165 research outputs found
Extended Inflation with a Curvature-Coupled Inflaton
We examine extended inflation models enhanced by the addition of a coupling
between the inflaton field and the space-time curvature. We examine two types
of model, where the underlying inflaton potential takes on second-order and
first-order form respectively. One aim is to provide models which satisfy the
solar system constraints on the Brans--Dicke parameter . This
constraint has proven very problematic in previous extended inflation models,
and we find circumstances where it can be successfully evaded, though the
constraint must be carefully assessed in our model and can be much stronger
than the usual . In the simplest versions of the model, one may
avoid the need to introduce a mass for the Brans--Dicke field in order to
ensure that it takes on the correct value at the present epoch, as seems to be
required in hyperextended inflation. We also briefly discuss aspects of the
formation of topological defects in the inflaton field itself.Comment: 24 pages, LaTeX (no figures), to appear, Physical Review D,
mishandling of the solar system constraint on extended gravity theories
corrected, SUSSEX-AST 93/6-
The Inflationary Energy Scale
The energy scale of inflation is of much interest, as it suggests the scale
of grand unified physics and also governs whether cosmological events such as
topological defect formation can occur after inflation. The COBE results are
used to limit the energy scale of inflation at around 60 -foldings from the
end of inflation. An exact dynamical treatment based on the Hamilton-Jacobi
equations is then used to translate this into limits on the energy scale at the
end of inflation. General constraints are given, and then tighter constraints
based on physically motivated assumptions regarding the allowed forms of
density perturbation and gravitational wave spectra. These are also compared
with the values of familiar models.Comment: 17 pages (plus three figures, available from the author as hard
copies only), standard LaTeX, SUSSEX-AST 93/7-
Influence of 1 and 25 Hz,1.5 mT Magnetic Fields on Antitumor Drug Potency in a Human Adenocarcinoma Cell Line
The resistance of tumor cells to antineoplastic agents is a major obstacle during cancer chemotherapy. Many authors have observed that some exposure protocols to pulsed electromagnetic fields (PEMF) can alter the efficacy of anticancer drugs; nevertheless, the observations are not clear. We have evaluated whether a group of PEMF pulses (1.5 mT peak, repeated at 1 and 25 Hz) produces alterations of drug potency on a multidrug resistant human colon adenocarcinoma (HCA) cell line, HCA-2/1 cch . The experiments were performed including (a) exposures to drug and PEMF exposure for 1 h at the same time, (b) drug exposure for 1 h, and then exposure to PEMF for the next 2 days (2 h/day). Drugs used were vincristine (VCR), mitomycin C (MMC), and cisplatin. Cell viability was measured by the neutral red stain cytotoxicity test. The results obtained were: (a) The 1 Hz PEMF increased VCR cytotoxicity (P < 0.01), exhibiting 6.1% of survival at 47.5 mg/ml, the highest dose for which sham exposed groups showed a 19.8% of survival. For MMC at 47.5 mg/ml, the % of survival changed significantly from 19.2% in sham exposed groups to 5.3% using 25 Hz (P < 0.001). Cisplatin showed a significant reduction in the % of survival (44.2-39.1%, P < 0.05) at 25 Hz and 47.5 mg/ml, and (b) Minor significant alterations were observed after nonsimultaneous exposure of cells to PEMF and drug. The data indicate that PEMF can induce modulation of cytostatic agents in HCA-2/1 cch , with an increased effect when PEMF was applied at the same time as the drug. The type of drug, dose, frequency, and duration of PEMF exposure could influence this modulation
Particle Physics Models of Inflation and the Cosmological Density Perturbation
This is a review of particle-theory models of inflation, and of their
predictions for the primordial density perturbation that is thought to be the
origin of structure in the Universe. It contains mini-reviews of the relevant
observational cosmology, of elementary field theory and of supersymmetry, that
may be of interest in their own right. The spectral index , specifying
the scale-dependence of the spectrum of the curvature perturbation, will be a
powerful discriminator between models, when it is measured by Planck with
accuracy . The usual formula for is derived, as well as
its less familiar extension to the case of a multi-component inflaton; in both
cases the key ingredient is the separate evolution of causally disconnected
regions of the Universe. Primordial gravitational waves will be an even more
powerful discriminator if they are observed, since most models of inflation
predict that they are completely negligible. We treat in detail the new wave of
models, which are firmly rooted in modern particle theory and have
supersymmetry as a crucial ingredient. The review is addressed to both
astrophysicists and particle physicists, and each section is fairly homogeneous
regarding the assumed background knowledge.Comment: 156 pages, after final proof corrections and addition
Light cone effect on the reionization 21-cm signal ā II. Evolution, anisotropies and observational implications
Measurements of the H I 21-cm power spectra from the reionization epoch will be influenced by the evolution of the signal along the line-of-sight direction of any observed volume. We use numerical as well as seminumerical simulations of reionization in a cubic volume of 607 Mpc across to study this so-called light-cone effect on the H I 21-cm power spectrum. We find that the light-cone effect has the largest impact at two different stages of reionization: one when reionization is ā¼20 per cent and other when it is ā¼80 per cent completed. We find a factor of ā¼4 amplification of the power spectrum at the largest scale available in our simulations. We do not find any significant anisotropy in the 21-cm power spectrum due to the light-cone effect. We argue that for the power spectrum to become anisotropic, the light-cone effect would have to make the ionized bubbles significantly elongated or compressed along the line of sight, which would require extreme reionization scenarios. We also calculate the two-point correlation functions parallel and perpendicular to the line of sight and find them to differ. Finally, we calculate an optimum frequency bandwidth below which the light-cone effect can be neglected when extracting power spectra from observations. We find that if one is willing to accept a 10 per cent error due to the light-cone effect, the optimum frequency bandwidth for k = 0.056 Mpcā1 is ā¼7.5 MHz. For k = 0.15 and 0.41 Mpcā1, the optimum bandwidth is ā¼11 and ā¼16 MHz, respectively
The Cosmological Constant
This is a review of the physics and cosmology of the cosmological constant.
Focusing on recent developments, I present a pedagogical overview of cosmology
in the presence of a cosmological constant, observational constraints on its
magnitude, and the physics of a small (and potentially nonzero) vacuum energy.Comment: 50 pages. Submitted to Living Reviews in Relativity
(http://www.livingreviews.org/), December 199
Characterizing Foreground for redshifted 21-cm radiation: 150 MHz GMRT observations
Foreground removal is a major challenge for detecting the redshifted 21-cm
neutral hydrogen (HI) signal from the Epoch of Reionization (EoR). We have used
150 MHz GMRT observations to characterize the statistical properties of the
foregrounds in four different fields of view. The measured multi-frequency
angular power spectrum C_l(Delta nu) is found to have values in the range 10^4
mK^2 to 2 x 10^4 mK^2 across 700 <= l <= 2 x 10^4 and Delta nu <= 2.5 MHz,
which is consistent with model predictions where point sources are the most
dominant foreground component. The measured C_l(Delta nu) does not show a
smooth Delta nu dependence, which poses a severe difficulty for foreground
removal using polynomial fitting.
The observational data was used to assess point source subtraction.
Considering the brightest source (~ 1 Jy) in each field, we find that the
residual artifacts are less than 1.5% in the most sensitive field (FIELD I). We
have used FIELD I, which has a rms noise of 1.3 mJy/Beam, to study the
properties of the radio source population to a limiting flux of 9 mJy. The
differential source count is well fitted with a single power law of slope -1.6.
We find there is no evidence for flattening of the source counts towards lower
flux densities which suggests that source population is dominated by the
classical radio-loud Active Galactic Nucleus (AGN).
The diffuse Galactic emission is revealed after the point sources are
subtracted out from FIELD I . We find C_l \propto l^{-2.34} for 253 <= l <= 800
which is characteristic of the Galactic synchrotron radiation measured at
higher frequencies and larger angular scales. We estimate the fluctuations in
the Galactic synchrotron emission to be sqrt{l(l+1)C_l/2 pi} ~ 10 K at l=800
(theta > 10'). The measured C_l is dominated by the residual point sources and
artifacts at smaller angular scales where C_l ~ 10^3 mK^2 for l > 800.Comment: 22 pages, 17 figures, 5 tables, accepted to MNRAS for publicatio
Disparities in appendicitis rupture rate among mentally ill patients
<p>Abstract</p> <p>Background</p> <p>Many studies have been carried out that focus on mental patients' access to care for their mental illness, but very few pay attention on these same patients' access to care for their physical diseases. Acute appendicitis is a common surgical emergency. Our population-based study was to test for any possible association between mental illness and perforated appendicitis. We hypothesized that there are significant disparities in access to timely surgical care between appendicitis patients with and without mental illness, and more specifically, between patients with schizophrenia and those with another major mental illness.</p> <p>Methods</p> <p>Using the National Health Insurance (NHI) hospital-discharge data, we compared the likelihood of perforated appendix among 97,589 adults aged 15 and over who were hospitalized for acute appendicitis in Taiwan between the years 1997 to 2001. Among all the patients admitted for appendicitis, the outcome measure was the odds of appendiceal rupture vs. appendicitis that did not result in a ruptured appendix.</p> <p>Results</p> <p>After adjusting for age, gender, ethnicity, socioeconomic status (SES) and hospital characteristics, the presence of schizophrenia was associated with a 2.83 times higher risk of having a ruptured appendix (odds ratio [OR], 2.83; 95% confidence interval [CI], 2.20ā3.64). However, the presence of affective psychoses (OR, 1.15; 95% CI: 0.77ā1.73) or other mental disorders (OR, 1.58; 95% CI: 0.89ā2.81) was not a significant predictor for a ruptured appendix.</p> <p>Conclusion</p> <p>These findings suggest that given the fact that the NHI program reduces financial barriers to care for mentally ill patients, they are still at a disadvantage for obtaining timely treatment for their physical diseases. Of patients with a major mental illness, schizophrenic patients may be the most vulnerable ones for obtaining timely surgical care.</p
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