• Korean Journal of Fisheries and Aquatic Sciences
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• v.12 no.1
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• pp.1-6
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• 1979

본연구에서는 그물어구의 상사를 지배하는 무차원수 K를 $$K=\frac{{\nu}^n\rho_wv^{2-n}}{{d^{1+n}(\rho-\rho_w)}$$ d, p: 재료의 직경 및 밀도 $\nu,\rho_w,v$: 물의 동점성계수, 밀도 및 속도으로 정하고, 여기에서의 직경의 비를 결정하는 방법에 따라 실물과 모형과의 상사를 완전하게 그리고 근사적으로 만족시키는 조건들을 구하였다. 즉, 원전한 상사한 경우는 직경의 비를 축척비와 같게 하고, 나아가서 다른 모든 치수의 비도 축척비와 같게 함으로써 만족된다고 하였으며, 측사적 상사의 경우느 직경의 비가 축척비 $(\frac{\lambda_2}{\lambda_1})$와 같지 않아도 된다고 하여, 그물실의 직경 d, 코의 크기 $\iota$ 및 콧수 N의 비를 $$\frac{d_2}{d_1}=\frac{\iota_2}{\iota_1}=\frac{\lambda_2}{\lambda_1}{\cdot}\frac{N_1}{N_2}$$ 으로, 줄의 직경 d', 길이 $\iota'$ 및 밀도 $\rho'$의 비를 $$\frac{d_2'}{d_1'}=\sqrt{{\frac{\lambda_2}{\lambda_1}}\cdot{\frac{d_2}{d_1}}\cdot{\frac{\rho_2-\rho_{w2}}{\rho_1-\rho_{w1}}\cdot{\frac{\rho_1'-\rho_{w1}}{\rho_2'-\rho_{w2}}}}$$, $\frac{\iota_2'}{\iota_1'}=\frac{\lambda_2}{\lambda_1}$로, 부속구의 치경 $d'$, 밀도 $\rho'$ 및 수 $N'$의 비를 $$\frac{N_2'}{N_1'}=(\frac{\lambda_2}{\lambda_1})^2(\frac{d_2}{d_1})(\frac{d_1'}{d_2'})\frac{(\rho_2-\rho_{w2})}{(\rho_1-\rho_{w1})}\frac{(\rho_1'-\rho_{w1})}{(\rho_2'-\rho_{w2})}$$으로 정하였다. 이렇게 정해진 모형어구에 대해 유속 v의 비느 $K_1=K_2$로부터 $$(\frac{u_2}{u_1})^{2-n}=(\frac{\nu_2}{\nu_1})^{-n}\;(\frac{\rho_{w1}}{\rho_{w2}})\;(\frac{\rho_2-\rho_{w2}}{\rho_1-\rho_{w1}})\;(\frac{d_2}{d_1})^{1+n}$$으로 주어지므로, 이를 이용하여 어구저항 D 및 그물감의 다리에서의 장력 $\tau$의 비를 $$\frac{D_2}{D_1}=\frac{d_2(\rho_2-\rho_{w2})}{d_1(\rho_1-\rho_{w1})}(\frac{\lambda_2}{\lambda_1})^2$$ $${\frac{\tau_2}{\tau_1}=\frac{d_2\iota_2(\rho_2-\rho_{w2})}{d_1\iota_1(\rho_1-\rho_{w1})}\;{\cdot}\frac{\lambda_2}{\lambda_1}$$로 정하였다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.1
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• pp.644-653
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• 2018

Landslides occur frequently due to the effects of heavy rainfall and typhoons caused by climate change. Erosion control measures are needed to effectively prevent landslide damage. In order to improve their efficiency, it is necessary to quantitatively measure the sediment discharge from the mountain stream. In this study, a load cell sensor was installed in a mountain stream and the measured values were compared according to the applicability and load test type in the mountain stream. The result of the load test showed that the effect of the loading type (load test 1, 2) was low at average (loadings) of 0.4kgf and 0.6kgf at sites 1 and 2, respectively. The load factor was also derived by regression analysis to increase the accuracy of the measured values. According to the results of the load factor (normalized) to the load-cell measurement value, the output value increased by 14.8% and 24.6% in sites 1 and 2, respectively, and was calculated to be similar to the reference value. The load cell sensor enabled us to quantitatively estimate the amount of sediment discharge in the mountain stream through time series analysis with the water level and rainfall information. If the monitoring is carried out for a long time, it can be used to find the sediment discharge mechanism for the mountain stream. In addition, applying sensors such as load-cells to a mountain stream is expected to contribute to the development of related industries, such as the manufacturing of measurement sensors.

• Journal of Korean Ophthalmic Optics Society
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• v.19 no.3
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• pp.285-293
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• 2014

Purpose: In order to find suitable size of soft contact lens for different ages group of elementary student to adults, visible iris diameter(horizontal, vertical) and palpebral aperture size were measured. Methods: Visible iris diameter (horizontal, vertical) and palpebral aperture size were measured in different age groups of total 514 subjects (1028 eyes) who have no eye disease and none history of surgery included cosmetic purpose. Results: No significant difference was found in iris diameter of both horizontal and vertical direction for different groups of age and sex but horizontal direction of palpebral aperture size in middle school students and university students groups and vertical direction of palpebral aperture size in high school student group shows significant difference (p<0.05) by sex. Horizontal visible iris diameter, vertical visible iris diameter, horizontal palpebral aperture size and vertical palpebral aperture size shows significant difference in difference age and sex. Conclusions: Visible iris diameter and palpebral aperture size are affective factor for soft contact lens diameter decision, especially it should considered more intensive for removing uncomfortable feeling of lens wearer.

• Current Research on Agriculture and Life Sciences
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• v.9
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• pp.87-94
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• 1991

An approximate analytical method to predict performance characteristics of the stirling engines in a preliminary design stage was investigated. In basic equations proposed by walker, typical temperatures of working fluids in expansion and compression spaces were treated the same as those of working fluids in heater and cooler respectively. While the temperature of working fluids in the expansion space was actually lower than that of working fluids in the heater, the temperature of working fluids in the compression space was higher than that of working fluids in the cooler. The aim of this study divided typical temperatures of working fluids in expansion and compression spaces into serval grades, and than evaluated the experimental engine. As the result, the case which working fluids temperature of expansion space was treated as lower than the heater temperature and which that of compression space was treated as higher than the cooler temperature, was much closer to the experimental value.

• Journal of KIISE
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• v.42 no.2
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• pp.242-254
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• 2015

In this paper, we address the problem of improving the performance of multi-step k-NN search using multi-dimensional indexes. Due to information loss by lower-dimensional transformations, existing multi-step k-NN search solutions produce a large tolerance (i.e., a large search range), and thus, incur a large number of candidates, which are retrieved by a range query. Those many candidates lead to overwhelming I/O and CPU overheads in the postprocessing step. To overcome this problem, we propose two efficient solutions that improve the search performance by reducing the tolerance of a range query, and accordingly, reducing the number of candidates. First, we propose a tolerance reduction-based (approximate) solution that forcibly decreases the tolerance, which is determined by a k-NN query on the index, by the average ratio of high- and low-dimensional distances. Second, we propose a coefficient control-based (exact) solution that uses c k instead of k in a k-NN query to obtain a tigher tolerance and performs a range query using this tigher tolerance. Experimental results show that the proposed solutions significantly reduce the number of candidates, and accordingly, improve the search performance in comparison with the existing multi-step k-NN solution.

• Journal of Korean Society of Steel Construction
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• v.27 no.1
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• pp.31-42
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• 2015

The plastic stress distribution method and the strain compatibility method are the two representative methods to calculate the P-M interaction strength of RCFT (rectangular concrete filled tube) columns. The plastic stress distribution method is approximate while the stress compatibility method should approach the exact solution if accurate constitutive relations of the materials involved are used. Recent study by the authors pointed out that, because of lack of accurate constitutive model for the concrete confined by the rectangular steel tube, no strain compatibility method according to the current structural provisions provides a satisfactory prediction of the P-M interaction strength of RCFT columns under various material combinations. An empirical constitutive model which can capture the stress-strain characteristics of the confined concrete of RCFT columns is proposed based on analyzing extensive exisitng test database. The key idea was to define the concrete crushing strain as a function of steel-to-concrete strength ratio and width-to-thickness ratio of steel tube. It was shown that the proposed model leads to more accurate and more consistent prediction of the P-M interaction strength of RCFT columns under general design conditions.

• Journal of the Korean Magnetics Society
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• v.18 no.5
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• pp.163-167
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• 2008

The electronic structure and magnetism of superlattice systems consisted of Heusler compound $Co_2MnSi$ (CMS) and zinc-blende MnAs (MA) are investigated by means of the all-electron full potential linearized augmented plane wave method within the generalized gradient approximation. Four superlattice systems are considered, that is CMS(m)/MA(n), where m and n, being either 2 or 4, denote the number of alternatingly arrayed layers of the compounds in a superlattice along [001] direction. From the calculated total magnetic moments as well as the total density of states, it is found that neither of the four systems is half-metallic. It is also found that the Mn atoms are antiferromagnetically coupled in the systems of CMS2/MA2 and CMS2/MA4. The total and atom-resolved density of states of the four superlattices are compared with those of the bulk $Co_2MnSi$ and MnAs, and the influences of the change in the systems symmetry on the magnetism and half-metallicity are discussed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.3
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• pp.269-281
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• 2014

In this paper, a systematic design of a low phase noise voltage-tuned dielectric resonator oscillator(VTDRO) using loop group delay is proposed. Designed VTDRO is closed-loop type and consists of a cascade connection of a resonator, phase shifter, and amplifier. Firstly, a reference VTDRO is fabricated and its phase noise and electrical frequency tuning range are measured. Both the phase noise and electrical frequency tuning range depend on the loop group delay. Then, a required value of loop group delay for a new VTDRO with a low phase noise can be systematically computed. In addition, its phase noise and electrical frequency tuning range can be theoretically estimated using those obtained from the measurement of the reference VTDRO. When the loop group delay increases, the phase noise decreases and the electrical frequency tuning range also decreases. The former predominantly depends on the resonator structure. Therefore we propose a systematic design procedure of a resonator with high group delay characteristics. The measured loop group delay of the new VTDRO is about 700 nsec. The measured phase noise of the new VTDRO show a state-of-the-art performance of 154.5 dBc/Hz at 100 kHz frequency offset and electrical frequency tuning range of 448 kHz for a voltage change of 0~10V. The oscillation power is about 4.39 dBm.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.26 no.6
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• pp.225-231
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• 2016

The valence band maximum (VBM) and conduction band minimum (CBM) of Al-doped GaInAsSb alloys substrated on GaSb are calculated by using an analytic approximation based on the tight binding method. The relative positions of the VBM and CBM between Al-GaInASSb and GaSb determine band alignement type, valence band offset (VBO) and conductin band offset (CBO) for the heterojunctions. In this study, aluminium doping is assumed to be substituted in the cation site and limited up to 20 % because it can easily oxidize and degrade materials. It is found that the Al-doped alloys exhibit type-II band alignments over the entire composition range and make the band gaps increase, whereas the VBO and CBO decrease. The decreasing rate of VBO is higher than that of CBO, which implies the Al components play a decisive role in controlling electrons at the interface. The Al-dopled GaInAsSb alloy has a direct band gap induced by $E({\Gamma})$ with a considerable distance from the E(L) and E(X), however, $E({\Gamma})$ approaches to E(L) and E(X) in the high Sb concentration (Sb > 0.7-0.8) which might affect the electron mobility and degrade the optical quality.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.6
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• pp.691-699
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• 2012

In this paper, we present a Vt-DRO with a low phase noise, which is achieved by improving the coupling structure between the dielectric resonator and microstrip line. The Vt-DRO is a closed-loop type and is composed of 3 blocks; dielectric resonator, phase shifter, and amplifier. We propose a mathematical estimation method of phase noise, using the group delay of the resonator. By modifying the coupling structure between the dielectric resonator and microstrip line, we achieved a group delay of 53 nsec. For convenience of measurement, wafer probes were inserted at each stage to measure the S-parameters of each block. The measured S-parameter of the Vt-DRO satisfies the open-loop oscillation condition. The Vt-DRO was implemented by connecting the input and output of the designed open-loop to form a closed-loop. As a result, the phase noise of the Vt-DRO was measured as -132.7 dBc/Hz(@ 100 kHz offset frequency), which approximates the predicted result at the center frequency of 5.3 GHz. The tuning-range of the Vt-DRO is about 5 MHz for tuning voltage of 0~10 V and the power is 4.5 dBm. PFTN-FOM is -31 dBm.