The initial stages of cave formation: Beyond the one-dimensional paradigm

The solutional origin of limestone caves was recognized over a century ago, but the short penetration length of an undersaturated solution made it seem impossible for long conduits to develop. This is contradicted by field observations, where extended conduits, sometimes several kilometers long, are found in karst environments. However, a sharp drop in the dissolution rate of CaCO_3 near saturation provides a mechanism for much deeper penetration of reactant. The notion of a "kinetic trigger" - a sudden change in rate constant over a narrow concentration range - has become a widely accepted paradigm in speleogenesis modeling. However, it is based on one-dimensional models for the fluid and solute transport inside the fracture, assuming that the dissolution front is planar in the direction perpendicular to the flow. Here we show that this assumption is incorrect; a planar dissolution front in an entirely uniform fracture is unstable to infinitesimal perturbations and inevitably breaks up into highly localized regions of dissolution. This provides an alternative mechanism for cave formation, even in the absence of a kinetic trigger. Our results suggest that there is an inherent wavelength to the erosion pattern in dissolving fractures, which depends on the reaction rate and flow rate, but is independent of the initial roughness. In contrast to one-dimensional models, two-dimensional simulations indicate that there is only a weak dependence of the breakthrough time on kinetic order; localization of the flow tends to keep the undersaturation in the dissolution front above the threshold for non-linear kinetics.Comment: to be published in Earth and Planetary Science Letter

Prosodic transcription of Glasgow English: an evaluation study of GlaToBI

GlaToBI, a version of the ToBI prosodic transcription system which can be used to transcribe the intonation patterns of western Scottish (Glasgow) English, is currently under development. An assessment of GlaToBI, similar to the evaluation studies that were undertaken for the original ToBI system [7], and for GToBI, a version developed for German [4], has been carried out to test the new system 's reliability, learnability and comprehensiveness. The results of this study show that this adaptation of the ToBI system can be applied with the expected level of reliability to the transcription of Glasgow English. 1. INTRODUCTION Very little corpus based work has been done on the prosodic features of English dialects other than Standard American and southern British (Received Pronunciation). However, with the creation of databases such as the University of Edinburgh's HCRC Map Task corpus [1], the predominant dialect of which is western Scottish (Glasgow) English, the opportunity has arisen..

Theory of physiological adaptation of poikilotherms to heat and cold

Cover title.Includes bibliographical references (pages 30-31)

A new model for simulating colloidal dynamics

We present a new hybrid lattice-Boltzmann and Langevin molecular dynamics scheme for simulating the dynamics of suspensions of spherical colloidal particles. The solvent is modeled on the level of the lattice-Boltzmann method while the molecular dynamics is done for the solute. The coupling between the two is implemented through a frictional force acting both on the solvent and on the solute, which depends on the relative velocity. A spherical colloidal particle is represented by interaction sites at its surface. We demonstrate that this scheme quantitatively reproduces the translational and rotational diffusion of a neutral spherical particle in a liquid and show preliminary results for a charged spherical particle. We argue that this method is especially advantageous in the case of charged colloids.Comment: For a movie click on the link below Fig

Numerical Simulations of Particulate Suspensions via a Discretized Boltzmann Equation Part II. Numerical Results

A new and very general technique for simulating solid-fluid suspensions has been described in a previous paper (Part I); the most important feature of the new method is that the computational cost scales with the number of particles. In this paper (Part II), extensive numerical tests of the method are described; for creeping flows, both with and without Brownian motion, and at finite Reynolds numbers. Hydrodynamic interactions, transport coefficients, and the short-time dynamics of random dispersions of up to 1024 colloidal particles have been simulated.Comment: Text and figures in uuencode-tar-compressed postcript Email [email protected]

The new cases of total color blindness.

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