Modified Tomographic Estimation of the lonosphere using Fewer Coefficients

Youngho Sohn,Changdon Kee 한국항공우주학회 2004 International Journal of Aeronautical and Space Sc Vol.5 No.1

Ionospheric time delay is the biggest error source for single-frequency DGPS applications, including time transfer and Wide Area Differential GPS (WADGPS). Currently, there are many attempts to develop real-time ionospheric time delay estimation techniques to reduce positioning error due to the ionospheric time delay. Klobuchar model is now widely used for ionospheric time delay calculation for single-frequency . users. It uses flat surface at night time and cosine surface at day time[1]. However, the model was developed for worldwide ionosphere fit, it is not adequate for local area single-frequency users who want to estimate ionospheric time delay accurately [2] Therefore, 3-D ionosphere model using tomographic estimation has been developed. 3-D tomographic inversion model shows better accuracy compared with prior algorithms[3]. But that existing 3-D model still has problem that it requires many coefficients and measurements for good accuracy. So, that algorithm has limitation with many coefficients in continuous estimation at the small region which is obliged to have fewer measurements. In this paper, we developed an modified 3-D ionospheric time delay model using tomography, which requires only fewer coefficients. Because the combinations of our base coefficients correspond to the full coefficients of the existing model, our model has equivalent accuracy to the existing. We confirmed our algorithm by simulations. The results proved that our modified algorithm can perform continuous estimation with fewer coefficients.

반도체 폐수의 탈질을 위한 다양한 외부탄소원의 적용

박영호 ( Youngho Park ),손동환 ( Donghwan Sohn ),조성완 ( Sungwan Cho ),이관용 ( Kwanyong Lee ),박기영 ( Ki Young Park ) 한국물환경학회(구 한국수질보전학회) 2019 한국물환경학회·대한상하수도학회 공동 춘계학술발표회 Vol.2019 No.-

Hydrothermal carbonization of lipid extracted algae for solid fuel production

( Donghwan Sohn ),( Jongkeun Lee ),( Junhee Ryu ),( Youngho Park ),( Sungwan Cho ),( Ki Young Park ) 한국폐기물자원순환학회(구 한국폐기물학회) 2019 한국폐기물자원순환학회 심포지움 Vol.2019 No.1

As the microalgae are used as the third generation biomass, the area of cultivation is narrow and the growth is fast, so much research is being conducted for the production of biodiesel. During biodiesel production, lipid extracted algae (LEA) is generated from the algal biodiesel production industries. The LEA residue, after the extraction of lipid, is commonly considered as waste. The objective of this study is to produce alternative solid fuels from LEAs via HTC process as a method of bio-carbon recovery and waste disposal. In this study, feedstocks were used LEA form Chlorella vulgaris were extracted by Dimethyl Ether (DME), and untreated C. vulgaris. Experiments were performed using a lab-scale reactor with a volume of 1 L, into which 300mL of LEA or C.vulgaris feedstock, mixed with an equal amount of distilled was water loaded. The anaerobic condition was achieved by purging the reactor with nitrogen gas for sufficient time before the HTC experiments. The operating temperature ranged between 180 to 270℃ with the reaction being maintained for 30 min in the presence of subcritical water. The contents of the reactor were mixed vigorously using an agitator, rotating at 200 rpm. After the HTC treatment, the residual steam was discharged from the reactor. The reaction time, as a result, the carbon contents of LEA and microalgae increased from 47.16% to 58.45% and from 50.91% to 59.36%, respectively, as the treatment temperature increased until 210℃. Also, the calorific value was also increased, indicating the highest value of 6,594 kcal/kg and 6,800 kcal/kg at 210℃. LEA has low carbon content and calorific value compare with C.vulgaris, but it has enough high carbon content and calorific value for using solid fuel. In addition, the characteristics of solid fuel of LEA are enhanced by HTC, and the product may be sufficient to use solid fuel.

관절염 무릎 보조기의 생체역학적 효과

손량희(Ryanghee Sohn),최희석(Heuseok Choi),조승관(Seungkwan Cho),김한성(Hansung Kim),김영호(Youngho Kim) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

We were performed the three dimensional motion analysis for the 'Arthritis Knee Brace(AKB)' which has widening effects on the knee joint condylar separation. The knee joint condylar separations were measured at 1.807㎜(lateral), 0.474㎜(center) and 2. 172㎜(medial) by the fluoroscopy. Finite elememt method result in condylar stress decrease at 3.951㎫ in femur and 4.556㎫ in tibia. However, three dimensional gait analysis showed that all three lower joints(hip, knee ankle) were more flexed during AKB walking, and ground reaction force was larger in AKB walking just before the push-off. In the future, the joint moment and power as well as the electromyogram have to be analyzed to find the biomechanical disadvantage of AKB.

Tomographic Estimation of the Ionosphere

Changdon Kee,Youngho Sohn 한국기상학회 2005 한국기상학회 학술대회 논문집 Vol.2005 No.-

Ionospheric time delay is the biggest error source for single-frequency DGPS applications, including time transfer and Wide Area Differential GPS (WADGPS). Currently, there are many attempts to develop real-time ionospheric time delay estimation techniques to reduce positioning error due to the ionospheric time delay. Klobuchar model is now widely used for ionospheric time delay calculation for single-frequency users. It uses flat surface at night time and cosine surface at daytime[1]. However, the model was developed for worldwide ionosphere fit, it is not adequate for local area single-frequency users who want to estimate ionospheric time delay accurately[2]. Therefore, 3-D ionosphere model using tomographic estimation has been developed. 3-D tomographic inversion model shows better accuracy compared with prior algorithms[3]. In this paper, we explained the basic algorithm of tomographic estimation of ionosphere and showed comparisons with other methods.

The balance recovery mechanisms against unexpected forward perturbation.

Hwang, Sungjae,Tae, Kisik,Sohn, Ryanghee,Kim, Jungyoon,Son, Jongsang,Kim, Youngho Pergamon Press [etc.] 2009 Annals of biomedical engineering Vol.37 No.8

<P>Falls are one of the main concerns of the elderly. Proper postural adjustments to maintain balance involve the activation of appropriate muscles to produce force and to relocate the center of body mass (CoM). In this study, biomechanical aspects of dynamic postural responses against forward perturbations were experimentally determined by simultaneous measurements of joint angles and EMG activations. Thirteen young and healthy volunteers took turns standing on a flat platform, and were directed to move in the forward direction by an AC servo-motor set at two different speeds (0.1 and 0.2 m/s). Joint motions were recorded, and they followed the sequence of ankle dorsiflexion, knee flexion, and then hip flexion during the later acceleration phase (AP) in order to maintain postural balance against forward perturbation. Tibialis anterior for the ankle dorsiflexion and biceps femoris for the knee flexion were activated during the second half of the AP as the primary muscles to recover balance. In addition, gastrocnemius, which was related to ankle plantarflexion, and rectus femoris, which was related to knee extension, were activated to maintain balance. Movements of the center of plantar pressure and ground reaction forces in fast-speed perturbation were significantly larger than those in slow-speed perturbation. As a result, the ankle strategy was used for slow-speed perturbation, but the mixed strategy consisting of both ankles and hip were used for fast-speed perturbation.</P>

Device Characteristics of a Ge-doped SbTe alloy for High-speed Phase-change Random Access Memory

Youngseok Kwon,최득성,엄재철,김진혁,Sujin Chae,Youngho Lee,Soo Gil Kim,Jachun Ku,Yongsun Sohn,Sungki Park 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.21

We investigated the influence of phase-change materials on the device performance for low-power and high-speed phase-change random access memory (PCRAM). The Ge-doped SbTe (Ge-ST) alloy was used as a phase-change material and was compared with the conventional Ge₂Sb₂Te_5 (GST225)alloy. An as-deposited Ge-ST film grown by using chemical vapor deposition had an amorphous phase which showed the superior gap-fill capability compared to as-deposited crystalline GST225. The crystallization time for the set operation was decreased to 80 ns, and the reset current reduced to 0.16 mA when Ge-ST was introduced in sub-40 nm a PCRAM. In addition, the Ge-ST alloy showed a good data retention property of 10 years guaranteed at 100 ℃. These results will enable us to realize low-power and high-speed PCRAM devices beyond the sub-40 nm design rule.

이동 Ad-Hoc 네트워크 환경에서 페어링 연산의 밀러 알고리듬에 대한 데이터 오류 공격

배기석(KiSeok Bae),손교용(GyoYong Sohn),박영호(YoungHo Park),문상재(SangJae Moon) 대한전자공학회 2013 전자공학회논문지 Vol.50 No.2

최근 이동 ad hoc 네트워크에 적합한 ID 기반의 암호시스템 구현을 위해서 다양한 페어링 연산들이 사용되고 있으며, 밀러 알고리듬은 Weil, Tate, Ate 페어링 연산에서 가장 많이 사용되는 알고리듬이다. 본 논문에서는 Whelan과 Scott에 의해 제안된 밀러 알고리듬의 중간 값에 대한 오류 공격을 구체화하여 라운드 위치와 상관없이 적용할 수 있는 데이터 오류 주입 공격의 가능성을 분석하였다. 시뮬레이션 결과, 제안하는 공격 방법이 라운드 위치나 사용하는 좌표계와 관계없이 적용 가능하여 효과적이며 강력한 오류 주입 공격 방법임을 확인하였다. Recently, there has been introduced various types of pairing computations to implement ID based cryptosystem for mobile ad hoc network. The Miller algorithm is the most popular algorithm for the typical pairing computation such as Weil, Tate and Ate. In this paper, we analyze the feasibility of concrete data fault injection attack, which was proposed by Whelan and Scott, in terms of regardless of round positions during the execution of the Miller algorithm. As the simulation results, the proposed attack that can be employed to regardless of round positions and coordinate systems is effective and powerful.

발뒤꿈치들기 시 근력 추정을 위한 혼합 정적 최적화

손종상(Jongsang Son),손량희(Ryanghee Sohn),김영호(Youngho Kim) Korean Society for Precision Engineering 2009 한국정밀공학회지 Vol.26 No.3

The estimation of muscle force is important to understand the roles of the muscles. The static optimization method can be used to figure out the individual muscle forces. However, muscle forces during the movement including muscle co-contraction cannot be considered by the static optimization. In this study, a hybrid static optimization method was introduced to find the well-matched muscle forces with EMG signals under muscle co-contraction conditions. To validate the developed algorithm, the 3D motion analysis and its corresponding inverse dynamics using the musculoskeletal modeling software (SIMM) were performed on heel-rise movements. Results showed that the developed algorithm could estimate the acceptable muscle forces during heel-rise movement. These results imply that a hybrid numerical approach is very useful to obtain the reasonable muscle forces under muscle co-contraction conditions.

마비환자의 보행훈련을 위한 로봇형 보행훈련 시스템 개발

황성재(Sungjae Hwang),김정윤(Jungyoon Kim),손종상(Jongsang Son),손량희(Ryanghee Sohn),김영호(Youngho Kim) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

In this study, we developed a robotic gait training system which induces the active gait training based on predefined continuous proper lower extremity joint movements for the paralysis. AC servo motors and linear actuators were used to control hip and knee joints of patients and the weight support system was used to support the patient's weight during the gait training. We also implemented a GUI program to set the gait training pattern with several training parameters and to confirm states of patients and the system through the visual feedback. The effectiveness of the gait training system will be determined by the long-term clinical experiments in the future. We expect that the developed robotic gait training system could be applied very practically to recover gait abilities for persons with gait disorder.