1,155 research outputs found
On-line multiobjective automatic control system generation by evolutionary algorithms
Evolutionary algorithms are applied to the on- line generation of servo-motor control systems. In this paper, the evolving population of controllers is evaluated at run-time via hardware in the loop, rather than on a simulated model. Disturbances are also introduced at run-time in order to pro- duce robust performance. Multiobjective optimisation of both PI and Fuzzy Logic controllers is considered. Finally an on-line implementation of Genetic Programming is presented based around the Simulink standard blockset. The on-line designed controllers are shown to be robust to both system noise and ex- ternal disturbances while still demonstrating excellent steady- state and dvnamic characteristics
Strong Effects of Weak Localization in Charge Density Wave/Normal Metal Hybrids
Collective transport through a multichannel disordered conductor in contact
with charge-density-wave electrodes is theoretically investigated. The
statistical distribution function of the threshold potential for charge-density
wave sliding is calculated by random matrix theory. In the diffusive regime
weak localization has a strong effect on the sliding motion.Comment: To be published in Physical Review
Maxwell - Chern - Simons topologically massive gauge fields in the first-order formalism
We find the canonical and Belinfante energy-momentum tensors and their
nonzero traces. We note that the dilatation symmetry is broken and the
divergence of the dilatation current is proportional to the topological mass of
the gauge field. It was demonstrated that the gauge field possesses the `scale
dimensionality' d=1/2. Maxwell - Chern - Simons topologically massive gauge
field theory in 2+1 dimensions is formulated in the first-order formalism. It
is shown that 6x6-matrices of the relativistic wave equation obey the Duffin -
Kemmer - Petiau algebra. The Hermitianizing matrix of the relativistic wave
equation is given. The projection operators extracting solutions of field
equations for states with definite energy-momentum and spin are obtained. The
5x5-matrix Schrodinger form of the equation is derived after the exclusion of
non-dynamical components, and the quantum-mechanical Hamiltonian is obtained.
Projection operators extracting physical states in the Schrodinger picture are
found.Comment: 18 pages, correction in Ref. [5
The non-commutative Landau problem
The Landau problem is discussed in two similar but still different
non-commutative frameworks. The ``standard'' one, where the coupling to the
gauge field is achieved using Poisson brackets, yields all Landau levels. The
``exotic'' approach, where the coupling to the gauge field is achieved using
the symplectic structure, only yields lowest-Landau level states, as advocated
by Peierls and used in the description of the ground states of the Fractional
Quantum Hall Effect. The same reduced model also describes vortex dynamics in a
superfluid He film. Remarkably, the spectrum depends crucially on the
quantization scheme. The system is symmetric w. r. t. area-preserving
diffeomorphisms.Comment: Published with shortened title as Ann. Phys. (N. Y.) 299, pp. 128-140
(2002) 14 pages, LaTex, no figure
Single parameter scaling in 1-D localized absorbing systems
Numerical study of the scaling of transmission fluctuations in the 1-D
localization problem in the presence of absorption is carried out. Violations
of single parameter scaling for lossy systems are found and explained on the
basis of a new criterion for different types of scaling behavior derived by
Deych et al [Phys. Rev. Lett., {\bf 84}, 2678 (2000)].Comment: 7 pages, 6 figures, RevTex, submitted to Phys. Rev.
The Basics of Water Waves Theory for Analogue Gravity
This chapter gives an introduction to the connection between the physics of
water waves and analogue gravity. Only a basic knowledge of fluid mechanics is
assumed as a prerequisite.Comment: 36 pages. Lecture Notes for the IX SIGRAV School on "Analogue
Gravity", Como (Italy), May 201
Disappearance of Ensemble-Averaged Josephson Current in Dirty SNS Junctions of d-wave Superconductors
We discuss the Josephson current in superconductor / dirty normal conductor /
superconductor junctions, where the superconductors have pairing
symmetry. The low-temperature behavior of the Josephson current depends on the
orientation angle between the crystalline axis and the normal of the junction
interface. We show that the ensemble-averaged Josephson current vanishes when
the orientation angle is and the normal conductor is in the diffusive
transport regime. The -wave pairing symmetry is responsible for
this fact.Comment: 8 pages, 5 figure
Microvascular Ultrasonic Imaging of Angiogenesis Identifies Tumors in a Murine Spontaneous Breast Cancer Model
The purpose of this study is to determine if microvascular tortuosity can be used as an imaging biomarker for the presence of tumor-associated angiogenesis and if imaging this biomarker can be used as a specific and sensitive method of locating solid tumors. Acoustic angiography, an ultrasound-based microvascular imaging technology, was used to visualize angiogenesis development of a spontaneous mouse model of breast cancer (n=48). A reader study was used to assess visual discrimination between image types, and quantitative methods utilized metrics of tortuosity and spatial clustering for tumor detection. The reader study resulted in an area under the curve of 0.8, while the clustering approach resulted in the best classification with an area under the curve of 0.95. Both the qualitative and quantitative methods produced a correlation between sensitivity and tumor diameter. Imaging of vascular geometry with acoustic angiography provides a robust method for discriminating between tumor and healthy tissue in a mouse model of breast cancer. Multiple methods of analysis have been presented for a wide range of tumor sizes. Application of these techniques to clinical imaging could improve breast cancer diagnosis, as well as improve specificity in assessing cancer in other tissues. The clustering approach may be beneficial for other types of morphological analysis beyond vascular ultrasound images
Isovector part of nuclear energy density functional from chiral two- and three-nucleon forces
A recent calculation of the nuclear energy density functional from chiral
two- and three-nucleon forces is extended to the isovector terms pertaining to
different proton and neutron densities. An improved density-matrix expansion is
adapted to the situation of small isospin-asymmetries and used to calculate in
the Hartree-Fock approximation the density-dependent strength functions
associated with the isovector terms. The two-body interaction comprises of
long-range multi-pion exchange contributions and a set of contact terms
contributing up to fourth power in momenta. In addition, the leading order
chiral three-nucleon interaction is employed with its parameters fixed in
computations of nuclear few-body systems. With this input one finds for the
asymmetry energy of nuclear matter the value MeV,
compatible with existing semi-empirical determinations. The strength functions
of the isovector surface and spin-orbit coupling terms come out much smaller
than those of the analogous isoscalar coupling terms and in the relevant
density range one finds agreement with phenomenological Skyrme forces. The
specific isospin- and density-dependences arising from the chiral two- and
three-nucleon interactions can be explored and tested in neutron-rich systems.Comment: 14 pages, 7 figures, to be published in European Physical Journal
Development of a Momentum Determined Electron Beam in the 1 -45 GeV Range
A beam line for electrons with energies in the range of 1 to 45 GeV, low
contamination of hadrons and muons and high intensity up to 10^6 per
accelerator spill at 27 GeV was setup at U70 accelerator in Protvino, Russia. A
beam tagging system based on drift chambers with 160 micron resolution was able
to measure relative electron beam momentum precisely. The resolution sigma_p p
was 0.13% at 45 GeV where multiple scattering is negligible. This test beam
setup provided the possibility to study properties of lead tungstate crystals
(PbWO_4) for the BTeV experiment at Fermilab.Comment: 12 pages, 8 figures; work done by the BTeV Electromagnetic
Calorimeter grou
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