• Korean Journal of Materials Research
• /
• v.29 no.5
• /
• pp.282-287
• /
• 2019

The photovoltaic properties of $TiO_2$ used for the electron transport layer in perovskite solar cells(PSCs) are compared according to the particle size. The PSCs are fabricated and prepared by employing 20 nm and 30 nm $TiO_2$ as well as a 1:1 mixture of these particles. To analyze the microstructure and pores of each $TiO_2$ layer, a field emission scanning electron microscope and the Brunauer-Emmett-Teller(BET) method are used. The absorbance and photovoltaic characteristic of the PSC device are examined over time using ultraviolet-visible-near-infrared spectroscopy and a solar simulator. The microstructural analysis shows that the $TiO_2$ shape and layer thicknesses are all similar, and the BET analysis results demonstrate that the size of $TiO_2$ and in surface pore size is very small. The results of the photovoltaic characterization show that the mean absorbance is similar, in a range of about 400-800 nm. However, the device employing 30 nm $TiO_2$ demonstrates the highest energy conversion efficiency(ECE) of 15.07 %. Furthermore, it is determined that all the ECEs decrease over time for the devices employing the respective types of $TiO_2$. Such differences in ECE based on particle size are due to differences in fill factor, which changes because of changes in interfacial resistance during electron movement owing to differences in the $TiO_2$ particle size, which is explained by a one-dimensional model of the electron path through various $TiO_2$ particles.

• Toxicological Research
• /
• v.35 no.2
• /
• pp.119-129
• /
• 2019

As the use of cosmetics has greatly increased in a daily life, safety issues with cosmetic ingredients have drawn an attention. Drometrizole [2-(2'-hydroxy-5'-methylphenyl)benzotriazole] is categorized as a sunscreen ingredient and is used in cosmetics and non-cosmetics as a UV light absorber. No significant toxicity has been observed in acute oral, inhalation, or dermal toxicity studies. In a 13-week oral toxicity study in beagle dogs, No observed adverse effect level (NOAEL) was determined as 31.75 mg/kg bw/day in males and 34.6 mg/kg bw/day in females, based on increased serum alanine aminotransferase activity. Although drometrizole was negative for skin sensitization in two Magnusson-Kligman maximization tests in guinea pigs, there were two case reports of consumers presenting with allergic contact dermatitis. Drometrizole showed no teratogenicity in reproductive and developmental toxicity studies in which rats and mice were treated for 6 to 15 days of the gestation period. Ames tests showed that drometrizole was not mutagenic. A long-term carcinogenicity study using mice and rats showed no significant carcinogenic effect. A nail product containing 0.03% drometrizole was nonirritating, non-sensitizing and non-photosensitizing in a test with 147 human subjects. For risk assessment, the NOAEL chosen was 31.75 mg/kg bw/day in a 13-week oral toxicity study. Systemic exposure dosages were 0.27228 mg/kg bw/day and 1.90598 mg/kg bw/day for 1% and 7% drometrizole in cosmetics, respectively. Risk characterization studies demonstrated that when cosmetic products contain 1.0% of drometrizole, the margin of safety was greater than 100. Based on the risk assessment data, the MFDS revised the regulatory concentration of drometrizole from 7% to 1% in 2015. Under current regulation, drometrizole is considered to be safe for use in cosmetics. If new toxicological data are obtained in the future, the risk assessment should be carried out to update the appropriate guidelines.

• Korean Journal of Metals and Materials
• /
• v.49 no.6
• /
• pp.498-504
• /
• 2011

We examined the microstructure and optical properties of crystallized ~30 nm-ZnO/~10 nm amorphous $TiO_2$ nano bilayered films as nano electrodes were deposited at extremely low substrate temperatures of $150-210^{\circ}C$. The bilayered films were deposited on silicon substrates with 10 cm diameters by ALD (atomic layer deposition) using DEZn (diethyl zinc(Zn(C2H5)2)) and TDMAT (tetrakis dimethyl-amid $titanium(Ti(N(CH_3)_2)_4)$ as the ZnO and $TiO_2$ precursors, respectively, and $H_2O$ as the oxidant. The microstructure, phase, and optical properties of the bilayered films were examined by FE-SEM, TEM, XRD, AES, and UV-VIS-NIR spectroscopy. FE-SEM and TEM showed that all bilayered films were deposited very uniformly and showed crystallized ZnO and amorphous $TiO_2$ layers. AES depth profiling showed that the ZnO and $TiO_2$ films had a stoichiometric composition of 1:1 and 1:2, respectively. These bilayered films have optical absorption properties in a wide range of ultraviolet wavelengths, 250-390 nm, whereas the single ZnO and $TiO_2$ films showed an absorption range of 350-380nm.

• Journal of Apiculture
• /
• v.34 no.2
• /
• pp.107-115
• /
• 2019

Bumblebees have apposition compound eyes (one on either side of the head) of about 6,000 ommatidia and three small single-lens ocelli on the frons of their head capsule. The surface of the eye is smooth and interommatidial hairs, as in the honeybee, are not developed. Each ommatidium (approx. 26 ㎛ in diameter) is capped by a hexagonal facet and contains in its centre a 3 ㎛ wide, columnar light-perceiving structure known as the rhabdom. Rhabdoms consist of thousands of regularly aligned, fingerlike microvilli, which in their membranes contain the photopigment molecules. Axons from each ommatidium transmit the information of their photic environment to the visual centres of the brain, where behavioural reactions may be initiated. Since bumblebee eyes possess three classes of spectrally different sensitivity peaks in a ratio of 1:1:6 (UV= 353 nm, blue= 430 nm and green=548 nm) per ommatidium, they use colour vision to find and select flower types that yield pollen and nectar. Ommatidial acceptance angles of at least 3° are used by the bumblebees to discriminate between different flower shapes and sizes, but their ability to detect polarized light appears to be used only for navigational purposes. A flicker fusion frequency of around 110Hz helps the fast flying bumblebee to avoid obstacles. The small ocelli are strongly sensitive to ultraviolet radiation and green wavelengths and appear to act as sensors for light levels akin to a photometer. Unlike the bumblebee's compound eyes, the ocelli would, however, be incapable of forming a useful image.

• Advances in nano research
• /
• v.10 no.2
• /
• pp.191-210
• /
• 2021

To compare the antifungal effect of two nanomaterials (NMs), nanoparticles of zinc oxide were synthesized by a chemical route and zinc oxide-based nanobiohybrids were obtained using green synthesis in an extract of garlic (Allium sativum). The techniques of X-Ray Diffraction (XRD), Infrared (IR) and Ultraviolet Visible (UV-Vis) absorption spectroscopies and Scanning (SEM) and Transmission Electron Microscopies (TEM) were used to determine the characteristics of the nanomaterials synthesized. The results showed that the samples obtained were of nanometric size (< 100 nm). To compare their antifungal capacity, their effect on Cercospora sp. was evaluated. Test results showed that both nanomaterials had an antifungal capacity. The nanobiohybrids (green route) gave an inhibition of fungal growth of ~72.4% while with the ZnO-NPs (chemical route), inhibition was ~87.1%. Microstructural studies using High Resolution Optical Microscopy (HROM) and ultra-structural analysis using TEM carried out on the treated strains demonstrated the effect of the nanofungicides on the vegetative and reproductive structures, as well as on their cell wall. To account for the antifungal effect presented by ZnO-NPs and ZnO nanobiohybrids on the fungi tested, effects reported in the literature related to the action of nanomaterials on biological entities were considered. Specifically, we discuss the electrical interaction of the ZnO-NPs with the cell membrane and the biomolecules (proteins) present in the fungi, taking into account the n-type nature of the ZnO semiconductor and the electrical behavior of the fungal cell membrane and that of the proteins that make up the protein crown.

• Korean Journal of Materials Research
• /
• v.31 no.12
• /
• pp.665-671
• /
• 2021

A 1.8 ㎛ thick polycrystalline diamond (PCD) thin film layer is prepared on a Si(100) substrate using hot-filament chemical vapor deposition. Thereafter, its thermal conductivity is measured using the conventional laser flash analysis (LFA) method, a LaserPIT-M2 instrument, and the newly proposed light source thermal analysis (LSTA) method. The LSTA method measures the thermal conductivity of the prepared PCD thin film layer using an ultraviolet (UV) lamp with a wavelength of 395 nm as the heat source and a thermocouple installed at a specific distance. In addition, the microstructure and quality of the prepared PCD thin films are evaluated using an optical microscope, a field emission scanning electron microscope, and a micro-Raman spectroscope. The LFA, LaserPIT-M2, and LSTA determine the thermal conductivities of the PCD thin films, which are 1.7, 1430, and 213.43 W/(m·K), respectively, indicating that the LFA method and LaserPIT-M2 are prone to errors. Considering the grain size of PCD, we conclude that the LSTA method is the most reliable one for determining the thermal conductivity of the fabricated PCD thin film layers. Therefore, the proposed LSTA method presents significant potential for the accurate and reliable measurement of the thermal conductivity of PCD thin films.

• Journal of Veterinary Science
• /
• v.23 no.4
• /
• pp.62.1-62.10
• /
• 2022

Background: The corneal and limbal morphology relevant to corneal epithelial maintenance in ten different species was examined using histological methods. Objectives: The presence of a Bowman's layer, limbal epithelial cell, and superficial stromal morphology was examined in the following species to evaluate the differences in corneal thickness and epithelium: Java sparrows, frogs, macaws, spoonbills, red pandas, penguins, horses, Dobermans, orangutans, and humans. Methods: Corneal sections (4 ㎛) were obtained from ten ocular globes from three different animal classes: Aves, Amphibia, and Mammalia. All sections were stained with hematoxylin and eosin and periodic acid-Schiff reaction. After microscopy, all stained slides were photographed and analyzed. Results: Significant morphological differences in the corneal and limbal epithelia and their underlying stroma between species were observed. The number of corneal epithelial cell layers and the overall corneal epithelial thickness varied significantly among the species. The presence of a Bowman's layer was only observed in primates (orangutans and humans). Presumed supranuclear melanin caps were noted in four species (orangutans, macaws, red pandas, and horses) in the limbal basal epithelial layer (putative site of corneal epithelial stem cells). The melanin granules covered the apex of the cell nucleus. Conclusions: Supranuclear melanin capping has been described as a process within the epidermis to reduce the concentration of ultraviolet-induced DNA photoproducts. Similarly, there may be a relationship between limbal stem cell melanin capping as a protective mechanism against ultra-violet radiation.

• Journal of Appropriate Technology
• /
• v.6 no.2
• /
• pp.226-237
• /
• 2020

As the number of reported COVID-19 cases rises around the world, regions affected by the virus are taking serious measures to contain its spread. Face shields are one of the highest-need personal protective equipment (PPE) during COVID-19 pandemic. Beyond traditional face masks, as known cases of the coronavirus soar, currently there is a significant shortage of face shields around the world. In response, the protective face shields were designed and fabricated with open-source 3D modelling software and 3D printing technology, respectively. Our face shield consisted of two parts only; a reusable 3D printed headband and a visor made of transparent plastic sheet, as barrier. The resulting 3D printed face shields are affordable, lightweight, one-size-fits-most and ready-to-wear with minimal assemblies, and go on easily over glass, goggle and face mask. To ensure being donated to the healthcare professionals without risk infected by any pathogens, the 3D printed face shields were successfully be disinfected with ultraviolet germicidal irradiation (UVGI dosage of 1000 mJ/cm²) and 70% alcohol. For routine disinfection a UVGI chamber was designed and optimized to provide uniform UV-C illumination with an appreciated fluence for complete decontamination. More than 1,000 face shields were produced already and donated to the special hospitals for COVID-19 patients, quarantines, government and medical agencies in Ethiopia as well as in East-African countries. With certainty, our intention goes beyond the hospitals and other first responders, but not limited for all those who have to stay in the service or be in contact with many other people in the time of COVID-19 pandemic.

• Journal of Microbiology and Biotechnology
• /
• v.31 no.7
• /
• pp.990-998
• /
• 2021

Melanin is a natural skin pigment produced by specialized cells called melanocytes via a multistage biochemical pathway known as melanogenesis, involving the oxidation and polymerization of tyrosine. Melanogenesis is initiated upon exposure to ultraviolet (UV) radiation, causing the skin to darken, which protects skin cells from UVB radiation damage. However, the abnormal accumulation of melanin may lead to the development of certain skin diseases, including skin cancer. In this study, the antioxidant and antimelanogenic activities of the cell-free supernatant (CFS) of twenty strains were evaluated. Based on the results of 60% 2,2-diphenyl-1-picrylhydrazyl scavenging activity, 21% 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) scavenging capacity, and a 50% ascorbic acid equivalent ferric reducing antioxidant power value, Limosilactobacillus fermentum JNU532 was selected as the strain with the highest antioxidant potential. No cytotoxicity was observed in cells treated with the CFS of L. fermentum JNU532. Tyrosinase activity was reduced by 16.7% in CFS-treated B16F10 cells (but not in the cell-free system), with >23.2% reduction in melanin content upon treatment with the L. fermentum JNU532-derived CFS. The inhibitory effect of the L. fermentum JNU532-derived CFS on B16F10 cell melanogenesis pathways was investigated using quantitative reverse transcription polymerase chain reaction and western blotting. The inhibitory effects of the L. fermentum JNU532-derived CFS were mediated by inhibiting the transcription of TYR, TRP-1, TRP-2, and MITF and the protein expression of TYR, TRP-1, TRP-2, and MITF. Therefore, L. fermentum JNU532 may be considered a potentially useful, natural depigmentation agent.

• The Korea Journal of Herbology
• /
• v.27 no.6
• /
• pp.43-48
• /
• 2012

Objectives : This study was investigated to determine the contents of pesticide residues and sulfur dioxide residues in commercial herbal medicines in Korea. Methods : Chromatographic test was performed on 100 samples consisted with 10 kinds of medicinal plants including improted and domestic products. To establish 19 pesticide residues (DDE, DDD, DDT, Dieldrin, Methoxychlor, BHC isomers, Aldrin, Endosulfan isomers, Endrin, Captan, Procymidone, Chlorpyrifos and Imidacloprid) in commercial herbal medicines, chromatographic equipments were used with the gas chromatography-mass detector and gas chromatography-electron capture detector for qualitative analysis. The imidacloprid analysis was performed by high performance liquid chromatograpgy-ultraviolet detector at 270 nm UV wavelength. The contents of sulfur dioxides were analyzed by modified Monnier-Williams method. All methods were based on notification procedure of Korea Food & Drug Administration (KFDA). Results : The residual pesticides were not founded in improted and domestic samples. Among 100 samples, the residues of sulfur dioxide in 73 samples were not detected and 25 samples showed contents in the range of 0~21.90 mg/kg. The excess samples of MRLs were 2 samples (30 mg/kg to medicinal herbs), Asiasari Radix et Rhizoma (Imported product) and the average amount of sulfur dioxide in 2 unsuitable samples were 14.83 mg/kg. These samples were found to transgress KFDA regulatory guidance of residual sulfur dioxide. Conclusion : These results are able to use as basic data to improve the reliability and value of commercial medicinal herbs.