• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.128.1-128.1
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• 2011

We present the results of the first simultaneous dual-frequency VLBI observation with KVN (Korean VLBI Network). The KVN has a unique multi-frequency receiving system performing simultaneous observations at four frequencies, such as 22, 43, 86, and 129 GHz, in order to calibrate the atmospheric phase fluctuations, which cause a severe degradation of an interferometric coherence in mm-VLBI regime. In order to test the multi-frequency phase referencing capability of KVN, we observe the bright continuum VLBI source, NRAO 150 at two different frequencies of 21.7 (K band) and 43.4 (Q band) GHz simultaneously. The VLBI fringe phases at K and Q bands show a tight correlation of phase behaviors and the results of phase referencing (residual phase, coherence etc) are promising for achieving excellent phase referencing observations with KVN. The KVN will be able to open new perspectives in the multi-frequency study of VLBI.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.489-494
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• 2001

In this thesis, the microstructure and electrical properties of ZnO varistors were investigated according to ZnO varistors with various formulation. A∼E's ZnO varistor ceramics were exhibited good density, 95% of theory density and low porosity, 5%, wholly. The average grain size of A-E's ZnO varistor ceramics exhibited 11.89$\mu\textrm{m}$, 13.57$\mu\textrm{m}$, 15.44$\mu\textrm{m}$, 11.92$\mu\textrm{m}$, 12.47$\mu\textrm{m}$, respectively. Grain size of C's ZnO varistor is larger and grain size of A and D's are smaller than other varistors. In the microstructure, A∼E's ZnO varistor ceramics sintered at l130$^{\circ}C$ was consisted of ZnO grain(ZnO), spinel phase(Zn$\sub$2.33/Sb$\sub$0.67/O$_4$), Bi-rich Phase(Bi$_2$O$_3$) and inergranular phase, wholly. Reference voltage of A∼E's ZnO varistor sintered at 1130$^{\circ}C$ decreased in order D, E > A > B > C's ZnO varistors. Nonlinear exponent of varistors exhibited high characteristics, above 30, wholly. Consequently, C's ZnO varistor exhibited good nonlinear exponent, 68. Lightning impulse residual voltage of A, B, C and E's ZnO varistors suited standard characteristics, below 12kV at current of 5kA.

• Journal of the Society of Disaster Information
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• v.13 no.2
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• pp.147-154
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• 2017

Duplex stainless steel finds increasing use as an alternative to austenitic stainless steel, particularly where chloride or sulphide stress corrosion cracking is of primary concern, due to the excellent combination of strength and corrosion resistance. During welding, duplex stainless steel does not create the same magnitude or distribution of weld-induced residual stresses as those in welded austenitic stainless steel due to the different physical and mechanical properties between them. In this work, an experimental study on the residual stresses in butt-welded duplex stainless steel is performed utilizing the layering technique to investigate the characteristics of residual stresses in the weldment.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.8
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• pp.248-261
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• 1999

The fatigue life of mechanical components and structures has been influenced by mechanical, material and environmental conditions. It is important to search out the load type and size for accurate cause of fracture at the damaged surface of material. The fractographic method by x-ray diffraction can utilize residual stress $\sigma$_r and half-value breadth B and find out the types and the mechanical conditions of fracture. This study showed the relationship between fracture mechanical parameters $\Delta$K, $K_{max}$ and X-ray residual stress $\sigma$_r for normalized SS41 steel with homogeneous crystal structure and M.E.F. dual phase steel(martensite encapsulated islands of ferrite). The fatigue crack propagation tests were carried out under stress ratios 0.1 and 0.5. The x-ray diffraction technique according to crack propatation direction was applied to fatigue fractured surface. Residual stress $\sigma$_r was independent on stress ratios by arrangement of $\Delta$K. The equation of $\sigma$_r$\Delta$K was established by the experimental data. Therefore, fracture mechanical parameters can be estimated can be estimated by the measurement of X-ray parameters.

• The Journal of Information Technology
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• v.8 no.3
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• pp.105-115
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• 2005

The CMA and MMA blind equalization algorithm has the inevitable large residual error caused by mismatching between the symbol constellation at a steady state after convergence. Stop-and-Go algorithm has a very superior residual error characteristics at a steady state but a relatively slow convergence characteristics. In this paper, we propose a SAG-Flagged MMA as a new adaptive blind equalization algorithm with a Stop-and-Go flag which follows a flagged MMA in update scheme of tap weights as appling the flag obtaining from Stop-and-Go algorithm to MMA. Using computer simulation, it is confirmed that the proposed algorithm has an enhancing performance from the viewpoint of residual ISI, residual error and convergence speed in comparison with MMA and Stop-and-Go algorithm. Algorithm has a new error function using the decided original constellation instead of the reduced constellation. By computer simulation, it is confirmed that the proposed algorithm has the performance superiority in terms of residual ISI and convergence speed compared with the adaptive blind equalization algorithm of CMA family, Constant Modulus Algorithm with Carrier Phase Recovery and Modified CMA(MCMA).

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1332-1336
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• 2005

It could make the LIghtweight Piezoelectric Composite Actuator (LIPCA) damageable by the cyclic large deformation. If the progressive microvoid coalescence of LIPCA interlaminar took place, the decrease of the stiffness and the weakness of stress transmission and fiber bridging effect would make the fatigue characteristics worse suddenly. Therefore, it is required to study the variation of fatigue behavior and interlaminar condition in LIPCA under resonant frequencies. These studies such as the changeable fatigue phase and interlaminar behavior of LIPCA affected by the resonant frequencies should be carried out due to the strong anisotropy of CFRP layer. Hence, these studies are as follows. 1) The residual stresses distribution of interlaminar in LIPCA using the Classical Lamination Theory (CLT). 2) Comparative analysis of interlaminar behavior for the intact LIPCA versus LIPCA containing an artificial delamination during resonant frequency.

• Journal of Food Hygiene and Safety
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• v.14 no.1
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• pp.76-83
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• 1999

Solid phase microextraction (SPME) was used for the determination of 6 standard solvents (methanol, isopropanol, methyl ethyl ketone, ethyl acetate, cyclohexane, toluene) in food packaging materials. SPME method is a solvent-free sample preparation technique in which a fused silica fiber coated with polymeric organic liquid is introduced into the headspace above the sample. SPME method using fiber coated polydimethylisiloxane (PDMS) was compared with static headspace (SHS) method used as a reference. It was found that the optimal adsorption condition using PDMS-SPME method was 2$0^{\circ}C$ for 15 minutes for the standard solvents. Detection limits, linearity, reproducibility and recovery of both SHS and PDMS-SPME methods have been determined using 6 standard solvents. Both methods were characterized by high reproducibility and good linearity. Using SHS methods, the mean recovery of the 6 standard solvents was ranged from 75.5% to 105.8% with a mean relative standard deviation (RSD) of 0.3% to 4.8%. With PDMS-SPME method, the mean recovery of the 6 standard solvents was ranged from 86.7% to 108.3% with a mean RSD of 0.4% to 2.5%. The detection limits of both methods were the same for toluene, cyclohexane and methyl ethyl ketone; those of PDMS-SPME method were higher than those of SHS method for methanol, isopropanol and ethyl acetate. PDMS-SPME fiber shoed excellent adsorption for non-polar solvents such as toluene, while it showed relatively low adsorption for polar solvents such as methanol.

• Journal of Advanced Navigation Technology
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• v.14 no.5
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• pp.668-676
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• 2010

Optimal net residual dispersions (NRDs) of inline dispersion management (DM) for compensating the signal distortion of $24{\times}40$ Gbps WDM channels in optical transmission links, in which optical phase conjugator (OPC) is placed from 250 km to 750 km by spacing 50 km in 1,000 km total transmission length of single mode fiber (SMF), are induced as a function of various ope positions. And, performance improvement of WDM channels in transmission links with the induced optimal NRD is investigated by comparing with that in transmission links with NRD = 0 ps/nm. It is confirmed that optimal NRDs are decided by displacement of OPC from mid-way of total transmission length, i.e. 500 km, and the determinating and applying of optimal NRD in case of ope displacement into transmitters is more stable and effective than that in case of ope displacement into receivers from 500 km. Also, it is shown that eye opening penalties (EOPs) of WDM channels in transmission links with optimal NRD are improved by 1.5 dB to 3 dB, which are related with OPC position, from that obtained in transmission links with fixed NRD of 0 ps/nm.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.12 s.354
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• pp.61-67
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• 2006

This paper proposes the algorithm for tracking of the residual phase errors incurred by carrier frequency offset and sampling frequency offset in the orthogonal frequency division multiplexing (OFDM) systems which are suitable for high data rate wireless communications. In the OFDM systems the subcarriers which are orthogonal to each other are modulated by digital data and transmitted simultaneously. The carrier frequency offset causes degradation of signal to noise ratio(SNR) performance and interference between the adjacent subcarriers. The errors in the sampling timing caused by the sampling frequency difference between the transmitter and the receiver sides also cause a major performance degradation in the OFDM systems. The residual error tracking and compensation mechanism is essential in the OFDM system since the carrier and the sampling frequency offset cause the loss of orthogonality resulting in the system performance loss. This paper proposes the scheme where the channel gain and the payload data information are reflected in the residual error tracking process which results in the reduction of the estimation error and the tracking performance improvements under the frequency selective fading wireless channels.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.535-540
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• 2006

The relationship between the observable noise model and the satellite elevation angle can be modeled quite well by an exponential function.[Jin, 1996] Noise size and dependence on the elevation angle are, however, different for each observation and receiver type. Therefore, the coefficient determination of this model is an issue, and various methods including PR-CP, single difference, and time difference have been suggested. The limitations of them are difficulty to model the carrier phase noise and to eliminate bias. To overcome these disadvantages for using Jin's model, we suggest zero baseline double difference (DD) and noise sorting algorithm. Data DD technique in zero baseline is useful to eliminate all the troublesome GPS biases, and the remaining error is the sum of GPS measurement noises from two satellites. These DD residuals for hours should be sorted by the combination of satellite elevation angles, and then variance value of the residual for each combination can be estimated. Using these values, we construct an over-determined linear equation whose solution is a set of noise variance for each satellite elevation angle. With 24hr Trimble 4000ssi data, we easily worked out the coefficients of the noise model not only for pseudorange but also for carrier phase. We estimated the standard deviation of the measurement DD using our model, and plotted 1 and 3 sigma lines for every epoch to verify the representation of the residual error. 63.3% of pseudorange residual and 65.9% of phase error did not exceed the 1 sigma lines. Additionally, 99.2% and 99.5% of them lied within 3sigma line. These figures prove that the Gaussian property of measurement noise, and that the suggested model by our algorithm corresponds to the observable noise information.