Direct numerical simulations of homogeneous sheared and stably stratified turbulence are considered to probe the asymptotic high dynamic range regime suggested by Gargett et al. J. Fluid Mech. 144, ...231 (1984)10.1017/S0022112084001592 and Shih et al. J. Fluid Mech. 525, 193 (1999)10.1017/S0022112004002587. We consider statistically stationary configurations of the flow that span three decades in dynamic range defined by the separation between the Ozmidov length scale L_{O}=sqrtε/N^{3} and the Kolmogorov length scale L_{K}=(ν^{3}/ε)^{1/4}, up to Re_{b}≡(L_{O}/L_{K})^{4/3}=ε/(νN^{2})∼O(1000), where ε is the mean turbulent kinetic energy dissipation rate, ν is the kinematic viscosity, and N is the buoyancy frequency. We isolate the effects of Re_{b}, particularly on irreversible mixing, from the effects of other flow parameters of stratified and sheared turbulence. Specifically, we evaluate the influence of dynamic range independent of initial conditions. We present evidence that the flow approaches an asymptotic state for Re_{b}⪆300, characterized both by an asymptotic partitioning between the potential and kinetic energies and by the approach of components of the dissipation rate to their expected values under the assumption of isotropy. As Re_{b} increases above 100, there is a slight decrease in the turbulent flux coefficient Γ=χ/ε, where χ is the dissipation rate of buoyancy variance, but, for this flow, there is no evidence of the commonly suggested Γ∝Re_{b}^{-1/2} dependence when 100≤Re_{b}≤1000.
The International Federation of Accountants (IFAC) requires its member professional accounting organisations and their authorised educators to adopt the overarching guidelines that are provided in ...the International Education Standards (IES). Despite these requirements, which include that accounting students develop several non-technical skills (NTS), students fail to adequately develop such skills. Furthermore, several studies advise that accounting programmes must incorporate emotional intelligence (EI) development initiatives, but this requirement is excluded from the IES. Resultantly, educators may disregard EI development within accounting programmes, especially since these programmes are already considered overloaded. This study investigates whether it is possible to advance the NTS of accounting students while facilitating the development of their EI competencies by aiming to answer the following question: which EI capabilities can improve the NTS of accounting students? By following a qualitative research approach and performing a systematic literature review, the study found that the enhancement of multiple EI capabilities can lead to the improvement of several NTS of accounting students. Educators that want to renew their NTS development offering, or introduce EI development initiatives within their accounting programmes, can use these findings as a guide to determine which EI capabilities (or combination thereof) can advance the essential NTS of accounting students.
We report on direct numerical simulations of the decay of initially isotropic, homogeneous turbulence subject to the application of stable density stratification. Flows were simulated for three ...different initial Reynolds numbers, but for the same initial Froude number. We find that the flows pass through three different dynamical regimes as they decay, depending on the local values of the Froude number and activity parameter. These regimes are analogous to those seen in the experimental study of Spedding (J. Fluid Mech., vol. 337, 1997, pp. 283–301) for the wake of a sphere. The flows initially decay with little influence of stratification, up to approximately one buoyancy period, when the local Froude number has dropped below 1. At this point the flows have adjusted to the density stratification, and, if the activity parameter is large enough, begin to decay at a slower rate and spread horizontally at a faster rate, consistent with the predictions of Davidson (J. Fluid Mech., vol. 663, 2010, pp. 268–292) and the scaling arguments of Billant & Chomaz (Phys. Fluids, vol. 13, 2001, pp. 1645–1651). We refer to this second regime as the stratified turbulence regime. As the flows continue to decay, ultimately the activity parameter drops below approximately 1 as viscous effects begin to dominate. In this regime, the flows have become quasi-horizontal, and approximately obey the scaling arguments of Godoy-Diana et al. (J. Fluid Mech., vol. 504, 2004, pp. 229–238).
Classical scaling arguments of Kolmogorov, Oboukhov and Corrsin (KOC) are evaluated for turbulence strongly influenced by stable stratification. The simulations are of forced homogeneous stratified ...turbulence resolved on up to
$8192\times 8192\times 4096$
grid points with buoyancy Reynolds numbers of
$\mathit{Re}_{b}=13$
, 48 and 220. A simulation of isotropic homogeneous turbulence with a mean scalar gradient resolved on
$8192^{3}$
grid points is used as a benchmark. The Prandtl number is unity. The stratified flows exhibit KOC scaling only for second-order statistics when
$\mathit{Re}_{b}=220$
; the
$4/5$
law is not observed. At lower
$\mathit{Re}_{b}$
, the
$-5/3$
slope in the spectra occurs at wavenumbers where the bottleneck effect occurs in unstratified cases, and KOC scaling is not observed in any of the structure functions. For the probability density functions (p.d.f.s) of the scalar and kinetic energy dissipation rates, the lognormal model works as well for the stratified cases with
$\mathit{Re}_{b}=48$
and 220 as it does for the unstratified case. For lower
$\mathit{Re}_{b}$
, the dominance of the vertical derivatives results in the p.d.f.s of the dissipation rates tending towards bimodal. The p.d.f.s of the dissipation rates locally averaged over spheres with radius in the inertial range tend towards bimodal regardless of
$\mathit{Re}_{b}$
. There is no broad scaling range, but the intermittency exponents at length scales near the Taylor length are in the range of
$0.25\pm 0.05$
and
$0.35\pm 0.1$
for the velocity and scalar respectively.
Nanomaterials have many advanced applications, from bio-medicine to flexible electronics to energy storage, and the broad interest in graphene-based materials and devices means that high annual ...tonnages will be required to meet this demand. However, manufacturing at the required scale remains unfeasible until economic and environmental obstacles are resolved. Liquid exfoliation of graphite is the preferred scalable method to prepare large quantities of good quality graphene, but only low concentrations are achieved and the solvents habitually employed are toxic. Furthermore, good dispersions of nanomaterials in organic solvents are crucial for the synthesis of many types of nanocomposites. To address the performance and safety issues of solvent use, a bespoke approach to solvent selection was developed and the renewable solvent Cyrene was identified as having excellent properties. Graphene dispersions in Cyrene were found to be an order of magnitude more concentrated than those achieved in N-methylpyrrolidinone (NMP). Key attributes to this success are optimum solvent polarity, and importantly a high viscosity. We report the role of viscosity as crucial for the creation of larger and less defective graphene flakes. These findings can equally be applied to the dispersion of other layered bi-dimensional materials, where alternative solvent options could be used as drop-in replacements for established processes without disruption or the need to use specialized equipment. Thus, the discovery of a benign yet high performance graphene processing solvent enhances the efficiency, sustainability and commercial potential of this ever-growing field, particularly in the area of bulk material processing for large volume applications.
Biorefineries are facilities that process biomass into fuels, power and value-added chemicals and with the increasing population and depleting petroleum reserves they are fast becoming more important ...to society. The technology required to process a wide variety of biomass types can be highly complex due to potentially unknown, varying or difficult to breakdown chemical structures within them. One of the prospective routes to a successful biorefinery, that can treat a wide range of biomass and produce products with good selectivity, is the use of nanoparticles as heterogeneous catalysts. The potential of nanoparticles to catalyse and modify chemical processes, thereby influencing both the nature of the products and their distribution is seen as highly promising. In this publication, we aim to give an overview of the use of a range of nano-catalysts and nano-enzymatic supports for greener biorefinery processing. Finally, future prospects of greener routes to nanoparticle production and their integration into biomass are discussed.
Biorefineries are facilities that process biomass into fuels, power and value-added chemicals and with the increasing population and depleting petroleum reserves they are fast becoming more important to society.
We present a new robust method for identifying three dynamically distinct regions in a stratified turbulent flow, which we characterise as quiescent flow, intermittent layers and turbulent patches. ...The method uses the cumulative filtered distribution function of the local density gradient to identify each region. We apply it to data from direct numerical simulations of homogeneous stratified turbulence, with unity Prandtl number, resolved on up to
$8192\times 8192\times 4096$
grid points. In addition to classifying regions consistently with contour plots of potential enstrophy, our method identifies quiescent regions as regions where
$\unicodeSTIX{x1D716}/\unicodeSTIX{x1D708}N^{2}\sim O(1)$
, layers as regions where
$\unicodeSTIX{x1D716}/\unicodeSTIX{x1D708}N^{2}\sim O(10)$
and patches as regions where
$\unicodeSTIX{x1D716}/\unicodeSTIX{x1D708}N^{2}\sim O(100)$
. Here,
$\unicodeSTIX{x1D716}$
is the dissipation rate of turbulence kinetic energy,
$\unicodeSTIX{x1D708}$
is the kinematic viscosity and
$N$
is the (overall) buoyancy frequency. By far the highest local dissipation and mixing rates, and the majority of dissipation and mixing, occur in patch regions, even when patch regions occupy only 5 % of the flow volume. We conjecture that treating stratified turbulence as an instantaneous assemblage of these different regions in varying proportions may explain some of the apparently highly scattered flow dynamics and statistics previously reported in the literature.
Stridor is a common symptom associated with foreign body aspiration. In most cases, this is due to the foreign bodies lodging in the supraglottis, glottis, subglottis, or high extra‐thoracic trachea. ...Infrequently, foreign bodies located in the esophagus cause stridor. The ingestion of button batteries (BBs) has been reported to cause multiple problems. The incidence has been estimated at 10.5 per million people per year with a case fatality rate of 0.5%. BBs predominantly cause esophageal mucosal injury. Mechanisms of injury include pressure necrosis, electrolysis, caustic exposure, or heavy metal toxicity. The reported complications include severe esophageal ulceration, trachea‐esophageal fistula or aorto‐esophageal fistula, and pneumonia. Vocal fold pathology after battery ingestion, other than edema of cords, has been rarely reported. We describe a case of acute bilateral vocal fold dysfunction and review the literature.
Abstract
Direct numerical simulations of stratified turbulence are used to test several fundamental assumptions involved in the Osborn, Osborn–Cox, and Thorpe methods commonly used to estimate the ...turbulent diffusivity from field measurements. The forced simulations in an idealized triply periodic computational domain exhibit characteristic features of stratified turbulence including intermittency and layer formation. When calculated using the volume-averaged dissipation rates from the simulations, the vertical diffusivities inferred from the Osborn and Osborn–Cox methods are within 40% of the value diagnosed using the volume-averaged buoyancy flux for all cases, while the Thorpe-scale method performs similarly well in the simulation with a relatively large buoyancy Reynolds number (Re
b
≃ 240) but significantly overestimates the vertical diffusivity in simulations with Re
b
< 60. The methods are also tested using a limited number of vertical profiles randomly selected from the computational volume. The Osborn, Osborn–Cox, and Thorpe-scale methods converge to their respective estimates based on volume-averaged statistics faster than the vertical diffusivity calculated directly from the buoyancy flux, which is contaminated with reversible contributions from internal waves. When applied to a small number of vertical profiles, several assumptions underlying the Osborn and Osborn–Cox methods are not well supported by the simulation data. However, the vertical diffusivity inferred from these methods compares reasonably well to the exact value from the simulations and outperforms the assumptions underlying these methods in terms of the relative error. Motivated by a recent theoretical development, it is speculated that the Osborn method might provide a reasonable approximation to the diffusivity associated with the
irreversible
buoyancy flux.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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