Formation and dynamics of magma reservoirs.

The emerging concept of a magma reservoir is one in which regions containing melt extend from the source of magma generation to the surface. The reservoir may contain regions of very low fraction intergranular melt, partially molten rock (mush) and melt lenses (or magma chambers) containing high melt fraction eruptible magma, as well as pockets of exsolved magmatic fluids. The various parts of the system may be separated by a sub-solidus rock or be connected and continuous. Magma reservoirs and their wall rocks span a vast array of rheological properties, covering as much as 25 orders of magnitude from high viscosity, sub-solidus crustal rocks to magmatic fluids. Time scales of processes within magma reservoirs range from very slow melt and fluid segregation within mush and magma chambers and deformation of surrounding host rocks to very rapid development of magma and fluid instability, transport and eruption. Developing a comprehensive model of these systems is a grand challenge that will require close collaboration between modellers, geophysicists, geochemists, geologists, volcanologists and petrologists. This article is part of the Theo Murphy meeting issue 'Magma reservoir architecture and dynamics'.

Maintained serum sodium in male ultra-marathoners--the role of fluid intake, vasopressin, and aldosterone in fluid and electrolyte regulation.

Exercise-associated hyponatremia (EAH) is a well know electrolyte disorder in endurance athletes. Although fluid overload is the most like etiology, recent studies, however, argued whether EAH is a disorder of vasopressin secretion. The aims of the present study were to investigate (i) the prevalence of EAH in male ultra-marathoners and (ii) whether fluid intake, aldosterone or vasopressin, as measured by copeptin, were associated with post-race serum sodium concentration ([Na+]). In 50 male ultra-marathoners in a 100 km ultra-marathon, serum [Na+], aldosterone, copeptin, serum and urine osmolality, and body mass were measured pre- and post-race. Fluid intake, renal function parameters and urine excretion were measured. No athlete developed EAH. Copeptin and aldosterone increased; a significant correlation was found between the change in copeptin and the change in serum [Na+], no correlation was found between aldosterone and serum [Na+]. Serum [Na+] increased by 1.6%; body mass decreased by 1.9 kg. The change in serum [Na+] and body mass correlated significantly and negatively. The fluid intake of ~ 0.58 l/h was positively related to the change in body mass and negatively to both post-race serum [Na+] and the change in serum [Na+]. We conclude that serum [Na+] was maintained by both the mechanisms of fluid intake and the hormonal regulation of vasopressin.

New model systems provide insights into Myc-induced transformation.

The ability of Myc to promote cellular transformation is well established; however, a better understanding of the mechanisms through which Myc mediates tumorigenesis is essential for the development of therapeutic approaches to target this potent oncoprotein. Structure-function studies in rodent fibroblast cells have provided the basis for much of our current understanding of these mechanisms. To build on these approaches, we have characterized three novel human cell line models of Myc-dependent transformation: MCF10A, SH-EP Tet21/N-Myc, and LF1/TERT/LT/ST cells. We have also evaluated Myc family proteins (c-Myc and L-Myc), a naturally occurring isoform of Myc (MycS), and a set of N-terminal domain mutants (ΔMBII, W135E, T58A) for their ability to promote anchorage-independent growth in these models. Taken together, these results provide the field with three new human cell-based models to study Myc activity, highlight the importance of cellular context, and challenge the paradigm that the ability of Myc to promote tumorigenesis is exclusively MBII-dependent.

Bubble shapes and orientations in low Re simple shear flow.

We present measurements of shape and orientation of air bubbles in a viscous Newtonian fluid deformed by simple shear. The apparatus is a variation of the "parallel band" device developed by G. I. Taylor. Previous experimental studies on low viscosity ratio, low Reynolds number (Re << 1) bubble deformation have focussed on either small or large deformations (mostly small deformation) and have only qualitatively examined the orientation of bubbles except for small deformations. Our data set spans both the theoretical small deformation and high deformation limits. With these data we confirm theoretical relationships and assess the range of capillary numbers (Ca) over which theoretical relationships for shape and orientation of bubbles are appropriate. We also examine the geometry of deformed bubbles as they relax to a spherical shape once shear stresses are removed. Our data indicate that for extremely small Reynolds numbers and viscosity ratios, the small deformation theoretical relationship first developed by Taylor, is a good approximation for Ca<0.5. The large deformation results for both shape and bubble orientation derived by Hinch and Acrivos agree with our data for Ca>1 and Ca>0.5, respectively.