Methanol Conversion into Dimethyl Ether on the Anatase TiO2(001) Surface

Exploring reactions of methanol on TiO₂ surfaces is of great importance in both C1 chemistry and photocatalysis. Reported herein is a combined experimental and theoretical calculation study of methanol adsorption and reaction on a mineral anatase TiO₂(001)‐(1×4) surface. The methanol‐to‐dimethyl ether (DME) reaction was unambiguously identified to occur by the dehydration coupling of methoxy species at the fourfold‐coordinated Ti⁴⁺ sites (Ti_4c), and for the first time confirms the predicted higher reactivity of this facet compared to other reported TiO₂ facets. Surface chemistry of methanol on the anatase TiO₂(001)‐(1×4) surface is seldom affected by co‐chemisorbed water. These results not only greatly deepen the fundamental understanding of elementary surface reactions of methanol on TiO₂ surfaces but also show that TiO₂ with a high density of Ti_4c sites is a potentially active and selective catalyst for the important methanol‐to‐DME reaction.     

Real-time distortion correction of fish-eye lens based on Bayer image signal

The imaging system based on a fish-eye lens generally has to correct the distortion of fish-eye images. The distortion correction based on the Bayer image signal is valuable, such as reducing the computation burden of image signal processing chips and providing a new imaging system structure of fish-eye lens. In this paper, a distortion correction method of fish-eye lens based on the Bayer image signal is proposed. Firstly, a distortion correction method that focuses on vertical straight lines and processing delay is proposed. Secondly, according to the correlation among color channels of the Bayer image, a novel Hermite interpolation method appropriate for Bayer image signal is proposed. Finally, a prototype system of fish-eye-lens-based imaging is established and the real-time field-programmable gate array (FPGA) implementation of the proposed method is demonstrated. The experiment demonstrates that the proposed distortion correction is not only characteristic of real-time processing and the smaller computation amount, but also applicable to embedded hardware.     

Influence of the deposition parameters on the properties of SnS2 films prepared by PECVD method combined with solid sources

We report a simple and rapid biological approach to synthesize water-soluble and highly roughened “meatball”-like Au nanoparticles using green tea extract under microwave irradiation. The synthesized Au meatball-like nanoparticles possess excellent monodispersity and uniform size (250 nm in diameter). Raman measurements show that these tea-generated meatball-like gold nanostructures with high active surface areas exhibit a high enhancement of surface-enhanced Raman scattering. In addition, the Au meatball-like nanoparticles demonstrate good biocompatibility and remarkable in vitro stability at the biological temperature. Meanwhile, the factors that influence the Au meatball-like nanoparticles morphology are investigated, and the mechanisms behind the nonspherical shape evolution are discussed.     

A general modal approach for the development of optimal multi-layer stacked vibration energy harvesters

Piezoelectric vibration energy harvesters with multi-layer stacked structures have been developed. They consist of multi-layer beams, of zigzag configurations, with rigid masses attached between the beams. The rigid masses, which also serve as spacers, are attached to each layer to tune the frequencies of the harvester. Close resonance frequencies and considerable power output can be achieved in multiple modes by varying the positions of the masses. A modal approach is introduced to determine the modal performance conveniently using the mass ratio and the modal electromechanical coupling coefficient, and the required modal parameters are derived using the finite element method. Mass ratio represents the influence of modal mechanical behaviour on the power density. Since the modes with larger mass ratios cause the remaining modes to have smaller mass ratios and lower power densities, a screening process using the modal approach is developed to determine the optimal or near-optimal performance of the harvesters when altering mass positions. This procedure obviates the need for full analysis by pre-selecting the harvester configurations with close resonances and favourable values of mass ratio initially. Furthermore, the multi-layer stacked designs using the modal approach can be used to develop harvesters with different sizes with the power ranging from microwatts to milliwatts.     

Characteristics analysis of extruded elliptical hole photonic crystal fibers with square air-core

An extruded elliptical hole photonic crystal fibers PCF with square air-core is proposed. By using a full vector finite-element method FV-FEM and anisotropic perfectly matched layers APML, the structure and optical properties of the proposed PCF are analyzed. Simulation results show that the birefringence of the proposed photonic crystal fiber can be up to the order of 10⁻², and has a flattened dispersion from 1.20 μm to 1.80 μm. The proposed PCF may have important application in super-continuum SC generation, dispersion compensation, fiber-optic sensing systems and other aspects.     

Relative density-based classification noise detection

Classification noise is a common byproduct of traditional data mining approaches, and no specialized approach for detecting classification noise is currently available. Methods for outlier detection are well-developed, but outliers and classification noise have characteristics different enough to make outlier detection algorithms unsuitable for classification noise detection. In this paper, a new, specialized approach to detect classification noise is proposed, named relative density based classification noise detection (RDBCND). Computational experiments in artificial data sets described herein show that RDBCND has time complexity of O(n log n), indicating greater efficiency than traditional approaches, which exhibit time complexity of at least O(n²). The use of classification noise detection to improve the generalization ability of common classifier algorithms is also described. In particular, a new unified approach based on RDBCND is compared to a cross validation approach applied to a BP neural network. Trials in both artificial and real-life datasets show that the RDBCND-based approach can greatly accelerate the process of identifying the best decision function. The novel method can also eliminate underfitting, as the algorithm simply searches for the highest training accuracy. The experiments also show that the RDBCND-based method has greater accuracy and lower cpu time in reaching global solutions than the cross-validation method. Since the relative density is a local concept, our new approach can be directly used in nonlinear datasets without data transformation. It is a great advantage compared to some linear classifier algorithms. As in current linear classifiers, the kernel functions or other transformations need to be used to make them suitable for non-linear datasets, and that will increase their complexity.     

Colossal enhancement in thermoelectric effect in a laterally coupled double-quantum-dot chain by the Coulomb interactions

Thermoelectric effects, including Seebeck coefficient (S), thermal conductance (κ), and figure of merit (ZT), in a laterally coupled double-quantum-dot (DQD) chain with two external nonmagnetic contacts are investigated theoretically by the nonequilibrium Green's function formalism. In this system, the DQD chain between two contacts forms a main channel for thermal electrons transporting, and each QD in the main chain couples laterally to a dangling one. The numerical calculations show that the Coulomb interactions not only lead to the splitting of the asymmetrical double-peak structure of the Seebeck coefficient, but also make the thermal spectrum show a strong violation of the Wiedemann–Franz law, leading to a colossal enhancement in ZT. These results indicate that the coupled DQD chain has potential applications in the thermoelectric devices with high thermal efficiency.     

Fiber-optic sensor based on evanescent wave absorbance around 2.7 μm for determining water content in polar organic solvents

The feasibility of sapphire fiber-optic sensors based on evanescent wave absorption spectroscopy in the infrared range for quantitative determination of water content in polar organic solvents has been investigated. Evanescent wave absorption spectra of sapphire fiber-optic sensors in glycerol, ethanol, and glycol with different water concentrations obtained and analyzed, respectively. Evanescent absorbance of the sensors in those organic solvents has been utilized to implement for in situ monitoring water concentration in organic solvents. The evanescent absorbance of sensors in glycerol and glycol has been found to vary linearly with water content in the range 0–30 % and in ethanol in the range 0–10 %, respectively. The fiber-optic sensors based on evanescent absorbance for monitoring water concentrations in those organic solvents are acceptably accurate, cost-effective, and reliable. Some methods to improve the accuracy of predicated water content in those organic solvents are also suggested. Overall, the results demonstrate that the sapphire fiber-optic sensor based on evanescent absorption spectroscopy is a promising candidate for prediction of water content in polar organic solvents in on-line and remote situation.     

耀变体S5 0716+714的混沌特性研究

长期观测显示,耀变体S5 0716+714具有复杂的光变行为.本文运用混沌理论,研究了S5 0716+714四个较大爆发阶段的射电、光学和X波段的光变曲线.分别计算了它们的关联维和Lyapunov指数.结果表明:1)光变曲线的关联维和Lyapunov指数都介于纯混沌系统与随机噪声之间;2)相轨迹是一个与Rossler吸引子相似的混沌系统,由于受到各种内在或外在因素的影响产生噪声,导致关联维和Lyapunov指数均比Rossler吸引子大,相轨迹出现紊乱.从这两个混沌判据上看,三个波段均表现出很强的混沌特性,因此推断S50714+716的光变是一个混沌现象.