• Korean Journal of Materials Research
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• v.27 no.12
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• pp.705-709
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• 2017

The electronic and optical characteristics of molybdenum disulphide ($MoS_2$) film significantly vary with its thickness, and thus a rapid and accurate estimation of the number of $MoS_2$ layers is critical in practical applications as well as in basic researches. Various existing methods are currently available for the thickness measurement, but each has drawbacks. Transmission electron microscopy allows actual counting of the $MoS_2$ layers, but is very complicated and requires destructive processing of the sample to the point where it will no longer be useable after characterization. Atomic force microscopy, particularly when operated in the tapping mode, is likewise time-consuming and suffers from certain anomalies caused by an improperly chosen set point, that is, free amplitude in air for the cantilever. Raman spectroscopy is a quick characterization method for identifying one to a few layers, but the laser irradiation causes structural degradation of the $MoS_2$. Optical microscopy works only when $MoS_2$ is on a silicon substrate covered with $SiO_2$ of 100~300 nm thickness. The last two optical methods are commonly limited in resolution to the micrometer range due to the diffraction limits of light. We report here a method of measuring the distribution of the number of $MoS_2$ layers using a low voltage field emission electron microscope with acceleration voltages no greater than 1 kV. We found a linear relationship between the FESEM contrast and the number of $MoS_2$ layers. This method can be used to characterize $MoS_2$ samples at nanometer-level spatial resolution, which is below the limits of other methods.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.9
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• pp.101-110
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• 1998

In process planning for 3D pocket machining, the critical issues for the optimal process planning are the generation of cutting layers and the tool selection for each cutting layers as well as the other factors such as the determination of machining types, tool path, etc. This paper describes the optimal tool selection on a single cutting layer for 2D pocket machining, the generation of cutting layers for 3D pocket machining, the determination of the thickness of each cutting layers, the determination of the tool combinations for each cutting layers and also the development of an algorithm for determining the machining sequence which reduces the number of tool exchanges, which are based on the backward approach. The branch and bound method is applied to select the optimal tools for each cutting layer, and an algorithmic procedure is developed to determine the machining sequence consisting of the pairs of the cutting layers and cutting tools to be used in the same operation.

• Geomechanics and Engineering
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• v.12 no.2
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• pp.327-346
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• 2017

Laminated plates have many applications in different industrials. Buckling analysis of these structures with the nano-scale reinforcement has not investigated yet. However, buckling analysis of embedded laminated plates with nanocomposite layers is studied in this paper. Considering the single-walled carbon nanotubes (SWCNTs) as reinforcement of layers, SWCNTs agglomeration effects and nonlinear analysis using numerical method are the main contributions of this paper. Mori-Tanaka model is applied for obtaining the equivalent material properties of structure and considering agglomeration effects. The elastic medium is simulated by spring and shear constants. Based on first order shear deformation theory (FSDT), the governing equations are derived based on energy method and Hamilton's principle. Differential quadrature method (DQM) is used for calculating the buckling load of system. The effects of different parameters such as the volume percent of SWCNTs, SWCNTs agglomeration, number of layers, orientation angle of layers, elastic medium, boundary conditions and axial mode number of plate on the buckling of the structure are shown. Results indicate that increasing volume percent of SWCNTs increases the buckling load of the plate. Furthermore, considering agglomeration effects decreases the buckling load of system. In addition, it is found that the present results have good agreement with other works.

• Journal of Environmental Science International
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• v.13 no.7
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• pp.611-618
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• 2004

The Neural Network Models which mathematically interpret human thought processes were applied to resolve the uncertainty of model parameters and to increase the model's output for the streamflow forecast model. In order to test and verify the flood discharge forecast model eight flood events observed at Kumho station located on the midstream of Kumho river were chosen. Six events of them were used as test data and two events for verification. In order to make an analysis the Levengerg-Marquart method was used to estimate the best parameter for the Neural Network model. The structure of the model was composed of five types of models by varying the number of hidden layers and the number of nodes of hidden layers. Moreover, a logarithmic-sigmoid varying function was used in first and second hidden layers, and a linear function was used for the output. As a result of applying Neural Networks models for the five models, the N10-6model was considered suitable when there is one hidden layer, and the Nl0-9-5model when there are two hidden layers. In addition, when all the Neural Network models were reviewed, the Nl0-9-5model, which has two hidden layers, gave the most preferable results in an actual hydro-event.

• 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.

• Journal of Biosystems Engineering
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• v.42 no.3
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• pp.136-146
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• 2017

Purpose: This paper presents an appropriate wrapping method by analyzing the pressure distribution applied to a bale surface, along with the change in pressure according to an increase in the number of film layers in rice straw bales, which account for 74% of the total bulky feed supply in Korea. Methods: A model with the shape of an actual bale was fabricated to analyze the distribution of surface pressure in bale wrapping, and the pressure was measured. Experiments were conducted to analyze the pressure using eight different layer numbers (2, 4, 6, 8 10, 12, 14, and 16 layers) at five wrapping speeds (27, 29, 31, 33, and 35 rpm). Results: The maximum pressure applied to a circular bale by the film occurred at the center of the end of the bale, whereas the minimum pressure occurred at the center of the bale side. An extreme value ratio between the minimum and maximum pressures was distributed as 8.5-56.6%, which was improved with an increase in rotation speed. The an uneven pressure distribution occurred because the number of film overlaps was 8.24-times greater at the center of the bale's end than at the center of the ba le side. At a level 5 rotation speed, the minimum pressure was $P_{LV5-M1}=0.0625{\sigma}^2+36.173{\sigma}-36.753$ ($R^2=0.9845$) at $M_1$, and the maximum pressure was $P_{LV5-M6}=5.5552{\sigma}^2+41.05{\sigma}-39.071$ at $M_2$, revealing a correlation of $R^2=0.9983$. Conclusions: To replace four layers with six layers, 2-4 layers were added only to the side of the bale, and the minimum pressure at $M_1$ was then improved from that at four layers to that at six layers, and the amount of film consumed for 4-6 layers was reduced by 84.6%.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.5
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• pp.737-748
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• 1995

In this paper, we studyed the variables in the design of multichip memory modules with 4M$\times$1bit DRAM chips to construct high capacity and high speed memory modules. The configuration of the module was 8 bit, 16 bit, and 32 bit DRAM modules with employing 0.6 W, 70 nsec 4M$\times$1 bit DRAM chips. We optimized routing area and wiring density by performing the routing experiment with the variables of the chip allocation, module I/O terminal, the number of wiring, and the number of mounting side of the chips. The multichip module was designed to be able to accept MCM-L techiques and low cost PCB materials. The module routing experiment showed that it was an efficient way to align chip I/O terminals and module I/O terminals in parallel when mounting bare chips, and in perpendicular when mounting packaged chips, to set module I/O terminals in two sides, to use double sided substrates, and to allocate chips in a row. The efficient number of wiring layer was 4 layers when designing single sided bare chip mounting modules and 6 layers when constructing double sided bare chip mounting modules whereas the number of wiring layer was 3 layers when using single sided packaged chip mounting substrates and 5 layers when constructing double sided packaged chip mounting substrates. The most efficient configuration was to mount bare chips on doubled substrates and also to increase the number of mounting chips. The fabrication of memory multichip module showed that the modules with bare chips can be reduced to a half in volume and one third in weight comparing to the module with packaged chips. The signal propagation delay time on module substrate was reduced to 0.5-1 nsec.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.29A no.3
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• pp.41-46
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• 1992

In this paper we report how to design integrated-mirror etalons for surface-emitting lasers and photonic switching without time-consuming numerical calculation. It consists of the following two-step process (step 1) find the minimum reflectance to achieve the maximum allowable linewidth. (step 2) find the number of the quarter-wave layers in each mirror to realize the reflectance given by step 1. The condition for maximum transmission in an integrated- mirror etalon is also derived. Under this condition we can achieve the required linewidth with the minimum number of quarterwave layers.

• Steel and Composite Structures
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• v.28 no.4
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• pp.495-508
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• 2018

In this paper, the effect of matrix cracks on the buckling of a hybrid laminated plate is investigated. The plate is composed of carbon nanotube reinforced functionally graded (CNTR-FG) layers and conventional fiber reinforced composite (FRC) layers. Different distributions of single walled carbon nanotubes (SWCNTs) through the thickness of layers are considered. The cracks are modeled as aligned slit cracks across the ply thickness and transverse to the laminate plane, and the distribution of cracks is assumed statistically homogeneous corresponding to an average crack density. The first-order shear deformation theory (FSDT) is employed to incorporate the effects of rotary inertia and transverse shear deformation, and the meshless kp-Ritz method is used to obtain the buckling solutions. Detailed parametric studies are conducted to investigate the effects of matrix crack density, CNTs distributions, CNT volume fraction, plate aspect ratio and plate length-to-thickness ratio, boundary conditions and number of layers on buckling behaviors of hybrid laminated plates containing CNTR-FG layers.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.7
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• pp.486-489
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• 2018

Solution-processed organic light-emitting diodes (OLEDs) have the advantages of low cost, fast fabrication, and large-area devices. However, most studies on solution-processed OLEDs have mainly focused on solution-processable hole transporting materials or emissive materials. Here, we report fully solution-processed green OLEDs including hole/electron transport layers and emissive layers. The electrical and optical properties of OLEDs based on solution-processed TPBi (2,2',2"-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)) as the electron transport layer were investigated with respect to the spin speed and the number of layers. The performance of OLEDs with solution-processed TPBi exhibits a power efficiency of 9.4 lm/W. We believe that the solution-processed electron transport layers can contribute to the development of efficient fully solution-processed multilayered OLEDs.