The EVN-MarkIV VLBI Data Processor     

R. T. Schilizzi  W. Aldrich  B. Anderson  A. Bos  R. M. Campbell  J. Canaris  R. Cappallo  J. L. Casse  A. Cattani  J. Goodman  H. J. van Langevelde  A. Maccafferri  R. Millenaar  R. G. Noble  F. Olnon  S. M. Parsley  C. Phillips  S. V. Pogrebenko  D. Smythe  A. Szomoru  H. Verkouter  A. R. Whitney 《Experimental Astronomy》2001,12(1):49-67

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The Preboreal climate reversal and a subsequent solar‐forced climate shift     

J. van der Plicht  B. van Geel  S. J. P. Bohncke  J. A. A. Bos  M. Blaauw  A. O. M. Speranza  R. Muscheler  S. Bjrck 《第四纪科学杂志》2004,19(3):263-269

Accurate chronologies are essential for linking palaeoclimate archives. Carbon‐14 wiggle‐match dating was used to produce an accurate chronology for part of an early Holocene peat sequence from the Borchert (The Netherlands). Following the Younger Dryas–Preboreal transition, two climatic shifts could be inferred. Around 11 400 cal. yr BP the expansion of birch (Betula) forest was interrupted by a dry continental phase with dominantly open grassland vegetation, coeval with the PBO (Preboreal Oscillation), as observed in the GRIP ice core. At 11 250 cal. yr BP a sudden shift to a humid climate occurred. This second change appears to be contemporaneous with: (i) a sharp increase of atmospheric ¹⁴C; (ii) a temporary decline of atmospheric CO₂; and (iii) an increase in the GRIP ¹⁰Be flux. The close correspondence with excursions of cosmogenic nuclides points to a decline in solar activity, which may have forced the changes in climate and vegetation at around 11 250 cal. yr BP. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

The relationship between zooplankton,conductivity and lake-water ionic composition in 111 lakes from the Interior Plateau of British Columbia,Canada   总被引：2，自引：0，他引：2  

Darren G. Bos  Brian F. Cumming  Christine E. Watters  John P. Smol 《International Journal of Salt Lake Research》1996,5(1):1-15

Zooplankton collected from vertical net tows were related to the environmental variables from 98 lakes from the Interior Plateau of British Columbia. Canonical correspondence analysis showed that both salinity and ionic composition (pH and Mg) of the lake-water made major and significant contributions to the first two ordination axes (=0.42 and 0.11 respectively,P<0.05). BothArtemia franciscana andMoina hutchinsoni had their highest relative abundance in meso-hypersaline waters. However,Artemia franciscana preferred waters that were higher in Mg and Ca, whileMoina hutchinsoni was found in waters that were lower in Mg and Ca. Similarly, at intermediate salinities,Daphnia pulex and the calanoid copepods preferred waters slightly lower in Mg and Ca, whereasCeriodaphnia laticaudata andSimocephalus spp. were relatively more common in waters higher in Mg and Ca. Because the freshest lakes studied varied much less in ionic composition, the zooplankton in these lakes did not show a preference to ionic composition. As expected, multi-generic groups, such as the calanoid copepods, cyclopoid copepods and nauplii, had wider tolerances to conductivity than groups identified to lower taxonomic levels. Significant weighted-averaging regression and calibration models of conductivity were developed based on zooplankton species composition from the study lakes (r ²=0.56,P<0.05). Samples composed largely of multi-generic taxa yielded the worst estimates of salinity in the reconstruction model. This study suggests that zooplankton community composition may be developed into a useful proxy for paleosalinity reconstruction.  相似文献   

Alkaline and ultramafic carbonate lamprophyres in Central Bohemian carboniferous basins,Czech Republic     

Dr. J. Ulrych  Dr. E. Pivec  Dr. K. Zák  Dr. J. Bendl  Dr. P. Bosák 《Mineralogy and Petrology》1993,48(1):65-81

Summary Dykes of alkaline and ultramafic carbonate lamprophyres (monchiquite-ouachitite and aillikite) intrude the Carboniferous sediments of Central Bohemia. Their characteristic feature is the presence of substantial amounts of a sodalite group mineral (presumably haüyne), carbonate and barite. Isotopic compositions of ¹³C (–3.4 to –6.2) and ¹⁸O ( + 13.5 to + 15.9) indicate that the carbonate is of primary magmatic origin and that fluids were formed at temperatures of 500 to 350°C. High contents of CO₂ (3.6 to 17.6 wt.%) and incompatible elements, high LREE/HREE ratios (30.0 to 57.7), and low Rb/Sr (0.025 to 0.078) and⁸⁷Sr/⁸⁶Sr (0.7038 to 0.7042) ratios suggest the ultramafic lamprophyres are related to deep-seated carbonated magmas of mantle origin. Low degree of partial melting ( < 1%) of the mantle peridotite is envisaged, with additional transport of fluids rich in incompatible elements into the crustal chamber. Alkaline lamprophyres are fractionated derivatives which originated from the same source. Magma intrusion from different levels of a magma chamber into fracture zones under horizontal tension without a central intrusion could result in variability in lamprophyre composition (cumulates or evolved derivatives).

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Alkalische und ultramafische Karbonat-Lamprophyre der zentralen böhmischen Karbonbecken, Tschische Republik

Zusammenfassung Alkalische und ultramafische Karbonat-Lamprophyrgänge (Monchiquit-Ouachitit und Aillikit) intrudieren in karbonische Sedimente Zentralböhmens. Sie sind charakterisiert durch das Auftreten von beträchtlichen Mengen an Mineralen der Sodalith-Gruppe (v.a. Haüyn), Karbonaten und Baryt. Ihre Isotopenzusammensetzung von ¹³C (–3.4 bis –6.2) und ¹⁸O (13.5 bis 15.9) zeigt, daß die Karbonate primär magmatischen Ursprungs sind und daß assoziierte Fluide in einem Temperaturbereich von 350 bis 500°C gebildet wurden. Hohe Gehalte an CO₂ (3.6 bis 17.6 Gew. %), inkompatiblen Elementen, hohe LREE/HREE-Verhältnisse (30.0 bis 57.7), sowie niedrige Rb/Sr—(0.025 bis 0.078) und⁸⁷Sr/⁸⁶Sr-(0.7038 bis 0.7042) Verhältnisse lassen vermuten, daß die ultramafischen Lamprophyre mit karbonatischen Magmen des Mantels in Beziehung stehen. Eine niedrige Aufschmelzungsrate ( < 1%) von Mantelperidotit mit zusätzlichem Transport von, an inkompatiblen Elementen angereicherten Fluiden, in die krustale Magmenkammer wird diskutiert. Alkalische Lamprophyre sind als stärker fraktionierte Magmen, die derselben Quelle entstammen, zu verstehen. Die Intrusion der aus verschiedenen Bereichen der Magmenkammer stammenden Magmen in durch horizontale Dehnung verursachte Störungszonen könnte das Fehlen eines zentralen Intrusionskörpers und die unterschiedliche Zusammensetzung der Lamprophyre (Kumulate oder entwickelte Derivate) erklären.

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With 8 Figures  相似文献   

Lake-Level Fluctuations and Small-Scale Vegetation Patterns During the Late Glacial in The Netherlands     

Johanna A. A. Bos  Sjoerd J. P. Bohncke  C. Roel Janssen 《Journal of Paleolimnology》2006,35(2):211-238

Late glacial changes in the vegetation were studied in and around a former lake on the southeastern side of a coversand ridge near Milheeze (southern Netherlands). Analyses of microfossils and macroremains and AMS ¹⁴C dating were performed on four sediment cores along a transect from sand ridge to the lake centre. Small-scale vegetation patterns and lake-level fluctuations were reconstructed in detail based on the information provided by the transect. For the first time in The Netherlands, cores along a transect within one lake were used to reconstruct the amplitude of late glacial lake-level fluctuations. Near Milheeze, a small and shallow lake was formed during the Bølling. The large increase in the water level during the Bølling and early Allerød, and the transition to more eutrophic conditions at the start of the Allerød, were probably related to the disappearance of permafrost. During the Allerød, open birch and pine woodlands developed in the area. In the lake, organic deposits accumulated, and the lake size and depth fluctuated. At the start of the Younger Dryas, higher lake water levels were recorded and woodlands became more open as a result of both a drop in the temperature and an increase in the effective precipitation. During the late Younger Dryas the lake water level dropped as the climate became drier and temperatures slightly increased. Accumulation of organic deposits in the lake ceased at the end of the Younger Dryas, which was caused by a drop in the water level in combination with the hydroseral succession process within the lake itself. The climatic signal reflected in the late glacial flora and lake-level fluctuations agree well with other published data from The Netherlands.  相似文献   

Investigating the use of spatial discretization of hydrological processes in conceptual rainfall runoff modelling: a case study for the meso‐scale     

H. Hellebrand  R. van den Bos 《水文研究》2008,22(16):2943-2952

In this study a simple modelling approach was applied to identify the need for spatial complexity in representing hydrological processes and their variability over different scales. A data set of 18 basins was used, ranging between 8 and 4011 km² in area, located in the Nahe basin (Germany), with daily discharge values for over 30 years. Two different parsimoniously structured models were applied in lumped as well as in spatially distributed according to two distribution classifications: (1) a simple classification based on the lithology expressed in three permeability types and (2) a more complex classification based on seven dominating runoff production processes. The objective of the study was to compare the performances of the models on a local and on a regional scale as well as between the models with a view to identifying the accuracy in capturing the spatial variability of the rainfall‐runoff relationships. It was shown that the presence of a specific basin characteristic or process of the distribution classification was not related with higher model performance; only a larger basin size promoted higher model performance. The results of this study also indicated that the permeability generally contained more useful information on the spatial heterogeneity of the hydrological behaviour of the natural system than did a more detailed classification on dominating runoff generation processes. Although model performance was slightly lower for the model that used permeability as a distribution classification, consistency in its parameter values was found, which was lacking with the more complex distribution classification. The latter distribution classification had a higher flexibility to optimize towards the variability of the runoff, which resulted in higher performance, however, process representation was applied inconsistently. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Broadband seismic source data acquisition and processing to delineate iron oxide deposits in the Blötberget mine-central Sweden     

Tatiana Pertuz  Alireza Malehmir  Jordan Bos  Bojan Brodic  Yinshuai Ding  Richard de Kunder  Paul Marsden 《Geophysical Prospecting》2022,70(1):79-94

A prototype electromagnetic vibrator, referred to here as E-Vib, was upgraded and developed for broadband hardrock and mineral exploration seismic surveys. We selected the iron oxide mine in Blötberget, central Sweden, for a test site in 2019 for the newly developed E-Vib because of the availability of earlier seismic datasets (from 2015 to 2016) for verification of its performance for hardrock imaging purposes. The two-dimensional data acquisition consisted of a fixed geometry with 550 receiver locations spaced at every 5 m, employing both cabled and wireless seismic recorders, along an approximately 2.7 km long profile. The E-Vib operated at every second receiver station (i.e. 10 m spacing) with a linear sweep of 2–180 Hz and with a peak force of 7 kN. The processing workflow took advantage of the broadband signal generated by the E-Vib in this challenging hardrock environment with varying ground conditions. The processed seismic section shows a set of reflections associated with the known iron oxide mineralization and a major crosscutting reflection interpreted to be from a fault system likely to be crosscutting the mineralization. The broadband source data acquisition and subsequent processing helped to improve signal quality and resolution in comparison with the earlier workflows and data where a drophammer seismic source was used as the seismic source. These results suggest new possibilities for the E-Vib source for improved targeting in hardrock geological settings.  相似文献   

Detection of individual normal modes of oscillation of the Sun in the period range from 2 hr to 10 min in solar diameter studies     

Bos  Randall J.  Hill  Henry A. 《Solar physics》1983,82(1-2):89-102

Solar Physics - New observations of solar oscillations are reported. Power density spectra derived from these observations reveal narrow-band oscillations that are spatially global, have spatial...  相似文献   

Optical dating of fluvio-deltaic clastic lake-fill sediments – A feasibility study in the Holocene Rhine delta (western Netherlands)     

Jakob Wallinga  Ingwer J. Bos 《Quaternary Geochronology》2010,5(5):602-610

We test the applicability of quartz optically stimulated luminescence (OSL) dating on clastic lake sediments to investigate whether this dating method can be applied to study the timing and rate of deposition in Holocene fluvio-deltaic lakes. Our study concerns the filling of a lake by the Angstel-Vecht system, part of the Rhine delta in the western Netherlands. Age constraints are provided by radiocarbon dates on the development and abandonment of the fluvial channels debouching into the lake. Results indicate that light exposure prior to deposition and burial was sufficient to reset the OSL signal of the vast majority of the quartz grains. Special attention was given to accurate estimation of the dose rate in the laminated and bedded deposits. The OSL ages obtained are in good agreement with the age constraints, especially for the relatively coarse sediments. OSL results indicate that the filling of the lake took about 700 years, with a sedimentation rate of ～3 mm per year. This study is a demonstration of the use of OSL dating of sand-sized quartz to determine the timing and rate of sedimentation in a Holocene fluvio-deltaic environment.  相似文献   

Fast error analysis of continuous GPS observations   总被引：4，自引：1，他引：3  

M. S. Bos  R. M. S. Fernandes  S. D. P. Williams  L. Bastos 《Journal of Geodesy》2008,82(3):157-166

It has been generally accepted that the noise in continuous GPS observations can be well described by a power-law plus white noise model. Using maximum likelihood estimation (MLE) the numerical values of the noise model can be estimated. Current methods require calculating the data covariance matrix and inverting it, which is a significant computational burden. Analysing 10 years of daily GPS solutions of a single station can take around 2 h on a regular computer such as a PC with an AMD Athlon^TM 64 X2 dual core processor. When one analyses large networks with hundreds of stations or when one analyses hourly instead of daily solutions, the long computation times becomes a problem. In case the signal only contains power-law noise, the MLE computations can be simplified to a process where N is the number of observations. For the general case of power-law plus white noise, we present a modification of the MLE equations that allows us to reduce the number of computations within the algorithm from a cubic to a quadratic function of the number of observations when there are no data gaps. For time-series of three and eight years, this means in practise a reduction factor of around 35 and 84 in computation time without loss of accuracy. In addition, this modification removes the implicit assumption that there is no environment noise before the first observation. Finally, we present an analytical expression for the uncertainty of the estimated trend if the data only contains power-law noise. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.  相似文献