Spatial patterns in the evolution of Cenozoic dynamic topography and its influence on the Antarctic continent

Our knowledge of dynamic topography in Antarctica remains in an infancy stage compared to other continents. We assess the space-time variability in dynamic topography in Antarctica by analysing grids of global dynamic topography in the Cenozoic (and late Cretaceous) based on the tomographic model S40RTS. Our model reveals that the Gamburtsev Province and Dronning Maud Land, two of the major nucleation sites for the East Antarctic Ice Sheet (EAIS) were ~500 m higher 60 Ma ago. The increased elevation may have facilitated ephemeral ice cap development in the early Cenozoic. Between ca 25 and 50 Ma the northern Wilkes Subglacial Basin was ca 200 m higher than today and a major increase in regional elevation (>600 m) occurred over the last 20-15 Ma over the northern and southern Victoria Land in the Transantarctic Mountains (TAM). The most prominent signal is observed over the Ross Sea Rift (RSR) where predicted Neogene dynamic topography exceeds 1,000 m. The flow of warm mantle from the West Antarctic Rift System (WARS)may have driven these dynamic topography effects over the TAM and RSR. However, we found that these effects are comparatively less significant over the Marie Byrd Land Dome and the interior of the WARS. If these contrasting dynamic topography effects are included, then the predicted elevations of the Ross Sea Embayment ca 20 Ma ago are more similar to the interior of the WARS, with significant implications for the early development of the West Antarctic Ice Sheet

Polaron and bipolaron dispersion curves in one dimension for intermediate coupling

Bipolaron energies are calculated as a function of wave vector by a variational method of Gurari appropriate for weak or intermediate coupling strengths, for a model with electron-phonon interactions independent of phonon wave vectors and a short-ranged Coulomb repulsion. It is assumed that the bare electrons have a constant effective mass. A two-parameter trial function is taken for the relative motion of the two electrons in the bipolaron. Energies of bipolarons are compared with those of two single polarons as a function of wave vector for various parameter values. Results for effective masses at the zone center are also obtained. Comparison is made with data of other authors for bipolarons in the Hubbard-Holstein model, which differs mainly from the present model in that it has a tight-binding band structure for the bare electrons.Comment: 11 pages including six figures. Physical Review B, to be publishe

Klein-Gordon Equation for Quark Pairs in Color Superconductor

The wave equation is derived for quark pairs in color superconductor in the regime of low density / strong coupling.Comment: 4 pages, no figure

Erosion at extended continental margins: Insights from new aerogeophysical data in eastern Dronning Maud Land

Modelling-, rock cooling-, sedimentation- and exposure-based interpretations of the mechanisms by which topography evolves at extended continental margins vary widely. Observations from the margin of Dronning Maud Land, Antarctica, have until now not strongly contributed to these interpretations. Here, we present new airborne gravity and radar data describing the eastern part of this margin. Inland of a tall (2.5 km) great escarpment, a plateau topped by a branching network of valleys suggests preservation of a fluvial landscape with SW-directed drainage beneath a cold-based ice sheet. The valley floor slopes show that this landscape was modified during a period of alpine-style glaciation prior to the onset of the current cold-based phase around 34 Ma. The volume of sediments in basins offshore in the Riiser-Larsen Sea balances with the volume of rock estimated to have been eroded and transported by north-directed drainage from between the escarpment and the continental shelf break. The stratigraphy of these basins shows that most of the erosion occurred during the ~40 Myr following late Jurassic continental breakup. This erosion is unlikely to have been dominated by backwearing because the required rate of escarpment retreat to its present location is faster than numerical models of landscape evolution suggest to be possible. We suggest an additional component of erosion by downwearing seawards of a pre-existing inland drainage divide. The eastern termination of the great escarpment and inland plateau is at the West Ragnhild trough, a 300 km long, 15–20 km wide and up to 1.6 km deep subglacial valley hosting the West Ragnhild glacier. Numerous overdeepened (by >300 m) segments of the valley floor testify to its experience of significant glacial erosion. Thick late Jurassic and early Cretaceous sediments fanning out from the trough's mouth into the eastern Riiser-Larsen Sea betray an earlier history as a river valley. The lack of late Jurassic relief-forming processes in this river's catchment in the interior of East Antarctica suggests this erosion was related to regional climatic change

Evaluation of the BCS Approximation for the Attractive Hubbard Model in One Dimension

The ground state energy and energy gap to the first excited state are calculated for the attractive Hubbard model in one dimension using both the Bethe Ansatz equations and the variational BCS wavefunction. Comparisons are provided as a function of coupling strength and electron density. While the ground state energies are always in very good agreement, the BCS energy gap is sometimes incorrect by an order of magnitude, particularly at half-filling. Finite size effects are also briefly discussed for cases where an exact solution in the thermodynamic limit is not possible. In general, the BCS result for the energy gap is poor compared to the exact result.Comment: 25 pages, 5 Postscript figure

Signatures of Superfluidity in Dilute Fermi Gases near a Feshbach Resonance

We present a brief account of the most salient properties of vortices in dilute atomic Fermi superfluids near a Feshbach resonance.Comment: 6 pages, 1 figure, and jltp.cls. Several typos and a couple of inaccuracies have been correcte

The pseudogap state in superconductors: Extended Hartree approach to time-dependent Ginzburg-Landau Theory

It is well known that conventional pairing fluctuation theory at the Hartree level leads to a normal state pseudogap in the fermionic spectrum. Our goal is to extend this Hartree approximated scheme to arrive at a generalized mean field theory of pseudogapped superconductors for all temperatures $T$. While an equivalent approach to the pseudogap has been derived elsewhere using a more formal Green's function decoupling scheme, in this paper we re-interpret this mean field theory and BCS theory as well, and demonstrate how they naturally relate to ideal Bose gas condensation. Here we recast the Hartree approximated Ginzburg-Landau self consistent equations in a T-matrix form. This recasting makes it possible to consider arbitrarily strong attractive coupling, where bosonic degrees of freedom appear at $T^*$ considerably above $T_c$. The implications for transport both above and below $T_c$ are discussed. Below $T_c$ we find two types of contributions. Those associated with fermionic excitations have the usual BCS functional form. That they depend on the magnitude of the excitation gap, nevertheless, leads to rather atypical transport properties in the strong coupling limit, where this gap (as distinct from the order parameter) is virtually $T$-independent. In addition, there are bosonic terms arising from non-condensed pairs whose transport properties are shown here to be reasonably well described by an effective time-dependent Ginzburg-Landau theory.Comment: 14 pages, 5 figures, REVTeX4, submitted to PRB; clarification of the diagrammatic technique added, one figure update

Selection of Forages for the Tropics (SoFT) - A Database and Selection Tool for Identifying Forages Adapted to Local Conditions in the Tropics and Subtropics

Rising populations and incomes in developing countries are likely to double demand for livestock products by 2020 (Delgado et al. 1999). This strong demand has potential to improve profitability for farmers but will require improved animal feeding in both semi-intensive crop-livestock and more extensive livestock systems. Forages usually are the most cost-effective option to supply feed demands, particularly for ruminant-, but also for pig- and poultry- production. It is critical to select the most suitable forages for the local system and conditions. Small- and even larger-scale farmers depend heavily on advice from extension and development agencies, and from seed companies, but this advice often is limited by inexperience and the difficulty in accessing reliable information. Expert information on an extensive range of tropical forages is now readily available through the SoFT database