433 research outputs found
Ultraslow light propagation in an inhomogeneously broadened rare-earth ion-doped crystal
We show that Coherent Population Oscillations effect allows to burn a narrow
spectral hole (26Hz) within the homogeneous absorption line of the optical
transition of an Erbium ion-doped crystal. The large dispersion of the index of
refraction associated with this hole permits to achieve a group velocity as low
as 2.7m/s with a ransmission of 40%. We especially benefit from the
inhomogeneous absorption broadening of the ions to tune both the transmission
coefficient, from 40% to 90%, and the light group velocity from 2.7m/s to
100m/s
Prioritising surveillance for alien organisms transported as stowaways on ships travelling to South Africa
The global shipping network facilitates the transportation and introduction of marine and terrestrial organisms to regions where they are not native, and some of these organisms become invasive. South Africa was used as a case study to evaluate the potential for shipping to contribute to the introduction and establishment of marine and terrestrial alien species (i.e. establishment debt) and to assess how this varies across shipping routes and seasons. As a proxy for the number of species introduced (i.e. 'colonisation pressure') shipping movement data were used to determine, for each season, the number of ships that visited South African ports from foreign ports and the number of days travelled between ports. Seasonal marine and terrestrial environmental similarity between South African and foreign ports was then used to estimate the likelihood that introduced species would establish. These data were used to determine the seasonal relative contribution of shipping routes to South Africa's marine and terrestrial establishment debt. Additionally, distribution data were used to identify marine and terrestrial species that are known to be invasive elsewhere and which might be introduced to each South African port through shipping routes that have a high relative contribution to establishment debt. Shipping routes from Asian ports, especially Singapore, have a particularly high relative contribution to South Africa's establishment debt, while among South African ports, Durban has the highest risk of being invaded. There was seasonal variation in the shipping routes that have a high relative contribution to the establishment debt of the South African ports. The presented method provides a simple way to prioritise surveillance effort and our results indicate that, for South Africa, port-specific prevention strategies should be developed, a large portion of the available resources should be allocated to Durban, and seasonal variations and their consequences for prevention strategies should be explored further. (Résumé d'auteur
Residence time and potential range : crucial considerations in modelling plant invasions
Wilson, J.R.U., et al. 2007. Residence time and potential range: crucial considerations in modelling plant invasions. Diversity and Distributions, 13:11-22. doi:10.1111/j.1366-9516.2006.00302.xThe original publication is available at https://onlinelibrary.wiley.com/journal/14724642A prime aim of invasion biology is to predict which species will become invasive, but
retrospective analyses have so far failed to develop robust generalizations. This is
because many biological, environmental, and anthropogenic factors interact to
determine the distribution of invasive species. However, in this paper we also argue
that many analyses of invasiveness have been flawed by not considering several
fundamental issues: (1) the range size of an invasive species depends on how much
time it has had to spread (its residence time); (2) the range size and spread rate are
mediated by the total extent of suitable (i.e. potentially invasible) habitat; and (3) the
range size and spread rate depend on the frequency and intensity of introductions
(propagule pressure), the position of founder populations in relation to the potential
range, and the spatial distribution of the potential range. We explored these considerations
using a large set of invasive alien plant species in South Africa for which accurate
distribution data and other relevant information were available.
Species introduced earlier and those with larger potential ranges had larger current
range sizes, but we found no significant effect of the spatial distribution of potential
ranges on current range sizes, and data on propagule pressure were largely unavailable.
However, crucially, we showed that: (1) including residence time and potential range
always significantly increases the explanatory power of the models; and (2) residence
time and potential range can affect which factors emerge as significant determinants
of invasiveness. Therefore, analyses not including potential range and residence time
can come to misleading conclusions. When these factors were taken into account, we
found that nitrogen-fixing plants and plants invading arid regions have spread faster
than other species, but these results were phylogenetically constrained. We also show
that, when analysed in the context of residence time and potential range, variation in
range size among invasive species is implicitly due to variation in spread rates, and,
that by explicitly assuming a particular model of spread, it is possible to estimate
changes in the rates of plant invasions through time.
We believe that invasion biology can develop generalizations that are useful
for management, but only in the context of a suitable null model.DST-NRF Centre of Excellence for Invasion Biology.
GDRI project ‘France South
Africa — Dynamics of biodiversity in Southern African ecosystems
and sustainable use in the context of global change: processes and
mechanisms involved’
ARC-Plant Protection Research Institute
provided funding for the SAPIA Project.https://onlinelibrary.wiley.com/doi/10.1111/j.1366-9516.2006.00302.xPublisher’s versio
Implementation of a science-action partnership to manage a threatened ecosystem in an urban context
Abstract: The gap between scientific knowledge and implementation of such knowledge in the fields of biodiversity conservation, environmental management and climate change adaptation, is widely recognized. The state of knowledge of urban ecosystems is generally quite poor, and there is a shortage of human capacity to implement scientifically-sound management practices at the local level, especially within institutions having the mandate of regulating land use planning. The need to bridge the science-action gap to improve decision-making for local land use planning and management, and thereby reduce the impacts of urbanization on ecosystems, has been recognized by eThekwini Municipality in the city of Durban, South Africa..
Finding music in music data : a summary of the DaCaRyH Project
The international research project, “Data science for the study of calypso-rhythm through history” (DaCaRyH), involved a collaboration between ethnomusicologists, computer scientists, and a composer. The primary aim of DaCaRyH was to explore how ethnomusicology could inform data science, and vice versa. Its secondary aim focused on creative applications of the results. This article summarises the results of the project, and more broadly discusses the benefits and challenges in such interdisciplinary research. It concludes with suggestions for reducing the barriers to similar work
Clinical, Biological and Genetic Analysis of Prepubertal Isolated Ovarian Cyst in 11 Girls
BACKGROUND: The cause of isolated gonadotropin-independent precocious puberty (PP) with an ovarian cyst is unknown in the majority of cases. Here, we describe 11 new cases of peripheral PP and, based on phenotypes observed in mouse models, we tested the hypothesis that mutations in the GNAS1, NR5A1, LHCGR, FSHR, NR5A1, StAR, DMRT4 and NOBOX may be associated with this phenotype. METHODOLOGY/PRINCIPAL FINDINGS: 11 girls with gonadotropin-independent PP were included in this study. Three girls were seen for a history of prenatal ovarian cyst, 6 girls for breast development, and 2 girls for vaginal bleeding. With one exception, all girls were seen before 8 years of age. In 8 cases, an ovarian cyst was detected, and in one case, suspected. One other case has polycystic ovaries, and the remaining case was referred for vaginal bleeding. Four patients had a familial history of ovarian anomalies and/or infertility. Mutations in the coding sequences of the candidate genes GNAS1, NR5A1, LHCGR, FSHR, NR5A1, StAR, DMRT4 and NOBOX were not observed. CONCLUSIONS/SIGNIFICANCE: Ovarian PP shows markedly different clinical features from central PP. Our data suggest that mutations in the GNAS1, NR5A1, LHCGR, FSHR StAR, DMRT4 and NOBOX genes are not responsible for ovarian PP. Further research, including the identification of familial cases, is needed to understand the etiology of ovarian PP
Assessing Biofuel Crop Invasiveness: A Case Study
BACKGROUND: There is widespread interest in biofuel crops as a solution to the world's energy needs, particularly in light of concerns over greenhouse-gas emissions. Despite reservations about their adverse environmental impacts, no attempt has been made to quantify actual, relative or potential invasiveness of terrestrial biofuel crops at an appropriate regional or international scale, and their planting continues to be largely unregulated. METHODOLOGY/PRINCIPAL FINDINGS: Using a widely accepted weed risk assessment system, we analyzed a comprehensive list of regionally suitable biofuel crops to show that seventy percent have a high risk of becoming invasive versus one-quarter of non-biofuel plant species and are two to four times more likely to establish wild populations locally or be invasive in Hawaii or in other locations with a similar climate. CONCLUSIONS/SIGNIFICANCE: Because of climatic and ecological similarities, predictions of biofuel crop invasiveness in Hawaii are applicable to other vulnerable island and subtropical ecosystems worldwide. We demonstrate the utility of an accessible and scientifically proven risk assessment protocol that allows users to predict if introduced species will become invasive in their region of interest. Other evidence supports the contention that propagule pressure created by extensive plantings will exacerbate invasions, a scenario expected with large-scale biofuel crop cultivation. Proactive measures, such as risk assessments, should be employed to predict invasion risks, which could then be mitigated via implementation of appropriate planting policies and adoption of the "polluter-pays" principle
Augmenting virtual spaces: affective feedback in computer games
Computer games can be considered a form of art insomuch as they are critiqued, revered and collected for their aesthetics in addition to their ludic qualities. Perhaps most significantly, computer games incite a plethora of emotional responses in their players as a deliberate and defining mechanism. However, unlike other forms of traditional media and art, another key feature of games is their intrinsic interactivity, reliance upon technology and non-linearity. These traits make them particularly noteworthy if one wishes to consider how art forms might respond and adapt to their audience’s emotions. The field of affective computing has been developing for several decades and many of its applications have been in the analysis and modelling of emotional responses to forms of media, such as music and film. In gaming, recent developments have led to an increasing number of consumer-grade biofeedback devices which are available on the market, some of which are explicitly sold as ‘gaming controllers’, giving rise to greater opportunity for affective feedback to be incorporated. In this chapter, a review is provided of the affective gaming field. Specifically, it is proposed that these developments give rise to interesting opportunities whereby virtual environments can be augmented with player affective and contextual information. An overview is provided of affective computing fundamentals and their manifestation in developments relating specifically to games. The chapter considers the impact this biometric information has upon games players, in terms of their experience of the game and the social connections between competitors. A number of associated practical and technological challenges are highlighted along with areas for future research and development activities. It is hoped that by exploring these developments in gaming that the longer established forms of art and media might be inspired to further embrace the possibilities offered by utilising affective feedback
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