Changes In Surface Topography Research Articles

Wind redistribution of snow impacts the Ka- and Ku-band radar signatures of Arctic sea ice

Abstract. Wind-driven redistribution of snow on sea ice alters its topography and microstructure, yet the impact of these processes on radar signatures is poorly understood. Here, we examine the effects of snow redistribution over Arctic sea ice on radar waveforms and backscatter signatures obtained from a surface-based, fully polarimetric Ka- and Ku-band radar at incidence angles between 0∘ (nadir) and 50∘. Two wind events in November 2019 during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition are evaluated. During both events, changes in Ka- and Ku-band radar waveforms and backscatter coefficients at nadir are observed, coincident with surface topography changes measured by a terrestrial laser scanner. At both frequencies, redistribution caused snow densification at the surface and the uppermost layers, increasing the scattering at the air–snow interface at nadir and its prevalence as the dominant radar scattering surface. The waveform data also detected the presence of previous air–snow interfaces, buried beneath newly deposited snow. The additional scattering from previous air–snow interfaces could therefore affect the range retrieved from Ka- and Ku-band satellite altimeters. With increasing incidence angles, the relative scattering contribution of the air–snow interface decreases, and the snow–sea ice interface scattering increases. Relative to pre-wind event conditions, azimuthally averaged backscatter at nadir during the wind events increases by up to 8 dB (Ka-band) and 5 dB (Ku-band). Results show substantial backscatter variability within the scan area at all incidence angles and polarizations, in response to increasing wind speed and changes in wind direction. Our results show that snow redistribution and wind compaction need to be accounted for to interpret airborne and satellite radar measurements of snow-covered sea ice.

Thermal transformation of bamboo sawdust for its advanced cementitious composites

This paper investigates a vacuum heat treatment (VHT) technology at 160℃, 200℃ and 240℃ for 6–14 h to modify bamboo sawdust (BS) and then BS/cement composites for the development of low carbon construction materials. The hydration process, thermal stability, micro-morphology and crystallinity, and chemical and mechanical changes for both VHT BS and composites are examined by FTIR, TG-DTG, XRD and SEM analyses. The mechanism of improving the mechanical properties of modified BS on composite materials is further elaborated together with the physical and mechanical properties and durability. The results show that the flexural strength and compressive strength of the modified BS/cement composites after VHT at 200℃ for 10 h are increased by 61.2% and 13.8%, respectively, compared with those in the untreated group, and the composites have better durability in the modified group. VHT resulted in cellulose and hemicellulose degradation to certain degrees, lignin undergoes cross-linked condensation reaction and cellulose crystallinity increases. These changes reduce the number of BS hydrophilic groups and result in changes in BS microstructure and surface topography, providing favorable conditions for the bonding and interface development of BS/cement composites. The impact of BS/cement composites on the carbon footprint in the production stage was analyzed, showing that the carbon emissions of BS/cement composites after VHT were reduced by 5.7% compared with that of the corresponding OPC composites.

Electrically Controlled Liquid Crystal Elastomer Surfaces for Dynamic Wrinkling

Liquid crystal elastomers (LCEs) are becoming increasingly popular as a shape memory material for soft robot actuators that operate in a contractile or flexural mode. There have been previously studies on the use of LCEs for reversible changes in surface topography. However, surface protrusions have typically been limited to the order of 1 μm or depend on light, heat, or electrical stimulation that are difficult to locally control or require relatively high voltage. This article presents a novel operation mode of LCE actuators based on the wrinkling behavior of an LCE‐elastomer bilayer architecture. Embedding a liquid‐metal‐based conductive ink within the LCE enables electrical control of surface wrinkling through Joule heating. The actuator cells can generate wrinkles with amplitudes ranging from 17 to 45 μm within 30 s under an input power of 2 W and a voltage on the order of 1 V. As the bilayer is composed entirely of soft materials, it is highly deformable, flexible, and can be integrated into a multi‐cell array capable of bending on curved surfaces.

Assessment of surface topographic changes of nickel–titanium rotary endodontic file at repeated usage: An in vitro study

ABSTRACT Aim: The current in vitro study aimed to assess the surface topography of Protaper gold NiTi files and compare changes in surface topography before and after root canal preparation in straight, moderately, and severely curved root canals. Methods: In this study, thirty Protaper gold S1 files were selected. These were divided into three groups of 10 each and were used to prepare 440 straight, moderately, and severely curved root canals. Optical profilometry was used to perform qualitative evaluations of file surfaces before and after root canal preparation at specified intervals. The statistical analysis was performed using the Mann–Whitney U-test for comparing two groups, the Friedman test for comparing within groups, the Kruskal–Wallis analysis of variance for multigroup comparisons, and the Bonferroni test for multiple pairwise comparisons. Results: The surface irregularities in the form of cracks and microcavities were higher in the used files when compared to the unused files. Similarly, the files used in severely curved canals exhibited more surface alterations at less no of uses when compared to the files used in straight and moderately curved canals. The difference obtained was statistically significant, that is, P = 0.000. Conclusion: From the findings, it was concluded that the file separation has been preceded with surface deterioration as a result of repeated cycles of cyclic fatigue.

Corrosion of copper nickel titanium archwire in chlorhexidine, sodium fluoride, and chitosan mouthwashes.

Copper (Cu), nickel (Ni), chromium (Cr) ion release, and surface topography change from the orthodontic wire are the initial processes of corrosion that may affect the mechanical properties of the archwire. In this study, we aim to evaluate the effect of CHX, NaF, and chitosan on the corrosion of CuNiTi wire nickel and copper ions released, surface roughness change, and archwire deflection. Ninety samples of CuNiTi Tanzo™ archwires were divided into five groups according to their immersion solution: Artificial Saliva, CHX, NaF, CHX-NaF, and chitosan group. Each group was further divided into three subgroups (n=6) corresponding immersion time, i.e., two, four, and six weeks. The corrosion of the samples was analyzed with an atomic absorption spectrophotometer (AAS), scanning electron microscope (SEM), and universal testing machine (UTM). The amount of nickel ion releases was increasing, but the copper ion releases were reduced by the time of observations. The highest nickel ion was released in the CHX-NaF group and the lowest in the chitosan group for six-week immersion. It also corresponded to the surface topography by SEM analysis which showed the most extended cracks and deep pits in the CHX-NaF group and a smoother surface in the chitosan group. Copper ion release showed the highest ion release in the NaF group and the lowest release in the chitosan group. The unloading force of CuNiTi archwire deflection remains the same at week two and week four for all mouthwashes. The use of mouthwashes that contained CHX, NaF, and chitosan could further alter the passive layer and cause higher nickel and copper ion release and increased CuNiTi archwire surface structure porosity. But there is no distinction between mouthwashes to release the unloading force within two until four weeks.

Operando Scanning Electrochemical Probe Microscopy during Electrocatalysis.

Scanning electrochemical probe microscopy (SEPM) techniques can disclose the local electrochemical reactivity of interfaces in single-entity and sub-entity studies. Operando SEPM measurements consist of using a SEPM tip to investigate the performance of electrocatalysts, while the reactivity of the interface is simultaneously modulated. This powerful combination can correlate electrochemical activity with changes in surface properties, e.g., topography and structure, as well as provide insight into reaction mechanisms. The focus of this review is to reveal the recent progress in local SEPM measurements of the catalytic activity of a surface toward the reduction and evolution of O2 and H2 and electrochemical conversion of CO2. The capabilities of SEPMs are showcased, and the possibility of coupling other techniques to SEPMs is presented. Emphasis is given to scanning electrochemical microscopy (SECM), scanning ion conductance microscopy (SICM), electrochemical scanning tunneling microscopy (EC-STM), and scanning electrochemical cell microscopy (SECCM).

Wear induced changes in surface topography during running-in of rolling-sliding contacts

Running-in occurs in rolling-sliding contacts under mixed-friction conditions and typically involves asperity smoothing through mild wear and plastic deformation. To improve the prediction of service life or friction of rolling-element bearings under mixed-friction conditions, knowledge of surface topography changes during running-in and their dependence on the operating condition is an important prerequisite. Therefore, this study aims to describe the surface mechanisms due to wear, during running-in and their dependence on one of the variables, slip.AISI 52100 steel specimens were tested in a mini traction machine (MTM) instrumented with friction and contact potential measurement in the presence of a PAO base oil, operating in the mixed lubrication regime. A novel method of pre and post-test surface relocation with 3-D optical profilometry and scanning electron microscopy (SEM) was implemented. Rolling-sliding tests were performed to study the effect of slide-roll ratio on the surface topography changes during running-in. Additional tests were conducted to track the changes to surface topography during this period.The results exhibit the rapid nature of running-in and how most of the surface topography changes occur in the first few load cycles. Surface topography transitions such as asperity removal due to wear, increase in the load-bearing area of the asperities and in tests with slip, plastic flow of material from peaks into adjacent valleys are shown at high magnification. Surface profilometry measurements show that the reduction in depth of the valleys due to plastic flow adds to the reduction in roughness, thus accurately identifying the surface mechanism, and redressing the consensus that the reduction in roughness during running-in is mainly due to wear and plastic deformation diminishing the height of the peaks, which is true for ideal running-in alone.

Exploring the Lunar Regolith's Thickness and Dielectric Properties Using Band‐Limited Impedance at Chang’E‐4 Landing Site

AbstractThe Yutu‐2 rover onboard China's Chang’E‐4 was the first to land in the Von Kármán crater on the lunar farside, where structural and dielectric properties may provide previously unknown clues to lunar formation and evolution. Based on the Lunar Penetrating Radar (LPR) with 500 MHz onboard the Yutu‐2 rover, we proposed a band‐limited impedance (BLIMP) inversion method to generate continuous dielectric 2‐D profiles with the help of dielectric constants retrieved from point reflectors (e.g., buried rocks), which provide low‐frequency information that may be lost or distorted in the LPR data pre‐processing. The dielectric constants retrieved from point reflectors were transformed from dielectric constant fitting curves, where these discrete dielectric constants were calculated using the hyperbolic fitting method. We estimated that the top fine‐grained regolith thickness along the rover path varies from ∼5.3 to ∼15.0 m in the first 27 lunar days of operation. The thickness variation could most likely be attributed to changes in ancient surface topography buried underground and ejecta from nearby craters. Compared to methods based on a singular dielectric constant, the estimated 2‐D dielectric profile in this study can reduce the uncertainties in lunar regolith thickness estimation, especially in the shallow layers. The BLIMP method and the estimated regolith thickness can improve our understanding of lunar subsurface structure and formation.

Correlative Analysis of Ion-Concentration Profile and Surface Nanoscale Topography Changes Using Operando Scanning Ion Conductance Microscopy.

Although various spectroscopic methods have been developed to capture ion-concentration profile changes, it is still difficult to visualize the ion-concentration profile and surface topographical changes simultaneously during the charging/discharging of lithium-ion batteries (LIBs). To tackle this issue, we have developed an operando scanning ion conductance microscopy (SICM) method that can directly visualize an ion-concentration profile and surface topography using a SICM nanopipette while controlling the sample potential or current with a potentiostat for characterizing the polarization state during charging/discharging. Using operando SICM on the negative electrode (anode) of LIBs, we have characterized ion-concentration profile changes and the reversible volume changes related to the phase transition during cyclic voltammetry (CV) and charge/discharge of the graphite anode. Operando SICM is a versatile technique that is likely to be of major value for evaluating the correlation between the electrolyte concentration profile and nanoscale surface topography changes.

Topography of high-speed steel substrates sputter cleaned by an Ar/Ti cathodic arc plasma

Hard coated high-speed steels are often used for tooling applications and consist of three different microstructural constituents: a martensitic matrix, M6C and MC carbides. The behavior of these three during the various tool manufacturing steps has a detrimental effect on the final tool performance. The focus of the current work is the surface topography change due to variation of the substrate bias voltage applied during the Ar/Ti arc plasma sputter cleaning process which changed the sputtering behavior of the high-speed steel's microstructural constituents and the appearance of droplets on the sputtered surface. The surface topography was characterized by laser confocal and scanning electron microscopy. Furthermore, microstructural analysis was carried out on cross-section lamellae prepared by a focus ion beam technique and analyzed by transmission electron microscopy. At each of the three investigated substrate bias voltages (Ub) of −600, −800 and −1000 V during the Ar/Ti arc plasma sputter cleaning process, the mentioned microstructural constituents behaved differently. At an Ub threshold of −600 V, sputter erosion starts at M6C carbides in an inhomogeneous material erosion pattern. At −800 V, a homogeneous sputter behavior was established for the entire sample. M6C carbides showed the highest sputter erosion rate, on MC carbides Ti deposition occurred instead of sputter erosion, and the martensitic matrix was smoothened, as peaks and exposed features were sputtered preferentially. As of Ub = −1000 V, the sputter erosion behavior of the martensitic matrix changed and exposed features were preserved. The reason for this change was identified to be Ti+ ion implantation indicated by Monte Carlo simulations and the associated increase of the matrix' cohesive strength, calculated using Density Functional Theory. The published results in this study will help to further utilize Ar/Ti arc plasma sputter cleaning processes for intentional surface topography design.

Corrosion of copper nickel titanium archwire in chlorhexidine, sodium fluoride, and chitosan mouthwashes

Background: Copper (Cu), nickel (Ni), chromium (Cr) ion release, and surface topography change from the orthodontic wire are the initial processes of corrosion that may affect the mechanical properties of the archwire. In this study, we aim to evaluate the effect of CHX, NaF, and chitosan on the corrosion of CuNiTi wire nickel and copper ions released, surface roughness change, and archwire deflection. Methods: Ninety samples of CuNiTi Tanzo™ archwires were divided into five groups according to their immersion solution: Artificial Saliva, CHX, NaF, CHX-NaF, and chitosan group. Each group was further divided into three subgroups (n=6) corresponding immersion time, i.e., two, four, and six weeks. The corrosion of the samples was analyzed with an atomic absorption spectrophotometer (AAS), scanning electron microscope (SEM), and universal testing machine (UTM). Results: The amount of nickel ion releases was increasing, but the copper ion releases were reduced by the time of observations. The highest nickel ion was released in the CHX-NaF group and the lowest in the chitosan group for six-week immersion. It also corresponded to the surface topography by SEM analysis which showed the most extended cracks and deep pits in the CHX-NaF group and a smoother surface in the chitosan group. Copper ion release showed the highest ion release in the NaF group and the lowest release in the chitosan group. The unloading force of CuNiTi archwire deflection remains the same at week two and week four for all mouthwashes. Conclusion: The use of mouthwashes that contained CHX, NaF, and chitosan could further alter the passive layer and cause higher nickel and copper ion release and increased CuNiTi archwire surface structure porosity. But there is no distinction between mouthwashes to release the unloading force within two until four weeks.

Photogrammetric Documentation of Stone Surface Topography Changes as a Tool in Conservation Praxis

Traces of stone working are an integral part of natural stone objects and artefacts of historical value. Each preserved trace does not only carry a value in determining the type of tool used, but also provides information about the historic stonemason’s work process and technology. For this reason, it is desirable to assess the restoration method’s influence on the change in surface topography. The effect of restoration interventions was investigated on five stone artefacts, three of ‘opuka’, one of sandstone and one of limestone, four of which showed historic working traces. For this purpose, selected restoration methods—chemical, mechanical and laser—were used. The examined artefacts were accurately photogrammetrically captured before and after the restoration interventions in order to assess and evaluate changes in the degree of preservation of the traces. Fine results using common tools were achieved in terms of geometric quality, level of detail and the documentation’s predictive power. The models’ geometric accuracy is in the single tenths of mm, as well as the matching of the two datasets (before and after).

Influences of surface topography of porous titanium scaffolds manufactured by powder bed fusion on osteogenesis

Powder bed fusion (PBF) has emerged as a useful metal-three-dimensional (3D) printing technology for manufacturing porous structures; it has been widely employed for the production of medical implants. Multiple previous reports have suggested that the bone ingrowth characteristics of porous structures, among the most important factors for medical implants, are affected by 3D printing parameters (e.g., pore shape). The topography of 3D-printed metal surfaces can also influence cellular responses, including osteoblast differentiation. The surface topography may change according to the shape of the printed pores. Nevertheless, it remains unclear how the surface topography changes. In addition, it is still unknown how the pore shape and the resulting surface topography can further impact the bone ingrowth efficiency of the porous structure. Therefore, to better understand the relationship, we prepared Ti–6Al–4V specimens with different pore shapes (i.e., circular, triangular, and rectangular) using the PBF method, then analyzed the surface topographies of these 3D scaffolds based on curvature and roughness profiles. Through subsequent in vitro studies, we investigated how changes in pore shape and surface topography affect the activity of Saos-2 human osteosarcoma cells. The results of this study confirmed that the curvature radii and local surface roughness change according to pore shape because of the characteristics of PBF. Furthermore, differences in local surface topography and pore shape led to differences in cell proliferation and differentiation. Through our findings, we anticipate that the meticulous design of pore shape and sophisticated control of the processing parameters, such as laser speed and paths, in the fabrication of orthopedic and dental implants will result in significantly enhanced bone ingrowth efficiency.

The Effect of Rhenium Content on Microstructural Changes and Irradiated Hardening in W-Re Alloy under High-Dose Ion Irradiation.

An amount of 100 dpa Si2+ irradiation was used to study the effect of transmutation rhenium content on irradiated microscopic defects and hardening in W-xRe (x = 0, 1, 3, 5 and 10 wt.%) alloys at 550 °C. The increase in Re content could significantly refine the grain in the W-xRe alloys, and no obvious surface topography change could be found after high-dose irradiation via the scanning electron microscope (SEM). The micro defects induced by high-dose irradiation in W and W-3Re alloys were observed using a transmission electron microscope (TEM). Dislocation loops with a size larger than 10 nm could be found in both W and W-3Re alloy, but the distribution of them was different. The distribution of the dislocation loops was more uniform in pure W, while they seemed to be clustered around some locations in W-3Re alloy. Voids (~2.4 nm) were observed in W-3Re alloy, while no void was investigated in W. High-dose irradiation induced obvious hardening with the hardening rate between 75% and 155% in all W-xRe alloys, but W-3Re alloy had the lowest hardening rate (75%). The main reasons might be related to the smallest grain size in W-3Re alloy, which suppressed the formation of defect clusters and induced smaller hardening than that in other samples.

Time-Varying Wear Calculation Method for Fractal Rough Surfaces of Friction Pairs

For the wear problem of the real rough surface during sliding friction, based on fractal theory and Hertz contact theory, a 3-D fractal rough surface with random characteristics is constructed, and the relationship between the wear deformation depth of the rough peak and its real contact area during the wear process is derived. Furthermore, considering the peak wear and pit scratch phenomena of rough surfaces in different contact states, the time-varying wear calculation model of the worn surface and the compensation wear calculation model of the unworn surface are established, respectively, and the relationship between the instantaneous wear amount and the dynamic change in the rough surface topography is comprehensively characterized. Combined with image digitization technology, the 3-D rough surface is converted into a 2-D discrete plane with 3-D information. According to the dynamic real-time update of the graph data, the iterative calculation of the wear cycle is completed, the time-varying wear calculation method for fractal rough surfaces of friction pairs is proposed, and the dynamic change in the wear amount and surface topography of the rough surface is simulated. The simulation results are experimentally verified and the influence of friction parameters on the surface topography is analyzed. The results show that after the wear simulation, the profile height of the rough surface is reduced, and the average wear depth is 0.02 mm. Increases in rotational speeds and external loads can exacerbate surface wear, surface topography tends to be flattened, and surface carrying capacity increases. This provides theoretical guidance for the development and manufacture of friction pairs.

Viscoplastic Modeling of Surface Relief Grating Growth on Isotropic and Preoriented Azopolymer Films.

We report on solving of two intriguing issues concerning the inscription of surface relief gratings within azopolymer thin films under irradiation with SS, PP and RL interference patterns. For this, we utilize the orientation approach and viscoplastic modeling in combination with experimental results, where the change in surface topography is acquired in situ during irradiation with modulated light. First, the initial orientation state of polymer backbones is proved to be responsible for the contradictory experimental reports on the efficiency of the SS interference pattern. Different orientation states can influence not only the phase of SS grating but also its height, which is experimentally confirmed by using special pretreatments. Second, the faster growth of gratings inscribed by the RL interference pattern is shown to be promoted by a weak photosoftening effect. Overall, the modeled results are in good agreement with the order of relative growth efficiency: RL-PP-SS.

Correlative high-resolution imaging of hydrogen in Mg2Ni hydrogen storage thin films

Nanometer scale imaging of hydrogen in solid materials remains an important challenge for the characterization of advanced materials, such as semiconductors, high-strength metallic alloys, and hydrogen storage materials. Within this work, we demonstrate high-resolution imaging of hydrogen and deuterium within Mg2Ni/Mg2NiH4 hydrogen storage thin films using an in-house developed secondary ion mass spectrometer (SIMS) system attached to a commercially available dual-beam focused ion beam - scanning electron microscope (FIB-SEM) instrument. We further demonstrate a novel approach to measure the size, shape, and distribution of the hydride phase in partially transformed films using laser scanning confocal microscopy (LSCM) to measure surface topography changes from the hydride phase volume expansion. Combining these techniques provides new insights on hydride nucleation and growth within the Mg2NiHx system. Finally, we demonstrate the efficacy of tracking deuterium as a hydrogen analog to reduce the background for SIMS imaging of hydrogen in high-vacuum chambers (∼10−6 mbar).

Guidelines for rail quality selection to increase service life based on wear and fatigue behavior of various wheel and rail materials

The Austrian rail network is very diverse: The lines in the alpine areas have very tight radii while the lines in the flat areas (east and north of Austria) are mainly straight high-speed lines. This leads to different levels of wheel and rail wear. Accordingly, the objective of this study was to experimentally model a laboratory-scale cyclic wheel-rail contact to investigate wear behavior and rolling contact fatigue at different radii (RCF).A novel test system was set up at AC2T research GmbH to reproduce unidirectional loading on a real track. Tribotests were performed with rail (grades R260, R350HT & R400HT) and wheel (grades ER7 & ER9) parts from the field. This newly designed principle is an effective method to characterize the wheel-rail contact. Wear characterization was done after defined testing cycles to detect (i) area loss and (ii) change in surface topography.

Direct observation of the dynamic reconstructed active phase of perovskite LaNiO3 for the oxygen-evolution reaction.

Ni-based transition metal oxides are promising oxygen-evolution reaction (OER) catalysts due to their abundance and high activity. Identification and manipulation of the chemical properties of the real active phase on the catalyst surface is crucial to improve the reaction kinetics and efficiency of the OER. Herein, we used electrochemical-scanning tunnelling microscopy (EC-STM) to directly observe structural dynamics during the OER on LaNiO3 (LNO) epitaxial thin films. Based on comparison of dynamic topographical changes in different compositions of LNO surface termination, we propose that reconstruction of surface morphology originated from transition of Ni species on LNO surface termination during the OER. Furthermore, we showed that the change in surface topography of LNO was induced by Ni(OH)2/NiOOH redox transformation by quantifying STM images. Our findings demonstrate that in situ characterization for visualization and quantification of thin films is very important for revealing the dynamic nature of the interface of catalysts under electrochemical conditions. This strategy is crucial for in-depth understanding of the intrinsic catalytic mechanism of the OER and rational design of high-efficiency electrocatalysts.

MViT-PCD: A Lightweight ViT-Based Network for Martian Surface Topographic Change Detection

Identifying the surface topographic changes accurately plays a vital role in the task of planetary exploration. In this study, a lightweight mobile vision transformer-based planetary image change detection (MViT-PCD) was proposed for monitoring dynamic surface changes using bitemporal images. The mobile vision transformer (MobileViT) was first introduced to make the most of the spatial information available. Subsequently, a multiscale feature differentiation and fusion (MFDF) block was adopted to improve the distinguishability of multilevel contextual information. Moreover, the strategy of information maximization (IM) was integrated to refine the model performance on the heterogeneous dataset. Then, experiments were conducted on the public Martian datasets. Compared with other state-of-the-art (SOTA) methods, the MViT-PCD provides favorable performance, with the highest accuracy of 97.2% and 82.9%, respectively, under the speed of 43.4 frame per second (FPS). Code is available at <uri xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">https://github.com/lynn1023-max/MViTPCD</uri> .