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ME Design and Freeform Fabrication of Compliant Cellular Materials with Graded Stiffness
Typically, cellular materials are designed for structural applications to provide stiffness or
absorb impact via permanent plastic deformation. Alternatively, it is possible to design compliant
cellular materials that absorb energy via recoverable elastic deformation, allowing the material to
spring back to its original configuration after the load is released. Potential applications include
automotive panels or prosthetic applications that require repeated, low-speed impact absorption
without permanent deformation. The key is to arrange solid base material in cellular topologies
that permit high levels of elastic deformation. To prevent plastic deformation, the topologies are
designed for contact between cell walls at predetermined load levels, resulting in customized,
graded stiffness profiles. Design techniques are established for synthesizing cellular topologies
with customized compliance for static or quasi-static applications. The design techniques
account for cell wall contact, large scale deformations, and material nonlinearities. Resulting
cellular material designs are fabricated with selective laser sintering, and their properties are
experimentally evaluated.Mechanical Engineerin
Design, fabrication, and characterization of deep-etched waveguide gratings
One-dimensional (1-D) deep-etched gratings on a specially grown AlGaAs wafer were designed and fabricated. The gratings were fabricated using state-of-the-art electron beam lithography and high-aspect-ratio reactive ion etching (RIE) in order to achieve the required narrow deep air slots with good accuracy and reproducibility. Since remarkable etch depths (up to 1.5 /spl mu/m), which completely cut through the waveguide core layer, have been attained, gratings composed of only five periods (and, thus, shorter than 6 /spl mu/m) have a bandgap larger than 100 nm. A defect was introduced by increasing the width of the central semiconductor tooth to create microcavities that exhibit a narrow transmission peak (less than 7 nm) around the wavelength of 1530 nm. The transmission spectra between 1460 and 1580 nm have been systematically measured, and the losses have been estimated for a set of gratings, both with and without a defect, for different periods and air slot dimensions. Numerical results obtained via a bidirectional beam propagation code allowed the evaluation of transmissivity, reflectivity, and diffraction losses. By comparing experimental results with the authors' numerical findings, a clear picture of the role of the grating's geometric parameters in determining its spectral features and diffractive losses is illustrated
OWA-based fuzzy m-ary adjacency relations in Social Network Analysis.
In this paper we propose an approach to Social Network Analysis (SNA) based on fuzzy m-ary adjacency relations. In particular, we show that the dimension of the analysis can naturally be increased and interesting results can be derived. Therefore, fuzzy m-ary adjacency relations can be computed starting from fuzzy binary relations and introducing OWA-based aggregations. The behavioral assumptions derived from the measure and the exam of individual propensity to connect with other suggest that OWA operators can be considered particularly suitable in characterizing such relationships.reciprocal relation; fuzzy preference relation; priority vector; normalization
Network reconstruction from infection cascades
International audienc
Probing turbulent superstructures in Rayleigh-B\'{e}nard convection by Lagrangian trajectory clusters
We analyze large-scale patterns in three-dimensional turbulent convection in
a horizontally extended square convection cell by Lagrangian particle
trajectories calculated in direct numerical simulations. A simulation run at a
Prandtl number Pr , a Rayleigh number Ra , and an aspect ratio
is therefore considered. These large-scale structures, which are
denoted as turbulent superstructures of convection, are detected by the
spectrum of the graph Laplacian matrix. Our investigation, which follows
Hadjighasem {\it et al.}, Phys. Rev. E {\bf 93}, 063107 (2016), builds a
weighted and undirected graph from the trajectory points of Lagrangian
particles. Weights at the edges of the graph are determined by a mean dynamical
distance between different particle trajectories. It is demonstrated that the
resulting trajectory clusters, which are obtained by a subsequent -means
clustering, coincide with the superstructures in the Eulerian frame of
reference. Furthermore, the characteristic times and lengths
of the superstructures in the Lagrangian frame of reference agree
very well with their Eulerian counterparts, and ,
respectively. This trajectory-based clustering is found to work for times
. Longer time periods require a
change of the analysis method to a density-based trajectory clustering by means
of time-averaged Lagrangian pseudo-trajectories, which is applied in this
context for the first time. A small coherent subset of the pseudo-trajectories
is obtained in this way consisting of those Lagrangian particles that are
trapped for long times in the core of the superstructure circulation rolls and
are thus not subject to ongoing turbulent dispersion.Comment: 12 pages, 7 downsized figures, to appear in Phys. Rev. Fluid
Power-law scaling in dimension-to-biomass relationship of fish schools
Motivated by the finding that there is some biological universality in the
relationship between school geometry and school biomass of various pelagic
fishes in various conditions, I here establish a scaling law for school
dimensions: the school diameter increases as a power-law function of school
biomass. The power-law exponent is extracted through the data collapse, and is
close to 3/5. This value of the exponent implies that the mean packing density
decreases as the school biomass increases, and the packing structure displays a
mass-fractal dimension of 5/3. By exploiting an analogy between school geometry
and polymer chain statistics, I examine the behavioral algorithm governing the
swollen conformation of large-sized schools of pelagics, and I explain the
value of the exponent.Comment: 25 pages, 6 figures, to appear in J. Theor. Bio
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