9,556 research outputs found
Neutrino Oscillations as a Probe of Dark Energy
We consider a class of theories in which neutrino masses depend significantly
on environment, as a result of interactions with the dark sector. Such theories
of mass varying neutrinos (MaVaNs) were recently introduced to explain the
origin of the cosmological dark energy density and why its magnitude is
apparently coincidental with that of neutrino mass splittings. In this Letter
we argue that in such theories neutrinos can exhibit different masses in matter
and in vacuum, dramatically affecting neutrino oscillations. Both long and
short baseline experiments are essential to test for these interactions. As an
example of modifications to the standard picture, we consider simple models
which may simultaneously account for the LSND anomaly, KamLAND, K2K and studies
of solar and atmospheric neutrinos, while providing motivation to continue to
search for neutrino oscillations in short baseline experiments such as BooNE.Comment: 5 pages, 1 figure, refs added, additional data considered, minor
change in conclusions about LSN
Recommended from our members
e‐Science Task Force Final Report
In several recent reports and solicitations, the National Science Foundation (NSF) has not only emphasized the importance of shared technological resources for academic work and research in all disciplines, but also pointed out the need to embed resources, tools, and services within a larger system—a cyberinfrastructure (CI). Based on networks, computers, and data storage, a CI’s foundation is the services, software, and human expertise that organize these resources to make them ubiquitously and seamlessly accessible to researchers, faculty, and students. Such a system aims to enable “distributed knowledge communities that collaborate and communicate across disciplines, distances, and cultures.” Echoing NSF, a research initiatives report solicited by the Computing Research Association in December 2008 recommends “a series of investments to create balanced high performance cyberinfrastructure for hundreds of U.S. colleges and universities which will stimulate the development, deployment, and application of a new generation of data‐intensive discovery.” Because, as the report states, “Research universities are the central engine of the innovation economy,” the task of “providing network enabled opportunities for students and faculty to work with large‐scale, data‐intensive computing and other cyberinfrastructure will yield high returns over many years.” Columbia must be in a position to take advantage of such national cyberinfrastructure investments should they occur
Approximating the Minimum Equivalent Digraph
The MEG (minimum equivalent graph) problem is, given a directed graph, to
find a small subset of the edges that maintains all reachability relations
between nodes. The problem is NP-hard. This paper gives an approximation
algorithm with performance guarantee of pi^2/6 ~ 1.64. The algorithm and its
analysis are based on the simple idea of contracting long cycles. (This result
is strengthened slightly in ``On strongly connected digraphs with bounded cycle
length'' (1996).) The analysis applies directly to 2-Exchange, a simple ``local
improvement'' algorithm, showing that its performance guarantee is 1.75.Comment: conference version in ACM-SIAM Symposium on Discrete Algorithms
(1994
The Far-Infrared/Radio Correlation in Nearby Abell Clusters
A comprehensive study of the effect of the cluster environment on the far-
infrared (FIR)/radio correlation in nearby Abell clusters is presented. Using
the cluster radio galaxy database from Miller & Owen (2001) and optical
spectroscopy and high resolution radio images to remove AGN, we assess the
FIR/radio correlation of cluster galaxies from the centers of the clusters out
well past the classical Abell radius. The FIR/radio correlation is shown to
hold quite well for star forming galaxies, and the FIR and radio fluxes for
cluster AGN are also well correlated. In the case of AGN, the relative radio-
to-FIR fluxes are greater and the scatter in the correlation is larger than
those seen for star forming galaxies. We also find that there is a rare but
statistically significant excess of star forming galaxies with enhanced radio
emission in the centers of the clusters, and that the degree of this
enhancement is typically a factor of two or three. The FIR/radio correlation
for cluster star forming galaxies is also tested against line-of-sight velocity
relative to the cluster systemic velocities, but no significant correlation is
found. While the radial dependence of the FIR/radio correlation is consistent
with the model wherein ram pressure increases the cluster galaxies' magnetic
field strengths through compression, the velocity data do not confirm this
model. Although a contribution from ram pressure can not be ruled out, the
thermal pressure due to the ICM alone is an equally viable alternative. The
high resolution radio images largely reject the hypothesis that the increased
radio emission arises from an AGN component, strengthening the claim that the
change in the correlation is caused by a change in the environment of the
galaxies.Comment: 26 pages, including 5 figures (uses AASTeX 5.0). Accepted for
publication in the Astronomical Journa
Cdc53p acts in concert with Cdc4p and Cdc34p to control the G1 to S phase transition and identifies a conserved family of proteins
Regulation of cell cycle progression occurs in part through the targeted degradation of both activating and inhibitory subunits of the cyclin-dependent kinases. During G1, CDC4, encoding a WD-40 repeat protein, and CDC34, encoding a ubiquitin-conjugating enzyme, are involved in the destruction of these regulators. Here we describe evidence indicating that CDC53 also is involved in this process. Mutations in CDC53 cause a phenotype indistinguishable from those of cdc4 and cdc34 mutations, numerous genetic interactions are seen between these genes, and the encoded proteins are found physically associated in vivo. Cdc53p defines a large family of proteins found in yeasts, nematodes, and humans whose molecular functions are uncharacterized. These results suggest a role for this family of proteins in regulating cell cycle proliferation through protein degradation
Herpetofaunal Inventory of Arkansas Post National Memorial, Arkansas County, Arkansas
The Arkansas Post National Memorial (ARPO) is a unique historical landmark with an interesting herpetofaunal community. We conducted an amphibian and reptile inventory of this national park from 2000-2002. We found eight amphibian and 21 reptilian species inhabiting the park. These included eight species not previously identified at ARPO. Overall species richness was highest at Alligator Slough, although the northern portion of ARPO was relatively rich. Aquatic trophic guilds included 7 (36.8%) piscivores, 7 (36.8%) omnivores, 4 (21.1%) insectivores, and one (5.3%) carnivore. The terrestrial trophic guilds included 13 (76.5%) insectivores, 2 (11.8%) carnivores, and 1 (5.9%) each of omnivores and generalized carnivores. We provide a species list, analysis of the distributions, diversity relationships and the trophic guilds present at ARPO, including management recommendations for the conservation of the herpetofauna community at ARPO
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