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Search Results: 1 - 10 of 318 matches for " Coskun Guclu "
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Influence of Aphids on the Epidemiology of Potato Virus Diseases (PVY, PVS and PLRV) in the High Altitude Areas of Turkey
Hidayet Bostan,Coskun Guclu,Erdogan Ozturk Isil Ozdemir,Havva Ilbagi
Pakistan Journal of Biological Sciences , 2006,
Abstract: Potato plants belonging to cv. Morfona were found infected with Potato leaf roll virus (PLRV), Potato virus Y (PVY) and Potato virus S (PVS) with the rates of 3.40, 6.47 and 5.30% in field conditions during the 2003 season. In order to determine the variations in the incidence rates of those potato viruses, harvested tubers from this field used for seed potato for the following seasons for the years of 2004 and 2005. Infection rates for 2004 and 2005 were determined as 7.66 and 22.33% for PLRV; 27.0 and 91.0% for PVY; 21.0 and 77.33% for PVS, respectively. While infection rates of those viruses were relatively low until 2003, the number of infected plants increased in following years. The results obtained from this study revealed that spreading rates of PVY and PVS were higher than PLRV as PVY higher than PVS. Winged aphid counts in the yellow-pan traps during the potato-growing seasons of 2004 and 2005 indicated that Myzus (Nectarosiphon) persicae (Sulzer, 1776), Therioaphis trifolii (Monell, 1882) and Aphis fabae (Scopoli, 1763) were the most abundant aphid species in Central District of Erzurum Province where field trails were established. Nevertheless there was not significant fluctuation of those aphid populations between 2004 and 2005. In addition to those aphids, Anoecia corni (Fabricius, Brachycaudus (Acaudus) cardui (Linnaeus), Cryptomyzus ribis (Linnaeus), Eulachnus rileyi (Williams, 1911), Hyperomyzus lactucae (Linnaeus, 1758) and Pterochloroides persicae (Cholodkovsky) species were collected from the pans but their number were very low.
Synchronization in Small-World-Connected Computer Networks
Hasan Guclu
Physics , 2006,
Abstract: In this thesis we study synchronization phenomena in natural and artificial coupled multi-component systems, applicable to the scalability of parallel discrete-event simulation for systems with asynchronous dynamics. We analyze the properties of the virtual time horizon or synchronization landscape (corresponding to the progress of the processing elements) of these networks by using the framework of non-equilibrium surface growth. When the communication topology mimics that of the short-range interacting underlying system, the virtual time horizon exhibits Kardar-Parisi-Zhang-like kinetic roughening. Although the virtual times, on average, progress at a nonzero rate, their statistical spread diverges with the number of processing elements, hindering efficient data collection. We show that when the synchronization topology is extended to include quenched random communication links (small-world links) between the processing elements, they make a close-to-uniform progress with a nonzero rate, without global synchronization. We also provide a coarse-grained description for the small-world-synchronized virtual-time horizon and compare the findings to those obtained by simulating the simulations based on the exact algorithmic rules. We also present numerical results for the evolution of the virtual-time horizon on scale-free Barabasi-Albert networks serving as communication topology among the processing elements. Finally, we investigate to what extent small-world couplings (extending the original local relaxational dynamics through the random links) lead to the suppression of extreme fluctuations in the synchronization landscape.
On the Inverse Problem of Dupire’s Equation with Nonlocal Boundary and Integral Conditions  [PDF]
Coskun Guler, Volkan Oban
Journal of Mathematical Finance (JMF) , 2017, DOI: 10.4236/jmf.2017.74051
Abstract: In this study, Inverse Problem for Dupire’s Equation with nonlocal boundary and integral conditions is studied. Then, by means of the some transformation, this equation is converted to diffusion equation. The conditions for the existence and uniqueness of a classical solution of the problem under consideration are established and continuous dependence of (p, v) on the data is shown. It is emphasized that this problem is well-posed.
Aflatoxin Regulations in a Network of Global Maize Trade
Felicia Wu, Hasan Guclu
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0045151
Abstract: Worldwide, food supplies often contain unavoidable contaminants, many of which adversely affect health and hence are subject to regulations of maximum tolerable levels in food. These regulations differ from nation to nation, and may affect patterns of food trade. We soughtto determine whether there is an association between nations' food safety regulations and global food trade patterns, with implications for public health and policymaking. We developed a network model of maize trade around the world. From maize import/export data for 217 nations from 2000–2009, we calculated basic statistics on volumes of trade; then examined how regulations of aflatoxin, a common contaminant of maize, are similar or different between pairs of nations engaging in significant amounts of maize trade. Globally, market segregation appears to occur among clusters of nations. The United States is at the center of one cluster; European countries make up another cluster with hardly any maize trade with the US; and Argentina, Brazil, and China export maize all over the world. Pairs of nations trading large amounts of maize have very similar aflatoxin regulations: nations with strict standards tend to trade maize with each other, while nations with more relaxed standards tend to trade maize with each other. Rarely among the top pairs of maize-trading nations do total aflatoxin standards (standards based on the sum of the levels of aflatoxins B1, B2, G1, and G2) differ by more than 5 μg/kg. These results suggest that, globally, separate maize trading communities emerge; and nations tend to trade with other nations that have very similar food safety standards.
Choice of drugs in the treatment of chronic hepatitis B in pregnancy
Ertugrul Guclu,Oguz Karabay
World Journal of Gastroenterology , 2013, DOI: 10.3748/wjg.v19.i10.1671
Abstract: The selection of antiviral drugs for chronic hepatitis B (CHB) treatment in pregnancy is very difficult since none of the drugs have been approved for use in pregnancy. Transmission from mother to newborn remains the most frequent route of infection in mothers with high viral load and positive hepatitis B e antigen status, even with the use of appropriate prophylaxis with hepatitis B virus (HBV) immunoglobulin and HBV vaccination. We read from the article written by Yi et al that lamivudine treatment in early pregnancy was safe and effective. However, we could not understand why adefovir dipivoxil (ADV) was used in three pregnancy cases, since ADV has been classified as pregnancy category C. In pregnancy, telbivudine or tenofovir should be selected when the treatment of CHB is necessary, since these drugs have been classified as Food and Drug Administration pregnancy risk category B.
Proximity Networks and Epidemics
Z. Toroczkai,H. Guclu
Physics , 2007, DOI: 10.1016/j.physa.2006.11.088
Abstract: Disease spread in most biological populations requires the proximity of agents. In populations where the individuals have spatial mobility, the contact graph is generated by the "collision dynamics" of the agents, and thus the evolution of epidemics couples directly to the spatial dynamics of the population. We first briefly review the properties and the methodology of an agent-based simulation (EPISIMS) to model disease spread in realistic urban dynamic contact networks. Using the data generated by this simulation, we introduce the notion of dynamic proximity networks which takes into account the relevant time scales for disease spread: contact duration, infectivity period and rate of contact creation. This approach promises to be a good candidate for a unified treatment of epidemic types that are driven by agent collision dynamics. In particular, using a simple model, we show that it can can account for the observed qualitative differences between the degree distributions of contact graphs of diseases with short infectivity period (such as air-transmitted diseases) or long infectivity periods (such as HIV).
Electromagnetic interactions at RHIC and LHC
M. C. Guclu
Physics , 2008,
Abstract: At LHC energies the Lorentz factor will be 3400 for the Pb + Pb collisions and the electromagnetic interactions will play important roles. Cross sections for the electromagnetic particle productions are very large and can not be ignored for the lifetimes of the beams and background. In this article, we are going to study some of the electromagnetic processes at RHIC and LHC and show the cross section calculations of the electron-positron pair production with the giant dipole resonance of the ions.
Extreme Fluctuations in Small-Worlds with Relaxational Dynamics
H. Guclu,G. Korniss
Physics , 2003, DOI: 10.1103/PhysRevE.69.065104
Abstract: We study the distribution and scaling of the extreme height fluctuations for Edwards-Wilkinson-type relaxation on small-world substrates. When random links are added to a one-dimensional lattice, the average size of the fluctuations becomes finite (synchronized state) and the extreme height diverges only logarithmically in the large system-size limit. This latter property ensures synchronization in a practical sense in small-world coupled multi-component autonomous systems. The statistics of the extreme heights is governed by the Fisher-Tippett-Gumbel distribution.
Scale-Free Overlay Topologies with Hard Cutoffs for Unstructured Peer-to-Peer Networks
Hasan Guclu,Murat Yuksel
Computer Science , 2006,
Abstract: In unstructured peer-to-peer (P2P) networks, the overlay topology (or connectivity graph) among peers is a crucial component in addition to the peer/data organization and search. Topological characteristics have profound impact on the efficiency of search on such unstructured P2P networks as well as other networks. It has been well-known that search on small-world topologies of N nodes can be as efficient as O(ln N), while scale-free (power-law) topologies offer even better search efficiencies like as good as O(lnln N) for a range of degree distribution exponents. However, generation and maintenance of such scale-free topologies are hard to realize in a distributed and potentially uncooperative environments as in the P2P networks. A key limitation of scale-free topologies is the high load (i.e. high degree) on very few number of hub nodes. In a typical unstructured P2P network, peers are not willing to maintain high degrees/loads as they may not want to store large number of entries for construction of the overlay topology. So, to achieve fairness and practicality among all peers, hard cutoffs on the number of entries are imposed by the individual peers, which limits scale-freeness of the overall topology. Thus, efficiency of the flooding search reduces as the size of the hard cutoff does. We investigate construction of scale-free topologies with hard cutoffs (i.e. there are not any major hubs) and effect of these hard cutoffs on the search efficiency. Interestingly, we observe that the efficiency of normalized flooding and random walk search algorithms increases as the hard cutoff decreases.
Stationary and Mobile Target Detection using Mobile Wireless Sensor Networks
Evsen Yanmaz,Hasan Guclu
Computer Science , 2010, DOI: 10.1109/INFCOMW.2010.5466620
Abstract: In this work, we study the target detection and tracking problem in mobile sensor networks, where the performance metrics of interest are probability of detection and tracking coverage, when the target can be stationary or mobile and its duration is finite. We propose a physical coverage-based mobility model, where the mobile sensor nodes move such that the overlap between the covered areas by different mobile nodes is small. It is shown that for stationary target scenario the proposed mobility model can achieve a desired detection probability with a significantly lower number of mobile nodes especially when the detection requirements are highly stringent. Similarly, when the target is mobile the coverage-based mobility model produces a consistently higher detection probability compared to other models under investigation.
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