• ETRI Journal
• /
• 제45권5호
• /
• pp.887-898
• /
• 2023

Aerial base stations (ABSs) seem promising to enhance the coverage and capacity of fifth-generation and upcoming networks. With the flexible mobility of ABSs, they can be positioned in air to maximize the number of users served with a guaranteed quality of service (QoS). However, ABSs may be overloaded or underutilized given inefficient placement, and user association has not been well addressed. Hence, we propose a three-dimensional ABS placement scheme with a delay-QoS-driven user association to balance loading among ABSs. First, a load balancing utility function is designed based on proportional fairness. Then, an optimization problem for joint ABS placement and user association is formulated to maximize the utility function subject to statistical delay QoS requirements and ABS collision avoidance constraints. To solve this problem, we introduce an efficient modified gray wolf optimizer for ABS placement with a greedy user association strategy. Simulation results demonstrate that the proposed scheme outperforms baselines in terms of load balancing and delay QoS provisioning.

• Ocean Systems Engineering
• /
• 제7권2호
• /
• pp.157-177
• /
• 2017

This research is based on the concept of safety airbag to design a self-rescue system for the autonomous underwater vehicle (AUV) using micro inertial sensing module. To reduce the possibility of losing the underwater vehicle and the difficulty of searching and rescuing, when the AUV self-rescue system (ASRS) detects that the AUV is crashing or encountering a serious collision, it can pump carbon dioxide into the airbag immediately to make the vehicle surface. ASRS consists of 10-DOF sensing module, sensing attitude algorithm and air-pumping mechanism. The attitude sensing modules are a nine-axis micro-inertial sensor and a barometer. The sensing attitude algorithm is designed to estimate failure attitude of AUV properly using sensor calibration and extended Kalman filter (SCEKF), feature extraction and backpropagation network (BPN) classify. SCEKF is proposed to be used subsequently to calibrate and fuse the data from the micro-inertial sensors. Feature extraction and BPN training algorithms for classification are used to determine the activity malfunction of AUV. When the accident of AUV occurred, the ASRS will immediately be initiated; the airbag is soon filled, and the AUV will surface due to the buoyancy. In the future, ASRS will be developed successfully to solve the problems such as the high losing rate and the high difficulty of the rescuing mission of AUV.

• 동력기계공학회지
• /
• 제12권4호
• /
• pp.64-71
• /
• 2008

This study is on pedestrian protection device using pneumatic cylinder and simple link mechanism when vehicle collide with pedestrian. This study ensured the safety space between engine and hood after it applies to simple link mechanism and pneumatic cylinder. It can absorb the damage which measure the specific device if vehicle collide with pedestrian. Combination of simple link mechanism and pneumatic cylinder was more superior than the present pedestrian protection device. Simple link mechanism could confirm superior height and survival probability than when only cylinder operated. It also ensured enough space between engine and hood. And if a cylinder is not working because of old cylinder, poor repair or damage of accident vertical cylinder would be difficult to execute because there exists the irregular space between engine and hood. If simple link mechanism operates with only one cylinder it could ensure the regular space because simple link mechanism set up at the middle of hood. So this device could confirm high safety for pedestrian.

• 상하수도학회지
• /
• 제19권4호
• /
• pp.437-445
• /
• 2005

Zeta potential is a key parameter of double layer repulsion for individual particles and can usually be used to interpret the trend of coagulation efficiency. This study focused on the measurement of zeta potential of algae and clay under various experimental conditions including water characteristics (pure water, stream water, reservoir water) and coagulant dose (10~50 mg/L). Results showed that the variation of zeta potential was highly sensitive depending on the water characteristics and coagulation conditions. Zeta potential of two genera of algae (anabaena sp. and microcystis sp.) were changed highly with coagulant dosage, especially. On the basis of trajectory analysis, bubble-floc collision efficiency simulated in terms of zeta potential was fitted well with removal efficiency of chlorophyll-a from algae particles. It was found that the control of zeta potential was important for effective removal of algae particles.

• 우주기술과 응용
• /
• 제3권2호
• /
• pp.118-143
• /
• 2023

우주공간은 안보공간의 역할에서 상업공간으로 역할을 급속히 넓혀가고 있다. 현실적인 제약들 때문에 늦게 출발했지만 우리나라는 최근 들어 비약적 기술발전과 함께 우주에 대한 국가적 관심이 커지고 있다. 2023년 5월 25일, 누리호는 7개의 위성을 성공적으로 550 km 고도의 태양동기궤도에 배치했다. 그런데, 이 근처 고도에는 이미 스타링크가 4,000대 이상의 위성을 배치시키고 상업적 서비스를 진행하고 있다. 따라서, 누리호 위성들은 스타링크위성들과의 위험상황발생 가능성에 대해 지속적으로 예측하고 만일의 경우에 대해서는 준비를 해야 한다. 본 논문은 누리호 위성들이 임무수행을 위해 궤도비행을 하면서 발생할 수 있는 충돌위험상황에 대해 수행한 연구의 계량적 분석결과를 보고한다. 분석결과에 따르면 누리호 위성들은 하루에 3회 정도 1 km 거리 이내로 스타링크위성에 접근하는 것으로 나타났으며, 이 상황에서의 충돌확률은 1.0E-5 이상인 것으로 계산되었고 크게는 1.0E-2 이상인 경우도 발생하고 있다. 2013년에 발사된 후 성공적으로 임무를 수행하고 있는 아리랑 5호에 대한 본 연구의 비교분석은 아리랑 5호와 누리호 위성들이 위험상황의 분포에 있어 중요한 차이가 있음을 보여준다. 본 연구는 스타링크가 회피기동을 할 때의 비용에 대한 계량적인 분석결과도 보고하며, 후발주자로서 우주산업에 진입하는 우리나라가 고려해야 할 전략도 제시했다. SpaceMap사에서 개발한 AstroOne 프로그램을 분석도구로 사용했으며, Celestrak사의 Socrates Plus에서 보고한 결과와 비교검증하였다. 우주물체데이터는 TLE(two line element)를 사용했다.

• 한국통신학회논문지
• /
• 제39C권6호
• /
• pp.457-465
• /
• 2014

본 논문에서는 수중음향센서네트워크의 수중 통신 프로토콜 시험을 위해 구축한 해상시험환경을 소개하고 상용 모뎀을 이용하여 실시한 및 매체접속제어기법(Medium Access Control: MAC)의 시험결과를 제시한다. 본 시험에서는 패킷 충돌을 회피하기 위해 기존 지상환경에서 많이 사용되는 반송파감지기반의 충돌회피기법(Carrier Sense Multiple Access/Collision Avoidance: CSMA/CA)을 사용하였으며 수중 통신 프로토콜로서의 가용성을 검증하였다. 시험에 사용된 네트워크 노드는 Benthos사의 상용 수중 모뎀과 ATmega2560 제어보드를 이용하여 구성하였다. 시험의 체계적 관리와 시험과정 관찰을 용이하게 하기 위해 각 노드가 GPS신호를 수신하여 자신의 위치를 파악할 수 있도록 하였으며 라디오주파수(Radio Frequency: RF) 인터페이스를 통해 위치정보 및 수중채널을 통해 송수신되는 패킷의 정보를 지상으로 보고할 수 있도록 했다. CSMA/CA 프로토콜을 수중환경에 적용하기 위해 4-way 핸드셰이킹동작에 사용되는 네 종류의 제어패킷 RTS(Request To Send), CTS(Clear to Send), DATA, ACK(Acknowledgement)을 수중환경에 맞게 설계했다. 시험을 통해 CSMA/CA 프로토콜의 실제 수중환경에서의 가용성을 검증할 수 있었다.

• Preventive Nutrition and Food Science
• /
• 제16권4호
• /
• pp.394-407
• /
• 2011

Better understanding of the complex factors leading to human diseases will be necessary for both long term prevention and for managing short and long-term health problems. The underlying causes, leading to a global health crisis in both acute and chronic diseases, include finite global health care resources for sustained healthy human survival, the population explosion, increased environmental pollution, decreased clean air, water, food distribution, diminishing opportunities for human self-esteem, increased median life span, and the interconnection of infectious and chronic diseases. The transition of our pre-human nutritional requirements for survival to our current culturally-shaped diet has created a biologically-mismatched human dietary experience. While individual genetic, gender, and developmental stage factors contribute to human diseases, various environmental and culturally-determined factors are now contributing to both acute and chronic diseases. The transition from the hunter-gatherer to an agricultural-dependent human being has brought about a global crisis in human health. Initially, early humans ate seasonally-dependent and calorically-restricted foods, during the day, in a "feast or famine" manner. Today, modern humans eat diets of caloric abundance, at all times of the day, with foods of all seasons and from all parts of the world, that have been processed and which have been contaminated by all kinds of factors. No longer can one view, as distinct, infectious agent-related human acute diseases from chronic diseases. Moreover, while dietary and environmental chemicals could, in principle, cause disease pathogenesis by mutagenic and cytotoxic mechanisms, the primary cause is via "epigenetic", or altered gene expression, modifications in the three types of cells (e.g., adult stem; progenitor and terminally-differentiated cells of each organ) during all stages of human development. Even more significantly, alteration in the quantity of adult stem cells during early development by epigenetic chemicals could either increase or decrease the risk to various stem cell-based diseases, such as cancer, later in life. A new concept, the Barker hypothesis, has emerged that indicates pre-natal maternal dietary exposures can now affect diseases later in life. Examples from the studies of the atomic bomb survivors should illustrate this insight.

• 대한기계학회논문집B
• /
• 제29권10호
• /
• pp.1156-1162
• /
• 2005

In this study, a noble method is proposed to prevent the edge overcoating (EOC) that may develop near the edge of the steel strip in the gas wiping process of continuous hot-dip galvanizing. In our past study (Trans. of the KSME (B), Vol. 27, No. 8, pp. $1105\~1113$), it was found that EOC is caused by the alternating vortices which are generated by the collision of two opposed jets in the region outside the steel strip. When the two opposed jets collide at an angle much less than $180^{o}$, non-alternating stable vortices are established symmetrically outside the steel strip, which lead to nearly uniform pressure on the strip surface. In order to deflect both jets downward by a certain angle, a cylinder with small diameter is installed tangentially to the exit of the lower lip of the two-dimensional jet. In order to find an optimum cylinder diameter, the three dimensional flow field is analysed numerically by using the commercial code, STAR-CD. And the coating thickness is calculated by using an integral analysis method to solve the boundary layer momentum equation. In order to compare the present noble method with the conventional baffle plate method to prevent the EOC, the flow field with a baffle plate is also calculated. The calculation results show that the tangentially installed cylinder at the bottom lip of the jet exit is more effective than the baffle plate to prevent EOC.

• 대기
• /
• 제18권4호
• /
• pp.317-338
• /
• 2008

Analyses of observational data and numerical simulations were performed to understand the mechanism of MCSs (Mesoscale Convective Systems) occurred on 13-14 July 2004 over Jindo area of the Korean Peninsula. Observations indicated that synoptic environment was favorable for the occurrence of heavy rainfall. This heavy rainfall appeared to have been enhanced by convergence around the Changma front and synoptic scale lifting. From the analyses of storm environment using Haenam upper-air observation data, it was confirmed that strong convective instability was present around the Jindo area. Instability indices such as K-index, SSI-index showed favorable condition for strong convection. In addition, warm advection in the lower troposphere and cold advection in the middle troposphere were detected from wind profiler data. The size of storm, that produced heavy rainfall over Jindo area, was smaller than $50{\times}50km^2$ according to radar observation. The storm developed more than 10 km in height, but high reflectivity (rain rate 30 mm/hr) was limited under 6 km. It can be judged that convection cells, which form cloud clusters, occurred on the inflow area of the Changma front. In numerical simulation, high CAPE (Convective Available Potential Energy) was found in the southwest of the Korean Peninsula. However, heavy rainfall was restricted to the Jindo area with high CIN (Convective INhibition) and high CAPE. From the observations of vertical drop size distribution from MRR (Micro Rain Radar) and the analyses of numerically simulated hydrometeors such as graupel etc., it can be inferred that melted graupels enhanced collision and coalescence process of heavy precipitation systems.

• 혜화의학회지
• /
• 제18권1호
• /
• pp.117-127
• /
• 2009

Study on correspondent of eastern and western astrology and Jung's psychological types, we obtain as follow as results. Western astrology is transmitted from China and developed, it influenced on the study of the Four Pillars(四柱學). Comparing assemble, gathering, punishment, destruction, collision, impair of Di-zhi(地支) in the study of Four Pillars with Xing-gong theory(星宮論) in the western astrology, can get the result that the Pillars study has close connection with astronomy and astrology. When we compared Jung's psychological types with astrology, the five elements(五行) and the four major factors, can be summarized like this. (1) intuition-fire sign-wood and fire-fire in the four major factors(四大), (2) sensation-earth sign-earth and metal-earth in the four major factors, (3) thinking-air sign-metal and water-wind in the four major factors, (4) feeling-water sign-water and wood-water in the four major factors. The four major factors of Buddhism is now understood as, earth, water and fire represent the state of solid(earth), liquid(water), gas(fire) and wind can be recognized as energy source help the changes. This is mentioned throughout the books, but only arranging the theory of four major factors.