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Search Results: 1 - 10 of 2730 matches for " Butun Ismail "
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Coherence time-based cooperative MAC protocol 1 for wireless ad hoc networks
Khalid Murad,Wang Yufeng,Butun Ismail,Kim Hyung-jin
EURASIP Journal on Wireless Communications and Networking , 2011,
Abstract: In this article, we address the goal of achieving performance gains under heavy-load and fast fading conditions. CoopMACI protocol proposed in Proceedings of the IEEE International Conference on Communications (ICC), Seoul, Korea, picks either direct path or relay path based on rate comparison to enhance average throughput and delay performances. However, CoopMACI performance deteriorates under fading conditions because of lower direct path or relay path reliability compared to UtdMAC (Agarwal et al. LNCS, 4479, 415-426, 2007). UtdMAC was shown to perform better than CoopMACI in terms of average throughput and delay performances because of improved transmission reliability provided by the backup relay path. Although better than CoopMACI, UtdMAC does not fully benefit from higher throughput relay path (compared to the direct path), since it uses relay path only as a secondary backup path. In this article, we develop a cooperative MAC protocol (termed as instantaneous relay-based cooperative MAC--IrcMAC) that uses channel coherence time and estimates signal-to-noise ratio (SNR) of source-to-relay, relay-to-destination, and source-to-destination links, to reliably choose between relay path or direct path for enhanced throughput and delay performances. Unique handshaking is used to estimate SNR and single bit feedbacks resolve contentions among relay nodes, which further provides source node with rate (based on SNR) information on source-to-destination, source-to-relay, and relay-to-destination links. Simulation results clearly show that IrcMAC significantly outperforms the existing CoopMACI and the UtdMAC protocols in wireless ad hoc network. Results show average throughput improvements of 41% and 64% and average delay improvementd of 98.5% and 99.7% compared with UtdMAC and CoopMACI, respectively.
An Examination of Variables Affecting the Social Behavior of Four and Five Year Old Pre-School Children
Neriman Aral,Aynur Butun Ayhan
The Social Sciences , 2013,
Abstract: This study reveals whether the social behavior of 4 and 5 year old pre-schoolers is affected by age, gender, number of siblings, time spent at school and mother s employment status. A total of 200, 4 and 5 year old children attending independent pre-schools affiliated to the Ministry of Education in Ankara city center were included in the study. Data about the children and families was gathered through the General Information Form prepared by the researchers. Children s social behavior scores were measured by using Behavior Ranking Scale. The results showed that age, gender and mother s employment status created a meaningful difference (p<0.05) in the cooperation and social relationships dimensions of 4 and 5 year olds social behavior scores.
A Comparative Study on the Visual Perceptions of Children with Attention Deficit Hyperactivity Disorder
Emine Ahmetoglu,Neriman Aral,Aynur Butun Ayhan
Journal of Applied Sciences , 2008,
Abstract: This study was conducted in order to (a) compare the visual perceptions of seven-year-old children diagnosed with attention deficit hyperactivity disorder with those of normally developing children of the same age and development level and (b) determine whether the visual perceptions of children with attention deficit hyperactivity disorder vary with respect to gender, having received preschool education and parents` educational level. A total of 60 children, 30 with attention deficit hyperactivity disorder and 30 with normal development, were assigned to the study. Data about children with attention deficit hyperactivity disorder and their families was collected by using a General Information Form and the visual perception of children was examined through the Frostig Developmental Test of Visual Perception. The Mann-Whitney U-test and Kruskal-Wallis variance analysis was used to determine whether there was a difference of between the visual perceptions of children with normal development and those diagnosed with attention deficit hyperactivity disorder and to discover whether the variables of gender, preschool education and parents` educational status affected the visual perceptions of children with attention deficit hyperactivity disorder. The results showed that there was a statistically meaningful difference between the visual perceptions of the two groups and that the visual perceptions of children with attention deficit hyperactivity disorder were affected meaningfully by gender, preschool education and parents` educational status.
Large-area, Lithography-Free Super Absorbers and Color Filters at Visible Frequencies Using Ultrathin Metallic Films
Zhongyang Li,Serkan Butun,Koray Aydin
Physics , 2014,
Abstract: Plasmonic materials and metamaterials have been widely utilized to achieve spectral transmission, reflection and absorption filters based on localized or delocalized resonances arising from the interaction of photons with nanostructured materials. Realization of visible-frequency, high-performance, large-area, optical filters based on nanoplasmonic materials is rather challenging due to nanofabrication related problems (cost, fabrication imperfection, surface roughness) and optical losses of metals. Here, we propose and demonstrate large-area perfect absorbers and transmission filters that overcome difficulties associated with the nanofabrication using a lithography-free approach. We also utilize and benefit from the optical losses in metals in our optical filter designs. Our resonant optical filter design is based on a modified, asymmetric metal-insulator-metal (MIM) based Fabry-Perot cavity with plasmonic, lossy ultra-thin (~30 nm) metallic films used as the top metallic layer. We demonstrated a narrow bandwidth (~17 nm) super absorber with 97% maximum absorption with a performance comparable to nanostructure/nanoparticle-based super absorbers. We also investigated transmission (color) filters using ultra-thin metallic films, in which different colors can be obtained by controlling the dielectric spacer thickness. With performance parameters of transmission peak intensity reaching 60% and a narrow-band of ~ 40 nm, our color filters exceed the performance of widely studied plasmonic nanohole array based color filters. Proposed asymmetric Fabry-Perot cavities using ultra-thin metallic films could find applications in spectrally selective optical (color and absorber) filters, optoelectronic devices with controlled bandwidth such as narrow-band photodetectors, and light-emitting devices.
Water Balance Analysis at Karangmumus River Basin Area (RBA) Samarinda City
Makara Seri Sains , 2009,
Abstract: Karangmumus RBA to getting degradation pressure being concrete drying and flooding so much to frighten. Climate data from BMG Temindung and SPAS Lempake has to water balance analysis based on Hewlett and Nutter methode. This region have the Area Class III (1500–2000 mm/year). With the bimodel or double wave rainfall models with C patern. The hight rainfall depth periode at December and April, therefore the low rainfall depth at September and November. Have level Q = ± 9.9%, or rainfall tipe A (very wet area with tropical wet vegetation) and E1 agroclimte zone. Water balance monthly indicated that this area have to water surplus 8 month, i.e. January (27.0 mm), February (57.3 mm), March (119.7 mm), April (72.8 mm), May (48.4 mm), Juni (19.6 mm), November (58.7 mm) and December (75.3 mm), or total amounts water surplus 478.8 mm/year. The water deficits at Juni (0.4 mm), July (0.3 mm), Augus (3.9 mm), September (13.6 mm) and October (26.7 mm) or total amount water deficits (44.5 mm/year).
Financial Risk Measurement for Turkish Insurance Companies Using VaR Models  [PDF]
Ismail Yildirim
Journal of Financial Risk Management (JFRM) , 2015, DOI: 10.4236/jfrm.2015.43013
Abstract: This study aims to measure the foreign exchange risks that the insurance companies are exposed to. In this context, this study analyzes 7 insurance companies listed in Borsa Istanbul (Istanbul Stock Exchange). The foreign exchange risks that the insurance companies are exposed to were measured using VaR models, Historical Simulation and Monte Carlo Simulation methods. Data obtained from the analysis show the losses that the insurance companies suffer due to exchange risk. The losses calculated using the Monte Carlo Simulation were found to be greater than the losses calculated using Historical Simulation.
A Very Rare Cause of Pleuritic Chest Pain: Bilateral Pleuritis as a First Sign of Familial Mediterranean Fever
Sevket Ozkaya,Saliha E. Butun,Serhat Findik,Atilla Atici
Case Reports in Pulmonology , 2013, DOI: 10.1155/2013/315751
Visible-frequency metasurfaces for broadband anomalous reflection and high-efficiency spectrum splitting
Zhongyang Li,Edgar Palacios,Serkan Butun,Koray Aydin
Physics , 2014,
Abstract: Ultrathin metasurfaces have recently emerged as promising materials to enable novel, flat optical components and surface-confined, miniature photonic devices. However, experimental realization of high-performance metasurfaces at visible frequencies has been a significant challenge due to high plasmonic losses and difficulties in high-uniformity nanofabrication. Here, we propose a highly-efficient yet simple metasurface design comprising of single gradient antenna as unit cell. We demonstrate visible broadband (450 - 850 nm) anomalous reflection and spectrum splitting with 85% conversion efficiency. Average power ratio of anomalous reflection to the strongest diffraction was calculated to be ~ 103 and measured to be ~ 10. The anomalous reflected photons and spectrum splitting performance have been visualized using CCD and characterized using angle-resolved measurement setup. Metasurface design proposed here is a clear departure from conventional metasurfaces utilizing multiple, anisotropic resonators, and could enable high-efficiency, broadband metasurfaces for achieving directional emitters, polarization/spectrum splitting surfaces for spectroscopy and photovoltaics.
Omnidirectional and broadband absorption enhancement from trapezoidal Mie resonators in semiconductor metasurfaces
Ragip A. Pala,Serkan Butun,Koray Aydin,Harry A. Atwater
Physics , 2015,
Abstract: Light trapping in planar ultrathin-film solar cells is limited due to a small number of optical modes available in the thin-film slab. A nanostructured thin-film design could surpass this limit by providing broadband increase in the local density of states in a subwavelength volume and maintaining efficient coupling of light. Here we report a broadband metasurface design, enabling efficient and broadband absorption enhancement by direct coupling of incoming light to resonant modes of subwavelength-scale Mie nanoresonators defined in the thin-film active layer. Absorption was investigated both theoretically and experimentally in prototypes consisting of lithographically patterned, two-dimensional periodic arrays of silicon nanoresonators on silica substrates. A crossed trapezoid resonator shape of rectangular cross section is used to excite broadband Mie resonances across the visible and near-IR spectra. Our numerical simulations, optical absorption measurements and photocurrent spectral response measurements demonstrate that crossed trapezoidal Mie resonant structures enable angle-insensitive, broadband absorption. A short circuit current density of 12.0 mA/cm2 is achieved in 210 nm thick patterned Si films, yielding a 4-fold increase compared to planar films of the same thickness. It is suggested that silicon metasurfaces with Mie resonator arrays can provide useful insights to guide future ultrathin-film solar cell designs incorporating nanostructured thin active layers.
Hydromorphological Mapping and Analysis for Characterizing Darfur Paleolake, NW Sudan Using Remote Sensing and GIS  [PDF]
Samy Ismail Elmahdy
International Journal of Geosciences (IJG) , 2012, DOI: 10.4236/ijg.2012.31004
Abstract: The north-western part of Sudan, which is the driest region on earth has revealed newly surface and near surface paleodrainage network underneath sand sheets indicating the possibilities for economic groundwater reservoirs. Advanced Space-born Thermal Radiometer (ASTER), the Shuttle Radar Topography Mission (SRTM ~90 m) DEMs and Quickbird images corroborate the presence of surface and near surface paleodrainage network. Bivariate quadratic surfaces with moving window size of 3 × 3 were fitted to the SRTM DEM. The second derivative surface curvature was calculated to reveal landform classes that may receive most of fossil water. The results showed that the new unnamed depression which recharges by a longitudinal paleodrainage network may receive vast amount of groundwater during humid phases. The results demonstrate that the D8 and curvature algorithms are very efficient tools for revealing and characterizing hydrological elements in arid and semi-arid regions and they provide information for hydrological exploration in remote deserts over large scale prior to geophysical survey.
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