199 research outputs found
(1+3) Covariant Dynamics of Scalar Perturbations in Braneworlds
We discuss the dynamics of linear, scalar perturbations in an almost
Friedmann-Robertson-Walker braneworld cosmology of Randall-Sundrum type II
using the 1+3 covariant approach. We derive a complete set of frame-independent
equations for the total matter variables, and a partial set of equations for
the non-local variables which arise from the projection of the Weyl tensor in
the bulk. The latter equations are incomplete since there is no propagation
equation for the non-local anisotropic stress. We supplement the equations for
the total matter variables with equations for the independent constituents in a
cold dark matter cosmology, and provide solutions in the high and low-energy
radiation-dominated phase under the assumption that the non-local anisotropic
stress vanishes. These solutions reveal the existence of new modes arising from
the two additional non-local degrees of freedom. Our solutions should prove
useful in setting up initial conditions for numerical codes aimed at exploring
the effect of braneworld corrections on the cosmic microwave background (CMB)
power spectrum. As a first step in this direction, we derive the covariant form
of the line of sight solution for the CMB temperature anisotropies in
braneworld cosmologies, and discuss possible mechanisms by which braneworld
effects may remain in the low-energy universe.Comment: 22 pages replaced with additional references and minor corrections in
Revtex4, and accepted for publication in Phys. Rev.
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Are Children With Birth Defects at Higher Risk of Childhood Cancers?
Birth defects may influence the risk of childhood cancer development through a variety of mechanisms. The rarity of both birth defects and childhood cancers makes it challenging to study these associations, particularly for the very rare instances of each. To address this limitation, the authors conducted a record linkage-based cohort study among Texas children born between 1996 and 2005. Birth defects in the cohort were identified through the Texas Birth Defects Registry, and children who developed cancer were identified by using record linkage with Texas Cancer Registry data. Over 3 million birth records were included; 115,686 subjects had birth defects, and there were 2,351 cancer cases. Overall, children with a birth defect had a 3-fold increased risk of developing cancer (incidence rate ratio (IRR) = 3.05, 95% confidence interval (CI): 2.65, 3.50), with germ cell tumors (IRR = 5.19, 95% CI: 2.67, 9.41), retinoblastomas (IRR = 2.34, 95% CI: 1.21, 4.16), soft-tissue sarcomas (IRR = 2.12, 95% CI: 1.09, 3.79), and leukemias (IRR = 1.39, 95% CI: 1.09, 1.75) having statistically significant elevated point estimates. All birth defect groups except for musculoskeletal had increased cancer incidence. Untangling the strong relation between birth defects and childhood cancers could lead to a better understanding of the genetic and environmental factors that affect both conditions.Keywords: congenital anomalies, childhood cancers, birth defectsKeywords: congenital anomalies, childhood cancers, birth defect
Natural Double Inflation in Supergravity
We propose a natural double inflation model in supergravity. In this model,
chaotic inflation first takes place by virtue of the Nambu-Goldstone-like shift
symmetry, which guarantees the absence of the exponential factor in the
potential for the inflaton field. During chaotic inflation, an initial value of
the second inflation (new inflation) is set. In this model, the initial value
of new inflation can be adequately far from the local maximum of the potential
for new inflation due to the small linear term of the inflaton in the K\"ahler
potential. Therefore, the primordial fluctuations within the present horizon
scale may be attributed to both inflations; that is, the first chaotic
inflation produces the primordial fluctuations on the large cosmological scales
while the second new inflation on the smaller scales. The successive decay of
the inflaton for new inflation leads to a reheating temperature low enough to
avoid the overproduction of gravitinos in a wide range of the gravitino mass.Comment: 13 pages, to appear in Phys. Rev.
Estimated Maternal Pesticide Exposure from Drinking Water and Heart Defects in Offspring
Our objective was to examine the relationship between estimated maternal exposure to pesticides in public drinking water and the risk of congenital heart defects (CHD). We used mixed-effects logistic regression to analyze data from 18,291 nonsyndromic cases with heart defects from the Texas Birth Defects Registry and 4414 randomly-selected controls delivered in Texas from 1999 through 2005. Water district-level pesticide exposure was estimated by linking each maternal residential address to the corresponding public water supply district’s measured atrazine levels. We repeated analyses among independent subjects from the National Birth Defects Prevention Study (NBDPS) (1620 nonsyndromic cases with heart defects and 1335 controls delivered from 1999 through 2005). No positive associations were observed between high versus low atrazine level and eight CHD subtypes or all included heart defects combined. These findings should be interpreted with caution, in light of potential misclassification and relatively large proportions of subjects with missing atrazine data. Thus, more consistent and complete monitoring and reporting of drinking water contaminants will aid in better understanding the relationships between pesticide water contaminants and birth defects
Maternal Exposure to Nitrogen Dioxide, Intake of Methyl Nutrients, and Congenital Heart Defects in Offspring
Nutrients that regulate methylation processes may modify susceptibility to the effects of air pollutants. Data from the National Birth Defects Prevention Study (United States, 1997-2006) were used to estimate associations between maternal exposure to nitrogen dioxide (NO2), dietary intake of methyl nutrients, and the odds of congenital heart defects in offspring. NO2 concentrations, a marker of traffic-related air pollution, averaged across postconception weeks 2-8, were assigned to 6,160 nondiabetic mothers of cases and controls using inverse distance-squared weighting of air monitors within 50 km of maternal residences. Intakes of choline, folate, methionine, and vitamins B6 and B12 were assessed using a food frequency questionnaire. Hierarchical regression models, which accounted for similarities across defects, were constructed, and relative excess risks due to interaction were calculated. Relative to women with the lowest NO2 exposure and high methionine intake, women with the highest NO2 exposure and lowest methionine intake had the greatest odds of offspring with a perimembranous ventricular septal defect (odds ratio = 3.23, 95% confidence interval: 1.74, 6.01; relative excess risk due to interaction = 2.15, 95% confidence interval: 0.39, 3.92). Considerable departure from additivity was not observed for other defects. These results provide modest evidence of interaction between nutrition and NO2 exposure during pregnancy
Adiabatic and entropy perturbations propagation in a bouncing Universe
By studying some bouncing universe models dominated by a specific class of
hydrodynamical fluids, we show that the primordial cosmological perturbations
may propagate smoothly through a general relativistic bounce. We also find that
the purely adiabatic modes, although almost always fruitfully investigated in
all other contexts in cosmology, are meaningless in the bounce or null energy
condition (NEC) violation cases since the entropy modes can never be neglected
in these situations: the adiabatic modes exhibit a fake divergence that is
compensated in the total Bardeen gravitational potential by inclusion of the
entropy perturbations.Comment: 25 pages, no figure, LaTe
Singular shell embedded into a cosmological model
We generalize Israel's formalism to cover singular shells embedded in a
non-vacuum Universe. That is, we deduce the relativistic equation of motion for
a thin shell embedded in a Schwarzschild/Friedmann-Lemaitre-Robertson-Walker
spacetime. Also, we review the embedding of a Schwarzschild mass into a
cosmological model using "curvature" coordinates and give solutions with
(Sch/FLRW) and without the embedded mass (FLRW).Comment: 25 pages, 2 figure
Maternal Occupational Exposure to Polycyclic Aromatic Hydrocarbons: Effects on Gastroschisis among Offspring in the National Birth Defects Prevention Study
Background: Exposure to polycyclic aromatic hydrocarbons (PAHs) occurs in many occupational settings. There is evidence in animal models that maternal exposure to PAHs during pregnancy is associated with gastroschisis in offspring; however, to our knowledge, no human studies examining this association have been conducted
Maternal occupational exposure to polycyclic aromatic hydrocarbons and risk of neural tube defect-affected pregnancies
This study evaluated whether there is an association between maternal occupational exposure to polycyclic aromatic hydrocarbons (PAHs) and neural tube defects (NTDs) in offspring. This is the first such study of which the authors are aware
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