A Water‐Soluble Mechanochromic Luminescent Pyrene Derivative Exhibiting Recovery of the Initial Photoluminescence Color in a High‐Humidity Environment

Switching of the luminescence properties of molecular materials in response to mechanical stimulation is of fundamental interest and also has a range of potential applications. Herein, a water‐soluble mechanochromic luminescent pyrene derivative having two hydrophilic dendrons is reported. This pyrene derivative is the first example of a mechanochromic luminescent organic compound that responds to relative humidity. Mechanical stimulation (grinding) of this pyrene derivative in the solid state results in a change of the photoluminescence from yellow to green. Subsequent exposure to water vapor induces recovery of the initial yellow photoluminescence. The color change is reversible through at least ten cycles. It is also demonstrated that this compound can be applied as a mechano‐sensing material in frictional wear testing for grease, owing to its immiscibility in non‐polar solvents and its non‐crystalline behavior. Transmission electron microscope and atomic force microscope observations of samples prepared from dilute aqueous solutions of the pyrene derivative on suitable substrates, together with dynamic light scattering measurements for the compound in aqueous solution, indicate that this amphiphilic dumbbell‐shaped molecule forms micelles in water.     

A consistent grayscale‐free topology optimization method using the level‐set method and zero‐level boundary tracking mesh

This paper proposes a level‐set based topology optimization method incorporating a boundary tracking mesh generating method and nonlinear programming. Because the boundary tracking mesh is always conformed to the structural boundary, good approximation to the boundary is maintained during optimization; therefore, structural design problems are solved completely without grayscale material. Previously, we introduced the boundary tracking mesh generating method into level‐set based topology optimization and updated the design variables by solving the level‐set equation. In order to adapt our previous method to general structural optimization frameworks, the incorporation of the method with nonlinear programming is investigated in this paper. To successfully incorporate nonlinear programming, the optimization problem is regularized using a double‐well potential. Furthermore, the sensitivities with respect to the design variables are strictly derived to maintain consistency in mathematical programming. We expect the investigation to open up a new class of grayscale‐free topology optimization. The usefulness of the proposed method is demonstrated using several numerical examples targeting two‐dimensional compliant mechanism and metallic waveguide design problems. Copyright © 2014 John Wiley & Sons, Ltd.     

General topology optimization method with continuous and discrete orientation design using isoparametric projection

A general topology optimization method, which is capable of simultaneous design of density and orientation of anisotropic material, is proposed by introducing orientation design variables in addition to the density design variable. In this work, the Cartesian components of the orientation vector are utilized as the orientation design variables. The proposed method supports continuous orientation design, which is out of the scope of discrete material optimization approaches, as well as design using discrete angle sets. The advantage of this approach is that vector element representation is less likely to fail into local optima because it depends less on designs of former steps, especially compared with using the angle as a design variable (Continuous Fiber Angle Optimization) by providing a flexible path from one angle to another with relaxation of orientation design space. An additional advantage is that it is compatible with various projection or filtering methods such as sensitivity filters and density filters because it is free from unphysical bound or discontinuity such as the one at θ = 2π and θ = 0 seen with direct angle representation. One complication of Cartesian component representation is the point‐wise quadratic bound of the design variables; that is, each pair of element values has to reside in a given circular bound. To overcome this issue, we propose an isoparametric projection method, which transforms box bounds into circular bounds by a coordinate transformation with isoparametric shape functions without having the singular point that is seen at the origin with polar coordinate representation. A new topology optimization method is built by taking advantage of the aforementioned features and modern topology optimization techniques. Several numerical examples are provided to demonstrate its capability. Copyright © 2014 John Wiley & Sons, Ltd.     

Laser brazing of a dissimilar joint of austenitic stainless steel and pure copper

In many industries, there are applications that require the joining of stainless steel and copper components; therefore, the welding of dissimilar stainless steel/copper joints is a common process. For this investigation, the optimal brazing conditions and suitable filler metals for laser brazing of stainless steel/copper lap joints were studied. Tensile shear force increases with increases in the laser spot diameter or in the laser irradiation angle, which is associated with increased bonding width; however, as bonding width approaches 2 mm, tensile shear force reaches a saturated value due to fracturing at the HAZ of the Cu base plate. In order to obtain joints with high tensile shear strength, laser brazing was optimized by using Cu–Si-based filler metal under the following conditions: laser power, 4 kW; spot diameter, 3 mm; laser irradiation angle, 80°; irradiation position shift, 0.6 mm; brazing speed, 0.30 m/min; and filler metal feed speed, 0.30 min. Concerning filler metals, it was found that the Ni–Cu type showed relatively large tensile shear force even at high welding speeds in comparison with those of the Cu–Si, Cu, Cu–Ni, Ni–Cu and Ni types, respectively.     

Normal Spectral Emissivity Measurement of Molten Cu–Co Alloy Using an Electromagnetic Levitator Superimposed with a Static Magnetic Field

The normal spectral emissivity of molten Cu–Co alloy with different compositions was measured in the wavelength range of 780 nm to 920 nm and in the temperature range of 1430 K to 1770 K including the undercooled condition by an electromagnetic levitator superimposed with a static magnetic field. The emissivity was determined as the ratio of the radiance from a levitated molten Cu–Co droplet measured by a spectrometer to the radiance from a blackbody calculated by Planck’s law at a given temperature, where a static magnetic field of 2.5 T to 4.5 T was applied to the levitated droplet to suppress the surface oscillation and translational motion of the sample. We found little temperature dependence of the normal spectral emissivity of molten Cu–Co alloy. Concerning the composition dependence, the emissivity decreased markedly above 80 at%Cu and reached that of pure Cu, although its dependence was low between 20 at%Cu and 80 at%Cu. In addition, this composition dependence of the emissivity of molten Cu–Co alloy can be explained well by the Drude free-electron model.     

Lingual Epithelial Stem Cells and Organoid Culture of Them

As tongue cancer is one of the major malignant cancers in the world, understanding the mechanism of maintenance of lingual epithelial tissue, which is known to be the origin of tongue cancer, is unquestionably important. However, the actual stem cells that are responsible for the long-term maintenance of the lingual epithelium have not been identified. Moreover, a simple and convenient culture method for lingual epithelial stem cells has not yet been established. Recently, we have shown that Bmi1-positive cells, residing at the second or third layer of the epithelial cell layer at the base of the interpapillary pit (IPP), were slow-cycling and could supply keratinized epithelial cells for over one year, indicating that Bmi1-positive cells are long-term lingual epithelial stem cells. In addition, we have developed a novel lingual epithelium organoid culture system using a three-dimensional matrix and growth factors. Here, we discuss current progress in the identification of lingual stem cells and future applications of the lingual culture system for studying the regulatory mechanisms of the lingual epithelium and for regenerative medicine.     

Mercury oxidation by hydrochloric acid over TiO2 supported metal oxide catalysts in coal combustion flue gas

Mercury oxidation by hydrochloric acid over the metal oxides supported by anatase type TiO₂ catalysts, 1 wt.% MO_x/TiO₂ where M = V, Cr, Mn, Fe, Ni, Cu, and Mo, was investigated by the Hg⁰ oxidation and the NO reduction measurements both in the presence and absence of NH₃. The catalysts were characterized by BET surface area measurement and Raman spectroscopy. The metal oxides added to the catalyst were observed to disperse well on the TiO₂ surface. For all catalysts studied, the Hg⁰ oxidation by hydrochloric acid was confirmed to proceed. The activity of the catalysts was found to follow the trend MoO₃ ~ V₂O₅ > Cr₂O₃ > Mn₂O₃ > Fe₂O₃ > CuO > NiO. The Hg⁰ oxidation activity of all catalysts was depressed considerably by adding NH₃ to the reactant stream. This suggests that the metal oxide catalysts undergo the inhibition effect by NH₃. The activity trend of the Hg⁰ oxidation in the presence of NH₃ was different from that observed in its absence. A good correlation was found between the NO reduction and the Hg⁰ oxidation activities in the NH₃ present condition. The catalyst having high NO reduction activity such as V₂O₅/TiO₂ showed high Hg⁰ oxidation activity. The result obtained in this study suggests that the oxidation of Hg⁰ proceeds through the reaction mechanism, in which HCl competes for the active catalyst sites against NH₃. NH₃ adsorption may predominate over the adsorption of HCl in the presence of NH₃.     

Azimuthal wave number control of oscillatory thermocapillary convection in a liquid bridge

Thermocapillary convection in a half‐zone liquid bridge of high Prandtl number fluid is widely known to exhibit a three‐dimensional oscillatory flow after the onset of oscillation. The oscillatory flow presents ‘standing’ and ‘traveling’ flows depending upon the temperature difference between the top and bottom rods. In the oscillatory state, the flow shows a modal structure with an azimuthal wave number that depends on the aspect ratio of the liquid bridge and the intensity of the thermocapillarity expressed by the Marangoni number. The present study attempted to control the azimuthal wave number by heating the free surface locally with a prescribed frequency and intensity. The flow in the liquid bridge exhibited different modal structures depending on the heating conditions and a relationship between the frequency and the modal structure was obtained. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(7): 460–469, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20086     

A Performance Comparison of Continuous and Discontinuous Finite Element Shallow Water Models

We present a comparative study of two finite element shallow water equation (SWE) models: a generalized wave continuity equation based continuous Galerkin (CG) model—an approach used by several existing SWE models—and a recently developed discontinuous Galerkin (DG) model. While DG methods are known to possess a number of favorable properties, such as local mass conservation, one commonly cited disadvantage is the larger number of degrees of freedom associated with the methods, which naturally translates into a greater computational cost compared to CG methods. However, in a series of numerical tests, we demonstrate that the DG SWE model is generally more efficient than the CG model (i) in terms of achieving a specified error level for a given computational cost and (ii) on large-scale parallel machines because of the inherently local structure of the method. Both models are verified on a series of analytic test cases and validated on a field-scale application.