• ETRI Journal
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• v.30 no.1
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• pp.21-32
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• 2008

Cognitive radio (CR) has been proposed as an effective technology for flexible use of the radio spectrum. The interference between primary users and CR users, however, becomes a critical problem when they are using adjacent frequency channels with different transmission power levels. In this paper, a robust CR orthogonal frequency division multiplexing (OFDM) architecture, which can effectively suppress interference to nearby primary users and overcome adjacent channel interference (ACI) to the CR user, is proposed. This new approach is characterized by adaptive data repetition for subcarriers under heavy ACI, and adaptive time spreading for subcarriers near the borders of the CR user's spectrum. The data repetition scheme provides extra power gain against the ACI coming from primary users. Time spreading guarantees an acceptable interference level to nearby primary users. By computer simulation, we demonstrate that, under a CR environment, the proposed CR OFDM architecture outperforms conventional OFDM systems in terms of throughput and BER performance.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.5
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• pp.1117-1122
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• 2005

This paper is studied the high-repetition rate optical-pulse stream generation using optical loop mirror coupler. With the recent development of the ultrahigh-speed optical time division multiplexed system, hish-repetition rate optical-pulse stream generation is necessary. This is different from conventional approaches, which use fiber or integrated waveguide delay line circuits. The high-repetition-rate optical-pulse multiplication phenomenon occurs when the optical pulse's spectral width is greater than the transfer bandwidth of the coupler used. From the analysis, the output repetition rate can be controlled by using fiber couplers with different equivalent transfer bandwidths. The pulse separation spacing is controlled by number of cascaded coupler in optical loop mirror coupler scheme.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.6
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• pp.360-364
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• 2015

Electronic systems based on solid state devices have changed to be more complicated and miniaturized as the electronic systems developed. If the electronic systems are exposed to HPEM (high power electromagnetics), the systems will be destroyed by the coupling effects of electromagnetic waves. Because the HPEM has fast rise time and high voltage of the pulse, the semiconductors are vulnerable to external stress factor such as the coupled electromagnetic pulse. Therefore, we will discuss about malfunction behavior and DFR (destruction failure rate) of the semiconductor caused by amplitude and repetition rate of the pulse. For this experiment, the pulses were injected into the pins of general purpose IC due to the fact that pulse injection test enables the phenomenon after the HPEM is coupled to power cables. These pulses were produced by pulse generator and their characteristics are 2.1 [ns] of pulse width, 1.1 [ns] of pulse rise time and 30, 60, 120 [Hz] of pulse repetition rate. The injected pulses have changed frequency, period and duty ratio of output generated by Timer IC. Also, as the pulse repetition rate increases the breakdown threshold point of the timer IC was reduced.

• Journal of electromagnetic engineering and science
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• v.13 no.3
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• pp.186-188
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• 2013

A triple 2-of-3 pulse repetition frequency (PRF) scheme is presented for medium PRF pulsed-Doppler airborne radars, and a real-time method is developed that searches for optimal or sub-optimal PRF sets according to momentary battle situations. The effectiveness of the real-time search method of PRF sets is demonstrated by the experimental results obtained using simulated data.

• Textile Coloration and Finishing
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• v.13 no.2
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• pp.7-7
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• 2001

This paper investigated the dyeability and surface color of silk and cotton fabrics dyed with chustnut bur extract. Some experiments were performed under the various dyeing conditions such as dyeing temperature, dyeing time, repetition of dyeing, dyeing pH, mordanting condition, washing fastness and light fastness with silk and cotton fabrics. The results obtained were as follows 1. △E value was increased when dyeing temperature and time was higher, value of munsell was shifted from Yellow to Yellow-Red at hither dyeing temperature and time in silk and cotton fabrics. 2. Optimal dyeing pH was increased with acidity of dyeing solution in silk and cotton fabrics, and repetition of dyeing did not change the dye-uptake. 3. When mordanting time and temperature was higher, △E value was larger in silk and cotton fabrics. Silk and cotton fabrics with Fe-premordanting treatment had best dyeability, but treatment with Sn-mordanting was worst. 4. Washing fastness and light fastness was excellent in various dyeing condition at silk fabric but cotton was without practical use.

• Textile Coloration and Finishing
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• v.13 no.2
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• pp.93-103
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• 2001

This paper investigated the dyeability and surface color of silk and cotton fabrics deed with chustnut bur extract. Some experiments were performed under the various dyeing conditions such as dyeing temperature, dyeing time, repetition of dyeing, dyeing pH, mordanting condition, washing fastness and light fastness with silk and cotton fabrics. The results obtained were as follows 1. $\Delta{E}$ value was increased when dyeing temperature and time was higher, value of munsell was shifted from Yellow to Yellow-Red at hither dyeing temperature and time In silk and cotton fabrics. 2. Optimal dyeing pH was increased with acidity of dyeing solution in silk and cotton fabrics, and repetition of dyeing did not change the dye-uptake. 3. When mordanting time and temperature was higher, $\Delta{E}$ value was larger in silk and cotton fabrics. Silk and cotton fabrics with Fe-premordanting treatment had best dyeability, but treatment with Sn-mordanting was worst. 4. Washing fastness and light fastness was excellent in various dyeing condition at silk fabric but cotton was without practical use.

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.1
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• pp.32-44
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• 2001

The purpose of this study was to investigate the effects of Er : YAG laser on cutting efficacy and temperature changes of dentin. We used the dentin specimens of human premolars and molars which contain the physiologic saline and maintain the pulpal pressure in dentinal tubules. Each specimen was exposed to Er : YAG laser with non-contact handpiece type delivery system under different treatment condition of irradiation energy, pulse repetition rate, and exposure time. Two procedures were conducted by the presence of water flow during lasing. The specimens were grouped by thickness of dentin. We investigated the cavity pattern, volume, and temperature change of dentin specimen to determine the cutting efficacy and temperature rise of Er : YAG laser, and obtained following results. 1. Cutting volume of dentin was increased by increasing the irradiation energy, pulse repetition rate, and exposure time(P<0.05). 2. Margins of abulated cavities were sharp and clean and floors of cavities were conical in shape and showing smooth surfaces. Upper diameter of abulated cavities were increasing as laser parameter of irradiation energy, pulse repetition rate, and exposure time were increased. A few cracks were observed on abulated surfaces under treatment condition of laser parameter with 150mJ, 5Hz, and 5sec. 3. Temperature was increased as laser parameter of irradiation energy, pulse repetition rate, and exposure time were increased, and temperature rise was decreased as dentin thickness was increased(P<0.05). 4. Temperature rise was decreased under water flow compared with no water flow during laser exposure(P<0.05). From these results, we think that the method of using a Er:YAG laser would be effective and safe in cutting dentin for clinical application.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.7
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• pp.85-91
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• 2016

Typically, radar systems change the pulse repetition interval of their modulated signal in order to avoid detection. On the other hand the radar-signal detection system tries to detect the modulation pattern. The histogram or auto-correlation methods are usually used to detect the PRI pattern of the radar signal. However these methods tend to lost the sequence information of the PRI pulses. This paper proposes a PRI-sequence detection algorithm based on the finite-state machine that could detect not only the PRI pattern but also their sequence.

• Journal of IKEEE
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• v.5 no.2 s.9
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• pp.201-210
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• 2001

Wavelength and repetition-rate tunable optical pulse-trains for ultrafast optical time- and wavelength division multiplexing are generated from a semiconductor fiber ring laser by optical injection mode-locking. The pulse trains show the pulse with of ${\sim}10$ ps and the wavelength tuning of wider than 30 nm at various repetition-rates of 10 GHz, 20 GHz, 30 GHz and 40 GHz, respectively.

• Speech Sciences
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• v.11 no.2
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• pp.105-117
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• 2004

Recently, many scholars have emphasized the importance of English listening ability for smoother communication. Most audio materials, however, were recorded in a quiet sound-proof booth. Therefore, students who have spent so much time listening to the ideal audio materials are expected to have difficulty communicating with native speakers in the real life. In this study, we examined how well thirty three Korean university students and five native speakers will repeat the recorded English sentences under noise and speed conditions. The subjects' production was scored by listening to each recorded sentence and counting the number of words correctly produced and determined the percent ratios of correctly produced words to the total words in each sentence. Results showed that the student group correctly repeated around 65% of all the words in each sentence while the native speakers demonstrated almost perfect match. It seemed that the students had difficulty perceiving and repeating function words in various conditions. Also, high-proficiency student group outperformed the low-proficiency student group particularly in their repetition of function words. In addition, the student subjects' accuracy of repetition remarkably dropped when the normal sentences were both sped up and mixed with noise. Finally, it was observed that the Korean students' percent correct ratio fell down as the stimulus sentence became longer.