Network protocol scalability via a topological Kadanoff transformation

A natural hierarchical framework for network topology abstraction is presented based on an analogy with the Kadanoff transformation and renormalisation group in theoretical physics. Some properties of the renormalisation group bear similarities to the scalability properties of network routing protocols (interactions). Central to our abstraction are two intimately connected and complementary path diversity units: simple cycles, and cycle adjacencies. A recursive network abstraction procedure is presented, together with an associated generic recursive routing protocol family that offers many desirable features.Comment: 4 pages, 5 figures, PhysComNet 2008 workshop submissio

Health-related quality of life and health behaviours in children and adolescents with sickle cell disease

Sickle cell disease (SCD) is an inherited blood disorder. Physical health problems include painful vaso-occlusive crises. Children and adolescents with SCD may also experience psychological distress, social isolation and an impaired health-related quality of life (HRQL). Physical health problems and psychosocial factors may be managed, to a certain degree by engaging in daily health behaviours and exacerbated by engaging in risky behaviours. However, children’s ability to engage in healthy behaviours may also be undermined by their condition, social influences, their environment and psychological factors. These behaviours have rarely been studied in paediatric SCD populations and both health behaviours and HRQL have rarely been examined in SCD by drawing on a theoretical approach. Therefore, the overall aim of this thesis was to gain a better understanding of HRQL by applying Gap theory (GT; which suggests that HRQL is based on the discrepancy between current and ideal self) and of health behaviours drawing on constructs from the Theory of Planned Behaviour (TPB). It also aimed to examine whether there is a relationship between health behaviours and HRQL. The research comprised two qualitative studies (one with children and healthy siblings using drawings and interviews and one with adolescents and healthy siblings using focus groups) and two quantitative studies using questionnaires focusing on children, adolescents and their parents. The findings from Study 1 suggested that children with SCD and healthy siblings had some discrepancies in different areas of their HRQL (physical vs. psychosocial domains respectively) but that this did not seem to manifest in adolescence (Study 2). Health behaviours were especially influenced by people in their lives and children and adolescents used some health behaviours to cope with their condition (Studies 1 and 2). In Study 3 GT was not applied and instead current perceived HRQL was predicted by greater disease severity (i.e. fewer days missed from school as well as crises only in adolescents) and increased moderate exercise only in children. There was no difference in HRQL between adolescents and children but there was some underestimation of their HRQL among their parents. In Study 4 the TPB constructs were more consistent at predicting behaviours in children than adolescents. Children’s weekly exercise was predicted by children’s TPB beliefs (although unexpectedly, more perceived barriers) and parental subjective norms (SN), whereas in adolescents, exercise was predicted by male gender and parental attitude. Child and parent attitude were also the key predictors of child/adolescent water consumption. Adolescents alcohol use was predicted by their attitude, older age, and unexpectedly, more perceived barriers. The combined findings of the thesis contribute towards a more comprehensive understanding of HRQL and health behaviours in SCD

Magnetic eddy viscosity of mean shear flows in two-dimensional magnetohydrodynamics

Magnetic induction in magnetohydrodynamic fluids at magnetic Reynolds number (Rm) less than~1 has long been known to cause magnetic drag. Here, we show that when $\mathrm{Rm} \gg 1$ and the fluid is in a hydrodynamic-dominated regime in which the magnetic energy is much smaller than the kinetic energy, induction due to a mean shear flow leads to a magnetic eddy viscosity. The magnetic viscosity is derived from simple physical arguments, where a coherent response due to shear flow builds up in the magnetic field until decorrelated by turbulent motion. The dynamic viscosity coefficient is approximately $(B_p^2/2\mu_0) \tau_{\rm corr}$, the poloidal magnetic energy density multiplied by the correlation time. We confirm the magnetic eddy viscosity through numerical simulations of two-dimensional incompressible magnetohydrodynamics. We also consider the three-dimensional case, and in cylindrical or spherical geometry, theoretical considerations similarly point to a nonzero viscosity whenever there is differential rotation. Hence, these results serve as a dynamical generalization of Ferraro's law of isorotation. The magnetic eddy viscosity leads to transport of angular momentum and may be of importance to zonal flows in astrophysical domains such as the interior of some gas giants.Comment: 16 pages, 8 figure