4,210 research outputs found
Coherent control using adaptive learning algorithms
We have constructed an automated learning apparatus to control quantum
systems. By directing intense shaped ultrafast laser pulses into a variety of
samples and using a measurement of the system as a feedback signal, we are able
to reshape the laser pulses to direct the system into a desired state. The
feedback signal is the input to an adaptive learning algorithm. This algorithm
programs a computer-controlled, acousto-optic modulator pulse shaper. The
learning algorithm generates new shaped laser pulses based on the success of
previous pulses in achieving a predetermined goal.Comment: 19 pages (including 14 figures), REVTeX 3.1, updated conten
Chaotic and integrable magnetic fields in one-dimensional hybrid Vlasov-Maxwell equilibria
In this paper, we develop a one-dimensional, quasineutral, hybrid
Vlasov-Maxwell equilibrium model with kinetic ions and massless fluid electrons
and derive associated solutions. The model allows for an electrostatic
potential that is expressed in terms of the vector potential components through
the quasineutrality condition. The equilibrium states are calculated upon
solving an inhomogeneous Beltrami equation that determines the magnetic field,
where the inhomogeneous term is the current density of the kinetic ions and the
homogeneous term represents the electron current density. We show that the
corresponding one-dimensional system is Hamiltonian, with position playing the
role of time, and its trajectories have a regular, periodic behavior for ion
distribution functions that are symmetric in the two conserved particle
canonical momenta. For asymmetric distribution functions, the system is
nonintegrable, resulting in irregular and chaotic behavior of the fields. The
electron current density can modify the magnetic field phase space structure,
inducing orbit trapping and the organization of orbits into large islands of
stability. Thus the electron contribution can be responsible for the emergence
of localized electric field structures that induce ion trapping. We also
provide a paradigm for the analytical construction of hybrid equilibria using a
rotating two-dimensional harmonic oscillator Hamiltonian, enabling the
calculation of analytic magnetic fields and the construction of the
corresponding distribution functions in terms of Hermite polynomials
Radio resource allocation for multicarrier-low density spreading multiple access
Multicarrier-low density spreading multiple access (MC-LDSMA) is a promising multiple access technique that enables near optimum multiuser detection. In MC-LDSMA, each user’s symbol spread on a small set of subcarriers, and each subcarrier is shared by multiple users. The unique structure of MC-LDSMA makes the radio resource allocation more challenging comparing to some well-known multiple access techniques. In this paper, we study the radio resource allocation for single-cell MC-LDSMA system. Firstly, we consider the single-user case, and derive the optimal power allocation and subcarriers partitioning schemes. Then, by capitalizing on the optimal power allocation of the Gaussian multiple access channel, we provide an optimal solution for MC-LDSMA that maximizes the users’ weighted sum-rate under relaxed constraints. Due to the prohibitive complexity of the optimal solution, suboptimal algorithms are proposed based on the guidelines inferred by the optimal solution. The performance of the proposed algorithms and the effect of subcarrier loading and spreading are evaluated through Monte Carlo simulations. Numerical results show that the proposed algorithms significantly outperform conventional static resource allocation, and MC-LDSMA can improve the system performance in terms of spectral efficiency and fairness in comparison with OFDMA
On 3-D inelastic analysis methods for hot section components (base program)
A 3-D Inelastic Analysis Method program is described. This program consists of a series of new computer codes embodying a progression of mathematical models (mechanics of materials, special finite element, boundary element) for streamlined analysis of: (1) combustor liners, (2) turbine blades, and (3) turbine vanes. These models address the effects of high temperatures and thermal/mechanical loadings on the local (stress/strain)and global (dynamics, buckling) structural behavior of the three selected components. Three computer codes, referred to as MOMM (Mechanics of Materials Model), MHOST (Marc-Hot Section Technology), and BEST (Boundary Element Stress Technology), have been developed and are briefly described in this report
Locking free and gradient robust H(div)-conforming HDG methods for linear elasticity
Robust discretization methods for (nearly-incompressible) linear elasticity are free of volume-locking and gradient-robust. While volume-locking is a well-known problem that can be dealt with in many different discretization approaches, the concept of gradient-robustness for linear elasticity is new. We discuss both aspects and propose novel Hybrid Discontinuous Galerkin (HDG) methods for linear elasticity. The starting point for these methods is a divergence-conforming discretization. As a consequence of its well-behaved Stokes limit the method is gradient-robust and free of volume-locking. To improve computational efficiency, we additionally consider discretizations with relaxed divergence-conformity and a modification which re-enables gradient-robustness, yielding a robust and quasi-optimal discretization also in the sense of HDG superconvergence
Review of Traveling Salesman Problem for the genetic algorithms
Genetic Algorithms (GAs) are an evolutionary technique that uses the operators like mutation, crossover and the selection of the most fitted element as solution for problems optimization. The Traveling Salesman Problem (TSP) finds a path with minimal length, closed within a weighted graph in all its nodes and it visits each of them once. This problem is found in many real world applications and where a good solution might help. There are applied many methods for finding a solution for the TSP, but during this study GAs are used as an approximate method of TSP
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