排序方式: 共有50条查询结果,搜索用时 31 毫秒
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Zinc(II) reacts with the anion of 3-cyano-2,4-pentanedione to form the coordinatively unsaturated bis(β-dionato)zinc(II) chelate that functions as Lewis acid and induces short-range site-bounded cohesion forces. Water molecules add to the metal center while others participate in specific interactions involving the terminal nitrogen atom. The X-ray structure analysis of the [Zn(H2O)2(NC-acac)2] · 2H2O entity (monoclinic, space group P21/c, a = 5.208(5), b = 21.359(5), c = 7.813(5) Å, β = 101.89(3)°, Z = 4, R = 0.0632, R w = 0.0679) revealed that zinc(II) exists in a centrosymmetric distorted tetragonal environment and that the entity performs as a building block of a supramolecular structure. 相似文献
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The response of a four-dimensional mammalian cold receptor model to different implementations of noise is studied across a wide temperature range. It is observed that for noisy activation kinetics, the parameter range decomposes into two regions in which the system reacts qualitatively completely different to small perturbations through noise, and these regions are separated by a homoclinic bifurcation. Noise implemented as an additional current yields a substantially different system response at low temperature values, while the response at high temperatures is comparable to activation-kinetic noise. We elucidate how this phenomenon can be understood in terms of state space dynamics and gives quantitative results on the statistics of interspike interval distributions across the relevant parameter range. 相似文献
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Artur Tyliszczak Davide E. Cavaliere Epaminondas Mastorakos 《Flow, Turbulence and Combustion》2014,92(1-2):237-267
Large Eddy Simulations of two-phase flames with the Conditional Moment Closure combustion model have been performed for flow conditions corresponding to stable and blow-off regimes in a swirl n-heptane spray burner. In the case of stable flame (i.e. low air velocity), the predicted mean and r.m.s. velocities and the location and shape of the flame agree reasonably well with experiment. In particular, the presence of localised extinctions is captured in agreement with experiment. Using model constants previously calibrated against piloted jet methane flames (Sandia F) with localised extinction, we obtain that at the experimentally determined blow-off velocity of the swirling spray flame, the predicted flame also blows off, demonstrating that the LES-CMC approach can capture the global extinction point in a realistic configuration. 相似文献
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Simulations and experiments on the ignition probability in turbulent premixed bluff-body flames 总被引:1,自引:0,他引:1
Michael Philip Sitte Ellen Bach James Kariuki Hans-Jörg Bauer Epaminondas Mastorakos 《Combustion Theory and Modelling》2016,20(3):548-565
The ignition characteristics of a premixed bluff-body burner under lean conditions were investigated experimentally and numerically with a physical model focusing on ignition probability. Visualisation of the flame with a 5 kHz OH* chemiluminescence camera confirmed that successful ignitions were those associated with the movement of the kernel upstream, consistent with previous work on non-premixed systems. Performing many separate ignition trials at the same spark position and flow conditions resulted in a quantification of the ignition probability Pign, which was found to decrease with increasing distance downstream of the bluff body and a decrease in equivalence ratio. Flows corresponding to flames close to the blow-off limit could not be ignited, although such flames were stable if reached from a richer already ignited condition. A detailed comparison with the local Karlovitz number and the mean velocity showed that regions of high Pign are associated with low Ka and negative bulk velocity (i.e. towards the bluff body), although a direct correlation was not possible. A modelling effort that takes convection and localised flame quenching into account by tracking stochastic virtual flame particles, previously validated for non-premixed and spray ignition, was used to estimate the ignition probability. The applicability of this approach to premixed flows was first evaluated by investigating the model's flame propagation mechanism in a uniform turbulence field, which showed that the model reproduces the bending behaviour of the ST-versus-u′ curve. Then ignition simulations of the bluff-body burner were carried out. The ignition probability map was computed and it was found that the model reproduces all main trends found in the experimental study. 相似文献
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Andrea Giusti Maria Kotzagianni Epaminondas Mastorakos 《Flow, Turbulence and Combustion》2016,97(4):1165-1184
Large Eddy Simulations (LES) with the Conditional Moment Closure (CMC) combustion model of swirling ethanol spray flames have been performed in conditions close to blow-off for which a wide database of experimental measurements is available for both flame and spray characterization. The solution of CMC equations exploits a three-dimensional unstructured code with a first order closure for chemical source terms. It is shown that LES/CMC is able to properly capture the flame structure at different conditions and agrees reasonably well with the measurements both in terms of mean flame shape and dynamic behaviour of the flame evaluated in terms of local extinctions and statistics of the lift-off height. Experimental measurements of the overall (liquid plus gaseous) mixture fraction, performed using the Laser-Induced Breakdown Spectroscopy technique, are also included allowing further assessment and validation of the numerical method. The sensitivity of the simulation results to the various boundary conditions is discussed. 相似文献
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Nilanjan Chakraborty Henrik Hesse Epaminondas Mastorakos 《Flow, Turbulence and Combustion》2010,84(1):125-166
The influences of fuel Lewis number Le F on localised forced ignition of inhomogeneous mixtures are analysed using three-dimensional compressible Direct Numerical Simulations (DNS) of turbulent mixing layers for Le F = 0.8, 1.0 and 1.2 and a range of different root-mean-square turbulent velocity fluctuation u′ values. For all Le F cases a tribrachial flame has been observed in case of successful ignition. However, the lean premixed branch tends to merge with the diffusion flame on the stoichiometric mixture fraction isosurface at later stages of the flame evolution. It has been observed that the maximum values of temperature and reaction rate increase with decreasing Le F during the period of external energy addition. Moreover, Le F is found to have a significant effect on the behaviours of mean temperature and fuel reaction rate magnitude conditional on mixture fraction values. It is also found that reaction rate and mixture fraction gradient magnitude \(\vert \nabla \xi \vert \) are negatively correlated at the most reactive region for all values of Le F explored. The probability of finding high values of \(\vert \nabla \xi \vert \) increases with increasing Le F . For a given value of u′, the extent of burning decreases with increasing Le F . A moderate increase in u′ gives rise to an increase in the extent of burning for Le F = 0.8 and 1.0, which starts to decrease with further increases in u′. For Le F = 1.2, the extent of burning decreases monotonically with increasing u′. The extent of edge flame propagation on the stoichiometric mixture fraction ξ = ξ st isosurface is characterised by the probability of finding burned gas on this isosurface, which decreases with increasing u′ and Le F . It has been found that it is easier to obtain self-sustained combustion following localised forced ignition in case of inhomogeneous mixtures than that in the case of homogeneous mixtures with the same energy input, energy deposition duration when the ignition centre is placed at the stoichiometric mixture. The difficultly to sustain combustion unaided by external energy addition in homogeneous mixture is particularly prevalent in the case of Le F = 1.2. 相似文献
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Different ways of transferring information regarding the mixture fraction, its sub-grid scale variance and the scalar dissipation
rate are examined in terms of a Large Eddy Simulation (LES)/Conditional Moment Closure (CMC) calculation. In such a simulation,
information must be transferred from a fine LES grid to a usually coarser CMC grid. Different options of calculating conditional
and unconditional quantities in the CMC resolution are assessed by filtering experimental mixture fraction and scalar dissipation
rate data at various resolutions. It was found that when a presumed shape for the Filtered Density Function at the CMC resolution
is used, special care must be given to the mixture fraction variance. It was also found that the Amplitude Mapping Closure
model can be used for the conditional scalar dissipation rate. LES/CMC with detailed chemistry of a bluff-body stabilised
burner was performed using two different ways of calculating the turbulent diffusivity. The structure of the flame is realistic,
with little difference noticed when using the two diffusivities. 相似文献
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Ioulia Georgiopoulou Soultana Tzima Georgia D. Pappa Vasiliki Louli Epaminondas Voutsas Kostis Magoulas 《Molecules (Basel, Switzerland)》2022,27(1)
Microalgae contain an abundance of valuable bioactive compounds such as chlorophylls, carotenoids, and phenolics and, consequently, present great commercial interest. The aim of this work is the study and optimization of recovering the aforementioned components from the microalgae species Chlorella vulgaris through conventional extraction in a laboratory-scale apparatus using a “green” mixture of ethanol/water 90/10 v/v. The effect of three operational conditions—namely, temperature (30–60 °C), duration (6–24 h) and solvent-to-biomass ratio (20–90 mLsolv/gbiom), was examined regarding the extracts’ yield (gravimetrically), antioxidant activity, phenolic, chlorophyll, and carotenoid contents (spectrophotometric assays), as well as concentration in key carotenoids, i.e., astaxanthin, lutein, and β-carotene (reversed-phase–high-performance liquid chromatography (RP–HPLC)). For this purpose, a face-centered central composite design (FC-CCD) was employed. Data analysis resulted in the optimal extraction conditions of 30 °C, for 24 h with 37 mLsolv/gbiom and validation of the predicted models led to 15.39% w/w yield, 52.58 mgextr/mgDPPH (IC50) antioxidant activity, total phenolic, chlorophyll, and carotenoid content of 18.23, 53.47 and 9.92 mg/gextr, respectively, and the total sum of key carotenoids equal to 4.12 mg/gextr. The experimental data and predicted results were considered comparable, and consequently, the corresponding regression models were sufficiently reliable for prediction. 相似文献
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