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Critical Limits (critical + limit)
Selected AbstractsPredicting potential impacts of climate change on the geographical distribution of enchytraeids: a meta-analysis approachGLOBAL CHANGE BIOLOGY, Issue 11 2007MARÍA JESÚS I. BRIONES Abstract The expectation that atmospheric warming will be most pronounced at higher latitudes means that Arctic and montane systems, with predominantly organic soils, will be particularly influenced by climate change. One group of soil fauna, the enchytraeids, is commonly the major soil faunal component in specific biomes, frequently exceeding above-ground fauna in biomass terms. These organisms have a crucial role in carbon turnover in organic rich soils and seem particularly sensitive to temperature changes. In order to predict the impacts of climate change on this important group of soil organisms we reviewed data from 44 published papers using a combination of conventional statistical techniques and meta-analysis. We focused on the effects of abiotic factors on total numbers of enchytraeids (a total of 611 observations) and, more specifically, concentrated on total numbers, vertical distribution and age groupings of the well-studied species Cognettia sphagnetorum (228 observations). The results highlight the importance of climatic factors, together with vegetation and soil type in determining global enchytraeid distribution; in particular, cold and wet environments with mild summers are consistently linked to greater densities of enchytraeids. Based on the upper temperature distribution limits reported in the literature, and identified from our meta-analyses, we also examined the probable future geographical limits of enchytraeid distribution in response to predicted global temperature changes using the HadCM3 model climate output for the period between 2010 and 2100. Based on the existing data we identify that a maximum mean annual temperature threshold of 16 °C could be a critical limit for present distribution of field populations, above which their presence would decline markedly, with certain key species, such as C. sphagnetorum, being totally lost from specific regions. We discuss the potential implications for carbon turnover in these organic soils where these organisms currently dominate and, consequently, their future role as C sink/source in response to climate change. [source] Advances in the free lunch methodJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2007Rocco Caliandro The most critical limit of macromolecular crystallography, the experimental data resolution, is partially `tricked' by the `free lunch method' (non-measured reflection extrapolation). The best electron density map available when only observed data are used may be employed to extrapolate moduli and phases of unobserved reflections behind and beyond the experimental resolution limit. The method is able to reduce the mean phase error of the observed reflections and to produce a more interpretable (in terms of a molecular model) electron density map. The main features of the free lunch method have been studied and its performance has been enhanced; it is beneficial even if data resolution is about 2,Ĺ. Furthermore, the technique has been parameterized so that it may be routinely used by other phasing programs. [source] H, long-term monitoring of the Be star , Cephei AaMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2008G. Catanzaro ABSTRACT Papers published in recent years have contributed to resolve the enigma of the hypothetical Be nature of the hot pulsating star , Cephei. This star shows variable emission in the H, line, typical for Be stars, but its projected rotational velocity is very much lower than the critical limit, contrary to what is expected for a typical Be star. The emission has been attributed to the secondary component of the , Cephei spectroscopic binary system. In this paper, using both our and archived spectra, we attempt to recover the H, profile of the secondary component and to analyse its behaviour with time for a long period. To accomplish this task, we first derive the atmospheric parameters of the primary, Teff= 24 000 ± 250 K and log g= 3.91 ± 0.10, and then we use these values to compute its synthetic H, profile, and finally we reconstruct the secondary's profile disentangling the observed one. The secondary's H, profile shows the typical two-peak emission of a Be star with a strong variability. We also analysed the behaviour versus time of some linewidth parameters: equivalent width, ratio of blue to red peak intensities, full width at half-maximum, peak separation and radial velocity of the central depression. The projected rotational velocity (v sin i) of the secondary and the dimension of the equatorial surrounding disc have also been estimated. [source] Comparison of analytical approaches for liquid chromatography/mass spectrometry determination of the alcohol biomarker ethyl glucuronide in urineRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2010Anders Helander Official guidelines originating from a European Union directive regulate requirements for analytical methods used to identify chemical compounds in biological matrices. This study compared different liquid chromatography/electropray ionization mass spectrometry (LC/ESI-MS) and tandem mass spectrometry (LC/ESI-MS/MS) procedures for accurate determination of the conjugated ethanol metabolite and alcohol biomarker ethyl glucuronide (EtG) in urine, and the value of combined EtG and ethyl sulfate (EtS) measurement. Analysis was carried out on 482 urines following solid-phase extraction (SPE) sample cleanup or using direct injection of a diluted sample. SPE combined with LC/MS/MS was demonstrated to be the most selective and sensitive method and was chosen as reference method. The EtG results by different methods showed good correlation (r,=,0.96,0.98). When comparing five reporting limits for EtG in the range 0.10,1.00,mg/L, the overall agreement with the reference method (frequency of true positives plus true negatives) was 82,97% for direct-injection LC/MS/MS, 90,97% for SPE-LC/MS, 86,98% for direct-injection LC/MS, and 86,98% for direct-injection LC/MS analysis of EtG and EtS. Most deviations were attributable to uncertainty in quantitation, when the value was close to a cutoff but the respective results were slightly above and below, or vice versa, the critical limit. However, for direct-injection LC/MS/MS, despite earning 4 identification points, equally many negative results were due to a product ion ratio outside the ±20% deviation accepted by the guidelines. These results indicate that the likelihood of different analytical methods to provide reliable analytical results depends on the reporting limit applied. Copyright © 2010 John Wiley & Sons, Ltd. [source] Developing a critical load approach for national risk assessments of atmospheric metal deposition,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2006Jane R. Hall Abstract The critical load approach has been proposed for evaluation of the need to reduce atmospheric emissions of metals that lead to transboundary transport and deposition across Europe. The present study demonstrates and evaluates the application of a critical load approach for national-scale risk assessment of metal deposition in the United Kingdom. Critical load maps, calculated using critical limits based on pH-dependent free metal ion activities, are presented. Current concentrations of lead and cadmium in soils are compared with two sets of critical limit values: First, limits based on the reactive soil concentration, and second, a pH-dependent free ion critical limit function, which takes into account variable soil characteristics across the country. The use of these two models leads to different conclusions about which areas of the United Kingdom are at greatest risk, partly because of differences in the range of values of pH and organic matter in soils used in ecotoxicological experiments and in the national database. Critical loads were calculated based on free ion critical limits; the critical loads were lowest in the south and east of the country and were associated with higher soil pH, lower runoff, and lower soil organic matter. [source] Comparison of critical limits for crop plant growth based on different indicators for the state of soil compactionJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 4 2010Manfred Kaufmann Abstract Soil compaction affects physical soil condition, in particular aeration, soil strength, and water availability and has adverse effects on plant growth. Bulk density is the most frequently used indicator to describe the state of compaction of a soil. However, this parameter lacks a direct functional relationship with plant growth. Various indicators have been proposed to simultaneously characterize the state of compaction of agricultural soil and its suitability for plant growth. This paper examines and compares the critical limits for crop plant growth based on three of these indicators: packing density, least limiting water range, and S parameter (the latter is the slope of the soil water-retention curve in the inflexion point). In a first step, we reviewed the literature for published optimum and limiting values of bulk density and found that these values were highly dependent on clay and silt content. Converting them into corresponding values of packing density (composite index of bulk density and clay content), a value of 1.70 was found to effectively distinguish between optimum and limiting soil conditions for plant growth. In a second step, the packing density of 59 soil horizons sampled in N Switzerland was compared with the least limiting water range and the S parameter of these soil horizons (both determined by means of pedotransfer functions taken from the literature). A linear relationship between the three parameters was found, which allowed for a comparison of the published critical limits for plant growth based on these parameters. The critical limits of the three indicators, which had been postulated independently of each other in the literature, were found to agree well with each other. This means that all of them could equally be used to describe the compaction state of a soil and its physical suitability for plant growth. However, the proposed critical limits of packing density, least limiting water range, and S parameter still need further validation by field studies relating plant growth to soil compaction. [source] | |||||||||||||