To stabilize the space debris problem, it's of great significance to perform Active Debris Removal (ADR) missions. The capturing phase plays a crucial role in the entire ADR mission. One of the greatest challenges is to capture the target in a simple manner. In this paper, a set of principal requirements are firstly established to guide the design of the capture mechanism. A malfunctioned satellite is chosen as the target due to increased collisions it may pose. Based on spatial overconstrained Bennett linkages that are linked by scissor elements, two types of 1-DOF linkage networks are built by tessellations. Both of the networks fold into bundles and deploy into "grippers", which also enables the deployment to be reversible with only one actuator. Without the need for latching devices, a novel concept of deployable capture mechanisms is proposed according to the networks. Besides, self-locking screw transmission and linkage mechanisms are compactly designed to drive the networks. Finally, simulations of the capturing operation are conducted to verify the compliance to the requirements, and the two types of mechanisms are compared to find their respective application occasions.
Along with the progression in technology, Internet of Things (IoT) has been dramatically developed in recent ten years. It connects physical world and digital world, which makes people's life more convenient. However, IoT devices have bring great vulnerability to Internet security since they usually under weak protection, which makes them easy to be exploited by criminals to launch multiple attacks. In fact, IoT devices have been a crucial part of botnets that launch horrible Distributed Denial of Service (DDoS) with explosive traffic. Unfortunately, traditional detection works have limited effectiveness face IoT botnets because of the restricted resources of IoT devices and unprecedented huge scale of IoT botnets. To mitigate the threat of IoT botnets, in this paper, we propose a lightweight system, named FastIoTBot, to discover compromised IoT devices in a fast way. FastIoTBot can distinguish compromised IoT devices instantly and prevent potential malicious behaviors by examining domain query activities. Specifically, FastIoTBot monitors the DNS query for a device and generates its NXDOMAIN query sequence. Then, for each domain in the sequence, FastIoTBot takes the domain name string as input and calculates its malicious score using long short-term memory (LSTM) model. Finally, FastIoTBot identifies compromised IoT devices through analyzing NXDOMAIN sequences with internal domains' malicious score leveraging threshold random walk (TRW) algorithm. The effectiveness of FastIoTBot is evaluate with real world DNS data of two large ISP networks. The results show that FastIoTBot perform well with over 99% accuracy.
A tactile sensor based varying contact point manipulation strategy that utilizes the mathematical models based on the assumption of fixed contact points is proposed to manipulate unknown objects with rolling contact for dexterous robot hand. In this strategy, fingertip tactile sensor is utilized to detect contact position and to update the size parameters about the finger end-link when rolling occurs. Experimental results show that the strategy can effectively improve the rolling contact manipulation performance when dexterous robot hand manipulates unknown objects.
A novel 3D-printing repair is proposed based on Fused Deposition Modeling (FDM) for improving the mechanical strength of the objects with surface cracks. Compared to the traditional FDM-based technique, the novelty of our proposed approach is that the extruding and moving directions of the printing nozzle are controllable and thus variable, eliminating any restriction of orthogonal alignment. This permits essential physical contact between the nozzle and the cracked area that allows the nozzle to remove surface material that might be covered by dust, as well as the heat transfer that preheats the inner material before being combined with the extruding one. Hence, the proposed approach can strengthen the bonding strength of materials to a great extent, particularly when the environmental temperature is not in a suitable range. Experimental results show that the mechanical strength of the objects with surface cracks is significantly improved by our proposed approach of 3D-printing repair compared to that produced by the traditional one.
Abstract Benefitting from the mature, cost‐effective, and scalable manufacturing capabilities of complementary metal‐oxide‐semiconductor (CMOS) technology, silicon photonics has facilitated the seamless and monolithic integration of diverse functionalities, including optical sources, modulators, and photodetectors. Microresonators can generate multiple coherent optical frequency comb lines and serve as optical sources. However, at the telecom band, silicon suffers from two‐photon absorption and free‐carrier absorption, which severely hampers the realization of microcombs from a single silicon chip at telecom wavelengths until now. In this paper, a novel approach is presented and demonstrated with near‐infrared dual‐band frequency combs from a multimode silicon resonator. With a single pumping configuration, dual‐band combs are generated from the interaction between the pump and Raman Stokes fields by involving two different optical mode families but with similar group velocities. It is observed that the pump power required to generate dual‐band combs is as low as 0.7 mW. The work in bringing telecom microcombs to the silicon platform will advance silicon photonics for the next generation of monolithically integrated technology based on a single silicon chip, enabling new possibilities for further exploring silicon photonics‐based applications in optical telecommunications, sensing, and quantum metrology in the telecom band using a monolithic single silicon chip.
Expansion Rod Capturing Nozzle Device based on Laser Range Finders Guidance is developed to capture the non-cooperative satellite by capturing the main engine nozzle. The capturing device is integrated with capturing mechanism of expansion rod, Field-Programmable Gate Array (FPGA) controller, multi-sensors with laser range finders and Force/Torque Sensor, which utilizes the design concept of the optics, mechanism and electricity unitization. In order to capture the nozzle by the "soft" contact way, six laser range finders are radially arranged in the capturing device to sense the nozzle pose. The measuring range of laser range finder is 25-350mm, and the measuring accuracy is 2%. By the finders, capturing device can achieve the function of accurately approaching and reaching the capturing and locking location in the capturing process of extremely close to nozzle, to capture the non-cooperative satellite. The experiments are carried out capture the nozzle by the capturing device utilizing the finders real-time measurement. The experiments demonstrate the capturing device has the ability to capture and lock the satellite nozzle.
Vehicular ad hoc network (VANET) has been brought out to revolutionize driving experiences and traffic flow control systems. In a VANET, roadside units (RSUs) are usually used to collect messages sent by nearby vehicles, which may include status information of vehicles and emergency events. Currently, batch verification is considered as an effective approach to verify these messages in VANETs. However, in existing batch verification scheme, the batch verification fails even one of the signed messages is invalid. In this paper, we introduce an efficient identity-based fault-tolerant batch verification scheme for cloud assisted VANETs.
Purpose The aim of this paper is to enhance the control performance of dexterous hands, enabling them to handle the high data flow from multiple sensors and to meet the deployment requirements of deep learning methods on dexterous hands. Design/methodology/approach A distributed control architecture was designed, comprising embedded motion control subsystems and a host control subsystem built on ROS. The design of embedded controller state machines and clock synchronization algorithms ensured the stable operation of the entire distributed control system. Findings Experiments demonstrate that the entire system can operate stably at 1KHz. Additionally, the host can accomplish learning-based estimates of contact position and force. Originality/value This distributed architecture provides foundational support for the large-scale application of machine learning algorithms on dexterous hands. Dexterity hands utilizing this architecture can be easily integrated with robotic arms.
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