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Yutu-2 rover conducted an exciting expedition on the 41st lunar day to investigate a fin-shaped rock at Longji site (45.44°S, 177.56°E) by extending its locomotion margin on perilous peaks. The varied locomotion encountered, especially multi-form wheel slippage, during the journey to the target rock, established unique conditions for a fin-grained lunar regolith analysis regarding bearing, shear and lateral properties based on terramechanics. Here, we show a tri-aspect characterization of lunar regolith and infer the rock’s origin using a digital twin. We estimate internal friction angle within 21.5°−42.0° and associated cohesion of 520-3154 Pa in the Chang’E-4 operational site. These findings suggest shear characteristics similar to Apollo 12 mission samples but notably higher cohesion compared to regolith investigated on most nearside lunar missions. We estimate external friction angle in lateral properties to be within 8.3°−16.5°, which fills the gaps of the lateral property estimation of the lunar farside regolith and serves as a foundational parameter for subsequent engineering verifications. Our in-situ spectral investigations of the target rock unveil its composition of iron/magnesium-rich low-calcium pyroxene, linking it to the Zhinyu crater (45.34°S, 176.15°E) ejecta. Our results indicate that the combination of in-situ measurements with robotics technology in planetary exploration reveal the possibility of additional source regions contributing to the local materials at the Chang’E-4 site, implying a more complicated geological history in the vicinity. Digital twins can be used to support planetary operations and analysis. Here, the authors show tri-aspect characterization of lunar far side regolith and investigate the origin of a fin-shaped rock via digital twin of Yutu-2 rover.

Terrain traversability analysis (TTA), the key to the navigation of planetary rovers, is significant to the safety of the rover. Therefore, owing to its complexity, the Martian terrain is worth analysing comprehensively based on the terrain variability and hazard level. In this work, we propose a novel method for terrain traversability analysis for the path planning of planetary rovers by integrating Martian terrain geometry features with terrain semantic information, which includes geometry and environmental perception (GEP). Specifically, we deploy semantic segmentation to classify common terrain types, such as rocks, bedrocks, and sand, obtaining semantic information as one part of terrain traversability analysis at the same time. Simultaneously, the point cloud is generated by using binocular images from the planetary rover navigation camera (Navcam) to construct a 2.5D elevation map of the environment to analyse the geometric characteristics of the terrain. Besides, we implement path planning based on the results of TTA-GEP. Overall, our proposed method improves the performance of the terrain traversability analysis and reduces the risk of planetary rovers while detecting in an unstructured environment.

Tianwen-1, China’s first Mars exploration mission, was successfully landed in the southern part of Utopia Planitia on 15 May 2021 (UTC+8). Timely and accurately determining the landing location is critical for the subsequent mission operations. For timely localization, the remote landmarks, selected from the panorama generated by the earliest received Navigation and Terrain Cameras (NaTeCam) images, were matched with the Digital Orthophoto Map (DOM) generated by high resolution imaging camera (HiRIC) images to obtain the initial result based on the triangulation method. Then, the initial localization result was refined by the descent images received later and the NaTeCam DOM. Finally, the lander location was determined to be (25.066°N, 109.925°E). Verified by the new orbital image with the lander and Zhurong rover visible, the localization accuracy was within a pixel of the HiRIC DOM.

The effect of inclined volute tongue on the aerodynamic noise and performance of a centrifugal fan was investigated by experimental test in this article. The present work highlights that the effect of both the clearance and the radius of the volute tongue has an influence on the performance and noise. The experimental tests of various models aim to obtain the aerodynamic noise and performance characteristics of several fan models. First, the experimental results of centrifugal fan performance are tested by the standard test equipment of aerodynamic performance. The experimental results of centrifugal fan aerodynamic noise are measured by the standard test equipment of experimental noise. Our experimental results mainly show that the generation of aerodynamic noise is significantly correlated with the clearance and radius of the volute tongue. Certain geometries of the volute tongue could reduce the noise of the centrifugal fan without decreasing the performance. It is experimentally demonstrated that the high A-weighted sound pressure levels mainly concentrate on a range of from 700 to 7000 Hz frequency by observing the each 1/3 octave band frequency for four fan models. The comparison of aerodynamic noise results also demonstrates that the inclined volute tongue may not only produce a deceasing of about 1.58 dB compared to that of the baseline model. We further obtain that the properly inclined volute tongue not only has positive performance features compared with the baseline model but also effectively controls the broadband frequency noise of single-inlet centrifugal fan.

Resistance spot welding (RSW) quality substantially influences the autobody’s mechanical properties and safety performance. Nondestructive testing (NDT) method is widely used to evaluate the quality of RSW, but the traditional ultrasonic testing method has high requirements for coupling conditions and flat surface of the weld part. The electromagnetic acoustic transducer (EMAT) is a novel NDT technology, which has advantages of noncontact, no coupling media, and low requirements for surface flatness of the workpiece. Therefore, the electromagnetic ultrasonic transverse wave (EUTW) is developed to realize the evaluation of RSW quality in this paper. Under the COMSOL platform, the finite element method (FEM) modeling is proposed by multiphysics simulation. The multiphysical fields include electromagnetic field, acoustic field, and solid mechanics. The generation mechanism and propagation rules of EUTW in various spot welds are studied by simulation analysis. The correctness of FEM modeling is validated by EUTW experiments; results show that the experimental waveforms of EUTW are consistent with the simulation waveforms. Finally, an evaluation method of the nugget size of RSW is proposed based on the simulation and experiments analysis of EUTW detection of RSW with different nugget diameter and indentation depth. The approach presented in this paper can provide the theoretical foundation and new method for the noncontact, high efficient, and low-cost detection of RSW quality of the autobody.

The steady and unsteady flow characteristics of internal flow in a backward centrifugal fan of double inlet at low flow-rate condition are investigated by computational fluid dynamics in this paper. The investigation aims to reveal insights into generation mechanisms and our physical understanding of the rotating stall and surge. The numerical results mainly demonstrate that, with decreasing flow rate, a large number of vortex flows almost increasingly occupy the internal flow of the impeller. The reverse flow and separation vortices increasingly appear near the outlet of volute, and the internal flow of the impeller is completely blocked by the separated vortex flow at low flow-rate conditions. Results indicate that, due to a synchronization of the impeller rotation and separation vortex, these separated vortices act intensely on the pressure surface of the blade with time evolution, and the interaction between the separated vortices and surface of blade increasingly yields small-scale eddies. It is further found that the amplitude of pressure and velocity fluctuations gradually increase with the decrease of flow rate in a certain range. The unsteady characteristics acting on the volute tongue gradually increase in a range of Qd to 0.3 Qd (Qd is the design volume flow rate) with the decrease of flow rate, and the unsteady characteristics acting on the volute tongue are weakened at the working condition of 0.15 Qd. These insights clearly explain the unsteady nature of the rotating stall and surge phenomenon in the double inlet backward centrifugal fan.

This article introduces papers published in the special collection of Water Resources Research on quantifying human interferences (or interventions in general) in hydrology and embedding them within large‐scale hydrological models. Starting with a list of instances of human interferences in various hydrologic processes, this article discusses the diverse perspectives of those papers, places the contributions in the context of related work, and distills insights and research perspectives. Eventually, this article goes beyond a typical special collection introduction and offers the author's perspective on human interferences in hydrologic processes.

BackgroundWith the development of micromanufacturing and 3D printing technologies, gut-on-a-chip provides a new method for studying intestinal diseases in vitro. Based on intestinal functions, gut-on-a-chip introduces modules with different parts, such as an injection pump for fluid flow and a pressure system for mechanical deformation. As a suitable platform for in vitro cell culture, microfluidic technology has attracted widespread attention in reconstructing various human organs, namely organ-on-a-chip technology. Compared to traditional model systems, gut-on-a-chip offers the capabilities of real-time observation, simulation of the intestinal microenvironment, adjustable fluid flow shear stress, and a host-microbiome interface.Methods‘Gut-on-a-chip’ can be divided into three types based on its structure. The first type of gut-on-a-chip consists of an upper microchannel, a lower microchannel, and a porous membrane in between. The second type of gut-on-a-chip comprises an upper microchannel, a lower microchannel, and a middle channel. The third type of gut-on-a-chip consists of a left microchannel, a right microchannel, and a middle channel filled with collagen gel. To further enhance the gut-on-a-chip’s ability to mimic the in vivo microenvironment, cells with different functions, oxygen concentration gradients, and scaffolds are incorporated.ResultsApplied an optimized immune-related cytokine trigger that simulates the effect of Escherichia coli-activated dendritic cells on intestinal epithelial cells to mimic inflammatory characteristics in this model. Additionally, IECs derived from human intestinal organoids were integrated with monocyte-derived macrophages onto the gut-on-a-chip platform. Lipopolysaccharide and interferon-γ were used to induce IBD markers. Under microfluidic conditions, it was determined that the transcriptome of the gut-on-a-chip resembled that of a normal adult human colon in vivo.ConclusionsGut-on-chip can be employed to resolve many of these challenges by extracting key parameters to simplify the whole system, combining different modules to uncover interactions, and realizing in vitro detection to monitor real-time dynamics. Therefore, the gut-on-a-chip can serve as a powerful platform for studying IBD.

Ubiquitous yet unique, lipid droplets are intracellular organelles that are increasingly being recognized for their versatility beyond energy storage. Advances uncovering the intricacies of their biogenesis and the diversity of their physiological and pathological roles have yielded new insights into lipid droplet biology. Despite these insights, the mechanisms governing the biogenesis and functions of lipid droplets remain incompletely understood. Moreover, the causal relationship between the biogenesis and function of lipid droplets and human diseases is poorly resolved. Here, we provide an update on the current understanding of the biogenesis and functions of lipid droplets in health and disease, highlighting a key role for lipid droplet biogenesis in alleviating cellular stresses. We also discuss therapeutic strategies of targeting lipid droplet biogenesis, growth or degradation that could be applied in the future to common diseases, such as cancer, hepatic steatosis and viral infection.This Review outlines our current understanding of the biogenesis and functions of lipid droplets in health and disease, highlighting a key role for lipid droplet biogenesis in alleviating cellular stress.

Likelihood cross-validation for kernel density estimation is known to be sensitive to extreme observations and heavy-tailed distributions. We propose a robust likelihood-based cross-validation method to select bandwidths in multivariate density estimations. We derive this bandwidth selector within the framework of robust maximum likelihood estimation. This method establishes a smooth transition from likelihood cross-validation for nonextreme observations to least squares cross-validation for extreme observations, thereby combining the efficiency of likelihood cross-validation and the robustness of least-squares cross-validation. We also suggest a simple rule to select the transition threshold. We demonstrate the finite sample performance and practical usefulness of the proposed method via Monte Carlo simulations and a real data application on Chinese air pollution.