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Yayın Temperature effect on drying and swelling of kappa carrageenan gels: A steady state fluorescence study(Wiley-V C H Verlag GMBH, 2008) Tarı İlgin, Özlem; Pekcan, Mehmet ÖnderA novel technique based on in situ steady state fluorescence (SSF) measurements is introduced for studying drying and swelling Of kappa(-) carrageenan (kappa carrageenan) gels at various temperatures. kappa(-) carrageenan gels were completely dried and then swelled in water vapor. Pyranine was embedded in kappa(-) carrageenan and used as a fluorescence probe. Scattered light intensities, I-SC and fluorescence intensities, I were monitored during the drying and swelling Of kappa(-) carrageenan gels. it was observed that the fluorescence intensity decreased linearly as drying time was increased. A simple model consisting of Case II diffusion was used to quantify the drying processes of the kappa(-) carrageenan gels. This moving boundary model provided packing constant, kappa(o). During swelling, fluorescence intensity increased exponentially as time is increased. The increase in I, was modeled using Li-Tanaka equation from which swelling time constants, tau(c) and cooperative diffusion coefficients, D-c were determined. It was observed that swelling time constants, tau(c) decreased and diffusion coefficients, D-c increased as the swelling temperature was increased. Activation energies for drying and swelling were also obtained and found to be 53.9 and 47.2 kJ mol(-1), respectively.Yayın In situ fluorescence study of swelling, sorption and desorption processes in and out of PAAm gels(Wiley-V C H Verlag GMBH, 2008-05) Evingür, Gülşen Akın; Karslı, Kadir; Pekcan, Mehmet ÖnderSmall molecule sorption and desorption in and out of polyacrylamide (PAAm) gels were studied at various temperatures. Pyranine (P(y)) dissolved in water used as a probe. Fluorescence emission intensity, I(p) from P(y) was monitored for studying sorption and desorption processes. Scattered light intensities, I(SC) from PAAm gel was also monitored to observed structural variations during sorption and desorption process. Li-Tanaka model was applied to produce the swelling time constants, tau(C) and sorption coefficients, D(C) for the swelling processes. on the other hand, sorption and desorption processes were studied and coefficients were produced by using Fickian model. Related activation energies were also calculated from the corresponding physical processes.Yayın Investigation of OSL signals from very deep traps in unfired and fired quartz samples(Elsevier Science BV, 2010-03-15) Kitis, George; Güneç Kıyak, Nafiye; Polymeris, George S.; Pagonis, VasilisThis paper presents an attempt to isolate experimentally optically stimulated luminescence (OSL) signals which may originate from very deep traps (VDT) in quartz samples. As VDT we consider those traps which are responsible for TL glow peaks with a peak maximum temperature above a TL readout temperature of 500 C. The basic experimental procedure used to isolate OSL signals from VDT is heating the quartz samples to 500 C immediately before measuring the OSL signal. The study was carried out on eight quartz samples of very different origins; it is found that all eight samples exhibit OSL signals from VDT, and for a wide region of OSL stimulation temperatures. The OSL signal from VDT depends strongly on the type of quartz sample studied and on whether the sample was fired at high temperatures or not. The behavior of the OSL signal from VDT as a function of the stimulation temperature is found to be very different in fired and unfired samples. The thermal activation energy E for the OSL signals from VDT is obtained in both fired and unfired samples. The OSL signal from VDT in quartz samples fired at 800 C for 1 h is very high, and the OSL curves consist of three well-defined components and a fourth slow component which is rather poorly resolved. The dose response of these components is obtained using a computerized deconvolution procedure for the dose region 0.5-300 Gy. The results are of importance for dating of ancient fired ceramics, since OSL signals from VDT could potentially extend appreciably the equivalent dose region toward both lower and higher values.Yayın Tectonic and climatic controls on Quaternary fluvial processes and river terrace formation in a Mediterranean setting, the Goksu River, southern Turkey(Cambridge University Press, 2019-03) Avşin Görendağlı, Nurcan; Vandenberghe, Jef; Van Balen, Ronald; Güneç Kıyak, Nafiye; Öztürk, TuğbaClimate and tectonics effect the fluvial evolution of the Mediterranean Mut basin. The basin contains a river terrace staircase of 16 levels (T16-T1) ranging from 365 to 10m above the current Goksu River in its middle and lower sections. These river terraces records tectonic uplift in the Mut basin. Optically stimulated luminescence (OSL) dating of the fluvial sediments of the youngest terrace (T16) provides a chronology for the assessment of the important impacts of climatic changes. The ages from the youngest river terrace deposits in T16 may be subdivided into two intervals: (1) 239-194.7 ka during the later part of Marine Oxygen Isotope Stage (MIS) 7, implying that the aggradation of T16 started in (the final phase of) this warm period; and (2) 187.9-171 ka during much of MIS 6. Thus, it appears that the Goksu River continued depositing sediment from an interglacial into a glacial time. The differences in climate-driven fluvial evolution between this Mediterranean fluvial system and the classical, well-studied temperate-periglacial river systems in Europe may be the result of different vegetation cover and greater thaw of more intense snowfalls.
