Hexagonal Rods Research Articles

LES and RANS Modeling of an 84-Pin Hexagonal Rod Bundle with Spacer Grid and Experimental Validation

As part of an ongoing integrated research project (IRP), detailed investigations of the flow characteristics of an 84-pin hexagonal rod bundle representing a potential modular gas-cooled fast reactor design have been performed. The rod bundle features a pitch-to-diameter ratio of 1.5 and a large central guide tube, along with simple spacer grids and an outer enclosure. The primary focus of the current work is modeling and simulation of this geometry using multiple computational techniques. These include high-fidelity large eddy simulation (LES) and advanced Reynolds-averaged Navier-Stokes (RANS) approaches. The flow predictions are validated at a Reynolds number of 12 000 using matched index of refraction particle image velocimetry experimental data that were also generated by Texas A&M University as part of the IRP. The comparison data include velocity magnitude and turbulent kinetic energy (TKE) at different lateral locations and at multiple distances downstream of the spacer grid. Many characteristics of the experimental flow are replicated in the LES and RANS runs, and a general agreement between simulation and experiment is shown. Except for the immediate vicinity of the grid, LES is able to capture the velocity magnitude within a 10% error and the TKE to within the experimental uncertainty. The LES shows notably better agreement with the experimental data than RANS, particularly regarding the TKE decay behavior downstream of the grid. Both methods show significant departures from the experiment in their predictions close to the central guide tube. The experimental and high-fidelity data will be used to inform closures for novel multiscale methodologies. The long-term goal of the work is to use the high-fidelity data to yield improved multiscale thermal analysis techniques for solving fuel performance problems of direct relevance to industry.

Influence Mechanism of Accelerator on the Hydration and Microstructural Properties of Portland Cement

Shotcrete is one of the most important types of concrete used in engineering construction, and its properties are significantly influenced by accelerators. This study investigates the effects of aluminum sulfate series alkali-free accelerator (AKF) and alkali accelerator (ALK) on the strength, hydration process, characteristic hydration products, and microstructure properties of shotcrete. Techniques such as setting time measurement, isothermal calorimetry, simultaneous thermal analysis, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDS), and mercury intrusion porosimetry (MIP) were utilized. The results indicate that both ALK and AKF significantly accelerate and increase the early hydration heat release rate and cumulative hydration heat of Portland cement, producing the characteristic hydration products hexagonal plate AFm and rod AFt, respectively. This acceleration notably speeds up the setting process of Portland cement. ALK negatively impacts the later-stage microstructural development and pore structure filling of hardened cement paste, leading to average reductions of 15.3% and 19.9% in flexural and compressive strengths at 28 days, respectively. Specifically, compared to ALK, AKF shows a faster hydration heat release rate during the induction period and a more significant increase in cumulative hydration heat during the hydration process; the cumulative hydration heat is on average 18.2% higher than AKF. Furthermore, AKF does not hinder the subsequent C3S hydration and C-S-H gel densification process. After 28 days of curing, EDS analysis indicates an average Ca/Si ratio of 1.171 for the AKF-treated shotcrete; the average Ca/Si ratio shows minimal variation from the reference group and is classified as the same type of C-S-H gel as the reference group. Therefore, the strength of hardened cement paste with AKF continues to increase steadily in the later stages. At 28 days, the average flexural strength increased by 10.2%, while the compressive strength decreased by only 3.0%. These findings suggest that AKF enhances the microstructural development and strength of shotcrete, making it a more effective accelerator for engineering applications.

Hydrothermal synthesis and morphological evolution of hexagonal ceria microrod structures

CeriaBTC (CeO2-1,3,5-Benzenetricarboxylic acid) microstructures have been synthesized through hydrothermal methods. Field Emission Scanning Electron Microscopy (FE-SEM) micrographs and X-ray diffraction (XRD) data reveal that the microstructure exhibit hexagonal rod-like structures with average diameters 1.9 ± 0.17 µm and length 5.7 ± 0.19 µm, synthesized at 130 °C for 72 h. Elevating the reaction temperature or duration leads to gradual morphological evolution in micromaterial shape and size (aspect ratio), stabilizing at 3.51. This signifies an ongoing chemical transformation driving morphological alteration. Fourier transform infrared spectroscopy (FT-IR) reveals the presence of an organic linker in the CeriaBTC microrods. Results from XRD, FE-SEM, FT-IR, and thermogravimetric analysis (TGA) suggest a chemical transformation from hexagonal type CeriaBTC to Ceria microrods at higher calcination temperatures of 400 °C for 4 h. The development of hierarchical morphologies, transitioning from hexagonal CeriaBTC rods to Ceria microstructure powder, has been observed to rely on both the orientation of the organic precursor (1,3,5-Benzenetricarboxylic acid) and the specific calcination temperature applied.

Electrocatalysis for Water Splitting Using Layered Zirconium Phosphate Nanomaterials

We are studying new applications of layered zirconium phosphate (ZrP) inorganic nanomaterials [1]. The θ phase of ZrP can be directly ion-exchanged with metal complexes and catalysts, producing intercalated phases useful for artificial photosynthesis schemes for water splitting, amperometric biosensors, and drug delivery applications. Recently, we have demonstrated improved electrocatalytic activity of ZrP nanomaterials loaded with metal ions suitable for the oxygen evolution reaction of water splitting. Electrocatalysts have been incorporated as intercalated species, surface bound, on exfoliated layers, and on nanoparticles of different morphologies (hexagonal platelets, cubes, rods, and spheres). Single and bimetallic electrocatalysts based on earth-abundant materials have been studied. Reduction in overpotentials and increases in mass activity have been achieved. Mixed metal NiFe-intercalated ZrP electrocatalysts at 90% Fe metal content proved to have superior OER electrocatalytic performance (decreased overpotentials, increased mass activities, reduced Tafel slopes) compared to adsorbed counterparts. We have recently prepared CoFe electrocatalysts systems and again the intercalated bimetallic system is more active than the surface-adsorbed one. We are starting to work also with Mn electrocatalysts. We are exploring OER activities of other mixed-metal catalysts on ZrP, bifunctional catalysts, and operando synchrotron X-ray absorption spectroscopy studies to elucidate the nature of the active species. We are also exploring efficient solar H2 production using these supports.Reference[1] M. V. Ramos-Garcés; J. González-Villegas; A. López-Cubero; J. L. Colón, Acc. Mater. Res. 2021, 2, 793-803. DOI: 10.1021/accountsmr.1c00102.

Scaffold microstructure evolution via freeze‐casting and hydrothermal phase transformation of calcium phosphate

AbstractExtensive research efforts have been focused on customizing the microstructure, macrostructure, and phase composition of calcium phosphate for enhanced biocompatibility and bioactivity in scaffolds for bone substitutes. Despite significant progress, achieving precise phase composition and microstructure remains a challenge, primarily due to the necessity of scaffold sintering. This study addresses the challenges in developing customized patient‐specific bone substitutes by proposing a sequential approach that reduces processing steps while providing control over the phase and morphology of the scaffolds’ structure. The methodology utilizes freeze‐casting and sintering for highly porous the scaffolds’ preparation, followed by hydrothermal treatment to modify the microstructure. The introduction of CaCO3 induces a phase transformation of tricalcium phosphate, increasing the hydroxyapatite content, while the overall macrostructure retains the characteristics of freeze‐casting. The surface morphology undergoes a transition from equiaxial grains to whiskers‐like structures and hexagonal rods, impacting compressive strength. Following hydrothermal treatment, the formation of whiskers‐like hydroxyapatite grains leads to a notable strength increase from 2.8 to 5.7 MPa. Remarkably, the scaffolds undergo nearly complete phase transformation, shifting from 100% tricalcium phosphate to 99% hydroxyapatite, all while conserving the macrostructure.

Investigation of ZnO@CdS nanocomposite with amplified photocatalytic H2 production under visible light irradiation

Researchers are trying to develop an efficient solar-powered catalytic water splitting system to solve the energy dilemma and generate green hydrogen. In this study, ZnO@CdS nano-heterostructures were synthesized using sol-gel and co-precipitation techniques. The pristine ZnO, CdS, and their heterostructures were characterized through various characterization tools such as XRD, SAED, XPS, FTIR, EDX, SEM, FE-TEM, UV–vis, Mott-Schottky, GCG, EIS, and PL, to know the crystal structure, chemical state, elemental composition, morphology, band gap, scheme mechanism, hydrogen production and charge transfer resistance characteristics of the samples, respectively. The SEM, FE-TEM, confirm that CdS NPs are well decorated on hexagonal ZnO rods. The efficient H2 production of 587.86 μmolg−1 h−1 were measured for the optimized sample which is 3.91 times greater than pure ZnO rods and 3.22 times than CdS NPs. Strong photo-cyclic stability test was carried out for 20 h in four cycles while, PL spectroscopy confirms the suppressed charge recombination. All of the above characterization prove that (ZC-20) optimized sample, has a potential to be used as an efficient and stable photocatalyst for H2 production via photocatalytic water splitting.

The influence of crystal facet on the catalytic performance of MOFs-derived NiO with different morphologies for the total oxidation of propane: The defect engineering dominated by solvent regulation effect

Crystal facet and defect engineering are crucial for designing heterogeneous catalysts. In this study, different solvents were utilized to generate NiO with distinct shapes (hexagonal layers, rods, and spheres) using nickel-based metal-organic frameworks (MOFs) as precursors. It was shown that the exposed crystal facets of NiO with different morphologies differed from each other. Various characterization techniques and density functional theory (DFT) calculations revealed that hexagonal-layered NiO (NiO-L) possessed excellent low-temperature reducibility and oxygen migration ability. The (111) crystal plane of NiO-L contained more lattice defects and oxygen vacancies, resulting in enhanced propane oxidation due to its highest O2 adsorption energy. Furthermore, the higher the surface active oxygen species and surface oxygen vacancy concentrations, the lower the C−H activation energy of the NiO catalyst and hence the better the catalytic activity for the oxidation of propane. Consequently, NiO-L exhibited remarkable catalytic activity and good stability for propane oxidation. This study provided a simple strategy for controlling NiO crystal facets, and demonstrated that the oxygen defects could be more easily formed on NiO(111) facets, thus would be beneficial for the activation of C−H bonds in propane. In addition, the results of this work can be extended to the other fields, such as propane oxidation to propene, fuel cells, and photocatalysis.

In situ transformation from metal-organic framework into iridium-iron hollow hexagonal rod to promote oxygen evolution reaction

Developing highly efficient and durable electrocatalysts for water oxidation in alkaline media is crucial for hydrogen production in industrialization. IrO2 is a highly promising electrocatalyst for oxygen evolution reaction (OER), but its large-scale is still limited to the sluggish OER kinetics in alkaline solution due to the multi-steps adsorption of -OH and H2O. Herein, we reported a novel in-situ generation from metal-organic framework strategy for preparing hollow hexagonal rod IrFex electrocatalysts (IrFex HHRs). Specifically, the optimized IrFe3 HHRs shows an excellent OER electrocatalytic activity, including low overpotential of 265, 295 and 307 mV at the current density of 10, 50 and 100 mA cm−2, and high stability (100 h). The experimental results revealed that the existent interfacial Fe-O-Ir bonds between Ir and MIL-88A (Fe) can promote electrons transport to improve the electrocatalyst activity. This work represents a new strategy for designing an efficiency electrocatalysts with low iridium content derived from Ir doped-bimetal MOF material.

Terahertz Polarization Isolator Using Two-Dimensional Square Lattice Tellurium Rod Array.

A novel terahertz polarization isolator using a two-dimensional square lattice tellurium rod array is numerically investigated at the interesting band of 0.22 THz in this short paper. The isolator is designed by inserting six hexagonal tellurium rods into a fully polarized photonic crystals waveguide with high efficiency of -0.34 dB. The TE and TM photonic band gaps of the 7 × 16 tellurium photonic crystals are computed based on the plane wave expansion method, which happen to coincide at the normalized frequency domain from 0.3859(a/λ) to 0.4033(a/λ), corresponding to the frequency domain from 0.2152 to 0.2249 THz. The operating bandwidth of the tellurium photonic crystals waveguide covers 0.2146 to 0.2247 THz, calculated by the finite element method. The six hexagonal tellurium rods with smaller circumradii of 0.16a serve to isolate transverse electric waves and turn a blind eye to transverse magnetic waves. The polarization isolation function and external characteristic curves of the envisaged structure are numerically simulated, which achieves the highest isolation of -33.49 dB at the central frequency of 0.2104 THz and the maximum reflection efficiency of 98.95 percent at the frequency of 0.2141 THz. The designed isolator with a unique function and high performance provides a promising approach for implementing fully polarized THz devices for future 6G communication systems.

Xylene adsorption behaviors of Co-MOF-74(X) synthesized from Co(II) salt with different anions

Xylene, a typical volatile organic compound (VOC) and primary raw material in the chemical industry, has been found to be a key component in ozone formation. Metal organic frameworks (MOFs) containing open metal sites are capable of binding to xylene. To recover xylene from waste solvent and to mitigate the environmental risks associated with it, three 1D coordination polymers (CPs), Co-MOF-74(X) (X = OAc–, Cl–, or NO3–), were synthesized using various cobalt salts of Co(OAc)2·4H2O, CoCl2·6H2O and Co(NO3)2·6H2O to investigate the influence of anions. Moreover, the liquid phase adsorptive performance for xylene was evaluated. The morphology features and structure differences of the resulting Co-MOF-74(X) were determined by SEM-EDS, XRD, N2/CO2 adsorption, FTIR and XPS. In situ DRIFT was applied to further distinguish the adsorption performance of Co-MOF-74(X) for xylene. The results indicated that Co-MOF-74(X) exhibits a different morphology. Co-MOF-74(OAc–) is flaky and agglomerated severely, while both Co-MOF-74(Cl–) and Co-MOF-74(NO3–) are hexagonal rod–like crystals. All of Co-MOF-74(X) showed microporous structures with high specific surface areas. A small amount of Cl– was retained in Co-MOF-74(Cl–), forming a Co–Cl bond with Co(II), and the active site of adsorption increased. Co-MOF-74(Cl–) shows the highest adsorption capacity of 1317.65 mg/g for the xylene mixture with excellent cyclic stability reported so far, which is 2.17 or 2.78 times more than Co-MOF-74(NO3–) or Co-MOF-74(OAc–). Therefore, it is anticipated to be a highly efficient adsorbent for removal or recovery of xylene.

Multiscale Modeling of Flow in Rod Bundles: From Direct Numerical Simulation and Subchannel to Coarse-Mesh CFD

Fast and accurate evaluation of flow and heat transfer phenomena in rod bundles is a problem of long-standing interest in nuclear engineering. Computational fluid dynamics (CFD) can provide accurate but relatively time-intensive estimates, such that simulations of very long transients with high spatial detail are infeasible. On the other hand, subchannel codes require relatively low computational time and can provide pin-level estimates, but have substantial empiricism in evaluating aspects such as crossflows and turbulent mixing coefficients. A multiscale method (SC+) for bridging this accuracy/speed gap, based on the Subchannel CFD (SubChCFD) method of Liu et al. [Nucl. Eng. Design, Vol. 355, paper 110318 (2019)], is demonstrated and developed here with a focus on a 5 × 5 square rod bundle geometry. The method has been newly implemented into the commercial code STAR-CCM+ and benchmarked against Liu et al.’s data. The 5 × 5 geometry was chosen in part due to the availability of direct numerical simulation (DNS) data at a relevant Reynolds number of a similar configuration for comparison. The SC+ results are variously compared against results from DNS, large eddy simulation, wall-resolved Reynolds-averaged Navier-Stokes, and coarse-mesh CFD methods. As an expansion to the original SubChCFD approach, a simple Hi2Lo approach is demonstrated using the DNS data as a correction to the original friction factor correlations employed. This is verified to improve the predictions. Additional test cases with geometric perturbations are pursued, illustrating the flexibility of SC+. The potential of this method for modeling the narrow gap vortex instability, which would represent an advancement over standard subchannel approaches, is also assessed. The method is expanded to include transverse flow losses, which was found to improve the results for modeling the gap instability. Initial extensions of SC+ for hexagonal rod bundles are also presented; some inaccuracies for the coarsest meshes prompted a detailed investigation of the mesh convergence behavior of the method. Geometric correction factors were devised that provided substantial improvement on these very coarse meshes, improving the prospects of SC+ for wider usage. Future work plans are to expand the methodology to wire-wrapped rod bundles and to implement the method into Pronghorn, with a unified pipeline via the Cardinal wrapper between the codes NekRS, Pronghorn, and BISON, to solve fuel performance problems of direct interest to industry.

Antimicrobial activity of Sargassum muticum incorporated nanohydroxyapatite hexagonal rods synthesized by co-precipitation method

The bio-functionality enhancement of nanohydroxyapatite (nHA) has currently become a major research field in the Health Care Industry. Researchers attempt to improve the antimicrobial activity by loading the antibiotics directly or doping the antimicrobial-enhancing ions such as Ag, ZnO, and Sr to nHA. There are few reports that Green synthesize also improves the same and not the morphology. Here we report, a two-step method of engineering the morphology of nHA using CTAB & SDS, and consequently, incorporating Sargassum muticum extract (SME), could promote the antimicrobial effect. Moreover, among the four methods of extraction, namely, hydrothermal, constant temperature bath and sonication, the extract obtained through sonication demonstrated potent antimicrobial activity against four pathogens tested, whereas, the extracts obtained through other methods exhibited activity only against two pathogens. The Minimum Inhibitory Concentration (MIC) for the SME-added nHA has successfully been determined against the pathogens S. aureus, E. faecalis, V. cholerae and S. typhi. Further, supportive studies, to confirm the composition, phase, morphology and porosity were also carried out and the results are discussed in detail.

Evaluation of pan‐epithelial viability in the whole porcine lens

Purpose: The lens has a monolayer of epithelial cells on its anterior surface that contributes to its homeostasis. A quantification of the viability of these cells is essential to evaluate the safety of new therapies targeting the lens (cataract, presbyopia). The observation of this whole tissue is made difficult by its optical properties (transparency and refraction) and only simplified models have been used until now to measure epithelial viability (primary cell cultures or partial surgical specimens).Aims: To develop a method to quantify the viability of epithelial cells on whole ex vivo lenses.Methods: Ten fresh pairs of 6‐month‐old porcine lens were retrieved from local slaughterhouse. For each pair, one lens was randomly selected to undergo a localized lesion and the other lens remained intact. The lesion was made on the anterior surface with a steel hexagonal rod (to make the mark easily identifiable) previously immersed in liquid nitrogen for one minute. Both lenses were incubated for 1 h at 20°C in a HEC mixture. Images were acquired with a macroscope and analysed with ImageJ. Calcein‐AM and Ethidium images were used to calculate the area covered by living epithelial cells. Hoescht images allowed to count cell nuclei per unit area. Viable epithelial cell density (vECD) was defined as the number of viable cells per unit area. The lenses were immersed (isotonic saline) inside a black container during the measurements to minimize reflections and refractive phenomena or drying of the samples.Results: The vECD median on the ten pairs was 2840 cells/mm2 [10th‐90th percentiles = 2479–3494] for cryo‐applied lenses versus 3364 cells/mm2 [2919–3739] for healthy lenses (p = 0.002).Conclusions: The triple HEC staining adapted to the whole lens provides an unrivalled measure of pan‐epithelial viability without the need for a tedious capsule dissection step that destroys the lens architecture. Other studies will be necessary to determine its ability to discriminate small variations or type of mortality.

Novel approach towards optically active and hexagonal plate morphology of Zinc doped Perylene Tetra Carboxylic Di Anhydride composite for high photovoltaic and flexible supercapacitor performances

This paper reports novel features like photo-voltaic and energy storage capacity as dual performance in Zinc-Perylene Tetra-Carboxylic Di-Anhydride (Zn-PTCDA) composite have synthesized via hydrothermal method. This follows escape-by-crafty mechanism chemical reaction that produces the orthorhombic crystal structure. The Morphology transformation from stacked pyramids of PTCDA into hexagonal plates and rod structures of Zn-PTCDA. The optical study suggest that Zn-PTCDA composite provide compelling evidence for the Dye sensitized solar cell (DSSC) with Power Conversion Efficiency (PCE) is lower 0.2 % due to charge carrier recombination and promote to utilize this as transport layer of any solar cell. The electrochemical performance of pure Zn-PTCDA exhibits capacitance retention of 44.2 % while Zn-PTCDA-Graphene Oxide (Zn-PTCDA-GO) has capacitance retention 84.5 % over 5000 Galvanostatic-Charging and Discharging (GCD) cycles. The best specific capacitance 561 F/g at 2 A/g along with discharge through light emitting diode (LED) illumination for 2–3 min and also excellent energy density 31.5 Whr/kg and power density 4.5 kW/kg values. The incorporation of Zinc into PTCDA dye demonstrates Metal Organic Frameworks can provide improvements in the performances of both supercapacitors and dye-sensitized solar cells. The integration of both can instant storage of converted energy is needed solution to solve energy demand in future.

Novel KOH treated Li-CuO as anode for the Application of Lithium-Ion Batteries

Lithiated CuO (Li-CuO) micro-structures were synthesized by the hydrothermal method using KOH as a reactive solution. The structural properties of pure Li-CuO and other KOH-reacted CuO samples were analysed using XRD analysis. Various vibrational bands were observed by FTIR spectra analysis. The SEM images indicated the formation of Li-CuO hexagonal rods of 1-2 µm dimension. The cyclic efficiencies of pure Li-CuO and 12 M KOH surfactant Li-CuO microstructures were observed to be 78.5% and 91.2%, respectively. The battery discharge characteristics revealed that after 50 cycles, the specific capacity of the battery based on a pure Li-CuO microstructure electrode showed 97 mAh g-1 whereas KOH surfactant Li-CuO microstructures electrode showed 150 mAh g-1 at a constant current density of 17.79 mA g-1 with a 1.0–4.0 V vs. Li/Li+ potential range. The enhancement of specific capacity and its stability due to a well-defined hexagonal crystal structure leads to increased Li+ ion kinetics during the insertion and extraction processes of batteries.

In situ synthesis of TiB2 rod crystal reinforced PcBN mechanical properties: First-principles calculations and experimental study

In this work, a combination of first-principles calculations and experiments is used to not only reveal the growth mechanism of hexagonal rod-shaped crystals TiB2 and its theoretical influencing factors, but also to experimentally regulate the growth of TiB2 rod-shaped crystals to obtain polycrystalline cubic boron nitride (PcBN) composites with excellent comprehensive mechanical properties. The calculation results reveal that under Ti-rich or B-rich conditions, both the surface energies of (0001) and (101̄0) are lower than the surface energy of (112̄0). The growth of TiB2 is interpreted at the atomic level as being composed of (0001) and (101̄0) surfaces, and it preferentially grows as rod crystals along the (0001) crystal plane. The calculations further indicate that the hexagonal morphology of TiB2 is determined by the atomic concentration within the melt. It exhibits a higher propensity for nucleation under Ti-rich conditions than under B-rich conditions. And it is predicted that a lower relative concentration of Ti atoms promotes the growth of TiB2 into hexagonal rod crystals. In addition, PcBN composites with TiB2 reinforced phase are synthesized in situ by modulating the Ti-Al molar ratio. The experimental results demonstrate that as the concentration of Ti atoms decreases, the nucleation of TiB2 decreases, while the growth of TiB2 rod crystals increases, which aligns with the predicted calculations. Moreover, the presence of rod crystals greatly enhances the densities and flexural strength of PcBN composites. When the Ti-Al molar ratio is adjusted to 1:2, a substantial quantity of high-quality TiB2 rod crystals are cultivated, leading to PcBN composites exhibiting outstanding mechanical properties.

Experimental characterization of pressure and friction factor in an interior subchannel of a 61-pin wire-wrapped rod bundle with a porous blockage

Comprehending and counteracting accident conditions presented by impedances of flow in diminutive subchannels of a Liquid Metal Fast Reactor (LMFR) hexagonal rod bundle are imperative toward their development and safety. Scarce experimental research currently exists in the literature to characterize the pressure and friction factor for partial blockages in LMFR assemblies. Experimental pressure measurements were conducted in a 61-pin prototypical LMFR fuel assembly using specialized instrumented wire-wrapped rods with a three-dimensional printed porous blockage installed. The pressure drop was measured for one helical pitch at four distinct interior subchannel locations: two in the blocked subchannel and two unblocked adjacent locations (near-center and near-wall of the assembly). A wide range of Reynolds numbers between 140 and 24 000 were studied to evaluate the blocked subchannel friction factor and to determine the flow regime boundaries for laminar-to-transition and transition-to-turbulent flows. Power spectral density analysis of the pressure fluctuations for three distinct locations (one upstream and two downstream of the porous blockage) revealed the mechanisms of coherent structure formations and transport, and dominant location-dependent Strouhal numbers. One-dimensional continuous wavelet transforms of the pressure fluctuations demarcated temporal instances of flow events with their frequency content. Temporal cross correlation quantified the temporal delay between the blocked subchannel pressure fluctuations in the blockage vicinity. The presented research provides first-of-its-kind datasets and fluid physics based-analyses for the interior LMFR subchannel in the presence of a porous blockage and provides a benchmark for the validation of computational flow models and predictive correlations for the safety enhancement of LMFR rod bundles.

Preparation of amine-incorporated hydroxyapatite through a single-step hydrothermal reaction

We report on the preparation of an amine-incorporated hydroxyapatite (NH2-HAP) by applying o-phosphorylethanolamine (PEA) as a phosphate source. By changing the ratio of PEA to normal phosphate source, three samples of NH2-HAPs having different contents of amine are synthesized. The TEM analysis confirmed that NH2-HAP exhibits elongated rod shape which is similar to the hexagonal rod of pure hydroxyapatite (HAP). As the concentration of PEA increases, the average size of NH2-HAP along (001) direction decreases approximately from 55.4(±10.39) to 31.2(±8.3) nm. The XRD patterns of NH2-HAPs are well matched with typical HAP patterns. Line broadening of XRD peaks in NH2-HAP seems to originate from low crystallinity and smaller size compared to pure HAP. Primary amine group on the surface of NH2-HAP is confirmed by both surface elemental analysis (XPS) and the ninhydrin test. The nitrogen content of NH2-HAP surface is approximately 0.6 ∼ 1.1 at.% based on XPS experiment.

Impact of particle elongation on the behavior of round and angular granular media: Consequences of particle rotation and force chain development

We developed a 2D discrete element model to simulate shearing response of elongated round and angular particles. Model was calibrated and validated by comparing numerical results with corresponding biaxial shearing tests on circular (round) and hexagonal (angular) rods at microscopic and macroscopic scales. Then, the systematic effect of particles aspect ratio was investigated on quasi-static shearing response of round and angular granular materials. Macroscopically, we observed a nonlinear tendency wherein as the aspect ratio decreased from 1, the critical state stress ratio initially increased, reaching a maximum, followed by a decreasing trend. This effect was more prominent in round samples. Microscopically, decreasing the aspect ratio from 1 reduced particle rotations and increased the mean coordination number. Elongated particles exhibited significant contact anisotropy, forming irregular force chains, facilitating interparticle sliding, and reducing overall strength. Additionally, we explored the impact of the interparticle friction coefficient. A high value of interparticle friction coefficient led to a monotonically increasing strength with elongation, underscoring the importance of accurately calibrating microscopic friction coefficients.

Characterization of ZnO/rGO Nanocomposite and Its Application for Photocatalytic Degradation

Zinc oxide (ZnO) nanorods (NRs) with reduced graphene oxide (rGO) were successfully synthesized using a hydrothermal method with an additional spray coating. This paper focuses on the effect of rGO coating on charge transfer and interaction between ZnO and rGO that remarkably contributes to the enhancement of the electrical and optical properties of ZnO-based NRs. The synthesized ZnO/rGO nanocomposite was characterized using FESEM, PL spectroscopy and XPS. FESEM analysis results showed that the surface morphology of the synthesized NRs had a hexagonal rod structure covered with rGO layers on the tip of the rod. The Tauc Plot analysis revealed that the rGO layers reduced the bandgap of ZnO NRs from 3.25 eV to 3.17 eV, where the light absorption increased. The chemical composition, electronic state, and interactions between the elements in the ZnO NRs/rGO nanocomposites were investigated using XPS. The presence of oxygen species due to the rGO deposition layers is indicated by the shift of the peak position toward a greater binding energy. The hybridization of this semiconductor and graphene material reduced the bandgap and lowered the PL emission. Finally, the photocatalytic activity of ZnO NRs/rGO has been studied for methylene blue degradation via oxidation. The results showed that the photocatalytic reaction rate constant of ZnO NRs/rGO > pristine ZnO NRs.