31 research outputs found
Generalized Cardassian Expansion: Models in Which the Universe is Flat, Matter Dominated, and Accelerating
The Cardassian universe is a proposed modification to the Friedmann Robertson
Walker (FRW) equation in which the universe is flat, matter dominated, and
accelerating. Here we generalize the original Cardassian proposal to include
additional variants on the FRW equation. Specific examples are presented.
In the ordinary FRW equation, the right hand side is a linear function of the
energy density, . Here, instead, the right hand side of the FRW
equation is a different function of the energy density, .
This function returns to ordinary FRW at early times, but modifies the
expansion at a late epoch of the universe. The only ingredients in this
universe are matter and radiation: in particular, there is {\it no} vacuum
contribution. Currently the modification of the FRW equation is such that the
universe accelerates. The universe can be flat and yet consist of only matter
and radiation, and still be compatible with observations. The energy density
required to close the universe is much smaller than in a standard cosmology, so
that matter can be sufficient to provide a flat geometry. The modifications may
arise, e.g., as a consequence of our observable universe living as a
3-dimensional brane in a higher dimensional universe. The Cardassian model
survives several observational tests, including the cosmic background
radiation, the age of the universe, the cluster baryon fraction, and structure
formation. As will be shown in future work, the predictions for observational
tests of the generalized Cardassian models can be very different from generic
quintessence models, whether the equation of state is constant or time
dependent.Comment: 5 pages, Conference Proceeding, Meeting on Sources and Detection of
Dark Matter and Dark Energy in the Universe, Marina del Rey, CA, February
200
Junior Recital: Katherine Riess, trombone
This recital is presented in partial fulfillment of requirements for the degree Bachelor of Music in Performance. Ms. Riess studies trombone with Wes Funderburk.https://digitalcommons.kennesaw.edu/musicprograms/1463/thumbnail.jp
Cardassian Expansion: a Model in which the Universe is Flat, Matter Dominated, and Accelerating
A modification to the Friedmann Robertson Walker equation is proposed in
which the universe is flat, matter dominated, and accelerating. An additional
term, which contains only matter or radiation (no vacuum contribution), becomes
the dominant driver of expansion at a late epoch of the universe. During the
epoch when the new term dominates, the universe accelerates; we call this
period of acceleration the Cardassian era. The universe can be flat and yet
consist of only matter and radiation, and still be compatible with
observations. The energy density required to close the universe is much smaller
than in a standard cosmology, so that matter can be sufficient to provide a
flat geometry. The new term required may arise, e.g., as a consequence of our
observable universe living as a 3-dimensional brane in a higher dimensional
universe. The Cardassian model survives several observational tests, including
the cosmic background radiation, the age of the universe, the cluster baryon
fraction, and structure formation.Comment: 12 pages, one eps figure. Accepted by Physics Lett.
Fallopia japonica and Impatiens glandulifera are colonized by species-poor root-associated fungal communities but have minor impacts on soil properties in riparian habitats
Fallopia japonica and Impatiens glandulifera are major plant invaders on a global scale that often become dominant in riparian areas. However, little is known about how these species affect interactions in soil-plant systems. The aim of this study was to investigate the impact of both species on abiotic and biotic soil properties, with a special focus on fungi. We investigated eight sites along small streams invaded by F. japonica and I. glandulifera, respectively, and compared each with nearby sites dominated by the native species Urtica dioica. Three different types of samples were collected: bulk soil, rhizosphere soil and roots from invasive and native stands at each site. Bulk soil samples were analysed for soil physicochemical, microbial properties (soil microbial respiration and ergosterol) and soil arthropod abundance (Acari and Collembola). Soil respiration was also evaluated in rhizosphere samples. The fungal community composition of both bulk soil and roots were analysed using a metabarcoding approach. Soil physicochemical properties as well as soil microbial activity, fungal biomass and soil fungal operational unit taxonomic unit (OTU) richness did not differ between invaded and native riparian habitats, indicating only minor belowground impacts of the two invasive plant species. Soil microbial activity, fungal biomass and soil fungal OTU richness were rather related to the soil physicochemical properties. In contrast, Acari abundance decreased by 68% in the presence of F. japonica, while Collembola abundance increased by 11% in I. glandulifera sites. Moreover, root-associated fungal communities differed between the invasive and native plants. In F. japonica roots, fungal OTU richness of all investigated ecological groups (mycorrhiza, endophytes, parasites, saprobes) were lower compared to U. dioica. However, in I. glandulifera roots only the OTU richness of mycorrhiza and saprobic fungi was lower. Overall, our findings show that F. japonica and I. glandulifera can influence the abundance of soil arthropods and are characterized by lower OTU richness of root-associated fungi
Cardassian Expansion: Dark Energy Density from Modified Friedmann Equations
The Cardassian universe is a proposed modification to the Friedmann equation
in which the universe is flat, matter dominated, and accelerating. In the
ordinary Friedmann equation, the right hand side is a linear function of the
energy density, . Here, instead, the right hand side of the
Friedmann equation is a different function of the energy density, . This function returns to ordinary Friedmann at early times, but
drives acceleration of the universe at the current epoch. The only ingredients
in this universe are matter and radiation: in particular, there is NO vacuum
contribution. The new term required may arise, e.g., as a consequence of our
observable universe living as a 3-dimensional brane in a higher dimensional
universe. A second possible interpretation of Cardassian expansion is
developed, in which we treat the modified Friedman equations as due to a fluid,
in which the energy density has new contributions with negative pressure
(possibly due to dark matter with self-interactions). Predictions are shown for
observational tests of generalized Cardassian models in future supernova
surveys.Comment: 7 pages, 1 figure, in press, New Astronomy Review
Devaluation: a dynamical mechanism for a naturally small cosmological constant
We propose a natural solution to the cosmological constant problem consistent
with the standard cosmology and successful over a broad range of energies. This
solution is based on the existence of a new field, the devaluton, with its
potential modeled on a tilted cosine. After inflation, the universe reheats and
populates the devaluton's many minima. As the universe cools, domain walls form
between different regions. The domain wall network then evolves and sweeps away
regions of higher vacuum energy in favor of lower energy ones. Gravitation
itself provides a cutoff at a minimum vacuum energy, thus leaving the universe
with a small cosmological constant comparable in magnitude to the present day
dark energy density.Comment: 6 pages and prepared in ReV-TeX added notes on eltro-weak breaking
and ds vacu
Probing Dark Energy Using Its Density Instead of Its Equation of State
The variation of dark energy density with redshift, , provides a
critical clue to the nature of dark energy. Since depends on the
dark energy equation of state through an integral, can be
constrained more tightly than given the same observational data. We
demonstrate this explicitly using current type Ia supernova (SN Ia) data [the
Tonry/Barris sample], together with the Cosmic Microwave Background (CMB) shift
parameter from CMB data (WMAP, CBI, and ACBAR), and the large scale structure
(LSS) growth factor from 2dF galaxy survey data. We assume a flat universe, and
use Markov Chain Monte Carlo (MCMC) technique in our analysis. We find that,
while extracted from current data is consistent with a cosmological
constant at 68% C.L., (which has far smaller uncertainties) is not.
Our results clearly show the advantage of using , instead of
, to probe dark energy.Comment: One color figure showing w_X(z) versus rho_X(z), reconstructed
model-independently from data. Submitte
Fluid Interpretation of Cardassian Expansion
A fluid interpretation of Cardassian expansion is developed. Here, the
Friedmann equation takes the form where contains
only matter and radiation (no vacuum). The function g(\rhom) returns to the
usual 8\pi\rhom/(3 m_{pl}^2) during the early history of the universe, but
takes a different form that drives an accelerated expansion after a redshift . One possible interpretation of this function (and of the right hand
side of Einstein's equations) is that it describes a fluid with total energy
density \rho_{tot} = {3 m_{pl}^2 \over 8 \pi} g(\rhom) = \rhom + \rho_K
containing not only matter density (mass times number density) but also
interaction terms . These interaction terms give rise to an effective
negative pressure which drives cosmological acceleration. These interactions
may be due to interacting dark matter, e.g. with a fifth force between
particles . Such interactions may be intrinsically four
dimensional or may result from higher dimensional physics. A fully relativistic
fluid model is developed here, with conservation of energy, momentum, and
particle number. A modified Poisson's equation is derived. A study of
fluctuations in the early universe is presented, although a fully relativistic
treatment of the perturbations including gauge choice is as yet incomplete.Comment: 25 pages, 1 figure. Replaced with published version. Title changed in
journa
Paraneoplastic thrombocytosis in ovarian cancer
<p>Background: The mechanisms of paraneoplastic thrombocytosis in ovarian cancer and the role that
platelets play in abetting cancer growth are unclear.</p>
<p>Methods: We analyzed clinical data on 619 patients with epithelial ovarian cancer to test associations between platelet counts and disease outcome. Human samples and mouse
models of epithelial ovarian cancer were used to explore the underlying mechanisms
of paraneoplastic thrombocytosis. The effects of platelets on tumor growth and angiogenesis were ascertained.</p>
<p>Results: Thrombocytosis was significantly associated with advanced disease and shortened
survival. Plasma levels of thrombopoietin and interleukin-6 were significantly elevated
in patients who had thrombocytosis as compared with those who did not. In mouse
models, increased hepatic thrombopoietin synthesis in response to tumor-derived
interleukin-6 was an underlying mechanism of paraneoplastic thrombocytosis. Tumorderived interleukin-6 and hepatic thrombopoietin were also linked to thrombocytosis
in patients. Silencing thrombopoietin and interleukin-6 abrogated thrombocytosis in
tumor-bearing mice. Antiâinterleukin-6 antibody treatment significantly reduced platelet counts in tumor-bearing mice and in patients with epithelial ovarian cancer. In
addition, neutralizing interleukin-6 significantly enhanced the therapeutic efficacy of
paclitaxel in mouse models of epithelial ovarian cancer. The use of an antiplatelet
antibody to halve platelet counts in tumor-bearing mice significantly reduced tumor
growth and angiogenesis.</p>
<p>Conclusions: These findings support the existence of a paracrine circuit wherein increased production of thrombopoietic cytokines in tumor and host tissue leads to paraneoplastic
thrombocytosis, which fuels tumor growth. We speculate that countering paraneoplastic thrombocytosis either directly or indirectly by targeting these cytokines may have
therapeutic potential. </p>
Growth, development, and phenotypic spectrum of individuals with deletions of 2q33.1 involving SATB2
SATB2-Associated syndrome (SAS) is an autosomal dominant, multisystemic, neurodevelopmental disorder due to alterations in SATB2 at 2q33.1. A limited number of individuals with 2q33.1 contiguous deletions encompassing SATB2 (ÎSAS) have been described in the literature. We describe 17 additional individuals with ÎSAS, review the phenotype of 33 previously published individuals with 2q33.1 deletions (n = 50, mean age = 8.5â±â7.8âyears), and provide a comprehensive comparison to individuals with other molecular mechanisms that result in SAS (non-ÎSAS). Individuals in the ÎSAS group were often underweight for age (20/41 = 49%) with a progressive decline in weight (95% CI = â2.3 to â1.1, pâ\u3câ0.0001) and height (95% CI = â2.3 to â1.0, pâ\u3câ0.0001) Z-score means from birth to last available measurement. ÎSAS individuals were often noted to have a broad spectrum of facial dysmorphism. A composite image of ÎSAS individuals generated by automated image analysis was distinct as compared to matched controls and non-ÎSAS individuals. We also present additional genotypeâphenotype correlations for individuals in the ÎSAS group such as an increased risk for aortic root/ascending aorta dilation and primary pulmonary hypertension for those individuals with contiguous gene deletions that include COL3A1/COL5A2 and BMPR2, respectively. Based on these findings, we provide additional care recommendations for individuals with ÎSAS variants