随机选取法计算化学反应流爆轰过程引起的参数涨落

利用ＲＣＭ（随机选取法）解反应流爆轰问题时,掌握影响流动参数随机涨落的主要因素是选择适当计算参数、保证得到正确结果的关键。各种流动参数的随机涨落相互关联,只需要搞清楚炸药未反应质量分数的随机涨落并做出分析,其它流动参数涨落的情况也就清楚了。给出了影响未反应质量分数涨落的因数,同时还给出了具体算例,检验所得结论的正确性。     

基于遗传算法和分布式计算的气动优化设计

采用求解NS方程作为气动优化设计的CFD分析方法,为了提高基于遗传算法的气动优化设计的效率,发展了一种基于分布式并行计算的混合遗传算法,并应用该方法进行了气动优化设计.设计实践表明,该方法是可行的,且由于采用了混合遗传算法和分布式并行计算而提高了优化的质量和效率.     

Leveraging Expertise in Thermal Catalysis to Understand Plasma Catalysis

Best practices in testing heterogeneous catalysts are translated to plasma-catalytic experiments. Independent determination of plasma-catalytic and plasma-chemical contributions is essential. Non-porous catalyst particles are preferred because active sites inside sub-micron pores cannot contribute. Temperature variation is needed to determine kinetics, despite the complexity of thermal effects in plasma. Rigorous checks on catalyst deactivation and mass balance are needed. Plasma enhanced reversed reactions should be minimized by keeping conversion low and far from thermodynamic equilibrium, preventing underestimation of the rate of forward reaction. In contrast, plasma-catalytic studies often aim at conversions surpassing thermodynamic equilibrium, not obtaining any information on kinetics. Calculation of catalyst activity per active sites (turn-over-frequency) requires also appropriate characterization to determine the number of active sites. The relationship between kinetics and thermodynamics for plasma-catalysis is discussed using endothermic decomposition of CO₂ and exothermic synthesis of ammonia from N₂ and H₂ as examples. Assuming Langmuir–Hinshelwood and Eley-Rideal mechanisms, the effect of excitation of reactant molecules on activation barriers and surface coverages are discussed, influencing reaction rates. The consequences of reversed reactions are considered. Plasma-catalysis with catalysts applied for thermal catalysis at much higher temperature should be avoided, as adsorbed species are bonded too strongly resulting in low rates.     

飞行器上层大气层空气动力特性探讨

针对近地轨道飞行器所面临的上层大气层(100～300 km)空气动力学问题,对几类典型航天器构型的上层大气层气动力特性进行了分析,给出了典型气动布局在该空域的气动力基本规律,取得了对上层大气层气动力关键影响因素的初步认识.在上层大气层,飞行器的绕流属于自由分子流状态.研究发现,气体分子与不同材质物面的相互作用反映出截然...     

Influence of Nucleation Agents Concentration on Crystallization Structure and Properties of Glass-ceramics

Deep color glass-ceramics is prepared by using gold tailings as the main raw material, and Cr2O3 is added as nucleation agent. Influence of different Cr2O3 additions on crystallization structure and properties of CaO-MgO-Al2O3-SiO2 glass-ceramics has been discussed so as to select optimum additions. DTA is employed to determine optimum crystallization and nucleation temperatures; XRD and SEM are used to characterize microstructure of each sample; and performance indexes, such as water absorption, bulk density, flexural strength and so on, are also determined. Experimental results show that when 3wt% Cr2O3 is introduced, fine glass-ceramics with diopside as the main crystal and Ca-Fe diopside as the second-crystal is obtained, and its corresponding performance indexes are as follows: water absorption 0.12%, bulk density 2.56 g/cm3, and flexural strength 70.01 Mpa.     

Atom interferometry gravity-gradiometer for the determination of the Newtonian gravitational constant G

We developed a gravity-gradiometer based on atom interferometry for the determination of the Newtonian gravitational constant G. The apparatus, combining a Rb fountain, Raman interferometry and a juggling scheme for fast launch of two atomic clouds, was specifically designed to reduce possible systematic effects. We present instrument performances and preliminary results for the measurement of G with a relative uncertainty of 1%. A discussion of projected accuracy for G measurement using this new scheme shows that the results of the experiment will be significant to discriminate between previous inconsistent values.     

Productions of X(1835) as baryonium with sizable gluon content

X(1835) has been treated as a baryonium with sizable gluon content, and to be almost flavor singlet. This picture allows us to rationally understand X(1835) production in J/ψ radiative decays, and its large couplings with pˉ, η^′ππ. The processes ϒ(1S) → γX(1835) and J/ψ → ωX(1835) have been examined. It has been found that Br(ϒ(1S) → γX(1835))Br(X(1835) → pˉ) < 6.45×10^-7, which is compatible with CLEO's recent experimental result (Phys. Rev. D 73, 032001 (2006) hep-ex/0510015). The branching fractions Br(J/ψ → ωX(1835)), Br(J/ψ → ρX(1835)) with X(1835) → pˉ and X(1835) → η^′π⁺π^- have been estimated by the quark-pair creation model. We show that they are heavily suppressed, so the signal of X(1835) is very difficult, if not impossible, to be observed in these processes. The experimental checks for these estimations are expected. The existence of the baryonium nonet is conjectured, and a model-independent derivation of their production branching fractions is presented.     

Upper limit on the flux of gravitational wave bursts

Summary The data obtained with three highly sensitive gravitational wave antennas have been used to establish an improved observational upper limit on the flux of impulsive gravitational waves. Preliminary results under the assumption of a source located in the center of the Galaxy are also reported. To speed up publication, the proofs were not sent to the authors and were superised by the Scientific Committee.     

Comparison of experimental data with the numerical simulation of planar entry flow: Role of the constitutive equation

The goal of this research was to determine whether there is any interaction between the type of constitutive equation used and the degree of mesh refinement, as well as how the type of constitutive equation might affect the convergence and quality of the solution, for a planar 4:1 contraction in the finite eiement method. Five constitutive equations were used in this work: the Phan-Thien–Tanner (PTT), Johnson–Segalman (JS), White–Metzner (WM), Leonov-like and upper convected Maxwell (UCM) models. A penalty Galerkin finite element technique was used to solve the system of non-linear differential equations. The constitutive equations were fitted to the steady shear viscosity and normal stress data for a polystyrene melt. In general it was found that the convergence limit based on the Deborah number De and the Weissenberg number We varied from model to model and from mesh to mesh. From a practical point of view it was observed that the wall shear stress in the downstream region should also be indicated at the point where convergence is lost, since this parameter reflects the throughput conditions. Because of the dependence of convergence on the combination of mesh size and constitutive equation, predictions of the computations were compared with birefringence data obtained for the same polystyrene melt flowing through a 4:1 planar contraction. Refinement in the mesh led to better agreement between the predictions using the PTT model and flow birefringence, but the oscillations became worse in the corner region as the mesh was further refined, eventually leading to the loss of convergence of the numerical algorithm. In comparing results using different models at the same wall shear stress conditions and on the same mesh, it was found that the PTT model gave less overshoot of the stresses at the re-entrant corner. Away from the corner there were very small differences between the quality of the solutions obtained using different models. All the models predicted solutions with oscillations. However, the values of the solutions oscillated around the experimental birefringence data, even when the numerical algorithm would not converge. Whereas the stresses are predicted to oscillate, the streamlines and velocity field remained smooth. Predictions for the existence of vortices as well as for the entrance pressure loss (ΔP_ent) varied from model to model. The UCM and WM models predicted negative values for ΔP_ent.     

A framework and algorithms for circular drawings of graphs

In this paper, we present a framework and two linear time algorithms for obtaining circular drawings of graphs. The first technique produces circular drawings of biconnected graphs and finds a zero crossing circular drawing if one exists. The second technique finds multiple embedding circle drawings. Techniques for the reduction of edge crossings are also discussed. Results of experimental studies are included.