As newly formed landscapes evolve, physical and biological changes occur that are collectively known as primary succession. Although succession is a fundamental concept in ecology, it is poorly ...understood in the context of aquatic environments. The prevailing view is that lakes become more enriched in nutrients as they age, leading to increased biological production. Here we report the opposite pattern of lake development, observed from the water chemistry of lakes that formed at various times within the past 10,000 years during glacial retreat at Glacier Bay, Alaska. The lakes have grown more dilute and acidic with time, accumulated dissolved organic carbon and undergone a transient rise in nitrogen concentration, all as a result of successional changes in surrounding vegetation and soils. Similar trends are evident from fossil diatom stratigraphy of lake sediment cores. These results demonstrate a tight hydrologic coupling between terrestrial and aquatic environments during the colonization of newly deglaciated landscapes, and provide a conceptual basis for mechanisms of primary succession in boreal lake ecosystems.
Context. We have obtained Herschel images at five wavelengths from 100 to 500 mu m of a similar to 5.5 x 2.5 degree area centred on the local galaxy M31 (Andromeda), our nearest neighbour spiral ...galaxy, as part of the Herschel guaranteed time project “HELGA”. The main goals of HELGA are to study the characteristics of the extended dust emission, focusing on larger scales than studied in previous observations of Andromeda at an increased spatial resolution, and the obscured star formation. Aims. In this paper we present data reduction and Herschel maps, and provide a description of the far-infrared morphology, comparing it with features seen at other wavelengths. Methods. We used high-resolution maps of the atomic hydrogen, fully covering our fields, to identify dust emission features that can be associated to M31 with confidence, distinguishing them from emission coming from the foreground Galactic cirrus. Results. Thanks to the very large extension of our maps we detect, for the first time at far-infrared wavelengths, three arc-like structures extending out to similar to 21, similar to 26 and similar to 31 kpc respectively, in the south-western part of M31. The presence of these features, hosting similar to 2.2 x 10(6) M-circle dot of dust, is safely confirmed by their detection in HI maps. Overall, we estimate a total dust mass of similar to 5.8 x 107 M-circle dot, about 78% of which is contained in the two main ring-like structures at 10 and 15 kpc, at an average temperature of 16.5 K. We find that the gas-to-dust ratio declines exponentially as a function of the galacto-centric distance, in agreement with the known metallicity gradient, with values ranging from 66 in the nucleus to similar to 275 in the outermost region. Conclusions. Dust in M31 extends significantly beyond its optical radius (similar to 21 kpc) and what was previously mapped in the farinfrared. An annular-like segment, located approximately at R-25, is clearly detected on both sides of the galaxy, and two other similar annular structures are undoubtedly detected on the south-west side even further out.
This article presents the scientific rationale for an ambitious ICDP drilling project to continuously sample Late Cretaceous to modern sediment in four different sedimentary basins that transect the ...equatorial Amazon of Brazil, from the Andean foreland to the Atlantic Ocean. The goals of this project are to document the evolution of plant biodiversity in the Amazon forests and to relate biotic diversification to changes in the physical environment, including climate, tectonism, and the surface landscape. These goals require long sedimentary records from each of the major sedimentary basins across the heart of the Brazilian Amazon, which can only be obtained by drilling because of the scarcity of Cenozoic outcrops. The proposed drilling will provide the first long, nearly continuous regional records of the Cenozoic history of the forests, their plant diversity, and the associated changes in climate and environment. It also will address fundamental questions about landscape evolution, including the history of Andean uplift and erosion as recorded in Andean foreland basins and the development of west-to-east hydrologic continuity between the Andes, the Amazon lowlands, and the equatorial Atlantic. Because many modern rivers of the Amazon basin flow along the major axes of the old sedimentary basins, we plan to locate drill sites on the margin of large rivers and to access the targeted drill sites by navigation along these rivers.
This review demonstrates current literature on pineal gland physiology, pathology, and animal model experiments to concisely explore future needs in research development with respect to pineal gland ...function and neuro-regenerative properties. The pineal gland plays an integral role in sleep and recovery by promoting physiologic circadian rhythms via production and release of melatonin. Yet, the current literature shows that the pineal gland has neuroprotective effects that modulate both peripheral and central nerve injuries through several direct and indirect mechanisms, such as angiogenesis and induction of growth factors and anti-inflammatory mediators. Animal models have also shown correlations between pineal gland function and metabolic homeostasis. Studies have shown that a functional pineal gland is essential in preventing and slowing the progression of certain diseases such as diabetes, osteoporosis, vertebral osteoarthritis, and neurodegenerative processes. Lastly, the array of cell culturing methods and animal models that can be used to further develop the study of pineal gland function and nervous system injury were reviewed.
We present the analysis of the broadened, flourescent iron Kα line in simultaneous XMM-Newton and RXTE data from the black hole Cygnus X-1. The XMM-Newton data were taken in a modified version of the ...timing mode of the EPIC-pn camera. In this mode the lower energy threshold of the instrument is increased to 2.8 keV to avoid telemetry drop outs due to the brightness of the source, while at the same time preserving the signal-to-noise ratio in the Fe Kα band. We find that the best-fit spectrum consists of the sum of an exponentially cutoff power-law and relativistically smeared, ionized reflection. The shape of the broadened Fe Kα feature is due to strong Compton broadening combined with relativistic broadening. Assuming a standard, thin accretion disk, the black hole is close to rotating maximally.
Peripheral nerve injury and the nerves’ subsequent repair and regeneration continues to be marked clinically by poor functional recovery. The analysis of nerve morphology is an aspect which may ...provide an impact on successful clinical outcomes through better prediction of donor and recipient matching. In this study, we evaluated the morphological aspects of the human obturator nerve for a better understanding of its potential in nerve transplantation. Morphological characteristics of donor obturator nerves were analysed, including nerve diameter and length, fascicle count and the ratio of neural to non‐neural tissue present within the cross‐sectional area of the nerve's epineurium, with respect to laterality and sex. Statistical significance (p < 0.10) was determined for male obturator nerves having an average diameter of 2.67 mm compared to female obturator nerves at 1.91 mm, as well as left obturator nerves having an average of 11.21 fascicles compared to the right having an average of 10.17 fascicles. Strong positive correlations were determined between cross‐sectional nerve area and limb size index, as well as between percentage of non‐neural tissue and area of non‐neural tissue, among males. Separately, strong correlation between percentage of non‐neural tissue and area of non‐neural tissue among right obturator nerves in males and females was determined . These findings indicate that there are associations and predictions that can be made about nerve morphology and that these when combined with other patient characteristics may enhance patient functional recovery following a peripheral nerve's repair.
Understanding the concept of habitability is clearly related to an evolutionary knowledge of the particular planet-in-question. However, additional indications so-called “systemic aspects” of the ...planetary system as a whole governs a particular planet׳s claim on habitability. In this paper we focus on such systemic aspects and discuss their relevance to the formation of an “Earth-like” habitable planet. This contribution summarizes our results obtained by lunar sample work and numerical models within the framework of the Research Alliance “Planetary Evolution and Life”. We consider various scenarios which simulate the dynamical evolution of the Solar System and discuss the consequences for the likelihood of forming an Earth-like world orbiting another star. Our model approach is constrained by observations of the modern Solar System and the knowledge of its history. Results suggest that on the one hand the long-term presence of terrestrial planets is jeopardized due to gravitational interactions if giant planets are present. On the other hand the habitability of inner rocky planets may be supported in those planetary systems hosting giant planets.
Gravitational interactions within a complex multiple-body structure including giant planets may supply terrestrial planets with materials which formed in the colder region of the proto-planetary disk. During these processes, water, the prime requisite for habitability, is delivered to the inner system. This may occur either during the main accretion phase of terrestrial planets or via impacts during a post-accretion bombardment. Results for both processes are summarized and discussed with reference to the lunar crater record.
Starting from a scenario involving migration of the giant planets this contribution discusses the delivery of water to Earth, the modification of atmospheres by impacts in a planetary system context and the likelihood of the existence of extrasolar Earth-like habitable worlds.
•Scenarios of the evolution of the Solar System are constrained by today׳s state.•“Grand Tack” and “Jumping Jupiter” describe orbital reconfigurations of our Solar System.•The impact history during the Heavy Bombardment Eon is constrained.•The importance of this impact scenario for the formation of life is examined.•Discuss likelihood of existence of habitable worlds in a planetary system context.
SUMMARY
This paper analyzes the influence of different static limits representation of generators on the load margins in voltage stability studies. Usually, a static representation of reactive power ...limits sets the reactive power generation at a machine to its maximum (or minimum) capacity. In this paper, an approach that considers the internal voltage of generators is presented, so both models are compared. These procedures are established using conventional bus type and the remote control bus type representations (PQV, P and θ bus type). These models are applied to a multi‐machine system under different operating conditions. This knowledge aggregates crucial information to the analysis of the operating limits of the system. Thus, the main contribution of this paper is the accurate determination of load margin when different generator reactive power limits models are considered. Hence, the role of the overexcitation of generators is highlighted as a function of the reactive power margin.
Fine-resolution fossil pollen and charcoal analyses reconstruct a vegetation and fire history in the area surrounding Lake Titicaca (3810 m, Peru/Bolivia) since ca. 27 500 cal yr BP (hereafter BP). ...Time control was based on 26 accelerator mass spectrometer (AMS) radiocarbon dates. Seventeen AMS dates and 155 pollen and charcoal samples between ca. 17 500 BP and ca. 3100 BP allow a centennial-scale reconstruction of deglacial and early- to mid-Holocene events. Local and regional fire signals were based on the separation of two charcoal size fractions, ≥180 μm and 179–65 μm. Charcoal abundance correlated closely with the proportion of woody taxa present in the pollen spectra. Little or no pollen was detected in the sedimentary record prior to ca. 21 000 BP. Very cold climatic conditions prevailed, with temperatures suggested to be at least 5–8°C cooler than present. Increases in pollen concentration suggest initial warming at ca. 21 000 BP with a more significant transition toward deglaciation ca. 17 700 BP. Between 17 700 BP and 13 700 BP, puna brava is progressively replaced by puna and sub-puna elements. The most significant changes between the Pleistocene and the Holocene floras were largely complete by 13 700 BP, providing an effective onset of near-modern conditions markedly earlier than in other Andean records. Fire first occurs in the catchment at ca. 17 700 BP and becomes progressively more important as fuel loads increase. No evidence is found of a rapid cooling and warming coincident with the Younger Dryas chron. A dry event between ca. 9000 BP and 3100 BP, with a peak between 6000 and 4000 BP, is inferred from changes in the composition of aquatics, and the marsh community as pollen of Cyperaceae is replaced by Poaceae, Apiaceae,
Plantago and the shrub
Polylepis. Human disturbance of the landscape is evident in the pollen spectra after ca. 3100 BP with the appearance of weed species.
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