Pulse radiolysis of 4,4'-bipyridyl aqueous solutions at elevated temperatures: spectral changes and reaction kinetics up to 400 degrees C

The spectral changes as well as the reaction kinetics of the transient species of 4,4'-bipyridyl (4,4'-bpy) have been experimentally investigated by pulse radiolysis techniques up to 400 degrees C. The results show that the transient species such as OH adduct 4,4'-bpyOH*, monoprotonated electron adduct 4,4'-bpyH*, and doubly protonated electron adduct 4,4'-bpyH2+* have 15-20 nm blue shifts from room temperature to 400 degrees C. For a deaerated neutral solution of 4,4'-bpy in the presence of tert-butyl alcohol, ethanol, or NaCOOH, the doubly protonated electron adduct is the main transient species at room temperature. But at temperatures > 350 degrees C, a monoprotonated form, the N-hydro radical 4,4'-bpyH*, becomes predominant. Interestingly, at room temperature, CO2-* could not efficiently react with 4,4'-bpy, but the reaction was accelerated with increasing temperature; at 350 degrees C, this reaction completed within 2 mus. Using an alkaline solution (pH = 11.5) of 4,4'-bpy in the presence of tert-butyl alcohol, we studied the N-hydro radical 4,4'-bpyH* from room temperature to 400 degrees C at 25 MPa. An estimation of the temperature-dependent G(e(aq)-) at 25 MPa agrees with our previous result with methyl viologen as a scavenger.     

Antianoxic action and active constituents of evodiae fructus

In order to develop new drugs from natural products, constituents of natural medicines were examined for their effectiveness in the KCN-induced anoxia model in mice. Methanol extract from a Chinese medicine, evodia (fruits of Evodia rutaecarpa Benth. or E. officinalis Dode), had a significant effect in the KCN-induced anoxia model in mice and therefore the active constituents were further examined. The results indicated that the antianoxic action of evodia was found in the fraction containing evodiamine. Further analysis of the active constituent indicated that evodiamine and rutaecarpine, indole-alkaloids found in large amounts in the Chinese medicine evodia, were mainly responsible for the antianoxic action.     

Determination of nickel in standard rocks and glasses by photon activation analysis with 30-MeV bremsstrahlung

The determination of nickel in various silicate rocks and glasses by photon activation analysis with a linear electron accelerator is described. Simultaneous irradiation of the sample and comparative standards produces the ⁵⁸Ni(γ, n)⁵⁷Ni reaction, and a post-irradiation chemical separation is used in conjunction with Ge(Li) γ-spectrometry. Nickel abundances for ten standard silicate rocks and two elementally doped glasses are presented and compared with the data previously published. The method is quite simple and gives good reproducible results for nickel down to sub-p.p.m. levels.     

Computation of transition to turbulence in the compression stage of a reciprocating engine

The transition to turbulent flow in the compression stage of a reciprocating engine is studied by obtaining the finite-difference numerical solutions to the governing Navier-Stokes equations without using explicit turbulence models. A computational method is developed under the assumption that the flow is in a low-subsonic regime with strong compression. The numerical method is a simple extension of the well known MAC method. Computations were performed for three different chamber geometries at the engine speed of 1400 rpm. The results of the computations clearly demonstrate the transient process in which large tumbling vortices break down into smaller ones near the end of the compression process. The transition process is also caught experimentally by using Mach-Zehnder interferometry.     

Antianoxic action and active constituents of atractylodis lanceae rhizoma

The screening test was carried out to identify new drugs from natural products for the KCN-induced anoxia model in mice. Acetone extract of Atractylodis Lanceae Rhizoma (Atractylodes lancea DC. var. Chinensis Kitamura) had a significant effect in the KCN-induced anoxia model and therefore the extract was selected for further study in order to identify the active principles. The result showed that beta-eudesmol was the active component in Atractylodis Lanceae Rhizoma.     

Time-resolved fluorescence study on the photomerocyanine form of spiropyran and its derivative with azobenzene

The excited state dynamics of the photomerocyanine (PMC) form originating from spirobenzopyran and the bi-functional photochromic compound spirobenzopyran–azobenzene (SpAz), containing typical photochromic molecules of spirobenzopyran (Sp) and azobenzene (Az), were investigated using picosecond time-resolved fluorescence measurements in solution at 200 and 285 K and in a PMMA polymer film at 298 K. While the fluorescence lifetimes of PMC were about twice as long as those of SpAz under all experimental conditions, both lifetimes showed similar strong dependence on viscosity rather than temperature. These results suggest that non-radiative decay to an intermediate state could be accompanied by a significant conformational change. The effect of the Az moiety in this relaxation process is also discussed. It is unlikely that an energy transfer from the PMC moiety to the Az moiety occurs. It was concluded that the PMC moiety in the bi-functional SpAz is independent from the Az moiety.     

Surface segregation of poly(2-methoxyethyl acrylate) in a mixture with poly(methyl methacrylate)

Poly(2-methoxyethyl acrylate) (PMEA) exhibits excellent blood compatibility. To understand why such a surface functionality exists, the surface of PMEA should be characterized in detail, structurally and dynamically, under not only ambient conditions, but also in water. However, a thin film of PMEA supported on a solid substrate can be easily broken, namely it is dewetted. Our strategy to overcome this difficulty is to mix PMEA with poly(methyl methacrylate) (PMMA). Differential scanning calorimetry and cloud point measurements revealed that the PMEA/PMMA blend has a phase diagram with a lower critical solution temperature. The blend surface was also characterized by X-ray photoelectron spectroscopy in conjunction with microscopic observations. Although PMEA is preferentially segregated over PMMA at the blend surface due to its lower surface free energy, the extent of segregation in the as-prepared films was not sufficient to cover the surface. Annealing the blend film at an appropriate temperature, higher than the glass transition temperature and lower than the phase-separation temperature of the blend, enabled us to prepare a stable and flat surface that was perfectly covered with PMEA.     

Photoreactive fluorinated polyimide protected by a tetrahydropyranyl group (THP) based on photo-induced acidolysis

A polyimide (6F-THP) with a tetrahydropyranyl group (THP) in its side chain has been synthesized. The THP group exhibits a high acidolysis rate in this polymer's film. This rate was faster than that of a tertbutoxycarbonyl group (t-BOC), which has been previously reported [1]. Furthermore, the deprotected fluorinated polyimide (6FDA-AHHFP) became soluble in an aqueous base due to the presence of a hydroxyl group attached to the phenyl group of the diamine segment. The polyimide thus provides high performance as a photopolymer when used in conjunction with a photoacid generator after the post-exposure baking process (PEB). The photoacid generators used in this study were p-nitrobenzyl-9,10-dimethoxyanthoracene-2-sulfonate (NBAS) and diphenyliodonium-9,10-dimethoxyanthoracene-2-sulfonate (DIAS). The quantum yields of photodissociation and photoacid generation were also measured. The photoacid-generating quantum yields closely corresponded to the photosensitivities of the photoreactive polyimide system. It was confirmed that the THP group was easily deprotected even in the 6F-THP film with p-toluenesulfonic acid as a model acid catalyst. The activation energy of the THP deprotection reaction was determined to be 12.8 kcal/mol (19.5 kcal/mol in the case of t-BOC). The relationships between the THP deprotecting rate constant (k_d) and acid molecular size and between k_d and polyimide structure were further investigated.     

Influence of the vacuum level upon the growth of carbon nanotubes on silicon carbide surface

We have investigated the influence of the vacuum level upon the growth of carbon nanotubes (CNTs) on 6H-SiC () surface.CNTs of about 160 nm in length were formed densely and uniformly on the 6H-SiC surface during annealing at 1700 °C in a high vacuum (∼10⁻² Pa). CNTs of about 1 μm in length were formed during annealing at 1700 °C in an ultra-high vacuum (∼10⁻⁷ Pa). However, CNTs were not formed and SiO₂ layers were formed on the SiC surface at 1700 °C in air. It is found that longer CNTs can grow up in an ultra-high vacuum, moreover, a little aligned and low-density graphite layers, or carbon nanofibers can also grow up.