ON THE GLOBAL AND LOCAL STRUCTURAL PROPERTIES OF PACKED BEDS OF NONEQUILATERAL CYLINDRICAL PARTICLES

The structure of a series of packed beds of non-equilateral cylindrical particles has been investigated and compared with those of beds of spheres and equilateral cylinders of similar dimensions. It is found that the mean voidage of beds of equilateral cylinders is consistently lower than the corresponding values for beds of spheres and non-equilateral cylinders of aspect ratios 0.25, 0.5, 2 and 3. End effects do not appear to be present in beds of cylinders of aspect ratios of 0.25 and 0.5 and generally, both wall and end effects are significantly weaker than corresponding effects in beds of spheres and equilateral cylinders. This suggests that chanelling is reduced in beds of non-equilateral cylindrical pellets. Whilst the axial voidage distribution of beds of non-equilateral cylinders appears to be almost uniform, the radial voidage distribution bears the effect of confining walls and an oscillatory profile is observed in most cases, but is seen to be irregular for aspect ratios 0.25 and 0.5. The orientation effect of particles of aspect ratio 0.25 in adjacent layers causes an irregular pattern in the axially averaged radial voidage distribution. Observed axially averaged radial voidage profiles suggest that a uniform structure may be achieved by modifying the basic cylindrical shape.     

Cutoff frequencies and noise power law model of spectral density:adaptation of the multivariance method for irregularly spaced timingdata using the lowest-mode estimator approach

The concept of structure functions, which is an extension of the variance approach, is useful to determine the variance (the structure function) which is optimized for a type of noise and for an order of drift. The multivariance method was developed to use different variances over the same signal. It is then possible to select a set of variances in which each variance is optimized to the determination of one parameter (of one noise level, drift, or cutoff frequency). Recently, we adapted this method to irregularly spaced timing data. In this connection, we replaced the structure functions by another method of spectral density estimation: the lowest-mode estimator, introduced by J.E. Deeter and P.E. Boynton (1982, 1984) for the analysis of pulsar timing data. Different lowest-mode estimators can be constructed according to two priorities: the order of drifts that must be removed and the type of noise for which the sensitivity must be maximum. Thus, a multivariance system is developed using a set of different estimators. The details of this method are described, and the results for different signals are discussed in this paper     

Some factors affecting the electrical properties of carbon-black-loaded butyl rubber during vulcanization

Butyl rubber mixtures loaded with 70 phr general purpose furnace black (GPF) and tetramethyl thiuram disulphide (TMTD)/S as vulcanizing system were prepared. The kinetics of their electrical conductivity development during the vulcanization process were followed by using an especially devised system. It was found that the increase in the electrical conductivity during vulcanization obeys an exponential growth function with time constant τ, which markedly decreases with increasing vulcanization temperature as well as with the efficiency of the vulcanizing system. After completion of the vulcanization process, about 80 min, the samples obtained possess reasonable stability and reproducibility of electrical conductivity.     

Mathematical analysis of dynamic channel selection in indoor mobilewireless communication systems

Dynamic channel selection (DCS) is an algorithm for flexible resource sharing in mobile radio systems. The digital enhanced cordless telecommunications (DECT) standard implements a version of DCS based on time as well as frequency multiplexing. In this paper, mathematical models are developed to evaluate the probabilities of channel availability, desired carrier power, and the carrier-to-interference ratio (CIR) for a constant traffic load. These results can be used to compute the call setup blocking probability. The models reported in this study are based on a decentralized DCS according to the DECT standard specifications. The results show that blocking due to availability of a channel (resource blocking), not interference blocking, generally is the most important factor in overall call blocking. Furthermore, it is seen that resource blocking is sensitive to the implementation of portable sets. Also, with homogeneous static traffic, this type of DCS ran be as good as fixed channel allocation (FCA) with respect to resource blocking     

The effect of surface roughness on the radiative properties ofpatterned silicon wafers

The radiative properties of patterned silicon wafers have a major impact on the two critical issues in rapid thermal processing (RTP), namely wafer temperature uniformity and wafer temperature measurement. The surface topography variation of the die area caused by patterning and the roughness of the wafer backside can have a significant effect on the radiative properties, but these effects are not well characterized. We report measurements of room temperature reflectance of a memory die, logic die, and various multilayered wafer backsides. The surface roughness of the die areas and wafer backsides is characterized using atomic force microscopy (AFM). These data are subsequently used to assess the effectiveness of thin film optics in providing approximations for the radiative properties of patterned wafers for RTP applications     

Microfabricated liquid chromatography columns based on collocated monolith support structures

There is great interest today in massively parallel analytical strategies as a way to accelerate the rate of discovery in biological research; among them being 'biochips' and 'laboratories-on-a-chip'. The concept in the 'chip' approach is that minaturization will allow large numbers of operations to be performed in parallel in a small space, as in electronics. Proceeding with the semiconductor analogy, this paper demonstrates that in situ micromachining can be used to simultaneously fabricate millions of micrometer size, particle like structures in multiple liquid chromatography columns on a single wafer. Reduction of this widely used bioanalytical tool to the nanoliter volume, parallel processing, chip format is a significant step toward laboratories-on-a-chip.