• ETRI Journal
• /
• v.21 no.1
• /
• pp.1-27
• /
• 1999

We present a new description of envelope-function equation of the superlattice (SL). The SL wave function and corresponding effective-mass equation are formulated in terms of a linear combination of Bloch states of the constituent material with smaller band gap. In this envelope-function formalism, we review the fundamental concept on the motion of a wave packet in the SL structure subjected to steady and uniform electric fields F. The review confirms that the average of SL crystal momentums K = ($k_x,k_y,q$), where ($K_x,k_y$) are bulk inplane wave vectors and q SL wave vector, included in a wave packet satisfies the equation of motion = $_0+Ft/h$; and that the velocity and acceleration theorems provide the same type of group velocity and definition of the effective mass tensor, respectively, as in the Bulk. Finally, Schlosser and Marcus's method for the band theory of metals has been by Altarelli to include the interface-matching condition in the variational calculation for the SL structure in the multi-band envelope-function approximation. We re-examine this procedure more thoroughly and present variational equations in both general and reduced forms for SLs, which agrees in form with the proposed envelope-function formalism. As an illustration of the application of the present work and also for a brief investigation of effects of band-parameter difference on the subband energy structure, we calculate by the proposed variational method energies of non-strained $GaAs/Al_{0.32}Ga_{0.68}As$ and strained $In_{0.63}Ga_{0.37}As/In_{0.73}Ga_{0.27}As_{0.58}P_{0.42}SLs$ with well/barrier widths of $60{\AA}/500{\AA}$ and 30${\AA}/30{\AA}$, respectively.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.11A
• /
• pp.918-923
• /
• 2009

In this paper, a design method of the compact narrow band filter on the microstrip board is proposed using complementary split-ring resonators(CSRRs). The design technique of this filter is based on cascading filter stages consisting of the combination of circular CSRRs, capacitive gaps between patches, and inductive grounded stubs with the meander configuration. By these means, it was possible to get the nearly symmetric frequency responses, adjustable bandwidths, compact sizes. And also excellent characteristic of the out-of-band rejection is achieved in contrast to the conventional filter design technique. The measured insertion shows good results about -4.0dB at the center frequency($f_0=1GHz$) and passband return loss is less than -9.4dB. The 3dB fractional bandwidth(FBW) is approximately 4%. The results of the frequency response measured on the fabricated band pass filter substrate show satisfactory agreement with the simulated frequency responses by the HFSS in the region of interest.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.7 no.2
• /
• pp.85-92
• /
• 1989

The aim of this study is to find out the combination of effective transformed data, applying Remote Sensing techniques, as to the classification and particular objects by transforming the MSS data and TM data of the satellite LANDSAT into several linearly transformed data. Since one of the problems in the processing of the LANDSAT data is the vastness of the data, the Linear Transformation could be a method to perform analysis of those vast data, more efficiently and economically. This method is carried out as follows : (1) offering the simplicity over complex data, (2) selectional processing over redundant data and removing unnecessary data, (3) emphasizing on the object of the study ; by transforming multispectral data through linear calculation and statistical transformation. In this study, the analysis and transformation of the data have been performed by means of Band Ratioing and Principal Component Analysis. As the classificatory consequence, Infrared/RED Ratioing which expands the characterization of green vegetation, has been useful for a distinctive classification among other classes. For the Principal Component Analysis, band 1,2,7 are efficient in the classification of the green vegetation.

• Journal of the Optical Society of Korea
• /
• v.18 no.3
• /
• pp.244-250
• /
• 2014

Due to the difficulty in measuring very low out-of-band cutoff depths of solar blind UV filters, we propose a cutoff depth adjustable measurement system (CDAM) to test deep cutoff filters with a large dynamic range. The CDAM utilizing the substitution method is elaborately composed of several parts, including narrow-band LED light sources, standard reflective neutral attenuators with known attenuation coefficients, and a photomultiplier (PMT). This paper also presents an attenuator combination method ensuring that the PMT works within its linear response range. In addition, numerical simulation testifies to the method, and experiment shows that the CDAM system can achieve an extension of dynamic range from 0-6 OD to 0-10 OD, which is sufficient for the measurement of out-of-band cutoff depths of solar blind UV filters. Above all, the CDAM system, being easily implemented, of wide dynamic range, and highly precise, could be widely used in the measurement of filter cutoff depth.

• Journal of Korea Water Resources Association
• /
• v.54 no.2
• /
• pp.121-133
• /
• 2021

Suspended Solids (SS) generated in rivers are mainly introduced from non-point pollutants or appear naturally in the water body, and are an important water quality factor that may cause long-term water pollution by being deposited. However, the conventional method of measuring the concentration of suspended solids is labor-intensive, and it is difficult to obtain a vast amount of data via point measurement. Therefore, in this study, a model for measuring the concentration of suspended solids based on remote sensing in the Nakdong River was developed using Sentinel-2 data that provides high-resolution multi-spectral satellite images. The proposed model considers the spectral bands and band ratios of various wavelength bands using a machine learning model, Support Vector Regression (SVR), to overcome the limitation of the existing remote sensing-based regression equations. The optimal combination of variables was derived using the Recursive Feature Elimination (RFE) and weight coefficients for each variable of SVR. The results show that the 705nm band belonging to the red-edge wavelength band was estimated as the most important spectral band, and the proposed SVR model produced the most accurate measurement compared with the previous regression equations. By using the RFE, the SVR model developed in this study reduces the variable dependence compared to the existing regression equations based on the single spectral band or band ratio and provides more accurate prediction of spatial distribution of suspended solids concentration.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.7 no.3
• /
• pp.56-61
• /
• 2008

Recently, although demands for an internal antenna applicable to DVB-H handhold terminals are increased, there are many difficulties in designing the antenna due to the long wavelength of $430{\sim}640mm$ and the wide bandwidth of $470MHz{\sim}702MHz$. Since the proposed DVB-H band antenna can be analyzed as an SDA (Supported structure Defined Antenna), it is designed by combination of the folded monopole radiator which has a wideband characteristics and the wing-type element which can reduce the resonant frequency effectively. The DVB-H band antenna has VSWR of 4 and obtains a good gain from -5 to 2 dBi, when it is built-in the mobile handset.

• International journal of advanced smart convergence
• /
• v.8 no.4
• /
• pp.34-39
• /
• 2019

Millimeter-wave (mmWave) and Non-orthogonal multiple access (NOMA) are expected to be the major techniques that lead to the next generation wireless communication. NOMA provides a high spectrum efficiency by sharing of spatial resources among users in the same frequency band. Meanwhile, millimeter-wave gives a huge underutilized bandwidth at extremely high frequency band (EHF) which covers 30GHz to 300GHz. These techniques have been proven in several recent literatures to achieve high data rates. The combination of NOMA and millimeter-wave techniques further improves average sum capacities, as well as reduces the interference compared to conventional wireless communication systems. In this paper, we focus on hybrid NOMA system working in millimeter-wave frequency. We propose a clustering algorithm used for a hybrid NOMA scheme to optimize the usage of wireless resources. The proposed clustering algorithm adds several conditions in grouping users and defining clusters to increase the probability of the successful superposition decoding process. The performance of the proposed clustering algorithm is investigated in hybrid NOMA system and compared with the conventional orthogonal multiple access (OMA) scheme.

• Journal of the Korean Ceramic Society
• /
• v.53 no.4
• /
• pp.456-462
• /
• 2016

$NaCaGd(MoO_4)_3:Ho^{3+}/Yb^{3+}$ ternary molybdates were successfully synthesized by microwave sol-gel method for the first time. Well-crystallized particles formed after heat-treatment at $900^{\circ}C$ for 16 h showed a fine and homogeneous morphology with particle sizes of $3-5{\mu}m$. Under excitation at 980 nm, the UC intensities of the doped samples exhibited strong yellow emissions based on the combination of strong emission bands at the 520-nm and 630-nm emission bands in the green and red spectral regions, respectively. The strong 520-nm emission band in the green region corresponds to the $^5S_2/^5F_4{\rightarrow}^5I_8$ transition of $Ho^{3+}$ ions, while the strong 630-nm emission band in the red region appears to be due to the $^5F_5{\rightarrow}^5I_8$ transition of the $Ho^{3+}$ ions. The optimal $Yb^{3+}:Ho^{3+}$ ratio was found at 9:1, as indicated by the composition-dependent quenching effect of $Ho^{3+}$ ions. The pump power dependence of the upconversion emission intensity and the Commission Internationale de L'Eclairage chromaticity coordinates of the phosphors were evaluated in detail.

• Fashion & Textile Research Journal
• /
• v.17 no.4
• /
• pp.604-612
• /
• 2015

This study investigates preferred bicycle wear designs that can satisfy active senior consumers. A survey was conducted on 50-60's women who periodically rode bicycles. The results indicated a preference for slim designs and red colors. Jacket designs preferences were for a tight fit for size tolerance, stand collar style, and elastic band details for cuff styles. Pants design preferences were for a whole band waist belt type with a tight fit style such as leggings in pants silhouette, zipper details on the side line and ankle length. They also preferred styles with pads attached to underpants in the pad style and the part of the back waist in the pocket position. The survey showed four kinds of jacket design drawings on an ordinal scale rating. Results indicated a preference for set-in variation jackets with the red and gray color combination. Finally, we demonstrated bicycle wear design suggestions. The jacket applied different armhole line colors connected to the sleeve to make the waist slimmer; in addition, stretchable material helped improve armpit part functionality.

• Transactions on Electrical and Electronic Materials
• /
• v.18 no.6
• /
• pp.364-369
• /
• 2017

Double molybdate $NaGd_{1-x}(MoO_4)_2:Ho^{3+}/Yb^{3+}$ phosphors with proper doping concentrations of $Ho^{3+}$ and $Yb^{3+}$ ($x=Ho^{3+}+Yb^{3+}$, $Ho^{3+}=0$ and 0.05, and $Yb^{3+}=0$, 0.35, 0.40, 0.45, and 0.50) were successfully synthesized using the microwave sol-gel method. Well-crystallized particles formed after heat-treatment at $800^{\circ}C$ for 16 h showed fine and homogeneous morphologies with particle sizes of $1{\sim}3{\mu}m$. The spectroscopic properties were examined using photoluminescence emission and Raman spectroscopy. Under excitation at 980 nm, the upconversion doped samples exhibited strong yellow emissions, from the combination of strong emission bands at 545 nm and 655 nm in the green and red spectral regions, respectively. The strong 545 nm emission band in the green region corresponded to the $^5S_2/^5F_4{\rightarrow}^5I_8$ transition in the $Ho^{3+}$ ions, while the strong 655 nm band in the red region appeared because of the $^5F_5{\rightarrow}^5I_8$ transition in the $Ho^{3+}$ ions. The pump power dependence and the Commission Internationale de L'Eclairage chromaticity of the upconversion emission intensity were evaluated in detail.