Symplectic Schemes for Birkhoffian System

A universal symplectic structure for a Newtonian system including nonconservative cases can be constructed in the framework of Birkhoffian generalization of Hamiltonian mechanics. In this paper the symplectic geometry structure of Birkhoffian system is discussed, then the symplecticity of Birkhoffian phase flow is presented. Based on these properties we give a way to construct symplectic schemes for Birkhoffian system by using the generating function method

Adaptive Integration of Audio and Visual Information Using Discrete and Semi-Continuous Hidden Markov Models in Audiovisual Automatic Speech Recognition

An audiovisual semi-continuous hidden Markov model (HMM)-based Automatic Speech Recognition (ASR) system and an improved method of integrating audio and visual information in an audiovisual discrete HMM-based ASR system are investigated. In the audiovisual discrete HMM, an adaptive integration formulation is employed, which incorporates the integration into the HMM at a pre-categorical stage. A visual weighting parameter is determined automatically, which allows the relative contribution of audio and visual information to be adjusted adaptively. Using an adaptive weight, the accuracy increased by 13% compared to the same model with no adaptive weight. The semi-continuous HMM is a class of models which includes both discrete and continuous mixture HMMs as its special forms and unifies vector quantization (VQ) the discrete HMM, and the continuous mixture HMM. It reduces the vector quantization distortion of discrete HMMs by using continuous output probability density functions represented by a combination of the discrete output probabilities of the model and the continuous Gaussian probability density functions (pdfs) associated with each VQ symbol. The parameters of the vector quantization codebook and the HMM can be optimized together to achieve a unified modeling approach. Experimental results show that the recognition performance could be improved significantly in a relatively low signal-to-noise ratio environment by using the semi-continuous HMMs and the accuracy could be increased 9% on average. The modified Gaussian pdfs, which are Gaussian within two standard deviation but have heavier Laplacian tails, is first used in the classification procedure of the semicontinuous HMM in this thesis. It is an efficient way to compensate for inadequate training of Gaussian pdfs, or different testing and training environments

Anisotropic intrinsic lattice thermal conductivity of phosphorene from first principles

Phosphorene, the single layer counterpart of black phosphorus, is a novel two-dimensional semiconductor with high carrier mobility and a large fundamental direct band gap, which has attracted tremendous interest recently. Its potential applications in nano-electronics and thermoelectrics call for a fundamental study of the phonon transport. Here, we calculate the intrinsic lattice thermal conductivity of phosphorene by solving the phonon Boltzmann transport equation (BTE) based on first-principles calculations. The thermal conductivity of phosphorene at $300\,\mathrm{K}$ is $30.15\,\mathrm{Wm^{-1}K^{-1}}$ (zigzag) and $13.65\,\mathrm{Wm^{-1}K^{-1}}$ (armchair), showing an obvious anisotropy along different directions. The calculated thermal conductivity fits perfectly to the inverse relation with temperature when the temperature is higher than Debye temperature ($\Theta_D = 278.66\,\mathrm{K}$). In comparison to graphene, the minor contribution around $5\%$ of the ZA mode is responsible for the low thermal conductivity of phosphorene. In addition, the representative mean free path (MFP), a critical size for phonon transport, is also obtained.Comment: 5 pages and 6 figures, Supplemental Material available as http://www.rsc.org/suppdata/cp/c4/c4cp04858j/c4cp04858j1.pd