• The Journal of the Acoustical Society of Korea
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• v.18 no.4
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• pp.23-30
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• 1999

In this study, we propose a new optimization algorithm for a withdrawal weighted SAW transversal filter to satisfy given, specifications such as bandwidth, ripple, insertion loss, and sidelobe rejection level. An analysis tool for the withdrawal weighted filter has been produced by means of the delta function model, and has been applied to the design of a filter consisting of an uniform input IDT and a withdrawal weighted output IDT. This optimization algorithm consists of three routines, which eventually determines eight design parameters to satisfy the performance specifications. At the first step, the number of input and output IDT fingers and their geometrical size are determined by the insertion loss specification. At the next step, the bandwidth is controlled by the change of the IDT finger position. Finally, the sidelobe rejection level is modified through the add/skip technique of IDT fingers. The algorithm in this paper is distinct from conventional techniques in that it can simultaneously consider all the specifications such as bandwidth, ripple, sidelobe rejection level and insertion loss, and optimize the geometry of the withdrawal weighted SAW filter.

• The Korean Journal of Food And Nutrition
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• v.20 no.2
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• pp.120-124
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• 2007

The thermal degradation kinetics of alpha-, gamma- and delta-tocopherols was studied during heating at 100, 150 200 and 250$^{\circ}C$ for 5, 15, 30 and 60 min in the absence of oxygen. The tocopherols were separated by HPLC using a reversed phase ${\mu}$-Bondapak C$_{18}$-column with two kinds of elution solvent system in a gradient mode. The kinetics for degradation of ${\alpha}$-, ${\gamma}$- and ${\delta}$-tocopherols was analyzed as a function of temperatures and times. The degradation of tocopherols was described by the first-order kinetics in the absence of oxygen. The rate of tocopherols degradation was dependent on heating temperatures. The degradation rate constants for ${\alpha}$-, ${\gamma}$ and ${\delta}$-tocopherols showed an increasing trend as the heating temperature increased. The magnitude order of the experimental activation energy was ${\delta}$->${\gamma}$->${\alpha}$-tocopherol.

• Korean Journal of Optics and Photonics
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• v.27 no.4
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• pp.143-150
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• 2016

The thickness of each layer in a multilayered system is determined by a Fourier-transform method using spectroscopic reflectance measurements. To verify this method, we first generate theoretical reflectance spectra for three layers, and these are fast-Fourier-transformed using our own Matlab program. Each peak of the Fourier-transformed delta function denotes the optical thickness of each layer, and these are transformed to physical thicknesses. The relative thickness error of the theoretical model is less than 1.0% while a layer's optical thickness is greater than 730 nm. A PI-(thin $SiO_2$)-PImultilayeredstructure produced by the bar-coating method was analyzed, and the thickness errors compared to SEM measurements. Even though this Fourier-transform method requires knowing the film order and the refractive index of each layer prior to analysis, it is a fast and nondestructive method for the analysis of multilayered structures.

• Geophysics and Geophysical Exploration
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• v.3 no.4
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• pp.119-124
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• 2000

A new fast algorithm for travel time calculation using mono-chromatic one-way wave equation was developed based on the delta function and the logarithms of the single frequency wavefield in the frequency domain. We found an empirical relation between grid spacing and frequency by trial and error method such that we can minimize travel time error. In comparison with other methods, travel time contours obtained by solving eikonal equation and the wave front edge of the snapshot by the finite difference modeling solution agree with our algorithm. Compared to the other two methods, this algorithm computes travel time of directly transmitted wave. We demonstrated our algorithm on migration so that we obtained good section showing good agreement with original model. our results show that this new algorithm is a faster travel time calculation method of the directly transmitted wave for imaging the subsurface and the transmission tomography.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.201-201
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• 2009

반도체 레이저 다이오드(laser diode)는 도파로 내부의 굴절률 변화로 발생하는 필라멘테이션(filamentation) 문제와 벽개면 손상으로 인한 catastrophic optical damage(COD) 문제로 고품위/고출력 발진이 제한된다. 양자점 (quantum dot) 레이저 다이오드는 델타 함수 형태의 상태 밀도를 갖기 때문에 이론적으로는 zero 값의 선폭증가요소 특성을 가져 고출력 동작 시 필라멘테이션 문제를 제거할 수 있다. 또한 고출력 동작을 위한 COD 문제는 낮은 광 밀도를 갖는 활성층/도파로 영역의 에피구조 최적화를 통해 해결할 수 있다. 본 논문에서는 고출력 808 nm 양자점 반도체 레이저 다이오드 개발을 위한 에피구조 설계 및 최적화 연구를 수행하였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.8
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• pp.1767-1775
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• 2003

The SAW device is extensively used as a electro$.$mechanical band­pass filter in which a two­pairs of interdigital transducers are provided over the surface of the piezoelectric substrate. For the design requirement, the central frequency and the bandwidth of the passband, and the attenuation level of the stopband region are specified. The configuration is made so as to satisfy the specification given. The central frequency is mainly determined by the distance between the pair of the finger electrodes. The design is considered as an optimization problem with which the error norm, the distance between the desired characteristics and the calculated for a given model is to be minimized. The delta function model and the electrical equivalent circuit model are utilized to represent the SAW filter characteristics. Genetic algorithm is used for optimization in which apodization of the transducer fingers is chosen as a design variable.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.4
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• pp.335-341
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• 2009

In this paper, review of developed MLS-based finite elements and a proposal for their applications are described. The shape functions and their derivatives of MLS-based finite elements are constructed using Moving-Least Square approximation. In MLS-based finite element, using the adequate influence domain of weight function used in MLS approximation, kronecker delta condition could be satisfied at the element boundary. Moreover, because of the characteristics of MLS approximation, we could easily add extra nodes at an arbitrary position in MLS-based finite elements. For these reasons, until now, several variable-node elements(2D variable element for linear case and quadratic case and 3D variable-node elements) and finite crack elements are developed using MLS-based finite elements concept. MLS-based finite elements could be extended to 2D variable-node triangle element, 2D finite crack triangle element, variable-node shell element, finite crack shell element, and 3D polyhedron element. In this paper, we showed the feasibility of 3D polyhedron element at the case of femur meshing.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.12
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• pp.1756-1761
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• 2021

Although the COVID-19 outbreak that occurred in Wuhan, Hubei around December 2019, seemed to be gradually decreasing, it was gradually increasing as of November 2020 and June 2021, and estimated confirmed cases were 192 million worldwide and approximately 184 thousand in South Korea. The Central Disaster and Safety Countermeasures Headquarters have been taking strong countermeasures by implementing level 4 social distancing. However, as the highly infectious COVID-19 variants, such as Delta mutation, have been on the rise, the number of daily confirmed cases in Korea has increased to 1,800. Therefore, the number of cumulative confirmed COVID-19 cases is predicted using ARIMA algorithms to emphasize the severity of COVID-19. In the process, differences are used to remove trends and seasonality, and p, d, and q values are determined and forecasted in ARIMA using MA, AR, autocorrelation functions, and partial autocorrelation functions. Finally, forecast and actual values are compared to evaluate how well it was forecasted.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.5
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• pp.2390-2395
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• 2011

For intersymbol interference (ISI) compensation from communication channels with multi-path fading and impulsive noise, a decision feedback equalizer algorithm that minimizes Euclidean distance of error probability is proposed. The Euclidean distance of error probability is defined as the quadratic distance between the probability error signal and Dirac-delta function. By minimizing the distance with respect to equalizer weight based on decision feedback structures, the proposed decision feedback algorithm has shown to have significant effect of residual ISI cancellation on severe multipath channels as well as robustness against impulsive noise.

• Economic and Environmental Geology
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• v.28 no.5
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• pp.481-485
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• 1995

This paper presents a new approaching method to determine the velocity and geometry of shallow subsurface from seismic refraction events. After picking the first breaks from seismic refraction data, we assume that field refraction seismogram can be replaced by the unit delta function having time shift of first break. Time curves are generated by shooting ray tracing. The partial derivatives seismogram for a damped least squares method is computed analytically at each step of the forward ray tracing. The technique is successfully tested on synthetic and real data. It has the advantage of real full waveform inversion, which is robust at low frequency band even if the initial guess is far from the true model.