Understanding the Performance Guarantee of Physical Topology Design for Optical Circuit Switched Data Centers

As a first step of designing O ptical-circuit-switched D ata C enters (ODC), physical topology design is critical as it determines the scalability and the performance limit of the entire ODC. However, prior works on ODC have not yet paid much attention to physical topology design, and the adopted physical topologies either scale poorly, or lack performance guarantee. We offer a mathematical foundation for the design and performance analysis of ODC physical topologies in this paper. We introduce a new performance metric β(G ) to evaluate the gap between a physical topology G and the ideal physical topology. We develop a coupling technique that bypasses a significant amount of computational complexity of calculating β(G). Using β(G ) and the coupling technique, we study four physical topologies that are representative of those in literature, analyze their scalabilities and prove their performance guarantees. Our analysis may provide new guidance for network operators to design better physical topologies for their ODCs.

Experimental design for verification and validation of harmonic vibration control systems

Verification and validation represent an important procedure for model-based systems engineering design processes. One of the crucial tasks for verification and validation is to test whether the control system has reached performance limit. This is challenging since complicated theories and complex steps are often involved to achieve such an objective; meanwhile, the state of the art for testing performance limit requires iterative procedures. A simple and one-off experimental design for telling whether a control system reaches its performance limit is thus necessitated. This article introduces a remarkable test criterion for fulfilling the requirement. Both theoretical foundation and experiment design procedures are presented. Numerical examples are illustrated for the proposed method, where it is also shown that the simple method can be generalized to determining performance limit maps over both frequencies and physical parameters.

Oxygen-Defect Enhanced Anion Adsorption Energy Toward Super-Rate and Durable Cathode for Ni–Zn Batteries

The alkaline zinc-based batteries with high energy density are becoming a research hotspot. However, the poor cycle stability and low-rate performance limit their wide application. Herein, ultra-thin CoNiO2 nanosheet with rich oxygen defects anchored on the vertically arranged Ni nanotube arrays (Od-CNO@Ni NTs) is used as a positive material for rechargeable alkaline Ni–Zn batteries. As the highly uniform Ni nanotube arrays provide a fast electron/ion transport path and abundant active sites, the Od-CNO@Ni NTs electrode delivers excellent capacity (432.7 mAh g−1) and rate capability (218.3 mAh g−1 at 60 A g−1). Moreover, our Od-CNO@Ni NTs//Zn battery is capable of an ultra-long lifespan (93.0% of initial capacity after 5000 cycles), extremely high energy density of 547.5 Wh kg−1 and power density of 92.9 kW kg−1 (based on the mass of cathode active substance). Meanwhile, the theoretical calculations reveal that the oxygen defects can enhance the interaction between electrode surface and electrolyte ions, contributing to higher capacity. This work opens a reasonable idea for the development of ultra-durable, ultra-fast, and high-energy Ni–Zn battery."Image missing"

Opposite Peak Ratio to Characterize Ground Motion Loading History for Performance-Based Design

Recent studies have revealed the impact of ground motion loading history on performance limit states of reinforced concrete (RC) bridge columns such as reinforcement bar-buckling and residual drift ratio. Conventional hazard characterizations such as peak ground acceleration, spectral acceleration, and spectral displacement only capture peak values of ground motion hazard and, therefore, fall short of providing the necessary information to account for these limit states. In this study, a parameter termed as the opposite peak ratio (Rop) is defined, explored, and shown to be useful in reproducing loading history characteristics of ground motions for displacement-based design. Several past ground motion records were analyzed to develop empirical models that can estimate Rop. These models provide the mean and confidence intervals of Rop as a function of earthquake magnitude, epicentral distance, structural period, hysteretic model, and displacement ductility. To motivate practitioners to make use of Rop, a design scenario and two case studies are discussed. In an RC bridge column design scenario, it is shown that having prior information about the expected Rop at the site could reduce the structural cost of the bridge. Next, case studies designed to investigate correlations between Rop and the performance limit states of RC bridge columns are discussed. By analyzing the results of nonlinear time-history analyses of numerical RC column models, it is established that Rop could potentially be a significant variable in generating fragility models for these limit-states.