Effect of strain on charge density wave order in α-U

The effect of strain on charge density wave (CDW) order in $\alpha$-U is investigated within the framework of relativistic density-functional theory. The energetical stability of $\alpha$-U with CDW distortion is enhanced by the tensile strain along $a$ and $b$ axes, which is similar to the case of negative pressure and normal. However, the tensile strain along $c$ axis suppresses the energetical stability of CDW phase. This abnormal effect could be understood from the emergence of a new one-dimensional atomic chain along $c$ axis in $\alpha$-U. Furthermore, this effect is supported by the calculations of Fermi surface and phonon mode, in which the topological objects and the dynamical instability show opposite behaviors between strains along $a$/$b$ and $c$ axes.     

化学教育硕士研究生的科学本质观研究*——基于对科普微视频的分析

以构建的科学本质要素框架作为分析工具,研究学生经科普微视频分析所呈现的科学本质观。结果表明,学生无法全面、深入分析视频呈现的科学本质,反映了局限的科学本质观,而经过讨论与汇报能在一定程度上提升其科学本质观。据此,为化学教育硕士研究生的培养工作提出3点建议,即将科普微视频作为科学本质教育的素材,促进学生形成完整且深刻的科学本质观,发展学生准确抽提课程资源中的科学本质的能力。     

Repairing force for deformed casing shaping with spinning casing swage and damage behaviour of cement sheath

In oil and gas fields, the repairing force (bit weight) is generally determined by experience when the deformed casing is repaired using the spinning casing swage. However, unreasonable repairing force easily damages the cement sheath around the deformed casing and causes pipe sticking, which results in failure of the wellbore integrity. Hence, based on the Hertz contact theory, the present study established a mechanical model to calculate the repairing force required to repair the deformed casing without a cement sheath by spinning casing swage, and the reshaping force was determined by combining the structural features of the spinning casing swage with the method of mechanics and kinetics analysis regarding axial loading and circumferential deformation of the deformed casing. Finally, a mechanical model was presented that could calculate the repairing force of the deformation casing with cement sheath using the inversion method. Repairing experiments involving three types of deformed casings (casing without cement sheath, casing with undamaged cement sheath and casing with damaged cement sheath) were performed, from which the accuracy and reliability of the mechanical model was validated. The damage behaviour of the cement sheath after casing repair was investigated based on the experimental results and the damage mechanism was analysed based on Saint-Venant's deformation compatibility principle. Analysis results showed that three types of damage, including micro-annulus, transverse fracture and longitudinal fracture, were caused by high contact pressure between the steel ball on the spinning casing swage and the internal wall of the deformed casing and pressure fluctuation during repairing. The research results provide important guidance and decision making for practical repairing measures.     

On the split common fixed point problem for strict quasi-ϕ-pseudocontractive mappings in Banach spaces

Numerical Algorithms - The purpose of this paper is to propose an algorithm for solving the split common fixed point problem for strict quasi-?-pseudocontractive mappings in Banach spaces. It...     

Hopf–Hopf bifurcation analysis based on resonance and non-resonance in a simplified railway wheelset model

Nonlinear Dynamics - This paper mainly investigates the dynamics of the non-resonant and near-resonant Hopf–Hopf bifurcations caused by the interaction of the lateral and yaw motion in a...     

Effects of longitudinal fire source locations on the maximum temperature and longitudinal temperature decay in a mountain tunnel with vertical shaft: an experimental investigation and empirical model

Journal of Thermal Analysis and Calorimetry - Few investigations have focused on the influence of longitudinal fire source location on the temperature profile of smoke induced by fire in a tunnel...