• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.6
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• pp.1522-1545
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• 2012

Call admission control (CAC) plays an important role in mobile cellular network to guarantee the quality of service (QoS). In this paper, a dynamic hybrid CAC scheme with integrated cutoff priority and handoff queue for mobile cellular network is proposed and some performance metrics are derived. The unique characteristic of the proposed CAC scheme is that it can support any number of service types and that the cutoff thresholds for handoff calls are dynamically adjusted according to the number of service types and service priority index. Moreover, timeouts of handoff calls in queues are also considered in our scheme. By modeling the proposed CAC scheme with a one-dimensional Markov chain (1DMC), some performance metrics are derived, which include new call blocking probability ($P_{nb}$), forced termination probability (PF), average queue length, average waiting time in queue, offered traffic utilization, wireless channel utilization and system performance which is defined as the ratio of channel utilization to Grade of Service (GoS) cost function. In order to validate the correctness of the derived analytical performance metrics, simulation is performed. It is shown that simulation results match closely with the derived analytic results in terms of $P_{nb}$ and PF. And then, to show the advantage of 1DMC modeling for the performance analysis of our proposed CAC scheme, the computing complexity of multi-dimensional Markov chain (MDMC) modeling in performance analysis is analyzed in detail. It is indicated that state-space cardinality, which reflects the computing complexity of MDMC, increases exponentially with the number of service types and total channels in a cell. However, the state-space cardinality of our 1DMC model for performance analysis is unrelated to the number of service types and is determined by total number of channels and queue capacity of the highest priority service in a cell. At last, the performance comparison between our CAC scheme and Mahmoud ASH's scheme is carried out. The results show that our CAC scheme performs well to some extend.

• YAKHAK HOEJI
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• v.60 no.2
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• pp.92-99
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• 2016

Parkinson's disease (PD) is one of the representative neurodegenerative movement disorders with the selective loss of dopaminergic neurons in the substantia nigra. 6-Hydroxydopamine (6-OHDA) is widely used as an experimental model system to mimic PD and has been reported to cause neuronal cell death via oxidative and/or nitrosative stress. Therefore, daily intake of dietary or medicinal plants which fortifies cellular antioxidant capacity can exert neuroprotective effects in PD. In the present study, we have investigated the protective effect of Korean red ginseng (KRG) against 6-OHDA-induced nitrosative death in C6 glioma cells. Treatment of C6 cells with 6-OHDA decreased cell viability and increased expression of inducible nitric oxide synthase, production of nitric oxide as well as peroxynitrite, and formation of nitrotyrosine. 6-OHDA led to apoptotic cell death as determined by decreased Bcl-2/Bax, phosphorylation of JNK, activation of caspase-3, and cleavage of PARP. Conversely, pretreatment of C6 cells with KRG attenuated 6-ODHA-induced cytotoxicity, apoptosis, and nitrosative damages. To further elucidate the molecular mechanism of KRG protection against 6-OHDA-induced nitrosative cell death, we have focused on the cellular self-defense molecules against exogenous noxious stimuli. KRG treatment up-regulated heme oxygenase-1 (HO-1), a key antioxidant enzyme essential for cellular defense against oxidative and/or nitrosative stress via activation of Nrf2. Taken together, these findings suggest KRG may have preventive and/or therapeutic potentials for the management of PD.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.8B
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• pp.687-694
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• 2012

In OFDMA-based cellular system, inter-cell interference (ICI) reduces system capacity by aggravating receiving performance of the users located in edge of the cell. Therefore, to mitigate ICI is very important issue in cellular system. To deal with ICI problem, fractional frequency reuse (FFR) is introduced. FFR is an interference management technique. It separates each cell into inner cell and outer cell. Then, it allocates whole system bandwidth to inner cell and different frequency partition to each sector of outer cell. By doing this, outer cell users can ignore interferences from adjacent cells. So, the receiving performance of the cell edge users can be fairly increased. However, using FFR technique has a fatal side effect. In order to use different frequency partition among three sectors of outer cell, they can use only a third of the whole system bandwidth. Then, the reduction of available bandwidth reduces the system throughput directly. To solve this problem, we propose a new FFR method that allocates partially overlapped frequency partition to each sector of outer cell. And then, we suggest a proper overlapping ratio for practical cellular system.

• Biomolecules & Therapeutics
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• v.27 no.3
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• pp.283-289
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• 2019

Brain aging induces neuropsychological changes, such as decreased memory capacity, language ability, and attention; and is also associated with neurodegenerative diseases. However, most of the studies on brain aging are focused on neurons, while senescence in astrocytes has received less attention. Astrocytes constitute the majority of cell types in the brain and perform various functions in the brain such as supporting brain structures, regulating blood-brain barrier permeability, transmitter uptake and regulation, and immunity modulation. Recent studies have shown that SIRT1 and SIRT2 play certain roles in cellular senescence in peripheral systems. Both SIRT1 and SIRT2 inhibitors delay tumor growth in vivo without significant general toxicity. In this study, we investigated the role of tenovin-1, an inhibitor of SIRT1 and SIRT2, on rat primary astrocytes where we observed senescence and other functional changes. Cellular senescence usually is characterized by irreversible cell cycle arrest and induces senescence- associated ${\beta}$-galactosidase (SA-${\beta}$-gal) activity. Tenovin-1-treated astrocytes showed increased SA-${\beta}$-gal-positive cell number, senescence-associated secretory phenotypes, including IL-6 and IL-$1{\beta}$, and cell cycle-related proteins like phospho-histone H3 and CDK2. Along with the molecular changes, tenovin-1 impaired the wound-healing activity of cultured primary astrocytes. These data suggest that tenovin-1 can induce cellular senescence in astrocytes possibly by inhibiting SIRT1 and SIRT2, which may play particular roles in brain aging and neurodegenerative conditions.

• BMB Reports
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• v.52 no.8
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• pp.520-525
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• 2019

Dihydroartemisinin (DHA) has been reported to possess anti-cancer activity against many cancers. However, the pharmacologic effect of DHA on HBV-positive hepatocellular carcinoma (HCC) remains unknown. Thus, the objective of the present study was to determine whether DHA could inhibit the proliferation of HepG2.2.15 cells and uncover the underlying mechanisms involved in the effect of DHA on HepG2.2.15 cells. We found that DHA effectively inhibited HepG2.2.15 HCC cell proliferation both in vivo and in vitro. DHA also reduced the migration and tumorigenicity capacity of HepG2.2.15 cells. Regarding the underlying mechanisms, results showed that DHA induced cellular senescence by up-regulating expression levels of proteins such as p-ATM, p-ATR, ${\gamma}-H_2AX$, P53, and P21 involved in DNA damage response. DHA also induced autophagy (green LC3 puncta gathered together and LC3II/LC3I ratio increased through AKT-mTOR pathway suppression). Results also revealed that DHA-induced autophagy was not linked to senescence or cell death. TPP1 (telomere shelterin) overexpression could not rescue DHA-induced anticancer activity (cell proliferation). Moreover, DHA down-regulated TPP1 expression. Gene knockdown of TPP1 caused similar phenotypes and mechanisms as DHA induced phenotypes and mechanisms in HepG2.2.15 cells. These results demonstrate that DHA might inhibit HepG2.2.15 cells proliferation through inducing cellular senescence and autophagy.

• Proceedings of the Acoustical Society of Korea Conference
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• 1994.06c
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• pp.205-209
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• 1994

This paper presents a variable rate speech coding method with phonetic segmentation, called for PSVXC. Multiple access techniques that require efficient encoding of speech to achieve capacity improvements are currently emerging in the cellular telephone system. The variable rate speech coder have the reduced average data rate required to transmit conversational speech. Each frame of active speech is classified into one of four phonetic classes. A distinct coding configuration and bit-rate is applied to each category. And also a split vector quantization is used to accurately quantize the LPC information using LSP parameters.

• Proceedings of the Korea Environmental Mutagen Society Conference
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• 2003.05a
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• pp.91-92
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• 2003

• Korean Management Science Review
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• v.18 no.2
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• pp.87-96
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• 2001

Mobility of service users makes Registration and Paging (R/P) procedures indispensable features in mobile communication networks. Importance of optimizing the configuration of R/P areas has been increased by the growth of R/P related signaling. Given the network topology (cell locations and adjacency between them) and R/P related traffics generated by each cell, we deal with the problem of finding optimal R/P areas minimizing the amount of R/P related signalling while the constraints on paging channel capacity and network configurations are satisfied.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.12A
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• pp.1806-1814
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• 2000

본 논문에서는 CDMA 계층구조 셀룰러 시스템에서 매크로 셀 기지국과 통신을 하는 고속 이동국과 마이크로 셀 기지국과 통신을 하는 저속 이동국의 비 그리고 소프트 핸드오프 영역 비에 따른 기지국이 받는 간섭전력과 시스템 용량을 구하였다. 매크로 셀 기지국과 통신을 하는 고속 이동국이 마이크로 셀 기지국과 통신을 하는 저속 이동국보다 많을수록 기지국이 받는 간섭전력은 증가하며 따라서 시스템 용량은 감소한다. 그러나 소프트 핸드오프 영역의 증가로 기지국이 받는 간섭전력은 감소하명 시스템 용량은 상당히 증가한다.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.22 no.49
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• pp.67-76
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• 1999

This research presents the relationship among machining time, cycle time and demand rate in a cellular manufacturing system. The manufacturing cell produces part families by automated machines. This paper discusses the cases of increasing demand rate in an existing cell and designing cell based on the demand rate. This research developed an algorithm for decision making such as cycle time, machines and workers in order to minimize the total machine capacity and the number of workers for any given demand rate. The proposed algorithm was successfully applied for the design and operation of cell manufacturing with a good result.