569 research outputs found
Robust Distributed Routing in Dynamical Flow Networks - Part I: Locally Responsive Policies and Weak Resilience
Robustness of distributed routing policies is studied for dynamical flow
networks, with respect to adversarial disturbances that reduce the link flow
capacities. A dynamical flow network is modeled as a system of ordinary
differential equations derived from mass conservation laws on a directed
acyclic graph with a single origin-destination pair and a constant inflow at
the origin. Routing policies regulate the way the inflow at a non-destination
node gets split among its outgoing links as a function of the current particle
density, while the outflow of a link is modeled to depend on the current
particle density on that link through a flow function. The dynamical flow
network is called partially transferring if the total inflow at the destination
node is asymptotically bounded away from zero, and its weak resilience is
measured as the minimum sum of the link-wise magnitude of all disturbances that
make it not partially transferring. The weak resilience of a dynamical flow
network with arbitrary routing policy is shown to be upper-bounded by the
network's min-cut capacity, independently of the initial flow conditions.
Moreover, a class of distributed routing policies that rely exclusively on
local information on the particle densities, and are locally responsive to
that, is shown to yield such maximal weak resilience. These results imply that
locality constraints on the information available to the routing policies do
not cause loss of weak resilience. Some fundamental properties of dynamical
flow networks driven by locally responsive distributed policies are analyzed in
detail, including global convergence to a unique limit flow.Comment: 32 pages, 5 figures, journal submissio
Breaking of general rotational symmetries by multi-dimensional classical ratchets
We demonstrate that a particle driven by a set of spatially uncorrelated,
independent colored noise forces in a bounded, multidimensional potential
exhibits rotations that are independent of the initial conditions. We calculate
the particle currents in terms of the noise statistics and the potential
asymmetries by deriving an n-dimensional Fokker-Planck equation in the small
correlation time limit. We analyze a variety of flow patterns for various
potential structures, generating various combinations of laminar and rotational
flows.Comment: Accepted, Physical Review
Nucleon Charge and Magnetization Densities from Sachs Form Factors
Relativistic prescriptions relating Sachs form factors to nucleon charge and
magnetization densities are used to fit recent data for both the proton and the
neutron. The analysis uses expansions in complete radial bases to minimize
model dependence and to estimate the uncertainties in radial densities due to
limitation of the range of momentum transfer. We find that the charge
distribution for the proton is significantly broad than its magnetization
density and that the magnetization density is slightly broader for the neutron
than the proton. The neutron charge form factor is consistent with the Galster
parametrization over the available range of Q^2, but relativistic inversion
produces a softer radial density. Discrete ambiguities in the inversion method
are analyzed in detail. The method of Mitra and Kumari ensures compatibility
with pQCD and is most useful for extrapolating form factors to large Q^2.Comment: To appear in Phys. Rev. C. Two new figures and accompanying text have
been added and several discussions have been clarified with no significant
changes to the conclusions. Now contains 47 pages including 21 figures and 2
table
A two-parameter wind speed algorithm for Ku-band altimeters
Globally distributed crossovers of altimeter and scatterometer observations clearly demonstrate that ocean altimeter backscatter correlates with both the near-surface wind speed and the sea state. Satellite data from TOPEX/Poseidon and NSCAT are used to develop an empirical altimeter wind speed model that attenuates the sea-state signature and improves upon the present operational altimeter wind model. The inversion is defined using a multilayer perceptron neural network with altimeter-derived backscatter and significant wave height as inputs. Comparisons between this new model and past single input routines indicates that the rms wind error is reduced by 10%–15% in tandem with the lowering of wind error residuals dependent on the sea state. Both model intercomparison and validation of the new routine are detailed, including the use of large independent data compilations that include the SeaWinds and ERS scatterometers, ECMWF wind fields, and buoy measurements. The model provides consistent improvement against these varied sources with a wind-independent bias below 0.3 m s?1. The continuous form of the defined function, along with the global data used in its derivation, suggest an algorithm suitable for operational application to Ku-band altimeters. Further model improvement through wave height inclusion is limited due to an inherent multivaluedness between any single realization of the altimeter measurement pair [?o, HS] and observed near-surface winds. This ambiguity indicates that HS is a limited proxy for variable gravity wave properties that impact upon altimeter backscatter
Modulation instability induced by cross-phase modulation in a dual-wavelength dispersion-managed soliton fiber ring laser
We report on the observation of modulation instability induced by cross-phase
modulation in a dual-wavelength operation dispersion-managed soliton fiber ring
laser with net negative cavity dispersion. The passively mode-locked operation
is achieved by using nonlinear polarization rotation technique. A new type of
dual-wavelength operation, where one is femtosecond pulse and the other is
picosecond pulse operation, is obtained by properly rotating the polarization
controllers. When the dual-wavelength pulses are simultaneously circulating in
the laser ring cavity, a series of stable modulation sidebands appears in the
picosecond pulse spectrum at longer wavelength with lower peak power due to
modulation instability induced by cross-phase modulation between the two lasing
wavelengths. Moreover, the intensities and wavelength shifts of the modulation
sidebands can be tuned by varying the power of the femtosecond pulse or the
lasing central wavelengths of the dual-wavelength pulses. The theoretical
analysis of the modulation instability induced by cross-phase modulation in our
fiber laser is also presented.Comment: 26 pages, 10 figure
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Reply to: New Meta- and Mega-analyses of Magnetic Resonance Imaging Findings in Schizophrenia: Do They Really Increase Our Knowledge About the Nature of the Disease Process?
This work was supported by National Institute of Biomedical Imaging and Bioengineering Grant No. U54EB020403 (to the ENIGMA consortium)
Search for supersymmetry with a dominant R-parity violating LQDbar couplings in e+e- collisions at centre-of-mass energies of 130GeV to 172 GeV
A search for pair-production of supersymmetric particles under the assumption
that R-parity is violated via a dominant LQDbar coupling has been performed
using the data collected by ALEPH at centre-of-mass energies of 130-172 GeV.
The observed candidate events in the data are in agreement with the Standard
Model expectation. This result is translated into lower limits on the masses of
charginos, neutralinos, sleptons, sneutrinos and squarks. For instance, for
m_0=500 GeV/c^2 and tan(beta)=sqrt(2) charginos with masses smaller than 81
GeV/c^2 and neutralinos with masses smaller than 29 GeV/c^2 are excluded at the
95% confidence level for any generation structure of the LQDbar coupling.Comment: 32 pages, 30 figure
Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment
This paper describes an analysis of the angular distribution of W->enu and
W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with
the ATLAS detector at the LHC in 2010, corresponding to an integrated
luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and
the missing transverse energy, the W decay angular distribution projected onto
the transverse plane is obtained and analysed in terms of helicity fractions
f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV
and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw
> 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour,
are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017
+/- 0.030, where the first uncertainties are statistical, and the second
include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables,
revised author list, matches European Journal of Physics C versio
Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS
The chi_b(nP) quarkonium states are produced in proton-proton collisions at
the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS
detector. Using a data sample corresponding to an integrated luminosity of 4.4
fb^-1, these states are reconstructed through their radiative decays to
Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks
corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new
structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is
also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes.
This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table,
corrected author list, matches final version in Physical Review Letter
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