The Interaction of High-Speed Turbulence with Flames: Global Properties and Internal Flame Structure

We study the dynamics and properties of a turbulent flame, formed in the presence of subsonic, high-speed, homogeneous, isotropic Kolmogorov-type turbulence in an unconfined system. Direct numerical simulations are performed with Athena-RFX, a massively parallel, fully compressible, high-order, dimensionally unsplit, reactive-flow code. A simplified reaction-diffusion model represents a stoichiometric H2-air mixture. The system being modeled represents turbulent combustion with the Damkohler number Da = 0.05 and with the turbulent velocity at the energy injection scale 30 times larger than the laminar flame speed. The simulations show that flame interaction with high-speed turbulence forms a steadily propagating turbulent flame with a flame brush width approximately twice the energy injection scale and a speed four times the laminar flame speed. A method for reconstructing the internal flame structure is described and used to show that the turbulent flame consists of tightly folded flamelets. The reaction zone structure of these is virtually identical to that of the planar laminar flame, while the preheat zone is broadened by approximately a factor of two. Consequently, the system evolution represents turbulent combustion in the thin-reaction zone regime. The turbulent cascade fails to penetrate the internal flame structure, and thus the action of small-scale turbulence is suppressed throughout most of the flame. Finally, our results suggest that for stoichiometric H2-air mixtures, any substantial flame broadening by the action of turbulence cannot be expected in all subsonic regimes.Comment: 30 pages, 9 figures; published in Combustion and Flam

Entanglement transfer from dissociated molecules to photons

We introduce and study the concept of a reversible transfer of the quantum state of two internally-translationally entangled fragments, formed by molecular dissociation, to a photon pair. The transfer is based on intracavity stimulated Raman adiabatic passage and it requires a combination of processes whose principles are well established.Comment: 5 pages, 3 figure

Foundations of Dissipative Particle Dynamics

We derive a mesoscopic modeling and simulation technique that is very close to the technique known as dissipative particle dynamics. The model is derived from molecular dynamics by means of a systematic coarse-graining procedure. Thus the rules governing our new form of dissipative particle dynamics reflect the underlying molecular dynamics; in particular all the underlying conservation laws carry over from the microscopic to the mesoscopic descriptions. Whereas previously the dissipative particles were spheres of fixed size and mass, now they are defined as cells on a Voronoi lattice with variable masses and sizes. This Voronoi lattice arises naturally from the coarse-graining procedure which may be applied iteratively and thus represents a form of renormalisation-group mapping. It enables us to select any desired local scale for the mesoscopic description of a given problem. Indeed, the method may be used to deal with situations in which several different length scales are simultaneously present. Simulations carried out with the present scheme show good agreement with theoretical predictions for the equilibrium behavior.Comment: 18 pages, 7 figure

The Interaction of High-Speed Turbulence with Flames: Turbulent Flame Speed

(Abridged) Direct numerical simulations of the interaction of a premixed flame with driven, subsonic, homogeneous, isotropic, Kolmogorov-type turbulence in an unconfined system are used to study the mechanisms determining the turbulent flame speed, S_T, in the thin reaction zone regime. High intensity turbulence is considered with the r.m.s. velocity 35 times the laminar flame speed, S_L, resulting in the Damkohler number Da = 0.05. Here we show that: (1) The flame brush has a complex internal structure, in which the isosurfaces of higher fuel mass fractions are folded on progressively smaller scales. (2) Global properties of the turbulent flame are best represented by the structure of the region of peak reaction rate, which defines the flame surface. (3) In the thin reaction zone regime, S_T is predominantly determined by the increase of the flame surface area, A_T, caused by turbulence. (4) The observed increase of S_T relative to S_L exceeds the corresponding increase of A_T relative to the surface area of the planar laminar flame, on average, by ~14%, varying from only a few percent to ~30%. (5) This exaggerated response is the result of tight flame packing by turbulence, which causes frequent flame collisions and formation of regions of high flame curvature, or "cusps." (6) The local flame speed in the cusps substantially exceeds its laminar value, which results in a disproportionately large contribution of cusps to S_T compared with the flame surface area in them. (7) A criterion is established for transition to the regime significantly influenced by cusp formation. In particular, at Karlovitz numbers Ka > 20, flame collisions provide an important mechanism controlling S_T, in addition to the increase of A_T by large-scale motions and the potential enhancement of diffusive transport by small-scale turbulence.Comment: 44 pages, 20 figures; published in Combustion and Flam

Langevin Simulation of Scalar Fields: Additive and Multiplicative Noises and Lattice Renormalization

We consider the Langevin lattice dynamics for a spontaneously broken lambda phi^4 scalar field theory where both additive and multiplicative noise terms are incorporated. The lattice renormalization for the corresponding stochastic Ginzburg-Landau-Langevin and the subtleties related to the multiplicative noise are investigated.Comment: 26 pages, 4 eps figures (Elsevier latex style

Comedy in Unfunny Times: News Parody and Carnival after 9/11

Comedy has a special role in helping societies manage crisis moments, and the U.S. media paid considerable attention to the proper role of comedy in public culture after the 9/11 tragedies. As has been well documented, many popular U.S. comic voices were paralyzed in trying to respond to 9/11 or disciplined by audiences when they did. Starting with these obstacles in mind, this essay analyzes early comic responses to 9/11, and particularly those of the print and online news parody The Onion, as an example of how “fake” news discourse could surmount the rhetorical chill that fell over public culture after the tragedies. By exposing the news as “mere” production and by setting an agenda for learning about Islamic culture and Middle East politics, The Onion avoided violating decorum and invited citizen participation. This kind of meta-discourse was crucial after 9/11, when shifting rules for decorum created controversy and as official voices in government and media honed frames and narratives for talking about the attacks

Effects of planting density on growth, light interception and yield of a photoperiod insensitive pigeon pea (Cajanus cajan)

A newly selected short-statured, early flowering, photoperiod insensitive line of pigeon pea was planted in February 1979 at four densities, viz. 2 × 105, 3 × 105, 5 × 105 and 1 × 106 plants ha-1. Maximum values of relative growth rate (RGR) (0.17 g g-1 day-1), net assimilation rate (NAR) (85 g m-2 week-1) and leaf area ratio (LAR) (1.6 dm2 g-1) were achieved by 25 days from planting at the lower densities. Maximum NAR and RGR at 1 × 106 density was delayed until day 36. By day 45 this density had almost complete light interception, and all densities had complete interception by day 85. This variety had a low extinction coefficient (0.3) suggesting that canopy structure was efficient in allowing light penetration. Since crop growth rate and leaf area index (LAI) were linearly related, highest dry matter yields were at the highest density. Highest seed yield per hectare (1300 kg) was at the 5 × 105 density, but overall, yields were not significantly different. Pod number per plant was the main determinant of yield. From the relationship of pod number per plant and density, an optimum density of 7.5 × 105 plants ha-1 was predicted. It was concluded on the basis of growth and leaf area data that this new material could support a higher photosynthetic demand if the objectives of a breeding program to increase seed size and/or seeds per pod could be achieved