ÖOÖzlem Orhan

Özlem Orhan

Bandırma Onyedi Eylül University
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Özlem Orhan has a total of 7 co-authors. Here are the top co-authors by number of shared publications:

Latest Publications

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    AMatrix-Algebraic Framework and Pairwise Asymmetry Multiplier for Quantifying Shock Propagation in Complex Production Networks

    by Özlem Orhan, Oya Mert Coşkun, Yasemin Demirel

    Scalar centrality measures assign one score to each sector of a production network and cannot compare its exposure to two shock sources. We develop a matrix-algebraic framework for this comparison. The Asymmetry Multiplier γj(α,β)=Ljα⊤/Ljβ⊤, the ratio of the price responses of a target sector to equal increments in unit value added at two sources, factors into a direct ratio and a network amplification ratio. Using sub-eigenvectors of the technical coefficient matrix, we derive lower and upper bounds that hold for every productive network and reduce to Perron–Frobenius bounds under irreducibility. We also prove that linear price responses bound those of competitive constant-returns economies from above and that no labeling-independent node-level measure determines the multiplier. A symmetric structural decomposition separates technological and final demand effects. As a proof of concept, the framework is applied to electricity and mining cost shocks in Türkiye. In 2022, the multiplier ranges from 0.20 to 1.86 across eleven sectors, indirect paths attenuate the direct ratio by a factor of 8 to 22 in six sectors, and Basic Metals is more exposed to mining than to electricity cost shocks, through imported mining inputs. For most sectors, the dominant channel is robust to disaggregation, coefficient perturbation and the annual tables of 2012–2022.

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    Integrability and Parametric Bifurcation of the Logarithmic Emden-Fowler Equation

    by Özlem Orhan

    This study investigates the generalized Emden-Fowler equation with logarithmic nonlinearity within the framework of complete integrability by means of the S-linearizability approach. Analytical proofs show that, for the fixed nonzero logarithmic source term, the quadratic-damping coefficient is the unique value within the family $a_2=k/\theta$ compatible with the integrability condition, and that, once this damping coefficient is fixed, every source term compatible with the integrability condition necessarily takes the form $\theta[\chi(t)+\Psi(t)\ln\theta]$, a family that contains source terms linear in $\theta$ as well as the logarithmic model investigated here. Under the parameter specialization that places the system in the scale-invariant regime, two functionally independent first integrals are constructed. These integrals are shown to generate equivalent closed-form general solutions through both a local point transformation and a generalized Sundman transformation, a result confirmed through symbolic substitution, internal consistency analysis, and independent numerical integration. The closed-form solution displays three distinct asymptotic regimes, determined by the sign of the discriminant of the characteristic equation. In particular, in contrast to the movable singularities observed in exponentially nonlinear equation classes, this family is shown to have no movable singularities; its only possible finite singular point is fixed at the origin. The S-linearizability framework provides a constructive coefficient-based route to the first integrals and the linearizing pair, consistent with the direct substitution $u=\ln\theta$. The conductivity relation provides structural motivation for possible heat-transfer applications, for which a physical interpretation requires a specified model.

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    Symmetry Classification and Exact Solutions of the Convective-Radiative Fin Equation with Variable Thermal Conductivity

    by Özlem Orhan

    Fins at large temperature differences lose heat by convection and radiation. With temperature-dependent conductivity, the nonlinear problem is usually treated numerically. Using λ-symmetries, the extended Prelle–Singer method and Lie symmetries, this study identifies the conductivity laws that make the problem linearizable. In this class, one relation gives the temperature for every heat-loss function, and the problem is well posed for heat loss with positive derivative, vanishing at ambient temperature. For power-law convection with Stefan–Boltzmann radiation, explicit solutions exist for purely convective or radiative loss and for constant heat transfer coefficients. They also exist for mixtures at negligible ambient temperature reducing to polynomials of degree at most four, including turbulent natural convection and nucleate boiling. Other mixtures have implicit exact solutions. The fin efficiency equals tanhμ/μ throughout the class, so the classical design relations hold. Tip losses and internal heat generation admit closed forms. For temperature-dependent heat loss, the class consists of the fin equations with maximal point symmetry sl(3,R). Within the Rosseland and thin-fin approximations, its constant-coefficient member is realized by semitransparent media of high refractive index satisfying a matching condition. A perturbation theory gives the efficiency correction outside the class. The exact solutions provide benchmarks for numerical methods.

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    ON THE SENSITIVITY AND CONVERGENCE PROPERTIES OF THE LEONTIEF INVERSE: A LINEAR-ALGEBRAIC APPROACH WITH A FOUR-SECTOR APPLICATION

    by Özlem Orhan

    This study explores the economy-wide consequences of changes in food-sector demand using a four-sector input-output framework intentionally simplified yet reflecting key structural characteristics of the Turkish economy. The analysis is confined to Agriculture, Food, Trade, and Transportation to make the main transmission mechanisms of demand shocks transparent. We establish a demand-driven Leontief model and assume that final demand for food products increases by 20% and then decreases by 20%. Subsequently, we monitored how this interest affected other aspects of the market through their interconnections. The results show that if food demand declines by 20%, the corresponding decline in overall output is approximately 23 billion TL. This demonstrates that a 1 lira decrease in demand for Food results in 1.99 liras in overall output. This shift influences various sectors of the economic structure differently. Agriculture is severely affected because it supplies many of the inputs required by the Food sector. Trade and Transport are not primarily influenced, as they don't directly produce it. Overall, this indicates that the Food industry, together with its vendors, is closely associated. Gradually, results have shown that input-output models are useful for analysing sectoral demand shocks.

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    A Comparative Performance Analysis of Dijkstra and Metaheuristic Algorithms for the Shortest Path Problem in Inter-District Transportation Networks

    by Rabia Korkmaz Tan, Oya Mert Coşkun, Yasemin Demirel, Özlem Orhan

    This study addresses the classical shortest path problem, a fundamental challenge in graph theory with critical applications in transportation networks. Using real inter-district distance data from southwestern Türkiye, particularly covering 13 districts of Muğla province, the region frequently affected by forest fires during summer, this study also emphasizes the importance of shortest path analyses for routing firefighting vehicles and emergency logistics. We compare the deterministic Dijkstra algorithm with four metaheuristic approaches: Genetic Algorithm (GA), Particle Swarm Optimization (PSO), Ant Colony Optimization (ACO), and Simulated Annealing (SA). The evaluation focuses on path length optimization, computational efficiency, and convergence behavior across multiple independent runs. Experimental findings confirm that Dijkstra consistently produces the optimal solution (200 km), while ACO achieves the same performance despite its stochastic nature. In contrast, GA (mean 621 km), PSO (mean 734 km), and SA (mean 759 km) exhibited significant deviations from the optimal solution, with varying convergence stability and computation times. These results highlight the robustness of Dijkstra in small-scale static problems, while also demonstrating the potential of ACO as a competitive metaheuristic for dynamic and large-scale applications. Furthermore, Dijkstra-Seeded (DS) hybrid variants of the three underperforming algorithms (DS-GA, DS-PSO, DS-SA) were developed to investigate whether informed initialization could improve solution quality. Experimental results revealed that Dijkstra-based seeding within a permutation-based encoding yielded mixed results, with DS-SA showing meaningful improvement (689 km mean, 9.22% better than original SA), while DS-GA (645 km mean, -3.86%) and DS-PSO (754 km mean, -2.72%) slightly deteriorated. These findings underscore the fundamental challenges of adapting continuous-space metaheuristics to discrete graph problems and highlight the importance of encoding-aware hybridization strategies.

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    Optimizing upper extremity reconstruction: outcomes of anterolateral thigh (ALT) flap in complex hand injuries

    by Numan Atilgan, Numan Duman, Ozlem Orhan

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    On the First Integrals and Linearization of Force-Free Duffing Van der Pol Equation

    by Ozlem Orhan

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    ON COMPARISON OF SOLUTION OF ORDINARY DIFFERENTIAL EQUATION WITH HAAR WAVELET METHOD AND THE MODIFIED ISHIKAWA ITERATION METHOD

    by Yasemi̇n Bakir, Oya Mert, Özlem Orhan