• Economic and Environmental Geology
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• v.39 no.4 s.179
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• pp.473-483
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• 2006

Although application of electrical methods in Korea began with observation of self potentials before World War II, the methods were developed slowly by the beginning of 1980's when a major burst of development activity took place. DC resistivity methods are applied in Korea more to geotechnical problems rather than to environmental ones unlike other developed countries. As with every other branch of technology, the evolving speed of the silicon chip and of streaming data to hard disk has revolutionized data collection and noise reduction processing. The last two decades saw major advances in data collection, processing, and interpretation of electrical data. Development of smooth-model two-dimensional (2D) resistivity inversion is one of the most visible changes to geophysical interpretation of the last 40 years and is now routinely applied to apparent resistivity data. The ability to represent resistivities in section rather than pseudosection view has revolutionized interpretation. Although calculation of sensitivities for general electromagnetic problems require numerous forward modelings, DC resistivity methods can enjoy computational efficiencies if sources and receivers occupy the same position, and previously intractable 3D inversion is now becoming available.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.4
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• pp.1504-1526
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• 2018

For uplink multi-user massive MIMO systems, conventional minimum mean square error (MMSE) linear detection method achieves near-optimal performance when the number of antennas at base station is much larger than that of the single-antenna users. However, MMSE detection involves complicated matrix inversion, thus making it cumbersome to be implemented cost-effectively and rapidly. In this paper, we first summarize in detail the state-of-the-art simplified MMSE detection algorithms that circumvent the complicated matrix inversion and hence reduce the computation complexity from ${\mathcal{O}}(K^3)$ to ${\mathcal{O}}(K^2)$ or ${\mathcal{O}}(NK)$ with some certain performance sacrifice. Meanwhile, we divide the simplified algorithms into two categories, namely the matrix inversion approximation and the classical iterative linear equation solving methods, and make comparisons between them in terms of detection performance and computation complexity. In order to further optimize the detection performance of the existing detection algorithms, we propose more proper solutions to set the initial values and relaxation parameters, and present a new way of reconstructing the exact effective noise variance to accelerate the convergence speed. Analysis and simulation results verify that with the help of proper initial values and parameters, the simplified matrix inversion based detection algorithms can achieve detection performance quite close to that of the ideal matrix inversion based MMSE algorithm with only a small number of series expansions or iterations.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.3-6
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• 2006

There are three types of frequency-domain loop-loop EM induction method, depending on the loop separation and their location relative to the ground surface: horizontal-loop EM (HLEM), fixed small-loop EM, and helicopter-borne EM (HEM) methods. Multidimensional inversion provides tomographic images of the subsurface resistivity structure and thus enhances the interpretational accuracy of loop-loop EM data. HLEM method is shown to be effective for exploring groundwater resources in weathered and fractured crystalline basement terrains in semi-arid regions. Also, HEM method is useful for locating weak zones in landslide areas. The applicability of inversion to small-loop EM data depends solely on the S/N ratio. The quadrature response of small-loop EM data can only give the equivalent conductivity of a homogenous half-space model, and thus the in-phase component is essential in inverting EM data. However, the in-phase response is much lower and decreases more rapidly with decreasing frequency than the quadrature response. Further work is needed to obtain conductivity-depth images from small-loop EM data.

• Bulletin of the Korean Chemical Society
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• v.26 no.9
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• pp.1339-1343
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• 2005

The N-inversion energies and nucleophilic ring-opening reactions of N-substituted aziridine compounds are investigated using B3LYP/6-31+$G^*$ methods, where substituents (R) on the nitrogen atom has been H (1), Me (2), Ph (3), Bn (4), CHMePh (5), $CO_2Me$ (6), COPh (7) and $SO_2Ph$ (8). The N-inversion energy with X group are decreased as the following order: R = CHMePh (17.06 kcal/mol) $\gt$ Me (16.97) $\gt$ Bn (16.70) $\gt$ H (16.64) $\gt$ $SO_2Ph$ (12.18) $\gt$ Ph (8.91) $\gt$ COPh (5.75) $\gt$ $CO_2Me$ (5.48). For reactivity of the ring opening toward cyanide ion, the aziridine 6 (R=$CO_2Me$) is shown to be the most reactive one. During the ring opening of aziridine 6 by CN$^{\ominus}$, the torsional OCNC angle becomes near to $180^{\circ}$, where the geometry allows for the effective incorporation of electrons of the nitrogen atom to the C=O bond. It would be a possible driving force for nucleophilic ring opening reaction as well as decreasing the N-inversion energy barrier. Regarding to the regioselectivity, the orientation of nucleophile in ring opening reaction appears to be different in the case of 9 and 10. The results are discussed in terms of steric/electronic effect of the $C_2$-substituents.

• Journal of Biosystems Engineering
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• v.39 no.4
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• pp.345-351
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• 2014

Purpose: Rapid detection of bacteria is very important in agricultural and food industries to prevent many foodborne illnesses. The objective of this study was to develop a portable nuclear magnetic resonance (NMR)-based system to detect foodborne pathogens (E. coli). This study was focused on developing a method to detect low concentrations of magnetic nanoparticles using NMR techniques. Methods: NMR relaxometry was performed to examine the NMR properties of iron nanoparticle mixtures with different concentrations by using a 1 T permanent magnet magnetic resonance imaging system. Exponential curve fitting (ECF) and inverse Laplace transform (ILT) methods were used to estimate the NMR relaxation time constants, $T_1$ and $T_2$, of guar gum solutions with different iron nanoparticle concentrations (0, $10^{-3}$, $10^{-4}$, $10^{-5}$, $10^{-6}$, and $10^{-7}M$). Results: The ECF and ILT methods did not show much difference in these values. Analysis of the NMR relaxation data showed that the ILT method is comparable to the classical ECF method and is more sensitive to the presence of iron nanoparticles. This study also showed that the spin-spin relaxation time constants acquired by a Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence are more useful for determining the concentration of iron nanoparticle solutions comparwith the spin-lattice relaxation time constants acquired by an inversion recovery pulse sequence. Conclusions: We conclude that NMR relaxometry that utilizes CPMG pulse sequence and ILT analysis is more suitable for detecting foodborne pathogens bound to magnetic nanoparticles in agricultural and food products than using inversion recovery pulse sequence and ECF analysis.

• Journal of the Korean earth science society
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• v.22 no.3
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• pp.179-185
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• 2001

Borehole tests are commonly used as a tool to obtain the physical properties of soils and rocks. The results of borehole tests are, however, discontinuous. Interpolation methods are applied to interpret the data gap between the borehole test points. The interpolation is valid only if the horizontal variations of the ground between the test points are small enough to ignore. A surface wave inversion method was used to study the S wave velocity of the very soft soil to provide the continuous 2 dimensional S wave velocity structure. The resolution of the S wave velocity structure was used to interpret the inversion results.

• Investigative Magnetic Resonance Imaging
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• v.19 no.2
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• pp.67-75
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• 2015

Purpose: To investigate the value of image post-processing software (FreeSurfer, IBASPM [individual brain atlases using statistical parametric mapping software]) and inversion time (TI) in volumetric analyses of the hippocampus and to identify differences in comparison with manual tracing. Materials and Methods: Brain images from 12 normal adults were acquired using magnetization prepared rapid acquisition gradient echo (MPRAGE) with a slice thickness of 1.3 mm and TI of 800, 900, 1000, and 1100 ms. Hippocampal volumes were measured using FreeSurfer, IBASPM and manual tracing. Statistical differences were examined using correlation analyses accounting for spatial interpretations percent volume overlap and percent volume difference. Results: FreeSurfer revealed a maximum percent volume overlap and maximum percent volume difference at TI = 800 ms ($77.1{\pm}2.9%$) and TI = 1100 ms ($13.1{\pm}2.1%$), respectively. The respective values for IBASPM were TI = 1100 ms ($55.3{\pm}9.1%$) and TI = 800 ms ($43.1{\pm}10.7%$). FreeSurfer presented a higher correlation than IBASPM but it was not statistically significant. Conclusion: FreeSurfer performed better in volumetric determination than IBASPM. Given the subjective nature of manual tracing, automated image acquisition and analysis image is accurate and preferable.

• Journal of Korean Society on Water Environment
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• v.31 no.3
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• pp.272-285
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• 2015

Accurate assessment of chlorophyll-a (Chl-a) concentrations in inland waters using remote sensing is challenging due to the optical complexity of case 2 waters. and the inherent optical properties (IOPs) of natural waters are the most significant factors affecting light propagation within water columns, and thus play indispensable roles on estimation of Chl-a concentrations. Despite its importance, no IOPs retrieval model was specifically developed for inland water bodies, although significant efforts were made on oceanic inversion models. So we have applied and validated a recently developed Red-NIR three-band model and an IOPs Inversion Model for estimating Chl-a concentration and deriving inland water IOPs in Lake Uiam. Three band and IOPs based Chl-a estimation model accuracy was assessed with samples collected in different seasons. The results indicate that this models can be used to accurately retrieve Chl-a concentration and absorption coefficients. For all datasets the determination coefficients of the 3-band models versus Chl-a concentration ranged 0.65 and 0.88 and IOPs based model versus Chl-a concentration varied from 0.73 to 0.83 respectively. and Comparison between 3-band and IOPs based models showed significant performance with decrease of root mean square error from 18% to 33.6%. The results of this study provides the potential of effective methods for remote monitoring and water quality management in turbid inland water bodies using hyper-spectral remote sensing.

• Geophysics and Geophysical Exploration
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• v.27 no.2
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• pp.129-143
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• 2024

In magnetotelluric (MT) surveys, small inhomogeneities near the surface cause a static shift in which apparent resistivities shift regardless of frequency. As the static shift in MT data leads to errors in subsurface structure interpretation, many studies have been conducted over the past few decades to mitigate or remove the distortions it caused. The most representative method involves removing static shifts from the data before inversion. Conversely, static shifts can be corrected during inversion or included in the inversion process. In addition, other geophysical data can be used to remove static shifts. However, the correction methods are limited to one-dimensional (1D) static responses, and limitations remain in two- or three-dimensional (2D or 3D) interpretation of distorted MT data owing to static shifts. This study provides a foundation for future studies on static shift by analyzing several previously published methods.

• Journal of Forest and Environmental Science
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• v.28 no.1
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• pp.24-29
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• 2012

This paper assesses the stmpage value of Korean white pine (Pinus koraiensis) stands in the Research Forest of Kangwon National University. Assessment was done by means of the cost value method (Faustmann formula) for age class I, Glaser method for age class II-V, and inversion market method for age class over VI. Generally the value of stumpage is calculated by the inversion market method in the market. However, immature trees and middle age class trees are not assessed in market, and the Korean forest is not old enough to harvest. So, when forests are damaged by attacks from forest fire, blight and harmful insects, the forest cannot be compensated for the loss from the government or insurance company. For this reason, the value of all-age class trees are calculated by using appropriate methods. As a result, the value of age I class stands (0.3 ha) is calculated as 1,786,305 (won), age II-Vclass stands (22.1 ha) 206,677,975 (won) and age VI class and over stands (24.8 ha) 523,789,603 (won).