737 research outputs found
Influence of gas compression on flame acceleration in the early stage of burning in tubes
The mechanism of finger flame acceleration at the early stage of burning in
tubes was studied experimentally by Clanet and Searby [Combust. Flame 105: 225
(1996)] for slow propane-air flames, and elucidated analytically and
computationally by Bychkov et al. [Combust. Flame 150: 263 (2007)] in the limit
of incompressible flow. We have now analytically, experimentally and
computationally studied the finger flame acceleration for fast burning flames,
when the gas compressibility assumes an important role. Specifically, we have
first developed a theory through small Mach number expansion up to the
first-order terms, demonstrating that gas compression reduces the acceleration
rate and the maximum flame tip velocity, and thereby moderates the finger flame
acceleration noticeably. This is an important quantitative correction to
previous theoretical analysis. We have also conducted experiments for
hydrogen-oxygen mixtures with considerable initial values of the Mach number,
showing finger flame acceleration with the acceleration rate much smaller than
those obtained previously for hydrocarbon flames. Furthermore, we have
performed numerical simulations for a wide range of initial laminar flame
velocities, with the results substantiating the experiments. It is shown that
the theory is in good quantitative agreement with numerical simulations for
small gas compression (small initial flame velocities). Similar to previous
works, the numerical simulation shows that finger flame acceleration is
followed by the formation of the "tulip" flame, which indicates termination of
the early acceleration process.Comment: 19 pages, 20 figure
Be Careful How You Treat Your Coworkers:The Reciprocal Relationship between Ethnic Outgroup Coworkers’ Reactions to Voice and Ethnic Majority Employees’ Attitudes regarding Immigrant Entitlements
Analysis of flame acceleration induced by wall friction in open tubes
Spontaneous flame acceleration leading to explosion triggering in open tubes/channels due to wall friction was analytically and computationally studied. It was first demonstrated that the acceleration is affected when the thermal expansion across the flame exceeds a critical value depending on the combustion configuration. For the axisymmetric flame propagation in cylindrical tubes with both ends open, a theory of the initial (exponential) stage of flame acceleration in the quasi-isobaric limit was developed and substantiated by extensive numerical simulation of the hydrodynamics and combustion with an Arrhenius reaction. The dynamics of the flame shape, velocity, and acceleration rate, as well as the velocity profile ahead and behind the flame, have been determined. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3425646
Mechanism of formation of polychlorinated dibenzo-p-dioxins and dibenzfurans in the catalyzed combustion of carbon.
Transgenerational plasticity is sex-dependent and persistent in yellow monkeyflower (Mimulus guttatus)
Transgenerational phenotypic plasticity, whereby environmental cues experienced by parents alter the phenotype of their progeny, has now been documented in diverse organisms. Transmission of environmentally determined responses is known to occur through both maternal and paternal gametes, but the underlying mechanisms have rarely been compared. In addition, the persistence of induction over multiple generations appears to vary widely, but has been characterized for relatively few systems. Yellow monkeyflower (Mimulus guttatus) is known to exhibit transgenerational induction of increased glandular trichome production in response to simulated insect damage. Here, we test for differences between maternal and paternal transmission of this response and examine its persistence over five generations following damage. Maternal and paternal damage resulted in similar and apparently additive increases in progeny trichome production. Treatment of germinating seeds with the genome-wide demethylating agent 5-azacytidine erased the effect of maternal but not paternal damage. The number of glandular trichomes remained elevated for three generations following damage. These results indicate that transgenerational transmission occurs through both maternal and paternal germ lines, but that they differ in the proximate mechanism of epigenetic inheritance. Our results also indicate that a wounding response can persist for multiple generations in the absence of subsequent damage
Fast electrochemical doping due to front instability in organic semiconductors
The electrochemical doping transformation in organic semiconductor devices is
studied in application to light-emitting cells. It is shown that the device
performance can be significantly improved by utilizing new fundamental
properties of the doping process. We obtain an instability, which distorts the
doping fronts and increases the doping rate considerably. We explain the
physical mechanism of the instability, develop theory, provide experimental
evidence, and perform numerical simulations. We further show how improved
device design can amplify the instability thus leading to a much faster doping
process and device kinetics.Comment: 4 pages, 4 figure
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