Testing cosmic opacity from SNe Ia and Hubble parameter through three cosmological-model-independent methods

We use the newly published 28 observational Hubble parameter data ($H(z)$) and current largest SNe Ia samples (Union2.1) to test whether the universe is transparent. Three cosmological-model-independent methods (nearby SNe Ia method, interpolation method and smoothing method) are proposed through comparing opacity-free distance modulus from Hubble parameter data and opacity-dependent distance modulus from SNe Ia . Two parameterizations, $\tau(z)=2\epsilon z$ and $\tau(z)=(1+z)^{2\epsilon}-1$ are adopted for the optical depth associated to the cosmic absorption. We find that the results are not sensitive to the methods and parameterizations. Our results support a transparent universe.Comment: 11 pages, 8 figures, 1 table, PLB(in press

The Effect of Honeycomb Cavity: Acoustic Performance of a Double-leaf Micro Perforated Panel

A micro perforated panel (MPP) is a device consisting of a thin plate and submillimeter perforations for reducing low frequency noise. MPPs have many advantages compared to traditional sound absorption materials, such as durability and designability, and they can be used in a variety of places such as room interior designs, passenger and crew compartments of aircrafts and combustion engines. The models in this study were designed and fabricated with the latest 3-D printing technology. The transmission loss and sound absorption coefficient of the 3-D printed double-leaf MPPs with honeycomb cavities were studied. According to the established theory, MPPs work well with the help of a backing and a cavity. Earlier experimental and theoretical developments have suggested that the acoustic performance of the MPPs can be improved by partitioning the backing cavity. A Brüel & Kjær type 4206 impedance tube was used for the experiments and the one-load method was implemented for calculating the absorption and transmission coefficients of the MPPs. A honeycomb structure was chosen to be placed in the cavity because it can provide the required partitions between perforated panels so that the overall transmission loss was expected to be higher than those without the cavity partitioning. Measured results indicated that use of the honeycomb structure in the cavity have improved the acoustic performance of the MPPs. The sound absorption coefficient of a double-leaf MPP was similar to that of a single-leaf MPP if the cavity was long enough. Future studies should involve an investigation of the acoustic performance of the MPPs at oblique angles of incidence because the current study only provides the pertinent information at normal incidence since the standing wave tubes were used in the experiments

Local Cyber-physical Attack with Leveraging Detection in Smart Grid

A well-designed attack in the power system can cause an initial failure and then results in large-scale cascade failure. Several works have discussed power system attack through false data injection, line-maintaining attack, and line-removing attack. However, the existing methods need to continuously attack the system for a long time, and, unfortunately, the performance cannot be guaranteed if the system states vary. To overcome this issue, we consider a new type of attack strategy called combinational attack which masks a line-outage at one position but misleads the control center on line outage at another position. Therefore, the topology information in the control center is interfered by our attack. We also offer a procedure of selecting the vulnerable lines of its kind. The proposed method can effectively and continuously deceive the control center in identifying the actual position of line-outage. The system under attack will be exposed to increasing risks as the attack continuously. Simulation results validate the efficiency of the proposed attack strategy.Comment: Accepted by IEEE SmartGridComm 201