Hexagonal Geometry Research Articles

Photocatalytic activity of ZnO nanoparticles and the role of the synthesis method on their physical and chemical properties

In the present study, we report on the effect of the synthesis method in the photoactivity of ZnO-NPs. The nanoparticles were prepared by precipitation and sol-gel procedures using zinc nitrate and zinc (II) acetylacetonate as ZnO precursors, respectively. The obtained samples were named as ZnO-PP (precipitation method) and ZnO-SG (sol-gel method). The powders were calcined at 500 °C and further characterized by Fourier Transform Infrared spectroscopy, X-ray Powder Diffraction, N2 adsorption, thermal analysis, Diffuse Reflectance UV-Vis spectroscopy, and Electron Microscopy. Both methods of synthesis lead to formation of pure ZnO with hexagonal-wurtzite crystalline structures with average crystallite sizes ∼30 nm. The specific surface area was affected by the synthesis method, since SBET values were 5 m2/g and 13 m2/g for sol-gel and precipitation method, respectively. The electron microscopy revealed significant changes in morphology for the obtained nanoparticles, as sol-gel directed the hexagonal rod-like geometries (∼50 nm in diameter) while quasi-spherical nanoparticles (∼100 nm in diameter) were formed using precipitation method. Photocatalytic activity was estimated by degrading phenol (50 ppm) as probe molecule under UVA irradiation (λ = 356 nm), the results demonstrated that ZnO-PP reached 100 % of degradation after 120 min and 90 % of the pollutant was mineralized, whereas for ZnO-SG the results were 80 % and 48 % respectively. Fluorescence test using terephthalic acid (TA) demonstrated higher formation of OH• radicals for ZnO synthesized by precipitation method, which could explain the higher photodegradation and mineralization observed. These results support that even slight differences in physical and chemical properties of ZnO, have a significant impact on the photocatalytic performance of such nanoparticles.

Adaptive time-step control for modal methods to integrate the neutron diffusion equation

The solution of the time-dependent neutron diffusion equation can be approximated using quasi-static methods that factorise the neutronic flux as the product of a time dependent function times a shape function that depends both on space and time. A generalization of this technique is the updated modal method. This strategy assumes that the neutron flux can be decomposed into a sum of amplitudes multiplied by some shape functions. These functions, known as modes, come from the solution of the eigenvalue problems associated with the static neutron diffusion equation that are being updated along the transient. In previous works, the time step used to update the modes is set to a fixed value and this implies the need of using small time-steps to obtain accurate results and, consequently, a high computational cost. In this work, we propose the use of an adaptive control time-step that reduces automatically the time-step when the algorithm detects large errors and increases this value when it is not necessary to use small steps. Several strategies to compute the modes updating time step are proposed and their performance is tested for different transients in benchmark reactors with rectangular and hexagonal geometry.

Abstract 3815: Cellular oxidative stress and immunological effects of carbon-based nanomaterials towards lung carcinogenicity

Abstract Lung cancer accounts for most number of cancer related death, reporting over 26.5% of all cancer deaths in United States alone. Among the risk factors, along with smoking, occupational as well as environmental exposure of carcinogens is considered as major driver of lung cancer in most cases. In that context, high aspect ratio nanomaterials (HARNs) with low density, such as carbon nanotubes (CNTs), remain efficient air-borne particulate matters during every step of their life cycle, from production to usage to disposal. Consequently, inhalation and potentially carcinogenic nanomaterial exposure to pulmonary tissues are anticipated, which may considerably facilitate lung cancer occurrence and mortality. Apart from pulmonary interaction, nanomaterial exposure via skin or oral route may play a significant role in adverse human health effects, especially when the use of nanomaterials in food and cosmetic industries are growing exponentially. CNTs are made of flat sheets of sp2 hybridized carbon atoms layered in hexagonal geometry that are rolled into unified cylindrical structures. CNTs are subdivided into single-walled (SWCNT), double-walled (DWCNT), or multi-walled carbon nanotube (MWCNT) based on the number of carbon layers in nanotubes. Size of CNTs can range from one to several nanometers in diameter and up to several micrometers in length, exhibiting a fibrous-like length-to-width (aspect) ratio similar to asbestos fibers and potentially harbor asbestos-like pulmonary fibrosis and lung cancer risks associated with their long-term exposure. Considerable efforts has been made to study Nano-toxicity but how cellular toxicological and immunological responses are affected by nanomaterial exposure is largely unknown. The present study investigated the effects of different CNT exposure on cellular proliferation, uptake, oxidative stress, DNA damage, Stem cell-like properties along with activation of cellular innate immune responses of human lung epithelial cells and immune cells to determine the underlying cross-talks. Using a physiologically relevant long-term-low-dose exposure model, we found that both single-walled and multi-walled carbon nanotubes, induced particle-specific cellular proliferation, tumor sphere formation, reactive oxygen species (ROS) and super oxide (SO), DNA-strand breaks, mitochondrial depolarization and reduced apoptosis, indicating the genotoxicity and carcinogenic potential of CNTs. We also determined distinct immune activation signature in these cells upon CNTs exposure that closely resembles “immune mediated” carcinogenesis signature as reported in “Inflammatory Cancer (C3)” subtypes. Finally, through in silico analyses and validation we have determined potential CNT exposure induced immune effectors to devise better targeted therapeutic intervention against nanomaterial exposure induced carcinogenesis. Citation Format: Rajib Ghosh, Liying W. Rojanasakul, Yon Rojanasakul. Cellular oxidative stress and immunological effects of carbon-based nanomaterials towards lung carcinogenicity [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3815.

Using the Hexagonal Layout Style for MOSFETs to Boost the Device Matching in Ionizing Radiation Environments

This paper describes an experimental comparative study of the matching between conventional (rectangular gate shape) and Diamond (hexagonal gate geometry) n-channel Metal-Oxide-Semiconductor (MOS) Field Effect Transistors (MOSFETs), which were manufactured in an 130 nm Silicon-Germanium Bulk Complementary MOS (CMOS) technology and exposed to different X-rays Total Ionizing Doses (TIDs). The results indicate that the Diamond layout style with alpha () angle equal to 90˚ for MOSFETs is capable of boosting the device matching by at least 17% regarding the electrical pa-rameters studied (Threshold Voltage and Subthreshold Slope) as compared with the conventional MOSFET counterparts, considering that they present the same gate area, channel width, bias conditions and for the same TID. This is due to the Longitudinal Corner Effect (LCE). Parallel MOSFETs with Different Channel Length Effect (PAMDLE) and Deactivation of Parasitic MOSFETs in the Bird’s Beak Regions Effect (DEPAMBBRE) present in the structure of Diamond MOSFETs. Therefore, the Diamond layout style can be consid-ered an alternative hardness-by-design (HBD) layout strategy to boost the electrical performance and TID tolerance of MOSFETs enabling analog or radio-frequency CMOS inte-grated circuits (ICs) applications.

Numerical solution of strongly guided modes propagating in sapphire crystal fibers (α-Al2O3) for UV, VIS/IR wave-guiding

A numerical solution, using the general formulation of the transcendental equation and eigenmode values, is proposed to demonstrate number of strongly guided modes propagating in sapphire crystal fibers (SCF). The SCF is considered to have hexagonal geometry of a single crystal and multimode step-index profile. Several distinguished characteristics are naturally embedded in SCF compared to other ordinary optical fibers. The eigenmodes of the SCF are numerically determined and are a combination of transverse electric, transverse magnetic, and hybrid modes. The numerical solution for wave-guiding in ultra-violet (UV), visible infrared (VIS/IR) spectrum, is investigated by the number of modal propagation under strongly guided approximation. The cross-sectional energy distribution of fundamental mode (FM) and higher order modes (HoM) describe the variation of the effective mode index with respect to the change in the core radius. The proposed waveguide is of ~35micron radius, exhibit −0.077 dB/m confinement loss at 200 nm. The simulations in this study are performed by the COMSOL multi-physics® software.

Stabilization of Plutonium(V) Within a Crown Ether Inclusion Complex

Crystalline coordination complexes of actinides, especially in atypical oxidation states, are not only fundamentally important for expanding the notably limited knowledge on the bonding nature of a...

CFD simulation of turbulent flows over wire-wrapped nuclear reactor bundles using immersed boundary method

A preliminary study for lead-bismuth eutectic (LBE) turbulent flows over wire-wrapped nuclear reactor bundles is performed. The 19-pin hexagonal bundle geometry, representative of NACIE-UP facility and adopted in the MYRRHA reactor [1, 2], is considered. The presence of the helical wire wrap has a strong effect on flow patterns inside the bundle geometry, with induced secondary flows and enhanced mixing [3]. From a computational point of view, the wire-wrapped geometry model is much more complex to realize than the bare rod configuration and simplified models are often used [4, 5]. In order to overcome the difficulties of the model generation, an hybrid body fitted immersed boundary method is used. A computational grid that fits the presence of bundle pins is generated, as for the case of the bare rod configuration, allowing a better control of mesh resolution in the regions close to wall boundaries. The immersed boundary method is used to model the presence of the helical wire wrap so that its effect on fluid motion can be taken into account.

Monolithic CMOS sensors for sub-nanosecond timing

In the ATTRACT project FASTPIX we investigate monolithic pixel sensors with small collection electrodes in CMOS technologies for fast signal collection and precise timing in the sub-nanosecond range.Deep submicron CMOS technologies allow tiny, sub-femtofarad collection electrodes, and large signal-to-noise ratios, essential for very precise timing. However, complex in-pixel circuits require some area, and one of the key limitations for precise timing is the longer drift time of signal charge generated near the pixel borders. Laying out the collection electrodes on a hexagonal grid and reducing the pixel pitch minimize the maximum distance from the pixel border to the collection electrode. The electric field optimized with TCAD simulations pulls the signal charge away from the pixel border towards the collection electrode as fast as possible. This also reduces charge sharing and maximizes the seed pixel signal hence reducing time-walk effects. Here the hexagonal geometry also contributes by limiting charge sharing at the pixel corners to only three pixels instead of four. We reach pixel pitches down to about 8.7μm between collection electrodes in this 180 nm technology by placing only a minimum amount of circuitry in the pixel and the rest at the matrix periphery. Consuming several tens of micro-ampere per pixel from a 1.8 V supply offers a time jitter of only a few tens of picoseconds. This allows detailed characterization of the sensor timing performance in a prototype chip with several mini matrices of 64 pixels each with amplifier, comparator and digital readout and 4 additional pixels with analog buffers. The aim is to prove sensor concepts before moving to a much finer line width technology and fully integrate the readout within the pixel at lower power consumption.

XRD structural studies on cobalt doped zinc oxide nanoparticles synthesized by coprecipitation method: Williamson-Hall and size-strain plot approaches

Cobalt doped Zinc Oxide (Zn1-xCoxO) (x = 0.03) nanoparticles have been synthesized by chemical co-precipitation method at room temperature and characterized by X-ray diffraction (XRD) study. The XRD pattern indicates that Co doped ZnO NPs are with hexagonal wurtzite geometry and diffraction peaks get shifted to higher angles which is the characteristic influence of dopant Co that has an ionic radius smaller than the host cation. The true values of lattice constants have been calculated using Nelson–Riley Function. Crystallite size calculated using Scherrer formula has been compared with that estimated by uniform deformation (UDM), uniform stress deformation (USDM) and uniform deformation energy density (UDEDM) models of Williamson – Hall method, and also by size-strain plot (SSP) method. The lattice strain has also been calculated. The surface morphology and elemental analysis of the product have been characterized by field emission scanning electron microscopy (FESEM) and energy dispersive (EDAX) spectra.

Geochemical composition and morphology study of Major Minerals of Angus Stone from Gamalama Mountain, Ternate Island, Indonesia

This research is aimed to recognize the chemical composition, type, and main mineral morphology that are consisted in Batu Angus. The analytical methods used are X-ray Fluorescence (XRF), X-ray Diffraction (XRD), Fourier Transform Infra-Red (FTIR), and Scanning Electronic Microscopic (SEM). The result of the research showed that the chemical composition of Angus stone consists of silicone mineral and iron. The kind of silicone mineral is identified as mineral quartz, cristobalite, and tridymite while the iron mineral is identified as maghemite. The silicone mineral morphology has tetragonal, cubic, orthorhombic, hexagonal, and trigonal geometry shapes.

Darcy and inertial fluid flow simulations in porous media using the non-orthogonal central moments lattice Boltzmann method

In this study, two-dimensional (2D) and three-dimensional (3D) lattice Boltzmann method (LBM) has been investigated using the non-orthogonal central moments collision method in order to study the Darcy and inertial (non-Darcy) fluid flow in porous media. A GPU parallel CUDA code has been developed and is employed to study the proposed method. A comparative study has been performed between the non-orthogonal central moments method and the Bhatnagar–Groos–Krook (BGK) method to measure the permeability. The effect of selecting sets of relaxation times and no-slip boundary conditions has been investigated using the 2D hexagonal and 3D body-centered cubic (BCC) structure, and an appropriate model has been presented for flow simulation in porous media. The comparison of the permeability obtained by the proposed numerical method with the analytical solutions shows that the proposed model is highly accurate and eliminates the dependence of permeability on the viscosity, which is one of the problems in the LBM. This model’s capability has been evaluated to simulate Darcy and inertial flows using 2D hexagonal geometry, 2D granular porous media with a random structure, 3D BCC geometry, 3D porous media with a random structure, and real porous media created by using computed tomography (CT) images. In addition, the apparent permeability, the non-Darcy β factor, and the onset of non-Darcy flow have been predicted to demonstrate the capability of the proposed method. The results show the high capability of the proposed model for fluid flow simulation in porous media with complex geometries; so, this model can be used as a powerful and stable tool with the capability of fluid flow simulation in porous media from the Darcy regime to large Reynolds numbers and the inertial regime.

Laser‐made 3D Auxetic Metamaterial Scaffolds for Tissue Engineering Applications

AbstractExploiting the unique properties of three‐dimensional (3D) auxetic scaffolds in tissue engineering and regenerative medicine applications provides new impetus to these fields. Herein, the results on the fabrication and characterization of 3D auxetic scaffolds for tissue engineering applications are presented. The scaffolds are based on the well‐known re‐entrant hexagonal geometry (bowtie) and they are fabricated by multiphoton lithography using the organic−inorganic photopolymer SZ2080. In situ scanning electron microscopy–microindentations and nanoindention experiments are employed to characterize the photocurable resin SZ2080 and the scaffolds fabricated with it. Despite SZ2080 being a stiff material with a positive Poisson’s ratio, the scaffolds exhibit a negative Poisson’s ratio and high elasticity due to their architecture. Next, mouse fibroblasts are used to seed the scaffolds, showing that they can readily penetrate them and proliferate in them, adapting the scaffold shape to suit the cells’ requirements. Moreover, the scaffold architecture provides the cells with a predilection to specific directions, an imperative parameter for regenerative medicine in many cell‐based applications. This research paves the way for the utility of 3D auxetic metamaterials as the next‐generation adaptable scaffolds for tissue engineering.

Majorana zero modes in nanowires with combined triangular and hexagonal geometry

The effects of geometry on the hosting of Majorana zero modes are explored in core–shell nanowires with a hexagonal core and a triangular shell, and vice versa. The energy interval separating electronic states localized in the corners from states localized on the sides of the shell is shown to be larger for a triangular nanowire with a hexagonal core, than a triangular one. We build the topological phase diagram for both cases and compare them to earlier work on prismatic nanowires with matching core and shell geometry. We suggest that a dual core nanowire is needed to allow for braiding operations of Majorana zero modes at the nanowire end plane.

Stress–strain state in α-Ga2O3 epitaxial films on α-Al2O3 substrates

We consider the stress–strain state in α-Ga2O3/α-Al2O3 heterostructures, in which both constituting phases belong to trigonal crystal system. We utilize the hexagonal geometry (hexagonal cell) to account for structural features of the materials and include in the analysis the complete set of six elastic constants Cij being typical for materials with rhombohedral crystal structure that differs from materials with hexagonal one by the presence of an additional constant C14. This allows us to derive analytical formulas for elastic strains and mechanical stresses in pseudomorphic α-Ga2O3 films on α-Al2O3 substrates with various growth orientations assuming nonzero constant C14.

Highly stretchable, stability, flexible yarn-fabric-based multi-scale negative Poisson’s ratio composites

In this paper, we report a new multi-scale NPR composite based on auxetic fabric/elastomer matrix (AF/EM) composite structure. The multi-scale AF was obtained via using helical auxetic yarn (HAY) as weft yarns and constructing re-entrant hexagonal (REH) geometry structure on the macro scale, then the AF was combined with EM to fabricate the auxetic composite (AC). The AF and AC exhibit the NPR of −1.492 and −0.379. Simultaneously, high tensile strain over 108% (AF) and 82% (AC) can be subjected, indicating good mechanical performance. The superior performance of the AC is its ability to maintain NPR and resilience, with elastic recovery ratio over 94% and work recovery coefficient with a stable value over 80% after 10 cycles. Also, the damping properties results further evidence the good elasticity of our AC. The paper shows that our AF and AC are promising candidates in protective composites.

Technical Note: Taking EGSnrc to new lows: Development of egs++ lattice geometry and testing with microscopic geometries.

This work introduces a new lattice geometry library, egs_lattice, into the EGSnrc Monte Carlo code, which can be used for both modeling very large (previously unfeasible) quantities of geometries (e.g., cells or gold nanoparticles (GNPs)) and establishing recursive boundary conditions. The reliability of egs_lattice, as well as EGSnrc in general, is cross-validated and tested at short length scales and low energies. New Bravais, cubic, and hexagonal lattice geometries are defined in egs_lattice and their transport algorithms are described. Simulations of cells and GNP-containing cavities are implemented to compare to independent, published Geant4-DNA and PENELOPE results. Recursive boundary conditions, implemented through a cubic lattice, are used to perform electron Fano cavity tests. The Fano test is performed on three different-sized cells containing GNPs in the region around the nucleus for three source energies. Lattices are successfully implemented in EGSnrc, and are used for validation. EGSnrc calculated the dose to cell cytoplasm and nucleus when irradiated by an internal electron source with a median difference of 0.6% compared to published Geant4-DNA results. EGSnrc calculated the ratio of dose to a microscopic cavity containing GNPs over dose to a cavity containing a homogeneous mixture of gold, and results generally agree (within 1%) with published PENELOPE results. The electron Fano cavity test is passed for all energies and cells considered, with sub-0.1% discrepancies between EGSnrc-calculated and expected values. Additionally, the recursive boundary conditions used for the Fano test provided a factor of over a million increase in efficiency in some cases. The egs_lattice geometry library, currently available as a pull request on the EGSnrc GitHub "develop" branch, is now freely accessible as open-source code. Lattice geometry implementations cross-validated with independent simulations in other MC codes and verified with the electron Fano cavity test demonstrate not only the reliability of egs_lattice, but also, by extension, EGSnrc's ability to simulate transport in nanometer geometries and score in microscopic cavities.

Development of a new hexagonal honeycomb steel damper

This paper presents a new metallic damper called hexagonal honeycomb steel damper (HHSD) for damage mitigation in structures subjected to earthquake excitations. The HHSD is composed of steel plates having several hexagonal and welded to the top and bottom anchor plates. The damper takes the advantages of hexagonal honeycomb geometry and steel material capability to dissipate seismic energy. The quasi-static cyclic test was performed experimentally and numerically on a series of specimens to evaluate the robustness of the HHSD. A three-dimensional finite element analysis of HHSD was carried out and verified with the experimental results. The results showed that the HHSD has low yield displacement, stable hysteretic behavior, a good range of ductility and high-energy dissipation capability. Additionally, the constitutive formulas of the damper are also derived based on the obtained results. Furthermore, it is found to have lightweight and inexpensive with ease of implementation as a potential alternative for new structures or seismic retrofitting of the existing structures.

Laser powder bed fusion manufacturing of aluminum honeycomb structures: Theory and testing

This paper addresses the theoretical and experimental assessment of thin-walled hexagonal structures manufactured by laser powder bed fusion which is a layerwise powder bed based additive manufacturing process. The lightweight potential and mechanical properties of such cellular structures are governed by their relative density for which the present literature only gives approximate values. Thus, a closed-form analytical solution is given which considers the cell wall overlaps that are neglected by the current models. Effective inplane elastic properties, i.e. two moduli of elasticity and two Poisson's ratios, are treated in the framework of a new closed-form analytical method that uses a homogenization approach applied to a representative volume element and is based on Timoshenko's beam theory by using the principle of the minimum of total complimentary elastic potential in conjunction with Castigliano's 2nd theorem. The general manufacturability of such cellular structures by laser powder bed fusion is investigated by establishing overhang restrictions and by manufacturing trial specimens for the assessment of maximum cell sizes and orientations in the build space of a laser powder bed fusion system. Extensive parameter studies are performed concerning the influence of laser power, scan speed and hatch distance on the resultant hexagon geometries, the surface quality, the occurrence of imperfections and the general limits of manufacturability which enables the targeted manufacturing of cellular structures with clearly defined properties. The resultant material density is determined by Archimedean density measurements, and the study of micrographs reveals degrees of porosity and the quality of the individual melt tracks. The closed-form analytical method for the determination of the effective elastic properties is finally validated by performing compression tests on selected specimens.

A response matrix method for the refined Analytic Function Expansion Nodal (AFEN) method in the two-dimensional hexagonal geometry and its numerical performance

In order to improve calculational efficiency of the CAPP code in the analysis of the hexagonal reactor core, we have tried to implement a refined AFEN method with transverse gradient basis functions and interface flux moments in the hexagonal geometry. The numerical scheme for the refined AFEN method adopted here is the response matrix method that uses the interface partial currents as nodal unknowns instead of the interface fluxes used in the original AFEN method. Since the response matrix method is single-node based, it has good properties such as good calculational efficiency and parallel computing affinity. Because a refined AFEN method equivalent nonlinear FDM response matrix method tried first could not provide a numerically stable solution, a direct formulation of the refined AFEN response matrix were developed. To show the numerical performance of this response matrix method against the original AFEN method, the numerical error analyses were performed for several benchmark problems including the VVER-440 LWR benchmark problem and the MHTGR-350 HTGR benchmark problem. The results showed a more than three times speedup in computing time for the LWR and HTGR benchmark problems due to good convergence and excellent calculational efficiency of the refined AFEN response matrix method.

A Multi-Core Fibre Photonic Lantern-Based Spectrograph for Raman Spectroscopy

We report on the development of a compact (volume $\approx$ 100\:cm$^3$), multimode diffraction-limited Raman spectrograph and probe designed to be compact as possible. The spectrograph uses `off the shelf' optics, a custom 3D-printed two-part housing and harnesses a multi-core fibre (MCF) photonic lantern (multimode to few-mode converter), which slices a large 40~\textmu m multimode input into a near-diffraction-limited 6~\textmu m aperture. Our unique design utilises the hexagonal geometry of our MCF, permitting high multimode collection efficiency with near-diffraction-limited performance in a compact design. Our approach does not require a complex reformatter or mask and thus preserves spectral information and throughput when forming the entrance slit of the spectrograph. We demonstrate the technology over the interval 800~nm to 940~nm (200~cm$^{-1}$ to 2000~cm$^{-1}$) with a resolution of 0.3\:nm (4\:cm$^{-1}$), but other spectral regions and resolutions from the UV to the near infrared are also possible. We demonstrate the performance of our system by recording the Raman spectra of several compounds, including the pharmaceuticals paracetamol and ibuprofen.