Mühendislik ve Doğa Bilimleri Fakültesi Koleksiyonu

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https://hdl.handle.net/20.500.12415/16

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Reductions of topologically massive gravity II. First order realizations of second order Lagrangians
(American Institute of Physics, 2020) Çağatay Uçgun, Filiz; Esen, Oğul; Gümral, Hasan
Second order degenerate Clement and Sarolu-Tekin Lagrangians are casted into forms of various first order Lagrangians. The structures of the iterated tangent bundle and acceleration bundle are presented as a suitable geometric framework. Hamiltonian analyses of these equivalent formalisms are performed by means of the Dirac-Bergmann constraint algorithm. All formulations are shown to possess only second class constraints.
A new systematic approach for warehouse management system evaluation
(UNIV OSIJEK, TECH FAC, 2016) Apak, Sinan; Tozan, Hakan; Vayvay, Ozalp
Warehouse management is one of the most important legs in supply chain operations and production management. To support that warehouse execution, a warehouse management system is required. Many warehouses have used various methods to handle this difficult and time consuming evaluation process. The purpose of this paper is to provide a decision support model to make a careful evaluation of warehouse management system. Purchasing an appropriate warehouse management system in a supply value chain is not an easy decision making and is related to fuzziness and uncertainty, which should be considered as a large number of complex factors in multiple evaluation criteria. A Fuzzy Multi Criteria Decision Making approach is adopted to effectively evaluate warehouse management systems. To provide a practical guidance for other companies a real life framework is presented with an application.
A Decision Making Model for the Evaluation of Supply Chain Execution and Management Systems
(ATLANTIS PRESS, 2013) Apak, Sinan; Vayvay, Ozalp; Feyzioglu, Orhan; Apak, Sinan
A Supply Chain Execution and Management (SCEM) system is an enterprise application that integrates all of the necessary supply chain functions into a single system. These functions range from common ones such as warehouse and transportation management to less known ones such as demand management. In order to execute and manage the supply chain processes successfully, organisations need a comprehensive evaluation approach to determine the most suitable system. The evaluation of an SCEM system involves numerous decision making criteria. Moreover, it is usually characterised with uncertainty and vagueness since it is very difficult to rate SCEM system alternatives with exact terms. To cope with this problem, a fuzzy logic-based approach is developed in this study. This approach main integrates the Fuzzy Analytic Hierarchy Process to weight the decision criteria and the Fuzzy Technique for Order Preference by Similarity to Ideal Solution to rate alternatives. A real life example is provided to demonstrate the capability of the proposed approach.
A bayesian approach proposal for inventory cost and demand forecasting
(2015) Apak, Sinan
Endüstriyel pazardaki teknolojinin kalıcı değişikliğinin ve ürün modellerinin farklılığının, yedek parçalar için yapılan talep tahmini üzerinde önemli bir etkisi vardır. Ürünlerin gelecekteki talep oranlarını ortaya koymak amacıyla envanter yöneticileri kendi tahminlerini sürekli güncellemektedir. Bayes modeli, önsel olasılık dağılımı kullanarak kabul edilebilir oranı birkaç dönem üzerinden optimum hesap yapmak için kullanmaktadır. Ancak, aralıklı talep gibi muhtelif talep oranlarının altında, Bayes Modelinin performansı analiz edilmemiştir. Bir araştırma sorusu yardımıyla, bu çalışma bu durum incelenmektedir.
Outstanding thermo-mechanical properties of graphene-like B3C3 and C3N3
(Springer, 2020) Şenturk, Ahmet Emin
Experimentally fabricated two-dimensional (2D) carbon-based nanomaterials have received significant attention because of their ultra-high physical properties, in recent years. In this manuscript, the thermal conductivity (TC) and mechanical response of 2D B3C3 and C3N3 structures are studied in detail, using molecular dynamics (MD) simulations. Their superior mechanical properties (Young’s modulus, ultimate tensile strength and failure strain) and TC make an excellent candidate for various applications of nanodevices. The mechanical properties of these 2D structures are also examined at five various temperatures up to 900 K along with the different loading directions and various strain rates from 107 to 109 s?1. MD results demonstrate that the mechanical properties of these 2D structures gradually decrease as temperature increases, due to the weakening effect of high temprerature. Additionally, when the strain rate increases, it is revealed that the mechanical properties show an increasing trend. Furthermore, at 300 K, the failure processes of these 2D structures are studied. MD simulations results demonstrate that these structures show brittle failure mechanism. On the other hand, various types of structural defects occurs during the production process and so these defects affect the physical properties of these structures adversely. Accordingly, the effects of various atom types, such as, N, B and C, vacancy defects on the mechanical properties and TC of these structures were investigated. The existence of vacancy defects in these structures reduces the TC and mechanical properties significantly by increasing the concentrations of defects. Finally, non-equilibrium MD simulations results indicate exceptionally high TC values of these structures.
Thermal conductivity and mechanical properties of graphene-like BC2, BC(3)and B4C3
(Taylor & Francis Online, 2020) Şentürk, Ahmet Emin; Öktem, Ahmet Sinan; Konukman, Alp Er S.
Recently, carbon-based 2D nanomaterials have received significant attention because of their superior physical properties. In this investigation, the thermal conductivity (TC) and mechanical properties of graphene-like BC2, BC(3)and B(4)C(3)structures are systematically examined, using molecular dynamics (MD) simulations. For graphene-like BC2, BC(3)and B(4)C(3)structures, our MD results predict remarkably high thermal and mechanical properties. Especially, graphene-like BC(3)structure indicates higher mechanical properties than graphene-like BC(2)and B(4)C(3)structures. Also, the mechanical properties of these graphene-like structures are investigated at four various temperatures from 200 to 900 K. Our results indicate that the mechanical properties of graphene-like structures gradually decrease as the temperature rises. In addition, the failure processes of graphene-like BC2, BC(3)and B(4)C(3)structures are examined at room temperature. According to the MD simulations, these graphene-like structures show brittle failure mechanism. In addition, graphene-like BC(3)structure is more stretchable than other structures. Remarkably, non-equilibrium MD simulation results demonstrate ultra high TC values of graphene-like BC2, BC(3)and B(4)C(3)structures and so propose them for thermal management of polymeric materials or in nanoelectronics. Similar to the mechanical properties, graphene-like BC(3)has higher TC value than others.
Reduction of inrush current in a shockwave non-thermal food processing system using an exponential clock pulse generator
(MDPI, 2020) Eguchi, Kei; Asadı, Farzin; Shibata, Akira; Abe, Hiroto; Oota, Ichirou
Recently, shockwave food processing is drawing much attention as a low-cost non-thermal food process technique. In shockwave non-thermal food processing, underwater shockwaves are generated by a high voltage generator. Therefore, high inrush currents and high voltage stress on circuit components significantly reduce the reliability and life expectancy of the circuit. However, to the best of our knowledge, stress reduction techniques and their experimental verification have not been studied yet in the shockwave non-thermal food processing system. In this paper, we propose a stress reduction technique for the shockwave non-thermal food processing system and investigate the effectiveness of the proposed technique experimentally. To achieve high reliability and life expectancy, a new high voltage multiplier with an exponential clock pulse generator is proposed for the shockwave non-thermal food processing system. By slowing down the rate at which the capacitors charge in the high voltage multiplier, the exponential clock pulse generator significantly reduces the inrush current. Furthermore, to perform shockwave non-thermal food processing continuously at a lower voltage level, we present a new electrode with a reset mechanism for wire electric discharge (WED), where a square-shaped metal wire swings on a hinge in the proposed electrode. The proposed electrode enables not only shockwave generation at a lower voltage level but also continuous non-thermal food processing, because the square-shaped metal wire is not melted in the WED process. To confirm the validity of the proposed techniques, some experiments are performed regarding the laboratory prototype of the shockwave non-thermal food processing system. In the performed experiments, reduction of inrush currents and effective food processing are confirmed.
Electrostatic theory of irregular conductance oscillations through a quantum constriction under Hall conditions
(Elsevier, 2020) Sıddıki, Afif
We propose a semi-classical explanation to the conductance oscillations () observed at gate-controlled quantum dots under quantized Hall conditions. Our approach is based on the self-consistent screening theory of the quantum Hall effect and originates either from the interference of electrons or from charging effects. In the interference regime electrons acquire an Aharonov–Bohm phase while propagating coherently along the evanescent incompressible stripes at a particular filling factor, where the stripes enclose a magnetic flux. The charging regime finds its ground in Coulomb blocked, where the transport electron generates an additional energy scale to conductance oscillations. Combining these two regimes, we found that the period of conductance oscillations in magnetic field () may increase, decrease or remain constant at different filling factors, as observed in the experiments. In addition it is shown that, a gate potential can shift the incompressible stripe along the gated edge spatially, thereby changing the enclosed flux, and can induce with a period . We demonstrate that our formulation is able to generate the superimposed - interferences in stripe or checkerboard patterns in agreement with experiments. We can account for further salient and peculiar features of experimental observations for example the surprising absence of oscillations at certain filling factors.
Interconnected conductive gel binder for high capacity silicon anode for Li-ion batteries
(Elsevier, 2020) Taşkın, Ömer Suat; Yuca, Neslihan; Papavasiliou, Joan; Avgouropoulos, George
A new design for conjugation and crosslinking combined with a conjugated polymer and its application for high capacity Li-ion battery are demonstrated. Polyfluorene (PF), poly(phenylene) (PP), with lateral substituents, namely carboxylic acids, as a potential building block for conjugation was synthesized and characterized. The synthesis was achieved through Suzuki polycondensation reaction in the presence of Pd(PPh3)4 catalyst by using dibromo benzoic acid in conjunction with dioctylfluorene-diboronic acid bis(1,3-propanediol) ester. Thermal chemical cross-linking between carboxylic acid in the polymer backbone and free hydroxyl groups in poly(vinyl alcohol) (PVA) has been performed in the presence of Si. This approach enables a polymer binder with multi-functionality providing a high electronic conductivity and good cycling stability. Overall, we report on a Si-anode with capacity of 1932 mAh/g at C/3, demonstrating the improvement of the electrode using gel polymer binder.
The electrochemical behavior of silicon and graphite anode materials with different cathodes for lithium ion cells
(Elsevier, 2020) Yuca, Neslihan
New material compositions with new electrode designs have the serious potential to improve the energy per weight and volume at reduced cost for lithium ion batteries. Herein, the advantage and disadvantage of electrode materials for LIBs were investigated in both half and full cells. It was found high capacity materials like silicon anode and Li-rich cathode provide higher specific capacity in mAh/g. In full cell configuration Graphite/Li-rich cathode had 92mAh/g specific capacity after 100 cycles at C/2.
How entrepreneurs utilize accelerators: a demographic factor analysis in Turkey using regression
(The Science and Information Organization, 2020) Çubukcu, Ceren; Gülseçen, Sevinç
Abstract: This study examines entrepreneurs participating into eight accelerator programs located in Istanbul, Turkey. Business accelerators are a new kind of incubation program built in particular to help technology entrepreneurs and assist them reach to the next level. In total eight accelerator programs are researched in this study. A survey is developed for this study and applied to entrepreneurs attending these eight accelerator programs. In this survey, the effectiveness of these programs are measured according to the demographics of entrepreneurs. The aim of this research is to analyze how entrepreneurs use the services given by the accelerator program. In relation to entrepreneurs’ age, gender, work experience, educational status and family background, several hypotheses have been identified for assessing the value of supports given in these accelerator programs. The data of this research have been examined via SPSS using Mann-Whitney and Kruskal-Wallis methods. According to the results of these tests, a regression model called Generalized Linear Mixed Model (GLMM) has been developed. This study adds to the literature by examining accelerator supports and facilities so that accelerators can set apart their programs in line with the requests of the entrepreneurs.
Optimization of PERC fabrication based on loss analysis in an industrially relevant environment: First results from GUNAM photovoltaic line (GPVL)
(PERGAMON-ELSEVIER SCIENCE LTD, 2020) Es, Firat; Semiz, Emel; Orhan, Efe; Genc, Ezgi; Kokbudak, Gamze; Baytemir, Gulsen; Turan, Rasit
Passivated emitter and rear cell (PERC) concept with an already developed roadmap for 24% efficiency will be leading the photovoltaics industry in the upcoming years. In a few industrial pilot lines, efficiencies above 22% have already been attained. Pilot lines have important roles in bridging lab scale proven concepts with the products which are ready for mass production. Therefore, GUNAM Photovoltaic Line which is specialized on PERC concepts has been established to overcome the barriers that hinder the performance of c-Si solar cells in PERC concepts in a relevant environment. The aim of this article is to show how a loss analysis can be employed in a practical way in an industrially relevant environment. The analysis depends on the first results of the studies from 6 months ramp up period of GPVL A batch of standard PERC type solar cells with p-type base and atomic layer deposited Al2O3 rear passivation have been fabricated during the ramp up of the line. A detailed gain-loss analysis was performed to address the optical, electrical and recombination losses in order to increase the cell efficiency. (C) 2019 Elsevier Ltd. All rights reserved.
Small divisors in the solar system
(Maltepe Üniversitesi, 2019) Zhivkov, Angel
Consider the Sun, Mercury, Venus, Earth+Moon, Mars, Jupiter, Saturn, Uranus and Neptune as point masses, moving according Newton’s inverse–square law of gravitation. Poincar´e proved [1] that the general solution of the N–body problem can be expressed as a formal Fourier series. But Poincar´e also proved that such a series generally diverges. This happens because some small divisors appear when we apply the method of variation of arbitrary constants [2, 3]. A divisor which may vanish during the next 1010 years we define as a small divisor. For each pair of planets, there always exists a principal small divisor which could spoil the stability of their orbits after certain time. Finally we estimate the impact of the small divisors to conclude that they would not destroy the stability of the solar system at least for the next 1010 years.
Total reduction of chiral oscillator and Its dirac analysis
(Maltepe Üniversitesi, 2019) Çağatay Uçgun, Filiz
In this study we present the Hamiltonian formulation of dynamical systems produced by second order degenerate Chiral Lagrangian. Chiral Lagrangian is reduced into first order Lagrangian and then for this reduced Lagrangian Dirac- Bergmann algorithm is employed.
Towards achieving reliable and efficıent green cloud computing using micro-smart grids to power internet data center
(Maltepe Üniversitesi, 2019) İbrahm, Mohammed Mansur
Energy generation and consumption are the main aspects of social life due to the fact that, modern people’s necessity for energy is a fundamental ingredient for existence. Therefore, energy efficiency is regarded as the best economical approach to provide safer and affordable energy for both utilities and consumers, through the enhancement of energy security and reduction of energy emissions. One of the problems of cloud computing service providers is the high rise in cost for energy, efficiency together with carbon emission with regards to the running of their internet data centres IDCs. In order to mitigate these issues, smart micro-grids was found to be suitable in increasing the energy efficiency, sustainability together with reliability of electrical services for the IDCs. We also found in our review how smart micro-grids can bring down the disturbing carbon emission by the IDC all in an effort to achieve a green cloud computing services from the service providers. In specific term we aim at achieving green ICT in the field of cloud computing with respect to energy efficiency, cost effectiveness and carbon emission reduction from cloud data centre’s perspective.
Security challenges for cloud computing and opportunities for implementation; with a case study
(Maltepe Üniversitesi, 2019) Hysenaj, Fehmi
Cloud computing is a new technology, which is created based on different requirements of businesses and academic institutions. It provides a virtual access to different services and resources worldwide, network security that should be treated seriously. The risk of our data manipulation from a third party is always present. In this paper, we will propose and develop variety of security mechanisms in different scenarios in the real network. The case study is based on AAB College network. The network configuration is performed using Opnet (Riverbed 17.5) and GNS3. Results from different scenarios are carefully analysed and compared. Until the Firewalls play an important role in the network security, we will treat a scenario where firewall is implemented and important recommendations will be given after final results.
Web-based system for supporting the management of the process of teaching students programming
(Maltepe Üniversitesi, 2019) Uulu, Nursutan Bolotbek
Web-based system for supporting the management of the process of teaching students programming is in the development stage system that will increase student’s knowledge base and help to improve their skills in programming, results in competitive programming and better understanding their major. This system will provide many educational materials that include not only theory, but also practices. Software engineering and programming consists of many algorithms that must be understood by students, if they want to be a highly qualified professionals and keep discover new things. So, knowing algorithms and to be able to apply them in solutions of problems are one the most important aspects of programming study. This system helps to achieve these goals. Let us dive deeper to understand, in what way this system will work. After getting logged in, you will choose what algorithm to learn. Everything is by your wish in this system, so there are not any constraints. You will not need to complete easiest ones to open more complex. This way we orienting for all type of users. Algorithm descriptions or lessons consist of only important and usable information, but for those, who interested the most; this system will provide additional links with extra data. Using the “Webbased system for supporting the management of the process of teaching students programming” we are going to improve our teaching methods and increase the education quality of our students. This system is based on the feedback term. For example, after reading new lesson or new algorithm student should solve the tasks described in the bottom of every tutorial. In addition, student will be able to post some thread or answer for someone’s. This will give us prepared and confident students to participate in lots of competitive programming events and every time improve their knowledge in the immense domain of computer science.
Ensuring information security and non-stop functioning of an e-wallet
(Maltepe Üniversitesi, 2019) Mukambetov, Zhankarach
This paper explores the security of electronic payment systems. The study is relevant due to the constant increase in the number of crimes in the field of electronic payments, which is confirmed by official statistics. Users of electronic payment systems need to have an idea about the security of these systems, and therefore, about the security of their funds stored in them. In the course of this work, various electronic payment systems were examined methods ensuring the security of systems were analyzed, and the advantages and disadvantages of their protection methods were identified. Electronic payment system (EPS) is a technology that is a combination of methods, agreements and sub-technologies and allows for payments between counter parties over data transmission networks. EPS is part of e-commerce. Currently the main threat to e-commerce are crimes in the field of information technology, or cybercrime. EPS are divided into mobile services (EPS applications for mobile devices) and non-mobile (browser EPS, desktop EPS applications). By type of payment, EPS is divided into card payment systems and electronic money operators. Payment gateways are a symbiosis of card payment systems and digital cash operators. Such systems allow making almost all possible transactions within one system. Most of the EPS can be considered as gateways, but usually each EPS specifies the main type of electronic payments. During the work the following were accomplished: • Main business processes implemented at the facility were identified; • important assets were identified that relate specifically to these business processes; • vulnerabilities of the described assets were identified. In the course of the work, an analysis was made of the methods protecting mobile and non-mobile EPS services, such as SSL and SET, combined SSL and SET, CVV2- and CVK2-code, Address Verification Service, one-step and two-step authentication, electronic user certificates, E-num, electronic tokens, IP binding, biometric data, etc. Analysis of the protection of mobile services EPS showed that most of the protection methods identified weaknesses and vulnerabilities that make the theft of user’s money possible. However, legislative and technical measures to restrict payments prevent the theft of large sums of money through mobile services.
Analysis of function-call graphs of open-source software systems using complex network analysis
(PAMUKKALE UNIV, 2020) Tunali, Volkan; Tuysuz, Mehmet Ali Aksoy
Software systems are usually designed in a modular and hierarchical fashion, where functional responsibility of a system is decomposed into multiple functional software elements optimally such as subsystems, modules, packages, classes, methods, and functions. These elements are coupled with each other with some kind of dependency relationships to some degree, and their interactions naturally form a graph or network structure. In this study, we generated the static function-call graphs of several open-source software systems, where functions were the most basic type of interacting elements calling each other. Then, we analyzed the call graphs both visually and topologically using the techniques of complex network analysis. We found the call graphs to reveal scale-free and small-world network properties similar to the findings of the previous studies. In addition, we identified the most central and important functions in each call-graph using several centrality measures. We also performed community analysis and found that the call graphs exhibited a tendency to form communities. Finally, we showed that analysis of static function-call graphs of software systems through complex network analysis has the potential to reveal useful information about them.
The comparison of surface temperature and air temperature trends using landsat 8 satellite images
(Maltepe Üniversitesi, 2019) Salehiyan, Sona; Khalaji, Amin
Surface temperature is an important indicator in the study of energy balance models on the Earth’s surface and also a strong indicator of the interactions between the Earth and its atmosphere on a regional and global scale. Surface temperature can be used in many environmental, agricultural, and meteorological applications. Traditional methods in field measurements of surface temperature are not capable of providing optimum spatial and temporal variations of the surface. Due to the coverage of the earth and other temperature conditions, the temperature at different points in one place could be several degrees lower or higher; in other words, physical conditions and land cover lead to the change in surface temperature. This requires the use of scientific methods (separate algorithms) that allow for calculating the temperature of each point of the earth so that researches and projects can be carried out in the Earth sciences fields in relation to surface temperature. Since meteorological stations only measure temperature data for specific points, infrared and thermal remote sensing images due to their extensive coverage are among the suitable information sources for the preparation of surface temperature maps at regional and global scales. The surface temperature (Ts) was calculated using a single-channel algorithm developed by JiménezMuñoz et al. Moreover, in order to calculate the air temperature (Ta), a linear relationship was first established between Ts and Ta. The comparison was implemented on seven Landsat 8 satellite images acquired in Ahvaz, Iran, in the period 2016 to 2018. The purpose in this study was to investigate trends of changes in Ta and Ts. The results showed that in the warm months of the year (July and October), according to the four pictures of 2016 and 2017, Ts was more than Ta. However, in the cold months of the year (according to the three pictures of 2017 and 2018), Ta was more than Ts. The results of the seasonal variation of the two parameters Ts and Ta were highly similar, and their changes were sinusoidally variable. Finally, the approximate equality of Ts derived from images taken in the same month in a year, as the images captured in July and October of 2016 and 2017, indicated the relative accuracy of the obtained temperatures.

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