60 research outputs found
Implicit reconstructions of thin leaf surfaces from large, noisy point clouds
Thin surfaces, such as the leaves of a plant, pose a significant challenge
for implicit surface reconstruction techniques, which typically assume a
closed, orientable surface. We show that by approximately interpolating a point
cloud of the surface (augmented with off-surface points) and restricting the
evaluation of the interpolant to a tight domain around the point cloud, we need
only require an orientable surface for the reconstruction. We use polyharmonic
smoothing splines to fit approximate interpolants to noisy data, and a
partition of unity method with an octree-like strategy for choosing subdomains.
This method enables us to interpolate an N-point dataset in O(N) operations. We
present results for point clouds of capsicum and tomato plants, scanned with a
handheld device. An important outcome of the work is that sufficiently smooth
leaf surfaces are generated that are amenable for droplet spreading
simulations
A high-throughput technique for determining grain boundary character non-destructively in microstructures with through-thickness grains
Grain boundaries (GBs) govern many properties of polycrystalline materials. However, because of their structural variability, our knowledge of GB constitutive relations is still very limited. We present a novel method to characterise the complete crystallography of individual GBs non-destructively, with high-throughput, and using commercially available tools. This method combines electron diffraction, optical reflectance and numerical image analysis to determine all five crystallographic parameters of numerous GBs in samples with through-thickness grains. We demonstrate the technique by measuring the crystallographic character of about 1,000 individual GBs in aluminum in a single run. Our method enables cost- and time-effective assembly of crystallography–property databases for thousands of individual GBs. Such databases are essential for identifying GB constitutive relations and for predicting GB-related behaviours of polycrystalline solids.United States. Department of Energy. Office of Basic Energy Sciences (award no DE-SC0008926)MIT International Science and Technology InitiativesNational Science Foundation (U.S.) (grant DMR-1003901
Materials Design for Hypersonics
Hypersonic vehicles must withstand extreme conditions during flights that
exceed five times the speed of sound. This class of vehicles has the potential
to facilitate rapid access to space, bolster defense capabilities, and create a
new paradigm for transcontinental earth-to-earth travel. However, the extreme
aerothermal environments resulting from high Mach number trajectories create
significant challenges for vehicle materials and structures. As hypersonic
systems advance, there is a critical need to develop novel materials that are
resilient to a combination of thermal and mechanical loads, aggressive
oxidizing environments, and rapid heating rates. This work aims to provide a
succinct discussion of emerging design strategies for refractory alloys,
composites, and ceramics used for hypersonic vehicles. We will highlight key
design principles for critical vehicle areas such as primary structures,
thermal protection, and propulsion systems; the role of theory and computation
in elucidating structure-property-processing relationships; and strategies for
advancing laboratory scale materials to flight-ready components such as
aerostructures and thermal protection systems
Data fusion for a multi-scale model of a wheat leaf surface: a unifying approach using a radial basis function partition of unity method
Realistic digital models of plant leaves are crucial to fluid dynamics
simulations of droplets for optimising agrochemical spray technologies. The
presence and nature of small features (on the order of 100)
such as ridges and hairs on the surface have been shown to significantly affect
the droplet evaporation, and thus the leaf's potential uptake of active
ingredients. We show that these microstructures can be captured by implicit
radial basis function partition of unity (RBFPU) surface reconstructions from
micro-CT scan datasets. However, scanning a whole leaf () at
micron resolutions is infeasible due to both extremely large data storage
requirements and scanner time constraints. Instead, we micro-CT scan only a
small segment of a wheat leaf (). We fit a RBFPU implicit
surface to this segment, and an explicit RBFPU surface to a lower resolution
laser scan of the whole leaf. Parameterising the leaf using a locally
orthogonal coordinate system, we then replicate the now resolved microstructure
many times across a larger, coarser, representation of the leaf surface that
captures important macroscale features, such as its size, shape, and
orientation. The edge of one segment of the microstructure model is blended
into its neighbour naturally by the partition of unity method. The result is
one implicit surface reconstruction that captures the wheat leaf's features at
both the micro- and macro-scales.Comment: 23 pages, 11 figure
Restoration of normal blood flow in atherosclerotic arteries promotes plaque stabilization
Blood flow is a key regulator of atherosclerosis. Disturbed blood flow promotes atherosclerotic plaque development, whereas normal blood flow protects against plaque development. We hypothesized that normal blood flow is also therapeutic, if it were able to be restored within atherosclerotic arteries. Apolipoprotein E-deficient (ApoE-/-) mice were initially instrumented with a blood flow-modifying cuff to induce plaque development and then five weeks later the cuffwas removed to allowrestoration of normal blood flow. Plaques in decuffed mice exhibited compositional changes that indicated increased stability compared to plaques in mice with the cuff maintained. The therapeutic benefit of decuffingwas comparable to atorvastatin and the combination had an additive effect. In addition, decuffing allowed restoration of lumen area, blood velocity, and wall shear stress to near baseline values, indicating restoration of normal blood flow. Our findings demonstrate that the mechanical effects of normal blood flow on atherosclerotic plaques promote stabilization
Smooth muscle cells affect differential nanoparticle accumulation in disturbed blood flow-induced murine atherosclerosis
Atherosclerosis is a lipid-driven chronic inflammatory disease that leads to the formation of plaques in the inner lining of arteries. Plaques form over a range of phenotypes, the most severe of which is vulnerable to rupture and causes most of the clinically significant events. In this study, we evaluated the efficacy of nanoparticles (NPs) to differentiate between two plaque phenotypes based on accumulation kinetics in a mouse model of atherosclerosis. This model uses a perivascular cuff to induce two regions of disturbed wall shear stress (WSS) on the inner lining of the instrumented artery, low (upstream) and multidirectional (downstream), which, in turn, cause the development of an unstable and stable plaque phenotype, respectively. To evaluate the influence of each WSS condition, in addition to the final plaque phenotype, in determining NP uptake, mice were injected with NPs at intermediate and fully developed stages of plaque growth. The kinetics of artery wall uptake were assessed in vivo using dynamic contrast-enhanced magnetic resonance imaging. At the intermediate stage, there was no difference in NP uptake between the two WSS conditions, although both were different from the control arteries. At the fully-developed stage, however, NP uptake was reduced in plaques induced by low WSS, but not multidirectional WSS. Histological evaluation of plaques induced by low WSS revealed a significant inverse correlation between the presence of smooth muscle cells and NP accumulation, particularly at the plaque-lumen interface, which did not exist with other constituents (lipid and collagen) and was not present in plaques induced by multidirectional WSS. These findings demonstrate that NP accumulation can be used to differentiate between unstable and stable murine atherosclerosis, but accumulation kinetics are not directly influenced by the WSS condition. This tool could be used as a diagnostic to evaluate the efficacy of experimental therapeutics for atherosclerosis
Improved reference genome for the domestic horse increases assembly contiguity and composition
Theodore Kalbfleisch et al. present an improved genome assembly for the domestic horse by combining short- and long-read data, as well as proximity ligation data. They improve contiguity of the assembly by 40-fold, with a 10-fold reduction in gaps
Improved reference genome for the domestic horse increases assembly contiguity and composition
Recent advances in genomic sequencing technology and computational assembly methods have allowed scientists to improve reference genome assemblies in terms of contiguity and composition. EquCab2, a reference genome for the domestic horse, was released in 2007. Although of equal or better quality compared to other first-generation Sanger assemblies, it had many of the shortcomings common to them. In 2014, the equine genomics research community began a project to improve the reference sequence for the horse, building upon the solid foundation of EquCab2 and incorporating new short-read data, long-read data, and proximity ligation data. Here, we present EquCab3. The count of non-N bases in the incorporated chromosomes is improved from 2.33 Gb in EquCab2 to 2.41 Gb in EquCab3. Contiguity has also been improved nearly 40-fold with a contig N50 of 4.5 Mb and scaffold contiguity enhanced to where all but one of the 32 chromosomes is comprised of a single scaffold
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