Now showing items 1-20 of 23

  • [2012-03-23] Long-time behavior of Ginzburg-Landau systems far from equilibrium 

    Coutsias, Evangelos A.; Huberman, B. A.
    Using singular-perturbation techniques, we study the stability of modulated structures generated by driving Ginzburg-Landau systems far from equilibrium. We show that, far from equilibrium, the steady-state behavior is ...
  • [2012-03-23] Effects of thermal spread on the space charge limit of an electron beam 

    Coutsias, Evangelos A.
    An asymptotic analysis is carried out to calculate the effects of a small thermal spread in the injection energy of an electron beam on its space charge limit. It is found that the space charge limit is lowered proportionally ...
  • [2012-03-23] Space charge limit instabilities in electron beams 

    Coutsias, Evangelos A.; Sullivan, D.J.
    The method of characteristics and multiple-scaling perturbation techniques are used to study the space-charge instability of electron beams. It is found that the stable oscillating state (virtual cathode) created when the ...
  • [2012-03-23] Non relativistic Kapitza-Dirac scattering 

    Coutsias, Evangelos A.; McIver, J.K.
    We use techniques of singular perturbation theory to investigate the scattering of nonrelativistic charged particles by a standing light wave (Kapitza-Dirac scattering). Unlike previous treatments, we give explicit results ...
  • [2012-03-23] Caustics and virtual cathodes in electron beams 

    Coutsias, Evangelos A.
    A simplified model is discussed that captures the basic physics of the phenomenon of oscillatory virtual cathodes in electron beams. A monoenergetic non-relativistic one-dimensional electron beam is injected through a ...
  • [2012-03-23] Acoustic-wave nonlinearity in stimulated Brillouin scattering 

    Coutsias, Evangelos A.; Masson, Bruce S.
    Stimulated Brillouin scattering is investigated here under conditions characterized by high optical pump intensity. Calculations are carried out at 1.3 and 3.8 /jm with pump intensities equal to approximately three times ...
  • [2012-03-22] AN EFFICIENT SPECTRAL METHOD FOR ORDINARY DIFFERENTIAL EQUATIONS WITH RATIONAL FUNCTION COEFFICIENTS 

    Coutsias, Evangelos A.; HAGSTROM, THOMAS; TORRES, DAVID
    We present some relations that allow the efficient approximate inversion of linear differential operators with rational function coefficients. We employ expansions in terms of a large class of orthogonal polynomial families, ...
  • [2012-03-22] Optimized preparation of quantum states by conditional measurements 

    Harel, G.; Kurizki, G.; Coutsias, Evangelos A.; McIver, J. K.
    We introduce a general strategy for preparation of arbitrary quantum states via optimal control of repeated conditional measurements. The effectiveness of this strategy in generating finite Fock-state superpositions with ...
  • [2012-03-22] The Approximate Functional Formula for the Theta Function and Diophantine Gauss Sums 

    Coutsias, Evangelos A.; Kazarinoff, N.D.
    By introducing the discrete curvature of the polygonal line, and by exploiting the similarity of segments of the line, for small w, to Cornu spirals (C-spirals), we prove the precise renormalization formula. This formula, ...
  • [2012-03-22] PSEUDOSPECTRAL SOLUTION OF THE TWO-DIMENSIONAL NAVIER{STOKES EQUATIONS IN A DISK 

    Coutsias, Evangelos A.; Torres, David J.
    An efficient and accurate algorithm for solving the two-dimensional (2D) incompressible Navier-Stokes equations on a disk with no-slip boundary conditions is described. The vorticity stream function formulation of these ...
  • [2012-03-22] Dynamical properties of forced shear layers in an annular geometry 

    Coutsias, Evangelos A.; Bergeron, Keith; Lynov, J.P.; Nielsen, A.H.
    Results of numerical simulations of a forced shear flow in an annular geometry are presented. The particular geometry used in this work reduces the effects of centrifugal and Coriolis forces. However, there are still a ...
  • [2012-03-22] Invertibility of current density from near-field electromagnetic data 

    Coutsias, Evangelos A.; Sheltraw, Daniel
    The problem of determining a current density confined to a volume from measurements of the magnetic and electric fields it produces exterior to that volume is known to have nonunique solutions. Despite the nonuniqueness ...
  • [2012-03-22] The Quaternions with an application to Rigid Body Dynamics 

    Coutsias, Evangelos A.; Romero, Louis
    William Rowan Hamilton invented the quaternions in 1843, in his effort to construct hypercomplex numbers, or higher dimensional generalizations of the complex numbers. Failing to construct a generalization in three dimensions ...
  • [2012-03-22] A reduced-order partial differential equation model for dynamics of the flow in athermosyphon 

    Coutsias, Evangelos A.; Burroughs, Elisabeth A.; Romero, L.
    Flow in a closed loop thermosyphon heated from below exhibits a sequence of bifurcations with increasing Grashof number. Using the Navier-Stokes equations in the Boussinesq approximation we have derived a model where, in ...
  • [2012-03-22] Algorithmic dimensionality reduction for molecular structure analysis 

    Coutsias, Evangelos A.; Brown, W. Michael; Martin, Shawn; Pollock, Sara N.; Watson, Jean-Paul
    Dimensionality reduction approaches have been used to exploit the redundancy in a Cartesian coordinate representation of molecular motion by producing low-dimensional representations of molecular motion. This has been used ...
  • [2012-03-22] Delay-induced destabilization of entrainment of nerve impulses on ephaptically coupled nerve fibers 

    Coutsias, Evangelos A.; Adhikari, Mohit H.; McIver, John K.
    We study the effect of delay on the synchronization of two nerve impulses traveling along two ephaptically coupled, unmyelinated nerve fibers. The system is modeled as a pair of delay-coupled Fitzhugh-Nagumo equations. A ...
  • [2012-03-22] Topology of cyclo-octane energy landscape 

    Coutsias, Evangelos A.; Martin, Shawn; Thompson, Aidan; Watson, Jean-Paul
    Understanding energy landscapes is a major challenge in chemistry and biology. Although a wide variety of methods have been invented and applied to this problem, very little is understood about the actual mathematical ...
  • [2012-03-20] The FALC-Loop web server for protein loop modeling 

    Coutsias, Evangelos A.; Ko, Junsu; Lee, Dongseon; Park, Hahnbeom; Lee, Julian; Seok, Chaok
    The FALC-Loop web server provides an online interface for protein loop modeling by employing an ab initio loop modeling method called FALC (fragment assembly and analytical loop closure). The server may be used to construct ...
  • [2013-11-25] Computing a logarithm of a unitary matrix with general spectrum [dataset] 

    Loring, Terry A.
    \begin{abstract} We analyze an algorithm for computing a skew-Hermitian logarithm of a unitary matrix, and also skew-Hermitian approximate logarithms for nearly unitary matrices. This algorithm is very easy to implement ...
  • [2013-12-02] Estimating norms of commutators 

    Loring, Terry A.; Vides, Freddy
    \begin{abstract} We find estimates on the norm of a commutator of the form $[f(x),y]$ in terms of the norm of $[x,y]$, assuming that $x$ and $y$ are bounded linear operators on Hilbert space, with $x$ normal and with ...