Fourier Analysis of Gapped Time Series: Improved Estimates of Solar and Stellar Oscillation Parameters     

Thorsten Stahn  Laurent Gizon 《Solar physics》2008,251(1-2):31-52

Quantitative helioseismology and asteroseismology require very precise measurements of the frequencies, amplitudes, and lifetimes of the global modes of stellar oscillation. The precision of these measurements depends on the total length (T), quality, and completeness of the observations. Except in a few simple cases, the effect of gaps in the data on measurement precision is poorly understood, in particular in Fourier space where the convolution of the observable with the observation window introduces correlations between different frequencies. Here we describe and implement a rather general method to retrieve maximum likelihood estimates of the oscillation parameters, taking into account the proper statistics of the observations. Our fitting method applies in complex Fourier space and exploits the phase information. We consider both solar-like stochastic oscillations and long-lived harmonic oscillations, plus random noise. Using numerical simulations, we demonstrate the existence of cases for which our improved fitting method is less biased and has a greater precision than when the frequency correlations are ignored. This is especially true of low signal-to-noise solar-like oscillations. For example, we discuss a case where the precision of the mode frequency estimate is increased by a factor of five, for a duty cycle of 15%. In the case of long-lived sinusoidal oscillations, a proper treatment of the frequency correlations does not provide any significant improvement; nevertheless, we confirm that the mode frequency can be measured from gapped data with a much better precision than the 1/T Rayleigh resolution.  相似文献   

A marine pebbly mudstone from the Swiss Alps: palaeotectonic implications and some consequences for the interpretation of Precambrian diamictites     

Dominik Letsch  Lea Kiefer 《Swiss Journal of Geoscience》2017,110(3):753-776

Pebbly mudstones are a conspicuous element of sedimentary sequences deposited in different tectonic settings and sedimentary environments. Whereas for many diamictites a glacial origin seems plausible, the problem to distinguish glacial from non-glacial diamictites is often difficult for Precambrian examples where palaeoclimatic constraints are generally lacking. This article documents an Eocene pebbly mudstone of the Southhelvetic nappes of eastern Central Switzerland (Blockmergel) for which a glacial origin can be firmly rejected and which may thus serve as an example for non-glacial marine diamictites and their sedimentary and palaeotectonic environment. The Blockmergel are interpreted as the product of gravitational deposition of single blocks across steep palaeo-slopes (subaqueous rockfall) into a basin otherwise dominated by suspension settling sedimentation. The Blockmergel occur within the basal part of the early fill of the North Alpine Foreland Basin, which constitutes a deepening upward sequence above basal shallow marine limestones. The Blockmergel demonstrate substantial Middle to Late Eocene sub-aerial erosion and fluvial transport (producing the rounded pebbles) and local extensional fault movements in the proximal part of the incipient North Alpine Foreland Basin. They are capped sharply by forced-regressive shoreface sandstones and the whole sequence thus demonstrates locally very shallow to subaerial conditions within an otherwise rather deep hemipelagic marine basin. This, and the extensional fault movements, are linked to a long-standing feature of Helvetic palaeogeography—the Southhelvetic swell zone. That this swell still operated during the Priabonian i.e. shortly before finally being overthrust by the orogenic wedge of the evolving Alpine orogen is a new element in Alpine palaeotectonics and seems to highlight the importance of the reactivation of inherited palaeotectonic faults. Finally, the example of the Blockmergel is suggested as a useful analogue to help distinguishing glacial-sourced from slope-derived diamictites in the Neoproterozoic sedimentary record and may thus help resolving the “diamictite dichotomy”.  相似文献   

Regime-dependent evaluation of accumulated precipitation in COSMO     

Tom Akkermans  Tim B?hme  Matthias Demuzere  Susanne Crewell  Christoph Selbach  Thorsten Reinhardt  Axel Seifert  Felix Ament  Nicole P. M. van Lipzig 《Theoretical and Applied Climatology》2012,108(1-2):39-52

Regime-dependent evaluation is a relatively new approach to assess model performance. It consists of classifying the model biases according to a discrete number of regimes and evaluating model output within each regime. In this paper, the regimes are firstly defined by the large-scale atmospheric circulation, based on the objective Jenkinson-Collison classification technique which distinguishes synoptic patterns by strength, direction and vorticity of the geostrophic flow. Eight directional and two vorticity circulation regimes (circulation types) are specified. In this way, it is possible to quantify the model performance for cases with for example westerly winds only, or with cyclonic circulation only. A second regime classification is based on temperature, which allows for detection of temperature-dependent model performance. Modelled accumulated precipitation (mm/6?h) is evaluated with rain gauges for the years 2007 and 2008. Two variants of the COSMO model are evaluated: a fine-resolution version (2.8?km, COSMO-DE) and a coarse-resolution version (7?km, COSMO-EU). In COSMO-EU, a windward/leeward effect becomes visible since circulation is related to dominant wind direction, hence to windward and lee side of orography. In COSMO-DE, no circulation dependent but a height-related bias is identified and further explored, making use of temperature-dependent evaluation which unveils a positive model bias related to solid precipitation.  相似文献   

A New,Well-Preserved Species of Glaresidae (Coleoptera:Scarabaeoidea) from the Jehol Biota of China   总被引：2，自引：1，他引：1  

BAI Ming  Frank Thorsten KRELL  REN Dong  and YANG Xingke 《《地质学报》英文版》2010,84(4):676-679

<正>Glaresis orthochilus sp.nov.(Scarabaeoidea:Glaresidae),the best preserved glaresid fossil,is described and illustrated from the Yixian Formation of western Liaoning province,north-east China.Glaresidae, the sister group of all extant Scarabaeoidea was established in the Upper Jurassic/Lower Cretaceous and contained larger species than those found today.  相似文献   

The replacement of plagioclase feldspars by albite: observations from hydrothermal experiments   总被引：7，自引：3，他引：4  

Jörn Hövelmann  Andrew Putnis  Thorsten Geisler  Burkhard C. Schmidt  Ute Golla-Schindler 《Contributions to Mineralogy and Petrology》2010,159(1):43-59

Oligoclase and labradorite crystals have been experimentally replaced by albite in an aqueous sodium silicate solution at 600°C and 2 kbars. The replacement is pseudomorphic and is characterised by a sharp chemical interface which progresses through the feldspar while preserving the crystallographic orientation. Reaction rims of albite, up to 50 μm thick, can be readily achieved within 14 days. Re-equilibration of plagioclase in an ¹⁸O-enriched sodium- and silica-bearing solution results in oxygen isotope redistribution within the feldspar framework structure. The observed characteristics of the reaction products are similar to naturally albitised plagioclase and are indicative of an interface-coupled dissolution–reprecipitation mechanism. Chemical analyses demonstrate that the albitisation is accompanied by the mobilisation of major, minor and trace elements also including elements such as Al and Ti which are commonly regarded as immobile during hydrothermal alteration. The results contribute to developing our understanding of the close association between large-scale albitisation and secondary ore mineralisation which is common in nature.  相似文献   

Early core formation in asteroids and late accretion of chondrite parent bodies: Evidence from Hf-W in CAIs, metal-rich chondrites, and iron meteorites     

Thorsten Kleine  Klaus Mezger  Erik Scherer 《Geochimica et cosmochimica acta》2005,69(24):5805-5818

The ¹⁸²Hf-¹⁸²W isotopic systematics of Ca-Al-rich inclusions (CAIs), metal-rich chondrites, and iron meteorites were investigated to constrain the relative timing of accretion of their parent asteroids. A regression of the Hf-W data for two bulk CAIs, various fragments of a single CAI, and carbonaceous chondrites constrains the ¹⁸²Hf/¹⁸⁰Hf and ε_W at the time of CAI formation to (1.07 ± 0.10) × 10⁻⁴ and −3.47 ± 0.20, respectively. All magmatic iron meteorites examined here have initial ε_W values that are similar to or slightly lower than the initial value of CAIs. These low ε_W values may in part reflect ¹⁸²W-burnout caused by the prolonged cosmic ray exposure of iron meteorites, but this effect is estimated to be less than ∼0.3 ε units for an exposure age of 600 Ma. The W isotope data, after correction for cosmic ray induced effects, indicate that core formation in the parent asteroids of the magmatic iron meteorites occurred less than ∼1.5 Myr after formation of CAIs. The nonmagmatic IAB-IIICD irons and the metal-rich CB chondrites have more radiogenic W isotope compositions, indicating formation several Myr after the oldest metal cores had segregated in some asteroids.Chondrule formation ∼2-5 Myr after CAIs, as constrained by published Pb-Pb and Al-Mg ages, postdates core formation in planetesimals, and indicates that chondrites do not represent the precursor material from which asteroids accreted and then differentiated. Chondrites instead derive from asteroids that accreted late, either farther from the Sun than the parent bodies of magmatic iron meteorites or by reaccretion of debris produced during collisional disruption of older asteroids. Alternatively, chondrites may represent material from the outermost layers of differentiated asteroids. The early thermal and chemical evolution of asteroids appears to be controlled by the decay of ²⁶Al, which was sufficiently abundant (initial ²⁶Al/²⁷Al >1.4 × 10⁻⁵) to rapidly melt early-formed planetesimals but could not raise the temperatures in the late-formed chondrite parent asteroids high enough to cause differentiation. The preservation of the primitive appearance of chondrites thus at least partially reflects their late formation rather than their early and primitive origin.  相似文献   

Constraints on fault slip rates of the southern California plate boundary from GPS velocity and stress inversions   总被引：2，自引：0，他引：2  

Thorsten W. Becker  Jeanne L. Hardebeck  Greg Anderson 《Geophysical Journal International》2005,160(2):634-650

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Biodegradation of forest floor organic matter bound to minerals via different binding mechanisms   总被引：6，自引：0，他引：6  

Robert Mikutta  Christian Mikutta  Thorsten Scheel  Reinhold Jahn 《Geochimica et cosmochimica acta》2007,71(10):2569-2590

Mineral-associated organic matter (OM) represents a large reservoir of organic carbon (OC) in natural environments. The factors controlling the extent of the mineral-mediated OC stabilization, however, are poorly understood. The protection of OM against biodegradation upon sorption to mineral phases is assumed to result from the formation of strong bonds that limit desorption. To test this, we studied the biodegradation of OM bound to goethite (α-FeOOH), pyrophyllite, and vermiculite via specific mechanisms as estimated from OC uptake in different background electrolytes and operationally defined as ‘ligand exchange’, ‘Ca²⁺ bridging’, and ‘van der Waals forces’. Organic matter extracted from an Oa forest floor horizon under Norway spruce (Picea abies (L.) Karst) was reacted with minerals at dissolved OC concentrations of ∼5-130 mg/L at pH 4. Goethite retained up to 30.1 mg OC/g predominantly by ‘ligand exchange’; pyrophyllite sorbed maximally 12.5 mg OC/g, largely via ‘van der Waals forces’ and ‘Ca²⁺ bridging’, while sorption of OM to vermiculite was 7.3 mg OC/g, mainly due to the formation of ‘Ca²⁺ bridges’. Aromatic OM components were selectively sorbed by all minerals (goethite ? phyllosilicates). The sorption of OM was strongly hysteretic with the desorption into 0.01 M NaCl being larger for OM held by ‘Ca²⁺ bridges’ and ‘van der Waals forces’ than by ‘ligand exchange’. Incubation experiments under aerobic conditions (initial pH 4; 90 days) revealed that OM mainly bound to minerals by ‘ligand exchange’ was more resistant against mineralization than OM held by non-columbic interactions (‘van der Waals forces’). Calcium bridges enhanced the stability of sorbed OM, especially for vermiculite, but less than the binding via ‘ligand exchange’. Combined evidence suggests that the extent and rate of mineralization of mineral-associated OM are governed by desorption. The intrinsic stability of sorbed OM as related to the presence of resistant, lignin-derived aromatic components appears less decisive for the sorptive stabilization of OM than the involved binding mechanisms. In a given environment, the type of minerals present and the solution chemistry determine the operating binding mechanisms, thereby the extent of OM sorption and desorption, and thus ultimately the bioavailability of mineral-associated OM.  相似文献   

History of subduction and back-arc extension in the Central Mediterranean   总被引：11，自引：0，他引：11  

Claudio Faccenna  Thorsten W. Becker  Francesco Pio Lucente  Laurent Jolivet  Federico Rossetti 《Geophysical Journal International》2001,145(3):809-820

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Two-dimensional modeling of exogenic mass transfer at the Calabrian active margin,southern Italy     

E. Kiefer 《International Journal of Earth Sciences》1994,83(2):334-347

Uplift caused by crustal growth at active plate margins triggers an exogenic mass transfer from the mountain ranges into arc-associated basins. This mass transfer comprises weathering and erosion of the source terranes, differentiation and transport of particles and finally deposition. The hydraulic populations produced by chemical dissolution and mechanical abrasion possess different recycling potentials: Coarse-grained particles are piled up in forearc accretionary wedges and recycled by subduction with the oceanic lithosphere. Fine-grained particles and the chemical load may leave the exogenic cycle by suspension and solution. Their recycling potential is low. For the Calabrian active margin a composite exogenic mass balance has been determined. Sedimentation rates were calculated by two-dimensional modeling of the forearc sedimentary wedge based on METEOR airgun sections. Erosion rates for the Calabrian Massif were evaluated by a morphometric volume balance. The total erosion of the Calabrian Massif is 178 m/Ma. About 28 m/Ma (16%) is removed by chemical dissolution and particle dispersion. The mean sedimentation rate in the forearc basin is 137 m/Ma. The remaining mass deficiency of 13 m/Ma (7%) is referred to sediment bypass to the abyssal plain through submarine canyons.  相似文献