A traversing micro‐erosion meter (TMEM) was used to measure short‐term microtopographic changes on a supratidal rock surface at Marengo, Australia. In order to describe the characteristics of rock surface behaviour at different temporal scales, the TMEM site was monitored at 2‐hourly, daily and multiday (3.5 days) periods. The rock surface was highly dynamic at 2‐hourly scale, repeatedly falling and rising by up to 0.644 mm. Two‐hourly surface change was also characterised by spatial heterogeneity, with contraction and expansion occurring concurrently at centimetre scale across the rock surface. Two‐hourly microtopographic change was linked to the microclimate with significant relationships between surface movement and relative humidity (R2 = 0.27) and air temperature (R2 = 0.24). Expansion was observed across the rock surface when there was a fluctuation of 18% in relative humidity, and when cloudy the rock surface remained active during the day. Temporal variability in surface movement was also observed over a 24 h period with three distinct periods observed: falling (06:00–12:00), rising (12:00–20:00) and stable (20:00–06:00). The daily surface change underwent no net microtopographic change (no loss of material). In contrast, an overall contraction was observed at multiday scale. Rock surface behaviour in coastal environments is therefore complex with many cycles of expansion and contraction acting concurrently albeit at different temporal scales from hours to multiple days. © 2018 John Wiley & Sons, Ltd.

This paper studies the synergistic effect of total ionizing dose (TID) and displacement damage dose (DDD) in enhancement-mode GaN high electron mobility transistor (HEMT) based on the p-GaN gate and cascode structure using neutron and 60Co gamma-ray irradiation. The results show that when the accumulated gamma-ray doses are up to 800k rad(Si), the leakage-current degradations of the two types of GaN HEMTs with 14 MeV neutron irradiation of 1.3 × 1012 n/cm2 and 3 × 1012 n/cm2 exhibit a lower degradation than the sum of the two separated effects. However, the threshold voltage shifts of the cascode structure GaN HEMT show a higher degradation when exposed to both TID and DDD effects. Moreover, the failure mechanisms of the synergistic effect in GaN HEMT are investigated using the scanning electron microscopy technique. It is shown that for the p-GaNHEMT, the increase in channel resistance and the degradation of two-dimensional electron gas mobility caused by neutron irradiation suppresses the increase in the TID leakage current. For the cascode structure HEMT, the neutron radiation-generated defects in the oxide layer of the metal–oxide–semiconductor field-effect transistor might capture holes induced by gamma-ray irradiation, resulting in a further increase in the number of trapped charges in the oxide layer.

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In this study laboratory experiments were used to explore the role of biofilms, formed by lithobiontic microorganism communities, in causing hourly surface changes of supratidal sandstone and the potential linkage to long‐term rock decay. To isolate the influence of individual environmental factors (temperature and humidity) on rock surface changes (expansion and contraction), a colonized (biofilm‐covered) and a non‐colonized sandstone block (biofilm‐free) underwent the same univariate microclimatic simulations closely controlled by an environmental chamber. Simulations were run under three different light conditions, with a natural light lamp on, on and off at 20‐min intervals and off, to investigate the impact of light on rock surface dynamics. Measured with a traversing micro‐erosion meter (TMEM), two‐hourly microtopographic fluctuations of these two sandstone blocks were compared in the same environment. Induced by microclimatic variations, surface movements of significantly higher magnitude (12–120% under varying tempeature and 121–154% under varying humidity) and different change patterns were observed on the colonized block, indicating the primary role of biofilm in driving microtopographic fluctuations of supratidal sandstone. However, thermally driven changes of similar magnitude and pattern were observed on both surfaces, suggesting other mechanisms also operating on the non‐colonized rock surface in this process. Due to the sensitivity of biofilm microorganism communities to light, the magnitude and pattern of surface changes was impacted by light condition. Because biofilms increased the magnitude and number of cycles of expansion and contraction of the experimental rock surface, we propose that lithobiontic biofilms facilitate the detachment of grains and granular disintegration on the rock surface, consequently contributing to rock decay and accelerating the rate of breakdown of supratidal rock. This short‐term episode therefore needs to be superimposed on longer term studies to fully understand the role of biofilms in rock surface change. © 2019 John Wiley & Sons, Ltd.