964 research outputs found
Obstacles to Preventing Obesity in Children Aged 2 to 5 Years: Latino Mothers’ and Fathers’ Experiences and Perceptions of Their Urban Environments
Background
The prevalence of obesity among Latino children is alarmingly high, when compared to non-Latino White children. Low-income Latino parents living in urban areas, even if they are well-educated, face obstacles that shape familial health behaviors. This study used qualitative methods to explore parents’ experiences in providing meals and opportunities to play to their children aged 2 to 5 years. In contrast to most prior studies, this study examined perceptions of familial behaviors among both mothers and fathers.
Methods
An ecological framework for exploring the associations of parental feeding behaviors and children’s weight informed this study. An interview guide was developed to explore parents’ experiences and perceptions about children’s eating and physical activity and administered to six focus groups in a community-based organization in the Mission District of San Francisco. Transcripts were coded and analyzed. Twenty seven mothers and 22 fathers of Latino children ages 2 to 5 participated.
Results
Mothers, fathers, and couples reported that employment, day care, neighborhood environments and community relationships were experienced, and perceived as obstacles to promoting health behavior among their children, including drinking water instead of soda and participating in organized playtime with other preschool-age children.
Conclusions
Results from this study suggest that the parents’ demographic, social and community characteristics influence what and how they feed their children, as well as how often and the types of opportunities they provide for physical activity, providing further evidence that an ecological framework is useful for guiding research with both mothers and fathers. Mothers and fathers identified numerous community and society-level constraints in their urban environments. The results point to the importance of standardized work hours, resources for day care providers, clean and safe streets and parks, strong community relationships, and reduced access to sugar-sweetened beverages in preventing the development of obesity in preschool-age Latino children
Low Genetic Differentiation across Three Major Ocean Populations of the Whale Shark, Rhincodon typus
BACKGROUND:Whale sharks are a declining species for which little biological data is available. While these animals are protected in many parts of their range, they are fished legally and illegally in some countries. Baseline biological and ecological data are needed to allow the formulation of an effective conservation plan for whale sharks. It is not known, for example, whether the whale shark is represented by a single worldwide panmictic population or by numerous, reproductively isolated populations. Genetic analysis of population structure is one essential component of the baseline data required for whale shark conservation. METHODOLOGY/PRINCIPAL FINDINGS:We have identified 8 polymorphic microsatellites in the whale shark and used these markers to assess genetic variation and population structure in a panel of whale sharks covering a broad geographic region. This is the first record of microsatellite loci in the whale shark, which displayed an average of 9 alleles per locus and mean H(o) = 0.66 and H(e) = 0.69. All but one of the eight loci meet the expectations of Hardy-Weinberg equilibrium. Analysis of these loci in whale sharks representing three major portions of their range, the Pacific (P), Caribbean (C), and Indian (I) Oceans, determined that there is little population differentiation between animals sampled in different geographic regions, indicating historical gene flow between populations. F(ST) values for inter-ocean comparisons were low (PxC = 0.0387, CxI = 0.0296 and PxI = -0.0022), and only CxI approached statistical significance (p = 0.0495). CONCLUSIONS/SIGNIFICANCE:We have shown only low levels of genetic differentiation between geographically distinct whale shark populations. Existing satellite tracking data have revealed both regional and long-range migration of whale sharks throughout their range, which supports the finding of gene flow between populations. Whale sharks traverse geographic and political boundaries during their life history and interbreed with animals from distant populations; conservation efforts must therefore target international protection for this species
Geometrical Constraints on the Cosmological Constant
The cosmological constant problem is examined under the assumption that the
extrinsic curvature of the space-time contributes to the vacuum. A compensation
mechanism based on a variable cosmological term is proposed. Under a suitable
hypothesis on the behavior of the extrinsic curvature, we find that an
initially large rolls down rapidly to zero during the early stages
of the universe. Using perturbation analysis, it is shown that such vacuum
behaves essentially as a spin-2 field which is independent of the metric.Comment: [email protected], 17 pages, Latex, 2 figures obtained by reques
Thermodynamics of Decaying Vacuum Cosmologies
The thermodynamic behavior of vacuum decaying cosmologies is investigated
within a manifestly covariant formulation. Such a process corresponds to a
continuous irreversible energy flow from the vacuum component to the created
matter constituents. It is shown that if the specific entropy per particle
remains constant during the process, the equilibrium relations are preserved.
In particular, if the vacuum decays into photons, the energy density and
average number density of photons scale with the temperature as and . The temperature law is determined and a generalized
Planckian type form of the spectrum, which is preserved in the course of the
evolution, is also proposed. Some consequences of these results for decaying
vacuum FRW type cosmologies as well as for models with ``adiabatic'' photon
creation are discussed.Comment: 21 pages, uses LATE
Beta, Dipole and Noncommutative Deformations of M-theory Backgrounds with One or More Parameters
We construct new M-theory solutions starting from those that contain 5 U(1)
isometries. We do this by reducing along one of the 5-torus directions, then
T-dualizing via the action of an O(4,4) matrix and lifting back to
11-dimensions. The particular T-duality transformation is a sequence of O(2,2)
transformations embedded in O(4,4), where the action of each O(2,2) gives a
Lunin-Maldacena deformation in 10-dimensions. We find general formulas for the
metric and 4-form field of single and multiparameter deformed solutions, when
the 4-form of the initial 11-dimensional background has at most one leg along
the 5-torus. All the deformation terms in the new solutions are given in terms
of subdeterminants of a 5x5 matrix, which represents the metric on the 5-torus.
We apply these results to several M-theory backgrounds of the type AdS_r x
X^{11-r}. By appropriate choices of the T-duality and reduction directions we
obtain analogues of beta, dipole and noncommutative deformations. We also
provide formulas for backgrounds with only 3 or 4 U(1) isometries and study a
case, for which our assumption for the 4-form field is violated.Comment: v2:minor corrections, v3:small improvements, v4:conclusions expanded,
to appear in Class. Quant. Gra
Nonsingular FRW cosmology and nonlinear electrodynamics
The possibility to avoid the cosmic initial singularity as a consequence of
nonlinear effects on the Maxwell eletromagnetic theory is discussed. For a flat
FRW geometry we derive the general nonsingular solution supported by a magnetic
field plus a cosmic fluid and a nonvanishing vacuum energy density. The
nonsingular behavior of solutions with a time-dependent -term are
also examined. As a general result, it is found that the functional dependence
of can uniquely be determined only if the magnetic field remains
constant. All these models are examples of bouncing universes which may exhibit
an inflationary dynamics driven by the nonlinear corrections of the magnetic
field.Comment: 20 pages, 7 figure
Transition Redshift: New Kinematic Constraints from Supernovae
The transition redshift (deceleration/acceleration) is discussed by expanding
the deceleration parameter to first order around its present value. A detailed
study is carried out by considering two different parameterizations: and , and the associated free parameters () are constrained by 3 different supernova samples. The previous analysis
by Riess {\it{et al.}} [ApJ 607, 665, 2004] using the first expansion is
slightly improved and confirmed in light of their recent data ({\emph{Gold}}07
sample). However, by fitting the model with the Supernova Legacy Survey (SNLS)
type Ia sample we find that the best fit to the redshift transition is instead of as derived by the High-z Supernovae Search
(HZSNS) team. This result based in the SNLS sample is also in good agreement
with the Davis {\it{et al.}} sample, ().
Such results are in line with some independent analyzes and accommodates more
easily the concordance flat model (CDM). For both parameterizations,
the three SNe type Ia samples considered favor recent acceleration and past
deceleration with a high degree of statistical confidence level. All the
kinematic results presented here depend neither on the validity of general
relativity nor the matter-energy contents of the Universe.Comment: 19 pages, 15 figures, 1 table, revised version accepted for
publication in MNRA
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