27,777 research outputs found
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Design Synthesis of Adaptive Mesoscopic Cellular Structures with Unit Truss Approach and Particle Swarm Optimization Algorithm
Cellular material structures have been engineered at the mesoscopic scale for high performance
and multifunctional capabilities. However, the design of adaptive cellular structures - structures with
cellular configurations, sizes, and shapes designed for a specific geometric and loading context - has
not been sufficiently investigated. In this paper, the authors present a design synthesis method with the
use of unit truss approach and particle swarm optimization algorithm to design adaptive cellular
structures. A critical review is presented to show the pros and cons of the new design synthesis method
and an existing homogenization method. The research extends the application of additive
manufacturing in the design of new materials for high performances and benefits its long-term growth.Mechanical Engineerin
Correlation between subgrains and coherently scattering domains
Crystallite size determined by X-ray line profile analysis is often smaller than the grain or subgrain size obtained by transmission electron microscopy, especially when the material has been produced by plastic deformation. It is shown that besides differences in orientation between grains or subgrains, dipolar dislocation walls without differences in orientation also break down coherency of X-rays scattering. This means that the coherently scattering domain size provided by X-ray line profile analysis provides subgrain or cell size bounded by dislocation boundaries or dipolar walls
Buckling of Carbon Nanotubes: A State of the Art Review
The nonlinear mechanical response of carbon nanotubes, referred to as their
"buckling" behavior, is a major topic in the nanotube research community.
Buckling means a deformation process in which a large strain beyond a threshold
causes an abrupt change in the strain energy vs. deformation profile. Thus far,
much effort has been devoted to analysis of the buckling of nanotubes under
various loading conditions: compression, bending, torsion, and their certain
combinations. Such extensive studies have been motivated by (i) the structural
resilience of nanotubes against buckling and (ii) the substantial influence of
buckling on their physical properties. In this contribution, I review the
dramatic progress in nanotube buckling research during the past few years.Comment: 38 pages, 21 figure
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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
Constrained CycleGAN for Effective Generation of Ultrasound Sector Images of Improved Spatial Resolution
Objective. A phased or a curvilinear array produces ultrasound (US) images
with a sector field of view (FOV), which inherently exhibits spatially-varying
image resolution with inferior quality in the far zone and towards the two
sides azimuthally. Sector US images with improved spatial resolutions are
favorable for accurate quantitative analysis of large and dynamic organs, such
as the heart. Therefore, this study aims to translate US images with
spatially-varying resolution to ones with less spatially-varying resolution.
CycleGAN has been a prominent choice for unpaired medical image translation;
however, it neither guarantees structural consistency nor preserves
backscattering patterns between input and generated images for unpaired US
images. Approach. To circumvent this limitation, we propose a constrained
CycleGAN (CCycleGAN), which directly performs US image generation with unpaired
images acquired by different ultrasound array probes. In addition to
conventional adversarial and cycle-consistency losses of CycleGAN, CCycleGAN
introduces an identical loss and a correlation coefficient loss based on
intrinsic US backscattered signal properties to constrain structural
consistency and backscattering patterns, respectively. Instead of
post-processed B-mode images, CCycleGAN uses envelope data directly obtained
from beamformed radio-frequency signals without any other non-linear
postprocessing. Main Results. In vitro phantom results demonstrate that
CCycleGAN successfully generates images with improved spatial resolution as
well as higher peak signal-to-noise ratio (PSNR) and structural similarity
(SSIM) compared with benchmarks. Significance. CCycleGAN-generated US images of
the in vivo human beating heart further facilitate higher quality heart wall
motion estimation than benchmarks-generated ones, particularly in deep regions
Shape transformations of lipid vesicles by insertion of bulky-head lipids
Lipid vesicles, in particular Giant Unilamellar Vesicles (GUVs), have been increasingly
important as compartments of artificial cells to reconstruct living cell-like systems in a
bottom-up fashion. Here, we report shape transformations of lipid vesicles induced by
polyethylene glycol-lipid conjugate (PEG lipids). Statistical analysis of deformed vesicle
shapes revealed that shapes vesicles tend to deform into depended on the concentration
of the PEG lipids. When compared with theoretically simulated vesicle shapes, those
shapes were found to be more energetically favorable, with lower membrane bending
energies than other shapes. This result suggests that the vesicle shape transformations
can be controlled by externally added membrane molecules, which can serve as a
potential method to control the replications of artificial cells
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