Acceleration of Non-Equidiffusive Flames in Channels: Computational Simulations and Analytical Studies

When a premixed flame front spreads in a narrow pipe, wall friction continuously distorts the flame shape. As a result, the flame front acquires a larger surface area, consumes more fuel per unit time and, thereby, propagates faster. While this mechanism of flame acceleration due to wall friction has widely been studied, especially within the last decade, the analytical and computational studies were mostly devoted to equidiffusive flames, where the Lewis number, defined as the thermal to mass diffusivity ratio, is unity, Le = 1. However, in reality thermal and mass diffusion are typically not balanced, especially in rich and lean mixtures. Hence, the micro-scale, diffusional-thermal effects may appear comparable with macro-scale phenomena such as wall friction. The present work sheds the light on the dynamics and morphology of Le ≠ 1 flames in channels. Specifically, it studies, by means of computational and analytical endeavors, how the interplay of finite flame thickness, stretch effect and the thermal-molecular diffusion influence the overall flame acceleration scenario. It is shown that Le \u3e 1 flames accelerate slower, due to an effective thickening of the flame front. In contrast, Le \u3c 1 flames exhibit faster acceleration due to effective flame channeling and other morphological deformations resembling the diffusional-thermal (DT) instability. The analysis also incorporates the internal transport flame properties into the theory of flame acceleration due to wall friction, by means of the Markstein number, Mk, that characterizes the flame response to curvature and stretch. Being a positive or negative function of thermal-chemical combustion parameters, such as the thermal expansion ratio and the Lewis and Zel\u27dovich numbers, the Markstein number either restrains or promotes the flame acceleration. While Mk may substantially facilitate the flame acceleration in narrow channels, this effects diminishes with the increase in the channel width. The analysis is accompanied by extensive numerical simulations of the Navier-Stokes and combustion equations, which clarify the impact of the Lewis number on the flame acceleration. It is obtained that, for Le lower than a certain critical value, at the initial stage of flame acceleration, globally-convex flame fronts split into two or more fingers , accompanied by a drastic increase in the flame surface area and associated enhancement of the flame acceleration. Later, however, the flame fingers meet, promptly consuming the troughs, which rapidly diminishes the flame surface area and moderates the acceleration. Eventually, this results in a single, globally-convex flame front that keeps accelerating. Overall, the thermal-diffusive effects facilitate the flame acceleration scenario, thereby advancing a potential deflagration-to-detonation transition

Comunicación corta. Efecto del momento de la recolección sobre la producción y la calidad del forraje en genotipos de colza y nabo

The effects of two different harvest stages (full flowering and full podding) on forage yield and quality of ten forage rape (Brassica napus L. var. oleifera) and three turnip (Brassica rapa L. var. rapa) cultivars were evaluated under rainfed conditions in a Mediterranean type climate at Bursa, Turkey, during the 2002/2003 and 2003/2004 growing seasons. Plant height, branches per plant, leaf length and width, plant part components, and dry matter (DM) and crude protein (CP) yield were measured. Significant differences were observed for the main effects cultivar and harvest stage on DM and protein yields. The CP content of the whole plant and vegetative parts of the Brassica genotypes decreased as plant maturity progressed. In general, turnip cultivars showed better performance in DM yield. Fall sown turnip produced 9.10 and 12.1 Mg/ha DM yield, with 15.1 and 9.10% CP concentrations, at full flowering and at podding stage, respectively. Significant differences were noted among cultivars for these two parameters. Protein content decreased dramatically in stem parts when maturity advanced from full flower to full pod stages. High leaf percentage and high protein content at full flowering suggest that this should be the preferred forage harvest stage for rape and turnip cultivars.Se evaluaron los efectos de dos momentos diferentes de la recolección (en flor o vaina completada) sobre la producción y calidad del forraje en 10 cultivares forrajeros de nabo (Brassica napus L. var. oleifera) y tres de colza (Brassica rapa L. var. rapa) en Bursa, Turquía, una zona de clima mediterráneo con precipitaciones, durante las campañas 2002/2003 y 2003/2004. Se midió la altura de las plantas, ramas por planta, longitud y anchura de hoja, componentes de partes de las plantas, y producción de materia seca (MS) y proteínas crudas (PC). Se observaros diferencias significativas para los principales efectos cultivar y momento de la recolección sobre el rendimiento en MS y PC. El contenido en PC de la planta completa y partes vegetativas de los genotipos de Brassica estudiados disminuyeron al avanzar la maduración de la planta. En general, los cultivares de nabo dieron mejor producción de MS. Nabos sembrados en otoño produjeron 9,10 y 12,1 Mg/ha de MS, con concentraciones de PC de 15,1 y 9,10%, en los momentos de flor o vaina completas, respectivamente. Para estos dos parámetros se observaron diferencias significativas entre cultivares. El contenido en proteínas disminuyó dramáticamente en partes del tallo cuando la planta pasó del estado de flor completa a vaina completa. La detección de un alto porcentaje de hojas y de contenido en proteínas en cultivares de colza y nabo en el estadío de flores completas sugieren que éste debe ser el momento preferido para la recolección

Parallel Rendering on Hybrid Multi-GPU Clusters

Achieving efficient scalable parallel rendering for interactive visualization applications on medium-sized graphics clusters remains a challenging problem. Framerates of up to 60hz require a carefully designed and fine-tuned parallel rendering implementation that fits all required operations into the 16ms time budget available for each rendered frame. Furthermore, modern commodity hardware embraces more and more a NUMA architecture, where multiple processor sockets each have their locally attached memory and where auxiliary devices such as GPUs and network interfaces are directly attached to one of the processors. Such so called fat NUMA processing and graphics nodes are increasingly used to build cost-effective hybrid shared/distributed memory visualization clusters. In this paper we present a thorough analysis of the asynchronous parallelization of the rendering stages and we derive and implement important optimizations to achieve highly interactive framerates on such hybrid multi-GPU clusters. We use both a benchmark program and a real-world scientific application used to visualize, navigate and interact with simulations of cortical neuron circuit models

Aspectos patológicos de miopatias em frangos de corte.

As alterações patológicas que ocorrem no músculo das aves são denominadas de miopatias. A primeira miopatia descrita foi a necrose do músculo peitoral profundo em perus e frangos, que podia ser reproduzida com estímulo para batimento de asas (1). Posteriormente foi identificada a alteração conhecida como ?white striping?, caracterizada por estrias brancas de gordura na superfície do músculo peitoral superficial. Mais recentemente foram observados novos quadros como o ?wooden breast - peito madeira? (2). Podem ocorrer também alterações na coloração ou tonalidade da carne de aves devido à queda brusca e acentuada do pH muscular, levando à condição conhecida como carne PSE (pale, soft and exudative) - carne pálida, mole e exudativa - ou quando por depleção de glicogênio no músculo ocorre a carne DFD (dark, firm and dry) - carne dura, firme e seca. O presente trabalho objetiva determinar se as condições observadas nas carcaças têm relação com causas microbianas e/ou infecciosas e avaliar se estas condições apresentam riscos para a saúde do consumidor

Search for intermediate mass black hole binaries in the first and second observing runs of the Advanced LIGO and Virgo network

Gravitational-wave astronomy has been firmly established with the detection of gravitational waves from the merger of ten stellar-mass binary black holes and a neutron star binary. This paper reports on the all-sky search for gravitational waves from intermediate mass black hole binaries in the first and second observing runs of the Advanced LIGO and Virgo network. The search uses three independent algorithms: two based on matched filtering of the data with waveform templates of gravitational-wave signals from compact binaries, and a third, model-independent algorithm that employs no signal model for the incoming signal. No intermediate mass black hole binary event is detected in this search. Consequently, we place upper limits on the merger rate density for a family of intermediate mass black hole binaries. In particular, we choose sources with total masses M=m1+m2ϵ[120,800] M and mass ratios q=m2/m1ϵ[0.1,1.0]. For the first time, this calculation is done using numerical relativity waveforms (which include higher modes) as models of the real emitted signal. We place a most stringent upper limit of 0.20 Gpc-3 yr-1 (in comoving units at the 90% confidence level) for equal-mass binaries with individual masses m1,2=100 M and dimensionless spins χ1,2=0.8 aligned with the orbital angular momentum of the binary. This improves by a factor of ∼5 that reported after Advanced LIGO's first observing run

All-sky search for short gravitational-wave bursts in the second Advanced LIGO and Advanced Virgo run

We present the results of a search for short-duration gravitational-wave transients in the data from the second observing run of Advanced LIGO and Advanced Virgo. We search for gravitational-wave transients with a duration of milliseconds to approximately one second in the 32-4096 Hz frequency band with minimal assumptions about the signal properties, thus targeting a wide variety of sources. We also perform a matched-filter search for gravitational-wave transients from cosmic string cusps for which the waveform is well modeled. The unmodeled search detected gravitational waves from several binary black hole mergers which have been identified by previous analyses. No other significant events have been found by either the unmodeled search or the cosmic string search. We thus present the search sensitivities for a variety of signal waveforms and report upper limits on the source rate density as a function of the characteristic frequency of the signal. These upper limits are a factor of 3 lower than the first observing run, with a 50% detection probability for gravitational-wave emissions with energies of ∼10-9 Mc2 at 153 Hz. For the search dedicated to cosmic string cusps we consider several loop distribution models, and present updated constraints from the same search done in the first observing run