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51.
52.
Time-relative positioning makes use of observations taken at two different epochs and stations with a single global positioning
system (GPS) receiver to determine the position of the unknown station with respect to the known station. The limitation of
this method is the degradation over time of the positioning accuracy due to the temporal variation of GPS errors (ionospheric
delay, satellite clock corrections, satellite ephemerides, and tropospheric delay). The impact of these errors is significantly
reduced by adding to the one-way move from the known to the unknown station, a back move to the known station. A loop misclosure
is computed from the coordinates obtained at the known station at the beginning and at the end of the loop, and is used to
correct the coordinates of the unknown station. The field tests, presented in this paper, show that using the loop misclosure
corrections, time-relative positioning accuracy can be improved by about 60% when using single frequency data, and by about
40% with dual frequency data. For a 4-min processing interval (an 8-min loop) and a 95% probability level, errors remain under
20 cm for the horizontal components and 36 cm for the vertical component with single frequency data; and under 11 cm for the
horizontal components and 29 cm for the vertical component with dual frequency data. 相似文献
53.
The completeness and the accuracy of the Brest sea level time series dating from 1807 make it suitable for long-term sea level trend studies. New data sets were recently discovered in the form of handwritten tabulations, including several decades of the eighteenth century. Sea level observations have been made in Brest since 1679. This paper presents the historical data sets which have been assembled so far. These data sets span approximately 300 years and together constitute the longest, near-continuous set of sea level information in France. However, an important question arises: Can we relate the past and the present-day records? We partially provide an answer to this question by analysing the documents of several historical libraries with the tidal data using a ‘data archaeology’ approach advocated by Woodworth (Geophys Res Lett 26:1589–1592, 1999b). A second question arises concerning the accuracy of such records. Careful editing was undertaken by examining the residuals between tidal predictions and observations. It proved useful to remove the worst effects of timing errors, in particular the sundial correction to be applied prior to August 1, 1714. A refined correction based on sundial literature [Savoie, La gnomique, Editions Les Belles Lettres, Paris, 2001] is proposed, which eliminates the systematic offsets seen in the discrepancies in timing of the sea level measurements. The tidal analysis has also shown that shallow-water tidal harmonics at Brest causes a systematic difference of 0.023 m between mean sea level (MSL) and mean tide level (MTL). Thus, MTL should not be mixed with the time series of MSL because of this systematic offset. The study of the trends in MTL and MSL however indicates that MTL can be used as a proxy for MSL. Three linear trend periods are distinguished in the Brest MTL time series over the period 1807–2004. Our results support the recent findings of Holgate and Woodworth (Geophys Res Lett) of an enhanced coastal sea level rise during the last decade compared to the global estimations of about 1.8 mm/year over longer periods (Douglas, J Geophys Res 96:6981–6992, 1991). The onset of the relatively large global sea level trends observed in the twentieth century is an important question in the science of climate change. Our findings point out to an ‘inflexion point’ at around 1890, which is remarkably close to that in 1880 found in the Liverpool record by Woodworth (Geophys Res Lett 26:1589–1592, 1999b). 相似文献
54.
In implementing into a molecular dynamics simulation code a simple interionic potential developed to describe the nine component system K2O-Na2O-CaO-MgO-FeO-Fe2O3-Al2O3-TiO2-SiO2 (KNCMFATS), it has been possible to reproduce satisfactorily a number of thermodynamic, structural and transport properties of a representative set of natural silicate melts. An important conclusion reached in this study is the good transferability of the potential from felsic to ultramafic compositions although this transferability becomes less accurate with high silica contents (rhyolitic composition and beyond) and with very iron-rich silicates (e.g. fayalite). A key feature of the simulation is to make the link between macroscopic properties of the melt and its microscopic structure and dynamics. We thus obtain a relationship between the molar volume of the melt, the number of network modifiers and the oxygen coordination number. The simulation also allows one to quantify the coordination environment around the cations as function of the melt composition. Furthermore, the electrical conductivity of the high temperature liquid is investigated. 相似文献
55.
Sung-Soo Cha Kang-Kun Lee Gwang-Ok Bae Dae-Hyuck Lee Nicolas Gatelier 《Engineering Geology》2007,93(3-4):117-129
Hydrogeological monitoring was conducted around a pilot cavern for underground cryogenic LNG (Liquefied Natural Gas) storage. The monitoring was mainly focused on the operation of a drainage and recharge system. After the operation of the drainage system commenced, the drainage rate decreased rapidly in the initial stages and then decreased gradually. Hydrogeological monitoring revealed that the rock drainage system operated effectively. During drainage, the water table was maintained below the cavern roof. The recharge for ice-ring formation was performed in two phases. The first phase involved the cessation of pumping in downward-drainage holes and the second involved the closure of upward boreholes. Since the water table was maintained below the cavern roof, artificial recharge was planned at first. However, it was not implemented due to heavy rainfall in the recharge stage. On the basis of hydrogeological monitoring and hydraulic tests, it was found that the fractures above the roof and on the right wall of the pilot cavern mainly affected seepage into the cavern and thermal variation due to the storage of liquid nitrogen. Thermal variation was examined by the thermometers installed around the pilot cavern. The cooling and thawing processes reveal the characteristics of thermal distribution in the rock and the 0 °C isotherm. The cooling phase lasted for six months, and the 0 °C isotherm progressed in time after the injection of liquid nitrogen into the cavern. The isotherm propagated up to about 4 m from the floor and the sidewall of the cavern and about 3 m from the cavern roof. The cooling rate of the rock mass above the cavern roof was lower than that of the other cavern sides due to the gaseous space in the upper part of the containment. The fractures were analyzed and considered for thermal modeling. A two-dimensional finite element analysis was performed to compare the field monitoring at the pilot cavern. The numerical modeling shows the distance between the ice ring and heat transfer pattern of the fractures around the pilot cavern. The propagation of the measured and calculated 0 °C isotherm reveals that the water-conveying joint on the right wall might affect thermal propagation through a thermal pipe. 相似文献
56.
Fabien Gibert Juan Cuesta Jun-Ichi Yano Nicolas Arnault Pierre H. Flamant 《Boundary-Layer Meteorology》2007,125(3):553-573
We question the correlation between vertical velocity (w) on the one hand and the occurrence of convective plumes in lidar reflectivity (i.e. range corrected backscatter signal Pz
2) and depolarization ratio (Δ) on the other hand in the convective boundary layer (CBL). Thermal vertical motion is directly
investigated using vertical velocities measured by a ground-based Doppler lidar operating at 2 μm. This lidar provides also
simultaneous measurements of lidar reflectivity. In addition, a second lidar 200 m away provides reflectivities at 0.53 and
1 μm and depolarization ratio at 0.53 μm. The time series from the two lidars are analyzed in terms of linear correlation
coefficient (ρ). The main result is that the plume-like structures provided by lidar reflectivity within the CBL as well as the CBL height
are not a clear signature of updrafts. It is shown that the lidar reflectivity within the CBL is frequently anti-correlated
(ρ (w, Pz
2 )) with the vertical velocity. On the contrary, the correlation coefficient between the depolarization ratio and the vertical
velocity ρ (w, Δ ) is always positive, showing that the depolarization ratio is a fair tracer of updrafts. The importance of relative humidity
on the correlation coefficient is discussed.
An erratum to this article can be found at 相似文献
57.
Climate extremes in Loess of China coupled with the strength of deep-water formation in the North Atlantic 总被引:1,自引:0,他引:1
Zhengtang Guo Tungsheng Liu Nicolas Fedoroff Lanying Wei Zhongli Ding Naiqin Wu Huoyuan Lu Wenying Jiang Zhisheng An 《Global and Planetary Change》1998,18(3-4)
The loess-paleosol sequences of the last 1.2 Ma in China have recorded two kinds of climate extremes: the strongly developed S4, S5-1 and S5-3 soils (corresponding to the marine δ18O stages 11, 13, and 15, respectively) as evidence of three episodes of great warmth and two coarse-grained loess units (L9 and L15, corresponding to the marine δ18O stages 22, 23, 24 and 38, respectively) which indicate severest glacial conditions. The climatic and geographical significance of these events are still unclear, and their cause remains a puzzle.Paleopedological, geochemical and magnetic susceptibility data from three loess sections (Xifeng, Changwu and Weinan) suggest that the S4, S5-1 and S5-3 soils were formed under sub-tropical semi-humid climates with a tentatively estimated mean annual temperature (MAT) of at least 4–6°C higher and a mean annual precipitation (MAP) of 200–300 mm higher than for the present-day, indicating a much strengthened summer monsoon. The annual rainfall was particularly accentuated for the southern-most part of the Loess Plateau, suggesting that the monsoon rain belt (the contact of the monsoonal northward warm-humid air mass with the dry-cold southward one) might have stood at the southern part of the Plateau for a relatively long period each year. The loess units L9 and L15 were deposited under semi-desertic environments with a tentatively estimated MAT and MAP of only about 1.5–3°C and 150–250 mm, indicating a much strengthened winter monsoon, and that the summer monsoon front could rarely penetrate into the Loess Plateau region.Correlation with marine carbon isotope records suggests that these climate extremes have large regional, even global, significance rather than being local phenomena in China. They match the periods with greatest/smallest Atlantic–Pacific δ13C gradients, respectively, indicating their relationships with the strength of Deep Water (NADW) production in the North Atlantic. These results suggest that the monsoon climate in the Loess Plateau region was significantly linked with the North Atlantic thermohaline circulation on timescales of 104 years. 相似文献
58.
Xavier Le Pichon Jacques Angelier Jean Aubouin Nicolas Lyberis Serge Monti Vincent Renard Henri Got Ken Hsu¨ Yossi Mart Jean Mascle Drummond Matthews Dimitri Mitropoulos Pandelis Tsoflias Georges Chronis 《Earth and Planetary Science Letters》1979,44(3):441-450
Preliminary results of a multi-narrow beam survey of the Hellenic trench system, in the Eastern Mediterranean, are presented. The southwestern Ionian branch is divided in small basins, partly filled with Pleistocene sediments. The morphology suggests that the basins are deformed by a compressional stress acting roughly perpendicularly to the trench along N50°E. This direction is the direction of the regional slip vector of the shallow thrust-type earthquakes. The structure of the southeastern Pliny-Strabo branch is quite different. Narrow en-e´chelon slots, oriented N40°E, have been mapped within the main troughs oriented N60°E. The regional earthquake slip vector is also oriented along N40°E. We conclude that the Hellenic trench system is an active subduction system, dominated by thrust along the Ionian branch and by transform motion along the Pliny-Strabo branch. 相似文献
59.
Adolphe Nicolas 《Tectonophysics》1976,32(1-2)
Flow mechanisms effective in the upper mantle and some of the parameters of the creep equation are determined from the study of peridotites from basalt and kimberlite xenoliths and alpine-type massifs. Creep controlled by dislocation climb, as inferred by Weertman, is the dominant mechanism. Evidence for superplastic flow is found in the deepest kimberlite xenoliths. Flow in the alpine-type massifs is ascribed either to intrusion in the crust when continental plates collide (lherzolite massifs) or to sea-floor spreading (harzburgite massifs included in ophiolites). The consideration of textures, crystal substructures and preferred orientations connected with P,T equilibrium conditions derived from pyroxenes, helps in deciphering the large-scale structure and flow of peridotites in the crust and in the mantle down to 200 km. For the first 150 km, the representative structures are those of the basalt xenoliths and the kimberlite xenoliths with a coarsegrained texture. They have many features in common and probably represent a static lithosphere with, in basalt xenoliths, possible evidence for the transition to the shear flowing asthenosphere. The porphyroclastic and mosaic-textured xenoliths, in kimberlites equilibrated at depth between 150 and 200 km and a few more superficial basalt xenoliths, reflect a much larger strain rate and applied stress and might be connected to vertical instabilities also responsible for magma genesis. 相似文献
60.
David L. COOK Meenakshi WADHWA Robert N. CLAYTON Nicolas DAUPHAS Philip E. JANNEY Andrew M. DAVIS 《Meteoritics & planetary science》2007,42(12):2067-2077
Abstract— We measured nickel isotopes via multicollector inductively coupled plasma mass spectrometry (MC‐ICPMS) in the bulk metal from 36 meteorites, including chondrites, pallasites, and irons (magmatic and non‐magmatic). The Ni isotopes in these meteorites are mass fractionated; the fractionation spans an overall range of ~0.4‰ amu?1. The ranges of Ni isotopic compositions (relative to the SRM 986 Ni isotopic standard) in metal from iron meteorites (~0.0 to ~0.3‰ amu?1) and chondrites (~0.0 to ~0.2‰ amu?1) are similar, whereas the range in pallasite metal (~–0.1 to 0.0‰ amu?1) appears distinct. The fractionation of Ni isotopes within a suite of fourteen IIIAB irons (~0.0 to ~0.3‰ amu?1) spans the entire range measured in all magmatic irons. However, the degree of Ni isotopic fractionation in these samples does not correlate with their Ni content, suggesting that core crystallization did not fractionate Ni isotopes in a systematic way. We also measured the Ni and Fe isotopes in adjacent kamacite and taenite from the Toluca IAB iron meteorite. Nickel isotopes show clearly resolvable fractionation between these two phases; kamacite is heavier relative to taenite by ~0.4‰ amu?1. In contrast, the Fe isotopes do not show a resolvable fractionation between kamacite and taenite. The observed isotopic compositions of kamacite and taenite can be understood in terms of kinetic fractionation due to diffusion of Ni during cooling of the Fe‐Ni alloy and the development of the Widmanstätten pattern. 相似文献