Implementation Of A Raptorq-Based Protocol For Peer To Peer Network

The object of this thesis is to develop and test a Ruby based implementation of the RaptorQP2P protocol. The RaptorQP2P protocol is a novel peer-to-peer protocol based on RaptorQ forward error correction. This protocol facilitates delivery of a single file to a large number of peers. It applies two levels of RaptorQ encoding to the source file before packet transmission. Download completion time using RaptorQP2P was found to be significantly improved comparing to BitTorrent. We developed a Ruby interface to the Qualcomm proprietary RaptorQ software development kit library. Then we achieved the two levels of RaptorQ encoding and decoding with the Ruby interface. Our implementation uses 5 threads to implement RaptorQP2P features. Thread 1 runs as a server to accept the connection requests from new peers. Thread 2 works as a client to connect to other peers. Thread 3 is used for sending data (pieces) and thread 4 is to receive data from neighboring peers. Thread 5 manages the piece map status, the peer list, and choking of a peer. We first tested communication modules of the implementation. Then we set up scheduled transmission tests to validate the intelligent symbol transmission scheduling design. Finally, we set up a multi-peer network for close to practical tests. We use 5 RaspberryvPi single-board computers to act as 1 seeder and 4 leechers. The seeder has the whole file and delivers the file to the 4 leechers simultaneously. The 4 leechers will also exchange part of the file with each other based on what they have received. Test results show that our implementation attains all the features of RaptorQP2P: the implementation uses two levels RaptorQ encoding; a peer is able to download a piece from multiple neighbors simultaneously; and a peer can send the received encoded symbols of a piece to other peers even if the peer does not have the full piece yet

An Analytical Model for the Normal Contact Stiffness of Mechanical Joint Surfaces Based on Parabolic Cylindrical Asperities

The analytical results of normal contact stiffness for mechanical joint surfaces are quite different from the experimental data. So, this paper proposes an analytical model based on parabolic cylindrical asperity that considers the micro-topography of machined surfaces and how they were made. First, the topography of a machined surface was considered. Then, the parabolic cylindrical asperity and Gaussian distribution were used to create a hypothetical surface that better matches the real topography. Second, based on the hypothetical surface, the relationship between indentation depth and contact force in the elastic, elastoplastic, and plastic deformation intervals of the asperity was recalculated, and the theoretical analytical model of normal contact stiffness was obtained. Finally, an experimental test platform was then constructed, and the numerical simulation results were compared with the experimental results. At the same time, the numerical simulation results of the proposed model, the J. A. Greenwood and J. B. P. Williamson (GW) model, the W. R. Chang, I. Etsion, and D. B. Bogy (CEB) model, and the L. Kogut and I. Etsion (KE) model were compared with the experimental results. The results show that when roughness is Sa 1.6 μm, the maximum relative errors are 2.56%, 157.9%, 134%, and 90.3%, respectively. When roughness is Sa 3.2 μm, the maximum relative errors are 2.92%, 152.4%, 108.4%, and 75.1%, respectively. When roughness is Sa 4.5 μm, the maximum relative errors are 2.89%, 158.07%, 68.4%, and 46.13%, respectively. When roughness is Sa 5.8 μm, the maximum relative errors are 2.89%, 201.57%, 110.26%, and 73.18%, respectively. The comparison results demonstrate that the suggested model is accurate. This new method for examining the contact characteristics of mechanical joint surfaces uses the proposed model in conjunction with a micro-topography examination of an actual machined surface

Extrusion deformation process of ground surface during the Lushan earthquake in China

Based on finite element method, the extrusion deformation process of ground surface during the Lushan earthquake (April 20, 2013) is investigated in this work. In order to construct the finite element model of Lushan earthquake structure, the geophysical layer model of Lushan area, the frictional characteristic of slip-weaken along the fault surface, and the Coulomb failure criterion are considered. Through the computation and the comparison with achievement on the Lushan focal dynamics, our researches indicate that: (1) The most extrusion deformation of ground surface occurred in the initial phase of earthquake procession, i.e., between the fourth and sixth seconds after the earthquake occurred. (2) Between the first and sixth seconds after the earthquake, the extrusion deformation concentrates on the surface projection of earthquake fault. (3) Between the first and third seconds after the earthquake, the extrusion deformation of ground surface is very tiny. Meanwhile, the extrusion deformation reaches maximum at the sixth second after earthquake. (4) After 6 s of Lushan earthquake, the extrusion deformation spread out of earthquake structure projection. (5) During the earthquake, the maximum of extrusion deformation on ground surface is larger than the final deformation of the post-earthquake, in other words, the ground extrusion deformation will lastly reach a relatively small value after the Lushan earthquake occurred

A Novel Simulation Method of Micro-Topography for Grinding Surface

A novel simulation method of microtopography for grinding surface was proposed in this paper. Based on the theory of wavelet analysis, multiscale decomposition of the measured topography was conducted. The topography was divided into high frequency band (HFB), theoretical frequency band (TFB), and low frequency band (LFB) by wavelet energy method. The high-frequency and the low-frequency topography were extracted to obtain the digital combination model. Combined with the digital combination model and the theoretical topography obtained by geometric simulation method, the simulation topography of grinding surface can be generated. Moreover, the roughness parameters of the measured topography and the simulation topography under different machining parameters were compared. The maximum relative error of Sa, Sq, Ssk and Sku were 1.79%, 2.24%, 4.69% and 4.73%, respectively, which verifies the feasibility and accuracy of the presented method

Novel Lithium-Ion Capacitor Based on a NiO-rGO Composite

Lithium-ion capacitors (LICs) have been widely explored for energy storage. Nevertheless, achieving good energy density, satisfactory power density, and stable cycle life is still challenging. For this study, we fabricated a novel LIC with a NiO-rGO composite as a negative material and commercial activated carbon (AC) as a positive material for energy storage. The NiO-rGO//AC system utilizes NiO nanoparticles uniformly distributed in rGO to achieve a high specific capacity (with a current density of 0.5 A g−1 and a charge capacity of 945.8 mA h g−1) and uses AC to provide a large specific surface area and adjustable pore structure, thereby achieving excellent electrochemical performance. In detail, the NiO-rGO//AC system (with a mass ratio of 1:3) can achieve a high energy density (98.15 W h kg−1), a high power density (10.94 kW kg−1), and a long cycle life (with 72.1% capacity retention after 10,000 cycles). This study outlines a new option for the manufacture of LIC devices that feature both high energy and high power densities

Design of LEO Constellations Providing Internet Services Based on SOC Method

Narrow-beamwidth antenna is applied to LEO satellite constellations to provide high-speed internet services for the globe. Low-altitude, limited coverage region of single satellite and large scale are the main features of them. In this paper, under the constraint of specified half-beam angle of antenna, both inclined and polar orbit constellations are analysed based on Streets-of-Coverage method to provide continuous coverage. The results indicate that the coverage performance of single satellite is the key factor which can affect the configuration and number of constellations. When the orbit altitude is 1200 km and half-beam angle is 32 degrees, up to thousands of satellites are required for constellations providing internet services for zonal region 60 degrees from the equator. Non-symmetrical polar constellations show the best performance of continuous coverage and require approximately half of the satellites of inclined orbit constellations. The required satellites with different single coverage performance are also investigated as a reference for future research

Design of LEO Constellations Providing Internet Services Based on SOC Method

Narrow-beamwidth antenna is applied to LEO satellite constellations to provide high-speed internet services for the globe. Low-altitude, limited coverage region of single satellite and large scale are the main features of them. In this paper, under the constraint of specified half-beam angle of antenna, both inclined and polar orbit constellations are analysed based on Streets-of-Coverage method to provide continuous coverage. The results indicate that the coverage performance of single satellite is the key factor which can affect the configuration and number of constellations. When the orbit altitude is 1200 km and half-beam angle is 32 degrees, up to thousands of satellites are required for constellations providing internet services for zonal region 60 degrees from the equator. Non-symmetrical polar constellations show the best performance of continuous coverage and require approximately half of the satellites of inclined orbit constellations. The required satellites with different single coverage performance are also investigated as a reference for future research

Novel gaussian mixture model based nonsingular terminal sliding mode control for spacecraft close-range proximity with complex shape obstacle

This paper is mainly focusing on the problem of spacecraft close-range proximity with obstacle avoidance in the presence of complex shape. A novel Gaussian Mixture Model based nonsingular terminal sliding mode control (GMM-NTSMC) is proposed. This is achieved by developing GMM-based potential func-tion with a switching surface of NTSMC. It is theoretically proved that the closed-loop system is global stable. The main contribution of this paper is that the GMM-based avoiding strategies, which include the GMM-based terminal sliding mode control (GMM-TSMC) and GMM-NTSMC, can solve the collision avoidance problem considering complex shape while the artificial potential function based terminal slid-ing model control (APF-TSMC) fails. Moreover, the GMM-NTSMC and the GMM-TSMC require less energy with respect to the APF-TSMC. Furthermore, the GMM-NTSMC retains the advantage of the NTSMC and can avoid singularity problem while GMM-TSMC cannot. Finally, numerical simulations are performed to verify the effectiveness and superiority of the proposed GMM-NTSMC