Linear/Quadratic Programming-Based Optimal Power Flow using Linear Power Flow and Absolute Loss Approximations

This paper presents novel methods to approximate the nonlinear AC optimal power flow (OPF) into tractable linear/quadratic programming (LP/QP) based OPF problems that can be used for power system planning and operation. We derive a linear power flow approximation and consider a convex reformulation of the power losses in the form of absolute value functions. We show four ways how to incorporate this approximation into LP/QP based OPF problems. In a comprehensive case study the usefulness of our OPF methods is analyzed and compared with an existing OPF relaxation and approximation method. As a result, the errors on voltage magnitudes and angles are reasonable, while obtaining near-optimal results for typical scenarios. We find that our methods reduce significantly the computational complexity compared to the nonlinear AC-OPF making them a good choice for planning purposes

On a Recently Introduced Fifth-Order Bi-Hamiltonian Equation and Trivially Related Hamiltonian Operators

We show that a recently introduced fifth-order bi-Hamiltonian equation with a differentially constrained arbitrary function by A. de Sole, V.G. Kac and M. Wakimoto is not a new one but a higher symmetry of a third-order equation. We give an exhaustive list of cases of the arbitrary function in this equation, in each of which the associated equation is inequivalent to the equations in the remaining cases. The equations in each of the cases are linked to equations known in the literature by invertible transformations. It is shown that the new Hamiltonian operator of order seven, using which the introduced equation is obtained, is trivially related to a known pair of fifth-order and third-order compatible Hamiltonian operators. Using the so-called trivial compositions of lower-order Hamiltonian operators, we give nonlocal generalizations of some higher-order Hamiltonian operators

Why did it work this time: a comparative analysis of transformation of Turkish economy after 2002

Turkey had several unsuccessful stabilization efforts during 1980s and 1990s. Thanks to policies that were put into practice after the 2001 crisis, which constitutes a turning point for Turkish economy, fiscal discipline was restored, single digit inflation was reached, and yet growth rate was doubled compared to the previous decade average. As a result investment climate improved and the economy benefited from substantial amount of foreign direct investment and other long-term capital inflows. However these developments had some adverse side effects as well. Real appreciation of domestic currency, deterioration of trade balance, and increasing private indebtedness generated vulnerability for sudden stops. Beside, increasing global integration and very rapid shift in the economic circumstances caused difficulties for traditional sectors. This paper analyzes the Turkish experience after 2001 and identifies underlying dynamics of the restructuring program, while denoting the costs of this transition. Turkish case provides evidence in favor of disinflation programs combined with sound fiscal policies in spite of some adverse effects in the short run.Turkish Economy, Crisis, Stabilization Policy, Macroeconomic Performance

Beyond the global financial crisis: central banking in a new global financial system

Since the outbreak of the global crisis in mid 2007, there has been an extensive discussion on root causes. Some blame the greed and corruption of financial actors. Others put the blame on central bankers for easy money or regulators who remained idle as too much risks accumulated in financial markets. According to advanced economies, global imbalances have been caused by emerging surplus countries that keep their currency undervalued and their domestic consumption restricted. It is unfortunate that all these arguments and counter arguments, which may be valid in their own way, prevents a more general discussion on the deep-seated conflicts and contradictions in the global economic, social and political paradigm upon which the world order is built. To put it another way, the problems we face today do not arise from some operational failures, but from the system itself and the underlying philosophical framework. In fact this is a crisis of three main pillars of our existing system: the crisis of the economic theory, the crisis of the globalization, and the crisis of market based financial system.global financial crisis, economic theory, financial system

Transmission Network Reduction Method using Nonlinear Optimization

This paper presents a new method to determine the susceptances of a reduced transmission network representation by using nonlinear optimization. We use Power Transfer Distribution Factors (PTDFs) to convert the original grid into a reduced version, from which we determine the susceptances. From our case studies we find that considering a reduced injection-independent evaluated PTDF matrix is the best approximation and is by far better than an injection-dependent evaluated PTDF matrix over a given set of arbitrarily-chosen power injection scenarios. We also compare our nonlinear approach with existing methods from literature in terms of the approximation error and computation time. On average, we find that our approach reduces the mean error of the power flow deviations between the original power system and its reduced version, while achieving higher but reasonable computation times

Turkey's response to the global economic crisis

Turkey was not affected by the financial crisis as much as the advanced economies and managed to rapidly exit the turmoil. The reasons behind the strong response and quick recovery of the Turkish economy were its low country risk and low currency risk premiums. This study shows the foundations of these low risk premiums and compares some measures of these risks of the Turkish economy with peer countries. Second, this paper demonstrates that all of Turkey’s economic sectors were very strong before the crisis and sustained this strength during the course of the crisis. Finally, it discusses the policies that have already been taken and planned to be taken by Turkey’s economic authorities. The government seems to be very determined in keeping fiscal discipline as tight as necessary while not being excessivefinancial crises, global economic crisis, Turkey, economic policies, financial markets

Enhanced transmission of electromagnetic waves through split-ring resonator-shaped apertures

The design of aperture shape is a promising approach for enhanced transmission through a subwavelength aperture. We designed split-ring-resonator (SRR)-shaped apertures in order to increase the transmission through subwavelength apertures by making use of the strong localization of the electromagnetic field in SRR-shaped apertures. We obtained a promising result of 104-fold enhancement by utilizing SRR-shaped apertures. It is possible to use these proposed structures at optical frequencies by making several modifications such as decreasing the sharpness of edges and increasing the gap width. Since SRRs are already being realized at optical frequencies, our proposed SRR-shaped aperture structures are promising candidates for novel applications