Phenomenological compensation of thermally caused position and orientation errors of rotary axes

Thermal errors of machine tools are one of the major sources of inaccuracy. Therefore, the reduction of temperature induced deviations or the compensation of the resulting tool center point (TCP) errors have been of strong interest to the manufacturing industry for a couple of years. Up to now, the observation of the environment, the main spindle, the linear axes and the machine bed were in the focus of research, but with the rising demand for 5-axis machine tools and the increasing requirements regarding their accuracy, the analysis of the thermal behavior of rotary axes becomes more and more important. This paper gives an overview of corresponding thermal measurements of machine tools. The thermal behavior of rotary and swiveling axes is analyzed in detail. A simulation model and an approach for a phenomenological compensation of the TCP error are introduced and verified by measurements.     

Distribution of organotin compounds in the bivalves of the Aegean Sea, Greece

Five bivalve species--Mytilus galloprovinciallis (Mediterranean mussels), Venus gallina (stripped venus), Modiola barbatus L. (bearded horse mussels), Pecten jacobeus (scallops) and Callista chione (hard clams)--were collected from seven areas in Aegean Sea, Greece, between August 2001 and January 2003 and analyzed for organotins (OTs). The concentrations (as geometric means) found were 17.1 ng g-1 for tributyltin (TBT), 18.8 ng g-1 for dibutytltin (DBT), 7.8 ng g-1 for monobutyltin (MBT) and 13.0 ng g-1 for triphenyltin (TPhT) (wet weight), which are at similar or lower levels than those reported worldwide. Studying OTs distribution between different bivalve species, lower concentrations were observed in mediterranean mussels, possibly due to their growth in water column (grown on sea net pens in mussel farms), in contrast to the free-ranging species, collected from fishing grounds. Concentrations of the OTs in the examined bivalves varied seasonally.     

General prevention and risk minimization in LCA A combined approach

Methods for life cycle assessment of products (LCA) are most often based on the general prevention principle, as opposed to the risk minimization principle. Here, the desirability and feasibility of a combined approach are discussed, along with the conditions for elaboration in the framework of LCA methodology, and the consequences for LCA practice. A combined approach provides a separate assessment of above and below threshold pollution, offering the possibility to combat above threshold impacts with priority. Spatial differentiation in fate, exposure, and effect modelling is identified to play a central role in the implementation. The collection of region-specific data turns out to be the most elaborate requirement for the implementation in both methodology and practice. A methodological framework for the construction of characterization factors is provided. Along with spatial differentiation of existing parameters, two newly introduced spatial parameters play a key role: the sensitivity factor and the threshold factor. The practicability of the proposed procedure is illustrated by an example of its application. Providing a reasonable data availability, the development of separate LCA characterization factors for the respective assessment of pollution levels above and below environmental threshold values seems to be a feasible task that may add to LCA credibility.     

Priority assessment of toxic substances in life cycle assessment. Part I: calculation of toxicity potentials for 181 substances with the nested multi-media fate, exposure and effects model USES-LCA

Toxicity potentials are standard values used in life cycle assessment (LCA) to enable a comparison of toxic impacts between substances. In most cases, toxicity potentials are calculated with multi-media fate models. Until now, unrealistic system settings were used for these calculations. The present paper outlines an improved model to calculate toxicity potentials: the global nested multi-media fate, exposure and effects model USES-LCA. It is based on the Uniform System for the Evaluation of Substances 2.0 (USES 2.0). USES-LCA was used to calculate for 181 substances toxicity potentials for the six impact categories freshwater aquatic ecotoxicity, marine aquatic ecotoxicity, freshwater sediment ecotoxicity, marine sediment ecotoxicity, terrestrial ecotoxicity and human toxicity, after initial emission to the compartments air, freshwater, seawater, industrial soil and agricultural soil, respectively. Differences of several orders of magnitude were found between the new toxicity potentials and those calculated previously.     

Cascading effects from predator removal depend on resource availability in a benthic food web

We tested joint effects of predator loss and increased resource availability on the grazers’ trophic level and the propagation of trophic interactions in a benthic food web by excluding larger predatory fish from cages and manipulating nutrients in the coastal zone of the Baltic Sea. The combination of nutrient enrichment and excluding larger predators induced an increase in medium-sized predatory fish (three-spined stickleback). The meso-predator fish in turn did not change the total abundance of the invertebrate herbivores, but did cause a substantial shift in their community composition towards the dominance of gastropods by reducing amphipods by 40–60%, while gastropods were left unchanged. The shift in grazer composition generated a 23 times higher producer biomass, but only under nutrient enrichment. Our results show that top-predator declines can substantially shift the species composition at the grazers’ level, but that cascading effects on producers by a trophic cascade strongly depend on resource availability.