Computer Engineering / Bilgisayar Mühendisliği

Permanent URI for this collectionhttps://hdl.handle.net/11147/10

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A New Embedded Controller for Data Acquisition and Control Applications
(1999) Ayav, Tolga; Aytaç, İsmail Sıtkı
Developing high performance data acquisition and control systems takes better tools than the industry normally provides. As the most common controllers, PLCs can be still weak in many applications, and especially they are not good choice for data acquisition due to their limited capability of computation, speed, memory and programming constraints. The fact that today s PCs have many advantages compared with their relatively low price made them very popular in industrial environments. In this project a PC based controller was designed for data acquisition and control purposes. Although such similar systems exist, this product with some advantages could be a good alternative to the existing ones.
Determination of Dose Profile Data With Film Dosimetry
(Institute of Electrical and Electronics Engineers Inc., 2001-10) Gökçe, Tuncay C.; Aytaç, Sıtkı; Gökçe, Tumay
Almost all external radiotherapy planning systems use dose profile data. There are various methods to measure these profiles. Direct measurements with semiconductor detectors are widely used. But this method takes lots of time especially at linear accelerators. We developed a simple method for this purpose. Dose profiles are measured with using radiographic films and verification films. Suitable modifications are done with derived sensitometric curve. Results are compared with original profiles. For the Co60, this method is found as an alternative to other methods with acceptable accuracy (%±2)
Neuro-Fuzzy Controller in Real-Time Feedback Schedulers
(Izmir Institute of Technology, 2002-06) Ayav, Tolga; Yılmaz, Sinan
Traditional scheduling algorithms worked on closed and highly predictable environments. However present day systems need to work in more open and unpredictable environments; such as mobile robots, on-line trading, e-commerce, multimedia that cannot be driven well with traditional open-loop algorithms. A new scheduling paradigm, feedback control scheduling, therefore has been presented recently to fulfil the requirements of such systems. This algorithm defines error terms for schedules, monitors the error, and continuously adjusts the schedule to maintain stable performance. When PID (Proportional-Integral-Derivative) controller is used to control the CPU utilization, one of the problems faced is that when utilization setpoint is closer to 100%, in severely overloaded conditions, systems can have a longer settling time than the analysis based on the linear model since utilization feedback saturates at 100%. To overcome this problem, a neuro-fuzzy controller is designed instead of PID. Simulations showed that settling time with the neuro-fuzzy controller is approximately four times shorter than the one with the PID controller.
Izmir Yüksek Teknoloji Enstitüsü'nün Bilgisayar Ağı için Bir Servis Kalitesi Uygulaması
(Türkiye Bilişim Derneği, 2002-09) Çağrıcı, Gökhan; Ayav, Tolga
Günümüzün gelişen bilgisayar ağları ve bu ağlarda oluşan trafik tiplerindeki çeşitlilik, Servis Kalitesi için büyük gereksinim doğuracak nitelikte sıkışıklıklar meydana getirmektedir. Nitekim, Servis Kalitesi’nin ne olduğu ve sıkışıklık yaşayan bilgisayar ağlarına neler sunduğu konuları hala tam bir açıklık kazanmamıştır. Ağ sistemleri üreticileri ve üniversite gibi bilimsel kuruluşlar, Servis Kalitesi mekanizmaları konusunda çeşitli araştırmalar yapmaktadır. Bu bildiride, Servis Kalitesi’nin anlamı genel hatlarıyla sunulacak ve İzmir Yüksek Teknoloji Enstitüsü’nün yerel bilgisayar ağı için geliştirilen bir Servis Kalitesi uygulaması açıklanacaktır.
Bir Ağ Yönetim Sistemi: Guardilan
(Türkiye Bilişim Derneği, 2003-09) Talay, Salih; Ayav, Tolga; Özardıç, Onur; Altıntaş, Erhan
Bilgisayar ağlarındaki hızlı gelişime rağmen ağ yönetim sistemleri bu gelişimin gerisinde kalmaktadır. Ağların hızla gelişmesi, ağda oluşan trafik tiplerindeki çeşitlilik, ve kaynaklardaki kısıtlılık Servis Kalitesi ve Network Yönetimi konularını daha önemli hale getirmiştir. Bu bildiride, İzmir Yüksek Teknoloji Enstitüsü’nün yerel bilgisayar ağı için geliştirilen GuardiLAN projesi sunulacaktır. GuardiLAN ilk aşamada 3 kısımdan oluşan, modüler ve web tabanlı bir ağ yönetim sistemidir. Birinci kısım ağ topolojisinin belirlenmesinden ve takibinden sorumlu olup, ikinci kısım kullanıcıların IP adreslerinin ve MAC adreslerinin düzenli olarak kontrolüyle ağ güvenliğinin yükseltilmesini sağlamaktadır. Son kısım ise geniş alan ağı bağlantısının etkin kullanımı için geliştirilmiş bir akıllı bant genişliği yönetim aracıdır.
Stability Properties of Adaptive Real-Time Feedback Scheduling: a Statistical Approach
(Nessuna, 2004-03) Ayav, Tolga; Ferrari-Trecate, Giancarlo; Yılmaz, Sinan
This paper focuses on the statistical analysis of an adaptive real-time feedback scheduling technique based on imprecise computation. We consider two-version tasks made of a mandatory and an optional part to be scheduled according to a feedback control rate-monotonic algorithm. A Proportional-Integral-Derivative (PID) control action provides the feedback strategy for deciding about the execution or rejection of the optional sub-tasks. By modelling the task execution times as random variables, we compute the probability density of the CPU utilization and derive conditions on PID parameters guaranteeing the stability of the overall system around a desired level of CPU utilization. This allows us to highlight the tasks statistics and the scheduling parameters that affect critically stability. The analysis is developed by first exploiting a number of simplifying assumptions that are progressively removed. The main results are also demonstrated through monte-carlo simulations of the scheduling algorithm.
Citation - WoS: 4
Citation - Scopus: 4
Merging Clustering Algorithms in Mobile Ad Hoc Networks
(Springer Verlag, 2005) Dağdeviren, Orhan; Erciyeş, Kayhan; Çokuslu, Deniz
Clustering is a widely used approach to ease implementation of various problems such as routing and resource management in mobile ad hoc networks (MANET)s. We first look at minimum spanning tree(MST) based algorithms and then propose a new algorithm for clustering in MANETs. The algorithm we propose merges clusters to form higher level clusters by increasing their levels. We show the operation of the algorithm and analyze its time and message complexities.
Implementation of a Cluster Based Routing Protocol for Mobile Networks
(Springer Verlag, 2005) Marshall, Geoffrey; Erciyeş, Kayhan
We show the implementation and the simulation results of a hierarchical, cluster based routing protocol for mobile ad hoc networks using Parallel Virtual Machine (PVM). The network represented by a graph is partitioned into clusters by a graph partitioning algorithm and the shortest routes are first calculated locally in each cluster in the first srep. The simplified network which consists only of the nodes that have connections to other clusters called the neighbor nodes is then formed and the shortest routes are calculated for this simple network as the second step. A complete route between the two nodes of different clusters is formed by the union of intra-cluster and inter-cluster routes. We show the implementation results using PVM where a workstation represents a cluster and each node is a PVM process. The results obtained support the theoretical considerations where the efficiency increases by the number of clusters in use.
Optimal Control for Real-Time Feedback Rate-Monotonic Schedulers
(Springer Verlag, 2005) Ayav, Tolga; Ferrari-Trecate, Giancarlo
This paper presents an optimal control scheme for a real-time feedback control rate-monotonic scheduling (FC-RMS) system. We consider two-version tasks composed of a mandatory and an optional part to be scheduled according to the FC-RMS. In FC-RMS, the controller provides a feedback strategy for deciding about the execution or rejection of the optional sub-tasks. By modeling the task execution times as random variables, we first find the statistical model of FC-RMS and then we design a pure optimal controller and an optimal controller with feedforward integral compensation. The comparison of these two schemes with common Proportional-Integral-Derivative (PID) controller highlights the benefit of the optimal scheme with integral compensation. The results are demonstrated through the real implementation of FC-RMS on RT-Linux.
Citation - Scopus: 2
Crympix: Cryptographic Multiprecision Library
(Springer Verlag, 2005) Koltuksuz, Ahmet; Hışıl, Hüseyin
This paper delineates the results gained throughout the development of a cryptographic multiprecision1 integer library, CRYMPIX. To obtain the know-how for cryptographic computation and thus being able to create the high level cryptographic protocols in an in-housefashion are the main reasons of this development. CRYMPIX is mainly designed to supply code readability and portability plus an increased performance over other similar libraries. The whole work is achieved by detailed investigation of current algorithms and multi-precision libraries. The selected algorithms are discussed by means of efficiency and various implementation techniques. The comparative performance measurements of CRYMPIX against other multiprecision libraries show that the overall performance of CRYMPIX is not behind its predecessors if not superior.
Citation - WoS: 6
Citation - Scopus: 8
A Cluster-Based Dynamic Load Balancing Middleware Protocol for Grids
(Springer Verlag, 2005) Erciyeş, Kayhan; Payli, Reşat Ümit
We describe a hierarchical dynamic load balancing protocol for Grids. The Grid consists of clusters and each cluster is represented by a coordinator. Each coordinator first attempts to balance the load in its cluster and if this fails, communicates with the other coordinators to perform transfer or reception of load. This process is repetaed periodically. We show the implementation and analyze the performance and scalability of the proposed protocol.
Citation - WoS: 10
Citation - Scopus: 26
Mobile Join Operators for Restricted Sources
(Hindawi Publishing Corporation, 2005) Özakar, Belgin; Morvan, Franck; Hameurlain, Abdelkader
We consider the problem of query execution when there is limited access to the relations, i.e. when binding patterns require values to be specified in order to get data from the relation. This problem is common in virtual data integration systems where there are heterogeneous sources with various restricted access patterns and query capabilities. Another problem is the lack of the statistical information about the sources and occurrence of unpredictable events. We introduce two mobile join operators, MDJoin and SMDJoin which are designed for restricted sources and implemented using ‘mobile agents’ in order to benefit from their autonomous and reactive characteristics. Mobile operators of restricted sources are capable to deal with restricted sources and react to the variations between the compile-time estimations and run-time computations of data during query execution. The difference between the two new query operators lies in their level of adaptation ability to the execution environment. Performance results show that mobile agent-based approach at operator level can lead to a significant reduction in response time with restricted sources.
Citation - WoS: 6
Citation - Scopus: 11
Dynamically Adaptive Partition-Based Data Distribution Management
(Institute of Electrical and Electronics Engineers Inc., 2005) Kumova, Bora İsmail
Performance and scalability of distributed simulations depends primarily on the effectiveness of the employed data distribution management (DDM) algorithm, which aims at reducing the overall computational and messaging effort on the shared data to a necessary minimum. Existing DDM approaches, which are variations and combinations of two basic techniques, namely region-based and grid-based techniques, perform purely in the presence of load differences. We introduce the partition-based technique that allows for variable-size partitioning shared data. Based on this technique, a novel DDM algorithm is introduced that is dynamically adaptive to cluster formations in the shared data as well as in the physical location of the simulation objects. Since the re-distribution is sensitive to inter-relationships between shared data and simulation objects, a balanced constellation has the additional advantage to be of minimal messaging effort. Furthermore, dynamic system scalability is facilitated, as bottlenecks are avoided.
Citation - WoS: 1
Citation - Scopus: 1
Multilevel Static Real-Time Scheduling Algorithms Using Graph Partitioning
(Springer Verlag, 2005) Erciyeş, Kayhan; Soysert, Zehra
We propose static task allocation algorithms for the periodic tasks of a distributed real-time system. The cyclic task consists of task threads which may communicate and share resources. A graph partitioning process and a thread sequencing algorithm are applied to these threads to yield local schedules. The exact analysis is then obtained and further refinements are performed if the worst case response time of a task is greater than its deadline.
Citation - WoS: 4
Citation - Scopus: 5
Query optimization: Mobile agents versus accuracy of the cost estimation
(CRL Publishing, 2005) Özakar, Belgin; Morvan, F.; Hameurlaint, A.
Since an increasing number of diverse sources of data and information become available through World Wide Web, the field of distributed heterogeneous query processing attracts attention of the researchers. One of the main concerns is to reduce the amount of communication and the volume of data transferred in terms of query optimization where it is a real challenge to have the statistics of the resources predictable and up-to-date. Autonomy, proactivity and mobility features of mobile agents seem promising under some conditions. In this paper we are interested in the study of the efficiency of the mobile agents in relation with the approach of the cost model used during the optimization process. We present an execution model based on mobile agents. Performance evaluation shows the efficiency intervals of the execution model according to the estimation errors and the current state of the system. The major contribution of this paper is to point out the effective use of an execution model based on mobile agents in relation with the approach of the cost model and with the query type. © 2005 CRL Publishing Ltd.
Gerçek-zamanlı Uyarlamacı Görev Planlaması Tekniğinin Rt-linux’ta Uygulanması
(Türkiye Bilişim Vakfı, 2005) Ayav, Tolga; Yılmaz, Sinan
Bu çalışma kesinleşmemiş hesaplamalar yöntemine dayalı olan gerçek-zamanlı geribesleme denetimli bir görev planlama tekniğinin ("Real Time Feedback Control Scheduling") Gerçek zamanlı Linux (Rt-Linux) üzerindeki uygulamasını sunmaktadır. Zorunlu ve seçmeli alt-görevlerden oluşan ve geribesleme denetimli "rate-monotonic" tekniğine göre planlanan iki-sürümlü görev modeli seçilmiştir. Oransal-Entegral-Türev (PID) denetim, seçmeli alt görevlerin çalıştırılması veya reddedilmesinde gerekli geribesleme stratejisini sağlamak için kullanılmıştır. Oluşturulan bu model RT-Linux işletim sistemine uygulanmış ve sistem başarımı yapay bir iş yükü altında sınanarak önerilen görev planlama modelinini sistemi öngörülen A/B kullanım oranı düzeyinde kararlı halde çalışabildiği gösterilmiştir.
Citation - WoS: 3
Citation - Scopus: 5
Serial and Parallel Multilevel Graph Partitioning Using Fixed Centers
(Springer Verlag, 2005) Erciyeş, Kayhan; Alp, Ali; Marshall, Geoffrey
We present new serial and parallel algorithms for multilevel graph partitioning. Our algorithm has coarsening, partitioning and uncoarsening phases like other multilevel partitioning methods. However, we choose fixed nodes which are at least a specified distance away from each other and coarsen them with their neighbor nodes in the coarsening phase using various heuristics. Using this algorithm, it is possible to obtain theoretically and experimentally much more balanced partitions with substantially decreased total edge costs between the partitions than other algorithms. We also developed a parallel method for the fixed centered partitioning algorithm. It is shown that parallel fixed centered partitioning obtains significant speedups compared to the serial case.
Citation - WoS: 1
On Defining Security Metrics for Information Systems
(Brill Academic Publishers, 2005) Koltuksuz, Ahmet
[No abstract available]
Citation - WoS: 1
Feedback Control Static Scheduling for Real-Time Distributed Embedded Systems
(Institute of Electrical and Electronics Engineers Inc., 2005-11-21) Ayav, Tolga; Sorel, Yves
This paper presents an implementation of feedback control strategy on distributed static scheduling. The static schedule is created taking into account the average execution times of the tasks. Feedback control algorithm handles the unestimated dynamic behaviors in the system and keeps the performance at a desired level. The approach of feedback control supporting static scheduling yields more flexible scheduling, low scheduling overhead and better resource utilization while preserving the realtime constraints.
Citation - WoS: 1
Citation - Scopus: 7
Intelligence analysis modeling
(Institute of Electrical and Electronics Engineers Inc., 2006) Koltuksuz, Ahmet; Tekir, Selma
Intelligence is the process of supporting the policymakers in making their decisions by providing them with the specific information they need. Intelligence analysis is the effort of extracting the nature of intelligence issue with the policy goal in mind. It is performed by intelligence analysts who form judgments that add value to the collected material. With the increased open source collection capabilities, there has emerged a need for a model of intelligence analysis that covers the basic elements of valuable information: relevancy, accuracy, and timeliness. There exist models such as vector space model of information retrieval which only addresses the relevancy aspect of information and cannot cope with nonlinear document spaces. In this paper, we discuss the requirements of an integrated model of intelligence analysis along with its peculiar characteristics.

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