• Journal of KSNVE
• /
• v.4 no.3
• /
• pp.377-384
• /
• 1994

This paper is an investigation of the performance of absorption diffusers to suppress the vent noise emitted when high pressure gas is throttled. First, experiment for the static performance is carried out. When there is no through-flow, the insertion loss has been obtained in terms of 1/3 octave band spectrum and the effect of the number of diffusers and the thickness of the absorption material on the static performance has been obtained. And the similarity in the spectrum of the static insertion loss is confirmed by comparing two similar models with different size. Second, the dynamic performance has been obtained by experiment using blow-down of compressed air from a storage tank through an orifice of diameter 10 mm. The back pressure by the diffuser is measured and compared with that of a single diffuser. It is found that the insertion loss of asingle diffuser is very low around 3 dB at high frequencies with negative value at low frequencies. By absorption material between the diffuser tubes, however, the performance is increased considerably. Without flow the static insertion loss increases by 3 - 4 dB by doubling the thickness or the density of the absorptionmaterial. With flow, however, the dynamic insertion loss increases. While, the back pressure by the diffuser is small enough to be neglected.

• Archives of Plastic Surgery
• /
• v.34 no.6
• /
• pp.719-723
• /
• 2007

Purpose: Blowout fracture can lead to functional impairments and esthetic deformities such as impairment of ocular movement, diplopia, visual loss and enophthalmos. The object of this study is to present a classification and its analysis according to the computed tomographic scan in blowout fractures. We classified blow out fractures into three types according to the anatomical location of fracture, the size of the bone defect and the degree of periosteal injury by using the computed tomography scan. Each progress and complications were analyzed more than mean 1 year. Methods: Among the 155 cases during 4 years, there were 11 cases of medial orbital wall fracture, 97 cases of inferior orbital wall fracture, 47 cases of combined type. The mean age of patients was 31.2 years, ranged from 8 to 84 years. Results: According to our classification, surgical treatments through the nasoendoscopic approach, the subciliary approach, the transconjunctival approach or their combinations were performed in 116 patients, and conservative treatments were done in 46 patients. Presurgical clinical findings of diplopia, impairment of ocular movement, enophthalmos of more than 2 mm were present in 62 patients. After surgical treatment, clinical findings were remained in 7 patients. Conclusion: We think that our classification according to computed tomographic scan is helpful for the indication and it may decrease the complications such as impairment of ocular movement, diplopia, visual loss and enophthalmos.

• The Korean Journal of Community Living Science
• /
• v.18 no.1
• /
• pp.63-70
• /
• 2007

The purpose of this study is to find out how family, school and community variables influence internet behavior problems in adolescents. By focusing on sex differences, this study analyzes female as well as male behavior problems. The data used in this study are gathered from 1,046 middle and high school students in a national sampling. The results are as follows. Internet addiction is the most frequently occurring problem. A chi-square test shows that male students have higher experience rates than female students in obscene chatting and violent games. A series of logistic regressions are performed to blow the relative influence of independent variables controlling for each other. In the case of male students' internet behavior problems, region, communications with their parents, interactions with their close friends, and satisfaction with community facilities are significant variables. Interactions with friends are significant in predicting behavior problems of both female and male students. Suggestions and implications with regard to intervention strategies for adolescents are discussed.

• Archives of Plastic Surgery
• /
• v.38 no.6
• /
• pp.879-882
• /
• 2011

Purpose: Superior orbital fissure syndrome is a rare neurological complex. Superior orbital fissure syndrome may result from a variety of inflammatory, infectious, neoplastic, iatrogenic, traumatic, vascular cause. The author report a patient who suffered from superior orbital fissure syndrome after inferior orbital wall reduction. Methods: A 26-year-old female suffered from inferior orbital wall fracture with inferior gaze limitation and orbital soft tissue herniation. On posttrauma 10 day, inferior orbital wall was reduced using endoscope and porous polyethylene ($Medpor^{(R)}$) was inserted. On immediate postoperation, she reported that extraocular movement was limited in almost any directions. She underwent exploration surgery to release the presence of extraocular muscle impingement. But, there was no observation of extraocular muscle impingement. On postoperative one day, high-dose steroid therapy was started to release superior orbital fissure syndrome which was defined in postoperative computed tomography. Results: After one month of high-dose steroid therapy, extraocular movement limitations improved progressively in all directions. In four months, extraocular movement recovered completely. Conclusion: Superior orbital fissure syndrome may occur after surgical procedure of orbital wall reduction. Prompt diagnosis and treatment with mega-dose corticosteroid is an effective option for avoiding disaster from compressive syndrome.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.15 no.2
• /
• pp.143-150
• /
• 2007

Ring and cylinder bore wear may not be a problem in most current automotive engines. However, a small change in ring face and cylinder bore diameter can significantly affect the lubrication characteristics and ring axial motion. This in turn can cause to change inter-ring pressure, blow-by and oil consumption in an engine. Therefore, by predicting the wear of piston ring face and cylinder bore altogether, the changed ring end gap and the changed volume of gas reservoir can be calculated. Then the excessive oil consumption can be predicted. Here, the oil amount through top ring gap into combustion chamber is estimated as engine oil consumption. Furthermore, the wear theories of ring and cylinder bore are included. The changed oil consumption caused by the new end gap and the new volume of oil reservoir around second land, can be calculated at some engine running interval. Meanwhile, the wear amount and oil consumption occurred during engine durability cycle are compared with the calculated values. The wear data of rings and cylinder bore are obtained from three engines after engine durability test. The calculated wear data of each part are turn out to be around the band of averaged test values or a little below. It is shown that the important factor regarding oil consumption increasement is the wear of ring face.

• Journal of the Korean Society of Safety
• /
• v.27 no.5
• /
• pp.35-41
• /
• 2012

The Numerical simulation was performed on the flow field around the two-dimensional rectangular bluff body in order to complement the previous experimental results of the bluff body stabilized flames [1]. For both fuel ejection configurations against an oxidizer stream, the flame stability was affected mainly by vortex structure and mixing field near bluff body. FDS(Fire Dynamic Simulator) based on the LES(Large Eddy Simulation) was employed to clarify the isothermal mixing characteristic and wake flow pattern around bluff body. The air used atmosphere and the fuel used methane. The result of counter flow configuration shows that the flow field depends on air velocity but the mixing field is influenced on the fuel velocity. At low fuel velocity the fuel mole fraction is below the flammable limit and hence the mixing is insufficient to react. Therefore, as the result, the flame formed at low fuel velocity is characterized by non-premixed flames. For the flow field of co-flow configuration, flame stability was affected by fuel velocity as well as air velocity. the vortex generated by fuel stream has counter rotating direction against the air stream. Therefore, the momentum ratio between air and fuel stream was important to decide the flame blow out limit, which is result in the characteristic of the partially premixed reacting wake near extinction.

• The Bulletin of The Korean Astronomical Society
• /
• v.41 no.2
• /
• pp.36.1-36.1
• /
• 2016

This is a presentation of the paper published as Kimm et al. 2016, ApJ, 823, 52. We investigate the formation of metal-poor globular clusters (GCs) at the center of two dark matter halos with $Mhalo{\sim}4{\times}107Msun$ at z>10 using cosmological radiation-hydrodynamics simulations. We find that very compact (${\leq}1$ pc) and massive (${\sim}6{\times}105Msun$) clusters form rapidly when pristine gas collapses isothermally with the aid of efficient $Ly{\alpha}$ emission during the transition from molecular-cooling halos to atomic-cooling halos. Because the local free-fall time of dense star-forming gas is very short (${\ll}1Myr$), a large fraction of the collapsed gas is turned into stars before stellar feedback processes blow out the gas and shut down star formation. Although the early stage of star formation is limited to a small region of the central star-forming disk, we find that the disk quickly fragments due to metal enrichment from supernovae. Sub-clusters formed in the fragmented clouds eventually merge with the main cluster at the center. The simulated clusters closely resemble the local GCs in mass and size but show a metallicity spread that is much wider than found in the local GCs. We discuss a role of pre-enrichment by Pop III and II stars as a potential solution to the latter issue. Although not without shortcomings, it is encouraging that a naive blind (not tuned) cosmological simulation presents a possible channel for the formation of at least some massive GCs.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.28 no.1
• /
• pp.9-15
• /
• 2004

$CO_2$ is a well-known green house gas as well as the major source of global warming. Many researchers have studied to reduce $CO_2$ emission in combustion processes. Among the method for reducing $CO_2$ emission, oxygen-enriched combustion has been proposed. Because its adiabatic flame temperature is relatively too high, existing facilities must be changed or the flame temperature in the combustion zone should be reduced. The combustion characteristics, composition in the flame zone, temperature profile and emission gases were investigated experimentally for the various oxygen-enriched ratios(OER) by the addition of $CO_2$, under constant $O_2$ flow rate. Results showed that the reaction zone was quenched and broadened as the addition of $CO_2$ was increased. The emission of NOx in flue gas was decreased as decreasing temperature in reaction zone. It was also shown that the reaction was delayed by the cooling effect. As the addition of $CO_2$ was increased, the composition of CO in the flame zone was increased due to the increase of reaction rate by increasing mixing effect of oxidant/fuel at OER=0％, but the composition of CO was decreased by quenching effect at OER=50％ and 100％.

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.1389-1394
• /
• 2003

$CO_2$ is a well-known green house gas, which is the major source of global warming. Many researchers have studied to reduce $CO_2$ emission in combustion processes. Among the method for reducing $CO_2$ emission, oxygen-enriched combustion has been proposed. But the adiabatic flame temperature is too high. So existing facilities must be changed, or the adiabatic flame temperature in the combustion zone should be reduced. The combustion characteristics, composition in the flame zone, temperature profile and emission gases were studied experimentally for the various oxygen-enriched mtios(OER) by addition of $CO_2$ under coustant $O_2$ flowrate. Results showed that the reaction zone was quenched, broadened, as addition of $CO_2$ was increased. Temperature has a large effect on the NOx emission. The emission of NOx in flue gas decreased due to the decreased temperature of reaction zone. It was also shown that the reaction was delayed by the cooling effect. As the addition of $CO_2$ was increased, the composition of CO in the flame zone increased due to the increase of reaction rate by increasing mixing effect of oxidant/fuel at OER=0, but the composition of CO decreased by quenching effect at OER=50 and 100%.

• Korea-Australia Rheology Journal
• /
• v.11 no.4
• /
• pp.305-311
• /
• 1999

The shear behavior of polymers obtained by means of devices such as capillary and cone-and-plate rheo-meters is commonly used to assess their processing performance and as a characterization tool. However, the number of instances when two polymers have the same shear properties but perform differently during certain types of processing operations (e.g. film blowing and sheet extrusion) indicate that shear properties alone may not be sufficient to characterize polymeric fluids. We begin by defining the kinematics of shear-free or extensional flow and the associated material functions. The extensional and shear behavior of three different types of polyethylene (PE) are then compared to illustrate the points that one cannot ascertain the extensional properties of polymer melts from their shear properties and, furthermore, there may not be a simple relation between properties obtained from one type of extensional flow and those of another type. The kinematics of most processing flows are extensional rather than shear in nature, and , hence, the performance of polymers during processes such as fiber spinning, film casting, film blowing, thermoforming, blow molding, and even extrusion is more readily accounted for through extensional viscosity measurements. Methods for carrying out extensional flow measurements are then reviewed including approximate methods. To illustrate the sensitivity of extensional viscosity measurements to subtle changes in the molecular architecture of PEs, results are presented for samples with a narrow molecular weight distribution but with varying numbers of long chain branches. Finally, constitutive equations which allow one to separate shear and extensional flow behavior are discussed as any attempts to simulate the subtle processing differences between two polymers will require constitutive equations of this nature.