Covalent assembly of metal nanoparticles on cellulose fabric and its antimicrobial activity

We develop an antimicrobial active robust metal-cellulose nanohybrid by covalent assembly of metal nanoparticles on cellulose fabric using a simple impregnation of thiol-modified cellulose fabric in colloidal silver (Ag) or palladium (Pd) nanoparticle solutions. The combined results of high resolution transmission electron microscopy (HR-TEM), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDXS) and inductively coupled plasma atomic emission spectrometry (ICP-AES) reveal that the nanoparticles are highly loaded and dispersed in the thiol-modified cellulose fabric, and X-ray photoelectron spectroscopy (XPS) analysis reveals that the nanoparticles are immobilized in the fabric by a strong and stable covalent bond with thiol functional group. This robust covalent linkage between the nanoparticles and the fabric leads to a remarkable suppression of the release of metal nanoparticles from the fabric. In addition, the metal-cellulose nanohybrids show high antimicrobial activity in excess of 99.9 % growth inhibition of the microorganism. Thus, we anticipate that our metal-cellulose nanohybrid may not only protect cell damage caused by penetration and fixation of metal nanoparticles into the human body but also act as a sustainable biomedical textile.     

Gravitational fermion production in inflationary cosmology

We revisit the gravitational production of massive Dirac fermions in inflationary cosmology with a focus on clarifying the analytic computation of the particle number density in both the large and the small mass regimes. For the case in which the masses of the gravitationally produced fermions are small compared to the Hubble expansion rate at the end of inflation, we obtain a universal result for the number density that is nearly independent of the details of the inflationary model. The result is identical to the case of conformally coupled scalars up to an overall multiplicative factor of order unity for reasons other than just counting the fermionic degrees of freedom.     

Synthesis and application of palladium stearates as precursors for the preparation of palladium nanoparticles

This report successfully demonstrates the synthesis and application of palladium stearates. It was found that the branching of the carboxylate anion of metal precursors could influence the size and shape of palladium nanoparticles (PdNPs). Worm‐like nanowires were formed when using the branched isomer palladium isostearate (PdISt₂), while triangular nanoparticles were produced in a majority when using the normal form: palladium stearate (PdSt₂). Furthermore, when applying CO₂ to the system, both types of PdNPs transformed into more spherical shapes with smaller sizes. The formation of carbamates from the amine stabilizer with CO₂ could prevent the further growth and aggregation of PdNPs. The PdNPs were tested as catalysts for the hydrogenation of styrene, and higher catalytic activities were achieved with PdNPs that were prepared with the assistance of CO₂. Copyright © 2012 John Wiley & Sons, Ltd.     

Influence of the height-to-diameter ratio on turbulent mixed convection in vertical cylinders

Turbulent mixed-convection mass transfer in vertical cylinders was measured using a sulfuric acid–copper sulfate electroplating technique. The Grashof numbers ranged from 5.3?×?10⁹ to 6.9?×?10¹⁰, the Reynolds numbers ranged from 4,000 to 14,000, and the Schmidt numbers were approximately 2,000. The test results under buoyancy-aided and buoyancy-opposed flow conditions successfully reproduced typical turbulent mixed-convection heat-transfer behavior and agreed well with existing studies performed by Ko et al. and Parlatan et al. Previous studies have used the cylinder diameter as the characteristic length for the buoyancy coefficient; however, this study focused on the influence of the cylinder height on the mixed-convection mass-transfer rates because the height determines the buoyancy. The tests performed for various heights with a fixed diameter or for various diameters with a fixed height demonstrated the influence of the height-to-diameter ratio on the mass-transfer rate, revealing that the height of the cylinder should be considered as a length scale. A new empirical correlation was derived for turbulent mixed-convection mass transfer that includes the influence of the height-to-diameter ratios.     

Heteroclinic connections in the 1:4 resonance problem using nonlinear transformation method

In this paper, the method of nonlinear time transformation is applied to obtain analytical approximation of heteroclinic connections in the problem of stability loss of self-oscillations near 1:4 resonance. As example, we consider the case of parametric and self-excited oscillator near the 1:4 subharmonic resonance. The method uses the unperturbed heteroclinic connection in the slow flow to determine conditions under which the perturbed heteroclinic connection persists. The results show that for small values of damping, the nonlinear time transformation method can predict well both the square and clover heteroclinic connection near the 1:4 resonance. The analytical finding is confirmed by comparisons to the results obtained by numerical simulations.     

Analytical derivation of earing in circular cup drawing based on simple tension properties

In the circular cylindrical cup drawing process of sheet materials, an earing profile develops, incurred by the planar anisotropic properties of sheets. Therefore, proper analysis of earing in cup drawing is important to evaluate anisotropic properties and also to control the development of earing. Even though anisotropic properties are commonly measured in the simple tension test, deformation in circular cylindrical cup drawing is in a near plane strain mode (at the flange) so that numerical simulations utilizing yield functions are common practices to analyze earing. In this work, simplified analytical derivation of earing development in circular cylindrical cup drawing is proposed, based on two simple tension anisotropic properties: the yield stress and the r-value. Good performance of the analytical derivation was verified for AA2090-T3, which has strong anisotropy and six ears in cup drawing. Since the current approach directly utilizes measured simple tension data without involving any yield functions, computational cost is significantly lower. Besides, the current derivation can handle any set of detailed anisotropic measurements in the simple tension test, unlike numerical approaches involving yield functions, which need the development of sophisticated yield functions in the first place.     

Visualization of natural convection heat transfer on horizontal cylinders

Natural convection heat transfer phenomena on horizontal cylinders were investigated experimentally in order to explore the applicability of analogy experimental method using the copper electroplating system and to visualize the local heat transfer depending on the angular position and the diameter of the horizontal cylinder. The diameters of the cylinders are varied from 0.01 to 0.15 m, which correspond to the Rayleigh numbers of 1.73 × 10⁷–5.69 × 10¹¹. The measured mass transfer coefficients show good agreements with the existing heat transfer correlations. The patterns of copper plated on the aluminum cathodes for various Rayleigh numbers reveal and visualize the local heat transfer depending on the angular position and show good agreement with the works of Kitamura et al. The hydrogen bubbles produced at higher applied potential visualize the plumes appeared on top region of the cylinders.     

Some basic problems in anisotropic bimaterials with a viscoelastic interface

This research is devoted to the study of anisotropic bimaterials with Kelvin-type viscoelastic interface under antiplane deformations. First we derive the Green’s function for a bimaterial with a Kelvin-type viscoelastic interface subjected to an antiplane force and a screw dislocation by means of the complex variable method. Explicit expressions are derived for the time-dependent stress field induced by the antiplane force and screw dislocation. Also presented is the time-dependent image force acting on the screw dislocation due to its interaction with the Kelvin-type viscoelastic interface. Second we investigate a rectangular inclusion with uniform antiplane eigenstrains embedded in one of the two bonded anisotropic half-planes by virtue of the derived Green’s function for a line force. The explicit expressions for the time-dependent stress field induced by the rectangular inclusion are obtained in terms of the simple logarithmic and exponential integral functions. It is observed that in general the stresses exhibit the logarithmic singularity at the four corners of the rectangular inclusion. Our results also show that when one side of the rectangular inclusion lies on the viscoelastic interface, the interfacial tractions are still regular at the two corners of the inclusion which are located on the interface. Last we address a finite Griffith crack normal to the viscoelastic interface by means of the obtained Green’s function for a screw dislocation. The crack problem is formulated in terms of a resulting singular integral equation which is solved numerically. The time-dependent stress intensity factors at the two crack tips are obtained and some interesting features are discussed.