Ekinci, H.; Kuryatkov, V.V.; Forgey, C.; Dabiran, A.; Jorgenson, R.; Nikishin, S.A.

High brightness colored LEDs based on InGaN multiple quantum wells have recently been an attractive topic of research to achieve high efficiency photonic devices. In this study, we investigated a 3-period InxGa1−xN/GaN multiple quantum well LED grown on special templates by metal-organic chemical vapor deposition. All epitaxial layers, including the InGaN/GaN multiple quantum well active region, n-GaN and p-GaN were realized using nitrogen alone as a carrier gas. The growth details and device fabrication steps were studied. High resolution X-ray diffraction was used to analyze the thickness of the barrier and well, and composition of indium in the multiple quantum well active region. The Hall effect measurements were used to analyze the electrical properties of the epitaxial layers. Electroluminescence measurements were performed to estimate the optical band-gap of the LED structure.

Atici, T.; Altun Çolak, D.

Today, occurrence of nanotechnology is making life easier, increasing the individual happiness and attracts attention to the benefits to be provided by it. As with any technology, nanotechnology also has risks, which are discussed here. In this study, toxic effects of ZnOTiO2 nanocomposite on various growth parameters of Drosophila melanogaster and removal of these effects by Cimin grape (Vitis vinifera L. ssp., Cimin) were investigated. For this purpose, assessment of the number of offspring and the survival rate were performed by feeding flies with ZnOTiO2 (1 mg/ml) and Cimin grape seed and fruit extracts (5 and 10 mg/ml). In the first stage, larvae of the the same age were put into the medium of each application group and the adult individuals were recorded. In the second stage, in order to determine the number of offspring in all treatment groups, in a set of experiments the grape extracts and ZnOTiO2 were only applied to the female members, while in another set of experiments, the grape extracts and ZnOTiO2 were applied only to male members, belonging to the same application group. The total number of flies developed from the eggs laid during ten days of pair mating was counted. As a result, survival rate and the offspring number in the application groups, that were only exposed to ZnOTiO2 were found to show a decline, compared with the other groups. At the same time, the values obtained from the groups, exposed to the ZnOTiO2 and grape extracts together, were close to control group values. This result supports the healing effects of Cimin grape, which is abundant in Erzincan.

Gürses, A.; Ejder-Korucu, M.; Doǧar, Ç.

Poly (ethylene oxide), PEO, which was used for a wide variety of applications is a flexible, crystalline, thermoplastic, water-soluble and non-ionic polymer. The most of studies on surfactant-modified activated carbon (SM-PAC) have been generally focused on the removal of contaminants. This study aims the preparation of PEO/(SM-PAC) composites, using solution-intercalation method. Firstly activated carbon was modified with cationic surfactant, Cetyltrimethylammonium Bromide (CTAB). Then PEO/(SM-PAC) composites were prepared using solution-intercalation method, with two different (SM-PAC) contents (1.0 and 2.0 wt.%). The characterization of the composites was made by X-ray diffraction (XRD), Fourier Infrared Spectroscopy (FT-IR), thermal analysis and tensile tests. The XRD patterns revealed that 2θ positions of the broad peaks belonging to the composites significantly shift to left compared with those of virgin PEO. The SEM images of the surfactant-modified powdered activated carbon (SM-PAC)/PEO composites prepared with the two different SM-PAC contents show that there is an intensive interaction between the CTA+ ions of modified activated carbon surface and the polymer chains. From the tensile tests, it was found that the unmodified powdered activated carbon dispersed into the polymer matrix made the ductile polymer more brittle. However, the tensile and yield strengths of the composite, prepared with modified powdered activated carbon, have decreased, and the strain percent value has significantly increased.

Gürses, A.; Eroǧlu, Z.; Güneş, K.; Doǧar, Ç.

In this study, the synthesis of aniline-formaldehyde resin, and its thermal and structural characterization, as well as the preparation and characterization of the resin-organoclay composites were carried out. For this, first, at 70 °C and acidic conditions the aniline formaldehyde prepolymer was prepared and then cured at 120 °C under vacuum. The structural and thermal characterization of the resin was made using FTIR and DSC techniques. By using the Cetyltrimethylammonium Bromide modified Montmorillonite (OMMT) and the synthesized resin, the resin-organoclay composites were prepared by melt intercalation method. Characterization of the resin-organoclay composites prepared with the different ratios of organoclay is made with the same techniques. The FTIR and thermal analysis results of the composites indicate that a cross-linked polymeric matrix was formed. The thermal behavior of the composites has also significantly changed compared to pure resin.

Ak, A.; Kaya, Ö.; Cosan, D.T.; Gülsoy, M.

Photodynamic therapy (PDT) is a minimally invasive treatment for cancer therapy. It can be administered in combination with other treatments such as chemotherapy, radiotherapy, and surgical excision. PDT involves a photosensitizing agent that is activated by exposure to a specific wavelength of light. PDT is a cold photochemical process, there is no tissue heating. In our study, we investigated whether different laser parameters with different concentrations of indocyanine green (ICG) have cytotoxic and anti-proliferative effects on neuroblastoma. Plates were divided groups as control, only ICG concentrations (25 and 50 μg/ml), only laser treatment I (50 J/cm2), only laser treatment II (100 J/cm2), 25 μg/ml ICG + laser treatment I and 25 μg/ml ICG + laser treatment II, 50 μg/ml ICG + laser treatment I and 50 μg/ml ICG + laser treatment II. Neuroblastoma cell lines were irradiated with an in-house developed diode laser system (= 809 nm, 70 mW/cm2, 50 & 100 J/cm2) in continuous wave operation mode after ICG application. Cell proliferation was measured by XTT assay after light irradiation. Cell proliferation was decreased in a dose-dependent manner in 25 and 50 μg/ml ICG concentrations when compared with control. The applied ICG concentrations (especially 50 μg/ml) had cytotoxic effects for neuroblastoma cell lines, SH-SY5Y. There was no difference between laser treatment groups (L 50 & 100 J/cm2). However, PDT groups (laser exposure with ICG) showed significant inhibition of cell viability (p < 0:05). Additionally, laser exposure did not increase the well temperature above the incubation parameter. In conclusion, PDT has cytotoxic effects in neuroblastoma cell lines. Appropriate ICG dose - laser parameter combinations must be determined for each cell type. Different energy densities may cause different effects of PDT on inhibition of cell viability.

Gürses, A.; Doʇar, Ç.; Köktepe, S.; Mindivan, F.; Güneş, K.; Aktürk, S.

Recently PF resins can be also prepared by the addition of urea because urea accelerates cure process of PF resin, reduces the cost and improves its strength performance. Clays have long been used as inorganic fillers in polymer systems because of low cost, availability and improved thermal properties of resulting polymer composites. Clay nanocomposites of different types yield a marked increase in a number of properties of thermoplastic and other resins and composites. This study investigates the variation of thermal properties of PUF/colored organoclay nanocomposites with increased colored clay ratio. For this the DSC, XRD, FT-IR and HRTEM analyses were made. The XRD patterns and HRTEM images showed that clay platelets were exfoliated at the lower contents of organoclay, whereas at the higher content of organo clay tactoids were observed. The XRD analysis results implied that the amorphous behaviour increased with increased content of colored organoclay. The DSC thermograms indicated that glassy transition temperature (Tg) was increased, appearing prominent crystallization peaks at the lower ratios of organoclay. The Tg value was partially decreased and the peak intensities gradually decreased with increased content of clay. The thermogram for composite with clay content of 20% was similar to the thermogram of virgin resin. This can be attributed to the shifting of the textural structure for this composite from prominent crystalline structure to amorphous one.

Dogar, C.; Gürses, A.; Köktepe, S.; Mindivan, F.; Güne, K.; Aktürk, S.

Recently, so-called "phenol-formaldehyde-urea resins", which are generally made only by mechanical blending of UF resin and alkaline type PF resins, have been used as adhesives for the manufacturing of wood products. Faster curing PF resins can be also prepared by the addition of urea during or after the resin synthesis to yield co- -condensed phenol-urea-formaldehyde (PUF) resins. In this study, resin/clay composites were prepared by in situ polymerization of phenol(18.2%)-urea(36.3%)-formaldehyde(45.5%) (PUF) with the various ratios of organoclay (7.69-45.45%) and colored organoclay (3.22-20.0%). The objective of our work is the investigation of the effect of addition of both organoclay and colored organoclay at different ratios on the textural characteristics. The composites are characterized by X-ray diffraction, Fourier transform infrared spectroscopy techniques and using high resolution transmission electron microscopy images of the samples. It was found that clay layers exfoliated in the resin matrix.

Gürses, A.; Karagöz, S.; Mindivan, F.; Güne, K.; Dogar, C.; Aktürk, S.

Urea-formaldehyde (UF) resin which is one of the most important wood adhesives is a polymeric condensation product of the chemical reaction of formaldehyde with urea, and considered as the most important type of adhesive resins for the production of particleboards. The present study is aimed to preparation and characterization of urea/ formaldehyde/Rosa Canina sp. seeds - and urea/formaldehyde/Rosa Canina sp. seeds/organo clay composites and also to determine the utility as an alternative and low cost material to manufacture particleboard. The synthesis of various composites was carried out using fresh Rosa Canina sp. seeds, typical agricultural waste, in its changing ratios from 7.7 to 83.3 wt%. Also, some of the composite mixtures were prepared by adding organo clay (0.17-3.3 wt%) in a constant ratio of 1/1 wt of urea and formaldehyde. The structural and mechanical characterization of samples was performed by X-ray diffraction, Fourier transform infrared spectra, high resolution transmission electron microscopy images and measurements of Shore D and scratch hardness. The analysis results conclude that organo clay platelets dispersed as simultaneously intercalated and exfoliated in resin matrix and also the increased organo clay ratio led to increase in the hardness values of samples.

Calik, A.; Duzgun, A.; Ekinci, A.E.; Karakas, S.; Ucar, N.

In this study, the hardness and wear behaviour of carburized and boronized AISI 8620 steels have been studied. The boronizing treatment increased the hardness of AISI 8620 steels from 395 HV0.1 to a maximal 1610 HV0.1 compared to the carburized steels and also significantly improved its wear behaviour. From obtained results, it can be concluded that boronizing is very effective surface hardening method for improving the wear properties of AISI 8620 steels.