43 results on '"Todd H. Weisgraber"'
Search Results
2. On the Network Topology of Cross-Linked Acrylate Photopolymers: A Molecular Dynamics Case Study
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James S. Oakdale, Magi Mettry, Maxim Shusteff, John J. Karnes, Juergen Biener, and Todd H. Weisgraber
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Acrylate polymer ,Acrylate ,Materials science ,Rational design ,Force field (chemistry) ,Surfaces, Coatings and Films ,chemistry.chemical_compound ,Molecular dynamics ,Monomer ,Photopolymer ,chemistry ,Polymerization ,Materials Chemistry ,Physical and Theoretical Chemistry ,Biological system - Abstract
A reactive molecular dynamics approach is used to simulate cross-linking of acrylate polymer networks. By employing the same force field and reactive scheme and studying three representative multifunctional acrylate monomers, we isolate the importance of the nonreactive moieties within these model monomers. Analyses of reactive trajectories benchmark the estimated gel points, cyclomatic character, and spatially resolved cross-linking tendencies of the acrylates as a function of conversion. These insights into the similarities and differences of the polymerization and resulting networks suggest molecular mechanics as a useful tool in the rational design of photopolymerization resins.
- Published
- 2020
3. Isolating Chemical Reaction Mechanism as a Variable with Reactive Coarse-Grained Molecular Dynamics: Step-Growth versus Chain-Growth Polymerization
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John J. Karnes, Todd H. Weisgraber, Caitlyn C. Cook, Daniel N. Wang, Jonathan C. Crowhurst, Christina A. Fox, Bradley S. Harris, James S. Oakdale, Roland Faller, and Maxim Shusteff
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Inorganic Chemistry ,Chemical Physics (physics.chem-ph) ,Condensed Matter - Materials Science ,Polymers and Plastics ,Physics - Chemical Physics ,Organic Chemistry ,Materials Chemistry ,Materials Science (cond-mat.mtrl-sci) ,Soft Condensed Matter (cond-mat.soft) ,FOS: Physical sciences ,Condensed Matter - Soft Condensed Matter - Abstract
We present a general approach to isolate chemical reaction mechanism as an independently controllable variable across chemically distinct systems. Modern approaches to reduce the computational expense of molecular dynamics simulations often group multiple atoms into a single "coarse-grained" interaction site, which leads to a loss of chemical resolution. In this work we convert this shortcoming into a feature and use identical coarse-grained models to represent molecules that share non-reactive characteristics but react by different mechanisms. As a proof of concept we use this approach to simulate and investigate distinct, yet similar, trifunctional isocyanurate resin formulations that polymerize by either chain- or step-growth. Since the underlying molecular mechanics of these models are identical, all emergent differences are a function of the reaction mechanism only. We find that the microscopic morphologies resemble related all-atom simulations and that simulated mechanical testing reasonably agrees with experiment.
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- 2022
- Full Text
- View/download PDF
4. A mechanical reduced order model for elastomeric 3D printed architectures
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Thomas S. Wilson, Todd H. Weisgraber, Christopher M. Spadaccini, Jeremy M. Lenhardt, Robert S. Maxwell, Eric B. Duoss, Thomas R. Metz, and Ward Small
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Optimal design ,Materials science ,Mechanical Engineering ,Stress–strain curve ,Stiffness ,Modulus ,Mechanical engineering ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Finite element method ,0104 chemical sciences ,Stress (mechanics) ,Shock absorber ,Mechanics of Materials ,medicine ,General Materials Science ,medicine.symptom ,0210 nano-technology ,Scaling - Abstract
Direct ink writing of silicone elastomers enables printing with precise control of porosity and mechanical properties of ordered cellular solids, suitable for shock absorption and stress mitigation applications. With the ability to manipulate structure and feedstock stiffness, the design space becomes challenging to parse to obtain a solution producing a desired mechanical response. Here, we derive an analytical design approach for a specific architecture. Results from finite element simulations and quasi-static mechanical tests of two different parallel strand architectures were analyzed to understand the structure-property relationships under uniaxial compression. Combining effective stiffness-density scaling with least squares optimization of the stress responses yielded general response curves parameterized by resin modulus and strand spacing. An analytical expression of these curves serves as a reduced order model, which, when optimized, provides a rapid design capability for filament-based 3D printed structures. As a demonstration, the optimal design of a face-centered tetragonal architecture is computed that satisfies prescribed minimum and maximum load constraints.
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- 2018
5. Simulating stochastic and additively manufactured foams at large strains and high strain rates (Progress Summary)
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Todd H. Weisgraber
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High strain ,Materials science ,Composite material - Published
- 2019
6. Progress Summary: Simulating stochastic and additively manufactured foams at large strains and high strain rates
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Todd H. Weisgraber
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High strain ,Materials science ,Composite material - Published
- 2018
7. Mesoscale Particle-Based Model of Electrophoresis
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Joshua D. Kuntz, Christopher M. Spadaccini, Andrew J. Pascall, Luis A. Zepeda-Ruiz, Brian Giera, and Todd H. Weisgraber
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Electrophoresis ,Renewable Energy, Sustainability and the Environment ,Chemical physics ,Chemistry ,Materials Chemistry ,Electrochemistry ,Mesoscale meteorology ,Particle ,Nanotechnology ,Condensed Matter Physics ,Nanomechanics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Published
- 2015
8. One-step volumetric additive manufacturing of complex polymer structures
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Brett Kelly, Robert M. Panas, Nicholas X. Fang, Johannes Henriksson, Christopher M. Spadaccini, Todd H. Weisgraber, Allison E. M. Browar, Maxim Shusteff, Massachusetts Institute of Technology. Department of Aeronautics and Astronautics, Massachusetts Institute of Technology. Department of Biological Engineering, Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology. Department of Mechanical Engineering, Massachusetts Institute of Technology. Department of Physics, Shusteff, Maxim, Panas, Robert M, Fang, Xuanlai, and Spadaccini, Christopher M.
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Work (thermodynamics) ,Fabrication ,Materials science ,Materials Science ,Holography ,One-Step ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,law.invention ,law ,Research Articles ,chemistry.chemical_classification ,Multidisciplinary ,business.industry ,SciAdv r-articles ,Polymer ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Photopolymer ,chemistry ,Optoelectronics ,0210 nano-technology ,business ,Layer (electronics) ,Photoinitiator ,Research Article - Abstract
Two limitations of additive manufacturing methods that arise from layer-based fabrication are slow speed and geometric constraints (which include poor surface quality). Both limitations are overcome in the work reported here, introducing a new volumetric additive fabrication paradigm that produces photopolymer structures with complex nonperiodic three-dimensional geometries on a time scale of seconds. We implement this approach using holographic patterning of light fields, demonstrate the fabrication of a variety of structures, and study the properties of the light patterns and photosensitive resins required for this fabrication approach. The results indicate that low-absorbing resins containing ~0.1% photoinitiator, illuminated at modest powers (~10 to 100 mW), may be successfully used to build full structures in ~1 to 10 s., United States. Department of Energy (contract DE-AC52-07NA27344), United States. Department of Energy (Laboratory Directed Research and Development funding 14-SI-004), United States. Department of Energy (Laboratory Directed Research and Development funding 7-ERD-116 (LLNL-JRNL-732526))
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- 2017
9. Addendum: Multiscale metallic metamaterials
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Nicholas X. Fang, Christopher M. Spadaccini, Nicholas Rodriguez, Da Chen, Todd H. Weisgraber, Julie A. Jackson, William L. Smith, Jianchao Ye, Xiaoyu Zheng, Huachen Cui, and Bryan D. Moran
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Mechanical Engineering ,Metamaterial ,Addendum ,Nanotechnology ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Mechanics of Materials ,General Materials Science ,0210 nano-technology - Published
- 2017
10. The Onset of Turbulence in Wall-bounded Flows with Surface Roughness and Fluctuations
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Todd H. Weisgraber, Pratanu Roy, and Berni J. Alder
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Physics ,Turbulence ,Bounded function ,Surface roughness ,Mechanics - Published
- 2017
11. Three-Dimensional Printing of Elastomeric, Cellular Architectures with Negative Stiffness
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Robert S. Maxwell, Ward Small, Eric B. Duoss, Keith Hearon, John J. Vericella, Cheng Zhu, Christopher M. Spadaccini, Joshua D. Kuntz, Holly D. Barth, Thomas S. Wilson, Thomas R. Metz, and Todd H. Weisgraber
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Absorption (acoustics) ,Materials science ,business.industry ,3D printing ,Cubic crystal system ,Condensed Matter Physics ,Elastomer ,Viscoelasticity ,Electronic, Optical and Magnetic Materials ,Biomaterials ,Tetragonal crystal system ,Electrochemistry ,Composite material ,Porosity ,business ,Mechanical energy - Abstract
Three-dimensional printing of viscoelastic inks to create porous, elastomeric architectures with mechanical properties governed by the ordered arrangement of their sub-millimeter struts is reported. Two layouts are patterned, one resembling a “simple cubic” (SC)-like structure and another akin to a “face-centered tetragonal” (FCT) configuration. These structures exhibit markedly distinct load response with directionally dependent behavior, including negative stiffness. More broadly, these findings suggest the ability to independently tailor mechanical response in cellular solids via micro-architected design. Such ordered materials may one day replace random foams in mechanical energy absorption applications.
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- 2014
12. Interpolation methods and the accuracy of lattice-Boltzmann mesh refinement
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Phillip Colella, Todd H. Weisgraber, Stephen M. Guzik, and Berni J. Alder
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Numerical Analysis ,Mathematical optimization ,Physics and Astronomy (miscellaneous) ,Adaptive mesh refinement ,Applied Mathematics ,MathematicsofComputing_NUMERICALANALYSIS ,Trilinear interpolation ,Lattice Boltzmann methods ,Grid ,Computer Science Applications ,Multivariate interpolation ,Computational Mathematics ,Modeling and Simulation ,Convergence (routing) ,Benchmark (computing) ,Algorithm ,ComputingMethodologies_COMPUTERGRAPHICS ,Mathematics ,Interpolation - Abstract
A lattice-Boltzmann model to solve the equivalent of the Navier-Stokes equations on adaptively refined grids is presented. A method for transferring information across interfaces between different grid resolutions was developed following established techniques for finite-volume representations. This new approach relies on a space-time interpolation and solving constrained least-squares problems to ensure conservation. The effectiveness of this method at maintaining the second order accuracy of lattice-Boltzmann is demonstrated through a series of benchmark simulations and detailed mesh refinement studies. These results exhibit smaller solution errors and improved convergence when compared with similar approaches relying only on spatial interpolation. Examples highlighting the mesh adaptivity of this method are also provided.
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- 2014
13. Universal Design Curves for Elastomeric Direct Ink-Writing Architectures
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Thomas S. Wilson, Thomas R. Metz, Christopher M. Spadaccini, Todd H. Weisgraber, Jeremy M. Lenhardt, Robert S. Maxwell, Eric B. Duoss, and Ward Small
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Inkwell ,Computer science ,Universal design ,Mechanical engineering ,Elastomer - Published
- 2016
14. Thermal aging of traditional and additively manufactured foams: analysis by time-temperature-superposition, constitutive, and finite-element models
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Ward Small, M. A. Pearson, Christopher M. Spadaccini, Todd H. Weisgraber, Eric B. Duoss, James P. Lewicki, Sarah C. Chinn, Robert S. Maxwell, Thomas S. Wilson, and Amitesh Maiti
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Stress (mechanics) ,Materials science ,Time–temperature superposition ,Thermal insulation ,business.industry ,Compression set ,Composite material ,Microstructure ,business ,Accelerated aging ,Finite element method ,Shock (mechanics) - Abstract
Cellular solids or foams are a very important class of materials with diverse applications ranging from thermal insulation and shock absorbing support cushions, to light-weight structural and floatation components, and constitute crucial components in a large number of industries including automotive, aerospace, electronics, marine, biomedical, packaging, and defense. In many of these applications the foam material is subjected to long periods of continuous stress, which can, over time, lead to a permanent change in structure and a degradation in performance. In this report we summarize our modeling efforts to date on polysiloxane foam materials that form an important component in our systems. Aging of the materials was characterized by two measured quantities, i.e., compression set and load retention. Results of accelerated aging experiments were analyzed by an automated time-temperaturesuperposition (TTS) approach, which creates a master curve that can be used for long-term predictions (over decades) under ambient conditions. When comparing such master curves for traditional (stochastic) foams with those for recently 3D-printed (i.e., additively manufactured, or AM) foams, it became clear that AM foams have superior aging behavior. To gain deeper understanding, we imaged the microstructure of both foams using X-ray computed tomography, and performed finite-element analysis of the mechanicalmore » response within these microstructures. This indicates a wider stress variation in the stochastic foam with points of more extreme local stress as compared to the 3D printed material.« less
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- 2016
15. Optimally Engineered Flow-through Electrodes Using Automatic Design Algorithms and Additive Manufacturing
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Victor A Beck, Todd H Weisgraber, Anna N Ivanovskaya, Swetha Chandrasekaran, Bryan D Moran, Seth E Watts, Dan A Tortorelli, Eric B Duoss, Juergen Biener, Michael Stadermann, and Marcus A. Worsley
- Abstract
Flow batteries are a promising technology for large scale energy storage and load balancing from intermittent power sources, but their viability hinges on our ability to attain high-power outputs while minimizing costs and meeting performance constraints. Controlling fluid flow, active species distribution, and mass transport in the electrode has a dramatic impact on cell power and efficiency. However, this control is often limited to changing a quasi-two-dimensional flow field and selecting bulk properties of a monolithic electrode. This can lead to non-uniform reaction rates, underutilized regions of the flow cell, and can limit the ultimate performance of the devices. We propose an alternative approach which seeks to control the fluid distribution in the cell by controlling the electrode geometry. Our approach is enabled by additive manufacturing techniques which allow us to directly build three-dimensional morphologies. Further, to determine effective electrode geometries, we employ topology optimization techniques that couple solution of the forward electrochemical problem over the full electrode domain with gradient-based optimization. The output of our code is a three-dimensional CAD representation which optimizes over specific performance metrics and which can be used to print functional electrodes. We will demonstrate the process for generating the electrodes using our optimization framework and present experiments comparing the performance of the optimized geometries across designs and against conventional electrodes. This work provides a systematic path toward automatic design of engineered electrodes with precise control over the fluid and species distribution. LLNL-ABS-764035 This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
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- 2019
16. Correction: Corrigendum: 3D printed cellular solid outperforms traditional stochastic foam in long-term mechanical response
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Ward Small, Todd H. Weisgraber, James P. Lewicki, M. A. Pearson, Robert S. Maxwell, Amitesh Maiti, Christopher M. Spadaccini, Sarah C. Chinn, Thomas S. Wilson, and Eric B. Duoss
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0301 basic medicine ,World Wide Web ,03 medical and health sciences ,3d printed ,030104 developmental biology ,Multidisciplinary ,National security ,Operations research ,Computer science ,business.industry ,Section (typography) ,business ,Term (time) - Abstract
Scientific Reports 6: Article number: 24871; Published online: 27 April 2016; Updated 25 May 2016 The Acknowledgements section in this Article is incomplete. “We would like to sincerely thank Dr. Jim Schneider of National Security Campus, MO (formerly Kansas City Plant) for giving us access to the results of their load retention study on the stochastic foam material.
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- 2016
17. Design of Nonperiodic Microarchitectured Materials That Achieve Graded Thermal Expansions
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Christopher M. Spadaccini, Lucas A. Shaw, Todd H. Weisgraber, George R. Farquar, Jonathan B. Hopkins, and Christopher D. Harvey
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010302 applied physics ,Materials science ,business.industry ,Mechanical Engineering ,Stiffness ,Young's modulus ,02 engineering and technology ,Structural engineering ,021001 nanoscience & nanotechnology ,01 natural sciences ,Finite element method ,Thermal expansion ,symbols.namesake ,0103 physical sciences ,Thermal ,symbols ,medicine ,medicine.symptom ,0210 nano-technology ,MATLAB ,business ,computer ,Topology (chemistry) ,computer.programming_language - Abstract
The aim of this paper is to introduce an approach for optimally organizing a variety of nonrepeating compliant-mechanism-like unit cells within a large deformable lattice such that the bulk behavior of the lattice exhibits a desired graded change in thermal expansion while achieving a desired uniform stiffness over its geometry. Such lattices with nonrepeating unit cells, called nonperiodic microarchitectured materials, could be sandwiched between two materials with different thermal expansion coefficients to accommodate their different expansions and/or contractions induced by changing ambient temperatures. This capability would reduce system-level failures within robots, mechanisms, electronic modules, or other layered coatings or structures made of different materials with mismatched thermal expansion coefficients. The closed-form analytical equations are provided, which are necessary to rapidly calculate the bulk thermal expansion coefficient and Young's modulus of general multimaterial lattices that consist first of repeating unit cells of the same design (i.e., periodic microarchitectured materials). Then, these equations are utilized in an iterative way to generate different rows of repeating unit cells of the same design that are layered together to achieve nonperiodic microarchitectured material lattices such that their top and bottom rows achieve the same desired thermal expansion coefficients as the two materials between which the lattice is sandwiched. A matlab tool is used to generate images of the undeformed and deformed lattices to verify their behavior and an example is provided as a case study. The theory provided is also verified and validated using finite-element analysis (FEA) and experimentation.
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- 2016
18. 3D printed cellular solid outperforms traditional stochastic foam in long-term mechanical response
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Eric B. Duoss, Robert S. Maxwell, James P. Lewicki, Ward Small, Thomas S. Wilson, Amitesh Maiti, Todd H. Weisgraber, Christopher M. Spadaccini, Sarah C. Chinn, and M. A. Pearson
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Multidisciplinary ,Materials science ,business.industry ,3D printing ,Compression set ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Microstructure ,Corrigenda ,01 natural sciences ,Stability (probability) ,Accelerated aging ,Article ,0104 chemical sciences ,Stress (mechanics) ,Compressibility ,Composite material ,0210 nano-technology ,business ,Elastic modulus - Abstract
3D printing of polymeric foams by direct-ink-write is a recent technological breakthrough that enables the creation of versatile compressible solids with programmable microstructure, customizable shapes, and tunable mechanical response including negative elastic modulus. However, in many applications the success of these 3D printed materials as a viable replacement for traditional stochastic foams critically depends on their mechanical performance and micro-architectural stability while deployed under long-term mechanical strain. To predict the long-term performance of the two types of foams we employed multi-year-long accelerated aging studies under compressive strain followed by a time-temperature-superposition analysis using a minimum-arc-length-based algorithm. The resulting master curves predict superior long-term performance of the 3D printed foam in terms of two different metrics, i.e., compression set and load retention. To gain deeper understanding, we imaged the microstructure of both foams using X-ray computed tomography, and performed finite-element analysis of the mechanical response within these microstructures. This indicates a wider stress variation in the stochastic foam with points of more extreme local stress as compared to the 3D printed material, which might explain the latter’s improved long-term stability and mechanical performance.
- Published
- 2016
19. Linking Network Microstructure to Macroscopic Properties of Siloxane Elastomers Using Combined Nuclear Magnetic Resonance and Mesoscale Computational Modeling
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Ward Small, Todd H. Weisgraber, James P. Lewicki, Robert S. Maxwell, Brian P. Mayer, and Sarah C. Chinn
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chemistry.chemical_classification ,Polymers and Plastics ,Organic Chemistry ,Mesoscale meteorology ,Polymer ,Elastomer ,Microstructure ,Inorganic Chemistry ,chemistry.chemical_compound ,Nuclear magnetic resonance ,chemistry ,Siloxane ,Materials Chemistry ,Mathematics::Metric Geometry - Abstract
It is well established that many fundamental properties of polymer materials are directly governed by chain dynamics, and both experimental and computational efforts to probe this motional spectrum...
- Published
- 2011
20. A mesoscopic network model for permanent set in crosslinked elastomers
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Robert S. Maxwell, Richard H. Gee, Sarah C. Chinn, Todd H. Weisgraber, Amitesh Maiti, and David S. Clague
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Mesoscopic physics ,Materials science ,Polymers and Plastics ,Organic Chemistry ,Elasticity (physics) ,Elastomer ,Condensed Matter::Soft Condensed Matter ,Rubber elasticity ,Materials Chemistry ,Polymer physics ,Composite material ,Elastic modulus ,Lattice model (physics) ,Network model - Abstract
A mesoscopic computational model for polymer networks and composites is developed as a very coarse-grained representation of the network microstructure. Unlike more complex molecular dynamics simulations, the model network is static unless undergoing deformation. The elastic modulus, which depends only on the crosslink density and parameters in the bond potential, is consistent with rubber elasticity theory, and the network response satisfies the independent network hypothesis of Tobolsky. The model, when applied to a commercial filled silicone elastomer, quantitatively reproduces the experimental permanent set and stress-strain response due to changes in the crosslinked network from irradiation.
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- 2009
21. Quantifying the potential exposure hazard due to energetic releases of CO2 from a failed sequestration well
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Carol J. Bruton, Martin J. Leach, Matthew Simpson, Todd H. Weisgraber, S. Julio Friedmann, and Roger D. Aines
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National Atmospheric Release Advisory Center ,Engineering ,Meteorology ,Energy(all) ,business.industry ,General Earth and Planetary Sciences ,Flux ,Tonne ,business ,Atmospheric sciences ,Casing ,Hazard ,General Environmental Science - Abstract
Wells are designed to bring fluids from depth to the earth’s surface quickly. As such they are the most likely pathway for CO2 to return to the surface in large quantities and present a hazard without adequate management. We surveyed oil industry experience of CO2 well failures, and separately, calculated the maximal CO2 flow rate from a 5000 ft depth supercritical CO2 reservoir. The calculated maximum of 20,000 tonne/day was set by the sound speed and the seven-inch well casing diameter, and was greater than any observed event. We used this flux to simulate atmospheric releases and the associated hazard utilizing the National Atmospheric Release Advisory Center (NARAC) tools and real meteorology at a representative location in the High Plains of the United States. Three cases representing a maximum hazard day (quiet winds
- Published
- 2009
- Full Text
- View/download PDF
22. Constitutive modeling of radiation effects on the permanent set in a silicone elastomer
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Amitesh Maiti, Richard H. Gee, Sarah C. Chinn, Robert S. Maxwell, and Todd H. Weisgraber
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Materials science ,Polymers and Plastics ,Composite number ,Constitutive equation ,Radiation ,Condensed Matter Physics ,Elastomer ,Set (abstract data type) ,chemistry.chemical_compound ,Silicone ,chemistry ,Mechanics of Materials ,Materials Chemistry ,Irradiation ,Composite material ,Elastic modulus - Abstract
When a networked polymeric composite under high stress is subjected to irradiation, the resulting chemical changes like chain scissioning and cross-link formation can lead to permanent set and altered elastic modulus. Using a commercial silicone elastomer as a specific example we show that a simple 2-stage Tobolsky model in conjunction with Fricker's stress-transfer function can quantitatively reproduce all experimental data as a function of radiation dosage and the static strain at which radiation is turned on, including permanent set, stress-strain response, and net cross-linking density.
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- 2008
23. Multiscale metallic metamaterials
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Xiaoyu Zheng, Jianchao Ye, Julie A. Jackson, Nicholas X. Fang, Christopher M. Spadaccini, Todd H. Weisgraber, Huachen Cui, Bryan D. Moran, Da Chen, Nicholas Rodriguez, and William L. Smith
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Materials science ,Orders of magnitude (temperature) ,Mechanical Engineering ,Metamaterial ,Nanotechnology ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,law.invention ,Specific strength ,Mechanics of Materials ,law ,Ultimate tensile strength ,Scalability ,Energy transformation ,General Materials Science ,Elasticity (economics) ,0210 nano-technology ,Stereolithography - Abstract
Materials with three-dimensional micro- and nanoarchitectures exhibit many beneficial mechanical, energy conversion and optical properties. However, these three-dimensional microarchitectures are significantly limited by their scalability. Efforts have only been successful only in demonstrating overall structure sizes of hundreds of micrometres, or contain size-scale gaps of several orders of magnitude. This results in degraded mechanical properties at the macroscale. Here we demonstrate hierarchical metamaterials with disparate three-dimensional features spanning seven orders of magnitude, from nanometres to centimetres. At the macroscale they achieve high tensile elasticity (>20%) not found in their brittle-like metallic constituents, and a near-constant specific strength. Creation of these materials is enabled by a high-resolution, large-area additive manufacturing technique with scalability not achievable by two-photon polymerization or traditional stereolithography. With overall part sizes approaching tens of centimetres, these unique nanostructured metamaterials might find use in a broad array of applications.
- Published
- 2015
24. Organizing Cells Within Non-Periodic Microarchitectured Materials That Achieve Graded Thermal Expansions
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Christopher M. Spadaccini, Christopher D. Harvey, Todd H. Weisgraber, Jonathan B. Hopkins, Lucas A. Shaw, and George R. Farquar
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Mathematical analysis ,Modulus ,Stiffness ,Young's modulus ,Geometry ,Finite element method ,Thermal expansion ,symbols.namesake ,Lattice (order) ,Thermal ,symbols ,medicine ,medicine.symptom ,MATLAB ,computer ,Mathematics ,computer.programming_language - Abstract
The aim of this paper is to introduce an approach for optimally organizing a variety of different unit cell designs within a large lattice such that the bulk behavior of the lattice exhibits a desired Young’s modulus with a graded change in thermal expansion over its geometry. This lattice, called a graded microarchitectured material, can be sandwiched between two other materials with different thermal expansion coefficients to accommodate their different expansions or contractions caused by changing temperature while achieving a desired uniform stiffness. First, this paper provides the theory necessary to calculate the thermal expansion and Young’s modulus of large multi-material lattices that consist of periodic (i.e., repeating) unit cells of the same design. Then it introduces the theory for calculating the graded thermal expansions of a large multimaterial lattice that consists of non-periodic unit cells of different designs. An approach is then provided for optimally designing and organizing different unit cells within a lattice such that both of its ends achieve the same thermal expansion as the two materials between which the lattice is sandwiched. A MATLAB tool is used to generate images of the undeformed and deformed lattices to verify their behavior and various examples are provided as case studies. The theory provided is also verified and validated using finite element analysis and experimentation.Copyright © 2015 by ASME
- Published
- 2015
25. Multi-Scale Fluid-Structure Interaction Simulations Based on Mesoscopic Approaches
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Stuart D.C. Walsh, Dennis Gottuso, Todd H. Weisgraber, and Kostas Karazis
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business.industry ,Adaptive mesh refinement ,Computer science ,Turbulence ,Lattice Boltzmann methods ,Reynolds number ,Computational fluid dynamics ,Computational science ,symbols.namesake ,Scalability ,Fluid–structure interaction ,Fluid dynamics ,symbols ,business ,Simulation - Abstract
Many challenging fluid-structure interaction problems in nuclear engineering remain unresolved because current CFD methodologies are unable to manage the number of computational cells needed and/or the difficulties associated with meshing changing geometries. One of the most promising recent methodologies for fluid dynamics modeling is the lattice-Boltzmann method — an approach that offers significant advantages over classical CFD methodologies by 1) greatly reducing meshing requirements, 2) offering great scalability, and 3) through relative ease of code parallelization. While LBM often requires increased numerical effort compared to other methods, this can be dramatically reduced by combining LBM with Adaptive Mesh Refinement (LB-AMR). This study describes an ongoing collaboration investigating nuclear fuel-assembly spacer grid performance. The LB-AMR method, used to simulate the flow field around a specific spacer grid design, is capable of describing turbulent flows for high Reynolds numbers, revealing rich flow dynamics in good qualitative agreement with experimental results. Prepared by LLNL under Contract DE-AC52-07NA27344.
- Published
- 2014
26. Modeling the mechanical and aging properties of silicone rubber and foam - stockpile-historical & additively manufactured materials
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Amitesh Maiti, Todd H. Weisgraber, and Richard H. Gee
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Stress (mechanics) ,Change over time ,chemistry.chemical_compound ,Silicone ,Materials science ,Manufactured material ,chemistry ,Stockpile ,Compression set ,Modulus ,Composite material ,Silicone rubber - Abstract
M97* and M9763 belong to the M97xx series of cellular silicone materials that have been deployed as stress cushions in some of the LLNL systems. Their purpose of these support foams is to distribute the stress between adjacent components, maintain relative positioning of various components, and mitigate the effects of component size variation due to manufacturing and temperature changes. In service these materials are subjected to a continuous compressive strain over long periods of time. In order to ensure their effectiveness, it is important to understand how their mechanical properties change over time. The properties we are primarily concerned about are: compression set, load retention, and stress-strain response (modulus).
- Published
- 2014
27. Ultralight, ultrastiff mechanical metamaterials
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Julie A. Jackson, Nicholas X. Fang, Maxim Shusteff, Christopher M. Spadaccini, Monika M. Biener, Todd H. Weisgraber, Joshua D. Kuntz, Qi Ge, Xiaoyu Zheng, Joshua R. Deotte, Sergei O. Kucheyev, Eric B. Duoss, Howon Lee, Massachusetts Institute of Technology. Department of Mechanical Engineering, Fang, Nicholas Xuanlai, Lee, Howon, and Ge, Qi (Kevin)
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Multidisciplinary ,Materials science ,Orders of magnitude (temperature) ,Isotropy ,Metamaterial ,engineering.material ,Compression (physics) ,Coating ,visual_art ,visual_art.visual_art_medium ,engineering ,Mechanical metamaterial ,Ceramic ,Composite material ,Microscale chemistry - Abstract
Microlattices make marvelous materials Framework or lattice structures can be remarkably strong despite their very low density. Using a very precise technique known as projection microstereolithography, Zheng et al. fabricated octet microlattices from polymers, metals, and ceramics. The design of the lattices meant that the individual struts making up the materials did not bend under pressure. The materials were therefore exceptionally stiff, strong, and lightweight. Science , this issue p. 1373
- Published
- 2014
28. Mullins effect in a filled elastomer under uniaxial tension
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Robert S. Maxwell, Richard H. Gee, Amitesh Maiti, Ward Small, Sarah C. Chinn, Thomas S. Wilson, and Todd H. Weisgraber
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chemistry.chemical_classification ,Materials science ,Mullins effect ,chemistry ,Cushion ,Volume fraction ,Constitutive equation ,Modulus ,Polymer ,Composite material ,Elastomer ,Softening - Abstract
Modulus softening and permanent set in filled polymeric materials due to cyclic loading and unloading, commonly known as the Mullins effect, can have a significant impact on their use as support cushions. A quantitative analysis of such behavior is essential to ensure the effectiveness of such materials in long-term deployment. In this work we combine existing ideas of filler-induced modulus enhancement, strain amplification, and irreversible deformation within a simple non-Gaussian constitutive model to quantitatively interpret recent measurements on a relevant PDMS-based elastomeric cushion. We find that the experimental stress-strain data is consistent with the picture that during stretching (loading) two effects take place simultaneously: (1) the physical constraints (entanglements) initially present in the polymer network get disentangled, thus leading to a gradual decrease in the effective cross-link density, and (2) the effective filler volume fraction gradually decreases with increasing strain due to the irreversible pulling out of an initially occluded volume of the soft polymer domain.
- Published
- 2014
29. Lightweight micro lattices with nanoscale features fabricated from Projection Microstereolithography
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Xiaoyu Zheng, Howon Lee, Maxim Shusteff, Todd H. Weisgraber, Joshua R. Deotte, John J. Vericella, Nicholas X. Fang, and Christopher M. Spadaccini
- Subjects
Honeycomb structure ,Materials science ,Fabrication ,law ,Active cooling ,Honeycomb ,Nanotechnology ,Projection (set theory) ,Stereolithography ,Efficient energy use ,Microfabrication ,law.invention - Abstract
Complex, three-dimensional lightweight cellular materials inspired by nature, such as honeycomb and foamlike structures are desirable for a broad array of applications such as structural components, catalysts supports and energy efficient materials. Additionally, when designed with interconnected porosity, the open volume in the architecture can be exploited for active cooling or energy storage, providing unique opportunities for multifunctionality. However, they are extremely difficult to fabricate with the current state-of-the-art fabrication techniques. This paper reports the fabrication of complex, three-dimensional cellular materials with nanoscale features using a novel additive manufacturing approach, namely Projection Microstereolithography (PμSL).
- Published
- 2014
30. Additive Micro-Manufacturing of Designer Materials
- Author
-
Joshua D. Kuntz, Jonathan B. Hopkins, Nicholas X. Fang, Howon Lee, Christopher M. Spadaccini, Todd H. Weisgraber, Jennifer A. Lewis, David B. Kolesky, Andrew J. Pascall, Cheng Zhu, Eric B. Duoss, James M. Frank, Joshua R. Deotte, Rayne Zheng, David Saintillan, John J. Vericella, Kyle T. Sullivan, and Daniel A. Tortorelli
- Subjects
Electrophoretic deposition ,Materials science ,Fracture toughness ,Thermal conductivity ,Inkwell ,Topology optimization ,Mechanical engineering ,Projection (set theory) ,Material properties ,Thermal expansion - Abstract
Material properties are governed by the chemical composition and spatial arrangement of constituent elements at multiple length scales. This fundamentally limits material properties with respect to each other creating trade-offs when selecting materials for a specific application. For example, strength and density are inherently linked so that, in general, the more dense the material, the stronger it is in bulk form. Other coupled material properties include thermal expansion and thermal conductivity, hardness and fracture toughness, strength and thermal expansion, etc. We are combining advanced microstructural design, using flexure and screw theory as well as topology optimization, with new additive micro- and nano-manufacturing techniques to create new material systems with previously unachievable property combinations. Our manufacturing techniques include Projection Microstereolithography (PμSL), Direct Ink Writing (DIW), and Electrophoretic Deposition (EPD). These processes are capable of reliably producing designed architectures that are highly three-dimensional, multi-scale, and often composed of multiple constituent materials.
- Published
- 2014
31. An Adaptive Mesh Refinement Strategy with Conservative Space-Time Coupling for the Lattice-Boltzmann Method
- Author
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Berni J. Alder, Xinfeng Gao, Todd H. Weisgraber, Stephen M. Guzik, and Phillip Colella
- Subjects
Coupling ,Mathematical optimization ,Spacetime ,Adaptive mesh refinement ,business.industry ,Space time ,MathematicsofComputing_NUMERICALANALYSIS ,Lattice Boltzmann methods ,Computational fluid dynamics ,Multivariate interpolation ,Applied mathematics ,business ,ComputingMethodologies_COMPUTERGRAPHICS ,Mathematics ,Interpolation - Abstract
A conservative lattice-Boltzmann method is presented for solving the time-dependent Navier-Stokes equations at low Mach numbers on lattices that are adaptively refined in space and time. A method for coupling the interfaces between grids at different resolutions was constructed following techniques established for finite-volume computational fluid dynamics methods. The effectiveness of the new coupling method, which relies on a spacetime interpolation and solving constrained least-squares problems to ensure conservation is compared against similar approaches relying only on spatial interpolation.
- Published
- 2013
32. Computer experiments on the onset of turbulence
- Author
-
Berni J. Alder and Todd H. Weisgraber
- Subjects
Physics::Fluid Dynamics ,Physics ,Computer simulation ,business.industry ,Turbulence ,K-epsilon turbulence model ,Numerical analysis ,Bounded function ,Lattice Boltzmann methods ,Statistical physics ,Surface finish ,Computational fluid dynamics ,business - Abstract
We are investigating if small amplitude distributed wall roughness, combined with fluctuations, could nucleate the onset of turbulence in bounded flows. Our direct numerical simulations of turbulent transition isolate the effects of the roughness since the only direct flow perturbations we consider are those due to natural hydrodynamic fluctuations. To properly resolve the range of length scales, we developed a conservative mesh refinement approach for the lattice-Boltzmann method.
- Published
- 2012
33. Radiation-induced mechanical property changes in filled rubber
- Author
-
Todd H. Weisgraber, Ward Small, C.T. Alviso, Sarah C. Chinn, Robert S. Maxwell, Amitesh Maiti, and Richard H. Gee
- Subjects
chemistry.chemical_classification ,Radiation ,Materials science ,Mullins effect ,Polymer ,Models, Theoretical ,Radiation Dosage ,Elastomer ,Condensed Matter::Materials Science ,Natural rubber ,chemistry ,Elastic Modulus ,visual_art ,visual_art.visual_art_medium ,Hardening (metallurgy) ,Rubber ,Stress, Mechanical ,Composite material ,Softening ,Elastic modulus ,Mechanical Phenomena - Abstract
In a recent paper we exposed a filled elastomer to controlled radiation dosages and explored changes in its cross-link density and molecular weight distribution between network junctions [A. Maiti et al., Phys. Rev. E 83, 031802 (2011)]. Here we report mechanical response measurements when the material is exposed to radiation while being under finite nonzero strain. We observe interesting hysteretic behavior and material softening representative of the Mullins effect, and materials hardening due to radiation. The net magnitude of the elastic modulus depends upon the radiation dosage, strain level, and strain-cycling history of the material. Using the framework of Tobolsky's two-stage independent network theory we develop a model that can quantitatively interpret the observed elastic modulus and its radiation and strain dependence.
- Published
- 2011
34. FY10 Engineering Innovations, Research and Technology Report
- Author
-
K Carlisle, C N Paulson, Timothy L. Houck, Joshua D. Kuntz, B Corey, Salvador M. Aceves, C Bennett, Carol Meyers, B L Guidry, B Y Chen, Christopher M. Spadaccini, J Kotovsky, Michael A. Puso, Daniel A. White, James V. Candy, Joel V. Bernier, D. Chen, Adam M. Conway, Rebecca J. Nikolic, M A Lane, Elizabeth K. Wheeler, J I Lin, Todd H. Weisgraber, Tracy D. Lemmond, Dietrich Dehlinger, B M Ng, Tang, R P Mariella, and A K Foudray
- Subjects
Engineering ,Engineering management ,National security ,Biological systems engineering ,Work (electrical) ,business.industry ,Value proposition ,Systems engineering ,Portfolio ,Health systems engineering ,Mechatronics ,Engineering research ,business - Abstract
This report summarizes key research, development, and technology advancements in Lawrence Livermore National Laboratory's Engineering Directorate for FY2010. These efforts exemplify Engineering's nearly 60-year history of developing and applying the technology innovations needed for the Laboratory's national security missions, and embody Engineering's mission to ''Enable program success today and ensure the Laboratory's vitality tomorrow.'' Leading off the report is a section featuring compelling engineering innovations. These innovations range from advanced hydrogen storage that enables clean vehicles, to new nuclear material detection technologies, to a landmine detection system using ultra-wideband ground-penetrating radar. Many have been recognized with RD all are examples of the forward-looking application of innovative engineering to pressing national problems and challenging customer requirements. Engineering's capability development strategy includes both fundamental research and technology development. Engineering research creates the competencies of the future where discovery-class groundwork is required. Our technology development (or reduction to practice) efforts enable many of the research breakthroughs across the Laboratory to translate from the world of basic research to the national security missions of the Laboratory. This portfolio approach produces new and advanced technological capabilities, and is a unique component of the value proposition of the Lawrence Livermore Laboratory.more » The balance of the report highlights this work in research and technology, organized into thematic technical areas: Computational Engineering; Micro/Nano-Devices and Structures; Measurement Technologies; Engineering Systems for Knowledge Discovery; and Energy Manipulation. Our investments in these areas serve not only known programmatic requirements of today and tomorrow, but also anticipate the breakthrough engineering innovations that will be needed in the future.« less
- Published
- 2011
35. Controlled manipulation of elastomers with radiation: Insights from multiquantum nuclear-magnetic-resonance data and mechanical measurements
- Author
-
Long N. Dinh, Todd H. Weisgraber, Richard H. Gee, Amitesh Maiti, Robert S. Maxwell, Thomas S. Wilson, and Sarah C. Chinn
- Subjects
Work (thermodynamics) ,Materials science ,Magnetic Resonance Spectroscopy ,Polymers ,Biocompatible Materials ,Elastomer ,Stress (mechanics) ,Natural rubber ,Tensile Strength ,Thermal ,chemistry.chemical_classification ,business.industry ,Temperature ,Reproducibility of Results ,Sterilization ,Polymer ,Characterization (materials science) ,Molecular Weight ,Cross-Linking Reagents ,chemistry ,Elastomers ,Equipment and Supplies ,Gamma Rays ,visual_art ,visual_art.visual_art_medium ,Optoelectronics ,Adhesive ,Rubber ,Stress, Mechanical ,business - Abstract
Filled and cross-linked elastomeric rubbers are versatile network materials with a multitude of applications ranging from artificial organs and biomedical devices to cushions, coatings, adhesives, interconnects, and seismic-isolation, thermal, and electrical barriers. External factors such as mechanical stress, temperature fluctuations, or radiation are known to create chemical changes in such materials that can directly affect the molecular weight distribution (MWD) of the polymer between cross-links and alter the structural and mechanical properties. From a materials science point of view it is highly desirable to understand, affect, and manipulate such property changes in a controlled manner. Unfortunately, that has not yet been possible due to the lack of experimental characterization of such networks under controlled environments. In this work we expose a known rubber material to controlled dosages of γ radiation and utilize a newly developed multiquantum nuclear-magnetic-resonance technique to characterize the MWD as a function of radiation. We show that such data along with mechanical stress-strain measurements are amenable to accurate analysis by simple network models and yield important insights into radiation-induced molecular-level processes.
- Published
- 2010
36. FY09 Engineering Research & Technology Report
- Author
-
Richard C. Montesanti, Jerry I. Lin, Rebecca J. Nikolic, Todd H. Weisgraber, Harry E. Martz, Robin Miles, Carol Meyers, James S. Stolken, Salvador M. Aceves, Christopher M. Spadaccini, Sean K. Lehman, Brenda Ng, Satinderpall S. Pannu, Michael A. Puso, John E. Heebner, Jerome Solberg, Gabriela G. Loots, Tracy D. Lemmond, Bob Corey, Klint A. Rose, R. Seugling, Joh M. Dzenitis, Joel V. Bernier, R. Sharpe, Nathan R. Barton, Timothy L. Houck, Michael J. King, James V. Candy, Vincent Tang, J.N. Florando, Adam M. Conway, and Daniel A. White
- Subjects
Engineering ,Engineering management ,business.industry ,Railway engineering ,Engineering research ,business - Published
- 2010
37. Environmental monitoring for biological threat agents using the autonomous pathogen detection system with multiplexed polymerase chain reaction
- Author
-
John Breneman, Benjamin J. Hindson, Thomas R. Metz, Bruce D. Henderer, Todd H. Corzett, Anthony J. Makarewicz, Dora M. Gutierrez, Ryan C. Mahnke, Todd H. Weisgraber, Dean R. Hadley, John M. Dzenitis, and John F. Regan
- Subjects
Biodefense ,Pathogen detection ,biology ,APDS ,Chemistry ,Yersinia pestis ,Real-time computing ,biology.organism_classification ,Multiplexing ,Bioterrorism ,Polymerase Chain Reaction ,Analytical Chemistry ,Bacillus anthracis ,law.invention ,Microsphere ,law ,Environmental monitoring ,cardiovascular system ,Polymerase chain reaction ,Environmental Monitoring - Abstract
We have developed and field-tested a now operational civilian biodefense capability that continuously monitors the air in high-risk locations for biological threat agents. This stand-alone instrument, called the Autonomous Pathogen Detection System (APDS), collects and selectively concentrates particles from the air into liquid samples and analyzes the samples using multiplexed PCR amplification coupled with microsphere array detection. During laboratory testing, we evaluated the APDS instrument's response to Bacillus anthracis and Yersinia pestis by spiking the liquid sample stream with viable spores and cells, bead-beaten lysates, and purified DNA extracts. APDS results were also compared to a manual real-time PCR method. Field data acquired during 74 days of continuous operation at a mass-transit subway station are presented to demonstrate the specificity and reliability of the APDS. The U.S. Department of Homeland Security recently selected the APDS reported herein as the first autonomous detector component of their BioWatch antiterrorism program. This sophisticated field-deployed surveillance capability now generates actionable data in one-tenth the time of manual filter collection and analysis.
- Published
- 2008
38. Convectively driven polymerase chain reaction thermal cycler
- Author
-
Fred P. Milanovich, A. Christian, J. Ortega, James B. Richards, A. Chen, William J. Benett, Todd H. Weisgraber, Kevin D. Ness, L. G. Li, Kenneth E. Goodson, Paul Stratton, and Elizabeth K. Wheeler
- Subjects
Buoyancy ,Time Factors ,Thermal cycler ,Chemistry ,Flow (psychology) ,Thermal cycle ,Mechanics ,engineering.material ,Polymerase Chain Reaction ,Finite element method ,Analytical Chemistry ,law.invention ,Electric Power Supplies ,Particle image velocimetry ,law ,Thermal ,engineering ,Polymerase chain reaction - Abstract
We have fabricated a low-cost disposable polymerase chain reaction thermal chamber that uses buoyancy forces to move the sample solution between the different temperatures necessary for amplification. Three-dimensional, unsteady finite element modeling and a simpler 1-D steady-state model are used together with digital particle image velocimetry data to characterize the flow within the device. Biological samples have been amplified using this novel thermal chamber. Time for amplification is less than 30 min. More importantly, an analysis of the energy consumption shows significant improvements over current technology.
- Published
- 2004
39. Cellular Solids: Three-Dimensional Printing of Elastomeric, Cellular Architectures with Negative Stiffness (Adv. Funct. Mater. 31/2014)
- Author
-
Christopher M. Spadaccini, Keith Hearon, Joshua D. Kuntz, Ward Small, Holly D. Barth, Todd H. Weisgraber, Cheng Zhu, Thomas S. Wilson, John J. Vericella, Thomas R. Metz, Robert S. Maxwell, and Eric B. Duoss
- Subjects
Biomaterials ,Materials science ,business.industry ,Three dimensional printing ,Negative stiffness ,Electrochemistry ,3D printing ,Nanotechnology ,Condensed Matter Physics ,business ,Elastomer ,Electronic, Optical and Magnetic Materials - Published
- 2014
40. Publisher's Note: 'Design and optimization of a light-emitting diode projection micro-stereolithography three-dimensional manufacturing system' [Rev. Sci. Instrum. 83, 125001 (2012)]
- Author
-
Howon Lee, Nicholas X. Fang, Christopher M. Spadaccini, Todd H. Weisgraber, Matthew P. Alonso, Joshua R. Deotte, Xiaoyu Zheng, George R. Farquar, and Steven Gemberling
- Subjects
Nanolithography ,Optics ,Materials science ,Projection micro-stereolithography ,business.industry ,law ,Optoelectronics ,business ,Manufacturing systems ,Instrumentation ,Stereolithography ,law.invention ,Light-emitting diode - Published
- 2013
41. Design and optimization of a light-emitting diode projection micro-stereolithography three-dimensional manufacturing system
- Author
-
Nicholas X. Fang, Christopher M. Spadaccini, Steven Gemberling, Joshua R. Deotte, George R. Farquar, Matthew P. Alonso, Howon Lee, Xiaoyu Zheng, and Todd H. Weisgraber
- Subjects
Fabrication ,Nanolithography ,Materials science ,Projection micro-stereolithography ,law ,Nanotechnology ,Projection (set theory) ,Instrumentation ,Throughput (business) ,Stereolithography ,law.invention ,Diode ,Light-emitting diode - Abstract
The rapid manufacture of complex three-dimensional micro-scale components has eluded researchers for decades. Several additive manufacturing options have been limited by either speed or the ability to fabricate true three-dimensional structures. Projection micro-stereolithography (PμSL) is a low cost, high throughput additive fabrication technique capable of generating three-dimensional microstructures in a bottom-up, layer by layer fashion. The PμSL system is reliable and capable of manufacturing a variety of highly complex, three-dimensional structures from micro- to meso-scales with micro-scale architecture and submicron precision. Our PμSL system utilizes a reconfigurable digital mask and a 395 nm light-emitting diode (LED) array to polymerize a liquid monomer in a layer-by-layer manufacturing process. This paper discusses the critical process parameters that influence polymerization depth and structure quality. Experimental characterization and performance of the LED-based PμSL system for fabricating highly complex three-dimensional structures for a large range of applications is presented.
- Published
- 2012
42. Tethered DNA dynamics in shear flow
- Author
-
Michael D. Graham, Berni J. Alder, Aleksandar Donev, Todd H. Weisgraber, Yu Zhang, and Juan J. de Pablo
- Subjects
Physics ,Polymers ,Stochastic process ,Lattice Boltzmann methods ,General Physics and Astronomy ,DNA ,Solutions ,Condensed Matter::Soft Condensed Matter ,Physics::Fluid Dynamics ,Shear rate ,Molecular dynamics ,Classical mechanics ,Models, Chemical ,Flow (mathematics) ,Brownian dynamics ,Computer Simulation ,Physical and Theoretical Chemistry ,Shear flow ,Algorithms ,Brownian motion - Abstract
We study the cyclic dynamics of a single polymer tethered to a hard wall in shear flow using Brownian dynamics, the lattice Boltzmann method, and a recent stochastic event-driven molecular dynamics algorithm. We focus on the dynamics of the free end (last bead) of the tethered chain and we examine the cross-correlation function and power spectral density of the chain extensions in the flow and gradient directions as a function of chain length N and dimensionless shear rate Wi. Extensive simulation results suggest a classical fluctuation-dissipation stochastic process and question the existence of periodicity of the cyclic dynamics, as previously claimed. We support our numerical findings with a simple analytical calculation for a harmonic dimer in shear flow.
- Published
- 2009
43. Linking Network Microstructure to Macroscopic Properties of Siloxane Elastomers Using Combined Nuclear Magnetic Resonance and Mesoscale Computational Modeling.
- Author
-
Brian P. Mayer, James P. Lewicki, Todd H. Weisgraber, Ward Small, Sarah C. Chinn, and Robert S. Maxwell
- Published
- 2011
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