Investigation of the Thermal Behavior of Polypyrrole/Carbon Nanotube Composites and Utilization as Capacitive Material or Support for Catalysts

In this study, polypyrrole (PPy)/carbon nanotube (CNT) composites were synthesized by in situ chemical oxidative polymerization of a pyrrole monomer on CNT. Two different types of CNT having different structural properties were used. The composites were characterized using BET surface area analysis, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) techniques. Thermal decomposition kinetics of PPy/CNT composites was studied by thermal gravimetric analysis techniques (TG/DTG (differential thermal gravimetric)) at different heating rates (2.5, 5, 7.5, and 10?K min^?1). Kinetic parameters of the composites were obtained from the TG and DTG curves using the Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) models. The electrochemical capacitive properties of the composites were investigated by the cyclic voltammetry (CV) technique. Pt nanoparticles were decorated on the plain CNTs and composite materials via the microwave irradiation method.     

Design and development of an innovative individualized adaptive and intelligent e-learning system for teaching–learning of probability unit: Details of UZWEBMAT

In this study, an innovative adaptive and intelligent web based e-learning system, UZWEBMAT (Turkish abbreviation of Adaptive and INtelligent WEB based MAThematics teaching–learning system) was designed, developed and implemented. This e-learning system was intended for learning and teaching secondary school level permutation-combination-binomial expansion and probability subjects. Content which was prepared according to Turkish curriculum for secondary school mathematics course was transformed into learning objects in three different ways in accordance with VAK (Visual–Auditory–Kinesthetic) learning styles. Primary/secondary/tertiary learning styles of learners registering the system are determined and each learner receives the content appropriate for his/her dominant learning style. Also, they can be directed to contents of other styles according to their performances thanks to an expert system. Learning objects constituting the content were prepared according to constructivist approach. An active role for the learner was the purpose. Tips and intelligent solution supports within the learning objects were presented with expert system support to the learners. With this structure, UZWEBMAT bears the characteristics of intelligent tutoring system as well as an adaptive e-learning environment. All the movements of learners studying with UZWEBMAT are recorded and the necessary information is reported to both learners and teachers in a visualized way.     

Modelling the Sliding Behaviour of Tribofilms Forming During Automotive Braking: Impact of Loading Parameters and Property Range of Constituents

The impact of pressure, sliding velocity and property variation of constituents on the sliding behaviour of a model tribofilm was studied with the method of movable cellular automata (MCA). Whereas a clear pressure dependency of the coefficient of friction (COF) was always observed and could be correlated with the structure formation in terms of varying thickness of a mechanically mixed layer, the impact of the other parameters was either negligible or rather weak. Only if a brittle-to-ductile transition of the oxide-based tribofilm was assumed, a significant decrease in the COF level was predicted. Temperature-dependent property changes can be neglected during MCA modelling, unless this transition takes place. For magnetite-based tribofilms, the transition temperature is beyond 800°C, i.e. a temperature leading to fading effects during braking anyway. Thus, it could be concluded that, except for very severe braking conditions, sliding simulations with the MCA method yield meaningful results without considering temperature-dependent mechanical properties.     

State space modelling and spectral analysis of cointegrated vector processes (evidence from the U.S. and Scandinavian economies)

We provide new evidence on the impact of the U.S. economy on two Scandinavian economies (Finland and Sweden). Initially, we test for the presence of unit roots among the observed input-output processes. Next, Granger causality and cointegra-tion of the system is explicitly tested, to justify the estimated vector-valued state space model. The trend and cyclical components of the endogenous vector are extracted by three alternative decomposition methods. Finally, the content of the cyclical component is analysed by spectral analysis.     

Wind turbine speed control of a contactless piezoelectric wind energy harvester

ABSTRACT

Wind turbine control is an important task to make the electricity generation secure in terms of energy demand and machine safety. It also yields to control the desired power level and optimized energy because of the assignment of turbine speed. The contactless piezoelectric wind energy harvester (CPWEH) used in this study has three piezoelectric layers located around the shaft with 120 degrees apart and they are buckled by the magnetic force without any physical contact. The superiority of this device is to generate energy for low wind speeds such as 1.5 m/s. However, for high speeds, high total harmonic distortions (THDs) govern the waveforms, thus controlling the turbine speed becomes necessary for optimizing the output power. Encouraged by this, a small low inertia dc generator is coupled with the wind turbine, and the generator terminals are connected to a resistor through a power switch to generate a braking torque that opposes to wind speed direction. By controlling the switch properly, turbine speed is ensured to remain within a certain band, which accordingly prevents the turbine from rotating very fast at damaging wind speeds. Several experiments are performed on the developed CPWEH with/without the presented control scheme which prove the existence of promising performance of our proposal.     

Experimental and Numerical Investigation of Flow Over Ogee Spillway

Ogee type spillway is one of the most preferred sluice types due to its functional suitability and high safety factor. It is used for controlling the flow rates and water levels in reservoirs, such as lowering the water level in emergency situations, maintaining normal river functions and discharging excess water. The main aim of this study is to investigate the flow over ogee type spillway by performing experiments in an open channel flume in the laboratory and simulating with numerical model. The numerical model having the same dimensions with the physical model is modeled with two different programs of ANSYS-Fluent and OpenFOAM. The flow depths of the models were measured at four points, H₁, H₂, H₃, H₄. In the numerical analysis, two different turbulence models, K-ε and K-ω SST turbulence model were used in order to investigate the accuracy of the turbulence models in the open channel. According to the results, R² values, obtained from ANSYS- Fluent for the each measurement points where H₁, H₂, H₃, H₄, are 0.9776, 0.9859, 0.9701, 0.9916 and obtained from OpenFOAM for the each measurement points 0.9920, 0.9687, 0.9855, 0.9926 respectively. The findings show that the numerical tools have been sufficiently developed to simulate flow depths and water surface profiles.

     

A BIM-GIS integrated pre-retrofit model for building data mapping

In response to rising energy costs and the impetus to reduce environmental impacts, upgrading the large building stock that is responsible for 40% of the total energy consumption to maximum energy efficiency is becoming an important task. Despite the many benefits associated with retrofit projects, they are still only slowly being implemented because of the many challenges that exist. One of these challenges is optimizing the decision between renovation scenarios based on economic and environmental goals, which can be made possible with an accurate pre-retrofit model. The intention of this paper is to introduce a pre-retrofit model that efficiently obtains and integrates multiple forms of building data as a critical step to develop a comprehensive understanding of a building to be renovated. Opportunities for utilizing building information modeling (BIM) and geographical information systems (GIS) for retrofitting projects were explored through the study of a historical campus building. With the use of as-is geometric data and as-is data, building data maps were obtained. The next step of this study is to use the model to conduct scenarios comparison and optimize renovation decision based on economic and environmental goals.     

Schwarz lemma for driving point impedance functions and its circuit applications

In this paper, a boundary version of the Schwarz lemma is investigated for driving point impedance functions and its circuit applications. It is known that driving point impedance function, Z(s) = 1 + c_p(s − 1)^p + c_{p + 1}(s − 1)^{p + 1} + ..., p > 1, is an analytic function defined on the right half of the s-plane. Two theorems are presented using the modulus of the derivative of driving point impedance function, |Z′(0)|, by assuming the Z(s) function is also analytic at the boundary point s = 0 on the imaginary axis with . In the obtained inequalities, the value of the function at s = 1 and the derivatives with different orders have been used. Finally, the sharpness of the inequalities obtained in the presented theorems is proved. Simple LC circuits are obtained using the obtained driving point impedance functions.