Isotopic mass dependence of metal cation diffusion coefficients in liquid water     

Ian C. Bourg  Frank M. Richter  Garrison Sposito 《Geochimica et cosmochimica acta》2010,74(8):2249-5818

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Conditions in the protoplanetary disk as seen by the type B CAIs     

Frank M. Richter  Ruslan A. Mendybaev  Andrew M. Davis 《Meteoritics & planetary science》2006,41(1):83-93

Abstract— Type B coarse‐grained calcium‐aluminum‐rich inclusions (CAIs) are the oldest known materials to have formed in the solar system and are a unique source of information regarding conditions and processes in the protoplanetary disk around the young sun. Recent experimental results on the crystallization and evaporation of type B‐like silicate melts allow us to place the following constraints on the conditions in the protoplanetary disk during the formation of type B CAIs. 1) Once type B CAIs precursors have been condensed from a solar composition gas, they were reheated at 1250–1450 °C, as is indicated by their igneous texture. 2) The melilite mantles characteristic of type B1 CAIs could be formed by crystallization of magnesium‐ and silicon‐depleted melt in the outer part of the partially molten droplets. Such depletion can arise when evaporation is fast compared to chemical diffusion in the melt. This requires the pressure of the surrounding solar composition gas to be at least 10⁻⁴ bars during the initial crystallization of melilite mantle. Type B2 CAIs with uniform distribution of melilite are expected to form at pressures less than 10⁻⁵ bars. 3) Evaporation calculations are used to place bounds on the thermal history of the type B CAIs. Observed compositional zoning in melilite suggests that the temperatures in the protoplanetary disk where the type B CAIs resided after crystallization could not have exceeded ˜1000 °C for more than a few tens of thousands of years. A recent calculation of the physical conditions associated with nebular shocks produced transient temperatures and gas pressures very much like what we find is required to melt reasonable CAI precursors and evaporate these sufficiently quickly to make a type B1 CAI.  相似文献   

GGOS-D: homogeneous reprocessing and rigorous combination of space geodetic observations   总被引：3，自引：3，他引：0  

M. Rothacher  D. Angermann  T. Artz  W. Bosch  H. Drewes  M. Gerstl  R. Kelm  D. K?nig  R. K?nig  B. Meisel  H. M��ller  A. Nothnagel  N. Panafidina  B. Richter  S. Rudenko  W. Schwegmann  M. Seitz  P. Steigenberger  S. Tesmer  V. Tesmer  D. Thaller 《Journal of Geodesy》2011,85(10):679-705

In preparation of activities planned for the realization of the Global Geodetic Observing System (GGOS), a group of German scientists has carried out a study under the acronym GGOS-D which closely resembles the ideas behind the GGOS initiative. The objective of the GGOS-D project was the investigation of the methodological and information-technological realization of a global geodetic-geophysical observing system and especially the integration and combination of the space geodetic observations. In the course of this project, highly consistent time series of GPS, VLBI, and SLR results were generated based on common state-of-the-art standards for modeling and parameterization. These series were then combined to consistently and accurately compute a Terrestrial Reference Frame (TRF). This TRF was subsequently used as the basis to produce time series of station coordinates, Earth orientation, and troposphere parameters. In this publication, we present results of processing algorithms and strategies for the integration of the space-geodetic observations which had been developed in the project GGOS-D serving as a prototype or a small and limited version of the data handling and processing part of a global geodetic observing system. From a comparison of the GGOS-D terrestrial reference frame results and the ITRF2005, the accuracy of the datum parameters is about 5?C7?mm for the positions and 1.0?C1.5?mm/year for the rates. The residuals of the station positions are about 3?mm and between 0.5 and 1.0?mm/year for the station velocities. Applying the GGOS-D TRF, the offset of the polar motion time series from GPS and VLBI is reduced to 50 ??as (equivalent to 1.5?mm at the Earth??s surface). With respect to troposphere parameter time series, the offset of the estimates of total zenith delays from co-located VLBI and GPS observations for most stations in this study is smaller than 1.5?mm. The combined polar motion components show a significantly better WRMS agreement with the IERS 05C04 series (96.0/96.0???as) than VLBI (109.0/100.7???as) or GPS (98.0/99.5???as) alone. The time series of the estimated parameters have not yet been combined and exploited to the extent that would be possible. However, the results presented here demonstrate that the experiences made by the GGOS-D project are very valuable for similar developments on an international level as part of the GGOS development.  相似文献   

Coastal tides in West Greenland derived from tide gauge records     

Andreas Richter  Søren Rysgaard  Reinhard Dietrich  John Mortensen  Dorthe Petersen 《Ocean Dynamics》2011,61(1):39-49

Based on pressure tide-gauge observations, sea-level records are derived for ten sites along the coast of West Greenland. The ocean tidal signal is extracted by a harmonic tidal analysis. The accuracy of the determined tidal constants is discussed in detail. The tides account for 85% of the observed sea-level standard deviation. The tide gauge records reveal significant shallow-water tidal effects, in particular compound and overtide amplitudes reaching 5 cm. The propagation of the tidal waves into the fjords depends strongly on local conditions and is in some cases accompanied by an amplification of the tidal amplitudes. The observed tidal signals are compared to the predictions of the global ocean tide model FES2004. At the outer coast, a good agreement is found. Inside the fjords, however, the model performs worse and tide gauge observations may still be indispensable when accurate tidal signals are required.  相似文献   

Mg and Si isotopic fractionation patterns in types B1 and B2 CAIs: Implications for formation under different nebular conditions     

Emma S. Bullock  Kim B. Knight  Frank M. Richter  Noriko T. Kita  Takayuki Ushikubo  Glenn J. MacPherson  Andrew M. Davis  Ruslan A. Mendybaev 《Meteoritics & planetary science》2013,48(8):1440-1458

Magnesium and silicon isotopic profiles across melilite grains in two type B1 and two type B2 calcium‐aluminum‐rich inclusions (CAIs) reveal differing but constant enrichments in heavy isotopes everywhere except ≤1000 μm from the CAI margins. There is no close correlation in the B1s or the B2s between isotopic composition and åkermanite content of the melilite, a measure of progressive igneous crystallization, yet such a correlation might be expected in a type B2: without a melilite mantle (as in B1s) to seal the interior off and prevent further evaporation, the melt would have maintained communication with the external gas. These observations indicate a model in which B1s and B2s solidified under differing conditions. The B2s solidified under lower hydrogen pressures ( ≤ 10^?4 – 10^?5 bars) than did B1s ( > 10^?4 bars), so surface volatilization was slower in the B2s and internal chemical and isotopic equilibrium was maintained over the interval of melilite crystallization. The outermost zones of the CAIs (≤1000 μm from the edge) are not consistently enriched in heavy isotopes relative to the interiors, as might be expected from diffusion‐limited surface evaporation of the melt. In all cases, the magnesium in the CAI margins is lighter than in the interiors. In one case, silicon in the margin also is lighter, but locally in some CAIs, it is isotopically heavier near the surface. If melt evaporation played a role in the formation of these outer zones, a later event in many cases caused isotopic re‐equilibration with an external and isotopically near‐normal reservoir.  相似文献   

LunarEX—a proposal to cosmic vision     

A. Smith  I. A. Crawford  R. A. Gowen  A. J. Ball  S. J. Barber  P. Church  A. J. Coates  Y. Gao  A. D. Griffiths  A. Hagermann  K. H. Joy  A. Phipps  W. T. Pike  R. Scott  S. Sheridan  M. Sweeting  D. Talboys  V. Tong  N. Wells  J. Biele  J. Chela-Flores  B. Dabrowski  J. Flannagan  M. Grande  J. Grygorczuk  G. Kargl  O. B. Khavroshkin  G. Klingelhoefer  M. Knapmeyer  W. Marczewski  S. McKenna-Lawlor  L. Richter  D. A. Rothery  K. Seweryn  S. Ulamec  R. Wawrzaszek  M. Wieczorek  I. P. Wright  M. Sims 《Experimental Astronomy》2009,23(3):711-740

While the surface missions to the Moon of the 1970s achieved a great deal, scientifically much was also left unresolved. The recent plethora of lunar missions (flown or proposed) reflects a resurgence in interest in the Moon, not only in its own right, but also as a record of the early solar system including the formation of the Earth. Results from recent orbiter missions have shown evidence of ice or at least hydrogen within shadowed craters at the lunar poles.  相似文献   

Simultaneous measurements of Martian plasma boundaries by Rosetta and Mars Express     

N.J.T. Edberg  A.I. Eriksson  U. Auster  S. Barabash  A. Bößwetter  C.M. Carr  S.W.H. Cowley  E. Cupido  M. Fränz  K.-H. Glassmeier  R. Goldstein  M. Lester  R. Lundin  R. Modolo  H. Nilsson  I. Richter  M. Samara  J.G. Trotignon 《Planetary and Space Science》2009,57(8-9):1085-1096

We present the first two-spacecraft near-simultaneous observations of the Martian bow shock (BS), magnetic pileup boundary (MPB) and photo-electron boundary (PEB) obtained by the plasma instruments onboard Rosetta and Mars Express during the Rosetta Mars flyby on February 25, 2007. Our observations are compared with shape models for the BS and MPB derived from previous statistical studies. The MPB is found at its expected position but the BS for this event is found significantly closer to the planet than expected for the rather slow and moderately dense solar wind. Cross-calibration of the density measurements on the two spacecraft gives a density profile through the magnetosheath, indicating an increasing solar wind flux during the Rosetta passage which is consistent with the multiple BS crossings at the Rosetta exit.  相似文献   

Late Holocene (0–2.4 ka BP) surface water temperature and salinity variability, Feni Drift, NE Atlantic Ocean     

T.O. Richter  F.J.C. Peeters  T.C.E. van Weering   《Quaternary Science Reviews》2009,28(19-20):1941-1955

Planktonic foraminiferal Mg/Ca ratios and oxygen isotopic compositions of a spliced sediment record from Feni Drift, NE Atlantic Ocean (box core M200309 and piston core ENAM9606) trace late Holocene sea surface temperature (SST) and salinity changes over the past 2400 years. At this location, the variability of SST and oxygen isotopic composition of seawater (δ¹⁸O_w) reflects variable northward advection of warm and saline surface waters, which appears linked to climate variability over the adjacent European continent. Our records reveal a general long-term cooling trend. Superimposed on this overall trend, partly higher temperatures and salinities from 180 to 560 AD and 750 to 1160 AD may be ascribed to the Roman and Medieval Warm Periods, respectively. Subsequently, our record displays highly variable surface water conditions; the main Little Ice Age SST minimum is restricted to the 15th and 16th centuries AD. Pervasive multidecadal- to centennial-scale variability throughout the sedimentary proxy records can be partly attributed to solar forcing and/or variable heat extraction from the surface ocean caused by shifts in the prevailing state of the North Atlantic Oscillation (NAO). High salinities in the 17th and 18th centuries are considered to reflect tropical anomalies linked to a southward shift of the Intertropical Convergence Zone, propagating across the North Atlantic Ocean.  相似文献   

Book reviews     

Dieter Richter  Axel Borsdorf  Olusegun Areola  Risto Laulajainen  L. Wahlstroem  Reinhard Stewig  Jonathan B. Laronne  Gösta A. Eriksson  Cesar N. Caviedes  John Gunn  Karl Mauder  G. Kunkel  John T. Pierce  Leszek A. Kosinski  G.orge H. Kakiuchi  Reiner Herrmann  W. M. Sackinger 《GeoJournal》1982,6(6):581-588

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Book reviews     

J. W. House  Engelbert Altenburger  D. Richter  W. U. Ehrmann  A. G. Koestler  U. C. Schreiber  Volker Kaminske 《GeoJournal》1984,9(1):64-98

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