562 research outputs found
Developing a preliminary recharge model of the Nile Basin to help interpret GRACE data
GRACE data provides a new and exciting opportunity to gain a direct and independent measure of water mass variation on a regional scale, but the data must be combined with hydrological modelling to indicate in which part of the water cycle the mass change has occurred. Processing GRACE data through a series of spectral filters indicates a seasonal variation to gravity mass (±0.005 mGal) thought to relate to the downstream movement of water in the catchment, and delayed storage from groundwater, following the wet season in the upper catchment.
To help interpret these data a groundwater recharge model was developed for the Nile Catchment using the model ZOODRM (a distributed modelling code for calculating spatial and temporal variations in groundwater recharge). ZOODRM was an appropriate model to use for this work, due to the lower data demands of the model, relative to other groundwater models, the ability of the model to use entirely remotely-sensed input data, and the added functionality of runoff routing. Rainfall (NOAA data) and ET data were sourced from the FEWS NET African Data Dissemination Service. Geological data was sourced from the digital geology map of the world, landuse data from the USGS and the DEM data from ESRI.
Initial model results indicate groundwater recharge across the basin of 0-4mma-1, with obvious considerable spatial variability. The results indicate the importance of groundwater in storing rainfall, and releasing it slowly throughout the year in different parts of the catchment. Only by modelling this process can GRACE data be reliably interpreted hydrologically. Despite only a qualitative interpretation of the GRACE data having been achieved within this preliminary study, the work has indicated that the ZOODRM model can be used with entirely remotely-sensed data, and that sufficient data exists for the Nile Basin to construct a plausible recharge model. Future work is now required to properly calibrate the model to enable closer comparison of the Nile GRACE data
Groundwater, flooding and hydrological functioning in the Findhorn floodplain, Scotland
A large floodplain of the River Findhorn, northeast Scotland, was investigated using hydrogeological and hydrochemical methods (including residence time indicators) to characterise groundwater/surface-water coupling and groundwater flooding. The study demonstrated widespread stratification within the floodplain: shallow (30 mm). Persistent groundwater flooding occurs within topographical lows and also in the discharge zone where it is largely managed with a series of drains constructed in the 19th century. The significant and complex role of groundwater in floodplains, demonstrated by this study, highlights the importance of fully considering groundwater in flood management schemes
Nondissipative Drag Conductance as a Topological Quantum Number
We show in this paper that the boundary condition averaged nondissipative
drag conductance of two coupled mesoscopic rings with no tunneling, evaluated
in a particular many-particle eigenstate, is a topological invariant
characterized by a Chern integer. Physical implications of this observation are
discussed.Comment: 4 pages, no figure. Title modified and significant revision made to
the text. Final version appeared in PR
Femtosecond laser writing in the monoclinic RbPb2Cl5:Dy3+ crystal
Monoclinic RbPb2Cl5:Dy single crystal was tested for femtosecond laser writing at wavelength of 800nm. Dependence of permanent refractive index change upon input pulse energy was investigated. Non-linear coefficients of multiphoton absorption and self-focusing were measured. Kerr non-linear coefficient was found to be as high as 4.0*10-6 cm2/GW
Transverse Wave Propagation in Relativistic Two-fluid Plasmas in de Sitter Space
We investigate transverse electromagnetic waves propagating in a plasma in
the de Sitter space. Using the 3+1 formalism we derive the relativistic
two-fluid equations to take account of the effects due to the horizon and
describe the set of simultaneous linear equations for the perturbations. We use
a local approximation to investigate the one-dimensional radial propagation of
Alfv\'en and high frequency electromagnetic waves and solve the dispersion
relation for these waves numerically.Comment: 19 pages, 12 figure
Isothermal Plasma Wave Properties of the Schwarzschild de-Sitter Black Hole in a Veselago Medium
In this paper, we study wave properties of isothermal plasma for the
Schwarzschild de-Sitter black hole in a Veselago medium. We use ADM 3+1
formalism to formulate general relativistic magnetohydrodynamical (GRMHD)
equations for the Schwarzschild de-Sitter spacetime in Rindler coordinates.
Further, Fourier analysis of the linearly perturbed GRMHD equations for the
rotating (non-magnetized and magnetized) background is taken whose determinant
leads to a dispersion relation. We investigate wave properties by using
graphical representation of the wave vector, the refractive index, change in
refractive index, phase and group velocities. Also, the modes of wave
dispersion are explored. The results indicate the existence of the Veselago
medium.Comment: 24 pages, 12 figures, accepted for publication in Astrophys. Space
Sci. arXiv admin note: text overlap with arXiv:1101.0884 and arxiv:1007.285
Electrical impedance spectroscopy in relation to seed viability and moisture content in snap bean (Phaseolus vulgaris L.)
Late Winter Biogeochemical Conditions Under Sea Ice in the Canadian High Arctic
With the Arctic summer sea-ice extent in decline, questions are arising as to how changes in sea-ice dynamics might affect biogeochemical cycling and phenomena such as carbon dioxide (CO2) uptake and ocean acidification. Recent field research in these areas has concentrated on biogeochemical and CO2 measurements during spring, summer or autumn, but there are few data for the winter or winter–spring transition, particularly in the High Arctic. Here, we present carbon and nutrient data within and under sea ice measured during the Catlin Arctic Survey, over 40 days in March and April 2010, off Ellef Ringnes Island (78° 43.11′ N, 104° 47.44′ W) in the Canadian High Arctic. Results show relatively low surface water (1–10 m) nitrate (<1.3 µM) and total inorganic carbon concentrations (mean±SD=2015±5.83 µmol kg−1), total alkalinity (mean±SD=2134±11.09 µmol kg−1) and under-ice pCO2sw (mean±SD=286±17 µatm). These surprisingly low wintertime carbon and nutrient conditions suggest that the outer Canadian Arctic Archipelago region is nitrate-limited on account of sluggish mixing among the multi-year ice regions of the High Arctic, which could temper the potential of widespread under-ice and open-water phytoplankton blooms later in the season
Skymrion lattice melting in the quantum Hall system
The melting and magnetic disordering of the skyrmion lattice in the quantum
Hall system at filling factor are studied. A
Berezinskii-Kosterlitz-Thouless renormalization group theory is employed to
describe the coupled magnetic and translational degrees of freedom. The
non-trivial magnetic properties of the skyrmion system stem from the in-plane
components of the non-collinear magnetization in the vicinity of skyrmions,
which are described by an antiferromagnetic XY model. In a Coulomb gas
formulation the `particles' are the topological defects of the XY model
(vortices) and of the lattice (dislocations and disclinations). The latter
frustrate the antiferromagnetic order and acquire fractional vorticity in order
to minimize their energy. We find a number of melting/disordering scenarios for
various lattice types. While these results do not depend on a particular model,
we also consider a simple classical model for the skyrmion system. It results
in a rich T=0 phase diagram. We propose that the triangular and square skyrmion
lattices are generically separated by a centered rectangular phase in the
quantum Hall system.Comment: 15 pages with 5 figures. Minor revisions. Important reference to M.
Rao, S. Sengupta, and R. Shankar, Phys. Rev. Lett. 79, 3998 (1997) adde
Coupling Optical and Electrical Measurements in Artificial Membranes: Lateral Diffusion of Lipids and Channel Forming Peptides in Planar Bilayers
Planar lipid bilayers (PLB) were prepared by the Montal-Mueller technique in a FRAP system designed to simultaneously measure conductivity across, and lateral diffusion of, the bilayer. In the first stage of the project the FRAP system was used to characterise the lateral dynamics of bilayer lipids with regards to phospholipid composition (headgroup, chain unsaturation etc.), presence of cholesterol and the effect of divalent cations on negatively-charged bilayers. In the second stage of the project, lateral diffusion of two fluorescently-labelled voltage-dependent pore-forming peptides (alamethicin and S4s from Shaker K(+) channel) was determined at rest and in the conducting state. This study demonstrates the feasibility of such experiments with PLBs, amenable to physical constraints, and thus offers new opportunities for systematic studies of structure-function relationships in membrane-associating molecules
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