1,076 research outputs found
Time trends in survival and readmission following coronary artery bypass grafting in Scotland, 1981-96: retrospective observational study
Improvements in coronary revascularisation techniques and an increase in the use of percutaneous interventions1 have led to a rise in the number of coronary artery bypass grafting operations in older patients with more severe cardiac disease and worse comorbidity and who have previously undergone revascularisation procedures. 2 3 Advances in surgical and anaesthetic techniques have prevented a worsening risk profile from being translated into an increase in perioperative deaths. 2 3 The aim of our study was to examine time trends in major outcomes up to two years after coronary artery bypass grafting
Observational constraints on an inflation model with a running mass
We explore a model of inflation where the inflaton mass-squared is generated
at a high scale by gravity-mediated soft supersymmetry breaking, and runs at
lower scales to the small value required for slow-roll inflation. The running
is supposed to come from the coupling of the inflaton to a non-Abelian gauge
field. In contrast with earlier work, we do not constrain the magnitude of the
supersymmetry breaking scale, and we find that the model might work even if
squark and slepton masses come from gauge-mediated supersymmetry breaking. With
the inflaton and gaugino masses in the expected range, and
in the range to (all at the high scale) the model can give
the observed cosmic microwave anisotropy, and a spectral index in the observed
range. The latter has significant variation with scale, which can confirm or
rule out the model in the forseeable future.Comment: Latex, 19 pages, 14 figures, uses epsf.st
Power Spectrum in Krein Space Quantization
The power spectrum of scalar field and space-time metric perturbations
produced in the process of inflation of universe, have been presented in this
paper by an alternative approach to field quantization namely, Krein space
quantization [1,2]. Auxiliary negative norm states, the modes of which do not
interact with the physical world, have been utilized in this method. Presence
of negative norm states play the role of an automatic renormalization device
for the theory.Comment: 8 pages, appear in Int. J. Theor. Phy
An Apparatus to Control and Monitor the Para-D2 Concentration in a Solid Deuterium, Superthermal Source of Ultra-cold Neutrons
Controlling and measuring the concentration of para-D2 is an essential step
toward realizing solid deuterium as an intense ultra-cold neutron (UCN) source.
To this end, we implemented an experimental technique to convert para- to
ortho-deuterium molecules by flowing D2 gas through a cryogenic cell filled
with paramagnetic hydrous ferric oxide granules. This process efficiently
reduced the para-D2 concentration from 33.3% to 1.5%. Rotational Raman
spectroscopy was applied to measure the residual para-D2 contamination to
better than 2 parts in 10^3, and the hydrogen contamination to 1 part in 10^3.
We also contrast our optical technique to conventional thermal conductivity
measurements of the para-D2 concentration, reporting some of the relevant
strengths and weaknesses of our implementation of each technique.Comment: accepted for publication in NIM
Particle physics models of inflation
Inflation models are compared with observation on the assumption that the
curvature perturbation is generated from the vacuum fluctuation of the inflaton
field. The focus is on single-field models with canonical kinetic terms,
classified as small- medium- and large-field according to the variation of the
inflaton field while cosmological scales leave the horizon. Small-field models
are constructed according to the usual paradigm for beyond Standard Model
physicsComment: Based on a talk given at the 22nd IAP Colloquium, ``Inflation +25'',
Paris, June 2006 Curve omitted from final Figur
Second-order corrections to slow-roll inflation in the brane cosmology
We calculate the power spectrum, spectral index, and running spectral index
for the RS-II brane inflation in the high-energy regime using the slow-roll
expansion. There exist several modifications. As an example, we take the
power-law inflation by choosing an inverse power-law potential. When comparing
these with those arisen in the standard inflation, we find that the power
spectrum is enhanced and the spectral index is suppressed, while the running
spectral index becomes zero as in the standard inflation. However, since
second-order corrections are rather small, these could not play a role of
distinguishing between standard and brane inflations.Comment: 6 page
The Detectability of Departures from the Inflationary Consistency Equation
We study the detectability, given CMB polarization maps, of departures from
the inflationary consistency equation, r \equiv T/S \simeq -5 n_T, where T and
S are the tensor and scalar contributions to the quadrupole variance,
respectively. The consistency equation holds if inflation is driven by a
slowly-rolling scalar field. Departures can be caused by: 1) higher-order terms
in the expansion in slow-roll parameters, 2) quantum loop corrections or 3)
multiple fields. Higher-order corrections in the first two slow-roll parameters
are undetectably small. Loop corrections are detectable if they are nearly
maximal and r \ga 0.1. Large departures (|\Delta n_T| \ga 0.1) can be seen if r
\ga 0.001. High angular resolution can be important for detecting non-zero
r+5n_T, even when not important for detecting non-zero r.Comment: 7 pages, 4 figures, submitted to PR
Improved Estimates of Cosmological Perturbations
We recently derived exact solutions for the scalar, vector and tensor mode
functions of a single, minimally coupled scalar plus gravity in an arbitrary
homogeneous and isotropic background. These solutions are applied to obtain
improved estimates for the primordial scalar and tensor power spectra of
anisotropies in the cosmic microwave background.Comment: 31 pages, 4 figures, LaTeX 2epsilon, this version corrects an
embarrasing mistake (in the published version) for the parameter q_C.
Affected eqns are 105, 109-110, 124, 148-153 and 155-15
Constraints on inflation in closed universe
We investigate inflation in closed Friedmann-Robertson-Walker universe filled
with the scalar field with power-law potential. For a wide range of powers and
parameters of the potential we numerically calculated the slow-roll parameters
and scalar spectral index at the epoch when present Hubble scale leaves the
horizon and at the end of inflation. Also we compare results of our numerical
calculations with recent observation data. This allows us to set a constraint
on the power of the potential: alpha < (3.5 - 4.5).Comment: 5 pages, 5 figures; extended versio
Bailing Out the Milky Way: Variation in the Properties of Massive Dwarfs Among Galaxy-Sized Systems
Recent kinematical constraints on the internal densities of the Milky Way's
dwarf satellites have revealed a discrepancy with the subhalo populations of
simulated Galaxy-scale halos in the standard CDM model of hierarchical
structure formation. This has been dubbed the "too big to fail" problem, with
reference to the improbability of large and invisible companions existing in
the Galactic environment. In this paper, we argue that both the Milky Way
observations and simulated subhalos are consistent with the predictions of the
standard model for structure formation. Specifically, we show that there is
significant variation in the properties of subhalos among distinct host halos
of fixed mass and suggest that this can reasonably account for the deficit of
dense satellites in the Milky Way. We exploit well-tested analytic techniques
to predict the properties in a large sample of distinct host halos with a
variety of masses spanning the range expected of the Galactic halo. The
analytic model produces subhalo populations consistent with both Via Lactea II
and Aquarius, and our results suggest that natural variation in subhalo
properties suffices to explain the discrepancy between Milky Way satellite
kinematics and these numerical simulations. At least ~10% of Milky Way-sized
halos host subhalo populations for which there is no "too big to fail" problem,
even when the host halo mass is as large as M_host = 10^12.2 h^-1 M_sun.
Follow-up studies consisting of high-resolution simulations of a large number
of Milky Way-sized hosts are necessary to confirm our predictions. In the
absence of such efforts, the "too big to fail" problem does not appear to be a
significant challenge to the standard model of hierarchical formation.
[abridged]Comment: 12 pages, 3 figures; accepted by JCAP. Replaced with published
versio
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