Browsing by Subject "Performance evaluation"

Now showing 1 - 20 of 22

Open Access
Adaptive source routing in multistage interconnection networks
(IEEE, 1996-04) Aydoğan, Yücel; Stunkel, C. B.; Aykanat, Cevdet; Abali, B.
We describe the adaptive source routing (ASR) method which is a first attempt to combine adaptive routing and source routing methods. In ASR, the adaptivity of each packet is determined at the source processor. Every packet can be routed in a fully adaptive or partially adaptive or non-adaptive manner, all within the same network at the same time. We evaluate and compare performance of the proposed adaptive source routing networks and oblivious routing networks by simulations. We also describe a route generation algorithm that determines maximally adaptive routes in multistage networks.
Open Access
Analysis of concurrency control protocols for real-time database systems
(Elsevier, 1998) Ulusoy, Özgür
This paper provides an approximate analytic solution method for evaluating the performance of concurrency control protocols developed for real-time database systems (RTDBSs). Transactions processed in a RTDBS are associated with timing constraints typically in the form of deadlines. The primary consideration in developing a RTDBS concurrency control protocol is the fact that satisfaction of the timing constraints of transactions is as important as maintaining the consistency of the underlying database. The proposed solution method provides the evaluation of the performance of concurrency control protocols in terms of the satisfaction rate of timing constraints. As a case study, a RTDBS concurrency control protocol, called High Priority, is analyzed using the proposed method. The accuracy of the performance results obtained is ascertained via simulation. The solution method is also used to investigate the real-time performance benefits of the High Priority over the ordinary Two-Phase Locking.
Open Access
Automatic ranking of information retrieval systems using data fusion
(Elsevier Ltd, 2006-05) Nuray, R.; Can, F.
Measuring effectiveness of information retrieval (IR) systems is essential for research and development and for monitoring search quality in dynamic environments. In this study, we employ new methods for automatic ranking of retrieval systems. In these methods, we merge the retrieval results of multiple systems using various data fusion algorithms, use the top-ranked documents in the merged result as the "(pseudo) relevant documents," and employ these documents to evaluate and rank the systems. Experiments using Text REtrieval Conference (TREC) data provide statistically significant strong correlations with human-based assessments of the same systems. We hypothesize that the selection of systems that would return documents different from the majority could eliminate the ordinary systems from data fusion and provide better discrimination among the documents and systems. This could improve the effectiveness of automatic ranking. Based on this intuition, we introduce a new method for the selection of systems to be used for data fusion. For this purpose, we use the bias concept that measures the deviation of a system from the norm or majority and employ the systems with higher bias in the data fusion process. This approach provides even higher correlations with the human-based results. We demonstrate that our approach outperforms the previously proposed automatic ranking methods. © 2005 Elsevier Ltd. All rights reserved.
Open Access
Cluster based collaborative filtering with inverted indexing
(2005) Subakan, Özlem Nurcan
Collectively, a population contains vast amounts of knowledge and modern communication technologies that increase the ease of communication. However, it is not feasible for a single person to aggregate the knowledge of thousands or millions of data and extract useful information from it. Collaborative information systems are attempts to harness the knowledge of a population and to present it in a simple, fast and fair manner. Collaborative filtering has been successfully used in domains where the information content is not easily parse-able and traditional information filtering techniques are difficult to apply. Collaborative filtering works over a database of ratings for the items which are rated by users. The computational complexity of these methods grows linearly with the number of customers which can reach to several millions in typical commercial applications. To address the scalability concern, we have developed an efficient collaborative filtering technique by applying user clustering and using a specific inverted index structure (so called cluster-skipping inverted index structure) that is tailored for clustered environments. We show that the predictive accuracy of the system is comparable with the collaborative filtering algorithms without clustering, whereas the efficiency is far more improved.
Open Access
Comparative analysis of power consumption in asynchronous wavelength modular optical switching fabrics
(Elsevier, 2011-04-02) Akar, N.; Eramo, V.; Raffaelli, C.
Next-generation optical routers will be designed to support the flexibility required by Future Internet services and, at the same time, to overcome the power consumption bottleneck which appears to limit throughput scalability in today routers. A model to evaluate average power consumption in asynchronous optical switching fabrics is here presented to compare these architectures with other synchronous and asynchronous solutions. The combination of wavelength modular switching fabrics with low spatial complexity and asynchronous operation is demonstrated to be the most power-efficient solution among those considered which employ wavelength converters, through presentation and discussion of a thorough set of numerical results.
Open Access
A comparison of epidemic algorithms in wireless sensor networks
(Elsevier BV, 2006-08-21) Akdere, M.; Bilgin, C. C.; Gerdaneri, O.; Korpeoglu, I.; Ulusoy, O.; Çetintemel, U.
We consider the problem of reliable data dissemination in the context of wireless sensor networks. For some application scenarios, reliable data dissemination to all nodes is necessary for propagating code updates, queries, and other sensitive information in wireless sensor networks. Epidemic algorithms are a natural approach for reliable distribution of information in such ad hoc, decentralized, and dynamic environments. In this paper we show the applicability of epidemic algorithms in the context of wireless sensor environments, and provide a comparative performance analysis of the three variants of epidemic algorithms in terms of message delivery rate, average message latency, and messaging overhead on the network. © 2006 Elsevier B.V. All rights reserved.
Open Access
Counteracting free riding in Peer-to-Peer networks
(Elsevier BV, 2008-03) Karakaya, M.; Körpeoǧlu, I.; Ulusoy, O.
The existence of a high degree of free riding is a serious threat to Peer-to-Peer (P2P) networks. In this paper, we propose a distributed framework to reduce the adverse effects of free riding on P2P networks. Our solution primarily focuses on locating free riders and taking actions against them. We propose a framework in which each peer monitors its neighbors, decides if they are free riders, and takes appropriate actions. Unlike other proposals against free riding, our framework does not require any permanent identification of peers or security infrastructures for maintaining a global reputation system. Our simulation results show that the framework can reduce the effects of free riding and can therefore increase the performance of a P2P network. © 2007 Elsevier B.V. All rights reserved.
Open Access
An evaluation of methodological issues in workflow management
(1998) Sotnikova, Anastasia
Workflow management is a diverse and rich technology being applied over an increasing number of industries. Despite this fact, workflow management systems (WFMSs) still have a long way to go before they can be regarded as mature technology. In this thesis, we try to analyze methodological aspects of WFMSs and contribute to the workflow management theory in terms of new functionality and structures of workflow schemas. A confirmation of our ideas is provided by simulation results of a workflow application which we have designed. Bringing the simulation stage in between design and implementation stages would let a schema designer assess a workflow system in terms of optimal system throughput, required facility capacities, and an efficient transactional representation of activities. Also, by allowing a schema designer to choose an effective structure of a workflow system, simulation results help to avoid possible future losses at early stages of the workflow schema design.
Open Access
The general behavior of pull production systems: the allocation problems
(Elsevier, 1999) Kırkavak, N.; Dinçer, C.
The design of tandem production systems has been well studied in the literature with the primary focus being on how to improve their e ciency. Considering the large costs associated, a slight improvement in e ciency can lead to very signi®cant savings over its life. Division of work and allocation of bu er capacities between workstations are two critical design problems that have attracted the attention of many researchers. In this study, ®rst an understanding into how the system works is to be provided. Except for the integration of two allocation problems, the basic model utilized here is essentially the same as the previous studies. Theoretical results that characterize the dynamics of these systems may also provide some heuristic support in the analysis of large-scale pull production systems. Ó 1999 Elsevier Science B.V. All rights reserved.
Open Access
Generic text summarization for Turkish
(Oxford University Press, 2010) Kutlu, M.; Cığır, C.; Cicekli, I.
In this paper, we propose a generic text summarization method that generates summaries of Turkish texts by ranking sentences according to their scores. Sentence scores are calculated using their surface-level features, and summaries are created by extracting the highest ranked sentences from the original documents. To extract sentences which form a summary with an extensive coverage of the main content of the text and less redundancy, we use features such as term frequency, key phrase (KP), centrality, title similarity and sentence position. The sentence rank is computed using a score function that uses its feature values and the weights of the features. The best feature weights are learned using machine-learning techniques with the help of human-constructed summaries. Performance evaluation is conducted by comparing summarization outputs with manual summaries of two newly created Turkish data sets. This paper presents one of the first Turkish summarization systems, and its results are promising. We introduce the usage of KP as a surface-level feature in text summarization, and we show the effectiveness of the centrality feature in text summarization. The effectiveness of the features in Turkish text summarization is also analyzed in detail. © The Author 2008. Published by Oxford University Press on behalf of The British Computer Society. All rights reserved.
Open Access
Land cover classification with multi-sensor fusion of partly missing data
(American Society for Photogrammetry and Remote Sensing, 2009-05) Aksoy, S.; Koperski, K.; Tusk, C.; Marchisio, G.
We describe a system that uses decision tree-based tools for seamless acquisition of knowledge for classification of remotely sensed imagery. We concentrate on three important problems in this process: information fusion, model understandability, and handling of missing data. Importance of multi-sensor information fusion and the use of decision tree classifiers for such problems have been well-studied in the literature. However, these studies have been limited to the cases where all data sources have a full coverage for the scene under consideration. Our contribution in this paper is to show how decision tree classifiers can be learned with alternative (surrogate) decision nodes and result in models that are capable of dealing with missing data during both training and classification to handle cases where one or more measurements do not exist for some locations. We present detailed performance evaluation regarding the effectiveness of these classifiers for information fusion and feature selection, and study three different methods for handling missing data in comparative experiments. The results show that surrogate decisions incorporated into decision tree classifiers provide powerful models for fusing information from different data layers while being robust to missing data. © 2009 American Society for Photogrammetry and Remote Sensing.
Open Access
Light-harvesting positively-charged nanocrystals for strong energy transfer to dye molecules
(IEEE, 2008-11) Mutlugün, Evren; Demir, Hilmi Volkan
In this work, water-soluble positively-charged CdSe/ZnS core/shell nanocrystals were presented, serving as light harvester (donor) for strong energy transfer to rhodamine B dye molecules (acceptor) in solution. In accordance with photoluminescence (PL) characterization, the emission of rhodamine B was enhanced at the laser pump wavelength, which may open up possibilities for lasers based on dye molecules pumped at different wavelengths.
Open Access
New event detection using chronological term ranking
(2009) Bağlıoğlu, Özgür
News web pages are an important resource for news consumers since the Internet provides the most up-to-date information. However, the abundance of this information is overwhelming. In order to solve this problem, news articles should be organized in various ways. For example, new event detection (NED) and tracking studies aim to solve this problem by categorizing news stories according to events. Generally, important issues are presented at the beginning of news articles. Based on this observation, we modify the term weighting component of the Okapi similarity measure in several different ways and use them in NED. We perform numerous experiments in Turkish using the BilCol2005 test collection that contains 209,305 documents from the entire year of 2005 and involves several events in which eighty of them are annotated by humans. In this study, we developed various chronological term ranking (CTR) functions using term positions with several parameters. Our experimental results show that CTR in combination with Okapi improves the effectiveness of a baseline system with a desirable performance up to 13%. We demonstrate that NED using CTR has a robust performance in different versions of TDT collection generated by N-pass detection evaluation. The tests indicate that the improvements are statistically significant.
Open Access
nOBS: an ns2 based simulation tool for performance Evaluation of TCP Traffic in OBS networks
(Springer-Verlag France, 2007) Gurel, G.; Alparslan, O.; Karasan, E.
Performance evaluation of TCP traffic in OBS networks has been under intensive study, since TCP constitutes the majority of Internet traffic. As a reliable and publicly available simulator, ns2 has been widely used for studying TCP/IP networks; however ns2 lacks many of the components for simulating optical burst switching networks. In this paper, an ns2 based OBS simulation tool (nOBS), which is built for studying burst assembly, scheduling and contention resolution algorithms in OBS networks is presented. The node and link objects in OBS are extended in nOBS for developing optical nodes and optical links. The ingress, core and egress node functionalities are combined into a common optical node architecture, which comprises agents responsible for burstification, routing and scheduling. The effects of burstification parameters, e.g., burstification timeout, burst size and number of burstification buffers per egress node, on TCP performance are investigated using nOBS for different TCP versions and different network topologies.
Open Access
Optimization of F2 layer parameters using IRI-Plas model and IONOLAB Total Electron Content
(IEEE, 2011) Sahin O.; Sezen, U.; Arikan F.; Arıkan, Orhan; Aktug, B.
In this study, the relation of the maximum ionization height (HmF2) and the critical frequency (FoF2) of F2 layer is examined within their parametric range through the International Reference Ionosphere extended towards the plasmasphere (IRI-Plas) model and the IONOLAB-TEC (Total Electron Content) observations. HmF2 and FoF2 are optimized using an iterational loop through Non-Linear Least Squares method by also using a physical relation constraint between these two parameters. Performance evaluation of optimization algorithm is performed separately for the cases running IRI-Plas with optimized parameters and TEC input; only with optimized parameters; only with TEC and finally with no optimized parameter and TEC input. As a conclusion, it is seen that using optimized parameters and TEC together as input produces best IRI-TEC estimates. But also using only optimized parameters (without TEC update) gives estimates with also very low RMS errors and is suitable to use in optimizations. HmF2 and FoF2 estimates are obtained separately for a quiet day, positively corrupted day, negatively corrupted day, a northern latitude and a southern latitude. HmF2 and FoF2 estimation results are compared with ionosonde data where available. This study enables the modification and update of empirical and deterministic IRI Model to include instantaneous variability of the ionosphere. © 2011 IEEE.
Open Access
A performance evaluation framework of a rate-controlled MPEG video transmission over UMTS networks
(IEEE, 2007-07) Akar, Nail; Barbera, M.; Budzisz, L.; Ferrùs, R.; Kankaya, Emre; Schembra, G.
UMTS is designed to offer high bandwidth radio access with QoS assurances for multimedia communications. In particular, real-time video communications services are expected to become a successful experience under UMTS networks. In this context, a video transmission service can be designed over the basis that UMTS can provide either a constant bit rate data channel or a dynamic variable bit rate data channel adapted to load conditions. In this latter approach, which is more efficient for both the user and the service provider, multimedia sources have to be timely designed in order to adapt their output rate to the instantaneous allowed channel rate. The target of this paper is to define an analytical model of adaptive real-time video sources in a UMTS network where system resources are dynamically shared among active users. © 2007 IEEE.
Open Access
A performance evaluation model for distributed real-time database
(Taylor & Francis Group, 1995) Ulusoy, Özgür; Belford, G. G.
A real-time database system (RTDBS) is designed to provide timely response to the transactions of data-intensive applications. Each transaction processed in an RTDBS is associated with a timing constraint in the form of a deadline. Efficient transaction-scheduling algorithms are required to minimize the number of missed transaction deadlines. In thls paper a performance evaluation model is provided to enable distributed RTDBS designers to analyze transaction scheduling algorithms. The model is developed progressing from a simple mathematical analysis to complicated simulations. The performance is expressed in terms of the fraction of satisfied transaction deadlines. The paper also provides an example simulation experiment implemented using the model presented.
Open Access
Performance evaluation models for single-item periodic pull production systems
(Palgrave Macmillan, 1996) Kırkavak, N.; Dinçer, C.
A number of pull production systems reported in the literature are found to be equivalent to a tandem- queue so that existing accurate tandem-queue approximation methods can be used to evaluate such systems. In this study, we consider developing an exact performance evaluation model for a non-tandem- queue equivalent pull production system using discrete-time Markov processes. It is a periodically con- trolled serial production system in which a single-item is processed at each stage with an exponential processing time in order to satisfy the Poisson finished product demand. The selected performance mea- sures are throughput, inventory levels, machine utilizations and service level of the system. For large systems, which are difficult to evaluate exactly because of large state-spaces involved, we also pro- pose a computationally feasible approximate decomposition technique together with some numerical experimentations.
Open Access
Performance evaluation of track association and maintenance for a MFPAR with doppler velocity measurements
(2010) Kural, F.; Arikan, F.; Arıkan, Orhan; Efe, M.
This study investigates the effects of incorporating Doppler velocity measurements directly into track association and maintenance parts for single and multiple target tracking unit in a multi function phased array radar (MFPAR). Since Doppler velocity is the major discriminant of clutter from a desired target, the measurement set has been expanded from range, azimuth and elevation angles to include Doppler velocity measurements. We have developed data association and maintenance part of a well known tracking method, Interacting Multiple Model Probabilistic Data Association.
Open Access
Performance measures for object detection evaluation
(Elsevier BV, 2010) Özdemir, B.; Aksoy, S.; Eckert, S.; Pesaresi, M.; Ehrlich, D.
We propose a new procedure for quantitative evaluation of object detection algorithms. The procedure consists of a matching stage for finding correspondences between reference and output objects, an accuracy score that is sensitive to object shapes as well as boundary and fragmentation errors, and a ranking step for final ordering of the algorithms using multiple performance indicators. The procedure is illustrated on a building detection task where the resulting rankings are consistent with the visual inspection of the detection maps. © 2009 Elsevier B.V. All rights reserved.