• 대한기계학회논문집
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• 제7권4호
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• pp.425-433
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• 1983

Fatigue tests by axial loading (R=0.1) were carried out to investigate fatigue crack growth properties of small surface cracks in mild steel at room temperature, 250.deg. C and 400.deg. C, by using flat specimens with a small artificial pit. All the data of the fatigue crack growth rate obtained in the present tests are determined as a function of the stress intensity factor range, so that the applicability of liner fracture mechanics to the fatigue crack growth of surface cracks at elevated temperatures is investigated and discussed in comparison with the data of type 304 stainless steel at room temperature and elevated temperature. The obtained results are as follows: 1) Relations of both surface fatigue crack length and its depth to cycle ratio fall within a narrow scatter band in spite of different stress levels. 2) The .DELTA. .sigma. .root. .pi. a-da/dN relation of surface fatigue crack growth at room temperature is independent of the stress level and can be plotted as a straight line at log-log diagram, but the relation at 400.deg. C depends partly on the stress level. 3) Relations of the fatigue crack growth into depth d(2b)/dN and is stress intensity factor range .DELTA. $K_{I}$, accounted for the aspect ratio variation, fall within a narrow scatter band for wide range of the applied stress levels. And .DELTA. $K_{I}$E-d(2b)/dN relations of mild steel at different stress level coincide relatively well with the data of type 304 stainless steel. 4) The value of aspect ratio obtained by a beach mark method and a temper coloring method approaches about 0.9 in common with crack growth and it is independent of stress level and temperatures. 5) The equi-crack length curve is parallel to S-N$_{f}$ curve at elevated temperatures.s.s.s.

• 한국정밀공학회지
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• 제9권3호
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• pp.140-148
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• 1992

The effect of mechanical, properties in the plastic zone near the crack-tip was investigated, under various controlled loading conditions, i.e., ${\Delta}K$ increasing, ${\Delta}K$ decreasing, and single overload test. For both ${\Delta}K$ decreasing test and ${\Delta}K$ increasing test with constant stress ratio, it is found that the ratio of material constant m'( ${\Delta}K$ decreasing test) to material constant m( ${\Delta}K$ increasing test) is larger than 1 for n<0.1, and it is equal to 1 for 0.10.2. A modified crack growth rate equation based on Forman's equation which applied stable region of fatigue crack propagation in ${\Delta}K$ decreasing test is proposed. Within the limit of this single overload test, an empirical relation between among the retardation ratio (Nd/ $N^{*}$), the strain hardening exponent (n) and the percent peak load (%PL) has been established.established.

• 한국결정성장학회지
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• 제17권5호
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• pp.187-191
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• 2007

The device performance of ZnO-thin film transistors(ZnO-TFTs) with gate dielectrics of $SiO_2,\;SiN_x$ and Polyvinylphenol(PVP) having a bottom gate configuration were investigated. ZnO-TFTs can induce high device performance with low intrinsic carrier concentration of ZnO only by controlling gas flow rates without additional doping or annealing processes. The field effect mobility and on/off ratio of ZnO-TFTs with $SiN_x$ were $20.2cm^2V^{-1}s^{-1}\;and\;5{\times}10^6$ respectively which is higher than those previously reported. The device adoptable values of the mobility of $1.37cm^2V^{-1}s^{-1}$ and the on/off ratio of $6{\times}10^3$ were evaluated from the device with organic PVP dielectric.

• ETRI Journal
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• 제37권6호
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• pp.1120-1128
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• 2015

We propose a pseudo optical N-level pulse-amplitude modulation (PO PAM-N) signal using a few externally-modulated lasers (EMLs) operating at different wavelengths, which is suitable for upgrading the transmission speed over an optical link of < 10 km single-mode fiber with low-cost components. To compare a PO PAM-N signal with that of a standard optical PAM-N signal, we perform experiments for evaluating the performance of a 51.56-Gb/s PO PAM-4 signal and standard 51.56-Gb/s optical PAM-4 signal. The receiver sensitivity (at $BER=10^{-5}$) of the PO PAM-4 signal is 1.5 dB better than the receiver sensitivity of a standard optical PAM-4 signal. We also investigate the feasibility of PO PAM-N (N = 4, 8, and 16) signals operating at 103.12 Gb/s, considering relative intensity noise, timing jitter, extinction ratio (ER) of EMLs, and dispersion. From the results, a PO PAM-8 signal performs better than PO PAM-4 and PO PAM-16 signals at 103.12 Gb/s. Finally, we suggest a timing control method to suppress the effect of dispersion in a PO PAM-N signal. We show that the tolerance to dispersion of a 103.12-Gb/s PO PAM-8 signal can be improved to ${\pm}40ps/nm$ by applying a proposed scheme.

• Bulletin of the Korean Chemical Society
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• 제34권1호
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• pp.225-230
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• 2013

A new heteropolyanion-based ionic ($[Hmim]_5PMo_{10}V_2O_{40}$) was synthesized by the reaction of molybdovanadophosphoric acid ($H_5PMo_{10}O_{40}$) with N-methylimidazole. [$[Hmim]_5PMo_{10}V_2O_{40}$ showed a high catalytic activity in the oxidative desulfurization of sulfur-containing compounds in 1-methylimidazolium tetrafluoroborate ($[Hmim]BF_4$) ionic liquid using 30% aqueous $H_2O_2$ as the oxidant. The catalytic system was of high activity, simplified workup and flexible recyclability. The catalytic oxidation reactivity of sulfur-containing compounds decreased in the order dibenzothiophene (DBT) > 4,6-dimethyldibenzothiophene (4,6-DMDBT) > benzothiophene (BT). The influences of various parameters including reaction time (t) and temperature (T), catalyst dosage, and oxidant to sulfur molar ratio n(O)/n(S) on the desulfurization of model oil were investigated in details. 99.1% of DBT conversion in the model oil was achieved at atmospheric pressure under the optimal conditions: n(O)/n(S) = 4:1, $60^{\circ}C$, 100 min and molar ratio of catalyst to sulfur of 0.062. The ionic liquid can be recycled six times without significant decrease in activity.

• Nutrition Research and Practice
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• 제10권1호
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• pp.67-73
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• 2016

BACKGROUND/OBJECTIVES: This study was aimed at examining the association between dietary flavanones intake and lipid profiles according to the presence of metabolic syndrome (MetS) in Korean women with type 2 diabetes mellitus (T2DM). SUBJECTS/METHODS: A cross-sectional analysis was performed among 502 female T2DM patients (non-MetS group; n = 129, MetS group; n = 373) who were recruited from the Huh's Diabetes Clinic in Seoul, Korea between 2005 and 2011. The dietary intake was assessed by a validated semi-quantitative food frequency questionnaire (FFQ) and the data was analyzed using the Computer Aided Nutritional Analysis program (CAN-Pro) version 4.0 software. The intake of flavanones was estimated on the basis of the flavonoid database. RESULTS: In the multiple linear regression analysis after adjustment for confounding factors, daily flavanones intake was negatively associated with CVD risk factors such as total cholesterol, LDL-cholesterol, and apoB and apoB/apoA1 ratio only in the MetS group but not in the non-MetS group. Multiple logistic regression analysis revealed that the odds ratio for a higher apoB/apoA1 ratio above the median (${\geq}0.74$) was significantly low in the $4^{th}$ quartile compared to that in the $1^{st}$ quartile of dietary flavanones intake [OR: 0.477, 95% CI: 0.255-0.894, P for trend = 0.0377] in the MetS group. CONCLUSIONS: Dietary flavanones intake was inversely associated with the apoB/apoA1 ratio, suggesting a potential protective effect of flavanones against CVD in T2DM women with MetS.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1997년도 가을 학술발표회 논문집
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• pp.261-266
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• 1997

• 한국안전학회지
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• 제7권1호
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• pp.20-29
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• 1992

Effects of strain hardening exponents on the retardation behavior of fatigue crack propagation are experimentally investigated. The retardation of fatigue crack propagation seems to be induced by the crack closure at crack tip. The phenomenon of crack closure becomes remarkable with the increment of strain hardening exponent and magnitude of percent peak load. The ratio of crack growth increment(a$\_$d//w$\_$d/) is influenced by a single overloading (a$\_$d/) and estimated plastic zone size (W$\_$d/=2r$\_$y/) is increased according with the increasing of strain ha.dening exponents. The number of retarded crack growth cycles were (N$\_$d/) decreased as the baseline stress intensity factor .ange( K$\_$b/) was increased. Within the limitation of these experimental results obtained under the single overload, an empirical relation between crack retardation ratio (Nd/N＊), strain hardening exponent (n) and percent peak load (％PL) has been proposed as; Nd/N＊＝ exp [PL $.$ PL$.$A(n)＋B(n) ] where, A(n)＝${\alpha}$n＋${\beta}$, B(n)＝${\gamma}$n＋$\delta$, PL＝％PL/100 and ${\alpha}$＝0.78, ${\beta}$＝0.54, ${\gamma}$＝0.58 and $\delta$＝-0.01, It is interesting to note that all these constants are identical for materials such as aluminum(A3203), steel(S4SC), steel(SS41) and stainless steel(SUS316) used in this experimental study.

• 지구물리와물리탐사
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• 제5권4호
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• pp.250-256
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• 2002

전기비저항 토모그래피는 지하의 전기비저항 분포를 영상화할 수 있는 매우 중요한 정밀 물리탐사법으로 지반조사 및 환경 오염대의 조사에 널리 사용되고 있다. 전기비저항 토모그래피 탐사의 경우 다양한 전극배열법이 사용될 수 있으며 각 배열법은 나름대로의 장단점을 가지고 있다. 예를 들어 단극배열의 경우에는 신호대 잡음비는 높으나 분해능이 벌어지며, 쌍극자배열의 경우에는 분해능은 높지만 신호대 잡음비가 너무 낮다. 단극-쌍극자 배열의 경우에는 중간정도의 분해능과 신호대 잡음비를 갖는다. 최근 개발된 변형된 단극-쌍극자 배열의 경우에는 단극-쌍극자 배열 수준의 신호대 잡음비와 분해능을 갖는다. 그러나 단극배열을 제외한 이들 전극배열법은 전류 및 전위 전극의 위치에 따라서는 겉보기 비저항이 발산할 수도 있다는 단점을 갖는다. 또한 단극배열의 경우에는 측정된 겉보기 비저항이 이상체의 전기비저항을 그대로 반영하지 못한다는 단점이 있다. 본 연구에서는 전류전극과 전위전극의 상대적인 위치에 따라 단극-쌍극자 배열과 변형된 단극-쌍극자 배열을 혼용하는 소위 혼합배열이라는 새로운 전극배열법을 제안하고자 한다. 이 새로운 전극배열법은 신호대 잡음비 및 분해능은 단극-쌍극자 배열의 수준을 유지하며, 측정 시추공상에서 겉보기 비저항이 발산하지 않는 특성을 갖는다. 또한 측정되는 겉보기 비저항은 항상 이상체의 전기비저항을 잘 반영한다.

• 한국식품영양과학회지
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• 제18권4호
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• pp.371-374
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• 1989

측백을 물로 추출하여 추출액를 토끼에게 4주간 급여하여 사육시키고 혈장을 분리하여 분석한 결과 다음과 같은 결론을 얻었다. 1. 실험식이 기간동안 체중변화는 대조군과 실험군이 큰 변화가 없이 증가되었으며 간장의 무게는 다같이 $43{\pm}5g$이었다. 2. 혈당, 콜레스테롤, 트리글리세라이드, 지질과산화물은 대조군에 있어서 보다 낮은 값을 보였고, $2m{\ell}/kg$을 급여한 실험군에 있어서 모두 낮은 값을 나타냈다. 3. 지방산 조성은 대조군과 실험군에 있어서 큰 차이는 없으나 $C_{16:0}$은 실험군에 있어서는 아주 높은 값(50%이상)을 보였고, n-3/n-6 ratio가 0.31이상으로 p/s ratio가 감소함을 보였다. 4. 이상의 결과로 측백의 물 추출액을 급여하면, 혈당, 콜레스테롤, 지질과 산화물. 트리글리세라이드를 감소시킬 수 있을 것으로 사료된다.