5,514 research outputs found
The nature and genesis of solution cavities (Makondos) in Transvaal Cave breccias
Main articleThe discovery of a large part of the cranium of a
hominid, evidently closely related to Homo habilis
(Hughes and Tobias 1977) in a solution cavity
within the calcified Member 5 of the Sterkfontein
Formation (Partridge 1978) has again drawn attention
to the frequent occurrence of these features
in the hominid-bearing breccias of the Transvaal.
The authors first studied these features at
Makapansgat (fig. 1) some fifteen years ago and
have since then become aware of their very widespread
occurrence in soluble rocks in many parts
of the world. All subsequent information has
served to confirm the origin of these features, but,
since these were never published, it is worthwhile
to place these findings on record.
Solution cavities, or Makondos, in the Transvaal
cave breccias are soil-filled pits shaped like an
inverted cone. Their walls and intervening areas of
the calcified cave deposit are usually rough, and
the coalescing of adjacent cavities below the surface
is common. They seldom exceed 2 m in diameter
and 6 m in depth and occur at intervals of 2 to
3 m in the calcified cave deposit.Non
Formal Solution of the Fourth Order Killing equations for Stationary Axisymmetric Vacuum Spacetimes
An analytic understanding of the geodesic structure around non-Kerr
spacetimes will result in a powerful tool that could make the mapping of
spacetime around massive quiescent compact objects possible. To this end, I
present an analytic closed form expression for the components of a the fourth
order Killing tensor for Stationary Axisymmetric Vacuum (SAV) Spacetimes. It is
as yet unclear what subset of SAV spacetimes admit this solution. The solution
is written in terms of an integral expression involving the metric functions
and two specific Greens functions. A second integral expression has to vanish
in order for the solution to be exact. In the event that the second integral
does not vanish it is likely that the best fourth order approximation to the
invariant has been found. This solution can be viewed as a generalized Carter
constant providing an explicit expression for the fourth invariant, in addition
to the energy, azimuthal angular momentum and rest mass, associated with
geodesic motion in SAV spacetimes, be it exact or approximate. I further
comment on the application of this result for the founding of a general
algorithm for mapping the spacetime around compact objects using gravitational
wave observatories.Comment: 5 Page
Inter-site Coulomb interaction and Heisenberg exchange
Based on exact diagonalization results for small clusters we discuss the
effect of inter-site Coulomb repulsion in Mott-Hubbard or charge transfer
insulators. Whereas the exchange constant J for direct exchange is
substantially enhanced by inter-site Coulomb interaction, that for
superexchange is suppressed. The enhancement of J in the single-band models
holds up to the critical value for the charge density wave (CDW) instability,
thus opening the way for large values of J. Single-band Hubbard models with
sufficiently strong inter-site repulsion to be near a CDW instability thus may
provide `physical' realizations of t-J like models with the `unphysical'
parameter ratio J/t=1.Comment: Revtex file, 4 PRB pages, with 5 embedded ps-files. To appear in PRB,
rapid communications. Hardcopies of figures or the entire manuscript may also
be obtained by e-mail request to: [email protected]
Electromagnetic Transition Strengths in Heavy Nuclei
We calculate reduced B(E2) and B(M1) electromagnetic transition strengths
within and between K-bands in support of a recently proposed model for the
structure of heavy nuclei. Previously, only spectra and a rough indication of
the largest B(E2) strengths were reported. The present more detailed
calculations should aid the experimental identification of the predicted ,
and bands and, in particular, act to confirm or refute the
suggestion that the model and bands correspond to the well known
and widespread beta and gamma bands. Furthermore they pinpoint transitions
which can indicate the presence of a so far elusive band by feeding
relatively strongly into or out of it. Some of these transitions may already
have been measured in Th, Th and U.Comment: 10 pages, 1 Figure, submitted to Physical Review
Twin building lattices do not have asymptotic cut-points
We show that twin building lattices have linear divergence, which implies
that all asymptotic cones are without cut-points.Comment: 7 page
Charged excitons in doped extended Hubbard model systems
We show that the charge transfer excitons in a Hubbard model system including
nearest neighbor Coulomb interactions effectively attain some charge in doped
systems and become visible in photoelectron and inverse photoelectron
spectroscopies. This shows that the description of a doped system by an
extended Hubbard model differs substantially from that of a simple Hubbard
model. Longer range Coulomb interactions cause satellites in the one electron
removal and addition spectra and the appearance of spectral weight if the gap
of doped systems at energies corresponding to the excitons of the undoped
systems. The spectral weight of the satellites is proportional to the doping
times the coordination number and therefore is strongly dependent on the
dimension.Comment: 10 pages revtex, 5 figures ps figures adde
Conformal Fixed Points of Unidentified Gauge Theories
In this article we discuss gauge/strings correspondence based on the
non-critical strings. With this goal we present several remarkable sigma models
with the AdS target spaces. The models have kappa symmetry and are completely
integrable. The radius of the AdS space is fixed and thus they describe
isolated fixed points of gauge theories in various dimensionsComment: 14 page
Measurement Of Quasiparticle Transport In Aluminum Films Using Tungsten Transition-Edge Sensors
We report new experimental studies to understand the physics of phonon
sensors which utilize quasiparticle diffusion in thin aluminum films into
tungsten transition-edge-sensors (TESs) operated at 35 mK. We show that basic
TES physics and a simple physical model of the overlap region between the W and
Al films in our devices enables us to accurately reproduce the experimentally
observed pulse shapes from x-rays absorbed in the Al films. We further estimate
quasiparticle loss in Al films using a simple diffusion equation approach.Comment: 5 pages, 6 figures, PRA
WKB approximation for multi-channel barrier penetrability
Using a method of local transmission matrix, we generalize the well-known WKB
formula for a barrier penetrability to multi-channel systems. We compare the
WKB penetrability with a solution of the coupled-channels equations, and show
that the WKB formula works well at energies well below the lowest adiabatic
barrier. We also discuss the eigen-channel approach to a multi-channel
tunneling, which may improve the performance of the WKB formula near and above
the barrier.Comment: 15 pages, 4 eps figure
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