液体火箭发动机中声腔抑制不稳定燃烧的声学分析

发展了声腔的分析和数值模型,对液体火箭发动机不稳定燃烧的抑制作用进行了评定,通过迭代计算研究了二维流动和温度分布变化对声腔调 谐和稳定性能的影响,对不同的声腔几何尺寸和温度梯度的稳定性计算结果表明,燃烧带有较大开口面积的声腔会更大程度地改变振荡的空间分布,这种改变而且影响了驱动和抑制燃烧的机理,讨论了在声腔设计安排中正确选择声腔的几何尺寸,且比较了不同长度和不同直径声腔的阻尼特性,通过考察声吸收系统的方法来最优化系统的阻尼,得到了可供设计参考的结论。     

Exact controllability of nodal profile for 1‐D first order quasilinear hyperbolic systems with internal controls

For 1‐D first order quasilinear hyperbolic systems without zero eigenvalues, based on the theory of exact boundary controllability of nodal profile, using an extension method, the exact controllability of nodal profile can be realized in a shorter time by means of additional internal controls acting on suitably small space‐time domains. On the other hand, using a perturbation method, the exact controllability of nodal profile for 1‐D first order quasilinear hyperbolic systems with zero eigenvalues can be realized by additional internal controls to the part of equations corresponding to zero eigenvalues. Furthermore, by adding suitable internal controls to all the equations on suitable domains, the exact controllability of nodal profile for systems with zero eigenvalues can be realized in a shorter time.     

Optical properties of strongly anisotropic metamaterials

We study the behavior of wave propagation in strongly anisotropic metamaterials with different principal dielectric constants. Analytical expressions of the dispersion relation, Poynting vector, and group velocity are derived theoretically. The light propagation properties for TM and TE waves in these metamaterials are explored, in which the backward wave, negative refraction, phase-compensation effects, and far-field propagation wave carrying subwavelength information are discussed. These theoretical results are supported by numerical simulation.     

傅里叶变换红外光谱对水溶性气溶胶复折射率的测量分析方法研究

当前大气气溶胶的成分比较复杂,其水溶性离子成分影响着大气质量,并且对人类健康不利。因此,对水溶性离子成分进行快速可靠的检测是环境科学领域中的一项重要研究工作。以SO24-为例,研究采用傅里叶变换红外光谱(FTIR)技术,对水溶性气溶胶离子的消光系数进行测量,并通过理论分析计算得到其复折射率N的过程。通过测量大气气溶胶水溶性SO24-离子的质量消光截面k和消光系数α,再根据消光系数α来计算复折射率N的虚部ni,使用KK(Kramers-Kronig)关系,来计算复折射率N的实部nr,并对实验结果进行了分析和讨论。     

A thioester substrate binds to the enzyme Arthrobacter thioesterase in two ionization states: evidence from Raman difference spectroscopy

4‐Hydroxybenzoyl‐CoA (4‐HB‐CoA) thioesterase from Arthrobacter is the final enzyme catalyzing the hydrolysis of 4‐HB‐CoA to produce coenzyme A and 4‐hydroxybenzoic acid in the bacterial 4‐chlorobenzoate dehalogenation pathway. Using a mutation E73A that blocks catalysis, stable complexes of the enzyme and its substrate can be analyzed by Raman difference spectroscopy. Here we have used Raman difference spectroscopy, in the non‐resonance regime, to characterize 4‐HB‐CoA bound in the active site of the E73A thioesterase. In addition, we have characterized complexes of the wild‐type enzyme complexed with the unreactive substrate analog 4‐hydroxyphenacyl‐CoA (4‐HP‐CoA). Both sets of complexes show evidence for two forms of the ligand in the active site: one population has the 4‐hydroxy group protonated, 4‐OH; while the second has the group as the hydroxide, 4‐O⁻. For bound 4‐HP‐CoA, X‐ray data show that glutamate 78 is close to the 4‐OH in the complex and it is likely that this is the proton acceptor for the 4‐OH proton. Although the pK_a of the 4‐OH group on the free substrate in aqueous solution is 8.6, the relative populations of ionized and neutral 4‐HB‐CoA bound to E73A remain invariant between pH 7.3 and 9.8. The invariance with pH suggests that the 4‐OH and the ‐COO⁻ of E78 constitute a tightly coupled pair where their separate pK_a ‘s lose their individual qualities. Narrow band profiles are seen in the CO double bond and C‐S regions, suggesting that the hydrolyzable thioester group is rigidly bound in the active site in a syn gauche conformation. Copyright © 2011 John Wiley & Sons, Ltd.     

The magnetization reversal behaviour for SmCo6.8Zr0.2 and SmCo6.8Zr0.2/α-（Fe,Co） nanocrystalline magnets at low temperature

This paper reports that the SmCo 6.8 Zr 0.2 nanocrystalline permanent magnets and SmCo 6.8 Zr 0.2 /α-(Fe,Co) nanocomposite permanent magnets are successfully produced by mechanical alloying and subsequently annealing at 700 C for 10 minutes.The x-ray diffraction results show that the phase structure of SmCo 6.8 Zr 0.2 nanocrystalline permanent magnets is composed of SmCo 7 phase and SmCo 6.8 Zr 0.2 /α-(Fe,Co) nanocomposite permanent magnets is composed of SmCo 7 and α-(Fe,Co) phases.The mechanism of magnetization reversal is mainly controlled by inhomogeneous domain wall pinning in SmCo 6.8 Zr 0.2 and SmCo 6.8 Zr 0.2 /α-(Fe,Co) magnets.The inter-grain exchange interaction at low temperature is investigated,which shows that the inter-grain exchange interaction of SmCo 6.8 Zr 0.2 /α-(Fe,Co) magnets increases greatly by the decrease of the measured temperature.According to Δm irr-H/H cj,Δm rev-H/H cj and χ irr-H/H cj curves at room temperature and 100 K,the changes of irreversible and reversible magnetization behaviours of SmCo 6.8 Zr 0.2 and SmCo 6.8 Zr 0.2 /α-(Fe,Co) magnets with the decreasing temperature are analysed in detail.The magnetic viscosity and the activation volume of SmCo 6.8 Zr 0.2 and SmCo 6.8 Zr 0.2 /α-(Fe,Co) magnets at different temperatures are also studied.     

A new model for electromigration grain boundary noise based on free volume

Grain boundary plays a key role in electromigration process of polycrystal interconnection. We take a free volume to represent a 'vacancy--ion complex' as a function of grain boundary specific resistivity, and develop a new characterisation model for grain boundary noise. This model reveals the internal relation between the boundary scattering section and electromigration noise. Comparing the simulation result with our experimental result, we find the source as well as the form of noise change in the electromigration process. In order to describe the noise enhancement at grain boundary quantitatively, we propose a new parameter-grain boundary noise enhancement factor, which reflects that the grain boundary noise can characterise the electromigration damage sensitively.     

一种制备单原子碳链的方案

考虑到迄今为止实验上尚不能制备含有上百个原子的自由单原子链,本文提出利用探针从graphene中拉伸较长单原子碳链的设想,并通过分子动力学计算发现,室温下可以利用C60探针以1 m/s的速度从graphene的zigzag边缘拉出较长的一维单原子碳链,为实验提供了一种制备单原子碳链的可能方案. 关键词： 碳链 一维 分子动力学 探针     

Contract and product quality in platform selling

More and more e-tailers (platforms) are allowing manufacturers direct access to customers. Two common contracts are offered by platforms to manufacturers: the revenue sharing contract where a platform appropriates a portion of the manufacturer’s revenue, and the fixed fee contract where a platform charges a fixed rent for each sale. Using an analytical model, this paper studies the interrelationship between a platform’s contract choice and a manufacturer’s product quality decision. We find that if product quality is exogenously given, the platform will always adopt the revenue sharing contract. If the manufacturer endogenously decides the quality, however, the platform’s contract choice may be changed. This is because the revenue sharing contract, compared to fixed fee, leads to a lower selling price of the manufacturer, whereas the fixed fee contract can motivate a higher quality than does revenue sharing. As a result, a large (small) market heterogeneity induces the platform to adopt the revenue sharing (fixed fee) contract. We also extend the model to several directions, finding that longer product line, manufacturer competition, lower marginal production cost, and higher platform cost all tend to induce the platform to put forward a fixed fee contract; while if quality decision is less flexible than contract decision, the platform is more ready to embrace revenue sharing. Besides, when there are two platforms competing for the same market, they should differentiate their contract choices so as to mitigate competition.     

基于PH服务的工作休假排队的流体模型

研究了带有单重工作休假的M/PH/1排队系统驱动的流体模型.首先,通过拟生灭过程和矩阵几何解法分别得到无穷小生成元和驱动过程的稳态队长分布.其次,建立并分析流体模型,根据平衡方程给出流体模型的稳态联合分布函数满足的矩阵微分方程组,利用Laplace变换（LT）和Laplace-Stieltjes变换（LST）的方法,推导出平稳缓冲器（库）容量的空库概率表达式和稳态条件下的缓冲器（库）容量的均值表达式.最后,给出模型在移动自组织网络（Ad Hoc）中的应用,并通过数值例子讨论系统参数对系统性能指标的影响.