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Practical Large-Scale Network Design with Variable Costs for Links and Switches
Get PDFThis paper considers communication network design problems that arise in the real world, with large numbers of nodes and link and switch costs dependent upon their traffic capacity. Such costs, in turn, depend upon network topology so are not fixed at the start of, or through, any optimisation process. Realistic topological restrictions are also discussed. The limitations of conventional approaches – both constructive and search based – are noted and the requirements of practical optimisation methods explored. Two workable approaches to network design - one an established local search variant, another a more novel geometric approach - are introduced. Five different algorithms, ranging from exhaustive search to fast heuristic are compared with experimental results given in conclusion
New Insights into the Mechanism of Gelation of Alginate and Pectin: Charge Annihilation and Reversal Mechanism
No full textStudies have been undertaken on the binding of Mn2+ ions to two alginate samples of different mannuronate:guluronate ratios (M:G), a sample of low-ester amidated pectin and poly(acrylic acid) (PAA). The binding of Ca2+ ions has also been included for the latter for comparison. The binding curves showed an initial steep rise at low additions of Mn2+ or Ca2+ indicating that all of the ions were bound to the polymer chains with none remaining in solution. At higher additions, the binding curves showed a plateau region and the maximum amount bound, θ, was found to be 0.2, 0.2, 0.25, and 0.33 mol M2+/mol COO- for high M:G alginate, low M:G alginate, pectin, and PAA, respectively. The binding curves for Mn2+ and Ca2+ with PAA were superimposable. In all cases, θ was less than the stoichiometric equivalent and also less than predicted by Manning counterion condensation theory. The linear charge density, ξ, for the polymers is 1.49, 1.55, 1.62, and 2.85, and it was found that at maximum binding the effective linear charge density, ξeffective, decreased to a value close to 1 in each case and not 0.5 as predicted from Manning's two-variable theory. The mobility of the PAA chains has been followed by electron spin resonance spectroscopy using nitroxide spin labels covalently attached to the polymer, and the gelation of the pectin and alginate samples has been monitored using small deformation oscillatory experiments. For PAA at maximum binding, it was noted that there was a loss of chain mobility and precipitation. For pectin and alginate, gelation occurred and the stoichiometric ratio for maximum binding corresponded to the stoichiometric ratio for the maximum in G‘. Precipitation and gelation are attributed to the formation of polymer−metal complexes involving one or two carboxylate groups resulting in charge reversal or charge annihilation
Hydrophobically Modified Associative Polymer Solutions: Rheology and Microstructure in the Presence of Nonionic Surfactants
No full textWe report on the rheology and morphology of a hydrophobically modified alkali-swellable emulsion (HASE) polymer solubilized in alkaline media containing nonionic surfactants. The HASE polymer consists of complex alkylaryl hydrophobes composed of oligomeric nonylphenol condensates attached to a poly(ethyl acrylate-co-methacrylic acid) backbone. The complex linear viscoelastic response of the polymer in alkaline solution suggests an unentangled network with an appreciable fraction of microgel. The concentration and hydrophile−lipophile balance (HLB) of nonionic surfactants profoundly affect the solution rheology. A surfactant of high HLB inhibits the dynamic network connectivity of the HASE polymer, as demonstrated by reductions of both the steady-shear viscosity and the dynamic storage modulus. The shear-induced structuring previously reported for this polymer is also progressively diminished as the surfactant concentration is increased. In contrast, the addition of a low-HLB surfactant promotes system structuring, as evidenced by (i) increases in the shear viscosity and the high-frequency plateau modulus and (ii) retention of the ability to undergo shear-induced structuring. We also employ cryofracture-replication transmission electron microscopy for the first time with regard to HASE associative polymers to examine the morphological characteristics of selected systems. The morphology of the HASE polymer in both latex and solubilized form appears more complex than previously anticipated, and a reasonable interpretation of these new data is provided
Molecular associations in acacia gums
Get PDFThe tendency of polysaccharides to associate in aqueous solution has long been recognised. Molecular associations can profoundly affect their performance in a given application due to its influence on the molecular weight, shape and size. This will ultimately determine how the molecules will interact with each other, with other molecules and with water. There are several factors, such as hydrogen bonding, hydrophobic association, ion mediated association, electrostatic interaction, concentration dependence and the presence of proteinaceous components, which affect this behaviour. Our objective is to highlight the role of the proteinaceous component, present in acacia gum, to promote associations when the gum is subjected to various processing treatments such as maturation, spray drying and irradiation. The results demonstrate the ability of the proteinaceous component to promote hydrophobic associations which influence the size and proportion of the arabinogalactan high molecular weight component (AGP). Heat treatment in solid state (maturation) increases the hydrophobic character of the gum and hence its emulsification performance. Spray drying also involves aggregation through hydrophobic association but changes the surface properties of peptide moieties to become more hydrophilic compared to the association promoted by the maturation treatment in the solid state. Irradiation induced cross-linking, in the presence of unsaturated gas, was used to introduce C-C bonds into the carbohydrate moiety and thus confirms the hydrophobic association prompted by the heat used in the maturation and spray drying. This association can be reversed by treatments such as filtration or high pressure homogenisation. The results reported here reconcile the contradiction about structure of gum arabic proposed by the wattle blossom and twisted hairy rope models and shows that the AGP fraction is basically an aggregated fraction made up of AG units stabilised by low molecular weight highly proteinaceous components.
A key to the future the attitudes and values of adolescent Europeans
Get PDFBased on original empirical data collected from adolescents in Europe (N = 9003) this paper focuses the lifeworlds of young people. It analyses negative and positive patterns of attitude and combines them with further concepts: personal life perspectives, various key values and political attitudes. Technically, the attitude towards Europe acts as the dependent variable whereas the remaining concepts are used as independent variables. The empirical results show Turkish and Polish adolescents are more critical towards Europe than adolescents living in 'old' Europe. Furthermore, the data show that those who hold negative expectations about their personal futures are likely also to be Eurosceptical
Students with Criminal Convictions: Policies and Practices in Social Work Education
No full textIn light of the Bichard Inquiry, this paper considers the vetting practices that apply in relation to those students with criminal convictions who apply to undertake social work education in England or Wales. The paper is organized primarily around the lessons that can be learnt from two case studies, and descriptions of how a range of social work programmes in England and Wales assess individuals with criminal convictions. It explores some of the reasons why the assessment of individuals with previous criminal convictions is important, some of the issues that might arise in relation to how it is currently carried out and what might constitute best practice in this area
Molecular interactions of plant and algal polysaccharides
Get PDFThis paper gives an overview of the interaction in solution of certain plant and algal polysaccharides with cations and also of their interaction in admixture with other polysaccharides and proteins. The mechanism of gelation of pectin and alginate in the presence of calcium ions is discussed together with the specific binding of potassium ions to kappa carrageenan and its influence on the coli-helix transition. The associative and segregative phase behaviour that is encountered in aqueous solutions of mixed polysaccharide systems is considered together with the formation of soluble and insoluble complexes in mixtures of polysaccharides and proteins
The “initial evidence”: implications of an empirical perspective in a British context
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Pebble on my wing
Get PDFQualitative research that explores the grief experience of bereaved mothers after the death of a child has revealed continuing bonds and the possibility of post-traumatic growth
An Investigation into Signal Strength of 802.11n WLAN
Get PDFWith the continual improvement in IEEE 802.11 standards wireless networks are being deployed in ever increasing numbers. As technology advances the data rates and coverage of Wi-Fi increases and so the usage for different high bandwidth requirement applications increases. These enhancements to the technology do provide network design engineers with some significant problems when designing the network infrastructure. Prior to the installation of Access Points it is difficult to predict whether access can be guaranteed at specific locations. Additionally, to increase the level of security, it is often preferable, despite the use of security protocols, to ensure that the signal strength is not large enough to enable connection in areas other than those designated. Experience with existing equipment may not be sufficient to ensure a secure design. It is shown that it is likely that equipment built to the anticipated IEEE 802.11n specification that uses MIMO provide a far more complex situation than equipment designed to previous standards.
By combining the theory of antennae and the measurement of the performance of equipment built to the IEEE 802.11n draft, it is possible to create a mathematical model that can predict the network coverage which should be extendable to the new standard. Additionally it is argued that due to the backward compatibility of equipment then the increased data rates are not going to be realised until the all intended clients have been upgraded