929 research outputs found
Coverage and Connectivity in Three-Dimensional Networks
Most wireless terrestrial networks are designed based on the assumption that
the nodes are deployed on a two-dimensional (2D) plane. However, this 2D
assumption is not valid in underwater, atmospheric, or space communications. In
fact, recent interest in underwater acoustic ad hoc and sensor networks hints
at the need to understand how to design networks in 3D. Unfortunately, the
design of 3D networks is surprisingly more difficult than the design of 2D
networks. For example, proofs of Kelvin's conjecture and Kepler's conjecture
required centuries of research to achieve breakthroughs, whereas their 2D
counterparts are trivial to solve. In this paper, we consider the coverage and
connectivity issues of 3D networks, where the goal is to find a node placement
strategy with 100% sensing coverage of a 3D space, while minimizing the number
of nodes required for surveillance. Our results indicate that the use of the
Voronoi tessellation of 3D space to create truncated octahedral cells results
in the best strategy. In this truncated octahedron placement strategy, the
transmission range must be at least 1.7889 times the sensing range in order to
maintain connectivity among nodes. If the transmission range is between 1.4142
and 1.7889 times the sensing range, then a hexagonal prism placement strategy
or a rhombic dodecahedron placement strategy should be used. Although the
required number of nodes in the hexagonal prism and the rhombic dodecahedron
placement strategies is the same, this number is 43.25% higher than the number
of nodes required by the truncated octahedron placement strategy. We verify by
simulation that our placement strategies indeed guarantee ubiquitous coverage.
We believe that our approach and our results presented in this paper could be
used for extending the processes of 2D network design to 3D networks.Comment: To appear in ACM Mobicom 200
Analysis of roles and groups in blogosphere
In the paper different roles of users in social media, taking into
consideration their strength of influence and different degrees of
cooperativeness, are introduced. Such identified roles are used for the
analysis of characteristics of groups of strongly connected entities. The
different classes of groups, considering the distribution of roles of users
belonging to them, are presented and discussed.Comment: 8th International Conference on Computer Recognition Systems, CORES
201
Multicomponent ceramic materials on the basis of PZT for the production of piezoelectric resonators
Investigations on the influence of the PbTiO3 content on the crystalline and domain structure of PZT-based four-component solid solutions have been performed. It has been shown that there is a close relation between the structure and temperature stability of the resonance frequency (fr) of the fabricated piezoceramic transducers. Better and more stable results have been obtained by doping and modifying the basic chemical composition obtaining Pb(Zr1¡xTix)O3. The compositions with minimal ¢fr=fr, within the temperature range T = 213–358 K (in relation to room temperature Tr = 293 K), exhibited (i) the smallest internal friction
(Q¡1 m ), (ii) the highest mechanical quality (Qm), (iii) high values of spontaneous deformation
of the elementary cell (±T and ±Re), (iv) the complex a-c-domain structure in the tetragonal
phase (T) and the simple domain structure in the rhombohedral phase (Re).
The practical result of the present work was the fabrication of piezoceramic electric band
filters exhibiting ¢fr=fr < 0:2% and a high mechanical quality factor (Qm = 3225)
DNA polymorphism analysis of Brucella lipopolysaccharide genes reveals marked differences in O-polysaccharide biosynthetic genes between smooth and rough Brucella species and novel species-specific markers
Background: The lipopolysaccharide is a major antigen and virulence factor of Brucella, an important bacterial pathogen. In smooth brucellae, lipopolysaccharide is made of lipid A-core oligosaccharide and N-formylperosamine O-polysaccharide. B. ovis and B. canis (rough species) lack the O-polysaccharide. Results: The polymorphism of O-polysaccharide genes wbkE, manA(O-Ag), manB(O-Ag), manC(O-Ag), wbkF and wbkD) and wbo (wboA and wboB), and core genes manB(core) and wa** was analyzed. Although most genes were highly conserved, species- and biovar-specific restriction patterns were found. There were no significant differences in putative N-formylperosamyl transferase genes, suggesting that Brucella A and M serotypes are not related to specific genes. In B. pinnipedialis and B. ceti (both smooth), manB(O-Ag) carried an IS711, confirming its dispensability for perosamine synthesis. Significant differences between smooth and rough species were found in wbkF and wbkD, two adjacent genes putatively related to bactoprenol priming for O-polysaccharide polymerization. B. ovis wbkF carried a frame-shift and B. canis had a long deletion partially encompassing both genes. In smooth brucellae, this region contains two direct repeats suggesting the deletion mechanism. Conclusion: The results define species and biovar markers, confirm the dispensability of manB(O-Ag) for O-polysaccharide synthesis and contribute to explain the lipopolysaccharide structure of rough and smooth Brucella species
The effects of growth hormone therapy on the somatic development of a group of Polish children with Silver-Russell syndrome
Spontaneous polarisation of the neutral interface for valence asymmetric coulombic systems
In this paper, we discuss the phenomenon of a spontaneous polarisation of a
neutral hard planar interface for valence asymmetric coulombic systems. Within
a field theoretical description, we account for the existence of non trivial
charge density and electric potential profiles. The analysis of the phenomenon
shows that the effect is related to combinatorics in relation with the
existence of the two independent species cations and anions. This simple and
basic feature is related to the quantum mechanical properties of the system.
The theoretical results are compared with numerical simulations data and are
shown to be in very good agreement, which a fortiori justifies our physical
interpretation.Comment: 12 pages, 11 figure
Cosmological vacuum selection and metastable susy breaking
We study gauge mediation in a wide class of O'Raifeartaigh type models where
supersymmetry breaking metastable vacuum is created by gravity and/or quantum
corrections. We examine their thermal evolution in the early universe and the
conditions under which the susy breaking vacuum can be selected. It is
demonstrated that thermalization typically makes the metastable supersymmetry
breaking cosmologically disfavoured but this is not always the case. Initial
conditions with the spurion displaced from the symmetric thermal minimum and a
small coupling to the messenger sector can result in the realization of the
susy breaking vacuum even if the reheating temperature is high. We show that
this can be achieved without jeopardizing the low energy phenomenology. In
addition, we have found that deforming the models by a supersymmetric mass term
for messengers in such a way that the susy breaking minimum and the susy
preserving minima are all far away from the origin does not change the
conclusions. The basic observations are expected to hold also in the case of
models with an anomalous U(1) group.Comment: 28 pages, 4 figures, plain Latex, journal versio
Beyond MFV in family symmetry theories of fermion masses
Minimal Flavour Violation (MFV) postulates that the only source of flavour
changing neutral currents and CP violation, as in the Standard Model, is the
CKM matrix. However it does not address the origin of fermion masses and mixing
and models that do usually have a structure that goes well beyond the MFV
framework. In this paper we compare the MFV predictions with those obtained in
models based on spontaneously broken (horizontal) family symmetries, both
Abelian and non-Abelian. The generic suppression of flavour changing processes
in these models turns out to be weaker than in the MFV hypothesis. Despite
this, in the supersymmetric case, the suppression may still be consistent with
a solution to the hierarchy problem, with masses of superpartners below 1 TeV.
A comparison of FCNC and CP violation in processes involving a variety of
different family quantum numbers should be able to distinguish between various
family symmetry models and models satisfying the MFV hypothesis.Comment: 34 pages, no figure
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