571 research outputs found
An emendation of some Cretaceous species of "Reophax" (Foraminiferida) from northwest Europe and Poland
The classification of some deep-water agglutinated foraminifera identified as Reophax minuta
Tappan, 1940 is revised based upon examination of type material. Lower Cretaceous specimens
formerly placed in Reophax minuta from northwest Europe and the Polish Carpathians in actuality
belong in Pseudonodosinella troyeri (Tappan, 1960). Upper Cretaceous forms formerly referred to R.
minuta are now placed in Pseudonodosinella parvula (Huss, 1966). A neotype for Pseudonodosinella
parvula is designated herein
Uppermost Jurassic to Lower Cretaceous benthic foraminiferal biostratigraphy at ODP Site 765 on the Argo Abyssal Plain.
Benthic foraminifers were studied in 99 samples collected from the lower 200 m of Hole 765C. The studied section
ranges from the Tithonian to Aptian, and benthic foraminifers can be subdivided into five assemblages on the basis of faunal diversity and stratigraphic ranges of distinctive species. Compared with deep-water assemblages from Atlantic DSDP sites and Poland, assemblages from the Argo Abyssal Plain display a higher diversity of agglutinated forms, which comprise the autochthonous assemblages. Assemblages at the base of Hole 765C are wholly composed of agglutinated forms, reflecting deposition beneath the carbonate compensation depth (CCD). Most calcareous benthic species are found in turbidite layers, and the presence of an upper Valanginian Praedorothia praehauteriviana Assemblage may indicate deposition at or just below the CCD. The P. praehauteriviana Assemblage from Hole 765C is the temporal equivalent of similar assemblages from DSDP Holes 534A, 416A, 370, 105, and 101 in the Atlantic Ocean and Hole 306 in the Pacific Ocean. Stratigraphic ranges of cosmopolitan agglutinated species at Site 765 generally overlap with their reported ranges in the Atlantic and in the bathyal flysch sequences of the Carpathians; however, several species from Hole 765C have not been previously reported from Uppermost Jurassic to Lower Cretaceous abyssal sediments
Quasistationary binary inspiral. I. Einstein equations for the two Killing vector spacetime
The geometry of two infinitely long lines of mass moving in a fixed circular
orbit is considered as a toy model for the inspiral of a binary system of
compact objects due to gravitational radiation. The two Killing fields in the
toy model are used, according to a formalism introduced by Geroch, to describe
the geometry entirely in terms of a set of tensor fields on the two-manifold of
Killing vector orbits. Geroch's derivation of the Einstein equations in this
formalism is streamlined and generalized. The explicit Einstein equations for
the toy model spacetime are derived in terms of the degrees of freedom which
remain after a particular choice of gauge.Comment: 37 pages, REVTeX, one PostScript Figure included with epsfig; minor
formatting changes and copyright notice added for journal publicatio
Discrete Group Actions on Spacetimes: Causality Conditions and the Causal Boundary
Suppose a spacetime is a quotient of a spacetime by a discrete group
of isometries. It is shown how causality conditions in the two spacetimes are
related, and how can one learn about the future causal boundary on by
studying structures in . The relations between the two are particularly
simple (the boundary of the quotient is the quotient of the boundary) if both
and have spacelike future boundaries and if it is known that the
quotient of the future completion of is past-distinguishing. (That last
assumption is automatic in the case of being multi-warped.)Comment: 32 page
Causally simple inextendible spacetimes are hole-free
It is shown that causally simple inextendible spacetimes are hole-free, thus
confirming the expectation that causal simplicity removes holes from spacetime.
This result is optimal in the sense that causal simplicity cannot be weakened
to causal continuity. Physically, it means that if there is some partial Cauchy
hypersurface which, for some reason, does not fully develop its influence, then
there is some discontinuity in the causal relation.Comment: Revtex4, 9 pages. v2: minor correction
Distorted charged dilaton black holes
We construct exact static, axisymmetric solutions of Einstein-Maxwell-dilaton
gravity presenting distorted charged dilaton black holes. The thermodynamics of
such distorted black holes is also discussed.Comment: 14 pages, latex; v2 typos corrected, references adde
Formation of closed timelike curves in a composite vacuum/dust asymptotically-flat spacetime
We present a new asymptotically-flat time-machine model made solely of vacuum
and dust. The spacetime evolves from a regular spacelike initial hypersurface S
and subsequently develops closed timelike curves. The initial hypersurface S is
asymptotically flat and topologically trivial. The chronology violation occurs
in a compact manner; namely the first closed causal curves form at the boundary
of the future domain of dependence of a compact region in S (the core). This
central core is empty, and so is the external asymptotically flat region. The
intermediate region surrounding the core (the envelope) is made of dust with
positive energy density. This model trivially satisfies the weak, dominant, and
strong energy conditions. Furthermore it is governed by a well-defined system
of field equations which possesses a well-posed initial-value problem.Comment: 15 pages; accepted to Phys. Rev. D (no modifications
On the Causality and Stability of the Relativistic Diffusion Equation
This paper examines the mathematical properties of the relativistic diffusion
equation. The peculiar solution which Hiscock and Lindblom identified as an
instability is shown to emerge from an ill-posed initial value problem. These
do not meet the mathematical conditions required for realistic physical
problems and can not serve as an argument against the relativistic
hydrodynamics of Landau and Lifshitz.Comment: 6 page
Conformal Invariance of Black Hole Temperature
It is shown that the surface gravity and temperature of a stationary black
hole are invariant under conformal transformations of the metric that are the
identity at infinity. More precisely, we find a conformal invariant definition
of the surface gravity of a conformal Killing horizon that agrees with the
usual definition(s) for a true Killing horizon and is proportional to the
temperature as defined by Hawking radiation. This result is reconciled with the
intimate relation between the trace anomaly and the Hawking effect, despite the
{\it non}invariance of the trace anomaly under conformal transformations.Comment: 8 pages, plain LaTeX, NSF-ITP-93-9
Quasi-Asimptotically Flat Spacetimes and Their ADM Mass
We define spacetimes that are asymptotically flat, except for a deficit solid
angle , and present a definition of their ``ADM'' mass, which is finite
for this class of spacetimes, and, in particular, coincides with the value of
the parameter of the global monopole spacetime studied by Vilenkin and
Barriola . Moreover, we show that the definition is coordinate independent, and
explain why it can, in some cases, be negative.Comment: Late
- …