1,758 research outputs found

    Pseudo-magic graphs

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    AbstractWe characterize graphs for which there is a labeling of the edges by pairwise different integer labels such that the sum of the labels of the edges incident with a vertex is independent of the particular vertex. We generalize to mixed graphs, and to labelings with values in an integral domain

    Lattice Boltzmann method to study the contraction of a viscous ligament

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    We employ a recently formulated axisymmetric version of the multiphase Shan-Chen (SC) lattice Boltzmann method (LBM) [Srivastava et al, in preparation (2013)] to simulate the contraction of a liquid ligament. We compare the axisymmetric LBM simulation against the slender jet (SJ) approximation model [T. Driessen and R. Jeurissen, IJCFD {\bf 25}, 333 (2011)]. We compare the retraction dynamics of the tail-end of the liquid ligament from the LBM simulation, the SJ model, Flow3D simulations and a simple model based on the force balance (FB). We find good agreement between the theoretical prediction (FB), the SJ model, and the LBM simulations

    Septic Arthritis Caused by Legionella dumoffii in a Patient with Systemic Lupus Erythematosus-Like Disease

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    We describe a patient with systemic lupus erythematosus (SLE)-like disease on immunosuppressive treatment who developed septic arthritis of the knee involving Legionella dumoffii. Cultures initially remained negative. A broad-range 16S PCR using synovial fluid revealed L. dumoffii rRNA genes, a finding that was subsequently confirmed by positive Legionella culture results

    Family ownership, innovation and other context variables as determinants of sustainable entrepreneurship in SMEs: An empirical research study

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    This study focuses on the prediction of sustainable entrepreneurship, that is, behavior which demonstrates a firm’s concern about the natural environment, especially among small and medium sized enterprises (SMEs). Using a random sample of 382 Dutch SMEs we examine how organizational context (firm sector, size, ownership structure) and innovativeness influence SMEs engagement in sustainable entrepreneurship. Results show that firms from more “tangible” sectors (manufacturing, construction and agriculture), larger firms, family-owned firms, and firms with a more innovative orientation are more likely to report positive activity related to the natural environment. The paper discusses implications of the obtained results.

    Beyond Size: Predicting engagement in environmental management practices of Dutch SMEs

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    This study focuses on the prediction of the engagement of small and medium sized enterprises (SMEs) in environmental management practices, based on a random sample of 689 SMEs. The study finds that several endogenous factors, including tangibility of sector, firm size, innovative orientation, family influence and perceived financial benefits from energy conservation, predict an SME’s level of engagement in selected environmental management practices. For family influence, this effect is found only in interaction with the number of owners. In addition to empirical research on SMEs’ environmental behavior, the article draws on the ecological modernization literature as well as the theory of planned behavior.

    Bubbles in inkjet printheads : analytical and numerical models

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    The phenomenon of nozzle failure of an inkjet printhead due to entrainment of air bubbles was studies using analytical and numerical models. The studied inkjet printheads consist of many channels in which an acoustic field is generated to eject a droplet. When an air bubble is entrained, it disrupts the droplet formation process. This phenomenon is called nozzle failure. A very simple analytical model of a bubble in a nozzle was shown to qualitatively capture the dependence of the droplet velocity on the bubble volume. A more advanced model in which the two-way coupling between the channel acoustics and the bubble volume oscillations is taken into account, is shown to quantitatively agree with experimental data. The two-way coupling between bubble volume oscillations and channel acoustics is essential in this case. To determine when two-way coupling can be neglected, a complete set of dimensionless groups is derived. This set of dimensionless groups yields sharp criteria for the significance of two-wat coupling and for nonlinearity in the volume oscillations. A fully nonlinear numerical model is developed to test the predictions from the dimensionless groups. The predictions are confirmed by the results from the numerical model. This model is extended to also calculate the translational motion of the bubble and its growth by rectified diffusion. The effects that cause air entrainment were also studied. The outside of the printhead is coated by a thin ink film. This ink film flows whenever the printhead is actuated due to Marangoni stress. This flow is the first link in a chain of events that causes air entrainment. A careful analysis of the governing equations shows that these thin Marangoni flows satisfy potential flow. This result is used to analytically calculate the evolution of a moving droplet and a fingering instability, and the theoretical predictions are confirmed by the observations

    Stability of viscous long liquid filaments

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    We study the collapse of an axisymmetric liquid filament both analytically and by means of a numerical model. The liquid filament, also known as ligament, may either collapse stably into a single droplet or break up into multiple droplets. The dynamics of the filament are governed by the viscosity and the aspect ratio, and the initial perturbations of its surface. We find that the instability of long viscous filaments can be completely explained by the Rayleigh-Plateau instability, whereas a low viscous filament can also break up due to end pinching. We analytically derive the transition between stable collapse and breakup in the Ohnesorge number versus aspect ratio phase space. Our result is confirmed by numerical simulations based on the slender jet approximation and explains recent experimental findings by Castrejon-Pita et al., PRL 108, 074506 (2012).Comment: 7 page
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