Influence of the seismic noise characteristics on noise correlations in the Baltic shield

International audienceIt has recently been shown that correlations of seismic noise can contain significant information about the Green's function along the station profile. Using an array of 38 temporary broad-band stations located in Finland between 1998 September and 1999 March, we study the resulting 703 noise correlations to understand how they are influenced by the directivity of the noise field. The latter information is obtained through f-k analysis of data from two permanent seismic arrays in Germany and Norway and from a subset of stations of the array in Finland. Both types of analysis confirm that the characteristics of the seismic noise is strongly frequency-dependent. At low frequencies (0.02–0.04 Hz), we observe diffuse noise and/or randomly distributed sources. In contrast, the noise is strongly direction-dependent and not fully diffuse in the intermediate period ranges (0.04–0.25 Hz) which correspond to the first and second microseismic peak, created at the Irish and Scottish coast and the western coast of Norway. In this frequency interval the noise is sufficiently close to a plane wave to introduce systematic errors in group velocities for station pairs which are not parallel to the direction of the dominant incident noise. Phase velocities calculated by slant stack over many traces are however correct, independently of profile direction. In the high-frequency band (0.25–1.0 Hz), the situation is a mix between the low-frequency and the intermediate frequency cases. Average phase velocities and individual group velocities from well-oriented profiles are in excellent agreement with results from Rayleigh wave studies of the area

The ac-Driven Motion of Dislocations in a Weakly Damped Frenkel-Kontorova Lattice

By means of numerical simulations, we demonstrate that ac field can support stably moving collective nonlinear excitations in the form of dislocations (topological solitons, or kinks) in the Frenkel-Kontorova (FK) lattice with weak friction, which was qualitatively predicted by Bonilla and Malomed [Phys. Rev. B{\bf 43}, 11539 (1991)]. Direct generation of the moving dislocations turns out to be virtually impossible; however, they can be generated initially in the lattice subject to an auxiliary spatial modulation of the on-site potential strength. Gradually relaxing the modulation, we are able to get the stable moving dislocations in the uniform FK lattice with the periodic boundary conditions, provided that the driving frequency is close to the gap frequency of the linear excitations in the uniform lattice. The excitations have a large and noninteger index of commensurability with the lattice (suggesting that its actual value is irrational). The simulations reveal two different types of the moving dislocations: broad ones, that extend, roughly, to half the full length of the periodic lattice (in that sense, they cannot be called solitons), and localized soliton-like dislocations, that can be found in an excited state, demonstrating strong persistent internal vibrations. The minimum (threshold) amplitude of the driving force necessary to support the traveling excitation is found as a function of the friction coefficient. Its extrapolation suggests that the threshold does not vanish at the zero friction, which may be explained by radiation losses. The moving dislocation can be observed experimentally in an array of coupled small Josephson junctions in the form of an {\it inverse Josephson effect}, i.e., a dc-voltage response to the uniformly applied ac bias current.Comment: Plain Latex, 13 pages + 9 PostScript figures. to appear on Journal of Physics: condensed matte

The digital challenge for multinational mobile network operators. More marginalization or rejuvenation?

Multinational mobile network operators (MNOs) rapidly emerged in the early 1990s and for a decade and a half were the dominant actors in their industry. We analyze the development and competitiveness of a typical MNO, Telenor. With the introduction of 4G in 2010, we show that Telenor, like other MNOs largely failed to respond to the opportunity that connectivity provided to develop digital services. Instead, these were developed by technology platform companies such as Amazon, Google and Microsoft. Telenor became a marginalized supplier of standardized internet connectivity. We argue that the ‘decade of lost opportunity’ (2010-2020) for Telenor was a product of a lack of ‘recombinant firm-specific advantages’ (FSARs). With the launch of 5G, an emerging global digital infrastructure, this sidelining is set to intensify unless Telenor responds to this new opportunity by developing B2B digital services. We analyze the FSARs that are necessary for a successful transition of capturing the value that 5G provides and the degree to which they are present, or potentially present, in Telenor

Considerations in Breeding Endophyte-Free Tall Fescue Forage Cultivars

Breeding tall fescue (Festuca arundinacea Schreb.) cultivars that are free of the endophytic fungus Acremonium coenophialum Morgan-Jones and Gams [previously identified and referred to as Epichloe typhina (Fries) Tulasne] is necessary to improve animal performance. The techniques used in developing new cultivars are not greatly different from those used previously, with one exception. Prior to the evaluation of new tall fescue lines or populations, the endophyte needs to be eliminated from the seed or the plants. Several techniques utilizing aging, heat, or chemical treatment are being used to effectively accomplish this in the seed. Methods for permanently eliminating the endophyte from plants are not available. The major new considerations in breeding endophyte-free tall fescue cultivars do not involve drastic changes in breeding methodology, but rather focus on new objectives. In the past, much effort was directed at overcoming the toxic effects of the endophyte. Now, breeders can focus their efforts on objectives such as increasing digestibility, physiological efficiency, mineral uptake, and insect and disease resistance. Losses in stress tolerance due to the elimination of the endophyte from tall fescue may also have to be addressed, especially in areas of marginal adaptation

Genetic manipulation of tall fescue

Genetic manipulation of tall fescue (Festuca arnndinacea Schreb.) has not been altered by the discovery of the Acremonium coenophialum (Morgan-Jones and Gams) / grass interaction. However, tall fescue breeding programs have been affected greatly. The basic methods for genetically manipulating the grass have remained static. Tall fescue is an obligate out-crossing species, and most improvements are, therefore, captured in the form of an improved population developed through some form of mass or recurrent selection. What has changed is the breeder\u27s ability to recognize genetic differences in the grass because of the confounding effect of A. coenophialum on plant phenotype. It is, therefore, critical that breeders recognize A. coenophialum status in their plants prior to selection. The other major change in tall fescue breeding since the discovery of the A. coenophialum/grass interaction is a tremendous increase in breeding activity

Genetic manipulation of tall fescue

Genetic manipulation of tall fescue (Festuca arnndinacea Schreb.) has not been altered by the discovery of the Acremonium coenophialum (Morgan-Jones and Gams) / grass interaction. However, tall fescue breeding programs have been affected greatly. The basic methods for genetically manipulating the grass have remained static. Tall fescue is an obligate out-crossing species, and most improvements are, therefore, captured in the form of an improved population developed through some form of mass or recurrent selection. What has changed is the breeder\u27s ability to recognize genetic differences in the grass because of the confounding effect of A. coenophialum on plant phenotype. It is, therefore, critical that breeders recognize A. coenophialum status in their plants prior to selection. The other major change in tall fescue breeding since the discovery of the A. coenophialum/grass interaction is a tremendous increase in breeding activity

Considerations in Breeding Endophyte-Free Tall Fescue Forage Cultivars

Breeding tall fescue (Festuca arundinacea Schreb.) cultivars that are free of the endophytic fungus Acremonium coenophialum Morgan-Jones and Gams [previously identified and referred to as Epichloe typhina (Fries) Tulasne] is necessary to improve animal performance. The techniques used in developing new cultivars are not greatly different from those used previously, with one exception. Prior to the evaluation of new tall fescue lines or populations, the endophyte needs to be eliminated from the seed or the plants. Several techniques utilizing aging, heat, or chemical treatment are being used to effectively accomplish this in the seed. Methods for permanently eliminating the endophyte from plants are not available. The major new considerations in breeding endophyte-free tall fescue cultivars do not involve drastic changes in breeding methodology, but rather focus on new objectives. In the past, much effort was directed at overcoming the toxic effects of the endophyte. Now, breeders can focus their efforts on objectives such as increasing digestibility, physiological efficiency, mineral uptake, and insect and disease resistance. Losses in stress tolerance due to the elimination of the endophyte from tall fescue may also have to be addressed, especially in areas of marginal adaptation

Experimental and numerical study of error fields in the CNT stellarator

Sources of error fields were indirectly inferred in a stellarator by reconciling computed and numerical flux surfaces. Sources considered so far include the displacements and tilts (but not the deformations, yet) of the four circular coils featured in the simple CNT stellarator. The flux surfaces were measured by means of an electron beam and phosphor rod, and were computed by means of a Biot-Savart field-line tracing code. If the ideal coil locations and orientations are used in the computation, agreement with measurements is poor. Discrepancies are ascribed to errors in the positioning and orientation of the in-vessel interlocked coils. To that end, an iterative numerical method was developed. A Newton-Raphson algorithm searches for the coils' displacements and tilts that minimize the discrepancy between the measured and computed flux surfaces. This method was verified by misplacing and tilting the coils in a numerical model of CNT, calculating the flux surfaces that they generated, and testing the algorithm's ability to deduce the coils' displacements and tilts. Subsequently, the numerical method was applied to the experimental data, arriving at a set of coil displacements whose resulting field errors exhibited significantly improved quantitative and qualitative agreement with experimental results.Comment: Special Issue on the 20th International Stellarator-Heliotron Worksho