1,720,963 research outputs found
From dust devils to lipid biomarkers: a planetary perspective of the Makgadikgadi Pans, Central Botswana
No full textThe Makgadikgadi Basin in Botswana hosts a system of salt lakes, which developed from the Upper Pleistocene onwards due to gradual shrinking of the giant Lake Palaeo-Makgadikgadi in the last 2 million years. This lake, in the central Kalahari is the key to understand the climatic variability in southern Africa in the Quaternary and holds important role for the evolution of numerous taxa. Stratigraphic and palaeoclimatic studies of this area are complicated by the influence of several factors, such as a complex history of regional tectonic activities, as well as climatic changes coupled with dryland diagenetic processes. In the Makgadikgadi Pans, in fact, there is an overlap of processes linked to groundwater upwelling, seasonal flooding and dry climate pedogenesis (including formation of calcretes and silcretes), all shaped by an intense aeolian activity.
It is the overlap of these morphological and geological factors that create a unique terrestrial analogue for the exploration of Mars where scientists can study adaptation strategies of extremophiles, diagenesis of biomarker, but also test sensors that were built to study the atmosphere of Mars and need calibration under certain environmental conditions.
Here we introduce the new frontiers of research conducted in the Makgadikgadi Pans and we provide a new background on the geology of the basin and the evolution of the sedimentary system in the Makgadikgadi. In particular, we provide detailed sedimentological analyses of the shallow sub-surface of the Makgadikgadi Pans combining physical and geochemical properties of the pan sediments with the first comprehensive study of paleontological proxies (ostracods) in order to establish trends in the environmental changes in the area from the Late Quaternary.
The research activities of the last few years in the Makgadikgadi Pans provided new benchmarking data that will not only shed light on one of the largest evaporitic basins in the world but also support further investigations in the field of planetary sciences and astrobiology
Biosensor-based Methods for Detection of Microcystins as Early Warning Systems
Get PDFCyanobacteria blooms are a water menace since they produce potent toxins that have been implicated in poisonings and deaths of humans and animals after consumption or contact with cyanotoxin-contaminated water. Of particular concern are cyanotoxins called microcystins, which are hepatotoxic cyclic peptides known to promote development of liver tumors in humans and animals. The high toxicity and increased occurrence of microcystins in drinking and surface waters have stimulated worldwide investigations and prompted the design of analytical techniques for the early stages of detection in order to protect human exposure to these fatal toxins. The major challenge for the accurate determination of microcystins is the large number of naturally occurring variants. To date, there are more than 80 different microcystin variants, and depending on the substituted amino acids in the structure, the hydrophobicity varies making it difficult for a single assay determination. Another problem is the low concentrations of individual toxins, which often are below the detection limits of existing assays. In order to achieve low concentrations detection, there is a need for a sensitive assay platform that gives a fast, quantitative determination of the microcystins below the stipulated limit. Regulations set for the monitoring of allowable microcystins levels in water are also becoming more stringent for water authorities to meet. Also, the predication of the algal blooming patterns becomes increasingly complicated. Of recent, algal blooms have shown to appear unexpectedly or come as late blooms due to changing weather patterns. Increased awareness of microcystin intoxications to the public that relies on surface waters has led to the World Health Organization (WHO) setting a guideline with a concentration limit for microcystins in drinking water of 1µg/L (10-9 M). Since these toxins are not efficiently removed during the conventional water treatment process, emphasis on alternative analytical methods are indeed required the protection of drinking water supplies. In addition, the detection of cyanotoxins at very low concentrations is necessary for making a rapid intervention before the toxin concentrations reach harmful levels. In this thesis work, biosensor-based methods for ultra-sensitive detection of microcystins have been developed. Different biosensor configurations were investigated where the first study involved the development of a capacitive immunoassay using specific antibodies able to recognize a special part in microcystin structure called 3-amino-9-methoxy-2,6,8-trymethyl-10-phenyldeca-4,6-dienoic acid (Adda). The study showed that microcystins could be detected at very low concentrations (down to 10-14 moles per liter) within 37 minutes. The developed biosensor was further applied for total analysis of microcystins produced in a batch culture of microcystin, aided by mass spectrometry to identify the different microcystin variants. A flow-ELISA-amperometric biosensor was also developed and investigated and showed an apparent rapid assay of 16 minutes (limit of detection 10-11 M). Finally, a micro-contact based molecularly imprinted polymer technique was explored as a cost-effective alternative for the expensive antibodies as ligands in the capacitive biosensor assay. In all cases, the developed biosensors showed both high selectivity and sensitivity and met the allowable detection limit set by WHO. In conclusion, the studies presented in this thesis demonstrated that low toxin determination with minimal sample preparation can be achieved using the investigated biosensor technology, and that miniaturization of the system can allow for portability and can be helpful for in situ monitoring of microcystins where sophisticated infrastructure is lacking. Also, the studies emphasize the need for more development of biorecognition molecules that will be able to monitor the group of microcystins at the same sensitivity while being able to discriminate against other non-related molecules. Automated and integrated system configurations used in all the experiments facilitated the analysis process by decreasing time and eliminating possible manual sampling handling errors
Biosensor-based Methods for Detection of Microcystins as Early Warning Systems [Elektronisk resurs]
No full textPopular Abstract in English Global invasion of our precious watercourses by cyanobacteria poses great threat to human- and animal health by deteriorating water systems. In fact, this problem is not likely to be solved in the near future as cyanobacteria are associated with pollution of waterways. Consequently, water sources are subject to contamination by natural toxins produced by abundant growth of cyanobacterial blooms all over the world. The produced toxins, which may be present at low levels without harm to humans or animals, can rapidly increase to become a dire health risk under certain environmental conditions. In addition, the rising global temperatures intensify the situation and excessive nutrient loading of watercourses through increased human activities by the expanding global populations, resulting in growth promotion of the potent toxin-producing blooms in surface waters. In most cases, surface water supplies potable water to communities and hence any bloom expansion raises concern over human health safety. Communities with resource-limited settings often depend directly on water sources with limited treatment infrastructure available. As such, the presence of these potent cyanotoxins especially microcystins limit the use of the water. Although potent microcystins are known to occur in surface waters, there is still no known general method for their removal from contaminated water when the concentration increases and reaches lethal levels, thus reflecting a need for emergent mitigations. Several detection methods are available for detecting microcystins but are neither sensitive enough to measure low concentrations nor user-friendly. Therefore, the pressure to detect these toxins in trace amounts has led to increased research on development of analytical systems such as biosensors to overcome this problem. In this thesis, sensitive biosensors have been developed for microcystin detection. Biosensor configurations combined with the advances in nanotechnology result in platforms with improved detection sensitivities compared to traditional analytical methods. It is expected that this new approach will dramatically reduce the analysis time, thereby reducing overall analysis costs without any loss of sensitivity and precision. These systems are made into small portable devices that can be taken to the site of contamination and quickly analyze the water. Mass production of such detection devices could help the communities out there who are in desperate need for clean and microcystin-free water.Cyanobacteria blooms are a water menace since they produce potent toxins that have been implicated in poisonings and deaths of humans and animals after consumption or contact with cyanotoxin-contaminated water. Of particular concern are cyanotoxins called microcystins, which are hepatotoxic cyclic peptides known to promote development of liver tumors in humans and animals. The high toxicity and increased occurrence of microcystins in drinking and surface waters have stimulated worldwide investigations and prompted the design of analytical techniques for the early stages of detection in order to protect human exposure to these fatal toxins. The major challenge for the accurate determination of microcystins is the large number of naturally occurring variants. To date, there are more than 80 different microcystin variants, and depending on the substituted amino acids in the structure, the hydrophobicity varies making it difficult for a single assay determination. Another problem is the low concentrations of individual toxins, which often are below the detection limits of existing assays. In order to achieve low concentrations detection, there is a need for a sensitive assay platform that gives a fast, quantitative determination of the microcystins below the stipulated limit. Regulations set for the monitoring of allowable microcystins levels in water are also becoming more stringent for water authorities to meet. Also, the predication of the algal blooming patterns becomes increasingly complicated. Of recent, algal blooms have shown to appear unexpectedly or come as late blooms due to changing weather patterns. Increased awareness of microcystin intoxications to the public that relies on surface waters has led to the World Health Organization (WHO) setting a guideline with a concentration limit for microcystins in drinking water of 1µg/L (10-9 M). Since these toxins are not efficiently removed during the conventional water treatment process, emphasis on alternative analytical methods are indeed required the protection of drinking water supplies. In addition, the detection of cyanotoxins at very low concentrations is necessary for making a rapid intervention before the toxin concentrations reach harmful levels. In this thesis work, biosensor-based methods for ultra-sensitive detection of microcystins have been developed. Different biosensor configurations were investigated where the first study involved the development of a capacitive immunoassay using specific antibodies able to recognize a special part in microcystin structure called 3-amino-9-methoxy-2,6,8-trymethyl-10-phenyldeca-4,6-dienoic acid (Adda). The study showed that microcystins could be detected at very low concentrations (down to 10-14 moles per liter) within 37 minutes. The developed biosensor was further applied for total analysis of microcystins produced in a batch culture of microcystin, aided by mass spectrometry to identify the different microcystin variants. A flow-ELISA-amperometric biosensor was also developed and investigated and showed an apparent rapid assay of 16 minutes (limit of detection 10-11 M). Finally, a micro-contact based molecularly imprinted polymer technique was explored as a cost-effective alternative for the expensive antibodies as ligands in the capacitive biosensor assay. In all cases, the developed biosensors showed both high selectivity and sensitivity and met the allowable detection limit set by WHO. In conclusion, the studies presented in this thesis demonstrated that low toxin determination with minimal sample preparation can be achieved using the investigated biosensor technology, and that miniaturization of the system can allow for portability and can be helpful for in situ monitoring of microcystins where sophisticated infrastructure is lacking. Also, the studies emphasize the need for more development of biorecognition molecules that will be able to monitor the group of microcystins at the same sensitivity while being able to discriminate against other non-related molecules. Automated and integrated system configurations used in all the experiments facilitated the analysis process by decreasing time and eliminating possible manual sampling handling errors
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Ethical considerations for analogue fieldwork in extreme environments
No full textRecent movements towards decolonizing the university and promoting racial justice and equality in social relations have highlighted and challenged the colonial influences on contemporary science and scientific knowledge production. These colonial legacies have a direct bearing on power relations between the Global North and the Global South, as well as collaborations and partnerships with local scholars and local communities. Astrobiology is one scholarly discipline that often makes use of remote sites in the Global South. Here we examine the ethical implications of carrying out fieldwork that involves accessing and sampling these extreme environments. Experiences of local and international collaborations in these sites have highlighted the importance of co-learning when engaging with diverse communities of scientists and right holders living on and around field sites. We argue that adopting an ethical approach to research in these environments is relevant also to research on other celestial bodies and to the future of space exploration. We propose that understanding space and Earth as interconnected domains, mutually shaped by scientific theories and practices, calls for a new terminology: ‘planetary ethics’, which places attention on this interconnection
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Diversity of Microbial Mats in the Makgadikgadi Salt Pans, Botswana
Get PDFThe Makgadikgadi Salt Pans are the remnants of a mega paleo-lake system in the central Kalahari, Botswana. Today, the Makgadikgadi Basin is an arid to semi-arid area receiving water of meteoric origin during the short, wet season. Large microbial mats, which support primary production, are formed due to desiccation during the dry season. This study aimed to characterise the microbial diversity of the microbial mats and the underlying sediment. The focus was the Ntwetwe Pan, located west of the Makgadikgadi Basin. Metagenomic analyses demonstrated that the mats consisted of a high relative abundance of Cyanobacteriota (synonym Cyanobacteria) (20.50–41.47%), Pseudomonadota (synonym Proteobacteria) (15.71 to 32.18%), and Actinomycetota (synonym Actinobacteria) (8.53–32.56%). In the underlying sediments, Pseudomonadota, Actinomycetota, and Euryarchaeota represented over 70% of the community. Localised fluctuations in water content and pH did not significantly affect the microbial diversity of the sediment or the mats
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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