• Journal of IKEEE
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• v.27 no.4
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• pp.650-656
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• 2023

This paper implements a channel model for mmWave bands using an NS-3-based 5G system-level simulator and analyzes the reliability and validity of the implemented model through RF performance verification. The channel model for RF performance verification in the mmWave bands consider parameters such as characteristics defined in 3GPP TR 38.901, beam-forming, antenna configuration, scenarios, among others. Furthermore, the simulation results verify compliance within the ranges permitted by the 3GPP standards and verify reliability in indoor environmental scenarios by exploiting the Radio Environment Map (REM). Therefore, the channel model implemented in this study is applicable to the actual design and establishment of 5G networks, presenting a method to evaluate and validate RF performance by adjusting various parameters.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.6
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• pp.38-47
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• 1989

A purely analytical model for HEMT's based on a two dimensional charge control simul-ation[4] is proposed. In this model proper treatment of diffusion effect of electron transport along a 2-DEG (two dimensional electron gas) channel is perfoemed. This diffusion effect is shown to effectively increase the bulk mibility and threshold voltage of the I-V curves compared to the existing models. The channel thickness and gate capacitance are expressed as functions of gate voltages covering subthreshold characteristics of HEMT's analytically. By introducing the finite channel opening and an effiective channel-length modulation, the solpe of the saturation region of the I-V curves ws modeled. The smooth transition of the I-V curves at linear-to-saturation regions of the I-V curves was possible using the continuous Troffimenkoff-type of field dependent mobility. Furthermore, a correction factor f was introduced to account for the finite transition section forming between a GCA and a saturated section. This factor removes large discrepancies in the saturation region of the I-V curve predicted by existing l-dimensional models.

• International Journal of Oral Biology
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• v.43 no.1
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• pp.43-51
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• 2018

$K^+$ channels are key components of the primary and secondary basolateral $Cl^-$ pump systems, which are important for secretion from the salivary glands. Paroxetine is a selective serotonin reuptake inhibitor (SSRI) for psychiatric disorders that can induce QT prolongation, which may lead to torsades de pointes. We studied the effects of paroxetine on a human $K^+$ channel, human ether-a-go-go-related gene (hERG), expressed in Xenopus oocytes and on action potential in guinea pig ventricular myocytes. The hERG encodes the pore-forming subunits of the rapidly-activating delayed rectifier $K^+$ channel ($I_{Kr}$) in the heart. Mutations in hERG reduce $I_{Kr}$ and cause type 2 long QT syndrome (LQT2), a disorder that predisposes individuals to life-threatening arrhythmias. Paroxetine induced concentration-dependent decreases in the current amplitude at the end of the voltage steps and hERG tail currents. The inhibition was concentration-dependent and time-dependent, but voltage-independent during each voltage pulse. In guinea pig ventricular myocytes held at $36^{\circ}C$, treatment with $0.4{\mu}M$ paroxetine for 5 min decreased the action potential duration at 90% of repolarization ($APD_{90}$) by 4.3%. Our results suggest that paroxetine is a blocker of the hERG channels, providing a molecular mechanism for the arrhythmogenic side effects of clinical administration of paroxetine.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.35 no.7
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• pp.139-146
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• 2019

This study examined the effect of various arrangement methods for forming peripheral closed hoops in the jacket section on the axial behavior of section enlargement strengthening columns. Four types of peripheral closed hoops arranged in the jacket section were prepared as follows: 1) Closed connection of prefabricated bar units (column P); 2) V-clip installation across the overlapped legs of channel-type bars (column V); 3) Use of glass fiber mesh for an alternative of steel bars (column F); and 4) combination of prefabricated bar units and glass fiber mesh (column PF). The V-clip is designed to form the closed hoops in the jacket section using the overlapped channel-type bars, preventing the opening of the channel bar legs. The glass fiber mesh is to examine the feasibility to apply for closed hoops in the jacket section as an alternative for steel bars, considering the easy construction. In the jacket section of all the strengthened columns, V-ties were arranged for supplementary ties, avoiding the interruption of the existing column. The axial stiffness and strength of the strengthened columns were insignificantly affected by the arrangement methods of closed hoops in the jacket section. The axial ductility ratio of the strengthened columns P, V, and PF was enhanced more than twice of that measured in the non-seismic existing column. However, the column F exhibited a lower ductility than the other strengthened columns because of the fracture of the mesh at the ultimate strength of the column. The V-clip approach was favorable to enhance the ductility of the strengthened column, preventing the opening of the legs of channel-type bars.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.36.1-36.1
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• 2016

This is a presentation of the paper published as Kimm et al. 2016, ApJ, 823, 52. We investigate the formation of metal-poor globular clusters (GCs) at the center of two dark matter halos with $Mhalo{\sim}4{\times}107Msun$ at z>10 using cosmological radiation-hydrodynamics simulations. We find that very compact (${\leq}1$ pc) and massive (${\sim}6{\times}105Msun$) clusters form rapidly when pristine gas collapses isothermally with the aid of efficient $Ly{\alpha}$ emission during the transition from molecular-cooling halos to atomic-cooling halos. Because the local free-fall time of dense star-forming gas is very short (${\ll}1Myr$), a large fraction of the collapsed gas is turned into stars before stellar feedback processes blow out the gas and shut down star formation. Although the early stage of star formation is limited to a small region of the central star-forming disk, we find that the disk quickly fragments due to metal enrichment from supernovae. Sub-clusters formed in the fragmented clouds eventually merge with the main cluster at the center. The simulated clusters closely resemble the local GCs in mass and size but show a metallicity spread that is much wider than found in the local GCs. We discuss a role of pre-enrichment by Pop III and II stars as a potential solution to the latter issue. Although not without shortcomings, it is encouraging that a naive blind (not tuned) cosmological simulation presents a possible channel for the formation of at least some massive GCs.

• Water for future
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• v.21 no.4
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• pp.399-406
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• 1988

Presented in this paper is a brief summary of the basic theory and observation from a laboratory investigation aimed at determining flow characteristics and ice jam topography in a sinuous channel, and in a single-bend channel. The sinuous channel comprised thirteen $90^{\circ}$ bends and was of comparatively small s\aspect ratio. The single-bend channel was a $180^{\circ}$ bend, which was an order of magnitude large in width as well as aspect ratios than the sinuous channel. The simulated ices were polyethylene and polypropylene beads and block. The streamwise velocities near the bottom were larger than that of surface in sinuous channel and forming ice jam in sinuous channel, this phenoumena were found strongly. Jams were generally thicker along the inner bank of bends. The path of maximum-streamwise velocity was displaced towards approachs side of the inner bank of bends. Radial variation of jam thickness was to be regular by increasing size of ice fragments. The rate of jam head progression around outer bank of the single bend was faster than that of inner bank and its velocity was roughly steady. With increasing Froude number, jm thickness became less uniformly distributed; being generally thicker along the inner bank and near the jam's toe. Two-layer model might be adaptable for the computing the streamwise velocity in shallow river bends. Two cells of secondary flow cound be expected in ice covered-river bends.

• Journal of the Korea Convergence Society
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• v.13 no.4
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• pp.287-292
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• 2022

In this paper, the stochastic distribution of the springback amount is investigated for the stamping process of a U-channel shaped-product with ultra-high strength steel. Using the reliability-based design optimization technique (RBDO), stochastic distribution of process parameters is considered in the analysis including material properties and process variation. Quantification of the springback scatters is carried out with the statistical analysis method according to the material strength. It is found that the scattering amount of springback decreases while the amount of springback increases as the tensile strength of the blank material increases, which is investigated by analyzing the strain and stress distribution of the punch and die shoulder. It is noted that the proposed scheme is capable of predicting and responding to the unavoidable scattering of springback in the sheet metal forming process.

• Journal of the Korean earth science society
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• v.33 no.3
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• pp.242-258
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• 2012

The Yellow Sea has sensitively responded to high-amplitude sea-level fluctuations during the late Quaternary. The repeated inundation and exposure have produced distinct transgression-regression successions with extensive exposure surfaces in Kyeonggi Bay. The late Quaternary strata consist of four seismic stratigraphic units, considered as depositional sequences (DS-1, DS-2, DS-3, and DS-4). DS-1 was interpreted as ridge-forming sediments of tidal-flat and estuarine channel-fill facies, formed during the Holocene highstand. DS-2 consists of shallow-marine facies in offshore area, which was formed during the regression of Marine Isotope Stage (MIS)-3 period. DS-3 comprises the lower transgressive facies and the upper highstand tidal-flat facies in proximal ridges and forced regression facies in distal ridges and offshore area. The lowermost DS-4 rests on acoustic basement rocks, considered as the shallow-marine and shelf deposits formed before the MIS-6 lowstand. This study suggests six depositional stages. During the first stage-A, MIS-6 lowstand, the Yellow Sea shelf was subaerially exposed with intensive fluvial incision and weathering. The subsequent rapid and high amplitude rise of sea level in stage-B until the MIS-5e highstand produced transgressive deposits in the lowermost part of the MIS-5 sequence, and the successive regression during the MIS-5d to -5a and the MIS-4 lowstand formed the upperpart of the MIS-5 sequence in stage-C. During the stage-D, from the MIS-4 lowstand to MIS-3c highstand period, the transgressive MIS-3 sequence formed in a subtidal environment characterized by repetitive fluvial incision and channel-fill deposition in exposed area. The subsequent sea-level fall culminating the last glacial maximum (Stage-E) made shallow-marine regressive deposits of MIS-3 sequence in offshore distal area, whereas it formed fluvial channel-fills and floodplain deposits in the proximal area. After the last glacial maximum, the overall Yellow Sea shelf was inundated by the Holocene transgression and highstand (Stage-F), forming the Holocene transgressive shelf sands and tidal ridges.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.2
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• pp.297-306
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• 2019

Since the centrifugal force acts on the flow in the curved channel, a transverse water surface gradient occurs and the thalweg is biased toward the outer bank. The submerged vanes may be used to solve various engineering problems of the curved channels. In order to analyze the influence of an attack angle and the distance between the vane arrays on the river bed variation and the superelevation in a bend, movable bed hydraulic experiments were conducted in a $90^{\circ}$ curved rectangular channel of a small-size gravel bed. Installing the submerged vanes in the bend increases the maximum scour depth. But if vanes are installed in a uniform obtuse angle, the scour depth may be reduced. If the flow rate in the channel bend with vanes equals to the channel forming discharge, the location of the maximum scour depth moved to the downstream and the superelevation increased. However if the flow rate is smaller than that, the location of the maximum scour depth moved upstream and the superelevation decreased. The channel bed change and the superelevation due to the installation of the submerged vanes have been dependent on the interaction of the attack angle, the flow rate, and the distance between the arrays.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.6
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• pp.3029-3045
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• 2017

The main processes of a cognitive radio system include spectrum sensing, spectrum decision, spectrum sharing, and spectrum conversion. Experimental results show that these stages introduce a time delay that affects the spectrum sensing accuracy, reducing its efficiency. To reduce the time delay, the frequency spectrum prediction was proposed to alleviate the burden on the spectrum sensing. In this paper, the deep recurrent neural network (DRNN) was proposed to predict the spectrum of multiple time slots, since the existing methods only predict the spectrum of one time slot. The continuous state of a channel is divided into a many time slots, forming a time series of the channel state. Since there are more hidden layers in the DRNN than in the RNN, the DRNN has fading memory in its bottom layer as well as in the past input. In addition, the extended Kalman filter was used to train the DRNN, which overcomes the problem of slow convergence and the vanishing gradient of the gradient descent method. The spectrum prediction based on the DRNN was verified with a WiFi signal, and the error of the prediction was analyzed. The simulation results proved that the multiple slot spectrum prediction improved the spectrum efficiency and reduced the energy consumption of spectrum sensing.