Exposing metal and silicate charges to electrical discharges: Did chondrules form by nebular lightning?     

Carsten Güttler  Torsten Poppe 《Icarus》2008,195(1):504-510

In order to investigate the hypothesis that dust aggregates were transformed to meteoritic chondrules by nebular lightning, we exposed silicatic and metallic dust samples to electrical discharges with energies of 120 to 500 J in air at pressures between 10 and 10⁵ Pa. The target charges consisted of powders of micrometer-sized particles and had dimensions of mm. The dust samples generally fragmented leaving the major fraction thermally unprocessed. A minor part formed sintered aggregates of 50 to 500 μm. In a few experiments melt spherules having sizes ?180 μm in diameter (and, generally, interior voids) were formed; the highest spherule fraction was obtained with metallic Ni. Our experiments indicate that chondrule formation by electric current or by particle bombardment inside a discharge channel is unlikely.  相似文献   

Sr and Nd isotope composition of Late Pleistocene sapropels and nonsapropelic sediments from the Eastern Mediterranean Sea: implications for detrital influx and climatic conditions in the source areas     

Syee Weldeab  Kay-Christian EmeisChristoph Hemleben  Torsten W VennemannHartmut Schulz 《Geochimica et cosmochimica acta》2002,66(20):3585-3598

Isotopic ratios of Sr and Nd from lithogenic components of three isochronous core sections recovered from an east-west transect in the Eastern Mediterranean Sea (EMS) have been analyzed. The data are used for a quantitative estimate of the temporal and spatial variation of detrital flux to the EMS, assuming Saharan dust and Aegean/Nile particulate matter as dominant end members. It was established that the carbonate-free Saharan dust flux during deposition of the nonsapropel layers of marine oxygen isotope stage 5.4 (MIS 5.4) was similar to the present flux. During the deposition of sapropels S5 and S6, however, the Saharan dust input was drastically reduced and was not balanced by a change in the riverine influx at this time. Denser vegetation cover during more humid conditions may have reduced physical erosion and sediment removal in the source area. During marine oxygen isotope stage 6.2 (MIS 6.2) a pronounced increase of Saharan dust and detrital influx from the Aegean region is evident and implies more arid conditions in the southern and northern catchment areas. During this period, intersite variations are interpreted in terms of their geographic location relative to the seaways connecting the Aegean Sea and EMS. The width of the straits and hence the amount of sediment entering the eastern basins may have been affected by a low sea level that impeded interbasin sediment dispersal.  相似文献   

Experience of geomagnetic field recording with a fluxgate magnetometer having a bridge sensor     

Torsten Bergmark 《Surveys in Geophysics》1984,6(3-4):381-391

A fluxgate magnetometer has been developed at the Geological Survey of Sweden. It measures the field in three orthogonal directions and has sensor elements forming bridges. The instrument can have direct readout in both digital and analogue form with a resolution of 0.1 nT.An instrument of this type has been adopted for stationary recording of geomagnetic elements in digital form. Special attention has been paid to insure good long term stability and high reliability. Experience from routine recording is described.  相似文献   

People at Risk of Flooding: Why Some Residents Take Precautionary Action While Others Do Not     

Torsten Grothmann  Fritz Reusswig 《Natural Hazards》2006,38(1-2):101-120

Self-protective behavior by residents of flood-prone urban areas can reduce monetary flood damage by 80%, and reduce the need for public risk management. But, research on the determinants of private households’ prevention of damage by natural hazards is rare, especially in Germany. To answer the question of why some people take precautionary action while others do not, a socio-psychological model based on Protection Motivation Theory (PMT) is developed, explaining private precautionary damage prevention by residents’ perceptions of previous flood experience, risk of future floods, reliability of public flood protection, the efficacy and costs of self-protective behavior, their perceived ability to perform these actions, and non-protective responses like wishful thinking. The validity of the proposed model is explored by means of representative quantitative telephone surveys and regression analyses, and compared with a socio-economic model (including residents’ age, gender, income, school degree and being owner or tenant). Participants were 157 residents of flood-prone homes in Cologne, Germany, a city that has traditionally been subject to minor and major flood events. Results of the study show the explanatory power of the socio-psychological model, with important implications for public risk communication efforts. To motivate residents in flood-prone areas to take their share in damage prevention, it is essential to communicate not only the risk of flooding and its potential consequences, but also the possibility, effectiveness and cost of private precautionary measures.  相似文献   

Geography and the study of interaction between nature and society     

Torsten Hgerstrand 《Geoforum》1976,7(5-6)

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Transient simulations,empirical reconstructions and forcing mechanisms for the Mid-holocene hydrological climate in southern Patagonia     

Sebastian Wagner  Martin Widmann  Julie Jones  Torsten Haberzettl  Andreas Lücke  Christoph Mayr  Christian Ohlendorf  Frank Schäbitz  Bernd Zolitschka 《Climate Dynamics》2007,29(4):333-355

This study investigates the atmospheric circulation in transient climate simulations with a coupled atmosphere–ocean general circulation model (GCM) for the mid-Holocene (MH) period 7–4.5 ka BP driven with combinations of orbital, solar and greenhouse gas forcings. The focus is on southern South America. Statistical downscaling models are derived from observational data and applied to the simulations to estimate precipitation in south-eastern Patagonia during the MH. These estimates are compared with lake level estimates for Laguna Potrok Aike (LPA) from sediments. Relative to pre-industrial conditions (i.e. 1550–1850), which show extraordinarily high lake levels, the proxy-based reconstructed lake levels during the MH are lower. The downscaled simulated circulation differences indicate higher LPA precipitation during the MH from March to August, higher annual means, and reduced precipitation from September to February. Thus the reconstructed lower LPA lake levels can not be explained solely by the simulated precipitation changes. Possible reasons for this discrepancy are discussed. Based on proxy data from southern South America hypotheses have also been proposed on the latitudinal position of the southern hemispheric westerlies (SHWs). In agreement with some of these hypotheses our simulations show an increased seasonal cycle of the latitudinal position of the SHWs during the MH, which can be explained by the orbital forcing. The simulations also show stronger SHWs over southern Patagonia during austral summer and weaker SHWs during winter. The downscaling model associates weaker SHWs with increased precipitation in the LPA region. However, this relationship is only moderate, and therefore the downscaling model does not support the assumption of a strong link between mean SHWs and precipitation over south-eastern Patagonia, which is the basis of many proxy-based hypotheses about the SHWs.  相似文献   

Influence of plastic fines content on the liquefaction susceptibility of sands: cyclic loading     

Goudarzy  Meisam  Sarkar  Debdeep  Wichtmann  Torsten 《Acta Geotechnica》2022,17(11):4977-4988

Acta Geotechnica - The paper presents an experimental study on the effect of plastic fines content on the undrained behavior and liquefaction susceptibility of sand-fines mixtures under cyclic...  相似文献   

Sound in media: audio drama and audio-guided tours as stimuli for the creation of place     

Torsten Wissmann  Stefan Zimmermann 《GeoJournal》2015,80(6):803-810

Mass media frequently makes use of more than the visual image. With the exception of music, movie scores, and radio news however, media geographers have largely ignored the impact sound in media has on shaping and characterizing our experience of the world. We address this lack by showcasing two types of audio media: audio drama and audio-guided tours. The former will be explored with the help of the world’s most successful audio drama series The Three Investigators to give a historical and theoretical introduction to the realm of sound within mass media. The latter will be illustrated using the example of the Austin Walking Tour as a representative production for city tourism.  相似文献   

Fully coupled generalised hybrid-mixed finite element approximation of two-phase two-component flow in porous media. Part II: numerical scheme and numerical results     

Estelle Marchand  Torsten Müller  Peter Knabner 《Computational Geosciences》2012,16(3):691-708

We consider the modeling and simulation of compositional two-phase flow in a porous medium, where one phase is allowed to vanish or appear. The modeling of Marchand et al. (in review) leads to a nonlinear system of two conservation equations. Each conservation equation contains several nonlinear diffusion terms, which in general cannot be written as a function of the gradients of the two principal unknowns. Also the diffusion coefficients are not necessarily explicit local functions of them. For the generalised mixed finite elements approximation, Lagrange multipliers associated to each principal unknown are introduced, the sum of the diffusive fluxes of each component is explicitly eliminated and the static condensation leads to a “global” nonlinear system of equations only in the Lagrange multipliers also including complementarity conditions to cope with vanishing or appearing phases. After time discretisation, this system can be solved at each time step using a semi-smooth Newton method. The static condensation involves “local” nonlinear systems of equations associated to each element, solved also by a semismooth Newton method. The algorithm is successfully applied to 1D and 2D examples of water–hydrogen flow involving gas phase appearance and disappearance.  相似文献   

Discrimination of induced seismicity by full moment tensor inversion and decomposition   总被引：3，自引：1，他引：2  

Simone Cesca  Alexander Rohr  Torsten Dahm 《Journal of Seismology》2013,17(1):147-163

Human activities, including operations related to mining and reservoir exploitation, may induce seismicity and pose a risk for population and infrastructures. While different observations are commonly used to assess the origin of earthquakes, there is a lack of rules and methods for the discrimination between natural and induced seismicity. The inversion and decomposition of the full moment tensor and the observation of relevant deviation from a pure double couple (DC) model may be an indicator for induced seismicity. We establish here a common procedure to analyse a set of natural and induced events of similar magnitude, which occurred in Germany and neighbouring regions. The procedure is based on an inversion method and on a consistent velocity model and recording network. Induced seismicity is recorded during different mining and/or reservoir exploitations. Moment tensors are inverted using a multi-step inversion approach. This method, which was successfully applied in previous studies at regional and teleseismic distances, is further developed here to account for full moment tensor analysis. We first find a best DC solution and then perform a full moment tensor inversion, fitting full waveforms amplitude spectra at regional distances. The moment tensor solution is decomposed into DC, compensated linear vector dipole and isotropic terms. The discrimination problem is then investigated through the evaluation of distributions of non-DC source components for natural and induced data sets. Results illustrate the potential of the inversion and discrimination approach. Additional detailed analyses are carried out for the two most significant induced earthquakes, and rupture models are compared with the full moment tensor solutions.  相似文献