ALBERT

Beschreibung: Zagros is a relatively young and active fold-thrust belt, which has formed due to convergence between the Eurasian and Arabian plates. Magnetotelluric (MT) soundings along a transect were carried out to determine the crustal structure in the collision zone of the two Palaeocontinents. MT data were analysed and modelled using 2-D inversion schemes. The models show clear conductive and resistive domains along the MT profile consistent to a great extent with documented tectonic features and surface geology. The models obtained from the joint inversion of transverse electric and transverse magnetic modes as well as the inversion of the determinant data show similar features along the profile. The new MT results reveal that the transition between two continents at the surface coincides with the western boundary of Sanandaj-Sirjan Zone (SSZ) at the Main Zagros Thrust (MZT). Along the profile towards northeast the conductors at top indicate massive Neogene sediments of the central domain (CD) while the very thick, shallow-located, resistive body (5–25 km thick and 100 km long) beneath is unlikely to be of oceanic affinity, but continental. Another main feature along the profile is the main resistive and conductive parts of the Arabian Plate, which coincide with the tectonic events of High Zagros Fault and Mountain Front Fault. Two highly conductive thick zones are recognized at the southwest part and in the middle of the profile apparently extending to a depth of about 50 km, possibly related to a downward smearing effect due to the presence of thick sedimentary columns in the upper crust. Along the profile, conductive features are recognized at the metamorphic SSZ and Urumieh-Dokhtar Magmatic Assemblage units as well as at CD. Below site 31 along the surface trace of the MZT, the transition between the two continents is distinguished by a complex sequence of conductive and resistive zones both varying laterally as well as vertically. The main difference between the two domains is that the Eurasian Plate seems to be more resistive than the Arabian Plate, although some part of the difference can be related to the thick sequence of conductive sedimentary rocks on the Arabian Plate.

Beschreibung: Motivation: Microtubules are dynamic polymers of tubulin dimers that undergo continuous assembly and disassembly. A mounting number of microtubule-associated proteins (MAPs) regulate the dynamic behavior of microtubules and hence the assembly and disassembly of disparate microtubule structures within the cell. Despite recent advances in identification and functional characterization of MAPs, a substantial number of microtubule accessory factors have not been functionally annotated. Here, using profile-to-profile comparisons and structure modeling, we show that the yeast outer kinetochore components NDC80 and NUF2 share evolutionary ancestry with a novel protein family in mammals comprising, besides NDC80/HEC1 and NUF2, three Intraflagellar Transport (IFT) complex B subunits (IFT81, IFT57, CLUAP1) as well as six proteins with poorly defined function (FAM98A-C, CCDC22, CCDC93 and C14orf166). We show that these proteins consist of a divergent N-terminal calponin homology (CH)-like domain adjoined to an array of C-terminal heptad repeats predicted to form a coiled-coil arrangement. We have named the divergent CH-like domain NN–CH after the founding members NDC80 and NUF2. Contact : kbschou@bio.ku.dk or lbpedersen@bio.ku.dk Supplementary information: Supplementary data are available at Bioinformatics online.

Beschreibung: We present an efficient approximate inversion scheme for near-surface loop-loop EM induction data (slingram) that can be applied to obtain 2D or 3D models on a normal desktop computer. Our approach is derived from a volume integral equation formulation with an arbitrarily conductive homogeneous half-space as a background model. The measurements are not required to fulfill the low induction number condition (low frequency and conductivity). The high efficiency of the method is achieved by invoking the Born approximation around a half-space background. The Born approximation renders the forward operator linear. The choice of a homogeneous half-space yields closed form expressions for the required electromagnetic normal fields. It also yields a translationally invariant forward operator, i.e., a highly redundant Jacobian. In connection with the application of a matrix-free conjugate gradient method, this allows for very low memory requirements during the inversion, even in three dimensions. As a consequence of the Born approximation, strong conductive deviations from the background model are underestimated. Highly resistive anomalies are in principle overestimated, but at the same time difficult to resolve with induction methods. In the case of extreme contrasts, our forward model may fail in simultaneously explaining all the data collected. We applied the method to EM34 data from a profile that has been extensively studied with other electromagnetic methods and compare the results. Then, we invert three conductivity maps from the same area in a 3D inversion.

Beschreibung: The Geological Survey of Sweden has been collecting airborne tensor very low frequency data (VLF) over several decades, covering large parts of the country. The data has been an invaluable source of information for identifying conductive structures that can among other things be related to water-filled fault zones, wet sediments that fill valleys or ore mineralizations. Because the method only uses two differently polarized plane waves of very similar frequency, vertical resolution is low and interpretation is in most cases limited to maps that are directly derived from the data. Occasionally, 2-D inversion is carried out along selected profiles. In this paper, we present for the first time a 3-D inversion for tensor VLF data in order to further increase the usefulness of the data set. The inversion is performed using a non-linear conjugate gradient scheme (Polak-Ribière) with an inexact line-search. The gradient is obtained by an algebraic adjoint method that requires one additional forward calculation involving the adjoint system matrix. The forward modelling is based on integral equations with an analytic formulation of the half-space Green's tensor. It avoids typically required Hankel transforms and is particularly amenable to singularity removal prior to the numerical integration over the volume elements. The system is solved iteratively, thus avoiding construction and storage of the dense system matrix. By using fast 3-D Fourier transforms on nested grids, subsequently farther away interactions are represented with less detail and therefore with less computational effort, enabling us to bridge the gap between the relatively short wavelengths of the fields (tens of metres) and the large model dimensions (several square kilometres). We find that the approximation of the fields can be off by several per cent, yet the transfer functions in the air are practically unaffected. We verify our code using synthetic calculations from well-established 2-D methods, and trade modelling accuracy off against computational effort in order to keep the inversion feasible in both respects. Our compromise is to limit the permissible resistivity to not fall below 100 m to maintain computational domains as large as 10 10 km 2 and computation times on the order of a few hours on standard PCs. We investigate the effect of possible local violations of these limits. Even though the conductivity magnitude can then not be recovered correctly, we do not observe any structural artefacts related to this in our tests. We invert a data set from northern Sweden, where we find an excellent agreement of known geological features, such as contacts or fault zones, with elongated conductive structures, while high resistivity is encountered in probably less disturbed geology, often related to topographic highs, which have survived predominantly glacial erosion processes. As expected from synthetic studies, the resolution is laterally high, but vertically limited down to the top of conductive structures.

Beschreibung: A 3-D model of the crustal electrical resistivity was constructed from the inversion of magnetotelluric data in the Kristineberg area, Skellefte district, the location of one of Sweden's most successful mining activities. Forward modelling of vertical magnetic transfer data supports our model which was derived from the magnetotelluric impedance only. The dominant features in the 3-D model are the strong conductors at various depth levels and resistive bodies of variable thickness occurring in the shallower subsurface. The deepest conductor, previously associated with the Skellefte crustal conductivity anomaly, is imaged in the southern part of the area as a north-dipping feature starting at ~4 km depth. Several shallow conductors are attributed to graphite in the black shales defining the contact between the metasedimentary rocks and the underlying metavolcanic rocks. Furthermore, an elongated intermediate depth conductor is possibly associated with alteration zones in the metavolcanic rocks that host the ore occurrences. The most prominent crustal resistors occur in the southern and northern part of the area, where their lateral extent on the surface coincides with the late-orogenic Revsund type intrusions. To the east, a resistive feature can be correlated to the early-orogenic Viterliden intrusion. The 3-D model is compared with two previous 2-D inversion models along two perpendicular profiles. The main electrical features are confirmed with the new model and previous uncertainties regarding 3-D effects, caused by off-profile conductors, can be better assessed in 3-D, although the resolution is lower due to a coarser model discretization. The comparison with seismic sections along two north–south profiles reveals structural correspondence between electrical features, zones of different reflectivity and geological units.

Beschreibung: A seismic reflection and MT survey was carried out along a 27-km long transect in northwestern Skellefte District, as part of a bigger 3D modeling project. The main motivation for the data acquisition is to elucidate the geologic relationship between the known mineralizations in the Adak mining camp to the north and in the well studied Kristineberg area south of the transect. The seismic reflection data were acquired with a VIBSIST system, and show reflectivity down to 3 s. Apart from the conventional processing for crystalline environments, the seismic data was also subject to an azimuthal binning procedure and cross-dip analysis, allowing the orientation of planar reflectors in 3D. Regarding the MT data, it is primarily of good quality along the 17 installed sites. The inversion of the determinant of the impedance tensor yielded a stable 2D resistivity model, dominated by resistors corresponding to the postorogenic intrusions along the transect. Adding the location of the analyzed seismic reflectors in the MT inversion rendered an integrated model that facilitated a preliminary joint interpretation of the data sets. Overall, the results are in good agreement with surface observations and reveal a crude configuration of the geologic units below the transect. The most prominent outcomes are the lateral and depth extent of the large postorogenic intrusions in the area reaching to 5- or 6-km depth, the dimensions of the nearly vertical Brännäs gabbro extending to 6-km depth, and the presence of enhanced conductivities along the transect at about 10 km depth. The latter is probably related to the deep conductor previously identified in the district.