Gas-Kinetic Schemes for Direct Numerical Simulations of Compressible Homogeneous Turbulence

We apply the gas-kinetic scheme (GKS) for the direct numerical simulations (DNSs) of compressible decaying homogeneous isotropic turbulence (DHIT). We intend to study the accuracy, stability, and efficiency of the gas-kinetic scheme for DNS of compressible homogeneous turbulence depending on both flow conditions and numerics. In particular, we study the GKS with multidimensional, quasi-one-dimensional, dimensional-splitting, and smooth-flow approximations. We simulate the compressible DHIT with the Taylor microscale Reynolds number Reλ =72.0 and the turbulence Mach number Mat between 0.1 and 0.6. We compute the low-order statistical quantities including the total kinetic energy K (t), the dissipation rate ε (t), the skewness Su (t), and the flatness Fu (t) of the velocity field u (x,t). We assess the effects on the turbulence statistics due to the approximations made in the treatment of fluxes, the flux limiter, the accuracy of the interpolation, and the bulk viscosity. Our results show that the GKS is adequate for DNS of compressible homogeneous turbulence as far as the low-order turbulence statistics are concerned. © 2009 The American Physical Society

Effects of Multitemperature Nonequilibrium on Compressible Homogeneous Turbulence

We study the effects of the rotational-translational energy exchange on the compressible decaying homogeneous isotropic turbulence (DHIT) in three dimensions through direct numerical simulations. We use the gas-kinetic scheme coupled with multitemperature nonequilibrium based on the Jeans-Landau-Teller model. We investigate the effects of the relaxation time of rotational temperature, ZR, and the initial ratio of the rotational and translational temperatures, TR0 / TL0, on the dynamics of various turbulence statistics including the kinetic energy K (t), the dissipation rate ε (t), the energy spectrum E (k,t), the root mean square of the velocity divergence θ′ (t), the skewness Su (t) and the flatness Fu (t) of the velocity derivatives, and the probability distribution functions of the local Mach number Ma and the shocklet strength χ. The larger the ZR is, the faster the compressibility decays after an initial time. Similarly, with a fixed TL0, the higher the initial energy ratio TR0 / TL0, the weaker is the compressibility in the flow. It is also observed that the effect of TR0 / TL0 is strong in all times in the decay, while the effect of ZR is severe only in the later times passing through the stage with strong nonlinearity. We also observe that the multitemperature model does not affect the self-similarities obeyed by the probability distribution functions of Ma and χ, which appear to be a robust feature of the compressible DHIT. © 2010 The American Physical Society

Numerics of the Lattice Boltzmann Method: Effects of Collision Models on the Lattice Boltzmann Simulations

We conduct a comparative study to evaluate several lattice Boltzmann (LB) models for solving the near incompressible Navier-Stokes equations, including the lattice Boltzmann equation with the multiple-relaxation-time (MRT), the two-relaxation-time (TRT), the single-relaxation-time (SRT) collision models, and the entropic lattice Boltzmann equation (ELBE). The lid-driven square cavity flow in two dimensions is used as a benchmark test. Our results demonstrate that the ELBE does not improve the numerical stability of the SRT or the lattice Bhatnagar-Gross-Krook (LBGK) model. Our results also show that the MRT and TRT LB models are superior to the ELBE and LBGK models in terms of accuracy, stability, and computational efficiency and that the ELBE scheme is the most inferior among the LB models tested in this study, thus is unfit for carrying out numerical simulations in practice. Our study suggests that, to optimize the accuracy, stability, and efficiency in the MRT model, it requires at least three independently adjustable relaxation rates: one for the shear viscosity ν (or the Reynolds number Re), one for the bulk viscosity ζ, and one to satisfy the criterion imposed by the Dirichlet boundary conditions which are realized by the bounce-back-type boundary conditions. © 2011 American Physical Society

1-Methyl-3-trifluoro­methyl-5-[(3-chloro­phen­yl)sulfanyl]-1H-pyrazole-4-carbaldehyde O-(4-chloro­benzo­yl)oxime

In the title compound, C19H12Cl2F3N3O2S, the 3-chloro­phenyl and 4-chloro­phenyl rings form dihedral angles 89.5 (2) and 11.4 (2)°, respectively, with the pyrazole ring. In the crystal, mol­ecules related by translation along the a axis are linked into chains via C—H⋯N hydrogen bonds

Kinetic and thermodynamic investigations of CO2 gasification of coal chars prepared via conventional and microwave pyrolysis

This study examined an isothermal CO2 gasification of four chars prepared via two different methods, i.e., conventional and microwave-assisted pyrolysis, by the approach of thermogravimetric analysis. Physical, chemical, and structural behaviours of chars were examined using ultimate analysis, X-ray diffraction, and scanning electronic microscopy. Kinetic parameters were calculated by applying the shrinking unreacted core (SCM) and random pore (RPM) models. Moreover, char-CO2 gasification was further simulated by using Aspen Plus to investigate thermodynamic performances in terms of syngas composition and cold gas efficiency (CGE). The microwave-induced char has the largest C/H mass ratio and most ordered carbon structure, but the smallest gasification reactivity. Kinetic analysis indicates that the RPM is better for describing both gasification conversion and reaction rates of the studied chars, and the activation energies and pre-exponential factors varied in the range of 78.45–194.72 kJ/mol and 3.15–102,231.99 s−1, respectively. In addition, a compensation effect was noted during gasification. Finally, the microwave-derived char exhibits better thermodynamic performances than the conventional chars, with the highest CGE and CO molar concentration of 1.30% and 86.18%, respectively. Increasing the pyrolysis temperature, gasification temperature, and CO2-to-carbon molar ratio improved the CGE

IC 225: a dwarf elliptical galaxy with a peculiar blue core

We present the discovery of a peculiar blue core in the elliptical galaxy IC 225 by using images and spectrum from the Sloan Digital Sky Survey (SDSS). The outer parts of the surface brightness profiles of u-, g-, r-, i- and z-band SDSS images for IC 225 are well fitted with an exponential function. The fitting results show that IC 225 follows the same relations between the magnitude, scale length and central surface brightness for dwarf elliptical galaxies. Its absolute blue magnitude (M_B) is -17.14 mag, all of which suggest that IC 225 is a typical dwarf elliptical galaxy. The g-r color profile indicates a very blue core with a radius of 2 arcseconds, which is also clearly seen in the RGB image made of g-, r- and i-band SDSS images. The SDSS optical spectrum exhibits strong and very narrow nebular emission lines. The metal abundances derived by the standard methods, which are 12+log(O/H) = 8.98, log(N/O) = -0.77 and 12+log(S+/H+) = 6.76, turn out to be significantly higher than that predicted by the well-known luminosity-metallicity relation. After carefully inspecting the central region of IC 225, we find that there are two distinct nuclei, separated by 1.4 arcseconds, the off-nucleated one is even bluer than the nucleus of IC 225. The asymmetric line profiles of higher-order Balmer lines indicate that the emission lines are bluer shifted relative to the absorption lines, suggesting that the line emission arises from the off-center core, whose nature is a metal-rich Hii region. To the best of our knowledge, it is the first high-metallicity Hii region detected in a dwarf elliptical galaxy.Comment: 7 figures, accepted for publication in A

5-(3-Chloro­phen­ylsulfan­yl)-1-methyl-3-trifluoro­methyl-1H-pyrazole-4-carbaldehyde O-[(2-chloro-1,3-thia­zol-5-yl)meth­yl]oxime

In the title compound, C16H11Cl2F3N4OS2, the benzene ring and the thia­zole ring make dihedral angles of 83.2 (3) and 78.3 (3)°, respectively, with the pyrazole ring. The crystal packing shows S⋯N contacts of 3.309 (2) Å

Preparation of poly(ethylene glycol)/polylactide hybrid fibrous scaffolds for bone tissue engineering

Polylactide (PLA) electrospun fibers have been reported as a scaffold for bone tissue engineering application, however, the great hydrophobicity limits its broad application. In this study, the hybrid amphiphilic poly(ethylene glycol) (PEG)/hydrophobic PLA fibrous scaffolds exhibited improved morphology with regular and continuous fibers compared to corresponding blank PLA fiber mats. The prepared PEG/PLA fibrous scaffolds favored mesenchymal stem cell (MSC) attachment and proliferation by providing an interconnected porous extracellular environment. Meanwhile, MSCs can penetrate into the fibrous scaffold through the interstitial pores and integrate well with the surrounding fibers, which is very important for favorable application in tissue engineering. More importantly, the electrospun hybrid PEG/PLA fibrous scaffolds can enhance MSCs to differentiate into bone-associated cells by comprehensively evaluating the representative markers of the osteogenic procedure with messenger ribonucleic acid quantitation and protein analysis. MSCs on the PEG/PLA fibrous scaffolds presented better differentiation potential with higher messenger ribonucleic acid expression of the earliest osteogenic marker Cbfa-1 and mid-stage osteogenic marker Col I. The significantly higher alkaline phosphatase activity of the PEG/PLA fibrous scaffolds indicated that these can enhance the differentiation of MSCs into osteoblast-like cells. Furthermore, the higher messenger ribonucleic acid level of the late osteogenic differentiation markers OCN (osteocalcin) and OPN (osteopontin), accompanied by the positive Alizarin red S staining, showed better maturation of osteogenic induction on the PEG/PLA fibrous scaffolds at the mineralization stage of differentiation. After transplantation into the thigh muscle pouches of rats, and evaluating the inflammatory cells surrounding the scaffolds and the physiological characteristics of the surrounding tissues, the PEG/PLA scaffolds presented good biocompatibility. Based on the good cellular response and excellent osteogenic potential in vitro, as well as the biocompatibility with the surrounding tissues in vivo, the electrospun PEG/PLA fibrous scaffolds could be one of the most promising candidates in bone tissue engineering

High speed self-testing quantum random number generation without detection loophole

Quantum mechanics provides means of generating genuine randomness that is impossible with deterministic classical processes. Remarkably, the unpredictability of randomness can be certified in a self-testing manner that is independent of implementation devices. Here, we present an experimental demonstration of self-testing quantum random number generation based on an detection-loophole free Bell test with entangled photons. In the randomness analysis, without the assumption of independent identical distribution, we consider the worst case scenario that the adversary launches the most powerful attacks against quantum adversary. After considering statistical fluctuations and applying an 80 Gb $\times$ 45.6 Mb Toeplitz matrix hashing, we achieve a final random bit rate of 114 bits/s, with a failure probability less than $10^{-5}$. Such self-testing random number generators mark a critical step towards realistic applications in cryptography and fundamental physics tests.Comment: 34 pages, 10 figure