3,552 research outputs found
Exploration versus Exploitation Using Kriging Surrogate Modelling in Electromagnetic Design
This paper discusses the use of kriging surrogate modelling in multiobjective design optimisation in electromagnetics. The importance of achieving appropriate balance between exploration and exploitation is emphasised when searching for the global optimum. It is argued that this approach will yield a procedure to solve time consuming electromagnetic design problems efficiently and will also assist the decision making process to achieve a robust design of practical devices considering tolerances and uncertainties
Numerical investigation of fano resonances in metamaterials with electric asymmetry
The excitation of high quality factor asymmetric Fano-type resonances on a double layer metafilm structure is investigated through numerical simulation. The paper demonstrates that it is possible to design simple structures capable to sustain a very high quality factor resonance by reducing their radiation losses. An equivalent circuit formed by two linearly coupled resonant RLC circuits is extracted in an attempt to explain the observed Fano resonance through classical circuit theory
Robust Global Optimization of Electromagnetic Designs Utilizing Gradient Indices and Kriging
Since uncertainties in design variables are inevitable an optimal solution must consider the robustness of the design. A methodology based on the use of first-order and second-order gradient indices is proposed introducing the notion of gradient sensitivity. A kriging method assisted by algorithms exploring the concept of rewards is utilized to facilitate function predictions for the robust optimization process. The performance of the proposed algorithms is assessed through a series of numerical experiments and the TEAM Workshop Problem 22
Origin and stability of the dipolar response in a family of tetragonal tungsten bronze relaxors
A new family of relaxor dielectrics with the tetragonal tungsten bronze
structure (nominal composition Ba6M3+Nb9O30, M3+ = Ga, Sc or In) were studied
using dielectric spectroscopy to probe the dynamic dipole response and
correlate this with the crystal structure as determined from powder neutron
diffraction. Independent analyses of real and imaginary parts of the complex
dielectric function were used to determine characteristic temperature
parameters, TVF, and TUDR, respectively. In each composition both these
temperatures correlated with the temperature of maximum crystallographic
strain, Tc/a determined from diffraction data. The overall behaviour is
consistent with dipole freezing and the data indicate that the dipole stability
increases with increasing M3+ cation size as a result of increased
tetragonality of the unit cell. Crystallographic data suggests that these
materials are uniaxial relaxors with the dipole moment predominantly restricted
to the B1 cation site in the structure. Possible origins of the relaxor
behaviour are discussed.Comment: Main article 32 pages, 8 figures; Supplementary data 24 pages, 4
figure
Considerations of uncertainty in robust optimisation of electromagnetic devices
Due to unavoidable uncertainties related to material properties and manufacturing processes, the robustness of the optimal solution must be considered when designing electromagnetic devices. In this paper, the worst-case optimisation (WCO) and the worst-vertex-based WCO are proposed to evaluate the robustness of both performance and constraints under uncertainty. To reduce computing times when searching for the robust solution a predicted objective function is used, obtained with the help of a kriging algorithm which explores the searching space using the concept of rewards. Finally, to avoid some of the shortcomings of WCO, the concept of average performance evaluation is developed
Using system and user performance features to improve emotion detection in spoken tutoring dialogs
In this study, we incorporate automatically obtained system/user performance features into machine learning experiments to detect student emotion in computer tutoring dialogs. Our results show a relative improvement of 2.7% on classification accuracy and 8.08% on Kappa over using standard lexical, prosodie, sequential, and identification features. This level of improvement is comparable to the performance improvement shown in previous studies by applying dialog acts or lexical/prosodic-/discourse- level contextual features
Spin-glass state and long-range magnetic order in Pb(Fe1/2Nb1/2)O3
We have investigated the magnetic ground-state of the multiferroic relaxor
ferroelectric \pfn with SR spectroscopy and neutron scattering. We find
that a transition to a partially disordered phase occurs below T=20 K that
coexists with long-range antiferromagnetic ordering. The disordered phase
resembles a spin-glass. No clustering of magnetic ions could be evidenced by
SR so that the coexistence appears homogeneous in the sample
Spectroscopy of P using the one-proton knockout reaction
The structure of P was studied with a one-proton knockout reaction
at88~MeV/u from a S projectile beam at NSCL. The rays from
thedepopulation of excited states in P were detected with GRETINA,
whilethe P nuclei were identified event-by-event in the focal plane of
theS800 spectrograph. The level scheme of P was deduced up to 7.5 MeV
using coincidences. The observed levels were attributed to
protonremovals from the -shell and also from the deeply-bound
orbital.The orbital angular momentum of each state was derived from the
comparisonbetween experimental and calculated shapes of individual
(-gated)parallel momentum distributions. Despite the use of different
reactions andtheir associate models, spectroscopic factors, , derived
from theS knockout reaction agree with those obtained earlier
fromS(,\nuc{3}{He}) transfer, if a reduction factor , as
deducedfrom inclusive one-nucleon removal cross sections, is applied to the
knockout transitions.In addition to the expected proton-hole configurations,
other states were observedwith individual cross sections of the order of
0.5~mb. Based on their shiftedparallel momentum distributions, their decay
modes to negative parity states,their high excitation energy (around 4.7~MeV)
and the fact that they were notobserved in the (,\nuc{3}{He}) reaction, we
propose that they may resultfrom a two-step mechanism or a nucleon-exchange
reaction with subsequent neutronevaporation. Regardless of the mechanism, that
could not yet be clarified, thesestates likely correspond to neutron core
excitations in \nuc{35}{P}. Thisnewly-identified pathway, although weak, offers
the possibility to selectivelypopulate certain intruder configurations that are
otherwise hard to produceand identify.Comment: 5 figures, 1 table, accepted for publication in Physical Review
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