1,721,211 research outputs found
Dyke emplacement in fractured media: application to the 2000 intrusion at Izu islands, Japan
No full textWe use a boundary element approach to study the problem of a large, magma-filled dyke embedded in a fractured, damaged medium. The numerical simulations show that the dyke opening and the crack extension force at the dyke tip increases with increasing fracture density. We show that this behaviour can at moderate fracture densities be predicted by an effective media model. Simple analytical formulae are given for the increasing average opening of the dyke and the decreasing fracture toughness as functions of increasing fracture density. The numerical and the theoretical results are found to be in good agreement. In a first application we tested the model by using GPS deformation and seismicity data from a recent lateral magma intrusion in Izu islands, Japan. This shows that a simple comparison of the distance change and the cumulative earthquake number enables the study of the stability of the dyke intrusion. The method seems to distinguish whether the dyke opening is actively driven by magma influx or passively driven by an expansion due to fracturing
Comment on "Spin dynamics of the electron-doped high-T(c) superconducting cuprates"
No full textDahm T, Eremin I. Comment on "Spin dynamics of the electron-doped high-T(c) superconducting cuprates". Physical Review Letters. 2006;97(23): 239701
Buoyancy-driven fracture ascent: Experiments in layered gelatine
No full textLaboratory experiments on air-filled fracture propagation in solidified homogeneous and layered gelatine have been carried out, providing an analogue model for magma-filled dikes ascending in the crust. The effects of layering on fracture velocity and shape have been analyzed in detail. The free surface is found to accelerate approaching fractures. Layering accelerates or decelerates fractures approaching discontinuities of the elastic parameters, depending on the value of the rigidity contrast. The shape of fractures are strongly influenced as they pass from one layer to another. The observed cross-sectional shape when crossing a layer interface and the acceleration with decreasing rigidity can be explained with theoretical models. Our experiments also reproduce the arrest of fractures in proximity of joints and the formation of sills in the layer below the interface. These findings could help in the interpretation of accelerated seismicity and deformation rates observed in volcanic areas
Critical Fluid Injection Volumes for Uncontrolled Fracture Ascent
Full text linkHydrofracturing is a routine industrial technique whose safety depends on fractures remaining confined within the target rock volume. Both observations and theoretical models show that, if the fluid volume is larger than a critical value, pockets of fluid can propagate large distances in the Earth's crust in a self-sustained, uncontrolled manner. Existing models for such critical volumes are unsatisfactory; most are two-dimensional and depend on poorly constrained parameters (typically the fracture length). Here we derive both analytically and numerically in three-dimensional scale-independent critical volumes as a function of only rock and fluid properties. We apply our model to gas, water, and magma injections in laboratory, industrial, and natural settings, showing that our critical volumes are consistent with observations and can be used as conservative estimates. We discuss competing mechanisms promoting fracture arrest, whose quantitative study could help to assess more comprehensively the safety of hydrofracturing operations
Optimal thickness of rectangular superconducting microtraps for cold atomic gases
Full text linkMarkowsky A, Zare A, Graber V, Dahm T. Optimal thickness of rectangular superconducting microtraps for cold atomic gases. Phys. Rev. A. 2012;86(2): 23412
Isotope effect in the presence of a pseudogap
No full textDahm T. Isotope effect in the presence of a pseudogap. Physical Review B. 2000;61(9):6381-6386.We investigate the question of whether the unusual doping dependence of the isotope exponent observed in underdoped high-T-c superconductors might be related to another unusual phenomenon observed in these systems: the pseudogap phenomenon. Within different approximations we study the influence of a phenomenological pseudogap on the isotope exponent and fmd that it generally strongly increases the isotope exponent, in qualitative agreement with experiments on underdoped high-T-c compounds. This result is stable against strong-coupling self-energy corrections and also holds for recently proposed spin-fluctuation exchange models, if a weak additional electron-phonon coupling is considered
Automated seismic event location by travel-time stacking: An application to mining induced seismicity
No full textA complex linear least-squares method to derive relative and absolute orientations of seismic sensors
No full textDetermining the relative orientation of the horizontal components of seismic sensors is a common problem that limits data analysis and interpretation for several acquisition setups, including linear arrays of geophones deployed in borehole installations or ocean bottom seismometers deployed at the seafloor. To solve this problem we propose a new inversion method based on a complex linear algebra approach. Relative orientation angles are retrieved by minimizing, in a least-squares sense, the l 2-norm between the complex traces (hodograms) of adjacent pairs of sensors. This methodology can be applied without restrictions only if the wavefield recorded by each pair of sensors is very similar. In most cases, it is possible to satisfy this condition by low-pass filtering the recorded waveforms. The main advantage of our methodology is that, in the complex domain, the relative orientations of seismic sensors can be viewed as a linear inverse problem, which ensures that the preferred solution corresponds to the global minimum of a misfit function. It is also possible to use simultaneously more than one independent data set (other seismic events) to better constrain the solution of the inverse problem. Furthermore, by a computational point of view, our method results faster than the relative orientation methods based on waveform cross-correlation. After several tests on synthetic data sets we applied successfully our methodology to different types of real data. These applications include the alignment of borehole sensors relative to a Vertical Seismic Profiling (VSP) acquisition and the orientation of Ocean Bottom Seismometers (OBS) relative to a neighbouring land station of known orientation. Using land stations, the absolute orientation of OBS can be retrieved. Finally, as a last application, we checked the correct orientation for land stations of a seismological array in Germany. © 2012 The Authors Geophysical Journal International © 2012 RAS
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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