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12. Enhanced transverse load sensitivity by using a highly birefringent photonic crystal fiber with larger air holes on one axis

Author

Kim, Hyun-Min, Kim, Tae-Hun, Kim, Bongkyun, and Chung, Youngjoo

Subjects
Photonics -- Research, Crystal whiskers -- Mechanical properties, Astronomy, Physics
Abstract

We report on a transverse load sensor with enhanced sensitivity through the use of a birefringent interferometer based on a highly birefringent photonic crystal fiber (HB-PCF). The transverse load sensitivity can be enhanced by using a fabricated HB-PCF having larger air holes on its fast axis. The transverse load sensitivity was measured to be high: ~2.17 nm/(N/cm). The temperature-induced undesirable effects can be ignored because transmission outputs of our HB-PCF were stable with the change of the temperature. The sensing probe can be compact because of its high birefringence with the order of [10.sup. -3] and no bending loss. OCIS codes: 060.2370, 060.2420, 060.5295.

Published
2010

16. MOVE MORE, GAIN LESS: EFFECT OF A RECREATIONAL TRAIL SYSTEM ON CHILDHOOD BMI.

Author

Kim, Bongkyun, Thomsen, Michael R., Nayga, Rodolfo M., Fang, Di, and Goudie, Anthony

Subjects
TRAILS, BODY mass index, CHILDHOOD obesity, STANDARD deviations, PHYSICAL activity
Abstract

We investigate the effect of residential proximity to recreational trails on childhood body mass index (BMI). We find that children living within 0.5 miles of recreational trails have BMI z‐scores that are 0.0412 to 0.0507 standard deviations lower than those who do not live within 0.5 miles of trails. We also find that living nearby trails reduces the probability of becoming obese by 1.6 percentage points. The impact for BMI z‐score is larger for children qualifying for free or reduced‐price meals and for Hispanic children. These findings suggest that improving neighborhood amenities conducive to physical activity may help reduce disparities in childhood obesity. [ABSTRACT FROM AUTHOR]

Published
2020
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24. Enhanced survival of ischemic skin flap by combined treatment with bone marrow-derived stem cells and low-level light irradiation.

Author

Moon, Jeong Hwan, Rhee, Yun-Hee, Ahn, Jin-Chul, Kim, Bongkyun, Lee, Sang Joon, and Chung, Phil-Sang

Subjects
VASCULAR endothelial growth factors, PEDICLE flaps (Surgery), EPITHELIAL cells, BLOOD platelets, WOUND healing, STEM cell transplantation, ANIMAL experimentation, ANIMALS, CONNECTIVE tissue cells, SURGICAL flaps, IMMUNOHISTOCHEMISTRY, ISCHEMIA, MICE, NECROSIS, NEOVASCULARIZATION, PERFUSION, RESEARCH evaluation, RESEARCH funding, PHYSIOLOGICAL effects of radiation
Abstract

The aim of this study is to examine the enhanced survival effect of ischemic skin flap by combined treatment with bone marrow-derived stem cells (BMSCs) and low-level light irradiation (LLLI). The neovasculogenic effect of BMSCs induced by LLLI was detected using a wound healing and tube formation assay. ICR mice were divided into four groups: control group, LLLI group, BMSCs group, and combine-treated group. The percentage of skin flap necrosis area was calculated on the seventh post-operative day. Specimens were harvested for histologic analyses. LLLI promoted BMSC migration and tube formation. The flap survival rate of combined treated group was significantly higher than that of the control group. Histologic results demonstrated a significant increase in neovascularization in the combined treatment group. This study demonstrates that combination treatment of BMSCs and LLLI could enhance the survival of ischemic skin flap in a mouse model. [ABSTRACT FROM AUTHOR]

Published
2018
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48. Tunable and switchable multi-wavelength fiber laser based on semiconductor optical amplifier and twin-core photonic crystal fiber

Author

Kim, Bongkyun, Han, Jihee, and Chung, Youngjoo

Abstract

Multi-wavelength fiber lasers have attracted a lot of interest, recently, because of their potential applications in wavelength-division-multiplexing (WDM) systems, optical fiber sensing, and fiber-optics instruments, due to their numerous advantages such as multiple wavelength operation, low cost, and compatibility with the fiber optic systems. Semiconductor optical amplifier (SOA)-based multi-wavelength fiber lasers exhibit stable operation because of the SOA has the property of primarily inhomogeneous broadening and thus can support simultaneous oscillation of multiple lasing wavelengths. In this letter, we propose and experimentally demonstrate a switchable multi-wavelength fiber laser employing a semiconductor optical amplifier and twin-core photonic crystal fiber (TC-PCF) based in-line interferometer comb filter. The fabricated two cores are not symmetric due to the associated fiber fabrication process such as nonuniform heat gradient in furnace and asymmetric microstructure expansion during the gas pressurization which results in different silica strut thickness and core size. The induced asymmetry between two cores considerably alters the linear power transfer, by seriously reducing it. These nominal twin cores form effective two optical paths and associated effective refractive index difference. The in-fiber comb filter is effectively constructed by splicing a section of TC-PCF between two single mode fibers (SMFs). The proposed laser can be designed to operate in stable multi-wavelength lasing states by adjusting the states of the polarization controller (PC). The lasing modes are switched by varying the state of PC and the change is reversible. In addition, we demonstrate a tunable multi-wavelength fiber laser operation by applying temperature changes to TC-PCF in the multi-channel filter.

Published
2012
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49. Essays in Applied Health Economics

Author

Kim, Bongkyun

Subjects
Environmental Studies, Health Economics
Abstract

I study how change in environmental factors and information provision about environmental risk effect on human capitals and individuals' behavior. Psychological maternal stress is thought to be a factor in poor infant health, but direct evidence is difficult to obtain. In first chapter, we posit that the 1994 Northridge earthquake in Los Angeles, California provides a natural test of the effect of mothers' stress on infants' birth weight and gestation. The Northridge disaster featured a low rate of injury and a quick recovery, but long-lasting and well documented consequences for mental health. Difference-in-difference results show that infants born closest to the epicenter were 0.2 percentage points more likely to be born with low birth weight. In second chapter, I examine the effect of air quality information on population change in counties of California, Oregon, and Washington State by measuring change in the number of air alerts days. Based on panel data between 1999-2014, the results find a negative relationship between more frequent air quality alerts and change in the total population of a county. In particular, only \Unhealthy" which is the air quality alert category that contains more polluted days than \Unhealthy for sensitive groups", has significant effect on the change in population. Those results are consistent with the idea that individuals are responsive to air quality and willing to move. Providing information is an important policy tool to encourage individuals' behavioral response. In my third paper, I focus on the role of prevalence and design of information by examining the effect of the EPA's map of radon zones, which is characterized as non- pervasive and unsophisticated in terms of its information on housing price in California counties. Using difference-in-difference estimator, I find that after the map is released, there is no difference in the house price between high radon level counties and low radon level counties. These results are consistent with the previous studies showing that individuals change their behavior when the information is well-specified as well as is widely available to the public.

Published
2017

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