• Computers and Concrete
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• v.22 no.5
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• pp.481-492
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• 2018

In this paper, a new hybrid fiber system (NHFS) is investigated for the application of slab. The steel fiber, polyvinyl alcohol (PVA) fiber and calcium carbonate ($CaCO_3$) whisker is added to form NHFS. The four-point bending test is carried out on the flexural properties of slab with plain, steel fiber, traditional hybrid fiber system (THFS) and NHFS reinforced cementitious composites. The flexural behavior is evaluated by ASTM C1018-97, JCI-SF4 and post-crack strength (PCS) technique. The evaluation parameters of flexural toughness such as toughness index (TI), equivalent flexural strength (EFS) and PCS are determined. The size of slab specimens is $15mm(thickness){\times}50mm(width){\times}200mm(length)$. The results show that adding $CaCO_3$ whisker to THFS can significantly improve the flexural strength, TI, EFS, PCS of the slab. The empirical relation between reinforcing index ($RI_v$) and flexural parameters show that flexural parameters of slabs increase first and then decrease; which indicates that optimum $RI_v$ values can be helpful in the considering the mix design of steel-PVA fibers-$CaCO_3$ whisker composites for achieving the desired flexural-related properties. The scanning electron microscopy is performed to observe the micro-morphological characteristics of the fracture surface, which proved the positive hybrid effect among the different fibers in cementitious composites. The NHFS can arrest the generation and propagation of the crack from micro to macro level.

• Journal of the Korean Applied Science and Technology
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• v.31 no.4
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• pp.688-693
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• 2014

This study is to increase the utilization of the ozonated water generator to make it easier to take advantage of the ozone water in the world today, there will be to develop a system that operates in one motion. Furthermore, olive oil and ozone is reacted with the wish to apply to the manufacturing technology. In the case of many existing products ozone generator driven mostly non-ozone system. In the case of ozone, but handwriting is implied general way pressure ozone gas leakage risks of suction force to the pump, it is the case of the challenge by using the injector, and limit the generation of ozone and ozone inhalation according to whether the water inlet leakage of existing products risk due to minimized. Despite the disadvantages of the injector system was found the effectiveness of the ozonated water production unit injector system used in this study to maintain the microbiological disinfection performance.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.387-387
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• 2013

Currently, the flash memory and the dynamic random access memory (DRAM) have been used in a variety of applications. However, the downsizing of devices and the increasing density of recording medias are now in progress. So there are many demands for development of new semiconductor memory for next generation. Magnetic random access memory (MRAM) is one of the prospective semiconductor memories with excellent features including non-volatility, fast access time, unlimited read/write endurance, low operating voltage, and high storage density. MRAM is composed of magnetic tunnel junction (MTJ) stack and complementary metal-oxide semiconductor (CMOS). The MTJ stack consists of various magnetic materials, metals, and a tunneling barrier layer. Recently, MgO thin films have attracted a great attention as the prominent candidates for a tunneling barrier layer in the MTJ stack instead of the conventional Al2O3 films, because it has low Gibbs energy, low dielectric constant and high tunneling magnetoresistance value. For the successful etching of high density MRAM, the etching characteristics of MgO thin films as a tunneling barrier layer should be developed. In this study, the etch characteristics of MgO thin films have been investigated in various gas mixes using an inductively coupled plasma reactive ion etching (ICPRIE). The Cl2/Ar, CH3OH/Ar, and CH4/Ar gas mix were employed to find an optimized etching gas for MgO thin film etching. TiN thin films were employed as a hard mask to increase the etch selectivity. The etch rates were obtained using surface profilometer and etch profiles were observed by using the field emission scanning electron microscopy (FESEM).

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.6
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• pp.34-40
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• 2011

From the present paper researched about the Design of Image Rejection SSB Modulator for X-Band Monopulse RADAR using Waveguide Hybrid Coupler. Generally, SSB modulator mixes IF(RF) and LO signals, and then it converts to RF(IF) frequency band. In this case, in order to transmit one sideband from RF band, SSB modulator is demanded the removal of image and LO signal. The balanced mixer was designed using waveguide hybrid coupler and crystal mixer diode to mix LO and IF signal. And also the IF Amplifier was designed for IF(+) and IF(-) signal generation which have $90^{\circ}$ phase differences which are suitable in two crystal mixer diode inputs. In order to maintain a high electric reliability from high frequency band the waveguide and IF amplifier's case were manufactured with aluminum using deep brazing techniques. The test result of SSB modulator, LO and sideband signal rejection ratio were 14.2dB and 18.5dB respectively.

• Journal of the Korea Concrete Institute
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• v.22 no.2
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• pp.171-177
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• 2010

Recently, Performance Based Design (PBD) method has been studied as a next generation structural design method, which enables a designed structure to satisfy the required performance during its service life. One method of deciding whether the required performance has been satisfied is Bayesian method, which has been commonly used in seismic analysis. Generally, it is presented as a conditional probability of exceeding some limit state (i.e., collapse) for a given ground motion. In PBD of concrete mixture design, the same methodology can be applied to assess concrete material performance based on some conditional parameters (i.e. strength, workability, carbonation, etc). In this paper, a detailed explanation of the procedure of drawing satisfaction curve by using Bayesian method based on various material parameters is shown. Also, a discussion of using the developed satisfaction curves for PBD for concrete mixture design is presented.

• Bulletin of the Korean Chemical Society
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• v.30 no.7
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• pp.1505-1515
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• 2009

A new method to semicontinuously determine $PM_{2.5}$ ionic species with a short time resolution is described in detail. In this system, a particle collection section (mixing part, particle collection chamber, and air/liquid separator) was developed. A Y-type connector was used to mix steam and an air sample. The particle collection chamber was constructed in the form of a helix coil and was cooled by a water circulation system. Particle size growth occurred due to the high relative humidity and water absorbed particles were efficiently collected in it. Liquid samples were drained out with a short residence time (0.08-0.1 s). The air/liquid separator was also newly designed to operate efficiently when the flow rate of the air sample was 16.7 L $min^{-1}$. For better performance, the system was optimized for particle collection efficiency with various types of test aerosols such as ($NH_4)_2SO_4,\;NaCl,\;NH_4HSO_4,\;and\;NH_4NO_3$. The particle collection efficiencies were almost 100% at different concentration levels in the range over 500 nm in diameter but 50-90% in the range of 50-500 nm under the following experimental conditions: 15 coil turns, a water flow rate for steam generation of 0.65 mL $min^{-1}$, and an air sample flow rate of 16.7 L $min^{-1}$. Finally, for atmospheric applications, chemical compositions of $PM_{2.5}$ were determined with a time resolution of 20 min on January 11-24, 2006 in Seoul, Korea, and the chemical characteristics of $PM_{2.5}$ ions were investigated.

• Advances in concrete construction
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• v.4 no.2
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• pp.123-143
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• 2016

Use of heavy fuel fly ash (HFFA) (diesel and cracked fuel) for power generation in Saudi Arabia has generated and accumulated large quantities of HFFA as a byproduct. In this research, HFFA is studied with the emphasis on the utilization of this waste material in concrete blocks and asphalt concrete mixes. Two types of mixes, one with low and other with high cement content, were studied for concrete blocks. Different mixes having varying percentages of HFFA (0% to 25%), as cement/sand replacement or as an additive, were studied. The performance of concrete blocks is evaluated in terms of compressive strength, water absorption, durability and environmental concerns. The results showed that blocks cannot be cast if more than 15% HFFA is used; also there is a marginal reduction in the strength of all the mixes before and after being exposed to the sulfate solution for a period of ten months. HFFA is studied in asphalt concrete mixes in two ways, as an asphalt modifier (3&5%) and as a filler (50%) replacement, the results showed an improvement in stiffness and fatigue life of mixes. However, the stability and indirect tensile strength loss were found to be high as compared to the control mix due to moisture damage, indicating a need of using antistripping agents. On environmental concerns, it was found that most of the concerned elements are within acceptable limits also it is observed that lower concentration of barium is leached out with the higher HFFA concentrations, which indicates that HFFA may work as an adsorbent for this leaching element.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.75-78
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• 2004

Various jet engines (Turbine engine family and RAM Jet engine) have been developed for high speed aircrafts. but their application to hypersonic flight is restricted by principle problems such as increase of total pressure loss and thermal stress. Therefore, the development of next generation propulsion system for hypersonic aircraft is a very important subject in the aerospace engineering field, SCRAM Jet engine based on a key technology, Supersonic Combustion. is supposed as the best choice for the hypersonic flight. Since Supersonic Combustion requires both rapid ignition and stable flame holding within supersonic air stream, much attention have to be given on the mixing state between air stream and fuel flow. However. the wider diffusion of fuel is expected with less total pressure loss in the supersonic air stream. So. in this study the direction of fuel injection is inclined 30 degree to downstream and the total pressure of jet is controlled for lower penetration height than thickness of boundary layer. Under these flow configuration both streams, fuel and supersonic air stream, would not mix enough. To spread fuel wider into supersonic air an aerodynamic force, baroclinic torque, is adopted. Baroclinic torque is generated by a spatial misalignment between pressure gradient (shock wave plane) and density gradient (mixing layer). A wedge is installed in downstream of injector orifice to induce an oblique shock. The schlieren optical visualization from side transparent wall and the total pressure measurement at exit cross section of combustor estimate how mixing is enhanced by the incidence of shock wave into supersonic boundary layer composed by fuel and air. In this study non-combustionable helium gas is injected with total pressure 0.66㎫ instead of flammable fuel to clarify mixing process. Mach number 1.8. total pressure O.5㎫, total temperature 288K are set up for supersonic air stream.

• Korea Journal of Hospital Management
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• v.4 no.2
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• pp.106-130
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• 1999

The main objective of this paper is to perform an empirical analysis on the relationship between various marketing activities and financial performance of Korean hospitals. A survey was conducted through structured questionnaire for 495 hospitals, and data from 218 hospitals were utilized in the final anaylsis.(response rate: 44%) Survey items include general characteristics of the hospitals(size, type, location), degree of competition, financial performance. marketing organization! budget, and level of various marketing activities in service development, access improvement, promotion, and pricing. We examine descriptive statistics of the response scores on marketing activities to evaluate the current status of marketing management of Korean hospitals, compare the results across hospital size, type and location, and perform regression analysis to investigate the relaionship between marketing and financial performance. Major findings are as follows: 1) About 46% of the responding hospitals have marketing departments although they are named as 'planning' or 'PR' departments, and the marketing budget on average represents 1.74% of the total expenditures. 2) Average level of marketing activities is calculated to be about 3.32 on 5-point scale, meaning that Korean hospitals implement their marketing programs 'somewhat actively'; however, the scores on the areas of marketing plannning and strategy are relatively low. 3) Large hospitals tend to be more active in marketing than small hospitals, and public hospitals' activities in marketing are not lower compared to private hospitals. 4) Level of overall marketing activities is positively related with financial performance measured by various finacial indicators except for profitability, implying that marketing is successful in revenue generation but needs to be more cost-effective. Also, when the marketing variables are separately included in the regression, no significant relationship is found, which means that various marketing activities are more effective when they are collectively implemented.

• Resources Recycling
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• v.21 no.6
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• pp.23-31
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• 2012

Removal work about weeds that grow naturally on road and industrial complex is attaining ordinary times but is suffering difficulty in weeding work by strong self-generation power. In the meantime, going side by side with these manual processing and weeding work through construction of weed-proof seat is attaining, but economic performance, limitation of application region and withdrawal processing problem are being blamed for shortcoming. The scope of this study is about the manufacture of weed-proof mortar using eco-friendly industrial byproducts characterized by an economic and simplicity for not limited to loss of function as a product recovered after treatment. After the carried out the various experiments and actual construction for the selection of mixing materials and derivation of appropriate mix, through the comparison and analysis of results, it was investigated the research results of weed-proof mortar for fundamental development.