• Environmental Engineering Research
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• v.25 no.4
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• pp.515-521
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• 2020

Nowadays, due to various pollution sources, it is essential for environmental scientists to monitor water quality. Phytoplanktons form the end of the food chain in water bodies and are one of the most important biological indicators in water pollution studies. Chlorophyll-A, a green pigment, is found in all phytoplankton. Chlorophyll-A concentration indicates phytoplankton biomass directly. Therefore, Chlorophyll-A is an indirect indicator of pollutants, including phosphorus and nitrogen, and their refinement and control are important. The present study, Moderate Resolution Imaging Spectroradiometer (MODIS) satellite images were used to estimate the chlorophyll-A concentration in southern coastal waters in the Caspian Sea. For this purpose, Multi-layer perceptron neural networks (NNs) were applied which contained three and four feed-forward layers. The best three-layer NN has 15 neurons in its hidden layer and the best four-layer one has 5 in each. The three- and four- layer networks both resulted in similar root mean square errors (RMSE), 0.1($\frac{{\mu}g}{l}$), however, the four-layer NNs proved superior in terms of R² and also required less training data. Accordingly, a four-layer feed-forward NN with 5 neurons in each hidden layer, is the best network structure for estimating Chlorophyll-A concentration in the southern coastal waters of the Caspian Sea.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.12 no.1
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• pp.111-122
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• 2009

Abatements of TN and ${NO_3}^-$-N in a horizontal subsurface-flow wetland with litter layer on its surface were compared with those without one. The wetland was constructed in 2001 on floodplain of the Gwangju Stream which flows through Gwangju City in Korea. Its dimensions were 29m in length, 9m in width and 0.65m in depth. A bottom layer of 45cm was filled with crushed granites (15~40mm in diameter) and a middle layer of 10cm had pea pebbles. An upper layer of 5cm contained coarse sands. Reeds (Phragmites australis) growing in natural wetlands were transplanted on its surface. Water of the stream was channelled into the wetland by gravity flow and its effluent was discharged back into the stream. Average Litter layer of 12.2cm was formed on its surface in 2007. The layer and above-ground parts of reeds were eliminated in April 2008. Volumes and water quality of influent and effluent of the wetland were analyzed from May to November in 2007 and 2008, respectively. Inflow into the wetland both in 2007 and 2008 averaged approximately 40$m^3$/day and hydraulic residence time both in 2007 and 2008 was about 1.5days. Influent TN concentration in 2007 and 2008 averaged 3.96 and 3.89mg/L, respectively and average influent ${NO_3}^-$-N concentration in 2007 and 2008 was 2.11 and 2.05mg/L, respectively. With a 0.05 significance level, influent concentrations of TN and ${NO_3}^-$-N, temperatures and pH of effluent, and heights and stem numbers of reeds showed no difference between the wetland with litter layer and without one. TN retention in the wetland with litter layer and without one averaged 64,76 and 54.69%, respectively and ${NO_3}^-$-N removal averaged 60.83 and 50.61%, respectively. Both TN and ${NO_3}^-$-N abatement rates in the wetland with litter layer were significantly high (TN abatement: p<0,001, ${NO_3}^-$-N abatement: p=0.001) when compared with those without one. The subsurface-flow wetland having litter layer on its surface was more efficient for TN and ${NO_3}^-$-N removal.

• Journal of Broadcast Engineering
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• v.3 no.2
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• pp.118-126
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• 1998

In order to fedice the computational complexity of the motion estimation for the spatio-temporal prediction of the higher layer, two estimation method are proposed. In the first one, the motion vector of the higher layer is estimated within the small search range by using the previously estimated motion vector in the lower layer as an innitial vector. Inthe second one, the notion vector is estimated by the spatio-temporally weighted search, which is combined with the previously estimated motion vector of the lower layer and the weight for spatial prediction. Simulation results show that the proposed methods give the smaller computational complexity without the degradation of the coding efficiency than the conventinal one.

• Journal of KSNVE
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• v.5 no.3
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• pp.313-325
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• 1995

Two active/passive vibration dampers were designed to control a cantilever beam first mode of vibration. The active element was a piezoelectric polymer, polyvinlidene fluoride (PVDF). The passive damping was provided by the application of a viscoelastic layer on the surface of the steel beam. Two substantially different damper configurations were designed and tested. One damper consisted of a piezoelectric actuator bonded to one face of the beam, with a viscoelastic layer applied to the other surface of the beam. The second one was composed of a layer viscoeastic layer with one surface bonded to the beam, and with other being constrained by nine piezoelectric actuators connected in parallel. A control law based on the sign of the angular velocity of the cantilever beam was implemented to control the beam first mode of vibration. The piezoelectric sensor output was digitally differentiated to obtain the transverse linear velocity, and its sign was used in the control algorith. Two dampers provided the system a damping increase of a factor of four for the first damper and three for the second damper. Both dampers were found to work well at low levels of vibration, suggesting that they can be used effectively to prevent resonant vibrations in flexible structure from initiating and building up.

• Journal of Sensor Science and Technology
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• v.17 no.5
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• pp.329-337
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• 2008

Simple, small and portable oxygen sensors were fabricated by tape casting technique. Yttria stabilized zirconia containing cordierite ceramics (YSZC) were used as a porous diffused layer of oxygen in pumping cell. Yttria stabilized zirconia (YSZ) solid electrolyte, YSZC porous diffusion layer and heater-patterned ceramic sheets were prepared by co- firing method. Limit current characteristics and the linear relationship of current to oxygen concentration were observed. Viscosity variation of the slurries both YSZ and YSZC showed a similar behavior, but micro pores in the fired sheet were increased with increasing of the cordierite amount. Molecular diffusion was dominated due to the formation of large pores in porous diffusion layer. The plateau range of limit current in porous-type oxygen sensor was narrow than the one of aperture-type oxygen sensor. However limit current curve was appeared in porous-type oxygen sensor even at the lower applied voltage. The plateau range of limit-current was widen as increasing the thickness of porous diffusion layer of the YSZ containing cordierite. Measuring temperature of $600{\sim}650^{\circ}C$ was recommended for limit-current oxygen sensor. Porous diffusion layer-type oxygen sensor showed faster response than the aperture-type one and was stable up to 30 days running without any crack at interface between the layers.

• Transactions on Electrical and Electronic Materials
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• v.13 no.1
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• pp.27-30
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• 2012

This paper proposes a micro gas sensor for measuring $H_2S$ gas. This is based on a $SnO_2$-CuO multi-layer thin film. The sensor has a silicon diaphragm, micro heater, and sensing layers. The micro heater is embedded in the sensing layer in order to increase the temperature to an operating temperature. The $SnO_2$-CuO multi layer film is prepared by the alternating deposition method and thermal oxidation which uses an electron beam evaporator and a thermal furnace. To determine the effect of the number of layers, five sets of films are prepared, each with different number of layers. The sensitivities are measured by applying $H_2S$ gas. It has a concentration of 1 ppm at an operating temperature of $270^{\circ}C$. At the same total thickness, the sensitivity of the sensor with multi sensing layers was improved, compared to the sensor with one sensing layer. The sensitivity of the sensor with five layers to 1 ppm of $H_2S$ gas is approximately 68%. This is approximately 12% more than that of a sensor with one-layer.

• Computers and Concrete
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• v.27 no.5
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• pp.417-435
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• 2021

The optimal distribution of steel fibers over different layers of concrete can be considered as an appropriate method in improving the structural performance and reducing the cost of fiber-reinforced concrete members. In addition, the use of waste tire rubber in concrete mixes, as one of the practical ways to address environmental problems, is highly significant. Thus, this study aimed to evaluate the flexural behavior of functionally graded steel fiber-reinforced concrete containing recycled tire crumb rubber, as a volume replacement of sand, after exposure to elevated temperatures. Little information is available in the literature regarding this subject. To achieve this goal, a set of 54 one-, two-, and three-layer concrete beam specimens with different fiber volume fractions (0, 0.25, 0.5, 1, and 1.25%), but the same overall fiber content, and different volume percentages of the waste tire rubber (0, 5, and 10%) were exposed to different temperatures (23, 300, and 600℃). Afterward, the parameters affecting the post-heating flexural performance of concrete, including flexural strength and stiffness, toughness, fracture energy, and load-deflection diagrams, along with the compressive strength and weight loss of concrete specimens, were evaluated. The results indicated that the flexural strength and stiffness of the three-layer concrete beams respectively increased by 10 and 7%, compared to the one-layer beam specimens with the same fiber content. However, the flexural performance of the two-layer beams was reduced relative to those with one layer and equal fiber content. Besides, the flexural strength, toughness, fracture energy, and stiffness were reduced by approximately 10% when a 10% of natural sand was replaced with tire rubber in the three-layer specimens compared to the corresponding beams without crumb rubber. Although the flexural properties of concrete specimens increased with increasing the temperature up to 300℃, these properties degraded significantly with elevating the temperature up to 600℃, leading to a sharp increase in the deflection at peak load.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.452-455
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• 2000

Superconducting power cable is one of the most promising energy application of high-T$_{c}$ superconductors (HTS). A prototype HTS cable have been constructed multi-layer cable using Bi-2223 tape and tested. The AC transport losses under self field were investigated at 77K on the 19 filamentary tape and multi-layer HTS cables. And we carried out numerical analysis using bean model. The result shows that the total transport current of HTS cable in L$N_2$ was 475[A], and transport current passed through almost the outer layer (2-layer). Also, AC transport losses in outer layer of HTS cable was proportion to I$^2$ and higher than losses of inner layer. In case of Ip=Ic, calculated numerical loss density was concentrated on the edge of tape and most of loss density in cable was distributed outer layer more than inner layer. As magnetic distribution was concentrated on outer layer.r.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1931-1934
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• 2006

The accuracy impact of using high-order Boussinesq-type model as compared to the typical order model is examined in this paper. The multi-layer model developed by Lynett and Liu(2004a) is used for simulating of wave breaking over a step region. The overall comparisons between the two-layer model and the hydraulic experiments are quite good. The one-layer model overshoals the wave near the breakpoint, while the two-layer model shoals at a rate more consistent with the experimental data.

• 제어로봇시스템학회:학술대회논문집
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• 1991.10a
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• pp.337-341
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• 1991

Fieldbus is a low level serial digital network which will be used for factory automation. This paper describes lower layer implementation of a Fieldbus network interface. Physical layer provides hardware interface between IBM-PC and Fieldbus. Also, physical layer uses manchester coding, shielded twisted pair lines and RS-485 electrical standard. Data link layer includes Intel's iDCX96 real time executive for 8797 one chip microcontroller and Fieldbus data link protocol software.