• Steel and Composite Structures
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• v.50 no.2
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• pp.159-181
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• 2024

In the present study, the effect of geometrical parameters of two different types of aluminum thin-walled structures on energy absorption under three-bending impact loading has been investigated experimentally and numerically. To evaluate the effect of parameters on the specific energy absorption (SEA), initial peak crushing force (IPCF), and the maximum crushing distance (δ), a design of experiment technique (DOE) with response surface method (RSM) was applied. Four different thin-walled structures have been tested under the low-velocity impact, and then they have simulated by ABAQUS software. An acceptable consistency between the numerical and experimental results was obtained. In this study, statistical analysis has been performed on various parameters of three different types of tubes. In the first and the second statistical analysis, the dimensional parameters of the cross-section, the number of holes, and the dimensional parameter of holes were considered as the design variables. The diameter reduction rate and the number of sections with different diameters are related to the third statistical analysis. All design points of the statistical method have been simulated by the finite element package, ABAQUS/Explicit. The final result shows that the height and thickness of tubes were more effective than other geometrical parameters, and despite the fact that the deformations of the cylindrical tubes were around forty percent greater than the rectangular tubes, the top desirability was relevant to the cylindrical tubes with reduced cross-sections.

• The Korean Journal of Ecology
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• v.15 no.3
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• pp.297-309
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• 1992

The growth of digitaria adscendens and eleusine indica, annual weeds common in japan, was experimentally analyzed under varying untrient conditions. compared with e. indica, d. adscendensshowed a higher the two under high nitrogen availability. Higher net assimilation rate(nar) in d. adscendens than e. india was responsible for high RGR in D. adscendens under the low nitrogen availability. The different of NAR in the two species was induced not by leaf nitrogen content but by nitrogen use efficiency. Under unfertilized conditions nitrogen uptake rate(nur) was greater in d. adscendens than e. indica. Specific absorption rate in two species was similar, but root mass was greater in d. adscendens than e. indica.d. adscendens allocated more dry matter to roots than e. india earlier stage of seedlings. The contributed to higher rot mass and in turn resulted in higher nur in d. adscendens than that in e. india. It is concluuded that the larger allocation of dry matter to roots at early seedling stage in d. adscendens plays an important role in obtaining nitrogen for the continuation of growth under low nitrogen availability.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.4
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• pp.208-213
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• 2009

Artificial lightweight aggregates were produced by using bottom ashes and dredged soils from coal power plant. The amount of glassy phases on the aggregate surfaces, specific gravities, absorption rates, and observations of cross-sectional surfaces were compared according to the compositions, sintering temperatures, and the amount of coating. It is concluded that surface modification by 10 % $CaCO_3$ coating on the aggregate surfaces enhances the properties of aggregates as follows: Specific gravities were controlled by depressing formation of large pores in the aggregates. Sticking phenomena among aggregates during the sintering process was drastically decreased by reducing glassy phases on the aggregate surfaces. Pumping problems during the application of ready-mix concretes containing lightweight aggregates having high value of absorption rates could be solved by reducing the absorption rate.

• Journal of electromagnetic engineering and science
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• v.16 no.2
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• pp.87-99
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• 2016

This paper describes an implementation method and the results of numerical mobile phone models representing real phone models that have been released on the Korean market since 2002. The aim is to estimate the electromagnetic absorption in the human brain for case-control studies to investigate health risks related to mobile phone use. Specific absorption rate (SAR) compliance test reports about commercial phone models were collected and classified in terms of elements such as the external body shape, the antenna, and the frequency band. The design criteria of a numerical phone model representing each type of phone group are as follows. The outer dimensions of the phone body are equal to the average dimensions of all commercial models with the same shape. The distance and direction of the maximum SAR from the earpiece and the area above -3 dB of the maximum SAR are fitted to achieve the average obtained by measuring the SAR distributions of the corresponding commercial models in a flat phantom. Spatial peak 1-g SAR values in the cheek and tilt positions against the specific anthropomorphic mannequin phantom agree with average data on all of the same type of commercial models. Second criterion was applied to only a few types of models because not many commercial models were available. The results show that, with the exception of one model, the implemented numerical phone models meet criteria within 30%.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.3
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• pp.125-130
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• 2008

If the properties of artificial lightweight aggregates produced by rotary kiln can be predicted by using a simulator equipped with a small electric furnace and a specially designed device for specimen movement, large amount of raw materials and plenty of test time can be saved to produce test products of lightweight aggregates. In this study a simulator for the accurate prediction of the artificial lightweight aggregates produced by rotary kiln was assembled by our own design and the properties of lightweight aggregates produced by both the simulator and rotary kiln were compared to speculate its usefulness. The average diameter of aggregates was 8 mm and atmosphere in the furnace was controlled by the amount of carbon powders. Specific gravity, absorption rate (%), black-core area in the cross-sectional view of both aggregates were measured and compared. Unlike oxydizing atmosphere, both specific gravity and absorption rate of the aggregates sintered at reducing atmosphere were increased with increasing carbon addition. It is concluded that the sintering atmosphere was the closest to that of the rotary kiln when the carbon addition was 0.7 g to make a reducing atmosphere in the furnace and the properties of both agreggates was also similar to each other.

• Journal of Magnetics
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• v.21 no.3
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• pp.460-467
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• 2016

Magnetic hyperthermia mediated by superparamagnetic particles is mainly based in sinusoidal waveforms as excitation signals. Temperature changes are conventionally explained by rotation of the particles in the surrounding medium. This is a hypothesis quite questionable since habitual experimental setups only produce changes in the magnetic module, not in the field lines trajectories. Theoretical results were tested by changing the waveform of the exciting signal in order to compare non-sinusoidal signals against sinusoidal signals. Experiments were done at different frequencies: 200 KHz, 400 KHz, 600 KHz, 800 KHz and 1 MHz. Superparamagnetic Iron Oxide samples (SPION), made of magnetite ($Fe_3O_4$) and suspended in water (100 mg/ml), were used. Magnetic field strength varies from $0.1{\pm}0.015KA/m$ to $0.6{\pm}0.015KA/m$. In this study was observed that the power loss depends on the applied frequency: for 1 to 2.5 RMS current the responses for each signal are part of the higher section of the exponential function, and for 3.5 to 8 RMS current the response is clearly the decrement exponential function's tale (under $1{\times}10^3LER/gr$).

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.8 s.99
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• pp.810-814
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• 2005

Input power for TEM cell apparatus due to SAR(Specific Absorption Rate) for culture blood cell is determined by the transmission and reflection measurement of blood into the TEM cell. Blood cell with skin cell are reference culture cells for the study of EM wave effect. Exposure RF power from exposure apparatus to culture cell should not only exact for SAR value, but also should be based on the theoretical theory. In this paper, insertion loss of 50 g blood was measured to know exposure power per gram for culture blood cell, and input power of TEM cell due to SAR 0.8, 1.6, 3, 4 mW/g using the measured data are delivered. This study is for applying to EM wave exposure apparatus to culture cell.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.1
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• pp.666-670
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• 2015

This paper presents radiation pattern reconfigurable antenna for Fitbit Flex wristband which detects vital signal. Also, the paper presents Specific Absorption Rate (SAR) from the loop-dipole radiation pattern reconfigurable antenna based on the position of human body. The proposed loop-dipole radiation pattern reconfigurable antenna produces two opposite side direction radiation pattern using two RF switches. The resonant frequency of the radiation pattern reconfigurable antenna is Bluetooth communication bandwidth (2.4 - 2.485 GHz) and the maximum gain of the proposed antenna is 1.96 dBi. The proposed antenna satisfied the standard SAR value of 1.6 W/kg in 1 g tissue of the human body when the Bluetooth communication input average power of 0.04 W is excited to five parts of human body (head, chest, stomach, back, wrist). The maximum SAR value of in this simulation is presented in the part of head.

• Biomedical Science Letters
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• v.12 no.1
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• pp.9-16
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• 2006

We investigated the effects of 835-MHz electromagnetic field (EMF), one of the most popular communication frequency band in Korean code-division multiple-access (CDMA) mobile phone system, on cellular signal transduction. For this, we examined the change of intracellular calcium $([Ca^{2+}]_i)$, reactive oxygen species (ROS) and F-actin polymerization after exposure to 835-MHz EMF followed by the treatment of agonists in Rat-2 fibroblast cells. Culture cells were pretreated with serum-tree medium and concomitantly exposed to 835-MHz at specific absorption rate (SAR) of 4.0 W/kg for 24 hr in a specialized designed apparatus based on Transverse Electro Magnetics (TEM) wave theory. Intracellular $Ca^{2+}$ responses to lysophosphatidic acid (LPA) and epidermal growth factor (EGF) in Rat-2 fibroblast after exposure to 835-MHz EMF were shown to be similar pattern as observed in normal cultured cells. However, the LPA-induced calcium spiking was slightly delayed to 7 sec and sustained thereafter to a little higher ground level under 835-MHz EMF radiation compared to unexposed cells. ROS production level by LPA in the exposed cells was not different from that in control. Furthermore, LPA induced the production of stress fibers with no significant difference in the exposed and unexposed cells. These results suggest that mobile phone radiation (835-MHz, SAR 4.0 W/kg) may not be directly related to signal transduction in Rat-2 fibroblasts except the slight effect of calcium spiking in LPA-induced cells but remain to be further elucidated for possible indirect intervention.

• Journal of the Korean Ceramic Society
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• v.39 no.8
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• pp.795-800
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• 2002

Yb:$YCa_4O(BO_3)_3$ (Yb:YCOB) single crystal, in which the concentration of $Yb^{3+}$ ion 20 at%, was grown by the Czocharalski method using an iridium crucible under N2 atmosphere. The optimum growth parameters to get a high quality of single crystals were found to be 1.5∼2 mm/h of pulling rate and 10∼20 rpm of rotation rate. According to the results of spectroscopic properties, absorption edge of Yb:YCOB was 236 nm. Two strong absorption line due to $Yb^{3+}$ ions were observed at 900 and 975 nm. Thermal expansion coefficients of Yb:YCOB crystal along a, b and c crystallographic axes from 320 to 650 K were 12.1${\times}10^{-6}$/K, 5.9${\times}10^{-6}$/K, 12.9${\times}10^{-6}$/K, respectively. Specific heat was 0.162 $cal/g{\cdot}K$ at 330 K.