• 한국연소학회:학술대회논문집
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• 2002.06a
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• pp.123-132
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• 2002

A numerical study was conducted to investigate the combustion phenomena of normal start and unstart processes based on ISL's RAMAC 30 experiments with different diluent amounts and fill pressures in a ram accelerator. The initial projectile launching speed was 1.8 km/s which corresponded to the superdetonative speed of the stoichiometric $H_2/O_2$ mixture diluted with 5 $CO_2$ or 4 $CO_2$. Experiments with same condition except for projectile surface material demonstrated that ignition was successful with an aluminum projectile, but no combustion was observed in case of a steel projectile. In this study, it was found that neither shock nor viscous heating was sufficient to ignite the mixture at a low speed of 1.8 km/s, as was found in the experiments using a steel projectile. However, we could succeed in igniting the mixtures by imposing a minimal amount of additional heat to the combustor section and simulate the normal start and unstart processes found in the experiments with an aluminum projectile. For the numerical simulation of supersonic combustion, multi-species Navier-Stokes equations coupled with a Baldwin-Lomax turbulence model and detailed chemistry reaction equations of $H_2/O_2/CO_2$ suitable for high-pressure gaseous combustion were considered. The governing equations were discretized by a high order accurate upwind scheme and solved in a fully coupled manner with a fully implicit, time accurate integration method. The numerical results matched almost exactly to the experimental results. As a result, it was found that the normal start and unstart processes depended on the strength of gas mixture, development of shock-induced combustion wave stabilized by the first separation bubble, and its size and location.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.1
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• pp.1-11
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• 2010

The definition of the speed of sound is reexamined since it is crucial in the numerical analysis of compressible real gas flows. The thermodynamic speed of sound (TSS), $a_{th}$, and the characteristic speed of sound (CSS), $a_{ch}$, are derived using generalized equation of state (EOS). It is found that the real gas EOS, for which pressure is not linearly dependent on density and temperature, results in slightly different TSS and CSS. in this formalism, Roe's approximate Riemann solver was derived again with corrections for real gases. The results show a little difference when the speeds of sound are applied to the Roe's scheme and Advection Upstream Splitting Method (AUSM) scheme, but a numerical instability is observed for a special case using AUSM scheme. It is considered reasonable to use of CSS for the mathematical consistency of the numerical schemes. The approach is applicable to multi-dimensional problems consistently.

• Structural Engineering and Mechanics
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• v.64 no.6
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• pp.703-721
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• 2017

The experimental study of the behavior of dry medium and loose sandy soil under the action of a single impulsive load is carried out. Different falling masses from different heights were conducted using the falling weight deflectometer (FWD) to provide the single pulse energy. The responses of soils were evaluated at different locations (vertically below the impact plate and horizontally away from it). These responses include; displacements, velocities, and accelerations that are developed due to the impact acting at top and different depth ratios within the soil using the falling weight deflectometer (FWD) and accelerometers (ARH-500A Waterproof, and Low capacity Acceleration Transducer) that are embedded in the soil and then recorded using the multi-recorder TMR-200. The behavior of medium and loose sandy soil was evaluated with different parameters, these are; footing embedment, depth ratios (D/B), diameter of the impact plate (B), and the applied energy. It was found that increasing footing embedment depth results in: amplitude of the force-time history increases by about 10-30%. due to increase in the degree of confinement with the increasing in the embedment, the displacement response of the soil will decrease by about 25-35% for loose sand, 35-40% for medium sand due to increase in the overburden pressure when the embedment depth increased. For surface foundation, the foundation is free to oscillate in vertical, horizontal and rocking modes. But, when embedding a footing, the surrounding soil restricts oscillation due to confinement which leads to increasing the natural frequency, moreover, soil density increases with depth because of compaction, that is, tendency to behave as a solid medium.

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.6
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• pp.2473-2476
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• 2014

Background: Little is known about the cancer screening prevalence and correlates in older adults from different racial backgrounds. In the context of heightened efforts for prevention and early diagnosis, we collected information on screening for two major types of cancers: cervical and breast cancer in order to establish their prevalence estimates and correlates among older South African women who participated in the Study of Global Ageing and Adults Health (SAGE) in 2008. Materials and Methods: We conducted a national population-based cross-sectional study with a multi-stage stratified cluster sample of 3,840 individuals aged 50 years or older in South Africa in 2008. In this analysis, we only considered the female subsample of (n=2202). The measures used included socio-demographic characteristics, health variables, anthropometric and blood pressure measurements. Multivariable regression analysis was performed to assess the association of socio-demographic factors, health variables and cancer screening. Results: Overall, regarding cervical cancer screening, 24.3% ever had a Papanicolaou (PAP) smear test, and regarding breast cancer screening, 15.5% ever had a mammography. In multivariate logistic regression analysis, younger age, higher education, being from the White or Coloured population group, urban residence, greater wealth, and suffering from two or more chronic conditions were associated with cervical cancer screening, and higher education, being from the White or Indian/Asian population group, greater wealth, having a health insurance, and suffering from two or more chronic condtions were associated with breast cancer screening. Conclusions: Cancer screening coverage remains low among elderly women in South Africa in spite of the national guideline recommendations for regular screening in order to reduce the risk of dying from these cancers if not detected early. There is a need to improve accessibility and affordability of early cervical and breast cancer screening for all women to ensure effective prevention and management of cervical and breast cancer.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.6
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• pp.1229-1236
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• 2009

Puretone audiometer, which is a machine used for measuring the minimum hearing threshold, can be cost-effectively implemented using computer with sound card and software. In this paper, we describe a puretone audiometer which has been designed and implemented based on a general PC with sound card. It supports air conduction and bone conduction test taking with automatic masking. It also provides multiple modes consisted of self-test, auto-test and manual test mode. Such multiple modes makes it possible to use in various environments like as home and/or hospital. Through measure of waveform of output voltage and sound pressure, we verified that puretone audiometer of this paper properly operates.

• Journal of Korean Society for Atmospheric Environment
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• v.28 no.2
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• pp.142-158
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• 2012

This paper investigates the physical and chemical characteristics of long-range transport (LRT) process of air pollutants by employing the MM5-CMAQ and its comparison with local emission dominant (LED) case over northeast Asia. We first classified high air pollution days into LRT and LED cases based on the synoptic meteorological variables of vorticity and geostrophic wind speed/direction at a geopotential level of over 850hPa. LRT cases are further categorized into three types of transport patterns (LRT-I-III) according to the air mass pathways from source regions. LRT-I-III are originated from northern, central, and southern China, respectively, identified by back trajectory analysis. Three LRT-I-III groups have different and unique locations of high pressure and transport pathways. The chemical characteristics showed that the simulated spatial distributions varied in terms of locations of maximum concentrations and the temporal variation of surface concentrations. The primary air pollutants such as $NO_x$, $PM_{10}$ and $SO_2$ of all of three LRT cases are well transported into Korea peninsula with different concentration levels. Of LRT cases, LRT-II has the greatest effect on air quality of Korea peninsula, followed by LRT-I and LRT-III. In comparison with LRT, the LED case shows relatively higher air pollution concentrations in general, but showed a variety of different air quality levels following the emission strength pattern. These widely varying patterns are impling the case dependent multi-directional approach for the development of indicators of long-range transport process over northeast Asia.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.1
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• pp.233-240
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• 2011

A field server was developed by using ubiquitous sensor network technology to monitor the abrupt weather variation in local or mountain area. The data transmissions between deployed field servers in local terrain are very important technology in disaster prevention monitoring system. Weather related information such as temperature, humidity, illumination, atmospheric pressure, dew point and meteorological data are collected from the designated field at a regular interval. The received information from the multiple sensors located at the sensor field is used flooding routing protocol transmission techniques and the sensing data is transferred to gateway through multi-hop method. Telosb sensor node are programmed by nesC language in TinyOS platform to monitor the weather parameters of the local terrain.

• Proceedings of the KIEE Conference
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• 2006.10c
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• pp.600-602
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• 2006

Some abnormal signals diagnostics and analysis through an important equivalent circuits modeling for passive elements under severe accident conditions have been performed. Unlike the design basis accidents, there are inherently some uncertainties in the instrumentation capabilities under the accident conditions. So, the circuit simulation analysis and diagnosis methods are used to assess instruments in detail when they give apparently abnormal readings as an accident alternative method. The simulations can be useful to investigate what the signal and circuit characteristics would be when similar to a variety of symptoms that can result from the environmental conditions such as high temperature, humidity, and pressure condition. In this paper, a new simulator through an analysis of the important equivalent circuits modeling under temperature accident conditions has been designed, the designed simulator is composed of the LabVIEW code as a main tool and the out-put file of the Multi-SIM code as an engine tool is exported to in-put file of the LabVIEW code. The procedure for the simulator design was divided into two design steps, of which the first step was the diagnosis method, the second step was the circuit simulator for the signal processing tool. It has three main functions which are a signal processing tool, an accident management tool, and an additional guide from the initial screen. This simulator should be possible that it could be applied a output signal analysis to some transient signal by variation of the resistance passive elements in the R-L-C equivalent circuit modeling under various degraded conditions in NPPs.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.392-396
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• 1999

Superconducting YBa$_2Cu_3O_{7-{\delta}}$(YBCO) thin films were grown on Hastelloy(Ni-Cr-Mo alloys) with CeO$_2$ buffer layer in-situ by pulsed laser deposition in a multi-target processing chamber. To apply superconducting property on power transmission line, we have deposited YBCO thin film on flexible metallic substrate. However, it is difficult to grow the YBCO films on flexible metallic substrates due to both interdiffusion problem between metallic substrate and superconducting overlayers and non-crystallization of YBCO on amorphous substrate. It is necessary to use a buffer layer to overcome the difficulties. We have chosen CeO$_2$ as a buffer layer which has cubic structure of 5.41 ${\AA}$ lattice parameter and only 0.2% of lattice mismatch with 3.82 ${\AA}$ of a-axis lattice parameter of YBCO on [110] direction of CeO$_2$ In order to enhance the crystallization of YBCO films on metallic substrates, we deposited CeO$_2$ buffer layers with varying temperature and 02 pressure. By XRD, it is observed that dominated film orientation is strongly depending on the deposition temperature of CeO$_2$ layer. The dominated orientation of CeO$_2$ buffer layer is changed from (200) to(111) by increasing the deposition temperature and this transition affects the crystallization of YBCO superconducting film on CeO$_2$ buffered Hastelloy.

• Korean Journal of Materials Research
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• v.15 no.2
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• pp.134-138
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• 2005

This study was performed to investigate the surface properties of electrochemically oxidized pure niobium by anodic oxide and hydrothermal treatment technique. Niobium specimens of $10mm\times10mm\times1.0mm$ in dimension were polished sequentially from $\#600,\;\#800,\;\#1000$ emery paper. The surface of pure niobium sperimens was anodized in an electrolytic solution that was dissolved calcium and phosphate in water. The electrolytic voltage was set in the range of 250 V and the current density was $10mA/cm^2$. The specimen was hydrothermal treated in high-pressure steam at $300^{\circ}C$ for 2 hours using an autoclave. And all specimens were immersed in the in the Hanks' solution nth pH 7.4 at $37^{\circ}C$ for 30 days. The surface of specimen was characterized by surface roughness, scanning electron microscope(SEM), energy dispersion X-ray analysis(EDX), X-ray photoemission spectroscopy(XPS) test. The value of surface roughness was the highest in the anodized sample and $0.41{\pm}0.04\;{\mu}m$. The results of the SEM observation show that oxide layers of the multi porosity in the anodized sample were piled up on another, and hydroxyapatite crystal was precipitate from the surface of the hydrothermal treated sample. In the XPS analysis, O, Nb, C peak and small amounts of N peak were found in the polished specimens while Ca and P peak in addition to O, Nb, C and peak were observed in the hydrothermal treated sample.