Stability analysis of the propagation of periodic parallel hydraulic fractures

When multiple fractures are propagating simultaneously, the fracture spacing may coarsen gradually resulting from loss of stability of the fracture system, which can also occur during the propagation of multiple hydraulic fractures (HFs). In this paper, the stability of the propagation of periodic parallel HFs in brittle solids is investigated based on a representative unit cell consisting two HFs. The fractures are driven to propagate by the inside fluid flow and fluid–solid coupling effect is involved. Both the stress interaction acting in the solid medium and the flow of fluid medium can influence the stability. Stability criterions are given based on the variations of the rates of change of the stress intensity factor with respect to facture velocities. Stability results are obtained by solving the system with fully coupled numerical method which considers the deformation of solid medium, fracture propagation, fluid flow in fractures, fluid partitioning into each fracture. Based on the numerical results, the influences of propagation regimes, fracture lengths and the fracture distance on the stability of HFs are investigated.     

Fabrication of large‐scale superhydrophobic composite films with enhanced tensile properties by multinozzle conveyor belt electrospinning

Large‐scale superhydrophobic composite films with enhanced tensile properties were prepared by multinozzle conveyor belt electrospinning. First, a strategy of conveyor belt electrospinning was introduced for large‐scale fabrication since the conveyor belt can expand the electrospinning area unlimitedly. During the electrospinning (or electrospraying) process, certain kinds of fibers are combined on the conveyor belt in one electrospinning (or electrospraying) step. The superhydrophobicity of electrospun film can be achieved by the presence of PS beads and bead‐on‐string PVDF fibers, while submicron PAN fibers are responsible for the improvement of mechanical properties. The result shows that CA value of the surface comprising of PS beads and bead‐on‐string PVDF fibers could reach up to 155.0°. As the submicron PAN fibers increased, the value of CA decreased, changing from 155.0° to 140.0°, meanwhile the tensile strength of composite film was enhanced from 1.14 to 4.12 MPa correspondingly which is beneficial to putting the films into practice. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39735.     

Acquiring real kinetics of reactions in the inhibitory atmosphere containing product gases using micro fluidized bed

This study proposed an isotope-tagging method to investigate reactions under the atmosphere of product gas. To illustrate this method, the calcination kinetics of calcium carbonate Ca¹³CO₃ in CO₂ atmospheres were investigated by monitoring ¹³CO₂ produced using a micro fluidized bed reaction analyzer (MFBRA). The results demonstrated that the presence of CO₂ in reaction atmosphere increases the apparent activation energy. The increase in the apparent activation energy is, however, significantly overestimated by the thermogravimetric analyzer (TGA) because of the excessive suppression by stagnated product gas inside the sample crucible. Comparatively, the apparent activation energy increases with CO₂ from the MFBRA due primarily to the thermal equilibrium limitation, because the gas diffusion in the MFBRA is essentially eliminated. It is thus concluded that the MFBRA is quite capable of acquiring the real kinetics of reactions in such inhibitory atmospheres.     

盾构隧道管片设计模型的改进

对现有管片计算模型的接头简化进行了改进,推导了改进惯用法模型的内力求解公式,并结合北京地铁十号线工程实例资料,对惯用法模型及其改进模型进行了对比分析,以供管片设计参考。     

A new macro-micro dual drive parallel robot for chromosome dissection

This paper presents a parallel-structure system dually driven by six servo motors and six piezoelectric actuators. Due to the combination of macro and micro manipulators which are both of orthogonal structures, the proposed system possesses a concise structure as well as actuation isolation and output motion decoupling properties. By using a glass needle mounted on a six-dimensional force sensor in endpoint operating, this system can be applied to chromosome dissection that to make the whole process more efficient and automatic. The glass needle tip has a stroke of 106 mm in three linear motions and 18.7-arc-degrees in three angle motion directions, with servo motors adopted. It also has the resolution of 20 nanometers with the adoption of piezoelectric actuators. The kinematics, isotropy, decoupling and design considerations of the proposed robot are discussed. Workspace and resolution of both macro and micro manipulators are measured separately. The experiments are also conducted to show its capability in dissecting chromosomes.     

Poly(acrylic acid)-modified silica nanoparticles as a nonmetal catalyst for NaBH4 methanolysis

In the present work, a SiO₂@PAA catalyst for NaBH₄ methanolysis composed of silica nanoparticles modified with poly(acrylic acid) has been developed. The morphology and composition of the prepared SiO₂@PAA catalyst were analyzed with transmission electron microscopy, Fourier transform-infrared spectroscopy, x-ray photoelectron spectroscopy and thermogravimetric analysis. This catalyst showed excellent catalytic performance for methanolysis of NaBH₄. The NaBH₄ methanolysis reaction catalyzed by SiO₂@PAA showed an average hydrogen generation rate 5.5 times as high as the reaction catalyzed by unmodified SiO₂ and 10.6 times as high as the uncatalyzed reaction, respectively. The activation energy for methanolysis of NaBH₄ catalyzed by this SiO₂@PAA catalyst was 24.03 kJ/mol. Moreover, although the catalytic activity of SiO₂@PAA catalyst partially lost after being used, it could be restored after being regenerated by washing with diluted hydrochloric acid solution.     

探析榆中青城镇古民居

该文主要从民居建筑的平面布局和环境特征、结构和外形特征、装饰装修和细部特征三个方面分别探讨了榆中青城镇古民居的特征，反映出了一个西北偏远古镇的文化历史价值。     

Two-dimensional nanomaterials for photocatalytic water disinfection: recent progress and future challenges

Photocatalysis has received ever-growing attention as a promising alternative to traditional water treatment technologies for waterborne biohazard inactivation. Due to unique optical, electronic, physicochemical properties and feasibility of functional architecture assembly, two-dimensional (2D) nanomaterials have become important in developing novel photocatalysts. This review summarizes the recent progress in configuring nanostructures with 2D materials as building blocks for photocatalytic water disinfection. In this review, five categories of 2D nanomaterials, that is, graphene, graphitic carbon nitride, 2D metal oxides and metallates, metal oxyhalides and transition metal dichalcogenides, for photocatalytic pathogen inactivation are introduced. First, the synthesis process, nanostructure engineering and disinfection performance of 2D-based photocatalysts are reviewed in categories. In the following section, the bacteria destruction mechanism based on the generation and roles of reactive species (RSs) is presented. Moreover, the effects of the chemical characteristics of the water matrix on photocatalytic bactericidal performance are discussed. Finally, the challenges regarding the development and application of 2D-based photocatalysts for highly efficient water sterilization are highlighted. © 2018 Society of Chemical Industry