Search NASA⌕ Search

SEARCH · Search NASA

Results for “ENFORCEMENT”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

microRNA-495 promotes bladder cancer cell growth and invasion by targeting phosphatase and tensin homolog

Accumulating evidence has linked deregulation of microRNA-495 (miR-495) to tumorigenesis; however, its function in tumor progression is controversial. This work was undertaken to explore the expression and biological roles of miR-495 in bladder cancer. The expression of miR-495 was examined in 67 pairs of bladder cancer and adjacent normal bladder tissues. The roles of miR-495 in bladder cancer cell proliferation and invasion in vitro and tumorigenesis in vivo were determined. Direct target gene(s) mediating the activity of miR-495 in bladder cancer cells was identified. It was found that miR-495 was expressed at greater levels in bladder tissues and cell lines. High expression of miR-495 was significantly associated with larger tumor size, advanced TNM stage, and lymph node metastasis. Overexpression of miR-495 significantly promoted bladder cancer cell proliferation and invasion, whereas inhibition of miR-495 suppressed cell proliferation and invasion. PTEN, a well-defined tumor suppressor was identified to be a target gene of miR-495. A significant inverse correlation between miR-495 and PTEN expression was noted in bladder cancer tissues (r = −0.3094, P = 0.0125). Overexpression of miR-495 led to reduction of PTEN expression in bladder cancer cells. Rescue experiments showed that enforced expression of PTEN impaired miR-495-mediated bladder cancer proliferation and invasion. In vivo mouse studies demonstrated that overexpression of miR-495 accelerated the growth of subcutaneous bladder cancer xenografts, which was associated with downregulation of PTEN. Overall, these findings indicate that miR-495 upregulation contributes to bladder cancer cell growth, invasion, and tumorigenesis by targeting PTEN and offer a potential therapeutic target for bladder cancer. - Highlights: • miR-495 upregulation induces aggressive phenotype in bladder cancer. • miR-495 is inversely correlated with PTEN in bladder cancer. • miR-495 promotes bladder cancer cell proliferation and invasion by targeting PTEN.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Production of ABA responses requires both the nuclear and cytoplasmic functional involvement of PYR1

Abscisic acid (ABA) enhances stress tolerant responses in plants against unfavorable environmental conditions. In Arabidopsis, ABA promotes interactions between PYR/PYL/RCARs and PP2C, thereby allowing SnRK2s to phosphorylate downstream components required for the regulation of gene expression or for gating ion channels. Because PYR1 is known to localize to nucleus and cytoplasm it is a question whether nuclear or cytoplasmic PYR1 confer different functions to the ABA signaling pathway, as has been previously shown for regulatory proteins. In order to answer this question, transgenic lines expressing nuclear PYR1 were generated in an ABA insensitive mutant background. Enforced nuclear expression of PYR1 was examined by confocal microscopy and western blot analysis. Physiological analyses of the transgenic lines demonstrated that nuclear PYR1 is sufficient to generate ABA responses, such as, the inhibition of seed germination, root growth inhibition, the induction of gene expression, and stomatal closing movement. However, for the full recovery of ABA responses in the mutant background cytoplasmic PYR1 was required. The study suggests both nuclear and cytoplasmic PYR1 participate in the control of ABA signal transduction. - Highlights: • Nuclear and cytoplasmic functions of PYR1 were studied in the mutant which lacked majority of ABA responses. • Nuclear PYR1 reconstituted partially the ABA responses during seed germination, root growth, and guard cell movement. • Both the nuclear and cytoplasmic functions of PYR1 were required for the full generation of ABA responses.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

25-hydroxycholesterol promotes RANKL-induced osteoclastogenesis through coordinating NFATc1 and Sp1 complex in the transcription of miR-139-5p

25-hydroxycholesterol (25-HC) is implicated in many processes, including lipid metabolism and the immune response. However, the role of 25-HC in RANKL-induced osteoclastogenesis remains largely unknown. Our results showed that 25-HC inhibited miR-139-5p expression in mouse bone marrow macrophages (BMMs) cultured in receptor activator of NF-κB ligand (RANKL) and monocyte macrophage colony-stimulating factor (M-CSF). Further investigation suggested that 25-HC promoted the expression of nuclear factor of activated T cell cytoplasmic 1 (NFATc1) and Sp1, especially in the presence of RANKL and M-CSF. Meanwhile, 25-HC induced nuclear translocation of NFATc1, resulting in the interaction between NFATc1 and Sp1 that was confirmed by co-immunoprecipitation. Chromatin immunoprecipitation assay indicated that Sp1 could bind to miR-139-5p promoter, but NFATc1 had no binding capacity. Although forming NFATc1/Sp1 complex increased its binding to miR-139-5p promoter, the complex inhibited the transcriptional activity of Sp1. Inhibition of NFATc1 increase the expression of miR-139-5p, which might be due to the release of free Sp1 that could bind to the promoter of miR-139-5p. Enforced expression of miR-139-5p impaired osteoclastogenesis induced by co-treatment with 25-HC and RANKL. These results suggested that 25-HC induced the interaction between NFATc1 and Sp1, reducing the level of free Sp1 to inhibit miR-139-5p expression and promote osteoclastogenesis. - Highlights: • 25-hydroxycholesterol inhibited miR-139-5p expression in bone marrow macrophages. • 25-hydroxycholesterol promoted the expression of NFATc1 and Sp1. • 25-hydroxycholesterol induced the interaction between NFATc1 and Sp1. • NFATc1/Sp1 complex inhibited the transcription of miR-139-5p. • MiR-139-5p impaired osteoclastogenesis induced by 25-hydroxycholesterol and RANKL.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Mitochondrial potassium channels in cell death

Highlights: • Mitochondria are the key organelles involved in several cellular processes. • Mitochondrial K{sup +} channels can modulate mitochondrial membrane potential. • Targeting of mitochondrial K{sup +} channels leads to mitochondrial ROS production. • Modulation of apoptosis by K{sup +} channels could be new strategy to kill cancer cells. Mitochondria are intracellular organelles involved in several processes from bioenergetics to cell death. In the latest years, ion channels are arising as new possible targets in controlling several cellular functions. The discovery that several plasma membrane located ion channels have intracellular counterparts, has now implemented this consideration and the number of studies enforcing the understanding of their role in different metabolic pathways. In this review, we will discuss the recent updates in the field, focusing our attention on the involvement of potassium channels during mitochondrial mediated apoptotic cell death. Since mitochondria are one of the key organelles involved in this process, it is not surprising that potassium channels located in their inner membrane could be involved in modulating mitochondrial membrane potential, ROS production, and respiratory chain complexes functions. Eventually, these events lead to changes in the mitochondrial fitness that prelude to the cytochrome c release and apoptosis. In this scenario, both the inhibition and the activation of mitochondrial potassium channels could cause cell death, and their targeting could be a novel pharmacological way to treat different human diseases.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

DOCK1 inhibition suppresses cancer cell invasion and macropinocytosis induced by self-activating Rac1P29S mutation

Highlights: • A guanine nucleotide exchange factor DOCK1 promotes GDP/GTP exchange of Rac1{sup P29S}. • DOCK1 deficiency cancels Rac1{sup P29S}-mediated invasion and macropinocytosis. • A DOCK1 inhibitor suppresses Rac1{sup P29S}-mediated invasion and macropinocytosis. Rac1 is a member of the Rho family of small GTPases that regulates cytoskeletal reorganization, membrane polarization, cell migration and proliferation. Recently, a self-activating mutation of Rac1, Rac1{sup P29S}, has been identified as a recurrent somatic mutation frequently found in sun-exposed melanomas, which possesses increased inherent GDP/GTP exchange activity and cell transforming ability. However, the role of cellular Rac1-interacting proteins in the transforming potential of Rac1{sup P29S} remains unclear. We found that the catalytic domain of DOCK1, a Rac-specific guanine nucleotide exchange factor (GEF) implicated in malignancy of a variety of cancers, can greatly accelerate the GDP/GTP exchange of Rac1{sup P29S}. Enforced expression of Rac1{sup P29S} induced matrix invasion and macropinocytosis in wild-type (WT) mouse embryonic fibroblasts (MEFs), but not in DOCK1-deficient MEFs. Consistently, a selective inhibitor of DOCK1 that blocks its GEF function suppressed the invasion and macropinocytosis in WT MEFs expressing Rac1{sup P29S}. Human melanoma IGR-1 and breast cancer MDA-MB-157 cells harbor Rac1{sup P29S} mutation and express DOCK1 endogenously. Genetic inactivation and pharmacological inhibition of DOCK1 suppressed their invasion and macropinocytosis. Taken together, these results indicate that DOCK1 is a critical regulator of the malignant phenotypes induced by Rac1{sup P29S}, and suggest that targeting DOCK1 might be an effective approach to treat cancers associated with Rac1{sup P29S} mutation.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

ATF3 mediates the inhibitory action of TNF-α on osteoblast differentiation through the JNK signaling pathway

Highlights: • TNF-α downregulated osteogenic markers, but upregulated the expression of ATF3. • Inhibition of ATF3 reversed the inhibition of osteoblast differentiation by TNF-α. • Overexpression of ATF3 enhances the inhibition of osteoblast differentiation by TNF-α. • ATF3 mediates the inhibitory action of TNF-α on osteoblast differentiation via JNK signaling pathway. Tumor necrosis factor (TNF)-α, which is a proinflammatory cytokine, inhibits osteoblast differentiation under diverse inflammatory conditions. Activating transcription factor 3 (ATF3), which is a member of the ATF/cAMP response element-binding protein family of transcription factors, has been implicated in the regulation of cell proliferation and differentiation. However, the precise interactions between ATF3 and the TNF-α signaling pathway in the regulation of osteoblast differentiation remain unclear. In this study, we examined the role of ATF3 in the TNF-α-mediated inhibition of osteoblast differentiation and investigated the signaling pathways involved. The treatment of cells with TNF-α downregulated osteogenic markers, but significantly upregulated the expression of Atf3. The inhibition of Atf3 by small interfering RNAs rescued osteogenesis, which was inhibited by TNF-α. Conversely, the enforced expression of Atf3 enhanced the TNF-α-mediated inhibition of osteoblast differentiation, as revealed by the measurement of osteogenic markers and alkaline phosphatase staining. Mechanistically, TNF-α-induced Atf3 expression was significantly suppressed by the inhibition of the c-Jun N-terminal kinase (JNK) pathway. Furthermore, the overexpression of Atf3 did not affect the rescue effect that inhibiting TNF-α expression using a JNK inhibitor had on alkaline phosphatase activity and mineralization. Taken together, these results indicate that ATF3 mediates the inhibitory action of TNF-α on osteoblast differentiation and that the TNF-α-activated JNK pathway is responsible for the induction of Atf3 expression.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

MicroRNA-124-3p represses cell growth and cell motility by targeting EphA2 in glioma

Highlights: • miR-124-3p inhibits glioma cell proliferation. • miR-124-3p inhibits glioma cell motility. • miR-124-3p suppresses glioma cell EMT. • EphA2 is a candidate target of miR-124-3p. MiR-124-3p and EphA2 are aberrantly expressed in glioma tissue specimens. In the present study, we firstly investigated that miR-124-3p inhibits EphA2 expression mediated by binding its 3′-UTR to regulate the progression of human glioma. The U87MG and LN229 cells were transfected with miR-124-3p mimics and/or siRNA-EphA2, and then the role of miR-124-3p and EphA2 in the colony-formation, cell-cycle, migration and invasion of glioma cells in vitro were examined. Proteins involved in the epithelial-mesenchymal transition were examined using western blot. The results showed that miR-124-3p was significantly downregulated in glioma tissues, whereas a marked upregulation of EphA2 expression was found. Colony-formation and flow cytometry assays demonstrated that EphA2 downregulation or miR-124-3p mimics caused growth and cell-cycle inhibition in glioma. Transwell migration and invasion assays demonstrated that EphA2 downregulation or miR-124-3p mimics suppressed the migration and invasion of glioma cells. EphA2 downregulation or miR-124-3p mimics reduced the level of vimentin in U87MG and LN229 cells. In conclusion, miR-124-3p was found to suppress the growth, migration and invasion of glioma cells in vitro via EphA2. Furthermore, we validated miR-124-3p enforced its biological modulation via targeting EphA2 through the rescue experiment. Conclusively, our study proclaimed that miR-124-3p can counteract the malignant phenotypes of glioma cells by the inhibitory effect of the EphA2.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

The miR-31-SOX10 axis regulates tumor growth and chemotherapy resistance of melanoma via PI3K/AKT pathway

Highlights: • Firstly found up-regulation of SOX10 and down-regulation of miR-31 in MM. • miR-31 regulated SOX10 by binding to its 3′UTR. • SOX10 regulated tumor growth and chemotherapy resistance of melanoma in vitro and in vivo. • The miR-31-SOX10 axis mediated tumor growth and drug resistance via activation of PI3K/AKT pathway. MicroRNAs were thought to play a regulatory role through complementarity to target messenger RNA (mRNA). Our previous study revealed a miR-31-SOX10 axis that regulated tumor growth and resistance to chemotherapy of melanoma. Up-regulation of SOX10 and down-regulation of miR-31 were found in melanoma tissues. SOX10 was further identified as a target of miR-31. Overexpression of SOX10 dramatically promoted melanoma cell proliferation and chemotherapy resistance both in vitro and in vivo. While enforced miR-31 expression suppressed cell growth and enhanced the chemosensitivity of melanoma cells, the re-expression of SOX10 rescued these effects by activating PI3K/AKT signaling pathway. In conclusion, our results demonstrated that SOX10 acted as an oncogene and was negatively regulated by miR-31, which supports the potential therapeutic strategy against melanoma by targeting the miR-31-SOX10 axis.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Long non-coding RNA SBF2-AS1 promotes hepatocellular carcinoma progression through regulation of miR-140-5p-TGFBR1 pathway

Highlights: • LncRNA SBF2-AS1 was overexpressed in HCC tissues and cell lines. • Up-regulation of lncRNA SBF2-AS1 was associated with poor clinical features and prognosis in HCC patients. • Knockdown of lncRNA SBF2-AS1 suppressed HCC progression by regulation of miR-140-5p-TGFBR1 pathway. A growing number of studies has suggested that long non-coding RNAs (lncRNAs) exert essential roles in the development and progression of hepatocellular carcinoma (HCC). However, the roles of lncRNA and its molecular mechanism in HCC are largely unknown. In the present study, the functions and molecular mechanisms of a novel lncRNA, SET-binding factor 2 (SBF2) antisense RNA1 (SBF2-AS1), were investigated in HCC tissues and cell lines. We found that the expression levels of SBF2-AS1 were significantly up-regulated in HCC tissues and correlated with poor prognosis. SBF2-AS1 knockdown could inhibit the proliferation of HCC cells and attenuate the development of HCC tumor in vivo. Moreover, wound healing and Transwell assays revealed that down-regulation of SBF2-AS1 suppressed the migration and invasion of HCC cells by modulating epithelial-mesenchymal transition (EMT) ability. Mechanistically, we observed that SBF2-AS1 served as a competing endogenous RNA (ceRNA) of miR-140–5p. Subsequently, transforming growth factor beta receptor 1 (TGFBR1) was certified as a direct target of miR-140–5p and enforcing SBF2-AS1 expression elevated TGFBR1 expression in HCC. Taken together, our study suggested that SBF2-AS1 modulated TGFBR1 through sponging miR-140–5p in HCC development and progression indicating that SBF2-AS1 might be further chosen as a potential anticancer therapeutic target and a promising prognostic biomarker for HCC.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Linkage between lipid droplet formation and nuclear deformation in HeLa human cervical cancer cells

Highlights: • Oleic acid (OA) induces cytoplasmic, but not nucleoplasmic, LDs in HeLa cells. • Cells harboring OA-induced cytoplasmic LDs exhibit deformity of the nucleus. • Multinucleation by paclitaxel and reversine treatment coincides with LD formation. • LD formation and nuclear deformation are mutually affectable. Because lipid droplets (LDs) and the nucleus are cellular organelles that regulate seemingly very different biochemical processes, very little attention has been focused on their possible interplay. Here, we report a correlation between nuclear morphology and cytoplasmic LD formation in HeLa human cervical cells. When the cells were treated with oleic acid (OA), LDs were formed in the cytoplasm, but not in the nucleoplasm. Interestingly, cells harboring OA-induced cytoplasmic LDs showed deformity of the nucleus, particularly at the nuclear rim. Conversely, when alteration from a single spherical nuclear shape to a multinucleated form was enforced by coadministration of paclitaxel and reversine, a significant amount of LDs was detected in the cytoplasm of the multinucleated cells. These two distinct pharmacological culture conditions not only allow analysis of the previously underappreciated organelle relationship, but also provide insights into the mutual affectability of LD formation and nuclear deformation.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

The positive feedback between lncRNA TNK2-AS1 and STAT3 enhances angiogenesis in non-small cell lung cancer

Highlights: • TNK2-AS1 promotes NSCLC. • TNK2-AS1 interacts with STAT3. • STAT3 induces TNK2-AS1 expression. Evidence has shown the importance of long non-coding RNAs (lncRNAs) during angiogenesis and lung cancer progression. However, the potential functions of TNK2-AS1 in non-small cell lung cancer (NSCLC) remain elusive. By lncRNA profiling, we identified TNK2-AS1 as a novel oncogenic lncRNA in NSCLC. TNK2-AS1 was significantly upregulated in NSCLC and correlated with poor prognosis. We found that TNK2-AS1 could increase viability and migration of NSCLC cells in vitro. TNK2-AS1 also promoted NSCLC xenograft tumor growth and metastasis in vivo. TNK2-AS1 could interact with STAT3 to increase its protein stability by protecting it from proteasome-mediated degradation. STAT3 could also bind TNK2-AS1 promoter to trigger its transcription. The positive feedback loop between STAT3 and TNK2-AS1 therefore augmented STAT3 signaling by elevating VEGFA expression to facilitate angiogenesis. Collectively, our work has elucidated a novel mechanism of TNK2-AS1-mediated angiogenesis by enforcing STAT3/VEGFA signaling and may provide a potential target for therapeutic intervention.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2025

SAXS Assistant: Automated SAXS analysis for structural discovery in biologics and polymeric nanoparticles

Small-angle x-ray scattering (SAXS) is a powerful technique for assessing macromolecular structure. High-throughput SAXS is limited by the time-consuming and, at times, subjective nature of SAXS data interpretation. Here, we present SAXS Assistant, a Python-based script that streamlines SAXS data analysis to extract features for machine learning (ML) and key structural parameters, including the Guinier radius of gyration (R g ), pair distance distribution function (PDDF)-derived R g , maximum particle dimension (D max ), and Kratky plots. The script builds upon BioXTAS RAW and validates reliability via Guinier/PDDF R g agreement, an important indicator of well-measured data sets. For assistance in D max estimation, a multilayer perceptron regressor was trained with 1940 data files from the Small Angle Scattering Biological Data Bank. The model achieved a test set performance R 2 = 0.90 and mean absolute error = 11.7 Å. Training exclusively with experimental data translates analyses from researchers, including experts in the field, to the ML model, which helps assess D max estimations from PDDF. Gaussian mixture model clustering was implemented to classify profiles into structural classes based on entries in the Small Angle Scattering Biological Data Bank. Users may therefore assess the similarity between experimental samples and known biomolecular shapes within the mapped repository entries. This probabilistic clustering aids in quantifying information from Kratky and generating shape-descriptive features. SAXS Assistant accelerates SAXS data analysis through enforced quality control, ML-ready outputs, and flags for low-confidence results. In addition to providing the ability to analyze large data sets at high throughput, this tool is versatile and may serve researchers in both biological and synthetic polymer research fields.

36 MATERIALS SCIENCE↗
DOE OSTI2018

An updated Lagrangian discontinuous Galerkin hydrodynamic method for gas dynamics

Here, we present a new Lagrangian discontinuous Galerkin (DG) hydrodynamic method for gas dynamics. The new method evolves conserved unknowns in the current configuration, which obviates the Jacobi matrix that maps the element in a reference coordinate system or the initial coordinate system to the current configuration. The density, momentum, and total energy (ρ, ρu, E ) are approximated with conservative higher-order Taylor expansions over the element and are limited toward a piecewise constant field near discontinuities using a limiter. Two new limiting methods are presented for enforcing the bounds on the primitive variables of density, velocity, and specific internal energy (ρ, u, e). The nodal velocity, and the corresponding forces, are calculated by solving an approximate Riemann problem at the element nodes. An explicit second-order method is used to temporally advance the solution. This new Lagrangian DG hydrodynamic method conserves mass, momentum, and total energy. 1D Cartesian coordinates test problem results are presented to demonstrate the accuracy and convergence order of the new DG method with the new limiters.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2024

Optimization-based, property-preserving algorithm for passive tracer transport

Here we present a new optimization-based property-preserving algorithm for passive tracer transport. The algorithm utilizes a semi-Lagrangian approach based on incremental remapping of the mass and the total tracer. However, unlike traditional semi-Lagrangian schemes, which remap the density and the tracer mixing ratio through monotone reconstruction or flux correction, we utilize an optimization-based remapping that enforces conservation and local bounds as optimization constraints. In so doing we separate accuracy considerations from preservation of physical properties to obtain a conservative, second-order accurate transport scheme that also has a notion of optimality. Moreover, we prove that the optimization-based algorithm preserves linear relationships between tracer mixing ratios. We illustrate the properties of the new algorithm using a series of standard tracer transport test problems in a plane and on a sphere.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

Multistage economic MPC for systems with a cyclic steady state: A gas network case study

Multistage model predictive control (MPC) provides a robust control strategy for dynamic systems with uncertainties and a setpoint tracking objective. Moreover, extending MPC to minimize an economic cost instead of tracking a pre-calculated optimal setpoint improves controller performance. This paper presents a novel multistage economic nonlinear model predictive control (E-NMPC) framework for dynamic systems operating under uncertainty, with specific application to natural gas transmission networks. A key innovation lies in the integration of cyclic steady-state (CSS) constraints within the multistage MPC formulation, enabling the controller to manage periodic operating conditions commonly observed in energy systems. A Lyapunov-based descent condition is enforced to ensure robust stability of the controller. The multistage economic MPC framework is validated on two gas pipeline case studies, where it successfully minimizes net energy consumption, respects operational constraints under uncertain demand profiles, and guides the network to optimal cyclic operation. The Lyapunov function remains bounded in both case studies, validating the robust stability of multistage E-NMPC.

03 NATURAL GAS↗
DOE OSTI2017

On domain symmetry and its use in homogenization

The present study focuses on solving partial differential equations in domains exhibiting symmetries and periodic boundary conditions for the purpose of homogenization. We show in a systematic manner how the symmetry can be exploited to significantly reduce the complexity of the problem and the computational burden. This is especially relevant in inverse problems, when one needs to solve the partial differential equation (the primal problem) many times in an optimization algorithm. The main motivation of our study is inverse homogenization used to design architected composite materials with novel properties which are being fabricated at ever increasing rates thanks to recent advances in additive manufacturing. For example, one may optimize the morphology of a two-phase composite unit cell to achieve isotropic homogenized properties with maximal bulk modulus and minimal Poisson ratio. Typically, the isotropy is enforced by applying constraints to the optimization problem. However, in two dimensions, one can alternatively optimize the morphology of an equilateral triangle and then rotate and reflect the triangle to form a space filling D 3 symmetric hexagonal unit cell that necessarily exhibits isotropic homogenized properties. One can further use this D 3 symmetry to reduce the computational expense by performing the “unit strain” periodic boundary condition simulations on the single triangle symmetry sector rather than the six fold larger hexagon. In this paper we use group representation theory to derive the necessary periodic boundary conditions on the symmetry sectors of unit cells. The developments are done in a general setting, and specialized to the two-dimensional dihedral symmetries of the abelian D 2 , i.e. orthotropic, square unit cell and nonabelian D 3 , i.e. trigonal, hexagon unit cell. We then demonstrate how this theory can be applied by evaluating the homogenized properties of a two-phase planar composite over the triangle symmetry sector of a D 3 symmetric hexagonal unit cell.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A gradient-based optimization approach for the detection of partially connected surfaces using vibration tests

The integrity of engineering structures is often compromised by embedded surfaces that result from incomplete bonding during the manufacturing process, or initiation of damage from fatigue or impact processes. Examples include delaminations in composite materials, incomplete weld bonds when joining two components, and internal crack planes that may form when a structure is damaged. In many cases the areas of the structure in question may not be easily accessible, thus precluding the direct assessment of structural integrity. In this paper, we present a gradient-based, partial differential equation (PDE)-constrained optimization approach for solving the inverse problem of interface detection in the context of steady-state dynamics. An objective function is defined that represents the difference between the model predictions of structural response at a set of spatial locations, and the experimentally measured responses. One of the contributions of our work is a novel representation of the design variables using a density field that takes values in the range [0, 1] and raised to an integer exponent that promotes solutions to be near the extrema of the range. The density field is combined with the penalty method for enforcing a zero gap condition and realizing partially bonded surfaces. Furthermore the use of the penalty method with a density field representation leads to objective functions that are continuously differentiable with respect to the unknown parameters, enabling the use of efficient gradient-based optimization algorithms. Numerical examples of delaminated plates are presented to demonstrate the feasibility of the approach.

42 ENGINEERING↗
DOE OSTI2020

Optimization-based, property-preserving finite element methods for scalar advection equations and their connection to Algebraic Flux Correction

In this paper, we continue our efforts to exploit optimization and control ideas as a common foundation for the development of property-preserving numerical methods. Here we focus on a class of scalar advection equations whose solutions have fixed mass in a given Eulerian region and constant bounds in any Lagrangian volume. Our approach separates discretization of the equations from the preservation of their solution properties by treating the latter as optimization constraints. This relieves the discretization process from having to comply with additional restrictions and makes stability and accuracy the sole considerations in its design. A property-preserving solution is then sought as a state that minimizes the distance to an optimally accurate but not property-preserving target solution computed by the scheme, subject to constraints enforcing discrete proxies of the desired properties. Furthermore, we consider two such formulations in which the optimization variables are given by the nodal solution values and suitably defined nodal fluxes, respectively. A key result of the paper reveals that a standard Algebraic Flux Correction (AFC) scheme is a modified version of the second formulation obtained by shrinking its feasible set to a hypercube. In conclusion, we present numerical studies illustrating the optimization-based formulations and comparing them with AFC

97 MATHEMATICS AND COMPUTING↗