A compact permanent‐magnet system for measuring magnetic circular dichroism in resonant inelastic soft X‐ray scattering

A compact and portable magnet system for measuring magnetic dichroism in resonant inelastic soft X‐ray scattering (SX‐RIXS) has been developed at the beamline BL07LSU in SPring‐8. A magnetic circuit composed of Nd–Fe–B permanent magnets, which realised ～0.25 T at the center of an 11 mm gap, was rotatable around the axis perpendicular to the X‐ray scattering plane. Using the system, a SX‐RIXS spectrum was obtained under the application of the magnetic field at an angle parallel, nearly 45° or perpendicular to the incident X‐rays. A dedicated sample stage was also designed to be as compact as possible, making it possible to perform SX‐RIXS measurements at arbitrary incident angles by rotating the sample stage in the gap between the magnetic poles. This system enables facile studies of magnetic dichroism in SX‐RIXS for various experimental geometries of the sample and the magnetic field. A brief demonstration of the application is presented.     

Calorimetric and dielectric studies of a phase transition in thallium dihydrogen phosphate: A nearly critical case

The heat capacity of thallium dihydrogen phosphate was measured from 12 to 300 K. A lambda anomaly with a small first order discontinuity was found at 229.76 K with the integrated enthalpy and entropy changes equal to 370 J mol^-1 and 1.8 J K^-1 mol^-1, respectively. The entropy discontinuity at the first order transition is 0.25 J K^-1 mol^-1. The Landau theory of phase transitions of the second kind reproduces closely the temperature dependence of the anomalous heat capacity. This, together with the small discontinuity in the entropy, implies that the phase transition is close to a classical critical point of higher order. The relative dielectric permittivity ?_r(b) along the b-axis at 1 kHz is anomalously large and strongly temperature dependent, while the ?_r(a¹) and ?_r(c) are not. A broad absorption centered at 1700 cm^-1 was observed in the infrared absorption spectrum, indicating presence of hydrogen bonding of the length ～ 0.25 nm. Occurrence of a phase transition at 127 ± 2 K was suggested by differential thermal analysis of thallium dideuterium phosphate.     

Disk Noise Measurement System for Optical Disks

We developed a system to measure disk noise as a function of both radial and angular position. In order to obtain an accurate disk noise measurement, crosstalk and intersymbol interference were avoided by recording regularly repeating pit patterns and the influence of electronic and laser noise was removed by averaging techniques. We found the system’s mapping ability and its high sensitivity to be very useful in investigating disk noise phenomena in the mastering process. We used the system to assess the accuracy and reproducibility of the photopolymerization replication and Al vapor deposition processes. Also, we investigated the choice of photoresist and found that photoresists with the combination of the narrowest molecular weight distribution and the highest photo-active compound content resulted in the lowest disk noise levels. Our system can, in principle, be adapted to evaluate magneto-optical and phase change disks.     

π–π Stacking Interaction in an Oxidized CuII–Salen Complex with a Side-Chain Indole Ring: An Approach to the Function of the Tryptophan in the Active Site of Galactose Oxidase

In order to gain new insights into the effect of the π–π stacking interaction of the indole ring with the Cu^II–phenoxyl radical as seen in the active form of galactose oxidase, we have prepared a Cu^II complex of a methoxy-substituted salen-type ligand, containing a pendent indole ring on the dinitrogen chelate backbone, and characterized its one-electron-oxidized forms. The X-ray crystal structures of the oxidized Cu^II complex exhibited the π–π stacking interaction of the indole ring mainly with one of the two phenolate moieties. The phenolate moiety in close contact with the indole moiety showed the characteristic phenoxyl radical structural features, indicating that the indole ring favors the π–π stacking interaction with the phenoxyl radical. The UV/Vis/NIR spectra of the oxidized Cu^II complex with the pendent indole ring was significantly different from those of the complex without the side-chain indole ring, and the absorption and CD spectra exhibited a solvent dependence, which is in line with the phenoxyl radical–indole stacking interaction in solution. The other physicochemical results and theoretical calculations strongly support that the indole ring, as an electron donor, stabilizes the phenoxyl radical by the π–π stacking interaction.     

Synthesis of nonplanar bipyridyls bridged by disilane and disiloxane and their phosphorescent copper complexes

Disilane- and disiloxane-bridged bipyridyls ( DSBPy and DSOBPy ) were prepared and their optical properties were investigated in comparison with those of previously reported monosilane- and monogermane-bridged counterparts. The UV–visible absorption and photoluminescence bands of DSBPy and DSOBPy were blue-shifted as a result of elongation of the bridging units from monosilane and monogermane to disilane and disiloxane, likely due to the enhanced twisting of the bipyridyl units. Phosphorescent complexes DSBPy–Cu and DSOBPy–Cu were prepared by the interaction of DSBPy and DSOBPy with Cu₂I₂(PPh₃)₂. X-ray diffraction studies of their single-crystal structures revealed polymeric structures composed of repeat units of DSBPy or DSOBPy and [Cu^II(PPh₃)]₂. Organic light-emitting diodes with the ITO/PEDOT:PSS/ DSBPy–Cu or DSOBPy–Cu :PCTSQ/TAZ/Al structure were fabricated to examine the applications of the complexes as electroluminescent materials. The devices emitted yellow light with emission maxima at approximately 600 nm, and maximal luminance reached 120 and 190 cd m⁻² for devices based on DSBPy–Cu and DSOBPy–Cu , respectively. The performance of the DSOBPy–Cu -based device was improved by using TAZ as the dopant of the emissive layer, and luminance was increased to 390 cd m⁻².     

Achievement of a 920-MHz high resolution NMR

We have developed a 920-MHz NMR system and performed the proton NMR measurement of H(2)O and ethylbenzene using the superconducting magnet operating at 21.6 T (920 MHz for proton), which is the highest field produced by a superconducting NMR magnet in the persistent mode. From the NMR measurements, it is verified that both homogeneity and stability of the magnet have a specification sufficient for a high resolution NMR.     

Signature of relations in mapping class groups and non-holomorphic Lefschetz fibrations

We introduce the notion of signature for relations in mapping class groups and show that the signature of a Lefschetz fibration over the 2-sphere is the sum of the signatures for basic relations contained in its monodromy. Combining explicit calculations of the signature cocycle with a technique of substituting positive relations, we give some new examples of non-holomorphic Lefschetz fibrations of genus and which violate slope bounds for non-hyperelliptic fibrations on algebraic surfaces of general type.

     

A combination of energy method and spectral analysis for study of equations of gas motion

There have been extensive studies on the large time behavior of solutions to systems on gas motions, such as the Navier-Stokes equations and the Boltzmann equation. Recently, an approach is introduced by combining the energy method and the spectral analysis to the study of the optimal rates of convergence to the asymptotic profiles. In this paper, we will first illustrate this method by using some simple model and then we will present some recent results on the Navier-Stokes equations and the Boltzmann equation. Precisely, we prove the stability of the non-trivial steady state for the Navier-Stokes equations with potential forces and also obtain the optimal rate of convergence of solutions toward the steady state. The same issue was also studied for the Boltzmann equation in the presence of the general time-space dependent forces. It is expected that this approach can also be applied to other dissipative systems in fluid dynamics and kinetic models such as the model system of radiating gas and the Vlasov-Poisson-Boltzmann system.      

Development of a small X-ray source using an ultraviolet laser and pyroelectric crystal

We investigate a miniaturized X-ray source using an ultraviolet (UV) laser and a pyroelectric crystal and discuss potential applications in medicine. The UV laser is the fourth harmonic of a Nd:YAG laser with a wavelength of 266 nm, repetition rate of 10 Hz, and pulse energy of 40 mJ. The pyroelectric crystal is a LiNbO₃ cylinder of diameter 10 mm and length 6 mm. The prototype X-ray source we fabricated is an aluminum parallelepiped of dimensions 3 × 3 × 5 cm. The X-ray count rate of the X-ray source is maximized at approximately 1,400 cps for UV laser irradiation of approximately 5 min. After 30 min of irradiation by the UV laser, the temperature of the pyroelectric crystal rose from 295 K to 312 K. The principles of X-ray generation ensure that X-ray sources using UV lasers and pyroelectric crystals offer ample opportunity for miniaturization. We believe the X-ray source developed in this work is suitable for medical applications, although further study is needed to address points such as increasing the X-ray count rate and adjusting the temperature of the pyroelectric crystal.