Doped colloidal photonic crystal structure with refractive index chirping to the [111] crystallographic axis

A three-dimensionally ordered array of close-packed colloidal spheres, a photonic crystal structure in which the refractive index of the medium interstitial lattice in a colloidal crystal spatially changes in the [111] crystallographic axis, is demonstrated. The colloidal photonic crystal structure with refractive index chirping was produced by infiltration of a monomer and organic dopants with a high refractive index into a silica opal, followed by interfacial gel polymerization. The resulting photonic crystal structure has a gradually varying stop band at each different (111) plane in the face-centered cubic (fcc) crystal structure at a normal incidence. This novel structure exhibited optical characteristics that have band-gap broadening by the superposition of stop bands at each plane of the crystal with different dielectric functions. Moreover, the refractive index perturbation in the [111] fcc opal also showed a defect state within a pseudo-photonic band gap. This new type of photonic crystal structure should be useful for the band-gap engineering of photonic-band-gap materials.     

Noise reduction in ultrasonic NDT using undecimated wavelet transforms

Translation-invariant wavelet processing is applied to grain noise reduction in ultrasonic non-destructive testing of materials. In particular, the undecimated wavelet transform (UWT), which is essentially a discrete wavelet transform (DWT) that avoids decimation, is used. Two different UWT processors have been specifically developed for that purpose, based on two UWT implementation schemes: the "à trous" algorithm and the cycle-spinning scheme. The performance of these two UWT processors is compared with that of a classical DWT processor, by using synthetic grain noise registers and experimental pulse-echo NDT traces. The synthetic ultrasonic traces have been generated by an own-developed frequency-domain model that includes frequency dependence in both material attenuation and scattering. The experimental ultrasonic traces have been obtained by inspecting a piece of carbon-fiber reinforced plastic composite in which we have mechanized artificial flaws. Decomposition level-dependent thresholds, which are suitable for correlated noise, are specifically determined in all cases. Soft thresholding, Daubechies db6 mother wavelet and the three well-known threshold selection rules, Universal, Minimax and SURE, are applied to the different decomposition levels. The performance of the different de-noising procedures for single echo detection has been comparatively evaluated in terms of signal-to-noise ratio enhancement.     

A novel image recovery method based on discrete cosine transform and matched blocks

In this paper, we propose a method for image recovery based on Discrete Cosine Transform (DCT) and finding the best matched blocks by using a part of the fractal compression algorithm. At the same time, we propose a new check algorithm for checking if image blocks are tampered. First, the original image is divided into small blocks. The best matched block of each small block is searched in a particular way. Then the matching information is embedded as backup into other blocks. For the ones that fail to find the best matched blocks, DCT is applied on them and then quantized to be the backup. In order to prevent the backup of the tampered blocks from damaging, we generate 3 backups for each block and embed them into different quadrants. On the receiving side, the tampering check bits are extracted to localize the tampered areas, and the backup bits are used to restore the contents of the tampered regions. The experimental results have proved a good restorability of this algorithm, and the lower the tampering rate is, the better quality of restored content can be obtained.     

Transmission of the spin-spin coupling constants through hydrogen bonds in ammonia clusters

Spin-spin coupling constants are reported using six ab initio and fifteen DFT methods for dimers and larger clusters of ammonia. An analysis of components (Fermi contact, spin dipole, paramagnetic spin-orbit, and diamagnetic spin-orbit) of more relevant coupling constants ¹J_NH′, ^1hJ_NH′ and ^2hJ_NN has been carried out. Fermi contact is the dominant term in the total value for all constants. For dimers, a relationship between the addition of direct and intermolecular coupling constants gives the direct constants of monomer. From the comparison of all ab initio and DFT methods for dimers, SOPPA(CCSD) and S55VWN5 methods are, respectively, more reliable taking into account their accuracy and the computing time. Both methods are employed for the analysis of the transmission of coupling constants through the hydrogen bond for ammonia clusters. A linear relation between the intermolecular constants ^1hJ_NH′ and the length of the hydrogen bond is found.     

Study of diffusion and local structure of sodium-silicate liquid: the molecular dynamic simulation

A systematic analysis on sodium-silicate melt with various silica contents was carried out. The simulation revealed two diffusion mechanisms occurred in the melt: the bond-breaking and hopping between sites. The local structure was analyzed through T-simplexes. It was revealed that T-clusters have a non-spherical shape and represent the diffusion channel, in which Na atoms are dominant, but no any O atoms are located. The SiO₂-poor melt acquires a long channel. In contrast, the SiO₂-rich melt consists of unconnected short channels. The simulation also revealed the immobile and mobile regions which differ in local structure and constituent composition. We propose a new CL-function to characterizing the spatial distribution of different atom component. The spatial distribution of mobile and immobile atoms is found quite different. In particular, the immobile atoms are concentrated in high-density regions possessing very large density of immobile atoms. The spatial distribution of mobile atoms in contrast is more homogeneous.     

A Versatile Iron–Tannin‐Framework Ink Coating Strategy to Fabricate Biomass‐Derived Iron Carbide/Fe‐N‐Carbon Catalysts for Efficient Oxygen Reduction

The conversion of biomass into valuable carbon composites as efficient non‐precious metal oxygen‐reduction electrocatalysts is attractive for the development of commercially viable polymer electrolyte membrane fuel‐cell technology. Herein, a versatile iron–tannin‐framework ink coating strategy is developed to fabricate cellulose‐derived Fe₃C/Fe‐N‐C catalysts using commercial filter paper, tissue, or cotton as a carbon source, an iron–tannin framework as an iron source, and dicyandiamide as a nitrogen source. The oxygen reduction performance of the resultant Fe₃C/Fe‐N‐C catalysts shows a high onset potential (i.e. 0.98 V vs the reversible hydrogen electrode (RHE)), and large kinetic current density normalized to both geometric electrode area and mass of catalysts (6.4 mA cm^?2 and 32 mA mg^?1 at 0.80 V vs RHE) in alkaline condition. This method can even be used to prepare efficient catalysts using waste carbon sources, such as used polyurethane foam.     

Electrical and dielectric properties of Al/p-Si and Al/perylene/p-Si type diodes in a wide frequency range

The perylene(C20H12) layer effect on the electrical and dielectric properties of Al/p-Si(MS) and Al/perylene/p-Si(MPS) diodes have been investigated and compared in the frequency range of 0.7 kHz–2 MHz. Experimental results show that C–V characteristics give an anomalous peak for two structures at low frequencies due to interface states(Nss) and series resistance(Rs). The increases in C and G/ω at low frequencies confirm that the charges at interface can easily follow an ac signal and yield excess capacitance and conductance. The frequency-dependent dielectric constant(ε) and dielectric loss(ε) are subtracted using C and G/ω data at 1.5 V. The ε and ε values are found to be strongly dependent on frequency and voltage, and their large values at low frequencies can be attributed to the excess polarization coming from charges at traps. Plots of ln(σac)–ln(ω) for two structures have two linear regions, with slopes of 0.369 and 1.166 for MS, and of 0.077 and 1.061 for MPS, respectively. From the C 2–V characteristics, the doping acceptor atom concentration(NA) and barrier height(ΦB) for Schottky barrier diodes(SBDs) of MS and MPS types are also obtained to be 1.484 × 1015 and 1.303 × 1015cm 3, and 1.10 and 1.13 eV, respectively.     

Semiclassical Inverse Spectral Theory for Singularities of Focus–Focus Type

We prove, assuming that the Bohr–Sommerfeld rules hold, that the joint spectrum near a focus–focus singular value of a quantum integrable system determines the classical Lagrangian foliation around the full focus–focus leaf. The result applies, for instance, to ?-pseudodifferential operators on cotangent bundles and Berezin–Toeplitz operators on prequantizable compact symplectic manifolds.     

静电式同位素辐射能量收集器的研究

针对目前无线传感网络节点对长寿命微能源的需求,提出了将同位素辐射能量转换为电能的静电式振动能量收集原理.该原理利用同位素63Niβ辐射能实现平行板悬浮-质量块结构的自由阻尼振动,并通过可变电容电路实现充-放电振荡循环,从而实现电能的转换.通过分析运动状态和能量转化过程,给出了结构的运动状态和能量输出方程,并使用Matlab/Simulink对输出特性进行了数值模拟和基于Ansys的结构优化设计.根据仿真和优化的结构尺寸设计出了满足最大平均输出功率的微电子机械器件结构.结果表明:所设计的结构在一阶固有频率为500 Hz,两极板间距离为75μm,外接电阻为90 k?时平均输出功率最大为0.416μW,转化效率8.25%.