• Journal of Advanced Navigation Technology
• /
• v.16 no.1
• /
• pp.16-26
• /
• 2012

Pseudolites are ground-based transmitters that can be configured to emit GPS-like signals for enhancing the GPS by providing increased accuracy, integrity, and availability. However, a pseudolite (PL) can interfere with GPS satellite signals while it is transmitting or cause saturation to automatic gain control circuit. To solve these problems pulsing scheme is used, which transmits PL signal during a short period of time. In this paper the effect of the number of PL and pulsing scheme on the software GPS L1 and L2C signal acquisition performance is studied for the three pulsing schemes such as static pulsing, sweep pulsing, and pseudo random pulsing. For GPS L1 signal, static pulsing shows the best signal acquisition and tracking performance with one PL, and random pulsing shows the best performance with more than or equal to two PLs. For GPS L2C signal, all three pulsing schemes show the similar signal acquisition and tracking performance, but static pulsing shows a little better performance. For GPS L1 and L2C signals, software GPS receivers can do positioning with up to three PLs.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.48 no.10
• /
• pp.809-819
• /
• 2020

In this study, the twist angle and wing planform shapes were selected as design variables and optimized to secure the stability of the flying-wing type UAV. Flying-wing aircraft has no separated fuselage and tails, which has advantages in aerodynamic characteristics and stealth performance, but it is difficult to secure the flight stability. In this paper, the sweep back angle and twist angle were optimized to obtain the lateral stability, the static margin and wing planform shapes were optimized to improve the longitudinal stability of the flying-wing, then effect of the twist angle was confirmed by comparing the stability of the shape with the winglet and the shape with the twist angle. In the optimization formulation, focusing on improving stability, constraints were established, objective functions and design variables were set, then design variable sensitivity analysis was performed using the Sobol method. AVL was used for aerodynamic analysis and stability analysis, and SQP was used for optimization. The CFD analysis of the optimized shape and the simulation of the dynamic stability proved that the twist angle can be applied to the improvement of the lateral stability as well as the stealth performance in the flying-wing instead of the winglet.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2003.07a
• /
• pp.319-322
• /
• 2003

To match the charge induced by the insulators $CeO_2$ with the remanent polarization of ferro electric SBT thin films, areas of Pt/SBT/Pt (MFM) and those of $Pt/CeO_2/Si$ (MIS) capacitors were ind ependently designed. The area $S_M$ of MIS capacitors to the area $S_F$ of MFM capacitors were varied from 1 to 10, 15, and 20. Top electrode Pt and SBT layers were etched with for various area ratios of $S_M\;/\;S_F$. Bottom electrode Pt and $CeO_2$ layers were respectively deposited by do and rf sputtering in-situ process. SBT thin film were prepared by the metal orgnic decomposition (MOD) technique. $Pt(100nm)/SBT(350nm)/Pt(300nm)/CeO_2(40nm)/p-Si$ (MFMIS) gate structures have been fabricated with the various $S_M\;/\;S_F$ ratios using inductively coupled plasma reactive ion etching (ICP-RIE). The leakage current density of MFMIS gate structures were improved to $6.32{\times}10^{-7}\;A/cm^2$ at the applied gate voltage of 10 V. It is shown that in the memory window increase with the area ratio $S_M\;/\;S_F$ of the MFMIS structures and a larger memory window of 3 V can be obtained for a voltage sweep of ${\pm}9\;V$ for MFMIS structures with an area ratio $S_M\;/\;S_F\;=\;6$ than that of 0.9 V of MFS at the same applied voltage. The maximum memory windows of MFMIS structures were 2.28 V, 3.35 V, and 3.7 V with the are a ratios 1, 2, and 6 at the applied gate voltage of 11 V, respectively. It is concluded that ferroelectric gate capacitors of MFMIS are good candidates for nondestructive readout-nonvolatile memories.

• Journal of the Korean Chemical Society
• /
• v.35 no.5
• /
• pp.545-552
• /
• 1991

A mercury ion-sensitive carbon-paste electrode (CPE) was constructed with l-sparteine. Mercury (II) ion was chemically deposited by the complexation with l-sparteine onto the CPE. The surface of CPEs was characterized by cyclic voltammetry and anodic stripping voltammetry in an acetate buffer solution, separately. Exposure of CPEs to acid solution could regenerate surface and reuse it for deposition. In 5 deposition/measurement/regeneration cycle, the response was reproducible and in licnear up to $2.0\;{\times}\;10^{-6}$ M with linear sweep voltammetry. In case of using the differential pulse technique, we have obtained the linear response up to $7.0 {\times}10^{-7}$ M with relative standard deviation of ${\pm}5.1$%. The detection limit was $5.0{\times}10^{-7}$ M for 20 minutes of the deposition. We have investigated the interference effect of various metal ions, which are expected to form the complex with ligand. Silver (I) ion of these has interfered with the analysis of Hg (II) ions. However, pretreatment of the silver (I) ion with potassium chloride led to no interference on the analysis of mercury ions in aqueous solution.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.02a
• /
• pp.27-27
• /
• 2011

For the design of real applicable molecular devices, current-voltage properties through molecular nanostructures such as metal-molecule-metal junctions (molecular junctions) have been studied extensively. In thiolate monolayers on the gold electrode, the chemical bonding of sulfur to gold and the van der Waals interactions between the alkyl chains of neighboring molecules are important factors in the formation of well-defined monolayers and in the control of the electron transport rate. Charge transport through the molecular junctions depends significantly on the energy levels of molecules relative to the Fermi levels of the contacts and the electronic structure of the molecule. It is important to understand the interfacial electron transport in accordance with the increased film thickness of alkyl chains that are known as an insulating layer, but are required for molecular device fabrication. Thiol-tethered RuII terpyridine complexes were synthesized for a voltage-driven molecular switch and used to understand the switch-on mechanism of the molecular switches of single metal complexes in the solid-state molecular junction in a vacuum. Electrochemical voltammetry and current-voltage (I-V) characteristics are measured to elucidate electron transport processes in the bistable conducting states of single molecular junctions of a molecular switch, Ru(II) terpyridine complexes. (1) On the basis of the Ru-centered electrochemical reaction data, the electron transport rate increases in the mixed self-assembled monolayer (SAM) of Ru(II) terpyridine complexes, indicating strong electronic coupling between the redox center and the substrate, along the molecules. (2) In a low-conducting state before switch-on, I-V characteristics are fitted to a direct tunneling model, and the estimated tunneling decay constant across the Ru(II) terpyridine complex is found to be smaller than that of alkanethiol. (3) The threshold voltages for the switch-on from low- to high-conducting states are identical, corresponding to the electron affinity of the molecules. (4) A high-conducting state after switch-on remains in the reverse voltage sweep, and a linear relationship of the current to the voltage is obtained. These results reveal electron transport paths via the redox centers of the Ru(II) terpyridine complexes, a molecular switch.

• Applied Chemistry for Engineering
• /
• v.8 no.6
• /
• pp.1022-1028
• /
• 1997

This work was performed to study the characteristics of electrochemical intercalation reactions occurring at the interface between the organic electrolyte and tungsten trioxide thin film (thickness of $4000{\AA}$) prepared by e-beam evaporation method as cathodically coloring oxide with regard to the electrochromism by the intercalating reactions of the lithium cation in the 1M $LiClO_4/PC$ organic solution. The characteristics of electrochemical intercalation reactions were investigated by various DC electrochemical methods such as cathodic Tafel polarization test, multiple and the single sweep cyclic voltammetry and the coulomety titrations method. The surfaces of thin films were observed with the patterns of X ray diffraction after the coloring and bleaching reactions. In comparison with the previous results that $WO_3$ thin film intersely detached from the surface of electrode when the hydrogen cation was intercalated into $WO_3$ thin film in the o.1N $H_2SO_4$ aqueous solution, the intercalation reaction of lithium cation into $WO_3$ thin film in the 1M $LiClO_4/PC$ organic solution was shown that the stable bleaching and coloration was appeared within 1.0V of the applied overpotential. When the overpotential of electrochromic reaction for lithium cation in the 1M $LiClO_4/PC$ organic solution had been applied up to 1.5V, the accumulation phenomenon of lithium in amorphous $WO_3$ thin film layer occurred because the inserted lithium into amorphous $WO_3$ thin layer for coloring process was not fully removed from the thin layer to the electrolyte during bleaching process. It was found that there is a limitation of applied overpotential for coloring process by the reduction of the current densities of bleaching and coloration after few number of coloring and bleaching cycles.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.48 no.8
• /
• pp.555-563
• /
• 2020

Foward-swept wings are known to possess superior aerodynamic performance compared to the conventional straight wings. However major concerns regarding forward-swept wings include divergence at lower airspeeds which require careful consideration at the design stage. As an endeavor to overcome such drawbacks, aeroelastic tailoring is attempted. In order to find an optimal ply sequence, recursive aeroelastic analyses is conducted and one-dimensional beam analysis coupled with simple aerodynamics is used for the improved computational efficiency and modelling convenience. The analysis used in this paper, DYMORE and analytic formula, both use one-dimensional beam model for the structure. Cross-sectional analysis for multi-cell NACA0015 airfoil section is conducted using VABS and oblique function is used for the sweep angle. Throughout the present aeroelastic tailoring, the maximum divergence speed of 290.2m/s is achieved which is increased by approximately 43% than that for the conventional ply configuration.

• Restorative Dentistry and Endodontics
• /
• v.25 no.3
• /
• pp.359-370
• /
• 2000

The purpose of this investigation was to observe the viscoelastic properties of five commercial flowable(Aeliteflo, Flow it, Revolution, Tetric flow, Compoglass flow), three conventional hybrid(Z-100, Z-250, P-60) and two condensable(Synergy compact, SureFil) resin composites. A dynamic oscillatory shear test was done to evaluate the storage shear modulus (G'), loss shear modulus(G"), loss tangent(tan ${\delta}$) and complex viscosity(${\eta}^*$) of the resin composites as a function of frequency - dynamic frequency sweep test from 0.01 to 100 rad/s at $25^{\circ}C$ - by using Advanced Rheometric Expansion System(ARES). To investigate the effect on the viscosity of resin composites of filler volume fraction, the filler weight % and volume % were measured by means of Archimedes' principle using a pyknometer. The results were as follows 1. The complex viscosity ${\eta}^*$ of flowable resins was lower than that of hybrid resins and significant differences were observed between brands. The complex viscosity ${\eta}^*$ of condensable resins was higher than that of hybrid resins. The order of complex viscosity ${\eta}^*$ at ${\omega}$=10 rad/s was as follows, Surefil, Synergy compact, P-60, Z-250, Z-100, Aeliteflo, Tetric flow, Compoglass flow, Flow it, Revolution. The relative complex viscosity of flowable resins compared to Z-100 was 0.04~0.56 but Surefil was 30.4 times higher than that of Z-100. 2. The storage shear modulus G' and the loss shear modulus G" of flowable resins were lower than those of hybrid resins but those of condensable resins were higher. The patterns of the change of loss tangent, tan ${\delta}$, of resin composites with increasing frequency were significantly different between brands. The phase angles, ${\delta}$, ranged from $30.2{\sim}78.1^{\circ}$ at ${\omega}$=10 rad/s. 3. All composite resins represent pseudoplastic nature with increasing shear rate. 4. The complex shear modulus $G^*$ and the phase angle ${\delta}$ was represented by the frequency domain phasor form, $G^*({\omega})=G^*e^{i{\delta}}=G^*{\angle}{\delta}$. The locus of frequency domain phasor plots in a complex plane was a valuable method that represent the viscoelastic properties of composite resins. 5. There was no direct linear correlationship but a weak positive relation was observed between filler volume % or weight % and the viscosity of the resin composites.

• Korean journal of applied entomology
• /
• v.51 no.1
• /
• pp.67-72
• /
• 2012

This study was conducted to evaluate the scouting methods for larva and adults of the alfalfa weevil, $Hypera$ $postica$ Gyllenhal on Chinese milkvetch, $Astragalus$ $sinicus$ L. in the field. Three sampling methods, shake-bucket, shake-picking, and a sweeping net were evaluated for collecting alfalfa weevil larvae. We found significant differences among scouting methods and date in all survey fields. Sweep-net sampling was less able to detect small larvae than large larvae, which were not detected until early April whereas the shake-bucket, and shake-picking methods efficiently collected larvae from middle March. A Pitfall trap with three different baits - no bait, kidney bean seeds and sprouting kidney beans were compared for collection efficiency of alfalfa weevil adults. Collection efficiencies were significantly different by bait(p<0.018). Traps baited with sprouting kidney beans were the most efficient for collecting the alfalfa weevil. The number of alfalfa weevil caught was not significantly different between kidney bean seed and no bait in the pitfall trap. Therefore, the shake-bucket method for larvae and a pitfall trap baited with sprouting kidney beans for adults are recommended for scouting of the alfalfa weevil in a Chinese milkvetch field.

• Journal of the Korean Chemical Society
• /
• v.37 no.10
• /
• pp.881-887
• /
• 1993

A cobalt(II) ion-selective carbon-paste electrode (CPE) was constructed with ${\iota}$-sparteine. Cobalt(II) ion in aqueous solution was chemically deposited through the complexation with ${\iota}$-sparteine onto the CPE. The surface of CPEs were characterized by cyclic voltammetry and differential pulse voltammetry in an acetate buffer solution, separately. Exposure of the CPEs to an acid solution could regenerate surface to reuse it for the deposition. In more than 5 deposition / measurement / regeneration cycles, the response was reproducible and linear up to $5.0{\times}10^{-6}$M with linear sweep voltammetry. The peaks at 0.17V / 0.27V were correspond to the redox of Co(II)-SP complex deposited on CPE. The anodic peak of which appeared after scan over the cathodic peak of 0.17 V to more negative scan. In case of using the differencial pulse voltammetry (DPV), we have obtained the linear response $2.0{\times}10^{-7}$M with relative standard deviation ${\pm}5.6%$. The detection limit was $1.0{times}10^{-7}$M for 20 minutes of the deposition. We have also investigated the interference effect of various metal ions, which are expected to form the complex with the ligand on the electrode.