Mean percentages of maximum heart rates (%HRmax) were considered of very light exercise intensity and ranged from 47.11 (± 7.18) to 50.15 (± 9.35) % for checking bona fides through to driving urgently respectively.
Of the 345 duty calls attended by participants, the four most commonly reported tasks were as follows: 'check bona fides' (n = 76 22%), 'driving urgently' (n = 45 13%), 'attending a domestic incident' (n = 37 10%), and 'attending a concern for welfare' (n = 30 8%). Descriptive data were recorded and analyzed by task and changes in physiological measures.
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Spanning nine police stations from the same Australian state, volunteers wore monitoring devices to collect physiological measures (heart rate, respiratory rate, and skin temperature) throughout the course of four consecutive shifts (two day shifts and two night shifts). The aim of this study was to investigate the physiological demands placed on Australian police officers carrying out common operational tasks.įorty participants (n = 40) from an Australian police force (mean age = 33.58 ± 7.78 years, mean height = 177.70 ± 7.28 cm, mean weight = 85.68 ± 14.52 kg, mean years of service: 6.74 ± 6.29 years) were recruited through preidentified local area commands. This increase in the amorphous fraction of the highly oriented polyethylene fibers has a synergistic effect with the thermo-oxidative degradation processes and contributes significantly to the decrease in their molar mass. Changes in the crystalline morphology of the UHMMPE fibers were also observed through wide-angle X-ray diffraction (WAXS), showing an increase in the amorphous regions, which promotes oxygen diffusion into the material, specifically through these areas.
These carbon-centered radicals result from a cascade of thermo-oxidative reactions that ultimately induce CC ruptures along the backbone of the polymer.
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The decrease in the molar mass was further supported by the presence of carbon-centered free radicals in the polyethylene that was detected using electron paramagnetic resonance (EPR) spectroscopy. This is the first comprehensive study on thermally aged UHMMPE fibers that measures their decrease in the average molar mass via high-temperature size exclusion chromatography (HT-SEC) analysis.
The objective of this work is to advance the field of lightweight and soft UHMMPE inserts used in various types of ballistic resistant-body armor via elucidating the mechanisms of chemical degradation and evaluating this chemical degradation, as well as the corresponding physical changes, of the UHMMPE fibers upon thermal aging. However, polymeric materials are susceptible to thermally induced degradation during storage and use, which can reduce the high strength of these fibers, and, thus, negatively impact their ballistic resistance. Ultra-high molar mass polyethylene (UHMMPE) is commonly used for ballistic-resistant body armor applications due to the superior strength of the fibers fabricated from this material combined with its low density.
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