10,851 research outputs found
Rapid Saline Permafrost Thaw Below a Shallow Thermokarst Lake in Arctic Alaska
Permafrost warming and degradation is well documented across the Arctic. However, observation- and model-based studies typically consider thaw to occur at 0°C, neglecting the widespread occurrence of saline permafrost in coastal plain regions. In this study, we document rapid saline permafrost thaw below a shallow arctic lake. Over the 15-year period, the lakebed subsided by 0.6 m as ice-rich, saline permafrost thawed. Repeat transient electromagnetic measurements show that near-surface bulk sediment electrical conductivity increased by 198% between 2016 and 2022. Analysis of wintertime Synthetic Aperture Radar satellite imagery indicates a transition from a bedfast to a floating ice lake with brackish water due to saline permafrost thaw. The regime shift likely contributed to the 65% increase in thermokarst lake lateral expansion rates. Our results indicate that thawing saline permafrost may be contributing to an increase in landscape change rates in the Arctic faster than anticipated
Harmonic functions, central quadrics, and twistor theory
Solutions to the -dimensional Laplace equation which are constant on a
central quadric are found. The associated twistor description of the case
is used to characterise Gibbons-Hawking metrics with tri-holomorphic SL(2,
\C) symmetry.Comment: Final version. To appear in CQ
Girls’ and women’s education within Unesco and the World Bank, 1945–2000
By 2000, girls’ and women’s education was a priority for international development organisations. While studies have examined the impact of recent campaigns and programmes, there has been less exploration of ideas about girls’ and women’s education within development thought in the immediate post?colonial period, and the political mechanisms through which this came to be a global concern. Through a study of policy documents, this paper investigates how the education of girls and women came to be prioritised within the two principle UN agencies involved with education since 1945, the World Bank and Unesco. A shift in priorities is evident, from ensuring formal rights and improving the status of women, to expanding the productive capacities of women, fertility control and poverty reduction. While the ascendance of human capital theory provided a space for a new perception of the role of women’s education in development, in other policy arenas women’s education was central to exploring more substantive, rights?based notions of gender equality. Ultimately, the goal of improving girls’ and women’s education fitted into diverse development agendas, paving the way for it to become a global development priority
Protein annotation and modelling servers at University College London
The UCL Bioinformatics Group web portal offers several high quality protein structure prediction and function annotation algorithms including PSIPRED, pGenTHREADER, pDomTHREADER, MEMSAT, MetSite, DISOPRED2, DomPred and FFPred for the prediction of secondary structure, protein fold, protein structural domain, transmembrane helix topology, metal binding sites, regions of protein disorder, protein domain boundaries and protein function, respectively. We also now offer a fully automated 3D modelling pipeline: BioSerf, which performed well in CASP8 and uses a fragment-assembly approach which placed it in the top five servers in the de novo modelling category. The servers are available via the group web site at http://bioinf.cs.ucl.ac.uk/
SDiff(2) Toda equation -- hierarchy, function, and symmetries
A continuum limit of the Toda lattice field theory, called the SDiff(2) Toda
equation, is shown to have a Lax formalism and an infinite hierarchy of higher
flows. The Lax formalism is very similar to the case of the self-dual vacuum
Einstein equation and its hyper-K\"ahler version, however now based upon a
symplectic structure and the group SDiff(2) of area preserving diffeomorphisms
on a cylinder . An analogue of the Toda lattice tau function is
introduced. The existence of hidden SDiff(2) symmetries are derived from a
Riemann-Hilbert problem in the SDiff(2) group. Symmetries of the tau function
turn out to have commutator anomalies, hence give a representation of a central
extension of the SDiff(2) algebra.Comment: 16 pages (``vanilla.sty" is attatched to the end of this file after
``\bye" command
Report of the Working Group on `W Mass and QCD' (Phenomenology Workshop on LEP2 Physics, Oxford, April 1997)
The W Mass and QCD Working Group discussed a wide variety of topics relating
to present and future measurements of M(W) at LEP2, including QCD backgrounds
to W+W- production. Particular attention was focused on experimental issues
concerning the direct reconstruction and threshold mass measurements, and on
theoretical and experimental issues concerning the four jet final state. This
report summarises the main conclusions.Comment: 43 pages LaTeX and 15 encapsulated postscript figures. Uses epsfig
and ioplppt macros. Full Proceedings to be published in Journal of Physics
Optical and submillimetre observations of Bok globules -- tracing the magnetic field from low to high density
We present optical and submillimetre polarimetry data of the Bok globule CB3
and optical polarimetry data of the Bok globule CB246. We use each set of
polarimetry data to infer the B-field orientation in each of the clouds. The
optical data can only be used in the low density, low extinction edge regions
of clouds. The submillimetre data can only be used in the high column-density,
central regions of the clouds.
It has previously been found that near-infrared polarisation mapping of
background stars does not accurately trace the magnetic field in dense cloud
regions. This may be due to a lack of aligned grains in dense regions. We test
this by comparing the field orientations measured by our two independent
polarimetry methods. We find that the field orientation deduced from the
optical data matches up well with the orientation estimated from the
submillimetre data. We therefore claim that both methods are accurately tracing
the same magnetic field in CB3. Hence, in this case, there must be significant
numbers of aligned dust grains in the high density region, and they do indeed
trace the magnetic field in the submillimetre.
We find an offset of 4014 degrees between the magnetic field orientation
and the short axis of the globule. This is consistent with the mean value of
313 degrees found in our previous work on prestellar cores, even though
CB3 is a protostellar core. Taken together, the six prestellar cores that we
have now studied in this way show a mean offset between magnetic field
orientation and core short axis of 3 degrees, in apparent
contradiction with some models of magnetically dominated star formation.Comment: 8 pages, 3 figures, accepted for publication in MNRA
Remarks on the waterbag model of dispersionless Toda Hierarchy
We construct the free energy associated with the waterbag model of dToda.
Also, the relations of conserved densities are investigatedComment: 12 page
The Paleocene-Eocene Thermal Maximum:how much carbon is enough?
The Paleocene-Eocene Thermal Maximum (PETM),55.53 million years before present, was an abrupt warming event that involved profound changes in the carbon cycle and led to major perturbations of marine and terrestrial ecosystems. The PETM was triggered by the release of a massive amount of carbon, and thus, the event provides an analog for future climate and environmental changes given the current anthropogenic CO2 emissions. Previous attempts to constrain the amount of carbon released have produced widely diverging results, between 2000 and 10,000 gigatons carbon (GtC). Here we use the UVic Earth System Climate Model in conjunction with a recently published compilation of PETM temperatures to constrain the initial atmospheric CO2 concentration as well as the total mass of carbon released during the event. Thirty-six simulations were initialized with varying ocean alkalinity, river runoff, and ocean sediment cover. Simulating various combinations of pre-PETM CO2 levels (840, 1680, and 2520 ppm) and total carbon releases (3000, 4500, 7000, and 10,000 GtC), we find that both the 840 ppm plus 7000 GtC and 1680 ppm plus 7000-10,000 GtC scenarios agree best with temperature reconstructions. Bottom waters outside the Arctic and North Atlantic Oceans remain well oxygenated in all of our simulations. While the recovery time and rates are highly dependent on ocean alkalinity and sediment cover, the maximum temperature anomaly, used here to constrain the amount of carbon released, is less dependent on this slow-acting feedback. Key PointsWe constrain pre-PETM CO2 concentration and total amount of carbon releasedData-model comparison with full OGCM including long-term transient simulationsOnly carbon-intensive scenarios are compatible with dat
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