• Journal of Mechanical Science and Technology
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• 제17권6호
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• pp.879-887
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• 2003

The flow in a parallel walled test channel, when obstructed with a geometry at the entrance, can be forward, reverse and stagnant depending on the position of the obstruction. This interesting flow phenomenon has potential benefit in the control of energy and various flows in the process industry In this experiment, the flat plate obstruction geometry was used as an obstruction at the entry of the test channel. The parameters that influence the flow inside and around the test channel were the gap (g) between the test channel and the obstruction geometry, the length (L) of the test channel and the Reynolds number (Re). The effect of the gap to channel width ratio (g/w) on the magnitude of the velocity ratio (V$\_$i/ / V$\_$o/ : velocity inside/ velocity outside the test channel) was investigated for a range of Reynolds numbers. The maximum reverse flow observed was nearly 20% to 60% of the outside velocity for Reynolds number ranging from 1000 to 9000 at g/w ratio of 1.5. The maximum forward velocity inside the test channel was found 80% of the outside velocity at higher g/w ratio of 8. The effect of the test channel length on the velocity ratio was investigated for different g/w ratios and a fixed Reynolds number of 4000. The influence of the Reynolds number on the velocity ratio is also discussed and presented for different gap to width ratio (g/w). The flow visualisation photographs showing fluid motion inside and around the test channel are also presented and discussed.

• 천문학논총
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• 제27권4호
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• pp.219-220
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• 2012

We present the results of far-infrared spectroscopic observations of the Large Magellanic Cloud (LMC) with FIS-FTS. We covered a large area across the LMC, including 30 Doradus (30 Dor) and N44 star-forming regions, by 191 pointings in total. As a result, we detect the [OIII] and [CII] line emission as well as far-infrared dust continuum emission throughout the LMC. We find that the [OIII] emission is widely distributed around 30 Dor. The observed size of the distribution is too large to be explained by massive stars in 30 Dor, which are assumed to be enshrouded by clouds with the constant gas density estimated from the [OIII] line intensities. Therefore the surrounding structure is likely to be highly clumpy. We also find a global correlation between the [OIII] and the far-infrared continuum emission, suggesting that the gas and dust are well mixed in the highly-ionized region where the dust survives in clumpy dense clouds shielded from energetic photons. Furthermore we find that the ratios of [CII]/CO are as high as 110,000 in 30 Dor, and 45,000 even on average, while they are typically 6,000 for star-forming regions in our Galaxy. The unusually high [CII]/CO is also consistent with the picture of clumpy small dense clouds.

• 한국세라믹학회지
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• 제39권10호
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• pp.981-987
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• 2002

$St\"{o}ber$ process를 이용하여 단분산 콜로이드 실리카를 제조하였다. 초기물질인 TEOS(Tetraethylorthosilicate)와 $NH_4OH$, 에탄올 및 증류수의 함유량을 조절하여 100 nm급, 200 nm급, 300 nm급 크기의 단분산 실리카 입자를 제조할 수 있었고, 제조된 실리카 입자는 Scanning Electron Microscope(SEM) 및 laser scattering particle analyzer를 통해 관찰하였다. Dipcoating 공정을 이용하여 제조된 300 nm 크기의 콜로이드 실리카의 자기 배열성(self-assembly) 형성에 관한 연구를 진행하였다. 다양한 코팅 공정 변수(표면장력, 표면전하, 입자의 함유량)의 조절을 통하여 dip coating시에 자기 배열성 단층막(monolayer)을 형성해 낼 수 있는 조건을 최적화하였고, SEM으로 관찰해 본 결과, 최적 조건 상태에서 비교적 넓은 영역 (1.5 mm ${\times}$ 1.5 mm)에서 hexagonally ordered packing된 콜로이드 입자 결정 단층막을 얻을 수 있었다.

• 자원환경지질
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• 제23권1호
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• pp.35-57
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• 1990

This study has been carried out on the Pegmatites, Naedeogri Granites, Nonggeori Granites and Metasedimentary rocks in the middle area of Taebaeksan region to investigate the geochemical properties and possibility of productivity. Pegmatites are characterized by metamorphosed anatectic pegmatite and differentiated magmatic pegmatite, and are mixed type of rare-element pegmatite and mica-bearing pegmatite by the classification of Ginsburg(1979). The petrological type of the igneous rocks is thought to be calcalkali, subalkaline and peralumious. According to chemical variations against D. I., differentiation trends from Naedeogri and Nonggeori Granites through non-mineralized pegmatites to mineralized pegmatites are supposed. From the relationship between oxided and $SiO_2$, pegmatites and Nonggeori Granite have shown similar tendencies and bulk composition of pegmatites and similar to metasedimentary rocks near the intrusives. By judging the correlations of trace elements, it is elucidated that pegmatites adjacent to Naedeogri and Nonggeori Granites have been originated in magma differentiation from these granites and the others have been differentiated by remelting or partial melting from metasedimentary rocks. $Sp_5$, $Sp_8$, and $Sp_9$ pegmatites are considered as productive rocks, and $Sp_4$, $Sp_6$, $Sp_7$, $Sp_{10}$, $Sp_{11}$, and $Sp_{12}$ pegmatites and granites are supposed to have a weak productivity, in terms of element ratios related with Sn mineralizations. Tourmalines in productive pegmatites are formed under the circumstance of Li-poor granitoids and associated with pegmatites, and the others are seemed to be originated in metapelites and metapsammites which are not coexisting with an Al-saturating phase. Three types of chemical zoning are noticed in tourmalines: (1) apparently homogeneous compositional patterns, (2) a continuous core-to-rim zoning and, (3) a discontinuous core-to-rim zoning. From results of EPMA of tourmalines, Al, Mg and Ca increase closer to rim, while Fe decreases.

• Journal of Biosystems Engineering
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• 제33권5호
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• pp.317-325
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• 2008

The electrocardiogram (ECG) measurement system consists of I/O interface to input the ECG signals from two electrodes, FPGA (Field programmable gate arrays) module to process the signal conditioning, and real time module to control the system. The algorithms based on wavelet transform were developed to remove the noise of the ECG signals and to determine the QRS-waves. Triangular wave tests were conducted to determine the optimal factors of the wavelet filter by analyzing the SNRs (signal to noise ratios) and RMSEs (root mean square errors). The hybrid rule, soft method, and symlets of order 5 were selected as thresholding rule, thresholding method, and mother wavelet, respectively. The developed wavelet filter showed good performance to remove the noise of the triangular waves with 10.98 dB of SNR and 0.140 mV of RMSE. The ECG signals from a total of 6 subjects were measured at different measuring postures such as lying, sitting, and standing. The durations of QRS-waves, the amplitudes of R-waves, the intervals of RR-waves were analyzed by using the finite impulse response (FIR) filter and the developed wavelet filter. The wavelet filter showed good performance to determine the features of QRS-waves, but the FIR filter had some problems to detect the peaks of Q and S waves. The measuring postures affected accuracy and precision of the ECG signals. The noises of the ECG signals were increased due to the movement of the subject during measurement. The results showed that the wavelet filter was a useful tool to remove the noise of the ECG signals and to determine the features of the QRS-waves.

• 천문학회지
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• 제41권6호
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• pp.163-172
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• 2008

Using the spectral data in the 3700 to $10050{\AA}$ wavelength range secured with the Hamilton Echelle Spectrograph (HES) at the Lick observatory, we have investigated the expansion velocities and the physical conditions of the elliptical planetary nebula NGC 6803. Various forbidden and permitted lines, e.g. HI, HeI, HeII, [OIII], [NII], [ArIII], and [SII], indicate complicated but systematic physical conditions variation: electron temperatures $T_{\varepsilon}\;{\sim}\;9000$ - 11000 K and electron number densities $N_{\varepsilon}\;{\sim}\;2000$ - $9000\;cm^{-3}$. The line profile analysis of these ions also indicates the systematic change or the acceleration of the expansion velocities in the range of 10 - $22\;km\;s^{-1}$. We show that the velocity gradient and physical condition found in various ions are closely related to the prolate ellipsoidal structure of NGC 6803. The expansion velocity and the ionic abundance of $O^{2+}$ were derived based on the OII and [OIII] lines. In spite of the discrepancy of ionic abundances derived by the two cases and their line profiles, the expansion velocities of them agree well. We find that the ratios of the red to blue line component of the HeII & OII lines are different from those of the [OIII] or other forbidden lines that indicates a possible involvement of emission of HeII & OII lines. This subtle difference and the different physical condition of the lines are likely to be caused by the elongated geometry and the latitude dependence of the emission zone.

• 천문학회지
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• 제41권5호
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• pp.121-137
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• 2008

We present optical and near-infrared imaging and long-slit spectroscopy for the blue compact dwarf galaxy (BCD) Mrk 49 in the Virgo Cluster. The surface brightness distribution analysis shows that Mrk 49 consists of an off-centered blue bright compact core of r = 10" and a red faint outer exponential envelope. The $H_{\alpha}$ image and color difference suggest that these two components have different stellar populations: a high surface brightness population of massive young stars and an underlying low surface brightness population of older stars. The redder near-infrared colors of the inner most region suggest that the near-infrared flux of Mrk 49 originates from evolved massive stars associated with the current star-forming activity. The total apparent magnitude is $B_T\;=\;14.32$ mag and the mean effective surface brightness is ${\mu}_{eff}(B)\;=\;21.56$ mag $arcsec^{-2}$. Long-slit spectroscopy shows that Mrk 49 rotates apparently as a solid body within r = 10" in a plane at position angle 55 degrees with an amplitude of about $20\;km\;sec^{-1}$. The measured radial velocity of Mrk 49 was derived as $1,535\;km\;sec^{-1}$; and the total mass of stars and gases is in the range of 3 to $6\;{\times}\;10^9\;M_{\odot}$. The mass-to-light ratios for the central region of Mrk 49 in I and B band are estimated 1.0 and 0.5, respectively. The upper limit of the dark matter to visible matter ratio seems to be < 5. The oxygen abundance is $12\;+\;\log(O/H)\;=\;8.21\;{\pm}\; 0.1$ which is about one quarter of the solar value while the relative helium abundance appears to be similar to that of the sun.

• 천문학회보
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• 제43권1호
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• pp.44.1-44.1
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• 2018

We present a spectroscopic study of the Galactic supernova remnant (SNR) Cygnus Loop using the fifth Data Release (DR5) of LAMOST. The LAMOST (Large Sky Area Multi-Object Fiber Spectroscopic Telescope) features both a large field-of-view (about 20 deg2) and a large aperture (~4 m in diameter), which allow us to obtain 4000 spectra simultaneously. Its wavelength coverage ranges from ${\sim}3700{\AA}$ to $9000{\AA}$ with a spectral resolution of $R{\approx}1800$. The Cygnus Loop is a prototype of middle-aged SNRs, which has advantages of being bright, large in angular size (${\sim}3.8^{\circ}{\times}3^{\circ}$), and relatively unobscured by dust. Along the line of sight of the Cygnus Loop, 2747 LAMOST DR5 spectra are found in total, which are spatially distributed over the entire remnant. Among them, 778 spectra are selected based on the presence of emission lines (i.e., [O III]${\lambda}5007$, Ha, and [S II]${\lambda}{\lambda}$ 6717, 6731) for further visual inspection. About half of them (336 spectra) show clear spectral features to confirm their association with the remnant, 370 spectra show stellar features only, and 72 spectra are ambiguous and need further investigation. For those associated with the remnant, we identify emission lines and measure their intensities. Spectral properties considerably vary within the remnant, and we compare them with theoretical models to derive physical properties of the SNR such as electron density and temperature, and shock velocity. While some line ratios are in good agreement with model prediction, others cannot be explained by simple shock models with a range of shock velocities. We discuss these discrepancies between model predictions and the observations and finally highlight the powerfulness of the LAMOST data to investigate spatial variations of physical properties of the Cygnus Loop.

• Carbon letters
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• 제15권1호
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• pp.57-66
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• 2014

Three activated carbons (ACs) were prepared using NaOH (N) as an activating agent. Hydrofluoric acid pre-leached rice husk was used as a precursor. After leaching, the precursor was washed with distilled water, dried, crushed, and then sieved; a size fraction of 0.3-0.5 mm was selected for carbonization in the absence of air at $600^{\circ}C$. The carbonization product (LC) was mixed with NaOH at ratios of 1:2, 1:3, and 1:4 (wt of LC: wt of NaOH) and the produced ACs after activation at $800^{\circ}C$ were designated NLC21, NLC31, and NLC41, respectively. Surface and textural properties were determined using nitrogen adsorption at $-196^{\circ}C$, scanning electron microscopy images, thermogravimetric analysis, and Fourier transform infrared spectra. These ACs were used as adsorbents for lead(II) from aqueous solutions. The effects of the textural properties and the chemistry of the carbon surfaces were investigated and the impact of the operation conditions on the capacity for lead(II) sorption was also considered. Modification of NLC41 with $H_2O_2$ and $HNO_3$ gave two other adsorbents, $H_{NLC41}$ and $N_{NLC41}$ respectively. These two new samples exhibited the highest removal capacities for lead(II), i.e.117.5 and 128.2 mg/g, respectively. The adsorption data fitted the Langmuir isotherm and the kinetic adsorption followed pseudo-second order kinetics. The thermodynamic parameters have been determined and they indicated a spontaneous endothermic process.

• 한국농공학회지
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• 제26권1호
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• pp.29-37
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• 1984

This study was made to find several significant relations among various physical and mechanical properties including cone penetration resistance. The alluvial clay samples were taken at the Daebul Reclaimed Tideland in Samhomyeon, Yeongamgun, Jeonranamdo. The results of the study are summarized as follows; 1.Most samples belong to medium or high plastic, inorganic, silty clay(clay contents;32-64%, silt contents; 36-68%, sand contents; 0-3%). The specific gravities range from 2.70 to 2.73, the unit weights from 1.45 to 1. 75g/cm$^3$, the natural moisture contents from 45 to 77%, the liquid limits from 32 to 56%. It is certain that the foundation is weak because the natural moisture contents are much higher than the liquid limits. 2.It is known from the shear tests that the unconfined compression strenghs vary from 0.09 to 0. 38kg/cm2, the cohesions from 0.05 to 0. 21kg/cm2, the internal friction angles from 0 to 3˚. 3.The consolidation tests show that the initial void ratios range from 1.25 to 2.28, the compression indeices from 0.43 to 0.84, the preconsolidation loads from 0.21 to 0.74kg/cm$^2$. 4.Cone penetration resistances are usually less than 5kg/cm$^2$ from ground surface to the depth of about 8m, and from S to l0kg/cm$^2$ in the layer below about 8m to hard layer. 5.The cohesion and cone penetration resistance are in proportion to the depth of soil layer. 6.The correlations between various physical and mechanical properties including cone penetration resistance for the alluvial clay samples are as follows; a) Wn=0.944C+ l2.733 (r=0.829) b) LL=0. 728Cy+6. 991 (r=0. 873) c) PI=0.659Cy-8.168 (r=0.860) d) rt=0. 0077(272-Wn) =2.092-0. 0077Wn (r=0. 859) e) 60=0. 035wn-0 447 (r=0. 893) f) C=0.380qw+0.031 (r=0.816) g) qu=0.0707qc+0.029 (r=0.810) h) C=0.018Z+0.055 (r=O.802) I) qc=0. 415Z+1, 438 (r=0. 943)