• Journal of the Korean Chemical Society
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• v.59 no.2
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• pp.117-124
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• 2015

The DFT and ab initio calculations have been performed to elucidate hydrogen interaction of hydrogen polyoxide dimers, $H_2O_n-H_2O_m$ (n=1-4, m=1-4). The optimized geometries, harmonic vibrational frequencies, and binding energies are predicted at various levels of theory. The harmonic vibrational frequencies of the molecules considered in this study show all real numbers implying true minima. The higher-order correlation effect were discussed to compare MP2 result with CCSD(T) single point energy. The binding energies were corrected for the zero-point vibrational energy (ZPVE) and basis set superposition errors (BSSE). The largest binding energy predicted at the CCSD(T)/cc-pVTZ level of theory is 8.18 kcal/mol for $H_2O_4-H_2O_3$ and the binding energy of water dimer is predicted to be 3.00 kcal/mol.

• Speech Sciences
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• v.10 no.4
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• pp.117-124
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• 2003

Speaker recognition is the technology that confirms the identification of speaker by using the characteristic of speech. Such technique is classified into speaker identification and speaker verification: The first method discriminates the speaker from the preregistered group and recognize the word, the second verifies the speaker who claims the identification. This method that extracts the information of speaker from the speech and confirms the individual identification becomes one of the most efficient technology as the service via telephone network is popularized. Some problems, however, must be solved for the real application as follows; The first thing is concerning that the safe method is necessary to reject the imposter because the recognition is not performed for the only preregistered customer. The second thing is about the fact that the characteristic of speech is changed as time goes by, So this fact causes the severe degradation of recognition rate and the inconvenience of users as the number of times to utter the text increases. The last thing is relating to the fact that the common characteristic among speakers causes the wrong recognition result. The silence parts being included the center of speech cause that identification rate is decreased. In this paper, to make improvement, We proposed identification rate can be improved by removing silence part before processing identification algorithm. The methods detecting speech area are zero crossing rate, energy of signal detect end point and starting point of the speech and process DTW algorithm by using two methods in this paper. As a result, the proposed method is obtained about 3% of improved recognition rate compare with the conventional methods.

• Bulletin of the Korean Chemical Society
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• v.35 no.3
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• pp.858-864
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• 2014

Recently, many researches have shown that even photosynthetic light-harvesting pigment-protein complexes can have quantum coherence in their excitonic energy transfer at cryogenic and physiological temperatures. Because the protein supplies such noisy environment around pigments that conventional wisdom expects very short lived quantum coherence, elucidating the mechanism and searching for an applicability of the coherence have become an interesting topic in both experiment and theory. We have previously studied the quantum coherence of a phycocyanin 645 complex in a marine algae harvesting light system, using Poisson mapping bracket equation (PBME). PBME is one of the applicable methods for solving quantum-classical Liouville equation, for following the dynamics of such pigment-protein complexes. However, it may suffer from many defects mostly from mapping quantum degrees of freedom into classical ones. To make improvements against such defects, benchmarking targets with more accurately described dynamics is highly needed. Here, we fall back to reduced hierarchical equation of motion (HEOM), for such a purpose. Even though HEOM is known to applicable only to simplified system that is coupled to a set of harmonic oscillators, it can provide ultimate accuracy within the regime of quantum-classical description, thus providing perfect benchmark targets for certain systems. We compare the evolution of the density matrix of pigment excited states by HEOM against the PBME results at physiological temperature, and observe more sophisticated changes of density matrix elements from HEOM. In PBME, the population of states with intermediate energies display only monotonically increasing behaviors. Most importantly, PBME suffers a serious issue of wrong population in the long time limit, likely generated by the zero-point energy leaking problem. Future prospects for developments are briefly discussed as a concluding remark.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.2
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• pp.59-68
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• 1987

Several series of fracture tests were conducted to explore the fracture characteristics and to determine the fracture energy of concrete. A stable three-point bend test was employed to generate the load-deflection curves. The fracture energy may then be calculated from the area under the complete load-deflection curve. The initial notch-to-beam depth ratio (${\alpha}_0$/H) was varied from zero to 0.6. The prediction formula for the fracture energy of concrete is also derived and is found to depend on the tensile strength and aggregate size. The proposed fracture energy formula can be used for the fracture analysis of concrete structures. The present study also devises an equivalent crack length concept to predict the maximum failure loads of concrete beams. A simple formula for the equivalent crack length is proposed.

• Journal of the Korean Solar Energy Society
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• v.25 no.4
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• pp.37-44
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• 2005

An experimental study was conducted to analyze performance of a heating system with variation of control logic of the system. The system uses a solar as heat source and composed with heat pump that uses R-22 as working fluid. The difference between the developed system and the commercially available heating system is working fluid. The solar assisted heating system which was widely distributed in the market uses water as a working fluid. It could be freezing in case of the temperature drops down under freezing point. The anti-freezing fluids such as methyl-alcohol or ethylene-glycol are mixed with the water to protect the freezing phenomena. However, the system developed in this study uses a refrigerant as a working fluid. It makes the system to run under zero degree temperature conditions. Another difference of the developed system compare with commercial available one is auxiliary heating method. The developed system has removed an auxiliary electric heater that has been used in conventional solar assisted heating system. Instead of the auxiliary electric heater, an air source heat exchanger which generally used as an evaporator of a heat pump was adapted as a backup heating device of the developed system. As results, an efficiency of the developed system is higher than a solar assisted heat pump with auxiliary electric heater. The merit of the developed system is on the performance increment when the system operates at a lower solar energy climate conditions. In case of the developed system operates at a normal condition, COP of the solar collector driven heat pump is higher than the air source heat exchanger driven heat pump's.

• Journal of Power Electronics
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• v.4 no.3
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• pp.138-151
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• 2004

In this paper, a constant frequency phase shifting PWM-controlled voltage source full bridge-type series load resonant high-frequency inverter using the $4^{th}$ generation IGBT power modules is presented for innovative consumer electromagnetic induction heating applications, such as a hot water producer, steamer and super heated steamer. The bridge arm side link passive capacitive snubbers in parallel with each power semiconductor device and AC load side linked active edge inductive snubber-assisted series load resonant tank soft switching inverter with a constant frequency phase shifted PWM control scheme is evaluated and discussed on the basis of the simulation and experimental results. It is proved from a practical point of view that the series load resonant and edge resonant hybrid high-frequency inverter topology, what is called, DE class type, including the variable-power variable-frequency regulation function can expand zero voltage soft switching commutation area even under low output power setting ranges, which is more suitable and acceptable for newly developed induction heated dual pack fluid heaters. Furthermore, even the lower output power regulation mode of this high-frequency load resonant tank inverter circuit is verified so that this inverter can achieve ZVS with the aid of the single auxiliary inductor snubber.

• Wind and Structures
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• v.31 no.4
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• pp.373-380
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• 2020

For large-scale 5MW offshore wind turbines, the discrete equation of fluid domain and the motion equation of structural domain with geometric nonlinearity were built, the three-dimensional modeling of the blade considering fluid-structure interaction (FSI) was achieved by using Unigraphics (UG) and Geometry modules, and the numerical simulation and the analysis of the vibration characteristics for wind turbine structure under rotating effect were carried out based on ANSYS software. The results indicate that the rotating effect has an apparent effect on displacement and Von Mises stress, and the response and the distribution of displacement and Von Mises stress for the blade in direction of wingspan increase nonlinearly with the equal increase of rotational speeds. Compared with the single blade model, the blade vibration period of the whole machine model is much longer. The structural coupling effect reduces the response peak value of the blade displacement and Von Mises stress, and the increase of rotational speed enhances this coupling effect. The maximum displacement difference between two models decreases first and then increases along wingspan direction, the trend is more visible with the equal increase of rotational speed, and the boundary point with zero displacement difference moves towards the blade root. Furthermore, the Von Mises stress difference increases gradually with the increase of rotational speed and decreases nonlinearly from the blade middle to both sides. The results can provide technical reference for the safe operation and optimal design of offshore wind turbines.

• Bulletin of the Korean Chemical Society
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• v.32 no.1
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• pp.277-280
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• 2011

We studied the relative stability and atomic structure of five $C_{20}^{2+}$ isomers obtained by two-electron ionization of a $C_{20}$ cage (the smallest fullerene). All the isomers are bond-stretch isomers, i.e., they differ in bond length. In particular, in one of the isomers with Ih symmetry, all the bond lengths are equal. Full geometry optimizations of the dipositive ion $C_{20}^{2+}$ were performed using the hybrid density functional (B3LYP/6-31G(d)) methods. All isomers were found to be true minima by frequency analysis at the level of B3LYP/6-31G(d) under the reinforced tight convergence criterion and a pruned (99,590) grid. The zero-point correction energy for the cage bond-stretch isomers was in the increasing order $D_{2h}<C_{2h}<C_2<T_h<I_h$ of $C_{20}^{2+}$. The energy difference among the isomers of cage dipositive ions was less than that among neutral cage isomers. Our results suggest that these isomers show bond-stretch isomerism and that they have an identical spin state and an identical potential energy curve. Although the predominant electronic configurations of the isomers are similar, the frontier orbital characteristics are different, implying that we could anticipate an entirely different set of characteristic chemical reactions for each type of HOMO and LUMO.

• Analytical Science and Technology
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• v.19 no.4
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• pp.285-289
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• 2006

In this study, the effect of an acidic treatment on granular activated carbon (GAC) and activated carbon fibers (ACF) was investigated for a $Pb^{2+}$ and $Ni^{2+}$ ion adsorption. 1.0 M nitric acid solution was used as the acid solution for the surface treatment. Surface properties of the GAC and ACF were characterized by the pH, elemental analysis and pHpzc (pH of the point of zero charge). Their specific surface area and the pore structure were also evaluated by the nitrogen adsorption data at 77K. As a result, the acidic treatment led to an increase of the oxygen-containing functional groups. Furthermore, the adsorption capacity of the acid-treated GAC and ACF was improved in the order of acidic-ACF > untreated-ACF > acidic-GAC > untreated-GAC, though the decrease in specific surface area induced by a pore blocking of the functional groups was observed.

• Journal of Power Electronics
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• v.4 no.1
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• pp.46-55
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• 2004

This paper presents a high-frequency ZVS-PWM boost chopper-fed DC-DC converter with a single active auxiliary edge resonant snubber in the load-side which can be designed for power conditioners such as solar photovoltaic generation, fuel cell generation, battery and super capacitor energy storages. Its principle operation in steady-state is described in addition to a prototype setup. The experimental results of ZVS-PWM boost chopper-fed DC-DC converter proposed here, are evaluated and verified with a practical design model in terms of its switching voltage and current waveforms, the switching v-i trajectory, the temperature performance of IGBT module, the actual power conversion efficiency and the EMI of radiated and conducted emissions. And then discussed and compared with the hard switching scheme from an experimental point of view. Finally, this paper proposes a practical method to suppress parasitic oscillation due to the active auxiliary resonant switch at ZCS turn off mode transition with the aid of an additional lossless clamping diode loop, and reduced the EMI conducted emission in this paper.