A graph-theoretic approach to a partial order of knots and links

We say that a link L₁ is an s-major of a link L₂ if any diagram of L₁ can be transformed into a diagram of L₂ by changing some crossings and smoothing some crossings. This relation is a partial ordering on the set of all prime alternating links. We determine this partial order for all prime alternating knots and links with the crossing number less than or equal to six. The proofs are given by graph-theoretic methods.     

Front shock behavior of stable curved detonation waves in rectangular-cross-section curved channels

The propagation of curved detonation waves of gaseous explosives stabilized in rectangular-cross-section curved channels is investigated. Three types of stoichiometric test gases, C₂H₄ + 3O₂, 2H₂ + O₂, and 2C₂H₂ + 5O₂ + 7Ar, are evaluated. The ratio of the inner radius of the curved channel (r_i) to the normal detonation cell width (λ) is an important factor in stabilizing curved detonation waves. The lower boundary of stabilization is around r_i/λ = 23, regardless of the test gas. The stabilized curved detonation waves eventually attain a specific curved shape as they propagate through the curved channels. The specific curved shapes of stabilized curved detonation waves are approximately formulated, and the normal detonation velocity (D_n)?curvature (κ) relations are evaluated. The D_n nondimensionalized by the Chapman–Jouguet (CJ) detonation velocity (D_CJ) is a function of the κ nondimensionalized by λ. The D_n/D_CJ?λκ relation does not depend on the type of test gas. The propagation behavior of the stabilized curved detonation waves is controlled by the D_n/D_CJ?λκ relation. Due to this propagation characteristic, the fully-developed, stabilized curved detonation waves propagate through the curved channels while maintaining a specific curved shape with a constant angular velocity. Self-similarity is seen in the front shock shapes of the stabilized curved detonation waves with the same r_i/λ, regardless of the curved channel and test gas.     

Dibenzoarsepins: Planarization of 8π‐Electron System in the Lowest Singlet Excited State

Dibenzo[b,f]arsepins possessing severely distorted cores compared to those of other heteropins were synthesized. These derivatives exhibited dual photoluminescence in the green‐to‐red region (500–700 nm) and the near‐ultraviolet region (<380 nm), which could be attributed to the planarization of the arsepin core in the lowest singlet excited (S₁) state. The computational approach for the assessment of the aromatic indices revealed that the dibenzoarsepins studied show aromaticity (8π system) in the S₁ states in line with Baird's rule. The lone pair electrons of the arsenic atoms play a crucial role in the aromaticity in the S₁ states.     

Finding Degradation Trigger Sites of Structural Materials for Airplanes Using X‐Ray Microscopy

Macroscopic properties of carbon fiber‐reinforced plastic (CFRP) and environmental barrier coating (EBC), widely used for airplanes, can be deteriorated by local cracks or degradation (“trigger sites”). We have tried to find these trigger sites using x‐ray microscopy (XM), which can provide the 2D or 3D images of the chemical states and microstructures. Crack initiation in CFRP was observed in a non‐destructive manner in multi‐scales (nm‐mm). 3D chemical‐state mapping of Yb in EBC was achieved with high resolution (<50 nm). In addition to XM, in‐situ observations at high temperatures were conducted for obtaining complementary information. X‐ray absorption spectroscopy (XAS) and x‐ray diffraction (XRD) analysis were performed simultaneously up to 1773 K. Dynamic XAS with short time‐resolution (<10 ns) was conducted to investigate changes in the local structure of metal. These approaches can help us identify degradation trigger sites in the materials.     

Thermal conductivity evidence for a dx2-y2 pairing symmetry in the heavy-fermion CeIrIn5 superconductor

The phase diagram of the quasi-2D Ce(Ir,Rh)In5 system contains two distinct superconducting domes. By the thermal transport measurements in rotating magnetic fields H, we pinned down the superconducting gap structure of CeIrIn5 in the second dome, located distant from the first dome in proximity to an antiferromagnetic quantum critical point. Clear fourfold oscillation was observed when H is rotated within the ab plane, while no oscillation was observed within the bc plane. In sharp contrast to previous reports, our results are most consistent with dx2-y2 symmetry, implying that the superconductivity in the second phase is also mediated by antiferromagnetic spin fluctuations.     

Temperature-dependent energy gap of the primary charge separation in photosystem I: study of delayed fluorescence at 77-268 K

The dynamics of fluorescence decay and charge recombination were studied in the ether-extracted photosystem I reaction center isolated from spinach with picosecond resolution over a wide time range up to 100 ns. At all temperatures from 268 to 77 K, a slow fluorescence decay component with a 30-40 ns lifetime was detected. This component was interpreted as a delayed fluorescence emitted from the singlet excited state of the primary donor P700*, which is repopulated through charge recombination that was increased by the lack of secondary acceptor phylloquinone in the sample. Analysis of the fluorescence kinetics allowed estimation of the standard free-energy difference -DeltaG between P700* and the primary radical pair (P700(+)A0(-)) state over a wide temperature range. The values of -DeltaG were estimated to be 160/36 meV at 268/77 K, indicating its high sensitivity to temperature. A temperature-dependent -DeltaG value was also estimated in the delayed fluorescence of the isolated photosystem I in which the secondary acceptor quinone was partially prereduced by preillumination in the presence of dithionite. The results revealed that the temperature-dependent -DeltaG is a universal phenomenon common with the purple bacterial reaction centers, photosystem II and photosystem I reaction centers.     

Construction of a pH-responsive artificial membrane fusion system by using designed coiled-coil polypeptides

In many viruses, pH-responsive coiled-coil domains in the specific fusion proteins play important roles in membrane fusion and the infection of viruses into host cells. To investigate the relationship between the conformational change of the coiled coil and the fusion process, we have introduced a de novo designed polypeptide as a model system of the coiled-coil domain. This system enables the systematic study of the dynamics of pH-responsive coiled-coil polypeptide-membrane interactions. First, we designed and synthesized pH-responsive isoleucine-zipper triple-stranded coiled-coil polypeptides. Then the relationship between the pH-induced conformational change of the polypeptide and the membrane's interactive properties was studied by physicochemical methods. Structural changes in the designed polypeptides were examined by means of circular dichroism measurements. And finally, the behavior of the membrane fusion was investigated by leakage of liposomal contents, turbidity analysis, dynamic light scattering, and lipid mixing experiments. Our data show that coiled-coil formation under acidic pH conditions enhances polypeptide-induced membrane fusion. The results in this study demonstrate that an artificial membrane fusion system can be constructed on a molecular level by the use of a pH-responsive isoleucine-zipper triple-stranded coiled-coil polypeptide.     

Preparation and mechanical properties of bacterial cellulose nanocomposites loaded with silica nanoparticles

Bacterial cellulose (BC), which is produced by Gluconacetobacter xylinus (Ga. xylinus) in culture, is made up of a three-dimensional network of ribbon-shaped bundles of cellulose microfibrils. In the current studies, we used two processes to prepare nanocomposites of BC filled with silica particles. In Process I, Ga. xylinus was incubated in medium containing silica sol Snowtex 0 (ST 0, pH 2–4) or Snowtex 20 (ST 20, pH 9.5–10.0). The elastic modulus at 20 °C was improved by keeping the amount of silica in the nanocomposites below 4% when ST 20 was used and below 8.7% when ST 0 was used. This process allowed incorporation of 50% silica in BC. Inclusion of higher amounts of silica reduced the modulus at 20 °C and the strength of the nanocomposites below that of BC. X-ray diffraction measurements revealed that the silica particles disturb the formation of ribbon-shaped fibrils and affect the preferential orientation of the ( ) plane. We also produced BC-silica nanocomposites by Process II, wherein the BC hydrogel was immersed in different concentrations of silica sols, allowing silica particles to diffuse into the BC hydrogel and lodge in the spaces between the ribbon-shaped fibrils. This method increased the modulus at 20°C and the strength compared to the BC matrix, but it was difficult to load the BC with more than 10% silica in this way.