Kinetic analysis of crystallization of zeolite beta synthesized by direct heating

To quantitatively investigate the initial crystallization of zeolite beta synthesized by direct heating, the extent of the reaction was precisely evaluated by X-ray diffraction measurements and Rietveld structural refinement, and a kinetic analysis of crystallization was performed using the Avrami-Erofe'ev equation. The activation energy for crystallization was lower than that for hydrothermal synthesis. Reaction and synthesis time curves revealed that the initial zeolite beta crystallization consisted of three stages. The first was an induction period with nucleation by the generation of building units and the formation of an initial coordinated structure. The second stage was crystal growth by a diffusion-controlled reaction, and the third stage involved slowing down of crystallization by the limitation of dehydrocondensation. These stages could be analyzed by calculation of the rate constant and Avrami exponent for each stage.     

Temperature-responsive culture surfaces for insect cell sheets to fabricate a bioactuator

ABSTRACT

For the first time, we have fabricated insect-derived cell sheets by using temperature-responsive culture surfaces having a phase-transition temperature below 25°C. We prepared the temperature-responsive cell culture surfaces (tissue culture polystyrene, TCPS) by grafting a copolymeric gel consisting of hydrophobic N-tert-butylacrylamide (tBAAm) and N-isopropylacrylamide (IPAAm) units. First, to characterize the hydrophilic and hydrophobic properties of the copolymeric gel-grafted surfaces, static water contact angles of each surface were measured at various temperatures. By increasing the amount of tBAAm in the grafted copolymeric gel, the transition temperature of the gel was shifted to lower temperatures. At 25°C, the grafted copolymeric gel was dehydrated, and the insect-derived cells (AeAl2 cells) adhered on all the copolymeric gel-grafted surfaces. At 20°C, AeAl2 cells cannot adhere on the P(IPAAm-1.62tBAAm)-TCPS surface (the initial molar ratio of IPAAm and tBAAm (tBAAm?=?1.62 mol%)) better than on other surfaces (TCPS and tBAAm?=?4.88, 8.17 mol%). These two findings implied that the lower critical solution temperature of the copolymeric gel-grafted-TCPS existed from 20°C to 25°C. The laminin-coated P(IPAAm-1.62tBAAm)-TCPS surface showed temperature-dependent cell attachment and detachment properties, while AeAl2 cells were not detached from the extracellular matrix uncoated P(IPAAm-1.62tBAAm)-TCPS surface. AeAl2 cells and insect muscle cells were harvested as the respective sheets.     

Quantitative evaluation of malignant gliomas damage induced by photoactivation of IR700 dye

The processes involved in malignant gliomas damage were quantitatively evaluated by microscopy. The near-infrared fluorescent dye IR700 that is conjugated to an anti-CD133 antibody (IR700-CD133) specifically targets malignant gliomas (U87MG) and stem cells (BT142) and is endocytosed into the cells. The gliomas are then photodamaged by the release of reactive oxygen species (ROS) and the heat induced by illumination of IR700 by a red laser, and the motility of the vesicles within these cells is altered as a result of cellular damage. To investigate these changes in motility, we developed a new method that measures fluctuations in the intensity of phase-contrast images obtained from small areas within cells. The intensity fluctuation in U87MG cells gradually decreased as cell damage progressed, whereas the fluctuation in BT142 cells increased. The endocytosed IR700 dye was co-localized in acidic organelles such as endosomes and lysosomes. The pH in U87MG cells, as monitored by a pH indicator, was decreased and then gradually increased by the illumination of IR700, while the pH in BT142 cells increased monotonically. In these experiments, the processes of cell damage were quantitatively evaluated according to the motility of vesicles and changes in pH.     

Effect of Cation Doping on the Superplastic Flow in Yttria-Stabilized Tetragonal Zirconia Polycrystals

The superplastic characteristics of various cation-doped yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) were examined. For 1 mol% cation doping the true stress of Y-TZP is very dependent on the ionic radii of the doped cations; for instance, smaller cation radii give rise to lower true stress when compared with the other compositions for the same grain size, strain rate, and testing temperature. The altered true stress level must be due to the change in diffusivity of the accommodation process for grain boundary sliding caused by the addition of cations in ZrO₂. The strain to failure of the doped zirconia is affected by both ionic radius and valence of the dopant cations.     

DESCRIPTION OF A THERMO-INELASTIC BODY WITH A MOVING SOLID/LIQUID INTERFACE AND SIMULATION OF THE WELDING PROCESS

Conservation laws of mass, momentum, and energy for the thermo-inelastic body in the region involving the moving interface between the solid and liquid are introduced to derive jump conditions of velocity, stress, and energy on the interface as the sequence of local form for the generalized Reynolds transport theorem. The jump condition of energy is revealed to be the generalized Stefan condition for moving interface problems. The finite element formulation is used to analyze the modes of flow, deformation, and stresses in a melting or solidifying process by employing a viscoplastic constitutive equation that describes the mechanical behavior of both the solid and liquid phases. The mathematical formalism is applied to simulate bead-on plate welding.     

Low-temperature thermionic emission from nitrogen-doped nanocrystalline diamond films on n-type Si grown by MPCVD

Temperature-dependent emission current–voltage measurements were carried out for nitrogen (N)-doped nanocrystalline diamond (NCD) films grown on n-type Si substrates by microwave plasma-assisted chemical vapor deposition (MP-CVD). Low threshold temperature (~ 260 °C) and low threshold electric field (~ 5 × 10^− 5 V/µm) were observed. Both the temperature dependence and the electric field dependence have shown that the obtained emission current was based on electron thermionic emission from N-doped NCD films. We have also studied the relation between nitrogen concentration and the saturation emission current. The saturation current obtained was as high as 1.4 mA at 5.6 × 10^− 3 V/µm at 670 °C when the nitrogen concentration was 2.4 × 10²⁰ cm^− 3. Low value of effective work function (1.99 eV) and relatively high value of Richardson constant (~ 70) were estimated by well fitting to Richardson–Dushman equation. The results of smaller φ and larger A′ suggest that N-doped NCD has great possibility of being a highly efficient thermionic emitter material.     

V–I characteristics of solid polymer electrolytic (SPE) dehumidifier

Measurements of the V–I characteristics of a solid polymer electrolytic (SPE) dehumidifier were done using a modified SPE dehumidifier with four electrodes which included two electrodes to carry the main current and the other two electrodes to measure the voltages applied to the electrical double layer, which are the boundary voltages between the electrodes and the SPE membrane. The measured results were analyzed using the Butler-Volmer equation to examine the validity of the measurements. The current flowing in the dehumidifier is produced by the decomposition of water near the anode. Therefore, under a steady-state condition, the current should be proportional to the supply rate of water to the anode. On the other hand, a two-layer model for the SPE dehumidifier presented in our previous article showed that the current flowing in the dehumidifier was roughly proportional to the water content in the vicinity of the anode. These results were introduced for interpretation of the V–I measurements of the SPE dehumidifier. It was concluded that the dehumidifier current was expressed in the form of a Butler-Volmer equation as a function of the electrode boundary voltages which were the voltages across the boundary between the electrodes and the SPE membrane. An experimental formula for the current under a steady-state condition was developed as a function of the water content near the anode and the boundary voltages.     

Microstructural Analysis of Liquid-Phase-Sintered β-Silicon Carbide

The microstructures of fine-grained β-SiC materials with α-SiC seeds annealed either with or without uniaxial pressure at 1900°C for 4 h in an argon atmosphere were investigated using analytical electron microscopy and high-resolution electron microscopy (HREM). An applied annealing pressure can greatly retard phase transformation and grain growth. The material annealed with pressure consisted of fine grains with β-SiC as a major phase. In contrast, the microstructure in the material annealed without pressure consisted of elongated grains with half α-SiC. Energy-dispersive X-ray analysis showed no differences in the amount of segregation of aluminum and oxygen atoms at grain boundaries, but did show a significant difference in the segregation of yttrium atoms at grain boundaries along SiC grains for the two materials. The increased segregation of yttrium ions at grain boundaries caused by the applied pressure might be the reason for the retarded phase transformation and grain growth. HREM showed a thin secondary phase of 1 nm at the grain boundary interface for both materials. The development of a composite grain consisting of a mixture of β/α polytypes during annealing was a feature common to both materials. The possible mechanisms for grain growth and phase transformation are discussed.