Fast iterative solution of large undrained soil‐structure interaction problems

In view of rapid developments in iterative solvers, it is timely to re‐examine the merits of using mixed formulation for incompressible problems. This paper presents extensive numerical studies to compare the accuracy of undrained solutions resulting from the standard displacement formulation with a penalty term and the two‐field mixed formulation. The standard displacement and two‐field mixed formulations are solved using both direct and iterative approaches to assess if it is cost‐effective to achieve more accurate solutions. Numerical studies of a simple footing problem show that the mixed formulation is able to solve the incompressible problem ‘exactly’, does not create pressure and stress instabilities, and obviate the need for an ad hoc penalty number. In addition, for large‐scale problems where it is not possible to perform direct solutions entirely within available random access memory, it turns out that the larger system of equations from mixed formulation also can be solved much more efficiently than the smaller system of equations arising from standard formulation by using the symmetric quasi‐minimal residual (SQMR) method with the generalized Jacobi (GJ) preconditioner. Iterative solution by SQMR with GJ preconditioning also is more elegant, faster, and more accurate than the popular Uzawa method. Copyright © 2003 John Wiley & Sons, Ltd.     

Calculating Internal Avalanche Velocities from Correlation with Error Analysis

Velocities inside avalanches have been calculated for many years by calculatingthe cross-correlation between opto-electronic sensors using a method pioneered by inlinecite Nishimura et al. and Dent et al. Their approachhas been widely adopted but there has been little discussion of the optimal designof such instruments and the best analysis techniques. This paper discusses some ofthe different sources of error that arise and how these can be mitigated. A statisticalframework that describes such instruments is developed and used to quantify the errors.     

North European last glacial–interglacial transition (LGIT; 15–9 ka) tephrochronology: extended limits and new events

High‐precision correlation of palaeoclimatic and palaeoenvironmental records is crucial for testing hypotheses of synchronous change. Although radiocarbon is the traditional method for dating late Quaternary sedimentary sequences, particularly during the last glacial–interglacial transition (LGIT; 15–9 ka), there are inherent problems with the method, particularly during periods of climate change which are often accompanied by major perturbations in atmospheric radiocarbon content. An alternative method is the use of tephras that act as time‐parallel marker horizons. Within Europe, numerous volcanic centres are known to have erupted during the LGIT, providing considerable potential for high‐precision correlation independent of past radiocarbon fluctuations. Here we report the first identification of the Vedde Ash and Askja Tephra in Ireland, significantly extending the known provenance of these events. We have also identified two new horizons (the Roddans Port Tephras A and B) and tentatively recognise an additional horizon from Vallensgård Mose (Denmark) that provide crucial additional chronological control for the LGIT. Two phases of the Laacher See Tephra (LST) are reported, the lower Laacher See Tephra (LLST) and probably the C2 phase of the Middle Laacher See Tephra (MLST‐C2) indicating a more northeasterly distribution of this fan than reported previously. Copyright © 2006 John Wiley & Sons, Ltd.     

The possiblity of detection of ultracool dwarfs with the UKIRT Infrared Deep Sky Survey

We present predictions for the numbers of ultracool dwarfs in the Galactic disc population that could be detected by the WFCAM/UKIDSS Large Area Survey and Ultra Deep Survey. Simulated samples of objects are created with masses and ages drawn from different mass functions and birthrates. Each object is then given absolute magnitudes in different passbands based on empirically derived bolometric correction versus effective temperature relationships (or model predictions for Y dwarfs). These are then combined with simulated space positions, velocities and photometric errors to yield observables such as apparent magnitudes and proper motions. Such observables are then passed through the survey selection mechanism to yield histograms in colour. This technique also produces predictions for the proper motion histograms for ultracool dwarfs and estimated numbers for the as yet undetected Y dwarfs. Finally, it is shown that these techniques could be used to constrain the ultra-low-mass mass function and birthrate of the Galactic disc population.     

Quintessential inflation models with a nonminimally coupled scalar field

The evolution of a homogeneous, isotropic cosmological model driven by a nonminimally coupled scalar field is studied. The potential for the quintessential inflation model proposed by Peebles and Vilenkin is selected as a scalar potential. Possible scenarios for the cosmological dynamics are described in the conformal Einstein and Jordan representations. It is shown that, unlike in models with a minimal scalar field, here a class of solutions exists for which the scalar field is fixed at finite values during cosmological expansion. __________ Translated from Astrofizika, Vol. 49, No. 3, pp. 487–498 (August 2006).