• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.18-19
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• 2000

Recently, coherent control of exciton populations has been demonstrated through terahertz, reflection, and four-wave-mixing experiments. However, the most direct probe of exciton population control is the absorption, which has been lacking in previous studies. In this report, we probe the time evolution of exciton population directly through a transmission experiment. In particular, using upconversion technique with both narrow (spectrally broad) and long (spectrally narrow) pulses, we can obtain both the temporal and the spectral information. The main thrust of our report is that when phase controlled, the second pulse can be either greatly enhanced or completely destroyed by gaining energy from exciton (thus destroying the exciton population) or giving all of its energy to the system (thus greatly increasing the exciton population), respectively. (omitted)

• Smart Structures and Systems
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• v.1 no.3
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• pp.257-266
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• 2005

In Lamb wave detection of damages in smart structures, the excitation pulse is usually designed as a narrow band burst wave for the convenience of analysis and recognition. However, the wideband excitation can excite more modes in plate/shell structure and thus provides extra information for changes of the structure. This paper presents a method that can extract information in wideband Lamb wave signals. By transforming the detected signals into various sub-frequency band, the measured signal can be converted to its equivalences of narrow band excitations, therefore, the information in different frequency bands can be acquired from a single test and in the same time the complicity of wideband signal can be simplified. Some test results are provided to verify this method.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.4
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• pp.517-522
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• 2013

The spurious electromagnetic radiation is generated due to the RF unbalanced current on a conductive cable connecting an electronic device to another. A metamaterial-based filtering geometry with frequency selectivity is suggested to reduce the radiation with a bandgap structure, where the right-handed inductance and capacitance stem from the transmission-like configuration between the cable and the metal protrusion, and the left-handed components come from the narrow cavities. The effect of the structure on the unbalanced current pulse and its spurious radiation is presented in the FDTD-method frame work.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.381-385
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• 2003

This paper presents the fabrication possibility of the micro actuator which uses a micro-thermal bubble, generated by a micro-heater under pulse heating. The micro-actuator is consist of three plate. The lower plate includes the channel and chamber are fabricated on high processability silicon wafer by the DRIE(Deep Reactive ion Etching) process. The middle plate includes the chamber and diaphragm, and the upper plate is the micro-heater. The micro-heater designed non-uniform width and results in periodic generation of stable single bubbles in D.I water. The single bubble appears precisely on the narrow part of the micro-heater and control is recorded.

• 전기의세계
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• v.26 no.3
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• pp.76-83
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• 1977

The choice of control method and circuit must be decided after a broad inspection with the characteristics of load and control elements as well as that of electric and mechanical nature. In the present study, Pulse width modulated(PWM) SCR chopper was chosen and for the electric commutation, Jones' forced method was taken bacause of its having enough reverse bias energy. Objectives of experimentation by this system are; 1) the condition of SCR as a gate trigger pulse. 2) the observation of phenomena at the time of forced commutation 3) the experimentation on characteristics of speed control by PWM chopper. Above experimentation shows good characteristics, however, in the limit of narrow gap between the ON and OFF pulses, a complete control was not possible. So, that must be the point to be studied further alone with the harmonics influence.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.265-269
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• 1994

The switching dead time avoiding a bridge leg short circuit in PWM voltage source inverter produces distortions of the controlling inverter output performance such as current waveform, voltage vector, and torque. In this paper, the influence of dead time is investigated. The on-line space voltage vector modulation method is used for current controller. It is possible to compensate dead time by space voltage vector modulation which generates additional pulse compensating voltage distortion caused by dead time. In addition, narrow pulse which is generally neglected can be compensated. All the algorithms, including field-oriented control are performed by one chip microprocessor 80C196MC and DSP TMS320C31. Experimental results probe that the proposed scheme provides a good inverter output performance.

• Bulletin of the Korean Chemical Society
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• v.25 no.12
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• pp.1829-1832
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• 2004

We have developed a new femtosecond probe technique by using stimulated Raman spectroscopy. The cross phase modulation in femtosecond time scale associated with off-resonant interaction was shown to be eliminated by integrating the transient gain/loss signal over the time delay between the Raman pump pulse and the continuum pulse. The stimulated Raman gain of neat cyclohexane was obtained to demonstrate the feasibility of the technique. Spectral and temporal widths of stimulated Raman spectra were controlled by using a narrow band pass filter. Femtosecond stimulated Raman spectroscopy was proposed as a highly useful probe in time-resolved vibrational spectroscopy.

• Bulletin of the Korean Chemical Society
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• v.16 no.3
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• pp.238-243
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• 1995

A pulsed molecular beam source having short pulse duration (typically 70 ${\mu}s)$ and narrow velocity distribution (${\Delta}$v/v=8% for helium) has been costructed utilizing a commercial fuel injector. Beam characteristics of helium and ammonia seeded in helium expansions are accomplished by the use of an electron impact time-or-flight mass spectrometer. The comparisons between experimental data and theoretical calculations show that the proper beam speed is important to predict the evolution of stream temperature and valve shutter function. The decreasing tendency of pulse duration with increasing cluster size leads to the conclusion that the cluster beam property is described as a function of cluster mass and disinct cluster temperature.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2008.05a
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• pp.148-150
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• 2008

In this paper, we report the improved driving methode using planar-gate for field emission light source. Due to the cold cathode in field emission device, it has advantage for driving system in terms of high speed pulse driving with narrow duty ratio. This paper shows that our driving method offers the stable and reliable driving system without rapid electric field variation for field emission light source.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.12A
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• pp.1189-1197
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• 2006

Ultra-wideband(UWB) is a killer technology for short-range wireless communications. In the past, most of the UWB research focused on physical layer but the unique characteristics of UWB make it different to design the upper layer protocols than conventional narrow band systems. Cross-layer protocols have received high attention for UWB networks. In this paper, we investigate the performance of two physical layer schemes: Time Hopping Binary Pulse Position Modulation(TH-BPPM) and Time Hopping Binary Pulse Amplitude Modulation (TH-BPAM) with proposed private MAC protocol for UWB ad-hoc networks. From pulse level to packet level simulation is done in network simulator ns-2 with realistic network environments for varying traffic load, mobility and network density. Our simulation result shows TH-BPAM outperforms TH-BPPM in high traffic load, mobility and dense network cases but in a low traffic load case identical performance is achieved.