Deep Crater Research Articles

Flexural and low‐velocity behavior of GFPP/DP980 honeycomb sandwich structure inspired by fiber metal laminates

AbstractWith the rapid development of electric vehicles, a hybrid composite structure has been designed for the battery pack bottom guard to enhance impact resistance and reduce weight. The glass fiber‐reinforced polypropylene (GFPP)/DP980 honeycomb sandwich structure consists of GFPP panels with a polypropylene honeycomb core. DP980 advanced high‐strength steel plate is encapsulated within the structure, inspired by fiber metal laminates. A lightweight and high‐strength sandwich composite lay‐up solution was determined through equivalent bending stiffness theory, finite element simulation and experiment. An asymmetric sandwich structure with the steel plate on the impacted side enhanced flexural strength and ductility, demonstrating different failure sequences and a higher bending strength of 77.64 MPa compared to 50.18 MPa when the steel plate was on the unimpacted side. As impact energy increased from 100 to 200 J, the sandwich structure showed higher peak impact load, deeper craters, and increased bulge height, with significant delamination up to 175 J, while gravel impact tests revealed minimal flexural strength reduction (4.92%) even after repeated impacts. This study confirms that the use of thermoplastic sandwich structures is a viable and promising option for crash safety and the lightweight design of battery pack bottom guards.Highlights The thermoplastic honeycomb sandwich structure is polypropylene‐based. The use of advanced high strength steel is inspired by fiber metal laminates. Both thickness and surface density are considered in the structural design. The steel plate placed on the impacted side improves the flexural behavior. The sandwich structure has excellent impact resistance and lightweight level.

Structural modification of high carbon Co−Cr−Mo alloy via chemical etching to enhance hydroxyapatite coating performance

AbstractNumerous papers have been reported on surface treatment of metallic implant to facilitate positive interaction between the implant and hard tissue interface. In this paper, surface treatment such as chemical etching was done on the biomedical grade cobalt‐based alloy prior to hydroxyapatite coating deposition to enhance its biocompatibility. The objective is to investigate which temperature possesses the positive effect in adhesion strength of hydroxyapatite coating without detrimental the surface hardness. Observation showed that acid etched at the highest temperature (80 °C) has successfully roughen the substrate surface from 0.168 μm ±0.1 μm to 1.383 μm ±0.2 μm. Vickers hardness measurement on surface treated at 80 °C exhibit an increment of surface hardness which is about 39 % compared to surface treated at lower temperature. The highest thickness of hydroxyapatite coating layer (~57 μm) was evidently formed on the substrate etched at 80 °C with minimal cracks and no delamination. This phenomenon happened due to chemical reaction were rigorously attack on the substrate surface have provide more micro‐pits, pores and deeper craters that trap more efficiently of hydroxyapatite particles for thicker and dense coating formation. It is worth to note that too long acid soaking will also detrimental the material properties.

A new model of crater degradation on Ceres involving ice sublimation and talus formation

We report on the widespread occurence of talus on cerean crater walls using Dawn framing camera images. This is unexpected for a planetary body with no atmosphere like Ceres since the dominant process in crater degradation was expected to be topographic diffusion associated with impact gardening, like on the Moon or Mercury. To investigate why talus deposits are so common, and whether they could be related to the particular nature of Ceres’ ice-rich crust, we mapped them over the entire surface and studied their morphological characteristics. We classified the features into three different types, indicating their degree of preservation. Our results show that there is no trend between the total surface area of talus (whatever their degree of preservation) and latitude or longitude. However, we found that talus deposits tend to be observed within deep and young impact craters, and that certain craters expose a particularly large surface area of talus deposits: Dantu, Ninsar, Occator, Kupalo and Juling craters. It was also noted that well-preserved talus have a larger surface area than more degraded ones, and have ≈20 % more consolidated outcrops per km2. Age estimates from crater size frequency distributions for the host craters completed these observations, giving a mean age of 20−4+4 Ma for the craters hosting the more preserved talus deposits, and 280−8+8 Ma for the craters hosting the more degraded ones. By studying the slope of the talus deposits, we obtained a value of the angle of repose of the cerean regolith: 34.5°± 2.8°. We also found that the talus facing the poles are approximately 5°steeper than those facing the equator, have an 18 % larger surface area, and exhibit three times as many outcrops compared to talus on crater walls facing other directions. This suggests that the degradation of outcrops, the source of the material making up the scree, is sensitive to insolation. If we assume that the outcrops are made cohesive by the ice they contain, then we can conclude that sublimation of this ice leads to their fragmentation, at the origin of the talus material. We suggest that outcrop wall retreat due to ice sublimation feeding talus slopes is a predominant process in the earlier phase of crater degradation on Ceres supplanting impact gardening and topographic diffusion for some tens of million years. Once the maximum extent of the talus is reached, the progressively reduced debris production leads to a decreasing talus activity. Impact gardening then takes over and talus deposits are slowly degraded during the next few hundreds million years before fully disappearing. This has an influence on age estimations of the surface of Ceres, as the diameters of the craters grow larger over time due to the ice sublimation, resulting in a slight overestimation of the age of the dated cerean areas. In addition, in the perspective of future missions to Ceres, one of whose objectives would be to precisely quantify the ice content of the crust, the outcrops facing the poles and not yet degraded would be among the most interesting targets to explore.

MARS CHRONOLOGY DERIVED FROM CRATERS HETEROGENEITY AT GALE CRATER

Craters sample into diachronic surfaces and different depths on Mars and other planetary surfaces. These surfaces are affected by cosmonuclide radiation that offers one of the most reliable age anchors to date. Craters also accumulate, evolve and display an universal characteristic that can be measured at any scale, regardless of the geologic unit they sample, in the form of the heterogeneity parameter (Capitan, 2021). Here we use an age equation, which is based on the measurements of craters diameter, depths and area they occupy, to derive the ages of deposits that are sampled by medium-scale craters (meters to few hundred meters in diameter). We show that units sampled by the deepest craters near MSL exploration area are formed during the early stages of Gale crater formation before 2870 Ma. In contrast, units sampled by shallower craters were formed during the stages that correspond to the time of sediment recycling and lithification periods, near 2129 Ma to present. Given the heterogeneity of initial formation conditions of craters of diverse diameters and their different depths of sampling, our proposed synchronous ages with ground-truth ages has the potential to redefine the paradigm of using the impact crater morphometry as a tool to date the planetary surfaces.

Drag Modeling Effects on Simulations of Supersonic Jet-Induced Cratering in a Soil

The impact of the drag model in the simulation of turbulent granular flows is studied using databases here created through simulations of supersonic jet-induced cratering in granular soil. The simulations are based on a previously developed model, which was shown to be hyperbolic, thus permitting the unhindered propagation of pressure waves critical to craters produced by supersonic plumes. The goal is to identify predicted quantities from these simulations that show sufficient differences among simulations performed with different drag models; these quantities would warrant future experimental investigations determining which model is correct. Among all drag models examined, only two models are found applicable to the regime of investigation. Examination of the databases is conducted from the viewpoint of global quantities and detailed quantities. The results show that isocontours and characteristic length scales are minimally affected by the employed drag law. In contrast, azimuthally averaged and root mean square ejecta-related quantities are more sensitive to the drag model employed, but only in the central part of the crater. This sensitivity is much larger for shallow craters having a parabolic cross section than for deep craters having a conical cross section, thus indicating the experimental configuration best suited to experimentally evaluating drag models.

Splashing impact of a falling liquid drop

The splashing phenomenon associated with the impact of a liquid drop on a liquid pool is investigated in this study using the volume of fluid method. The different outcomes of this phenomena largely depend on the height (/depth) of a liquid pool and the impinging drop velocity. The impingement angle, drop shape, fluid properties, and other non-isothermal effects also play a role, but we have eliminated those dependencies by considering no variation in these parameters. The different phenomena that are observed when a drop impacts a liquid pool are controlled by (i) crater depth and wave-swell (rim of the crater) expansion, (ii) wave-swell retraction followed by crater side retraction, and (iii) crater base retraction. During splashing, a deep crater is produced in the receiving liquid after the drop impact. At its rim, a crown-like cylindrical liquid film is ejected out of the crater. Small droplets are normally shed from this rim. It is seen that the depth of the pool has dramatic effects on the dynamics of the crown formed during splashing. When observed even more comprehensively, the physical attributes of the crown, such as crown height and crown radius, are found to strongly relate to the velocity of the falling drop. Finally, we try to demarcate the regions of splashing with and without the formation of secondary droplets on the regime map of Weber number–dimensionless pool depth.

Investigating laser beam shadowing and powder particle dynamics in directed energy deposition through high-fidelity modelling and high-speed imaging

Laser beam shadowing in directed energy deposition process occurs when in-flight powder particles partially block the laser beam, preventing it from fully reaching the melt pool. This blockage alters the beam's profile, introducing spatio-temporal randomness in heat transfer to the melt pool and affecting its stability. This study utilizes a novel high-fidelity multiphysics model to quantitatively analyze gas-powder stream dynamics and laser-particle interactions. It specifically focuses on dynamic variations in laser beam shadowing, attenuation, and reflection of the laser beam radiant energy, along with powder particles temperature prediction from in-flight heating, accounting for multiple reflection phenomena. Gas-particle dynamics is modeled using a fully coupled CFD-DEM approach, while laser-particle in-flight interactions are predicted using a ray-tracing-based photon discretization method. Modeling predicted that interactions between the laser beam and the in-flight powder stream could result in energy losses up to approximately 70 % due to shadowing and attenuation. The study comprehensively explored the spatio-temporal variations in the attenuated laser beam profile, revealing significant deviations from its initial Gaussian profile and substantial stochasticity and randomness over time. To confirm the modeling results and correlate computational predictions with experimental data, high-speed visible imaging of the powder stream, both with and without the melt pool, along with laser beam attenuation measurements using a photodiode system, were conducted. The model's predictions of particle velocity and laser beam attenuation characteristics aligned with the results from these experiments. Modeling and high-speed imaging demonstrated that in-flight heating caused some particles to melt and few others to reach the vaporization threshold. High-speed imaging further validated these numerical findings by examining the interaction of heated particles with the melt pool across different phases (solid, liquid, and partially vaporized). A significant observation was the increased velocities of partially vaporized particles due to recoil pressure from selective vaporization, which led to the formation of deep craters in the melt pool resulting from high-speed impact.

Understanding stratification and turnover dynamics of a tropical lake using extensive field observations and 3D hydrodynamic simulations

The stratification and turnover dynamics of a tropical lake were evaluated using field observations and 3D hydrodynamic simulations. Located in the Philippines, Sampaloc Lake is a 104-ha and 27-m deep volcanic crater lake with enclosed watershed, which is at risk of the impacts of intensive aquaculture, rapid urbanization and climate change. Temperature, dissolved oxygen (DO) and chlorophyll-a (Chl-a) were measured at seven sampling stations using a multiprobe. Kruskal-Wallis test revealed that the three parameters are not significantly different among stations, indicating that one sampling station can represent the water quality of the whole lake. Schmidt's Stability Index (SSI) and thermocline strength, together with DO and Chl-a gradients decreased from October 2022 (stratified) to January 2023 (turnover). After successfully verifying the 3D numerical model, sensitivity analyses of water temperature to varying weather, together with particle tracking simulations, were implemented to determine the timing of isothermal state, upwelling, partial mixing, and full turnover. Compared to air temperature, variations in wind speed have more pronounced effects on the delay or progression of isothermal conditions in the lake based on SSI, Lake Number and Wedderburn Number. Isothermal conditions do not necessarily coincide with the timing of full turnover, with the latter being delayed by two days than the former, on average. Results revealed that full turnover can occur several weeks earlier with the decrease in AT and increase in WS. This study can advance the understanding of thermal and turnover dynamics of stratified tropical lakes, leading to better management of the water quality of these water bodies.

Parametric analysis, modeling and optimization of the process parameters in electric discharge machining of aluminium metal matrix composite

Optimizing electric discharge machining (EDM) for aluminum/SiCp metal matrix composites poses challenges due to intricate machine parameters and process complexity, impacting process economy and elevating product costs. The research aims to find the optimal combination of process parameters which include pulse on-time, pulse current, duty cycle (%), gap voltage, sensitivity and flushing pressure for EDM of Al/SiCp-MMC using a copper electrode for the selected response factors such as material erosion rate and surface roughness, Ra. The experiments were designed using the central composite design of response surface methodology and an advanced optimization technique known as Teaching–learning-based optimization (TLBO), is applied to find the optimal combination of process parameters to obtain maximum material erosion rate subject to the desired range of surface roughness (SR), Ra. The combination of the high pulse on-time (i.e. 150 μs) and high pulse current (i.e. 12A) results in high material removal rate with deep craters on the machined surface clearly visible in SEM images contrasting the minimized surface roughness at lower values of pulse on-time (50 μs) and the pulse current (4A). Pulse on - time (Ton) is found to be the most significant factor for material erosion rate and surface roughness with percentage contribution of 70.86 and 54.9 respectively for optimization of the response. The regression models were developed at 95% confidence level for material removal rate and surface roughness with R2 value of 0.93 and 0.95 respectively signifying high degree of accuracy in predicting the response. Confirmation tests conducted to check the adequacy of the established models revealed that the percentage error between the predicted and experimental responses is found to be within acceptable levels. Electron discharge machining of the aluminium metal matrix composite at the optimized conditions could provide economical aspect in the aerospace and automobile industry.

Crater Triangle Matching Algorithm Based on Fused Geometric and Regional Features

Craters are regarded as significant navigation landmarks during the descent and landing process in small body exploration missions for their universality. Recognizing and matching craters is a crucial prerequisite for visual and LIDAR-based navigation tasks. Compared to traditional algorithms, deep learning-based crater detection algorithms can achieve a higher recognition rate. However, matching crater detection results under various image transformations still poses challenges. To address the problem, a composite feature-matching algorithm that combines geometric descriptors and region descriptors (extracting normalized region pixel gradient features as feature vectors) is proposed. First, the geometric configuration map is constructed based on the crater detection results. Then, geometric descriptors and region descriptors are established within each feature primitive of the map. Subsequently, taking the salience of geometric features into consideration, composite feature descriptors with scale, rotation, and illumination invariance are generated through fusion geometric and region descriptors. Finally, descriptor matching is accomplished by computing the relative distances between descriptors and adhering to the nearest neighbor principle. Experimental results show that the composite feature descriptor proposed in this paper has better matching performance than only using shape descriptors or region descriptors, and can achieve a more than 90% correct matching rate, which can provide technical support for the small body visual navigation task.

Wear behavior of ultrafine WC-Co cemented carbide end mills during milling of Inconel 718

Two innovative ultrafine cemented carbide end mills, denoted C1 and C2, were synthesized through spark plasma sintering, featuring compositions of WC-8Co-0.4VC-0.4Cr3C2 and WC-40(Ti,W)–8Co-0.4VC-0.4Cr3C2, respectively. Their wear behaviors were delved into during the precision machining of Inconel 718, and distinct disparities in wear evolution and tool longevity were unveiled. C1 exhibits exceptional wear resistance, surpassing C2 by a striking margin of 7.4–9.5, depending on the cutting speed employed. The sharp cutting edge of C1, characterized by a single hard phase of WC, minimal grain size, and high hardness, demonstrates excellent wear resistance and deformation resistance, thereby minimizing the onset of notch wear. In contrast, C2 experiences severe adhesive and diffusive wear phenomena, which culminate in substantial flank wear and cutting edge chipping. The addition of 40 wt% of (Ti,W)C exacerbates adhesion, flaking, and notch wear during machining. The prolonged and intensified adhesive wear witnessed in C2 leads to the deterioration of the tool surface and the formation of deep wear craters on the flank face. A comparison evaluation involving the prepared novel tools and commercially available end mills reveals that C1 boasts a longer tool life that outstrip those of its commercial counterparts by approximately 1.7–3.5 times under identical cutting conditions.

Experimental investigation on the surface quality of WEDM machined 20MnCr5 steel for gear application

This experimental study investigates the Wire-cut Electrical Discharge Machining (WEDM) of 20MnCr5 steel, a low alloy steel grade material which is intended for the production of gears, shafts and other parts which need high surface hardness and wear resistance. WEDM is a crucial manufacturing process for producing gears, shafts, spindles, and various mechanical components. The investigation focuses on three key performance parameters: profile error, material removal rate (MRR), and surface roughness (SR), employing five WEDM parameters—wire feed (Wf), wire tension (Wt), servo voltage (SV), discharge arc-off time (Toff), and arc-on time (Ton) - by employing the Taguchi L27 orthogonal array. The study reveals that, in comparison to arc-on time and servo voltage, wire feed rate and tension have a lesser impact. Higher arc-on time and servo voltage result in increased profile error, while reduced wire tension values elevate surface roughness. Recast layer formation has been explored under different WEDM input parameters, revealing its dependence on arc-on time, voltage, wire tension, and feed rate. Higher voltage leads to uneven surfaces with larger globules and deep craters, contributing to a thicker recast layer at higher arc-on time and servo voltage.

Droplet–jet collision following the monodispersedly dripping of coaxial binary droplets above a pool surface

In the present study, the collision between a falling droplet and a rising Worthington jet was experimentally studied. The event is followed by the monodispersedly dripping of coaxial binary droplets into a quiescent pool of glycerol solution. Different concentrations of the solution are considered. Unique droplet–jet collision characteristics are observed when the dripping flow rate is manipulated to release binary droplets. When the first droplet impacts the pool, a significant disturbance is imposed onto the pool, forming a deep crater followed by a Worthington jet. The second droplet is timed to collide with the rising jet to create a unique mushroom-shaped droplet–jet collision. Two jet pinch-off modes (tip pinch-off and no pinch-off) and four distinct collision regimes (partial rebounding, end-pinching, elongated, and clotted central jet collision) are recognized. Liquid viscosity and jetting mode significantly influence the collision dynamics and splattering characteristics. To achieve partial rebounding collision at low Weber number, a high-impact coefficient incorporating characteristic dimensions of the droplets and the Worthington jet is required, whereas a low-impact coefficient is required at high Weber number to attain clotted jet collision. The overall end-pinching phenomenon occurs due to the interaction between liquid flow toward the jet tip and the retraction of the tip, which causes the jet neck diameter to decrease on a capillary timescale. As the impact parameter decreases, the Worthington jet is inhibited, and the mushroom-shaped collision splash spreading is suppressed.

Wettability, reactivity, and interface structure in Mg/Ni system

The sessile drop method was applied to the experimental investigation of the wetting and spreading behaviors of liquid Mg drops on pure Ni substrates. For comparison, the experiments were performed in two variants: (1) using the Capillary Purification (CP) procedure, which allows the non-contact heating and squeezing of a pure oxide-free Mg drop; (2) by classical Contact Heating (CH) procedure. The high-temperature tests were performed under isothermal conditions (CP: 760 °C for 30 s; CH: 715 °C for 300 s) using Ar + 5 wt% H2 atmosphere. During the sessile drop tests, images of the Mg/Ni couples were recorded by CCD cameras (57 fps), which were then applied to calculate the contact angles of metal/substrate couples. Scanning and transmission electron microscopy analyses, both coupled with energy-dispersive X-ray spectroscopy, were used for detailed structural characterization of the solidified couples.It was found that an oxide-free Mg drop obtained by the CP procedure showed a wetting phenomenon on the Ni substrate (an average contact angle θ < 90° in < 1 s), followed by fast spreading and good wetting over the Ni substrate (θ(CP) ∼ 20° in 5 s) to form a final contact angle of θf(CP) ∼ 18°. In contrast, a different wetting behavior was observed for the CH procedure, where the unavoidable primary oxide film on the Mg surface blocked the spreading of liquid Mg showing apparently non-wetting behavior after 300 s contact at the test temperature.However, in both cases, the deep craters formed in the Ni substrates under the Mg drops and significant change in the structure of initially pure Mg drops to Mg-Ni alloys suggest a strong dissolution of Ni in liquid Mg and apparent values of the final contact angles measured for the Mg/Ni system.

Comparison of Doses in Lunar Habitats Located at the Surface and in Crater

As humanity prepares for extended lunar exploration, understanding the radiation environment on the Moon is important for astronaut safety. This study utilized the Particle and Heavy-Ion Transport code System (PHITS), a stochastic Monte Carlo-based radiation transport code, to simulate the radiation environment inside a habitat, focusing on the impact of galactic cosmic rays (GCRs) interacting with local lunar and habitat material, and to calculate the effective dose equivalent. Placing a lunar base in a crater can provide additional shielding by reducing the GCR flux incident on the base. Furthermore, the secondary radiation field created by GCR interactions may be altered by the local topological features. GCR transport calculations were performed for a hypothetical base on a flat surface and in shallow and deep craters to determine the overall efficacy in dose reduction gained by placing a base in a 100 m diameter crater. Our findings indicate that the depth of lunar habitats significantly influences the effective dose equivalent, with deeper locations offering substantial protection. Specifically, alongside a crater wall at a deep depth (15 m), in solar minimum conditions, the total dose was reduced by approximately 44.9% compared to the dose at the surface. Similarly, at a shallow depth (5 m), a reduction of approximately 10.7% was observed. As the depth of the crater increased, the neutron contribution to the total dose also increased. Comparing the simulated doses to NASA’s lifetime exposure limits provides insights into mission planning and astronaut safety, emphasizing the importance of strategic habitat placement and design.

Optimizing the contributing electro-erosive discharge parameters for reducing the electrode wear and geometric dimensional deviation in EDM of Ti-based superalloy

The low thermal conductivity, the small magnitude of modulus of elasticity, and the high chemical reactivity of Ti-6Al-4V make it difficult to machine this material using traditional processes. The intended requirements for the applications of the said alloy, like in biomedical and aerospace, further complicate its processing. Thereof, electric discharge machining (EDM) opted for this alloy. However, intrinsic issues of EDM, that is, electrode wear rate (EWR) and dimensional overcuts, restricted its utilization. Therefore, the potential of three powder-based additives and dielectric fluids against different electrode materials has been deeply envisaged to address the abovementioned issues. Because the choice of best dielectric has a direct bearing on heat input to the electrode which influences the melting/vaporization of the tool wear of the electrode. It is worth mentioning that these concerns have not been discussed so far in such a broad spectrum. Taguchi’s experimental design is used for experimentation. The results show that transformer oil performance is best rated compared to other dielectrics. Overall, the reduction in tool wear rate and overcut obtained with transformer oil is 21.3% and 21.4%, respectively, in contrast to the other dielectrics. The electrode of Cu outperforms for yielding the smaller value of overcut and tool wear rate. In the case of micro-additives, alumina has proved its potential for lowering the electrode wear rate. Deep and wide craters of a depth of 150 µm have been observed by using the brass electrode in kerosene oil, whereas the small and shallow craters of 38 µm depth have been encountered using the Cu electrode in the presence of transformer oil.

Impact analysis of electrode materials and EDM variables on the surface characteristics of SS316L for biomedical applications

The biocompatibility of the SS316L makes it an alluring alternative for orthopaedic and other biomedical applications. In such applications, surface characteristics of the materials are key considerations for bacterial adhesion at the surface of the metallic implant. Therefore, the current study focuses on the investigation of surface roughness and microhardness of SS316L in the electric discharge machining process using adequate electrode/tool material. Machining is performed with brass, copper, and aluminum electrodes to limit the surface roughness and enhance the microhardness of machining surfaces. Besides this, process variables including peak current, pulse off time, pulse on time and spark voltage are also optimized to obtain superior surface characteristics. Results show that adequate surface roughness of 1.08 μm can be attained with the aluminum electrode while brass electrodes offered increased microhardness of 1270.6 HV of machined surfaces. Microstructural analysis shows that aluminum electrode yields shallow and small-sized craters and few micro-cavities while brass electrode generates high peaks and valleys on the machined surface due to the deep craters, micro cracks, and cavities. The composite desirability function approach suggests that aluminum electrode along with the optimal setting of process variables such as peak current = 25 A, pulse off time = 50 μs, pulse on time = 55 μs and spark voltage = 2 V offers reasonable values of surface roughness 4.09 μm and microhardness 1051.2 HV after trading off.

Dual-wavelength femtosecond laser-induced single-shot damage and ablation of silicon

An experimental and theoretical study of laser-induced damage and ablation of silicon by two individual femtosecond pulses of different wavelengths, 1030 and 515 nm, is performed to address the physical mechanisms of dual-wavelength ablation and reveal possibilities for increasing the ablation efficiency. The produced craters and damaged areas are analyzed as a function of laser fluence and time separation between the pulses and are compared with monochromatic irradiation. The order of pulses is demonstrated to be essential in bi-color ablation with higher material removal rates when a shorter-wavelength pulse arrives first at the surface. Simulations based on the two-temperature model show that the visible pulse is profitable for the generation of the electron-hole plasma while the delayed IR pulse is efficiently absorbed in the plasma enhancing energy coupling to the target. At long delays of 30–100 ps, the dual-wavelength ablation is found to be particularly strong with formation of deep smooth craters. This is explained by the expansion of a hot liquid layer produced by the first pulse with a drastic decrease in the surface reflectivity at this timescale. The results provide insight into the processes of dual-wavelength laser ablation offering a better control of the energy deposition into material.

Tissue Ablation with Multi‐Millimeter Depth and Cellular‐Scale Collateral Damage by a Femtosecond Mid‐Infrared Laser Tuned to the Amide‐I Vibration

AbstractLaser ablation of bio‐tissues is the key technology of future surgeries, owing to the merits of submicron accuracy, non‐contact operation, and precision control assisted by automation and computer intelligence. Excellent efficiency, minimal collateral damage, biological safety, and tissue selectivity are the ideal parameters for delicate surgical applications. Here, by exploring the mid‐infrared (MIR) resonant ablation and the femtosecond cold processing, tissue ablation with multi‐millimeter depth and cellular collateral damage, enabled by a tabletop femtosecond MIR optical parametric amplifier operating at the amide‐I resonant wavelength of 6.1 µm, is demonstrated. Remarkably, the collateral damage is observed to be 15, &lt;4, and &lt;1 µm in the porcine cornea, sclera, and articular cartilage, respectively, with multi‐millimeter incision depth. In addition, preliminary proof‐of‐concept experiments of tissue‐selective ablation, microchannels on cartilage for drug delivery, laser glaucoma, keratotomy, neurologic tissue incision, dentin deep crater formation, and hypertrophic scarring ablation are demonstrated, which pave the way for high‐precision surgical applications with a tabletop solution.

Impact Crater Morphometry on Pluto: Implications for Surface Composition and Evolution

New Horizons showed that Pluto exhibits a wide range of geologic groups, with much of the surface modified by volatile ice processes. Impact craters are a valuable tool to investigate how these regions have evolved, as they record the effects of various modification mechanisms and retain information on the properties of the bedrock ice(s). In this work, we use Pluto’s crater population to quantify the extent of surface modification and identify variations in surface properties on Pluto. In this study, we have measured the relative depth of Pluto’s craters compared to minimally modified water-ice craters to interpret how the craters may have evolved and/or what the information tells us about the surface properties of the bedrock. We found a trend of increasing crater relative depth from southeast to northwest that may reflect the conditions of an ancient surface when a thicker layer of volatile ice may have existed, possibly changed by polar wander after the Sputnik impact. We have identified anomalously deep craters across Pluto’s surface, with a concentration in Cthulhu Macula, suggesting different bedrock-ice properties in this region. Other deep craters may be influenced by extraneous factors, such as impactor speed. Overall, this study expands on our understanding of the evolution and composition of Pluto’s surface and sets a road map for further investigations into Pluto’s surface evolution.