184 research outputs found
Transition from decelerated to accelerated cosmic expansion in braneworld universes
Braneworld theory provides a natural setting to treat, at a classical level,
the cosmological effects of vacuum energy. Non-static extra dimensions can
generally lead to a variable vacuum energy, which in turn may explain the
present accelerated cosmic expansion. We concentrate our attention in models
where the vacuum energy decreases as an inverse power law of the scale factor.
These models agree with the observed accelerating universe, while fitting
simultaneously the observational data for the density and deceleration
parameter. The redshift at which the vacuum energy can start to dominate
depends on the mass density of ordinary matter. For Omega = 0.3, the transition
from decelerated to accelerated cosmic expansion occurs at z approx 0.48 +/-
0.20, which is compatible with SNe data. We set a lower bound on the
deceleration parameter today, namely q > - 1 + 3 Omega/2, i.e., q > - 0.55 for
Omega = 0.3. The future evolution of the universe crucially depends on the time
when vacuum starts to dominate over ordinary matter. If it dominates only
recently, at an epoch z < 0.64, then the universe is accelerating today and
will continue that way forever. If vacuum dominates earlier, at z > 0.64, then
the deceleration comes back and the universe recollapses at some point in the
distant future. In the first case, quintessence and Cardassian expansion can be
formally interpreted as the low energy limit of our model, although they are
entirely different in philosophy. In the second case there is no correspondence
between these models and ours.Comment: In V2 typos are corrected and one reference is added for section 1.
To appear in General Relativity and Gravitatio
Accelerated expansion from braneworld models with variable vacuum energy
In braneworld models a variable vacuum energy may appear if the size of the
extra dimension changes during the evolution of the universe. In this scenario
the acceleration of the universe is related not only to the variation of the
cosmological term, but also to the time evolution of and, possibly, to the
variation of other fundamental "constants" as well. This is because the
expansion rate of the extra dimension appears in different contexts, notably in
expressions concerning the variation of rest mass and electric charge. We
concentrate our attention on spatially-flat, homogeneous and isotropic,
brane-universes where the matter density decreases as an inverse power of the
scale factor, similar (but at different rate) to the power law in FRW-universes
of general relativity.
We show that these braneworld cosmologies are consistent with the observed
accelerating universe and other observational requirements. In particular,
becomes constant and asymptotically in
time. Another important feature is that the models contain no "adjustable"
parameters. All the quantities, even the five-dimensional ones, can be
evaluated by means of measurements in 4D. We provide precise constrains on the
cosmological parameters and demonstrate that the "effective" equation of state
of the universe can, in principle, be determined by measurements of the
deceleration parameter alone. We give an explicit expression relating the
density parameters , and the deceleration
parameter . These results constitute concrete predictions that may help in
observations for an experimental/observational test of the model.Comment: References added, typos correcte
Increasing incidence of invasive and in situ cervical adenocarcinoma in the Netherlands during 2004-2013
In the developed world, the incidence of cervical squamous cell carcinoma has decreased, however, the incidence of adenocarcinoma in situ (AIS) and invasive adenocarcinoma increased, predominantly in young females. The goal of this study was to evaluate the most recent incidence rates of AIS, adenocarcinoma, and squamous cell carcinoma of the uterine cervix in the Netherlands in 2004-2013. By using Dutch national pathology and cancer registries, we calculated European standardized incidence rates (ESR) and estimated annual percentage changes (EAPC) for AIS during 2004-2013 and for invasive cervical carcinomas during 1989-2013. For AIS, presence or absence of concomitant cervical intraepithelial neoplasia (CIN) was explored. The estimated annual percentage change (EAPC) of squamous cell carcinoma decreased significantly in 1989-2013, predominantly in 1989-2003. The EAPC of invasive adenocarcinoma decreased in 1989-2003, but remained stable in 2004-2013. The EAPC of AIS increased significantly, predominantly in women of 25-39 years old. Of these AIS cases, 58.9% had concomitant CIN and AIS with concomitant CIN showed a significantly higher EAPC compared to AIS without CIN. Our conclusion is that despite a nationwide screening program for cancer of the uterine cervix, the incidence of adenocarcinoma in the Netherlands remained stable during 2004-2013 and the incidence of adenocarcinoma in situ increased. This was most predominant in cases with concomitant CIN and in younger females. The incidence of squamous cell carcinoma decreased in the same timeframe
Evaluating the softness of animal fibers
Softness is an important property of textile fibers, and animal fibers in particular. At present, there is no reliable method for objectively evaluating fiber softness. This paper examines a simple technique of such evaluations by pulling a bundle of parallel fibers through a series of pins. Softer fibers with lower bending rigidities and smoother surfaces should have lower pulling forces. Alpaca and wool fibers are used in this study to validate this technique, and the results suggest that pulling force measurements can reflect differences in fiber softness
Relativistic anisotropic charged fluid spheres with varying cosmological constant
Static spherically symmetric anisotropic source has been studied for the
Einstein-Maxwell field equations assuming the erstwhile cosmological constant to be a space-variable scalar, viz., . Two
cases have been examined out of which one reduces to isotropic sphere. The
solutions thus obtained are shown to be electromagnetic in origin as a
particular case. It is also shown that the generally used pure charge
condition, viz., is not always required for constructing
electromagnetic mass models.Comment: 15 pages, 3 eps figure
FRW Cosmology From Five Dimensional Vacuum Brans-Dicke Theory
We follow approach of induced matter theory for 5D vacuum BD, introduce
induced matter and potential in 4D hypersurfaces, and employ generalized FRW
type solution. We confine ourselves to scalar field and scale factors be
functions of the time. This makes the induced potential, by its definition,
vanishes. When the scale factor of fifth dimension and scalar field are not
constants, 5D eqs for any geometry admit a power law relation between scalar
field and scale factor of fifth dimension. Hence the procedure exhibits that 5D
vacuum FRW like eqs are equivalent, in general, to corresponding 4D vacuum ones
with the same spatial scale factor but new scalar field and coupling constant.
We show that 5D vacuum FRW like eqs or its equivalent 4D vacuum ones admit
accelerated solutions. For constant scalar field, eqs reduce to usual FRW eqs
with typical radiation dominated universe. For this situation we obtain
dynamics of scale factors for any geometry without any priori assumption. For
nonconstant scalar fields and spatially flat geometries, solutions are found to
be power law and exponential ones. We also employ weak energy condition for
induced matter, that allows negative/positive pressures. All types of solutions
fulfill WEC in different ranges. The power law solutions with negative/positive
pressures admit both decelerating and accelerating ones. Some solutions accept
shrinking extra dimension. By considering nonghost scalar fields and recent
observational measurements, solutions are more restricted. We illustrate that
accelerating power law solutions, which satisfy WEC and have nonghost fields,
are compatible with recent observations in ranges -4/3 < \omega </- -1.3151 and
1.5208 </- n < 1.9583 for dependence of fifth dimension scale factor with usual
scale factor. These ranges also fulfill condition nonghost fields in the
equivalent 4D vacuum BD eqs.Comment: 18 pages, 16 figures, 11 table
Minimum mass-radius ratio for charged gravitational objects
We rigorously prove that for compact charged general relativistic objects
there is a lower bound for the mass-radius ratio. This result follows from the
same Buchdahl type inequality for charged objects, which has been extensively
used for the proof of the existence of an upper bound for the mass-radius
ratio. The effect of the vacuum energy (a cosmological constant) on the minimum
mass is also taken into account. Several bounds on the total charge, mass and
the vacuum energy for compact charged objects are obtained from the study of
the Ricci scalar invariants. The total energy (including the gravitational one)
and the stability of the objects with minimum mass-radius ratio is also
considered, leading to a representation of the mass and radius of the charged
objects with minimum mass-radius ratio in terms of the charge and vacuum energy
only.Comment: 19 pages, accepted by GRG, references corrected and adde
Interacting Kasner-type cosmologies
It is well known that Kasner-type cosmologies provide a useful framework for
analyzing the three-dimensional anisotropic expansion because of the
simplification of the anisotropic dynamics. In this paper relativistic
multi-fluid Kasner-type scenarios are studied. We first consider the general
case of a superposition of two ideal cosmic fluids, as well as the particular
cases of non-interacting and interacting ones, by introducing a
phenomenological coupling function . For two-fluid cosmological scenarios
there exist only cosmological scaling solutions, while for three-fluid
configurations there exist not only cosmological scaling ones, but also more
general solutions. In the case of triply interacting cosmic fluids we can have
energy transfer from two fluids to a third one, or energy transfer from one
cosmic fluid to the other two. It is shown that by requiring the positivity of
energy densities there always is a matter component which violates the dominant
energy condition in this kind of anisotropic cosmological scenarios.Comment: Accepted for publication in Astrophysics &Space Science, 8 page
A Weyl-Dirac Cosmological Model with DM and DE
In the Weyl-Dirac (W-D) framework a spatially closed cosmological model is
considered. It is assumed that the space-time of the universe has a chaotic
Weylian microstructure but is described on a large scale by Riemannian
geometry. Locally fields of the Weyl connection vector act as creators of
massive bosons having spin 1. It is suggested that these bosons, called
weylons, provide most of the dark matter in the universe. At the beginning the
universe is a spherically symmetric geometric entity without matter. Primary
matter is created by Dirac's gauge function very close to the beginning. In the
early epoch, when the temperature of the universe achieves its maximum,
chaotically oriented Weyl vector fields being localized in micro-cells create
weylons. In the dust dominated period Dirac's gauge function is giving rise to
dark energy, the latter causing the cosmic acceleration at present. This
oscillatory universe has an initial radius identical to the Plank length =
1.616 exp (-33) cm, at present the cosmic scale factor is 3.21 exp (28) cm,
while its maximum value is 8.54 exp (28) cm. All forms of matter are created by
geometrically based functions of the W-D theory.Comment: 25 pages. Submitted to GR
Transcatheter aortic valve implantation in failed bioprosthetic surgical valves.
IMPORTANCE: Owing to a considerable shift toward bioprosthesis implantation rather than mechanical valves, it is expected that patients will increasingly present with degenerated bioprostheses in the next few years. Transcatheter aortic valve-in-valve implantation is a less invasive approach for patients with structural valve deterioration; however, a comprehensive evaluation of survival after the procedure has not yet been performed.
OBJECTIVE: To determine the survival of patients after transcatheter valve-in-valve implantation inside failed surgical bioprosthetic valves.
DESIGN, SETTING, AND PARTICIPANTS: Correlates for survival were evaluated using a multinational valve-in-valve registry that included 459 patients with degenerated bioprosthetic valves undergoing valve-in-valve implantation between 2007 and May 2013 in 55 centers (mean age, 77.6 [SD, 9.8] years; 56% men; median Society of Thoracic Surgeons mortality prediction score, 9.8% [interquartile range, 7.7%-16%]). Surgical valves were classified as small (≤21 mm; 29.7%), intermediate (>21 and <25 mm; 39.3%), and large (≥25 mm; 31%). Implanted devices included both balloon- and self-expandable valves.
MAIN OUTCOMES AND MEASURES: Survival, stroke, and New York Heart Association functional class.
RESULTS: Modes of bioprosthesis failure were stenosis (n = 181 [39.4%]), regurgitation (n = 139 [30.3%]), and combined (n = 139 [30.3%]). The stenosis group had a higher percentage of small valves (37% vs 20.9% and 26.6% in the regurgitation and combined groups, respectively; P = .005). Within 1 month following valve-in-valve implantation, 35 (7.6%) patients died, 8 (1.7%) had major stroke, and 313 (92.6%) of surviving patients had good functional status (New York Heart Association class I/II). The overall 1-year Kaplan-Meier survival rate was 83.2% (95% CI, 80.8%-84.7%; 62 death events; 228 survivors). Patients in the stenosis group had worse 1-year survival (76.6%; 95% CI, 68.9%-83.1%; 34 deaths; 86 survivors) in comparison with the regurgitation group (91.2%; 95% CI, 85.7%-96.7%; 10 deaths; 76 survivors) and the combined group (83.9%; 95% CI, 76.8%-91%; 18 deaths; 66 survivors) (P = .01). Similarly, patients with small valves had worse 1-year survival (74.8% [95% CI, 66.2%-83.4%]; 27 deaths; 57 survivors) vs with intermediate-sized valves (81.8%; 95% CI, 75.3%-88.3%; 26 deaths; 92 survivors) and with large valves (93.3%; 95% CI, 85.7%-96.7%; 7 deaths; 73 survivors) (P = .001). Factors associated with mortality within 1 year included having small surgical bioprosthesis (≤21 mm; hazard ratio, 2.04; 95% CI, 1.14-3.67; P = .02) and baseline stenosis (vs regurgitation; hazard ratio, 3.07; 95% CI, 1.33-7.08; P = .008).
CONCLUSIONS AND RELEVANCE: In this registry of patients who underwent transcatheter valve-in-valve implantation for degenerated bioprosthetic aortic valves, overall 1-year survival was 83.2%. Survival was lower among patients with small bioprostheses and those with predominant surgical valve stenosis
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