• Nuclear Engineering and Technology
• /
• 제5권2호
• /
• pp.77-82
• /
• 1973

Fermi통계를 도입한 새로운 밀도행렬을 정의함으로써 전자들의 Partition 함수를 구하는 방법이 마련되었다. 새 밀도행렬에 대응하는 Bloch방정식이 형성되었고 약한 Potential에 대하여 이것을 푸는 방법이 얻어겼다. 이 이론은 액체금속의 모델이 될 수 있는 구조적 불규칙계에 적용되었다.

• Bulletin of the Korean Chemical Society
• /
• 제8권2호
• /
• pp.111-114
• /
• 1987

Temperature-dependent, solution EPR spectra of two mixed-valence copper(II)-copper(I) complexes have been simulated by using modified Bloch equations. The transition probability for the intramolecular electron transfer is determined from the simulation. The transition probabilities have been fitted to the Arrhenius equation to derive the activation energies. The transition probability also varies according to the solvent used.

• Bulletin of the Korean Chemical Society
• /
• 제17권2호
• /
• pp.188-192
• /
• 1996

It is shown that the inversion of the undamped Bloch equation for an amplitude-modulated broadband π/2 pulse can be precisely treated as an inverse scattering problem for a Schrodinger equation on the positive semiaxis. The pulse envelope is closely related to the central potential and asymptotically the wave function takes the form of a regular solution of the radial Schrodinger equation for s-wave scattering. An integral equation, which allows the calculation of the pulse amplitude (the potential) from the phase shift of the asymptotic solution, is derived. An exact analytical inversion of the integral equation shows that the detuning-independent π/2 pulse amplitude is given by a delta function. The equation also provides a means to calculate numerically approximate π/2 pulses for broadband excitation.

• 대한수학회보
• /
• 제60권5호
• /
• pp.1335-1364
• /
• 2023

The aim of this paper is to investigate the spectral instability of roll waves bifurcating from an equilibrium in the 2-dimensional generalized Swift-Hohenberg equation. We characterize unstable Bloch wave vectors to prove that the rolls are spectrally unstable in the whole parameter region where the rolls exist, while they are Eckhaus stable in 1 dimension [13]. As compared to [18], showing that the stability of the rolls in the 2-dimensional Swift-Hohenberg equation without a quadratic nonlinearity is determined by Eckhaus and zigzag curves, our result says that the quadratic nonlinearity of the equation is the cause of such instability of the rolls.

• Bulletin of the Korean Chemical Society
• /
• 제34권12호
• /
• pp.3895-3898
• /
• 2013

• Investigative Magnetic Resonance Imaging
• /
• 제3권1호
• /
• pp.13-19
• /
• 1999

MRI imaging provides many benefits such as noninvasive, 3-dimensional imaging capabilities. But it has relatively serious drawback that is the long data collection time, compared with other imaging modality. Many studies have been performed for fast MR imaging. But EPI and SEPI (4-6) are required to expensive hardware. In this paper, we introduce to Burst imaging technique. It can reduce imaging time by use of a mulitple RF excitation technique. Further it is easily implemented to the normal MRI system. But a pixel profile in the conventional burst sequence is so poor that excited area by burst sequence is a small portion of a pixel. This causes poor signal to noise ratio in burst image. therefore frequency sweeping of RF pulse for burst imaging sequence is proposed to improve pixel profile. A burst pulse train is shaped by liner or nonlinear frequency sweeping function so that all the spins within a pixel are excited, thereby improving the signal to noise ratio. It also shows that the pixel profiles are dependent on how frequency sweep is made. Computer simulations with Bloch equation and experimental results obtained using a 1.0 T NMR imaging system are presented.

• 한국광학회지
• /
• 제8권3호
• /
• pp.204-208
• /
• 1997

고리형 레이저에서 단일모드로 발진되는 양방향 광속의 출력세기를 맥스웰-블로흐 방정식을 사용한 준고전적 모형으로 분석하였다. Nd:YAG를 레이저 매질로 설정하고, 한쪽 방향의 광속이 반대 방향의 광속에 미치는 영향을 고려하여, 펌핑률과 감쇄율 및 진동수 어긋남에 따른 레이저 발진의 안정성과 출력변조를 조사하였다. 특히, 전산시늉을 통하여 진동수 어긋남에 따른 출력광속의 변화를 조사하고, 안정한 연속발진 조건을 규명하였다.

• ETRI Journal
• /
• 제21권1호
• /
• pp.1-27
• /
• 1999

We present a new description of envelope-function equation of the superlattice (SL). The SL wave function and corresponding effective-mass equation are formulated in terms of a linear combination of Bloch states of the constituent material with smaller band gap. In this envelope-function formalism, we review the fundamental concept on the motion of a wave packet in the SL structure subjected to steady and uniform electric fields F. The review confirms that the average of SL crystal momentums K = ($k_x,k_y,q$), where ($K_x,k_y$) are bulk inplane wave vectors and q SL wave vector, included in a wave packet satisfies the equation of motion = $_0+Ft/h$; and that the velocity and acceleration theorems provide the same type of group velocity and definition of the effective mass tensor, respectively, as in the Bulk. Finally, Schlosser and Marcus's method for the band theory of metals has been by Altarelli to include the interface-matching condition in the variational calculation for the SL structure in the multi-band envelope-function approximation. We re-examine this procedure more thoroughly and present variational equations in both general and reduced forms for SLs, which agrees in form with the proposed envelope-function formalism. As an illustration of the application of the present work and also for a brief investigation of effects of band-parameter difference on the subband energy structure, we calculate by the proposed variational method energies of non-strained $GaAs/Al_{0.32}Ga_{0.68}As$ and strained $In_{0.63}Ga_{0.37}As/In_{0.73}Ga_{0.27}As_{0.58}P_{0.42}SLs$ with well/barrier widths of $60{\AA}/500{\AA}$ and 30${\AA}/30{\AA}$, respectively.

• 대한수의학회지
• /
• 제27권1호
• /
• pp.101-108
• /
• 1987

국내(國內)에서 사육(飼育)하고 있는 토끼중 시장(市場)으로부터 구입(購入)되어 가축위생연구소(家畜衛生硏究所)에서 여러가지 연구(硏究) 목적(目的)으로 공시(供試)되고 있는 실험용(實驗用) 토끼를 대상으로하여 실험전(實驗前) 자연폐사(自然斃死) 또는 시험종결후(試驗終了後) 폐기(廢棄)되는 때에 부검(剖檢)하여 두상조충(豆狀條蟲)(Taenia pisiformis)의 유생기(幼生期)인 두상낭미충(豆狀囊尾蟲)(Cysticercus pisiformis)에 대한 감염실태(感染實態) 양상(樣相)을 조사(調査)하였으며 충체내부(蟲體內部)의 두부(頭部)를 관찰(觀察)한바 그 결과(結果)를 요약(要約)하면 다음과 같다. 1. 1981년(年) 7월(月)부터 1986년(年) 6월(月)까지 5개년간(個年間) 조사된 총(總) 213수(首)의 토끼중 46수(首)가 감염(感染)되어 평균(平均) 21.6%의 감염율(感染率)을 나타 냈으며 연차별(年次別)로 증가(增加)되는 추세를 인정(認定)할 수 있었다. 2. 계절별(季節別) 및 성별(性別)에 따른 차이(差異)는 인정(認定)되지 아니 하였으나, 품종별(品種別)로는 단모종(短毛種)(28.4%)에서 장모종(長毛種)(6.2%)보다 높았다. 3. 기생부위별(寄生部位別)로는 간(肝)에의 기생(寄生)이 가장 많았으며, 장간막, 위(胃), 신장(腎臟)의 순(順)이었는데 두장기에 복합 감염된 예(例)도 있었다. 4. 분리(分離)된 충체(蟲體)는 길이(평균(平均) 7.04mm)가 폭(평균(平均) 4.62mm)보다 1.5배(培) 가량 길었으며 내부(內部)에는 두부(頭部)(scolex)가 형성(形成)되어 있었다. 5. 두부(頭部)에는 4개(個)의 흡반(吸盤)이 붙어있고 상부중앙(上部中央)에 구기돌출물(口器突出物)(rostellum)이 있으며 내측(內側)(큰 것)과 외측(外側)(작은 것) 2예(列)로 갈쿠리(hooks)가 정렬되어 있었는데, 큰 것은 $250{\mu}m$ 정도, 작은것은 $150{\mu}m$ 정도이었다.