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Sparse Representation Approach to Inverse Halftoning in Terms of DCT Dictionary
Yuhri Ohta,Toshiaki Aida 제어로봇시스템학회 2014 제어로봇시스템학회 국제학술대회 논문집 Vol.2014 No.10
The problem of inverse halftoning is approached on the basis of compressed sensing, which enables us to make significantly efficient inference through the sparse representation of data to be inferred. For this purpose, we have adopted a DCT dictionary as a basis to represent image patches. In the Bayesian formulation of the problem taking the sparse representation into account, the MAP estimate is found to lead to an inverse halftoning algorithm which can be interpreted as a linear programming problem. Numerical simulations have successfully confirmed the effectiveness of the algorithm, which allows us to conclude that the compressed sensing approach is efficient to the problem of inverse halftoning.
Degradation mechanism of LiCoO<sub>2</sub> in aqueous lithium-ion batteries
오현정,나무늬,( Keisuke Yamanaka ),( Toshiaki Ohta ),변혜령 한국공업화학회 2018 한국공업화학회 연구논문 초록집 Vol.2018 No.0
Since the safety issues of nonaqueous lithium-ion batteries, aqueous rechargeable lithium batteries(ARLB) have been highlighted. However, the conventional positive electrodes of layer-structured lithium transi-tion- metal oxide such as LiCoO<sub>2</sub>(LCO) have suffered from poor cyclability in aqueous electrolyte solution, especially at low pH, which may be attributed to surface degradation from water or H<sup>+</sup> intercalation. The fundamental understanding of degradation process of such positive electrodes is still superficial. Here we shed light on irrever-sibility of LCO electrode during charge and discharge process using various X-ray measurement techniques(XANES, XPS and XRD). LCO electrodes in three different environments are examined; aqueous (pH=7), basic(pH=10) solution and nonaqueous solution. The LCO with neutral aqueous electrolyte solution exhibits capacity fading during cycling due to the insignificant presence of CEI layer and distortion of oxygen for both surface and bulk LCO.
김성현,강광훈,Kim, Seong Hyeon,Toshiaki Ohta,Gang, Gwang Hun Korean Chemical Society 2000 Bulletin of the Korean Chemical Society Vol.21 No.6
Structural changes of an iron phthalocyanine (FePC) monolayer induced by adsorption and externally applied potential on high area carbon surface have been investigated in situ by iron K-edge X-ray absorption fine structure (XAFS) in 0.5 M $H_2S0_4.$ Fine structures shown in the X-ray absorption near edge structure (XANES) for microcrystalline FePC decreased upon adsorption and further diminished under electrochemical conditions. Fe(II)PC(-2) showed a 1s ${\rightarrow}$ 4p transition as poorly resolved shoulder to the main absorption edge rather than a distinct peak and a weak 1s ${\rightarrow}$ 3d transition. The absorption edge position measured at half maximum was shifted from 7121.8 eV for Fe(lI)PC(-2) to 7124.8 eV for $[Fe(III)PC(-2)]^+$ as well as the 1s ${\rightarrow}$ 3d pre-edge peak being slightly enhanced. However, essentially no absorption edge shift was observed by the 1-electron reduction of Fe(Il)PC(-2), indicating that the species formed is $[Fe(II)PC(-3)]^-$. Structural parameters were obtained by analyzing extended X-ray absorption fine structure (EXAFS) oscillations with theoretical phases and amplitudes calculated from FEFF 6.01 using multiple-scattering theory. When applied to the powder FePC, the average iron-to-phthalocyanine nitrogen distance, d(Fe-$N_p$) and the coordination number were found to be 1.933 $\AA$ and 3.2, respectively, and these values are the same, within experimental error, as those reported ( $1.927\AA$ and 4). Virtually no structural changes were found upon adsorption except for the increased Debye-Wailer factor of $0.005\AA^2$ from $0.003\AA^2.$ Oxidation of Fe(II)PC(-2) to $[Fe(III)PC(-2)]^+$ yielded an increased d(Fe-Np) (1 $.98\AA)$ and Debye-Wailer factor $(0.005\AA^2).$ The formation of $[Fe(II)PC(-3)]^-$, however, produced a shorter d(Fe-$N_p$) of $1.91\AA$ the same as that of crystalline FePC within experimental error, and about the same DebyeWaller $factor(0.006\AA^2)$.
Wong, Raymond A.,Dutta, Arghya,Yang, Chunzhen,Yamanaka, Keisuke,Ohta, Toshiaki,Nakao, Aiko,Waki, Keiko,Byon, Hye Ryung American Chemical Society 2016 Chemistry of materials Vol.28 No.21
<P>In lithium oxygen (Li-O-2) batteries, controlling the structure of lithium peroxide (Li2O2) can reduce the large overpotential of the charge process as this affects the ionic and electronic conductivities of Li2O2. We demonstrate, for the first time, the in situ structural tuning of Li2O2 during the discharge process by virtue of the surface properties of carbon nanotube electrodes. We tailored carbon nanotube surfaces to decouple oxygen functional groups, defective edges, and graphitization, which directly influence the surface-binding affinity of O-2 and LiO2. Consequently, conformal and completely amorphous Li2O2 films form in the presence of oxygen functional groups, which can facilely decompose in the subsequent charge. In contrast, crystalline Li2O2 particles grow in more ordered carbon electrodes and consequently require higher overpotential for decomposition. Our comprehensive study reveals the possibility of facile decomposition of Li2O2 by the surface engineering of carbon electrode and gives insights into the parameters to improve Li-O-2 cell performance without any additional promoters such as nanoparticles or soluble redox mediators. In all, this work provides improved understanding of the general role of carbonaceous electrode surfaces toward the enhancement of discharge capacity, charge potential, and stability.</P>
Yang, Chunzhen,Wong, Raymond A.,Hong, Misun,Yamanaka, Keisuke,Ohta, Toshiaki,Byon, Hye Ryung American Chemical Society 2016 NANO LETTERS Vol.16 No.5
<P>In lithium-oxygen (Li-O-2) batteries, it is believed that lithium peroxide (Li2O2) electrochemically forms thin films with thicknesses less than 10 nm resulting in capacity restrictions due to limitations in charge transport. Here we show unexpected Li2O2 film growth with thicknesses of similar to 60 nm on a three-dimensional carbon nanotube (CNT) electrode incorporated with cerium dioxide (ceria) nanoparticles (CeO2 NPs). The CeO2 NPs favor Li2O2 surface nucleation owing to their strong binding toward reactive oxygen species (e.g., O-2 and LiO2). The subsequent film growth results in thicknesses of similar to 40 nm (at cutoff potential of 2.2 V vs Li/Li+), which further increases up to similar to 60 nm with the addition of trace amounts of H2O that enhances the solution free energy. This suggests the involvement of solvated superoxide species (LiO2(sol)) that precipitates on the existing Li2O2 films to form thicker films via disproportionation. By comparing toroidal Li2O2 formed solely from LiO2(sol), the thick Li2O2 films formed from surface-mediated nucleation/thin-film growth following by LiO2(sol) deposition provides the benefits of higher reversibility and rapid surface decomposition during recharge.</P>