2,107 research outputs found

    Energy and Information

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    Routing Protocols for Underwater Acoustic Sensor Networks: A Survey from an Application Perspective

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    Underwater acoustic communications are different from terrestrial radio communications; acoustic channel is asymmetric and has large and variable end‐to‐end propagation delays, distance‐dependent limited bandwidth, high bit error rates, and multi‐path fading. Besides, nodes’ mobility and limited battery power also cause problems for networking protocol design. Among them, routing in underwater acoustic networks is a challenging task, and many protocols have been proposed. In this chapter, we first classify the routing protocols according to application scenarios, which are classified according to the number of sinks that an underwater acoustic sensor network (UASN) may use, namely single‐sink, multi‐sink, and no‐sink. We review some typical routing strategies proposed for these application scenarios, such as cross‐layer and reinforcement learning as well as opportunistic routing. Finally, some remaining key issues are highlighted

    Decentralized Convex Optimization for Wireless Sensor Networks

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    Many real-world applications arising in domains such as large-scale machine learning, wired and wireless networks can be formulated as distributed linear least-squares over a large network. These problems often have their data naturally distributed. For instance applications such as seismic imaging, smart grid have the sensors geographically distributed and the current algorithms to analyze these data rely on centralized approach. The data is either gathered manually, or relayed by expensive broadband stations, and then processed at a base station. This approach is time-consuming (weeks to months) and hazardous as the task involves manual data gathering in extreme conditions. To obtain the solution in real-time, we require decentralized algorithms that do not rely on a fusion center, cluster heads, or multi-hop communication. In this thesis, we propose several decentralized least squares optimization algorithm that are suitable for performing real-time seismic imaging in a sensor network. The algorithms are evaluated and tested using both synthetic and real-data traces. The results validate that our distributed algorithm is able to obtain a satisfactory image similar to centralized computation under constraints of network resources, while distributing the computational burden to sensor nodes

    A Survey on Issues and Challenges in Congestion Adaptive Routing in Mobile Ad hoc Network

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    Mobile ad hoc networks is the future wireless communication systems have recently emerged as an important trend. Mobile adhoc network is self-configurable and adaptive. Due to the mobility of nodes, the network congestion occurs and it is difficult to predict load on the network which leads to congestion. Mobile adhoc network suffers from a severe congestion controlling problem due to the nature of shared communication and mobility. Standard TCP controlling mechanism for congestion is not fit to the dynamic changing topology of MANETs. This provides a wide scope of research work in mobile ad hoc network. The purpose of this survey is to study and analyze various issues and challenges in congestion control mechanisms in adaptive routing protocols in Mobile Adhoc Network (MANET)

    Implementation of Captcha as Graphical Passwords For Multi Security

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    To validate human users, passwords play a vital role in computer security. Graphical passwords offer more security than text-based passwords, this is due to the reason that the user replies on graphical passwords. Normal users choose regular or unforgettable passwords which can be easy to guess and are prone to Artificial Intelligence problems. Many harder to guess passwords involve more mathematical or computational complications. To counter these hard AI problems a new Captcha technology known as, Captcha as Graphical Password (CaRP), from a novel family of graphical password systems has been developed. CaRP is both a Captcha and graphical password scheme in one. CaRP mainly helps in hard AI problems and security issues like online guess attacks, relay attacks, and shoulder-surfing attacks if combined with dual view technologies. Pass-points, a new methodology from CaRP, addresses the image hotspot problem in graphical password systems which lead to weak passwords. CaRP also implements a combination of images or colors with text which generates session passwords, that helps in authentication because with session passwords every time a new password is generated and is used only once. To counter shoulder surfing, CaRP provides cheap security and usability and thus improves online security. CaRP is not a panacea; however, it gives protection and usability to some online applications for improving online security

    Midfrontal theta transcranial alternating current stimulation modulates behavioural adjustment after error execution

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    Cognitive control during conflict monitoring, error processing, and post-error adjustment appear to be associated with the occurrence of midfrontal theta (MFÏŽ). While this association is supported by correlational EEG studies, much less is known about the possible causal link between MFÏŽ and error and conflict processing. In the present study, we aimed to explore the role of band-specific effects in modulating the error system during a conflict resolution. In turn, we delivered transcranial alternating current stimulation (tACS) at different frequency bands (delta ÎŽ, theta Ξ, alpha α, beta ÎČ, gamma Îł) and sham stimulation over the medial frontal cortex (MFC) in 36 healthy participants performing a modified version of the Flanker task. Task performance and reports about the sensations (e.g. visual flickering, cutaneous burning) induced by the different frequency bands, were also recorded. We found that online Ξ-tACS increased the response speed to congruent stimuli after error execution with respect to sham stimulation. Importantly, the accuracy following the errors did not decrease because of speed-accuracy trade off. Moreover, tACS evoked visual and somatosensory sensations were significantly stronger at α-tACS and ÎČ-tACS compared to other frequencies. Our findings suggest that theta activity plays a causative role in modulating behavioural adjustments during perceptual choices in a stimulus-response conflict task. © 2018 Federation of European Neuroscience Societies and John Wiley & Sons Lt

    Schnelle Löser fĂŒr Partielle Differentialgleichungen

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    This workshop was well attended by 52 participants with broad geographic representation from 11 countries and 3 continents. It was a nice blend of researchers with various backgrounds
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