스핀-S 단일 스핀모델의 시간에 따른 행태

오석근 忠北大學校部設基礎科學硏究所 1987 自然科學硏究 Vol.1 No.1

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IoT 기반 기온, 상대습도, 강수 탐지 관측 품질평가 - 2020년 여름 서울을 중심으로 -

오석근,손석우,김선영,박준상,이종원 건국대학교 기후연구소 2021 기후연구 Vol.16 No.3

This study evaluates the quality of surface air temperature, relative humidity, and precipitation detection observed by 22 internet of thing (IoT)-based mini-weather stations in Seoul in 2020 summer. The automatic weather station (AWS) closest to each IoT-based station is used as reference. The IoT-based observations show surface air temperature and relative humidity are about 0.2-4.0°C higher and about -1--22% lower than the AWS observations, respectively. However, they exhibit temporal variability similar to the AWS observations on both diurnal and daily time scales, with daily correlations greater than 0.90 for temperature and 0.82 for relative humidity. Given these strong linear relationships, it show that temperature and relative humidity biases can be effectively corrected by applying a simple bias correction method. For IoT-based precipitation detection, we found that precipitation conductivity value (PCV) during precipitation events is well separated from that during non-precipitation events, providing a basis for distinguishing precipitation events from non-precipitation events. When the PCV threshold is set to 250 for precipitation detection, the highest critical success index and the bias score index close to one, suitable for operational precipitation detection, are obtained. These results demonstrate that IoT-based mini-weather stations can successfully measure surface air temperature, relative humidity, and precipitation detection with appropriate bias corrections.

감쇄항이 없는 고전적인 Bloch 방정식의 정확한 해: 초기조건 의존성

오석근 한국물리학회 2008 새물리 Vol.57 No.1

The classical Bloch equations without damping terms originating from a model of noninteracting classical spins in a time-dependent rotating magnetic field are investigated. The nonequilibrium magnetization is calculated to see its dependence on the initial conditions. We adopted three physically realizable, but different, initial conditions, namely, completely ordered, completely disordered, and equilibrium states, and we found a distinct initial-condition dependence of the nonequilibrium magnetization. For different magnitudes and angular frequencies of a transverse rotating magnetic field, we found a distinct initial condition dependence of the nonequilibrium magnetization. For the completely disordered states as initial conditions, the magnetization remains zero, irrespective of both the magnitude and the angular frequency of the rotating field. For the completely ordered state as the initial condition, all the components of the magnetization oscillate as a function of time. For the equilibrium states as initial conditions, at low temperatures, the nonequilibrium behaviors of the components of the magnetization are similar to these for the completely ordered initial state, whereas the nonequilibrium behaviors of the components of the magnetization at high temperatures are similar to that of completely disordered initial states. Especially, for small rotating fields, compared to a static field along the z-axis, the nonequilibrium magnetization shows a remarkable increase in the oscillation amplitude at the resonance frequency. However, due to the competition between the static field and the rotating field, the oscillation amplitude increases monotonically for large rotating fields as the angular frequency is increased beyond the resonance angular frequency, so no resonance phenomena will be seen. 상호작용하지 않는 고전 스핀들에 회전 자기장이 걸려 있는 모델을 선택하여, 감쇄항이 없는 Bloch 방정식을 유도하였다. 그리고 이 방정식에서 자기화가 초기조건에 따라서 어떤 영향을 받는지를 조사하였다. 물리적으로 실현하기 쉬운, 완전 정렬상태, 완전 무질서 상태, 평형상태의 세 초기조건을 택하여 조사한 결과 비평형 자기화가 초기조건에 따라서 크게 영향을 받는것을 보았다. 구체적으로는 여러 크기의 가로방향 (transverse) 회전 자기장과 회전 각진동수에 대하여, 비평형 자기화가 초기조건에 크게 의존함을 보았다. 초기조건이 완전 무질서 상태인 경우에는 회전 자기장의 크기나 각진동수에 무관하게 자기화의 값이 0을 유지하였다. 그러나 초기조건이 완전 정렬상태인 경우에는 모든 조건아래서 자기화의 성분이 시간에 따라서 진동함을 보였다. 평형상태가 초기조건인 경우에 아주 낮은 온도에서는 완전 정렬상태가 초기조건인 경우와 비슷한 행태를 보였고, 그리고 아주 높은 온도에서는 완전 무질서 상태가 초기조건인 경우와 비슷한 행태를 보였다. 또한 z-축 정자기장에 비하여 작은 크기의 회전 자기장내에서는 공진 각진동수에서 비평형 자기화의 진동진폭이 놀랄 만큼 크게 증가함을 보았다.그렇지만, 정자기장과 가로방향 회전 자기장의 경쟁효과때문에 각진동수가 공진 각진동수보다 커지게 될 경우에 커다란 회전자기장에 대해서 단조적으로 진동폭이 증가하여 더이상 공진효과를 얻을 수 없음을 보았다.

시간에 따라서 진동하는 자기장이 걸려있는 무한범위 Glauber 운동학적 Ising 모델에서의 겪음 현상 : 몬테칼로 전산시늉 vs. Master 방정식 방법

오석근 한국물리학회 2006 새물리 Vol.53 No.5

Hysteresis curves obtained from both Monte Carlo simulations and from the master equation approach via the Tom\'{e} and de Oliveira equation for the infinite-range Glauber kinetic Ising model in the presence of time-dependent external oscillating magnetic fields are compared. We found that these hysteresis curves cannot be related by simply introducing the re-scaled time. The difference between lagging phases for the hysteresis curves turns out to be another piece of information necessary to relate the hysteresis obtained in the two ways curves. 시간에 따라서 진동하는 자기장이 걸려있는무한범위 Glauber 운동학 모델을 마스터 (Master) 방정식으로 접근한여얻은 Tom\'{e} 와 de Oliveira의 방정식과 몬테칼로 전산시늉에서 얻은자기겪음 (magnetic hysteresis) 곡선을 비교하였다. 우리는 이들겪음곳선이 단순한 시간의 재축척에 의해서 관련 지울 수 없음을발견하였다. 그리고 두 겪음고선 사이의 지연된 위상차가 이들을연관지울 수 있는 고리임이 확인하였다.

CORDEX 동아시아 영역에서 경계조건 및 적운모수화방안이 RegCM4를 이용한 남한 지역 기후모의에 미치는 영향 분석

오석근,서명석,명지수,차동현 한국지구과학회 2011 한국지구과학회지 Vol.32 No.4

In this study, four types of sensitivity experiments (EG, EE, NG, NE; E: ERA-Interim, N: NCEP/DOE2, G:Grell scheme, E: Emanuel scheme) were performed to evaluate the simulation skills of RegCM4 released in July 2010over the CORDEX (COordinated Regional Downscaling EXperiment) East Asia domain based on the combinations of boundary conditions (BC: ERA-Interim, NCEP/DOE2) and the cumulus parameterization schemes (CPS: Grell, Emanuel)for the 1989. The surface air temperature and precipitation data observed by the Korea Meteorological Adminstration were used to validate the simulation results over South Korea. The RegCM4 well simulates the seasonal and spatial variations of temperature but it fails to capture the seasonal and spatial variations of precipitation without consideration of the BC and CPS. Especially the simulated summer precipitation amount is significantly less in EG, NG, and NE experiments. But the seasonal variation of precipitation including summer precipitation is relatively well simulated in the EE experiment. The EE experiment shows a better skill in the seasonal march of East Asia summer monsoon, distribution of precipitation intensity and frequency than other experiments. In general, the skills of RegCM4 for temperature and precipitation are better during winter than summer, and in Emanuel than Grell schemes. The simulation results are more impacted by cumulus parameterization schemes than boundary conditions. 본 연구에서는 CORDEX 동아시아 영역에서 경계조건(ERA-Interim, NCEP/DOE2) 및 적운모수화방안(Grell,Emanuel)이 2010년 7월에 공개된 지역기후모델(RegCM4)의 모의성능에 미치는 영향을 평가하기 위해 1989년에 대해총 4개의 민감도 실험(EG, EE, NG, NE)을 수행하였다. 남한에서의 기온, 강수에 대한 RegCM4의 모의성능을 분석하기위해 기상청의 기온, 강수자료를 이용하였다. RegCM4는 경계조건 및 적운모수화방안에 관계없이 기온의 공간분포, 계절변동을 잘 모의한 반면, 모든 실험에서 강수의 시·공간 분포를 적절히 모의하지 못하였다. 특히, EG, NG, NE 실험은 여름 강수를 관측보다 현저히 적게 모의하는 등 강수의 계절변동을 전혀 모의하지 못하고 있다. 하지만 EE 실험에서는 여름 강수를 포함하여 계절변동을 상대적으로 잘 모의하였다. 동아시아 여름 몬순 및 강수강도별 강수량, 강수빈도 모의에서도 EE 실험이 우수한 모의성능을 보였다. RegCM4는 경계조건에 관계없이 기온, 강수 모두 여름보다는 겨울에, Grell 보다는 Emanuel 방안을 적용할 때 높은 모의성능을 보였다. 또한 전체적으로 모의성능은 경계조건보다는적운모수화방안에 더 큰 영향을 받는다.

Geometric Algorithm for the Classical Spin van der Waals Model in Transverse Magnetic Fields

오석근 한국물리학회 2014 새물리 Vol.64 No.5

Geometric algorithms for solving the nonlinear equations of motion for classical spin systems with a Poisson structure are developed in detail. The higher-order exponential operator product decomposition method of Suzuki and Hatano is utilized in developing higher-order geometric algorithms. The exactly solvable classical spin van der Waals model in transverse fields, which is exactly solvable, is adopted to illustrate the algorithms up to fourth order and to check their validity. The higher-order algorithm is confirmed to be working properly even for larger time-steps.

Closer Look at Linear Response Theory via an Exactly Solvable Model of Classical Spins in a Rotating Magnetic Field

오석근 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.2

Linear response theory is examined through an exactly solvable model of noninteracting classical spins in a rotating magnetic field. The nonequilibrium magnetizations obtained via linear response theory and exact calculation are compared to see explicitly how close their values are. We found that the nonequilibrium magnetization obtained via linear response theory had a value close to that of the exact calulation for very small fields and small angular frequencies far away from the resonance frequency. Furthermore, both magnetizations are again very close to each other for small fields, but very large angular frequencies far away from the resonance angular frequency. However, at or near the resonance angular frequency, the nonequilibrium magnetization obtained via linear response theory is markedly different from that of the exact calculation, irrespective of the magnitude of the magnetic field.

Linear Response Theory of the Classical Spin van der Waals Model in a Rotating Magnetic Field

오석근 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.5

The effect of interactions on the validity of linear response theory is examined via the classical spin van der Waals model in a rotating magnetic field. First, the nonequilibrium magnetization was calculated within the linear response theory by choosing a rotating magnetic field as a perturbation source. Secondly, since the equations of motion for the full Hamiltonian are not exactly solvable except in the Heisenberg limit, a spin dynamics simulation method was adopted to calculate the nonequilibrium magnetization for the full Hamiltonian in the XY and the Ising limits, and then together with the exact results in the Heisenberg limit they are compared with those obtained from the linear response theory. It turns out that, for small rotating magnetic fields and small angular frequencies, the linear response theory works well in the Heisenberg and Ising limits. Nonetheless, in the XY limit, it does not work at low temperatures because the initial ordering along the x-direction is suddenly increased by a discontinuously switched-on magnetic field along the x-direction at t = 0, further enhancing the ordering in the x-direction and thereby causing the results of the linear response theory to move further away from the spin dynamics simulation results. However, it is still good at high temperatures, with no initial ordering in the xy-plane.

Continuous vs. Discontinuous Field-switching Dependence of Linear Response Theory for an Exactly Solvable Model of Noninteracting Classical Spins

오석근 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.2

The e®ect of ¯eld-switching at t = 0 on the consequences of linear response theory (LRT) was examined through an exactly solvable model of noninteracting classical spins in a very small rotat-ing magnetic ¯eld. Both continuous and discontinuous switching ¯elds at time t = 0 were used to get the trajectories of a single spin and nonequilibrium magnetization within LRT, and they were compared with the exact nonequilibrium results. By making use of an arbitrarily chosen set of same initial single spin components, we found that the microscopic single spin trajectories obtained from the LRT for both types of switching ¯elds were almost identical to each other up to some time away from the resonance angular frequency. Surprisingly, the discontinuous ¯eld-switching case agrees with the exact case for longer time intervals. When the initial values of the magnetization components were chosen from the equilibrium magnetization for the judiciously chosen unperturbed Hamiltonian, the nonequilibrium magnetization within the LRT were in close agreement with ex-act solutions away from the resonance angular frequency; i.e., unlike the microscopic single time trajectory calculation, continuous ¯eld-switching yields magnetization components agreeing better with the exact results. However, near the resonance angular frequency, the LRT results for the nonequilibrium magnetization in the presence of both switching ¯elds were quite di®erent from the exact results.

Nonequilibrium Statistical Mechanics of Noninteracting Classical Spins in a Rotating Magnetic Field

오석근 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.6

A model of noninteracting classical spins in a time-dependent rotating magnetic field is investigated. The nonequilibrium magnetization, equal-time correlation functions, time-displaced correlation functions, and the energy are calculated to see their dependences on the magnitude of a transverse rotating magnetic field and a rotating angular frequency. For small rotating fields, compared to a static field along the $z$-axis, all the nonequilibrium quantities show remarkable increases in the oscillation amplitudes at the resonance frequency. However, due to the competition between the static field and the rotating field, the oscillation amplitude increases monotonically for large rotating fields as we increase the angular frequency beyond the resonance angular frequency and no resonance phenomena are seen.