Carrier dynamics in bulk GaN

Carrier dynamics in hydride vapor phase epitaxy grown bulk GaN with very low density of dislocations, 5–8 × 105 cm−2, have been investigated by time-resolved photoluminescence (PL), free carrier absorption, and light-induced transient grating techniques in the carrier density range of 1015 to ∼1019 cm−3 under single and two photon excitation. For two-photon carrier injection to the bulk (527 nm excitation), diffusivity dependence on the excess carrier density revealed a transfer from minority to ambipolar carrier transport with the ambipolar diffusion coefficient D a saturating at 1.6 cm2/s at room temperature. An extremely long lifetime value of 40 ns, corresponding to an ambipolar diffusion length of 2.5 μm, was measured at 300 K. A nearly linear increase of carrier lifetime with temperature in the 80–800 K range and gradual decrease of D pointed out a prevailing mechanism of diffusion-governed nonradiative recombination due to carrier diffusive flow to plausibly the grain boundaries. Under single photon excitation (266 and 351 nm), subnanosecond transients of PL decay and their numerical modeling revealed fast processes of vertical carrier diffusion, surface recombination, and reabsorption of emission, which mask access to pure radiative decay

Renkli Görüntülerin Ortalama Tabanlı Çok Seviyeli Eşiklenmesi

Eşikleme görüntü sınıflandırmanın en kararlı yöntemlerinden biridir. Ancak her bir görüntü için uygun eşik seçimi hesap maliyeti açısından zorlu bir süreçtir. Ayrıca günümüze kadar önerilen yöntemler gri seviyeli görüntüler için uygulanabilmiştir. Bu çalışmada hem gri ölçekli hem de renkli görüntülerin otomatik olarak çok seviyeli eşiklenmesini sağlayan bir algoritma geliştirilmiştir. Sayısal görüntülerin her bir kanalına ait histogram bilgileri ve tekrarlı ortalama yaklaşımı temel alınmıştır. Öncelikle görüntünün genel ortalaması bulunmuş ve takip eden aşamalarda önceki basamakta bulunan ortalama bilgileri tekrar kullanılmıştır. Böylece her bir aşamada elde edilen eşik sayısı artmıştır. Başka bir ifade ile tespit edilen eşik sayısı kullanılan aşama sayısı ile orantılı hale gelmiştir. Her bir kanal için elde edilen eşik bilgileri yardımıyla kırmızı, yeşil ve mavi renk uzayı (Red, Green, Blue:RGB) alt prizmalara bölünmüş ve ilgili prizma içerisinde kalan pikseller aynı sınıfa atanmıştır

Saf ve Ru-katkılı TiO2 Nanofiberlerin Gaz ve Nemlilik Duyarlılık Özellikleri

TiO2 and Ru-doped TiO2 nanofibers were fabricated by calcining electrospun TiO2-PVP hybrid fibers at 600 o C. Their humidity and O2 sensing properties were investigated. The morphologies of nanofibers were characterized by scanning electron microscopy (SEM), which showed that the nanofibers with diameter of 260 nm formed a non-woven mat structure. Phase structures of the nanofibers were characterized by X-Ray difractometer (XRD) which showed that TiO2 nanofibers are polycrystalline with a mixture of anatase and rutile structure at 600o C. The effects of Ru doping in TiO2 sensing properties were investigated. The results show that humidity and O2 gas sensing properties of TiO2 nanofibers are effectively enhanced by Ru doping

Azelaic acid loaded chitosan and HPMC based hydrogels for treatment of acne: Formulation, characterization, in vitro-ex vivo evaluation

In this study, hydrogels containing azelaic acid were developed using chitosan or HPMC (1-7%) for local treatment of acne vulgaris. Physicochemical properties such as viscosity, pH and mechanical properties were evaluated. In vitro release and ex vivo permeability studies were performed using the Franz diffusion cell system. The pH of the hydrogels was highly compatible with the skin pH and varied between 4.38 and 5.84. The cumulative release percentages of the hydrogels at the end of 6 hours were 65-78%, whereas the marketed product yielded 50% drug release. According to the ex vivo permeability results, azelaic acid accumulated in the skin was found to be 9.38 +/- 0.65% (marketed cream), 19.53 +/- 1.06% (K3), 10.96 +/- 1.91% (H6). The antiacne studies with Cutibacterium acnes revealed that K3 (29.45 +/- 0.95) and H6 (32.35 +/- 0.15) had higher inhibition zones compared to the marketed cream (24.50 +/- 0.90). Additionally, the gels were found to be highly stable as a result of the stability studies for 6 months. Among the hydrogels that were prepared based on experimental findings, K3 (3% Chitosan) and H6 (6% HPMC) represented elevated in vitro release profile, higher permeability and increased antiacne activity. The findings of this research suggest that the developed hydrogels might be an alternative to the marketed product

Saf ve Ru-katkılı TiO2 Nanofiberlerin Gaz ve Nemlilik Duyarlılık Özellikleri

TiO2 and Ru-doped TiO2 nanofibers were fabricated by calcining electrospun TiO2-PVP hybrid fibers at 600 o C. Their humidity and O2 sensing properties were investigated. The morphologies of nanofibers were characterized by scanning electron microscopy (SEM), which showed that the nanofibers with diameter of 260 nm formed a non-woven mat structure. Phase structures of the nanofibers were characterized by X-Ray difractometer (XRD) which showed that TiO2 nanofibers are polycrystalline with a mixture of anatase and rutile structure at 600o C. The effects of Ru doping in TiO2 sensing properties were investigated. The results show that humidity and O2 gas sensing properties of TiO2 nanofibers are effectively enhanced by Ru doping