• Korean Chemical Engineering Research
• /
• v.57 no.5
• /
• pp.723-729
• /
• 2019

A theoretical analysis was conducted of convective instability driven by buoyancy forces under transient temperature fields in an annular porous medium bounded by coaxial vertical cylinders. Darcy's law and Boussinesq approximation are used to explain the characteristics of fluid motion and linear stability theory is employed to predict the onset of buoyancy-driven motion. The linear stability equations are derived in a global domain, and then cast into in a self-similar domain. Using a spectral expansion method, the stability equations are reformed as a system of ordinary differential equations and solved analytically and numerically. The critical Darcy-Rayleigh number is founded as a function of the radius ratio. Also, the onset time and corresponding wavelength are obtained for the various cases. The critical time becomes smaller with increasing the Darcy-Rayleigh number and follows the asymptotic relation derived in the infinite horizontal porous layer.

• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.1
• /
• pp.48.1-48.1
• /
• 2019

Mass and radius of a neutron star in low-mass X-ray binary (LMXB) can be estimated simultaneously when the observed light curve and spectrum show the photospheric radius expansion feature. This method has been applied to 4U 1746-37 and the mass and radius were found to be unusually small in comparison with typical neutron stars. We re-estimate the mass and radius of this target by considering that the observed light curve and spectrum can be affected by other X-ray sources because this LMXB belongs to a very crowded globular cluster NGC 6441. The new estimation increases the mass and radius but they do not reach the typical values yet.

• Journal of the Korean Ceramic Society
• /
• v.56 no.1
• /
• pp.77-83
• /
• 2019

MgO-C refractories are used in basic furnaces and steel ladles due to their many desirable properties, such as excellent thermal shock resistance via low thermal expansion, and high thermal conductivity. However, the mechanical and thermal properties of the refractory continuously deteriorate by spalling phenomena and pore generation due to the oxidation of graphite, used as a carbon source, indicating that the characteristics and performance of MgO-C refractories need to be improved by using a new material or composition. In this study, the use of a Hertzian indentation test as a method for determining the damage and fracture behavior of an MgO-C refractory is described. The results highlight that Hertzain indentation tests can be one of the important evaluation tools for quasi-plastic damage accumulation of MgO-C refractories during falling process of scrap metal.

• Computers and Concrete
• /
• v.24 no.5
• /
• pp.437-444
• /
• 2019

PLC and its expansion module, electric ball valve and cooling pipe, electric heating steel plate and various components of the system, which is used to control test and process data. By automatically adjusting the opening of the valve, the system makes the top temperature and cooling speed develop along the ideal temperature diachronic curve. Moreover, the system enables the temperature difference between inside and surface of test block limited in a given range by automatically controlling the surface board heating. The method of physical simulation test by sandbox with built-in cooling water pipe and heating rod is adopted. On the premise of a given standard value, the operation of the system is checked under different working conditions. Further, an extension of this system is proposed, which enables its application to obtain some thermal parameters when cooperating with numerical simulation.

• Journal of Korean Neurosurgical Society
• /
• v.64 no.1
• /
• pp.136-141
• /
• 2021

The crossing Y-stent method is one of the indispensable techniques to achieve sufficient neck coverage during coil embolization of bifurcation aneurysms with a wide neck and/or branch incorporation. However, the inevitable hourglass-like expansion of the second stent at the crossing point can result in insufficient vessel wall apposition, reduced aneurysm neck coverage, delayed endothelialization, and subsequent higher risks of acute or delayed thrombosis. It also interferes with engagement of the microcatheter into the aneurysm after stent installation. We expected to be able to reduce these disadvantages by installing a noncrossing type Y-stent using the Solitaire AB stent, which is fully retrievable with a tapered proximal end. Here we report the techniques and two successful cases.

• Bulletin of the Korean Chemical Society
• /
• v.7 no.3
• /
• pp.231-235
• /
• 1986

MNDO and ab initio calculations for gas phase reactions of alkoxide-exchange at silicon and carbon centers have been performed. Results show that MNDO values of ${\Delta}$E's of these reactions closely parallel those of the STO-3G method. The alkoxide-exchange at silicon is shown to be facile due to the formation of stable five-coordinate intermediate while the reaction at carbon is predicted to proceed with high barrier; the difference in this substitution behavior between carbon and silicon is shown to be due to an easy valence shell expansion of silicon in accommodating an extra bond in the formation of stable five-coordinate intermediates.

• Infection and chemotherapy
• /
• v.50 no.4
• /
• pp.346-349
• /
• 2018

In 2015, rapid human immunodeficiency virus (HIV) testing was implemented in all 25 public health centers in Seoul. During March and December 2015, 20,987 rapid HIV tests were performed, of which 116 (0.5%) were positive. Compared to those of the period before application of the rapid HIV test in place of conventional enzyme immunoassay method, the number of HIV tests performed and the number of positive results increased by sevenfold and twofold, respectively. In conclusion, expansion of the provision of rapid HIV tests in public health centers increased the number of voluntary HIV tests.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.6 no.4
• /
• pp.85-96
• /
• 1996

In this paper, a simple method to increase securities of DES against DC and LC will be proposed. Our implementation results that the proposed algorithm is as fast as DES.

• Journal of applied mathematics & informatics
• /
• v.39 no.1_2
• /
• pp.31-43
• /
• 2021

A homogeneous circular disk undergoing a contact force is considered to investigate the thermo-elastic characteristics, and the inquiry is based on the variations of outer surface temperature and angular velocity. The intensity of stresses grows with the increase of outer surface temperature, and the circumferential strain reacts more sensitively to the change of outer surface temperature than the radial strain. In general, higher angular velocity produces; (i) larger expansion in the radial direction, (ii) smaller displacement in the circumferential, (iii) diminished intensity in the stresses. It is demonstrated that outer surface temperature and angular velocity are critical factors in the determination of thermo-elastic characteristics of homogeneous circular disks subjecting to a contact force. The results obtained can be applied on the design of a homogeneous circular cutter to promote proper and reliable thermos-elastic characteristics in service by the proper operation of these parameters.

• Journal of Korea Multimedia Society
• /
• v.24 no.5
• /
• pp.709-716
• /
• 2021

The current trend of entertainment programs is an "Sub-character." This study is to find out which strategies were chosen, considering the entertainment program "Hang Out With Yoo" as the beginning and front-runner of craze for Sub-characters. The following results were deduced: implementation of trendy characters, aggressive acceptance of growth narrative and expansion of episodes. The success or failure of an entertainment program depends on the implementation method of differentiated characters. At this point in time when Sub-characters are continuously developed, this program is meaningful in that it has presented the strategies for Sub-characters reflecting the demand of audience.