Oxidation and Fracture Strength of High-Purity Reaction-Bonded Silicon Nitride

Reaction-bonded Si₃N₄ (RBSN) made from high-purity Si powder is unusually resistant to degradation caused by exposures to air for up to 50 h at temperatures up to 1400°C. The weight gain during oxidation of this SiH₄-originating RBSN is approximately 10 times less than conventional RBSN. Contrary to normally observed strength degradations, room-temperature strengths of this high-purity, oxidized RBSN (avg = 435 MPa, max. = 668 MPa) remained at their unusually high, as-processed levels after 1000° and 1400°C oxidizing exposures. Fracture toughness values were unaffected by oxidation ( K _IC= 2.3 to 2.4 MPa · m^1/2). This superior oxidation resistance results from the high purity and the small diameter pore channels (0.01 to 0.06 μm) achieved in this SiH₄-originating RBSN.     

Transient behaviour of encapsulated enzyme reactor systems

Mathematical models are developed for the transient behaviour of encapsulated enzyme reactor systems such as the continuous stirred tank reactor (CSTR) and the packed bed tubular reactor. The rate processes taking place in the encapsulated enzyme bed are approximated by using a combined rate control model of enzyme reaction and membrane diffusion. The change in transient substrate concentration is obtained by using the developed rate expression in the material balance over the substrate as a function of time for the CSTR and as a function of time and position for the packed bed tubular reactor. The effects of various parameters such as the enzymic reaction rate constant, Michaelis constant, diffusional resistance of membranes, and Peclet number on the substrate concentration distribution, which varies with respect to operating time, are investigated. This study affords insight into the transient operating characteristics of the encapsulated enzyme reactor system. The results should be useful in understanding the start-up performance of the reactor systems and to control such reactor systems at desired operating conditions.     

Investigation of Flow Patterns in Continuous‐flow Stirred Vessels by Laser Doppler Velocimetry

The flow structure of a continuous‐flow reactor stirred by a Rushton turbine was investigated by laser Doppler velocimetry for two different mean residence time‐mixing time ratios. Velocity measurements were obtained for two inlet locations, corresponding to the incoming liquid stream being fed co‐currently or counter‐currently to the flow discharged by the turbine. In all investigated configurations and for all operating conditions, it was found that the flow disruption caused by the incoming liquid stream was observable mainly in the first vessel quarter, which followed the feed‐tube plane. From comparison of the velocities encountered in the various planes in the continuous‐flow reactor to the velocities of the batch reactor, it was also concluded that it may be possible to intensify the usage of the turbine‐stirred vessel by decreasing the characteristic times ratio, without considerable flow by‐pass and/or short‐circuiting problems.     

Universal variable length coding for an integrated approach to image coding

We propose a new entropy coding scheme, denoted in this paper as the UVLC (universal variable length coding). It is universal in the sense that its efficiency is close to one for a large class of images. The UVLC, when it is applied to block orthogonal transforms, processes groups of blocks at the bit level, using universal codes designed for binary memoryless sources. It can be used for every video coding application, from high definition TV (HDTV) to high quality videotelephony (above 2 Mbit/s) for transform or subband coding. Last but not least, its implementation is very regular and can be realized in a single chip for the encoding oftv at theccir 601 format.     

Issues in the replacement of lead-bearing solders

The use of soft solders, particularly those containing lead, dates back nearly 5,000 years. Solders similar to the materials used to seal the aqueducts of ancient Rome are now an important building block in the manufacture of high-speed computer assemblies. This history attests to the technological versatility of soft solders and, in particular, the solder alloys that contain lead. However, the health effects of prolonged exposure to lead have also been documented; measures to limit human exposure—at the work place and indirectly through the environment—are being considered. The successful introduction of lead-free solders into future electronic products will rely heavily upon their solderability, which can be evaluated by test procedures such as the meniscometer/wetting balance technique and the capillary flow test.     

Aesthetics and complexity in digital layout systems

Abstract

The layout of pages which carry information is the bread and butter of the graphic design profession. The rationale of what elements are chosen and where they are placed is based on tacit knowledge gained over a number of years of experience. The aesthetics associated with the overall finished design are often based on a style. Important elements of style are complexity and aesthetic value. In this paper I explore how various mathematical aesthetic functions can use complexity as an arousal enhancing or limiting mechanism in the application of layout designs.     

Use of a dark object concept and support vector machines to automate forest cover change analysis

An automated method was developed for mapping forest cover change using satellite remote sensing data sets. This multi-temporal classification method consists of a training data automation (TDA) procedure and uses the advanced support vector machines (SVM) algorithm. The TDA procedure automatically generates training data using input satellite images and existing land cover products. The derived high quality training data allow the SVM to produce reliable forest cover change products. This approach was tested in 19 study areas selected from major forest biomes across the globe. In each area a forest cover change map was produced using a pair of Landsat images acquired around 1990 and 2000. High resolution IKONOS images and independently developed reference data sets were available for evaluating the derived change products in 7 of those areas. The overall accuracy values were over 90% for 5 areas, and were 89.4% and 89.6% for the remaining two areas. The user's and producer's accuracies of the forest loss class were over 80% for all 7 study areas, demonstrating that this method is especially effective for mapping major disturbances with low commission errors. IKONOS images were also available in the remaining 12 study areas but they were either located in non-forest areas or in forest areas that did not experience forest cover change between 1990 and 2000. For those areas the IKONOS images were used to assist visual interpretation of the Landsat images in assessing the derived change products. This visual assessment revealed that for most of those areas the derived change products likely were as reliable as those in the 7 areas where accuracy assessment was conducted. The results also suggest that images acquired during leaf-off seasons should not be used in forest cover change analysis in areas where deciduous forests exist. Being highly automatic and with demonstrated capability to produce reliable change products, the TDA-SVM method should be especially useful for quantifying forest cover change over large areas.     

Reducing control points in lofted B-spline surface interpolation using common knot vector determination

A new algorithm for reducing control points in lofted surface interpolation to rows of data points is presented in this paper. The key step of surface lofting is to obtain a set of compatible B-spline curves interpolating each row. Given a set of points and their parameterization, a necessary and sufficient condition is proposed to determine the existence of interpolating B-spline curves defined on a given knot vector. Based on this condition, we first properly construct a common knot vector that guarantees the existence of interpolating B-spline curves to each row of points. Then we calculate a set of interpolating B-spline curves defined on the common knot vector by energy minimization. Using this method, fewer control points are employed while maintaining a visually pleasing shape of the lofted surface. Several experimental results demonstrate the usability and quality of the proposed method.