12,755 research outputs found
Poor Man's Content Centric Networking (with TCP)
A number of different architectures have been proposed in support of data-oriented or information-centric networking. Besides a similar visions, they share the need for designing a new networking architecture. We present an incrementally deployable approach to content-centric networking based upon TCP. Content-aware senders cooperate with probabilistically operating routers for scalable content delivery (to unmodified clients), effectively supporting opportunistic caching for time-shifted access as well as de-facto synchronous multicast delivery. Our approach is application protocol-independent and provides support beyond HTTP caching or managed CDNs. We present our protocol design along with a Linux-based implementation and some initial feasibility checks
Multifractal clustering of passive tracers on a surface flow
We study the anomalous scaling of the mass density measure of Lagrangian
tracers in a compressible flow realized on the free surface on top of a three
dimensional flow. The full two dimensional probability distribution of local
stretching rates is measured. The intermittency exponents which quantify the
fluctuations of the mass measure of tracers at small scales are calculated from
the large deviation form of stretching rate fluctuations. The results indicate
the existence of a critical exponent above which exponents
saturate, in agreement with what has been predicted by an analytically solvable
model. Direct evaluation of the multi-fractal dimensions by reconstructing the
coarse-grained particle density supports the results for low order moments.Comment: 7 pages, 4 figures, submitted to EP
Extending holographic LEED to ordered small unit cell superstructures
Following on the success of the recent application of holographic LEED to the
determination of the 3D atomic geometry of Si adatoms on a SiC(111) p(3x3)
surface, which enabled that structure to be solved, we show in this paper that
a similar technique allows the direct recovery of the local geometry of
adsorbates forming superstructures as small as p(2x2), even in the presence of
a local substrate reconstruction.Comment: 10 pages, 5 figures postscript included, revtex, Phys. Rev. B in
pres
Direct observation of impurity-induced magnetism in an S = 1/2 antiferromagnetic Heisenberg 2-leg spin ladder
Nuclear magnetic resonance and magnetization measurements were used to probe
the magnetic features of single-crystalline Bi(Cu(1-x)Znx)2PO6 with 0<x<0.05 at
temperatures between 2.6 K and 300 K. The simple lineshape of the 31P NMR
signals of the pristine compound changes considerably for x>0 and we present
clear evidence for a temperature dependent variation of the local magnetization
close to the Zn sites. The generic nature of this observation is indicated by
results of model calculations on appropriate spin systems of limited size
employing QMC methods.Comment: 4 pages, 4 figure
The Influence of Thermal Pressure on Equilibrium Models of Hypermassive Neutron Star Merger Remnants
The merger of two neutron stars leaves behind a rapidly spinning hypermassive
object whose survival is believed to depend on the maximum mass supported by
the nuclear equation of state, angular momentum redistribution by
(magneto-)rotational instabilities, and spindown by gravitational waves. The
high temperatures (~5-40 MeV) prevailing in the merger remnant may provide
thermal pressure support that could increase its maximum mass and, thus, its
life on a neutrino-cooling timescale. We investigate the role of thermal
pressure support in hypermassive merger remnants by computing sequences of
spherically-symmetric and axisymmetric uniformly and differentially rotating
equilibrium solutions to the general-relativistic stellar structure equations.
Using a set of finite-temperature nuclear equations of state, we find that hot
maximum-mass critically spinning configurations generally do not support larger
baryonic masses than their cold counterparts. However, subcritically spinning
configurations with mean density of less than a few times nuclear saturation
density yield a significantly thermally enhanced mass. Even without decreasing
the maximum mass, cooling and other forms of energy loss can drive the remnant
to an unstable state. We infer secular instability by identifying approximate
energy turning points in equilibrium sequences of constant baryonic mass
parametrized by maximum density. Energy loss carries the remnant along the
direction of decreasing gravitational mass and higher density until instability
triggers collapse. Since configurations with more thermal pressure support are
less compact and thus begin their evolution at a lower maximum density, they
remain stable for longer periods after merger.Comment: 20 pages, 12 figures. Accepted for publication in Ap
Chaos in a modified Henon-Heiles system describing geodesics in gravitational waves
A Hamiltonian system with a modified Henon-Heiles potential is investigated.
This describes the motion of free test particles in vacuum gravitational
pp-wave spacetimes with both quadratic ("homogeneous") and cubic
("non-homogeneous") terms in the structural function. It is shown that, for
energies above a certain value, the motion is chaotic in the sense that the
boundaries separating the basins of possible escapes become fractal.
Similarities and differences with the standard Henon-Heiles and the monkey
saddle systems are discussed. The box-counting dimension of the basin
boundaries is also calculated.Comment: 11 pages, 7 figures, LaTeX. To appear in Phys. Lett.
Dynamical trapping and chaotic scattering of the harmonically driven barrier
A detailed analysis of the classical nonlinear dynamics of a single driven
square potential barrier with harmonically oscillating position is performed.
The system exhibits dynamical trapping which is associated with the existence
of a stable island in phase space. Due to the unstable periodic orbits of the
KAM-structure, the driven barrier is a chaotic scatterer and shows stickiness
of scattering trajectories in the vicinity of the stable island. The
transmission function of a suitably prepared ensemble yields results which are
very similar to tunneling resonances in the quantum mechanical regime. However,
the origin of these resonances is different in the classical regime.Comment: 14 page
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