Multi-Objective Redundancy Optimization of Continuous-Point Robot Milling Path in Shipbuilding

The 6-DOF manipulator provides a new option for traditional shipbuilding for its advantages of vast working space,low power consumption,and excellent flexibility.However,the rotation of the end effector along the tool axis is functionally redundant when using a robotic arm for five-axis machining.In the process of ship construction,the performance of the parts’protective coating needs to bemachined tomeet the Performance Standard of Protective Coatings(PSPC).The arbitrary redundancy configuration in path planning will result in drastic fluctuations in the robot joint angle,greatly reducing machining quality and efficiency.There have been some studies on singleobjective optimization of redundant variables,However,the quality and efficiency of milling are not affected by a single factor,it is usually influenced by several factors,such as the manipulator stiffness,the joint motion smoothness,and the energy consumption.To solve this problem,this paper proposed a new path optimization method for the industrial robot when it is used for five-axis machining.The path smoothness performance index and the energy consumption index are established based on the joint acceleration and the joint velocity,respectively.The path planning issue is formulated as a constrained multi-objective optimization problem by taking into account the constraints of joint limits and singularity avoidance.Then,the path is split into multiple segments for optimization to avoid the slow convergence rate caused by the high dimension.An algorithm combining the non-dominated sorting genetic algorithm(NSGA-II)and the differential evolution(DE)algorithm is employed to solve the above optimization problem.The simulations validate the effectiveness of the algorithm,showing the improvement of smoothness and the reduction of energy consumption.

The Importance of Ecological Redundancy for Ecosystems Restoration

Restoration ecology is a multidisciplinary science that exchanges several concepts with other scientific fields to improve its practices.In this article,I discuss the ecological redundancy concept and its implications and appli­cations on ecological restoration.Ecological redundancy was coined in the early 1990s to characterize those species that play similar(equivalent)func­tions in the ecosystem.The concept made it possible to segregate species into functional groups that operate in maintaining the system.I searched the literature and found that although some restoration models naturally consider this concept,studies in areas undergoing restoration which di­rectly measure and test the ecological redundancy are still rare(n=14).I provide evidence that distinguishing redundant species and identifying key species is feasible for ecological restoration.Additionally,I suggest that redundancy should also be part of the restoration monitoring,for example,by checking if functional groups have been recovered.Theory predicts that if ecological redundancy is correctly incorporated in restoration,projects with more chances of success will be created because redundancy tends to increase ecosystem resilience.Resilience is a crucial factor for restoration sustainability in a changing environment.

Resilience and functional redundancy of methanogenic digestion microbiome safeguard recovery of methanogenesis activity under the stress induced by microplastics

Microplastics and nanoplastics are emerging pollutants that substantially influence biological element cycling in natural ecosystems.Plastics are also prevalent in sewage,and they accumulate in waste-activated sludge(WAS).However,the impacts of plastics on the methanogenic digestion of WAS and the underpinning microbiome remain underexplored,particularly during long-term operation.In this study,we found that short-term exposure to individual microplastics and nanoplastics(polyethylene,polyvinyl chloride,polystyrene,and polylactic acid)at a low concentration(10 particles/g sludge)slightly enhanced methanogenesis by 2.1%−9.0%,whereas higher levels(30−200 particles/g sludge)suppressed methanogenesis by 15.2%−30.1%.Notably,the coexistence of multiple plastics,particularly at low concentrations,showed synergistic suppression of methanogenesis.Unexpectedly,methanogenesis activity completely recovered after long-term exposure to plastics,despite obvious suppression of methanogenesis by initial plastic exposure.The inhibition of methanogenesis by plastics could be attributed to the stimulated generation of reactive oxygen species.The stress induced by plastics dramatically decreased the relative abundance of methanogens but showed marginal influence on putative hydrolytic and fermentation populations.Nonetheless,the digestion sludge microbiome exhibited resilience and functional redundancy,contributing to the recovery of methanogenesis during the long-term operation of digesters.Plastics also increased the complexity,modularity,and negative interaction ratios of digestion sludge microbiome networks,but their influence on community assembly varied.Interestingly,a unique plastisphere was observed,the networks and assembly of which were distinct from the sludge microbiome.Collectively,the comprehensive evaluation of the influence of microplastics and nanoplastics on methanogenic digestion,together with the novel ecological insights,contribute to better understanding and manipulating this engineered ecosystem in the face of increasing plastic pollution.

Genome-Wide Identification and Functional Analysis of Genes Expressed Ubiquitously in Rice

Genes that are expressed ubiquitously throughout all developmental stages are thought to be necessary for basic biological or cellular functions. Therefore, determining their biological roles is a great challenge. We identified 4034 of these genes in rice after studying the results of Agilent 44K and Affymetrix meta- anatomical expression profiles. Among 105 genes that were characterized by loss-of-function analysis, 79 were classified as members of gene families, the majority of which were predominantly expressed. Using T-DNA insertional mutants, we examined 43 genes and found that loss of expression of six genes caused developing seedor seedling-defective phenotypes. Of these, three are singletons without similar family members and defective phenotypes are expected from mutations. Phylogenomic analyses integrating genome-wide transcriptome data revealed the functional dominance of three ubiquitously expressed fam- ily genes. Among them, we investigated the function of OsO3g19890, which is involved in ATP generation within the mitochondria during endosperm development. We also created and evaluated functional net- works associated with this gene to understand the molecular mechanism. Our study provides a useful strategy for pheonome analysis of ubiquitously expressed genes in rice.

The diversity and ecological significance of microbial traits potentially involved in B_(12) biosynthesis in the global ocean

Cobalamin(B_(12)),an essential nutrient and growth cofactor for many living organisms on Earth,can be fully synthesized only by selected prokaryotes in nature.Therefore,microbial communities related to B_(12) biosynthesis could serve as an example subsystem to disentangle the underlying ecological mechanisms balancing the function and taxonomic make-up of complex functional assemblages.By anchoring microbial traits potentially involved in B_(12) biosynthesis,we depict the biogeographic patterns of B_(12) biosynthesis genes and the taxa harboring them in the global ocean,despite the limitations of detecting de novo B_(12) synthesizers via metagenomes alone.Both the taxonomic and functional composition of B_(12) biosynthesis genes were strongly shaped by depth,differentiating the epipelagic zones from the mesopelagic layers.Functional genes related to B_(12) biosynthesis were relatively stably distributed across different oceans,but the taxa harboring them varied considerably,showing clear functional redundancy among microbial systems.Microbial taxa carrying B_(12) biosynthesis genes in the surface water were influenced by environmental factors such as temperature,oxygen,and nitrate.However,the composition of functional genes was only weakly associated with these environmental factors.Null model analyses demonstrated that determinism governed the variations in B_(12) biosynthesis genes,whereas a higher degree of stochasticity was associated with taxonomic variations.Significant associations were observed between the chlorophyll a concentration and B_(12) biosynthesis,confirming its importance in primary production in the global ocean.The results of this study reveal an essential ecological mechanism governing the assembly of microbes in nature:the environment selects for function rather than taxonomy;functional redundancy underlies stochastic community assembly.

Smoothness-oriented path optimization for robotic milling processes

Industrial robots are increasingly used for five-axis machining operations, where the rotation of the end effector along the toolaxis direction is functionally redundant. This functional redundancy should be carefully resolved when planning the robot path according to the tool path generated by a computer-aided manufacturing(CAM) system. Improper planning of the redundancy may cause drastic variations of the joint motions, which could significantly decrease the machining efficiency as well as the machining accuracy. To tackle this problem, this paper presents a new optimization-based methodology to globally resolve the functional redundancy for the robotic milling process. Firstly, a global performance index concerning the smoothness of the robot path at the joint acceleration level is proposed. By minimizing the smoothness performance index while considering the avoidance of joint limits and the singularity and the constraint of the stiffness performance, the resolution of the redundancy is formulated as a constrained optimization problem. To efficiently solve the problem, the sequential linearization programming method is employed to improve the initial solution provided by the conventional graph-based method. Then, simulations for a given tool path are presented. Compared with the graph-based method, the proposed method can generate a smoother robot path in which a significant reduction of the magnitude of the maximum joint acceleration is obtained, resulting in a smoother tool-tip feedrate profile. Finally, the experiment on the robotic milling system is also presented. The results show that the optimized robot path of the proposed method obtains better surface quality and higher machining efficiency, which verifies the effectiveness of the proposed method.

Driver Model-Based Fault-Tolerant Control of Independent Driving Electric Vehicle Suffering Steering Failure

This paper presents a fault-tolerant control(FTC)strategy for a four-wheel independent driving electric vehicle suffering steering failure.The method is based on the functional redundancy of driving and braking actuators to recover the vehicle’s steering ability.A dynamic vehicle model is derived with the function of four-wheel driving.A sliding mode controller with a combined sliding surface is employed as a motion controller,allowing the desired vehicle motion to be tracked by the adaptive drivermodel.An extended Kalman filter-based state estimator is adopted to virtually measure the sideslip anglewhile considering the nonlinear tire force.A new allocation strategy,involving two distribution modes of coordination,is designed.In addition,a weight coefficient adjustment strategy is implemented in optimal mode based on the lateral load transfer,thus improving the steering performance.Simulations are conducted to verify the proposed FTC algorithm.The results demonstrate that steering failure can be effectively covered by the functional redundancy of the driving/braking actuators.