10 sonuçlar
Arama Sonuçları
Listeleniyor 1 - 10 / 10
Yayın Synthesis and liquid crystalline behavior of random copolymer of poly(ethylene oxide) macromonomer and liquid crystalline monomer by the photon transmission technique(Taylor & Francis Inc, 2005-12) Yıldız, Sevtap; Yılmaz, Faruk; Özbek, Haluk; Pekcan, Mehmet Önder; Ito, Koichi; Yağcı, YusufRandom copolymers of poly(ethylene oxide) macromonomer with p-vinylbenzyl end-functional group (PEOVB) and liquid crystalline monomer, namely 6-(4-cyanobiphenyl-4'-oxy)hexyl acrylate (COA), were prepared by conventional free radical polymerization. A living anionic polymerization technique was employed for the synthesis of PEO macromonomers bearing p-vinylbenzyl moiety at one end. The photon transmission method was also applied to study the phase transitions of COA monomer and its random copolymer with PEO. It was found that, for both samples, the nematic-smectic A transition is continuous, but the critical fluctuation regions do not allow to obtain 3D XY values. Instead, we have obtained the values close to mean field regime. Scaling of thermal hystersis for random copolymer sample near the nematic-isotropic transition was studied as well. Thermal hysteresis loops were produced under linearly varying temperature. It was shown that the areas of the hysteresis loops scale with the temperature scanning rate with an exponent being equal to 0.614 which is in good agreement with the field-theoretical value.Yayın Development of externalizing behaviors in the context of family and non-family relationships(Springer New York, 2016-02-04) Akçinar Yayla, Berna; Baydar, NazlıA longitudinal model was presented, that included reciprocal associations between physically harsh parenting by the mother, child externalizing problems, and support from the father, the extended family, and the neighbors. This transactional process was estimated for the years preceding school entry. The data were from a 4-years longitudinal and nationally representative study of 1009 children and their mothers in Turkey. The results indicated that concurrently, physically harsh parenting and child externalizing problems were strongly associated. Controlling for their within domain stability and cross-domain concurrent correlation, changes in harsh parenting and changes in child externalizing behaviors had significant reciprocal effects in early childhood, although these effects were small. These reciprocal effects were smaller for observer reported harsh parenting than maternal reports. There was a role of the mesosystem in this developmental process. Increases in the support from the father, and the extended family and the neighbors predicted declines in the child externalizing behaviors subsequently. Reciprocally, high child externalizing and maternal physically harsh parenting predicted subsequent declines in the support from these sources. These results were consistent with the hypotheses that negative mother–child relationships could spill over to the other relationships of the mothers, and that positive and supportive relationships of the mother could constitute positive role models for the child.Yayın Small molecule diffusion into swelling Iota-Carrageenan gels: A fluorescence study(Taylor & Francis Group, 2007-04) Ataman, Evren; Pekcan, Mehmet ÖnderSmall molecule diffusion into Iota-Carrageenan gel was studied by using steady-state fluorescence (SSF) technique. Pyranine, dissolved in water was used as fluorescence probe. Fluorescence emission intensity, I-p, and scattered light intensity, I-sc, were monitored to study diffusion and swelling processes at various temperatures respectively. Fickian and Li-Tanaka models were elaborated to produce diffusion, D, and collective diffusion, D-0, coefficients. Diffusion and swelling activation energies were also obtained and found to be 20.5 kj mol(-1) and 28.2 kj mol(-1). respectively.Yayın Progressive damage analyses of masonry buildings by dynamic analyses(Springer International Publishing AG, 2020-08) Aras, Fuat; Akbaş, Tolga; Ekşi, Hızır; Çeribaşı, SeyitThis study investigates the effects of prescribed damage on the walls of masonry buildings by experimental and numerical methods. Ambient vibration survey method was applied to an existing, two-story, unreinforced masonry building to determine its dynamic characteristics, such as mode shapes and natural frequencies. Then, the walls on two exterior sides of the building were demolished, and dynamic testing was repeated for the damaged building. As the next step, the amount of damage on the building was increased by more impacts, and the dynamic characteristics of the heavily damaged building were identified. The results obtained from the undamaged, damaged and heavily damaged building were compared, and the damage effect on the natural frequencies of the building was noted. Besides, finite element analyses of the undamaged, damaged and heavily damaged buildings were performed. It was found that, the numerical models, constructed with code-based material properties, do not sufficiently represent the dynamic behavior of masonry buildings. Secondly, as the result of the sustained damage, while the experimental and the numerical modal analyses revealed the decrease in the dominant frequencies of the building, the difference between them increases with the severity of the damage. With the framework presented in this study, the behavior of masonry buildings can better be determined and used for analysis purposes.Yayın Numerical calculations of relativistic electron drift loss effect(Amer Geophysical Union, 2008-09-09) Kim, Kyung Chan; Lee, Daeyoung; Kim, Heejeong; Lyons, Larry R.; Lee, Ensang; Öztürk, Mehmet Kaan; Choi, CheongrimIt has been suggested that drift loss to the magnetopause can be one of the major loss mechanisms contributing to relativistic electron flux dropouts. In this study, we examine details of relativistic electrons' drift physics to determine the extent to which the drift loss through the magnetopause is important to the total loss of the outer radiation belt. We have numerically computed drift paths of relativistic electrons' guiding center for various pitch angles, various measurement positions, and different solar wind conditions using the Tsyganenko T02 model. We specifically demonstrate how the drift loss effect depends on these various parameters. Most importantly, we present various estimates of relative changes of the omnidirectional flux of 1 MeV electrons between two different solar wind conditions based on a simple form of the directional flux function. For a change of the dynamic pressure from 4 nPa to 10 nPa with a fixed IMF B-Z = 0 nT, our estimate indicates that after this increase in pressure, the equatorial omnidirectional flux at midnight near geosynchronous altitude decreases by similar to 56 to similar to 97%, depending on the specific pitch angle dependence of the directional flux. The effect rapidly decreases at regions earthward of geosynchronous orbit and shows a general trend of decrease away from midnight. For a change of the IMF BZ from 0 nT to -15 nT with a fixed dynamic pressure of 4 nPa, the relative decrease of the omnidirectional flux at geosynchronous altitude on the nightside is much smaller than that for the pressure increase, but its effect becomes substantial only beyond geosynchronous orbit. Possibilities exist that our results may change to some extent for a different magnetospheric model than the one used here.Yayın Projected changes in extreme temperature and precipitation indices over CORDEX-MENA domain(MDPI AG, 2021-05) Öztürk, Tuğba; Saygılı Aracı, Fatma Sibel; Kurnaz, Mehmet LeventIn this study, projected changes in climate extreme indices defined by the Expert Team on Climate Change Detection and Indices were investigated over Middle East and North Africa. Changes in the daily maximum and minimum temperature-and precipitation-based extreme indices were analyzed for the end of the 21st century compared to the reference period 1971–2000 using regional climate model simulations. Regional climate model, RegCM4.4 was used to downscale two different global climate model outputs to 50 km resolution under RCP4.5 and RCP8.5 scenarios. Results generally indicate an intensification of temperature-and precipitation-based extreme indices with increasing radiative forcing. In particular, an increase in annual minimum of daily minimum temperatures is more pronounced over the northern part of Mediterranean Basin and tropics. High increase in warm nights and warm spell duration all over the region with a pronounced increase in tropics are projected for the period of 2071–2100 together with decrease or no change in cold extremes. According to the results, a decrease in total wet-day precipitation and increase in dry spells are expected for the end of the century.Yayın Phase transitions of kappa-carrageenan gels in various types of salts(John Wiley & Sons Inc, 2006-11-05) Kara, Selim; Arda, Ertan; Kavzak, Burhan; Pekcan, Mehmet ÖnderSol-gel and gel-sol phase transitions of K-carrageenan in various types of salts were studied using photon transmission technique. Here, LiCl, NaCl, KCl, MgCl2, CaCl2, and SrCl2 were chosen as the proper salts for the K-carrageenan-water system. Photon transmission intensity, I-tr was monitored against temperature to determine the sol-gel and gel-sol temperatures (T-sg and T-gs) and activation energies (Delta E-sg and Delta E-gs). It was observed that T-gs temperatures were notably higher than T-sg due to the hysteresis on the phase transition loops. It was observed that stronger carrageenan gels are formed in the presence of KCl compared to the others.Yayın Impact of climate change on natural snow reliability, snowmaking capacities, and wind conditions of ski Resorts in Northeast Turkey: a dynamical downscaling approach(Mdpi Ag, 2016-04) Demiroğlu, Osman Cenk; Turp, Mustafa Tufan; Öztürk, Tuğba; Kurnaz, Mehmet LeventMany ski resorts worldwide are going through deteriorating snow cover conditions due to anthropogenic warming trends. As the natural and the artificially supported, i.e., technical, snow reliability of ski resorts diminish, the industry approaches a deadlock. For this reason, impact assessment studies have become vital for understanding vulnerability of ski tourism. This study considers three resorts at one of the rapidly emerging ski destinations, Northeast Turkey, for snow reliability analyses. Initially one global circulation model is dynamically downscaled by using the regional climate model RegCM4.4 for 1971-2000 and 2021-2050 periods along the RCP4.5 greenhouse gas concentration pathway. Next, the projected climate outputs are converted into indicators of natural snow reliability, snowmaking capacity, and wind conditions. The results show an overall decline in the frequencies of naturally snow reliable days and snowmaking capacities between the two periods. Despite the decrease, only the lower altitudes of one ski resort would face the risk of losing natural snow reliability and snowmaking could still compensate for forming the base layer before the critical New Year's week. On the other hand, adverse high wind conditions improve as to reduce the number of lift closure days at all resorts. Overall, this particular region seems to be relatively resilient against climate change.Yayın Calculation of the T-X phase diagram for a mixture of liquid crystals(Pergamon-Elsevier Science, 2000-12) Yurtseven, Hasan Hamit; Enginer, Yücel; Salihoğlu, SelamiIn this study we calculate the T-X phase diagram for a mixture of liquid crystals. In this calculation we use a mean field theory We fit our calculated phase line equations to the experimental data from the literature. There is a very good agreement between our calculated and the experimentally observed phase diagram.Yayın Universality of sol-gel phase transition of kappa-carrageenan in various salts: a steady state fluorescence study(Taylor & Francis Ltd, 2007-08) Pekcan, Mehmet Önder; Tarı İlgin, ÖzlemThermal phase transitions of kappa-carrageenan in NaCl, KCl and CaCl2 solutions were studied using steady state fluorescence (SSF) technique. Pyranine was introduced as a fluorescence probe for studying sol-gel phase transitions. Scattered light, I-sc and fluorescence intensity, I was monitored against temperature to determine the sol-gel (T-sg) phase transition temperatures. It was observed that T-sg values are strongly correlated to NaCl, KCl and CaCl2 contents. The weight average degree of polymerization, DPw, and gel fraction G, exponents (gamma and beta) were measured and found to be in accord with the classical Flory-Stockmayer model, i.e., gamma and beta were found to be close to 1.0, independent of salt content.
