• Bulletin of the Korean Chemical Society
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• 제26권1호
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• pp.19-31
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• 2005

During the last decade, the exploration of nanoscale device and circuitry based on molecules has gained increasing interest. In parallel with this, considerable effort is being devoted to the development of molecular photonic/electronic materials based on various porphyrin arrays. This involves light as an input/output signal and excitation energy migration as a mechanism for signal transmission. Absorption of a photon at the light collector end of the porphyrin array yields the excited state, which migrates among the intervening pigments until reaching the emitter, whereupon another photon is emitted. As a consequence, it is relevant to understand the excitation energy transfer (EET) processes occurring in various forms of porphyrin arrays for the applications as artificial light harvesting arrays and molecular photonic/electronic wires. Since the excitonic (dipole) and electronic (conjugation) couplings between the adjacent porphyrin moieties in porphyrin arrays govern the EET processes, we have characterized the EET rates of various forms of multiporphyrin arrays (linear, cyclic, and box) based on various time-resolved spectroscopic measurements. We believe that our observations provide a platform for further development of molecular photonic/electronic materials based on porphyrin arrays.

• Bulletin of the Korean Chemical Society
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• 제22권8호
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• pp.837-841
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• 2001

The electronic absorption and Raman spectra of $\alpha\omega-diphenylpolyenyl$, anions Ph(CH)nPh- (DPn- , n = 3, 5, 7, 9, and 13), with odd number of carbons at the polyene part, have been studied in the tetrahydrofuran (THF) solutions and in their solid film states, respectively. In the case of Raman spectra for DPn- , the frequencies and relative intensities of some Raman peaks regularly change with the increase of polyene chain length. The spectral patterns of anions (DPn- ) are very similar with those of radical anion (DPn${\cdot}$- ). However, the C=C stretching peaks of DPn- anions are observed in the 25-35 cm-1 higher frequency region than those of DPn${\cdot}$- radical anions. In the case of long chain models such as DP9- and DP13- , the C=C stretching peaks are observed in even higher frequency region than those of the corresponding neutral polyenes such as DP8, DP10, and DP12. The Raman patterns of DPn- anions in the THF solutions are similar with those in their solid film states. On the other hand, their electronic absorption spectra show a considerable difference each other. The n- ${\pi}*$ electronic absorption bands of DPn- anions in the THF solutions have been observed in the 0.27-0.39 eV lower energy region than those in their solid film states due to the solvent effects on polyene anions.

• ETRI Journal
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• 제43권2호
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• pp.357-370
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• 2021

The evolution of blockchain-based systems has enabled researchers to develop nextgeneration e-voting systems. However, the classical consensus method of blockchain, that is, Proof-of-Work, as implemented in Bitcoin, has a significant impact on energy consumption and compromises the scalability, efficiency, and latency of the system. In this paper, we propose a hybrid consensus model (PSC-Bchain) composed of Proof of Credibility and Proof of Stake that work mutually to address the aforementioned problems to secure e-voting systems. Smart contracts are used to provide a trustworthy public bulletin board and a secure computing environment to ensure the accuracy of the ballot outcome. We combine a sharding mechanism with the PSC-Bchain hybrid approach to emphasize security, thus enhancing the scalability and performance of the blockchain-based e-voting system. Furthermore, we compare and discuss the execution of attacks on the classical blockchain and our proposed hybrid blockchain, and analyze the security. Our experiments yielded new observations on the overall security, performance, and scalability of blockchain-based e-voting systems.

• Bulletin of the Korean Chemical Society
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• 제27권6호
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• pp.881-885
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• 2006

We have employed a technique of corona excited supersonic expansion to generate electronically excited but jet-cooled o-tolunitrile. The vibronically well-resolved emission spectrum of the jet-cooled o-tolunitrile in the $S_{1}\rightarrow S_{0}$ transition was recorded in the uv region using a Fourier transform spectrometer equipped with a Quartz-uv beam splitter. The electronic transition and vibrational mode frequencies in the ground electronic state were accurately determined from the analysis of the spectra observed.

• Bulletin of the Korean Chemical Society
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• 제27권9호
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• pp.1377-1380
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• 2006

The technique of corona-excited supersonic expansion was applied to produce electronically excited but rovibrationally cooled m-tolunitrile. The well-resolved vibronic emission spectrum of the jet-cooled m-tolunitrile in the $S_1\;\rightarrow \;S_0$ transition was recorded in the uv region using a Fourier transform spectrometer equipped with a Quartz-uv beam splitter. From an analysis of the spectrum observed, it was confirmed that the electronic transition and vibrational mode frequencies in the ground electronic state were accurately determined.

• Bulletin of the Korean Chemical Society
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• 제33권3호
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• pp.997-1008
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• 2012

This work provides an alternative derivation of third order response functions in four wave mixing spectroscopy of multichromophoric macromolecular systems considering only single exciton states. For the case of harmonic oscillator bath linearly and diagonally coupled to exciton states, closed form expressions showing all the explicit time dependences are derived. These expressions can provide more solid physical basis for understanding 2-dimensional electronic spectroscopy signals. For more general cases of system-bath coupling, the quantum master equation (QME) approach is employed for the derivation of multistep time evolution equations for Green function-like operators. Solution of these equations is feasible at the level of 2nd order non-Markovian QME, and the new approach can account for inter-exciton coupling, dephasing, relaxation, and non-Markovian effects in a consistent manner.

• Bulletin of the Korean Chemical Society
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• 제33권3호
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• pp.993-996
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• 2012

We investigated fluorescence and fluorescence excitation of diphenylsilane (DPS) in a solution and molecular beams in combination with the aid of the DFT method. When the molecule was photoexcited at 250 nm in a cyclohexane solution, normal and excimer fluorescences were observed in the ranges of 260-320 and 330-450 nm, respectively. The fluorescence excitation spectrum indicates that the channel leading to the intramolecular excimer formation is not efficient in comparison with the normal fluorescence. Vibrationally resolved fluorescence excitation spectra were measured for the DPS molecules cooled in pulsed supersonic expansion of He in the range 262.2-271.7 nm, in which we can see several electronic excitation spectra exhibiting the electronic band origins. We found that the simulated absorption spectrum based on the time-dependent densityfunctional theory calculations accords well with the absorption spectrum.

• Bulletin of the Korean Chemical Society
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• 제24권8호
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• pp.1111-1118
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• 2003

We present one-color nonlinear wavepacket interferometry (WPI) signal calculations for a system of two electronic levels and one vibrational degree of freedom. We consider two cases, a displaced harmonic oscillator system, which can be treated analytically, and a model photodissociative system, whose WPI signal must be calculated by numerical wavepacket propagation. We show how signals obtained with different combinations of intrapulse-pair phase shifts can be combined to isolate the complex-valued overlap between a given onepulse target wavepacket and a variable three-pulse reference wavepacket. We demonstrate that with a range of inter- and intrapulse-pair delays the complex overlaps and variable reference states can be used to reconstruct the target wavepacket. We compare our results with previous methods for vibronic state reconstruction based on linear WPI and discuss further generalizations of our method.

• Bulletin of the Korean Chemical Society
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• 제32권6호
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• pp.1879-1883
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• 2011

The electronic structure and bonding in $Ti_2Pd$ and $Pd_2Ti$ alloys with and without hydrogen as an interstitial atom were studied by performing extended Huckel tight-binding band calculations. The hydrogen absorption near an octahedral site is found to be a favorable process in $Ti_2Pd$ rather than in $Pd_2Ti$. In metal hydrides, the metal-hydrogen bonding contribution is crucial to the stability of the system. The stronger interaction of hydrogen with Ti atoms in $Ti_2PdH_2$ than with Pd atoms in $Pd_2TiH_2$ is analyzed by perturbation theory.

• Bulletin of the Korean Chemical Society
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• 제34권3호
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• pp.912-916
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• 2013

The electronic structure of LaFeAsO was analyzed by tight-binding band calculation based upon the normal and shrunk lattices. A strong Fermi surface nesting was found in the normal LaFeAsO, while most of the nesting area was disappeared in the shrunk LaFeAsO. It was found, therefore, high pressure atmosphere is required to become a superconductor for LaFeAsO by suppressing the SDW (spin density wave) state through the disappearance of the Fermi surface nesting.