Three-dimensional micro-droplet collision simulation using the Lattice Boltzmann method

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.The modelling of binary droplet collisions has important applications in many engineering problems, including spray coating and fuel injection. The Lattice Boltzmann method (LBM) is a well established technique for modelling multiphase fluids, and does so without the difficulties of explicit interface tracking found in other CFD methods. However, simulating droplet collisions under realistic conditions remains a complex problem. Challenges include reproducing the different collision outcomes observed experimentally (Qian and Law, 1997), and maintaining a stable simulation at sufficiently high Reynolds and Weber numbers, and with a high density ratio between the liquid and gas phases. Although previous studies have achieved these goals individually, they have not been successfully combined to simulate droplet collisions with realistic physical parameters. A number of different methods for extending the LBM for multiphase flow exist, with the Shan-Chen interparticle potential method (Shan and Chen, 1993) being the basic model used here. Many extensions to improve the original Shan-Chen method have been proposed, to improve achievable Reynolds number and density ratio. Using combinations of these, both coalescence and separation of two-dimensional droplets were successfully simulated at density ratios of order 1000, and high Weber numbers (Lycett-Brown et al., 2011). In this study, the developed methodologies in Lycett-Brown et al. (2011) are extended to simulate three dimensional micro-droplet collisions by making use of the LBM’s excellent scalability on massively parallel computers. These high-resolution simulations are also compared with low-resolution three-dimensional simulations using a multiple-relaxation-time LBM approach (Monaco and Luo, 2008).This study is funded by the Engineering and Physical Sciences Research Council for Grant No. EP/I000801/1 and a HEC Studentship

Multiphase cascaded lattice Boltzmann method

To improve the stability of the lattice Boltzmann method (LBM) at high Reynolds number the cascaded LBM has recently been introduced. As in the multiple relaxation time (MRT) method the cascaded LBM introduces additional relaxation times into the collision operator, but does so in a co-moving reference frame. This has been shown to significantly increase stability at low viscosity in the single phase case. Here the cascaded LBM is further developed to include multiphase flow. For this the force term is calculated by the interaction potential method, and introduced into the collision operator via the exact difference method (EDM). Comparisons are made with the lattice Bhatnagar–Gross–Krook (LBGK) method, and an MRT implementation. Both the cascaded and MRT methods are shown to significantly reduce spurious velocities over the LBGK method. For the particular case of the Shan–Chen interparticle force term calculation with the EDM, the cascaded LBM is successfully combined with a multiphase method, and shown to perform as well as the more established MRT method. The cascaded LBM is found to be a considerably improved approach to the simulation of multiphase flow over the LBGK, significantly increasing the stability range of both density ratio and Reynolds number. Additionally the importance of including third order velocity terms in the equilibria of both the cascaded and MRT methods is discussed

Resonance structure in the {\gamma}{\gamma} and π0π0\pi^0\pi^0 systems in dC interactions

Along with $\pi^0$ and {\eta} mesons, a resonance structure in the invariant mass spectrum of two photons at M{\gamma}{\gamma} = 360 \pm 7 \pm 9 MeV is observed in the reaction d + C \rightarrow {\gamma} + {\gamma} + X at momentum 2.75 GeV/c per nucleon. Estimates of its width and production cross section are {\Gamma} = 64 \pm 18 MeV and $\sigma_{\gamma\gamma}$ = 98 \pm 24 {\mu}b, respectively. The collected statistics amount to 2339 \pm 340 events of 1.5 \cdot 10^6 triggered interactions of a total number ~ 10^12 of dC-interactions. The results on observation of the resonance in the invariant mass spectra of two $\pi^0$ mesons are presented: the data obtained in the d + C \rightarrow {\gamma} + {\gamma} reaction is confirmed by the d + C \rightarrow $\pi^0$ + $\pi^0$ reaction: $M_{\pi^0\pi^0}$ = 359.2 \pm 1.9 MeV, {\Gamma} = 48.9 \pm 4.9 MeV; the ratio of Br(R\rightarrow{\gamma}{\gamma}) / Br(R\rightarrow$\pi^0\pi^0$) = (1.8 {\div} 3.7)\cdot10^-3.Comment: 10 pages, 11 figure

Improved forcing scheme in pseudopotential lattice Boltzmann methods for multiphase flow at arbitrarily high density ratios

The pseudopotential lattice Boltzmann method has been widely used to simulate many multiphase flow applications. However, there still exist problems with reproducing realistic values of density ratio and surface tension. In this study, a higher-order analysis of a general forcing term is derived. A forcing scheme is then constructed for the pseudopotential method that is able to accurately reproduce the full range of coexistence curves. As a result, multiphase flow of arbitrarily high density ratios independent of the surface tension can be simulated. Furthermore, the interface width can be tuned to allow for grid refinement and systematic error reduction. Numerical results confirm that the proposed scheme enables independent control of density ratio, surface tension, and interface width simultaneously

On compression of Bruhat-Tits buildings

We obtain an analog of the compression of angles theorem in symmetric spaces for Bruhat--Tits buildings of the type $A$. More precisely, consider a $p$-adic linear space $V$ and the set $Lat(V)$ of all lattices in $V$. The complex distance in $Lat(V)$ is a complete system of invariants of a pair of points of $Lat(V)$ under the action of the complete linear group. An element of a Nazarov semigroup is a lattice in the duplicated linear space $V\oplus V$. We investigate behavior of the complex distance under the action of the Nazarov semigroup on the set $Lat(V)$.Comment: 6 page

Hsf1 and Hsp90 orchestrate temperature-dependent global transcriptional remodelling and chromatin architecture in Candida albicans

This is the final version. Available from Nature Research via the DOI in this record.RNA-sequencing data sets are available at ArrayExpress (www.ebi.ac.uk) under accession code E-MTAB-4075. ChIP-seq data sets are available at the NCBI SRA database (http://www.ncbi.nlm.nih.gov) under accession code SRP071687. The authors declare that all other data supporting the findings of this study are available within the article and its supplementary information files, or from the corresponding author upon request.Fever is a universal response to infection, and opportunistic pathogens such as Candida albicans have evolved complex circuitry to sense and respond to heat. Here we harness RNA-seq and ChIP-seq to discover that the heat shock transcription factor, Hsf1, binds distinct motifs in nucleosome-depleted promoter regions to regulate heat shock genes and genes involved in virulence in C. albicans. Consequently, heat shock increases C. albicans host cell adhesion, damage and virulence. Hsf1 activation depends upon the molecular chaperone Hsp90 under basal and heat shock conditions, but the effects are opposite and in part controlled at the level of Hsf1 expression and DNA binding. Finally, we demonstrate that Hsp90 regulates global transcription programs by modulating nucleosome levels at promoters of stress-responsive genes. Thus, we describe a mechanism by which C. albicans responds to temperature via Hsf1 and Hsp90 to orchestrate gene expression and chromatin architecture, thereby enabling thermal adaptation and virulence.Wellcome TrustCanadian Institutes of Health ResearchCanadian Institutes of Health ResearchBiotechnology and Biological Sciences Research Council (BBSRC)European Research Council (ERC)Science and Technology Development Fund of Macau S.A.R (FDCT)Research and Development Administrative Office of the University of MacauNational Institutes of Health (NIH

Coevolved mutations reveal distinct architectures for two core proteins in the bacterial flagellar motor

Switching of bacterial flagellar rotation is caused by large domain movements of the FliG protein triggered by binding of the signal protein CheY to FliM. FliG and FliM form adjacent multi-subunit arrays within the basal body C-ring. The movements alter the interaction of the FliG C-terminal (FliGC) "torque" helix with the stator complexes. Atomic models based on the Salmonella entrovar C-ring electron microscopy reconstruction have implications for switching, but lack consensus on the relative locations of the FliG armadillo (ARM) domains (amino-terminal (FliGN), middle (FliGM) and FliGC) as well as changes during chemotaxis. The generality of the Salmonella model is challenged by the variation in motor morphology and response between species. We studied coevolved residue mutations to determine the unifying elements of switch architecture. Residue interactions, measured by their coevolution, were formalized as a network, guided by structural data. Our measurements reveal a common design with dedicated switch and motor modules. The FliM middle domain (FliMM) has extensive connectivity most simply explained by conserved intra and inter-subunit contacts. In contrast, FliG has patchy, complex architecture. Conserved structural motifs form interacting nodes in the coevolution network that wire FliMM to the FliGC C-terminal, four-helix motor module (C3-6). FliG C3-6 coevolution is organized around the torque helix, differently from other ARM domains. The nodes form separated, surface-proximal patches that are targeted by deleterious mutations as in other allosteric systems. The dominant node is formed by the EHPQ motif at the FliMMFliGM contact interface and adjacent helix residues at a central location within FliGM. The node interacts with nodes in the N-terminal FliGc α-helix triad (ARM-C) and FliGN. ARM-C, separated from C3-6 by the MFVF motif, has poor intra-network connectivity consistent with its variable orientation revealed by structural data. ARM-C could be the convertor element that provides mechanistic and species diversity.JK was supported by Medical Research Council grant U117581331. SK was supported by seed funds from Lahore University of Managment Sciences (LUMS) and the Molecular Biology Consortium

Beaver: Nature's ecosystem engineers

This is the final version. Available on open access from Wiley via the DOI in this record. Beavers have the ability to modify ecosystems profoundly to meet their ecological needs, with significant associated hydrological, geomorphological, ecological, and societal impacts. To bring together understanding of the role that beavers may play in the management of water resources, freshwater, and terrestrial ecosystems, this article reviews the state-of-the-art scientific understanding of the beaver as the quintessential ecosystem engineer. This review has a European focus but examines key research considering both Castor fiber—the Eurasian beaver and Castor canadensis—its North American counterpart. In recent decades species reintroductions across Europe, concurrent with natural expansion of refugia populations has led to the return of C. fiber to much of its European range with recent reviews estimating that the C. fiber population in Europe numbers over 1.5 million individuals. As such, there is an increasing need for understanding of the impacts of beaver in intensively populated and managed, contemporary European landscapes. This review summarizes how beaver impact: (a) ecosystem structure and geomorphology, (b) hydrology and water resources, (c) water quality, (d) freshwater ecology, and (e) humans and society. It concludes by examining future considerations that may need to be resolved as beavers further expand in the northern hemisphere with an emphasis upon the ecosystem services that they can provide and the associated management that will be necessary to maximize the benefits and minimize conflicts.Natural Environment Research Council (NERC)Wellcome TrustDevon Wildlife TrustPlymouth City CouncilCornwall Wildlife TrustUniversity of Exete

Extracting statistical distributions of RTN originating from both acceptor-like and donor-like traps

The impact of Random Telegraph Noise (RTN) on devices increases, as the device sizes are downscaled. Against a reference level, it is commonly observed that RTN can fluctuate both below and above this level. The modelling of RTN, however, was typically carried out only in the direction where drain current reduces. In reality, this current reduction can be compensated by simultaneous current increases. This calls the accuracy of the onedirectional RTN modelling into questions. Separating the fluctuation in one direction from the other is difficult experimentally. In this paper, we review the recently proposed integral methodology for achieving this separation. In contrast with early works, the integral methodology does not require selecting devices with fluctuation only in one direction. The RTN in all devices are measured and grouped together to form one dataset. It is then statically analyzed by assuming the presence of fluctuation in both directions. In this way, the separation is carried out numerically, rather than experimentally. Based on the maximum likelihood estimation, the popular statistical distributions are tested against experimental data. It is found that the General Extreme Value (GEV) distribution agrees best with the experimental threshold voltage shift, when compared with the Exponential and Lognormal distributions