Cation-promoted supramolecular assembly of bivalent metal tetra-15-crown-5-phthalocyaninates: Controlling the architecture of supramolecular aggregates

Cation-promoted supramolecular assembly of cobalt(II) and ruthenium(II) tetra-15-crown-5-phthalocyaninates is comparatively studied using the electronic absorption and infrared spectroscopy. The effects of the nature of the receptor and substrate on the architecture of the supramolecular aggregates formed are discovered. By contrast to Cu(II), Zn(II), and Ni(II) tetra-15-crown-5-phthalocyaninates, Co(II) and Ru(II) complexes are found to demonstrate sodium-potassium selectivity determined by the peculiarities of supramolecular structures formed upon the interaction with the cations.     

Modeling of microstructure effects on the mechanical behavior of ultrafine-grained nickels processed by hot isostatic pressing

Bulk ultrafine-grained nickel specimens having grain sizes in the range of 0.25-5 μm were consolidated by hot isostatic pressing technique. The resulting microstructures were characterized by transmission electron microscopy and X-ray diffraction analysis. Compression tests were carried out at room temperature and at strain rate of 1.6×10⁻⁴ s⁻¹. It was found that the measured yield strength does not follow the Hall-Petch law as a consequence of the presence of oxide phase. Therefore, the use of micromechanics based model, which takes into account only the Hall-Petch relationship at grain level for predicting the grain sized effects on mechanical behavior of this kind of materials, is not accurate yet. In this study, a modification made to the generalized self-consistent model was proposed for studying both grain size and oxide phase dependence of ultrafine-grained materials behavior. Because of the novel modification, an optimization procedure with two steps was required to identify the parameters of micromechanical model. An acceptable agreement between experimental and numerical results was achieved. Moreover, the influence of texture on the yield strength and the application of the proposed model to the spark plasma sintering processed materials were also discussed.     

Amphiphilic and photocatalytic behaviors of TiO2 nanotube arrays on Ti prepared via electrochemical oxidation

Amphiphilic TiO₂ nanotube arrays (TiO₂ NTs) were fabricated through electrochemical oxidation of Ti in solution containing H₃PO₄ and NaF. Scanning electron microscopic analysis shows that the as-prepared TiO₂ NTs have an average pore diameter of 100 nm and a wall thickness of 15 nm. The electrochemical oxidation of Ti can be divided into four stages. In the first stage, when the potential is very low, oxygen formation and Ti dissolution are the major reactions. The second stage corresponds to a slightly higher potential, but less than 2.5 V. In this stage, the formation of TiO₂ film occurs. When the potential is increased to the even higher range from 2.5 V to 6 V, the TiO₂ film dissolves and nanoporous surface structure is generated. This is the third stage. Further increase of the potential enters stage four. The high potentials cause the self-organization of the nanostructure and allow the formation of well-aligned TiO₂ NTs. We also found that the change in surface condition of Ti by annealing heat treatment affects the film dissolution kinetics. As compared with TiO₂ thin film, the TiO2 NTs show higher photocatalytic activity on decomposing Rhodamine B. The surface of the TiO₂ NTs can be wetted by both water and oil. Such an amphiphilic property comes from the capillary effect of the nanochannel structure of the TiO₂ NTs. Because of the amphiphilic property and the photocatalytic activity, we conclude that the TiO₂ NTs have the capability of self-cleaning.     

Dynamic behavior of a Zr-based metallic glass at cryogenic temperature

The dynamic behavior of a Zr-based bulk metallic glass at cryogenic temperature is investigated by a miniaturized split Hopkinson pressure bar apparatus. As that at room temperature, the failure stress decreases suddenly and then tends to hold steady along with increasing strain rate at cryogenic temperature, but the strain rate regime corresponding to the sudden decrease of the failure stress moves up. The failure stress also increases along with decreasing temperature, whereas there is no obvious change for the plasticity.     

Increasing the accuracy of level-based volume detection of medical liquids in test tubes by including the optical effect of the meniscus

A novel system for liquid volume detection is reported in this paper. The system uses two lasers with different wavelengths to scan the entire height of tubes. By detecting the shape and position of the meniscus that is formed at the liquid-air interface, the volume of liquid in a tube of known geometry can be determined. To increase the accuracy of this level-based volume detection, the shape of the meniscus must be considered. The optical effect of the meniscus in such a system was modeled and its effect on the volume detection simulated. A laboratory prototype was built and the biggest difference between the measured power of the transmitted light through the meniscus and the simulated data was less than 8%.     

Strategic justification of advanced manufacturing technology using an extended AHP model

Layered manufacturing has emerged as a highly versatile process to produce complex parts compared with conventional manufacturing processes, which are either too costly to implement or just downright not possible. However, this relatively new manufacturing process is characterized by a few outstanding issues that have kept the process from being widely applied. One such issue is the reduced part accuracy caused by the primitive method of generating the layer contours. Current practice generates the layer contours by simply intersecting a set of parallel planes through the computer model of the design part. The volumetric geometry of each layer is then constructed by extruding the layer contour by the layer thickness in the part building direction. This practice often leads to distorted part geometry due to the unidirectional bias of the extruded layers. This paper proposes a novel scheme to correct the systematic part distortion of layered manufactured parts resulting from the improperly generated layer contours. A new layer contour generation method utilizing the sectional projected data of a point cloud representation of the part surface is introduced. The systematic part distortion is reduced by extruding the outer boundary of the projected point data into the layer volumetric geometry. The boundary contour construction algorithm is able to adapt to changing density of the point set in order to keep the captured level of detail consistent. Specifically devised case studies were carried out to validate the proposed method.     

Measuring spatial dispersion: exact results on the variance of random spatial distributions

Measuring the spatial distribution of locations of many entities (trees, atoms, economic activities, etc.), and, more precisely, the deviations from purely random configurations, is a powerful method to unravel their underlying interactions. Several coefficients have been developed in the past to quantify the possible deviations. It is important to quantify the variances of the coefficients for random distributions, to ascertain the statistical significance of an empirical deviation. By lack of a proper analytical expression, the significance is usually obtained by simulating many random configurations by Monte Carlo simulations. In the present paper, we present an exact analytical expression for the variance of several spatial coefficients for random distributions, and we rigorously show that these distributions asymptotically follow a Normal law. These two results eliminate the need for cumbersome Monte Carlo simulations. They also allow to understand qualitatively the main factors that may change the variance: number of sites, spatial inhomogeneity, etc.     

W-based versus latent variables spatial autoregressive models: evidence from Monte Carlo simulations

In this paper, we compare by means of Monte Carlo simulations two approaches to take spatial autocorrelation into account: the classical spatial autoregressive model and the structural equations model with latent variables. The former accounts for spatial dependence and spillover effects in georeferenced data by means of a spatial weights matrix W. The latter represents spatial dependence and spillover effects by means of a latent variable in the structural (regression) model while the observed spatially lagged variables are related to the latent spatial dependence variable in the measurement model. The simulation results based on Anselin’s Columbus, Ohio, crime data set show that the misspecified latent variables approach slightly trails the correctly specified classical approach in terms of bias and root mean squared error of the coefficient estimators.