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Fluoreszenzfarbstoffe mit Dioxolobenzodioxol-Grundgerüst: Synthese, Untersuchungen und Anwendungen
(2013)
The nutrition of animal consumers is an important regulator of ecological processes due to its effects on their physiology, life-history and behaviour. Understanding the ecological effects of poor nutrition depends on correctly diagnosing the nature and strength of nutritional limitation. Despite the need to assess nutritional limitation, current approaches to delineating nutritional constraints can be non-specific and imprecise. Here, we consider the need and potential to develop new complementary approaches to the study of nutritional constraints on animal consumers by studying and using a suite of established and emerging biochemical and molecular responses. These nutritional indicators include gene expression, transcript regulators, protein profiling and activity, and gross biochemical and elemental composition. The potential applications of nutritional indicators to ecological studies are highlighted to demonstrate the value that this approach would have to future studies in community and ecosystem ecology.
Context. The Tarantula Nebula (a.k.a. 30 Dor) is a spectacular star-forming region in the Large Magellanic Cloud (LMC), seen through gas in the Galactic disc and halo. Diffuse interstellar bands (DIBs) offer a unique probe of the diffuse, cool-warm gas in these regions.
Aims. The aim is to use DIBs as diagnostics of the local interstellar conditions, whilst at the same time deriving properties of the yet-unknown carriers of these enigmatic spectral features.
Methods. Spectra of over 800 early-type stars from the Very Large Telescope Flames Tarantula Survey (VFTS) were analysed. Maps were created, separately, for the Galactic and LMC absorption in the DIBs at 4428 and 6614 angstrom and - in a smaller region near the central cluster R 136 - neutral sodium (the Na ID doublet); we also measured the DIBs at 5780 and 5797 angstrom.
Results. The maps show strong 4428 and 6614 angstrom DIBs in the quiescent cloud complex to the south of 30 Dor but weak absorption in the harsher environments to the north (bubbles) and near the OB associations. The Na maps show at least five kinematic components in the LMC and a shell-like structure surrounding R 136, and small-scale structure in the Milky Way. The strengths of the 4428, 5780, 5797 and 6614 angstrom DIBs are correlated, also with Na absorption and visual extinction. The strong 4428 angstrom DIB is present already at low Na column density but the 6614, 5780 and 5797 angstrom DIBs start to be detectable at subsequently larger Na column densities.
Conclusions. The carriers of the 4428, 6614, 5780 and 5797 angstrom DIBs are increasingly prone to removal from irradiated gas. The relative strength of the 5780 and 5797 angstrom DIBs clearly confirm the Tarantula Nebula as well as Galactic high-latitude gas to represent a harsh radiation environment. The resilience of the 4428 angstrom DIB suggests its carrier is large, compact and neutral. Structure is detected in the distribution of cool-warm gas on scales between one and > 100 pc in the LMC and as little as 0.01 pc in the Sun's vicinity. Stellar winds from the central cluster R 136 have created an expanding shell; some infalling gas is also detected, reminiscent of a galactic "fountain".
The near-infrared is an important part of the spectrum in astronomy, especially in cosmology because the light from objects in the early universe is redshifted to these wavelengths. However, deep near-infrared observations are extremely difficult to make from ground-based telescopes due to the bright background from the atmosphere. Nearly all of this background comes from the bright and narrow emission lines of atmospheric hydroxyl (OH) molecules. The atmospheric background cannot be easily removed from data because the brightness fluctuates unpredictably on short timescales. The sensitivity of ground-based optical astronomy far exceeds that of near-infrared astronomy because of this long-standing problem. GNOSIS is a prototype astrophotonic instrument that utilizes "OH suppression fibers" consisting of fiber Bragg gratings and photonic lanterns to suppress the 103 brightest atmospheric emission doublets between 1.47 and 1.7 mu m. GNOSIS was commissioned at the 3.9 m Anglo-Australian Telescope with the IRIS2 spectrograph to demonstrate the potential of OH suppression fibers, but may be potentially used with any telescope and spectrograph combination. Unlike previous atmospheric suppression techniques GNOSIS suppresses the lines before dispersion and in a manner that depends purely on wavelength. We present the instrument design and report the results of laboratory and on-sky tests from commissioning. While these tests demonstrated high throughput (approximate to 60%) and excellent suppression of the skylines by the OH suppression fibers, surprisingly GNOSIS produced no significant reduction in the interline background and the sensitivity of GNOSIS+IRIS2 is about the same as IRIS2. It is unclear whether the lack of reduction in the interline background is due to physical sources or systematic errors as the observations are detector noise dominated. OH suppression fibers could potentially impact ground-based astronomy at the level of adaptive optics or greater. However, until a clear reduction in the interline background and the corresponding increasing in sensitivity is demonstrated optimized OH suppression fibers paired with a fiber-fed spectrograph will at least provide a real benefit at low resolving powers.
A considerable fraction of the central stars of planetary nebulae (CSPNe) are hydrogen-deficient. Almost all of these H-deficient central stars (CSs) display spectra with strong carbon and helium lines. Most of them exhibit emission-line spectra resembling those of massive WC stars. Therefore these stars are classed as CSPNe of spectral type [WC]. Recently, quantitative spectral analysis of two emission-line CSs, PB 8 and IC 4663, revealed that these stars do not belong to the [WC] class. Instead PB 8 has been classified as [WN/WC] type and IC 4663 as [WN] type. In this work we report the spectroscopic identification of another rare [WN] star, the CS of Abell 48. We performed a spectral analysis of Abell 48 with the Potsdam Wolf-Rayet (PoWR) models for expanding atmospheres. We find that the expanding atmosphere of Abell 48 is mainly composed of helium (85 per cent by mass), hydrogen (10 per cent) and nitrogen (5 per cent). The residual hydrogen and the enhanced nitrogen abundance make this object different from the other [WN] star IC 4663. We discuss the possible origin of this atmospheric composition.
We report observations of dusty clouds in Saturn's rings, which we interpret as resulting from impacts onto the rings that occurred between 1 and 50 hours before the clouds were observed. The largest of these clouds was observed twice; its brightness and cant angle evolved in a manner consistent with this hypothesis. Several arguments suggest that these clouds cannot be due to the primary impact of one solid meteoroid onto the rings, but rather are due to the impact of a compact stream of Saturn-orbiting material derived from previous breakup of a meteoroid. The responsible interplanetary meteoroids were initially between 1 centimeter and several meters in size, and their influx rate is consistent with the sparse prior knowledge of smaller meteoroids in the outer solar system.
A unified understanding of the relationship between disturbance and biodiversity is needed to predict biotic responses to global change. Recent advances have identified the need to deconstruct traditional models of disturbance into intensity and frequency to reconcile empirical studies that appear to generate contradictory associations between species diversity and disturbance. We integrate results from theoretical simulation modelling, field-based surveys of 5176 vegetation plots from 48 transects across 6 sites, and experimental pot-based manipulations of flooding to identify how disturbance drives species diversity within ephemeral wetlands in South Island, New Zealand. We find empirical, hump-shaped and positive relationships between species diversity and both disturbance intensity and frequency, mirroring patterns from a simulation model in which species differed in their demographic responses to disturbance. More generally, our simulations show that the relationships between diversity and disturbance shift from positive to hump-shaped to negative as species that are favored at low disturbance because of their resistance strategies, defined by low mortality and recruitment, decline within communities relative to resilient species. Resilient species with higher mortality and recruitment rates are instead favored as disturbance intensity and frequency intensify. Our theoretical findings suggest that sites must also have a third group of unique species with intermediate resilience and resistance. Analyses of community composition along our disturbance gradients support this prediction, emphasizing that shifts in community-level resistance and resilience drive empirical associations between diversity and disturbance. Overall, terrestrial plants may be unable to resist intense and frequent flooding, even with specialized traits. Only fast-growing species with high regeneration from seed may respond once flooding subsides and dominate community composition in these situations, especially on nutrient-rich soils. However, different strategies can co-occur at intermediate disturbance, ultimately increasing species richness. As disturbances become more pervasive globally, our results suggest that differences in the niches of species, rather than demographic stochasticity, drive biodiversity patterns. These niche-based processes may especially prevail, without accompanying losses in species richness, where sites are initially dominated by resistant taxa or life history strategies that balance resistance and resilience.
We report the discovery of an unidentified, extended source of very-high-energy gamma-ray emission, VER J2019+407, within the radio shell of the supernova remnant SNR G78.2+2.1, using 21.4 hr of data taken by the VERITAS gamma-ray observatory in 2009. These data confirm the preliminary indications of gamma-ray emission previously seen in a two-year (2007-2009) blind survey of the Cygnus region by VERITAS. VER J2019+407, which is detected at a post-trials significance of 7.5 standard deviations in the 2009 data, is localized to the northwestern rim of the remnant in a region of enhanced radio and X-ray emission. It has an intrinsic extent of 0 degrees.23 +/- 0 degrees.03(stat-0 degrees.02sys)(+0 degrees.04) and its spectrum is well-characterized by a differential power law (dN/dE = N-0 x (E/TeV)-Gamma) with a photon index of Gamma = 2.37 +/- 0.14(stat) +/- 0.20(sys) and a flux normalization of N-0 = 1.5 +/- 0.2(stat) +/- 0.4(sys) x 10(-12) photon TeV-1 cm(-2) s(-1). This yields an integral flux of 5.2 +/- 0.8(stat) +/- 1.4(sys) x 10(-12) photon cm(-2) s(-1) above 320 GeV, corresponding to 3.7% of the Crab Nebula flux. We consider the relationship of the TeV gamma-ray emission with the GeV gamma-ray emission seen from SNR G78.2+2.1 as well as that seen from a nearby cocoon of freshly accelerated cosmic rays. Multiple scenarios are considered as possible origins for the TeV gamma-ray emission, including hadronic particle acceleration at the SNR shock.
Based on joint consideration of S receiver functions and surface-wave anisotropy we present evidence for the existence of a thick and layered lithosphere beneath the Kalahari Craton. Our results show that frozen-in anisotropy and compositional changes can generate sharp Mid-Lithospheric Discontinuities (MLD) at depths of 85 and 150-200 km, respectively. We found that a 50 km thick anisotropic layer, containing 3% S wave anisotropy and with a fast-velocity axis different from that in the layer beneath, can account for the first MLD at about 85 km depth. Significant correlation between the depths of an apparent boundary separating the depleted and metasomatised lithosphere, as inferred from chemical tomography, and those of our second MLD led us to characterize it as a compositional boundary, most likely due to the modification of the cratonic mantle lithosphere by magma infiltration. The deepening of this boundary from 150 to 200 km is spatially correlated with the surficial expression of the Thabazimbi-Murchison Lineament (TML), implying that the TML isolates the lithosphere of the Limpopo terrane from that of the ancient Kaapvaal terrane. The largest velocity contrast (3.6-4.7%) is observed at a boundary located at depths of 260-280 km beneath the Archean domains and the older Proterozoic belt. This boundary most likely represents the lithosphere-asthenosphere boundary, which shallows to about 200 km beneath the younger Proterozoic belt. Thus, the Kalahari lithosphere may have survived multiple episodes of intense magmatism and collisional rifting during the billions of years of its history, which left their imprint in its internal layering.
We introduce an invariant phase description of stochastic oscillations by generalizing the concept of standard isophases. The average isophases are constructed as sections in the state space, having a constant mean first return time. The approach allows us to obtain a global phase variable of noisy oscillations, even in the cases where the phase is ill defined in the deterministic limit. A simple numerical method for finding the isophases is illustrated for noise-induced switching between two coexisting limit cycles, and for noise-induced oscillation in an excitable system. We also discuss how to determine isophases of observed irregular oscillations, providing a basis for a refined phase description in data analysis.