• 제목/요약/키워드: $NO_2/NO_x$ ratio

검색결과 545건 처리시간 0.03초

PET/CT에서 Pitch와 Rotation Time의 변화를 이용한 능동적인 프로토콜 사용에 대한 연구 (A Study on the Use of Active Protocol Using the Change of Pitch and Rotation Time in PET/CT)

  • 장의순;곽인석;박선명;최춘기;이혁;김수영;최성욱
    • 핵의학기술
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    • 제17권2호
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    • pp.67-71
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    • 2013
  • PET/CT검사에서 CT촬영조건의 변화는 영상의 화질 및 환자가 받는 피폭선량에 영향을 미친다. 본 연구는 CT 매개 변수 중 Pitch와 X-선관 회전시간 변화에 따른 선량대비 CT 영상의 질과 이로 인해 PET상에서 SUV에 미치는 영향을 비교 평가하고자 하였다. Discovery STe PET/CT 장비를 이용하여 영상을 획득하였다. QA Phantom과 AAPM Phantom을 이용한 CT 영상 획득 시 Pitch는 0.562, 0.938, 1.375, 1.75:1로 4단계, X-선관 회전시간은 0.5에서 1.0까지 0.1초씩 증가시켜 6단계로 나누어 총 24개 조합을 적용한 영상을 각각 획득하였다. PET 영상은 $^{18}F-FDG$ 5.3 kBq/mL가 채워진 1994 NEMA PET Phantom을 이용하여 프레임당 2분 30초의 방출영상을 획득하였다. 각 조합의 CT 영상에 관심영역을 설정하고 CT number의 표준편차를 측정하였다. 동일한 영상에서 DLP변화에 따른 영상잡음의 예측값을 계산하여 예측값 대비 실측값의 비율을 구해 선량대비 영상잡음 효과를 비교하는 척도로 사용하였다. AAPM Phantom 영상에서 1.0 mm까지 식별이 가능한 지 확인하였다. NEMA PET Phantom의 방출영상에 관심영 역을 설정하고 SUV를 비교 평가하였다. Pitch가 0.562, 0.938, 1.375, 1.75:1로 변화할 때 영상잡음 효과는 QA Phantom에서 1.00, 1.03, 1.01, 0.96, AAPM Phantom에서 1.00, 1.04, 1.02, 0.97로 측정되었다. 회전시간의 증가에 따른 경우 QA Phantom에서 0.99, 1.02, 1.00, 1.00, 0.99, 0.99이었고, AAPM Phantom에서 1.01, 1.01, 0.99, 1.01, 1.01, 1.01로 SPSS Ver. 18을 이용하여 상관관계를 분석한 결과 피어슨 상관계수는 -0.059로 나타났다. 공간분해능에 대한 평가는 24개의 조합 모두에서 1.0 mm까지 육안으로 구별이 가능하였다. SUV의 경우 평균 SUV는 모든 조합에서 1.1로 모두 동일한 값을 나타내었다. Pitch 변화에 따른 CT 영상 평가에서 1.75:1을 적용 시 선량대비 가장 적은 영상잡음 효과를 보이며 공간분해능과 SUV에는 영향을 미치지 않는다. 그러나 회전시간 변화가 영상에 미치는 영향에는 유의한 차이가 없음을 알 수 있다. 결과에서와 같이 각 장비에 따른 선량대비 영상잡음이 적은 Pitch를 사용하고 환자의 체격에 따른 적절한 X-선관 회전시간을 이용한다면 환자의 피폭선량을 줄이면서 최적의 화질을 얻을 수 있는 프로토콜을 구성하는데 도움이 될 것이라 사료된다.

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대동맥박리의 임상적 고찰 (Clinical Observation of Aortic Dissection)

  • 장병익;박진호;신동구;김영조;심봉섭;이현우;김수현;한승세
    • Journal of Yeungnam Medical Science
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    • 제9권2호
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    • pp.334-341
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    • 1992
  • 저자는 1983년 3월부터 1992년 4월까지 영남대학교 의과대학 부속병원에 입원하여 대동맥박리로 진단받은 34례를 대상으로 이들의 임상상을 관찰한 결과를 요약하면 다음과 같다. 1. 총 대상환자 34명중 남자가 22명, 여자가 12명으로 남녀의 비는 1.83 : 1로 남자가 많았으며, 호발연령은 60대, 70대, 50대 순이었다. 2. 원인질환으로는 고혈압 및 대동맥 경화증이 79%로 대다수를 차지하였다. 3. 증상은 흉하부 혹은 배복부동통이 가장 많아 73%에서 관찰되었고, 이학적 검사상 복부의 박동성종괴가 type III 환자 22명중 66%를 차지하였다. 4. 심전도 소견상 심허혈소견이 6명, 심부정맥이 5명, 좌심실비대의 소견이 4명이었으며, 정상심전도의 소견을 가진예가 16명이었다. 5. 흉부방사선 소견상 대동맥 윤곽이상이 10명에서 관찰되었고, Type III의 63%에서 정상흉부방사선소견을 보였다. 6. 가장 많이 사용된 진단 방법은 심 혹은 복부 초음파도로 26명에서 시행되었고, 대동맥조영술은 47%에서 시행되었다. 7. 전체대상환자의 평균사망율은 20%였고 수술사망율은 18%이며, 내과적치료의 적용증이 되어 내과적치료를 받은 환자중 사망한 례는 없었다.

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보건지소(保健支所) 진료활동(診療活動)에 관(關)한 연구(硏究) (Study of Medical Carein Health Subcenter)

  • 김문식;김한중;김영기;김일순
    • Journal of Preventive Medicine and Public Health
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    • 제9권1호
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    • pp.109-116
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    • 1976
  • Reorganization of myun health care service is one of the main issues in health care delivery in rural Korea. The fundamenta, concept of the role and function of the myun health subcenter is that it is the basic unit of rural health care service and is to provide comprehensive health care service through the integration of curative and preventive services. The aim of this study is to analyze the patterns of curative activities in the myun health subcenter in terms of the most prevalent types of diseases, necessary diagnostic methods and required equipment, types of treatment, necessary drugs and materials, and finally the cost of curative services. The population on which this study was done was the 1596 patients who visited the two myun health subcenters (Sunwon Myun and Naega Myun) in Kang Wha County, the area of the Yonsei University Community Health Teaching Project, during period from May 1, 1975 to June 10, 1976. For the patient's record in the clinic, problem oriented medical records were used. Decisions regarding the disease classification, the diagnostic methods used and selection of the most appropriate and adequate medical treatment were made by a group of three experienced physicians after reviewing the medical records which had been written by public physicians who were treating patients in the study area. The records were reviewed by resident staff members of the Department of Preventive Medicine, of Yonsei University College of Medicine. A brief summary of results of the study is as follow: 1. 29.9% of the patients who visited the clinics were ages between 0-4. No sex difference was observed among patients less than 20 years of age. However, among patients over 20 years old, females predominated. Thus it is evident that the majority of patients were either children or mothers and grandmothers. 2. The distance from the individual villages to the myun health subcenter was one of important factors in determining the ratio of clinic visits. However, other factors such as the activities of the health workers also affected the rates substantially. 3. The most common 25 diseases comprised 90.2% of all the diseases recorded. Acute respiratory infection (25.5%), Skin (12.7%) , diarrheal diseases (6.8%), neuralgia and back pain (4.9%) and. all other injuries (3.9%) were the five most common diseases. 4. Of all the diseases diagnosed and treated, 9.2% required simple laboratory tests for diagnosis, 6.5% required X-ray examination, and altogether 13.6% required either laboratory test or X-ray examination. 5. Treatment and management of 42.0% of the cases could be accomplished with simple, inexpensive drugs, 12.8% required the use of more expensive drugs (mostly antibiotics) and injections were required in 19.7% of the cases. Minor surgery and referral were necessary in 5% of the cases. 6. The cost for diagnosis and treatment was estimated with a standard which was set by general concensus. The average cost of diagnosis was 144 per case and the cost of treatment was 726 per case, The Total average cost per visit was 870.

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Effects of L-Carnitine on the Nutritive Value of Extruded Full-Fat Soybean in Weaned Pigs

  • Piao, X.S.;Kim, J.H.;Jin, J.;Kim, J.D.;Lee, J.H.;Shin, I.S.;Han, In K.
    • Asian-Australasian Journal of Animal Sciences
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    • 제13권9호
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    • pp.1263-1271
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    • 2000
  • A total of 80 piglets ($5.85{\pm}0.62kg$ BW; 21 d of age) were used to study the effect of carnitine addition to extruded full-fat soybean (EFS) diets on the growth of weaned pigs. Pigs were allotted into five treatments based on body weight, in a completely randomized block design. Each treatment has 4 replicates of 4 heads each. Treatments were 1) SBM (positive control), 2) EFS without carnitine (negative control), 3) EFS with 50 ppm carnitine, 4) EFS with 100 ppm carnitine and 5) EFS with 150 ppm carnitine. During d 0 to 14, piglets were fed diets containing 3,400 kcal ME, 23% crude protein, 1.65% lysine, 0.9% Ca and 0.8% P and for the period of d 15 to 28, piglets were fed diets supplying 3,300 kcal ME, 20% crude protein, 1.55% lysine, 0.9% Ca and 0.8% P. The urease activity of EFS (0.18) were three times higher than SBM (0.07). During d 0-14, pigs fed SBM had greater ADG and ADFI compared to pigs fed extruded full-fat soybean diets (p<0.05). Feed conversion ratio was not different among treatments. No linear or quadratic effect of carnitine addition was found in growth performance. During d 15-28, piglets fed SBM diet also showed better ADG and FCR with no significant differences among treatments. Feed intake tended to increase as carnitine addition level was increased (p=0.10). For overall period (d o to 28), the best performance was observed in pigs fed SBM diet. CP digestibility was higher in pigs fed SBM diet than piglets fed EFS diet at d 14, and DM and CP digestibility tended to be higher in pigs fed SBM diet at d 28. Blood metabolites (BUN, glucose and cholesterol)were not affected by treatments. In conclusion, based on the results of this study piglets at 21 d of age appeared to be not ready for extruded full-fat soybean (FFSB) in their diets. Piglets fed extruded FFSB showed decreased growth rate compared to piglets fed SBM diet. Nutrient utilization was also poor in piglets fed extruded FFSB diets. L-carnitine addition at the level of 50 to 150 ppm was not effective in improving the growth performance of pigs fed EFS diets.

CT 검사에서 대동맥박리(aortic dissection)의 발생빈도에 관한 고찰 (A Study on the Frequency of Occurrence of the Aortic Dissection using CT)

  • 동경래;최성관;장영일;노상호
    • 대한방사선기술학회지:방사선기술과학
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    • 제31권2호
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    • pp.115-121
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    • 2008
  • 목적: 혈관의 내층과 외층을 급속히 해리시키는 예후가 매우 위험한 질환으로 대동맥 박리증(aortic dissection)의 임상적 진단을 위해 CT를 시행하여 대동맥 박리 증으로 판명된 환자 수와 연령별로 발생 빈도를 조사하고자 하였다. 방법 및 대상: 2005년 1월부터 2006년 12월까지 2년간 C대학병원에 내원한 환자 중 CT를 시행한 환자 112명을 대상으로 연도별로 증감 추세를 조사해 보고, 성별, 연령별, 진료과별로 조사 해 보았으며, 정확한 관찰을 위해 CT scan 후의 재구성 영상인 MIP와 SSD 그리고 VRT영상을 획득하여 CT와 일반 Chest PA 상을 비교하여 결과를 조사 연구하였다. 결과 및 결론: 1. CT를 시행한 환자 112명을 대상으로 연도별 검사건수는 2005년도 37명으로 41.9%를 보였고, 2006년도는 65명으로 58.1%로 2005년에 비해 2006년에 1.4배 증가되었다. 2. CT를 시행한 환자의 성별분포는 남성이 45명으로 40.1%, 여성이 67명으로 59.9%를 차지하고 있고 남성 45명 중 대동맥 박리증 환자는 9명으로 20%, 여성은 67명 중 21명으로 31.3%로 대동맥 박리증 환자가 남성에 비해 여성이 1.6배 많이 발생되었다. 또한 검사자 수도 남성에 비해 여성이 1.5배 많은 것으로 나타났다. 3. CT를 시행한 환자의 연령별 분포는 30세 미만에서는 거의 볼 수 없었으며 41세에서 80세까지가 전체에 88.3%를 차지하였으며 연령이 높을수록 대동맥 박리증 질환의 발생빈도가 높게 나타났다. 연령별 발생빈도의 차이는 통계적으로 유의하였다(p < 0.01). 4. CT를 의뢰한 과는 응급의학과에서 46명(41.1%), 순환기 내과에서 37명(33.0%), 흉부외과에서 13명(11.6%), 기타 과에서 16명(14.3%)으로 응급의학과와 순환기내과가 전체의 74.1%로 나타났다. 따라서 대동맥 박리증 질환의 환자는 주로 응급실로 내원하는 매우 위험한 질환이라는 것을 알 수 있다. 5. 대동맥 박리 환자 30명 중 22명(73.3%)은 일반 X-ray상 정상으로 판독되었고, 8명(26.7%)만이 일반 X-ray상 이상소견이 나왔다. 따라서 대동맥 박리 질환을 정확히 평가하기 위해서는 반듯이 CT를 시행해야 할 것으로 사료되었다.

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실시간 에어로졸 질량분석기를 이용한 PM1.0의 화학적성분의 특성에 관한 연구 (A Study on the Characteristics of PM1.0 Chemical Components Using a Real-time Aerosol Mass Spectrometer)

  • 박진수;최진수;김현재;오준;성민영;안준영;이상보;김정호
    • 한국도시환경학회지
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    • 제18권4호
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    • pp.485-494
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    • 2018
  • 2017년 겨울철 인천에서 미세먼지($PM_{1.0}$)의 화학적 성분과 산화특성을 파악하였다. 측정기간 대기오염물질 농도는 $PM_{10}$ $46{\pm}22{\mu}g/m^3$, $PM_{2.5}$ $29{\pm}18{\mu}g/m^3$, $SO_2$ 5(${\pm}3$) ppb, CO 0.56(${\pm}0.24$) ppm, $O_3$ 21(${\pm}13$) ppb, $NO_2$ 28(${\pm}17$) ppb이었다. $PM_{1.0}$ 화학적 성분은 organic 성분이 $3.2{\mu}g/m^3$, nitrate $1.9{\mu}g/m^3$로 주요성분으로 나타났다. 주간과 야간에서 대부분 야간에 높은 농도를 나타냈다. 측정기간 NOR(nitrate oxidation rate)은 0.06 이었고, SOR(sulfate oxidation rate)은 0.11이었다. 고농도기간, NOR은 0.6까지 증가하였으며, nitrate 성분도 증가하였다. $NOx/SO_2$ 비는 평균 8.7이었으며, nitrate/sulfate 비율은 평균 2.1로서 측정지점에 위치한 발전소, 산업 보일러를 포함한 고정오염원과 이동오염원인 자동차로부터 배출된 NOx가 기여요인으로 작용한 것으로 판단된다.

복부 전후 방향 검사의 자동노출제어 사용 시 선량 비교 연구 (Comparison of Exposure Dose by Using AEC Mode of Abdomen AP Study in Radiography)

  • 김기원;권용락;서승원;권경태;오주영;손순룡;손진현;민정환
    • 대한방사선기술학회지:방사선기술과학
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    • 제38권3호
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    • pp.205-211
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    • 2015
  • 복부 전후 방향 검사 시 automatic exposure control (AEC) mode에서 조사시간을 제한하지 않고 검사를 하는 방법 (non-time limit, NTL) 과 조사시간을 제한하고 검사하는 방법 (time limit, TL)에 대해서 영상 품질 평가인 신호 대 잡음비 (signal to noise ratio, SNR), 대조도 대 잡음비 (contrast to ratio, CNR)를 측정하여 TL 방법과 NTL방법을 비교 평가하고자 하였다. 실험 기기는 XGEO GC 80 (Samsung, Korea), Unfors ThinX RAD (Unfors, Sweden), Rando Phantom (alderson research laboratories, USA)과 $5.5{\times}9{\times}0.1cm^3$ 크기의 차폐재를 사용하였으며, AEC mode에서 전리함 (ionization chamber)를 상단 2 개만 작동하도록 설정하고 관전압은 80 kVp로 설정하였다. TL 방법의 경우에는 조사시간을 51 msec로 제한하였으며, 전리함에 차폐재를 부착하지 않은 상태와 부착한 상태에서 NTL AEC mode와 TL AEC mode의 영상을 획득하였다. 또한 'Image J"를 이용하여 영상 평가방법인 SNR과 CNR로 평가하였다. 결론적으로 차폐재를 부착했을 때 NTL AEC mode가 다른 실험 방법보다 선량이 최대 130.7% 최소 80%까지 증가한 결과 값을 보였으며, TL AEC mode는 NTL AEC mode보다 mAs와 피폭선량에서 각 각 43.8%, 44.4% 감소한 값을 보였다. 통계적으로는 SNR과 CNR은 유의한 차이를 보이지 않았다($p{\geq}0.05$). 그러므로, 본 연구에서는 BMI 지수가 높은 환자나 수술 후 인체 내에 금속물질이 있는 환자를 검사할 경우에는 TL AEC mode가 유효한 검사법이라고 사료된다.

Effects of Keratinase on Performance, Nutrient Utilization, Intestinal Morphology, Intestinal Ecology and Inflammatory Response of Weaned Piglets Fed Diets with Different Levels of Crude Protein

  • Wang, D.;Piao, X.S.;Zeng, Z.K.;Lu, T.;Zhang, Q.;Li, P.F.;Xue, L.F.;Kim, S.W.
    • Asian-Australasian Journal of Animal Sciences
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    • 제24권12호
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    • pp.1718-1728
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    • 2011
  • Two experiments were conducted to investigate the in vitro ability of keratinase to hydrolyze soybean glycinin and ${\beta}$-conglycinin and to evaluate the in vivo effects of keratinase when included in corn-soybean diets with different levels of crude protein and fed to nursery pigs. In experiment 1, a saturated keratinase solution (1 ml) was added to two blank controls of either glycinin or ${\beta}$-conglycinin resulting in the hydrolysis of 94.74% glycinin and 88.89% ${\beta}$-conglycinin. In experiment 2, 190 pigs (8.3${\pm}$0.63 kg BW) were allotted to one of four treatments in a 2${\times}$2 factorial arrangement on the basis of body weight, and sex was balanced among the pens. The effects of crude protein (19 vs. 22%) and keratinase (0 vs. 0.05%) were studied. Each treatment was applied to six pens with seven (two pens) or eight pigs per pen. Pigs were fed the experimental diets for 21 d. Weight gain and feed conversion ratio were improved (p<0.05) with keratinase supplementation while feed intake was reduced (p<0.05). Keratinase supplementation increased (p<0.05) the apparent total tract digestibility of dry matter, energy, crude protein and phosphorus. Keratinase supplementation also increased n-butyric acid in the cecum and colon, lactobacilli and total anaerobe counts in the colon as well as the ratio of villus height to crypt depth in the ileum. Additionally, fecal score, ammonia nitrogen and branch chain volatile fatty acids in the colon, E. coli and total aerobe counts in the colon, crypt depth in the jejunum and ileum as well as serum interleukin-1 and interleukin-6 concentrations were also decreased (p<0.05) by keratinase supplementation. A reduction in dietary crude protein decreased (p<0.05) colon ammonia nitrogen concentration and cecal propionic acid and branch chain volatile fatty acid concentrations. In addition, cecal E. coli counts, colon total anaerobe counts, ileal crypt depth, and serum interleukin-1 and interleukin-6 concentrations were also decreased (p<0.05) with the reduction of dietary crude protein. With the exception of fecal scores, there were no significant interactions between crude protein and keratinase. This study provides evidence that dietary keratinase supplementation improved nursery pig performance by improving intestinal morphology and ecology, thus improving nutrient digestibility and alleviating the inflammatory response.

Effects of Different Mycotoxin Adsorbents on Performance, Meat Characteristics and Blood Profiles of Avian Broilers Fed Mold Contaminated Corn

  • Wang, R.J.;Fui, S.X.;Miao, C.H.;Feng, D.Y.
    • Asian-Australasian Journal of Animal Sciences
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    • 제19권1호
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    • pp.72-79
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    • 2006
  • 1,225 healthy day-old avian broiler chicks were used to investigate the effects of activated charcoal (AC, made from willow tree), hydrated sodium calcium aluminosilicates (HSCAS) and esterified glucomannan (EGM) supplementation on broiler performance, blood profiles and meat characteristics when less moldy or moldy corn was included to formulate seven isocaloric and isonitrogenous diets: Positive Control (less moldy corn diet, PC), PC+2% AC, Negative Control (moldy corn, NC), NC+0.05% EGM, NC+0.1% EGM, NC+0.5% HSCAS and NC+1% AC. PC+2% AC resulted in lower growth rate, poorer feed conversion ratio (FCR), more leg problems and higher mortality of birds than those fed PC diet (p<0.05). Inclusion of 0.05% EGM, 0.1% EGM, 0.5% HSCAS and 1% AC in NC diet did not improve average daily weight gain (ADG) or affect feed intake of birds during the first or the second three-week periods. However, 0.05% EGM tended to (p>0.05) and 0.1% EGM significantly (p<0.05) improved FCR during the first three-week period. Breast meat of NC birds had higher Minolta $L^*$ values (white) but lower $a^*$ (reddish) and $b^*$ (yellowish) values (p<0.01) than the PC birds. Addition of 0.05% EGM and 0.1% EGM in NC diet reduced the $L^*$ values (p<0.05), improved $a^*$ and $b^*$ values (p<0.05) of breast meat of birds fed NC diet, but had no effect on meat color when 0.5% HSCAS or 1% AC was included (p>0.05). Relative weight of liver to body was reduced by feeding NC diet (p<0.05) and could not be normalized by different mycotoxin adsorbents (p>0.05) to the ratio of the PC birds. Relative weight of cholecyst of NC birds was increased compared with PC birds and could only be normalized by addition of 0.05% EGM and 1% AC (p<0.05) in NC diet. NC birds had lower serum albumin level than the PC birds (p<0.05) and addition of 0.05% EGM or 1% AC in NC diet did normalize serum albumin level. Addition of 0.5% HSCAS in NC diet further reduced serum albumin, globulin, total protein and uric acid levels (p<0.05). It was concluded that lower FCR during the first three-week period of growth and deterioration of meat quality observed in bird fed moldy corn with moderate T2 and fuminisin contamination and damaged nutrients and pigment availability, might be improved by dietary supplementation of 0.05% to 0.1% EGM, but not by 1% AC or 0.5% HSCAS supplementation.

Hybrid MBE Growth of Crack-Free GaN Layers on Si (110) Substrates

  • 박철현;오재응;노영균;이상태;김문덕
    • 한국진공학회:학술대회논문집
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    • 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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    • pp.183-184
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    • 2013
  • Two main MBE growth techniques have been used: plasma-assisted MBE (PA-MBE), which utilizes a rf plasma to supply active nitrogen, and ammonia MBE, in which nitrogen is supplied by pyrolysis of NH3 on the sample surface during growth. PA-MBE is typically performed under metal-rich growth conditions, which results in the formation of gallium droplets on the sample surface and a narrow range of conditions for optimal growth. In contrast, high-quality GaN films can be grown by ammonia MBE under an excess nitrogen flux, which in principle should result in improved device uniformity due to the elimination of droplets and wider range of stable growth conditions. A drawback of ammonia MBE, on the other hand, is a serious memory effect of NH3 condensed on the cryo-panels and the vicinity of heaters, which ruins the control of critical growth stages, i.e. the native oxide desorption and the surface reconstruction, and the accurate control of V/III ratio, especially in the initial stage of seed layer growth. In this paper, we demonstrate that the reliable and reproducible growth of GaN on Si (110) substrates is successfully achieved by combining two MBE growth technologies using rf plasma and ammonia and setting a proper growth protocol. Samples were grown in a MBE system equipped with both a nitrogen rf plasma source (SVT) and an ammonia source. The ammonia gas purity was >99.9999% and further purified by using a getter filter. The custom-made injector designed to focus the ammonia flux onto the substrate was used for the gas delivery, while aluminum and gallium were provided via conventional effusion cells. The growth sequence to minimize the residual ammonia and subsequent memory effects is the following: (1) Native oxides are desorbed at $750^{\circ}C$ (Fig. (a) for [$1^-10$] and [001] azimuth) (2) 40 nm thick AlN is first grown using nitrogen rf plasma source at $900^{\circ}C$ nder the optimized condition to maintain the layer by layer growth of AlN buffer layer and slightly Al-rich condition. (Fig. (b)) (3) After switching to ammonia source, GaN growth is initiated with different V/III ratio and temperature conditions. A streaky RHEED pattern with an appearance of a weak ($2{\times}2$) reconstruction characteristic of Ga-polarity is observed all along the growth of subsequent GaN layer under optimized conditions. (Fig. (c)) The structural properties as well as dislocation densities as a function of growth conditions have been investigated using symmetrical and asymmetrical x-ray rocking curves. The electrical characteristics as a function of buffer and GaN layer growth conditions as well as the growth sequence will be also discussed. Figure: (a) RHEED pattern after oxide desorption (b) after 40 nm thick AlN growth using nitrogen rf plasma source and (c) after 600 nm thick GaN growth using ammonia source for (upper) [110] and (lower) [001] azimuth.

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