High Aspect Ratio Cells Research Articles

Cell morphology as a biological fingerprint of chondrocyte phenotype in control and inflammatory conditions.

Little is known how inflammatory processes quantitatively affect chondrocyte morphology and how single cell morphometric data could be used as a biological fingerprint of phenotype. We investigated whether trainable high-throughput quantitative single cell morphology profiling combined with population-based gene expression analysis can be used to identify biological fingerprints that are discriminatory of control vs. inflammatory phenotypes. The shape of a large number of chondrocytes isolated from bovine healthy and human osteoarthritic (OA) cartilages was quantified under control and inflammatory (IL-1β) conditions using a trainable image analysis technique measuring a panel of cell shape descriptors (area, length, width, circularity, aspect ratio, roundness, solidity). The expression profiles of phenotypically relevant markers were quantified by ddPCR. Statistical analysis, multivariate data exploration, and projection-based modelling were used for identifying specific morphological fingerprints indicative of phenotype. Cell morphology was sensitive to both cell density and IL-1β. In both cell types, all shape descriptors correlated with expression of extracellular matrix (ECM)- and inflammatory-regulating genes. A hierarchical clustered image map revealed that individual samples sometimes responded differently in control or IL-1β conditions than the overall population. Despite these variances, discriminative projection-based modeling revealed distinct morphological fingerprints that discriminated between control and inflammatory chondrocyte phenotypes: the most essential morphological characteristics attributable to non-treated control cells was a higher cell aspect ratio in healthy bovine chondrocytes and roundness in OA human chondrocytes. In contrast, a higher circularity and width in healthy bovine chondrocytes and length and area in OA human chondrocytes indicated an inflammatory (IL-1β) phenotype. When comparing the two species/health conditions, bovine healthy and human OA chondrocytes exhibited comparable IL-1β-induced morphologies in roundness, a widely recognized marker of chondrocyte phenotype, and aspect ratio. Overall, cell morphology can be used as a biological fingerprint for describing chondrocyte phenotype. Quantitative single cell morphometry in conjunction with advanced methods for multivariate data analysis allows identifying morphological fingerprints that can discriminate between control and inflammatory chondrocyte phenotypes. This approach could be used to assess how culture conditions, inflammatory mediators, and therapeutic modulators regulate cell phenotype and function.

Optimization of methacrylated gelatin /layered double hydroxides nanocomposite cell-laden hydrogel bioinks with high printability for 3D extrusion bioprinting.

Layered double hydroxides (LDHs) offer unique source of inspiration for design of bone mimetic biomaterials due to their superior mechanical properties, drug delivery capability and regulation cellular behaviors, particularly by divalent metal cations in their structure. Three-dimensional (3D) bioprinting of LDHs holds great promise as a novel strategy thanks to highly tunable physiochemical properties and shear-thinning ability of LDHs, which allow shape fidelity after deposition. Herein, we introduce a straightforward strategy for extrusion bioprinting of cell laden nanocomposite hydrogel bioink of gelatin methacryloyl (GelMA) biopolymer and LDHs nanoparticles. First, we synthesized LDHs by co-precipitation process and systematically examined the effect of LDHs addition on printing parameters such as printing pressure, extrusion rate, printing speed, and finally bioink printability in creating grid-like constructs. The developed hydrogel bioinks provided precise control over extrudability, extrusion uniformity, and structural integrity after deposition. Based on the printability and rheological analysis, the printability could be altered by controlling the concentration of LDHs, and printability was found to be ideal with the addition of 3 wt % LDHs. The addition of LDHs resulted in remarkably enhanced compressive strength from 652 kPa (G-LDH0) to 1168 kPa (G-LDH3). It was shown that the printed nanocomposite hydrogel scaffolds were able to support encapsulated osteoblast survival, spreading, and proliferation in the absence of any osteoinductive factors taking advantage of LDHs. In addition, cells encapsulated in G-LDH3 had a larger cell spreading area and higher cell aspect ratio than those encapsulated in G-LDH0. Altogether, the results demonstrated that the developed GelMA/LDHs nanocomposite hydrogel bioink revealed a high potential for extrusion bioprinting with high structural fidelity to fabricate implantable 3D hydrogel constructs for repair of bone defects.

Non-modal analysis of linear multigrid schemes for the high-order Flux Reconstruction method

We present a numerical analysis of linear multigrid operators for the high-order Flux Reconstruction method. The non-modal analysis is used to assess the short-term numerical dissipation in the context of 1D and 2D linear convection-diffusion. The effect of several parameters, namely the number of coarse-level iterations, the polynomial order and the combination of h- and p-multigrid is explored in an effort to identify the most efficient configurations. V-cycle p-multigrid is shown to have increased efficiency at higher polynomial orders, and the use of W-cycles and/or hp-multigrid appear to offer additional advantages. The effect of high Péclet numbers and high aspect-ratio cells is also explored in 2D, and both factors are shown to decrease the error dissipation. Finally, we relate the non-modal dissipation to the convergence rate of the multigrid in a series of manufactured solutions.

Enhanced Light Absorption by Horizontally Oriented Diatom Colonies

Through \textit{in situ} holographic imaging of undisturbed water, diatom colonies with high aspect ratios have been found to exhibit preferential horizontal orientation within high biomass subsurface layers. We analyzed holographic video to determine the abundance, size, and orientation of colonies over several vertical profiles from the surface to $\sim$25 m depth. A geometric optics model based on these measurements was then used to estimate light absorption by phytoplankton throughout the water column. Results show a substantial increase in absorption of downwelling irradiance (up to 24.5\%) for horizontally oriented colonies when compared to randomized orientations. The effect can be attributed to maximization of the projected area of colonies when oriented perpendicular to the direction of incident light. Formation of high aspect ratio cells and colonies may represent an adaptation to maximize light harvesting in low light environments through interaction with the low velocity shear fields commonly found along pycnoclines at the base of the surface mixed layer. The effect of orientation on light absorption by large chain forming diatoms could influence their abundance and distribution in the ocean as well as the broader structure and function of marine ecosystems.

Strong fluid–solid interactions with segregated CFD solvers

Purpose This paper aims to present a fluid-structure coupling partitioned scheme involving rigid bodies supported by spring-damper systems. This scheme can be used with already existing fluid flow solvers without the need to modify them. Design/methodology/approach The scheme is based on a modified Broyden method. It solves the equations of solid body motion in which the external forces coming from the flow are provided by a segregated flow solver used as a black box. The whole scheme is implicit. Findings The proposed partitioned method is stable even in the ultimate case of very strong fluid–solid interactions involving a massless cylinder oscillating with no structural damping. The overhead associated with the coupling scheme represents an execution time increase by a factor of about 2 to 5, depending on the context. The scheme also has the advantage of being able to incorporate turbulence modeling directly through the flow solver. It has been tested successfully with URANS simulations without wall law, thus involving thin high aspect-ratio cells near the wall. Originality/value Such problems are known to be very difficult to solve and previous studies usually rely on monolithic approaches. To the authors' knowledge, this is the first time a partitioned scheme is used to solve fluid–solid interactions involving massless components.

Current Density Distribution in Electrochemical Cells with Small Cell Heights and Coplanar Thin Electrodes as Used in ec-S/TEM Cell Geometries

The electrochemical engineering aspects of high aspect ratio cells, such as those used in in situ electrochemical scanning transmission microscopy (ec-S/TEM) were examined, focusing on aspects that could cause non-uniform current distribution. Having a uniform current distribution across the working electrode is important for any spectroelectrochemical technique in order to provide accurate electrochemical information as well as structural electrolyte-electrode interface information. An analytical model was developed to determine current density distribution and a Wagner number was derived for a small cell height with coplanar electrodes. The main assumptions of this analysis are: 1) mass transport effects are negligible, 2) a uniform potential distribution in the direction of the cell height due to their small size, and 3) the working electrode potential is constant across its length. With our analysis, the assumptions were found to be reasonable. In addition, the effect of the conductivity and thickness of the thin film electrode and its potential effect on current density distribution have been analyzed. Now, with this work, high aspect ratio cells with a small cell heights and coplanar thin electrodes can be analyzed to determine their current density distribution.

Towards a generalised dual-mesh hybrid LES/RANS framework with improved consistency

This paper presents a combined RANS and LES methodology, which automates the dual-mesh hybrid LES/RANS approach and circumvents the need for wall-functions. Unlike RANS, wall-resolved LES is still unaffordable for studying high Reynolds number complex flows in industry and requires much user expertise when turbulence features are unknown a priori. The present approach avoids these issues by concurrently solving the LES and unsteady RANS equations on separate meshes, which are adapted to each model and are overlapping over the entire domain.The RANS solution guides the LES where its mesh is too coarse, and vice-versa where the LES is well-resolved. The driver- and driven-simulation locally swap roles automatically, depending on which one is deemed more reliable by a blending function. Consistency between the RANS solution and a temporal average of the LES solution is enforced by drift terms, whose strength depend on relaxation times-scales that are provided by the RANS model.Predictions for fully-developed channel flows and the flow through periodic hills are shown to be in excellent agreement with reference data. The LES grids are deliberately too coarse for wall-resolved LES, while the independent RANS mesh uses high aspect-ratio cells to economically resolve the near-wall layer.

Application of a wall function to simulate turbulent flows in foil bearings at high rotational speeds

For turbulent simulations in hydrodynamic applications, a fine mesh close to wall boundaries is required to correctly predict the friction and heat fluxes. This results in a remarkable increase of computational cost due to the high aspect ratio cells and reduced allowable time step. To reduce the computational cost, a compressible wall function is introduced and validated with the representative flows. Moreover, high aspect ratio cells lead to simulation instabilities. These spurious oscillations are smoothed through the addition of a fourth-order artificial dissipation term. To verify that the solution accuracy is not affected, the method of manufactured solution is applied. These two additions result in a fast and stable solver for turbulent simulations of foil thrust bearings.

Lagrangian transported MDF methods for compressible high speed flows

This paper deals with the application of thermochemical Lagrangian MDF (mass density function) methods for compressible sub- and supersonic RANS (Reynolds Averaged Navier–Stokes) simulations. A new approach to treat molecular transport is presented. This technique on the one hand ensures numerical stability of the particle solver in laminar regions of the flow field (e.g. in the viscous sublayer) and on the other hand takes differential diffusion into account. It is shown in a detailed analysis, that the new method correctly predicts first and second-order moments on the basis of conventional modeling approaches. Moreover, a number of challenges for MDF particle methods in high speed flows is discussed, e.g. high cell aspect ratio grids close to solid walls, wall heat transfer, shock resolution, and problems from statistical noise which may cause artificial shock systems in supersonic flows. A Mach 2 supersonic mixing channel with multiple shock reflection and a model rocket combustor simulation demonstrate the eligibility of this technique to practical applications. Both test cases are simulated successfully for the first time with a hybrid finite-volume (FV)/Lagrangian particle solver (PS).

Effect of Processing Conditions on the Cellular Morphology of Polypropylene Foamed Films for Piezoelectric Applications

In this work, continuous extrusion-calendering was used to produce polypropylene (PP) foam films for piezoelectric applications. The setup is based on physical foaming using supercritical nitrogen (SC-N2) and calcium carbonate (CaCO3) as nucleating agent. In particular, the extrusion parameters (screw design, temperature profile, blowing agent and nucleating agent content) and post-extrusion conditions (calendaring temperature and speed) were optimized to achieve a specific stretched eye-like cellular structure with uniform cell size distribution. The morphology in both machine and transverse directions, as well as tensile properties were characterized. The results show that a cellular structure with a higher cell aspect ratio has a lower Young's modulus, which is appropriate for piezoelectric cellular films. Generally, the developed foam morphology presents high potential for the production of ferroelectret PP films used in different piezoelectric applications.

Polymer ferroelectret based on polypropylene foam: Piezoelectric properties improvement using post‐processing thermomechanical treatment

ABSTRACTIn this work, the effect of post‐processing parameters (time, temperature, and pressure) on the morphology as well as mechanical and piezoelectric properties of foamed polypropylene (PP) films were studied. Two different post‐processing methods, based on the saturation of a foamed film with supercritical nitrogen (N2), were used to obtain an optimized eye‐like cellular structure with a high cell aspect ratio (AR). The results showed that, when the PP‐foamed films were exposed to a gradual temperature and pressure increase, an appropriate cellular structure with high AR value (about 6.6) was obtained. This structure led to a high quasi‐static piezoelectric d33 coefficient of 800 pC/N (45% higher than for untreated ones) indicating the importance of the post‐processing treatment on the piezoelectric behavior of these films. On the other hand, when the treatment was performed in steps, cell morphology changed from an eye‐like to a less elongated shape, resulting in lower d33 values. The tensile characterization showed that higher cell aspect ratio led to lower Young's modulus, which is suitable to achieve higher piezoelectric properties. Finally, dynamic mechanical analysis (DMA) was used as a simple method to correlate mechanical and piezoelectric properties of cellular PP. This was done via the ratio of the storage moduli in the longitudinal and transverse directions, which is directly related to film anisotropy (AR value) and thus to the piezoelectric behavior. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44577.

Double side read-out technique for mitigation of radiation damage effects in PbWO4 crystals

Test beam results of a calorimetric module based on 3×3×22 cm3 PbWO4 crystals, identical to those used in the CMS ECAL Endcaps, read out by a pair of photodetectors coupled to the two opposite sides (front and rear) of each crystal are presented. Nine crystals with different level of induced absorption, from 0 to 20 m−1, have been tested using electrons in the 50–200 GeV energy range. Photomultiplier tubes have been chosen as photodetectors to allow for a precise measurement of highly damaged crystals. The information provided by this double side read-out configuration allows to correct for event-by-event fluctuations of the longitudinal development of electromagnetic showers. By strongly mitigating the effect of non-uniform light collection efficiency induced by radiation damage, the double side read-out technique significantly improves the energy resolution with respect to a single side read-out configuration. The non-linearity of the response arising in damaged crystals is also corrected by a double side read-out configuration and the response linearity of irradiated crystals is restored. In high radiation environments at future colliders, as it will be the case for detectors operating during the High Luminosity phase of the Large Hadron Collider, defects can be created inside the scintillator volume leading to a non-uniform response of the calorimetric cell. The double side read-out technique presented in this study provides a valuable way to improve the performance of calorimeters based on scintillators whose active volumes are characterized by high aspect ratio cells similar to those used in this study.

Applications of Dynamic Cartesian Grids Method on Unsteady Flows Involving Moving Boundaries

A mesh deformation algorithm for unstructured Cartesian grids is presented. Given a surface deformation, the method efficiently recalculates new locations of high aspect ratio cells that make up the viscous layers of the grid and then deforms the inviscid part of the grid using an established method based on a spring analogy technique. The unsteady Navier-Stokes equations are solved on dynamic Cartesian grid by an explicit, finite-volume, upwind method. This dynamic, unstructured flow solver is validated by computing the flow about NACA 0012 airfoil and M6 wing undergoing a forced periodic motion in angle of attack.

Discontinuous diffusion synthetic acceleration for [formula omitted] transport on 2D arbitrary polygonal meshes

In this paper, a Diffusion Synthetic Acceleration (DSA) technique applied to the Sn radiation transport equation is developed using Piece-Wise Linear Discontinuous (PWLD) finite elements on arbitrary polygonal grids. The discretization of the DSA equations employs an Interior Penalty technique, as is classically done for the stabilization of the diffusion equation using discontinuous finite element approximations. The penalty method yields a system of linear equations that is Symmetric Positive Definite (SPD). Thus, solution techniques such as Preconditioned Conjugate Gradient (PCG) can be effectively employed. Algebraic MultiGrid (AMG) and Symmetric Gauss–Seidel (SGS) are employed as conjugate gradient preconditioners for the DSA system. AMG is shown to be significantly more efficient than SGS. Fourier analyses are carried out and we show that this discontinuous finite element DSA scheme is always stable and effective at reducing the spectral radius for iterative transport solves, even for grids with high-aspect ratio cells. Numerical results are presented for different grid types: quadrilateral, hexagonal, and polygonal grids as well as grids with local mesh adaptivity.

Efficient unsteady high Reynolds number flow computations on unstructured grids

Despite the advances in computer power and numerical algorithms over the last decades, solutions to unsteady flow problems remain computing time intensive. Especially for high Reynolds number flows, nonlinear multigrid, which is commonly used to solve the nonlinear systems of equations, converges slowly. The stiffness induced by the high-aspect ratio cells and turbulence is not tackled well by this solution method. In this paper, it is investigated if a Jacobian-free Newton–Krylov ( jfnk) solution method can speed up unsteady flow computations at high Reynolds numbers. Preconditioning of the linear systems that arise after Newton linearization is commonly performed with matrix-free preconditioners or approximate factorizations based on crude approximations of the Jacobian. Approximate factorizations based on a Jacobian that matches the target residual operator are unpopular because these preconditioners consume a large amount of memory and can suffer from robustness issues. However, these preconditioners remain appealing because they closely resemble A - 1 . In this paper, it is shown that a jfnk solution method with an approximate factorization preconditioner based on a Jacobian that approximately matches the target residual operator enables a speed up of a factor 2.5–12 over nonlinear multigrid for two-dimensional high Reynolds number flows. The solution method performs equally well as nonlinear multigrid for three-dimensional laminar problems. A modest memory consumption is achieved with partly lumping the Jacobian before constructing the approximate factorization preconditioner, whereas robustness is ensured with enhanced diagonal dominance.

A quadratic least‐squares solution reconstruction in a boundary layer region

AbstractA local weighted least‐squares (LS) method is often used to approximate a solution function in computational aerodynamics problems. In our paper we study LS approximation by a quadratic polynomial on unstructured grids that have the high cell aspect ratio. It will be shown in the paper that an LS method degrades to unacceptable accuracy on stretched meshes and weighting of distant stencil points does not result in a more accurate reconstruction. A concept of numerically distant points will be employed to explain the reasons behind the method's poor performance and an approach will be discussed that allows one to improve the results of a quadratic LS reconstruction in a boundary layer region. Copyright © 2009 John Wiley & Sons, Ltd.

Cartesian-Like Grids Using a Novel Grid-Stitching Algorithm for Viscous Flow Computations

A novel grid-stitching algorithm has been developed for generating Cartesian-like grids for viscous flow calculations. A grid is generated by recursive division of Cartesian cells. Unlike the conventional Cartesian-mesh calculations that involve unit aspect ratio cells, stretching is used to get the high aspect ratio cells and smooth grid near the body. The grid data are collected in an unstructured format. This novel approach, along with an unstructured mesh-based flow solver (HIFUN-2D, developed in-house), has been successfully used for numerical simulations. This grid is successfully used for Euler and laminar flowcomputations. Partial success has been achieved for turbulent flow simulations.

Interaction effect on switching behaviors of paired "Pac-Man" array

Interactions between neighboring cells become increasingly important due to the miniaturization of magnetoelectronic devices. This paper studies the effect of magnetic interaction on the switching behaviors in two different configurations of paired Pac-man shape Permalloy elements: back-to-back and face-to-face configurations. From as-patterned state MFM images, it is observed that the face-to-face configuration is prone to form either two single domains with an antiferromagnetic configuration, one single domain with one vortex or a double vortex configuration. MOKE hysteresis loops show that the coercivity for the face-to-face configuration is smaller than the back-to-back configuration. These experimental results indicate that the back-to-back configuration has weaker interaction between the two Pac-man elements than the face-to-face configuration. We further varied the aspect ratio of Pac-man elements in the pair arrays to tune the magnetic interaction. It was found that the coercivity of pair array increased with the higher cell aspect ratio. Micromagnetic simulation was also performed to simulate the switching process for the two different configurations. Overall, the back-to-back configuration is recommended for applications that demands less inter-cell interactions.

Development of magnetic tunnel junction for toggle MRAM

Toggle switching mode MRAM is tested and characterized with respect to the free- and pinned-layer material and thickness. With magnetization curves, we were able to find the optimum thickness combinations of free-layer and spacer materials. For CoFeB where the intrinsic anisotropy field ( Hi) is about 20-30 Oe, one needs to have a reasonably high exchange coupling field (Hex) to ensure large switching margin. In case of an NiFe/Ru/NiFe free-layer, Hi is usually much smaller than Hex, so that further decrease of Hex between two magnetic layers is needed. The pinned-layer roughness and thickness are other factors to be optimized to reduce the toggle switching field. High cell aspect ratio /spl ges/3.0 helps to minimize the switching distribution and enhance the switching stability.

Parallelization of Rotorcraft Aerodynamics Navier-Stokes Codes

The modie cation of unsteady three-dimensional Navier ‐Stokes codes for application on massively parallel and distributed computing environments is investigated. Previously, theEulermode of theNavier ‐Stokescode TURNS hasbeenparallelized. Fortheefe cientimplementation oftheNavier ‐StokesmodeofTURNS onparallelcomputing systems, several algorithmic changes should be made. The main modie cation is done on the implicit operator, lower‐upper symmetric Gauss ‐Seidel. Two new implicit operators are used because of convergence problems of traditional operators with high cell aspect ratio grids needed for viscous calculations. Results for Navier ‐Stokes cases are presented for various operators. The message passing interface protocol is used because of its portability to various parallel architectures. Nomenclature a = speed of sound e = total energy p = pressure Pr = Prandtl number Re = Reynolds number u;v;w = Cartesian velocities x; y;z = Cartesian coordinates ° = specie c heat ratio π = dynamic viscosity »;´;‡ = generalized coordinates Ω = density 9 = rotor azimuth angle