62,419 research outputs found
An adaptive directed query dissemination scheme for wireless sensor networks
This paper describes a directed query dissemination scheme, DirQ that routes queries to the appropriate source nodes based on both constant and dynamic-valued attributes such as sensor types and sensor values. Unlike certain other query dissemination schemes, location information is not essential for the operation of DirQ. DirQ uses only locally available information in order to route queries accurately. Nodes running DirQ are able to adapt autonomously to changes in network topology due to certain cross-layer features that allow it to exchange information with the underlying MAC protocol. DirQ allows nodes to autonomously control the rate of sending update messages in order to keep the routing information updated. The rate of sending updates is dependent on both the number of queries injected into the network and the rate of variation of the measured physical parameter. Our results show that DirQ spends between 45% and 55% the cost of flooding
Epidemic processes in complex networks
In recent years the research community has accumulated overwhelming evidence
for the emergence of complex and heterogeneous connectivity patterns in a wide
range of biological and sociotechnical systems. The complex properties of
real-world networks have a profound impact on the behavior of equilibrium and
nonequilibrium phenomena occurring in various systems, and the study of
epidemic spreading is central to our understanding of the unfolding of
dynamical processes in complex networks. The theoretical analysis of epidemic
spreading in heterogeneous networks requires the development of novel
analytical frameworks, and it has produced results of conceptual and practical
relevance. A coherent and comprehensive review of the vast research activity
concerning epidemic processes is presented, detailing the successful
theoretical approaches as well as making their limits and assumptions clear.
Physicists, mathematicians, epidemiologists, computer, and social scientists
share a common interest in studying epidemic spreading and rely on similar
models for the description of the diffusion of pathogens, knowledge, and
innovation. For this reason, while focusing on the main results and the
paradigmatic models in infectious disease modeling, the major results
concerning generalized social contagion processes are also presented. Finally,
the research activity at the forefront in the study of epidemic spreading in
coevolving, coupled, and time-varying networks is reported.Comment: 62 pages, 15 figures, final versio
Survey on Data-Centric based Routing Protocols for Wireless Sensor Networks
The great concern for energy that grew with the technological advances in the
field of networks and especially in sensor network has triggered various
approaches and protocols that relate to sensor networks. In this context, the
routing protocols were of great interest. The aim of the present paper is to
discuss routing protocols for sensor networks. This paper will focus mainly on
the discussion of the data-centric approach (COUGAR, rumor, SPIN, flooding and
Gossiping), while shedding light on the other approaches occasionally. The
functions of the nodes will be discussed as well. The methodology selected for
this paper is based on a close description and discussion of the protocol. As a
conclusion, open research questions and limitations are proposed to the reader
at the end of this paper
Active-to-absorbing state phase transition in the presence of fluctuating environments: Weak and strong dynamic scaling
We investigate the scaling properties of phase transitions between survival
and extinction (active-to-absorbing state phase transition, AAPT) in a model,
that by itself belongs to the directed percolation (DP) universality class,
interacting with a spatio-temporally fluctuating environment having its own
non-trivial dynamics. We model the environment by (i) a randomly stirred fluid,
governed by the Navier-Stokes (NS) equation, and (ii) a fluctuating surface,
described either by the Kardar-Parisi-Zhang (KPZ) or the Edward-Wilkinson (EW)
equations. We show, by using a one-loop perturbative field theoretic set up,
that depending upon the spatial scaling of the variance of the external forces
that drive the environment (i.e., the NS, KPZ or EW equations), the system may
show {\em weak} or {\em strong dynamic scaling} at the critical point of active
to absorbing state phase transitions. In the former case AAPT displays scaling
belonging to the DP universality class, whereas in the latter case the
universal behavior is different.Comment: 17 pages, 2 figures, accepted in PR
Giant Coulomb broadening and Raman lasing on ionic transitions
CW generation of anti-Stokes Raman laser on a number of blue-green argon-ion
lines (4p-4s, 4p-3d) has been demonstrated with optical pumping from metastable
levels 3d'^2G, 3d^4F. It is found, that the population transfer rate is
increased by a factor of 3-5 (and hence, the output power of such Raman laser)
owing to Coulomb diffusion in the velocity space. Measured are the excitation
and relaxation rates for the metastable level. The Bennett hole on the
metastable level has been recorded using the probe field technique. It has been
shown that the Coulomb diffusion changes shape of the contour to exponential
cusp profile while its width becomes 100 times the Lorentzian one and reaches
values close to the Doppler width. Such a giant broadening is also confirmed by
the shape of the absorption saturation curve.Comment: RevTex 18 pages, 5 figure
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