• Research in Mathematical Education
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• v.9 no.2 s.22
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• pp.153-173
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• 2005

Recently Bianshi problems, math isomorphic problems by changing the conditions, conclusions or deduction process of the three components of the example problem, are consistently identified as an important element in Chinese math education, characteristics in Chinese math education culture and form a hot point in China, 5 main factors related to reasons why is regarded as CULTURE characteristics in Chinese math education are discussed: (a) Exam goal (b) the curriculum objectives (c) traditional mode and conception, (d) Chinese situation, (e) Chinese math tradition.

• Proceedings of the Korean Society of Grassland Science Conference
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• 2005.06a
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• pp.148-149
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• 2005

• Wind and Structures
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• v.27 no.6
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• pp.439-449
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• 2018

Wind loading of a tall building built amidst a group of buildings in urban environment is always greatly affected by shielding effects. Wind tunnel tests were carried out to assess the shielding provided by a row of low-rise or medium-rise buildings upstream a square-section tall building of height-to-breadth ratio 6. Mean and dynamic wind loads on the tall building were measured at different wind incidence angles and presented as interference factors (IFs). It is found that presence of a row of upstream buildings provides significant shielding to the tall building. At normal wind incidence, the mean along-wind loads and all components of fluctuating wind loads on the tall building are always reduced by shielding. Vortex shedding seems to still occur on the upper exposed part of the tall building but the vortex excitation levels are largely reduced. The degree of shielding is found to depend on a number of arrangement parameters of the row of upstream buildings. Empirical equations are proposed to quantify the shielding effect based on the wind tunnel data.

• ETRI Journal
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• v.16 no.4
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• pp.1-11
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• 1995

A GaAs power metal semiconductor field effect transistor (MESFET) operating at a voltage as low as 3.3V has been developed with the best performance for digital handheld phone. The device has been fabricated on an epitaxial layer with a low-high doped structure grown by molecular beam epitaxy. The MESFET, fabricated using $0.8{\mu}m$ design rule, showed a maximum drain current density of 330 mA/mm at $V_{gs}$ =0.5V and a gate-to-drain breakdown volt-age of 28 V. The MESFET tested at a 3.3 V drain bias and a 900 MHz operation frequency displayed an output power of 32.5-dBm and a power added efficiency of 68%. The associate power gain at 20 dBm input power and the linear gain were 12.5dB and 16.5dB, respectively. Two tone testing measured at 900.00MHz and 900.03MHz showed that a third-order intercept point is 49.5 dBm. The power MESFET developed in this work is expected to be useful as a power amplifying device for digital hand-held phone because the high linear gain can deliver a high power added efficiency in the linear operation region of output power and the high third-order intercept point can reduce the third-order intermodulation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.9
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• pp.1335-1341
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• 2003

This paper describes the process of nanoparticle synthesis by laser ablation of microparticles and consolidated sample. We have generated nanoparticles by high-power pulsed laser ablation of AI, Cu and Ag microparticles using a Q-switched Nd:YAG laser (wavelength 355nm, FWHM 6ns, fluence $0.8{\sim}2.0J/cm^2$). Microparticles of mean diameter $18{\sim}80{\mu}m$ are ablated in the ambient air. The generated nanoparticles are collected on a glass substrate and the size distribution and morphology are examined using a scanning electron microscope and a transmission electron microscope. The effect of laser fluence, collector position and compacting pressure on the distribution of particle size is investigated. To better understand the process of laser ablation of microparticle(LAM), we investigated the Nd: YAG laser-induced breakdown of Cu microparticle using time-resolved optical shadow images. Nanosecond time-resolved images of the ablation process are also obtained by laser flash shadowgraphy. Based on the experimental results, discussions are made on the dynamics of ablation plume.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.8B
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• pp.755-761
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• 2004

Currently, Wireless LAN(WLAN) service is widely deployed to provide high speed wireless Internet access through the mobile stations such as notebook and PDA. To provide enhanced security and user access control in the public WLAN area, WLAM access points should have the capability of IEEE 802.1x-based user authentication and authorization functionality. In this paper, we provide a brief understanding of IEEE 802. 1x standards and related protocols likeEAPoL(Extended Authentication Protocol Over LAN), EAP, RADIUS and describe how the IEEE 802.1x is designed and implemented in our embedded linux-based WLAN AP which is named i-WiNG.(Intelligent Wireless Internet Gateway).

• Journal of the Korean Society for Precision Engineering
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• v.11 no.5
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• pp.33-41
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• 1994

For the establishment of large force standard and the accurate measurement of large force, 2MN hydraulic force standard machine which consists of loading frame, deadweight machine, two ram/cylinder systems and hydraulic control system was designed and fabricated. Measurement results of shapes for tow ram/cylinders reveal that the ratio of effective area is 200.094. The relative deviation of force stability for the machine is about .+-. 0.01% at 2MN and is less than .+-. 0.005% below 2MN. This machine may be widely used to calibrate the force measuring devices in industry and to test the force sensors.

• Asian-Australasian Journal of Animal Sciences
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• v.30 no.2
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• pp.198-205
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• 2017

Objective: This study aimed to investigate the effects of single or/and double strains of probiotic supplement on feed efficiency, growth performance, and microbial population in distal gastrointestinal tract (GIT) of weaning rabbits. Methods: Sixty-four weaning (28 days old) New Zealand White rabbits were randomly distributed into four groups with treatments including: basal diet without probiotic supplement (control) or supplemented as follows: $1{\times}10^6cfu/g$ B. subtilis (BS group), $1{\times}10^7cfu/g$ L. acidophilus (LA group), or $0.5{\times}10^6cfu/g$ B. subtilis plus $0.5{\times}10^7cfu/g$ L. acidophilus (BL group). During the research, the male and female rabbits were fed separately. Body weight of the rabbits was recorded at 28, 42, and 70 d of age. Results: There was an increase (p<0.05) in body weight gain for the LA group at 42 d. Rabbits fed BL responsed with a greater growth (p<0.05) and better feed conversion ratio (p<0.05) than those fed with no probiotic. Digestibility coefficients of dry matter, organic matter, crude protein, neutral detergent fiber, and gross energy were higher (p<0.05) in LA and BL groups than those in the control group. Male rabbits had higher (p<0.05) Bacilli spp. and Coliformis spp. in the ileum than female rabbits. Rabbits supplemented with BS had greater (p<0.05) numbers of bacilli in all intestinal segments than those receiving no probiotic, whereas intestinal Lactobacilli populations were greater (p<0.001) in the LA and BL diets compared to control. Average intestinal coliform populations were lowest (p<0.05) in the rabbits supplemented with LA as compared to those fed the control and BS. Conclusion: Supplementation of L. acidophilus alone or in combination with B. subtilis at a half of dose could enhance number of gut beneficial bacteria populations, nutrient digestibility, cecal fermentation, feed efficiency, and growth performance, but rabbits receiving only B. subtilis alone were not different from the controls without probiotic.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.6A
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• pp.697-704
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• 2004

This paper describes the design and fabrication of an MMIC variable gain LNA for 5GHz wireless LAN applications, using 0.5${\mu}{\textrm}{m}$ gate length GaAs MESFET transistors. The advantages of high gain and low noise performance of E-MESFETS and excellent linear performance of D-MESFETS are combined as a cascode topology in this design. Behavioral model equations are derived from the MESFET nonlinear current voltage characteristics by using Turlington's asymptote method in a cascode configuration. Using the behavioral model equations, a 4${\times}$50${\mu}{\textrm}{m}$ E-MESFET as a common source amplifier and a 2${\times}$50${\mu}{\textrm}{m}$ D-MESFET as a common gate amplifier are determined for the cascode amplifier. The fabricated variable gain LNA shows a noise figure of 2.4dB, variable gain range of more than 17dB, IIP3 of -4.8dBm at 4.9GHz, and power consumption of 12.8mW.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.12C
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• pp.1248-1255
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• 2005

We investigate the OFDM-based wireless LAN systems operating in the 60 GHz frequency band as part of the fourth-generation (4G) systems. The 60 GHz band is of much interest since this is the band in which a massive amount of spectral space has been allocated worldwide for dense wireless local communications. This paper gives an overview of 60 GHz bandchannel characteristics and an effect on phase noise. The performance of OFDM system is severely degraded by the local oscillator phase noise, which causes both common phase error and inter-carrier interference. In this paper, we apply phase noise suppression (PNS) algorithm that is easy for implementation to OFDM based 60 GHz wireless LAM system and analyze the SER performance. In case of using the PNS algorithm, SER performance is improved about 6dB, 7.5dB, respectively in 16, 64-QAM.