5,223 research outputs found
Computing NodeTrix Representations of Clustered Graphs
NodeTrix representations are a popular way to visualize clustered graphs;
they represent clusters as adjacency matrices and inter-cluster edges as curves
connecting the matrix boundaries. We study the complexity of constructing
NodeTrix representations focusing on planarity testing problems, and we show
several NP-completeness results and some polynomial-time algorithms. Building
on such algorithms we develop a JavaScript library for NodeTrix representations
aimed at reducing the crossings between edges incident to the same matrix.Comment: Appears in the Proceedings of the 24th International Symposium on
Graph Drawing and Network Visualization (GD 2016
High Frequency dynamics in metallic glasses
Using Inelastic X-ray Scattering we studied the collective dynamics of the
glassy alloy NiZr in the first pseudo Brillouin zone, an
energy-momentum region still unexplored in metallic glasses. We determine key
properties such as the momentum transfer dependence of the sound velocity and
of the acoustic damping, discussing the results in the general context of
recently proposed pictures for acoustic dynamics in glasses. Specifically, we
demonstrate the existence in this strong glass of well defined (in the Ioffe
Regel sense) acoustic-like excitations well above the Boson Peak energy.Comment: 4 pages, 4 .eps figures, accepted in Phys. Rev. Let
Il corpo nelle diverse culture e tradizioni religiose
Conoscere e comprendere il senso della pratica delle Mutilazioni Genitali Femminili (MGF) attraverso il coinvolgimento delle comunità religiose e dei suoi rappresentanti per meglio contrastare tale fenomeno, richiede il contatto e l’ascolto a riguardo di religiosi e capi comunità rappresentanti delle comunità religiose presenti sul territorio. Al fine di acquisire elementi di base della relazione corpo-religione nelle religioni maggiormente rappresentate tra le comunità straniere
Simultaneous Orthogonal Planarity
We introduce and study the problem: Given planar
graphs each with maximum degree 4 and the same vertex set, do they admit an
OrthoSEFE, that is, is there an assignment of the vertices to grid points and
of the edges to paths on the grid such that the same edges in distinct graphs
are assigned the same path and such that the assignment induces a planar
orthogonal drawing of each of the graphs?
We show that the problem is NP-complete for even if the shared
graph is a Hamiltonian cycle and has sunflower intersection and for
even if the shared graph consists of a cycle and of isolated vertices. Whereas
the problem is polynomial-time solvable for when the union graph has
maximum degree five and the shared graph is biconnected. Further, when the
shared graph is biconnected and has sunflower intersection, we show that every
positive instance has an OrthoSEFE with at most three bends per edge.Comment: Appears in the Proceedings of the 24th International Symposium on
Graph Drawing and Network Visualization (GD 2016
Competing interactions in arrested states of colloidal clays
Using experiments, theory and simulations, we show that the arrested state
observed in a colloidal clay at intermediate concentrations is stabilized by
the screened Coulomb repulsion (Wigner glass). Dilution experiments allow us to
distinguish this high-concentration disconnected state, which melts upon
addition of water, from a low-concentration gel state, which does not melt.
Theoretical modelling and simulations reproduce the measured Small Angle X-Ray
Scattering static structure factors and confirm the long-range electrostatic
nature of the arrested structure. These findings are attributed to the
different timescales controlling the competing attractive and repulsive
interactions.Comment: Accepted for publication in Physical Review Letter
Arrested state of clay-water suspensions: gel or glass?
The aging of a charged colloidal system has been studied by Small Angle
X-rays Scattering, in the exchanged momentum range Q=0.03 - 5 nm-1, and by
Dynamic Light Scattering, at different clay concentrations (Cw =0.6 % - 2.8 %).
The static structure factor, S(Q), has been determined as a function of both
aging time and concentration. This is the first direct experimental evidence of
the existence and evolution with aging time of two different arrested states in
a single system simply obtained only by changing its volume fraction: an
inhomogeneous state is reached at low concentrations, while a homogenous one is
found at high concentrations.Comment: 5 pages, 2 figure
Ordered Level Planarity, Geodesic Planarity and Bi-Monotonicity
We introduce and study the problem Ordered Level Planarity which asks for a
planar drawing of a graph such that vertices are placed at prescribed positions
in the plane and such that every edge is realized as a y-monotone curve. This
can be interpreted as a variant of Level Planarity in which the vertices on
each level appear in a prescribed total order. We establish a complexity
dichotomy with respect to both the maximum degree and the level-width, that is,
the maximum number of vertices that share a level. Our study of Ordered Level
Planarity is motivated by connections to several other graph drawing problems.
Geodesic Planarity asks for a planar drawing of a graph such that vertices
are placed at prescribed positions in the plane and such that every edge is
realized as a polygonal path composed of line segments with two adjacent
directions from a given set of directions symmetric with respect to the
origin. Our results on Ordered Level Planarity imply -hardness for any
with even if the given graph is a matching. Katz, Krug, Rutter and
Wolff claimed that for matchings Manhattan Geodesic Planarity, the case where
contains precisely the horizontal and vertical directions, can be solved in
polynomial time [GD'09]. Our results imply that this is incorrect unless
. Our reduction extends to settle the complexity of the Bi-Monotonicity
problem, which was proposed by Fulek, Pelsmajer, Schaefer and
\v{S}tefankovi\v{c}.
Ordered Level Planarity turns out to be a special case of T-Level Planarity,
Clustered Level Planarity and Constrained Level Planarity. Thus, our results
strengthen previous hardness results. In particular, our reduction to Clustered
Level Planarity generates instances with only two non-trivial clusters. This
answers a question posed by Angelini, Da Lozzo, Di Battista, Frati and Roselli.Comment: Appears in the Proceedings of the 25th International Symposium on
Graph Drawing and Network Visualization (GD 2017
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