• ETRI Journal
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• v.37 no.1
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• pp.147-156
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• 2015

A typical solid-state drive contains several independent channels that can be operated in parallel. To exploit this channel-level parallelism, a variety of works proposed to split consecutive write sequences into small segments and schedule them to different channels. This scheme exploits the parallelism but breaks the spatial locality of write traffic; thus, it is able to significantly degrade the efficiency of garbage collection. This paper proposes a channel-aware write reordering (CAWR) mechanism to schedule write requests to different channels more intelligently. The novel mechanism encapsulates correlated pages into a cluster beforehand. All pages belonging to a cluster are scheduled to the same channels to exploit spatial locality, while different clusters are scheduled to different channels to exploit the parallelism. As CAWR covers both garbage collection and I/O performance, it outperforms existing schemes significantly. Trace-driven simulation results demonstrate that the CAWR mechanism reduces the average response time by 26% on average and decreases the valid page copies by 10% on average, while achieving a similar hit ratio to that of existing mechanisms.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.7
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• pp.2435-2453
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• 2015

Independent component analysis (ICA) is a signal processing technique used for un-mixing of the mixed recorded signals. In wireless communication, ICA is mainly used in multiple input multiple output (MIMO) systems. Most of the existing work regarding the ICA applications in MIMO systems assumed static or quasi static wireless channels. Performance of the ICA algorithms degrades in case of time varying wireless channels and is further degraded if the data block lengths are reduced to get the quasi stationarity. In this paper, we propose an ICA based MIMO transceiver that performs well in time varying wireless channels, even for smaller data blocks. Simulation is performed over quadrature amplitude modulated (QAM) signals. Results show that the proposed transceiver system outperforms the existing MIMO system utilizing the FastICA and the OBAICA algorithms in both the transceiver systems for time varying wireless channels. Performance improvement is observed for different data blocks lengths and signal to noise ratios (SNRs).

• The Korean Journal of Physiology and Pharmacology
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• v.13 no.3
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• pp.215-220
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• 2009

Chlorpheniramine is a potent first-generation histamine $H_1$ receptor antagonist that can increase action potential duration and induce QT prolongation in several animal models. Since block of cardiac human ether-a-go-go-related gene (hERG) channels is one of leading causes of acquired long QT syndrome, we investigated the acute effects of chlorpheniramine on hERG channels to determine the electrophysiological basis for its proarrhythmic potential. We examined the effects of chlorpheniramine on the hERG channels expressed in Xenopus oocytes using two-microelectrode voltage-clamp techniques. Chlorpheniramine induced a concentration-dependent decrease of the current amplitude at the end of the voltage steps and hERG tail currents. The $IC_{50}$ of chlorpheniramine-dependent hERG block in Xenopus oocytes decreased progressively relative to the degree of depolarization. Chlorpheniramine affected the channels in the activated and inactivated states but not in the closed states. The S6 domain mutations Y652A and F656A partially attenuated (Y652A) or abolished (F656A) the hERG current block. These results suggest that the $H_1$ antihistamine, chlorpheniramine is a blocker of the hERG channels, providing a molecular mechanism for the drug-induced arrhythmogenic side effects.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2006.11a
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• pp.288-300
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• 2006

In this paper, we consider a channel ordering problem that seeks to minimize the total interference in mobile radio networks. If a base station receives connection request from a mobile user, one of the empty channels that are fixed to the base station is assigned to the mobile user. Among several channels available, we can choose one that seems to make least interference with other channels assigned to adjacent base stations. However, a pair of channels that are not separated enough do not generate interference if both of them are not simultaneously used by mobile users. That is, interference between channels may vary depending on the channel assignment sequence for each base station and on the distribution of mobile users. To find a channel assignment sequence that seems to generate minimum interference, we develop an optimization model considering various scenarios of mobile user distribution. Simulation results show that channel assignment sequence determined by the scenario based optimization model significantly reduces the interference provided that scenarios and interference costs are properly generated.

• The Korean Journal of Physiology and Pharmacology
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• v.8 no.1
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• pp.33-41
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• 2004

We developed a cardiac cell model to explain the phenomenon of mechano-electric feedback (MEF), based on the experimental data with rat atrial myocytes. It incorporated the activity of ion channels, pumps, exchangers, and changes of intracellular ion concentration. Changes in membrane excitability and $Ca^{2+}$ transients could then be calculated. In the model, the major ion channels responsible for the stretch-induced changes in electrical activity were the stretch-activated channels (SACs). The relationship between the extent of stretch and activation of SACs was formulated based on the experimental findings. Then, the effects of mechanical stretch on the electrical activity were reproduced. The shape of the action potential (AP) was significantly changed by stretch in the model simulation. The duration was decreased at initial fast phase of repolarization (AP duration at 20% repolarization level from 3.7 to 2.5 ms) and increased at late slow phase of repolarization (AP duration at 90% repolarization level from 62 to 178 ms). The resting potential was depolarized from -75 to -61 mV. This mathematical model of SACs may quantitatively predict changes in cardiomyocytes by mechanical stretch.

• Journal of Korea Water Resources Association
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• v.41 no.4
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• pp.395-404
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• 2008

It is important to understand the complex, various migration features of the alluvial channels for river engineering. In this study, the morphological changes and migration features of alluvial channels were investigated by analyzing the aerial photographs of active channels between 1972 and 2004 in Hapyeong Intake Station, Nakdong river. The lower channels were migrated from left bank to right bank and showed the features of braided channel in 2004. The instability of lower channels was increased due to the increased channel slope and width. The sinuosity of lower channels was decreased with time. As time increased, the increasing rate of lower channel and lateral migration rate were decreased. As a result of meso-scale regime analysis by using bankfull discharge, multiple row bars were developed, and suspended sediment load was governed in the flow as a sand bed channel.

• BMB Reports
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• v.53 no.5
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• pp.260-265
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• 2020

Scorpion venom comprises a cocktail of toxins that have proven to be useful molecular tools for studying the pharmacological properties of membrane ion channels. HelaTx1, a short peptide neurotoxin isolated recently from the venom of the scorpion Heterometrus laoticus, is a 25 amino acid peptide with two disulfide bonds that shares low sequence homology with other scorpion toxins. HelaTx1 effectively decreases the amplitude of the K⁺ currents of voltage-gated Kv1.1 and Kv1.6 channels expressed in Xenopus oocytes, and was identified as the first toxin member of the κ-KTx5 subfamily, based on a sequence comparison and phylogenetic analysis. In the present study, we report the NMR solution structure of HelaTx1, and the major interaction points for its binding to voltage-gated Kv1.1 channels. The NMR results indicate that HelaTx1 adopts a helix-loop-helix fold linked by two disulfide bonds without any β-sheets, resembling the molecular folding of other cysteine-stabilized helix-loop-helix (Cs α/α) scorpion toxins such as κ-hefutoxin, HeTx, and OmTx, as well as conotoxin pl14a. A series of alanine-scanning analogs revealed a broad surface on the toxin molecule largely comprising positively-charged residues that is crucial for interaction with voltage-gated Kv1.1 channels. Interestingly, the functional dyad, a key molecular determinant for activity against voltage-gated potassium channels in other toxins, is not present in HelaTx1.

• Proceedings of the Korean Biophysical Society Conference
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• 2003.06a
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• pp.42-42
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• 2003

Large-conductance $Ca^{2+}$-activated potassium channels ($BK_{Ca}$ are a widely distributed and play key roles in various cell functions. In nerve cells, $BK_{Ca}$ channels shorten the duration of action potentials and block $Ca^{2+}$ entry thereby repolarizing excitable cells after excitation. $BK_{Ca}$ channel opening has been postulated to confer neuroprotection during stroke, and has attracted attention as a means for therapeutic intervention in asthma, hypertension, convulsions, and traumatic brain injury. Several natural and synthetic compounds including a steroid hormone, $\beta$-estradiol, have been identified as the activators of $BK_{Ca}$ channels. Based on the structural features of the previously reported activators of $BK_{Ca}$ channels, we designed several lead compounds, synthesized chemically, and tested their functional activity on cloned $BK_{Ca}$ channels. The $\alpha$ subunit of rat $BK_{Ca}$ channel was expressed alone or with different $\beta$ subunits in Xenopus oocytes and the effects of the compounds were tested electrophysiological means. One of the lead compounds affected the activity of the $\alpha$ subunit of $BK_{Ca}$ channel in a $\beta$ subunit-specific manner. While the activity of B $K_{ca}$ channel $\alpha$ subunit was Potentiated, the channel composed of $\alpha$ and $\beta$1 subunits were inhibited by this compound. We are currently investigating the mechanism of the $\beta$ subunit-dependent effects and planning to localize the receptor site of the lead compound.f the lead compound.

• Journal of Ginseng Research
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• v.32 no.2
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• pp.99-106
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• 2008

A ligand - whether an endogenous hormone, neurotransmitter, exogenous toxin or synthetic drug - binds to plasma membrane proteins (e.g., ion channels, receptors or other functional proteins) to exert its physiological or pharmacological effects. Ligands can also have functional groups, showing stereospecificity for interaction sites on their counterpart plasma membrane proteins. Previous reports have shown that the ginsenoside Rg$_3$, a bioactive ginsenoside, meets these criteria in that: 1) an aliphatic side chain of $Rg_3$ plays a role as a functional group, 2) Rg$_3$ regulates voltage- and ligand-gated ion channels in a stereospecific manner with respect to carbon-20, and 3) $Rg_3$ regulates subsets of ligand-gated and voltage-gated ion channels through specific interactions with identified amino acid residues inside the channel pore, in the outer pore entryway, or in toxin binding sites. Rg$_3$, therefore, could be a candidate for a novel ginseng-derived glycosidic ligand regulating ion channels and receptors. This review will examine how Rg$_3$ regulates voltage-gated and ligand-gated ion channels through interactions with its target proteins in the plasma membrane. Hopefully, this review will advance understanding of ginseng pharmacology at the cellular and molecular levels.

• The Korean Journal of Physiology and Pharmacology
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• v.21 no.2
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• pp.259-265
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• 2017

Excessive influx and the subsequent rapid cytosolic elevation of $Ca^{2+}$ in neurons is the major cause to induce hyperexcitability and irreversible cell damage although it is an essential ion for cellular signalings. Therefore, most neurons exhibit several cellular mechanisms to homeostatically regulate cytosolic $Ca^{2+}$ level in normal as well as pathological conditions. Delayed rectifier $K^+$ channels ($I_{DR}$ channels) play a role to suppress membrane excitability by inducing $K^+$ outflow in various conditions, indicating their potential role in preventing pathogenic conditions and cell damage under $Ca^{2+}$-mediated excitotoxic conditions. In the present study, we electrophysiologically evaluated the response of $I_{DR}$ channels to hyperexcitable conditions induced by high $Ca^{2+}$ pretreatment (3.6 mM, for 24 hours) in cultured hippocampal neurons. In results, high $Ca^{2+}$-treatment significantly increased the amplitude of $I_{DR}$ without changes of gating kinetics. Nimodipine but not APV blocked $Ca^{2+}$-induced $I_{DR}$ enhancement, confirming that the change of $I_{DR}$ might be targeted by $Ca^{2+}$ influx through voltage-dependent $Ca^{2+}$ channels (VDCCs) rather than NMDA receptors (NMDARs). The VDCC-mediated $I_{DR}$ enhancement was not affected by either $Ca^{2+}$-induced $Ca^{2+}$ release (CICR) or small conductance $Ca^{2+}$-activated $K^+$ channels (SK channels). Furthermore, PP2 but not H89 completely abolished $I_{DR}$ enhancement under high $Ca^{2+}$ condition, indicating that the activation of Src family tyrosine kinases (SFKs) is required for $Ca^{2+}$-mediated $I_{DR}$ enhancement. Thus, SFKs may be sensitive to excessive $Ca^{2+}$ influx through VDCCs and enhance $I_{DR}$ to activate a neuroprotective mechanism against $Ca^{2+}$-mediated hyperexcitability in neurons.