Gultekin H.,TOBB University of Economics and Technology
International Journal of Production Economics | Year: 2012
This study considers the throughput optimization in a two-machine flowshop producing identical jobs. Unlike the general trend in the scheduling literature, the machines are assumed to be capable of performing different operations. As a consequence, one of the three operations that a job requires can only be processed by the first and another operation can only be processed by the second machine. These are called fixed operations. The remaining one is called the flexible operation and can be processed by any one of the machines. The machines are assumed to have different technological properties, i.e. non-identical, so that the processing time of the flexible operation has different values on the two machines. We first consider the problem of assigning the flexible operations to the machines for each job in order to maximize the throughput rate. We develop constant time solution algorithms for infinite and zero capacity buffer spaces in between the machines. We then analyze the benefits of flexibility. Managerial insights are provided regarding the changes in the makespan as well as the associated cost with respect to the increase in the level of flexibility. © 2012 Elsevier B.V. All rights reserved.
Efe M.O.,TOBB University of Economics and Technology
Transactions of the Institute of Measurement and Control | Year: 2011
We consider integral sliding mode control with a fractional order reaching law in this paper. The reaching law approach is followed and stability of the sliding manifold is shown graphically. We choose a quadrotor-type unmanned aerial vehicle (UAV) to validate the design. The attitude dynamics of the vehicle is controlled by the proposed scheme and it is seen that the proposed form of the control system gives much better results compared with its integer order counterpart. The contribution of the study is to report a highly robust control scheme utilizing the fractional order differintegration operators. © 2010 The Institute of Measurement and Control.
Bagci G.B.,TOBB University of Economics and Technology
Physica A: Statistical Mechanics and its Applications | Year: 2015
Absrtact Bento et al. (2015) recently proposed to use the third law of thermodynamics as a test for the generalized entropies, since the third law should be respected by any statistical mechanical entropy regardless of the explicit form of the Hamiltonian. We first consider the Rényi entropy which is the sole additive generalized entropy, and show that it violates the third law for q>1. Interestingly, this is exactly the interval where the Rényi entropy is neither concave nor convex. We then consider the homogeneous entropy and show that it also violates the third law for 0
Yuksel M.,TOBB University of Economics and Technology |
Erkip E.,New York University
IEEE Transactions on Wireless Communications | Year: 2011
In this paper the fading multiple antenna (MIMO) wire-tap channel is investigated under short term power constraints. The secret diversity gain and the secret multiplexing gain are defined. Using these definitions, the secret diversity-multiplexing tradeoff DMT) is calculated analytically for no transmitter side channel state information (CSI) and for full CSI. When there is no CSI at the transmitter, under the assumption of Gaussian codebooks, it is shown that the eavesdropper steals both transmitter and receiver antennas, and the secret DMT depends on the remaining degrees of freedom. When CSI is available at the transmitter (CSIT), the eavesdropper steals only transmitter antennas. This dependence on the availability of CSI is unlike the DMT results without secrecy constraints, where the DMT remains the same for no CSI and full CSI at the transmitter under short term power constraints. A zero-forcing type scheme is shown to achieve the secret DMT when CSIT is available. © 2011 IEEE.
Yalta A.T.,TOBB University of Economics and Technology
Energy Economics | Year: 2011
We employ a maximum entropy bootstrap based framework to analyze the energy consumption and real GDP nexus between 1950 and 2006 in Turkey. Our approach provides more accurate inference in comparison to conventional hypothesis tests based on asymptotic theory. It also avoids preliminary testing and shape-destroying transformations such as differencing and detrending. The bivariate analysis as well as a multivariate framework controlling for exchange rate and oil prices shows no evidence of a causal relation. Our results are robust to both the number of lags and the time period chosen. We also perform a cointegration analysis of the data and point out a common misunderstanding in the literature regarding the concept of causation. © 2010 Elsevier B.V.