1,219 research outputs found
Stability of planar flames as gasdynamic discontinuities
No full textThe stability of a steadily propagating planar premixed flame has been the subject of numerous studies since Darrieus and Landau showed that in their model flames are unstable to perturbations of any wavelength. Moreover, the instability was shown to persist even for very small wavelengths, i.e. there was no high-wavenumber cutoff of the instability. In addition to the Darrieus-Landau instability, which results from thermal expansion, analysis of the diffusional thermal model indicates that premixed flames may exhibit cellular and pulsating instabilities as a consequence of preferential diffusion. However, no previous theory captured all the instabilities including a high-wavenumber cutoff for each. In Class, Matkowsky & Klimenko (2003) a unified theory is proposed which, in appropriate limits and under appropriate assumptions, recovers all the relevant previous theories. It also includes additional new terms, not present in previous theories. In the present paper we consider the stability of a uniformly propagating planar flame as a solution of the unified model. The results are then compared to those based on the models of Darrieus-Landau, Sivashinsky and Matalon-Matkowsky. In particular, it is shown that the unified model is the only model to capture the Darrieus-Landau, cellular and pulsating instabilities including a high-wavenumber cutoff for each
Near-axis asymptote of the bathtub-type inviscid vortical flows
No full textThe near-axis asymptotic behavior of a vortical, laminar, bathtub-type flow is analyzed for large values of the Reynolds number. It is shown that only two exponents α=2 and α=4/3 can be expected for the near-axis inviscid asymptote of a given stream function
Aye–ay: An Anglo-Frisian Parallel
No full textThe most widespread form for neutral “yes” in the Survey of English Dialects is not yea or yes, but aye. It is used not only in the North and Midlands, but also in areas of the South of England. It is a feature of Scottish English, and is familiar from government in many English-speaking countries. We also find the aye-like ayuh in Northeast America. “Aye” appears suddenly about 1575 and is “exceedingly common” around 1600; it is initially written I and its origin, like yes, is uncertain. Ay is also found in Old Frisian, as well as Sater Frisian today (öäi, a'äi etc.). This study reviews a number of proposed etymologies, examining which can account for the occurrence or development of ay(e) in both languages. Based on a wider study of change in forms of “yes” and “no” in English, the author argues that aye–ay is a parallel development of interjection + particle. The study also suggests functional and phonological overlap with the pronominal echo I in English, but not Frisian, with the vocalic form of the pronoun and diphthongisation in the “Great Vowel Shift”, accounting for the popularity and spelling I of “aye” around 1600.</jats:p
Examining the cascade hypothesis for turbulent premixed combustion
No full textThe cascade hypothesis, which was introduced in application for premixed combustion by Yakhot (1988) and Sivashinsky (1988), is examined against the correlations of the turbulent burning velocity data by Bradley, Lau and Lawes (1992) (BLL data). A new, less restrictive formulation of the cascade hypothesis is suggested. The formulation is shown to be consistent with the BLL data. Various flame characteristics- fractal dimensions, inner cutoffs, main asymptotic regimes - are determined form the BLL data on the basis of the cascade hypothesis
Fucoxanthin promotes translocation and induction of glucose transporter 4 in skeletal muscles of diabetic/obese KK-Ay mice
No full textFucoxanthin (Fx) isolated from Undaria pinnatifida suppresses the development of hyperglycemia and hyperinsulinemia of diabetic/obese KK-Ay mice after two weeks of feeding 0.2% Fx-containing diet. In the soleus muscle of KK-Ay mice that were fed Fx, glucose transporter 4 (GLUT4) translocation to plasma membranes from cytosol was promoted. On the other hand, Fx increased GLUT4 expression levels in the extensor digitorum longus (EDL) muscle, although GLUT4 translocation tended to increase. The expression levels of insulin receptor (IR) mRNA and phosphorylation of Akt, which are in upstream of the insulin signaling pathway regulating GLUT4 translocation, were also enhanced in the soleus and EDL muscles of the mice fed Fx. Furthermore, Fx induced peroxisome proliferator activated receptor γ coactivator-1α (PGC-1α), which has been reported to increase GLUT4 expression, in both soleus and EDL muscles. These results suggest that in diabetic/obese KK-Ay mice, Fx improves hyperglycemia by activating the insulin signaling pathway, including GLUT4 translocation, and inducing GLUT4 expression in the soleus and EDL muscles, respectively, of diabetic/obese KK-Ay mice
Conditional methods in application for Lagrangian modeling
No full textThe exact unclosed equation for the phase-space density function (or corresponding Lagrangian pdf) in turbulent flows is obtained using conditional techniques. The equation has direct implications for stochastic Lagrangian models based on the assumption of similarity with a Markov process. The problem of random particle sources is examined and the appropriate correcting term is suggested. (C) 1998 American Institute of Physics
A small disturbance in the strong vortex flow
No full textA small disturbance in the axisymmetric, bathtub-like flow with strong vorticity is considered and the asymptotic representation of the solution is found. It is shown that if the disturbance is smaller than a certain critical scale, the conventional strong vortex approximation cannot describe the field generated by the disturbance not only in the vicinity of the disturbance but also at the distances much larger than the critical scale. (C) 2001 American Institute of Physics
Matching the conditional variance as a criterion for selecting parameters in the simplest multiple mapping conditioning models
No full textThe simplest model within the multiple mapping conditioning (MMC) approach, that involves a single mixture-fraction-like reference variable, is considered in the Brief Communication. An important parameter-the minor dissipation time-remains unknown in the probabilistic version of the model. The present work demonstrates by the specially developed asymptotic analysis that the simplest MMC possesses an ability (although somewhat limited) to match the physical intensity of the conditional fluctuations and this match represents the criterion for proper selection of the minor dissipation time. (C) American Institute of Physics
Modified associate formalism without entropy paradox Part II. Comparison with similar models
No full textThe modified associate formalism is compared with similar models, such as the classical associate model, the associate species model and the modified quasichemical model. Advantages of the modified associate formalism are demonstrated
Propagation of nonstationary curved and stretched premixed flames with multistep reaction mechanisms
No full textThe propagation speed of a thin premixed flame disturbed by an unsteady fluid flow of a larger scale is considered. The flame may also have a general shape but the reaction zone is assumed to be thin compared to the flame thickness. Unlike in preceding publications, the presented asymptotic analysis is performed for a general multistep reaction mechanism and, at the same time, the flame front is curved by the fluid flow. The resulting equations define the propagation speed of disturbed flames in terms of the properties of undisturbed planar flames and the flame stretch. Special attention is paid to the near-equidiffusion limit. In this case, the flame propagation speed is shown to depend on the effective Zeldovich number Z(f) , and the flame stretch. Unlike the conventional Zeldovich number, the effective Zeldovich number is not necessarily linked directly to the activation energies of the reactions. Several examples of determining the effective Zeldovich number for reduced combustion mechanisms are given while, for realistic reactions, the effective Zeldovich number is determined from experiments. Another feature of the present approach is represented by the relatively simple asymptotic technique based on the adaptive generalized curvilinear system of coordinates attached to the flame (i.e., intrinsic disturbed flame equations [IDFE])
- …
