• 천문학회보
• /
• 제41권2호
• /
• pp.53.2-53.2
• /
• 2016

We present our experiences with open-source spatio-temporal database systems for managing and analyzing big astronomical data acquired by wide-field time-domain sky surveys. Considering performance, cost, difficulty, and scalability of the database systems, we conduct comparison studies of open-source spatio-temporal databases such as GeoMesa and PostGIS that are already being used for handling big geographical data. Our experiments include ingesting, indexing, and querying millions or billions of astronomical spatio-temporal data. We choose the public VVV (VISTA Variables in the Via Lactea) catalogs of billions measurements for hundreds of millions objects as the test data. We discuss issues of how these spatio-temporal database systems can be adopted in the astronomy community.

• 한국초전도ㆍ저온공학회논문지
• /
• 제15권1호
• /
• pp.11-13
• /
• 2013

We have developed a terahertz time-domain spectroscopy (THz-TDS) system for transmission and reflection measurements of metallic thin films. Using our THz-TDS system, we studied the conventional superconductor niobium (Nb) in the normal state in the spectral range from 5 to $50cm^{-1}$. Both the real and imaginary parts of the conductivity are acquired without Kramers-Kronig analysis. Nb exhibits a nearly frequency independent real conductivity spectrum in the terahertz range, with a very small imaginary part.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 2000년도 가을 학술발표회논문집
• /
• pp.18-23
• /
• 2000

The radar method is becoming one of the major nondestructive testing (NDT) techniques for concrete structures. Numerical modeling of electromagnetic wave is needed to analyze radar measurement results and to study the influence of measurement parameters on the radar measurements. Finite difference-time domain (FD-TD) method is used to simulate electromagnetic wave propagation through concrete specimens. Three concrete specimens with a 19.1 mm rebar embedded at 40 mm, 60 mm, and 80 mm depth are modeled in 3-dimension. As results, 2-D image processing scheme of modeling data has been developed and applied to the imaging of steel bars inside concrete.

• Smart Structures and Systems
• /
• 제8권2호
• /
• pp.157-172
• /
• 2011

A new method for both local damage(s) identification and input excitation force identification of beam structures is presented using the dynamic response sensitivity-based finite element model updating method. The state-space approach is used to calculate both the structural dynamic responses and the responses sensitivities with respect to structural physical parameters such as elemental flexural rigidity and with respect to the force parameters as well. The sensitivities of displacement and acceleration responses with respect to structural physical parameters are calculated in time domain and compared to those by using Newmark method in the forward analysis. In the inverse analysis, both the input excitation force and the local damage are identified from only several acceleration measurements. Local damages and the input excitation force are identified in a gradient-based model updating method based on dynamic response sensitivity. Both computation simulations and the laboratory work illustrate the effectiveness and robustness of the proposed method.

• 천문학논총
• /
• 제30권2호
• /
• pp.611-616
• /
• 2015

The Antarctic high plateau offers exceptional conditions for infrared and terahertz astronomy, as well as for programs requiring long, uninterrupted periods for measurements made with high cadence and photometric precision (i.e. time domain astronomy). In this review we summarise the special conditions of the Antarctic plateau which facilitate these observing regimes. We also outline some high profile science programs in each that could be conducted most effectively from the Antarctic high plateau, involving the first light in the Universe, the life cycle of our Galaxy, and the equation of state for the Universe. Three high plateau sites are under particular consideration for furthering such scientific programs{Dome A, Dome F and Ridge A. We summarise the activity underway at each site, which includes the building of new stations and the construction of facilities for optical, infrared and terahertz astronomy, as well as the plans for their future development.

• Journal of the Optical Society of Korea
• /
• 제8권1호
• /
• pp.34-52
• /
• 2004

Over the past decade the experimental technique of THz time domain spectroscopy (㎔- TDS) has proved to be a versatile method for investigating a wide range of phenomena in the ㎔ or far infrared spectral region from 100 ㎓ to 5 ㎔. This paper reviews some recent results of the Ultrafast ㎔ Research Group at Oklahoma State University using ㎔-TDS as a characterization tool. The experimental technique is described along with recent results on ㎔ beam propagation and how ㎔ beam profiles arise from propagation of pulse fronts along caustics. To illustrate how spatio-temporal electric field measurements can determine material properties over a wide spectral range, propagation of ㎔ pulses through systems exhibiting frustrated total internal reflection (FTIR) are reviewed. Finally two potential metrology applications of ㎔-TDS are discussed, thin film characterization and non-destructive evaluation of ceramics. Although ㎔-TDS has been confined to the research laboratory, the focus on application may stimulate the adoption of ㎔- TDS for industrial or metrology applications.

• 한국광학회지
• /
• 제18권3호
• /
• pp.196-201
• /
• 2007

두 대의 펄스 레이저를 사용한 BOTDA(Brillouin optical time-domain analysis)의 이론적 연구가 수행되었다. 비록 펌프 펄스 주기동안 한 점의 정보만을 측정할 수 있지만 시스템의 동적 범위 성능은 광섬유 길이가 140 km이고 스톡스(Stokes) 전력이 1 mW일 때 펄스와 CW 레이저를 사용한 시스템 보다 5 dB 큰 것으로 분석되었다.

• Earthquakes and Structures
• /
• 제2권4호
• /
• pp.323-336
• /
• 2011

The problem of reconstruction of complete building response from a limited number of response measurements is considered. The response at the intermediate degrees of freedom is reconstructed by using piecewise cubic Hermite polynomial interpolation in time domain. The piecewise cubic Hermite polynomial interpolation is preferred over the spline interpolation due to its trend preserving character. It has been shown that factorization of response data in variable separable form via singular value decomposition can be used to derive the complete set of normal modes of the structural system. The time domain principal components can be used to derive empirical transfer functions from which the natural frequencies of the structural system can be identified by peak-picking technique. A reduced-rank approximation for the system flexibility matrix can be readily constructed from the identified mass-orthonormal mode shapes and natural frequencies.

• Journal of Power Electronics
• /
• 제10권6호
• /
• pp.635-642
• /
• 2010

The paper presents a multimedia educational program of DC servo drives for distant learning with a special emphasis on sliding mode control. The program contains of three parts: animation, simulation and internet based measurement. The animation program explains the operation of DC motors, gives its time- and frequency-domain equations, transfer functions and the theoretical background necessary for controller design for DC servo motors. The simulation model of the DC servo motor and the controller can be designed by the students based on the animation program. The students can also test their controllers through the internet based measurement, which is the most important part from engineering point of view. After the measurements are executed, the students can download the measured data and compare them to the simulation results.

• Steel and Composite Structures
• /
• 제10권6호
• /
• pp.541-561
• /
• 2010

This paper presents finite element analyses, experimental measurements and finite element model updating of an arch type steel laboratory bridge model using semi-rigid connections. The laboratory bridge model is a single span and fixed base structure with a length of 6.1 m and width of 1.1m. The height of the bridge column is 0.85 m and the maximum arch height is 0.95 m. Firstly, a finite element model of the bridge is created in SAP2000 program and analytical dynamic characteristics such as natural frequencies and mode shapes are determined. Then, experimental measurements using ambient vibration tests are performed and dynamic characteristics (natural frequencies, mode shapes and damping ratios) are obtained. Ambient vibration tests are performed under natural excitations such as wind and small impact effects. The Enhanced Frequency Domain Decomposition method in the frequency domain and the Stochastic Subspace Identification method in the time domain are used to extract the dynamic characteristics. Then the finite element model of the bridge is updated using linear elastic rotational springs in the supports and structural element connections to minimize the differences between analytically and experimentally estimated dynamic characteristics. At the end of the study, maximum differences in the natural frequencies are reduced on average from 47% to 2.6%. It is seen that there is a good agreement between analytical and experimental results after finite element model updating. Also, connection percentages of the all structural elements to joints are determined depending on the rotational spring stiffness.