1,908 research outputs found
Stabilization, pointing and command control of a balloon-borne 1-meter telescope
A 1-meter balloon-borne telescope has been constructed and flown to observe far-infrared radiation from celestial sources. The attitude control systems must perform to the diffraction limit of the telescope for stabilization and have positioning capability for source acquisition. These and associated systems are discussed in detail, as is the command control of the payload as a whole
Identifying predictable foraging habitats for a wide-ranging marine predator using ensemble ecological niche models
Aim
Ecological niche modelling can provide valuable insight into species' environmental preferences and aid the identification of key habitats for populations of conservation concern. Here, we integrate biologging, satellite remote-sensing and ensemble ecological niche models (EENMs) to identify predictable foraging habitats for a globally important population of the grey-headed albatross (GHA) Thalassarche chrysostoma.
Location
Bird Island, South Georgia; Southern Atlantic Ocean.
Methods
GPS and geolocation-immersion loggers were used to track at-sea movements and activity patterns of GHA over two breeding seasons (n = 55; brood-guard). Immersion frequency (landings per 10-min interval) was used to define foraging events. EENM combining Generalized Additive Models (GAM), MaxEnt, Random Forest (RF) and Boosted Regression Trees (BRT) identified the biophysical conditions characterizing the locations of foraging events, using time-matched oceanographic predictors (Sea Surface Temperature, SST; chlorophyll a, chl-a; thermal front frequency, TFreq; depth). Model performance was assessed through iterative cross-validation and extrapolative performance through cross-validation among years.
Results
Predictable foraging habitats identified by EENM spanned neritic ( 0.5 mg mâ3) and frequent manifestation of mesoscale thermal fronts. Our results confirm previous indications that GHA exploit enhanced foraging opportunities associated with frontal systems and objectively identify the APFZ as a region of high foraging habitat suitability. Moreover, at the spatial and temporal scales investigated here, the performance of multi-model ensembles was superior to that of single-algorithm models, and cross-validation among years indicated reasonable extrapolative performance.
Main conclusions
EENM techniques are useful for integrating the predictions of several single-algorithm models, reducing potential bias and increasing confidence in predictions. Our analysis highlights the value of EENM for use with movement data in identifying at-sea habitats of wide-ranging marine predators, with clear implications for conservation and management
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âIf you look the part youâll get the jobâ: should career professionals help clients to enhance their career image?
This article presents a critical exploration of the role of career professionals in supporting people to reflect on and enhance their appearance, attractiveness and self-presentation (career image). The article is conceptual and based on a review of the broader literature on career success, appearance and attractiveness. It explores the evidence for a relationship between attractiveness and career, and the authors propose a conceptual framework in which career image is comprised of three elements (interpersonal skills, aesthetic presentation and beauty). The paper examines a possible role for career professionals in relation to this and then critically examines this role and concludes with the proposition of a research agenda in this area
High-pressure investigations of CaTiO3 up to 60 GPa using X-ray diffraction and Raman spectroscopy
In this work, we investigate calcium titanate (CaTiO3 - CTO) using X-ray
diffraction and Raman spectroscopy up to 60 and 55 GPa respectively. Both
experiments show that the orthorhombic Pnma structure remains stable up to the
highest pressures measured, in contradiction to ab-initio predictions. A fit of
the compression data with a second-order Birch-Murnaghan equation of state
yields a bulk modulus K0 of 181.0(6) GPa. The orthorhombic distortion is found
to increase slightly with pressure, in agreement with previous experiments at
lower pressures and the general rules for the evolution of perovskites under
pressure. High-pressure polarized Raman spectra also enable us to clarify the
Raman mode assignment of CTO and identify the modes corresponding to rigid
rotation of the octahedra, A-cation shifts and Ti-O bond stretching. The Raman
signature is then discussed in terms of compression mechanisms.Comment: 11 pages, 6 figures, 4 table
Siglec receptors impact mammalian lifespan by modulating oxidative stress.
Aging is a multifactorial process that includes the lifelong accumulation of molecular damage, leading to age-related frailty, disability and disease, and eventually death. In this study, we report evidence of a significant correlation between the number of genes encoding the immunomodulatory CD33-related sialic acid-binding immunoglobulin-like receptors (CD33rSiglecs) and maximum lifespan in mammals. In keeping with this, we show that mice lacking Siglec-E, the main member of the CD33rSiglec family, exhibit reduced survival. Removal of Siglec-E causes the development of exaggerated signs of aging at the molecular, structural, and cognitive level. We found that accelerated aging was related both to an unbalanced ROS metabolism, and to a secondary impairment in detoxification of reactive molecules, ultimately leading to increased damage to cellular DNA, proteins, and lipids. Taken together, our data suggest that CD33rSiglecs co-evolved in mammals to achieve a better management of oxidative stress during inflammation, which in turn reduces molecular damage and extends lifespan
Aircraft-borne, laser-induced fluorescence instrument for the in situ detection of hydroxyl and hydroperoxyl radicals
The odd-hydrogen radicals OH and HO2 are central to most of the gas-phase chemical transformations that occur in the atmosphere. Of particular interest is the role that these species play in controlling the concentration of stratospheric ozone. This paper describes an instrument that measures both of these species at volume mixing ratios below one part in 10(exp 14) in the upper troposphere and lower stratosphere. The hydroxyl radical (OH) is measured by laser induced fluorescence at 309 nm. Tunable UV light is used to pump OH to the first electric state near 282 nm. the laser light is produced by a high-repetition rate pulsed dye-laser powered with all solid-state pump lasers. HO2 is measured as OH after gas-phase titration with nitric oxide. Measurements aboard a NASA ER-2 aircraft demonstrate the capability of this instrument to perform reliably with very high signal-to-noise ratios (greater than 30) achieved in short integration times (less than 20 sec)
Towards a global understanding of the drivers of marine and terrestrial biodiversity
Understanding the distribution of lifeâs variety has driven naturalists and scientists for centuries, yet this has been constrained both by the available data and the models needed for their analysis. Here we compiled data for over 67,000 marine and terrestrial species and used artificial neural networks to model species richness with the state and variability of climate, productivity, and multiple other environmental variables. We find terrestrial diversity is better predicted by the available environmental drivers than is marine diversity, and that marine diversity can be predicted with a smaller set of variables. Ecological mechanisms such as geographic isolation and structural complexity appear to explain model residuals and also identify regions and processes that deserve further attention at the global scale. Improving estimates of the relationships between the patterns of global biodiversity, and the environmental mechanisms that support them, should help in efforts to mitigate the impacts of climate change and provide guidance for adapting to life in the Anthropocene
Landau theory applied to phase transitions in calcium orthotungstate and isostructural compounds
The pressure-driven tetragonal-to-monoclinic phase transition in CaWO4 and
related scheelite-structured orthotungstates is analysed in terms of
spontaneous strains. Based upon our previous high-pressure x-ray diffraction
results and the Landau theory, it is suggested that the
scheelite-to-fergusonite transition is of second order in nature.Comment: 14 pages, 3 figure
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