Natural gas demand in Turkey

On average, energy demand of Turkey is mounting by 8% annually, one of the highest rates in the world. Among primary energy sources, natural gas is the fastest growing one in Turkey. Gas consumption started at 0.5 bcm (billion cubic meters) in 1987 and reached approximately 35 bcm in 2007. Turkish natural gas usage is projected to further increase remarkably in coming years. The present paper focuses the characteristics of this demand and estimates short and long-run price and income elasticities of sectoral natural gas demand in Turkey. The future growth in this demand is also forecasted using an ARIMA modelling and the results are compared with official projections. The paper reveals that natural gas demand elasticities are quite low, meaning that consumers do not respond possible abusive price increases by decreasing their demand or substituting natural gas with other energy sources. Since consumers are prone to monopoly abuse by incumbent, there is a need for market regulation in Turkish natural gas market. Based on forecasts obtained, it is clear that the current official projections do not over/under-estimate natural gas demand although past official projections highly overestimated it.     

Computational modeling of airflow patterns and heat transfer prediction through stacked layers' products in a vented box during cooling

Efficiency of forced-air cooling processes is measured by process time and product temperature uniformity. Ventilated packaging is required to achieve a rapid and uniform cooling process. Product type, produce positioning and orientation and container venting have significant effects on airflow patterns. To optimize the design, airflow patterns and temperature distributions inside a ventilated package should be known. The objective of this study was to determine airflow patterns and temperature distribution in ventilated containers including stacked layers of spheres using computational fluid dynamics and turbulence model. Effects of flow dimensionality, turbulence intensity, mesh sensitivity, opening size and ratios for venting and air inflow rate were investigated. This study is expected to provide a better method for analyzing cooling performance of ventilated packages.     

Numerical simulation for heat transfer and velocity field characteristics of two-phase flow systems in axially rotating horizontal cans

Volume of fluid (VOF) element method coupled with a finite volume (FV) discretization technique was used to simulate two-dimensional, transient, two-phase flow patterns (air–water and air–food material) in an axially rotating horizontal can for rotational speeds of 10–160 rpm. Rotational Reynolds number ranged from 1700 to 27200 and 0.88 to 14.1 for water and food phases, respectively. FV solution was performed on a moving mesh system representing the can motion in on-axis axial rotation with respect to an inertial-fixed frame. Since the two-phase flow pattern prediction was an important aspect of modeling fluid mixing and improved heat transfer in canning process, reliable time- and spatially-dependent flow pattern maps were given to identify the rotational effects on two-phase flow characteristics and to determine flow patterns prevailing at different rotational speeds. Single-phase and food-phase flow computations with the corresponding flow patterns were also provided for a direct comparison with air–water results to further determine the physical limitations of the rotational effects. Numerical results demonstrated that two-phase flow patterns were significantly influenced by increasing rotational speeds leading to distinguishable flow patterns in terms of air–liquid (water/food material) interface characteristics and associated headspace air bubble movement through the liquid phase.     

Re-design of a failed clutch fork using topology and shape optimisation by the response surface method

This paper presents a framework for re-designing a failed automotive component subjected to cyclic loading. In the automotive industry, some parts fail before completing their design life. These failed components have to be re-designed using modern optimisation tools. In this paper, a failed clutch fork was completely re-designed using topology and the shape optimisation approach. Stress-life fatigue analysis was conducted to correlate the crack location between the failed component and the simulation model. A new design proposal was determined with the topology optimisation approach, and then design optimisation by response surface methodology was effectively used to improve the new clutch fork design. The mass reduction obtained was 24%. A maximum stress reduction of 9% was achieved, and the rigidity was improved up to 37% in comparison to the original clutch fork.     

On the wind energy in Turkey

Increase in negative effects of fossil fuels on the environment has forced many countries, including Turkey, to use renewable energy sources. Today, clean, domestic and renewable energy is commonly accepted as the key for future life, not only for Turkey but also for the world. As wind energy is an alternative clean energy source compared to the fossil fuels that pollute the atmosphere, systems that convert wind energy to electricity have developed rapidly. Turkey is an energy importing country, more than half of the energy requirement has been supplied by imports. Turkey's domestic fossil fuel resources are extremely limited. In addition, Turkey's geographical location has several advantages for extensive use of wind power. In this context, renewable energy resources appear to be one of the most efficient and effective solutions for sustainable energy development and environmental pollution prevention in Turkey. Since wind energy will be used more and more in the future, its current potential, usage, and assessment in Turkey is the focus of the present study. The paper not only presents a review of the potential and utilization of the wind power in Turkey but also provides some guidelines for policy makers.     

Note on Niederreiter-Xing's Propagation Rule for Linear Codes

We present a simple construction of long linear codes from shorter ones. Our approach is related to the product code construction; it generalizes and simplifies substantially the recent “Propagation Rule” by Niederreiter and Xing. Many optimal codes can be produced by our method. Received: June 23, 2000     

Graph‐Based Dwell Time Computation Methods for Discrete‐Time Switched Linear Systems

Analytical computation methods are proposed for evaluating the minimum dwell time and the average dwell time guaranteeing the asymptotic stability of a discrete‐time switched linear system whose switchings are assumed to respect a given directed graph. The minimum and average dwell time can be found using the graph that governs the switchings, and the associated weights. This approach, which is used in a previous work for continuous‐time systems having non‐defective subsystems, has been adapted to discrete‐time switched systems and generalized to allow defective subsystems. Moreover, we present a novel method to improve the dwell time estimation in the case of bimodal switched systems. In this method, scaling algorithms to minimize the condition number have been used to give better minimum dwell time and average dwell time estimates.     

An empirical study on evolutionary feature selection in intelligent tutors for learning concept detection

Concept map mining (CMM) has emerged as a new research area with recent developments in computational intelligence in educational technology. CMM includes the following steps: extracting the learning concepts from educational content, specifying relations among them, and generating a concept map as a result. The purpose of this study was to develop a mechanism using data mining technique to determine the features that characterize a learning concept extracted automatically from a single educational text. The 3 major features that distinguish the real learning concepts from other sequences of strings are detected by using a hybrid system of a feed‐forward neural network and some evolutionary algorithms. Ant colony optimization and genetic algorithm and particle swarm optimization are used as a binary feature selection method. In addition, the aforementioned methods are hybridized to get better accuracy and precision. The performance comparisons with two different state‐of‐the‐art algorithms have been made from the viewpoint of a typical classification problem.