400 years of astrometry: from Tycho Brahe to Hipparcos     

Erik Høg 《Experimental Astronomy》2009,25(1-3):225-240

Galileo Galilei’s use of the newly invented telescope for astronomical observation resulted immediately in epochal discoveries about the physical nature of celestial bodies, but the advantage for astrometry came much later. The quadrant and sextant were pre-telescopic instruments for measurement of large angles between stars, improved by Tycho Brahe in the years 1570–1590. Fitted with telescopic sights after 1660, such instruments were quite successful, especially in the hands of John Flamsteed. The meridian circle was a new type of astrometric instrument, already invented and used by Ole Rømer in about 1705, but it took a hundred years before it could fully take over. The centuries-long evolution of techniques is reviewed, including the use of photoelectric astrometry and space technology in the first astrometry satellite, Hipparcos, launched by ESA in 1989. Hipparcos made accurate measurement of large angles a million times more efficiently than could be done in about 1950 from the ground, and it will soon be followed by Gaia which is expected to be another one million times more efficient for optical astrometry.  相似文献   

Rapid incorporation of lipids into macromolecules during experimental decay of invertebrates: Initiation of geopolymer formation     

Neal S. Gupta  George D. Cody  O. Erik Tetlie  Derek E.G. Briggs  Roger E. Summons 《Organic Geochemistry》2009,40(5):589-594

Diagenetic alteration is critical for the preservation of fossil cuticles of plant and animal origin and to the formation of kerogen. The process takes place over millions of years, but the stage at which it is initiated is not known. Laboratory decay experiments were carried out on shrimps, scorpions and cockroaches to monitor changes in the chitin–protein of the arthropod cuticle and associated lipids. The cockroach and scorpion exoskeleton remained largely unaltered morphologically, but the shrimp experienced rapid decomposition within a month, which progressed through the 44 week duration of the experiment as revealed using electron microscopy. Mass spectrometry and ¹³C NMR (nuclear magnetic resonance) spectroscopy revealed the association of an n-alkyl component with labile lipids, such as fatty acids with up to 24 carbon atoms, which were incorporated into the decaying macromolecule. The scorpion and cockroach cuticle did not reveal the incorporation of additional lipids, indicating that decay is important in initiating in situ lipid association. This experiment provides evidence that lipids can become associated with carbohydrate and proteinaceous macromolecules during the very early stages of decay, representing the first stage in the transformation process that contributes to the aliphatic rich composition ubiquitous in organic fossils and kerogen.  相似文献   

An analytical model of surface mass densities of cold dark matter haloes – with an application to MACHO microlensing optical depths     

Janne Holopainen  Erik Zackrisson  Alexander Knebe  Pasi Nurmi  Pekka Heinämäki  Chris Flynn  Stuart Gill  Teresa Riehm 《Monthly notices of the Royal Astronomical Society》2008,383(2):720-728

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Spacecraft Reconnaissance of Asteroid and Comet Interiors     

Erik Asphaug  Louise Prockter 《Meteoritics & planetary science》2008,43(6):995-996

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Thermal evolution of an ancient subduction interface revealed by Lue Hf garnet geochronology,Halilba■? Complex(Anatolia)     

Amaury Pourteau  Erik E.Scherer  Simon Schorn  Rebecca Bast  Alexander Schmidt  Lisa Ebert 《地学前缘(英文版)》2019,(1)

The thermal structure of subduction zones exerts a major influence on deep-seated mechanical and chemical processes controlling arc magmatism, seismicity, and global element cycles. Accretionary complexes exposed inland may comprise tectonic blocks with contrasting pressureetemperature(Pe T)histories, making it possible to investigate the dynamics and thermal evolution of former subduction interfaces. With this aim, we present new Lue Hf geochronological results for mafic rocks of the Halilbag?Complex(Anatolia) that evolved along different thermal gradients. Samples include a lawsoniteeepidote blueschist, a lawsoniteeepidote eclogite, and an epidote eclogite(all with counter-clockwise Pe T paths),a prograde lawsonite blueschist with a "hairpin"-type Pe T path, and a garnet amphibolite from the overlying sub-ophiolitic metamorphic sole. Equilibrium phase diagrams suggest that the garnet amphibolite formed at w0.6 -0.7 GPa and 800 -850℃, whereas the prograde lawsonite blueschist records burial from 2.1 GPa and 420℃ to 2.6 GPa and 520℃. Well-defined Lue Hf isochrons were obtained for the epidote eclogite(92.38 ± 0.22 Ma) and the lawsoniteeepidote blueschist(90.19 ± 0.54 Ma),suggesting rapid garnet growth. The lawsoniteeepidote eclogite(87.30 ± 0.39 Ma) and the prograde lawsonite blueschist(ca. 86 Ma) are younger, whereas the garnet amphibolite(104.5 ± 3.5 Ma) is older.Our data reveal a consistent trend of progressively decreasing geothermal gradient from granulite-facies conditions at ~104 Ma to the epidote-eclogite facies around 92 Ma, and the lawsonite blueschist-facies between 90 Ma and 86 Ma. Three Lue Hf garnet dates(between 92 Ma and 87 Ma) weighted toward the growth of post-peak rims(as indicated by Lu distribution in garnet) suggest that the HP/LT rocks were exhumed continuously and not episodically. We infer that HP/LT metamorphic rocks within the Halilbag?Complex were subjected to continuous return flow, with "warm" rocks being exhumed during the tectonic burial of "cold" ones. Our results, combined with regional geological constraints, allow us to speculate that subduction started at a transform fault near a mid-oceanic spreading centre. Following its formation, this ancient subduction interface evolved thermally over more than 15 Myr, most likely as a result of heat dissipation rather than crustal underplating.  相似文献   

A new archival infrastructure for highly-structured astronomical data     

Erik Dovgan  Cristina Knapic  Massimo Sponza  Riccardo Smareglia 《Experimental Astronomy》2018,45(1):41-55

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High‐resolution bathymetric mapping reveals subaqueous glacial landforms in the Arctic alpine lake Tarfala,Sweden     

Nina Kirchner  Riko Noormets  Jakob Kuttenkeuler  Elias Strandell Erstorp  Erik Schytt Holmlund  Gunhild Rosqvist  Per Holmlund  Marika Wennbom  Torbjrn Karlin 《第四纪科学杂志》2019,34(6):452-462

In Arctic alpine regions, glacio‐lacustrine environments respond sensitively to variations in climate conditions, impacting, for example,glacier extent and rendering former ice‐contact lakes into ice distal lakes and vice versa. Lakefloors may hold morphological records of past glacier extent, but remoteness and long periods of ice cover on such lakes make acquisition of high‐resolution bathymetric datasets challenging. Lake Tarfala and Kebnepakte Glacier, located in the Kebnekaise mountains, northern Sweden, comprise a small, dynamic glacio‐lacustrine system holding a climate archive that is not well studied. Using an autonomous surface vessel, a high‐resolution bathymetric dataset for Lake Tarfala was acquired in 2016, from which previously undiscovered end moraines and a potential grounding line feature were identified. For Kebnepakte Glacier, structure‐from‐motion photogrammetry was used to reconstruct its shape from photographs taken in 1910 and 1945. Combining these methods connects the glacial landform record identified at the lakefloor with the centennial‐scale dynamic behaviour of Kebnepakte Glacier. During its maximum 20^th century extent, attained c. 1910, Kebnepakte Glacier reached far into Lake Tarfala, but had retreated onto land by 1945, at an average of 7.9 m year^–1. Copyright © 2019 John Wiley & Sons, Ltd.  相似文献   

High-precision stellar abundances of the elements: methods and applications     

Poul Erik Nissen  Bengt Gustafsson 《Astronomy and Astrophysics Review》2018,26(1):6

Efficient spectrographs at large telescopes have made it possible to obtain high-resolution spectra of stars with high signal-to-noise ratio and advances in model atmosphere analyses have enabled estimates of high-precision differential abundances of the elements from these spectra, i.e. with errors in the range 0.01–0.03 dex for F, G, and K stars. Methods to determine such high-precision abundances together with precise values of effective temperatures and surface gravities from equivalent widths of spectral lines or by spectrum synthesis techniques are outlined, and effects on abundance determinations from using a 3D non-LTE analysis instead of a classical 1D LTE analysis are considered. The determination of high-precision stellar abundances of the elements has led to the discovery of unexpected phenomena and relations with important bearings on the astrophysics of galaxies, stars, and planets, i.e. (i) Existence of discrete stellar populations within each of the main Galactic components (disk, halo, and bulge) providing new constraints on models for the formation of the Milky Way. (ii) Differences in the relation between abundances and elemental condensation temperature for the Sun and solar twins suggesting dust-cleansing effects in proto-planetary disks and/or engulfment of planets by stars; (iii) Differences in chemical composition between binary star components and between members of open or globular clusters showing that star- and cluster-formation processes are more complicated than previously thought; (iv) Tight relations between some abundance ratios and age for solar-like stars providing new constraints on nucleosynthesis and Galactic chemical evolution models as well as the composition of terrestrial exoplanets. We conclude that if stellar abundances with precisions of 0.01–0.03 dex can be achieved in studies of more distant stars and stars on the giant and supergiant branches, many more interesting future applications, of great relevance to stellar and galaxy evolution, are probable. Hence, in planning abundance surveys, it is important to carefully balance the need for large samples of stars against the spectral resolution and signal-to-noise ratio needed to obtain high-precision abundances. Furthermore, it is an advantage to work differentially on stars with similar atmospheric parameters, because then a simple 1D LTE analysis of stellar spectra may be sufficient. However, when determining high-precision absolute abundances or differential abundance between stars having more widely different parameters, e.g. metal-poor stars compared to the Sun or giants to dwarfs, then 3D non-LTE effects must be taken into account.  相似文献   

Inherited basement canyons: Impact on sediment distribution in the North Atlantic     

Gregers Dam  Martin Snderholm  Erik Vest Srensen 《地学学报》2020,32(4):272-280

Studies of basement‐bounded canyons in West Greenland show that these were long‐lasting features that extended inland for several hundreds of kilometres, acting as prominent sediment conduits sourcing the Albian–Palaeocene Nuussuaq Basin during several phases of basin evolution. The Ilulissat Icefjord canyon was the major conduit for sediment into the basin and provenance data indicate that it had a huge catchment area that extended to East Greenland. The Uparuaqqusuitsut canyon was also an important conduit for sediment in the northern part of the basin. It is suggested that the initial canyon formation occurred during uplift events in the Late Triassic and Late Jurassic when the deeply weathered basement surface formed during Early–Middle Triassic time was eroded. The recognition of these canyons as long‐lasting sediment conduits have huge implications for understanding the sediment distribution, source‐to‐sink studies and the palaeogeography of the North Atlantic basins.  相似文献   

Public perceptions of biodiversity in Norway: From recognition to stewardship?     

Bjørn P. Kaltenborn  Vegard Gundersen  Erik Stange  Dagmar Hagen  Ketil Skogen 《Norsk geografisk tidsskrift. Norwegian journal of geography》2016,70(1):54-61

The authors surveyed a representative sample of the Norwegian population (N = 4077) to examine perceptions of biodiversity loss and management, the relative importance of biodiversity loss to other environmental issues, and perceived implications of biodiversity loss. The results showed that 50% of the sample population saw biodiversity as a reality and major environmental issue, and 75% recognized that biodiversity loss occurs. Biodiversity loss was perceived as a lesser global environmental problem than environmental toxins, climate change, air and water pollution, and loss of rainforest, despite the fact that these topics can be difficult to separate since biodiversity loss is a function of other environmental problems. Loss of biodiversity was seen to have negative impacts on people's relationship to the natural environment, to impact environmental resilience, to be at least partly human-induced, and to be an issue of importance and relevance to the general public, not merely to the scientific community. Self-reported levels of knowledge of environmental topics were associated with increasing concern about consequences of reductions in species diversity. The authors conclude that efforts to increase public support for biodiversity conservation can be strengthened by increased emphasis on aesthetic, emotional and cultural aspects of biodiversity.  相似文献