RESUMEN
The rapid drainage of supraglacial lakes injects substantial volumes of water to the bed of the Greenland ice sheet over short timescales. The effect of these water pulses on the development of basal hydrological systems is largely unknown. To address this, we develop a lake drainage model incorporating both (1) a subglacial radial flux element driven by elastic hydraulic jacking and (2) downstream drainage through a linked channelized and distributed system. Here we present the model and examine whether substantial, efficient subglacial channels can form during or following lake drainage events and their effect on the water pressure in the surrounding distributed system. We force the model with field data from a lake drainage site, 70 km from the terminus of Russell Glacier in West Greenland. The model outputs suggest that efficient subglacial channels do not readily form in the vicinity of the lake during rapid drainage and instead water is evacuated primarily by a transient turbulent sheet and the distributed system. Following lake drainage, channels grow but are not large enough to reduce the water pressure in the surrounding distributed system, unless preexisting channels are present throughout the domain. Our results have implications for the analysis of subglacial hydrological systems in regions where rapid lake drainage provides the primary mechanism for surface-to-bed connections. KEY POINTS: Model for subglacial hydrological analysis of rapid lake drainage eventsLimited subglacial channel growth during and following rapid lake drainagePersistence of distributed drainage in inland areas where channel growth is limited.
RESUMEN
The aim of this study was to evaluate the retention of fixed orthodontic appliances bonded without liquid resin with the use of a retrospective study design. Patients from each of 2 consultant orthodontists in the same specialty clinic were chosen under strict selection criteria. In the test group (n = 37), composite material (Phase II) without liquid resin was used to bond full arch fixed appliances onto patients' upper teeth. Patients' appliances, which were bonded with Phase II composite and liquid resin, were used as the control group (n = 37). The duration of the appliance survival, from the date of appliance bonding to the date of first accidental bracket loss, was analyzed by Kaplan-Meier product limit method and log-rank test. Our data suggested that supragingival orthodontic metal brackets seemed to bond on healthy enamel surfaces and to work equally well either with or without the use of liquid resin. The total percentages of bond failure, roughly 6%, were similar in both test and control groups. Approximately 73% of all patients in the test group and 57% of the patients in the control group experienced no bond failure at all throughout the entire course of treatment.