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Yayın Yayın Optimal project duration for resource leveling(Işık Üniversitesi, 2017-07-13) Eren, Elif; Atan, Sabri Tankut; Işık Üniversitesi, Fen Bilimleri Enstitüsü, Endüstri Mühendisliği - Yöneylem Araştırması Yüksek Lisans ProgramıResource leveling is important in project management as resource fluctuations are costly and undesired. Typically, schedules with better resource profiles are obtained using the schedule found by Critical Path Method and then shifting the activities within their oat times. However, if the project duration can be extended, it is plausible to find a schedule with enhanced resource leveling since a longer duration allows for more oat time for all activities. In this thesis, we investigate what the duration for the best leveled schedule should be. We provide mixed-integer linear models for several objectives including the Release and Rehire metric. We show that not all metrics used for leveling under fixed durations may be appropriate when the project duration becomes a decision variable. Optimal solutions from smaller problems are used to find the magnitude of the extension needed and benefits obtained thereby. Since the problem is a NP-hard problem for which exact solutions cannot be obtained for big networks, we modify Burgess-Killebrew heuristic to solve larger problems. Computational experiments with benchmark problems from the literature indicate that the more the number of resource types is increased, the less levelling benefits are gained from extending the project. The optimal project durations can also be significantly different for different metrics.Yayın Power control in the cognitive cooperative multiple access channel(IEEE, 2012) Kaya, Onur; İşleyen, MuratWe extend several encoding and decoding techniques from cooperative communications framework, to a cognitive radio system consisting of a primary user (PU) and a secondary user (SU), sending their messages to a common receiver. Assuming that the transmitters and the receiver have full channel state information (CSI) collected and distributed by the common receiver, and that the SU knows the PU's codebook, the cooperation is obtained by block Markov superposition coding, and backwards decoding, which yield a causal overlay scenario. We formulate two rate optimization problems with the aim of, (i) maximizing the sum rate of the system, and (ii) maximizing the rate of the secondary user. We obtain the optimal power allocations for both cases, and the resulting rate regions. The power controlled cooperation turns out to be especially useful when maximizing the sum rate of the system, as it gives the PU significant rate rewards for allowing the cognitive transmitter to access its resources.Yayın A split-step Fourier scheme for the dissipative Kundu-Eckhaus equation and its rogue wave dynamics(Işık University Press, 2021-01) Bayındır, Cihan; Yurtbak, HazalWe investigate the rogue wave dynamics of the dissipative Kundu-Eckhaus equation. With this motivation, we propose a split-step Fourier scheme for its numerical solution. After testing the accuracy and stability of the scheme using an analytical solution as a benchmark problem, we analyze the chaotic wave fields generated by the modulation instability within the frame of the dissipative Kundu-Eckhaus equation. We discuss the effects of various parameters on rogue wave formation probability and we also discuss the role of dissipation on occurrences of such waves.
