Concerned with the surge of contentcentric applications,it is challenging to balance network traffic and cater to low-delay requirements.Hierarchical caching architecture of both edge network(EN)and core network(CN)em...Concerned with the surge of contentcentric applications,it is challenging to balance network traffic and cater to low-delay requirements.Hierarchical caching architecture of both edge network(EN)and core network(CN)emerges and leverages caching resources to reduce the delivery delay of contents.Most previous work takes an impractical assumption to treat the CN as a content provider,which neglects the collaboration by intermediate CN caches.Most importantly,it is still necessary to thoroughly study the tradeoff between CN delay and edge delay for files delivery so as to minimize the overall delivery delay across the network.In this paper,we consider a hierarchical caching network with distributed CN nodes and edge nodes,where cooperative transmission is enabled for edge nodes to transmit multi-files simultaneously.This poses a joint optimization problem of hierarchical file caching and fetching to minimize the overall delivery delay of requests.Since the problem is NP-hard,we decompose the original problem and design an iterative algorithm to address it.Numerical results validate that the proposed scheme can find a balanced solution between lowering edge delay by utilizing coordinated CN caching and lowering CN delay by solely relying on edge caching.展开更多
The metamaterial constructed by Helmholtz resonators (HR) has low-frequency acoustic forbidden bands and possesses negative mass density and effective bulk modulus at particular frequencies. The resonant modes in one-...The metamaterial constructed by Helmholtz resonators (HR) has low-frequency acoustic forbidden bands and possesses negative mass density and effective bulk modulus at particular frequencies. The resonant modes in one-dimensional HR structure with point defect were studied using finite element method (FEM). The results show that the acoustic energy is localized between the resonant HR and the opening in the local-resonant-type gap. There is a high pressure area around the defect resonator at the frequency of defect mode. In the Bragg type gap, the energy mainly distributes in the waveguide with harmonic attenuation due to the multi-scattering. Phase opposition demonstrates the existence of negative dynamic mass density. Local negative parameter is observed in the pass band due to the defect mode. Based on further investigation of the acoustic intensity and phase distributions in the resonators corresponding to two different forbidden bands, only one local resonant mode is verified, which is different from the three-component local resonant phononics. This work will be useful for understanding the mechanisms of acoustic forbidden bands and negative parameters in the HR metamaterial, and of help for designing new functional acoustic devices.展开更多
Numerical methods can provide extremely powerful tools for analysis and design of engineering systems with complex factors that are not possible or very difficult with the use of the conventional methods. In this pape...Numerical methods can provide extremely powerful tools for analysis and design of engineering systems with complex factors that are not possible or very difficult with the use of the conventional methods. In this paper, we use the 2-D boundary element method (BEM) program to model elastic wave excited by a point explosive source propagating in cracked rocks. As an example, we consider the typical crack distributions in rocks, both models for the real crack structure are also talked about. The elastic wave propagating in rocks with aligned cracks and parallel fractures is assumed. Effects of different crack parameters, such as crack scale length and crack density are analyzed. Numerical results show that the BEM is a powerful interpretive tool for understanding the complicated wave propagation and interaction in cracked solids.展开更多
基金supported by National Key R&D Program of China under grant No.2021YFB2900200China Postdoctoral Science Foundation under grant No.2022M713475。
文摘Concerned with the surge of contentcentric applications,it is challenging to balance network traffic and cater to low-delay requirements.Hierarchical caching architecture of both edge network(EN)and core network(CN)emerges and leverages caching resources to reduce the delivery delay of contents.Most previous work takes an impractical assumption to treat the CN as a content provider,which neglects the collaboration by intermediate CN caches.Most importantly,it is still necessary to thoroughly study the tradeoff between CN delay and edge delay for files delivery so as to minimize the overall delivery delay across the network.In this paper,we consider a hierarchical caching network with distributed CN nodes and edge nodes,where cooperative transmission is enabled for edge nodes to transmit multi-files simultaneously.This poses a joint optimization problem of hierarchical file caching and fetching to minimize the overall delivery delay of requests.Since the problem is NP-hard,we decompose the original problem and design an iterative algorithm to address it.Numerical results validate that the proposed scheme can find a balanced solution between lowering edge delay by utilizing coordinated CN caching and lowering CN delay by solely relying on edge caching.
文摘The metamaterial constructed by Helmholtz resonators (HR) has low-frequency acoustic forbidden bands and possesses negative mass density and effective bulk modulus at particular frequencies. The resonant modes in one-dimensional HR structure with point defect were studied using finite element method (FEM). The results show that the acoustic energy is localized between the resonant HR and the opening in the local-resonant-type gap. There is a high pressure area around the defect resonator at the frequency of defect mode. In the Bragg type gap, the energy mainly distributes in the waveguide with harmonic attenuation due to the multi-scattering. Phase opposition demonstrates the existence of negative dynamic mass density. Local negative parameter is observed in the pass band due to the defect mode. Based on further investigation of the acoustic intensity and phase distributions in the resonators corresponding to two different forbidden bands, only one local resonant mode is verified, which is different from the three-component local resonant phononics. This work will be useful for understanding the mechanisms of acoustic forbidden bands and negative parameters in the HR metamaterial, and of help for designing new functional acoustic devices.
文摘Numerical methods can provide extremely powerful tools for analysis and design of engineering systems with complex factors that are not possible or very difficult with the use of the conventional methods. In this paper, we use the 2-D boundary element method (BEM) program to model elastic wave excited by a point explosive source propagating in cracked rocks. As an example, we consider the typical crack distributions in rocks, both models for the real crack structure are also talked about. The elastic wave propagating in rocks with aligned cracks and parallel fractures is assumed. Effects of different crack parameters, such as crack scale length and crack density are analyzed. Numerical results show that the BEM is a powerful interpretive tool for understanding the complicated wave propagation and interaction in cracked solids.
