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Citation Count: 970
Electrospinning of polyurethane fibers
(Elsevier BV, 2002) Demir M.M.; Yilgor I.; Yilgor E.; Erman, B.
A segmented polyurethaneurea based on poly(tetramethylene oxide)glycol, a cycloaliphatic diisocyanate and an unsymmetrical diamine were prepared. Urea content of the copolymer was 35 wt%. Electrospinning behavior of this elastomeric polyurethaneurea copolymer in solution was studied. The effects of electrical field, temperature, conductivity and viscosity of the solution on the electrospinning process and morphology and property of the fibers obtained were investigated. Results of observations made by optical microscope, atomic force microscope and scanning electron microscope were interpreted and compared with literature data available on the electrospinning behavior of other polymeric systems. © 2002 Elsevier Science Ltd. All rights reserved.
Citation Count: 2
Dimensions of polystyrene particles deposited on mica from dilute cyclohexane solution at different temperatures
(2002) Demir M.M.; Erman, B.
Using atomic force microscopy, the height, diameter, and volume of polystyrene particles deposited on mica from dilute cyclohexane solution at different temperatures are determined. Dimensions exhibit a strong temperature dependence. The heights of the deposited particles are only a few atomic diameters, the major dimension being parallel to the mica surface. The number of single polystyrene molecules in a deposited particle cannot be determined directly by atomic force microscopy. However, the maximum number of molecules that may be present in a particle may be estimated. Below 35 °C, the particles possibly consist of single collapsed molecules. This number increases with temperature and becomes as large as about 30 molecules per particle at 80 °C. The volume occupied by a single chain in solvent is calculated as a function of temperature and compared with observed volumes of dry particles on mica. A linear relationship is observed between single chain volumes in solvent and corresponding particle volumes on mica. On the average, the volume of a single chain in solution is 10 times the volume of a dry particle at the corresponding temperature. Fluctuations of chain volumes that are dominant in solution are also present in the volumes of particles deposited and dried on mica.
Citation Count: 1
Polyurethane nanofiber webs for sensor and actuator applications in MicroElectroMechanical Systems (MEMS)
(Materials Research Society, 2003) Demir M.M.; Naseer M.; Bechteler T.F.; Gurbuz Y.; Menceloglu, Y.Z.
Sensor application of Polyurethane Nanofiber Webs (PNW) has been explored in this study. PNW were prepared by electrospinning of the polyurethane solution in dimethylformamide. Silver nanoparticles with a size of 60 nm on PNW were produced by precipitation of AgNO3 in alkaline media. A micromachined capacitive pressure sensor has been designed using a special elastic and conducting thin membrane (PNW) as an active electrode sensing the pressure. With an additional inductor and a metal-semiconductor field effect transistor (MESFET), a microwave oscillator has also been designed as part of the system. The capacity variation due to changing pressure results in a frequency shift of this oscillator. This frequency shift is measured and corresponds to the pressure. The simulations performed on this structure show a very good linearity over a wide range of applied pressure which could be detected by change in oscillator frequency. These results indicate that an implementation of PNW as an active material in capacitative sensing applications of MicroElectroMechanical Systems (MEMS) could be feasible.
Citation Count: 285
Palladium Nanoparticles by Electrospinning from Poly(acrylonitrile-co-acrylic acid)-PdCl2 Solutions. Relations between Preparation Conditions, Particle Size, and Catalytic Activity
(2004) Demir M.M.; Gulgun M.A.; Menceloglu Y.Z.; Erman B.; Abramchuk S.S.; Makhaeva E.E.; Khokhlov A.R.; Matveeva V.G.; Sulman, M.G.
Catalytic palladium (Pd) nanoparticles on electrospun copolymers of acrylonitrile and acrylic acid (PAN-AA) mats were produced via reduction of PdCl2 with hydrazine. Fiber mats were electrospun from homogeneous solutions of PAN-AA and PdCl2 in dimethylformamide (DMF). Pd cations were reduced to Pd metals when fiber mats were treated in an aqueous hydrazine solution at room temperature. Pd atoms nucleate and form small crystallites whose sizes were estimated from the peak broadening of X-ray diffraction peaks. Two to four crystallites adhere together and form agglomerates. Agglomerate sizes and fiber diameters were determined by scanning and transmission electron microscopy. Spherical Pd nanoparticles were dispersed homogeneously on the electrospun nanofibers, The effects of copolymer composition and amount of PdCl2 on particle size were investigated. Pd particle size mainly depends on the amount of acrylic acid functional groups and PdCl2 concentration in the spinning solution. Increasing acrylic acid concentration on polymer chains leads to larger Pd nanoparticles. In addition, Pd particle size becomes larger with increasing PdCl2 concentration in the spinning solution. Hence, it is possible to tune the number density and the size of metal nanoparticles. The catalytic activity of the Pd nanoparticles in electrospun mats was determined by selective hydrogenation of dehydrolinalool (3,7-dimethyloct-6-ene-l-yne-3-ol, DHL) in toluene at 90°C. Electrospun fibers with Pd particles have 4.5 times higher catalytic activity than the current PoVAl2O3 catalyst.
Citation Count: 25
On some lizard species of the Western Taurus Range
(2004) Kumlutaş,Y.; Öz,M.; Durmuş,H.; Tunç,M.R.; Özdemir,A.; Düşen,S.
A total of 282 specimens belonging to 13 lizard species from the Western Taurus Range were investigated. Morphological and biological data as well as missing pieces of information about the species were sought to be completed with the addition of a large number of new localities. Moreover, the data obtained were compared with those in the relevant literature in an attempt to shed light on the taxonomical status of the species. © TÜBITAK.
Citation Count: 5
First record of eumeces schneiderii (Daudin, 1802) (Sauria: Scincidae) from Western Anatolia
(2004) Kumlutaş,Y.; Kaska,Y.; Ilgaz,Ç.; Böhme,W.
[No abstract available]
Citation Count: 16
On snake species of the Western Taurus range, Turkey
(Croatian Natural History Museum, 2004) Kumlutas,Y.; Öz,M.; Tunç,M.R.; Kaska,Y.; Özdemir,A.; Düsen,S.
A total of 85 specimens belonging to 14 snake species collected from the Western Taurus Mountain Range were examined in this study. Along with morphological information about the species, the study contains some topographical observations concerning the localities. The collection of material from a number of new localities helped efforts to complete missing information related to the distribution of species in this region. Moreover, the data obtained were compared with those contained in the relevant literature with the purpose of shedding light on the taxonomical status of the species.
Citation Count: 8
The case of a cyst hydatid localized within the interatrial septum
(2004) Karabay,Ö.; Önen,A.; Yildiz,F.; Yilmaz,E.; Erdal,A.C.; Şanli,A.; Açikel,Ü.
The ratio of cardiac involvement of Echinoccocus granulosus is 0.02-2% and although seen rarely, involvement of the interatrial septum has also been reported in the published literature. The present case was a 19-year-old male university student admitted to hospital with complaints of headache and dizziness. Computerized tomography of the cranium revealed a cystic mass located at the frontal region and enucleation of the cyst was performed during surgery. A cystic lesion 5 × 4 cm in size was detected within the interatrial septum on two-dimensional transthoracic echocardiography during the postoperative period and the patient was referred to our clinic. Open heart surgery was performed and a hydatid cyst that involved the interatrial septum was enucleated. The cyst wall was sutured to the interatrial septum. No complications developed during the postoperative period. The patient was discharged on the fifth day of hospitalization and medical therapy was started with albendazole. Copyright © 2004 by the Japanese Heart Journal.
Citation Count: 11
The amphibian and reptile species of Bozdaǧ (Ödemiş)
(2004) Kumlutaş,Y.; Özdemir,A.; Ilgaz,Ç.; Tosunoǧlu,M.
The herpetofauna of Bozdaǧ in western Anatolia was investigated. In the study area, 152 samples belonging to 22 species from 14 amphibian and reptile families were described. One of these species is an urodelan, 5 are anurans, 1 is a tortoise, 10 are lizards and 5 are snakes. A specimen of Eumeces schneideri was found at Bozdaǧ for the first time. © TÜBİTAK.
Citation Count: 13
Probing Nanoscale Domains of J-Aggregates Deposited on a Mica Surface
(American Chemical Society, 2004) Özçelik S.; Demir M.M.; Birkan, B.
J-aggregates of 1,1′,3,3′-tetraethyl-5,5′,6,6′- tetrachlorobenzimidazolocarbocyanine (TTBC) were deposited on a mica surface and probed by atomic force microscopy operated at tapping mode in air. Optical spectra showed that J-aggregates were formed in aqueous solutions. Atomic force microscopy images revealed that J-aggregates deposited on mica surfaces mainly present single domains with a mean height of 2.00 ± 0.25 nm and an average diameter of 100 ± 20 nm. Quantitative analysis of the morphology of images indicated that the single domain of J-aggregates exhibits very uniform height and diameter distributions with polydispersity indices of 1.02 and 1.04, respectively. Based on the results, we propose a two-dimensional nanostructure in which TTBC J-aggregates could be arranged in a monolayer.
Citation Count: 46
Effect of filler amount on thermoelastic properties of poly(dimethylsiloxane) networks
(Elsevier BV, 2005) Demir M.M.; Menceloglu Y.Z.; Erman, B.
End-linked poly(dimethylsiloxane) (PDMS) networks were prepared in the presence of fumed silica particles with hydroxyl groups at their surfaces. The silica particles were introduced into the polymer solution prior to end-linking. Hydroxyl ended PDMS chains were end-linked via the tetra functional crosslinker, tetraethoxysilane. The filler content varied in the range 0-5 wt%. Atomic Force Microscopy was used to image and characterize the silica particles. Swelling, stress-strain and thermoelasticity experiments were performed. The temperature coefficient and the energetic part of the force in uniaxial extension are found to increase with increasing silica amount. This observation is ascribed to effects contributed possibly by the adsorption layer around the silica particles. © 2005 Elsevier Ltd. All rights reserved.
Citation Count: 1
Feedback control static scheduling for real-time distributed embedded systems
(2005) Ayav, T.; Sorel, Y.; Ayav, Tolga; Bilgisayar Mühendisliği Bölümü
This paper presents an implementation of feedback control strategy on distributed static scheduling. The static schedule is created taking into account the average execution times of the tasks. Feedback control algorithm handles the unestimated dynamic behaviors in the system and keeps the performance at a desired level. The approach of feedback control supporting static scheduling yields more flexible scheduling, low scheduling overhead and better resource utilization while preserving the realtime constraints. © 2005 IEEE.
Optimal control for real-time feedback rate-monotonic schedulers
(2005) Ayav, T.; Ferrari-Trecate, G.; Ayav, Tolga; Bilgisayar Mühendisliği Bölümü
This paper presents an optimal control scheme for a real-time feedback control rate-monotonie scheduling (FC-RMS) system. We consider two-version tasks composed of a mandatory and an optional part to be scheduled according to the FC-RMS. In FC-RMS, the controller provides a feedback strategy for deciding about the execution or rejection of the optional sub-tasks. By modeling the task execution times as random variables, we first find the statistical model of FC-RMS and then we design a pure optimal controller and an optimal controller with feedforward integral compensation. The comparison of these two schemes with common Proportional-Integral-Derivative (PID) controller highlights the benefit of the optimal scheme with integral compensation. The results are demonstrated through the real implementation of FC-RMS on RT-Linux. © Springer-Verlag Berlin Heidelberg 2005.
Citation Count: 178
PMMA/zinc oxide nanocomposites prepared by in-situ bulk polymerization
(2006) Demir M.M.; Memesa M.; Castignolles P.; Wegner, G.
Dispersing surface-modified zinc oxide nano-particles (ZnO) in methyl methacrylate (MMA) improves the free radical bulk polymerization process as well as the thermal stability of the formed polymer. Hydroxy groups available on the ZnO surface may induce a degenerative transfer. This suppresses the gel effect, which leads to a better control of the heat evolution during the late stages of polymerization. The formation of chains having vinylidene end groups and head-to-head links is suppressed, which shifts the onset of thermal decomposition to the regime where decomposition occurs by random chain scission. © 2006 WILEY-VCH Verlag GmbH & co. KGaA.
Citation Count: 15
Aggregation of fillers blended into random elastomeric networks: Theory and comparison with experiments
(2006) Demir M.M.; Menceloglu Y.Z.; Erman, B.
A theoretical model describing aggregation of filler particles in amorphous elastomers is proposed. The model is based on a counting technique originally used in genome analysis to characterize the size and distribution of overlapping segments randomly placed on a DNA molecule. In the present model, the particles are first assumed to aggregate randomly upon mixing into the elastomer and then-sizes are calculated. The sizes and distributions of aggregates are also studied in the presence of attractive interparticle forces. Results of the proposed model are compared with experimental data on silica-filled end-linked poly(dimethyl-siloxane) networks. Comparison of the theory and experiment shows that the random aggregation assumption where no attractive forces exist between the particles is not valid and a significant attraction between the silica particles is needed in the theory to justify the experimental data obtained using atomic force microscopy. For filler content below 1.45 vol.-%, the model agrees, qualitatively, with experiment and shows the increase in cluster size with increasing amount of filler. It also explains the increase in the dispersion of aggregate sizes with increasing amount of filler. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.
Citation Count: 6
End-to-end security implementation for mobile devices using TLS protocol
(Springer France, 2006) Kayayurt, Baris; Tuglular, Tugkan; Tuğlular, Tuğkan; Bilgisayar Mühendisliği Bölümü
End-to-end security has been an emerging need for mobile devices with the widespread use of personal digital assistants and mobile phones. Transport Layer Security Protocol (TLS) is an end-to-end security protocol that is commonly used on the Internet, together with its predecessor, SSL protocol. By implementing TLS protocol in the mobile world, the advantage of the proven security model of this protocol can be utilized. The main design goals of mobile end-to-end security protocol are maintainability and extensibility. Cryptographic operations are performed with a free library, Bouncy Castle Cryptography Package. The object oriented architecture of proposed end-to-end security protocol implementation makes the replacement of this library with another cryptography package easier. The implementation has been experimented with different cases, which represent use of different cryptographic algorithms.
Citation Count: 89
Precipitation of monodisperse ZnO nanocrystals via acid-catalyzed esterification of zinc acetate
(2006) Demir M.M.; Muñoz-Espí R.; Lieberwirth I.; Wegner, G.
A wet-chemical method to produce zinc oxide nanocrystals of monodisperse size distribution (diameter range of 20-80 nm) is presented. The synthesis starts from zinc acetate dihydrate which is converted to ZnO in the presence of 1-pentanol in m-xylene at 130 °C. We report for the first time catalysis of this reaction by p-toluene sulfonic acid monohydrate (p-TSA), which allows a shorter reaction time and improves both the reproducibility of the particle size distribution and the crystallinity of the particles. The reaction can be scaled up to give multigram quantities of product per batch. Particles were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and photoluminesence (PL) spectroscopy. Room temperature PL spectra of ZnO prepared without catalyst exhibit a strong and sharp UV emission band at ca. 385 nm and a weak and very broad green-yellow visible emission centered at ca. 550-560 nm. However, for nanoparticles precipitated in the presence of p-TSA, the UV emission is enhanced by a factor of 4, which can be correlated with the improvement of crystal perfection. A particle formation mechanism is discussed. © The Royal Society of Chemistry 2006.
Citation Count: 186
Optical properties of composites of PMMA and surface-modified zincite nanoparticles
(2007) Demir M.M.; Koynov K.; Akbey Ü.; Bubeck C.; Park I.; Lieberwirth I.; Wegner, G.
Composites that show visible light transmittance, UV absorption, and moderately high refractive index, based on poly(methyl methacrylate) (PMMA) and zinc oxide (zincite, ZnO) nanoparticles, were prepared in two steps. First, surface-modified ZnO nanoparticles with 22 nm average diameter were nucleated by controlled precipitation via acid-catalyzed esterification of zinc acetate dihydrate with pentan-1-ol. The surface of growing crystalline particles was modified with tert-butylphosphonic acid (tBuPO3H2) in situ by monolayer coverage. Particle size and graft density of -PO3H 2 on the particle surface were controlled by the amount of surfactant applied to the reaction solution. Second, the surface-modified particles were incorporated into PMMA by in-situ bulk polymerization. Free radical polymerization was carried out in the presence of these particles using AIBN as initiator. Volume fraction (0) of the particles was varied from 0.10 to 7.76% (0.5 to 30 wt %). Although the particles are homogeneously dispersed in monomer, segregation of the individual particles upon polymerization was observed. Optical constants of the films ca. 2.0 μm including absorption and scattering efficiencies, indices of refraction, and dispersion constants were determined. The absorption coefficient at 350 nm increases linearly with ZnO, obeying Beer's law at low particle contents. However, it levels off toward a value of about 5000 cm-1 and shows a negative deviation at high concentrations because of aggregation of the individual particles. Waveguide propagation loss coefficients of the composite films were examined by prism coupling. A steep increase of the loss coefficient was found with a slope of 52 dB cm-1 vol %-1 as the volume fraction of the particle increases. The refractive index of the composites depends linearly on volume fraction of ZnO and varies from 1.487 to 1.507 (φ = 7.76%) at 633 nm. The dispersion of refractive index was found to be consistent with Cauchy's formula. © 2007 American Chemical Society.
Citation Count: 27
No association of interleukin-6 gene polymorphism (-174 G/C) with premature coronary artery disease in a Turkish cohort
(2007) Sekuri,C.; Cam,F.S.; Sagcan,A.; Ercan,E.; Tengiz,I.; Alioglu,E.; Berdeli,A.
OBJECTIVES: Interleukin-6 (IL-6) may contribute to the inflammatory response by activating endothelial cells and stimulating the synthesis of fibrinogen. It might thus be important in the pathogenesis of inflammation associated with coronary artery disease (CAD). Several studies suggested that the -174 C allele was associated with an increased prevalence of coronary heart disease. The aim of this study was to investigate further the association of the IL-6 -174 G/C allele status with premature CAD. METHODS: A total of 120 patients and 105 controls were included in the study. The IL-6 -174 G/C polymorphism was genotyped using PCR-restriction fragment length polymorphism. RESULTS: The genotype distribution of the -174 G/C polymorphism was not different in premature CAD patients (GG: 53%; GC: 42.6%; CC: 4.3%) and controls (GG: 54.3%; GC: 39%; CC: 6.7%) (P=0.72). The prevalence of the C allele was 25.6% in patients and 26.1% in controls. By multiple regression analysis, family history, smoking, diabetes, and hypertension were independent risk factors of premature CAD, but not IL-6 genotype. CONCLUSIONS: We conclude that the IL-6 -174 G/C polymorphism is not associated with the risk of premature CAD, and does not contribute to cardiovascular risk stratification. © 2007 Lippincott Williams & Wilkins, Inc.
Citation Count: 12
A new subspecies, Eumeces schneiderii barani n. ssp (Reptilia: Sauria: Scincidae) from Turkey
(Magnolia Press, 2007) Kumlutaş,Y.; Arikan,H.; Ilgaz,Ç.; Kaska,Y.
This study describes a new subspecies of lizard, Eumeces schneiderii barani n. ssp., from western Anatolia, Turkey. The new subspecies is differentiated from other two subspecies in Anatolia (E. s. princeps and E. s. pavimentatus) by its characteristic colour and colour-pattern as well as by the scales along the dorsal midline. Results obtained from polyacrylamide gel disc electrophoresis support this differentiation. Copyright © 2007 · Magnolia Press.

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