Quantitative XAFS/EELS analyses of nitrogen species in titanium oxide photocatalysts

With a view to rational designing of a highly functional visible-light TiO₂ photocatalyst, nitrogen atoms were doped into TiO₂ samples by an ion implantation technique which enables to control the depth and concentration of dopants. Although the absorbance in the visible-light region of the sample increased by the nitrogen doping, photocatalytic activity of the sample was not directly connected with the photo-absorbance. The N K-edge X-ray absorption near edge structure (XANES) spectrum of the photocatalytic active sample (A-cat) showed a characteristic double peak at 398 and 401 eV, and the XANES spectrum of the inactive sample (I-cat) a distinct single peak around 401 eV. These features of the XANES spectra were well reproduced by theoretical simulations based on the model where an O atom in TiO₂ was replaced by N ((N)s) for A-cat, and that of quasi NO₂ molecule ((NO₂)s) for I-cat. Therefore, we have concluded that the nitrogen atom occupying the oxygen site of TiO₂ is photocatalytic active species effective for visible light photocatalysis. In addition, the quantitative XANES/ELNES analysis has revealed that the photo-absorbance ratio of I-cat to A-cat corresponds well to the ratio of total doped nitrogen concentration rather than photocatalytic active nitrogen ((N)s) concentration. This result indicates that not only (N)s but also (NO₂)s also absorb the visible light. Thus, the absorbance in the visible-light region is not necessarily an indication of the visible-light response of a photocatalyst.     

Synthesis of N,N′-bridged azacalixarenes

The one-pot reaction between bis(hydroxymethyl)phenol derivatives and diamines or triamines afforded novel azacalixarenes with bridged structures. Basket-type macrocycles of cone conformations, molecules that contained two aza[3.1.1.1]calixarene skeletons connected by a chain, or novel saucer-type azacalixarenes were obtained from the reaction. Structures of some of them were determined by crystallographic analyses.     

A Designer Axially Chiral Amino Sulfonamide as an Efficient Organocatalyst for Direct Asymmetric anti‐Selective Mannich Reactions and syn‐Selective Cross‐Aldol Reactions

Amino sulfonamide catalyst : A distal proton of the axially chiral amino sulfonamide (S)‐ 1 realized the opposite diastereoselectivity in Mannich and cross‐aldol reactions compared with that observed in proline‐catalyzed reactions. The reactions catalyzed by (S)‐ 1 proceeded smoothly to give the anti‐Mannich and syn‐aldol adducts in excellent enantioselectivity (see scheme).

     

Biometric Identification Systems with Noisy Enrollment for Gaussian Sources and Channels

In the present paper, we investigate the fundamental trade-off of identification, secret-key, storage, and privacy-leakage rates in biometric identification systems for remote or hidden Gaussian sources. We use a technique of converting the system to one where the data flow is in one-way direction to derive the capacity region of these rates. Also, we provide numerical calculations of three different examples for the system. The numerical results imply that it seems hard to achieve both high secret-key and small privacy-leakage rates simultaneously.     

Observation of quasi-two-dimensional nonlinear interactions in a drift-wave streamer

A streamer, which is a bunching of drift-wave fluctuations, and its mediator, which generates the streamer by coupling with other fluctuations, have been observed in a cylindrical magnetized plasma. Their radial structures were investigated in detail by using the biphase analysis. Their quasi-two-dimensional structures were revealed to be equivalent with a pair of fast and slow modes predicted by a nonlinear Schr?dinger equation based on the Hasegawa-Mima model.     

Indirectly illuminated X-ray area detector for X-ray photon correlation spectroscopy

An indirectly illuminated X-ray area detector is employed for X-ray photon correlation spectroscopy (XPCS). The detector consists of a phosphor screen, an image intensifier (microchannel plate), a coupling lens and either a CCD or CMOS image sensor. By changing the gain of the image intensifier, both photon-counting and integrating measurements can be performed. Speckle patterns with a high signal-to-noise ratio can be observed in a single shot in the integrating mode, while XPCS measurement can be performed with much fewer photons in the photon-counting mode. By switching the image sensor, various combinations of frame rate, dynamic range and active area can be obtained. By virtue of these characteristics, this detector can be used for XPCS measurements of various types of samples that show slow or fast dynamics, a high or low scattering intensity, and a wide or narrow range of scattering angles.     

First observation of natural circular dichroism spectra in the extreme ultraviolet region using a polarizing undulator‐based optical system and its polarization characteristics

Natural circular dichroism (CD) spectra in the extreme ultraviolet (EUV) region down to a wavelength of 80 nm have been observed for the first time, using an alanine thin film deposited on sodium salicylate coated glass as a sample. Calibrated EUV‐CD spectra of l ‐alanine exhibited a large negative peak at around 120 nm and a positive CD signal below 90 nm, which were roughly predicted by theoretical calculations. A CD measurement system with an Onuki‐type polarizing undulator was used to obtain the EUV‐CD spectra. This CD system, the development of which took five years, can be used to observe even weak natural CD spectra. The polarization characteristics of this system were also evaluated in order to calibrate the recorded CD spectra.     

Application of X-ray radiography to study the segregation process of iron from silicate under high pressure and high temperature

X-ray radiography was applied to observe the segregation process of iron from silicate at high pressure and high temperature in mixtures containing light elements. As the temperature of the hydrogen-containing sample increases, the molten iron becomes coherent. Small droplets of iron sink to the bottom of the chamber, where they merge into a single, large droplet. The small iron droplets exhibit complex motion, moving in random directions. Markedly different behavior is found in the sulfur-containing sample, where no clear motion of the molten iron is observed. Instead, as the sample temperature is increased, the concentration of iron near the wall of the sample chamber gradually increases. These observations demonstrate that the behavior of molten iron changes according to the dissolved elements. This X-ray radiography experiment represents a powerful technique to study the segregation process of molten iron from solid or partially molten silicate, particularly when combined with high-resolution tomography techniques.     

Effects of water content on magnesium deposition from a Grignard reagent-based tetrahydrofuran electrolyte

It is well known that water causes decomposition of Grignard reagents. When these reagents are used, water or moisture should be eliminated. However, it is possible that a very small amount of water, for example, trapped in the walls of the glassware used, can enter the system even in a well-controlled Ar glove box. Therefore, in this work, the effect of very low concentrations of water on Mg deposition from a Grignard reagent-based electrolyte was studied. It was shown that a minute amount of water, although insufficient to cause destruction of the Grignard reagent, affects the overpotential for Mg deposition, resulting in Mg deposits of different morphology. For reproducible and reversible Mg deposition and dissolution, it is desirable that the water content of the electrolyte is kept as low as possible and the electrolyte is left to stand for at least several hours after preparation.