Wave dispersion and dissipation performance of locally resonant acoustic metamaterials using an internal variable model

Engineering structures for different dispersion and dissipation levels of wave propagation use internal variable models, which may enhance the performance of acoustic metamaterials (AMMs). In this study, the wave dispersion and dissipation performance of AMMs is studied using an anelastic displacement fields (ADF) model. A symmetric state-space method based on Floquet-Bloch’s theorem for a nonviscously damped unit cell is developed. The study also constructs Bloch’s eigenvalue problems built from the symmetric state-space formulation to obtain the wavevector-dependent damped frequency and damping ratio for wave propagation analysis of periodic structures. The effects of wave dispersion and dissipation on the performance of AMMs are studied by using two numerical examples of mass-in-mass lattice systems containing multiple resonators. It is shown that nonviscous damping increases the wave dispersion performance of AMM. It is also shown that the metadamping phenomenon enhances the wave dissipation performance of AMM. It is demonstrated that the new method in symmetric form is applicable for performance analysis of periodic phononic crystal.     

The advantage of indices of dispersion in queueing approximations

A recent robust queueing approximation for open queueing networks exploits partial characterizations of each arrival process by its rate and index of dispersion for counts (IDC), which is a scaled version of the variance–time curve. Even though only means and variances (as functions of time) are involved, we show that the IDC provides a basis for more accurate approximations than traditional two-moment partial characterizations. For the $GI∕GI∕1$ queue, this approach applied to the arrival and service processes fully characterizes the model.     

如何通过跨学科多元整合模式培养新型博士*——以麻省理工学院化学工程实践博士项目为例

1999年,麻省理工学院启动了化学工程实践博士项目,迄今已有20余年的历史。该项目是麻省理工学院的独创,其模式较为新颖,有典型性与代表性。该模式突破了钟摆现象二元分割范式的制约,体现出跨学科多元整合的特色。在实践中,多元整合的特色体现在历史演进、培养目标、培养内容及培养路径方面。在新一轮工业革命竞争日趋激烈的背景下,创新高层次化学相关专业研究生人才培养模式意义重大。可运用跨学科多元整合模式,从树立多样化人才培养理念、打造跨学科教师队伍、构建校企协同育人机制等方面出发,打破化学相关专业研究生高层次人才培养的二元分割范式,整合多重资源,创新人才培养新理念,构建新时代化学工程研究生人才培养新模式。