• Nuclear Engineering and Technology
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• v.56 no.2
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• pp.463-471
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• 2024

Average and local convective heat transfer coefficients of nitrogen are measured experimentally in an electrically heated circular tube for a range of Reynolds number from 1.08 × 10⁴ to 3.60 × 10⁴, and wall-to-bulk temperature ratio from 1.01 to 1.77. The exit Mach number is up to 0.17, and the heat flux is up to 46 kW·m^-2. The molybdenum test section has a 62 diameters heated section with an inside diameter of 5 mm and a 30 diameters entrance section to ensure the fully-developed flow. Uncertainty of Nusselt number is less than 1.6 % in this study. The results indicate that the average heat transfer correlations evaluated by both the bulk and the modified film Reynolds numbers agree well with the experimental data. The local heat transfer results based on bulk properties are compared with previous empirical correlations. New prediction correlations are recommended which are significantly affected by the property variation and heated length. The comparison between the proposed correlations and experimental points shows that 88 % of experimental data fall into an error of 10 %, and almost all data are within an error of 20 %.

• Asian-Australasian Journal of Animal Sciences
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• v.22 no.12
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• pp.1703-1708
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• 2009

Deproteinization has been recognized as a prerequisite for amino acid analysis of plasma samples. For plasma stored at room temperature, delaying deproteinization for 30, 60 or 120 minutes did not result in significant changes in the mean CV (coefficient of variation), which ranged from 4.4 to 5.6%. However the mean CV of aspartic acid, ${\alpha}$-aminoadipic acid, alanine and lysine was about 10%. When the plasma was stored frozen at -20${^{\circ}C}$, the CV was increased at 0 and 120 minutes after thawing, to 12.4% (range, 4.1 to 35.3%) and 8.0% (2.5 to 30.7%), respectively. The concentrations in plasma during storage at room temperature of all the amino acids analyzed showed significant changes. In plasma stored for 30 minutes at room temperature, 17 amino acids increased in concentrations and two decreased. Extending this period to 60 or 120 minutes increased the instability as compare to the reference group. Storing plasma at -20${^{\circ}C}$ for 2 weeks resulted in significantly greater changes in the amino acid concentrations than at room temperature. On extending the storage time at room temperature, after thawing, to 30, 60, and 120 minutes, 21, 20, and all 22 amino acids respectively changed significantly (p<0.01). The present study indicates that methodological errors occur in the concentrations determined for all amino acids when plasma is left at room temperature. The storage of frozen non-deproteinized plasma accompanied more significant changes in most amino acid concentrations and thus should be avoided. Deproteinization should be performed as soon as possible after plasma collection.

• Journal of Forest and Environmental Science
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• v.28 no.3
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• pp.158-169
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• 2012

Sabah has experienced a rapid decline in the extent of forest cover. The precise impact of habitat loss on the conservation status of the plants of Sabah is uncertain. In this study we use the niche modelling algorithm MAXENT to construct preliminary, revised and final ecological niche models for Dipterocarpus lamellatus and Dipterocarpus ochraceus and combined these models with data on current land-use to derive conservation assessments for each species. Preliminary models were based on herbarium data alone. Ground surveys were conducted to evaluate the performance of these preliminary models, and a revised niche model was generated from the combined herbarium and ground survey data. The final model was obtained by constraining the predictions of the revised models by filters. The range overlap between the preliminary and revised models was 0.47 for D. lamellatus and 0.39 for D. ochraceus, suggesting poor agreement between them. There was substantial variation in estimates of habitat loss for D. ochraceus, among the preliminary, revised and constrained models, and this has the potential to lead to incorrect threat assessments. From these estimates of habitat loss, the historic distribution and estimates of population size we determine that both species should be classified as Critically Endangered under IUCN Red List guidelines. Our results suggest that ground-truthing of ecological niche models is essential, especially if the models are being used for conservation decision making.

• Journal of the Korean Geosynthetics Society
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• v.11 no.3
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• pp.27-35
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• 2012

In this paper, the frost heaving and thawing characteristics of flexible pavement structure were evaluated in the large scale freezer which have a specification of temperature range $-20^{\circ}C{\sim}10^{\circ}C$ and $3.2m(L){\times}3.2m(B){\times}2.4m(H)$ in size. The insulated steel box with the size of $0.9m(L){\times}0.9m(B){\times}0.9m(H)$ was used to simulate actual pavement road structure. The variation of temperature, frost heave amount and frost heave pressure were measured through the instrument of TDS-602 data logger. LFWD (light falling weight deflectometer) was used to determine the change of deflection due to the frost heaving and thawing. Furthermore, the influence of aggregate layer to the freezing of the subgrade soil was studied to verify the function and effectiveness of the anti-freezing layer.

• 한국해양학회지
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• v.30 no.6
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• pp.543-549
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• 1995

The inverse method has been used to estimate a surface velocity field from sequential AVHRR/SST data. In the model, equation system was composed of heat equation and horizontal divergence minimization and the velocity field contained in the advective term of the heat equation, which was linearized in grid system, was estimated. A constraint was the minimization of horizontal divergence with weighting factor and introduced to compensate the null space(Menke, 1984) of the velocity solutions for the heat equation. The experiments were carried out to set up the range of weighting factor and the matrix equation was solved by SVD(Singular Value Decomposion). In the experiment, the scales of horizontal temperature gradient and divergence of synthetic velocity field were approximated to those of real field. The neglected diffusive effect and the horizontal variation of heat flux in the heat equation were regarded as random temperature errors. According to the result of experiments, the minimum of relative error was more desirable than the minimum of misfit as the criteria of setting up the weighting factor and the error of estimated velocity field became small when the weighting factor was order of $10^{-1}$

• Journal of Korean Society on Water Environment
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• v.28 no.1
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• pp.10-17
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• 2012

The middle and lower reaches of the Kum River system become stagnant in dry seasons with florishing of phytoplankton. In this study primary productivity of phytoplankton were measured by the C-14 uptake method and the P-I model method at seven main stream sites of the Kum River from the Daechung Dam outet to the river mouth. Nutrients (TN, TP, DIP, TIN) concentrations were measured in the mainstream and tributaries and compared with the variation of assimilation number. The range of primary productivity was $40{\sim}4,558mgC{\cdot}m^{-2}{\cdot}day^{-1}$ and it was higher than those of lentic ecosystems in Korea. Average TN and TP were $4.1mgN{\cdot}L^{-1}$, $70.6mgP{\cdot}m^{-3}$, respectively. Tributaries showed higher nutrient concentrations than the main stream. After two major tributaries merged with the discharging water of the Daechung Dam phyotplankton biomass and productivity increased drastically and remained at the similar eutrophic level through the downstream reach to the river mouth. Both dissolved phosphorus and nitrogen concentrations showed positive correlation with assimilation number of phytoplankton. In conclusion phytoplankton productivity is at the level of eutrophic water and it was higher than usual lentic habitats. Nutrient concentrations are critical factors in controlling productivity in the lower reach of the Kum River.

• Journal of Korean Society of Water and Wastewater
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• v.29 no.4
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• pp.469-479
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• 2015

This study have been conducted to analyze the feasibility of establishing Contamination Warning System(CWS) that is capable of monitoring early natural or intentional water quality accidents, and providing active and quick responses for domestic C_water supply system. In order to evaluate the water quality data set, pH, turbidity and free residual chlorine concentration data were collected and each statistical value(mean, variation, range) was calculated, then the seasonal variability of those were analyzed using the independent t-test. From the results of analyzing the distribution of outliers in the measurement data using a high-pass filter, it could be confirmed that a lot of lower outliers appeared due to data missing. In addition, linear filter model based on autoregressive model(AR(1) and AR(2)) was applied for the state estimation of each water quality data set. From the results of analyzing the variability of the autocorrelation coefficient structure according to the change of window size(6hours~48hours), at least the window size longer than 12hours should be necessary for estimating the state of water quality data satisfactorily.

• Korean Journal of Materials Research
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• v.3 no.4
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• pp.319-326
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• 1993

The effects of $SnO_2$ crystallite size on the powder characteristics, the resistance in air and the sensitivity to 0.5 vol % $H_2$, CO-air mixture were observed. The size of SnO, powder was controlled by calcining temperature variation ($500^{\circ}C$ ~$1100^{\circ}C$) of $\alpha$-stannic acid fabricated from $SnCl_4 \cdot xH_2O$. Its crystallite size. evaluated from TEM image, was in the range of 8-54nm. With the reduction of crystallite size, the adsoption peak of $H_2O$ on FTIR curve became more clear while the lattice parameters were invariable. As the crystallite size decreased, with elements of thick film, the temperatures showing a minimum resistance in air and a maximum sensitivity to H, gas reduced. The temperature variations were assigned to the changes of activation energy of the active adsorbates, and it was suggested that the decrease of activation energy can be one of the reasons for the' sensitivity increase with the' fine powder.

• Journal of the Korean Institute of Gas
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• v.9 no.3 s.28
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• pp.1-8
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• 2005

We studied on the nondestructive evaluation of the elastic wave signals of locally wall thinned straight pipe. Wavelet transform was applied for the time-frequency analysis of waveforms obtained by fracture wave detector due to the dropping steel ball. The time-frequency analysis provides time variation of each frequency component involved in a waveform, which makes it possible to evaluate the shape of local wall thinning at each frequency. In this study, comparison by wavelet transform of the AE signals and monotonic bending tests without internal pressure are conducted on 1.91 inch diameter full-scale carbon steel pipe specimens. As the results of tests, fracture behaviors could be shown by the characteristic of mechanical strength of locally wall thinned pipes and the waveforms could be evaluated for the integrity insurance of the piping system according to the length and depth range of the deffeted shape pipes in the real field.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.7
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• pp.568-573
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• 2011

AZO (Al doped ZnO) thin films were deposited on the quartz substrates with thickness variation from 25 to 300 nm by using PLD (pulsed laser deposition). XRD (x-ray diffractometer), SPM (scanning probe microscopy), Hall effect measurement and uv-visible spectrophotometer were employed to investigate the structural, morphological, electrical and optical properties of the thin films. XRD results demonstrated that films were preferrentially oriented along the c-axis and crystallinity of film was improved with increase of film thickness. As for the surface morphologies, the mean diameter and root mean square of grains were increased as the film thickness was increased. When the film thickness was 200 nm, the lowest resistivity of $4.25{\times}10^{-4}\;{\Omega}cm$ obtained with carrier concentration of $6.84{\times}10^{20}\;cm^{-3}$ and mobility of $21.4\;cm^2/V{\cdot}S$. All samples showed more than 80% of transmittance in the visible range. Upon these results, it is found that the samples thickness can affect their structural, morphological, optical and electrical properties. This study suggests that the resistivity can be improved by controlling film thickness.