• Journal of Environmental Health Sciences
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• v.44 no.5
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• pp.480-490
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• 2018

Objective: This study aimed to report the level of extremely low frequency-magnetic field (ELF-MF) emitted by portable hand-held fans (HHF) and to discuss the methodologies for determining the health risk of ELF-MF for HHF products. Method: ELF-MF was monitored at eight locations by distances in the vicinity of HHFs. A total of 13 HHF brands on the market were randomly selected. A portable ELF-MF monitor MDEX II was used to measure the ELF-MF level in the range of 40-800 Hz with a resolution of $0.01{\mu}T$. This study also examined the frequency results of a total of 45 HHF products investigated by the Korean Ministry of Science and ICT (KMSICT). Results: ELF-MF higher than $0.3{\mu}T$ was found to be emitted at a distance of less than 20 cm from 12 HHF. ELF-MF emitted from four products was found to exceed the reference level ($83.3{\mu}T$ based on 60 Hz) recommended by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). KMSIT reported that the principle frequency emitted from the HHFs ranged from 54 Hz to 284 kHz, without the level of LEF-MF. Unscientifically, the KMSICT used the reference level by ICNIRP as the chronic level and concluded that all HHFs are safe with a basis of 1.2-36.0% less than the reference level. Conclusion: The HHF emitted much higher levels of ELF-MF than $0.3-0.4{\mu}T$, which is regarded as the reference level for childhood leukemia. The risk of HHF should be examined in terms of whether they can be used by the general public, including children and pregnant woman.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.1
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• pp.150-155
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• 2009

Hysteresis current regulator has been used widely because of its simple principle and structure. However, when the current band width is too narrow or the applied voltage is relatively too high, the switching frequency increases abruptly and it makes large amount of heat. In this study, for single phase current control, the hysteresis current control is executed by adding 0 mode state and comparing the slope of the current reference, which decreases the switching frequency so much and make the current control much stable. These were proved with computer simulations.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.2
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• pp.67-75
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• 2012

Different from other natural hazards including floods, drought advances slowly and spreads widely, so that the preparedness is quite important and effective to mitigate the impacts from drought. Evaluation and forecast the status of drought for the present and future utilizing the meteorological scenario for agricultural drought can be useful to set a plan for agricultural drought mitigation in agriculture water resource management. In this study, drought climate scenario model on the basis of historical drought records for preparing agricultural drought mitigation was developed. To consider dependency and correlation between various climate variables, this model was utilized the historical climate pattern using reference year setting of four drought levels. The reference year for drought level was determined based on the frequency analysis result of monthly effective rainfall. On the basis of this model, drought climate scenarios at Suwon and Icheon station were set up and these scenarios were applied on the water balance simulation of reservoir water storage for Madun reservoir as well as the soil moisture model for Gosam reservoir watershed. The results showed that drought climate scenarios in this study could be more useful for long-term forecast of longer than 2~3 months period rather than short-term forecast of below one month.

• Korean Journal of Optics and Photonics
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• v.11 no.5
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• pp.347-352
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• 2000

We have stabIhzed the laser frequency of a commercial dIode laser using a ULE (Ultra-low expansion material) reference cavIty and the cunent modulation charactenstics of the dIode itself The liuewIdth of the frce running laser was about a 1 MHz (rms) for a sampling time of 1 s and the drift rate was 300 kHz/s. Vvhen the laser is locked to oue sIde of the transmission signal from the ULE reference cavity, the lincwidth was reduced to 46 kHz (nus) for a sampling time longer than 10 ms. The root Allan variance was less than 2 kHz for a sampling time langeI than10 ms. 10 ms.

• Journal of electromagnetic engineering and science
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• v.9 no.3
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• pp.118-123
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• 2009

This paper discusses the design and fabrication of a reference signal generator for a naval radar system, including the vibration environment test. The transmit signals of the S-band radar system are synthesized by the reference signal and the phase noise must lower than - 130 dBc/Hz at a 10 kHz offset frequency. To achieve this specification, the phase noise of the reference signal needs to be less than -165 dBc/Hz at a 10 kHz offset. For achieving very low phase noise performance by the reference signal generator, the phase locked loop technique is applied with a 10 Hz loop bandwidth. Also, this reference signal generator has ${\pm}0.35\;ppb$ short-term stability to minimize instant phase errors and high vibration sensitivity against a ship's shaking, unbalanced rotating of antennas and so on.

• Journal of IKEEE
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• v.19 no.2
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• pp.176-185
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• 2015

The study aims to a design hybrid frequency synthesizer in spectrum analyzer and to propose new techniques designed for evasion of in-band spurious. The study focuses on calculating the exact location of multiple phase locked loop of hybrid frequency synthesizer and spurious of direct digital synthesizer to evade in-band spurious outside of frequency range that the user wants to see and thereby simulating technique to improve input related spurious of spectrum analyzer for algorithm. The proposed technique is designed to calculate spurious evasion algorithm in central processing system when in-band spurious arises, and to move output frequency of DDS(direct digital synthesizer) into the place where no in-band spurious exists thereby improving performance of frequency synthesizer. The study used simulation and result representation to prove the effectiveness of the proposed technique.

• International Journal of Knowledge Content Development & Technology
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• v.14 no.2
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• pp.81-97
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• 2024

The study investigated computer literacy skills as a determinant of electronic reference sources utilization among selected secondary school students in Ado-Odo Ota Local Government, Ogun State, Nigeria. Four specific objectives with conforming research questions guided the study. Descriptive survey research design was adopted for the study. The population of the study comprises of SSS3 students of the three selected Community Secondary Schools in Ado Odo Ota. A sample size of 150 was used for the study. The instrument for data collection was a self-developed structured questionnaire. Data collected was analyzed using frequency and percentages. Findings of the study revealed that majority of secondary school students were not aware of the availability of electronic reference sources. It also revealed that the level of their computer literacy skills was below average. Majority of them have never used computer before and the few of them that have used computer before used it in their homes, their friend's homes or in the cyber café. It was found that lack of formal training on the use of electronic reference sources, lack of access to computer, lack of awareness of availability of electronic reference sources, lack of funds for internet subscriptions, over dependency on printed reference sources and lack of motivation to use electronic reference sources were the major hindrances to the use of electronic reference sources among secondary school students. It was recommended that the school librarians and teachers should play a role in creating awareness among secondary school students about the availability of online/ electronic reference sources among others.

• Proceedings of the IEEK Conference
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• 2004.06b
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• pp.557-560
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• 2004

In this study, we design the one-chip PWM IC for SMPS (Switching Mode Power Supply) application. We determine the IC spec. and simulated each block of PWM IC (Reference, Error amp., Comparator, Oscillator) with Smart Spice (SILVACO Circuit Simulation Tool). Reference circuits generate constant voltage(5V) in the various of power supply and temperature condition. Error amp. is designed with large DC gain (${\simeq}65dB$), unity frequency (${\simeq}190kHz$) and large PM($75^{\circ}$).Saw tooth generators operate with 20K oscillation frequency (external resistor, capacitor).

• Proceedings of the IEEK Conference
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• 2005.11a
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• pp.841-844
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• 2005

Multi-output VC-TCXO (Voltage Controlled-Temperature Compensated Crystal Oscillator) for WCDMA has integrated the additional CMOS inverter, so it can be normal clipped sinewave output and additional CMOS output and it can be satisfied the VC-TCXO Characteristics that WCDMA system required. In this paper, however 26MHz is used for reference frequency, similarly and practically, it is usable from 10MHz to 40MHz, Most important factor to integrate CMOS inverter internally is the isolation between normal output and additional output. For this, it is separated in package design, due to this, when it isn't used additional output, it shows the same electrical performance, when it is used additional output, it has minimum-rized the interference. and then the important characteristics in reference oscillator are met to WCDMA system's requirements, like phase noise and frequency short term stability.

• Proceedings of the KIEE Conference
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• 2004.11c
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• pp.672-674
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• 2004

Many nonlinear controllers for the power system are based on nonlinear models involving the power angle as an element of the state, and therefore the reference value for the power angle is needed. As this reference value is not generally available, it is difficult to apply such nonlinear control methods in practice. To deal with this problem, we present an input-output feedback linearizing control scheme by selecting the output as a combination of the squared voltage and the relative frequency. It is shown that the internal dynamics are locally stable with controllable damping, and that the frequency remains bounded for all time. Simulations illustrate the effectiveness of the proposed method.