1,213 research outputs found
Perturbative analysis of anharmonic chains of oscillators out of equilibrium
We compute the first-order correction to the correlation functions of the
stationary state of a stochastically forced harmonic chain out of equilibrium
when a small on-site anharmonic potential is added. This is achieved by
deriving a suitable formula for the covariance matrix of the invariant state.
We find that the first-order correction of the heat current does not depend on
the size of the system. Second, the temperature profile is linear when the
harmonic part of the on-site potential is zero. The sign of the gradient of the
profile, however, is opposite to the sign of the temperature difference of the
two heat baths.Comment: 26 pages, 2 figures, corrected typo
Real-time Text Queries with Tunable Term Pair Indexes
Term proximity scoring is an established means in information retrieval for improving result quality of full-text queries. Integrating such proximity scores into efficient query processing, however, has not been equally well studied. Existing methods make use of precomputed lists of documents where tuples of terms, usually pairs, occur together, usually incurring a huge index size compared to term-only indexes. This paper introduces a joint framework for trading off index size and result quality, and provides optimization techniques for tuning precomputed indexes towards either maximal result quality or maximal query processing performance, given an upper bound for the index size. The framework allows to selectively materialize lists for pairs based on a query log to further reduce index size. Extensive experiments with two large text collections demonstrate runtime improvements of several orders of magnitude over existing text-based processing techniques with reasonable index sizes
Normal Heat Conductivity in a strongly pinned chain of anharmonic oscillators
We consider a chain of coupled and strongly pinned anharmonic oscillators
subject to a non-equilibrium random forcing. Assuming that the stationary state
is approximately Gaussian, we first derive a stationary Boltzmann equation. By
localizing the involved resonances, we next invert the linearized collision
operator and compute the heat conductivity. In particular, we show that the
Gaussian approximation yields a finite conductivity
, for the anharmonic coupling
strength.Comment: Introduction and conclusion modifie
Surface code architecture for donors and dots in silicon with imprecise and nonuniform qubit couplings
A scaled quantum computer with donor spins in silicon would benefit from a
viable semiconductor framework and a strong inherent decoupling of the qubits
from the noisy environment. Coupling neighbouring spins via the natural
exchange interaction according to current designs requires gate control
structures with extremely small length scales. We present a silicon
architecture where bismuth donors with long coherence times are coupled to
electrons that can shuttle between adjacent quantum dots, thus relaxing the
pitch requirements and allowing space between donors for classical control
devices. An adiabatic SWAP operation within each donor/dot pair solves the
scalability issues intrinsic to exchange-based two-qubit gates, as it does not
rely on sub-nanometer precision in donor placement and is robust against noise
in the control fields. We use this SWAP together with well established global
microwave Rabi pulses and parallel electron shuttling to construct a surface
code that needs minimal, feasible local control.Comment: Published version - more detailed discussions, robustness to
dephasing pointed out additionall
Development of a Compact Neutron Source based on Field Ionization Processes
The authors report on the use of carbon nanofiber nanoemitters to ionize
deuterium atoms for the generation of neutrons in a deuterium-deuterium
reaction in a preloaded target. Acceleration voltages in the range of 50-80 kV
are used. Field emission of electrons is investigated to characterize the
emitters. The experimental setup and sample preparation are described and first
data of neutron production are presented. Ongoing experiments to increase
neutron production yields by optimizing the field emitter geometry and surface
conditions are discussed.Comment: 4 pages, 5 figures; IVNC 201
Comparison between estimation of breeding values and fixed effects using Bayesian and empirical BLUP estimation under selection on parents and missing pedigree information
Bayesian (via Gibbs sampling) and empirical BLUP (EBLUP) estimation of fixed effects and breeding values were compared by simulation. Combinations of two simulation models (with or without effect of contemporary group (CG)), three selection schemes (random, phenotypic and BLUP selection), two levels of heritability (0.20 and 0.50) and two levels of pedigree information (0% and 15% randomly missing) were considered. Populations consisted of 450 animals spread over six discrete generations. An infinitesimal additive genetic animal model was assumed while simulating data. EBLUP and Bayesian estimates of CG effects and breeding values were, in all situations, essentially the same with respect to Spearman's rank correlation between true and estimated values. Bias and mean square error (MSE) of EBLUP and Bayesian estimates of CG effects and breeding values showed the same pattern over the range of simulated scenarios. Methods were not biased by phenotypic and BLUP selection when pedigree information was complete, albeit MSE of estimated breeding values increased for situations where CG effects were present. Estimation of breeding values by Bayesian and EBLUP was similarly affected by joint effect of phenotypic or BLUP selection and randomly missing pedigree information. For both methods, bias and MSE of estimated breeding values and CG effects substantially increased across generations
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