Unitary Cell Research Articles

A ONE-WAY COUPLED APPROACH FOR MULTISCALE CHARACTERIZATION OF FILLING OF DUAL-SCALE FIBROUS REINFORCEMENTS CONSIDERING AIR COMPRESSIBILITY AND DISSOLUTION IN LUMPED FASHION

The filling characterization of dual-scale fibrous reinforcements is challenging due to the presence of subdomains with dissimilar permeabilities, existence of wicking effects, and combination of air compressibility and dissolution phenomena. These factors cause flow imbalances inside the representative unitary cell (RUC), which lead to void formation and influence the behavior of macroscopic field variables, affecting the parts manufacturing by liquid composite molding (LCM). Here, the filling characterization of woven fabrics used in LCM is done using one-way coupled simulations. Once RUC geometry is characterized by scanning-electron microscopy (SEM), and stereomicroscopy, standard thickness test, and resin viscosity are measured, the multiphase finite volume method-volume of fluid (FVM-VOF) model of ANSYS Fluent is used for the three-dimensional filling of the RUC, incorporating an experimentally calibrated air entrapment parameter (λ) to consider air compressibility and dissolution; then, a lumped function for the coupling term with macroscopic equations is obtained in terms of volume-averaged variables. This function is used in the equivalent Darcy macroscopic model, which is solved using a dual-reciprocity boundary element method (DR-BEM) algorithm. By considering a single value of λ during the simulation, neglecting wicking effects, and normalizing physical variables, unified injection pressure-independent results for the local tows saturation and normalized pressure fields at mesoscopic scale were obtained, as well as for global tows saturation and normalized pressure and fluid front profiles at macroscopic scale, thus simplifying the filling characterization of reinforcements. Numerical results are coherent with unidirectional injection experiments at both scales.

Understanding of the Effect of the Adsorption of Atom and Cluster Silver on Chitosan: An In Silico Analysis.

In this work, the structural, electronic, and optical stability properties of the chitosan monomer (M-Ch) and atomic silver complex are reported, as well as a unitary cell of a silver cluster in the gas phase and acetic acid. The generalized gradient approximation HSEh1PBE/def2-TZVPP50 results established the structures' anionic charge (Q = -1|e|) and the doublet state (M = 2). The high cohesive energy indicates structural stability, and the quantum-mechanical descriptors show a high polarity and low chemical reactivity. Also, the quantum-mechanical descriptors present a low work function that shows the structures are suitable for applications in light-emitting diodes. Finally, the electronic behavior observed by the |HOMO-LUMO| gap energy changes depending on the atomic silver incorporated into the complex.

New approach for filling simulations of dual-scale preforms used in the manufacturing of composites materials.

Some fibrous reinforcements used in the manufacturing of parts by Liquid Composite Molding (LCM) have a dual-scale nature, which supposes flow imbalances between the tows and channels at mesoscopic scale, which in turn, cause uncontrolled defects (voids, dry points, among others) and could considerably affect the global flow behavior during the filling of cavities at macroscopic scale. In the present work, a new approach to conduct filling simulations of dual-scale fibrous reinforcements at mesoscopic scale is proposed. This consists of prescribing a pressure gradient along the Representative Unitary Cell, and imposing Stokes-Darcy matching conditions between the tows and the channel sub-domains to determine the filling of the former ones. Contrarily to the traditional approach, where a uniform pressure is assumed for the channels and only the porous media fluid is modeled, the present one allows considering the fluid pressure gradient at channels (fluid motion), air compressibility and dissolution, flow-direction dependent capillary pressure, and vacuum pressure, as well as capturing several phenomena involved in the dynamic evolution of intra-tow voids, namely, compression, mobilization at constant volume and migration from tows towards channel. The velocity vectors and streamlines in the tows and channel subdomains, when these phenomena take place, are analyzed as well.

Crossings. Flying Over Antisymmetric Truchet Friezes

Symmetry and antisymmetry are resources used by humans since pre-historic times in their artistic creations. In this work we start by introducing antisymmetry and the 17 possible asso- ciated groups. We then present some counts of friezes, built with a particular module, the Truchet tile, which is itself antisymmetric. These counts take into consideration the frieze antisymmetry group and the number of tiles composing the unitary cell which originates the frieze by translation. These Truchet friezes led to the creation of a set of 5 paintings, named Crossings, which illustrate all the possible groups, in an artistic context.

Anatomy embroiders function in Purkinje cells

The anatomy of the human cerebellar Purkinje cell, as captured by Ramón y Cajal in a drawing, inspired the spectacular cover embroidery by Lisa Stoneman (Roanoke College, Roanoke, VA, USA) in the October issue of The Lancet Neurology. 1 Mehta AR Abbott CM Chandran S Haley JE The Cajal Embroidery Project: celebrating neuroscience. Lancet Neurol. 2020; 19: 979 Summary Full Text Full Text PDF Scopus (6) Google Scholar Like contemporary confocal microscopy images do, this anatomical representation also raises fascinating questions about the function served by the complex array of dendrites in this cell type. Each Purkinje cell, in rodents, receives about 174 000 synaptic inputs from the parallel fibre axons of the far tinier cerebellar granule cells, along with a single powerful input from the climbing fibre arising from the inferior olivary nucleus. 2 Howarth C Gleeson P Attwell D Updated energy budgets for neural computation in the neocortex and cerebellum. J Cereb Blood Flow Metab. 2012; 32: 1222-1232 Crossref PubMed Scopus (337) Google Scholar Even though a large fraction of those synapses can become inactive with learning, 3 Isope P Barbour B Properties of unitary granule cell→Purkinje cell synapses in adult rat cerebellar slices. J Neurosci. 2002; 22: 9668-9678 Crossref PubMed Google Scholar it is remarkable that the information processed from such a large number of inputs, which are even more numerous in human beings, is ultimately channelled down a single inhibitory axon to the deep cerebellar nuclei, as denoted by the label a in Cajal's original 1894 drawing (appendix).

SUSTAINABLE ALKALINE MEMBRANE FUEL CELL

This work proposes a sustainable alkaline membrane fuel cell (SAMFC) comprising a traditional AMFC coupled to a hydrogen generation reactor. The reactor uses recycled aluminum from soda cans to split the water molecule via oxidation catalyzed by NaOH, and an innovative cellulose membrane eliminates the undesirable characteristics of liquid electrolytes and asbestos or ammonia---common constituents of alkaline electrolyte membranes that are toxic and carcinogenic. Oxygen is supplied to the cell by first directing the ambient air through KOH aqueous solution to remove CO2 and thus to avoid the formation of K­2CO3. In this paper, an SAMFC system with one unitary cell, reactor, and CO2 purifier was designed, built, and tested in the laboratory, and the system was compared experimentally against traditional AMFCs driven by commercial hydrogen and by the hydrogen derived from commercial aluminum. According to experimental polarization and power curves, the SAMFC delivered 0.9V in open circuit and approximately 0.42W of maximum power with recycled aluminum. The study thereby demonstrates the economic potential and competitive performance of the proposed SAMFC against traditional fuel cells.

Negative electrical permittivity in metamaterials for a wire of rectangular cross-sectional: an application to antennas design

In this article, we propose a model to obtain negative electrical permittivity in metamaterials using a conductor wire of rectangular cross-sectional geometry. Plasma frequency in the GHz range is determined in terms of the wire geometry. This new composite dielectric, which has the property of negative electrical permittivity below the plasma frequency, opens new possibilities for GHz devices. Finally, we show a unitary metamaterial cell where the refractive index takes negative values over a wide frequency range.

Positive, zero and negative Poisson’s ratio non-stochastic metallic cellular solids: Dependence between static and dynamic mechanical properties

Cellular solids are attractive materials due to their high specific static and dynamic mechanical properties. Even though these mechanical domains are interdependent, they are generally studied separately. This study uses a combination of additive manufacturing and vacuum assisted investment casting to manufacture low specific density (0.042–0.098) non-stochastic metallic cellular solids. An in-situ unitary cell geometric control is used to produce samples with positive, zero and negative Poisson’s ratios. The different values of this elastic constant allow the analysis of the distinct deformation in auxetic and non-auxetic behaviors. Deformation models are used to describe the static and dynamic behavior of the referred samples. It is shown that auxetic samples display higher values of apparent modulus and plastic collapse stress due to their densification effect. In terms of dynamic properties, samples with slightly negative and zero rib angles show higher values of damping. This is attributed to the more favorable flexure component of deformation and variations in material volume that influence the hysteretic damping. Overall, it is suggested that the most beneficial combination of specific density, static and dynamic mechanical properties is observed in samples with a rib angle of −10° and a Poisson’s ratio of −0.34.

Investigation of Unitary Degradation Cells for Li Batteries Diagnosis

Lithium ion Batteries (LIBs) are the most popular tools as energy storage systems for electric vehicles (EVs), large-scale energy storage system (ESS) owing to their high energy density, power properties. However, LIBs are complex systems which are not yet revealed completely for their degradation mechanism. In general, the loss of Lithium during cycling, depletion and decomposition of the electrolyte, structural collapse of active materials and resistance increase are the most probable reasons for the degradation of LIBs. To diagnose LIBs, we have focused to make a unitary degradation cell which has referred reason during cycling. Herein, we fabricate Li loss cell intentionally as specified value and figure out how different capacities between intended values and real value in cells. Furthermore, we investigate what different in electrochemical impedance between the fresh cell and the unitary degradation cell.

Compact and Low-Loss V-Band Waveguide Phase Shifter Based on Glide-Symmetric Pin Configuration

This paper presents a compact and low-loss V-band waveguide phase shifter based on glide-symmetric pin configuration. This kind of higher symmetry permits the control and improvement of the electromagnetic behavior or radiofrequency devices, as it is the case of the proposed phase shifter. The study of the dispersion diagram of the phase shifter unitary cell demonstrates that the pin configuration is a proper option for introducing a phase shift in a waveguide-based system. There is a significant increase in terms of phase shift when using a glide-symmetric pin distribution compared to its corresponding non-glide-symmetric configuration. Through this paper, the key geometrical parameters are also determined. The complete phase shifter is composed of an optimized cascade of tailored unitary cells so that the desired final phase shift value is achieved. A prototype has been manufactured in order to validate the theoretical approach through the comparison of phased shifters with both non-glide-symmetric and glide-symmetric configurations. The measurement results demonstrate the higher performance and compactness of the glide-symmetric phase shifter. For the same distance, the glide-symmetric version of the phase shifter provides more than 60% of phase shifting compared to the non-glide-symmetric phase shifter. Both phase shifters have a good impedance matching between 46 and 60 GHz and an insertion loss lower than 1 dB, thus clearly enabled as a 5G technology.

Size-effect on the optical behavior of Fe-doped CuO nanoparticles synthesized by a freeze-drying process

Cu1-xFexO nanoparticles were prepared by freeze-drying an aqueous solution of copper and iron acetates, followed by a heat treatment. The material was characterized regarding structural, morphological and optical properties by high-resolution X-ray diffraction, transmission electron microscopy and, UV-Vis diffuse reflectance. All samples prepared in the 0 ≤ x ≤ 0.04 concentration range exhibited a single phase, corresponding to monoclinic structure (space group C2/c). Increasing the iron doping level resulted in the contraction of the unitary cell volume and in the decrease of the particle size and bandgap. The correlation between particle size, bandgap and, iron concentration represents a key information to tuning the material for semiconductor applications.

Comparative performance assessment of plate heat exchangers with triangular corrugation

A three-dimensional computational fluid dynamics approach with the Reynolds stress model is considered to investigate the influence of the apex angle on the thermal and hydraulic features of triangular cross-corrugated heat exchangers for a range of Reynolds numbers 310–2064. The influence of the intensity and complexity of the recirculation zones along with the turbulence intensity on those characteristics and corresponding viscous and pressure forces are studied. The choice of the computational domain as a unitary cell with periodic boundary condition versus a long channel with several cells is discussed. One on one comparison between the Reynolds stress model and experimental results shows less than 5% deviation, which is within the uncertainty of the experiment. By increasing the apex angle both pressure drop and heat transfer coefficient increase, due to the increase of the pressure force and the vorticity magnitude along the flow direction. The pressure force is the dominant force, contrary to pipe flow, where the viscous force is dominant. The influence of the apex angle on the friction factor and the Colburn j factor follows two distinguished trends. The apex angles around of 90°–100° are the transitional angles for the flow regime. Peak of turbulence intensity, friction factor and Colburn j factor are observed around these angles. The ratio between pressure and viscous forces decays after angle 100°, resulting in a smaller recirculation zone and lower turbulence intensity. Finally, the thermo-hydraulic performance of the considered geometries is compared with respect to each other based on a performance evaluation criterion. It is found that the geometry with the largest apex angle has the highest thermo-hydraulic performance.

Covalent and Ionic Capacity of MOFs To Sorb Small Gas Molecules.

In this work, the aim is to characterize how an Fe-based metal-organic framework (MOF) behaves when gases, like carbon dioxide, are inserted through their channels and to characterize the nature and strength of those interactions. Despite the computational nature of the project, it is based on the experimental results obtained in 2016 by Mı́nguez-Espallargas and co-workers ( J. Am. Chem. Soc. 2013, 135, 15986 - 15989 ). Those MOFs were found to selectively allocate/adsorb CO2, having as a drawback that apparently each cavity allocates only one CO2 molecule. Despite truncating the MOF to its unitary cell, the whole cavity of the MOF can be described in detail by precise ab initio calculations. Another computational goal is to unravel why experimentally CO2 was preferred with respect to N2, and for the sake of consistency, a list of common gases will be further studied, such as H2, O2, H2O, CH4, C2H6, N2O, or NO.

Boundary Element Method for the dynamic evolution of intra-tow voids in dual-scale fibrous reinforcements using a Stokes–Darcy formulation

The Boundary Element Method (BEM) is implemented in the simulation of compression, displacement, migration and splitting of intra-tow voids in dual-scale fibrous reinforcements. The last three processes have not been simulated at mesoscopic scale in previous works due to the consideration of a constant pressure in the channels of the Representative Unitary Cell. In this work, both the channels and tows are modeled using the Stokes and Darcy equations, respectively, a pressure gradient is prescribed along the fluid motion, and full air compressibility is deemed, thereby allowing to consider these three processes. The void migration process from the weft towards the channel is analyzed in terms of the ratio between the average air migration velocity and the average liquid velocity, and of the normalized air rate from the weft towards the channel. According to BEM results, the bubble can migrate at both lower and higher velocities with respect to the liquid velocity, and the void removal out of the tows can occur after several stages of compression–displacement–migration–splitting; additionally, the bubble breaks up after several cycles of expansion and compression. BEM results also show that the liquid surface tension, pressure gradient and average channel pressure have important influence in the void migration process.

Direct Recording of Dendrodendritic Excitation in the Olfactory Bulb: Divergent Properties of Local and External Glutamatergic Inputs Govern Synaptic Integration in Granule Cells.

The olfactory bulb contains excitatory principal cells (mitral and tufted cells) that project to cortical targets as well as inhibitory interneurons. How the local circuitry in this region facilitates odor-specific output is not known, but previous work suggests that GABAergic granule cells plays an important role, especially during fine odor discrimination. Principal cells interact with granule cells through reciprocal dendrodendritic connections that are poorly understood. While many studies examined the GABAergic output side of these reciprocal connections, little is known about how granule cells are excited. Only two previous studies reported monosynaptically coupled mitral/granule cell connections and neither attempted to determine the fundamental properties of these synapses. Using dual intracellular recordings and a custom-built loose-patch amplifier, we have recorded unitary granule cell EPSPs evoked in response to mitral cell action potentials in rat (both sexes) brain slices. We find that the unitary dendrodendritic input is relatively weak with highly variable release probability and short-term depression. In contrast with the weak dendrodendritic input, the facilitating cortical input to granule cells is more powerful and less variable. Our computational simulations suggest that dendrodendritic synaptic properties prevent individual principal cells from strongly depolarizing granule cells, which likely discharge in response to either concerted activity among a large proportion of inputs or coactivation of a smaller subset of local dendrodendritic inputs with coincidence excitation from olfactory cortex. This dual-pathway requirement likely enables the sparse mitral/granule cell interconnections to develop highly odor-specific responses that facilitate fine olfactory discrimination.SIGNIFICANCE STATEMENT The olfactory bulb plays a central role in converting broad, highly overlapping, sensory input patterns into odor-selective population responses. How this occurs is not known, but experimental and theoretical studies suggest that local inhibition often plays a central role. Very little is known about how the most common local interneuron subtype, the granule cell, is excited during odor processing beyond the unusual anatomical arraignment of the interconnections (reciprocal dendrodendritic synapses). Using paired recordings and two-photon imaging, we determined the properties of the primary input to granule cells for the first time and show that these connections bias interneurons to fire in response to spiking in large populations of principal cells rather than a small group of highly active cells.

The critical neck spacing in ductile plates subjected to dynamic biaxial loading: On the interplay between loading path and inertia effects

In this work we have investigated the emergence of a critical wavelength which characterizes the localization pattern in ductile plates subjected to dynamic biaxial loading. For that task we have used a linear stability analysis and finite element calculations. The linear stability analysis follows the 2D approach developed by Zaera et al. (2015) which includes specific features to account for inertia and stress triaxiality effects inside the necking. Two different finite element models are built: (1) a unitary cell model in which the localization is favoured by a sinusoidal geometrical perturbation and (2) a plate with constant cross section which allows to assess the collective behaviour of multiple necks. A wide spectrum of loading paths which range from plane strain to (almost) biaxial stretching has been explored. We have demonstrated that, if inertia plays a dominant role in the loading process, the influence of geometrical perturbations in the necking inception is substantially reduced and the necking pattern shows a deterministic nature. The deterministic nature is directly connected to the emergence of a critical wavelength which characterizes the neck spacing at high strain rates. This critical wavelength increases (i.e. the neck spacing increases) and becomes less prevailing (i.e. the necking pattern becomes less uniform) as we move away from plane strain to biaxial stretching. This is a key outcome of our investigation that, from the authors’ knowledge, has not been previously reported in the literature.

A numerical micro-mechanical study of the influence of fiber–matrix interphase failure on carbon/epoxy material properties

A finite element micromechanical study of unidirectional carbon–epoxy system is performed in order to investigate the role of fiber–matrix debonding in the degradation of mechanical properties and in the onset of failure for this class of composite materials.The presence of interphase flaws, that can be induced during the manufacturing processes, into micro-scale FE models is obtained by means of an original damage injection technique developed by the authors. The fibers are considered as transversally isotropic solids and the matrix is modeled as an isotropic, elasto-plastic, material with damage.The effect of fiber–matrix debonding is analyzed by means of a quasi 3-D unitary cell with a single fiber, with periodic boundary conditions, for different loading cases. Subsequently, multi-fiber representative volume elements are investigated with the same boundary and loading conditions. Finally, the effect of a 3-D debonding propagation is studied via single fiber model with an increased fiber-wise depth.

The design and application of the tripole array metamaterial unitary cell

ABSTRACTPeriodic structures are widely used in order to provide different behavior on devices that operate in high frequencies. Some of them, are capable to change the constitutive parameters ε and µ, so that, the incident wave can assume a different behavior. Therefore, in this work, the tripole array is presented as an alternative tool to improve the performance of microwave systems, in terms of bandwidth, gain and resonance frequency. The equivalent circuit method in conjunction with the full‐wave simulation method was used in order to characterize the tripole array topology, for normal and oblique incidence. Measurements and simulated results are compared. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1786–1790, 2016

Normal-State Optical Features Study of Nd123 and Gd1212 HTSC Materials for Photonics and Metamaterials Fabrication

YBCO-like Nd123 and Gd1212 superconductors in the normal state, in the visible and infrared regime, have been analyzed in this work. Superconductors, particularly high-temperature superconductors (HTSCs), hold indeed a great interest in the highly innovative research field of metamaterials and photonics with important applications. Indeed nanostructured devices suffer from increasing resistivity with frequency in metals, and superconducting materials provide a viable route to approach this problem. Moreover, HTSCs are plasmonic materials at nonzero temperature, and their features, not available in conventional materials, make them very attractive for metamaterials use. In particular, we investigate Nd123, for its high T c , and Gd1212, for the coexistence, in its unitary cell, of magnetic order and superconductivity. Samples were extracted from top-seeded melt-textured growth bulk pellets and bars. Fourier transform infrared spectroscopy analysis, performed in the far-infrared, shows articulated peak structures with k <; k min and a plateau for higher k, allowing for Nd123 and Gd1212 pseudogap measurement. Raman spectroscopy and microscopy provided a structural mapping of our Nd123 samples, allowing for distinguishing the superconducting matrix from nonsuperconducting phase inclusions (precipitates) and providing an instrument to discriminate among optical responses of the different compounds.

Study on the turbulence model sensitivity for various cross-corrugated surfaces applied to matrix type heat exchanger

Diverse cross-corrugated surface geometries were considered to estimate the sensitivity of four variants of k-e turbulence models (Low Reynolds, standard, RNG and realizable models). The cross-corrugated surfaces considered in this study are a conventional sinusoidal shape and two different asymmetric shapes. The numerical simulations using the steady incompressible Reynolds-averaged Navier- Stokes (RANS) equations were carried out to obtain the steady solutions of the flow and thermal fields in the unitary cell of the heat exchanger matrix. In addition, the experimental test for the measurement of local convective heat transfer coefficients on the heat transfer surfaces was performed by means of the Transient liquid crystal (TLC) technique in order to compare the numerical results with the measured data. The features on detailed flow structure and corresponding heat transfer in the unitary cell of the matrix type heat exchanger are compared and analyzed against four different turbulence models considered in this study.