Efficient RRT*-based Safety-Constrained Motion Planning for Continuum Robots in Dynamic Environments

Continuum robots, characterized by their high flexibility and infinite degrees of freedom (DoFs), have gained prominence in applications such as minimally invasive surgery and hazardous environment exploration. However, the intrinsic complexity of continuum robots requires a significant amount of time for their motion planning, posing a hurdle to their practical implementation. To tackle these challenges, efficient motion planning methods such as Rapidly Exploring Random Trees (RRT) and its variant, RRT*, have been employed. This paper introduces a unique RRT*-based motion control method tailored for continuum robots. Our approach embeds safety constraints derived from the robots' posture states, facilitating autonomous navigation and obstacle avoidance in rapidly changing environments. Simulation results show efficient trajectory planning amidst multiple dynamic obstacles and provide a robust performance evaluation based on the generated postures. Finally, preliminary tests were conducted on a two-segment cable-driven continuum robot prototype, confirming the effectiveness of the proposed planning approach. This method is versatile and can be adapted and deployed for various types of continuum robots through parameter adjustments

Diverse phylogeny and morphology of magnetite biomineralized by magnetotactic cocci

Magnetotactic bacteria (MTB) are diverse prokaryotes that produce magnetic nanocrystals within intracellular membranes (magnetosomes). Here, we present a large‐scale analysis of diversity and magnetosome biomineralization in modern magnetotactic cocci, which are the most abundant MTB morphotypes in nature. Nineteen novel magnetotactic cocci species are identified phylogenetically and structurally at the single‐cell level. Phylogenetic analysis demonstrates that the cocci cluster into an independent branch from other Alphaproteobacteria MTB, that is, within the Etaproteobacteria class in the Proteobacteria phylum. Statistical analysis reveals species‐specific biomineralization of magnetosomal magnetite morphologies. This further confirms that magnetosome biomineralization is controlled strictly by the MTB cell and differs among species or strains. The post‐mortem remains of MTB are often preserved as magnetofossils within sediments or sedimentary rocks, yet paleobiological and geological interpretation of their fossil record remains challenging. Our results indicate that magnetofossil morphology could be a promising proxy for retrieving paleobiological information about ancient MTB.This study was supported financially by the National Natural Science Foundation of China (grants 41920104009, 41890843 and 41621004), The Senior User Project of RVKEXUE2019GZ06 (Centre for Ocean Mega-Science, Chinese Academy of Sciences), The Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology (grant MGQNLM201704) and the Australian Research Council (grants DP140104544 and DP200100765)

The Ventral Intermediate Nucleus Differently Modulates Subtype-Related Networks in Parkinson’s Disease

Background: Posture instability gait difficulty-dominant (PIGD) and tremor-dominant (TD) are two subtypes of Parkinson’s disease (PD). The thalamus is involved in the neural circuits of both subtypes. However, which subregion of the thalamus has an influence on the PD subtypes remains unclear.Objective: To explore the core subregion of the thalamus showing a significant influence on the PD subtypes and its directional interaction between the PD subtypes.Methods: A total of 79 PD patients (43 TD and 36 PIGD) and 31 normal controls (NC) were enrolled, and the gray matter volume and perfusion characteristics in the thalamus were compared between the three groups. The subregion of the thalamus with significantly different perfusion and volume among three groups was used as the seed of a Granger causality analysis (GCA) to compare the causal connectivity between different subtypes.Results: Perfusion with an increased gradient among the three groups (TD > PIGD > NC) in the bilateral ventral intermediate nucleus (Vim) was observed, which was positively correlated with the clinical tremor scores. The GCA revealed that TD patients had enhanced causal connectivity from the bilateral Vim to the bilateral paracentral gyrus, M1 and the cerebellum compared with the NC group, while the PIGD subtype revealed an increased causal connectivity from the bilateral Vim to the bilateral premotor cortex (preM) and putamen. Additionally, there were positive correlations between the tremor scores and a causal connectivity from the Vim to the cerebellum. The connectivity from the right Vim to the right preM and the right putamen was positively correlated with the PIGD scores.Conclusion: This multilevel analysis showed that the Vim had a significant influence on the PD subtypes and that it differentially mediated the TD and PIGD-related causal connectivity pattern in PD

The hydration of slag in complex binder and the microstructural variation of hardened paste under the condition of leaching of soft water

The hydration of slag in complex binder with different dosage was studied by identifying Ca(OH)2 content in hardened paste and Ca/Si ratio of formed C-A-S-H gel. The results shows that: elevated temperature curing could improve the slag’s reaction degree in early ages, but hinder the further hydration in late time. Some Ca(OH)2 is consumed when the outer hydrate is formed in early hydrating time, so the Ca(OH)2 content in the hardened paste decreases and Ca/Si ratio of C-A-S-H gel decreases. In the late hydrating time, the inner hydrate is formed, it no longer consumes a significant amount of Ca(OH)2, then Ca/Si ratio of C-A-S-H gel decreases more and Ca(OH)2 content tends to increase in the hardened paste. The Ca(OH)2 content in pastes is abundant, the Ca/Si ratio of C-A-S-H gel slightly decreases but there is not the decomposition sign of C-A-S-H gel after leaching of soft water for long time. The porosity of cement-slag complex binder pastes is low. The cement-slag complex binder containing no more than 70% slag shows good leaching resistance

The Influence of Ground Fly Ash on Cement Hydration and Mechanical Property of Mortar

In this study, the ground fly ash is made of ordinary grade I fly ash by grinding. Compared with grade I fly ash, the influence of ground fly ash on cement hydration and mechanical property of mortar was investigated. The results show that ground fly ash can improve the hydration of cement at all the ages compared with grade I fly ash, and not only does its pozzolanic reaction start earlier, but the reaction degree is higher and the speed is quicker. Before 3 days, the contribution of ground fly ash to the strength is mainly due to physical filling and microaggregate effect. After that, the contribution of pozzolanic effect to the strength becomes obvious and can significantly increase the compressive strength after 60 days and the flexural strength after 28 days. The ground fly ash is better than grade I fly ash to optimize the pore structure of hardened pastes. It can significantly reduce the number of harmful pores (>20 nm) and increase the number of harmless pores (<20 nm), which refines the pore structure and makes the structure denser

Investigation of Freeze-Thaw Resistance of Stabilized Saline Soil

In this paper, three freezing-thawing tests are designed to study the freeze-thaw resistance of stabilized sulfate type saline soil. The results show that different destructive modes and erosion extents are caused by different freeze-thaw conditions. The destructive effect from salt tends to be limited if there is no external water intrusion. When sufficient water is provided, ice expansion, dissolution recrystallization of salts, and ettringite growth during the thawing phase may take place. Soil water potential is used for analysis and explanation of the driving force and water migration in the stabilized soil. Pressure potential caused by the air sealed in the stabilized soil specimen leads to early water concentration in the outer parts of the specimen, and the surface layer is first eroded under the freeze-thaw cycles. A high percentage of soil stabilizer can improve the freeze-thaw resistance of stabilized soil, but a sufficiently long curing period plays a more important role. This study provides useful insights for improving the freeze-thaw resistance of solidified saline soil in road engineering

Comparative Study of Different Measurement Methods for Characterizing Rheological Properties of Lubrication Layer

The lubrication layer plays a governing role in predicting the pumpability of fresh concrete. To determine the effect of measurement methods on the characterization of the rheological properties of the lubrication layer, different measurement systems, including Sliper, tribometer, and the utilization of a mortar rheometer, were employed. The rheological properties and workability of bulk concrete were measured in parallel to investigate the correlation between them and the rheological properties of the lubrication layer. The results show that the measured values of the rheological parameters of the lubrication layer differ due to the systematic deviation between different measurement methods. The results obtained by both tribometer and mortar rheometer were well-correlated, having a linear relationship with the rheological parameters of bulk concrete. The correlation coefficient between results gained with Sliper and rheological parameters of concrete or lubrication layer determined with other methods was not high enough. Addition friction led to the large accidental error and overestimated yield stress obtained with Sliper. The workability of concrete is only suitable for characterizing the rheological properties of bulk concrete

Effects of Mineral Admixtures on the Evolution of Static Yield Stress of Different Composite Pastes

The effects of different mineral admixtures on the evolution of static yield stress of common composite cementitious material paste and ultra-high-performance concrete (UHPC)-based paste were investigated. The results show that there are obvious differences in the role of mineral admixtures in the common paste and the UHPC-based paste. Adding mineral admixtures can change the initial static yield stress of the paste by affecting the particle size, particle shape and the charged particles. The addition of mineral admixtures with small particle size such as silica fume and ultrafine slag can increase the initial static yield stress of common paste but reduce that of UHPC-based paste. Adding mineral admixtures changes the evolution of static yield stress of the paste by affecting the particle spacing and the formation and growth rate of hydration products. In turn, the addition of ultrafine slag or silica fume increases the growth of the static yield stress of common paste. Adding slag, fly ash or fly ash microbeads successively reduces the static yield stress of common paste at the later stage. Affected by the content of PCE, the static yield stress of UHPC-based paste containing fly ash microbeads, slag, ultrafine slag and fly ash increases sequentially compared with the blank group at the later stage. The effect of silica fume with different dosages on the evolution of static yield stress of UHPC-based paste is significantly different