Comment on “Thermal Conductivity Measurements of Some Synthetic Al2O3-CaO-SiO2 Slags by Means of a Front-Heating and Front-Detection Laser-Flash Method”

In a previous research, it was pointed out that the thermal conductivity of molten silicate may be misled, due to the current leakage through the molten sample and the error in the resistance of the hot-wire. The applicability of the hot-wire method could be verified by the prediction of the current leakage through the sample and the comparison between the measured and the reference values of the hot-wire resistance.     

Preparation and physical properties of transparent organic–inorganic nanohybrid materials based on urethane dimethacrylate

The aim of this study was to prepare transparent organic–inorganic nanohybrid materials with improved physical properties in comparison with the matrix polymer. Polymerizable silica nanoparticles were synthesized via the reaction of silanol groups on the surface of silica nanoparticles (particle diameter ≈ 12 nm) with isocyanate groups of 2‐(methacryloyloxy)ethyl isocyanate (MOI) in ethyl acetate. In addition, the matrix monomer, urethane dimethacrylate, was prepared by the reaction of an MOI isocyanate group with the hydroxyl group of 2‐hydroxyethyl methacrylate, and novel organic–inorganic nanohybrid materials were obtained at various silica contents with bulk polymerization. The surface treatment of the silica nanoparticles and preparation of the matrix monomer were carried out in a one‐pot reaction. The prepared hybrid materials retained high transparency, and the elastic modulus and surface hardness improved with increasing silica content. Moreover, the strength of the material containing 20 wt % silica was up to 30 MPa higher than that of the matrix polymer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Intestinal absorption and biological effects of orally administered amorphous silica particles

Although amorphous silica nanoparticles are widely used in the production of food products (e.g., as anticaking agents), there is little information available about their absorption and biological effects after oral exposure. Here, we examined the in vitro intestinal absorption and in vivo biological effects in mice of orally administered amorphous silica particles with diameters of 70, 300, and 1,000 nm (nSP70, mSP300, and mSP1000, respectively) and of nSP70 that had been surface-modified with carboxyl or amine groups (nSP70-C and nSP70-N, respectively). Analysis of intestinal absorption by means of the everted gut sac method combined with an inductively coupled plasma optical emission spectrometer showed that the intestinal absorption of nSP70-C was significantly greater than that of nSP70. The absorption of nSP70-N tended to be greater than that of nSP70; however, the results were not statistically significant. Our results indicate that silica nanoparticles can be absorbed through the intestine and that particle diameter and surface properties are major determinants of the degree of absorption. We also examined the biological effects of the silica particles after 28-day oral exposure in mice. Hematological, histopathological, and biochemical analyses showed no significant differences between control mice and mice treated with the silica particles, suggesting that the silica nanoparticles evaluated in this study are safe for use in food production.     

Performance Evaluation of Flexible Manufacturing Systems with Finite Local Buffers: Fixed and Dynamic Routings

This article evaluates the performance of flexible manufacturing systems with finite local buffers and fixed or dynamic routing rules, and addresses the optimal design or system configuration problem of maximizing the system throughput. The costs include machine cost, part (or pallet) cost, and local buffers cost. First, the system throughputs and their behaviors are considered with both queueing network analysis and simulation, and it is shown for a fixed routing model that the system throughput in the case of finite local buffers is greater than in the case of infinite local buffers. For a fixed versus dynamic routing rule, it is also found that the throughput in the former case can be close to the one in the latter case by changing the setting parameters. Next, the design problems of maximizing the system throughput are considered numerically for fixed and dynamic routing cases. Then, it is seen that better combination of design variables is a class of the monotonicity in local buffers, service rates, and routing probabilities.     

Determination of correlations to predict the minimum agitation speed for complete solid suspension in agitated vessels

Experiments were conducted to determine the effects of impeller clearance, impeller diameter, and other operating variables on the minimum agitation speed for off-bottom solid suspension in agitated vessels, N_js, for disc turbines (DTs) and flat-blade turbines (FBTs). Only data for which the impellers produced recirculation flows above and below the impeller (the so-called “double-eight” flow pattern) were considered. Regression equations for N_js were obtained, in which explicit terms for impeller clearance and vessel diameter-to-impeller diameter ratio (T/D) were included. Modified Zwietering equations (Zwietering, 1958) were also obtained, in which Zwietering's parameter S was mathematically expressed as a function of vessel diameter-to-impeller clearance ratio and T/D ratio. When used together with the correlations of Armenante and Uehara Nagamine (1998) for impellers close to the vessel bottom, the equations presented here can be used to calculate N_js for DTs and FBTs for any typical impeller clearance.     

Scanning magnetic microscope system utilizing a magneto-impedance sensor for a nondestructive diagnostic tool of geological samples

We have developed a scanning magneto-impedance (MI) magnetic microscope to image surface stray magnetic fields of room-temperature geological samples with submillimeter resolution. The instrument consists of a small, 30 microm diameter, 5 mm length amorphous wire-based magneto- impedance (MI) sensor without any cooling mechanisms. The spacing between the sensor head and the sample was less than 300 microm. The length of the amorphous wire and sample-to-wire distance limits the spatial resolution. We have achieved a spatial resolution of 400 microm with a magnetic resolution of 10 nT. This instrument enables us to map a two-dimensional out-of-page component of a stray magnetic field of a natural remanent magnetization over a millimeter-thick slab of a primitive ordinary chondrite meteorite, documenting dipolelike features. A comparison of element mapping images with the stray field of the meteorites reveals what individual metals carry the dipolar remanences in the meteorites. These results suggest that the scanning MI microscope offers a room-temperature operable, small, low-maintenance alternative to the scanning SQUID microscope, and can aid in the interpretation of the magnetic remanence acquisition process of a meteorite.     

A wind-tunnel study on exhaust gas dispersion from road vehicles—Part I: Velocity and concentration fields behind single vehicles

By a reduced-scale model in a wind tunnel, we investigate the dispersion behavior of exhaust gas from automobiles. Two types of vehicles are considered, a passenger car and a small-size truck. Tracer gas experiments show that the exhaust gas dispersion is enhanced significantly by the vehicle wake compared to the case when the vehicle body is absent. The passenger car and the truck promote dispersion in the horizontal and the vertical direction, respectively. The wake field is analyzed by particle image velocimetry (PIV), and the distribution of the mean and the fluctuation fields is found to conform to the concentration field of the exhaust gas. The buoyancy of the exhaust gas has minor effect except on the vertical spread behind the truck whose wake flow amplifies the vertical displacement generated near the pipe exit.     

Characterization of flexible switchable mirror film prepared by DC magnetron sputtering

An electrochromic switchable mirror on a flexible plastic sheet was developed taking into consideration practical use, low cost and high adaptability. The mirror has a multilayer of Mg₄Ni/Pd/Al/Ta₂O₅/WO₃, which was fabricated by DC magnetron sputtering on an ITO-coated PET sheet. In the previous research, when the mirror was exposed to air for a long period of time, its optical switching properties disappeared. This work focused on the mechanism of degradation of the mirror in different environments. When the mirror was stored in a desiccator for 50 days as a means of preservation, its switching speed was seven times higher as compared with the mirror exposed to air. It is also well known that oxygen and moisture in air easily penetrate PET sheets. The features of the PET sheet strongly affected the durability of the optical switching layer. When the state of the optical switching layer was changed to nonmetallic due to the formation of oxide and hydroxide, the optical switching properties almost disappeared.     

Improvement of Low‐Temperature zT in a Mg3Sb2–Mg3Bi2 Solid Solution via Mg‐Vapor Annealing

Materials with high zT over a wide temperature range are essential for thermoelectric applications. n‐Type Mg₃Sb₂‐based compounds have been shown to achieve high zT at 700 K, but their performance at low temperatures (<500 K) is compromised due to their highly resistive grain boundaries. Syntheses and optimization processes to mitigate this grain‐boundary effect has been limited due to loss of Mg, which hinders a sample's n‐type dopability. A Mg‐vapor anneal processing step that grows a sample's grain size and preserves its n‐type carrier concentration during annealing is demonstrated. The electrical conductivity and mobility of the samples with large grain size follows a phonon‐scattering‐dominated T^?3/2 trend over a large temperature range, further supporting the conclusion that the temperature‐activated mobility in Mg₃Sb₂‐based materials is caused by resistive grain boundaries. The measured Hall mobility of electrons reaches 170 cm² V^?1 s^?1 in annealed 800 °C sintered Mg_{3 + δ}Sb_1.49Bi_0.5Te_0.01, the highest ever reported for Mg₃Sb₂‐based thermoelectric materials. In particular, a sample with grain size >30 mm has a zT 0.8 at 300 K, which is comparable to commercial thermoelectric materials used at room temperature (n‐type Bi₂Te₃) while reaching zT 1.4 at 700 K, allowing applications over a wider temperature scale.