Shock wave formation from head-on collision of two subsonic vortex rings.

Vortex ring collisions have attracted intense interest in both water and air studies (Baird in Proc R Soc Lond Ser Math Phys Sci 409:59-65, 1987, Poudel et al. in Phys Fluids 33:096105, 2021, Lim and Nickels in Nature 357:225, 1992, New et al. in Exp Fluids 57:109, 2016, Suzuki et al. in Geophys Res Lett 34, 2007, Yan et al. in J Fluids Eng 140:054502, 2018, New et al. in J Fluid Mech 899, 2020, Cheng et al. in Phys Fluids 31:067107, 2019, Hernández and Reyes in 29:103604, 2017, Mishra et al. in Phys Rev Fluids, 2021, Zednikova et al. in Chem Eng Technol 42:843-850, 2019, Kwon et al. in Nature 600:64-69, 2021). These toroidal structures spin around a central axis and travel in the original direction of impulse while spinning around the core until inertial forces become predominant causing the vortex flow to spontaneously decay to turbulence (Vortex Rings, https://projects.iq.harvard.edu/smrlab/vortex-rings ). Previous studies have shown the collision of subsonic vortex rings resulting in reconnected vortex rings, but the production of a shock wave from the collision has not been demonstrated visibly (Lim and Nickels in Nature 357:225, 1992, Cheng et al. in Phys Fluids 31:067107, 2019). Here we present the formation of a shock wave due to the collision of explosively formed subsonic vortex rings. As the vortex rings travel at Mach 0.66 toward the collision point, they begin to trap high pressure air between them. Upon collision, high pressure air was imploded and released radially away from the axis of the collision, generating a visible shock wave traveling through and away from the colliding vortices at Mach 1.22. Our results demonstrate a pressure gradient with high pressure release creating a shock wave. We anticipate our study to be a starting point for more explosively formed vortex collisions. For example, explosives with different velocities of detonation could be tested to produce vortex rings of varying velocities.

Explosive Fragmentation of Luminescent Diamond Particles.

Development of efficient and cost-effective mass-production techniques for size reduction of high- pressure, high-temperature (HPHT) diamonds with sizes from tens to hundreds of micrometers remains one of the primary goals towards commercial production of fluorescent submicron and nanodiamond (fND). fNDs offer great advantages for many applications, especially in labelling, tracing, and biomedical imaging, owing to their brightness, exceptional photostability, mechanical robustness and intrinsic biocompatibility. This study proposes a novel processing method utilizing explosive fragmentation that can potentially be used for the fabrication of submicron to nanoscale size fluorescent diamond particles. In the proposed method, synthetic HPHT 20 pm and 150 pm microcystalline diamond particles containing color centers are rapidly fragmented in conditions of high explosive detonation. X-ray diffraction and Raman spectroscopy show that the detonation fragmented diamond particles consist of good quality submicron diamonds of ~420-800 nm in size, while fluorescence spectroscopy shows photoluminescence spectra with noticeable changes for large (150 µm) starting microcrystalline diamond particles, and no significant changes in photoluminescence properties for smaller (20 µm) starting microcrystalline diamond particles. The proposed detonation method shows potential as an efficient, cost effective, and industrially scalable alternative to milling for the fragmentation of fluorescent diamond microcrystals into submicron- to nano-size domain.

Ultrastructural brain abnormalities and associated behavioral changes in mice after low-intensity blast exposure.

Explosive blast-induced mild traumatic brain injury (mTBI), a "signature wound" of recent military conflicts, commonly affects service members. While past blast injury studies have provided insights into TBI with moderate- to high-intensity explosions, the impact of primary low-intensity blast (LIB)-mediated pathobiology on neurological deficits requires further investigation. Our prior considerations of blast physics predicted ultrastructural injuries at nanoscale levels. Here, we provide quantitative data using a primary LIB injury murine model exposed to open field detonation of 350 g of high-energy explosive C4. We quantified ultrastructural and behavioral changes up to 30 days post blast injury (DPI). The use of an open-field experimental blast generated a primary blast wave with a peak overpressure of 6.76 PSI (46.6 kPa) at a 3-m distance from the center of the explosion, a positive phase duration of approximate 3.0 milliseconds (ms), a maximal impulse of 8.7 PSI × ms and a sharp rising time of 9 × 10-3 ms, with no apparent impact/acceleration in exposed animals. Neuropathologically, myelinated axonal damage was observed in blast-exposed groups at 7 DPI. Using transmission electron microscopy, we observed and quantified myelin sheath defects and mitochondrial abnormalities at 7 and 30 DPI. Inverse correlations between blast intensities and neurobehavioral outcomes including motor activities, anxiety levels, nesting behavior, spatial learning and memory occurred. These observations uncover unique ultrastructural brain abnormalities and associated behavioral changes due to primary blast injury and provide key insights into its pathogenesis and potential treatment.