Variance decomposition in two-stage plot sampling: theoretical and empirical results

The statistical properties of two-stage plot sampling estimators of abundance are considered. In the first stage, some spatial units are selected over the whole study area according to a suitable sampling design, while in the second stage, the selected units are surveyed with floating plot sampling to estimate the abundance within. Some insights into the accuracy of the resulting estimators are obtained by splitting the sample variance into the first and second-stage components, while performance is empirically checked by means of a simulation study. Simulation results show that, in most situations, a relevant amount of the overall variance is due to the second stage sampling.     

Correction to: High-capacity adsorbents from stainless steel slag for the control of dye pollutants in water

Environmental Science and Pollution Research - A Correction to this paper has been published: https://doi.org/10.1007/s11356-021-12759-3     

Differential effect of ultraviolet exposure (UVR) in the stress response of the Dinophycea Gymnodinium sp. and the Chlorophyta Dunaliella tertiolecta: mortality versus survival

Dunaliella tertiolecta (Chlorophyta) and Gymnodinium sp. (Dinophyceae) cells were exposed to ultraviolet radiation (UVR) (PAR, UVA and UVB: PAB) for 6 days either continuously or during a photoperiod. Both UVR treatments were harmful to Gymnodinium but exposure to continuous PAB had the most dramatic effects. Although a number of lesions/damage could have happened during the first few hours of exposure to UVR, in less than 24 h, Gymnodinium lost its ability to detoxify ROS efficiently, photoinhibition occurred, thymine dimers formed in the DNA, caspase-like enzymatic activities DEVDase sharply increased and cells died as determined by SYTOX-green staining. Superoxide dismutase activity did not significantly change with time, and although the catalase activity augmented in both treatments, cells still suffered from the UVR stress. Clearly, UVR was fatal to the dinoflagellate. For the chlorophyte, however, cell numbers increased regardless of the UVR treatment and mortality remained low (<20 %). F _v/F _m showed an initial decrease but then remained constant for both light treatments. After 6 days of continuous PAB exposure, however, signs of stress (thymine dimers, oxidative stress) paralleled a drop in catalase activity. Results obtained here demonstrate that the dinoflagellate Gymnodinium was much more sensitive and was harmed more rapidly by UVR exposure than the chlorophyte D. tertiolecta. The increased tolerance to UVR exposure of the chlorophyte may provide advantages over other more sensitive phytoplankton species within the photic zone. We provide strong support in the present study for repair being an important component of UV resistance in this species.     

Bioaccumulation and toxic effects of copper in common onion Allium cepa L.

The aim of this study was to investigate the potential utility of Allium cepa L. as a bioindicator organism for measuring copper bioaccumulation and toxicity in laboratory conditions. Onions were exposed to increasing concentrations of the metal (0, 0.1, 0.5, 1, 5 and 10 μg mL^?1) for 7 days. Root and leaf development were chosen as biological endpoints, while bioaccumulation was evaluated in roots, bulbs and leaves. Copper caused inhibition of root elongation with increasing effects at the higher doses, growth being reduced by almost 60% at 0.1 μg mL^?1 and up to 95% at 10 μg mL^?1. The elongation of leaves was significantly lower only in specimens exposed at 0.5 μg mL^?1, but a total absence of newly formed tissues was observed at 10 μg mL^?1. A marked bioaccumulation of copper was measured in roots, with values increasing up to almost four orders of magnitude compared to controls; only slight or even no significant differences were observed for copper levels in leaves and bulbs of treated A. cepa. Multiple linear correlations revealed a significant inverse relationship between copper concentrations and tissue length in both the roots and leaves, evidencing a sensitive responsiveness of this biological model. The overall results suggest the suitability of A. cepa as a robust species for easy and simple ecotoxicological bioassays to test the toxic effects and bioavailability of environmental pollutants, especially trace metals.     

Adjustment of female reproductive investment according to male carotenoid-based ornamentation in a gallinaceous bird

Carotenoid-based ornaments (many yellow–orange–red colourations) may signal the genetic or parental quality of the bearer. Thus, their expression could influence the amount of resources/energy that the mate will invest in the production of offspring, thereby optimising its reproductive fitness. The differential allocation hypothesis (DAH) predicts that females mated with more attractive males should lay more and better eggs. This has been explored only in few bird species with carotenoid-based traits. We tested this hypothesis in the red-legged partridge (Alectoris rufa), a gallinacean with very variable laying capacity. Both sexes display carotenoid-based ornamentation that gradually fades throughout the laying period. Here, the redness of beak and eye rings of captive males was intensified after mating by means of paint. The proportion of females that laid eggs did not differ between treatments. Amongst laying females, those mated with colour-enhanced males (experimental females) tended to lay earlier and produced significantly more eggs than controls, but of similar quality (egg mass and composition). We additionally investigated whether male attractiveness influenced egg components depending on the clutch size and laying sequence. The testosterone level in eggs from experimental females was positively related to the laying order, whereas control eggs did not show any trend. Our results provided mixed support for the DAH, but nevertheless revealed that female red-legged partridges may adjust their breeding investment according to male carotenoid-based ornamentation.     

Assessing the reliability of diverse fault-tolerant software-based systems

We discuss a problem in the safety assessment of automatic control and protection systems. There is an increasing dependence on software for performing safety-critical functions, like the safety shut-down of dangerous plants. Software brings increased risk of design defects and thus systematic failures; redundancy with diversity between redundant channels is a possible defence. While diversity techniques can improve the dependability of software-based systems, they do not alleviate the difficulties of assessing whether such a system is safe enough for operation. We study this problem for a simple safety protection system consisting of two diverse channels performing the same function. The problem is evaluating its probability of failure in demand. Assuming failure independence between dangerous failures of the channels is unrealistic. One can instead use evidence from the observation of the whole system's behaviour under realistic test conditions. Standard inference procedures can then estimate system reliability, but they take no advantage of a system's fault-tolerant structure. We show how to extend these techniques to take account of fault tolerance by a conceptually straightforward application of Bayesian inference. Unfortunately, the method is computationally complex and requires the conceptually difficult step of specifying ‘prior’ distributions for the parameters of interest. This paper presents the correct inference procedure, exemplifies possible pitfalls in its application and clarifies some non-intuitive issues about reliability assessment for fault-tolerant software.     

External heating closed-volume thermally activated tube forming: A fundamentally new approach for hydroforming thick-walled tubes

The underlying principles of water’s equation of state (ES) and its associated pressure–volume–temperature (PVT) relationship, are employed for the purpose of producing “ultra-high” pressure within the closed volume of a thick-walled metal tube, resulting in a new and innovative hydroforming process. The process, called “Closed-Volume Thermally Activated” (CVTA) Tube Hydroforming, involves conducting a high level of heat through the walls of a thick-walled, metallic, water-containing closed tube. Experimental validation of the concept is presented, and potential applications are discussed. This work represents a break-through in manufacturing technology, which, when further developed, is expected to enable manufacturers to expand significantly their manufacturing capability.     

Guidelines for routine mercury speciation analysis in seafood by gas chromatography coupled to a home-modified AFS detector. Application to the Andalusian coast (south Spain)

A home-modified atomic fluorescence detector (mAFS) has been employed for mercury and methylmercury determination in bivalves from the Andalusian coast (south Spain). This modification consists on the inclusion of a quartz flow cell into the detector, which increases the concentration of mercury atoms in the detector and therefore enhances sensitivity about two fold. Two analytical approaches for mercury speciation based on the coupling of gas chromatography on-line pyrolysis and mAFS (GC-Pyro-mAFS) have been tested. The first approach (Method 1) is based on aqueous ethylation followed by extraction into an organic solvent, and the second one (Method 2) in the extraction of monoalkylated mercury as chloride. Method 1 is a rapid procedure but not sensitive enough for the analysis of methylmercury in non-polluted sites (detection limit: 20 ng g(-1) as mercury, wet basis). The second one is quite more sensitive (detection limit: 0.2 ng g(-1), wet weight), but sample treatment is cumbersome and time-consuming. The optimum range for mercury determination for both methods are complementary and exhibit an overlapping measurable concentration range (OMCR) in which methylmercury can be indistinctly determined (75-100 ng g(-1) as mercury, wet basis). The suitability of both methods has been assayed with spiking experiences at levels within the OMCR with good recoveries. Both approaches have been validated with two certified reference materials (BCR-463, mercury and methylmercury in tuna fish; and NIST-2977, organic contaminants and trace metals in mussel tissue). Both procedures have been used for the analysis of three species of bivalve molluscs collected along the Andalusian coast (south Spain), all of them employed for human consumption (Chamelea gallina, Donax trunculus and Scrobicularia plana), and their potential use in routine analysis has been established.     

Mathematical modelling for conservation and management of gorgonians corals: youngs and olds,could they coexist?

Gorgonian corals are long-lived, slow-growing marine species dominating Mediterranean rocky bottoms. Endowed with complex morphologies they give a structure to the whole community, moreover, being efficient suspension feeders, they play a key role in plankton-benthos energy flow and CO₂${\text{CO}}_2$ storage. Thus, the structure and the development of benthic, hard bottom communities are linked to gorgonian survival. The red coral Corallium rubrum (L. 1758) is a precious gorgonian endemic to the Mediterranean Sea. Harvested and traded world-wide since ancient times red coral is a clear example of overexploited marine resource. This species is structured into self-seeding, genetically differentiated populations, some of which, living in the shallower part of the species bathymetric distribution, was recently affected by anomalous mortality events linked to global climate change. The co-occurrence of overharvesting and mass mortality could dramatically affect such populations. Demographic population models, widely applied by conservation biologists to check population viability and to project population trends over time are fundamental to foster survival of such populations matching harvesting to population growth rates. Therefore we set out a dynamic model of a genetically differentiated red coral population living in shallow waters. This population is characterised by small/young, crowded colonies and high recruitment rate. On the basis of the size–age structure determined for this population, a static life-history table, in which survival and reproduction coefficients of the different size–age classes were reported, has been set out. Demographic data were included in a non-linear, discrete, age-structured dynamic model, based on a Leslie-Lewis transition matrix. Our field data indicate that the recruits-to-larvae ratio is actually density-dependent. Such dependence, positive for low and negative for high density values, was included into the model and the effect of colonies of different size–age classes on recruits-to-larvae ratio was considered to be proportional to the number of polyps they have. We applied such model to simulate the trends of the studied population under different increases of survival and life-span. As some populations of gorgonians actually show the dominance of sparse, big/old colonies and low recruitment rate, while others are characterised by crowded, small/young colonies and high recruitment rate, we simulated the shift from the former to the latter structure increasing survival and life-span. Our results suggest that a dramatic mortality increase of bigger–older colonies (due, in the case of red coral to overfishing) could have determined the population structure we found.