Highly Elastic and Deformable Hydrogel Formed from Tetra‐arm Polymers

After decades of efforts by many researchers, we have succeeded in realizing a near‐ideal polymer network. This network, the Tetra network, is made by cross‐end‐coupling of tetra‐arm polymer modules. The mechanical energy dissipation was extremely low (tan δ ≈ 10⁻⁴). The macroscopic stress–strain relationship of the Tetra network was in good agreement with that of microscopic elastic blobs. The maximum breaking strength was extremely high (≥27 MPa). These results indicate that the Tetra network is closer to an ideal polymer network than any other conventional model networks. Because the Tetra network can be treated as uniformly packed elastic blobs, it should help apply the knowledge of single polymer chains seamlessly to the design of polymer materials and help further develop the theory of rubber elasticity.

     

Influence of temperature and photon energy on quantum yield of photoemission from real iron surfaces

The influence of temperature and incident photon energy on the photoemission quantum yield, Y _s, of real iron surfaces has been investigated by thermally assisted photoemission (TAPE). Measurements were carried out using a Geiger counter under a gaseous atmosphere of He containing 1 % isobutane vapor at normal atmospheric pressure in the temperature range 25–353 °C under UV irradiation with wavelengths of 200, 210, 220, and 230 nm. The Y _s obtained under irradiation at a given wavelength was found to increase with temperature, particularly more rapidly with wavelengths of greater photon energy. From the Arrhenius plots, the Y _s values were found to have activation energies of 0.112–0.040 eV, depending on the photon energy. The chemical composition of the surfaces after TAPE measurements at different temperatures was examined by X-ray photoelectron spectroscopy (XPS). The intensity of species thermally removed from the surface was also measured by temperature desorption spectroscopy (TDS). XPS and TDS results showed the removal of the surface water and weakly bound carbon material from the surface with temperature. It was concluded that the removal of these species with increasing temperature enabled the incident light to penetrate through the surface into the metal, causing the increase in the Y _s. The dependence of the activation energies on the photon energy was explained by the change of UV light absorption spectra of the surface water, and the enhancement of the Y _s with temperature was also attributed to the influence of iron cations (Fe³⁺) corresponding to positive holes produced in the surface oxide layer by UV light.     

Narrowband solid state vuv coherent source for laser cooling of antihydrogen

We describe the design and performance of a solid-state pulsed source of narrowband (< 100 MHz) Lyman-α radiation designed for the purpose of laser cooling magnetically trapped antihydrogen. Our source utilizes an injection seeded Ti:Sapphire amplifier cavity to generate intense radiation at 729.4 nm, which is then sent through a frequency doubling stage and a frequency tripling stage to generate 121.56 nm light. Although the pulse energy at 121.56 nm is currently limited to 12 nJ with a repetition rate of 10 Hz, we expect to obtain greater than 0.1 μJ per pulse at 10 Hz by further optimizing the alignment of the pulse amplifier and the efficiency of the frequency tripling stage. Such a power will be sufficient for cooling a trapped antihydrogen atom from 500 mK to 20mK.     

Growth of epitaxial TmFeCuO4 thin films by pulsed laser deposition

Epitaxial thin films of TmFeCuO₄ with a two-dimensional triangular lattice structure were successfully grown on yttria-stabilized-zirconia substrates by pulsed laser deposition and ex situ annealing in air. The films as-deposited below 500 °C showed no TmFeCuO₄ phase and the subsequent annealing resulted in the decomposition of film components. On the other hand, as-grown films deposited at 800 °C showed an amorphous nature. Thermal annealing converted the amorphous films into highly (0 0 1)-oriented epitaxial films. The results of scanning electron microscopic analysis suggest that the crystal growth process during thermal annealing is dominated by the regrowth of non-uniformly shaped islands to the distinct uniform islands of hexagonal base.     

Disturbance-free laser diode Sagnac interferometer using direct phase modulation

We exploited the wavelength tunability of the laser diode of a phase-shifting Sagnac interferometer to realize disturbance-free measurements. The Sagnac interferometer is robust against mechanical disturbances because it has a common path configuration and requires no special references. An unbalanced optical path was introduced between p- and s-polarized beams to enable easy phase shifting by direct current modulation. The experimental results indicate that the proposed system is effective for performing precise disturbance-free measurements.     

Selective Hydroperoxygenation of Olefins Realized by a Coinage Multimetallic 1-Nanometer Catalyst

The science of particles on a sub-nanometer (ca. 1 nm) scale has attracted worldwide attention. However, it has remained unexplored because of the technical difficulty in the precise synthesis of sub-nanoparticles (SNPs). We recently developed the “atom-hybridization method (AHM)” for the precise synthesis of SNPs by using a suitably designed macromolecule as a template. We have now investigated the chemical reactivity of alloy SNPs obtained by the AHM. Focusing on the coinage metal elements, we systematically evaluated the oxidation reaction of an olefin catalyzed by these SNPs. The SNPs showed high catalytic performance even under milder conditions than those used with conventional catalysts. Additionally, the hybridization of multiple elements enhanced the turnover frequency and the selectivity for the formation of the hydroperoxide derivative. We discuss the unique quantum-sized catalysts providing generally unstable hydroperoxides from the viewpoint of the miniaturization and hybridization of materials.     

Optimum measurements for discrimination among symmetric quantum states and parameter estimation

An optimum quantum measurement that minimizes the average probability of error is considered for symmetric quantum states. The positive operator-valued measure (POM) which satisfies the necessary and sufficient condition for the minimization of the average probability of error is derived by using the quantum Bayes strategy. It is also shown that the mutual information obtained in the optimum quantum measurement becomes extremum. Furthermore, an optimum quantum measurement for parameter estimation is found for symmetric quantum states by applying the maximum-likelihood estimation. The optimum POM for the parameter estimation has the same structure as that for the quantum state discrimination.     

Enzymatic cyclizations of squalene analogs with threo- and erythro-diols at the 6,7- or 10,11-positions by recombinant squalene cyclase. Trapping of carbocation intermediates and mechanistic insights into the product and substrate specificities

In order to trap the carbocation intermediates formed during the squalene cyclization cascade, squalene analogs with threo- and erythro-diols at the 6,7- and 10,11-positions were incubated with the recombinant squalene cyclase from Alicyclobacillus acidocaldarius, leading to the construction of the triterpenes with tetrahydropyran, octahydrochromene, decahydronaphthalene with a carbonyl group, dodecahydrobenzo[f]chromene, tetradecahydronaphtho[2,1-b]oxepine and malabaricane skeletons, almost of which are novel compounds. These products indicate that 6-membered monocyclic, 6/6-fused bicyclic and 6/6/5-fused tricyclic cations were involved in the cyclization reaction in addition to acyclic cation. All the trapped cations were the stable tertiary cation, but not the secondary one, indicating that the polycyclization reaction proceeds with a Markovnikov closure. The product profiles revealed that the cyclization reactions proceeded with the product and substrate specificities in addition to enantioselectivity. Mechanistic insight into the observed stereochemical specificities indicated that the pre-organized chair-conformation of squalene-diols is tightly constricted by the cyclase and a free motion or a conformational change is not allowed in the reaction cavity, thus, the substrate and product specificities are dominantly directed by the least motion of the nucleophilic hydroxyl group toward the intermediary carbocation; a small rotation of the hydroxyl group afforded the cyclization products in a good yield, but a large rotation of the hydroxyl group gave a marginal or no detectable amount of products.     

Photoswitching properties of photonic band gap material containing azo-polymer liquid crystal

A photochemically tunable photonic crystal was prepared by infiltration of the polymer liquid crystal (LC) having azo-chromophores in a SiO₂ inverse opal structure. The SiO₂ inverse opal film infiltrated with the polymer LC reflected a light corresponding to the periodicity as well as the refractive indices of the inverse opal structure. Linearly polarized light irradiation caused the shift of the reflection band to longer wavelength more than 15 nm. This is caused by the formation of uniaxially anisotropic molecular orientation of the polymer LC. The switched state was stable under interior light, and reversible switching of the reflection band can be achieved by the linearly and circularly polarized light irradiation. This photoswitching property will be suitable not only for various optical materials, but also for introduction of defects in the photonic crystals.