Quantifying the Effect of Atmospherically-Induced Pointing Errors in Optical Geostationary Satellite Feeder Links Using Transmitter Diversity

Optical links to geostationary (GEO) satellites suffer from atmospherically-induced beam wander which leads to pointing errors at the satellite causing deep fades. In this paper, we show the benefit of transmitter diversity in reducing the fades caused by beam wander. We derive an analytical expression for the reduction of overall scintillation index for a given number of transmitted beams with Gaussian profile in a multiple-input single-output (MISO) system considering solely the effect of beam wander. The transmitted power, beam divergence angle and pointing jitter are kept as free parameters as in the real situation. Moreover, the optimized ratio of transmitted powers between multiple beams is obtained though simulations for a two-fold transmitter diversity to obtain minimum overall power scintillation index (PSI)

High Treosulfan Exposure is Associated with Early Toxicity in Pediatric Hematopoietic Stem Cell Transplantation: A Prospective Multicenter Study

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Synthesis of bicyclic tripeptides inspired by the ABC-ring system of vancomycin through ruthenium-based cyclization chemistries

The synthesis of a bicyclic tripeptide that mimics the ABC ring system of vancomycin is described by using a ring closing metathesis (RCM) – peptide coupling – ruthenium-catalyzed azide-alkyne cycloaddition (RuAAC) strategy

A horizon scan of global biological conservation issues for 2024

We present the results of our 15th horizon scan of novel issues that could influence biological conservation in the future. From an initial list of 96 issues, our international panel of scientists and practitioners identified 15 that we consider important for societies worldwide to track and potentially respond to. Issues are novel within conservation or represent a substantial positive or negative step-change with global or regional extents. For example, new sources of hydrogen fuel and changes in deep-sea currents may have profound impacts on marine and terrestrial ecosystems. Technological advances that may be positive include benchtop DNA printers and the industrialisation of approaches that can create high-protein food from air, potentially reducing the pressure on land for food production

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

The role of regeneration in plant niche differentiation and habitat specialization

To predict the effects of environmental change and nature management on the distribution of plant species, it is crucial to understand the mechanisms of plant niche differentiation and habitat specialization. The importance to habitat specialization of particular plant traits and requirement of the regenerative phase of the plants life has received scanty interest. Our experiments on seed germination and seedling establishment have shown that plant strategies in the regenerative phase contribute strongly to the habitat specialization of species. A conceptual model explains how germination strategies and seasonal environmental conditions interact to allow certain species to establish in forests, whereas other species are effectively excluded from establishing under the prevailing adverse conditions that characterize forest floor environments throughout the year. Also the specific adaptations in the seedling stage contribute to the specialization of species to their habitat. Specialization to shaded habitats was associated with more conservative growth strategy, i.e. showing a more modest growth response to increasing light. Species from open habitats showed a stronger shade avoidance response than forest species, which is more adaptive in herbaceous vegetation than in a forest floor herb layer. Seed size also appeared to be important for the recruitment success of plants in different habitats. Seed size is a compromise between a numeric advantage of producing many seeds against a recruitment advantage, e.g. higher resistance to environmental adverse conditions, of larger seeds. In our study, the recruitment advantage of larger seeded species relative to smaller seeded species appeared to increase with from meadows and open forests to closed canopy-forest. Besides the responses of individual plant species to the environment, community assembly processes and the resulting species and trait composition of local assemblages has also been studied in this thesis. Within-community trait variation appeared to be larger than between-community traits variation for seed mass, plant height, lateral spread and species indices of competition, stress and ruderality in rocky habitat vegetation. This would indicate that limiting similarity plays a role in structuring plant communities in rocky habitats if the underlying environmental gradient was mainly varying in productivity. However, due to the shallow soils, rocky habitats are drought-prone by nature and chemical stress from aluminium increases towards low soil pH parallel to phosphorus. In the last paper, we studied the effect of deterministic processes on the reproducibility of species assemblages, when the stochastic factor of seed dispersal is controlled for. In synthetically assembled plant communities, patterns in species composition were highly repeatable at each level of soil fertility, indicating strong deterministic processes in community assembly. A severe drought resulted in disproportionately high mortality in the high soil fertility microcosms, where a dense sward of fast-grown and hence drought-susceptible plant individuals was formed. The findings in this thesis reveal an important role of regeneration in niche differentiation between species and the resulting habitat specialization. Plants strategies in the regenerative phase contribute strongly to the habitat specialization of species and their adaptation to specific habitats. The abiotic environment causes species to separate along productivity gradients, and simultaneously affect local biotic interactions by governing species’ relative abundances

Spectrally Efficient Transmitter Diversity Scheme for Optical Satellite Feeder Links Employing Multiple Signal Sidebands

Optical links between ground stations and geostationary orbit (GEO) satellites suffer from the atmospherically induced phase piston and intensity fluctuations. This aggravates stable signal detection in the uplink scenario. In this work transmitter diversity is studied as a fading mitigation technique in GEO satellite feeder uplinks. A single sideband scheme is used as a spectrally efficient frequency division technique compatible with intensity modulation and direct detection. A spectral efficiency of 0.56 bit/s/Hz with twofold diversity gaining 2.3 dB at BER = 10-3 was obtained by simulation

Recruitment advantage of large seeds is greater in shaded habitats

Large seeds are assumed to have higher probability of successful recruitment than small seeds. This is because larger seeds give rise to larger seedlings and larger seedlings better withstand environmental hazards like deep shade and drought. Biotic and abiotic limitations to seedling growth and survival, and conversely availability of safe sites for recruitment, vary along environmental gradients and between habitat types. Thus, the value to plant species of possessing large seeds may differ between plant communities. We analyzed the relationship between seed mass and per-seed recruitment success (seedlings established per number of seeds produced) along an environmental gradient from open grassland to closed-canopy forest using data collected by Uuno Perttula in southern Finland in 1934. We found that larger seeds have greater recruitment success relative to smaller seeds in all investigated communities. However, the recruitment success of large seeds relative to small seeds strongly increased from grassland and open forest to closed-canopy forest. Of the measured environmental variables, canopy closure most strongly explained this increase. This indicates a strong direct effect of deep shade on seedling survival in natural plant communities. Additional explanatory power was associated with soil moisture. Litter cover, moss cover, and soil pH did not contribute to explaining the variation in relative recruitment success of larger seeds. Thus, the advantage of large seeds in recruitment success is pronounced in deeply shaded forest but may be insignificant in open vegetation

Seedling stage strategies as a means of habitat specialization in herbaceous plants.

The regeneration niche has been little investigated in studies of community assembly and plant distribution. We examined adaptive associations between seedling traits and habitat specialization. Two habitat contrasts were investigated across several evolutionary lineages of angiosperms: species specialized to forest vs. open habitats and to dry vs. wet habitats. We also tested whether effects of shade and drought vary independently or, alternatively, if shade may amplify effects on drought-stressed plants. Seedling response in terms of growth rate, height, slenderness, specific leaf area (SLA) and degree of elongation (longest internode; petiole or leaf-sheath depending on species' morphology) to light and watering treatments was assessed. We used a factorial design involving three light regimes and two watering frequencies. The open-shaded habitat contrast and the dry-wet habitat contrast were investigated using six and five pairs of congeneric species, respectively. The congeneric species pair design controlled for confounding effects of evolutionary history prior to divergence in habitat specialization. Seedling growth rate generally decreased with shade and reduced watering frequency. Plant height was generally largest at intermediate light. Specialization to shaded habitats was associated with a more conservative growth strategy, i.e. showing a more modest growth response to increasing light. Species from all habitats showed the highest relative elongation at intermediate light, except for the moist-habitat species, for which elongation increased with shade. Contrary to our expectations, species from dry habitats grew bigger than species from moist habitats in all treatments. SLA responded to the light treatment, but not to watering regime. The contrasting light and moisture conditions across habitats appear to not have selected for differences in SLA. We conclude that seedling phase strategies of resource allocation in temperate herbs contribute to their habitat specialization. Habitat-specific seedling strategies and trade-offs in response to resource availability and environmental conditions may be important to adaptive specialization