Hexagonal Cross-section Research Articles

A model for a set of porous fins on a long rotating cylinder considering thermal radiation and natural convection

This article proposes a method to estimate the heat transfer and temperature distribution from a porous fin placed on a constantly rotating long cylinder with a hexagonal cross section. Moreover, both radiation and natural convection are considered, as well as radiation interchange between the cylinder and the fin and among the porous fins themselves, giving rise to an Integro-Differential problem. Time-averaged thermal properties are employed since the proposed problem is periodic. The numerical simulation is validated by comparing three different numerical methods: Finite Difference Method (FDM), Finite Volumes Method (FVM), and Spectral Collocation Method with Chebyshev interpolation polynomials (CGL). The three methods demonstrated good agreement among themselves. They provided results according to the existing literature concerning heat transfer and temperature distribution on porous fins, such as showing that convection, as the convective parameter grows from 0 to 10, can quickly become the dominant mode of heat transfer instead of the radiation parameter, which ranged from 0 to 50. The impact on the temperature at the tip ranged from less than 4% to 18.9%, depending on the changes made to thermal and physical parameters under similar conditions. The dimensionless temperature stayed in the stipulated variation from 0 to 1.

Rebuildable Silver Nanoparticles Employed as Seeds for Synthesis of Pure Silver Nanopillars with Hexagonal Cross-Sections under Room Temperature

Silver nanopillars with strong plasmonic effects are used for localized electromagnetic field enhancement and regulation and have wide potential applications in sensing, bioimaging, and surface-enhanced spectroscopy. Normally, the controlled synthesis of silver nanopillars is mainly achieved using heterometallic nanoparticles, including Au nanobipyramids and Pd decahedra, as seeds for inducing nanostructure growth. However, the seed materials are usually doped in silver nanopillar products. Herein, the synthesis of pure silver nanopillars with hexagonal cross-sections is achieved by employing rebuildable silver nanoparticles as seeds. An environmentally friendly, stable, and reproducible synthetic route for obtaining silver nanopillars is proposed using sodium dodecyl sulfate as the surface stabilizer. Furthermore, the seed particles induce the formation of regular structures at different temperatures, and, specifically, room temperature is beneficial for the growth of nanopillars. The availability of silver nanoparticle seeds using sodium alginate as a carrier at different temperatures was verified. A reproducible method was developed to synthesize pure silver nanopillars from silver nanoparticles at room temperature, which can provide a strategy for designing plasmonic nanostructures for chemical and biological applications.

Selective Area Growth of GaAs Nanowires and Microplatelet Arrays on Silicon by Hydride Vapor-Phase Epitaxy

In this work, we demonstrate the growth of vertically oriented GaAs nanowires (NWs) and microplatelets directly on a patterned SiO2/Si(111) substrate by hydride vapor-phase epitaxy (HVPE). Direct condensation of GaAs on Si was achieved through a critical surface preparation under an As-controlled atmosphere. GaAs NWs were grown along the ⟨111⟩B direction with a hexagonal cross section when the hole opening diameter (D) in the SiO2 mask was below 350 nm. Larger apertures (D ≥ 500 nm) resulted in uniform microplatelets. This study highlights the capability of HVPE for selective area growth of GaAs directly on Si and thus the potential of HVPE as a generic heterointegration process for III–V semiconductors on silicon.

Ultraviolet Exciton-Polariton Light-Emitting Diode in a ZnO Microwire Homojunction.

Low-dimensional ZnO, possessing well-defined side facets and optical gain properties, has emerged as a promising material to develop ultraviolet coherent light sources. However, the realization of electrically driven ZnO homojunction luminescence and laser devices is still a challenge due to the absence of a reliable p-type ZnO. Herein, the sample of p-type ZnO microwires doped by Sb (ZnO:Sb MWs) was synthesized individually. Subsequently, the p-type conductivity was examined using a single-MW field-effect transistor. Upon optical pumping, a ZnO:Sb MW showing a regular hexagonal cross-section and smooth sidewall facets can feature as an optical microcavity, which is evidenced by the achievement of whispering-gallery-mode lasing. By combining an n-type ZnO layer, a single ZnO:Sb MW homojunction light-emitting diode (LED), which exhibited a typical ultraviolet emission at a wavelength of 379.0 nm and a line-width of approximately 23.5 nm, was constructed. We further illustrated that strong exciton-photon coupling can occur in the as-constructed p-ZnO:Sb MW/n-ZnO homojunction LED by researching spatially resolved electroluminescence spectra, contributing to the exciton-polariton effect. Particularly, varying the cross-sectional dimensions of ZnO:Sb wires can further modulate the exciton-photon coupling strengths. We anticipate that the results can provide an effective exemplification to realize reliable p-type ZnO and tremendously promote the development of low-dimensional ZnO homojunction optoelectronic devices.

Development of Bi-hexagonal hybrid crash box subjected to axial loading for enhancement of crashworthiness

Crash box design had been developed to increase crashwortiness performance. The crash box cross section is one important parameter to increase the energy absorption as crashwortiness performance. In the previous study, hexagonal cross section provide the higher energy absorption than other cross section. One of strategy to increase cross section is using two cross section put together in one component of crash box design. Bi-tubular crash box shows higher energy absorption with easy manufacture opportunity. In other study, hybrid crash box is investigated to reduce crash box mass. In this study, development of bi-hexagonal hybrid crash box subjected to axial loading to enhance crashworthiness were investigated. Analysis of crash box design is developed by using computer simulation with ANSYS Workbench 19.2. The crash box materials used are Aluminum Alloy and carbon-epoxy woven. The material modeling in the crash box is assumed as deformable body while the impactor is a rigid body. The axial loading is modelled by setting impactor impact the crash box with a speed of 7.67 m/s. Fixed support is set on the bottom of crash box. Nine of frontal test models were simulated for the bi-hexagonal hybrid crash box with different layups orientation angle and composite hexagonal tube diameter. Energy absorption and deformation patterns were observed. The results indicated that the highest energy absorption and specific energy absorption is occured on the A60 model with layups orientation angle of [0/60/0/60] and composite hexagonal tube diameter of 41 mm are 3693.8 J and 19.121 kJ/kg. The deformation pattern in the aluminum part is diamond mode, while in the composite part, the deformation pattern produce transverse shearing, lamina bending, brittle fracturing and local buckling mode

A mathematical approach to calculate the absolute total detection efficiency of a 4[formula omitted] NaI(Tl) sum spin spectrometer

The absolute total detection efficiency of a detector for gamma rays intensely depends on the solid angle subtended by the detector’s front surface at the gamma source. In the present work, we have developed, for the first time, a new mathematical formalism to calculate the solid angle subtended by an n-sided polygonal detector at the point source when the source is placed along the axis of the detector. The method is based on the subtraction of the solid angle in which gamma rays do not enter the detector from that of the circular cross-section. The solid angle formula, so derived, has been applied to calculate the absolute total detection efficiency of NaI(Tl) scintillation detectors of pentagonal and hexagonal cross-sections for monoenergetic gamma rays. These efficiencies are then used to calculate the absolute total detection efficiency of 4π sum-spin spectrometer for gamma rays up to energy 20 MeV. The spectrometer is an array of 32 conical NaI(Tl) detectors of pentagonal and hexagonal cross-sections. To validate the formalism developed, the theoretically calculated efficiencies are compared with those obtained from realistic GEANT4 simulations and experimental measurements considering 137Cs and 60Co gamma sources. The reasonably good agreement clearly validates the developed formalism.

Heat Transfer and Pressure Loss of Additively Manufactured Internal Cooling Channels With Various Shapes

AbstractAdditive manufacturing (AM) provides the ability to fabricate highly customized internal cooling passages that are relevant to gas turbine components. This experimental study examines the pressure loss and heat transfer performance of a range of fundamental channel shapes that were produced using direct metal laser sintering. Circular, hexagonal, pentagonal, elliptical, diamond, square, rectangular, trapezoidal, and triangular channel cross sections were investigated. To maintain the same convective surface area between shapes, the wetted perimeters of the channel cross sections were kept constant. Parallel computational fluid dynamic simulations were performed to understand the relationships in cooling performance between several channel shapes. Several characteristic length scales were evaluated to scale the pressure loss and heat transfer measurements. Among the channel shapes investigated, the diamond channel showed the lowest Nusselt number and friction factor. The pentagon exhibited a similar Nusselt number as the circular channel despite having a lower friction factor. There was no difference in scaling the friction factor or Nusselt number results of the different channel shapes between using the square root of cross-sectional area compared to hydraulic diameter as the characteristic length scale

Re-appearance of precipitated aragonite crystal fans as evidence for expansion of oceanic dissolved inorganic carbon reservoir in the aftermath of the Lomagundi-Jatuli Event

The initial accumulation of atmospheric oxygen is marked by the unprecedented positive δ13Ccarb excursions of the Lomagundi-Jatuli Event (LJE) and records an interval of abnormal O2 production through elevated rates of organic carbon burial. Emerging evidence suggests that the post-LJE atmosphere-ocean system might have suffered a significant deoxygenation. These dynamic perturbations in the oceanic redox state and biogeochemical cycles would have led to fundamental changes in carbonate precipitation dynamics. Here, we report the discovery of centimeter-sized crystal fans in the post-LJE Huaiyincun Formation, Hutuo Supergroup in the North China Craton. The hexagonal cross-sections and square terminations suggest that these fan-like dolomitic structures were originally aragonite crystal fans (ACF). Variations of stromatolite morphology and frequent occurrences of storm-related deposits in the Huaiyincun Formation point to repeated cycles of sea level changes. The bedding-parallel distribution of the ACF and the homogeneous δ13C values of the ACF-bearing dolostones are consistent with a primary depositional origin for the ACF. An updated compilation of published records of ACF throughout geological history highlights a clear absence of ACF from the initiation of the Paleoproterozoic Great Oxidation Event until the end of the LJE, and a global reappearance of ACF in the post-LJE late Paleoproterozoic. We propose that the reappearance of ACF is in agreement with the expansion of the oceanic dissolved inorganic carbon reservoir. At the same time, consumption of dissolved oxygen during the oxidation of organic matter might have been stimulated by ferruginous deep seawater, facilitating the formation of Huiayincun ACF.

Numerical Study About Nanofluids of Spherical and Tube-Shaped TiO2 Nanomaterials on the Thermal Performance and Entropy Generation of Different Cross-Section Microchannel Heat Sinks

We numerically evaluated the thermal performance of microchannel heat sinks, considering rectangular, hexagonal, and circular cross-sections. Moreover, as a passive heat transfer augmentation technique, dimples were added to improve the rectangular microchannel heat sinks. These simulations use nanofluids based on TiO2 nanoparticles or nanotubes dispersed in bidistilled water as working fluids. The mathematical model considered variable thermophysical properties of the nanofluids; for this purpose, polynomial fittings correlate the dependence of the thermophysical properties on the temperature. We considered a heat flux of q″ = 50 W/cm2 at the microchannel’s lower surface as a boundary condition along with laminar flow conditions. The numerical simulations allowed the Nusselt numbers and entropy generation calculation, which were the basis for the thermal performance calculation. Regarding the effect of TiO2 nanoparticles shape, spherical TiO2 nanoparticles based nanofluids using rectangular microchannels improve the Nusselt number. Moreover, the frictional entropy decreases with nanofluids based on TiO2 nanotubes, but the thermal entropy decreases with nanofluids based on TiO2 nanotubes. Incorporating dimples in the rectangular microchannel enhances the Nusselt numbers and lowers the entropy generation. Considering the Reynolds number range and from the perspective of Nusselt number and entropy generation, we concluded that the microchannels must be operated at a high Reynolds number to improve the microchannel heat sinks thermal performance.

Numerical investigation of crash behavior of vehicle side door beams under high-speed pole side impacts

In side vehicle accidents, there is a very short distance between the impactor and the passenger. In such accidents, car manufacturers place impact energy absorber beams inside the door so that the passengers do not suffer from loss of life or major damage. In this study, the crashworthiness performances of impact energy absorber beams were investigated. Comparisons were made by changing the beams’ angles, materials, thickness, and cross-sections. Among the materials used (Aluminum 6061-T6 and A36 steel), Aluminum 6061T6 material stood out with its high Specific Energy Absorption (SEA) value, low reaction force, and low permanent deformation performance. The best Velocity Absorption Time (VAT) value was obtained in the combination where the angle between the two beams defined by A36 steel was 25°. It has been stated that the hexagonal cross-section door beam used is superior to the circular beam and is open to improvement.

Dynamic Composite Materials Characterisation with Hopkinson Bars: Design and Development of New Dynamic Compression Systems

The split Hopkinson pressure bars (SHPB) system is the most commonly employed machine to study the dynamic characteristics of different materials under high strain rates. In this research, a numerical investigation is carried out to study different bar shapes such as square, hexagonal, and triangular cross-sections and to compare them with the standard cylindrical bars. The 3D finite element model developed for circular cross-sectional shapes was first validated with the experimental results and then compared with the other proposed shapes. In most scientific research, cylindrical cross-section bars with a square cross-section specimen are traditionally used as they have several advantages, such as in situ imaging of the side surfaces of the specimen during stress wave propagation. Moreover, the flat surfaces of the proposed shapes counter the problem of debonding strain gauges, especially at high impact pressures. Comparison of the results showed an excellent confirmation of the sample dynamic behaviour and different geometric shapes of the bar geometries, which validates the choice of the appropriate system.

Luminescent hexagonal microtubes prepared through water-induced self-assembly of a polymorphic organoboron compound: formation mechanism and waveguide behaviour.

Tetra-coordinated organoboron (TCOB) compounds are promising candidates for developing high-performance optical devices due to their excellent optoelectronic performance. Fabricating TCOB-based nanomaterials of controlled and defined morphology through rapid and easy-to-execute protocols can significantly accelerate their practical utility in the aforesaid applications. Herein, we report water-induced self-assembly (WISA) to convert a polymorphic TCOB complex (HNBI-B, derived from a 2-(2'-hydroxy-naphthyl)-benzimidazole precursor) into two unique nanomorphologies viz. nanodiscoids (NDs) and fluorescent microtubes with hexagonal cross-sections (HMTs). Detailed electron microscopic investigations revealed that oriented assembly and fusion of the initially formed NDs yield the blue emissive HMTs (SSQY = 26.7%) that exhibited highly promising photophysical behaviour. For example, the HMTs outperformed all the crystal polymorphs of HNBI-B obtained from CHCl3, EtOAc and MeOH in emissivity and also exhibited superior waveguide behaviour, with a much lower optical loss coefficient α' = 1.692 dB mm-1 compared to the rod-shaped microcrystals of HNBI-B obtained from MeOH (α' = 1.853 dB mm-1). Thus, this work reports rapid access to high performance optical nanomaterials through WISA, opening new avenues for creating useful nanomaterial morphologies with superior optical performance.

Temperature-controlled and shape-dependent ZnO/TiO2 heterojunction for photocathodic protection of nickel-coated magnesium alloys

Using nanomaterials to design and prepare photoanodes could enhance photoelectrochemical and photocathodic protection (PCP) performances. However, little is known about how the detailed nanostructure correlates with performance. Here, we report a morphologically tunable nano-ZnO semiconductor grown on a TiO2 nanotube array (ZnO/TiO2) for the PCP of nickel-coated magnesium alloy by manipulating the hydrothermal reaction temperature. While irregular ZnO nanosheet clusters were observed at relatively low and high temperatures, a smooth array of nanorods with a hexagonal cross-section structure was obtained at a moderate reaction temperature. Such nanostructure exhibited the optimum photoelectrochemical and PCP capacities, showing the highest photogenerated current density, which is 4.2 times higher than the single-component TiO2 photoanode. The apparent enhancement in the performance of the ZnO/TiO2 composite was related to the morphological regulation of the nano-ZnO and the formation of staggered gap heterojunction between ZnO and TiO2. This assessment is supported by the results from several characterizations, including a high-resolution transmission electron microscope, Mott-Schottky, and valence band X-ray photoelectron spectroscopy. These findings give a new insight into the relationship between the structure and photoelectrochemical performances of nano-ZnO, which has significant implications for designing and preparing high-efficiency photoanode in photocatalysis and corrosion protection.

Thick-Panel Origami Tubes With Hexagonal Cross-Sections

Abstract Rigidly foldable origami tubes can be kinematically regarded as assemblies of spherical linkages. They have exhibited excellent properties for deployable structures. Yet, for the engineering applications, the corresponding thick-panel forms have to be designed. In this paper, the spherical 4R linkages in tubes with hexagonal cross-sections are partially replaced by spatial linkages, leading to a method to construct the thick-panel tubes, which can reproduce kinematic motions equivalent to those realized using zero-thickness origami. Based on the D–H matrix method, the rotational symmetric and symmetric tubes are introduced, together with their four types of vertexes, where the specific spherical 4R linkages are replaced by Bennett and Bricard linkages to obtain the thick-panel foldable tubes. The approach can be applied to multilayered tubes with a straight or curved profile, whose manufacture can be simplified by removing extra links. The results can be readily utilized to the design of deployable tubular structures whose thickness cannot be disregarded.

Fabrication of ZnO nanorods decorated Au nanoparticles by hydrothermal and magnetron sputter techniques

In this study, ZnO nanorods decorated with gold (Au) nanoparticles with the desired size parameters were fabricated using a simple, low-cost, and highly efficient method. The ZnO nanorod structure was fabricated using a hydrothermal method on a ZnO seed layer with hydrothermal solution concentrations varying from 20 mM to 90 mM. Au nanoparticles were coated on the ZnO nanorod structure by magnetron sputtering with a sputtering time from the 40s to 70 s. The characteristics of the fabricated samples were investigated through SEM images and optical absorption spectroscopy. The results show that the fabricated ZnO nanorods are relatively uniform, with a cylindrical shape and hexagonal cross-section when the solution concentration is less than 70 mM. Au nanoparticles were attached to the surface of the ZnO nanorods with average sizes of 30-50 nm. The optical absorption spectroscopy results showed that the ZnO nanorods’ absorption edge appeared at a wavelength of approximately 395 nm. In addition, the exciton absorption peak of Au nanoparticles was between 550 nm and 600 nm and there was a shift towards shorter wavelengths as the size of the Au nanoparticle decreased. This result opens up potential applications of this material such as increasing photocatalytic efficiency and its, use in photonic devices, etc.

Impact of dielectric substrates on chipless RFID tag performance

AbstractA five-slot hexagonal shape chipless RFID tag is designed, simulated, and manufactured on FR4 substrate. The designed tag's copper geometry was replicated on a wide range of dielectric substrate to quantify the impact on resonance quality factor (RQF) and resonating frequencies. The tag's performance was assessed in three configurations. First, a hexagonal shape tag's radar cross section (RCS) was studied over different dielectric substrates. The various dielectric substrate effects were investigated over the maximum read range, resonant frequencies and RQF. In the second evaluation, the physical geometry of the tag was adjusted to achieve the spectral signatures in 2–7 GHz frequency band with high RQF. In step three, the optimized tag geometry was manufactured on FR4, Roger Duroid 5880, and polyethylene naphthalate (PEN) substrates. Denford milling machine for PCB engraving and inkjet printing for silver nanoparticles deposition were used for tags manufacturing. During tag manufacturing, copper and silver were used as conducting materials for RCS backscattering. The tag RCS response was measured by vector network analyzer with bi-static antenna setup. The analysis of different dielectric substrate provides a pathway of designing a novel substrate by using various nanomaterials.

Surface Morphology and Structure in ZnO films doped with Ga and In impurities

The ZnO:Ga:In nanocrystal (NC) films co-doped with Ga and In donor type impurities have been investigated The films were produced by spray pyrolysis ultrasonic on Si substrates kept at 400°C. The group of samples was grown with permanent In content of 1at% in the films, and with various Ga contents of 0.5 at% up to 2.5 at% Ga. All samples for better crystallization have been further annealed in a nitrogen flow (5 L/min) at 400°C during 4h.The non-monotonous varying the surface morphology has been detected in ZnO:Ga:In NC films. With a small Ga content (≤1.0 at%) and a high Ga content (≥2.0 at%), the grains have the form of small sheets distributed randomly on the surface. The sheet like shape changes to nanorod with hexagonal cross sections of the size 50-100 nm in films with 1.5 at% Ga. With all Ga concentrations the ZnO films studied demonstrated the crystal structures of wurtzite. However, the XRD peak positions and ZnO lattice parameters change non monotonically versus Ga contents. The factors that favor the non-monotonic change of the parameters of the ZnO crystal lattice have been analysed. The Ga/In doping concentrations necessary to obtain ZnO films with low roughness and flat surface morphology have been estimated.

Flexural Behavior of Concrete-Filled Double-Skin Hexagonal Tubular Beams Using Finite Element Analysis

The Concete-Filled Double Steel Tube (CFDST) members usually prepared from Concrete-Filled Steel Tube (CFST) member with additional internal steel tube, in order to increase strength and reduce the selfweight of the composite member. The conventional square cross-sections are usually used for the CFDST beams. However, these sectionsthis square section are usually facing an outward buckling failure at the compression zone stress that usually occurred at the top flange of the CFDST beams under high bending loads. Additionally, using cross-section shapes with hexagonal and/or octagonal and/or decagonal could be to reduce the flatness width of the CFDST beam’s top flangem since they have smaller flatness width of their flanges than the square/rectangular tube’s cross section. Therefore, the aim of this research is to numerically study the flexural behavior of CFDST beam with hexagonal tubular cross-section under pure bending static loads by using finite element (FE) software named ABAQUS. First, the FE model was devloped and verified with the rated experimental tested results, then devloped and analysed additional models of hexagonal CFDST beams to investigate further parameters that not yet been investiated. Generally a total of 19 hexagonal CFDST models were analysed for this project to investigate the influnce of varied tube’s thickness (t), steel yielding strength (fy), concrete strength (fcu), inner to outer tube’s dimensions ratio (Di/Do), and different inner tube’s cross-sections shape (hexagon, square and circle). The result of the paper showed that by using double steel tube for the beam, the failure due to outward buckling can be reduced significantly. The ultimate bending capacity of the hexagon CFDST models were increased with increases of their steel/concrete strength, tube’s thickness and Di/Do ratio. For example, increasing the tube thickness from 1.5 mm 2.5 mm achieved an improvement in Mu values of about 41%. Meanwhile less improvement percentages was recorded when only the concrete strength increased. Furthermore, there are no much improvements have been recorded in the model’s bending capacity when used square or circle shape of inner tube’s cross-section the than the hexagonal shape. The energy absorption of the hexagon CFDST model have been improved according to the improvement of their loading strength capacities

Magnetic and Electrical Properties of Ni3Te2 Single Crystals Grown by Physical Vapor Transport Technique

The transition metal tellurides (TMTs) have attracted much attention due to their rich properties in both fundamental research and applications. Among all the TMTs, the study of Ni3Te2 large single crystals is rare. By using the physical vapor transport technique, Zhe Li, Jun-Yi Ge, and co-workers have successfully grown Ni3Te2 single crystals with unique hexagonal cross section and a tubular shape (see article number 2200037). The crystal structure, the electrical transport and magnetic properties, and band structures are investigated in detail. It is revealed that Ni3Te2 exhibits a metallic behavior with the coexistence of ferromagnetism and antiferromagnetism.

A simulation study of polarization characteristics of ultrathin CsPbBr3 nanowires with different cross-section shapes and sizes

The polarization characteristics of ultrathin CsPbBr3 nanowires are investigated. Especially, for the height of cross-section of nanowires between 2 nm and 25 nm, the normalized intensity and polarization ratio ρ of CsPbBr3 nanowires with triangular, square and hexagonal cross-section shapes are compared. The results show that, along with the increase of the height of cross-section, the polarization ratios of these three nanowires decrease until T = 15 nm, and increase afterwards. Also, along with the increase of the cross-section area up to 100 nm2, the polarization ratios of these three nanowires increase too. In general, for the same height or area, the polarization ratio ρ of these nanowires follows ρ hexagon > ρ square > ρ triangle. Therefore, the nanowire with the hexagonal cross-section should be chosen, where for a cross-section height of 2 nm and a length-height ratio of 20:1, the maximal polarization ratio is 0.951 at the longitudinal center of the NW. Further, for the hexagonal NW with a cross-section height of 10 nm, the hexagonal NW with a length-height ratio of 45:1 exhibits the maximal polarization ratio at the longitudinal center of the NW. These simulation results predict the feasible size and shape of CsPbBr3 nanowire devices with high polarization ratios.