• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.44 no.7 s.361
• /
• pp.37-44
• /
• 2007

A low-voltage high-linear bipolar OTA and its application to IF bandpass filter for GSM cellular telephone are presented. The OTA consists of a low-voltage linear transconductor, a translinear current gain cell, and three current mirrors. The bandpass filter is composed of two cascaded identical second-order bandpass filters, which consist of a resistor, a capacitor, and a grounded simulated inductor realized with two OTA's and a grounded capacitor. SPICE simulations using an 8 GHz bipolar transistor-array parameter show that the OTA with a transconductance of 1 mS exhibits a linearity error of less than ${\pm}2%$ over an input voltage range of ${\pm}0.65\;V$ at supply voltages of ${\pm}2.0\;V$. Temperature coefficient of the transconductance is less than $-90ppm/^{\circ}C$. The bandpass filter has a center frequency of 85 MHz and Q-factor of 80. Temperature coefficient of the center frequency is less than $-182ppm/^{\circ}C$. The power dissipation of the filter is 128 mW.

• Journal of Ecology and Environment
• /
• v.44 no.4
• /
• pp.229-240
• /
• 2020

Background: Genus Quercus is a successful group that has occupied the largest area of forest around the world including South Korea. The acorns are an important food source for both wild animals and humans. Although the reproductive characteristics of this genus are highly variable, it had been rarely studied in South Korea. Therefore, in Seoraksan and Odaesan National Parks (i) we measured the acorn production of Quercus mongolica, an overwhelmingly dominant species in South Korea, for 3 years (2017-2019), (ii) evaluated the spatial-temporal variation of acorn production, and (iii) analyzed the effects of oak- and site-related variables on the acorn production. Results: The annual acorn production of Q. mongolica increased 36 times from 1.2 g m-2 in 2017 to 43.2 g m-2 in 2018, and decreased to 16.7 g m-2 in 2019, resulting in an annual coefficient of variation of 104%. The coefficient of spatial variation was high and reached a maximum of 142%, and the tree size was the greatest influencing factor. That is, with an increase in tree size, acorn production increased significantly (2018 F = 16.3, p < 0.001; 2019 F = 8.2, p < 0.01). Elevation and slope also significantly affected the production in 2019. However, since elevation and tree size showed a positive correlation (r = 0.517, p < 0.001), the increase in acorn production with increasing elevation was possibly due to the effect of tree size. The acorn production of Odaesan for 3 years was 2.2 times greater than that of Seoraksan. This was presumed that there are more distribution of thick oak trees and more favorable site conditions such as deep soil A-layer depth, high organic matter, and slower slopes. Conclusion: As reported for other species of the genus Quercus, the acorn production of Q. mongolica showed large spatial and annual variations. The temporal variability was presumed to be a weather-influenced masting, while the spatial variability was mainly caused by oak tree size.

• The Korean Journal of Ecology
• /
• v.25 no.3 s.107
• /
• pp.153-161
• /
• 2002

This study was carried out to classify forest vegetation of the Mt. Naeyeon with phytosociological analysis of ZM school and to explain ordination of communities with CCA. The research sites were located between the northern part of Pohang-si area and the southern part of Yeongdeok-gun area. The 70 plots consisted of 253 species were investigated. The forest vegetation was classified into Quercus mongolica community, Q. variabilis community, Pinus densiflora community, Carpinus laxiflora community and Zelkova serrata community. Q. mongolica community was divided into 2 groups such as Rhododendron schlippenbachii group and Euonymus oxyphyllus group and Q. variabilis community was divided into 3 groups such as Syneilesis palmata group, Lespedeza$\times$tomentilia group and Tilia mandshurica group, and Z. serrata community was divided into 2 groups such as Carpinus cordata group and Diospyros lotus group. According to the results of CCA ordination, Q. mongolica community showed high positive correlation to altitude and topography, whereas it showed negative correlation to bare rock. But Z. serrata community showed the opposite tendency to Q. mongolica community, Altitude was considered as the most important factor among 5 environmental variables in the correlation with axes.

• Journal of Wetlands Research
• /
• v.25 no.2
• /
• pp.159-165
• /
• 2023

This study measured the ecological niche overlap between two deciduous oak species(Quercus acutissmia and Q. dentata) according to the change in growth responses after treating with the moisture and nutrient contents of the soil at four gradients, and interpreted the degree of competition between the two oak species by ordination method. In the moisture environment gradient, the ecological niche overlap of the two species was high in the photosynthesis-related leaf organs and low in plant architecture such as shoot length. In addition, in case of competition between two oaks, Q. dentata was remarkably dominant in soil moisture gradient, but Q. acutissimia slightly was slightly advantageous over Q. dentata in the soil nutrient gradient. These results show that even in a similar taxonomical group growing in a similar habitat, the response to the organ system of the plant varies depending on the type of environment factor, resulting in different competitive differences among plants.

• Journal of the Institute of Electronics Engineers of Korea SC
• /
• v.42 no.1
• /
• pp.23-31
• /
• 2005

Recently, the multimedia and high speed telecommunication systems needs a high frequency and high stability oscillator. The VCXO(voltage controlled -crystal oscillator) have continually downsized to gratify a thin and small size of the telecommunication systems. In his paper, we have developed the small ceramic PECL(positive emitter-coupled logic) VCXO of the 5×7 mm size for gratifying the requested specifications from user, and then use the multilayer ceramic SMD(surface mounted device) package technology. The ceramic SMD PECL VCXO is operating at the 3.3 Voltage and have the frequency range of 120MHz～180MHz. The Q factor is over 5K and it has the low jitter characteristics of 3.5 ps and low phase noise.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.28 no.7
• /
• pp.419-423
• /
• 2015

Sintering, microstructure, thermal conductivity and microwave dielectric properties of xLiF-(1-x)MgO ceramics (x=0.03~0.10 mol) were investigated. The high density was obtained in the specimens of $x{\geq}0.06$, i.e., 0.04 LiF-0.96 MgO in mol, whereas the amount of 0.03 mol LiF was insufficient to densify. From the result that the contact flattening in the sintered specimen was observed, the densification occurred through the liquid-phase sintering. The specimen of x=0.06 showed the highest room-temperature thermal conductivity. Relative density, thermal conductivity, dielectric constant, and quality factor ($Q{\times}f$) of the specimen for x=0.06 sintered at $900^{\circ}C$ for 4 h were 97.8%, $39.2Wm^{-1}K^{-1}$, 9.45, and 14,671 GHz, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.07a
• /
• pp.127-130
• /
• 2002

In this study, development of a new LTCC material using a non-glassy system was attempted with respect to reducing the fabrication process steps and cost down. Lowering the sintering temperature can be achieved by liquid phase sintering. For LTCC application, the starting material must have quality factor as high as possible in microwave frequency range. And also, the material should have a low dielectric constant for enhancing the signal propagation speed. Regarding these factors, dielectric constants of various materials were estimated by the Clausius-Mosotti equation. Among them, CaWO$_4$ was tamed out the suitable LTCC material. CaWO$_4$ can be sintered up to 98% of full density at 1200$^{\circ}C$ for 3 hours. It's measured dielectric constant, quality factor, and temperature coefficient of resonant frequency were 10.15, 62880GHz, and -27.8ppm/$^{\circ}C$, respectively. In order to modify the dielectric properties and densification temperature, 0.5∼1.5 wt% LiF were added to CaWO$_4$. LiF addition reduced the sintering temperature/time down to 800$^{\circ}C$/10∼30min due to the reactive liquid phase sintering. Dielectric constant lowered from 10.15 to 9.38 and Q x fo increased up to 92000GHz with increasing LiF content.

• Wind and Structures
• /
• v.14 no.3
• /
• pp.253-283
• /
• 2011

This paper presents the field measurement results of wind effects on a super-tall building (CITIC Plaza, 391 m high) located in Guangzhou. The field data such as wind speed, wind direction and acceleration responses were simultaneously and continuously recorded from the tall building by a wind and vibration monitoring system during two typhoons. The typhoon-generated wind characteristics including turbulence intensity, gust factor, peak factor, turbulence integral length scale and power spectral density of fluctuating wind speed were presented and discussed. The dynamic characteristics of the tall building were determined based on the field measurements and compared with those calculated from a 3D finite element model of the building. The measured natural frequencies of the two fundamental sway modes of the building were found to be larger than those calculated. The damping ratios of the building were evaluated by the random decrement technique, which demonstrated amplitude-dependent characteristics. The field measured acceleration responses were compared with wind tunnel test results, which were found to be consistent with the model test data. Finally, the serviceability performance of the super-tall building was assessed based on the field measurement results.

• Journal of Environmental Health Sciences
• /
• v.27 no.2
• /
• pp.30-36
• /
• 2001

This review begins with a brief expression of aerosol capture mechanism of fibrous filter(s) and performance of particulate removing respirators. The more complicated and detailed discussion is not included in this articles. Filtration efficiency and pressure drop are introduced as quality factor ( $q_{F}$) and the way in which filtration efficiency varies with particle size is discussed. Quality factors fro filters recently certified in USA were found to be very higher than those of filters made in Korea, China and USA filters certified with old certified standards. Electrically charged filters are widely used because they have high filtration efficiency and low pressure drop, but their efficiency decreases sharply at the condition occurring wet and oil mist. A discussion is given of respirator leakage through face seal and filter media with fit testing and total inward leakage testing. Since fit factor (FF) refers to the reciprocal of the fraction of the total air entering a respirator through face seal leakage , the degree of fitting performance for respirators is expected with FF. Because respirators made in Korea had generally lower FFs than respirators made in USA, it is necessary to develope respirators that fit properly for Koreans or establish regulations for fit testing.g.

• Geomechanics and Engineering
• /
• v.16 no.6
• /
• pp.655-667
• /
• 2018

To evaluate the stability of a rock slope with one pre-exiting vertical crack, this paper performs corresponding probabilistic stability analysis. The existence of cracks is generally ignored in traditional deterministic stability analysis. However, they are widely found in either cohesive soil or rock slopes. The influence of one pre-exiting vertical crack on a rock slope is considered in this study. The safety factor, which is usually adopted to quantity the stability of slopes, is derived through the deterministic computation based on the strength reduction technique. The generalized Hoek-Brown (HB) failure criterion is adopted to characterize the failure of rock masses. Considering high nonlinearity of the limit state function as using nonlinear HB criterion, the multivariate adaptive regression splines (MARS) is used to accurately approximate the implicit limit state function of a rock slope. Then the MARS is integrated with Monte Carlo simulation to implement reliability analysis, and the influences of distribution types, level of uncertainty, and constants on the probability density functions and failure probability are discussed. It is found that distribution types of random variables have little influence on reliability results. The reliability results are affected by a combination of the uncertainty level and the constants. Finally, a reliability-based design figure is provided to evaluate the safety factor of a slope required for a target failure probability.