• Bulletin of the Korean Chemical Society
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• v.29 no.6
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• pp.1233-1242
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• 2008

The hydration effect on the intrinsic magnetism of natural salmon double-strand DNA was explored using electron magnetic resonance (EMR) spectroscopy and superconducting quantum interference device (SQUID) magnetic measurements. We learned from this study that the magnetic properties of DNA are roughly classified into two distinct groups depending on their water content: One group is of higher water content in the range of 2.6-24 water molecules per nucleotide (wpn), where all the EMR parameters and SQUID susceptibilities are dominated by spin species experiencing quasi one-dimensional diffusive motion and are independent of the water content. The other group is of lower water content in the range of 1.4-0.5 wpn. In this group, the magnetic properties are most probably dominated by cyclotron motion of spin species along the helical π -way, which is possible when the momentum scattering time (${\tau}_k$) is long enough not only to satisfy the cyclotron resonance condition (${\omega}_c{\tau}_k$ > 1) but also to induce a constructive interference between the neighboring double helices. The same effect is reflected in the S-shaped magnetization-magnetic field strength (M-H) curves superimposed with the linear background obtained by SQUID measurements, which leads to larger susceptibilities at 1000 G when compared with the values at 10,000 G. In particular, we propose that the spin-orbital coupling and Faraday's mutual inductive effect can be utilized to interpret the dimensional crossover of spin motions from quasi 1D in the hydrate state to 3D in the dry state of dsDNA.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.4
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• pp.86-92
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• 1999

A SiGe p-channel MESFET using $\delta$-doped layers is designed and the considerabel enhancement of the current driving capability of the device is observed from the result of simulation. The channel consists of double $\delta$-doped layers separated by a low-doped spacer which consists of Si and SiGe. A quantum well is formed in the valence band of the Si/SiGe heterojunction and much more holes are accumulated in the SiGe spacer than those in the Si spacer. The saturation current is enhanced by the contribution of the holes in the spacer. Among the design parameters that affect the performance of the device, the thickness of the SiGe layer and the Ge composition are studied. The thickness of 0~300$\AA$ and the Ge composition of 0~30% are investigated, and saturation current is observed to be increased by 45% compared with a double $\delta$-doped Si p-channel MESFET.

• Journal of Radiation Protection and Research
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• v.42 no.1
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• pp.16-20
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• 2017

Background: The design of deuteron accelerator neutron source facilities requires reliable yield estimation of gamma-rays as well as neutrons from deuteron-induced reactions. We have so foar measured systematically double-differential thick target neutron yields (DDTTNYs) for carbon, aluminum, titanium, copper, niobium, and SUS304 targets. In the neutron data analysis, the events of gamma-rays taken simultaneously were treated as backgrounds. In the present work, we have re-analyzed the experimental data for a thick carbon target with particular attention to gamma-ray events. Materials and Methods: Double-differential thick target gamma-ray yields from carbon irradiated by 5 and 9 MeV deuterons were measured using an NE213 liquid organic scintillator at the Kyushu University Tandem accelerator Laboratory. The gamma-ray energy spectra were obtained by an unfolding method using FORIST code. The response functions of the NE213 detector were calculated by EGS5 incorporated in PHITS code. Results and Discussion: The measured gamma-ray spectra show some pronounced peaks corresponding to gamma-ray transitions between discrete levels in residual nuclei, and the measured angular distributions are almost isotropic for both the incident energies. Conclusion: PHITS calculations using INCL, GEM, and EBITEM models reproduce the spectral shapes and the angular distributions generally well, although they underestimate the absolute gamma-ray yields by about 20%.

• Bulletin of the Korean Chemical Society
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• v.12 no.5
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• pp.554-559
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• 1991

The photophysical and photochemical properties of khellin were compared with those of 8-methoxypsoralen (8-MOP). Quantum yields of fluorescence and triplet formation decreases as solvent polarity increases, which is opposite to 8-MOP, and photocycloadditivity of khellin to olefins is much lower than that of 8-MOP. Electron ejection from khellin by laser flash was not observed, but observed from 8-MOP. As models of 4',5'-monoadducts of khellin or 8-MOP with thymine base, khellin<>dimethylfumarate 4',5'-monoadduct (KDF) was also compared with 8-MOP<>thymidine 4',5'-monoadduct (F-2) in those properties to give some insight on the second-step biadduct formation resulting in cross-links of DNA duplex. KDF and F-2 were very similar to khellin and 8-MOP in photophysical properties, respectively. However, KDF did not form adducts with various olefins, and thus it is thought that 2,3-double bond of chromone moiety in khellin is hardly reactive in contrast with 3,4-double bond of coumarin moiety in 8-MOP. These results indicate that khellin is fairly photostable compound, a poor type Ⅰ photodynamic sensitizer and producer of ${O_2}^{-}$ which is some cause of phototoxic erythemal reactions and undesirable side effects. Therefore khellin is safer to use than 8-MOP in photochemotherapy of some skin diseases. Although khellin is much less reactive than 8-MOP, khellin must be also a monofunctional drug. Since khellin is, however, as effective as 8-MOP in photochemotherapy of some skin diseases, it is suggested that khellin may be different from 8-MOP in the action mechanism.

• Korean Journal of Optics and Photonics
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• v.35 no.5
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• pp.241-249
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• 2024

In this study, we demonstrate compact mode-locked laser operations using three different kinds of Yb³⁺-doped potassium double tungstate laser crystals, Yb:KGdW, Yb:KYW and Yb:KLuW, operating near 1040 nm at a repetition rate of 405 MHz. We utilized a semiconductor saturable absorber mirror as a mode locker, successfully maintaining mode-locked states for several hours without any Q-switching instabilities for all types of laser crystals. Notably, the Yb:KGdW mode-locked laser produces the shortest pulse with a duration of 108 fs, delivering 125 mW of output power. Additionally, we conducted a numerical analysis by solving the Haus master equation, which incorporates the effect of group delay dispersion and self-phase modulation, using the standard split-step Fourier method.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.174-175
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• 2012

(In, Ga) N-based III-nitride semiconductor materials have been viewed as the most promising materials for the applications of blue and green light emitting devices such as light-emitting diodes (LEDs) and laser diodes. Although the InGaN alloy can have wide range of visible wavelength by changing the In composition, it is very hard to grow high quality epilayers of In-rich InGaN because of the thermal instability as well as the large lattice and thermal mismatches. In order to avoid phase separation of InGaN, various kinds of structures of InGaN have been studied. If high-quality In-rich InGaN/GaN multiple quantum well (MQW) structures are available, it is expected to achieve highly efficient phosphor-free white LEDs. In this study, we proposed a novel InGaN double hetero-structure grown on GaN nano-pyramids to generate broad-band red-color emission with high quantum efficiency. In this work, we systematically studied the optical properties of the InGaN pyramid structures. The nano-sized hexagonal pyramid structures were grown on the n-type GaN template by metalorganic chemical vapor deposition. SiNx mask was formed on the n-type GaN template with uniformly patterned circle pattern by laser holography. GaN pyramid structures were selectively grown on the opening area of mask by lateral over-growth followed by growth of InGaN/GaN double hetero-structure. The bird's eye-view scanning electron microscope (SEM) image shows that uniform hexagonal pyramid structures are well arranged. We showed that the pyramid structures have high crystal quality and the thickness of InGaN is varied along the height of pyramids via transmission electron microscope. Because the InGaN/GaN double hetero-structure was grown on the nano-pyramid GaN and on the planar GaN, simultaneously, we investigated the comparative study of the optical properties. Photoluminescence (PL) spectra of nano-pyramid sample and planar sample measured at 10 K. Although the growth condition were exactly the same for two samples, the nano-pyramid sample have much lower energy emission centered at 615 nm, compared to 438 nm for planar sample. Moreover, nano-pyramid sample shows broad-band spectrum, which is originate from structural properties of nano-pyramid structure. To study thermal activation energy and potential fluctuation, we measured PL with changing temperature from 10 K to 300 K. We also measured PL with changing the excitation power from 48 ${\mu}W$ to 48 mW. We can discriminate the origin of the broad-band spectra from the defect-related yellow luminescence of GaN by carrying out PL excitation experiments. The nano-pyramid structure provided highly efficient broad-band red-color emission for the future applications of phosphor-free white LEDs.

• Journal of the Optical Society of Korea
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• v.1 no.2
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• pp.116-119
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• 1997

Highly quantum efficient and multi-color emissible polymer light emitting devices have been realized utilizing poly (1-dodecyloxy-4-methyl-1, 3-phenylene)(2, 5"-terthienylene)(hereafter, mPTTh polymer) as an emitting layer and tris(8-hydroxyquinoline) aluminum (Alq3) as an electron transport layer. A single layer EL device of mPTTh polymer emits orange-colored light. EL efficiency increases as the thickness of Alq3 layer increases, but the emission color becomes visually broad when the Alq3 layer thickness is greater than 30nm since the relative peak intensity of green EL from Alq3 layer grows. EL color is changed from orange to greenish orange as the thickness of Alq3 layer grows. EL color is changed from orange to greenish orange as the thickness of Alq3 layer increases. EL efficiency of the double layer device was greatly enhanced by 3000 times compared with that of a single layer device. Alq3 layer in device acts as a hole blocking electron transporting layer and an emitting layer as a function of the thickness of Alq3 layer.ayer.

• Korean Journal of Optics and Photonics
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• v.20 no.1
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• pp.41-47
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• 2009

We report the spectral characteristics of Multimode Interferometer (MMI)-coupled semicondoctor square ring resonators. The epitaxial layers of the proposed semiconductor ring resonator consists of $1.55{\mu}m$ GaInAsP-InP multiple quantum wells. The lasing characteristics were observed by varying the structure parameters of the MMI-coupled square ring resonators. It is concluded that the MMI-coupled scheme selects a single spectral lasing mode in the double square ring cavities.

• Journal of the Korean Applied Science and Technology
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• v.16 no.2
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• pp.127-133
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• 1999

New electroluminescent materials base on anthracene chromophore, [9.10-bis(${\alpha}$-naph -thylethenyl) anthracene (${\alpha}$-BNA)] were newly synthesized. The anthracene derivatives with bulky substituent possessed high melting point and they gave stable amorphous films through vacuum - sublimation methods. Three types of electroluminescent devices were fabricated with double layer and triple layer structure : ITO/TPD/emission layer/MgAg, ITO/emission layer/ OXD-7 and ITO/ TPD/ emission layer/OXD-7/MgAg, respectively. In three types of devices with the emissive layer of ${\alpha}$-BNA, efficient orange electroluminescence was observed. In the triple layer device whit a emitting layer of 20 nm thickness , maximum luminance was about 10000 cd/ $m^2$ at an applied voltage of 10v and maximum external quantum efficiency was 1.0%.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.27-32
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• 1999

We developed a 40-channel superconducting quantum interference device (SQUID) system for neuromagnetic measurements. The main features of the system are use of double relaxation oscillation SQUID (DROS), and planar gradiometer for measuring tangential field components. The DROSS with high flux-to-voltage transfers enabled direct readout of the SQUID output by room-temperature electronics and simple flux-locked loop circuits could be used for SQUID operation. The pickup coil is an integrated first-order planar gradiometer with a baseline of 40 mm. The average noise of the 40 channels is around 1.2 fT/cm/${\sqrt{Hz}}$ at 100 Hz, corresponding to the field noise of 5 fT/${\sqrt{Hz}}$ at 100 Hz, operated inside a magnetically shielded room. The 40-Channel system was applied to measure auditory-evoked neuromagnetic fields.