Maintaining Path Stability with Node Failure in Mobile Ad Hoc Networks

AbstractAs the demand for mobile ad hoc wireless network (MANET) applications grows, so does their use for many important services where reliability and stability of the communication paths are of great importance. Therefore, a MANET must be able to establish reliable communication channels which are protected by failure recovery protocols. One approach for existing failure recovery protocols is based on using backup paths, or multi-paths. This technique provides for more stable communication channels for wireless services, in particular for MANET applications. But work on such multi-path protocols has focused on stability in the presence of link failure for MANETs. In this paper, we extend such protocols to maintain connection stability in the presence of node failure. Our work is focused on protecting the route of mobile wireless communications in the presence of node failure in order to improve their use in MANETs applications by discovering efficient stable communication channels with longer lifetimes and increased number of packets delivered

CONNECTION SURVIVAL USING POSITION-BASED ROUTING IN MOBILE AD HOC NETWORKS

Connection Survival using Position-Based Routing in Mobile Ad Hoc Networks Abedalmotaleb Zadin Concordia University, 2015 Mobile ad hoc networks (MANETs) have witnessed a tremendous growth in the recent years thanks to technological advancements and energy saving techniques that have made possible the creation of autonomous mobile communicating systems. Still, MANETs face many challenges in terms of stability, power consumption and quality of service. Typically, stability is assured through the use of reliable communication channels protected by failure recovery protocols. In this thesis, we examine the stability problem by the elaboration of new position based routing algorithms that maintain stable connections between nodes in MANETs. The positions of the nodes are updated by the regular beacon broadcasts. Specifically, we have extended the backup path mechanism used by Yang et al.'s 2011 Greedy- Based stable multi-path Routing protocol (GBR), that have been recently used in MANETs. In terms of stability alone, our algorithms have explored using more general backup paths; re-establishing broken paths from the last reachable node; or using a conservative range for neighbor next-hop selection. The latter protocol (GBR-CNR), using a Conservative Neighborhood Range (CNR), is the most efficient in simulations. To be able to accommodate energy constraints typical in MANETs, we study energy efficient variations of these stable position-based routing algorithms. We study the use of Dynamic Transmission Ranges (DTR) or energy-aware neighbor next-hop selection, such as the LEARN algorithm, to assure energy efficiency while preserving connection stability. Out of all the algorithms considered, the combination of CNR and DTR, GBR-CNR-DTR, outperforms the rest in simulation. Concerning the Quality of Service (QoS), we consider variations of GBR-CNR that improve QoS through the reduction of interference that affect the quality of communications. We develop stable communication protocols that mitigate interference between mobile nodes by minimizing the number of corrupted packets through the use of different techniques such as defining new methods to choose the hereafter hop in a communication process. Overall, this thesis presents several new stable position-based routing algorithms that improve energy consumption and QoS in MANETs. Several of the introduced algorithms are shown to have better capabilities than previously published algorithms as demonstrated in the simulation results

SISTEM REM PADA MOBIL GARUDA URBAN GASOLINE GUNA KOMPETISI SHELL ECO MARATHON ASIA SINGAPURA 2018

Tujuan penyusunan proyek akhir Sistem Rem Pada Mobil Garuda Urban Gasoline Guna Kompetisi Shell Eco Marathon Asia Singapura 2018, yakni mampu melakukan perancangan dan pembuatan sistem pengereman sesuai dengan kebutuhan dan regulasi kompetisi Shell Eco Marathon Asia 2018. Pembuatan sistem rem ini terdiri dari proses perancangan, pembuatan dan pengujian sistem rem pada Mobil Garuda Urban Gasoline 18. Pembuatan sistem rem ini meliputi pemasangan, master silinder, kaliper, return spring, sistem hidrolik, dan hand rem. Pengujian sistem rem digunakan untuk menganalisis adanya kesenjangan dalam proses pembuatan baik dari desain sampai ke hasil akhir yakni pengujian. Setelah dipastikan semua sudah sesuai dan sistem rem dapat bekerja dengan baik maka terakhir dilakukan pengujian yang mengacu pada hasil dari pembuatan sistem rem yang berupa pengujian statis dan pengujian dinamis. Hasil pengujian dari sistem rem yaitu sistem sudah sesuai dengan kebutuhan dan regulasi kompetisi Shell Eco Marathon Asia 2018 hal ini didasarkan pada hasil pengujian pada bidang miring dan pengujian hand rem. Untuk pengujian celah kampas rem didapatkan hasil perbedaan celah kampas rem yang menggunakan return spring dan tidak menggunakan return spring sebesar 5-6 mm. Dari hasil kalkulasi rancangan sistem rem besarnya gaya pengereman yang dibutuhkan sebesar 1120 N dengan torsi pengereman roda depan sebesar 195,91 Nm dan torsi pengereman roda belakang sebesar 97,63 Nm. Untuk pengujian jarak pengereman didapatkan 18 m dari 20 m braking area dan untuk daya gelinding terbaik didapatkan sebesar 310 m

Abrupt elastic-to-plastic transition in pentagonal nanowires under bending

MD modeling and calculations were supported by Russian Science Foundation project grant 18-19-00645 “Adhesion of polymer-based soft materials: from liquid to solid”; mechanical testing and FEM simulations were supported by Estonian Research Council projects PUT1689 and PUT1372.In this study, pentagonal Ag and Au nanowires (NWs) were bent in cantilever beam configuration inside a scanning electron microscope. We demonstrated an unusual, abrupt elastic-to-plastic transition, observed as a sudden change of the NW profile from smooth arc-shaped to angled knee-like during the bending in the narrow range of bending angles. In contrast to the behavior of NWs in the tensile and three-point bending tests, where extensive elastic deformation was followed by brittle fracture, in our case, after the abrupt plastic event, the NW was still far from fracture and enabled further bending without breaking. A possible explanation is that the five-fold twinned structure prevents propagation of critical defects, leading to dislocation pile up that may lead to sudden stress release, which is observed as an abrupt plastic event. Moreover, we found that if the NWs are coated with alumina, the abrupt plastic event is not observed and the NWs can withstand severe deformation in the elastic regime without fracture. The coating may possibly prevent formation of dislocations. Mechanical durability under high and inhomogeneous strain fields is an important aspect of exploiting Ag and Au NWs in applications like waveguiding or conductive networks in flexible polymer composite materials.Eesti Teadusagentuur PUT1372,PUT1689; Russian Science Foundation 18-19-00645; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Thermal runaway of metal nano-tips during intense electron emission

When an electron emitting tip is subjected to very high electric fields, plasma forms even under ultra high vacuum conditions. This phenomenon, known as vacuum arc, causes catastrophic surface modifications and constitutes a major limiting factor not only for modern electron sources, but also for many large-scale applications such as particle accelerators, fusion reactors etc. Although vacuum arcs have been studied thoroughly, the physical mechanisms that lead from intense electron emission to plasma ignition are still unclear. In this article, we give insights to the atomic scale processes taking place in metal nanotips under intense field emission conditions. We use multi-scale atomistic simulations that concurrently include field-induced forces, electron emission with finite-size and space-charge effects, Nottingham and Joule heating. We find that when a sufficiently high electric field is applied to the tip, the emission-generated heat partially melts it and the field-induced force elongates and sharpens it. This initiates a positive feedback thermal runaway process, which eventually causes evaporation of large fractions of the tip. The reported mechanism can explain the origin of neutral atoms necessary to initiate plasma, a missing key process required to explain the ignition of a vacuum arc. Our simulations provide a quantitative description of in the conditions leading to runaway, which shall be valuable for both field emission applications and vacuum arc studies.Peer reviewe

Application of artificial neural networks for rigid lattice kinetic Monte Carlo studies of Cu surface diffusion

Kinetic Monte Carlo (KMC) is a powerful method for simulation of diffusion processes in various systems. The accuracy of the method, however, relies on the extent of details used for the parameterization of the model. Migration barriers are often used to describe diffusion on atomic scale, but the full set of these barriers may become easily unmanageable in materials with increased chemical complexity or a large number of defects. This work is a feasibility study for applying a machine learning approach for Cu surface diffusion. We train an artificial neural network on a subset of the large set of 2(26) barriers needed to correctly describe the surface diffusion in Cu. Our KMC simulations using the obtained barrier predictor show sufficient accuracy in modelling processes on the low-index surfaces and display the correct thermodynamical stability of these surfaces.Peer reviewe