Optimization design of a micro-perforated panel absorber with 8.6 octave bands

In order to improve low-frequency characteristics of micro-perforated panel absorbers, sound absorption structures composed of micro-perforated panels and expansion chambers are design, and an optimization design method is constructed based on the transfer function model and the simulated annealing algorithm. First, a single-chamber structure composed of a micro-perforated panel and an expansion chamber is build, and the sound absorption curve is simulated by the finite element method. Second, for the sake of enlarging the continuous absorption bandwidth with absorption coefficients not less than 0.8, a three-chamber structure is designed, which has a sound absorption bandwidth of 1277Hz (27-1304Hz) covering 5.6 octave bands. Then, the transfer function model of the structure is established, and a series of theoretical formulae are derived to calculate the absorption coefficients. Subsequently, the sound absorption bandwidths calculated by the theoretical formulae and the finite element method are compared, and the relative error is 3.68%. Finally, an optimization design method is constructed by combining the transfer function model and the simulated annealing algorithm, where the optimization objective is to maximize the absorption bandwidth and the optimization variables are structural parameters of the three-chamber structure. The results show, after optimization, the three-chamber structure exhibits an excellent sound absorption performance, with a continuous bandwidth of 1591Hz (4-1595Hz), realizing 8.6 octave bands

Platform-Based Online Services, Competitive Actions, And E-Marketplace Seller Performance

Platform-based services are online services provided by e-marketplace operators to online sellers for them to compete and enhance performance. This paper aims at examining two important questions in the context of e-marketplace: (1) what kind of platform-based services can be used by online retail sellers as competitive moves? and (2) to what extent does the usage of these platform-based services impact online seller’s performance? Drawing on competitive dynamics theory, we argue that sellers that undertake a larger number of, more complex and heterogeneous platform-based services achieve better performance in e-marketplace. Using data of 1046 sellers, who open online retail stores and sell cosmetics on Taobao, a Chinese e-marketplace, we found that while undertaking more complex platform-based services is important by itself, it is more important to be strategic by undertaking a large number of platform-based services and these services had better be different from its competitors and the industry. Implications for practice and research and suggestions for future research on improving sellers’ competitiveness are discussed. This research was supported in part by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China (No. CityU 141809)

High-efficiency photoelectric detector based on a p-n homojunction of monolayer black phosphorus

We numerically investigate the high-efficiency photovoltaic effect in lateral p-n homojunction based on monolayer black phosphorus (MBP) by using the non-equilibrium Green's function combined with the density functional theory. Due to the built-in electric field of the p-n junction and the wrinkle structure of MBP, the photocurrent excited by either linearly or elliptically polarized light is significantly enhanced in a wide photon energy range. Moreover, because of the electron-photon interaction, the photocurrent is related to atomic orbitals through the polarizing angle of polarized light. Therefore, we can read the orbital information of the band structure from the polarizing angular distribution of photocurrent. These findings suggest the promising application of MBP-based p-n homojunction in high-efficiency photoelectric devices and orbital-resolved photovoltaic detection

3,3,6,6,9,9-Hexamethyl-2,3,4,5,6,7,8,9-octa­hydro-1H-xanthene-1,8-dione

The title compound, C19H26O3, was synthesized directly from the condensation of 5,5-dimethyl­cyclo­hexane-1,3-dione with malononitrile catalysed by palladium chloride: there are two molecules in the asymmetric unit

Improved belief propagation decoding algorithm based on decoupling representation of Pauli operators for quantum LDPC codes

We propose a new method called decoupling representation to represent Pauli operators as vectors over GF(2), based on which we propose partially decoupled belief propagation and fully decoupled belief propagation decoding algorithm for quantum low density parity-check codes. Under the assumption that there is no measurement error, compared with traditional belief propagation algorithm in symplectic representation over GF(2), within the same number of iterations, the decoding accuracy of partially decoupled belief propagation and fully decoupled belief propagation algorithm is significantly improved in pure Y noise channel and depolarizing noise channel, which supports that decoding algorithms of quantum error correcting codes might have better performance in decoupling representation than in symplectic representation. The impressive performance of fully decoupled belief propagation algorithm might promote the realization of quantum error correcting codes in engineering

Fast Computation of Single Scattering in Participating Media with Refractive Boundaries using Frequency Analysis

International audienceMany materials combine a refractive boundary and a participating media on the interior. If the material has a low opacity, single scattering effects dominate in its appearance. Refraction at the boundary concentrates the incoming light, resulting in an important phenomenon called volume caustics. This phenomenon is hard to simulate. Previous methods used point-based light transport, but attributed point samples inefficiently, resulting in long computation time. In this paper, we use frequency analysis of light transport to allocate point samples efficiently. Our method works in two steps: in the first step, we compute volume samples along with their covariance matrices, encoding the illumination frequency content in a compact way. In the rendering step, we use the covariance matrices to compute the kernel size for each volume sample: small kernel for high-frequency single scattering, large kernel for lower frequencies. Our algorithm computes volume caustics with fewer volume samples, with no loss of quality. Our method is both faster and uses less memory than the original method. It is roughly twice as fast and uses one fifth of the memory. The extra cost of computing covariance matrices for frequency information is negligible