Catalytic activity and characterizations of Ni/K2TixOy–Al2O3 catalyst for steam methane reforming

Nickel catalysts supported on the K₂Ti_xO_y–Al₂O₃ were prepared by the wet impregnation method for steam methane reforming to produce hydrogen. X-ray diffraction, N₂ physisorption, scanning electron microscopy with energy dispersive spectroscopy, the H₂ temperature-programed reduction technique, and X-ray photoelectron spectroscopy were employed for the characterization of catalyst samples. The results revealed that the performance of the Ni/K₂Ti_xO_y–Al₂O₃ catalysts was comparable to that of commercial FCR-4 for steam methane reforming under the mild condition. In particular, a catalytic stability test at 800 °C and in the reactant flow with the steam-to-carbon (S/C) feed ratio of 1.0 indicated that the Ni/K₂Ti_xO_y–Al₂O₃ catalysts were more active, thermally stable and resistant to deactivation than the non-promoted Ni/Al₂O₃. It is considered that the appropriate interaction strength between nickel and the modified support and proper K₂Ti_xO_y phases with a surface monolayer coverage achieved at ca. 15 wt.% loading in the support play important roles in promoting the steam methane reforming activity as well as suppressing the sintering of the catalyst.     

Evaluation of directivity for planar antenna arrays

In this paper, the directivity, including phase shift factors, for several types of uniformly excited planar arrays is obtained. Four types of dipole arrays are considered: arrays of collinear short dipoles, and of parallel short dipoles; and broadside and end-fire arrays of crosses of short dipoles. Curves of directivity versus inter-element spacing and scan angle for planar arrays with these element power patterns are presented     

Quantitative measurements of active and passive mechanical properties of adult cardiac myocytes

Cytoskeletal displacement, mechanical coupling between the cytoskeleton and the extracellular matrix, as well as nuclear mechanics can be independently quantified using novel methods based on high-resolution tracking of cellular structures and receptor bound magnetic beads in response to applied forces. These techniques can be applied to study the interaction between known protein function and specific changes in cellular mechanical properties and their role in cardiac hypertrophy.     

Simultaneous occurrence of hereditary angioneurotic edema and Crohn disease

Hereditary C1 esterase inhibitor deficiency is often associated with immunpathologic disorders. The authors present a case of the rare coincidence of hereditary angioedema (HAE) and Crohn's disease. The history of the patient is analysed along with the familial occurrence of the disease. Characteristic abdominal manifestations of C1 esterase inhibitor deficiency are compared to the clinical signs of Crohn's disease. Differential diagnostic pitfalls are described along with efficatious therapeutic options.     

Ultrasonic properties of fluorosilicate glass-ceramics at cryogenic temperatures

The longitudinal ultrasonic wave velocity and attenuation, and shear wave velocity for machinable fluorosilicate glass-ceramic (MACOR) samples (regular shelf stock, annealed to 900°C, and 1000°C for 10 hrs) were measured as the functions of frequency and temperature with the pulse-echo method. The frequency and temperature range used were 5 MHz to 50 MHz, and 100 K to 300 K respectively. Both velocities for three samples decrease linearly with temperature, and the ultrasonic attenuation increases linearly with the frequency square, and decreases monotonically with increasing temperature. These data were used to calculate the elastic moduli, Lame parameter, and Poisson's ratio for the materials.     

Simple and efficient microstrip-to-waveguide transition

A new microstrip-to-waveguide transition is investigated experimentally. The coupling is achieved by virtue of a slot-coupled dielectric resonator (DR) at the microstrip-waveguide boundary. Since the DR loss is very small, the new transition can be operated efficiently. A net transition loss of 0.38 dB is obtained. The effects of the slot offset and slot length on the characteristics of the transition are measured and discussed     

Achievable diversity order by space-time trellis coding combined with MLED and OFDM over frequency selective fading channels

Space-time trellis code (STTC) in frequency selective fading channel using maximum likelihood equalization and detection (MLED), and orthogonal frequency division multiplexing (OFDM) are compared in this paper for channels with arbitrary delay profile. The performance bound for both schemes are first derived and their performances are compared both analytically and through simulations. Code design, receiver complexity, interleaver design and the robustness issues are addressed in these comparisons.     

A hybrid electronically coupled current comparator

A new versatile electronically coupled current comparator is presented in the paper. Its simpler design is more convenient for manufacturing yet it retains high accuracy in either manual or automated version. It provides a resolution of one part in 10/sup 6/ and has an estimated uncertainty less than 5/spl middot/10/sup -6/ in magnitude and less than 5 /spl mu/rad in phase at power frequencies.     

A new algorithm for explicit adaptation of time delay

By using an adaptive technique similar to the one developed by Etter and Stearns (1981), a novel constrained algorithm for explicit time delay estimation (TDE) is derived. The adaptive process provides an unbiased delay estimate and its respective performance surface, learning characteristics and delay variance will be given. The mean-square error surface, though a function of the estimated delay only, is multimodal and proper initialization is required to guarantee global convergence. Simulation results are included to validate the convergence behavior of the TDE system