• Journal of the Korean Solar Energy Society
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• v.39 no.4
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• pp.11-24
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• 2019

The total solar irradiation on horizontal surfaces is separated into the beam and diffuses components. Although horizontal global irradiance is a commonly measured parameter for many sites, horizontal diffuse irradiance is not so readily obtainable. For such sites that measure global irradiation alone, a simple but reasonably accurate method is required to estimate diffuse irradiance from its global counterpart. This study investigates the applicability of correlation coefficients models correlating hourly diffuse and beam fraction and hourly clearness index in Daejeon. The three diffuse to global correlation coefficients models (Orgill and Holland model, CIBSE Guide J model, and Erbs et al. model) are selected and the three modified beam to global correlation coefficients models are generated. MBE, RMSE, r-squared of Daejeon and Daejeon boundary site-fitted models are compared with the case of original coefficients. The comparison result shows that the beam and diffuse to global solar irradiation correlation coefficients models with boundary site-fitted coefficients are best suitable for Daejeon. Further researches will be conducted to find the boundary site-fitting method using measured data of other cities and correlation coefficients models using solar altitude, cloud cover, and sunshine duration.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.12A
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• pp.1251-1260
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• 2008

Diffuse wireless optical communication offers more robust optical links in terms of coverage and shadowing than line-of-sight links. However, traditional diffuse wireless infrared (IR) transceiver systems are more susceptible to multi-path distortion and great power decrease, which results in limiting high-speed performance. Multi-beam is an effective technique to compensate for multi-path distortion in a wireless infrared environment. The goal of this paper is to analyze the transmission characteristics by replacing traditional diffuse system (TDS) which contains single wide angle transmitter and single element receiver by system consisting of three-beam transmitter and non-imaging receiver (TNS) attached with compound parabolic concentrator (CPC). In the simulation, we use the recursive model developed by Barry and Kahn and build the scenario based on 10 different cases which have been listed in Table 1. Moreover, we also check the reliability of the TNS diffuse link channel by BER test on the basis of different receiver positions and room sizes. The simulation results not only show the basic transmission characteristics of TNS diffuse link, but also are references to design more efficient and reliable indoor infrared transmission systems.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.6
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• pp.94-101
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• 2004

From the Beckmann's reflection model of wave incident, reflected light from a surface is known to have not only specular but also diffuse components. The specular component dominant a surface for a mirror-like surface is distributed on the almost the same area as the spot on the surface, but the diffuse component region dominant f3r a rough surface spreads scattered on the larger areas than the spot. Therefore, statistic parameters from the scattered light distribution are more meaningful in the diffuse region, while the magnitude of rather meaning in the specular region. In usual, there need two sensors to acquire two kinds of information: Photo-detector for light intensity magnitude and image sensor for light intensity distribution. But dual sensor scheme requires a beam splitter usually to feed light to each sensor, and moreover there is not a combination rule to relieve the different sensor characteristics. In this study a new method is proposed for acquisition of the dual information using only an image sensor. Specular region is established on an image area being distinguished from a diffuse component, and laser power is adjusted so that no pixel of the image sensor in the specular region is saturated. Simulation based on the light reflection theory and the experimental results are quite well matched, and thus the proposed method was proved to be very useful for mirror-like surface measurement.

• Radiation Oncology Journal
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• v.25 no.4
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• pp.278-282
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• 2007

Purpose: Diffuse pigmented villonodular synovitis (PVNS) is an uncommon aggressive synovial proliferative disorder of unknown etiology affecting the joint linings. Though a histologically benign inflammatory process, because of its aggressive growth with bone destruction or recurrence, it is frequently suggested to occur as a low malignant neoplasm. Optimal treatment is surgery, but the local recurrence rate after radical synovectomy for diffuse PVNS is relatively high due to the infiltrative growth pattern. External beam radiotherapy with moderate doses or intra-articular instillation of radioactive isotopes may improve the likelihood of local control and long-term function in patients with incompletely resected or recurrent diffuse PVNS. I report one case of diffuse PVNS of the right knee joint treated with arthroscopic synovectomy and external beam radiotherapy is presented.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1294-1299
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• 2004

Transient radiative heat transfer is analyzed in a one-dimensional slab using finite volume method (FVM). In this study, the step, $2^{nd}$ order upwind, and QUICK schemes are used for incident diffuse radiation and collimated beam, respectively. The results for diffuse radiation show that all schemes applied in this study give good agreements with available published results. In case of collimated beam, however, the results show deviations from the analytical solutions. To successfully describe the propagations of collimated beam, shock capturing schemes such as TVD scheme are need to be developed.

• 한국신재생에너지학회:학술대회논문집
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• 2005.11a
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• pp.595-598
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• 2005

The thermal performance of glass evacuated tube solar collectors are numerically and experimentally investigated. Four different shapes of solar collectors are considered and the performances of these solar collectors are compared. Dealing with a single collector tube, the effects of not only the shapes of the absorber tube but also the incidence angle of solar irradiation (beam radiation) on thermal performance of the collector are studied. However the solar irradiation consists of the beam radiation as well as the diffuse radiation. Also, the interference of solar irradiation and heat transfer interaction between the tubes exist in an actual solar collector. These effects are considered in this study experimentally and numerically the accuracy of the numerical model is verified by the experimental results. The result shows that the thermal performance of the absorber used a plate fin and U-tube is the best.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.3 s.246
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• pp.201-207
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• 2006

Transient radiative heat transfer is analyzed in a one-dimensional slab using finite volume method (FVM). In this study, the step, $2^{nd}$ order upwind, and QUICK schemes are used for incident diffuse radiation and collimated beam, respectively. The results fer diffuse radiation show that all schemes applied in this study give good agreements with available published results. In case of collimated beam however, the results show deviations from the analytical solutions. To successfully describe the propagations of collimated beam shock capturing schemes such as TVD scheme are need to be developed.

• New & Renewable Energy
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• v.2 no.1 s.5
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• pp.56-65
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• 2006

The thermal performance of glass evacuated tube solar collectors are numerically and experimentally investigated. Four different shapes of solar collectors are considered and the performances of these solar collectors are compared. Dealing with a single collector tube, the effects of not only the shapes of the absorber tube but also the incidence angle of solar irradiation (beam irradiation) on thermal performance of the collector are studied. However, the solar irradiation consists of the beam irradiation as well as the diffuse irradiation. Also, the interference of solar irradiation and heat transfer interaction between the tubes exist in an actual solar collector, These effects are considered in this study experimentally and numerically. The accuracy of the numerical model is verified by the experimental results. The result shows that the thermal performance of the absorber used a plate fin and U-tube is the best.

• Proceedings of the Materials Research Society of Korea Conference
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• 1997.05a
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• pp.37-37
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• 1997

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.581-584
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• 2005

Ion beam processing is one of the key technologies to realize mastless and resistless sub 50nm nano fabrication. Unwanted effects, however, may occur since an energetic ion can interact with a target surface in various ways. Depending on the ion energy, the interaction can be swelling, deposition, sputtering, re-deposition, implantation, damage, backscattering and nuclear reaction. Sputtering is the fundamental mechanisms in ion beam induced direct patterning. Re-deposition and backscattering are unwanted mechanisms to avoid. Therefore understanding of ion beam-solid interaction should be advanced for further ion beam related research. In this paper we simulate some important interaction mechanisms between energetic incident ions and solid surfaces and the results are compared with experimental data. The simulation results are agreed well with experimental data.