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Search Results: 1 - 10 of 354368 matches for " J. W. Choi "
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Determination of Integrated Risk Degrees in Product Development Project
D. W. Choi,J. S. Kim,H. G Choi
Lecture Notes in Engineering and Computer Science , 2009,
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.
Autophagy in Inflammatory Diseases
Alexander J. S. Choi,Stefan W. Ryter
International Journal of Cell Biology , 2011, DOI: 10.1155/2011/732798
Abstract: Autophagy provides a mechanism for the turnover of cellular organelles and proteins through a lysosome-dependent degradation pathway. During starvation, autophagy exerts a homeostatic function that promotes cell survival by recycling metabolic precursors. Additionally, autophagy can interact with other vital processes such as programmed cell death, inflammation, and adaptive immune mechanisms, and thereby potentially influence disease pathogenesis. Macrophages deficient in autophagic proteins display enhanced caspase-1-dependent proinflammatory cytokine production and the activation of the inflammasome. Autophagy provides a functional role in infectious diseases and sepsis by promoting intracellular bacterial clearance. Mutations in autophagy-related genes, leading to loss of autophagic function, have been implicated in the pathogenesis of Crohn's disease. Furthermore, autophagy-dependent mechanisms have been proposed in the pathogenesis of several pulmonary diseases that involve inflammation, including cystic fibrosis and pulmonary hypertension. Strategies aimed at modulating autophagy may lead to therapeutic interventions for diseases associated with inflammation. 1. Introduction 1.1. Inflammation Acute inflammation acts as part of the host’s innate protective response to infection or tissue injury. Endothelial cell injury or microbial infection causes changes in vascular permeability, local edema, and in the distribution of chemoattractants [1, 2]. The activation of endothelial cells allows the transmigration of leukocytes, initially primarily neutrophils (polymorphonuclear (PMN) cells), to the site of tissue injury [3]. Finally, macrophages uptake apoptotic PMN cells, cellular debris, and invasive pathogens via phagocytosis during the resolution of acute inflammation, which leads to neutrophil clearance and the release of anti-inflammatory cytokines such as transforming growth factor-β1. The resolution program ends with the efflux of macrophages from the site of inflammation through lymphatics [4]. However, aberrant inflammatory responses can be associated with a wide range of acute, chronic, and systemic inflammatory disorders, such as cardiovascular disease, asthma, inflammatory bowel disease, rheumatoid arthritis [1], and cystic fibrosis [5]. In recent years, emerging evidence has indicated that the process of macroautophagy may play an essential role for the host during bacterial clearance [6] as well as interact with inflammatory processes, and thereby potentially impact the outcome of disease progression. 1.2. Autophagy Macroautophagy
Thermoelectric power of MgB$_{2-x}$Be$_x$
J. S. Ahn,E. S. Choi,W. Kang,D. J. Singh,E. J. Choi
Physics , 2002, DOI: 10.1103/PhysRevB.65.214534
Abstract: We investigated thermoelectric power $S(T)$ of MgB$_{2-x}$Be$_{x}$ ($x=0$, 0.2, 0.3, 0.4, and 0.6). $S(T)$ decreases systematically with $x$, suggesting that the hole density increases. Our band calculation shows that the increase occurs in the $\sigma $-band. With the hole-doping, $T_{c}$ decreases. Implication of this phenomenon is discussed within the BCS framework. While the Mott formula explains only the linear part of $S(T)$ at low temperature, incorporation of electron-phonon interaction enables us to explain $S(T)$ over wide temperature range including the anomalous behavior at high temperature.
Impurity Effects of Aerogel in Superfluid $^{3}$He
W. P. Halperin,H. Choi,J. P. Davis,J. Pollanen
Physics , 2008, DOI: 10.1143/JPSJ.77.111002
Abstract: The discovery of superfluid $^{3}$He in high porosity silica aerogels, and subsequent experimental and theoretical work, have led to a better general understanding of quasiparticle scattering from impurities in unconventional pairing systems. It is immensely helpful for understanding impurity effects in the case of superfluid $^{3}$He that the structure of its order parameter is well-established. An overview of impurity effects is presented with emphasis on those experiments which have a quantitative interpretation in terms of theoretical models for homogeneous and inhomogeneous scattering. The latter can account successfully for most experimental results.
Acoustic Spectroscopy of Superfluid 3He in Aerogel
J. P. Davis,H. Choi,J. Pollanen,W. P. Halperin
Physics , 2006, DOI: 10.1063/1.2354682
Abstract: We have designed an experiment to study the role of global anisotropic quasiparticle scattering on the dirty aerogel superfluid 3He system. We observe significant regions of two stable phases at temperatures below the superfluid transition at a pressure of 25 bar for a 98% aerogel.
Imaginary Squashing Mode Spectroscopy of Helium Three B
J. P. Davis,H. Choi,J. Pollanen,W. P. Halperin
Physics , 2006, DOI: 10.1007/s10909-007-9417-7
Abstract: We have made precision measurements of the frequency of a collective mode of the superfluid 3He-B order parameter, the J=2- imaginary squashing mode. Measurements were performed at multiple pressures using interference of transverse sound in an acoustic cavity. Transverse waves propagate in the vicinity of this order parameter mode owing to off-resonant coupling. At the crossing of the sound mode and the order parameter mode, the sound wave is strongly attenuated. We use both velocity and attenuation measurements to determine precise values of the mode frequency with a resolution between 0.1% and 0.25%.
High frequency sound in superfluid 3He-B
J. P. Davis,H. Choi,J. Pollanen,W. P. Halperin
Physics , 2008, DOI: 10.1007/s10909-008-9819-1
Abstract: We present measurements of the absolute phase velocity of transverse and longitudinal sound in superfluid 3He-B at low temperature, extending from the imaginary squashing mode to near pair-breaking. Changes in the transverse phase velocity near pair-breaking have been explained in terms of an order parameter collective mode that arises from f-wave pairing interactions, the so-called J=4- mode. Using these measurements, we establish lower bounds on the energy gap in the B-phase. Measurement of attenuation of longitudinal sound at low temperature and energies far above the pair-breaking threshold, are in agreement with the lower bounds set on pair-breaking. Finally, we discuss our estimations for the strength of the f-wave pairing interactions and the Fermi liquid parameter, F4s.
Collective Modes and f-wave Pairing Interactions in Superfluid 3He
J. P. Davis,H. Choi,J. Pollanen,W. P. Halperin
Physics , 2006, DOI: 10.1103/PhysRevLett.97.115301
Abstract: Precision measurements of a collective mode in superfluid 3He B are sensitive to quasiparticle and f wave pairing interactions. Measurements were performed at various pressures using interference of transverse sound in an acoustic cavity. We fit the measured collective mode frequencies, which depend on the strength of f wave pairing and the Fermi liquid parameter F2s, to theoretical predictions and discuss what implications these values have for observing new order parameter collective modes.
Magneto-Acoustic Spectroscopy in Superfluid 3He-B
J. P. Davis,H. Choi,J. Pollanen,W. P. Halperin
Physics , 2007, DOI: 10.1103/PhysRevLett.100.015301
Abstract: We have used the recently discovered acoustic Faraday effect in superfluid 3He to perform high resolution spectroscopy of an excited state of the superfluid condensate. With acoustic cavity interferometry we measure the rotation of the plane of polarization of a transverse sound wave propagating in the direction of magnetic field from which we determine the Zeeman energy of the excited state. We interpret the Lande g-factor, combined with the zero-field energies of the state, using the theory of Sauls and Serene to calculate the strength of f -wave interactions in 3He.
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