Effect of Alloying Elements on Nb-Rich Portion of Nb-Si-X Ternary Systems and In Situ Crack Observation of Nb-Si-Based Alloys

To find a new route for microstructure control and to find additive elements beneficial for improving high-temperature strength, a systematic investigation is performed on hypoeutectic Nb-15 at. pct Si-X ternary alloys containing a transition element, Fe, Co, Ni, Cu, Ru, Rh, Pd, Re, Os, Ir, Pt, or Au. Information on phase equilibrium is classified in terms of phase stability of silicide phases, α Nb₅Si₃, Nb₄SiX, and Nb₃Si, and the relationship between microstructure and mechanical properties both at room temperature and high temperature is investigated. All the additive elements are found to stabilize either α Nb₅Si₃ or Nb₄SiX but destabilize Nb₃Si. A microstructure of Nb_ss/α Nb₅Si₃ alloy composed of spheroidized α Nb₅Si₃ phase embedded in the Nb_ss matrix is effective for toughening, regardless of the initial as-cast microstructure. Also the plastic deformation of Nb_ss dendrites may effectively suppress the propagation of longer cracks. High-temperature strength of alloys is governed by the deformation of Nb_ss phase and increases with higher melting point additives.     

Functional Properties of the Catalytic Domain of Mouse Acidic Mammalian Chitinase Expressed in Escherichia coli

Mouse acidic mammalian chitinase (AMCase) plays important physiological roles in defense and nutrition. AMCase is composed of an N-terminal catalytic domain (CatD) and a C-terminal chitin-binding domain (CBD). We expressed CatD of mouse AMCase as a recombinant fusion protein with Protein A and V5-His in Escherichia coli (Protein A-CatD-V5-His), evaluated its functional properties and compared them to the full-length AMCase (Protein A-AMCase-V5-His). Under our experimental conditions, the chitinolytic activity of both proteins against 4-nitrophenyl N,N''-diacetyl-β-d-chitobioside was equivalent with regard to their specific enzymatic activities, optimal pH and temperature as well as to the pH and temperature stability. CatD bound to chitin beads and cleaved the N-acetylglucosamine hexamer, colloidal and crystalline chitin as well as the shrimp shell, and released primarily N,N''-diacetylchitobiose fragments at pH 2.0. These results indicate that the primary structure of CatD is sufficient to form a proper tertiary structure required for chitinolytic activity, recognize chitin substrates and degrade them in the absence of a CBD. Our recombinant proteins can be used for further studies evaluating pathophysiological roles of AMCase in different diseases.     

Homomorphic characterizations of recursively enumerable languages with very small language classes

In this paper, we attempt to characterize the class of recursively enumerable languages with much smaller language classes than that of linear languages. Language classes, and , of (i,j) linear languages and (i,j) minimal linear languages are defined by posing restrictions on the form of production rules and the number of nonterminals. Then the homomorphic characterizations of the class of recursively enumerable languages are obtained using these classes and a class, , of minimal linear languages. That is, for any recursively enumerable language L over Σ, an alphabet Δ, a homomorphism h : Δ^*→Σ^* and two languages L₁ and L₂ over Δ in some classes mentioned above can be found such that L = h(L₁∩L₂). The membership relations of L₁ and L₂ of the main results are as follows:(I) For posing restrictions on the forms of production rules, the following result is obtained:(1) and .This result is the best one and cannot be improved using . However, with posing more restriction on L₂, this result can be improved and the follwing statement is obtained.(2) and .(II) For posing restrictions on the numbers of nonterminals, the follwing result is obtained.(3) and .We believe this result is also the best.     

Rheological Study on Gelatin Gelation

Abstract

Changes in the rheological properties of a gelatin solution during gelation were studied. Samples with various concentrations (0.1-6.0 wt%) were cooled from 45°C to 10 °C at a constant cooling rate and then kept at 10 °c. When the sample was cooled to a certain temperature, the viscosity started to increase. A steep rise in rigidity was observed after the viseosity increase. The vatlie of tanδ of each sampIe first increased and then decreased and converged to a characteristic vallie. We can understand this behaviour well in the framrwork of percolation transition theory. Concentration dependence of the rheological behaviour in the gelation process suggests that the gel structure of < 1.5 wt% samples and that of > 1.5wt% samples are different. In the higher concentration region, almost all the crosslinking points take part in the gel network formation, and thus the gels all feature an essentially similar structure. In the lower concentration region, some of the crosslinking points become dangling bOnds and do not contribute to rigidity, resulting in a mechanically weak gel network. A 0.1 wt%-order sample, that never gells macroscopically, also showed a rise in rigidity whell cooled, suggesting formation of a gel network of infinite size even in this low concentration range.     

Mechanical Properties of Gelatin Film

Abstract

The mechanical properties of gelatin films were investigated. We prepared gelatin films under various conditions, such as changing temperature, storage time and humidity. The stress-strain curves were obtained by measuring the tensile-strength of sample films at various humidities. These results suggest that mechanical properties of gelatin films depend on the structure and water content of the sample. It was found that the structure of gelatin films was influenced by the drying process and the thermal history of the gelatin.     

Numerical verification of a simplified model for vapor bubble lift-off from a hydrophilic heated flat-wall

Three-dimensional interface tracking simulations were carried out to investigate the role of surface tension force in the process of vapor bubble lift-off from a hydrophilic heated surface in nucleate boiling. Since bubbles are frequently flattened along the heated surface in photographic experiments reported in literature, a bubble was assumed to be spheroidal in shape in the initial condition. The effect of phase change at the bubble interface was not taken into consideration for the sake of simplicity. In the present numerical simulations, the initially spheroidal bubble approached the spherical shape due to the surface tension force and was eventually lifted off the surface. The change in bubble shape induced local liquid flow directing toward the bubble base, that was the direct cause of the occurrence of the bubble lift-off. The dependence of the bubble migration velocity on several important parameters including the bubble size, surface tension coefficient and the density of surrounding liquid was also investigated. The change in bubble shape from flattened to more rounded causes the reduction of the surface energy, while the formation of local liquid flow leads to an increase in the kinetic energy. It was demonstrated that the bubble migration velocity after the lift-off can successfully be interpreted from the standpoint of energy conservation during the lift-off process.     

Freezing phenomena of supercooled water under impacts of ultrasonic waves

In order to clarify effects of ultrasonic waves on supercoold water, ultrasonic waves were applied to supercooled water. Frequency of the ultrasonic waves applied was 45 kHz, and the intensities of the waves were 0.13 and 0.28 W cm⁻², respectively. Four cases of experimental conditions were selected; a case of a free surface, a case of an oil-water surface, a case of a free surface with a dipped metal bar and a case of an oil–water surface with a dipped metal bar. For each experimental condition, water was cooled at a constant cooling rate and the ultrasonic wave was applied from underneath until the water in a test tube solidified. It was found that in the case of 0.28 W cm⁻², the ultrasonic wave had distinct effects on freezing of supercooled water for all experimental conditions. On the other hand, in the case of 0.13 W cm⁻², the ultrasonic wave had an effect on freezing of supercooled water only under existence of a free surface and a metal bar.