• Nuclear Engineering and Technology
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• v.5 no.2
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• pp.77-82
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• 1973

A method of obtaining the partition function for a system of electrons is developed by defining a new density matrix, in which the Fermi statistics is explicitly incorporated. The corresponding Bloch equation is formulated and a practical method of solving the equation is obtained for weak potential. This theory is applied to structurally disordered ststems which might be reasonable models for liquid metals.

• Bulletin of the Korean Chemical Society
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• v.8 no.2
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• pp.111-114
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• 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
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• v.17 no.2
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• pp.188-192
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• 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.

• Bulletin of the Korean Mathematical Society
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• v.60 no.5
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• pp.1335-1364
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• 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
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• v.34 no.12
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• pp.3895-3898
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• 2013

• Investigative Magnetic Resonance Imaging
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• v.3 no.1
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• pp.13-19
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• 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.

• Korean Journal of Optics and Photonics
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• v.8 no.3
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• pp.204-208
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• 1997

We analyze the intensity characteristics of the output beams of the ring laser, in which only one mode is generated in each direction, within the neoclassical model by using the Maxwell-Bloch equation. Considering the Nd:YAG crystal as a gain medium, we investigate the stability and the modulation of the output beam intensity as the pumping rate, the relaxation or the decay rate, and the frequency detuning vary, upon taking into account the effect of the beam in one beam in one direction onto the beam in the other direction. In particular, we examine the variation of the output beam intensity and the stability condition through a computer simulation.

• ETRI Journal
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• v.21 no.1
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• pp.1-27
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• 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.

• Korean Journal of Veterinary Research
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• v.27 no.1
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• pp.101-108
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• 1987

A total of 213 rabbits was investigated from July 1981 to June 1986, for the survey on the incidence of Cysticercus pisiformis infections and the morphological characteristics were observed for the descriptions on the scolexes of the cysts collected. The results obtained were summarized as follows; The overall infection rate was revealed as high as 21.6% and it increased annually with the secular trend equation Y=7.45X+5.87 when, Y=infection rate estimated, X=year 0(1981) to 5 (1986). The incidence was no relation with the sexes of the host, but it was higher in the short-haired New Zealand White than in the long-haired Angola. It was also revealed that the liver was the most parasitized organ (39.1%) and that 48 cases were double infections in two organs, such as the mesentery, the stomach or the kidney. The mean size of the cysts measured was 7.04mm in length and 4.62mm in width. There were four suckers and a rostellum on the top of the scolex identified inside the cyst. The hooks were arranged in two rows, the large-type inner hooks (mean $250{\mu}m$ in length) and the small-type outer hooks (mean $150{\mu}m$ in length).