Tsuyoshi Kato

Asymmetric Gaussian and Its Application to Pattern Recognition

In this paper, we propose a new probability model, asymmetric Gaussian(AG), which can capture spatially asymmetric distributions. It is also extended to mixture of AGs. The values of its parameters can be determined by Expectation-Conditional Maximization algorithm. We apply the AGs to a pattern classification problem and show that the AGs outperform Gaussian models.

Molecular alignment in a liquid induced by a nonresonant laser field: Molecular dynamics simulation.

We carried out molecular dynamics (MD) simulations for a dilute aqueous solution of pyrimidine in order to investigate the mechanisms of field-induced molecular alignment in a liquid phase. An anisotopically polarizable molecule can be aligned in a liquid phase by the interaction with a nonresonant intense laser field. We derived the effective forces induced by a nonresonant field on the basis of the concept of the average of the total potential over one optical cycle. The results of MD simulations show that a pyrimidine molecule is aligned in an aqueous solution by a linearly polarized field of light intensity I approximately 10(13) W/cm2 and wavelength lambda = 800 nm. The temporal behavior of field-induced alignment is adequately reproduced by the solution of the Fokker-Planck equation for a model system in which environmental fluctuations are represented by Gaussian white noise. From this analysis, we have revealed that the time required for alignment in a liquid phase is in the order of the reciprocals of rotational diffusion coefficients of a solute molecule. The degree of alignment is determined by the anisotropy of the polarizability of a molecule, light intensity, and temperature. We also discuss differences between the mechanisms of optical alignment in a gas phase and a liquid phase.

Optimal laser control of ultrafast photodissociation of I2- in water: mixed quantum/classical molecular dynamics simulation.

A linearized optimal control method in combination with mixed quantum/classical molecular dynamics simulation is used for numerically investigating the possibility of controlling photodissociation wave packets of I(2)(-) in water. Optimal pulses are designed using an ensemble of photodissociation samples, aiming at the creation of localized dissociation wave packets. Numerical results clearly show the effectiveness of the control although the control achievement is reduced with an increase in the internuclear distance associated with a target region. We introduce effective optimal pulses that are designed using a statistically averaged effective dissociation potential, and show that they semiquantitatively reproduce the control achievements calculated by using optimal pulses. The control mechanisms are interpreted from the time- and frequency-resolved spectra of the effective optimal pulses.

Intermolecular interaction-induced quantum beats in femtosecond time-resolved light scattering from molecules: photon-polarization and inhomogeneous effects

Abstract We present a quantum statistical theory of intermolecular interaction-induced quantum beats in ultrashort time-resolved light scattering (TRLS) from an ensemble of two interacting molecules (chromophores). An expression for the profile of TRLS is derived based on the generalized master equation in Liouville space. The expression takes into account the initial excitation process as well as the dephasing process. Model calculations of femtosecond TRLS profiles in resonant conditions and an intermolecular degree of coherence are performed to show how the quantum beats appear as a result of intermolecular coherent energy transfer. Effects of photon-polarization on the TRLS profile are investigated. It is shown that under the magic angle condition the interaction-induced quantum beats disappear regardless of the relative orientation between two interacting molecules. Effects of inhomogeneity in interacting molecular pairs on the TRLS profile are also investigated. Finally, inhomogeneity effects on the quantum beats in time-dependent anisotropic absorption observed by Zhu et al. (J. Chem. Phys. 98 (1993) 1042) are discussed.

Absolute Quantification of Lipophilic Shellfish Toxins by Quantitative Nuclear Magnetic Resonance Using Removable Internal Reference Substance with SI Traceability

Okadaic acid (OA), a lipophilic shellfish toxin, was accurately quantified using quantitative nuclear magnetic resonance with internal standards for the development of an authentic reference standard. Pyridine and the residual proton in methanol-d4 were used as removable internal standards to limit any contamination. They were calibrated based on a maleic acid certified reference material. Thus, the concentration of OA was traceable to the SI units through accurate quantitative NMR with an internal reference substance. Signals from the protons on the oxygenated and unsaturated carbons of OA were used for quantification. A reasonable accuracy was obtained by integrating between the lower and upper (13)C satellite signal range when more than 4 mg of OA was used. The best-determined purity was 97.4% (0.16% RSD) when 20 mg of OA was used. Dinophysistoxin-1, a methylated analog of OA having an almost identical spectrum, was also quantified by using the same methodology.

Precise hand-printed character recognition using elastic models via nonlinear transformation

Distorted character recognition is a difficult but inevitable problem in hand-printed character recognition. In this paper, we propose a character recognition method using elastic models for recognizing cursive characters with intricate structure. The models are fitted to unknown input patterns by applying the EM algorithm to minimize a measure of fitness. To avoid falling into local minima, multiresolution approach is introduced. Moreover, nonlinear transformation is adopted to realize more flexible matching. Experiments performed on Japanese characters show effectiveness of the proposed method.

Adiabatic theory of laser-induced vibrational predesorption of physisorbed molecules: Application to a CO/NaCl system

Laser-induced vibrational predesorption of molecules physisorbed on insulating substrates is theoretically investigated based on the Markoff master equation. The system vibrations, which consist of intramolecular vibrations of an admolecule and admolecule-surface vibrations, are divided by the adiabatic approximation, whereby the predesorption is represented by the nonadiabatic transitions from the bound states to the desorption continuum. By using the projection operator in the double(Liouville)-space representation, the bound-continuum couplings due to the nonadiabatic and the optical interactions are explicitly included in the master equation. The adiabatic theory is applied to CO physisorbed on a NaCl(100) surface, in which CO stretching and CO-surface vibration are chosen as the system vibrations. This two-dimensional model with a shallow Morse potential for the CO-surface potential gives a desorption rate of ∼10−4 s−1, which agrees with the experimentally measured rate by Chang and Ewing [Chem. Phys...

Quantification of Representative Ciguatoxins in the Pacific Using Quantitative Nuclear Magnetic Resonance Spectroscopy

The absolute quantification of five toxins involved in ciguatera fish poisoning (CFP) in the Pacific was carried out by quantitative 1H-NMR. The targeted toxins were ciguatoxin-1B (CTX1B), 52-epi-54-deoxyciguatoxin-1B (epideoxyCTX1B), ciguatoxin-3C (CTX3C), 51-hydroxyciguatoxin-3C (51OHCTX3C), and ciguatoxin-4A (CTX4A). We first calibrated the residual protons of pyridine-d5 using certified reference material, 1,4-BTMSB-d4, prepared the toxin solutions with the calibrated pyridin-d5, measured the 1H-NMR spectra, and quantified the toxin using the calibrated residual protons as the internal standard. The absolute quantification was carried out by comparing the signal intensities between the selected protons of the target toxin and the residual protons of the calibrated pyridine-d5. The proton signals residing on the ciguatoxins (CTXs) to be used for quantification were carefully selected for those that were well separated from adjacent signals including impurities and that exhibited an effective intensity. To quantify CTX1B and its congeners, the olefin protons in the side chain were judged appropriate for use. The quantification was achievable with nano-molar solutions. The probable errors for uncertainty, calculated on respective toxins, ranged between 3% and 16%. The contamination of the precious toxins with nonvolatile internal standards was thus avoided. After the evaporation of pyridine-d5, the calibrated CTXs were ready for use as the reference standard in the quantitative analysis of ciguatoxins by LC/MS.

Quantitative 31 P NMR Method for Individual and Concomitant Determination of Phospholipid Classes in Polar Lipid Samples

Herein, to achieve individual and concomitant quantifications of phospholipid classes, an absolute quantification 31P NMR method using an internal standard was examined. Phospholipid standards and dietary foods were dispersed to prepare test solutions in an anionic surfactant (sodium cholate) solution containing EDTA, as a modification based on a reported method. Each phospholipid class showed a reproducible chemical shift at a near-neutral test solution pH of 6.90±0.04 and temperature of 30.0±0.1°C. The quantity of synthetic phosphatidylcholine measured using 31P NMR was consistent with that measured by 1H NMR using an internal standard. As the principal phospholipid class of soybean and egg yolk lecithin is phosphatidylcholine, the measurement conditions of 31P NMR (pulse interval time and number of scans) were optimized such that minor phospholipids, including lysophospholipids, also present in lecithin could be quantified simultaneously. Phospholipid classes in commercial polar lipid samples derived from porcine brain, yeast, and soybean were individually quantified using the above conditions. Using phosphoserine as the internal standard material allowed the absolute molar quantity of the phospholipid class to be precisely determined with traceability to the SI. The determined molar amounts of phospholipid classes were then translated to the weight amount by assuming that each phospholipid class contained two stearic acid molecules as the constituent fatty acid. The calculated total contents of each phospholipid class by 31P NMR were in good agreement with those obtained by molybdenum blue colorimetry. Furthermore, the quantitative values of the principal phospholipid classes in the polar lipid samples obtained by 31P NMR corresponded in a broad view, however, was more informative for the separation of individual phospholipid species rather than the quantitative 2D thin-layer chromatography.

Numerical Synthesis of Optimal Laser Pulses for Manipulating Dissociation Wave Packets of I2− in Water

A linearlized optimal control method in combination with mixed quantum/classical molecular dynamics simulation is used for numerically investigating the possibility of controlling dissociation wave packets of diiodide ions (I2-) in water.