751 research outputs found
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Intelligent Learning Algorithms for Active Vibration Control
YesThis correspondence presents an investigation into the
comparative performance of an active vibration control (AVC) system
using a number of intelligent learning algorithms. Recursive least square
(RLS), evolutionary genetic algorithms (GAs), general regression neural
network (GRNN), and adaptive neuro-fuzzy inference system (ANFIS)
algorithms are proposed to develop the mechanisms of an AVC system.
The controller is designed on the basis of optimal vibration suppression
using a plant model. A simulation platform of a flexible beam system
in transverse vibration using a finite difference method is considered to
demonstrate the capabilities of the AVC system using RLS, GAs, GRNN,
and ANFIS. The simulation model of the AVC system is implemented,
tested, and its performance is assessed for the system identification models
using the proposed algorithms. Finally, a comparative performance of the
algorithms in implementing the model of the AVC system is presented and
discussed through a set of experiments
Symmetry and optical selection rules in graphene quantum dots
Graphene quantum dots (GQD's) have optical properties which are very
different from those of an extended graphene sheet. In this Article we explore
how the size, shape and edge--structure of a GQD affect its optical
conductivity. Using representation theory, we derive optical selection rules
for regular-shaped dots, starting from the symmetry properties of the current
operator. We find that, where the x- and y-components of the current operator
transform with the same irreducible representation (irrep) of the point group -
for example in triangular or hexagonal GQD's - the optical conductivity is
independent of the polarisation of the light. On the other hand, where these
components transform with different irreps - for example in rectangular GQD's -
the optical conductivity depends on the polarisation of light. We find that
GQD's with non-commuting point-group operations - for example dots of
rectangular shape - can be distinguished from GQD's with commuting point-group
operations - for example dots of triangular or hexagonal shape - by using
polarized light. We carry out explicit calculations of the optical conductivity
of GQD's described by a simple tight--binding model and, for dots of
intermediate size, \textcolor{blue}{()}
find an absorption peak in the low--frequency range of the spectrum which
allows us to distinguish between dots with zigzag and armchair edges. We also
clarify the one-dimensional nature of states at the van Hove singularity in
graphene, providing a possible explanation for very high exciton-binding
energies. Finally we discuss the role of atomic vacancies and shape asymmetry.Comment: 24 pages, 15 figure
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Intelligent Active Vibration Control for a Flexible Beam System
YesThis paper presents an investigation into the
development of an intelligent active vibration control
(AVC) system. Evolutionary Genetic algorithms (GAs)
and Adaptive Neuro-Fuzzy Inference system (ANFIS)
algorithms are used to develop mechanisms of an AVC
system, where the controller is designed on the basis of
optimal vibration suppression using the plant model. A
simulation platform of a flexible beam system in
transverse vibration using finite difference (FD) method
is considered to demonstrate the capabilities of the AVC
system using GAs and ANFIS. MATLAB GA tool box for
GAs and Fuzzy Logic tool box for ANFIS function are
used for AVC system design. The system is then
implemented, tested and its performance assessed for GAs
and ANFIS based design. Finally a comparative
performance of the algorithm in implementing AVC
system using GAs and ANFIS is presented and discussed
through a set of experiments
Toward the Gravity Dual of Heterotic Small Instantons
The question of what happens when the heterotic SO(32) instanton becomes
small was answered sometime back by Witten. The heterotic theory develops an
enhanced Sp(2k) gauge symmetry for k small instantons, besides the allowed
SO(32) gauge symmetry. An interesting question now is to ask what happens when
we take the large k limit. In this paper we argue that in some special cases,
where Gauss' law allows the large k limit, the dynamics of the large k small
instantons can be captured by a dual gravitational description. For the cases
that we elaborate in this paper, the gravity duals are non-Kahler manifolds
although in general they could be non-geometric. These small instantons are
heterotic five-branes and the duality allows us to study the strongly coupled
field theories on these five-branes. We review and elaborate on some of the
recent observations pointing towards this duality, and argue that in certain
cases the gauge/gravity duality may be understood as small instanton
transitions under which the instantons smoothen out and consequently lose the
Sp(2k) gauge symmetry. This may explain how branes disappear on the dual side
and are replaced by fluxes. We analyse the torsion classes before and after the
transitions, and discuss briefly how the ADHM sigma model and related vector
bundles could be studied for these scenarios.Comment: 47 pages, 3 eps figures, LaTex, JHEP3 file; v2: Another consistency
check added, typos corrected and a reference added; v3: Text expanded a bit,
minor typos corrected and a few references updated. Final version to appear
in Phys. Rev.
Ultrafast Control of the Dimensionality of Exciton-Exciton Annihilation in Atomically Thin Black Phosphorus
Using microtransient absorption spectroscopy, we show that the dynamical form of exciton-exciton annihilation in atomically thin black phosphorous can be made to switch between time varying 1D scattering and time-independent 2D scattering. At low carrier densities, anisotropy drives the 1D behavior, but as the photoexcitation density approaches the exciton saturation limit, the 2D nature of exciton-exciton scattering takes over. Furthermore, lowering the temperature provides a handle on the ultrafast timescale at which the 1D to 2D transition occurs. We understand our results quantitatively using a diffusion based model of exciton-exciton scattering
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Scheduling of tasks in multiprocessor system using hybrid genetic algorithms
This paper presents an investigation into the optimal scheduling of realtime
tasks of a multiprocessor system using hybrid genetic algorithms (GAs). A comparative
study of heuristic approaches such as `Earliest Deadline First (EDF)¿ and
`Shortest Computation Time First (SCTF)¿ and genetic algorithm is explored and
demonstrated. The results of the simulation study using MATLAB is presented and
discussed. Finally, conclusions are drawn from the results obtained that genetic algorithm
can be used for scheduling of real-time tasks to meet deadlines, in turn to obtain
high processor utilization
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Impact of algorithm design in implementing real-time active control systems
This paper presents an investigation into the impact of algorithm design
for real-time active control systems. An active vibration control (AVC) algorithm
for flexible beam systems is employed to demonstrate the critical design
impact for real-time control applications. The AVC algorithm is analyzed, designed
in various forms and implemented to explore the impact. Finally, a comparative
real-time computing performance of the algorithms is presented and
discussed to demonstrate the merits of different design mechanisms through a
set of experiments
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