Wind effects on noise propagation for complicated geographical and road configurations

Outdoor propagation from roads is influenced by wind, temperature and humidity. It is necessary to predict wind effects to simulate long-term environmental noise accurately. Noise levels have been measured in conjunction with wind speed and wind direction measurements. These noise levels showed noticeable daily changes. Excess attenuations of noise levels were found to depend on the vector wind (U_vec). By relating the vector wind and observed sound attenuations under all wind conditions, the influence of wind can be more accurately predicted for purposes of simulating noise propagation.     

Long-Distance Transmission at Zero Dispersion: Exact Expressions for One-Time Statistical Properties

We study the transmission of a signal through a dispersionless fiber with in-line amplifiers. The nonlinearities of the fiber and the noise generated at each amplifier are taken into account. Exact analytical expressions are obtained for the field averages. From these results we obtain the distributed amplification approximation, and study the conditions under which this approximation is valid.     

Frequency– and Time-domain BEM Analysis of Rigid Track on a Half-Space with Vibration Barriers

The rapid development of high-speed trains like the TGV or the ICE in recent years results in high dynamic loads causing vibrations which propagate from the train-track structure into the ground and further into nearby buildings. In this context it is important to develop rigid tracks with improved dynamic behaviour and to investigate possible means of vibration reduction. The boundary element method in frequency and time domain is used to simulate train-track structures subjected to dynamic loading and the reduction of vibrations which for instance can be achieved via a trench running parallel to the rigid track. In this context the non-causality error, which arises when the time-domain BEM algorithm is applied to mathematically concave domains, is discussed and the substructure method is proposed as a solution to this problem. A two-layered cylindrical elastic structure on a half-space with a trench is added as an example of a possible application.     

Nonlinear optical properties of C<Subscript>60</Subscript> with explicit time-dependent electron dynamics

An explicit electron dynamics approach has been used to calculate the nonlinear optical properties of C₆₀ and its radical anion. An external perturbation, in the form of an oscillating electric field, induces the time-evolution of the molecular wavefunction. The time-averaged instantaneous dipole moment of the systems gives the molecular response to perturbations of varying field intensities and frequency of oscillation. The polarizabilities and the second-order hyperpolarizabilties have been calculated and are in good qualitative agreement with experimentally available data. In line with previous theoretical and experimental studies, the nonlinear effect is enhanced for the radical species. Contribution to the Fernando Bernardi Memorial Issue.     

飞秒激光脉冲在正色散固体材料中的自压缩

实验研究了正色散固体介质中的激光脉冲自压缩现象,证明了无需任何外加色散补偿情况下，固体透明介质中的自聚焦传输过程可使高功率飞秒激光脉冲实现时域脉冲压缩，并详细研究了输出脉冲的时域和频域特性随入射脉冲强度的演化规律.实验结果表明脉冲自压缩量随入射脉冲强度的增加呈递增趋势，然而当入射光强增大到足以引起超连续谱及锥形辐射产生时，脉冲时域形状会发生分裂.此外还发现发散光束入射情况下同样可以观察到脉冲自压缩现象. 关键词： 超短激光脉冲 脉冲压缩 非线性传输     

K9光学玻璃化学钢化技术研究

为提高K9光学玻璃在一些特殊应用领域（如高压、温度变化剧烈等）的力学性能,并保证其光学性能符合精密光学仪器要求,对K9光学玻璃进行了化学钢化技术研究。以脆性材料断裂过程微裂纹扩展理论为基础,导出化学钢化玻璃强度应力因子计算模型,分析化学钢化表面应力与表面微裂纹深度、韧性之间的关系,指出化学钢化工艺应注意的事项。通过实验研究,分析化学钢化温度和钢化时间对K9光学玻璃抗弯强度、表面应力及应力层厚度的影响,优化得出K9光学玻璃化学钢化温度为400 ℃、钢化时间为40 h。采用优化工艺,获得了表面应力为500 MPa、应力层厚度为50 μm量级及规格为220 mm×110 mm×22 mm的化学钢化K9光学玻璃样件。钢化后,样件抗弯强度提高了3.5倍以上,且表面疵病、光学鉴别率、透过率等光学性能指标未见明显变化。     

Dynamics of a stochastic rumor propagation model incorporating media coverage and driven by Lévy noise

With the development of information technology, rumors propagate faster and more widely than in the past. In this paper, a stochastic rumor propagation model incorporating media coverage and driven by Lévy noise is proposed. The global positivity of the solution process is proved, and further the basic reproductive number R₀ is obtained. When R₀ < 1, the dynamical process of system with Lévy jump tends to the rumor-free equilibrium point of the deterministic system, and the rumor tends to extinction; when R₀ > 1, the rumor will keep spreading and the system will oscillate randomly near the rumor equilibrium point of the deterministic system. The results show that the oscillation amplitude is related to the disturbance of the system. In addition, increasing media coverage can effectively reduce the final spread of rumors. Finally, the above results are verified by numerical simulation.     

Viewing the noise propagation mechanism in a unidirectional transition cascade from the perspective of stability

Noise and noise propagation are inevitable and play a constructive role in various biological processes. The stability of cell homeostasis is also a critical issue. In the unidirectional transition cascade of colon cells, stem cells (SCs) are the source. They differentiate into transit-amplifying cells (TACs), and TACs differentiate into fully differentiated cells (FDCs). Two differentiation processes are irreversible. The stability factor is introduced so that the noise propagation mechanism from the perspective of stability is studied according to the noise propagation formulas. It is found that the value of the stability factor corresponding to the minimum noise in FDCs may be the best choice to enable colon cells to maintain high stability and low noise of the cascade. Moreover, for the source cell, the total noise only includes intrinsic noise; for the downstream cell with self-proliferation capability, the total noise mainly depends on its intrinsic noise and transmitted noise from upstream cells, and its intrinsic noise is dominant. For the downstream cell without self-proliferation capability, the total noise is mainly determined by transmitted noises from upstream cells, and there is a minimum value. This work provides a new approach for studying the mechanism of noise propagation while considering the stability of cell homeostasis in biological systems.     

复杂网络上的意见动力学对谣言传播的影响

通过在SIR(susceptible-infected-recovered)模型中引入抑制者对谣言的辟谣机制研究了在线社交网络上的意见动力学对谣言传播的影响.在这一模型中,节点可以与自身的邻居组成1个群,传播者可以通过该群传播信息,抑制者也可以在此群中对信息发表意见进行辟谣.辟谣机制在降低未知者对于谣言的接受概率的同时也可以促使传播者向抑制者转变.本文采用ER(Erd?s-Rényi)随机网络、无标度网络以及真实的社交网络研究了抑制者的沉默概率对于谣言传播范围的影响.首先发现,谣言传播的过程以传播者的峰值为界可以分为两个阶段,即谣言自由传播的前期以及抑制者和传播者互相制衡的后期;其次,谣言的传播会随着抑制者的沉默概率的增大而突然暴发.在谣言暴发阈值之下,沉默概率的增大不会导致谣言传播范围显著增大,这是由于未知者在感知到谣言并转变为传播者后又迅速转变为抑制者;而当沉默概率达到谣言暴发阈值时,抑制者将不能控制传播者对谣言的传播从而导致抑制者的降低和谣言的暴发;最后,无标度上的谣言自由传播的前期阶段比随机网络持续的时间更短,从而使无标度上的谣言更难以暴发.本文的模型综合考虑了意见动力学和谣言传播的相互作用,更加真实地模拟了真实世界社交网络中的谣言传播过程.为谣言传播的控制和干预提供了一些有用的思路和见解.