Large wood potential,piece characteristics,and flood effects in Swiss mountain streams     

Christian Rickli  Alexandre Badoux  Dieter Rickenmann  Nicolas Steeb  Peter Waldner 《自然地理学》2018,39(6):542-564

We present results of two studies on the (1) potential wood load in steep headwater streams and (2) properties of large wood (LW) transported in mountain rivers during the large August 2005 flood event in Switzerland. Ten headwater reaches of 1000 m length were surveyed in different regions of Switzerland. The potential wood load was estimated for in-channel deadwood, and possible driving factors were explored. Correlations were found with dead wood volume on hillslopes and mean channel width. We established size distributions of LW pieces and identified probable recruitment processes. Four reaches were resurveyed after an exceptionally severe flood in August 2005, showing limited LW transport in channels but considerable wood input by mass wasting processes. In addition, characteristics of deposits of LW along mountain rivers affected by the 2005 flood were investigated. Diameter and length distribution of transported and deposited pieces were comparable to those of LW from steep headwater streams, yet with considerably fewer long pieces in the deposits of mountain rivers. Most LW pieces were fresh wood, indicating that the portion of in-channel deadwood transported during the 2005 flood was limited. Findings of the study contribute to a better understanding of LW dynamics in Alpine mountain streams.  相似文献   

Gravity studies of Aphrodite Terra on Venus     

Janle  Peter  Jannsen  Dieter 《Earth, Moon, and Planets》1986,36(3):275-287

Aphrodite Terra is the largest highland area on Venus of the size of Africa. It is traversed by the Aphrodite-Beta belt of troughs with a length of 21 000 km. There are two other large belts of troughs on Venus: Themis-Atla, 14 000 km long, and Beta-Phoebe, 8000 km long. In this paper, four gravity profiles across Aphrodite Terra are studied and compared with the morphology.Western Aphrodite and Niobe Planitia to the north seem to be in isostatic equilibrium under the assumption of Airy compensation with a mean crustal thickness of T = 50 km. The graben area in the middle part of Aphrodite Terra shows negative isostatic gravity anomalies indicating deficit masses. The adjacent Atla Regio to the east is regionally Airy compensated with T = 50 km, and the mountains Nokomis, Maat and Ozza Montes are locally undercompensated, i.e. they are associated with surplus masses in the depth. Ulfrun Regio, a hilly terrain just east of Atla Regio is Airy compensated with T = 30 km. These results give a mean crustal thickness around 50 km for Aphrodite Terra. The isostatic disturbed zones in the middle of Aphrodite (grabens) and Atla Regio as well as the undercompensated Beta Regio have been associated with recent volcanism from the observation of the concentrations of electrical discharges in these areas. Atla and Beta Regiones are both located at intersections of the systems of troughs described above.Contribution No. 308, Institut für Geophysik der Universität Kiel, F.R.G.  相似文献   

Ceres’ spectral link to carbonaceous chondrites—Analysis of the dark background materials          下载免费PDF全文

Michael Schäfer  Tanja Schäfer  Matthew R. M. Izawa  Edward A. Cloutis  Stefan E. Schröder  Thomas Roatsch  Frank Preusker  Katrin Stephan  Klaus‐Dieter Matz  Carol A. Raymond  Christopher T. Russell 《Meteoritics & planetary science》2018,53(9):1925-1945

Ceres’ surface has commonly been linked with carbonaceous chondrites (CCs) by ground‐based telescopic observations, because of its low albedo, flat to red‐sloped spectra in the visible and near‐infrared (VIS/NIR) wavelength region, and the absence of distinct absorption bands, though no currently known meteorites provide complete spectral matches to Ceres. Spatially resolved data of the Dawn Framing Camera (FC) reveal a generally dark surface covered with bright spots exhibiting reflectance values several times higher than Ceres’ background. In this work, we investigated FC data from High Altitude Mapping Orbit (HAMO) and Ceres eXtended Juling (CXJ) orbit (~140 m/pixel) for global spectral variations. We found that the cerean surface mainly differs by spectral slope over the whole FC wavelength region (0.4–1.0 μm). Areas exhibiting slopes ?1 constitute only ~3% of the cerean surface and mainly occur in the bright material in and around young craters, whereas slopes ≥?10% μm^?1 occur on more than 90% of the cerean surface; the latter being denoted as Ceres’ background material in this work. FC and Visible and Infrared Spectrometer (VIR) spectra of this background material were compared to the suite of CCs spectrally investigated so far regarding their VIS/NIR region and 2.7 μm absorption, as well as their reflectance at 0.653 μm. This resulted in a good match to heated CI Ivuna (heated to 200–300 °C) and a better match for CM1 meteorites, especially Moapa Valley. This possibly indicates that the alteration of CM2 to CM1 took place on Ceres.  相似文献   

A multi-wavelength study of the evolution of early-type galaxies in groups: the ultraviolet view     

R. Rampazzo  P. Mazzei  A. Marino  L. Bianchi  H. Plana  G. Trinchieri  M. Uslenghi  A. Wolter 《Astrophysics and Space Science》2018,363(4):80

The ultraviolet–optical colour magnitude diagram of rich galaxy groups is characterised by a well developed Red Sequence, a Blue Cloud and the so-called Green Valley. Loose, less evolved groups of galaxies which are probably not virialised yet may lack a well defined Red Sequence. This is actually explained in the framework of galaxy evolution. We are focussing on understanding galaxy migration towards the Red Sequence, checking for signatures of such a transition in their photometric and morphological properties. We report on the ultraviolet properties of a sample of early-type (ellipticals+S0s) galaxies inhabiting the Red Sequence. The analysis of their structures, as derived by fitting a Sérsic law to their ultraviolet luminosity profiles, suggests the presence of an underlying disk. This is the hallmark of dissipation processes that still must have a role to play in the evolution of this class of galaxies. Smooth particle hydrodynamic simulations with chemo-photometric implementations able to match the global properties of our targets are used to derive their evolutionary paths through ultraviolet–optical colour magnitude diagrams, providing some fundamental information such as the crossing time through the Green Valley, which depends on their luminosity. The transition from the Blue Cloud to the Red Sequence takes several Gyrs, being about 3–5 Gyr for the brightest galaxies and longer for fainter ones, if occurring.The photometric study of nearby galaxy structures in the ultraviolet is seriously hampered by either the limited field of view of the cameras (e.g., in Hubble Space Telescope) or by the low spatial resolution of the images (e.g., in the Galaxy Evolution Explorer). Current missions equipped with telescopes and cameras sensitive to ultraviolet wavelengths, such as Swift-UVOT and Astrosat-UVIT, provide a relatively large field of view and a better resolution than the Galaxy Evolution Explorer. More powerful ultraviolet instruments (size, resolution and field of view) are obviously bound to yield fundamental advances in the accuracy and depth of the surface photometry and in the characterisation of the galaxy environment.  相似文献   

Micromechanical analysis of non-coaxiality between stress and strain increment in granular materials     

Shi  Jingshan  Guo  Peijun  Stolle  Dieter 《Acta Geotechnica》2020,15(9):2559-2574

Acta Geotechnica - It is known that non-coaxiality between the directions of the principal stresses and the principal plastic strain increments in granular material is physically resulted from the...  相似文献   

Comment on the Guzmán-Bianchi type-VII h solutions     

Dieter Lorenz-Petzold 《Astrophysics and Space Science》1989,161(1):163-164

It is shown that the recently presented Brans-Dicke-Bianchi type-VII _h perfect fluid solutions by Guzmán (1989) are nothing but the solutions given already by us in our previous paper (Lorenz-Petzold, 1984).  相似文献   

Field experiments yield new insights into gas exchange and excess air formation in natural porous media     

Stephan Klump  Yama Tomonaga  Wolfgang Kinzelbach  Dieter M. Imboden 《Geochimica et cosmochimica acta》2007,71(6):1385-1397

Gas exchange between seepage water and soil air within the unsaturated and quasi-saturated zones is fundamentally different from gas exchange between water and gas across a free boundary layer, e.g., in lakes or rivers. In addition to the atmospheric equilibrium fraction, most groundwater samples contain an excess of dissolved atmospheric gases which is called “excess air”. Excess air in groundwater is not only of crucial importance for the interpretation of gaseous environmental tracer data, but also for other aspects of groundwater hydrology, e.g., for oxygen availability in bio-remediation and in connection with changes in transport dynamics caused by the presence of entrapped air bubbles. Whereas atmospheric solubility equilibrium is controlled mainly by local soil temperature, the excess air component is characterized by the (hydrostatic) pressure acting on entrapped air bubbles within the quasi-saturated zone. Here we present the results of preliminary field experiments in which we investigated gas exchange and excess air formation in natural porous media. The experimental data suggest that the formation of excess air depends significantly on soil properties and on infiltration mechanisms. Excess air was produced by the partial dissolution of entrapped air bubbles during a sprinkling experiment in fine-grained sediments, whereas similar experiments conducted in coarse sand and gravel did not lead to the formation of excess air in the infiltrating water. Furthermore, the experiments revealed that the noble gas temperatures determined from noble gases dissolved in seepage water at different depths are identical to the corresponding in situ soil temperatures. This finding is important for all applications of noble gases as a paleotemperature indicator in groundwater since these applications are always based on the assumption that the noble gas temperature is identical to the (past) soil temperature.  相似文献   

Potential future changes in water limitations of the terrestrial biosphere     

Dieter Gerten  Sibyll Schaphoff  Wolfgang Lucht 《Climatic change》2007,80(3-4):277-299

This study explores the effects of atmospheric CO₂ enrichment and climate change on soil moisture (W _r ) and biome-level water limitation (L _TA), using a dynamic global vegetation and water balance model forced by five different scenarios of change in temperature, precipitation, radiation, and atmospheric CO₂ concentration, all based on the same IS92a emission scenario. L _TA is defined as an index that quantifies the degree to which transpiration and photosynthesis are co-limited by soil water shortage (high values indicate low water limitation). Soil moisture decreases in many regions by 2071–2100 compared to 1961–1990, though the regional pattern of change differs substantially among the scenarios due primarily to differences in GCM-specific precipitation changes. In terms of L _TA, ecosystems in northern temperate latitudes are at greatest risk of increasing water limitation, while in most other latitudes L _TA tends to increase (but again varies the regional pattern of change among the scenarios). The frequently opposite direction of change in W _r and L _TA suggests that decreases in W _r are not necessarily felt by actual vegetation, which is attributable mainly to the physiological vegetation response to elevated CO₂. Without this beneficial effect, the sign of change in L _TA would be reversed from predominantly positive to predominantly negative.  相似文献   

Eine Bestimmungsmethode für die radioaktiven Isotope60Co,54Mn und65Zn in Meerwasser     

Dieter E. Schmitt 《Ocean Dynamics》1966,19(1):28-38

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The abundances of the heavy elements     

Hans E. Suess  H. Dieter Zeh 《Astrophysics and Space Science》1973,23(1):173-187

Abundance regularities for heavy nuclei (A>58) are investigated and formulated as abundance rules. Abundance values of carbonaceous chondrites of type 1 and 2 as well as most probable values for primordial abundances are listed. The abundance rules definitely require minor connections of the empirical values. A measurement of the (n, ) cross-section of Pd¹⁰⁴ would make possible to decide whether type-1 or type-2 carbonaceous chondrites have a more primitive elemental composition.Paper dedicated to Prof. Harold C. Urey on the occasion of his 80th birthday on 29 April, 1973.  相似文献