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11.
Progress in Carrier Phase Time Transfer 总被引:1,自引:0,他引:1
Jim Ray Felicitas Arias Gérard Petit Tim Springer Thomas Schildknecht Jon Clarke Jan Johansson 《GPS Solutions》2001,4(4):47-54
The progress of the joint Pilot Project for time transfer, formed by the International GPS Service (IGS) and the Bureal International
des Poids et Mesures (BIPM), was recently reviewed. Three notable milestones were set. (1) The IGS will implement, at least
in a test mode, an internally realized time scale based on an integration of combined frequency standards within the IGS network.
This will eventually become the reference time scale for all IGS clock products (instead of the current GPS broadcast time).
(2) A new procedure for combined receiver and satellite clock products will be implemented officially in November 2000. Receiver
clocks are an entirely new product of the IGS. (3) The BIPM will coordinate an effort to calibrate all Ashtech Z12-T (and
possibly other) receivers suitable for time transfer applications, either differentially or absolutely. Progress reports will
be presented publicly in the spring 2001. ? 2001 John Wiley & Sons, Inc. 相似文献
12.
The stability constants K1 and K12 of phosphoric acid were determined for artificial seawater of six different salinities (5, 10, 20, 30, 35, 40‰) and in 0.2, 0.4 and 0.7 M NaCl at three temperatures (5, 15, 25°C). The results are compared with those of Kester and Pytkowicz (1967), Atlas et al. (1976) and Dickson and Riley (1979). The ionic product of water, Kw, was determined in sodium chloride media at 5, 15 and 25°C. Complex formation among Ca2+, Mg2+, HPO42? and PO43? is discussed. 相似文献
13.
Paleomagnetic samples were collected from 190 m of the Late Carboniferous/Early Permian Casper Formation in southeastern Wyoming. A total of 549 samples was drilled near the vicinity of Horse Creek Station at an average stratigraphic interval of 33 cm. All samples were reversely magnetized. Rock magnetic analyses indicate that the primary carrier of remanence in the formation is hematite. A selection criterion applied to the partial demagnetized data restricted the sample population to 233, resulting in a paleomagnetic North Pole located at 47.4°N, 127.4°E (δp=0.7;δm=1.4). The Casper pole agrees well with other Late Carboniferous/Early Permian poles for cratonic North America. The tight clustering of these paleomagnetic poles suggests that little apparent polar motion with respect to North America occurred during this time. Comparing the stable North American poles with paleomagnetic poles from Late Carboniferous/Early Permian strata of the New England-Canadian Maritime region (Acadia) indicates that this region did not reach its present position relative to North America until at least the Early Permian. 相似文献
14.
Kurt Johansson Rune B. Larsen Markku J. Lehtinen Lars Persson Mika Raeisaenen Stig A. Schack Pedersen Paer Weihed Nils-Gunnar Wik 《《幕》》2008,31(1):133-139
The Nordic countries, including Greenland, have a long tradition in mining. The industrial minerals sector is expanding in most Nordic countries and extensive development has taken place during the last few years. The main commodities mined are carbonate rocks, quartz, feldspar, apatite, olivine and talc.
A number of diferent types of dimension stones are quarried in all countries. Rock aggregates are increasingly important, replacing sand and gravel aggregate as construction materials in some countries due to the need to protect ground water supplies. 相似文献
A number of diferent types of dimension stones are quarried in all countries. Rock aggregates are increasingly important, replacing sand and gravel aggregate as construction materials in some countries due to the need to protect ground water supplies. 相似文献
15.
S. V. Kalenskii S. Kurtz V. I. Slysh P. Hofner C. M. Walmsley L. E. B. Johansson P. Bergman 《Astronomy Reports》2010,54(10):932-939
We present the results of VLA observations of a maser candidate in the low-mass star formation region L1157 in the 70-61
A
+ transition at 44 GHz. The line is emitted by a compact, undoubtedly maser source associated with clump B0a, which is seen
in maps of L1157 in thermal lines of methanol and other molecules. A much weaker compact source is associated with clump B1a,
which is brighter than B0a in thermal methanol lines. The newly detected masers may form in thin layers of turbulent post-shock
gas. In this case, the maser emission may be beamed, so that only an observer located in or near the planes of the layers
can observe strong masers. On the other hand, the maser lines are double with a “red” asymmetry, indicating that the masers
may form in collapsing clumps. A detailed analysis of collapsing-cloud maser models and their applicability to the masers
in L1157 will be developed in subsequent papers. 相似文献
16.
Spatio-temporal trends of heavy metals and source apportionment in Tolo Harbour,Hong Kong 总被引:1,自引:1,他引:0
This study provided a picture of the spatial and temporal distributions of Cr, Co, Ni Cu, Zn, As, Cd and Pb in bottom sediments
of Tolo Harbour. The concentrations of the eight heavy metals differed significantly between sites due to the poor tidal flushing
in Tolo Harbour. The levels of Cu, Zn, Cd and Pb were generally enriched in sediments from inner Tolo Harbour, while sediments
from outer Tolo Harbour (Tolo Channel) had higher levels of Cr, Co and Ni. The redox sensitive element arsenic showed no distinct
spatial pattern in Tolo Harbour. The decreasing levels of Cu, Zn, Pb and Cd in sediments with increasing distance from land
demonstrated a typical diffusion pattern from land to the direction of sea. Two hot spots of Cu, Zn, Pb and Cd in sediments
were located near Tai Po and Sha Tin new town, indicating that Cu, Zn, Pb and Zn were from land-derived sources. The sites
with relatively high levels of Cr, Co and Ni in sediments were located in areas close to waste spoil in sea floor. The natural
and anthropogenic inputs from Sha Tin and Tai Po to Tolo Harbour were mostly responsible for Cu, Zn, Cd and Pb enrichment
in sediments from inner Tolo Harbour. The waste spoil in sea floor was believed to contribute to the Cr, Co and Ni in outer
Tolo Harbour. The results of correlation coefficient between the eight heavy metals showed that Cu, Zn, Cd and Pb were strongly
positively correlated, and Cr, Co and Ni were also significantly correlated with each other. The best explanation of strong
correlation was their similar source. As, however, is not well correlated with the other seven heavy metals. The average concentrations
of Cu and Zn displayed general increasing trends from 1978 to 2006 in Tolo Harbour, while the mean levels of Cr and Pb displayed
a substantial decrease from 1978 to 1987, then a slight increase after 1987. No distinct temporal trends of the concentrations
of Ni and As were observed from 1978 due to the inconsecutive data. On the other hand, the increasing trends of Cr, Cu, Zn,
Cd and Pb were observed since 1996. 相似文献
17.
For agriculture, there are three major options for mitigating greenhouse gas (GHG) emissions: 1) productivity improvements, particularly in the livestock sector; 2) dedicated technical mitigation measures; and 3) human dietary changes. The aim of the paper is to estimate long-term agricultural GHG emissions, under different mitigation scenarios, and to relate them to the emissions space compatible with the 2 °C temperature target. Our estimates include emissions up to 2070 from agricultural soils, manure management, enteric fermentation and paddy rice fields, and are based on IPCC Tier 2 methodology. We find that baseline agricultural CO2-equivalent emissions (using Global Warming Potentials with a 100 year time horizon) will be approximately 13 Gton CO2eq/year in 2070, compared to 7.1 Gton CO2eq/year 2000. However, if faster growth in livestock productivity is combined with dedicated technical mitigation measures, emissions may be kept to 7.7 Gton CO2eq/year in 2070. If structural changes in human diets are included, emissions may be reduced further, to 3–5 Gton CO2eq/year in 2070. The total annual emissions for meeting the 2 °C target with a chance above 50 % is in the order of 13 Gton CO2eq/year or less in 2070, for all sectors combined. We conclude that reduced ruminant meat and dairy consumption will be indispensable for reaching the 2 °C target with a high probability, unless unprecedented advances in technology take place. 相似文献
18.
Seawater intrusion has been an important topic in hydrogeology in China in recent decades. The rapid growth of the population and economy in the coastal regions has been consuming a tremendous amount of groundwater resources and has increased the extent of seawater intrusion. The spatial discrepancy of water resource distribution has caused the studies of seawater intrusion into China to mainly be concentrated on the area around the Bohai Sea in the northern part of China. The total area of seawater-intruded land due to excessive groundwater utilization in the area was estimated to be approximately 2,457 km2 in 2003. Great efforts have been made to mitigate the extent of seawater intrusion and to secure more freshwater resources, including building monitoring networks, subsurface barrier and groundwater reservoirs, and artificial infiltration facilities. Management projects over the years were evaluated to satisfy the objectives and to provide valuable experiences for future research and planning. It is expected that the coastal groundwater conditions of the northern region will improve through the development of a national water resource plan, such as the ongoing south-to-north water diversion project. 相似文献
19.
20.
Qiule He Xingxing Kuang Jiachang Chen Jiu Jimmy Jiao Sihai Liang Chunmiao Zheng 《Ground water》2022,60(3):434-450
Glaciers on the Tibetan Plateau play an important role in the local hydrological cycle. However, there are only few studies on groundwater in the alpine basins in the Tibetan Plateau which considered the effects of glaciers. Glaciers are extensively distributed in the Dongkemadi River Basin, which is a representative alpine basin in the Yangtze River source region. This study focuses on building a numerical groundwater flow model with glaciations using HydroGeoSphere (HGS) to simulate subglacial meltwater recharge to groundwater in the Dongkemadi River Basin in response to future climate changes. Effects of hydraulic conductivity, precipitation, and temperature on subglacial meltwater recharge to groundwater were discussed. Glacier changes in the future 50 years were predicted under different climate change scenarios. Results show that: (1) the average thickness of the glacier will change significantly; (2) the simulated rate of annual mean subglacial meltwater recharge to groundwater is 4.58 mm, which accounts for 6.33% of total groundwater recharge; and (3) hydraulic conductivity has the largest influence on subglacial meltwater recharge to groundwater, followed by temperature and precipitation. Results of this study are also important to sustainable water resource usage in the Yangtze River source region. 相似文献