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  • Weitere Quellen  (15)
  • Univ. Freiburg (Breisgau)  (9)
  • Institut für Geologie 〈Freiberg〉  (6)
  • Englisch  (15)
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  • 2010-2014  (15)
  • 2000-2004
  • 1
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    Institut für Geologie 〈Freiberg〉
    Publikationsdatum: 2021-03-29
    Beschreibung: research
    Schlagwort(e): 551.4 ; VEJ 100 ; Indischer Subkontinent {Geologie}
    Sprache: Englisch
    Materialart: article
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  • 2
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    Univ. Freiburg (Breisgau)
    Publikationsdatum: 2021-03-29
    Beschreibung: Observations of the solar corona show loop-like structures formed by plasma at temperatures of one million degrees and higher. Since the solar surface is much cooler than the corona, a heating mechanism must be responsible for the high temperatures. The dissipation of magnetic fields in the corona could provide such a heating mechanism. However, the process of transforming magnetic energy into thermal energy is still not yet understood in detail. To investigate this process and its impact on the heating of the corona, we employ a three-dimensional magneto-hydrodynamical model. This numerical model synthesizes the temporal evolution of the magnetic field above an Active Region. It includes the solar atmosphere from the photosphere up to the corona. The magnetic field in the corona is braided by foot point motions in the photosphere. This is done imilarly to the braiding through granulation in reality. The stressed agnetic field induces currents which are then dissipated in the corona. This dea is known as the DC model (direct current) and was proposed by Parker in 1972. The model reaches a quasi-stationary state, i.e. the energy input by hotospheric motions is counterbalanced by radiative losses in the optically thin corona. As a result, the described heating process creates and sustains a hot corona with a temperature of one million degrees and higher ...
    Beschreibung: thesis
    Schlagwort(e): 523 ; TGC 765 ; TGC 800 ; Korona {Astronomie: Sonne} ; Magnetfelder {Astronomie: Sonne}
    Sprache: Englisch
    Materialart: monograph , publishedVersion
    Format: 108 S.
    Format: application/pdf
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  • 3
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    Univ. Freiburg (Breisgau)
    Publikationsdatum: 2021-03-29
    Beschreibung: The CERN Axion Solar Telescope (CAST) is searching for solar axions, which could be produced in the core of the Sun via the so-called Primakoff effect. For this purpose, CAST uses a decommissioned LHC prototype magnet. In its magnetic field of 9 Tesla axions could be reconverted into X-ray photons. The magnet is mounted on a structure built to follow the Sun during sunrise and sunset for a total of about 3 hours per day. The analysis of the data acquired during the first phase of the experiment with vacuum in the magnetic field region yielded the best experimental upper limit on the axion-to-photon coupling constant for axion masses up to about 0.02 eV. In order to extend the sensitivity of the experiment to a wider mass range, the CAST experiment continued its search for axions with helium in the magnet bores. In this way it is possible to restore coherence for larger masses. Changing the pressure of the helium gas enables the experiment to scan different axion masses. In the first part of this second phase of CAST, helium-4 has been used and the axion mass region was extended up to 0.4 eV ...
    Beschreibung: thesis
    Schlagwort(e): 523 ; TII 100 ; TCE 380 ; Dunkle Materie {Astronomie: Interstellare Materie} ; CCD, Photodetektoren {Astronomische Instrumente}
    Sprache: Englisch
    Materialart: monograph , publishedVersion
    Format: 266 S.
    Format: application/pdf
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  • 4
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    Univ. Freiburg (Breisgau)
    Publikationsdatum: 2021-03-29
    Beschreibung: The solar surface outside sunspots and active regions, i.e., the quiet Sun, shows the ubiquitous pattern of granulation in the photosphere. The quiet solar photosphere harbors small-scale magnetic structures inside and between granules. This thesis presents thermodynamic properties of the small-scale magnetic flux concentrations in the quiet Sun using high spatial and temporal resolution observations along with numerical simulations. Spectral line profiles of the Fe I 630 nm pair and Ca II H were used to trace the photospheric and chromospheric layers of the magnetic elements. In the presence of magnetic field spectral lines split and are polarized via the Zeeman effect. The difference of a spectral line profile, measured in left and right circular polarized light, is a Stokes-V profile with two lobes. In the absence of any gradients of velocity or magnetic field along the line of sight, Stokes-V profiles are anti-symmetric. The different area of the two lobes, the Stokes-V area asymmetry, provides information about the gradients of the magnetic and velocity fields along the line of sight. Comparing high resolution spectropolarimetric data with synthetic maps of a 3D MHD simulation, we found several magnetic elements in the photosphere showing a central region of negative Stokes-V area asymmetry surrounded by a peripheral region with larger positive asymmetry ...
    Beschreibung: thesis
    Schlagwort(e): 523 ; TGC 745 ; TGC 755 ; TGC 800 ; Photosphäre {Astronomie: Sonne} ; Chromosphäre {Astronomie: Sonne} ; Magnetfelder {Astronomie: Sonne}
    Sprache: Englisch
    Materialart: monograph , publishedVersion
    Format: 146 S.
    Format: application/pdf
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  • 5
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    Univ. Freiburg (Breisgau)
    Publikationsdatum: 2021-03-29
    Beschreibung: Observations of the sun are almost always impaired by the turbulent motion of air in Earth's atmosphere. The turbulence would limit the theoretical resolution of modern large telescopes to that of amateur telescopes without additional tools.Today however, high-resolution data of the Sun are necessary to invesitgate its small-scale structure. This structure is likely to be connected to the radially outward increasing temparature distribution of the solar atmosphere. An introduction into further details of this topic that has also been the motivation for this work is presented in Chapt. 1. A theory of atmospheric turbulence that builds the basis for several results of this work is described in Chapt. 2. Here, two modern tools to enhance the resolution of groundbased observations are reviewed, on the one hand adaptive optics (AO) systems and on the other hand speckle interferometry. Until recently, these two techniques were only used separately. In Chapt. 3 the necessary modifications for analytical models of transfer functions are developed that include the changes made by an AO system to the incoming wave front, thus making a combination of AO systems and speckle interferometry possible ...
    Beschreibung: thesis
    Schlagwort(e): 523 ; TGC 100 ; TGC 740 ; Sonnenbeobachtung {Astronomie} ; Sonnenatmosphäre
    Sprache: Englisch
    Materialart: monograph , publishedVersion
    Format: 137 S.
    Format: application/pdf
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  • 6
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    Univ. Freiburg (Breisgau)
    Publikationsdatum: 2021-03-29
    Beschreibung: Photospheric bright points are proxies for small-scale magnetic flux concentrations.These magnetic elements are thought to be the building blocks of the solar magnetic field and are important to understand many physical processes on the Sun, e.g. the variability of the solar irradiance.Because of their small size (100-200 km in diameter) the observations of photospheric bright points put special requirements on the seeing conditions, instrumental setup and post-processing techniques ...
    Beschreibung: thesis
    Schlagwort(e): 523 ; TGC 800 ; TGC 745 ; Magnetfelder {Astronomie: Sonne} ; Photosphäre {Astronomie: Sonne}
    Sprache: Englisch
    Materialart: monograph , publishedVersion
    Format: 105 S.
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  • 7
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    Institut für Geologie 〈Freiberg〉
    Publikationsdatum: 2021-03-29
    Beschreibung: The present work deals with two challenging problems of applied geostatistics: (i) Stationarity assumptions often do not hold under real-world conditions. (ii) Geostatistical methods have to be linked with spatial databases in order to be applicable in non-stationary situations. Solutions for both problems are proposed and implemented. (i) A central assumption in geostatistics is the stationarity of the process. However the spatial variability of many natural phenomena heavily depends on the local geology, which is nonstationary in most cases. To deal with this, the concept of process stationarity is replaced by a stationarity of the governing influence relating the local semivariogram and the local geology as stored in a Geographical Information System (GIS). A construction method is used, which can meaningfully incorporate additional spatial information from GIS, e.g. smoothly varying geology in the investigated area, spatially varying anisotropy induced by mountainous morphology, or geological faults interrupting continuity. Least-squares parameter estimation is used for fitting instationary semivariogram models in typical example situations, leading to non-linear optimization problems. Furthermore, a method for semivariogram parameter estimation in the present of linear trend is proposed. (ii) Geostatistical tools that make use of the local geology need direct access to the data stored in the GIS. A link between the presented geostatistical tools and the GIS software ArcView was established. Thus, spatial data such as measured contaminant concentrations, soil properties and morphology can be incorporated in geostatistical analyses. R code that fits instationary semivariogram models and performs kriging was implemented and can be obtained from the author. It is applied to simulated datasets.
    Beschreibung: Die vorliegende Diplomarbeit befasst sich mit zwei wichtigen Problemen der angewandten Geostatistik: (i) Stationaritätsannahmen werden unter realweltlichen Bedingungen oft nicht erfüllt. (ii) Geostatistische Methoden müssen mit räumlichen Datenbanken verbunden werden, um unter nichtstationären Bedingungen anwendbar zu sein. Lösungen für beide Probleme werden vorgeschlagen und implementiert. (i) In der Geostatistik ist die Stationarität des Prozesses eine zentrale Annahme. Die räumliche Variabilität vieler Phänomene in unserer Umwelt hängt jedoch stark von lokalen geologischen Verhältnissen ab, die meist aber instationär sind. Um damit umgehen zu können, wird das Konzept der Stationarität des Prozesses ersetzt durch eine Stationarität des Einflusses der lokalen Geologie, wie sie in einem GIS gespeichert ist, auf das lokale Semivariogramm. Es wird eine Konstruktionsmethode benutzt, die auf sinnvolle Art räumliche Informationen aus dem GIS in Semivariogrammmodelle einbinden kann, etwa sich über das Untersuchungsgebiet gleichmäßig verändernde geologische Verhältnisse, sich räumlich verändernde Anisotropie im Gebirgsrelief oder geologische Störungen, die die Kontinuität unterbrechen. Kleinste-Quadrate Schätzung wird für die Anpassung instationärer Semivariogrammmodelle in typischen Beispielsituationen verwendet. Dies führt zu nichtlinearen Optimierungsproblemen. Des weiteren wird eine Methode der Schätzung von Semivariogrammparametern in Modellen mit linearem Trend vorgestellt. (ii) Geostatistische Werkzeuge, die lokalen geologischen Verh¨ältnisse berücksichtigen, benötigen einen direkten Zugang zu Daten, die in einem GIS gespeichert sind. Im Rahmen dieser Arbeit wurde eine Verbindung zwischen den vorgestellten geostatistischen Werkzeugen und dem GIS Programm ArcView erstellt. Auf diese Weise können räumliche Daten wie etwa Schadstoffkonzentrationen, Bodeneigenschaften oder die Morphologie in geostatistische Analysen einbezogen werden. R-Code, der instationäre Semivariogrammmodelle anpasst und Kriging durchführt, wurde erstellt und auf simulierte Datensätze angewandt. Der Code kann über den Author bezogen werden.
    Beschreibung: research
    Schlagwort(e): 551.4 ; QBD 700 ; QBK 000 ; VJA 310 ; VBD 000 ; VJA 100 ; VKB 311 ; QFC 430 ; Geoinformationssysteme {Geographie} ; Mathematische Geographie ; Statistische Auswertung {Geochemie} ; Mathematische und Statistische Geologie ; Probennahme, Probenaufbereitung {Geochemie} ; Untersuchungsmethoden und Probennahme im Gelände {Sedimentologie} ; Methoden und Techniken der Umweltforschung {Angewandte Geographie} ; geographic information systems ; geostatistics ; combination ; spatial distribution ; sampling
    Sprache: Englisch
    Materialart: article , publishedVersion , publishedVersion
    Format: application/pdf
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  • 8
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    Institut für Geologie 〈Freiberg〉
    Publikationsdatum: 2021-03-29
    Beschreibung: Deutsche Forschungsgemeinschaft
    Beschreibung: research
    Schlagwort(e): 551.4 ; VJC 000 ; VQ 600 ; VJF 000 ; Aquatische Geochemie ; Grenzgebiete. Beziehungen. Einflüsse. Wirkungen. {Lagerstättenkunde} ; Umweltgeochemie insgesamt ; uranium ; geochemistry ; hydrochemistry ; hydrogeochemistry ; physicochemical properties ; isotope fractionation ; isotope fractionation ; spectroscopy
    Sprache: Englisch
    Materialart: article , publishedVersion
    Format: application/pdf
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  • 9
    Publikationsdatum: 2021-03-29
    Beschreibung: Human activities result in climate changes with various impacts on forest ecosystems. An increase in global surface temperature, compared to pre-industrial levels, is already recorded and further elevation is expected. Extreme events, such as hot and dry periods, would increase in frequency and duration in near future. Due to the low adaptive capacity of forest ecosystems to rapid climate changes, high priority is given to the assessment of their responses. Particularly, studies on forests dominated by the drought susceptible European beech, especially when grown on limestone-derived soils with low water storage capacity, being common in Central and Southern Europe, are important. Moreover, climate models emphasize the significance of management practices for the adaptation to the expected changes, since they could contribute to the mitigation of possible adverse effects of climate change. The present study assessed the effects of different climatic conditions on the nitrogen and water status of natural beech regeneration grown in managed (thinned) and not managed (control) stands in a forest in Southern Germany. A SW-exposed site, characterized by low water availability and high temperature and radiation interception, was regarded as representative of the climate conditions expected in the future, whereas a NE-exposed site was used as typical of present climatic conditions...
    Beschreibung: thesis
    Schlagwort(e): 551.6 ; TUG 000 ; Biometeteorologie und Bioklimatologie
    Sprache: Englisch
    Materialart: monograph , publishedVersion
    Format: 41 S.
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  • 10
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    Institut für Geologie 〈Freiberg〉
    Publikationsdatum: 2021-03-29
    Beschreibung: research
    Schlagwort(e): 551.4 ; VBQ 900 ; UD 340 ; UBG 200 ; UBG 600 ; UBG 300 ; VEI 400 ; Hydrogeologie einzelner Regionen ; Aride und semiaride Zone {Hydrologie} ; Grundwasserbildung {Hydrologie, Unterirdische Gewässer} ; Grundwasserhaushalt {Hydrologie, Unterirdische Gewässer} ; Grundwassereigenschaften {Hydrologie, Unterirdische Gewässer} ; Israel, Palästina {Geologie} ; Jordan ; ground water ; recharge ; hydrogeology ; hydrogeochemistry ; PHREEQE
    Sprache: Englisch
    Materialart: article
    Format: application/pdf
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  • 11
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    Institut für Geologie 〈Freiberg〉
    Publikationsdatum: 2021-03-29
    Beschreibung: Computer simulations have become increasingly popular in many different areas over the years, owing mainly to more effective and cheaper machines. In many cases, the trend seems to be that computer simulations are replacing experiments, at least in areas in which experiments are very difficult (expensive) or impossible. One such area is that of attempting to foresee what will happen in the future. Such analyses are very important for a durable construction such as a repository for spent nuclear fuel, for example. In the modelling effort, several computer codes are used and input data are often used without scrutiny. However, this work shows that even the rather simple task of calculating the solubility of a solid phase in a given water is encumbered with the effects of different uncertainties. These uncertainties may make the calculated solubility vary by several orders of magnitude. Thus the input to the more complex codes, simulating processes in connection with the repository, will also be affected. This report presents some computer programs for uncertainty and sensitivity analysis of solubility calculations. They are then illustrated by numerical simulations and estimation of uncertainty intervals for a case at the Äspö site in Sweden. Some of the input data treated as uncertain parameters are the stability constants for the reactions between the metal ion concerned and the elements present in the selected water or the rock. Stability constants and the enthalpies and entropies of reaction for the thoriumwater-acetylacetone-phosphate system have been determined experimentally. In addition to the values determined for these entities, uncertainty intervals are also estimated. A complexing mechanism for the thorium-phosphates at pH 8 is also suggested.
    Beschreibung: research
    Schlagwort(e): 551.4 ; VJC 000 ; VBE 000 ; VJH 200 ; Aquatische Geochemie ; Modellierung von Prozessen in der Geosphäre ; Thermodynamische Prozesse, Verteilungskoeffizienten {Physikalische Geochemie} ; uncertainty analysis ; sensitivity analysis ; SENVAR ; UNCCON ; MINVAR ; thorium hydrolysis ; thorium phosphate complexes ; solvent extraction ; potentiometric titrations
    Sprache: Englisch
    Materialart: article
    Format: application/pdf
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  • 12
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    Univ. Freiburg (Breisgau)
    Publikationsdatum: 2021-03-29
    Beschreibung: The most prominent features on the surface of the solar disc are the sunspots, which have been studied since their detection in the 17th century. Despite this years and centuries of scientific investigations, surprisingly many facets of sunspots are not well understood. In this thesis, the properties of a sunspots' penumbra are derived from the observed spectra by means of an inversion, a forward modeling technique. A method for the construction of a 3-dimensional model of the field topology from the inversion results is presented. It offers the possibility to build a toy-model of the spot. This allows to investigate the relationships between the geometry and other properties of the sunspot like flow velocities, intensity, temperature, or field strength. The application of the procedure to time series of observations will allow to study the temporal evolution of the geometry and the other properties, to determine the physical processes happening and their respective drivers. A second part of the thesis is devoted to the analysis of isolated field concentrations in the surroundings of the sunspot. These isolated magnetic elements are assumed to be the elementary building blocks of the solar surface magnetism. In the turbulent surroundings of the solar atmosphere, only relatively strong concentrations with a field strength above 1 kG are assumed to be stable at all ...
    Beschreibung: thesis
    Schlagwort(e): 523 ; TGC 800 ; Magnetfelder {Astronomie: Sonne}
    Sprache: Englisch
    Materialart: monograph , publishedVersion
    Format: 166 S.
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  • 13
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    Univ. Freiburg (Breisgau)
    Publikationsdatum: 2021-03-29
    Beschreibung: Satellite observations with high spatial and temporal resolution have revealed the highly dynamic nature of the solar corona and enabled us to study physical processes in the outer atmosphere of our mother star in great detail. This thesis deals with dynamic processes in coronal loops, i.e. magnetic structures which may be thought of as the elementary building blocks of the solar corona. Using computational fluid dynamics as a tool, I calculate time-dependent models of solar coronal loops in order to address the following questions: Are dynamic processes in coronal loops, such as flows and transient brightenings, necessarily the result of a time-dependent driving mechanism? Can various observations of fast downflows be explained by a common mechanism? Which parameters determine the dynamics of coronal loops? It is found that coronal loops which are predominantly heated around their footpoints can develop a thermal instability in the upper part of the loop. This instability results in a self-amplifying catastrophic cooling process and leads to the formation of dense, cool plasma condensations. The first part of the work focuses on plasma condensations in short cool loops, which presumably constitute the solar transition region, and describes how the catastrophic cooling process leads to transient brightenings in spectral lines formed in the transition region ...
    Beschreibung: thesis
    Schlagwort(e): 523 ; TGC 765 ; TBI 000 ; Korona {Astronomie: Sonne} ; Ultraviolett-Astronomie
    Sprache: Englisch
    Materialart: monograph , publishedVersion
    Format: 161 S.
    Format: application/pdf
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  • 14
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    Univ. Freiburg (Breisgau)
    Publikationsdatum: 2021-03-29
    Beschreibung: In this study we present a finite-volumen scheme for solving the equations of radiation magnetohydrodynamics in two and three space dimensions. Among other applications this system is used to model the plasma in the solar convection zone and in the solar photosphere. It is a non--linear system of balance laws derived from the Euler equations of gas dynamics and the Maxwell equations; the energy transport through radiation is also included in the model. The starting point of our presentation is a standard explicit first and second order finite-volume scheme on both structured and unstructured grids. We first study the convergence of a finite-volume scheme applied to a scalar model problem for the full system of radiation magnetohydrodynamics. We then present modifications of the base scheme. These make it possible to approximate the system of magnetohydrodynamics with an arbitrary equation of state; they reduce errors due to a violation of the divergence constraint on the magnetic field, and they lead to an improved accuracy in the approximation of solution near an equilibrium state. These modifications significantly increase the robustness of the scheme and are essential for an accurate simulation of processes in the solar atmosphere ...
    Beschreibung: thesis
    Schlagwort(e): 523 ; TGC 400 ; Strahlung der Sonne {Astronomie}
    Sprache: Englisch
    Materialart: monograph , publishedVersion
    Format: 305 S.
    Format: application/pdf
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  • 15
    Publikationsdatum: 2021-07-14
    Beschreibung: This dictionary was compiled by hydrogeologists from Germany, Mexico and Nicaragua. German and Spanish expressions were established by native speakers, all of them with a good knowledge of English and some French. However no native English or French speaker has reviewed the dictionary so far. Using the dictionary you will additionally recognize that some translations are still missing in one or more languages while they are already available in others. Further some special expressions you are looking for might be neglected at all. The dictionary is published by now in order to make it available to as many scientists in the field of applied geology as possible, however it is still under construction and probably will ever be. We do think about adding definitions for at least part of the words and a more convenient way to query. If you find any mistakes, missing words or if you have any additional suggestions or want to participate in our multilingual dictionary project (e.g. with a further language) please feel free to contact Prof. Dr. Broder Merkel (merkel@geo.tufreiberg. de). At the end of this four lingual introduction you will find the dictionary applied geology in four versions, all of them contain all four languages, sorted by the language listed in the file name (“English dictionary”: expressions sorted by the first column English; “Deutsches Wörterbuch”: expressions sorted by the first column German, etc.). You may download each dictionary and use the search function of the Acrobat Reader to look for the desired expression. Articles are indicated behind each word with (f) for feminine, (m) for masculine, (n) for neutral. For some words several translations exist in one language or the other. They are listed in different lines below each other. All copyrights belong to the authors. Neither the whole dictionary nor parts of it are to be published by any other user. We hope this dictionary helps you working in the multilingual field of applied geology and you will help us to further improve it. Enjoy!
    Beschreibung: research
    Schlagwort(e): 551.4 ; VB 000 ; V 200 ; VBQ 100 ; Angewandte Geowissenschaften ; Wissenschaftsorganisation und -Pflege {Geologische Wissenschaften} ; Methodik, Untersuchungsverfahren und Instrumente {Hydrogeologie} ; geology ; hydrogeology ; dictionary ; english ; french ; german ; spanish
    Sprache: Englisch
    Materialart: article , publishedVersion
    Format: application/pdf
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