Surface Evolution Research Articles

Morphological Characterization of Decimeter‐ to Hectometer‐Scale Impact Craters at the Chang’E‐3/4/5 Landing Sites

AbstractThe morphology of impact craters on the Moon is important for understanding impact cratering process and lunar surface properties. Though the morphology of lunar impact craters at hectometer scales and larger is extensively investigated and well understood, the morphology of very small craters is rarely studied due to the lack of high‐resolution data. In this study, we investigated the morphology of 1,513 craters at decimeter to hectometer scales using the 5 mm/pixel–0.5 m/pixel topographic data of the Chang’E‐3/4/5 (CE‐3/4/5) landing regions. Our results show that crater depth, rim height, and inner wall slope increase with the diameter and that the mean values of depth/diameter ratio, rim height/diameter ratio, and inner wall slope are 0.065, 0.017, and 10.5°, respectively. These morphometric parameters are smaller than those of large craters above hectometer scales, which is probably due to low‐strength surficial regolith and rapid topographic degradation. The comparison of the morphometric parameters among the three regions suggests that the CE‐4, CE‐3, and CE‐5 landing regions have the highest, intermediate, and lowest regolith strengths, respectively. In addition, we first observed widespread meter‐scale concentric and flat‐bottomed craters in optical images, which are most probably formed due to strength heterogeneity within the regolith layer. Our results can help to understand near‐surface properties of the regolith layer, lunar surface evolution, and impact cratering process in the strength regime.

A novel machine learning fingerprinting method using sparse representation for provenance detection in delta sediments

Quantitative research on the sediment source to sink process is critical to revealing the evolution of the Earth’s surface. The fingerprinting technique is useful for sediment source detection, and machine learning methods are being used with this technique. However, paleo-provenance research with limited measured data from sediment cores is not adequate for big data analysis which demands a large amount of data. Hence, determining how to assess authentic source contributions by using fingerprinting techniques based on very limited measurement data is a key scientific task. Sparse representation (SR), a machine learning method with advantages in feature extraction that treats the source as a linear combination of multiple tracers, has the potential to provide satisfactory answers. In this paper, a sparse representation-based sediment fingerprinting (SRSF) method is introduced. Based on size-specific magnetic and geochemical characterizations, we applied this method to quantize the provenance of three sediment cores from the Yangtze River Delta (YRD), where Yellow River sediment has contributed to delta formation over the past 400–600 years. Our results showed that the sediments of the Yellow River contributed 19.3 ± 5.8 % of the clay and fine silt (<16 μm) and 23.5 ± 9.2 % of the medium silt (16–32 μm) in the delta, which was consistent with previously published results. This study improves the current fingerprinting technique in the feature extraction and selection stage by leveraging SR and provides reference data for the development of the modern YZD delta. The SRSF method has many potential applications, especially in paleo-provenance detection with highly limited measurement data, which could help expand our understanding of paleo-Earth surface evolution.

Analyzing of the Evolution and the Scaling Properties of a Sinusoidal Mound

The evolution of an initial surface (below its roughening temperature) bounded by a sinusoidal function and consisting of concentric circular steps in two dimensions has been investigated in the Diffusion Limited (DL) regime. Assuming that there were entropic interactions between steps and the local mass transfer took place due to the surface diffusion, the solution of the diffusion equation has been obtained by using polar coordinates in two dimensions. The results obtained in this investigation with analyzing the surface height’s evolution as a function of time are as follows: The surface’s height approximately decreases as τ^α (α≈0.35) and α is independent of the amplitude and the wavelength of the initial surface. The variations in the heights of the surfaces which have different amplitudes (A_01,A_02 ) and wavelengths (λ_1,λ_2 ) scale as (A_01⁄A_02 ) (λ_1⁄λ_2 )^3.

Rayleigh–Taylor instability of viscoelastic self-rewetting film flowing down a temperature-controlled inclined substrate

Rayleigh–Taylor (RT) instability of gravity-driven viscoelastic self-rewetting film flowing under an inclined substrate uniformly heated or cooled is considered. The surface tension of self-rewetting film is considered as a quadratic function of temperature. The long wave hypothesis is used to derive a nonlinear free surface evolution equation of the thin viscoelastic film. Linear stability analysis shows that for a prescribed the viscoelastic coefficient, substrate cooling products instability, while substrate heating remains stability. Furthermore, we analyze the influence of viscoelastic coefficient on RT instability. Results show that the viscoelastic coefficient reinforces the RT instability whether the substrate is heated or cooled. Moreover, we use the line method to numerically simulate the nonlinear evolution equation and systematically examine the space-time variation of the film free surface. The numerical results illustrate that increasing the viscoelastic coefficient can enhance the disturbance amplitude and wave frequency. This means that the viscoelastic coefficient makes the system unstable, which is consistent with result of the linear stability analysis. In addition, the oscillation tends to accumulate downstream of the inclined substrate when the evolution time is long enough. Finally, the variation of film thickness with related parameters for different viscoelastic coefficients is investigated.

Impact Induced Oxidation and Its Implications for Early Mars Climate

AbstractH2 in a CO2 atmosphere may serve as a potential solution to the early Mars climate paradox, but its unknown sources cast doubts on the proposed mechanism. Impact cratering is an energetic process that may modify the surface redox budget. Here, we investigate the potential influence of impact‐related melt oxidation and serpentinization on global climate conditions. We show that impact melt and the projectile's significant oxidizing potential during basin‐forming impacts (Basin size ≥1,250 km) result in sufficient H2 to raise the global mean temperature to above 273K, which lasts for up to 105 − 106 yr considering rate‐limited regime. Impact‐induced serpentinization has limited consequences on the global climate in comparison. Episodic warming after large impacts may have enabled the presence of liquid water for up to several million years in the Noachian, resulting in the chemical evolution of the planet's surface co‐evolving with the planetary atmosphere in an episodic manner.

Mouthpart palp sensilla of basal Trichoptera families

A comparative SEM study of palp sensory surfaces in 25 caddisfly species representing seven families reveals seven types of sensilla: long trichoid, blunt chaetoid, campaniform, mushroom-like pseudoplacoid, petaloid, thick basiconic and thin basiconic sensilla. Long trichoid and chaetoid sensilla are present on all segments of both pairs of palps. First and second segments of maxillary palps bear groups of long and sclerotised chaetoid sensilla on their medial surface. Other segments of maxillary palps and all segments of labial palps have shorter and thinner chaetoid sensilla mainly on their ventromedial surfaces. Campaniform sensilla usually occur on the first segment of labial palps and second segment of maxillary palps. Mushroom-like pseudoplacoid sensilla may occupy all palp segments or only distal ones. Petaloid sensilla form sensory fields on apical segments of both pairs of palps in most studied species. Thick basiconic sensilla occur only in apical sensory complexes on tips of maxillary and labial palps. A comparison with the Lepidoptera suggests the similarity in palp sensilla and conservative evolution of the palp surface. The reconstructed ground plan for the palp sensory surfaces in Trichoptera and Amphiesmenoptera is provided.

Stable CuIn alloy for electrochemical CO2 reduction to CO with high-selectivity

High-selective and stable electrocatalysts are highly desired for CO2 reduction in large scale. To achieve CO2 reduction to CO with high selectivity and longtime running stability, CuIn alloy nanowires (NWs) is prepared by the combining of chemical oxidation and electrodeposition method. More importantly, due to electrochemical pretreatment during synthesis process, the CuIn alloy shows remarkable stability and its structure remains unchanged under harsh negative bias during CO2 reduction. In addition, the alloy NWs achieve the optimal CO2 to CO selectivity with a Faradaic efficiency of 86% at −1.0 V vs. RHE. Through DFT calculation, it is found that the stable CuIn alloy surface is crucial for the modulation of *COOH intermediate bonding to catalyst for easier formation of *CO, and the *CO dimerization is inhibited by CuIn alloy surface due to the weaker *CO adsorption compared to metallic Cu. We believe this work will shed light on the preparation of stable electrocatalysts for CO2 reduction with high selectivity, and deep understanding of metal surface evolution under electrochemical environment.

Assessment of surface and subsurface evolution under rolling contact fatigue of a pearlitic steel

The assessment of surface and subsurface evolution of rolling/sliding elements manufactured of pearlitic rail steel is investigated using a rolling contact fatigue (RCF) test. The experiments are carried out under different contact pressures in boundary lubricated condition, with 0 % and 2 % slide-to-roll ratios (SRR). The micro-pit area on the contact surface was greater for 2 % SRR than for 0 % SRR. As the load cycles continue, these micro-pits are going to become macro-pits. Under higher load and more SRR, these macro-pits link to form surface-initiated spalls in subsequent RCF tests. The anisotropic surface was destroyed with applied SRR conditions in each RCF test, as the distribution of power spectral density (PSD) became nearly uniform in each direction after the RCF test. The rolling element's subsurface shows the breaking and bending of pearlite. Plastic shakedown and ratcheting response are accountable for deforming subsurface, and as a result, subsurface hardness increases. Subsurface fatigue cracks are visible from MnS inclusion. Changes in surface topography characteristics are also investigated since they impact surface fatigue.

Evolution of Mineral-Accessible Surface Area Induced by Geochemical Reactions

Mineral dissolution and precipitation reactions occur in a wide range of porous media systems, driven by deviations from an equilibrium between solid and fluid phases. Reactions occur at mineral surfaces in contact with reactive fluids or accessible mineral surface areas. These mineral surface areas can be determined using a multiscale imaging approach and have been shown to improve the simulation of mineral reaction rates in porous media compared to other estimates of reactive surface area. As reactions progress, mineral surface area evolves, and reactive transport simulations often use a simplified model assuming spherical grains to estimate mineral surface area evolution. This, however, does not depict the evolution of reactive surfaces in porous media systems with varying mineral accessibility. This work aims to quantitatively assess the evolution of accessible mineral surface area in porous media for a multimineralic system undergoing mineral dissolution reactions induced by acid exposure. Before and after the reaction, accessible mineral surface areas are determined from 2D scanning electron microscopy, and 3D X-ray computed tomography imaging of a sandstone sample. The quantified evolution of accessible surface area is compared to the calculated mineral surface area evolution using current approaches. Results show an overall increase in total surface area due to the reaction; however, individual mineral surface areas may increase or decrease. Variation is observed in mineral surface area values measured from imaging and equations used in models. The evolution of mineral surface area is largely impacted by the total surface area as well as the pore connectivity rather than porosity and volume fraction evolution.

Describing and Modeling Rough Composites Surfaces by Using Topological Data Analysis and Fractional Brownian Motion.

Many composite manufacturing processes employ the consolidation of pre-impregnated preforms. However, in order to obtain adequate performance of the formed part, intimate contact and molecular diffusion across the different composites' preform layers must be ensured. The latter takes place as soon as the intimate contact occurs and the temperature remains high enough during the molecular reptation characteristic time. The former, in turn, depends on the applied compression force, the temperature and the composite rheology, which, during the processing, induce the flow of asperities, promoting the intimate contact. Thus, the initial roughness and its evolution during the process, become critical factors in the composite consolidation. Processing optimization and control are needed for an adequate model, enabling it to infer the consolidation degree from the material and process features. The parameters associated with the process are easily identifiable and measurable (e.g., temperature, compression force, process time, ⋯). The ones concerning the materials are also accessible; however, describing the surface roughness remains an issue. Usual statistical descriptors are too poor and, moreover, they are too far from the involved physics. The present paper focuses on the use of advanced descriptors out-performing usual statistical descriptors, in particular those based on the use of homology persistence (at the heart of the so-called topological data analysis-TDA), and their connection with fractional Brownian surfaces. The latter constitutes a performance surface generator able to represent the surface evolution all along the consolidation process, as the present paper emphasizes.

Surface Evolution of Vermicular Cast Iron in High Frequent Cyclic Plasma and Different Facial Cooling Airflows

The surface evolution of vermicular cast iron in a high frequent cyclic plasma and facial cooling airflow was studied to understand the behavior and mechanism in different cooling conditions under a unique thermal shock environment. Results indicated that both the mass and linear loss presented titled inverted V-shaped relationships with the flux of the cooling airflow, while the change in roughness decreased continuously. As the cooling airflow rose, the eroded zone was reduced, the iron oxides lessened, and fluctuation of the surface temperature weakened. In combination with the thermodynamic calculations and thermal analysis, it was confirmed that the oxidation and mechanical erosion had contrary tendencies with the rising flux in the facial cooling airflow. The transformation of the dominant factor from oxidation to peeling off by thermal stress and scouring resulted in the evolution of mass and thickness. The surface oxides dominated the change in the roughness.

Self-Sustained Constant Anodic Dissolution Rate on Iron Electrode Under a Magnetic Field

The evolution of the wavy surface of an iron electrode with anodic polarization time in a sulfuric acid solution under a 0.4 T magnetic field is quantified by 3D tomographic depth profile measurements. The electrode surface after anodic dissolution under a magnetic field is irregular and the 3D profile changes with the anodic polarization time. The anodic dissolution rate is specific to the geometrical location on the electrode, which is, in general, insensitive to the polarization time as well as the surface irregularity.

Level-set topology optimization for Ductile and Brittle fracture resistance using the phase-field method

This work presents a rigorous mathematical formulation for topology optimization of a macro structure undergoing ductile failure. The prediction of ductile solid materials which exhibit dominant plastic deformation is an intriguingly challenging task and plays an extremely important role in various engineering applications. Here, we rely on the phase-field approach to fracture which is a widely adopted framework for modeling and computing the fracture failure phenomena in solids. The first objective is to optimize the topology of the structure in order to minimize its mass, while accounting for structural damage. To do so, the topological phase transition function (between solid and void phases) is introduced, thus resulting in an extension of all the governing equations. Our second objective is to additionally enhance the fracture resistance of the structure. Accordingly, two different formulations are proposed. One requires only the residual force vector of the deformation field as a constraint, while in the second formulation, the residual force vector of the deformation and phase-field fracture simultaneously have been imposed. An incremental minimization principles for a class of gradient-type dissipative materials are used to derive the governing equations. Thereafter, to obtain optimal topology to enhance the structural resistance due to fracture, the level-set-based formulation is formulated. The level-set-based topology optimization is employed to seek an optimal layout with smooth and clear boundaries. Sensitivities are derived using the analytical gradient-based adjoint method to update the level-set surface for both formulations. Here, the evolution of the level-set surface is realized by the reaction–diffusion equation to maximize the strain energy of the structure while a certain volume of design domain is prescribed. Several three-dimensional numerical examples are presented to substantiate our algorithmic developments.

Revealing Surface and Interface Evolution of Molybdenum Nitride as Carrier-Selective Contacts for Crystalline Silicon Solar Cells

Molybdenum nitride (MoNx) was perceived as carrier-selective contacts (CSCs) for crystalline silicon (c-Si) solar cells due to having proper work functions and excellent conductivities. However, the poor passivation and non-Ohmic contact at the c-Si/MoNx interface endow an inferior hole selectivity. Here, the surface, interface, and bulk structures of MoNx films are systematically investigated by X-ray scattering, surface spectroscopy, and electron microscope analysis to reveal the carrier-selective features. Surface layers with the composition of MoO2.51N0.21 form upon air exposure, which induces the overestimated work function and explains the origin of inferior hole selectivities. The c-Si/MoNx interface is confirmed to adopt long-term stability, providing guidance for designing stable CSCs. A detailed evolution of the scattering length density, domain sizes, and crystallinity in the bulk phase is presented to elucidate its superior conductivity. These multiscale structural investigations offer a clear structure-function correlation of MoNx films, providing key inspiration for developing excellent CSCs for c-Si solar cells.

Structural transformation and performance analysis of PPS-based bag filters in coal-fired power plants

Owing to the complicated environments, the service life of bag-filter or electrostatic-bag composite precipitators with polyphenylene sulfide (PPS) is greatly deviated from the ideal time. In this paper, the structural transformation of PPS-based bag filter materials collected from the coal-fired power plants with different loading units were investigated systematically. As the SO2 content increases, the surface evolution of PPS fibers from smoothness to crack occurs. An opposite trend is observed for melting point and cross breaking strength. The major reason for the failure of PPS-based bag filters is that working temperature (T) often passes through acid dew gas point (Ta), and the SO3 would be produced during the condensing of H2SO4 when T is lower than Ta. The SO3 with strong oxidation would attack the weak C-S bonds of PPS, resulting in the oxidation or even sulfonation of PPS-based bag filters. This work discloses the actual structural evolution of PPS and some corresponding rules under the complicated corrosive gases with high temperatures, which provides a guidance for prolonging the service life of PPS-based bag filters during the usage of coal-fired power plants.

A bounding surface viscoplastic damage model for time-dependent rock deformation

A novel bounding surface viscoplastic damage (BS-VPD) framework is proposed in this study for capturing the time-dependent rock deformation driven by subcritical cracking. Our constitutive creep model has been established via imposing effective control over stress-state evolution with respect to the characteristic surfaces while enforcing strictly the thermodynamic constraint. In particular, a new viscoplastic flow rule is first developed by upscaling the microscopic subcritical cracking towards macroscopic creep characterization based on the bounding surface concept. A continuum damage criterion has then been deduced from the maximum dissipation principle for capturing realistically the strain hardening and damage softening during sustained creep loading. By further completing the model with a novel strategy for regulating the interactive surface evolution, we have thus reproduced successfully the progressive transition from stable subcritical cracking characteristic of decelerating creep into unstable propagation during accelerating rupture. In addition, a hierarchical procedure has also been formulated in this study to facilitate straightforward calibration via conventional laboratory testing, and the applicability of our BS-VPD model is then verified against constant strain-rate and creep tests of brittle rocks representing distinct lithologies (i.e., granite, sandstone, and gneiss). The close agreement between model simulation and experimental measurement suggests that the proposed BS-VPD framework is able to capture faithfully the trimodal creep behaviour of brittle rocks across primary, secondary, and tertiary regimes.

Fractal characterizations of MeV ion treated CaF2 thin films.

We present the morphological evolution and fractal characterizations of CaF2 thin-film surfaces modified by bombardment with 100 MeV Au+8 ions at various fluences. Atomic force microscopy (AFM) combined with line profile and two-dimensional power spectral density (2D-PSD) analysis was utilized to investigate the evolution of surface morphology as a function of fluence. The AFM images were utilized to investigate the relationship between fractal dimension, roughness exponent, lateral correlation length, and ion fluence. The surface erosion owing to sputtering was depicted using Rutherford backscattering spectrometry. The structural characteristics' dependency on fluence was explored with the help of glancing angle x-ray diffraction measurements on virgin and irradiated samples. Tensile stress calculated using a peak shift in the glancing angle x-ray diffractogram showed an increase in tensile stress with fluence that caused the surface to crack after the fracture strength of the surface was crossed. 2D-PSD analysis signified the role of sputtering over surface diffusion for the observed surface modifications. Fractal dimensions first increased and then decreased with ion fluence. The lateral correlation length decreased, while the roughness exponent increased with fluence after the threshold value.

Surface and bulk relaxation of vapor-deposited polystyrene glasses.

We have studied the liquid-like response of the surface of vapor-deposited glassy films of polystyrene to the introduction of gold nanoparticles on the surface. The build-up of polymer material was measured as a function of time and temperature for both as-deposited films, as well as films that have been rejuvenated to become normal glasses cooled from the equilibrium liquid. The temporal evolution of the surface profile is well described by the characteristic power law of capillary-driven surface flows. In all cases, the surface evolution of the as-deposited films and the rejuvenated films is enhanced compared to bulk and is not easily distinguishable from each other. The temperature dependence of the measured relaxation times determined from the surface evolution is found to be quantitatively comparable to similar studies for high molecular weight spincast polystyrene. Comparisons to numerical solutions of the glassy thin film equation provide quantitative estimates of the surface mobility. For temperatures sufficiently close to the glass-transition temperature, particle embedding is also measured and used as a probe of bulk dynamics, and, in particular, bulk viscosity.

Modeling the moving boundary value problem of electrochemical machining

AbstractTwo evolving surfaces define the moving boundary value problem in electrochemical machining. On the side of the work piece, the anodic dissolution yields the evolution of the machined surface. A novel approach for modeling the dissolution process of the anode has recently been proposed by [6], which is based on internal variables and effective material parameters that are inserted into the balance equation of electric charge. Thereby, the resulting distributions of the electric current densities ‐ the driving forces of the dissolution process ‐ are accurately captured without the necessity to adapt the finite element mesh in each time step. On the tool side, an efficient methodology to incorporate the movement of the cathode into the simulation without remeshing had been lacking so far. Thus, we proposed to extend the modeling approach of [6] to model the cathode also based on effective material parameters whilst using a constant finite element mesh (see [7]). The procedure allows for the consideration of arbitrarily complex geometries that additionally may possess differently oriented feed vectors. In this paper, a new anisotropic rule of mixture is put forward. The presented example is restricted to a stationary cathode, but focuses on a detailed investigation of the new methodology and a comparison with existing rules of mixture, which are a key component of the methodology and equivalently applicable to moving boundary value problems.

Updated Radiative Transfer Model for Titan in the Near-infrared Wavelength Range: Validation against Huygens Atmospheric and Surface Measurements and Application to the Cassini/VIMS Observations of the Dragonfly Landing Area

We present an analysis of Titan data acquired by the Cassini Visual and Infrared Mapping Spectrometer (VIMS) at the landing site of the Dragonfly mission, using a new version of our radiative transfer model for Titan, with significant updates for the spectroscopic parameters of atmospheric gases and photochemical aerosols. Our updated radiative transfer model is validated against the in situ spectroscopic measurements of the Huygens probe during its descent and once landed. We confirm that aerosols with a fractal dimension of 2.3–2.4 provide the best fit to the observations. We apply our radiative transfer model to four VIMS data cubes over the Selk crater region including the Dragonfly landing and exploration areas, further validating our model by producing consistent aerosol population and surface albedo maps. These infrared albedo maps, further corrected from the photometry, enable us to study the Selk crater region in terms of surface composition, landscape formation, and evolution. Our results suggest that the Selk crater is in an intermediate state of degradation and that the mountainous terrains of the area (including the crater rim and ejecta) are likely to be dominated by fine grains of tholin-like sediment. This organic sediment would be transported to the lowlands (crater floor and surrounding plains), possibly with water ice particles, by rivers, and further deposited and processed to form the sand particles that feed the neighboring dune fields. These results provide information for the operational and scientific preparation of the Dragonfly mission, paving the way for future exploration of Titan’s surface composition and geology.