Characterization of active layer water contents in the McMurdo Sound region, Antarctica

The liquid soil water contents in the seasonally thawed layer (active layer) were characterized from seven soil climate monitoring sites - four coastal sites from south to north (Minna Bluff, Scott Base, Marble Point and Granite Harbour), and inland sites from low to high altitude (Wright Valley, Victoria Valley and Mount Fleming). Mean water contents ranged from 0.013 m³ m⁻³ near the surface at Victoria Valley to 0.013 m³ m⁻³ near the ice-cemented layer at Granite Harbour. The coastal sites have greater soil water contents than the McMurdo Dry Valley and Mount Fleming sites, and moisture contents increase with depth in the active layer. The Wright Valley site receives very little infiltration from snowmelt, with none in most years. All other sites, except Mount Fleming, received between one and four wetting events per summer, and infiltrated water moved to greater depths (≈ 10–25 cm). The Scott Base and Granite Harbour sites are on sloping ground and receive a subsurface flow of water along the ice-cemented permafrost. Our findings indicate that water contents are low with very little recharge, are greatly influenced by the local microclimate and topography, and show no significant increasing or decreasing trend over 10 years of monitoring

Temporal and spatial variation in active layer depth in the McMurdo Sound Region, Antarctica

A soil climate monitoring network, consisting of seven automated weather stations, was established between 1999 and 2003, ranging from Minna Bluff to Granite Harbour and from near sea level to about 1700m on the edge of the polar plateau. Active layer depth was calculated for each site for eight successive summers from 1999/2000 to 2006/2007. The active layer depth varied from year to year and was deepest in the warm summer of 2001–02 at all recording sites. No trends of overall increase or decrease in active layer depth were evident across the up-to-eight years of data investigated. Average active layer depth decreased with increasing latitude from Granite Harbour (778S, active layer depth of.90 cm) to Minna Bluff (78.58S, active layer depth of 22 ± 0.4 cm), and decreased with increasing altitude from Marble Point (50m altitude, active layer depth of 49 ± 9 cm) through to Mount Fleming (1700m altitude, active layer depth of 6 ± 2 cm). When all data from the sites were grouped together and used to predict active layer depth the mean summer air temperature, mean winter air temperature, total summer solar radiation and mean summer wind speed explained 73% of the variation (R250.73)

New constraints from U–Pb dating of detrital zircons on the palaeogeographic origin of metasediments in the Talea Ori, central Crete

High-pressure low-temperature metamorphic sediments of the Phyllite–Quartzite unit sensu stricto and the Talea Ori group are investigated in the field, microstructurally and by U–Pb dating of detrital zircons to shed light on their palaeogeographic origin. Zircon age spectra with ages >450 Ma of the Phyllite–Quartzite unit sensu stricto indicate a palaeogeographic origin at the northern margin of East Gondwana. In contrast, the lower stratigraphic, siliciclastic formations of the Talea Ori group show a high number of well-rounded Cambrian to Early Carboniferous aged zircons and a Neoproterozoic zircon age spectrum with East Gondwana affinity. Based on the comparison of zircon age data, a possible distal sediment source is the Sakarya Zone at the southern active margin of Eurasia. To reconcile the zircon data with the geological observations we propose different alternative models, or a combination of these, including sediment transport from the Sakarya Zone and/or a westerly source towards the northern margin of Gondwana as well as terrane-displacement of the Sakarya Zone. Also, a palaeogeographic origin of the Talea Ori group at the southern active margin of Eurasia cannot be excluded. This alternative, however, would not be consistent with the usually assumed association of the Talea Ori group with the Plattenkalk unit characterized by a palaeogeographic origin at the northern margin of Gondwana

Establishing RNAi in a non-model organism: The Antarctic nematode Panagrolaimus sp. DAW1

The Antarctic nematode Panagrolaimus sp. DAW1 is one of the only organisms known to survive extensive intracellular freezing throughout its tissues. Although the physiological mechanisms of this extreme adaptation are partly understood, the molecular mechanisms remain largely unknown. RNAi is a method that allows the examination of gene function in a direct, targeted manner, by knocking out specific mRNAs and revealing the effects on the phenotype. In this study we have explored the viability of RNAi in Panagrolaimus sp. DAW1. In the first trial, nematodes were fed E. coli expressing Panagrolaimus sp. DAW1 dsRNA of the embryonic lethal genes rps-2 and dhc, and the blister gene duox. Pd-rps-2(RNAi)-treated nematodes showed a significant decrease in larval hatching. However, qPCR showed no significant decrease in the amount of rps-2 mRNA in Pd-rps-2(RNAi)-treated animals. Several soaking protocols for dsRNA uptake were investigated using the fluorescent dye FITC. Desiccation-enhanced soaking showed the strongest uptake of FITC and resulted in a significant and consistent decrease of mRNA levels of two of the four tested genes (rps-2 and tps-2a), suggesting effective uptake of dsRNA-containing solution by the nematode. These findings suggest that RNAi by desiccation-enhanced soaking is viable in Panagrolaimus sp. DAW1 and provide the first functional genomic approach to investigate freezing tolerance in this non-model organism. RNAi, in conjunction with qPCR, can be used to screen for candidate genes involved in intracellular freezing tolerance in Panagrolaimus sp. DAW1

The influence of a weight-bearing platform on the mechanical behavior of two Ilizarov ring fixators: tensioned wires vs. half-pins

<p>Abstract</p> <p>Background</p> <p>A weight-bearing platform applied at the distal end of an Ilizarov external frame allows patients with hindfoot transfixations, foot deformities or plantar skin lesions to bear weight. This leads to an indirect loading of the fracture or osteotomy site. However, the effect on the fracture/osteotomy site's motion or compressive loads is unknown. The aim of this study was to analyze the mechanical effects of a weight-bearing platform on the traditional all-wire, four-ring frame in comparison to a two-ring frame consisting of half-pins.</p> <p>Methods</p> <p>Two frame configurations, with either anatomically positioned wires or half-pins, were analyzed with and without a weight-bearing platform applied underneath the distal ring. Composite tibiae with a mid-diaphyseal osteotomy of 3.5 mm were used in all the experiments. An axial load was applied with the use of a universal test machine (UTS^®). Interfragmentary movements, the relative movements of bone fragments and movements between rings were recorded using displacement transducers. Compressive loads at the osteotomy site were recorded with loading cells.</p> <p>Results</p> <p>Indirect loading with a weight-bearing platform altered the force transmission through the osteotomy. Indirect loading of the tibiae decreased the extent of the axial micro-motion by 50% under the applied weight load when compared to direct weight loading (p < 0.05). The half pin frame was 25% stiffer than the wire frame under both direct and indirect loading of the tibiae (p < 0.05). Compressive loads under indirect loading were reduced by 67% in the wire frame and by 57% in the half-pin frames compared to direct loading of the bones (p < 0.05). While axial loading in the wire frames resulted in plain axial movements at the site of the osteotomy, it was coupled with translational movements and angular displacements in the half pin mountings. This effect was more apparent in the case of indirect loading.</p> <p>Conclusions</p> <p>A weight-bearing platform has substantial influence on the biomechanical performance of an Ilizarov external fixator. Half-pins induce greater stiffness to the Ilizarov external fixator and allow the usage of only one ring per bone segment, but shear stresses at the osteotomy under axial loading should be considered. The results allow an estimation of the size and direction of interfragmentary movements based on the extent of weight bearing.</p

Galerkin FEM for fractional order parabolic equations with initial data in H−s, 0<s≤1H^{-s},~0 < s \le 1

We investigate semi-discrete numerical schemes based on the standard Galerkin and lumped mass Galerkin finite element methods for an initial-boundary value problem for homogeneous fractional diffusion problems with non-smooth initial data. We assume that $\Omega\subset \mathbb{R}^d$, $d=1,2,3$ is a convex polygonal (polyhedral) domain. We theoretically justify optimal order error estimates in $L_2$- and $H^1$-norms for initial data in $H^{-s}(\Omega),~0\le s \le 1$. We confirm our theoretical findings with a number of numerical tests that include initial data $v$ being a Dirac $\delta$-function supported on a $(d-1)$-dimensional manifold.Comment: 13 pages, 3 figure