Browsing by Subject "Computer networks"
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Item Open Access 3D forest fire propagation simulation(IEEE, 2008-05) Köse, Kıvanç; Grammalidis, N.; Yılmaz, E.; Çetin, A. EnisThe increase in the number of forest fires in the last few years dispatch governments to take precautions. Besides prevention, early intervention is also very important in fire fighting. If the firefighters know where the fire will be in some time, it would be easier for them to stop the fire. Therefore a big need for simulating the fire behavior exists. In this paper we are proposing a system which can simulate the propagation of fire in time. Also this system can visualize the propagation of fire in any 3D-GIS environment, that accepts KMZ as a file format. Besides, any user demanded data can be visualized on the map of the system. This gives the chance of fire planning to firefighters. The system can visualize its results on 3D screens in 3D. Therefore, a better understanding of the terrain can be obtained. ©2008 IEEE.Item Open Access Animation of boiling phenomena(IEEE, 2008-05) Bülbül, Abdullah; Küçüktunç, Onur; Özgüç, BülentPhenomenon of boiling is a challenging topic for computer graphics due to its complex hydrodynamics and formulation. Realistic fluid animations require very heavy three-dimensional fluid flow calculations, and surface estimations as well. However, realism and performance are the two important objectives of the boiling animation for a real-time application. We present an efficient method for the simulation of boiling water in this paper. The method is based on modeling the bubbles and waves as particles. Grid-based approach is used both for the heating and the fluid surface. Our technique makes it possible to produce the animation of boiling phenomena nearly in real-time. ©2008 IEEE.Item Open Access BilKristal 4.0: A tool for crystal parameters extraction and defect quantification(Elsevier, 2015) Okuyan, E.; Okuyan, C.In this paper, we present a revised version of BilKristal 3.0 tool. Raycast screenshot functionality is added to provide improved visual analysis. We added atomic distance analysis functionality to assess crystalline defects. We improved visualization capabilities by adding high level cut function definitions. Discovered bugs are fixed and small performance optimizations are made. © 2015 Elsevier B.V. All rights reserved.Item Open Access Camera tamper detection using wavelet analysis for video surveillance(IEEE, 2007-09) Aksay, A.; Temizel, A.; Çetin, A. EnisIt is generally accepted that video surveillance system operators lose their concentration after a short period of time and may miss important events taking place. In addition, many surveillance systems are frequently left unattended. Because of these reasons, automated analysis of the live video feed and automatic detection of suspicious activity have recently gained importance. To prevent capture of their images, criminals resort to several techniques such as deliberately obscuring the camera view, covering the lens with a foreign object, spraying or defocusing the camera lens. In this paper, we propose some computationally efficient wavelet domain methods for rapid camera tamper detection and identify some real-life problems and propose solutions to these. © 2007 IEEE.Item Open Access Design and implementation of a DMD based volumetric 3D display(IEEE, 2008-05) Yücesoy, Veysel; Tunaoǧlu, Doruk; Kovachev, Metodi; Ilieva, Rossitza; Onural, LeventA real image swept-volume volumetric display is developed. A piston type moving screen is used to obtain the desired volume. A commercially available DMD device is used to project 2D slices of a 3D frame. There is a varying magnification effect during the projection because of the optical design of the system; raw 3D video frames are processed by a software to generate the appropriate 2D slices by also correcting the magnification. Synchronization between the hardware and the software is achieved via a microcontroller. The overall system is capable of printing 12 3D frames per second where a 3D frame consists of 90 2D slices with a resolution varying from 512x512 to 450x450 (approx. 20M voxels per one 3D frame). Although some flickering effect is observed due to rather low 3D frame rate, results are visually satisfactory. ©2008 IEEE.Item Open Access A distributed and measurement-based framework against free riding in peer-to-peer networks(IEEE, 2004) Karakaya, Murat; Korpeoglu, İbrahim; Ulusoy, ÖzgürIn this paper, we propose a distributed and measurement-based method to reduce the degree of free riding in P2P networks. We primarily focus on developing schemes to locate free riders and on determining policies that can be used to take actions against them. Our proposed schemes require each peer to monitor its neighboring peers, make decisions if they exhibit any kind of free riding, and take appropriate actions if required.Item Open Access Distributed construction and maintenance of bandwidth-efficient bluetooth scatternets(IEEE, 2005-05) Tekkalmaz, Metin; Sözer, Hasan; Körpeoǧlu, İbrahimBluetooth networks can be constructed as piconets or scatternets depending on the number of nodes in the network. Although piconet construction is a well-defined process specified in Bluetooth standards, scatternet construction policies and algorithms are not well specified. Among many solution proposals for this problem, only a few of them focus on efficient usage of bandwidth in the resulting scatternets. In this paper, we propose a distributed algorithm for scatternet construction problem, that dynamically constructs and maintains a scatternet based on estimated traffic flow rates between nodes. The algorithm is adaptive to changes and maintains a constructed scatternet for bandwidth-efficiency when nodes come and go or when traffic flow rates change. Based on simulations, the paper also presents the improvements in bandwidth-efficiency provided by the proposed algorithm. © 2005 IEEE.Item Open Access Dynamic congestion control in interconnected computer networks(IEEE, 1988-10) Ulusoy, Özgür; Baray, MehmetThe authors evaluate a window-based congestion control mechanism in an internetwork environment. They also propose and study two dynamic-window congestion-control algorithms. These algorithms provide further control to the window mechanism by adjusting the window size in accordance with the availability of the network resources at the destination. A comparison of dynamic algorithms with fixed window control is provided in terms of throughput and delay performance. It is shown that dynamic algorithms have considerable performance advantages over fixed-window control.Item Open Access An evaluation of a client-server real-time database system(ACM, 1996) Ulusoy, ÖzgürA real-time database system (RTDBS) can be defined as a database system where transactions are associated with real-time constraints. In this paper, we investigate various performance issues in a RTDBS constructed on a client-server system architecture. In a client-server database management system the whole database is stored on the server disks, and copies of database items can be cached in the client memories. We provide a detailed simulation model of a client-server RTDBS, and present the initial results of a performance work that evaluates the effects of various workload parameters and design alternatives. Index Terms - Real-time database systems, client-server architecture, transaction scheduling, timing constraints.Item Open Access Mesh topology design in overlay virtual private networks(IET, 2002) Karasan, E.; Ekin-Karasan, O.; Akar, N.; Pinar, M. C.The mesh topology design problem in overlay virtual private networks is studied. Given a set of customer nodes and an associated traffic matrix, tunnels that connect node pairs through a service provider network are determined such that the total multi-hopped traffic is minimised. A tabu search based heuristic is proposed.Item Open Access Model-free adaptive hysteresis for dynamic bandwidth reservation(IEEE, 2007-10) Akar, NailDynamic bandwidth reservation refers to the process of dynamically updating the bandwidth allocation to a connection between two network end points on the basis of actual aggregate traffic demand of the connection. We assume a scenario in which bandwidth updates for the connection should not be performed too frequently and the frequency of updates are thus limited to a so-called desired update rate. We propose an asynchronous model-free adaptive hysteresis algorithm for dynamic bandwidth reservations with such update frequency constraints. We validate the effectiveness of the proposed approach by comparing its bandwidth efficiency with that of a synchronous model-based dynamic bandwidth reservation mechanism from the existing literature.Item Open Access Moderating effects of climate and external support on transformational leadership and technological innovation: An investigation in creative ventures in Turkey(IEEE, 2006) Gümüsluoğlu, Lale T.; Ilsev, A.The purpose of this study was to investigate the influence of transformational leadership on technological innovation at the organizational level. Specifically, it was proposed that transformational leadership would have a positive effect on organizational innovation. Furthermore, this effect was proposed to be moderated by an innovation-supporting climate and support received from external organizations. These relationships were tested on 163 R&D personnel and managers of 43 micro- and small-sized Turkish entrepreneurial software development companies. The results confirmed the positive impact of transformational leadership on organizational innovation, which was measured with a market-oriented criterion developed specifically for developing countries and newly developing industries. Furthermore, the relationship between transformational leadership and organizational innovation was stronger when external support was at high levels than when there was no external support. The moderating effect of an innovation-supporting climate was not significant. Managerial implications as well as policy recommendations are provided, for micro and small-sized enterprises in particular. (c) 2006 PICMET.Item Open Access Negative refraction and subwavelength focusing using left-handed composite metamaterials(SPIE, 2008-01) Özbay, Ekmel; Aydın, KorayWe review experimental studies performed on left-handed metamaterials (LHM) at microwave frequencies. The metamaterial structure is composed of periodic arrays of split-ring resonators and wire meshes and exhibits a left-handed propagation band at frequencies of negative permittivity and negative permeability. Negative refraction is verified using prism shaped LHM and also by beam-shifting method. Subwavelength focusing of a point source is achieved with a resolution of 0.13λ, through a flat LHM superlens.Item Open Access A peer-to-peer file search and download protocol for wireless ad-hoc networks(Elsevier BV, 2009-01) Sözer, H.; Tekkalmaz, M.; Korpeoglu, I.Deployment of traditional peer-to-peer file sharing systems on a wireless ad-hoc network introduces several challenges. Information and workload distribution as well as routing are major problems for members of a wireless ad-hoc network, which are only aware of their immediate neighborhood. In this paper, we propose a file sharing system that is able to answer location queries, and also discover and maintain the routing information that is used to transfer files from a source peer to another peer. We present a cross-layer design, where the lookup and routing functionality are unified. The system works according to peer-to-peer principles, distributes the location information of the shared files among the members of the network. The paper includes a sample scenario to make the operations of the system clearer. The performance of the system is evaluated using simulation results and analysis is provided for comparing our approach with a flooding-based, unstructured approach. © 2008 Elsevier B.V. All rights reserved.Item Open Access Pole-zero computation in microwave circuits using multipoint Padé approximation(Institute of Electrical and Electronics Engineers, 1995-01) Celik, M.; Ocali, O.; Tan, M. A.; Atalar, AbdullahA new method is proposed for dominant pole- zero (or pole-residue) analysis of large linear microwave circuits containing both lumped and distributed elements. The method is based on a multipoint Padé approximation. It finds a reduced-order rational s-domain transfer function using a data set obtained by solving the circuit at only a few frequency points. We propose two techniques in order to obtain the coefficients of the transfer function from the data set. The proposed method provides a more efficient computation of both transient and frequency domain responses than conventional simulators and more accurate results than the techniques based on single-point Padé approximation such as asymptotic waveform evaluation.Item Open Access Privacy threats and practical solutions for genetic risk tests(IEEE, 2015) Barman, L.; Elgraini, M.-T.; Raisaro, J. L.; Hubaux, J. -P.; Ayday, ErmanRecently, several solutions have been proposed to address the complex challenge of protecting individuals' genetic data during personalized medicine tests. In this short paper, we analyze different privacy threats and propose simple countermeasures for the generic architecture mainly used in the literature. In particular, we present and evaluate a new practical solution against a critical attack of a malicious medical center trying to actively infer raw genetic information of patients. © 2015 IEEE.Item Open Access Reducing Router-Crossings in a Mobile Intranet(Springer, 1998) Korpeoglu, I.; Dube, R.; Tripathi, S. K.Current general purpose mobility solutions like Mobile-IP involve multiple router-crossings even when the mobile host moves within an intranet from one subnet of a router to another. An environment consisting of a large number of mobile hosts would congest the router causing hosts to experience high latency and jitter. This paper presents a mechanism to eliminate multiple router-crossings in a mobile intranet by making the routers aware of mobility, which reduces the load on the routers and the hand-off and data latency at the mobile hosts.Item Open Access A reputation-based trust management system for P2P networks(IEEE, 2004) Selçuk, Ali Aydin; Uzun, Ersin; Pariente, Mark ReşatThe open and anonymous nature of a P2P network makes it an ideal medium for attackers to spread malicious content. In this paper, we describe a reputation-based trust management protocol for P2P networks where users rate the reliability of parties they deal with, and share this information with their peers. The protocol helps establishing trust among good peers as well as identifying the malicious ones. Results of various simulation experiments show that the proposed system can be highly effective in preventing the spread of malicious content in P2P networks.Item Open Access rtPS uplink scheduling algorithms for IEEE 802.16 networks(Boğaziçi University, 2008-06) Ertürk, Mustafa Cenk; Akar, NailIEEE 802.16 MAC provides flexible bandwidth allocation and QoS mechanisms for users with different requirements. However, QoS scheduling is not specified by the 802.16 standard and is thus left open for vendors' implementation. In this paper, we propose an uplink scheduler to be used in WiMAX Base Station (BS) for rtPS type of connections. We propose that the base station maintains a leaky bucket for each rtPS connection to police and schedule rtPS traffic for uplink traffic management. The proposed scheduler is studied via simulations in MATLAB and throughput and fairness properties of the scheduler are demonstrated. Copyright ©2008 by Boǧaziçi University.Item Open Access SeaSpider: Automated information gathering on vessel movements in support of marine intelligence, surveillance, and reconnaissance(Spie, 2008-03) Tatar, Serhan; Chapman, D. M. F.SeaSpider is an R&D tool to investigate the development of a software agent that would aid an operator in gathering information about marine vessels from public sources on the Internet. This information would supplement sensor information used for Intelligence, Surveillance, and Reconnaissance (ISR) to enhance Maritime Domain Awareness (MDA) and to complete the Recognized Maritime Picture (RMP). Specifically, SeaSpider is fine-tuned to search for, extract, integrate, and display information about locations (ports), dates and times, and activities (arrival, in berth, departure). One module manages World Wide Web (WWW) searches and retrieves the web pages; another module extracts relevant ship activities, integrates them and populates a database; a third module retrieves information from the database in response to user-generated queries. In this paper, the SeaSpider concept is introduced, the design details of the prototype are presented, and performance is analyzed, with a view towards future research.