Half-flat structures on indecomposable Lie groups

This article can be viewed as a continuation of the articles arXiv:0912.3486 and arXiv:1012.3714 where the decomposable Lie algebras admitting half-flat SU(3)-structures are classified. The new main result is the classification of the indecomposable six-dimensional Lie algebras with five-dimensional nilradical which admit a half-flat SU(3)-structure. As an important step of the proof, a considerable refinement of the classification of six-dimensional Lie algebras with five-dimensional non-Abelian nilradical is established. Additionally, it is proved that all non-solvable six-dimensional Lie algebras admit half-flat SU(3)-structures.Comment: 25 pages, v2: minor corrections due to the new classification of the six-dimensional Lie algebras with five-dimensional nilradical by Shabanskay

Half-flat structures on decomposable Lie groups

Half-flat SU(3)-structures are the natural initial values for Hitchin's evolution equations whose solutions define parallel G_2-structures. Together with the results of arXiv:0912.3486v1, the results of this article completely solve the existence problem of left-invariant half-flat SU(3)-structures on decomposable Lie groups. The proof is supported by the calculation of the Lie algebra cohomology for all indecomposable five-dimensional Lie algebras which refines and clarifies the existing classification of five-dimensional Lie algebras.Comment: 15 pages, v2: minor corrections and improved presentatio

The arginine deiminase pathway in the wine lactic acid bacteria Lactobacillus hilgardii X1B: structural and functional study of the arcABC genes

The genes implicated in the catabolism of the amino acid arginine by Lactobacillus hilgardiiX1Bwere investigated to assess the potential for formation of ethyl carbamate precursors in wine. L. hilgardii X1B can use arginine via the arginine deiminase pathway. The complete nucleotide sequence of the arc genes involved in this pathway has been determined. They are clustered in an operon-like structure in the order arcABC. No evidence was found for the presence of a homologue of the arcD gene, coding for the arginine/ornithine antiporter. The arc genes have been expressed in Escherichia coli resulting in arginine deiminase (ArcA), ornithine carbamoyltransferase (ArcB) and carbamate kinase (ArcC) activities. The results indicate the need for caution in the selection of lactic acid bacteria for conducting malolactic fermentation in wine since arginine degradation could result in high amounts of ethyl carbamate.This work was supported by grant VIN00-016 from the Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA) and Consejo de Investigaciones de la Universidad Nacional de Tucumán (CIUNT). M.E. Arena was a recipient of a Contrato UNT-Proyecto FOMEC 1214 from the Programa de Reforma de la Educación Superior. The nucleotide sequence of the arcABC gene cluster has been deposited in the EMBL/GenBank/DDBJ databases under accession number AJ421514.Peer reviewe

Magnetotellurische Studien im Nordwestdeutschen Becken: Ein Beitrag zur paläogeographischen Entwicklung des Unterkarbons

Diese Arbeit leistet einen Beitrag zur paläogeographischen Entwicklung des Unterkarbons im Nordwestdeutschen Becken. Ausgehend von Magnetotellurik-Sondierungen werden elektrisch leitfähige Schichten in präpermischen Sedimenten aufgezeigt. Anhand der räumlichen Verbreitung dieser Schichten konnten Informationen zur Verbesserung des Verständnisses der sedimentären Fazies-Entwicklung und die Verbreitung präwestfaler Muttergesteine gewonnen werden. Das Ergebnis wird in einer präziseren Karte der Fazies-Verteilung des Unterkarbons präsentiert, die zwei Bereiche aufzeigt, in denen leitfähige Schwarzschiefer auftreten: im Nordosten des Beckens die Skandinavischen Alaunschiefer und weiter südwestlich die Rhenoherzynischen Alaunschiefer. Da Schwarzschiefer als potentielle Erdöl-/Erdgas-Muttergesteine angesehen werden, sind die Magnetotellurik-Ergebnisse von spezieller Bedeutung für die Einschätzung der Erdgas-Höffigkeit im Nordwestdeutschen Becken

Undoing seamlessness : exploring seams for critical visualization

While seamful design has been part of discourses and work within HCI contexts for some time, it has not yet been fully explored in data visualization design. At the same time, critics of visualization have been arguing that the representation of data as contextual, contingent, relational, partial, heterogeneous, and situated is currently lacking in visualization. Seamful visualization promises a fresh perspective on visualization design as we seek to find more expressive encodings and novel approaches to representing data that acknowledge their wider qualities and limitations. By consulting seams in other realms and exploring existing seams and seamfulness in visualization, this paper offers a foundation for conceptualizing seamful visualization, points towards the value of seams and seamfulness in critical visualization, and proposes principles for engaging with seamful visualization in practice and research

Half-flat structures on products of three-dimensional Lie groups

We classify six-dimensional Lie groups which admit a left-invariant half-flat SU(3)-structure and which split in a direct product of three-dimensional factors. Moreover, a complete list of those direct products is obtained which admit a left-invariant half-flat SU(3)-structure such that the three-dimensional factors are orthogonal. Similar classification results are proved for left-invariant half-flat SL(3,R)-structures on direct products with either definite and orthogonal or isotropic factors.Comment: 19 page

Solvable Lie algebras are not that hypo

We study a type of left-invariant structure on Lie groups, or equivalently on Lie algebras. We introduce obstructions to the existence of a hypo structure, namely the 5-dimensional geometry of hypersurfaces in manifolds with holonomy SU(3). The choice of a splitting g^*=V_1 + V_2, and the vanishing of certain associated cohomology groups, determine a first obstruction. We also construct necessary conditions for the existence of a hypo structure with a fixed almost-contact form. For non-unimodular Lie algebras, we derive an obstruction to the existence of a hypo structure, with no choice involved. We apply these methods to classify solvable Lie algebras that admit a hypo structure.Comment: 21 pages; v2: presentation improved, typos corrected, notational conflicts eliminated. To appear in Transformation Group

The Use of the Multi-channel Analysis of Surface Waves (MASW) Method as an Initial Estimator of Liquefaction Susceptibility in Greymouth, New Zealand

Combined analysis of the geomorphic evolution of Greymouth with Multi-channel Analysis of Surface Waves (MASW) provides new insight into the geotechnical implications of reclamation work. The MASW method utilises the frequency dependent velocity (dispersion) of planar Rayleigh waves created by a seismic source as a way of assessing the stiffness of the subsurface material. The surface wave is inverted to calculate a shear wave velocity (Park et al., 1999). Once corrected, these shear-wave (Vs) velocities can be used to obtain a factor of safety for liquefaction susceptibility based on a design earthquake. The primary study site was the township of Greymouth, on the West Coast of New Zealand’s South Island. Greymouth is built on geologically young (Holocene-age) deposits of beach and river sands and gravels, and estuarine and lagoonal silts (Dowrick et al., 2004). Greymouth is also in a tectonically active region, with the high seismic hazard imposed by the Alpine Fault and other nearby faults, along with the age and type of sediment, mean the probability of liquefaction occurring is high particularly for the low-lying areas around the estuary and coastline. Repeated mapping over 150 years shows that the geomorphology of the Greymouth Township has been heavily modified during that timeframe, with both anthropogenic and natural processes developing the land into its current form. Identification of changes in the landscape was based on historical maps for the area and interpreting them to be either anthropogenic or natural changes, such as reclamation work or removal of material through natural events. This study focuses on the effect that anthropogenic and natural geomorphic processes have on the stiffness of subsurface material and its liquefaction susceptibility for three different design earthquake events. Areas of natural ground and areas of reclaimed land, with differing ages, were investigated through the use of the MASW method, allowing an initial estimation of the relationship between landscape modification and liquefaction susceptibility. The susceptibility to liquefaction of these different materials is important to critical infrastructure, such as the St. John Ambulance Building and Greymouth Aerodrome, which must remain functional following an earthquake. Areas of early reclamation at the Greymouth Aerodrome site have factors of safety less than 1 and will liquefy in most plausible earthquake scenarios, although the majority of the runway has a high factor of safety and should resist liquefaction. The land west of the St. John’s building has slightly to moderately positive factors of safety. Other areas have factors of safety that reflect the different geology and reclamation history