A convenient synthesis of long-chain 1-O-Alkyl glyceryl ethers

A convenient and economical procedure for synthesis of long-chain 1-O-alkyl glyceryl ethers (V) is described. Alkyl glycidyl ethers (II) which were derived from the reaction of alcohols (I) with epichlorohydrin using a phase transfer catalyst were first converted into the corresponding dioxolanes (III) or 1-O-alkyl-2,3-di-O-acetylglycerols (IV). Subsequent hydrolysis of the resultant products provided 1-O-alkyl glyceryl ethers (V) in high yields.     

Influence of the Compositional Profile of Functionally Graded Material on the Crack Path under Thermal Shock

Thermal cracking under a transient-temperature field in a ceramic/metal functionally graded plate is discussed. When the functionally graded plate is cooled from high-temperature, curved or straight crack paths often occur on the ceramic surface. It is shown that the crack paths are influenced by the compositional profile of the functionally graded plate. Transient-thermal stresses are treated as a linear quasi-static thermoelastic problem for a plane strain state. The crack paths are obtained using finite element method with Mode I and Mode II stress intensity factors.     

THERMO-ELASTO-PLASTIC STRESSES OF FUNCTIONALLY GRADED MATERIAL PLATE WITH A SUBSTRATE AND A COATING

Functionally graded material (FGM) has an excellent ability to reduce thermal stresses, especially in high-temperature applications such as the international thermo-nuclear experimental reactor (ITER). In the present study, the thermo-elasto-plastic behaviors of a particle-reinforced FGM plate (FGP) with substrate and coating layers are presented in the fabrication process. The thermo-elasto-plastic constitutive equation of a particle-reinforced composite taking temperature change and damage process into consideration is used to calculate the thermo-elasto-plastic stresses. The macroscopic stress components as well as the microscopic stress components are obtained using the temperature-dependent properties of the constituent materials. The FGP consists of the coating layer, the FGM layer, and the substrate layer. The FGM layer is divided into three regions. First, the region near the metal substrate is metal rich; and the metal is considered a matrix, while the ceramic is considered particles. Second, the region near the ceramic coating is ceramic rich, so the materials of the matrix and the particle are opposite those of the first region. Third, the middle region between the previous two regions is metal and ceramic that are perfectly mixed. In the third region the macroscopic analysis is made because the difference between the volume fractions of the ceramic and the metal is so small that it is difficult to consider one of them as a matrix or particles. The substrate and coating effects on the thermo-elasto-plastic stresses and optimal profile of the volume fraction of the ceramic are presented using the finite element method.     

THERMAL STRESSES IN FUNCTIONALLY GRADED MATERIALS

The thermal stress problems of functionally graded materials (FGMs), as one of the advanced high-temperature materials capable of withstanding the extreme temperature environments, are discussed. The FGMs consist of the continuously changing composi tion of two different materials. For example, one is an engineering ceramic to resist the severe thermal loading from the high-temperature environment, and the other is a light metal to maintain the structural rigidity. When the FGMs are subjected to extremely severe thermal loading, large thermal stresses are produced in the FGMs. Therefore, one of the most important problems of FGMs is how to decrease thermal stresses and how to increase heat resistance. The optimal composition profile problems of the FGMs in decreasing thermal stresses are discussed in detail. When FGMs are subjected to extremely severe thermal loading, the FGMs are damaged. The crack initiates on the ceramic surface and propagates in the FGMs. It is important to discuss the thermal stresses in the FGMs with various types of cracks. The thermal stress intensity factors in the FGMs with various types of crack are treated analytically and numerically. The optimal composition profile problems of the FGMs in decreasing thermal stress intensity factor are studied. Finally, the crack propagation paths due to thermal shock are discussed.     

Multiple degrees-of-freedom arm with passive joints for on-the-machine measurement system by calibrating with geometric solids

To fabricate three-dimensional profiles with high accuracy, on-the-machine measurement is useful. Methods for the on-the-machine measurement by calibration with geometric solids used for references have been developed. In this paper, an arm with passive joints for on-the-machine measurement is proposed. As a prototype, the arm has 4 degrees of freedom (DOF) including two passive joints. The probing system has 7 DOF, including the DOF of the machine tool, in total. Angles of the passive joints are changed by driving the numerically controlled (NC) table and the main spindle of the machine tool, where the arm is mounted. To calculate the optimal posture of the arm for the shape to be measured, a numerical method of the inverse kinematics is also proposed. The arm has enough positioning accuracy to calibrate its posture. Shapes can be automatically measured with the accuracy of micrometer order by the on-the-machine measurement method as well as a commercial three-dimensional (3-D) coordinate measuring machine and a profilometer.     

Thermal shock analysis for a functionally graded plate with a surface crack

Summary The fracture behavior of a functionally graded material (FGM) plate subjected to a thermal shock is studied. A surface crack is considered. The thermomechanical properties of the FGM plate are assumed to vary along the thickness direction. By using a perturbation method, the transient temperature field is solved. Then the transient thermal stresses and the corresponding thermal stress intensity factor (TSIF) are obtained. The transient thermal stresses and TSIF in an FGM ceramic/metal (ZrO₂/Ti-6Al-4V) plate are shown in figures. Dedicated to Professor Franz Ziegler on the occasion of his 70th birthday     

An analytical method for thermal stresses of a functionally graded material cylindrical shell under a thermal shock

In this paper, the thermal stresses of a thin functionally graded material (FGM) cylindrical shell subjected to a thermal shock are studied. An analytical method is developed. The studied problem for an FGM cylindrical shell is reduced to a plane problem. A perturbation method is used to solve the thermal diffusion equation for FGMs with general thermal properties. Then, the transient thermal stresses are obtained. The results show that the thermal shock is much easier to result in failure than the steady thermal loading. The present method can also be used to solve the crack problem of an FGM cylindrical shell with general thermal properties.     

Rho and Rab small G proteins coordinately reorganize stress fibers and focal adhesions in MDCK cells

The Rho subfamily of the Rho small G protein family (Rho) regulates formation of stress fibers and focal adhesions in many types of cultured cells. In moving cells, dynamic and coordinate disassembly and reassembly of stress fibers and focal adhesions are observed, but the precise mechanisms in the regulation of these processes are poorly understood. We previously showed that 12-O-tetradecanoylphorbol-13-acetate (TPA) first induced disassembly of stress fibers and focal adhesions followed by their reassembly in MDCK cells. The reassembled stress fibers showed radial-like morphology that was apparently different from the original. We analyzed here the mechanisms of these TPA-induced processes. Rho inactivation and activation were necessary for the TPA-induced disassembly and reassembly, respectively, of stress fibers and focal adhesions. Both inactivation and activation of the Rac subfamily of the Rho family (Rac) inhibited the TPA-induced reassembly of stress fibers and focal adhesions but not their TPA-induced disassembly. Moreover, microinjection or transient expression of Rab GDI, a regulator of all the Rab small G protein family members, inhibited the TPA-induced reassembly of stress fibers and focal adhesions but not their TPA-induced disassembly, indicating that, furthermore, activation of some Rab family members is necessary for their TPA-induced reassembly. Of the Rab family members, at least Rab5 activation was necessary for the TPA-induced reassembly of stress fibers and focal adhesions. The TPA-induced, small G protein-mediated reorganization of stress fibers and focal adhesions was closely related to the TPA-induced cell motility. These results indicate that the Rho and Rab family members coordinately regulate the TPA-induced reorganization of stress fibers and focal adhesions that may cause cell motility.