11,635 research outputs found
Survey of Different Data Dependence Analysis Techniques
Dependency analysis is a technique to detect dependencies between tasks that prevent these tasks from running in parallel. It is an important aspect of parallel programming tools. Dependency analysis techniques are used to determine how much of the code is parallelizable.
Literature shows that number of data dependence test has been proposed for parallelizing loops in case of arrays with linear subscripts, however less work has been done for arrays with nonlinear subscripts. GCD test, Banerjee method, Omega test, I-test dependence decision algorithms are used for one-dimensional arrays under constant or variable bounds. However, these approaches perform well only for nested loop with linear array subscripts. The Quadratic programming (QP) test, polynomial variable interval (PVI) test, Range test are typical techniques for nonlinear subscripts. The paper presents survey of these different data dependence analysis tests
Compact nonlinear model of an implantable electrode array for spinal cord stimulation (SCS)
We describe the construction of a model of the electrode-electrolyte interface and surrounding electrolyte in the case of a platinum-electrode array intended for spinal-cord stimulation (SCS) application. We show that a finite, two dimensional, resistor array provides a satisfactory model of the bulk electrolyte, and we identify the complexity required of that resistor array. The electrode-electrolyte interface is modelled in a fashion suitable for commonly-available, compact simulators using a nonlinear extension of the model of Franks et al. that incorporates diodes and a memristor. The electrode-electrolyte interface model accounts for the nonlinear current-overpotential characteristic and diffusion-limiting effects. We characterise a commercial, implantable, electrode array, fit the model to it, and show that the model successfully predicts subtle operational characteristics
Cosmic-ray acceleration in supernova remnants: non-linear theory revised
A rapidly growing amount of evidences, mostly coming from the recent
gamma-ray observations of Galactic supernova remnants (SNRs), is seriously
challenging our understanding of how particles are accelerated at fast shocks.
The cosmic-ray (CR) spectra required to account for the observed phenomenology
are in fact as steep as , i.e., steeper than the
test-particle prediction of first-order Fermi acceleration, and significantly
steeper than what expected in a more refined non-linear theory of diffusive
shock acceleration. By accounting for the dynamical back-reaction of the
non-thermal particles, such a theory in fact predicts that the more efficient
the particle acceleration, the flatter the CR spectrum. In this work we put
forward a self-consistent scenario in which the account for the magnetic field
amplification induced by CR streaming produces the conditions for reversing
such a trend, allowing --- at the same time --- for rather steep spectra and CR
acceleration efficiencies (about 20%) consistent with the hypothesis that SNRs
are the sources of Galactic CRs. In particular, we quantitatively work out the
details of instantaneous and cumulative CR spectra during the evolution of a
typical SNR, also stressing the implications of the observed levels of
magnetization on both the expected maximum energy and the predicted CR
acceleration efficiency. The latter naturally turns out to saturate around
10-30%, almost independently of the fraction of particles injected into the
acceleration process as long as this fraction is larger than about .Comment: 24 pages, 5 figures, accepted for publication in JCA
Nonthermal Radiation from Type Ia Supernova Remnants
We present calculations of expected continuum emissions from Sedov-Taylor
phase Type Ia supernova remnants (SNRs), using the energy spectra of cosmic ray
(CR) electrons and protons from nonlinear diffusive shock acceleration (DSA)
simulations. A new, general-purpose radiative process code, Cosmicp, was
employed to calculate the radiation expected from CR electrons and protons and
their secondary products. These radio, X-ray and gamma-ray emissions are
generally consistent with current observations of Type Ia SNRs. The emissions
from electrons in these models dominate the radio through X-ray bands. Decays
of \pi^0 s from p-p collisions mostly dominate the gamma-ray range, although
for a hot, low density ISM case (n_{ISM}=0.003 cm^{-3}), the pion decay
contribution is reduced sufficiently to reveal the inverse Compton contribution
to TeV gamma-rays. In addition, we present simple scalings for the contributing
emission processes to allow a crude exploration of model parameter space,
enabling these results to be used more broadly. We also discuss the radial
surface brightness profiles expected for these model SNRs in the X-ray and
gamma-ray bands.Comment: 37 pages, 7 figures, accepted in MNRA
A wavelength-tunable fiber-coupled source of narrowband entangled photons
We demonstrate a wavelength-tunable, fiber-coupled source of
polarization-entangled photons with extremely high spectral brightness and
quality of entanglement. Using a 25 mm PPKTP crystal inside a polarization
Sagnac interferometer we detect a spectral brightness of 273000 pairs/(s mW
nm), a factor of 28 better than comparable previous sources while state
tomography showed the two-photon state to have a tangle of T=0.987. This
improvement was achieved by use of a long crystal, careful selection of
focusing parameters and single-mode fiber coupling. We demonstrate that, due to
the particular geometry of the setup, the signal and idler wavelengths can be
tuned over a wide range without loss of entanglement.Comment: 10 pages, 5 figures. Article rewritten, added Fig.(1a-1b). Published
in Optics Express, comments welcom
Direct Numerical Simulation of Receptivity to Roughness in a Swept-Wing Boundary Layer at High Reynolds Numbers
Direct numerical simulations (DNS) are performed to examine the receptivity to roughness in a spatially developing three-dimensional boundary layer over an in finite-swept natural-laminar-flow wing at a free stream Mach number of 0:75 and a chord Reynolds number of approximately 25 million based on the long, swept chord. Stationary cross ow disturbances are excited by applying either critically spaced discrete cylinders of micron size or naturally occurring distributed roughness in the leading-edge region. The DNS data show that the spanwise spectral content of the excited cross ow disturbances is highly dependent upon the shape of roughness elements, and the initial growth of the cross ow structures is a nonlinear function of the element height. The linear growth rate of the excited cross ow disturbances predicted by DNS shows good agreement with linear parabolized stability equations. The receptivity study lays the foundation for investigating the stabilization of the naturally most unstable steady cross ow mode by using spanwise periodic DREs
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