Explicit cosmological coarse graining via spatial averaging

The present matter density of the Universe, while highly inhomogeneous on small scales, displays approximate homogeneity on large scales. We propose that whereas it is justified to use the Friedmann–Lemaître–Robertson–Walker (FLRW) line element (which describes an exactly homogeneous and isotropic universe) as a template to construct luminosity distances in order to compare observations with theory, the evolution of the scale factor in such a construction must be governed not by the standard Einstein equations for the FLRW metric, but by the modified Friedmann equations derived by Buchert (Gen Relat Gravit 32:105, 2000; 33:1381, 2001) in the context of spatial averaging in Cosmology. Furthermore, we argue that this scale factor, defined in the spatially averaged cosmology, will correspond to the effective FLRW metric provided the size of the averaging domain coincides with the scale at which cosmological homogeneity arises. This allows us, in principle, to compare predictions of a spatially averaged cosmology with observations, in the standard manner, for instance by computing the luminosity distance versus red-shift relation. The predictions of the spatially averaged cosmology would in general differ from standard FLRW cosmology, because the scale-factor now obeys the modified FLRW equations. This could help determine, by comparing with observations, whether or not cosmological inhomogeneities are an alternative explanation for the observed cosmic acceleration.     

Depth-adaptive regularized reconstruction for reflection diffuse optical tomography

We study reflection diffuse optical tomography using two-dimensional (2D) continuous-wave source-detector arrays on the surface of semi-infinite medium, aiming at imaging the perfusion and the hemoglobin oxygen saturation variation of human cerebral cortex with brain activation. We had previously formulated the inverse problem with Moore-Penrose inversion. When we use simple regularization in this inverse problem, the reconstruction sensitivity decreases markedly with the depth so that the signal in the deep range may be masked by an unwanted signal in the shallow range. In this paper, we propose a depth-adaptive regularized reconstruction, in which we assign a smaller regularization parameter with the depth. We demonstrate improvement of the three-dimensional (3D) reconstruction uniformity using the proposed scheme.     

Brownian Approximation and Monte Carlo Simulation of the Non-Cutoff Kac Equation

The non-cutoff Boltzmann equation can be simulated using the DSMC method, by a truncation of the collision term. However, even for computing stationary solutions this may be very time consuming, in particular in situations far from equilibrium. By adding an appropriate diffusion, to the DSMC-method, the rate of convergence when the truncation is removed, may be greatly improved. We illustrate the technique on a toy model, the Kac equation, as well as on the full Boltzmann equation in a special case.     

Time Evolution of Spontaneous Emission Rate of Two Undistinguished Radiators

The behavior of the system of radiators at short and long time intervals in comparison with the retardation between them is studied. The entanglement behavior of atomic states in the process of spontaneous emission is determined. It is demonstrated that at a short time interval the rate of spontaneous emission in an oscillatory manner tends to the exponential law of spontaneous emission. The simple kinetic equation, which describes this stage of system evolution, is obtained.     

Pulsed laser deposition of high-quality ZnO films using a high temperature deposited ZnO buffer layer

High-quality ZnO film growth on sapphire was achieved by pulsed laser deposition using a high temperature deposited ZnO buffer layer. This high temperature deposited buffer layer remarkably improves crystallinity of subsequent films. In particular, the full width at half-maximum of X-ray diffraction ω-rocking curves for ZnO films grown with the buffer layer is 0.0076° (27.36 arcsec) and 0.1242° (447.12 arcsec) for the out-of-plane (002) and in-plane (102) reflections, respectively. In addition, ZnO films grown with this buffer layer showed a carrier mobility of 88 cm²/V s, which is three times higher than that realized for ZnO films grown without the buffer layer. The room temperature photoluminescence spectra showed strong band edge emission with little or no defect-related visible emission. PACS 78.55.Et; 81.05.Dz     

Grafting of PMMA brushes on titania nanoparticulate surface via surface-initiated conventional radical and “controlled” radical polymerization (ATRP)

Stable dispersion of titania nanoparticles in organic solvents are obtained by grafting poly(methyl methacrylate) layer on to the surface. Titania nanoparticles are synthesized through the hydrolysis of titanium (IV) isopropoxide. The average size of the titania particles is found to be 15 ± 2 nm. The polymer layer was introduced onto the surface by immobilizing the initiating moiety. Azo initiator moiety required for surface-initiated conventional free radical polymerization and a tertiary bromide initiator moiety required for ATRP are attached covalently to the titania nanoparticulate surface through the surface hydroxyl groups. The “encapsulation” of PMMA layer results in the steric stabilization of the titania nanoparticles. Another important finding is that it is possible to grow polymer layer in a controlled fashion.     

Evolution in shapes of a series of (111)-based In<Subscript>2</Subscript>O<Subscript>3</Subscript> particles

In₂O₃ particles with different morphology were controllably synthesized on silicon substrates by thermal evaporation of In grains at 900 °C. The structure and morphology of the In₂O₃ particles were evaluated using X-ray diffraction, and scanning and transmission electron microscopies. The evolution in shapes as the ratio of {100} relative to {111} increases is clearly observed. The photoluminescence spectrum of the obtained In₂O₃ structures exhibits UV emission centered at about 378 nm and wide-band emission covering the green and orange regions with three peaks around 525, 572, and 604 nm. PACS 81.05.Hd; 81.07.Bc; 81.16.-c; 61.46.-w; 81.40.Gh     

一种新颖的取样光纤光栅振幅版的研制

提出了一种新颖的用于制作取样光纤光栅的取样振幅版的设计方案,其特点是具有渐变的取样周期和不变的占空比,利用这种振幅版可以简单灵活地制作出反射峰波长间隔不同的取样光栅梳状滤波器,有利于提高取样光栅的制作灵活性并降低成本.对这种方法可能存在的不足也进行了分析.利用制作出的取样光栅,基于全光纤结构实现了具有游标尺式波长调谐机理的可选波长光纤激光器. 关键词： 取样光纤光栅 梳状滤波器 可选波长光纤激光器 振幅版     

聚龙一号装置上首次铝套筒Z箍缩X射线背光照相实验

在聚龙一号脉冲功率装置上首次完成了对带正弦扰动铝套筒Z箍缩的X射线背光照相实验。实验采用千焦耳激光器（1053 nm, 1 kJ, 1 ns）驱动固体靶材产生X射线, 然后利用基于球面晶体的单色背光照相技术以及直接点投影背光照相技术, 成功观测到约7.5 MA电流驱动条件下, Z箍缩铝套筒的外边界不稳定性发展情况。该实验验证了在聚龙一号装置上联合千焦耳激光器开展X射线背光照相实验的能力, 为后续精密Z箍缩物理研究奠定了基础。     

PSO优化LS-SVM在模拟电路故障预测中的应用

针对模拟电路故障预测的特点,提出一种基于PSO优化LS-SVM惩罚因子和核参数的模拟电路故障预测方法。利用小波包分解重构构造能量特征向量,通过计算PPMCC和欧氏距离来表征电路中元件的健康程度,定义为健康度,由此推导出电路发生故障时该元件的故障阈值。应用PSO优化的LS-SVM模型来实现模拟电路的故障预测,预测各个时间点的健康度变化轨迹并估计模拟电路的剩余寿命。通过仿真实验得知,该方法简单便捷,能够有效实现模拟电路的故障预测,具有较好的实用性。