Tip Radius Research Articles

Research on methylene blue degradation based on multineedle-to-plane liquid dielectric barrier discharge mode

Advanced oxidation processes (AOPs) focusing on non-thermal plasma induced by dielectric barrier discharge (DBD) are adequate sources of diverse reactive oxygen species beneficial for water and wastewater treatment. The degradation of methylene blue (MB) was investigated using plasma liquid dielectric barrier discharge with a multineedle-to-plane reactor. MB at 20 mg/L concentration was almost completely degraded after 40 min of treatment. In this study, several important parameters, such as input voltage, initial concentration, initial pH, discharge gap, tip radius of curvature, and presence of radical, were evaluated, and their effects on MB degradation rate were investigated. The degradation rate of MB increased with initial pH. By contrast, the degradation rate showed a downward trend with increasing initial concentration, discharge distance, and tip curvature radius. O3 and H2O2 produced during the degradation process considerably influenced the entire degradation process, especially when the quenching agents of HO⋅, O2·- and e− were added, and the degradation efficiency was obviously reduced. According to the measured spectrum, the possible process of the discharge process was analyzed, and the COMSOL finite element simulation is performed to obtain the visualization of the discharge model. This work can provide exploratory platforms for comprehensively understanding and enhancing MB degradation in DBD plasma technology.

Research on calculation of grinding surface roughness

In machining processes, grinding is often chosen as the final machining method. Grinding is often chosen as the final machining method. This process has many advantages such as high precision and low surface roughness. It depends on many parameters including grinding parameters, dressing parameters and lubrication conditions. In grinding, the surface roughness of a workpiece has a significant influence on quality of the part. This paper presents a study of the grinding surface roughness predictions of workpieces. Based on the previous studies, the study built a relationship between the abrasive grain tip radius and the Standard marking systems of the grinding wheel for conventional and superabrasive grinding wheels (diamond and CBN abrasive). Based on this, the grinding surface roughness was predicted. The proposed model was verified by comparing the predicted and experimental results. Appling the research results, the surface roughness when grinding three types of steel D3, A295M and SAE 420 with Al2O3 and CBN grinding wheels were predicted. The predicted surface roughness values were close to the experimental values, the average deviation between predictive results and experimental results is 15.11 % for the use of Al2O3 grinding wheels and 24.29 % for the case of using CBN grinding wheels. The results of the comparison between the predicted model and the experiment show that the method of surface roughness presented in this study can be used to predict surface roughness in each specific case. The proposed model was verified by comparing the predicted and measured results of surface hardness. This model can be used to predict the surface hardness when surface grinding

Parallel-GPU-accelerated adaptive mesh refinement for three-dimensional phase-field simulation of dendritic growth during solidification of binary alloy

In the phase-field simulation of dendrite growth during the solidification of an alloy, the computational cost becomes extremely high when the diffusion length is significantly larger than the curvature radius of a dendrite tip. In such cases, the adaptive mesh refinement (AMR) method is effective for improving the computational performance. In this study, we perform a three-dimensional dendrite growth phase-field simulation in which AMR is implemented via parallel computing using multiple graphics processing units (GPUs), which provide high parallel computation performance. In the parallel GPU computation, we apply dynamic load balancing to parallel computing to equalize the computational cost per GPU. The accuracy of an AMR refinement condition is confirmed through the single-GPU computations of columnar dendrite growth during the directional solidification of a binary alloy. Next, we evaluate the efficiency of dynamic load balancing by performing multiple-GPU parallel computations for three different directional solidification simulations using a moving frame algorithm. Finally, weak scaling tests are performed to confirm the parallel efficiency of the developed code.

Force‐Electric Coupling of Nanoscale Ferroelectric Domains Based on Piezoelectric Force Microscopy (PFM)

Piezoelectric and ferroelectric materials are widely used in various types of microelectronics due to their excellent mechanical and electrical coupling characteristics. In recent years, piezoelectric force microscopy has developed into a powerful tool for analyzing nanoscale ferroelectric materials. However, quantitative analysis based on PFM is difficult to properly study it. This article studies the related issues of PFM quantitative analysis. First, the relationship between the effective piezoelectric coefficient and piezoelectric coefficient of different materials is analyzed from the PFM nanometer scale to analyze the force‐electric coupling effect. The study found that the effective piezoelectric coefficient is closely related to the intrinsic electroelastic constant of the material. Secondly, the analysis of the nanoscale piezoelectric deformation of ferroelectric materials shows that under the conductive SPM probe, as the clustering with the probe increases, the in‐plane displacement first increases and then decreases, and the out‐of‐plane displacement gradually decreases. Finally, the half‐width region of the nanoscale ferroelectric response domain was analyzed by PFM. Taking the in‐plane and out‐of‐plane domains of 180° and 90° domains as examples, the relationship between the response boundary domain and the tip radius was analyzed, and the results showed that whether the PFM can effectively solve the problem of detection and analysis depends on the half‐width of the response boundary domain, and the resolution of the vertical PFM is higher than that of the lateral PFM.

口絞り成形時のローラー先端曲率半径が加工欠陥の発生に及ぼす影響

口絞り成形時のローラー先端曲率半径が加工欠陥の発生に及ぼす影響

Shortcomings of the Derjaguin–Muller–Toporov model in dynamic atomic force microscopy

Force–distance curves recorded by frequency modulated atomic force microscopy (FM AFM) provide insight into the tip–sample mechanics. For quantitative analysis, FM AFM is able to separate conservative from dissipative forces by simultaneously measuring amplitude–distance and frequency–distance curves. Here, we report on the conservative forces in the gentle tip–sample contact of mesoscopic tips at low Tabor parameters. We introduce an analytical expression for the frequency shift based on the Derjaguin–Muller–Toporov (DMT) contact model to simplify the comparison between the experiment and theory. From the analytical formulas, a scaling law between the tip radius and minimal frequency shift is found, which is supported by experimental data. Although excellent fits for full frequency–distance curves are possible, the resulting material properties do not match the accepted literature values. We suspect that these flaws are a consequence of the incomplete treatment of attractive forces and DMT’s strain-stiffness approximation, rendering DMT-based models inappropriate to measure material properties by dynamic AFM in gentle contact.

Quantitative Mapping of Unmodulated Temperature Fields with Nanometer Resolution.

Quantitative mapping of temperature fields with nanometric resolution is critical in various areas of scientific research and emerging technology, such as nanoelectronics, surface chemistry, plasmonic devices, and quantum systems. A key challenge in achieving quantitative thermal imaging with scanning thermal microscopy (SThM) is the lack of knowledge of the tip-sample thermal resistance (RTS), which varies with local topography and is critical for quantifying the sample temperature. Recent advances in SThM have enabled simultaneous quantification of RTS and topography in situations where the temperature field is modulated enabling quantitative thermometry even when topographical features cause significant variations in RTS. However, such an approach is not applicable to situations where the temperature modulation of the device is not readily possible. Here we show, using custom-fabricated scanning thermal probes (STPs) with a sharp tip (radius ∼25 nm) and an integrated heater/thermometer, that one can quantitatively map unmodulated temperature fields, in a single scan, with ∼7 nm spatial resolution and ∼50 mK temperature resolution in a bandwidth of 1 Hz. This is accomplished by introducing a modulated heat input to the STP and measuring the AC and DC responses of the probe's temperature which allow for simultaneous mapping of the tip-sample thermal resistance and sample surface temperature. The approach presented here─contact resistance resolved scanning thermal microscopy (CR-SThM)─can greatly facilitate temperature mapping of a variety of microdevices under practical operating conditions.

Predictive Analytical Modeling of Thermo-Mechanical Effects in Orthogonal Machining.

Factor relationships in a machining system do not work in pairs. Varying the cutting parameters, materials machined, or volumes produced will influence many machining characteristics. For this reason, we are attempting to better understand the effect of the Johnson-Cook (J-C) law of behavior on cutting temperature prediction. Thus, the objective of the present study is to investigate, experimentally and theoretically, the tool/material interactions and their effects on dust emission during orthogonal cutting. The proposed approach is built on three steps. First, we established an experimental design to analyze, experimentally, the cutting conditions effects on the cutting temperature under dry condition. The empirical model which is based on the response surface methodology was used to generate a large amount of data depending on the machining conditions. Through this step, we were able to analyze the sensitivity of the cutting temperature to different cutting parameters. It was found that cutting speed, tool tip radius, rake angle, and the interaction between the cutting speed and the rake angle explain more than 84.66% of the cutting temperature variation. The cutting temperature will be considered as a reference to validate the analytical model. Hence, a temperature prediction model is important as a second step. The modeling of orthogonal machining using the J-C plasticity model showed a good correlation between the predicted cutting temperature and that obtained by the proposed empirical model. The calculated deviations for the different cutting conditions tested are relatively acceptable (with a less than 10% error). Finally, the established analytical model was then applied to the machining processes in order to optimize the cutting parameters and, at the same time, minimize the generated dust. The evaluation of the dust generation revealed that the dust emission is closely related to the variation of the cutting temperature. We also noticed that the dust generation can indicate different phenomena of fine and ultrafine particles generation during the cutting process, related to the heat source or temperature during orthogonal machining. Finally, the effective strategy to limit dust emissions at the source is to avoid the critical temperature zone. For this purpose, the two-sided values can be seen as combinations to limit dust emissions at the source.

Mechanical tailoring of dislocation densities in SrTiO3 at room temperature

AbstractDislocation‐tuned functional properties such as electrical conductivity, thermal conductivity, and ferroelectric properties in oxides are attracting increasing research interest. A prerequisite for harvesting these functional properties in oxides requires successful introduction and control of dislocation density and arrangement without forming cracks, which is a great challenge due to their brittle nature. Here, we report a simple method to mechanically tailor the dislocation densities in single‐crystal perovskite SrTiO3. By using a millimeter‐sized Brinell indenter, dislocation densities from ∼1010 to ∼1013 m−2 are achieved by increasing the number of indenting cycles. Depending on tip radius and indenting load, large and crack‐free plastic zones over hundreds of micrometers are created. The dislocation multiplication mechanisms are discussed, and the work hardening in the plastic zone is evaluated by micro‐hardness measurement as a function of dislocation density. This simple approach opens many new opportunities in the area of dislocation‐tuned functional and mechanical studies.

Crack root radius effect on stress fields under nonlinear

The influence of crack root radius and plastic material properties on the crack tip fields was evaluated by strain gradient plasticity theory, and classical plasticity theory. A conventional mechanism-based strain gradient (CMSG) plasticity theory was used in the study. The stress fields in single edge tension specimen are investigated numerically for a wide range of the crack tip radius variations. Five values of the crack tip curvature radius ρ = 0 (mathematical notch); ρ = 25 nm, ρ = 30 nm, ρ = 60 nm and ρ = 100 nm were investigated. The strain hardening exponent varied from N = 0.075 to N = 0.4. A stress analysis by CMSG plasticity was performed for two values of the Taylor’s length parameter l = 1μm and l = 10μm. The boundaries of the local areas, where the influence of the crack tip radius is realized were determined for both HRR and CMSG plasticity. The sizes of the dominance area of the strain gradient plasticity were established and their approximation equations were presented. The influence of the plastic properties and the Taylor’s length scale parameter on the stress fields in the vicinity of rhe crack tip was estimated for the strain gradient plasticity.

Chemically characterizing the cortical cell nano-structure of human hair using atomic force microscopy integrated with infrared spectroscopy (AFM-IR).

The use of conventional microscopy and vibrational spectroscopy in the optical region to investigate the chemical nature of hair fibres on a nanometre scale is frustrated by the diffraction limit of light, prohibiting the spectral elucidation of nanoscale sub-structures that contribute to the bulk properties of hair. The aim of this work was to overcome this limitation and gain unprecedented chemical resolution of cortical cell nano-structure of hair. The hybrid technique of AFM-IR, combining atomic force microscopy with an IR laser, circumvents the diffraction limit of light and achieves nanoscale chemical resolution down to the AFM tip radius. In this work, AFM-IR was employed on ultra-thin microtomed cross-sections of human hair fibres to spectrally distinguish and characterize the specific protein structures and environments within the nanoscale components of cortical cells. At first, a topographical and chemical distinction between the macrofibrils and the surrounding intermacrofibillar matrix was achieved based on 2.5×2.5μm maps of cortical cell cross-sections. It was found that the intermacrofibrillar matrix has a large protein content and specific cysteine-related residues, whereas the macrofibrils showed bigger contributions from aliphatic amino acid residues and acidic-/ester-containing species (e.g. lipids). Localized spectra recorded at a spatial resolution of the order of the AFM tip radius enabled the chemical composition of each region to be determined following deconvolution of the Amide-I and Amide-II bands. This provided specific evidence for a greater proportion of α-helices in the macrofibrils and correspondingly larger contributions of β-sheet secondary structures in the intermacrofibrillar matrix, as inferred in earlier studies. Analysis of the parallel and antiparallel β-sheet structures, and of selected dominant amino acid residues, yielded further novel composition and conformation results for both regions. In this work, we overcome the diffraction limit of light using atomic force microscopy integrated with IR laser spectroscopy (AFM-IR) to characterize sub-micron features of the hair cortex at ultra-high spatial resolution. The resulting spectral analysis shows clear distinctions in the Amide bands in the macrofibrils and surrounding intermacrofibrillar matrix, yielding novel insight into the molecular structure and intermolecular stabilization interactions of the constituent proteins within each cortical component.

Constructal design for dual-pressure axial-flow turbine in organic Rankine cycle

Dual-pressure organic Rankine cycle (ORC) has great advantages in low-temperature waste heat utilization systems. There are few studies on optimizing the performance and structure of the dual-pressure turbine, which is a key part of the dual-pressure ORC. The constructal design is performed for a dual-pressure axial-flow turbine (AFT) in a dual-pressure ORC to improve the turbine and cycle performances. Total power is taken as optimization objective function, volume ratio of the high-pressure turbine (HPT) and inlet pressure of the low-pressure turbine (LPT) are chosen as optimization variables, and total volume is employed as a constraint. After obtaining the optimization results, the impacts of some flow and structure parameters are analyzed. Furthermore, performances of the dual- and single-pressure AFTs are contrasted. The results demonstrate that the total powers of the dual-pressure AFT after the primary and twice optimizations are increased by 0.97% and 1.69% compared with the initial value, respectively. After the twice optimization, the optimal construct of the dual-pressure AFT is that the volume ratio of the HPT and inlet pressure of the LPT are 0.072 and 695 kPa, respectively. The nozzle inlet hub to tip radius ratios of the two turbines and the working-fluid mass flow rate ratio positively impact the total power, while the total volume hurts it. Besides, the dual-pressure AFT has a better performance advantage than the single-pressure AFT, and the total power of the former is 16.59% higher than that of the latter. The results confirm that the dual pressure is more suitable for low-temperature waste heat utilization systems than the single pressure and provide strategies for improving the turbine performance.

Size Effect of CeO2 Particle on Nanoscale Single-Asperity Sliding Friction

The size of abrasive particle has a great impact on the fundamental friction behavior and mechanical properties of the abrasive during ultra-precision polishing performance. Here, the size effect of the tribological behavior and mechanical properties of CeO2 single abrasive were studied. Experimental results show that the size effect plays a role on coefficient of friction (COF) of each regime in single-asperity sliding friction, especially in ploughing and cutting regimes. The residual depth of the scratch and COF both decrease with the increase of the CeO2 tip radius. These results relate to the mechanical properties of CeO2 nanoparticles. We found that the effective modulus increases with the decrease of abrasive size, which corresponds to the size effect of the single-asperity sliding friction experiment.

Electrical Tree Driven Breakdown of XLPE Under Step Stress Breakdown Test at Multiple Frequencies

The electrical treeing of a 33 kV XLPE cable is investigated on a pin-plane electrode system in the frequency range of 50–650 Hz. Cable specimens are created with needle electrodes having a tip radius of 1 µm and a tip distance of 0.75 ± 0.1 mm. Step stress tests are conducted at a step increase of 1 kV peak voltage for step times of 15 seconds and 75 seconds. The breakdown instances of the specimens are recorded to obtain the time to breakdown (TTB), breakdown voltage and the polarity of the breakdown voltage. In addition, the breakdown path is observed using a stereo microscope. It is found that the normalized TTB and the breakdown voltage exhibit a decreasing trend with respect to the frequency for step stress tests. A high percentage of samples are broken down in the negative half cycle of the applied voltage. Microscopic imaging shows that the corresponding electrical trees are branch type trees for all the frequencies. The observations for normalized TTB and voltage variation is attributed to the phenomenon of space charge limiting electrical field variation with frequency.

Numerical Study on the Effect of Electric Field Non-uniformity on the Pulse Characteristics of Positive Corona Discharge in SF6/N2 Gas Mixtures

This paper establishes a two-dimensional axisymmetric needle-to-plane geometry model in SF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> /N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> gas mixtures to simulate the effect of the electric field non-uniformity on the pulse characteristics of positive corona discharge. By changing the needle tip radii from 25 µm to 300 µm, the corona discharge process under different electric field non-uniformity is simulated. Meanwhile, the simulated results are verified by the experiments on a corona discharge experimental setup. The results show that the rising and falling edges of positive corona current pulses correspond to the development and termination of streamers, respectively. The sub-pulse will be generated during the formation of the first current pulse, and this phenomenon is closely related to the applied voltage. The generation of sub-pulse is expected to be a feature of positive corona discharge in SF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> /N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> gas mixtures entering the brush-pulse stage. With increasing the electric field non-uniformity, the onset voltages of two characteristic pulse stages, including the streamer-pulse stage and brush-pulse stage, decrease. Moreover, the first current pulse amplitude increases, and the pulse-repetition rate presents an approximate exponential increasing trend.

Hydration Dynamics and the Future of Small-Amplitude AFM Imaging in Air.

Here, we discuss the effects that the dynamics of the hydration layer and other variables, such as the tip radius, have on the availability of imaging regimes in dynamic AFM—including multifrequency AFM. Since small amplitudes are required for high-resolution imaging, we focus on these cases. It is possible to fully immerse a sharp tip under the hydration layer and image with amplitudes similar to or smaller than the height of the hydration layer, i.e., ~1 nm. When mica or HOPG surfaces are only cleaved, molecules adhere to their surfaces, and reaching a thermodynamically stable state for imaging might take hours. During these first hours, different possibilities for imaging emerge and change, implying that these conditions must be considered and reported when imaging.

Compound jetting from bubble bursting at an air-oil-water interface

Bursting of bubbles at a liquid surface is ubiquitous in a wide range of physical, biological, and geological phenomena, as a key source of aerosol droplets for mass transport across the interface. However, how a structurally complex interface, widely present in nature, mediates the bursting process remains largely unknown. Here, we document the bubble-bursting jet dynamics at an oil-covered aqueous surface, which typifies the sea surface microlayer as well as an oil spill on the ocean. The jet tip radius and velocity are altered with even a thin oil layer, and oily aerosol droplets are produced. We provide evidence that the coupling of oil spreading and cavity collapse dynamics results in a multi-phase jet and the follow-up droplet size change. The oil spreading influences the effective viscous damping, and scaling laws are proposed to quantify the jetting dynamics. Our study not only advances the fundamental understanding of bubble bursting dynamics, but also may shed light on the airborne transmission of organic matters in nature related to aerosol production.

Aerodynamic port-aligned fins to enhance thermal-hydraulic performance of jet impingement arrays

Jet impingement arrays with interspersed fluid extraction ports can suffer degraded heat transfer near outlets due to flow separation. This study explores the potential to integrate aerodynamic port-aligned fins on the impingement surface to maintain wall-jet attachment and increase heat transfer area. Such fins may also enhance local transport under inlet nozzles. Laminar-flow conjugate heat transfer simulations are performed for a range of Reynolds numbers and geometries to characterize this concept for slot jet impingement arrays. The simulation methodology is validated with conventional slot jet data from the literature and demonstrated to achieve mesh convergence. Overall flow characteristics are evaluated for a representative geometry, and results show a significant increase in relative average Nusselt number (Nu∗‾)and a reduction in peak temperature of the cooled surface. Conjugate heat transfer effects are evaluated, and are found to be significant for lower conductivity fin materials. Parametric studies are performed to generate performance maps for relative average Nusselt number and pressure drop as functions of Reynolds number, fin height, base width, and tip radius. Pareto curves are generated for the geometries that optimally trade heat transfer enhancement and pressure drop penalty to guide design. Teardrop shaped fins are found to be optimal for low Re, whereas continuously narrowing fins are preferable for higher Re. This jet impingement enhancement is shown to deliver up to 25% enhancement in Nu∗‾ at baseline pressure drop.

Phase-field modeling of dendritic growth of magnesium alloys with a parallel-adaptive mesh refinement algorithm

A two-dimensional phase field (PF) model was developed to simulate the dendritic solidification in magnesium alloy with hcp crystal structure. By applying a parallel-adaptive mesh refinement (Para-AMR) algorithm, the computational efficiency of the numerical model was greatly improved. Based on the PF model, a series of simulation cases were conducted and the results showed that the anisotropy coefficient and coupling coefficient had a great influence on the dendritic morphology of magnesium alloy. The dendritic growth kinetics was determined by the undercooling and equilibrium solute partition coefficient. A significant finding is acquired that with a large undercooling, the maximum solute concentration is located on both sides of the dendrite tip in the liquid, whereas the maximum solute concentration gradient is located right ahead of the dendrite tip in the liquid. The dendrite tip growth velocity decreases with the increase of the equilibrium solute partition coefficient, while the variation trend of the dendrite tip radius is the opposite. Quantitative analysis was carried out relating to the dendritic morphology and growth kinetics, and the simulated results are consistent with the theoretical models proposed in the previously published works.

Mechanical properties of α-quartz using nanoindentation tests and molecular dynamics simulations

Understanding the mechanical properties of α-quartz is of vital importance to rock engineering because α-quartz is the main component of igneous, metamorphic and sedimentary rocks. Molecular dynamics simulations (MDs) of nanoindentation tests on α-quartz were performed to investigate the effects of indenter tip radius and penetration depth on the mechanical properties of α-quartz. Indentation load-penetration depth (P-h) curves were plotted, from which Reduced Young’s modulus ( E r ) , hardness ( H ) were obtained and these mechanical parameters were then compared with the laboratory nanoindentation results. The mechanical results obtained from MDs are in good agreement with the experimental values. It can be found that E r and H increase with indentation depth at shallow contact depth while they decrease with indenter tip size. To the authors’ knowledge, this is the first MDs of nanoindentation test of hard rock-forming minerals reported and we believe that this study can shed light on the precise measurement of the mechanical properties of rock minerals at micro- and nano-scales.