Tingfeng Wang

Mesoporous Transition Metal Oxides for Supercapacitors

Recently, transition metal oxides, such as ruthenium oxide (RuO2), manganese dioxide (MnO2), nickel oxides (NiO) and cobalt oxide (Co3O4), have been widely investigated as electrode materials for pseudo-capacitors. In particular, these metal oxides with mesoporous structures have become very hot nanomaterials in the field of supercapacitors owing to their large specific surface areas and suitable pore size distributions. The high specific capacities of these mesoporous metal oxides are resulted from the effective contacts between electrode materials and electrolytes as well as fast transportation of ions and electrons in the bulk of electrode and at the interface of electrode and electrolyte. During the past decade, many achievements on mesoporous transition metal oxides have been made. In this mini-review, we select several typical nanomaterials, such as RuO2, MnO2, NiO, Co3O4 and nickel cobaltite (NiCo2O4), and briefly summarize the recent research progress of these mesoporous transition metal oxides-based electrodes in the field of supercapacitors.

Phase matching analysis of noncollinear optical parametric process in nonlinear anisotropic crystals

Phase matching for noncollinear optical parametric generation is investigated. All the possible phase matching configurations and existence conditions for general noncollinear three-wave mixing interactions are derived for propagation within the crystal principal planes. Numerical expressions for the critical phase matching angles are presented wherever possible. Finally, as an application of these expressions, several numerical calculations of the phase matching angles for general noncollinear phase matched optical parametric amplification in the nonlinear-optical crystals such as beta -BaB2O4, LiB3O5 and KTiOPO4 are completed. and the results are graphically presented

Optimally enhanced optical emission in laser-induced air plasma by femtosecond double-pulse

In laser-induced breakdown spectroscopy, a femtosecond double-pulse laser was used to induce air plasma. The plasma spectroscopy was observed to lead to significant increase of the intensity and reproducibility of the optical emission signal compared to femtosecond single-pulse laser. In particular, the optical emission intensity can be optimized by adjusting the delay time of femtosecond double-pulse. An appropriate pulse-to-pulse delay was selected, that was typically about 50 ps. This effect can be especially advantageous in the context of femtosecond laser-induced breakdown spectroscopy, plasma channel, and so on.

Comparison of plasma temperature and electron density on nanosecond laser ablation of Cu and nano-Cu

Laser-induced breakdown spectroscopy is performed through the collection of spectra by spectral detection equipment at different delay times and distances from targets composed of Cu and nano-Cu, which are ablated using a Nd:YAG laser (532 nm, 10 ns, 10 Hz) in our experiments. The measured wavelength range is from 475 nm to 525 nm. Using the local thermodynamic equilibrium model, we analyze the characteristics of the plasma temperature and the electron number density for different distances between the target surface and the lens. The results show that when compared with the nano-Cu plasma case, the temperature of the Cu plasma is higher, while its electron number density is lower.

A novel single multiplicative neuron model trained by an improved glowworm swarm optimization algorithm for time series prediction

To better predict time series, in this paper the single multiplicative recurrent neuron (SMRN) is constructed by adding feedforward and feedback links at the nodes of the original single multiplicative neuron (SMN). Glowworm swarm optimization (GSO) algorithm as a method for training the parameters of various kinds of neural network models gets easily into locally optimal traps during optimization process and its movement stability is also poor because of no memory about search history. To overcome the aforementioned disadvantages, firstly the linearly declining inertia weight is incorporated into the location update formula of standard GSO (LWGSO). After that in order to further enhance the robustness capability, differential evolution (DE) algorithm is introduced into LWGSO forming LWGSODE. Standard unimodal and multi-modal static test functions in high dimensions have been used to test its properties. The statistically experimental results show that the proposed LWGSODE approach performs much better than basic GSO whatever in terms of solutions precision, robustness or convergence speed. Moreover, the function optimization results are also competitive when compared with other state-of-the-art methods in the literature. Finally, the LWGSODE algorithm is used to train SMRN for time series prediction, and approximation results have improved significantly. All the results obtained reveal the novel SMRN model combined with the proposed LWGSODE algorithm provides a promising means to approximate nonlinear series in the future.

Mathematic model analysis of Gaussian beam propagation through an arbitrary thickness random phase screen.

In order to research the statistical properties of Gaussian beam propagation through an arbitrary thickness random phase screen for adaptive optics and laser communication application in the laboratory, we establish mathematic models of statistical quantities, which are based on the Rytov method and the thin phase screen model, involved in the propagation process. And the analytic results are developed for an arbitrary thickness phase screen based on the Kolmogorov power spectrum. The comparison between the arbitrary thickness phase screen and the thin phase screen shows that it is more suitable for our results to describe the generalized case, especially the scintillation index.

Carbon-based optical limiting materials

In this mini-review, special attention has been paid to carbon-based optical limiting materials. After a brief introduction to optical limiting mechanisms of carbon-based optical materials and their characterization technique, this mini-review presents the recent progress of carbon-based optical limiting materials including carbon black suspensions (CBS), carbon nanotubes (CNTs), fullerenes, graphene and detonation nanodiamond. Finally, perspectives on carbon-based optical limiting are given.

Global μ-stability of impulsive reaction–diffusion neural networks with unbounded time-varying delays and bounded continuously distributed delays☆

Abstract This paper investigates the global μ-stability for impulsive cellular neural networks with reaction–diffusion terms and mixed delays, where mixed delays consist of unbounded time-varying delays and bounded continuously distributed delays. The model under consideration is more general than those investigated in most existing literature. By establishing a novel Lyapunov–Krasovskii functional and employing the delay differential inequality with impulsive initial conditions, boundary conditions and LMI, we obtain two concise and sufficient conditions ensuring global μ-stability of the impulsive reaction–diffusion cellular neural networks with mixed delays. The newly obtained criteria are concerned with the reaction–diffusion coefficients and the regional feature. However, they are independent of boundaries of variable time delays. Several corollaries are also presented. Finally, three concrete numerical examples are given to demonstrate the effectiveness and superiority of our main results.

Optimization of distances between the target surface and focal point on spatially confined laser-induced breakdown spectroscopy with a cylindrical cavity

The spatial confinement effect in laser-induced plasma with different distances between the target surface and focal point is investigated by optical emission spectroscopy. A Nd:YAG laser is used to produce plasma from a silicon sample in air atmosphere. When the appropriate distance is selected, the duration of spectral emission enhancement is much longer, and the enhancement effect is much stronger. The phenomenon is attributed to the aspect ratio of the lateral to axial direction of the plasma plume. The plasma plume of a large aspect ratio will interact with the reflected shockwave in a long range of delay time, leading to high particle density. This provided a better understanding about the effect of the distance between the target surface and focal point, leading to better conditions for spatially confined laser-induced breakdown spectroscopy.

Linear equations method for modal decomposition using intensity information

The linear equations method is proposed to calculate the complete modal content of the partially coherent laser beam using only the intensity information. This method could give not only the incoherent expansion coefficients of the modal decomposition but also the cross-correlation expansion coefficients using the intensity profiles in several planes of finite distance along the propagation direction. A simulation is also presented to verify the validity of this theory. In our algorithm, the minimum and maximum mode orders should be known a priori, so we provide an estimation method for the two parameters.