Octagonal Shape Research Articles

Riesenkampf's vortex solution revisited for 2-D commingling of groundwater in a three-layered aquifer: Vertical-inclined-horizontal seepage in aquitard

Using exact and explicit analytical solutions and MODFLOW simulations we show that downstream of an unconformity (transition from an aquifuge layer to a homogeneous aquitard) groundwater seeps at varying angles with respect to the layering. As a generalization of the Anderson (2003) two-layered composite, a steady, 2-D Darcian flow in a three-layered aquifer is studied. This flow is generated by different inlet piezometric heads in thick upper and lower strata and a cross-flow through an aquitard sandwiched between them. Analytically, a line vortex combined with a dipole at infinity describes commingling between the strata with refraction (continuity of head and normal flux component) along the upper and lower boundaries of the aquitard. The Fourier method by Riesenkampf (1940) gives explicit expressions for the specific discharge vector fields in the three media. MODFLOW models finite lengths composites of rectangular and octagonal shapes. The Dupuit–Forchheimer approximation is illustrated to oversimplify the flow topology.

Morphological control and kinetics in three dimensions for hierarchical nanostructures growth by screw dislocations

The precise control and in-depth understanding of the anisotropic crystal screw dislocation growth could yield further optimization of nanomaterial design and broader applications, yet the studies of rational control and kinetics for more complex nanostructures are still insufficient. In this work, by programming synthesis conditions, we achieve a controllable three-dimensional (3D) screw dislocation growth of hierarchical nanostructures, including nanowires, nanoplates, and previously unreported hierarchical hollow nanobelts, via a facile chemical vapor deposition approach. Notably, the screw dislocation growth in nanobelts is confirmed by the clear observations of the stepwise spiral terraces with initial hexagonal to octagonal shapes and the hollow cores in the growth spiral centers, as well as the fundamental Burton-Cabrera-Frank crystal growth theoretical calculations. The formation of the nanowires and nanoplates can be well interpreted by the previously reported screw dislocation growth model, while a new 3D screw dislocation growth model with considering of transition in growth velocities and directions is proposed to interpret the formation of the nanobelts and other potential complex nanostructures. This study not only enriches our understanding of the screw dislocation growth kinetics but also guides us to achieve the precise morphological design and control in nanosynthesis.

Crashworthiness Performance of Stiffened Foam-filled Tapered Structures under Axial and Oblique Dynamic Loads

Abstract This paper aims to explore crashworthiness performance of new designed foam-filled tapered structures under axial and oblique impact load conditions. The structures consisted of inner and outer tapered tubes connected together by four stiffening plates. They also included square, hexagonal, octagonal, decagonal and circular cross-sectional shapes with different ratios of a/b (ratio of the inner tube side length to the outer tube one). The ratio of a/b was assumed to be 0, 0.25, 0.5, 0.75 and 1. Crashworthiness criteria of specific energy absorption (SEA), peak collapse force (Fmax) and crash force efficiency (CFE) were obtained for these structures using the experimentally validated model in LS-DYNA. Based on the numerical results, semi-foam filled structures (i.e. those with the ratio of a/b=0.5) demonstrated greater crashworthiness performance than foam filled single-cell ones. Furthermore, according to the TOPSIS calculations, cross sectional shape of decagonal was found to be an outstanding potential profile for the automobile structural components.

Experimental investigation on octagonal concrete filled steel stub columns under uniaxial compression

Concrete filled steel tubes (CFST) have been widely used in modern constructions. The cross-section shapes of circular and rectangular are mostly used. This paper presents an investigation on CFST with a new cross-section shape - octagonal shape which combines both advantages from circular and square cross-sections. In this study, 21 CFST stub columns were tested accompanying with 9 plain concrete columns under uniaxial compression. Three cross-section shapes, octagonal, circular and square sections were considered. In parallel, 10 associated CFST stub columns with octagonal cross-sections from literature were also complied. The measured steel yield strength was between 383 MPa to 485 MPa. Both normal and high strength concrete were used with measured cylinder compressive strengths ranging from 38 MPa to 112 MPa. The key investigation focuses on the relationship between the cross-section shapes and confinement effectiveness which can provide an understanding on the difference in load bearing capacity of CFST with those three section shapes. Design formulae for the cross-section capacity in the current code of practice were assessed by the experimental results and modification was proposed to the existing formula for circular cross-section which could be adopted for the CFST with octagonal cross-section.

Controlling Octagon-to-Square Wetting Interface Transition of Evaporating Sessile Droplet through Surfactant on Microtextured Surface.

Producing and maintaining specific liquid patterns during evaporation holds great potential for techniques of printing and coating. Here we report the control over the evolution of surfactant solution droplets on the micropyramid substrates during evaporation. The polygonal droplet shape is achieved during the drying rather than solely at the beginning. As the initial surfactant concentration is 0.04 mM, the droplet maintains its initial octagonal shape throughout the lifetime. Interestingly, the initial octagonal shape transforms into a square during the evaporation as the initial surfactant concentration reaches 0.8 mM. These findings can shed light on wetting pattern control for complex solutions required in various applications.

Prilling and Coating of Ammonium Dinitramide (ADN) Solid Green Propellant in Toluene Mixture Using Ultrasound Sonication

Ammonium Dinitramide (ADN) in its generic form has a long needle shaped structure, which hinders higher solid loading. Therefore, it is of utmost importance to optimize its crystal morphology into octagonal shapes. Moreover, the low critical humidity level of ADN renders it unusable in a humid climate. Hence, encapsulation with a hydrophobic polymer is necessary. In the present work, ADN was synthesized by nitration of potassium sulfamate with mixed acid nitration. The product was then mixed with toluene, graphene, citryl ammonium butyl, Cab-o-sil, and coating polymer (Polystyrene or HTPB) and treated with ultrasound to obtain semi-spherical ADN-coated particles. The method offers a reduction in operating temperature and elimination of ADN melting in the shape-altering process. In addition, the ADN product has a similar particle size and thermal stability compared to those in a conventional ADN melt-prilling method. The ADN product investigated under SEM confirms the particle morphological change from long needles into semi-spherical shapes. The particle size obtained, in the micrometer range, is ideal for higher theoretical maximum density. Furthermore, the ultrasound-treated ADN particles show significant reduction in moisture absorption, from 68% to 16% at 65% relative humidity. The DSC result shows no degradation of thermal stability of the coated particles.

Improving Behavior of Castellated Beam by Adding Spacer Plat and Steel Rings

Castellated steel beams are those members which are made from hot rolled steel I-section firstly by cutting the web in zigzag pattern and rejoining the two halves by welding together to form a hexagonal castellated beam such that the depth of section will be increased. Generally, the openings made in the web are with hexagonal shape; however, octagonal shape of web openings is typically obtained by providing spacer plate which is utilized to increase the depth of beam. Nowadays, using castellated beams in building construction becomes very popular because of their useful functions such as ease of service provision, strength and low cost. This study focuses on improving the behavior of hexagonal and octagonal castellated beam with spacer plate. The ultimate strength of the original (parent) I- section beam increases due to the increasing its depth. The increment of castellated beam depth; however, leads to post buckling in its web and to many other modes of failure when these beams are subjected for loading. Hexagonal and octagonal castellated beams which are fabricated using parent I-section (IPN140) are analyzed using finite element model (FEM).The analysis results revealed that using ring stiffeners around edge of holes contributes effectively in strengthening the web. It was found that using ring steel stiffeners can reduce the stress concentration around the edge of holes and improve the behavior of these beams by increasing the ultimate strength and minimizing the deflection. From the numerical (FEM) results obtained by using ANSYS14, it is concluded that ultimate strength of castellated beam can be improved by providing spacer plate and ring stiffeners around the web hole. Also, the results showed that ultimate strength of octagonal castellated steel beam can be increased up to (53%) more than the parent beam (IPN140) with providing only (13.0%) weight of steel (spacer plate plus ring steel stiffeners).

Analysis of subsonic wind tunnel with variation shape rectangular and octagonal on test section

The need for good design in the aerodynamics field required a wind tunnel design. The wind tunnel design required in this case is capable of generating laminar flow. In this research searched for wind tunnel models with rectangular and octagonal variations with objectives to generate laminar flow in the test section. The research method used numerical approach of CFD (Computational Fluid Dynamics) and manual analysis to analyze internal flow in test section. By CFD simulation results and manual analysis to generate laminar flow in the test section is a design that has an octagonal shape without filled for optimal design.

Finite element analysis of large diameter high strength octagonal CFST short columns

Octagonal masonry columns have been broadly used in outstanding architectural heritage due to their aesthetical appearance and to support high loads. Nowadays, concrete-filled steel tubular (CFST) columns have been utilised to carry such high load. However, a recent trend in the construction of the CFST columns is to use the high strength concrete (HSC) to increase the usable floor spaces in different buildings due to the global limited land areas. Therefore, this paper combines the architectural demand of the octagonal column shape with the advantages of the CFST columns by investigating numerically, by means of finite element (FE) modelling, the octagonal CFST short columns. Accordingly, validated FE models for the octagonal CFST short columns are employed to perform parametric studies to widen the available knowledge about their behaviour. The paper is mainly devoted for investigating large diameter columns using extensive series of diameter-to-thickness (D/t) ratios ranging from 40 to 200, most of which filled with HSC up to 100MPa. The ultimate strengths, based on available experiments in literature and current FE investigation, are compared with the existing design models. This comparison indicates that the existing design models are conservative and their accuracy is affected by the D/t ratios. Therefore, a new design model is suggested based on the existing provisions by taking the D/t ratios of the columns into account. This suggested design model is validated by using the existing experimental results and is found to give excellent results. The important factors that affect the strength and behaviour of the octagonal CFST short columns filled with HSCs are additionally discussed in detail, with new conclusions added to literature for the first time.

A New Compact Octagonal Shape Perfect Metamaterial Absorber for Microwave Applications

A new compact octagonal shape perfect metamaterial absorber (PMA) design, numerical simulation, fabrication, and investigational verification of unit cell that is based on a simple structure are presented in this paper. The suggested structure comprised of three layers, in which interact to produce the plasmonic resonances. The finite-integration technique (FIT) based Computer Simulation Technology (CST) microwave electromagnetic simulator was utilized to examine the design parameters and conduct absorption analysis. The design structure exhibited peak absorption values as 99.64% and 99.95% at frequencies 8.08 GHz and 11.41 GHz, respectively. The absorption characteristics were analysed using the polarization angle of the structure, layer thickness, PMA with resistive load, and number of rings. An N5227A vector network analyser was used for the measurement. The measured results of the fabricated prototype were in good agreement with the simulation results. The suggested perfect absorber structure enables innumerable application aimed at X-band for applications like, defence, security, and stealth technology.

Characterization and formation mechanism of pits on diamond {100} face etched by molten potassium nitrite

The morphology of diamond surface etched by molten potassium nitrate was investigated and the formantion mechanism of etched pits was disscussed. The inverted pyramid and square-shaped pits were formed on the {111} face and {100} face of diamond particles, respectively. The size and depth of etching pits on {100} face were apparently smaller than that of {111} face, which suggests {100} face has higher stability due to the role of oxygen functional groups absorb on the structure. At a low etching temperature (600°C), square-shaped pits were firstly formed on {100} face and then gradually changed into octagon shape with the increasing of etching time. The change of shape can be attributed to the configuration of atomic on {100} face of diamond and the change of oxygen partial in molten salt during the etching process. When etch temperature up to 700°C, the edges direction of the preferentially formed square shape pit became an angle of 45°with the edges of later formed square shape pit which indicated that partial oxygen pressure can effect stability of diamond surface and etching direction.

Crashworthiness investigation of bitubal columns reinforced with several inside ribs under axial and oblique impact loads

This paper deals with the crashworthiness capability of newly designed bitubal columns with different polygonal cross-sections (i.e. triangular, square, hexagonal, octagonal, decagonal and circular) reinforced with several inside ribs. A large number of finite element analyses were performed on these columns under axial and oblique impact loads using LS-DYNA to find the crashworthiness indicators. These columns were studied with five different size ratios (the ratios of the perimeter a of the inner tube to the perimeter b of the outer tube), namely a/ b = 0, 0.25, 0.5, 0.75 and 1. A decision-making method, which in this case is the technique for ordering preferences by similarity to the ideal solution, was then employed to select the better columns which possessed a higher energy absorption and a lower peak force. The bitubal columns with size ratios a/ b of 0.5, 0.25 and 0.75 were generally found to be the best cases. Furthermore, the multi-cell columns with the decagonal and octagonal cross-sectional shapes were selected as the best energy absorbers.

Octagonal Wetting Interface Evolution of Evaporating Saline Droplets on a Micropyramid Patterned Surface.

Textured surfaces have been extensively employed to investigate the dynamics, wetting phenomena, and shape of liquid droplets. Droplet shape can be controlled via the manipulation of topographic or chemical heterogeneity of a solid surface by anchoring the three-phase line at specific sites. In this study, we demonstrate that droplet shape on a topographically patterned surface can be modified by varying the concentration of salt potassium chloride (KCl) in the droplet solution. It is found that at the beginning of evaporation the octagonal shape of the solid-liquid interface is changed to a rectangle with corners cut upon increasing the salt concentration. Such a variation in the solid-liquid interface versus the salt concentration is explained by the analysis of free energy difference. It indicates that the increases in solid-liquid and liquid-vapor surface tensions by raising the salt concentration result in a favored extension of the three-phase line intersecting the micropyramid bottom sides than the counterpart intersecting the micropyramid diagonal edges. The saline droplets experience a pinning stage at first and a depinning one afterward. The onset of depinning is delayed, and at which the instantaneous contact angle is larger upon raising the salt concentration. The three-phase line which intersects the micropyramid diagonal edges recedes ahead of the one along the micropyramid bottom sides, making the octagonal wetting interface evolve toward a circle. A close view at the droplet edge indicates that the three-phase line repeats "slow slip-rapid slip" across row by row of micropyramids during the depinning stage.

Biosynthesis of gold nanoparticles by two bacterial and fungal strains, Bacillus cereus and Fusarium oxysporum, and assessment and comparison of their nanotoxicity in vitro by direct and indirect assays

Background: Although nanoparticles (NPs) have many advantages, it has been proved that they may be absorbed by and have toxic effects on the human body. Recent research has tried to evaluate and compare the nanotoxicity of gold nanoparticles (AuNPs) produced by two types of microorganisms in vitro by two different methods. AuNPs were produced by Bacillus cereus and Fusarium oxysporum , and their production was confirmed by visible spectral, transmission electron microscope, and X-ray diffraction (XRD) analyses. The human fibroblast cell line CIRC-HLF was treated with AuNPs, and the induced nanotoxicity was measured using direct microscopic and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. Results: The results showed that the produced AuNPs had a maximum absorbance peak around 510–530 nanometer (nm), with spherical, hexagonal, and octagonal shapes and average sizes around 20–50 nm. The XRD results confirmed the presence of GNPs in the microbial culture supernatants. An MTT assay showed that GNPs had dose-dependent toxic effects, and microscopic analysis showed that GNPs induced cell abnormalities in doses lower than the determined half-maximal inhibitory concentrations (IC50s). Conclusions: In conclusion, the biologically produced AuNPs had toxic effects in the cell culture, and direct techniques such as microscopic evaluation instead of indirect methods such as MTT assay were more useful for assessing the nanotoxicity of the biologically produced AuNPs. Thus, the use of only MTT assay for nanotoxicity evaluation of AuNPs is not desirable. Normal 0 false false false ES-CL X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:Tabla normal; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin-top:0cm; mso-para-margin-right:0cm; mso-para-margin-bottom:8.0pt; mso-para-margin-left:0cm; line-height:107%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:Calibri,sans-serif; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:Times New Roman; mso-bidi-theme-font:minor-bidi; mso-ansi-language:ES-CL;}

A Computational Simulation Study of Fluid Mechanics of Low-Speed Wind Tunnel Contractions

In this work, the fluid mechanics performance of four different contraction wall shapes has been studied and compared side-by-side by computational simulation, and the effect of contraction cross-sectional shape on the flow uniformity at the contraction exit has been included as well. A different contraction wall shape could result in up to an extra 4% pressure drop of a closed-loop wind tunnel, and the contraction wall shape has a stronger influence on the pressure loss than the contraction cross-sectional shape. The first and the second derivatives from different wall shape equations could provide a hint for qualitatively comparing the flow uniformity at the contraction exits. A wind tunnel contraction with an octagonal shape provides not only better fluid mechanics performance than that with a circular or a square cross-sectional shape, but also lower manufacturing costs. Moreover, a smaller blockage ratio within the test section can be achieved by employing an octagonal cross-sectional shape instead of a circular cross-sectional shape under the same hydraulic diameter circumstance. A wind tunnel contraction with an octagonal cross-sectional shape is recommended to be a design candidate.

Hexagonal Hollow Tube Based Energy Absorbing Crash Buffers for Roadside Fixed Objects

The purpose of this study was to investigate the deformation of the energy absorbing hexagonal hollow tubes in a lateral compression. The aim is to design cost effective and high energy-absorbing buffer systems, which are capable of controlling out-of-control vehicles in high-speed zones. A nonlinear quasi-static finite element analysis was applied to determine the deformation and energy absorption capacity. The main parameters in the design were diameter and wall thickness of the tubes. Experimental test simulating the lateral compressive loading on a single tube was performed. Results show that as the diameter and the thickness increase, the deformation strength increases. Hexagonal tube with diameter of 219 mm and thickness of 4 mm is shown to have the highest energy absorption capability. Compared to existing cylindrical and octagonal shapes, the hexagonal tubes show the highest energy absorption capacity. Hexagonal tubes therefore can be regarded as a potential candidate for buffer designs in high speed zones. In addition, they would be compact, cost effective and facilitate ease of installation.

Octagonal CMOS Image Sensor for Endoscopic Applications

An octagonal shaped CMOS image sensor (CIS) has been developed for endoscopic applications. The octagonal shape of the outlined die is also applied to the pixel matrix which has suppressed corners, resulting in an octagonal pixel matrix of 422'640 effective pixels. The sensor die fits on a circumference of 3.2 mm diameter being this the best die cut ratio between the cut corners and the pixel placement. The missing pixels on the corners are internally compensated by the readout electronics to maintain a rectangular image output format of 680x680 pixels. This paper presents the solutions found to overcome the layout challenges of fitting both row and column logic on the same side of the diagonally cut corners. Furthermore, the sensor features an area efficient column parallel ADC converter, having on the column readout side, only 402 μm overhead total space between the utmost pixel row until the edge of the silicon die. This space is used to place CDS, ADC, column addressing, readout, additional electronics and power routing. The sensor also has a fully autonomous operation, requiring only an external clock supply to drive the internal state machine. The interface requires just 6 connections: 2 for power supply, 2 for bidirectional data and 2 for main clock supply. The frame rate and the exposure are configurable by register. The maximum frame rate is 50 frames per second (FPS) and data is delivered over LVDS serial data link. The integration time can be configured from 147 μs to 20.1 ms. The power supply is 3.3 V with internal Power-On-Reset (POR) and has a power consumption of 91 mW manufactured in 180 nm CIS process.

Analysing the Impact of Horizontal Shading Device – A Case of Octagonal Shape Building

Analysing the Impact of Horizontal Shading Device – A Case of Octagonal Shape Building

A Wideband Base Station Antenna Element With Stable Radiation Pattern and Reduced Beam Squint

This paper presents the design procedure, optimization strategy, theoretical analysis, and experimental results of a wideband dual-polarized base station antenna element with superior performance. The proposed antenna element consists of four electric folded dipoles arranged in an octagon shape that are excited simultaneously for each polarization. It provides ±45° slant-polarized radiation that meets all the requirements for base station antenna elements, including stable radiation patterns, low cross polarization level, high port-to-port isolation, and excellent matching across the wide band. The problem of beam squint for beam-tilted arrays is discussed and it is found that the geometry of this element serves to reduce beam squint. Experimental results show that this element has a wide bandwidth of 46.4% from 1.69 to 2.71 GHz with ≥15-dB return loss and 9.8 ± 0.9-dBi gain. Across this wide band, the variations of the half-power-beamwidths of the two polarizations are all within 66.5° ± 5.5°, the port-to-port isolation is >28 dB, the cross-polarization discrimination is >25 dB, and most importantly, the beam squint is <4° with a maximum 10° down-tilt.

Design of a Microstrip Series Power Divider for Sequentially Rotated Nonuniform Antenna Array

This paper deals with the design of a microstrip series power divider for circularly polarized sequential rotational antenna array. The theoretical description of the design is firstly proposed, comprising the cases of nonuniform weighted antenna arrays. A more flexible open octagon shape instead of the classical open ring is suggested, highlighting benefits in the case of nonuniform power distribution. A design example of an ultra-high frequency (UHF) band 4×4 sequentially rotated Tschebischeff antenna array finally demonstrates the effectiveness of the proposed implementation.