The effect of milling time on the sintering kinetics of Si3N4 based nanocomposites

Multi-walled carbon nanotube (MWCNT) reinforced silicon nitride composites have been prepared by hot isostatic pressing at 20 MPa and gas pressure sintering at 2 MPa. To assure a good dispersion of the MWCNTs a highly efficient attritor milling was employed in the preparation process of the powder mixtures. The morphological and micro-structural evolution of the powder particles during the high-energy milling was monitored.We have found that the milling time has a complex influence on the structure and mechanical properties of the resulting nanocomposites through affecting both the dispersion and degradation of the nanoscale filler as well as the phase transformations of the ceramic host.     

Treatments of Lignocellulosic Hydrolysates and Continuous‐Flow Hydrogenation of Xylose to Xylitol

Xylitol is produced by the heterogeneous catalytic hydrogenation of xylose over Raney nickel. The hydrogenation must typically be followed by several purification steps, which makes the chemical production relatively complex and expensive. In this study, activated carbon and bio‐purification treatments of corn stover hydrolysates and subsequent nickel‐catalyzed hydrogenation of xylose to xylitol were investigated. The activated carbon treatment was used to eliminate inhibitory compounds and increase the efficiency of the bio‐purification step. It was found that the glucose could be completely eliminated from the hydrolysate. The hydrogenation reactions of corn stover hydrolysate demonstrated that a high reaction temperature resulted in high sugar alcohol yields and selectivity. At a given temperature, the flow rate had no significant effect on xylitol yield.     

Dielectric Response of Embedded Fullerenes: A Classical Approach

The optical properties of fullerenes embedded in other media is explored, assuming that a single fullerene behaves as a microscopic crystallite. The justification for this assumption is discussed, and various experimental results are compared to test the limits of this approximation. The effective medium theory is used to calculate the optical response of exemplary composite systems.     

Topographic cellular active contour techniques: theory,implementations and comparisons

This paper overviews some massively parallel topographic cellular computational approaches proposed for contour localization and tracking. When implemented on a focal plane cellular array microprocessor, these algorithms offer real‐time object contour localization and tracking—even at very high frame rates. Three specific methods (Constrained Wave Computing, Pixel Level Snakes and Moving Patch Method) will be described and compared along with their associated hardware–software architectures. Computational complexity, implementation, and performance related issues are discussed on a common platform (ACE‐BOX with the ACEx CNN‐UM chips). In conclusion, a novel architecture is proposed incorporating the best solutions learned from this comparative study. Copyright © 2006 John Wiley & Sons, Ltd.     

A query processing algorithm for a system of heterogeneous distributed databases

This paper presents a query processing algorithm, formulated and developed in support of the prototype architecture of the Distributed Access View Integrated Database (DAVID) which is a heterogeneous distributed database management system. The objective of the proposed query processing algorithm is to produce an inexpensive strategy for a given query. The inexpensive query strategy is obtained primarily by computing the most profitable semi-joins and by determining the best sequence of join operations per processing site. The latter is obtained by applying a zero-one integer linear program that uses a non-parametric statistical estimation technique to compute the sizes of the temporary clusters. A cluster is a subset of the cartesian product of a list of atomic and non-atomic domains and is the structure that can represent in a uniform way data stored in relational, hierarchical and network databases.Following some background information on the development of the DAVID prototype, this paper introduces the schema architecture. The schema architecture describes the mechanism by which the component heterogeneous database schemata are mapped into the uniform global schema. This is followed by the formulation of the query processing algorithm, its implementation and an illustration of its use in the context of NASA's Astrophysics Data System.Recommended by: Y. Breitbart     

Pixel‐level snakes on the CNNUM: algorithm design,on‐chip implementation and applications

In this paper, a new algorithm for the cellular active contour technique called pixel‐level snakes is proposed. The motivation is twofold: on the one hand, a higher efficiency and flexibility in the contour evolution towards the boundaries of interest are pursued. On the other hand, a higher performance and suitability for its hardware implementation onto a cellular neural network (CNN) chip‐set architecture are also required. Based on the analysis of previous schemes the contour evolution is improved and a new approach to manage the topological transformations is incorporated. Furthermore, new capabilities in the contour guiding are introduced by the incorporation of inflating/deflating terms based on the balloon forces for the parametric active contours. The entire algorithm has been implemented on a CNN universal machine (CNNUM) chip set architecture for which the results of the time performance measurements are also given. To illustrate the validity and efficiency of the new scheme several examples are discussed including real applications from medical imaging. Copyright © 2005 John Wiley & Sons, Ltd.     

Polymodal Transient Receptor Potential Vanilloid (TRPV) Ion Channels in Chondrogenic Cells

Mature and developing chondrocytes exist in a microenvironment where mechanical load, changes of temperature, osmolarity and acidic pH may influence cellular metabolism. Polymodal Transient Receptor Potential Vanilloid (TRPV) receptors are environmental sensors mediating responses through activation of linked intracellular signalling pathways. In chondrogenic high density cultures established from limb buds of chicken and mouse embryos, we identified TRPV1, TRPV2, TRPV3, TRPV4 and TRPV6 mRNA expression with RT-PCR. In both cultures, a switch in the expression pattern of TRPVs was observed during cartilage formation. The inhibition of TRPVs with the non-selective calcium channel blocker ruthenium red diminished chondrogenesis and caused significant inhibition of proliferation. Incubating cell cultures at 41 °C elevated the expression of TRPV1, and increased cartilage matrix production. When chondrogenic cells were exposed to mechanical load at the time of their differentiation into matrix producing chondrocytes, we detected increased mRNA levels of TRPV3. Our results demonstrate that developing chondrocytes express a full palette of TRPV channels and the switch in the expression pattern suggests differentiation stage-dependent roles of TRPVs during cartilage formation. As TRPV1 and TRPV3 expression was altered by thermal and mechanical stimuli, respectively, these are candidate channels that contribute to the transduction of environmental stimuli in chondrogenic cells.