Mullite Formation by Endothermic Reaction of α-Alumina/Silica Microcomposite Particles

The formation of mullite was investigated using microcomposite powders which consist of α-alumina cores and amorphous silica coatings. Differential thermal analysis and X-ray diffraction showed that the mullitization reaction was endothermic. In contrast, mullite forms exothermically in samples prepared by sol-gel processing. The results are shown to be consistent with available thermodynamic data for mullite formation from different alumina and silica phases.     

Value analysis of intermittent generation sources from the systemoperations perspective

The objective of this study is to determine the economic and operational impact on energy cost of incorporating large photovoltaic (PV) and wind energy conversion systems (WECS) into the electric utility generation mix. In most cases, PV and WECS power outputs are subtracted from the utility load with the expectation that conventional generation would meet the residual load. This approach is valid for small penetration levels and/or for PV and WECS facilities connected near load centers, However, several constraints such as thermal generation characteristics, fuel supply and delivery, spinning reserve requirements, and hydro availability are not adequately represented in this process. To determine the optimal value of large-scale PV and WECS applications, a new methodology that would take into account the aforementioned constraints as well as a more global penetration is developed. Results indicate that while high hydro availability increases PV penetration levels, high ramping rates can also significantly increase penetration levels     

Three-dimensional CMOS NAND with three stacked channels

A process-inherent NAND2 device is presented for a three-dimensional CMOS integration with epitaxial lateral overgrowth and chemo-mechanical polishing. The required 'OR' function of the two PMOS transistors is achieved by one silicon volume, which is controlled by a back gate and a conventional front gate. Almost symmetrical characteristics are measured for the front and the back gates.<>     

1.3 μm InAsyP1-y-InPstrained-layer quantum-well laser diodes grown by metalorganic chemicalvapor deposition

The authors have fabricated 1.3-μm InAsP-InP separate-confinement-heterostructure (SCH) strained-layer double-quantum-well (SL-DQW) laser diodes (LDs) by metalorganic chemical vapor deposition (MOCVD). A low threshold current density of 410 A/cm ² was obtained. The CW threshold current was as low as 1.8 mA at 20°C, and maximum CW operating temperature of 120°C was obtained. These characteristics are almost the same as those of well-designed GaInAsP-InP SL-QW LDs. Further improvement of the characteristics of InAsP-InP LDs is expected by optimizing the device structure     

The correlation of texture and magnetic properties in Co-Cr films

This investigation focuses on the correlation between the crystallographic orientation of grains with respect to magnetic properties in Co-Cr films. Based on a distribution measured for the (0002) crystallographic pole densities, modified formulae describing the texture were used to calculate the coercivity Hc, the squareness ratio Rs (Mr⊥/TMs) and the anisotropy field Ha for Co-Cr films. In general, calculated values for the coercive force He agreed well with the measured values. The calculated Rs⊥. values were much larger than the measured ones, however, indicating that the influence of the demagnetizing field and the magnetostriction on the orientation of the magnetization cannot be neglected. On leave from Institute of Computing Technology, Academia Sinica, P.O.Box 2704-6, Beijing, P.R. China.     

An analytic expression of fmax for HBTs

An analytic expression of f_max is derived based on a practical HBT circuit model where collector junction capacitance is split up into internal and external parts. It shows that for advanced HBTs, f_max is well characterized by the product of the base resistance and internal collector capacitance. In other words, the external collector capacitance has only a small impact on the determination of f_max. Good agreement between experimental results and numerical circuit simulation confirms the validity of the HBT circuit model. The influence of the external collector capacitance on maximum available gain is also described     

A hybrid spreading/despreading function with good SNR performancefor band-limited DS-CDMA

Code-division multiple-access (CDMA) implemented with direct-sequence spread spectrum (DS/SS) signaling is a promising multiplexing technique for cellular telecommunications services. The efficiency of a direct-sequence spread-spectrum code-division multiple-access (DS-CDMA) system depends heavily on the shape of the spectrum of the spread signal. Maximum efficiency is obtained with an ideal brick-wall bandpass spectrum. There are two approaches toward achieving such a spectrum. One is to use a simple spreader that produces a broad spectrum and then follow it with a precise, high order filter to band limit the spectrum. A second approach, which is the approach taken in this paper, is to use a spreader that produces a spectrum close to the ideal spectrum and then employ a simple filter to control the out-of-band power. The proposed spreader/despreader is based on a simple hybrid function and can be easily implemented. An analysis provides a compact expression for the signal-to-noise ratio (SNR) of a RAKE receiver. The expression includes the effects of baseband, intermediate frequency (IF) and RF filtering as well as the effects of the spectral densities of the spreading/despreading functions. The analysis shows that the proposed spreader/despreader yields superior performance over a conventional pseudo noise (PN) spreading/despreading mechanism     

Étude du refroidissement avec solidification d'un fluide pseudoplastique thermodépendant

Heat transfer of highly consistent shear-thinning fluids flowing in a horizontal cylindrical channel has been investigated numerically and experimentally when the outer channel wall is subjected to a constant convective heat exchange. The case considered being cooling, a possible ice deposit must be taken into account. The variation of the rheological properties with temperature must be considered as well.