• 대한기계학회논문집A
• /
• 제34권9호
• /
• pp.1257-1263
• /
• 2010

함정구조물은 함내 엔진 및 프로펠러 추진력의 환경진동에 노출되어 있다. 일반적으로 함상구조물은 함상진동규격인 MIL-STD-167-1A 에 따라 개발되고 있으며, 장기간 사용을 목적으로 하는 함상구조물의 진동에 대한 피로수명은 해석적 접근법과 진동실험을 통해 반드시 평가되야 한다. 본 논문에서는 함상구조재로 사용된 주조 알루미늄합금인 A356 의 피로강도를 14 S-N 법으로 평가하고, 구조물의 작용응력은 함상진동규격에 준하는 주파수응답해석을 통해 분석되었다. 최대등가응력의 주파수는 최대실험주파수에서 나타났으며, 함상장비의 진동피로수명은 누적손상법에 의해 평가되었다.

• 대한전자공학회:학술대회논문집
• /
• 대한전자공학회 2006년도 하계종합학술대회
• /
• pp.227-228
• /
• 2006

In this paper, we introduce the design and fabrication of 60 GHz low noise amplifier MMIC for IEEE802.15.3c WPAN system. The 60 GHz LNA was designed using ETRI's $0.12{\mu}m$ PHEMT process. The PHEMT shows a peak transconductance ($G_{m,peak}$) of 500 mS/mm, a threshold voltage of -1.2 V, and a drain saturation current of 49 mA for 2 fingers and $100{\mu}m$ total gate width (2f100) at $V_{ds}$=2 V. The RF characteristics of the PHEMT show a cutoff frequency, $f_T$, of 97 GHz, and a maximum oscillation frequency, $f_{max}$, of 166 GHz. The performances of the fabricated 60 GHz LNA MMIC are operating frequency of $60.5{\sim}62.0\;GHz$, small signal gain ($S_{21}$) of $17.4{\sim}18.1\;dB$, gain flatness of 0.7 dB, an input reflection coefficient ($S_{11}$) of $-14{\sim}-3\;dB$, output reflection coefficient ($S_{22}$) of $-11{\sim}-5\;dB$ and noise figure (NF) of 4.5 dB at 60.75 GHz. The chip size of the amplifier MMIC was $3.8{\times}1.4\;mm^2$.

• 전자공학회논문지A
• /
• 제30A권12호
• /
• pp.51-59
• /
• 1993

A 4${\times}10^{19}cm^{3}$ carbon-doped base AlGaAs/GaAs HBY was grown using carbontetracholoride(CCl$_4$) by atmospheric pressure MOCVD. Abruptness of emitter-base junction was characterized by SIMS(secondary ion mass spectorscopy) and the doping concentration of base layer was confirmed by DXRD(double crystal X-ray diffractometry). Mesa-type HBTs were fabricated using wet etching and lift-off technique. The base sheet resistance of R$_{sheet}$=550${\Omega}$/square was measured using TLM(transmission line model) method. The fabricated transistor achieved a collector-base junction breakdown voltage of BV$_{CBO}$=25V and a critical collector current density of J$_{O}$=40kA/cm$^2$ at V$_{CE}$=2V. The 50$\times$100$\mu$$^2$ emitter transistor showed a common emitter DC current gain of h$_{FE}$=30 at a collector current density of JS1CT=5kA/cm$^2$ and a base current ideality factor of ηS1EBT=1.4. The high frequency characterization of 5$\times$50$\mu$m$^2$ emitter transistor was carried out by on-wafer S-parameter measurement at 0.1~18.1GHz. Current gain cutoff frequency of f$_{T}$=27GHz and maximum oscillation frequency of f$_{max}$=16GHz were obtained from the measured Sparameter and device parameters of small-signal lumped-element equivalent network were extracted using Libra software. The fabricated HBT was proved to be useful to high speed and power spplications.

• 한국진공학회지
• /
• 제15권6호
• /
• pp.637-641
• /
• 2006

본 논문에서는 100 nm 게이트 길이를 갖는 InGaAs/InAlAs/GaAs MHEMT(metamorphic high electron mobility transistors)m의 DC와 RF 특성을 분석 하였다. 이중 노광 방법으로 ZEP520/P(MMA-MAA)/PMMA 3층 구조의 레지스터와 게이트 길이 100 nm인 게이트를 제작하였다. 게이트의 단위 폭이 $70\;{\mu}m$인 2개의 게이트와 길이가 100 nm로 제작된 MHEMT를 DC 및 RF특성을 조사하였다. 최대 드레인 전류 밀도는 465 mA/mm, 상호전달 컨덕턴스는 844 mS/mm이, RF 측정으로부터 전류 이득 차단 주파수는 192 GHz와 최대 진동주파수 310 GHz인 특성을 보였다.

• 한국동물위생학회지
• /
• 제42권2호
• /
• pp.67-71
• /
• 2019

A variety of livestock feed resources were used in Korean dairy farm due to a lack of the endemic feed. However, there is inadequate real farm data to support farmers' decisions on the choice of options. The main objective of this study was to evaluate the nutritional value of total mixed ration (TMR) as well as the metabolic diseases status in Korean dairy farms. TMR samples were collected from nine feed companies and eight selected self-formulated by the dairy farms. The nutrient contents were examined by AOAC methods. The frequency of metabolic diseases such as ketosis and hypocalcemia were surveyed. The average moisture content was 36.2% although the min. and max. value were varied from 21.7% and 50.6% among farms. The mean${\pm}$standard deviation of crude fiber (CF), crude ash (CA), ether extract (EE), and crude protein (CP) were $21.4{\pm}2.5$, $4.6{\pm}0.4$, $3.2{\pm}0.5$ and $9.8{\pm}1.7$, respectively. However, the average ADF and NDF was $17.3{\pm}3.7$ and $31.0{\pm}5.7$, respectively. The compositions of TMR were varied significantly among the dairy farms. The frequency of clinical Ketosis (CK), subclinical ketosis (SCK) and hypocalcemia were higher in early lactation period with 4.5%, 11.0% and 3.0%, respectively. Also, the frequency of SCK was higher than CK and hypocalcemia throughout the lactation. Periodic TMR nutrient analysis based on herd production or physiology change would maximize the effects of TMR feeding. Furthermore, the study results would be useful to the farm practitioner and producer for their farm management.

• 천문학회보
• /
• 제46권1호
• /
• pp.52.1-52.1
• /
• 2021

We present the results of multi-epoch, multi-frequency monitoring of a blazar 4C +29.45, which was regularly monitored as part of the Interferometric Monitoring of GAmma-ray Bright AGNs program - a key science program of the Korean Very long baseline interferometry Network (KVN). Observations were conducted simultaneously at 22, 43, 86 and 129 GHz during the 4 years from December 2012 to December 2016. We also used additional data from the 15 GHz Owens Valley Radio Observatory (OVRO) monitoring program. From the 15 GHz light curve, we estimated the variability time scales of the source during several radio flux enhancements. We found that the source experiencesd 6 radio flux enhancements with variability time scales of 9-187 days during the observing period, yielding corresponding variability Doppler factors of 9-27. From the multi-frequency simultaneous KVN observations, we were able to obtain accurate radio spectra of the source and hence to more precisely measure the turnover frequencies 𝜈_r of synchrotron self-absorbed (SSA) emission with a mean value of ${\bar{\nu}_r}=28.9GHz$. Using jet geometry assumptions, we estimated the size of the emitting region at the turnover frequency. Taking into account these results, we found that the equipartition magnetic field strength is up to two orders of magnitudes higher than the SSA magnetic field strength (0.6-99 mG). This is consistent with the source being particle dominated.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회B
• /
• pp.3506-3511
• /
• 2007

The energy harvesting using smart materials has been extensively investigated to supply electric power to wireless sensor systems. In this paper, the energy harvesting using eddy current was studied with the integrated magnetic cantilever beam system. If a large conductive metal plate moves through a magnetic field which intersects perpendicularly to the sheet, the magnetic field will induce small rings of current which will actually create internal magnetic fields opposing the change. This eddy current that was induced in the coiled conductive sheet from the mechanical vibration was converted to chemical energy by charging batteries. The experimental results show that the eddy current generated the electric power up to max 31.2mW. Additionally the vibration reduction of the mechanical cantilever beam was observed by the energy dissipation in the electro-magnetic coupled system. The present result shows that the vibration level of the first natural frequency was reduced up to 7.7dB

• ETRI Journal
• /
• 제40권2호
• /
• pp.180-187
• /
• 2018

In this paper, we introduce a ground radiation antenna that uses controlled endless metal rim modes. In the proposed technique, the metal rim mode is tuned and excited as a one-wavelength radiator by a small ground radiation antenna. The proposed antenna occupies a clearance of $1mm{\times}4mm$ in a $30mm{\times}20mm$ ground plane. A metal rim with dimensions of $34mm{\times}24mm$ surrounds the ground plane, and the metal rim is separated from the ground plane by a gap of 2 mm. In addition, a lumped capacitor is inserted between the metal rim and the ground plane to control the characteristic mode of the metal rim such that the resonance of the metal rim is tuned to be equal to the operating frequency. By performing simulations and measurements, we compare the performance of the proposed antenna with that of a reference antenna that does not have an inserted capacitor between the metal rim and the ground plane. The results show that a significant improvement of the radiation performance is obtained by employing the proposed technique.

• 한국지진공학회:학술대회논문집
• /
• 한국지진공학회 2002년도 춘계 학술발표회 논문집
• /
• pp.42-50
• /
• 2002

The duration and H/V ratio(the amplitude ratio of the horizontal to vertical components) of ground motions caused by earthquakes in southern Korea are analyzed. Total 329 seismograms of horizontal component recorded at hypocentral distances of 10 to 350 km from 27 earthquakes with local magnitude 2 to 4 are used for the analysis. Simplified relation between the duration of ground motion( $T_{d}$) and the ratio($\chi$) of Arias intensity( $I_{A}$) and squared maximum acceleration($\alpha$$_{max}$$^{2}$) is determined to be $T_{d}$ = 3.423$\chi$$^2$+ 8.200$\chi$ + 0.029, which is useful for the estimation of the duration in southern Korea. There are three distinct distance ranges with different linear variations of the duration in hypocentral distance. They are distance intervals of 10~80km, 80~140km, and the distance greater than 140km. The duration in southern Korea shows clear proportionality to the local magnitude at magnitudes greater than 3.1. The value 1.37 of the H/V ratio obtained in southern Korea is similar to the value 1.4 of ENA(Eastern North America). The H/V ratio in southern Korea increases in the frequency range from 0.3 to 10Hz. The duration and H/V ratio of ground motions derived in this study could be used in the stochastic simulation of strong ground motion.ion.n.n.

• Journal of Applied Biological Chemistry
• /
• 제44권4호
• /
• pp.167-172
• /
• 2001

A cDNA fragment encoding the chloroplastic fructose-1, 6-bisphosphatase (FBPase) was cloned via PCR from the cDNA library of pea leaves. The cloned cDNA, about 1.05 kbp without signal sequence, was introduced into a pET-28a vector for expression in E. coli strain BL21(DE3)pLysS. The recombinant FBPase was purified through $Ni^+-NTA$ affinity chromatography and characterized. Molecular mass of the monomer was about 42,000. Enzymatic activity of the purified enzyme as the native pea chloroplastic FBPase was the highest at alkaline pH (pH 9.0). The recombinant enzyme was activated by a reducing agent DTT and was insensitive to AMP. The activation energy (Ea) and Arrehenius frequency factor were 42.67 kcal/mol and $2.65{\times}10^{14}/s$, respectively, slightly higher than those of the native enzyme. $K_M$ and $V_{max}$ were $99.98{\mu}M$ and $52.9{\mu}M/min$, respectively, which were comparable with the native enzyme.