360 research outputs found
Simulation technique for available bandwidth estimation
The paper proposes a method for measuring available bandwidth, based on
testing network packets of various sizes (Variable Packet Size method, VPS).
The boundaries of applicability of the model have been found, which are based
on the accuracy of measurements of packet delays, also we have derived a
formula of measuring the upper limit of bandwidth. The computer simulation has
been performed and relationship between the measurement error of available
bandwidth and the number of measurements has been found. Experimental
verification with the use of RIPE Test Box measuring system has shown that the
suggested method has advantages over existing measurement techniques. Pathload
utility has been chosen as an alternative technique of measurement, and to
ensure reliable results statistics by SNMP agent has been withdrawn directly
from the router
Variation principle and the universal metric of dynamic routing
In this paper the variation principles from theoretical physics is considered
that would describe the process of routing in computer networks. The total
traffic which is currently served on all hops of the route has been chosen as
the quantity to minimize. Universal metric function has been found for dynamic
routing taking into account the packet loss effect. An attempt to derive the
metric of the most popular dynamic routing protocols such as RIP, OSPF, EIGRP
from universal metric was made.Comment: 4 pages, 3 figures, 14 equation
Influence of distortions of key frames on video transfer in wireless networks
In this paper it is shown that for substantial increase of video quality in
wireless network it is necessary to execute two obligatory points on
modernization of the communication scheme. The player on the received part
should throw back automatically duplicated RTP packets, server of streaming
video should duplicate the packets containing the information of key frames.
Coefficients of the mathematical model describing video quality in wireless
network have been found for WiFi and 3G standards and codecs MPEG-2 and MPEG-4
(DivX). The special experimental technique which has allowed collecting and
processing the data has been developed for calculation of values of factors.Comment: 6 pages, 4 figures, 2 Table
Coercivity reduction in a two-dimensional array of nanoparticles
We report on theoretical investigation of the magnetization reversal in
two-dimensional arrays of ferromagnetic nano-particles with parameters of
cobalt. The system was optimized for achieving the lowest coercivity in an
array of particles located in the nodes of triangular, hexagonal and square
grids. Based on the numerical solution of the non-stochastic
Landau-Lifshitz-Gilbert equation we show that each particle distribution type
is characterized with a proper optimal distance, allowing to lower the
coercivity values for approximately 30% compared with the reference value
obtained for a single nano-particle. It was shown that the reduction of
coercivity occurs even if the particle position in the array is not very
precise. In particular, the triangular particle arrangement maintained the same
optimal distance between the particles under up to 20% random displacements of
their position within the array.Comment: 7 pages, 5 figure
Magnetophononics: ultrafast spin control through the lattice
Using a combination of first-principles and magnetization-dynamics
calculations, we study the effect of the intense optical excitation of phonons
on the magnetic behavior in insulating magnetic materials. Taking the
prototypical magnetoelectric \CrO\ as our model system, we show that excitation
of a polar mode at 17 THz causes a pronounced modification of the magnetic
exchange interactions through a change in the average Cr-Cr distance. In
particular, the quasi-static deformation induced by nonlinear phononic coupling
yields a structure with a modified magnetic state, which persists for the
duration of the phonon excitation. In addition, our time-dependent
magnetization dynamics computations show that systematic modulation of the
magnetic exchange interaction by the phonon excitation modifies the
magnetization dynamics. This temporal modulation of the magnetic exchange
interaction strengths using phonons provides a new route to creating
non-equilibrium magnetic states and suggests new avenues for fast manipulation
of spin arrangements and dynamics.Comment: 11 pages with 7 figure
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