259 research outputs found
Influence of different permafrost processes on the large-scale energy and water cycles over Siberia
Did Cosmology Trigger the Origin of the Solar System?
It is a matter of curious coincidence that the Solar System formed 4.6 billion years ago around the same epoch that the Friedmann-Lemaitre (FL) universe became -dominated or dark-energy-dominated, where is the cosmological constant. This observation was made in the context of known gravitational anomalies that affect spacecraft orbits during planetary flyby's and the Pioneer anomaly, both possibly having connections with cosmology. In addition, it has been known for some time that the Universe is not only expanding but accelerating as well. Hence one must add the onset of cosmological acceleration in the FL universe as having a possible influence on the origin of the Solar System. These connections will now be examined in greater detail
Quasi-normal modes of AdS black holes : A superpotential approach
A novel method, based on superpotentials is proposed for obtaining the
quasi-normal modes of anti-de Sitter black holes. This is inspired by the case
of the three-dimensional BTZ black hole, where the quasi-normal modes can be
obtained exactly and are proportional to the surface gravity. Using this
approach, the quasi-normal modes of the five dimensional Schwarzschild
anti-deSitter black hole are computed numerically. The modes again seem to be
proportional to the surface gravity for very small and very large black holes.
They reflect the well-known instability of small black holes in anti-deSitter
space.Comment: LaTeX, 17 pages, 5 eps figures, 1 eepic figure, minor typos correcte
Belief, Credence and Statistical Evidence
According to the Rational Threshold View, a rational agent believes p if and only if her credence in p is equal to or greater than a certain threshold. One of the most serious challenges for this view is the problem of statistical evidence: statistical evidence is often not sufficient to make an outright belief rational, no matter how probable the target proposition is given such evidence. This indicates that rational belief is not as sensitive to statistical evidence as rational credence. The aim of this paper is twofold. First, we argue that, in addition to playing a decisive role in rationalizing outright belief, non-statistical evidence also plays a preponderant role in rationalizing credence. More precisely, when both types of evidence are present in a context, non-statistical evidence should receive a heavier weight than statistical evidence in determining rational credence. Second, based on this result, we argue that a modified version of the Rational Threshold View can avoid the problem of statistical evidence. We conclude by suggesting a possible explanation of the varying sensitivity to different types of evidence for belief and credence based on the respective aims of these attitudes
A detailed study of quasinormal frequencies of the Kerr black hole
We compute the quasinormal frequencies of the Kerr black hole using a
continued fraction method. The continued fraction method first proposed by
Leaver is still the only known method stable and accurate for the numerical
determination of the Kerr quasinormal frequencies. We numerically obtain not
only the slowly but also the rapidly damped quasinormal frequencies and analyze
the peculiar behavior of these frequencies at the Kerr limit. We also calculate
the algebraically special frequency first identified by Chandrasekhar and
confirm that it coincide with the quasinormal frequency only at the
Schwarzschild limit.Comment: REVTEX, 15 pages, 7 eps figure
Continuous 1.3-Million-Year Record of East African Hydroclimate, and Implications for Patterns of Evolution and Biodiversity
The transport of moisture in the tropics is a critical process for the global energy budget and on geologic timescales, has markedly influenced continental landscapes, migratory pathways, and biological evolution. Here we present a continuous, first-of-its-kind 1.3-My record of continental hydroclimate and lake-level variability derived from drill core data from Lake Malawi, East Africa (9â15° S). Over the Quaternary, we observe dramatic shifts in effective moisture, resulting in large-scale changes in one of the worldâs largest lakes and most diverse freshwater ecosystems. Results show evidence for 24 lake level drops of more than 200 m during the Late Quaternary, including 15 lowstands when water levels were more than 400 m lower than modern. A dramatic shift is observed at the Mid-Pleistocene Transition (MPT), consistent with far-field climate forcing, which separates vastly different hydroclimate regimes before and after âŒ800,000 years ago. Before 800 ka, lake levels were lower, indicating a climate drier than today, and water levels changed frequently. Following the MPT high-amplitude lake level variations dominate the record. From 800 to 100 ka, a deep, often overfilled lake occupied the basin, indicating a wetter climate, but these highstands were interrupted by prolonged intervals of extreme drought. Periods of high lake level are observed during times of high eccentricity. The extreme hydroclimate variability exerted a profound influence on the Lake Malawi endemic cichlid fish species flock; the geographically extensive habitat reconfiguration provided novel ecological opportunities, enabling new populations to differentiate rapidly to distinct species
Black Hole Decay and Quantum Instantons
We study the analytic structure of the S-matrix which is obtained from the
reduced Wheeler-DeWitt wave function describing spherically symmetric
gravitational collapse of massless scalar fields. The complex simple poles in
the S-matrix lead to the wave functions that satisfy the same boundary
condition as quasi-normal modes of a black hole, and correspond to the bounded
states of the Euclidean Wheeler-DeWitt equation. These wave function are
interpreted as quantum instantons.Comment: RevTex, 7 pages, no figure; The wave functions of gr-qc/9912115 are
newly interpreted as quantum instantons describing a black hole decay.
Replaced by the version to be published in Phys. Rev. D, in which the
boundary condition on the apparent horizon is clarifie
A Mission to Explore the Pioneer Anomaly
The Pioneer 10 and 11 spacecraft yielded the most precise navigation in deep
space to date. These spacecraft had exceptional acceleration sensitivity.
However, analysis of their radio-metric tracking data has consistently
indicated that at heliocentric distances of astronomical units,
the orbit determinations indicated the presence of a small, anomalous, Doppler
frequency drift. The drift is a blue-shift, uniformly changing with a rate of
Hz/s, which can be interpreted as a
constant sunward acceleration of each particular spacecraft of . This signal has become known as the Pioneer
anomaly. The inability to explain the anomalous behavior of the Pioneers with
conventional physics has contributed to growing discussion about its origin.
There is now an increasing number of proposals that attempt to explain the
anomaly outside conventional physics. This progress emphasizes the need for a
new experiment to explore the detected signal. Furthermore, the recent
extensive efforts led to the conclusion that only a dedicated experiment could
ultimately determine the nature of the found signal. We discuss the Pioneer
anomaly and present the next steps towards an understanding of its origin. We
specifically focus on the development of a mission to explore the Pioneer
Anomaly in a dedicated experiment conducted in deep space.Comment: 8 pages, 9 figures; invited talk given at the 2005 ESLAB Symposium
"Trends in Space Science and Cosmic Vision 2020", 19-21 April 2005, ESTEC,
Noordwijk, The Netherland
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