Stabilization of hyperbolic systems using concentrated sensors and actuators

Certain hyperbolic systems of partial differential equations which are known to be uniformly asymptotically stabilizable using point sensors/actuators (S/A) are considered. The issue to be investigated is the effect on stability when point S/A's are replaced by "concentrated" S/ A's, that is, S/A's which average over small regions of the spatial domain. Although it is known that passing from point to concentrated S/ A's necessarily destroys uniform stability, a necessary and sufficient condition for strong stability is obtained in terms of the S/A weighting functions. In addition, in the special case of a cantilevered beam controlled by a single sensor/actuator pair concentrated at the free end, another, more robust type of stability is shown to hold, even when strong stability does not. The latter result shows that the system energy is bounded by a part which goes uniformly to zero at infinity and a residual which can be explicitly estimated in terms of the support of the weight functions and the initial energy. Furthermore, the residual energy converges to zero as the support reduces to the point at the free end of the beam.     

Physical, Chemical and Sensory Changes in Irradiated Fresh Pork Packaged in Modified Atmosphere

The effects of irradiation dose (0, 0.5 and 1.0 kGy), headspace oxygen (0, 10 and 20% O₂, balance nitrogen) and storage temperature (5, 15 and 25°C) on the physical, chemical and sensory changes in fresh pork were studied using factorial design experiments. Irradiation in the absence of oxygen extended the sensory shelf life of pork from 9 to 26 days at 5°C and from & lt; 2 to 2 days at 25°C. Oxygen in the package headspace combined with irradiation adversely affected physical, chemical and sensory characteristics of the end product.     

On the VLSI implementation of real-time order statistic filters

Real-time implementation of an order-statistic filter (OSF) or ranked order filter requires the computation of the order statistic (ranked order) of the samples in a window which gets periodically updated with the arrival of a new sample(s). The authors give an algorithm for the computation of the running order statistic. A highly parallel architecture suitable for VLSI implementation is presented. The architecture is very versatile, with programmable window size and rank order. An expansion algorithm and its VLSI architecture, which permit the usage of two r-bit OSFs to implement an (r+1)-bit OSF, where r is the resolution of the input signal samples, are given. In a special case where one is satisfied with at most one LSB error, the hardware complexity of the proposed architecture can be reduced by almost one half. It is further shown how a VLSI chip incorporating the proposed architecture can be used as the basic building block in the real-time implementation of other forms of nonlinear filters     

Fast algorithms for computing the diameter of a finite planar set

Three algorithms for computing the diameter of a finite planar set are proposed. Although all three algorithms have (O(n ²) worst-case running time, an expected-complexity analysis shows that, under reasonable probabilistic assumptions, all three algorithms have linear expected running time. Experimental results indicate that two of these algorithms perform very well for some distributions, and are competitive with an existing method. Finally, we exhibit situations where these exact algorithms out-perform a published approximate algorithm.Research of the first author was supported by grant NSERC A 2422. Research of the second author was supported by grants NSERC A 9293, FCAC EQ-1678 and a Killam Senior Research Fellowship awarded by the Canada Council     

Pyramid collaborative filtering technique for an intelligent autonomous guide agent

This article presents an autonomous guide agent that can observe a community of learners on the web, interpret the learners' inputs, and then assess their sharing. The goal of this agent is to find a reliable helper (tutor or other learner) to assist a learner in solving his task. Despite the growing number of Internet users, the ability to find helpers is still a challenging and important problem. Although helpers could have much useful information about courses to be taught, many learners fail to understand their presentations. For that, the agent must be able to deal autonomously with the following challenges: Do helpers have information that the learners need? Will helpers present information that learners can understand? And can we guarantee that these helpers will collaborate effectively with learners? We have developed a new filtering framework, called a pyramid collaborative filtering model, to whittle the number of helpers down to just one. We have proposed four levels for the pyramid. Moving from one level to another depends on three filtering techniques: domain model filtering, user model filtering, and credibility model filtering. A new technique is filtering according to helpers' credibilities. Our experiments show that this method greatly improves filtering effectiveness. © 2007 Wiley Periodicals, Inc. Int J Int Syst 22: 1065–1082, 2007.     

An investigation of carbon nanotube jet grinding

Since their observation in 1976 and 1991, carbon nanotubes (CNTs) have generated much interest due to their properties and potential applications. CNTs are tubular carbon molecules with remarkable mechanical, electrical, chemical and thermal properties, which make them useful in various applications. Industries producing CNTs via the fluidized bed chemical vapor deposition technique face challenges related to the size of CNT bundles. The two main challenges are agglomeration and agglomerate size distribution control. A solution to these challenges involves the use of jet mills to grind the CNT agglomerates. The goal of this study was to determine whether the nanotubes could be ground with air jets using a commercial jet mill and apply a two-parameter model to describe the grinding process. The present study has indicated that air-jet grinding of CNTs is feasible with a typical commercial jet mill. This paper presents the effect of operational parameters on the arithmetic mean diameter of the ground product. Sonic velocity through the grinding nozzles was required to obtain reasonable grinding rates and relatively narrow particle size distributions. This occurs at high air to solids feedrate ratios. Additionally, a simple attrition model can describe the grinding process in the spiral jet mill.     

A fluidelastic model for the dynamics of cantilevered plates with an additional spring support in axial flow

A fluidelastic model has been developed for studying the dynamics of cantilevered plates in axial flow, with an additional spring support at the plate trailing edge. The plate is supposed to be two-dimensional; a nonlinear equation of motion based on the inextensibility condition is used to account for the possible large vibration amplitude. For the fluid-dynamic part, an unsteady lumped vortex model is used for calculating the fluid loads acting on the plate undergoing deformation; the longitudinal displacement of the plate associated with lateral motions is also taken into account. The fluidelastic model is first validated through comparisons with experimental data published for systems without the spring support; it is then used to investigate the dynamics of cantilevered plates in axial flow with an additional spring support at the plate trailing edge. Some interesting results of the dynamics of the fluid–structure system are presented.     

Bile acids as constituents for dental composites: in vitro cytotoxicity of (meth)acrylate and other ester derivatives of bile acids.

Methacrylic derivatives of bile acids have been synthesized for use as monomers in dental composites. Polymeric dental materials are known to leach cytotoxic unreacted monomers and degradation products. In this study, the in vitro cytotoxicity of bile acids and their derivatives towards 3T3 fibroblasts has been evaluated by colorimetric MTT assay and compared with that of the common dental monomers BisGMA, UDMA and TEGDMA. In general, the bile acids and their derivatives induced mitochondrial dysfunction at similar or higher concentrations than the commercial dental monomers. Certain monomers did not influence MTT response over their entire range of solubility.     

Nondestructive Online In Vitro Monitoring of Pre-Osteoblast Cell Proliferation Within Microporous Polymer Scaffolds

We present a system for the online, in vitro, nondestructive monitoring of tissue growth within microporous polymer scaffolds. The system is based on measuring the admittance of the sample over a frequency range of 10-200 MHz using an open-ended coaxial probe and impedance analyzer. The sample admittance is related to the sample complex permittivity (CP) by a quasi-static model of the probe's aperture admittance. A modified effective medium approximation is then used to relate the CP to the cell volume fraction. The change of cell volume fraction is used as a measure of tissue growth inside the scaffold. The system detected relative cell concentration differences between microporous polymer scaffolds seeded with 0.4, 0.45, 0.5, and 0.6 x 10⁶ pre-osteoblast cells. In addition, the pre-osteoblast proliferation within 56 scaffolds over 14 days was recorded by the system and a concurrent DNA assay. Both techniques produced cell proliferation curves that corresponded to those found in literature. Thus, our data confirmed that the new system can assess relative cell concentration differences in microporous scaffolds enabling online nondestructive tissue growth monitoring.     

Pitting corrosion resistance of La added 316L stainless steel in simulated body fluids

Lanthanum (La), a rare earth element with anticoagulative and antiphlogistic function, was added into the medical grade 316L stainless steel in order to improve its biocompatibility. The corrosion resistance of the La added 316L steel in two different simulated body fluids, simulated blood plasma and Hank's solution, was evaluated. The result showed that the addition of La in the steel could largely affect the corrosion behavior of the steel. The steel with 0.01% La showed the widest passive region and the best resistance to pitting attack, within the addition range of La from 0.01% to 0.08%. The corrosion resistance improvement of La added 316L stainless steel is probably due to the effect of La on the purification of the steel, the modification of inclusions, and the passive film formation in the simulated body fluids.