Design and loading of dragline buckets

Draglines are an expensive and essential part of open cut coal mining. Small improvements in performance can produce substantial savings. The design of the bucket and the way in which it fills with overburden are very important to the overall dragline performance. Here we use a numerical model to simulate this filling process and to differentiate between the flow patterns of two different buckets. Extensions to the model are explored

PVC autoclave model

The batch reaction of polyvinyl chloride (PVC) in a pressure autoclave is modelled by considering the various mechanisms for conversion from vinyl chloride monomer (VCM) to the polymer during the middle phase of the industrial process. A key step is to determine at what stage the droplets of VCM stop contracting because of the density difference between VCM and PVC - this is known as the 'freeze point'. A model is proposed that locates the freeze point as that point where the unfavourable energy due to wetting of the PVC by water is dominated by the energy required to compress the gel network inside the droplets. Preliminary investigations support this explanation and suggest avenues for further work. A corollary of this model is an explanation of the role of 'secondary granulating agents' in controlling the porosity of the final product

Efficient homogenisation of photographic dispersions

The formation of fine droplets in a photographic emulsion which is forced through an orifice disperser consisting of a tube with one or more abrupt constrictions is considered. Some design ideas for reducing the droplet size are presented

Manning condensation in two dimensions

We consider a macroion confined to a cylindrical cell and neutralized by oppositely charged counterions. Exact results are obtained for the two-dimensional version of this problem, in which ion-ion and ion-macroion interactions are logarithmic. In particular, the threshold for counterion condensation is found to be the same as predicted by mean-field theory. With further increase of the macroion charge, a series of single-ion condensation transitions takes place. Our analytical results are expected to be exact in the vicinity of these transitions and are in very good agreement with recent Monte-Carlo simulation data.Comment: 4 pages, 4 figure

Wetting of Curved Surfaces

As a first step towards a microscopic understanding of the effective interaction between colloidal particles suspended in a solvent we study the wetting behavior of one-component fluids at spheres and fibers. We describe these phenomena within density functional theory which keeps track of the microscopic interaction potentials governing these systems. In particular we properly take into account the power-law decay of both the fluid-fluid interaction potentials and the substrate potentials. The thicknesses of the wetting films as a function of temperature and chemical potential as well as the wetting phase diagrams are determined by minimizing an effective interface potential which we obtain by applying a sharp-kink approximation to the density functional. We compare our results with previous approaches to this problem.Comment: 54 pages, 17 figures, accepted for publication in Physica

The articulation of lexical palatalization in Scottish Gaelic

Session 4aSC - Speech Communication: Cross-Language Topics in Speech Communication (Poster Session) - Contributed Paper: 4aSC6Scottish Gaelic (Gàidhlig, henceforth SG) exhibits a rich system of consonant mutation, which is mostly governed by its morphology (Ladefoged et al. 1998; Gillies 2002; Stewart 2004). For instance, bàta “boat” changes to [v] when the word undergoes morphological inflection—e.g., a bhàta “his boat”, in which the sound spelled bh is pronounced as [v]. Using ultrasound imaging, the present study investigates palatalization in SG, which is considered as one of lexicalized consonant mutation types. Experimental data was collected in Sabhal Mòr Ostaig, a college on the Isle of Skye. Preliminary results show a clear sign of palatalization across different consonant types in palatalization environments (i.e., when morphologically conditioned), represented by higher tongue contours in the front region of tongue. While the articulatory distinction between plain and palatalized consonants is significant, different syllabic positions (i.e., word-initial vs. -final palatalization) often yield individualized patterns.published_or_final_versio

Many-body interactions and melting of colloidal crystals

We study the melting behavior of charged colloidal crystals, using a simulation technique that combines a continuous mean-field Poisson-Boltzmann description for the microscopic electrolyte ions with a Brownian-dynamics simulation for the mesoscopic colloids. This technique ensures that many-body interactions between the colloids are fully taken into account, and thus allows us to investigate how many-body interactions affect the solid-liquid phase behavior of charged colloids. Using the Lindemann criterion, we determine the melting line in a phase-diagram spanned by the colloidal charge and the salt concentration. We compare our results to predictions based on the established description of colloidal suspensions in terms of pairwise additive Yukawa potentials, and find good agreement at high-salt, but not at low-salt concentration. Analyzing the effective pair-interaction between two colloids in a crystalline environment, we demonstrate that the difference in the melting behavior observed at low salt is due to many-body interactions

Effect of many-body interactions on the solid-liquid phase-behavior of charge-stabilized colloidal suspensions

The solid-liquid phase-diagram of charge-stabilized colloidal suspensions is calculated using a technique that combines a continuous Poisson-Boltzmann description for the microscopic electrolyte ions with a molecular-dynamics simulation for the macroionic colloidal spheres. While correlations between the microions are neglected in this approach, many-body interactions between the colloids are fully included. The solid-liquid transition is determined at a high colloid volume fraction where many-body interactions are expected to be strong. With a view to the Derjaguin-Landau-Verwey-Overbeek theory predicting that colloids interact via Yukawa pair-potentials, we compare our results with the phase diagram of a simple Yukawa liquid. Good agreement is found at high salt conditions, while at low ionic strength considerable deviations are observed. By calculating effective colloid-colloid pair-interactions it is demonstrated that these differences are due to many-body interactions. We suggest a density-dependent pair-potential in the form of a truncated Yukawa potential, and show that it offers a considerably improved description of the solid-liquid phase-behavior of concentrated colloidal suspensions

Classical Coulomb Systems:Screening and Correlations Revisited

From the laws of macroscopic electrostatics of conductors (in particular the existence of screening) taken for granted, one can deduce universal properties for the thermal fluctuations in a classical Coulomb system at equilibrium. The universality is especially apparent in the long-range correlations of the electrical potentials and fields. The charge fluctuations are derived from the field fluctuations. This is a convenient way for studying the surface charge fluctuations on a conductor with boundaries. Explicit results are given for simple geometries. The potentials and the fields have Gaussian fluctuations, except for a short-distance cutoff.Comment: 17 pages,TE

Interaction between macroions mediated by divalent rod-like ions

Attractive interactions between identical like-charged macroions in aqueous multivalent salt solution arise due to ion-ion correlations. The mean-field level Poisson-Boltzmann (PB) theory does not predict such behavior for point-like structureless ions. Various multivalent ions, such as certain DNA condensing agents or short stiff polyelectrolytes, do have an internal, often rod-like, structure. Applying PB theory to the generic case of divalent rod-like salt ions, we find attraction between like-charged macroions above a critical distance between the two individual charges of the rod-like ions. We calculate this distance analytically within linearized PB theory. Numerical results for the non-linear PB theory indicate strong enhancement of the tendency to mediate attractive interactions