5,272 research outputs found
Kinematics of the South Atlantic rift
The South Atlantic rift basin evolved as branch of a large
Jurassic-Cretaceous intraplate rift zone between the African and South American
plates during the final breakup of western Gondwana. By quantitatively
accounting for crustal deformation in the Central and West African rift zone,
we indirectly construct the kinematic history of the pre-breakup evolution of
the conjugate West African-Brazilian margins. Our model suggests a causal link
between changes in extension direction and velocity during continental
extension and the generation of marginal structures such as the enigmatic
Pre-salt sag basin and the S\~ao Paulo High. We model an initial E-W directed
extension between South America and Africa (fixed in present-day position) at
very low extensional velocities until Upper Hauterivian times (126 Ma)
when rift activity along in the equatorial Atlantic domain started to increase
significantly. During this initial 17 Myr-long stretching episode the
Pre-salt basin width on the conjugate Brazilian and West African margins is
generated. An intermediate stage between 126.57 Ma and Base Aptian is
characterised by strain localisation, rapid lithospheric weakening in the
equatorial Atlantic domain, resulting in both progressively increasing
extensional velocities as well as a significant rotation of the extension
direction to NE-SW. Final breakup between South America and Africa occurred in
the conjugate Santos--Benguela margin segment at around 113 Ma and in the
Equatorial Atlantic domain between the Ghanaian Ridge and the Piau\'i-Cear\'a
margin at 103 Ma. We conclude that such a multi-velocity, multi-directional
rift history exerts primary control on the evolution of this conjugate passive
margins systems and can explain the first order tectonic structures along the
South Atlantic and possibly other passive margins.Comment: 46 Pages, 22 figures. Submitted to Solid Earth
(http://www.solid-earth.net). Abstract shortened due to arXiv restrictions.
New version contains revisions and amendments as per reviewers requests.
Supplementary data is available at
http://datahub.io/en/dataset/southatlanticrif
Effect of Particle Shape and Charge on Bulk Rheology of Nanoparticle Suspensions
The rheology of nanoparticle suspensions for nanoparticles of various shapes
with equal mass is studied using molecular dynamics simulations. The
equilibrium structure and the response to imposed shear are analyzed for
suspensions of spheres, rods, plates, and jacks in an explicit solvent for both
charged and uncharged nanoparticles. For the volume fraction studied,
?, the uncharged systems are all in their isotropic phase and
the viscosity is only weakly dependent on shape for spheres, rods, and plate
whereas for the jacks the viscosity is an order of magnitude larger than for
the other three shapes. The introduction of charge increases the viscosity for
all four nanoparticle shapes with the increase being the largest for rods and
plates. The presence of a repulsive charge between the particles decreases the
amount of stress reduction that can be achieved by particle reorientation.Comment: 15 pages, 9 figures, in pres
Invariance of density correlations with charge density in polyelectrolyte solutions
We present a theory for the equilibrium structure of polyelectrolyte
solutions. The main element is a simple, new optimization scheme that allows
theories such as the random phase approximation (RPA) to handle the harsh
repulsive forces present in such systems. Comparison is made with data from
recent neutron scattering experiments of randomly charged, hydrophilic polymers
in salt-free, semi-dilute solution at various charge densities. Models with
varying degrees of realism are examined. The usual explanation of the
invariance observed at high charge density has been counterion condensation.
However, when polymer-polymer correlations are treated properly, we find that
modeling polymer-counterion correlations at the level of Debye-Huckel theory is
sufficient.Comment: 4 pages, 2 figure
Competition between Kondo screening and quantum Hall edge reconstruction
We report on a Kondo correlated quantum dot connected to two-dimensional
leads where we demonstrate the renormalization of the g-factor in the pure
Zeeman case i.e, for magnetic fields parallel to the plane of the quantum dot.
For the same system we study the influence of orbital effects by investigating
the quantum Hall regime i.e. a perpendicular magnetic field is applied. In this
case an unusual behaviour of the suppression of the Kondo effect and of the
split zero-bias anomaly is observed. The splitting decreases with magnetic
field and shows discontinuous changes which are attributed to the intricate
interplay between Kondo screening and the quantum Hall edge structure
originating from electrostatic screening. This edge structure made up of
compressible and incompressible stripes strongly affects the Kondo temperature
of the quantum dot and thereby influences the renormalized g-factor
Flight/ground sample comparison relating to flight experiment M552, exothermic brazing
Comparisons were made between Skylab and ground-based specimens of nickel and stainless steel which were vacuum brazed using silver-copper-lithium alloy with various joint configurations. It was established that the absence of gravity greatly extends the scope of brazing since capillary flow can proceed without gravity interference. There was also evidence of enhanced transport, primarily in that liquid silver copper alloy dissolves nickel to a much greater extent in the zero gravity environment
Local Phonon Density of States in an Elastic Substrate
The local, eigenfunction-weighted acoustic phonon density of states (DOS)
tensor is calculated for a model substrate consisting of a semi-infinite
isotropic elastic continuum with a stress-free surface. On the surface, the
local DOS is proportional to the square of the frequency, as for the
three-dimensional Debye model, but with a constant of proportionality that is
considerably enhanced compared to the Debye value, a consequence of the
Rayleigh surface modes. The local DOS tensor at the surface is also
anisotropic, as expected. Inside the substrate the local DOS is both spatially
anisotropic and non-quadratic in frequency. However, at large depths, the local
DOS approaches the isotropic Debye value. The results are applied to a Si
substrate.Comment: 7 pages, 2 figures, RevTe
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