Class Refinement as Semantics of Correct Object Substitutability

Subtype polymorphism, based on syntactic conformance of objects' methods and used for substituting subtype objects for supertype objects, is a characteristic feature of the object-oriented programming style. While certainly very useful, typechecking of syntactic conformance of subtype objects to supertype objects is insufficient to guarantee correctness of object substitutability. In addition, the behaviour of subtype objects must be constrained to achieve correctness. In class-based systems classes specify the behaviour of the objects they instantiate. In this paper we define the class refinement relation which captures the semantic constraints that must be imposed on classes to guarantee correctness of substitutability in all clients of the objects these classes instantiate. Clients of class instances are modelled as programs making an iterative choice over invocation of class methods, and we formally prove that when a class C′ refines a class C, substituting instances of C′ for instances of C is refinement for the clients. Received May 1999 / Accepted in revised form March 2000     

Rapid synthesis of nanostructured porous silicon carbide from biogenic silica

Nanostructured silicon carbide (SiC) is an exceptional material with numerous applications, for example, in catalysis, biomedicine, high-performance composites, and sensing. In this study, a fast and scalable method of producing nanostructured SiC from plant materials by magnesiothermic reduction via self-propagating high-temperature synthesis (SHS) route was developed. The produced biogenic material possessed a high surface area above 200 m²/g with a SiC crystallite size below 10 nm, which has not been done previously by SHS. This method enables affordable synthesis of the material plant-based precursors in a reaction that only takes a few seconds, thereby paving a way for nanostructured SiC production in high volumes using renewable resources. The material was also functionalized with carboxylic acid and bisphosphonate moieties, and its use as metal adsorbent in applications such as wastewater remediation was demonstrated.     

Stabilizing Active Edge Sites in Semicrystalline Molybdenum Sulfide by Anchorage on Nitrogen‐Doped Carbon Nanotubes for Hydrogen Evolution Reaction

Finding an abundant and cost‐effective electrocatalyst for the hydrogen evolution reaction (HER) is crucial for a global production of hydrogen from water electrolysis. This work reports an exceptionally large surface area hybrid catalyst electrode comprising semicrystalline molybdenum sulfide (MoS_2+x) catalyst attached on a substrate based on nitrogen‐doped carbon nanotubes (N‐CNTs), which are directly grown on carbon fiber paper (CP). It is shown here that nitrogen‐doping of the carbon nanotubes improves the anchoring of MoS_2+x catalyst compared to undoped carbon nanotubes and concurrently stabilizes a semicrystalline structure of MoS_2+x with a high exposure of active sites for HER. The well‐connected constituents of the hybrid catalyst are shown to facilitate electron transport and as a result of the good attributes, the MoS_2+x/N‐CNT/CP electrode exhibits an onset potential of ?135 mV for HER in 0.5 m H₂SO₄, a Tafel slope of 36 mV dec^?1, and high stability at a current density of ?10 mA cm^?2.     

Evolutionary conservation of human drug targets in organisms used for environmental risk assessments

Pharmaceuticals are typically found in very low concentrations in the aquatic environment. Accordingly, environmental effects clearly assigned to residual drugs are consistent with high affinity interactions with conserved targets in affected wildlife species rather than with a general toxic effect. Thus, evolutionarily well-conserved targets in a given species are associated with an increased risk. In this study orthologs for 1318 human drug targets were predicted in 16 species of which several are relevant for ecotoxicity testing. The conservation of different functional categories of targets was also analyzed. Zebrafish had orthologs to 86% of the drug targets while only 61% were conserved in Daphnia and 35% in green alga. The predicted presence and absence of orthologs agrees well with published experimental data on the potential for specific drug target interaction in various species. Based on the conservation of targets we propose that aquatic environmental risk assessments for human drugs should always include comprehensive studies on aquatic vertebrates. Furthermore, individual targets, especially enzymes, are well conserved suggesting that tests on evolutionarily distant organisms would be highly relevant for certain drugs. We propose that the results can guide environmental risk assessments by improving the possibilities to identify species sensitive to certain types of pharmaceuticals or to other contaminants that act through well defined mechanisms of action. Moreover, we suggest that the results can be used to interpret the relevance of existing ecotoxicity data.     

Effects of aluminum treatment on phosphorus, carbon, and nitrogen distribution in lake sediment: a 31P NMR study

The effects of aluminum (Al) treatment on sediment composition of carbon (C), nitrogen (N) and phosphorus (P) were investigated in sediment representing pre- and post-treatment years in the Danish Lake S?nderby. 31P NMR spectroscopy analysis of EDTA-NaOH extracts revealed six functional P groups. Direct effects of the Al treatment were reflected in the orthophosphate profile revealing increased amounts of Al-P in the sediment layers representing the post-treatment period, as well as changes in organic P groups due to precipitation of phytoplankton and bacteria at the time of Al addition. Furthermore, changes in phytoplankton community structure and lowered production due to the Al treatment resulted in decreased concentrations of sediment organic P groups and total C. Exponential regressions were used to describe the diagenesis of C, N, and P in the sediment. From these regressions, half-life degradation times and C, N, and P burial rates were determined.     

Angle-resolved optical characterisation of an electrochromic device

An electrochromic prototype with WO₃ and NiO as electrochromic layers was analysed in an absolute spectrophotometer. The electrochromic glazing was measured in combination with a clear float glass and a low-e glass in order to simulate a ‘real’ window. Similar measurements were performed on a commercial electrochromic product, i.e., a Gentex Night Vision Safety™ (NVS^®) mirror from Gentex Corporation, and the results were compared. The spectral transmittance was measured, in bleached and coloured state, over the solar wavelength range at the angles of incidence, φ=0, 40, 60 and 70°. The direct solar transmittance, T_sol, the visual transmittance, T_vis, and the angular dependence for these parameters were calculated.     

Two-dimensional electrophoretic separation of yeast proteins using a non-linear wide range (pH 3–10) immobilized pH gradient in the first dimension; reproducibility and evidence for isoelectric focusing of alkaline (pI >7) proteins

The proteome of the yeast Saccharomyces cerevisiae was analysed by two-dimensional (2D) polyacrylamide gel electrophoresis utilizing a non-linear immobilized pH gradient (3–10) in the first-dimensional separation. Cells were labelled by [³⁵S]methionine incorporation in the respiro-fermentative phase during exponential growth on glucose. Gels were run, visualized with phosphoimager technology and all resolved proteins automatically quantified. Proteins were well resolved over the whole pH interval, and evidence for isoelectric focusing on the basic side of the pattern was generated by sequencing of some spots, revealing the 2D positions of Tef1p, Pgk1p, Gpm1p, Tdh1p and Shm2p. Roughly 25% of the spots were resolved at the alkaline side of the pattern (pI>7). The position reproducibility was high and in the range 1–2 mm in the x-and y-dimension, respectively. No quantitative variation was linked to a certain size or charge class of resolved proteins, and the average quantitative standard deviation was 17±11%. The obtained immobilized pH gradient based pattern could easily be compared to the old ampholine-based 2D pattern, and the previously reported identifications could thus be transferred. Our yeast pattern currently contains 43 known proteins, all identified by protein sequencing. Utilizing these identified proteins, relevant pI and Mr scales in the pattern were constructed. Normalization of the expression of identified spots by compensating for the number of methionine residues a protein contains allowed stoichiometric comparisons. The most dominant proteins under these growth conditions were Tdh3p, Fba1p, Eno2p and Tef1p/Tef2p, all being expressed at more than 500 000 copies per cell. The differential carbon source response during exponential growth on either glucose, galactose or ethanol was examined for the alkaline proteins identified by micro-sequencing in this study. © 1997 John Wiley & Sons, Ltd.