The Dynamics of a Roll Press Nip

The problem presented concerned the dynamics of a roll press nip, a crucial component in a paper-making machine. Modern commercial paper-making machines are huge items of equipment. They may be as long as a football field and cost many millions of dollars each. Integrity of the process is extremely important; the paper in such a machine travels so fast (up to 20 km/sec) that a break is viewed as a major calamity and may take many man-hours and dollars to recover from. The size and speed of the machines means that it is not easy to make measurements as the paper passes through. The hostility of the environment therefore dictates that a thorough theoretical understanding of the important parts of the process is crucial if the processes involved are to be optimized. In this study we do not seek to answer anyone specific question, but rather wish to propose a general framework for modeling the flow and deformation under a roll press nip. Because of the difficulty of making measurements in the nip region and the need to closely control the process, the distributions of pressure, velocity and felt porosity within the nip have traditionally been subjects of great debate. Previous treatments have included lubrication theory models and "Bernoulli" based models. Although some progress may be made using thin layer theory, we shall show the required modeling does not take the form of standard lubrication theory. As far as models based on Bernoulli's equation are concerned, we simply note that the discussion below shows that the drag force exerted by the felt on the liquid is a key physical component of the flow process. Clearly, a full three-phase flow treatment is required. In this study we will thus address the following questions: (i) Is it possible to propose a general theoretical treatment of the roll press nip? (ii) What determines the physics of the water movement within the paper and felt in the roll press nip and how is this connected to the details of the air movement and the deformation of the felt? (iii) When a general model has been proposed, is it possible exploit the geometry within the nip to generate some simple exact solutions? (iv) What are the key non-dimensional parameters in the problem and how large are they likely to be for realistic paper-making machines? A further matter of interest concerns the influence that the size, shape and separation of the rollers have on the whole process. We approach the modeling from a rather general point of view, beginning by including all effects that might be important and then making clearly defined assumptions to simplify the equations. In this way it is possible to make changes to the model if circumstances change

Mathematical Modelling of flow in Schlemm's canal and its influence on primary open angle glaucoma

POAG (Primary Open Angle Glaucoma) is a major cause of blindness. This normally occurs when the IOP (intraocular pressure) increases. High pressure can be caused by an imbalance in the production and drainage of fluid (aqueous humour, AH) in the eye. AH is continually being produced but sometimes cannot be drained because of improperly functioning drainage channels (trabecular meshwork, TM). A mathematical model is presented for the flow of AH through the TM and into the SC (canal of Schlemm) and to couple this flow in order to predict changes in IOP. The governing equations have been developed by using the lubrication theory limit of the Navier-Stokes equations. To close the model, Friedenwald’s law has been used to predict changes of IOP. Several different cases have been examined in the model, relating AH flow to changes in IOP for various submodels: (i) the permeability, k in Darcy’s law may be either constant or not constant; (ii) the TM may be deformable so that the general theory of a beam under axial load is applicable - a number of different subcases where either ? or ?, may be either large or small have been considered. However only the subcase ? is small has been discussed in this study by assuming the permeability, k is constant and the TM is deformable. This subcase has been solved by using the regular perturbation method. The results show that the IOP rises continually when ? is small and may cause blindness

The application of cellular automata to weather radar

A possible cellular automaton approach to weather (and in particular rainfall) modelling is considered. After posing a paradigm problem in a manner reminiscent of a numerical PDE solver and showing that the general approach appears to be valid, we consider some more detailed modelling and comment on how this could be used to construct a genuine finite-state cellular automaton

Inertial levitation

We consider the steady levitation of a rigid plate on a thin air cushion with prescribed injection velocity. This injection velocity is assumed to be much larger than that in a conventional Prandtl boundary layer, so that inertial effects dominate. After applying the classical ‘blowhard’ theory of Cole & Aroesty (1968) to the two-dimensional version of the problem, it is shown that in three dimensions the flow may be foliated into streamline surfaces using Lagrangian variables. An example is given of how this may be exploited to solve the three-dimensional problem when the injection pressure distribution is known

Pharmacokinetics and efficacy of oral versus intravenous mixed-micellar phylloquinone (vitamin K-1) in severe acute liver disease

Background/Aims: In patients with severe acute liver dysfunction, i.v. phylloquinone (vitamin K-1) may be given to exclude vitamin K deficiency, rather than impaired hepatic synthesis of coagulation factors alone, as the cause of the coagulopathy. However, there have been no studies of the pharmacokinetics or efficacy of i.v. or oral K-1 in such patients.Methods: 49 adults with severe acute liver disease were randomised double-blind to a single 10 mg dose of i.v. or oral mixed-micellar K-1, or placebo. Serum levels of phylloquinone and undercarboxylated prothrombin (PIVKA-II) were assessed before and after treatment.Results: At admission, 13 patients (27 %) had either low serum K-1 levels or elevated PIVKA-II concentrations, indicative of subclinical vitamin K deficiency. In the 16 patients who received i.v. K-1, there was one (6 %) treatment failure (K-1 rise < 10 ng/ml above baseline), compared with 12 of the 15 (80 %) who received oral K, (P < 0.0001). One patient in the placebo group developed overt vitamin K deficiency.Conclusions: A minority of patients with severe acute liver dysfunction have subclinical vitamin K deficiency at the time of presentation, which is corrected by a single dose of i.v. K-1. The intestinal absorption of mixed-micellar K, is unreliable in adults with severe acute liver dysfunction. (c) 2004 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved

Effect of Ammonium-supplemented Seawater on Glutamine Synthetase and Glutamate Dehydrogenase Activities in Host Tissue and Zooxanthellae of Pocillopora damicornis and on Ammonium Uptake Rates of the Zooxanthellae

Host glutamine synthetase activity decreases in Pocillopora damicornis (Linnaeus) following exposure of the coral to seawater containing elevated ammonium (20 uM). Zooxanthellae isolated from these corals exhibited lower ammonium uptake capacity and glutamine synthetase activity compared with those from the control corals. Ammonium concentration of the surrounding seawater had no effect on the NADPH-dependent glutamate dehydrogenase activity in the host

Void elimination in screen printed thick film dielectric pastes

The problem is to understand the mechanisms for the formation and evolution of defects in wet screen printed layers. The primary objective is to know how best to alter the properties of the paste (rather than the geometry of the screen printing process itself) in order to eliminate the defects. With these goals in mind the work done during the Study Group reported here was as follows; to describe a simple model for the closure of craters, a model for the partial closure of vias, a possible mechanism for the formation of pinholes and finally a more detailed consideration of the screen printing process

Host pathogen interactions in relation to management of light leaf spot disease (caused by Pyrenopeziza brassicae) on Brassica species

Light leaf spot, caused by Pyrenopeziza brassicae, is currently the most damaging disease problem in oilseed rape in the UK. According to recent survey data, the severity of epidemics has increased progressively across the UK, with current yield losses of up to £160M per annum in England and more severe epidemics in Scotland. Light leaf spot is a polycyclic disease with primary inoculum consisting of air-borne ascospores produced on diseased debris from the previous cropping season. Splash-dispersed conidia produced on diseased leaves are the main component of the secondary inoculum. P. brassicae is also able to infect and cause considerable yield losses on vegetable brassicas, especially Brussels sprouts. There may be spread of light leaf spot among different brassica species. Since they have a wide host range, Pyrenopeziza brassicae populations are likely to have considerable genetic diversity and there is evidence suggesting population variations between different regions, which need further study. Available disease-management tools are not sufficient to provide adequate control of the disease. There is a need to identify new sources of resistance, which can be integrated with fungicide applications to achieve sustainable management of light leaf spot. Several major resistance genes and quantitative trait loci have been identified in previous studies, but rapid improvements in the understanding of molecular mechanisms underpinning B. napus – P. brassicae interactions can be expected through exploitation of novel genetic and genomic information for brassicas and extracellular fungal pathogens.Peer reviewe