Synthesis of ordered mesoporous carbon thin films at various temperatures in vapor infiltration method

Mesoporous carbon thin films with ordered structures were prepared by using resorcinol-surfactant self-assembly. A mixture of resorcinol, surfactant, and ethanol coated on silicon substrates was exposed to formaldehyde vapor as a cross-linking agent to form structured resorcinol/formaldehyde resin films. The films were then carbonized at 800 °C in an inert atmosphere to remove the surfactant and to obtain structured carbon materials. With this vapor infiltration method, thin films with several structures were obtained from the same precursor solution by employing different vapor infiltration temperatures. The results were interpreted from the transformation of the self-assembly during the vapor infiltration process.     

A statistical evaluation of the free energy of Fe-base ternary ordering alloys

The free energy of the Fe-base ternary ordering alloys whereB2 andD0₃ ordered structures are formed is evaluated. The statistical theory is employed using a pairwise interaction approximation taking into account not only the atomic interaction but also the magnetic interaction, based upon the Bragg-Williams-Gorsky model. The application of this model on Fe-Si-Co ordering alloys are demonstrated. The propriety of the calculation results are performed by comparing the experimental results. The influences of the magnetic energy to the stability of ordered structures are also demonstrated.     

An adaptive array utilizing an adaptive spatial averaging technique for multipath environments

When the interference is coherent with the desired signal, the conventional adaptive arrays working under the guiding principle of output power minimization tend to cancel the desired signal by using the coherent interference. A technique is described which enables the adaptive array to function even under such an environment. The array is divided into subarrays, whose input correlation matrices are adaptively averaged so as to produce a Toeplitz matrix which would be obtained when the interference did not correlate with the desired signal. The averaged matrix is now free from correlation terms between the desired signal and interference, and therefore may be used to derive the optimum weight for the array element just as in the ordinary radio environment of incoherent interference. Numerical examples show that the new adaptive array is highly capable to suppress the coherent interferences as well as incoherent ones.     

CMOS retinal prosthesis with on-chip electrode impedance measurement

A retinal prosthesis device with built-in self-test capability is proposed and demonstrated. The measurement of electrode impedance as a self-test is achieved without increasing the chip area by employing analogue multiplexers to allow the electrodes to be used for both stimulation of retinal cells and measurement of impedance. Measurement is performed using a four-terminal method to ensure good accuracy. A prototype stimulus chip with 16/spl times/16 channels is fabricated using standard 0.6 /spl mu/m CMOS technology, and is demonstrated to provide self-test functionality with error of as little as 0.05% in the frequency range of 100 Hz to 100 kHz.     

Microstructures of Annealed TiNiSn-Based Alloy Ribbons

The thermoelectric half-Heusler compounds Ti _x NiSn_0.998Sb_0.002 (x = 1.0 to 1.2) and Ti _y Zr_0.25Hf_0.25NiSn_0.998Sb_0.002 (y = 0.5 to 0.65) with nonstoichiometric nominal compositions were prepared by spin-casting and subsequent annealing at 1073 K for 24 h. The dimensionless figure of merit ZT at room temperature was maximized at x = 1.1 and y = 0.6 in Ti-rich compounds through an increase in absolute Seebeck coefficients despite a decrease in electrical conductivities. ZT reached 0.07 at x = 1.1 and 0.14 at y = 0.6. In powder x-ray diffraction analysis, minor phases of β-Sn, TiNi, Ti₂Sn, and Ti₅Sn₃ were observed in addition to a major phase of half-Heusler. The quantity of the minor phases was minimized at x = 1.1 and y = 0.55, where the absolute Seebeck coefficients are maximized. In transmission electron microscopic (TEM) analysis of Ti_0.55Zr_0.25Hf_0.25NiSn_0.998Sb_0.002, crystal grains of the half-Heusler phase, from several hundred nanometers to several micrometers in size, were observed. TEM energy-dispersive spectroscopy measurements indicated that fluctuations of Ti, Zr, and Hf compositions within the Ti-site in the half-Heusler phase may occur. Thermoelectric properties were improved at x = 1.1 and y = 0.6 rather than at the stoichiometric compositions of x = 1.0 and y = 0.5 due to minimization of the precipitate quantities.     

International mobility of researchers in robotics,computer vision and electron devices: A quantitative and comparative analysis

We investigated author information in scientific articles by approximately 7,000 researchers for a quantitative analysis of researchers’ international mobility. From top journals, we traced the movements of more than 2,200 researchers in the research domains of robotics, computer vision and electron devices. We categorized countries’ characteristics for the balance between the inflow and the outflow of researchers moving internationally. Flow patterns of international mobility confirm that the United States, China and India exhibit the greatest global flows of researchers, with Singapore and Hong Kong attracting remarkable numbers of researchers from other countries. International mobility focusing on institutions reveals that universities in Singapore receive as many foreign researchers as do research universities in the United States. Furthermore, firms and international collaborative research institutes act as alternative receivers to the universities in the electron devices research domain.     

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.     

Microstructure and Thermoelectric Properties of Dense YB<Subscript>22</Subscript>C<Subscript>2</Subscript>N Samples Fabricated Through Spark Plasma Sintering

Dense samples of the higher boride YB₂₂C₂N have been fabricated through the spark plasma sintering (SPS) method with different sintering aids. YB₂₂C₂N is a representative of a series of newly discovered rare-earth borocarbonitrides, which may be the long-awaited n-type counterpart of boron carbide, “B₄C.” The effect of Si, SiC, Al, and TiC additions on the sintering process of YB₂₂C₂N has been studied. The best sintered bodies with densities higher than 90% of theoretical density were obtained by means of SPS at 1700°C. We show that the additive choice and pressure have an effect on grain size and density. An investigation of the effect of atmosphere on the sintering behavior has also been carried out. It was found that sinterability is enhanced under nitrogen atmosphere. Thermoelectric properties of the materials sintered with additives have been evaluated, and we discuss their dependences on the fabrication process route.