A time-space discretization method in milling stability prediction of thin-walled component

The stability prediction of thin-walled workpiece milling is an awkward problem due to the time variant of dynamic characteristics during milling process. Integrating the time discretization method for stability prediction mentioned in many articles, a novel time-space discretization method for thin-walled component milling stability prediction is proposed based on thin plate theory and mode superposition principle, which includes the effects of the engagement position between cutter and workpiece and multi-modes of the system. The results show that the method presented is very reliable and efficient, and its accuracy is also in good agreement with experimental results. Additionally, the method can be used to handle various complex boundary conditions by means of the updated Rayleigh-Ritz solutions together with the penalty method. Two case studies are performed to explain the validation of the method as well as milling experiments of a half-clamped thin plate.     

Phase-pure iron pyrite nanocrystals for low-cost photodetectors

Earth-abundant iron pyrite (FeS₂) shows great potential as a light absorber for solar cells and photodetectors due to their high absorption coefficient (>10⁵ cm^-1). In this paper, high-quality phase-pure and single crystalline pyrite nanocrystals were synthesized via facile, low-cost, and environment friendly hydrothermal method. The molar ratio of sulphur to iron and the reaction time play a crucial role in determining the quality and morphology of FeS₂ nanocrystals. X-ray diffraction and high-resolution transmission electron microscopy confirm that phase-pure and single crystalline pyrite nanocrystals can be synthesized with high sulphur to iron molar ratio and sufficient reaction time. For the first time, a crystalline nanogap pyrite photodetector with promising photocurrent and UV-visible photoresponse has been fabricated. This work further demonstrates a facile route to synthesize high-quality FeS₂ nanomaterials and their potential in optoelectronic applications.     

高职院校顶岗实习指导教师结构的研究与实践——以唐山工业职业技术学院为例

以唐山工业职业技术学院数控技术专业为例,通过对顶岗实习过程中指导教师在年龄结构、专业知识结构、实践能力结构上的调查研究与实践,说明合理的顶岗实习指导教师结构是改善顶岗实习效果,全面提升学生职业能力的重要保证。     

Synthesis of highly transparent and heat‐resistant polyimides containing bulky pendant moieties

A new diamine with bulky pendant biphenyl and ortho‐position dimethyl structures, 4,4′‐((1,1′‐biphenyl)‐4‐ylmethylene)bis(2,6‐dimethylaniline), was synthesized via a one‐pot reaction of 4‐biphenyl carboxaldehyde and 2,6‐dimethylaniline. The diamine was employed to polymerize with several dianhydrides via one‐step condensation under high‐temperature conditions. The light yellow or colorless polyimide (PI) films obtained were found to have cut‐off wavelengths in the range 286–358 nm and transmittance over 80% in the visible region (400–780 nm). Meanwhile, these PIs possessed excellent solubility in common organic solvents, even in low‐boiling‐point solvents such as chloroform (CHCl₃), dichloromethane (CH₂Cl₂) and tetrahydrofuran. The glass transition temperatures (T_g) of the PIs were determined to exceed 343 °C, even to 456 °C. All PI films were flexible with a tensile strength of 78–119 MPa, a Young's modulus of 2.0–2.5 GPa and elongation at break of 4.0%–8.2%. Therefore, these colorless PIs can be used as candidate materials for flexible display substrates. © 2019 Society of Chemical Industry     

A survey on decision making for task migration in mobile cloud environments

The key idea of MCC is using powerful back-end computing nodes to enhance capabilities of small mobile devices and provide better user experiences. An effective and widely used approach to realize this is task migrations. Decision making is an important aspect of migrations which affects the feasibility and effectiveness of task migrations. There have been a number of research efforts to MCC which help make decisions for task migrations. In this paper, we present a comprehensive survey on decision making for task migrations in MCC, including decision factors and algorithms. We observe that there are still some challenges such as comprehensive context awareness, unified migration standards, large-scale experiments, more involvement of latest achievements from artificial intelligence, and flexible decision-making mechanisms. The paper highlights these issues and challenges to attract more efforts to work on MCC.     

Limit requirements simulation of sundial solar tracking machine

Sundial solar tracking machines are machines that tracking the sun,and can promote sunshine receiving efficiency of solar panels.Their operations are strongly influenced by wind load.Previous studies w...     

抽水蓄能电站机组C级检修后的故障分析与处理

介绍了华东宜兴抽水蓄能有限公司1号机组和3号机组在C级检修后发生的两起故障,虽然故障表象不同,但是根据实际情况采取不同措施分别对轴瓦与轴颈间隙进行调整,均取得了非常好的效果,由于这两台机组发生故障的主要原因在同类型的机组中非常典型,因此其诊断及处理过程,值得同类型机组在运行和管理中借鉴.     

Solvothermal synthesis of Mn3O4 as an anode material for lithium ion batteries

Journal of Electroceramics - The nanoparticles of Mn3O4 has been self-assembly synthesized by the mixed solvothermal method. The PEO-PPO-PEO(P123) and hexamethylenetetramine (HMTA) were used as...     

Principle of a two-output-difference interferometer for removing the most important interference distortions

This paper presents a two-output-difference interferometer for removing the most important interference distortions caused by nonlinear detectors. These distortions can be removed not only because the resulting interferogram is composed of the difference between the signals of the two detectors, but also because the modulated signals at each output have the same amplitude and opposite phases. Due to the use of two corner-cube mirrors fixed as a single moving element, the tilt and shearing problem will disappear. The effect of the corner-cube mirror deviation angle and the plane mirror tilt angle are investigated in detail, and the formulas of their tolerance are derived by means of modulation depth and phase error. The advantage of the interferometer enables it to be suitable for Fourier transform spectrometers.