaches to achieve distributed burning at realisable conditions are
discussed; factors that increase the likelihood of realising distributed
burning are higher pressure, lower equivalence ratio, higher Lewis number, and
lower reactant temperature
Phase Control of Trapped Ion Quantum Gates
There are several known schemes for entangling trapped ion quantum bits for
large-scale quantum computation. Most are based on an interaction between the
ions and external optical fields, coupling internal qubit states of
trapped-ions to their Coulomb-coupled motion. In this paper, we examine the
sensitivity of these motional gate schemes to phase fluctuations introduced
through noisy external control fields, and suggest techniques to suppress the
resulting phase decoherence.Comment: 21 pages 12 figure
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