22 research outputs found
Modification of turbulent dissipation rates by a deep Southern Ocean eddy
This is the final version. Available from AGU via the DOI in this recordAll data used in this study are available by communication with the author and will be archived at British Oceanographic Data CentreThe impact of a mesoscale eddy on the magnitude and spatial distribution of diapycnal ocean mixing is investigated using a set of hydrographic and microstructure measurements collected in the Southern Ocean. These data sampled a baroclinic, middepth eddy formed during the disintegration of a deep boundary current. Turbulent dissipation is suppressed within the eddy but is elevated by up to an order of magnitude along the upper and lower eddy boundaries. A ray tracing approximation is employed as a heuristic device to elucidate how the internal wave field evolves in the ambient velocity and stratification conditions accompanying the eddy. These calculations are consistent with the observations, suggesting reflection of internal wave energy from the eddy center and enhanced breaking through critical layer processes along the eddy boundaries. These results have important implications for understanding where and how internal wave energy is dissipated in the presence of energetic deep geostrophic flows.DIMES is supported by the Natural Environment Research Council (NERC) grants NE/E007058/1 and NE/E005667/1 and U.S. National Science Foundation grants OCE‐1231803, OCE‐0927583, and OCE‐1030309. K.L.S. and J.A.B. are supported by NERC
A classification of the torsion tensors on almost contact manifolds with B-metric
The space of the torsion (0,3)-tensors of the linear connections on almost
contact manifolds with B-metric is decomposed in 15 orthogonal and invariant
subspaces with respect to the action of the structure group. Three known
connections, preserving the structure, are characterized regarding this
classification.Comment: 17 pages, exposition clarified, references adde
On conformal submersions with geodesic or minimal fibers
We prove that every conformal submersion from a round sphere onto an Einstein manifold
with fbers being geodesics is—up to an isometry—the Hopf fbration composed with a
conformal difeomorphism of the complex projective space of appropriate dimension. We
also show that there are no conformal submersions with minimal fbers between manifolds
satisfying certain curvature assumptions
Vigorous lateral export of the meltwater outflow from beneath an Antarctic ice shelf
The instability and accelerated melting of the Antarctic Ice Sheet are among the foremost elements of contemporary global climate change1, 2. The increased freshwater output from Antarctica is important in determining sea level rise1, the fate of Antarctic sea ice and its effect on the Earth’s albedo4, 5, ongoing changes in global deep-ocean ventilation6, and the evolution of Southern Ocean ecosystems and carbon cycling7, 8. A key uncertainty in assessing and predicting the impacts of Antarctic Ice Sheet melting concerns the vertical distribution of the exported meltwater. This is usually represented by climate-scale models3–5, 9 as a near-surface freshwater input to the ocean, yet measurements around Antarctica reveal the meltwater to be concentrated at deeper levels10, 11, 12, 13, 14. Here we use observations of the turbulent properties of the meltwater outflows from beneath a rapidly melting Antarctic ice shelf to identify the mechanism responsible for the depth of the meltwater. We show that the initial ascent of the meltwater outflow from the ice shelf cavity triggers a centrifugal overturning instability that grows by extracting kinetic energy from the lateral shear of the background oceanic flow. The instability promotes vigorous lateral export, rapid dilution by turbulent mixing, and finally settling of meltwater at depth. We use an idealized ocean circulation model to show that this mechanism is relevant to a broad spectrum of Antarctic ice shelves. Our findings demonstrate that the mechanism producing meltwater at depth is a dynamically robust feature of Antarctic melting that should be incorporated into climate-scale models
The impact of transposable element activity on therapeutically relevant human stem cells
Human stem cells harbor significant potential for basic and clinical translational research as well as regenerative
medicine. Currently ~ 3000 adult and ~ 30 pluripotent stem cell-based, interventional clinical trials are ongoing
worldwide, and numbers are increasing continuously. Although stem cells are promising cell sources to treat a
wide range of human diseases, there are also concerns regarding potential risks associated with their clinical use,
including genomic instability and tumorigenesis concerns. Thus, a deeper understanding of the factors and
molecular mechanisms contributing to stem cell genome stability are a prerequisite to harnessing their therapeutic
potential for degenerative diseases. Chemical and physical factors are known to influence the stability of stem cell
genomes, together with random mutations and Copy Number Variants (CNVs) that accumulated in cultured human
stem cells. Here we review the activity of endogenous transposable elements (TEs) in human multipotent and
pluripotent stem cells, and the consequences of their mobility for genomic integrity and host gene expression. We
describe transcriptional and post-transcriptional mechanisms antagonizing the spread of TEs in the human genome,
and highlight those that are more prevalent in multipotent and pluripotent stem cells. Notably, TEs do not only
represent a source of mutations/CNVs in genomes, but are also often harnessed as tools to engineer the stem cell
genome; thus, we also describe and discuss the most widely applied transposon-based tools and highlight the
most relevant areas of their biomedical applications in stem cells. Taken together, this review will contribute to the
assessment of the risk that endogenous TE activity and the application of genetically engineered TEs constitute for
the biosafety of stem cells to be used for substitutive and regenerative cell therapiesS.R.H. and P.T.R. are funded by the Government of Spain (MINECO, RYC-2016-
21395 and SAF2015–71589-P [S.R.H.]; PEJ-2014-A-31985 and SAF2015–71589-
P [P.T.R.]). GGS is supported by a grant from the Ministry of Health of the
Federal Republic of Germany (FKZ2518FSB403)