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1.
Qiang Xiao Aliou Sow Brian M. Maxwell Matei I. Radulescu 《Proceedings of the Combustion Institute》2021,38(3):3641-3649
We evaluate the effect of boundary layer losses on two-dimensional H2/O2/Ar cellular detonations obtained in narrow channels. The experiments provide the details of the cellular structure and the detonation speed deficits from the ideal CJ speed. We model the effect of the boundary layer losses by incorporating the flow divergence in the third dimension due to the negative boundary layer displacement thickness, modeled using Mirels’ theory. The cellular structures obtained numerically with the resulting quasi-2D formulation of the reactive Euler equations with two-step chain-branching chemistry are found in excellent agreement with experiment, both in terms of cell dynamics and velocity deficits, provided the boundary layer constant of Mirels is modified by a factor of 2. A significant increase in the cell size is found with increasing velocity deficit. This is found to be very well captured by the induction zone increase in slower detonations due to the lower temperatures in the induction zone. 相似文献
2.
Doubly‐Charged Xe Ions Evidenced by Time Resolved RPA Measurement in the Far Field Plume of a Low‐Power HET 下载免费PDF全文
A low power Hall Effect Thruster (HET), based on a permanent magnet circuit, was investigated in the GREMI laboratory facility. The thruster operated in the working range between 50 and 300 W and the previously measured thrust is between 4 and 16 mN for an anodic efficiency respectively between 15% and 27%. The pulsed character of the thruster current is an important feature of this HET. The ion current's bursts are recorded at 30 and 70 cm from the exit plane in the thruster plume and are time‐resolved, which lead to a preliminary analysis of the time of flight (TOF) phenomena. This paper presents a detailed study of these bursts of ion current in the plume. The total ion current is shown to be a superposition of 2 distinct contributions of charged species. In complement, a controlled single current interruption in stable anodic current condition leads to exactly the same features than in oscillating mode. This crucial verification garantees the validity of the time of flight origine of the two distinct contributions. Then, the slower one is the more intense and is proportional to the ion Xe+ current whereas the faster one could be attributed either to doubly‐charged Xe++ or to superfast Xe+. The work presents a way to determine unambiguously the nature of the fast contribution by recording the Retardated Potential Analyser (RPA) signals at various repelling grid potentials with respect to time. The energy distribution of the 2 wellseparated contributions are reconstructed and confirms the contribution of doubly‐charged xenon ions (Xe++) in the plume. This way of RPA collecting data and interpretation presents the main advantage tobe an easy way for the identification of the nature of the charged species in the plume. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
3.
In this work, we study the existence, uniqueness, and exponential asymptotic behavior of mild solutions to stochastic integrodifferential delay evolution equations. We assume that the non-delay part generates a C0-semigroup. 相似文献
4.
5.
Thomas Horseman Mehdi Tajvidi Cherif I. K. Diop Douglas J. Gardner 《Cellulose (London, England)》2017,24(6):2455-2468
Lignocellulose nanofibrils (LCNF) were produced from thermo-mechanical pulp (TMP) using a micro-grinder and were characterized with respect to fiber diameter and thermal stability. The initial water content in the TMP affected the defibrillation process and longer grinding time was necessary for the air-dried TMP, resulting in LCNF with higher fibril diameter. As compared to the reference cellulose nanofibrils (CNF) produced through a refining process, LCNF was less thermally stable and started to degrade at a temperature that was 30 °C lower than that of CNF. LCNF obtained from the never-dried TMP was combined with various additives (10 wt%) to produce composite films. The neat LCNF and composite films did not reach the mechanical properties of the neat CNF film that was evaluated as reference. However, the addition of poly(vinyl alcohol) (PVA) at 10 wt% on a dry basis did cause a 46 and 25% increase in tensile strength and elastic modulus, respectively. Other additives including cellulose nanocrystals, bentonite and CNF were also found to increase to some extent the Young’s modulus and ductility of the LCNF composite films whereas the addition of talc did not improve the film performance. Water absorption of neat LCNF films was lower than the reference CNF and was negatively affected by the addition of PVA. 相似文献
6.
A PDE based and interpolation-free framework for modeling the sifting process in a continuous domain
El Hadji S. Diop Radjesvarane Alexandre Valérie Perrier 《Advances in Computational Mathematics》2013,38(4):801-835
The empirical mode decomposition (EMD) is a powerful tool in signal processing. Despite its algorithmic origin making its theoretical analysis and formulation very difficult, a few recent works has contributed to its theoretical framework. Herein, the former local mean is formulated in a more convenient way by introducing operators to calculate local upper and lower envelopes. This enables the use of differential calculus and other classical calculations on the new local mean. Based on its more accurate formulation, a partial differential equation (PDE) consistency result is provided to approximate the sifting process iterations, without any envelope interpolation. In addition, a new stopping criterion based on the introduced local mean is proposed. This new criterion is a local measure and resolves the null integral conservative property of the previous derived PDE, which made any signal having a null integral be a PDE-based mode. Moreover, the δ inner model parameter is now linked to the signal intrinsic properties, providing to the latter a physical meaning and making the proposed model keep the auto-adaptive property of the EMD. New decomposition modes are now analytically and fully characterized, and also interpolation free. Finally, properties of the interpolation free PDE model are presented. Results obtained with our proposed approach by explicit computations thanks to the eigendecomposition of the Laplacian operator, and also by numerical resolution of the derived PDE, show noticeable improvements for both stationary and non stationary signals, in comparison to the former EMD algorithm. 相似文献
7.
S. A. Ould Abdi S. Dabo-Niang A. Diop A. Ould Abdi 《Mathematical Methods of Statistics》2010,19(1):1-21
Given a stationary multidimensional spatial process (Z
i
= (X
i
, Y
i
) ∈ ℝ
d
× ℝ, i ∈ ℤ
N
), we investigate a kernel estimate of the spatial conditional quantile function of the response variable Y
i
given the explicative variable X
i
. Almost complete convergence and consistency in L
2r
norm (r ∈ ℕ*) of the kernel estimate are obtained when the sample considered is an α-mixing sequence. 相似文献
8.
I. Diop N. David J.M. Fiorani R. Podor M. Vilasi 《The Journal of chemical thermodynamics》2009,41(3):420-432
In the present work, the experimental characterization of the pseudo-binary PbO–Bi2O3 cut has been performed by differential thermal analysis (DTA), isothermal annealing, powder X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). A thermodynamic assessment according to the Calphad method was also performed based on the present results as well as previous experimental data using the ThermoCalc software. 相似文献
9.
Delahaye É Eyele-Mezui S Diop M Leuvrey C Rabu P Rogez G 《Dalton transactions (Cambridge, England : 2003)》2010,39(44):10577-10580
Synthesis of new heterometallic layered magnets with controlled chirality have been achieved by insertion of chiral and non-chiral salen-type Ni(II) complexes into copper and cobalt layered simple hydroxides. 相似文献
10.
We consider a threshold autoregressive stochastic volatility model where the driving noises are sequences of iid regularly
random variables. We prove that both the right and the left tails of the marginal distribution of the log-volatility process
(αt)t are regularly varying with tail exponent −α with α > 0. We also determine the exact values of the coefficients in the tail behaviour of the process (αt)t.
AMS 2000 Subject Classification. Primary—62G32, 62PO5 相似文献