#psuphysics

Jack Straton earned a Bachelor of Fine Arts degree in photography from the University of Oregon in 1977, worked as a professional jazz drummer for three years, and then returned to the U of O in the 1980s to earn a doctorate in quantum theory. Both as a volunteer and professional diversity trainer over the past 18 years, he has presented several hundred workshops on ending sexual assault and racism. Jack founded Men Against Rape groups in Eugene, Oregon, Washington, D.C., and Manhattan, Kansas. He has published extensively in professional journals from his research in Quantum Scattering Theory, Gender Equity, and Diversity Training Methods. He has served as co-chair of the National Organization for Men Against Sexism (NOMAS) and, as coordinator of the NOMAS Task Group on Child Custody Issues, is recognized as one of the leading writers and speakers in the country with expertise on ethical and public policy issues related to the overlap between child custody, child abuse, and woman abuse.

Shear-force acoustic near-field microscopy (SANM) and Whispering Gallery Acoustic Sensing have recently been introduced as a tandem system to characterize the viscoelastic response of fluids confined between two solid-boundaries in relative oscillatory lateral motion. SANM uses a) a laterally oscillating tapered probe (attached to a quartz tuning fork QTF) as one of the trapping boundaries, and b) an acoustic sensor (attached to the other flat-substrate boundary) that independently monitors the fluid’s acoustic emission. On the other and, WGAS is another technique that uses an acoustic transducer (attached to the frame holding the probe) to monitor the probe’s lateral motion amplitude. Steps towards improving the standing of the SANM/WGAS system as a nanometrology tool include i) to integrate frequency modulation methods, to thus be able to discriminate the elastic from the inelastic component of the probe-fluid interactions, and ii) evaluate the integrity and robustness of the probe to endure such surface interactions, since eventual deformation of the probe affect the reproducibility of the measurements. Here we report using the WGAS signal (or alternatively the QTF electrical response) to control the probe’s motion in frequency modulation modality. In addition, systematic evaluation of eventual probe damage (acquiring scanning electron micrograph before and after the probe exerts one approach/retraction trip to/from the substrate) are also presented. The non-monotonic behavior of the fluid’s acoustic emission (first increasing and then decreasing) as the probe approaches the sample—which occurs before the probe touches the surface, as revealed by the lack of damaged observed on the probe— constitutes one of the main findings reported here. The acoustic signal provides clues on the fluid’s dynamic response when subjected to nanoscale confinement. 

Shear-force Acoustic Near-field Microscopy (SANM) was recently introduced as a metrology tool to characterize the dynamic behavior of mesoscopic fluids trapped between two solid boundaries under relative shear motion. SANM measurements emphasize, in particular, the near-field detection of acoustic waves emitted from a trapped mesoscopic fluid[1,2], which offers complementary information to the simultaneously acquired shear-force also intervening in the probe-fluids interactions. This scenario is akin to interfacial friction phenomena (wear-less friction[3]) where the dissipation of energy is attributed to inelastic interactions between the solid boundaries and the confined fluid layer (with no solid-probe and solid-substrate contact.) The added acoustic detection capability brought by the new SANM technique allows contrasting the acoustic signal emitted by the fluid with the information obtained from the simultaneously acquired damping shear-force acting on the probe, which illustrates the improved metrology capabilities offered by SANM. Still, at its current state of development, this new technique lacks the ability to measure the normal force component of the solid-fluid interactions. This shortcoming is addressed herein.

Ethylene, which regulates fruit ripening processes in some species, is a molecule of central interest to postharvest researchers and technologists. There is a need for a portable, inexpensive, accurate, and repeatable sensor for infield or storeroom measurements. To help ensure repeatable results, we developed a field calibration protocol for a portable electrochemical gas sensor that combines ethephon (2-chloroethylphosphonic acid) with a buffering agent to release a controlled amount of ethylene gas (1–4 μL/L). The ethephon reaction provides an economical source of standard gas for device calibration. This work addresses device selectivity issues through the use of an inline aqueous trap to remove polar volatile organics (50% reduction, as reported by an electrochemical sensor), interfering with the ethylene detection. A complementary gas chromatographic (GC) assay provided an independent validation of these results. A post-harvest study of ethylene production of apples as detected by the electrochemical sensor illustrates significant improvements in the accuracy and precision of these measurements.