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351.
Zhang Suihan Johansson Fredrik Stille Håkan 《Geotechnical and Geological Engineering》2022,40(4):2167-2186
Geotechnical and Geological Engineering - Grout curtains are commonly constructed under dams to reduce the seepage through the rock foundation. In the design of grout curtains, empirical methods... 相似文献
352.
Observations of Comet 9P/Tempel 1 around the Deep Impact event by the OSIRIS cameras onboard Rosetta
Horst Uwe Keller Sonia Fornasier Stubbe F. Hviid Jörg Knollenberg Miriam Rengel Gabriele Cremonese Detlef Koschny Ekkehard Kührt Holger Sierks Cesare Barbieri Hans Rickman Michael F. A'Hearn Maria-Antonella Barucci Vania da Deppo Björn J.R. Davidsson Stefano Debei Fritz Gliem José J. Lopez Moreno Giampiero Naletto Angel Sanz Andrés 《Icarus》2007,187(1):87-103
The OSIRIS cameras on the Rosetta spacecraft observed Comet 9P/Tempel 1 from 5 days before to 10 days after it was hit by the Deep Impact projectile. The Narrow Angle Camera (NAC) monitored the cometary dust in 5 different filters. The Wide Angle Camera (WAC) observed through filters sensitive to emissions from OH, CN, Na, and OI together with the associated continuum. Before and after the impact the comet showed regular variations in intensity. The period of the brightness changes is consistent with the rotation period of Tempel 1. The overall brightness of Tempel 1 decreased by about 10% during the OSIRIS observations. The analysis of the impact ejecta shows that no new permanent coma structures were created by the impact. Most of the material moved with . Much of it left the comet in the form of icy grains which sublimated and fragmented within the first hour after the impact. The light curve of the comet after the impact and the amount of material leaving the comet ( of water ice and a presumably larger amount of dust) suggest that the impact ejecta were quickly accelerated by collisions with gas molecules. Therefore, the motion of the bulk of the ejecta cannot be described by ballistic trajectories, and the validity of determinations of the density and tensile strength of the nucleus of Tempel 1 with models using ballistic ejection of particles is uncertain. 相似文献
353.
In a previous paper (Gayon and Bois 2008a), we have shown the general efficiency of retrograde resonances for stabilizing
compact planetary systems. Such retrograde resonances can be found when two-planets of a three-body planetary system are both
in mean motion resonance and revolve in opposite directions. For a particular two-planet system, we have also obtained a new
orbital fit involving such a counter-revolving configuration and consistent with the observational data. In the present paper,
we analytically investigate the three-body problem in this particular case of retrograde resonances. We therefore define a
new set of canonical variables allowing to express correctly the resonance angles and obtain the Hamiltonian of a system harboring
planets revolving in opposite directions. The acquiring of an analytical “rail” may notably contribute to a deeper understanding
of our numerical investigation and provides the major structures related to the stability properties. A comparison between
our analytical and numerical results is also carried out. 相似文献
354.
Tracing glacier wastage in the Northern Tien Shan (Kyrgyzstan/Central Asia) over the last 40 years 总被引:2,自引:1,他引:1
Peter Niederer Viktor Bilenko Natasha Ershova Hans Hurni Sergeji Yerokhin Daniel Maselli 《Climatic change》2008,86(1-2):227-234
The status and dynamics of glaciers are crucial for agriculture in semiarid parts of Central Asia, since river flow is characterized
by major runoff in spring and summer, supplied by glacier- and snowmelt. Ideally, this coincides with the critical period
of water demand for irrigation. The present study shows a clear trend in glacier retreat between 1963 and 2000 in the Sokoluk
watershed, a catchment of the Northern Tien Shan mountain range in Kyrgyzstan. The overall area loss of 28% observed for the
period 1963–2000, and a clear acceleration of wastage since the 1980s, correlate with the results of previous studies in other
regions of the Tien Shan as well as the Alps. In particular, glaciers smaller than 0.5 km2 have exhibited this phenomenon most starkly. While they registered a medium decrease of only 9.1% for 1963–1986, they lost
41.5% of their surface area between 1986 and 2000. Furthermore, a general increase in the minimum glacier elevation of 78 m
has been observed over the last three decades. This corresponds to about one-third of the entire retreat of the minimum glacier
elevation in the Northern Tien Shan since the Little Ice Age maximum. 相似文献
355.
Phenological data have shown an increase of ca. 10 days in European growing season length in the latter part of the twentieth
century. In general, these changes have been associated with global warming. Here we present a study of thermal growing season
(GS) trends in the Greater Baltic Area, northern Europe. Yearly dates for the start, end and length of the GS were computed
for 49 stations in the studied area, using daily mean temperature measurements. Trends and tendencies of the GS parameters
were analysed within the twentieth century. We also examined GS trends in long records (starting before 1850) from the region.
The results show a general increase of the length of the GS of ca one week since 1951 in the area, where the most considerable
change has occurred in spring (starting ∼6 days earlier). The largest increases were found at stations adjacent to the Baltic
Sea and North Sea, where some Danish stations showed significant increasing trends in the length of the GS of more than 20 days.
The only tendency for a shorter GS was found in Archangelsk, north western Russia. The three longest records displayed large
inter-annual and decadal variability, with tendencies for increased frequencies of longer growing seasons since the 1950s. 相似文献
356.
River discharge and freshwater runoff to the Barents Sea under present and future climate conditions
River discharge forms a major freshwater input into the Arctic Ocean, and as such it has the potential to influence the oceanic
circulation. As the hydrology of Arctic river basins is dominated by cryospheric processes such as snow accumulation and snowmelt,
it may also be highly sensitive to a change in climate. Estimating the water balance of these river basins is therefore important,
but it is complicated by the sparseness of observations and the large uncertainties related to the measurement of snowfalls.
This study aims at simulating the water balance of the Barents Sea drainage basin in Northern Europe under present and future
climate conditions. We used a regional climate model to drive a large-scale hydrological model of the area. Using simulated
precipitation derived from a climate model led to an overestimation of the annual discharge in most river basins, but not
in all. Under the B2 scenario of climate change, the model simulated a 25% increase in freshwater runoff, which is proportionally
larger than the projected precipitation increase. As the snow season is 30–50 day shorter, the spring discharge peak is shifted
by about 2–3 weeks, but the hydrological regime of the rivers remains dominated by snowmelt. 相似文献
357.
358.
LINET—An international lightning detection network in Europe 总被引:1,自引:0,他引:1
Hans D. Betz Kersten Schmidt Pierre Laroche Patrice Blanchet Wolf P. Oettinger Eric Defer Z. Dziewit J. Konarski 《Atmospheric Research》2009,91(2-4):564-573
During the past years a VLF/LF lightning detection network (LINET) was developed at the University of Munich, which provides continuous data for both research and operational purposes. In particular, the network introduces five new features: a) total lightning capability: both cloud-to-ground strokes (CG) and cloud lightning (IC) are measured; b) low-amplitude reporting: weak lightning events from discharge channel with currents well below 5 kA are detected within the central part of the network, whereby IC events dominate; c) new 3D-discrimination: a time-of-arrival method is utilized to separate CG from IC with good reliability, provided that the sensor baseline does not exceed ~ 250 km; d) IC emission height: for each cloud event a height is determined which is thought to reflect the central region of the involved channel; and e) optimised location accuracy: due to precision and combined action of all influential network components, complemented by site-error corrections, the position accuracy of strokes reaches an average value as small as ~ 150 m, whereby false locations (‘outliers’) rarely occur. During international co-operations LINET has been deployed in four continents: Europe (initially Germany), South America (area of Bauru, Brazil), Australia (around Darwin), and Central Africa (Benin). Since the features quoted above could be verified in the tests, a 65-sensor network was established in Europe and started on May 1, 2006, in co-operation with the service company nowcast. LINET covers a wide area approximately from longitude − 10° to 25° to latitude 35° to 66°; it is available for scientific projects and officially utilized by the German Weather Service for operational purposes. Meanwhile, the network was extended by deployment of additional sites so that it comprises about 90 sensors in 17 countries. 相似文献
359.
Manfred Birke Uwe Rauch Bodo Harazim Hans Lorenz Wolfgang Glatte 《Journal of Geochemical Exploration》2010
The market for mineral water has been growing steadily over the last few years. Germany is the country with the highest number of bottled mineral water brands (908 bottled water samples from 502 wells/brands were analyzed). The per capita consumption of mineral water in Germany in 2003 was 129 L. A wide range of values of one to seven orders of magnitude was determined for 71 elements in the bottled water samples analyzed by ICP-QMS, ICP-AES, IC, titration, photometric, conductometric and potentiometric methods. A comparison of the element concentrations and the legal limits for both bottled and tap water (EU, Germany, US EPA, WHO) shows that only 70% of the 908 mineral water samples fulfill the German and EU drinking water (i.e., tap water) regulations for all parameters (not including pH) for which action levels are defined. Nearly 5% of the bottled water samples not fulfill the German and EU regulations for mineral and table water. Comparison of our results with the current German and European action levels for mineral and table water shows that only 42 of the bottled water samples exceed the limits for one or more of the following elements: arsenic, nitrate, nitrite, manganese, nickel and barium concentrations. Ten of the bottled water samples contain uranium concentrations above the 10 μg/L recommended limit. 相似文献
360.
Bj?rn Sandstr?m Hans Annersten Eva-Lena Tullborg 《International Journal of Earth Sciences》2010,99(1):1-25
Red-staining of rocks due to fluid–rock interaction during hydrothermal circulation in fractures is a common feature in crystalline
sequences. In this study, red-stained metagranitic rock adjacent to fractures in Forsmark, central Sweden, has been studied
with emphasis on the mineral reactions and associated element mobility occurring during the alteration. The main mineral reactions
associated with the hydrothermal alteration are an almost complete saussuritization of plagioclase accompanied by total chloritization
of biotite. Magnetite has been partly replaced by hematite whereas quartz and K-feldspar were relatively unaffected by the
hydrothermal alteration. We show that redistribution of elements on the whole rock scale was very limited and is mainly manifested
by enrichment of Na2O and volatiles and depletion of CaO, FeO and SiO2 in the red-stained rock. However, on the microscale, element redistribution was more extensive, with both intragranular and
intergranular migration of e.g. Ca, K, Na, Al, Si, Fe, Ba, Cs, Rb, Sr, Ti and REEs. The altered rock shows a shift towards
higher total oxidation factors, but the change is smaller than 1σ and the red-staining of the rock is due to hematite dissemination
rather than a significant oxidation of the rock. An increase in the connected porosity is also observed in the altered rock. 相似文献