6,290 research outputs found
Effective t-J Hamiltonian for the Copper Oxides
Starting from the Emery model, which is assumed to describe the copper oxygen
planes, and including direct oxygen hopping matrix elements, we have been able
to derive the effective t-J Hamiltonian for the copper orbitals using the
Linked Cluster Expansion Method up to fourth order in the hybridization matrix
element.Comment: (ps version of the dvi file, resubmitted because previous
uucompressed version was corrupted), 9 page
Absence of a structural transition up to 40 Gpa in MgB2 and the relevance of magnesium non-stoichiometry
We report measurements on MgB2 up to ~40GPa. Increasing pressure yields a
monotonous decrease of the lattice parameters and of the c/a ratio, but no
structural transition down to parameters smaller than those of AlB2. The
transition superconducting temperature also decreases with temperature in a
sample dependent way. The results are explained by an increase of the filling
of the 2D pxy bands with pressure, the Mg stoichiometry determining the
starting position of the Fermi level. Our measurements indicate that these hole
bands are the relevant ones for superconductivity.Comment: submitted March 9th 2001, PRB accepte
Constraint and gauge shocks in one-dimensional numerical relativity
We study how different types of blowups can occur in systems of hyperbolic evolution equations of the type found in general relativity. In particular, we discuss two independent criteria that can be used to determine when such blowups can be expected. One criteria is related to the so-called geometric blowup leading to gradient catastrophes, while the other is based upon the ODE-mechanism leading to blowups within finite time. We show how both mechanisms work in the case of a simple one-dimensional wave equation with a dynamic wave speed and sources, and later explore how those blowups can appear in one-dimensional numerical relativity. In the latter case we recover the well known "gauge shocks" associated with Bona-Massó–type slicing conditions. However, a crucial result of this study has been the identification of a second family of blowups associated with the way in which the constraints have been used to construct a hyperbolic formulation. We call these blowups "constraint shocks" and show that they are formulation specific, and that choices can be made to eliminate them or at least make them less severe
Seismic structure of the southern Rivera plate and Jalisco block subduction zone
Structural and tectonic features in the Pacific Coast of Mexico generate a
high level of seismic activity in the Jalisco block (JB) region, making it one
of the most attractive areas of the world for geophysical investigations. The
Rivera North America contact zone has been the object of different tectonic
studies in recent years framed within the TsuJal project. To this day, this
project is generating numerous crucial geophysical results, which significantly
improve our understanding of the region. Our study is focused on the
interaction between the south of the JB and Rivera plate (RP), which crosses
the Middle America trench. We also cover an offshore onshore transect of 130 km
length between the eastern Rivera fracture zone and La Huerta region, in the
Jalisco state. To characterize this region,we interpreted wide angle seismic,
multichannel seismic, and multibeam bathymetry data. The integration of these
results, with the local and regional seismicity recorded by the Jalisco Seismic
Accelerometric Telemetric Network and by the Mapping the Rivera Subduction Zone
experiment, provides new insights into the geometry of the southern RP, which
is dipping 12 14 degrees under the JB in the northeast southwest direction.
Moreover, our results provide new seismic images of the accretionary wedge, the
shallow crust, the deep crust, and the upper-mantle structure along this
profile.Comment: Seismological Research Letters 201
- …