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Distribution by Scientific Domains

Chemistry	50%

Selected Abstracts

ACE4k: An analog I/O 64×64 visual microprocessor chip with 7-bit analog accuracy

INTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 2-3 2002
G. Liñán
Abstract This paper describes a full-custom mixed-signal chip which embeds distributed optical signal acquisition, digitally-programmable analog parallel processing, and distributed image memory cache on a common silicon substrate. This chip, designed in a 0.5 µm standard CMOS technology contains around 1.000.000 transistors, of which operate in analog mode; it is hence one the most complex mixed-signal chip reported to now. Chip functional features are: local interactions, spatial-invariant array architecture; programmable local interactions among cells; randomly-selectable memory of instructions (elementary instructions are defined by specific values of the cell local interactions); random storage/retrieval of intermediate images; capability to complete algorithmic image processing tasks controlled by the user-selected stored instructions and interacting with the cache memory, etc. Thus, as illustrated in this paper, the chip is capable to complete complex spatio-temporal image processing tasks within short computation time (<300 ns for linear convolutions) and using a low power budget (<1.2 W for the complete chip). The internal circuitry of the chip has been designed to operate in robust manner with >7-bits equivalent accuracy in the internal analog operations, which has been confirmed by experimental measurements. Such 7-bits accuracy is enough for most image processing applications. ACE4k has been demonstrated capable to implement up to 30 template,-either directly or through template decomposition. This means the 100% of the 3×3 linear templates reported in Roska et al. 1998, [1]. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Incremental identification of fluid multi-phase reaction systems

AICHE JOURNAL, Issue 4 2009
Claas Michalik
Abstract Despite their importance, rigorous process models are rarely available for reaction and especially multi-phase reaction systems. The high complexity of these systems, which is due to the superposed effects of mass transfer and intrinsic reaction, is the major barrier for the development of process models. A methodology that allows thesystematic decomposition of mass transfer and chemical reaction and thus enables the efficient identification of multi-phase reaction systems is proposed in this work. The method is based on the so-called Incremental Identification Method, recently presented by Brendel et al., Chem Eng Sci. 2006;61:5404-5420. The method allows to easily test the identifiability of a system based on the available measurement data. If identifiability is given, the intrinsic reaction kinetics can be identified in a sound and numerically robust manner. These benefits are illustrated using a simulated 2-phase enzyme reaction system. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Improving the assessment of species compositional dissimilarity in a priori ecological classifications: evaluating map scale, sampling intensity and improvement in a hierarchical classification

APPLIED VEGETATION SCIENCE, Issue 4 2010
B.E. Lawson
Abstract Question: Can species compositional dissimilarity analyses be used to assess and improve the representation of biodiversity patterns in a priori ecological classifications? Location: The case study examined the northern-half of the South-east Queensland Bioregion, eastern Australia. Methods: Site-based floristic presence,absence data were used to construct species dissimilarity matrices (Kulczynski metric) for three levels of Queensland's bioregional hierarchy , subregions (1:500 000 scale), land zones (1:250 000 scale) and regional ecosystems (1:100 000 scale). Within- and between-class dissimilarities were compiled for each level to elucidate species compositional patterns. Randomized subsampling was used to determine the minimum site sampling intensity for each hierarchy level, and the effects of lumping and splitting illustrated for several classes. Results: Consistent dissimilarity estimates were obtained with five or more sites per regional ecosystem, 10 or more sites per land zone, and more than 15 sites per subregion. On average, subregions represented 4% dissimilarity in floristic composition, land zones approximately 10%, and regional ecosystems over 19%. Splitting classes with a low dissimilarity increased dissimilarity levels closer to average, while merging ecologically similar classes with high dissimilarities reduced dissimilarity levels closer to average levels. Conclusions: This approach demonstrates a robust and repeatable means of analysing species compositional dissimilarity, determining site sampling requirements for classifications and guiding decisions about ,lumping' or ,splitting' of classes. This will allow more informed decisions on selecting and improving classifications and map scales in an ecologically and statistically robust manner. [source]

Separation of Homogeneous Azeotropic Mixtures by Pressure Swing Distillation , Analysis of the Operation Performance

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 10 2005
J.-U. Repke
Abstract The complex separation of a homogenous azeotropic mixture by pressure swing distillation is analyzed based on a rigorous dynamic model considering the system acetonitrile/water. The model is validated with our own experimental data. Investigations showed that the process can be operated in a very stable and robust manner even when large disturbances set the feed concentration to the other distillation region. [source]