Rectangular Cell Research Articles

Three-Dimensional Convective Planforms for Inclined Darcy-Bénard Convection

We investigate the onset of convection in an inclined Darcy-Bénard layer. When such a layer is unbounded in the spanwise direction it is generally known that longitudinal rolls comprise the most unstable planform. On the other hand, when a layer has a sufficiently small spanwise width, then transverse rolls form the most unstable planform. However, the layer remains stable to transverse roll disturbances when the inclination is above roughly 31 degrees from the horizontal. This paper considers the transition between these two extreme cases where the spanwise width takes moderate values and where rectangular cells are considered. It is found that the most unstable planform is quite strongly sensitive to the magnitude of the spanwise width and that there are large regions of parameter space within which three-dimensional convection patterns have the smallest critical Darcy-Rayleigh number.

A new species of moss emerges from molecular and morphological data: Schistidium memnonium sp. nov. (Grimmiaceae, Bryophyta)

Schistidium memnonium is described as a new species from Europe, based on molecular and morphological data. The species is described and illustrated, its affinities are discussed, and its current distribution mapped. The species is distinguished by its ovate to ovate-triangular leaves, unistratose lamina in lower part, occasionally with 2-stratose spots or short striae, in central and upper part varying from 1-stratose to 2-stratose in spots and striae, recurved leaf margins from the base to near the apex on both sides, in lower part mostly 1-2˗stratose for 1(2) rows, in upper and central part 2-3˗stratose for 1–2 rows and oblong to long rectangular or long obovate exothecial cells in central part. A table with characters to distinguish this species from S. brunnescens (both subspecies), two taxa morphologically very similar, and a phylogenetic analysis in order to detect relationships of the new species with nearby taxa, based on rDNA ITS region, are provided.

Detail description of Lithophyllum okamurae (Lithophylloideae, Corallinales), a widely distributed crustose coralline alga in marine ecosystems

Lithophyllum okamurae is one of the important encrusting coralline algae, which plays important roles as primary producer, carbonate sediment builder, and habitat provider in the marine ecosystems. In this study, L. okamurae was collected from tropical coast of Sanya, and firstly described based on both detailed morph-anatomical characteristics and molecular studies of typic DNA sequences. The structure of the thalli of L. okamurae was pseudoparenchymatous construction with radially organized dimerous organizations in the crustose portion. The pseudoparenchymatous construction were composed of three parts, including 1 to 3 layers of epithelia cells which had flatten to round outermost walls, one layer of square or rectangular cells of the hypothallia and multiple layers of square or elongated rectangular peripheral cells. Palisade cells were observed, and the cells of the contiguous vegetative filaments were connected by secondary pit-connections with cell fusions absent. The carposporangial conceptacles, the spermatangial conceptacles, the bisporangial conceptacles and the tetrasporangial conceptacles were observed, and all these four kinds of conceptacles were uniporate. The spermatangial conceptacles were slightly convex and buried at shallow depths in the thalli tissues, and the carposporangial conceptacles and asexual conceptacles were protruding and conical. Phylogenetic studies based on DNA barcoding markers of 18S rDNA, COI, rbcL and psbA revealed that L. okamurae clustered with the closest relation of L. atlanticum, and formed a distinct branch. Based on the comparative anatomical features and the molecular data, the detailed description of the valid species of L. okamurae was firstly given in this study to provide theoretical basis for algae resources utilization and conservation in marine ecosystems.

Broadband linear‐to‐circular polarisation conversion using the diamond‐shaped reflecting metasurface

To overcome the narrow axial ratio (AR) bandwidth inherent in conventional linearly to circularly polarised converters, this research proposes a metasurface (MS) with a diamond-shaped configuration that can mitigate the effect of surface wave (SW) along the MS edge and achieve a wider 3 dB AR bandwidth. The diamond-shaped MS structure is realised by slanting a square MS by 45°, and it consists of constituent unit cells of rectangular and arbitrary shapes. The rectangular unit cells are positioned 45° to the square dielectric substrate, and the unit cells along the MS edge are partially cut into arbitrary shape to be perfectly aligned along the edge. The 3 dB AR bandwidths and degradation of the MS are characterised by SW and magnetic current distribution. Simulations are carried out and an MS prototype is fabricated to verify the results. The effects of partially cut unit cells (PCUCs) along the MS edge on the SW are characterised. The simulation and measured 3 dB AR bandwidths of the diamond-shaped MS are 37.6 and 28.8%, respectively. The novelty of the proposed diamond-shaped MS polarisation converter lies in the implementation of arbitrary-shaped PCUCs and the use of the diamond-shaped configuration in place of conventional square geometry to realise wider AR bandwidth.

Crashworthiness optimization of honeycomb structures under out‐of‐plane impact using radial basis functions

AbstractCrashworthiness design and development of lightweight structures have become important engineering challenges because of the high standards of energy consumption and safety regulations. Within this context, the use of honeycomb structures as crush absorber is continuously growing in automotive and aircraft industries, once honeycombs are known for their high strength‐to‐weight ratio and excellent energy absorbing capacity. Thus, this paper presents a method that combines radial basis functions with expected improvement to optimize the specific energy absorption of honeycomb cellular materials, while the peak crush force is constrained at low levels for safety reasons. Honeycomb's cell size, cell shape and thickness are the design variables. Concerning the cell shape, the results indicate the hexagonal configuration has a higher out‐of‐plane performance compared to auxetic and rectangular cells in terms of energy absorption capacity. Lastly, a multi‐objective optimization using only the radial basis function predictor (without sequential sampling) is carried out to seek simultaneously for optimal solutions with minimum peak force and maximum specific energy absorption.

Peak instability in an elastic interface ferrofluid

The instability of an elastic interface separating a ferrofluid and a nonmagnetic fluid subjected to an applied magnetic field perpendicular to the initially undisturbed interface is investigated in the effectively two-dimensional environment of a vertical, rectangular Hele-Shaw cell. By using a third-order mode-coupling perturbative scheme, and considering that the elastic interface has a curvature-dependent bending rigidity, the emergence of elastic ferrofluid peaks is detected at the onset of nonlinearities. In this context, the approximate profile of the interface is obtained. It is also shown that the morphology of the resulting peaks is sensitive to changes in a dimensionless magnetoelastic number (relative measure of magnetic and elastic forces), as well as in a bending rigidity fraction parameter, which expresses variations in the bending rigidity with the local interface curvature.

Evolution and Phylogeny of Altingiaceae: Anatomically Preserved Infructescences from Late Cretaceous Deposits of Vancouver Island, British Columbia, Canada

Premise of research. Five permineralized specimens of infructescences and dispersed fruits assignable to the Altingiaceae have been identified from the Late Cretaceous (Coniacian) Eden Main Quarry on Vancouver Island, British Columbia, Canada. Two infructescences and three isolated two-loculed fruits are preserved in calcium carbonate marine concretions.Methodology. Concretions were sectioned using the cellulose acetate peel technique and were included in a phylogenetic analysis employing morphological characters using TNT.Pivotal results. Infructescences are globose ca. 1 cm in diameter with at least 24 two-loculed fruits and a broad central axis. We have been unable to identify any perianth parts, but there are knob-like extrafloral processes similar to the phyllomes of other altingiaceous infructescences. The inner carpel lining consists of a single palisade layer of elongate rectangular cells. The endocarp also contains several layers of thick-walled, elongate sclerenchyma. The mesocarp is well differentiated, with fiber bundles interspersed with parenchyma and resin canals. There are at least 16 seeds (ovules) per carpel with axile placentation, but most of these are immature or aborted. Fruits have septicidal and ventricidal dehiscence. Specimens are assigned to Protoaltingia comoxense Scharfstein, Stockey & Rothwell gen. et. sp. nov.Conclusions. These fossils represent the second-most ancient occurrence of Altingiaceae, and phylogenetic analysis of morphological characters confirms that P. comoxense is most similar to species of Altingia. Results of morphological analyses resolve Altingia and Liquidambar as sister clades, placing P. comoxense as the basal member of the Altingia clade and sister to Altingia spp., thus documenting that evolutionary diversification of the core eudicot family Altingiaceae (Saxifragales) was well underway by the mid–Upper Cretaceous.

A Review on Macroscopy, Microscopy and Pharmacological Activity of Cayratiatrifolia Linn.

Cayratiatrifolia (Linn.)Domin is a perennial climber, family Vitaceae, found in India, Asia and Australia. The plant is found in hilly regions as well as the hotter part of India from Jammu and Rajasthan to Assam. It is commonly known as fox grape in English, Amalbel, Ramchana in Hindi and Amlavetash in Sanskrit. The plant has trifoliated leaves with (2-3cm) long petioles and ovate to oblong-ovate leaflets. Flowers are small greenish white and brown in colour. Fruits are fleshy, juicy, spherical, about 1 cm in diameter of dark purple or black colour.The stem composed of cork cells on the outer side and composed of small size sclerenchymatous cells. The cortex is wide and has parenchymatous cells. Numbers of sclereids are widely distributed in the cortex region. Cortex also shows the presence of calcium oxalate crystals.The leaf surface shows the stomata covered with guard cells followed by epidermis layer (Figure2A). Epidermal cells are rectangular, thin and straight walled cells. Stomata are anisocytic or unequal celled stomata, three subsidiary cells, one is smaller than other two. Leaf surface analysis also shows the presence of veins, vein islet and vein termination (Figure2B). Transverse section of leaf shows the epidermis layer followed by cuticle layer and vascular bundles (xylem and phloem).The leaf powder is pale green in color, with a characteristic odour and bitter taste.This plant also contains kaempferol, myricetin, quercetin, triterpenes and epifriedelanol. Whole plant of Cayratiatrifolia has been reported to contain yellow waxy oil, steroids/terpenoids, flavonoids, tannins. Plant shows the antioxidant, antidiabetic, antibacterial, antiviral and anticancer activity.
 

A paradox in Hele-Shaw displacements

The Saffman–Taylor instability occurs when a less viscous Stokes fluid is displacing a more viscous one, in a rectangular Hele-Shaw cell. We study the case when all surface tensions on the interfaces are zero. Consider N liquid-layers with constant viscosities, inserted between the two initial fluids. The corresponding growth constants become infinite with increasing wave numbers, even if N is very large. On the contrary, a single intermediate liquid with a suitable variable viscosity gives us an almost stable flow. We compute the total amount of intermediate liquid used in both models.

<p><strong>Morpho-anatomy of the cypselae of native species of Mutisieae (Asteraceae) from Mexico</strong></p>

The aims of this study were to describe and illustrate cypselae of 15 Mexican species of Mutisieae from observations using optical and scanning electron microscopy. The cypselae are heteromorphic with pilose, sericeous or glandular indumentum. The primary sculpture of the surface has two microstructural patterns: reticulate and plicate. The secondary sculpture is striate in 13 taxa, but in two species, Chaptalia estribensis and C. mexicana, differences were found in the secondary sculpture of the external and internal cypselae. The most distinctive anatomical trait is in the epicarp, which has rectangular or square-shaped cells that have a convex periclinal wall in most species of Chaptalia. The mesocarp has vascular bundles with fibers in all species of Chaptalia, but fibers are absent in Adenocaulon, Gerbera and Leibnitzia. In addition, the cells of the mesocarp inner layer have either thick walls or only an anticlinal wall in nine species of Chaptalia. The micromorphological characteristics of the primary or secondary sculpture of the surface, the type of trichomes and the variation they present have taxonomical value for recognizing closely-related taxa, whereas anatomical traits of the mesocarp distinguish Adenocaulon, Gerbera and Leibnitzia from most Chaptalia species.

Transient freezing of water between two parallel plates: A combined experimental and modelling study

The transient freezing/solidification of water subjected to shear flow inside a rectangular cell is investigated under laminar flow conditions. A flow of freezing water is established inside the cell by cooling the top surface of the conductive, copper plate that forms the cell’s top side by contact with boiling liquid nitrogen (−197∘C). This heat removal results in an ice layer that forms and grows gradually on the ceiling of the cell, which is subjected to shear from the flow below it inside the channel. The spatiotemporal characteristics of the ice layer are recorded with optical, laser-based measurements and are compared with predictions from a transient freezing model that is developed for this purpose. Furthermore, tracer particles are introduced into the flow to aid the tracking of the ice layer and to allow for measurements based on particle image velocimetry (PIV) of the velocity field inside the flow during the ice-layer evolution. After an initial time-lag/‘buffer’ period (of 5−40 s) that depends on the flow conditions, a quasi-linear growth of the ice layer is observed; at longer times the thickness of the ice layer reaches a maximum and then decreases again. The increase in the thickness, and hence thermal resistance, of the ice layer is counter-balanced by a decrease in the temperature of the copper plate and, therefore, a decrease in the temperature difference across the ice layer. Furthermore, it is found that the flow is associated with symmetric velocity profiles, recorded along the vertical spanwise length between the ice layer at the top of the cell and the floor of the cell, while an increase of the velocity maxima is recorded as the ice layer gradually thickens and, consequently, the flow cross-section is reduced. A constant heat flux of 19.7 × 103 W m−2 is measured on the top side of the channel, while the heat transfer coefficient on the top side of the channel is found to be in the range of 90–110 W m−2 K−1, depending on the wall temperature. Finally, from comparisons against the experimental data, it is concluded that the model developed herein is able to predict the freezing of water and the growth of the ice layer in these flows over a range of water inlet temperatures and Reynolds numbers. This model can be incorporated in thermohydraulic codes for the design of relevant heat-exchange components in the precence of freezing/solidification.

Broadband Low-Profile L-Probe Fed Metasurface Antenna With TM Leaky Wave and TE Surface Wave Resonances

A broadband low-profile L-probe fed metasurface antenna is proposed by well exciting both transverse magnetic (TM) leaky wave and transverse electric (TE) surface wave resonances. The metasurface is composed of an array of rectangular metallic patch cells. An L-shaped probe positioned underneath the finite metasurface is utilized to excite a TM leaky wave resonance and a TE surface wave resonance simultaneously for broadband operation. The dispersion properties of the TM leaky wave and TE surface wave are used to analyze the dual resonance modes. The proposed L-probe fed metasurface antenna achieves a broad −10 dB impedance bandwidth of 34.5% with the peak gain of 10.3 dBi and the front-to-back ratio larger than 18 dB with a low profile of $0.06\lambda _{0}$ , where $\lambda _{0}$ is the free-space wavelength at the center operating frequency.

Extension of the fast multipole method for the rectangular cells with an anisotropic partition tree structure.

The fast multipole method (FMM) is an order N method for the numerically rigorous calculation of the electrostatic interactions among point charges in a system of interest. The FMM is utilized for massively parallelized software for molecular dynamics (MD) calculations. However, an inconvenient limitation is imposed on the implementation of the FMM: In three-dimensional case, a cubic MD unit cell is hierarchically divided by the octree partitioning under isotropic periodic boundary conditions along three axes. Here, we extended the FMM algorithm adaptive to a rectangular MD unit cell with different periodicity along the axes by applying an anisotropic hierarchical partitioning. The algorithm was implemented into the parallelized general-purpose MD calculation software designed for a system with uniform distribution of point charges in the unit cell. The partition tree can be a mixture of binary and ternary branches, the branches being chosen arbitrarily with respect to the coordinate axes at any levels. Errors in the calculated electrostatic interactions are discussed in detail for a selected partition tree structure. The extension enables us to execute MD calculations under more general conditions for the shape of the unit cell, partition tree, and boundary conditions, keeping the accuracy of the calculated electrostatic interactions as high as that with the conventional FMM. An extension of the present FMM algorithm to other prime number branches, such as 5 and 7, is straightforward.

Moment-of-fluid analytic reconstruction on 3D rectangular hexahedrons

The moment-of-fluid method (MOF) is a second-order accurate interface reconstruction method which can be seen as an extension of the volume-of-fluid method with piecewise linear interface construction (VOF-PLIC). MOF involves a computationally intensive minimization problem that needs to be solved on every cell containing several materials. We propose a new fast and robust reconstruction algorithm to tackle this problem on rectangular hexahedral cells. Our approach uses explicit analytic formulas of the objective function that does not use any geometric computations such as half-space–polyhedron intersections. The numerical results show that the proposed method is more robust and more than 200 times faster than the original approach. Additionally, we propose a faster reconstruction algorithm on convex polyhedral cells. All the methods presented in this article have been implemented and verified on the open-source code Notus.

Rapid polarization mapping in ferroelectrics using Fourier masking.

Ferroelectric materials, and more specifically ferroelectric domain walls (DWs) have become an area of intense research in recent years. Novel physical phenomena have been discovered at these nanoscale topological polarization discontinuities by mapping out the polarization in each atomic unit cell around the DW in a scanning transmission electron microscope (STEM). However, identifying these features requires an understanding of the polarization in the overall domain structure of the TEM sample, which is often a time-consuming process. Here, a fast method of polarization mapping in the TEM is presented, which can be applied to a range of ferroelectric materials. Due to the coupling of polarization to spontaneous strain, we can isolate different strain states and demonstrate the fast mapping of the domain structure in ferroelectric lead titanate (PTO). The method only requires a high-resolution TEM or STEM image and is less sensitive to zone axis or local strain effects, which may affect other techniques. Thus, it is easily applicable to in-situ experiments. The complimentary benefits of Fourier masking with more advanced mapping strategies and its application to other materials are discussed. These results imply that Fourier masked polarization mapping will be a useful tool for electron microscopists in streamlining their analysis of ferroelectric TEM samples. LAY DESCRIPTION: This paper addresses a problem that often occurs when looking at a ferroelectric material in the Transmission Electron Microscope (TEM). Ferroelectric samples are interesting because they form tiny areas inside themselves with arrow of charge in each one. The thinner the sample, the smaller these regions, called "domains" become. These arrows of charge point in different directions in each domain of the sample. The boundary where these domains meet have interesting properties to study in a TEM but it's important to figure out which way the arrows point in the domains around the boundary. What causes the arrows in the different domains is tiny shifts of different atoms in unit cell away from their neutral position, usually because they're being squeezed by pressure from the domains nearby. The problem is that these tiny atoms moving are difficult to measure and see where the charged arrow is pointing, often it's hard to know how many different domains are even in the sample and where they begin. This paper discusses a method called "Fourier masking" to quickly see what's going on in the overall TEM sample, where the domains are and roughly where the arrows point. It does this by looking at the spacings of the atoms from a magnification where you can just about see the lines of atoms. In lead titanate the unit cell is a rectangle and the arrow always points in line with the long side of the rectangle. The Fourier masking lets you see which direction the long side of the rectangular unit cell is pointing in different parts of your TEM image. The big advantage is that it takes about two minutes to do and uses software that almost every TEM already has. That lets the TEM user quickly know where the domains are in their TEM samples and roughly which way the arrows of charge are pointing. Then they can choose the most interesting features focus on for higher resolution analysis.

Two-satellite formation flying control by cell-structured solar sail

The method of simultaneous relative motion and attitude control by a solar radiation pressure is proposed. The control goal is to stabilize the given closed relative orbit. The principle idea is to use special materials for solar sail that able to change their optical properties. The solar sail consists of a number of rectangular cells. Each of them can change its optical properties. The necessary control force is produced by varying the average reflectivity of solar sail, and the control torque is achieved by the appropriate pattern of black and white cells.

The AquiFR hydrometeorological modelling platform as a tool for improving groundwater resource monitoring over France: evaluation over a 60-year period

Abstract. The new AquiFR hydrometeorological modelling platform was developed to provide short-to-long-term forecasts for groundwater resource management in France. This study aims to describe and assess this new tool over a long period of 60 years. This platform gathers in a single numerical tool several hydrogeological models covering much of the French metropolitan area. A total of 11 aquifer systems are simulated through spatially distributed models using either the MARTHE (Modélisation d'Aquifères avec un maillage Rectangulaire, Transport et HydrodynamiquE; Modelling Aquifers with Rectangular cells, Transport and Hydrodynamics) groundwater modelling software programme or the EauDyssée hydrogeological platform. A total of 23 karstic systems are simulated by a lumped reservoir approach using the EROS (Ensemble de Rivières Organisés en Sous-bassins; set of rivers organized in sub-basins) software programme. AquiFR computes the groundwater level, the groundwater–surface-water exchanges and the river flows. A simulation covering a 60-year period from 1958 to 2018 is achieved in order to evaluate the performance of this platform. The 8 km resolution SAFRAN (Système d'Analyse Fournissant des Renseignements Adaptés à la Nivologie) meteorological analysis provides the atmospheric variables needed by the SURFEX (SURFace EXternalisée) land surface model in order to compute surface runoff and groundwater recharge used by the hydrogeological models. The assessment is based on more than 600 piezometers and more than 300 gauging stations corresponding to simulated rivers and outlets of karstic systems. For the simulated piezometric heads, 42 % and 60 % of the absolute biases are lower than 2 and 4 m respectively. The standardized piezometric level index (SPLI) was computed to assess the ability of AquiFR to identify extreme events such as groundwater floods or droughts in the long-term simulation over a set of piezometers used for groundwater resource management. A total of 56 % of the Nash–Sutcliffe efficiency (NSE; Ef) coefficient calculations between the observed and simulated SPLI time series are greater than 0.5. The quality of the results makes it possible to consider using the platform for real-time monitoring and seasonal forecasts of groundwater resources as well as for climate change impact assessments.

Spoof surface plasmonic transmission line with high isolation and low propagation loss.

A novel compact spoof surface plasmonic (SSP) transmission line (TL) consisting of a stem-shaped periodic structure is proposed to achieve high field confinement in the higher frequency range (microwave to terahertz). The dispersion characteristic of the proposed stem-shaped SSP unit cell exhibits much lower asymptotic frequency and higher field confinement than the conventional coplanar waveguide (CPW) and the rectangular SSP unit cell structure without increasing the overall transverse dimension, i.e., improved signal propagation performance with reduced cross-sectional area. The numerical study of the multi-conductor line based on the proposed stem-shaped SSP unit cell shows that it has improved propagation and isolation features in comparison to the conventional TL structures. Here, the improved isolation is characterized in terms of the mutual coupling (MC) between the two adjacent lines designed using the stem-shaped SSP unit cell, which is not found to significantly increase with an increase in the coupling length unlikely in the conventional TLs. For the proposed SSP-based multi-conductor line, the MCs for 1.6, 2.25, and 4.15λ coupling lengths with fixed separation of 0.175λ are found to be 22, -19.8, and -17.55dB, respectively.

Observation of the domain wall propagation in CoFe and CoFeB nanowires driven by sub-nanosecond magnetic pulse using micromagnetic simulation

In this study, we have observed the domain wall (DW) propagation in CoFe and CoFeB nanowires driven by sub-nanosecond magnetic pulse using micromagnetic simulation approach. The length of the nanowire is 2000 nm, the widths are varied of 50, 100, and 150 nm, and the thicknesses are 2.5 and 5.0 nm. The simulation was performed using a rectangular cell size of 5×5×t nm3 with t is the thickness of the nanowire and the damping factor is 0.05. The sub-nanosecond magnetic pulse length of 0.5 ns was used to move DW through the nanowire. We found that the DW velocity increased as the magnitude of magnetic pulse increased then abruptly decreased which known as the Walker Breakdown (H WB). The transverse type DW structure is observed below the H WB field while vortex/anti-vortex wall structure was formed above H WB. We found that the H WB value of CoFe and CoFeB decreased as the width and thickness of the nanowire increased. The increasing of nanowire thickness also caused the velocity reduction of DW. The energy competition between exchange and demagnetization energy contributed to the DW structure during propagation. The exchange energy is higher than the demagnetization energy as the formation of vortex/anti-vortex wall.

An Innovative Miniature Pulsating Emulsification Device: Flow Characterization and Measurement of Emulsion Stability

The aim of this study is the development of an emulsification device for two immiscible liquids with a total volume of approximately 3 mL. The heart of the device is a piston, with an aluminum plate fixed at its tip, which moves periodically up and down inside a rectangular cell. The plate geometry (uniform or non-uniform height) affects significantly both the emulsions stability and the size of the droplets of the prepared emulsions. Five parameters are examined during testing (surfactant type, surfactant concentration, proportion of immiscible liquids, piston stroke frequency, duration of emulsification) and all of them appear to have an important role in the resulting droplet size distribution. A macroscopic theoretical model is developed for the determination of the main hydrodynamic parameters of the innovative device. It is shown that the non-uniform height plate achieves higher shear rates when compared to the uniform height plate because of the smaller gap between the plate and the cell walls. However, the benefits of the higher shear rate are overturned by the larger effective breakage time encountered in the uniform height plate resulting from the larger surface area of its sides. The results of the emulsification experiments are analyzed using the parameter values derived by the developed model.