Browsing by Subject "Heat equation"

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    A novel method for thermal conductivity measurement of two dimensional materials
    (2019-09) Çakıroğlu, Onur
    Thermal conductivity is a quantity which governs the heat transfer in a material. After increasing importance of efficiency in power generation systems and cooling mechanisms in micro-structures, many measurement methods have been developed to explore the thermal conductivity in micro and nano-sized materials. However, complexity in experimental setups, difficulties in the fabrication of devices required for measurements, and lacking exact solutions to thermal equations limit the usability of the methods to a class of materials. It is particularly challenging to study atomically thin metallic materials. To tackle this challenge, we have developed a new thermal conductivity measurement method based on the temperature dependent electrical resistance change and analyzed our method analytically and numerically by finite element method. We applied our method to 2H-TaS2 and found thermal conductivity as 9.55 1.27 W/m.K. Thermal conductivity value of TaS2, a metallic transition metal dichalcogenide was measured for the first time. This is supported by Wiedemann-Franz law and thermal conductivity of similar materials such as 2H-TaSe2 and 1T-TaS2. The method can be applied to semiconducting thin materials as well and is superior to other methods in various ways.
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    Stability analysis of the heat equation with time-delayed feedback
    (IFAC, 2009-06) Çalışkan, Sina Yamaç; Özbay, Hitay
    In this paper we consider the heat equation with time delayed feedback. Recently, stability analysis of this system, with possibly time-varying delay, is done by Fridman and Orlov (2007, 2009); and a sufficient condition is obtained for stability in terms of a linear matrix inequality. Here we consider the same system, but with constant delay, and perform the stability analysis in the frequency domain. A necessary and sufficient condition is obtained in terms of the system parameters. The result is illustrated with numerical examples. © 2009 IFAC.