Constant depth microfluidic networks based on a generalised Murray’s law for Newtonian and power-law fluids

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Microfluidic bifurcating networks of rectangular cross-sectional channels are designed using a novel biomimetic rule, based on Murray’s law. Murray’s principle is extended to consider the flow of power-law fluids in planar geometries (i.e. of constant depth rectangular cross-section) typical of lab-on-a-chip applications. The proposed design offers the ability to control precisely the shear-stress distributions and to predict the flow resistance along the network. We use an in-house code to perform computational fluid dynamics simulations in order to assess the extent of the validity of the proposed design for Newtonian, shear-thinning and shear-thickening fluids under different flow conditions

Disease progression in Plasmodium knowlesi malaria is linked to variation in invasion gene family members.

Emerging pathogens undermine initiatives to control the global health impact of infectious diseases. Zoonotic malaria is no exception. Plasmodium knowlesi, a malaria parasite of Southeast Asian macaques, has entered the human population. P. knowlesi, like Plasmodium falciparum, can reach high parasitaemia in human infections, and the World Health Organization guidelines for severe malaria list hyperparasitaemia among the measures of severe malaria in both infections. Not all patients with P. knowlesi infections develop hyperparasitaemia, and it is important to determine why. Between isolate variability in erythrocyte invasion, efficiency seems key. Here we investigate the idea that particular alleles of two P. knowlesi erythrocyte invasion genes, P. knowlesi normocyte binding protein Pknbpxa and Pknbpxb, influence parasitaemia and human disease progression. Pknbpxa and Pknbpxb reference DNA sequences were generated from five geographically and temporally distinct P. knowlesi patient isolates. Polymorphic regions of each gene (approximately 800 bp) were identified by haplotyping 147 patient isolates at each locus. Parasitaemia in the study cohort was associated with markers of disease severity including liver and renal dysfunction, haemoglobin, platelets and lactate, (r = ≥ 0.34, p =  <0.0001 for all). Seventy-five and 51 Pknbpxa and Pknbpxb haplotypes were resolved in 138 (94%) and 134 (92%) patient isolates respectively. The haplotypes formed twelve Pknbpxa and two Pknbpxb allelic groups. Patients infected with parasites with particular Pknbpxa and Pknbpxb alleles within the groups had significantly higher parasitaemia and other markers of disease severity. Our study strongly suggests that P. knowlesi invasion gene variants contribute to parasite virulence. We focused on two invasion genes, and we anticipate that additional virulent loci will be identified in pathogen genome-wide studies. The multiple sustained entries of this diverse pathogen into the human population must give cause for concern to malaria elimination strategists in the Southeast Asian region

Numerical modelling of jet-forced circulation in reservoirs using boundary-fitted coordinate systems

Throughout the past decade, interest has grown in the use of boundary-fitted coordinate systems in many areas of computational fluid dynamics. The boundary-fitted technique provides an exact method of implementing finite-difference numerical schemes in curved flow geometries and offers an alternative solution procedure to the finite-element method. The unavoidable large bandwidth of the global stiffness matrix, employed in finite-element algorithms, means that they are computationally less efficient than corresponding finite-difference schemes. As a consequence, the boundary-fitted method offers a more efficient process for solving partial differential flow equations in awkwardly shaped regions. This thesis describes a versatile finite-difference numerical scheme for the solution of the shallow water equations on arbitrary boundary-fitted non-orthogonal curvilinear grids. The model is capable of simulating flows in irregular geometries typically encountered in river basin management. Validation tests have been conducted against the severe condition of jet-forced flow in a circular reservoir with vertical side walls, where initial reflections of free surface waves pose major problems in achieving a stable solution. Furthermore, the validation exercises have been designed to test the computer model for artificial diffusion which may be a consequence of the numerical scheme adopted to stabilise the shallow water equations. The thesis also describes two subsidiary numerical studies of jet-forced recirculating flow in circular cylinders. The first of these implements a Biot-Savart discrete vortex method for simulating the vorticity in the shear layers of the inflow jet, whereas the second employs a stream function/vorticity-transport finite-difference procedure for solving the two-dimensional Navier-Stokes equations on a distorted orthogonal polar mesh. Although the predictions from the stream function/vorticity-transport model are confined to low Reynolds number flows, they provide a valuable set of benchmark velocity fields which are used to confirm the validity of the boundary-fitted shallow water equation solver

Balancing the dilution and oddity effects: Decisions depend on body size

Background Grouping behaviour, common across the animal kingdom, is known to reduce an individual's risk of predation; particularly through dilution of individual risk and predator confusion (predator inability to single out an individual for attack). Theory predicts greater risk of predation to individuals more conspicuous to predators by difference in appearance from the group (the ‘oddity’ effect). Thus, animals should choose group mates close in appearance to themselves (eg. similar size), whilst also choosing a large group. Methodology and Principal Findings We used the Trinidadian guppy (Poecilia reticulata), a well known model species of group-living freshwater fish, in a series of binary choice trials investigating the outcome of conflict between preferences for large and phenotypically matched groups along a predation risk gradient. We found body-size dependent differences in the resultant social decisions. Large fish preferred shoaling with size-matched individuals, while small fish demonstrated no preference. There was a trend towards reduced preferences for the matched shoal under increased predation risk. Small fish were more active than large fish, moving between shoals more frequently. Activity levels increased as predation risk decreased. We found no effect of unmatched shoal size on preferences or activity. Conclusions and Significance Our results suggest that predation risk and individual body size act together to influence shoaling decisions. Oddity was more important for large than small fish, reducing in importance at higher predation risks. Dilution was potentially of limited importance at these shoal sizes. Activity levels may relate to how much sampling of each shoal was needed by the test fish during decision making. Predation pressure may select for better decision makers to survive to larger size, or that older, larger fish have learned to make shoaling decisions more efficiently, and this, combined with their size relative to shoal-mates, and attractiveness as prey items influences shoaling decisions

The Spin Structure of the Nucleon

We present an overview of recent experimental and theoretical advances in our understanding of the spin structure of protons and neutrons.Comment: 84 pages, 29 figure

Adult videogame consumption as individualised, episodic progress

Drawing from phenomenological interviews with 24 adult videogamers, we explore videogame consumption as a source of individualised, episodic progress. We first consider the relationship between play, progress, technology and the market. We then document adults' accounts of progress through the acquisition of new consoles and software, in the accumulation of in-game resources, and in creative achievements within videogames. Alongside an understanding of technological improvements as representing both technological and personal progress, we see how individuals may also turn to videogames in search of quick and easy episodes of achievement; here, progress is not some grand plan, but a series of small events helpfully structured by the latest game releases. Thus, in a society which aspires to a life where things ‘get better’ and time is usefully spent, adults who fail to actualise progress elsewhere may use videogames and related hardware to perform the idea of achievement as individualised episodes of play. In integrating the accepted cultural idea of progress, perceptions of adult play as ‘frivolous’ can be overcome and such practices may be normalised as a legitimate adult activity. However, play emerges from its frivolousness as legitimate only in compensating for working practices that remain alienated through technology-driven productivity, and through the latest technological commodities. The enjoyable nature of games as a leisure pursuit can become overshadowed by an obligation to achieve at the same time as distancing players from areas of their lives where progress is not experienced

Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

The inclusive and dijet production cross-sections have been measured for jets containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The measurements use data corresponding to an integrated luminosity of 34 pb^-1. The b-jets are identified using either a lifetime-based method, where secondary decay vertices of b-hadrons in jets are reconstructed using information from the tracking detectors, or a muon-based method where the presence of a muon is used to identify semileptonic decays of b-hadrons inside jets. The inclusive b-jet cross-section is measured as a function of transverse momentum in the range 20 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-dijet cross-section is measured as a function of the dijet invariant mass in the range 110 < m_jj < 760 GeV, the azimuthal angle difference between the two jets and the angular variable chi in two dijet mass regions. The results are compared with next-to-leading-order QCD predictions. Good agreement is observed between the measured cross-sections and the predictions obtained using POWHEG + Pythia. MC@NLO + Herwig shows good agreement with the measured bbbar-dijet cross-section. However, it does not reproduce the measured inclusive cross-section well, particularly for central b-jets with large transverse momenta.Comment: 10 pages plus author list (21 pages total), 8 figures, 1 table, final version published in European Physical Journal

Observation of associated near-side and away-side long-range correlations in √sNN=5.02 TeV proton-lead collisions with the ATLAS detector

Two-particle correlations in relative azimuthal angle (Δϕ) and pseudorapidity (Δη) are measured in √sNN=5.02  TeV p+Pb collisions using the ATLAS detector at the LHC. The measurements are performed using approximately 1  μb-1 of data as a function of transverse momentum (pT) and the transverse energy (ΣETPb) summed over 3.1<η<4.9 in the direction of the Pb beam. The correlation function, constructed from charged particles, exhibits a long-range (2<|Δη|<5) “near-side” (Δϕ∼0) correlation that grows rapidly with increasing ΣETPb. A long-range “away-side” (Δϕ∼π) correlation, obtained by subtracting the expected contributions from recoiling dijets and other sources estimated using events with small ΣETPb, is found to match the near-side correlation in magnitude, shape (in Δη and Δϕ) and ΣETPb dependence. The resultant Δϕ correlation is approximately symmetric about π/2, and is consistent with a dominant cos⁡2Δϕ modulation for all ΣETPb ranges and particle pT

Observing interactions between children and adolescents and their parents: the effects of anxiety disorder and age

Parental behaviors, most notably overcontrol, lack of warmth and expressed anxiety, have been implicated in models of the development and maintenance of anxiety disorders in children and young people. Theories of normative development have proposed that different parental responses are required to support emotional development in childhood and adolescence, yet age has not typically been taken into account in studies of parenting and anxiety disorders. In order to identify whether associations between anxiety disorder status and parenting differ in children and adolescents, we compared observed behaviors of parents of children (7–10 years) and adolescents (13–16 years) with and without anxiety disorders (n=120), while they undertook a series of mildly anxiety-provoking tasks. Parents of adolescents showed significantly lower levels of expressed anxiety, intrusiveness and warm engagement than parents of children. Furthermore, offspring age moderated the association between anxiety disorder status and parenting behaviors. Specifically, parents of adolescents with anxiety disorders showed higher intrusiveness and lower warm engagement than parents of non-anxious adolescents. A similar relationship between these parenting behaviors and anxiety disorder status was not observed among parents of children. The findings suggest that theoretical accounts of the role of parental behaviors in anxiety disorders in children and adolescents should distinguish between these different developmental periods. Further experimental research to establish causality, however, would be required before committing additional resources to targeting parenting factors within treatment