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Search Results: 1 - 10 of 15643 matches for " Jong Ho Park "
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Radio Variability and Random Walk Noise Properties of Four Blazars
Jong-Ho Park,Sascha Trippe
Physics , 2014, DOI: 10.1088/0004-637X/785/1/76
Abstract: We present the results of a time series analysis of the long-term radio lightcurves of four blazars: 3C 279, 3C 345, 3C 446, and BL Lacertae. We exploit the data base of the University of Michigan Radio Astronomy Observatory (UMRAO) monitoring program which provides densely sampled lightcurves spanning 32 years in time in three frequency bands located at 4.8, 8, and 14.5 GHz. Our sources show mostly flat or inverted (spectral indices -0.5 < alpha < 0) spectra, in agreement with optically thick emission. All lightcurves show strong variability on all time scales. Analyzing the time lags between the lightcurves from different frequency bands, we find that we can distinguish high-peaking flares and low-peaking flares in accord with the classification of Valtaoja et al. (1992). The periodograms (temporal power spectra) of the observed lightcurves are consistent with random-walk powerlaw noise without any indication of (quasi-)periodic variability. The fact that all four sources studied are in agreement with being random-walk noise emitters at radio wavelengths suggests that such behavior is a general property of blazars.
Multiple Emission States in Active Galactic Nuclei
Jong-Ho Park,Sascha Trippe
Physics , 2012, DOI: 10.5303/JKAS.2012.45.6.147
Abstract: We present a test of the emission statistics of active galactic nuclei (AGN), probing the connection between red-noise temporal power spectra and multi-modal flux distributions known from observations. We simulate AGN lightcurves under the assumption of uniform stochastic emission processes for different power-law indices of their power spectra. For sufficiently shallow slopes (power-law indices beta < 1), the flux distributions (histograms) of the resulting lightcurves are approximately Gaussian. For indices corresponding to steeper slopes (beta > 1), the flux distributions become multi-modal. This finding disagrees systematically with results of recent mm/radio observations. Accordingly, we conclude that the emission from AGN does not necessarily originate from uniform stochastic processes even if their power spectra suggest this. Possible mechanisms are transitions between different activity states and/or the presence of multiple, spatially disconnected, emission regions.
An Efficient Method of Vibration Diagnostics For Rotating Machinery Using a Decision Tree
Bo Suk Yang,Chul Hyun Park,Ho Jong Kim
International Journal of Rotating Machinery , 2000, DOI: 10.1155/s1023621x00000038
Abstract: This paper describes an efficient method to automatize vibration diagnosis for rotating machinery using a decision tree, which is applicable to vibration diagnosis expert system. Decision tree is a widely known formalism for expressing classification knowledge and has been used successfully in many diverse areas such as character recognition, medical diagnosis, and expert systems, etc. In order to build a decision tree for vibration diagnosis, we have to define classes and attributes. A set of cases based on past experiences is also needed. This training set is inducted using a result-cause matrix newly developed in the present work instead of using a conventionally implemented cause-result matrix. This method was applied to diagnostics for various cases taken from published work. It is found that the present method predicts causes of the abnormal vibration for test cases with high reliability.
Exact Null Controllability of KdV-Burgers Equation with Memory Effect Systems
Rajagounder Ravi Kumar,Kil To Chong,Jong Ho Park
Abstract and Applied Analysis , 2012, DOI: 10.1155/2012/531659
Abstract:
Carabid beetle species as a biological indicator for different habitat types of agricultural landscapes in Korea
Banghun Kang*,Joon-Ho Lee,Jong-Kyun Park
Journal of Ecology and Field Biology , 2012,
Abstract: In the current study, several carabid beetle species were proposed as potential biological indicators for different habitattypes (levee, upland dike, hillock, and streamside) of agricultural landscapes focusing on agrobiont species. Synuchusarcuaticollis and Synuchus orbicollis were found in all habitat types, indicating that they are general species for all habitattypes. Harpalus eous and Synuchus cycloderus are potential bioindicator species for the paddy levee and hillock habitats,respectively. Amara pseudosimplicidens, Anisodactylus punctatipennis, and Chlaenius ocreatus, which occurred widely,and Bembidion morawitzi, which occurred only in the streamside habitat, are potential bioindicators for the streamsidehabitat.
Exact Null Controllability of KdV-Burgers Equation with Memory Effect Systems
Rajagounder Ravi Kumar,Kil To Chong,Jong Ho Park
Abstract and Applied Analysis , 2012, DOI: 10.1155/2012/531659
Abstract: This paper is concerned with exact null controllability analysis of nonlinear KdV-Burgers equation with memory. The proposed approach relies upon regression tool to prove controllability property of linearized KdV-Burgers equation via Carleman estimates. The control is distributed along with subdomain and the external control acts on the key role of observability inequality with memory. This description finally showed the exact null controllability guaranteeing the stability. 1. Introduction In recent years there has been rapidly increasing interest in mathematical studies of dynamical and statistical property of nonlinear fields described by the Burgers equation (see [1–4]) and it has been motivated by several developments. As Burgers [5] noticed, the Burgers equation is a convenient analytical model for the physical turbulence, which is simultaneously taken into an account of two competing mechanisms: to determine properties of the strong hydrodynamic turbulence: the interior nonlinearity and viscosity. Moreover, the quantitative description in many physical processes leads to the Burgers equation. One example here is an intense acoustical noise, such as the jet noise [6], where knowledge of dynamical and statistical properties of the Burgers turbulence can be directly applied to an analysis of nonlinear distortions. Another phenomenon is adequately for the nonlinear evolution of gravitational instability and the related characteristic of large-scale cellular structures (see [1, 7]). Many problems have been modelled on nonlinear Burgers equations. There has been an enormous on-going research and it is directly investigating some nonlinear effects. For example, the simpler model equation with higher dimension, which encapsulates to essential features of the problem. But it is impossible to solve it directly in a higher dimension. After few years, these issues were carried out by Fernández-Cara et al. [8] and it has been discussed via Korteweg-de Vries (KdV). The KdV equation is a prototype of such a model also describing the competition between nonlinear and disperse effects in water waves. The KdV equations are not directly related to the disperse waves, the density fields in Burgers turbulence, and it is rather difficult to do in higher dimensions. Although the KdV equation of analytical model is not a convenient and also nonefficient model of the strong turbulence, it holds at least one serious drawback from the viewpoint of physical applications (see [6]). Namely, it does not take into account pressure forces that could lead to smoothing of
A spectral approach to compute the mean performance measures of the queue with low-order input
Ho Woo Lee,Jong Min Moon,Jong Keun Park,Byung Kyu Kim
International Journal of Stochastic Analysis , 2003, DOI: 10.1155/s1048953303000273
Abstract: This paper targets engineers and practitioners who want a simple procedure to compute the mean performance measures of the Batch Markovian Arrival process (BMAP/G/1) queueing system when the parameter matrices order is very low. We develop a set of system equations and derive the vector generating function of the queue length. Starting from the generating function, we propose a spectral approach that can be understandable to those who have basic knowledge of M/G/1 queues and eigenvalue algebra.
Ferroelectric Phase Transition of Lead Free (1-x)(Na0.5K0.5)NbO3- xLiNbO3 Ceramics
Jong-Ho Park,Hui-Jin Park,Byung-Chun Choi
Transactions on Electrical and Electronic Materials , 2012,
Abstract: Lead-free (1-x)(Na0.5K0.5)NbO3-xLiNbO3, i.e., NKN-LNx (x =0.0, 0.1, 0.2, 0.3, 0.4 mol) was prepared using theconventional solid state reaction method. The effects of LN mixing on the ferroelectric properties of NKN-LNxceramics were studied using a dielectric constant and P-E (Polarization-electric field) measurements. Ferroelectricitywas observed in the composition for x approximately varying between 0.0 and 0.4. Minimum remanent polarization2Pr=5 C/cm2 was achieved in the composition for x = 0.2. The ferroelectric phase transition temperature TC increasedwith increasing LN content. The ferroelectric phase transition of NKN-LNx (x ≥ 0.1) is a second-order phase transition,and that of NKN-LNx (x ≤ 0.2) is a first-order phase transition. These results indicate that the ferroelectric phasetransition temperature of NKN-LNx change from that of second-order to weak first-order phase transition accordingto the LN content.
Gas Nozzle Effect on the Deposition of Polysilicon by Monosilane Siemens Reactor
Seung Oh Kang,Uk June Lee,Seung Hyun Kim,Ho Jung You,Kun Park,Sung Eun Park,Jong Hoon Park
International Journal of Photoenergy , 2012, DOI: 10.1155/2012/697653
Abstract: Deposition of polysilicon (poly-Si) was tried to increase productivity of poly-Si by using two different types of gas nozzle in a monosilane Bell-jar Siemens (MS-Siemens) reactor. In a mass production of poly-Si, deposition rate and energy consumption are very important factors because they are main performance indicators of Siemens reactor and they are directly related with the production cost of poly-Si. Type A and B nozzles were used for investigating gas nozzle effect on the deposition of poly-Si in a MS-Siemens reactor. Nozzle design was analyzed by computation cluid dynamics (CFD). Deposition rate and energy consumption of poly-Si were increased when the type B nozzle was used. The highest deposition rate was 1 mm/h, and the lowest energy consumption was 72kWh?kg−1 in this study.
Residual tumor after the salvage surgery is the major risk factors for primary treatment failure in malignant ovarian germ cell tumors: A retrospective study of single institution
Chung Won Lee, Min Jong Song, Sung Taek Park, Eun Young Ki, Sung Jong Lee, Keun Ho Lee, Ki Sung Ryu, Jong Sup Park, Soo Young Hur
World Journal of Surgical Oncology , 2011, DOI: 10.1186/1477-7819-9-123
Abstract: The medical records of 57 patients with stages I to IV malignant ovarian germ cell tumor were retrospectively reviewed, and their clinicopathologic and treatment-related data were collected and analyzed.The median age at the diagnosis was 23.3 years (range: 8-65 years), and the median follow-up period was 108 months (range: 48-205 months). The histological types of the tumors were immature teratoma (n = 24), dysgerminoma (n = 20), endodermal sinus tumor (n = 8), mixed germ cell tumor (n = 4), and choriocarcinoma (n = 1). 66.7% of the patients had stage I disease; 5.2%, stage II; 26.3%, stage III; and 1.8%, stage IV. After the initial surgery, 49 patients (86%) received cisplatin-based chemotherapy. The five-year survival rate was 96.5%. There were six primary treatment failures, with two of the patients dying of the disease, and the median time to the recurrence was 8 months. The histological diagnosis (P < 0.0001), tumor stage (P = 0.0052), elevation of beta-hCG (P = 0.0134), operation methods (P = 0.0006), and residual tumor after the salvage surgery (P < 0.0001) were significantly associated with the risk of primary treatment failure in the univariate analysis. In the multivariate analysis, the residual tumor after the salvage surgery was the only significant variable associated with primary treatment failure (P = 0.0011, Hazard ratio = 29.046, 95% Confidence interval 3.832-220.181).Most malignant ovarian germ cell tumors have excellent prognoses with primary treatment, and good reproductive outcomes can be expected. Because primary treatment failure is associated with the residual disease after the salvage surgery, knowledge of the presence or absence of this risk factor may be helpful in risk stratification and individualization of adjuvant therapy in malignant ovarian germ cell tumors. Further large-scale prospective studies to confirm these results should be performed.Malignant ovarian germ cell tumors (MOGCTs) are a heterogeneous group of tumors that have se
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