扩散模型中扩散系数的非参数组合估计

为了提高扩散系数估计的准确度, 我们利用动态组合时间域与状态域信息提出一个新的组合估计量. 我们发现所提组合估计量能有效估计扩散模型的扩散系数, 正如在本文中模拟所示. 在一定的条件下, 建立了估计量的渐进正态性, 并证明了时间域估计量与状态域估计量是渐进独立的. 大量的模拟展示了所提组合估计量优于单域估计量, 也优于本文所提估计量.     

工科力学如何训练及培养学生探索未知的能力

本文介绍了作者在工科力学教学中进行的三层次训练与考核,并阐述了它们在训练及培养学生探索未知的能力方面的重要作用。     

Well-posedness and dynamics of fractional FitzHugh-Nagumo systems on ℝN driven by nonlinear noise

This article is concerned with the well-posedness as well as long-term dynamics of a wide class of non-autonomous, non-local, fractional, stochastic FitzHugh-Nagumo systems driven by nonlinear noise defined on the entire space?R^N. The well-posedness is proved for the systems with polynomial drift terms of arbitrary order as well as locally Lipschitz nonlinear diffusion terms by utilizing the pathwise and mean square uniform estimates. The mean random dynamical system generated by the solution operators is proved to possess a unique weak pullback mean random attractor in a Bochner space. The existence of invariant measures is also established for the autonomous systems with globally Lipschitz continuous diffusion terms. The idea of uniform tail-estimates of the solutions in the appropriate spaces is employed to derive the tightness of a family of probability distributions of the solutions in order to overcome the non-compactness of the standard Sobolev embeddings on ?^N as well as the lack of smoothing effect on one component of the solutions. The results of this paper are new even when the fractional Laplacian is replaced by the standard Laplacian.

     

工科力学教学如何讲科学思想与思维方法

本文通过能量和时空二个基本观点,以及稳定性、对称性和等效性三性,探索在工科力学教学中如何对学生进行科学思想和思维方法的教学。     

中国化工实业家──范旭东

1 早年留日 创办盐碱 范旭东(1$83-1945),原名范源让,字明俊,1883年10月25日生于湖南长沙东乡。早年留学日本,改名范锐,字旭东,1901年在日本清华学堂学习日语,1905年毕业于和歌山中学,同年考入岗山第六高等学校学习医学,1908年考入日本京都帝国大学应用化学科。     

How to Look for Compounds: Predictive Screening and in situ Studies in Na−Zn−Bi System

Here, the combination of theoretical computations followed by rapid experimental screening and in situ diffraction studies is demonstrated as a powerful strategy for novel compounds discovery. When applied for the previously “empty” Na−Zn−Bi system, such an approach led to four novel phases. The compositional space of this system was rapidly screened via the hydride route method and the theoretically predicted NaZnBi (PbClF type, P4/nmm) and Na₁₁Zn₂Bi₅ (Na₁₁Cd₂Sb₅ type, P ) phases were successfully synthesized, while other computationally generated compounds on the list were rejected. In addition, single crystal X-ray diffraction studies of NaZnBi indicate minor deviations from the stoichiometric 1 : 1 : 1 molar ratio. As a result, two isostructural (PbClF type, P4/nmm) Zn-deficient phases with similar compositions, but distinctly different unit cell parameters were discovered. The vacancies on Zn sites and unit cell expansion were rationalized from bonding analysis using electronic structure calculations on stoichiometric “NaZnBi”. In-situ synchrotron powder X-ray diffraction studies shed light on complex equilibria in the Na−Zn−Bi system at elevated temperatures. In particular, the high-temperature polymorph HT-Na₃Bi (BiF₃ type, Fm m) was obtained as a product of Na₁₁Zn₂Bi₅ decomposition above 611 K. HT-Na₃Bi cannot be stabilized at room temperature by quenching, and this type of structure was earlier observed in the high-pressure polymorph HP-Na₃Bi above 0.5 GPa. The aforementioned approach of predictive synthesis can be extended to other multinary systems.     

工科力学要大力发展典型模型教学

本文指出了典型模型在工科力学教学中的重要作用,并以各类具体模型为例,介绍作者在华中科技大学如何发展力学中的模型教学。     

Asymptotic autonomy of random attractors for BBM equations with Laplace-multiplier noise

We study asymptotic autonomy of random attractors for possibly non-autonomous Benjamin-Bona-Mahony equations perturbed by Laplace-multiplier noise. We assume that the time-indexed force converges to the time-independent force as the time-parameter tends to negative infinity, and then show that the time-indexed force is backward tempered and backward tail-small. These properties allow us to show that the asymptotic compactness of the non-autonomous system is uniform in the past, and then obtain a backward compact random attractor when the attracted universe consists of all backward tempered sets. More importantly, we prove backward convergence from time-fibers of the non-autonomous attractor to the autonomous attractor. Measurability of solution mapping, absorbing set and attractor is rigorously proved by using Egoroff, Lusin and Riesz theorems.     

A power allocation method for $$2 \times 2$$ VLC-MIMO indoor communication

Visible light communication (VLC) has been a promising field of optical communications which focuses on visible light spectrum that humans can see. Unlike existing studies which mainly discuss point-to-point communication, in this paper, we consider a VLC network, in particular a \(2 \times 2\) system. Our focus is on dealing with interference in this network. The objective is to maximize the signal to interference plus noise ratio (SINR) of one receiver for a given SINR of another receiver. We formulate a power allocation optimization problem to deal with such interference, and introduce dichotomy to solve this optimization problem. Simulation results have twofold meaning: First, \(\mathrm{SINR}_1\) increases with the growth of \(\mathrm{SINR}_2\), which are the SINR of the two receivers, respectively. Second, our proposed scheme outperforms the classical time-division multiple access technique in terms of transmit powers of both light sources when the data rate for these two schemes are set to be identical for each user, respectively.     

茶与化学

饮茶在我国有数千年历史 ,且经久不衰 ,现在几乎普及至世界所有国家和地区 ,这是基于茶叶中含有 6 0 0多种化学成分 ,其中大多数成分对人体有营养保健作用以及对许多疾病有预防和治疗功效。