Flood magnitude-frequency and lithologic control on bedrock river incision in post-orogenic terrain

Mixed bedrock-alluvial rivers - bedrock channels lined with a discontinuous alluvial cover - are key agents in the shaping of mountain belt topography by bedrock fluvial incision. Whereas much research focuses upon the erosional dynamics of such rivers in the context of rapidly uplifting orogenic landscapes, the present study investigates river incision processes in a post-orogenic (cratonic) landscape undergoing extremely low rates of incision (> 5 m/Ma). River incision processes are examined as a function of substrate lithology and the magnitude and frequency of formative flows along Sandy Creek gorge, a mixed bedrock-alluvial stream in arid SE-central Australia. Incision is focused along a bedrock channel with a partial alluvial cover arranged into riffle-pool macrobedforms that reflect interactions between rock structure and large-flood hydraulics. Variations in channel width and gradient determine longitudinal trends in mean shear stress (τb) and therefore also patterns of sediment transport and deposition. A steep and narrow, non-propagating knickzone (with 5% alluvial cover) coincides with a resistant quartzite unit that subdivides the gorge into three reaches according to different rock erodibility and channel morphology. The three reaches also separate distinct erosional styles: bedrock plucking (i.e. detachment-limited erosion) prevails along the knickzone, whereas along the upper and lower gorge rock incision is dependent upon large formative floods exceeding critical erosion thresholds (τc) for coarse boulder deposits that line 70% of the channel thalweg (i.e. transport-limited erosion). The mobility of coarse bed materials (up to 2 m diameter) during late Holocene palaeofloods of known magnitude and age is evaluated using step-backwater flow modelling in conjunction with two selective entrainment equations. A new approach for quantifying the formative flood magnitude in mixed bedrock-alluvial rivers is described here based on the mobility of a key coarse fraction of the bed materials; in this case the d84 size fraction. A 350 m3/s formative flood fully mobilises the coarse alluvial cover with τb200-300 N/m2 across the upper and lower gorge riffles, peaking over 500 N/m2 in the knickzone. Such floods have an annual exceedance probability much less than 10- 2 and possibly as low as 10- 3. The role of coarse alluvial cover in the gorge is discussed at two scales: (1) modulation of bedrock exposure at the reach-scale, coupled with adjustment to channel width and gradient, accommodates uniform incision across rocks of different erodibility in steady-state fashion; and (2) at the sub-reach scale where coarse boulder deposits (corresponding to <i>τ</i><sub>b</sub> minima) cap topographic convexities in the rock floor, thereby restricting bedrock incision to rare large floods. While recent studies postulate that decreasing uplift rates during post-orogenic topographic decay might drive a shift to transport-limited conditions in river networks, observations here and elsewhere in post-orogenic settings suggest, to the contrary, that extremely low erosion rates are maintained with substantial bedrock channel exposure. Although bed material mobility is known to be rate-limiting for bedrock river incision under low sediment flux conditions, exactly how a partial alluvial cover might be spatially distributed to either optimise or impede the rate of bedrock incision is open to speculation. Observations here suggest that the small volume of very stable bed materials lining Sandy Creek gorge is distributed so as to minimise the rate of bedrock fluvial incision over time

Patterns of eye-movements when Male and Female observers judge female attractiveness, body fat and waist-to-hip ratio

Behavioural studies of the perceptual cues for female physical attractiveness have suggested two potentially important features; body fat distribution (the waist-to-hip ratio or WHR) and overall body fat (often estimated by the body mass index or BMI). However none of these studies tell us directly which regions of the stimulus images inform observers’ judgments. Therefore, we recorded the eye-movements of 3 groups of 10 male observers and 3 groups of 10 female observers, when they rated a set of 46 photographs of female bodies. The first sets of observers rated the images for attractiveness, the second sets rated for body fat and the third sets for WHR. If either WHR and/or body fat are used to judge attractiveness, then observers rating attractiveness should look at those areas of the body which allow assessment of these features, and they should look in the same areas when they are directly asked to estimate WHR and body fat. So we are able to compare the fixation patterns for the explicit judgments with those for attractiveness judgments, and infer which features were used for attractiveness. Prior to group analysis of the eye-movement data, the locations of individual eye fixations were transformed into a common reference space to permit comparisons of fixation density at high resolution across all stimuli. This manipulation allowed us to use spatial statistical analysis techniques to show: 1) Observers’ fixations for attractiveness and body fat clustered in the central and upper abdomen and chest, but not the pelvic or hip areas, consistent with the finding that WHR had little influence over attractiveness judgments. 2) The pattern of fixations for attractiveness ratings was very similar to the fixation patterns for body fat judgments. 3) The fixations for WHR ratings were significantly different from those for attractiveness and body fat

Lipopolysaccharide exposure modifies high tidal volume ventilation-induced proinflammatory mediator expression in newborn rat lungs

Infection/inflammation and mechanical ventilation have both independently been shown to increase cytokine/chemokine levels in lung tissue and blood samples of premature patients. Little is known about the combined effect of systemic inflammation and mechanical ventilation on cytokine expression in the lung. We tested whether pre-existing inflammation induced by lipopolysaccharide (LPS) exposure would modify cytokine/chemokine response in newborn rat lungs to high tidal volume ventilation (HTVV). Newborn rats were randomly assigned to four groups: groups I and II (saline); groups III and IV: 3 mg/kg LPS. Groups II and IV were 24h later subjected to 3h of ventilation with a tidal volume of 25 mL/kg. HTVV alone increased IL-1beta, IL-6 and the chemokine (C-X-C motif) ligand 2 (CXCL2) mRNA expression. Although the cytokine response to LPS alone had disappeared after 24 h, the combination of LPS pretreatment and HTVV significantly increased the expression of IL-6 and IL-1beta mRNA when compared with HTVV alone. TNF-alpha expression was increased neither by HTVV alone nor in combination with LPS. IL-6 protein content in bronchoalveolar lavage increased due to the combined treatment. Thus, a subtle pre-existing inflammation combined with HTVV amplifies the proinflammatory cytokine/chemokine expression in the newborn rat lung compared with HTVV alone