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Search Results: 1 - 10 of 439132 matches for " K. S. Kim "
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Organic carbon efflux from a deciduous forest catchment in Korea
S. J. Kim, J. Kim,K. Kim
Biogeosciences (BG) & Discussions (BGD) , 2010,
Abstract: Soil infiltration and surface discharge of precipitation are critical processes that affect the efflux of Dissolved Organic Carbon (DOC) and Particulate Organic Carbon (POC) in forested catchments. Concentrations of DOC and POC can be very high in the soil surface in most forest ecosystems and their efflux may not be negligible particularly under the monsoon climate. In East Asia, however, there are little data available to evaluate the role of such processes in forest carbon budget. In this paper, we address two basic questions: (1) how does stream discharge respond to storm events in a forest catchment? and (2) how much DOC and POC are exported from the catchment particularly during the summer monsoon period? To answer these questions, we collected hydrological data (e.g., precipitation, soil moisture, runoff discharge, groundwater level) and conducted hydrochemical analyses (including DOC, POC, and six tracers) in a deciduous forest catchment in Gwangneung National Arboretum in west-central Korea. Based on the end-member mixing analysis of the six storm events during the summer monsoon in 2005, the surface discharge was estimated as 30 to 80% of the total runoff discharge. The stream discharge responded to precipitation within 12 h during these storm events. The annual efflux of DOC and POC from the catchment was estimated as 0.04 and 0.05 t C ha 1 yr 1, respectively. Approximately 70% of the annual organic carbon efflux occurred during the summer monsoon period. Overall, the annual efflux of organic carbon was estimated to be about 10% of the Net Ecosystem carbon Exchange (NEE) obtained by eddy covariance measurement at the same site. Considering the current trends of increasing intensity and amount of summer rainfall and the large interannual variability in NEE, ignoring the organic carbon efflux from forest catchments would result in an inaccurate estimation of the carbon sink strength of forest ecosystems in the monsoon East Asia.
Organic carbon sequestration and discharge from a deciduous forest catchment in Korea
S. J. Kim,J. Kim,K. Kim
Biogeosciences Discussions , 2009,
Abstract: Soil infiltration and surface discharge of precipitation are critical processes that affect the sequestration and discharge of dissolved organic carbon (DOC) and particulate organic carbon (POC) in forested catchments. Both DOC and POC are highly concentrated in the soil surface in most forest ecosystems and their discharge may not be negligible particularly under the monsoon climate. In East Asia, however, there are little data available to evaluate the role of such processes in forest carbon budget. In this paper, we address two basic questions: 1) how does stream discharge respond to storm events in a forest catchment? and 2) how much DOC and POC are discharged from the catchment particularly during the summer monsoon period? To answer these questions, we collected hydrological data (e.g., precipitation, soil moisture, runoff discharge, groundwater level) and conducted hydrochemical analyses (including DOC, POC, and six tracers) for a deciduous forest catchment in Gwangneung National Arboretum in west-central Korea. Based on the end-member mixing analysis of the six storm events during the summer monsoon in 2005, the surface discharge was estimated as 30 to 80% of the total runoff discharge. The stream discharge responded to precipitation within 12 h during these storm events. The annual discharge of DOC and POC from the catchment was estimated as 0.04 and 0.05 t C ha 1 yr 1, respectively. Approximately 70% of the annual organic carbon efflux occurred during the summer monsoon period. Overall, the annual discharge of organic carbon was estimated to be 4 to 14% of the net ecosystem carbon exchange (NEE) obtained by eddy covariance technique at the same site. Considering the current trends of increasing intensity and amount of summer rainfall and the large interannual variability in NEE, ignoring the organic carbon discharge from forest ecosystems would result in an overestimation (underestimation) of the strength of forests as a carbon sink (source) in the monsoon East Asia.
Evaluation of Accuracy and Precision of IRMS by Using Standard Materials and Applications  [PDF]
J. Y. Hwang, B. K. Kim, M. S. Kim, J. W. Choi, T. S. Kim, W. S. Lee
Journal of Agricultural Chemistry and Environment (JACEN) , 2016, DOI: 10.4236/jacen.2016.54022
Abstract: The isotope ratio mass spectrometer (IRMS) is an instrument that measures both of the elemental contents and isotope ratios of hydrogen, oxygen, carbon, nitrogen and sulfur in environmental samples at the same time. In this study, we want to try to get two main goals; first, to make up for setting the analytical conditions such as accuracy and precision, second, to apply for comparing of the carbon and nitrogen isotope ratio of sediments in the abandoned mine located in middle province of Korea. For the first goal, a recently introduced IRMS was used to analyze CRM (certified reference materials), which helped to make up the analytical conditions of carbon and nitrogen isotope ratios. So, the accuracy and precision of isotope ratios and elemental contents were also assessed simultaneously, and also the results were very satisfactory. The analytical results of carbon reference materials (EMA-P2) showed an accuracy of -2.801 × 10‰ ± 0.01‰ (2σ) and a precision of 0.009‰ in the mass range from 0.008 μg - 0.162 μg. For nitrogen reference materials (EMA-P2), an accuracy of -1.632‰ ± 0.72‰ (2σ) was obtained in the mass range from 0.082 - 0.162 mg. These values of accuracy and precision are higher than those reported by other studies. For the second goal, carbon and nitrogen isotopes in river sediment near abandoned mines were analyzed based on the established analytical conditions. The result suggested that carbon isotope ratios ranged from -22.5‰ - -7.5‰ and nitrogen isotope ratios from -1.9‰ - 7.9‰. By comparing the isotope ratios and sampling sites of sediment, we know that the nitrogen isotope values in samples of entrance area of mine are greater than those of the farm house area, which is indicating the effects of organic materials. So, we could guess that the newly accumulated organic materials were much more in the farm house area than mine entrance area. And a result of this study, the accuracy and precision tests of IRMS using certified reference materials were very satisfactory and optimum analytical conditions were established well. And also, it was found that the applications of isotopic analysis for environmental samples by using the IRMS could be very useful for the studies on tracing pollution sources.
Analysis of Dynamic Cross Response between Spindles in a Dual Spindle Type Multi-Functional Turning Machine  [PDF]
Y. H. Choi, S. T. Kim, T. Y. Seo, K. H. Kim
Journal of Power and Energy Engineering (JPEE) , 2013, DOI: 10.4236/jpee.2013.17004
Abstract:

In order to meet increasing demand for higher productivity and flexibility, recently many kinds of multi-functional machine tools, which are capable of multiple machining functions or different kinds of machining processes on one machine, have been developed and widely used in manufacturing industries. In this study, a multi-functional turning lathe, which has two spindles and two turrets so that multiple turning operations and various machining processes could be performed simultaneously, has been developed. Furthermore, the equations of correlation between whole responses and cross responses of the two spindles have been derived to examine to what extent the two spindles affect each other’s vibrations.

Structural and mechanical properties of cellulose acetate/graphene hybrid nanofibers: Spectroscopic investigations
B. S. Kim,I. S. Kim,K. Zeeshan,K. Fujimori
eXPRESS Polymer Letters , 2013, DOI: 10.3144/expresspolymlett.2013.52
Abstract: Cellulose acetate/graphene (CA/graphene) and cellulose acetate/graphene-COOH (CA/graphene-COOH) hybrid nanofibers were fabricated via electrospinning technique, and their morphologies, crystallinity and mechanical properties were investigated. The added amounts of graphene and graphene-COOH were varied from 0.5 to 5.0 wt%. The crystal structures and morphologies of the resultant hybrid nanofibers were investigated by wide angle X-ray diffraction (WAXD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. Graphene-COOH incorporated CA nanofiber mats showed higher Young’s modulus of about 910 MPa among than those of CA/graphene nanofibers, which is due to molecular interactions between –COOH groups in acid-treated graphene and C=O groups in CA via hydrogen bonding. This specific interaction was demonstrated by spectroscopic studies (Raman and Fourier transform infrared (FT-IR) spectroscopies).
Experimental Studies of Neural Network Control for One-Wheel Mobile Robot
P. K. Kim,S. Jung
Journal of Control Science and Engineering , 2012, DOI: 10.1155/2012/194397
Abstract: This paper presents development and control of a disc-typed one-wheel mobile robot, called GYROBO. Several models of the one-wheel mobile robot are designed, developed, and controlled. The current version of GYROBO is successfully balanced and controlled to follow the straight line. GYROBO has three actuators to balance and move. Two actuators are used for balancing control by virtue of gyro effect and one actuator for driving movements. Since the space is limited and weight balance is an important factor for the successful balancing control, careful mechanical design is considered. To compensate for uncertainties in robot dynamics, a neural network is added to the nonmodel-based PD-controlled system. The reference compensation technique (RCT) is used for the neural network controller to help GYROBO to improve balancing and tracking performances. Experimental studies of a self-balancing task and a line tracking task are conducted to demonstrate the control performances of GYROBO. 1. Introduction Mobile robots are considered as quite a useful robot system for conducting conveying objects, conducting surveillance, and carrying objects to the desired destination. Service robots must have the mobility to serve human beings in many aspects. Most of mobile robots have a two-actuated wheel structure with three- or four-point contact on the ground to maintain stable pose on the plane. Recently, the balancing mechanism becomes an important issue in the mobile robot research. Evolving from the inverted pendulum system, the mobile-inverted pendulum system (MIPS) has a combined structure of two systems: an inverted pendulum system and a mobile robot system. Relying on the balancing mechanism of the MIPS, a personal transportation vehicle has been introduced [1]. The MIPS has two-point contact to stabilize itself. Advantages of the MIPS include robust balancing against small obstacles on the ground and possible narrow turns while three- or four-point contact mobile robots are not able to do so. In research on balancing robots, two-point contact mobile robots are designed and controlled [1–5]. A series of balancing robots has been implemented and demonstrated their performances [3–5]. Currently, successful navigation and balancing control performances with carrying a human operator as a transportation vehicle have been reported [5]. More challengingly, one-wheel mobile robots are developed. A one-wheel robot is a rolling disk that requires balancing while running on the ground [6]. Gyrover is a typical disc-typed mobile robot that has been developed and presented for
Quantum Boltzman equation study for the Kondo breakdown quantum critical point
K. -S. Kim,C. Pepin
Physics , 2009, DOI: 10.1088/0953-8984/22/2/025601
Abstract: We develop the quantum Boltzman equation approach for the Kondo breakdown quantum critical point, involved with two bands for conduction electrons and localized fermions. Particularly, the role of vertex corrections in transport is addressed, crucial for non-Fermi liquid transport of temperature linear dependence. Only one band of spinons may be considered for scattering with gauge fluctuations, and their associated vertex corrections are introduced in the usual way, where divergence of self-energy corrections is cancelled by that of vertex corrections, giving rise to the physically meaningful result in the gauge invariant expression for conductivity. On the other hand, two bands should be taken into account for scattering with hybridization excitations, giving rise to coupled quantum Boltzman equations. We find that vertex corrections associated with hybridization fluctuations turn out to be irrelevant due to heavy mass of spinons in the so called decoupling limit, consistent with the diagrammatic approach showing the non-Fermi liquid transport.
The thermopower as a fingerprint of the Kondo breakdown quantum critical point
K. -S. Kim,C. Pepin
Physics , 2010, DOI: 10.1103/PhysRevB.83.073104
Abstract: We propose that the thermoelectric power distinguishes two competing scenarios for quantum phase transitions in heavy fermions : the spin-density-wave (SDW) theory and breakdown of the Kondo effect. In the Kondo breakdown scenario, the Seebeck coefficient turns out to collapse from the temperature scale $E^{*}$, associated with quantum fluctuations of the Fermi surface reconfiguration. This feature differs radically from the physics of the SDW theory, where no reconstruction of the Fermi surface occurs, and can be considered as the hallmark of the Kondo breakdown theory. We test these ideas, upon experimental results for YbRh$_2$Si$_2$.
Quantization of electromagnetic fields in a circular cylindrical cavity
K. Kakazu,Y. S. Kim
Physics , 1995,
Abstract: We present a quantization procedure for the electromagnetic field in a circular cylindrical cavity with perfectly conducting walls, which is based on the decomposition of the field. A new decomposition procedure is proposed; all vector mode functions satisfying the boundary conditions are obtained with the help of this decomposition. After expanding the quantized field in terms of the vector mode functions, it is possible to derive the Hamiltonian for this quantized system.
Kinematics of a cascade decay for the precision measurement of $^{29}{\rm Si}$ binding energy
Yongkyu Ko,K. S. Kim
Physics , 2011,
Abstract: Comparison of a Penning trap and a flat-crystal spectrometer experiments gives a direct test of $E=mc^2$. The result is $1-\Delta mc^2/E =(-1.4 \pm 4.4) \times 10^{-7}$ for $^{29}{\rm Si}$ and $^{33}{\rm S}$. The dominant uncertainty is on the $\gamma$-ray measurement in neutron capture reactions, and the secondary $\gamma$-ray has the uncertainty 4.0 eV for $^{29}{\rm Si}$. We calculated the Doppler effect of the secondary $\gamma$-ray as $-646.9 \cos \theta$ eV from the relativistic energy momentum relation of the $^{28}{\rm Si}(n,\gamma)^{29}{\rm Si}$ reaction. This corresponds to the full wave of half maximum of 431.3 eV. The error 4.0 eV comes mainly from the Bragg angle measurement between the centroids of the linewidths which means that only the most probable part of the whole data has been considered. It is necessary to confirm the assumption of the isotropy for the object to measure. We discussed a coincidence measurement as one of the methods to overcome the assumption.
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