• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.151.2-151.2
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• 2014

Broadband impedances for the 3-GeV pohang light source-II (PLS-II) storage ring have been numerically estimated using a full three dimensional finite-difference time-domain code, CST particle studio. The total broadband impedance of all the vacuum components was estimated as 0.256 ohm, which is a small fraction of the total machine impedance budget.

• Nuclear Engineering and Technology
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• v.52 no.9
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• pp.2107-2118
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• 2020

The nuclear reactor coupled with supercritical carbon dioxide (S-CO₂) Brayton cycle has good prospects in generation IV reactors. Turbomachineries (turbine and compressor) are important work equipment in circulatory system, whose performances are critical to the efficiency of the energy conversion system. However, the sharp variations of S-CO₂ thermophysical properties make turbomachinery performances more complex than that of traditional working fluids. Meanwhile, almost no systematic analysis has considered the effects of turbomachinery efficiency under different conditions. In this paper, an in-house code was developed to realize the geometric design and performance prediction of S-CO₂ turbomachinery, and was coupled with systematic code for Brayton cycle characteristics analysis. The models and methodology adopted in calculation code were validated by experimental data. The effects of recompressed fraction, pressure and temperature on S-CO₂ recompression Brayton cycle were studied based on detailed design of turbomachinery. The results demonstrate that the recompressed fraction affects the turbomachinery characteristic by changing the mass flow and effects the system performance eventually. By contrast, the turbomachinery efficiency is insensitive to variation in pressure and temperature due to almost constant mass flow. In addition, the S-CO₂ thermophysical properties and the position of minimum temperature difference are significant influential factors of cyclic performance.

• Proceedings of the IEEK Conference
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• 2000.07a
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• pp.289-293
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• 2000

We propose two new algorithms for parallelism-independent scheduling. The machine code generated from the compiler using these algorithms in its scheduling phase is parallelism-independent code, executable in minimum time regardless of the number of the processors in the parallel computer. Our new algorithms have the following phases: finding the minimum number of processors on which the program can be executed in minimal time, scheduling by an heuristic algorithm for this predefined number of processors, and serialization of the parallel schedule according to the earliest start time of the tasks. At run time tasks are taken from the serialized schedule and assigned to the processor which allows the earliest start time of the task. The order of the tasks decided at compile time is not changed at run time regardless of the number of the available processors which means there is no out-of-order issue and execution. The scheduling is done predominantly at compile time and dynamic scheduling is minimized and diminished to allocation of the tasks to the processors. We evaluate the proposed algorithms by comparing them in terms of schedule length to the CP/MISF algorithm. For performance evaluation we use both randomly generated DAGs (directed acyclic graphs) and DACs representing real applications. From practical point of view, the algorithms we propose can be successfully used for scheduling programs for in-order superscalar processors and shared memory multiprocessor systems. Superscalar processors with any number of functional units can execute the parallelism-independent code in minimum time without necessity for dynamic scheduling and out-of-order issue hardware. This means that the use of our algorithms will lead to reducing the complexity of the hardware of the processors and the run-time overhead related to the dynamic scheduling.

• ETRI Journal
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• v.24 no.6
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• pp.415-428
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• 2002

This paper presents a new satellite radio interface, satellite code division multiple access (SAT-CDMA), for the satellite component of IMT-2000. The SAT-CDMA was proposed by Korea and was based on wideband CDMA (WCDMA) for a high degree of commonality with the terrestrial component of IMT-2000. Because a satellite link has a longer round trip delay and a higher Doppler shift than a terrestrial link, we developed new technologies that would make the satellite component especially efficient. We present the main features of the SAT-CDMA radio interface by focusing on satellite-specific schemes. We also demonstrate with extensive comparison results the performance of the main technologies in the SAT-CDMA radio interface.

• Proceedings of the Korea Information Processing Society Conference
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• 2003.11c
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• pp.1657-1660
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• 2003

엔터프라이즈 컴퓨팅 환경에서 넘쳐나는 다양한 플랫폼과 언어, 프레임워크가 소프트웨어 개발에 대한 중복 투자를 야기하고 있다. 이종 플랫폼, 나아가 이종 개발 플랫폼을 자유로이 연동시킬 수 있는 개발 방법에 대한 필요성이 대두되면서 등장한 MDA 개념은 개발된 모델을 특정 플랫폼에 알맞은 형태로 변환함으로써 개발 모델 및 코드의 재사용성을 극대화한다. 본 논문에서는 MDA 개발 방법에 있어서 특정 플랫폼에 알맞은 로드를 동적으로 생성하면서 PSM 이나 프로그래밍 언어에 대한 중립성을 가지기 위한 방안으로 템플릿과 언어 처리기를 복합적으로 사용하는 방안을 제시한다.

• Journal of Communications and Networks
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• v.18 no.2
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• pp.218-226
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• 2016

Coordination among users is an inevitable but time-consuming operation in wireless networks. It severely limit the system performance when the data rate is high. We present FC-MAC, a novel MAC protocol that can complete a contention within one contention slot over a joint frequency-code domain. When a node takes part in the contention, it generates randomly a contention vector (CV), which is a binary sequence of length equal to the number of available orthogonal frequency division multiplexing (OFDM) subcarriers. In FC-MAC, different user is assigned with a distinct signature (i.e., PN sequence). A node sends the signature at specific subcarriers and uses the sequence of the ON/OFF states of all subcarriers to indicate the chosen CV. Meanwhile, every node uses the redundant antennas to detect the CVs of other nodes. The node with the minimum CV becomes the winner. The experimental results show that, the collision probability of FC-MAC is as low as 0.05% when the network has 100 nodes. In comparison with IEEE 802.11, contention time is reduced by 50-80% and the throughput gain is up to 200%.

• Nuclear Engineering and Technology
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• v.51 no.8
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• pp.1871-1885
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• 2019

The deterministic MOC code STREAM of the Computational Reactor Physics and Experiment (CORE) laboratory of Ulsan National Institute of Science and Technology (UNIST), was initially designed for the calculation of pressurized water reactor two- and three-dimensional assemblies and cores. Since fast reactors play an important role in the generation-IV concept, it was decided that the code should be upgraded for the analysis of fast neutron spectrum reactors. This paper presents a coupled code - TULIP/STREAM, developed for the fast reactor assembly and core calculations. The TULIP code produces self-shielded multi-group cross-sections using a one-dimensional cylindrical model. The generated cross-section library is used in the STREAM code which solves eigenvalue problems for a two-dimensional assembly and a multi-assembly whole reactor core. Multiplication factors and steady-state power distributions were compared with the reference solutions obtained by the continuous energy Monte-Carlo code MCS. With the developed code, a sensitivity study of the number of energy groups, the order of anisotropic P_N scattering, and the multi-group cross-section generation model was performed on the k_eff and power distribution. The 2D core simulation calculations show that the TULIP/STREAM code gives a k_eff error smaller than 200 pcm and the root mean square errors of the pin-wise power distributions within 2%.

• Journal of Korean Ophthalmic Optics Society
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• v.10 no.4
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• pp.357-364
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• 2005

To develope the assessment equpiments of an optical system using adaptive optics, we developed the program of wavefront reconstruction for an optical system like eye. We used matlab in order to program the wavefront reconstruction for an optical system and presented the wavefront function of optical system by the zemike polynomials using modal method. To test the developed program, we calculated the zemike coefficient(n=7) of cooke triplet using code V, and compared the wavefront shape and the zemike polynomials using code V to those using the developed program. In this case, the used zemike coefficients were n=2, 3, 4, 5, 6, 7, 8, 9, and 10 and the number of sub-aperture were 1,253. From these results, we know that the reconstructed wavefronts were similar to the wavefront of cooke triplet as n was the larger than 4 and the zemike coefficient was equal to that of cooke triplet as n was 7. The developed program is able to be applied to the core technology to develope the assessment equipment of an optical system using the adaptive optics.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.12
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• pp.1700-1706
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• 2016

To improve the number of simultaneous transmissions of machine-to-machine traffic in a spread spectrum ALOHA channel, we propose a new spreading technique called doubly truncated cyclic code shift keying (DTCCSK). By truncating the codeset of cyclic code shift keying, DTCCSK freely adjusts the spreading factor and the symbol length. As a result, DTCCSK exhibits both a high spectral efficiency of M-ary signaling and low implementation complexity of a direct sequence.

• Nuclear Engineering and Technology
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• v.41 no.6
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• pp.797-806
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• 2009

The Multichannel Analyzer for Transient and steady-state in Rod Array - Liquid Metal Reactor for Flow Blockage analysis (MATRA-LMR-FB) code for the analysis of a subchannel blockage has been developed and evaluated through several experiments. The current version of the code is improved here by the implementation of a distributed resistance model which accurately considers the effect of flow resistance on wire spacers, by the addition of a turbulent mixing model, and by the application of a hybrid scheme for low flow regions. Validation calculations for the MATRA-LMR-FB code were performed for Oak Ridge National Laboratory (ORNL) 19-pin tests with wire spacers and Karlsruhe 169-pin tests with grid spacers. The analysis of the ORNL 19-pin tests conducted using the code reveals that the code has sufficient predictive accuracy, within a range of 5 $^{\circ}C$, for the experimental data with a blockage. As for the results of the analyses, the standard deviation for the Karlsruhe 169-pin tests, 0.316, was larger than the standard deviation for the ORNL 19-pin tests, 0.047.