• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.357-361
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• 2010

When high-pressure gas is exhausted through nozzle exit to the atmosphere, expanded supersonic jet is formed with the Mach disk at a specific condition. In two-dimensional supersonic jets, the hysteresis phenomenon of the reflected shock waves is found to occur under quasi-steady flow conditions. Transitional pressure ratio between the regular reflection and Mach reflection in the jet is affected by this phenomenon. In the present study, experiments are carried out on internal flow in a supersonic nozzle to clarify the hysteresis phenomena for the shock waves and to discuss its interdependence on the rate of the change of pressure ratio with time. Flow visualization is carried out separately on the straight and divergent channels downstream of the nozzle throat section. The influence that the hysteresis phenomena have on the location of shock wave in a supersonic nozzle is also investigated experimentally.

• The Korean Journal of Zoology
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• v.30 no.4
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• pp.417-431
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• 1987

Isozyme analysis, morphometric comparison, and artificial hybridization test wereperformed to elucidate the patterns of genic variation, morphological differentiation, genetic incompatibility, and a probable path in speciation between two MDH allelotypes (MM type and MS type) of the Dark Chub Zacco temmincki, a fresh water fish inhabiting in Korean waters. The degree of genic variation of MS type(HD=.023, HG=.021) was twofold higher than that of MM type (HD=.013, HG=.014) but both allelotypes were far less than the average genic variation of fresh water Bish in general. The average genetic similarities among 7 populations of MM type and 6 Populations of MS type were S=.947 and S=.966 respectively, whereas the value between two allelotypes was S=.853. Presumed divergent time of two allelotypes was estimated to be about 700 thousand years ago. Discriminant function analysis based on 18 morphometric characters of 302 specimens representing 12 populations revealed no morphological difference between two allelotypes. Artificial hybridization test indicates that there is an obvious genetic incogpatibility between two allelotypes and therefore it is assumed that isolating mechanism is completed.

• The Korean Journal of Zoology
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• v.39 no.2
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• pp.147-158
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• 1996

Since the floating goby, Choenogobius onnuloris, has intricate and diverse morphological variations, allozymic analysis at 25 loci was carried out for their populations in Korea to clarify its taxonomic status. A genetic assay carried out revealed that the floating gobies were clearly divided into three genetic groups (Tvpe-A, Tvpe-B and Tvpe-C) in Korea. Alternative alleles were fated at six loci (Aco, 6pgd, Ldh-1, Got-1, Gpf, Gp3l. Some loci had considerable heterogeneitv among three types and no evidence of gene exchange in slunpatric populations was found from statistical analyses. The genetic similarity (Rogers'S) among three types was lower than 0.80 and divergent time estimate indicates that they were speciated during 1.2-1.8 million year before present (WBP). ASso, these three types of C. unnuluris were distinguished morpholosicallv from each other by several characters such as band ornamentations. In conclusion, the evidences presented here support recognition of three types of Chuenogobius annularis as typical discrete species.

• The Journal of Information Technology and Database
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• v.5 no.1
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• pp.51-67
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• 1998

There exist a number of information systems planning(ISP) methodologies. As the level of market competition gets intensified, firms are more likely to engage in organizational transformations such as BPR and CPI(continuous process improvement). Because this new requirement should be incorporated into ISP methodology, the number of ISP methodologies available will be continually increasing. However, we could not find a framework for understanding and classifying these divergent methodologies. So, we here present a framework for classifying ISP methodology classes. With this framework, we categorize different classes of ISP methodologies and identify their limitations in terms of missing elements and links. And we move on to present new technical innovations and other methodological advances that, if properly integrated with ISP methodologies, would help us derive an IT infrastructure plan more effectively. Furthermore, in search of software tools or aids supporting the application of ISP methodologies, we identify requirements of ISP-supporting software tools and evaluate functions of existing software tools, then suggesting a future direction to that end.

• Journal of Biomedical Engineering Research
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• v.15 no.2
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• pp.143-150
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• 1994

Wall shear rate or stress is believed to be a major hemodynamic variable influencing atherosclerosis and artery-graft anastomic intimal hyperplasia. The purpose of this study is to verify the effects of radial wall motion, artery-graft compliance and diameter mismatch, and impedance phase angle on the wall shear rate distribution near an end-to-end artery-graft anastomosis model. The results show that radial wall motion of the elastic artery model lowers the mean wall shear rates under pulsatile flow condition by 15 to 20 % comparing to those under steady flow condition at the same mean flow rate. Impedance phase angle seems to have small effects on the mean and amplitude of the wall shear rate distribution. In order to study the effects of compliance and diameter mismatch on the wall shear rates, two models are studied-Model I has 6% and Model I has 6% and Model II has 11% smaller graft diameter. Divergent geometry caused by diameter mismatch near the distal sites reduces the mean wall shear rates significantly, and this low shear region is believed to be prone to intimal hyperplasia.

• Journal of Species Research
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• v.9 no.2
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• pp.174-179
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• 2020

Larvae and pupae of Simulium (Eusimulium) satsumense were collected and recorded from Korea for the first time. Detailed descriptions and photographs of both immatures are provided. Currently, 42 species are known from the subgenus Eusimulium, which is found globally, mainly in the Holarctic Region, but unknown from Korea. Members of the subgenus Eusimulium are morphologically homogeneous in male, female, and pupa, making them extremely difficult to distinguish from one another. S. (E.) satsumense can be distinguished from other Korean black flies by the following combination of the characteristics: Pupa: Gill of four slender filaments, dorsalmost filament strongly divergent from other filaments; cocoon slipper shaped without anterodorsal projection; Larva: Head spots distinctly positive; postgenal cleft short, apically rounded or squared; antenna with proximal segment brown; abdominal segments IX with prominent ventral tubercles; and rectal papillae of three simple lobes. In addition to descriptions for larvae and pupae of the species, a key to genera and subgenera of Simulium of Korean black flies are also provided.

• The Mathematical Education
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• v.51 no.4
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• pp.337-349
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• 2012

The purpose of this study is to survey and analyze conception on creativity carried out from elementary school teachers in Seoul and Gyeonggi-do area. As results, first, most of teachers replied divergent thinking, creative problem solving, and new creation as general creativity and mathematical creativity. Secondly, they showed that thinking process would be related to transfer and cognition in terms of mathematical creativity factors. Lastly, there are significant differences among groups according to gender, teaching career, and age, even though most teachers expressed sympathy for need of creativity education in mathematics education.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.1052-1060
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• 1989

Using a vortex stretching invariant term, the two-layer k-.epsilon. model has been modified to account for the extra staining of turbulence due to the mean-flow convergence and divergence. The calculations of turbulent boundary layers in a plane of symmetry are compared for experimental cases which are an axisymmetric body at an incidence of 15.deg.. The comparisons between the calculations and experimental data show that additional modifications to the dissipation rate equation have brought the significant improvement to the prediction of plane of symmetry boundary layers in the strong mean-flow convergence and divergence.

• Proceedings of the Optical Society of Korea Conference
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• 1989.02a
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• pp.81-84
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• 1989

EHZP is a kind of holographic optical element, which is generated by the interference of two divergent spherical waves from point sources on the same axis. It has the spherical aberration that the focal power increases as the radial distance r increases. By using this property, optimal design of EHZP was performed for f-$\theta$ lens. As the result of optimization, the f-$\theta$ condition and the field flattening condition were well satisfied when EHZP has f0=0.803f, faR=4.076f, 1=0.406f. It was assumed for calculation of field flattening condition that the incident wave was a plane wave with the diameter of 1mm.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.12
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• pp.28-33
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• 2020

Oil-related products have provided many benefits to humanity, but are significant contributors to environmental pollution. As per the International Maritime Organization (IMO) requirements, in the future, all ships must be equipped with filtering equipment and 5ppm bilge alarms that can help remove or reduce oil products during wastewater treatment. In this study, a UV fluorescence measurement system that can detect the oil components in wastewater containing both water and oil was developed. When an excitation wavelength of 254nm was used to irradiate the wastewater, the amount of UV at a divergent wavelength of 360nm was measured to measure the contamination. Based on the measurement, it was concluded that this system is suitable for use as the 5ppm bilge alarm proposed by IMO.