277 research outputs found
Expanding Cosmologies in Brane Geometries
Five dimensional gravity coupled, both in the bulk and on a brane, to a
scalar Liouville field yields a geometry confined to a strip around the brane
and with time dependent scale factors for the four geometry. In various limits
known models can be recovered as well as a temporally expanding four geometry
with a warp factor falling exponentially away from the brane. The effective
theory on the brane has a time dependent Planck mass and ``cosmological
constant''. Although the scale factor expands, the expansion is not an
acceleration.Comment: 7 pages, LaTex/RevTex
The Major Roles of DNA Polymerases Epsilon and Delta at the Eukaryotic Replication Fork Are Evolutionarily Conserved
Coordinated replication of eukaryotic genomes is intrinsically asymmetric, with continuous leading strand synthesis preceding discontinuous lagging strand synthesis. Here we provide two types of evidence indicating that, in fission yeast, these two biosynthetic tasks are performed by two different replicases. First, in Schizosaccharomyces pombe strains encoding a polδ-L591M mutator allele, base substitutions in reporter genes placed in opposite orientations relative to a well-characterized replication origin are strand-specific and distributed in patterns implying that Polδ is primarily involved in lagging strand replication. Second, in strains encoding a polε-M630F allele and lacking the ability to repair rNMPs in DNA due to a defect in RNase H2, rNMPs are selectively observed in nascent leading strand DNA. The latter observation demonstrates that abundant rNMP incorporation during replication can be tolerated and that they are normally removed in an RNase H2-dependent manner. This provides strong physical evidence that Polε is the primary leading strand replicase. Collectively, these data and earlier results in budding yeast indicate that the major roles of Polδ and Polε at the eukaryotic replication fork are evolutionarily conserved
Charge conservation and time-varying speed of light
It has been recently claimed that cosmologies with time dependent speed of
light might solve some of the problems of the standard cosmological scenario,
as well as inflationary scenarios. In this letter we show that most of these
models, when analyzed in a consistent way, lead to large violations of charge
conservation. Thus, they are severly constrained by experiment, including those
where is a power of the scale factor and those whose source term is the
trace of the energy-momentum tensor. In addition, early Universe scenarios with
a sudden change of related to baryogenesis are discarded.Comment: 4 page
Unique Signature of Dark Matter in Ancient Mica
Mica can store (for >1 Gy) etchable tracks caused by atoms recoiling from
WIMPs. Because a background from fission neutrons will eventually limit this
technique, a unique signature for WIMPs in ancient mica is needed. Our motion
around the center of the Galaxy causes WIMPs, unlike neutrons, to enter the
mica from a preferred direction on the sky. Mica is a directional detector and
despite the complex rotations that natural mica crystals make with respect to
this WIMP ``wind,'' there is a substantial dependence of etch pit density on
present day mica orientation.Comment: 5 pages, LaTeX, 2 figures. Accepted for publication at Phys. Rev.
Let
Molecular Phylogeny and Biogeography of the Native Rodents of Madagascar (Muridae: Nesomyinae): A Test of the Single-Origin Hypothesis
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72349/1/j.1096-0031.1999.tb00267.x.pd
The fundamental constants and their variation: observational status and theoretical motivations
This article describes the various experimental bounds on the variation of
the fundamental constants of nature. After a discussion on the role of
fundamental constants, of their definition and link with metrology, the various
constraints on the variation of the fine structure constant, the gravitational,
weak and strong interactions couplings and the electron to proton mass ratio
are reviewed. This review aims (1) to provide the basics of each measurement,
(2) to show as clearly as possible why it constrains a given constant and (3)
to point out the underlying hypotheses. Such an investigation is of importance
to compare the different results, particularly in view of understanding the
recent claims of the detections of a variation of the fine structure constant
and of the electron to proton mass ratio in quasar absorption spectra. The
theoretical models leading to the prediction of such variation are also
reviewed, including Kaluza-Klein theories, string theories and other
alternative theories and cosmological implications of these results are
discussed. The links with the tests of general relativity are emphasized.Comment: 56 pages, l7 figures, submitted to Rev. Mod. Phy
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