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Analysis of Spatial Correlation between Surface Temperature and Absorbed Solar Radiation Using Drone - Focusing on Cool Roof Performance - (드론을 활용한 지표온도와 흡수일사 간 공간적 상관관계 분석 - 쿨루프 효과 분석을 중심으로 -)

  • Cho, Young-Il;Yoon, Donghyeon;Lee, Moung-Jin
    • Korean Journal of Remote Sensing
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    • v.38 no.6_2
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    • pp.1607-1622
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    • 2022
  • The purpose of this study is to determine the actual performance of cool roof in preventing absorbed solar radiation. The spatial correlation between surface temperature and absorbed solar radiation is the method by which the performance of a cool roof can be understood and evaluated. The research area of this study is the vicinity of Jangyu Mugye-dong, Gimhae-si, Gyeongsangnam-do, where an actual cool roof is applied. FLIR Vue Pro R thermal infrared sensor, Micasense Red-Edge multi-spectral sensor and DJI H20T visible spectral sensor was used for aerial photography, with attached to the drone DJI Matrice 300 RTK. To perform the spatial correlation analysis, thermal infrared orthomosaics, absorbed solar radiation distribution maps were constructed, and land cover features of roof were extracted based on the drone aerial photographs. The temporal scope of this research ranged over 9 points of time at intervals of about 1 hour and 30 minutes from 7:15 to 19:15 on July 27, 2021. The correlation coefficient values of 0.550 for the normal roof and 0.387 for the cool roof were obtained on a daily average basis. However, at 11:30 and 13:00, when the Solar altitude was high on the date of analysis, the difference in correlation coefficient values between the normal roof and the cool roof was 0.022, 0.024, showing similar correlations. In other time series, the values of the correlation coefficient of the normal roof are about 0.1 higher than that of the cool roof. This study assessed and evaluated the potential of an actual cool roof to prevent solar radiation heating a rooftop through correlation comparison with a normal roof, which serves as a control group, by using high-resolution drone images. The results of this research can be used as reference data when local governments or communities seek to adopt strategies to eliminate the phenomenon of urban heat islands.

A Comparative Study on the Ways of Enjoying Xīsāishān Mountain, Scenic Site and Euisang(意象: Images) of it Shown on a Number of the Historic Korean and Chinese Literatures (한중 역대 문집에 나타난 명승(名勝) 서새산(西塞山) 향유방식과 의상(意象) 비교 고찰)

  • Park, So-Hyun
    • Journal of the Korean Institute of Traditional Landscape Architecture
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    • v.40 no.2
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    • pp.24-33
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    • 2022
  • The travel notes and nature poems found in historic literary men's works can be considered historical records related to scenic sites. Such travel notes and nature poems are based on the writers' personal characters, experiences, learning and etc. Such works clearly show the characters of each literature, information of the related objects and the writers' thoughts of the objects. This study, thus, looked into Euisang on Xīsāishān Mountain that could be the origin of Eobusa(漁父詞) loved and sung by Korean historic literary men, and found that the Korean and Chinese literary men's thoughts were shown through their ways to enjoy Xīsāishān Mountain and their Euisang on the mountain, which was different between the Korean and Chinese literary men depending on the geographical locations described in their poems. In detail, the study results are: 1. Such difference of the ways to enjoy Xīsāishān Mountain, the scenic site described in historic Korean and Chinese literary men's work is broadly classified into the ways to enjoy the scenic site by seeing it in person and the ways to enjoy it under the mental structure of speculation. 2. Xīsāishān Mountain in Wuxing is the background of Yújiāzi(漁家子) of the painting Zhāngzhìhé, is boasting its distinguished beautiful nature, and is the place where the Confucian Study of Hú(湖學) was originated. It is also the place known of its warmhearted climate. Therefore, Euisang on Xīsāishān Mountain under such beautiful and warmhearted circumstance are realized as the complete freedom and seclusion in Taoism and the satisfaction with the given environment and position in Confucianism. 3. Xīsāishān Mountain in Wǔchāng is a military strategic point with rugged mountain terrain and scenery that has been a historic ferocious battlefield and related with the loyal civil servant Qū Yuán. The Euisang on Xīsāishān Mountain in Wǔchāng, therefore, represents the nature scenery of a rugged fortress and patriotism of Confucianism. 4. The Korean literary men's way to enjoy Xīsāishān Mountain is Shinyu(神遊: spiritual travel), so that their Euisang is formed according to the direction of the writer's values. Especially it is noted that Korean Euisang on Xīsāishān Mountain is originally based on the painting Zhāngzhìhé that shows the complete free mood of Taoism; and the Euisang on Xīsāishān Mountain that came from the mindful image by the poet monk Qíjǐ of Tang dynasty and Kim Si-seup appears with such Buddhist ways to seek the truth as SakGongIlYeo(色空一如: Being full is essentially as same as being vacant) and GyeonSeongSeongBul(見性成佛: Everybody can become Buddha by enlightenment).

Influence of Erythropoiesis Factors, BDNF, Cognitive Function and Working Memory by Intensity Aerobic Exercise in Middle Aged Women (강도별 유산소운동이 중년여성의 적혈구생성인자, BDNF와 인지기능, 작업기억에 미치는 영향)

  • Cho, Won-Je
    • 한국체육학회지인문사회과학편
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    • v.54 no.1
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    • pp.553-566
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    • 2015
  • This study was performed to identify the effects of different intensities of regular aerobic exercise on erythropoietin (EPO) and BDNF levels, and cognitive function and working memory in middle-aged women. Women aged 40 to 60 years residing in G-gu, Y-si, Gyeonggi-do were divided into 3 groups: control group, moderate-intensity aerobic exercise group and high-intensity aerobic exercise. All groups were asked to exercise at the given intensities, twice a week for a total of 12 weeks. Blood samples were collected from participants on week 0 (before exercising), week 6 and week 12, and then cognitive function and working memory tests were followed to measure erythropoietin (EPO) and BDNF levels, cognitive function and working memory. Repeated measures ANOVA, univariate analysis and follow-up test were performed on all data to compare the group, period and interaction through a SPSS. As a result, a significant difference over time was observed in EPO, BDNF, cognitive function and working memory; therefore, a follow-up one-way ANOVA analysis was performed on each group. As a result of analysis, a significant increase in erythrocyte, hematocrit, BDNF level and working memory was observed in moderate-intensity aerobic exercise group while erythrocyte and working memory were significantly increased inhigh-intensity aerobic exercise group. When comparing the results between the groups, the level of hematocrit was shown to be significantly higher in both moderate-and high-intensity aerobic group than the control group and also the higher level of hemoglobin was observed in both moderate-and high-intensity aerobic group comparing to control group. Considering the results of this study, therefore, a 12-week long aerobic exercise at moderate to high intensity positively affected EPO and BDNF levels, cognitive function and working memory in middle-aged women.

The factors to impact on the satisfaction of field practice among dental hygiene students (일부 치위생(학)과 학생들의 현장임상실습 만족도의 영향을 미치는 요인)

  • Sim, Seon-Ju;Baek, Ha-Oung;Um, Jung-Sun;Jung, Ha-Yan;Ji, Hey Mi;Hwang, Si-Nae;Han, Ji-Hey
    • Journal of Korean Academy of Dental Administration
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    • v.5 no.1
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    • pp.22-30
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    • 2017
  • Objective: The purpose is to study the factors to impact on the satisfaction of field practice among dental hygiene students and to provide the basic data for the quality improvement of the field practices for dental hygiene students. Methods: A self-reported questionnaires were filled out by 108 dental hygiene students in C city. Questionnaires were composed with the general characteristics, satisfaction to major, and satisfaction to field clinical practice. The data was analyzed by chi-square statistics using SPSS 20.0 program. Results: The higher satisfaction to communication with professor or seniors in department was associated with the higher satisfaction to field clinical practice (p<0.05). The higher satisfaction to field clinical practice hours per week was associated with the higher satisfaction to field clinical practice (p<0.05). The higher interest to major subjects and the satisfaction to the laboratory environment were associated with the higher satisfaction to field clinical practice (p<0.05). Conclusions: The higher satisfaction to major was associated with the higher satisfaction to field clinical practice. Therefore, the systematic curriculum development is needed to improve the satisfaction with major and clinical practice.

Predictors of Latent Class of Longitudinal Medical Expenses of Older People and the Effects on Subjective Health (노인 의료비 변화궤적의 잠재계층 유형: 예측요인과 주관적 건강에 대한 영향)

  • Song, Si Young;Jun, Hey Jung;Choi, Bo Mi
    • 한국노년학
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    • v.39 no.3
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    • pp.467-484
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    • 2019
  • The purpose of this study is to explore latent classes of longitudinal medical expenses of older people and to analyze its predictors and its effects on subjective health. Among participants of the Korean Health Panel, the sample of this study includes 1,119 people who is 65-year-old or older and reported their medical expenses for nine consecutive years. The analyses were conducted in three steps. First, Growth Mixture Model (GMM) was applied to find distinct subgroups showing similar patterns in medical expenses. The results showed four groups which were classified as high medical expenditure maintenance group, medical expenditure increase group, low medical expenditure maintenance group, and medical expenditure reduction group. Second, the multinominal logistic regression found that the presence of spouse, economic participation, the number of chronic diseases, and the type of health insurance were significant predictors of latent classes in medical expenses. In particular, the greater the number of chronic diseases, the higher the likelihood of belonging to the high medical expenditure maintenance group. In addition, medical benefit recipients are more likely to belong to the low medical cost maintenance and medical cost reduction groups. Third, multiple regression analysis revealed that the older people in the groups with low or reducing expenses reported better subjective health than people with higher expenses. This study has its meanings in exploring the heterogeneity in longitudinal medical expenses among older people and its predictors and its associations with health outcome. The results of this research provide background information in establishing public health policy for older people.

Distribution and Remineralization Ratio of Inorganic Nutrients in the Divergence Zone($7^{\circ}{\sim}10.5^{\circ}N$), Northeastern Pacific (북동태평양 발산대 해역($7^{\circ}{\sim}10.5^{\circ}N$)의 무기영양염 분포와 재무기질화 비율)

  • Son, Ju-Won;Kim, Kyeong-Hong;Kim, Mi-Jin;Son, Seung-Kyu;Chi, Sang-Bum;Hwang, Keun-Choon;Park, Yong-Chul
    • The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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    • v.13 no.3
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    • pp.178-189
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    • 2008
  • The distribution of inorganic nutrients and their remineralization ratio in the divergence zone ($7^{\circ}{\sim}10.5^{\circ}N$) of the northeastern Pacific were investigated from July 2003 to July 2007. A divergence zone along the boundary of the North Equatorial Counter Current (NECC) and North Equatorial Current (NEC) at $10^{\circ}N$ was observed in July 2007 when the La Nina event and divergence-related upwelling was strong. The mean depth of oligotrophic surface mixed layer in the divergence zone was 46, 61, and 30 m in July 2003, August 2005, and July 2007, respectively. Below the surface mixed layer, a nutricline was clearly observed. The depth integrated value of nitrate including nitrite (DIVn) in the upper layer($0{\sim}100$ m depth) ranged from 5.51 to 21.71 $gN/m^2$(mean 12.82 $gN/m^2$) in July 2003, from 5.62 to 8.46 $gN/m^2$ (mean 7.15 $gN/m^2$) in August 2005, and from 8.98 to 27.80 $gN/m^2$(mean 21.12 $gN/m^2$) in July 2007. The maximum DIVn was observed at the divergence zone. The distributions of phosphate(DIVp) and silicate(DIVsi) were similar to that of DIVn and the DIVn/DIVsi ratio was $0.87{\pm}0.11$ in the upper layer. The limiting nutrient for phytoplankton growth in the study area was identified as nitrogen(N/P ratio=14.6). The nitrate (including nitrite) concentrations were lower in the region mainly affected by NEC than in the region affected by NECC. The study area of low silicate concentrations was also considered to be Si-limiting environment. The remineralization ratios of nutrients were $P/N/-O_2=1/14.6{\pm}1.1/100.4{\pm}8.8(23.44{\leq}Sigma-{\theta}{\leq}26.38)$ in the study area. These ratios suggested remineralization process in the surface layer of divergence zone.

A Study on the Conservation State and Plans for Stone Cultural Properties in the Unjusa Temple, Korea (운주사 석조문화재의 보존상태와 보존방안에 대한 연구)

  • Sa-Duk, Kim;Chan-Hee, Lee;Seok-Won, Choi;Eun-Jeong, Shin
    • Korean Journal of Heritage: History & Science
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    • v.37
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    • pp.285-307
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    • 2004
  • Synthesize and examine petrological characteristic and geochemical characteristic by weathering formation of rock and progress of weathering laying stress on stone cultural properties of Unjusa temple of Chonnam Hwasun county site in this research. Examine closely weathering element that influence mechanical, chemical, mineralogical and physical weathering of rocks that accomplish stone cultural properties and these do quantification, wish to utilize by a basic knowledge for conservation scientific research of stone cultural properties by these result. Enforced component analysis of rock and mineralogical survey about 18 samples (pyroclastic tuff; 7, ash tuff; 4, granite ; 4, granitic gneiss; 3) all to search petrological characteristic and geochemical characteristic by weathering of Unjusa temple precinct stone cultural properties and recorded deterioration degree about each stone cultural properties observing naked eye. Major rock that constitution Unjusa temple one great geological features has strike of N30-40W and dip of 10-20NE being pyroclastic tuff. This pyroclastic tuff is ranging very extensively laying center on Unjusa temple and stone cultural properties of precinct is modeled by this pyroclastic tuff. Stone cultural propertieses of present Unjusa temple precinct are accomplishing structural imbalance with serious crack, and because weathering of rock with serious biological pollution is gone fairly, rubble break away and weathering and deterioration phenomenon such as fall off of a particle of mineral are appearing extremely. Also, a piece of iron and cement mortar of stone cultural properties everywhere are forming precipitate of reddish brown and light gray being oxidized. About these stone cultural properties, most stone cultural propertieses show SD(severe damage) to MD(moderate damage) as result that record Deterioration degree. X-ray diffraction analysis result samples of each rock are consisted of mineral of quartz, orthoclase,plagioclase, calcite, magnetite etc. Quartz and feldspar alterated extremely in a microscopic analysis, and biotite that show crystalline form of anhedral shows state that become chloritization that is secondary weathering mineral being weathered. Also, see that show iron precipitate of reddish brown to crack zone of tuff everywhere preview rock that weathering is gone deep. Tuffs that accomplish stone cultural properties of study area is illustrated to field of Subalkaline and Peraluminous, $SiO_2$(wt.%) extent of samples pyroclastic tuff 70.08-73.69, ash tuff extent of 70.26-78.42 show. In calculate Chemical Index of Alteration(CIA) and Weathering Potential Index(WPI) about major elements extent of CIA pyroclastic tuff 55.05-60.75, ash tuff 52.10-58.70, granite 49.49-51.06 granitic gneiss shows value of 53.25-67.14 and these have high value gneiss and tuffs. WPI previews that is see as thing which is illustrated being approximated in 0 lines and 0 lines low samples of tuffs and gneiss is receiving esaily weathering process as appear in CIA. As clay mineral of smectite, zeolite that is secondary weathering produce of rock as result that pick powdering of rock and clothing material of stone cultural properties observed by scanning electron micrographs (SEM). And roots of lichen and spore of hyphae that is weathering element are observed together. This rock deep organism being coating to add mechanical weathering process of stone cultural properties do, and is assumed that change the clay mineral is gone fairly in stone cultural properties with these. As the weathering of rocks is under a serious condition, the damage by the natural environment such as rain, wind, trees and the ground is accelerated. As a counter-measure, the first necessary thing is to build the ground environment about protecting water invasion by making the drainage and checking the surrounding environment. The second thing are building hardening and extirpation process that strengthens the rock, dealing biologically by reducing lichens, and sticking crevice part restoration using synthetic resin. Moreover, it is assumed to be desirable to build the protection facility that can block wind, sunlight, and rain which are the cause of the weathering, and that goes well with the surrounding environment.

MR T2 Map Technique: How to Assess Changes in Cartilage of Patients with Osteoarthritis of the Knee (MR T2 Map 기법을 이용한 슬관절염 환자의 연골 변화 평가)

  • Cho, Jae-Hwan;Park, Cheol-Soo;Lee, Sun-Yeob;Kim, Bo-Hui
    • Progress in Medical Physics
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    • v.20 no.4
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    • pp.298-307
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    • 2009
  • By using the MR T2 map technique, this study intends, first, to measure the change of T2 values of cartilage between healthy people and patients with osteoarthritis and, second, to assess the form and the damage of cartilage in the knee-joint, through which this study would consider the utility of the T2 map technique. Thirty healthy people were selected based on their clinical history and current status and another thirty patients with osteoarthritis of the knee who were screened by simple X-ray from November 2007 to December 2008 were selected. Their T2 Spin Echo (SE hereafter) images for the cartilage of the knee joint were collected by using the T2 SE sequence, one of the multi-echo methods (TR: 1,000 ms; TE values: 6.5, 13, 19.5, 26, 32.5. 40, 45.5, 52). Based on these images, the changes in the signal intensity (SI hereafter) for each section of the cartilage of the knee joint were measured, which yielded average values of T2 through the Origin 7.0 Professional (Northampton, MA 01060 USA). With these T2s, the independent samples T-test was performed by SPSS Window version 12.0 to run the quantitative analysis and to test the statistical significance between the healthy group and the patient group. Closely looking at T2 values for each anterior and lateral articular cartilage of the sagittal plane and the coronal plane, in the sagittal plane, the average T2 of the femoral cartilage in the patient group with arthritis of the knee ($42.22{\pm}2.91$) was higher than the average T2 of the healthy group ($36.26{\pm}5.01$). Also, the average T2 of the tibial cartilage in the patient group ($43.83{\pm}1.43$) was higher than the average T2 in the healthy group ($36.45{\pm}3.15$). In the case of the coronal plane, the average T2 of the medial femoral cartilage in the patient group ($45.65{\pm}7.10$) was higher than the healthy group ($36.49{\pm}8.41$) and so did the average T2 of the anterior tibial cartilage (i.e., $44.46{\pm}3.44$ for the patient group vs. $37.61{\pm}1.97$ for the healthy group). As for the lateral femoral cartilage in the coronal plane, the patient group displayed the higher T2 ($43.41{\pm}4.99$) than the healthy group did ($37.64{\pm}4.02$) and this tendency was similar in the lateral tibial cartilage (i.e., $43.78{\pm}8.08$ for the patient group vs. $36.62{\pm}7.81$ for the healthy group). Along with the morphological MR imaging technique previously used, the T2 map technique seems to help patients with cartilage problems, in particular, those with the arthritis of the knee for early diagnosis by quantitatively analyzing the structural and functional changes of the cartilage.

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A Study on the Cultural Landscape Metamorphosis of ChoYeon Pavilion's Garden in SoonCheon City (순천 초연정(超然亭) 원림의 문화경관 변용 양상)

  • Kahng, Byung-Seon;Lee, Seung-Yoen;Shin, Sang-Sup
    • Journal of the Korean Institute of Traditional Landscape Architecture
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    • v.35 no.3
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    • pp.13-21
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    • 2017
  • The Cho-yeon Pavilion located in the Wangdae village in Samcheong-ri, Songgwang-myeon, Suncheon-si, was transformed into a place of refuge, a shrine, a vacation home, a lecture hall for kings. Based on the change, the current study has explored the periodic changing placeness and the transformation of cultural landscape and has figured out the meaning. The result of this study is as follows. First, "Cho-yeon", named by Yeonjae Song, Byeong-Seon, originated from Tao Te Ching of Lao Tzu. The concept is found not only in the Cho-yeon Pavilion in Suncheon but also in various places, such as, the Cho-yeon-dae in Pocheon, of the Cho-yeon-dae in Gapyeong, of the Cho-yeon-dae of the embankment behind the Gioheon of Changdeok-gung Garden, Cho-Yeon-Mul-Oe old buildings, including Jung(亭), Dae(臺), Gak(閣), of Ockriukag in Yuseong, etc. This shows that taoistic Poongrhu was naturally grafted onto confucian places, which is one of the examples of the fusion of Confucianism, Buddhism, and Taoism. Second, the placeness of the Cho-yeon Pavilion area is related to a legend that King Gong-min sought refuge here at the end of the Koryo Dynasty. The legend is based on the Wangdae village(king's region), Yu-Gyeong(留京)(the place where kings stayed), rock inscription of Wang-Dae-Sa-Jeok, Oh-Jang-Dae (the place where admiral flags were planted), and the Mohusan Mountain. Third, the Cho-yeon Pavilion not only has a base(the vacation home) that reflects confucian values from the rock inscription(趙鎭忠別業, 趙秉翼, 宋秉璿) of the beautiful rock walls and torrents but also has territoriality as taoistic Abode of the Immortals (there are places where people believe taoist hermits with miraculous powers live within 1km of the pavillion: Wol-Cheong(月靑), Pung-Cheong(風靑), Su-Cheong(水靑), Dong-Cheon(洞天). The Cho-yeon Pavilion also reflects the heaven of Neo-Confucianism for, pursuing study, and improving aesthetic sense by expanding its outer area and establishing the nine Gok: Se-Rok-Gyo(洗鹿橋)., Bong-Il-Dae(捧日臺), Ja-Mi-Gu(紫薇鳩), Un-Mae-Dae(雲梅臺), Wa-Ryong-Chong(臥龍叢), Gwang-Seok-Dae(廣石臺), Eun-Seon-Gul(隱仙窟), Byeok-Ok-Dam(碧玉潭), and Wa-Seok-Po(臥石布). In sum, the Cho-yeon Pavilion is a complex cultural landscape. Fourth, the usage of the Cho-yeon Pavilion was expanded and transformed: (1)Buddhist monastery${\rightarrow}$(2)Confucian vacation home${\rightarrow}$(3)Vacation home+Taoistic Poongrhu Place${\rightarrow}$(4)Vacation Home+Taoistic Poongrhu Place+Lecture Hall(the heaven of Neo-Confucianism). To illustrate, in 7978, the place served as Buddist Monk Kwang-Sa's monastery; in 1863, Cho, Jin-Choong established a vacation home by building a shrine in front of the tomb of his ancestor; in 1864, Cho, Jae-Ho expanded its usage to a vacation home to serve ancestors as a taoistic place by repairing the pavilion with roof tiles; and after 1890, Cho, Jun-Sup received the name of the pavilion, Cho-yeon, from his teacher Song, Byeong-Seon, and used the Pavilion for a lecture hall.

Clinical Efficacy of Clomiphene Citrate and Letrozole Combined with Gonadotropins for Superovulation in Patients with Clomiphene-Induced Thin Endometrium (클로미펜에 얇은 자궁내막을 보이는 환자에서 성선자극호르몬 병합 과배란유도시 클로미펜과 레트로졸의 임상적 효용성)

  • Lee, Eun-Joo;Park, Hyun-Jong;Yang, Hyo-In;Lee, Kyung-Eun;Seo, Seok-Kyo;Kim, Hye-Yeon;Cho, Si-Hyun;Choi, Young-Sik;Lee, Byung-Seok;Park, Ki-Hyun;Cho, Dong-Jae
    • Clinical and Experimental Reproductive Medicine
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    • v.36 no.2
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    • pp.111-119
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    • 2009
  • Objective: The aim of this study was to compare the clinical efficacy of clomiphene citrate (CC) and letrozole combined with gonadotropins for controlled ovarian stimulation (COS) in patients with CC-induced thin endometrium Methods: Fifty-one intrauterine insemination cycles performed in patients who previously had a thin endometrium (<8 mm) to ovulation induction using CC were included in this study. A CC 100 mg/day (CC+gonadotropin group, n=26) or letrozole 2.5 or 5 mg/day (letrozole+gonadotropin group, n=25) was administered on day 3~7 of the menstrual cycle, combined with gonadotropins at dose 75~150 IU every other day starting on day 5~7. We compared total dose of gonadotropin used, endometrial thickness, endometrial pattern, number of follicles ${\geq}14\;mm$ on hCG day, pregnancy rate and multiple pregnancy rate between the two groups, which were statistically analyzed using Mann-Whitney U test or Fisher's exact test, where appropriate. Results: There were no significant differences in clinical characteristics such as age, duration of infertility, number of previous IUI cycles, basal serum hormone levels and cause of infertility between the two groups. In both groups, the endometrium was significantly thicker than that of previous ovulation induction cycles using CC. No significant differences were found in the total dose of gonadotropin used, day of hCG administration, the rate of triple endometrium and pregnancy rate. The number of follicles ${\geq}14\;mm$ was significantly lower ($3.7{\pm}1.7$ vs. $2.8{\pm}1.7$, p=0.03) and the endometrium on hCG day was significantly thicker ($7.7{\pm}1.5$ vs. $9.1{\pm}1.7$, p=0.001) in letrozole+gonadotropin group compared to CC+gonadotropin group. Conclusion: The clomiphene citrate and letrozole combined with gonadotropins appear to avoid the undesirable effects on the endometrium frequently seen with CC for ovulation induction. However, in terms of adequate endometrial development or optimal follicular growth, letrozole may be more beneficial than CC for gonadotropin-combined COS in patients with CC-induced thin endometrium. Further prospective randomized controlled studies in a larger scale will be necessary to confirm our findings.