Three-dimensional receptivity of boundary layers

The paper presents a review of results of some recent (mainly experimental) studies devoted to a quantitative investigation of the problem of receptivity of the 2D and 3D boundary layers with respect to various 3D (in general) external perturbations. The paper concentrates on the mechanisms of excitation and development of stationary and travelling instability modes in a 3D boundary layer on a swept wing, as well as in 2D boundary layers including the Blasius flow and a self-similar boundary layer with an adverse pressure gradient. In particular, the following problems of the boundary-layer receptivity are discussed: (i) receptivity to localized 3D surface roughness, (ii) receptivity to localized 3D surface vibrations, (iii) acoustic receptivity in presence of 3D surface roughness, and (iv) acoustic receptivity in the presence of 3D surface vibrations. All experiments described in the paper were conducted using controlled disturbance conditions with the help of simulation of the stationary and non-stationary perturbations by means of several disturbance generators. This approach gives us the possibility to obtain quantitative results which are independent of any uncontrolled background perturbations of the flow and the experimental model. In contrast to the data obtained at “natural” environmental conditions these results can be directly compared with calculations without any significant assumptions about the physical nature of the disturbances under investigation. The complex (amplitude and phase) coefficients of the boundary-layer receptivity to external perturbations, obtained as functions of the disturbance frequency and the spanwise wavenumber (or the wave propagation angle), represent the main results of the experiments described. These results can be used for the evaluation of the initial amplitudes and phases of the instability modes generated by various external perturbations, as well as for quantitative verification of linear receptivity theories. Several examples of the comparison of experimental results with calculations are also presented in this paper. A brief analysis of the state-of-art in the field is performed and some general properties of different receptivity mechanisms are discussed.     

FKKM-型定理的推广及应用

本文得到ＦＫＫＭ－型定理的几个新的推广定理,并将所得结果应用于研究重合点问题．文中的结果统一和包含了一些作者的最新成果．     

Effect of electric field on the electronic spectrum and the persistent current of a quantum ring with two electrons

The effect of an electric field E on a narrow quantum ring that contains two electrons and is threaded by a magnetic flux B has been investigated. Localization of the electronic distribution and suppression of the Aharonov--Bohm oscillation (ABO) are found in the two-electron ring, which are similar to those found in a one-electron ring. However, the period of ABO in a two-electron ring is reduced by half compared with that in a one-electron ring. Furthermore, during the variation of B, the persistent current of the ground state may undergo a sudden change in sign. This change is associated with a singlet--triplet transition and has no counterpart in one-electron rings. For a given E, there exists a threshold of energy. When the energy of the excited state exceeds the threshold, the localization would disappear and the ABO would recover. The value of the threshold is proportional to the magnitude of E. Once the threshold is exceeded, the persistent current is much stronger than the current of the ground state at E=0.     

分子发光法研究空间位阻效应对包络物形成的影响

利用分子发光法研究了正丁醇(n-butanol,n-Bu)和苯酚(phenol,ph)存在下空间位阻效应对β-环糊精(Cyclodextrin,β-CD)和溴代萘(Bromonaphthalene,BrN)包络物形成的影响。在各自最佳实验条件下,2-BrN/β-CD/n-Bu/ph体系的室温磷光(RTP)强度不及1-BrN/β-CD/n-Bu/ph体系的三分之一;而其荧光发射光谱较1-BrN/β-CD/n-Bu/ph发射光谱红移5～10 nm,表明BrN中溴的空间位置对包络物的形成有显著的影响。两四元体系包络常数(K_f)的测定结果也进一步说明这一点。据此,讨论了上述包络物的形成机理。     

A chiral cyclohex-2-enone carrying a hexofuranosyl substituent which directs highly stereoselective 1,4-conjugate additions

The reaction of (Z)-3-deoxy-3-C-[(hydroxymethyl)methylene]-1,2:5,6-di-O-isopropylidene-α-D-ribo-hexo-furanose, prepared from D-glucose, with 1,1-dimethoxycyclohexane in the presence of propanoic acid at 135°C, then at 200°C, provided two Claisen rearrangement products, namely (2R,3R,4S,5S)-2,3-(isopropylidene)dioxy-5-[(1R)-1,2-(isopropylidene)dioxyethyl]-4-[(1S)- and (1R)-2-oxocyclohexyl]-4-vinyltetrahydrofuran in a ratio of 3.3:1. L-Selectride^® reduction of the major product gave the corresponding (S)-cyclohexanol exclusively. In contrast, the Claisen rearrangement of the aforementioned allylic alcohol with 3,3-dimethoxycyclohexene proceeded with complete stereoselectivity to provide the corresponding 4-[(1S)-2-oxocyclohex-3-enyl]-4-vinyltetrahydrofuran exclusively. The 1,4-conjugate additions to the thus formed cyclohexenone derivative with dimethyl and divinylcuprates proceeded with complete π-facial selection to provide the 3-methylated and 3-vinylated cyclohexanone derivatives, both in high yields.     

Local electric field and configuration of CO molecules adsorbed on a nanostructured surface with nanocones

Based on the nanostructured surface model that the (platinum, Pt) nanocones grow out symmetrically from a plane substrate, the local electric field near the conical nanoparticle surface is computed and discussed. On the basis of these results, the adsorbed CO molecules are modelled as dipoles, and three kinds of interactions, i.e. interactions between dipoles and local electric field, between dipoles and dipoles, as well as between dipoles and nanostructured substrate, are taken into account. The spatial configuration of CO molecules adsorbed on the nanocone surface is then given by Monte-Carlo simulation. Our results show that the CO molecules adsorbed on the nanocone surface cause local agglomeration under the action of an external electric field, and this agglomeration becomes more compact with decreasing conical angle, which results in a stronger interaction among molecules. These results serve as a basis for explaining abnormal phenomena such as the abnormal infrared effect (AIRE), which was found when CO molecules were adsorbed on the nanostructured transition-metal surface.     

新型四羧基铝酞菁-二氧化硅荧光纳米粒子的合成及在酸度测定中的应用

首次制备出红区荧光染料四羧基铝酞菁掺杂的二氧化硅纳米粒子,并对其进行了表征。将环己烷、正己醇和表面活性剂Triton X-100按一定体积比(12.3∶1.04∶1)混合均匀,形成清澈透明的溶液;将适量的四羧基铝酞菁溶解到浓氨水中,加入到上述混合溶液中,形成反向胶束。搅拌10 m in后加入一定量的四乙氧基硅烷,加快搅拌速度,促使四乙氧基硅烷进入反相胶束中的“纳米水池”,在碱性条件下,四乙氧基硅烷水解形成二氧化硅纳米粒子。采用该方法制备的核壳荧光纳米颗粒荧光稳定性强,生物相容性高,抗干扰能力强。将一定量四羧基铝酞菁掺杂的二氧化硅纳米粒子溶于水溶液中,随溶液pH值的增加,荧光强度增强,并在pH 5.02~11.98的范围内,荧光强度与溶液酸度有良好的线性关系。该法已成功地用于自来水和模拟生物体系中pH的测定。预期该技术有望用于细胞内H 的实时监测。     

Hg2+在大鼠组织器官中的分布及其存在形态研究

汞是环境中重要的污染物之一,对人类的健康构成了巨大的威胁。文章通过建立电感耦合等离子体质谱及凝胶排阻色谱分离法与紫外和电感耦合等离子体质谱在线检测的联用技术,研究大鼠灌喂HgCl2后Hg在大鼠中的分布累积规律和及其与蛋白的结合,实验结果表明肝脏和肾脏中在Hg刺激下诱导产生大量硫蛋白,大量产生的金属硫蛋白可能因此而优先与通过胃肠吸收摄入的Hg结合,减少了Hg对其它蛋白的正常作用的干扰,从而大大降低了Hg^2＋的毒性。     

Investigation of electrical properties (ac and dc) of organic zinc phthalocyanine,ZnPc, semiconductor thin films

We report measurements on the electrical properties of thermally evaporated zinc phthalocyanine, ZnPc, semiconductor thin films. Aluminum and gold metal electrodes were used and both proved to act as ohmic contacts. A relative permittivity, ε_r, of 1.56 was estimated from the dependence of capacitance on film thickness. The room temperature current density–voltage measurements indicated an ohmic conduction at low voltages, while a space–charge-limited conduction at higher voltages. An average value of a thermally generated hole concentration of the order 10¹³ m⁻³ was estimated at room temperature.The ac conductivity, capacitance and loss tangent were measured over a wide range of temperature (from 170 to 430 K) and frequency (between 0.1 and 20 kHz). The ac conductivity of ZnPc films was observed to be proportional to ω^s, where ω is the angular frequency, and the index s is a temperature and frequency-dependent constant. At low temperatures and for higher frequencies the ac conduction was due to hopping. The capacitance, as well as the loss tangent, was found to be dependent on both temperature and frequency, but was constant for all frequencies at low temperatures. Such dependences were accounted for the equivalent-circuit model consisting of inherent capacitance in parallel with a temperature dependent resistive element.     

Phase space reconstruction of chaotic dynamical system based on wavelet decomposition

In view of the disadvantages of the traditional phase space reconstruction method,this paper presents the method of phase space reconstruction based on the wavelet decomposition and indicates that the wavelet decomposition of chaotic dynamical system is essentially a projection of chaotic attractor on the axes of space opened by the wavelet filter vectors,which corresponds to the time-delayed embedding method of phase space reconstruction proposed by Packard and Takens.The experimental results show that,the structure of dynamical trajectory of chaotic system on the wavelet space is much similar to the original system,and the nonlinear invariants such as correlation dimension,Lyapunov exponent and Kolmogorov entropy are still reserved.It demonstrates that wavelet decomposition is effective for characterizing chaotic dynamical system.