16,012 research outputs found
Code and accessories for 'Subcritical instabilities in plane Poiseuille flow of an Oldroyd-B fluid'
No full textRecently, detailed experiments on visco-elastic channel flow have provided convincing evidence for a nonlinear instability scenario which we had argued for based on calculations for visco-elastic Couette flow. Motivated by these experiments we extend the previous calculations to the case of visco-elastic Poiseuille flow, using the Oldroyd-B constitutive model. Our results confirm that the subcritical instability scenario is similar for both types of flow, and that the nonlinear transition occurs for Weissenberg numbers somewhat larger than one. We provide detailed results for the convergence of our expansion and for the spatial structure of the mode that drives the instability. This also gives insight into possible similarities with the mechanism of the transition to turbulence in Newtonian pipe flow
Data and movies accompanying 'Kinetic theory of pattern formation in mixtures of microtubules and molecular motors'
No full textIn this study we formulate a theoretical approach, based on a Boltzmann-like kinetic equation, to describe pattern formation in two-dimensional mixtures of microtubular filaments and molecular motors. Following the previous work by Aranson and Tsimring [Phys. Rev. E {\bf 74}, 031915 (2006) https://doi.org/10.1103/PhysRevE.74.031915 ] we model the motor-induced reorientation of microtubules as collision rules, and devise a semi-analytical method to calculate the corresponding interaction integrals. This procedure yields an infinite hierarchy of kinetic equations that we terminate by employing a well-established closure strategy, developed in the pattern-formation community and based on a power-counting argument. We thus arrive at a closed set of coupled equations for slowly varying local density and orientation of the microtubules, and study its behaviour by performing a linear stability analysis and direct numerical simulations. By comparing our method with the work of Aranson and Tsimring, we assess the validity of the assumptions required to derive their and our theories. We demonstrate that our approximation-free evaluation of the interaction integrals and our choice of a systematic closure strategy result in a rather different dynamical behaviour than was previously reported. Based on our theory, we discuss the ensuing phase diagram and the patterns observed.See readme.txt file for details
Harpyia nadiae Morozov 2013
No full text51. Harpyia nadiae Morozov, 2013 (new record for India) (Figs. 23, 51) Harpyia nadiae Morozov, 2013; Tinea 22: 182. TL: China, West Yunnan, Wudingshan, N-Xiangyan. Material examined. India: 1 ♂, Manipur, Ukhrul district, Shirui Hill (Site 1), 25.1264°N 94.4357°E, 1930 m, 13.III.2019, in coll NCZ, ZSI, Registration no. 11532/H10; 2 ♂♂, Shirui Hill (Site 2), 25.1236°N 94.4408°E, 2036 m, 24.VII.2019; 1 ♂, Shirui Hill (Site 3), 25.1171°N 94.4456°E, 2190 m, 13.III.2019; 1 ♂, Shirui Hill (Site 4), 25.1112°N 94.4534°E, 2425 m, 25.VII.2019, genitalia slide no. JSI-GP 338; leg. JS Irungbam, India, (NCZ, ZSI). Diagnosis. The Harpyia longipennis complex was revised by Morozov (2013), raising H. formosicola (from Taiwan) and H. yunnanensis (from China, Yunnan, Vietnam, and Thailand) to valid species. The male genitalia of our examined specimens are different from all other species of the H. longipennis group by having a prominent apical valva process. 8 th sternite bears a central projection on the posterior margin. Externally, H. nadiae is not distinguishable from H. longipennis. Distribution. India: Manipur (In the present study). Elsewhere: China, Vietnam (Morozov 2013).Published as part of Irungbam, Jatishwor Singh, Schintlmeister, Alexander & Fric, Zdenek Faltynek, 2022, New and less known Notodontidae from Manipur, India (Lepidoptera: Noctuoidea), pp. 61-93 in Zootaxa 5196 (1) on page 86, DOI: 10.11646/zootaxa.5196.1.3, http://zenodo.org/record/722413
The role of correlations in the collective behaviour of microswimmer suspensions
No full textIn this work, we study the collective behaviour of a large number of self-propelled microswimmers immersed in a fluid. Using unprecedently large-scale lattice Boltzmann simulations, we reproduce the transition to bacterial turbulence. We show that, even well below the transition, swimmers move in a correlated fashion that cannot be described by a mean-field approach. We develop a novel kinetic theory that captures these correlations and is non-perturbative in the swimmer density. To provide an experimentally accessible measure of correlations, we calculate the diffusivity of passive tracers and reveal its non-trivial density dependence. The theory is in quantitative agreement with the lattice Boltzmann simulations and captures the asymmetry between pusher and puller swimmers below the transition to turbulence
Rate constants of the fulvenallenyl recombination with propargyl and its role in PAH formation: a theoretical and kinetic modeling study
No full textThe temperature- and pressure-dependent rate constants of the reaction of fulvenallenyl (C7H5) and propargyl (C3H3) radicals have been explored using advanced electronic structure methods and kinetics theories. The results show that the head-C3H3 + tail-C7H5 addition is the fastest, followed by the tail + tail addition, and that at typical combustion conditions of 1500 K and 1 atm, the reaction mostly results in collisional stabilization of entrance channel adducts without further cyclization, whereas the well-skipping pathway to fulvalene - a precursor to naphthalene, prevails at high temperatures. The formation of the aromatic two-ring isomers, naphthalene, methylene-indenes, and azulene, can be enhanced only at high temperatures and much lower pressures, when the collisional stabilization of the intermediate wells is not efficient. The computed phenomenological rate constants were consequently simplified using master equation-based lumping and the pseudo steady state approximation to reduce the size of the system. This post-processing confirmed fulvalene as the main two-ring aromatic product and thus, its contribution should be considered in kinetic models. While naphthalene is only a trace product of the C7H5 + C3H3 reaction, it can be formed from fulvalene via H-assisted isomerization. The impact of the updated thermochemistry and rate constants in CRECK and ITV kinetic models on mole fractions of relevant cyclic aromatic species was also analyzed. The results suggest that the relevance of the C7H5 + C3H3 reaction has been likely overestimated in the current literature and needs to be carefully reevaluated by revising the pathways involving the formation and consumption of C7H6 and C7H5 and improving predictions of their precursors, such as unsaturated C4 species in flames
Douglas Alexander Stewart, poet, author and playwright
No full textDouglas Alexander Stewart, poet, author and playwrigh
Intersection numbers on M¯ g,n and BKP hierarchy
No full text© 2021, The Author(s).In their recent inspiring paper, Mironov and Morozov claim a surprisingly simple expansion formula for the Kontsevich-Witten tau-function in terms of the Schur Q-functions. Here we provide a similar description for the Brézin-Gross-Witten tau-function. Moreover, we identify both tau-functions of the KdV hierarchy, which describe intersection numbers on the moduli spaces of punctured Riemann surfaces, with the hypergeometric solutions of the BKP hierarchy.11Nsciescopu
Lid-driven cavity flow of viscoelastic liquids
No full textThe lid-driven cavity flow is a well-known benchmark problem for the validation of new numerical methods and techniques. In experimental and numerical studies with viscoelastic fluids in such lid-driven flows, purely-elastic instabilities have been shown to appear even at very low Reynolds numbers. In this work, a finite-volume viscoelastic code, using the log-conformation formulation, is used to probe the effect of viscoelasticity on the appearance of such instabilities in lid-driven cavities for a wide range of aspect ratios (0.125 ≤ Λ ≤ 4.0) at different Deborah number under creeping-flow conditions. The effect of the viscoelasticity on the steady-state results and on the critical conditions for the onset of the elastic instabilities are described and compared to experimental results
Swimming suppresses correlations in dilute suspensions of pusher microorganisms
No full textActive matter exhibits various forms of non-equilibrium states in the absence of external forcing, including macroscopic steady-state currents. Such states are often too complex to be modelled from first principles and our understanding of their physics relies heavily on minimal models. These have mostly been studied in the case of “dry” active matter, where particle dynamics are dominated by friction with their surroundings. Significantly less is known about systems with long-range hydro- dynamic interactions that belong to “wet” active matter. Dilute suspensions of motile bacteria, modelled as self-propelled dipolar particles interacting solely through long-ranged hydrodynamic fields, are arguably the most studied example from this class of active systems. Their phenomenol- ogy is well-established: at sufficiently high density of bacteria, there appear large-scale vortices and jets comprising many individual organisms, forming a chaotic state commonly known as bac- terial turbulence. As revealed by computer simulations, below the onset of collective motion, the suspension exhibits very strong correlations between individual microswimmers stemming from the long-ranged nature of dipolar fields. Here we demonstrate that this phenomenology is captured by the minimal model of microswimmers. We develop a kinetic theory that goes beyond the com- monly used mean-field assumption, and explicitly takes into account such correlations. Notably, these can be computed exactly within our theory. We calculate the fluid velocity variance, spatial and temporal correlation functions, the fluid velocity spectrum, and the enhanced diffusivity of tracer particles. We find that correlations are suppressed by particle self-propulsion, although the mean-field behaviour is not restored even in the limit of very fast swimming. Our theory is not perturbative and is valid for any value of the micro-swimmer density below the onset of collective motion. This work constitutes a significant methodological advance and allows us to make qual- itative and quantitative predictions that can be directly compared to experiments and computer simulations of micro-swimmer suspensions
Author inscription in William Hazlitt, essayist and critic; selections from his writings, with a memoir, biographical and critical by Alexander Ireland
No full textAuthor's gift inscription, "To W. C. Hazlitt Esq with kind regards, from Alexr Ireland," with tipped-in review of the book.ASU Library edition has inscription from Ireland to Hazlitt [a child of William Hazlitt?].
Hazlitt , William, 1778-1830.
Ireland, Alexander, 1810-1894
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