Browsing by Subject "Performance"
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Item Open Access 45 GHz bandwidth-efficiency resonant cavity enhanced ITO-Schottky photodiodes(OSA, 2001) Bıyıklı, Necmi; Kimukin, İbrahim; Aytür, Orhan; Özbay, Ekmel; Gökkavas, M.; Ünlü, M. S.We demonstrated high-performance resonant cavity enhanced ITO-Schottky photodiodes. We achieved a peak efficiency of 75% around 820 nm with a 3-dB bandwidth of 60 GHz resulting in a bandwidth-efficiency product of 45 GHz.Item Open Access Âşik Ali Cemali repertuvarindan parçalarin performans teorisi kapsaminda değerlendirilmesi(2002) Dündar, HülyaBu çalışmada Aşık Ali Cemali'nin söylediği türküler ve anlattığı kısa hikayeler Performans Teorisi çerçevesinde incelenmiştir Çalışma dört bölümden oluşmakta olup bu bölümlerde anlatanın, dinleyicinin, anlatım ortamının ve ses kayıt cihazının aşığın performansı üzerindeki etkileri araştınlmıştır.Item Open Access Automatic performance evaluation of Web search engines(Elsevier, 2004) Can, F.; Nuray, R.; Sevdik, A. B.Measuring the information retrieval effectiveness of World Wide Web search engines is costly because of human relevance judgments involved. However, both for business enterprises and people it is important to know the most effective Web search engines, since such search engines help their users find higher number of relevant Web pages with less effort. Furthermore, this information can be used for several practical purposes. In this study we introduce automatic Web search engine evaluation method as an efficient and effective assessment tool of such systems. The experiments based on eight Web search engines, 25 queries, and binary user relevance judgments show that our method provides results consistent with human-based evaluations. It is shown that the observed consistencies are statistically significant. This indicates that the new method can be successfully used in the evaluation of Web search engines. © 2003 Elsevier Ltd. All rights reserved.Item Open Access Cache-based query processing for search engines(Association for Computing Machinery, 2012-11-01) Cambazoglu, B. B.; Altıngovde, I. S.; Ozcan, R.; Ulusoy, ÖzgürIn practice, a search engine may fail to serve a query due to various reasons such as hardware/network failures, excessive query load, lack of matching documents, or service contract limitations (e.g., the query rate limits for third-party users of a search service). In this kind of scenarios, where the backend search system is unable to generate answers to queries, approximate answers can be generated by exploiting the previously computed query results available in the result cache of the search engine.In this work, we propose two alternative strategies to implement this cache-based query processing idea. The first strategy aggregates the results of similar queries that are previously cached in order to create synthetic results for new queries. The second strategy forms an inverted index over the textual information (i.e., query terms and result snippets) present in the result cache and uses this index to answer new queries. Both approaches achieve reasonable result qualities compared to processing queries with an inverted index built on the collection. © 2012 ACM.Item Open Access Circuit partitioning using mean field annealing(Elsevier, 1995) Bultan, T.; Aykanat, CevdetMean field annealing (MFA) algorithm, proposed for solving combinatorial optimization problems, combines the characteristics of neural networks and simulated annealing. Previous works on MFA resulted with successful mapping of the algorithm to some classic optimization problems such as traveling salesperson problem, scheduling problem, knapsack problem and graph partitioning problem. In this paper, MFA is formulated for the circuit partitioning problem using the so called net-cut model. Hence, the deficiencies of using the graph representation for electrical circuits are avoided. An efficient implementation scheme, which decreases the complexity of the proposed algorithm by asymptotical factors is also developed. Comparative performance analysis of the proposed algorithm with two wellknown heuristics, simulated annealing and Kernighan-Lin, indicates that MFA is a successful alternative heuristic for the circuit partitioning problem. © 1995.Item Open Access Compact optical temporal processors(Optical Society of America, 1995) Mendlovic, D.; Melamed, O.; Özaktaş, Haldun M.Optical signal processing can be done with time-lens devices. A temporal processor based on chirp-z transformers is suggested. This configuration is more compact than a conventional 4-f temporal processor. On the basis of implementation aspects of such a temporal processor, we did a performance analysis. This analysis leads to the conclusion that an ultrafast optical temporal processor can be implemented.Item Open Access A comparative study of computational procedures for the resource constrained project scheduling problem(Elsevier, 1994) Oğuz, O.; Bala, H.Performance of two new integer programming based heuristics together with some special purpose algorithms for project scheduling are tested from a computational point of view. The objective of the study is to compare the quality of solutions obtained by using these algorithms and reach conclusions about their relative merits on this specific problem. © 1994.Item Open Access Comparison of local and global computation and its implications for the role of optical interconnections in future nanoelectronic systems(Elsevier, 1993) Özaktaş, Haldun M.; Goodman J. W.Various methods of simulating diffusion phenomena with parallel hardware are discussed. In particular methods are compared requiring local and global communication among the processors in terms of total computation time. Systolic convolution on a locally connected array is seen to exhibit an asymptotic advantage over Fourier methods on a globally connected array. Whereas this may translate into a numerical advantage for extremely large numbers of ultrafast devices for two-dimensional systems, this is unlikely for three-dimensional systems. Thus global Fourier methods will be advantageous for three-dimensional systems for foreseeable device speeds and system sizes. The fact that optical interconnections are potentially advantageous for implementing the longer connections of such globally connected systems suggests that they can be beneficially employed in future nanoelectronic computers. Heat removal considerations play an important role in our conclusions.Item Open Access Compiler directed network-on-chip reliability enhancement for chip multiprocessors(Association for Computing Machinery, 2010-04) Ozturk, O.; Kandemir, M.; Irwin, M. J.; Narayanan, S.H. K.Chip multiprocessors (CMPs) are expected to be the building blocks for future computer systems. While architecting these emerging CMPs is a challenging problem on its own, programming them is even more challenging. As the number of cores accommodated in chip multiprocessors increases, network-on-chip (NoC) type communication fabrics are expected to replace traditional point-to-point buses. Most of the prior software related work so far targeting CMPs focus on performance and power aspects. However, as technology scales, components of a CMP are being increasingly exposed to both transient and permanent hardware failures. This paper presents and evaluates a compiler-directed power-performance aware reliability enhancement scheme for network-on-chip (NoC) based chip multiprocessors (CMPs). The proposed scheme improves on-chip communication reliability by duplicating messages traveling across CMP nodes such that, for each original message, its duplicate uses a different set of communication links as much as possible (to satisfy performance constraint). In addition, our approach tries to reuse communication links across the different phases of the program to maximize link shutdown opportunities for the NoC (to satisfy power constraint). Our results show that the proposed approach is very effective in improving on-chip network reliability, without causing excessive power or performance degradation. In our experiments, we also evaluate the performance oriented and energy oriented versions of our compiler-directed reliability enhancement scheme, and compare it to two pure hardware based fault tolerant routing schemes. © 2010 ACM.Item Open Access Corporate social responsibility: why bother?(Elsevier, 2014) Isaksson, I.; Kiessling, T.; Harvey, M.Corporate Social Responsibility (CSR) is not a new concept, but unfortunately has been defined in so many ways, it is often misinterpreted. In fact it has had 40 years to evolve from a somewhat infant concept to a successful managerial tool to build a company's reputation in the global market arena. Corporate social responsibility has become corporate strategic responsibility - an imperative element of corporate global business strategies. Many leaders, entrepreneurs, investors, executives and politicians now recognize CSR's potential for differentiation and positioning in the global marketplace. In the 21st century, we find CSR to have a remarkable acceptance among practicing managers; publicly traded corporations especially label CSR an essential tool for their long-term legitimacy and profitability. CSR has matured from its infancy, becoming a corporate reputational adding value strategy for firms.Item Open Access Data replication versus timing constraints in distributed database systems(ACM, 1994-03) Ulusoy, ÖzgürIn a database system supporting a real-time application, each transaction is associated with a timing constraint, typically in the form of a deadline. Replicated database systems possess desirable features for real-time applications, such as a high level of data availability, and potentially improved response time for queries. On the other hand, multiple copy updates lead to a considerable overhead due to the communication required among the data sites holding the copies. In this paper, we investigate the impact of storing multiple copies of data on satisfying the timing constraints of real-time transactions. A detailed performance model of a distributed database system is employed in evaluating the effects of various workload parameters and design alternatives on the system performance. The performance is expressed in terms of the fraction of satisfied transaction deadlines.Item Open Access Deriving feasible deployment alternatives for parallel and distributed simulation systems(Association for Computing Machinery, 2013-07) Çelik, T.; Tekinerdogan, B.; Imre, K.Parallel and distributed simulations (PADS) realize the distributed execution of a simulation system over multiple physical resources. To realize the execution of PADS, different simulation infrastructures such as HLA, DIS and TENA have been defined. Recently, the Distributed Simulation Engineering and Execution Process (DSEEP) that supports the mapping of the simulations on the infrastructures has been defined. An important recommended task in DSEEP is the evaluation of the performance of the simulation systems at the design phase. In general, the performance of a simulation is largely influenced by the allocation of member applications to the resources. Usually, the deployment of the applications to the resources can be done in many different ways. DSEEP does not provide a concrete approach for evaluating the deployment alternatives. Moreover, current approaches that can be used for realizing various DSEEP activities do not yet provide adequate support for this purpose. We provide a concrete approach for deriving feasible deployment alternatives based on the simulation system and the available resources. In the approach, first the simulation components and the resources are designed. The design is used to define alternative execution configurations, and based on the design and the execution configuration; a feasible deployment alternative can be algorithmically derived. Tool support is developed for the simulation design, the execution configuration definition and the automatic generation of feasible deployment alternatives. The approach has been applied within a large-scale industrial case study for simulating Electronic Warfare systems. © 2013 ACM.Item Open Access Document replication strategies for geographically distributed web search engines(Elsevier Ltd., 2013) Kayaaslan, E.; Cambazoglu, B. B.; Aykanat, CevdetLarge-scale web search engines are composed of multiple data centers that are geographically distant to each other. Typically, a user query is processed in a data center that is geographically close to the origin of the query, over a replica of the entire web index. Compared to a centralized, single-center search engine, this architecture offers lower query response times as the network latencies between the users and data centers are reduced. However, it does not scale well with increasing index sizes and query traffic volumes because queries are evaluated on the entire web index, which has to be replicated and maintained in all data centers. As a remedy to this scalability problem, we propose a document replication framework in which documents are selectively replicated on data centers based on regional user interests. Within this framework, we propose three different document replication strategies, each optimizing a different objective: reducing the potential search quality loss, the average query response time, or the total query workload of the search system. For all three strategies, we consider two alternative types of capacity constraints on index sizes of data centers. Moreover, we investigate the performance impact of query forwarding and result caching. We evaluate our strategies via detailed simulations, using a large query log and a document collection obtained from the Yahoo! web search engine. (C) 2012 Elsevier Ltd. All rights reserved.Item Open Access Effect of load, processing time and due date variation on the effectiveness of scheduling rules(Taylor & Francis, 2002) Lejmi, T.; Sabuncuoğlu, İ.In real manufacturing environments, variations in production factors (i.e. pro- cessing time, demand, due-dates) are inevitable facts. All these dynamic changes, together with random disturbances (e.g. machine breakdowns) can seriously a ect the system performance. In this paper we focus on load, processing time and due date variation and analyse their impacts on a scheduling system. Speci®cally, we investigate the impact of variation on dispatching policies in a job shop environ- ment via simulation. The statistical analysis of the results leads to two major conclusions: ®rst, the relative performance of rules is not threatened much by PV (processing time variation), LV (load variation) or DDV (due date variation) Ð a result that can be a consolation for practitioners in the ®eld. Secondly, the performance of the rules deteriorates, in particular at high levels of PV, LV and DDV Ð a result that can provide new insights into the problem and produces useful information for researchers in their continuous e ort to develop better dispatching rules.Item Open Access Effect of shell thickness on small-molecule solar cells enhanced by dual plasmonic gold-silica nanorods(AIP Publishing, 2014-09-19) Xu, X.; Du, Q.; Peng, B.; Xiong, Q.; Hong, L.; Demir, Hilmi Volkan; Wong, T. K. S.; Kyaw, A. K. K.; Sun, X. W.Chemically synthesized gold (Au)-silica nanorods with shell thickness of 0 nm-10 nm were incorporated into the bulk heterojunction of a small-molecule organic solar cell. At optimal (1 wt. %) concentration, Au-silica nanorods with 5 nm shell thickness resulted in the highest power conversion efficiency of 8.29% with 27% relative enhancement. Finite-difference time-domain simulation shows that the localized electric field intensity at the silica shell-organic layer interface decreases with the increase of shell thickness for both 520 nm and 680 nm resonance peaks. The enhanced haze factor for transmission/reflection of the organic layer is not strongly dependent on the shell thickness. Bare Au nanorods yielded the lowest efficiency of 5.4%. Light intensity dependence measurement of the short-circuit current density shows that the silica shell reduces bimolecular recombination at the Au surface. As a result, both localized field intensity and light scattering are involved in efficiency enhancement for an optimized shell thickness of 5 nm.Item Open Access Efficiency and effectiveness of query processing in cluster-based retrieval(Elsevier, 2004) Can, F.; Altingövde I.S.; Demir, E.Our research shows that for large databases, without considerable additional storage overhead, cluster-based retrieval (CBR) can compete with the time efficiency and effectiveness of the inverted index-based full search (FS). The proposed CBR method employs a storage structure that blends the cluster membership information into the inverted file posting lists. This approach significantly reduces the cost of similarity calculations for document ranking during query processing and improves efficiency. For example, in terms of in-memory computations, our new approach can reduce query processing time to 39% of FS. The experiments confirm that the approach is scalable and system performance improves with increasing database size. In the experiments, we use the cover coefficient-based clustering methodology (C3M), and the Financial Times database of TREC containing 210158 documents of size 564 MB defined by 229748 terms with total of 29545234 inverted index elements. This study provides CBR efficiency and effectiveness experiments using the largest corpus in an environment that employs no user interaction or user behavior assumption for clustering. © 2003 Elsevier Ltd. All rights reserved.Item Open Access Efficient fast hartley transform algorithms for hypercube-connected multicomputers(IEEE, 1995) Aykanat, Cevdet; Derviş, A.Although fast Hartley transform (FHT) provides efficient spectral analysis of real discrete signals, the literature that addresses the parallelization of FHT is extremely rare. FHT is a real transformation and does not necessitate any complex arithmetics. On the other hand, FHT algorithm has an irregular computational structure which makes efficient parallelization harder. In this paper, we propose a efficient restructuring for the sequential FHT algorithm which brings regularity and symmetry to the computational structure of the FHT. Then, we propose an efficient parallel FHT algorithm for medium-to-coarse grain hypercube multicomputers by introducing a dynamic mapping scheme for the restructured FHT. The proposed parallel algorithm achieves perfect load-balance, minimizes both the number and volume of concurrent communications, allows only nearest-neighbor communications and achieves in-place computation and communication. The proposed algorithm is implemented on a 32-node iPSC/21 hypercube multicomputer. High-efficiency values are obtained even for small size FHT problems. © 1995 IEEEItem Open Access Equity ownership structure and its consequences : an empirical investigation in Turkish firms(Bilkent University, 2001) Gürsoy, GünerThe study describes the main characteristics of ownership structure of the Turkish nonfinancial firms listed on the Istanbul Stock Exchange (ISE) and examines the impact of ownership structure on performance and risk-taking behavior of Turkish firms. Turkish corporations can be characterized as highly concentrated, family owned firms attached to a group of companies generally owned by the same family or a group of families. Ownership structure is defined along two attributes: concentration and identity of the owner(s). We conclude that there is a significant impact of ownership structure - ownership concentration and ownership mix- on both performance and risk-taking behavior of the firms in our sample. Higher concentration leads to better market performance but lower accounting performance. Family-owned firms, contrast to conglomerate affiliates, seem to have lower performance with lower risk. Governmentowned firms have lower accounting, but higher market performance with higher risk.Item Open Access Equity ownership structure, risk taking, and performance: an empirical investigation in Turkish listed companies(Routledge, 2002) Gürsoy, G.; Aydoğan, K.The paper describes the main characteristics of ownership structure of Turkish nonfinancial firms listed on the Istanbul Stock Exchange (ISE) and examines the impact of ownership structure on performance and risk-taking behavior of Turkish firms. Turkish corporations can be characterized as highly concentrated, family owned firms attached to a group of companies generally owned by the same family or a group of families. Ownership structure is defined along two attributes: concentration and identity of the owner(s). We conclude that there is a significant impact of ownership structure—ownership concentration and ownership mix—on both performance and risk-taking behavior of the firms in our sample. Higher concentration leads to better market performance but lower accounting performance. Family owned firms, in contrast to conglomerate affiliates, seem to have lower performance with lower risk. Government-owned firms have lower accounting but higher market performance with higher risk.Item Open Access Evaluation of army corps artillery ammunition supply systems via simulation(IEEE, 2002) Sabuncuoğlu, İhsan; Utku, D. H.The purpose of this paper is to discuss the evaluation of different alternatives for the implementation of Turkish army corps artillery ammunition supply system. The objective is to see whether the alternative systems operate properly and to select the best system design. We find that the first alternative system cannot supply the units for all phases of an eight-day battle time while the second, the third, and the fourth systems can supply and yield better results. The third system is less costly than the second and the fourth systems. However, it has the drawback of too many vehicles in the convoy (i.e. congestion) which makes it susceptible to the enemy long distance and air assaults. The fourth system is the best of all from the point of the performance it yields; but, it costs more compared to the other systems.
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