• Journal of Astronomy and Space Sciences
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• 제8권2호
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• pp.141-148
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• 1991

In order to obtain a complete picture of the time dependent dynamic of 360 fragments in space, the program IODS (ISSA Orbit Determination System) has been set up. Using The program IODS, all fragments orbits of one break-up event can be generated. Perturbations due to the Earth's asymmetrical potential, the Sun, moon, air drag and solar radiation force are considered. We summarize our results as follows : I) Due to J2 term, precessional motion of all fragment orbits are (수식생략) ii) The other perturbations have very small effects.

• 천문학회보
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• 제46권1호
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• pp.37.3-38
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• 2021

Radiation pressure noise of photon and photon shot noise are quantum noise limitation in interferometric gravita-tional wave detectors. Since relationship between the two noises is position and momentum of the Heisenberg uncertainty principle, quantum non-demolition (QND) technique is required to reduce the two noises at the same time. Frequency dependent squeezing using a filter cavity is one of realistic solutions for QND measurement and experimental results show that its cutting-edge performance is sufficient to apply to the current gravitational wave detectors. A 300m filter cavity is under construction at adv-LIGO. KAGRA (gravitational wave detector in Japan) has also started international collaboration to build a filter cavity. Recently we joined the filter cavity project for KAGRA. Current status of squeezing and filter cavity research at KASI and details of the KAGRA filter cavity project will be presented.

• 한국정밀공학회지
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• 제18권7호
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• pp.127-133
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• 2001

The effects of triangular and rectangular discharge current waveforms on anode erosion in wire electric discharge machining is investigated based on heat transfer analysis of half-space subject to time and space-dependent heat flux. The thermal load on the anode is simulated by a hear flux that is calculated from time-dependent discharge channel radius and energy. Evolution of the melting front during discharge, the molten volume at the experimental result for qualitative verification of the analysis. It is demonstrated that the triangular current waveform is more efficient in eroding the anode than the rectangular one.

• Structural Engineering and Mechanics
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• 제76권5호
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• pp.599-611
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• 2020

A state-space method is developed to investigate the time-dependent behaviors of an angle-ply cylindrical shell in cylindrical bending with surface-bonded piezoelectric layers. Both the interfacial diffusion and sliding are considered to describe the properties of the imperfect interfaces. Particularly, a matrix reduction technique is adopted to establish the transfer relations between the elastic and piezoelectric layers of the laminated shell. Very different from our previous paper, in which an approximate numerical technique, i.e. power series expansion method, is used to deal with the time-dependent problems, the exact solutions are derived in the present analysis based on the piezoelasticity equations without any assumptions. Numerical results are finally obtained and the effects of imperfect interfaces on the electro-mechanical responses of the laminated shell are discussed.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2010년도 한국우주과학회보 제19권1호
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• pp.38.3-39
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• 2010

While major solar proton events (SPEs) come from the coronal mass eject (CME)-driven shocks in solar wind, there are many evidences that potentiality of CMEs to generate SPEs depends on its early evolution near the Sun and on different solar activities observed around the CME liftoff time. To decipher origin of SPE release, we have investigated onset time comparison of the SPE with CME, metric type II radio burst, and hard X-ray flare. For this, we select 30 SPEs observed from 1997 to 2006 by using the particle instrument ERNE onboard SOHO, which allows proton flux anisotropy measurement in the energy range ~10 - 50MeV. Onset time of the SPEs is inferred by considering the energy-dependent proton transport time. As results, we found that (1) SPE onset time is comparable to that of type II but later than type III onset time and HXR start time, (2) SPE onset time is mostly later than the peak time of HXR flare, (3) almost half of the SPE onsets occurred after the HXR emission, and (4) there are two groups of CME height at the onset time of SPE; one is the height below 5 Rs (low corona) and the other is above 5Rs (high corona). In this talk, we will present the onset time comparison and discuss about the origin of the SPE onset.

• Steel and Composite Structures
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• 제45권4호
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• pp.535-546
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• 2022

The memory response of nonlocal systematical formulation size-dependent coupling of viscoelastic deformation and thermal fields for piezoelectric materials with dual-phase lag heat conduction law is constructed. The method of the matrix exponential, which constitutes the basis of the state-space approach of modern control theory, is applied to the non-dimensional equations. The resulting formulation together with the Laplace transform technique is applied to solve a problem of a semi-infinite piezoelectric rod subjected to a continuous heat flux with constant time rates. The inversion of the Laplace transforms is carried out using a numerical approach. Some comparisons of the impacts of nonlocal parameters and time-delay constants for various forms of kernel functions on thermal spreads and thermo-viscoelastic response are illustrated graphically.

• Nuclear Engineering and Technology
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• 제53권2호
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• pp.399-413
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• 2021

The solution of the time-dependent neutron diffusion equation can be approximated using quasi-static methods that factorise the neutronic flux as the product of a time dependent function times a shape function that depends both on space and time. A generalization of this technique is the updated modal method. This strategy assumes that the neutron flux can be decomposed into a sum of amplitudes multiplied by some shape functions. These functions, known as modes, come from the solution of the eigenvalue problems associated with the static neutron diffusion equation that are being updated along the transient. In previous works, the time step used to update the modes is set to a fixed value and this implies the need of using small time-steps to obtain accurate results and, consequently, a high computational cost. In this work, we propose the use of an adaptive control time-step that reduces automatically the time-step when the algorithm detects large errors and increases this value when it is not necessary to use small steps. Several strategies to compute the modes updating time step are proposed and their performance is tested for different transients in benchmark reactors with rectangular and hexagonal geometry.

• Steel and Composite Structures
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• 제25권2호
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• pp.177-186
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• 2017

In this work, the model of magneto-thermoelasticity based on memory-dependent derivative (MDD) is applied to a one-dimensional thermal shock problem for a functionally graded half-space whose surface is assumed to be traction free and subjected to an arbitrary thermal loading. The $Lam{\acute{e}}^{\prime}s$ modulii are taken as functions of the vertical distance from the surface of thermoelastic perfect conducting medium in the presence of a uniform magnetic field. Laplace transform and the perturbation techniques are used to derive the solution in the Laplace transform domain. A numerical method is employed for the inversion of the Laplace transforms. The effects of the time-delay on the temperature, stress and displacement distribution for different linear forms of Kernel functions are discussed. Numerical results are represented graphically and discussed.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.347-354
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• 2001

Extradosed PSC Box bridges, newly emerging type of structures in construction market, have a characteristic in that external tendons are used for strengthening PSC Box girder like stay cables in cable stayed bridges. In this study, a series of constructions stage analysis procedure, including initial shape analysis, backward analysis and forward analysis, have been performed in order to investigate long-term behavior of extradosed PSC box bridges, using PCCAP-a computer program for time-dependent stage analysis of PSC cable stayed bridges. CEB-FIP 1978 model was used for the consideration of time-dependent effect of concrete material. Showing the validity of the analysis results with RM SPACE FRAME, it has been confirmd that time-dependent effects become less consequential as the stiffness of girder becomes larger.

• 대한음성학회지:말소리
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• 제53호
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• pp.143-156
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• 2005

Speaker adaptation in eigenvoice space is a popular method for rapid speaker adaptation. To improve the performance of the method, the number of speaker dependent models should be increased and eigenvoices should be re-estimated. However, principal component analysis takes much time to find eigenvoices, especially in a continuous speech recognition system. This paper describes a method to reduce computation time to estimate eigenvoices only for supplementary speaker dependent models and to merge them with the used eigenvoices. Experiment results show that the computation time is reduced by 73.7% while the performance is almost the same in case that the number of speaker dependent models is the same as used ones.