• Agricultural and Biosystems Engineering
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• v.2 no.2
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• pp.63-68
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• 2001

The objective of this study was to develop a real-time soil moisture meter using RF impedance. The impedance suchas capacitance and resistance (or conductance) was analyzed using parallel cylinder type capacitance probe(C-probe) and Q-meter (HP4342). The capacitance and conductance of soil increased as volumetric water content increased. The 5 MHz of modified Colpitts type crystal oscillator was designed to detect the capacitance change of the C-probe with moist soil. A third order polynomial regression model was proposed to describe the relationship between RF impedance and volumetric water content. The prototype real time moisture meter consisted of the C-probe, sample container, oscillator, frequency counter and related signal processing units. The calibration equation for measurement of volumetric moisture content of soil was developed and validated. The correlation coefficient and root mean square error between measured volumetric water content by oven method and predicted values by prototype moisture meter for unknown soil samples were 0.984 and 0.032$cm^3$$cm\^3$, respectively.

• Journal of the Korean Institute of Telematics and Electronics
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• v.8 no.3
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• pp.15-26
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• 1971

The paper presents a new method for analyzing oscillation regions of transistor oscillators. In transistor feedback oscillators oscillation region appears as a circle in feedback impedance complex plane. When the resistive component of feedback impedance is fixed and the reactive component of feedback impedance is varied or vice versa, the locus of maximum negative output conductance becomes hyperbola. In transistor crystal oscillators oscillation region is determined by two circles which make real part and imaginary part of input impedance zero in load impedance complex plane. When the resistive compoment of load impedance is fixed and the reactive colnponent of load impedance is varied or vice versa, the loci of maximum or minimum resistive component of input impedance become straight lines.

• The Korean Journal of Physiology and Pharmacology
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• v.1 no.6
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• pp.783-796
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• 1997

The relaxation induced by stimulation of the inhibitory non-adrenergic, non-cholinergic (iNANC) nerve is mediated by the release of iNANC neurotransmitters such as nitric oxide (NO), vasoactive intestinal peptide (VIP) and adenosine triphosphate (ATP). The mechanisms of NO, VIP or ATP-induced relaxation have been partly determined in previous studies, but the detailed mechanism remains unknown. We tried to identify the nature of iNANC neurotransmitters in the smooth muscle of guinea pig ileum and to determine the mechanism of the inhibitory effect of nitric oxide. We measured the effect of NO-donors VIP and ATP on the intracellular $Ca^{2+}$ concentration$([Ca^{2+}]_i)$, by means of a fluorescence dye(fura 2) and tension simultaneously in the isolated guinea pig ileal smooth muscle. Following are the results obtained. 1. Sodium nitroprusside $(SNP:10^{-5}\;M)$ or S -nitro-N-acetyl-penicillamine $(SNP:10^{-5}\;M)$ decreased resting $[Ca^{2+}]_i$ I and tension of muscle. SNP or SNAP also inhibited rhythmic oscillation of $[Ca^{2+}]_i$ and tension. In 40mM $K^+$ solution or carbachol ($(CCh:10^{-6}\;M)$-induced precontracted muscle, SNP decreased muscle tension. VIP did not change $[Ca^{2+}]_i$ and tension in the resting or precontracted muscle, but ATP increased resting $[Ca^{2+}]_i$ and tension in the resting muscle. 2. 1H-[1,2,4]oxadiazol(4,3-a)quinoxalin-1-one $(ODQ:1\;{\mu}M)$, a specific inhibitor of soluble guanylate cyclase, limited the inhibitory effect of SNP 3. Glibenclamide $(10\;{\mu}M)$, a blocker of $K_{ATP}$ channel, and 4-aminopyridine (4-AP:5 mM), a blocker of delayed rectifier K channel, apamin $(0.1\;{\mu}M)$, a blocker of small conductance $K_{Ca}$ channel had no effect on the inhibitory effect of SNP. Iberiotoxin $(0.1\;{\mu}M)$, a blocker of large conductance $K_{Ca}$ channel, significantly increased the resting $[Ca^{2+}]_i$, and tension, and limited the inhibitory effect of SNP. 4. Nifedipine $(1\;{\mu}M)$ or elimination of external $Ca^{2+}$ decreased not only resting $[Ca^{2+}]_i$ and tension but also oscillation of $[Ca^{2+}]_i$ and tension. Ryanodine $(5\;{\mu}M)$ and cyclopiazonic acid $(10\;{\mu}M)$ decreased oscillation of $[Ca^{2+}]_i$ and tension. 5. SNP decreased $Ca^{2+}$ sensitivity of contractile protein. In conclusion, these results suggest that 1) NO is an inhibitory neurotransmitter in the guinea pig ileum, 2) the inhibitory effect of SNP on the $[Ca^{2+}]_i$ and tension of the muscle is due to a decrease in $[Ca^{2+}]_i$ by activation of the large conductance $K_{Ca}$ channel and a decrease in the sensitivity of contractile elements to $Ca^{2+}$ through activation of G-kinase.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.8
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• pp.1885-1890
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• 2013

In this paper, the electrical properties of nanoscale junctionless p-channel MuGFET at cryogenic temperature have been analyzed experimentally. The experiment was performed using a cryogenic probe station which uses the liquid Helium. It has been observed that the drain current oscillation at low drain voltage and cryogenic temperature was more pronounced in junctionless transistor than in accumulation mode transistor. The reason for more marked oscillation is due to the smaller electrical cross section area of the inversion channel which is formed at the center of silicon film in junctionless transistor. It was also observed that the drain current and maximum transconductance were increased as the measurement temperature increased. This is resulted from the increase of hole mobility and the decrease of the threshold voltage as the measurement temperature increases. The drain current oscillation due to the quantum effects can be occurred up to the room temperature when the device size scales down to the nanometer level.

• Proceedings of the IEEK Conference
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• 2002.07a
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• pp.337-340
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• 2002

This paper describes a phase compensation technique for the low power consumption OTA. Power consumption of the low power OTA is lower than that of the conventional Wang's OTA. However. this circuit has an oscillation problem. The phase margin is -24deg. By using the phase compensation capacitor, the phase margin becomes 52deg. As a result, the low power consumption OTA circuit becomes to have an enough phase margin and to operate stably.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.10
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• pp.14-22
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• 2010

The source/channel/drain regions are formed by ion implantation with different dopant types of $n^+/p^{(+)}/n^+$ in the fabrication of the conventional n-type metal-oxide-semiconductor field effect transistor(NMOSFET). In implementing the ultra-small devices with channel length of sub-30 nm, in order to achieve the designed effective channel length accurately, low thermal budget should be considered in the fabrication processes for minimizing the lateral diffusion of dopants although the implanted ions should be activated as completely as possible for higher on-current level. Junctionless (JL) MOSFETs fully capable of the the conventional NMOSFET operations without p-type channel for enlarging the process margin are under researches. In this paper, the optimum design of the JL MOSFET based on silicon nanowire (SNW) structure is carried out by 3-D device simulation and the basic radio frequency (RF) characteristics such as conductance, maximum oscillation frequency($f_{max}$), current gain cut-off frequency($f_T$) for the optimized device. The channel length was 30 run and the design variables were the channel doping concentration and SNW radius. For the optimally designed JL SNW NMOSFET, $f_T$ and $f_{max}$ high as 367.5 GHz and 602.5 GHz could be obtained, respectively, at the operating bias condition $V_{GS}$ = $V_{DS}$ = 1.0 V).

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.16 no.4
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• pp.281-292
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• 2016

The proposed scheme is based on the modified perturb and observe (P&O) algorithm combined with the sliding mode technique. A modified P&O algorithm based sliding mode controller is developed to study the effects of partial shade, temperature, and insolation on the performance of maximum power point tracking (MPPT) used in photovoltaic (PV) systems. Under partially shaded conditions and temperature, the energy conversion efficiency of a PV array is very low, leading to significant power losses. Consequently, increasing efficiency by means of MPPT is particularly important. Conventional techniques are easy to implement but produce oscillations at MPP. The proposed method is applied to a model to simulate the performance of the PV system for solar energy usage, which is compared to the conventional methods under non-uniform insolation improving the PV system utilization efficiency and allowing optimization of the system performance. The modified perturb and observe sliding mode controller successfully overcomes the issues presented by non-uniform conditions and tracks the global MPP. Compared to MPPT techniques, the proposed technique is more efficient; it produces less oscillation at MPP in the steady state, and provides more precise tracking.

• The Korean Journal of Physiology
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• v.28 no.2
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• pp.151-157
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• 1994

Intracellular free $Ca^{2+}$ contributes to regulation of various events occurring in vascular smooth muscle cells. One of these events is modulating the membrane iou currents. Single smooth muscle cells were isolated from rabbit mesenteric artery. Three kinds of $Ca^{2+}-activated\;current$ were studied with the patch clamp method. $Ca^{2+}-activated\;K^+\;current$ with a large oscillation was recorded in the depolarized potential range. The single channel conductance of this current was about 250 pS. It was abolished by replacing intracellular $K^+\;with\;Cs^+$. A $Ca^{2+}-activated$ nonselective cation current was observed in both the depolarized and hyperpolarized potential ranges. And it was blocked by replacement of extracellular $Na^+$ with N-methylglucamine (NMG) or extracellular application of $Cd^{2+}$. $Ca^{2+}-activated\;Cl^-\;current$ was revealed in the whole voltage range and was blocked by niflumic acid. These results indicate that at least three kinds of $Ca^{2+}-activated$ ionic currents exist in smooth muscle cells from rabbit superior mesenteric artery.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.12-12
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• 2010

By using scanning tunneling microscopy/spectroscopy (STM/S), we can make images of various physical properties in nanometer-scale spatial resolutions. Here, I demonstrate imaging of two electron-correlated subjects; screening and superconductivity by STM/S. The electrostatic potential around a charge is described with the Coulomb potential. When the charge is located in a metal, the potential is modified because of the free electrons in the host. The potential modification, called screening, is one of the fundamental phenomena in the condensed matter physics. Using low-temperature STM we have developed a method to measure electrostatic potential in high spatial and energy resolutions, and observed the potential around external charges screened by two-dimensional surface electronic states. Characteristic potential decay and the Friedel oscillation were clearly observed around the charges [1]. Superconductivity of nano-size materials, whose dimensions are comparable with the coherence length, is quite different from their bulk. We investigated superconductivity of ultra-thin Pb islands by directly measuring the superconducting gaps using STM. The obtained tunneling spectra exhibit a variation of zero bias conductance (ZBC) with a magnetic field, and spatial mappings of ZBC revealed the vortex formation [2]. Size dependence of the vortex formation will be discussed at the presentation.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.12
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• pp.1-6
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• 2007

In this study, we have performed the channel modification of the conventional MHEMT (metamorphic high electron mobility transistor) to improve the breakdown characteristics. The Modified channel consists of the InxGal-xAs channel and the InP sub channel instead of the InxGa1-xAs channel. Since InP has the lower impact ionization coefficient in comparison with In0.53Ga0.47As, we have adopted the InP-composite channel in the modified MHEMT. We have investigated the breakdown mechanism and the RF characteristics for the conventional and the InP- composite channel MHEMTs. From the measurement results, we have obtained the enhanced on and off-state breakdown voltages of 2.4 and 5.7 V, respectively. Also, the increased RF characteristics have brought about the decreased output conductance for the InP-composite channel MHEMT. The cut-off frequency (fT) and the maximum oscillation frequency (fmax) for the InP-composite Channel MHEMT were 160 GHz and 230 GHz, respectively. It has been shown that the InP-composite channel MHEMT has the potential applications for the millimeter wave power device.