25,376 research outputs found
A distributed scheme to detect wormhole attacks in mobile wireless sensor networks
Due to mostly being unattended, sensor nodes become open to physical attacks such as wormhole attack, which is our focus in this paper. Various solutions are proposed for wormhole attacks in sensor networks, but only a few of them take mobility of sensor nodes into account. We propose a distributed wormhole detection scheme for mobile wireless sensor networks in which mobility of sensor nodes is utilized to estimate two network features (i.e. network node density, standard deviation in network node density) through using neighboring information in a local manner. Wormhole attack is detected via observing anomalies in the neighbor nodes’ behaviors based on the estimated network features and the neighboring information. We analyze the performance of proposed scheme via simulations. The results show that our scheme achieves a detection rate up to 100% with very small false positive rate (at most 1.5%) if the system parameters are chosen accordingly. Moreover, our solution requires neither additional hardware nor tight clock synchronization which are both costly for sensor networks
Indirect stabilization of weakly coupled systems with hybrid boundary conditions
We investigate stability properties of indirectly damped systems of evolution
equations in Hilbert spaces, under new compatibility assumptions. We prove
polynomial decay for the energy of solutions and optimize our results by
interpolation techniques, obtaining a full range of power-like decay rates. In
particular, we give explicit estimates with respect to the initial data. We
discuss several applications to hyperbolic systems with {\em hybrid} boundary
conditions, including the coupling of two wave equations subject to Dirichlet
and Robin type boundary conditions, respectively
A universal ribbon surface in B^4
We construct an orientable ribbon surface F in B^4, which is universal in the
following sense: any compact orientable pl 4-manifold having a handle
decomposition with 0-, 1- and 2-handles can be represented as a cover of B^4
branched over F.Comment: 19 pages, 28 figures, 28 references. LaTeX 2.09 file. Uses:
amstext.sty amscd.sty geom.sty epsf.st
Anticipation and the Non-linear Dynamics of Meaning-Processing in Social Systems
Social order does not exist as a stable phenomenon, but can be considered as
"an order of reproduced expectations." When anticipations operate upon one
another, they can generate a non-linear dynamics which processes meaning.
Although specific meanings can be stabilized, for example in social
institutions, all meaning arises from a global horizon of possible meanings.
Using Luhmann's (1984) social systems theory and Rosen's (1985) theory of
anticipatory systems, I submit algorithms for modeling the non-linear dynamics
of meaning in social systems. First, a self-referential system can use a model
of itself for the anticipation. Under the condition of functional
differentiation, the social system can be expected to entertain a set of
models; each model can also contain a model of the other models. Two
anticipatory mechanisms are then possible: a transversal one between the
models, and a longitudinal one providing the system with a variety of meanings.
A system containing two anticipatory mechanisms can become hyper-incursive.
Without making decisions, however, a hyper-incursive system would be overloaded
with uncertainty. Under this pressure, informed decisions tend to replace the
"natural preferences" of agents and a knowledge-based order can increasingly be
shaped
Representing Dehn twists with branched coverings
We show that any homologically non-trivial Dehn twist of a compact surface F
with boundary is the lifting of a half-twist in the braid group B_n, with
respect to a suitable branched covering p : F -> B^2. In particular, we allow
the surface to have disconnected boundary. As a consequence, any allowable
Lefschetz fibration on B^2 is a branched covering of B^2 x B^2.Comment: Major revision. It has been added Corollary 3 about the lifting
homomorphism. Are been added also some remarks and are given some other
definitions. There are now 19 figures and 23 page
Self Assembly of Soft Matter Quasicrystals and Their Approximants
The surprising recent discoveries of quasicrystals and their approximants in
soft matter systems poses the intriguing possibility that these structures can
be realized in a broad range of nano- and micro-scale assemblies. It has been
theorized that soft matter quasicrystals and approximants are largely
entropically stabilized, but the thermodynamic mechanism underlying their
formation remains elusive. Here, we use computer simulation and free energy
calculations to demonstrate a simple design heuristic for assembling
quasicrystals and approximants in soft matter systems. Our study builds on
previous simulation studies of the self-assembly of dodecagonal quasicrystals
and approximants in minimal systems of spherical particles with complex,
highly-specific interaction potentials. We demonstrate an alternative
entropy-based approach for assembling dodecagonal quasicrystals and
approximants based solely on particle functionalization and shape, thereby
recasting the interaction-potential-based assembly strategy in terms of
simpler-to-achieve bonded and excluded-volume interactions. Here, spherical
building blocks are functionalized with mobile surface entities to encourage
the formation of structures with low surface contact area, including
non-close-packed and polytetrahedral structures. The building blocks also
possess shape polydispersity, where a subset of the building blocks deviate
from the ideal spherical shape, discouraging the formation of close-packed
crystals. We show that three different model systems with both of these
features -- mobile surface entities and shape polydispersity -- consistently
assemble quasicrystals and/or approximants. We argue that this design strategy
can be widely exploited to assemble quasicrystals and approximants on the nano-
and micro- scales. In addition, our results further elucidate the formation of
soft matter quasicrystals in experiment.Comment: 12 pages 6 figure
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