CNGI/ChinaFLUX: an IPv6-based Terrestrial Ecosystem Flux Research Network in China

In this manuscript, we introduce the first-step research and development onCNGI/ChinaFLUX, which is supported by CNGI (China Next Generation Internet)Project. From May 2012, we set up an IPv6-based real-time carbon flux observationsystem in ten sites, based on the Chinese Terrestrial Ecosystem Flux ResearchNetwork (ChinaFLUX). The hardware environment construction includes IPv6-baseddata transmission network platform, data acquisition system, data storage andprocessing system. The software environment construction includes IPv6-basedobservation device monitoring system, data storage and management system.Researchers develop a series of research applications in CNGI/ChinaFLUX network

Collaborative Planning for Catching and Transporting Objects in Unstructured Environments

Multi-robot teams have attracted attention from industry and academia for their ability to perform collaborative tasks in unstructured environments, such as wilderness rescue and collaborative transportation.In this paper, we propose a trajectory planning method for a non-holonomic robotic team with collaboration in unstructured environments.For the adaptive state collaboration of a robot team to catch and transport targets to be rescued using a net, we model the process of catching the falling target with a net in a continuous and differentiable form.This enables the robot team to fully exploit the kinematic potential, thereby adaptively catching the target in an appropriate state.Furthermore, the size safety and topological safety of the net, resulting from the collaborative support of the robots, are guaranteed through geometric constraints.We integrate our algorithm on a car-like robot team and test it in simulations and real-world experiments to validate our performance.Our method is compared to state-of-the-art multi-vehicle trajectory planning methods, demonstrating significant performance in efficiency and trajectory quality

Application of light diffraction theory to qualify the downstream light field modulation property of mitigated KDP crystals

Micro-milling can effectively remove laser damage sites on a KDP (potassium dihydrogen phosphate) surface and then improve the laser damage resistance of the components. However, the repaired KDP surface could cause light propagating turbulence and downstream light intensification with the potential risk to damage downstream optics. In order to analyze the downstream light field modulation caused by Gaussian mitigation pits on KDP crystals, a computational model of the downstream light diffraction based on the angular spectrum theory and the Gaussian repair contour is established. The results show that the phase offset caused by the repaired surface produces a large light field modulation near the rear KDP surface. The modulation generated in the whole downstream light field is greater than that caused by the amplitude change. Therefore, the phase characteristics of the outgoing light could be suggested as a vital research topic for future research on the downstream light field modulation caused by mitigation contours. Significantly, the experimental results on the downstream light intensity distribution have good agreement with the simulation ones, which proves the validity of the established downstream light diffraction model. The phase characterization of the outgoing light is proposed as an evaluation tool in the repair of KDP crystals. The developed analytical method and numerical discrete algorithm could be also applicable in qualifying the repair quality of other optical components applied in high-power laser systems

An Efficient Spatial-Temporal Trajectory Planner for Autonomous Vehicles in Unstructured Environments

As a core part of autonomous driving systems, motion planning has received extensive attention from academia and industry. However, real-time trajectory planning capable of spatial-temporal joint optimization is challenged by nonholonomic dynamics, particularly in the presence of unstructured environments and dynamic obstacles. To bridge the gap, we propose a real-time trajectory optimization method that can generate a high-quality whole-body trajectory under arbitrary environmental constraints. By leveraging the differential flatness property of car-like robots, we simplify the trajectory representation and analytically formulate the planning problem while maintaining the feasibility of the nonholonomic dynamics. Moreover, we achieve efficient obstacle avoidance with a safe driving corridor for unmodelled obstacles and signed distance approximations for dynamic moving objects. We present comprehensive benchmarks with State-of-the-Art methods, demonstrating the significance of the proposed method in terms of efficiency and trajectory quality. Real-world experiments verify the practicality of our algorithm. We will release our codes for the research communit

Model development for nanosecond laser-induced damage caused by manufacturing-induced defects on potassium dihydrogen phosphate crystals

Nanosecond laser-induced damage on (potassium dihydrogen phosphate) KDP crystals is a complex process, which involves coupled actions of multi-physics fields. However, the mechanisms governing the laser damage behaviors have not been fully understood and there have been no available models to accurately describe this complex process. In this work, based on the theories of electromagnetic, thermodynamic, and hydrodynamic fields, a coupled multi-physics model is developed to describe the transient behavior of laser-supported energy deposition and diffusion accompanied by the surface defect (e.g., surface cracks)-initiated laser damage process. It is found that the light intensification caused by the defects near the crystal surface plays a significant role in triggering the laser-induced damage, and a large amount of energy is quickly deposited via the light intensity-activated nonlinear excitation. Using the developed model, the maximum temperature of the crystal material irradiated by a 3 ns pulse laser is calculated, which agrees well with previously reported experimental results. Furthermore, the modeling results suggest that physical processes such as material melting, boiling, and flowing have effects on the evolution of the laser damage process. In addition, the experimentally measured morphology of laser damage sites exhibits damage features of boiling cores, molten regions, and fracture zones, which are direct evidence of bowl-shaped higherature expansion predicted by the model. These results well validate that the proposed coupled multi-physics model is competent to describe the dynamic behaviors of laser damage, which can serve as a powerful tool to understand the general mechanisms of laser interactions with KDP optical crystals in the presence of different defects

Secondary peak of downstream light field modulation caused by Gaussian mitigation pits on the rear KDP surface

Micro-milling has been proved to be the most effective method to mitigate the growth of laser-induced surface damage on potassium dihydrogen phosphate (KDP) crystals used in high power laser systems. However, the secondary peak of downstream light field modulation caused by Gaussian mitigation pits on the rear KDP surface would cause potential risk to damage downstream optics. In order to explore the effect of the mitigation pits on the secondary peak, we numerically calculated the downstream light field modulations caused by Gaussian mitigation pits on the rear KDP surface based on the angular spectrum diffraction theory. The results suggest that the secondary peaks are dependent on the parameters of the width, depth, depth error and title error. Among them, the tilt error and depth have greater influence on the mitigation effect. To reduce the laser damage risk caused by the secondary peak, the depth of the pre-designed mitigated contour should be optimized according to the actual operating conditions. The tilt error and depth error are proposed to be controlled within 10 and 2 μm, respectively, during the micro-milling. Also, the experiments verified the calculation results of downstream modulations and the effects of these parameters on the secondary peak. This work can not only provide available models for evaluating the laser damage risk of secondary peak caused by mitigation pits on the KDP surface but also contribute to the development of optimal micro-milling parameters for laser damage mitigation as well as the installation strategy of optical components employed in the high power laser systems

Ultra-small topological spin textures with size of 1.3nm at above room temperature in Fe78Si9B13 amorphous alloy

Topologically protected spin textures, such as skyrmions1,2 and vortices3,4, are robust against perturbations, serving as the building blocks for a range of topological devices5-9. In order to implement these topological devices, it is necessary to find ultra-small topological spin textures at room temperature, because small size implies the higher topological charge density, stronger signal of topological transport10,11 and the higher memory density or integration for topological quantum devices5-9. However, finding ultra-small topological spin textures at high temperatures is still a great challenge up to now. Here we find ultra-small topological spin textures in Fe78Si9B13 amorphous alloy. We measured a large topological Hall effect (THE) up to above room temperature, indicating the existence of highly densed and ultra-small topological spin textures in the samples. Further measurements by small-angle neutron scattering (SANS) reveal that the average size of ultra-small magnetic texture is around 1.3nm. Our Monte Carlo simulations show that such ultra-small spin texture is topologically equivalent to skyrmions, which originate from competing frustration and Dzyaloshinskii-Moriya interaction12,13 coming from amorphous structure14-17. Taking a single topological spin texture as one bit and ignoring the distance between them, we evaluated the ideal memory density of Fe78Si9B13, which reaches up to 4.44*104 gigabits (43.4 TB) per in2 and is 2 times of the value of GdRu2Si218 at 5K. More important, such high memory density can be obtained at above room temperature, which is 4 orders of magnitude larger than the value of other materials at the same temperature. These findings provide a unique candidate for magnetic memory devices with ultra-high density.Comment: 26 pages, 4 figure