• Nuclear Engineering and Technology
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• v.53 no.4
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• pp.1119-1126
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• 2021

Spacer grid with mixing vane had been widely used in nuclear reactor core. One of the main feather of spacer grid with mixing vane was that strong swirl flow was formed after the spacer grid. The swirl flow not only changed the bubble generation in the near wall field, but also affected the bubble behaviors in the center region of the subchannel. The interaction between bubble and the swirl flow was one of the basic phenomena for the two phase flow modeling in fuel assembly. To obatin better understanding on the bubble behaviors in swirl flow, full three dimension numerical simulations were conducted in the present paper. The swirl flow was assumed in the cylindral calculation domain. The bubble interface was captured by Volume Of Fluid (VOF) method. The properties of saturated water and steam at different pressure were applied in the simulation. The bubble trajectory, motion, shape and force were obtained based on the bubble parameters captured by VOF. The simulation cases in the present study included single bubble with different size, at different angular velocity conditions and at different pressure conditions. The results indicated that bubble migrated to the center in swirl flow with spiral motion type. The lateral migration was mainly related to shear stress magnitude and bubble size. The bubble moved toward the center with high velocity when the swirl magnitude was high. The largest bubble had the highest lateral migration velocity in the present study range. The effect of pressure was small when bubble size was the same. The prelimenery simulation result would be beneficial for better understanding complex two phase flow phenomena in fuel assembly with spacer grid.

• International Journal of Computer Science & Network Security
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• v.21 no.6
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• pp.47-53
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• 2021

The article deals with the problems of application of microwave methods in systems of geoecological monitoring of natural environments and resources of the agro-industrial complex. It is noted that the methods of microwave radiometry make it possible, by the power of the measured intrinsic radio-thermal radiation of the atmosphere, when solving inverse problems using empirical and semi-empirical models, to determine such parameters of the atmosphere as thermodynamic temperature, humidity, water content, moisture content, precipitation intensity, and the presence of different fractions of clouds.In addition to assessing the meteorological parameters of the atmosphere and the geophysical parameters of the underlying surface based on the data of microwave radiometric measurements, it is possible to promptly detect and study pollution of both the atmosphere and the earth's surface. A technique has been developed for the analysis of sources of measurement error and their numerical evaluation, because they have a significant effect on the accuracy of solving inverse problems of reconstructing the values of the physical parameters of the probed media.To analyze the degree of influence of the limited spatial selectivity of the antenna of the microwave radiometric system on the measurement error, we calculated the relative measurement error of the ratio of radio brightness contrasts in two angular directions. It has been determined that in the system of geoecological monitoring of natural environments, the effect of background noise is maximal with small changes in the radiobrightness temperature during angular scanning and high sensitivity of the receiving equipment.

• The Journal of the Acoustical Society of Korea
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• v.28 no.5
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• pp.432-440
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• 2009

Recently, the necessity of underwater acoustic communication and demand for transmitting and receiving various data such as voice or high resolution image data are increasing as well. The performance of underwater acoustic communication system is influenced by underwater channel characteristic. Especially, a delay spread caused by reverberation and multi-path induces the ISI (Inter-Symbol-Interference) and reduces the communication performance. In this paper, we study the OFDM (Orthogonal Frequency Division Multiplexing) technique for robust the delay spread in underwater channel. We also use the clipping method to overcome the performance degradation in high PAPR (Peak-to-Average Power Ratio). We confirm the performances of underwater communication system by the underwater channel model simulation model and experiment in small water tank. As a result, the multi-carrier modulation with clipping method presented low BER and the previous single carrier modulation had high BER.

• Advances in nano research
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• v.16 no.3
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• pp.231-249
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• 2024

When the amplitude of the vibrations is equivalent to that clearance, the vibrations for small amplitudes will really be significantly nonlinear. Nonlinearities will not be significant for amplitudes that are rather modest. Finally, nonlinearities will become crucial once again for big amplitudes. Therefore, the concrete panel system may experience a big amplitude in this work as a result of the high temperature. Based on the 3D modeling of the shell theory, the current work shows the influences of the von Kármán strain-displacement kinematic nonlinearity on the constitutive laws of the structure. The system's governing Equations in the nonlinear form are solved using Kronecker and Hadamard products, the discretization of Equations on the space domain, and Duffing-type Equations. Thermo-elasticity Equations. are used to represent the system's temperature. The harmonic solution technique for the displacement domain and the multiple-scale approach for the time domain are both covered in the section on solution procedures for solving nonlinear Equations. An effective data-driven solution is often utilized to predict how different systems would behave. The number of hidden layers and the learning rate are two hyperparameters for the network that are often chosen manually when required. Additionally, the data-driven method is offered for addressing the nonlinear vibration issue in order to reduce the computing cost of the current study. The conclusions of the present study may be validated by contrasting them with those of data-driven solutions and other published articles. The findings show that certain physical and geometrical characteristics have a significant effect on the existing concrete panel structure's susceptibility to temperature change and GPL weight fraction. For building construction industries, several useful recommendations for improving the thermo-mechanics' behavior of structural concrete panels are presented.

• Toxicological Research
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• v.18 no.1
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• pp.13-22
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• 2002

In Korea, 2,320 tonnes of acetanilide were mostly wed as intermediates for synthesis in phar-maceuticals or additives in synthesizing hydrogen peroxide, varnishes, polymers and rubber. Only small amount of 120 kg were wed as a stabilizer for hydrogen peroxide solution for hair colouring agents in 1998. Readily available environmental or human exposure data do not exist in Korea at the present time. However, potential human exposures from drinking water, food, ambient water and in work places are expected to be negligible because this chemical is produced in the closed system in only one company in Korea and the processing factory is equipped with local ventilation and air filtering system. Acetanilide could be distributed mainly to water based on EQC model. This substance is readily biodegradable and its bioaccumulation is low. Acute toxicity of acetanilide is low since the L $D_{50}$ of oral exposure in rats is 1,959 mg/kg bw. The chemical is not irritating to skin, but slightly irritating to the eyes of rabbits. horn repeated dose toxicity, the adverse effects in rats were red pulp hyperplasia of spleen, bone marrow hyperplasia of femur and decreased hemoglobin, hematocrit and mean corpuscular hemoglobin concentration. The LOAEL for repeated dose toxicity in rats was 22 mg/kg/day for both sexes. Acetanilide is not considered to be genotoxic. In a reproductive/developmental toxicity study, no treatment-related changes in precoital time and rate of copulation, impregnation, pregnancy were shown in all treated groups. The NOAELs for reproduction and developmental toxicity (off-spring toxicity) are considered to be 200 mg/kg bw/day and 67 mg/kg bw/day, respectively. Ecotoxicity data has been generated in a limited number of aquatic species of algae (72 hr- $E_{b}$ $C_{50}$; 13.5 mg/l), daphnid (48hr-E $C_{50}$ > 100 mg/l) and fish (Oryzias latipes, 96hr-L $C_{50}$; 100 mg/l). Form the acute toxicity values, the predicted no effect concentration (PNEC) of 0.135 mg/1 was derived win an assessment factor of 100. On the basis of these data, acetanilide was suggested as currently of low priority for further post-SIDS work in OECD.in OECD.D.

• Journal of Korean Society of Forest Science
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• v.99 no.1
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• pp.75-84
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• 2010

For policies and actions associated promotion of social and environmental benefits of forest in Korea, various polices have been progressed based on newly established ordinances along with full progresses of subdivision of the Forest Law since reorganization of regulatory system by functions focused on the Basic Forestry Act. In these policies, water resource conserving function and national land conserving function which have little close relation to the people's daily life including formation of forest for conservation of water supply and erosion control have continued to be promoted since 1970s. Especially in recently years, the policy of biodiversity conserving function according to importance of health and recreation function and conservation management of forest ecosystem and animal and plant are being promoted actively. Among them, the health and recreation functions is featured for various policies to be promoted in spite of small budget for responding actively to various forest recreation demands after settlement of 5-day workweek system. It seems because the health and recreation function could obtain visible results of governmental investment and high responses from the peoples as a function having close relationship with the people's daily life.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.15 no.1
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• pp.25-35
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• 2010

The biodiversity of eukaryotic plankton has commonly been used to evaluate the status of aquatic ecosystems. Therefore, an accurate and rapid method for species identification is needed to reveal the biodiversity of environmental water samples. To date, molecular methods have provided a great deal of information that has enabled identification of the hidden biodiversity in environmental samples. In this study, we utilized environmental polymerase chain reaction (PCR) and constructed the 18S nuclear ribosomal RNA clone library from environmental water samples in order to develop more efficient methods for species identification. For the molecular analysis, water samples were collected from the Seonakdong River (Gimhae Bridge) and the coast of Namhae，(Namhaedo). Colony PCR and restriction fragment length polymorphism of PCR (PCR-RFLP) were then adopted to isolate unique clones from the 18S rDNA clone library. Restriction fragment length polymorphism pattern analysis of the Gimhae Bridge sample revealed 44 unique clones from a total of 60 randomly selected clones, while analysis of the Namhae sample revealed 27 unique clones from 150 clones selected at random. A BLAST search and subsequent phylogenetic analysis conducted using the sequences of these clones revealed hidden biodiversity containing a wide range of taxonomic groups (Heterokontophyta (7), Ciliophora (23), Dinophyta (1), Chytridiomycota (1), Rotifera (1) and Arthropoda (11) in the Gimhae Bridge samples Ciliophora (4), Dinophyta (3), Cryptophyta (1), Arthropoda (19) in the Namhae samples). Therefore, the molecular monitoring method developed here can provide additional information regarding the biodiversity and community structure of eukaryotic plankton in environmental samples and helps construct a useful database of biodiversity for aquatic ecosystems.

• Journal of Navigation and Port Research
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• v.30 no.10 s.116
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• pp.861-867
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• 2006

In connection with redevelopment of Busan North Port, there has been lots of studies and efforts for the development of superannuated North general piers into a center of marine tourism and waterfront for the citizens of Busan. Recently it has moved to the stage of execution, after several trials to find concrete solutions. On the other hand, the change of flow field and tidal exchange cuased by redevelopment is one of the important investigation subjects. This study deals with the change of flow field and water exchange after redevelopment using numerical simulation technique, based on the general data which were collected and analyzed. As a result of simulation, the speed of tidal currents are tended to decrease near the North and inner-port and increase at the main waterway. Furthermore, the tidal exchange had a tendency to be small both before and after redevelopment by about 77% in a quasi steady state, which is about 15 days after.

• Korean Journal of Ecology and Environment
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• v.36 no.4 s.105
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• pp.420-426
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• 2003

During a three-year study (2000-2002), dramatic changes in the phytoplankton biomass and high transparency were repeatedly observed during mid-spring in the lower part of the Nakdong River. Rotifers (Brachionus, Keratella, Polyarthra) , sharply increased toward the middle and end of spring. As hydrologic retention time increased (to near 20 days) and water temperature increased from $10^{\circ}C$ to > $20^{\circ}C$ toward the end of spring, small cladocerans noticeably increased. Once phytoplankton biomass passed their peak stage in the mid-spring, a short period (one or two weeks) of relatively low phytoplankton biomass and high Secchi transparencies occurred. Grazing by the zooplankton was highest in spring, thus, it seems that high grazing activities of zooplankton grazing regulated phytoplankton dynamics in the river. The results indicate that the role of zooplankton grazing in controlling the phytoplankton biomass becomes more important during the spring when river water is relatively stagnant.

• Progress in Medical Physics
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• v.14 no.1
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• pp.1-7
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• 2003

In this work we developed a EGS4 control code to calculate the dose distributions for high energy electron beams in water phantom applied longitudinal magnetic field. We reviewed the electron's motion in magnetic field and delivered equations for direction changs of the electron by the external magnetic field. The mathematical results are inserted into the EGS4 code system to account for the presence of external magnetic fields in phantom. The electron pencil beam paths of 6 MeV in water phantom are calculated for magnetic fields of 1-3 T and the dose distributions for a field of 1.0 cm in diameter are calculated for magnetic fields of 0.6-1 T using the code. From the results of path calculations we found that the lateral ranges of the electrons are reduced in the magnetic field of 3 T. For a field of 1 cm diameter and a magnetic field of 1 T, the small dose enhancement near the range of the electrons on the depth dose and the penumbra reduction of 0.15 cm on the beam profile are observed. We discussed and evaluated the results from the theoretical concepts.