346,887 research outputs found
Controlling synchrony by delay coupling in networks: from in-phase to splay and cluster states
We study synchronization in delay-coupled oscillator networks, using a master
stability function approach. Within a generic model of Stuart-Landau
oscillators (normal form of super- or subcritical Hopf bifurcation) we derive
analytical stability conditions and demonstrate that by tuning the coupling
phase one can easily control the stability of synchronous periodic states. We
propose the coupling phase as a crucial control parameter to switch between
in-phase synchronization or desynchronization for general network topologies,
or between in-phase, cluster, or splay states in unidirectional rings. Our
results are robust even for slightly nonidentical elements of the network.Comment: 4 pages, 4 figure
Non Mean-Field Quantum Critical Points from Holography
We construct a class of quantum critical points with non-mean-field critical
exponents via holography. Our approach is phenomenological. Beginning with the
D3/D5 system at nonzero density and magnetic field which has a chiral phase
transition, we simulate the addition of a third control parameter. We then
identify a line of quantum critical points in the phase diagram of this theory,
provided that the simulated control parameter has dimension less than two. This
line smoothly interpolates between a second-order transition with mean-field
exponents at zero magnetic field to a holographic
Berezinskii-Kosterlitz-Thouless transition at larger magnetic fields. The
critical exponents of these transitions only depend upon the parameters of an
emergent infrared theory. Moreover, the non-mean-field scaling is destroyed at
any nonzero temperature. We discuss how generic these transitions are.Comment: 15 pages, 7 figures, v2: Added reference
Systems identification technology development for large space systems
A methodology for synthesizinng systems identification, both parameter and state, estimation and related control schemes for flexible aerospace structures is developed with emphasis on the Maypole hoop column antenna as a real world application. Modeling studies of the Maypole cable hoop membrane type antenna are conducted using a transfer matrix numerical analysis approach. This methodology was chosen as particularly well suited for handling a large number of antenna configurations of a generic type. A dedicated transfer matrix analysis, both by virtue of its specialization and the inherently easy compartmentalization of the formulation and numerical procedures, is significantly more efficient not only in computer time required but, more importantly, in the time needed to review and interpret the results
Exploring Holographic General Gauge Mediation
We study models of gauge mediation with strongly coupled hidden sectors,
employing a hard wall background as an holographic dual description. The
structure of the soft spectrum depends crucially on the boundary conditions one
imposes on bulk fields at the IR wall. Generically, vector and fermion
correlators have poles at zero momentum, leading to gauge mediation by massive
vector messengers and/or generating Dirac gaugino masses. Instead, non-generic
choices of boundary conditions let one cover all of GGM parameter space.
Enriching the background with R-symmetry breaking scalars, the SSM soft term
structure becomes more constrained and similar to previously studied top-down
models, while retaining the more analytic control the present bottom-up
approach offers.Comment: 28 pages, 4 figures; v2: typos corrected and refs adde
From Parameter Tuning to Dynamic Heuristic Selection
The importance of balance between exploration and exploitation plays a crucial role while solving combinatorial optimization problems. This balance is reached by two general techniques: by using an appropriate problem solver and by setting its proper parameters. Both problems were widely studied in the past and the research process continues up until now. The latest studies in the field of automated machine learning propose merging both problems, solving them at design time, and later strengthening the results at runtime. To the best of our knowledge, the generalized approach for solving the parameter setting problem in heuristic solvers has not yet been proposed. Therefore, the concept of merging heuristic selection and parameter control have not been introduced.
In this thesis, we propose an approach for generic parameter control in meta-heuristics by means of reinforcement learning (RL). Making a step further, we suggest a technique for merging the heuristic selection and parameter control problems and solving them at runtime using RL-based hyper-heuristic. The evaluation of the proposed parameter control technique on a symmetric traveling salesman problem (TSP) revealed its applicability by reaching the performance of tuned in online and used in isolation underlying meta-heuristic. Our approach provides the results on par with the best underlying heuristics with tuned parameters.:1 Introduction 1
1.1 Motivation 1
1.2 Research objective 2
1.3 Solution overview 2
2 Background and RelatedWork Analysis 3
2.1 Optimization Problems and their Solvers 3
2.2 Heuristic Solvers for Optimization Problems 9
2.3 Setting Algorithm Parameters 19
2.4 Combined Algorithm Selection and Hyper-Parameter Tuning Problem 27
2.5 Conclusion on Background and Related Work Analysis 28
3 Online Selection Hyper-Heuristic with Generic Parameter Control 31
3.1 Combined Parameter Control and Algorithm Selection Problem 31
3.2 Search Space Structure 32
3.3 Parameter Prediction Process 34
3.4 Low-Level Heuristics 35
3.5 Conclusion of Concept 36
4 Implementation Details 37
4.2 Search Space 40
4.3 Prediction Process 43
4.4 Low Level Heuristics 48
4.5 Conclusion 52
5 Evaluation 55
5.1 Optimization Problem 55
5.2 Environment Setup 56
5.3 Meta-heuristics Tuning 56
5.4 Concept Evaluation 60
5.5 Analysis of HH-PC Settings 74
5.6 Conclusion 79
6 Conclusion 81
7 FutureWork 83
7.1 Prediction Process 83
7.2 Search Space 84
7.3 Evaluations and Benchmarks 84
Bibliography 87
A Evaluation Results 99
A.1 Results in Figures 99
A.2 Results in numbers 10
A unified framework for solving a general class of conditional and robust set-membership estimation problems
In this paper we present a unified framework for solving a general class of
problems arising in the context of set-membership estimation/identification
theory. More precisely, the paper aims at providing an original approach for
the computation of optimal conditional and robust projection estimates in a
nonlinear estimation setting where the operator relating the data and the
parameter to be estimated is assumed to be a generic multivariate polynomial
function and the uncertainties affecting the data are assumed to belong to
semialgebraic sets. By noticing that the computation of both the conditional
and the robust projection optimal estimators requires the solution to min-max
optimization problems that share the same structure, we propose a unified
two-stage approach based on semidefinite-relaxation techniques for solving such
estimation problems. The key idea of the proposed procedure is to recognize
that the optimal functional of the inner optimization problems can be
approximated to any desired precision by a multivariate polynomial function by
suitably exploiting recently proposed results in the field of parametric
optimization. Two simulation examples are reported to show the effectiveness of
the proposed approach.Comment: Accpeted for publication in the IEEE Transactions on Automatic
Control (2014
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