1,850 research outputs found
Online Differential Thermal Isotope Analysis of Hydration Water in Minerals by Cavity Ringdown Laser Spectroscopy.
We have developed a new method for measuring the isotopic composition (ÎŽ18O and ÎŽD) of different types of bonded water (e.g., molecular water, hydroxyl) contained in hydrated minerals by coupling a thermal gravimeter (TG) and a cavity ringdown laser spectrometer (CRDS). The method involves precisely step-heating a mineral sample, allowing the separation of the different types of waters that are released at different temperatures. Simultaneously, the water vapor evolved from the mineral sample is analyzed for oxygen and hydrogen isotopes by CRDS. Isotopic values for the separate peaks are calculated by integrating the product of the water amounts and its isotopic values, after correcting for background. We provide examples of the application of the differential thermal isotope analysis (DTIA) method to a variety of hydrous minerals and mineraloids including gypsum, clays, and amorphous silica (opal). The isotopic compositions of the total water evolved from a set of natural gypsum samples by DTIA are compared with the results of a conventional offline water extraction method followed by CRDS analysis. The results from both methods are in excellent agreement, and precisions (1Ï) for ÎŽ18O (±0.12â°) and ÎŽD (±0.8â°) of the total gypsum hydration water from the DTIA method are comparable to that obtained by the offline method. A range of analytical challenges and solutions (e.g., spectroscopic interferences produced by VOCs in natural samples, isotopic exchange with structural oxygen, etc.) are discussed. The DTIA method has wide ranging applications for addressing fundamental problems across many disciplines in earth and planetary sciences, including paleoclimatology, sedimentology, volcanology, water exchange between the solid earth and hydrosphere, and water on Mars and other planetary bodies
Conceptual Ecological Modelling of Sublittoral Rock Habitats to Inform Indicator Selection
The purpose of this study is to produce a series of Conceptual Ecological Models (CEMs)
that represent sublittoral rock habitats in the UK. CEMs are diagrammatic representations of
the influences and processes that occur within an ecosystem. They can be used to identify
critical aspects of an ecosystem that may be studied further, or serve as the basis for the
selection of indicators for environmental monitoring purposes. The models produced by this
project are control diagrams, representing the unimpacted state of the environment free from
anthropogenic pressures.
It is intended that the models produced by this project will be used to guide indicator
selection for the monitoring of this habitat in UK waters. CEMs may eventually be produced
for a range of habitat types defined under the UK Marine Biodiversity Monitoring R&D
Programme (UKMBMP), which, along with stressor models, are designed to show the
interactions within impacted habitats, would form the basis of a robust method for indicator
selection. This project builds on the work to develop CEMs for shallow sublittoral coarse
sediment habitats (Alexander et al 2014).
The project scope included those habitats defined as âsublittoral rockâ. This definition
includes those habitats that fall into the EUNIS Level 3 classifications A3.1 Atlantic and
Mediterranean high energy infralittoral rock, A3.2 Atlantic and Mediterranean moderate
energy infralittoral rock, A3.3 Atlantic and Mediterranean low energy infralittoral rock, A4.1
Atlantic and Mediterranean high energy circalittoral rock, A4.2 Atlantic and Mediterranean
moderate energy circalittoral rock, and A4.3 Atlantic and Mediterranean low energy
circalittoral rock as well as the constituent Level 4 and 5 biotopes that are relevant to UK
waters. A species list of characterising fauna to be included within the scope of the models
was identified using an iterative process to refine the full list of species found within the
relevant Level 5 biotopes.
A literature review was conducted using a pragmatic and iterative approach to gather
evidence regarding species traits and information that would be used to inform the models
and characterise the interactions that occur within the sublittoral rock habitat. All information
gathered during the literature review was entered into a data logging pro-forma spreadsheet
that accompanies this report. Wherever possible, attempts were made to collect information
from UK-specific peer-reviewed studies, although other sources were used where
necessary. All data gathered was subject to a detailed confidence assessment. Expert
judgement by the project team was utilised to provide information for aspects of the models
for which references could not be sourced within the project timeframe.
A multivariate analysis approach was adopted to assess ecologically similar groups (based
on ecological and life history traits) of fauna from the identified species to form the basis of
the models. A model hierarchy was developed based on these ecological groups. One
general control model was produced that indicated the high-level drivers, inputs, biological
assemblages, ecosystem processes and outputs that occur in sublittoral rock habitats. In
addition to this, seven detailed sub-models were produced, which each focussed on a
particular ecological group of fauna within the habitat: âmacroalgaeâ, âtemporarily or
permanently attached active filter feedersâ, âtemporarily or permanently attached passive
filter feedersâ, âbivalves, brachiopods and other encrusting filter feedersâ, âtube building
faunaâ, âscavengers and predatory faunaâ, and ânon-predatory mobile faunaâ. Each sub-model
is accompanied by an associated confidence model that presents confidence in the links
between each model component. The models are split into seven levels and take spatial and
temporal scale into account through their design, as well as magnitude and direction of
influence. The seven levels include regional to global drivers, water column processes, local
inputs/processes at the seabed, habitat and biological assemblage, output processes, local
ecosystem functions, and regional to global ecosystem functions.
The models indicate that whilst the high level drivers that affect each ecological group are
largely similar, the output processes performed by the biota and the resulting ecosystem
functions vary both in number and importance between groups. Confidence within the
models as a whole is generally high, reflecting the level of information gathered during the
literature review.
Physical drivers which influence the ecosystem were found to be of high importance for the
sublittoral rock habitat, with factors such as wave exposure, water depth and water currents
noted to be crucial in defining the biological assemblages. Other important factors such as
recruitment/propagule supply, and those which affect primary production, such as
suspended sediments, light attenuation and water chemistry and temperature, were also
noted to be key and act to influence the food sources consumed by the biological
assemblages of the habitat, and the biological assemblages themselves.
Output processes performed by the biological assemblages are variable between ecological
groups depending on the specific flora and fauna present and the role they perform within
the ecosystem. Of particular importance are the outputs performed by the macroalgae
group, which are diverse in nature and exert influence over other ecological groups in the
habitat. Important output processes from the habitat as a whole include primary and
secondary production, bioengineering, biodeposition (in mixed sediment habitats) and the
supply of propagules; these in turn influence ecosystem functions at the local scale such as
nutrient and biogeochemical cycling, supply of food resources, sediment stability (in mixed
sediment habitats), habitat provision and population and algae control. The export of
biodiversity and organic matter, biodiversity enhancement and biotope stability are the
resulting ecosystem functions that occur at the regional to global scale.
Features within the models that are most useful for monitoring habitat status and change
due to natural variation have been identified, as have those that may be useful for monitoring
to identify anthropogenic causes of change within the ecosystem. Biological, physical and
chemical features of the ecosystem have been identified as potential indicators to monitor
natural variation, whereas biological factors and those physical /chemical factors most likely
to affect primary production have predominantly been identified as most likely to indicate
change due to anthropogenic pressures
Integrated ecologicalâeconomic fisheries modelsâEvaluation, review and challenges for implementation
Marine ecosystems evolve under many interconnected and area-specific pressures. To fulfil society's intensifying and diversifying needs while ensuring ecologically sustainable development, more effective marine spatial planning and broader-scope management of marine resources is necessary. Integrated ecological-economic fisheries models (IEEFMs) of marine systems are needed to evaluate impacts and sustainability of potential management actions and understand, and anticipate ecological, economic and social dynamics at a range of scales from local to national and regional. To make these models most effective, it is important to determine how model characteristics and methods of communicating results influence the model implementation, the nature of the advice that can be provided and the impact on decisions taken by managers. This article presents a global review and comparative evaluation of 35 IEEFMs applied to marine fisheries and marine ecosystem resources to identify the characteristics that determine their usefulness, effectiveness and implementation. The focus is on fully integrated models that allow for feedbacks between ecological and human processes although not all the models reviewed achieve that. Modellers must invest more time to make models user friendly and to participate in management fora where models and model results can be explained and discussed. Such involvement is beneficial to all parties, leading to improvement of mo-dels and more effective implementation of advice, but demands substantial resources which must be built into the governance process. It takes time to develop effective processes for using IEEFMs requiring a long-term commitment to integrating multidisciplinary modelling advice into management decision-making.</p
Plants lacking the main light-harvesting complex retain photosystem II macro-organization
Photosystem II (PSII) is a key component of photosynthesis, the process of converting sunlight into the chemical energy of life. In plant cells, it forms a unique oligomeric macrostructure in membranes of the chloroplasts. Several light-harvesting antenna complexes are organized precisely in the PSII macrostructureâthe major trimeric complexes (LHCII) that bind 70% of PSII chlorophyll and three minor monomeric complexesâwhich together form PSII supercomplexes. The antenna complexes are essential for collecting sunlight and regulating photosynthesis, but the relationship between these functions and their molecular architecture is unresolved. Here we report that antisense Arabidopsis plants lacking the proteins that form LHCII trimers have PSII supercomplexes with almost identical abundance and structure to those found in wild-type plants. The place of LHCII is taken by a normally minor and monomeric complex, CP26, which is synthesized in large amounts and organized into trimers. Trimerization is clearly not a specific attribute of LHCII. Our results highlight the importance of the PSII macrostructure: in the absence of one of its main components, another protein is recruited to allow it to assemble and function
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Early Ultraviolet Observations of Type IIn Supernovae Constrain the Asphericity of Their Circumstellar Material
© 2020. The American Astronomical Society. All rights reserved.. We present a survey of the early evolution of 12 Type IIn supernovae (SNe IIn) at ultraviolet and visible light wavelengths. We use this survey to constrain the geometry of the circumstellar material (CSM) surrounding SN IIn explosions, which may shed light on their progenitor diversity. In order to distinguish between aspherical and spherical CSM, we estimate the blackbody radius temporal evolution of the SNe IIn of our sample, following the method introduced by Soumagnac et al. We find that higher-luminosity objects tend to show evidence for aspherical CSM. Depending on whether this correlation is due to physical reasons or to some selection bias, we derive a lower limit between 35% and 66% for the fraction of SNe IIn showing evidence for aspherical CSM. This result suggests that asphericity of the CSM surrounding SNe IIn is common - consistent with data from resolved images of stars undergoing considerable mass loss. It should be taken into account for more realistic modeling of these events
Visual outcomes and predictors in optic pathway glioma: a single centre study
BACKGROUND/AIMS: Optic pathway gliomas (OPGs) may cause progressive visual loss despite chemotherapy. Newer, less toxic treatments might be given earlier, depending on visual prognosis. We aimed to investigate the prognostic value of visual evoked potentials (VEP) and optical coherence tomography (OCT). METHODS: A retrospective study of OPG patients (treated 2003â2017) was conducted. Primary outcome was PEDIG category visual acuity in better and worse eyes (goodââ=â0.7 logMAR). Binary logistic regression analysis was used to identify predictors of these outcomes. RESULTS: 60 patients (32 Neurofibromatosis type 1 [NF1] and 28 sporadic) had median presentation age 49 months (range 17â183) (NF1) and 27 months (range 4â92) (sporadic). Median follow up was 82 months (range 12â189 months). At follow up 24/32 (75%) of NF1 children and 14/28 (50%) of sporadic children had good better eye visual acuity and 11/32 (34%) of NF1 children and 15/28 (54%) of sporadics had poor worse eye acuity. Mean peripapillary retinal nerve fibre layer (RNFL) thickness predicted good better eye final acuity (OR 0.799, 95%CI 0.646â0.987, pâ=â0.038). Presenting with visual symptoms (OR 0.22 95% CI 0.001â0.508, pâ=â0.017) and poorer VEP scores (OR 2.35 95% CI 1.1â5.03, pâ=â0.027) predicted poor worse eye final acuity. 16 children had homonymous hemianopias at follow up, predicted by poor presenting binocular VEP score (OR 1.449 95%CI 1.052â1.995, pâ=â0.02). CONCLUSIONS: We found that both RNFL thickness on OCT and VEP were useful in predicting future visual acuity and vision and potentially in planning treatment. We had a high prevalence of homonymous hemianopia
Standard decomposition of expansive ergodically supported dynamics
In this work we introduce the notion of weak quasigroups, that are quasigroup
operations defined almost everywhere on some set. Then we prove that the
topological entropy and the ergodic period of an invertible expansive
ergodically supported dynamical system with the shadowing property
establishes a sufficient criterion for the existence of quasigroup operations
defined almost everywhere outside of universally null sets and for which is
an automorphism. Furthermore, we find a decomposition of the dynamics of in
terms of -invariant weak topological subquasigroups.Comment: 18 pages, the conditions on the entropy in Theorem 3.5 was improved.
Some small changes in the text, by adding more explanation
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