Rectangular Cell Research Articles

Gel growth of aqueous konjac glucomannan solution containing sodium trimetaphosphate dialyzed with dilute sodium hydroxide

The growth rate of the hydrogel of the aqueous konjac glucomannan (KGM) solution containing sodium trimetaphosphate (STMP) dialyzed with aqueous NaOH was investigated in a rectangular cell. The growth rate of the KGM-STMP gel depended on both the KGM and STMP concentrations in addition to the NaOH concentration. The initial growth rate of the KGM-STMP gel was closely related to the diffusion of NaOH into the KGM-STMP solution, leading to the ring-opening reaction of STMP and the deacetylation of KGM at the interface. The time course of the gelation of the KGM-STMP solution was analyzed on the basis of the moving boundary picture theory by introducing the characteristic length to express the consumption of NaOH in the gel layer accompanying the decomposition of STMP. Dynamic mechanical measurements were performed to compare the gelation of the KGM-STMP solution mixed homogeneously with dilute NaOH and the gel dynamics by the dialysis method.

Variations in the cellular magnetic domain structure in Fe–Ga alloys

The so-called cellular magnetic domain structure has been widely observed in Fe–Ga alloys of different compositions and heat treatment. It has attracted attention for producing desirable magnetic properties and also for arousing controversy over its cause and identity. Two existing models, one based on novel charge density waves and the other based on traditional V-lines from the classical magnetic domain theory, give contradictory interpretations of the cellular domains in Fe–Ga alloys, which remain to be clarified. The cellular domains observed in Fe–Ga alloys so far are highly periodic, consisting of parallel chains of rectangular cells. This paper reports on the presence of various deviations in the cellular domains from the previously known ideal periodic cellular structure in Fe–Ga alloys and explores the implications of those variations. The variations include changes in the cell shape, spacing, branching, and nesting. It is shown that the observed variations in the cellular domains can be explained well by the V-line model where the competition between elastic and wall energy drives the pattern formation process. In comparison, the disagreements of the charge density wave model with the experimental observations are addressed. Similar cellular domain variations observed previously in Fe–Si alloys are also discussed, confirming the generic aspects of the cellular domains and their variations in cubic magnetostrictive materials. The findings provide insights into the magnetic domain phenomena in Fe–Ga alloys.

Unravelling the structural changes of phospholipid membranes in presence of graphene oxide

Graphene-based nano-technology is the future of biomedical devices including biosensors and, hence, it is essential to unravel the interaction of graphene oxide (GO) with cellular membrane. Here, the structural reorganization of lipid molecules, which are the building blocks of a cellular membrane, has been demonstrated in presence of GO flakes. The membrane is mimicked by forming a stack of lipid bilayers of zwitterionic phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and its structures have been probed by X-ray reflectivity and grazing incidence X-ray diffraction techniques. Lipid-GO composites have exhibited two sets of lamellar diffraction peaks illustrating GO-rich micro-domains in the matrix of phospholipid bilayers (GO-poor phase). In these domains, the GO flakes are observed to penetrate into hydrophobic core of the bilayer altering the thickness along with the overall electron density profile of the lipid layer. The GO-poor bilayer is closely related to the phase formed by pristine lipid molecules. The lattice parameters of a body-centred rectangular unit cell formed by chains of saturated phospholipids are found to be modified in presence of GO with a significant effect on molecular tilt. The structural description of GO-membrane interaction may pave the way of discerning the physical behaviour of the composites.

BASIC TOMO: an educational tool for investigating the role of controlling parameters and observation geometry in tomography problems

The paper presents an educational version of the tomography algorithm BASIC TOMO, which is aimed at demonstration of the role of different controlling parameters in inversion. The algorithm uses a simplified approximation of rays with straight lines and a model parameterization with the use of rectangular cells. The tomography procedure is reduced to solving a system of linear equations, which is performed using the LSQR method. This study presents several exercises showing the role of different factors in inversion, such as grid spacing, smoothing, ray configuration, and noise in the data. The calculations are performed for different types of synthetic models. All the results can be easily reproduced using the appended version of the BASIC TOMO code.

Revealing Molecular Mechanisms in Hierarchical Nanoporous Carbon via Nuclear Magnetic Resonance

Author(s): Mao, H; Tang, J; Xu, J; Peng, Y; Chen, J; Wu, B; Jiang, Y; Hou, K; Chen, S; Wang, J; Lee, HR; Halat, DM; Zhang, B; Chen, W; Plantz, AZ; Lu, Z; Cui, Y; Reimer, JA | Abstract: Hierarchical nanoporous carbons combining pore sizes of different length scales are highly important for separation processes. However, critical questions remain regarding the hierarchical structure regulation and the molecular mechanisms of gaseous adsorbate uptake and interactions within the hierarchical nanoporous carbons. These materials present characterization challenges in that there are no experimental techniques that can elucidate the molecular mechanisms of the organic compounds and CO within the materials. We deployed multidimensional solid-state nuclear magnetic resonance (NMR) to generate maps of guest-framework interactions as a function of adsorbate concentrations and adsorption times. The NMR spectra provide insight toward the design of effective hierarchical pore structures. Our materials show a high volatile organic compounds/CO physisorption capacity, which reveals promising application to carbon-capture strategies to mitigate global warming. 2 2

Recent improvements in straw neutron detectors for large-scale neutron science instruments

Modified boron-coated straw (BCS) detector configurations are introduced, in order to improve detection efficiency, and reduce the number of layers required to match the response of high-pressure 3He tubes, in large-scale neutron science instruments. A new 7-straw design employing thin-walled aluminum tubes facilitates operation in vacuum, and substantially reduces the scattering material by a factor of 5 compared with the flow-through design of the Multi-Grid detector. Another design introduces 18 radial walls inside each straw, coated on both sides with enriched boron carbide, to increase the coated wall perimeter 4.3 times. The so-called Pie straw offers a significant benefit in detection efficiency compared with round straws used in LoKI. An example of such a straw having 18 septa is explored in modeling and experimental studies, that can potentially reduce the number of layers needed in large-scale instruments like LoKI by a factor of 2.8. In a parallel development, a totally new configuration of boron-coated detectors is introduced, aimed to address the need for high spatial resolution, and high-rate capability in single crystal diffractometers, like MaNDi and TOPAZ at the SNS, and in neutron reflectometers. The proposed structure is a close-packed array of rectangular cells, each fabricated by wrapping copper foil having a coating of 10B4C on one side and electroplated tin on the other side, around precisely machined rectangular bars. The array is pressed together and then vacuum brazed together. The resulting structure is quite strong and precise in geometry. This so-called Microcell Straw Array can be configured with channel dimensions as small as 0.5 mm × 2.5 mm. Due to its ultra thin walls (25 μm) secondary scattering of neutrons is minimized. It is sealed inside a fully welded thin aluminum containment vessel that allows convenient operation in vacuum. A mature low power readout system capable of an estimated count rate of 22 MHz in a 15 × 15 cm2 detector is also proposed. The improvements are the result of recent advances in BCS design, spurred by the development of compact, high-sensitivity monitors for homeland security and military applications.

Nodal Integral method for multi-group neutron diffusion equation in three dimensional cylindrical coordinate system

Due to their high accuracy, the nodal methods are quite extensively used for solving neutron diffusion and transport equations. However, their use is mainly restricted to the geometries which can be mapped by rectangular (cuboidal in 3D) or hexagonal cells. For several Generation IV reactors the equations are solved in cylindrical geometries, needing fine meshing near the boundaries if traditional nodal methods are used. Therefore, a Nodal Integral Method (NIM) for one group neutron diffusion in 2D polar coordinates was developed recently. Here, the method is extended to multi-group neutron diffusion in 3D cylindrical coordinates. Unlike the Cartesian geometries, each direction needs separate treatment in case of the cylindrical geometries. Therefore, the extension is neither trivial nor straightforward. The developed method is tested by solving three different problems for which analytical or benchmark solutions exist. It is observed that the methodology preserves its high accuracy for multi-group 3D problems.

A new periodic cell model of aerosol diffusion deposition in a fibrous filter

A new periodic cell model for the convective-diffusive transport of small aerosol particles in a fibrous filter is developed. The proposed periodic model takes into account the influence of the fiber diffusion wake on the particle deposition. This allows us to predict the efficiency of a filter more accurately compared to the single-fiber approximations. The fluid flow is described in the framework of Stokes flow in a rectangular periodic cell. New form of periodic boundary conditions for the particle transport equation in the cell is suggested. The equations of fluid flow and particle transport are solved using the Boundary Element Method (BEM) and Boundary Domain Integral Method (BDIM).The diffusive deposition of nanoaerosols in the filter, modeled as a row of the large number of circular cylinders located perpendicular to the flow direction, is studied numerically using the many fibers model. It is shown, that predictions of the new periodic model are in the better agreement with the many fibers model for the filters of greater length. It is also shown, that the widely used approximation for single fiber deposition efficiency (Stechkina, 1967) overestimates the efficiency of multi-fiber filter compared to periodic model. The overestimation increases with increase of Peclet number.The approximate formula for the single fiber particle deposition efficiency in a periodic cell for a square and staggered cylinder arrays is derived. The formula accounts for the effect of the Peclet number and the hydrodynamic factor. The predictions of the derived formula are compared to the numerical data from the work of Hosseini and Tafreshi (2010) for the fibrous filter comprised of many randomly arranged cylinders. The predictions of the diffusive deposition efficiency obtained using the derived formula for the staggered fibers array are shown to be in a good agreement with the numerical model predictions.

Development of magnetoelastic fingering patterns in a rectangular Hele-Shaw cell

A ferrofluid and a nonmagnetic fluid flow in a rectangular Hele-Shaw cell subjected to an in-plane magnetic field. A chemical reaction occurs, and the two-fluid interface becomes elastic. The produced patterns range from straight front to sharp tip ones, and they differ from usual Saffman-Taylor fingers.

GRID: GRID Resample by Information Distribution

This paper exploits a concise yet efficient initialization strategy to optimize grid sampling-based superpixel segmentation algorithms. Rather than straight distributing all initial seeds evenly, it adopts a context-aware approach to modify their positions and total number via a coarse-to-fine manner. Firstly, half the expected number of seeds are regularly sampled on the image grid, thereby creating a rough distribution of color information for all rectangular cells. A series of fission is then performed on cells that contain excessive color information recursively. In each cell, the local color uniformity is balanced by a dichotomy on one original seed, which generates two new seeds and settles them to spatially symmetrical sub-regions. Therefore, the local concentration of seeds is adaptive to the complexity of regional information. In addition, by calculating the amount of color via a summed area table (SAT), the informative regions can be located at a very low time cost. As a result, superpixels are produced from ideal original seeds with an exact number and exhibit better boundary adherence. Experiments demonstrate that the proposed strategy effectively promotes the performance of simple linear iterative clustering (SLIC) and its variants in terms of several quality measures.

Separation of glucose, other reducing sugars and phenolics from natural extract by nanofiltration: Effect of pressure and cross-flow velocity

This study considers the effect of cross-flow velocity and transmembrane pressure on flux and rejection behavior during nanofiltration of Eurasian water milfoil hydrolysate. Fractionation by nanofiltration was applied to obtain a glucose-rich permeate solution and a concentrated retentate solution of other sugars and phenolics. Nanofiltration was performed in a cross-flow rectangular flat-sheet cell (MaxiMem, Prozesstechnik GmbH). Membrane Microdyn Nadir™ NP030 with molecular weight cut-off 500 Da was used. The velocity and shear stress distribution on the membrane surface was modelled by CFD simulations. Mild hydrodynamic conditions (cross-flow velocity and pressure) are recommended based on the observed permeate flux and rejection difference between the targeted groups of compounds. The results are discussed in rapport with existing experimental observations in the literature.

Morphology and microstructure of Pellites hamiensis nov. sp., a Middle Jurassic liverwort from northwestern China and its evolutionary significance

Pelliales is a basal lineage of the simple thalloid liverworts. Here, we describe a simple thalloid liverwort from the Middle Jurassic Xishanyao Formation of the Turpan–Hami Basin, Xinjiang Uygur Autonomous Region in northwestern China. The thalloid fossil liverwort is described as a new species: Pellites hamiensis (Pelliaceae, Pelliales). Pellites hamiensis nov. sp. resembles the extant species of Pelliaceae in having ribbon-like segments, conspicuous costae that appear as ridges on the ventral surface, rectangular cells with thickened walls adjacent to the margin, and elongated cells in the middle part of the thallus. The occurrence of P. hamiensis nov. sp. extends the fossil records of Pellites back to the Aalenian-Bajocian or Bajocian (ca. 170 Ma) and suggests that the divergence time of the Pelliaceae is no later than the Middle Jurassic.

Computational Study of Magnetic Switching Mechanism of Nanoscale MRAM Cells

Investigation of magnetic switching of nanoscale single MRAM cells of different shapes and sizes is imperative for their applications in future magnetic memory devices. To this end, we have investigated the magnetic switching mechanism of nanoscale single MRAM cells of two different shapes with varying lateral aspect ratios by computational micromagnetic simulation. We have analysed how various parameters such as the coercive field, remanence and saturation field were affected by the variation in magnetic field. We have also analysed the change in shape of the hysteresis loops of the various samples. The magnetization reversal states were simulated to justify the spatial coherence of magnetization switching. As a result, the cells with higher aspect ratio show the Py and Fe layers forming antiparallel states in the plateau similar to synthetic antiferromagnets. As we reduce the aspect ratio, more complex quasi-uniform magnetic states are observed which are even more complicated for elliptical cells. The rectangular cell with the highest aspect ratio of 2.5 shows the most coherent and predictable switching behaviour, showing its suitability for the application of MRAM cells.

Oxide at the Al-rich Fe0.85Al0.15(110) surface

The formation of an ultra-thin aluminum oxide film at Fe0.85Al0.15(110) surface (A2 random alloy) has been studied by a variety of surface sensitive techniques (X-ray photoemission, low-energy electron diffraction, surface X-ray diffraction and scanning tunneling microscopy) supplemented by ab initio atomistic simulations. Since iron is not oxidized in the used conditions, the study focused on the coupling between aluminum oxidation and segregation processes. Compared to the bare surface, whose average composition (Fe0.6Al0.4) is closer to the B2-CsCl structure over a ∼ 3 nm depth, the oxidation hardly affects the subsurface segregation of aluminum. All the structural and chemical fingerprints point to an oxide film similar to that found on NiAl(110). It is a bilayer (∼ 7.5A thick) with a composition close to Al10O13 and a large (18.8 × 10.7)A 2 nearly rectangular unit cell; an almost perfect match between substrate periodicity and the (1 × 2) oxide supercell is found. Nevertheless, microscopy reveals the presence of anti-phase domain boundaries. Measured Al 2p and O 1s core level shifts match calculated ones; their origin and the relative contributions of initial/final state effects are discussed. The ubiquity of the present oxide on different supports asks for the origin of its stability.

Experimental study of capillary penetration in rectangular Hele-Shaw cells closed by two edges

Here is studied the capillary penetration of a viscous liquid between two vertical, rectangular close together plates. In experiments the plates were joined simultaneously along two edges, and the liquid has penetrated from the bottom. Spacers with different geometries like circular, triangular and rectangular shape, were used to check their aects on the rise proles in a dynamic way, it was noticed that when time evolves, the proles are stabilized in a catenary and the instabilities induced by efforts present in the plates disappear. Also, it is observed a rate of ascent that diers of classical values of t^1/3 or t^1/2, depending of gravity effect.

Pressure drop analysis on the positive half-cell of a cerium redox flow battery using computational fluid dynamics: Mathematical and modelling aspects of porous media

Description of electrolyte fluid dynamics in the electrode compartments by mathematical models can be a powerful tool in the development of redox flow batteries (RFBs) and other electrochemical reactors. In order to determine their predictive capability, turbulent Reynolds-averaged Navier-Stokes (RANS) and free flow plus porous media (Brinkman) models were applied to compute local fluid velocities taking place in a rectangular channel electrochemical flow cell used as the positive half-cell of a cerium-based RFB for laboratory studies. Two different platinized titanium electrodes were considered, a plate plus a turbulence promoter and an expanded metal mesh. Calculated pressure drop was validated against experimental data obtained with typical cerium electrolytes. It was found that the pressure drop values were better described by the RANS approach, whereas the validity of Brinkman equations was strongly dependent on porosity and permeability values of the porous media.

Design of Large‐Scale Rectangular Cells for Rechargeable Seawater Batteries

AbstractRechargeable seawater batteries (SWBs) are regarded as sustainable alternatives to Li‐ion batteries due to the use of an unlimited and free source of Na ion active materials. Although many approaches including the introduction of new catalysts have successfully improved the performance of SWBs, reconsidering the cell design is an urgent requirement to improve the performance and scale up the production of practical batteries. In this study, by adjusting the maximum space efficiency, a rectangular cell is developed which due to its unique architecture, benefits from optimized contact to improve the overall charge transfer in the system. In view of the rigidity of the solid electrolyte, the novel cell model is intended to have adequate flexibility to be easily transported and practically utilized. Furthermore, the enhanced efficiency of the parallel stacked modules, indicates the capability of this cell in practical use. The designed catalyst‐free cell system shows a record capacity of 3.8 Ah (47.5 Ah kg−1), energy of 11 Wh (137.5 Wh kg−1), and peak power of 523 mW for individual unit cell, while it also retains performance up to 100 cycles. This design paves the way for commercializing rechargeable seawater batteries.

Tunable elastic wave propagation in planar functionally graded metamaterials

Structures made of functionally graded materials (FGM) are successful attempts to enhance the mechanical properties of homogeneous materials. On the other hand, periodically architected structures provide phenomenal opportunities to design structures much lighter than their bulk counterparts showing exceptional mechanical characteristics. In the present study, to utilize the advantages of both technologies, wave propagation properties of functionally graded metamaterials (FGMM), i.e., periodically architected structures made of FGM, are investigated for three different planar topologies, and their vibration filtering performances are analyzed. The mathematical formulations to obtain the equation of motion for the FGMM are developed using the finite element method, and Floquet–Bloch’s theorem is employed to find their dispersion curves. Periodically architected structures with hexagonal, rectangular, and triangular unit cells are considered, and the effects of the FGM on their stop-band percentages are investigated. A comparison between band structures of pure steel (St), pure alumina ( $$\hbox {Al}_{2}\hbox {O}_{3}$$ ) and $$\hbox {St}{-}\hbox {Al}_{2}\hbox {O}_{3}$$ reveals that using FGM in the periodically architected structures can greatly enhance wave propagation properties by opening new stop-band regions leading to structures with much more versatility and tunability. The material distribution is assumed to vary according to both power-law and exponential-law rules along the beam axis and thickness, and the effects of Young’s modulus ratio, density ratio, relative density, and non-negative power-law exponent are scrutinized on the bandgap properties. The results indicate that periodically architected structures made of FGM exhibit much higher percentages of stop-bands, and playing with corresponding FGM parameters can tune this value for desired engineering needs. In addition, a mathematical approach is presented to investigate the polarization of the studied FGMM in the longitudinal, transverse, and rotational directions, and to measure the effects of material distribution on the polarization of the first three branches of the dispersion curves. It is revealed that the polarization factors of the three first dispersion branches are mainly geometry-dependent and change slightly with the material distribution.

<p><strong>New and endemic species of<em> Brachymenium </em>(Bryaceae, Bryophyta) in the Atlantic Rainforest of Brazil</strong></p>

The present study describes and illustrates two newly identified moss species of Brachymenium, endemic to the Atlantic Rainforest of the South and Southeastern regions of Brazil. The first is Brachymenium elimbatum, a medium-sized plant with leaf apex ending in a short to long arista, margins not bordered, plane, entire, costa tapering above and sub-percurrent. The second is Brachymenium sublineare, a medium-sized plant with leaves often asymmetrically curved in the distal half, margins bordered by 1–3 rows of narrow rectangular cells and serrate at distal half, costa short-excurrent, flagelliform branches occasionally present and exostome teeth sub-linear. A key is presented with the most similar Brazilian Brachymenium species.

Design and fabrication of a low-loss microstrip lowpass-bandpass diplexer for WiMAX applications

This work presents a compact low-pass-bandpass microstrip diplexer with a novel configuration. It consists of a lowpass filter integrated with a bandpass filter via a simple compact junction. The proposed bandpass filter consists of four rectangular patch cells and some thin strips. The step impedance structures, with a radial cell, are applied to achieve a lowpass frequency response. The lowpass channel of the introduced diplexer has 2.64 GHz cut-off frequency, whereas, the bandpass channel center frequency is 3.73 GHz for WiMAX applications and covers the frequencies 3.31 GHz to 4 GHz. In addition to having novel structures, both filters have other advantages in terms of high return loss, low insertion loss and high selectivity. The presented microstrip diplexer has the compact size of 29 mm × 13.8 mm × 0.762 mm, calculated at 2.64 GHz. The obtained insertion losses are 0.20 dB (for the first channel) and 0.25 dB (for the second channel), which make the proposed diplexer suitable for energy harvesting. The stopband properties of both bandpass and lowpass filters are improved by creating several transmission zeros. The comparison results show that the lowest insertion losses, the minimum gap between channels, good return losses, and good isolation are obtained.