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Archived Theses
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Archived Theses
Investigation of amazon and google for fault tolerance strategies in cloud computing services
Cloud computing has recently become an attractive topic due to its ability to offer information technology solutions through virtual machines as on-demand services to share and consume resources over the Internet. As a result of rapid development in such services, the necessity of fault tolerance in the cloud is a major concern with reliability, availability and dependability is more critical to this new service type. This thesis investigates techniques and means of tolerating cloud services as well as cloud customers' systems/enterprises execution over the cloud safe from failures. As one of this findings shows, failures in cloud enabled services should be expected to occur hence they should be handled. The essential features of implementing fault tolerance strategies guarantee the business continuity, avoid financial lost, recovering systems from failures, and provide disaster recovery as well. The specific focus is to explore scenarios of avoiding/recovering from failures through redundancy, checkpoint and replication. Commercial IaaS providers such as Amazon's AWS and v Google's GCE are taken as examples as they tolerate their infrastructure from failures; in this way a robust architecture with fault tolerance property could be proposed for a system/enterprise. Hence, a general conceptual model with fault tolerance considerations has been proposed. With this basis, addressing potential failures in detail, implementing fault tolerance techniques, organizing teamwork to setup business policies are left for future work. Such limitations can be addressed through online questionnaires to collect information for case studies.
Döviz kuru ve enflasyon ilişkisi: Türkiye örneği
Bu çalışmada, Türkiye ekonomisinde döviz kuru değişimlerinin yurt içi enflasyon üzerindeki etkisi incelenmiştir. Analizler, 2013-2021 döneminin aylık verilerini kapsamaktadır. İncelemelerde, 2013-2021 yılları arasında en çok ithalat yapılan 10 ülke verileri baz alınarak çalışılmıştır. Bu 10 ülke için döviz türlerine göre ithalat oranlarının ağırlıkları hesaplanmış ve bunun sonucunda ağırlıklandırılmış döviz kuru olarak Dolar ve Euro baz alınmıştır. Enflasyonu ölçmek için genel Tüketici Fiyat Endeksi (TÜFE) ve TÜFE'nin alt grupları kullanılmıştır. Gagnon ve Ihrig (2004) çalışmasından yola çıkılarak regresyon analizleri yapılmıştır. Regresyon için kullanılan modelde hem tüketici fiyat endeksi hem de kur dalgalanmalarının yerel piyasaya etkisini gözlemlemek amaçlanmıştır. Analizlerde R programlama dili kullanılmıştır. Literatür araştırmaları sonucu görüldüğü üzere, döviz kuru geçişkenliği özellikle yüksek ve belirsiz enflasyon dönemlerinde önem kazanmaktadır. Analiz sonuçlarında da, döviz kuru geçişkenliğinin ele alınan dönemde genel tüketici fiyatlarına etki ettiği görülmüştür. Kısa dönem ve uzun dönem geçişkenliğin sonuçlarından da bahsedilmektedir.
Ekonomik haberlerin sürü davranışı üzerindeki etkileri
Sürü davranışı, Etkin Piyasa Hipotezinin (EPH) ileri sürdüğü argümanlara ters düştüğü için finans literatüründe geçmişte yoğun bir şekilde araştırılmıştır ve günümüzde de bu araştırmalar devam etmektedir. Sürü davranışı, yatırımcıların kendi bilgileri yerine bir kişi/kurum/grup yatırımcı kararlarına daha fazla güvenip onların yatırım kararlarını takip etmesini veya piyasanın artış ve azalışlarına göre karar vermelerini ifade etmektedir. Aynı zamanda, yatırımcıların davranışlarının belli dönemlerde benzerlik göstermesi (yüksek korelasyonun olması) sürü davranışı gibi kendini gösterse de bu gerçekten sürü davranışı olarak değerlendirilmemelidir. Dolayısıyla, gerçek sürü davranışının var olması EPH'den uzaklaşıldığını ve yatırımcıların rasyonel davranmaktan uzaklaştığını ifade edebilir. Eğer piyasa da takip edilen ve sürü davranışına yol açan aktörler daha fazla bilgiye sahip ise sürü davranışının rasyonel olduğu söylenebilir. Sürü davranışının sermaye piyasasında baskın olması piyasa etkinliğine engel olabilir ve piyasa fiyatlarının karar vermede kullanılacak temel bir istatistik olarak kullanılmasının yetersizliğine yol açabilir. Bu çalışma sürü davranışını incelemek için piyasa hareketlerini (herding towards the market) kullanmayı amaçlamaktadır. Bu amaç için yoğun olarak kullanılan üç yöntem vardır. Bu yöntemlerden ilk ikisi yatay kesit standart sapma (CSSD-cross sectional standard deviation) ve yatay kesit mutlak sapma (CSAD-cross sectional absolute deviation) yöntemleri olarak sıralanabilir. Bu iki yöntemde sapmalar piyasa getirisinden uzaklaşma olarak hesaplanmaktadır. Üçüncü yöntem de CSSD hesaplaması getiri yerine sistematik risk kullanılarak yapılmakta ve sürü davranışı değişkeni bir gizli değişken olarak tahmin edilmektedir.
Experimental analysis of effects of different network parameters on TCP / IP networks
Today, the Internet is actively used in almost every aspect of life and stands out as an indispensable component of the digital age. With Internet technologies, instant access to information is possible, and global communication processes are significantly simplified. Computer networks are structured by using different topologies depending on their purpose and scale. In this thesis, the use of the preferred Mesh topology in complex and large-scale network structures has been deemed appropriate. Using mesh topology has been a logical choice due to its high connection level and reliability. However, in these mesh topologies it is important that the network performance must be in good condition to provide network security and high efficiency. Therefore, having better system performance is one of the fundamental rules to maintain proficient network management. In the thesis GNS3 simulation environment is used, which is frequently used by network engineers. Thanks to this simulation environment we can investigate various network parameters' performance on TCP/IP based networks, and we are able to compare performances of each parameter with using different routing protocols. In network management, the most common routing protocols are used such as RIP (Routing Information Protocol), OSPF (Open Shortest Path First), EIGRP (Enhanced Interior Gateway Routing Protocol) and BGP (Border Gateway Protocol). These protocols are analyzed by comparing each one's throughput, packet data volume and their packet loss performances. Statistical data which is acquired by graphs is designed in MATLAB environment. In the conclusion of this thesis, it can be seen that routing algorithms perform differently with respect to consecutive packet data amount. Thus, we can conclude to a study that which routing protocol performs better in which environment and this enables us to make clear judgements for them as well. The main purpose of this study is to monitor different routing protocols in simulation environments and understand differences of their performances. This study may be clarifying the way and can work as a guidebook for those who would like to create real network design.
Characterization of under-hood airflow in construction equipment using experimental techniques
This thesis investigates the effects of hot air accumulation beneath the hood in excavator-type construction machinery during engine operation and proposes a practical design solution to improve airflow. Accumulated thermal energy under the hood negatively impacts the operational efficiency of the engine and surrounding components, potentially leading to reduced performance and shorter component lifespan over time. To address this issue, ventilation openings were strategically added to the hood structure, allowing heated air to be directed outward more effectively.The study not only evaluates the thermal improvement achieved through these modifications but also considers the impact on noise emission.Noise measurements were conducted according to relevant standards, and the results were analyzed to determine whether the values remained within legally acceptable thresholds.The findings demonstrate that the addition of ventilation vents effectively reduced the under-hood temperature, contributing to better thermal management. At the same time, the noise levels recorded after the modification were observed to remain within permissible limits. These results suggest that it is possible to enhance thermal flow characteristics without compromising compliance with environmental noise regulations. Keywords: Under-Hood Flow, Thermal Management, Noise Measurement, Thermal Analysis, Construction Machinery,
Engelleyi̇ci̇ LEDli̇ Güvenli̇k Si̇stemi̇
In this thesis, we designed and developed a prototype of a non-lethal system using light emitting diodes (LEDs) as the light source. The system, which is called a Blocker Security System with LEDs (BSSL), sends a light beam whose color and light intensity are changed in time (spectrally, temporally) according with certain pre-programmed patterns. It was observed in the literature that these changes in light patterns cause headache, nausea, dizziness and visual defects on people who are exposed to them.These effects are observed when the change in light pattern from the LEDs is fast enough so that human's brain could not process properly the information transmitted, and therefore, it cannot decode the changes in the speed they come. In the thesis, experiments are made, and measurements are performed by using the designed and developed Blocker Security System's prototype, and assessments of the experimental data have been performed to find the most effective patterns of the light. We searched the patterns that cause the desired effects on the people and tried to find the best pattern. The subsystems of the BSSL, mainly the LEDs, the optical system that guides the light beams from the LEDs, the cooling system, the battery system, the body, and the LED drivers that generate the required light patterns were investigated. We focused mostly on the drivers that not only provide the necessary forward currents to the LEDs, but also generate the lighting patterns required from them. In doing this, we developed the embedded software required to form the lighting patterns through the driver.
Detecting subthreshold signals in field effect transistors by using stochastic resonance phenomenon
Until recently it is accepted that noise is always a degrading factor for the performance of electronic communication and signal processing systems. For this reason many of the studies on signal processing and communication systems focused on eliminating the negative effects of noise signal on information bearing signal. However, recently it is discovered that noise can play a positive role for the detection of weak signals for electronic systems employing nonlinear electronic devices. It is seen that the detection of the weak signals in nonlinear systems is possible when an optimum amount of noise is added to the information bearing signal before passing the signal through the nonlinear system. And this concept is named as stochastic resonance, i.e., SR. In this thesis it is shown that it is possible to develop a training based model for the SR systems that decides optimum noise signal to be added to the weak information signal directly for the best system performance. In the second part of the thesis study a practical application of the SR concept on a nonlinear electronic device, field effect transistor (FET), is demonstrated. For this purpose a user interface program using C# is developed and some part of the signal processing is done using the field programmable gate arrays (FPGA).
An exploratory study to assess analytical and logical thinking skills of the software practitioners using a gamification perspective
The link between analytical and logical thinking skills and success of software practitioners attracted an increasing attention in the last decade. Several studies report that the ability to think logically is a requirement for improving software development skills, which exhibits a strong reasoning. Additionally, analytical thinking is a vital part of software development for example while dividing a task into elemental parts with respect to basic rules and principles. Using the basic essence of gamification, this study proposes a mobile testing platform for assessing analytical and logical thinking skills of software practitioners as well as computer engineering students. The assessment questions were taken from the literature and transformed into a gamified tool based on the software requirements. A focus group study was conducted to capture the requirements. Using the Delphi method, these requirements were discussed by a group of experts to reach a multidisciplinary understanding where a level of moderate agreement has been achieved. In light of these, an assessment tool was developed, which was tested on both software practitioners from the industry and senior computer engineering students. Preliminary results suggest that individuals who exhibit skills in analytical and logical thinking are also more inclined to be successful in software development.
Prevailing factors of successful design in library spaces
The purpose of this thesis is to discuss and outline the functional suggestions on the important factors that need to be considered while designing interior libraries. These important factors can affect considerably to interior environment and designing of libraries. These important factors include lighting, color and materials. Each factors could change designing of interior library easily. In this thesis, all these factors are investigated in separate sections, and there are standards of interior libraries which are explained in each section. Moreover, the history of university library in Turkey is explained and the role of the libraries in society and history of library are investigated. Furthermore, there are different kind of libraries which are explained in separate parts. Consequently, a case studies have been studied under the headlines of this thesis, which are located in Çankaya University in Ankara. Keywords: Library, interior, design, environment.
Authentication mechanism of Electronic Health Record (EHR) in the cloud
Electronic health record (EHR) is a system that contains patients' complete medical related records from birth to death. These records consist of diagnoses, medications, laboratory tests, and results. The records are created by the patients and accessed by health providers such as doctors, nurses, pharmacies, etc. The advantages of using cloud computing has helped the health organizations to dispense the local servers and shift all their data to the cloud, which helped them save space, energy, and cost, as well as provide the benefit of accessing the data by patients and healthcare providers from anywhere at any time. Exchanging medical records in the cloud, however, has threatened the security and privacy of e-health systems where the authentication, access control, and integrity of the medical records are the main challenges in e-health clouds. In this thesis, we study the authentication mechanism of an EHR system and investigate an improved version using attribute based encryption ABE. Patients have full control over their medical records which are stored in a semi trusted servers. The system also works on access policies in case of emergency.