基于改进的PHT-样条自适应等几何配点法

将传统等几何配点法扩展至任意高阶单元并且满足自适应局部细分功能,提出一种基于改进的PHT样条单元的自适应等几何配点法.改进的PHT样条单元依然具有传统PHT样条单元局部细分功能,但因为传统PHT样条函数在层级网格划分后需要对部分基函数的定义域进行截断处理,所以在层级细分过于频繁区域,部分函数可能因为严重变形而影响计算稳...     

High performance organic field-effect transistors using ambient deposition of tetracene single crystals

Organic molecular crystals (OMCs) are of significant interest due to their potential use in transistors, photovoltaic devices, light emitting diodes, and other applications. However, conventional vacuum-based methods of growing crystalline OMC films are costly and provide limited control over crystal growth. In this study, we present a new method for preparing high performance single-crystal tetracene field-effect transistors under near-ambient conditions using organic vapor-liquid-solid (OVLS) deposition. We find that the mobility of OVLS-grown tetracene is comparable to high quality crystalline films prepared by physical vapor deposition. These results establish OVLS deposition as a relatively low cost, low substrate temperature, and ambient pressure method for growing high quality OMC films for device applications.     

舰载机拦阻系统动力学建模与控制

提出了一种液压吸能和滑轮机构相结合的舰载机拦阻系统模型,然后建立了计入拦阻索弹性的拦阻系统非线性动力学模型．基于高斯伪谱方法获得了舰载机拦阻过程的最优控制轨迹,并应用线性二次型最优控制跟踪该最优轨迹,数值结果验证了该方法的可行性,最后讨论了空气阻力与甲板摩擦力对控制过程的影响．     

NMR research on deterioration characteristics of microscopic structure of sandstones in freeze–thaw cycles

In order to study the deterioration characteristics of the microscopic structure of sandstones in freeze–thaw cycles, tests of 180 freeze–thaw cycles were performed on sandstone specimens. The nuclear magnetic resonance (NMR) technique was applied to the measurement of sandstone specimens and analysis of the magnetic resonance imaging. Then, the fractal theory was employed to compute the fractal dimension values of pore development of rocks after different freeze–thaw cycles. The results show that the mass and porosity of rocks grow with the increase of freeze–thaw cycles. According to the NMR T₂ distribution of sandstones, the pore sizes of rock specimens increase after 180 freeze–thaw cycles, especially that of the medium-sized and small-sized pores. The spatial distribution of sandstone pores after freeze–thaw cycles has fractal features within certain range, and the fractal dimension of sandstones tends to increase gradually.     

Fabrication and thermal stability of NH4HF2-etched Ti3C2 MXene

MXene, a new family of 2D transition metal carbides and carbonitrides, has been proved to possess excellent electrical conductivity and hydrophilicity. In this work, a single-step method to produce the larger interplanar spacing 2D MXene Ti₃C₂ by etching Ti₃AlC₂ with NH₄HF₂ was demonstrated, and the optimal reaction conditions between Ti₃AlC₂ and NH₄HF₂ were systematically researched. The morphology and microstructure of samples were characterized by scanning electron smicroscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD). The thermal stability of Ti₃C₂ was investigated by the thermogravimetry (TG) and differential thermal analyzer (DTA). It was found that the lattice parameter c of obtained Ti₃C₂ was up to 24.9 Å, and the larger interplanar spacing Ti₃C₂ was more stable than the sample exfoliated by HF. The transition temperature in air from NH₄HF₂-etched Ti₃C₂ to anatase TiO₂ thoroughly is more than 500 ℃, and the multilayered structure of Ti₃C₂ could be well retained even afer 900 ℃ heat treatment, while the value of HF-etched Ti₃C₂ is less than 350 ℃. This work is important for exploring a safe synthesis method and well understanding the thermal stability of 2D MXene materials.     

Methods of ranking search results for searches based on multiple search concepts carried out in multiple databases

If a patent prior art search produces several hundred results, it can be annoying when the best document turns out to be the last one. Ideally the most relevant search result should be brought to the top of the list. This article discusses the particular problems which searches for multiple concepts entail, explains what ranking is and compares some ways to rank, or reorder, search results. In particular, the article deals with a special technique which examiners at the European Patent Office (EPO) can use and which has been found to work well, especially when there are several search concepts and several technical fields to be searched. This ranking technique, called Horváth–Materne ranking or pivot ranking, is based on the assumption that the best documents will not only mention the search concepts in full-text databases, but will also mention at least some of the concepts in corresponding abstract databases. The more concepts present in the abstracts, the greater the probability that the document is relevant. In principle the technique could be used to rank results in any database where both full-text and abstracts are available. The technique can be broadened by including an automatic concept extraction.     

Photoelectrochemical performance of CdS nanorods grafted vertically aligned TiO2 nanorods

In this study, TiO₂ nanorods/CdS nanorods composite samples were successfully synthesized by grafting CdS nanorods on vertically aligned TiO₂ nanorods. A two-step hydrothermal method was used to prepare the samples. Some properties of the samples, such as morphological, structural, and optical properties were characterized by energy-dispersive X-ray detection, field emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and ultraviolet-visible spectroscopy. Moreover, photoelectrochemical properties were studied via current-voltage and photocurrent spectrum measurements. The results showed that CdS nanorods grafted on top of TiO₂ nanorods like a lawn. The amount grafted as well as the diameter and crystallinity of CdS nanorods increased first and then decreased as the grafting time increased, due to Ostwald ripening. Under the back-side illumination, the composite film with 2 h grafting time exhibited the highest photocurrent density which was almost twice of that of the pure TiO₂ nanorods.     

An improved unified viscoplastic constitutive model for strain-rate sensitivity in high temperature fatigue

An improved unified cyclic viscoplastic material model for high temperature fatigue of P91 steel is presented. The primary enhancement over existing models is in relation to strain-rate independence of parameters, for accurate interpolation and extrapolation across a range of strain-rates and stress regimes, as relevant to flexible operation of high temperature power generation plant. The model combines a hyperbolic sine constitutive equation with anisothermal cyclic evolution of isotropic and kinematic hardening variables. The material model is developed from a thermodynamic framework and is implemented in multi-axial form within a user material subroutine. The user material subroutine is calibrated and validated for P91 steel across a range of cyclic (isothermal fatigue and thermo-mechanical fatigue) and non-cyclic high temperature loading conditions. A novel method for the identification of the cyclic viscoplastic material parameters is also presented.