Modeling and Simulation of the Impact Response of Linear Cellular Alloys for Structural Energetic Material Applications

We investigate the deformation and fracture as well as stress transfer behavior of 250 maraging steel linear cellular alloys (LCAs) undergoing high velocity impact upon a rigid target. Of paramount importance for application as a ballistic delivery mechanism for thermite powders, is the ability to transfer stress along the inner length of the cell walls. Additionally, outward fragmentation of the LCA body upon impact must be controlled. Parameters for a Johnson-Cook strength model of 250 maraging steel are determined in conjunction with 3-dimensional Lagrangian based finite element analysis on a solid cylinder. These parameters are then applied to four, 25% theoretical density LCA geometries: hollow cylinder, pie, reinforced pie, and 9-cell waffle. Verification of the validity of the Johnson-Cook parameters determined from the solid cylinder experiments and simulations is analyzed through comparison of experiments of the four LCA geometries, produced using a direct reduction technique with corresponding simulations. Upon verification of the Johnson-Cook strength model for maraging steel, the deformation and fracture as well as the stress transfer response of the LCAs during impact is analyzed. Through transient analysis of finite element simulations, it has been determined that the 9-cell waffle geometry displays optimal stress transfer behavior as well as limited outward fragmentation.Thadhani, Naresh - Faculty Mentor ; Carter, Brent - Committee Member/Second Reade

The Analysis of Drive Systems in Unmanned Underwater Vehicles Towards Identifying the Method of Drive Transmission

This is the first part of the material concerned with the analysis of drive systems in remotely controlled unmanned underwater vehicles. The paper discusses the problem of classification of UUVs, mainly remotely controlled, with an indication of four different approaches to this issue. Moreover, the article discusses the nomenclature used in relation to various components of the discussed drive systems and thrusters, as well as indicates the functionality of such systems along with the advantages and disadvantages of the analysed design solutions. The method of analysis of drive systems, its methodology and the results will be the subject of a subsequent publication of the authors

Climate Change and Angling Behavior on the North Shore of Lake Superior

Angling in Minnesota’s North Shore faces unique threats from the impacts of climate change. These impacts, such as changes in the presence and/or abundance of specific species, present management challenges which might also influence the demand for recreational angling throughout the region. Anglers’ adaptations to climate change in the North Shore region could shift densities, timing, and spatial use of the region’s fish populations, increasing the stress on ecological systems. Developing an empirically grounded understanding of the contingent behaviors of anglers is imperative if the region’s fish populations are to be managed sustainably. Using a travel cost model, we measure the demand for angling under current conditions and potential future climate and environmental conditions. Our research also explores the adaptive and coping behaviors of anglers. Results suggest North Shore anglers are not likely to alter the total number of trips they take to the region in the future as climate and environmental conditions change. Among the adaptive and coping behaviors we asked about, anglers indicated they are most likely to engage in a different activity (activity substitution) as conditions change; they also indicated a willingness to fish elsewhere (spatial substitution). Rescheduling or canceling angling trips (temporal substitution) was the least preferred adaptive/coping behavior. Further research is needed to understand why anglers’ future trip-taking behaviors are not responsive to changes in climate and environmental conditions, though their adaptive and coping behaviors are. Our findings can be used to help managers maintain the satisfaction, experiences, and participation of future generations of anglers

Functional Maturation of Induced Pluripotent Stem Cell Hepatocytes in Extracellular Matrix—A Comparative Analysis of Bioartificial Liver Microenvironments

Induced pluripotent stem cells (iPSCs) are new diagnostic and potentially therapeutic tools to model disease and assess the toxicity of pharmaceutical medications. A common limitation of cell lineages derived from iPSCs is a blunted phenotype compared with fully developed, endogenous cells. We examined the influence of novel three-dimensional bioartificial microenvironments on function and maturation of hepatocyte-like cells differentiated from iPSCs and grown within an acellular, liver-derived extracellular matrix (ECM) scaffold. In parallel, we also compared a bioplotted poly-l-lactic acid (PLLA) scaffold that allows for cell growth in three dimensions and formation of cell-cell contacts but is infused with type I collagen (PLLA-collagen scaffold) alone as a “deconstructed” control scaffold with narrowed biological diversity. iPSC-derived hepatocytes cultured within both scaffolds remained viable, became polarized, and formed bile canaliculi-like structures; however, cells grown within ECM scaffolds had significantly higher P450 (CYP2C9, CYP3A4, CYP1A2) mRNA levels and metabolic enzyme activity compared with iPSC hepatocytes grown in either bioplotted PLLA collagen or Matrigel sandwich control culture. Additionally, the rate of albumin synthesis approached the level of primary cryopreserved hepatocytes with lower transcription of fetal-specific genes, α-fetoprotein and CYP3A7, compared with either PLLA-collagen scaffolds or sandwich culture. These studies show that two acellular, three-dimensional culture systems increase the function of iPSC-derived hepatocytes. However, scaffolds derived from ECM alone induced further hepatocyte maturation compared with bioplotted PLLA-collagen scaffolds. This effect is likely mediated by the complex composition of ECM scaffolds in contrast to bioplotted scaffolds, suggesting their utility for in vitro hepatocyte assays or drug discovery. SIGNIFICANCE: Through the use of novel technology to develop three-dimensional (3D) scaffolds, the present study demonstrated that hepatocyte-like cells derived via induced pluripotent stem cell (iPSC) technology mature on 3D extracellular matrix scaffolds as a result of 3D matrix structure and scaffold biology. The result is an improved hepatic phenotype with increased synthetic and catalytic potency, an improvement on the blunted phenotype of iPSC-derived hepatocytes, a critical limitation of iPSC technology. These findings provide insight into the influence of 3D microenvironments on the viability, proliferation, and function of iPSC hepatocytes to yield a more mature population of cells for cell toxicity studies and disease modeling

Voltaglue bioadhesives energized with interdigitated 3D‐graphene electrodes

Soft tissue fixation of implant and bioelectrodes relies on mechanical means (e.g., sutures, staples, and screws), with associated complications of tissue perforation, scarring, and interfacial stress concentrations. Adhesive bioelectrodes address these shortcomings with voltage cured carbene-based bioadhesives, locally energized through graphene interdigitated electrodes. Electrorheometry and adhesion structure activity relationships are explored with respect to voltage and electrolyte on bioelectrodes synthesized from graphene 3D-printed onto resorbable polyester substrates. Adhesive leachates effects on in vitro metabolism and human-derived platelet-rich plasma response serves to qualitatively assess biological response. The voltage activated bioadhesives are found to have gelation times of 60 s or less with maximum shear storage modulus (G') of 3 kPa. Shear modulus mimics reported values for human soft tissues (0.1-10 kPa). The maximum adhesion strength achieved for the ≈50 mg bioelectrode films is 170 g cm-2 (17 kPa), which exceeds the force required for tethering of electrodes on dynamic soft tissues. The method provides the groundwork for implantable bio/electrodes that may be permanently incorporated into soft tissues, vis-à-vis graphene backscattering wireless electronics since all components are bioresorbable.MOE (Min. of Education, S’pore)Accepted versio

Three-Dimensional Printing of Cytocompatible, Thermally Conductive Hexagonal Boron Nitride Nanocomposites

Hexagonal boron nitride (hBN) is a thermally conductive yet electrically insulating two-dimensional layered nanomaterial that has attracted significant attention as a dielectric for high-performance electronics in addition to playing a central role in thermal management applications. Here, we report a high-content hBN-polymer nanocomposite ink, which can be 3D printed to form mechanically robust, self-supporting constructs. In particular, hBN is dispersed in poly­(lactic-<i>co</i>-glycolic acid) and 3D printed at room temperature through an extrusion process to form complex architectures. These constructs can be 3D printed with a composition of up to 60% vol hBN (solids content) while maintaining high mechanical flexibility and stretchability. The presence of hBN within the matrix results in enhanced thermal conductivity (up to 2.1 W K^–1 m^–1) directly after 3D printing with minimal postprocessing steps, suggesting utility in thermal management applications. Furthermore, the constructs show high levels of cytocompatibility, making them suitable for use in the field of printed bioelectronics