91 research outputs found
Towards Geometric Motion Planning for High-Dimensional Systems: Gait-Based Coordinate Optimization and Local Metrics
Geometric motion planning offers effective and interpretable gait analysis
and optimization tools for locomoting systems. However, due to the curse of
dimensionality in coordinate optimization, a key component of geometric motion
planning, it is almost infeasible to apply current geometric motion planning to
high-dimensional systems. In this paper, we propose a gait-based coordinate
optimization method that overcomes the curse of dimensionality. We also
identify a unified geometric representation of locomotion by generalizing
various nonholonomic constraints into local metrics. By combining these two
approaches, we take a step towards geometric motion planning for
high-dimensional systems. We test our method in two classes of high-dimensional
systems - low Reynolds number swimmers and free-falling Cassie - with up to
11-dimensional shape variables. The resulting optimal gait in the
high-dimensional system shows better efficiency compared to that of the
reduced-order model. Furthermore, we provide a geometric optimality
interpretation of the optimal gait.Comment: 7 pages, 6 figures, submitted to the 2024 IEEE International
Conference on Robotics and Automation (ICRA 2024
Geometric Gait Optimization for Inertia-Dominated Systems With Nonzero Net Momentum
Inertia-dominated mechanical systems can achieve net displacement by 1)
periodically changing their shape (known as kinematic gait) and 2) adjusting
their inertia distribution to utilize the existing nonzero net momentum (known
as momentum gait). Therefore, finding the gait that most effectively utilizes
the two types of locomotion in terms of the magnitude of the net momentum is a
significant topic in the study of locomotion. For kinematic locomotion with
zero net momentum, the geometry of optimal gaits is expressed as the equilibria
of system constraint curvature flux through the surface bounded by the gait,
and the cost associated with executing the gait in the metric space. In this
paper, we identify the geometry of optimal gaits with nonzero net momentum
effects by lifting the gait description to a time-parameterized curve in
shape-time space. We also propose the variational gait optimization algorithm
corresponding to the lifted geometric structure, and identify two distinct
patterns in the optimal motion, determined by whether or not the kinematic and
momentum gaits are concentric. The examples of systems with and without
fluid-added mass demonstrate that the proposed algorithm can efficiently solve
forward and turning locomotion gaits in the presence of nonzero net momentum.
At any given momentum and effort limit, the proposed optimal gait that takes
into account both momentum and kinematic effects outperforms the reference
gaits that each only considers one of these effects.Comment: 8 pages, 9 figures, accepted to IEEE/RSJ International Conference on
Intelligent Robots and Systems (IROS) 202
Recent progress in Ti-based nanocomposite anodes for lithium ion batteries
Studying on the anode materials with high energy densities for next-generation lithium-ion batteries (LIBs) is the key for the wide application for electrochemical energy storage devices. Ti-based compounds as promising anode materials are known for their outstanding high-rate capacity and cycling stability as well as improved safety over graphite. However, Ti-based materials still suffer from the low capacity, thus largely limiting their commercialized application. Here, we present an overview of the recent development of Ti-based anode materials in LIBs, and special emphasis is placed on capacity enhancement by rational design of hybrid nanocomposites with conversion-/ alloying-type anodes. This review is expected to provide a guidance for designing novel Ti-based materials for energy storage and conversion. Keywords: lithium-ion batteries (LIBs) anode titania lithium titanateNational Natural Science Foundation (China) (51472137)National Natural Science Foundation (China) (51772163
Proprioception and Tail Control Enable Extreme Terrain Traversal by Quadruped Robots
Legged robots leverage ground contacts and the reaction forces they provide
to achieve agile locomotion. However, uncertainty coupled with contact
discontinuities can lead to failure, especially in real-world environments with
unexpected height variations such as rocky hills or curbs. To enable dynamic
traversal of extreme terrain, this work introduces 1) a proprioception-based
gait planner for estimating unknown hybrid events due to elevation changes and
responding by modifying contact schedules and planned footholds online, and 2)
a two-degree-of-freedom tail for improving contact-independent control and a
corresponding decoupled control scheme for better versatility and efficiency.
Simulation results show that the gait planner significantly improves stability
under unforeseen terrain height changes compared to methods that assume fixed
contact schedules and footholds. Further, tests have shown that the tail is
particularly effective at maintaining stability when encountering a terrain
change with an initial angular disturbance. The results show that these
approaches work synergistically to stabilize locomotion with elevation changes
up to 1.5 times the leg length and tilted initial states.Comment: 8 pages, 9 figures, accepted to IEEE/RSJ International Conference on
Intelligent Robots and Systems (IROS) 202
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A wafer-scale two-dimensional platinum monosulfide ultrathin film via metal sulfurization for high performance photoelectronics
2D nonlayered materials have attracted enormous research interests due to their novel physical and chemical properties with confined dimensions. Platinum monosulfide as one of the most common platinum-group minerals has been less studied due to either the low purity in the natural product or the extremely high-pressure conditions for synthesis. Recently, platinum monosulfide (PtS) 2D membranes have emerged as rising-star materials for fundamental Raman and X-ray photoelectron spectral analysis as well as device exploration. However, a large-area homogeneous synthesis route has not yet been proposed and released. In this communication, we report a facile metal sulfurization strategy for the synthesis of a 4-inch wafer-scale PtS film. Enhanced characterization tools have been employed for thorough analysis of the crystal structure, chemical environment, vibrational modes, and atomic configuration. Furthermore, through theoretical calculations the phase diagram of the Pt–S compound has been plotted for showing the successful formation of PtS in our synthesis conditions. Eventually, a high-quality PtS film has been reflected in device demonstration by a photodetector. Our approach may shed light on the mass production of PtS films with precise control of their thickness and homogeneity as well as van der Waals heterostructures and related electronic devices
Heterogeneity matching and IDH prediction in adult-type diffuse gliomas: a DKI-based habitat analysis
ObjectiveTo explain adult-type diffuse gliomas heterogeneity through diffusion kurtosis imaging-based habitat characteristics and develop and validate a comprehensive model for predicting isocitrate dehydrogenase (IDH) status.Materials and methodsIn this prospective secondary analysis, 103 participants (mean age, 52 years; range, 21-77; 54 [52%] male) pathologically diagnosed with adult-type diffuse gliomas were enrolled between June 2018 and February 2022. The Otsu method was used to generate habitat maps with mean diffusivity (MD) and mean kurtosis (MK) for a total of 4 subhabitats containing 16 habitat features. Habitat heatmaps were created based on the Pearson correlation coefficient. The Habitat imAging aNd clinicraD INtegrated prEdiction SyStem (HANDINESS) was created by combining clinical features, conventional MRI morphological features, and habitat image features. ROC, calibration curve, and decision curve analyses were used to select the optimal model after 32 pipelines for model training and validation.ResultsIn the restricted diffusion and high-density subhabitat, MK was highly correlated with MD (R2Â =Â 0.999), volume (0.608) and percentage of volume (0.663), and this region had the highest MK value (P<.001). The unrestricted diffusion and low-density subhabitat had the highest MD value (P<.001). When MK was less than the Otsu threshold, there was still a difference between restricted diffusion and low-density and unrestricted diffusion and low-density subhabitats (P<.01). The HANDINESS enabled more accurate prediction of the IDH status in the training (AUC=0.951 [0.902-0.987]) and internal validation cohorts (0.938 [0.881-0.949]). AUC values for single-modality models and independent factors ranged from 0.593 to 0.916. Calibration and decision curve analyses showed that the HANDINESS demonstrated a high level of clinical applicability and predictive consistency.ConclusionDiffusion kurtosis imaging-based habitat analysis provides additional important information on microscopic tumor spatial heterogeneity. The HANDINESS has higher diagnostic performance and robustness than single-modality models
Research on accessibility of port collection and distribution system from the perspective of carbon emissions
Port accessibility is an important factor in the efficiency of a port collection and distribution systems. And the carbon emission of the collection and transportation system is large, which is an important factor that cannot be ignored when constructing the collection and transportation system. In order to analyze the carbon emission characteristics of the port collection and distribution system, the paper incorporates the carbon emission factor into the accessibility measurement of the port collection and distribution system. To solve the problem of unbalanced demand of each logistics node, the distribution of logistics demand in the system is realized by the method based on the appropriate freight volume. The carbon emission cost factor is introduced, and the accessibility measurement model based on the generalized cost impedance function is constructed. Taking the collection and distribution system of Douala Port in West Africa as an example to verify, the results show that, after adding the carbon emission factor, the accessibility of each logistics node shows different degrees of decline which shows that the addition of the carbon emission factor can be more comprehensive and can reflect the accessibility of the system
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