Fast solver for some computational imaging problems: A regularized weighted least-squares approach

In this paper we propose to solve a range of computational imaging problems under a unified perspective of a regularized weighted least-squares (RWLS) framework. These problems include data smoothing and completion, edge-preserving filtering, gradient-vector flow estimation, and image registration. Although originally very different, they are special cases of the RWLS model using different data weightings and regularization penalties. Numerically, we propose a preconditioned conjugate gradient scheme which is particularly efficient in solving RWLS problems. We provide a detailed analysis of the system conditioning justifying our choice of the preconditioner that improves the convergence. This numerical solver, which is simple, scalable and parallelizable, is found to outperform most of the existing schemes for these imaging problems in terms of convergence rate.     

考虑应力敏感的致密气藏水平井产能计算方法

除启动压力梯度外致密气藏还存在应力敏感,在实验确定应力敏感参数的基础上,引入虚拟裂缝概念,利用保角变换方法,考虑应力敏感和启动压力梯度建立了气藏水平井产能方程,同时分析了应力敏感、启动压力梯度、水平井长度等对产能的影响。结果表明:产能方程与试采产能的误差小于7%,验证了产能方程的可靠性;应力敏感和启动压力梯度均使产能降低,其中应力敏感占主要作用;应力敏感在低井底流压时对产能影响严重,启动压力梯度在高井底流压时对产能影响较大;水平井长度是影响产能的主控因素。该研究丰富了致密气藏水平井产能计算方法,并为水平井长度和生产压差的优化提供了理论指导。     

CoPtx‐loaded Zn0.5Cd0.5S nanocomposites for enhanced visible light photocatalytic H2 production

Zn_0.5Cd_0.5S solid solution, modified with bimetallic CoPt_x nanoparticles, has been prepared using a two‐step organic solution method. The photocatalytic H₂ production rate of CoPt_x–Zn_0.5Cd_0.5S nanocomposites with different composition and percentage of CoPt_x was investigated. The results showed that the 1 wt% CoPt₃–Zn_0.5Cd_0.5S sample had the best activity which was 4.7 times higher than that of pure Zn_0.5Cd_0.5S and 1.2 times higher than that of Pt–Zn_0.5Cd_0.5S for photocatalytic H₂ production. The transient photocurrent response of the Zn_0.5Cd_0.5S showed an obvious increase in the current density after CoPt_x loading. Electrochemical impedance spectra measurements showed that the CoPt_x–Zn_0.5Cd_0.5S nanocomposites with x = 2 and 3 had lower charge transfer resistance R_t than that of Pt–Zn_0.5Cd_0.5S. The enhanced catalytic properties of the CoPt_x–Zn_0.5Cd_0.5S nanocomposites are attributed to their better accumulation ability for photoexcited electrons and higher rate for charge separation and transportation. Copyright © 2016 John Wiley & Sons, Ltd.     

Electrodeposited Pt nanorods on a novel flowered-like nanostructured NiCo alloy as an electrocatalyst for methanol oxidation

For the first time, a novel system of Pt nanorods supported on nano flowered-like structure NiCo alloy has been successfully electro-synthesized onto a glassy carbon electrode for the electrocatalytic oxidation of methanol. The electrodeposited system has been characterized using scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). The electrocatalytic efficiency of the electro-fabricated system of Pt/NiCo/GCE have been confirmed by cyclic voltammetric (CV) and current-time methods. It is discovered that the electrodeposited nano flowered NiCo alloy substrate has a great effect on the electrocatalytic properties of the electrodeposited Pt nanorods. The electrocatalytic efficiency of the new system for methanol oxidation reaction (MOR) is found to be 174 A/g_Pt. The effect of electrodeposition time for NiCo alloy has been studied. Also, the effect of pH, temperature, and concentration for the electrodeposition of Pt catalyst on the electrocatalytic properties of the Pt/NiCo/GCE have been studied for detection the optimum conditions. The mechanism of the electrocatalytic oxidation of methanol has been discussed. Furthermore, the stability and the corrosion resistance test of the Pt/NiCo/GCE system have been investigated by electrochemical impedance spectroscopy (EIS), Tafel plot and current-time methods.     

The dual capacity of the NiSn alloy/MWCNT nanocomposite for sodium and hydrogen ions storage using porous Cu foam as a current collector

A nanostructured NiSn alloy/multi-walled carbon nanotube (MWCNT) composite was successfully synthesized for highly reversible sodium and hydrogen ions storage by using an electrochemical deposition process on porous Cu foam. The surface morphology of the resulting NiSn alloy/MWCNT nanocomposite was characterized using a field-emission scanning electron microscope, indicating the formation of sphere-like NiSn alloy nanoparticles with an average size of 190 nm. On the other hand, X-ray diffraction analysis, energy dispersive and Fourier transform infrared spectroscopies were employed to determine the crystalline structure, elemental surface and chemical composition of the nanocomposite electrode. The initial sodium discharge capacity of the electrode was maximized at ∼550 mAh g⁻¹ under the current density of 1000 mA g⁻¹, and a high hydrogen discharge capacity of 5200 mAh g⁻¹ was obtained at 1100 mA g⁻¹ after 20 cycles. A comprehensive comparison between the sodium and hydrogen ions capacities in this study and those of the literature for different materials and structures was also performed. Accordingly, the resulting nanocomposite electrode with dual capacity may offer promising applications in both sodium-ion battery and hydrogen storage.     

Titanium-iron-manganese (TiFe0.85Mn0.15) alloy for hydrogen storage: Reactivation upon oxidation

Titanium-iron (TiFe) is known to be a low-cost alloy that can be reactivated to nearly full hydrogen storage capacity after oxidation. However, this reactivation requires multiple heat treatments at high temperatures under vacuum even upon partial substitution of Fe with a small amount of manganese to form TiFe_0.85Mn_0.15. This process is cumbersome in the context of practical applications, and better strategies for the facile activation of TiFe are required. Herein, we report on an improvement in the reactivation strategy of TiFe_0.85Mn_0.15 by using a single heat treatment process after air oxidation of the alloy. After full oxidation of the material under air for 2 h, reactivation was achieved in a single step by heating the alloy to 300 °C under hydrogen pressure. During that process, the reduction of Fe was believed to lead to new reactive paths at the surface of the alloy facilitating the permeation of hydrogen. As a result, full cycling capability of the material was quickly re-gained, and the hydrogen capacity loss was of only 0.1 mass%.