• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.174-174
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• 2014

Memristor devices are one of the most promising candidate approaches to next-generation memory technologies. Memristive switching phenomena usually rely on repeated electrical resistive switching between non-volatile resistance states in an active material under the application of an electrical stimulus, such as a voltage or current. Recent reports have explored the use of variety of external operating parameters, such as the modulation of an applied magnetic field, temperature, or illumination conditions to activate changes in the memristive switching behaviors. Among these possible choices of signal controlling factors of memristor, photon is particularly attractive because photonic signals are not only easier to reach directly over long distances than electrical signal, but they also efficiently manage the interactions between logic devices without any signal interference. Furthermore, due to the inherent wave characteristics of photons, the facile manipulation of the light ray enables incident light angle controlled memristive switching. So that, in the tautological sense, device orienting position with regard to a photon source determines the occurrence of memristive switching as well. To demonstrate this position controlled memory device functionality, we have fabricated a metal-semiconductor-metal memristive switching nanodevice using ZnO nanorods. Superhydrophobicity employed in this memristor gives rise to illumination direction selectivity as an extra controlling parameter which is important feature in emerging. When light irradiates from a point source in water to the surface treated device, refraction of light ray takes place at the water/air interface because of the optical density differences in two media (water/air). When incident light travels through a higher refractive index medium (water; n=1.33) to lower one (air; n=1), a total reflection occurs for incidence angles over the critical value. Thus, when we watch the submerged NW arrays at the view angles over the critical angle, a mirror-like surface is observed due to the presence of air pocket layer. From this processes, the reversible switching characteristics were verified by modulating the light incident angle between the resistor and memristor.

• 천문학회보
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• 제41권1호
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• pp.65.1-65.1
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• 2016

We present results of long-term multi-wavelength polarization observations of the powerful blazar 3C 279 after its ${\gamma}$-ray flare on 2013 December 20. We followed up this flare by means of single-dish polarization observations with two 21-m telescopes of the Korean VLBI Network, carried out weekly from 2013 December 25 to January 11, and at 22, 43, and 86 GHz, simultaneously. These observations were part of the Monitoring Of GAmma-ray Bright AGNs (MOGABA) program. We Measured 3C 279 total flux densities at 22, 43, and 86 GHz, showing a mild variability of a factor of ${\leq}50%$ over the period of our observations. The spectral index ranged from -0.13 to -0.36 at between 22 and 86 GHz. The degree of linear polarization was in the range of 6 ~ 12 %, and slightly decreased with time at all frequencies. We found Faraday rotation measures (RM) of -300 to $-1200rad\;m^{-2}$ between 22 and 43 GHz, and -800 to $-5100rad\;m^{-2}$ between 43 and 86 GHz. The RM values follow a power law ${\mid}RM{\mid}{\propto}{\nu}^{\alpha}$, with a mean ${\alpha}$ of 2.2, implying that the polarized emission at these frequencies travels through a Faraday screen in or near the jet. We conclude that the regions emitting polarized radio emission may be different from the region responsible for the 2013 December ${\gamma}$-ray flare, and that these regions are maintained by the dominant magnetic field perpendicular to the direction of the radio jet at milliarcsecond scales.

• 천문학회지
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• 제28권2호
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• pp.245-253
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• 1995

We have analyzed the time series of Ca II H,K and ${\lambda}8498$ line profiles taken for a sunspot (SPO 5007) with the Echelle spectrograph attached to Vacuum Tower Telescope at Sacramento Peak Solar Observatory. Each set of spectra was taken simultaneously for 20 minutes at a time interval of 30 seconds. A total of 40 photographic films for each line was scanned by a PDS at Korea Astronomy Observatory. The central peak intensity of Ca II H ($I_{max}$), the intensity measured at ${\Delta}{\lambda}=-0.1{\AA}$ from the line center of ${\lambda}8498(I_{{\lambda}8489})$, the radial velocity ($V_r$) and the Doppler width (${\Delta}{\lambda}_D$) estimated from Ca II H have been measured to study the dynamical behaviors of the sunspot chromosphere. Fourier analysis has been carried out for these measured quantities. Our main results are as follows: (1) We have confirmed the 3-minute oscillation being dominant throughout the umbra. The period of oscillations jumps from 180 sec in the umbra to 500 to 1000 sec in the penumbra. (2) The nonlinear character of the umbral oscillation is noted from the observed sawtooth shaped radial velocity fluctuations with amplitudes reaching up to $5{\sim}6\;km/sec$. (3) The spatial distribution of the maximum powers shows that the power of oscillations is stronger in the umbra than in the penumbra. (4) The spatial distributions of the time averaged < $I_{max}$ > and < $V_r$ > across the spot are found to be nearly axially symmetric, implying that the physical quantities derived from the line profiles of Ca II H and ${\lambda}8498$ are inherently associated with the geometry of the magnetic field distribution of the spot. (5) The central peaks of the CaII H emission core lead the upward motions of the umbral atmosphere by $90^{\circ}$, while no phase delay is found in intensities between $I_{max}$ and $I_{{\lambda}8498}$, suggesting that the umbral oscillation is of standing waves.

• 한국추진공학회지
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• 제25권5호
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• pp.65-72
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• 2021

소형위성의 궤도조정 및 궤도유지에 활용될 수 있는 700 W급 홀추력기 랩모델을 개발하였다. 스케일링 방정식을 사용하여 방전채널의 크기를 선정하였으며, 자기장이 방전채널 중심선을 기준으로 대칭성을 가지면서 방전채널 바깥에서 최대가 되도록 설계하였다. 개발된 홀추력기의 방전시험은 2.0×10^-5 Torr 이하의 배경압력을 갖는 진공 환경에서 수행되었으며 추력 스탠드를 이용하여 추력을 측정하였다. 양극전압을 300 V로 고정하고 양극유량과 코일전류를 변수로 하여 추력을 측정하였으며, 양극유량 2.36 mg/s, 코일전류 2.4 A 조건에서 양극전력 620 W에서 추력 38 mN, 통합비추력 1,540 s, 양극효율 50 %로 가장 높은 성능을 보였다.

• 자원환경지질
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• 제30권6호
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• pp.613-624
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• 1997

A study of anisotropy of magnetic susceptibility (AMS) was conducted on the Ordovician-Eocene strata in the Taebaek area. The study area is a northeastern part of the Okchon belt, sometimes called as Paegunsan Synclinal Area. A total of 600 independently oriented samples were collected from 60 sites covering the whole area. With a few exception of late Cretaceous-Eocene volcanic rocks, all the sampled strata are nonmetamorphosed sedimentary rocks, mainly sandstones. Among the 60 sites, 5 sites showed flow lineation lying on the bedding plane, 11 sites showed load foliation parallel to the bedding plane, and 21 sites showed tectonic foliation unrelated to the bedding plane. The tectonic foliations are defined by $k_1-k_2$ ($k_{max}-k_{int}$) anisotropy plane, and are considered as a result of tectonic forces acted perpendicularly to the foliation plane in the geologic past. Regardless of sample-site locations, tectonic force directions defined by $k_3$ ($k_{min}$) axis perpendicular to the tectonic foliation are consistent among the strata of the same geologic age. In the course of geologic time, however, the tectonic force directions showed a clockwise rotation: approximately E-W in the Ordovician sites, NW-SE in the Permian sites, N-S in the Triassic sites, and lastly NE-SW in the late Cretaceous-Eocene sites. The pre-Permian directions showed better clustering in the in-situ (geographic) coordinates, while the younger directions become better clustered after the bedding-tilt correction. It is interpreted that the major tectonic structures of the Taebaek area were controlled by the above-mentioned tectonic forces: The Paegunsan Syncline and the Hambaeksan Fault must have been generated by the NW-SE force of late Permian-early Triassic time. It was then reactivated in the reverse (dextral) sense by the N-S force of Triassic time. The Osipchon Fault in the eastern part of the study area was either generated or reactivated by the NE-SW force of late Cretaceous-Eocene time. The Permo-Triassic NW-SE force should be an expression of the Songnim Disturbance in the Korean peninsula, which is in turn related with the SCB/NCB collision in China.

• 한국방사선학회논문지
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• 제9권5호
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• pp.307-314
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• 2015

유방 자기공명영상검사 시 확산강조영상에서 발생하는 심장과 폐에 의한 불수의적 움직임 인공물과 감소된 영상영역 에코평면영상기법으로 발생하는 둘러겹침 인공물을 추가적인 사전포화기법을 사용하여 이를 저감화시키고자 하였다. 2014년 08월 1일부터 11월 30일까지 여성 환자 38명을 대상으로 하였으며 사용 장비로는 유방 검사에 최적화된 3.0T와 유방 전용 코일을 사용하였다. 영상의 평가와 분석은 정량적, 정성적 분석을 하였으며 통계적 유의성은 Paired T-test와 Wilcoxon rank test를 하였다. 결과적으로 추가적인 사전포화펄스의 사용으로 정량적인 평가에서는 병변에서 15.69%, 병변 근접 부위에서 13.72%, 지방에서 20.63%의 증가를 보였으며, 대조도 대 잡음비의 경우는 병변과 병변 근접 부위에서 10.58%, 병변과 지방 부위에서 12.03%의 증가로 나타났다. 정성적인 평가에서는 확산경사계수 0에서 22.05%, 1000에서 21.42%, 현성확산계수에서 16.10%의 증가로 나타났으며, 통계적 평가에서는 신호 대 잡음비와 대조도 잡음비, 확산경사계수와 현성확산계수에서 모두 유의한 결과로 나타났다(p<0.05). 따라서 사전포화펄스의 추가적인 사용으로 유방 자기공명영상 검사에서 확산강조영상 획득 시 위상 부호화 방향으로 발생하는 불수의적 움직임 인공물과 둘러겹침 인공물이 감소가 되어 최적의 영상을 얻을 수 있을 것으로 판단된다.

• 천문학논총
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• 제30권2호
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• pp.559-563
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• 2015

Monitor of All-sky X-ray Image (MAXI) is a Japanese X-ray all-sky surveyer mounted on the International Space Station (ISS). It has been scanning the whole sky since 2009 during every 92-minute ISS rotation. X-ray transients are quickly found by the real-time nova-search program. As a result, MAXI has issued 133 Astronomer's Telegrams and 44 Gamma-ray burst Coordinated Networks so far. MAXI has discovered six new black holes (BH) in 4.5 years. Long-term behaviors of the MAXI BHs can be classified into two types by their outbursts; a fast-rise exponential-decay type and a fast-rise flat-top one. The slit camera is suitable for accumulating data over a long time. MAXI issued a 37-month catalog containing 500 sources above a ~0.6 mCrab detection limit at 4-10 keV in the region ${\mid}{b}{\mid}$ > $10^{\circ}$. The SSC instrument utilizing an X-ray CCD has detected diffuse soft X-rays extending over a large solid angle, such as the Cygnus super bubble. MAXI/SSC has also detcted a Ne emission line from the rapid soft X-ray nova MAXI J0158-744. The overall shapes of outbursts in Be X-ray binaries (BeXRB) are precisely observed with MAXI/GSC. BeXRB have two kinds of outbursts, a normal outburst and a giant one. The peak dates of the subsequent giant outbursts of A0535+26 repeated with a different period than the orbital one. The Be stellar disk is considered to either have a precession motion or a distorted shape. The long-term behaviors of low-mass X-ray binaries (LMXB) containing weakly magnetized neutron stars are investigated. Transient LMXBs (Aql X-1 and 4U 1608-52) repeated outbursts every 200-1000 days, which is understood by the limit-cycle of hydrogen ionization states in the outer accretion disk. A third state (very dim state) in Aql X-1 and 4U 1608-52 was interpreted as the propeller effect in the unified picture of LMXB. Cir X-1 is a peculiar source in the sense that its long-term behavior is not like typical LMXBs. The luminosity sometimes decreases suddenly at periastron. It might be explained by the stripping of the outer accretion disk by a clumpy stellar wind. MAXI observed 64 large flares from 22 active stars (RS CVns, dMe stars, Argol types, young stellar objects) over 4 years. The total energies are $10^{34}-10^{36}$ erg $s^{-1}$. Since MAXI can measure the spectrum (temperature and emission measure), we can estimate the size of the plasma and the magnetic fields. The size sometimes exceeds the size of the star. The magnetic field is in the range of 10-100 gauss, which is a typical value for solar flares.

• 자원리싸이클링
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• 제16권3호
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• pp.19-26
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• 2007

도심지에서 발생하는 생활폐기물들은 재활용 가능한 목재나 iron 등을 분리시킨 후 소각장으로 보내지기 때문에 자기류나 유리류 그리고 가장 많은 양을 차지하고 있는 가연성 물질로 존재하게 된다. 하지만 소각 전 분리 공정에도 불구하고 생활폐기물에서의 iron의 함유량은 약 $3{\sim}11%$에 달하고 있다. 이러한 iron은 소각로에서 소각 처리될 경우 약 $1000^{\circ}C$의 온도(로의 내부 온도)에서 산화반응에 의해 표면에 산화물 층을 형성하게 된다. 소각된 바닥재는 water-cooling냉각 처리를 통해 냉각되며 물과 접촉한 iron 표면의 산화물 층은 심한 붕괴가 일어나 부식작용이 더욱 활발히 일어나며 많은 양의 ferrous material($Fe_3O_4,\;Fe_2O_3,\;FeS_2$)을 생성하게 된다. 이러한 iron과 ferrous material은 산화 환원 작용에 의해 부피변화를 일으키기 때문에 시멘트 골재 등으로의 재활용 시 많은 문제점을 일으킬 수 있다. 따라서 본 연구에서는 소각 바닥재를 이용하여 각 입도별 자력선별에 따른 ferrous material의 분리 특성에 대해 연구하였다. 그 결과 전체 바닥재의 약 18.7%(ferrous product; $Fe_3O_4,\;Fe_2O_3,\;FeS_2$, iron)가 자력선별(자력세기:3800gauss)에 의해 분리 되었으며 1.18mm이상의 입도에서 전체 ferrous product의 87.7%가 분포하였다. iron의 경우 전체 바닥재의 약 3.8%의 함유량을 보였으며 1.18mm이상의 입도에서 전체 iron의 99%이상이 존재하였다.

• 한국자기학회지
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• 제13권5호
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• pp.187-192
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• 2003

IrMn에 Mn을 첨가시킨 N $i_{80}$F $e_{20}$/[I $r_{22}$M $n_{78}$-Mn] $Co_{75}$F $e_{25}$ 다층박막을 상온에서 이온빔 증착(ion beam deposition: IBD)법으로 제작하여 그 자기적 및 열적 특성을 연구하였다. Mn이 첨가된 NiFe/[IrMn-Mn]/CoFe다층박막은 Mn이 첨가되지 않은 순수 합금 IrMn 박막 위의 CoFe 고정층 보다 큰 교환결합력( $H_{ex}$)과 방해온도(blocking temperature: $T_{b}$)을 가지고 있었다. Mn이 첨가되지 않는 I $r_{22}$M $n_{78}$ 와 CoFe 사이의 $H_{ex}$는 상온에서 거의 없었으나, 25$0^{\circ}C$ 열처리 후 100 Oe로 나타났다. IrMn 내에서 76.8-78.1 vol% Mn일 때, $H_{ex}$와 $T_{b}$는 크게 향상되었고, Mn이 0.6 vol%씩 증가함에 따라 크게 줄어들었다. NiFe/[IrMn-Mn]/CoFe 다층박막 구조에서 [(111)CoFe, NiFe]/(111)IrM $n_3$인 x-선 회절 피크비 평균값은 75.5, 77.5, 79.3 vol% Mn일 때 각각 1.4, 0.8, 0.6였다. 특히, 열처리 전 77.5과 78.7 vol% Mn일 때, $H_{ex}$는 각각 259와 150 Oe였다. 77.5 vol% Mn인 경우, $H_{ex}$가 열처리 온도 35$0^{\circ}C$까지 475 Oe였으며, 450 $^{\circ}C$에서는 200 Oe로 크게 감소하였다. 따라서 합금형 반강자성체 IrMn에서 높은 $H_{ex}$와 $T_{b}$을 얻을 수 있는 최적의 Mn 함유량의 존재를 확인하였다.다.다. 확인하였다.다.하였다.다.

• 한국지구과학회지
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• 제39권6호
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• pp.519-532
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• 2018

우리는 오리온 분자운 복합체의 북부 필라멘트(이하 NF)에 대하여 $^{12}CO$ (J=1-0) 분자선의 자료를 이용하여 은하 평면이 분자의 운동과 운동학에 미치는 영향을 연구하였다. 6 m 서울대학교 전파망원경(Seoul Radio Astronomy Observatory, SRAO)을 이용하여 2arcmin 공간분해능으로 은하면으로부터 먼 순서로 NF1, NF2, NF3 세 곳을 총 270시간 동안 관측된 자료를 사용하였다. 은하면과 OMC NF는 $^{12}CO$ (J=2-1) 경우 3% 밀도에서, 티끌의 경우 9% 밝기 수준에서 자기장을 따라 서로 연결되어 있었다. $^{12}CO$ (J=1-0), $^{12}CO$ (J=2-1), 성간 티끌 관측결과를 비교해본 결과, 세 경우 모두 NF3에서는 고루 분포했지만, NF1과 NF2에서는 비교적 밀도가 높은 특정 영역에서만 함께 나타났다. NF는 단일 구조를 보였으며, NF1에서는 부분 수축 운동을, NF2에서는 하단에서 회전 운동이 나타났고, NF3에서는 유일하게 명확히 자기장에 연관된 나선형 회전이 보였다. 위치-속도 분석 결과, $^{12}CO$ (J=1-0)를 비롯한 물질들은 NF2와 NF3을 따라 은하면을 향하여 흐를 가능성이 있음을 확인할 수 있었다. 은하면을 향하여 물질이 흐르는 명백한 원인을 이번 연구결과에서 볼 수 없었지만 추후의 더 정교한 관측결과가 NF1과 NF2 상단부의 회전 운동을 확인 할 수 있겠다.