• JSTS:Journal of Semiconductor Technology and Science
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• v.15 no.5
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• pp.497-503
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• 2015

It is essential to acquire an accurate and simple technique for extracting the interface trap density ($D_{it}$) in order to characterize the normally-off gate-recessed AlGaN/GaN hetero field-effect transistors (HFETs) because they can undergo interface trap generation induced by the etch damage in each interfacial layer provoking the degradation of device performance as well as serious instability. Here, the frequency-dependent capacitance-voltage (C-V) method (FDCM) is proposed as a simple and fast technique for extracting $D_{it}$ and demonstrated in normally-off gate-recessed AlGaN/GaN HFETs. The FDCM is found to be not only simpler than the conductance method along with the same precision, but also much useful for a simple C-V model for AlGaN/GaN HFETs because it identifies frequency-independent and bias-dependent capacitance components.

• The Korean Journal of Physiology and Pharmacology
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• v.12 no.6
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• pp.323-330
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• 2008

The properties of voltage dependent $Ca^{2+}$ current (VDCC) were investigated in interstitial cells of Cajal (ICC) distributed in the myenteric layer (ICC-MY) of guinea-pig antrum. In tissue, ICC-MY showed c-Kit positive reactions and produced driving potentials with the amplitude and frequency of about 62 mV and 2 times $min^{-1}$ respectively, in the presence of $1{\mu}M$ nifedipine. Single ICC-MY isolated by enzyme treatment also showed c-Kit immunohistochemical reactivity. These cells were also identified by generation of spontaneous inward current under $K^+$ -rich pipette solution. The voltage clamp experiments revealed the amplitude of - 329 pA inward current at irregular frequency. With $Cs^+$-rich pipette solution at $V_h=-80\;mV$, ICC-MY produced voltage-dependent inward currents (VDIC), and nifedipine ($1{\mu}M$) blocked VDIC. Therefore, we successfully isolated c-Kit positive single ICC from guinea-pig stomach, and found that ICC-MY potently produced dihydropiridine sensitive L-type voltage-dependent $Ca^{2+}$ currents ($VDCC_L$).

• Journal of the Korean Society of Tobacco Science
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• v.25 no.2
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• pp.128-136
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• 2003

Although tobacco smoke has been known to have genotoxicity as well as cytotoxicity, the sensitivity of the cell lines used against cigarette smoke is poorly understood. The objective of this study was to evaluate and compare the genotoxicity of several cell lines, which are routinely used in the in vitro assays, with cigarette smoke condensate(CSC) of Kentucky Reference Cigarette 1R4F. In the micronucleus(MN) induction assays, murine(CHO-K1, V79, BALB/c 3T3) cell lines and human(MCF-7, A549) ones were used. As a result, the CSC exhibited cytotoxicity with a concentration-dependent response in all cell lines. EC$_{50}$ of CSC in CHO-K1, V79, BALB/c 3T3, MCF-7 and A549 were 140, 125, 100, 116 and 109 $\mu\textrm{g}$/mL, respectively. On the other hand, the spontaneous micronucleated cell(MNC) frequency was stable and reproducible in every cell lines tested in this study. The dose-response of various cell lines to the induction of MN by CSC was estimated using linear regression analysis. CSC(0～100 $\mu\textrm{g}$/mL) caused a dose-dependent MN induction in CHO-K1, V79, BALB/c 3T3 and MCF-7 cell lines. Putting together all the data obtained and linear regression analysis of the data, we concluded that V79 cells are more susceptible to the accurate assessment of CSC-induced MN than the others.s.

• KIEE International Transactions on Electrophysics and Applications
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• v.11C no.3
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• pp.70-74
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• 2001

Admittance or impedance spectroscopy is one of the powerful tools to study dielectric relaxation and loss processes in organic and inorganic materials. In this study, the frequency dependent properties of an indium tin oxide/tris(8-hydroxyquinoline) aluminum($Alq_3$)/aluminum structure have been studied. The conductance of the $Alq_3$ film increases with the DC applied voltage up to 4V and decreases above 4V in the low frequency region. This indicates that the resistance of the device decreases with the applied bias due to the carrier injection enhancement, thereafter the injected carriers form the space charge and the additional injection of carriers is prevented. The Cole-Cole plot of the admittance takes a one-semicircle shape, which means that the device can be modeled as a parallel resistor-capacitor network. The resistance and capacitance were estimated as 8.62k${\Omega}$ and 2.7nF, respectively, at 3V in the low frequency region. The dielectric constant ( ${\epsilon}'$ ) of the $Alq_3$ film is independent of the frequency in the low frequency region below 100kHz, while the frequency dependency was observed at above 100kHz. The dielectric loss factor ( ${\epsilon}"$ ) of the $Alq_3$ film shows the dielectric dispersion below 100kHz and dielectric absorption in higher frequency domain. The dispersion is thought to be related to the hopping process of the carriers. The ${\epsilon}"$ is proportional to the reciprocal of the frequency. The dielectric relaxation time was extracted to about 0.318${\mu}s$ from the dielectric absorption spectrum.

• Bulletin of the Korean Chemical Society
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• v.23 no.5
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• pp.741-744
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• 2002

Single phase of multicomponent oxide ZrTiO4 film could be prepared through surface sol-gel route simply by coating the mixture of 100 mM zirconium butoxide and titanium butoxide on $Pt/Ti/SiO_2Si(100)$ substrate, following pyro lysis at $450^{\circ}C$, and annealing it at 770 $^{\circ}C.$ The dielectric constant of the film was reduced as the film thickness decreased due to of the interfacial effects caused by layer/electrode and a few voids inside the multilayer. However, the dielectric property was independent of applied dc bias sweeps voltage (-2 to +2 V).The dielectric constant of bulk film, 31.9, estimated using series-connected capacitor model was independent of film thickness and frequency in the measurement range, but theoretical interfacial thickness, ti, was dependent on the frequency. It reached a saturated ti value, $6.9{\AA}$, at high frequency by extraction of some capacitance component formed at low frequency range. The dielectric constant of bulk ZrTiO4 pellet-shaped material was 33.7 and very stable with frequency promising as good applicable devices.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.35C no.8
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• pp.42-51
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• 1998

An 8th-order elliptic low-pass filter with cutoff frequency of 3.13kHz is presented. The design procedure is based on teh 1/s impedance transformation which is applied to a minimum capacitor LC ladder network.The tranformed network is implemented with resistors and high Q frequency-dependent negative resistors (FDNR's). The high Q FDNR is realized with two transadmittance amplifiers. Detailed SPICE simulations show that the iflter has pass-band ripple of 0.18dB, stop-band attenuation over 100dB, cutoff frequency of 3.13 khz, and cutoff frequency temperature coefficient of 8.5ppm/.deg. C at supply voltage of .+-.5V.

• Genomics & Informatics
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• v.18 no.4
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• pp.44.1-44.7
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• 2020

The severity of coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), greatly varies from patient to patient. In the present study, we explored and compared mutation profiles of SARS-CoV-2 isolated from mildly affected and severely affected COVID-19 patients in order to explore any relationship between mutation profile and disease severity. Genomic sequences of SARS-CoV-2 were downloaded from Global Initiative on Sharing Avian Influenza Data (GISAID) database. With the help of Genome Detective Coronavirus Typing Tool, genomic sequences were aligned with the Wuhan seafood market pneumonia virus reference sequence and all the mutations were identified. Distribution of mutant variants was then compared between mildly and severely affected groups. Among the numerous mutations detected, 14408C>T and 23403A>G mutations resulting in RNA-dependent RNA polymerase (RdRp) P323L and spike protein D614G mutations, respectively, were found predominantly in severely affected group (>82%) compared with mildly affected group (<46%, p < 0.001). The 241C>T mutation in the non-coding region of the genome was also found predominantly in severely affected group (p < 0.001). The 3037C>T, a silent mutation, also appeared in relatively high frequency in severely affected group compared with mildly affected group, but the difference was not statistically significant (p = 0.06). We concluded that spike protein D614G and RdRp P323L mutations in SARS-CoV-2 are associated with severity of COVID-19. Further studies will be required to explore whether these mutations have any impact on the severity of disease.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.149.2-149.2
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• 2011

We performed the cross-correlation analysis on energy-dependent light curves of the Z-type source GX 5-1. We observed X-ray delays of a few hundred seconds between hard (16-30 keV) and soft (2-5 keV) X-ray light curves. During these phenomena, the centroid frequency of horizontal branch oscillation (HBO) was found to shift to lower or higher frequency indicating towards the dynamical movement of a Compton cloud or an inner disk front. Both eastern and western approaches were used to unfold the X-ray continuum and systematic changes were observed in soft and hard X-ray spectral components. Simultaneous energy spectral and power density spectral study shows that the production of HBOs is closely related to the Comptonizing region rather than the accretion disk. We discuss the results in the context of re-condensation of coronal material in the inner accretion disk region.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.451-454
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• 2002

A silicone rubber has been used so many dielectric materials for extremely high voltage(EBW) electric appliances. The reason why it is very stable in the thermal, mechanical and electrical environment. In this paper, we have studied the dependence of dielectric characteristics of silicone rubber on frequency-dependent variation. The dielectric characteristics were measured in the temperature range of 25[$^{\circ}C$] and 150[$^{\circ}C$]. Also we measured in the voltage range of 1[V] and 20[V]. The energy of activation on the dielectric loss obtained 2.44[kcal/mol], 2.1[kcal/mol], 1.63[kcal/mol] and 1.57[kcal/mol] by appling respectively.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.12
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• pp.24-29
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• 2009

In order to model the high temperature dependence of the cutoff frequency $f_T$ in $0.18{\mu}m$ deep n-well isolated bulk NMOSFET, high temperature data of electron velocity of bulk MOSFETs from $30^{\circ}C$ to $250^{\circ}C$ are obtained by an accurate RF extraction method using measured S-parameters. From these data, an improved temperature-dependent electron velocity equation is developed and implemented in a BSIM3v3 SPICE model to eliminate modeling error of a conventional one in the high temperature range. Better agreement with measured $f_T$ data from $30^{\circ}C$ to $250^{\circ}C$ are achieved by using the SPICE model with the improved equation rather than the conventional one, verifying its accuracy of the improved one.