• Journal of Hydrospace Technology
• /
• 제2권2호
• /
• pp.44-56
• /
• 1996

The effects of the air on the reductions in resistance when supplied under the bottom of a semi-planing ship with a step are investigated in the present study. A 1.275m long FRP model is constructed and the pressure and viscous tangential stresses over the planing surface of the hull with and without air supply are measured through measuring holes carefully selected at the towing tank of Seoul National University. Locations of holes most suitable for air injection are surveyed in front of the planing surface of the model with careful examinations of the limiting streamlines and pressure distributions measured without air supply. At those locations, found to be just front of the step, air has been supplied into a wake region to form an air filled cavity of fixed type. Flow rates and pressure of the supplied air as well as the local pressure and shear stress distributions on the hull surface are measured to understand the physics involved as well as to determine the conditions most effective in resistance reduction at the design speed. It has been found that total resistance of the stepped semi-planing hull can be considerably reduced if an air cavity generated by an adequate air injection at the bottom of the hull near the step. After the cavity optimized at the given speed, air bubbles also have been generated right behind the point where dividing streamlines re-attach to further reduce the frictional resistance but found to be not so effective as the air cavity in resistance reductions.

• 한국식품영양과학회지
• /
• 제24권2호
• /
• pp.346-353
• /
• 1995

The dietary requirement for zinc to maintain optimally the various metabolic and physiological funcitons is still under study. Human beings adapt to reductions in zinc intake by reducing the rate of growth or zinc excretion. Reductions in dietary zinc beyond the capacity to maintain homeostasis lead to utilization of zinc from an exchangeable pool. Loss of a small, critical amount of zinc from this pool leads to both biochemical and clinical signs of zinc deficiency. Zinc requirements have been assessed by balance studies and factorial method. As tissue zinc status influences endogenous losses and the dietary needs, individuls in good status may require higher amounts of zinc than those in poor status. While plasma zinc is insensitive to reducitons in dietary zinc, it is regarded as a valid, useful indicator of the exchangeable pool of zinc. Plasma metallothionein concentrations may prove useful for identifying poor zinc status. It has been suggested that functional end point measurement is the new direciton for zinc requirement. However, determination of the functional response to a marginal zinc intake is difficult because of the lack of a specific, sensitive indicator of zinc status. Presently, no good method for assessment of human zinc requirements exists.

• Environmental Engineering Research
• /
• 제15권1호
• /
• pp.29-33
• /
• 2010

In 2004, the Korean government launched comprehensive measures for nonpoint pollution that were intended to reduce their amount by 34.3% over of those forecast by 2020. During the first and second stages of their implementation; from 2004 to 2011, nonpoint source (NPS) measures have focused on systemic improvements and project management, as well as the introduction of optimal management techniques; accordingly, reductions have been small. However, during the third stage in 2011, serious reductions will be pursued. Accordingly, the gradual expansion of sites subject to NPS measures has focused on the establishment of a basis for reduction measures in connection with model projects during the first half of the plan, with full scale enforcement due in the second half. For Korea, rather than commencing NPS management en masse, it has been more appropriate to gradate NPS management into stages tailored to the different needs of new and existing businesses, as well as to the needs of large and small-scale businesses, in consideration of their specific circumstances. This has allowed sufficient time for such businesses to become accustomed to the concept of NPS management.

• Advances in concrete construction
• /
• 제7권1호
• /
• pp.31-37
• /
• 2019

This paper evaluates the workability and hardened properties of self-compacting concrete (SCC) containing silica fume as the partial replacement of cement. SCC mixtures with 0, 2, 4, 6, 8 and 10% silica fume were tested for fresh and hardened properties. Slump flow with $T_{500}$ time, L-box and V-funnel tests were performed for evaluating the workability properties of SCC mixtures. Compressive strength, splitting tensile strength and modulus of rupture were performed on hardened SCC mixtures. Experiments revealed that replacement of cement by silica fume equal to and more than 4% reduced the slump flow diameter and increased the $T_{500}$ and V-funnel time linearly. Compressive strength, splitting tensile strength and modulus of rupture increased with increasing the replacement level of cement by silica fume and were found to be maximum for SCC mixture with 10% silica fume. Further, residual hardened properties of SCC mixture yielding maximum strengths (i.e., SCC with 10% silica fume) were determined experimentally after heating the concrete samples up to 200, 400, 600 and $800^{\circ}C$. Reductions in hardened properties up to $200^{\circ}C$ were found to be very close to normal vibrated concrete (NVC). For 400 and $600^{\circ}C$ reductions in hardened properties of SCC were found to be more than NVC of the same strength. Explosive spalling occurred in concrete specimens before reaching $800^{\circ}C$.

• East Asian Economic Review
• /
• 제23권1호
• /
• pp.27-53
• /
• 2019

I employ search-and-matching to a multi-country and multi-sector Ricardian model with input-output linkages, trade in intermediate goods, and sectoral heterogeneity, in order to quantify the welfare effects from tariff changes. The paper shows that labor market frictions can be a source of comparative advantage in the sense that better labor market conditions contribute to lower cost in production. Labor market frictions play a critical role in determining the probability of exporting goods to trading partners, and interact with bilateral trade share, price, expenditures, etc. Unemployment and changes in unemployment rates due to tariff reductions contribute welfare changes across countries, implying that welfare effects based on quantitative trade models with full-employment are likely to be biased. I confirm the biased welfare effects by revisiting Caliendo and Parro (2015), who conduct an analysis of the welfare effects from the NAFTA from 1993 to 2005. I show that the welfare gap between theirs and mine has a positive correlation with changes in observed unemployment rates across countries. With the constructed model, I further conduct counterfactual exercises by asking what would happen if China's tariffs remain unchanged from 2006 to 2015. It turns out that there are mild welfare effects to trading partners in the world trading system.

• Steel and Composite Structures
• /
• 제46권5호
• /
• pp.709-718
• /
• 2023

The absence of an important portion of the web plate in steel beams with multiple circular perforations, cellular beams, causes the web plate to undergo distortions prior to and during lateral torsional buckling (LTB). The conventional LTB equations in the codes and literature underestimate the buckling moments of cellular beams due to web distortions. The present study is an attempt to develop analytical methods for estimating the elastic buckling moments of cellular beams. The proposed methods rely on the reductions in the torsional and warping rigidities of the beams due to web distortions and the reductions in the weak-axis bending and torsional rigidities due to the presence of web openings. To test the accuracy of the analytical estimates from proposed solutions, a total of 114 finite element analyses were conducted for six different standard IPEO sections and varying unbraced lengths within the elastic limits. These analyses clearly indicated that the LTB solutions in the AISC 360-16 and AS4100:2020 codes overestimate the buckling loads of cellular beams within elastic limits, particularly at shorter span lengths. The LDB solutions in the literature and the Eurocode 3 LTB solution, on the other hand, provided conservative buckling moment estimates along the entire range of elastic buckling.

• 한국환경과학회지
• /
• 제32권6호
• /
• pp.419-428
• /
• 2023

This study estimates the greenhouse gases (GHGs) emissions from energy sector of Changwon city from 2012 to 2020 and scenario analysis of GHGs reductions pathways in the context of the goal of 2030 NDC and 2050 carbon neutral scenario in Korea. As a result, the GHG emissions as a reference year of carbon neutral in 2018 were estimated as 8,872,641 tonCO_2eq accounting for 3,851,786 tonCO_2eq (43.6%) of direct source (scope 1) and 4,975,855 tonCO_2eq (56.4%) of indirect source (scope 2). Especially, among indirect sources as purchased electricity, manufacturing sector emitted the largest GHG accounting for 33.0%(2,915 thousands tonCO_2eq) of the total emissions from all energy sectors, scenario analysis of GHG reductions potential from the energy was analyzed 8,473,614 tonCO_2eq and the residual emissions were 354,027 tonCO_2eq. Purchased electricity and industry sector reducted the largest GHG accounting for 58.7%(4,976 thousands tonCO_2eq) and 42.1%(3,565 thousands tonCO_2eq) of the total emissions from all energy sectors, respectively.

• Structural Engineering and Mechanics
• /
• 제87권4호
• /
• pp.305-315
• /
• 2023

The idea of the combination of the fractional-order operators with the brain emotional learning-based intelligent controller (BELBIC) is developed for implementation in seismic-excited structures equipped with active mass damper (AMD). For this purpose, a new design framework of the mentioned combination namely fractional-order BEBIC (FOBELBIC) is proposed based on a modified-teaching-learning-based optimization (MTLBO) algorithm. The seismic performance of the proposed controller is then evaluated for a 15-story building equipped with AMD subjected to two far-field and two near-field earthquakes. An optimal BELBIC based on the MTLBO algorithm is also introduced for comparison purposes. In comparison with the structure equipped with a passive tuned mass damper (TMD), an average reduction of 44.7% and 42.8% are obtained in terms of the maximum absolute and RMS top floor displacement for FOBELBIC, while these reductions are obtained as 30.4% and 30.1% for the optimal BELBIC, respectively. Similarly, the optimal FOBELBIC results in an average reduction of 42.6% and 39.4% in terms of the maximum absolute and RMS top floor acceleration, while these reductions are given as 37.9% and 30.5%, for the optimal BELBIC, respectively. Consequently, the superiority of the FOBELBIC over the BELBIC is concluded in the reduction of maximum and RMS seismic responses.

• KDI Journal of Economic Policy
• /
• 제45권2호
• /
• pp.1-20
• /
• 2023

Carbon pricing is in the spotlight as an economically efficient policy to limit global warming and reduce greenhouse gas emissions. We examine how policymakers can improve social acceptance of a carbon tax, which is the main obstacle in implementing the policy. We conduct a survey experiment to analyze this topic and adopt two different interventions focusing on the use of revenue from a carbon tax and types of information to be provided. Regarding revenue use, we consider 1) tax reductions, 2) lump-sum transfers, and 3) green project investments. For information types, we focus on 1) the economic value of a carbon tax, and 2) the environmental value of a carbon tax. We find that lump-sum transfers have negative impacts on social acceptance of a carbon tax. For those who perceive climate change as a serious issue, moreover, both lump-sum transfers and tax reductions have negative impacts on acceptability. Regardless of the type of information provided, on the other hand, the social acceptance of a carbon tax is increased after the provision of information. Furthermore, the impact of information provision on the social acceptance interacts with the revenue use impacts. When the revenue use and the type of information are consistent with the aim of the policy, the effects of these strategies can be amplified.

• 대한기계학회논문집
• /
• 제17권5호
• /
• pp.1054-1065
• /
• 1993

본 연구에서는 정상상태의 단일 주파수에서의 임의의 음압분포로 조화가진되 는 3차원 정방형 밀폐계 음장의 경우에 대한 능동제어를 시도함으로써 사무실과 같은 실내 공간에 대한 능동적 소음저감의 응용 가능성을 검토하고자 하였다. 또한 변환기 의 위치선정을 위하여 상태공간 모드 모델의 모드 근사화에 따른 계수행렬의 요소를 평가함으로써 가제어성과 가광측성을 만족하는 최적한 변환기 (부가음원, 마이크로폰) 의 위치를 선정하였다. 밀폐계 내부의 음압을 저감시키는 목적함수로는 전체 시간평 균 음향 포텐셜에너지를 사용하였으며 폐공간의 음압변동을 이론적으로 규명함으로써 부가적인 음원의 복소세기를 적절히 선정하여 이 음향 포텐셜 에너지의 양을 최소화 시킬 수 있음을 보였다.