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  • Gajduk, Andrej  (11)
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  • 1
    Description: The ability to extract public opinion from web portals such as review sites, social networks and blogs will enable companies and individuals to form a view, an attitude and make decisions without having to do lengthy and costly researches and surveys. In this paper machine learning techniques are used for determining the polarity of forum posts on kajgana which are written in Macedonian language. The posts are classified as being positive, negative or neutral. We test different feature metrics and classifiers and provide detailed evaluation of their participation in improving the overall performance on a manually generated dataset. By achieving 92% accuracy, we show that the performance of systems for automated opinion mining is comparable to a human evaluator, thus making it a viable option for text data analysis. Finally, we present a few statistics derived from the forum posts using the developed system. Comment: In press, MASA proceedings
    Keywords: Computer Science - Computation And Language
    Source: Cornell University
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  • 2
    Language: English
    In: The European Physical Journal Special Topics, 2014, Vol.223(12), pp.2387-2409
    Description: Transient stability and steady-state (small signal) stability in power girds are reviewed. Transient stability concepts are illustrated with simple examples; in particular, we consider three methods for computing region of attraction: time-simulations, extended Lyapunov function, and sum of squares optimization method. We discuss steady state stability in power systems, and present an example of a feedback control via a communication network for the 10 Unit 39 Bus New England Test system.
    Keywords: Electrical Engineering ; Computer Science;
    ISSN: 1951-6355
    E-ISSN: 1951-6401
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  • 3
    Description: Efficient control of power systems is becoming increasingly difficult as they gain in complexity and size. We propose an automatic control strategy that regulates the mechanical power output of the generators in a power grid based on information obtained via a communication infrastructure. An algorithm that optimizes steady-state stability of a power grid by iteratively adding communication links is presented. The proposed control scheme is successfully applied to the IEEE New England and IEEE RTS 96 power systems, leading to a significant increase in the steady-state stability of the systems and an improvement in their overall robustness. The resulting communication network topology differs significantly from the transmission grid topology. This shows how complex the steady- state control for power systems is, influenced by the generators configuration, the transmission network topology, and the manner by which control is executed. Comment: Submitted and currently under review in IEEE Transactions on Circuits and Systems - 2
    Keywords: Computer Science - Systems And Control ; Mathematics - Optimization And Control ; Nonlinear Sciences - Adaptation And Self-Organizing Systems
    Source: Cornell University
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  • 4
    Language: English
    In: IEEE Journal on Emerging and Selected Topics in Circuits and Systems, September 2017, Vol.7(3), pp.349-358
    Description: Efficient control of power systems is becoming increasingly difficult as they gain in complexity and size. By considering a power grid and a communication infrastructure as a multiplex network, we propose an automatic control strategy that regulates the mechanical power output of the generators based on information obtained via communication links (wireless or wired). An algorithm that optimizes steady-state stability of a power grid by iteratively adding communication links is presented. The proposed control scheme is successfully applied to the IEEE New England and the IEEE RTS 96 power systems, leading to a significant increase in the steady-state stability of the systems and an improvement in their overall robustness. The resulting communication network topology differs significantly from the transmission grid topology. This shows how complex the steady-state control for power systems is, influenced by the generators' configuration, the transmission network topology, and the manner by which control is executed.
    Keywords: Power System Stability ; Multiplexing ; Power Grids ; Steady-State ; Stability Criteria ; Generators ; Power Systems ; Smart Grid ; Control ; Stability ; Multiplex Networks ; Engineering
    ISSN: 2156-3357
    E-ISSN: 2156-3365
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  • 5
    Language: English
    In: New Journal of Physics, 2014, Vol.16(11), p.115011 (14pp)
    Description: Plug-in electric vehicles (PEVs) can serve in discharge mode as distributed energy and power resources operating as vehicle-to-grid (V2G) devices and in charge mode as loads or grid-to-vehicle devices. It has been documented that PEVs serving as V2G systems can offer possible backup for renewable power sources, can provide reactive power support, active power regulation, load balancing, peak load shaving, can reduce utility operating costs and can generate revenue. Here we show that PEVs can even improve power grid transient stability, that is, stability when the power grid is subjected to large disturbances, including bus faults, generator and branch tripping, and sudden large load changes. A control strategy that regulates the power output of a fleet of PEVs based on the speed of generator turbines is proposed and tested on the New England 10-unit 39-bus power system. By regulating the power output of the PEVs we show that (1) speed and voltage fluctuations resulting from large disturbances can be significantly reduced up to five times, and (2) the critical clearing time can be extended by 20–40%. Overall, the PEVs control strategy makes the power grid more robust.
    Keywords: Computer Science - Systems And Control ; Mathematics - Optimization And Control ; Nonlinear Sciences - Adaptation And Self-Organizing Systems;
    E-ISSN: 1367-2630
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  • 6
    Language: English
    In: Physica A: Statistical Mechanics and its Applications, 01 April 2017, Vol.471, pp.825-836
    Description: We show that three basic actor characteristics, namely normalized reciprocity, three cycles, and triplets, can be expressed using an unified framework that is based on computing the similarity index between two sets associated with the actor: the set of her/his friends and the set of those considering her/him as a friend. These metrics are extended to multiplex networks and then computed for two friendship networks generated by collecting data from two groups of undergraduate students. We found that in offline communication strong and weak ties are (almost) equally presented, while in online communication weak ties are dominant. Moreover, weak ties are much less reciprocal than strong ties. However, across different layers of the multiplex network reciprocities are preserved, while triads (measured with normalized three cycles and triplets) are not significant.
    Keywords: Multiplex Analysis ; Social Networks ; Graph Theory ; Physics
    ISSN: 0378-4371
    E-ISSN: 1873-2119
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  • 7
    Description: Energy efficiency is gaining importance in wireless communication networks which have nodes with limited energy supply and signal processing capabilities. We present a numerical study of cooperative communication scenarios based on simple local rules. This is in contrast to most of the approaches in the literature which enforce cooperation by using complex algorithms and require strategic complexity of the network nodes. The approach is motivated by recent results in evolutionary biology which suggest that, if certain mechanism is at work, cooperation can be favoured by natural selection, i. e. even selfish actions of the individual nodes can lead to emergence of cooperative behaviour in the network. The results of the simulations in the context of wireless communication networks verify these observations and indicate that uncomplicated local rules, followed by simple fitness evaluation, can generate network behaviour which yields global energy efficiency. Comment: The paper is accepted for publication at the International Workshop on Physics-inspired Paradigms in Wireless Communications and Networks - PHYSCOMNET 2014, in conjunction with the 12th Intl. Symposium on Modelling and Optimization in Mobile, Ad Hoc, and Wireless Networks - WIOPT, May 12-16, 2014, Hammamet, Tunisia
    Keywords: Computer Science - Networking And Internet Architecture ; Computer Science - Computer Science And Game Theory
    Source: Cornell University
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  • 8
    Description: We develop a game-theoretic framework to investigate the effect of cooperation on the energy efficiency in wireless networks. We address two examples of network architectures, resembling ad-hoc network and network with central infrastructure node. Most present approaches address the issue of energy efficiency in communication networks by using complex algorithms to enforce cooperation in the network, followed by extensive signal processing at the network nodes. Instead, we address cooperative communication scenarios which are governed by simple, evolutionary-like, local rules, and do not require strategic complexity of the network nodes. The approach is motivated by recent results in evolutionary biology which suggest that cooperation can emerge in Nature by evolution, i. e. can be favoured by natural selection, if certain mechanism is at work. As result, we are able to show by experiments that cooperative behavior can indeed emerge and persist in wireless networks, even if the behavior of the individual nodes is driven by selfish decision making. The results from this work indicate that uncomplicated local rules, followed by simple fitness evaluation, can promote cooperation and generate network behavior which yields global energy efficiency in certain wireless networks. Comment: This work has been submitted to the IEEE/ACM Transactions on Networking
    Keywords: Computer Science - Networking And Internet Architecture
    Source: Cornell University
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  • 9
    Description: Plug-in electrical vehicles (PEV) are capable of both grid-to-vehicle (G2V) and vehicle-to-grid (V2G) power transfer. The advantages of developing V2G include an additional revenue stream for cleaner vehicles, increased stability and reliability of the electric grid, lower electric system costs, and eventually, inexpensive storage and backup for renewable electricity. Here we show how smart control of PEVs can improve the stability of power grids using only local frequency measurements. We evaluate the proposed control strategy on the IEEE Case 3 and the IEEE New England power systems. The results show that V2G leads to improved steady-state stability, larger region of stability, reduced frequency and voltage fluctuations during transients and longer critical clearing times. Comment: 18 pages, 7 figures, subbmited for review in Elsevier's International Journal of Electrical Power & Energy Systems
    Keywords: Computer Science - Systems And Control
    Source: Cornell University
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  • 10
    Description: We consider an integration of renewable energy into transport and electricity sectors through vehicle to grid (V2G) technologies for an energy system that is predominantly based on lignite. The national energy system of Macedonia is modeled using EnergyPLAN which integrates energy for electricity, transport and heat, and includes hourly fluctuations in human needs and the environment. We show that electric-vehicles can provide the necessary storage enabling a fully renewable energy profile for Macedonia that can match the country's growing demand for energy. Furthermore, a large penetration of electric vehicles leads to a dramatic reduction of 47% of small particles and other air pollutants generated by car traffic in 2050. Comment: 15 pages, 9 figures. The paper is accepted for publication in the European Physics Journal - Special Topics
    Keywords: Physics - Physics And Society
    ISSN: 19516355
    E-ISSN: 19516401
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