• Structural Engineering and Mechanics
• /
• 제71권3호
• /
• pp.271-282
• /
• 2019

The span record of cable-stayed bridges has exceeded 1,000 m, which makes research on the maximum possible span length of cable-stayed bridges an important topic in the engineering community. In this paper, span limit is discussed from two perspectives: the theoretical span limit determined by the strength-to-density ratio of the cable and girder, and the engineering span limit, which depends not only on the strength-to-density ratio of materials but also on the actual loading conditions. Closed form equations of both theoretical and engineering span limits of cable-stayed bridges determined by the cable and girder are derived and a detailed parametric analysis is conducted to assess the engineering span limit under current technical conditions. The results show that the engineering span limit of cable-stayed bridges is about 2,200 m based on materials used available today. The girder is the critical member restricting further increase in the span length; its compressive stress is the limiting factor. Approaches to increasing the engineering span limit are also presented based on the analysis results.

• 한국전기전자재료학회논문지
• /
• 제35권4호
• /
• pp.322-332
• /
• 2022

Energy storage capacitors based on dielectric ceramics with superior polarization properties and dielectric constant can provide much higher output power density due to their very fast energy charging/discharging rates, which are particularly suitable for operating pulsed-power devices. For an outstanding energy storage performance of dielectric capacitor, a large recoverable energy density could be derived by introducing a slim polarization-electric field hysteresis loop into dielectric materials by various technical approaches. Many research teams have explored various dielectric capacitor technologies to demonstrate high output power density and ultrafast charging/discharging behavior. This article reviews the recent research progress in high-performance dielectric capacitors for pulsed-power electronic applications.

• 반도체디스플레이기술학회지
• /
• 제20권4호
• /
• pp.146-150
• /
• 2021

Plasma information based virtual metrology (PI-VM) that predicts wafer-to-wafer etch rate variation after wet cleaning of plasma facing parts was developed. As input parameters, plasma information (PI) variables such as electron temperature, fluorine density and hydrogen density were extracted from optical emission spectroscopy (OES) data for etch plasma. The PI-VM model was trained by stepwise variable selection method and multi-linear regression method. The expected etch rate by PI-VM showed high correlation coefficient with measured etch rate from SEM image analysis. The PI-VM model revealed that the root cause of etch rate variation after the wet cleaning was desorption of hydrogen from the cleaned parts as hydrogen combined with fluorine and decreased etchant density and etch rate.

• 대한영양사협회학술지
• /
• 제9권1호
• /
• pp.71-80
• /
• 2003

Food intake patterns and iron nutritional status of male and female college students were studied based on dietary iron density. Dietary data were collected using the method of 24-hour recalls for 3 consecutive days from 106 students, and fasting blood were drawn to measure iron nutritional status indicators such as total iron binding capacity, serum iron, hematocrit, hemoglobin, and red blood cell count. Mean daily iron intakes of male and female students were 13.3㎎ and 10.0㎎, which were 107% and 63% of the RDA, respectively. However, dietary iron density were similar between male and female students as 5.9㎎/1,000㎉ and 5.7㎎/1,000㎉, respectively. The diets were divided into two groups according to iron density; high iron density group (6㎎/1,000㎉ or more) and low iron density group (less than 6㎎/1,000㎉). The students in high density group had lower intakes of energy, especially fat, than those in low density group. Female students in high density group showed significantly higher intakes of iron, and non-heme iron and folate than those of low density group. The students in high density group consumed more rice, hamburger, and eggs, while those in low density group consumed more Ra-myon and alcoholic beverages. The students in high density group consumed greater proportions of iron from plant-origin foods. Vegetables, legumes and seasonings were the food groups that female students in high density group consumed significantly more than those in low density group. Also the percentages of female students with iron deficiency were higher in low density group. These results suggest that diet with high iron density is important to improve iron nutritional status of women, and further research about the effective way to increase iron density in our diet is needed.

• 한국물환경학회지
• /
• 제35권6호
• /
• pp.557-566
• /
• 2019

Paldang is a river reservoir in the Midwest of Korea, which is a drinking water source for the metropolitan area. Since the Paldang Reservoir is shallow, and has a short hydraulic residence time, its water quality is directly impacted by two incoming rivers, the north Han River (NHR) and the south Han River (SHR). The NHR has different seasonal patterns of water temperature from the SHR because the NHR is greatly impacted by the discharge water from upstream dams. The electrical conductivity (EC) and other material concentrations of the SHR are usually higher than those of the NHR because its basin is limestone-based. The difference in water temperature in the two rivers causes density flow, and the distribution of the EC within the reservoir can be an indicator for monitoring density flow. From the vertical gradient of the EC at the dam site, from spring to fall, it was confirmed that the SHR flowed into the upper layer, and the NHR flowed into the lower layer, and vice versa at other times. The relative difference (RD) of the EC between the upper layer and the lower layer at the dam site was used as an indicator for density flow. The RD of the EC showed a very significant correlation with the RD of total organic carbon (r = 0.70, p < 0.001) and the RD of total nitrogen (r = 0.58, p < 0.01). This relationship is based on the assumption that the difference in electrical conductivity and water quality between the SHR and the NHR is constant. However, in many cases this assumption is inconsistent. Thus, further study is needed on more suitable indicators to evaluate the impact of density flow on water quality.

• Journal of Preventive Medicine and Public Health
• /
• 제49권6호
• /
• pp.367-375
• /
• 2016

Objectives: The established theory that breast density is an independent predictor of breast cancer risk is based on studies targeting white women in the West. More Asian women than Western women have dense breasts, but the incidence of breast cancer is lower among Asian women. This meta-analysis investigated the association between breast density in mammography and breast cancer risk in Asian women. Methods: PubMed and Scopus were searched, and the final date of publication was set as December 31, 2015. The effect size in each article was calculated using the interval-collapse method. Summary effect sizes (sESs) and 95% confidence intervals (CIs) were calculated by conducting a meta-analysis applying a random effect model. To investigate the dose-response relationship, random effect dose-response meta-regression (RE-DRMR) was conducted. Results: Six analytical epidemiology studies in total were selected, including one cohort study and five case-control studies. A total of 17 datasets were constructed by type of breast density index and menopausal status. In analyzing the subgroups of premenopausal vs. postmenopausal women, the percent density (PD) index was confirmed to be associated with a significantly elevated risk for breast cancer (sES, 2.21; 95% CI, 1.52 to 3.21; $I^2=50.0%$). The RE-DRMR results showed that the risk of breast cancer increased 1.73 times for each 25% increase in PD in postmenopausal women (95% CI, 1.20 to 2.47). Conclusions: In Asian women, breast cancer risk increased with breast density measured using the PD index, regardless of menopausal status. We propose the further development of a breast cancer risk prediction model based on the application of PD in Asian women.

• 한국지반환경공학회 논문집
• /
• 제8권5호
• /
• pp.23-29
• /
• 2007

약액으로 개량된 지반의 액상화 저항은 약액의 농도에 따라 달라지며 현재는 일축압축강도를 기준으로 농도가 결정되는 것이 일반적이다. 하지만 액상화에 대한 저항력을 나타내는 강성저하율을 적극적으로 평가하여 합리적이고 경제적인 설계를 확립해야 할 필요성이 몇몇 연구자들에 의해 지적되어 왔다. 이에 본 논문에서는 반복전단 삼축압축시험을 이용하여 개량토의 강성저하율을 평가하였으며 이를 바탕으로 약액 농도 산정의 합리성을 검토하였다. 실험결과, 개량토는 유효응력의 감소, 강성의 저하 측면에서 모두 액상화에 대한 저항력을 갖고 있었으며, 설계에서 사용하는 5~6%의 약액 농도보다 적은 2%의 약액 농도에서도 액상화 저항이 향상되었다. 이러한 점을 바탕으로 생각하면, 기존의 일축압축강도를 기준으로 한 약액농도의 설정은 과다설계의 가능성이 있는 것으로 판단되었으며, 결국 과도하게 일축압축강도를 증가 시키지 않고도 강성저하가 방지되며 이를 반영한다면 약액 농도를 보다 합리적으로 줄여 갈 수 있을 것으로 기대한다.

• 한국환경과학회지
• /
• 제25권12호
• /
• pp.1689-1699
• /
• 2016

The growth conditions of planted trees, invasion of nuisance herbaceous species, competition between species, and effects of erosion control were monitored over five years in a riparian greenspace in Gapyeong County that was established through multilayered and grouped ecological planting. Of 156 trees planted in the upper and middle layers, 5.8% died. This tree death was attributed to poor drainage or aeration in the rooting zone from the clay-added root ball and too deep planting as well as a small-sized root ball and scanty fine roots. Of all the trees, 21.6% grew poorly due to transplant stress in the first year after planting, but they started to grow vigorously in the third year. This good growth was largely associated with soil improvement before planting, selection of appropriate tree species based on growth ground, and control of dryness and invasive climbing plants through surface mulching and multilayered/grouped planting. Mixed planting of fast-growing species as temporary trees was desirable for accelerating planting effect and increasing planting density. Thinning of fast-growing trees was required in the fifth year after planting to avoid considerable competition with target species. To reduce the invasion of herbaceous and climbing plants that oppress normal growth of planted trees, higher density planting of trees (crown opening of about 15%), woodchip mulching to a 10-cm depth, and edge planting 2 m wide were more effective than lower density planting (crown opening of 70%), no surface mulching, and no edge planting, respectively. This reduction effect was especially great during the first three years after planting. Nuisance herbaceous plants rarely invaded higher density planting with woodchip mulching over the five years. Higher density planting or woodchip mulching also showed much greater erosion control through rainfall interception and buffering than lower density planting with no mulching did. Based on these results, desirable planting and management strategies are suggested to improve the functions of riparian greenspaces.

• 정보처리학회논문지B
• /
• 제11B권2호
• /
• pp.213-220
• /
• 2004

진화 알고리즘은 여러 개의 상충하는 목적을 갖는 다목적 최적화 문제를 해결하기에 적합한 방법이다. 특히, 파레토 지배관계에 기초하여 개체의 적합도를 평가하는 파레토 기반 진화알고리즘들은 그 성능에 있어서 우수한 평가를 받고 있다. 최근의 파레토 기반 진화알고리즘들은 전체 파레토 프론트에 균일하게 분포하는 해집합의 생성을 위해 개체들의 밀도를 개체의 적합도를 평가하기 위한 하나의 요소로 사용하고 있다. 그러나 밀도의 역할은 전체 진화과정에서 중요한 요소가 되기보다는 파레토 프론트에 어느 정도 수렴된 후, 개체의 균일 분포를 만들기 위해 사용된다. 본 논문에서 우리는 파레토 지배 순위와 밀도에 대한 임의가중치를 적용한 다목적 최적화 진화알고리즘을 제안한다. 제안한 알고리즘은 진화 개체의 적합도를 평가하기 위해 파레토 순위와 밀도에 대한 임의의 가중치를 적용하므로 전체 진화과정에서 파레토 순위와 밀도가 비슷한 영향을 미치도록 하였다. 또한, 제안한 방법을 6개의 다목적 최적화 문제에 적용한 결과 비교적 우수한 결과를 보였다.

• 대한토목학회논문집
• /
• 제28권3D호
• /
• pp.287-293
• /
• 2008

국내의 경우 현재 연결로 접속부의 서비스수준 분석은 2005년에 제정된 우리나라의 도로용량편람(KHCM)에서 제시하고 있는 영향권 내 밀도를 효과척도로 하여 분석하고 있다. 국내의 경우 현재 연결로 접속부의 서비스수준 분석은 2005년에 개정된 KHCM에서 제시하고 있는 영향권 내 밀도를 효과척도로 하여 분석하고 있다. KHCM의 영향권 내 밀도추정모형은 고속도로만을 대상으로 구축된 것으로 도시고속도로와는 특성의 차이가 상당하여 KHCM에서 제시한 모형을 도시고속도로에 적용하는데 검증이 필요한 것으로 판단된다. 따라서 이 연구의 목적은 고속도로와는 다른 특성을 가진 도시고속도로상의 유입연결로 합류영향권내 실시간 교통특성 자료를 바탕으로 연결로 접속부의 서비스수준 평가를 위한 효과척도인 영향권 내 밀도를 보다 정확하게 추정하는 분석모델을 개발하고 2005년 의 KHCM모형과 더불어 2000년에 개정된 미국의 도로용량편람(USHCM)에서 제시하고 있는 모형을 도시고속도로(번영로)에 적용하여 그 타당성을 검토하는데 있다.