A semi-supervised approach to visualizing and manipulating overlapping communities

When evaluating a network topology, occasionally data structures cannot be segmented into absolute, heterogeneous groups. There may be a spectrum to the dataset that does not allow for this hard clustering approach and may need to segment using fuzzy/overlapping communities or cliques. Even to this degree, when group members can belong to multiple cliques, there leaves an ever present layer of doubt, noise, and outliers caused by the overlapping clustering algorithms. These imperfections can either be corrected by an expert user to enhance the clustering algorithm or to preserve their own mental models of the communities. Presented is a visualization that models overlapping community membership and provides an interactive interface to facilitate a quick and efficient means of both sorting through large network topologies and preserving the user's mental model of the structure. © 2013 IEEE

Adaptive visualization of research communities

Adaptive visualization approaches attempt to tune the content and the topology of information visualization to various user characteristics. While adapting visualization to user cognitive traits, goals, or knowledge has been relatively well explored, some other user characteristics have received no attention. This paper presents a methodology to adapt a traditional cluster-based visualization of communities to user individual model of community organization. This class of user-adapted visualization is not only achievable, but expected due to real world situation where users cannot be segmented into heterogeneous communities since many users have affinity to more than one group. An interactive clustering and visualization approach presented in the paper allows the user communicate their personal mental models of overlapping communities to the clustering algorithm itself and obtain a community visualization image that more realistically fits their prospects

Ignition of uniform droplet-laden weakly turbulent flows following a laser spark

The forced ignition process has a stochastic nature, which can be intensi ed due to turbulence and mixture uctuations. Although fuel droplets represent strong inhomogeneities which are generally detrimental to ignition, the presence of small droplets has been found to enhance ame speeds, decrease minimum ignition energy, and improve the ignitability of overall lean mixtures. In order to understand which factors are conducive to ignition of sprays, a spherically expanding ame is investigated, which is produced by a laser spark in a uniform dispersion of ethanol droplets in turbulent air. The ame is visualised by schlieren and OH*-chemiluminescence for overall equivalence ratios of 0.8 to 2, Sauter mean diameter of approximately 25 m, and u0=SL ranging from 0.9 to 1.3, where u0 and SL denote the rms axial velocity and laminar burning velocity, respectively. The timescales of the spark's effects on the ame are measured, as well as quenching timescales and initial kernel sizes conditional on ignition or failure. Small kernels quenched faster than approximately 0.6 ms, that is, the duration of the ame overdrive, and a minimum kernel radius for ignition of 1mm was observed. The short-mode of ignition failure was suppressed by increasing the laser energy and, consequently, the initial kernel size. Nevertheless, the ignitability of lean mixtures was only e ectively improved through high-energy sparks and partial prevaporisation of the fuel. Virtually all kernels ignited once prevaporisation was increased, and the gas-phase equivalence ratio was approximately 75% of the lower ammability limit, with ignition being limited only by laser breakdown.European Commission Clean Sky project AMEL (641453); Brazilian Space Agency and Brazil's National Council for Scientific and Technological Developmen

South African foreign policy: the challenge of international political economy

In this article attention will firstly be given to tbe general trends and characteristics of the study of international political economy and secondly to an interpretation of Soutb Africa's foreign policy in that context. The consideration of specific relations with tbe European Community, the United States, East Asia, otber developing countries, tbe middle east as well as witb tbe southern African region are receiving much attention at this stage. One area which is relatively ignored relates to tbe tendencies in the international political economic relations between states and how it could have an impact upon South Africa's foreign policy

Study of Optimal Perimetric Testing In Children (OPTIC): Normative visual field values in children

Purpose: We sought to define normative visual field (VF) values for children using common clinical test protocols for kinetic and static perimetry. Design: Prospective, observational study. Subjects: We recruited 154 children aged 5 to 15 years without any ophthalmic condition that would affect the VF (controls) from pediatric clinics at Moorfields Eye Hospital. Methods: Children performed perimetric assessments in a randomized order using Goldmann and Octopus kinetic perimetry, and Humphrey static perimetry (Swedish Interactive Thresholding Algorithm [SITA] 24-2 FAST), in a single sitting, using standardized clinical protocols, with assessment by a single examiner. Unreliable results (assessed qualitatively) were excluded from the normative data analysis. Linear, piecewise, and quantile mixed-effects regression models were used. We developed a method to display age-specific normative isopters graphically on a VF plot to aid interpretation. Main Outcome Measures: Summary measures and graphical plots describing normative VF data for 3 common perimetric tests. Results: Visual field area increased with age on testing with Goldmann isopters III4e, I4e, and I2e (linear regression; P < 0.001) and for Octopus isopters III4e and I4e (linear regression; P < 0.005). Visual field development occurs predominately in the infero-temporal field. Humphrey mean deviation (MD) showed an increase of 0.3 decibels (dB; 95% CI, 0.21-0.40) MD per year up to 12 years of age, when adult MD values were reached and thereafter maintained. Conclusions: Visual field size and sensitivity increase with age in patterns that are specific to the perimetric approach used. These developmental changes should be accounted for when interpreting perimetric test results in children, particularly when monitoring change over time

Selection bias: neighbourhood controls and controls selected from those presenting to a Health Unit in a case control study of efficacy of BCG revaccination.

BACKGROUND: In most case control studies the hardest decision is the choice of the control group, as in the ideal control group the proportion exposed is the same as in the population that produced the cases. METHODS: A comparison of two control groups in a case control study of the efficacy of BCG revaccination. One group was selected from subjects presenting to the heath unit the case attended for routine prevention and care; the second group was selected from the neighbourhood of cases. All Health Units from which controls were selected offered BCG revaccination. Efficacy estimated in a randomized control trial of BCG revaccination was used to establish that the neighbourhood control group was the one that gave unbiased results. RESULTS: The proportion of controls with scars indicating BCG revaccination was higher among the control group selected from Health Unit attenders than among neighbourhood controls. This excess was not removed after control for social variables and history of exposure to tuberculosis, and appears to have resulted from the fact that people attending the Health Unit were more likely to have been revaccinated than neighbourhood controls, although we can not exclude an effect of other unmeasured variables. CONCLUSION: In this study, controls selected from people presenting to a Health Unit overrepresented exposure to BCG revaccination. Had the results from the HU attenders control group been accepted this would have resulted in overestimation of vaccine efficacy. When the exposure of interest is offered in a health facility, selection of controls from attenders at the facility may result in over representation of exposure in controls and selection bias

The Mechanics and Statistics of Active Matter

Active particles contain internal degrees of freedom with the ability to take in and dissipate energy and, in the process, execute systematic movement. Examples include all living organisms and their motile constituents such as molecular motors. This article reviews recent progress in applying the principles of nonequilibrium statistical mechanics and hydrodynamics to form a systematic theory of the behaviour of collections of active particles -- active matter -- with only minimal regard to microscopic details. A unified view of the many kinds of active matter is presented, encompassing not only living systems but inanimate analogues. Theory and experiment are discussed side by side.Comment: This review is to appear in volume 1 of the Annual Review of Condensed Matter Physics in July 2010 and is posted here with permission from that journa

Mechanisms of flame propagation in jet fuel sprays as revealed by OH/fuel planar laser-induced fluorescence and OH* chemiluminescence

© 2019 The Combustion Institute Previous work on spray flames has shown that different propagation mechanisms may occur depending on the size and number density of droplets. In this work, the structure and propagation of flames in uniformly dispersed sprays of low-volatility fuels is experimentally examined. The effect of the Sauter mean diameter (SMD) of the spray (16–33 µm) on the propagation modes, flame speed, and flame curvature is assessed in weakly turbulent sprays, with the ratio of axial velocity rms to the gaseous laminar burning velocity uz′/SL,g ranging from 0.5–2.5, and overall equivalence ratio ϕ of 0.8, 1, and 1.4. The growth of the flame is evaluated from OH*-chemiluminescence and schlieren visualisation, which combined with OH/fuel planar laser-induced fluorescence visualisation reveal details of the propagation mechanisms. The aviation fuels investigated – Jet A and a renewable alternative, ATJ-8 – exhibited similar flame speed behaviour due to changes in SMD in each of the propagation modes identified: the droplet, inter-droplet, and gaseous-like modes. Concentrated reactions around large droplets found in lean conditions (ϕ = 0.8) allowed for a slowly propagating flame front which, in turn, ignited new droplets. Stoichiometric to rich conditions (ϕ = 1, 1.4) were marked by stronger evaporation ahead of the flame and, therefore, higher and more uniform heat release across the flame. Still, droplets penetrated the flame, locally inducing regions of negative flame curvature and continuing to evaporate in the burnt products. The droplet-induced effects disappeared at low SMD (16 µm, ϕ = 1.4), giving rise to a fully gaseous layer ahead of the flame and the highest flame speeds. At rich conditions and high SMD, Jet A had a lower flame speed than ATJ-8

Effect of spark location and laminar flame speed on the ignition transient of a premixed annular combustor

The flame expansion process (``light-round'') during the ignition transient in annular combustors depends on a number of parameters such as equivalence ratio (and hence laminar burning velocity, $S_L$, of the mixture), turbulent intensity, mean flow magnitude and direction, geometry, and spark location. Here, an experimental study on a fully premixed, swirled, bluff-body stabilised annular combustor is carried out to identify the sensitivity of the light-round to these parameters. A wide range of conditions were assessed: two inter-burner spacing distances, two fuels (methane and ethylene), bulk velocities from 10 to 30 m/s, and $\phi$ between 0.75 and 1 for methane and 0.58 and 0.9 for ethylene. The spark location was varied longitudinally ($x/D$ = 0.5 and $x/D$ = 5, where $D$ is the bluff body diameter, expected to lie inside and downstream of the inner recirculation zone of a single burner, respectively) and azimuthally. The propagation of the flame during the ignition transient was investigated via high speed (10 kHz) OH$^*$ chemiluminescence using two cameras to simultaneously image the annular chamber from axially downstream and from the side of the combustor. The pattern of flame propagation depended on the initial longitudinal spark location and comprised of burner-to-burner propagation close to the bluff bodies and upstream propagation of the flame front. The spark azimuthal position\textcolor{red}{, in this horizontal configuration,} had a negligible impact on the light-round time ($\tau_{LR}$), thus buoyancy plays a minor role in the process. In contrast, sparking at $x/D$ = 5 resulted in an increase in $\tau_{LR}$ by $\sim$30-40\% for all the conditions examined. The inter-burner spacing had a negligible effect on $\tau_{LR}$. When increasing bulk velocity, $\tau_{LR}$ decreased. For a constant bulk velocity, $\tau_{LR}$ depended strongly on $S_L$ and it was found that mixtures with the same $S_L$ from different fuels resulted in the same $\tau_{LR}$. Further, the observed propagation speed, corrected for dilatation, was approximately proportional to $S_L$ and was within 30\% of estimates of the turbulent flame speed at the same conditions. These findings suggest that $S_L$ is one of the controlling parameters of the light-round process; hence turbulent flame propagation has a major role in the light-round process, in addition to dilatation and flame advection by the mean flow. The results reported in the study help explain the mechanism of light-round and can assist the development of efficient ignition procedures in aviation gas turbines.EU project ANNULIGHT (765998

Ignition probability and lean ignition behaviour of a swirled premixed bluff body stabilised annular combustor

Abstract An experimental investigation was performed in a premixed annular combustor equipped with multiple swirl, bluff body burners to assess the ignition probability and to provide insights into the mechanisms of failure and of successful propagation. The experiments are done at conditions that are close to the lean blow-off limit (LBO) and hence the ignition is difficult and close to the limiting condition when ignition is not possible. Two configurations were employed, with 12 and 18 burners, the mixture velocity was varied between 10 and 30 m/s, and the equivalence ratio (ϕ) between 0.58 and 0.68. Ignition was initiated by a sequence of sparks (2 mm gap, 10 sparks of 10 ms each) and “ignition” is defined as successful ignition of the whole annular combustor. The mechanism of success and failure of the ignition process and the flame propagation patterns were investigated via high-speed imaging (10 kHz) of OH* chemiluminescence. The lean ignition limits were evaluated and compared to the lean blow-off limits, finding the 12-burner configuration is more stable than the 18-burner. It was found that failure is linked to the trapping of the initial flame kernel inside the inner recirculation zone (IRZ) of a single burner adjacent to the spark, followed by localised quenching on the bluff body probably due to heat losses. In contrast, for a successful ignition, it was necessary for the flame kernel to propagate to the adjacent burner or for a flame pocket to be convected downstream in the chamber to grow and start propagating upwards. Finally, the ignition probability (Pign) was obtained for different spark locations. It was found that sparking inside the recirculation zone resulted in Pign ∼ 0 for most conditions, while Pign increased moving the spark away from the bluff-body or placing it between two burners and peaked to Pign ∼ 1 when the spark was located downstream in the combustion chamber, where the velocities are lower and the turbulence less intense. The results provide information on the most favourable conditions for achieving ignition in a complex multi-burner geometry and could help the design and optimisation of realistic gas turbine combustors.EU Project ANNULIGHT (765998