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Department: search.filters.department.Department of MathematicsSubject: search.filters.subject.Software engineering

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    Exact performance measures for peer-to-peer epidemic information diffusion
    (Springer-Verlag Berlin, 2006) N/A; Department of Computer Engineering; Department of Mathematics; Department of Mathematics; Department of Mathematics; Özkasap, Öznur; Yazıcı, Emine Şule; Küçükçifçi, Selda; Çağlar, Mine; Faculty Member; Faculty Member; Faculty Member; Faculty Member; Department of Computer Engineering; Department of Mathematics; College of Engineering; College of Sciences; College of Sciences; College of Sciences; 113507; 27432; 105252; 105131
    We consider peer-to-peer anti-entropy paradigms for epidemic information diffusion, namely pull, push and hybrid cases, and provide exact performance measures for them. Major benefits of the proposed epidemic algorithms are that they are fully distributed, utilize local information only via pair-wise interactions, and provide eventual consistency, scalability and communication topology-independence. Our contribution is the derivation of exact expressions for infection probabilities through elaborated counting techniques on a digraph. Considering the first passage times of a Markov chain based on these probabilities, we find the expected message delay experienced by each peer and its overall mean as a function of initial number of infectious peers. In terms of these criteria, the hybrid approach outperforms pull and push paradigms, and push is better than the pull case. Such theoretical results would be beneficial when integrating the models in several peer-to-peer distributed application scenarios.
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    Principles and performance analysis of second: a system for epidemic peer-to-peer content distribution
    (Academic Press Ltd- Elsevier Science Ltd, 2009) N/A; Department of Computer Engineering; Department of Mathematics; Department of Computer Engineering; Özkasap, Öznur; Çağlar, Mine; Alagöz, Ali; Faculty Member; Faculty Member; Other; Department of Mathematics; Department of Computer Engineering; College of Engineering; College of Sciences; College of Engineering; 113507; 105131; N/A
    We propose and design a peer-to-peer system, SeCond, addressing the distribution of large sized content to a large number of end systems in an efficient manner. In contrast to prior work, it employs a self-organizing epidemic dissemination scheme for state propagation of available blocks and initiation of block transmissions. in order to exploit heterogeneity of peers, enhance the utilization of system resources and for the ease of deployment, scalability, and adaptivity to dynamic peer arrivals/departures, we propose mechanisms for adjusting protocol parameters dynamically according to the bandwidth usages. We describe design and analysis details of our protocol SeCond. Comprehensive performance evaluations and comparison with the BitTorrent system model have been accomplished for a wide range of scenarios. Performance results include scalability analysis for different arrival/departure patterns, flash-crowd scenario, overhead analysis, and fairness ratio. The major metrics we study include the average file download time, load on the primary seed, uplink/downlink utilization. and communication overhead. We show that SeCond is a scalable and adaptive protocol which takes the heterogeneity of the peers into account. The protocol is as fair as BitTorrent although it has no explicit strategy addressing free-riding. We also illustrate the applicability of an analytical fluid model to the behavior of SeCond.
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    Statistical analysis of cortical morphometrics using pooled distances based on labeled cortical distance maps
    (Springer, 2011) Hosakere, M.; Nishino, T.; Alexopoulos, J.; Todd, R. D.; Botteron, K. N.; Miller, M. I.; Ratnanather, J. Tilak; Department of Mathematics; Ceyhan, Elvan; Faculty Member; Department of Mathematics; College of Sciences; N/A
    Neuropsychiatric disorders have been demonstrated to manifest shape differences in cortical structures. Labeled Cortical Distance Mapping (LCDM) is a powerful tool in quantifying such morphometric differences and characterizes the morphometry of the laminar cortical mantle of cortical structures. Specifically, LCDM data are distances of labeled gray matter (GM) voxels with respect to the gray/white matter cortical surface. Volumes and descriptive measures (such as means and variances for each subject) based on LCDM distances provide descriptive summary information on some of the shape characteristics. However, additional morphometrics are contained in the data and their analysis may provide additional clues to underlying differences in cortical characteristics. To use more of this information, we pool (merge) LCDM distances from subjects in the same group. These pooled distances can help detect morphometric differences between groups, but do not provide information about the locations of such differences in the tissue in question. In this article, we check for the influence of the assumption violations on the analysis of pooled LCDM distances. We demonstrate that the classical parametric tests are robust to the non-normality and within sample dependence of LCDM distances and nonparametric tests are robust to within sample dependence of LCDM distances. We specify the types of alternatives for which the tests are more sensitive. We also show that the pooled LCDM distances provide powerful results for group differences in distribution of LCDM distances. As an illustrative example, we use GM in the ventral medial prefrontal cortex (VMPFC) in subjects with major depressive disorder (MDD), subjects at high risk (HR) of MDD, and healthy subjects. Significant morphometric differences were found in VMPFC due to MDD or being at HR. In particular, the analysis indicated that distances in left and right VMPFCs tend to decrease due to MDD or being at HR, possibly as a result of thinning. The methodology can also be applied to other cortical structures.
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    Structural stability and decay estimate for marine riser equations
    (2011) Çelebi, A. O.; Gür, S.; Department of Mathematics; Kalantarov, Varga; Faculty Member; Department of Mathematics; College of Sciences; 117655
    We study the problem of the continuous dependence of weak and strong solutions to the initial boundary value problem for multidimensional marine riser equations on the parameters of the equation. The continuous dependence of solutions on the coefficient of the effective tension, on the coefficient of the nonlinear drag, and on the coefficients of the Coriolis force is established.