• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.28 no.6
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• pp.573-578
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• 2010

Precise determination of satellite positions is necessary to improve positioning accuracy in GNSS. In this study, GLONASS orbits were predicted from broadcast ephemeris using the 4th-order Runge-Kutta numerical integration method and their accuracy dependence on the integration step and the integration time was analyzed. The 3D RMS (Root Mean Square) differences between the results from I-second integration step and 300-second integration step was about 3 cm, but the processing time was one hundred times less for the I-second integration time case. For trials of different integration times, the 3D RMS errors were 8.3 m, 187.3 m, and 661.5 m for 30-, 150-, and 300-minutes of integration time, respectively. Though this integration-time analysis, we concluded that the accuracy gets higher with a shorter integration time. Thus we suggest forward and backward integration methods to improve GLONASS positioning accuracy, and with this method we can achieve a 5-meter level of 3-D orbit accuracy.

• Korean Journal of Remote Sensing
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• v.27 no.1
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• pp.25-31
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• 2011

Precise control of antenna position is very critical in ArcSAR system which uses an arc-rail as a platform for the antenna movement instead of linear rail. In order to minimize the antenna positional error, we improved the motion driving system and applied a newly developed motion control S/W which utilizes the real time antenna position information from magnetic linear scale and encoder. The experimental results showed that the rotational RMS error was reduced to $0.0062^{\circ}$ from $0.0432^{\circ}$. In terms of antenna positional RMS error for the arm length of 3m, it was reduced to 0.324mm from 2.262mm. It is expected that the ArcSAR system can be used to monitor the sub-millimetric displacement of terrain and structural targets.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.5
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• pp.15-20
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• 2009

Hot-firing tests were performed on two 30 tonf-class regenerative cooling combustion chambers, with different injector distribution and wall cooling method. In the paper, the combustion stability test results were analyzed and presented. The pressure fluctuation and stability rating test(SRT) results of the combustion chambers were examined to evaluate combustion stability. The combustion chambers exhibited satisfactory results on combustion stability. The RMS values of the chamber pressure fluctuation were less than 3% of the chamber pressure and the decay time of artificial pressure peaks was measured to be around 10% of the reference decay time. It is interesting that the RMS values of pressure fluctuation in the combustion chamber with film cooling are smaller than those in the chamber with cooling injectors at the periphery row.

• Journal of radiological science and technology
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• v.32 no.1
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• pp.17-24
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• 2009

Noise evaluation for an image has been performed by root mean square (RMS) granularity, autocorrelation function (ACF), and Wiener spectrum. RMS granularity stands for standard deviation of photon data and ACF is acquired by integration of 1 D function of distance variation. Fourier transform of ACF results in noise power spectrum which is called Wiener spectrum in image quality evaluation. Wiener spectrum represents noise itself. In addition, along with MTF, it is an important factor to produce detective quantum efficiency (DQE). The proposed evaluation method using Wiener spectrum is expected to contribute to educate the concept of Wiener spectrum in educational organizations, choose the appropriate imaging detectors for clinical applications, and maintain image quality in digital imaging systems.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.6
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• pp.814-822
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• 2012

To improve the flow and mixing characteristics of marine SCR system, two different mixer including up-down and swirl type mixer were considered. The purpose of this study is to analyse turbulence intensity and uniformity index in detail and to improve the performance of SCR with respect to the mixer structure. The results showed that, the concentration uniformity index is improved by about 5% with the utilization of both mixers in the front of catalyst part. Although the RMS value and relative turbulence intensity increased after the up-down type mixer, it could observed that the value of two parameters decreased with the flow proceeding forward to the downstream. For the case of swirl type mixer, the decrease of RMS value and relative turbulence intensity were relatively smaller than that of up-down type mixer, and uniform distribution of relative turbulence intensity was observed. As a results, it could be concluded that the mixing effects and the distance of the two kinds of mixer were different.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.3
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• pp.158-164
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• 2002

2-6 GHz digital phase shifter module has been designed and fabricated. For the broadband operation and performance, MMIC phase shifter chip for phase shifter module was designed and fabricated by using the reflection-type circuits with Lange coupler. The fabricated phase shifter module shows 6.1$^{\circ}$RMS phase error, 13.5 dB maximum insertion loss, and 8 dB and 10 dB input and output return losses, respectively. Computer controlled measurement systems are realized in order to get the measured data of 32 phase states. The RMS insertion phase error and the average insertion loss deviation among 8${\times}$8 modules for the phased-array system are less than ${\pm}$0.5$^{\circ}$and ${\pm}$0.5 dB, respectively. The size of fabricated phase shifter module is 45 ${\times}$ 22.5 ${\times}$60㎣.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.51.2-51.2
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• 2010

We have investigated 63 intense geomagnetic storms (Dst $\leq$ -100 nT) that occurred from 1998 to 2006. Using these events, we compared Dst forecast models: Burton et al. (1975), Fenrich and Luhmann (1998), O'Brien and McPherron (2000a), Wang et al. (2003), and Temerin and Li (2002, 2006) models. For comparison, we examined a linear correlation coefficient, RMS error, the difference of Dst minimum value (${\Delta}$peak), and the difference of Dst minimum time (${\Delta}$peak_time) between the observed and the predicted during geomagnetic storm period. As a result, we found that Temerin and Li model is mostly much better than other models. The model produces a linear correlation coefficient of 0.94, a RMS (Root Mean Square) error of 14.89 nT, a MAD (Mean Absolute Deviation) of ${\Delta}$peak of 12.54 nT, and a MAD of ${\Delta}$peak_time of 1.44 hour. Also, we classified storm events as five groups according to their interplanetary origin structures: 17 sMC events (IP shock and MC), 18 SH events (sheath field), 10 SH+MC events (Sheath field and MC), 8 CIR events, and 10 nonMC events (non-MC type ICME). We found that Temerin and Li model is also best for all structures. The RMS error and MAD of ${\Delta}$peak of their model depend on their associated interplanetary structures like; 19.1 nT and 16.7 nT for sMC, 12.5 nT and 7.8 nT for SH, 17.6 nT and 15.8 nT for SH+MC, 11.8 nT and 8.6 nT for CIR, and 11.9 nT and 10.5 nT for nonMC. One interesting thing is that MC-associated storms produce larger errors than the other-associated ones. Especially, the values of RMS error and MAD of ${\Delta}$peak of SH structure of Temerin and Li model are very lower than those of other models.

• Proceedings of the KIEE Conference
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• 1999.11d
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• pp.981-983
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• 1999

In this paper, the electrical characteristics of $\lambda$ vibration-mode piezoelectric transformer for applying to CCFL driving inverter was investigated. Piezoelectric transformer was made of PZT - PMN - 0.5wt% $Nb_{2}O_{5}$ composition. As a results of the electrical characteristics of piezoelectric transformer, when applied voltage was $35[V_{rms}]$ in $100[k{\Omega}]$ load resistance, output voltage was about $710[V_{rms}]$ and output power was more than 2[W]. As output power increased, step-up ratio and temperature was very stable until output power was 2.5[W]. Also, Efficiency was maximum in $70[k{\Omega}]$ load resistance, and about 89[%]. Also, when CCFL was used as load, the maintaining voltage was $700[V_{rms}]$ and the luminescence was $2000[cd/m^2]$ in applying $25[V_{rms}]$ to piezoelectric transformer. Conclusively, piezoelectric transformer fabricated in this paper can be applied to piezoelectric inverter for CCFL driving.

• Korean Journal of Applied Biomechanics
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• v.27 no.1
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• pp.53-58
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• 2017

Objective: The purpose of this study was to compare the accuracy of stride time and stride length provided by a commercial APDM inertial sensor system (APDM) with the results of three dimensional motion capture system (3D motion) during treadmill walking. Method: Five healthy men participated in this experiment. All subjects walked on the treadmill for 3 minutes at their preferred walking speed. The 3D motion and the APDM were simultaneously used for extracting gait variables such as stride time and stride length. Mean difference and root mean squared (RMS) difference were used to compare the measured gait variables from the two measurement devices. The regression equation derived from the range of motion of the lower limb was also applied to correct the error of stride length. Results: The stride time extracted from the APDM was almost the same as that from the 3D motion (the mean difference and RMS difference were less than 0.0001 sec and 0.0085 sec, respectively). For stride length, mean difference and RMS difference were less than 0.1141 m and 0.1254 m, respectively. However, after correction of the stride length error using the derived regression equation, the mean difference and the RMS difference decreased to 0.0134 m and 0.0556 m or less, respectively. Conclusion: In this study, we confirmed the possibility of using the temporal variables provided from the APDM during treadmill walking. By applying the regression equation derived only from the range of motion provided by the APDM, the error of the spatial variable could be reduced. Although further studies are needed with additional subjects and various walking speeds, these results may provide the basic data necessary for using APDM in treadmill walking.

• Korean Journal of Optics and Photonics
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• v.9 no.2
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• pp.51-58
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• 1998

We investigated surface-relief profiles of the TPHK(telecentric paraxial holographic kinofrm) used as a Fourier-transform lens employing exact geometrical raytracing. For the TPHK of F/8 and focal length of 15 mm, we consider the cases where the thickness of the substrate is 0 and 50 ${\mu}{\textrm}{m}$, dividing the surface-relif profiles into fifty steps from plano-convex to convexplano shapes and varying the angle of incidence($0^{\circ},{2.5}^{\circ},5^{\circ}$). In order to identify appropriate surface-relief profiles, we employ, as criteria of performance, rms spot size, rms deviation from $f{\sin}{\theta}$, peak position and FWHM(full width at half maximum), number of rays abandoned from raytracing etc., which are determined from the result of exact raytracing. It is found that the profile with 80% of its relief thickness facing the image plane gives the best performance regardless of the presence of substrate.