Surface Configuration Research Articles

A 10-m resolution impervious surface area map for the greater Mekong subregion from remote sensing images

High-resolution and multi-temporal impervious surface area maps are crucial for capturing rapidly developing urbanization patterns. However, the currently available relevant maps for the greater Mekong subregion suffer from coarse resolution and low accuracy. Addressing this issue, our study focuses on the development of accurate impervious surface area maps at 10-m resolution for this region for the period 2016–2022. To accomplish this, we present a new machine-learning framework implemented on the Google Earth Engine platform that merges Sentinel-1 Synthetic Aperture Radar images and Sentinel-2 Multispectral images to extract impervious surfaces. Furthermore, we also introduce a training sample migration strategy that eliminates the collection of additional training samples and automates multi-temporal impervious surface area mapping. Finally, we perform a quantitative assessment with validation samples interpreted from Google Earth. Results show that the overall accuracy and kappa coefficient of the final impervious surface area maps range from 92.75% to 92.93% and 0.854 to 0.857, respectively. This dataset provides comprehensive measurements of impervious surface coverage and configuration that will help to inform urban studies.

Effect of the acoustic manipulation on single phase immersion cooling performance of discretely heated vertical plate

In the cooling of high heat capacity systems, immersion cooling systems are increasing importance due to the insufficient heat dissipation rates of conventional cooling systems. In this study, the effects of ultrasonic sound waves on cooling performance in single-phase immersion cooling systems were investigated. Experimental study was carried out with ultrasonic sound waves for 9.6 kHz, 14.4 kHz, 19.2 kHz, 24 kHz and silent conditions. In addition, the effects of discrete heat sources on thermal performance were investigated by changing the surface (embedded, 2 mm protruding, 4 mm protruding) and location configurations. According to the results obtained, the highest heat transfer coefficient was calculated as 1703.36 W/m2 °C for the embedded heat source closest to the tank bottom for at 24 kHz frequency. The lowest heat transfer coefficient was calculated as 373.28 W/m2 °C for the maximum protrusion amont heat source closest to the tank upper and when ultrasound manipulation was not applied. In addition, the immersion cooling heat transfer coefficient was increased by 107.49% with ultrasonic sound wave. The heat transfer coefficient increased with increasing ultrasound frequency and decreased with increasing protrusion thickness.

Advancement in biomaterials used in implants

Implants are an important factor in one life as the loss of any part of the body leads to reduced activity of the body thus making the person feel uncomfortable and underconfident. The pharmaceutical industry aims to restore a person to normal function and health regardless of disease or injury he/she is suffering from. This leads to constantly and continuously striving to find new ways and methods which can help in order to overcome such problems. Implants are a method that is been used since the early times. Later on, gold teeth were used as an implant for teeth and slowly the implants became important and widely used. The biocompatibility of an implant is its compatibility with a biological environment. It should be compatible with the body so it is necessary to find materials that are compatible with it and do not cause any harm to the body. For an implant to show its optimum activity it is essential that its physical characteristics, its propensity to corrode in tissue environments, and other important factors such as surface configuration, tissue induction, and their capacity to trigger an inflammatory or rejection function properly. With advances in science and technology, the materials that can be used for making implants have also improved.

Intelligent Reflecting Surface for MIMO VLC: Joint Design of Surface Configuration and Transceiver Signal Processing

With the capability of reconfiguring the wireless electromagnetic environment, intelligent reflecting surface (IRS) becomes a new paradigm for designing future wireless communication systems. In this paper, we consider optical IRS for improving the performance of visible light communication (VLC) under a multiple-input and multiple-output (MIMO) setting, where the mean square error (MSE) of the IRS-aided MIMO VLC is minimized by jointly designing the IRS and transceiver signal processing. To this end, the MIMO channel gains of the IRS-aided VLC are first derived under the point source assumption, based on which the MSE minimization problem is formulated subject to the emission power constraints and the IRS configuration constraints. Next, we propose an alternating optimization algorithm, which decomposes the original problem into three subproblems, to iteratively optimize the IRS configuration, the precoding and detection matrices for minimizing the MSE. Moreover, theoretical analysis on the performance of the proposed algorithm in high and low signal-to-noise ratio (SNR) regimes is investigated, revealing that the joint optimization process can be simplified in such special cases, and the algorithm’s convergence property and computational complexity are also discussed. Finally, numerical results show that IRS-aided schemes significantly reduce the MSE as compared to their counterparts without IRS, and the proposed algorithm outperforms other baseline schemes.

Ultrathin and Bendable mm-Wave Chipless Tags Based on Grounded Periodic Surfaces

Depolarizing mm-wave chipless RFID tags based on grounded dipole resonators characterized by an extremely thin profile are proposed. The use of thin grounded substrate (below 0.15 mm) makes the tags bendable. The presence of the ground plane allows to isolate the response of the tag from surrounding objects making the proposed configuration suitable for non-planar lossy objects like filled water bottles or containers. The periodic surface configuration is employed to obtain a sufficiently large RCS to increase the read range of the tags. The proposed tags operate between 26 GHz and 40 GHz, which allows to achieve the miniaturization necessary for practical scenarios. Toward low cost, thermal printing fabrication is investigated taking lithographic one as a reference. The associated severely loss (introduced by both ultra thin substrate and thermal printing), and the rotation sensitivity of depolarizing label are discussed theoretically and well addressed experimentally. Rotation insensitivity up to 5 degrees and long read range up to 150 cm are experimentally verified. The readability of the proposed ultra-thin tags applied to filled bottles is successfully assessed comparing the performance of tags with and without ground plane.

Optimasi Sudut Baji, Kecepatan Pemakanan & Rpm Terhadap Kekasaran Permukaan Material SCM 440 Dengan Metode Respon Surface (RSM)

The development of manufacturing technology has developed so rapidly. In this study, SCM 440 steel material was used, which is an alloy steel of chromium molybdenum. This steel has the advantages of stable composition,low harmful elements,high steel purity. Surface roughness is important, surface roughness is defined as the irregularity of surface configuration in an object resulting from a finishing process. This study aims to determine the influence of process variables on the surface roughness rate of SCM 440 material by varying the total cutting angles of 700,750 and 800 then variations in feeding speed of 0.08mm, 0.09mm, and 0.10mm and spindle speed or RPM, namely 160,220, and 280 puts / min in the RSM method. The Rspon Surface method is a set of mathematical and statistical techniques that are useful for analyzing problems where several independent variables affect the response variable and determine the optimal value of the process variable. From the results of the study, the value of the Second order yˆ = + 0.092224 X1² + 0.208515 X2² - 0.03661 X3² was obtained. With stationary point value X0 = ( total Cut angle ) = - 0.382409, X0 = (feeding) = 0.161715, X0 = (RPM) = 0.578250. and found the optimal values of Wedge Angle (78.212), Feeding Speed (0.095 mm) and RPM (278.29 put/min). Then it can be analyzed the optimal value that is different from the value of the RSM method framework and if the values are the same then the research fails.

Rice husk coated with copper oxide nanoparticles for 17α-ethinylestradiol removal from an aqueous solution: adsorption mechanisms and kinetics.

The 17 α-ethinylestradiol (EE2) adsorption from aqueous solution was examined using a novel adsorbent made from rice husk powder coated with CuO nanoparticles (CRH). Advanced analyses of FTIR, XRD, SEM, and EDSwere used to identify the classification parameters of a CRH-like surface morphology, configuration, and functional groups. The rice husk was coated with CuO nanoparticles, allowing it to create large surface area materials with significantly improved textural qualities with regard to functional use and adsorption performance, according to a detailed characterization of the synthesized materials. The adsorption process was applied successfully with elimination effectiveness of 100% which can be kept up to 61.3%. The parameters of adsorption were affecting the adsorption process significantly. Thermodynamic data stated that the process of adsorption was endothermic, spontaneous, chemisorption and the molecules of EE2 show affinity with the CRH. It was discovered that the adsorption process controlled by a pseudo-second-order kinetic model demonstrates that the chemisorption process was controlling EE2 removal. The Sips model is regarded as optimal for representing this practice, exhibiting a significantly high determination coefficient of 0.948. This coefficient implies that the adsorption mechanism indicates the occurrence of both heterogeneous and homogeneous adsorption. According to the findings, biomass can serve as a cheap, operative sorbent to remove estrogen from liquified solutions.

Optimal bi-planar gradient coil configurations for diamond nitrogen-vacancy based diffusion-weighted NMR experiments

IntroductionDiffusion weighting in optically detected magnetic resonance experiments involving diamond nitrogen-vacancy (NV) centers can provide valuable microstructural information. Bi-planar gradient coils employed for diffusion weighting afford excellent spatial access, essential for integrating the NV-NMR components. Nevertheless, owing to the polar tilt of roughly 55^{circ } of the diamond NV center, the primary magnetic field direction must be taken into account accordingly.MethodsTo determine the most effective bi-planar gradient coil configurations, we conducted an investigation into the impact of various factors, including the square side length, surface separation, and surface orientation. This was accomplished by generating over 500 bi-planar surface configurations using automated methods.ResultsWe successfully generated and evaluated coil layouts in terms of sensitivity and field accuracy. Interestingly, inclined bi-planar orientations close to the NV–NMR setup’s requirement, showed higher sensitivity for the transverse gradient channels than horizontal or vertical orientations. We fabricated a suitable solution as a three-channel bi-planar double-layered PCB system and experimentally validated the sensitivities at 28.7 mathrm mT/m/A and 26.8 mathrm mT/m/A for the transverse G_{x} and G_{y} gradients, and 26 mathrm mT/m/A for the G_{z} gradient.DiscussionWe found that the chosen relative bi-planar tilt of 35^{circ } represents a reasonable compromise in terms of overall performance and allows for easier coil implementation with a straight, horizontal alignment within the overall experimental setup.

Defective Au nanoparticles manipulated by Au-MgxAl-LDH interplay for alkali-free oxidation of benzyl alcohol

Supported gold catalyst, especially in terms of nanosized particles with defective surface and low-coordinated structure, plays a vital role in the heterogeneous catalysis. However, such defective Au nanoparticles are hardly acquired when supporting on non-reducible metal oxides/hydroxides due to insufficient Au-support interaction. In this work, we found that the defective Au NPs could be fabricated via the strong interplay between Au and crystal lattices of layered double hydroxides-MgxAl-LDH. Experimental and theoretical evidences revealed that the formation of a preferential-oriented LDH(015) plane enabled the surface configuration for defective Au centers with the maximized number of step sites at Mg/Al ratio of 3.0–3.5. The optimized Au/Mg3.5Al-LDH catalyst shows a boosting catalytic activity for benzyl alcohol oxidation (TOF, 1008 h−1) at only 80 °C with the lowest activation energy in the absence of alkali. The work provides a new insight for manipulating the defective-enriched Au particles via the fine-tuning Au-LDH interplay for alkali-free selective oxidations.

Enhancement and localization of atomistic polarity and polarizability memory in light scattering upon hydrogenation of luminescent spherical 1 nm Si nanoparticles

The classical light interactions of nanosilicon, which is a dielectric material, are exceedingly weak for radius r ≪ λ (wavelength), scaling as r6. It exhibits geometrical anisotropy-based depolarization, which is the basis for the very weak response in isotropic structures (nanosphere). Recently, surface enhanced Raman scattering (SERS) in DNA decorated with ultrasmall Si nanoparticles has been demonstrated, affording an effective alternative to plasmon–metal particles. In this paper, we execute fundamental quantum atomistic computation of 1 nm hydrogenated Si particles, with different surface reconstruction and termination, including Si–H, H–Si–Si–H (dimer molecules), or oxygenated dimer bridges (H–Si–O–Si–H). We obtain the mechanical vibrational modes of the particles. Our results show that by changing the surface configuration one can control the symmetry and normal vibration modes, and enhance the polarizability, polarity, and light interactions (scattering, absorption, and depolarization/memory). The low frequency polarizability (Raman scattering) shifts spatially from the interior to the surface, while the infrared polarity remains on the surface, but its bandwidth narrows spectrally. The results support previous infrared absorption and light scattering and depolarization measurements, as well recent SERS, which enable Si nanoparticles to be an effective alternative to plasmonic metal particles. Molecular surface reconstruction in terms of Si dimers and bridges were suggested as the source of the novel nonlinear and anisotropic luminescence and photonic properties of Si nanoparticles. Such control affords potential for optimizing the design and operation of a wide range of opto-electronic advanced scattering and luminescence devices.

Stepwise dissolution of silica surface in alkaline solution revealed by molecular modeling

AbstractThe atomic scale solid–liquid interfacial process dominates the macro‐dissolution of silica, yet its direct experimental observation is challenging. Here we employed the reactive molecular dynamics to model this process in alkaline condition. An elevated temperature strategy under canonical ensemble (NVT) was applied to accelerate the process for sufficient sampling at temporal domain. A stepwise transformation from fully linked SiO4 network (Q3 and Q4) to reduced linkage and eventually aqueous species (Q0) was revealed. The simulated dissolution rate agrees well with the value predicted by empirical model. By tracing hydrogen atoms, we found that the dehydroxylated silica surfaces in alkaline electrolyte solutions underwent a transition from Si–O–Si bond cleavage‐dominated (mainly reacted with OH−) to hydroxylation‐dominated surface reactions. The free‐energy reconstruction of well‐tempered metadynamics reveals that 1500 K accelerates dissolution without altering the reaction pathways. These findings offer novel insights into the evolution of atomic‐scale surface configurations during the dissolution kinetics of silica.

Modulating the electronic structures of cobalt-organic frameworks for efficient electrocatalytic oxygen evolution

The oxygen evolution reaction (OER) is a key process in various energy storage/generation technologies. Tuning the electronic structures of catalysts is an effective approach to improve the catalyst’s activity. In this work, we synthesized Ce-doped cobalt-organic frameworks with benzene-1, 4-dicarboxylic acid (BDC) as the ligand as efficient OER electrocatalysts (denoted as Co3Ce1 BDC) with excellent stability and improved catalytic performance. The introduced Ce in Co3Ce1 BDC changes the surface configuration and tunes electronic structures of the active Co site, leading to enhanced interaction between intermediates and catalysts. Besides, the specific surface area, reaction kinetics, charge transfer efficiency, and turnover frequency are also improved in the presence of Ce. As a result, the Co3Ce1 BDC demonstrated excellent performance with a low overpotential of 285 mV at a current of 10 mA·cm−2, a preferable Tafel slope of 56.1 mV·dec−1, and an excellent durability in 1 M KOH, indicating the potential for practical applications in water splitting and other energy storage technologies wherein the OER plays a critical role. Comprehensive theoretical calculations and modeling further identified the key role of Ce in modulating the electronic structure and OER activity of cobalt-organic frameworks. Most importantly, this work provides a new strategy to the development of efficient cobalt-organic framework catalysts in OER-related applications.

A step toward correct interpretation of XPS results in metal oxides: A case study aided by first-principles method in ZnO.

Metal oxide semiconductors constitute a vast group of materials whose physical properties are greatly affected by native defects. For decades, x-ray photoelectron spectroscopy (XPS) has been widely used in defect analysis. However, correct interpretation of XPS results remains a difficult task. In this work, we present a detailed first-principles study on the core-level shift of the most stable and commonly cited crystal imperfections in ZnO, including O and -OH species at the surface with different coverages and bulk defects, including O interstitial (Oi), O vacancy in the +2 charge state (Vo2+), and the neutral vacancy (Vo0). The O1s core level spectrum is simulated and compared with experiments to understand the correlation between local atomic structures and features in the O1s spectrum. In particular, our results indicate that the widely adopted assignment in the defect analysis of ZnO, which links the defect peak in XPS to Vo, the most stable defect, is very likely a misinterpretation. Theoretical analysis indicates that there are no distinguishable XPS features arising from the Vo defect. Furthermore, we show that the commonly observed defect-related peak instead arises due to Oi or specific surface configurations. Given the importance of native defects in materials performance, misinterpretation of XPS results may lead to erroneous conclusions regarding materials properties. This work provides a first-principles basis for the analysis of oxide defects through XPS.

Flow boiling heat transfer enhancement in vertical minichannel heat sink with non-uniform microcavity arrays under electric field

Effects of electrohydrodynamics (EHD) on the bubble behavior and enhanced heat dissipation mechanism for four surface configurations and various heat fluxes in an upward flowing minichannel heat sink were studied experimentally. Three different minichannel configurations with microcavities array were fabricated using direct metal laser sintering. Flow boiling experiments of nanofluid (SiO2-R141b) under different nonuniform electric fields were performed. Homogeneity test of Variance Analysis was introduced to analyze the effect of design and operation parameters on heat transfer. Coupled effect of microcavity and electric field was further found to improve boiling heat transfer efficiency. Visualization shows that the diameter of small bubbles leaving microcavity increased under electric field. The bubbles wiggled between wire electrode and heated wall by action of electric field in bubbly flow district. Furthermore, the mechanism of perturbation of small bubbles flowing along the heating wall under electric field was discussed. It was revealed that the micro-concave cavity array distributed dense downstream and sparse upstream had a large impact on heat transfer coefficient (HTC), especially under electric field. The maximum synthetic enhancement factor of 2.11 was obtained for given flow conditions. Furthermore, a new predictive equation was proposed by a nonlinear regression equation to consider the effects of micro-concave cavity distribution and electric field factors on thermal transfer performance, and this correlation can predict the HTC affected by non-uniform micro-concave arrays well within the ± 10% error band.

Current Advances on the Single-Atom Nanozyme and Its Bioapplications.

Nanozymes, a class of nanomaterials mimicking the function of enzymes, have aroused much attention as the candidate in diverse fields with the arbitrarily tunable features owing to the diversity of crystalline nanostructures, composition, and surface configurations. However, the uncertainty of their active sites and the lower intrinsic deficiencies of nanomaterial-initiated catalysis compared with the natural enzymes promote the pursuing of alternatives by imitating the biological active centers. Single-atom nanozymes (SAzymes) maximize the atom utilization with the well-defined structure, providing an important bridge to investigate mechanism and the relationship between structure and catalytic activity. They have risen as the new burgeoning alternative to the natural enzyme from in vitro bioanalytical tool to in vivo therapy owing to the flexible atomic engineering structure. Here, focus is mainly on the three parts. First, a detailed overview of single-atom catalyst synthesis strategies including bottom-up and top-down approaches is given. Then, according to the structural feature of single-atom nanocatalysts, the influence factors such as central metal atom, coordination number, heteroatom doping, and the metal-support interaction are discussed and the representative biological applications (including antibacterial/antiviral performance, cancer therapy, and biosensing) are highlighted. In the end, the future perspective and challenge facing are demonstrated.

Numerical Simulations of the Driving Process of a Wheeled Machine Tire on a Snow-Covered Road

Wheeled machines, such as agricultural tractors, snowplows, and wheeled mobile robots, usually work on icy or snow-covered roads. Therefore, it is very important to study the driving and slip resistance of the tires of these machines. In this paper, we investigate the driving behavior of tires on snow-covered terrain by means of numerical simulations. A high-fidelity snow-covered road model is established, and smoothed particle hydrodynamics (SPH) and the finite element method (FEM) are employed to account for the behaviors of the snow layers and the pavement, respectively. We use the node-to-surface algorithm for the contact interactions between the snow and the pavement. The SPH parameters for the snow are calibrated by means of a triaxial compression experiment. A simplified tire model is established as well, using the FEM, and the effectiveness of the model is demonstrated via comparisons with the experimental data in terms of stiffness. Finally, the tire driving performance on the snow-covered road is simulated, and the influence of the tire surface configuration, external load, inflation pressure, and snowpack compression on the tire traction behaviors is systematically investigated.

Ultrasensitive Surface Plasmon Resonance Sensor with a Feature of Dynamically Tunable Sensitivity and High Figure of Merit for Cancer Detection.

Cancer is one of the leading causes of death worldwide, and it is well known that an early detection of cancer in a human body will provide an opportunity to cure the cancer. Early detection of cancer depends on the sensitivity of the measuring device and method, where the lowest detectable concentration of the cancerous cell in a test sample becomes a matter of high importance. Recently, Surface Plasmon Resonance (SPR) has proven to be a promising method to detect cancerous cells. The SPR method is based on the detection of changes in refractive indices of samples under testing and the sensitivity of such a SPR based sensor is related to the smallest detectable change in the refractive index of the sample. There exist many techniques where different combinations of metals, metal alloys and different configurations have been shown to lead to high sensitivities of the SPR sensors. Based on the difference in the refractive index between a normal healthy cell and a cancerous cell, recently, SPR method has been shown to be applicable to detect different types of cancers. In this work, we propose a new sensor surface configuration that comprises of gold-silver-graphene-black phosphorus to detect different cancerous cells based on the SPR method. Additionally, recently we proposed that the application of electric field across gold-graphene layers that form the SPR sensor surface can provide enhanced sensitivity than that is possible without the application of electrical bias. We utilized the same concept and numerically studied the impact of electrical bias across the gold-graphene layers combined with silver and black Phosphorus layers which forms the SPR sensor surface. Our numerical results have shown that electrical bias across the sensor surface in this new heterostructure can provide enhanced sensitivity compared to the original unbiased sensor surface. Not only that, our results have shown that as the electrical bias increases, the sensitivity increases up to a certain value and stabilizes at a still improved sensitivity value. Such dependence of sensitivity on the applied bias provides a dynamic tunability of the sensitivity and figure-of-merit (FOM) of the sensor to detect different types of cancer. In this work, we used the proposed heterostructure to detect six different types of cancers: Basal, Hela, Jurkat, PC12, MDA-MB-231, and MCF-7. Comparing our results to work published recently, we were able to achieve an enhanced sensitivity ranging from 97.2 to 1851.4 (deg/RIU) and FOM values ranging from 62.13 to 89.81 far above the values presented recently by other researchers.

Bond performance of fiber reinforced polymer bars in normal- and high-strength concrete

The structural performance of reinforced concrete (RC) members depends on the bond between the reinforcing bars and surrounding concrete. Unlike steel bars, fiber-reinforced polymer (FRP) bars are manufactured with different fiber types (glass, basalt, carbon, and aramid) and have different mechanical properties and surface configurations (sand-coated, deformed, grooved, sand-coated over helical wrapping). These differences impact the bond performance between the FRP bars and concrete. This paper investigates the bond performance of new generation and different FRP bars embedded in concrete. A total of 87 pullout specimens were constructed and tested until failure. The test results are presented and discussed. The test parameters include (i) fiber type (glass or carbon), (ii) surface configuration (sand-coated, deformed, or grooved), (iii) No. 4 to No. 8 (13 to 25.4 mm diameter) bar diameters), and (iv) concrete strength (normal- or high-strength concrete: NSC or HSC). Specimens with deformed 10 M or 15 M steel bars were also fabricated as controls and tested for comparison. The embedment length and block dimensions were also considered to ensure pullout-failure mode. The test results reveal that increasing the bar diameter generally reduced the bond strength of the FRP bars, while the bar diameter had insignificant impact on the steel bars. There was a positive relationship between the concrete compressive strength and the bond strength gained. The anticipated failure modes with the high concrete strength were at the fiber resin interface due to the high confinement generated by high-strength concrete. With the lower strength, failure usually occurred at the resin–concrete interface. In addition, the test results were used to assess different analytical models for bond stress-slip relationships.

Hybridized nanofluidic convection in umbrella-shaped porous thermal systems with identical heating and cooling surfaces

PurposeThis study aims to investigate the impact of different heater geometries (flat, rectangular, semi-elliptical and triangular) on hybrid nanofluidic (Cu–Al2O3–H2O) convection in novel umbrella-shaped porous thermal systems. The system is top-cooled, and the identical heater surfaces are provided centrally at the bottom to identify the most enhanced configuration.Design/methodology/approachThe thermal-fluid flow analysis is performed using a finite volume-based indigenous code, solving the nonlinear coupled transport equations with the Darcy number (10–5 ≤ Da ≤ 10–1), modified Rayleigh number (10 ≤ Ram ≤ 104) and Hartmann number (0 ≤ Ha ≤ 70) as the dimensionless operating parameters. The semi-implicit method for pressure linked equations algorithm is used to solve the discretized transport equations over staggered nonuniform meshes.FindingsThe study demonstrates that altering the heater surface geometry improves heat transfer by up to 224% compared with a flat surface configuration. The triangular-shaped heating surface is the most effective in enhancing both heat transfer and flow strength. In general, flow strength and heat transfer increase with rising Ram and decrease with increasing Da and Ha. The study also proposes a mathematical correlation to predict thermal characteristics by integrating all geometric and flow control variables.Research limitations/implicationsThe present concept can be extended to further explore thermal performance with different curvature effects, orientations, boundary conditions, etc., numerically or experimentally.Practical implicationsThe present geometry configurations can be applied in various engineering applications such as heat exchangers, crystallization, micro-electronic devices, energy storage systems, mixing processes, food processing and different biomedical systems (blood flow control, cancer treatment, medical equipment, targeted drug delivery, etc.).Originality/valueThis investigation contributes by exploring the effect of various geometric shapes of the heated bottom on the hydromagnetic convection of Cu–Al2O3–H2O hybrid nanofluid flow in a complex umbrella-shaped porous thermal system involving curved surfaces and multiphysical conditions.

Effect of modifiers on the structure formation and properties of nickel-phosphorus coatings applied to powder steels

The paper shows the effect of solution temperature on the deposition rate of applying composite nickel-phosphorus coatings modified with boron nitride and polytetrafluoroethylene to powder samples made of improved P40, P40Kh and P40KhN steels obtained by hot stamping of porous sintered blanks. It has been experimentally established that within the range of 70–90 °C, the average deposition rate of modified BN and (C2F4)n coatings is 15–19 μm/h, while the chemical composition of the improved steels and the surface configuration of the samples have no effect on the coating build-up rate. The mechanism of the formation of the structure and properties of nickel-phosphorus coatings (NiPC) without additives and those of NiPC modified with boron nitride and polytetrafluoroethylene during deposition, sintering and running-in is revealed. It has been established that immediately after deposition, Ni–P coating has an amorphous structure with inclusions of nickel particles, and its microhardness does not exceed 380–390 MPa with no modifiers added. In the dry friction mode at the running-in stage, Ni12P5 and Ni2P phases are formed in the modified Ni–P coatings, allowing to improve their tribological properties, and in the steady-state mode, the phase disordering of the modified NiPC proceeds. It has been experimentally revealed that the coefficient of friction and wear decrease by 1.3 times when only (C2F4)n is introduced into Ni–P coating, these indices decrease by 1.6 times when only BN is added, and they decrease almost twice when BN and (C2F4)n are introduced together. It has been established that upon the combined (complex) modification of NiPC with BN and (C2F4)n after the heat treatment, there is almost no nickel oxide phase, nickel boride of NiB type is formed in the coating during running-in, and its content does not decrease when entering the stationary friction mode, thus increasing tribotechnical properties of the coating. During running-in, the coefficient of friction of Ni–P + BN + (C2F4)n coating decreases from 0.28 to 0.19, and the wear rate of such a coating in the stationary friction mode is 1.5 mg/h. The efficiency of applying the antifriction nickel-phosphorus coatings modified with BN + (C2F4)n to the products made of the improved structural steels obtained by various methods has been theoretically and experimentally substantiated.