Information techniques for irrigation systems: Selected proceedings of the Second International Network Meeting on Information Techniques for Irrigation Systems held in Lahore/Bahawalnagar, Pakistan, 5-8 December 1994

Irrigation management / Irrigation systems / Decision support tools / Decision making / Information systems / Computer techniques / Models / Water management / Malaysia / Pakistan / Sri Lanka

Modelled subglacial floods and tunnel valleys control the life cycle of transitory ice streams

Ice streams are corridors of fast-flowing ice that control mass transfers from continental ice sheets to oceans. Their flow speeds are known to accelerate and decelerate, their activity can switch on and off, and even their locations can shift entirely. Our analogue physical experiments reveal that a life cycle incorporating evolving subglacial meltwater routing and bed erosion can govern this complex transitory behaviour. The modelled ice streams switch on and accelerate when subglacial water pockets drain as marginal outburst floods (basal decoupling). Then they decelerate when the lubricating water drainage system spontaneously organizes itself into channels that create tunnel valleys (partial basal recoupling). The ice streams surge or jump in location when these water drainage systems maintain low discharge but they ultimately switch off when tunnel valleys have expanded to develop efficient drainage systems. Beyond reconciling previously disconnected observations of modern and ancient ice streams into a single life cycle, the modelling suggests that tunnel valley development may be crucial in stabilizing portions of ice sheets during periods of climate change

Detection of mild papilloedema in posterior uveitis using spectral domain optical coherence tomography

Objective To compare two methods for diagnosing mild papilloedema (PO) using peripapillary total retinal (PTR) and retinal nerve fibre layer (RNFL) thickness measurement by spectral domain optical coherence tomography (OCT) in patients suffering from posterior uveitis. Methods 17 eyes in 17 patients with PO caused by posterior uveitis, 15 eyes in 15 patients with uveitis but with no PO based on slit lamp analysis were studied. High-quality OCT fundus images were analysed and graded by three masked observers using the Modified Frisen Scale. Eyes with PO were divided into two subgroups: mild (n= 15) and moderate-severe PO (n= 2). Two measurement methods were evaluated and compared: RNFL and PTR thickness measurements centred on the optic disc. Thickness values were calculated overall and for each quadrant and compared between groups. The main outcome measures were RNFL and PTR thickness, and thickness variation between control and affected patients for both protocols. Results Average RNFL and PTR thickness in the moderate-severe PO, mild PO and control groups were 274.5 +/- 54.45 mm, 134 +/- 31.69 mm, 97.4 +/- 14.43 mm and 722.25 +/- 29.34 mm, 437.53 +/- 84.47 mm, 327.8 +/- 25.92 mm, respectively. Mild PO differed from the control groups according to both the RNLF (p= 0.0006) and the PTR (p= 0.0002) measurements. The average thickness variation between control and mild PO was significantly different between RNFL and PTR measurements: 36.6 mm vs 109.73 mm (p< 0.0001), respectively. Conclusions PTR thickness measurement increases the sensitivity of detection of mild PO and could be useful for diagnosing and monitoring papillitis. A new protocol should be developed to measure PTR in the same 3.5 mm disc as the RNFL measurement