4,935 research outputs found
A New Scheme for Minimizing Malicious Behavior of Mobile Nodes in Mobile Ad Hoc Networks
The performance of Mobile Ad hoc networks (MANET) depends on the cooperation
of all active nodes. However, supporting a MANET is a cost-intensive activity
for a mobile node. From a single mobile node perspective, the detection of
routes as well as forwarding packets consume local CPU time, memory,
network-bandwidth, and last but not least energy. We believe that this is one
of the main factors that strongly motivate a mobile node to deny packet
forwarding for others, while at the same time use their services to deliver its
own data. This behavior of an independent mobile node is commonly known as
misbehaving or selfishness. A vast amount of research has already been done for
minimizing malicious behavior of mobile nodes. However, most of them focused on
the methods/techniques/algorithms to remove such nodes from the MANET. We
believe that the frequent elimination of such miss-behaving nodes never allowed
a free and faster growth of MANET. This paper provides a critical analysis of
the recent research wok and its impact on the overall performance of a MANET.
In this paper, we clarify some of the misconceptions in the understating of
selfishness and miss-behavior of nodes. Moreover, we propose a mathematical
model that based on the time division technique to minimize the malicious
behavior of mobile nodes by avoiding unnecessary elimination of bad nodes. Our
proposed approach not only improves the resource sharing but also creates a
consistent trust and cooperation (CTC) environment among the mobile nodes. The
simulation results demonstrate the success of the proposed approach that
significantly minimizes the malicious nodes and consequently maximizes the
overall throughput of MANET than other well known schemes.Comment: 10 pages IEEE format, International Journal of Computer Science and
Information Security, IJCSIS July 2009, ISSN 1947 5500, Impact Factor 0.42
Multiscale turbulence effects in supersonic jets exhausting into still air
A modified version of the multiscale turbulence model of Hanjalic has been applied to the problem of supersonic jets exhausting into still air. In particular, the problem of shock-cell decay through turbulent interaction with the mixing layer has been studied for both mildly interacting and strongly resonant jet conditions. The modified Hanjalic model takes into account the nonequilibrium energy transfer between two different turbulent spectral scales. The turbulence model was incorporated into an existing shock-capturing, parabolized Navier-Stokes computational model in order to perform numerical experiments. The results show that the two-scale turbulence model provides significant improvement over one-scale models in the prediction of plume shock structure for underexpanded supersonic (Mach 2) and sonic (Mach 1) jets. For the supersonic jet, excellent agreement with experiment was obtained for the centerline shock-cell pressure decay up to 40 jet radii. For the sonic jet, the agreement with experiment was not so good, but the two-scale model still showed significant improvement over the one-scale model. It is shown that by relating some of the coefficients in the turbulent-transport equations to the relative time scale for transfer of energy between scales the two-scale model can provide predictions that bound the measured shock-cell decay rate for the sonic jet
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