Incompatible magnetic behaviour of fine-grained natural haematite samples prepared in similar ways     

Eduard Petrovský  Mark J. Dekkers  Vladimír Kropáček  Pavel Hejda  Tomáš Zelinka 《Studia Geophysica et Geodaetica》1994,38(1):46-56

Summary The results of a magnetic study of two batches of sized natural haematite fractions (from Kada, Czech Republic) are reported. One of the sample batches was prepared by ultrasonic micro precision sieving in propanon (acetone), the other in ethanol (alcohol). Surprisingly, the magnetic behaviour of the ethanol-sieved fractions was much softer (e.g. H_cr 20 kA/m) as compared with the propanon-sieved fractions (H_cr > 200 kA/m). Thermomagnetic measurements suggest a maghemite portion is present in the material used for the preparation of the ethanol-sieved samples. Possible causes of this puzzling behaviour are discussed. However, no definite conclusion can be drawn on the basis of the data presently available.Presented at 3rd Biennial Meeting on New Trends in Geomagnetism, Smolenice Castle, West Slovakia, June 22–29, 1992.  相似文献   

Probable tsunami origin for a Shell and Sand Sheet from marine ponds on Anegada, British Virgin Islands     

Eduard G. Reinhardt  Jessica Pilarczyk  Alyson Brown 《Natural Hazards》2012,63(1):101-117

A distinctive Shell and Sand Sheet found beneath the marine ponds of Anegada, British Virgin Islands, was formed by a post-1650 AD overwash event, but its origin (tsunami or hurricane) was unclear. This study assesses the taphonomic characters of the shell and large clast material (>2?mm) to determine its provenance and origin. Pond-wide stratigraphic units (Shelly Mud, Shell and Sand Sheet, Mud Cap) were analyzed (12 samples) at four sites in Bumber Well and Red Pond along with eight samples from the Shell and Sand Sheet in a 2-km transect of Bumber Well. Mollusks in the pond muds include Anomalocardia spp. and cerithids with no allochthonous shells from the offshore reef-flat. Results show that the shells and clasts (>2?mm) are derived from the erosion and winnowing of the underlying Shelly Mud of the former marine pond, forming a distinctive sheet-like deposit with Homotrema sand. The Shell and Sand Sheet contains articulated Anomalocardia bivalves and moderate numbers of angular fragments (approximately 35%) that are likely from crab predation. Radiocarbon dates of articulated Anomalocardia specimens from the Shell and Sand Sheet range widely (approximately 4000?years), with shell condition (pristine to variably preserved) showing no correlation with age. The articulated condition of the bivalves with the wide-ranging dates suggests erosion and winnowing of the underlying Shelly Mud but minimal transport of the bivalves. The Shell and Sand Sheet has taphonomic characteristics indicative of a widespread tsunami overwash (sheet-like extent and articulated specimens) but lacks allochthonous reef-flat shells. Reef-flat shell material may not have penetrated the pond, as a tsunami would have to cross the reef-flat and overtop high dunes (2.2?m) hindering transport of larger shell material but allowing the Homotrema sand to penetrate. Processes including hurricane overwash, pond wave action, or tidal channel opening and closure are not favoured interpretations as they would not produce extensive sheet-like deposits. Taphonomic analysis is hampered by the limited (400?C500?years BP) depositional history from Anegada??s ponds and the lack of comparative data from other Caribbean locations.  相似文献   

Analyzing bank filtration by deconvoluting time series of electric conductivity   总被引：4，自引：0，他引：4  

Cirpka OA  Fienen MN  Hofer M  Hoehn E  Tessarini A  Kipfer R  Kitanidis PK 《Ground water》2007,45(3):318-328

Knowing the travel-time distributions from infiltrating rivers to pumping wells is important in the management of alluvial aquifers. Commonly, travel-time distributions are determined by releasing a tracer pulse into the river and measuring the breakthrough curve in the wells. As an alternative, one may measure signals of a time-varying natural tracer in the river and in adjacent wells and infer the travel-time distributions by deconvolution. Traditionally this is done by fitting a parametric function such as the solution of the one-dimensional advection-dispersion equation to the data. By choosing a certain parameterization, it is impossible to determine features of the travel-time distribution that do not follow the general shape of the parameterization, i.e., multiple peaks. We present a method to determine travel-time distributions by nonparametric deconvolution of electric-conductivity time series. Smoothness of the inferred transfer function is achieved by a geostatistical approach, in which the transfer function is assumed as a second-order intrinsic random time variable. Nonnegativity is enforced by the method of Lagrange multipliers. We present an approach to directly compute the best nonnegative estimate and to generate sets of plausible solutions. We show how the smoothness of the transfer function can be estimated from the data. The approach is applied to electric-conductivity measurements taken at River Thur, Switzerland, and five wells in the adjacent aquifer, but the method can also be applied to other time-varying natural tracers such as temperature. At our field site, electric-conductivity fluctuations appear to be an excellent natural tracer.  相似文献   

Uniform asymptotic Green's functions for efficient modeling of cracks in elastic layers with relative shear deformation controlled by linear springs     

Anthony P. Peirce  Hongren Gu  Eduard Siebrits 《国际地质力学数值与分析法杂志》2009,33(3):285-308

We present a uniform asymptotic solution (UAS) for a displacement discontinuity (DD) that lies within the middle layer of a three‐layer elastic medium in which relative shear deformation between parallel interfaces is controlled by linear springs. The DD is assumed to be normal to the two interfaces between the elastic media. Using the Fourier transform method we construct a leading term in the asymptotic expansion for the spectral coefficient functions for a DD in a three‐layer‐spring medium. Although a closed‐form solution will require a solution in terms of an infinite series, we demonstrate how this UAS can be used to construct highly efficient and accurate solutions even in the case in which the DD actually touches the interface. We compare the results using the Green's function UAS solution for a crack crossing a soft interface with results obtained using a multi‐layer boundary element method. We also present results from an implementation of the UAS Green's function approach in a pseudo‐3D hydraulic fracturing simulator to analyze the effect of interface shear deformation on the fracture propagation process. These results are compared with field measurements. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Consequences of climate change for the soil climate in Central Europe and the central plains of the United States   总被引：2，自引：0，他引：2  

Miroslav Trnka  Kurt Christian Kersebaum  Josef Eitzinger  Michael Hayes  Petr Hlavinka  Mark Svoboda  Martin Dubrovský  Daniela Semerádová  Brian Wardlow  Eduard Pokorný  Martin Možný  Don Wilhite  Zdeněk Žalud 《Climatic change》2013,120(1-2):405-418

This study aims to evaluate soil climate quantitatively under present and projected climatic conditions across Central Europe (12.1°–18.9° E and 46.8°–51.1° N) and the U.S. Central Plains (90°–104° W and 37°–49° N), with a special focus on soil temperature, hydric regime, drought risk and potential productivity (assessed as a period suitable for crop growth). The analysis was completed for the baselines (1961–1990 for Europe and 1985–2005 for the U.S.) and time horizons of 2025, 2050 and 2100 based on the outputs of three global circulation models using two levels of climate sensitivity. The results indicate that the soil climate (soil temperature and hydric soil regimes) will change dramatically in both regions, with significant consequences for soil genesis. However, the predicted changes of the pathways are very uncertain because of the range of future climate systems predicted by climate models. Nevertheless, our findings suggest that the risk of unfavourable dry years will increase, resulting in greater risk of soil erosion and lower productivity. The projected increase in the variability of dry and wet events combined with the uncertainty (particularly in the U.S.) poses a challenge for selecting the most appropriate adaptation strategies and for setting adequate policies. The results also suggest that the soil resources are likely be under increased pressure from changes in climate.  相似文献   

Carbon flows in the benthic food web at the deep-sea observatory HAUSGARTEN (Fram Strait)     

Dick van Oevelen  Melanie Bergmann  Karline Soetaert  Eduard Bauerfeind  Christiane Hasemann  Michael Klages  Ingo Schewe  Thomas Soltwedel  Nataliya E. Budaeva 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(11):1069-1083

The HAUSGARTEN observatory is located in the eastern Fram Strait (Arctic Ocean) and used as long-term monitoring site to follow changes in the Arctic benthic ecosystem. Linear inverse modelling was applied to decipher carbon flows among the compartments of the benthic food web at the central HAUSGARTEN station (2500 m) based on an empirical data set consisting of data on biomass, prokaryote production, total carbon deposition and community respiration. The model resolved 99 carbon flows among 4 abiotic and 10 biotic compartments, ranging from prokaryotes up to megafauna. Total carbon input was 3.78±0.31 mmol C m⁻² d⁻¹, which is a comparatively small fraction of total primary production in the area. The community respiration of 3.26±0.20 mmol C m⁻² d⁻¹ is dominated by prokaryotes (93%) and has lower contributions from surface-deposit feeding macro- (1.7%) and suspension feeding megafauna (1.9%), whereas contributions from nematode and other macro- and megabenthic compartments were limited to <1%. The high prokaryotic contribution to carbon processing suggests that functioning of the benthic food web at the central HAUSGARTEN station is comparable to abyssal plain sediments that are characterised by strong energy limitation. Faunal diet compositions suggest that labile detritus is important for deposit-feeding nematodes (24% of their diet) and surface-deposit feeding macrofauna (∼44%), but that semi-labile detritus is more important in the diets of deposit-feeding macro- and megafauna. Dependency indices on these food sources were also calculated as these integrate direct (i.e. direct grazing and predator–prey interactions) and indirect (i.e. longer loops in the food web) pathways in the food web. Projected sea-ice retreats for the Arctic Ocean typically anticipate a decrease in the labile detritus flux to the already food-limited benthic food web. The dependency indices indicate that faunal compartments depend similarly on labile and semi-labile detritus, which suggests that the benthic biota may be more sensitive to changes in labile detritus inputs than when assessed from diet composition alone. Species-specific responses to different types of labile detritus inputs, e.g. pelagic algae versus sympagic algae, however, are presently unknown and are needed to assess the vulnerability of individual components of the benthic food web.  相似文献   

Sociological Profile of Astronomers in Spain     

Julio Iglesias de Ussel  Antonio Trinidad  Diego RuIz  Eduardo Battaner  Antonio J. Delgado  José M. Rodriguez-Espinosa  Eduard Salvador-Solé  José M. Torrelles 《Astrophysics and Space Science》1997,257(2):237-248

In this paper the main findings are presented of a recent study made by a team of sociologists from the University of Granada on the professional astronomers currently working in Spain. Despite the peculiarities of this group – its youth, twentyfold increase in size over the last 20 years, and extremely high rate of specialization abroad – in comparison with other Spanish professionals, this is the first time that the sociological characteristics of the group have been studied discretely. The most significant results of the study are presented in the following sections. Section 1 gives a brief historical background of the development of Astronomy in Spain. Section 2 analyzes the socio-demographic profile of Spanish Astronomy professionals (sex, age, marital status, etc.). Sections 3–5 are devoted to the college education and study programs followed by Spanish astronomers, focusing on the features and evaluations of the training received, and pre- and postdoctoral study trips made to research centers abroad. The results for the latter clearly show the importance that Spanish astronomers place on having experience abroad. Special attention is paid to scientific papers published as a result of joint research projects carried out with colleagues from centers abroad as a result of these study trips. Section 6 describes the situation of Astronomy professionals within the Spanish job market, the different positions available and the time taken to find a job after graduation. Section 7 examines Astronomy as a discipline in Spain, including the astronomers' own opinions of the social status of the discipline within Spanish society. Particular attention is paid to how Spanish astronomers view the status of Astronomy in Spain in comparison with that of other European countries. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Nonuniform Target Ionization and Fitting Thick Target Electron Injection Spectra to RHESSI Data     

Kontar  Eduard P.  Brown  John C.  McArthur  Guillian K. 《Solar physics》2002,210(1-2):419-429

Past analyses of flare hard X-ray (HXR) spectra have largely ignored the effect of nonuniform ionization along the electron paths in the thick-target model, though it is very significant for well-resolved spectra. The inverse problem (photon spectrum to electron injection spectrum F ₀(E ₀)) is disturbingly non-unique. However, we show that it is relatively simple to allow for the effect in forward fitting of parametric models of F ₀(E ₀)) and provide an expression to evaluate it for the usual single power-law form of F ₀(E ₀)).The expression involves the column depth N _* of the transition region in the flare loop as one of the parameters so data fitting can enable derivation of N _* (and its evaporative evolution) as part of the fitting procedure. The fit to RHESSI data on four flares for a single power law F ₀(E ₀)) is much improved when ionization structure is included compared to when the usual fully ionized approximation is used. This removes the need, in these events at least, to invoke broken power laws, or other forms, of the acceleration spectrum F ₀(E ₀)) to explain the observed photon spectrum  相似文献   

First GOCE gravity field models derived by three different approaches   总被引：28，自引：10，他引：18  

Roland Pail  Sean Bruinsma  Federica Migliaccio  Christoph F?rste  Helmut Goiginger  Wolf-Dieter Schuh  Eduard H?ck  Mirko Reguzzoni  Jan Martin Brockmann  Oleg Abrikosov  Martin Veicherts  Thomas Fecher  Reinhard Mayrhofer  Ina Krasbutter  Fernando Sans��  Carl Christian Tscherning 《Journal of Geodesy》2011,85(11):819-843

Three gravity field models, parameterized in terms of spherical harmonic coefficients, have been computed from 71 days of GOCE (Gravity field and steady-state Ocean Circulation Explorer) orbit and gradiometer data by applying independent gravity field processing methods. These gravity models are one major output of the European Space Agency (ESA) project GOCE High-level Processing Facility (HPF). The processing philosophies and architectures of these three complementary methods are presented and discussed, emphasizing the specific features of the three approaches. The resulting GOCE gravity field models, representing the first models containing the novel measurement type of gravity gradiometry ever computed, are analysed and assessed in detail. Together with the coefficient estimates, full variance-covariance matrices provide error information about the coefficient solutions. A comparison with state-of-the-art GRACE and combined gravity field models reveals the additional contribution of GOCE based on only 71 days of data. Compared with combined gravity field models, large deviations appear in regions where the terrestrial gravity data are known to be of low accuracy. The GOCE performance, assessed against the GRACE-only model ITG-Grace2010s, becomes superior at degree 150, and beyond. GOCE provides significant additional information of the global Earth gravity field, with an accuracy of the 2-month GOCE gravity field models of 10?cm in terms of geoid heights, and 3?mGal in terms of gravity anomalies, globally at a resolution of 100?km (degree/order 200).  相似文献   

Experimental study of fly-ash migration by using magnetic method     

Aleš Kapička  Radka Kodešová  Eduard Petrovský  Zdeněk Hůlka  Hana Grison  Martin Kaška 《Studia Geophysica et Geodaetica》2011,55(4):683-696

Several studies have shown that magnetic measurements can be used in assessing soil contamination due to atmospheric deposition of pollutants. Reliable spatial mapping of magnetic susceptibility of soils assumes high temporal stability of deposited particles, accumulated in top-soil horizons. One of the main methodological concerns is whether the migration of deposited anthropogenic ferrimagnetic particles may bias the measured values. Measurements carried out on high-porosity (sandy) soils, or on soils with a very variable water regime may yield inconsistent values of top-soil magnetic susceptibility as the indicator of contamination. This study focuses on the laboratory examination of migration of fly ashes from a coal-burning power plant in sands of different porosity and under a simulated rain regime. Columns of sand of different grain sizes, placed in plastic cylinders, were contaminated on the surface by the fly ash. The vertical migration of magnetic particles was monitored using measurements of magnetic susceptibility with an SM400 Kappameter. Calibration measurements in the water environment showed an erroneous performance and resulted in the technical improvement of the used susceptibility meter (Model 2009). Our results show that the vertical distribution of flyash particles deposited on fine sand is very stable even after repeated rain simulation. The peak value of magnetic susceptibility is located in a stable position a few millimeters under the surface. Hence, standard top-soil magnetic mapping is in such a case reliable and fully representative. Contrary to that, in case of coarse sand, the peak value of magnetic susceptibility migrates by more than 10 cm. The results will be further used for numerical modeling of contaminant transport in porous media.  相似文献