• Tuberculosis and Respiratory Diseases
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• v.71 no.5
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• pp.355-358
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• 2011

Endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) is a useful, safe diagnostic modality for evaluating mediastinal and hilar lymphadenopathy. We report a 51-year-old male who presented with a left renal mass and multiple pleural masses without lung parenchymal lesions. The pleural masses were thought to be metastatic tumors or malignant mesothelioma. The patient underwent two percutaneous needle biopsies of the pleural mass, but the specimens were insufficient for a histopathological diagnosis. Because one pleural mass was adjacent to the right main bronchus, we decided to perform EBUS-TBNA for the pleural mass. As a result, sufficient core tissue was obtained with no complications, and the histopathological findings were consistent with metastatic papillary renal cell carcinoma. To our knowledge, this is the first case of using EBUS-TBNA for a pleural mass.

• International Journal of Highway Engineering
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• v.17 no.6
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• pp.27-32
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• 2015

PURPOSES : It is difficult to estimate tunnel stability because of lack of timely information during tunnel excavation. Tunnel deformability refers to the capacity of rock to strain under applied loads or unloads during tunnel excavation. This study was conducted to analyze a methods of pre-evaluation of stability during tunnel construction using the critical strain concept, which is applied to the results of tunnel settlement data and unconfined compression strength of intact rock or rock mass at the tunnel construction site. METHODS : Based on the critical strain concept, the pre-evaluation of stability of a tunnel was performed in the Daegu region, at a tunnel through andesite and granite rock. The critical strain concept is a method of predicting tunnel behavior from tunnel crown settlement data using the critical strain chart that is obtained from the relationship between strain and the unconfined compression strength of intact rock in a laboratory. RESULTS : In a pre-evaluation of stability of a tunnel, only actually measured crown settlement data is plotted on the lower position of the critical strain chart, to be compared with the total displacement of crown settlement, including precedent settlement and displacement data from before the settlement measurement. However, both cases show almost the same tunnel behavior. In an evaluation using rock mass instead of intact rock, the data for the rock mass strength is plotted on the lower portion of the critical strain chart, as a way to compare to the data for intact rock strength. CONCLUSIONS : From the results of the pre-evaluation of stability of the tunnel using the critical strain chart, we reaffirmed that it is possible to promptly evaluate the stability of a tunnel under construction. Moreover, this research shows that a safety evaluation using the actual instrumented crown settlement data with the unconfined compression strength of intact rock, rather than with the unconfined compression strength of a rock mass in the tunnel working face, is more conservative.

• The Bulletin of The Korean Astronomical Society
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• v.3
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• pp.18-23
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• 1978

The evolutionary tracks of a protostar of one solar mass under quasi-hydrostatic equilibrium are computed with mass-accretion time scales of $10^3,\;10^4,\;10^5\;and\;10^6$ years, and their resulting behaviors in the H-R diagram are discussed. It is found that there exists a critical time scale of mass accretion, which reverses the course of their evolutionary tracks. A value of the critical time scale appears to lie between $10^3\;and\;10^4$ years. The physical cause for the presence of the critical time scale is discussed. Finally, it is proposed that star formation requires at least several $10^3$ years before any star is born out of dark dense interstellar clouds.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.12
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• pp.956-964
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• 2003

The paper describes the relationship between the eigenvalue branches and the corresponding flutter modes of cantilevered pipes with a tip mass conveying fluid. Governing equations of motion are derived by extended Hamilton's principle, and the numerical scheme using finite element method is applied to obtain the discretized equations. The flutter configurations of the pipes at the critical flow velocities are drawn graphically at every twelfth period to define the order of quasi-mode of flutter configuration. The critical mass ratios, at which the transference of the eigenvalue branches related to flutter takes place. are definitely determined. Also, in the case of haying internal damping, the critical tip mass ratios, at which the consistency between eigenvalue braches and quasi-modes occurs. are thoroughly obtained.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.6
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• pp.99-107
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• 2008

In this paper, the stability of a cracked cantilever Timoshenko beam with a tip mass subjected to follower force is investigated. In addition, an analysis of the flutter instability(flutter critical follower force) and a critical natural frequency of a cracked cantilever Euler / Timoshenko beam with a tip mass subjected to a follower force is presented. The vibration analysis on such cracked beam is conducted to identify the critical follower force for flutter instability based on the variation of the first two resonant frequencies of the beam. Therefore, the effect of the crack's intensity, location and a tip mass on the flutter follower force is studied. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations.

• 유체기계공업학회:학술대회논문집
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• 2003.12a
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• pp.167-173
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• 2003

For the measurement of mass flow rate at a wide range of operation conditions, it is required that the critical nozzle gas different diameters, since the mass flow rate through the critical nozzle depends on the nozzle supply conditions and the nozzle throat diameter. In the present study, both computational and experimental investigations are performed to explore the variable critical nozzle. Computational work using the 2-dimensional, axisymmetric, compressible Navier-Stokes equations are carried out to simulate the gas flow through variable critical nozzle. In experimnet, a cylinder with several different diameters is inserted into the critical nozzle to vary the nozzle throat diameter. Computational results are compared with the experimented ones. The computed results are in close agreement with experiment. It is found that the displacement and momentum thickness of variable critical nozzle are given as a function of Reynolds numbers. The discharge coefficient of the variable critical nozzle is predicted using an empirical equation.

• Nuclear Engineering and Technology
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• v.5 no.2
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• pp.115-131
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• 1973

L.S. Pontryagin's maximum principle is applied to the minimum critical mass problem without any restriction on the ranges of uranium enrichment. For the analysis, two group diffusion equation is adopted for a cylindrical reactor neglecting the vertical axis consideration. The result shows that the three-zoned reactor turns out to be most optimal: the inner and outer zones with the minimum enrichment ; whereas the middle 3one with the maximum enrichment. With the given three-zoned reactor, critical condition is derived, which leads to the calculation of the determinant. By finding the roots of the determinant the numerical calculation of the minimum critical mass is carried out for the case of Kori reactor geometry changing the minimum or the maximum enrichment. It is found from many computed values that the least possible critical mass turns out to be the case of 1.2% maximum enrichment for the middle zone and 0.65% minimum enrichment for the inner and out zones.

• Nuclear Engineering and Technology
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• v.34 no.4
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• pp.382-395
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• 2002

An experimental study on transient critical heat flux (CHF) under flow coastdown has been performed for the water flow in a non-uniformly heated vertical annulus under low flow and a wide range of pressure conditions. The objectives of this study are to systematically investigate the effect of the flow transient on the CHF and to compare the transient CHF with steady-state CHF The transient CHF experiments have been performed for three kinds of flow transient modes based on the coastdown data of a nuclear power plant reactor coolant pump. At the same inlet subcooling, system pressure and heat flux, the effect of the initial mass flux on the critical mass flux can be negligible. However, the effect of the initial mass flux on the time-to- CHF becomes large as the heat flux decreases. The critical mass flux has the largest value for slow flow reduction rate. There is a pressure effect on the ratio of the transient CHF data to steady-state CHF data. Except under low system pressure conditions, the flow transient CHF was revealed to be conservative compared with the steady-state CHF data. Bowling CHF correlation and thermal hydraulic system code MARS show promising results for the prediction of CHF occurrence .

• Journal of Mechanical Science and Technology
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• v.17 no.8
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• pp.1171-1184
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• 2003

An experimental study on critical heat flux (CHF) has been performed in an internally heated vertical annulus with non-uniform heating. The CHF data for the chopped cosine heat flux have been compared with those for uniform heat flux obtained from the previous study of the authors, in order to investigate the effect of axial heat flux distribution on CHF. The local CHF with the parameters such as mass flux and critical quality shows an irregular behavior. However, the total critical power with mass flux and the average CHF with critical quality are represented by a unique curve without the irregularity. The effect of the heat flux distribution on CHF is large at low pressure conditions but becomes rapidly smaller as the pressure increases. The relationship between the critical quality and the boiling length is represented by a single curve, independent of the axial heat flux distribution. For non-uniform axial heat flux distribution, the prediction results from Doerffer et al.'s and Bowling's CHF correlations have considerably large errors, compared to the prediction for uniform heat flux distribution.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.1
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• pp.101-109
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• 2008

The stability of a rotating cantilever pipe conveying fluid with a crack and tip mass is investigated by the numerical method. That is, the effects of the rotating angular velocity, mass ratio, crack severity and tip mass on the critical flow velocity for flutter instability of system are studied. The equations of motion of rotating pipe are derived by using the Euler-Bernoulli beam theory and the extended Hamilton's principle. The crack section of pipe is represented by a local flexibility matrix connecting two undamaged pipe segments. Also, the crack is assumed to be in the first mode of fracture and always opened during the vibrations. When the tip mass and crack are constant, the critical flow velocity for flutter is proportional to the rotating angular velocity of pipe. In addition, the stability maps of the rotating pipe system as a rotating angular velocity and mass ratio ${\beta}$ are presented.