Effect of temperature on the frequency dependency of crack propagation velocity in delayed failure under cyclic load

The crack propagation velocity and the incubation time in delayed failure under repeating load were examined at various frequency ƒ(0–800 cpm) and temperature T(5–80°C) using the pre-cracked specimen of JIS SNCM8 quenched and tempered. The crack propagation velocity under repeating load (da/dt)_R decreased with increase of frequency ƒ and revealed a minimum value (da/dt)_minat a certain ƒ. The activation energy obtained from the Arrhenius plot of (da/dt)_min vs 1/T was about 10,000 cal/mol, which was a little larger than 8100 cal/mol obtained from the relation between the crack propagation velocity under static load and 1/T. The reason for the existence of the minimum value in the crack propagation velocity was explained by assuming the interaction between hydrogen atoms invaded from crack tip and the cyclic change of the position with tri-axial tensile stress. The incubation time under repeating load did not seem to be controlled by the diffusion or concentration process of hydrogen atoms.     

Evaluation of retained products of conception using pulsed continuous arterial spin-labeling MRI: clinical feasibility and initial results

Objectives

We evaluated the vascularity of retained products of conception (RPOC) using arterial spin-labeling magnetic resonance imaging (ASL-MRI) to clarify the clinical feasibility of this approach.

Materials and methods

A pulsed-continuous ASL sequence with echo-planar imaging (EPI) acquisitions was used. Ten consecutive patients with RPOC were enrolled. All ASL images were evaluated visually and semiquantitatively and compared with the findings of Doppler ultrasound (US) and dynamic contrast-enhanced MRI (DCE-MRI).

Results

The technical success rate was 93.7% (15/16 scans). One failed case was excluded from the analysis. Six patients showed quite high signals over RPOC, while three patients showed no abnormal signals. Doppler US alone failed to detect the hypervascular area in two cases, and ASL-MRI alone failed in three. A significant linear correlation was found between semiquantitative values of ASL-MRI and DCE-MRI. All six patients showing high signals on ASL-MRI underwent follow-up MRI after therapy. High signals in five patients decreased visually and semiquantitatively, while one patient showed signal increases.

Conclusion

Evaluation of RPOC using ASL-MRI was clinically feasible and response to therapy could be evaluated. However, the clinical advantages over conventional imaging remain unclear and need to be evaluated.

     

Direct Nanoimprint Lithography of Polyethersulfone Using Cellulose‐Based Mold

Polyethersulfone (PES) with a glass transition temperature of 224 °C is a class of high‐performance super engineering plastics with excellent heat resistance, as well as mechanical, electrical, and optical properties. However, the nanopatterning of PES using thermal nanoimprint lithography at a high temperature can induce technical difficulties. High‐accuracy 900‐nm line patterning of PES is fabricated 50 times using both a solvent‐permeable cellulose‐based mold and dimethylformamide as a dilution solvent in direct thermal nanoimprint lithography. The use of dilution solvents in PES has yet been limited in the nanoimprint lithography, and the developed processes expand the surface patterning of super engineering plastic.