Macroscopic effects of microscopic roughness in suspensions

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.We study a model suspension consisting of a monolayer of identical spheres in a viscous medium without Brownian effects. In the absence of inertia, and under the influence of finite forces, perfectly smooth spheres will never come into contact because of the strength of the lubrication interaction. Indeed, an interaction between two spheres is perfectly reversible. However, this ideal is not achieved in practice: careful experiments with just two spheres show that some irreversible interaction occurs. We treat this interaction as a simple contact between the spheres: we assume that they are microscopically rough and have surface asperities which are too sparse to affect the hydrodynamics of the system, but which prevent the particles from approaching beyond some nominal surface separation. For a dilute suspensions in steady shear flow, a calculation to order c(2) in the particle area concentration shows that roughness actually lowers the viscosity of the suspension relative to its value for smooth spheres; this is because the excluded parts of configuration space are those with very close particles, where the lubrication layers cause high dissipation. Negative normal stress differences are also introduced by the roughness. At higher concentrations we use Stokesian Dynamics to simulate the suspension dynamics. We find that rough- ness increases the viscosity above an area concentration of around 40% and the normal stress differences be- come very sensitive to particle configuration, and fluctuate strongly with time

Investigation of a single vapour bubble confined between superheated or subcooled parallel plates

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.We investigate the evolution of a single vapour bubble confined between two parallel plates. The experimental study involves generating a single vapour bubble and recording its evolution using a high speed camera. The working fluid used is FC-72, and the plates are held at controlled temperatures that can be either superheated or subcooled. The speed of growth or collapse of the bubble is determined from the recorded images. A simple theoretical model is presented, the predictions of which are found to be in good agreement with the experimental results for the collapse of a bubble between subcooled plates at high subcooling

Search for lepton flavor violating decays of a heavy neutral particle in p-pbar collisions at root(s)=1.8 TeV

We report on a search for a high mass, narrow width particle that decays directly to e+mu, e+tau, or mu+tau. We use approximately 110 pb^-1 of data collected with the Collider Detector at Fermilab from 1992 to 1995. No evidence of lepton flavor violating decays is found. Limits are set on the production and decay of sneutrinos with R-parity violating interactions.Comment: Figure 2 fixed. Reference 4 fixed. Minor changes to tex

Measurement of Resonance Parameters of Orbitally Excited Narrow B^0 Mesons

We report a measurement of resonance parameters of the orbitally excited (L=1) narrow B^0 mesons in decays to B^{(*)+}\pi^- using 1.7/fb of data collected by the CDF II detector at the Fermilab Tevatron. The mass and width of the B^{*0}_2 state are measured to be m(B^{*0}_2) = 5740.2^{+1.7}_{-1.8}(stat.) ^{+0.9}_{-0.8}(syst.) MeV/c^2 and \Gamma(B^{*0}_2) = 22.7^{+3.8}_{-3.2}(stat.) ^{+3.2}_{-10.2}(syst.) MeV/c^2. The mass difference between the B^{*0}_2 and B^0_1 states is measured to be 14.9^{+2.2}_{-2.5}(stat.) ^{+1.2}_{-1.4}(syst.) MeV/c^2, resulting in a B^0_1 mass of 5725.3^{+1.6}_{-2.2}(stat.) ^{+1.4}_{-1.5}(syst.) MeV/c^2. This is currently the most precise measurement of the masses of these states and the first measurement of the B^{*0}_2 width.Comment: 7 pages, 1 figure, 1 table. Submitted to Phys.Rev.Let

Measurement of the fraction of t-tbar production via gluon-gluon fusion in p-pbar collisions at sqrt(s)=1.96 TeV

We present a measurement of the ratio of t-tbar production cross section via gluon-gluon fusion to the total t-tbar production cross section in p-pbar collisions at sqrt{s}=1.96 TeV at the Tevatron. Using a data sample with an integrated luminosity of 955/pb recorded by the CDF II detector at Fermilab, we select events based on the t-tbar decay to lepton+jets. Using an artificial neural network technique we discriminate between t-tbar events produced via q-qbar annihilation and gluon-gluon fusion, and find Cf=(gg->ttbar)/(pp->ttbar)<0.33 at the 68% confidence level. This result is combined with a previous measurement to obtain the most precise measurement of this quantity, Cf=0.07+0.15-0.07.Comment: submitted to Phys. Rev.

Risk, commercialism and social purpose: Repositioning the English housing association sector

Originally seen as the ‘third arm’ of UK housing policy, the independent, not-for-profit housing association sector had long been seen as effective in ‘filling the gap’ where the state or market were unable to provide for households in need. Since the 1980s in particular, successive governments had viewed housing associations in favourable terms as efficient, semi-autonomous social businesses, capable of leveraging significant private funding. By 2015, in contrast, central government had come to perceive the sector as inefficient, bureaucratic and wasteful of public subsidy. Making use of institutional theory, this paper considers this paradigm shift and examines the organisational responses to an increasingly challenging operating environment. By focusing, in particular, on large London housing associations, the paper analyses their strategic decision-making to address the opportunities and threats presented. The paper argues that in facing an era of minimal subsidy, low security and high risk, the 2015 reforms represent a critical juncture for the sector. Housing organisations face a stark dilemma about whether to continue a strategy of ‘profit for purpose’ or to embrace an unambiguously commercial ethos. The article contends that the trajectory of decision-making (although not unidirectional) leads ultimately towards an increased exposure to risk and vulnerability to changes in the housing market. More fundamentally, the attempt to reconcile social and commercial logics is likely to have wider consequences for the legitimacy of the sector

Feeling Safe in the Dark : Examining the Effect of Entrapment, Lighting Levels, and Gender on Feelings of Safety and Lighting Policy Acceptability

This research examined to what extent physical factors, notably lighting and entrapment (blocked escape), and individual factors, notably gender, affect feelings of safety and the acceptability of reduced lighting levels. The authors reasoned that acceptability of reduced street lighting depends on perceived safety, which in turn depends on entrapment, lighting, and gender. Virtual representations of a residential street were used, systematically manipulating entrapment and lighting levels. As expected, people felt less safe in lower lighting and higher entrapment settings, and these settings were evaluated as less acceptable. Although women perceived a situation as less safe compared with men, the authors found no gender differences in acceptability, which extends previous research. Importantly, as hypothesized, perceived safety mediated the effect of lighting on acceptability levels, suggesting that people can accept lower lighting levels when social safety is not threatened

Critical Realism and Statistical Methods: A Response to Nash

This article offers a defence of critical realism in the face of objections Nash (2005) makes to it in a recent edition of this journal. It is argued that critical and scientific realisms are closely related and that both are opposed to statistical positivism. However, the suggestion is made that scientific realism retains (from statistical positivism) a number of elements that result in misleading accounts of social processes and events: indicators are used which do not reflect the close relationship between structure and agency; indicators refer to reified and not real properties of both structures and agents; and indicators do not refer to causal properties of objects and entities. In order to develop a narrative of causal processes, as Nash argues researchers should, then some adjustments need to be made to the principles that underpin scientific realism

Circles of support and accountability: the characteristics of core members in England and Wales

Background Circles of support and accountability, or Circles, use community volunteers to help reintegrate sex offenders at risk of reoffending in the community. Aims The aims of this study are to describe the first 275 male sex offenders (‘core members’) in England and Wales supported by a Circle and to compare those attending the five largest Circles. Methods As part of their monitoring activity, 10 Circles extracted data from case files, anonymised it and submitted it to Circles UK, the national oversight body. Results Circles have expanded rapidly with 165 (60%) of Circles commencing in the three years 2011–2013 compared with 110 in the nine years 2002–2010. Most core members were referred from the Probation Service (82%). Circles were provided to men with a range of predicted risks of reoffending – from low (26%) to very high (12%). There were some positive changes between the beginning and end of Circles, such as fewer men being unemployed and more living in their own chosen accommodation. Conclusions/implications for practice Circles have been used to support the reintegration of a wide range of sex offenders. Given their rapid growth and flexibility, consistent recording standards are required across. These standards should be reviewed periodically to ensure all important fields of change are captured, including frequency of attendance, length per session and quality of engagement in the work