Gauss-Hermite quadratures and accuracy of lattice Boltzmann models for non-equilibrium gas flows

Recently, kinetic theory-based lattice Boltzmann (LB) models have been developed to model nonequilibrium gas flows. Depending on the order of quadratures, a hierarchy of LB models can be constructed which we have previously shown to capture rarefaction effects in the standing-shearwave problems. Here, we further examine the capability of high-order LB models in modeling nonequilibrium flows considering gas and surface interactions and their effect on the bulk flow. The Maxwellian gas and surface interaction model, which has been commonly used in other kinetic methods including the direct simulation Monte Carlo method, is used in the LB simulations. In general, the LB models with high-order Gauss-Hermite quadratures can capture flow characteristics in the Knudsen layer and higher order quadratures give more accurate prediction. However, for the Gauss-Hermite quadratures, the present simulation results show that the LB models with the quadratures obtained from the even-order Hermite polynomials perform significantly better than those from the odd-order polynomials. This may be attributed to the zero-velocity component in the odd-order discrete set, which does not participate in wall and gas collisions, and thus underestimates the wall effect

Accuracy analysis of high-order lattice Boltzmann models for rarefied gas flows

In this work, we have theoretically analyzed and numerically evaluated the accuracy of high-order lattice Boltzmann (LB) models for capturing non-equilibrium effects in rarefied gas flows. In the incompressible limit, the LB equation is shown to be able to reduce to the linearized Bhatnagar–Gross–Krook (BGK) equation. Therefore, when the same Gauss–Hermite quadrature is used, LB method closely resembles the discrete velocity method (DVM). In addition, the order of Hermite expansion for the equilibrium distribution function is found not to be directly correlated with the approximation order in terms of the Knudsen number to the BGK equation for incompressible flows. Meanwhile, we have numerically evaluated the LB models for a standing-shear-wave problem, which is designed specifically for assessing model accuracy by excluding the influence of gas molecule/surface interactions at wall boundaries. The numerical simulation results confirm that the high-order terms in the discrete equilibrium distribution function play a negligible role in capturing non-equilibrium effect for low-speed flows. By contrast, appropriate Gauss–Hermite quadrature has the most significant effect on whether LB models can describe the essential flow physics of rarefied gas accurately. Our simulation results, where the effect of wall/gas interactions is excluded, can lead to conclusion on the LB modeling capability that the models with higher-order quadratures provide more accurate results. For the same order Gauss–Hermite quadrature, the exact abscissae will also modestly influence numerical accuracy. Using the same Gauss–Hermite quadrature, the numerical results of both LB and DVM methods are in excellent agreement for flows across a broad range of the Knudsen numbers, which confirms that the LB simulation is similar to the DVM process. Therefore, LB method can offer flexible models suitable for simulating continuum flows at the Navier–Stokes level and rarefied gas flows at the linearized Boltzmann model equation level

Analytical solution of axi-symmetrical lattice Boltzmann model for cylindrical Couette flows

Analytical solution for the axi-symmetrical lattice Boltzmann model is obtained for the low-Mach number cylindrical Couette flows. In the hydrodynamic limit, the present solution is in excellent agreement with the result of the Navier-Stokes equation. Since the kinetic boundary condition is used, the present analytical solution using nine discrete velocities can describe flows with the Knudsen number up to 0.1. Meanwhile, the comparison with the simulation data obtained by the direct simulation Monte Carlo method shows that higher-order lattice Boltzmann models with more discrete velocities are needed for highly rarefied flows

Pathogenetic role of tissue factor in graft-versus-host disease

Graft-versus-host disease (GVHD) is a serious complication after allogeneic stem cell transplantation, the mechanism of it is still not elucidated. Recent findings suggest that host endothelial cells are a target of alloreactive donor cytotoxic T lymphocytes in GVHD and tissue factor (TF) plays an important role not only in coagulation-inflammation cycle, but also in transplant immunology. We postulate TF expression in vascular endothelial cells(VEC) may play an pivotal role in the pathogenesis of GVHD. TF gene andprotein expression in target organs of GVHD in aGVHD mice was significantly elevated compared to that of controls as determined by real-time PCR and Western blotting. Allogeneic CD4^+^T cell and CD8^+^T cells enhanced TF, VCAM-1, TNF-[alpha], IFN-[gamma] and IL-6 expression in TNF-[alpha] prestimulated HUVECs compared to controls as determined by flowcytometry and real-time PCR. JNK and p38MAPK mediated allogeneic T cells-induced TF expression in HUVECs. These effects were largely prevented by monoclonal antibody against TF, SB203580 and SP600125. In concert, these data provide strong evidence that upregulated TF expression is related to tissue damage caused by GVHD, TF isthe key factor in GVHD mediated by endothelial cells and allogeneic T cells-induced TF and consecutive proinflammatory cytokines expression in VEC contribute to the pathogenesis of GVHD

Forced or Inspired: Understanding Consumers’ Cognitive Appraisals and Behavioral Responses towards Online Advertising

Drawing upon the coping theory and the stimulus-organism-response (S-O-R) model, this paper proposes a research model to understand consumers’ behavioral responses toward online ads. We posit that a combination of primary appraisals (perceived gain/loss) and secondary appraisals (perceived control) of ads’ design features influences consumers’ emotional states (positive affect vs. negative affect) and motivational states (reactance vs. inspiration) that further lead to their behavioral responses. The behavioral responses are conceptualized along two dimensions: behavioral directions (approach vs. avoidance) and intensity of behavioral efforts (active vs. passive). This study contributes to the extant literature by emphasizing both the negative and positive aspects of consumers’ interactions with online ads and incorporates the effects of emotional and motivational states in mediating and influencing consumer behaviors. It can also potentially have practical implications in improving online advertising design

Chiral topological excitonic insulator in semiconductor quantum wells

We present a scheme to realize the chiral topological excitonic insulator in semiconductor heterostructures which can be experimentally fabricated with a coupled quantum well adjacent to twoferromagnetic insulating films. The different mean-field chiral topological orders, which are due to the change in the directions of the magnetization of the ferromagnetic films, can be characterized by the TKNN numbers in the bulk system as well as by the winding numbers of the gapless states in the edged system. Furthermore, we propose an experimental scheme to detect the emergence of the chiral gapless edge state and distinguish different chiral topological orders by measuring the thermal conductance.Comment: 14 pages, 4 figure