ALBERT

Description: 〈span〉〈div〉SUMMARY〈/div〉The localization of passive seismic sources in form of microseismic tremors as well as large-scale earthquakes is a key issue in seismology. While most previous studies are assuming fairly good knowledge of the underlying velocity model, we propose an automatic spatial localization and joint velocity model building scheme that is independent of detailed 〈span〉a priori〈/span〉 information. The first step is a coherence analysis, estimating so-called wavefront attributes to locally describe the wavefield in terms of slopes and curvatures. In a similar fashion, we also obtain an initial guess of the source excitation times of the recorded events. The wavefront attributes constitute the input for wavefront tomography which represents the next step of the workflow and allows for a refinement of the previously evaluated source excitation times while simultaneously approximating the velocity distribution. In a last step, we use the final estimate of the velocity distribution and compute the respective image function by reverse time modelling to gain the source locations. This paper introduces the theoretical concept of our proposed approach for the general 3-D case. We analyse the feasibility of our strategy and the influences of different acquisition settings by means of a synthetic 2-D data example. In a final 3-D field data example we use the workflow to localize a deep earthquake without relying on a given velocity model. The approach can deal with high levels of noise and low signal amplitudes, respectively, as well as sparse geophone sampling. The workflow generally delivers good approximations of the long-wavelength velocity variations along with accurate source locations.〈/span〉

Description: As an analogue of the mineral pollucite (CsAlSi 2 O 6 ), CsTiSi 2 O 6.5 is a potential host phase for radioactive Cs. However, as 137 Cs and 135 Cs transmute to 137 Ba and 135 Ba, respectively, through the beta decay, it is essential to study the structure and stability of this phase upon Cs Ba substitution. In this work, two series of Ba/Ti-substituted samples, Cs x Ba (1− x )/2 TiSi 2 O 6.5 and Cs x Ba 1− x TiSi 2 O 7−0.5 x , ( x  = 0.9 and 0.7), were synthesized by high-temperature crystallization from their respective precursors. Synchrotron X-ray diffraction and Rietveld analysis reveal that while Cs x Ba (1− x )/2 TiSi 2 O 6.5 samples are phase-pure, Cs x Ba 1− x TiSi 2 O 7−0.5 x samples contain Cs 3 x /(2+ x ) Ba (1− x )/(2+ x ) TiSi 2 O 6.5 pollucites (i.e., also two-Cs-to-one-Ba substitution) and a secondary phase, fresnoite (Ba 2 TiSi 2 O 8 ). Thus, the Cs x Ba 1− x TiSi 2 O 7−0.5 x series is energetically less favorable than Cs x Ba (1− x )/2 TiSi 2 O 6.5 . To study the stability systematics of Cs x Ba (1− x )/2 TiSi 2 O 6.5 pollucites, high-temperature calorimetric experiments were performed at 973 K with or without the lead borate solvent. Enthalpies of formation from the constituent oxides (and elements) have thus been derived. The results show that with increasing Ba/(Cs + Ba) ratio, the thermodynamic stability of these phases decreases with respect to their component oxides. Hence, from the energetic viewpoint, continued Cs Ba transmutation tends to destabilize the parent silicotitanate pollucite structure. However, the Ba-substituted pollucite co-forms with fresnoite (which incorporates the excess Ba), thereby providing viable ceramic waste forms for all the Ba decay products.

Description: Genes involved in detoxification of foreign compounds exhibit complex spatiotemporal expression patterns in liver. Cytochrome P450 1A1 ( CYP1A1 ), for example, is restricted to the pericentral region of liver lobules in response to the interplay between aryl hydrocarbon receptor (AhR) and Wnt/β-catenin signaling pathways. However, the mechanisms by which the two pathways orchestrate gene expression are still poorly understood. With the help of 29 mutant constructs of the human CYP1A1 promoter and a mathematical model that combines Wnt/β-catenin and AhR signaling with the statistical mechanics of the promoter, we systematically quantified the regulatory influence of different transcription factor binding sites on gene induction within the promoter. The model unveils how different binding sites cooperate and how they establish the promoter logic; it quantitatively predicts two-dimensional stimulus-response curves. Furthermore, it shows that crosstalk between Wnt/β-catenin and AhR signaling is crucial to understand the complex zonated expression patterns found in liver lobules. This study exemplifies how statistical mechanical modeling together with combinatorial reporter assays has the capacity to disentangle the promoter logic that establishes physiological gene expression patterns.

Description: 〈span〉〈div〉Summary〈/div〉The localisation of passive seismic sources in form of microseismic tremors as well as large-scale earthquakes is a key issue in seismology. While most previous studies are assuming fairly good knowledge of the underlying velocity model, we propose an automatic spatial localisation and joint velocity model building scheme that is independent of detailed a priori information. The first step is a coherence analysis, estimating so-called wavefront attributes to locally describe the wavefield in terms of slopes and curvatures. In a similar fashion, we also obtain an initial guess of the source excitation times of the recorded events. The wavefront attributes constitute the input for wavefront tomography which represents the next step of the workflow and allows for a refinement of the previously evaluated source excitation times while simultaneously approximating the velocity distribution. In a last step, we use the final estimate of the velocity distribution and compute the respective image function by reverse time modelling to gain the source locations. This paper introduces the theoretical concept of our proposed approach for the general 3D case. We analyse the feasibility of our strategy and the influences of different acquisition settings by means of a synthetic 2D data example. In a final 3D field data example we use the workflow to localise a deep earthquake without relying on a given velocity model. The approach can deal with high levels of noise and low signal amplitudes, respectively, as well as sparse geophone sampling. The workflow generally delivers good approximations of the long-wavelength velocity variations along with accurate source locations.〈/span〉