Mechanical Properties of a Typical Jurassic Shaximiao Sandstone Under Subzero and Deep in situ Temperature Conditions

Insight into the difference between the mechanical properties of rocks at low and in situ deep reservoir temperatures is vital for achieving a better understanding of fracking technologies with supercritical CO2 and liquid nitrogen. To address this issue, the fracking-related mechanical properties of the Shaximiao Formation sandstone (SS) were investigated through direct tension, uniaxial compression, and three-point bending fracture tests at a typical low temperature (Tlow) of −10°C and a reservoir temperature (Tin situ) of 70°C. The results showed that the tensile strength σt, compressive strength σc, and fracture toughness KIC of the SS were all higher at Tlow than at Tin situ, although to different extents. The KIC of the SS increased slightly more than σt at the lower temperature, while both σt and KIC of the SS increased significantly more than σc at the lower temperature. In addition to the strength, the stiffness (particularly the tensile stiffness) and the brittleness indices of SS were similarly higher at Tlow than at Tin situ. In situ monitoring using the digital image correlation technique revealed that a highly strained band (HSB) always appeared at the crack front. However, because of the inhomogeneous microstructure of the SS, the HSB did not always develop along the line connecting the notch tip to the loading point. This was a possible cause of the highly dispersed KIC values of the SS. The HSB at the crack front was notably narrower at Tlow than at Tin situ, suggesting that low temperatures suppress the plastic deformation of rocks and are therefore beneficial to reservoir stimulation.

Polarized Raman spectroscopy of GaP nanowires under 5% elastic strain

Optical porperties of highly-strained gallium phosphide nanowires were investigated via polarized Raman spectroscopy. 5% elastic strain was created in individual nanowire lying on nickel substrate by the means of atomic force microscopy. Micro-Raman mapping along the nanowire cross section in parallel and perpendicular polarization was carried out. Strain-induced effects on transverse optical mode position and shape were analyzed. The pronounced splitting of the mode due to high level of strain was observed. It was found that in parallel polarization the mode shape is sensitive to the position of the pumping spot which can be attributed to enhanced light-nanowire coupling effects.

The mechanochemical origins of the microtubule sliding motility within the kinesin-5 domain organization

The conserved kinesin-5 bipolar tetrameric motors slide apart microtubules during mitotic spindle assembly and elongation. Kinesin-5 bipolar organization originates from its conserved tetrameric helical minifilament, which position the C-terminal tail domains of two subunits near the N-terminal motor domains of two anti-parallel subunits (Scholey et al, 2014). This unique tetrameric structure enables kinesin-5 to simultaneously engage two microtubules and transmit forces between them, and for multiple kinesin-5 motors to organize via tail to motor interactions during microtubule sliding (Bodrug et al, 2020). Here, we show how these two structural adaptations, the kinesin-5 tail-motor domain interactions and the length of the tetrameric minifilament, determine critical aspects of kinesin-5 motility and sliding mechanisms. An x-ray structure of the 34-nm kinesin-5 minifilament reveals how the dual dimeric N-terminal coiled-coils emerge from the tetrameric central bundle. Using this structure, we generated active bipolar mini-tetrameric motors from Drosophila and human orthologs, which are half the length of native kinesin-5. Using single-molecule motility assays, we show that kinesin-5 tail domains promote mini-tetramers static pauses that punctuate processive motility. During such pauses, kinesin-5 mini-tetramers form multi-motor clusters mediated via tail to motor domain cross-interactions. These clusters undergo slow and highly processive motility and accumulate at microtubule plus-ends. In contrast to native kinesin-5, mini-tetramers require tail domains to initiate microtubule crosslinking. Although mini-tetramers are highly strained in initially aligning microtubules, they slide microtubules more efficiently than native kinesin-5, due to their decreased minifilament flexibility. Our studies reveal that the conserved kinesin-5 motor-tail mediated clustering and the length of the tetrameric minifilament are key features for sliding motility and are critical in organizing microtubules during mitotic spindle assembly and elongation.

Controlling of Lattice Strains for Crack-Free and Strong Ferroelectric Barium Titanate Films by Post-Thermal Treatment

In this study, we experimentally demonstrate the fabrication of ultra-smooth and crystalline barium titanate (BTO) films on magnesium oxide (MgO) substrates by engineering the lattice strain and the crystal structure via thermal treatment. We first grow crack-free BTO thin films at oxygen-depleted condition, and enhance the ferroelectric characteristics by post-annealing at high temperature. The roughened surface due to recrystallization during post-annealing is controlled by chemical-mechanical polishing (CMP) to retain the ultra-smooth surface morphology. Oxygen-depleted deposition allows a highly strained BTO film to grow on a MgO substrate with an ultra-smooth surface, and post-annealing relaxes the strain, resulting in the enhancement of the ferroelectricity. From Raman spectroscopy, reciprocal space map (RSM), and capacitance–voltage (C–V) curve measurements, we observe that the ferroelectricity of the BTO film strongly depends on the lattice strain relaxation and the phase transition from a-axis to c-axis oriented crystal structure.

Strain-Induced Transformations of Bicyclo[3.1.0]hex-1-enes

Bicyclo[3.1.0]hex-1-ene is a highly strained bicyclic intermediate that generates trimethylenemethane (TMM) diradical through breaking the C–C bond of its methylene cyclopropane moiety. The reactivity of bicyclo[3.1.0]hex-1-enes and trimethylenemethane (TMM) diradicals depend on the reaction temperature and substitution patterns. This short review covers various strain-induced transformations of bicyclo[3.1.0]hex-1-enes and their formal [3+2] cycloadditions through TMM diradicals and presents synthetic applications to natural products containing triquinane and tropone structures.1 Introduction2 Early Reports on Bicyclo[3.1.0]hex-1-enes3 Approaches to Form Bicyclo[3.1.0]hex-1-enes4 Structure and Reactivity of Bicyclo[3.1.0]hex-1-enes4.1 Isomerization4.2 Dimerization4.3 [3+2] Cycloaddition4.4 [4+2] Cycloaddition5 Synthetic Applications to Natural Products6 Summary and Outlook