312 research outputs found
Gas Seepage and Pockmark Formation From Subsurface Reservoirs:Insights From Table-Top Experiments
Pockmarks are morphological depressions commonly observed in ocean and lake floors. Pockmarks form by fluid (typically gas) seepage thorough a sealing sedimentary layer, deforming and breaching the layer. The seepage-induced sediment deformation mechanisms, and their links to the resulting pockmarks morphology, are not well understood. To bridge this gap, we conduct laboratory experiments in which gas seeps through a granular (sand) reservoir, overlaid by a (clay) seal, both submerged under water. We find that gas rises through the reservoir and accumulates at the seal base. Once sufficient gas over-pressure is achieved, gas deforms the seal, and finally escapes via either: (a) doming of the seal followed by dome breaching via fracturing; (b) brittle faulting, delineating a plug, which is lifted by the gas seeping through the bounding faults; or (c) plastic deformation by bubbles ascending through the seal. The preferred mechanism is found to depend on the seal thickness and stiffness: in stiff seals, a transition from doming and fracturing to brittle faulting occurs as the thickness increases, whereas bubble rise is preferred in the most compliant, thickest seals. Seepage can also occur by mixed modes, such as bubbles rising in faults. Repeated seepage events suspend the sediment at the surface and create pockmarks. We present a quantitative analysis that explains the tendency for the various modes of deformation observed experimentally. Finally, we connect simple theoretical arguments with field observations, highlighting similarities and differences that bound the applicability of laboratory experiments to natural pockmarks.</p
Ulta-slow relaxation in discontinuous-film based electron glasses
We present field effect measurements on discontinuous 2D thin films which are
composed of a sub monolayer of nano-grains of Au, Ni, Ag or Al. Like other
electron glasses these systems exhibit slow conductance relaxation and memory
effects. However, unlike other systems, the discontinuous films exhibit a
dramatic slowing down of the dynamics below a characteristic temperature .
is typically between 10-50K and is sample dependent. For the
sample exhibits a few other peculiar features such as repeatable conductance
fluctuations in millimeter size samples. We suggest that the enhanced system
sluggishness is related to the current carrying network becoming very dilute in
discontinuous films so that the system contains many parts which are
electrically very weakly connected and the transport is dominated by very few
weak links. This enables studying the glassy properties of the sample as it
transitions from a macroscopic sample to a mesocopic sample, hence, the results
provide new insight on the underlying physics of electron glasses.Comment: 4 pages, 4 figure
Time Dependent Development of the Coulomb Gap
We show that the time development of the Coulomb gap in a Coulomb glass can
involve very long relaxation times due to electron rearrangement and hopping.
We find that an applied magnetic field reduces the rate of electron hopping
and, hence, Coulomb gap formation. These results are consistent with recent
conductance experiments on thin semiconducting and metallic films.Comment: 4 pages, Latex, 3 encapsulated postscript figure
Density Functional Application to Strongly Correlated Electron Systems
The LSDA+U approach to density functional theory is carefully reanalyzed. Its
possible link to single-particle Green's function theory is occasionally
discussed. A simple and elegant derivation of the important sum rules for the
on-site interaction matrix elements linking them to the values of U and J is
presented. All necessary expressions for an implementation of LSDA+U into a
non-orthogonal basis solver for the Kohn-Sham equations are given, and
implementation into the FPLO solver is made. Results of application to several
planar cuprate structures are reported in detail and conclusions on the
interpretation of the physics of the electronic structure of the cuprates are
drawn.Comment: invited paper in Journal of Solid State Chemistr
Commensurate-Incommensurate Magnetic Phase Transition in Magnetoelectric Single Crystal LiNiPO
Neutron scattering studies of single-crystal LiNiPO reveal a spontaneous
first-order commensurate-incommensurate magnetic phase transition. Short- and
long-range incommensurate phases are intermediate between the high temperature
paramagnetic and the low temperature antiferromagnetic phases. The modulated
structure has a predominant antiferromagnetic component, giving rise to
satellite peaks in the vicinity of the fundamental antiferromagnetic Bragg
reflection, and a ferromagnetic component giving rise to peaks at small
momentum-transfers around the origin at . The wavelength of the
modulated magnetic structure varies continuously with temperature. It is argued
that the incommensurate short- and long-range phases are due to
spin-dimensionality crossover from a continuous to the discrete Ising state.
These observations explain the anomalous first-order transition seen in the
magnetoelectric effect of this system
A COMPARATIVE MATCHED-ANALYSIS OF MAJOR CLINICAL OUTCOMES USING DIFFERENT DRUG-ELUTING STENTS VS. BARE-METAL STENTS IN A LARGE CONSECUTIVE PATIENT COHORT
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