Yun-Soo Choi

An alternative measure of public transport accessibility based on space syntax

The local governments of major cities in Korea are giving focus on public transportation to reduce congestion and improve accessibility in city areas. In this regards, the proper measurement of accessibility is now a key policy requirement for reorganizing the public transport network. However, Public transport routing problems are considered to be highly complicated since a multi-mode travel generates different combinations of accessibility. While most of the previous research efforts on measuring transport accessibility are found at zone-levels, an alternative approach at a finer scale such as bus links and stops is presented in this study. We propose a method to compute the optimal route choice of origin-destination pairs and measure the accessibility of the chosen mode combination based on topological configuration. The genetic algorithm is used for the computation of the journey paths, whereas the space syntax theory is used for the accessibility. The resulting accessibilities of bus stops are calibrated by O-D survey data and the proposed process is tested on a CBD of Seoul using the city GIS network data.

FABRICATION AND CHARACTERIZATION OF MFIS-FET USING Bi3.25La0.75Ti3O12/ZrO2/Si STRUCTURE

ABSTRACT A metal-ferroelectric-insulator-semiconductor structure (MFIS) has been fabricated by ZrO2and Bi3.25La0.75Ti3O12 as the buffer layer and ferroelectric film in forming MFIS diodes on Si(100) substrates, respectively. ZrO2 films were prepared by a sol-gel method. Then, they were carried out dry O2 annealing in a rapid thermal annealing (RTA) furnace at 700°C for 10 min. On the ZrO2/Si structures, Bi3.25La0.75Ti3O12 films were deposited by sol-gel method and they crystallized rapid thermal annealing in O2 atmosphere at 750°C for 30 min. They were characterized by X-ray diffraction analysis (XRD) and atomic force microscopy (AFM). The memory window width in capacitance-voltage(C-V) curve of the Au/BLT/ZrO2/Si diode was about 1.0 V for a voltage sweep of ± 4 V. Base on these results, we fabricated the MFIS-FET structure. The memory window width in drain current–gate voltage (ID–VG) curve of the MFIS-FET was about 0.7 V.

The effect of resident-perceived neighborhood boundary on the equity of public parks distribution: using GIS

Because of the ready availability of various data at residence level, census tracts have been the spatial units most commonly selected. In some cases, municipally defined service districts have also been selected, and they are, in fact, only the aggregates of several neighboring census tracts. The problem encountered in the current study is that Census-based Neighborhoods such as census tracts and the aggregations of census tracts frequently do not correspond with commonly recognized neighborhoods experienced informally in daily life. The primary purpose of this study was to investigate the effects of Resident-perceived Neighborhood Boundaries (as the alternative unit of analysis to conventionally-used Census-based Neighborhood Units) on the accessibility to public parks based on equity consideration. The result indicates that when Resident-perceived Neighborhood Boundaries are adopted, there is no significant change the equity of accessibility to public park distribution among neighborhoods of different social strata.

Toward generalized planetary stereo analysis scheme—Prototype implementation with multi-resolution Martian stereo imagery

Stereo analysis of orbital imagery is highly valuable for scientific research in planetary surface. Thus, the processing of planetary stereo imagery has been progressed with various approaches and resulted in a series of uncontrolled topographic products. In order to fully utilize the data derived from image systems carried on various planetary orbiters, the generalized algorithms of stereo image processing and Digital Terrain Model (DTM) extraction have been developed. Based on Kim and Muller’s approach (2009), the algorithms were updated employing the feed-forwarded model-based matcher and the generic sensor model. It is a sort of iterative stereo procedure delivering the reference data to next stage for 3D zoom-up. Thus the system is capable of processing various stereo data sets with the generic approach and achieves stable photogrammetric accuracy of resultant DTMs. To demonstrate the potential of this stereo processing routine, the DTMs obtained from various Mars orbital images covering some sample test sites were processed with the prototype processor. As the result, the processed DTMs clearly illustrated detailed geological features and high agreement with the height spots of Mars Obiter Laser Altimeter (MOLA). It was proved that the overall processing strategy in this paper was effective and the topographic products were accurate and reliable.

Investigation of Potential Volcanic Risk from Mt. Baekdu by DInSAR Time Series Analysis and Atmospheric Correction

Mt. Baekdu is a volcano near the North Korea-Chinese border that experienced a few destructive eruptions over the course of its history, including the well-known 1702 A.D eruption. However, signals of unrest, including seismic activity, gas emission and intense geothermal activity, have been occurring with increasing frequency over the last few years. Due to its close vicinity to a densely populated area and the high magnitude of historical volcanic eruptions, its potential for destructive volcanic activity has drawn wide public attention. However, direct field surveying in the area is limited due to logistic challenges. In order to compensate for the limited coverage of ground observations, comprehensive measurements using remote sensing techniques are required. Among these techniques, Differential Interferometric SAR (DInSAR) analysis is the most effective method for monitoring surface deformation and is employed in this study. Through advanced atmospheric error correction and time series analysis, the accuracy of the detected displacements was improved. As a result, clear uplift up to 20 mm/year was identified around Mt. Baekdu and was further used to estimate the possible deformation source, which is considered as a consequence of magma and fault interaction. Since the method for tracing deformation was proved feasible, continuous DInSAR monitoring employing upcoming SAR missions and advanced error regulation algorithms will be of great value in monitoring comprehensive surface deformation over Mt. Baekdu and in general world-wide active volcanoes.

Fabrication and Characterization of MFIS-FET Using Au/BLT/LZO/Si Structures

We fabricated the n-channel metal-ferroelectric-insulator-semiconductor field-effect transistor (MFIS-FET) using an Au/(Bi,La) 4 Ti 3 O 12 /LaZrO x /Si(100) gate structure. We observed that the LaZrO x thin film had the equivalent oxide thickness value of around 8.7 nm. The 420-nm-thick (Bi,La) 4 Ti 3 O 12 film on a LaZrO x /Si structure, showed a good ferroelectric property and had the width of the memory window of 1.2 V for a bias voltage sweeping of ± 7 V. The drain current-gate voltage (I D -V G ) of an Au/(Bi,La) 4 Ti 3 O 12/ LaZrO x /Si(100) MFIS-FET showed threshold voltage shift (memory window width) owing to the ferroelectric (Bi,La) 4 Ti 3 O 12 film. The drain current-drain voltage (I D -V D ) characteristic curves exhibit typical n-channel field-effect transistor current-voltage characteristic. However, relatively large leakage current observed in the I D –V G and the I D –V D characteristic curves, might be caused by the high density of pores in the BLT film.

Thin Film Properties of Sol-Gel Derived High-K Lanthanum-Doped Zirconium Oxides

The lanthanum zirconium oxide thin films were prepared on p-type Si(100) by a sol-gel wet method. Sol-gel solutions of La x Zr 1 − x O y with La atomic fractions of x = 0, 0.05, 0.1, 0.3, and 0.5 were synthesized for film deposition. Thin films were characterized using x-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM). Electrical property characterization was performed with metal-insulator-semiconductor (MIS) structures through capacitance-voltage (C-V) and current density-voltage (J-V) measurements. The thin film showed a good surface morphology. Equivalent oxide thickness (EOT) values of 30 nm-thick La x Zr 1 − x O y thin films annealed at 700°C were about 8.8–10.5 nm. C-V measurements revealed that curves shifted left when the film has a larger content of La or was annealed at a higher temperature. The leakage current density was below 1.0 × 10−6 A/cm 2 at 1 MV/cm for all samples.

BLT/STA/Si Structure for MFIS in an NDRO-Type Ferroelectric Random Access Memory

Ferroelectric (Bi,La) 4 Ti 3 O 12 (BLT) thin films were prepared on a p-type Si (100) wafer with a SrTa 2 O 6 (STA) buffer layer for a metal-ferroelectric-insulator-silicon (MFIS) structure. The STA buffer layer was completely crystallized at the high temperature over 800°C. We observed that STA thin films fabricated at 900°C for 3 minutes in O 2 ambient had good insulating properties. Their EOT value was about 5.7 nm. Considering the distribution of the bias voltage on a series capacitor, the ferroelectric BLT and the dielectric STA, BLT thin films with a different thickness were formed on STA/Si structures and characterized by C-V measurement including memory windows. It was found that the memory window width was about 1.5 V for the ±5 V bias sweeping with the 600 nm thick BLT films on STA/Si structure. The leakage current density was about 1.0 × 10−7 A/cm 2 at 5 V. These results are useful and promise the realization of a MFIS structure with the BLT and a STA layer for non-destructive read-out (NDRO) type ferroelectric memories.

Automatic Building Extraction from LIDAR Data and Digital Maps

As the use of building models are rapidly increased for various applications, many studies have been performed to develop a practical and nearly automatic method to extract such models from various sensory and GIS data. Nevertheless, it is still a difficult problem to extract the models of large-complex buildings in particular. The purpose of this study is thus to develop a fully automatic method to extract the detail models of buildings from LIDAR data and a digital map. This extraction consisting of primitive extraction and modeling is mainly based on robust segmentation of planar patches from numerous LIDAR points. These primary primitives are used as the references to generate secondary primitives such as edges and corners and then refined based on these secondary primitives to form a complete polyhedral model. The proposed method was successfully applied to extracting large-complex buildings from real data in the test site. It can be a promising time- and cost-effective solution for a country to enhance their traditional map to include 3D models of buildings.

The GIS Strategy for Urban Infrastructure Management in Korea

With the rapid development of IT, the society is becoming highly information-based and community development is depending on the level of computerization. Also, with the growth of the cities, more reasonable decision-making is required based on efficient information management of basic facilities such as urban space and underground utilities. Korean government organized a steering committee for the master plan of the National Geographic Information Systems (NGIS) so that government departments, autonomous bodies and enterprises may cooperatively establish a firm foothold to develop and utilize the GIS. The 1st NGIS master plan was established in May, 1995 and was carried out through 2000. The 2nd NGIS (2001–2005) is under way at present. Each municipality has been trying to utilize the GIS systematically in management of basic facilities such as water, sewage pipeline, road and transportation to enhance administrative affairs and administrative services for citizens. Also, they are striving to use the GIS to minimize natural or man-made disasters and to deal with internal and external environmental changes. This study presents the strategy to reform GIS construction for the better urban infrastructure-especially underground facilities-management on the basis of problems found in the GIS projects that were previously carried out.