Cathodoluminescence, electron microscopy, and Raman spectroscopy of experimentally shock-metamorphosed zircon     

Arnold GucsikChristian Koeberl  Franz BrandstätterWolf Uwe Reimold  Eugen Libowitzky 《Earth and Planetary Science Letters》2002,202(2):495-509

Thorough understanding of the shock metamorphic signatures of zircon could be the basis for the use of this mineral as a powerful tool for the study of old, deeply eroded, and metamorphically overprinted impact structures and formations. This study of the cathodoluminescence (CL) and Raman spectroscopic signatures of experimentally (20-60 GPa) shock-metamorphosed zircon single crystals contributes to the understanding of high-pressure microdeformation in zircon. For all samples, an inverse relationship between the brightness of the backscattered electron (BSE) signal and the corresponding cathodoluminescence intensity was observed. The unshocked sample shows crosscutting, irregular fractures. The 20 GPa sample displays some kind of mosaic texture of CL brighter and darker domains, but does not exhibit any shock metamorphic features in BSE or CL images. The 40 GPa sample shows a high density of lamellar features, which might be explained by the phase transformation between zircon- and scheelite-structure phases of zircon and resulting differences in the energy levels of the activator elements. The CL spectra of unshocked and shocked (20, 40, and 60 GPa) zircon samples are dominated by narrow emission lines and broad bands in the region of visible light and in the near-UV range. The emission lines result from rare earth element activators and the broad bands might be associated with lattice defects. Raman spectra revealed that the unshocked and 20 GPa samples represent zircon-structure material, whereas the 40 GPa sample yielded additional peaks with relatively high peak intensities, which are indicative of the presence of the scheelite-type high-pressure phase. The 60 GPa sample has a Raman signature that is similar to that of an amorphous phase, in contrast to the observations of an earlier TEM study that the crystalline scheelite-structure phase is stable at this shock pressure. The 60 GPa Raman signature cannot be explained at this stage. The results show a clear dependence of the CL and Raman properties of zircon on shock pressure, which confirm the possible usage of these methods as shock indicators.  相似文献   

Evaluation of the wave transformation in an open bay with two spectral models   总被引：1，自引：0，他引：1  

Eugen Rusu 《Ocean Engineering》2011,38(16):1763-1781

An evaluation of two state of the art phase averaged wave models for the transformation scale, SWAN and STWAVE, is carried out in the present work. The target area is the Obidos Bay located in the central part of the Portuguese continental nearshore. The wave input for the two models is provided by an offshore buoy. In order to compare the nearshore outputs of the wave models against in-situ measurements, a directional buoy and an ADCP, operating in intermediate water depth, are used. The wave parameters considered for comparisons are significant wave height, peak period and wave direction. Sensitivity analyses studies and evaluations in the spectral and geographical spaces concerning the results of the two models are also carried out in both intermediate and shallow water. The present study provides some information on the performances of the two wave models in different forcing conditions as well as on their sensitivity in relationship with various input parameters and some physical processes. STWAVE appears to be faster and more robust than SWAN, which on the other hand has more options and flexibility. In statistical terms the results are comparable.  相似文献   

Perception of flood risk in Danube Delta,Romania   总被引：1，自引：1，他引：0  

Iuliana Armaş  Eugen Avram 《Natural Hazards》2009,50(2):269-287

For exposed and vulnerable communities, the perception of natural risk is an essential link in the analysis of man–environment coping relationship and also an important parameter in the quantification of complex vulnerability as a central predictive variable in the risk equation. The topic of flood risk in related perception is of considerable interest, as some recently published papers have proven (Messner and Meyer 2005, 2006; Raaijmakers et al. 2008). The aim of the current study is to reveal the conscious and unconscious attitudes towards the flood risk for the inhabitants of the Danube Delta/Romania. These attitudes, defined by different degrees of psychological vulnerability, represent the background for a series of psycho-behavioural patterns that generate certain adjustment mechanisms and strategies. Application of a specially designed questionnaire and the statistical analysis of the results revealed two psychological factors as essential in establishing the psychosocial vulnerability degree of the interviewed subjects: (i) an internal control factor and (ii) an external control factor. The persons characterized by inner control have a significantly reduced general anxiety level in comparison to individuals with the control factor placed externally. As confidence diminishes, it increases the tendency of the individual to rely on the external factors for support and security. The lack of resources (indicating lower resilience) and mistrust in the support given emphasizes non-adaptive behaviours.

Iuliana ArmaşEmail:

  相似文献   

Principles of quantitative absorbance measurements in anisotropic crystals   总被引：1，自引：0，他引：1  

Eugen Libowitzky  George R. Rossman 《Physics and Chemistry of Minerals》1996,23(6):319-327

The accurate measurement of absorbance (A=-log T; T=I/I ₀) in anisotropic materials like crystals is highly important for the determination of the concentration and orientation of the oscillator (absorber) under investigation. The absorbance in isotropic material is linearly dependent on the concentration of the absorber and on the thickness of the sample (A=?·c·t). Measurement of absorbance in anisotropic media is more complicated, but it can be obtained from polarized spectra (i) on three random, but orthogonal sections of a crystal, or (ii) preferably on two orthogonal sections oriented parallel to each of two axes of the indicatrix ellipsoid. To compare among different crystal classes (including cubic symmetry) it is useful to convert measured absorbance values to one common basis (the total absorbance A _tot), wherein all absorbers are corrected as if they were aligned parallel to the E-vector of the incident light. The total absorption coefficient (a _tot=A _tot/t) is calculated by $$\left( {\text{i}} \right)a_{{\text{tot}}} = \sum\limits_{i = 1}^3 {(a_{\max ,i} + a_{\min ,i} )} /2, {\text{or}} {\text{by}} {\text{(ii) }}a_{{\text{tot}}} = a_x + a_y + a_z .$$ Only in special circumstances will unpolarized measurements of absorbance provide data useful for quantitative studies of anisotropic material. The orientation of the absorber with respect to the axes of the indicatrix ellipsoid is calculated according to A _x/A _tot=cos² (x < absorber), and analogously for A _yand A _z. In this way, correct angles are obtained for all cases of symmetry. The extinction ratio of the polarizer (Pe=I _crossed/I _parallel) has considerable influence on the measured amplitude of absorption bands, especially in cases of strong anisotropic absorbance. However, if Pe is known, the true absorbance values can be calculated even with polarizers of low extinction ratio, according to A _max=?log[(T _max,obs?0.5·Pe·T _min,obs)/(1?0.5·Pe)], and similar for A _min. The theoretical approach is confirmed by measurements on calcite and topaz.  相似文献   

Evolutionary processes in protoplanetary accretion disks: the propagation of axisymmetric shock waves     

Eugen Willerding 《Planetary and Space Science》1998,46(11-12)

In this paper we investigate both the global and the local hydrodynamics of axisymmetric accretion disks around young stellar objects under the simultaneous action of viscosity, self-gravity and pressure forces. For simplicity, we take for the global model a polytropic equation of state, make the infinitely thin disk approximation and characterize the surface density and temperature profiles in the disk as power laws in the radial distance r from the protostar. We solve the problem of the general density profile of a Keplerian disk showing that self-gravity could not be an important factor for the fast formation of the rocky cores of giant gaseous planets in our solar system. Under the hypothesis that the unperturbed rotation curve of the disk is nearly Keplerian throughout the radial extent, we can estimate with our polytropic model a lower limit for the resulting masses M_d(r) of stable disks up to 100 AU. These masses are in the range of the so-called minimum mass solar nebular (_d/M_s ≈ 0.01–0.02).By adopting a simplified viscosity model, where the height-integrated turbulent dynamical viscosity ν is a function of the surface density σ like η ∝ σ^Γ, we derive in the local shearing sheet model linearized evolution equations for small density perturbations describing both a diffusion process and the propagation of acoustic density waves. We solve a special initial value problem and calculate the appropriate Green's function. The analytical solutions so obtained describe in the case Γ < 0 the successive formation of quasi-stationary ring-shaped density structures in a disk with a definite mode of maximum instability, whereas in the case Γ > Γ_c the density wave equation describes the propagation of an “overstable” ring-shaped acoustic density wavelet to the outer ranges of the accretion disk. Whereas the group velocity of the wave packet is subsonic, the phase velocities of individual wave crests in the wave packet are supersonic. The mode of maximum instability, the growth rate and the number of growing waves in the wavelet are controlled by Γ and α. Our present knowledge concerning turbulent viscosity in protoplanetary disks is not sufficient to decide whether or not the case Γ > Γ_c is realized.The suggested structuring processes in the linear theory should initiate in the non-linear regime the formation of narrow ring-shaped density shock waves moving through the protoplanetary disk. These non-linear waves could produce extremely spatially and temporally heterogeneous temperature regions in the disk. We speculate that ring-shaped density waves, excited by inner boundary conditions and which have dominated the disk's evolution at early times, are responsible both for the fast growth of dust to planetesimals and at least for the rapid accretion of the rocky cores of giant gaseous planets in the protoplanetary accretion disk (shock wave trigger hypothesis). We derive provisional scaling rules for planetary systems regarding the spacing of orbits as a function of the mass ratio of the protoplanetary disk to the protostar. However, further analytical work and linear as well as nonlinear numerical simulations of density waves excited by inner boundary conditions are needed to consolidate the results and speculations of our linear wave mechanics in the future.  相似文献   

A forecast of public water scarcity on Leu-Rotunda Plain,Romania, for the end of the 21st century     

Bianca Mitrică  Istvan Bogardi  Eugen Mitrică  Irena Mocanu  Marin Minciună 《Norsk geografisk tidsskrift. Norwegian journal of geography》2017,71(1):12-29

The article examines the risk of water shortages due to the climate change on Leu-Rotunda Plain, which is part of Oltenia Plain in Romania. The region has been exposed to several extreme climatic phenomena, mostly droughts, which has created several problems related to water quality and quantity. The authors defined climate change scenarios using two regional climate models. Water resources under climate change were estimated by a regional numerical groundwater model covering a deep aquifer. The water demand components were estimated for households, industries, services, and livestock, based on specific socio-economic assumptions. A non-probabilistic risk assessment, using simplified fuzzy sets mathematics, was used to estimate water supply, water demand, and the consequences of water shortages. The results of the study revealed significant vulnerability in the water supply, a limited territorial expansion of sewerage networks, an expected increase in households’ demand, an expected increase in industrial and services water demand, a relatively stable demand for water for livestock farming, and an important water shortage in the study area. The authors conclude by highlighting a set of actions to mitigate the risk of the potential crisis.  相似文献   

Melt in the impact breccias from the Eyreville drill cores,Chesapeake Bay impact structure,USA     

Katerina BARTOSOVA  Lutz HECHT  Christian KOEBERL  Eugen LIBOWITZKY  Wolf Uwe REIMOLD 《Meteoritics & planetary science》2011,46(3):396-430

The center of the 35.3 Ma Chesapeake Bay impact structure (85 km diameter) was drilled during 2005/2006 in an ICDP–USGS drilling project. The Eyreville drill cores include polymict impact breccias and associated rocks (1397–1551 m depth). Tens of melt particles from these impactites were studied by optical and electron microscopy, electron microprobe, and microRaman spectroscopy, and classified into six groups: m1—clear or brownish melt, m2—brownish melt altered to phyllosilicates, m3—colorless silica melt, m4—melt with pyroxene and plagioclase crystallites, m5—dark brown melt, and m6—melt with globular texture. These melt types have partly overlapping major element abundances, and large compositional variations due to the presence of schlieren, poorly mixed melt phases, partly digested clasts, and variable crystallization and alteration. The different melt types also vary in their abundance with depth in the drill core. Based on the chemical data, mixing calculations were performed to determine possible precursors of these melt particles. The calculations suggest that most melt types formed mainly from the thick sedimentary section of the target sequence (mainly the Potomac Formation), but an additional crystalline basement (schist/gneiss) precursor is likely for the most abundant melt types m2 and m5. Sedimentary rocks with compositions similar to those of the melt particles are present among the Eyreville core samples. Therefore, sedimentary target rocks were the main precursor of the Eyreville melt particles. However, the composition of the melt particles is not only the result of the precursor composition but also the result of changes during melting and solidification, as well as postimpact alteration, which must also be considered. The variability of the melt particle compositions reflects the variety of target rocks and indicates that there was no uniform melt source. Original heterogeneities, resulting from melting of different target rocks, may be preserved in impactites of some large impact structures that formed in volatile‐rich targets, because no large melt body exists, in which homogenization would have taken place.  相似文献   

Analysis of Croatian geomagnetic repeat station surveys in 2004 and 2007     

Eugen Vujić  Mario Brkić  Nikol Radović 《Studia Geophysica et Geodaetica》2011,55(4):737-753

Surveys of the geomagnetic declination, inclination and total field intensity were carried out at eight stations of the Croatian Geomagnetic Repeat Stations Network in 2004 and 2007. The total field time series at repeat stations and observatories were compared by use of the multi-linear regression and linear correlation coefficients. The surveys’ data were reduced to 2004.5 and 2007.5 epochs by a simple method proposed here, assuming the secular variations at the repeat station and observatory are equal or different, respectively. These reductions, obtained in reference to L’Aquila, Fürstenfeldbruck and Tihany observatories, and corresponding weighted as well as non-weighted averages, were compared. The preferred geomagnetic field elements as well as the corresponding annual changes between 2004.5 and 2007.5 epochs, were compared to the latest International Geomagnetic Reference Field. Additionally, the Croatian Geomagnetic Normal Reference Fields for 2004.5 and 2007.5 epochs were presented.  相似文献   

Regional Geomagnetic Field Model for Croatia at 2009.5     

Eugen Vujić  Mario Brkić  Peter Kovács 《Acta Geophysica》2016,64(1):26-42

Geomagnetic data of north, east, and vertical components at Croatian repeat stations and ground survey sites, as well as European geomagnetic observatories and repeat stations, were used to obtain a regional geomagnetic model over Croatia at 2009.5 epoch. Different models were derived, depending on input data, and three modelling techniques were used: Taylor Polynomial, Adjusted Spherical Harmonic Analysis, and Spherical Harmonic Analysis. It was derived that the most accurate model over Croatia was the one when only Croatian data were used, and by using the Adjusted Spherical Harmonic Analysis. Based on Croatian repeat stations’ data in the interval 2007.5–2010.5, and a global Enhanced Magnetic Model, it was possible to estimate the crustal field at those sites. It was also done by taking into account the empirical adjustment for long-term external field variations. The higher crustal field values were found at those stations which are on or close to the Adriatic anomaly.  相似文献   

Determination of the Croatian geomagnetic observatory location     

Giuliana Verbanac  Eugen Vujić 《Acta Geophysica》2012,60(2):337-356

Ground survey within the Nature Park Lonjsko Polje, placed in the middle-northern Croatia was performed during the time interval 2007–2010 in order to find the best location for installing the geomagnetic observatory. The total magnetic field has been measured a few times using the Overhauser proton magnetometers. The horizontal and vertical gradients of the total field, and its temporal behaviour were investigated over the restricted region that we estimated as suitable for the observatory. The results obtained from thoroughly conducted measurements allowed us to find definitive positions for the instrument pillars. These results are in agreement with previously suggested location found based on combination of Comprehensive CM4 model prediction and measurements conducted from 2003 to 2005. This study contributes to the development of geomagnetism in Croatia and paves a way to install the first geomagnetic observatory in Croatia.  相似文献