Transfer Function for Relative Blast Overpressure Through Porcine and Human Skulls In Situ

ABSTRACT Introduction The overarching objective of the Office of Naval Research sponsored Blast Load Assessment Sense and Test (BLAST) program was to quantify neurofunctional risk from repeated blast exposure. However, human studies have limitations in data collection that can only be addressed by animal models. To utilize a large animal model in this work, researchers developed an approach for scaling blast exposure data from animal to human-equivalent loading. For this study, energy interacting with the brain tissue was selected as a translation metric because of the hypothesized association between observed neurological changes and energy transmitted through the skull. This article describes the methodology used to derive an energy-based transfer function capable of serving as a global correspondence rule for primary blast injury exposure, allowing researchers to derive human-appropriate thresholds from animal data. Methods and Materials To generate data for the development of the transfer functions, three disarticulated cadaveric Yucatan minipigs and three postmortem human surrogate heads were exposed to blast overpressure using a large bore, compressed-gas shock tube. Pressure gauges in the free field, on the skull surface, and pressure probes within the brain cavity filled with Sylgard silicone gel recorded the pressure propagation through the skull of each specimen. The frequency components of the freefield and brain cavity measurements from the pig and human surrogates were interrogated in the frequency domain. Doing so quantifies the differences in the amount of energy, in each frequency band, transmitted through both the porcine and the human skull, and the transfer function was calculated to quantify those differences. Results Nonlinear energy transmission was observed for both the porcine and human skulls, indicating that linear scaling would not be appropriate for developing porcine to human transfer functions. This study demonstrated similar responses between species with little to no attenuation at frequencies below 30 Hz. The phase of the pressure transmission to the brain is also similar for both species up to approximately 10 kHz. There were two notable differences between the porcine and human surrogates. First, in the 40-100 Hz range, human subjects have approximately 8 dB more pressure transmitted through the skull relative to porcine subjects. Second, in the 1-10 kHz range, human subjects have up to 10 dB more pressure transmitted into the brain (10 dB more attenuation) relative to the porcine subjects. Conclusions The fundamental goal of this study was to develop pig-to-human transfer functions to allow researchers to interpret data collected from large animal studies and aid in deriving risk functions for repeated blast exposures. Similarities in porcine and human brain physiology make the minipig experimental model an excellent candidate for blast research. However, differences in the skull geometry have historically made the interpretation of animal data difficult for the purposes of characterizing potential neurological risk in humans. Human equivalent loading conditions are critical so that the thresholds are not over- or underpredicted due to differences in porcine skull geometry. This research provides a solution to this challenge, providing a robust methodology for interpreting animal data for blast research.

Preparation of Fe(II)/MOF-5 Catalyst for Highly Selective Catalytic Hydroxylation of Phenol by Equivalent Loading at Room Temperature

The metal-organic framework MOF-5 was synthesized by self-assembling of Zn(NO3)2·7H2O and H2BDC using DMF as solvent by the direct precipitation method and loaded with Fe2+ by the equivalent loading method at room temperature to prepare Fe(II)/MOF-5 catalyst and the microstructure, phases, and pore size of which was characterized by IR, XRD, SEM, TEM, and BET. It was found that Fe(II)/MOF-5 had high specific surface and porosity like MOF-5 and uniform pore distribution, and the pore size is 1.2 nm. In order to study the catalytic activity and reaction conditions of Fe(II)/MOF-5, it was used to catalyze the hydroxylation reaction of phenol with hydrogen peroxide. The results showed that the dihydroxybenzene yield of 53.2% and the catechol selectivity of 98.6% were obtained at the Fe2+ content of 3 wt.%, the mass ratio of Fe(II)/MOF-5 to phenol of 0.053, the reaction temperature of 80°C, and the reaction time of 2 h.

Comparative biomechanical analysis demonstrates functional convergence between slender-snouted crocodilians and phytosaurs

Morphological similarities between the extinct Triassic archosauriform clade Phytosauria and extant crocodilians have formed the basis of long-proposed hypotheses of evolutionary convergence. These hypotheses have informed the reconstructions of phytosaur ecology and biology, including feeding preferences, body mass, soft tissue systems, mating behaviours, and environmental preferences. However, phytosaurs possess numerous cranial apomorphies that distinguish them from modern crocodilians and potentially limit ecomorphological comparisons. Here, we present the first computational mechanical comparison of phytosaur cranial strength to several extant crocodilian taxa using two biomechanical approaches: beam theory and finite element analysis. We demonstrate mechanical convergence between the slender-snouted phytosaur Ebrachosuchus neukami and modern slender-snouted crocodilians. We provide evidence that the phytosaurian premaxillary palate is functionally equivalent to the crocodilian secondary palate. The premaxillary palate is associated with greater resistance to biting induced stress, lower strain energy, higher resistance to bending and torsion, as well as increased performance under tension. In all tests, Ebrachosuchus performed worse than all tested crocodilians, showing higher stress under equivalent loading conditions. These findings have implications for the proposed feeding ecology of slender-snouted phytosaurs and corroborate previous broad assessments of phytosaur ecology based on morphological comparisons to crocodilians; however, we urge caution in overextending those assessments given the current paucity of comparative functional data.

Comparative biomechanical analysis demonstrates functional convergence between slender-snouted crocodilians and phytosaurs

Morphological similarities between the extinct Triassic archosauriform clade Phytosauria and extant crocodilians have formed the basis of long-proposed hypotheses of evolutionary convergence. These hypotheses have informed the reconstructions of phytosaur ecology and biology, including feeding preferences, body mass, soft tissue systems, mating behaviours, and environmental preferences. However, phytosaurs possess numerous cranial apomorphies that distinguish them from modern crocodilians and potentially limit ecomorphological comparisons. Here, we present the first computational mechanical comparison of phytosaur cranial strength to several extant crocodilian taxa using two biomechanical approaches: beam theory and finite element analysis. We demonstrate mechanical convergence between the slender-snouted phytosaur Ebrachosuchus neukami and modern slender-snouted crocodilians. We provide evidence that the phytosaurian premaxillary palate is functionally equivalent to the crocodilian secondary palate. The premaxillary palate is associated with greater resistance to biting induced stress, lower strain energy, higher resistance to bending and torsion, as well as increased performance under tension. In all tests, Ebrachosuchus performed worse than all tested crocodilians, showing higher stress under equivalent loading conditions. These findings have implications for the proposed feeding ecology of slender-snouted phytosaurs and corroborate previous broad assessments of phytosaur ecology based on morphological comparisons to crocodilians; however, we urge caution in overextending those assessments given the current paucity of comparative functional data.