26,279 research outputs found
An isogeometric analysis for elliptic homogenization problems
A novel and efficient approach which is based on the framework of
isogeometric analysis for elliptic homogenization problems is proposed. These
problems possess highly oscillating coefficients leading to extremely high
computational expenses while using traditional finite element methods. The
isogeometric analysis heterogeneous multiscale method (IGA-HMM) investigated in
this paper is regarded as an alternative approach to the standard Finite
Element Heterogeneous Multiscale Method (FE-HMM) which is currently an
effective framework to solve these problems. The method utilizes non-uniform
rational B-splines (NURBS) in both macro and micro levels instead of standard
Lagrange basis. Beside the ability to describe exactly the geometry, it
tremendously facilitates high-order macroscopic/microscopic discretizations
thanks to the flexibility of refinement and degree elevation with an arbitrary
continuity level provided by NURBS basis functions. A priori error estimates of
the discretization error coming from macro and micro meshes and optimal micro
refinement strategies for macro/micro NURBS basis functions of arbitrary orders
are derived. Numerical results show the excellent performance of the proposed
method
Satellite analog FDMA/FM to digital TDMA conversion
The results of a study which investigated design issues regarding the use of analog to digital (A/D) conversion on board a satellite are presented. The need for A/D, and of course D/A as well, conversion arose from a satellite design which required analog FDMA/FM up and down links to/from a digitally modulated intersatellite link. There are also some advantages when one must interconnect a large number of various spot beams which are using analog, and therefore cannot take advantage of SS/TDMA switching among the beams, thus resulting in low fill factors. Various tradeoffs were performed regarding the implementation of on-board A/D processing, including mass, power, and costs. The various technologies which were considered included flash ADCs, surface acoustic wave (SAW) devices, and digital signal processing (DSP) chips. Impact analyses were also performed to determine the effect on ground stations to convert to digital if the A/D approach were not implemented
Inhibition of DNA ejection from bacteriophage by Mg+2 counterions
The problem of inhibiting viral DNA ejection from bacteriophages by
multivalent counterions, specifically Mg counterions, is studied.
Experimentally, it is known that MgSO salt has a strong and non-monotonic
effect on the amount of DNA ejected. There exists an optimal concentration at
which the minimum amount of DNA is ejected from the virus. At lower or higher
concentrations, more DNA is ejected from the capsid. We propose that this
phenomenon is the result of DNA overcharging by Mg multivalent
counterions. As Mg concentration increases from zero, the net charge of
DNA changes from negative to positive. The optimal inhibition corresponds to
the Mg concentration where DNA is neutral. At lower/higher
concentrations, DNA genome is charged. It prefers to be in solution to lower
its electrostatic self-energy, which consequently leads to an increase in DNA
ejection. By fitting our theory to available experimental data, the strength of
DNADNA short range attraction energies, mediated by Mg, is found to
be 0.004 per nucleotide base. This and other fitted parameters agree
well with known values from other experiments and computer simulations. The
parameters are also in aggreement qualitatively with values for tri- and
tetra-valent counterions.Comment: 17 pages, 4 figures, improved manuscript. Submitted to J. Chem. Phys
(2010
Dynamics of horizontal-like maps in higher dimension
We study the regularity of the Green currents and of the equilibrium measure
associated to a horizontal-like map in C^k, under a natural assumption on the
dynamical degrees. We estimate the speed of convergence towards the Green
currents, the decay of correlations for the equilibrium measure and the
Lyapounov exponents. We show in particular that the equilibrium measure is
hyperbolic. We also show that the Green currents are the unique invariant
vertical and horizontal positive closed currents. The results apply, in
particular, to Henon-like maps, to regular polynomial automorphisms of C^k and
to their small pertubations.Comment: Dedicated to Professor Gennadi Henkin on the occasion of his 65th
birthday, 37 pages, to appear in Advances in Mat
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