• The Korean Journal of Applied Statistics
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• v.30 no.3
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• pp.453-462
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• 2017

Double propensity score adjustment is an analytic solution to address bias due to incomplete matching. However, it is difficult to estimate the standard error of the estimated treatment effect when using double propensity score adjustment. In this study, we propose two bootstrap methods to estimate the standard error. The first is a simple bootstrap method that involves drawing bootstrap samples from the matched sample using the propensity score as well as estimating the standard error from the bootstrapped samples. The second is a complex bootstrap method that draws bootstrap samples first from the original sample and then applies the propensity score matching to each bootstrapped sample. We examined the performances of the two methods using simulations under various scenarios. The estimates of standard error using the complex bootstrap were closer to the empirical standard error than those using the simple bootstrap. The simple bootstrap methods tended to underestimate. In addition, the coverage rates of a 95% confidence interval using the complex bootstrap were closer to the advertised rate of 0.95. We applied the two methods to a real data example and found also that the estimate of the standard error using the simple bootstrap was smaller than that using the complex bootstrap.

• Journal of the Korean Magnetics Society
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• v.11 no.1
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• pp.14-20
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• 2001

The structure, shape, size, and magnetic properties of Ni$_{0.5}$Cu$_{0.1}$Zn$_{0.4}$Fe$_2$O$_4$ have been investigated as a function of annealing temperatures. In order to control the microwave absorbing properties of ferrite-rubber composite and the complex losses (magnetic loss and conduction loss), the effect of carbon addition was also studied. It was found that the coercive force decreased with increasing heat-treatment temperatures. Relative complex permeability and reflection loss were measured by the network analyzer. As a result, the natural resonance occurred in the low frequency tinge, and the matching frequency of the ferrite-rubber composite prepared at 130$0^{\circ}C$ was found to be lower. As heat-treatment temperatures were increased, the magnetic loss ($\mu$$_{r}$", $\mu$$_{r}$′) and the dielectric loss ($\varepsilon$$_{r}$"/$\varepsilon$$_{r}$′) were increased. It was caused that the absorption characteristics of the absorber were improved. The conduction loss and magnetic loss were expected to be occurred together because two matching frequencies were shown with carbon addition. It was confirmed that the matching frequency of the microwave absorber could be controlled by controlling heat-treatment temperatures and carbon additions.ons.tions.

• Journal of Korea Multimedia Society
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• v.10 no.11
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• pp.1439-1445
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• 2007

In this paper, we propose a fast motion estimation algorithm using initial matching errors by sorting square sub-blocks to find complex sub-block area adaptively based on partial calculation of SAD(sum of absolute difference) while keeping the same prediction quality compared with the PDE(partial distortion elimination) algorithm. We reduced unnecessary calculations with square sub-block adaptive matching scan based initial SAD calculation of square sub-block in each matching block. Our algorithm reduces about 45% of computations for block matching error compared with conventional PDE(partial distortion elimination) algorithm without any degradation of prediction quality, and for algorithm will be useful to real-time video coding applications using MPEG-4 AVC or MPEG-2.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.42 no.4 s.304
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• pp.1-10
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• 2005

This paper presents a map matching method using multiple hypothesis technique(MHT) to identify the road that a land vehicle is located on. To realize a map matching method using MHT, Pseudo-measurements are generated utilizing adjacent roads of GPS/DR position and the MHT is reformulated as a single target problem. Since pseudo-measurements are generated using digital map, topological properties such as road connection, direction, and road facility information are considered in calculating probabilities of hypotheses. In order to improve the map matching performance under when bias errors exist in digital road map data, a Kalman filter is employed to estimate the biases. Field experimental results show that the proposed map matching method provides the consistent performance even in complex downtown areas, overpass/underpass areas, and in the areas where roads are adjacent in parallel.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2007.04a
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• pp.201-205
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• 2007

In the post-Cold War era, acquisition technique of high-resolution satellite imagery (HRSI) has begun to commercialize. IKONOS-2 satellite imaging data is supplied for the first time in the 21st century. Many researchers testified mapping possibility of the HRSI data instead of aerial photography. It is easy to renew and automate a topographical map because HRSI not only can be more taken widely and periodically than aerial photography, but also can be directly supplied as digital image. In this study matching size of IKONOS Geo-level stereo image is presented lot production of digital elevation model (DEM). We applied area based matching method using correlation coefficient of pixel brightness value between the two images. After matching line (where "matching line" implies straight line that is approximated to complex non-linear epipolar geometry) is established by exterior orientation parameters (EOPs) to minimize search area, the matching is tarried out based on this line. The experiment on matching size is performed according to land cover property, which is divided off into four areas (water, urban land, forest land and agricultural land). In each of the test areas, window size for the highest correlation coefficient is selected as propel size for matching. As the results of experiment, the proper size was selected as $123{\times}123$ pixels window, $13{\times}13$ pixels window, $129{\times}129$ pixels window and $81{\times}81$ pixels window in the water area, urban land, forest land and agricultural land, respectively. Of course, determination of the matching size by the correlation coefficient may be not absolute appraisal method. Optimum matching size using the geometric accuracy therefore, will be presented by the further work.

• Journal of KIISE:Software and Applications
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• v.32 no.10
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• pp.949-955
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• 2005

In this Paper, we propose fast block matching algorithm by dividing complex areas based on complexity order of reference block and square sub-block to reduce an amount of computation of full starch(FS) algorithm for fast motion estimation, while keeping the same prediction quality compared with the full search algorithm. By using the fact that matching error is proportional to the gradient of reference block, we reduced unnecessary computations with square sub-block adaptive matching scan based image complexity instead of conventional sequential matching scan and row/column based matching scan. Our algorithm reduces about $30\%$ of computations for block matching error compared with the conventional partial distortion elimination(PDE) algorithm without any prediction quality, and our algorithm will be useful in real-time video coding applications using MPEG-4 AVC or MPEG-2.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3183-3186
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• 2007

Taylor-Couette flow may appear when the angular velocity is different between two concentric rotating cylinders. This kind of Taylor-vortex flow can be easily seen in lots of engineering problems. In general the geometries of rotating cylinders are generally complex in these cases. In this study, we investigated Taylor-Couette flow when the outer cylinder has the slit along the annulus. The radius ratio and aspect ratio of the experimental model used was 0.825 and 48, respectively. The depth of slits is 5mm and total 18 slits are azimuthally located along the inner wall of outer cylinder. We used PIV method to measure the flow and applied index matching method to resolve the complex geometry effect. The results show the model with slit has no stable wavy vortex region above Re=143.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.25 no.6_2
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• pp.587-597
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• 2007

This study determines matching size for digital elevation model (DEM) production according to land cover property from IKONOS Geo-level stereo image. We applied area based matching method using correlation coefficient of pixel brightness value between the two images. After matching line (where "matching line" implies straight line that is approximated to complex non-linear epipolar geometry) is established by exterior orientation parameters to minimize search area, the matching is carried out based on this line. The experiment is performed according to land cover property, which is divided off into four areas (water, urban land, forest land and agricultural land). In each of the test areas, matching size is selected using a correlation-coefficient image and parallax image. As the results, optimum matching size of the images was selected as $81{\times}81$ pixels window, $21{\times}21$ pixels window, $119{\times}119$ pixels window and $51{\times}51$ pixels window in the water area, urban land, forest land and agricultural land, respectively.

• Journal of the Korean Magnetics Society
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• v.5 no.1
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• pp.21-26
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• 1995

The systematic variation of complex permeability and complex permittivity and their relationship with micro-wave absorbing properties are investigated in sintered Ni-Zn ferrites of non-stoichiometric composition. The specirrens of ${(Ni_{0.5}Zn_{0.5}O)}_{1-x}(Fe_{2}O_{3})_{1+x}$ spinels were prepared by a conventional ceramic processing technique. In the present study. complex permeability and permittivity can be controlled by the variation of ${\alpha}-Fe_{2}O_{3}$ contents in the spinel lattice. The primary effect of the excess ${\alpha}-Fe_{2}O_{3}$ is to increase the dielectric constant. while the notable decrease of magnetic loss is observed in the iron-deficient ferrites. The results suggest that the matching fre-queocyand matching thickness could be controlled by the variation of ${\alpha}-Fe_{2}O_{3}$ contents in the Ni-Zn ferrite.

• Journal of the Optical Society of Korea
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• v.5 no.3
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• pp.99-109
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• 2001

This paper presents a phase-only modulation scheme for a three-dimensional (3-D) image matching system to improve optical efficiency of the system. The 3-D image matching system is based on the two mask heterodyne scanning. A hologram of the 3-D reference object is first created and then the phase of the hologram is extracted. The phase of the hologram is represented as one mask with the other mask being a plane wave. The superposition of each beam modulated by the two masks generated a scanning beam pattern. This beam pattern scans the 3-D target object to be recognized. The output of the scanning system gives out the correlation of the phase-only hologram of the reference object and the complex hologram of the target object. Since a hologram contains 3-D information of an object as a form of fringe pattern, the correlation of holograms matches whole 3-D aspect of the objects. Computer simulations are performed with additive gaussian noise and without noise for the complex hologram modulation scheme and the phase-only hologram modulation scheme. The computer simulation results show that the phase-only hologram modulation scheme improves the optical efficiency. Thus the system with the phase-only hologram modulation scheme is more robust than the system with the complex hologram modulation scheme.