• Title, Summary, Keyword: Purcell effect

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Numerical Investigation of Purcell Enhancement of the Internal Quantum Efficiency of GaN-based Green LED Structures

  • Choi, Young-Hwan;Ryu, Guen-Hwan;Ryu, Han-Youl
    • Current Optics and Photonics
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    • v.1 no.6
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    • pp.626-630
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    • 2017
  • GaN-based green light-emitting diode (LED) structures suffer from low internal quantum efficiency (IQE), known as the "green gap" problem. The IQE of LED structures is expected to be improved to some extent by exploiting the Purcell effect. In this study, the Purcell effect on the IQE of green LED structures is investigated numerically using a finite-difference time-domain simulation. The Purcell factor of flip-chip LED structures is found to be more than three times as high as that of epi-up LED structures, which is attributed to the high-reflectance mirror near the active region in the flip-chip LED structures. When the unmodified IQE is 20%, the relative enhancement of IQE can be greater than 50%, without utilizing the surface-plasmon coupling effect. Based on the simulation results, the "green gap" problem of GaN-based green LEDs is expected to be mitigated significantly by optimizing flip-chip LED structures to maximize the Purcell effect.

Electron Beam Bunching Effect in Smith-Purcell Radiation as a FIR Light Source (Smith-Purcell 효과를 이용한 원적외선 광원에서 전자빔 군집의 효과)

  • 임영경;이희제;김선국;이병철;정영욱;조성오;차병헌;이종민
    • Proceedings of the Optical Society of Korea Conference
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    • pp.50-51
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    • 2000
  • 가속된 전자빔을 금속회절격자의 위로 통과시킬 때 결맞은 복사광(coherent radiation)이 발생하는데 이를 Smith- Purcell 효과라고 한다. 이때 발생하는 전자기파의 파장은 회절격자의 주기, 전자빔의 속도 및 복사광의 방출각도에 관계된다$^{(1)}$ . 그리고 방출된 복사광의 출력세기는 전자빔의 군집을 고려하지 않는 경우, 회절이론(diffraction theory)에 의해 얻을 수 있는데, 그 세기는 입사시킨 전자빔의 전류세기에 선형적으로 비례한다$^{(2)}$ . (중략)

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The Effect of Ankle Kinesio Taping on Postural Control Functions in University Students: a randomized control trial (발목관절의 키네지오 테이핑 적용이 대학생들의 운동 수행 시 자세조절기능에 미치는 영향)

  • Eom, Se-Young;Lee, Won-Jun;Lee, Jae-Il;Lee, Eun-Hee;Lee, Hye-Young;Chung, Eun-Jung
    • Journal of Korean Physical Therapy Science
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    • v.25 no.1
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    • pp.11-19
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    • 2018
  • Purpose : The purpose of this study was to examine the effects of ankle kinesio taping on postural control function during exercise in university students. Method : Thirty subjects were randomly allocated to three groups: Y taping group (n=20), I taping group (n=20) and Non-taping group (n=20). All groups underwent the same exercise program including stretching for 30 minutes. The exercise program proceeded in the following order: five minutes of stretching, a 20-minutes exercise program, and additional five 5 minutes of stretching. Of the eight exercise methods suggested by Purcell et al, seven were chosen (lateral shuffle, forward & backward running, agility ladder, figure-of-8, forward jogging while jumping over cones, wall jumps and zigzags); $90^{\circ}$ cuts with lateral shuffle were omitted. The postural control functions was measured participants's perceptions of stability, confidence, and reassurance using methods suggested by Purcell et al,. Result : The confidence was significant difference in I taping group compared to Non taping group. The reassurance was significant difference in Y taping group and I taping group compared to Non taping group. Conclusion : The Kinesio taping increased confidence, and reassurance during exercise in university students. Additional research on Kinesio taping for improving range of motion and agility is need.

Modeling the effects of excess water on soybean growth in converted paddy field in Japan. 2. modeling the effect of excess water on the leaf area development and biomass production of soybean

  • Nakano, Satoshi;Kato, Chihiro;Purcell, Larry C.;Shiraiwa, Tatsuhiko
    • Proceedings of the Korean Society of Crop Science Conference
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    • pp.308-308
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    • 2017
  • The low and unstable yield of soybean has been a major problem in Japan. Excess soil moisture conditions are one of the major factors to restrict soybean productivity. More than 80 % of soybean crops are cultivated in converted paddy fields which often have poor drainage. In central and eastern regions of Japan, the early vegetative growth of soybean tends to be restricted by the flooding damage because the early growth period is overlapped with the rainy season. Field observation shows that induced excess water stress in early vegetative stage reduces dry matter production by decreasing intercepted radiation by leaf and radiation use efficiency (RUE) (Bajgain et al., 2015). Therefore, it is necessary to evaluate the responses of soybean growth for excess water conditions to assess these effects on soybean productions. In this study, we aim to modify the soybean crop model (Sinclair et al., 2003) by adding the components of the restriction of leaf area development and RUE for adaptable to excess water conditions. This model was consist of five components, phenological model, leaf area development model, dry matter production model, plant nitrogen model and soil water balance model. The model structures and parameters were estimated from the data obtained from the field experiment in Tsukuba. The excess water effects on the leaf area development were modeled with consideration of decrease of blanch emergence and individual leaf expansion as a function of temperature and ground water level from pot experiments. The nitrogen fixation and nitrogen absorption from soil were assumed to be inhibited by excess water stress and the RUE was assumed to be decreasing according to the decline of leaf nitrogen concentration. The results of the modified model were better agreement with the field observations of the induced excess water stress in paddy field. By coupling the crop model and the ground water level model, it may be possible to assess the impact of excess water conditions for soybean production quantitatively.

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The effect of ankle Kinesio taping on range of motion and agility during exercise in university students

  • Eom, Se Young;Lee, Won Jun;Lee, Jae Il;Lee, Eun Hee;Lee, Hye Young;Chung, Eun Jung
    • Physical Therapy Rehabilitation Science
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    • v.3 no.1
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    • pp.63-68
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    • 2014
  • Objective: The purpose of this study was to examine the effects of ankle Kinesio taping on range of motion and agility during exercise in university students. Design: Cross-sectional study. Methods: Thirty subjects were randomly allocated to two groups: taping group (n=15) and non-taping group (n=15). All groups underwent the same exercise program including stretching for 30 minutes. The exercise program proceeded in the following order: five minutes of stretching, a 20-minutes exercise program, and additional five minutes of stretching. Of the eight exercise methods suggested by Purcell et al, seven were chosen (lateral shuffle, forward and backward running, agility ladder, figure-of-8, forward jogging while jumping over cones, wall jumps and zigzags); $90^{\circ}$ cuts with lateral shuffle were omitted. The range of motion of ankle dorsiflexion and plantarflexion was measured using the goniometer. Agility was measured using the side hop test. Results: For ankle range of motion, the taping group showed significant differences in dorsiflexion and plantarflexion on both sides (p<0.05). The non-taping group showed significant differences only in left plantarflexion (p<0.05). There was a significant difference in dorsiflexion on both sides between the taping group and the non-taping group (p<0.05). All groups showed significant differences in agility on the left and right ankle (p<0.05). There was a significant difference in left ankles between the taping group and the non-taping group (p<0.05). Conclusions: Kinesio taping increased range of motion and agility during exercise in university students. Additional research on Kinesio taping for improving range of motion and agility is needed.

$^{17}O$ NMR Study On Water Excharge Rate of Paramagnetic Contrast Agents ($^{17}O$ NMR 기법을 이용한 상자성 자기공명조영제의 물분자 교환에 관한 연구)

  • Yongmin Chang;Sung Wook Hong;Moon Jung Hwang;Il Soo Rhee;Duk-Sik Kang
    • Investigative Magnetic Resonance Imaging
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    • v.5 no.1
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    • pp.33-37
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    • 2001
  • Purpose : The water exchange rate between bulk water and bound water is an important parameter in deciding the efficiency of paramagnetic contrast agents. In this study, we evaluated the water exchange rates of various Gd-chelates using oxygen-17 NMR technique. Material and Methods : The samples (Gd-DTPA, Gd-DTPA-BMA, Gd-DOTA, Gd-EOB-DTPA) were prepared by mixing 5% $^{17}O-enriched$ water (Isotech, USA). The pH of the samples was adjusted to physiological value [pH=7.0] by buffer solution. The variable temperature $^{17}O-NMR$ measurements were performed using Bruker-600 (14.1 T, 81.3 MHz) spectrometer. Bruker VT-1000 temperature control units were used to stabilize the temperature. The $^{17}O$ spin-spin relaxation times (T2) were measured using Carr-Purcell-Meiboom-Gill (CPMG)I pulse sequence with 24 echo trains. The variable temperature T2 relaxation data were then fitted into Solomon-Bloembergen equations using least square fit algorithm to estimate the water exchange times. Results : From the measured $^{17}O-NMR$ relaxation rates, the determined water exchange rates at 300K are $0.42{\;}{\mu}s$ for Gd-DTPA, $1.99{\;}{\mu}s$ for Gd-DTPA-BMA, $0.27{\;}{\mu}s$ for Gd-DOTA, and $0.11{\;}{\mu}s$ for Gd-EOB-DTPA. The Gd-DTPA-BMA showed slowest exchange whereas Gd-EOB-DTPA had fastest water exchange rate. In addition, it was found that the water exchange rates (${\tau}_m$) of all samples had exponential temperature dependence with different decay constant. Conclusion : $^{17}O-NMR$ relaxation rate measurements, when combined with variable temperature technique, provide a solid tool for studying water exchange rate, which is very important in investigating the detailed mechanism of relaxation enhancement effect of the paramagnetic contrast agents.

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Study of Localized Surface Plasmon Polariton Effect on Radiative Decay Rate of InGaN/GaN Pyramid Structures

  • Gong, Su-Hyun;Ko, Young-Ho;Kim, Je-Hyung;Jin, Li-Hua;Kim, Joo-Sung;Kim, Taek;Cho, Yong-Hoon
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.184-184
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    • 2012
  • Recently, InGaN/GaN multi-quantum well grown on GaN pyramid structures have attracted much attention due to their hybrid characteristics of quantum well, quantum wire, and quantum dot. This gives us broad band emission which will be useful for phosphor-free white light emitting diode. On the other hand, by using quantum dot emission on top of the pyramid, site selective single photon source could be realized. However, these structures still have several limitations for the single photon source. For instance, the quantum efficiency of quantum dot emission should be improved further. As detection systems have limited numerical aperture, collection efficiency is also important issue. It has been known that micro-cavities can be utilized to modify the radiative decay rate and to control the radiation pattern of quantum dot. Researchers have also been interested in nano-cavities using localized surface plasmon. Although the plasmonic cavities have small quality factor due to high loss of metal, it could have small mode volume because plasmonic wavelength is much smaller than the wavelength in the dielectric cavities. In this work, we used localized surface plasmon to improve efficiency of InGaN qunatum dot as a single photon emitter. We could easily get the localized surface plasmon mode after deposit the metal thin film because lnGaN/GaN multi quantum well has the pyramidal geometry. With numerical simulation (i.e., Finite Difference Time Domain method), we observed highly enhanced decay rate and modified radiation pattern. To confirm these localized surface plasmon effect experimentally, we deposited metal thin films on InGaN/GaN pyramid structures using e-beam deposition. Then, photoluminescence and time-resolved photoluminescence were carried out to measure the improvement of radiative decay rate (Purcell factor). By carrying out cathodoluminescence (CL) experiments, spatial-resolved CL images could also be obtained. As we mentioned before, collection efficiency is also important issue to make an efficient single photon emitter. To confirm the radiation pattern of quantum dot, Fourier optics system was used to capture the angular property of emission. We believe that highly focused localized surface plasmon around site-selective InGaN quantum dot could be a feasible single photon emitter.

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The Magnetic Relaxation Properties of DTPA-bis(4-carboxycyclohexyl) amide Paramagnetic Gd-chelates (DTPA-bis(4-carboxycyclohexyl)amide 상자성 복합체의 자기이완특성에 관한 연구)

  • Kim, In-Sung;Lee, Young-Ju;Lee, Jae-Jun;Kim, Ju-Hyun;Kim, Yoo-Kyung;Sujit, Dutta;Kim, Suk-Kyung;Kim, Tae-Jeong;Kang, Duk-Sik;Chang, Yong-Min
    • Investigative Magnetic Resonance Imaging
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    • v.10 no.1
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    • pp.20-25
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    • 2006
  • Purpose : To evaluate the NMR relaxation properties of newly developed high performance paramagnetic complexes. Materials and methods : 4-aminomethylcyclohexane carboxylic acid (0.63g, 4 mmol) was mixed with the suspension solution of DMF (15mL) and DTPA-bis-anhydride (0.71g, 2 mmol) to synthesize the ligand. The ligand was then mixed with Gd2O3 (0.18g, 0.5 mmol) to synthesize Gd-chelate. For the measurement of magnetic relaxivity of paramagnetic compounds, the compounds were diluted to 1mM and then the relaxation times were measured at 1.5T(64 MHz). Inversion-recovery pulse sequence was employed for T1 relaxation measurement and CPMG(Carr-Purcell-Meiboon-Gill) pulse sequence was employed for T2 relaxation measurement. Using MATLAB(Version 7.1) program, T1 magnetic relaxation map, R1 map, T2 magnetic relaxation map and R2 map were developed to represent magnetic relaxation time and magnetic relaxivity as image. Results : Compared to $R1=4.9mM^{-1}sec^{-1}$ and $R2=4.8mM^{-1}sec^{-1}$ of Omniscan (Gadodiamide), which is commercially available paramagnetic MR agent, R1 of SUK090(Gd-C32H74N5O24) was $12.46mM^{-1}sec^{-1}$ and R1 of SUK091(Gd-C34H78N5O24) was $12.77mM^{-1}sec^{-1}$. However, R1 of SUK092(Gd-C30H56N5O17) was decreased to $2.09mM^{-1}sec^{-1}$. In case of R2, SUK090(Gd-C32H74N5O24) was $8.76mM^{-1}sec^{-1}$ and SUK091(Gd-C34H78N5O24) was $7.60mM^{-}1sec^{-1}$ whereas SUK092(Gd-C30H56N5O17) was decreased to $1.82mM^{-1}sec^{-1}$. Conclusion : Among three new paramagnetic complexes, SUK090(Gd-C32H74N5O24) and SUK091(Gd-C34H78N5O24) showed higher T1, T2 magnetic relaxation rates than that of commercially available paramagnetic MR agent and thus expected to have more contrast enhancement effect.

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