25,882 research outputs found
Dynamic weight parameter for the Random Early Detection (RED) in TCP networks
This paper presents the Weighted Random Early Detection (WTRED) strategy for congestion handling in TCP networks. WTRED provides an adjustable weight parameter to increase the sensitivity of the average queue size in RED gateways to the changes in the actual queue size. This modification, over the original RED proposal, helps gateways minimize the mismatch between average and actual queue sizes in router buffers. WTRED is compared with RED and FRED strategies using the NS-2 simulator. The results suggest that WTRED outperforms RED and FRED. Network performance has been measured using throughput, link utilization, packet loss and delay
A consistent design procedure for supercritical airfoils in free air and a wind tunnel
A computational inverse procedure for transonic airfoils in which shapes are determined supporting prescribed pressure distributions is presented. The method uses the small disturbance equation and a consistent analysis-design differencing procedure at the airfoil surface. This avoids the intermediate analysis-design-analysis iterations. The effect of any openness at the trailing edge is taken onto account by adding an effective source term in the far field. The final results from a systematic expansion procedure which models the far field for solid, ideal slotted, and free jet tunnel walls are presented along with some design results for the associated boundary conditions and those for a free flight
Observation of non-Markovian micro-mechanical Brownian motion
All physical systems are to some extent open and interacting with their
environment. This insight, basic as it may seem, gives rise to the necessity of
protecting quantum systems from decoherence in quantum technologies and is at
the heart of the emergence of classical properties in quantum physics. The
precise decoherence mechanisms, however, are often unknown for a given system.
In this work, we make use of an opto-mechanical resonator to obtain key
information about spectral densities of its condensed-matter heat bath. In
sharp contrast to what is commonly assumed in high-temperature quantum Brownian
motion describing the dynamics of the mechanical degree of freedom, based on a
statistical analysis of the emitted light, it is shown that this spectral
density is highly non-Ohmic, reflected by non-Markovian dynamics, which we
quantify. We conclude by elaborating on further applications of opto-mechanical
systems in open system identification.Comment: 5+6 pages, 3 figures. Replaced by final versio
Measuring the galaxy power spectrum and scale-scale correlations with multiresolution-decomposed covariance -- I. method
We present a method of measuring galaxy power spectrum based on the
multiresolution analysis of the discrete wavelet transformation (DWT). Since
the DWT representation has strong capability of suppressing the off-diagonal
components of the covariance for selfsimilar clustering, the DWT covariance for
popular models of the cold dark matter cosmogony generally is diagonal, or
(scale)-diagonal in the scale range, in which the second scale-scale
correlations are weak. In this range, the DWT covariance gives a lossless
estimation of the power spectrum, which is equal to the corresponding Fourier
power spectrum banded with a logarithmical scaling. In the scale range, in
which the scale-scale correlation is significant, the accuracy of a power
spectrum detection depends on the scale-scale or band-band correlations. This
is, for a precision measurements of the power spectrum, a measurement of the
scale-scale or band-band correlations is needed. We show that the DWT
covariance can be employed to measuring both the band-power spectrum and second
order scale-scale correlation. We also present the DWT algorithm of the binning
and Poisson sampling with real observational data. We show that the alias
effect appeared in usual binning schemes can exactly be eliminated by the DWT
binning. Since Poisson process possesses diagonal covariance in the DWT
representation, the Poisson sampling and selection effects on the power
spectrum and second order scale-scale correlation detection are suppressed into
minimum. Moreover, the effect of the non-Gaussian features of the Poisson
sampling can be calculated in this frame.Comment: AAS Latex file, 44 pages, accepted for publication in Ap
Unusually Large Fluctuations in the Statistics of Galaxy Formation at High Redshift
We show that various milestones of high-redshift galaxy formation, such as
the formation of the first stars or the complete reionization of the
intergalactic medium, occurred at different times in different regions of the
universe. The predicted spread in redshift, caused by large-scale fluctuations
in the number density of galaxies, is at least an order of magnitude larger
than previous expectations that argued for a sharp end to reionization. This
cosmic scatter in the abundance of galaxies introduces new features that affect
the nature of reionization and the expectations for future probes of
reionization, and may help explain the present properties of dwarf galaxies in
different environments. The predictions can be tested by future numerical
simulations and may be verified by upcoming observations. Current simulations,
limited to relatively small volumes and periodic boundary conditions, largely
omit cosmic scatter and its consequences. In particular, they artificially
produce a sudden end to reionization, and they underestimate the number of
galaxies by up to an order of magnitude at redshift 20.Comment: 8 ApJ pages, 4 figures, ApJ. Minor changes in revised version.
Originally first submitted for publication on Aug. 29, 200
Instanton Theory of Burgers Shocks and Intermittency
A lagrangian approach to Burgers turbulence is carried out along the lines of
the field theoretical Martin-Siggia-Rose formalism of stochastic hydrodynamics.
We derive, from an analysis based on the hypothesis of unbroken galilean
invariance, the asymptotic form of the probability distribution function of
negative velocity-differences. The origin of Burgers intermittency is found to
rely on the dynamical coupling between shocks, identified to instantons, and
non-coherent background fluctuations, which, then, cannot be discarded in a
consistent statistical description of the flow.Comment: 7 pages; LaTe
Beyond capitalism and liberal democracy: on the relevance of GDH Cole’s sociological critique and alternative
This article argues for a return to the social thought of the often ignored early 20th-century English thinker GDH Cole. The authors contend that Cole combined a sociological critique of capitalism and liberal democracy with a well-developed alternative in his work on guild socialism bearing particular relevance to advanced capitalist societies. Both of these, with their focus on the limitations on ‘free communal service’ in associations and the inability of capitalism to yield emancipation in either production or consumption, are relevant to social theorists looking to understand, critique and contribute to the subversion of neoliberalism. Therefore, the authors suggest that Cole’s associational sociology, and the invitation it provides to think of formations beyond capitalism and liberal democracy, is a timely and valuable resource which should be returned to
Electrostatic considerations affecting the calculated HOMO-LUMO gap in protein molecules.
A detailed study of energy differences between the highest occupied and
lowest unoccupied molecular orbitals (HOMO-LUMO gaps) in protein systems and
water clusters is presented. Recent work questioning the applicability of
Kohn-Sham density-functional theory to proteins and large water clusters (E.
Rudberg, J. Phys.: Condens. Mat. 2012, 24, 072202) has demonstrated vanishing
HOMO-LUMO gaps for these systems, which is generally attributed to the
treatment of exchange in the functional used. The present work shows that the
vanishing gap is, in fact, an electrostatic artefact of the method used to
prepare the system. Practical solutions for ensuring the gap is maintained when
the system size is increased are demonstrated. This work has important
implications for the use of large-scale density-functional theory in
biomolecular systems, particularly in the simulation of photoemission, optical
absorption and electronic transport, all of which depend critically on
differences between energies of molecular orbitals.Comment: 13 pages, 4 figure
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