• Proceedings of the KSME Conference
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• 2000.04b
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• pp.548-554
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• 2000

The aim of this paper is to understand the time averaged pressure distributions in a high-speed centrifugal compressor channel diffuser at design and off-design flow rates. Pressure distributions from the impeller exit to the channel diffuser exit are measured and discussed far various flow rates from choke to near surge condition, and the effect of operating condition is discussed. The strong non-uniformity in the pressure distribution is obtained over the vaneless space and semi-vaneless space caused by the impeller-diffuser interaction. As the flow rate increases, flow separation near the throat, due to large incidence angle at the vane leading edge, increases aerodynamic blockage and reduces the aerodynamic flow area downstream. Thus the minimum pressure location occurs downstream of the geometric throat, and it is named as the aerodynamic throat. And at choke condition, normal shock occurs downstream of this aerodynamic throat. The variation in the location of the aerodynamic throat is discussed.

• Proceedings of the KIEE Conference
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• 1987.11a
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• pp.286-289
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• 1987

The measurements of prebreakdown currents and breakdown voltages have been made for smooth rough, protrusion plane parallel stainless steel electrodes in vacuum ($10^{-5}$ torr), as a function of electrode separation, in the range $0.4{\sim}2.4mm$ using DC source($0{\sim}200KV$). Thee prebreakdwon currents of a each condition are found to be consistent with the Fouler-Nondheim field emission theory. The effect of the electrode surface condition on the local field enhancement factors, prebreakdown currents, and on the breakdown voltages are shown. The breakdown mechanism of a small vacuum gap was ascertained as the field emission corresponding the F-N theory. Therefore, these results suggest that the field emission currents following the electrode surface condition play a major role for initiation of DC breakdown.

• Journal of applied mathematics & informatics
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• v.42 no.3
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• pp.583-605
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• 2024

This paper discusses the properties of attractors of Type 1 IFS which construct self similar fractals on product spaces. General results like continuity theorem and Collage theorem for Type 1 IFS are established. An algebraic equivalent condition for the open set condition is studied to characterize the points outside a feasible open set. Connectedness properties of Type 1 IFS are mainly discussed. Equivalence condition for connectedness, arc wise connectedness and locally connectedness of a Type 1 IFS is established. A relation connecting separation properties and topological properties of Type 1 IFS attractors is studied using a generalized address system in product spaces. A construction of 3D fractal images is proposed as an application of the Type 1 IFS theory.

• Applied Chemistry for Engineering
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• v.8 no.4
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• pp.694-699
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• 1997

Normal-phase HPLC was used to separate the useful phospholipids, PE, PI and PC in soybean lecithin. The mobile phase used in this experiments were haxane, isopropanol and methanol, the gradient mode was applied as the three components could not be separated by the isocratic mode. To find the optimum separation condition, the concentration profiles of effluents were calculated from the plate theory and the capacity factor in step-gradient mode. From the calculated results, PE was separated with hexane/isopropanol/methanol = 90/5/5vol.% in isocratic mode and PI and PC were resolved in the conditions of 10min gradient time and the second mobile phase of hexane/isopropanol/methanol=50/20/30vol.% in step-gradient mode. The agreement between the calculated concentration profile and experimental data was good, so the methodology developed in this work can be used to obtain the optimum separation condition in gradient mode.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2015.10a
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• pp.1079-1082
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• 2015

In Article 23 of Technical regulations for Telecommunication Line and Facilities, we have criteria of separation distance between telecommunication lines and power lines, and its related exceptional conditions. However, this is a conflicts condition with Article 32 that provides the type of indoor telecommunication cables such as twisted-pair cables and optical fiber cables. Also, it is frequently raised that exceptional condition related the PoE cables with up to 15.4W is improved to accept PoE cables with up to 30W. In this paper, we have proposed improvement plans of Technical regulations for separation distance between telecommunication lines and power lines by analyzing the variety of standard specifications at home and abroad.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.195-201
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• 2008

In the jet engines on the aircrafts cruising at high altitude over 20 km and subsonic speed, the Reynolds number in terms of the compressor blades becomes very low. In such an operating condition with low Reynolds number, it is widely reported that total pressure loss of the air flow through the compressor cascades increases dramatically due to separation of the boundary layer and the secondary-flow. But the detail of flow mechanisms causes the total pressure loss has not been fully understood yet. In the present study, two series of numerical investigations were conducted to study the effects of Reynolds number on the aerodynamic characteristics of compressor cascades. At first, the incompressible flow fields in the two-dimensional compressor cascade composed of C4 airfoils were numerically simulated with various values of Reynolds number. Compared with the corresponding experimental data, the numerically estimated trend of total pressure loss as a function of Reynolds number showed good agreement with that of experiment. From the visualized numerical results, the thickness of boundary layer and wake were found to increase with the decrease of Reynolds number. Especially at very low Reynolds number, the separation of boundary layer and vortex shedding were observed. The other series, as the preparatory investigation, the flow fields in the transonic compressor, NASA Rotor 37, were simulated under the several conditions, which corresponded to the operation at sea level static and at 10 km of altitude with low density and temperature. It was found that, in the case of operation at high altitude, the separation region on the blade surface became lager, and that the radial and reverse flow around the trailing edge become stronger than those under sea level static condition.

• Resources Recycling
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• v.19 no.3
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• pp.9-15
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• 2010

Domestic gold mine tailings, generally, contain a lot of non-metallic silica and clay minerals. These minerals can be separated from the tailings by various physical separation methods and used as raw materials for cements and ceramic products. In these physical separation procedures, metallic complex sulfides, in which Au and metallic constituents such as Pb, As and Fe were concentrated, were obtained as a by-product. These metallic constituents should be removed or separated from the by-product to extract Au efficiently. In this work, removal and separation processes of Pb, As, and Fe from the by-product were investigated. Pb was removed to under 3% by using alkaline oxidative leaching at the leaching condition of $120^{\circ}C$, 2M NaOH, 100psi $Po_2$, 250r.p.m., 4 wt.% solid and 30 min. leaching time. The leached residue was roasted and separated magnetically to obtain a non-magnetic product contained <0.2% As, <3% Fe and high concentrated Au more than 8,000 ppm.

• Earthquakes and Structures
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• v.15 no.2
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• pp.193-202
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• 2018

This paper studied the probability of pounding occurred between decks and abutments of a long span high-pier continuous rigid fame bridge subjected to ground motions with local soil effect. A pounding probability analysis methodology has been proposed using peak acceleration at bedrock as intensity measure (IM) for multi-support seismic analysis. The bridge nonlinear finite element (FE) models was built with four different separation distances. Effect of actual site condition and non-uniform spatial soil profiles on seismic wave propagating from bedrock to ground surface is modelled. Pounding probability of the high-pier bridge under multi-support seismic excitations (MSSE) is analyzed based on the nonlinear incremental dynamic analysis (n-IDA). Pounding probability results under uniform excitations (UE) without actual local site effect are compared with that under MSSE with site effect. The study indicates that the required design separation length between deck and abutment under uniform excitations is larger than that under MSSE as the peak acceleration at bedrock increases. As the increase of both separation distance between deck and abutment and the peak acceleration, the probability of pounding occurred at a single abutment or at two abutments simultaneously under MSSE is less than that under UE. It is of great significance considering actual local site effect for determining the separation distance between deck and abutment through the probability pounding analysis of the high-pier bridge under MSSE.

• Journal of Microbiology and Biotechnology
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• v.23 no.7
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• pp.942-952
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• 2013

Monoliths are functional porous materials with a three-dimensional continuous interconnected pore structure in a single piece. A monolith with uniform shape based on poly(${\gamma}$-glutamic acid) (PGA) has been prepared via a thermally induced phase separation technique using a mixture of dimethyl sulfoxide, water, and ethanol as solvent. The morphology of the obtained monolith was observed by scanning electron microscopy and the surface area of the monolith was evaluated by the Brunauer Emmett Teller method. The effects of fabrication parameters such as the concentration and molecular mass of PGA and the solvent composition have been systematically investigated. The PGA monolith was cross-linked with hexamethylene diisocyanate to produce the water-insoluble monolith. The addition of sodium chloride to the phase separation solvent affected the properties of the cross-linked monolith. The swelling ratio of the cross-linked monolith toward aqueous solutions depended on the buffer pH as well as the monolith fabrication condition. Copper(II) ion was efficiently adsorbed on the cross-linked PGA monolith, and the obtained copper-immobilized monolith showed strong antibacterial activity for Escherichia coli. By combination of the characteristic properties of PGA (e.g., high biocompatibility and biodegradability) and the unique features of monoliths (e.g., through-pore structure, large surface area, and high porosity with small pore size), the PGA monolith possesses large potentials for various industrial applications in the biomedical, environmental, analytical, and separation fields.

• Applied Chemistry for Engineering
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• v.9 no.5
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• pp.698-703
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• 1998

The pervaporation experiments of aqueous solutions of trichloroethylene (TCE) and chlorobenzene (CB) through the silicone rubber (polydimethylsiloxane, PDMS) membrane were carried out and the effect of concentration polarization on the separation characteristics was investigated. The resistance-in-series model was used to explain the boundary layer resistance. It was clear that the concentration polarization phenomenon had a significant effect on the permeation behavior in the pervaporation separation of the trace organic chlorides from aqueous solutions. With the same membrane thickness, the permeation of TCE, which has a stronger affinity for the PDMS, appeared to be more influenced by the boundary layer resistance than that of CB. The effect of boundary layer resistance was reduced and the membrane resistance became dominant with increasing membrane thickness at a given hydrodynamic condition. The separation factor was increased to approach the intrinsic separation factor of the membrane with its thickness.