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Search Results: 1 - 10 of 26901 matches for " Jae-Young Kim "
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VIMAP: an Interactive Program Providing Radio Spectral Index Maps of Active Galactic Nuclei
Jae-Young Kim,Sascha Trippe
Physics , 2014, DOI: 10.5303/JKAS.2014.47.5.195
Abstract: We present a GUI-based interactive Python program, VIMAP, which generates radio spectral index maps of active galactic nuclei (AGN) from Very Long Baseline Interferometry (VLBI) maps obtained at different frequencies. VIMAP is a handy tool for the spectral analysis of synchrotron emission from AGN jets, specifically of spectral index distributions, turn-over frequencies, and core-shifts. In general, the required accurate image alignment is difficult to achieve because of a loss of absolute spatial coordinate information during VLBI data reduction (self-calibration) and/or intrinsic variations of source structure as function of frequency. These issues are overcome by VIMAP which in turn is based on the two-dimensional cross-correlation algorithm of Croke and Gabuzda (2008). In this paper, we briefly review the problem of aligning VLBI AGN maps, describe the workflow of VIMAP, and present an analysis of archival VLBI maps of the active nucleus 3C 120.
How To Monitor AGN Intra-Day Variability at 230 GHz
Jae-Young Kim,Sascha Trippe
Physics , 2013, DOI: 10.5303/JKAS.2013.46.2.65
Abstract: We probe the feasibility of high-frequency radio observations of very rapid flux variations in compact active galactic nuclei (AGN). Our study assumes observations at 230 GHz with a small 6-meter class observatory, using the SNU Radio Astronomical Observatory (SRAO) as example. We find that 33 radio-bright sources are observable with signal-to-noise ratios larger than ten. We derive statistical detection limits via exhaustive Monte Carlo simulations assuming (a) periodic, and (b) episodic flaring flux variations on time-scales as small as tens of minutes. We conclude that a wide range of flux variations is observable. This makes high-frequency radio observations - even with small observatories - a powerful probe of AGN intra-day variability; especially, those observations complement observations at lower radio frequencies with larger observatories like the Korean VLBI Network (KVN).
Stability of Jensen-Type Functional Equations on Restricted Domains in a Group and Their Asymptotic Behaviors
Jae-Young Chung,Dohan Kim,John Michael Rassias
Journal of Applied Mathematics , 2012, DOI: 10.1155/2012/691981
Abstract: We consider the Hyers-Ulam stability problems for the Jensen-type functional equations in general restricted domains. The main purpose of this paper is to find the restricted domains for which the functional inequality satisfied in those domains extends to the inequality for whole domain. As consequences of the results we obtain asymptotic behavior of the equations.
Broad Band-Stop Filter Using Frequency Selective Surfaces in Uniplanar Microwave Transmission Line
Jae-Young Kim;Jung Han Choi;Chang Won Jung
PIER Letters , 2012, DOI: 10.2528/PIERL12022705
Abstract: We present a band-stop filter (BSF) by using a periodic structure property of frequency selective surfaces (FSSs) embedded in a microstrip transmission line. The proposed BSF is designed with FSS unit cells modifying the cross-loop slots. The center frequency (f) of the BSF is 6.6 GHz, and the 3-dB bandwidth varies by the number of cascading unit cells. The BSF is interpreted with an equivalent circuit model and a dispersion diagram, and exhibits uniplanar geometry, low return loss, simple fabrication, smaller size, and wide bandwidth.
Discrete denoising of heterogenous two-dimensional data
Taesup Moon,Tsachy Weissman,Jae-Young Kim
Mathematics , 2010,
Abstract: We consider discrete denoising of two-dimensional data with characteristics that may be varying abruptly between regions. Using a quadtree decomposition technique and space-filling curves, we extend the recently developed S-DUDE (Shifting Discrete Universal DEnoiser), which was tailored to one-dimensional data, to the two-dimensional case. Our scheme competes with a genie that has access, in addition to the noisy data, also to the underlying noiseless data, and can employ $m$ different two-dimensional sliding window denoisers along $m$ distinct regions obtained by a quadtree decomposition with $m$ leaves, in a way that minimizes the overall loss. We show that, regardless of what the underlying noiseless data may be, the two-dimensional S-DUDE performs essentially as well as this genie, provided that the number of distinct regions satisfies $m=o(n)$, where $n$ is the total size of the data. The resulting algorithm complexity is still linear in both $n$ and $m$, as in the one-dimensional case. Our experimental results show that the two-dimensional S-DUDE can be effective when the characteristics of the underlying clean image vary across different regions in the data.
Forest Fire Model as a Supercritical Dynamic Model in Financial Systems
Deokjae Lee,Jae-Young Kim,Jeho Lee,B. Kahng
Quantitative Finance , 2015, DOI: 10.1103/PhysRevE.91.022806
Abstract: Recently, large-scale cascading failures in complex systems have garnered substantial attention. Such extreme events have been treated as an integral part of the self-organized criticality (SOC). Recent empirical work has suggested that some extreme events systematically deviate from the SOC paradigm, requiring a different theoretical framework. We shed additional theoretical light on this possibility by studying financial crisis. We build our model of financial crisis on the well-known forest fire model in scale-free networks. Our analysis shows a non-trivial scaling feature indicating supercritical behavior, which is independent of system size. Extreme events in the supercritical state result from bursting of a fat bubble, seeds of which are sown by a protracted period of a benign financial environment with few shocks. Our findings suggest that policymakers can control the magnitude of financial meltdowns by keeping the economy operating within reasonable duration of a benign environment.
Wide Tuning Range VCDRO and Low Phase Noise DRO in InGaP/GaAs HBT Technology
Lee Jae-Young,Shrestha Bhnau,Yoon Jae-Ho,Kim Nam-Young
IETE Technical Review , 2007,
Abstract: A monolithic microwave integrated circuit voltage-controlled dielectric resonator oscillator (MMIC-VCDRO) is demonstrated at Ku-band for a low noise block down-converter (LNB) system in InGaP/GaAs HBT process with on-chip varactors. The fabricated VCDRO achieves high output power of 6.45 to 5.31 dBm with frequency tuning range of 165 MHz and also achieves low phase noise of under -95 dBc/Hz at 100 kHz offset and -115 dBc/Hz at 1 MHz offset. Also InGaP/GaAs HBT monolithic DRO with the same topology of the proposed VCDRO is fabricated which exhibits the output power of 1.33 dBm, and extremely low phase noise of -109 dBc/Hz at 100 kHz and -131 dBc/Hz at 1 MHz offset at the 10.75 GHz oscillation frequency.
The Beneficial Effect of Vanillic Acid on Ulcerative Colitis
Su-Jin Kim,Min-Cheol Kim,Jae-Young Um,Seung-Heon Hong
Molecules , 2010, DOI: 10.3390/molecules15107208
Abstract: Vanillic acid, an oxidized form of vanillin, is a benzoic acid derivative used as a flavoring agent. The objective of this study was to determine whether vanillic acid has beneficial effects against dextran sulfate sodium (DSS)-induced ulcerative colitis. Our results showed that vanillic acid reduced the severity of the clinical signs of DSS-induced colitis, including weight loss and shortening of colon length, and the disease activity index. The results of this study showed that vanillic acid significantly suppressed the expression of cyclooxygenase-2 and the activation of transcription nuclear factor-kB p65 in DSS-treated colon tissues. In addition, we observed that the plasma levels of interleukin (IL)-6 were higher in the DSS-treated group than in the control group, but these increased levels were reduced by the administration of vanillic acid. Taken together, these findings suggest that vanillic acid has a beneficial effect on DSS-induced ulcerative colitis, thereby indicating its usefulness in the regulation of chronic intestinal inflammation.
Intestinal Epithelial-Derived TAK1 Signaling Is Essential for Cytoprotection against Chemical-Induced Colitis
Jae-Young Kim, Rie Kajino-Sakamoto, Emily Omori, Christian Jobin, Jun Ninomiya-Tsuji
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0004561
Abstract: Background We have previously reported that intestinal epithelium-specific TAK1 deleted mice exhibit severe inflammation and mortality at postnatal day 1 due to TNF-induced epithelial cell death. Although deletion of TNF receptor 1 (TNFR1) can largely rescue those neonatal phenotypes, mice harboring double deletion of TNF receptor 1 (TNFR1) and intestinal epithelium-specific deletion of TAK1 (TNFR1KO/TAK1IEKO) still occasionally show increased inflammation. This indicates that TAK1 is important for TNF-independent regulation of intestinal integrity. Methodology/Principal Findings In this study, we investigated the TNF-independent role of TAK1 in the intestinal epithelium. Because the inflammatory conditions were sporadically developed in the double mutant TNFR1KO/TAK1IEKO mice, we hypothesize that epithelial TAK1 signaling is important for preventing stress-induced barrier dysfunction. To test this hypothesis, the TNFR1KO/TAK1IEKO mice were subjected to acute colitis by administration of dextran sulfate sodium (DSS). We found that loss of TAK1 significantly augments DSS-induced experimental colitis. DSS induced weight loss, intestinal damages and inflammatory markers in TNFR1KO/TAK1IEKO mice at higher levels compared to the TNFR1KO control mice. Apoptosis was strongly induced and epithelial cell proliferation was decreased in the TAK1-deficient intestinal epithelium upon DSS exposure. These suggest that epithelial-derived TAK1 signaling is important for cytoprotection and repair against injury. Finally, we showed that TAK1 is essential for interleukin 1- and bacterial components-induced expression of cytoprotective factors such as interleukin 6 and cycloxygenase 2. Conclusions Homeostatic cytokines and microbes-induced intestinal epithelial TAK1 signaling regulates cytoprotective factors and cell proliferation, which is pivotal for protecting the intestinal epithelium against injury.
Physical characteristics and age structure of Mongolian racerunner(Eremias argus; Larcertidae; Reptilia)
Ja-Kyoung Kim,Jae-Young Song,Jung-Hyun Lee,Daesik Park
Journal of Ecology and Field Biology , 2010,
Abstract: In this study, we have evaluated the physical characteristics of neonate, female, and male Mongolian racerunners (Eremiasargus) and determined the age structure of a population of the species in a field located in Taean-gun, Chungnam,South Korea. The physical parameters of females and males, including snout-vent length (SVL), head length, head width,and body mass were found to be significantly interrelated. Male Mongolian racerunners exhibited significantly longerheads than the females, but other physical parameters, such as SVL, head width, and body mass did not differ betweenthe female and male specimens. In the study population, the females ranged in age from two to eleven years old and themales ranged between two to eight years of age. The number of females and males, when separated into different ageclasses, did not differ within each age class. Male Mongolian racerunners evidenced greater SVL growth coefficients thanthe females, but asymptotic SVL did not differ between the females and males.
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