5,809 research outputs found

    Real-time diffuse optical tomography using reduced-order light propagation models based on a priori anatomical and functional information

    Get PDF
    This paper proposes a new fast 3D image reconstruction algorithm for Diffuse Optical Tomography using reduced order polynomial mappings from the space of optical tissue parameters into the space of flux measurements at the detector locations. The polynomial mappings are constructed through an iterative estimation process involving structure detection, parameter estimation and cross-validation using data generated by simulating a diffusion approximation of the radiative transfer equation incorporating a priori anatomical and functional information provided by MR scans and prior psychological evidence. Numerical simulation studies demonstrate that reconstructed images are remarkably similar in quality as those obtained using the standard approach, but obtained at a fraction of the time

    Beyond conventional factorization: Non-Hermitian Hamiltonians with radial oscillator spectrum

    Full text link
    The eigenvalue problem of the spherically symmetric oscillator Hamiltonian is revisited in the context of canonical raising and lowering operators. The Hamiltonian is then factorized in terms of two not mutually adjoint factorizing operators which, in turn, give rise to a non-Hermitian radial Hamiltonian. The set of eigenvalues of this new Hamiltonian is exactly the same as the energy spectrum of the radial oscillator and the new square-integrable eigenfunctions are complex Darboux-deformations of the associated Laguerre polynomials.Comment: 13 pages, 7 figure

    Exactly Solvable Hydrogen-like Potentials and Factorization Method

    Get PDF
    A set of factorization energies is introduced, giving rise to a generalization of the Schr\"{o}dinger (or Infeld and Hull) factorization for the radial hydrogen-like Hamiltonian. An algebraic intertwining technique involving such factorization energies leads to derive nn-parametric families of potentials in general almost-isospectral to the hydrogen-like radial Hamiltonians. The construction of SUSY partner Hamiltonians with ground state energies greater than the corresponding ground state energy of the initial Hamiltonian is also explicitly performed.Comment: LaTex file, 21 pages, 2 PostScript figures and some references added. To be published in J. Phys. A: Math. Gen. (1998

    Cycling diversity, accessibility, and equality: An analysis of cycling commuting in Bogotá

    Get PDF
    In a context of rising awareness for environmental concerns and promotion policies targeting non-motorized travel as a sustainable mobility solution, the bicycle has increasingly become an attractive transport mode in cities. However, accessibility to opportunities for people who cycle is not necessarily the same across socioeconomically different population segments, and it tends to be further constrained by high costs associated with the travel distance through the road network. This research examines equality in the accessibility to employment and education among cycle-user adults in Bogotá. Using 968 reported bicycle trips with these travel purposes in the 2015 Bogotá Household Travel Survey, we estimate a potential accessibility indicator and horizontal and vertical equality indicators. First, we identify three clusters through the K-prototypes method to classify bicycle commuters based on trip and socioeconomic characteristics, and second, we calculate potential accessibility using GIS-based trip distance decay functions, which is later assessed through equality indices such as Lorenz Curves, Gini index and Palma Ratio. Results show marked differences in potential accessibility to work and study opportunities between and within clusters, where up to 90% of the analyzed population of a cyclists' cluster has access to 30% of the job and study opportunities, indicating social and spatial inequalities produced by the urban structure and individual and household characteristics of regular cyclists. Results can guide in the implementation of accurate transport policies towards more equitable and sustainable transport in cities that are experiencing increases in bicycle ridership

    Quantum mechanical spectral engineering by scaling intertwining

    Full text link
    Using the concept of spectral engineering we explore the possibilities of building potentials with prescribed spectra offered by a modified intertwining technique involving operators which are the product of a standard first-order intertwiner and a unitary scaling. In the same context we study the iterations of such transformations finding that the scaling intertwining provides a different and richer mechanism in designing quantum spectra with respect to that given by the standard intertwiningComment: 8 twocolumn pages, 5 figure

    Analog implementation of a robust control strategy for mechanical systems

    Get PDF
    An analog implementation of a control structure with disturbance identification for mechanical systems is presented. This control structure is based on a discontinuous observer that estimates the state and the disturbances in the plant, improving the robustness of the closed loop system which also displays a control input free from chattering. The control structure, built with operational amplifiers, is simple, showing good performance for stabilization, regulation, and tracking objectives. The performance of the circuit is compared with a digital implementation based on a real-time data acquisition card to control a simple pendulum. In addition, the circuit performance is illustrated on an industrial 2-DOF robot
    corecore