Gravitational scattering of stars and clusters and the heating of the Galactic disk

Could the velocity spread, increasing with time, in the Galactic disk be explained as a result of gravitational interactions of stars with giant molecular clouds (GMCs) and spiral arms? Do the old open clusters high above the Galactic plane provide clues to this question? We explore the effects on stellar orbits of scattering by inhomogeneities in the Galactic potential due to GMCs, spiral arms and the Galactic bar, and whether high-altitude clusters could have formed in orbits closer to the Galactic plane and later been scattered. Simulations of test-particle motions are performed in a realistic Galactic potential. The effects of the internal structure of GMCs are explored. The destruction of clusters in GMC collisions is treated in detail with N-body simulations of the clusters. The observed velocity dispersions of stars as a function of time are well reproduced. The GMC structure is found to be significant, but adequate models produce considerable scattering effects. The fraction of simulated massive old open clusters, scattered into orbits with |z| > 400 pc, is typically 0:5%, in agreement with the observed number of high-altitude clusters and consistent with the present formation rate of massive open clusters. The heating of the thin Galactic disk is well explained by gravitational scattering by GMCs and spiral arms, if the local correlation between the GMC mass and the corresponding voids in the gas is not very strong. Our results suggest that the high-altitude metal-rich clusters were formed in orbits close to the Galactic plane and later scattered to higher orbits. It is possible, though not very probable, that the Sun formed in such a cluster before scattering occurred.Comment: 19 pages, 15 figure

Design and Construction of Anchored and Strutted Sheet Pile Walls in Soft Clay

The design and construction of anchored and strutted sheet pile walls in soft clay are reviewed in the paper based on experience gained mainly in Singapore during the last 10 years where mainly strutted sheet pile walls and contiguous bored piles are used. It is important to consider in the design also the high lateral earth pressures on the sheet piles below the bottom of the excavation when the depth of the excavation is large compared with the shear strength of the clay. The strut loads and the maximum bending moment in the sheet piles can be considerable higher than indicated by a conventional analysis. Different methods to increase the stability have also been investigated. With jet grouting, embankment piles and excavation under water it is possible to reduce significantly the maximum bending moment, the strut loads, the settlements outside the excavated area and the heave within the excavation

The Swedish-Turkish Parallel Corpus and Tools for its Creation

Proceedings of the 16th Nordic Conference of Computational Linguistics NODALIDA-2007. Editors: Joakim Nivre, Heiki-Jaan Kaalep, Kadri Muischnek and Mare Koit. University of Tartu, Tartu, 2007. ISBN 978-9985-4-0513-0 (online) ISBN 978-9985-4-0514-7 (CD-ROM) pp. 136-143

Use of Ground Anchors in Residual Soils

In the past decade the use of ground anchors in deep basements has increased in most parts of the world, while their applications in Singapore have been very limited so far because of their interference with adjacent properties. Empirical design methods which are adequate in most cases are still commonly used. Analytical design methods and finite element analysis (FEM) which give better insight into the soil-anchor interaction are gaining popularity. Post grouting is often used for anchors in residual soils and has been found successful. Some case histories from Singapore are presented in this paper

Stable Computations with Flat Radial Basis Functions Using Vector-Valued Rational Approximations

One commonly finds in applications of smooth radial basis functions (RBFs) that scaling the kernels so they are \u27flat\u27 leads to smaller discretization errors. However, the direct numerical approach for computing with flat RBFs (RBF-Direct) is severely ill-conditioned. We present an algorithm for bypassing this ill-conditioning that is based on a new method for rational approximation (RA) of vector-valued analytic functions with the property that all components of the vector share the same singularities. This new algorithm (RBF-RA) is more accurate, robust, and easier to implement than the Contour-Padé method, which is similarly based on vector-valued rational approximation. In contrast to the stable RBF-QR and RBF-GA algorithms, which are based on finding a better conditioned base in the same RBF-space, the new algorithm can be used with any type of smooth radial kernel, and it is also applicable to a wider range of tasks (including calculating Hermite type implicit RBF-FD stencils). We present a series of numerical experiments demonstrating the effectiveness of this new method for computing RBF interpolants in the flat regime. We also demonstrate the flexibility of the method by using it to compute implicit RBF-FD formulas in the flat regime and then using these for solving Poisson\u27s equation in a 3-D spherical shell

Damage Criteria for Small Amplitude Ground Vibrations

European codes and recommendations have been reviewed with respect to critical vibration levels, causing damage to buildings. It was found that the variation of the vibration threshold levels was large between the different codes. A rational approach to assess the damage caused by ground vibrations is proposed, based on wave propagation theory. The wave length appears to be the most important parameter. The damage potential was found to be greatest when the length of the propagating wave is equal to or shorter than the length of the building. The wave length can be determined from the frequency and wave propagation velocity. The critical dynamic ground distortion has been back-calculated from the requirements in the different codes and from published recommendations. The critical vertical particle velocity, causing damage, can be calculated if the wave propagation velocity is known. Also other factors such as the source of the vibrations, the building conditions and the degree of damage have been considered. A comparison of the proposed relationship with existing vibration criteria shows surprisingly good agreement

Relaxed thiol substrate specificity of glutathione transferase effected by a non-substrate glutathione derivative

AbstractRat glutathione transferase 4-4 catalysed the conjugation of 2-mercaptoethanol with 1-chloro-2,4-dinitrobenzene in the presence of S-methyl-glutathione. The reaction was linearly dependent on enzyme concentration and saturation was seen with respect to both 2-mercaptoethanol and S-methyl-glutathione concentration. High concentrations of S-methyl-gluta-thione were inhibitory. The results suggest that the natural substrate glutathione has two distinct functions in the normal catalytic reaction, (i) induction of a catalytically competent conformation of the enzyme and (ii) provision of the substrate sulfhydryl group in the reaction catalyzed

Advances in behavioral genetics modeling using Mplus: Applications of factor mixture modeling to twin data.

This article discusses new latent variable techniques developed by the authors. As an illustration, a new factor mixture model is applied to the monozygotic-dizygotic twin analysis of binary items measuring alcohol-use disorder. In this model, heritability is simultaneously studied with respect to latent class membership and within-class severity dimensions. Different latent classes of individuals are allowed to have different heritability for the severity dimensions. The factor mixture approach appears to have great potential for the genetic analyses of heterogeneous populations. Generalizations for longitudinal data are also outlined