High level modelling and design of asynchronous interface logic

Asynchronous digital interface circuits exhibit a high degree of concurrency. Self-timed implementation is the most appropriate design discipline for such circuits. Their complexity demands that a formal design methodology, amenable to automation, is used to design them. Existing specification models suffer from severe limitations when it comes to describing the circuit function at a high level, which requires decomposing the specification into intercommunicating sub-modules and synthesizing a logic circuit implementation of that function. We propose a new methodology to design asynchronous circuits that is divided in two stages: abstract synthesis and logic synthesis. The first stage is carried out by refining an abstract model, based on logic predicates describing the correct input-output behavior of the circuit, into a labeled Petri net and then into a formalization of timing diagrams (the Signal Transition Graph). This refinement involves hierarchical decomposition of the initial i..

Effects of sedimentary soot-like materials on bioaccumulation and sorption of polychlorinated biphenyls

Bioaccumulation of hydrophobic organic chemicals from sediments containing soot or sootlike materials has been hypothesized to be limited by strong sorption of the chemicals to the soot matrixes. To test this hypothesis, we quantified bioaccumulation of 11 polychlorinated biphenyls (PCBs) into the aquatic oligochaete Limnodrilus sp. exposed to spiked sediment with and without the sootlike materials coal and charcoal. In addition, sorption experiments with sediment containing varying amounts of coal or charcoal were performed to elucidate the accumulation mechanism. Results showed that coal and charcoal (at realistic levels of 1.5% on a dry-wt basis) reduced PCB accumulation in worms 1.2 to 8.5 times when expressed oil a mass basis. Moreover, whereas bioaccumulation from pure sediment increased with molecular planarity of the PCBs (toxic potency), it decreased in case of sediments containing coal and charcoal. In contrast to this advantageous effect, it was hypothesized that coal and charcoal had an adverse influence on the habitat quality of oligochaetes: Organisms inhabiting sediment containing coal or charcoal had significantly reduced lipid contents as compared to organisms from pure sediment. Because of these reduced lipid contents, lipid-normalized PCB concentrations in worms and biota-to-sediment accumulation factors (BSAFs) for most PCBs were higher in sediments containing the sootlike materials as compared to those for reference sediment. Also, measured BSAFs for coal- and charcoal-containing sediments appeared to be much higher than estimated on the basis of equilibrium partitioning theory. Sorption experiments revealed that this was caused by much weaker sorption to the sediment-coal/charcoal mixture than calculated assuming linear additivity of sorption capacities of the distinct phases. It was hypothesized that this weaker sorption resulted from competition between PCBs and dissolved organic carbon molecules for sorption sites on coal/charcoal. This points to a sorption process that is much more complicated than generally assumed

Plastic debris and policy: Using current scientific understanding to invoke positive change

Captain Charles Moore introduced the world to the "Great Pacific Garbage Patch" in the mid-1990s. Since then, there has been increasing interest from scientists, the public and policy makers regarding plastic debris in the environment. A focus article in the July issue of the Society of Environmental Toxicology and Chemistry's journal, Environmental Toxicology and Chemistry, outlines the current research, identifies research gaps on plastic debris and reviews some of the weight of evidence regarding contamination, fate and effects of the materia

Use of a theorem prover for transformational synthesis

SIGLEAvailable from British Library Document Supply Centre- DSC:8724.9(UNUT-CL-TRS--426) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Microplastics in Freshwater Biota: A Critical Review of Isolation, Characterization and Assessment Methods

Freshwater systems provide key pathways for microplastic (MP) pollution, and although existing studies have demonstrated the susceptibility of freshwater biota to ingestion, translocation, and trophic transfer, specific challenges pertaining to methodological standardization remain largely unresolved, particularly with respect to isolating, characterizing, and assessing MPs. Here, a critical review is performed outlining the challenges and limitations currently faced by freshwater MP researchers, which may well apply across the MP research spectrum. Recommendations are provided for methodological standardization, particularly in MP characterization, quality assurance, and quality control (QA/QC) procedures as well as reporting. Considerations for the assessment of MPs in freshwater biota as a means of improving comparisons between studies are discussed. Technological advancements, including the improvement of laboratory infrastructure for identifying MPs within the smaller size range as well as methodological standardization are essential in providing policy makers with tools and measures necessary to determine the distribution of MPs within freshwater ecosystems, while also allowing for comparability and providing compliance for future monitoring requirements