Au Nanoparticles Research Articles

Successively enhanced photoelectrochemical performance from plasmonic Au nanoparticles decorated Ta3N5-TiO2 heterostructure

Semiconductor-based photocatalysts innovation and heterojunction design incorporating novel materials have shed light on the enhancement of the photoelectrochemical performances concerning energy fields, among which the plasmonic metal/semiconductor nanostructure raised extensive research attentions due to further PEC performance enhancement. In this work, an innovatively sandwiched structure composed of Ta3N5 nanorods/ultrathin TiO2/Au nanoparticles was designed with successive PEC enhancement. The successful combination between the Ta3N5 nanorods and the dielectric TiO2 layer represented carriers’ migration, in addition with the heterojunction between TiO2 and Au NPs contributed to the synergistically suppression of the charge carriers’ recombination. Au NPs could further serve as the plasmonic absorber underlying their localized surface plasma resonance effect, expanding the light absorption over the whole visible range, and inducing hot electrons injection to the TiO2 layer effectively. The hierarchical performance improvement via surface plasmon enhanced photoelectrochemical activity in the well-designed heterostructure propose strong potential for the development of novel photocatalysts.

Magnetically-assembled multifunctional Fe3O4@SiO2@Au particles for SERS detection of low-concentration dye molecules

Abstract Surface-enhanced Raman scattering (SERS) is a sensitive spectroscopic method to detect low concentration-low volume analytes. Owing to this, there has been a rising interest in developing improved as well as novel nanostructured substrates for SERS applications. For SERS applications, it is desirable to have large-scale assemblies of such nanostructures that can sustain multiple electromagnetic ‘hotspots’ for improved sensitivity. In this work, we use magnetic-field aided large-scale assembly of multifunctional magnetic-plasmonic particles to generate a large area SERS substrate. The particles, composed of a Fe3O4 core with a thin silica coating followed by Au nanoparticles (Fe3O4@SiO2@Au), were synthesized by simple chemical methods. The multifunctional particles were characterized using powder x-ray diffraction, transmission electron microscopy, Raman spectroscopy, and SQUID magnetometer. Magnetic assembly of the composite particles, carried out using a bi-electromagnet setup, was used for SERS detection of organic dyes such as rhodamine B and methylene blue. Using this scheme, it was possible to detect ultra-low concentrations (up to 1fM) of the dye molecules. This method is promising for applications such as chemical sensors, biomolecular detection, cancer detection, and hyperthermia treatment, forensic investigations, and drug delivery.

Fabrication of Periodically Ordered MnO2 Arrays Decorated with Au Nanoparticles for Interference Enhanced SPR-Mediated Visible-Light Responsive Photocatalysis

Fabrication of Periodically Ordered MnO2 Arrays Decorated with Au Nanoparticles for Interference Enhanced SPR-Mediated Visible-Light Responsive Photocatalysis

Utilizing DNA Logic Device for Precise Detection of Circulating Tumor Cells via High Catalytic Activity Au Nanoparticle Anchoring.

As medical advancements turn most cancers into manageable chronic diseases, new challenges arise in cancer recurrence monitoring. Detecting circulating tumor cells (CTCs) is crucial for monitoring cancer recurrence, but the current methods are cumbersome and costly. This study developed a new CTC detection system combining DNA aptamer recognition, hybridization chain reaction (HCR) technology, and DNA logic devices, enabling the one-step recognition of CTCs by identifying multiple membrane proteins. After catalytically active Au nanoparticles were attached through reduction synthesis in situ onto the DNA hybridization strands of the CTCs surface, a 3,3',5,5'-tetramethylbenzidine (TMB) colorimetric reaction was used to detect CTCs concentration via peroxidase-like catalysis. With this CTCs detection reporting system, we achieved an LOD of 4 cells/mL using an ultraviolet-visible (UV-vis) spectrophotometer. At certain concentrations, CTCs could even be detected visually without the need for an instrument. The development of this CTCs detection reporting system provided a convenient, reliable, and cost-effective detection strategy for widespread CTCs-based cancer recurrence monitoring.

Optimization of NC-LSPR coupled MoS2 phototransistors for high-performance broad-spectrum detection

Abstract In this work, negative-capacitance (NC) and local surface plasmon resonance (LSPR) coupled MoS2 phototransistors with a gate stack of HZO/AuNPs/Al2O3/MoS2 are fabricated, and the impacts of Al2O3 interlayer-thickness (T AlO) on the LSPR effect, the tensile strain on MoS2 from the Au nanoparticles (AuNPs), the capacitance matching of the NC effect from Hf0.5Zr0.5O2 (HZO) ferroelectric layer and the optoelectrical properties of the relevant devices are investigated. Through optimizing T AlO, excellent optoelectrical properties of phototransistors with a T AlO of 3 nm are achieved: a subthreshold swing (SS) of 25.76 mV/dec and ultrahigh detectivity of over 1014 Jones under 740 nm illumination. This is primarily because the NC-LSPR coupled structure can achieve an ultra-low SS through capacitance matching and a good interface passivation through optimizing Al2O3 interlayer to maintain effective LSPR and strain effects cross the MoS2 to enhance optical absorption and detection range. This work provides a comprehensive analysis on effective distance range of the non-direct-contacted LSPR effect and its combination with capacitance matching of NC effect, culminating in an optimized NC-LSPR coupled MoS2 phototransistor with a good consistency across an array of 30 devices, and offering a viable solution for the preparation of large-area, high-performance and broad-spectrum response 2D phototransistor array.

Au/CeO2 Nanozyme Scaffold Boosts Electron and Hydrogen Transfer for NIR-Enhanced Chemodynamic Therapy.

CeO2 nanozymes have demonstrated the potential to enhance biological scaffolds with chemodynamic therapy. However, their catalytic efficacy is limited by the slow conversion of Ce4+ to Ce3+ and the lack of substrates like H2O2 and H+. To address these challenges, we adopted a dual-pronged strategy that utilized the plasmonic resonance of Au nanoparticles and their glucose-oxidase mimicry to boost electron and hydrogen transfer. Specifically, we integrated Au/CeO2 nanozymes into poly-l-lactic acid scaffolds via selective laser sintering. This conversion of Ce3+ to Ce4+ in the scaffolds enhanced the reduction of H2O2 to a hydroxyl radical, inducing oxidative stress in tumor cells. The Au nanoparticles played a crucial role in boosting the Ce3+/Ce4+ catalytic cycle by providing both the energy and the catalytic substrates. They recycled Ce4+ back to Ce3+ by exploiting plasmonic-induced hot electrons and catalyzed glucose oxidation to supply H2O2 and H+. Our nanoscale and atomic-scale simulations confirmed that the Au/CeO2 hybrid structure utilized near-field coupling to amplify the plasmonic resonance and the Au-O-Ce bridge reduced the electron transfer barrier. Consequently, the Au/CeO2 scaffold decreased the activation energy from 22.57 to 9.92 kJ/mol. These findings highlight the significant promise of the Au/CeO2 nanozyme scaffold for NIR-enhanced chemodynamic therapy.

Precise Control of Polyaniline Nanohelices with Chirality Continuum and Their Correlation on Catalytic Performance.

Left- and right-handed chiral molecule inducers have been frequently used to guide the formation of chiral nanomaterials with binary chiral shapes. However, the transition of chiral nanomaterials from discrete to continuously tunable chiral shapes is imperative but challenging and will contribute to a deep understanding of the fundamental relations between chiral nanostructures and their chemical properties. This study shows that chiral polyaniline nanohelices (PANI NHs) with similar aspect ratios (∼5.0) but continuously tunable screw pitches (293 to ∞ nm) and tilt angles (33° to 0°) can be fabricated by adjusting the enantiomer excess of S/R-camphorsulfonic acid used as a chiral molecule inducer. After Au nanoparticles were loaded on the surface of chiral PANI NHs, the chiral morphology-dependent catalytic performances of PANI-Au NHs are studied in reduction, oxidation, and enantioselective catalytic reactions, showing that the larger the helical twist degree, the higher the catalytic activity and enantioselectivity of PANI-Au NHs.

Inside Back Cover: Gapped and Rotated Grain Boundary Revealed in Ultra‐small Au Nanoparticles for Enhancing Electrochemical CO2 Reduction

Inside Back Cover: Gapped and Rotated Grain Boundary Revealed in Ultra‐small Au Nanoparticles for Enhancing Electrochemical CO2 Reduction

Inside Back Cover: Gapped and Rotated Grain Boundary Revealed in Ultra‐small Au Nanoparticles for Enhancing Electrochemical CO2 Reduction

Inside Back Cover: Gapped and Rotated Grain Boundary Revealed in Ultra‐small Au Nanoparticles for Enhancing Electrochemical CO2 Reduction

Controllable Synthesis of Amino-Functionalized Silica Particles via Co-condensation of Tetraethoxysilane and (3-Aminopropyl)triethoxysilane.

Amino-functionalized silica has attracted a great deal of interest due to its high surface reactivity and potential for diverse applications across various fields. While the classical co-condensation method is commonly used to synthesize amino-functionalized silica particles, the mechanism of the reaction between (3-aminopropyl)triethoxysilane (APTES) and tetraethoxysilane under different conditions remains unclear, leading to unexpected self-nucleation or cross-linking between silica particles and consequently hindering rational control over the extent of functionalization. To address this issue, we systematically explored the co-condensation growth mechanism of amino-functionalized silica particles in the Stöber method by investigating the effects of APTES concentration and water content on the hydrolysis and condensation of silanes. The experimental results revealed that APTES could decrease the rate of hydrolysis/condensation, while the moderate water content promoted both the rate of hydrolysis/condensation and the overall quality of the silica particles. Consequently, we successfully demonstrated the rational synthesis of amino-functionalized silica particles with diameters ranging from 213 to 670 nm and a nitrogen content of ≤2.8 wt %. The relationship between the APTES concentration and particle properties exhibited a biphasic trend. At low APTES concentrations (≤2.0 mM), the particle size remained stable while the isoelectric point increased rapidly. Further increasing the APTES concentration from 2.0 to 100.0 mM induced a decrease in particle size due to APTES's inhibitory effect on silica growth, with nitrogen content continuing to increase even after the isoelectric point remained unchanged. These silica particles, featuring varying surface amino group densities, were utilized as matrices for loading Au nanoparticles. The resulting functionalized particles exhibited distinctive catalytic ability in the reduction of 4-nitroaniline, demonstrating significant potential for applications across various fields.

Facet engineering in Au nanoparticles buried in Cu2O nanocubes for enhanced catalytic degradation of rhodamine B and larvicidal application

Water systems around the world are significantly impacted by organic pollutants from industrial activities. In this study, we report a novel and promising approach utilizing a cost-effective and simple chemical co-precipitation method for the synthesis of Cu2O@Au nanocubes. The characterization of these nanocubes was conducted using various advanced techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL). These analyses revealed the formation of crystalline nanocube-structured catalyst, confirming their purity, chemical state, and electronic structure. The synthesized Cu2O@Au nanocubes, particularly with 5 % Au over Cu2O, showed the highest catalytic efficiency in degrading Rhodamine B (RhB), achieving about 99.6 % degradation in 7 min. The deposition of Au significantly enhanced the electron mobility, thereby increasing the catalytic efficiency of the catalyst. GC/MS analysis performed to identify the intermediates formed and a possible degradation pathway of RhB was proposed. In addition, the toxicity of intermediates also evaluated by ECOSAR software. Reusability tests were conducted to assess the consistency and practical application of Cu2O@Au-5 % nanocubes. The results indicated high stability and sustained catalytic performance over multiple cycles. Additionally, the multifunctional properties of the synthesized material were validated through larvicidal activity tests, demonstrating its potential for broader environmental applications. Overall, Cu2O@Au-5 % presents a highly efficient and versatile catalyst for environmental remediation and other practical applications, demonstrating significant potential for large-scale use. These findings underscore the promise of Cu2O@Au as a multifunctional catalyst, capable of delivering substantial advancements in both environmental and public health domains.

Photoactivity Enhancement of WO3 Photoanodes Using the Combined Effect of Plasmonic Au and Photoluminescent Y2O3:Eu3+ Nanoparticles.

The WO3 photoanode has great potential application for solar photoelectrochemical water oxidation due to suitable band edge positions with water oxidation potentials. However, it suffers from poor light absorbance in the visible region. Here, we use Eu3+-doped Y2O3 nanoparticles (NPs) in combination with plasmonic gold (Au) NPs to better utilize and adsorb photons from UV and visible regions of sunlight. We attached plasmonic Au NPs on WO3 to enhance the photocatalytic properties due to the plasmon resonance mechanism. Additional deposition of Y2O3:Eu3+ NPs on Au NPs/WO3 improved the photoactivity of the photoanode further. Y2O3:Eu3+ NPs' downconversion property, along with their light-scattering effect, converts ultraviolet-region photons into visible-region photons and enforces the plasmon resonance mechanism of Au NPs. Experimental results show the increase of absorbance, improvement of electron-hole separation, and enhancement in photocurrent generation of the resultant photoelectrode.

Metal-phenolic nanoparticles enhance low temperature photothermal therapy for bacterial biofilm in superficial infections

Bacterial infections, especially induced by multidrug-resistant pathogens, have become a significant global health concern. In the infected tissues, biofilms not only serve as a source of nutrients but also act as protective barriers that impede antibiotic penetration. Herein, we developed tea polyphenols epigallocatechin gallate (EGCG) Au nanoparticles (E-Au NPs) through direct one-step self-assembly methods by EGCG chelating with Au ions to eradicate antibiotic-resistant bacteria methicillin-resistant Staphylococcus aureus (MRSA) and prevent the formation of biofilm under near-infrared (NIR) irradiation. The outstanding antibacterial effect involved in mild photothermal therapy, reactive oxygen species production, pathogenicity-related genes regulation, and quinoprotein formation that were specific to the polyphenol-based NPs. The excellent antibacterial and anti-inflammatory therapeutic efficacy of E-Au NPs was validated and topically applied in murine MRSA-infected skin wounds and keratitis model in vivo to kill bacteria, reduce the inflammation response and promote wound healing. Furthermore, the ophthalmic and systemic biosafety profiles were thoroughly evaluated while no significant side effects were revealed achieving a balance between high-efficiency antibacterial properties and biocompatibility. This study provides an effective therapeutic agent of metal-phenolic materials for superficial tissue infection with favorable prognosis and potential in clinical translation.Graphical abstract

Label-free electrochemical biosensor with magnetic self-assembly constructed via PNA-DNA hybridization process on α-Fe2O3/Fe3O4 nanosheets for APOE ε4 genes ultrasensitive detection

A label-free electrochemical DNA detection strategy based on self-assembled α-Fe2O3/Fe3O4 nanosheets with PNA-DNA hybridization process was developed for ultrasensitive detection of APOE ε4 gene, one of the most robust genetic risks for Alzheimer’s Disease (AD). In this work, magnetic α-Fe2O3/Fe3O4 heterogeneous nanosheets were prepared by hydrothermal-calcined reduction method and loaded with Au nanoparticles (AuNPs) on their surfaces. The magnetic α-Fe2O3/Fe3O4@Au nanocomposites significantly enhanced the electrochemical response as a signal amplification matrix and were able to bind to the magnetic glassy carbon electrode (MGCE) surface by magnetic self-assembly. Moreover, owing to the high specificity and stable binding capacity of PNA with respect to the target DNA, the biosensor not only enabled accurate (the limit of detection was estimated to be 0.147 pM) and rapid detection of the APOE ε4 gene, but also exhibited excellent specificity, stability and regeneration capability. Additional, the satisfactory recoveries were also obtained in real samples of human serum, ranging from 92.83 % to 106.22 % with relative standard deviation (RSD) between 0.25 % and 1.85 %. The results possessed important reference value for exploring the application of DNA biosensor technology in the diagnosis of APOE gene mutation.

Remarkably Boosted High‐Temperature Electrostatic Energy Storage of Polyetherimide Film Induced by TiO2@Au@AlOx@Au Core‐shell Nanofibers

AbstractPolymer dielectrics have broad applications in advanced electronics and power systems. However, they suffer from low energy density and poor breakdown performance at high temperatures, limiting their applications in high‐temperature environments. Herein, TiO2@Au@AlOx@Au nanofibers with double coulomb blockade nanolayers are obtained via a physical sputtering strategy to improve the high‐temperature energy storage performance of polyetherimide composites. Experimental studies and finite elemenet phase‐field simulations demonstrate that the double‐layer coulomb blockade effect and micro‐capacitor effect of Au nanoparticles synergistically enhance the breakdown strength and dielectric permittivity of polyetherimide composite at high temperatures. Notably, the composite exhibits ultra‐high discharged energy densities of 11.33 and 9.70 J cm−3 at 150 and 200 °C, respectively, along with high charge–discharge efficiencies of 93.4% and 84%, which far exceed that of the polymer nanocomposites reported so far. Furthermore, the composite exhibits excellent charge–discharge cycling performance (>50000 cycles at 400 MV m−1) and high‐power density (1.16 MW cm−3) at 200 °C, making it an ideal candidate for high‐temperature capacitors. Hopefully, these nanofibers not only serve as excellent nanofillers for high‐temperature energy storage dielectric composites but also holds tremendous potential and inspirational significance for other applications such as electronics, biomedical fields, optics, and catalysis.

Realizing Bidirectional Photocurrent in Monolithic Dual‐Mode Device for Neuromorphic Vision and Logically‐Encrypted Transmission

AbstractDue to significant response contradictions, unidirectional carrier transmission of typical semiconductor p‐n junctions limits integrated sensors and artificial synapses in a monolithic device. In this work, a bipolar p‐n junction designed by employing the hydrogel/p‐GaN local contact interface with p‐GaN/(In,Ga)N heterojunction, demonstrating the bidirectional photocurrent and sensor/artificial synapse dual‐mode device successfully. After modifying Au nanoparticles, the negative (positive) photocurrent is increased by 900% (300%) under 365 nm (520 nm) light to achieve a more balanced bipolar carrier dynamic. Such a regulation of photocurrent is found to be attributed to the promotion of hydrogen evolution reaction (HER) at the hydrogel/Au/p‐GaN interface. Thus, the device achieves the ultrahigh paired‐pulse facilitation (PPF) index of 243% under self‐powered condition. Moreover, the implementation of plasticity from short‐term to long‐term demonstrates its adaptability in neural morphology visual recognition. Beyond independent working mode, the function of five classic logic gates is achieved under three‐terminal operation. Finally, an encrypted wireless communication system using dual‐channel light signals demonstrates the extensive application potential of the monolithic device. Therefore, this work presents a viable construction blueprint to meet the demands of next‐generation all‐in‐one optoelectronics for intricate application scenarios.

Engineering MXene Surface via Oxygen Functionalization and Au Nanoparticle Deposition for Enhanced Electrocatalytic Hydrogen Evolution Reaction.

MXene, a family of 2D transition metal carbides and nitrides, presents promising applications in electrocatalysis. Maximizing its large surface area is key to developing efficient non-noble-metal catalysts for the hydrogen evolution reaction (HER). In this study, oxygen-functionalized Ti3C2Tx MXene (Ti3C2Ox) is synthesized and deposited gold nanoparticles (Au NPs) onto it, forming a novel composite material, Au-Ti3C2Ox. By selectively removing other functional groups, mainly -O functional groups are retained on the surface, directing electron transfer from Au NPs to MXene due to electronic metal-support interaction (EMSI), thereby improving the catalytic activity of the MXene surface. Additionally, the interaction between Au NPs and -O functional groups further enhanced the overall catalytic activity, achieving an overpotential of 62 mV and a Tafel slope of 40.1 mV dec-1 at a current density of -10 mA cm-2 in 0.5 m H2SO4 solution. Density functional theory calculations and scanning electrochemical microscopy with ≤150 nm resolution confirmed the enhanced catalytic efficiency due to the specific interaction between Au NPs and Ti3C2Ox. This work provides a surface modification strategy to fully utilize the MXene surface and enhance the overall catalytic activity of MXene-based catalysts.

Probing the Effect of pH Value and Voltage on the Near‐Surface Proton Concentration at the Electrochemical Interface by In Situ Electrochemical Surface‐Enhanced Raman Spectroscopy (EC‐SERS)

ABSTRACTUnderstanding the variation of proton concentration near the surface of the electrochemical interface is of great significance for understanding the mechanism of electrochemical reactions. In this work, 4‐Mpy molecules that are protonated and deprotonated depending on the surrounding pH value adsorb on the Au nanoparticle film electrode with high SERS activity, and by virtue of the highly interfacial‐sensitive EC‐SERS technique, we systematically studied the effects of electrolyte pH value and external voltage on the protonation and deprotonation of 4‐Mpy at the interface between Au‐NP film electrode and phosphate buffer, to analyze the changes of near‐surface proton concentration at the electrochemical interface. It is found that the pH value of the electrolyte plays a decisive role in the protonation process of 4‐Mpy at the electrode interface at low reduction voltage (< −0.1 V). In acidic and neutral solution, 4‐Mpy exists mainly in protonated form on the electrode surface. However, in alkaline solutions, 4‐Mpy exists mainly on the electrode surface in the form of deprotonation. At high reduction voltage (≥ −0.1 V), the protonation and deprotonation of 4‐Mpy on the electrode surface are mainly determined by the adsorption structure of 4‐Mpy on the electrode surface. At the same time, we conducted a comparative study of 2‐Mpy and 4‐Mpy molecules and found that the adsorption modes were different depending on the position of the N atom. 2‐Mpy is inclined adsorbed on the surface of the Au‐NP film electrode, and 4‐Mpy is vertically adsorbed on the surface of the Au‐NP film electrode.

Biosynthesis of gold and silver nanoparticle using water hyacinth (Eichhornia crassipes) extract for photocatalytic degradation of organophosphate and organochlorine pesticide

The study aimed to assess the efficiency of synthesized gold (Au) and silver (Ag) nanoparticles in the degradation of organochlorine and organophosphate pesticides through photocatalysis. The synthesis of gold and silver nanoparticles was achieved using Eichhornia crassipes (water hyacinth extract). Photocatalytic degradation tests were conducted on organochlorine and organophosphate pesticides using gold and silver nanoparticles, with the absorbance of the samples measured by a UV spectrophotometer. The photocatalytic degradation rates of organochlorine and organophosphate were determined, with varied concentrations of the synthesized nanoparticles. The results showed high degradation rates at lower concentrations (10–20 ppm), with degradations of 51.789%, 47.954%, 47.983%, 44.088%, 41.565%, and 36.749% for 25/75, 50/50, and 75/25 Au nanoparticle ratios, respectively. The results also revealed that higher degradation rates were observed at longer reaction times (70–80 minutes), with percentage degradations of 44.344% and 49.987%, 41.754% and 45.937%, 36.773% and 40.458% for 25/75, 50/50, and 75/25 Au nanoparticle ratios, respectively. Lower degradation efficiencies were observed at shorter reaction times (10–20 minutes), with percentage degradations of 15.356% and 19.982%, 13.746% and 17.082%, and 10.976% and 15.167% for 25/75, 50/50, and 75/25 ratios, respectively. Additionally, the results showed high degradation rates at lower concentrations (10–20 ppm) for Ag nanoparticles, with percentage degradations ranging from 40.814% to 44.822% across AgNP ratios (25/75, 50/50, 75/25), indicating efficient degradation at lower concentrations. Conversely, at higher concentrations (60–80 ppm), the degradation efficiency was notably lower, with percentage degradations ranging from 7.004% to 13.539% across different AgNP ratios. In conclusion, Au nanoparticles exhibited higher photocatalytic efficiency than Ag nanoparticles, particularly in degrading organophosphate (Sniper) pesticides. It is recommended that these synthesized nanoparticles be considered as environmentally friendly and cost-effective options for pesticide degradation.

Simulation of blood flow in a tapered artery with ternary hybrid nanofluid and Jeffrey model

This research simulates flow of blood in a tapered peristaltic artery integrating ternary hybrid nanofluid using the Jeffrey fluid model. The simulation examines the effects of Au, Fe3O4, and Ag nanoparticles on the flow. The artery, modeled as a peristaltic channel, is subjected to nonlinear thermal radiation, magnetic forces, and heat source. The problem is formulated using non-linear Cartesian partial differential equations, which are then transformed into dimensionless form without approximations. Adomian Decomposition Method (ADM) is employed to solve these equations, revealing how normal and shear stress, normal and axial velocities, induced magnetic fields, and temperature profiles vary with changes in relevant parameters. Additionally, biological factors are considered to graph streamlines, providing a comprehensive analysis of the flow dynamics. Some notable results include that adding ternary nanoparticles increases the Nusselt number by 26.03% in Newtonian fluids and 158.69% in Jeffrey fluids, and increasing tapering parameters and wavenumber improves axial and normal velocities, heat transfer, and flow complexity.