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Search Results: 1 - 10 of 11130 matches for " Chul-Sik Pan "
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Regulation of cerebrospinal fluid production by caffeine consumption
Myoung-Eun Han, Hak-Jin Kim, Young-Suk Lee, Dong-Hyun Kim, Joo-Taek Choi, Chul-Sik Pan, Sik Yoon, Sun-Yong Baek, Bong-Seon Kim, Jae-Bong Kim, Sae-Ock Oh
BMC Neuroscience , 2009, DOI: 10.1186/1471-2202-10-110
Abstract: In the present study we found that the long-term consumption of caffeine can induce ventriculomegaly; this was observed in 40% of the study rats. In the caffeine-treated rats with ventriculomegaly, there was increased production of CSF, associated with the increased expression of Na+, K+-ATPase and increased cerebral blood flow (CBF). In contrast to the chronic effects, acute treatment with caffeine decreased the production of CSF, suggesting 'effect inversion' associated with caffeine, which was mediated by increased expression of the A1 adenosine receptor, in the choroid plexus of rats chronically treated with caffeine. The involvement of the A1 adenosine receptor in the effect inversion of caffeine was further supported by the induction of ventriculomegaly and Na+, K+-ATPase, in A1 agonist-treated rats.The results of this study show that long-term consumption of caffeine can induce ventriculomegaly, which is mediated in part by increased production of CSF. Moreover, we also showed that adenosine receptor signaling can regulate the production of CSF by controlling the expression of Na+, K+-ATPase and CBF.Methylxanthine caffeine is present in many common beverages, and is widely consumed worldwide [1,4]. Caffeine consumption has been estimated to be 76 mg per person per day worldwide, as high as 238 mg per person per day in the United States and Canada, and more than 400 mg per person per day in Sweden and Finland [5,6]. Caffeine is absorbed rapidly after oral administration and distributed to various organs and tissues. In the liver, caffeine is metabolized to dimethyl- and monomethylxanthines, dimethyl and monomethyl uric acids, trimethyl- and dimethylallantoin, and uracil derivatives. Some metabolites of caffeine including 1,3-dimethylxanthine (theophylline) and 1,7-dimethylxanthine (paraxanthine) have pharmacological activity similar to caffeine [4]. The half-life of caffeine is ~5 hours in humans and ~1 hour in rats [4,7].The main mechanism of action of caffei
Effects of High EGR Rate on Dimethyl Ether (DME) Combustion and Pollutant Emission Characteristics in a Direct Injection Diesel Engine
Seung Hyun Yoon,Seung Chul Han,Chang Sik Lee
Energies , 2013, DOI: 10.3390/en6105157
Abstract: This study investigated the effects of high exhaust gas recirculation (EGR) rates on dimethyl ether (DME) fuel combustion performance, exhaust emissions and particle emission characteristics in a small direct injection diesel engine under various injection timings. To examine the effect of EGR and injection timings, the experiment was performed under high EGR rates (0%, 30%, 50%) and injection timings were varied from 40° before top dead center (BTDC) to top dead center (TDC) of the crank angle to examine the effects of early injection of DME fuel. The combustion pressures and heat release rates for different EGR rates followed similar trends. As the injection timing was advanced, the indicated mean effective pressure (IMEP) differed little in response to EGR rate in the range from TDC to 25° BTDC, and more for crank angles beyond 25° BTDC. DME combustion exhibited very little soot emission, but soot emission increased slightly with EGR rate. The use of high EGR during combustion produced very low NO x concentrations but increased HC and CO emissions for advanced injection timings from 25° BTDC to 40° BTDC. The use of EGR increased both the emissions of total particle number and particle volume over the whole range of the injection timings; for all cases, total particle volume decreased as injection timing was advanced.
Finite temperature many-particle theory of condensed matter systems in the functional Schroedinger picture
Hyun Sik Noh,Sang Koo You,Chul Koo Kim
Physics , 1997,
Abstract: A finite temperature many-particle theory of condensed matter systems is formulated using the functional Schroedinger picture. Using the interacting electron gas as a model system, we solve the equation of motion for the density matrix variationally with a Gaussian type trial density matrix. We show that the present formalism yields the finite temperature Hartree-Fock results both for the para- and ferromagnetic states in a simple and convenient fashion. Implications of the present results and future prospects are also discussed.
Phosphorus in the Young Supernova Remnant Cassiopeia A
Bon-Chul Koo,Yong-Hyun Lee,Dae-Sik Moon,Sung-Chul Yoon,John C. Raymond
Physics , 2013, DOI: 10.1126/science.1243823
Abstract: Phosphorus ($^{31}$P), which is essential for life, is thought to be synthesized in massive stars and dispersed into interstellar space when these stars explode as supernovae (SNe). Here we report on near-infrared spectroscopic observations of the young SN remnant Cassiopeia A, which show that the abundance ratio of phosphorus to the major nucleosynthetic product iron ($^{56}$Fe) in SN material is up to 100 times the average ratio of the Milky Way, confirming that phosphorus is produced in SNe. The observed range is compatible with predictions from SN nucleosynthetic models but not with the scenario in which the chemical elements in the inner SN layers are completely mixed by hydrodynamic instabilities during the explosion.
Major Achievements and Prospect of the ATLAS Integral Effect Tests
Ki-Yong Choi,Yeon-Sik Kim,Chul-Hwa Song,Won-Pil Baek
Science and Technology of Nuclear Installations , 2012, DOI: 10.1155/2012/375070
Abstract: A large-scale thermal-hydraulic integral effect test facility, ATLAS (Advanced Thermal-hydraulic Test Loop for Accident Simulation), has been operated by KAERI. The reference plant of ATLAS is the APR1400 (Advanced Power Reactor, 1400?MWe). Since 2007, an extensive series of experimental works were successfully carried out, including large break loss of coolant accident tests, small break loss of coolant accident tests at various break locations, steam generator tube rupture tests, feed line break tests, and steam line break tests. These tests contributed toward an understanding of the unique thermal-hydraulic behavior, resolving the safety-related concerns and providing validation data for evaluation of the safety analysis codes and methodology for the advanced pressurized water reactor, APR1400. Major discoveries and lessons found in the past integral effect tests are summarized in this paper. As the demand for integral effect tests is on the rise due to the active national nuclear R&D program in Korea, the future prospects of the application of the ATLAS facility are also discussed. 1. Introduction ATLAS (Advanced Thermal-Hydraulic Test Loop for Accident Simulation) is a large-scale integral effect test facility with a reference plant of APR1400 (Advanced Power Reactor, 1400?MWe), which is under construction in Korea [1]. It was designed to have the capability of simulating various transients and accident conditions at full pressure and temperature conditions, including loss of coolant accident (LOCA) series as well as non-LOCA series. The ATLAS program started in 1997 under a nuclear R&D program funded by the Korean government. The complete installation of ATLAS was finished in 2005. In 2006, extensive commissioning operations were carried out, including startup tests and preliminary tests [2]. In 2007, ATLAS was used for a wide range of integral effect tests on the reflood phase of a large break LOCA to resolve the safety issues of the APR1400 raised by a regulatory body [3]. Afterwards, at the beginning of 2008, ATLAS was modified to have a configuration for simulating the direct vessel injection (DVI) line break accidents of the APR1400. One of the unique design features of ATLAS is its ability to simulate the DVI of the emergency core cooling water. Sensitivity tests for different DVI line break sizes were performed and an integral effect database was established for various break sizes of 5%, 25%, 50%, and 100% [4]. After a series of DVI line break tests were completed, small break LOCA (SBLOCA) tests commenced at the end of 2008. In order to
Non-invasive algorithm for bowel motility estimation using a back-propagation neural network model of bowel sounds
Keo-Sik Kim, Jeong-Hwan Seo, Chul-Gyu Song
BioMedical Engineering OnLine , 2011, DOI: 10.1186/1475-925x-10-69
Abstract: Twelve healthy males (age: 24.8 ± 2.7 years) and 6 patients with spinal cord injury (6 males, age: 55.3 ± 7.1 years) were examined. BS signals generated during the digestive process were recorded from 3 colonic segments (ascending, descending and sigmoid colon), and then, the acoustical features (jitter and shimmer) of the individual BS segment were obtained. Only 6 features (J1, 3, J3, 3, S1, 2, S2, 1, S2, 2, S3, 2), which are highly correlated to the CTTs measured by the conventional method, were used as the features of the input vector for the BPNN.As a results, both the jitters and shimmers of the normal subjects were relatively higher than those of the patients, whereas the CTTs of the normal subjects were relatively lower than those of the patients (p < 0.01). Also, through k-fold cross validation, the correlation coefficient and mean average error between the CTTs measured by a conventional radiograph and the values estimated by our algorithm were 0.89 and 10.6 hours, respectively.The jitter and shimmer of the BS signals generated during the peristalsis could be clinically useful for the discriminative parameters of bowel motility. Also, the devised algorithm showed good potential for the continuous monitoring and estimation of bowel motility, instead of conventional radiography, and thus, it could be used as a complementary tool for the non-invasive measurement of bowel motility.Radiological scoring methods such as the Barr and Blethyn scores [1] and colon transit time (CTT) [2,3], which operate by means of X-rays and magnetic resonance imaging (MRI), have generally been used for the assessment of bowel motility. Among these methods, the CTT described by Metcalf [2] is considered to be the gold-standard. It is simply assessed by measuring the movement of radiopaque markers taken at a fixed time after their ingestion. This test is highly reproducible and most useful in determining whether constipation symptoms are associated with normal or slow transit. Howev
Design for PCS Antenna Based on Wibro-MIMO
Kyeong-Sik Min;Min-Seong Kim;Chul-Keun Park;Manh Dat Vu
PIER Letters , 2008, DOI: 10.2528/PIERL07111810
Abstract: This paper presents a design of wireless broadband (WiBro)-multi-input multi-output (MIMO) and personal communication service (PCS) antenna for practical mobile phone. To decrease the mutual coupling of WiBro-MIMO antenna, it is considered on the projected ground structure. In addition, two type PCS antennas for multi-function mobile phone are designed. The proposed antennas are well resonated in each operating frequency band. The measured bandwidths of 3-dimensional (3D) and 2-dimensional (2D) PCS antennas are 110MHz and 130MHz below -10 dB, respectively. The isolations between WiBro-MIMO and two PCS antenna are below -15dB by 2D antenna type and -20dB by 3D antenna type, respectively. The printed IFA has shown a better performance than modified planner IFA with spiral and shorting strip.
Fluctuation correction to the ground state energy density of a dilute Bose gas in the functional Schr?dinger picture
Sang-Hoon Kim,Hyun Sik Noh,Dae Kwan Kim,Chul Koo Kim,Kyun Nahm
Physics , 1998,
Abstract: A dilute Bose gas system is studied using the functional Schr\"{o}dinger picture theory. The ground state properties are obtained by solving the infinite dimensional Schr\"{o}dinger equation variationally. It is shown that a shifted Gaussian trial wavefunctional enables us to calculate a higher order correction, which corresponds to the fluctuation contribution from the condensate. The obtained term is compared with the quantum correction arising from the low energy $3 \to 3$ scattering.
A variational perturbation scheme for many-particle systems in the functional integral approach
Sang Koo You,Chul Koo Kim,Kyun Nahm,Hyun Sik Noh
Physics , 2000, DOI: 10.1103/PhysRevC.62.045503
Abstract: A variational Perturbation theory based on the functional integral approach is formulated for many-particle systems. Using the variational action obtained through Jensen-Peierls' inequality, a perturbative expansion scheme for the thermodynamic potential is established. A modified Wick's theorem is obtained for the variational perturbation expansions. This theorem allows one to carry out systematic calculations of higher order terms without worrying about the double counting problem. A model numerical calculation was carried out on a nucleon gas system interacting through the Yukawa-type potential to test the efficiency of the present method.
Near-Infrared Spectroscopy of Infrared-Excess Stellar Objects in the Young Supernova Remnant G54.1+0.3
Hyun-Jeong Kim,Bon-Chul Koo,Dae-Sik Moon
Physics , 2013, DOI: 10.1088/0004-637X/774/1/5
Abstract: We present the results of broadband near-infrared spectroscopic observations of the recently discovered mysterious stellar objects in the young supernova remnant G54.1+0.3. These objects, which show significant mid-infrared excess emission, are embedded in a diffuse loop structure of ~1 arcmin in radius. Their near-infrared spectra reveal characteristics of late O- or early B-type stars with numerous H and He I absorption lines, and we classify their spectral types to be between O9 and B2 based on an empirical relation derived here between the equivalent widths of the H lines and stellar photospheric temperatures. The spectral types, combined with the results of spectral energy distribution fits, constrain the distance to the objects to be 6.0 +/- 0.4 kpc. The photometric spectral types of the objects are consistent with those from the spectroscopic analyses, and the extinction distributions indicate a local enhancement of matter in the western part of the loop. If these objects originate via triggered formation by the progenitor star of G54.1+0.3, then their formations likely began during the later evolutionary stages of the progenitor, although a rather earlier formation may still be possible. If the objects and the progenitor belong to the same cluster of stars, then our results constrain the progenitor mass of G54.1+0.3 to be between 18 and ~35 M_sun and suggest that G54.1+0.3 was either a Type IIP supernova or, with a relatively lower possibility, Type Ib/c from a binary system.
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