302 research outputs found
Relativistic stars in f(R) gravity, and absence thereof
Several f(R) modified gravity models have been proposed which realize the
correct cosmological evolution and satisfy solar system and laboratory tests.
Although nonrelativistic stellar configurations can be constructed, we argue
that relativistic stars cannot be present in such f(R) theories. This problem
appears due to the dynamics of the effective scalar degree of freedom in the
strong gravity regime. Our claim thus raises doubts on the viability of f(R)
models.Comment: 9 pages, 7 figures, v2: references added, minor corrections, version
accepted for publication in PR
Strong ground motions from an Mj 6.1 inland crustal earthquake in Hokkaido, Japan: the 2004 Rumoi earthquake
Can higher curvature corrections cure the singularity problem in f(R) gravity?
Although modified gravity models can be made to satisfy solar system
and cosmological constraints, it has been shown that they have the serious
drawback of the nonexistence of stars with strong gravitational fields. In this
paper, we discuss whether or not higher curvature corrections can remedy the
nonexistence consistently. The following problems are shown to arise as the
costs one must pay for the models that allow for neutrons stars: (i) the
leading correction must be fine-tuned to have the typical energy scale GeV, which essentially comes from the free fall time of a
relativistic star; (ii) the leading correction must be further fine-tuned so
that it is not given by the quadratic curvature term. The second problem is
caused because there appears an intermediate curvature scale and laboratory
experiments of gravity will be under the influence of higher curvature
corrections. Our analysis thus implies that it is a challenge to construct
viable models without very careful and unnatural fine-tuning.Comment: 9 pages, 9 figures, v2: minor modifications, version accepted for
publication in Phys. Rev.
The Optical/Near-Infrared Light Curves of SN 2002ap for the First 1.5 Years after Discovery
Late-time BVRIJHK photometry of the peculiar Type Ic SN 2002ap, taken between
2002 June 12 and 2003 August 29 with the MAGNUM telescope, is presented. The
light curve decline rate is derived in each band and the color evolution is
studied through comparison with nebular spectra and with SN 1998bw. Using the
photometry, the OIR bolometric light curve is built, extending from before
light maximum to day 580 after explosion. The light curve has a late-time shape
strikingly similar to that of the hypernova SN 1998bw. The decline rate changes
from 0.018 mag/day between day 130 and 230 to 0.014 mag/day between day 270 and
580. To reproduce the late-time light curve, a dense core must be added to the
1-D hypernova model that best fits the early-time observations, bringing the
ejecta mass from 2.5 Msun to 3 Msun without much change in the kinetic energy,
which is 4 times 10^51 ergs. This is similar to the case of other hypernovae
and suggests asymmetry. A large H-band bump developed in the spectral energy
distribution after about day 300, probably caused by strong [Si I] 1.646 micron
and 1.608 micron emissions. The near-infrared flux contribution increased
simultaneously from 50% at day 580. The near-infrared light curves
were compared with those of other Type Ib/c supernovae, among which SN 1983I
seems similar to SN 2002ap both in the near-infrared and in the optical.Comment: 24pages, 9 figures, ApJ in press (10 June 2006, v644 1 issue).
Acknowledgements update
Blood pressure in heart failure management and prevention
Hypertension is a leading cause of heart failure and other cardiovascular diseases. Its role in the pathogenesis of heart failure with reduced ejection fraction (HFrEF) differs from that in heart failure with preserved ejection fraction (HFpEF). Moreover, rigorous blood pressure control may reduce the incidence of heart failure. However, once heart failure develops, prognosis is affected by blood pressure, which may differ between patients with and without heart failure. Therefore, the association between guideline-directed medical therapy (GDMT) for heart failure and its uptitration must be considered for blood pressure management and should not be overlooked. Heart failure medications affect the blood pressure and efficacy per baseline blood pressure value. This review discusses the potential mechanisms by which hypertension leads to HFrEF or HFpEF, the impact of hypertension on incident heart failure, and the recommended approaches for blood pressure management in patients with heart failure. </p
Analysis of the Wheeler-DeWitt Equation beyond Planck Scale and Dimensional Reduction
We solve the Wheeler-DeWitt equation for {\it four}-dimensional Einstein
gravity as an expansion in powers of the Planck mass by means of a heat kernel
regularization. Our results suggest that in the universe with a very small
radius or with a very large curvature beyond a Planck scale expectation values
of operators are reduced to calculations in a path integral representation of
{\it three}-dimensional Einstein gravity.Comment: 9 pages, latex file, KOBE-TH-94-0
Loss of Parp-1 affects gene expression profile in a genome-wide manner in ES cells and liver cells
BACKGROUND: Many lines of evidence suggest that poly(ADP-ribose) polymerase-1 (Parp-1) is involved in transcriptional regulation of various genes as a coactivator or a corepressor by modulating chromatin structure. However, the impact of Parp-1-deficiency on the regulation of genome-wide gene expression has not been fully studied yet. RESULTS: We employed a microarray analysis covering 12,488 genes and ESTs using mouse Parp-1-deficient (Parp-1(-/-)) embryonic stem (ES) cell lines and the livers of Parp-1(-/- )mice and their wild-type (Parp-1(+/+)) counterparts. Here, we demonstrate that of the 9,907 genes analyzed, in Parp-1(-/- )ES cells, 9.6% showed altered gene expression. Of these, 6.3% and 3.3% of the genes were down- or up-regulated by 2-fold or greater, respectively, compared with Parp-1(+/+ )ES cells (p < 0.05). In the livers of Parp-1(-/- )mice, of the 12,353 genes that were analyzed, 2.0% or 1.3% were down- and up-regulated, respectively (p < 0.05). Notably, the number of down-regulated genes was higher in both ES cells and livers, than that of the up-regulated genes. The genes that showed altered expression in ES cells or in the livers are ascribed to various cellular processes, including metabolism, signal transduction, cell cycle control and transcription. We also observed expression of the genes involved in the pathway of extraembryonic tissue development is augmented in Parp-1(-/- )ES cells, including H19. After withdrawal of leukemia inhibitory factor, expression of H19 as well as other trophoblast marker genes were further up-regulated in Parp-1(-/- )ES cells compared to Parp-1(+/+ )ES cells. CONCLUSION: These results suggest that Parp-1 is required to maintain transcriptional regulation of a wide variety of genes on a genome-wide scale. The gene expression profiles in Parp-1-deficient cells may be useful to delineate the functional role of Parp-1 in epigenetic regulation of the genomes involved in various biological phenomena
Risk factors for initial antibiotic treatment failure in patients with aspiration pneumonia
Sulbactam/ampicillin (SBT/ABPC) and ceftriaxone (CTRX) are the initial antibiotics recommended for treating aspiration pneumonia without risk factors for drug-resistant pathogens. However, the condition of some patients does not improve with these antibiotics. Therefore, we investigated the new risk factors associated with failure of initial antibiotic treatment in patients with aspiration pneumonia. This study included 487 patients diagnosed with aspiration pneumonia who received initial antibiotic treatment with SBT/ABPC or CTRX, and were hospitalized at the Respiratory Medicine Department of the Yokohama City Minato Red Cross Hospital. The outcome was initial antibiotic treatment failure, which was defined as a change from initial to secondary antibiotic treatment. The characteristics of patients with and without antibiotic treatment failure were compared using univariate analyses, and significant independent risk factors for the initial antibiotic treatment failure were selected using multivariate analyses. The mean age of the patients was 84.1 ± 9.6 years; 302 (62%) of them were men and 93 patients experienced antibiotic treatment failure. Logistic regression analysis extracted no restriction of diet on admission (odds ratio [OR], 3.23; 95% confidence interval [CI], 1.35-7.74), history of hospitalization due to aspiration pneumonia (OR, 1.81; 95%CI, 1.12-2.93), the severity of pneumonia (OR, 1.37; 95%CI, 1.01-1.86), and C-reactive protein (CRP) level (OR, 1.26; 95%CI, 1.09-1.45) as risk factors for initial antibiotic treatment failure. Our results suggested that no restriction of diet on admission, history of hospitalization due to aspiration pneumonia, severity of pneumonia, and increased CRP levels were the risk factors associated with failure of initial antibiotic treatment in patients with aspiration pneumonia. These factors will be useful for determining an effective initial treatment strategy for patients with aspiration pneumonia
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