50,530 research outputs found
Newton like: Minimal residual methods applied to transonic flow calculations
A computational technique for the solution of the full potential equation is presented. The method consists of outer and inner iterations. The outer iterate is based on a Newton like algorithm, and a preconditioned Minimal Residual method is used to seek an approximate solution of the system of linear equations arising at each inner iterate. The present iterative scheme is formulated so that the uncertainties and difficulties associated with many iterative techniques, namely the requirements of acceleration parameters and the treatment of additional boundary conditions for the intermediate variables, are eliminated. Numerical experiments based on the new method for transonic potential flows around the NACA 0012 airfoil at different Mach numbers and different angles of attack are presented, and these results are compared with those obtained by the Approximate Factorization technique. Extention to three dimensional flow calculations and application in finite element methods for fluid dynamics problems by the present method are also discussed. The Inexact Newton like method produces a smoother reduction in the residual norm, and the number of supersonic points and circulations are rapidly established as the number of iterations is increased
Momentum Kick Model Description of the Ridge in (Delta-phi)-(Delta eta) Correlation in pp Collisions at 7 TeV
The near-side ridge structure in the (Delta phi)-(Delta eta) correlation
observed by the CMS Collaboration for pp collisions at 7 TeV at LHC can be
explained by the momentum kick model in which the ridge particles are medium
partons that suffer a collision with the jet and acquire a momentum kick along
the jet direction. Similar to the early medium parton momentum distribution
obtained in previous analysis for nucleus-nucleus collisions at 0.2 TeV, the
early medium parton momentum distribution in pp collisions at 7 TeV exhibits a
rapidity plateau as arising from particle production in a flux tube.Comment: Talk presented at Workshop on High-pT Probes of High-Density QCD at
the LHC, Palaiseau, May 30-June2, 201
Axion hot dark matter bounds
We derive cosmological limits on two-component hot dark matter consisting of
neutrinos and axions. We restrict the large-scale structure data to the safely
linear regime, excluding the Lyman-alpha forest. We derive Bayesian credible
regions in the two-parameter space consisting of m_a and sum(m_nu).
Marginalizing over sum(m_nu) provides m_a<1.02 eV (95% CL). In the absence of
axions the same data and methods give sum(m_nu)< 0.63 eV (95% CL).Comment: Contribution to Proc. 4th Patras Workshop on Axions, WIMPs and WISPs
(18-21 June 2008, DESY
Cascades of Dynamical Transitions in an Adaptive Population
In an adaptive population which models financial markets and distributed
control, we consider how the dynamics depends on the diversity of the agents'
initial preferences of strategies. When the diversity decreases, more agents
tend to adapt their strategies together. This change in the environment results
in dynamical transitions from vanishing to non-vanishing step sizes. When the
diversity decreases further, we find a cascade of dynamical transitions for the
different signal dimensions, supported by good agreement between simulations
and theory. Besides, the signal of the largest step size at the steady state is
likely to be the initial signal.Comment: 4 pages, 8 figure
Observing trans-Planckian ripples in the primordial power spectrum with future large scale structure probes
We revisit the issue of ripples in the primordial power spectra caused by
trans-Planckian physics, and the potential for their detection by future
cosmological probes. We find that for reasonably large values of the first
slow-roll parameter epsilon (> 0.001), a positive detection of trans-Planckian
ripples can be made even if the amplitude is as low as 10^-4. Data from the
Large Synoptic Survey Telescope (LSST) and the proposed future 21 cm survey
with the Fast Fourier Transform Telescope (FFTT) will be particularly useful in
this regard. If the scale of inflation is close to its present upper bound, a
scale of new physics as high as 0.2 M_Planck could lead to observable
signatures.Comment: 20 pages, 3 figures, uses iopart.cls; v2: 21 pages, added references,
to appear in JCA
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